Macrophage-derived glutamine boosts satellite cells and muscle regeneration.

Muscle regeneration is sustained by infiltrating macrophages and the consequent activation of satellite cells1-4. Macrophages and satellite cells communicate in different ways1-5, but their metabolic interplay has not been investigated. Here we show, in a mouse model, that muscle injuries and ageing are characterized by intra-tissue restrictions of glutamine. Low levels of glutamine endow macrophages with the metabolic ability to secrete glutamine via enhanced glutamine synthetase (GS) activity, at the expense of glutamine oxidation mediated by glutamate dehydrogenase 1 (GLUD1). Glud1-knockout macrophages display constitutively high GS activity, which prevents glutamine shortages. The uptake of macrophage-derived glutamine by satellite cells through the glutamine transporter SLC1A5 activates mTOR and promotes the proliferation and differentiation of satellite cells. Consequently, macrophage-specific deletion or pharmacological inhibition of GLUD1 improves muscle regeneration and functional recovery in response to acute injury, ischaemia or ageing. Conversely, SLC1A5 blockade in satellite cells or GS inactivation in macrophages negatively affects satellite cell functions and muscle regeneration. These results highlight the metabolic crosstalk between satellite cells and macrophages, in which macrophage-derived glutamine sustains the functions of satellite cells. Thus, the targeting of GLUD1 may offer therapeutic opportunities for the regeneration of injured or aged muscles.

High-intensity interval training in hypoxia does not affect muscle HIF responses to acute hypoxia in humans.

PURPOSE: The myocellular response to hypoxia is primarily regulated by hypoxia-inducible factors (HIFs). HIFs thus conceivably are implicated in muscular adaptation to altitude training. Therefore, we investigated the effect of hypoxic versus normoxic training during a period of prolonged hypoxia ('living high') on muscle HIF activation during acute ischaemia. METHODS: Ten young male volunteers lived in normobaric hypoxia for 5 weeks (5 days per week, ~ 15.5 h per day, FiO2: 16.4-14.0%). One leg was trained in hypoxia (TRHYP, 12.3% FiO2) whilst the other leg was trained in normoxia (TRNOR, 20.9% FiO2). Training sessions (3 per week) consisted of intermittent unilateral knee extensions at 20-25% of the 1-repetition maximum. Before and after the intervention, a 10-min arterial occlusion and reperfusion of the leg was performed. Muscle oxygenation status was continuously measured by near-infrared spectroscopy. Biopsies were taken from m. vastus lateralis before and at the end of the occlusion. RESULTS: Irrespective of training, occlusion elevated the fraction of HIF-1α expressing myonuclei from ~ 54 to ~ 64% (P < 0.05). However, neither muscle HIF-1α or HIF-2α protein abundance, nor the expression of HIF-1α or downstream targets selected increased in any experimental condition. Training in both TRNOR and TRHYP raised muscular oxygen extraction rate upon occlusion by ~ 30%, whilst muscle hyperperfusion immediately following the occlusion increased by ~ 25% in either group (P < 0.05). CONCLUSION: Ten minutes of arterial occlusion increased HIF-1α-expressing myonuclei. However, neither normoxic nor hypoxic training during 'living high' altered muscle HIF translocation, stabilisation, or transcription in response to acute hypoxia induced by arterial occlusion.

Ether-Oxygen Containing Electrospun Microfibrous and Sub-Microfibrous Scaffolds Based on Poly(butylene 1,4-cyclohexanedicarboxylate) for Skeletal Muscle Tissue Engineering.

