NPR3 is regulated by gonadotropins and modulates bovine cumulus cell expansion

The natriuretic peptide system, particularly the C-type natriuretic peptide (CNP) and natriuretic peptide receptor 2 (NPR2), plays a critical role in regulating mammalian ovarian functions, including oocyte-cumulus cell communication and meiotic maturation. However, the contribution of natriuretic peptide receptor 3 (NPR3) to these processes has not been thoroughly investigated. Data from this study provide compelling evidence that NPR3 is involved in modulating gonadotropin signaling and regulating cumulus cell expansion in cattle.

The significant role of CNP and its receptor 2 (NPR2) in regulating oocyte meiotic maturation and facilitating communication between oocytes and surrounding cumulus cells has been well documented in various mammalian species including mice, cattle and swine. However, further investigation is needed to ascertain whether natriuretic peptide receptors (NPRs) are involved in regulating other essential ovarian functions. Hence, this study aimed to explore the potential involvement of NPRs in the regulation of cumulus expansion and oocyte meiotic maturation in bovine cumulus-oocyte complexes (COCs). The findings revealed that NPR3 mRNA abundance was downregulated by follicle-stimulating hormone and luteinizing hormone in cumulus cells of bovine COCs during in vitro maturation (IVM), while NPR2 mRNA levels were not affected by gonadotropins. Inhibition of the epidermal growth factor receptor (EGFR) during IVM of COCs prevented the NPR3 mRNA downregulation induced by gonadotropins in cumulus cells. Additionally, treatment of COCs during IVM with an NPR3 agonist (cANP4-23) inhibited cumulus expansion induced by gonadotropins. This inhibitory effect was further intensified when COCs were cotreated with cANP4-23 and CNP. These findings provide robust evidence indicating that normal cumulus expansion in bovine COCs involves an inhibitory effect of gonadotropins on NPR3 mRNA expression, which is mediated via EGFR signaling. The study also provides evidence that CNP and NPR3 interact synergistically to regulate cumulus expansion in response to gonadotropins.