ID3 mediates the TGF‐β1‐induced suppression of matrix metalloproteinase‐1 in human granulosa cells

In the mammalian ovary, matrix metalloproteinase‐1 (MMP1) is expressed in growing ovarian follicles, and MMP1‐mediated extracellular matrix (ECM) remodeling plays a functional role in regulating the formation of corpus luteum. Transforming growth factor‐β1 (TGF‐β1) is an intraovarian growth factor that acts as a negative regulator of luteinization and progesterone production in human granulosa‐lutein (hGL) cells. At present, whether TGF‐β1 regulates the expression of MMP1 and thus affects ECM remodeling during corpus luteum formation remains largely unknown. The aim of this study was to investigate the effects of TGF‐β1 and the molecular mechanisms by which it regulates the expression of MMP1 in immortalized human granulosa cells lines (SVOG) and primary hGL cells (obtained from consenting patients undergoing IVF treatment). We used inhibition approaches including a competitive antagonist for endogenous TGF‐β type II receptor, pharmacological inhibitors (SB431542 and dorsomorphin), and specific small interfering RNA‐targeted knockdown of ALK5 type I receptor and SMAD4 to demonstrate that TGF‐β1 downregulates the expression and production of MMP1 via a TβRII/ALK5‐mediated SMAD‐dependent signaling pathway in hGL cells. Additionally, our results show that the suppressive effect of TGF‐β1 on the expression of MMP1 is mediated by a transcription factor, the inhibitor of differentiation 3 (ID3) protein. Our findings provide insights into the molecular interactions and mechanisms of TGF‐β1 and ID3 during the regulation of MMP1 in hGL cells. TGF‐β1 binds to complex of type I (ALK5) and type II (TβRII) receptors leading to the activation of canonical SMAD2/3 signaling pathway. The activation of receptor complexes containing ALK5 and TβRII leads to the phosphorylation of SMAD2/3, which complexes with common SMAD4 and translocates into the nucleus to increase the transcription of ID3, which in turn suppresses the transcriptional expression of MMP1 that inhibits type I collagen degradation and modulates ECM remodeling.