Cachectic Skeletal Muscle Research Articles

Integrative study of skeletal muscle mitochondrial dysfunction in a murine pancreatic cancer-induced cachexia model

Pancreatic ductal adenocarcinoma (PDAC), the most common pancreatic cancer, is a deadly cancer, often diagnosed late and resistant to current therapies. PDAC patients are frequently affected by cachexia characterized by muscle mass and strength loss (sarcopenia) contributing to patient frailty and poor therapeutic response. This study assesses the mechanisms underlying mitochondrial remodeling in the cachectic skeletal muscle, through an integrative exploration combining functional, morphological, and omics-based evaluation of gastrocnemius muscle from KIC genetically engineered mice developing autochthonous pancreatic tumor and cachexia. Cachectic PDAC KIC mice exhibit severe sarcopenia with loss of muscle mass and strength associated with reduced muscle fiber’s size and induction of protein degradation processes. Mitochondria in PDAC atrophied muscles show reduced respiratory capacities and structural alterations, associated with deregulation of oxidative phosphorylation and mitochondrial dynamics pathways. Beyond the metabolic pathways known to be altered in sarcopenic muscle (carbohydrates, proteins, and redox), lipid and nucleic acid metabolisms are also affected. Although the number of mitochondria per cell is not altered, mitochondrial mass shows a twofold decrease and the mitochondrial DNA threefold, suggesting a defect in mitochondrial genome homeostasis. In conclusion, this work provides a framework to guide toward the most relevant targets in the clinic to limit PDAC-induced cachexia.

Integrative study of skeletal muscle mitochondrial dysfunction in a murine pancreatic cancer-induced cachexia model.

Pancreatic ductal adenocarcinoma (PDAC), the most common pancreatic cancer, is a deadly cancer, often diagnosed late and resistant to current therapies. PDAC patients are frequently affected by cachexia characterized by muscle mass and strength loss (sarcopenia) contributing to patient frailty and poor therapeutic response. This study assesses the mechanisms underlying mitochondrial remodeling in the cachectic skeletal muscle, through an integrative exploration combining functional, morphological, and omics-based evaluation of gastrocnemius muscle from KIC genetically engineered mice developing autochthonous pancreatic tumor and cachexia. Cachectic PDAC KIC mice exhibit severe sarcopenia with loss of muscle mass and strength associated with reduced muscle fiber's size and induction of protein degradation processes. Mitochondria in PDAC atrophied muscles show reduced respiratory capacities and structural alterations, associated with deregulation of oxidative phosphorylation and mitochondrial dynamics pathways. Beyond the metabolic pathways known to be altered in sarcopenic muscle (carbohydrates, proteins, and redox), lipid and nucleic acid metabolisms are also affected. Although the number of mitochondria per cell is not altered, mitochondrial mass shows a twofold decrease and the mitochondrial DNA threefold, suggesting a defect in mitochondrial genome homeostasis. In conclusion, this work provides a framework to guide toward the most relevant targets in the clinic to limit PDAC-induced cachexia.

Molecular mechanisms of cancer cachexia-related loss of skeletal muscle mass: data analysis from preclinical and clinical studies.

Cancer cachexia is a systemic hypoanabolic and catabolic syndrome that diminishes the quality of life of cancer patients, decreases the efficiency of therapeutic strategies and ultimately contributes to decrease their lifespan. The depletion of skeletal muscle compartment, which represents the primary site of protein loss during cancer cachexia, is of very poor prognostic in cancer patients. In this review, we provide an extensive and comparative analysis of the molecular mechanisms involved in the regulation of skeletal muscle mass in human cachectic cancer patients and in animal models of cancer cachexia. We summarize data from preclinical and clinical studies investigating how the protein turnover is regulated in cachectic skeletal muscle and question to what extent the transcriptional and translational capacities, as well as the proteolytic capacity (ubiquitin-proteasome system, autophagy-lysosome system and calpains) of skeletal muscle are involved in the cachectic syndrome in human and animals. We also wonder how regulatory mechanisms such as insulin/IGF1-AKT-mTOR pathway, endoplasmic reticulum stress and unfolded protein response, oxidative stress, inflammation (cytokines and downstream IL1ß/TNFα-NF-κB and IL6-JAK-STAT3 pathways), TGF-ß signalling pathways (myostatin/activin A-SMAD2/3 and BMP-SMAD1/5/8 pathways), as well as glucocorticoid signalling, modulate skeletal muscle proteostasis in cachectic cancer patients and animals. Finally, a brief description of the effects of various therapeutic strategies in preclinical models is also provided. Differences in the molecular and biochemical responses of skeletal muscle to cancer cachexia between human and animals (protein turnover rates, regulation of ubiquitin-proteasome system and myostatin/activin A-SMAD2/3 signalling pathways) are highlighted and discussed. Identifying the various and intertwined mechanisms that are deregulated during cancer cachexia and understanding why they are decontrolled will provide therapeutic targets for the treatment of skeletal muscle wasting in cancer patients.

