Extracellular Vesicles and Exosomes in the Control of the Musculoskeletal Health.

PURPOSE OF REVIEW: The present review will highlight recent reports supporting the relevance of extracellular vesicles to the musculoskeletal system in health and disease. RECENT FINDINGS: Preserving the health of the musculoskeletal system is important to maintain a good quality of life, and the bone-muscle crosstalk is crucial in this regard. This latter is largely mediated by extracellular vesicles released by the different cell populations residing in muscle and bone, which deliver cargoes, microRNAs, and proteins being the most relevant ones, to target cells. Extracellular vesicles could be exploited as therapeutic tools, in view of their resistance to destruction in the biological fluid and of the possibility to be functionalized according to the need. Extracellular vesicles are recognized as crucial players in the bone-muscle cross-talk. Additional studies however are required to refine their use as biomarkers of early alterations of the musculoskeletal system, and as potential therapeutic tools.

Liquid Biopsy for Cancer Cachexia: Focus on Muscle-Derived microRNAs.

Cancer cachexia displays a complex nature in which systemic inflammation, impaired energy metabolism, loss of muscle and adipose tissues result in unintentional body weight loss. Cachectic patients have a poor prognosis and the presence of cachexia reduces the tolerability of chemo/radio-therapy treatments and it is frequently the primary cause of death in advanced cancer patients. Early detection of this condition could make treatments more effective. However, early diagnostic biomarkers of cachexia are currently lacking. In recent years, although solid biopsy still remains the "gold standard" for diagnosis of cancer, liquid biopsy is gaining increasing interest as a source of easily accessible potential biomarkers. Moreover, the growing interest in circulating microRNAs (miRNAs), has made these molecules attractive for the diagnosis of several diseases, including cancer. Some muscle-derived circulating miRNA might play a pivotal role in the onset/progression of cancer cachexia. This topic is of great interest since circulating miRNAs might be easily detectable by means of liquid biopsies and might allow an early diagnosis of this syndrome. We here summarize the current knowledge on circulating muscular miRNAs involved in muscle atrophy, since they might represent easily accessible and promising biomarkers of cachexia.

Moderate exercise in mice improves cancer plus chemotherapy-induced muscle wasting and mitochondrial alterations.

Cancer cachexia is a multifactorial syndrome characterized by anorexia, body wasting, and muscle and adipose tissue loss, impairing patient's tolerance to anticancer treatments and survival. The aim of the present study was to compare the effects induced in mice by tumor growth alone (C26) or in combination with chemotherapy [C26 oxaliplatin and 5-fluorouracil (oxfu)] and to evaluate the potential of moderate exercise. Oxfu administration to C26 mice exacerbated muscle wasting and triggered autophagy or mitophagy, decreased protein synthesis, and induced mitochondrial alterations. Exercise in C26 oxfu mice counteracted the loss of muscle mass and strength, partially rescuing autophagy and mitochondrial function. Nevertheless, exercise worsened survival in C26 oxfu mice in late stages of cachexia. In summary, chemotherapy further impinges on cancer-induced alterations, worsening muscle wasting. An ideal multifactorial and early intervention to prevent cancer cachexia could take advantage of exercise, improving patient's energy metabolism, mobility, and quality of life.-Ballarò, R., Beltrà, M., De Lucia, S., Pin, F., Ranjbar, K., Hulmi, J. J., Costelli, P., Penna, F. Moderate exercise in mice improves cancer plus chemotherapy-induced muscle wasting and mitochondrial alterations.

Effects of chronic sugar consumption on lipid accumulation and autophagy in the skeletal muscle.

