The immune system in Duchenne muscular dystrophy: Friend or foe

Benfotiamine improves dystrophic pathology and exercise capacity in mdx mice by reducing inflammation and fibrosis

Duchenne Muscular Dystrophy (DMD) is a progressive and fatal neuromuscular disease. Cycles of myofibre degeneration and regeneration are hallmarks of the disease where immune cells infiltrate to repair damaged skeletal muscle. Benfotiamine is a lipid soluble precursor to thiamine, shown clinically to reduce inflammation in diabetic related complications. We assessed whether benfotiamine administration could reduce inflammation related dystrophic pathology. Benfotiamine (10 mg/kg/day) was fed to male mdx mice (n = 7) for 15 weeks from 4 weeks of age. Treated mice had an increased growth weight (5-7 weeks) and myofibre size at treatment completion. Markers of dystrophic pathology (area of damaged necrotic tissue, central nuclei) were reduced in benfotiamine mdx quadriceps. Grip strength was increased and improved exercise capacity was found in mdx treated with benfotiamine for 12 weeks, before being placed into individual cages and allowed access to an exercise wheel for 3 weeks. Global gene expression profiling (RNAseq) in the gastrocnemius revealed benfotiamine regulated signalling pathways relevant to dystrophic pathology (Inflammatory Response, Myogenesis) and fibrotic gene markers (Col1a1, Col1a2, Col4a5, Col5a2, Col6a2, Col6a2, Col6a3, Lum) towards wildtype levels. In addition, we observed a reduction in gene expression of inflammatory gene markers in the quadriceps (Emr1, Cd163, Cd4, Cd8, Ifng). Overall, these data suggest that benfotiamine reduces dystrophic pathology by acting on inflammatory and fibrotic gene markers and signalling pathways. Given benfotiamine's excellent safety profile and current clinical use, it could be used in combination with glucocorticoids to treat DMD patients.

How Can Proteomics Help to Elucidate the Pathophysiological Crosstalk in Muscular Dystrophy and Associated Multi-System Dysfunction?

This perspective article is concerned with the question of how proteomics, which is a core technique of systems biology that is deeply embedded in the multi-omics field of modern bioresearch, can help us better understand the molecular pathogenesis of complex diseases. As an illustrative example of a monogenetic disorder that primarily affects the neuromuscular system but is characterized by a plethora of multi-system pathophysiological alterations, the muscle-wasting disease Duchenne muscular dystrophy was examined. Recent achievements in the field of dystrophinopathy research are described with special reference to the proteome-wide complexity of neuromuscular changes and body-wide alterations/adaptations. Based on a description of the current applications of top-down versus bottom-up proteomic approaches and their technical challenges, future systems biological approaches are outlined. The envisaged holistic and integromic bioanalysis would encompass the integration of diverse omics-type studies including inter- and intra-proteomics as the core disciplines for systematic protein evaluations, with sophisticated biomolecular analyses, including physiology, molecular biology, biochemistry and histochemistry. Integrated proteomic findings promise to be instrumental in improving our detailed knowledge of pathogenic mechanisms and multi-system dysfunction, widening the available biomarker signature of dystrophinopathy for improved diagnostic/prognostic procedures, and advancing the identification of novel therapeutic targets to treat Duchenne muscular dystrophy.

Identifying hub genes and dysregulated pathways in Duchenne muscular dystrophy

PURPOSE

The aim of this study was to identify the hub genes and dysregulated pathways in the progression of duchenne muscular dystrophy (DMD) and to unveil detailedly the cellular and molecular mechanisms associated with DMD for developing efficacious treatments in the future.

MATERIAL AND METHODS

Three mRNA microarray datasets (GSE13608, GSE38417 and GSE109178) were downloaded from Gene Expression Omnibus (GEO). The differentially expressed genes (DEGs) between DMD and normal tissues were obtained via R package. Function enrichment analyses were implemented respectively using DAVID online database. The network analysis of protein-protein interaction network (PPI) was conducted using String. Cytoscape and String were used to analyse modules and screen hub genes. The expression of the identified hub genes was confirmed in mdx mice through using qRT-PCR.

RESULTS

In total, 519 DEGs were identified, consisting of 393 upregulated genes and 126 downregulated genes. The enriched functions and pathways of the DEGs mainly involve extracellular matrix organization, collagen fibril organization, interferon-gamma-mediated signaling pathway, muscle contraction, endoplasmic reticulum lumen, MHC class II receptor activity, phagosome, graft-versus-host disease, cardiomyocytes, calcium signaling pathway. Twelve hub genes were discovered and biological process analysis proved that these genes were mainly enriched cell cycle, cell division. The result of qRT-PCR suggested that increase in expression of CD44, ECT2, TYMS, MAGEL2, HLA-DMA, SERPINH1, TNNT2 was confirmed in mdx mice and the downregulation of ASB2 and LEPREL1 was also observed.

CONCLUSION

In conclusion, DEGs and hub genes identified in the current research help us probe the molecular mechanisms underlying the pathogenesis and progression of DMD, and provide candidate targets for diagnosis and treatment of DMD.

Association between blood eosinophil count and Duchenne muscular dystrophy severity and prognosis: a retrospective cohort study

BACKGROUND

Duchenne muscular dystrophy (DMD) is a rare hereditary muscular disease. The role of eosinophils in DMD has not been clarified. This study aims to evaluate the association between peripheral blood eosinophil count and severity and prognosis of DMD.

METHODS

A retrospective cohort study was performed for 145 DMD patients between January 2012 and December 2020. Clinical data of 150 healthy children were collected as a control group. Logistic regression and Cox regression analyses were used to explore the influences of eosinophil count on DMD severity and prognosis.

RESULTS

Eosinophil count in DMD group was lower than the control group (Z = 2.163, P = 0.031). It was negatively correlated with Vignos scale score, Spearman correlation coefficient was p = 0.245, P = 0.040 (at admission), p = 0.137, P = 0.032 (at follow-up); was a protective factor for high Vignos scale score at admission [odds ratio (OR) = 0.038, 95%CI: 0.002-0.752, P = 0.032] and follow-up (OR = 0.033,95%CI: 0.001-0.121, P = 0.039). The Cox regression analysis indicated that elevated eosinophil count was correlated with better therapeutic efficacy for DMD patients [hazard ratio (HR) = 2.218, 95%CI: 1.154-3.924, P = 0.016].

CONCLUSION

Eosinophil count in peripheral blood was correlated with the severity of DMD. It could indicate the therapeutic efficacy and prognosis of DMD patients to a certain extent. Eosinophils may be a potentially valuable biomarker or therapeutic target for DMD.

Duchenne muscular dystrophy: disease mechanism and therapeutic strategies

Duchenne muscular dystrophy (DMD) is a severe, progressive, and ultimately fatal disease of skeletal muscle wasting, respiratory insufficiency, and cardiomyopathy. The identification of the dystrophin gene as central to DMD pathogenesis has led to the understanding of the muscle membrane and the proteins involved in membrane stability as the focal point of the disease. The lessons learned from decades of research in human genetics, biochemistry, and physiology have culminated in establishing the myriad functionalities of dystrophin in striated muscle biology. Here, we review the pathophysiological basis of DMD and discuss recent progress toward the development of therapeutic strategies for DMD that are currently close to or are in human clinical trials. The first section of the review focuses on DMD and the mechanisms contributing to membrane instability, inflammation, and fibrosis. The second section discusses therapeutic strategies currently used to treat DMD. This includes a focus on outlining the strengths and limitations of approaches directed at correcting the genetic defect through dystrophin gene replacement, modification, repair, and/or a range of dystrophin-independent approaches. The final section highlights the different therapeutic strategies for DMD currently in clinical trials.

Regulatory T cells-centered regulatory networks of skeletal muscle inflammation and regeneration

As the understanding of skeletal muscle inflammation is increasingly clarified, the role of Treg cells in the treatment of skeletal muscle diseases has attracted more attention in recent years. A consensus has been reached that the regulation of Treg cells is the key to completing the switch of inflammation and repair of skeletal muscle, whose presence directly determine the repairing quality of the injured skeletal muscle. However, the functioning process of Treg cells remains unreported, thereby making it necessary to summarize the current role of Treg cells in skeletal muscle. In this review, the characteristics, origins, and cellular kinetics of these Treg cells are firstly described; Then, the relationship between Treg cells and muscle satellite cells (MuSCs), conventional T cells (Tconv) is discussed (the former is involved in the entire repair and regeneration process, while the latter matters considerably in causing most skeletal muscle autoimmune diseases); Next, focus is placed on the control of Treg cells on the phenotypic switch of macrophages, which is the key to the switch of inflammation; Finally, factors regulating the functional process of Treg cells are analyzed, and a regulatory network centered on Treg cells is summarized. The present study summarizes the cell-mediated interactions in skeletal muscle repair over the past decade, and elucidates the central role of regulatory T cells in this process, so that other researchers can more quickly and comprehensively understand the development and direction of this very field. It is believed that the hereby proposed viewpoints and problems can provide fresh visions for the latecomers.

