Regulation of muscle protein synthesis during sepsis and inflammation

Association of Psoas Muscle Mass at Intensive Care Unit Admission With Physical Function and Post-discharge Destination in Survivors of Critical Illness

OBJECTIVE

Survivors of critical illness may have physical impairments, known as post-intensive care syndrome (PICS). Early screening for the risk of PICS is recommended to prevent PICS. Skeletal muscle mass is a clinically important indicator associated with various outcomes. This study aimed to examine the association of psoas muscle mass at intensive care unit (ICU) admission with the destination and physical function at hospital discharge.

METHODS

In this single-center retrospective cohort study, we reviewed the medical records of adult patients who had required emergency ICU admission and who had been intubated and mechanically ventilated. Psoas major muscle was measured as an indicator of skeletal muscle mass from abdominal computed tomography images at ICU admission. Physical function was assessed using the functional status score for the ICU and ICU mobility scale at hospital discharge. Multinomial logistic and multivariable linear regression were used to analyze the associations of the psoas muscle mass with the discharge destination and physical function at discharge.

RESULTS

We enrolled 124 patients (79 men and 45 women) with a median (interquartile range) age of 72.0 (62.0-80.0) years; 39 (31.5%) were discharged to home, 50 (40.3%) were transferred to rehabilitation wards, and 35 (28.2%) were transferred to long-term care settings. The psoas muscle area and volume were 16.9 (11.3-20.6) cm2 and 228.3 (180.2-282.0) cm3 in home discharge patients, 17.5 (11.5-21.5) cm2 and 248.4 (162.0-311.4) cm3 in rehabilitation ward patients, and 15.9 (10.3-19.5) cm2 and 184.0 (137.0-251.1) cm3 in long-term care patients. The areas and volumes of the psoas muscle were not significantly different in the three groups. Furthermore, psoas muscle mass was not significantly associated with the discharge destination and physical function.

CONCLUSIONS

Discharge destination and physical function at hospital discharge were not significantly associated with psoas muscle mass at ICU admission.

Increased Dietary Trp, Thr, and Met Supplementation Improves Performance, Health, and Protein Metabolism of Weaned Piglets under Mixed Management and Poor Housing Conditions

A sanitary challenge was carried out to induce suboptimal herd health while investigating the effect of amino acids supplementation on piglet responses. Weaned piglets of high sanitary status (6.33 ± 0.91 kg of BW) were distributed in a 2 × 2 factorial arrangement into two similar facilities with contrasting sanitary conditions and two different diets. Our results suggest that increased Trp, Thr, and Met dietary supplementation could support the immune systems of piglets under a sanitary challenge. In this manner, AA+ supplementation improved the performance and metabolism of piglets under mixed management and poor sanitary conditions. No major temporal microbiome changes were associated with differences in performance regardless of sanitary conditions or diets. Since piglets often become mixed in multiple-site production systems and facility hygiene is also often neglected, this study suggests that increased Trp, Thr, and Met (AA+) dietary supplementation could contribute to mitigating the side effects of these harmful risk factors in modern pig farms.

Development of novel liver-targeting glucocorticoid prodrugs

Background

Glucocorticoids (GCs) are widely used in the treatment of inflammatory liver diseases and sepsis, but GC's various side effects on extrahepatic tissues limit their clinical benefits. Liver-targeting GC therapy may have multiple advantages over systemic GC therapy. The purpose of this study was to develop novel liver-targeting GC prodrugs as improved treatment for inflammatory liver diseases and sepsis.

Methods

A hydrophilic linker or an ultra-hydrophilic zwitterionic linker carboxylic betaine (CB) was used to bridge cholic acid (CA) and dexamethasone (DEX) to generate transporter-dependent liver-targeting GC prodrugs CA-DEX and the highly hydrophilic CA-CB-DEX. The efficacy of liver-targeting DEX prodrugs and DEX were determined in primary human hepatocytes (PHH), macrophages, human whole blood, and/or mice with sepsis induced by cecal ligation and puncture.

Results

CA-DEX was moderately water soluble, whereas CA-CB-DEX was highly water soluble. CA-CB-DEX and CA-DEX displayed highly transporter-dependent activities in reporter assays. Data mining found marked dysregulation of many GR-target genes important for lipid catabolism, cytoprotection, and inflammation in patients with severe alcoholic hepatitis. These key GR-target genes were similarly and rapidly (within 6 h) induced or down-regulated by CA-CB-DEX and DEX in PHH. CA-CB-DEX had much weaker inhibitory effects than DEX on endotoxin-induced cytokines in mouse macrophages and human whole blood. In contrast, CA-CB-DEX exerted more potent anti-inflammatory effects than DEX in livers of septic mice.

Conclusions

CA-CB-DEX demonstrated good hepatocyte-selectivity in vitro and better anti-inflammatory effects in vivo. Further test of CA-CB-DEX as a novel liver-targeting GC prodrug for inflammatory liver diseases and sepsis is warranted.

Combining proteins with n-3 PUFAs (EPA + DHA) and their inflammation pro-resolution mediators for preservation of skeletal muscle mass

The optimal feeding strategy for critically ill patients is still debated, but feeding must be adapted to individual patient needs. Critically ill patients are at risk of muscle catabolism, leading to loss of muscle mass and its consequent clinical impacts. Timing of introduction of feeding and protein targets have been explored in recent trials. These suggest that "moderate" protein provision (maximum 1.2 g/kg/day) is best during the initial stages of illness. Unresolved inflammation may be a key factor in driving muscle catabolism. The omega-3 (n-3) fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are substrates for synthesis of mediators termed specialized pro-resolving mediators or SPMs that actively resolve inflammation. There is evidence from other settings that high-dose oral EPA + DHA increases muscle protein synthesis, decreases muscle protein breakdown, and maintains muscle mass. SPMs may be responsible for some of these effects, especially upon muscle protein breakdown. Given these findings, provision of EPA and DHA as part of medical nutritional therapy in critically ill patients at risk of loss of muscle mass seems to be a strategy to prevent the persistence of inflammation and the related anabolic resistance and muscle loss.

Intensive care unit-acquired weakness: Recent insights

Intensive care unit-acquired weakness (ICU-AW) is a common complication in critically ill patients and is associated with a variety of adverse outcomes. These include the need for prolonged mechanical ventilation and ICU stay; higher ICU, in-hospital, and 1-year mortality; and increased in-hospital costs. ICU-AW is associated with multiple risk factors including age, underlying disease, severity of illness, organ failure, sepsis, immobilization, receipt of mechanical ventilation, and other factors related to critical care. The pathological mechanism of ICU-AW remains unclear and may be considerably varied. This review aimed to evaluate recent insights into ICU-AW from several aspects including risk factors, pathophysiology, diagnosis, and treatment strategies; this provides new perspectives for future research.

Moderate exercise-induced dynamics on key sepsis-associated signaling pathways in the liver

BACKGROUND

There is a clear relationship between quantitative measures of fitness (e.g., VO₂ max) and outcomes after surgical procedures. Whether or not fitness is a modifiable risk factor and what underlying biological processes drive these changes are not known. The purpose of this study was to evaluate the moderate exercise training effect on sepsis outcomes (survival) as well as the hepatic biological response. We chose to study the liver because it plays a central role in the regulation of immune defense during systemic infection and receives blood flow directly from the origin of infection (gut) in the cecal ligation and puncture (CLP) model.

METHODS

We randomized 50 male (♂) and female (♀) Sprague-Dawley rats (10 weeks, 340 g) to 3 weeks of treadmill exercise training, performed CLP to induce polymicrobial "sepsis," and monitored survival for five days (Part I). In parallel (Part II), we randomized 60 rats to control/sedentary (G1), exercise (G2), exercise + sham surgery (G3), CLP/sepsis (G4), exercise + CLP [12 h (G5) and 24 h (G6)], euthanized at 12 or 24 h, and explored molecular pathways related to exercise and sepsis survival in hepatic tissue and serum.

RESULTS

Three weeks of exercise training significantly increased rat survival following CLP (polymicrobial sepsis). CLP increased inflammatory markers (e.g., TNF-a, IL-6), which were attenuated by exercise. Sepsis suppressed the SOD and Nrf2 expression, and exercise before sepsis restored SOD and Nrf2 levels near the baseline. CLP led to increased HIF1a expression and oxidative and nitrosative stress, the latter of which were attenuated by exercise. Haptoglobin expression levels were increased in CLP animals, which was significantly amplified in exercise + CLP (24 h) rats.

CONCLUSIONS

Moderate exercise training (3 weeks) increased the survival in rats exposed to CLP, which was associated with less inflammation, less oxidative and nitrosative stress, and activation of antioxidant defense pathways.

The association of dietary inflammatory potential with skeletal muscle strength, mass, and sarcopenia: a meta-analysis

Aims

Evidence suggested that dietary inflammatory potential may be associated with age-related skeletal muscle decline, but the results remained controversial. To summarize the evidence for the relationships between dietary inflammatory potential and skeletal muscle strength, mass, and sarcopenia in adults we conducted this meta-analysis.

Methods

Embase, Pubmed, and Web of Science were searched from inception up to 12 March 2023 for studies that evaluated the associations of dietary inflammatory potential [estimated by the Dietary inflammatory index (DII)] with skeletal muscle strength, mass, and sarcopenia. A meta-analysis was then performed to calculate the pooled regression coefficient (β) and odds ratio (OR). The non-linear dose-response relation between DII and sarcopenia was assessed using random-effects dose-response meta-analysis.

