Nutrient and hormonal regulation of proteolysis through FOXO signaling pathways in rainbow trout

Authors: Cleveland, Beth; Weber, Gregory - Greg

Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2010
Publication Date: 3/1/2010
Citation: Cleveland, B.M., Weber, G.M. 2010. Nutrient and hormonal regulation of proteolysis through FOXO signaling pathways in rainbow trout. Aquaculture America Conference. Paper No. 00.

Interpretive Summary:

Technical Abstract: It is established in mammals that insulin like growth factor-I (IGF-I) and insulin promote protein accretion by both increasing rates of protein synthesis and decreasing rates of protein degradation. The suppression of ubiquitin ligase expression is a mechanism that contributes to the effects that these anabolic hormones have on protein degradation. In fish it is known that IGF-I increases protein synthesis, but it has not been determined how IGF-I and insulin affect protein degradation and ubiquitin ligase expression. Since rates of protein degradation impact protein accretion, a better understanding of the regulation of proteolysis is important for the development of feeding strategies or husbandry practices that optimize fish growth and feed efficiency. The effects of IGF-I, insulin, and leucine on protein turnover and pathways that regulate proteolytic gene expression and protein polyubiquitination were investigated in primary cultures of four day old rainbow trout myocytes. Supplementing media with 100 nM IGF-I or 1 M insulin increased protein synthesis and decreased protein degradation. IGF-I and insulin also reduced the abundance of the ubiquitin ligase transcripts for Fbx32, Fbx25, and MuRF1. IGF-I and insulin increased phosphorylation of FOXO1 and FOXO4 (P<0.05), which was inhibited by the PI3K inhibitor wortmannin, and decreased the abundance of polyubiquitinated proteins by 10%-20% (P<0.05). Supplementing media containing 0.6 mM leucine with an additional 2.5 mM leucine did not increase rates of protein synthesis but reduced rates of protein degradation by 8% (P<0.05). Leucine supplementation reduced Fbx32 expression by 25% (P<0.05) but did not affect Fbx25 nor MuRF1 transcript abundance. Serum deprivation decreased rates of protein synthesis by 60% (P<0.05), increased protein degradation by 40% (P<0.05), and increased expression of all ubiquitin ligases. These data suggest that, similar to mammals, the inhibitory effects of IGF-I and insulin on proteolysis are partially responsible for the ability of these compounds to promote protein accretion.