Notch2 Regulates the Function of Bovine Follicular Granulosa Cells via the Wnt2/ß-Catenin Signaling Pathway.

Ovarian follicular GCs are strongly implicated in the growth, development, and atresia of ovarian follicles. The Wnt/ß-catenin and Notch signaling pathways participate in GC proliferation, differentiation, apoptosis, and steroid hormone production during follicular development. However, the crosstalk between Wnt and Notch signaling in GCs remains unclear. This study investigated this crosstalk and the roles of these pathways in apoptosis, cell cycle progression, cell proliferation, and steroid hormone secretion in bovine follicular GCs. The interaction between ß-catenin and Notch2 in GCs was assessed by overexpressing CTNNB1, which encodes ß-catenin. The results showed that inhibiting the Notch pathway by Notch2 silencing in GCs arrested the cell cycle, promoted apoptosis, reduced progesterone (P4) production, and inhibited the Wnt2-mediated Wnt/ß-catenin pathway in GCs. IWR-1 inhibited Wnt2/ß-catenin and Notch signaling, reduced GC proliferation, stimulated apoptosis, induced G1 cell cycle arrest, and reduced P4 production. CTNNB1 overexpression had the opposite effect and increased 17ß-estradiol (E2) production and Notch2 protein expression. Co-immunoprecipitation assays revealed that Notch2 interacted with ß-catenin. These results elucidate the crosstalk between the Wnt/ß-catenin and Notch pathways and the role of these pathways in bovine follicular GC development.

Cross-talk between NOTCH2 and BMP4/SMAD signaling pathways in bovine follicular granulosa cells.

NOTCH and bone morphogenetic protein (BMP)/SMAD signaling play key regulatory roles in mammalian ovarian development. The study aimed to investigate interregulatory mechanisms between NOTCH2 and BMP4/SMAD signaling pathways in bovine follicular granulosa cells (GCs). The results showed that NOTCH2 silence reduced the mRNA expression of SMAD1, SMAD5, SMAD8 (also known as SMAD9) and Mg2+/Mn2+- dependent Protein Phosphatase 1A (PPM1A), which are effectors of BMP/SMAD signaling pathway (P < 0.01). Overexpressing NOTCH2 intracellular sequence increased the mRNA expression of BMPR1A, SMAD1, SMAD4, SMAD5, SMAD8 and PPM1A (P < 0.01). Meanwhile, treating GCs with BMP4 inhibited the mRNA expression of its downstream gene SMAD1 and steroidogenesis genes STAR and CYP11A1 in the presence of follicular stimulating hormone (FSH) (P < 0.01). Moreover, BMP4 inhibited the mRNA expression of NOTCH signaling pathway target gene HES1 (P < 0.05), while the increase in NOTCH2 may be due to negative feedback of HES1. By and large, these results indicated that NOTCH2 up-regulated key genes of BMP/SMAD signaling in bovine follicle GCs, while BMP4 inhibited its downstream signaling factors and NOTCH signaling pathway target gene HES1. This study suggests there are complex synergistic and antagonistic effects between the two signaling pathways, which jointly participate in regulating bovine follicular development through regulating follicular GCs.

Neddylation inactivation affects cell cycle and apoptosis in sheep follicular granulosa cells.

Protein neddylation inactivation is a novel topic in cancer research. However, there are few studies on the mechanism of neddylation underlying the development of sheep follicular granulosa cells (GCs). In this study, the development of follicular GCs in sheep was inactivated by MLN4924, a neddylation-specific inhibitor, which significantly attenuated the proliferation and cell index of sheep follicular GCs. Further, the inactivation of neddylation by MLN4924 caused the accumulation of the cullin ring ligase (CRLs) substrates Wee1 and c-Myc, which could upregulate NOXA protein expression. Meanwhile, the B-cell lymphoma/leukemia 2 (BCL2) family members Bcl-2 and MCL-1 were downregulated, subsequently inducing apoptosis in follicular GCs of sheep. Increasing Wee1 levels caused G2/M-phase arrest. The effects of neddylation inactivation on Akt, the JAK2/STAT3 signaling pathway, and Forkhead box class O(FOXO) family members were evaluated. Neddylation inactivation by MLN4924 increased the levels of phospho-Akt, JAK2, phospho-STAT3, and FOXO1 (p < 0.05) and decreased the levels of phospho-FOXO3a and STAT3 (p < 0.05). In addition, MLN4924 could alter the mitochondrial morphology of GCs, increase cellular glucose utilization and lactate production, increase reactive oxygen species (ROS) generation, and promote sheep follicular GCs glycolysis, thus causing changes in mitochondrial functions. Together, these findings point to an unrecognized role of neddylation in regulating follicular GCs proliferation in sheep.