Results

This meta-analysis included 24 studies involving 56,536 participants. It was found that high DII was associated with low skeletal muscle strength [OR 1.435, 95% confidence interval (CI) 1.247-1.651, P < 0.001, I² = 4.97%]. There was a negative association of DII with skeletal muscle strength (β-0.031, 95% CI -0.056 to -0.006, P = 0.017, I² = 72.69%). High DII was also associated with low skeletal muscle mass (OR 1.106, 95% CI 1.058-1.157, P < 0.001, I² = 0%). DII had a negative relationship with skeletal muscle mass with high heterogeneity (β-0.099, 95% CI -0.145 to -0.053, P < 0.001, I² = 88.67%); we downgraded the inconsistency in the subgroup analysis of overweight/obese participants (β-0.042, 95% CI -0.065 to -0.019, I² = 12.54%). Finally, the pooled results suggested that high DII was significantly associated with sarcopenia with significant heterogeneity (OR 1.530, 95% CI 1.245-1.880, P < 0.001, I² = 69.46%); age and BMI may contribute partially to the heterogeneity since heterogeneity was decreased in the subgroup of older age (OR 1.939, 95% CI 1.232-3.051, I² = 0%) and the group of overweight/obesity (OR 1.853, 95% CI 1.398-2.456, I² = 0%). There was a non-linear dose-response association between DII and sarcopenia (P = 0.012 for non-linearity).

Conclusion

This meta-analysis suggested that higher dietary inflammatory potential was significantly associated with lower skeletal muscle strength, mass, and risk of sarcopenia. Future studies with consistent assessment and standardized methodology are needed for further analysis.

IMPORTANCE OF THE INNATE IMMUNE RESPONSE IN SKELETAL MUSCLE TO SEPSIS-INDUCED ALTERATIONS IN PROTEIN BALANCE

ABSTRACT

There is growing appreciation that skeletal muscle is a fully functional component of the body's innate immune system with the potential to actively participate in the host response to invading bacteria as opposed to being a passive target. In this regard, skeletal muscle in general and myocytes specifically possess an afferent limb that recognizes a wide variety of host pathogens via their interaction with multiple classes of cell membrane-bound and intracellular receptors, including toll-like receptors, cytokine receptors, NOD-like receptors, and the NLRP inflammasome. The efferent limb of the innate immune system in muscle is equally robust and with an increased synthesis and secretion of a variety of myocyte-derived cytokines (i.e., myokines), including TNF-α, IL-1, IL-6, and NO as well as multiple chemokines in response to appropriate stimulation. Herein, the current narrative review focuses primarily on the immune response of myocytes per se as opposed to other cell types within whole muscle. Moreover, because there are important differences, this review focuses specifically on systemic infection and inflammation as opposed to the response of muscle to direct injury and various types of muscular dystrophies. To date, however, there are few definitive muscle-specific studies that are necessary to directly address the relative importance of muscle-derived immune activation as a contributor to either the systemic immune response or the local immune microenvironment within muscle during sepsis and the resultant downstream metabolic disturbances.

Melatonin: A potential adjuvant therapy for septic myopathy

Septic myopathy, also known as ICU acquired weakness (ICU-AW), is a characteristic clinical symptom of patients with sepsis, mainly manifested as skeletal muscle weakness and muscular atrophy, which affects the respiratory and motor systems of patients, reduces the quality of life, and even threatens the survival of patients. Melatonin is one of the hormones secreted by the pineal gland. Previous studies have found that melatonin has anti-inflammatory, free radical scavenging, antioxidant stress, autophagic lysosome regulation, mitochondrial protection, and other multiple biological functions and plays a protective role in sepsis-related multiple organ dysfunction. Given the results of previous studies, we believe that melatonin may play an excellent regulatory role in the repair and regeneration of skeletal muscle atrophy in septic myopathy. Melatonin, as an over-the-counter drug, has the potential to be an early, complementary treatment for clinical trials. Based on previous research results, this article aims to critically discuss and review the effects of melatonin on sepsis and skeletal muscle depletion.

Construction of m7G subtype classification on heterogeneity of sepsis

Sepsis is a highly heterogeneous disease and a major factor in increasing mortality from infection. N7-Methylguanosine (m7G) is a widely RNA modification in eukaryotes, which involved in regulation of different biological processes. Researchers have found that m7G methylation contributes to a variety of human diseases, but its research in sepsis is still limited. Here, we aim to establish the molecular classification of m7G gene-related sepsis, reveal its heterogeneity and explore the underlying mechanism. We first identified eight m7G related prognostic genes, and identified two different molecular subtypes of sepsis through Consensus Clustering. Among them, the prognosis of C2 subtype is worse than that of C1 subtype. The signal pathways enriched by the two subtypes were analyzed by ssGSEA, and the results showed that the amino acid metabolism activity of C2 subtype was more active than that of C1 subtype. In addition, the difference of immune microenvironment among different subtypes was explored through CIBERSORT algorithm, and the results showed that the contents of macrophages M0 and NK cells activated were significantly increased in C2 subtype, while the content of NK cells resting decreased significantly in C2 subtype. We further explored the relationship between immune regulatory genes and inflammation related genes between C2 subtype and C1 subtype, and found that C2 subtype showed higher expression of immune regulatory genes and inflammation related genes. Finally, we screened the key genes in sepsis by WGCNA analysis, namely NUDT4 and PARN, and verified their expression patterns in sepsis in the datasets GSE131761 and GSE65682. The RT-PCR test further confirmed the increased expression of NUDTA4 in sepsis patients. In conclusion, sepsis clustering based on eight m7G-related genes can well distinguish the heterogeneity of sepsis patients and help guide the personalized treatment of sepsis patients.

Tidy up - The unfolded protein response in sepsis

Pathogens, their toxic byproducts, and the subsequent immune reaction exert different forms of stress and damage to the tissue of the infected host. This stress can trigger specific transcriptional and post-transcriptional programs that have evolved to limit the pathogenesis of infectious diseases by conferring tissue damage control. If these programs fail, infectious diseases can take a severe course including organ dysfunction and damage, a phenomenon that is known as sepsis and which is associated with high mortality. One of the key adaptive mechanisms to counter infection-associated stress is the unfolded protein response (UPR), aiming to reduce endoplasmic reticulum stress and restore protein homeostasis. This is mediated via a set of diverse and complementary mechanisms, i.e. the reduction of protein translation, increase of protein folding capacity, and increase of polyubiquitination of misfolded proteins and subsequent proteasomal degradation. However, UPR is not exclusively beneficial since its enhanced or prolonged activation might lead to detrimental effects such as cell death. Thus, fine-tuning and time-restricted regulation of the UPR should diminish disease severity of infectious disease and improve the outcome of sepsis while not bearing long-term consequences. In this review, we describe the current knowledge of the UPR, its role in infectious diseases, regulation mechanisms, and further clinical implications in sepsis.

Anti-inflammatory Streptococcus thermophilus CNRZ160 limits sarcopenia induced by low-grade inflammation in older adult rats

Background and aims

Aging is characterized, at the systemic level, by the development of low-grade inflammation, which has been identified as determining sarcopenia by blunting postprandial muscle anabolism. The causes of this “inflammageing” is still not clearly defined. An increased intestinal permeability, a microbiota dysbiosis and subsequent generation of intestinal then generalized inflammation have been hypothesized. The objective of this study was to test in vivo during aging if (1) a chronic low-grade intestinal inflammation can lead to anabolic resistance and muscle loss and (2) if a bacterial strain presenting anti-inflammatory properties could prevent these adverse effects.

Methods

Young adult (6 m) and elderly rats (18 m) received Dextran Sodium Sulfate (DSS) for 28 days to generate low-grade intestinal inflammation, and received (PB1 or PB2 groups) or not (DSS group) one of the two S. Thermophilus strains (5 × 109 CFU/day) previously shown to present an anti-inflammatory potential in vitro. They were compared to pair fed control (PF). Muscle and colon weights and protein synthesis (using 13C Valine) were measured at slaughter. Muscle proteolysis, gut permeability and inflammatory markers were assessed only in old animals by RT-PCR or proteins quantifications (ELISA).

Results

In both adult and old rats, DSS reduced absolute protein synthesis (ASR) in gastrocnemius muscle [−12.4% (PB1) and −9.5% (PB2) vs. PF, P &lt; 0.05] and increased ASR in colon (+86% and +30.5%, respectively vs. PF, P &lt; 0.05). PB1 (CNRZ160 strain) but not PB2 resulted in a higher muscle ASR as compared to DSS in adults (+18%, P &lt; 0.05), a trend also observed for PB1 in old animals (+12%, P = 0.10). This was associated with a blunted increase in colon ASR. In old rats, PB1 also significantly decreased expression of markers of autophagy and ubiquitin-proteasome pathways vs. DSS groups and improved gut permeability (assessed by Occludin, Zonula Occludens 1 and Claudin 1 expression, P &lt; 0.05) and alleviated systemic inflammation (A2M: −48% vs. DSS, P &lt; 0.05).

Conclusion

The loss of muscle anabolism associated with low-grade intestinal inflammation can be prevented by supplementation with anti-inflammatory CNRZ160 strain. We propose that the moderated gut inflammation by CNRZ160 may result in curtailed amino acids (AA) utilization by the gut, and subsequent restored AA systemic availability to support muscle protein accretion. Therefore, CNRZ160 could be considered as an efficient probiotic to modulate muscle mass loss and limit sarcopenia during aging.

Narrative Review: Glucocorticoids in Alcoholic Hepatitis—Benefits, Side Effects, and Mechanisms

Alcoholic hepatitis is a major health and economic burden worldwide. Glucocorticoids (GCs) are the only first-line drugs recommended to treat severe alcoholic hepatitis (sAH), with limited short-term efficacy and significant side effects. In this review, I summarize the major benefits and side effects of GC therapy in sAH and the potential underlying mechanisms. The review of the literature and data mining clearly indicate that the hepatic signaling of glucocorticoid receptor (GR) is markedly impaired in sAH patients. The impaired GR signaling causes hepatic down-regulation of genes essential for gluconeogenesis, lipid catabolism, cytoprotection, and anti-inflammation in sAH patients. The efficacy of GCs in sAH may be compromised by GC resistance and/or GC’s extrahepatic side effects, particularly the side effects of intestinal epithelial GR on gut permeability and inflammation in AH. Prednisolone, a major GC used for sAH, activates both the GR and mineralocorticoid receptor (MR). When GC non-responsiveness occurs in sAH patients, the activation of MR by prednisolone might increase the risk of alcohol abuse, liver fibrosis, and acute kidney injury. To improve the GC therapy of sAH, the effort should be focused on developing the biomarker(s) for GC responsiveness, liver-targeting GR agonists, and strategies to overcome GC non-responsiveness and prevent alcohol relapse in sAH patients.