Creatine modulates cellular energy metabolism and protects against cancer cachexia-associated muscle wasting.

Cancer cachexia is a multifactorial syndrome defined by progressive loss of body weight with specific depletion of skeletal muscle and adipose tissue. Since there are no FDA-approved drugs that are available, nutritional intervention is recommended as a supporting therapy. Creatine supplementation has an ergogenic effect in various types of sports training, but the regulatory effects of creatine supplementation in cancer cachexia remain unknown. In this study, we investigated the impact of creatine supplementation on cachectic weight loss and muscle loss protection in a tumor-bearing cachectic mouse model, and the underlying molecular mechanism of body weight protection was further assessed. We observed decreased serum creatine levels in patients with cancer cachexia, and the creatine content in skeletal muscle was also significantly decreased in cachectic skeletal muscle in the C26 tumor-bearing mouse model. Creatine supplementation protected against cancer cachexia-associated body weight loss and muscle wasting and induced greater improvements in grip strength. Mechanistically, creatine treatment altered the dysfunction and morphological abnormalities of mitochondria, thus protecting against cachectic muscle wasting by inhibiting the abnormal overactivation of the ubiquitin proteasome system (UPS) and autophagic lysosomal system (ALS). In addition, electron microscopy revealed that creatine supplementation alleviated the observed increase in the percentage of damaged mitochondria in C26 mice, indicating that nutritional intervention with creatine supplementation effectively counteracts mitochondrial dysfunction to mitigate muscle loss in cancer cachexia. These results uncover a previously uncharacterized role for creatine in cachectic muscle wasting by modulating cellular energy metabolism to reduce the level of muscle cell atrophy.

PGC1α overexpression preserves muscle mass and function in cisplatin-induced cachexia.

BackgroundChemotherapy induces a cachectic‐like phenotype, accompanied by skeletal muscle wasting, weakness and mitochondrial dysfunction. Peroxisome proliferator‐activated receptor‐gamma coactivator‐1 alpha (PGC1α), a regulator of mitochondrial biogenesis, is often reduced in cachectic skeletal muscle. Overexpression of PGC1α has yielded mixed beneficial results in cancer cachexia, yet investigations using such approach in a chemotherapy setting are limited. Utilizing transgenic mice, we assessed whether overexpression of PGC1α could combat the skeletal muscle consequences of cisplatin.MethodsYoung (2 month) and old (18 month) wild‐type (WT) and PGC1α transgenic male and female mice (Tg) were injected with cisplatin (C; 2.5 mg/kg) for 2 weeks, while control animals received saline (n = 5–9/group). Animals were assessed for muscle mass and force, motor unit connectivity, and expression of mitochondrial proteins.ResultsYoung WT + C mice displayed reduced gastrocnemius mass (male: −16%, P < 0.0001; female: −11%, P < 0.001), muscle force (−6%, P < 0.05, both sexes), and motor unit number estimation (MUNE; male: −53%, P < 0.01; female: −51%, P < 0.01). Old WT + C male and female mice exhibited gastrocnemius wasting (male: −22%, P < 0.05; female: −27%, P < 0.05), muscle weakness (male: −20%, P < 0.0001; female: −17%, P < 0.01), and loss of MUNE (male: −82%, P < 0.01; female: −62%, P < 0.05), suggesting exacerbated cachexia compared with younger animals. Overexpression of PGC1α had mild protective effects on muscle mass in young Tg + C male only (gastrocnemius: +10%, P < 0.05); however, force and MUNE were unchanged in both young Tg + C male and female, suggesting preservation of neuromuscular function. In older male, protective effects associated with PGC1α overexpression were heighted with Tg + C demonstrating preserved muscle mass (gastrocnemius: +34%, P < 0.001), muscle force (+13%, P < 0.01), and MUNE (+3‐fold, P < 0.05). Similarly, old female Tg + C did not exhibit muscle wasting or reductions in MUNE, and had preserved muscle force (+11%, P < 0.05) compared with female WT + C. Follow‐up molecular analysis demonstrated that aged WT animals were more susceptible to cisplatin‐induced loss of mitochondrial proteins, including PGC1α, OPA1, cytochrome‐C, and Cox IV.ConclusionsIn our study, the negative effects of cisplatin were heighted in aged animals, whereas overexpression of PGC1α was sufficient to combat the neuromuscular dysfunction caused by cisplatin, especially in older animals. Hence, our observations indicate that aged animals may be more susceptible to develop chemotherapy side toxicities and that mitochondria‐targeted strategies may serve as a tool to prevent chemotherapy‐induced muscle wasting and weakness.

