The Mature COC Promotes the Ampullary NPPC Required for Sperm Release from Porcine Oviduct Cells

Abstract

Porcine spermatozoa are stored in the oviductal isthmus after natural mating, and the number of spermatozoa is increased in the oviductal ampulla when the mature cumulus-oocyte complexes (COCs) are transferred into the ampulla. However, the mechanism is unclear. Herein, natriuretic peptide type C (NPPC) was mainly expressed in porcine ampullary epithelial cells, whereas its cognate receptor natriuretic peptide receptor 2 (NPR2) was located on the neck and the midpiece of porcine spermatozoa. NPPC increased sperm motility and intracellular Ca2+ levels, and induced sperm release from oviduct isthmic cell aggregates. These actions of NPPC were blocked by the cyclic guanosine monophosphate (cGMP)-sensitive cyclic nucleotide-gated (CNG) channel inhibitor l-cis-Diltiazem. Moreover, porcine COCs acquired the ability to promote NPPC expression in the ampullary epithelial cells when the immature COCs were induced to maturation by epidermal growth factor (EGF). Simultaneously, transforming growth factor-β ligand 1 (TGFB1) levels were dramatically increased in the cumulus cells of the mature COCs. The addition of TGFB1 promoted NPPC expression in the ampullary epithelial cells, and the mature COC-induced NPPC was blocked by the transforming growth factor-β type 1 receptor (TGFBR1) inhibitor SD208. Taken together, the mature COCs promote NPPC expression in the ampullae via TGF-β signaling, and NPPC is required for the release of porcine spermatozoa from the oviduct isthmic cells.

The molecular regulatory mechanisms of meiotic arrest and resumption in Oocyte development and maturation

“…The natriuretic peptide receptors (NPRs) in mammalian follicles play a critical role in regulating oocyte meiotic arrest. NPR2, a major member of the NPR family, is mainly located on CGCs, whereas its ligand, known as natriuretic peptide precursor C (NPPC), is expressed in MGCs in mice [41], humans [42], and pigs [43]. Natriuretic peptide precursor C inhibits spontaneous GVBD in COCs but exerts little inhibitory effect on DOs.…”

“…Therefore, degradation of cyclin B leads to both the inactivation of CDK1 phosphorylation and a decrease in MPF activity, which together arrest oocytes at MI [63]. Recently, some cyclin B1-deficient oocytes were shown to resume and complete MI via a mechanism in which cyclin B2 compensates for the CDK1-activation activity of cyclin B1 during the oocyte meiotic G2/M transition [43,64].…”