Multifactorial Mechanism of Sarcopenia and Sarcopenic Obesity. Role of Physical Exercise, Microbiota and Myokines

Obesity and ageing place a tremendous strain on the global healthcare system. Age-related sarcopenia is characterized by decreased muscular strength, decreased muscle quantity, quality, and decreased functional performance. Sarcopenic obesity (SO) is a condition that combines sarcopenia and obesity and has a substantial influence on the older adults’ health. Because of the complicated pathophysiology, there are disagreements and challenges in identifying and diagnosing SO. Recently, it has become clear that dysbiosis may play a role in the onset and progression of sarcopenia and SO. Skeletal muscle secretes myokines during contraction, which play an important role in controlling muscle growth, function, and metabolic balance. Myokine dysfunction can cause and aggravate obesity, sarcopenia, and SO. The only ways to prevent and slow the progression of sarcopenia, particularly sarcopenic obesity, are physical activity and correct nutritional support. While exercise cannot completely prevent sarcopenia and age-related loss in muscular function, it can certainly delay development and slow down the rate of sarcopenia. The purpose of this review was to discuss potential pathways to muscle deterioration in obese individuals. We also want to present the current understanding of the role of various factors, including microbiota and myokines, in the process of sarcopenia and SO.

Skeletal muscle wasting: the estrogen side of sexual dimorphism

The importance of defining sex differences across various biological and physiological mechanisms is more pervasive now than it has been over the past 15-20 years. As the muscle biology field pushes to identify small molecules and interventions to prevent, attenuate, or even reverse muscle wasting, we must consider the effect of sex as a biological variable. It should not be assumed that a therapeutic will affect males and females with equal efficacy or equivalent target affinities under conditions where muscle wasting is observed. With that said, it is not surprising to find that we have an unclear or even a poor understanding of the effects of sex or sex hormones on muscle wasting conditions. Although recent investigations are beginning to establish experimental approaches that will allow investigators to assess the impact of sex-specific hormones on muscle wasting, the field still needs rigorous scientific tools that will allow the community to address critical hypotheses centered around sex hormones. The focus of this review is on female sex hormones, specifically estrogens, and the roles that these hormones and their receptors play in skeletal muscle wasting conditions. With the overall review goal of assembling the current knowledge in the area of sexual dimorphism driven by estrogens with an effort to provide insights to interested physiologists on necessary considerations when trying to assess models for potential sex differences in cellular and molecular mechanisms of muscle wasting.

Molecular Mechanisms of Muscle Fatigue

Muscle fatigue (MF) declines the capacity of muscles to complete a task over time at a constant load. MF is usually short-lasting, reversible, and is experienced as a feeling of tiredness or lack of energy. The leading causes of short-lasting fatigue are related to overtraining, undertraining/deconditioning, or physical injury. Conversely, MF can be persistent and more serious when associated with pathological states or following chronic exposure to certain medication or toxic composites. In conjunction with chronic fatigue, the muscle feels floppy, and the force generated by muscles is always low, causing the individual to feel frail constantly. The leading cause underpinning the development of chronic fatigue is related to muscle wasting mediated by aging, immobilization, insulin resistance (through high-fat dietary intake or pharmacologically mediated Peroxisome Proliferator-Activated Receptor (PPAR) agonism), diseases associated with systemic inflammation (arthritis, sepsis, infections, trauma, cardiovascular and respiratory disorders (heart failure, chronic obstructive pulmonary disease (COPD))), chronic kidney failure, muscle dystrophies, muscle myopathies, multiple sclerosis, and, more recently, coronavirus disease 2019 (COVID-19). The primary outcome of displaying chronic muscle fatigue is a poor quality of life. This type of fatigue represents a significant daily challenge for those affected and for the national health authorities through the financial burden attached to patient support. Although the origin of chronic fatigue is multifactorial, the MF in illness conditions is intrinsically linked to the occurrence of muscle loss. The sequence of events leading to chronic fatigue can be schematically denoted as: trigger (genetic or pathological) -> molecular outcome within the muscle cell -> muscle wasting -> loss of muscle function -> occurrence of chronic muscle fatigue. The present review will only highlight and discuss current knowledge on the molecular mechanisms that contribute to the upregulation of muscle wasting, thereby helping us understand how we could prevent or treat this debilitating condition.

Sarcopenia and frailty in decompensated cirrhosis

In patients with decompensated cirrhosis, sarcopenia and frailty are prevalent. Although several definitions exist for these terms, in the field of hepatology, sarcopenia has commonly been defined as loss of muscle mass, and frailty has been broadly defined as the phenotypic manifestation of the loss of muscle function. Prompt recognition and accurate assessment of these conditions are critical as they are both strongly associated with morbidity, mortality, poor quality of life and worse post-liver transplant outcomes in patients with cirrhosis. In this review, we describe the complex pathophysiology that underlies the clinical phenotypes of sarcopenia and frailty, their association with decompensation, and provide an overview of tools to assess these conditions in patients with cirrhosis. When available, we highlight data focusing on patients with acutely decompensated cirrhosis, such as inpatients, as this is an area of unmet clinical need. Finally, we discuss management strategies to reverse and/or prevent the development of sarcopenia and frailty, which include adequate nutritional intake of calories and protein, as well as regular exercise of at least moderate intensity, with a mix of aerobic and resistance training. Key knowledge gaps in our understanding of sarcopenia and frailty in decompensated cirrhosis remain, including best methods to measure muscle mass and function in the inpatient setting, racial/ethnic variation in the development and presentation of sarcopenia and frailty, and optimal clinical metrics to assess response to therapeutic interventions that translate into a reduction in adverse outcomes associated with these conditions.

Resistance Exercise After Laparoscopic Surgery Enhances Improvement in Exercise Tolerance in Geriatric Patients With Gastrointestinal Cancer

INTRODUCTION

 Early mobilization after cancer surgery is generally recommended. However, the effects of postoperative resistance exercise during a hospital stay have been rarely investigated. This study aimed to clarify the effects of resistance exercise after laparoscopic surgery on exercise tolerance and skeletal muscle mass in geriatric patients with gastrointestinal cancer.

METHODS

This single-center retrospective observational study included patients with gastrointestinal cancer who admitted for laparoscopic surgery. Exercise tolerance and skeletal muscle mass were assessed using a six-minute walking test (6MWT) and skeletal muscle index (SMI) at admission and discharge, respectively. Intergroup comparisons of absolute changes in 6MWT and SMI were analyzed by the unpaired t-test or Mann-Whitney U test according to whether resistance exercise was performed or not. Multivariable linear regression analyses were used to analyze the association of resistance exercise with changes in 6MWT and SMI. The analyses were adjusted for age, sex, cancer stage, postoperative complication, and preoperative exercise tolerance and skeletal muscle mass.

RESULTS

Altogether, 66 patients (mean age 69.9 years; 60.6% men) were recruited. Of them, 72.7% performed the resistance exercise and started at a median of 4.5 postoperative days. There were no significant intergroup differences in absolute changes in the 6MWT and the SMI (p = 0.153, p = 0.476, respectively). Multivariable linear regression analysis showed that resistance exercise was independently and positively associated with the 6MWT at discharge (β = 1.70, 95% confidence interval, 1.88 to 71.09) and did not significantly contribute to the SMI at discharge (95% confidence interval, -0.21 to 0.27).

CONCLUSION

Resistance exercise may enhance the improvement in postoperative exercise tolerance in geriatric patients with gastrointestinal cancer who underwent laparoscopic surgery.

TGF-β Pathway Inhibition Protects the Diaphragm From Sepsis-Induced Wasting and Weakness in Rat

Sepsis is a frequent complication in patients in intensive care units (ICU). Diaphragm weakness, one of the most common symptoms observed, can lead to weaning problems during mechanical ventilation. Over the last couple of years, members of the transforming growth factor (TGF) β family, such as myostatin, activin A, and TGF-β1, have been reported to strongly trigger the activation of protein breakdown involved in muscle wasting. The aim of this study was to investigate the effect of TGF-β inhibitor LY364947 on the diaphragm during chronic sepsis.Rats were separated into four groups exposed to different experimental conditions: Control group, Septic group, Septic group with inhibitor from day 0 (LY D0), and Septic group with inhibitor from day 1 (LY D1). Sepsis was induced in rats by cecal ligation and puncture, and carried out for 7 days.Chronic sepsis was responsible for a decrease in body weight, food intake and diaphragm's mass. The inhibitor was able to abolish diaphragm wasting only in the LY D1 group. Similarly, LY364947 had a beneficial effect on the diaphragm contraction only for the LY D1 group. SMAD3 was over-expressed and phosphorylated within rats in the Septic group; however, this effect was reversed by LY364947. Calpain-1 and -2 as well as MAFbx were over-expressed within individuals in the Septic group. Yet, calpain-1 and MAFbx expressions were decreased by LY364947.With this work, we demonstrate for the first time that the inhibition of TGF-β pathway during chronic sepsis protects the diaphragm from wasting and weakness as early as one day post infection. This could lead to more efficient treatment and care for septic patients in ICU.