We report the study of novel biodegradable electrospun scaffolds from poly(butylene 1,4-cyclohexandicarboxylate-co-triethylene cyclohexanedicarboxylate) (P(BCE-co-TECE)) as support for in vitro and in vivo muscle tissue regeneration. We demonstrate that chemical composition, i.e., the amount of TECE co-units (constituted of polyethylene glycol-like moieties), and fibre morphology, i.e., aligned microfibrous or sub-microfibrous scaffolds, are crucial in determining the material biocompatibility. Indeed, the presence of ether linkages influences surface wettability, mechanical properties, hydrolytic degradation rate, and density of cell anchoring points of the studied materials. On the other hand, electrospun scaffolds improve cell adhesion, proliferation, and differentiation by favouring cell alignment along fibre direction (fibre morphology), also allowing for better cell infiltration and oxygen and nutrient diffusion (fibre size). Overall, C2C12 myogenic cells highly differentiated into mature myotubes when cultured on microfibres realised with the copolymer richest in TECE co-units (micro-P73 mat). Lastly, when transplanted in the tibialis anterior muscles of healthy, injured, or dystrophic mice, micro-P73 mat appeared highly vascularised, colonised by murine cells and perfectly integrated with host muscles, thus confirming the suitability of P(BCE-co-TECE) scaffolds as substrates for skeletal muscle tissue engineering.

Myogenic induction of adult and pluripotent stem cells using recombinant proteins.

Met Activating Genetically Improved Chimeric Factor 1 (Magic-F1) is a human recombinant protein, derived from dimerization of the receptor-binding domain of hepatocyte growth factor. Previous experiments demonstrate that in transgenic mice, the skeletal muscle specific expression of Magic-F1 can induce a constitutive muscular hypertrophy, improving running performance and accelerating muscle regeneration after injury. In order to evaluate the therapeutic potential of Magic-F1, we tested its effect on multipotent and pluripotent stem cells. In murine mesoangioblasts (adult vessel-associated stem cells), the presence of Magic-F1 did not alter their osteogenic, adipogenic or smooth muscle differentiation ability. However, when analyzing their myogenic potential, mesoangioblasts expressing Magic-F1 differentiated spontaneously into myotubes. Finally, Magic-F1 inducible cassette was inserted into a murine embryonic stem cell line by homologous recombination. When embryonic stem cells were subjected to myogenic differentiation, the presence of Magic-F1 resulted in the upregulation of Pax3 and Pax7 that enhanced the myogenic commitment of transgenic pluripotent stem cells. Taken together our results candidate Magic-F1 as a potent myogenic stimulator, able to enhance muscular differentiation from both adult and pluripotent stem cells.

Alpha sarcoglycan is required for FGF-dependent myogenic progenitor cell proliferation in vitro and in vivo.

Mice deficient in α-sarcoglycan (Sgca-null mice) develop progressive muscular dystrophy and serve as a model for human limb girdle muscular dystrophy type 2D. Sgca-null mice suffer a more severe myopathy than that of mdx mice, the model for Duchenne muscular dystrophy. This is the opposite of what is observed in humans and the reason for this is unknown. In an attempt to understand the cellular basis of this severe muscular dystrophy, we isolated clonal populations of myogenic progenitor cells (MPCs), the resident postnatal muscle progenitors of dystrophic and wild-type mice. MPCs from Sgca-null mice generated much smaller clones than MPCs from wild-type or mdx dystrophic mice. Impaired proliferation of Sgca-null myogenic precursors was confirmed by single fiber analysis and this difference correlated with Sgca expression during MPC proliferation. In the absence of dystrophin and associated proteins, which are only expressed after differentiation, SGCA complexes with and stabilizes FGFR1. Deficiency of Sgca leads to an absence of FGFR1 expression at the membrane and impaired MPC proliferation in response to bFGF. The low proliferation rate of Sgca-null MPCs was rescued by transduction with Sgca-expressing lentiviral vectors. When transplanted into dystrophic muscle, Sgca-null MPCs exhibited reduced engraftment. The reduced proliferative ability of Sgca-null MPCs explains, at least in part, the severity of this muscular dystrophy and also why wild-type donor progenitor cells engraft efficiently and consequently ameliorate disease.

PI3K/mTOR inhibition induces tumour microenvironment remodelling and sensitises pS6high uterine leiomyosarcoma to PD-1 blockade.

