Fat-derived cells Enhance the Bone-Forming Capacity of Hypertrophic Cartilage Matrices


Treating particular bone defects or injuries present a substantial challenges for clinicians. The method of choice usually involves the use of an “autologous” bone graft (“autologous” simply means that the graft comes from the patient’s own bone). However, autologous bone grafts have plenty of limitations. For example, if a patient has a large enough bone defect, there is no way the orthopedist and take bone from a donor site without causing a good deal of risk to the donor site. Even with small bone grafts, so-called “donor site morbidity” remains a risk. Having said that, plenty of patients have had autologous bone grafts that have worked well, but larger bone injuries or defects are not treatable with autologous bone grafts.

The answer: bone substitute materials. Bone substitute materials include tricalcium phosphate, hydroxyapatite, cement, ceramics, bioglass, hydrogels, polylactides, PMMA or poly(methy methacrylate) and other acrylates,, and a cadre of commercially available granules, blocks, pastes, cements, and membranes. Some of these materials are experimental, but others do work, even if do not work every time. The main problem with bone substitute materials is that, well, they are not bone, and, therefore lack the intrinsic ability to induce the growth of new bone (so-called osteoinductive potential) and their ability to integrate into new bone is also a problem at times.

We must admit that a good deal of progress has been made in this area and it’s a good thing too. Many of our fabulous men and women-at-arms have returned home with severe injuries from explosives and wounds from large-caliber weapons that have shattered their bones. These courageous men and women have been the recipient of these technologies. However, the clinician is sometimes left asking herself, “can we do better?”

A new paper from the laboratories of Ivan Martin and Claude Jaquiery from the University Hospital of Basel suggests that we can. This paper appeared in Stem Cells Translational Medicine and describes the use of a hypertrophic cartilage matrix that was seeded with cells derived from the stromal vascular faction of fat to not only make bone in the laboratory, but to also heal skull defects in laboratory animals. While this work benefitted laboratory animals, it was performed with human cells and materials, which suggests that this technique, if it can be efficiently and cheaply scaled up, might be usable in human patients.
The two lead authors of this paper, Atanas Todorov and Matthias Kreutz and their colleagues made hypertrophic cartilage matrices from human bone marrow mesenchymal stem cells (from human donors) that were induced to make cartilage. Fortunately, protocols have been very well worked out and making cartilage plugs with chondrocytes that are enlarged (hypertrophic) is something that has been successfully done in many laboratories. After growing the mesenchymal stem cells in culture, half a million cells were induced to form cartilage with dexamethasone, ascorbic acid 2-phosphate, and the growth factor TGF-beta1. After three weeks, the cartilage plugs were subjected to hypertrophic medium, which causes the cartilage cells to enlarge.

Chondrocyte enlargement is a prolegomena to the formation of bone and during development, many of our long bones (femur, humerus, fibula, radius, etc.), initially form as cartilage exemplars that are replaced by bone as the chondrocytes enlarge. Ossification begins when a hollow cylinder forms in the center of the bone (known as the periosteal collar). The underlying chondrocytes degenerate and die, thus releasing the matrix upon which calcium phosphate crystals accrete. The primary ossification center commences with the calcification of the central shaft of the bone and erosion of the matrix by the invasion of a blood vessel. The blood vessels bring osteoprogenitor cells that differentiate into osteoblasts and begin to deposit the bone matrix.

Next, Todorov and his crew isolated the stromal vascular fraction from fat that was donated by 12 volunteers who had fat taken from them by means of liposuction. The fat is then minced, digested with enzymes, centrifuged, filtered and then counted. This remaining fraction is called the stromal vascular fraction or SVF, and it consists of a pastiche of blood vessel-forming cells, mesenchymal stem cells, and bone-forming cells (and probably a few other cells types too). These SVF cells were seeded onto the hypertrophic cartilage plugs and used for the experiments in this paper.

First, the SVF-seeded plugs were used to grow bone in laboratory rodents. The cartilage plugs were implanted into the backs for nude mice. Different cartilage plugs were used that had been seeded with gradually increasing number of SVF cells. The implanted plugs definitely made ectopic bone, but the amount of bone they made was directly proportional to the number of SVF cells with which they had been seeded. Staining experimental also showed that some of the newly-grown bone came from the implanted SVF cells.

Ectopic bone formation. Grafts based on devitalized hypertrophic cartilage pellets were embedded in fibrin gel without or with stromal vascular fraction cells from adipose tissue and implanted subcutaneously in nude mice. (A): Representative hematoxylin and eosin, Masson-Tri-Chrome, and Safranin-O (Saf-O) staining and in situ hybridization for human ALU sequences (dark blue = positive) after 12 weeks in vivo. Saf-O stainings are blue-green because of lack of glycosaminoglycans and counterstaining with fast green. Osteoid matrix and bone marrow are visible. Scale bars = 200 µm. (B): Stainings for metalloproteinase (MMP)13 and MMP9, as well as for the N-terminal neoepitope at the major MMP cleavage site (DIPEN) after 12 weeks in vivo (red/pink = positive). Scale bars = 50 µm. +, osteoid matrix; ⋆, bone marrow. Abbreviations: ALU, Arthrobacter luteus; H&E, hematoxylin and eosin; Masson, Masson’s trichrome; MMP, metalloproteinase; Saf-O, Safranin-O; SVF, stromal vascular fraction.
Ectopic bone formation. Grafts based on devitalized hypertrophic cartilage pellets were embedded in fibrin gel without or with stromal vascular fraction cells from adipose tissue and implanted subcutaneously in nude mice. (A): Representative hematoxylin and eosin, Masson-Tri-Chrome, and Safranin-O (Saf-O) staining and in situ hybridization for human ALU sequences (dark blue = positive) after 12 weeks in vivo. Saf-O stainings are blue-green because of lack of glycosaminoglycans and counterstaining with fast green. Osteoid matrix and bone marrow are visible. Scale bars = 200 µm. (B): Stainings for metalloproteinase (MMP)13 and MMP9, as well as for the N-terminal neoepitope at the major MMP cleavage site (DIPEN) after 12 weeks in vivo (red/pink = positive). Scale bars = 50 µm. +, osteoid matrix; ⋆, bone marrow. Abbreviations: ALU, Arthrobacter luteus; H&E, hematoxylin and eosin; Masson, Masson’s trichrome; MMP, metalloproteinase; Saf-O, Safranin-O; SVF, stromal vascular fraction.

In the second experiment, Todorov and Kreutz used these SVF-seeded cartilage plugs to repair skull lesions in rats. Once again, the quantity of bone produced was directly proportional to the number of SVFs seeded into the cartilage matrices prior to implantation. In both experiments, the density of SVF cells positively correlates with the bone-forming cells in the grafts and the percentage of SVF-derived blood vessel-forming cells correlates with the amount of deposited mineralized matrix.

Bone repair capacity. Devitalized hypertrophic cartilage pellets were embedded in fibrin gel without or with stromal vascular fraction (SVF) cells from adipose tissue and implanted in rat calvarial defects. (A): Mineralized volume quantified by microtomography (n = 9 grafts assessed per group). (B): Bone area assessed in histological sections, expressed as percentage of total defect area (n = at least 24 sections assessed per group). ∗∗∗∗, p < .0001. (C, D): Representative three-dimensional microtomography reconstructions (left) and hematoxylin/eosin (H&E) staining (right) of the calvarial defects filled with devitalized grafts, implanted without (C) or with (D) activation by SVF cells after 4 weeks. Dotted circles indicate the defect borders (4 mm diameter). Scale bars = 500 µm. (E): Microtomography (left) and H&E staining (middle and right) displaying the bridging between hypertrophic matrix and bone of the calvarium, or the fusion of single pellets (right) in activated grafts. White bar = 850 µm; black bars = 500 µm. Dotted lines indicate the edge of the calvarium. (F): In situ hybridization for Arthrobacter luteus sequences showing the presence of human cells (dark blue, positive) in the explants. Scale bar = 200 µm. Abbreviations: C, calvarium; dev, fibrin gel without stromal vascular fraction; dev + SVF, fibrin gel with stromal vascular fraction; P, hypertrophic matrix; SVF, stromal vascular fraction.
Bone repair capacity. Devitalized hypertrophic cartilage pellets were embedded in fibrin gel without or with stromal vascular fraction (SVF) cells from adipose tissue and implanted in rat calvarial defects. (A): Mineralized volume quantified by microtomography (n = 9 grafts assessed per group). (B): Bone area assessed in histological sections, expressed as percentage of total defect area (n = at least 24 sections assessed per group). ∗∗∗∗, p < .0001. (C, D): Representative three-dimensional microtomography reconstructions (left) and hematoxylin/eosin (H&E) staining (right) of the calvarial defects filled with devitalized grafts, implanted without (C) or with (D) activation by SVF cells after 4 weeks. Dotted circles indicate the defect borders (4 mm diameter). Scale bars = 500 µm. (E): Microtomography (left) and H&E staining (middle and right) displaying the bridging between hypertrophic matrix and bone of the calvarium, or the fusion of single pellets (right) in activated grafts. White bar = 850 µm; black bars = 500 µm. Dotted lines indicate the edge of the calvarium. (F): In situ hybridization for Arthrobacter luteus sequences showing the presence of human cells (dark blue, positive) in the explants. Scale bar = 200 µm. Abbreviations: C, calvarium; dev, fibrin gel without stromal vascular fraction; dev + SVF, fibrin gel with stromal vascular fraction; P, hypertrophic matrix; SVF, stromal vascular fraction.