Leucine Reconstitutes Phagocytosis-Induced Cell Death in E. coli-Infected Neonatal Monocytes-Effects on Energy Metabolism and mTOR Signaling

MΦ differentiate from circulating monocytes (Mo). The reduced ability of neonatal Mo to undergo apoptosis after E. coli infection (phagocytosis-induced cell death (PICD)) could contribute to sustained inflammatory processes. The objective of our study was to investigate whether immune metabolism in Mo can be modified to gain access to pro-apoptotic signaling. To this end, we supplemented Mo from neonates and from adults with the branched amino acid leucine. In neonatal Mo, we observed increased energy production via oxidative phosphorylation (Oxphos) after E. coli infection via Seahorse assay. Leucine did not change phagocytic properties. In neonatal Mo, we detected temporal activation of the AKT and mTOR pathways, accompanied with subsequent activation of downstream targets S6 Kinase (S6K) and S6. FACS analyses showed that once mTOR activation was terminated, the level of anti-apoptotic BCL-2 family proteins (BCL-2; BCL-X_L) decreased. Release of cytochrome C and cleavage of caspase-3 indicated involvement of the intrinsic apoptotic pathway. Concomitantly, the PICD of neonatal Mo was initiated, as detected by hypodiploid DNA. This process was sensitive to rapamycin and metformin, suggesting a functional link between AKT, mTOR and the control of intrinsic apoptotic signaling. These features were unique to neonatal Mo and could not be observed in adult Mo. Supplementation with leucine therefore could be beneficial to reduce sustained inflammation in septic neonates.

Implication of the NLRP3 Inflammasome in Bovine Age-Related Sarcopenia

Sarcopenia is defined as the age-related loss of skeletal muscle mass, quality, and strength. The pathophysiological mechanisms underlying sarcopenia are still not completely understood. The aim of this work was to evaluate, for the first time, the expression of NLRP3 inflammasome in bovine skeletal muscle in order to investigate the hypothesis that inflammasome activation may trigger and sustain a pro-inflammatory environment leading to sarcopenia. Samples of skeletal muscle were collected from 60 cattle belonging to three age-based groups. Morphologic, immunohistochemical and molecular analysis were performed to assess the presence of age-related pathologic changes and chronic inflammation, the expression of NLRP3 inflammasome and to determine the levels of interleukin-1β, interleukin-18 and tumor necrosis factor alpha in muscle tissue. Our results revealed the presence of morphologic sarcopenia hallmark, chronic lymphocytic inflammation and a type II fibers-selective NLRP3 expression associated to a significant decreased number of immunolabeled-fibers in aged animals. Moreover, we found a statistically significant age-related increase of pro-inflammatory cytokines such as interleukin-1β and interleukin-18 suggesting the activation of NLRP3 inflammasome. Taken together, our data suggest that NLRP3 inflammasome components may be normally expressed in skeletal muscle, but its priming and activation during aging may contribute to enhance a pro-inflammatory environment altering normal muscular anabolism and metabolism.

Local immune responses to VAA DNA vaccine against Listonella anguillarum in flounder (Paralichthys olivaceus)

The efficacy of DNA vaccine is associated closely with the expression of the antigen and the intensity of local immune responses. In our previous study, a recombinant DNA plasmid expressing the VAA protein (pVAA) of Listonella anguillarum has been proved to have a good protection against the infection of L. anguillarum. In the present study, the local immune responses eliciting by immunizing flounder with intramuscular (I.M.) injection of pVAA was investigated at the cellular and genetic level, the muscle at the injection site at 7th post vaccination day was sampled and analyzed by hematoxylin-eosin (H&E) staining, immunohistochemistry (IHC), flow cytometry (FCM), RNA sequencing (RNA-Seq)-based transcriptomics and RT-qPCR. Then variations on the specific antibodies in serum at 1st-6th post vaccination week and the relative percent survival rate (RPS) at following 14 days after challenge were measured. The H&E results showed that inflammatory cells and immune cells significantly increased at the injection site. The IHC using monoclonal antibody against T cell markers revealed that both CD4-1⁺ and CD4-2⁺ T lymphocytes were recruited to the injection site and FCM results showed that the proportion of CD4-1⁺ cells in pVAA immunized group was 28.6 %, in the control group was 8.7 %, and that of CD4-2⁺ cells in two groups was 21.2 % and 8.5 %, respectively. These results indicating that the proportion of CD4⁺ cells in the immune group was significantly increased compared with the control group. Moreover, there were 2551 genes differently expressed in pVAA immunized group, KEGG analysis showed the genes involved in the signal transduction and immune system, and surface markers for B-cells genes, T-cells and antigen presenting cells (APCs) genes were highly upregulated, suggesting the activation of the systemic immune responses. Antibody specific anti-L. anguillarum or anti-rVAA antibodies were significantly induced at 2nd post-immunization week, that reached a peak at 4-5th week. RPS in pVAA group was 53.85±3.64 %. In conclusion, pVAA induced effective local immune responses and then the systematic response. This probably is the main contribution of pVAA to effective protection against L. anguillarum.

Barth syndrome cardiomyopathy: targeting the mitochondria with elamipretide

Barth syndrome (BTHS) is a rare, X-linked recessive, infantile-onset debilitating disorder characterized by early-onset cardiomyopathy, skeletal muscle myopathy, growth delay, and neutropenia, with a worldwide incidence of 1/300,000-400,000 live births. The high mortality rate throughout infancy in BTHS patients is related primarily to progressive cardiomyopathy and a weakened immune system. BTHS is caused by defects in the TAZ gene that encodes tafazzin, a transacylase responsible for the remodeling and maturation of the mitochondrial phospholipid cardiolipin (CL), which is critical to normal mitochondrial structure and function (i.e., ATP generation). A deficiency in tafazzin results in up to a 95% reduction in levels of structurally mature CL. Because the heart is the most metabolically active organ in the body, with the highest mitochondrial content of any tissue, mitochondrial dysfunction plays a key role in the development of heart failure in patients with BTHS. Changes in mitochondrial oxidative phosphorylation reduce the ability of mitochondria to meet the ATP demands of the human heart as well as skeletal muscle, namely ATP synthesis does not match the rate of ATP consumption. The presence of several cardiomyopathic phenotypes have been described in BTHS, including dilated cardiomyopathy, left ventricular noncompaction, either alone or in conjunction with other cardiomyopathic phenotypes, endocardial fibroelastosis, hypertrophic cardiomyopathy, and an apical form of hypertrophic cardiomyopathy, among others, all of which can be directly attributed to the lack of CL synthesis, remodeling, and maturation with subsequent mitochondrial dysfunction. Several mechanisms by which these cardiomyopathic phenotypes exist have been proposed, thereby identifying potential targets for treatment. Dysfunction of the sarcoplasmic reticulum Ca2+-ATPase pump and inflammation potentially triggered by circulating mitochondrial components have been identified. Currently, treatment modalities are aimed at addressing symptomatology of HF in BTHS, but do not address the underlying pathology. One novel therapeutic approach includes elamipretide, which crosses the mitochondrial outer membrane to localize to the inner membrane where it associates with cardiolipin to enhance ATP synthesis in several organs, including the heart. Encouraging clinical results of the use of elamipretide in treating patients with BTHS support the potential use of this drug for management of this rare disease.

Improved recovery from skeletal muscle damage is largely unexplained by myofibrillar protein synthesis or inflammatory and regenerative gene expression pathways

The contribution of myofibrillar protein synthesis (MyoPS) to recovery from skeletal muscle damage in humans is unknown. Recreationally active men and women consumed a daily protein-polyphenol beverage targeted at increasing amino acid availability and reducing inflammation (PPB; n = 9), both known to affect MyoPS, or an isocaloric placebo (PLA; n = 9) during 168 h of recovery from 300 maximal unilateral eccentric contractions (EE). Muscle function was assessed daily. Muscle biopsies were collected for 24, 27, 36, 72, and 168 h for MyoPS measurements using ²H₂O and expression of 224 genes using RT-qPCR and pathway analysis. PPB improved recovery of muscle function, which was impaired for 5 days after EE in PLA (interaction P < 0.05). Acute postprandial MyoPS rates were unaffected by nutritional intervention (24-27 h). EE increased overnight (27-36 h) MyoPS versus the control leg (PLA: 33 ± 19%; PPB: 79 ± 25%; leg P < 0.01), and PPB tended to increase this further (interaction P = 0.06). Daily MyoPS rates were greater with PPB between 72 and 168 h after EE, albeit after function had recovered. Inflammatory and regenerative signaling pathways were dramatically upregulated and clustered after EE but were unaffected by nutritional intervention. These results suggest that accelerated recovery from EE is not explained by elevated MyoPS or suppression of inflammation.NEW & NOTEWORTHY The present study investigated the contribution of myofibrillar protein synthesis (MyoPS) and associated gene signaling to recovery from 300 muscle-damaging, eccentric contractions. Measured with ²H₂O, MyoPS rates were elevated during recovery and observed alongside expression of inflammatory and regenerative signaling pathways. A nutritional intervention accelerated recovery; however, MyoPS and gene signaling were unchanged compared with placebo. These data indicate that MyoPS and associated signaling do not explain accelerated recovery from muscle damage.

