Severe wounds are typically treated with full thickness skin grafts. Some new work by researchers from Michigan Tech and the First Affiliated Hospital of Sun Yat Sen University in Guangzhou, China might provide a way to use a patient’s own stem cells to make split thickness skin grafts (STSG). If this technique pans out, it would eliminate the needs for donors and could work well for large or complicated injury sites.
This work made new engineered tissues were able to capitalize on the body’s natural healing power. Dr. Feng Zhao at Michigan Tech and her Chinese colleagues used specially engineered skin that was “prevascularized, which is to say that Zhao and other designed it so that it could grow its own veins, capillaries and lymphatic channels.
This innovation is a very important one because on of the main reasons grafted tissues or implanted fabricated tissues fail to integrate into the recipient’s body is that the grafted tissue lacks proper vascular support. This leads to a condition called graft ischemia. Therefore, getting the skin to form its own vasculature is vital for the success of STSG.
STSG is a rather versatile procedure that can be used under unfavorable conditions, as in the case of patients who have a wound that has been infected, or in cases where the graft site possess less vasculature, where the chances of a full thickness skin graft successfully integrating would be rather low. Unfortunately, STSGs are more fragile than full thickness skin grafts and can contract significantly during the healing process.
In order to solve the problem of graft contraction and poor vascularization, Zhao and others grew sheets of human mesenchymal stem cells (MSCs) and mixed in with those MSCs, human umbilical cord vascular endothelial cells or HUVECs. HUVECs readily form blood vessels when induced, and growing mesenchymal stem cells tend to synthesize the right cocktail of factors to induce HUVECs to form blood vessels. Therefore this type of skin is truly poised to form its own vasculature and is rightly designated as “prevascularized” tissue.
Zhao and others tested their MSC/HUVEC sheets on the tails of mice that had lost some of their skin because of burns. The prevascularized MSC/HUVEC sheets significantly outperformed MSC-only sheets when it came to repairing the skin of these laboratory mice.
When implanted, the MSC/HUVEC sheets produced less contracted and puckered skin, lower amounts of inflammation, a thinner outer skin (epidermal) thickness along with more robust blood microcirculation in the skin tissue. And if that wasn’t enough, the MSC/HUVEC sheets also preserved skin-specific features like hair follicles and oil glands.
The success of the mixed MSC/HUVEC cell sheets was almost certainly due to the elevated levels of growth factors and small, signaling proteins called cytokines in the prevascularized stem cell sheets that stimulated significant healing in surrounding tissue. The greatest challenge regarding this method is that both STSG and the stem cell sheets are fragile and difficult to harvest.
An important next step in this research is to improve the mechanical properties of the cell sheets and devise new techniques to harvest these cells more easily.
According to Dr. Zhao: “The engineered stem cell sheet will overcome the limitation of current treatments for extensive and severe wounds, such as for acute burn injuries, and significantly improve the quality of life for patients suffering from burns.”
This paper can be found here: Lei Chen et al., “Pre-vascularization Enhances Therapeutic Effects of Human Mesenchymal Stem Cell Sheets in Full Thickness Skin Wound Re-pair,” Theranostics, October 2016 DOI: 10.7150/ thno.17031.
As we age, the capacity of our stem cells to heal and replace damaged cells and tissues decline. This age-associated decrease in adult stem cell function seems to be a major contributor to the physiological decline during aging. A new paper, by Efstathios Gonos and his colleagues at the National Hellenic Research Foundation in Athens, Greece gives one possible technique that might improve the function of stem cells in an aging body.
Cells contain a multiprotein complex called the “proteasome” that degrades unneeded or defective proteins. The proteasome controls protein half-lives, function, and the protein composition of the cell. Functional failure of the proteasome has been linked to various biological phenomena including senescence and aging. The role of the proteasome in stem cells aging, however has received little attention to date.
Gonos and his coworkers used mesenchymal stem cells from umbilical cord Wharton’s Jelly and human fat. Because they were able to compare the proteasome activity in very young and aged stem cells, Gonos and others discovered a significant age-related decline in proteasome content and activity between these two types of stem cells. The proteasome from Warton’s Jelly mesenchymal stem cells were consistently more active and displayed more normal function and activity than those from human fat. In fact, not only were the protease activities of the proteasomes from the aging stem cells decreased, but they also displayed structural alterations.
These differences in proteasomal activity were not only reproducible, but when the proteasome of young stem cells were compromised, the “stemness,” or capacity of the stem cells to act as undifferentiated cells, was negatively affected.