This is not the first time scientists have proposed the use of cartilage plugs to induce the formation of new bone. Van der Stok and others and Bahney and colleagues were able to repair segmental bone defects in laboratory rodents. Is this technique transferable to human patients? Possibly. Hypertrophic cartilage is relatively easy to make and it is completely conceivable that hypertrophic cartilage wedges can be sold as “off-the-shelf” products for bone treatments. SVF can also be derived from the patient or can be derived from donors.

Furthermore, the protocols in this paper all used human cells and grew the products in immunodeficient rats and mice. Therefore, in addition to scaling this process up, we have a potentially useful protocol that might very well be adaptable to the clinic.

The efficacy of this technique must be confirmed in larger animal model system before human trials can be considered. Hopefully human trials are in the future for this fascinating technique.

New Study Validates Cellular Bone Allograft Technology


In a study in laboratory rats that had defects in their femurs (upper leg bone) showed new bone formation after they were treated with adipose-derived mesenchymal stromal cells that had been seeded on demineralized bone matrix and implanted.  Implanted stem cells were detected for up to 84 days in areas of new formation and had differentiated within the bony repair tissue.

According to AlloSource, the procedures used similar technology to the company’s AlloStem Cellular Bone Allograft process.

Surgical oncologist Nicole Ehrhart of Colorado State University presented these data at the State of Spine Surgery annual symposium and at the Korean American Spine Society meeting.

AlloStem is partially demineralized allograft bone combined with adipose-derived mesenchymal stem cells.  AlloStem is suitable for general bone grafting applications, and is similar to autograft bone because it provides the three key properties necessary for bone formation: osteoconduction, osteoinduction and osteogenesis.

Ehrhart’s study has been accepted for publication in Journal of Biomaterials and Tissue Engineering.

AlloSource provides 200 types of precise cartilage, cellular, bone, skin and soft-tissue allografts.

Key Molecules Tha Control Stem Cell Fate Identified


Adult stem cells, such as mesenchymal stem cells and blood-vessel-associated pericytes represent patient-specific stem cells that are excellent candidates for regenerative medicine. To that end being able to control the differentiation of these stem cells with drugs or small molecules is extremely desirable for eliciting targeted tissue and organ regeneration.

However, identifying these stem-cell-inducing molecules is time-consuming, expensive, and fraught with dead ends. Is there an easier way to control the behavior of stem cells in culture or in your own body?

Research from the City University of New York (CUNY) suggests that the answer to this question might be “yes.” According to Rein Ulijn from CUNY, “Simple small metabolites present in the body already can dictate cell behavior.”

In collaboration with Matthew Dalby from the University of Glasgow, Ulijn and his colleagues discovered that when they grew stem cells on a gel-like medium, the stiffness of which could be easily adjusted, they found molecules that could direct the differentiation of cultured stem cells. As an added bonus, they could direct the differentiation of cultured stem cells much more cheaply.

Ulijn and Dalby began their collaboration in 2011 after other laboratories had demonstrated that the stiffness of the medium could affect the differentiation of stem cells. “On a stiff gel you might get bone-like differentiation,” Ulijn explained. “On a softer gel differentiation into neurons is more likely.” They wanted to use such a system to identify small molecules that can control stem cell differentiation in culture. Such a finding could also “aid the discovery of natural metabolite-based drugs,” added Ulijn added. Such natural-based drugs could be used to, for example, reinforce bones in osteoporosis.

Dalby was interested in the role metabolites played in this stem cell differentiation. Unfortunately, these metabolites are present in fleetingly low concentrations. To complicate the picture, the different formulations of stiffer and floppier materials can mask subtle changes in metabolite concentration. Ulijn found a way around this problem by turning to the two-component peptide gels made by Biogelx (full disclosure: Ulijn serves as the chief scientific officer for Biogelx). Fine-tuning the concentration of the two different gel components changes the rigidity of the gel without changing any other components of the gel that might mask metabolite variation.

The researchers therefore studied concentration changes of hundreds of metabolites during stiffness-controlled stem cell differentiation of stem cells into bone or cartilage. Several metabolites that seemed to make a significant difference for stem cell differentiation were lysophosphatidic acid, which drove stem cells to form cartilage and cholesterol sulfate, which helped stem cells form bone. When Ulijn and his coworkers fed these metabolites to standard stem cell cultures, they differentiated into the desired cell type.

Helena Azevedo of Queen Mary University of London, said, “We will see, for sure, studies exploiting these metabolites for inducing controlled differentiation of stem cells.” She went on to called this study “highly innovative” and said that it might directly influence future stem cell differentiation experiments; particularly those that involve the formation of cartilage or bone.

Making Cartilage to Heal Broken Bones


Gage Crump and his colleagues at the University of Southern California have used the regeneration of zebrafish jawbone to demonstrate that the regeneration of damaged bones does not necessarily require a recapitulation of the same processes that occur during embryonic development. Even though this work used zebrafish as a model system, it may provide some of the underlying principles for treating difficult fractures.

Cartilage production is critical for healing full-thickness bone injuries. In order to understand how this bone-producing cartilage is generated, Crump and his coworkers turned to the genetically malleable and relatively more simple zebrafish system. Zebrafish are vertebrates, like humans, but these animals retain a remarkable capacity to regenerate many of their organs.

When human bones fracture, a small cartilage callus forms that is replaced by bone that bridges small, but not large, gaps in the bone.

In zebrafish, however, the cartilage callus continues to expand and fills even very large gaps in broken bones. This cartilage is replaced throughout the bone by bone. This allows zebrafish to heal even very large fractures.

These days, patients with severe bone fractures may have a surgeon insert metal pins and even plates to help set bone. In more severe cases, bone grafts are used to span gaps, and stem cell-based treatments have been tested in a few clinical trials as well.

About six million people in the U.S. suffer bone breaks each year, and even though most of these patients recover fully, about 300,000 are slow to heal and some may not heal at all. Complications include post-traumatic arthritis, growth abnormalities, delayed union and misaligned union.

Hundreds of professional football players have invested in stem cell treatments to treat injuries, even though the evidence for the efficacy of such treatments is, sometimes, sparse. One report even tells of an NFL linebacker who paid $6,000 for a 1-milliliter vial of donated placenta tissue containing stem cells to be injected into his injured knee.

The bone surface contains thin lining called the “periosteum” that contains a stem cell population that helps maintain bone mass throughout one’s life. In Gage’s laboratory, his team identified a gene called Indian Hedgehog a (IHHa), which is responsible for inducing these periosteal stem cells to switch from bone production to cartilage production. Mutant zebrafish strains that lack the IHHa gene are unable to make cartilage in response to bone injury and heal poorly from bone fractures.

Periosteum

Crump said that an “exciting finding from our work is that, somewhat counterintuitively, cartilage is critical for healing full thickness bone injuries. By understanding how this bone-producing cartilage is generated in the simpler zebrafish model, we hope to find ways to create more of this unique cartilage tissue in patients to better heal their bones.”

According to this paper, which was published in the journal Development, 2016; dev.131292 DOI: 10.1242/dev.121292; instead of the more traditional approach of using bone cells or bone-like materials to heal broken bones, stimulating endogenous bone-based stem cells that make this special kind of fracture-healing cartilage might be a more effective strategy.

A Common Osteoporosis Drug Protects Bone Marrow Stem Cells from DNA Damage


A commonly used treatment for osteoporosis can protect stem cells in bone from the ravages of aging, according to a new study from the University of Sheffield.

