Triclosan-induced abnormal expression of miR-30b regulates fto-mediated m6A methylation level to cause lipid metabolism disorder in zebrafish

Chronic exposure of triclosan (TCS) to zebrafish triggers high incidence of fatty liver and hepatitis; however, the underlying molecular mechanisms remain unclear. Herein, we identified miR-30b as a sensitive biomarker to TCS stress, reflecting in that its decreased expression caused metabolic toxicity, abnormal development and behavior, and lipid-metabolism disorder. By microinjecting the inhibitor and mimic experiments, miR-30b was proved to regulate lipid metabolism by its main target gene fto . Over-expression of FTO resulted in fat accumulation, elevation of the TG and TC levels and up-regulation of the PPARγ and CEBPα, as well as decrease of the global m 6 A level in larvae. On the contrary, the knock-down of FTO using MO caused the anti-lipogenic effect, decrease of the TG and T-CHO levels, and abnormal changes of cebpɑ , acsl 5, fasn , ppap 2c and ppar γ etc. Further fortification tests of cycloleucine and betaine evidenced that the toxic effect was strongly dependent on regulation of the m 6 A level. The toxicity effects in the treatments of methylated donors and receptors were consistent with the changes in physiological functions of FTO knockdown and overexpression. The effects of cycloleucine on m 6 A level and lipid metabolism generally consisted with those of FTO, but this was not the case for betaine, reflecting in increased m 6 A level and lipid accumulation in larval liver. Consequently, we posit that TCS exposure caused zebrafish lipid-metabolism disorder by decreasing miR-30b expression to regulate fto-mediated m 6 A methylation level. These findings contribute to our deep understanding of the underlying molecular mechanisms regarding contaminant-originating fatty liver and hepatocellular carcinoma, and also have practical significance in pollution warning and target therapy for related diseases.