Duchenne muscular dystrophy (DMD) is a fatal disorder caused by loss of dystrophin, a protein essential for muscle cell integrity. To date, no therapeutic has restored full-length dystrophin. Suppress...

Gioftsidi, Hayashi, et al. uncover that in mouse neonatal hindlimb muscles Pax7 progenitors generate both myogenic and non-myogenic cells, including a specific subpopulation of fibroblast-like cells, ...

Cell and gene therapy are of interest to treat age-related diseases. Here the authors developed subcutaneous transplantation of autologous myocytes to form myografts. Myografts showed a mature vascularized structure, contracted continuously and induced improvements in systemic muscle function, metabolic regulation and tissue regeneration in aged and obese mouse models.

Ewachiw et al. have provided the field with critical insight into the function of TDP-43 in satellite cells. They bred mice that allowed for the specific and conditional deletion of TDP-43 specificall...

Antisense oligonucleotide-mediated exon skipping in Duchenne muscular dystrophy is limited by low dystrophin restoration, partly due to 5’-3’ DMD transcript imbalance and limited transcript availabili...

Background Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disorder for which monitoring biomarkers are urgently needed. We aimed to evaluate whether proteins in serum can accurately monitor patients' function within the duration of a clinical trial. Methods In this study, we evaluated longitudinal serum proteins of DMD patients participating in the FOR-DMD clinical trial, comparing daily and intermittent corticosteroid regimens in boys aged 4–8 years at baseline. Using the aptamer-based protein platform SomaScan, we profiled 1500 proteins. Associations between protein levels and motor function outcomes, such as Rise from the Floor Velocity (RFV), 10-Meter Run/Walk Velocity (10MRWV), and North Star Ambulatory Assessment (NSAA), were assessed using linear mixed models. In particular, we explored whether patients with higher protein levels also tended to have better functional scores (across-patients analysis), and whether changes in protein levels within the same patient over time were linked to changes in their functional performance (within-patient analysis). Finally, penalized (lasso) mixed models were applied to evaluate the predictive function of the proteins. The prediction accuracy of the models (evaluated by optimism-corrected Root Mean Squared Error) was compared to that of a simpler model with only age and treatment as predictors. Results Across-patients and within-patient analyses revealed consistent associations with three functional tests for a subset of proteins, notably RGMA, ART3, ANTXR2, and CFB. Multivariate models incorporating the proteins significantly associated with at least two tests, improved prediction accuracy by 12% for NSAA, and by 33–35% for RFV and 10MRWV. These models also revealed a subset of proteins that were consistently selected. Quantification of CFB, RGMA, ANTXR2, SERPINF1 and ATP5PF using SomaScan showed strong agreement with measurements obtained using orthogonal methods such as ELISA, MRM-MS and an in-house developed bead-based sandwich immunoassay. Conclusions These findings support the utility of serum protein signatures as objective, quantitative tools for monitoring disease progression and treatment response in DMD during clinical visits and clinical trials. Trial registration The FOR-DMD clinical trial was registered at ClinicalTrials.gov (registration no. NCT01603407). First submission: 03/04/2012.

The gut microbiome from exercise-trained mice protects against muscle atrophy when transferred to immobilized mice. Two microbial metabolites, pipecolic acid and succinate, are identified as exercise ...

