Dataset Information

Alcohol-induced autophagy contributes to loss in skeletal muscle mass.

ABSTRACT: Patients with alcoholic cirrhosis and hepatitis have severe muscle loss. Since ethanol impairs skeletal muscle protein synthesis but does not increase ubiquitin proteasome-mediated proteolysis, we investigated whether alcohol-induced autophagy contributes to muscle loss. Autophagy induction was studied in: A) Human skeletal muscle biopsies from alcoholic cirrhotics and controls, B) Gastrocnemius muscle from ethanol and pair-fed mice, and C) Ethanol-exposed murine C2C12 myotubes, by examining the expression of autophagy markers assessed by immunoblotting and real-time PCR. Expression of autophagy genes and markers were increased in skeletal muscle from humans and ethanol-fed mice, and in myotubes following ethanol exposure. Importantly, pulse-chase experiments showed suppression of myotube proteolysis upon ethanol-treatment with the autophagy inhibitor, 3-methyladenine (3MA) and not by MG132, a proteasome inhibitor. Correspondingly, ethanol-treated C2C12 myotubes stably expressing GFP-LC3B showed increased autophagy flux as measured by accumulation of GFP-LC3B vesicles with confocal microscopy. The ethanol-induced increase in LC3B lipidation was reversed upon knockdown of Atg7, a critical autophagy gene and was associated with reversal of the ethanol-induced decrease in myotube diameter. Consistently, CT image analysis of muscle area in alcoholic cirrhotics was significantly reduced compared with control subjects. In order to determine whether ethanol per se or its metabolic product, acetaldehyde, stimulates autophagy, C2C12 myotubes were treated with ethanol in the presence of the alcohol dehydrogenase inhibitor (4-methylpyrazole) or the acetaldehyde dehydrogenase inhibitor (cyanamide). LC3B lipidation increased with acetaldehyde treatment and increased further with the addition of cyanamide. We conclude that muscle autophagy is increased by ethanol exposure and contributes to sarcopenia.

SUBMITTER: Thapaliya S

PROVIDER: S-EPMC4091154 | biostudies-literature | 2014 Apr

REPOSITORIES: biostudies-literature

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Alcohol-induced autophagy contributes to loss in skeletal muscle mass.

Thapaliya Samjhana S Runkana Ashok A McMullen Megan R MR Nagy Laura E LE McDonald Christine C Naga Prasad Sathyamangla V SV Dasarathy Srinivasan S

Autophagy 20140131 4

Patients with alcoholic cirrhosis and hepatitis have severe muscle loss. Since ethanol impairs skeletal muscle protein synthesis but does not increase ubiquitin proteasome-mediated proteolysis, we investigated whether alcohol-induced autophagy contributes to muscle loss. Autophagy induction was studied in: A) Human skeletal muscle biopsies from alcoholic cirrhotics and controls, B) Gastrocnemius muscle from ethanol and pair-fed mice, and C) Ethanol-exposed murine C2C12 myotubes, by examining the ...[more]

PMID: 24492484

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Project description:BackgroundIncreasing evidence suggests that severe skeletal muscle index (SMI) loss (sarcopenia) is associated with poor overall survival in metastatic colorectal cancer patients, but its mechanisms are unknown. We recently found, using data of the randomized phase 3 CAIRO3 study, that SMI loss was related with shorter time to disease progression and overall survival during first-line maintenance treatment with capecitabine + bevacizumab (CAP-B) or observation and during more intensive capecitabine + oxaliplatin + bevacizumab (CAPOX-B) reintroduction treatment. As a potential risk factor for reduced survival, we explored whether sarcopenia and SMI loss were associated with dose-limiting toxicities (DLTs) during CAP-B and CAPOX-B.MethodsSarcopenia status and SMI loss were assessed by using consecutive computed tomography scans. DLTs were defined as any dose delay/reduction/discontinuation of systemic treatment because of reported CTCAE (version 3.0) toxicities at the start or during treatment. Poisson regression models were used to study whether sarcopenia and body mass index (BMI) at the start of treatment and SMI and BMI loss during treatment were associated with DLTs.ResultsOne hundred eighty-two patients (mean age 63.0 ± 8.8 years, 37% female) received CAP-B, and 232 patients (mean age 63.0 ± 9.0 years, 34% female) received CAPOX-B. At the start of CAP-B and CAPOX-B, 54% and 46% of patients were sarcopenic, respectively. Mean BMI was lower in sarcopenic patients, although patients were on average still overweight (sarcopenic vs. non-sarcopenic at the start of CAP-B 25.0 ± 3.9 vs. 26.7 ± 4.1 and CAPOX-B 25.8 ± 3.8 vs. 27.1 ± 3.8 kg/m2 ). Sarcopenia at the start of CAP-B was not associated with DLTs [relative risk 0.87 (95% confidence interval 0.64-1.19)], whereas patients with >2% SMI loss had a significantly higher risk of DLTs [1.29 (1.01-1.66)]. At the start of subsequent CAPOX-B, 25% of patients received a dose reduction, and the risk of dose reduction was significantly higher for patients with preceding SMI loss [1.78 (1.06-3.01)] or sarcopenia [1.75 (1.08-2.86)]. After the received dose reductions, sarcopenia or SMI loss was not significantly associated with a higher risk of DLTs during CAPOX-B [sarcopenia vs. non-sarcopenic: 0.86 (0.69-1.08) and SMI loss vs. stable/gain: 0.83 (0.65-1.07)]. In contrast, BMI (loss) at the start or during either treatment was not associated with an increased risk of DLTs.ConclusionsIn this large longitudinal study in metastatic colorectal cancer patients during palliative systemic treatment, sarcopenia and/or muscle loss was associated with an increased risk of DLTs. BMI was not associated with DLTs and could not detect sarcopenia or SMI loss. Prospective (randomized) studies should reveal whether normalizing chemotherapeutic doses to muscle mass or muscle mass preservation (by exercise and nutritional interventions) increases chemotherapeutic tolerance and improves survival.

Dataset Information

Alcohol-induced autophagy contributes to loss in skeletal muscle mass.

Publications

Alcohol-induced autophagy contributes to loss in skeletal muscle mass.

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