miR-4433a-3p promotes granulosa cell apoptosis by targeting peroxisome proliferator–activated receptor alpha and inducing immune cell infiltration in polycystic ovarian syndrome

Background Granulosa cell (GC) proliferation and apoptosis are critical events of the ovum energy supply, which lead to follicular growth retardation or atresia, and various ovulatory obstacles, eventually resulting in the development of ovarian disorders such as polycystic ovarian syndrome (PCOS). Apoptosis and dysregulated miRNA expression in GCs are manifestations of PCOS. miR-4433a-3p has been reported to be involved in apoptosis. However, there is no study reporting the roles of miR-4433a-3p in GC apoptosis and PCOS progression. Methods miR-4433a-3p and peroxisome proliferator–activated receptor alpha (PPAR-α) levels in GCs of PCOS patients or in tissues of a PCOS rat model were examined by quantitative polymerase chain reaction and immunohistochemistry. Bioinformatics analyses and luciferase assays were used to examine the association between miR-4433a-3p and PPAR-α, as well as PPAR-α and immune cell infiltration, in PCOS patients. Results miR-4433a-3p expression in GCs of PCOS patients was increased. miR-4433a-3p overexpression inhibited the growth of the human granulosa-like tumor cell line (KGN) and promoted apoptosis, while co-treatment with PPAR-α and miR-4433a-3p mimic rescued miR-4433a-3p-induced apoptosis. PPAR-α was a direct target of miR-4433a-3p and its expression was decreased in PCOS patients. PPAR-α expression was also positively correlated with the infiltration of activated CD4 + T cells, eosinophils, B cells, gamma delta T cells, macrophages, and mast cells, but negatively correlated with the infiltration of activated CD8 + T cells, CD56 + bright natural killer cells, immature dendritic cells, monocytes, plasmacytoid dendritic cells, neutrophils, and type 1 T helper cells in PCOS patients. Conclusion The miR-4433a-3p/PPAR-α/immune cell infiltration axis may function as a novel cascade to alter GC apoptosis in PCOS.