Immunoproteasome Inhibition Ameliorates Aged Dystrophic Mouse Muscle Environment

Muscle wasting is a major pathological feature observed in Duchenne muscular dystrophy (DMD) and is the result of the concerted effects of inflammation, oxidative stress and cell senescence. The inducible form of proteasome, or immunoproteasome (IP), is involved in all the above mentioned processes, regulating antigen presentation, cytokine production and immune cell response. IP inhibition has been previously shown to dampen the altered molecular, histological and functional features of 3-month-old mdx mice, the animal model for DMD. In this study, we described the role of ONX-0914, a selective inhibitor of the PSMB8 subunit of immunoproteasome, in ameliorating the pathological traits that could promote muscle wasting progression in older, 9-month-old mdx mice. ONX-0914 reduces the number of macrophages and effector memory T cells in muscle and spleen, while increasing the number of regulatory T cells. It modulates inflammatory markers both in skeletal and cardiac muscle, possibly counteracting heart remodeling and hypertrophy. Moreover, it buffers oxidative stress by improving mitochondrial efficiency. These changes ultimately lead to a marked decrease of fibrosis and, potentially, to more controlled myofiber degeneration/regeneration cycles. Therefore, ONX-0914 is a promising molecule that may slow down muscle mass loss, with relatively low side effects, in dystrophic patients with moderate to advanced disease.

Next-Generation SINE Compound KPT-8602 Ameliorates Dystrophic Pathology in Zebrafish and Mouse Models of DMD

Duchenne muscular dystrophy (DMD) is a progressive, X-linked childhood neuromuscular disorder that results from loss-of-function mutations in the DYSTROPHIN gene. DMD patients exhibit muscle necrosis, cardiomyopathy, respiratory failure, and loss of ambulation. One of the major driving forces of DMD disease pathology is chronic inflammation. The current DMD standard of care is corticosteroids; however, there are serious side effects with long-term use, thus identifying novel anti-inflammatory and anti-fibrotic treatments for DMD is of high priority. We investigated the next-generation SINE compound, KPT-8602 (eltanexor) as an oral therapeutic to alleviate dystrophic symptoms. We performed pre-clinical evaluation of the effects of KPT-8602 in DMD zebrafish (sapje) and mouse (D2-mdx) models. KPT-8602 improved dystrophic skeletal muscle pathologies, muscle architecture and integrity, and overall outcomes in both animal models. KPT-8602 treatment ameliorated DMD pathology in D2-mdx mice, with increased locomotor behavior and improved muscle histology. KPT-8602 altered the immunological profile of the dystrophic mice, and reduced circulating osteopontin serum levels. These findings demonstrate KPT-8602 as an effective therapeutic in DMD through by promotion of an anti-inflammatory environment and overall improvement of DMD pathological outcomes.

Selective ablation of Nfix in macrophages attenuates muscular dystrophy by inhibiting fibro-adipogenic progenitor-dependent fibrosis

Muscular dystrophies are genetic diseases characterized by chronic inflammation and fibrosis. Macrophages are immune cells that sustain muscle regeneration upon acute injury but seem deleterious in the context of chronic muscle injury such as in muscular dystrophies. Here, we observed that the number of macrophages expressing the transcription factor Nfix increases in two distinct mouse models of muscular dystrophies. We showed that the deletion of Nfix in macrophages in dystrophic mice delays the establishment of fibrosis and muscle wasting, and increases grasp force. Macrophages lacking Nfix expressed more TNFα and less TGFβ1, thus promoting apoptosis of fibro‐adipogenic progenitors. Moreover, pharmacological treatment of dystrophic mice with a ROCK inhibitor accelerated fibrosis through the increase of Nfix expression by macrophages. Thus, we have identified Nfix as a macrophage profibrotic factor in muscular dystrophies, whose inhibition could be a therapeutic route to reduce severity of the dystrophic disease. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Treating Duchenne Muscular Dystrophy: The Promise of Stem Cells, Artificial Intelligence, and Multi-Omics

Muscular dystrophies are chronic and debilitating disorders caused by progressive muscle wasting. Duchenne muscular dystrophy (DMD) is the most common type. DMD is a well-characterized genetic disorder caused by the absence of dystrophin. Although some therapies exist to treat the symptoms and there are ongoing efforts to correct the underlying molecular defect, patients with muscular dystrophies would greatly benefit from new therapies that target the specific pathways contributing directly to the muscle disorders. Three new advances are poised to change the landscape of therapies for muscular dystrophies such as DMD. First, the advent of human induced pluripotent stem cells (iPSCs) allows researchers to design effective treatment strategies that make up for the gaps missed by conventional “one size fits all” strategies. By characterizing tissue alterations with single-cell resolution and having molecular profiles for therapeutic treatments for a variety of cell types, clinical researchers can design multi-pronged interventions to not just delay degenerative processes, but regenerate healthy tissues. Second, artificial intelligence (AI) will play a significant role in developing future therapies by allowing the aggregation and synthesis of large and disparate datasets to help reveal underlying molecular mechanisms. Third, disease models using a high volume of multi-omics data gathered from diverse sources carry valuable information about converging and diverging pathways. Using these new tools, the results of previous and emerging studies will catalyze precision medicine-based drug development that can tackle devastating disorders such as DMD.

Inhibition of PKCθ Improves Dystrophic Heart Phenotype and Function in a Novel Model of DMD Cardiomyopathy

Chronic cardiac muscle inflammation and subsequent fibrotic tissue deposition are key features in Duchenne Muscular Dystrophy (DMD). The treatment of choice for delaying DMD progression both in skeletal and cardiac muscle are corticosteroids, supporting the notion that chronic inflammation in the heart plays a pivotal role in fibrosis deposition and subsequent cardiac dysfunction. Nevertheless, considering the adverse effects associated with long-term corticosteroid treatments, there is a need for novel anti-inflammatory therapies. In this study, we used our recently described exercised mdx (ex mdx) mouse model characterised by accelerated heart pathology, and the specific PKCθ inhibitor Compound 20 (C20), to show that inhibition of this kinase leads to a significant reduction in the number of immune cells infiltrating the heart, as well as necrosis and fibrosis. Functionally, C20 treatment also prevented the reduction in left ventricle fractional shortening, which was typically observed in the vehicle-treated ex mdx mice. Based on these findings, we propose that PKCθ pharmacological inhibition could be an attractive therapeutic approach to treating dystrophic cardiomyopathy

P2X7 Receptor Antagonist Reduces Fibrosis and Inflammation in a Mouse Model of Alpha-Sarcoglycan Muscular Dystrophy

Limb-girdle muscular dystrophy R3, a rare genetic disorder affecting the limb proximal muscles, is caused by mutations in the α-sarcoglycan gene (Sgca) and aggravated by an immune-mediated damage, finely modulated by the extracellular (e)ATP/purinoceptors axis. Currently, no specific drugs are available. The aim of this study was to evaluate the therapeutic effectiveness of a selective P2X7 purinoreceptor antagonist, A438079. Sgca knockout mice were treated with A438079 every two days at 3 mg/Kg for 24 weeks. The P2X7 antagonist improved clinical parameters by ameliorating mice motor function and decreasing serum creatine kinase levels. Histological analysis of muscle morphology indicated a significant reduction of the percentage of central nuclei, of fiber size variability and of the extent of local fibrosis and inflammation. A cytometric characterization of the muscle inflammatory infiltrates showed that A438079 significantly decreased innate immune cells and upregulated the immunosuppressive regulatory T cell subpopulation. In α-sarcoglycan null mice, the selective P2X7 antagonist A438079 has been shown to be effective to counteract the progression of the dystrophic phenotype and to reduce the inflammatory response. P2X7 antagonism via selective inhibitors could be included in the immunosuppressant strategies aimed to dampen the basal immune-mediated damage and to favor a better engraftment of gene-cell therapies.

