Mechanisms Underlying Muscle Protein Imbalance Induced by Alcohol

Post-natal muscle growth and protein turnover: a narrative review of current understanding

A model explaining the dietary-protein-driven post-natal skeletal muscle growth and protein turnover in the rat is updated, and the mechanisms involved are described, in this narrative review. Dietary protein controls both bone length and muscle growth, which are interrelated through mechanotransduction mechanisms with muscle growth induced both from stretching subsequent to bone length growth and from internal work against gravity. This induces satellite cell activation, myogenesis and remodelling of the extracellular matrix, establishing a growth capacity for myofibre length and cross-sectional area. Protein deposition within this capacity is enabled by adequate dietary protein and other key nutrients. After briefly reviewing the experimental animal origins of the growth model, key concepts and processes important for growth are reviewed. These include the growth in number and size of the myonuclear domain, satellite cell activity during post-natal development and the autocrine/paracrine action of IGF-1. Regulatory and signalling pathways reviewed include developmental mechanotransduction, signalling through the insulin/IGF-1-PI3K-Akt and the Ras-MAPK pathways in the myofibre and during mechanotransduction of satellite cells. Likely pathways activated by maximal-intensity muscle contractions are highlighted and the regulation of the capacity for protein synthesis in terms of ribosome assembly and the translational regulation of 5-TOPmRNA classes by mTORC1 and LARP1 are discussed. Evidence for and potential mechanisms by which volume limitation of muscle growth can occur which would limit protein deposition within the myofibre are reviewed. An understanding of how muscle growth is achieved allows better nutritional management of its growth in health and disease.

The relationship between physical performance and alcohol consumption levels in Russian adults

Investigating the relationship between alcohol consumption and physical performance, we used data from the 2015-2018 Know Your Heart study on 4215 adults aged 35-69 from Arkhangelsk and Novosibirsk, Russia. We classified participants' drinking status into non-drinking, non-problem drinking, hazardous drinking, and harmful drinking based on their self-reported drinking behaviors. To evaluate physical performance, we developed a Composite Physical Performance Scale (CPPS), which combined the results of three functional tests: grip strength (GS), closed-eyes balance, and chair rises (CR). We applied multivariable linear regression to assess the relationship between alcohol consumption and CPPS score, and ordinal logistic regression to explore the associations between alcohol consumption and the three functional tests separately. The results showed that harmful drinking was associated with lower CPPS scores compared to non-problem drinking. Among harmful drinking men, the decrease in CPPS scores was explained by all three tests equally and exceptionally by GS among women. Non-drinking was also associated with decreased CPPS, linked to lower GS and CR scores in men, and only lower GS scores in women. The study revealed a reduced physical performance in the non-drinking and harmful drinking groups compared to non-problem drinking.

Alcohol and Skeletal Muscle in Health and Disease

PURPOSE

Alcohol-related myopathy is one of the earliest alcohol-associated pathological tissue changes that is progressively exacerbated by cumulative long-term alcohol misuse. Acute and chronic alcohol use leads to changes in skeletal muscle mass and function. As discussed in this evidence-based review, alcohol-mediated mechanisms are multifactorial with effects on anabolic and catabolic signaling, mitochondrial bioenergetics, extracellular matrix remodeling, and epigenomic alterations. However, systematic studies are limited, especially regarding the acute effects of alcohol on skeletal muscle.

SEARCH METHODS

This review focuses on peer-reviewed manuscripts published between January 2012 and November 2022 using the search terms "alcohol" or "ethanol" and "skeletal muscle" in MEDLINE, PubMed, and Web of Science using EndNote reference management software.

SEARCH RESULTS

Eligible manuscripts included full-length research papers that discussed acute and chronic effects of alcohol on skeletal muscle mass and function in both clinical and preclinical studies. The review also includes alcohol-mediated skeletal muscle effects in the context of comorbidities. The three databases together yielded 708 manuscripts. Of these, the authors excluded from this review 548 papers that did not have "alcohol" or "muscle" in the title and 64 papers that were duplicates or did not discuss skeletal muscle. Thus, of all the manuscripts considered for this review, 96 are included and 612 are excluded. Additionally, relevant papers published earlier than 2012 are included to provide context to the review.

DISCUSSION AND CONCLUSIONS

Both acute and chronic alcohol use decrease protein synthesis and increase protein degradation. Alcohol also impairs mitochondrial function and extracellular matrix remodeling. However, there is a gap in the literature on the known alcohol-mediated mechanisms, including senescence, role of immune activation, and interorgan communication, on the development of alcohol-related myopathy. With increased life expectancy, changing alcohol use patterns, and increasing frequency of alcohol use among females, current observational studies are needed on the prevalence of alcohol-related myopathy. Additionally, the compounding effects of acute and chronic alcohol use on skeletal muscle with aging or exercise, in response to injury or disuse, and in the context of comorbidities including diabetes and human immunodeficiency virus (HIV), call for further investigation. Though evidence suggests that abstinence or reducing alcohol use can improve muscle mass and function, they are not restored to normal levels. Hence, understanding the pathophysiological mechanisms can help in the design of therapeutic strategies to improve skeletal muscle health.