Even more surprisingly, once after mesenchymal stem cells from human donors lost their ability to proliferate and act as stem cells (their stemness, that is) their decline could be counteracted by artificially activating their proteasomes. Activating the proteasome seems to help the cell “clean house,” get rid of junk proteins, and rejuvenate themselves.
Gonos and his team found that the stem cell-specific protein, Oct4, binds to the promoter region of the genes that encode the β2 and β5 proteasome subunits. Oct4 might very well regulate the expression of these proteasome-specific genes.
From this paper, it seems that a better understanding the mechanisms regulating protein turnover in stem cells might bring forth a way to stem cell-based interventions that can improve health during old age and lifespan.
Dr. Ronald J. Buckanovich, professor of hematology/oncology and gynecologic oncology at the University of Michigan Medical School, and his colleagues have identified a protein that help ovarian cancer cells multiply and spread to other organs. When he and his coworkers inhibited this protein with an antibody they were able to stop the spread of ovarian cancer cold.
The EGFL6 or epidermal growth factor like 6 precursor protein, which is also known as MAEG, maps to human Xp22 chromosome. The EGFL6 protein is expressed primarily in fetal tissues and during early development (see YeungG., et al., (1999) Genomics 62, 304–307; and BuchnerG., et al., (2000) Genomics 65, 16–23). The expression of MAEG has also been detected in several tissues, including the dermis of the trunk, hair follicles, and the mesenchyme of the cranio-facial region (see BuchnerG., and others, (2000) Mech. Dev. 98, 179–182). EGFL6 protein has been proposed as a possible biomarker in ovarian cancer (BuckanovichR. J., and others, (2007) J. Clin. Oncol. 25, 852–861).
In this paper, which appeared in Cancer Research, Buckanovich and others amplified the expression of EGFL6 in ovarian cancer cells. Increased EGFL6 expression stimulated cancer growth some two-three times. This effect was observed in cultured ovarian cancer cells and in a mouse model of ovarian cancer. Conversely, elimination of EGFL6 greatly reduced ovarian cancer growth, decreasing the rate of growth some four-fold.
EGFL6 specifically acts in cancer stem cells. To review, in tumors, not all cancer cells are the same. Inside malignant tumors or even among circulating cancerous cells (as in the case of leukemia) there are usually a variety of different types of cancer cells. The stem cell theory of cancer proposes that among cancerous cells, a small population among them act as stem cells that reproduce themselves and sustain the cancer. Cancer stem cells, therefore, are like normal stem cells that renew and sustain our organs and tissues. Therefore, cancer cells that are not stem cells can certainly adversely affect health, but they cannot sustain the cancer long-term. Therefore, cancer stem cells fuel the growth and spread of cancers and also are often resistant to chemotherapy and radiation treatments.
Further experiments by Buckanovich and his colleagues showed that EGFL6 cause cancer stem cells to divide asymmetrically so that the one of the daughter cells remains a cancer stem cell while the other daughter cell is a cancer cell that can affect the patient but cannot sustain the cancer. This asymmetric cell division also generates a good deal of diversity among cancer cells.
Buckanovich noted: “What this means is that the stem cell population remains stable. But the daughter cells, which can have a burst of growth, multiply, and allow the cancer to grow.”.
EGFL6 does more than just promote cancer cell proliferation. EGFL6 is also a promoter of cancer stem cell migration. When blood vessels were engineered to express EGFL6, tumor metastasis (spread) was even more robust.
Treatment of tumor-afflicted mice with an antibody that specifically binds to EGFL6 and inactivates it caused a 35% reduction in cancer stem cells and significantly reduced overall tumor growth. Additionally, the antibody also prevented tumor metastasis.
Buckanovich thinks that targeting EGFL6 might be a potential therapy for women with stage 3 ovarian cancer. Such a treatment might control the growth and spread of ovarian cancers.
Dr. Buckanovich added: “The bigger implication is for women at high risk of ovarian cancer. These patients could be treated before cancer develops, potentially blocking cancer from developing or preventing it from spreading. If cancer did develop, it could be diagnosed at an early stage, which would improve patient outcomes.”.
The next step for Buckanovich and his colleagues is developing an antibody that can properly work in human cancer patients.
Stress urinary incontinence affects 25%-50% of the female population and is defined as the leakage of the bladder upon exertion. The exertions that can cause the bladder to leak can be as simple as laughing, coughing, sneezing, hiccups, yelling, or even jumping up and down. Stress urinary incontinence costs Americans some $12 billion a year and also causes a good deal of embarrassment and compromises quality of life. Unsurprisingly, stress urinary incontinence also is associated with an increased incidence of anxiety, stress, and depression.