BACKGROUND: Uterine leiomyosarcomas (uLMS) are aggressive tumours with poor prognosis and limited treatment options. Although immune checkpoint blockade (ICB) has proven effective in some 'challenging-to-treat' cancers, clinical trials showed that uLMS do not respond to ICB. Emerging evidence suggests that aberrant PI3K/mTOR signalling can drive resistance to ICB. We therefore explored the relevance of the PI3K/mTOR pathway for ICB treatment in uLMS and explored pharmacological inhibition of this pathway to sensitise these tumours to ICB. METHODS: We performed an integrated multiomics analysis based on TCGA data to explore the correlation between PI3K/mTOR dysregulation and immune infiltration in 101 LMS. We assessed response to PI3K/mTOR inhibitors in immunodeficient and humanized uLMS patient-derived xenografts (PDXs) by evaluating tumour microenvironment modulation using multiplex immunofluorescence. We explored response to single-agent and a combination of PI3K/mTOR inhibitors with PD-1 blockade in humanized uLMS PDXs. We mapped intratumoural dynamics using single-cell RNA/TCR sequencing of serially collected biopsies. RESULTS: PI3K/mTOR over-activation (pS6high) associated with lymphocyte depletion and wound healing immune landscapes in (u)LMS, suggesting it contributes to immune evasion. In contrast, PI3K/mTOR inhibition induced profound tumour microenvironment remodelling in an ICB-resistant humanized uLMS PDX model, fostering adaptive anti-tumour immune responses. Indeed, PI3K/mTOR inhibition induced macrophage repolarisation towards an anti-tumourigenic phenotype and increased antigen presentation on dendritic and tumour cells, but also promoted infiltration of PD-1+ T cells displaying an exhausted phenotype. When combined with anti-PD-1, PI3K/mTOR inhibition led to partial or complete tumour responses, whereas no response to single-agent anti-PD-1 was observed. Combination therapy reinvigorated exhausted T cells and induced clonal hyper-expansion of a cytotoxic CD8+ T-cell population supported by a CD4+ Th1 niche. CONCLUSIONS: Our findings indicate that aberrant PI3K/mTOR pathway activation contributes to immune escape in uLMS and provides a rationale for combining PI3K/mTOR inhibition with ICB for the treatment of this patient population.

Nucleotide metabolism in cancer cells fuels a UDP-driven macrophage cross-talk, promoting immunosuppression and immunotherapy resistance.

Many individuals with cancer are resistant to immunotherapies. Here, we identify the gene encoding the pyrimidine salvage pathway enzyme cytidine deaminase (CDA) among the top upregulated metabolic genes in several immunotherapy-resistant tumors. We show that CDA in cancer cells contributes to the uridine diphosphate (UDP) pool. Extracellular UDP hijacks immunosuppressive tumor-associated macrophages (TAMs) through its receptor P2Y6. Pharmacologic or genetic inhibition of CDA in cancer cells (or P2Y6 in TAMs) disrupts TAM-mediated immunosuppression, promoting cytotoxic T cell entry and susceptibility to anti-programmed cell death protein 1 (anti-PD-1) treatment in resistant pancreatic ductal adenocarcinoma (PDAC) and melanoma models. Conversely, CDA overexpression in CDA-depleted PDACs or anti-PD-1-responsive colorectal tumors or systemic UDP administration (re)establishes resistance. In individuals with PDAC, high CDA levels in cancer cells correlate with increased TAMs, lower cytotoxic T cells and possibly anti-PD-1 resistance. In a pan-cancer single-cell atlas, CDAhigh cancer cells match with T cell cytotoxicity dysfunction and P2RY6high TAMs. Overall, we suggest CDA and P2Y6 as potential targets for cancer immunotherapy.

Substrains of inbred mice differ in their physical activity as a behavior.

Recent studies strengthen the belief that physical activity as a behavior has a genetic basis. Screening wheel-running behavior in inbred mouse strains highlighted differences among strains, showing that even very limited genetic differences deeply affect mouse behavior. We extended this observation to substrains of the same inbred mouse strain, that is, BALB/c mice. We found that only a minority of the population of one of these substrains, the BALB/c J, performs spontaneous physical activity. In addition, the runners of this substrain cover a significantly smaller distance than the average runners of two other substrains, namely, the BALB/c ByJ and the BALB/c AnNCrl. The latter shows a striking level of voluntary activity, with the average distance run/day reaching up to about 12 kilometers. These runners are not outstanders, but they represent the majority of the population, with important scientific and economic fallouts to be taken into account during experimental planning. Spontaneous activity persists in pathological conditions, such as cancer-associated cachexia. This important amount of physical activity results in a minor muscle adaptation to endurance exercise over a three-week period; indeed, only a nonsignificant increase in NADH transferase+ fibers occurs in this time frame.

