Skeletal muscle mitochondrial uncoupling in a murine cancer cachexia model

Immunomodulation: A new approach to cancer cachexia, potentially suitable for aging

Cancer cachexia is the prototypical example of comorbidity, occurring in most of cancer patients. It is a direct consequence of tumor growth and of the associated inflammatory/immune response. Cachexia can be exacerbated by anti-cancer therapies, frequently resulting in dose limitation and/or treatment delay or discontinuation. The pathogenesis of cancer cachexia is still unclear and includes nutritional, metabolic, hormonal and immunological components. Tumor ability to shape the immune response to its own advantage is now well accepted, while the possibility that such an altered immune response could play a role in the onset of cachexia is still an undefined issue. Indeed, most of the immune-related research on cachexia mainly focused on pro-inflammatory mediators, almost totally disregarding the interactions among immune cells and the homeostasis of peripheral tissues. The present review provides an overview of the immune system dysregulations occurring in cancer cachexia, focusing on the possibility that immunomodulating strategies, mainly developed to stimulate the anti-cancer immune response, could be useful to counteract cachexia as well. Cancer and cachexia are frequent comorbidities of aging. Along this line, cancer- and aging-associated muscle wasting likely coexist in the same patients. Since both conditions share some of the underlying mechanisms, the potential effectiveness of immunomodulation on sarcopenia of aging is discussed.

Exploring heterogeneity: a dive into preclinical models of cancer cachexia

Cancer cachexia (CC) is a multifactorial and complex syndrome experienced by up to 80% of patients with cancer and implicated in ∼40% of cancer-related deaths. Given its significant impact on patients' quality of life and prognosis, there has been a growing emphasis on elucidating the underlying mechanisms of CC using preclinical models. However, the mechanisms of cachexia appear to differ across several variables including tumor type and model and biologic variables such as sex. These differences may be exacerbated by variance in experimental approaches and data reporting. This review examines literature spanning from 2011 to March 2024, focusing on common preclinical models of CC, including Lewis Lung Carcinoma, pancreatic KPC, and colorectal colon-26 and Apcmin/+ models. Our analysis reveals considerable heterogeneity in phenotypic outcomes, and investigated mechanisms within each model, with particular attention to sex differences that may be exacerbated through methodological differences. Although searching for unified mechanisms is critical, we posit that effective treatment approaches are likely to leverage the heterogeneity presented by the tumor and pertinent biological variables to direct specific interventions. In exploring this heterogeneity, it becomes critical to consider methodological and data reporting approaches to best inform further research.

CCL2 signaling promotes skeletal muscle wasting in non-tumor and breast tumor models

Despite advancements in treatment, approximately 25% of patients with breast cancer experience long-term skeletal muscle wasting (SMW), which limits mobility, reduces drug tolerance and adversely impacts survival. By understanding the underlying molecular mechanisms of SMW, we may be able to develop new strategies to alleviate this condition and improve the lives of patients with breast cancer. Chemokines are small soluble factors that regulate homing of immune cells to tissues during inflammation. In breast cancers, overexpression of C-C chemokine ligand 2 (CCL2) correlates with unfavorable prognosis. Elevated levels of CCL2 in peripheral blood indicate possible systemic effects of this chemokine in patients with breast cancer. Here, we investigated the role of CCL2 signaling on SMW in tumor and non-tumor contexts. In vitro, increasing concentrations of CCL2 inhibited myoblast and myotube function through C-C chemokine receptor 2 (CCR2)-dependent mechanisms involving JNK, SMAD3 and AMPK signaling. In healthy mice, delivery of recombinant CCL2 protein promoted SMW in a dose-dependent manner. In vivo knockdown of breast tumor-derived CCL2 partially protected against SMW. Overall, chronic, upregulated CCL2-CCR2 signaling positively regulates SMW, with implications for therapeutic targeting.

Caprylic Acid Inhibits High Mobility Group Box-1-Induced Mitochondrial Damage in Myocardial Tubes

Myocardial damage significantly impacts the prognosis of patients with cancer; however, the mechanisms of myocardial damage induced by cancer and its treatment remain unknown. We previously reported that medium-chain fatty acids (MCFAs) improve cancer-induced myocardial damage but did not evaluate the differences in effect according to MCFA type. Therefore, this study investigated the role of inflammatory cytokines in cancer-induced myocardial damage and the effects of three types of MCFAs (caprylic acid [C8], capric acid [C10], and lauric acid [C12]). In a mouse model, the C8 diet showed a greater effect on improving myocardial damage compared with C10 and C12 diets. Myocardial tubes differentiated from H9C2 cardiomyoblasts demonstrated increased mitochondrial oxidative stress, decreased membrane potential and mitochondrial volume, and inhibited myocardial tube differentiation following treatment with high-mobility group box-1 (HMGB1) but not interleukin-6 and tumor necrosis factor-α cytokines. However, HMGB1 treatment combined with C8 improved HMGB1-induced mitochondrial damage, enhanced autophagy, and increased mitochondrial biogenesis and maturation. However, these effects were only partial when combined with beta-hydroxybutyrate, a C8 metabolite. Thus, HMGB1 may play an important role in cancer-related myocardial damage. C8 counteracts HMGB1's effects and improves cancer-related myocardial damage. Further clinical studies are required to investigate the effects of C8.

Transcutaneous carbon dioxide suppresses skeletal muscle atrophy in a mouse model of oral squamous cell carcinoma

Cancer cachexia causes skeletal muscle atrophy, impacting the treatment and prognosis of patients with advanced cancer, but no treatment has yet been established to control cancer cachexia. We demonstrated that transcutaneous application of carbon dioxide (CO2) could improve local blood flow and reduce skeletal muscle atrophy in a fracture model. However, the effects of transcutaneous application of CO2 in cancer-bearing conditions are not yet known. In this study, we calculated fat-free body mass (FFM), defined as the skeletal muscle mass, and evaluated the expression of muscle atrophy markers and uncoupling protein markers as well as the cross-sectional area (CSA) to investigate whether transcutaneous application of CO2 to skeletal muscle could suppress skeletal muscle atrophy in cancer-bearing mice. Human oral squamous cell carcinoma was transplanted subcutaneously into the upper dorsal region of nude mice, and 1 week later, CO2 gas was applied to the legs twice a week for 4 weeks and FFM was calculated by bioimpedance spectroscopy. After the experiment concluded, the quadriceps were extracted, and muscle atrophy markers (muscle atrophy F-box protein (MAFbx), muscle RING-finger protein 1 (MuRF-1)) and uncoupling protein markers (uncoupling protein 2 (UCP2) and uncoupling protein 3 (UCP3)) were evaluated by real-time polymerase chain reaction and immunohistochemical staining, and CSA by hematoxylin and eosin staining. The CO2-treated group exhibited significant mRNA and protein expression inhibition of the four markers. Furthermore, immunohistochemical staining showed decreased MAFbx, MuRF-1, UCP2, and UCP3 in the CO2-treated group. In fact, the CSA in hematoxylin and eosin staining and the FFM revealed significant suppression of skeletal muscle atrophy in the CO2-treated group. We suggest that transcutaneous application of CO2 to skeletal muscle suppresses skeletal muscle atrophy in a mouse model of oral squamous cell carcinoma.

Mitochondria transcription and cancer

Mitochondria are major organelles involved in several processes related to energy supply, metabolism, and cell proliferation. The mitochondria function is transcriptionally regulated by mitochondria DNA (mtDNA), which encodes the key proteins in the electron transport chain that is indispensable for oxidative phosphorylation (OXPHOS). Mitochondrial transcriptional abnormalities are closely related to a variety of human diseases, such as cardiovascular diseases, and diabetes. The mitochondria transcription is regulated by the mtDNA, mitochondrial RNA polymerase (POLRMT), two transcription factors (TFAM and TF2BM), one transcription elongation (TEFM), and one known transcription termination factor (mTERFs). Dysregulation of these factors directly leads to altered expression of mtDNA in tumor cells, resulting in cellular metabolic reprogramming and mitochondrial dysfunction. This dysregulation plays a role in modulating tumor progression. Therefore, understanding the role of mitochondrial transcription in cancer can have implications for cancer diagnosis, prognosis, and treatment. Targeting mitochondrial transcription or related pathways may provide potential therapeutic strategies for cancer treatment. Additionally, assessing mitochondrial transcriptional profiles or biomarkers in cancer cells or patient samples may offer diagnostic or prognostic information.