The Immune System in Duchenne Muscular Dystrophy Pathogenesis

Growing evidence demonstrates the crosstalk between the immune system and the skeletal muscle in inflammatory muscle diseases and dystrophic conditions such as Duchenne Muscular Dystrophy (DMD), as well as during normal muscle regeneration. The rising of inflammation and the consequent activation of the immune system are hallmarks of DMD: several efforts identified the immune cells that invade skeletal muscle as CD4+ and CD8+ T cells, Tregs, macrophages, eosinophils and natural killer T cells. The severity of muscle injury and inflammation dictates the impairment of muscle regeneration and the successive replacement of myofibers with connective and adipose tissue. Since immune system activation was traditionally considered as a consequence of muscular wasting, we recently demonstrated a defect in central tolerance caused by thymus alteration and the presence of autoreactive T-lymphocytes in DMD. Although the study of innate and adaptive immune responses and their complex relationship in DMD attracted the interest of many researchers in the last years, the results are so far barely exhaustive and sometimes contradictory. In this review, we describe the most recent improvements in the knowledge of immune system involvement in DMD pathogenesis, leading to new opportunities from a clinical point-of-view.

Role of Immunoglobulins in Muscular Dystrophies and Inflammatory Myopathies

Muscular dystrophies and inflammatory myopathies are heterogeneous muscular disorders characterized by progressive muscle weakness and mass loss. Despite the high variability of etiology, inflammation and involvement of both innate and adaptive immune response are shared features. The best understood immune mechanisms involved in these pathologies include complement cascade activation, auto-antibodies directed against muscular proteins or de-novo expressed antigens in myofibers, MHC-I overexpression in myofibers, and lymphocytes-mediated cytotoxicity. Intravenous immunoglobulins (IVIGs) administration could represent a suitable immunomodulator with this respect. Here we focus on mechanisms of action of immunoglobulins in muscular dystrophies and inflammatory myopathies highlighting results of IVIGs from pre-clinical and case reports evidences.

The Interplay of Mitophagy and Inflammation in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is an X-linked neuromuscular disease caused by a pathogenic disruption of the DYSTROPHIN gene that results in non-functional dystrophin protein. DMD patients experience loss of ambulation, cardiac arrhythmia, metabolic syndrome, and respiratory failure. At the molecular level, the lack of dystrophin in the muscle results in myofiber death, fibrotic infiltration, and mitochondrial dysfunction. There is no cure for DMD, although dystrophin-replacement gene therapies and exon-skipping approaches are being pursued in clinical trials. Mitochondrial dysfunction is one of the first cellular changes seen in DMD myofibers, occurring prior to muscle disease onset and progresses with disease severity. This is seen by reduced mitochondrial function, abnormal mitochondrial morphology and impaired mitophagy (degradation of damaged mitochondria). Dysfunctional mitochondria release high levels of reactive oxygen species (ROS), which can activate pro-inflammatory pathways such as IL-1β and IL-6. Impaired mitophagy in DMD results in increased inflammation and further aggravates disease pathology, evidenced by increased muscle damage and increased fibrosis. This review will focus on the critical interplay between mitophagy and inflammation in Duchenne muscular dystrophy as a pathological mechanism, as well as describe both candidate and established therapeutic targets that regulate these pathways.

Inflammation, fibrosis and skeletal muscle regeneration in LGMDR9 are orchestrated by macrophages

AIMS

Variable degrees of inflammation, necrosis, regeneration and fibrofatty replacement are part of the pathological spectrum of the dystrophic process in alpha dystroglycanopathy LGMDR9 (FKRP-related, OMIM #607155), one of the most prevailing types of LGMDs worldwide. Inflammatory processes and their complex interplay with vascular, myogenic and mesenchymal cells may have a major impact on disease development. The purpose of our study is to describe the specific immune morphological features in muscle tissue of patients with LGMDR9 to enable a better understanding of the phenotype of muscle damage leading to disease progression.

METHODS

We have analysed skeletal muscle biopsies of 17 patients genetically confirmed as having LGMDR9 by histopathological and molecular techniques.

RESULTS

We identified CD206⁺ MHC class II⁺ and STAT6⁺ immune-repressed macrophages dominating the endomysial infiltrate in areas of myofibre regeneration and fibrosis. Additionally, PDGFRβ⁺ pericytes were located around MHC class II⁺ activated capillaries residing in close proximity to areas of fibrosis and regenerating fibres. Expression of VEGF was found on many regenerating neonatal myosin⁺ fibres, myofibres and CD206⁺ macrophages also co-expressed VEGF.

CONCLUSION

Our results show characteristic immune inflammatory features in LGMDR9 and more specifically shed light on the predominant role of macrophages and their function in vascular organisation, fibrosis and myogenesis. Understanding disease-specific immune phenomena potentially inform about possibilities for anti-fibrotic and anti-inflammatory therapeutic strategies, which may complement Ribitol replacement and gene therapies for LGMDR9 that may be available in the future.

Defective dystrophic thymus determines degenerative changes in skeletal muscle

In Duchenne muscular dystrophy (DMD), sarcolemma fragility and myofiber necrosis produce cellular debris that attract inflammatory cells. Macrophages and T-lymphocytes infiltrate muscles in response to damage-associated molecular pattern signalling and the release of TNF-α, TGF-β and interleukins prevent skeletal muscle improvement from the inflammation. This immunological scenario was extended by the discovery of a specific response to muscle antigens and a role for regulatory T cells (Tregs) in muscle regeneration. Normally, autoimmunity is avoided by autoreactive T-lymphocyte deletion within thymus, while in the periphery Tregs monitor effector T-cells escaping from central regulatory control. Here, we report impairment of thymus architecture of mdx mice together with decreased expression of ghrelin, autophagy dysfunction and AIRE down-regulation. Transplantation of dystrophic thymus in recipient nude mice determine the up-regulation of inflammatory/fibrotic markers, marked metabolic breakdown that leads to muscle atrophy and loss of force. These results indicate that involution of dystrophic thymus exacerbates muscular dystrophy by altering central immune tolerance.

A stromal progenitor and ILC2 niche promotes muscle eosinophilia and fibrosis-associated gene expression

Despite the well-accepted view that chronic inflammation contributes to the pathogenesis of Duchenne muscular dystrophy (DMD), the function and regulation of eosinophils remain an unclear facet of type II innate immunity in dystrophic muscle. We report the observation that group 2 innate lymphoid cells (ILC2s) are present in skeletal muscle and are the principal regulators of muscle eosinophils during muscular dystrophy. Eosinophils were elevated in DMD patients and dystrophic mice along with interleukin (IL)-5, a major eosinophil survival factor that was predominantly expressed by muscle ILC2s. We also find that IL-33 was upregulated in dystrophic muscle and was predominantly produced by fibrogenic/adipogenic progenitors (FAPs). Exogenous IL-33 and IL-2 complex (IL-2c) expanded muscle ILC2s and eosinophils, decreased the cross-sectional area (CSA) of regenerating myofibers, and increased the expression of genes associated with muscle fibrosis. The deletion of ILC2s in dystrophic mice mitigated muscle eosinophilia and impaired the induction of IL-5 and fibrosis-associated genes. Our findings highlight a FAP/ILC2/eosinophil axis that promotes type II innate immunity, which influences the balance between regenerative and fibrotic responses during muscular dystrophy.

Immune cells that comprise type II innate immunity coalesce to regulate tissue repair and fibrosis. Kastenschmidt et al. report that ILC2s reside in skeletal muscle, are activated in muscular dystrophy, and promote muscle eosinophilia. Stromal progenitors expressed IL-33, which expanded ILC2s and promoted a transcriptional program associated with muscle fibrosis.

Proteome-wide Changes in the mdx-4cv Spleen due to Pathophysiological Cross Talk with Dystrophin-Deficient Skeletal Muscle

Duchenne muscular dystrophy is primarily characterized by progressive muscle wasting due to deficiency in the membrane cytoskeletal protein dystrophin but is also associated with body-wide cellular disturbances in a variety of non-muscle tissues. In this study, we have focused on the comparative proteomic analysis of the spleen and established considerable changes in this crucial secondary lymphoid organ from the genetic mdx-4cv mouse model of dystrophinopathy. An apparent short isoform of dystrophin and associated glycoproteins were identified in spleen by mass spectrometry but appear not be affected in muscular dystrophy. In contrast, the mdx-4cv spleen showed significant proteome-wide changes in other protein species that are involved in metabolism, signaling, and cellular architecture. Since the spleen plays a key role in the immune response, these proteomic alterations may reflect pathophysiological cross talk between the lymphoid system and dystrophic muscles, which are affected by both fiber degeneration and inflammation.

