Serum biochemistry, liver histology and transcriptome profiling of bighead carp Aristichthys nobilis following different dietary protein levels

Abstract

ABSTRACT Dietary protein plays a major role in determining the rate of fish growth and overall health. Given that the liver is an important organ for metabolism and detoxification, we hypothesized that optimal dietary protein levels may benefit liver function. Herein, we investigated the effects of dietary protein level on serum biochemistry, liver histology and transcriptome profiling of juvenile bighead carp Aristichthys nobilis fed for 8 weeks on a diet supplemented with high protein (HP, 40%), low protein (LP, 24%) or optimal protein (OP, 32%; controls). The results revealed a significant change in liver morphology in LP and HP groups compared with the OP group, coupled with increased serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activity. RNA sequencing (RNA‐Seq) analysis of the liver transcriptome yielded 47 million high‐quality reads using an Illumina platform, which were de novo assembled into 80,777 unique transcript fragments (unigenes) with an average length of 1021 bp. Subsequent bioinformatics analysis identified 878 and 733 differentially expressed unigenes (DEGs) in liver in response to LP and HP diets, respectively. KEGG enrichment analysis of DEGs identified immune and metabolism‐related pathways, including Toll‐like receptor signaling, PI3K‐Akt signaling, NF‐&kgr;B signaling, complement and coagulation, peroxisome, nitrogen metabolism, PPAR signaling, and glycolysis and gluconeogenesis pathways. Transcriptome profiling results were validated by quantitative real‐time PCR for 16 selected DEGs. The findings expand our understanding of the molecular mechanisms underlying the effects of dietary protein level on liver function in bighead carp. HighlightsThe effects of dietary protein level on liver function in bighead carp were explored.A high protein diet caused hepatic injury, and an optimal protein diet did not.Many differentially expressed genes were linked to immune responses and metabolism.KEGG analysis identified inflammatory and Toll‐like receptor signaling pathways.