PURPOSE: In recent years, the increasing consumption of soft drinks containing high-fructose corn syrup or sucrose has caused a rise in fructose intake, which has been related to the epidemic of metabolic diseases. As fructose and glucose intake varies in parallel, it is still unclear what the effects of the increased consumption of the two single sugars are. In the present study, the impact of chronic consumption of glucose or fructose on skeletal muscle of healthy mice was investigated. METHODS: C57BL/6J male mice received water (C), 15 % fructose (ChF) or 15 % glucose (ChG) to drink for up to 7 months. Lipid metabolism and markers of inflammation and autophagy were assessed in gastrocnemius muscle. RESULTS: Increased body weight and gastrocnemius muscle mass, as well as circulating glucose, insulin, and lipid plasma levels were observed in sugar-drinking mice. Although triglycerides increased in the gastrocnemius muscle of both ChF and ChG mice (+32 and +26 %, vs C, respectively), intramyocellular lipids accumulated to a significantly greater extent in ChF than in ChG animals (ChF +10 % vs ChG). Such perturbations were associated with increased muscle interleukin-6 levels (threefold of C) and with the activation of autophagy, as demonstrated by the overexpression of LC3B-II (ChF, threefold and ChG, twofold of C) and beclin-1 (ChF, sevenfold and ChG, tenfold of C). CONCLUSIONS: The present results suggest that intramyocellular lipids and the pro-inflammatory signaling could contribute to the onset of insulin resistance and lead to the induction of autophagy, which could be an adaptive response to lipotoxicity.

Role of Inflammation in Muscle Homeostasis and Myogenesis.

Skeletal muscle mass is subject to rapid changes according to growth stimuli inducing both hypertrophy, through increased protein synthesis, and hyperplasia, activating the myogenic program. Muscle wasting, characteristic of several pathological states associated with local or systemic inflammation, has been for long considered to rely on the alteration of myofiber intracellular pathways regulated by both hormones and cytokines, eventually leading to impaired anabolism and increased protein breakdown. However, there are increasing evidences that even alterations of the myogenic/regenerative program play a role in the onset of muscle wasting, even though the precise mechanisms involved are far from being fully elucidated. The comprehension of the links potentially occurring between impaired myogenesis and increased catabolism would allow the definition of effective strategies aimed at counteracting muscle wasting. The first part of this review gives an overview of skeletal muscle intracellular pathways determining fiber size, while the second part considers the cells and the regulatory pathways involved in the myogenic program. In both parts are discussed the evidences supporting the role of inflammation in impairing muscle homeostasis and myogenesis, potentially determining muscle atrophy.

Autophagic degradation contributes to muscle wasting in cancer cachexia.

Muscle protein wasting in cancer cachexia is a critical problem. The underlying mechanisms are still unclear, although the ubiquitin-proteasome system has been involved in the degradation of bulk myofibrillar proteins. The present work has been aimed to investigate whether autophagic degradation also plays a role in the onset of muscle depletion in cancer-bearing animals and in glucocorticoid-induced atrophy and sarcopenia of aging. The results show that autophagy is induced in muscle in three different models of cancer cachexia and in glucocorticoid-treated mice. In contrast, autophagic degradation in the muscle of sarcopenic animals is impaired but can be reactivated by calorie restriction. These results further demonstrate that different mechanisms are involved in pathologic muscle wasting and that autophagy, either excessive or defective, contributes to the complicated network that leads to muscle atrophy. In this regard, particularly intriguing is the observation that in cancer hosts and tumor necrosis factor α-treated C2C12 myotubes, insulin can only partially blunt autophagy induction. This finding suggests that autophagy is triggered through mechanisms that cannot be circumvented by using classic upstream modulators, prompting us to identify more effective approaches to target this proteolytic system.

Coming back: autophagy in cachexia.

PURPOSE OF REVIEW: Cachexia is a complex syndrome characterized by body weight loss, tissue wasting, systemic inflammation, metabolic abnormalities, and altered nutritional status. One of the most prominent features of cachexia is the loss of muscle mass, mainly because of increased protein degradation rates. This review is aimed at discussing the involvement of autophagy in the pathogenesis of muscle wasting in cachexia. RECENT FINDINGS: Modulations of muscle mass in the adult reflect an imbalance between protein synthesis and degradation rates. Muscle depletion in cachexia is associated with increased protein breakdown, mainly involving the pathways dependent on ubiquitin-proteasome and autophagy-lysosomes. This latter, in particular, was considered not relevant for a long time. Just in the last years, autophagy was shown to contribute to the pathogenesis of muscle wasting not only in myopathies because of intrinsic muscle defects, but also in muscle depletion associated with conditions such as sepsis, chronic obstructive pulmonary disease, glucocorticoid treatment, cancer cachexia, and aging. SUMMARY: The present review highlights that both excess and defective autophagy are relevant to the onset of muscle depletion, and draws some considerations about possible therapeutic intervention aimed at modulating autophagy in order to improve muscle trophism. VIDEO ABSTRACT: http://links.lww.com/COCN/A5.

