Hypoxia alters steroidogenesis in female marine medaka through miRNAs regulation

Hypoxia is a worldwide environmental problem in marine ecosystems, leading to serious declines in fishery production over large areas. Our previous studies demonstrated that hypoxia is an endocrine disruptor which can cause reproductive impairment through the regulation of miRNAs, suggesting the functional role of miRNAs in reproductive systems in response to hypoxia. In this study, we used small RNA sequencing to determine the change in miRNA profile in ovary of marine medaka Oryzias melastigma under hypoxic stress. A total of 509 miRNAs were found in the ovary of marine medaka, in which, 33 and 10 miRNAs were found to be statistically significant upregulated and downregulated under hypoxia, respectively. Bioinformatics analysis highlighted that a large number of hypoxia-suppressed miRNAs that target a variety of steroidogenic enzymes including steroidogenic acute regulatory protein, aromatase, and 17-alpha-monooxygenase. Also, estrogen receptor 2 and androgen receptor were found to be targeted by hypoxia-responsive miRNAs. For the first time, our results showed that hypoxia may upregulate specific steroidogenic enzymes and hormone receptors through actions of miRNA, and hence provide a novel mechanism for the observed female reproductive impairment caused by hypoxia.