Acute and chronic effects of alcohol exposure on skeletal muscle c-myc, p53, and Bcl-2 mRNA expression

Abstract

Skeletal muscle atrophy is a common feature in alcoholism that affects up to two-thirds of alcohol misusers, and women appear to be particularly susceptible. There is also some evidence to suggest that malnutrition exacerbates the effects of alcohol on muscle. However, the mechanisms responsible for the myopathy remain elusive, and some studies suggest that acetaldehyde, rather than alcohol, is the principal pathogenic perturbant. Previous reports on rats dosed acutely with ethanol (<24 h) have suggested that increased proto-oncogene expression (i.e., c-myc) may be a causative process, possibly via activating preapoptotic or transcriptional pathways. We hypothesized that 1) increases in c-myc mRNA levels also occur in muscle exposed chronically to alcohol, 2) muscle of female rats is more sensitive than that from male rats, 3) raising acetaldehyde will also increase c-myc, 4) prior starvation will cause further increases in c-myc mRNA expression in response to ethanol, and 5) other genes involved in apoptosis (i.e., p53 and Bcl-2) would also be affected by alcohol. To test this, we measured c-myc mRNA levels in skeletal muscle of rats dosed either chronically (6–7 wk; ethanol as 35% of total dietary energy) or acutely (2.5 h; ethanol as 75 mmol/kg body wt ip) with ethanol. All experiments were carried out in male Wistar rats (∼0.1–0.15 kg body wt) except the study that examined gender susceptibility in male and female rats. At the end of the studies, rats were killed, and c-myc, p53, and Bcl-2 mRNA was analyzed in skeletal muscle by RT-PCR with an endogenous internal standard, GAPDH. The results showed that 1) in male rats fed ethanol chronically, there were no increases in c-myc mRNA; 2) increases, however, occurred in c-myc mRNA in muscle from female rats fed ethanol chronically; 3) raising endogenous acetaldehyde with cyanamide increased c-myc mRNA in acute studies; 4) starvation per se increased c-myc mRNA levels and at 1 day potentiated the acute effects of ethanol, indicative of a sensitization response; 5) the only effect seen with p53 mRNA levels was a decrease in muscle of rats starved for 1 day compared with fed rats, and there was no statistically significant effect on Bcl-2 mRNA in any of the experimental conditions. The increases in c-myc may well represent a preapoptotic effect, or even a nonspecific cellular stress response to alcohol and/or acetaldehyde. These data are important in our understanding of a common muscle pathology induced by alcohol.

Spontaneous and In Vitro Induced Apoptosis of Lymphocytes and Neutrophils in Patients with Alcohol Dependence

“…These results are in good agreement with the data of other authors on apoptosis disorders in various cells in alcoholism [11,14]. This pattern of reaction with more intense apoptosis processes for immunocompetent cells explains low resistance of the immune system of alcoholics to infections and a high risk of tumors, viral and autoimmune diseases for this population, and is presumably one of the mechanisms of immunodefi ciency developing in patients with addictions.…”

Upregulation of β‐Catenin Levels in Superior Frontal Cortex of Chronic Alcoholics

“…The upregulation of Myc level in chronic alcoholics is in line with previous studies of Myc mRNA and protein in animal models and cell treatment (Leach et al, 1999;Nakahara et al, 2003;Paice et al, 2002;Saunders et al, 1995). Since Myc is a proto-oncogene, our results suggest that chronic alcohol misuse might increase the risk of brain tumorigenesis.…”

“…Further studies will also be required to determine whether changes in a-catenin, b-catenin, and Myc levels are restricted to the pathologically vulnerable superior frontal cortex or evident in other mesolimbic areas that are involved in drug addictions. Available evidence suggests that, at least for Myc, the changes might not be restricted in extent, since alcohol-induced increase of Myc mRNA and protein levels have been found in mouse hippocampus (Saunders et al, 1995) and rat muscle tissue (Nakahara et al, 2003;Paice et al, 2002).…”

Id2 and p53 participate in apoptosis during unloading-induced muscle atrophy

“…Furthermore, p53 protein levels increase in atrophied rat skeletal muscles after a 14-day spaceflight (42). However, a consensus regarding the role of p53 in muscle remodeling is still lacking, because p53 has been reported to be unchanged in skeletal muscles during atrophy induced by nerve injury, steroid, or alcohol (28,32,38).…”

“…It was recognized recently that p53 is one of the central modulators in cell cycling and apoptosis (53). Although most research in p53 has been conducted in active dividing cells, a few studies have attempted to investigate the response of p53 during disuse, laser irradiation, and ischemia in postmitotic skeletal myocytes (20,28,38,42,49). However, the possible role of p53 in regulating the apoptotic signaling pathway during unloading-induced muscle atrophy is still unclear.…”