Determination and risk assessment of phthalates in face masks. An Italian study.

Serious human health concerns have been recently raised from daily use of face masks, due to the possible presence of hazardous compounds as the phthalic acid esters (PAEs). In this study, the content of 11 PAEs in 35 commercial masks was assessed by applying a specific and accurate method, using Gas Chromatography/Mass Spectrometry. Surgical, FFP2 and non-surgical models, for both adults and children were collected from the Italian market. Analyses showed that four of the target analytes were detected in all tested samples with median total concentrations ranging between 23.6 mg/kg and 54.3 mg/kg. Results obtained from the experimental analysis were used in the risk assessment studies carried out for both carcinogenic and non-carcinogenic effects. Doses of exposure (Dexp) of PAEs ranged from 6.43 × 10-5 mg/kg bw/day to 1.43 × 10-2 mg/kg bw/day. Cumulative risk assessment was performed for non-carcinogenic and carcinogenic effects. No potential risk was found for non-carcinogenic effects, yet the 20% of the mask samples showed potential carcinogenic effects for humans. A refined exposure assessment was performed showing no risk for carcinogenic effects. This paper presents a risk assessment approach for the identification of potential risks associated to the use of face masks.

miRNAs in ESC differentiation.

MicroRNAs (miRNAs) are small sequences of noncoding RNAs that regulate gene expression by two basic processes: direct degradation of mRNA and translation inhibition. miRNAs are key molecules in gene regulation for embryonic stem cells, since they are able to repress target pluripotent mRNA genes, including Oct4, Sox2, and Nanog. miRNAs are unlike other small noncoding RNAs in their biogenesis, since they derive from precursors that fold back to form a distinctive hairpin structure, whereas other classes of small RNAs are formed from longer hairpins or bimolecular RNA duplexes (siRNAs) or precursors without double-stranded character (piRNAs). An increasing amount of evidence suggests that miRNAs may have a critical role in the maintenance of the pluripotent cell state and in the regulation of early mammalian development. This review gives an overview of the current state of the art of miRNA expression and regulation in embryonic stem cell differentiation. Current insights on controlling stem cell fate toward mesodermal, endodermal and ectodermal differentiation, and cell reprogramming are also highlighted.

Targeting the bicarbonate transporter SLC4A4 overcomes immunosuppression and immunotherapy resistance in pancreatic cancer.

Solid tumors are generally characterized by an acidic tumor microenvironment (TME) that favors cancer progression, therapy resistance and immune evasion. By single-cell RNA-sequencing analysis in individuals with pancreatic ductal adenocarcinoma (PDAC), we reveal solute carrier family 4 member 4 (SLC4A4) as the most abundant bicarbonate transporter, predominantly expressed by epithelial ductal cells. Functionally, SLC4A4 inhibition in PDAC cancer cells mitigates the acidosis of the TME due to bicarbonate accumulation in the extracellular space and a decrease in lactate production by cancer cells as the result of reduced glycolysis. In PDAC-bearing mice, genetic or pharmacological SLC4A4 targeting improves T cell-mediated immune response and breaches macrophage-mediated immunosuppression, thus inhibiting tumor growth and metastases. In addition, Slc4a4 targeting in combination with immune checkpoint blockade is able to overcome immunotherapy resistance and prolong survival. Overall, our data propose SLC4A4 as a therapeutic target to unleash an antitumor immune response in PDAC.

Serine metabolism remodeling after platinum-based chemotherapy identifies vulnerabilities in a subgroup of resistant ovarian cancers.