Unveiling the Role of the Proton Gateway, Uncoupling Proteins (UCPs), in Cancer Cachexia

Uncoupling proteins (UCPs) are identified as carriers of proton ions between the mitochondrial inner membrane and the mitochondrial matrix. ATP is mainly generated through oxidative phosphorylation in mitochondria. The proton gradient is generated across the inner mitochondrial membrane and the mitochondrial matrix, which facilitates a smooth transfer of electrons across ETC complexes. Until now, it was thought that the role of UCPs was to break the electron transport chain and thereby inhibit the synthesis of ATP. UCPs allow protons to pass from the inner mitochondrial membrane to the mitochondrial matrix and decrease the proton gradient across the membrane, which results in decreased ATP synthesis and increased production of heat by mitochondria. In recent years, the role of UCPs in other physiological processes has been deciphered. In this review, we first highlighted the different types of UCPs and their precise location across the body. Second, we summarized the role of UCPs in different diseases, mainly metabolic disorders such as obesity and diabetes, cardiovascular complications, cancer, wasting syndrome, neurodegenerative diseases, and kidney complications. Based on our findings, we conclude that UCPs play a major role in maintaining energy homeostasis, mitochondrial functions, ROS production, and apoptosis. Finally, our findings reveal that mitochondrial uncoupling by UCPs may treat many diseases, and extensive clinical studies are required to meet the unmet need of certain diseases.

Impact of cancer cachexia on respiratory muscle function and the therapeutic potential of exercise

Cancer cachexia is defined as a multi-factorial syndrome characterised by an ongoing loss of skeletal muscle mass and progressive functional impairment, estimated to affect 50-80% of patients and responsible for 20% of cancer deaths. Elevations in the morbidity and mortality rates of cachectic cancer patients has been linked to respiratory failure due to atrophy and dysfunction of the ventilatory muscles. Despite this, there is a distinct scarcity of research investigating the structural and functional condition of the respiratory musculature in cancer, with the majority of studies exclusively focusing on limb muscle. Treatment strategies are largely ineffective in mitigating the cachectic state. It is now widely accepted that an efficacious intervention will likely combine elements of pharmacology, nutrition and exercise. However, of these approaches, exercise has received comparatively little attention. Therefore, it is unlikely to be implemented optimally, whether in isolation or combination. In consideration of these limitations, the current review describes the mechanistic basis of cancer cachexia and subsequently explores the available respiratory- and exercise-focused literature within this context. The molecular basis of cachexia is thoroughly reviewed. The pivotal role of inflammatory mediators is described. Unravelling the mechanisms of exercise-induced support of muscle via antioxidant and anti-inflammatory effects in addition to promoting efficient energy metabolism via increased mitochondrial biogenesis, mitochondrial function and muscle glucose uptake provide avenues for interventional studies. Currently available pre-clinical mouse models including novel transgenic animals provide a platform for the development of multi-modal therapeutic strategies to protect respiratory muscles in people with cancer.

PGC-1α overexpression is not sufficient to mitigate cancer cachexia in either male or female mice

Cancer-cachexia accounts for 20-40% of cancer-related deaths. Mitochondrial aberrations have been shown to precede muscle atrophy in different atrophy models, including cancer. Therefore, this study investigated potential protection from the cachectic phenotype through overexpression of PGC-1α. First, to establish potential of mitochondria-based approaches we showed that the mitochondrial antioxidant mitoTEMPO attenuates myotube atrophy induced by Lewis Lung Carcinoma (LLC) cell conditioned media. Next, cachexia was induced in muscle specific PGC-1α overexpressing (MCK-PCG1α) or wildtype (WT) littermate mice by LLC implantation. MCK-PCG1α did not protect LLC-induced muscle mass loss. In plantaris, Atrogin mRNA content was 6.2-fold and ~11-fold greater in WT-LLC vs. WT-PBS for males and females, respectively (p<0.05). MitoTimer red:green ratio for male PGC was ~65% higher than WT groups (p<0.05), with ~3-fold more red puncta in LLC than PBS (p<0.05). Red:green ratio was ~56% lower in females WT-LLC vs. PGC-LLC (p<0.05). In females, no change in red puncta was noted across conditions. Lc3 mRNA content was ~ 73% and 2-fold higher in male and female LLC mice respectively vs. PBS (p<0.05). While MitoTEMPO could mitigate cancer-induced atrophy in vitro, PGC1α overexpression was insufficient to protect muscle mass and mitochondrial health in vivo despite mitigation of cachexia-associated signaling pathways.

Skeletal Muscle Deconditioning in Breast Cancer Patients Undergoing Chemotherapy: Current Knowledge and Insights From Other Cancers

Breast cancer represents the most commonly diagnosed cancer while neoadjuvant and adjuvant chemotherapies are extensively used in order to reduce tumor development and improve disease-free survival. However, chemotherapy also leads to severe off-target side-effects resulting, together with the tumor itself, in major skeletal muscle deconditioning. This review first focuses on recent advances in both macroscopic changes and cellular mechanisms implicated in skeletal muscle deconditioning of breast cancer patients, particularly as a consequence of the chemotherapy treatment. To date, only six clinical studies used muscle biopsies in breast cancer patients and highlighted several important aspects of muscle deconditioning such as a decrease in muscle fibers cross-sectional area, a dysregulation of protein turnover balance and mitochondrial alterations. However, in comparison with the knowledge accumulated through decades of intensive research with many different animal and human models of muscle atrophy, more studies are necessary to obtain a comprehensive understanding of the cellular processes implicated in breast cancer-mediated muscle deconditioning. This understanding is indeed essential to ultimately lead to the implementation of efficient preventive strategies such as exercise, nutrition or pharmacological treatments. We therefore also discuss potential mechanisms implicated in muscle deconditioning by drawing a parallel with other cancer cachexia models of muscle wasting, both at the pre-clinical and clinical levels.

Phosphorylation of Dynamin-Related Protein 1 (DRP1) Regulates Mitochondrial Dynamics and Skeletal Muscle Wasting in Cancer Cachexia

Background

Cancer-associated cachexia (CAC) is a syndrome characterized by skeletal muscle atrophy, and the underlying mechanisms are still unclear. Recent research studies have shed light on a noteworthy link between mitochondrial dynamics and muscle physiology. In the present study, we investigate the role of dynamin-related protein 1 (DRP1), a pivotal factor of mitochondrial dynamics, in myotube atrophy during cancer-associated cachexia.

Methods

Seventy-six surgical patients, including gastrointestinal tumor and benign disease, were enrolled in the study and divided to three groups: control, non-cachexia, and cancer-associated cachexia. Demographic data were collected. Their rectus abdominis samples were acquired intraoperatively. Muscle fiber size, markers of ubiquitin proteasome system (UPS), mitochondrial ultrastructure, and markers of mitochondrial function and dynamics were assayed. A cachexia model in vitro was established via coculturing a C2C12 myotube with media from C26 colon cancer cells. A specific DRP1 inhibitor, Mdivi-1, and a lentivirus of DRP1 knockdown/overexpression were used to regulate the expression of DRP1. Muscle diameter, mitochondrial morphology, mass, reactive oxygen species (ROS), membrane potential, and markers of UPS, mitochondrial function, and dynamics were determined.

Results

Patients of cachexia suffered from a conspicuous worsened nutrition status and muscle loss compared to patients of other groups. Severe mitochondrial swelling and enlarged area were observed, and partial alterations in mitochondrial function were found in muscle. Analysis of mitochondrial dynamics indicated an upregulation of phosphorylated DRP1 at the ser616 site. In vitro, cancer media resulted in the atrophy of myotube. This was accompanied with a prominent unbalance of mitochondrial dynamics, as well as enhanced mitochondrial ROS and decreased mitochondrial function and membrane potential. However, certain concentrations of Mdivi-1 and DRP1 knockdown rebalanced the mitochondrial dynamics, mitigating this negative phenotype caused by cachexia. Moreover, overexpression of DRP1 aggravated these phenomena.

Conclusion

In clinical patients, cachexia induces abnormal mitochondrial changes and possible fission activation for the atrophied muscle. Our cachexia model in vitro further demonstrates that unbalanced mitochondrial dynamics contributes to this atrophy and mitochondrial impairment, and rebuilding the balance by regulating of DRP1 could ameliorate these alterations.

Metabolic Remodeling in Skeletal Muscle Atrophy as a Therapeutic Target

Skeletal muscle is a highly responsive tissue, able to remodel its size and metabolism in response to external demand. Muscle fibers can vary from fast glycolytic to slow oxidative, and their frequency in a specific muscle is tightly regulated by fiber maturation, innervation, or external causes. Atrophic conditions, including aging, amyotrophic lateral sclerosis, and cancer-induced cachexia, differ in the causative factors and molecular signaling leading to muscle wasting; nevertheless, all of these conditions are characterized by metabolic remodeling, which contributes to the pathological progression of muscle atrophy. Here, we discuss how changes in muscle metabolism can be used as a therapeutic target and review the evidence in support of nutritional interventions and/or physical exercise as tools for counteracting muscle wasting in atrophic conditions.

