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Adipose-derived Stromal Cells Within Transplanted Fat Hone To Blood Vessels And Assume A Pericyte Structure
Mimi R. Borrelli, MBBs, MSc, Sandeep Adem, MS, Nestor M. Diaz Deleon, Michael Januszyk, MD, PhD, Dung Nguyen, Arash Momeni, MD, PhD, Michael T. Longaker, MD, MA, Derrick C. Wan, MD.
Stanford, menlo park, CA, USA.

PURPOSE: Fat grafting can restore volume defects and improve the texture, quality, and appearance of overlying skin. The adipose-derived stromal cells (ASCs) within transplanted fat are thought to drive these regenerative effects, either by direct differentiation or by paracrine signaling. The survival and differentiation fate of transplanted ASCs post grafting, however, remains incompletely understood. We therefore performed lineage tracing of transplanted human ASCs in vivo using a mouse model of fat grafting. METHODS: ASCs were isolated from human lipoaspirate and transduced to express green fluorescent protein (GFP) (Fig. 1A). Successfully labeled cells were isolated using fluorescence-activated cells sorting (FACS) (Fig. 1B). Next, CD1 nude mice were grafted with fresh human lipoaspirate enriched with GFP+ ASCs (10,000 cells/200ul lipoaspirate/graft). Mice were harvested at 2, 4, 6, and 8 weeks (n=5 mice/group). Grafted fat was explanted and assessed by whole tissue mounting, confocal microscopy, and image reconstruction software to characterize the three-dimensional structure of fat with reference to the GFP+ ASCs. RESULTS: Transplanted ASCs were evident in whole mount sections through 6-weeks post transplantation. GFP+ ASCs grouped together and honed to blood vessels, and adipocyte size was correlated with proximity to GFP+ ASCs (Fig. 1C). ASCs co-stained for the known pericytes markers Tie2, smooth muscle actin (SMA), and nerve growth factor 2 (NGF2). Although ASCs became fewer in number with time post grafting, fat enriched with ASCs was more vascular throughout the graft compared to fat not enriched with ASCs. CONCLUSIONS: In this mouse model of fat grafting we show that the transplanted human ASCs may survive and hone to blood vessels, assuming a pericyte-like position. These data suggest a role for ASCs in directing and supporting angiogenesis and neovascularization by direct differentiation. Future work may further profile the exact cytokine profile of transplanted ASCs throughout grafting to determine the mechanism by which they drive their regenerative effects.


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