David Atashroo

Aging disrupts cell subpopulation dynamics and diminishes the function of mesenchymal stem cells

Advanced age is associated with an increased risk of vascular morbidity, attributable in part to impairments in new blood vessel formation. Mesenchymal stem cells (MSCs) have previously been shown to play an important role in neovascularization and deficiencies in these cells have been described in aged patients. Here we utilize single cell transcriptional analysis to determine the effect of aging on MSC population dynamics. We identify an age-related depletion of a subpopulation of MSCs characterized by a pro-vascular transcriptional profile. Supporting this finding, we demonstrate that aged MSCs are also significantly compromised in their ability to support vascular network formation in vitro and in vivo. Finally, aged MSCs are unable to rescue age-associated impairments in cutaneous wound healing. Taken together, these data suggest that age-related changes in MSC population dynamics result in impaired therapeutic potential of aged progenitor cells. These findings have critical implications for therapeutic cell source decisions (autologous versus allogeneic) and indicate the necessity of strategies to improve functionality of aged MSCs.

Biomaterials for Craniofacial Bone Engineering

Conditions such as congenital anomalies, cancers, and trauma can all result in devastating deficits of bone in the craniofacial skeleton. This can lead to significant alteration in function and appearance that may have significant implications for patients. In addition, large bone defects in this area can pose serious clinical dilemmas, which prove difficult to remedy, even with current gold standard surgical treatments. The craniofacial skeleton is complex and serves important functional demands. The necessity to develop new approaches for craniofacial reconstruction arises from the fact that traditional therapeutic modalities, such as autologous bone grafting, present myriad limitations and carry with them the potential for significant complications. While the optimal bone construct for tissue regeneration remains to be elucidated, much progress has been made in the past decade. Advances in tissue engineering have led to innovative scaffold design, complemented by progress in the understanding of stem cell–based therapy and growth factor enhancement of the healing cascade. This review focuses on the role of biomaterials for craniofacial bone engineering, highlighting key advances in scaffold design and development.

Nanotechnology in bone tissue engineering

UNLABELLED Nanotechnology represents a major frontier with potential to significantly advance the field of bone tissue engineering. Current limitations in regenerative strategies include impaired cellular proliferation and differentiation, insufficient mechanical strength of scaffolds, and inadequate production of extrinsic factors necessary for efficient osteogenesis. Here we review several major areas of research in nanotechnology with potential implications in bone regeneration: 1) nanoparticle-based methods for delivery of bioactive molecules, growth factors, and genetic material, 2) nanoparticle-mediated cell labeling and targeting, and 3) nano-based scaffold construction and modification to enhance physicochemical interactions, biocompatibility, mechanical stability, and cellular attachment/survival. As these technologies continue to evolve, ultimate translation to the clinical environment may allow for improved therapeutic outcomes in patients with large bone deficits and osteodegenerative diseases. FROM THE CLINICAL EDITOR Traditionally, the reconstruction of bony defects has relied on the use of bone grafts. With advances in nanotechnology, there has been significant development of synthetic biomaterials. In this article, the authors provided a comprehensive review on current research in nanoparticle-based therapies for bone tissue engineering, which should be useful reading for clinicians as well as researchers in this field.

Scarless wound healing: chasing the holy grail.

Summary: Over 100 million patients acquire scars in the industrialized world each year, primarily as a result of elective operations. Although undefined, the global incidence of scarring is even larger, extending to significant numbers of burn and other trauma-related wounds. Scars have the potential to exert a profound psychological and physical impact on the individual. Beyond aesthetic considerations and potential disfigurement, scarring can result in restriction of movement and reduced quality of life. The formation of a scar following skin injury is a consequence of wound healing occurring through reparative rather than regenerative mechanisms. In this article, the authors review the basic stages of wound healing; differences between adult and fetal wound healing; various mechanical, genetic, and pharmacologic strategies to reduce scarring; and the biology of skin stem/progenitor cells that may hold the key to scarless regeneration.

