Sex-dependent effects of subacute mercuric chloride exposure on histology, antioxidant status and immune-related gene expression in the liver of adult zebrafish (Danio rerio).

Mercury (Hg) is a global pollutant that causes negative health effects. In order to assess Hg-induced hepatotoxicity in fish and examine whether gender differences existed in response to Hg exposure, adult zebrafish were exposed to 0, 15 and 30 µg L-1 Hg2+ for 30 days, and histology, antioxidant status and the transcription levels of several immune-related genes were examined in the liver. Hg2+ exposure caused a dose-dependent increase in histopathological lesions of the liver, including vacuolization, parenchyma disorganization and pyknotic nucleus, and these lesions were more severe in males than in females. In females, Hg2+ exposure decreased CAT activity and its mRNA levels, while increased GSH content and the expressions of sod1, gpx1a, gstr and keap1. In males, the decrease in cat1 expression and the increase in GST activity, GSH and MDA contents as well as gpx1a, gstr, nrf2 and keap1 mRNA levels were observed in Hg2+-exposed groups, but the activities of CAT, SOD and GPX were only stimulated in the 15 µg L-1 Hg2+ group. Moreover, both in females and males, Hg2+ exposure down-regulated il-8 expression while up-regulated il-10 and lyz mRNAs. However, the down-regulation of il-1ß and tnfα was detected only in males under Hg2+ treatments. Thus, our results indicated that HgCl2 exposure induced histopathological damage, oxidative stress and immunotoxicity in the liver of zebrafish. Different response patterns of histology, antioxidant status and immune defenses to Hg2+ between females and males suggested sex-dependent effects of Hg, and males showed more vulnerable to Hg2+ exposure than females.