Introduction In patients with Duchenne muscular dystrophy (DMD), the gene transfer therapy delandistrogene moxeparvovec delivers a functional form of dystrophin, which has been shown to stabilize or slow disease progression. Methods We assessed cardiac safety of delandistrogene moxeparvovec in clinical trials with ≤ 5 years of follow-up. Data were collected from clinical trials 101 (NCT03375164, n = 4), 102 (NCT03769116, n = 41), ENDEAVOR (NCT04626674, n = 48), and EMBARK (NCT05096221, n = 125), which excluded patients with left ventricular ejection fraction (LVEF) < 40%. Adverse events and cardiac echocardiography were assessed regularly in all trials. Troponin I was assessed regularly in ENDEAVOR and EMBARK. Cardiac magnetic resonance imaging (MRI; without gadolinium enhancement) was assessed within an EMBARK substudy. Results Of 218 patients (baseline mean age [range], 6.4 [3.2–20.2] years; mean LVEF [range], 63.8% [48.9–78.0%]), 210 (96%) were ambulatory; 216 received delandistrogene moxeparvovec treatment. Two myocarditis cases were reported within 4 days after delandistrogene moxeparvovec infusion; both resolved within 3 weeks. Except in the two myocarditis cases, troponin I fluctuations were asymptomatic. Thirteen patients with baseline and postbaseline echocardiography data had elevated troponin I at baseline; 1 year post infusion, only one of these patients had LVEF < 50%. LVEF in all four patients with 5-year follow-up remained > 50%. Although cardiac MRI without gadolinium revealed no relevant differences in heart function between patients 1 or 2 years after delandistrogene moxeparvovec versus patients 1 year after placebo infusion, subclinical fibrosis cannot be ruled out. Conclusion Results from delandistrogene moxeparvovec trials with 1 to 5 years of follow-up suggest a manageable cardiac safety profile in this study population of predominantly younger, ambulatory patients with DMD who had no signs of persistent treatment-related cardiac injury.

Background Duchenne muscular dystrophy (DMD) is a devastating disease manifested in skeletal muscle by repetitious myonecrosis and regeneration. Because the regenerative process is closely linked to the cumulative severity of muscle damage, which is variably distributed within and between muscle groups, accurately quantifying muscle regeneration has remained a significant challenge. Methods Myofibers are delineated by immunostaining for laminin, and subsequent image analysis employed to generate a masked outline precisely within each myofiber boundary. Morphometric parameters including minimal Feret’s diameter, cross-sectional area, and circularity were measured for each myofiber. In addition, the number of Pax7-expressing satellite cells were quantified. To evaluate regenerative activity, newly formed myofibers were identified by immunostaining for expression of embryonic myosin heavy chain (eMHC). Necrotic myofibers were enumerated by immunofluorescent detection of immunoglobulin G (IgG) infiltration. The Regenerative Index (RI) was calculated as the number of regenerating (eMHC+) myofibers divided by the number of necrotic (IgG+) myofibers. Determination of RI was performed on muscle biopsies obtained from 10 boys with DMD and 3 age-matched non-DMD controls. Results A trend toward an increasing minimal Feret’s diameter, cross-sectional area and circularity was observed with increasing age in DMD boys, with circularity showing the strongest trend. Furthermore, compared to DMD boys 7- to 8-years old, the boys 9- to 11-years old had increased myofiber circularity. Pax7-expressing cells per myofiber were elevated in DMD boys compared to control boys of similar ages, without any observation of age-related changes. The Regenerative Index in DMD boys exhibited a decline between 7 and 11 years of age, with an inverse correlation between RI and age. Conclusions The use of eMHC and IgG immunostaining to calculate RI appears to provide a way to assess regeneration across biopsies that differ in histopathologic severity. Using this approach, RI showed a negative correlation with age in DMD boys aged 7 to 11 years which requires further investigation.

In this article, Barton and colleagues show that FAPs are an important source of IGF-I for skeletal muscle. The loss of FAP IGF-I has autocrine consequences, including blunted proliferation, delayed f...

Mice carry the Dutch founder variant in Kbtbd13, phenocopy major human NEM6 pathology, and show reversal of muscle dysfunction with shRNA treatment.