Ilaria Bellantuono and her colleagues have discovered that zoledronate can extend the lifespan of bone marrow mesenchymal stem cells by reducing the degree of DNA damage experienced by these stem cells.

As stem cells age, they accumulate DNA damage, and this seems to be one of the most important mechanisms of aging. DNA damage can cause stem cells to lose their capacity to maintain tissues and repair them when those tissues are damaged. This new research from Bellantuono’s laboratory shows that zoledronate can protect mesenchymal stem cells from DNA damage, which enhances their survival and maintains their function.

According the Professor Bellantuono, “The drug enhances the repair of the damage in DNA occurring with age in stem cells in the bone. It is also likely to work in other stem cells too.”

She continued: “This drug has been shown to delay mortality in patients affected by osteoporosis but until now we didn’t know why. These findings provide an explanation as to why it may help people to live longer.

“Now we want to understand whether the drug can be used to delay or revert the aging in stem cells in older people and improve the maintenance of tissues such as the heart, the muscle and immune cells, keeping them healthier for longer.

“We want to understand whether it improves the ability of stem cells to repair those tissues after injury, such as when older patients with cancer undergo radiotherapy.”

Almost half of elderly patients over 75 years of age have three or more diseases at the same time, such as osteoporosis, diabetes, cardiovascular disease, infections, and muscle weakness. However, work like this suggests that drugs like zoledronate could be used to treat, prevent or perhaps even delay the onset of such diseases.

Dr Bellantuono added: “We are hopeful that this research will pave the way for a better cure for cancer patients and keeping older people healthier for longer by reducing the risk of developing multiple age-related diseases.”

How Stem Cell Therapy Protects Bone In Lupus


Systemic Lupus Erythematosis, otherwise known as lupus, is an autoimmune disease cause your own immune system attacking various cells and tissues in your body. Lupus patients can suffer from fatigue, joint pain and selling and show a marked increased risk or osteoporosis.

Clinical trials have established that infusions of mesenchymal stem cells (MSCs) can significantly improve the condition of lupus patients, but exactly why these cells help these patients is not completely clear. Certainly suppression of inflammation is probably part of the mechanism by which these cells help lupus patients, but how do these cells improve the bone health of lupus patients?

Songtao Shi and his team at the University of Pennsylvania have used an animal model of lupus to investigate this very question. In their hands, transplanted MSCs improve the function of bone marrow stem cells by providing a source of the FAS protein. FAS stimulates bone marrow stem cell function by means of a multi-step, epigenetic mechanism.

This work by Shi and his colleagues has implications for other cell-based treatment strategies for not only lupus, but other diseases as well.

“When we used transplanted stem cells for these diseases, we didn’t know exactly what they were doing, but saw that they were effective,” said Shi. “Now we’ve seen in a model of lupus that bone-forming mesenchymal stem cell function was rescued by a mechanism that was totally unexpected.”

In earlier work, Shi and his group showed that mesenchymal stem cell infusions can be used to treat various autoimmune diseases in particular animals models. While these were certainly highly desirable results, no one could fully understand why these cells worked as well as they did. Shi began to suspect that some sort of epigenetic mechanism was at work since the infused MSCs seemed to permanently recalibrate the gene expression patterns in cells.

In order to test this possibility, Shi and others found that lupus mice had a malfunctioning FAS protein that prevented their bone marrow MSCs from releasing pro-bone molecules that are integral for bone maintenance and deposition.

A deficiency for the FAS protein prevents bone marrow stem cells from releasing a microRNA called miR-29b.  The failure to release miR-29b causes its concentrations to increase inside the cells.  miR-29b can down-regulate an enzyme called DNA methyltransferase 1 (Dnmt1), and the buildup of miR-29b inhibits Dnmt1, which causes decreased methylation of the Notch1 promoter and activation of Notch signaling.  Methylation of the promoters of genes tends to shut down gene expression, and the lack of methylation of the Notch promoter increases Notch gene expression, activating Notch signaling.  Unfortunately, increased Notch signaling impaired the differentiation of bone marrow stem cells into bone-making cells.  Transplantation of MSCs brings FAS protein to the bone marrow stem cells by means of exosomes secreted by the MSCs.  The FAS protein in the MSC-provided exosomes reduce intracellular levels of miR-29b, which leads to higher levels of Dnmt1.  Dnmt1 methylates the Notch1 promoter, thus shutting down the expression of the Notch gene, and restoring bone-specific differentiation.

Shi and others are presently investigating if this FAS-dependent process is also at work in other autoimmune diseases.  If so, then stem cell treatments might convey similar bone-specific benefits.

Faster Bone Regeneration With a Little Wnt


Nick Evans and his colleagues at the University of Southampton, UK have discovered that transient stimulation of the Wnt signaling pathway in bone marrow stem cells expands them and enhances their bone-making ability. This finding has led to an intense search for drugs that can stimulate the Wnt pathway in order to stimulate bone formation in wounded patients.

The Wnt pathway is a highly conserved pathway found in sponges, starfish, sharks, and people. Wnt signaling controls pattern formation during development, and the growth of stem cells during healing.

When it comes to healing, bone fractures represent a sizeable societal problem, particularly among the aged. While most fractures heal on their own, approximately 10 percent of all fractures take over six months to heal or never heal at all. In the worse cases, fracture patients can require several surgeries or might need amputation in desperate cases.

According the Evans, he and his research group are screening a wide range of chemicals to determine if they stimulate Wnt signaling. If such chemicals prove safe to use in laboratory animals, then they might become clinical tools to help stimulate bone formation and healing in patients with recalcitrant fractures.

Research from Evans’ group has shown that transient stimulation of the Wnt signaling pathway in isolated bone marrow cells increases the number of bone-making progenitor cells. However, if the Wnt pathway is activated for too long a time period, this regenerative effect is lost or even reversed. Hence the need to develop treatments that deliver small molecules that stimulate Wnt signaling in bone marrow cells for a specified period of time and in a targeted fashion.

Evans and his group have used nanoparticles loaded with Wnt proteins to do exactly that. The feasibility of this technology and its effectiveness requires further work, but the promise is there and the idea is more than a little intriguing.

Forcing Stem Cells to Make Bone


Researchers in the laboratory of Janet Rubin from the University of North Carolina School of Medicine have discovered that a compound from mold can drive mesenchymal stem cells (MSCs) to become osteoblasts, which are the cells that make bone.

MSCs are found in many different tissues without our bodies, ranging from bone marrow, to fat, to tendons, to liver, muscle, brain, and the heart. MSCs have the ability to readily differentiate into bone, fat, and cartilage, and with a little coaxing in the laboratory, they can also form smooth muscle, blood vessels, and even neurons. The key to using these cells is fine-tuning their differentiation in the clinic to efficiently make one cell type over and above another.

Rubin and her colleagues showed that by treating MSCs with cytochalasin D, the cells overwhelmingly became bone cells (osteoblasts). Furthermore, when cytochalasin D was injected into the bone cavity inside bones, it also triggered the formation of bone.

Rubin commented that the “bone forms quickly. The data and images are so clear; you don’t have to be a bone biologist to see what cytochalasin D does in one week in a mouse.”

Rubin continued: “This is not what we expected. This was not what we were trying to do in the lab. But what we’ve found could become an amazing way to jump-start local bone formation. However, this will not address osteoporosis, which involves bone loss throughout the skeleton.”

Cytochalasins are known to target the major cytoskeletal protein actin. Actin self-assembles to form long chain known as microfilaments, and are involved in such vital cell processes as movement, cell shape, cell extensions, vesicle trafficking, and other essential processes in the cell. Cytochalasins disassemble actin microfilaments, which increases the pool of actin monomers in the cell. Rubin and her team showed that these actin monomers went into the cell nucleus and regulated gene expression. Specifically, they turned on the genes responsible for osteoblasts differentiation.

This a novel use of actin by cells, since actin is not normally known to traffic to the nucleus and affect gene expression.

If Rubin and her group disassembled the actin cytoskeleton but prevented actin from trafficking to the nucleus, the MSCs nerve differentiated into osteoblasts.

Cytochalasin D also worked in live mice to drive the formation of bone.

Because bone formation is largely the same in humans and mice, this research is probably translatable. Even though clinicians may not want to use cytochalasin D in human patients, screening compounds that trigger the transport of monomeric actin into the nucleus might be a good way to induce MSCs to form bone cells.

