Transcriptome analysis provides insights into the molecular mechanism of hepatocyte apoptosis in response to feeding restriction in juvenile largemouth bass Micropterus salmoides

Feeding restriction (FR) is a scientific strategy to attenuate nutrient excess-mediated liver metabolic syndromes in human beings. However, it is still unclear whether liver health could benefit from FR in cultured animals including fish. In this regard, the regulatory role of FR in liver health of juvenile largemouth bass Micropterus salmoides were investigated in this study using single-molecule real-time sequencing and next-generation sequencing. Groups of fish (20 fish per group) with an initial body weight of 6.9 g were randomly allocated into 12 rectangular tanks (250 L each) operating as a recirculating aquaculture system. The satiation (ST) fish was fed to satiation, while ration levels of the moderately restricted (MR) and highly restricted (HR) fish were maintained at 85% and 70% of the ST fish, respectively. All fish were fed a commercial extruded diet containing 49.9% crude protein and 13.2% crude lipid. After a 9-week feeding trial, growth performance of the MR fish was not affected through improving the feed utilization as compared with the ST fish. Even though feed utilization was further improved, growth of the HR fish was still impaired. The MR fish obtained superior antioxidant status in the plasma and liver (based on glutathione or malondialdehyde concentration, and total antioxidant capacity and superoxide dismutase activities) together with better liver integrity (based on HE and TUNEL staining) than the other treatments. A total of 38,909 full-length transcripts were generated from the sequencing. GO enrichment analysis of the differentially expressed genes (DEGs) showed that many terms related to immunization and wound repair were enriched in the feed restricted fish (especially the MR fish). A total of 701 DEGs were identified in the liver of the MR fish as compared with the ST fish, and the apoptosis was enriched as the prominent pathway by KEGG pathway analysis. Our results suggested that the intrinsic apoptosis pathway played an important role in the hepatocyte apoptosis inhibition in the MR fish. Specifically, the activation of Akt might mediate an anti-apoptosis role through inhibiting the release of direct IAP binding protein with low pI (DIABLO) from mitochondria and promoting the transcription of pro-survival genes such as X-linked inhibitor-of-apoptosis protein (xiap), which coordinately activated the inhibitor of apoptosis protein (IAP). Besides the intrinsic apoptosis pathway, our results indicated that the lysosome pathway and endoplasmic reticulum stress pathway might also participate in regulating hepatocyte apoptosis inhibition of the MR fish.