Comparative genomic and functional analyses of the insulin signaling pathway in response to high-carbohydrate feeding in largemouth bass (Micropterus salmoides)

Abstract

Limited carbohydrate utilization is a common metabolic challenge in carnivorous fish, including largemouth bass (Micropterus salmoides). This study integrated in vivo feeding trials, in vitro primary hepatocyte experiments, and comparative genomic analyses to investigate the mechanisms underlying limited carbohydrate utilization in this species. Prolonged high-carbohydrate feeding decreased serum insulin levels and increased hepatic glycogen levels, accompanied by alterations in hepatic insulin signaling and glucose metabolism. A high-carbohydrate diet suppressed hepatic insulin signaling, including components of the IR/PI3K/AKT pathway, downregulated glycolytic genes (gk and pk), and differentially regulated gluconeogenic genes (pepck, fbp1, and g6pc), indicating limited glucose utilization and altered regulation of gluconeogenesis. Comparative genomic analysis across 18 teleost species revealed that key insulin signaling genes (ins, ir, irs, pi3k, and akt) were highly conserved in largemouth bass, although ins exhibited greater evolutionary divergence, suggesting lineage-specific diversification. In in vitro, insulin supplementation partially ameliorated high-glucose-induced alterations by upregulating irs and pik3r1 expressions and restoring akt1 expression, indicating that insulin pathway responsiveness was retained. Western blot further confirmed insulin-mediated modulation of INSR, PI3K, and AKT1 phosphorylation. Meanwhile, the selective recovery of glycolytic and gluconeogenic gene expression indicated pathway-specific sensitivity to insulin. These findings indicate that largemouth bass exhibit reduced serum insulin levels and widespread suppression of hepatic insulin signaling under high-carbohydrate conditions, whereas exogenous insulin partially restores the associated metabolic alterations.

Keywords

High-carbohydrate feeding / Insulin pathway / Glucose metabolism / Genome-wide identification / Micropterus salmoides

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