Considering the requirement for the proper level of expression for each of these enzymes involved in HOX gene regulation, it is conceivable that each state is the result of a combined activity of histone modifying enzymes

y, glucose uptake and cell surface and mRNA levels of trout GLUT4 in skeletal muscle cells suggest that the reported hypoglycemic effects of metformin administration in rainbow trout may result from the direct action of this compound on white skeletal muscle, increasing its ability to take up glucose through a mechanism involving AMPK activation and increased GLUT4 cell surface and mRNA levels. AMPK activation may drive glucose towards the glycolytic pathway for energy generation In skeletal muscle, once glucose enters the cells it is rapidly phosphorylated to glucose-6-phosphate by HK. The fate of G6P is then two-fold: G6P can either be directed towards the synthesis of glycogen or, alternatively, G6P can be used for the direct generation of ATP by glycolysis and the TCA cycle. Our results show that pharmacological activation of AMPK by AICAR increased the mRNA levels of HK in trout myotubes, suggesting that activation of AMPK stimulates the entry as well as the metabolism of glucose in trout skeletal muscle cells, as it is the case in the mammalian muscle in response to exercise. Our results are also consistent with those of a recent study showing that in vivo administration of metformin in rainbow trout fed a highcarbohydrate diet LGX818 web increases the mRNA levels and activity of HK in white skeletal muscle. Interestingly, our results also show that the glycogen content in trout myotubes was not affected by the AMPK activators AICAR and metformin and that the mRNA levels of GS were not affected by AICAR. Our results are consistent with studies in mammals that have shown that AMPK activation induces the phosphorylation of GS, decreasing its activity and, consequently, glycogen synthesis in skeletal muscle. However, other studies in mammals have reported the opposite effect, with ” AICAR stimulating allosterically GS by increasing the concentration of glucose-6-phosphate and, therefore, overriding the inhibitory phosphorylation of GS. Although there is no direct evidence in fish on the regulation of GS activity by AMPK activators, the inability of AMPK activators to February 2012 | Volume 7 | Issue 2 | e31219 Metabolic Effects of AMPK on Fish Skeletal 17062696” Muscle muscle and may involve the phosphorylation of PGC-1a by AMPK and the binding of myocyte enhancer factor 2 to the GLUT4 promoter to increase the transcription of the GLUT4 gene. Additionally, recent studies suggest that exercise and pharmacological activation of AMPK also serve as important signals in regulating the expression of PGC-1a in skeletal muscle. PGC-1a is also involved in the transcriptional regulation of several genes implicated in the generation of ATP, mainly from oxidative metabolism. In particular, PGC-1a is known to mediate the stimulatory effects of AMPK on fatty acid oxidation in skeletal muscle. In the present study we show that AICAR increases PGC-1a mRNA levels in trout myotubes, which agrees with the described effect of this AMPK activator in the mammalian muscle. The observation that AMPK activation in trout myotubes results in increased PGC-1a and CS mRNA levels, coupled with recent data showing that exercise increases PGC-1a and CS mRNA levels in the skeletal muscle of zebrafish, suggest that AMPK could be involved in mediating the stimulatory effects of exercise on PGC-1a and CS expression in fish skeletal muscle. It will be interesting to determine in future studies if the pharmacological activation of AMPK in trout myotubes, or even in vivo conditions that may res