Effects of Notch2 on proliferation, apoptosis and steroidogenesis in bovine luteinized granulosa cells.

Notch signaling pathway plays an important regulatory role in the development of mammalian follicles. This study aimed to explore the effect of Notch2 on the function of bovine follicles luteinized granulosa cells (LGCs). We detected that the coding sequence (CDS) of bovine Notch2 gene is 7416 bp, encoding 2471 amino acids (AA). The homology of Notch2 AA sequence between bovine and other species is 86.04%-98.75%, indicating high conservatism. Immunohistochemistry found that Notch2 receptor and its ligand Jagged2 localize in granulosa cells (GCs) and theca cells in bovine antral follicles. And immunofluorescence found that positive signals of Notch2 and Jagged2 overlap in bovine LGCs, speculating that Notch2 receptor may react with Jagged2 ligand to activate Notch signaling pathway and play an important role in bovine LGCs. To further investigate the function of Notch2, Notch2 gene was silenced by short hairpin RNA (shRNA) and CCK-8 analysis showed that the proliferation rate of LGCs was downregulated significantly (P < 0.01). Quantitative reverse transcription polymerase chain reaction (qRT-PCR) showed that the mRNA expression of apoptosis related gene Bcl-2/Bax decreased (P < 0.01) and Caspase3 increased (P < 0.05), cell cycle related gene CyclinD2/CDK4 complex decreased (P < 0.01) and P21 increased (P < 0.05), steroidogenesis gene STAR and 3ß-HSD decreased (P < 0.01) while CYP19A1 and CYP11A1 had no significant difference (P > 0.05). In addition, Enzyme-linked immunosorbent assay (ELISA) showed that there was no difference in estradiol (E2) secretion (P > 0.05) while the progesterone (P4) secretion decreased (P < 0.01). In conclusion, Notch2 plays an important role in regulating bovine LGCs development.

Effects of FOXO1 on the proliferation and cell cycle-, apoptosis- and steroidogenesis-related genes expression in sheep granulosa cells.

Forkhead boxO (FOXO) transcription factors regulate diverse biological processes, including cellular metabolism, cell apoptosis, and the cell cycle. Results from several studies indicate FOXO1 regulates different granulosa cell (GC) pathways involved in proliferation, survival and differentiation. Functions and mechanisms of FOXO1 regulation of sheep GCs remain unclear. This study was conducted to analyze the function of FOXO1 in regulation of sheep GCs. In this study, the 1827 bp sheep FOXO1 coding sequence was cloned from sheep GCs. Multiple sequence alignment and phylogenetic analysis indicated that the FOXO1 protein sequence is highly homologous to FOXO1 protein sequences from other species. The results obtained from using CCK-8 assays indicated sheep GC proliferation increased when there was suppression of FOXO1 gene expression. When there was induced expression of the FOXO1 gene in sheep GCs, there was a resulting increased abundance of P21 and P27 mRNA transcript, whereas suppression of the FOXO1 gene expression had the opposite effect. Furthermore, the relative abundance in vitro of apoptosis-related protein mRNA transcripts (caspase3, caspase8, caspase9, Bax/Bcl-2) was markedly increased or decreased when there was induction or suppression of FOXO1 gene expression, respectively,(P < 0.05). Induction of FOXO1 gene expression resulted in an increase in abundance of steroidogenic protein mRNA transcripts (CYP11A1, 3ß-HSD), while suppression of FOXO1 gene expresion resulted in a decrease abundance of the CYP11A1, STAR mRNA transcripts. Results from the present study indicated that FOXO1 inhibited the proliferation of sheep GCs and affected mRNA transcript abundance for proteins involved in regulation of apoptosis, the cell cycle and steroidogenesis.