In most cases of stress urinary incontinence, injury to the internal sphincter muscles of the urethra or to the nerves that innervate these muscles (both smooth and voluntary muscles) significantly contribute to the condition. Conservative management of stress urinary incontinence can work at first, but can fail later on. The other option is corrective surgery that reconstructs the urethral sphincter and increases urethral support. However, even though such surgeries can and often do work, recurrence of the incontinence is rather common. Is there a better way?
Yan Wen from Stanford University School of Medicine and colleagues and collaborators from College of Medicine of Case Western Reserve in Cleveland, Ohio, Southern Medical University in Guangzhou, China, and Montana State University have used a novel stem cell-based technique to treat laboratory Rowett nude rats that had a surgically-induced form of stress urinary incontinence. While the results are not overwhelming, they suggest that a stem cell-based approach might be a step in the right direction.
Wen and others used a human embryonic stem cell line called H9 and two different types of induced pluripotent stem cell lines to make, in culture, human smooth muscle progenitor cells (pSMCs). Fortunately, protocols for differentiating pluripotent stem cells into smooth muscle cells is well worked out and rather well understood. These pSMCs were also tagged with a firefly luciferase gene that allowed visualization of the cells after implantation.
Six groups of rats were treated in various ways. The first group had stress urinary incontinence and were only treated with saline solutions. The second group of animals also had stress urinary incontinence and were treated with cultured human pSMCs that were derived from human bladders. The third group of animals also had stress urinary incontinence and were treated with pSMCs made from H9 human embryonic stem cells. The next two groups also had stress urinary incontinence and were treated with two different induced pluripotent stem cell lines; one of which was induced with a retroviral vector and the second of which was made with episomal DNA. Both lines were originally derived from dermal fibroblasts. The final group of rats did not have stress urinary incontinence and were used as a control group.
The cells were introduced into the mice by means of injections into the urethra under anesthesia. Two million cells were introduced in each case, three weeks after the induction of stress urinary incontinence. All animals were examined five weeks after the cells were injected into the animals.
Because the cells were tagged with firefly luciferase, the animals could be given an injection of luciferin, which is the substrate for luciferase. Luciferase catalyzes a reaction with luciferin, and the cells glow. This glow is easily detected by means of a machine called the Xenogen Imaging System. Such experiments showed that the injected cells did not survive terribly well, and by 9 days after the injections, they were usually not detectable. Two rats that had been injected with retrovirally-induced induced pluripotent stem cell-derived pSMCs lasted until 35 days after injection, but these rats were the exception and not the rule.
Did the cells integrate into the urethral sphincter by the signal is too low to be detected using luciferase? The answer to this question was certainly yes, but the amount of integration was nothing to write home about. Small patches of cells showed up in the urethra sphincters that expressed human gene products, and therefore, had to be derived from the injected cells.
The exciting part about these results, however, was that when Wen and others examined the rat urethral sphincters for the presence of things like elastin and other proteins that make for a healthy urethral sphincter, there was a good deal of elastin, but it was not human elastin but rat elastin. Therefore, this elastin synthesis was INDUCED by the implanted cells even though it was not made by the implanted cells. Instead, the implanted cells seemed to signal to the native cells to beef up their own production of sphincter-specific gene products, which made from a better sphincter. This was not the case in animals that received injections of human pSMCs derived from human bladders.
Because these mice were sacrificed five weeks after the injections, Wen and others could not assess the urethral function of these animals. Therefore, it is uncertain if the improved tissue architecture of the urethral sphincter properly translated into improved function even though it is reasonable to assume that it would. Having said that, it is possible that the experiments that detected the presence of increased amounts of elastin and collagen in the sphincters of these rats was complicated by the presence of bladder tissue in the preparations. Since bladder tissue was included in all trials of this experiment, it is unlikely that bladder tissue is the sole cause of increase elastin and collagen in the stem cell-treated rats. Secondly, rat regenerative properties may not properly match the regenerative properties in older human patients. Here again, unless such an experiment is attempted in larger animal models and then in human patients, we will never know if this procedure is viable for regenerative treatments in the future.
For now, it is an interesting observation, and perhaps a promising start to might someday become a viable regenerative treatment for human patients.
Bone marrow-derived mesenchymal stem cells (MSCs) can be induced to make cartilage by incubating the cells with particular growth factors. Unfortunately, batches of MSCs show respectable variability from patient-to-patient. Therefore the growth factor-dependent method suffers from poor efficacy, limited reproducibility from batch-to-batch, and the cell types that are induced are not always terribly stable. Finding a better way to make cartilage would certainly be a welcome addition to regenerative treatments,
Cartilage that coats the ends of bones is known as articulate cartilage, and articular cartilage lacks blood vessels. Therefore, is it possible that inhibiting blood vessel formation could conveniently push MSCs to differentiate into cartilage-making chondrocytes?