Myostatin deficiency not only prevents muscle wasting but also improves survival in septic mice

Sepsis remains a leading cause of mortality in critically ill patients. Muscle wasting is a major complication of sepsis and negatively affects clinical outcomes. Despite intense investigation for many years, the molecular mechanisms underlying sepsis-related muscle wasting are not fully understood. In addition, a potential role of muscle wasting in disease development of sepsis has not been studied. Myostatin is a myokine that downregulates skeletal muscle mass. We studied the effects of myostatin deficiency on muscle wasting and other clinically relevant outcomes, including mortality and bacterial clearance, in mice. Myostatin deficiency prevented muscle atrophy along with inhibition of increases in muscle-specific RING finger protein 1 (MuRF-1) and atrogin-1 expression and phosphorylation of signal transducer and activator of transcription protein 3 (STAT3; major players of muscle wasting) in septic mice. Moreover, myostatin deficiency improved survival and bacterial clearance of septic mice. Sepsis-induced liver dysfunction, acute kidney injury, and neutrophil infiltration into the liver and kidney were consistently mitigated by myostatin deficiency, as indicated by plasma concentrations of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and neutrophil gelatinase-associated lipocalin (NGAL) and myeloperoxidase activity in the organs. Myostatin deficiency also inhibited sepsis-induced increases in plasma high-mobility group protein B1 (HMGB1) and macrophage inhibitory cytokine (MIC)-1/growth differentiation factor (GDF)-15 concentrations. These results indicate that myostatin plays an important role not only in muscle wasting but also in other clinically relevant outcomes in septic mice. Furthermore, our data raise the possibility that muscle wasting may not be simply a complication, but myostatin-mediated muscle cachexia and related changes in muscle may actually drive the development of sepsis as well.NEW & NOTEWORTHY Muscle wasting is a major complication of sepsis, but its role in the disease development is not known. Myostatin deficiency improved bacterial clearance and survival and mitigated damage in the liver and kidney in septic mice, which paralleled prevention of muscle wasting. These results raise the possibility that muscle wasting may not simply be a complication of sepsis, but myostatin-mediated cachexic changes may have a role in impaired bacterial clearance and mortality in septic mice.

Association between appendicular skeletal muscle index and leukocyte telomere length in adults: A study from National Health and Nutrition Examination Survey (NHANES) 1999-2002

BACKGROUND

A higher body mass index (BMI) is associated with shorter telomeres. The loss of muscle mass with aging is associated with adverse outcomes. The appendicular skeletal muscle index (ASMI) is currently used to quantify muscle mass.

OBJECTIVE

We investigated the association of the ASMI with leukocyte telomere length in adult Americans.

METHODS

This cross-sectional study used the National Health and Nutrition Examination Survey (NHANES) 1999-2002 dataset. Body composition was measured by dual-energy X-ray absorptiometry. Low muscle mass was defined using sex-specific thresholds of the appendicular skeletal muscle mass index (ASMI). The telomere-to-single-copy gene ratio (T/S ratio) was converted to base pairs. Generalized linear models were performed to evaluate the association of ASMI with telomere length.

RESULTS

In multivariable adjustment regression models, higher ASMI was associated with longer telomeres in US adults (β = 70.2, P < 0.001, P trend<0.001). In participants with preserved muscle mass, the ASMI was related to longer telomere length (β = 75.1, P < 0.001), but not significantly in low muscle mass participants (β = 68.7, P = 0.30). Further subgroup analysis by a combination of age groups and muscle mass status showed positive association with young-preserved muscle mass (β = 82.6, P < 0.001), old-preserved muscle mass (β = 44.4, P = 0.12), young-low muscle mass (β = 135.4, P = 0.20), and old-low muscle mass (β = 52.7, P = 0.55). Because each additional year of chronological age was associated with telomeres that were 15.3 base pairs shorter, on average, this would equate to 5.4 fewer years of biological aging (82.6 ÷ 15.3) in the young-preserved muscle mass participants.

CONCLUSIONS

A higher ASMI is associated with longer telomeres. The prevention of skeletal muscle loss has the potential to delay telomere shortening and account for less biological aging.

Perioperative physical and nutritional therapy for tongue cancer-induced malnutrition and muscle atrophy: A case report

Malnutrition is a common complication in patients with tongue cancer who experience dysphagia and can steadily lead to skeletal muscle atrophy. Additionally, skeletal muscle loss commonly occurs in patients after invasive surgery. Therefore, patients with tongue cancer are at high risk of skeletal muscle atrophy during the perioperative phase of treatment. Over time, physical and nutritional therapy are expected to increase skeletal muscle mass and improve nutritional status. However, immediate benefits for patients in the perioperative phase of treatment are largely unknown. This case report aimed to evaluate the combined effects of physical and nutritional therapy for a patient in the perioperative phase of treatment for tongue cancer. We describe a 48-year-old woman diagnosed with tongue cancer. Her increasing difficulty with eating and swallowing led to malnutrition. After hospital admission for oral surgery, physical and nutritional therapy were initiated. Skeletal muscle mass measured by body composition analyzer and ultrasound apparatus showed increases, whereas blood tests to indicate nutritional status showed no improvement. This case suggests that physical and nutritional therapy are effective for increasing skeletal muscle during perioperative phase treatment in malnourished patients with tongue cancer and assessment of skeletal muscle mass is a reliable method for clinical evaluation.

Ultrasound Measurement of Septic Shock-induced Acute Skeletal Muscle Atrophy in Intensive Care Unit

BACKGROUND

Skeletal muscle wasting progresses rapidly during critical care. However, the effect of skeletal muscle changes on physical function during intensive care remain poorly understood.

OBJECTIVE

To examine the changes in skeletal muscle thickness of patients admitted to the intensive care unit (ICU) for septic shock and the relationship between skeletal muscle thickness and physical function following intensive care.

DESIGN

Longitudinal observational study.

SETTING

Single emergency hospital.

PATIENTS

Ten septic shock patients who were mechanically ventilated in the ICU were recruited.

INTERVENTIONS

Not applicable.

METHODS

Ultrasound measurements of thickness of rectus femoris (RF) were conducted within 24 hours after admission and repeated every two days until the 14th hospital day. The correlations between TRF and various parametric data (i.e., age, severity classification, mechanically ventilated period, length of stay (LOS) at the ICU, and physical function) correlations were assessed with Pearson's product moment coefficient of correlation.

MAIN OUTCOME MEASURE(S)

Curve estimation for best fit for chronological changes in TRF with respect to the HD and the correlation between TRF and clinical indicators.

RESULTS

Eight septic shock patients were observed completely for 14 days. TRF decreased linearly by 30.6% (IQR: 23.9-45.7) during the first 14 days. The correlation between TRF at admission and physical function at the 30th hospital day was close to significant. The TRF at the 14th hospital day was negatively correlated with disease severity and age. A positive correlation was observed between the decrease in rate of TRF and LOS at the ICU.

CONCLUSION

Skeletal muscle thickness of septic shock patients rapidly decreased in a linear manner over 14 days and may predict physical function after critical care.

Sepsis Increases Muscle Proteolysis in Severely Burned Adults, but Does not Impact Whole-Body Lipid or Carbohydrate Kinetics

Sepsis is a common and often fatal consequence of severe burn injury, but its exact effects on whole body and muscle metabolism in the burn patient is unclear. To address this, 13 septic and 11 nonseptic patients (age: 36.9 ± 13.0 years) with burns encompassing >30% of their total body surface area underwent muscle protein kinetic studies under postabsorptive conditions using bolus injections of ring-C6 and N phenylalanine isotopes. In parallel, whole-body lipid and carbohydrate kinetics were assessed using constant infusions of [U-C6]palmitate, [6,6-H2]glucose, and [H5]glycerol, and during a 2-h hyperinsulinemic euglycemic clamp. Muscle mRNA levels of genes implicated in the development of muscle cachexia were assessed by qPCR. Fractional breakdown rates of mixed-muscle proteins were found to be 2.4-fold greater in septic versus nonseptic patients (P < 0.05). No discernable differences in fractional synthetic rate of mixed-muscle proteins or rate of appearance of plasma free fatty acids, glycerol, or glucose could be observed between patient groups, although the latter was significantly associated with burn size (P < 0.05). Hyperinsulinemia stimulated whole-body glucose uptake and suppressed endogenous glucose production and whole-body lipolytic rate to equivalent degrees in both groups. Muscle mRNA levels of genes spanning autophagy, lysosomal, and ubiquitin proteasome-mediated proteolysis were not enhanced in septic versus nonseptic patients. Our results demonstrate that accelerated muscle proteolysis appears to be the principal metabolic consequence of sepsis in severe burn patients and could be a contributing factor to the accelerated loss of muscle mass in these individuals. The exact mechanistic basis for these changes remains unclear.

TGF-β1-induced expression of collagen type II and ACAN is regulated by 4E-BP1, a repressor of translation

Eukaryotic initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1) binds eIF4E and represses protein translation by displacing it from the mRNA. In this study, we investigated the influence of 4E-BP1 translational apparatus on the regulation of transforming growth factor-beta 1 (TGF-β1)-induced anabolic signaling in chondrocytes. The level of 4E-BP1 expression was significantly higher in human OA cartilage than normal cartilage. TGF-β1 increased total protein synthesis, including aggrecan (ACAN) and collagen type II (Col II), together with activation of Akt/mTOR signaling pathway. mTOR silencing significantly suppressed ACAN and Col II expressions through decreasing TGF-β1-induced phosphorylation of 4E-BP1. On the contrary, 4E-BP1 knockdown promoted total protein synthesis but suppressed Col II and ACAN expressions with decreased expression of Smad2/3 and Smad4 and increased expression of inhibitory Smad6 and Smad7. TGF-β1 suppressed the interaction of 4E-BP1 and eIF4E and subsequently enhanced protein synthesis. Furthermore, 4E-BP1 regulated translation levels of inhibitory Smads, which decreased the accumulation of nuclear Smad2/3 complexes on the promoter of ACAN and Col II genes, subsequently affecting transcription of ACAN and Col II. These results demonstrated that TGF-β1-modulated phosphorylation of 4EBP1 plays a role in the expression of Col II and ACAN through differential alteration of Smad signaling pathway.

