Clusterin-carrying extracellular vesicles derived from human umbilical cord mesenchymal stem cells restore the ovarian function of premature ovarian failure mice through activating the PI3K/AKT pathway

Emerging evidence has highlighted the therapeutic potential of human umbilical cord mesenchymal stem cells (UC-MSCs) in chemotherapy-induced premature ovarian failure (POF). This study was designed to investigate the appropriate timing and molecular mechanism of UC-MSCs treatment for chemotherapy-induced POF. Ovarian structure and function of mice were assessed every 3 days after injections with cyclophosphamide (CTX) and busulfan (BUS). UC-MSCs and UC-MSCs-derived extracellular vesicles (EVs) were infused into mice via the tail vein, respectively. Ovarian function was analyzed by follicle counts, the serum levels of hormones and ovarian morphology. The apoptosis and proliferation of ovarian granulosa cells were analyzed in vitro and in vivo. Label-free quantitative proteomics was used to detect the differentially expressed proteins in UC-MSC-derived EVs. After CTX/BUS injection, we observed that the ovarian function of POF mice was significantly deteriorated on day 9 after CTX/BUS infusion. TUNEL assay indicated that the number of apoptotic cells in the ovaries of POF mice was significantly higher than that in normal mice on day 3 after CTX/BUS injection. Transplantation of UC-MSCs on day 6 after CTX/BUS injection significantly improved ovarian function, enhanced proliferation and inhibited apoptosis of ovarian granulosa cells, whereas the therapeutic effect of UC-MSCs transplantation decreased on day 9, or day 12 after CTX/BUS injection. Moreover, EVs derived from UC-MSCs exerted similar therapeutic effects on POF. UC-MSCs-derived EVs could activate the PI3K/AKT signaling pathway and reduce ovarian granulosa cell apoptosis. Quantitative proteomics analysis revealed that clusterin (CLU) was highly expressed in the EVs of UC-MSCs. The supplementation of CLU proteins prevented ovarian granulosa cells from chemotherapy-induced apoptosis. Further mechanistic analysis showed that CLU-knockdown blocked the PI3K/AKT signaling and reversed the protective effects of UC-MSCs-derived EVs. Administration of UC-MSCs and UC-MSCs-derived EVs on day 6 of CTX/BUS injection could effectively improve the ovarian function of POF mice. UC-MSCs-derived EVs carrying CLU promoted proliferation and inhibited apoptosis of ovarian granulosa cells through activating the PI3K/AKT pathway. This study identifies a previously unrecognized molecular mechanism of UC-MSCs-mediated protective effects on POF, which pave the way for the use of cell-free therapeutic approach for POF.