Journal of Cachexia, Sarcopenia and Muscle

Background and AimsOver 80% of patients with pancreatic cancer experience cachexia, characterized by severe muscle and fat loss. While all the mechanistic understanding comes from preclinical models, the translatable nature of these findings to humans remains a critical gap due to the limited knowledge of human cachexia biology. MethodsWe generated matched gene and microRNA profiles from rectus abdominis muscle of 55 pancreatic ductal adenocarcinoma and 18 control subjects. Differentially expressed genes and microRNAs were identified at 1.5-fold change and p<0.05. ResultsGene expression results revealed a striking sex-specific difference at the expression and pathway levels. In both sexes, co-expression gene network analysis identified more significant modules and hub genes at 1-month of weight loss than the traditionally used six months, suggesting that gene alterations may be more dynamic in the early stages of the disease progression. When comparing hub genes from humans to experimental models of cachexia, genes such as RELA, DDX21, WDR75, PTPN1, and CRIP3 exhibited similar patterns of expression, suggesting their potential role in cachexia. microRNAs also exhibited sex-specific expression. Although several common miRNAs were identified between sexes, their gene targets differed, indicating that microRNAs may regulate gene targets in a sex-specific manner. ConclusionsThe dataset can serve as a resource for validating preclinical findings and exploring previously unexplored molecules in cachexia. Future studies will functionally characterize the role of the hub genes and microRNAs in cachexia. This is the first study to identify sex-specific genes and microRNAs from a single cancer type.

Cancer cachexia is a highly prevalent wasting syndrome in cancer patients. Inflammation is hallmarks of symptomatic cachexia, however early stages of cachexia are not well understood, including differences between biological sexes. In a mouse model of early cachexia, muscle from males showed strong mitochondrial defects, whereas females were characterized by inflammatory and stress response. We demonstrate a novel link between the increase in purinergic receptor P26Y, and dysregulated Ca2+ homeostasis, mitochondrial dysfunction and damage, and inflammation during early stages of cancer cachexia. Low levels of miR-379-3p were associated with poor survival of patients with lung cancer. Restoring miR-379-3p levels in mice prevented loss of muscle mass and function. miR-379-3p targeted P2r6y and restored mitochondrial content and function, inhibited type II interferon response, and regulated the expression of Ca2+-related and apoptotic markers. This supports miR-379-3p as a hub regulating multiple processes underlying cachexia and represent a therapeutic target for cancer patients.

RationaleMechanical ventilation plays an important role in critical illness-associated diaphragm weakness. Weakness contributes to difficult weaning and is associated with increased morbidity and mortality. Diaphragm weakness is caused by a combination of atrophy and dysfunction of myofibers, which are large syncytial cells maintained by a population of myonuclei. Each myonucleus provides gene transcripts to a finite fiber volume, termed the myonuclear domain. Changes in myonuclear number in myofibers undergoing atrophy has not been investigated in mechanically ventilated ICU patients. Myonuclear number is a determinant of transcriptional capacity, and therefore critical for muscle regeneration after atrophy. ObjectivesOur objective was to investigate if and how myonuclear number changes in the diaphragm of mechanically ventilated ICU patients and whether changes are associated with myofiber atrophy. MethodsWe used a combination of transcriptomics, immunohistochemistry, and confocal microscopy to study myonuclear alterations in diaphragm and quadriceps biopsies from mechanically ventilated ICU patients. ResultsMyonuclear number and myonuclear domain were reduced in patients with diaphragm myofiber atrophy. Intrinsic apoptotic pathway activation was identified as a mechanism underlying myonuclear removal in the diaphragm of mechanically ventilated ICU patients. Total transcriptional activity in myofibers decreased with myonuclear loss. Furthermore, muscle stem cell number was reduced in the patients with diaphragm atrophy. ConclusionWe identified myonuclear loss due to intrinsic apoptotic pathway activation as a potential mechanism underlying diaphragm atrophy in mechanically ventilated patients. This provides novel insights in diaphragm weakness of ICU patients. Targeted therapies may limit development of diaphragm weakness and improve weaning outcome.

