Immunobiology of Inherited Muscular Dystrophies

Blood Transcriptome Profiling Links Immunity to Disease Severity in Myotonic Dystrophy Type 1 (DM1)

The blood transcriptome was examined in relation to disease severity in type I myotonic dystrophy (DM1) patients who participated in the Observational Prolonged Trial In DM1 to Improve QoL- Standards (OPTIMISTIC) study. This sought to (a) ascertain if transcriptome changes were associated with increasing disease severity, as measured by the muscle impairment rating scale (MIRS), and (b) establish if these changes in mRNA expression and associated biological pathways were also observed in the Dystrophia Myotonica Biomarker Discovery Initiative (DMBDI) microarray dataset in blood (with equivalent MIRS/DMPK repeat length). The changes in gene expression were compared using a number of complementary pathways, gene ontology and upstream regulator analyses, which suggested that symptom severity in DM1 was linked to transcriptomic alterations in innate and adaptive immunity associated with muscle-wasting. Future studies should explore the role of immunity in DM1 in more detail to assess its relevance to DM1.

Myeloid mineralocorticoid receptors contribute to skeletal muscle repair in muscular dystrophy and acute muscle injury

Suppressing mineralocorticoid receptor (MR) activity with MR antagonists is therapeutic for chronic skeletal muscle pathology in Duchenne muscular dystrophy (DMD) mouse models. Although mechanisms underlying clinical MR antagonist efficacy for DMD cardiomyopathy and other cardiac diseases are defined, mechanisms in skeletal muscles are not fully elucidated. Myofiber MR knockout improves skeletal muscle force and a subset of dystrophic pathology. However, MR signaling in myeloid cells is known to be a major contributor to cardiac efficacy. To define contributions of myeloid MR in skeletal muscle function and disease, we performed parallel assessments of muscle pathology, cytokine levels, and myeloid cell populations resulting from myeloid MR genetic knockout in muscular dystrophy and acute muscle injury. Myeloid MR knockout led to lower levels of C-C motif chemokine receptor 2 (CCR2)-expressing macrophages, resulting in sustained myofiber damage after acute injury of normal muscle. In acute injury, myeloid MR knockout also led to increased local muscle levels of the enzyme that produces the endogenous MR agonist aldosterone, further supporting important contributions of MR signaling in normal muscle repair. In muscular dystrophy, myeloid MR knockout altered cytokine levels differentially between quadriceps and diaphragm muscles, which contain different myeloid populations. Myeloid MR knockout led to higher levels of fibrosis in dystrophic diaphragm. These results support important contributions of myeloid MR signaling to skeletal muscle repair in acute and chronic injuries and highlight the useful information gained from cell-specific genetic knockouts to delineate mechanisms of pharmacological efficacy.

The ratio of cardiac troponin T to troponin I may indicate non-necrotic troponin release among COVID-19 patients

BACKGROUND

Although cardiac troponin T (cTnT) and troponin I(cTnI) are expressed to similar amount in cardiac tissue, cTnI often reach ten-times higher peak levels compared to cTnT in patients with myocardial necrosis such as in acute myocardial infarction (MI). In contrast, similar levels of cTnT and cTnI are observed in other situations such as stable atrial fibrillation and after strenuous exercise.

OBJECTIVE

Examine cTnT and cTnI levels in relation to COVID-19 disease and MI.

METHODS

Clinical and laboratory data from the local hospital from an observational cohort study of 27 patients admitted with COVID-19 and 15 patients with myocardial infarction (MI) that were analyzed with paired cTnT and cTnI measurement during hospital care.

RESULTS

Levels of cTnI were lower than cTnT in COVID-19 patients (TnI/TnT ratio 0.3, IQR: 0.1-0.6). In contrast, levels of cTnI were 11 times higher compared to cTnT in 15 patients with MI (TnI/TnT ratio 11, IQR: 7-14). The peak cTnI/cTnT ratio among the patients with MI following successful percutaneous intervention were 14 (TnI/TnT ratio 14, IQR: 12-23). The 5 COVID-19 patient samples collected under possible necrotic events had a cTnI/cTnT ratio of 5,5 (IQR: 1,9-8,3).

CONCLUSIONS

In patients with COVID-19, cTnT is often elevated to higher levels than cTnI in sharp contrast to patients with MI, indicating that the release of cardiac troponin has a different cause in COVID-19 patients.

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.

Hydrogen sulfide as a therapeutic option for the treatment of Duchenne muscular dystrophy and other muscle-related diseases

Hydrogen sulfide (H₂S) has been known for years as a poisoning gas and until recently evoked mostly negative associations. However, the discovery of its gasotransmitter functions suggested its contribution to various physiological and pathological processes. Although H₂S has been found to exert cytoprotective effects through modulation of antioxidant, anti-inflammatory, anti-apoptotic, and pro-angiogenic responses in a variety of conditions, its role in the pathophysiology of skeletal muscles has not been broadly elucidated so far. The classical example of muscle-related disorders is Duchenne muscular dystrophy (DMD), the most common and severe type of muscular dystrophy. Mutations in the DMD gene that encodes dystrophin, a cytoskeletal protein that protects muscle fibers from contraction-induced damage, lead to prominent dysfunctions in the structure and functions of the skeletal muscle. However, the main cause of death is associated with cardiorespiratory failure, and DMD remains an incurable disease. Taking into account a wide range of physiological functions of H₂S and recent literature data on its possible protective role in DMD, we focused on the description of the 'old' and 'new' functions of H₂S, especially in muscle pathophysiology. Although the number of studies showing its essential regulatory action in dystrophic muscles is still limited, we propose that H₂S-based therapy has the potential to attenuate the progression of DMD and other muscle-related disorders.