The Impact of Immune Cells on the Skeletal Muscle Microenvironment During Cancer Cachexia

Progressive weight loss combined with skeletal muscle atrophy, termed cachexia, is a common comorbidity associated with cancer that results in adverse consequences for the patient related to decreased chemotherapy responsiveness and increased mortality. Cachexia's complexity has provided a barrier for developing successful therapies to prevent or treat the condition, since a large number of systemic disruptions that can regulate muscle mass are often present. Furthermore, considerable effort has focused on investigating how tumor derived factors and inflammatory mediators directly signal skeletal muscle to disrupt protein turnover regulation. Currently, there is developing appreciation for understanding how cancer alters skeletal muscle's complex microenvironment and the tightly regulated interactions between multiple cell types. Skeletal muscle microenvironment interactions have established functions in muscle response to regeneration from injury, growth, aging, overload-induced hypertrophy, and exercise. This review explores the growing body of evidence for immune cell modulation of the skeletal muscle microenvironment during cancer-induced muscle wasting. Emphasis is placed on the regulatory network that integrates physiological responses between immune cells with other muscle cell types including satellite cells, fibroblast cells, and endothelial cells to regulate myofiber size and plasticity. The overall goal of this review is to provide an understanding of how different cell types that constitute the muscle microenvironment and their signaling mediators contribute to cancer and chemotherapy-induced muscle wasting.

Long-term human IgG treatment improves heart and muscle function in a mouse model of Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease caused by mutations in the dystrophin gene, which leads to structural instability of the dystrophin-glycoprotein-complex with subsequent muscle degeneration. In addition, muscle inflammation has been implicated in disease progression and therapeutically addressed with glucocorticosteroids. These have numerous adverse effects. Treatment with human immunoglobulin G (IgG) improved clinical and para-clinical parameters in the early disease phase in the well-established mdx mouse model. The aim of the present study was to confirm the efficacy of IgG in a long-term pre-clinical study in mdx mice.

METHODS

IgG (2 g/kg body weight) or NaCl solution as control was administered monthly over 18 months by intraperitoneal injection in mdx mice beginning at 3 weeks of age. Several clinical outcome measures including endurance, muscle strength, and echocardiography were assessed. After 18 months, the animals were sacrificed, blood was collected for analysis, and muscle samples were obtained for ex vivo muscle contraction tests, quantitative PCR, and histology.

RESULTS

IgG significantly improved the daily voluntary running performance (1.9 m more total daily running distance, P < 0.0001) and slowed the decrease in grip strength by 0.1 mN, (P = 0.018). IgG reduced fatigability of the diaphragm (improved ratio to maximum force by 0.09 ± 0.04, P = 0.044), but specific tetanic force remained unchanged in the ex vivo muscle contraction test. Cardiac function was significantly better after IgG, especially fractional area shortening (P = 0.012). These results were accompanied by a reduction in cardiac fibrosis and the infiltration of T cells (P = 0.0002) and macrophages (P = 0.0027). In addition, treatment with IgG resulted in a significant reduction of the infiltration of T cells (P ≤ 0.036) in the diaphragm, gastrocnemius, quadriceps, and a similar trend in tibialis anterior and macrophages (P ≤ 0.045) in gastrocnemius, quadriceps, tibialis anterior, and a similar trend in the diaphragm, as well as a decrease in myopathic changes as reflected by a reduced central nuclear index in the diaphragm, tibialis anterior, and quadriceps (P ≤ 0.002 in all).

CONCLUSIONS

The present study underscores the importance of an inflammatory contribution to the disease progression of DMD. The data demonstrate the long-term efficacy of IgG in the mdx mouse. IgG is well tolerated by humans and could preferentially complement gene therapy in DMD. The data call for a clinical trial with IgG in DMD.

Arrhythmogenic Cardiomyopathy and Skeletal Muscle Dystrophies: Shared Histopathological Features and Pathogenic Mechanisms

Arrhythmogenic cardiomyopathy (ACM) is a heritable cardiac disease characterized by fibrotic or fibrofatty myocardial replacement, associated with an increased risk of ventricular arrhythmias and sudden cardiac death. Originally described as a disease of the right ventricle, ACM is currently recognized as a biventricular entity, due to the increasing numbers of reports of predominant left ventricular or biventricular involvement. Research over the last 20 years has significantly advanced our knowledge of the etiology and pathogenesis of ACM. Several etiopathogenetic theories have been proposed; among them, the most attractive one is the dystrophic theory, based on the observation of similar histopathological features between ACM and skeletal muscle dystrophies (SMDs), such as progressive muscular degeneration, inflammation, and tissue replacement by fatty and fibrous tissue. This review will describe the pathophysiological and molecular similarities shared by ACM with SMDs.

Group 2 Innate Lymphoid Cells: Central Players in a Recurring Theme of Repair and Regeneration

Innate lymphoid cells (ILCs) are recently discovered innate counterparts to the well-established T helper cell subsets and are most abundant at barrier surfaces, where they participate in tissue homeostasis and inflammatory responses against invading pathogens. Group 2 innate lymphoid cells (ILC2s) share cytokine and transcription factor expression profiles with type-2 helper T cells and are primarily associated with immune responses against allergens and helminth infections. Emerging data, however, suggests that ILC2s are also key regulators in other inflammatory settings; both in a beneficial context, such as the establishment of neonatal immunity, tissue repair, and homeostasis, and in the context of pathological tissue damage and disease, such as fibrosis development. This review focuses on the interactions of ILC2s with stromal cells, eosinophils, macrophages, and T regulatory cells that are common to the different settings in which type-2 immunity has been explored. We further discuss how an understanding of these interactions can reveal new avenues of therapeutic tissue regeneration, where the role of ILC2s is yet to be fully established.

Role of Insulin-Like Growth Factor Receptor 2 across Muscle Homeostasis: Implications for Treating Muscular Dystrophy

The insulin-like growth factor 2 receptor (IGF2R) plays a major role in binding and regulating the circulating and tissue levels of the mitogenic peptide insulin-like growth factor 2 (IGF2). IGF2/IGF2R interaction influences cell growth, survival, and migration in normal tissue development, and the deregulation of IGF2R expression has been associated with growth-related disease and cancer. IGF2R overexpression has been implicated in heart and muscle disease progression. Recent research findings suggest novel approaches to target IGF2R action. This review highlights recent advances in the understanding of the IGF2R structure and pathways related to muscle homeostasis.

Underlying Immune Disorder May Predispose Some Transthyretin Amyloidosis Subjects to Inotersen-Mediated Thrombocytopenia

Inotersen, a 2'-O-methoxyethyl (2'-MOE) phosphorothioate antisense oligonucleotide, reduced disease progression and improved quality of life in patients with hereditary transthyretin amyloidosis with polyneuropathy (hATTR-PN) in the NEURO-TTR and NEURO-TTR open-label extension (OLE) trials. However, 300 mg/week inotersen treatment was associated with platelet count reductions in several patients. Mean platelet counts in patients in the NEURO-TTR-inotersen group remained ≥140 × 10⁹/L in 50% and ≥100 × 10⁹/L in 80% of the subjects. However, grade 4 thrombocytopenia (<25 × 10⁹/L) occurred in three subjects in NEURO-TTR trial, and one of these suffered a fatal intracranial hemorrhage. The two others were treated successfully with corticosteroids and discontinuation of inotersen. Investigations in a subset of subjects in NEURO-TTR (n = 17 placebo; n = 31 inotersen) and OLE (n = 33) trials ruled out direct myelotoxicity, consumptive coagulopathy, and heparin-induced thrombocytopenia. Antiplatelet immunoglobulin G (IgG) antibodies were detected at baseline in 5 of 31 (16%) inotersen-treated subjects in NEURO-TTR, 4 of whom eventually developed grade 1 or 2 thrombocytopenia while on the drug. In addition, 24 subjects in the same group developed treatment-emergent antiplatelet IgG antibodies, of which 2 developed grade 2, and 3 developed grade 4 thrombocytopenia. Antiplatelet IgG antibodies in two of the three grade 4 thrombocytopenia subjects targeted GPIIb/IIIa. Plasma cytokines previously implicated in immune dysregulation, such as interleukin (IL)-23 and a proliferation-inducing ligand (APRIL) were often above the normal range at baseline. Collectively, these findings suggest an underlying immunologic dysregulation predisposing some individuals to immune-mediated thrombocytopenia during inotersen treatment.

Splenic Ly6Chi monocytes are critical players in dystrophic muscle injury and repair

Dystrophic muscle is characterized by chronic injury and a steady recruitment of inflammatory Ly6Chi monocytes. Recent studies have identified the spleen as the dominant reservoir of these cells during chronic inflammation. Here, we investigated the contribution of splenic Ly6Chi monocytes to dystrophic muscle pathology. Using the mdx mouse model of muscular dystrophy, we show that Ly6Chi monocytes accumulate in great numbers in the spleen over the course of the disease. The chemokine receptor CCR2 was upregulated on Ly6Chi monocytes in mdx spleen before disease onset, thereby enabling their recruitment to dystrophic muscle. Splenectomy performed before disease onset significantly reduced the number of Ly6Chi monocytes infiltrating dystrophic limb muscle. Moreover, in the absence of splenic Ly6Chi monocytes there was a significant reduction in dystrophic muscle inflammation and necrosis, along with improved regeneration during early disease. However, during late disease, a lack of splenic Ly6Chi monocytes adversely affected muscle fiber repair, due to a delay in the phenotypic shift of proinflammatory F4/80+Ly6ChiCD206lo to antiinflammatory F4/80+Ly6CloCD206+ macrophages. Overall, we show that the spleen is an indispensable source of Ly6Chi monocytes in muscular dystrophy and that splenic monocytes are critical players in both muscle fiber injury and repair.

