Small extracellular vesicles from human adipose-derived mesenchymal stromal cells: a potential promoter of fat graft survival

Background Small extracellular vesicles (sEVs) with genetic information secreted by cells play a crucial role in the cellular microenvironment. In this study, our purpose is to explore the characteristics of the small extracellular vesicles of human adipose-derived mesenchymal stromal cells (hADMSC-sEVs) and studied the role of hADMSC-sEVs in improving the survival rate of grafted fat. Methods In the present study, we used the transmission electron microscopy, nano-tracking analysis, nanoflow surface protein analysis, and zeta potential value to identify sEVs. SEVs' trajectory was traced dynamically to verify whether hADMSC-sEVs can be internalized into human umbilical vein endothelial cells (HUVECs) in vitro at different times. The angiogenic property of hADMSC-sEVs was observed by measuring the volume, weight, and histological analysis of the grafted fats in nude mouse models. Results Our research showed that the hADMSC-sEVs were sEVs with double-layer membrane structure and the diameter of which is within 30-150 nm. hADMSC-sEVs exert biological influence mainly through internalization into cells. Compared with the control group, the hADMSC-sEVs group had a significantly higher survival rate of grafted fat, morphological integrity, and a lower degree of inflammation and fibrosis. And immunohistochemistry showed that hADMSC-sEVs significantly increased the neovascularisation and the expression of CD34, VEGFR2, and Ki-67 in the graft tissue. Conclusions As a potential nanomaterial, hADMSC-sEVs have been explored in the field of cell-free application of stem cell technology. hADMSC-sEVs promoted the survival of grafted fats by promoting the formation of new blood vessels, which is another promising progress in the field of regenerative medicine. We believe that hADMSC-sEVs will have a broad application prospect in the field of regenerative medicine in the future.