Background Muscle passive and active function is dependent on the extracellular matrix (ECM). In diseases characterized by muscle fibrosis, namely Duchenne Muscular Dystrophy (DMD), the ECM contributes to deficits in muscle mechanical function and regeneration. Because fibrosis is often viewed as irreversible in DMD and other muscle diseases, there is great incentive to develop anti-fibrotic therapies to prevent or reverse fibrosis. Methods In this study we tested the effectiveness of intramuscular injections of non-specific Clostridium histolyticum collagenase (CCH) on reducing ECM contents and rescuing muscle mechanical function in D2.mdx mice, models of DMD. We performed unilateral injections of collagenase into the tibialis anterior and gastrocnemius in WT and D2.mdx mice. We measured in vivo plantarflexion strength, ex vivo muscle mechanical function, immunohistochemistry, and total and cross-linked collagen content. Results We found that crude CCH was effective at digesting the muscle ECM but did not provide a therapeutic benefit evidenced by induction of muscle weakness and bleeding within 24 h after CCH injections, and a thickened basal lamina after 7 days. Conclusions We conclude that future studies testing collagenase as an anti-fibrotic should use a collagenase specific to fibrillar collagens and a paired physical therapy protocol to better preserve muscle function while reducing fibrosis.

Proceedings of the National Academy of Sciences (PNAS), a peer reviewed journal of the National Academy of Sciences (NAS) - an authoritative source of high-impact, original research that broadly spans...

Proceedings of the National Academy of Sciences (PNAS), a peer reviewed journal of the National Academy of Sciences (NAS) - an authoritative source of high-impact, original research that broadly spans...

Proceedings of the National Academy of Sciences (PNAS), a peer reviewed journal of the National Academy of Sciences (NAS) - an authoritative source of high-impact, original research that broadly spans...

Circular ADAR-recruiting RNAs enable programmable exon skipping to bypass out-of-frame mutations in Duchenne muscular dystrophy and restore dystrophin expression. LEAPER 2.0 shows sustained efficacy i...

Congenital megaconial muscular dystrophy (OMIM #602541) is an autosomal recessive disease caused by rare variants in the CHKB gene. McMaster and colleagues carried out a dose-ranging study of rAAV9 ge...

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Proceedings of the National Academy of Sciences (PNAS), a peer reviewed journal of the National Academy of Sciences (NAS) - an authoritative source of high-impact, original research that broadly spans...

Prostate cancer and androgen deprivation therapy (ADT) impair muscle function and quality of life, yet mitochondrial involvement remains unclear. The authors show that greater mitochondrial function correlates with better endurance, quality of life, and smaller declines in these parameters post-ADT

Dysferlinopathy is an age-dependent muscular dystrophy caused by loss of the membrane-associated protein dysferlin. Disease severity increases with age and selectively affects specific muscle groups, yet the molecular basis for this vulnerability remains unclear. Since lipid remodeling is a hallmark of dysferlinopathy and aging, we investigated how age, sex, and muscle fiber type interact to shape the muscle lipidome in dysferlin-deficient mice. We performed omics-scale lipid profiling across 738 lipid species and 30 lipid classes in quadriceps and gastrocnemius (fast-twitch muscles exhibiting pronounced pathology), soleus (slow-twitch) and extensor digitorum longus (EDL; fast-twitch, relatively spared) muscles from male and female dysferlin-deficient (BLA/J) and wildtype C57BL/6J (WT) mice aged 3, 10, and 26 months. Normal aging was associated with broad lipid remodeling, however, in the absence of dysferlin markedly amplified this remodeling, leading to elevations in specific triglycerides, diglycerides, cholesterol esters, gangliosides, ceramides, and sphingomyelin compared to WT muscle. Interestingly, we observed minimal sex differences between dysferlin-deficient muscles. Fast-twitch muscles, particularly quadriceps and gastrocnemius, exhibited the most extensive lipid alterations, whereas the slow-twitch soleus muscle showed relative lipid stability even at advanced age. Thus, fast-glycolytic muscles are more susceptible to age- and dysferlin-dependent lipid dysregulation than slow oxidative muscle. The preferential vulnerability of fast-twitch muscles to muscle wasting in dysferlinopathy suggests that fiber-type-dependent lipid handling contributes to selective muscle degeneration. This work defines a comprehensive lipidomic signature of disease progression and provides a framework for understanding how aging, sex, and muscle phenotype interact in muscular dystrophy.