Exercise Protects Against Cancer-Induced Gastrocnemius Metabolic Alterations

Cancer cachexia is a complex metabolic wasting disease. Currently, there are no clear diagnostic criteria, its effects are irreversible, and it cannot be treated. However, exercise has been shown to be beneficial for wasting disorders. PURPOSE: To determine how cancer cachexia alters muscle metabolism and whether aerobic exercise can protect against cancer-cachexia mediated alterations. METHODS: Male ApcMin mice (Apc) and litter-matched non-carrier mice (WT) underwent a 10-week voluntary wheel run (Ex) exercise regimen or remained sedentary (SED). At 15 weeks, gastrocnemius tissues were analyzed for metabolite signatures via non-targeted GC/MS metabolomics. RESULTS: Analysis identified 135 metabolites in the gastrocnemius of cachectic (SED + Apc) mice with 3 metabolites significantly (P < 0.05) increased compared to SED + WT mice: hydroxyproline, ornithine, and lysine. One metabolite was significantly (P < .01) decreased in SED + Apc compared to SED + WT mice: 1-5-1-5-anhydroglucitol. Variable Importance in Projection (VIP) analysis and pathway analysis revealed that the urea cycle, Warburg metabolism, inositol phosphate metabolism, and arginine and proline biosynthesis were affected by cancer cachexia. Following exercise, Ex+Apc gastrocnemius ornithine and hydroxyproline were significantly decreased (P < 0.01) compared to SED + Apc. Conversely, Ex+Apc gastrocnemius 1-5-anhydroglucitol was significantly (P < 0.01) increased compared to SED + Apc. CONCLUSION: These data indicate that cancer cachexia significantly disrupts arginine and proline metabolism, inositol phosphate metabolism, and the urea cycle in cachectic skeletal muscle. Interestingly, aerobic exercise appears to abolish many metabolic perturbations imposed by cancer cachexia. Hydroxyproline (elevated in SED + Apc) has been shown to be increased during times of metabolic stress, however exercise reversed this signal. 1-5-anhydroglucitol (decreased in SED + Apc) is a marker of glycemic control and was restored to basal levels with exercise. Such data may provide a valuable steppingstone in understanding the metabolic consequence of cancer cachexia as well as the identification of metabolic biomarkers. Furthermore, these data shed important light on the mechanisms of the benefits of exercise in cancer survivors.

Phenotypic features of cancer cachexia-related loss of skeletal muscle mass and function: lessons from human and animal studies.

Cancer cachexia is a complex multi‐organ catabolic syndrome that reduces mobility, increases fatigue, decreases the efficiency of therapeutic strategies, diminishes the quality of life, and increases the mortality of cancer patients. This review provides an exhaustive and comprehensive analysis of cancer cachexia‐related phenotypic changes in skeletal muscle at both the cellular and subcellular levels in human cancer patients, as well as in animal models of cancer cachexia. Cancer cachexia is characterized by a major decrease in skeletal muscle mass in human and animals that depends on the severity of the disease/model and the localization of the tumour. It affects both type 1 and type 2 muscle fibres, even if some animal studies suggest that type 2 muscle fibres would be more prone to atrophy. Animal studies indicate an impairment in mitochondrial oxidative metabolism resulting from a decrease in mitochondrial content, an alteration in mitochondria morphology, and a reduction in mitochondrial metabolic fluxes. Immuno‐histological analyses in human and animal models also suggest that a faulty mechanism of skeletal muscle repair would contribute to muscle mass loss. An increase in collagen deposit, an accumulation of fat depot outside and inside the muscle fibre, and a disrupted contractile machinery structure are also phenotypic features that have been consistently reported in cachectic skeletal muscle. Muscle function is also profoundly altered during cancer cachexia with a strong reduction in skeletal muscle force. Even though the loss of skeletal muscle mass largely contributes to the loss of muscle function, other factors such as muscle–nerve interaction and calcium handling are probably involved in the decrease in muscle force. Longitudinal analyses of skeletal muscle mass by imaging technics and skeletal muscle force in cancer patients, but also in animal models of cancer cachexia, are necessary to determine the respective kinetics and functional involvements of these factors. Our analysis also emphasizes that measuring skeletal muscle force through standardized tests could provide a simple and robust mean to early diagnose cachexia in cancer patients. That would be of great benefit to cancer patient's quality of life and health care systems.