Background: Skeletal muscle atrophy and low physical performance are associated with disease progression and higher mortality rates in multiple pathological conditions. Here, we determined whether body composition and physical performance would predict mortality in metastatic non-small cell lung cancer (NSCLC) patients. In addition, we defined whether plasma samples from NSCLC patients would directly affect the homeostasis of skeletal muscle cells. Methods: The prospective cohort included 55 metastatic NSCLC patients and seven age-matched control subjects. We assessed clinical characteristics, body composition, cancer cachexia, and quality of life (QoL). We determined physical performance with a series of functional tests. We analyzed skeletal muscle and adipose tissue areas. Finally, we evaluated the overall survival rate, and additional blood samples were collected from a subcohort of eighteen patients for further studies in cell culture and metabolomic analysis. Results: We found that physical performance, not body composition, was associated with overall survival in this cohort. Moreover, incubation with plasma derived from NSCLC patients with low physical performance impaired the metabolism and proliferation of primary human myotubes. Unbiased metabolomics revealed several metabolites differentially expressed in the plasma of NSCLC patients with low physical performance compared to healthy control subjects, with serine and N2,N2-dimethylguanosine (M22G) being the most reduced and increased metabolites, respectively. Conclusion: These novel findings confirm physical performance as a significant predictor of overall survival in metastatic NSCLC patients and provide insights into cancer-induced circulating factors that can directly affect skeletal muscle homeostasis and prognosis.

Cancer cachexia affects up to 80% of cancer patients and results in reduced quality of life and survival. We previously demonstrated that the transcriptional repressor Forkhead box P1 (FoxP1) is upregulated in skeletal muscle of cachectic mice and people with cancer, and when overexpressed in skeletal muscle is sufficient to induce pathological features characteristic of cachexia. However, the role of myofiber-derived FoxP1 in both normal muscle physiology and cancer-induced muscle wasting remains largely unexplored. To address this gap, we generated a conditional mouse line with myofiber-specific ablation of FoxP1 (FoxP1SkmKO) and found that in cancer-free mice, deletion of FoxP1 in skeletal myofibers resulted in increased myofiber size in both males and females, with a significant increase in muscle mass in males. In response to murine KPC pancreatic tumor burden, we found that myofiber-derived FoxP1 is required for cancer-induced muscle wasting and diaphragm muscle weakness in male mice. In summary, our findings identify myofiber-specific FoxP1 as a negative regulator of skeletal muscle with sex-specific differences in the context of cancer. NEW & NOTEWORTHYHere we identify myofiber-derived FoxP1 as a negative regulator of skeletal muscle with sex-specific effects in cancer. Under cancer-free conditions, FoxP1 knockout increased myofiber size in male and female mice. However, in response to pancreatic cancer, FoxP1 was required for muscle wasting and weakness in males but not females. This highlights the need to consider sexual dimorphism in cancer-induced muscle pathologies and provides evidence suggesting that targeting FoxP1 could help mitigate these effects in males.

The cellular and molecular consequences of lack of dystrophin in humans are only partially known, which is crucial for the development of new therapies aiming to slow or stop the progression Duchenne and Becker muscular dystrophies. We analyzed muscle biopsies of DMD patients and controls using single nuclei RNA sequencing (snRNAseq) and correlated the results with clinical data. DMD samples displayed an increase in regenerative fibers, satellite cells and fibro-adipogenic progenitor cells (FAPs) and a decrease in slow fibers and smooth muscle cells. Samples from patients with stable mild weakness were characterized by an increase in regenerative fibers, while those from patients with progressive weakness had fewer muscle fibers and increased FAPs. DMD muscle fibers displayed a strong regenerative signature, while DMD FAPs upregulated genes producing extracellular matrix and molecules involved in several signaling pathways. An analysis of intercellular communication profile identified FAPs as a key regulator of cell signaling in DMD samples. We show significant differences in the gene expression profiled of the different cell populations present in DMD muscle samples compared to controls.