MitoTEMPOL, a mitochondrial targeted antioxidant, prevents sepsis-induced diaphragm dysfunction

Clinical studies indicate that sepsis-induced diaphragm dysfunction is a major contributor to respiratory failure in mechanically ventilated patients. Currently there is no drug to treat this form of diaphragm weakness. Sepsis-induced muscle dysfunction is thought to be triggered by excessive mitochondrial free radical generation; we therefore hypothesized that therapies that target mitochondrial free radical production may prevent sepsis-induced diaphragm weakness. The present study determined whether MitoTEMPOL, a mitochondrially targeted free radical scavenger, could reduce sepsis-induced diaphragm dysfunction. Using an animal model of sepsis, we compared four groups of mice: 1) sham-operated controls, 2) animals with sepsis induced by cecal ligation puncture (CLP), 3) sham controls given MitoTEMPOL (10 mg·kg^-1·day^-1 ip), and 4) CLP animals given MitoTEMPOL. At 48 h after surgery, we measured diaphragm force generation, mitochondrial function, proteolytic enzyme activities, and myosin heavy chain (MHC) content. We also examined the effects of delayed administration of MitoTEMPOL (by 6 h) on CLP-induced diaphragm weakness. The effects of MitoTEMPOL on cytokine-mediated alterations on muscle cell superoxide generation and cell size in vitro were also assessed. Sepsis markedly reduced diaphragm force generation. Both immediate and delayed MitoTEMPOL administration prevented sepsis-induced diaphragm weakness. MitoTEMPOL reversed sepsis-mediated reductions in mitochondrial function, activation of proteolytic pathways, and decreases in MHC content. Cytokines increased muscle cell superoxide generation and decreased cell size, effects that were ablated by MitoTEMPOL. MitoTEMPOL and other compounds that target mitochondrial free radical generation may be useful therapies for sepsis-induced diaphragm weakness.

AMPK activation suppresses mTOR/S6K1 phosphorylation and induces leucine resistance in rats with sepsis

Although it has been known that protein synthesis is suppressed in sepsis, which cannot be corrected by leucine supplement (also known as leucine resistance), the molecular signaling mechanism remains unclear. This study aimed to investigate the AMP-activated protein kinase/mammalian target of rapamycin (AMPK/mTOR) pathway in sepsis-induced leucine resistance and its upstream signals, and to seek a way to correct leucine resistance in sepsis. Sepsis was produced by cecal ligation and puncture (CLP) model in rat. Both septic rats and sham operation rat received total parenteral nutrition (TPN) with or without leucine for 24 h, and then protein synthesis and AMPK/mTOR and protein kinase B (PKB) were tested. In vitro C2C12 cells were treated with or without leucine, and we tested the AMPK/mTOR pathway and protein synthesis. We blocked AMPK by compound C and stimulated it by 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) individually. The results showed that AMPK was highly phosphorylated and suppressed mTOR/S6K1 activation in CLP rats. In vitro when AMPK was activated by AICAR, protein synthesis was suppressed and leucine resistance was observed. High phosphorylation of AMPK was accompanied by PKB inactivation in CLP rats. When PKB was blocked, both AMPK activation and leucine resistance were observed. In CLP rats, nutrition support with intensive insulin therapy reversed leucine resistance by activating PKB and suppressing AMPK phosphorylation. These findings suggest that high phosphorylation of AMPK induced by PKB inactivation in sepsis suppresses mTOR, S6K1 phosphorylation, and protein synthesis and leads to leucine resistance. Intensive insulin treatment can reverse leucine resistance by suppressing AMPK activation through activation of PKB.

Effects of aging and lifelong aerobic exercise on basal and exercise-induced inflammation

Age-associated chronic basal inflammation compromises muscle mass and adaptability, but exercise training may exert an anti-inflammatory effect. This investigation assessed basal and exercise-induced inflammation in three cohorts of men: young exercisers [YE; n = 10 men; 25 ± 1 yr; maximal oxygen consumption (V̇o2max), 53 ± 3 mL·kg-1·min-1; quadriceps area, 78 ± 3 cm2; means ± SE], old healthy nonexercisers (OH; n = 10; 75 ± 1 yr; V̇o2max, 22 ± 1 mL·kg-1·min-1; quadriceps area, 56 ± 3 cm2), and lifelong exercisers with an aerobic training history of 53 ± 1 yr (LLE; n = 21; 74 ± 1 yr; V̇o2max, 34 ± 1 mL·kg-1·min-1; quadriceps area, 67 ± 2 cm2). Resting serum IL-6, TNF-α, C-reactive protein, and IGF-1 levels were measured. Vastus lateralis muscle biopsies were obtained at rest (basal) and 4 h after an acute exercise challenge (3 × 10 repetitions, 70% 1-repetition maximum) to assess gene expression of cytokines [IL-6, TNF-α, IL-1β, IL-10, IL-4, interleukin-1 receptor antagonist (IL-1Ra), and transforming growth factor-β (TGF-β)], chemokines [IL-8 and monocyte chemoattractant protein-1 (MCP-1)], cyclooxygenase enzymes [cyclooxygenase-1 and -2 (COX-1 and COX-2, respectively), prostaglandin E2 synthases [microsomal prostaglandin E synthase 1 (mPGES-1) and cytosolic prostaglandin E2 synthase (cPGES)] and receptors [prostaglandin E2 receptor EP3 and EP4 subtypes (EP3 and EP4, respectively), and macrophage markers [cluster of differentiation 16b (CD16b) and CD163], as well as basal macrophage abundance (CD68+ cells). Aging led to higher (P ≤ 0.05) circulating IL-6 and skeletal muscle COX-1, mPGES-1, and CD163 expression. However, LLE had significantly lower serum IL-6 levels (P ≤ 0.05 vs. OH) and a predominantly anti-inflammatory muscle profile [higher IL-10 (P ≤ 0.05 vs. YE), TNF-α, TGF-β, and EP4 levels (P ≤ 0.05 vs. OH)]. In OH only, acute exercise increased expression of proinflammatory factors TNF-α, TGF-β, and IL-8 (P ≤ 0.05). LLE had postexercise gene expression similar to YE, except lower IL-10 (P ≤ 0.10), mPGES-1, and EP3 expression (P ≤ 0.05). Thus, although aging led to a proinflammatory profile within blood and muscle, lifelong exercise partially prevented this and generally preserved the acute inflammatory response to exercise seen in young exercising men. Lifelong exercise may positively impact muscle health throughout aging by promoting anti-inflammation in skeletal muscle.NEW & NOTEWORTHY This study assessed a unique population of lifelong aerobic exercising men and demonstrated that their activity status exerts an anti-inflammatory effect in skeletal muscle and circulation. Furthermore, we provide evidence that the inflammatory response to acute exercise is dysregulated by aging but preserved with lifelong exercise, which might improve skeletal muscle resilience to unaccustomed loading and adaptability into late life.

Chronic muscle weakness and mitochondrial dysfunction in the absence of sustained atrophy in a preclinical sepsis model

Chronic critical illness is a global clinical issue affecting millions of sepsis survivors annually. Survivors report chronic skeletal muscle weakness and development of new functional limitations that persist for years. To delineate mechanisms of sepsis-induced chronic weakness, we first surpassed a critical barrier by establishing a murine model of sepsis with ICU-like interventions that allows for the study of survivors. We show that sepsis survivors have profound weakness for at least 1 month, even after recovery of muscle mass. Abnormal mitochondrial ultrastructure, impaired respiration and electron transport chain activities, and persistent protein oxidative damage were evident in the muscle of survivors. Our data suggest that sustained mitochondrial dysfunction, rather than atrophy alone, underlies chronic sepsis-induced muscle weakness. This study emphasizes that conventional efforts that aim to recover muscle quantity will likely remain ineffective for regaining strength and improving quality of life after sepsis until deficiencies in muscle quality are addressed.

Inverse relationship between serum hsCRP concentration and hand grip strength in older adults: a nationwide population-based study

Despite the potential detrimental effects of systemic inflammation on muscle mass, which is mainly observed in patients with pathologic diseases, its role in muscle strength, especially in a healthy general population reflecting subclinical low-grade inflammation, is unclear. This is a nationally representative population-based, cross-sectional study from the Korea National Health and Nutrition Examination Survey, which enrolled 1,036 men aged ≥50 years and 1,080 postmenopausal women. After adjustment for confounders, serum high-sensitivity C-reactive protein (hsCRP) level was inversely associated with hand grip strength (HGS) in men. Consistently, compared with men in the lowest serum hsCRP quartile, those in the highest quartile showed a significant lower HGS, with a linear decrease of HGS across increasing serum hsCRP quartiles. Men with low muscle strength had 74.2% higher serum hsCRP than those without, and each standard deviation increment in serum hsCRP was associated with a multivariate-adjusted odds ratio of 1.35 for the risk of low muscle strength in men. However, these associations were not statistically significant in women. These findings provide clinical evidence that chronic subclinical low-grade inflammation may contribute to the deterioration of muscle strength seen with aging, especially in men.

Differential regulation of myofibrillar proteins in skeletal muscles of septic mice

Sepsis elicits skeletal muscle atrophy as a result of decreased total protein synthesis and/or increased total protein degradation. It is unknown how and whether sepsis differentially affects the expression of specific myofibrillar proteins in respiratory and limb muscles. In this study, we measured the effects of sepsis myofibrillar mRNAs and their corresponding protein levels in the diaphragm (DIA) and tibialis anterior (TA) muscles in a murine cecal ligation and perforation (CLP) model of sepsis. Male mice (C57/BL6j) underwent CLP-induced sepsis. Sham-operated mice were subjected to the same surgical procedures, except for CLP. Mice were euthanized 24, 48, or 96 h postsurgery. Transcript and protein levels of autophagy-related genes, ubiquitin E3 ligases, and several myofibrillar genes were quantified. Sepsis elicited transient fiber atrophy in the DIA and prolonged atrophy in the TA. Atrophy was coincident with increased autophagy and ubiquitin E3 ligase expression. Myosin heavy chain isoforms decreased at 24 h in the DIA and across the time-course in the TA, myosin light chain isoforms decreased across the time-course in both muscles, and troponins T and C as well as tropomyosin decreased after 24 and 48 h in both the DIA and TA. α-Actin and troponin I were unaffected by sepsis. Sepsis-induced decreases in myofibrillar protein levels coincided with decreased mRNA expressions of these proteins, suggesting that transcriptional inhibition is involved. We hypothesize that sepsis-induced muscle atrophy is mediated by decreased transcription and enhanced degradation of specific myofibrillar proteins, including myosin heavy and light chains, troponin C, troponin T, and tropomyosin.