Wang and colleagues show that a cyclic peptide-conjugated antisense oligonucleotide rapidly rescues mis-splicing in a mouse model of myotonic dystrophy. Computational modeling and in vivo nascent RNA ...

Nature - Spinal neuromotor rehabilitation using a portable isokinetic training robot

The authors investigated metabolic remodeling in response to stem cell activation and the effect of aging on this response. Aging muscle stem cells lose a key glutamine-fueled metabolic pathway that powers de novo lipogenesis needed for activation. This study shows that reductive TCA cycling helps preserve stem cell function and may offer a new target against sarcopenia.

Parks and colleagues show that the concentration of nanoparticles in blood plasma and cerebrospinal fluid tend to be elevated in individuals with spinal muscular atrophy (SMA), which declined followin...

Jeong et al. establish a high-resolution in vitro fate-map of porcine skeletal muscle formation from embryonic stem cells, uncovering dynamics of the developmental continuum at the single-cell level a...

Tang et al. demonstrate that disease progression in Duchenne muscular dystrophy is driven not only by dystrophin deficiency but also by ANXA11-mediated failure of regenerative myofiber maturation. Targeting ANXA11 improves muscle regeneration and function in mdx mice.

Background Caloric restriction (CR), achieved by reducing energy intake without malnutrition, has been shown to preserve muscle function and delay age-related declines in strength and mobility by modulating key metabolic and molecular pathways involved in muscle maintenance. While most initial research on CR was done in rodents, non-human primates (NHPs) offer a higher translatable animal model for understanding CR effects due to their close genetic, physiological and cognitive similarities to humans. Methods In this cross-sectional study, we investigated skeletal muscle gene expression changes induced by 30% CR in skeletal muscle in rhesus monkeys (n = 18 CR, n = 18 control). We performed high-depth RNA sequencing to profile gene expression and alternative splicing variants and identify pathways linked to aging, regeneration/degeneration, and energy metabolism. Results Transcriptomic profiling revealed widespread gene expression differences between CR animals compared to controls. Genes that were overexpressed were mainly involved in pathways related to energy metabolism, mitochondrial function, signaling, and oxidative stress response. Conversely, underexpressed genes were connected to immune response, extracellular matrix organization, apoptosis, and ribosomal RNA processing. Further, we identify alternative splicing as a major mechanism by which CR modulates genes involved in muscle function, metabolism, and aging. Conclusions Caloric restriction preserves skeletal muscle by enhancing metabolism, limiting degeneration and inflammation, and engaging conserved mechanisms across species.

Mori and Imai demonstrate that skeletal muscle-derived Mimecan regulates the inter-organ communication between hypothalamus, skeletal muscle, and brown adipose tissue by activating a specific subset o...

Suzuki and Yoshioka et al. show that the garlic-derived metabolite S-1-propenyl-L-cysteine (S1PC) increases circulating eNAMPT, a key NAD+ biosynthetic enzyme, in mice and humans by activating a criti...

Periodontitis is common in aging populations and linked to systemic diseases, yet its impact on skeletal muscle is unclear. Here, the authors show that increased gingiva-derived activin A in periodontitis triggers muscle loss in male mice.