Skeletal muscle regeneration is a cardinal feature of muscle pathologies and is crucial for post-exercise recovery and traumatic sports injuries. Regeneration of damaged muscle in humans is a prolonged process and is accompanied by pain and physical dysfunction, highlighting the unmet need for effective interventions to accelerate the regenerative process. Through cellular and preclinical models, we have previously identified nicotinamide (NAM) and pyridoxine (PN) as potent stimulators of Muscle Stem Cells (MuSCs). Herein we investigated if a combination of NAM and PN could enhance MuSC activity and improve muscle regeneration in healthy volunteers during recovery from eccentric contractions. MethodsThis randomized, double-blind, placebo-controlled trial enrolled male participants aged 18-50 years supplemented daily with 714mg NAM and 19mg PN (NAM/PN) or placebo for 8 days following unilateral eccentric muscle contractions using Neuromuscular Electrical Stimulation (NMES). MuSC was quantified by immunohistofluorescence on vastus lateralis muscle biopsies. Results39 out of 43 enrolled participants completed the study. Supplementation of NAM/PN was well tolerated and increased blood concentrations of NAM and PN vitamers. The NMES protocol caused myofiber necrosis and triggered a strong MuSC response. After 8 days, the number of Pax7, MyoD, and myogenin positive cells per damaged fiber was significantly higher in NAM/PN vs placebo groups (+29-67%). NAM/PN also increased the proportion of regenerating fibers re-expressing embryonic myosin (+37%). ConclusionDaily oral NAM/PN supplementation following eccentric muscle damaging contractions enhances MuSC activity and accelerates muscle regeneration. These findings provide new possibilities for targeted therapeutic interventions in muscle repair. Trial registrationNCT04874662 One Sentence SummaryMuscle regeneration is enhanced by nicotinamide and pyridoxine supplementation, accelerating recovery and offering therapeutic potential.

BackgroundCancer-associated cachexia, a frequent complication of solid tumours, is not recorded in cancer registries. Cachexia affects patients diagnosed with non-small cell lung cancer (NSCLC); however, a detailed characterization of nutritional and body composition parameters matched with blood-based, non-invasive markers is lacking. We hypothesized that a systematic characterization of cachectic patients may facilitate the development of interventions aimed to improve clinical outcomes. MethodsWe conducted a prospective study of 51 patients diagnosed with locally advanced unresectable NSCLC who underwent concurrent chemoradiotherapy followed by immunotherapy at the HUB-ICO Comprehensive Cancer Centre from 2022 to 2024. The primary objectives were (1) to determine the prevalence of cachexia according to Fearons criteria and (2) to comprehensively characterize patients before and after completing chemoradiotherapy in terms of nutritional status, metabolic parameters, body composition and circulating cytokine levels. Here, we report the baseline assessment results. ResultsMost patients were male (80%), ever smokers (98%) with a median age of 68 years. All patients completed the planned concurrent chemoradiotherapy regimen, while only 43% initiated durvalumab consolidation therapy. At baseline, 53% of patients met the diagnostic criteria for cachexia. Women were more likely to have cachexia at baseline compared to men, although these differences were not statistically significant. Cachexia was significantly associated with tumor stage (p < 0.001), performance status (p = 0.027), lower skeletal muscle index (p = 9e-4) and total adipose tissue index (p = 0.004), elevated C-Reactive Protein blood levels (p = 0.004), moderate to severe malnutrition (p < 0.001), reduced caloric intake (p = 0.007) and diminished physical strength (p=0.001). Proteomic profiling using the O-link platform revealed significant differences in circulating cytokine levels between cachectic and non-cachectic patients. Cachexia was significantly associated with elevated levels of CCL23, IL-6, IL-11, Oncostatin M (OSM), pentraxin-related protein 3 (PTX3), and agouti-related protein (AGRP), among others, demonstrating varying degrees of correlation with caloric intake. GDF15 was associated with weight loss (p = 0.00014), but not with calorie intake or body composition. ConclusionsThis prospective study reveals that cancer cachexia is highly prevalent in patients with unresectable locally advanced NSCLC. In addition to previously known cytokines, we identified several understudied cytokines, which may contribute to a more comprehensive characterization of the cachexia phenotype and help uncover potential targets for therapeutic interventions.

Skeletal muscle wasting results from numerous conditions, such as sarcopenia, glucocorticoid therapy or intensive care. It prevents independent living in the elderly, predisposes to secondary diseases, and ultimately reduces lifespan. There is no approved drug therapy and the major causative mechanisms are not fully understood. Dual specificity phosphatase 22 (DUSP22) is a pleiotropic signaling molecule that plays important roles in immunity and cancer. However, the role of DUSP22 in skeletal muscle wasting is unknown. In this study, DUSP22 was found to be upregulated in sarcopenia patients and models of skeletal muscle wasting. DUSP22 knockdown or pharmacological inhibition prevented multiple forms of muscle wasting. Mechanistically, targeting DUSP22 suppressed FOXO3a, a master regulator of skeletal muscle wasting, via downregulation of the stress-activated kinase JNK, which occurred independently of aberrant Akt activation. DUSP22 targeting was also effective in human skeletal muscle cells undergoing atrophy. In conclusion, phosphatase DUSP22 is a novel target for preventing skeletal muscle wasting. The DUSP22-JNK-FOXO3a axis could be exploited to treat sarcopenia or related aging disorders.

