Gremlin 1 regulates granulosa cell apoptosis through the TGF-β/SMAD signaling pathway during bovine follicular atresia.

Gremlin 1 is a highly conserved secretory glycoprotein of the DAN family that plays significant roles in human and mouse follicular development and ovulation through both BMP-dependent and BMP-independent pathways. However, its function and mechanisms in bovine follicular development and atresia remain unclear. This study investigated its specific molecular mechanism during follicular development in bovines. Gremlin 1 protein is expressed in ovarian follicles at various developmental stages, with both its mRNA and protein levels increasing in correlation with the progression of follicular atresia. Following Si-RNA mediated knockdown of Gremlin 1 expression, a reduction in apoptosis and an enhancement in proliferative activity were observed in granulosa cells (GCs). In contrast, recombinant human Gremlin 1 (Rh-Gremlin 1) protein significantly induced apoptosis of GCs and inhibited cell proliferation. Previous studies have shown that Gremlin 1 can mediate apoptosis in a variety of cells through the TGF-β/SMAD signaling pathway. In our study, we observed that Gremlin 1 was associated with the phosphorylation levels of SMAD-2/3, and treatment with the TGF-β signaling pathway inhibitor SB431542 partially reversed Gremlin 1-induced apoptosis of GCs. Moreover, SB431542 significantly restored the proliferative viability and cell cycle progression of GCs. The results showed that Gremlin 1 was involved in follicular atresia-related processes by regulating the apoptosis and proliferation of GCs, and partially mediated this process through the TGF-β/SMAD signaling pathway. This provides a new avenue for further exploration of its role in follicular development.