title: Reproductive toxicity of inorganic mercury exposure in adult zebrafish: Histological damage, oxidative stress, and alterations of sex hormone and gene expression in the hypothalamic-pituitary-gonadal axis.
abstract: Mercury (Hg) is a prominent environmental contaminant that causes a variety of adverse effects on aquatic organisms. However, the mechanisms underlying inorganic Hg-induced reproductive impairment in fish remains largely unknown. In this study, adult zebrafish were exposed to 0 (control), 15 and 30μg Hg/l (added as mercuric chloride, HgCl2) for 30days, and the effects on histological structure, antioxidant status and sex hormone levels in the ovary and testis, as well as the mRNA expression of genes involved in the hypothalamic-pituitary-gonadal (HPG) axis were analyzed. Exposure to Hg caused pathological lesions in zebrafish gonads, and changed the activities and mRNA levels of antioxidant enzymes (catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx)) as well as the content of glutathione (GSH) and malondialdehyde (MDA). In females, although ovarian 17β-estradiol (E2) content remained relatively stable, significant down-regulation of lhβ, gnrh2, gnrh3, lhr and erα were observed. In males, testosterone (T) levels in the testis significantly decreased after Hg exposure, accompanied by down-regulated expression of gnrh2, gnrh3, fshβ and lhβ in the brain as well as fshr, lhr, ar, cyp17 and cyp11b in the testis. Thus, our study indicated that waterborne inorganic Hg exposure caused histological damage and oxidative stress in the gonads of zebrafish, and altered sex hormone levels by disrupting the transcription of related HPG-axis genes, which could subsequently impair the reproduction of fish. Different response of the antioxidant defense system, sex hormone and HPG-axis genes between females and males exposed to inorganic Hg indicated the gender-specific regulatory effect by Hg. To our knowledge, this is the first time to explore the effects and mechanisms of inorganic Hg exposure on reproduction at the histological, enzymatic and molecular levels, which will greatly extend our understanding on the mechanisms underlying of reproductive toxicity of inorganic Hg in fish.
authors.affiliation: Chongqing Key Laboratory of Animal Biology, School of Life Sciences, Chongqing Normal University, Chongqing 401331, China.
authors.forename: Qun-Fang
authors.initials: QF
authors.lastname: Zhang
authors.affiliation: Chongqing Key Laboratory of Animal Biology, School of Life Sciences, Chongqing Normal University, Chongqing 401331, China.
authors.forename: Ying-Wen
authors.initials: YW
authors.lastname: Li
authors.affiliation: Chongqing Key Laboratory of Animal Biology, School of Life Sciences, Chongqing Normal University, Chongqing 401331, China.
authors.forename: Zhi-Hao
authors.initials: ZH
authors.lastname: Liu
authors.affiliation: Chongqing Key Laboratory of Animal Biology, School of Life Sciences, Chongqing Normal University, Chongqing 401331, China. Electronic address: xncql@126.com.
authors.forename: Qi-Liang
authors.initials: QL
authors.lastname: Chen
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D001921:Brain / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D004958:Estradiol / Q000378:metabolism; D005260:Female; D015870:Gene Expression / Q000187:drug effects*; D012739:Gonadal Steroid Hormones / Q000235:genetics / Q000378:metabolism; D006066:Gonads / Q000187:drug effects / Q000378:metabolism; D007028:Hypothalamic Hormones / Q000235:genetics / Q000378:metabolism; D008297:Male; D008628:Mercury / Q000633:toxicity*; D010053:Ovary / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D018384:Oxidative Stress / Q000187:drug effects*; D012333:RNA, Messenger / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D013737:Testis / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D013739:Testosterone / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000633:toxicity*; D015027:Zebrafish / Q000502:physiology
chemical_list: D000975:Antioxidants; D012739:Gonadal Steroid Hormones; D007028:Hypothalamic Hormones; D012333:RNA, Messenger; D014874:Water Pollutants, Chemical; D013739:Testosterone; D004958:Estradiol; D008628:Mercury
keywords: Histological damage; Hypothalamic-pituitary-gonadal axis; Inorganic Hg exposure; Oxidative stress; Reproductive toxicity