Patients with chronic obstructive pulmonary disease (COPD)-pulmonary emphysema often develop locomotor muscle dysfunction, which is independently associated with disability and higher mortality in that population. Muscle dysfunction entails reduced muscle mass and force-generation capacity, which are influenced by fibers integrity. Myogenesis, which is muscle turnover driven by progenitor cells such as satellite cells, contributes to the maintenance of muscle integrity in the context of organ development and injury-repair cycles. Injurious events crucially occur in COPD patients skeletal muscles in the setting of exacerbations and infections which lead to acute decompensations for limited periods of time after which, patients typically fail to recover the baseline status they had before the acute event. Autophagy, which is dysregulated in muscles from COPD patients, is a key regulator of satellite cells activation and myogenesis, yet very little research has so far investigated the mechanistic role of autophagy dysregulation in COPD muscles. Using a genetically inducible murine model of COPD-driven muscle dysfunction and confirmed with a second genetic animal model, we found a significant myogenic dysfunction associated with a reduced proliferative capacity of freshly isolated satellite cells. Transplantation experiments followed by lineage tracing suggest that an intrinsic defect in satellite cells, and not in the COPD environment, plays a dominant role in the observed myogenic dysfunction. RNA sequencing analysis of freshly isolated satellite cells suggests dysregulation of transcripts associated with control of cell cycle and autophagy, which is confirmed by a direct observation of COPD mice satellite cells fluorescent-tracked autophagosome formation. Moreover, spermidine-induced autophagy stimulation leads to improved satellite cells autophagosome turnover, replication rate and myogenesis. Our data suggests that pulmonary emphysema causes a disrupted myogenesis, which could be improved with stimulation of autophagy and satellite cells activation, leading to an attenuated muscle dysfunction in this context.

BackgroundCancer cachexia is a complex metabolic syndrome that severely impacts patient mobility, treatment strategies, and quality of life. However, no treatments are available to mitigate the debilitating consequences of cancer cachexia. Unacylated ghrelin (UnAG), the main circulating form of ghrelin, enhances muscle growth and mitochondrial function in various diseases, but its effects in cancer cachexia remain to be tested. MethodsMale C57Bl6/N mice were assigned to one of three treatment groups: non-tumor-bearing (NTB), tumor-bearing (TB), or tumor-bearing treated with unacylated ghrelin (TB+UnAG). Over four weeks, we monitored body weight, food intake, and tumor size. We assessed muscle mass, contractility, mitochondrial oxygen consumption rate (OCR), and reactive oxygen species (ROS) production. Proteomic analysis was performed to elucidate the downstream effects of UnAG. Cell culture assays were performed to measure the in vitro effects of cancer cell-secreted factors and UnAG on myoblasts. ResultsGastrocnemius and quadriceps muscle masses were reduced by 20-30% in TB mice compared to NTB controls; however, UnAG treatment prevented approximately 50% of this loss. Beyond muscle mass, UnAG enhanced the isometric maximum specific force of the extensor digitorum longus by 70% in TB mice. This improvement in muscle quality was associated with preferential upregulation of myosin heavy chain expression in TB+UnAG mice. UnAG also increased mitochondrial OCR while reducing ROS production. Mitochondrial DNA (mtDNA) copy number, which was reduced in TB mice, was restored by UnAG, while the reduced mtDNA mutation frequency in TB mice was maintained with treatment, indicating improved mtDNA integrity. Consistent with enhanced mitochondrial function, treadmill running time was significantly increased in TB+UnAG mice. Proteomic analysis revealed that UnAG downregulated proteins associated with proteolysis, while normalizing antioxidant enzyme thioredoxin and proteins involved in calcium handling. Cancer cell-conditioned medium reduced myotube width in vitro, but UnAG treatment preserved myotube structure.. ConclusionUnAG protects against cancer cachexia by targeting multiple risk factors, including myosin heavy chain expression, mitochondrial bioenergetics, and modulation of protein degradation pathways.