Withaferin A attenuates ovarian cancer-induced cardiac cachexia.

Cachexia is a common multifactorial syndrome in the advanced stages of cancer and accounts for approximately 20–30% of all cancer-related fatalities. In addition to the progressive loss of skeletal muscle mass, cancer results in impairments in cardiac function. We recently demonstrated that WFA attenuates the cachectic skeletal muscle phenotype induced by ovarian cancer. The purpose of this study was to investigate whether ovarian cancer induces cardiac cachexia, the possible pathway involved, and whether WFA attenuates cardiac cachexia. Xenografting of ovarian cancer induced cardiac cachexia, leading to the loss of normal heart functions. Treatment with WFA rescued the heart weight. Further, ovarian cancer induced systolic dysfunction and diastolic dysfunction Treatment with WFA preserved systolic function in tumor-bearing mice, but diastolic dysfunction was partially improved. In addition, WFA abrogated the ovarian cancer-induced reduction in cardiomyocyte cross-sectional area. Finally, treatment with WFA ameliorated fibrotic deposition in the hearts of tumor-bearing animals. We observed a tumor-induced MHC isoform switching from the adult MHCα to the embryonic MHCβ isoform, which was prevented by WFA treatment. Circulating Ang II level was increased significantly in the tumor-bearing, which was lowered by WFA treatment. Our results clearly demonstrated the induction of cardiac cachexia in response to ovarian tumors in female NSG mice. Further, we observed induction of proinflammatory markers through the AT1R pathway, which was ameliorated by WFA, in addition to amelioration of the cachectic phenotype, suggesting WFA as a potential therapeutic agent for cardiac cachexia in oncological paradigms.

The ERG1 Potassium Channel is Abundant in Cachectic Human Skeletal Muscle

IntroductionA heteromultimer of the ERG1a/1b potassium channel is known to contribute to repolarization of the cardiac action potential. A homomultimer of the ERG1a subunit has been detected in the atrophying skeletal muscle of mice experiencing muscle disuse and cancer cachexia and has been shown to contribute to muscle atrophy by enhancing ubiquitin proteolysis; however, to our knowledge, ERG1 has not been reported in human skeletal muscle.Methods and ResultsHere, using immunohistochemistry we detect ERG1 immunofluorescence at low levels in Rectus abdominis muscle of young adult humans and show that it trends toward greater levels (10.6%) in the same muscle of healthy aged adults. Further, we detect ERG1 immunofluorescence at a statistically greater level (53.6%; p&lt;0.05) in the Rectus abdominis muscle of older people having cancer cachexia than in age‐matched adults. Additionally, we observe ERG1 immunofluorescence in skeletal muscle sarcolemma and detect that its fluorescent pattern is consistent with I‐band localization.DiscussionThe data suggest that ERG1 may be related to muscle loss in humans and may be located in t‐tubules where it could influence calcium handling.Support or Funding InformationThis work was supported in part by Southern Illinois University School of Medicine (Research Seed Grant to ALP). The work was also supported in part by the Italian Society for Cancer Research (AIRC grant number 17388 to M Sandri) and by Austrian national co‐financing of the Austrian Federal Ministry of Science and Research; Ludwig Boltzmann Society (Vienna, Austria) to H Kern. PK would like to acknowledge National Science Foundation (CHE 0748676), NIH (GM 106364) for partial financial support of this research. The authors wish to thank Dr. Don Caspary who graciously provided FBN rat muscles. Human Pectoralis minor muscle samples were provided by the SIU School of Medicine Tissue Bank, a Simmons Cancer Institute funded program. Other investigators may have received samples from these same tissue specimens. UC thanks the IRCCS Fondazione Ospedale San Camillo, Venezia, Italy and the A&amp;C M‐C Foundation for Translational Research for scientific support.