Immune System Stimulation Reduces the Efficiency of Whole-Body Protein Deposition and Alters Muscle Fiber Characteristics in Growing Pigs

Simple Summary

Disease reduces growth and protein retention in pigs. Protein retention is the balance between two energy-consuming processes in the body of pigs: protein synthesis and breakdown. Previous reports on the effects of disease on these components of protein metabolism and their consecutive effects on protein retention are inconsistent. In addition, limited information is available about the effects of disease on the composition of muscle fibers in pigs. Thus, we evaluated these parameters, since they help us to understand protein metabolism during disease in pigs. We used twelve gilts; five were used as a control and seven were made ill. Experimental diets were designed to supply nutrients that closely met the daily requirements of each group. Protein synthesis, protein breakdown, and protein retention were measured over 72 h. Pigs were then euthanized and various muscles were sampled. Our findings suggested that disease not only reduces protein retention by decreasing protein synthesis and protein breakdown, but also by reducing the efficiency of protein deposition. In other words, ill pigs synthesize more protein per unit of protein retention, compared to healthy pigs. In addition, disease reduces muscle mass and changes the composition of the muscle fibers. The latter might negatively affect pork quality.

Abstract

The effects of immune system stimulation (ISS), induced by repeated injection of Escherichia coli lipopolysaccharide, on the whole-body protein synthesis versus degradation rates, the efficiency of protein deposition (PD), and muscle fiber characteristics in pigs were evaluated. Twelve growing gilts were assigned to two levels of amino acid intake that was predicted based on the potential of each group’s health status for PD and feed intake. Isotope tracer, nitrogen balance, and immunohistochemical staining techniques were used to determine protein turnover, PD, and muscle fiber characteristics, respectively. Protein synthesis, degradation, and PD were lower in immune-challenged pigs than in control pigs (p < 0.05). Strong tendencies for a higher protein synthesis-to-PD ratio (p = 0.055) and a lower protein synthesis-to-degradation ratio (p = 0.065) were observed in immune-challenged pigs. A decrease in muscle cross-sectional area of fibers and a shift from myosin heavy chain (MHC)-II towards MHC-I fibers (p < 0.05) were observed in immune-challenged pigs. These results indicated that ISS reduces PD not only by suppressing the whole-body protein synthesis and degradation rates, but also by decreasing the efficiency of PD in growing pigs. In addition, ISS induces atrophy in skeletal muscles and favors a slow-twitch oxidative fiber type composition.

MicroRNA-140 inhibits skeletal muscle glycolysis and atrophy in endotoxin-induced sepsis in mice via the WNT signaling pathway

Sepsis is a systemic inflammatory response syndrome resulting from infection. This study aimed at exploring the role of microRNA-140 (miR-140) in septic mice. Wnt family member 11 (WNT11) was verified to be a target gene of miR-140 after bioinformatic prediction and dual luciferase reporter gene assay. Importantly, miR-140 negatively regulated WNT11. We initially induced the model of sepsis by endotoxin, and then ectopic expression and knockdown experiments were performed to explore the functional role of miR-140 in sepsis. Additionally, cross-sectional areas of muscle fiber, lactic acid production, 3-methylhistidine (3-MH) and tyrosine (Tyr) production in extensor digitorium longus (EDL) muscles, and serum levels of inflammatory factors were examined. The effect of miR-140 on the expression of WNT signaling pathway-related and apoptosis-related factors in skeletal muscle tissue was determined. The experimental results indicated that upregulated miR-140 or silenced WNT11 increased cross-sectional areas of muscle fiber while decreasing lactic acid production, skeletal muscle cell apoptosis [corresponding to downregulated B cell lymphoma 2 (Bcl-2)-associated X protein (Bax) and caspase-3 and upregulated Bcl-2], and the proteolytic rate of Tyr and 3-MH. Also, overexpressed miR-140 or silenced WNT11 reduced inflammation as reflected by decreased serum levels of IL-6, IL-10, and TNF-α. Furthermore, overexpression of miR-140 was shown to suppress the activation of the WNT signaling pathway, accompanied by decreased expression of WNT11, β-catenin, and GSK-3β. Taken together, upregulation of miR-140 could potentially inhibit skeletal muscle lactate release, an indirect measure of glycolysis, and atrophy in septic mice through suppressing the WNT signaling pathway via inhibiting WNT11 expression.

Sepsis-Induced Channelopathy in Skeletal Muscles is Associated with Expression of Non-Selective Channels

Skeletal muscles (∼50% of the body weight) are affected during acute and late sepsis and represent one sepsis associate organ dysfunction. Cell membrane changes have been proposed to result from a channelopathy of yet unknown cause associated with mitochondrial dysfunction and muscle atrophy. We hypothesize that the channelopathy might be explained at least in part by the expression of non-selective channels. Here, this possibility was studied in a characterized mice model of late sepsis with evident skeletal muscle atrophy induced by cecal ligation and puncture (CLP). At day seven after CLP, skeletal myofibers were found to present de novo expression (immunofluorescence) of connexins 39, 43, and 45 and P2X7 receptor whereas pannexin1 did not show significant changes. These changes were associated with increased sarcolemma permeability (∼4 fold higher dye uptake assay), ∼25% elevated in intracellular free-Ca concentration (FURA-2), activation of protein degradation via ubiquitin proteasome pathway (Murf and Atrogin 1 reactivity), moderate reduction in oxygen consumption not explained by changes in levels of relevant respiratory proteins, ∼3 fold decreased mitochondrial membrane potential (MitoTracker Red CMXRos) and ∼4 fold increased mitochondrial superoxide production (MitoSox). Since connexin hemichannels and P2X7 receptors are permeable to ions and small molecules, it is likely that they are main protagonists in the channelopathy by reducing the electrochemical gradient across the cell membrane resulting in detrimental metabolic changes and muscular atrophy.

Molecular Mechanisms Responsible for the Rescue Effects of Pamidronate on Muscle Atrophy in Pediatric Burn Patients

Not only has pamidronate been shown to prevent inflammation associated bone resorption following burn injury, it also reduces protein breakdown in muscle. The aim of this study was to identify the molecular mechanisms responsible for muscle mass rescue in pamidronate treated compared to placebo/standard of care-treated burn patients. Mature myotubes, generated by differentiating murine C2C12 myoblasts, were exposed for 48 h to 1 or 5% serum obtained from 3 groups of children: normal unburned, burned receiving standard of care, and burned receiving standard of care with pamidronate. Exposure to serum from burned patients caused dose-dependent myotube atrophy compared to normal serum as expected based on previous observations of muscle atrophy induced by burn injury in humans and animals. The size of C2C12 myotubes was partially protected upon exposure to the serum from patients treated with pamidronate correlating with the rescue of muscle size previously observed in these patients. At the molecular signaling level, serum from both pamidronate and non-pamidronate-treated burn patients increased pSTAT3/STAT3 and pERK1/2/ERK1/2 compared to normal serum with no significant differences between the two groups of burn patients indicating elevated production of inflammatory cytokines. However, serum from pamidronate-treated patients restored the phosphorylation of AKT and mTOR and reduced protein ubiquitination when compared to burn serum alone, suggesting a prevention of muscle catabolism and a restoration of muscle anabolism. Myotube atrophy induced by burn serum was partially rescued after exposure to a pan anti-TGFβ-1/2/3 antibody, suggesting that this signaling pathway is partially responsible for the atrophy and that bisphosphonate protection of bones from resorption during burn injury prevents the release of muscle pro-catabolic factors such as TGFβ into the circulation.

Elevated serum Activin A in chronic obstructive pulmonary disease with skeletal muscle wasting

OBJECTIVE

Muscle wasting contributes to the reduced quality of life and increased mortality in chronic obstructive pulmonary disease (COPD). Muscle atrophy in mice with cachexia was caused by Activin A binding to ActRIIB. The role of circulating Activin A leading to muscle atrophy in COPD remains elusive.

METHODS

In the present study, we evaluated the relationship between serum levels of Activin A and skeletal muscle wasting in COPD patients. The expression levels of serum Activin A were measured in 78 stable COPD patients and in 60 healthy controls via ELISA, which was also used to determine the expression of circulating TNF-α levels. Total skeletal muscle mass (SMM) was calculated according to a validated formula by age and anthropometric measurements. The fat-free mass index (FFMI) was determined as the fat-free mass (FFM) corrected for body surface area.

RESULTS

Compared to the healthy controls, COPD patients had upregulated Activin A expression. The elevated levels of Activin A were correlated with TNF-α expression, while total SMM and FFMI were significantly decreased in COPD patients. Furthermore, serum Activin A expression in COPD patients was negatively associated with both FFMI and BMI.

CONCLUSION

The above results showed an association between increased circulating Activin A in COPD patients and the presence of muscle atrophy. Given our previous knowledge, we speculate that Activin A contributes to skeletal muscle wasting in COPD.