Voluntary exercise prevents abnormal muscle mitochondrial morphology in cancer cachexia mice

This study aimed to examine the effects of voluntary wheel running on cancer cachexia-induced mitochondrial alterations in mouse skeletal muscle. Mice bearing colon 26 adenocarcinoma (C26) were used as a model of cancer cachexia. C26 mice showed a lower gastrocnemius and plantaris muscle weight, but 4 weeks of voluntary exercise rescued these changes. Further, voluntary exercise attenuated observed declines in the levels of oxidative phosphorylation proteins and activities of citrate synthase and cytochrome c oxidase in the skeletal muscle of C26 mice. Among mitochondrial morphology regulatory proteins, mitofusin 2 (Mfn2) and dynamin-related protein 1 (Drp1) were decreased in the skeletal muscle of C26 mice, but exercise resulted in similar improvements as seen in markers of mitochondrial content. In isolated mitochondria, 4-hydroxynonenal and protein carbonyls were elevated in C26 mice, but exercise blunted the increases in these markers of oxidative stress. In addition, electron microscopy revealed that exercise alleviated the observed increase in the percentage of damaged mitochondria in C26 mice. These results suggest that voluntary exercise effectively counteracts mitochondrial dysfunction to mitigate muscle loss in cachexia.

Pharmacological or genetic inhibition of iNOS prevents cachexia-mediated muscle wasting and its associated metabolism defects

Cachexia syndrome develops in patients with diseases such as cancer and sepsis and is characterized by progressive muscle wasting. While iNOS is one of the main effectors of cachexia, its mechanism of action and whether it could be targeted for therapy remains unexplored. Here, we show that iNOS knockout mice and mice treated with the clinically tested iNOS inhibitor GW274150 are protected against muscle wasting in models of both septic and cancer cachexia. We demonstrate that iNOS triggers muscle wasting by disrupting mitochondrial content, morphology, and energy production processes such as the TCA cycle and acylcarnitine transport. Notably, iNOS inhibits oxidative phosphorylation through impairment of complexes II and IV of the electron transport chain and reduces ATP production, leading to energetic stress, activation of AMPK, suppression of mTOR, and, ultimately, muscle atrophy. Importantly, all these effects were reversed by GW274150. Therefore, our data establish how iNOS induces muscle wasting under cachectic conditions and provide a proof of principle for the repurposing of iNOS inhibitors, such as GW274150 for the treatment of cachexia.

A Metabolic Change towards Fermentation Drives Cancer Cachexia in Myotubes

Cachexia is a disorder associated with several pathologies, including cancer. In this paper, we describe how cachexia is induced in myotubes by a metabolic shift towards fermentation, and the block of this metabolic modification prevents the onset of the cachectic phenotype. Cachectic myotubes, obtained by the treatment with conditioned medium from murine colon carcinoma cells CT26, show increased glucose uptake, decreased oxygen consumption, altered mitochondria, and increased lactate production. Interestingly, the block of glycolysis by 2-deoxy-glucose or lactate dehydrogenase inhibition by oxamate prevents the induction of cachexia, thus suggesting that this metabolic change is greatly involved in cachexia activation. The treatment with 2-deoxy-glucose or oxamate induces positive effects also in mitochondria, where mitochondrial membrane potential and pyruvate dehydrogenase activity became similar to control myotubes. Moreover, in myotubes treated with interleukin-6, cachectic phenotype is associated with a fermentative metabolism, and the inhibition of lactate dehydrogenase by oxamate prevents cachectic features. The same results have been achieved by treating myotubes with conditioned media from human colon HCT116 and human pancreatic MIAPaCa-2 cancer cell lines, thus showing that what has been observed with murine-conditioned media is a wide phenomenon. These findings demonstrate that cachexia induction in myotubes is linked with a metabolic shift towards fermentation, and inhibition of lactate formation impedes cachexia and highlights lactate dehydrogenase as a possible new tool for counteracting the onset of this pathology.

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.

Methylarginine metabolites are associated with attenuated muscle protein synthesis in cancer-associated muscle wasting

Cancer cachexia is characterized by reductions in peripheral lean muscle mass. Prior studies have primarily focused on increased protein breakdown as the driver of cancer-associated muscle wasting. Therapeutic interventions targeting catabolic pathways have, however, largely failed to preserve muscle mass in cachexia, suggesting that other mechanisms might be involved. In pursuit of novel pathways, we used untargeted metabolomics to search for metabolite signatures that may be linked with muscle atrophy. We injected 7-week-old C57/BL6 mice with LLC1 tumor cells or vehicle. After 21 days, tumor-bearing mice exhibited reduced body and muscle mass and impaired grip strength compared with controls, which was accompanied by lower synthesis rates of mixed muscle protein and the myofibrillar and sarcoplasmic muscle fractions. Reductions in protein synthesis were accompanied by mitochondrial enlargement and reduced coupling efficiency in tumor-bearing mice. To generate mechanistic insights into impaired protein synthesis, we performed untargeted metabolomic analyses of plasma and muscle and found increased concentrations of two methylarginines, asymmetric dimethylarginine (ADMA) and N^G-monomethyl-l-arginine, in tumor-bearing mice compared with control mice. Compared with healthy controls, human cancer patients were also found to have higher levels of ADMA in the skeletal muscle. Treatment of C2C12 myotubes with ADMA impaired protein synthesis and reduced mitochondrial protein quality. These results suggest that increased levels of ADMA and mitochondrial changes may contribute to impaired muscle protein synthesis in cancer cachexia and could point to novel therapeutic targets by which to mitigate cancer cachexia.

Disease-associated metabolic alterations that impact satellite cells and muscle regeneration: perspectives and therapeutic outlook

Many chronic disease patients experience a concurrent loss of lean muscle mass. Skeletal muscle is a dynamic tissue maintained by continuous protein turnover and progenitor cell activity. Muscle stem cells, or satellite cells, differentiate (by a process called myogenesis) and fuse to repair and regenerate muscle. During myogenesis, satellite cells undergo extensive metabolic alterations; therefore, pathologies characterized by metabolic derangements have the potential to impair myogenesis, and consequently exacerbate skeletal muscle wasting. How disease-associated metabolic disruptions in satellite cells might be contributing to wasting is an important question that is largely neglected. With this review we highlight the impact of various metabolic disruptions in disease on myogenesis and skeletal muscle regeneration. We also discuss metabolic therapies with the potential to improve myogenesis, skeletal muscle regeneration, and ultimately muscle mass.

Exosomal microRNAs in cancer-related sarcopenia: Tumor-derived exosomal microRNAs in muscle atrophy

Cancer-associated sarcopenia is a complex metabolic syndrome marked by muscle mass wasting. Muscle wasting is a serious complication that is a primary contributor to cancer-related mortality. The underlying molecular mechanisms of cancer-associated sarcopenia have not been completely described to date. In general, evidence shows that the main pathophysiological alterations in sarcopenia are associated with the degradation of cellular components, an exceptional inflammatory secretome and mitochondrial dysfunction. Importantly, we highlight the prospect that several miRNAs carried by tumor-derived exosomes that have shown the ability to promote inflammatory secretion, activate catabolism, and even participate in the regulation of cellular degradation pathways can be delivered to and exert effects on muscle cells. In this review, we aim to describe the current knowledge about the functions of exosomal miRNAs in the induction of cancer-associated muscle wasting and propose potential treatment strategies.

Molecular Basis for the Therapeutic Effects of Exercise on Mitochondrial Defects

Mitochondrial dysfunction is common to many organ system disorders, including skeletal muscle. Aging muscle and diseases of muscle are often accompanied by defective mitochondrial ATP production. This manuscript will focus on the pre-clinical evidence supporting the use of regular exercise to improve defective mitochondrial metabolism and function in skeletal muscle, through the stimulation of mitochondrial turnover. Examples from aging muscle, muscle-specific mutations and cancer cachexia will be discussed. We will also examine the effects of exercise on the important mitochondrial regulators PGC-1α, and Parkin, and summarize the effects of exercise to reverse mitochondrial dysfunction (e.g., ROS production, apoptotic susceptibility, cardiolipin synthesis) in muscle pathology. This paper will illustrate the breadth and benefits of exercise to serve as "mitochondrial medicine" with age and disease.