Wound healing: an update

Wounds, both chronic and acute, continue to be a tremendous socioeconomic burden. As such, technologies drawn from many disciplines within science and engineering are constantly being incorporated into innovative wound healing therapies. While many of these therapies are experimental, they have resulted in new insights into the pathophysiology of wound healing, and in turn the development of more specialized treatments for both normal and abnormal wound healing states. Herein, we review some of the emerging technologies that are currently being developed to aid and improve wound healing after cutaneous injury.

Studies in fat grafting: Part IV. Adipose-derived stromal cell gene expression in cell-assisted lipotransfer.

Background: Fat graft volume retention remains highly unpredictable, but addition of adipose-derived stromal cells to fat grafts has been shown to improve retention. The present study aimed to investigate the mechanisms involved in adipose-derived stromal cell enhancement of fat grafting. Methods: Adipose-derived stromal cells isolated from human lipoaspirate were labeled with green fluorescent protein and luciferase. Fat grafts enhanced with adipose-derived stromal cells were injected into the scalp and bioluminescent imaging was performed to follow retention of adipose-derived stromal cells within the fat graft. Fat grafts were also explanted at days 1, 5, and 10 after grafting for adipose-derived stromal cell extraction and single-cell gene analysis. Finally, CD31 immunohistochemical staining was performed on fat grafts enriched with adipose-derived stromal cells. Results: Bioluminescent imaging demonstrated significant reduction in luciferase-positive adipose-derived stromal cells within fat grafts at 5 days after grafting. A similar reduction in viable green fluorescent protein–positive adipose-derived stromal cells retrieved from explanted grafts was also noted. Single-cell analysis revealed expression of multiple genes/markers related to cell survival and angiogenesis, including BMPR2, CD90, CD105, FGF2, CD248, TGFß1, and VEGFA. Genes involved in adipogenesis were not expressed by adipose-derived stromal cells. Finally, CD31 staining revealed significantly higher vascular density in fat grafts explanted at day 10 after grafting. Conclusions: Although adipose-derived stromal cell survival in the hypoxic graft environment decreases significantly over time, these cells provide multiple angiogenic growth factors. Therefore, improved fat graft volume retention with adipose-derived stromal cell enrichment may be attributable to improved graft vascularization.

Studies in Fat Grafting: Part V. Cell-Assisted Lipotransfer to Enhance Fat Graft Retention is Dose Dependent

Background: Cell-assisted lipotransfer has shown much promise as a technique for improving fat graft take. However, the concentration of stromal vascular fraction cells required to optimally enhance fat graft retention remains unknown. Methods: Human lipoaspirate was processed for both fat transfer and harvest of stromal vascular fraction cells. Cells were then mixed back with fat at varying concentrations ranging from 10,000 to 10 million cells per 200 &mgr;l of fat. Fat graft volume retention was assessed by means of computed tomographic scanning over 8 weeks, and then fat grafts were explanted and compared histologically for overall architecture and vascularity. Results: Maximum fat graft retention was seen at a concentration of 10,000 cells per 200 &mgr;l of fat. The addition of higher number of cells negatively impacted fat graft retention, with supplementation of 10 million cells producing the lowest final volumes, lower than fat alone. Interestingly, fat grafts supplemented with 10,000 cells showed significantly increased vascularity and decreased inflammation, whereas fat grafts supplemented with 10 million cells showed significant lipodegeneration compared with fat alone Conclusions: The authors’ study demonstrates dose dependence in the number of stromal vascular fraction cells that can be added to a fat graft to enhance retention. Although cell-assisted lipotransfer may help promote graft survival, this effect may need to be balanced with the increased metabolic load of added cells that may compete with adipocytes for nutrients during the postgraft period.

Studies in fat grafting: Part I. Effects of injection technique on in vitro fat viability and in vivo volume retention.