Formoterol treatment prevents the effects of endotoxin on muscle TNF/NF-kB, Akt/mTOR, and proteolytic pathways in a rat model. Role of IGF-I and miRNA 29b

Inflammatory diseases are associated with muscle wasting as a result of an increase in proteolysis. The purpose of this study was to elucidate whether administration of a β2 adrenergic agonist, formoterol, was able to prevent the acute effects of sepsis induced by liposaccharide (LPS) injection on rat gastrocnemius muscle and to evaluate the possible roles of corticosterone, IGF-I, miR-23a, and miR-29b. For this purpose, male Wistar rats were injected with LPS and/or formoterol. Formoterol treatment decreased LPS-induced increase in serum corticosterone, TNFα upregulation, and NF-κB(p65) and Forkhead box protein O1 activation in the gastrocnemius. Atrogin-1, muscle RING-finger protein-1, microtubule-associated protein-1 light chain 3b (LC3b), and the lipidation of LC3b-I to LC3b-II were increased by LPS, and formoterol blocked these effects. Serum IGF-I and its mRNA levels in the gastrocnemius were decreased, whereas mecano growth factor and IGF binding protein 3 mRNA levels were increased in the rats injected with LPS but not in the rats that received LPS and formoterol. Similarly, LPS decreased Akt and mammalian target of rapamycin phosphorylation, and formoterol blocked these decreases. Finally, miR-29b expression in the gastrocnemius was upregulated by endotoxin injection, whereas miR-23a was not significantly different. Formoterol treatment did not significantly modify LPS-induced increase in muscle miR-29b. Furthermore, in control rats formoterol increased the expression of this miRNA. We conclude that formoterol decreases endotoxin-induced inflammation and proteolysis in rat skeletal muscle. Those responses can be a direct effect of β2 adrenergic receptor stimulation or/and of blocking the effects of LPS on corticosterone and IGF-I. Muscle miR-23a and -29b do not seem to play an important role in those responses.

Muscle Atrophy Due to Nerve Damage Is Accompanied by Elevated Myofibrillar Protein Synthesis Rates

Muscle loss is a severe complication of many medical conditions such as cancer, cardiac failure, muscular dystrophies, and nerve damage. The contribution of myofibrillar protein synthesis (MPS) to the loss of muscle mass after nerve damage is not clear. Using deuterium oxide (D₂O) labeling, we demonstrate that MPS is significantly increased in rat m.tibialis anterior (TA) compared to control (3.23 ± 0.72 [damaged] to 2.09 ± 0.26%^∗day⁻¹ [control]) after 4 weeks of nerve constriction injury. This is the case despite substantial loss of mass of the TA (350 ± 96 mg [damaged] to 946 ± 361 mg [control]). We also show that expression of regulatory proteins involved with MPS (p70s6k1: 2.4 ± 0.3 AU [damaged] to 1.8 ± 0.2 AU [control]) and muscle protein breakdown (MPB) (MAFbx: 5.3 ± 1.2 AU [damaged] to 1.4 ± 0.4 AU [control]) are increased in nerve damaged muscle. Furthermore, the expression of p70s6k1 correlates with MPS rates (r² = 0.57). In conclusion, this study shows that severe muscle wasting following nerve damage is accompanied by increased as opposed to decreased MPS.

Repurposing Thioridazine (TDZ) as an anti-inflammatory agent

Nuclear factor-kB (NF-kB) is a crucial transcription factor in the signal transduction cascade of the inflammatory signaling. Activation of NF-κB depends on the phosphorylation of IκBα by IκB kinase (IKKβ) followed by subsequent ubiquitination and degradation. This leads to the nuclear translocation of the p50- p65 subunits of NF-κB, and further triggers pro-inflammatory cytokine gene expression. Thus, in the need of a more effective therapy for the treatment of inflammatory diseases, specific inhibition of IKKβ represents a rational alternative strategy to the current therapies. A computer-aided drug identification protocol was followed to identify novel IKKβ inhibitors from a database of over 1500 Food and Drug Administration (FDA) drugs. The best scoring compounds were compared with the already known high-potency IKKβ inhibitors for their ability to bind and inhibit IKKβ by evaluating their docking energy. Finally, Thioridazinehydrochloride (TDZ), a potent antipsychotic drug against Schizophrenia was selected and its efficiency in inhibiting IκBα protein degradation and NF-κB activation was experimentally validated. Our study has demonstrated that TDZ blocks IκBα protein degradation and subsequent NF-κB activation to inhibit inflammation. Thus, it is a potential repurposed drug against inflammation.

Pulmonary inflammation-induced loss and subsequent recovery of skeletal muscle mass require functional poly-ubiquitin conjugation

BACKGROUND

Pulmonary inflammation in response to respiratory infections can evoke muscle wasting. Increased activity of the ubiquitin (Ub)-proteasome system (UPS) and the autophagy lysosome pathway (ALP) have been implicated in inflammation-induced muscle atrophy. Since poly-Ub conjugation is required for UPS-mediated proteolysis and has been implicated in the ALP, we assessed the effect of impaired ubiquitin conjugation on muscle atrophy and recovery following pulmonary inflammation, and compared activation and suppression of these proteolytic systems to protein synthesis regulation.

METHODS

Pulmonary inflammation was induced in mice by an intratracheal instillation of LPS. Proteolysis (UPS and ALP) and synthesis signaling were examined in gastrocnemius muscle homogenates. Ub-conjugation-dependency of muscle atrophy and recovery was addressed using Ub-K48R (K48R) mice with attenuated poly-ubiquitin conjugation, and compared to UBWT control mice.

RESULTS

Pulmonary inflammation caused a decrease in skeletal muscle mass which was accompanied by a rapid increase in expression of UPS and ALP constituents and reduction in protein synthesis signaling acutely after LPS. Muscle atrophy was attenuated in K48R mice, while ALP and protein synthesis signaling were not affected. Muscle mass recovery starting 72 h post LPS, correlated with reduced expression of UPS and ALP constituents and restoration of protein synthesis signaling. K48R mice however displayed impaired recovery of muscle mass.

CONCLUSION

Pulmonary inflammation-induced muscle atrophy is in part attributable to UPS-mediated proteolysis, as activation of ALP- and suppression of protein synthesis signaling occur independently of poly-Ub conjugation during muscle atrophy. Recovery of muscle mass following pulmonary inflammation involves inverse regulation of proteolysis and protein synthesis signaling, and requires a functional poly-Ub conjugation.

miR-424-5p reduces ribosomal RNA and protein synthesis in muscle wasting

BACKGROUND

A loss of muscle mass occurs as a consequence of a range of chronic and acute diseases as well as in older age. This wasting results from an imbalance of protein synthesis and degradation with a reduction in synthesis and resistance to anabolic stimulation often reported features. Ribosomes are required for protein synthesis, so changes in the control of ribosome synthesis are potential contributors to muscle wasting. MicroRNAs (miRNAs) are known regulators of muscle phenotype and have been shown to modulate components of the protein synthetic pathway. One miRNA that is predicted to target a number of components of protein synthetic pathway is miR-424-5p, which is elevated in the quadriceps of patients with chronic obstructive pulmonary disease (COPD).

METHODS

Targets of miR-424-5p were identified by Argonaute2 pull down, and the effects of the miRNA on RNA and protein expression were determined by quantitative polymerase chain reaction and western blotting in muscle cells in vitro. Protein synthesis was determined by puromycin incorporation in vitro. The miRNA was over-expressed in the tibialis anterior muscle of mice by electroporation and the effects quantified. Finally, quadriceps expression of the miRNA was determined by quantitative polymerase chain reaction in patients with COPD and intensive care unit (ICU)-acquired weakness and in patients undergoing aortic surgery as well as in individuals from the Hertfordshire Sarcopenia Study.

RESULTS

Pull-down assays showed that miR-424-5p bound to messenger RNAs encoding proteins associated with muscle protein synthesis. The most highly enriched messenger RNAs encoded proteins required for the Pol I RNA pre-initiation complex required for ribosomal RNA (rRNA) transcription, (PolR1A and upstream binding transcription factor). In vitro, miR-424-5p reduced the expression of these RNAs, reduced rRNA levels, and inhibited protein synthesis. In mice, over-expression of miR-322 (rodent miR-424 orthologue) caused fibre atrophy and reduced upstream binding transcription factor expression and rRNA levels. In humans, elevated miR-424-5p associated with markers of disease severity in COPD (FEV₁ %), in patients undergoing aortic surgery (LVEF%), and in patients with ICU-acquired weakness (days in ICU). In patients undergoing aortic surgery, preoperative miR-424-5p expression in skeletal muscle was associated with muscle loss over the following 7 days.

CONCLUSIONS

These data suggest that miR-424-5p regulates rRNA synthesis by inhibiting Pol I pre-initiation complex formation. Increased miR-424-5p expression in patients with conditions associated with muscle wasting is likely to contribute to the inhibition of protein synthesis and loss of muscle mass.

Restorative Mechanisms Regulating Protein Balance in Skeletal Muscle During Recovery From Sepsis

Muscle deconditioning is commonly observed in patients surviving sepsis. Little is known regarding the molecular mechanisms regulating muscle protein homeostasis during the recovery or convalescence phase. We adapted a sepsis-recovery mouse model that uses cecal ligation and puncture (CLP), followed 24 h later by cecal resection and antibiotic treatment, to identify putative cellular pathways regulating protein synthesis and breakdown in skeletal muscle. Ten days after CLP, body weight and food consumption did not differ between control and sepsis-recovery mice, but gastrocnemius weight was reduced. During sepsis-recovery, muscle protein synthesis was increased 2-fold and associated with enhanced mTOR kinase activity (4E-BP1 and S6K1 phosphorylation). The sepsis-induced increase in 4E-BP1 was associated with enhanced formation of the eIF4E-eIF4G active cap-dependent complex, while the increased S6K1 was associated with increased phosphorylation of downstream targets S6 and eIF4B. Proximal to mTOR, sepsis-recovery increased Akt and TSC2 phosphorylation, did not alter AMPK phosphorylation, and decreased REDD1 protein content. Despite the decreased mRNA content for the E3 ubiquitin ligases atrogin-1 and muscle RING-finger 1, proteasomal activity was increased 50%. In contrast, sepsis-recovery was associated with an apparent decrease in autophagy (e.g., increased ULK-1 phosphorylation, decreased LCB3-II, and increased p62). The mRNA content for IL-1β, IL-18, TNFα, and IL-6 in muscle was elevated in sepsis-recovery. During recovery after sepsis skeletal muscle responds with an increase in Akt-TSC2-mTOR-dependent protein synthesis and decreased autophagy, but full restoration of muscle protein content may be slowed by the continued stimulation of ubiquitin-proteasome activity.