An in vivo and in vitro assessment of autophagy-related gene expression in muscle of rainbow trout (Oncorhynchus mykiss)

In mammals, new evidence has demonstrated the important role of the autophagic/lysosomal pathway in regulating muscle mass and identified the transcription factor FoxO3 as a key factor of the control of this proteolytic system by inducing several autophagy-related genes. In contrast, the mechanisms responsible for the regulation of autophagy have not been investigated in teleosts, known to exhibit different muscle growth dynamics. The present work aimed to characterize both in vivo and in vitro the transcriptional regulation of several major genes involved in autophagy (LC3B, gabarapl1, atg12l, atg4b) in the white skeletal muscle of rainbow trout. We found that fasting fish for 14 days or serum depletion of trout myocytes strongly induces the expression of all studied genes. Our in vitro study on trout myocytes indicated that IGF1 induces FoxO3 phosphorylation but has a low or no effect on autophagy-related gene expression, suggesting a moderate role for this transcription factor on the autophagic/lysosomal pathway in this species. Data reported here show for the first time in a lower vertebrate, the existence and the regulation of several major genes involved in the autophagy, opening a new area of research on the molecular bases of muscle protein degradation in teleosts.