This work was published in the journal Stem Cells 2015; 33(10:3065.

Fetal Stem Cell Therapy Trial for Brittle Bone Disease


Dr. Cecilia Gӧtherström works as a medical researcher at the Karolinska Institutet in Stockholm, Sweden. Earlier this month, Dr Gӧtherström announced the commencement of the first clinical trial that utilizes fetal stem cell transplants to treat the brittle bone disease, Osteogenesis Imperfecta.

Osteogenesis imperfect (OI) was made famous by the Bruce Willis/Samuel Jackson movie “Unbreakable.” In this movie, Samuel Jackson played a wheel-chair bound savant whose bones were incredibly fragile, but acted as a mentor to Bruce Willis’ character who had a tendency to not become injured despite being in accidents and other traumatic events. Willis becomes a kind of local protector of the weak and innocent in his community under Jackson’s tutelage. I will not give away the surprising ending, but the fact that Jackson’s character had OI and his bones broke so easily put OI in the public’s consciousness.

OI is actually a group of genetic disorders that affects an estimated 6 to 7 per 100,000 people worldwide and prevents the bones from forming properly. This disease results from mutations in the COL1A1, COL1A2, CRTAP, and P3H1 genes. More than 90 percent of all cases of OI result from mutations in the COL1A1 and COL1A2 genes. The COL1A1 and COL1A2 genes encode the type I collagen proteins. Collagen is the most abundant protein in bone, skin, and other connective tissues. Patients with OI have fragile bones that break easily, sometimes with no apparent cause. OI can also cause loose joints, fatigue, early hearing loss, and respiratory problems. Multiple fractures are common, and in severe cases, can occur even before birth. Milder cases may involve only a few fractures over a person’s lifetime.

The publication SelectScience interviewed Dr. Gӧtherström who is the coordinator of this clinical trial that will use stem cell therapy to treat babies diagnosed with OI before they are ever born. Dr Gӧtherström told SelectScience that she and her colleagues selected OI as a disease to attack with stem cell treatment because “no good treatment exists.” Dr. Gӧtherström continued: “OI is a chronic disorder that affects the patient throughout their lifetime with reduced quality of life.” Also, because OI causes poor bone mineralization, fractures and malformation of the bones commences by the time the baby is born. Therefore, physicians can diagnose OI during pregnancy, and once it has been diagnosed, it is crucial to initiate treatment as soon as possible.

Dr. Gӧtherström and her colleagues will infuse stem cells into the fetal bodies of babies afflicted with OI by employing the same protocol that is generally used for blood transfusions during pregnancy. This is a very well-tested technique that carries a very little risk to the mother and her baby. According to Dr. Gӧtherström, there is a theoretical risk of the donor cells acquiring mutations that causing cancer in the mother, but this is very unlikely.

Fetal stem cell therapy has some benefits over other types of stem cell therapy. According to Dr. Gӧtherström, “Fetuses do not have a fully developed immune system, so the donor cells may have a better engraftment potential.” Also, fetal Mesenchymal Stem Cells (MSC) have a far better ability to form bone tissue than adult stem cells.

“If this proves to be safe and efficient, we will explore other disorders that can be treated prenatally, such as other skeletal dysplasias, or metabolic disorders,” Dr Gӧtherström explained. The success of this trial could open up new avenues for prenatal therapies to become more common. Dr. Gӧtherström believes that prenatal diagnosis of similar chronic disorders will shift, from delaying or slowing down the onset of a condition to actually treating it.

3D Printing of Stem Cells on Bioceramic Molds to Reconstruct Skulls


Skull defects or injuries can be very difficult to repair. However, an Australian research team has pioneered a new technique that can regrow skulls by applying stem cells to a premade scaffold with a 3D printer.

This research team consists of a surgeon, a neurosurgeon, two engineers, and a chief scientist. This five-person team is collaborating with a 3D printing firm that is based in Vienna in order to manufacture exact replicas of bone taken from the skulls of patients.

The protocol for this procedure utilizes stem cells and 3D printers, and is funded by a $1.5 million research grant that is aimed at reducing costs and improving efficiency of the Australian public health service.

The first subjects for this procedure will include patients whose skulls were severely damaged, or had a piece of their skull removed for brain surgery, and require cranial reconstruction. The skull reconstructions will take place at the Royal Perth Hospital. The first trial will commence next year. If this procedure proves to be successful it could reduce the risk of complications and surgical time, and provide massive cost savings.

If a patient has a skull injury or some other skull issue, pieces of skull bone were removed bone and stored it in a freezer for later implantation into the skull. Unfortunately, this procedure often resulted in infection or resorption of the bone. Alternatively, titanium plates can be used but these eventually they degrade, and therefore, are not ideal.

Neurosurgeon Marc Coughlan, who is a member of the five-person research team that developed this procedure, said this protocol represents the first time stem cells have been used on a 3D printed scaffold to regrow bone. “What we’re trying to do is take it one step further and have the ceramic resorb and then be only left with the patient’s bone, which would be exactly the same as having the skull back,” Coughlan told The Australian.

If this procedure proves successful, it could revolutionize cranial reconstruction surgeries. According to health minister Kim Hames, “This project highlights some of the innovative and groundbreaking research that is under way in WA’s public health system, and the commitment of the government to supporting this crucial work.”

We will keep tabs on this clinical trial to determine if it works as well as reported.

Porous Hydrogels Boost Stem Cell-Based Bone Production


Regenerative medicine relies upon the ability to isolate, manipulate, and exploit stem cells from our own bodies or from the bodies of stem cell donors. A present obstacle to present therapeutic strategies is the poor survival of implanted stem cells. There are also worries of about properly directing the differentiation of transplanted stem cells. After all, if implanted stem cells do not differentiate into the terminal cell types you want to be replaced, the use of such cells seems pointless.

To address this problem, David Mooney from the Wyss Institute and his colleagues have designed a three-dimensional system that might keep transplanted stem cells alive and happy, ready to heal.

Mooney’s group has adopted a strategy based on the concept of stem cell “niches.”. In our bodies, stem cells have particular places where they live. These stem cell-specific microenvironments provide unique support systems for stem cells and typically include extracellular matrix molecules to which stem cells attach.

Mooney and others have identified chemical and physical cues that act in concert to promote stem cell growth and survival. The chemical cues found in stem cell niches are relatively well-known but the physical and mechanical properties are less well understood at the present time.

Stem cells in places like bone, cartilage, or muscle, when cultured in the laboratory, display particular mechanical sensitivities and they must rest on a substrate with a defined elasticity and stiffness in order to proliferate and mature. As you might guess, reproducing the right physical properties in the laboratory is no mean feat. However, several laboratories have used hydrogels to generate the right combination of chemical and physical properties.

Mooney and his colleagues have made two hydrogels with very different properties. A stable, “bulk” gel is filled with small bubbles of a pore-making molecule called a “porogen,” which degrades quickly and leaves porous cavities in its wake. When the bulk hydrogel is combined with extracellular matrix molecules from stem cell niches and filled with tissue-specific stem cells, and the porogen, Mooney and his team can make an artificial bone-forming stem cell niche. The porous cavities in the hydrogel, in combination with the chemical signals, drive the stem cells to grow, and divide while expanding into the open spaces in the gel. Then the cell move from the hydrogel to form mineralized bone.

In small animal experiments, Mooney and his colleagues showed that a porous hydrogel with the correct chemical and elastic properties provides better bone regeneration than transplanting stem cells alone. The maturing stem cells deployed by the hydrogel also induce neighboring stem cell populations to contribute to the bone repair, which further amplifies their regenerative effects.

This study provides the first demonstration that adjusting the physical properties of a biomaterial can not only help deliver stem cells but also tune the behavior of those cells in a living organism. Even though Mooney has primarily focused on bone formation, he and his group believe that the hydrogel concept can be broadly applied to other regenerative process as well.

This work was published in Nature Materials 2015; DOI: 10.1038/nmat4407.

MSC Transplantation Reduces Bone Loss via Epigenetic Regulation of Notch Signaling in Lupus


Mesenchymal stem cells from bone marrow, fat, and other tissues have been used in many clinical trials, experiments, and treatment regimens. While these cells are not magic bullets, they do have the ability to suppress unwanted inflammation, differentiate into bone, cartilage, tendon, smooth muscle, and fat, and can release a variety of healing molecules that help organs from hearts to kidneys heal themselves.