BackgroundSkeletal muscle atrophy is prevalent worldwide and is a major detractor from length and quality of life. It is often diagnosed and treated as a single disorder, but the causal stimuli and progression of atrophy vary widely. Malnutrition and disuse are two common causes of muscle atrophy, and despite their prevalence and extensive characterization, there have been no direct comparisons of how these two types of atrophy progress and whether they differentially affect skeletal muscle fiber types. The purpose of this study is to directly compare atrophy from fasting and disuse and provide a transcriptomic resource for future research on both conditions. MethodsWe fasted or hindlimb suspended (HS) two cohorts of 12-week-old female C57/bl6 mice. Mice were fasted for up to 72 hours to induce malnutrition atrophy or were hindlimb suspended for 0, 3, 7, 14, or 28 days to induce disuse atrophy. At each timepoint, mice were euthanized and three muscles (tibialis anterior (TA), extensor digitorum longus (EDL), and soleus) were weighed and collected for RNA sequencing. Atrophy progression and gene expression changes were compared across muscle fiber types and atrophy stimuli. ResultsWe found differences in atrophy progression between muscle fiber types based on fiber twitch speed and atrophy stimulus. Fasted mice lost 25% of their body weight and 23% of fast-twitch TA mass with little change in soleus. In contrast, HS mice lost 40% of the slower-twitch soleus but the effect on the TA was negligible. Gene expression varied in response to both atrophy stimuli, but a greater number of genes changed with fasting compared to HS in the EDL and soleus. By muscle type, a greater transcriptional shift occurred in the EDL with fasting while the soleus showed more gene changes during HS. Enrichment analysis of transcriptional changes showed similarities (downregulation in muscle growth pathways) and differences (increased fatty acid metabolism in fasting and increased neuronal activity in HS) between atrophy stimuli. ConclusionsAtrophy progression varies based on stimuli and muscle fiber type. This study provides a large, matched data set where the effects of different atrophic stimuli can be easily and directly compared in multiple fiber types. To our knowledge, this is the first study to closely compare these two atrophy stimuli in a muscle type-specific context. This work demonstrates that atrophy is not a single disorder and that the development of therapies may need to be tailored to the atrophic stimulus.

ObjectiveDuchenne Muscular Dystrophy (DMD) is characterized by progressive muscle wasting leading to early loss of motor function. Functional tests monitor disease progression and serve as clinical trial endpoints, but are influenced by maturation in younger patients, variability, and patient motivation. Blood biomarkers, that can predict disease progression and objectively evaluate treatment responses, offer a valuable alternative. In this study, we investigated whether longitudinal observations of biomarkers myostatin and the creatine/creatinine ratio (Cr/Crn) are associated with functional tests, such as 6-minute walk test, North Star Ambulatory Assessment (NSAA), 10-meter walk-run test velocity, Performance of Upper Limb (PUL2.0), and disease milestones like loss of ambulation (LoA), overhead reach. and hand-to-mouth function. MethodsWe used real-world longitudinal data from 74 DMD patients followed for up to 11 years with annual visits to the LUMC outpatient clinic, linked to 408 serum samples. Associations between biomarkers, functional tests, and clinical milestones were assessed using linear mixed models and time-dependent Cox models, respectively. ResultsLower Cr/Crn levels and higher myostatin levels were associated with better functional performance and a less rapid decline in ambulation, given fixed treatment and BMI. Children with one-unit higher log2-myostatin levels had, on average, 4.73 points higher NSAA and 3.40 points higher PUL2.0 (both p < 0.001), and were 42% less likely to lose ambulation over the following year. Conversely, children with one-unit lower log2-ratio levels had, on average, 7.18 points higher NSAA and 11.40 points higher PUL2.0 (both p < 0.001), and were 3.67 times more likely to remain ambulant. We also proved that incorporating log2-myostatin and log2-Cr/Crn as endpoints could reduce the required sample size for clinical trials by more than half without compromising statistical power. For instance, to detect a yearly drop of 3 points in the NSAA with 80% power, recruitment requires almost 80 participants in a 1:1 randomized trial, in contrast to a little more than 50 patients for the respective value of log2-myostatin or log2-Cr/Crn. InterpretationThese findings support the potential of myostatin and Cr/Crn as prognostic biomarkers to enhance trial design and endpoint in clinical and interventional trials for DMD.

