Meeting Abstract
Insulin-like growth factor-1 (Igf1) regulates skeletal muscle growth in fishes by increasing protein synthesis and promoting muscle hypertrophy. In the wild, fish can experience periods of insufficient food intake that can lead to slower muscle growth or muscle wasting, and those changes are linked in part to nutritional modulation of Igf1 signaling. Here, we examined how food deprivation (fasting) affects Igf1 regulation of skeletal muscle gene expression in gopher rockfish (Sebastes carnatus) to understanding how food limitation affects Igf-mediated muscle growth. Juvenile rockfish were either fasted or fed (9% mass feed ration per d per g wet fish mass) for 14 d, after which a subset of fish from each group was injected with recombinant Igf1 (1 μg per g body mass) from sea bream (Sparus aurata). Fasted fish lost body mass and had a lower body condition factor (k), lower hepatosomatic index, reduced plasma Igf1 concentrations, and lower relative mRNA levels for igf1 in skeletal muscle. Fasted fish also showed elevated mRNA levels for Igf1 receptors A (igf1rA) and B (igf1rB) in skeletal muscle, and >4-fold higher gene transcript abundance for muscle-specific F-box protein 32 (fbxo32, also called atrogin-1), a ubiquitin ligase involved in myofibrillar protein degradation and muscle atrophy. Injection with recombinant sea bream Igf1 increased plasma Igf1 concentrations in both fasted and fed rockfish, and strongly down-regulated gene transcript abundance for fbxo32, suggesting that elevated muscle protein degradation during food restriction is mediated in part by a reduced availability of Igf1.
