Melatonin-Nrf2 Signaling Activates Peroxisomal Activities in Porcine Cumulus Cell-Oocyte Complexes

Abstract

Melatonin and Nrf2 signaling synergistically improve mammalian oocyte maturation and embryonic development. Furthermore, previous studies have suggested an interplay between peroxisomes and Nrf2 signaling in cells, but it is still unclear whether peroxisomes are involved in oocyte maturation. The aim of the present study was to identify the possible roles of peroxisomes in the melatonin-Nrf2 signaling pathway during in vitro maturation (IVM) of porcine oocytes. Porcine oocytes were treated with melatonin (10−9 M) and brusatol, a Nrf2 specific inhibitor, in order to investigate the mechanism. Then, the rates of maturation and related gene and protein expression were analyzed. During oocyte maturation, melatonin upregulated the expression of gene and protein related to Nrf2 signaling and peroxisomal activities; RNA sequencing partially validated these results. Our results demonstrate that melatonin can activate Nrf2 signaling by binding to melatonin receptor 2, resulting in the upregulation of catalase. Moreover, peroxisomes were also found to be activated in response to melatonin treatment, causing the activation of catalase; together with Nrf2 signaling, peroxisomes synergistically prevented the generation of reactive oxygen species and enhanced oocyte quality. Thus, we suggest that a crosstalk might exist between Nrf2 signaling and peroxisomal activities in porcine oocytes.

Melatonin Restores the Developmental Competence of Heat Stressed Porcine Oocytes, and Alters the Expression of Genes Related to Oocyte Maturation

“…Brusatol (an Nrf2 specific inhibitor) inhibits expression of Nrf2, and modulates Cyclin B1 level to disturb proper spindle assembly and chromosome condensation in mouse oocytes [ 13 ]. Melatonin increases the Nrf2 expression, but Brusatol neutralizes the effects on Nrf2 expression induced by melatonin in porcine COCs [ 48 ]. Therefore, HS may induce overexpression of NRF2 , and have negative effects on the porcine oocytes, but melatonin treatment may have beneficial effects through attenuating NRF2 overexpression.…”

Melatonin Promotes In Vitro Maturation of Vitrified-Warmed Mouse Germinal Vesicle Oocytes, Potentially by Reducing Oxidative Stress through the Nrf2 Pathway

“…Vitrification had no significant effect on GCLM and SOD2 genes, indicating that these genes were more stable and perhaps either produced a strong response to cold stimulation or had differences related to the timeliness of their functions [ 62 ]. Melatonin can enhance the expression of genes related to the intracellular Nrf2 pathway in response to oxidative stress [ 25 , 35 , 63 ]. Similarly, in this study, melatonin restored levels of Nrf2 and SOD1 genes during in vitro development of vitrified-warmed mouse GV oocytes.…”

“…During in vitro maturation of vitrified-warmed mouse GV oocytes, 10 −7 M melatonin restored the expression levels of Nrf2 and HO-1, indicating that melatonin can reduce the intracellular oxidative stress by protecting proteins related to the Nrf2 signaling pathway. Similarly, melatonin-enhanced Nrf2 and downstream proteins in response to injury stress on porcine COC oocytes [ 35 ], rat hippocampus [ 68 ], human alveolar epithelial cells [ 23 ], and rat bladders [ 69 ], etc. Melatonin can regulate Nrf2 signaling pathway-related proteins to respond to stress through its receptors [ 38 , 39 ].…”

“…Melatonin receptors, MT1 (MEL-1A) and MT2 (MEL-1B), are mainly distributed on the cell membrane [ 32 , 33 , 34 , 35 ]. Melatonin can have an antioxidant role in cells through receptors, such as by protecting against cisplatin-induced ovarian damage in mice [ 36 ] and delaying the fertility decline in female animals [ 37 ].…”

Crosstalk between Peroxisomal Activities and Nrf2 Signaling in Porcine Embryos

“…The entire process of porcine IVM has been previously described [ 34 ]. In brief, ovaries from a local abattoir were collected and delivered to the laboratory.…”