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1 Department of Nutritional Sciences, University of Wisconsin, Madison, WI, USA
2 Department of Kinesiology, University of Wisconsin, Madison, WI, USA
3 Department of Nutritional Sciences, University of Wisconsin, Madison, WI, USA; Department of Kinesiology, University of Wisconsin, Madison, WI, USA
* To whom correspondence should be addressed. E-mail: cartee{at}education.wisc.edu.
Skeletal muscle insulin sensitivity improves with short-term reduction in calorie intake. The goal of this study was to evaluate changes in the abundance and phosphorylation of Akt1 and Akt2 as a potential mechanism for enhanced insulin action after 20 days of moderate calorie restriction [CR:60% ad libitum (AL)intake]in rat skeletal muscle. We also assessed changes in the abundance of SH2-domain containing protein (SHIP2), a negative regulator of insulin signaling. Fisher 344 Brown Norway rats were assigned to an AL control group or a CR treatment group for 20 days. Epitrochlearis muscles were dissected and incubated with or without insulin (500µU/ml). Total Akt serine and threonine phosphorylation was significantly increased by 32% (p<0.01) and 30% (p<0.005) in insulin-stimulated muscles from CR vs. AL. Despite an increase in total Akt phosphorylation, there was no difference in Akt1 serine- or Akt1 threonine- phosphorylation between CR and AL insulin-treated muscles. However, there was a 30% decrease (p<0.05) in Akt1 abundance for CR vs. AL. In contrast, there was no change in Akt2 protein abundance, and there was a 94% increase(p<0.05) in Akt2 serine- phosphorylation and an increase of 75% (p<0.05) in Akt2 threonine-phosphorylation of insulin-stimulated CR muscles compared to AL. There was no diet-effect on SHIP2 abundance in skeletal muscle. These results suggest that with brief CR, enhanced Akt2 phosphorylation may play a role in increasing insulin sensitivity in rat skeletal muscles.
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