Resistance to platinum-based chemotherapy represents a major clinical challenge for many tumors, including epithelial ovarian cancer. Patients often experience several response-relapse events, until tumors become resistant and life expectancy drops to 12-15 months. Despite improved knowledge of the molecular determinants of platinum resistance, the lack of clinical applicability limits exploitation of many potential targets, leaving patients with limited options. Serine biosynthesis has been linked to cancer growth and poor prognosis in various cancer types, however its role in platinum-resistant ovarian cancer is not known. Here, we show that a subgroup of resistant tumors decreases phosphoglycerate dehydrogenase (PHGDH) expression at relapse after platinum-based chemotherapy. Mechanistically, we observe that this phenomenon is accompanied by a specific oxidized nicotinamide adenine dinucleotide (NAD+) regenerating phenotype, which helps tumor cells in sustaining Poly (ADP-ribose) polymerase (PARP) activity under platinum treatment. Our findings reveal metabolic vulnerabilities with clinical implications for a subset of platinum resistant ovarian cancers.

A Pound of Flesh: What Cachexia Is and What It Is Not.

Body weight loss, mostly due to the wasting of skeletal muscle and adipose tissue, is the hallmark of the so-called cachexia syndrome. Cachexia is associated with several acute and chronic disease states such as cancer, chronic obstructive pulmonary disease (COPD), heart and kidney failure, and acquired and autoimmune diseases and also pharmacological treatments such as chemotherapy. The clinical relevance of cachexia and its impact on patients' quality of life has been neglected for decades. Only recently did the international community agree upon a definition of the term cachexia, and we are still awaiting the standardization of markers and tests for the diagnosis and staging of cancer-related cachexia. In this review, we discuss cachexia, considering the evolving use of the term for diagnostic purposes and the implications it has for clinical biomarkers, to provide a comprehensive overview of its biology and clinical management. Advances and tools developed so far for the in vitro testing of cachexia and drug screening will be described. We will also evaluate the nomenclature of different forms of muscle wasting and degeneration and discuss features that distinguish cachexia from other forms of muscle wasting in the context of different conditions.

Molecular, cellular and physiological characterization of the cancer cachexia-inducing C26 colon carcinoma in mouse.

BACKGROUND: The majority of cancer patients experience dramatic weight loss, due to cachexia and consisting of skeletal muscle and fat tissue wasting. Cachexia is a negative prognostic factor, interferes with therapy and worsens the patients' quality of life by affecting muscle function. Mice bearing ectopically-implanted C26 colon carcinoma are widely used as an experimental model of cancer cachexia. As part of the search for novel clinical and basic research applications for this experimental model, we characterized novel cellular and molecular features of C26-bearing mice. METHODS: A fragment of C26 tumor was subcutaneously grafted in isogenic BALB/c mice. The mass growth and proliferation rate of the tumor were analyzed. Histological and cytofluorometric analyses were used to assess cell death, ploidy and differentiation of the tumor cells. The main features of skeletal muscle atrophy, which were highlighted by immunohistochemical and electron microscopy analyses, correlated with biochemical alterations. Muscle force and resistance to fatigue were measured and analyzed as major functional deficits of the cachectic musculature. RESULTS: We found that the C26 tumor, ectopically implanted in mice, is an undifferentiated carcinoma, which should be referred to as such and not as adenocarcinoma, a common misconception. The C26 tumor displays aneuploidy and histological features typical of transformed cells, incorporates BrdU and induces severe weight loss in the host, which is largely caused by muscle wasting. The latter appears to be due to proteasome-mediated protein degradation, which disrupts the sarcomeric structure and muscle fiber-extracellular matrix interactions. A pivotal functional deficit of cachectic muscle consists in increased fatigability, while the reported loss of tetanic force is not statistically significant following normalization for decreased muscle fiber size. CONCLUSIONS: We conclude, on the basis of the definition of cachexia, that ectopically-implanted C26 carcinoma represents a well standardized experimental model for research on cancer cachexia. We wish to point out that scientists using the C26 model to study cancer and those using the same model to study cachexia may be unaware of each other's works because they use different keywords; we present strategies to eliminate this gap and discuss the benefits of such an exchange of knowledge.

Skeletal muscle is enriched in hematopoietic stem cells and not inflammatory cells in cachectic mice.