Oleocanthal Protects C2C12 Myotubes against the Pro-Catabolic and Anti-Myogenic Action of Stimuli Able to Induce Muscle Wasting In Vivo.

Oleocanthal (OC) is a monophenol of extra-virgin olive oil (EVOO) endowed with antibiotic, cardioprotective and anticancer effects, among others, mainly in view of its antioxidant and anti-inflammatory properties. OC has been largely investigated in terms of its anticancer activity, in Alzheimer disease and in collagen-induced arthritis; however, the possibility that it can also affect muscle biology has been totally overlooked so far. This study is the first to describe that OC modulates alterations induced in C2C12 myotubes by stimuli known to induce muscle wasting in vivo, namely TNF-α, or in the medium conditioned by the C26 cachexia-inducing tumor (CM-C26). C2C12 myotubes were exposed to CM-C26 or TNF-α in the presence or absence of OC for 24 and 48 h and analyzed by immunofluorescence and Western blotting. In combination with TNF-α or CM-C26, OC was revealed to be able to restore both the myotube's original size and morphology and normal levels of both atrogin-1 and MuRF1. OC seems unable to impinge on the autophagic-lysosomal proteolytic system or protein synthesis. Modulations towards normal levels of the expression of molecules involved in myogenesis, such as Pax7, myogenin and MyHC, were also observed in the myotube cultures exposed to OC and TNF-α or CM-C26. In conclusion, the data presented here show that OC exerts a protective action in C2C12 myotubes exposed to TNF-α or CM-C26, with mechanisms likely involving the downregulation of ubiquitin-proteasome-dependent proteolysis and the partial relief of myogenic differentiation impairment.

Erythropoietin administration partially prevents adipose tissue loss in experimental cancer cachexia models.

Cancer-associated cachexia is characterized, among other symptoms, by a dramatic loss of both muscle and fat. In addition, the cachectic syndrome is often associated with anemia. The object of the present investigation was to assess the effects of erythropoietin (EPO) treatment on experimental cancer cachexia models. The results clearly show that, in addition to the improvement of the hematocrit, EPO treatment promoted a partial preservation of adipose tissue while exerting negligible effects on muscle loss. Administration of EPO to tumor-bearing animals resulted in a significant increase of lipoprotein lipase (LPL) activity in adipose tissue, suggesting that the treatment favored triacylglycerol (TAG) accumulation in the adipose tissue. In vitro experiments using both adipose tissue slices and 3T3-L1 adipocytes suggests that EPO is able to increase the lipogenic rate through the activation of its specific receptor (EPOR). This metabolic pathway, in addition to TAG uptake by LPL, may contribute to the beneficial effects of EPO on fat preservation in cancer cachexia.

Early changes of muscle insulin-like growth factor-1 and myostatin gene expression in gastric cancer patients.

INTRODUCTION: Cachexia increases morbidity and mortality of cancer patients. The progressive loss of muscle mass negatively affects physical function and quality of life. We previously showed reduced muscle insulin-like growth factor-1 (IGF-1) expression and enhanced myostatin signaling in tumor-bearing animals. This study was aimed at investigating whether similar perturbations occur in gastric cancer patients. METHODS: Early perturbations of myostatin and IGF-1 signaling (including the expression of muscle-specific ubiquitin ligases) were investigated in 16 gastric cancer patients and in 6 controls by analyzing muscle mRNA expression with semiquantitative reverse transcriptase polymerase chain reaction (PCR) and real-time PCR. RESULTS: In gastric cancer patients, muscle mRNA levels for IGF-1, myostatin, and atrogin-1 were reduced irrespective of weight loss (≤5% or >5%), whereas MuRF1 expression was unchanged. CONCLUSIONS: IGF-1 and myostatin mRNA levels are downregulated in gastric cancer patients who have minimal or no weight loss. These early alterations are particularly relevant in order to devise preventive and therapeutic strategies for cancer cachexia.