Background: Fat grafting has become increasingly popular for the correction of soft-tissue deficits at many sites throughout the body. Long-term outcomes, however, depend on delivery of fat in the least traumatic fashion to optimize viability of the transplanted tissue. In this study, the authors compare the biological properties of fat following injection using two methods. Methods: Lipoaspiration samples were obtained from five female donors, and cellular viability, proliferation, and lipolysis were evaluated following injection using either a modified Coleman technique or an automated, low-shear device. Comparisons were made to minimally processed, uninjected fat. Volume retention was also measured over 12 weeks after injection of fat under the scalp of immunodeficient mice using either the modified Coleman technique or the Adipose Tissue Injector. Finally, fat grafts were analyzed histologically. Results: Fat viability and cellular proliferation were both significantly greater with the Adipose Tissue Injector relative to injection with the modified Coleman technique. In contrast, significantly less lipolysis was noted using the automated device. In vivo fat volume retention was significantly greater than with the modified Coleman technique at the 4-, 6-, 8-, and 12-week time points. This corresponded to significantly greater histologic scores for healthy fat and lower scores for injury following injection with the device. Conclusion: Biological properties of injected tissues reflect how disruptive and harmful techniques for placement of fat may be, and the authors’ in vitro and in vivo data both support the use of the automated, low-shear devices compared with the modified Coleman technique.

The role of stem cells in aesthetic surgery: fact or fiction?

Background: Stem cells are attractive candidates for the development of novel therapies, targeting indications that involve functional restoration of defective tissue. Although most stem cell therapies are new and highly experimental, there are clinics around the world that exploit vulnerable patients with the hope of offering supposed stem cell therapies, many of which operate without credible scientific merit, oversight, or other patient protection. Methods: The authors review the potential and the drawbacks of incorporation of stem cells in cosmetic procedures. A review of U.S. Food and Drug Administration–approved indications and ongoing clinical trials with adipose stem cells is provided. Furthermore, a “snapshot” analysis of Web sites using the search terms “stem cell therapy” or “stem cell treatment” or “stem cell facelift” was performed. Results: Despite the protective net cast by regulatory agencies such as the U.S. Food and Drug Administration and professional societies such as the American Society of Plastic Surgeons, the authors are witnessing worrying advertisements for procedures such as stem cell face lifts, stem cell breast augmentations, and even stem cell vaginal rejuvenation. The marketing and promotion of stem cell procedures in aesthetic surgery is not adequately supported by clinical evidence in the majority of cases. Conclusions: Stem cells offer tremendous potential, but the marketplace is saturated with unsubstantiated and sometimes fraudulent claims that may place patients at risk. With plastic surgeons at the forefront of stem cell–based regenerative medicine, it is critically important that they provide an example of a rigorous approach to research, data collection, and advertising of stem cell therapies.

Cell‐Assisted Lipotransfer Improves Volume Retention in Irradiated Recipient Sites and Rescues Radiation‐Induced Skin Changes

Radiation therapy is not only a mainstay in the treatment of many malignancies but also results in collateral obliteration of microvasculature and dermal/subcutaneous fibrosis. Soft tissue reconstruction of hypovascular, irradiated recipient sites through fat grafting remains challenging; however, a coincident improvement in surrounding skin quality has been noted. Cell‐assisted lipotransfer (CAL), the enrichment of fat with additional adipose‐derived stem cells (ASCs) from the stromal vascular fraction, has been shown to improve fat volume retention, and enhanced outcomes may also be achieved with CAL at irradiated sites. Supplementing fat grafts with additional ASCs may also augment the regenerative effect on radiation‐damaged skin. In this study, we demonstrate the ability for CAL to enhance fat graft volume retention when placed beneath the irradiated scalps of immunocompromised mice. Histologic metrics of fat graft survival were also appreciated, with improved structural qualities and vascularity. Finally, rehabilitation of radiation‐induced soft tissue changes were also noted, as enhanced amelioration of dermal thickness, collagen content, skin vascularity, and biomechanical measures were all observed with CAL compared to unsupplemented fat grafts. Supplementation of fat grafts with ASCs therefore shows promise for reconstruction of complex soft tissue defects following adjuvant radiotherapy. Stem Cells 2016;34:668–673