Binge drinking leads to an oxidative and metabolic imbalance in skeletal muscle during adolescence in rats: endocrine repercussion

Binge drinking (BD) is an especially pro-oxidant model of alcohol consumption, mainly used by adolescents. It has recently been related to the hepatic IR-process. Skeletal muscle is known to be involved in insulin action and modulation through myokine secretion. However, there is no information on muscle metabolism and myokine secretion after BD exposure in adolescents. Two experimental groups of adolescent rats have been used: control and BD-exposed one. Oxidative balance, energy status and lipid, and protein metabolism have been analyzed in muscle, together with myokine serum levels (IL-6, myostatin, LIF, IL-5, fractalkine, FGF21, irisin, BDNF, FSTL1, apelin, FABP3, osteocrin, osteonectin (SPARC), and oncostatin). In muscle, BD affects the antioxidant enzyme balance leading to lipid and protein oxidation. Besides, it also increases the activation of AMPK and thus contributes to decrease SREBP1 and pmTOR and to increase FOXO3a expressions, promoting lipid and protein degradation. These alterations deeply affect the myokine secretion pattern. This is the first study to examine a general myokine response after exposure to BD. BD not only caused a detrimental imbalance in myokines related to muscle turnover, decreased those contributing to increase IR-process, decreased FST-1 and apelin and their cardioprotective function but also reduced the neuroprotective BDNF. Consequently, BD leads to an important metabolic and energetic disequilibrium in skeletal muscle, which contributes to exacerbate a general IR-process.

Longitudinal assessment of strength and body composition in a mouse model of chronic alcohol-related myopathy

BACKGROUND

Excessive, chronic alcohol consumption can result in muscle atrophy and weakness (i.e., alcoholic myopathy) that impairs the quality of life. However, the precise mechanisms responsible for ethanol's detrimental impact on skeletal muscle have not been fully elucidated, in part due because the time course of disease development and progression are not well established. Therefore, we examined muscle strength and body composition longitudinally using an established preclinical mouse model of chronic alcoholic myopathy.

METHODS

To establish a time course of chronic alcoholic myopathy, we fed High Drinking in the Dark (HDID) female mice (n = 7) 20% ethanol for ~32 weeks (following a 2-week ethanol ramping period). We assessed in vivo isometric contractility of the left ankle dorsiflexor and lean mass via NMR every 4 weeks. Outcomes were compared with age-matched control HDID mice that did not consume ethanol (n = 8).

RESULTS

At study completion, mice who consumed ethanol were 12% weaker than control mice (p = 0.015). Compared to baseline, consuming ethanol resulted in an acute transient reduction in dorsiflexion torque at Week 4 (p = 0.032) that was followed by a second, more sustained reduction at Week 20 (p < 0.001). Changes in lean mass paralleled those of dorsiflexor torque, with ~40% of the variance in dorsiflexor torque being explained by the variance in lean mass of the ethanol group (p < 0.001). Dorsiflexor torque normalized to lean mass (mN·m/g lean mass) did not differ between the ethanol and control groups from Weeks 4 to 32 (p ≥ 0.498).

CONCLUSIONS

These results indicate that reductions in muscle mass and strength due to chronic, excessive ethanol intake are dynamic, not necessarily linear, processes. Moreover, the findings confirm that ethanol-induced weakness is primarily driven by muscle atrophy (i.e., loss of muscle quantity). Future studies should consider how chronic alcoholic myopathy develops and progresses rather than identifying changes after it has been diagnosed.

Alcohol, White Adipose Tissue, and Brown Adipose Tissue: Mechanistic Links to Lipogenesis and Lipolysis

According to data from the World Health Organization, there were about 3 million deaths caused by alcohol consumption worldwide in 2016, of which about 50% were related to liver disease. Alcohol consumption interfering with the normal function of adipocytes has an important impact on the pathogenesis of alcoholic liver disease. There has been increasing recognition of the crucial role of adipose tissue in regulating systemic metabolism, far beyond that of an inert energy storage organ in recent years. The endocrine function of adipose tissue is widely recognized, and the significance of the proteins it produces and releases is still being investigated. Alcohol consumption may affect white adipose tissue (WAT) and brown adipose tissue (BAT), which interact with surrounding tissues such as the liver and intestines. This review briefly introduces the basic concept and classification of adipose tissue and summarizes the mechanism of alcohol affecting lipolysis and lipogenesis in WAT and BAT. The adipose tissue-liver axis is crucial in maintaining lipid homeostasis within the body. Therefore, this review also demonstrates the effects of alcohol consumption on the adipose tissue-liver axis to explore the role of alcohol consumption in the crosstalk between adipose tissue and the liver.

Excessive Ethanol Intake in Mice Does Not Impair Recovery of Torque after Repeated Bouts of Eccentric Contractions

PURPOSE

Alcoholics develop muscle atrophy and weakness from excessive ethanol (EtOH) intake. To date, most research has examined outcomes of alcohol-induced atrophy and weakness under basal or unstressed conditions despite physical stress being a normal occurrence in a physiological setting. Therefore, this study set out to determine if recovery of torque is impaired after repetitive bouts of physical stress in skeletal muscle during excessive short-term (experiment 1) and long-term (experiment 2) EtOH consumption.

METHODS

Twenty male and female mice were assigned to receive either 20% EtOH in their drinking water or 100% water. Short- and long-term consumption was predetermined to be EtOH intake starting at 4 and 26 wk, respectively. Anterior crural muscles performed repeated bouts of physical stress using in vivo eccentric contractions, with tetanic isometric torque being measured immediately pre- and postinjury. A total of 10 bouts were completed with 14 d between each bout within bouts 1-5 (experiment 1) and bouts 6-10 (experiment 2), and 12 wk between bouts 5 and 6.

RESULTS

Mice consuming EtOH had blood alcohol concentrations up to 270 mg·dL -1 . In experiment 1, five bouts of eccentric contractions did not reduce recovery of torque, regardless of sex or EtOH treatment ( P ≥ 0.173). Similarly, in experiment 2, preinjury torques did not differ from day 14 values regardless of sex or treatment ( P ≥ 0.322). However, there was a group effect in female mice for bouts 6 and 10 during experiment 2, with female EtOH mice being weaker than controls ( P ≤ 0.002).