MuRF-1 and p-GSK3ß expression in muscle atrophy of cirrhosis.

BACKGROUND: Chronic diseases, including cirrhosis, are often accompanied by protein-energy malnutrition and muscle loss, which in turn negatively affect quality of life, morbidity and mortality. Unlike other chronic conditions, few data are available on the molecular mechanisms underlying muscle wasting in this clinical setting. AIMS: To assess mechanisms of muscle atrophy in patients with cirrhosis. METHODS: Nutritional [subjective global assessment (SGA) and anthropometry] and metabolic assessment was performed in 30 cirrhotic patients awaiting liver transplantation. Rectus abdominis biopsies were obtained intraoperatively in 22 cirrhotic patients and in 10 well-nourished subjects undergoing elective surgery for non-neoplastic disease, as a control group. Total RNA was extracted and mRNA for atrogenes (MuRF-1, Atrogin-1/MAFbx), myostatin (MSTN), GSK3ß and IGF-1 was assayed. RESULTS: A total of 50% of cirrhotic patients were malnourished based on SGA, while 53% were muscle-depleted according to mid-arm muscle area (MAMA<5th percentile). MuRF-1 RNA expression was significantly increased in malnourished cirrhotic patients (SGA-B/C) vs. well-nourished patients (SGA-A) (P = 0.01). The phosphorylation of GSK3ß was up-regulated in cirrhotic patients with hepatocellular carcinoma (HCC) vs. patients without tumour (P < 0.05). CONCLUSIONS: Muscle loss is frequently found in end-stage liver disease patients. Molecular factors pertaining to signalling pathways known to be involved in the regulation of muscle mass are altered during cirrhosis and HCC.

Pharmacotherapeutic options for cancer cachexia: emerging drugs and recent approvals.

INTRODUCTION: Cachexia is a complex multi-factorial syndrome characterized by anorexia, inflammation, body, and skeletal muscle wasting. Early diagnosis and intervention via a multimodal approach combining nutritional counseling, exercise, and pharmacological agents is advisable. However, no effective treatment options are currently available in the clinical setting. AREAS COVERED: The present work is a review of emerging treatment options for cancer cachexia, including mainly, but not only, pharmacological approaches. The main interest is on drugs currently investigated in clinical trials; however, promising pre-clinical options are presented as well. Data were collected using PubMed and ClinicalTrials.gov databases, including studies of the last 20 years and active clinical trials. EXPERT OPINION: The lack of effective therapeutic approaches against cachexia results from several issues, among which a reduced number of studies focused on new drugs. Furthermore, the translation of pre-clinical results in the clinical practice is a hard mission, and it must be considered whether drugs target cachexia as a consequence of acting directly on the tumor. Indeed, dissecting antineoplastics from direct anti-cachexia effects is needed to elucidate the mechanisms of action of specific drugs. This is necessary for their inclusion into multimodal approaches, which nowadays are considered the best way to tackle cachexia.

Small non-coding RNA profiling in patients with gastrointestinal cancer.

