<i>In vitro</i> effect of omentin-1 on porcine ovarian follicular steroidogenesis: Role of insulin receptor, extracellular signal-regulated kinase 1/2 and protein kinase A signaling pathways.

Omentin-1 (ITLN1) is an adipokine involved in energy metabolism and insulin resistance; its expression has been demonstrated in the ovary, but its effect on ovarian endocrine function remains unknown. Therefore, this study aimed to determine the effect of ITLN1 alone or with follicle stimulating hormone (FSH) or luteinising hormone (LH) on secretion of progesterone (P⁴), testosterone (T), estradiol (E²); mRNA, protein expression of StAR, CYP11A1, HSD3B, CYP19A1; mRNA levels of receptors for gonadotropins and steroid hormones in ovarian follicle cells of normal weight Large White and fat Meishan pigs. Moreover, we studied the involvement of insulin receptor (INSR), extracellular signal-regulated kinase 1/2 (ERK1/2), protein kinase A (PKA) in ITLN1-mediated steroidogenesis. Ovarian follicle cells were treated with ITLN1 (10-100 ng/mL) alone or FSH/LH (100 ng/mL) preincubated or not with pharmacological inhibitors of INSR, ERK1/2, PKA to investigate the mechanism of ITLN1 action in ovarian cells. The concentration of steroids, mRNA and protein expression of steroidogenic markers were determined using ELISA, RT-qPCR or Western blotting. For E₂ secretion, StAR, HSD3B, CYP19A1 protein expression, all main effects of ITLN1 dose, breed, and their interactions were significant. When combined with FSH/LH, ITLN1 significantly influenced E₂, T secretion, <i>CYP11A1</i> mRNA expression, StAR, CYP19A1 protein levels, with all main effects (FSH, LH, ITLN1 dose, breed) and interactions being significant. This suggests that ITLN1's impact on steroidogenesis is strongly dependent on breed, ITLN1 dose and hormonal context. Furthermore, the increase in E₂ synthesis indicates a potential role of ITLN1 in enhancing steroidogenesis, potentially <i>via</i> ERK1/2, PKA, and INSR pathways. Therefore, ITLN1 may play a role in the regulation of steroidogenesis in ovarian follicle cells.