Disruption of Trib1 Results in Granulosa Cells Steroid Hormone Synthesis Dysfunction and Infertility in Female Mice via Downregulations of FOSL2 Expression

Proper steroid hormone synthesis is essential for maintaining fertility in female animals. Tribbles pseudokinase 1 (Trib1), a member of the Tribbles pseudokinase family, exerts its functions mainly through interacting with other molecules. Numerous studies have shown that Trib1 plays a central role in regulating cell proliferation. In mammals, the proliferation of granulosa cells (GCs) is a hallmark event in follicular development, which is essential for follicular maturation and successful ovulation. However, whether Trib1 regulates ovarian steroid hormone synthesis remains largely unexplored. In this study, we found that Trib1 is predominantly expressed in ovarian GCs. Knockdown of Trib1 in GCs significantly reduced their capacity for steroid hormone synthesis. Furthermore, Trib1 KO female mice were completely infertile, exhibiting impaired transition from primary to antral follicles, increased follicle atresia, and defective steroid hormone secretion. Ovarian RNA-Seq analysis revealed that differential expressed genes (DEGs) were significantly enriched in cholesterol metabolism and steroid biosynthesis pathways following Trib1 deletion. Notably, FOSL2, a transcription factor that potentially bound to the promoters of the pivotal steroidogenic genes Star and Cyp11a1, was significantly down-regulated in Trib1 KO mice. Crucially, overexpression of FOSL2 in Trib1-deficient GCs restored Star and Cyp11a1 expression and significantly rescued the ability of steroid hormone synthesis in GCs. Our findings unveil a novel Trib1 gene governing steroidogenesis in GCs and is essential for fertility in female mice, providing profound insights into the female reproductive endocrinology and potential therapeutic targets.