BACKGROUND: Small non-coding (snc)RNAs, including microRNAs and P-element induced wimpy testis (PIWI)-interacting-RNAs (piRNAs), crucially regulate gene expression in both physiological and pathological conditions. In particular, some muscle-specific microRNAs (myomiRs) have been involved in the pathogenesis of cancer-induced muscle wasting. The aims of the present study were (i) to profile sncRNAs in both skeletal muscle and plasma of gastrointestinal cancer patients and (ii) to investigate the association among differentially expressed sncRNAs and the level of muscularity at body composition analysis. METHODS: Surgical patients with gastrointestinal cancer or benign disease were recruited. Blood samples and muscle biopsies (rectus abdominis) were collected during surgery. Low muscularity patients were those at the lowest tertile of skeletal muscle index (SMI; CT-scan), whereas moderate/high muscularity patients were in the middle and highest SMI tertiles. SncRNAs in the muscle were assessed by RNAseq, circulating microRNAs were evaluated by qPCR. RESULTS: Cancer patients (n = 25; 13 females, 52%) showed a mean age of 71.6 ± 11.2 years, a median body weight loss of 4.2% and a mean BMI of 27.0 ± 3.2 kg/m2 . Control group (n = 15; 9 females, 60%) showed a mean age 58.1 ± 13.9 years and a mean BMI of 28.0 ± 4.3 kg/m2 . In cancer patients, the median L3-SMI (cm2 /m2 ) was 42.52 (34.42; 49.07). Males showed a median L3-SMI of 46.08 (41.17-51.79) and females a median L3-SMI of 40.77 (33.73-42.87). Moderate-high and low muscularity groups included 17 and 8 patients, respectively. As for circulating microRNAs, miR-21-5p and miR-133a-3p were up-regulated in patients compared with controls, whereas miR-15b-5p resulted down-regulated in the same comparison (about 30% of control values). Sample clustering by muscularity and sex revealed increased miR-133a-3p and miR-206 only in moderate-high muscularity males. SncRNA profiling in the muscle identified 373 microRNAs and 190 piRNAs (72.5% and 18.7% of raw reads, respectively). As for microRNAs, 10 were up-regulated, and 56 were down-regulated in cancer patients versus controls. Among the 24 dysregulated piRNAs, the majority were down-regulated, including the top two most expressed piRNAs in the muscle (piR-12790 and piR-2106). Network analysis on validated mRNA targets of down-regulated microRNAs revealed miR-15b-5p, miR-106a-5p and miR-106b-5p as main interactors of genes related to ubiquitin ligase/transferase activities. CONCLUSIONS: These results show dysregulation of both muscle microRNAs and piRNAs in cancer patients compared with controls, the former following a sex-specific pattern. Changes in circulating microRNAs are associated with the degree of muscularity rather than body weight loss.

Point mutated caveolin-3 form (P104L) impairs myoblast differentiation via Akt and p38 signalling reduction, leading to an immature cell signature.

Unbalanced levels of caveolin-3 (Cav3) are involved in muscular disorders. In the present study we show that differentiation of immortalized myoblasts is affected by either lack or overexpression of Cav3. Nevertheless, depletion of Cav3 induced by delivery of the dominant-negative Cav3 (P104L) form elicited a more severe phenotype, characterized by the simultaneous attenuation of the Akt and p38 signalling networks, leading to an immature cell and molecular signature. Accordingly, differentiation of myoblasts harbouring Cav3 (P104L) was improved by countering the reduced Akt and p38 signalling network via administration of IGF-1 or trichostatin A. Furthermore, loss of Cav3 correlated with a deregulation of the TGF-ß-induced Smad2 and Erk1/2 pathways, confirming that Cav3 controls TGF-ß signalling at the plasma membrane. Overall, these data suggest that loss of Cav3, primarily causing attenuation of both Akt and p38 pathways, contributes to impair myoblast fusion.

Changes in myostatin signaling in non-weight-losing cancer patients.

BACKGROUND: Myostatin is a negative regulator of skeletal muscle mass. We recently demonstrated that myostatin expression is upregulated in an experimental model of cancer cachexia, suggesting that modulations of this pathway might play a pathogenic role in cancer-related muscle wasting. The present study was designed to investigate whether myostatin signaling is modulated in the muscle of non-weight-losing (nWL) patients with lung and gastric cancer. METHODS: Myostatin signaling was studied in muscle biopsies obtained during surgical procedure from nWL patients affected by gastric (n=16) or lung (n=17) cancer. Western blotting was applied to test both the total expression of myostatin and the expression of phosphorylated form of GSK-3beta and Smad2/3. RESULTS: In patients with gastric cancer, the expression of both myostatin and phosphorylated GSK-3beta (p-GSK3ß) were significantly increased. By contrast, in patients with lung cancer, myostatin levels were comparable to controls, whereas the expression of p-GSK3ß significantly decreased in patients with disease stage III/IV. CONCLUSIONS: Myostatin signaling is altered in nWL cancer patients. Different tumor types may give rise to different patterns of molecular changes within the muscle, which occur even before cachexia becomes clinically apparent.

Extracellular vesicles derived from tumour cells as a trigger of energy crisis in the skeletal muscle.

