Microcystin-LR Interferes With The Reproductive Endocrine System:In Vivo And In Vitro Studies

Microcystins(MCs) are a family of the most frequent occurrence, the highest output and the most serious harm cyanobacterial toxins in algae blooms. Recent studies have documented that MCs can cause gonadal pathological damage and disrupt the balance of sex steroid hormone levels, and thus are one of potential environmental endocrine disruptors. In the present study, using MC-LR as experiment toxin, both in vivo and in vitro experiments were carried out to investigate the toxic effect of MC-LR on the reproductive system and the potential mechanism in endocrine disruption at the levels of the histological structure, hormone levels and gene expression related to the synthesis and regulation of sex steroid hormone.In in vivo experiment, zebrafish hatchlings(5 d post-fertilization) were exposed to 0, 0.3, 3 and 30 μg/L MC-LR for 90 d until they reached sexual maturity. Male zebrafish were selected and the changes in growth and developmental parameters, testis histological structure and the levels of gonadal steroid hormones as well as the related-gene transcriptional responses in the hypothalamic-pituitary-gonadal axis(HPG-axis) were studied. The results for the first time showed a life cycle exposure to MC-LR caused the growth inhibition, testicular damage and delayed sperm maturation. A significant decrease in T/E2 ratio indicated that MC-LR disrupted sex steroid hormones balance. The changes in transcriptional responses of HPG-axis related genes(gnrh2, gnrh3, fshβ, lhβ, ar and cyp19a1b) revealed that MC-LR promoted the conversion of T to E2 in circulating blood. It was also noted that vtg1 m RNA expression in the liver were all up-regulated, which implied that MC-LR could induce estrogenic-like effects at environmentally relevant concentrations and long-term exposure. Our findings indicated that a life cycle exposure to MC-LR cause endocrine disruption and organic and functional damage of the testis, which might compromise quality of life of the survivors and pose a potent threat on fish reproduction and thus population dynamics in MCs-contaminated aquatic environment.In in vitro experiment, it is the first time using H295 R human adenocarcinoma cells to determine the potential effects of MC-LR on steroidogenesis. H295 R cells were exposed to MC-LR at the concentrations of 0, 1, 10, 100, 500, 1000, 5000 n M for 48 h respectively. And the cells and culture medium were collected, respectively. Sex hormone levels and steroidogenic gene transcriptions were measured. Results showed that MC-LR upregulated the expression of the steroidogenic genes like St AR, HMGR, CYP11 A, CYP17, 17β-HSD1, 17β-HSD4 and CYP19 at all MC-LR-treated groups, suggesting MC-LR caused the endocrine disruption in vitro. At the low concentration groups(1 and 10 n M MC-LR), the levels of both 17-estradiol(E2) and testosterone(T) were significant increased along with the significantly up-regulated CYP19, indicating that low concentration of MC-LR enhanced the conversion to E2 by altering the expression of CYP19 and caused an estrogenic-like responses in H295 R cell. In conclusion, the regulation of MC-LR on steroid synthesis pathways may be one mechanism of its reproductive toxicology and endocrinedisrupting effects.