Expression and positive impact of omentin-1 on in vitro porcine oocyte maturation via the ERK1/2 and PRKAA1.

In brief: Omentin-1 enhanced in vitro oocyte maturation by increasing the percentage of oocytes in metaphase II, progesterone levels, mitochondrial functions, and lipolysis via extracellular signal-regulated kinase 1/2 and AMP-activated protein kinase alpha 1, without effect on preimplantation embryo development. Abstract: Oocyte maturation is a critical stage in embryo development and female reproduction, and is regulated by adipokines-hormones produced by adipose tissue. Omentin-1 (ITLN1) is an adipokine known to regulate ovarian follicle function, however its role in oocyte maturation remains unclear. This study investigated ITLN1 expression in porcine oocytes and cumulus cells before and after in vitro maturation (quatitiative real-time PCR, western blotting, immunofluorescence) and the effect of ITLN1 on: oocyte maturation by assessing the percentage of oocytes in metaphase II (M2) (4',6-diamidino-2-phenylindole, DAPI) and progesterone (P4) secretion (enzyme-linked immunosorbent assay); glucose metabolism, including glucose transporter type 4 (GLUT4) expression, glucose and lactate secretion, and mitochondrial function (Seahorse Test); lipid metabolism, as assessed by lipid droplet area (Nile Red), and adipose differentiation-related protein and adipose triglyceride lipase (ATGL) expression; extracellular signal-regulated kinase 1/2 (ERK1/2) and AMP-activated protein kinase alpha 1 (PRKAA1) phosphorylation, which mediate the effects of ITLN1 on oocyte maturation. Moreover, the effect of ITLN1 on preimplantation embryo development was also examined. ITLN1 expression increased after maturation in both oocytes and cumulus cells, with strong immunofluorescence signals in both cells. ITLN1 increased oocyte maturation to the M2 stage and P4 secretion. It enhanced glucose metabolism by upregulating GLUT4 and reducing glucose and lactate levels, improved mitochondrial function, reduced lipid droplet area, upregulated ATGL expression, and stimulated ERK1/2 and PRKAA1 phosphorylation. However, ITLN1 had no significant effect on preimplantation embryo development. In conclusion, ITLN1 positively regulates porcine oocyte maturation in vitro through coordinated modulation of energy metabolism, mitochondrial activity, lipid utilization, and ERK1/2-PRKAA1 signalling.