Development and progression of cancer cachexia: Perspectives from bench to bedside

Cancer cachexia (CC) is a devastating syndrome characterized by weight loss, reduced fat mass and muscle mass that affects approximately 80% of cancer patients and is responsible for 22%-30% of cancer-associated deaths. Understanding underlying mechanisms for the development of CC are crucial to advance therapies to treat CC and improve cancer outcomes. CC is a multi-organ syndrome that results in extensive skeletal muscle and adipose tissue wasting; however, CC can impair other organs such as the liver, heart, brain, and bone as well. A considerable amount of CC research focuses on changes that occur within the muscle, but cancer-related impairments in other organ systems are understudied. Furthermore, metabolic changes in organ systems other than muscle may contribute to CC. Therefore, the purpose of this review is to address degenerative mechanisms which occur during CC from a whole-body perspective. Outlining the information known about metabolic changes that occur in response to cancer is necessary to develop and enhance therapies to treat CC. As much of the current evidences in CC are from pre-clinical models we should note the majority of the data reviewed here are from preclinical models.

Muscle Stem Cell-Derived Extracellular Vesicles Reverse Hydrogen Peroxide-Induced Mitochondrial Dysfunction in Mouse Myotubes

Muscle stem cells (MuSCs) hold great potential as a regenerative therapeutic but have met numerous challenges in treating systemic muscle diseases. Muscle stem cell-derived extracellular vesicles (MuSC-EVs) may overcome these limitations. We assessed the number and size distribution of extracellular vesicles (EVs) released by MuSCs ex vivo, determined the extent to which MuSC-EVs deliver molecular cargo to myotubes in vitro, and quantified MuSC-EV-mediated restoration of mitochondrial function following oxidative injury. MuSCs released an abundance of EVs in culture. MuSC-EVs delivered protein cargo into myotubes within 2 h of incubation. Fluorescent labeling of intracellular mitochondria showed co-localization of delivered protein and mitochondria. Oxidatively injured myotubes demonstrated a significant decline in maximal oxygen consumption rate and spare respiratory capacity relative to untreated myotubes. Remarkably, subsequent treatment with MuSC-EVs significantly improved maximal oxygen consumption rate and spare respiratory capacity relative to the myotubes that were damaged but received no subsequent treatment. Surprisingly, MuSC-EVs did not affect mitochondrial function in undamaged myotubes, suggesting the cargo delivered is able to repair but does not expand the existing mitochondrial network. These data demonstrate that MuSC-EVs rapidly deliver proteins into myotubes, a portion of which co-localizes with mitochondria, and reverses mitochondria dysfunction in oxidatively-damaged myotubes.

Evaluation of cancer-derived myocardial impairments using a mouse model

Myocardial damage in cancer patients is emphasized as a cause of death; however, there are not many murine cachexia models to evaluate cancer-derived heart disorder. Using the mouse cachexia model that we established previously, we investigated myocardial damage in tumor-bearing mice. In cachexic mice, decreased heart weight and myocardial volume, and dilated left ventricular lumen, and atrophied cardiomyocytes were noted. The cardiomyocytes also showed accumulated 8-hydroxydeoxyguanosine, decreased leucine zipper and EF-hand-containing transmembrane protein-1, and increased microtubule-associated protein light chain3-II. Levels of tumor necrosis factor-α and high-mobility group box-1 proteins in the myocardium were increased, and nuclear factor κB, a signaling molecule associated with these proteins, was activated. When rat cardiomyoblasts (H9c2 cells) were treated with mouse cachexia model ascites and subjected to flux analysis, both oxidative phosphorylation and glycolysis were suppressed, and the cells were in a quiescent state. These results are in good agreement with those previously reported on cancerous myocardial damage. The established mouse cachexia model can therefore be considered useful for analyzing cancer-derived myocardial damage.

Combined administration of lauric acid and glucose improved cancer-derived cardiac atrophy in a mouse cachexia model

Cancer‐derived myocardial damage is an important cause of death in cancer patients. However, the development of dietary interventions for treating such damage has not been advanced. Here, we investigated the effect of dietary intervention with lauric acid (LAA) and glucose, which was effective against skeletal muscle sarcopenia in a mouse cachexia model, on myocardial damage. Treatment of H9c2 rat cardiomyoblasts with lauric acid promoted mitochondrial respiration and increased ATP production by Seahorse flux analysis, but did not increase oxidative stress. Glycolysis was also promoted by LAA. In contrast, mitochondrial respiration and ATP production were suppressed, and oxidative stress was increased in an in vitro cachexia model in which cardiomyoblasts were treated with mouse cachexia ascites. Ascites‐treated H9c2 cells with concurrent treatment with LAA and high glucose showed that mitochondrial respiration and glycolysis were promoted more than that of the control, and ATP was restored to the level of the control. Oxidative stress was also reduced by the combined treatment. In the mouse cachexia model, myocardiac atrophy and decreased levels of a marker of muscle maturity, SDS‐soluble MYL1, were observed. When LAA in CE‐2 diet was orally administered alone, no significant rescue was observed in the cancer‐derived myocardial disorder. In contrast, combined oral administration of LAA and glucose recovered myocardial atrophy and MYL1 to levels observed in the control without increase in the cancer weight. Therefore, it is suggested that dietary intervention using a combination of LAA and glucose for cancer cachexia might improve cancer‐derived myocardial damage.

The Etiology and Impact of Muscle Wasting in Metastatic Cancer

Metastasis arises when cancer cells disseminate from their site of origin and invade distant organs. While cancer cells rarely colonize muscle, they often induce a debilitating muscle-wasting condition known as cachexia that compromises feeding, breathing, and cardiac function in metastatic cancer patients. In fact, nearly 80% of metastatic cancer patients experience a spectrum of muscle-wasting states, which deteriorates the quality of life and overall survival of cancer patients. Muscle wasting in cancer results from increased muscle catabolism induced by circulating tumor factors and a systemic metabolic dysfunction. In addition, muscle loss can be exacerbated by the exposure to antineoplastic therapies and the process of aging. With no approved therapies to alleviate cachexia, muscle health, therefore, becomes a key determinant of prognosis, treatment response, and survival in metastatic cancer patients. This review will discuss the current understanding of cancer-associated cachexia and highlight promising therapeutic strategies to treat muscle wasting in the context of metastatic cancers.

The Redox Balance: A Target for Interventions Against Muscle Wasting in Cancer Cachexia?

Significance: The management of cancer patients is frequently complicated by the occurrence of a complex syndrome known as cachexia. It is mainly characterized by muscle wasting, a condition that associates with enhanced protein breakdown and with negative energy balance. While the mechanisms underlying cachexia have been only partially elucidated, understanding the pathogenesis of muscle wasting in cancer hosts is mandatory to design new targeted therapeutic strategies. Indeed, most of cancer patients will experience cachexia during the course of their disease, and about 25% of cancer-related deaths are due to this syndrome, rather than to the tumor itself. Recent Advances: Compelling evidence suggests that an altered redox homeostasis likely contributes to cancer-induced muscle protein depletion, directly or indirectly activating the intracellular degradative pathways. In addition, oxidative stress impinges on both mitochondrial number and function; the other way round, altered mitochondria lead to enhanced redox imbalance, creating a vicious loop that eventually results in negative energy metabolism. Critical Issues: The present review focuses on the possibility that pharmacological and nonpharmacological strategies able to restore a physiologic redox balance could be useful components of treatment schedules aimed at counteracting cancer-induced muscle wasting. Future Directions: Exercise and the use of exercise mimetic drugs represent the most promising approaches capable of reinforcing the muscle antioxidant defenses of cancer patients. The results from ongoing and new clinical trials are needed to validate the preclinical studies and provide effective therapies for cancer cachexia. Antioxid. Redox Signal. 33, 542-558.

Mitochondrial Metabolism in Cancer Cachexia: Novel Drug Target

BACKGROUND

Cancer cachexia is a metabolic syndrome prevalent in the majority of the advanced cancers and is associated with complications such as anorexia, early satiety, weakness, anaemia, and edema, thereby reducing performance and impairing quality of life. Skeletal muscle wasting is a characteristic feature of cancer-cachexia and mitochondria is responsible for regulating total protein turnover in skeletal muscle tissue.

METHODS

We carried out exhaustive search for cancer cachexia and role of mitochondria in the same in various databases. All the relevant articles were gathered and the pertinent information was extracted out and compiled which was further structured into different sub-sections.

RESULTS

Various findings on the mitochondrial alterations in connection to its disturbed normal physiology in various models of cancer-cachexia have been recently reported, suggesting a significant role of the organelle in the pathogenesis of the complications involved in the disorder. It has also been reported that reduced mitochondrial oxidative capacity is due to reduced mitochondrial biogenesis as well as altered balance between fusion and fission protein activities. Moreover, autophagy in mitochondria (termed as mitophagy) is reported to play an important role in cancer cachexia.