OBJECTIVE: Cachexia, a debilitating syndrome characterized by skeletal muscle wasting, is associated to many chronic diseases and diminishes the quality of life and survival of patients. Tumor-derived factors and proinflammatory cytokines, including TNF-alpha, IL-6 and IL-1 beta, mediate cachexia. In response to elevated cytokine levels, increased proteasome-mediated proteolysis and auto-phagocytosis result in muscle wasting. The histologic features of muscle cachexia are not fully elucidated. Therefore, we analysed alterations of different cell populations in cachectic muscle. METHODS: By immunohistochemical and cytological approaches, we characterized changes in the abundance of cellular populations in the musculature of a murine model of cancer cachexia (C26-bearing mice). RESULTS: Cachectic muscle displayed a decreased DNA content proportional to muscle mass wastage. A decrease in the number of nuclei occurred in the muscular but not in the stromal compartment. Cachectic muscle showed: mild modulation of myeloperoxidase activity, a neutrophil marker; reduction of macrophages in the endomysium; decrease in CD3(+) lymphocyte number. Conversely, a statistically significant enrichment in Sca-1(+) CD45(+) hematopoietic stem cells (HSCs) occurred in cachectic muscle. DISCUSSION: The elevated levels of cytokines which characterize cachexia may represent a trigger for inflammatory cell activation. However, we find that in cachexia, inflammatory cells in muscle are not increased while muscle tissue nuclei decline. Our data suggest that the inflammatory cell-mediated stress is not an etiologic component of muscle wasting in cachexia. The relative increase in HSCs in cachectic skeletal muscle suggests an attempt to maintain muscle homeostasis by recruitment and/or activation of stem cells.

Differential modulation of PPARalpha and gamma target gene expression in the liver and kidney of rats treated with aspirin.

Aspirin modified peroxisomal enzymatic activities both in the liver and renal cortex of rats, producing typical effects of peroxisomal proliferators (PPs). Although similar increments in beta-oxidation system and catalase activities were observed in both organs, induction of mRNA-Cyp4a10 and mRNA-FAT/CD36, target genes for peroxisome proliferator-activated receptors alpha (PPARalpha) and gamma (PPARgamma), respectively, was only present in the liver. There was no effect on liver mRNA-PPARalpha, while mRNA-PPARgamma was down-regulated, probably as a result of enzymatic inhibition of cyclooxygenases (COXs) by aspirin which has been shown to decrease the levels of PGJ2 and its metabolites, known as strong endogenous ligands for PPARgamma. Typical PP alterations in cell replication and apoptosis were not found during aspirin treatment or after withdrawal, suggesting that peroxisome proliferation occurs without inducing cell cycle alterations. Probably, the synergic action of both PPARalpha and PPARgamma receptors might reduce the impact on cell proliferation and apoptosis.

A noninterfering system to measure in-cage spontaneous physical activity in mice.

Due to lack of low-cost and convenient measurement procedures, uncontrolled changes in spontaneous physical activity (SPA) level often are insufficiently considered as a confounding factor in rodent studies. Nonetheless, alterations in SPA can significantly impact on a wide range of physiological measurements. Therefore, we developed an accurate, low-cost video tracking procedure to allow routine assessment of SPA in the home cage of experimental animals (i.e., mice) and in the absence of any distress that might cause alterations in SPA. SPA parameters acquired (movement distance, movement time, and movement speed) with the novel tracking system were identical to those simultaneously obtained with a high-end and well-validated movement-tracking device (mean error = 0.15 ± 0.07%, r = 0.99, P < 0.001). To further validate the setup, we also demonstrated caffeine-induced stimulation of SPA (195% more activity compared with vehicle, P < 0.01), we adequately reproduced typical SPA fluctuations inherent to day/night cycles (146 and 702% more active during nocturnal compared with diurnal cycle for Balb/c and C57BL/6J mice, respectively, P < 0.001), and we confirmed previously documented SPA differences between animal strains (24% less activity in C57BL/6J mice compared with Balb/c mice, P < 0.05). Taken together, we provide data to prove that this novel low-cost methodology can be conveniently used in any mouse experiment where uncontrolled changes in SPA due to experimental interventions might confound data interpretation. By analogy, the system can be used to document a beneficial impact of therapeutic interventions on SPA in any disease mouse model. NEW & NOTEWORTHY We developed a low-cost procedure to routinely measure SPA in mice. The procedure maintains normal SPA because the animals continue to stay in their home cage in the absence of any external manipulation by the investigators and under habitual dark/light ambient conditions. This novel methodology can be conveniently used in any mouse experiment to quantify experimentally induced alterations in SPA or to assess natural variations in SPA that might confound data interpretation.