The SINE Compound KPT-350 Blocks Dystrophic Pathologies in DMD Zebrafish and Mice

Duchenne muscular dystrophy (DMD) is an X-linked muscle wasting disease that is caused by the loss of functional dystrophin protein in cardiac and skeletal muscles. DMD patient muscles become weakened, leading to eventual myofiber breakdown and replacement with fibrotic and adipose tissues. Inflammation drives the pathogenic processes through releasing inflammatory cytokines and other factors that promote skeletal muscle degeneration and contributing to the loss of motor function. Selective inhibitors of nuclear export (SINEs) are a class of compounds that function by inhibiting the nuclear export protein exportin 1 (XPO1). The XPO1 protein is an important regulator of key inflammatory and neurological factors that drive inflammation and neurotoxicity in various neurological and neuromuscular diseases. Here, we demonstrate that SINE compound KPT-350 can ameliorate dystrophic-associated pathologies in the muscles of DMD models of zebrafish and mice. Thus, SINE compounds are a promising novel strategy for blocking dystrophic symptoms and could be used in combinatorial treatments for DMD.

Free intramuscular Mg2+ concentration calculated using both 31 P and 1 H NMRS-based pH in the skeletal muscle of Duchenne muscular dystrophy patients

Early studies have demonstrated that (total) magnesium was decreased in skeletal muscle of Duchenne muscular dystrophy (DMD) patients. Free intramuscular Mg²⁺ can be derived from ³¹ P NMRS measurements. The value of free intramuscular magnesium concentration ([Mg²⁺ ]) is highly dependent on precise knowledge of intracellular pH, which is abnormally alkaline in dystrophic muscle, possibly due to an expanded interstitial space, potentially causing an underestimation of [Mg²⁺ ]. We have recently shown that intracellular pH can be derived using ¹ H NMRS of carnosine. Our aim was to determine whether ³¹ P NMRS-based [Mg²⁺ ] is, in fact, abnormally low in DMD patients, taking advantage of the ¹ H NMRS-based pH. A comparative analysis was, therefore, made between [Mg²⁺ ] values calculated with both ¹ H and ³¹ P NMRS-based approaches to determine pH in 25 DMD patients, on a 3-T clinical NMR scanner. [Mg²⁺ ] was also assessed with ³¹ P NMRS only in (forearm or leg) skeletal muscle of 60 DMD patients and 63 age-matched controls. Additionally, phosphodiester levels as well as quantitative NMRI indices including water T₂ , fat fraction, contractile cross-sectional area and one-year changes were evaluated. The main finding was that the significant difference in [Mg²⁺ ] between DMD patients and controls was preserved even when the intracellular pH determined with ¹ H NMRS was similar in both groups. Consequently, we observed that [Mg²⁺ ] is significantly lower in DMD patients compared with controls in the larger database where only ³¹ P NMRS data were obtained. Significant yet weak correlations existed between [Mg²⁺ ] and PDE, water T₂ and fat fraction. We concluded that low [Mg²⁺ ] is an actual finding in DMD, whether intracellular pH is normal or alkaline, and that it is a likely consequence of membrane leakiness. The response of Mg²⁺ to therapeutic treatment remains to be investigated in neuromuscular disorders. Free [Mg²⁺ ] determination with ³¹ P NMRS is highly dependent on a precise knowledge of intracellular pH. The pH of Duchenne muscular dystrophy (DMD) patients, as determined by ³¹ P NMRS, is abnormally alkaline. We have recently shown that intracellular pH could be determined using ¹ H NMRS of carnosine, and that intracellular pH was alkaline in a proportion of, but not all, DMD patients with a ³¹ P NMRS-based alkaline pH. Taking advantage of this ¹ H NMRS-based intracellular pH, we found that free intramuscular [Mg²⁺ ] is in fact abnormally low in DMD patients.

Dystrophin deficiency promotes leukocyte recruitment in mdx mice

BACKGROUND

A growing body of evidence defines inflammation as a hallmark feature of disease pathogenesis of Duchenne muscular dystrophy. To tailor potential immune modulatory interventions, a better understanding of immune dysregulation in Duchenne muscular dystrophy is needed. We now asked whether dystrophin deficiency affects the cascade of leukocyte recruitment.

METHODS

We performed intravital microscopy on the cremaster muscle of wild-type and dystrophin-deficient mdx mice. Recruitment was triggered by preparation alone (traumatic inflammation) or in combination with scrotal TNFα injections. Neutrophilic infiltration of the cremaster muscle was assessed on tissue sections. Integrin expression on circulating neutrophils and serum levels of pro-inflammatory cytokines were measured by flow cytometry.

RESULTS

Mdx mice show increased rolling and adhesion at baseline (traumatic inflammation) and a more profound response upon TNFα injection compared with wild-type animals. In both models, neutrophilic infiltration of the cremaster muscle is increased. Upregulation of the integrins LFA-1 and Mac-1 on circulating leukocytes and pro-inflammatory cytokines IL-6 and CCL2 in the serum points toward systemically altered immune regulation in mdx mice.

CONCLUSION

We are the first to show exaggerated activation of the leukocyte recruitment cascade in a dystrophin-deficient organism in vivo.

Preliminary Evidences of Safety and Efficacy of Flavonoids- and Omega 3-Based Compound for Muscular Dystrophies Treatment: A Randomized Double-Blind Placebo Controlled Pilot Clinical Trial

Background: Nutritional compounds can exert both anti-inflammatory and anti-oxidant effects. Since these events exacerbate the pathophysiology of muscular dystrophies, we investigated nutraceutical supplementation as an adjuvant therapy in dystrophic patients, to low costs and easy route of administration. Moreover, this treatment could represent an alternative therapeutic strategy for dystrophic patients who do not respond to corticosteroid treatment.

Objective: A 24 weeks randomized double-blind placebo-controlled clinical study was aimed at evaluating the safety and efficacy of daily oral administration of flavonoids- and omega3-based natural supplement (FLAVOMEGA) in patients affected by muscular dystrophy with recognized muscle inflammation.

Design: We screened 60 patients diagnosed for Duchenne (DMD), Facioscapulohumeral (FSHD), and Limb Girdle Muscular Dystrophy (LGMD). Using a computer-generated random allocation sequence, we stratified patients in a 2:1:1 ratio (DMD:FSHD:LGMD) to one of two treatment groups: continuous FLAVOMEGA, continuous placebo. Of 29 patients included, only 24 completed the study: 15 were given FLAVOMEGA, 14 placebo.

Results: FLAVOMEGA was well tolerated with no reported adverse events. Significant treatment differences in the change from baseline in 6 min walk distance (6MWD; secondary efficacy endpoint) (P = 0.033) and in isokinetic knee extension (P = 0.039) (primary efficacy endpoint) were observed in LGMD and FSHD subjects. Serum CK levels (secondary efficacy endpoint) decreased in all FLAVOMEGA treated groups with significant difference in DMD subjects (P = 0.039).

Conclusions: Although the small number of patients and the wide range of disease severity among patients reduced statistical significance, we obtained an optimal profile of safety and tolerability for the compound, showing valuable data of efficacy in primary and secondary endpoints.

Trial registration number: NCT03317171

Retrospectively registered 25/10/2017

Eosinophils Do Not Drive Acute Muscle Pathology in the mdx Mouse Model of Duchenne Muscular Dystrophy

Eosinophils are present in muscle lesions associated with Duchenne muscular dystrophy and dystrophin-deficient mdx mice that phenocopy this disorder. Although it has been hypothesized that eosinophils promote characteristic inflammatory muscle damage, this has not been fully examined. In this study, we generated mice with the dystrophin mutation introduced into PHIL, a strain with a transgene that directs lineage-specific eosinophil ablation. We also explored the impact of eosinophil overabundance on dystrophinopathy by introducing the dystrophin mutation into IL-5 transgenic mice. We evaluated the degree of eosinophil infiltration in association with myofiber size distribution, centralized nuclei, serum creatine kinase, and quantitative histopathology scores. Among our findings, eosinophils were prominent in the quadriceps muscles of 4-wk-old male mdx mice but no profound differences were observed in the quantitative measures of muscle damage when comparing mdx versus mdx.PHIL versus mdx.IL5tg mice, despite dramatic differences in eosinophil infiltration (CD45+CD11c-Gr1-MHC class IIloSiglecF+ eosinophils at 1.2 ± 0.34% versus <0.1% versus 20 ± 7.6% of total cells, respectively). Further evaluation revealed elevated levels of eosinophil chemoatttractants eotaxin-1 and RANTES in the muscle tissue of all three dystrophin-deficient strains; eotaxin-1 concentration in muscle correlated inversely with age. Cytokines IL-4 and IL-1R antagonist were also detected in association with eosinophils in muscle. Taken together, our findings challenge the long-held perception of eosinophils as cytotoxic in dystrophin-deficient muscle; we show clearly that eosinophil infiltration is not a driving force behind acute muscle damage in the mdx mouse strain. Ongoing studies will focus on the functional properties of eosinophils in this unique microenvironment.