CONCLUSION

The present review aims to put forth the changes occurring in mitochondria and hence explore possible targets which can be exploited in cancer-induced cachexia for treatment of such a debilitating condition.

The wasting-associated metabolite succinate disrupts myogenesis and impairs skeletal muscle regeneration

BACKGROUND

Muscle wasting is a debilitating co-morbidity affecting most advanced cancer patients. Alongside enhanced muscle catabolism, defects in muscle repair/regeneration contribute to cancer-associated wasting. Among the factors implicated in suppression of muscle regeneration are cytokines that interfere with myogenic signal transduction pathways. Less understood is how other cancer/wasting-associated cues, such as metabolites, contribute to muscle dysfunction. This study investigates how the metabolite succinate affects myogenesis and muscle regeneration.

METHODS

We leveraged an established ectopic metabolite treatment (cell permeable dimethyl-succinate) strategy to evaluate the ability of intracellular succinate elevation to 1) affect myoblast homeostasis (proliferation, apoptosis), 2) disrupt protein dynamics and induce wasting-associated atrophy, and 3) modulate in vitro myogenesis. In vivo succinate supplementation experiments (2% succinate, 1% sucrose vehicle) were used to corroborate and extend in vitro observations. Metabolic profiling and functional metabolic studies were then performed to investigate the impact of succinate elevation on mitochondria function.

RESULTS

We found that in vitro succinate supplementation elevated intracellular succinate about 2-fold, and did not have an impact on proliferation or apoptosis of C2C12 myoblasts. Elevated succinate had minor effects on protein homeostasis (~25% decrease in protein synthesis assessed by OPP staining), and no significant effect on myotube atrophy. Succinate elevation interfered with in vitro myoblast differentiation, characterized by significant decreases in late markers of myogenesis and fewer nuclei per myosin heavy chain positive structure (assessed by immunofluorescence staining). While mice orally administered succinate did not exhibit changes in overall body composition or whole muscle weights, these mice displayed smaller muscle myofiber diameters (~6% decrease in the mean of non-linear regression curves fit to the histograms of minimum feret diameter distribution), which was exacerbated when muscle regeneration was induced with barium chloride injury. Significant decreases in the mean of non-linear regression curves fit to the histograms of minimum feret diameter distributions were observed 7 days and 28 days post injury. Elevated numbers of myogenin positive cells (3-fold increase) supportive of the differentiation defects observed in vitro were observed 28 days post injury. Metabolic profiling and functional metabolic assessment of myoblasts revealed that succinate elevation caused both widespread metabolic changes and significantly lowered maximal cellular respiration (~35% decrease).

CONCLUSIONS

This study broadens the repertoire of wasting-associated factors that can directly modulate muscle progenitor cell function and strengthens the hypothesis that metabolic derangements are significant contributors to impaired muscle regeneration, an important aspect of cancer-associated muscle wasting.

Early detection of skeletal muscle bioenergetic deficit by magnetic resonance spectroscopy in cigarette smoke-exposed mice

Skeletal muscle dysfunction is a common complication and an important prognostic factor in patients with chronic obstructive pulmonary disease (COPD). It is associated with intrinsic muscular abnormalities of the lower extremities, but it is not known whether there is an easy way to predict its presence. Using a mouse model of chronic cigarette smoke exposure, we tested the hypothesis that magnetic resonance spectroscopy allows us to detect muscle bioenergetic deficit in early stages of lung disease. We employed this technique to evaluate the synthesis rate of adenosine triphosphate (ATP) and characterize concomitant mitochondrial dynamics patterns in the gastrocnemius muscle of emphysematous mice. The fibers type composition and citrate synthase (CtS) and cytochrome c oxidase subunit IV (COX4) enzymatic activities were evaluated. We found that the rate of ATP synthesis was reduced in the distal skeletal muscle of mice exposed to cigarette smoke. Emphysematous mice showed a significant reduction in body weight gain, in the cross-sectional area of the total fiber and in the COX4 to CtS activity ratio, due to a significant increase in CtS activity of the gastrocnemius muscle. Taken together, these data support the hypothesis that in the early stage of lung disease, we can detect a decrease in ATP synthesis in skeletal muscle, partly caused by high oxidative mitochondrial enzyme activity. These findings may be relevant to predict the presence of skeletal bioenergetic deficit in the early stage of lung disease besides placing the mitochondria as a potential therapeutic target for the treatment of COPD comorbidities.

Repeated eccentric contractions positively regulate muscle oxidative metabolism and protein synthesis during cancer cachexia in mice

Cancer-induced wasting is accompanied by disruptions to muscle oxidative metabolism and protein turnover that have been associated with systemic inflammation, whereas exercise and stimulated muscle contractions can positively regulate muscle protein synthesis and mitochondrial homeostasis. In preclinical cancer cachexia models, a single bout of eccentric contractions (ECCs) can induce protein synthesis and repeated ECC bouts prevent myofiber atrophy. The cellular mechanisms providing this protection from atrophy have not been resolved. Therefore, the purpose of this study was to determine whether repeated stimulated ECC bouts affect basal muscle oxidative metabolism and protein synthesis during cancer cachexia, and if these changes were associated with plasma IL-6 levels. Male Apc^Min/+ (MIN; n = 10) mice initiating cachexia and healthy C57BL/6 (B6; n = 11) control mice performed repeated ECC bouts over 2 wk. MIN mice exhibited body weight loss and elevated plasma IL-6 before and during repeated ECC bouts. Control MIN muscle demonstrated disrupted signaling related to inflammation, oxidative capacity, and protein synthesis regulation, which were all improved by repeated ECC bouts. With cachexia, plasma IL-6 levels were negatively correlated with myofiber cross-sectional area, oxidative capacity, and protein synthesis. Interestingly, ECC improvements in these outcomes were positively correlated with plasma IL-6 levels in MIN mice. There was also a positive relationship between muscle oxidative capacity and protein synthesis after repeated ECC bouts in MIN mice. Collectively, repeated ECC bouts altered the cachectic muscle phenotype independent of systemic wasting, and there was a strong association between muscle oxidative capacity and protein synthesis in this adaptive response.NEW & NOTEWORTHY Cancer-induced muscle wasting is accompanied by disruptions to muscle oxidative metabolism and protein turnover regulation, whereas exercise is a potent stimulator of muscle protein synthesis and mitochondrial homeostasis. In a preclinical model of cancer cachexia, we report that cachectic muscle retains anabolic and metabolic plasticity to repeated eccentric contraction bouts despite an overall systemic wasting environment. The attenuation of muscle atrophy is linked to improved oxidative capacity and protein synthesis during cancer cachexia progression.

Exercise training reverses cancer-induced oxidative stress and decrease in muscle COPS2/TRIP15/ALIEN

OBJECTIVE

We tested the hypothesis that exercise training would attenuate metabolic impairment in a model of severe cancer cachexia.

METHODS

We used multiple in vivo and in vitro methods to explore the mechanisms underlying the beneficial effects induced by exercise training in tumor-bearing rats.

RESULTS

Exercise training improved running capacity, prolonged lifespan, reduced oxidative stress, and normalized muscle mass and contractile function in tumor-bearing rats. An unbiased proteomic screening revealed COP9 signalosome complex subunit 2 (COPS2) as one of the most downregulated proteins in skeletal muscle at the early stage of cancer cachexia. Exercise training normalized muscle COPS2 protein expression in tumor-bearing rats and mice. Lung cancer patients with low endurance capacity had low muscle COPS2 protein expression as compared to age-matched control subjects. To test whether decrease in COPS2 protein levels could aggravate or be an intrinsic compensatory mechanism to protect myotubes from cancer effects, we performed experiments in vitro using primary myotubes. COPS2 knockdown in human myotubes affected multiple cellular pathways, including regulation of actin cytoskeleton. Incubation of cancer-conditioned media in mouse myotubes decreased F-actin expression, which was partially restored by COPS2 knockdown. Direct repeat 4 (DR4) response elements have been shown to positively regulate gene expression. COPS2 overexpression decreased the DR4 activity in mouse myoblasts, and COPS2 knockdown inhibited the effects of cancer-conditioned media on DR4 activity.

CONCLUSIONS

These studies demonstrated that exercise training may be an important adjuvant therapy to counteract cancer cachexia and uncovered novel mechanisms involving COPS2 to regulate myotube homeostasis in cancer cachexia.

