title: Melatonin-induced increase of lipid droplets accumulation and in vitro maturation in porcine oocytes is mediated by mitochondrial quiescence.
abstract: Melatonin, the major pineal secretory product, has a significant impact on the female reproductive system. Recently, the beneficial effects of melatonin on mammalian oocyte maturation and embryonic development have drawn increased attention. However, the exact underlying mechanisms remain to be fully elucidated. This study demonstrates that supplementing melatonin to in vitro maturation (IVM) medium enhances IVM rate, lipid droplets (LDs) accumulation as well as triglyceride content in porcine oocytes. Decrease of mitochondrial membrane potential, mitochondrial respiratory chain complex IV activity as well as mitochondrial reactive oxygen species (mROS) content indicated that melatonin induced a decrease of mitochondrial activity. The copy number of mitochondrial DNA (mtDNA) which encodes essential subunits of oxidative phosphorylation (OXPHOS), was not affected by melatonin. However, the expression of mtDNA-encoded genes was significantly down-regulated after melatonin treatment. The DNA methyltransferase DNMT1, which regulates methylation and expression of mtDNA, was increased and translocated into the mitochondria in melatonin-treated oocytes. The inhibitory effect of melatonin on the expression of mtDNA was significantly prevented by simultaneous addition of DNMT1 inhibitor, which suggests that melatonin regulates the transcription of mtDNA through up-regulation of DNMT1 and mtDNA methylation. Increase of triglyceride contents after inhibition of OXPHOS indicated that mitochondrial quiescence is crucial for LDs accumulation in oocytes. Taken together, our results suggest that melatonin-induced reduction in mROS production and increase in IVM, and LDs accumulation in porcine oocytes is mediated by mitochondrial quiescence.
authors.affiliation: Key Laboratory of Animal Physiology and Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, Nanjing, P. R. China.
authors.forename: Bin
authors.initials: B
authors.lastname: He
authors.affiliation: Key Laboratory of Animal Physiology and Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, Nanjing, P. R. China.
authors.forename: Chao
authors.initials: C
authors.lastname: Yin
authors.affiliation: Key Laboratory of Animal Physiology and Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, Nanjing, P. R. China.
authors.forename: Yabin
authors.initials: Y
authors.lastname: Gong
authors.affiliation: Key Laboratory of Animal Physiology and Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, Nanjing, P. R. China.
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.affiliation: Key Laboratory of Animal Physiology and Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, Nanjing, P. R. China.
authors.forename: Huiduo
authors.initials: H
authors.lastname: Guo
authors.affiliation: Key Laboratory of Animal Physiology and Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, Nanjing, P. R. China.|Jiangsu Collaborative Innovation Center of Meat Production and Processing, Quality and Safety Control, Nanjing, P. R. China.
authors.forename: Ruqian
authors.identifier: http://orcid.org/0000-0001-8019-8480
authors.initials: R
authors.lastname: Zhao
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation; D004272:DNA, Mitochondrial / Q000235:genetics / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000378:metabolism; D004734:Energy Metabolism / Q000187:drug effects*; D005260:Female; D005786:Gene Expression Regulation; D059471:In Vitro Oocyte Maturation Techniques; D066292:Lipid Droplets / Q000187:drug effects* / Q000378:metabolism; D008550:Melatonin / Q000494:pharmacology*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D009865:Oocytes / Q000187:drug effects* / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D034421:Sus scrofa; D014280:Triglycerides / Q000378:metabolism
chemical_list: D004272:DNA, Mitochondrial; D017382:Reactive Oxygen Species; D014280:Triglycerides; D003576:Electron Transport Complex IV; D004248:DNA (Cytosine-5-)-Methyltransferases; D008550:Melatonin
keywords: DNA methyltransferase 1; in vitro maturation; melatonin; mitochondrial quiescence; oocyte