CONCLUSIONS

Excessive short- or long-term EtOH misuse in a mouse model did not affect the muscle's ability to regain strength after repeated bouts of eccentric contractions, suggesting that EtOH may not be as detrimental to recovery as once predicted.

A multi-organ analysis of the role of mTOR in fetal alcohol spectrum disorders

Alcohol exposure during gestation can lead to fetal alcohol spectrum disorders (FASD), an array of cognitive and physical developmental impairments. Over the past two and a half decades, Mammalian Target of Rapamycin (mTOR) has emerged at the nexus of many fields of study, and has recently been implicated in FASD etiology. mTOR plays an integral role in modulating anabolic and catabolic activities, including protein synthesis and autophagy. These processes are vital for proper development and can have long lasting effects following alcohol exposure, such as impaired hippocampal and synapse formation, reduced brain size, as well as cognitive, behavioral, and memory impairments. We highlight recent advances in the field of FASD, primarily with regard to animal model discoveries and discuss the interaction between alcohol and mTOR in the context of various tissues, including brain, placenta, bone, and muscle, with respect to developmental alcohol exposure paradigms. The current review focuses on novel FASD research within the context of the mTOR signaling and sheds light on mechanistic etiologies at various biological levels including molecular, cellular, and functional, across multiple stages of development and illuminates the dichotomy between the different mTOR complexes and their unique signaling roles.

The effects of voluntary binge-patterned ethanol ingestion and daily wheel running on signaling of muscle protein synthesis and degradation in female mice

Excessive ethanol ingestion can reduce skeletal muscle protein synthesis (MPS) through the disruption of signaling along the Akt-mTOR pathway and increase muscle protein degradation (MPD) through the Ubiquitin Proteasome Pathway (UPP) and autophagy. Identification of interventions that curb the disrupting effects of alcohol misuse on MPS and MPD are of central importance for the prevention of chronic health complications that arise from muscle loss. Physical activity is one potential strategy to combat the deleterious effects of alcohol on skeletal muscle. Therefore, the purpose of this study was to investigate the interaction between daily wheel running and binge-patterned ethanol consumption, through episodes of voluntary binge-patterned ethanol drinking, on signaling factors along the Akt-mTOR, Ubiquitin-Proteasome, and autophagy pathways. Adult female C57BL/6J mice received daily access to cages with or without running wheels for 2.5 h/day for five weeks. During the final five days of the study, mice received 2-4 h of daily access to sipper tubes containing water (n = 14 sedentary; n = 15 running) or 20% ethanol (n = 14 sedentary; n = 16 running) 30 min after running wheel access, using the "Drinking in the Dark" (DID) model of binge-patterned ethanol consumption. Immediately after the final episode of DID, gastrocnemius muscle was extracted. Western blotting was performed to measure proteins along Akt-mTOR, Ubiquitin-Proteasome, and autophagy pathways, and PCR was used to assess mRNA expression of atrogenes. Ethanol access increased expression of MAFbx by 82% (p = 0.048), but did not robustly influence Akt-mTOR or UPP signaling. Daily wheel access did not prevent alcohol-induced MAFbx expression; however, ethanol access decreased the phosphorylation of p70S6K by 45% in running mice (p = 0.020). These results suggest that physical activity may be insufficient to prevent alcohol-induced changes to signaling factors along pathways involved in muscle loss. Instead, binge-patterned ethanol ingestion may impair the benefits of physical activity on factors involved in MPS.

Neuromuscular mechanisms of weakness in a mouse model of chronic alcoholic myopathy

BACKGROUND

Weakness is a common clinical symptom reported in individuals with chronic alcohol use disorder. However, it remains unclear whether low strength in these individuals is directly related to excessive ethanol intake, other deleterious factors (lifestyle, environment, genetics, etc.), or a combination of both. Therefore, we examined whether (and how) ethanol reduces the muscle's force-producing capacity using a controlled in vivo preclinical mouse model of excessive ethanol intake.

METHODS

To establish whether chronic ethanol consumption causes weakness, C57BL/6 female mice consumed 20% ethanol for 40 weeks (following a 2-week ethanol ramping period), and various measures of muscular force were quantified. Functional measures included all-limb grip strength and in vivo contractility of the left ankle dorsiflexors and plantarflexors. Once confirmed that mice consuming ethanol were weaker than age-matched controls, we sought to determine the potential neuromuscular mechanisms of muscle dysfunction by assessing neuromuscular excitation, muscle quantity, and muscle quality.

RESULTS

Mice consuming chronic ethanol were 13 to 16% weaker (p ≤ 0.016) than controls (i.e., mice consuming 100% water) with the negative impact of ethanol on voluntary grip strength (ƞ²  = 0.603) being slightly larger than that of electrically stimulated muscle contractility (ƞ²  = 0.482). Relative to controls, lean mass and muscle wet masses were 9 to 16% lower in ethanol-consuming mice (p ≤ 0.048, ƞ²  ≥ 0.268). No significant changes were observed between groups for indices of neuromuscular excitation at the level of the motor unit, neuromuscular junction, or plasmalemma (p ≥ 0.259, ƞ²  ≤ 0.097), nor was muscle quality altered after 40 weeks of 20% ethanol consumption (p ≥ 0.695, ƞ²  ≤ 0.012).

CONCLUSIONS

Together, these findings establish that chronic ethanol consumption in mice induces a substantial weakness in vivo that we interpret to be primarily due to muscle atrophy (i.e., reduced muscle quantity) and possibly, to a lesser degree, loss of central neural drive.