Mesenchymal stem cell transplantation (MSCT) is the main means by which mesenchymal stem cells are delivered to patients for therapeutic purposes. However, the precise mechanisms that underlie the success of these cells are not fully understood. In a paper by from the University Of Pennsylvania School Of Dental Medicine published in the journal Cell Metabolism, MSCT were able to re-establish the bone marrow function in MRL/lpr mice. The MRL/lpr mouse is a genetic model of a generalized autoimmune disease sharing many features and organ pathology with systemic lupus erythematosus (SLE). Such mice show bone loss and poor bone deposition, a condition known as “osteopenia.” Because mesenchymal stem cells are usually the cells in bone marrow that differentiate into osteoblasts (which make bone) a condition like osteopenia results from defective mesenchymal stem cell function.

In this paper, Shi and his coworkers and collaborators showed that the lack of the Fas protein in the mesenchymal stem cells from MRL/lpr mice prevents them from releasing a regulatory molecule called “miR-29b.” This regulatory molecule, mir-29b, is a small RNA molecule known as a microRNA. MicroRNAs regulate the expression of other genes, and the failure to release miR-29b increases the intracellular levels of miR-29b. This build-up in the levels of miR-29b causes the downregulation of an enzyme called “DNA methyltransferase 1” or Dnmt1. This is not surprising, since this is precisely what microRNAs do – they regulate genes. Dnmt1 attaches methyl groups (CH3 molecules) to the promoter or control regions of genes.

Decrease in the levels of Dnmt1 causes hypomethylation of the Notch1 promoter. When promoters are heavily methylated, genes are poorly expressed. When very methyl groups are attached to the promoters, then the gene has a greater chance of being highly expressed. Robust expression of the Notch1 genes activates Notch signaling. Increased Notch signaling leads to impaired bone production, since differentiation into bone-making cells requires mesenchymal stem cells to down-regulate Notch signaling.

When normal mesenchymal stem cells are transplanted into the bone marrow of MRL/lpr mice, they release small vesicles called exosomes that transfer the Fas protein to recipient MRL/lpr bone marrow mesenchymal stem cells. The presence of the Fas protein reduces intracellular levels of miR-29b, and this increases Dnmt1-mediated methylation of the Notch1 promoter. This decreases the expression of Notch1 and improves MRL/lpr BMMSC function.

fx1

These findings elucidate the means by which MSCT rescues MRL/lpr BMMSC function. Since MRL/lpr mice are a model system for lupus, it suggests that donor mesenchymal stem cell transplantation into lupus patients provides Fas protein to the defective, native mesenchymal stem cells, thereby regulating the miR-29b/Dnmt1/Notch epigenetic cascade that increases differentiation of mesenchymal stem cells into osteoblasts and bone deposition rates.

Genetically Engineered Stem Cells to Treat Osteoporosis in Mice


Osteoporosis is a nasty condition characterized by weak and brittle bones often leading to devastating bone fractures and other injuries. Unfortunately, millions of people worldwide have been diagnosed with osteoporosis.

Osteoporosis

Contrary to popular belief, out bones are dynamic organs that undergo constant remodeling consisting of bone resorption and renewal. However, once bone resorption rates outpace bone renewal, bone densities decrease, which puts bones at risk of fractures. Medical researchers are would like to find new ways to not only discourage bone resorption, but generate new bone material to replace demineralized bone. Ideally, therapies would rejuvenate bone growth so that it the bone reverts back to its original density levels.

Now a promising strategy to accomplish this goal is relies on stem cell therapy. A collaborative study by Xiao-Bing Zhang and his colleagues from Loma Linda University and Jerry L. Pettis from the Memorial VA Medical Center has built on their prior work with genetically modified hematopoietic stem cells (HSCs) that identified a growth factor that caused a 45% increase in bone strength in mouse models. This work was published in the journal Proceedings of the National Academy of Sciences, USA.

Zhang and his coworkers wanted to find a gene therapy that promotes bone growth while minimizing side effects. To that end, Zhang’s group focused on a growth factor called PGDFB or “platelet-derived growth factor, subunit B.” The properties of this growth factor make it a promising candidate, since it is already FDA approved for treating bone defects in the jaw and mouth.

platelet-derived growth factor, subunit B
platelet-derived growth factor, subunit B

First, Zhang and others isolated HSCs from the bone marrow of donor mice. HSCs were chosen because they can be given intravenously, after which they will home in to one of the major sites of bone loss (the endosteal bone surface). The isolated HSCs were then genetically engineered to overexpress the growth factor PGDFB. Experimental mice were then irradiated to wipe out their own HSCs, and then these same mice were transplanted with the modified HSCs.

After four weeks, the upper leg bones of the mice (femur) were tested. Zhang and his colleagues found that PGDFB promoted new trabecular bone formation, but because the PGDFB was expressed at high levels, it negatively affected bone mineral density. Zhang and others then used weaker promoters to optimize the dosage of PGDFB expression in the HSCs. They discovered that the phosphoglycerate kinase promoter (PGK) worked well to mitigate the amount of PGDFB that is expressed in cells. When these HSCs were transplanted into irradiated mice, they observed increases in trabecular bone volume, thickness, and number as well as increases in connectivity density. Additionally, cortical bone volume increased by 20-30% while cortical porosity was reduced by 40%. Importantly, the lower dosage of PGDFB resulted in no observed decreases in bone mineral density due to osteomalacia or hyperparathyroidism.

These treated femurs and a control sample underwent three-point mechanical testing to test the integrity of the new bone. The PGK-PGDFB-treated femur displayed a 45% increase in maximum load-to-failure in the midshaft of the femur and a 46% increase in stiffness, indicating quality bone formation. Thus the new bone that is deposited it also of high quality.

The next step in this work would like to determine why this combination of a PGK promotor and PDGFB worked so well. Zhang and others have discovered that PDGFB promotes bone marrow mesenchymal stem cell formation and angiogenesis, which are two important factors in bone growth. They also found that optimizing the dosage of PDGFB is quite important for promoting osteoblast (bone-forming) cell formation.

Finally Zhang’s group investigated how osteoclastogenesis, or the creation of cells that reabsorb bone (osteoclasts) is affected by PDGFB with a PGK promotor. The treated femurs also had an increase in biomarkers for osteoclasts. This increase in both osteoblasts and osteoclasts indicates that the treated bones undergo the normal bone rebuilding and remodeling cycle.

Overall, this research provides a compelling investigational pathway for future cell therapies to treat osteoporosis. Mouse models show a fast-acting technique that result in bone formation and increasing bone strength.

Stem Cell-Tweaking Drug Might Treat Osteoporosis


A research group from the Florida campus of The Scripps Research Institute (TSRI) has identified a new therapeutic approach that could promote the development of new bone-forming cells in patients suffering from bone loss.

The study was published in the journal Nature Communications, and it focused on a protein called PPARγ, which is a master regulator of fat, and the impact of this molecule on the fate of mesenchymal stem cells derived from bone marrow. Since these mesenchymal stem cells can differentiate into several different cell types, including fat, connective tissues, bone and cartilage. Consequently mesenchymal stem cells have a number of potentially important therapeutic applications.

A partial loss of PPARγ in a genetically modified mouse model led to increased bone formation. Could the use of drugs to inhibit PPARγ and potentially mimic that effect? This group combined a variety of structural biology approaches and then tried to design drugs that could fit PPARγ. This type of strategy is called “rational design,” and this yielded a new compound that could repress the biological activity of PPARγ.

The new drug, SR2595 (SR=Scripps Research), when applied to mesenchymal stem cells, significantly increased bone cell or osteoblast formation, a cell type known to form bone.

“These findings demonstrate for the first time a new therapeutic application for drugs targeting PPARy, which has been the focus of efforts to develop insulin sensitizers to treat type 2 diabetes,” said Patrick Griffin, chair of the Department of Molecular Therapeutics and director of the Translational Research Institute at Scripps Florida. “We have already demonstrated SR2595 has suitable properties for testing in mice; the next step is to perform an in-depth analysis of the drug’s efficacy in animal models of bone loss, aging, obesity and diabetes.”

In addition to identifying a new, potential therapeutic use for bone loss, this study may have even broader implications.

“Because PPARG is so closely related to several proteins with known roles in disease, we can potentially apply these structural insights to design new compounds for a variety of therapeutic applications,” said David P. Marciano, first author of the study, a recent graduate of TSRI’s PhD program and former member of the Griffin lab. “In addition, we now better understand how natural molecules in our bodies regulate metabolic and bone homeostasis, and how unwanted changes can underlie the pathogenesis of a disease.” Marciano will focus on this subject in his postdoctoral work in the Department of Genetics at Stanford University.