ER Stress and Unfolded Protein Response in Cancer Cachexia

Cancer cachexia is a devastating syndrome characterized by unintentional weight loss attributed to extensive skeletal muscle wasting. The pathogenesis of cachexia is multifactorial because of complex interactions of tumor and host factors. The irreversible wasting syndrome has been ascribed to systemic inflammation, insulin resistance, dysfunctional mitochondria, oxidative stress, and heightened activation of ubiquitin-proteasome system and macroautophagy. Accumulating evidence suggests that deviant regulation of an array of signaling pathways engenders cancer cachexia where the human body is sustained in an incessant self-consuming catabolic state. Recent studies have further suggested that several components of endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR) are activated in skeletal muscle of animal models and muscle biopsies of cachectic cancer patients. However, the exact role of ER stress and the individual arms of the UPR in the regulation of skeletal muscle mass in various catabolic states including cancer has just begun to be elucidated. This review provides a succinct overview of emerging roles of ER stress and the UPR in cancer-induced skeletal muscle wasting.

Breast cancer-released exosomes trigger cancer-associated cachexia to promote tumor progression

Cancer-secreted exosomes are emerging mediators of cancer-associated cachexia. Here, we show that miR-155 secreted by breast cancer cells is a potent role on the catabolism of adipocytes and muscle cells through targeting the PPARγ. After cocultivated with mature adipocytes or C2C12, tumour cells exhibit an aggressive phenotype via inducing epithelial-mesenchymal transition while breast cancer-derived exosomes increased catabolism and release the metabolites in adipocytes and muscle cells. In adipocytes, cancer cell-secreted miR-155 promotes beige/brown differentiation and remodel metabolism in resident adipocytes by downregulating the PPARγ expression, but does not significantly affect biological conversion in C2C12. Likewise, propranolol ameliorates tumour exosomes-associated cachectic wasting through upregulating the PPARγ expression. In summary, we have demonstrated that the transfer of miR-155 from exosomes acts as an oncogenic signal reprograming systemic energy metabolism and leading to cancer-associated cachexia in breast cancer.

Muscle alterations in the development and progression of cancer-induced muscle atrophy: a review

Cancer cachexia-cancer-associated body weight and muscle loss-is a significant predictor of mortality and morbidity in cancer patients across a variety of cancer types. However, despite the negative prognosis associated with cachexia onset, there are no clinical therapies approved to treat or prevent cachexia. This lack of treatment may be partially due to the relative dearth of literature on mechanisms occurring within the muscle before the onset of muscle wasting. Therefore, the purpose of this review is to compile the current scientific literature on mechanisms contributing to the development and progression of cancer cachexia, including protein turnover, inflammatory signaling, and mitochondrial dysfunction. We define "development" as changes in cell function occurring before the onset of cachexia and "progression" as alterations to cell function that coincide with the exacerbation of muscle wasting. Overall, the current literature suggests that multiple aspects of cellular function, such as protein turnover, inflammatory signaling, and mitochondrial quality, are altered before the onset of muscle loss during cancer cachexia and clearly highlights the need to study more thoroughly the developmental stages of cachexia. The studying of these early aberrations will allow for the development of effective therapeutics to prevent the onset of cachexia and improve health outcomes in cancer patients.

Exercise training counteracts urothelial carcinoma-induced alterations in skeletal muscle mitochondria phospholipidome in an animal model

Cancer associated body wasting is the cause of physical disability, reduced tolerance to anticancer therapy and reduced survival of cancer patients and, similarly to cancer, its incidence is increasing. There is no cure for this clinical condition, and the pathophysiological process involved is largely unknown. Exercise training appears as the gold standard non-pharmacological therapy for the management of this wasting syndrome. Herein we used a lipidomics approach based on liquid chromatography coupled with high-resolution mass spectrometry (LC-HR-MS) to study the effect of exercise in the modulation of phospholipids profile of mitochondria isolated from gastrocnemius muscle of a pre-clinical model of urothelial carcinoma-related body wasting (BBN induced), submitted to 13 weeks of treadmill exercise after diagnosis. Multivariate analysis showed a close relationship between the BBN exercise group and both control groups (control sedentary and control exercise), while the BBN sedentary group was significantly separated from the control groups and the BBN exercise group. Univariate statistical analysis revealed differences mainly in phosphatidylserine (PS) and cardiolipin (CL), although some differences were also observed in phosphatidylinositol (PI, LPI) and phosphatidylcholine (PC) phospholipids. PS with shorter fatty acyl chains were up-regulated in the BBN sedentary group, while the other species of PS with longer FA and a higher degree of unsaturation were down-regulated, but the BBN exercise group was mostly similar to control groups. Remarkably, exercise training prevented these alterations and had a positive impact on the ability of mitochondria to produce ATP, restoring the healthy phospholipid profile. The remodelling of mitochondria phospholipid profile in rats with urothelial carcinoma allowed confirming the importance of the lipid metabolism in mitochondria dysfunction in cancer-induced skeletal muscle remodelling. The regulation of phospholipid biosynthetic pathways observed in the BBN exercise group supported the current perspective that exercise is an adequate therapeutic approach for the management of cancer-related muscle remodeling.

Treatment with Soluble Activin Receptor Type IIB Alters Metabolic Response in Chemotherapy-Induced Cachexia

Some chemotherapeutic agents have been shown to lead to the severe wasting syndrome known as cachexia resulting in dramatic losses of both skeletal muscle and adipose tissue. Previous studies have shown that chemotherapy-induced cachexia is characterized by unique metabolic alterations. Recent results from our laboratory and others have shown that the use of ACVR2B/Fc, a soluble form of the activin receptor 2B (ACVR2B), can mitigate muscle wasting induced by chemotherapy, although the underlying mechanisms responsible for such protective effects are unclear. In order to understand the biochemical mechanisms through which ACVR2B/Fc functions, we employed a comprehensive, multi-platform metabolomics approach. Using both nuclear magnetic resonance (NMR) and mass-spectrometry (MS), we profiled the metabolome of both serum and muscle tissue from four groups of mice including (1) vehicle, (2) the chemotherapeutic agent, Folfiri, (3) ACVR2B/Fc alone, and (4) combined treatment with both Folfiri and ACVR2B/Fc. The metabolic profiles demonstrated large effects with Folfiri treatment and much weaker effects with ACVR2B/Fc treatment. Interestingly, a number of significant effects were observed in the co-treatment group, with the addition of ACVR2B/Fc providing some level of rescue to the perturbations induced by Folfiri alone. The most prominent of these were a normalization of systemic glucose and lipid metabolism. Identification of these pathways provides important insights into the mechanism by which ACVR2B/Fc protects against chemotherapy-induced cachexia.

Mitophagy in Cancer: A Tale of Adaptation

：In the past years, we have learnt that tumors co-evolve with their microenvironment, and that the active interaction between cancer cells and stromal cells plays a pivotal role in cancer initiation, progression and treatment response. Among the players involved, the pathways regulating mitochondrial functions have been shown to be crucial for both cancer and stromal cells. This is perhaps not surprising, considering that mitochondria in both cancerous and non-cancerous cells are decisive for vital metabolic and bioenergetic functions and to elicit cell death. The central part played by mitochondria also implies the existence of stringent mitochondrial quality control mechanisms, where a specialized autophagy pathway (mitophagy) ensures the selective removal of damaged or dysfunctional mitochondria. Although the molecular underpinnings of mitophagy regulation in mammalian cells remain incomplete, it is becoming clear that mitophagy pathways are intricately linked to the metabolic rewiring of cancer cells to support the high bioenergetic demand of the tumor. In this review, after a brief introduction of the main mitophagy regulators operating in mammalian cells, we discuss emerging cell autonomous roles of mitochondria quality control in cancer onset and progression. We also discuss the relevance of mitophagy in the cellular crosstalk with the tumor microenvironment and in anti-cancer therapy responses.

Muscle and serum metabolomes are dysregulated in colon-26 tumor-bearing mice despite amelioration of cachexia with activin receptor type 2B ligand blockade

Cancer-associated cachexia reduces survival, which has been attenuated by blocking the activin receptor type 2B (ACVR2B) ligands in mice. The purpose of this study was to unravel the underlying physiology and novel cachexia biomarkers by use of the colon-26 (C26) carcinoma model of cancer cachexia. Male BALB/c mice were subcutaneously inoculated with C26 cancer cells or vehicle control. Tumor-bearing mice were treated with vehicle (C26+PBS) or soluble ACVR2B either before (C26+sACVR/b) or before and after (C26+sACVR/c) tumor formation. Skeletal muscle and serum metabolomics analysis was conducted by gas chromatography-mass spectrometry. Cancer altered various biologically functional groups representing 1) amino acids, 2) energy sources, and 3) nucleotide-related intermediates. Muscle metabolomics revealed increased content of free phenylalanine in cancer that strongly correlated with the loss of body mass within the last 2 days of the experiment. This correlation was also detected in serum. Decreased ribosomal RNA content and phosphorylation of a marker of pyrimidine synthesis revealed changes in nucleotide metabolism in cancer. Overall, the effect of the experimental C26 cancer predominated over blocking ACVR2B ligands in both muscle and serum. However, the level of methyl phosphate, which was decreased in muscle in cancer, was restored by sACVR2B-Fc treatment. In conclusion, experimental cancer affected muscle and blood metabolomes mostly independently of blocking ACVR2B ligands. Of the affected metabolites, we have identified free phenylalanine as a promising biomarker of muscle atrophy or cachexia. Finally, the decreased capacity for pyrimidine nucleotide and protein synthesis in tumor-bearing mice opens up new avenues in cachexia research.

