Melatonin Alleviates the Suppressive Effect of Hypoxanthine on Oocyte Nuclear Maturation and Restores Meiosis via the Melatonin Receptor 1 (MT1)-Mediated Pathway

Abstract

It is well known that hypoxanthine (HX) inhibits nuclear maturation of oocytes by elevating the intracellular cAMP level, while melatonin (MT) is a molecule that reduces cAMP production, which may physiologically antagonize this inhibition and restore the meiosis process. We conducted in vitro and in vivo studies to examine this hypothesis. The results showed that 10–3 M MT potentiated the inhibitory effect of HX on mouse oocyte meiosis by lowering the rate of germinal vesicle breakdown (GVBD) and the first polar body (PB1). However, 10–5 M and 10–7 M MT significantly alleviated the nuclear suppression induced by HX and restored meiosis in 3- and 6-week-old mouse oocytes, respectively. We identified that the rate-limiting melatonin synthetic enzyme AANAT and melatonin membrane receptor MT1 were both expressed in oocytes and cumulus cells at the GV and MII stages. Luzindole, a non-selective melatonin membrane receptor antagonist, blocked the activity of MT on oocyte meiotic recovery (P < 0.05). This observation indicated that the activity of melatonin was mediated by the MT1 receptor. To understand the molecular mechanism further, MT1 knockout (KO) mice were constructed. In this MT1 KO animal model, the PB1 rate was significantly reduced with the excessive expression of cAPM synthases (Adcy2, Adcy6, Adcy7, and Adcy9) in the ovaries of these animals. The mRNA levels of Nppc and Npr2 were upregulated while the genes related to progesterone synthesis (Cyp11a11), cholesterol biosynthesis (Insig1), and feedback (Lhcgr, Prlr, and Atg7) were downregulated in the granulosa cells of MT1 KO mice (P < 0.05). The altered gene expression may be attributed to the suppression of oocyte maturation. In summary, melatonin protects against nuclear inhibition caused by HX and restores oocyte meiosis via MT1 by reducing the intracellular concentration of cAMP.

Maternal obesity may disrupt offspring metabolism by inducing oocyte genome hyper-methylation via increased DNMTs

“…Melatonin receptors (MT1 and 2), which couples with inhibitor G-protein (Gi), are identified in oocytes and granulosa cells ( 27, 28 ). The activated Gi inhibits the activation of adenylyl cyclases (ADCYs), resulting in decrease of cAMP (cyclic adenosine monophosphate), which regulates the activation of protein kinase A (PKA) and CREB (cAMP response element-binding protein) ( 29 ).…”

“…Nevertheless, the molecular mechanism of melatonin regulating DNA methylation in oocytes is still covered. Melatonin has two receptors, MT1 and MT2, both of which have been identified in oocytes ( 27 ). Melatonin receptors couple with inhibitor G-protein and can regulate gene expression via cAMP/PKA/CREB pathway ( 29 ).…”

Prolonged Administration of Melatonin Ameliorates Liver Phenotypes in Cholestatic Murine Model

“…14 Several studies in other cell systems have shown that melatonin effects are mediated by interaction with the MT1 receptor. 41,42 MT1-melatonin interaction also ameliorates liver injury caused by alcohol gastric perfusion reducing lipid peroxidation through down-regulation of cAMP, but enhanced the activity of AMPK. 41 Moreover, melatonin-MT1 interaction inhibits insulin secretion in rat insulinoma cells and mouse pancreatic islets through decreased phosphorylation of CREB protein.…”

In Vivo and In Vitro Matured Oocytes From Mice of Advanced Reproductive Age Exhibit Alternative Splicing Processes for Mitochondrial Oxidative Phosphorylation

“…For IVM, oocytes were cultured in M16 medium (Sigma, M7292) under paraffin oil for 12 h at 37°C in a 5% CO 2 incubator. For melatonin treatment, oocytes were cultured in M16 medium at a final concentration of 1 mM melatonin (Sigma, M5250) in accordance with previous studies (38,39). For IVO, mice injected with PMSG were further injected with 5 IU of human chorionic gonadotropin (hCG) 46 h later.…”