A Small RNA that Increases Bone Formation in Osteoporotic Bone-Making Cells


We normally think of bone as a very static tissue that does not change very much. However bone is actually a very dynamic tissue is constantly being remodeled in response to the needs of the organism. Bone remodeling is mediated by two different types of cells: osteoblasts that build bone and osteoclasts that resorb bone. Osteoblasts are derived from mesenchymal stem cells in the stroma of the bone marrow. The differentiation of mesenchymal stem cells into osteoblasts is mediated by molecules made by bone cells when bone is damaged. Osteoclasts come from pre-osteoclast cells that are monocyte-derived cells that fuse into multinucleate osteoclasts in response to the death of osteocytes (bone cells).

In healthy bone, osteocytes secrete a molecule called sclerostin, which prevents any new bone deposition. A break in bone causes the death of osteocytes near the site of the break, and the nearby osteocytes stop secreting sclerostin and start producing growth factors, nitric oxide and prostaglandins.

Bone deposition

The lining cells of the bone marrow cavity detach and fuse with blood vessels. The mesenchymal stromal cells, under influence from IL-1, become pre-osteoblasts, and they start to secrete M-CSF, which prepares the pre-osteoclasts to fuse and become multinucleate osteoclasts. Pre-osteoclasts then express a molecule called RANKL, which binds to the RANK receptor on the surface of pre-osteoclasts and this induces them to fuse, and become mature osteoclasts. The osteoclasts secrete acid and cathepsin K to dissolve the damaged bone. The osteoclasts stop eating bone when the pre-osteoblasts mature into full-fledged osteoblasts that stop making RANKL and start making OPG, which binds to RANK, but does not activate it. Without this stimulation, the osteoclasts die. Then the osteoblasts divide, fill the cavity made by the now-deceased osteoclasts, and remake the bone. Some of the osteoblasts become entrapped in the bone matrix and become osteocytes. The bone takes several months to remineralize and 3-4 years to completely remineralize.  See here for a video of this.

Bone resorption-deposition

If there is a relative increase in bone resportion relative to bone deposition, the result is fragile, poorly mineralized bones, and this condition is known as osteoporosis. Decreased bone mass and bone strength causes an increased incidence of bone fractures, which often leads to further disability and early mortality. Bone healing is also impaired.

To treat osteoporosis, clinicians usually prescribe anti-resorptive agents that exert their effect by decreasing the rate of bone resorption. This strategy, however, has drawbacks, since as noted above, bone deposition relies on bone resorption. Inhibition of bone resorption also inhibits bone deposition, and bone tends to remain static and heal poorly.

A new paper has examined osteoporosis from the perspective of osteoblasts. It has been well established that in osteoblasts function is diminished in osteoporotic patients. Therefore increase osteoblast function is of chief interest. Work from the laboratories of Jihua Chen and Yan Jin from the Fourth Medical University has shown that a miniature RNA molecule called miR-26a plays a critical role in modulating bone formation during osteoporosis. Chen and Jin and others discovered that miR-26a treatment of mesenchymal stem cells effectively improved the osteogenic differentiation capability of these mesenchymal stem cells. In these experiments, they isolated mesenchymal stem cells from female mice that had their ovaries removed. Such mice are prone to undergo osteoporosis because they lack the hormone estrogen that stimulates osteoblast function. When these stem cells were treated with MiR-26a, they increased their bone-making capacities by in culture and when injected into live mice.

Further work showed that MiR-26a directly targets a gene called Tob1. Tob1 negatively regulates the BMP/Smad signaling pathway, and MiR-26a binds to the rear mRNA (3′-untranslated region) of Tob1, and prevents Tob1 translation.

These findings indicate that miR-26a is a potentially promising therapeutic candidate to enhance bone formation in order to treat osteoporosis and to promote bone regeneration in osteoporotic fracture healing.

For the article, go here.

Stem Cell-Extracted Proteins Promote Bone Regrowth


Scientists from the Gladstone Institutes have found a new technique to regrow bone by using the protein signals produced by stem cells. This new technology could potentially help treat victims who have experienced major trauma to a limb, such as soldiers wounded in combat or casualties of a natural disaster. This new protocol improves older therapies by providing a sustainable source for fresh tissue that also reduces the risk of tumor formation that can arise with stem cell transplants.

This study was published in a journal called Scientific Reports, and it is the first study that successfully extracted bone-producing growth factors from stem cells and showed that these proteins are sufficient to create new bone. This stem cell-based approach was as effective as the current standard treatment in terms of the amount of bone created.

“This proof-of-principle work establishes a novel bone formation therapy that exploits the regenerative potential of stem cells,” says senior author Todd McDevitt, PhD, a senior investigator at the Gladstone Institutes. “With this technique, we can produce new tissue that is completely stem cell-derived and that performs similarly with the gold standard in the field.”

Rather than using stem cells, the Gladstone scientists extracted the proteins that the stem cells secrete, such as a protein called bone morphogenetic protein (BMP). By extracting these proteins, they hoped to harness their regenerative power. McDevitt and his colleagues treated stem cells with a chemical that helped drove them to begin to differentiate into early bone cells. Then they analyzed the secreted factors produced by these cells that signal to other cells to regenerate new tissue. Afterwards, they took these isolated proteins and injected then into mouse muscle tissue to facilitate new bone growth.

Currently, laboratory technicians grind up old bones and extract the available proteins and growth factors that can induce the growth of new bone. Unfortunately, this approach relies on bones taken from cadavers, which are highly variable when it comes to the quality of the available tissue and how much of the necessary signals they still produce. Also, cadaver tissue is not always available.

“These limitations motivate the need for more consistent and reproducible source material for tissue regeneration,” says Dr. McDevitt, who conducted the research while he was a professor at the Georgia Institute of Technology. “As a renewable resource that is both scalable and consistent in manufacturing, pluripotent stem cells are an ideal solution.”

Skull Suture Stem Cells Can Heal Birth Defect and Facial Injuries


A research group from the University of Southern California (USC) School of Dentistry have identified a new stem cell population that is responsible for a particular birth defect and might someday help treat wounded soldiers, accident victims and other patients recover from disfiguring facial injuries.

“This has a lot more implication than what we initially thought,” said Yang Chai, a lead researcher on the study at the Herman Ostrow School of Dentistry of USC. “We can take advantage of these stem cells not only to repair a birth defect, but to provide facial regeneration for veterans or other people who have suffered traumatic injury.”

According to Chai, treatments of human patients that utilize the new stem cell population he and his colleagues identified could become available within the next five to 10 years, but it must pass through the intense hurdles of clinical trials with human patients.

In their mouse studies, Chai and his team noticed a stem cell population that expresses the transcription factor Gli1+. These Gli1+ stem cells appear within the tissues that eventually fuse the craniofacial bones together. However, in mice that have a shortage or even absence of the Gli1+ stem cells, the skull bones prematurely fused together to cause “craniosynostosis,” a birth defect that locks the skull into a small structure can cannot accommodate the growing brain and can hinder brain development. Chai and his colleagues also found that these Gli+ stem cells are activated when the skull is injured. Therefore, they transplanted Gli1+ stem cells into injured mice, and within weeks, it was clear that the Gli1+ stem cells had migrated to the injured parts of the skull and were repairing those damaged areas.

“It is a very minimal procedure to just cut off a strip of bone instead of cutting the entire calvaria [skull-cap],” Chai said. A stem cell treatment “will truly restore the normal anatomy, which will then be able to respond to the continuous brain growth and the patient can live a normal life.”

These findings also have upset the bone development apple cart, according to Hu Zhao, the first author of this publication. “Before our findings, people just assumed the bones all around the body are the same,” Zhao said. “We are now showing that they are all totally different, that they have a different source of stem cells and a different healing mechanism.”

The discovery of these Gli1+ stem cells and their ability to regenerate craniofacial injuries might mean that physicians will be able to use them to treat people who have suffered disfiguring facial injuries and infants diagnosed with craniosynostosis through biological means instead of multiple, high-risk surgeries.

Presently, the surgeons, unknowingly, were destroying the regenerative stem cells that could potentially help the patient when they operated on craniosynostosis patients. During a typical craniosynostosis surgery, doctors break the skull into multiple pieces, staple them together and then discard the suture tissues as waste. Zhao said the procedure, intended to aid brain growth, actually interferes with healing because the Gli1+ stem cells are lost.