Polydatin attenuates chronic alcohol consumption-induced cardiomyopathy through a SIRT6-dependent mechanism

Polydatin has attracted much attention as a potential cardioprotective agent against ischemic heart disease and diabetic cardiomyopathy. However, the effect and mechanism of polydatin supplementation on alcoholic cardiomyopathy (ACM) are still unknown. This study aimed to determine the therapeutic effect of polydatin against ACM and to explore the molecular mechanisms with a focus on SIRT6-AMP-activated protein kinase (AMPK) signaling and mitochondrial function. The ACM model was established by feeding C57/BL6 mice with an ethanol Lieber-DeCarli diet for 12 weeks. The mice received polydatin (20 mg kg^-1) or vehicle treatment. We showed that polydatin treatment not only improved cardiac function but also reduced myocardial fibrosis and dynamin-related protein 1 (Drp-1)-mediated mitochondrial fission, and enhanced PTEN-induced putative kinase 1 (PINK1)-Parkin-dependent mitophagy in alcohol-treated myocardium. Importantly, these beneficial effects were mimicked by SIRT6 overexpression but abolished by the infection of recombinant serotype 9 adeno-associated virus (AAV9) carrying SIRT6-specific small hairpin RNA. Mechanistically, alcohol consumption induced a gradual decrease in the myocardial SIRT6 level, while polydatin effectively activated SIRT6-AMPK signaling and modulated mitochondrial dynamics and mitophagy, thus reducing oxidative stress damage and preserving mitochondrial function. In summary, these data present new information regarding the therapeutic actions of polydatin, suggesting that the activation of SIRT6 signaling may represent a new approach for tackling ACM-related cardiac dysfunction.

Association of Modifiable Lifestyle Factors with Plasma Branched-Chain Amino Acid Metabolites in Women

BACKGROUND

Circulating branched-chain amino acids (BCAAs-isoleucine, leucine, and valine) are strongly associated with higher risk of incident type 2 diabetes (T2D); however, determinants of elevated fasting BCAA concentrations are largely unknown.

OBJECTIVES

We aimed to characterize the modifiable lifestyle factors related to plasma BCAAs.

METHODS

We performed a cross-sectional analysis among n = 18,897 women (mean ± SD age: 54.9 ± 7.2 y) in the Women's Health Study, free of T2D and cardiovascular disease at baseline blood draw. Lifestyle factors, weight, and height were self-reported via questionnaire, including smoking status, alcohol, leisure-time physical activity (LTPA), diet quality scores [2010 Alternative Healthy Eating Index (without alcohol) (aHEI); alternate Mediterranean Diet (aMED)], and dietary sources of BCAAs. Plasma BCAAs were quantified via NMR spectroscopy. We calculated multivariable-adjusted percentage mean differences (95% CIs) and P values for linear trend of BCAAs stratified by categoric lifestyle factors. We estimated R2 from univariate cubic spline regression models to estimate the variability in BCAAs explained.

RESULTS

Compared with women with BMI (in kg/m2) <25.0, BCAAs were 8.6% (95% CI: 8.0%, 9.3%), 15.3% (95% CI: 14.4%, 16.3%), and 21.0% (95% CI: 18.2%, 23.9%) higher for the BMI strata 25.0-29.9, 30.0-39.9, and ≥40.0, respectively (P-trend < 0.0001). Women with higher LTPA and higher alcohol intake compared with lower had modestly (∼1%) lower plasma BCAAs (P-trend = 0.014 and 0.0003, respectively). Differences in smoking status, aHEI, and aMED score were not related to plasma BCAAs. Women with higher dietary BCAAs had dose-response higher plasma BCAA concentrations, 3.4% (95% CI: 2.5%, 4.4%) higher when comparing the highest with the lowest quintile (P-trend < 0.0001). BMI explained 11.6% of the variability of BCAAs, whereas other factors explained between 0.1% and 1%.

CONCLUSIONS

Our findings among a large cohort of US women indicate that BMI, but less so diet, physical activity, and other lifestyle factors, is related to plasma BCAAs.This trial was registered at clinicaltrials.gov as NCT00000479.

Factors Associated with Handgrip Strength Among Older Adults in Malaysia

Purpose

Handgrip strength (HGS) is indicative of overall physical health among older adults. A decrease in HGS may be associated with an increased risk of disease. The aim of this study is to determine the factors associated with HGS among older adults in Malaysia.

Patients and Methods

One thousand two hundred four (1204) participants from urban and rural areas in Selangor state, Malaysia, were recruited. Sociodemographic and health-related conditions were gathered through a comprehensive face-to-face interview, followed by HGS assessments by a handgrip dynamometer. Subsequently, multiple linear regression was used to test the main association with the HGS.

Results

A total of 691 participants (57.4%) were male, and 513 (42.6%) were female. Males had a mean HGS of 30.0 (SD 7.53) kg, and females had a mean HGS of 19.4 (SD 5.28) kg. Males’ handgrip strength was significantly reduced with increasing age, physically inactive, and diabetes (all at the level p<0.001) after adjusting for social-demographic characteristics and health-related variables. Meanwhile, for females, the HGS was significantly decreased with age (p<0.001), physically inactive (p<0.001) and hypertension (p=0.03). However, female HGS was positively related to BMI (p<0.001).

Conclusion

The study contributed to a better understanding of factors associated with HGS, and thus, the HGS is recommended as a section in the health evaluation among high-risk older adults as the strategy of disease control and prevention.

