230
M.L. Cancela et al.
fish oil replacement (100%) with vegetable oil for 62 weeks from first feeding in
rainbow trout has also been shown to decrease the expression of two genes involved
in lipid metabolism: fatty acid synthase and long-chain fatty acid elongase (Panserat
et al. 2008b). In addition to changes in genes involved in lipogenesis, complete
fish oil replacement caused changes in the hepatic expression of genes involved in
steroid synthesis, xenobiotic detoxification, protein catabolism and transcriptional
regulation, interestingly in the absence of changes in body weight, feed efficiency
and feed intake (Panserat et al. 2008a,b). In contrast, replacement of animal proteins
(fish meal) with plant proteins in the diet caused a reduction of growth rates and feed
efficiency and increased feed intake in rainbow trout, which was accompanied by
altered expression of genes involved in protein and amino acid metabolism (Panserat
et al. 2008b). Not surprisingly, similar changes were observed in the liver of rainbow trout after a 3-week fasting period: decreased expression of genes involved in
protein biosynthesis and increase in the machinery needed for protein degradation
(Salem et al. 2007).
7.4.4.2 Changes in the Liver Proteome in Relation to Nutrition and Growth
In view of the limited transcriptional response of the teleost liver to growth and
nutritional stimuli, studies on the hepatic proteome are needed to detect posttranscriptional changes. To date, studies have evaluated the response of the hepatic
proteome of rainbow trout to fasting and to diets in which fish protein is replaced
by protein of plant origin. In response to fasting, 24 differentially expressed proteins were detected in the rainbow trout liver. Among the proteins with increased
abundance after fasting were enolase and cytochrome C oxidase, on one hand, and
cathepsin D, on the other hand, most likely related to the higher energy requirements and protein degradation, respectively, that takes place during fasting (Martin
et al. 2001). Using the same proteomic approach, effects of dietary substitution of
fish meal by vegetable protein sources were tested on growth performance and liver
protein content in trout (Martin et al. 2003, Vilhelmsson et al. 2004). In one study,
adaptation of trout to a diet with a partial (30%) substitution of fish meal with soybean meal for 12 weeks resulted in unaltered growth rates but increased protein
catabolism, higher protein turnover and higher protein catabolism, accompanied by
changes in the abundance of 33 protein spots (Martin et al. 2003). Although not all
spots were identified, this study reported changes in the abundance of structural proteins (e.g. keratin and tubulin), lipid binding proteins (e.g. apolipoprotein A) and,
most notably, heat shock proteins, which are indicative of a stress response probably
induced by the presence of anti-nutritional factors in soy (Martin et al. 2003). In a
subsequent study, trout fed a diet in which fish meal was substituted with a mixture of vegetable proteins showed a reduction in growth rate, despite unaltered feed
intake, and decreased feed efficiency, mostly due to a decrease in protein utilization
(Vilhelmsson et al. 2004). These changes in nutritional parameters were accompanied by changes in protein production, in particular, proteins involved in primary
energy metabolism (e.g. production of NADPH and ATP), as well as two proteasome subunits, indicative of an increase in protein degradation. Overall, changes
M.L. Cancela et al.
fish oil replacement (100%) with vegetable oil for 62 weeks from first feeding in
rainbow trout has also been shown to decrease the expression of two genes involved
in lipid metabolism: fatty acid synthase and long-chain fatty acid elongase (Panserat
et al. 2008b). In addition to changes in genes involved in lipogenesis, complete
fish oil replacement caused changes in the hepatic expression of genes involved in
steroid synthesis, xenobiotic detoxification, protein catabolism and transcriptional
regulation, interestingly in the absence of changes in body weight, feed efficiency
and feed intake (Panserat et al. 2008a,b). In contrast, replacement of animal proteins
(fish meal) with plant proteins in the diet caused a reduction of growth rates and feed
efficiency and increased feed intake in rainbow trout, which was accompanied by
altered expression of genes involved in protein and amino acid metabolism (Panserat
et al. 2008b). Not surprisingly, similar changes were observed in the liver of rainbow trout after a 3-week fasting period: decreased expression of genes involved in
protein biosynthesis and increase in the machinery needed for protein degradation
(Salem et al. 2007).
7.4.4.2 Changes in the Liver Proteome in Relation to Nutrition and Growth
In view of the limited transcriptional response of the teleost liver to growth and
nutritional stimuli, studies on the hepatic proteome are needed to detect posttranscriptional changes. To date, studies have evaluated the response of the hepatic
proteome of rainbow trout to fasting and to diets in which fish protein is replaced
by protein of plant origin. In response to fasting, 24 differentially expressed proteins were detected in the rainbow trout liver. Among the proteins with increased
abundance after fasting were enolase and cytochrome C oxidase, on one hand, and
cathepsin D, on the other hand, most likely related to the higher energy requirements and protein degradation, respectively, that takes place during fasting (Martin
et al. 2001). Using the same proteomic approach, effects of dietary substitution of
fish meal by vegetable protein sources were tested on growth performance and liver
protein content in trout (Martin et al. 2003, Vilhelmsson et al. 2004). In one study,
adaptation of trout to a diet with a partial (30%) substitution of fish meal with soybean meal for 12 weeks resulted in unaltered growth rates but increased protein
catabolism, higher protein turnover and higher protein catabolism, accompanied by
changes in the abundance of 33 protein spots (Martin et al. 2003). Although not all
spots were identified, this study reported changes in the abundance of structural proteins (e.g. keratin and tubulin), lipid binding proteins (e.g. apolipoprotein A) and,
most notably, heat shock proteins, which are indicative of a stress response probably
induced by the presence of anti-nutritional factors in soy (Martin et al. 2003). In a
subsequent study, trout fed a diet in which fish meal was substituted with a mixture of vegetable proteins showed a reduction in growth rate, despite unaltered feed
intake, and decreased feed efficiency, mostly due to a decrease in protein utilization
(Vilhelmsson et al. 2004). These changes in nutritional parameters were accompanied by changes in protein production, in particular, proteins involved in primary
energy metabolism (e.g. production of NADPH and ATP), as well as two proteasome subunits, indicative of an increase in protein degradation. Overall, changes