Selective spermatozoa movement from storage of the oviduct to fertilization site is suggested to be a result of chemotaxis. In the present study, Natriuretic peptide precursor A (NPPA) induced sperm chemotaxis in capillaries and enhanced intracellular Ca(2+) level, both of which could be blocked by the Natriuretic Peptide Receptor 1 (NPR1) inhibitor anantin and the cGMP-dependent protein kinase (PKG) inhibitors, KT5823 and Rp-8-Br-PET-cGMPS. NPPA also increased spermatozoa kinetic parameters of VAP, VSL, LIN, STR, and BCF. Only 2.0% of positive staining for NPR1 was detected in fresh spermatozoa. The positive rate was increased in capacitated spermatozoa (20.5%), and further increased in spermatozoa of NPPA treatment (70.2%). Nppa mRNA level in the ampullae was significantly higher compared with that in isthmus and uterotubal junction, and NPPA protein had an ascending gradient (AG) from the uterotubal junction to ampullae in gonadotropin-treated mice. NPPA induced sperm chemotaxis in diestrus oviducts without a NPPA gradient, and sperm chemotaxis occurred in the oviducts of gonadotropin-treated mice. These effects were inhibited by anantin. Meanwhile, sperm chemotaxis also occurred in unilateral ovariectomized oviducts of gonadotropin-treated mice, in which the possible effect of follicular fluid and oocyte-cumulus mass were eliminated when ovulation occurs. Furthermore, anantin significantly decreased the rate of fertilization in a dose-dependent manner (0.1 µM, 57.1%; 1 µM, 33.8%) compared with control (78.5%). These results suggest that a NPPA gradient originating in the oviduct induces sperm chemotaxis by binding to its receptor NPR1 and then activating PKG pathway, and plays a physiological role in fertilization.
Many studies have shown that cyclic adenosine-5′-monophosphate (cAMP)-dependent protein kinase A (PKA) and G-protein-coupled receptor 3 (GPR3) are crucial for controlling meiotic arrest in oocytes. However, it is unclear how gonadotropins modulate these factors to regulate oocyte maturation, especially by gap junctional communication (GJC). Using an in vitro meiosis-arrested mouse cumulus-oocyte complex (COC) culture model, we showed that there is a close relationship between follicle-stimulating hormone (FSH) and the PKA type I (PKAI) and GPR3. The effect of FSH on oocyte maturation was biphasic, initially inhibitory and then stimulatory. During FSH-induced maturation, rapid cAMP surges were observed in both cumulus cells and oocyte. Most GJC between cumulus cells and oocyte ceased immediately after FSH stimulation and recommenced after the cAMP surge. FSH-induced maturation was blocked by PKAI activator 8-AHA-cAMP. Levels of PKAI regulatory subunits and GPR3 decreased and increased, respectively, after FSH stimulation. In the presence of the GJC inhibitor carbenoxolone (CBX), FSH failed to induce the meiotic resumption and the changes in PKAI, GPR3 and cAMP surge in oocyte were no longer detected. Furthermore, GPR3 was upregulated by high cAMP levels, but not by PKAI activation. When applied after FSH stimulation, the specific phosphodiesterase 3A (PDE3A) inhibitor cilostamide immediately blocked meiotic induction, regardless of when it was administered. PKAI activation inhibited mitogen-activated protein kinase (MAPK) phosphorylation in the oocytes of COCs, which participated in the initiation of FSH-induced meiotic maturation in vitro. Just before FSH-induced meiotic maturation, cAMP, PKAI, and GPR3 returned to basal levels, and PDE3A activity and MAPK phosphorylation increased markedly. These experiments show that FSH induces a transient increase in cAMP levels and regulates GJC to control PKAI and GPR3 activities, thereby creating an inhibitory phase. After PDE3A and MAPK activities increase, meiosis resumes.
Nest breakdown and primordial folliculogenesis of the mouse ovary can be inhibited by progesterone (P4) and Notch signaling inhibitors. However, the relationship between these two signals during this process remains unknown. In the present study, transcript levels of Jagged2, Notch1, and their target, Hey2, increased markedly in ovaries during the beginning stage of folliculogenesis (17.5 days post coitus (dpc) to birth). Maternal P4 levels decreased simultaneously. We found that maternal midpregnancy P4 levels significantly inhibited Jagged2, Notch1, and Hey2 expression, and follicle formation in vitro. Maintaining high maternal P4 levels by daily injection also significantly suppressed the expression of Jagged2, Notch1, and Hey2, and follicle formation during late pregnancy. Based on immunohistochemistry, Jagged2 was localized in oocytes and Notch1 was strongly stained in pre-granulosa cells in 19.5 dpc ovaries. Suppression of their function by antibody addition and RNAi markedly inhibited nest breakdown and follicle formation. Taken together, these results demonstrate that maternal P4 levels during midpregnancy can inhibit the expression of Jagged2 and Notch1, which are involved in primordial folliculogenesis, in the mouse fetal ovary.
Acute fasting impairs meiotic resumption and glucose consumption in mouse cumulus cell and oocyte complexes (COCs). This study examines the effects of acute fasting on the regulation of glucose transporter 1 (GLUT1) expression and glucose consumption in oocyte maturation. Our results indicate that the restriction of glucose utilisation by 2-deoxyglucose (2-DG) mimicked the inhibitory effects of acute fasting on oocyte meiotic resumption and cumulus cell expansion, effects that were rescued by high glucose concentrations in the culture medium. GLUT1 protein levels were higher in cumulus cells compared with oocytes, and GLUT1 expression in COCs increased with FSH treatment in vitro. However, under acute fasting conditions, GLUT1 expression in COCs decreased and the response to FSH disappeared. Exposure to high glucose conditions (27.5mM and 55mM), significantly increased both glucose consumption and GLUT1 levels in COCs. Inhibition of GLUT1 function using an anti-GLUT1 antibody significantly inhibited FSH-induced oocyte meiotic resumption. Taken together, these results suggest that acute fasting decreases GLUT1 expression and glucose utilisation, inhibiting the processes of oocyte maturation and cumulus cell expansion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.