According to Chai, a biological approach that transplants Gli1+ stem cells into targeted areas could give infants with craniosynostosis the flexibility that they need for their brains to grow normally. For those patients who have suffered head trauma or facial disfigurement, the Gli1+ stem cells could repair fractured or injured areas.

Chai acknowledges the need to conduct additional experiments before such a treatment is tested in clinical trials with patients.

“One of our ideas is that we could probably use those healthy sutures and the healthy pieces from them and transplant them on the injured sides,” Zhao said.

New Bone Marrow-Based Stem Cell Identified in Mice that Regenerates Bones and Cartilage in Adults


Researchers at Columbia University Medical Center (CUMC) have discovered a bone marrow-based stem cell capable of regenerating both bone and cartilage in mice. The discovery appeared in the online issue of the journal Cell.

These cells have been called osteochondroreticular (OCR) stem cells, and they were identified in experiments that tracked a protein expressed by these cells. By using this specific protein as a marker for OCR stem cells, the Columbia team found that OCR cells self-renew and produce key bone and cartilage cells, including osteoblasts and chondrocytes. Furthermore, when OCR stem cells are transplanted to a fracture site, they dutifully contribute to bone repair.

“We are now trying to figure out whether we can persuade these cells to specifically regenerate after injury. If you make a fracture in the mouse, these cells will come alive again, generate both bone and cartilage in the mouse—and repair the fracture. The question is, could this happen in humans,” says Siddhartha Mukherjee, MD, PhD, assistant professor of medicine at CUMC and a senior author of the study.

Since mice and humans have similar bone biology, Mukherjee and his colleagues are quite confident that OCR stem cells exist in human bone marrow. Further studies could uncover new and effective ways to exploit OCR cells to provide greater ways to prevent and treat osteoporosis, osteoarthritis, or bone fractures.

“Our findings raise the possibility that drugs or other therapies can be developed to stimulate the production of OCR stem cells and improve the body’s ability to repair bone injury—a process that declines significantly in old age,” says Timothy C. Wang, MD, the Dorothy L. and Daniel H. Silberberg Professor of Medicine at CUMC, who initiated this research. Wang and his team previously found an analogous stem cell in the intestinal tract and observed that it was also abundant in the bone.

“These cells are particularly active during development, but they also increase in number in adulthood after bone injury,” says Gerard Karsenty, MD, PhD, the Paul A. Marks Professor of Genetics and Development, chair of the Department of Genetics & Development, and a member of the research team.

Mukherjee and his coworkers also showed that adult OCR stem cells are distinct from mesenchymal stem cells (MSCs). MSCs play essential roles in bone generation during development and adulthood. Therefore, researchers thought that MSCs gave rise to all bone, cartilage, and fat, but recent studies have shown that MSCs do not generate young bone and cartilage. This study by Mukherjee and his colleagues suggests that OCR stem cells actually make young bone and cartilage, but both OCR stems cells and MSCs contribute to bone maintenance and repair in adults.

Mukherjee also suspects that OCR cells may play a role in soft tissue cancers.

A research team from Stanford University School of Medicine just released a similar study that used a different methodology to identify the same stem cell type.

Bone Progenitor Cells Discovered – Might Help Children Who Need Corective Facial Surgery


In children, bone grow thicker and longer and get stronger and denser. When children reach adolescence, they know that the time has come to stop growing longer and stronger. However, even into adulthood, bones still retain the capacity to heal. Why the differences between adolescents and adults? This is a question that has long fed the imaginations of scientists.

Recently, a collaborative team of biomedical researchers from the University of Michigan, Kyoto University and Harvard University has made the answer to this question a little clearer.

Dr. Noriaki Ono, U-M assistant professor of dentistry, and his collaborators discovered that a certain subset of cartilage-making cells – cells known as chondrocytes – proliferate and differentiate into other bone cells that drive bone growth. These discoveries could lead to new treatments for children with facial deformities who normally have to wait until adulthood for corrective surgery. This study appeared in the journal Nature Cell Biology.

A long-held view is that bone-making chondrocytes die once children reach adolescence and their bones stop growing. However, in adults, bone still heal without the benefit of these bone-making chondrocytes. How does this occur? This question has generated a fair amount of disagreement between researchers.

Ono’s group discovered that some of these bone-making chondrocytes don’t die. Instead, they are transformed into other types of bone-growing and bone-healing cells.

“Up until now, the cells that drive this bone growth have not been understood very well. As an orthodontist myself, I have special interest in this aspect, especially for finding a cure for severe bone deformities of the face in children,” he said. “If we can find a way to make bones that continue to grow along with the child, maybe we would be able to put these pieces of growing bones back into children and make their faces look much better than they do.”

According to Ono, one of the challenges in bone and cartilage medicine is that resident stem cells haven’t really been identified. The only widely accepted idea is that certain stem cells like mesenchymal stem cells help bones heal and other help them grow, but the progenitor cells for these cell populations and what goes wrong with them in conditions such as osteoporosis remains mysterious.

Ono and his team used a technique called “fate mapping,” which labels cells genetically and them follows them throughout development. Ono and others came upon a specific precursor cell that gives rise to fetal chondrocytes, and all the other later bone-making cells and . By mesenchymal stromal cells later in life. Most exciting, Ono and his coworkers found a way to identify the cells responsible for growing bone. By identifying these cells, isolating them and even implanting them into the skull or long bones of a child with a bone deformity condition, the cells would make bone that would also grow with the child.

Many factors cause craniofacial deformities. These types of deformities can place pressure on the brain, eyes, or other structures and prevent them from developing normally. For example, children with Goldenhar syndrome have underdeveloped facial tissues that can harm the developing jawbone. Another bone deformity called deformational plagiocephaly causes a child’s head to grow asymmetrically. Maybe the implantation of such cells can provide a way to restart the abnormally growing bones in these children.

Bone-Making Ability of Amniotic Epithelial Cells


Human amniotic epithelial cells (hAECs) develop from the embryo as early as eight days after fertilization. hAECs have been shown to possess remarkable plasticity, or the ability to form many cell types. Mattioli and others showed that AECs from sheep have capacity to differentiate into bone cells (see Cell Biol Int 2012;36:7-19). Therefore, it is possible that these cells could be developed into a source of cells for regenerative treatments.

Steve Shen from the Shanghai Jiao Tong University School of Medicine and his coworkers have examined the ability of cultured hAECs to make bone in culture, and then applied their techniques to an animal system to test the ability of cultured hAECs to restore tooth sockets and facial bone.

To begin, hAECs were isolated from healthy mothers who had undergone childbirth by cesarean section. These cells were cultured in a standard cell culture medium (DMEM/F12 for those who are interested), expanded in culture, and then subjected to flow cytometry to isolate those cells with all the right cell surface markers.

These cells wee then placed into a specialized culture medium designed to convert mesenchymal stem cells into bone-making cells. This osteogenic induction medium was changed every three days for 21 days.  The figure below shows how well the bone-induction worked.  A red stain called alizarin red binds to calcium and therefore stains forming bone matrices rather well.  As you can see in the panel labeled “G” below, the hAECs grown in the osteogenic medium stain red rather well, which shows that they are making bone.

