Small extracellular vesicles secreted by urine-derived stem cells enhanced wound healing in aged mice by ameliorating cellular senescence

Regeneration of chronic skin wounds in tissue is still a key challenge in regenerative medicine because of the accumulation of senescent cells and increasing secretion of "senescence-associated secretory phenotype"-(SASP) in the wound site. Recently, some studies have reported that small extracellular vesicles (sEVs) derived from stem cells can alleviate cellular senescence with very low risk of tumorigenesis and immune responses. As our previous studies have shown that urine-derived stem cells (USCs) can be obtained easily and noninvasively and sEVs derived from USCs (USC-sEVs) have capabilities of regenerating tissue injuries, using USC-sEVs to enhance chronic skin wound healing in aged tissue might be a feasible and efficient strategy. Therefore, in this study, the USC-sEVs were collected and firstly loaded in a human acellular amniotic membrane (HAAM) for controlled releasing and locating the USC-sEVs in the wound site before they were implanted into a chronic skin wound in aged mice. In vivo results showed that the USC-sEVs in HAAM could effectively accelerate the wound healing by ameliorating cellular senescence and reducing the secretion of SASP in the aged skin wounds. To elucidate the mechanism, USC-sEVs were used to in vitro culture human dermal fibroblasts (HDFs) and results showed that USC-sEVs could rejuvenate senescent fibroblasts by reversing the aging phenotypes of senescent HDFs and efficiently reducing the secretion of SASP after they activated the Sirt1 pathway. Therefore, USC-sEVs are efficient for enhancing wound healing in aged mice by ameliorating cellular senescence.