Wnt7a Counteracts Cancer Cachexia

Cancer cachexia is a complex metabolic disease so far lacking effective therapy, and it accounts for approximately one third of all cancer-related deaths worldwide. The extracellular ligand Wnt7a has a dual function in skeletal muscle, inducing the anabolic AKT/mammalian target of rapamycin (mTOR) pathway in myofibers and driving muscle stem cell expansion in skeletal muscle, making it a promising candidate for treatment of muscle wasting diseases. In murine and human myotubes, Wnt7a activates the anabolic AKT/mTOR pathway, thereby preventing cachexia-induced atrophy with a single application being sufficient to prevent atrophy independently of the tumor cell type causing cachexia. Addition of Wnt7a also improved activation and differentiation of muscle stem cells in cancer cachexia, a condition under which skeletal muscle regeneration is severely impaired due to stalled muscle stem cell differentiation. Finally, we show that Wnt7a prevents cancer cachexia in an in vivo mouse model based on C26 colon carcinoma cells. Wnt7a has a dual role in cachectic skeletal muscle; that is, it effectively counteracts muscle wasting through activation of the anabolic AKT/mTOR pathway and, furthermore, reverts the loss of muscle stem cell functionality due to cancer cachexia, making Wnt7a a promising candidate for an ameliorative treatment of cancer cachexia.

Derangements of amino acids in cachectic skeletal muscle are caused by mitochondrial dysfunction.

BackgroundCachexia is the direct cause of at least 20% of cancer‐associated deaths. Muscle wasting in skeletal muscle results in weakness, immobility, and death secondary to impaired respiratory muscle function. Muscle proteins are massively degraded in cachexia; nevertheless, the molecular mechanisms related to this process are poorly understood. Previous studies have reported conflicting results regarding the amino acid abundances in cachectic skeletal muscle tissues. There is a clear need to identify the molecular processes of muscle metabolism in the context of cachexia, especially how different types of molecules are involved in the muscle wasting process.MethodsNew in situ ‐omics techniques were used to produce a more comprehensive picture of amino acid metabolism in cachectic muscles by determining the quantities of amino acids, proteins, and cellular metabolites. Using matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry imaging, we determined the in situ concentrations of amino acids and proteins, as well as energy and other cellular metabolites, in skeletal muscle tissues from genetic mouse cancer models (n = 21) and from patients with cancer (n = 6). Combined results from three individual MALDI mass spectrometry imaging methods were obtained and interpreted. Immunohistochemistry staining for mitochondrial proteins and myosin heavy chain expression, digital image analysis, and transmission electron microscopy complemented the MALDI mass spectrometry imaging results.ResultsMetabolic derangements in cachectic mouse muscle tissues were detected, with significantly increased quantities of lysine, arginine, proline, and tyrosine (P = 0.0037, P = 0.0048, P = 0.0430, and P = 0.0357, respectively) and significantly reduced quantities of glutamate and aspartate (P = 0.0008 and P = 0.0124). Human skeletal muscle tissues revealed similar tendencies. A majority of altered amino acids were released by the breakdown of proteins involved in oxidative phosphorylation. Decreased energy charge was observed in cachectic muscle tissues (P = 0.0101), which was related to the breakdown of specific proteins. Additionally, expression of the cationic amino acid transporter CAT1 was significantly decreased in the mitochondria of cachectic mouse muscles (P = 0.0133); this decrease may play an important role in the alterations of cationic amino acid metabolism and decreased quantity of glutamate observed in cachexia.ConclusionsOur results suggest that mitochondrial dysfunction has a substantial influence on amino acid metabolism in cachectic skeletal muscles, which appears to be triggered by diminished CAT1 expression, as well as the degradation of mitochondrial proteins. These findings provide new insights into the pathobiochemistry of muscle wasting.

Inflammatory signalling regulates eccentric contraction-induced protein synthesis in cachectic skeletal muscle.

