MiR-let-7d-3p inhibits granulosa cell proliferation by targeting TLR4 in polycystic ovary syndrome

•Next-generation sequencing (NGS) is performed to find new target miRNAs in granulosa cells of PCOS.•MiR-let-7d-3p in granulosa cells of PCOS patients was significantly increased.•MiR-let-7d-3p may mediate TLR4 to inhibit granulosa cell proliferation in PCOS. Polycystic ovary syndrome (PCOS) is a typical reproductive and endocrinological disorder of women at child-bearing age. In this study, we used miRNA sequencing technology and verified miR-let-7d-3p as a vital miRNA in PCOS. RT-qPCR confirmed miR-let-7d-3p was significantly increased in granulosa cells (GCs) of PCOS. Cell counting kit-8 (CCK-8) identified the suppression of miR-let-7d-3p mimic in KGN cell proliferation and PI3K/Akt signaling pathway. Dual luciferase reporter assay proved that Toll-like receptor 4 (TLR4) was a target of miR-let-7d-3p, and TLR4 was significantly down-regulated by miR-let-7d-3p. Furthermore, over-expression of TLR4 promoted KGN cell proliferation and rescued the inhibition of miR-let-7d-3p on KGN cells. In conclusion, miR-let-7d-3p was a crucial miRNA up-regulated in GCs of PCOS, and inhibited cell proliferation by targeting TLR4 gene.