Nitric Oxide Synthase Activity Is Critical for the LH-Induced Ovulatory Cascade in Bovine Granulosa Cells.
Notice bibliographique
Résumé
Fertility in dairy and beef cows is negatively affected by stressors such as lamness and high milk yield, and one site of action of these stressors is the process of ovulation. Rupture of the follicle is initiated by the preovulatory surge of LH, which stimulates granulosa cell release of the EGF-like ligands epiregulin (EREG) and amphiregulin (AREG), which activate EGF receptors in granulosa and cumulus cells to stimulate prostaglandin synthase 2 (PTGS2, also known as COX2) expression, prostaglandin secretion and downstream expression of cumulus expansion genes. Various factors have been implicated in the control of this process, including endogenous nitric oxide (NO). In rodents, NO has been associated either positively or negatively with ovulation. The objectives of the present study were to determine (1) if endogenous NO is critical for expression of genes critical for the ovulatory cascade in bovine granulosa cells, (2) and to determine if nitric oxide synthase (NOS) enzymes are regulated by LH. We employed a short-term bovine granulosa cell (GC) culture system in which AREG, EREG and PTGS2 mRNA levels are acutely upregulated by LH. The first series of experiments was performed to determine the importance of NO in the preovulatory cascade. Pretreatment of cells with a NOS inhibitor, L-NAME, effectively blocked the effect of LH on EREG, AREG and PTGS2 mRNA abundance at 6 hours post-LH, and on PTGS2 protein levels at 12 hours post LH challenge (P<0.05). To determine if NO is necessary for downstream, EGFR-dependent signaling, cells were pretreated with L-NAME and challenged with EGF; EGF alone increased mRNA encoding EREG within 1 h, and this was inhibited by pretreatment with L-NAME. EGF alone increased abundance of mRNA encoding AREG and the nuclear orphan receptors NR5A1 and NR5A2 after 8 h, and L-NAME inhibited the effect of EGF. A second series of experiments was performed to determine the regulation of NOS mRNA abundance in bovine GC. Time- and dose-response experiments demonstrated that LH had a significant stimulatory effect on NOS3 (eNOS) mRNA abundance (P<0.05), although transcriptional regulation of NOS3 was not observed until 12 h of LH treatment, much later than that of EREG mRNA (1-3 h). Messenger RNA encoding NOS2 (iNOS) was detected at very low levels and was not investigated further. Further experiments demonstrated that EGF stimulated NOS3 mRNA levels in a dose-dependent manner (P<0.05). As some studies report a positive feedback loop between prostaglandin E2 (PGE2) and EGF-like factors in cumulus cells, we tested whether PGE2 stimulates NOS3 mRNA levels in mural granulosa cells. The results confirmed that PGE2 stimulates EREG and also NOS3 mRNA levels (P<0.05). Moreover, when cells were pretreated with indomethacin, a PTGS2 inhibitor, EGF was not capable of inducing NOS3 and EREG mRNA levels (P<0.05), suggesting that the transcriptional regulation of NOS3 is prostaglandin dependent. To our knowledge, this is the first study indicating an interaction between nitric oxide and EGF-like factors during the preovulatory period. Taken together, these results suggest that endogenous NOS activity is critical for LH-induced ovulatory cascade in granulosa cells and NO may be essential for ovulation in cattle. Supported by FRQNT and NSERC Canada.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».