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.

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.

Bone Therapeutics Cleared to Test ALLOB in Spinal Fusion Trial

Bone Therapeutics is a biotechnology company that specializes in regenerative therapies for orthopaedic conditions. Founded in 2006, Bone Therapeutics is headquartered in Gosselies, Belgium. One of the products developed by Bone Therapeutics is called ALLOB, which is a bone making (osteoblastic) cell product that has the ability to regenerate bone, and has been developed for the treatment of bone diseases. ALLOB is meant to be an off-the-shelf product that can be used to treat patients with various types of bone diseases.

Bone Therapeutics has recently announced that it has received approval from the Belgium regulatory agencies for a phase II proof-of-concept study to assess the safety and efficacy of ALLOB in spinal fusion procedures that are commonly used to treat degenerative lumbar disc disease. The hope is that this clinical trial will demonstrate that ALLOB improves spinal fusion surgery outcomes. Bone Therapeutics hopes to market ALLOB as an off-the-shelf treatment for spinal fusion surgery.

In previous studies, ALLOB has shown that it can enhance bone formation, and that it is a safe product in laboratory animals. Currently ALLOB is being evaluated in a phase I/IIa trial for delayed-union fractures. This is a pilot proof-of-concept study that examines 16 patients with symptomatic degenerative lumbar disc disease, all of whom require interbody vertebral fusion. These patients will be treated with a single dose of ALLOB mixed with bioceramic granules to promote bone formation and fusion at the within the degenerative discs. The bioceramic scaffold in this trials promotes bone formation by guiding bone growth in three dimensions and restoring a healthy bone environment. Patients will be enrolled in this trial at four different centres. The safety and efficacy of the treatment will be monitored over 12 months by clinical and radiological means. Additionally, there will be a 24-month post-study follow-up.

Back pain is a widespread medical disorder in industrialized societies that sometimes requires spinal surgery. Around 1.3 million spinal fusions are performed each year in Europe and the USA, the majority of which are to address degenerative lumbar disc disease. Despite the frequency of this surgery, non-union of bone and persistent pain following the intervention is still somewhat common. Further improvements to this procedure would be most welcome to patients and medical practitioners alike.

Enrico Bastianelli, CEO of Bone Therapeutics commented, “This new clinical trial clearance from the Competent Authorities in Belgium is an important milestone in the development of ALLOB® and further validates Bone Therapeutics’ clinical, regulatory and manufacturing capabilities.”

Synthetic Matrices that Induce Stem Cell-Mediated Bone Formation

Biomimetic matrices resemble living structures even though they are made from synthetic materials. Researchers in the laboratory of Shyni Varghese at the UC San Diego Jacobs School of Engineering have used calcium phosphate to direct mesenchymal stem cells to form bone. In doing so, Varghese and his colleagues have identified a surprising pathway from biomaterials to bone.

Varghese and his colleagues think that their work may point out new targets for treating bone defects, such as major fractures, and bone metabolic disorders such as osteoporosis.

The first goal of this research was to use materials to build something that looked like bone. This way, stem cells harvested from bone marrow (the squishy stuff inside our bones) could sense the presence of bone and differentiate into osteoblasts, the cells in our bodies that build bone.

“We knew for years that calcium phosphate-based materials promote osteogenic differentiation of stem cells, but none of use knew why.” said Varghese. “As engineers, we want to build something that is reproducible and consistent, so we need to know how building factors contribute to this end.”

Varghese and co-workers discovered that phosphate ions dissolved from calcium phosphate-based materials and these stray phosphate ions are taken up by the stem cells and used for the production of adenosine triphosphate or ATP. ATP is the energy currency of the cell, and it is the way cells store energy in a form that is readily usable for powering other reactions.

In stem cells, the generation of ATP eventually increases the intracellular concentration of the ATP breakdown product adenosine, and adenosine signals to stem cells to differentiate into osteoblasts and make bone.

Varghese said that she was surprised that “the biomaterials were connected to metabolic pathways. And we didn’t know how these metabolic pathways could influence stem cells,” and their commitment to bone formation.

These results also explain another clinical observation. Plastic surgeons have been using fat-based stem cells for eyelid lifts, breast augmentation, and other types of reconstructive surgeries. In once case, a plastic surgeon injected a dermal filler that contained calcium hydroxyapatite with the fat-based stem cells into a woman’s eyelid to provide an eye lift. However, the stem cells formed bone, and the poor lady’s lid painfully clicked every time she blinked and she had to have surgery to remove the ectopic bone. These results from Varghese’s laboratory explains why these fat-based stem cells formed bone in this case, and great care should be taken to never use such fillers in fat-based transplantation procedures.

Artificial Bones From Umbilical Cord Stem Cells

I am back from vacation. We visited some colleges in Indiana for my daughter who will be a senior this year. She really liked Taylor University and Anderson University. We’ll see if the tuition exchange works out.

Now to blogging.

Scientists from Granada, Spain have patented a hew biomaterial that consists of activated carbon cloth that just happens to be able to support the growth of cells that have the ability to regenerate bone. These results came from experiments that were conducted outside any living animals, but they hope to confirm these results in a living animal in the near future.

This new biomaterial facilitates the growth of bone-making cells derived from umbilical cord stem cells. This activated carbon cloth acts as a scaffold for cells that differentiate into “osteoblasts,” which are bone-building cells. This activated carbon cloth gives the osteoblasts a proper surface upon which to promote the growth of new bone.

Bone loss as a result of cancer, trauma, or degenerative bone diseases requires replacement bone to heal to damaged bone. Making new bone in the laboratory that can be transplanted is an optimal strategy for treating these patients.

Even though this laboratory-made bone was not used in living laboratory animals to date, the laboratory results look quite impressive. In the future, such techniques could help manufacture medicines or other sources of material to repair bone or lost cartilage. Once such artificial bone has been made in the laboratory, the Spanish team hopes to transplant it into rats or rabbits to determine if it can regenerate bone in such creatures.

Presently, no materials exist to replace lost bone. The method used to make bone by the research team from Granada uses a three-dimensional support that facilitates the production of those cell types that regenerate bone without the need for additional growth factors.

The growth of these umbilical cord stem cells on activated carbon cloth produced a product that could produce organic bone, but also mineralize the organic bone matrix. This patent could have numerous clinical applications in regenerative medicine and the Granada group hopes to obtain funding to continue this work and achieve their ultimate objective: to regenerate bones by implanting biomaterial in patients with bone diseases.