BackgroundSkeletal muscle responds to eccentric contractions (ECC) with an anabolic response that involves the induction of protein synthesis through the mechanistic target of rapamycin complex 1. While we have reported that repeated ECC bouts after cachexia initiation attenuated muscle mass loss and inflammatory signalling, cachectic muscle's capacity to induce protein synthesis in response to ECC has not been determined. Therefore, we examined cachectic muscle's ability to induce mechano‐sensitive pathways and protein synthesis in response to an anabolic stimulus involving ECC and determined the role of muscle signal transducer and activator of transcription 3 (STAT3)/nuclear factor kappa‐light‐chain‐enhancer of activated B cells (NFκB) signalling on ECC‐induced anabolic signalling.MethodsMechano‐sensitive pathways and anabolic signalling were examined immediately post or 3 h after a single ECC bout in cachectic male Apc Min/+ mice (n = 17; 16 ± 1% body weight loss). Muscle STAT3/NFκB regulation of basal and ECC‐induced anabolic signalling was also examined in an additional cohort of Apc Min/+ mice (n = 10; 16 ± 1% body weight loss) that received pyrrolidine dithiocarbamate 24 h prior to a single ECC bout. In all experiments, the left tibialis anterior performed ECC while the right tibialis anterior served as intra‐animal control. Data were analysed by Student's t‐test or two‐way repeated measures analysis of variance with Student‐Newman‐Keuls post‐hoc when appropriate. The accepted level of significance was set at P < 0.05 for all analysis.Results Apc Min/+ mice exhibited a cachectic muscle signature demonstrated by perturbed proteostasis (Ribosomal Protein S6 (RPS6), P70S6K, Atrogin‐1, and Muscle RING‐finger protein‐1 (MuRF1)), metabolic (adenosine monophosphate‐activated protein kinase, Peroxisome proliferator‐activated receptor gamma coactivator 1‐alpha (PGC‐1α), and Cytochrome c oxidase subunit IV (COXIV)), and inflammatory (STAT3, NFκB, extracellular signal‐regulated kinases 1 and 2, and P38) signalling pathway regulation. Nonetheless, mechano‐sensitive signalling pathways (P38, extracellular signal‐regulated kinases 1 and 2, and Protein kinase B (AKT)) were activated immediately post‐ECC irrespective of cachexia. While cachexia did not attenuate ECC‐induced P70S6K activation, the protein synthesis induction remained suppressed compared with healthy controls. However, muscle STAT3/NFκB inhibition increased basal and ECC‐induced protein synthesis in cachectic Apc Min/+ mice.ConclusionsThese studies demonstrate that mechano‐sensitive signalling is maintained in cachectic skeletal muscle, but chronic STAT3/NFκB signalling serves to attenuate basal and ECC‐induced protein synthesis.

Understanding the Role of Exercise in Cancer Cachexia Therapy.

Cachexia, the unintentional loss of body weight, is prevalent in many cancer types, and the associated skeletal muscle mass depletion increases patient morbidity and mortality. While anorexia can be present, cachexia is not reversible with nutritional therapies alone. Pharmacological agents have been proposed to treat this condition, but there are currently no approved treatments. Nonetheless, the hallmark characteristics associated with cancer cachexia remain viable foundations for future therapies. Regular physical activity holds a promising future as a nonpharmacological alternative to improve patient survival through cachexia prevention. Evidence suggests exercise training is beneficial during cancer treatment and survival. However, the mechanistic examination of cachectic skeletal muscle's response to exercise is both needed and justified. The primary objective of this review is to discuss the role of exercise for the prevention and treatment of cancer-associated muscle wasting. Initially, we provide an overview of systemic alterations induced by cancer and their role in the regulation of wasting processes during cachexia progression. We then discuss how exercise could alter disrupted regulatory pathways related to growth and metabolism during cancer-induced muscle atrophy. Last, we outline current exercise prescription guidelines and how exercise could be a potential behavioral therapy to curtail cachexia development in cancer patients.

Inflammatory Signaling Regulation of Eccentric Contraction–induced Muscle Protein Synthesis in Cachectic Skeletal Muscle

Eccentric muscle contractions (ECC) induce growth that is associated with increased protein synthesis regulated by mTORC1. While disrupted muscle protein turnover occurs during cancer cachexia, cachectic muscle's capacity to respond to ECC is not well understood. Repeated ECC bouts during the progression of cachexia can attenuate muscle mass loss, reduce muscle inflammatory signaling, and decrease AMPK activation. However, cachectic muscle's ability to induce protein synthesis through mTORC1 has not examined. Therefore, we examined if cancer‐induced muscle inflammatory signaling involving STAT3 and NFkB could disrupt ECC‐induced protein synthesis. Either pharmacological (PDTC, a STAT3/NFkB inhibitor) or non‐pharmacological (ECC training) treatments were used to alter muscle inflammatory signaling. mTORC1 signaling and protein synthesis was examined 3h after a single bout of ECC in C57BL/6 (B6; N=9) and cachectic ApcMin/+ (MIN; N=9; 16% BW loss) mice. A subset of MIN mice (N=6; 17% BW loss) also received a single PDTC injection 24h prior to acute muscle contraction. The acute response after ECC training (8 bouts over 2 weeks) in C57BL/6 (N=8) and MIN mice (N=9; 15% BW loss) was also examined. In all experiments the left tibialis anterior (TA) performed ECC while the right TA served as intra‐animal control. Cachexia decreased TA muscle mass, mTORC1 signaling, and protein synthesis when compared to B6 controls. While the ECC induction of p70S6K(T389) phosphorylation was not attenuated by cachexia, the protein synthesis induction by ECC remained suppressed compared to B6 controls. Inhibition of STAT3/NFkB signaling increased basal muscle protein synthesis in MIN mice, which was further enhanced by ECC. The acute ECC induction of muscle protein synthesis was not altered by training. These data demonstrate that basal muscle protein synthesis in cachectic muscle is regulated by muscle inflammatory signaling. However, cachectic muscle inflammatory signaling does not alter the ECC induction of mTORC1 signaling and muscle protein synthesis.Support or Funding InformationSupported by NCI R01‐CA121249 (JAC) and an ACSM Foundation Research Grant (JPH).

