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Shining a new light onto adipose stromal/stem cells

2020; Wiley; Volume: 230; Issue: 1 Linguagem: Inglês

10.1111/apha.13536

1748-1716

Jeffrey M. Gimble, Trivia Frazier, António J. Salgado,

Body Contouring and Surgery

In the current issue of Acta Physiologica, Fan et al report that light activation enhances and prolongs the regenerative properties of adipose-derived stromal/stem cells in a murine hindlimb ischaemia model through mechanisms involving secretion of angiogenic and vasculogenic factors.1 To understand why this finding merits a highlight, it helps to take a flashlight into the tunnels of time and get a historical perspective. In 2001, human ASC took centre stage in the spotlight of regenerative medicine with a landmark publication from the University of Pittsburgh and the University of California-Los Angeles.2 In this seminal study, Patricia Zuk, Adam Katz and their colleagues presented compelling evidence documenting the robust ability of ASC to differentiate along the adipocyte, chondrocyte, myocyte and osteoblast lineage pathways.2 This supported the authors’ novel hypothesis that adipose tissue, harvested from healthy donors during elective liposuction surgery, was a rich reservoir for cells with regenerative properties. While Alexander Friedenstein had first described bone-marrow-derived mesenchymal stromal/stem cells (MSC) with similar or identical properties in the 1960s, their frequency within a bone marrow aspirate was one to three orders of magnitude less abundant. In 2004, three laboratories in rapid succession shed light on the endothelial cell functionality of ASC. First, Planat-Bernard et al showed that human stromal vascular fraction (SVF) cells, the precursors of culture expanded ASC, formed vasculogenic structures when cultured in three-dimensional Matrigel scaffolds in vitro.3 Furthermore, when injected intramuscularly in vivo, the SVF cells enhanced circulatory recovery in a nude mouse model of hindlimb ischemia.3 Next, Rehman et al reported that human ASC secreted angiogenic cytokines including hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF) and transforming growth factor β (TGFβ) in vitro and postulated that these accounted for the pro-angiogenic effects of ASC when injected intramuscularly into a hindlimb ischemic mice.4 Shortly thereafter, Miranville et al independently confirmed that human SVF cells differentiated into endothelial cells in vitro and improved vasculogenic recovery when injected intramuscularly into a murine hindlimb ischemic model.5 By 2006, Zvonic et al began using mass spectrometry to define the heterogeneous content of the ASC secretome, detecting adiponectin, angiotensinogen, stromal-derived growth factor and serpins, among other proteins.6 Flashing forward to 2008, Tomchuck, Betancourt and colleagues showed that it was possible to educate bone marrow MSC by manipulating their exposure to toll-like receptor (TLR) ligands.7 In the presence of endotoxin or lipopolysaccharide (LPS), the agonist for TLR-4, MSC secreted pro-inflammatory cytokines while in the presence of single chain DNA, an agonist for TLR-3, MSC secreted immunosuppressive or anti-inflammatory cytokines. This team went on to distinguish these two phenotypes as MSC1 (pro-inflammatory) and MSC2 (immunosuppressive), similar to the distinction between type 1 (M1) and type 2 (M2) macrophages.7 Betancourt and her colleagues have since founded their biotechnology company, Commence Bio, based on this intellectual property and have begun exploring MSC1 therapy for cancer targets and MSC2 immunosuppressive therapy for inflammatory bowel disease and related autoimmune disorders. By combining these individual glimmers from the past, Fan et al have now extended and advanced the stromal/stem cell field by demonstrating a non-invasive physical means to educate and manipulate the regenerative functionality of ASC.1 After exposure to photoactivation for 30 minutes, murine ASC displayed increased proliferative potential in vitro compared to untreated controls (figure 1).1 When a murine hindlimb ischaemia model was injected intravenously with phosphate-buffered saline alone, blood flow did not return to normal. While injection of untreated and photoactivated ASC significantly improved blood flow within 2 weeks, this increase persisted up to 38 days only with the photoactivated ASC (figure 3). Analyses of the skeletal muscle at this final timepoint by qRT-PCR indicated a significant increase in mRNA encoding angiopoietin 2, platelet-derived growth factor-BB, and VEGFA and VEGFC (figure 4). Subsequent unbiased mass spectrometry analysis of the conditioned medium of human ASC detected >80 proteins associated with angiogenesis as well as heat shock protein 90 (HSP90) isoforms which were selectively induced following light exposure (table 1). Based on their findings, Fan et al conclude that photoactivation can serve as a low-cost physical manipulation of ASC to improve their efficacy as a cell therapy for peripheral artery disease, a frequent complication in type 2 diabetic and atherosclerotic patients. While the use of ASC and MSC in regenerative medicine is still in its infancy, adult cell therapy has gained some momentum. There is a growing industry to isolate, expand and package human stromal/stem cells in accordance with the Good Manufacturing Practice (GMP) standards necessary to address regulatory authority concerns regarding patient safety and product efficacy. Since the ASC and MSC release both cytokines and exosomes that contribute paracrine regenerative effects, there is a need to further explore and understand the secretome content with respect to tissue repair mechanisms. The secretome can potentially be harvested, cryopreserved and lyophilized as a stable, off the shelf product that can be delivered at point of care to patients as a substitute or supplement to live cell therapies. The ability to standardize and quantify the process of cell manipulation and media conditioning using physical as opposed to biological or chemical means has practical applications. Thus, the ability to insure a proliferative and secretory advantage to ASC by photoactivation has commercial and clinical translational appeal. Theoretically, such a treatment regimen could be applied to any cell therapy, including autologous SVF cells isolated and processed using a closed-system device at the point of care by a surgeon practicing medicine within an operating room. Before such an approach can be put into practice, further studies will be necessary. The time course and dosage of light exposure to the ASC and SVF cells will need to be validated in vitro using cells prepared from multiple donors, not just one lot isolated from a single individual as reported in the current manuscript. Likewise, the ability of photoactivation to persist following cryopreservation of the cell product will likewise merit investigation as this will have value in generating a stable, off the shelf product. Fortunately, there is precedent to suggest that this may be a likely outcome. Studies by have demonstrated that ASC exposed to a physical temperature of 43°C prior to cryopreservation display induced levels of HSP and enhanced viability post-thaw relative to untreated controls. Thus, the concept of photoactivation as described by Fan et al in this issue of Acta Physiologica holds potential clinical translation as a quantifiable and low budget method for educating and modulating the functionality of ASC and other cell types for a wide range of regenerative medical therapies. JMG and TPF are the co-owners, co-founders and Chief Scientific Officer and Chief Executive Officer, respectively of Obatala Sciences Inc; JMG holds these same roles in LaCell LLC. Both are for profit biotech companies focusing on adipose-derived cells and products designed for research and clinical translation in regenerative medicine, metabolism and obesity. JMG is also co-owner and co-founder of Talaria Antibodies Inc, a research antibody production company as well as a member of the board of the International Federation of Adipose Therapeutics and Science (IFATS), an editorial board member of Stem Cells and Development and JTERM, and editor for Biochimie. JMG and TPF are inventors on numerous patents relating to the use of human adipose stromal/stem cells in regenerative medicine as well as human biomaterial scaffolds.