Characterization of hAECs in vitro. (A, B): hAECs at passages 0 and 1 displayed a cobblestone-like morphology. (C): Some hAECs changed into fibroblast-like cells after 7 days of osteoblastic culture. (D): hAECs showed significant morphological changes and settled on superimposed layers after 21 days of osteoblastic culture. (E): Cell proliferation of hAECs at passage 1 was significantly higher than at passages 0 and 5 from day 4 to day 12; hAECs at passage 5 displayed the lowest proliferation rate from day 6 to day 14 (☆, p < .05). (F): Flow cytometry analysis showed that hAECs expressed CD44, CD90, CD105, and SSEA-4 and did not express CD34, CD45, and HLA-DR. Values represent the percentages of all assessed cells positively stained by the indicated antigens (bottom of each graph). Nonspecific fluorescence was determined as the blank control using isotype-matched monoclonal antibodies (PE blank, FITC blank). (G): Representative images of microscopic and general photographs for ALP and ARS staining in osteogenic and control groups indicated the osteogenic differentiation of hAECs in vitro. Scale bar = 200 μm. Abbreviations: ALP, alkaline phosphatase; ARS, alizarin red S; FITC, fluorescein isothiocyanate; hAEC, human amniotic epithelial cell; OD, optical density; p, passage; PE, phycoerythrin.
Characterization of hAECs in vitro. (A, B): hAECs at passages 0 and 1 displayed a cobblestone-like morphology. (C): Some hAECs changed into fibroblast-like cells after 7 days of osteoblastic culture. (D): hAECs showed significant morphological changes and settled on superimposed layers after 21 days of osteoblastic culture. (E): Cell proliferation of hAECs at passage 1 was significantly higher than at passages 0 and 5 from day 4 to day 12; hAECs at passage 5 displayed the lowest proliferation rate from day 6 to day 14 (☆, p < .05). (F): Flow cytometry analysis showed that hAECs expressed CD44, CD90, CD105, and SSEA-4 and did not express CD34, CD45, and HLA-DR. Values represent the percentages of all assessed cells positively stained by the indicated antigens (bottom of each graph). Nonspecific fluorescence was determined as the blank control using isotype-matched monoclonal antibodies (PE blank, FITC blank). (G): Representative images of microscopic and general photographs for ALP and ARS staining in osteogenic and control groups indicated the osteogenic differentiation of hAECs in vitro. Scale bar = 200 μm. Abbreviations: ALP, alkaline phosphatase; ARS, alizarin red S; FITC, fluorescein isothiocyanate; hAEC, human amniotic epithelial cell; OD, optical density; p, passage; PE, phycoerythrin.

When hAECs were subjected to gene expression assays, it was clear that the cells grown in the osteogenic medium expressed a whole host of bone-specific genes.  Therefore, the formation of bone was not a fluke, since these cells not only concentrated calcium, but also increased their expression of bone-specific genes (these include osterix, Runx2, Alkaline phosphatase, Collagen I, and osteoprotegerin).

Additionally, those hAECs grown in osteogenic medium stopped forming sheets of cells and began to grow as individual cells.  This is an important transformation for the synthesis of bone because bone-making cells secrete a bone-specific protein matrix upon which calcium phosphate-based crystals deposit to form bone.  If the cells were organized in sheets, then bone deposition would not be possible.  When isolated from amniotic membranes, hAECs grow as sheets of cells that are known as epithelia.  In order to become bone-making cells, the hAECs must undergo an “epithelial-to-mesenchymal transformation” or EMT.  This requires turning on new genes and turning off others.  Gene expression assays of hAECs grown in the osteogenic medium, show extensive evidence of EMT.  For example, a protein called E-cadherin is essential for cells growing in sheets, because it helps cells stick to each other.  However, in hAECs grown in the osteogenic medium, E-cadherin expression was quite low.  Also, a protein called vimentin is highly expressed during EMT, and the hAECs grown in osteogenic medium showed high expression of vimentin.  Thus, these hAECs were undergoing all the necessary changes in order to become bone-making cells,, making all the right genes, and made bone in culture to boot.

This is certainly interesting, but can these hAECs repair bone in a living animal?  Shen’s group tried that very experiment.  The hAECs that were grown in the osteogenic medium were loaded on tricalcium phosphate scaffolds and implanted into rodents with tooth socket lesions.  Control animals were implanted with tricalcium phosphate scaffolds without cells.  The scaffold with cells significantly increased bone formation in the rodents, and showed much more infilling with mineralized tissue.  There was also extensive evidence of the formation of new vasculature and wandering cells called macrophages that are important for the degradation of the implanted scaffold required for new bone formation.  Tissue samples were examined 4 to 8 weeks after the implants were placed.

In vivo healing process in alveolar defect at 4 and 8 weeks postoperatively. (A): Representative three-dimensional micro-computed tomography (CT) reconstruction images of hAECs+β-TCP scaffold (EXP) and β-TCP scaffold (CTR) at 4 and 8 weeks postoperatively. Scale bar = 1 mm. (B): Micro-CT parameters acquired among β-TCP scaffold in vitro, hAECs+β-TCP scaffold in vivo, and β-TCP scaffold alone in vivo at 4 and 8 weeks postoperatively (☆, p < .05). (C): Hematoxylin and eosin staining of the rat alveolar defect at 4 and 8 weeks postoperatively revealed more active new bone formation in the EXP group than in the CTR group (×50 and ×200 magnification). Alveolar defect treated with hAECs+β-TCP scaffold exhibited a more mature lamellae-bone formation at 8 weeks postoperatively. Scale bar = 200 μm. (D): ANA-positive cells, visible as green fluorescence in the nuclei, were observed within the newly deposited OCN, and OPN-positive bone tissue, visible as red fluorescence, in the EXP group at 4 weeks postoperatively, indicating a mature osteoblastic function of these hAEC-derived cells. Scale bar = 50 μm. (E): Representative images of immunohistochemical staining of sections with anti-VEGF antibody and anti-CD68 antibody in hAECs+β-TCP scaffold (EXP) and β-TCP scaffold (CTR) at 4 and 8 weeks postoperatively. Scale bar = 200 μm. (F): The histomorphometric quantification of the relative new bone area, VEGF-positive area, and CD68-positive area showed that more bone tissue regeneration was observed in the EXP group than in the CTR group at 4 and 8 weeks postoperatively. The positive signal of VEGF and CD68 in the EXP group was much weaker at 4 weeks postoperatively and became more intense at 8 weeks postoperatively compared with the CTR group (☆, p < .05). Abbreviations: ANA, anti-nuclear antibody; BV/TV, bone volume/tissue volume ratio; BMD, bone mineralization density; hAECs, human amniotic epithelial cells; OPN, osteopontin; post op, postoperatively; SMI, structure model index; Tb.Th., trabecular thickness; Tb.N., trabecular number; Tb.Sp., trabecular separation; β-TCP, β-tricalcium phosphate; VEGF, vascular endothelial growth factor.
In vivo healing process in alveolar defect at 4 and 8 weeks postoperatively. (A): Representative three-dimensional micro-computed tomography (CT) reconstruction images of hAECs+β-TCP scaffold (EXP) and β-TCP scaffold (CTR) at 4 and 8 weeks postoperatively. Scale bar = 1 mm. (B): Micro-CT parameters acquired among β-TCP scaffold in vitro, hAECs+β-TCP scaffold in vivo, and β-TCP scaffold alone in vivo at 4 and 8 weeks postoperatively (☆, p < .05). (C): Hematoxylin and eosin staining of the rat alveolar defect at 4 and 8 weeks postoperatively revealed more active new bone formation in the EXP group than in the CTR group (×50 and ×200 magnification). Alveolar defect treated with hAECs+β-TCP scaffold exhibited a more mature lamellae-bone formation at 8 weeks postoperatively. Scale bar = 200 μm. (D): ANA-positive cells, visible as green fluorescence in the nuclei, were observed within the newly deposited OCN, and OPN-positive bone tissue, visible as red fluorescence, in the EXP group at 4 weeks postoperatively, indicating a mature osteoblastic function of these hAEC-derived cells. Scale bar = 50 μm. (E): Representative images of immunohistochemical staining of sections with anti-VEGF antibody and anti-CD68 antibody in hAECs+β-TCP scaffold (EXP) and β-TCP scaffold (CTR) at 4 and 8 weeks postoperatively. Scale bar = 200 μm. (F): The histomorphometric quantification of the relative new bone area, VEGF-positive area, and CD68-positive area showed that more bone tissue regeneration was observed in the EXP group than in the CTR group at 4 and 8 weeks postoperatively. The positive signal of VEGF and CD68 in the EXP group was much weaker at 4 weeks postoperatively and became more intense at 8 weeks postoperatively compared with the CTR group (☆, p < .05). Abbreviations: ANA, anti-nuclear antibody; BV/TV, bone volume/tissue volume ratio; BMD, bone mineralization density; hAECs, human amniotic epithelial cells; OPN, osteopontin; post op, postoperatively; SMI, structure model index; Tb.Th., trabecular thickness; Tb.N., trabecular number; Tb.Sp., trabecular separation; β-TCP, β-tricalcium phosphate; VEGF, vascular endothelial growth factor.

hAECs are typically not recognized by the immune system as foreign and they also have anti-scarring capabilities.  Not only can they effectively form bone in culture, but they can also repair an alveolar defect in a rodent model.  Clearly these cells show promise for clinical applications.  However, before they can be used in the clinic more has to be known about their culture conditions, how many cells are required for transplantation, the best cell dose, at what passages they need to be used, and so on.  Thus, this paper represents a good start for hAECs, but they have to be better understood before they can come to the clinic.