Enrichment of Newly Synthesized Proteins following treatment of C2C12 Myotubes with Endotoxin and Interferon-γ

Inflammation in muscle induces the synthesis of mediators that can impair protein synthesis and enhance proteolysis, and when sustained lead to muscle atrophy. Furthermore, muscle-derived mediators that are secreted may participate in disrupting the function of other peripheral organs. Selective identification of newly synthesized proteins can provide insight on biological processes that depend on the continued synthesis of specific proteins to maintain homeostasis as well as those proteins that are up- or down-regulated in response to inflammation. We used puromycin-associated nascent chain proteomics (PUNCH-P) to characterize new protein synthesis in C2C12 myotubes and changes resulting from their exposure to the inflammatory mediators lipopolysaccharide (LPS) and interferon (IFN)-γ for either a short (4 h) or prolonged (16 h) time period. We identified sequences of nascent polypeptide chains belonging to a total of 1523 proteins and report their detection from three independent samples of each condition at each time point. The identified nascent proteins correspond to approximately 15% of presently known proteins in C2C12 myotubes and are enriched in specific cellular components and pathways. A subset of these proteins was identified only in treated samples and has functional characteristics consistent with the synthesis of specific new proteins in response to LPS/IFNγ. Thus, the identification of proteins from their nascent polypeptide chains provides a resource to analyze the role of new synthesis of proteins in both protein homeostasis and in proteome responses to stimuli in C2C12 myotubes. Our results reveal a profile of actively translating proteins for specific cellular components and biological processes in normal C2C12 myotubes and a different enrichment of proteins in response to LPS/IFNγ. Collectively, our data disclose a highly interconnected network that integrates the regulation of cellular proteostasis and reveal a diverse immune response to inflammation in muscle which may underlie the concomitantly observed atrophy and be important in inter-organ communication.

Alcohol Use Disorders and Their Harmful Effects on the Contractility of Skeletal, Cardiac and Smooth Muscles

Alcohol misuse has deleterious effects on personal health, family, societal units, and global economies. Moreover, alcohol misuse usually leads to several diseases and conditions, including alcoholism, which is a chronic condition and a form of addiction. Alcohol misuse, whether as acute intoxication or alcoholism, adversely affects skeletal, cardiac and/or smooth muscle contraction. Ethanol (ethyl alcohol) is the main effector of alcohol-induced dysregulation of muscle contractility, regardless of alcoholic beverage type or the ethanol metabolite (with acetaldehyde being a notable exception). Ethanol, however, is a simple and "promiscuous" ligand that affects many targets to mediate a single biological effect. In this review, we firstly summarize the processes of excitation-contraction coupling and calcium homeostasis which are critical for the regulation of contractility in all muscle types. Secondly, we present the effects of acute and chronic alcohol exposure on the contractility of skeletal, cardiac, and vascular/ nonvascular smooth muscles. Distinctions are made between in vivo and in vitro experiments, intoxicating vs. sub-intoxicating ethanol levels, and human subjects vs. animal models. The differential effects of alcohol on biological sexes are also examined. Lastly, we show that alcohol-mediated disruption of muscle contractility, involves a wide variety of molecular players, including contractile proteins, their regulatory factors, membrane ion channels and pumps, and several signaling molecules. Clear identification of these molecular players constitutes a first step for a rationale design of pharmacotherapeutics to prevent, ameliorate and/or reverse the negative effects of alcohol on muscle contractility.

The alcohol marker phosphatidylethanol is closely related to AST, GGT, ferritin and HDL-C

BACKGROUND

The aim of this study was to evaluate the quantitative relation between common clinical chemical analyses and ethanol use, measured by a combination of the two alcohol markers phosphatidylethanol (PEth) and carbohydrate-deficient transferrin (CDT).

METHODS

Results of PEth and CDT in whole blood and serum, respectively, were included, together with information on 10 different commonly measured clinical chemical analytes, as well as age and sex. PEth was analysed by UPC² -MS/MS and CDT was measured by capillary electrophoresis.

RESULTS

Samples from 4873 patients were included. The strongest relation to alcohol consumption as measured by PEth, when correcting for age and sex, was found for HDL-C (standardized β = 0.472, p < 0.001), AST (standardized β = 0.372, p < 0.001), ferritin (standardized β = 0.332, p < 0.001) and GGT (standardized β = 0.325, p < 0.001). The relation to PEth was weak for total cholesterol, TG and ALP. No relation was found for Hb and LDL-C.

CONCLUSIONS

When using PEth as a marker for alcohol consumption, this study demonstrated the quantitative relation to commonly used test as AST or GGT, but also an important relation to ferritin or HDL-C. In clinical practice, elevated levels of these clinical chemical analytes should initiate further work-up on possibly harmful alcohol use.

Soluble RANKL exaggerates hindlimb suspension-induced osteopenia but not muscle protein balance

We examined the hypothesis that exaggerating unloading-induced bone loss using a combination of hindlimb suspension (HLS) and exogenous injections of receptor activator of nuclear factor-κB ligand (RANKL) also exaggerates gastrocnemius and quadriceps muscle loss. Forty, male C57Bl/6J mice (16 weeks) were subjected to HLS or normal ambulation (ground control, GC) for 14 days. Mice received three intraperitoneal injections of either human recombinant soluble RANKL or phosphate-buffered saline as control (n = 10/group) at 24 h intervals starting on Day 1 of HLS. GC + RANKL and HLS mice exhibited similar decreases in trabecular bone volume and density in both proximal tibias and distal femurs. However, RANKL affected trabecular number, separation, and connectivity density, while HLS decreased trabecular thickness. The combination of RANKL and HLS exacerbated these changes. Similarly, GC + RANKL and HLS mice saw comparable decreases in cortical bone volume, thickness, and strength in femur midshafts, and combination treatment exacerbated these changes. Plasma concentrations of P1NP were increased in both groups receiving RANKL, while CTX concentrations were unchanged. HLS decreased gastrocnemius weight and was associated with a reduction in global protein synthesis, and no change in proteasome activity. This change was correlated with a decrease in S6K1 and S6 phosphorylation, but no change in 4E-BP1 phosphorylation. Injection of RANKL did not alter gastrocnemius or quadriceps muscle protein metabolism in GC or HLS mice. Our results suggest that injection of soluble RANKL exacerbates unloading-induced bone loss, but not unloading-induced gastrocnemius or quadriceps muscle loss.