Simultaneous Enrichment Analysis of all Possible Gene-sets: Unifying Self-Contained and Competitive Methods

Studying sets of genomic features is increasingly popular in genomics, proteomics and metabolomics since analyzing at set level not only creates a natural connection to biological knowledge but also offers more statistical power. Currently, there are two gene-set testing approaches, self-contained and competitive, both of which have their advantages and disadvantages, but neither offers the final solution. We introduce simultaneous enrichment analysis (SEA), a new approach for analysis of feature sets in genomics and other omics based on a new unified null hypothesis, which includes the self-contained and competitive null hypotheses as special cases. We employ closed testing using Simes tests to test this new hypothesis. For every feature set, the proportion of active features is estimated, and a confidence bound is provided. Also, for every unified null hypotheses, a \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$P$\end{document}-value is calculated, which is adjusted for family-wise error rate. SEA does not need to assume that the features are independent. Moreover, users are allowed to choose the feature set(s) of interest after observing the data. We develop a novel pipeline and apply it on RNA-seq data of dystrophin-deficient mdx mice, showcasing the flexibility of the method. Finally, the power properties of the method are evaluated through simulation studies.

The Role of Metabolic Remodeling in Macrophage Polarization and Its Effect on Skeletal Muscle Regeneration

Significance: Macrophages are crucial for tissue homeostasis. Based on their activation, they might display classical/M1 or alternative/M2 phenotypes. M1 macrophages produce pro-inflammatory cytokines, reactive oxygen species (ROS), and nitric oxide (NO). M2 macrophages upregulate arginase-1 and reduce NO and ROS levels; they also release anti-inflammatory cytokines, growth factors, and polyamines, thus promoting angiogenesis and tissue healing. Moreover, M1 and M2 display key metabolic differences; M1 polarization is characterized by an enhancement in glycolysis and in the pentose phosphate pathway (PPP) along with a decreased oxidative phosphorylation (OxPhos), whereas M2 are characterized by an efficient OxPhos and reduced PPP. Recent Advances: The glutamine-related metabolism has been discovered as crucial for M2 polarization. Vice versa, flux discontinuities in the Krebs cycle are considered additional M1 features; they lead to increased levels of immunoresponsive gene 1 and itaconic acid, to isocitrate dehydrogenase 1-downregulation and to succinate, citrate, and isocitrate over-expression. Critical Issues: A macrophage classification problem, particularly in vivo, originating from a gap in the knowledge of the several intermediate polarization statuses between the M1 and M2 extremes, characterizes this field. Moreover, the detailed features of metabolic reprogramming crucial for macrophage polarization are largely unknown; in particular, the role of β-oxidation is highly controversial. Future Directions: Manipulating the metabolism to redirect macrophage polarization might be useful in various pathologies, including an efficient skeletal muscle regeneration. Unraveling the complexity pertaining to metabolic signatures that are specific for the different macrophage subsets is crucial for identifying new compounds that are able to trigger macrophage polarization and that might be used for therapeutical purposes.

A tissue communication network coordinating innate immune response during muscle stress

Complex tissue communication networks function throughout an organism's lifespan to maintain tissue homeostasis. Using the genetic model Drosophila melanogaster, we have defined a network of immune responses that are activated following the induction of muscle stresses, including hypercontraction, detachment and oxidative stress. Of these stressors, loss of the genes that cause muscle detachment produced the strongest levels of JAK-STAT activation. In one of these mutants, fondue (fon), we also observe hemocyte recruitment and the accumulation of melanin at muscle attachment sites (MASs), indicating a broad involvement of innate immune responses upon muscle detachment. Loss of fon results in pathogen-independent Toll signaling in the fat body and increased expression of the Toll-dependent antimicrobial peptide Drosomycin. Interestingly, genetic interactions between fon and various Toll pathway components enhance muscle detachment. Finally, we show that JAK-STAT and Toll signaling are capable of reciprocal activation in larval tissues. We propose a model of tissue communication for the integration of immune responses at the local and systemic level in response to altered muscle physiology.

Biological scaffold-mediated delivery of myostatin inhibitor promotes a regenerative immune response in an animal model of Duchenne muscular dystrophy

Recent studies have reported that the immune system significantly mediates skeletal muscle repair and regeneration. Additionally, biological scaffolds have been shown to play a role in polarizing the immune microenvironment toward pro-myogenic outcomes. Moreover, myostatin inhibitors are known to promote muscle regeneration and ameliorate fibrosis in animal models of Duchenne muscular dystrophy (DMD), a human disease characterized by chronic muscle degeneration. Biological scaffolds and myostatin inhibition can potentially influence immune-mediated regeneration in the dystrophic environment, but have not been evaluated together. Toward this end, here we created an injectable biological scaffold composed of hyaluronic acid and processed skeletal muscle extracellular matrix. This material formed a cytocompatible hydrogel at physiological temperatures in vitro When injected subfascially above the tibialis anterior muscles of both WT and dystrophic mdx-5^Cv mice, a murine model of DMD, the hydrogel spreads across the entire muscle before completely degrading at 3 weeks in vivo We found that the hydrogel is associated with CD206⁺ pro-regenerative macrophage polarization and elevated anti-inflammatory cytokine expression in both WT and dystrophic mice. Co-injection of both hydrogel and myostatin inhibitor significantly increased FoxP3⁺ regulatory T cell modulation and Foxp3 gene expression in the scaffold immune microenvironment. Finally, delivery of myostatin inhibitor with the hydrogel increased its bioactivity in vivo, and transplantation of immortalized human myoblasts with the hydrogel promoted their survival in vivo This study identifies a key role for biological scaffolds and myostatin inhibitors in modulating a pro-regenerative immune microenvironment in dystrophic muscle.

Agent-based model illustrates the role of the microenvironment in regeneration in healthy and mdx skeletal muscle

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease with no effective treatment. Multiple mechanisms are thought to contribute to muscle wasting, including increased susceptibility to contraction-induced damage, chronic inflammation, fibrosis, altered satellite stem cell (SSC) dynamics, and impaired regenerative capacity. The goals of this project were to 1) develop an agent-based model of skeletal muscle that predicts the dynamic regenerative response of muscle cells, fibroblasts, SSCs, and inflammatory cells as a result of contraction-induced injury, 2) calibrate and validate the model parameters based on comparisons with published experimental measurements, and 3) use the model to investigate how changing isolated and combined factors known to be associated with DMD (e.g., altered fibroblast or SSC behaviors) influence muscle regeneration. Our predictions revealed that the percent of injured muscle that recovered 28 days after injury was dependent on the peak SSC counts following injury. In simulations with near-full cross-sectional area recovery (healthy, 4-wk mdx, 3-mo mdx), the SSC counts correlated with the extent of initial injury; however, in simulations with impaired regeneration (9-mo mdx), the peak SSC counts were suppressed relative to initial injury. The differences in SSC counts between these groups were emergent predictions dependent on altered microenvironment factors known to be associated with DMD. Multiple cell types influenced the peak number of SSCs, but no individual parameter predicted the differences in SSC counts. This finding suggests that interventions to target the microenvironment rather than SSCs directly could be an effective method for improving regeneration in impaired muscle. NEW & NOTEWORTHY A computational model predicted that satellite stem cell (SSC) counts are correlated with muscle cross-sectional area (CSA) recovery following injury. In simulations with impaired CSA recovery, SSC counts are suppressed relative to healthy muscle. The suppressed SSC counts were an emergent model prediction, because all simulations had equal initial SSC counts. Fibroblast and anti-inflammatory macrophage counts influenced SSC counts, but no single factor was able to predict the pathological differences in SSC counts that lead to impaired regeneration.

