Nitrite-induced hepatotoxicity in Bluntsnout bream (Megalobrama amblycephala): The mechanistic insight from transcriptome to physiology analysis

Previous studies have investigated the physiological responses to acute nitrite exposure in fish; however, little information is available for the underlying molecular mechanisms of nitrite toxicity in aquatic ecosystems. In an effort to understand the underlying mechanisms of nitrite tolerance and to illuminate global gene expression patterns modulated by nitrite toxicity, we sampled livers from juvenile Megalobrama amblycephala exposed in 0.1, 15 and 30mgL^-1 nitrite and performed short read (100bp) next generation RNA sequencing (RNA-seq). The RNA-seq reads from all the exposures (24million reads) were assembled into unigenes datasets according to an available reference transcriptome. Using reads from each nitrite concentration, we performed RNA-seq based gene expression analysis that identified a total of 357 differentially expressed genes. The differentially expressed genes were related to oxidative stress, apoptotic pathway, oxygen transport, immune responses and the metabolism of proteins and fats. Quantitative real-time polymerase chain reaction using six genes independently verified the RNA-seq results, the present study suggests several new candidate genes commonly regulated in liver of M. amblycephala. In addition to liver histology examinations, this study provides important mechanistic insights into nitrite-induced liver toxicity in a whole-animal physiology context, which will help in understanding the syndromes caused by nitrite poisoning.