Multiomics-Identified Intervention to Restore Ethanol-Induced Dysregulated Proteostasis and Secondary Sarcopenia in Alcoholic Liver Disease

BACKGROUND/AIMS

Signaling and metabolic perturbations contribute to dysregulated skeletal muscle protein homeostasis and secondary sarcopenia in response to a number of cellular stressors including ethanol exposure. Using an innovative multiomics-based curating of unbiased data, we identified molecular and metabolic therapeutic targets and experimentally validated restoration of protein homeostasis in an ethanol-fed mouse model of liver disease.

METHODS

Studies were performed in ethanol-treated differentiated C2C12 myotubes and physiological relevance established in an ethanol-fed mouse model of alcohol-related liver disease (mALD) or pair-fed control C57BL/6 mice. Transcriptome and proteome from ethanol treated-myotubes and gastrocnemius muscle from mALD and pair-fed mice were analyzed to identify target pathways and molecules. Readouts including signaling responses and autophagy markers by immunoblots, mitochondrial oxidative function and free radical generation, and metabolic studies by gas chromatography-mass spectrometry and sarcopenic phenotype by imaging.

RESULTS

Multiomics analyses showed that ethanol impaired skeletal muscle mTORC1 signaling, mitochondrial oxidative pathways, including intermediary metabolite regulatory genes, interleukin-6, and amino acid degradation pathways are β-hydroxymethyl-butyrate targets. Ethanol decreased mTORC1 signaling, increased autophagy flux, impaired mitochondrial oxidative function with decreased tricarboxylic acid cycle intermediary metabolites, ATP synthesis, protein synthesis and myotube diameter that were reversed by HMB. Consistently, skeletal muscle from mALD had decreased mTORC1 signaling, reduced fractional and total muscle protein synthesis rates, increased autophagy markers, lower intermediary metabolite concentrations, and lower muscle mass and fiber diameter that were reversed by β-hydroxymethyl-butyrate treatment.

CONCLUSION

An innovative multiomics approach followed by experimental validation showed that β-hydroxymethyl-butyrate restores muscle protein homeostasis in liver disease.

Alcohol Acutely Antagonizes Refeeding-Induced Alterations in the Rag GTPase-Ragulator Complex in Skeletal Muscle

The Ragulator protein complex is critical for directing the Rag GTPase proteins and mTORC1 to the lysosome membrane mediating amino acid-stimulated protein synthesis. As there is a lack of evidence on alcohol's effect on the Rag-Ragulator complex as a possible mechanism for the development of alcoholic skeletal muscle wasting, the aim of our study was to examine alterations in various protein-protein complexes in the Rag-Ragulator pathway produced acutely by feeding and how these are altered by alcohol under in vivo conditions. Mice (C57Bl/6; adult males) were fasted, and then provided rodent chow for 30 min ("refed") or remained food-deprived ("fasted"). Mice subsequently received ethanol (3 g/kg ethanol) or saline intraperitoneally, and hindlimb muscles were collected 1 h thereafter for analysis. Refeeding-induced increases in myofibrillar and sarcoplasmic protein synthesis, and mTOR and S6K1 phosphorylation, were prevented by alcohol. This inhibition was not associated with a differential rise in the intracellular leucine concentration or plasma leucine or insulin levels. Alcohol increased the amount of the Sestrin1•GATOR2 complex in the fasted state and prevented the refeeding-induced decrease in Sestrin1•GATOR2 seen in control mice. Alcohol antagonized the increase in the RagA/C•Raptor complex formation seen in the refed state. Alcohol antagonized the increase in Raptor with immunoprecipitated LAMPTOR1 (part of the Ragulator complex) after refeeding and decreased the association of RagC with LAMPTOR1. Finally, alcohol increased the association of the V1 domain of v-ATPase with LAMPTOR1 and prevented the refeeding-induced decrease in v-ATPase V1 with LAMPTOR1. Overall, these data demonstrate that acute alcohol intake disrupts multiple protein-protein complexes within the Rag-Ragulator complex, which are associated with and consistent with the concomitant decline in nutrient-stimulated muscle protein synthesis under in vivo conditions.

Empagliflozin alleviates ethanol-induced cardiomyocyte injury through inhibition of mitochondrial apoptosis via a SIRT1/PTEN/Akt pathway

Ethanol-induced myocardial injury involves multiple pathophysiological processes including apoptosis. Empagliflozin (EMPA), is a novel hypoglycaemic drug which possesses multiple pharmacologically relevant protective effects, including anti-apoptotic, anti-inflammatory and antioxidant effects. However, whether EMPA treatment has a protective effect on ethanol-induced myocardial injury has not been assessed, to the best of our knowledge. Therefore, the aim of this study was to determine the effect of EMPA treatment on ethanol-induced myocardial injury and the underlying mechanism. An ethanol-induced myocardial injury model was established by culturing H9c2 cells treated with 200 mmol/L ethanol for 24 hours, and additional groups of ethanol treated cells were also treated with EMPA with or without SIRT1 inhibitors prior to ethanol treatment. Cell viability and apoptosis were assessed using a CCK-8 assay and flow cytometry, respectively. The expression of apoptosis-related proteins was assessed using western blotting. The results showed that EMPA pretreatment resulted in increased cell viability and a decrease in LDH activity. Moreover, EMPA pretreatment significantly reduced apoptosis of cardiomyocytes, and reduced the expression of cleaved caspase 3. Furthermore, EMPA increased the expression of SIRT1, increased the phosphorylation levels of Akt, and reduced the expression of PTEN. EMPA also reduced ethanol-induced mitochondrial apoptosis, increasing the Bcl-2/Bax ratio and the mitochondrial membrane potential. However, the cardioprotective effects of EMPA were abrogated when cells were pretreated with a SIRT1 inhibitor. In conclusion, EMPA can alleviate ethanol-induced myocardial injury by inhibiting mitochondrial apoptosis via the SIRT1/PTEN/Akt pathway. Therefore, EMPA may be a novel target for treatment of ethanol-induced myocardial injury.