Tissue-specific dysregulation of mitochondrial respiratory capacity and coupling control in colon-26 tumor-induced cachexia

In addition to skeletal muscle dysfunction, cancer cachexia is a systemic disease involving remodeling of nonmuscle organs such as adipose and liver. Impairment of mitochondrial function is associated with multiple chronic diseases. The tissue-specific control of mitochondrial function in cancer cachexia is not well defined. This study determined mitochondrial respiratory capacity and coupling control of skeletal muscle, white adipose tissue (WAT), and liver in colon-26 (C26) tumor-induced cachexia. Tissues were collected from PBS-injected weight-stable mice, C26 weight-stable mice and C26 mice with moderate (10% weight loss) and severe cachexia (20% weight loss). The respiratory control ratio [(RCR) an index of oxidative phosphorylation (OXPHOS) coupling efficiency] was low in WAT during the induction of cachexia because of high nonphosphorylating LEAK respiration. Liver RCR was low in C26 weight-stable and moderately cachexic mice because of reduced OXPHOS. Liver RCR was further reduced with severe cachexia, where Ant2 but not Ucp2 expression was increased. Ant2 was inversely correlated with RCR in the liver (r = -0.547, P < 0.01). Liver cardiolipin increased in moderate and severe cachexia, suggesting this early event may also contribute to mitochondrial uncoupling. Impaired skeletal muscle mitochondrial respiration occurred predominantly in severe cachexia, at complex I. These findings suggest that mitochondrial function is subject to tissue-specific control during cancer cachexia, whereby remodeling in WAT and liver arise early and may contribute to altered energy balance, followed by impaired skeletal muscle respiration. We highlight an under-recognized role of liver and WAT mitochondrial function in cancer cachexia and suggest mitochondrial function of multiple tissues to be therapeutic targets.

The AMPK agonist 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), but not metformin, prevents inflammation-associated cachectic muscle wasting

Activation of AMPK has been associated with pro-atrophic signaling in muscle. However, AMPK also has anti-inflammatory effects, suggesting that in cachexia, a syndrome of inflammatory-driven muscle wasting, AMPK activation could be beneficial. Here we show that the AMPK agonist AICAR suppresses IFNγ/TNFα-induced atrophy, while the mitochondrial inhibitor metformin does not. IFNγ/TNFα impair mitochondrial oxidative respiration in myotubes and promote a metabolic shift to aerobic glycolysis, similarly to metformin. In contrast, AICAR partially restored metabolic function. The effects of AICAR were prevented by the AMPK inhibitor Compound C and were reproduced with A-769662, a specific AMPK activator. AICAR and A-769662 co-treatment was found to be synergistic, suggesting that the anti-cachectic effects of these drugs are mediated through AMPK activation. AICAR spared muscle mass in mouse models of cancer and LPS induced atrophy. Together, our findings suggest a dual function for AMPK during inflammation-driven atrophy, wherein it can play a protective role when activated exogenously early in disease progression, but may contribute to anabolic suppression and atrophy when activated later through mitochondrial dysfunction and subsequent metabolic stress.

Colon 26 adenocarcinoma (C26)-induced cancer cachexia impairs skeletal muscle mitochondrial function and content

The present study aimed to determine the impact of colon 26 adenocarcinoma (C26)-induced cancer cachexia on skeletal muscle mitochondrial respiration and content. Twelve male CD2F1 mice were injected with C26-cells (tumor bearing (TB) group), whereas 12 age-matched mice received PBS vehicle injection (non-tumor bearing (N-TB) group). Mitochondrial respiration was studied in saponin-permeabilized soleus myofibers. TB mice showed lower body weight (~ 20%) as well as lower soleus, gastrocnemius-plantaris complex and tibialis anterior masses versus N-TB mice (p < 0.05). Soleus maximal state III mitochondrial respiration was 20% lower (10 mM glutamate, 5 mM malate, 5 mM adenosine diphosphate; p < 0.05) and acceptor control ratio (state III/state II) was 15% lower in the TB vs. N-TB (p < 0.05), with the latter suggesting uncoupling. Lower VDAC protein content suggested reduced mitochondrial content in TB versus N-TB (p < 0.05). Skeletal muscle in C26-induced cancer cachexia exhibits reductions in: maximal mitochondrial respiration capacity, mitochondrial coupling and mitochondrial content.

Mediators of cachexia in cancer patients

Alterations in amino acid and protein metabolism-particularly in skeletal muscle-are a key feature of cancer that contributes to the cachexia syndrome. Thus, skeletal muscle protein turnover is characterized by an exacerbated rate of protein degradation, promoted by an activation of different proteolytic systems that include the ubiquitin-proteasome and the autophagic-lysosomal pathways. These changes are promoted by both hormonal alterations and inflammatory mediators released as a result of the systemic inflammatory response induced by the tumor. Other events, such as alterations in the rate of myogenesis/apoptosis and decreased regeneration potential also affect skeletal muscle in patients with cancer. Mitochondrial dysfunction also contributes to changes in skeletal muscle metabolism and further contributes to the exacerbation of the cancer-wasting syndrome. Different inflammatory mediators-either released by the tumor or by the patient's healthy cells-are responsible for the activation of these catabolic processes that take place in skeletal muscle and in other tissues/organs, such as liver or adipose tissues. Indeed, white adipose tissue is also subject to extensive wasting and "browning" of some of the white adipocytes into beige cells; therefore increasing the energetic inefficiency of the patient with cancer. Recently, an interest in the role of micromRNAs-either free or transported into exosomes-has been related to the events that take place in white adipose tissue during cancer cachexia.

PDK4 drives metabolic alterations and muscle atrophy in cancer cachexia

Cachexia is frequently accompanied by severe metabolic derangements, although the mechanisms responsible for this debilitating condition remain unclear. Pyruvate dehydrogenase kinase (PDK)4, a critical regulator of cellular energetic metabolism, was found elevated in experimental models of cancer, starvation, diabetes, and sepsis. Here we aimed to investigate the link between PDK4 and the changes in muscle size in cancer cachexia. High PDK4 and abnormal energetic metabolism were found in the skeletal muscle of colon-26 tumor hosts, as well as in mice fed a diet enriched in Pirinixic acid, previously shown to increase PDK4 levels. Viral-mediated PDK4 overexpression in myotube cultures was sufficient to promote myofiber shrinkage, consistent with enhanced protein catabolism and mitochondrial abnormalities. On the contrary, blockade of PDK4 was sufficient to restore myotube size in C2C12 cultures exposed to tumor media. Our data support, for the first time, a direct role for PDK4 in promoting cancer-associated muscle metabolic alterations and skeletal muscle atrophy.-Pin, F., Novinger, L. J., Huot, J. R., Harris, R. A., Couch, M. E., O'Connell, T. M., Bonetto, A. PDK4 drives metabolic alterations and muscle atrophy in cancer cachexia.

The Skeletal Muscle as an Active Player Against Cancer Cachexia

The management of cancer patients is frequently complicated by the occurrence of cachexia. This is a complex syndrome that markedly impacts on quality of life as well as on tolerance and response to anticancer treatments. Loss of body weight, wasting of both adipose tissue and skeletal muscle and reduced survival rates are among the main features of cachexia. Skeletal muscle wasting has been shown to depend, mainly at least, on the induction of protein degradation rates above physiological levels. Such hypercatabolic pattern is driven by overactivation of different intracellular proteolytic systems, among which those dependent on ubiquitin-proteasome and autophagy. Selective rather than bulk degradation of altered proteins and organelles was also proposed to occur. Within the picture described above, the muscle is frequently considered a sort of by-stander tissue where external stimuli, directly or indirectly, can poise protein metabolism toward a catabolic setting. By contrast, several observations suggest that the muscle reacts to the wasting drive imposed by cancer growth by activating different compensatory strategies that include anabolic capacity, the activation of autophagy and myogenesis. Even if muscle response is eventually ill-fated, its occurrence supports the idea that in the presence of appropriate treatments the development of cancer-induced wasting might not be an ineluctable event in tumor hosts.

