Brain derived neurotrophic factor promotes oocyte maturation through the TrkB-MAPK-PI3K pathway in zebrafish

Brain-derived neurotrophic factor (BDNF) was previously reported as a positive modulator of zebrafish reproduction, yet the mechanism of action of BDNF that elicits this function is unknown. We hypothesized that the pro-reproductive effects of BDNF in female zebrafish are mediated by TrkB signaling. In zebrafish liver (ZFL) cells, a TrkB antagonist (ANA-12) blocked the stimulatory effect of BDNF on transcript abundance of vitellogenin (vtg1, 2, 4, and 7) and steroidogenic factor 1 (sf-1). No changes were observed in hepatocyte nuclear factor 4 alpha, specificity protein 1, cAMP response element-binding protein 1a, or forkhead box L2. Blocking the mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K), and phospholipase C gamma (PLC-γ) pathways significantly attenuated BDNF-induced upregulation of vtg and sf-1 transcripts. Total vtg protein was increased by BDNF, an effect that was blunted when TrkB, MAPK, PI3K, or PLC-γ were blocked. The estrogen receptor alpha (Esrα) fluorescence immunoreactivity in the ZFL cells treated with BDNF was significantly reduced in the presence of ANA-12. In the zebrafish follicles, BDNF-induced oocyte maturation was attenuated by TrkB, MAPK-, and PI3K inhibitors, but not a PLC-γ blocker. Similarly, the positive effects of BDNF on maturation-related genes 3β-hydroxysteroid dehydrogenase 2 enzyme (3bhsd2), cytochrome P450 family 17, hyaluronan synthase 2, luteinizing hormone receptor, and prostaglandin synthase 2 were significantly attenuated when TrkB, MAPK, or PI3K was blocked. PLC-γ inhibition prevented the BDNF-induced upregulation of 3bhsd1 in the oocytes. This study demonstrates that BDNF promotes vitellogenesis via the TrkB-MAPK/PI3K/PLC-γ signaling pathways. Meanwhile, BNDF enhances oocyte maturation through the TrkB-MAPK/PI3K pathways in zebrafish.