BACKGROUND: Cachexia, a syndrome frequently occurring in cancer patients, is characterized by muscle wasting, altered energy and protein metabolism and impaired myogenesis. Tumour-derived microvesicles (TMVs) containing proteins, messenger RNAs (mRNAs), and non-coding RNAs could contribute to cancer-induced muscle wasting. METHODS: Differential ultracentrifugation was used to isolate TMVs from the conditioned medium of Lewis lung carcinoma and C26 colon carcinoma cell cultures. TMVs were added to the culture medium of C2C12 myoblasts and myotubes for 24-48-72 h, and the effects on protein and energy metabolism were assessed. TMVs were also isolated from the blood of C26-bearing mice. MicroRNA (miR) profile of TMVs was obtained by RNA-seq and validated by digital drop PCR. Selected miRs were overexpressed in C2C12 myoblasts to assess the effects on myogenic differentiation. RESULTS: Differentiation was delayed in C2C12 myoblasts exposed to TMVs, according to reduced expression of myosin heavy chain (MyHC; about 62% of controls at Day 4) and myogenin (about 68% of controls at Day 4). As for myotubes, TMVs did not affect the expression of MyHC, while revealed able to modulate mitochondria and oxidative metabolism. Indeed, reduced mRNA levels of PGC-1α (C = 1 ± 0.2, TMV = 0.57 ± 0.06, normalized fold change, P < 0.05) and Cytochrome C (C = 1 ± 0.2, TMV = 0.65 ± 0.04, normalized fold change, P < 0.05), associated with increased BNIP3 expression (C = 1 ± 0.1, TMV = 1.29 ± 0.2, normalized fold change, P < 0.05), were observed, suggesting reduced mitochondrial biogenesis/amount and enhanced mitophagy. These changes were paralleled by decreased oxygen consumption (C = 686.9 ± 44 pmol/min, TMV = 552.25 ± 24 pmol/min, P < 0.01) and increased lactate levels (C = 0.0063 ± 0.00045 nmol/µL, TMV = 0.0094 ± 0.00087 nmol/µL, P < 0.01). A total of 118 miRs were found in MVs derived from the plasma of the C26 hosts; however, only three of them were down-regulated (RNA-seq): miR-181a-5p (-1.46 fold change), miR-375-3p (-2.52 fold change), and miR-455-5p (-3.87 fold change). No correlation could be observed among miRs in the MVs obtained from the blood of the C26 host and those released by C26 cells in the culture medium. Overexpression of miR-148a-3p and miR-181a-5p in C2C12 myoblasts revealed the ability to impinge on the mRNA levels of Myf5, Myog, and MyHC (Myh4 and Myh7). CONCLUSIONS: These results show that in C2C12 cultures, TMVs are able to affect both differentiation and the mitochondrial system. Such effects could be related to TMV-contained miRs.

PGC-1α in the myofibers regulates the balance between myogenic and adipogenic progenitors affecting muscle regeneration.

Skeletal muscle repair is accomplished by satellite cells (MuSCs) in cooperation with interstitial stromal cells (ISCs), but the relationship between the function of these cells and the metabolic state of myofibers remains unclear. This study reports an altered proportion of MuSCs and ISCs (including adipogenesis-regulatory cells; Aregs) induced by the transgenic overexpression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) in the myofibers (MCK-PGC-1α mice). Although PGC-1α-driven increase of MuSCs does not accelerate muscle regeneration, myogenic progenitors isolated from MCK-PGC-1α mice and transplanted into intact and regenerating muscles are more prone to fuse with recipient myofibers than those derived from wild-type donors. Moreover, both young and aged MCK-PGC-1α animals exhibit reduced perilipin-positive areas when challenged with an adipogenic stimulus, demonstrating low propensity to accumulate adipocytes within the muscle. Overall, these results unveil that increased PGC-1α expression in the myofibers favors pro-myogenic and anti-adipogenic cell populations in the skeletal muscle.

Glutamine prevents myostatin hyperexpression and protein hypercatabolism induced in C2C12 myotubes by tumor necrosis factor-α.