Cachexia induced by cancer and chemotherapy yield distinct perturbations to energy metabolism

BACKGROUND

Cancer cachexia is a metabolic disorder involving perturbed energy balance and altered mitochondrial function. Chemotherapy is a primary treatment option for many types of cancer, but there is substantial evidence that some chemotherapeutic agents can also lead to the development and progression of cachexia. In this study, we apply a comprehensive and systems level metabolomics approach to characterize the metabolic perturbations in murine models of cancer-induced and chemotherapy-induced cachexia. Knowledge of the unique pathways through which cancer and chemotherapy drive cachexia is necessary in order to develop effective treatments.

METHODS

The murine Colon26 (C26) adenocarcinoma xenograft model was used to study the metabolic derangements associated with cancer-induced cachexia. In vivo administration of Folfiri (5-fluorouracil, irinotecan, and leucovorin) was used to model chemotherapy-induced cachexia. Comprehensive metabolic profiling was carried out using both nuclear magnetic resonance-based and mass spectrometry-based platforms. Analyses included plasma, muscle, and liver tissue to provide a systems level profiling.

RESULTS

The study involved four groups of CD2F1 male mice (n = 4-5), including vehicle treated (V), C26 tumour hosts (CC), Folfiri treated (F), and C26 tumour hosts treated with Folfiri (CCF). Significant weight loss including skeletal muscle was observed for each of the experimental groups with the tumour hosts showing the most dramatic change (-3.74 g vs. initial body weight in the CC group). Skeletal muscle loss was evident in all experimental groups compared with V, with the CCF combination resulting in the most severe depletion of quadriceps mass (-38% vs. V; P < 0.001). All experimental groups were characterized by an increased systemic glucose demand as evidenced by decreased levels of circulating glucose (-47% in CC vs. V; P < 0.001) and depletion of liver glucose (-51% in CC vs. V; P < 0.001) and glycogen (-74% in CC vs. V; P < 0.001). The cancer-induced and chemotherapy-induced cachexia models displayed unique alterations in flux through the tricarboxylic acid cycle and β-oxidation pathways. Cancer-induced cachexia was uniquely characterized by a dramatic elevation in low-density lipoprotein particles (+6.9-fold vs. V; P < 0.001) and a significant increase in the inflammatory marker, GlycA (+33% vs. V; P < 0.001).

CONCLUSIONS

The results of this study demonstrated for the first time that cancer-induced and chemotherapy-induced cachexia is characterized by a number of distinct metabolic derangements. Effective therapeutic interventions for cancer-induced and chemotherapy-induced cachexia must take into account the specific metabolic defects imposed by the pathological or pharmacological drivers of cachexia.

Assessing Metabolic Dysregulation in Muscle During Cachexia

Cancer cachexia is a metabolic disease characterized by a negative energy balance associated with systemic weight loss and poor quality of life.In particular, skeletal muscle, which represents almost 50% of the total body mass, is strongly affected, and metabolic alterations therein (e.g., insulin resistance and mitochondrial dysfunction) can eventually support tumor growth by facilitating nutrient scavenging by the growing mass. Interestingly, metabolic interventions on wasting muscle have been proven to be protective, advocating for the importance of metabolic regulation in the wasting muscle.Here, we will briefly define the current knowledge of metabolic regulation in cachexia and provide a protocol to grow and differentiate in vitro myotubes for the assessment of mitochondrial metabolism during cachexia.

Dysregulation of metabolic-associated pathways in muscle of breast cancer patients: preclinical evaluation of interleukin-15 targeting fatigue

BACKGROUND

Breast cancer patients report a perception of increased muscle fatigue, which can persist following surgery and standardized therapies. In a clinical experiment, we tested the hypothesis that pathways regulating skeletal muscle fatigue are down-regulated in skeletal muscle of breast cancer patients and that different muscle gene expression patterns exist between breast tumour subtypes. In a preclinical study, we tested the hypothesis that mammary tumour growth in mice induces skeletal muscle fatigue and that overexpression of the cytokine interleukin-15 (IL-15) can attenuate mammary tumour-induced muscle fatigue.

METHODS

Early stage non-metastatic female breast cancer patients (n = 14) and female non-cancer patients (n = 6) provided a muscle biopsy of the pectoralis major muscle during mastectomy, lumpectomy, or breast reconstruction surgeries. The breast cancer patients were diagnosed with either luminal (ER⁺ /PR⁺ , n = 6), triple positive (ER⁺ /PR⁺ /Her2/neu⁺ , n = 5), or triple negative (ER^- /PR^- /Her2/neu^- , n = 3) breast tumours and were being treated with curative intent either with neoadjuvant chemotherapy followed by surgery or surgery followed by standard post-operative therapy. Biopsies were used for RNA-sequencing to compare the skeletal muscle gene expression patterns between breast cancer patients and non-cancer patients. The C57BL/6 mouse syngeneic mammary tumour cell line, E0771, was used to induce mammary tumours in immunocompetent mice, and isometric muscle contractile properties and fatigue properties were analysed following 4 weeks of tumour growth.

RESULTS

RNA-sequencing and subsequent bioinformatics analyses revealed a dysregulation of canonical pathways involved in oxidative phosphorylation, mitochondrial dysfunction, peroxisome proliferator-activated receptor signalling and activation, and IL-15 signalling and production. In a preclinical mouse model of breast cancer, the rate of muscle fatigue was greater in mice exposed to mammary tumour growth for 4 weeks, and this greater muscle fatigue was attenuated in transgenic mice that overexpressed the cytokine IL-15.

CONCLUSIONS

Our data identify novel genes and pathways dysregulated in the muscles of breast cancer patients with early stage non-metastatic disease, with particularly aberrant expression among genes that would predispose these patients to greater muscle fatigue. Furthermore, we demonstrate that IL-15 overexpression can attenuate muscle fatigue associated with mammary tumour growth in a preclinical mouse model of breast cancer. Therefore, we propose that skeletal muscle fatigue is an inherent consequence of breast tumour growth, and this greater fatigue can be targeted therapeutically.

Mitochondrial dynamics in cancer-induced cachexia

Cancer-induced cachexia has a negative impact on quality of life and adversely affects therapeutic outcomes and survival rates. It is characterized by, often severe, loss of muscle, with or without loss of fat mass. Insight in the pathophysiology of this complex metabolic syndrome and direct treatment options are still limited, which creates a research demand. Results from recent studies point towards a significant involvement of muscle mitochondrial networks. However, data are scattered and a comprehensive overview is lacking. This paper aims to fill existing knowledge gaps by integrating published data sets on muscle protein or gene expression from cancer-induced cachexia animal models. To this end, a database was compiled from 94 research papers, comprising 11 different rodent models. This was combined with four genome-wide transcriptome datasets of cancer-induced cachexia rodent models. Analysis showed that the expression of genes involved in mitochondrial fusion, fission, ATP production and mitochondrial density is decreased, while that of genes involved ROS detoxification and mitophagy is increased. Our results underline the relevance of including post-translational modifications of key proteins involved in mitochondrial functioning in future studies on cancer-induced cachexia.

The High Costs of Low-Grade Inflammation: Persistent Fatigue as a Consequence of Reduced Cellular-Energy Availability and Non-adaptive Energy Expenditure

Chronic or persistent fatigue is a common, debilitating symptom of several diseases. Persistent fatigue has been associated with low-grade inflammation in several models of fatigue, including cancer-related fatigue and chronic fatigue syndrome. However, it is unclear how low-grade inflammation leads to the experience of fatigue. We here propose a model of an imbalance in energy availability and energy expenditure as a consequence of low-grade inflammation. In this narrative review, we discuss how chronic low-grade inflammation can lead to reduced cellular-energy availability. Low-grade inflammation induces a metabolic switch from energy-efficient oxidative phosphorylation to fast-acting, but less efficient, aerobic glycolytic energy production; increases reactive oxygen species; and reduces insulin sensitivity. These effects result in reduced glucose availability and, thereby, reduced cellular energy. In addition, emerging evidence suggests that chronic low-grade inflammation is associated with increased willingness to exert effort under specific circumstances. Circadian-rhythm changes and sleep disturbances might mediate the effects of inflammation on cellular-energy availability and non-adaptive energy expenditure. In the second part of the review, we present evidence for these metabolic pathways in models of persistent fatigue, focusing on chronic fatigue syndrome and cancer-related fatigue. Most evidence for reduced cellular-energy availability in relation to fatigue comes from studies on chronic fatigue syndrome. While the mechanistic evidence from the cancer-related fatigue literature is still limited, the sparse results point to reduced cellular-energy availability as well. There is also mounting evidence that behavioral-energy expenditure exceeds the reduced cellular-energy availability in patients with persistent fatigue. This suggests that an inability to adjust energy expenditure to available resources might be one mechanism underlying persistent fatigue.