More than 85% of patients with pancreatic ductal adenocarcinoma (PDAC) suffer from cachexia, a debilitating syndrome characterized by the loss of muscle and fat and remains an unmet medical need. While chemotherapy remains an effective treatment option, it can also induce weight and muscle loss in patients with cancer. Gemcitabine combined with nab paclitaxel (GnP) is a first line treatment option for patients with PDAC but GnPs effect on cachexia has not been comprehensively investigated. We interrogated the effects of GnP in a murine model of pancreatic cancer cachexia. Mice were orthotopically implanted with the cachexia inducing pancreatic cell line (KPC) and were administered GnP or vehicle. The controls underwent sham surgery. We defined GnP effects on cachexia and tumor burden by evaluating muscle and cardiac mass and function, fat mass, bone morphometry, and hematology measurements. We completed RNA sequencing and deep proteome profiling in skeletal and cardiac muscle. KPC+GnP reduced tumor burden over 50% and increased survival compared to KPC. KPC vehicle group had more than 15% muscle mass loss and decreased left ventricular mass, this was not present in KPC+GnP when compared to controls. RNA Seq and deep proteomics analyses suggested that muscle and cardiac dysfunction pathways activated in KPC group were either reversed or decreased in KPC+GnP. In all, our data suggests that GnP protects against muscle and cardiac wasting in an experimental model of PDAC cachexia. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=98 SRC="FIGDIR/small/536434v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@1d394f7org.highwire.dtl.DTLVardef@1d8fdaforg.highwire.dtl.DTLVardef@f709d4org.highwire.dtl.DTLVardef@a668e0_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical AbstractC_FLOATNO C_FIG

The adult skeletal muscle regenerates robustly upon injury, but this regenerative capacity rapidly declines with age. In this study, we identify the lanthionine synthetase C-Like (LanCL) proteins, mammalian homologs of the bacterial peptide cyclase LanC, as positive regulators of muscle regeneration in middle-aged mice. In a barium chloride-induced injury model, we found the protein levels of LanCL1 and LanCL2 to increase during an early phase of regeneration in middle-aged (12-month-old) but not young adult (4-month-old) mice. Utilizing a mouse line lacking all three LanCL proteins (LanCL triple KO or LTKO), we examined a potential role of LanCL in injury-induced muscle regeneration. Consistent with an age-dependent function of LanCL, we observed a delayed regeneration of the tibialis anterior (TA) muscle after injury, as reflected by reduced sizes of regenerating myofibers in middle-aged (but not young) LTKO compared to age-matched WT mice. Although the pool size of quiescent satellite cells (Pax7+) was comparable between 12-month-old LTKO and WT muscles without injury, the number of Pax7+ cells was significantly higher in regenerating LTKO muscles at day 5 after injury, accompanied by drastically decreased numbers of MyoD+ and MyoG+ cells, as well as increased numbers of proliferating cells. In addition, we detected elevated expression of pro-inflammatory cytokines in regenerating LTKO muscles, while the number of macrophages was similar comparing LTKO and WT muscles. Taken together, our observations suggest that in aging muscles LanCLs are important for proper timing of inflammation resolution and regeneration upon injury. New & NoteworthyPhysiological roles of the mammalian homologs of bacterial LanC, LanCLs, are poorly understood. Our work uncovers a function of LanCLs in post-injury regeneration of aging skeletal muscles. Middle-aged LanCL triple KO mice displayed a delay in satellite cell differentiation and regenerative myofiber formation, as well as persistent inflammatory cytokine expression, suggesting that LanCLs may have an age-dependent role in modulating inflammation in the injured muscles to facilitate regeneration.

BackgroundAgeing is accompanied by progressive declines in skeletal muscle mass and strength, culminating in sarcopenia, a condition that contributes to frailty, multimorbidity, and mortality. Age-related changes to mitochondria lead to oxidative damage and dysfunction and are proposed to occur early in the trajectory of sarcopenia, supporting the candidacy of mitochondrial-protective therapies. Here, we test the efficacy of mitochondrial uncoupler BAM15 in age-dependent sarcopenic mouse models. MethodsMale and female MitoQC mice aged 24 months received either standard chow or chow supplemented with BAM15 (0.033% mg/g) ad libitum for eight weeks (n=13-14/group). Young (3-month-old) mice served as reference controls (n=8/group). Muscle mitochondrial respiration was assessed in permeabilized fib res, and contractile function was measured in isolated extensor digitorum longus and soleus muscles. Mitophagy was quantified by immunofluorescence confocal microscopy. Data were analyzed using one-or two-way ANOVA followed by Dunnetts or Bonferronis multiple comparison tests. ResultsAged male and female mice exhibited reduced gastrocnemius muscle mass relative to body mass compared with young controls (p<0.05; [~]18% and [~]32% loss, respectively). BAM15 did not alter muscle size but reversed the age-related loss of contractile function in EDL muscles, to that of the young reference controls in both sexes (p<0.05; [~]33% in males, [~]16% in females). In male mice, BAM15 improved mitochondrial efficiency, evidenced by restoration of Complex I-linked respiration and decreased proton leak ([~]52% improvement; p<0.05), and normalized protein levels of oxidative stress marker 4 -HNE, without changes in mitophagy or mitochondrial content. In females, BAM15 did not improve mitochondrial parameters, which may be, in part, due to aged female muscle exhibiting unchanged Complex I leak and 4-HNE protein abundance, alongside lower complex I subunit (NDUFB8) protein abundance. ConclusionsBAM15 improved skeletal muscle mitochondrial efficiency and contractile function in aged male mice, supporting the potential of mitochondrial uncoupling as a therapeutic strategy for sarcopenia.