Disrupted Skeletal Muscle Mitochondrial Dynamics, Mitophagy, and Biogenesis during Cancer Cachexia: A Role for Inflammation.

Chronic inflammation is a hallmark of cancer cachexia in both patients and preclinical models. Cachexia is prevalent in roughly 80% of cancer patients and accounts for up to 20% of all cancer-related deaths. Proinflammatory cytokines IL-6, TNF-α, and TGF-β have been widely examined for their regulation of cancer cachexia. An established characteristic of cachectic skeletal muscle is a disrupted capacity for oxidative metabolism, which is thought to contribute to cancer patient fatigue, diminished metabolic function, and muscle mass loss. This review's primary objective is to highlight emerging evidence linking cancer-induced inflammation to the dysfunctional regulation of mitochondrial dynamics, mitophagy, and biogenesis in cachectic muscle. The potential for either muscle inactivity or exercise to alter mitochondrial dysfunction during cancer cachexia will also be discussed.

Mouse Cachectic Skeletal Muscle mTORC1 Signaling in Response to Acute Eccentric Contractions

Eccentric contraction (EC) induced skeletal muscle hypertrophy involves the activation of protein synthesis through mTORC1 signaling. Cancer cachexia disruption of muscle protein turnover regulation is well established, but whether increased use regulates suppressed muscle protein synthesis warrants further investigation. We recently demonstrated severely cachectic muscle can initiate a growth response to repeated ECs. However, the EC activation of mTORC1 signaling in cachectic muscle has not been investigated. The purpose of this study was to determine if mTORC1 signaling and protein synthesis in cachectic muscle from 2 distinct preclinical cancer cachexia models could respond to EC. Male, ApcMin/+ (N=5; 15% body weight loss) and Lewis Lung Carcinoma (LLC) tumor‐bearing (N=8; 14% body weight loss) mice performed 1 bout (10 sets of 6 repetitions) of EC and were sacrificed 3h post‐contraction. The left TA performed EC while the right TA served as intra‐animal control. C57BL/6 (WT) mice served as controls. In control muscle ApcMin/+ and LLC mice had decreased muscle mass, p70S6K(T389) phosphorylation, and protein synthesis compared to WT controls. Cachexia did not inhibit the acute EC‐induction of p70S6K(T389) phosphorylation in ApcMin/+ or LLC mice. While EC induced protein synthesis in ApcMin/+ mice, protein synthesis remained suppressed compared to WT mice. Interestingly, EC did not stimulate muscle protein synthesis in LLC mice. Although cachexia suppressed muscle anabolic signaling, cachectic muscle maintains the ability to activate mTORC1 signaling by EC. However, in LLC‐induced cachexia there is a disconnect between mTORC1 activation and the induction of protein synthesis. Further studies are required to determine the tumor specific effects that regulate the anabolic response to eccentric contractions in cachectic muscle.Support or Funding InformationSupported by NIH/NCI R01‐CA121249

Eccentric contraction-induced myofiber growth in tumor-bearing mice.

