Low-density small extracellular vesicles in bovine follicular fluid carrying let-7i target FASLG to inhibit granulosa cells apoptosis

Apoptosis of granulosa cells is a key factor in mammalian follicular atresia. It has a significant impact on oocyte development and maturation. Extracellular vesicles (EVs) are a group of highly heterogeneous population. Previous studies have found that ovarian follicular fluid is rich in EVs. In the present study, the follicular fluid of 3–5 mm follicles from bovine ovaries without corpus luteum was collected, and a subtype of small EVs (sEVs), low-density small EVs (LD-sEVs), was successfully isolated by differential ultracentrifugation combined with iodixanol density gradient centrifugation. LD-sEVs were identified using transmission electron microscope, nanoparticle tracking analysis and Western blot. Flow cytometry, Quantitative reverse transcription PCR (RT-qPCR), Western blot, and other methods were used to detect the effect of LD-sEVs on follicular granulosa cell apoptosis. After that, let-7i, a highly expressed miRNA component in LD-sEVs, was screened and target validation was carried out in granulosa cells. The results showed that LD-sEVs could be taken up by granulosa cells and inhibited the apoptosis. Further research found that let-7i inhibits the apoptosis of granulosa cells by targeting FASLG. It plays an important role in regulating the apoptosis of follicular granulosa cells, which may affect follicular development.