Background The progressive skeletal muscle degeneration observed in Duchenne Muscular Dystrophy (DMD) patients requires multiple cycles of satellite cells (SCs) activation to promote tissue regeneration. Dystrophic SCs present intrinsic defects, and the disrupting fibrotic niche hinders appropriate muscle recovery. Traditional 2D culture systems face challenges in modeling the DMD muscle niche and SCs behavior. Our aim was to validate a 3D culture of skeletal muscle spheroids (iSMS) for DMD modeling, as compared to the traditional 2D culture, while investigating the pathophysiological mechanisms of dystrophin deficiency in vitro. Methods To compare iSMS with traditional 2D myogenic differentiation, we differentiated wild-type (WT), dystrophic (DMD) isogenic induced pluripotent stem cells (iPSCs), as well as iPSCs derived from DMD patients, characterized myogenic markers levels and assessed differences in proliferation and differentiation using RT-qPCR, immunofluorescence, and flow cytometry. Results Our data showed that iSMS improved PAX7 expression in vitro, while MYOD1, MYOG, MYF5, and MYH3 expression were significantly reduced. These findings suggest that, at three weeks of myogenic differentiation, iSMS cultures retained satellite-like cells in a less activated, progenitor-like state. Accordingly, we identified higher expression of canonical Notch signaling genes such as JAG1 and NOTCH1 in iSMS compared to 2D. We also characterized the response of 2D and iSMS to terminal differentiation medium, providing a valuable comparison with muscle fibers derived from human adult myoblasts. Additionally, we showed that DMD iSMS-derived progenitors proliferated at reduced levels compared with WT, a characteristic not observed in progenitors derived from 2D cultures. Finally, we performed iSMS and 2D myogenic differentiation of iPSC lines from three patients with DMD. Conclusion Our results highlight important advantages of using the iSMS differentiation platform over 2D for DMD in vitro modeling. Exploring these 3D systems may help to gain a deeper understanding of SCs behavior to advance in novel treatments for DMD, which might be applicable to other forms of muscular disorders.

Background Duchenne Muscular Dystrophy (DMD) is characterized by the formation of fibrosis and fat deposits that progressively replace muscle fibers, resulting in the loss of muscle function. Both fibrosis and adipogenesis are operated by fibroadipogenic precursors (FAPs), but the molecular regulation and interactions between the two processes are not fully understood. Methods Adipogenesis was investigated in vivo in the D2-mdx mouse, and in vitro using FAPs isolated from WT (DBA/2) and D2-mdx muscles. Epithelial Growth Factor (EGF) was overexpressed in the D2-mdx muscle via electroporation of an expression plasmid. Results We found that the D2-mdx gastrocnemius muscle showed fat deposition from 10 weeks of age and increased until 18 weeks of age, coinciding with fibrosis. Fat deposition was exclusively found within fibrotic areas. In vitro, D2-mdx FAPs proliferated more, and were more prone to adipogenesis than WT FAPs. Cells from both genotypes showed equal fibrogenesis. Analysis of normal muscle snRNAseq data showed that the Epithelial Growth Factor Receptor (EGFR) was primarily expressed by FAPs. Both EGFR expression and EGFR-phosphorylation were decreased in D2-mdx FAPs as compared with WT FAPs. Stimulating FAPs with EGF decreased adipogenesis, more efficiently in D2-mdx FAPs than in WT FAPs. However, EGF stimulation of EGFR had no effect on their fibrogenic differentiation. Finally, in vivo overexpression of EGF in D2-mdx gastrocnemius muscles reduced both adipogenesis and fibrosis, and was associated with an increased muscle force. Conclusions In a DMD context, FAPs are more likely to differentiate into adipocytes than in normal muscle, which is associated with decreased EGFR signaling. Stimulating EGFR signaling decreased adipogenesis in vitro and fat deposition in vivo. The impact of EGFR signaling on fibrogenesis is unclear, the reduced fibrosis observed in vivo may be due to indirect mechanisms. This study identifies EGFR signaling as a new molecular mechanism for controlling adipogenesis in skeletal muscle FAPs.

Skeletal Muscle - Duchenne muscular dystrophy (DMD) is a severe X-linked genetic disease characterized by progressive muscle degeneration, exhaustion of the muscle stem cell pool, and extensive...

Skeletal muscle fiber type is key to metabolic health. Zhou et al. reveal that the protein BRD4 dictates muscle fiber identity, blocking it promotes energy-burning slow fibers and prevents obesity in mice, offering a new target for metabolic disease.

Background The restoration of uniformly distributed dystrophin protein expression is an important consideration for the development of advanced therapeutics for Duchenne muscular dystrophy (DMD). ...