<i>Smad8</i> is involvement in follicular development via the regulation of granulosa cell growth and steroidogenesis in mice

Abstract

Background: SMAD family proteins (SMADs) are crucial transcription factors downstream of transforming growth factor beta (TGF-ß)/SMAD signaling pathways that have been reported to play a pivotal role in mammalian reproduction. However, the role of SMAD family member 8 (SMAD8, also known as SMAD9), a member of the SMAD family, in mammalian reproduction remains unclear. Methods: We employed RNA interference techniques to knock down Smad8 expression in mouse granulosa cells (GCs) to investigate the effects of Smad8 on GC growth and steroidogenesis. Results: Our findings revealed a significant decrease in the proliferative capacity and a substantial increase in the apoptosis rate of GCs after transfection with Smad8-siRNA for 48 h. Subsequent hormone assays demonstrated a significant decrease in estradiol (E2) levels, whereas progesterone (P4) remained unchanged. Further mechanistic analysis showed that the mRNA expression of proliferating cell nuclear antigen (Pcna), Cyclin D2, cell cycle-dependent kinase 4 (Cdk4), B-cell lymphoma-2 (Bcl-2), estrogen receptor (Er), luteinizing hormone receptor (Lhr) and cytochrome P450 family 19 subfamily A member 1 (Cyp19a1) significantly decreased. Conversely, the mRNA of cysteine aspartate proteinase 3 (Caspase 3) significantly increased, wheras Bcl2-associated X (Bax), follicle-stimulating hormone receptor (Fshr) and cytochrome P450 family 11 subfamily A member 1 (Cyp11a1) remained unchanged compared to the controls. Conclusion: This study indicates that Smad8 knockdown inhibits cell proliferation, promotes apoptosis, reduces Er and Lhr transcription, and decreases E2 production in mouse GCs. These findings suggest that Smad8 may serve as a novel genetic marker for mammalian reproduction.