The effects of acute stress and repeated bouts of ethanol consumption on rates of muscle protein synthesis and related signaling in male mice

Abstract

Stress and alcohol misuse can negatively impact skeletal muscle, and unfortunately, stress can often precipitate alcohol misuse. Due to their catabolic nature, the combination of these factors may lead to significant dysregulation of skeletal muscle signaling involved in preservation of muscle mass. The aim of the current study, therefore, was to examine the unexplored effects of repeated bouts of ethanol consumption and an acute stressful event on markers of muscle protein synthesis and degradation. We hypothesized stress and alcohol individually would decrease rates of protein synthesis and related signaling along the Akt-mTOR pathway and that the combination of these factors may cause further disruption. To test this hypothesis, male C57BL/6 mice (9-10 weeks old) underwent a modified Drinking in the Dark (DID) protocol. Mice had limited voluntary access to 20% ethanol or water for 4 days. Three days later, half of the mice were exposed to 100 inescapable tail shocks, allowed to recover for 3 days, then completed 10 more days of DID as before. This design resulted in 4 groups: No stress-water, stress-water, no stress-ethanol, and stress-ethanol (n=9/group). On the final day of drinking, gastrocnemius muscle was excised and frozen for western blot analysis. Although 2 weeks post-stress, rates of muscle protein synthesis were significantly reduced by stress exposure ( P=0.008) as was the phosphorylation of Akt ( P=0.039). There was a significant interaction between stress and ethanol on the phosphorylation of mTOR ( P=0.032) and ethanol tended to decrease mTOR phosphorylation in non-stressed mice ( P=0.079) by ~41%. Furthermore, there tended to be an interaction between stress and ethanol ( P=0.067) on P70S6K phosphorylation, and ethanol significantly reduced P70S6K phosphorylation ( P=0.033). Phosphorylation of 4E-BP1, interestingly, was unchanged with stress or ethanol. Myostatin, which can influence both muscle protein synthesis and degradation signaling, was unchanged with by stress or alcohol consumption . Ubiquitination of proteins and markers of the Ubiquitin Proteasome Pathway, involved in protein degradation, were also unchanged by the individual or combined effects of stress and ethanol. Interestingly, HSP70, a protein whose expression is increased as a response to cellular stress to maintain muscle fiber health, was profoundly increased ( P<0.001) by stress exposure. In conclusion, it appears that a single acute stressful event results in prolonged reductions in rates of protein synthesis and signaling along the Akt-mTOR pathway. Ethanol consumption, in the form of binge-pattern drinking, modestly reduced phosphorylation of several proteins along the Akt-mTOR pathway, but did not exacerbate the effects of acute stress exposure. No funding to report. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.