Combined use of protein biomarkers and network analysis unveils deregulated regulatory circuits in Duchenne muscular dystrophy

Although the genetic basis of Duchenne muscular dystrophy has been known for almost thirty years, the cellular and molecular mechanisms characterizing the disease are not completely understood and an efficacious treatment remains to be developed. In this study we analyzed proteomics data obtained with the SomaLogic technology from blood serum of a cohort of patients and matched healthy subjects. We developed a workflow based on biomarker identification and network-based pathway analysis that allowed us to describe different deregulated pathways. In addition to muscle-related functions, we identified other biological processes such as apoptosis, signaling in the immune system and neurotrophin signaling as significantly modulated in patients compared with controls. Moreover, our network-based analysis identified the involvement of FoxO transcription factors as putative regulators of different pathways. On the whole, this study provided a global view of the molecular processes involved in Duchenne muscular dystrophy that are decipherable from serum proteome.

1 H NMRS of carnosine combined with 31 P NMRS to better characterize skeletal muscle pH dysregulation in Duchenne muscular dystrophy

In recent years, quantitative nuclear magnetic resonance imaging and spectroscopy (NMRI and NMRS) have been used more systematically as outcome measures in natural history and clinical trial studies for Duchenne muscular dystrophy (DMD). Whereas most of these studies have emphasized the evaluation of the fat fraction as an assessment for disease severity, less focus has been placed on metabolic indices measured by NMRS. ³¹ P NMRS in DMD reveals an alkaline inorganic phosphate (P_i ) pool, originating from either leaky dystrophic myocytes or an increased interstitial space. ¹ H NMRS, exploiting the pH-sensitive proton resonances of carnosine, an intracellular dipeptide, was used to distinguish between these two hypotheses. NMR data were obtained in 23 patients with DMD and 14 healthy subjects on a 3-T clinical NMR system. Both ³¹ P and ¹ H NMRS data were acquired at the level of the gastrocnemius medialis muscle. A multi-slice multi-echo imaging acquisition was performed for the determination of water T₂ and fat fraction in the same region of interest. Whereas nearly all patients with DMD showed an elevated pH compared with healthy controls when using ³¹ P NMRS, ¹ H NMRS-determined pH was not systematically increased. As expected, the carnosine-based intracellular pH was never found to be alkaline in the absence of a concurrent P_i -based pH elevation. In addition, abnormal intracellular pH, based on carnosine, was never associated with normal water T₂ values. We conclude that, in one group of patients, both ¹ H and ³¹ P NMRS showed an alkaline pH, originating from the intracellular compartment and reflecting ionic dysregulation in dystrophic myocytes. In the other patients with DMD, intracellular pH was normal, but an alkaline P_i pool was still present, suggesting an extracellular origin, probably revealing an expanded interstitial volume fraction, often associated with fibrotic changes. The data demonstrate that ¹ H NMRS could serve as a biomarker to assess the normalization of intramyocytic pH and sarcolemmal permeability following therapy inducing dystrophin expression in patients with DMD.

The Muscle Stem Cell Niche in Health and Disease

The regulation of stem cells that maintain and regenerate postnatal tissues depends on extrinsic signals originating from their microenvironment, commonly referred to as the stem cell niche. Complex higher-order regulatory interrelationships with the tissue and factors in the systemic circulation are integrated and propagated to the stem cells through the niche. The stem cell niche in skeletal muscle tissue is both a paradigm for a structurally and functionally relatively static niche that maintains stem cell quiescence during tissue homeostasis, and a highly dynamic regenerative niche that is subject to extensive structural remodeling and a flux of different support cell populations. Conditions ranging from aging to chronically degenerative skeletal muscle diseases affect the composition of the niche and thereby impair the regenerative potential of muscle stem cells. A holistic and integrative understanding of the extrinsic mechanisms regulating muscle stem cells in health and disease in a broad systemic context will be imperative for the identification of regulatory hubs in the niche interactome that can be targeted to maintain, restore, or enhance the regenerative capacity of muscle tissue. Here, we review the microenvironmental regulation of muscle stem cells, summarize how niche dysfunction can contribute to disease, and discuss emerging therapeutic implications.

Immunoglobulin therapy ameliorates the phenotype and increases lifespan in the severely affected dystrophin-utrophin double knockout mice

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder, caused by mutations in the dystrophin gene, affecting 1:3500-5000 boys worldwide. The lack of dystrophin induces degeneration of muscle cells and elicits an immune response characterized by an intensive secretion of pro-inflammatory cytokines. Immunoglobulins modulate the inflammatory response through several mechanisms and have been widely used as an adjuvant therapy for autoimmune diseases. Here we evaluated the effect of immunoglobulin G (IG) injected intraperitoneally in a severely affected double knockout (dko) mouse model for Duchenne muscular dystrophy. The IG dko treated mice were compared regarding activity rates, survival and histopathology with a control untreated group. Additionally, dendritic cells and naïve lymphocytes from these two groups and WT mice were obtained to study in vitro the role of the immune system associated to DMD pathophysiology. We show that IG therapy significantly enhances activity rate and lifespan of dko mice. It diminishes muscle tissue inflammation by decreasing the expression of costimulatory molecules MHC, CD86 and CD40 and reducing Th1-related cytokines IFN-γ, IL-1β and TNF-α release. IG therapy dampens the effector immune responses supporting the hypothesis according to which the immune response accelerates DMD progression. As IG therapy is already approved by FDA for treating autoimmune disorders, with less side-effects than currently used glucocorticoids, our results may open a new therapeutic option aiming to improve life quality and lifespan of DMD patients.

Restoration of pharyngeal dilator muscle force in dystrophin-deficient (mdx) mice following co-treatment with neutralizing interleukin-6 receptor antibodies and urocortin 2

NEW FINDINGS

What is the central question of this study? We previously reported impaired upper airway dilator muscle function in the mdx mouse model of Duchenne muscular dystrophy (DMD). Our aim was to assess the effect of blocking interleukin-6 receptor signalling and stimulating corticotrophin-releasing factor receptor 2 signalling on mdx sternohyoid muscle structure and function. What is the main finding and its importance? The interventional treatment had a positive inotropic effect on sternohyoid muscle force, restoring mechanical work and power to wild-type values, reduced myofibre central nucleation and preserved the myosin heavy chain type IIb fibre complement of mdx sternohyoid muscle. These data might have implications for development of pharmacotherapies for DMD with relevance to respiratory muscle performance. The mdx mouse model of Duchenne muscular dystrophy shows evidence of impaired pharyngeal dilator muscle function. We hypothesized that inflammatory and stress-related factors are implicated in airway dilator muscle dysfunction. Six-week-old mdx (n = 26) and wild-type (WT; n = 26) mice received either saline (0.9% w/v) or a co-administration of neutralizing interleukin-6 receptor antibodies (0.2 mg kg^-1 ) and corticotrophin-releasing factor receptor 2 agonist (urocortin 2; 30 μg kg^-1 ) over 2 weeks. Sternohyoid muscle isometric and isotonic contractile function was examined ex vivo. Muscle fibre centronucleation and muscle cellular infiltration, collagen content, fibre-type distribution and fibre cross-sectional area were determined by histology and immunofluorescence. Muscle chemokine content was examined by use of a multiplex assay. Sternohyoid peak specific force at 100 Hz was significantly reduced in mdx compared with WT. Drug treatment completely restored force in mdx sternohyoid to WT levels. The percentage of centrally nucleated muscle fibres was significantly increased in mdx, and this was partly ameliorated after drug treatment. The areal density of infiltrates and collagen content were significantly increased in mdx sternohyoid; both indices were unaffected by drug treatment. The abundance of myosin heavy chain type IIb fibres was significantly decreased in mdx sternohyoid; drug treatment preserved myosin heavy chain type IIb complement in mdx muscle. The chemokines macrophage inflammatory protein 2, interferon-γ-induced protein 10 and macrophage inflammatory protein 3α were significantly increased in mdx sternohyoid compared with WT. Drug treatment significantly increased chemokine expression in mdx but not WT sternohyoid. Recovery of contractile function was impressive in our study, with implications for Duchenne muscular dystrophy. The precise molecular mechanisms by which the drug treatment exerts an inotropic effect on mdx sternohyoid muscle remain to be elucidated.