Duchenne Muscular Dystrophy (DMD) is the most common childhood muscular disorder. Mitochondrial dysfunctions are key disease features of the disease, and strategies that improve mitochondrial health have emerged as promising to slow disease progression. Emerging evidence indicates that impaired/insufficient mitophagy may contribute to the accumulation of mitochondrial dysfunction seen in patients and animal models of DMD. We therefore hypothesized that overexpressing Parkin, a key mitophagy regulator, may improve mitochondrial and muscle health in a mouse model of DMD. To this end, Parkin was overexpressed using intramuscular injections of adeno-associated viruses performed in 5-week-old and 18-week-old D2.B10-Dmdmdx/J mice (D2.mdx), a widely used mouse model of DMD. Four and 16 weeks of Parkin overexpression initiated in 5-week-old and 18-week-old D2.mdx, respectively, resulted in muscle hypertrophy, as indicated by an increase in muscle mass and fiber cross-sectional area. While Parkin overexpression did not impact maximal mitochondrial respiration or mitochondrial content, it increased the Acceptor Control Ratio, an index of mitochondrial bioenergetic efficiency. Parkin overexpression also decreased mitochondrial H2O2 emission, a surrogate for mitochondrial ROS production. However, Parkin overexpression failed to reduce the proportion of fibers with central nuclei and markers of muscle damage and/or necrosis. Taken all together, our results indicate that Parkin overexpression can attenuate muscle atrophy, improve mitochondrial bioenergetics and lower mitochondrial ROS production in a mouse model of DMD. These findings showcase the partial beneficial effects of overexpressing Parkin in ameliorating some, but not all, pathological features observed in a mouse model of DMD. Graphical abstractImpact of AAV-mediated Parkin overexpression on Duchenne Muscular Dystrophy (DMD) progression in skeletal muscle of D2.mdx (a mouse model of DMD). Parkin overexpression attenuated muscle atrophy, reduced mitochondrial H2O2 emissions and improved an index of mitochondrial coupling efficiency. Created with BioRender.com. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=179 SRC="FIGDIR/small/659533v3_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@143f08borg.highwire.dtl.DTLVardef@16543a9org.highwire.dtl.DTLVardef@13d1110org.highwire.dtl.DTLVardef@2b5e2e_HPS_FORMAT_FIGEXP M_FIG C_FIG

BackgroundOxidative phosphorylation (OXPHOS) is a central function and a key indicator of mitochondrial fitness, yet studies in human tissue remain limited. Inclusion body myositis (IBM) is a progressive myopathy that lies at the intersection of aging, inflammation and mitochondrial dysfunction. We aimed to perform a comprehensive profiling of mitochondrial respiration in muscle tissue from patients with IBM. MethodsA wide battery of complementary tests from RNA level to high-resolution respirometry on permeabilized muscle fibers was performed. The relationship between respiration, mitochondrial content, mitochondrial DNA (mtDNA) abnormalities and mitophagy was examined, along with the correlation with various clinical parameters to determine the clinical significance of the findings. ResultsThe study included a total of 67 patients with IBM and 45 controls. IBM muscle tissue exhibited reduced maximal respiration per tissue weight in State 3 (high substrates, high ADP) and uncoupled state with decreased coupling efficiency and higher leak control ratios. When adjusting for citrate synthase reflecting mitochondrial content, males had decreased State 3 intrinsic respiration, whereas females had greater intrinsic respiration in leak states. Complex II control ratio strongly correlated with disease duration and severity only in females. IBM was associated with decreased RNA and protein expression of OXPHOS complexes. Complex I activity was decreased mainly in females. IBM samples exhibited lower maximal H2O2 emission, accompanied by a higher total antioxidant capacity that correlated with disease duration in females. In IBM, there was decreased mtDNA content, and impaired mitophagy, both of which strongly correlated with respirometry measures and markers of disease severity, indicating these pathways are likely interconnected and of clinical significance. ConclusionIBM is characterized by multilevel impairments in mitochondrial coupling efficiency, revealing several potential therapeutic targets to improve mitochondrial fitness, while accounting for sex-specific differences.

