TGF-β1 suppresses de novo cholesterol biosynthesis in granulosa-lutein cells by down-regulating DHCR24 expression via the GSK-3β/EZH2/H3K27me3 signaling pathway

Abstract

Cholesterol is a precursor to steroid hormones and can be obtained from serum LDL or de novo synthesis in steroidogenic cells. Before luteinizing hormone (LH) surge-induced ovulation, follicles remain avascular, and cholesterol required for progesterone production in granulosa cells (GCs) is derived from de novo biosynthesis. Previous studies have verified that the intrafollicular TGF-β1 plays inhibitory roles in GCs luteinization, vascularization, and progesterone production. Nevertheless, the regulatory function of TGF-β1 on de novo cholesterol synthesis in granulosa-lutein (GL) cells remains largely unknown. We aim to investigate this aspect in this study using in vivo cultured human GL cells. Our results suggested that TGF-β1 significantly suppresses intracellular cholesterol levels and down-regulates the expression of the final step enzyme, DHCR24, that catalyzes de novo cholesterol synthesis. We used specific inhibitors and siRNA-mediated knockdown approaches demonstrate that TGF-β1 suppression of DHCR24 expression in GL cells is mediated by the GSK-3β/EZH2/H3K27me3 signaling pathway. Further ChIP assays revealed that elevated H3K27me3 levels in the promoter region of DHCR24 play a vital role in TGF-β1-induced DHCR24 down-regulation, and RNA-sequencing results confirmed these findings. Notably, our study provides a novel insight into the molecular mechanisms by which TGF-β1 suppresses de novo cholesterol biosynthesis in GL cells.