Proteomic profiling of mdx-4cv serum reveals highly elevated levels of the inflammation-induced plasma marker haptoglobin in muscular dystrophy

X-linked muscular dystrophy is caused by primary abnormalities in the Dmd gene and is characterized by the almost complete loss of the membrane cytoskeletal protein dystrophin, which triggers sarcolemmal instability, abnormal calcium homeostasis, increased proteolysis and impaired excitation-contraction coupling. In addition to progressive necrosis, crucial secondary pathologies are represented by myofibrosis and the invasion of immune cells in damaged muscle fibres. In order to determine whether these substantial changes within the skeletal musculature are reflected by an altered rate of protein release into the circulatory system or other plasma fluctuations, we used label-free mass spectrometry to characterize serum from the mdx-4cv model of Duchenne muscular dystrophy. Comparative proteomics revealed a large number of increased vs. decreased protein species in mdx-4cv serum. A serum component with greatly elevated levels was identified as the inflammation-inducible plasma marker haptoglobin. This acute phase response protein is usually secreted in relation to tissue damage and sterile inflammation. Both immunoblot analyses and enzyme-linked immunosorbent assays confirmed the increased concentration of haptoglobin in crude mdx-4cv serum. This suggests that haptoglobin, in conjunction with other altered serum proteins, represents a novel diagnostic, prognostic and/or therapy-monitoring biomarker candidate to evaluate the inflammatory response in the mdx-4cv animal model of dystrophinopathy.

Pharmacological Inhibition of PKCθ Counteracts Muscle Disease in a Mouse Model of Duchenne Muscular Dystrophy

Inflammation plays a considerable role in the progression of Duchenne Muscular Dystrophy (DMD), a severe muscle disease caused by a mutation in the dystrophin gene. We previously showed that genetic ablation of Protein Kinase C θ (PKCθ) in mdx, the mouse model of DMD, improves muscle healing and regeneration, preventing massive inflammation. To establish whether pharmacological targeting of PKCθ in DMD can be proposed as a therapeutic option, in this study we treated young mdx mice with the PKCθ inhibitor Compound 20 (C20). We show that C20 treatment led to a significant reduction in muscle damage associated with reduced immune cells infiltration, reduced inflammatory pathways activation, and maintained muscle regeneration. Importantly, C20 treatment is efficient in recovering muscle performance in mdx mice, by preserving muscle integrity. Together, these results provide proof of principle that pharmacological inhibition of PKCθ in DMD can be considered an attractive strategy to modulate immune response and prevent the progression of the disease.

Research in context

Duchenne muscular dystrophy (DMD) is a severe muscle disease affecting 1:3500 male births. DMD is caused by a mutation in dystrophin gene, coding for a protein required for skeletal and cardiac muscle integrity. Lack of a functional dystrophin is primarily responsible for the muscle eccentric contraction-induced muscle damage, observed in dystrophic muscle. However, inflammation plays a considerable role in the progression of DMD. Glucocorticoids, which have anti-inflammatory properties, are being used to treat DMD with some success; however, long term treatment with these drugs induces muscle atrophy and wasting, outweighing their benefit. The identification of specific targets for anti-inflammatory therapies is one of the ongoing therapeutic options. Although blunting inflammation would not be a “cure” for the disease, the emerging clue is that multiple strategies, addressing different aspects of the pathology, which may eventually converge, may be successful. In this context, we previously showed that genetic ablation of Protein Kinase C θ (PKCθ), an enzyme known to be involved in immune response, in mdx, the mouse model of DMD, improves muscle healing and regeneration, preventing massive inflammation. To establish whether pharmacological targeting of PKCθ in DMD can be proposed as a therapeutic option, in this study we treated young mdx mice with the PKCθ inhibitor Compound 20 (C20). We show that C20 treatment led to a significant reduction in muscle damage associated with reduced immune cells infiltration, reduced inflammatory pathways activation, and maintained muscle regeneration. Importantly, C20 treatment is efficient in recovering muscle performance in mdx mice, by preserving muscle integrity. Together, these results provide proof of principle that pharmacological inhibition of PKCθ in DMD can be considered an attractive strategy to modulate immune response and prevent the progression of the disease.

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Immune-cell intrinsic PKCθ activity might play a hitherto unrecognized role of in the development of DMD.

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Mdx dystrophic mice were treated with the PKCθ inhibitor C20.

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C20 treatment prevents damage and inflammation in dystrophic muscle, while improving muscle regeneration.

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C20 treatment prevents drop in force and ameliorates fatigue resistance in dystrophic mice.

Anti-inflammatory drugs for Duchenne muscular dystrophy: focus on skeletal muscle-releasing factors

Duchenne muscular dystrophy (DMD), an incurable and a progressive muscle wasting disease, is caused by the absence of dystrophin protein, leading to recurrent muscle fiber damage during contraction. The inflammatory response to fiber damage is a compelling candidate mechanism for disease exacerbation. The only established pharmacological treatment for DMD is corticosteroids to suppress muscle inflammation, however this treatment is limited by its insufficient therapeutic efficacy and considerable side effects. Recent reports show the therapeutic potential of inhibiting or enhancing pro- or anti-inflammatory factors released from DMD skeletal muscles, resulting in significant recovery from muscle atrophy and dysfunction. We discuss and review the recent findings of DMD inflammation and opportunities for drug development targeting specific releasing factors from skeletal muscles. It has been speculated that nonsteroidal anti-inflammatory drugs targeting specific inflammatory factors are more effective and have less side effects for DMD compared with steroidal drugs. For example, calcium channels, reactive oxygen species, and nuclear factor-κB signaling factors are the most promising targets as master regulators of inflammatory response in DMD skeletal muscles. If they are combined with an oligonucleotide-based exon skipping therapy to restore dystrophin expression, the anti-inflammatory drug therapies may address the present therapeutic limitation of low efficiency for DMD.

[Inflammation and muscle regeneration, a double-edged sword]

Muscle injuries are very frequent and are associated with an inflammatory reaction that varies in intensity. Classically the inflammatory process was considered harmful for muscle regeneration and anti-inflammatory agents are still part of a conventional therapy. Over the last decades, it has been demonstrated under some conditions that the inflammatory response could be detrimental for the musculoskeletal tissue. However, accumulating evidence indicate that controlled and efficient inflammatory response is necessary for an optimal muscle recovery. Among the resident and infiltrating leukocytes that participate into the inflammatory process, macrophages play a critical role in muscle regeneration due to their ability to switch from pro-inflammatory to anti-inflammatory phenotypes depending on their microenvironment. The present review synthesizes the recent advances regarding the interactions of the different infiltrating and resident leukocytes on myogenic cell function and muscle regeneration.

Understanding the molecular consequences of inherited muscular dystrophies: advancements through proteomic experimentation

INTRODUCTION

Proteomic techniques offer insights into the molecular perturbations occurring in muscular-dystrophies (MD). Revisiting published datasets can highlight conserved downstream molecular alterations, which may be worth re-assessing to determine whether their experimental manipulation is capable of modulating disease severity.

AREAS COVERED

Here, we review the MD literature, highlighting conserved molecular insights warranting mechanistic investigation for therapeutic potential. We also describe a workflow currently proving effective for efficient identification of biomarkers & therapeutic targets in other neurodegenerative conditions, upon which future MD proteomic investigations could be modelled. Expert commentary: Studying disease models can be useful for identifying biomarkers and model specific degenerative cascades, but rarely offer translatable mechanistic insights into disease pathology. Conversely, direct analysis of human samples undergoing degeneration presents challenges derived from complex chronic degenerative molecular processes. This requires a carefully planed & reproducible experimental paradigm accounting for patient selection through to grouping by disease severity and ending with proteomic data filtering and processing.

Dystrophin: The dead calm of a dogma

Duchenne muscular dystrophy (DMD) is the most common inherited muscle disease leading to severe disability and death of young men. Current interventions are palliative as no treatment improves the long-term outcome. Therefore, new therapeutic modalities with translational potential are urgently needed and abnormalities downstream from the absence of dystrophin are realistic targets. It has been shown that DMD mutations alter extracellular ATP (eATP) signaling via P2RX7 purinoceptor upregulation, which leads to autophagic death of dystrophic muscle cells. Furthermore, the eATP-P2RX7 axis contributes to DMD pathology by stimulating harmful inflammatory responses. We demonstrated recently that genetic ablation or pharmacological inhibition of P2RX7 in the mdx mouse model of DMD produced functional attenuation of both muscle and non-muscle symptoms, establishing this receptor as an attractive therapeutic target. Central to the argument presented here, this purinergic phenotype affects dystrophic myoblasts. Muscle cells were believed not to be affected at this stage of differentiation, as they do not produce detectable dystrophin protein. Our findings contradict the central hypothesis stating that aberrant dystrophin expression is inconsequential in myoblasts and the DMD pathology results from effects such as sarcolemma fragility, due to the absence of dystrophin, in differentiated myofibres. However, we discuss here the evidence that, already in myogenic cells, DMD mutations produce a plethora of abnormalities, including in cell proliferation, differentiation, energy metabolism, Ca(2+) homeostasis and death, leading to impaired muscle regeneration. We hope that this discussion may bring to light further results that will help re-evaluating the established belief. Clearly, understanding how DMD mutations alter such a range of functions in myogenic cells is vital for developing effective therapies.