Depletion of skeletal muscle protein mainly results from enhanced protein breakdown, caused by activation of proteolytic systems such as the Ca2+-dependent and the ATP-ubiquitin-dependent ones. In the last few years, enhanced expression and bioactivity of myostatin have been reported in several pathologies characterized by marked skeletal muscle depletion. More recently, high myostatin levels have been associated with glucocorticoid-induced hypercatabolism. The search for therapeutical strategies aimed at preventing/correcting protein hypercatabolism has been directed to inhibit humoral mediators known for their pro-catabolic action, such as TNFα. The present study has been aimed to investigate the involvement of TNFα in the regulation of both myostatin expression and intracellular protein catabolism, and the possibility to interfere with such modulations by means of amino acid supplementation. For this purpose, C2C12 myotubes exposed to TNFα in the presence or in the absence of amino acid (glutamine or leucine) supplementation have been used. Myotube treatment with TNFα leads to both hyperexpression of the muscle-specific ubiquitin ligase atrogin-1, and enhanced activity of the Ca(2+)-dependent proteolytic system. These changes are associated with increased myostatin expression. Glutamine supplementation effectively prevents TNFα-induced muscle protein loss and restores normal myostatin levels. The results shown in the present study indicate a direct involvement of TNFα in the onset of myotube protein loss and in the perturbation of myostatin-dependent signaling. In addition, the protective effect exerted by glutamine suggests that amino acid supplementation could represent a possible strategy to improve muscle mass.

Mitochondrial Dysfunction in Cancer Cachexia: Impact on Muscle Health and Regeneration.

Cancer cachexia is a frequently neglected debilitating syndrome that, beyond representing a primary cause of death and cancer therapy failure, negatively impacts on patients' quality of life. Given the complexity of its multisystemic pathogenesis, affecting several organs beyond the skeletal muscle, defining an effective therapeutic approach has failed so far. Revamped attention of the scientific community working on cancer cachexia has focused on mitochondrial alterations occurring in the skeletal muscle as potential triggers of the complex metabolic derangements, eventually leading to hypercatabolism and tissue wasting. Mitochondrial dysfunction may be simplistically viewed as a cause of energy failure, thus inducing protein catabolism as a compensatory mechanism; however, other peculiar cachexia features may depend on mitochondria. On the one side, chemotherapy also impacts on muscle mitochondrial function while, on the other side, muscle-impaired regeneration may result from insufficient energy production from damaged mitochondria. Boosting mitochondrial function could thus improve the energetic status and chemotherapy tolerance, and relieve the myogenic process in cancer cachexia. In the present work, a focused review of the available literature on mitochondrial dysfunction in cancer cachexia is presented along with preliminary data dissecting the potential role of stimulating mitochondrial biogenesis via PGC-1α overexpression in distinct aspects of cancer-induced muscle wasting.

Control of Skeletal Muscle Atrophy Associated to Cancer or Corticosteroids by Ceramide Kinase.

Apart from cytokines and chemokines, sphingolipid mediators, particularly sphingosine-1-phosphate (S1P) and ceramide 1-phosphate (C1P), contribute to cancer and inflammation. Cancer, as well as other inflammatory conditions, are associated with skeletal muscle (SkM) atrophy, which is characterized by the unbalance between protein synthesis and degradation. Although the signaling pathways involved in SkM mass wasting are multiple, the regulatory role of simple sphingolipids is limited. Here, we report the impairment of ceramide kinase (CerK), the enzyme responsible for the phosphorylation of ceramide to C1P, associated with the accomplishment of atrophic phenotype in various experimental models of SkM atrophy: in vivo animal model bearing the C26 adenocarcinoma or Lewis lung carcinoma tumors, in human and murine SkM cells treated with the conditioned medium obtained from cancer cells or with the glucocorticoid dexamethasone. Notably, we demonstrate in all the three experimental approaches a drastic decrease of CerK expression. Gene silencing of CerK promotes the up-regulation of atrogin-1/MAFbx expression, which was also observed after cell treatment with C8-ceramide, a biologically active ceramide analogue. Conversely, C1P treatment significantly reduced the corticosteroid's effects. Altogether, these findings provide evidence that CerK, acting as a molecular modulator, may be a new possible target for SkM mass regulation associated with cancer or corticosteroids.