Cancer cachexia is characterized by the progressive loss of skeletal muscle mass. While mouse skeletal muscle's response to an acute bout of stimulated low-frequency concentric muscle contractions is disrupted by cachexia, gaps remain in our understanding of cachexia's effects on eccentric contraction-induced muscle growth. The purpose of this study was to determine whether repeated bouts of stimulated high-frequency eccentric muscle contractions [high-frequency electrical muscle stimulation (HFES)] could stimulate myofiber growth during cancer cachexia progression, and whether this training disrupted muscle signaling associated with wasting. Male Apc(Min/+) mice initiating cachexia (N = 9) performed seven bouts of HFES-induced eccentric contractions of the left tibialis anterior muscle over 2 wk. The right tibialis anterior served as the control, and mice were killed 48 h after the last stimulation. Age-matched C57BL/6 mice (N = 9) served as wild-type controls. Apc(Min/+) mice lost body weight, muscle mass, and type IIA, IIX, and IIB myofiber cross-sectional area. HFES increased myofiber cross-sectional area of all fiber types, regardless of cachexia. Cachexia increased muscle noncontractile tissue, which was attenuated by HFES. Cachexia decreased the percentage of high succinate dehydrogenase activity myofibers, which was increased by HFES, regardless of cachexia. While cachexia activated AMP kinase, STAT3, and ERK1/2 signaling, HFES decreased AMP kinase phosphorylation, independent of the suppression of STAT3. These results demonstrate that cachectic skeletal muscle can initiate a growth response to repeated eccentric muscle contractions, despite the presence of a systemic cachectic environment.

Cardiac and skeletal muscles show molecularly distinct responses to cancer cachexia.

Cancer cachexia is a systemic, paraneoplastic syndrome seen in patients with advanced cancer. There is growing interest in the altered muscle pathophysiology experienced by cachectic patients. This study reports the microarray analysis of gene expression in cardiac and skeletal muscle in the colon 26 (C26) carcinoma mouse model of cancer cachexia. A total of 268 genes were found to be differentially expressed in cardiac muscle tissue, compared with nontumor-bearing controls. This was fewer than the 1,533 genes that changed in cachectic skeletal muscle. In addition to different numbers of genes changing, different cellular functions were seen to change in each tissue. The cachectic heart showed signs of inflammation, similar to cachectic skeletal muscle, but did not show the upregulation of ubiquitin-dependent protein catabolic processes or downregulation of genes involved in cellular energetics and muscle regeneration that characterizes skeletal muscle cachexia. Quantitative PCR was used to investigate a subset of inflammatory genes in the cardiac and skeletal muscle of independent cachectic samples; this revealed that B4galt1, C1s, Serpina3n, and Vsig4 were significantly upregulated in cardiac tissue, whereas C1s and Serpina3n were significantly upregulated in skeletal tissue. Our skeletal muscle microarray results were also compared with those from three published microarray studies and found to be consistent in terms of the genes differentially expressed and the functional processes affected. Our study highlights that skeletal and cardiac muscles are affected differently in the C26 mouse model of cachexia and that therapeutic strategies cannot assume that both muscle types will show a similar response.

Cachectic Skeletal Muscle Response To Eccentric and Concentric Contractions

Cachectic Skeletal Muscle Response To Eccentric and Concentric Contractions

STAT3 Regulation In Cachectic Skeletal Muscle After Repeated Eccentric Contractions

Introduction The cachectic muscle's response to multiple bouts of eccentric contractions (ECC) has not been examined. We examined if 2 weeks of repeated ECC training could alter STAT3 regulation in cachectic muscle. Methods Male C57BL/6 (B6; N=9) and ApcMin/+ mice were subjected to 7 bouts of high-frequency electrical stimulation (100 Hz, 6-12V, 10 sets of 6 repetitions) over 2 weeks. The left tibialis anterior (TA) muscle performed ECC while the right TA served as an intra-animal control. ApcMin/+ mice were stratified into mild (7%; N=5) and severe (16% loss; N=4) cachexia based on the percentage of body weight loss at the end of the study. Results ApcMin/+ mice had smaller control TA muscle mass (-26%; P<.01) and type IIA and IIB myofiber cross-sectional area (CSA) compared to B6 mice. Cachexia increased control TA muscle STAT3 phosphorylation (9-fold; P<.05), p42/44 MAPK phosphorylation (8-fold; P<.05), and Atrogin-1 protein expression (9-fold; P<.05). Independent of cachexia ECC increased TA muscle mass and type IIA and IIB myofiber CSA. ECC had no effect on TA muscle STAT3 phosphorylation in mildly cachectic mice, but there was a 30% reduction (P<.01) in severely cachectic mice. ECC had no effect on muscle p42/p44 MAPK phosphorylation in ApcMin/+ mice. The induction of Atrogin-1 protein expression was attenuated 31% (P<.01) by ECC in severely cachectic mice. Conclusion These results suggest that repeated bouts of ECC can alter cachexia-induced muscle signaling. The contraction-induced regulation of STAT3 signaling during cachexia progression warrants further investigation. Supported by NIH/NCI R01CA121249 to JAC.