A new paper by Ivan Martin and Andrea Basil from the University Hospital Basel and their colleagues have used this very strategy to induce cartilage formation in MSCs from bone marrow.
Martin and others isolated MSCs from bone marrow aspirates from human donors. These cultured human MSCs were then genetically engineered with modified viruses to express a receptor for soluble vascular endothelial growth factor (VEGF) that binds this growth factor, but fails to induce any intracellular signals. Such a receptor that binds the growth factor but does not induce any biological effects is called a “decoy receptor,” and decoy receptors efficiently sequester or vacuum up all the endogenous VEGF. VEGF is the major blood vessel-inducing growth factor and it is heavily expressed during development, by cancer cells, and during healing.
After expressing the decoy VEGF receptor in these human MSCs, these genetically engineered cells were grown on collagen sponges and then implanted in immunodeficient mice. If the implanted MSCs were not genetically engineered to express decoy VEGF receptors, they induced for formation of vascularized fibrous tissue. However, the implantation of genetically engineered MSCs that expressed the decoy VEGF receptor efficiently and reproducibly differentiated into chondrocytes and formed hyaline cartilage. This is significant because headline cartilage is the very type of cartilage found at articular surfaces where the ends of bones come together to form joints.
This articular cartilage was quite stable and showed no signs of undergoing the chondrocytes enlargement found in terminally differentiated cartilage that is ready to form bone. This stability was maintained for up to 12 weeks.
Why did inhibition of VEGF signaling induce cartilage? Inhibition of angiogenesis induced low oxygen tensions, which activated a growth factor called transforming growth factor-β. Activation of the TGF-beta pathway robustly enhanced the formation of articular cartilage.
Cartilage formation from MSCs was induced by blocking VEGF-mediated angiogenesis. These results represent a remarkable advance in cartilage formation that can be used for regenerative treatments. This cartilage formation was spontaneous and efficient and if it can be carried out with VEGF-inhibiting drugs rather than genetic engineering techniques, then we might have a transferable technique for making cartilage in the laboratory to treat osteoarthritis and other joint-based maladies. Clinical trials will be required, but this is certainly an auspicious start.
It has been over ten years since the development of cultured skin substitutes or CSSs. CSSs consist of cultured epidermis from the patients and dermal fibroblasts that can form a good epidermal layer. However, CSSs do not form hair follicles or sebaceous glands which makes for mighty dry skin. Therefore, it is highly preferable to make at skin substitute that can form such epidermal appendages.
Fortunately the skin possesses several types of stem cells for use in regenerative medicine. Epidermal stem cells (Epi-SCs) in the basal layer of the epidermis that constantly provide new cells to the epidermis (the uppermost layer of the skin). Unfortunately, adult Epi-SCs cannot form hair follicles, but they can if they are combined with embryonic or newborn dermal cells. Dermal papilla (DP) cells can induce hair follicles, but the availability of DP cells has greatly limited work with them. Adult dermal skin also contains multipotent SKPs or skin-derived precursors. Injection of SKPs underneath the skin of mice, leads to the induction of new hair follicles (Biernaskie et al., 2009, Cell Stem Cell 5:610-623). This suggests that SKPs might be applicable in a clinical setting to induce hair follicles in cultured skin substitutes.
A new paper by Yaojiong Wu and coworker from the Shenzhen Key Laboratory of Health Sciences and Technology, in collaboration with Edward E. Tredget from University College Dublin has successfully induced the growth of hair follicles and sebaceous glands in a cultured skin substitute. They combined cultured Epi-SCs and SKPs, from mice and humans, and embedded them into a hydrogel. These stem cell-embedded hydrogels were then implanted into immunodeficient mice with substantial skin wounds.
The results were remarkable. The implants able to induce the formation of new epidermis with hair follicles. Furthermore, when Epi-SCs and SKPs taken from human scalps were used in these experiments, they worked just as well as those taken from mice.
Additionally, when the ability of Epi-SCs to differentiate into sebaceous glands was examined, Wu and others showed that Epi-SCs can form the precursors to sebaceous glands, sebocytes. Additionally, the oils secreted by these Epi-SC-derived sebocytes were chemically similar to sebaceous glands from native skin.
Thus, a combination of Epi-SCs and SKPs from human or mouse skin were sufficient to generate newly formed hair follicles and functional sebaceous glands. These results provide knowledge that is potentially transferable to clinical applications for regenerating damaged skin.
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.
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.
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.