BackgroundDuchenne Muscular Dystrophy (DMD) is a severe muscle disease caused by impaired expression of dystrophin. While mitochondrial dysfunction is thought to play an important role in DMD, the mechanism of this dysfunction remains to be clarified. We recently identified in DMD and in other muscular dystrophies the upregulation of a large number of the Dlk1-Dio3 clustered miRNAs (DD-miRNAs), in both the muscle and the serum. The objective of the present study was to define the biological functions of DD-miRNAs in skeletal muscle, particularly in the context of muscular dystrophy. MethodsDD-miRNAs expression pattern was characterized in vitro and in vivo, in normal and dystrophic situations. Epigenomic characterization was performed, to elucidate the molecular control of DD-miRNAs dysregulation. The biological effect of muscle DD-miRNAs dysregulation was investigated by an in vivo simultaneous overexpression of 14 DD-miRNAs in the wild-type muscle, together with CRISPR-Cas9-based knockdown of the entire DD-miRNA cluster in an iPS-derived myotubes. Omics data and bioinformatics tools were used for the prediction of DD-miRNAs biological functions, and functional characterization of mitochondrial pathways was performed. ResultsWe found that DD-miRNAs dysregulation is not specific to DMD since observed in mouse models for other muscular dystrophies. We showed that DD-miRNAs expression in mdx, is reduced in satellite cells, but highly upregulated in regenerating myofibers, suggesting a myofibers origin of DD6miRNA upregulation in muscular dystrophy in both muscles and serum. We demonstrated that upregulation of DD-miRNAs in the dystrophic muscle is controlled epigenetically by DNA and histone methylation (p<0.0001 and p=0.001, respectively) at the Intergenic Differentially Methylated Region (IG-DMR) of Dlk1-Dio3 locus. Transcriptomic analysis revealed a substantial overlap between the dystrophic muscle of the mdx mouse and the normal muscle that overexpressed 14 DD-miRNAs. Bioinformatics analysis predicted that DD-miRNAs could regulate mitochondrial functions. The ectopic overexpression of 14 DD-miRNAs, in the healthy muscle, resulted in a drastic downregulation of mitochondrial oxidative phosphorylation (OxPhos) (NES=-2.8, p=8.7E-17), similarly to the level in dystrophic muscles of mdx mice and DMD patients (NES=-2.88, p=7.7E-28). Knocking down the entire DD-miRNA cluster in iPS-derived myotubes resulted in increased mitochondrial OxPhos expression and activities. ConclusionsThe present study provides evidence for the modulation of mitochondrial activity in the dystrophic muscle by the upregulated DD-miRNAs and supports an updated model for mitochondrial dysfunction in DMD. The regulation of mitochondrial OxPhos by DD-miRNAs may have a broader impact beyond DMD in physiological and pathological situations of muscle adaptation and regeneration.

BACKGROUNDVitamin B3 analogue nicotinamide riboside (NR) has been suggested to have beneficial effects on muscle pathology in a mouse model for Duchenne muscular dystrophy (DMD). In muscle dystrophy, NR is thought to act acts by increasing levels of NAD+, to improve mitochondrial functioning and reduce muscle pathology. OBJECTIVEWe here aimed to validate the effects of NR to improve muscle quality after eight weeks of treatment in two different mouse models for DMD: the commonly used mdx mouse on a C57BL/10 background (BL10mdx) and the more severely affected mdx mouse on a DBA/2J background (D2-mdx). METHODSTo study in more detail whether NR treatment had an impact on muscle pathology, we assessed the expression levels of several markers for DMD pathology (fibrosis, regeneration and inflammation) in diaphragm. RESULTSOur data showed a trend for increase in NAD+-levels in blood; only in the D2-mdx NR-treated mice the NAD+-levels were slightly increased. These markers were elevated in mdx models compared to controls, but not affected by the NR treatment. Histological analysis of muscle tissues indicated a mild treatment effect in D2-mdx mice. CONCLUSIONSBased on our results, testing NR treatment in clinical trials in DMD patients is not warranted.