Spontaneous Physical Activity Downregulates Pax7 in Cancer Cachexia.

Emerging evidence suggests that the muscle microenvironment plays a prominent role in cancer cachexia. We recently showed that NF-kB-induced Pax7 overexpression impairs the myogenic potential of muscle precursors in cachectic mice, suggesting that lowering Pax7 expression may be beneficial in cancer cachexia. We evaluated the muscle regenerative potential after acute injury in C26 colon carcinoma tumor-bearing mice and healthy controls. Our analyses confirmed that the delayed muscle regeneration observed in muscles form tumor-bearing mice was associated with a persistent local inflammation and Pax7 overexpression. Physical activity is known to exert positive effects on cachectic muscles. However, the mechanism by which a moderate voluntary exercise ameliorates muscle wasting is not fully elucidated. To verify if physical activity affects Pax7 expression, we hosted control and C26-bearing mice in wheel-equipped cages and we found that voluntary wheel running downregulated Pax7 expression in muscles from tumor-bearing mice. As expected, downregulation of Pax7 expression was associated with a rescue of muscle mass and fiber size. Our findings shed light on the molecular basis of the beneficial effect exerted by a moderate physical exercise on muscle stem cells in cancer cachexia. Furthermore, we propose voluntary exercise as a physiological tool to counteract the overexpression of Pax7 observed in cancer cachexia.

Physical Activity Counteracts Tumor Cell Growth in Colon Carcinoma C26-Injected Muscles: An Interim Report.

Skeletal muscle tissue is a rare site of tumor metastasis but is the main target of the degenerative processes occurring in cancer-associated cachexia syndrome. Beneficial effects of physical activity in counteracting cancer-related muscle wasting have been described in the last decades. Recently it has been shown that, in tumor xeno-transplanted mouse models, physical activity is able to directly affect tumor growth by modulating inflammatory responses in the tumor mass microenvironment. Here, we investigated the effect of physical activity on tumor cell growth in colon carcinoma C26 cells injected tibialis anterior muscles of BALB/c mice. Histological analyses revealed that 4 days of voluntary wheel running significantly counteracts tumor cell growth in C26-injected muscles compared to the non-injected sedentary controls. Since striated skeletal muscle tissue is the site of voluntary contraction, our results confirm that physical activity can also directly counteract tumor cell growth in a metabolically active tissue that is usually not a target for metastasis.

Aerobic Exercise and Pharmacological Treatments Counteract Cachexia by Modulating Autophagy in Colon Cancer.

Recent studies have correlated physical activity with a better prognosis in cachectic patients, although the underlying mechanisms are not yet understood. In order to identify the pathways involved in the physical activity-mediated rescue of skeletal muscle mass and function, we investigated the effects of voluntary exercise on cachexia in colon carcinoma (C26)-bearing mice. Voluntary exercise prevented loss of muscle mass and function, ultimately increasing survival of C26-bearing mice. We found that the autophagic flux is overloaded in skeletal muscle of both colon carcinoma murine models and patients, but not in running C26-bearing mice, thus suggesting that exercise may release the autophagic flux and ultimately rescue muscle homeostasis. Treatment of C26-bearing mice with either AICAR or rapamycin, two drugs that trigger the autophagic flux, also rescued muscle mass and prevented atrogene induction. Similar effects were reproduced on myotubes in vitro, which displayed atrophy following exposure to C26-conditioned medium, a phenomenon that was rescued by AICAR or rapamycin treatment and relies on autophagosome-lysosome fusion (inhibited by chloroquine). Since AICAR, rapamycin and exercise equally affect the autophagic system and counteract cachexia, we believe autophagy-triggering drugs may be exploited to treat cachexia in conditions in which exercise cannot be prescribed.