Low-Dose Ethanol Has Impacts on Plasma Levels of Metabolites Relating to Chronic Disease Risk in SAMP8 mice

The effects of low-dose alcohol on experimental animals are unclear. This study examined plasma metabolites in senescence-accelerated mice 8 (SAMP8) given low-dose ethanol, and compared them with aging progress and skeletal muscle strength. Male SAMP8 mice (10-wk-old) were given drinking water containing 0% (control), 1%, 2%, or 5% (v/v) ethanol for 14 wk. Compared with the control group, only mice who consumed 1% ethanol experienced a lower senescence score at 18 and 23 wk, as well as an increased limb grip strength at 21 wk. Plasma metabolites of control, 1% and 2% ethanol groups were analyzed by capillary electrophoresis-time-of-flight mass spectrometry (CE-TOF/MS). Among the 7 metabolites affected by ethanol, notewhorthy is the positive association of the ethanol levels in drinking water with the levels of α-ketoglutarate (antioxidant and anti-inflammatory metabolite) and hippurate (antioxidant and microbial co-metabolite) (p<0.05). Intriguingly, the levels of 2-hydroxyisobutyrate (the biomarker of energy metabolism and microbial co-metabolite) were higher in the 1% ethanol group (p<0.05), but not in the 2% ethanol group as compared to the control. Furthermore, the levels of some of the metabolites affected were correlated with some variables in the grading score of senescence and muscle strength. This study provides a novel insight into how low-dose ethanol in SAMP8 mice modulates the levels of circulating metabolites relating to chronic disease risk.

Strength training protects against prostate injury in alcoholic rats

Alcoholic injury can alter the hormonal signaling pathway and lead to glucose and lipid metabolism disorders. In this study, we investigated whether the strength training could exert protective effects against the alterations caused by ethanol consumption on prostatic metabolism. A UChB, ethanol-preferring rats were used in this study. Strength training was conducted for 3 days per week for 13 weeks, rats performed jumps in water carrying a weight load strapped to their chests as part of a strength training protocol. The reduced alcohol consumption by strength training was accompanied by increased glucose, serum lipid profile, total protein levels, and reduced hormonal levels. The results of protein expression of prostatic tissues in the ethanol- and strength training-treated groups indicated that "steroidal hormone receptors," "fatty acid translocation," and "cell regulation" were significantly different between ethanol- and strength training-treated groups. Taken together, these findings show that strength training effectively ameliorated prostatic injuries in alcoholic rats at least partially by acting on lipids receptors and steroidal hormone receptors pathway, suggesting the strength training as a potential novel therapeutic strategy for treating prostate injuries caused by ethanol.

Mechanical loading recovers bone but not muscle lost during unloading

Space travel and prolonged bed rest are examples of mechanical unloading that induce significant muscle and bone loss. The compromised structure and function of bone and muscle owing to unloading make the reloading period a high risk for injury. To explore interactions between skeletal bone and muscle during reloading, we hypothesized that acute external mechanical loading of bone in combination with re-ambulation facilitates the proportional recovery of bone and muscle lost during hind limb suspension (HLS) unloading. Adult male C57Bl/6J mice were randomly assigned to a HLS or time-matched ground control (GC) group. After 2-weeks of HLS, separate groups of mice were studied at day 14 (no re-ambulation), day 28 (14 days re-ambulation) and day 56 (42 days re-ambulation); throughout the re-ambulation period, one limb received compressive mechanical loading and the contralateral limb served as an internal control. HLS induced loss of trabecular bone volume (BV/TV; -51 ± 2%) and muscle weight (-15 ± 2%) compared to GC at day 14. At day 28, the left tibia (re-ambulation only) of HLS mice had recovered approximately 20% of BV/TV lost during HLS, while the right tibia (re-ambulation and acute external mechanical loading) recovered to GC values of BV/TV (~100% recovery). At day 56, the right tibia continued to recover bone for some outcomes (trabecular BV/TV, trabecular thickness), while the left limb did not. Cortical bone displayed a delayed response to HLS, with a 10% greater decrease in BV/TV at day 28 compared to day 14. In contrast to bone, acute external mechanical loading during the re-ambulation period did not significantly increase muscle mass or protein synthesis in the gastrocnemius, compared to re-ambulation alone. Our results suggest acute external mechanical loading facilitates the recovery of bone during reloading following HLS unloading, but this does not translate to a concomitant recovery of muscle mass.

The Estrogen-Responsive Transcriptome of Female Secondary Sexual Traits in the Gulf Pipefish

Sexual dimorphism often results from hormonally regulated trait differences between the sexes. In sex-role-reversed vertebrates, females often have ornaments used in mating competition that are expected to be under hormonal control. Males of the sex-role-reversed Gulf pipefish (Syngnathus scovelli) develop female-typical traits when they are exposed to estrogens. We aimed to identify genes whose expression levels changed during the development and maintenance of female-specific ornaments. We performed RNA-sequencing on skin and muscle tissue in male Gulf pipefish with and without exposure to estrogen to investigate the transcriptome of the sexually dimorphic ornament of vertical iridescent bands found in females and estrogen-exposed males. We further compared differential gene expression patterns between males and females to generate a list of genes putatively involved in the female secondary sex traits of bands and body depth. A detailed analysis of estrogen-receptor binding sites demonstrates that estrogen-regulated genes tend to have nearby cis-regulatory elements. Our results identified a number of genes that differed between the sexes and confirmed that many of these were estrogen-responsive. These estrogen-regulated genes may be involved in the arrangement of chromatophores for color patterning, as well as in the growth of muscles to achieve the greater body depth typical of females in this species. In addition, anaerobic respiration and adipose tissue could be involved in the rigors of female courtship and mating competition. Overall, this study generates a number of interesting hypotheses regarding the genetic basis of a female ornament in a sex-role-reversed pipefish.

