Reply: Supplementation with Extracellular Vesicles Derived from Adipose-Derived Stem Cells Increases Fat Graft Survival and Browning in Mice: A Cell-Free Approach to Construct Beige Fat from White Fat Grafting.

Abstract

Background Growing evidence has demonstrated that adipose-derived stem cell-derived extracellular vesicles enhance the survival of fat grafts and the browning of white adipose tissue. We evaluated whether supplementation with adipose-derived stem cell-derived extracellular vesicles promotes the survival and browning of fat grafts. Methods Extracellular vesicles derived from adipose-derived stem cells were injected into fat grafts of C57BL/6 mice once per week until postgraft week 12. The grafts were collected and weighed after postgraft weeks 2, 4, and 12. The histological morphology, neovascularization, and the proportion of M2 macrophages of grafts were evaluated. The ability of extracellular vesicles to promote macrophage polarization and catecholamine secretion was detected. Whether the inducement of browning adipose differentiation is extracellular vesicles or the paracrine effect of M2 macrophages polarized by extracellular vesicles was also verified. Results Grafts treated by extracellular vesicles derived from adipose-derived stem cells showed enhanced beige adipose regeneration with increased neovascularization, M2 macrophage proportion, and norepinephrine secretion at postgraft week 4. Increased retention and decreased fibrosis and necrosis were noted at postgraft week 12. The extracellular vesicles uptake by macrophages promoted M2 type polarization and catecholamine secretion while suppressing M1 type polarization. Of note, browning adipose differentiation with enhanced energy expenditure could be promoted only by the conditioned medium from extracellular vesicle-polarized M2 macrophages but not by extracellular vesicles themselves. Conclusions Supplementation with extracellular vesicles derived from adipose-derived stem cells increases fat graft survival and browning by which extracellular vesicles-polarized M2 macrophages secrete catecholamines to promote beige adipose regeneration.