Alcohol induces mitochondrial fragmentation and stress responses to maintain normal muscle function in Caenorhabditis elegans

Chronic excessive ethanol consumption has distinct toxic and adverse effects on a variety of tissues. In skeletal muscle, ethanol causes alcoholic myopathy, which is characterized by myofiber atrophy and the loss of muscle strength. Alcoholic myopathy is more prevalent than all inherited muscle diseases combined. Current evidence indicates that ethanol directly impairs muscle organization and function. However, the underlying mechanism by which ethanol causes toxicity in muscle is poorly understood. Here, we show that the nematode Caenorhabditis elegans exhibits the key features of alcoholic myopathy when exposed to ethanol. As in mammals, ethanol exposure impairs muscle strength and induces the expression of protective genes, including oxidative stress response genes. In addition, ethanol exposure causes the fragmentation of mitochondrial networks aligned with myofibril lattices. This ethanol-induced mitochondrial fragmentation is dependent on the mitochondrial fission factor DRP-1 (dynamin-related protein 1) and its receptor proteins on the outer mitochondrial membrane. Our data indicate that this fragmentation contributes to the activation of the mitochondrial unfolded protein response (UPR). We also found that robust, perpetual mitochondrial UPR activation effectively reduces muscle weakness caused by ethanol exposure. Our results strongly suggest that the modulation of mitochondrial stress responses may provide a method to ameliorate alcohol toxicity and damage to muscle.

Chronic Alcohol Consumption, but not Acute Intoxication, Decreases In Vitro Skeletal Muscle Contractile Function

BACKGROUND

Skeletal muscle myopathy accompanying chronic alcohol misuse results in part from a decrease in protein synthesis typically observed in type II-rich muscles that leads to muscle weakness. However, there is a paucity of studies investigating whether the alcohol-induced weakness is intrinsic to the muscle or results primarily from the loss of muscle mass. The present study determines whether acute alcohol (ethanol) intoxication or chronic alcohol consumption decreases the intrinsic contractile function of muscle.

METHODS

Adult male mice were randomly assigned to the chronic alcohol group or given a binge dose of alcohol, and contractile characteristics of the extensor digitorum longus (EDL) were determined in vitro.

RESULTS

The weight and physiological cross-sectional area (PCSA) of the EDL were decreased in alcohol-fed mice. Maximum twitch and tetanic tension were also reduced, and there was a downward shift of the absolute force-frequency curve in alcohol-fed mice. However, no alcohol-induced changes were noted when these contractile parameters were normalized for the lower PCSA. Alcohol-fed mice demonstrated greater fatigability, and alcohol-induced decreases in postfatigue specific twitch and tetanic force were independent of a decreased PCSA. Furthermore, postfatigue recovery of muscle force over time was reduced. While alcohol did not alter the content of high-energy phosphates or oxidative phosphorylation complexes I-V, it did reduce myosin heavy chain and troponin-T content. In contrast, contractile properties were not altered when examined 2 hours after binge alcohol.

CONCLUSIONS

These data demonstrate chronic alcohol consumption decreases isometric and tetanic tension development due to a reduction in muscle CSA, whereas the increased fatigability observed was independent of muscle mass. As none of the functional changes were produced by acute alcohol, which produced higher blood alcohol levels than chronic ingestion, our data suggest defects in intrinsic muscle contractility require sustained intake and appear independent of defects in basal energy production.

Ethanol acutely antagonizes the refeeding-induced increase in mTOR-dependent protein synthesis and decrease in autophagy in skeletal muscle

The purpose of this study was to determine the impact of acute ethanol administration on the major signal transduction pathways in skeletal muscle responsible for regulating the protein synthetic and degradative response to refeeding. Adult male C57Bl/6 mice were fasted overnight; mice were then either refed normal rodent chow for 30 min or a separate group of mice remained food deprived (i.e., fasted). Thereafter, mice were administered either 3 g/kg ethanol or saline. Gastrocnemius/plantaris was collected 1 h later and analyzed. Acute ethanol decreased basal and prevented the refeeding-induced increase in muscle protein synthesis. While ethanol prevented a nutrient-stimulated increase in S6K1 phosphorylation, it did not alter the increase in 4E-BP1 phosphorylation. Downstream of S6K1, ethanol also attenuated the refeeding-induced increase in S6 and eIF4B phosphorylation, as well as the decrease in eEF2 phosphorylation. Although ethanol decreased ERK and p90 RSK phosphorylation, activation of this signaling pathway was not altered by refeeding in either control or ethanol-treated mice. Related to protein degradation, in vitro-determined proteasome activity and the content of total ubiquitinated proteins were not altered by ethanol and/or refeeding. Control mice appeared to exhibit a refeeding-induced decrease in autophagy as suggested by the increased FoxO3 and ULK1 phosphorylation and total p62 protein as well as decreased LC3B-II; however, ethanol blunted these refeeding-induced changes. These data suggest that ethanol can acutely prevent the normally observed mTOR-dependent increase in protein synthesis and reduction in autophagy in response to nutrient stimulation, but does not appear to acutely alter proteasome activity.