Macrophage plasticity in Duchenne muscular dystrophy: a nexus of pathological remodelling with therapeutic implications

Duchenne muscular dystrophy (DMD) is characterized by chronic skeletal muscle necrosis, leading to muscle regeneration failure and fibrosis. Although macrophages (MPs) are normally essential for muscle regeneration, dysregulated MP function promotes pathological muscle remodelling. Infiltrating MPs can be predominantly pro-inflammatory (M1 biased), anti-inflammatory (M2 biased) or of a mixed phenotype and can originate from the adult bone marrow (monocyte dependent) or embryonic precursors (monocyte independent). In mdx mice (genetic model of DMD) lacking either Toll-like receptor (Tlr) 2 or Tlr4, it is found that MP infiltration of dystrophic muscle is significantly reduced and that the MP phenotype is shifted toward a more anti-inflammatory profile. This is accompanied by significant improvements in muscle histology and force production. Lack of the chemokine receptor CCR2, which impedes monocyte release from the bone marrow, leads to similar beneficial effects in mdx mice. Evidence was also found for Tlr4-regulated induction of trained innate immunity in MPs cultured from the bone marrow of mdx mice before their entry into the muscle. These MPs exhibit epigenetic and metabolic alterations, accompanied by non-specific hyper-responsiveness to multiple stimuli, which is manifested by potentiated upregulation of both pro- and anti-inflammatory genes. In summary, exaggerated recruitment of monocyte-derived MPs and signs of trained innate immunity at the level of the bone marrow are features of the immunophenotype associated with dystrophic muscle disease. These phenomena are regulated by Toll-like receptors that bind endogenous damage-associated molecular pattern (DAMP) molecules, suggesting that DAMP release from dystrophic muscles modulates MP plasticity at the bone marrow level through Toll-like receptor-driven mechanisms.

Deficiency of MMP-10 Aggravates the Diseased Phenotype of Aged Dystrophic Mice

Matrix metalloproteinases (MMPs) have been implicated in the progression of muscular dystrophy, and recent studies have reported the role of MMP-10 in skeletal muscle pathology of young dystrophic mice. Nevertheless, its involvement in dystrophin-deficient hearts remains unexplored. Here, we aimed to investigate the involvement of MMP-10 in the progression of severe muscular dystrophy and to characterize MMP-10 loss in skeletal and cardiac muscles of aged dystrophic mice. We examined the histopathological effect of MMP-10 ablation in aged mdx mice, both in the hind limb muscles and heart tissues. We found that MMP-10 loss compromises survival rates of aged mdx mice, with skeletal and cardiac muscles developing a chronic inflammatory response. Our findings indicate that MMP-10 is implicated in severe muscular dystrophy progression, thus identifying a new area of research that could lead to future therapies for dystrophic muscles.

Sertoli Cells Improve Myogenic Differentiation, Reduce Fibrogenic Markers, and Induce Utrophin Expression in Human DMD Myoblasts

Duchenne muscular dystrophy (DMD) is an X-linked disease caused by mutations in DMD gene translating in lack of functional dystrophin and resulting in susceptibility of myofibers to rupture during contraction. Inflammation and fibrosis are critical hallmarks of DMD muscles, which undergo progressive degeneration leading to loss of independent ambulation in childhood and death by early adulthood. We reported that intraperitoneal injection of microencapsulated Sertoli cells (SeC) in dystrophic mice translates into recovery of muscle morphology and performance thanks to anti-inflammatory effects and induction of the dystrophin paralogue, utrophin at the muscle level, opening new avenues in the treatment of DMD. The aim of this study is to obtain information about the direct effects of SeC on myoblasts/myotubes, as a necessary step in view of a translational application of SeC-based approaches to DMD. We show that (i) SeC-derived factors stimulate cell proliferation in the early phase of differentiation in C2C12, and human healthy and DMD myoblasts; (ii) SeC delay the expression of differentiation markers in the early phase nevertheless stimulating terminal differentiation in DMD myoblasts; (iii) SeC restrain the fibrogenic potential of fibroblasts, and inhibit myoblast-myofibroblast transdifferentiation; and, (iv) SeC provide functional replacement of dystrophin in preformed DMD myotubes regardless of the mutation by inducing heregulin β1/ErbB2/ERK1/2-dependent utrophin expression. Altogether, these results show that SeC are endowed with promyogenic and antifibrotic effects on dystrophic myoblasts, further supporting their potential use in the treatment of DMD patients. Our data also suggest that SeC-based approaches might be useful in improving the early phase of muscle regeneration, during which myoblasts have to adequately proliferate to replace the damaged muscle mass.

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.

Inflammation in Duchenne Muscular Dystrophy-Exploring the Role of Neutrophils in Muscle Damage and Regeneration

Duchenne muscular dystrophy (DMD) is a severe and progressive, X-linked, neuromuscular disorder caused by mutations in the dystrophin gene. In DMD, the lack of functional dystrophin protein makes the muscle membrane fragile, leaving the muscle fibers prone to damage during contraction. Muscle degeneration in DMD patients is closely associated with a prolonged inflammatory response, and while this is important to stimulate regeneration, inflammation is also thought to exacerbate muscle damage. Neutrophils are one of the first immune cells to be recruited to the damaged muscle and are the first line of defense during tissue injury or infection. Neutrophils can promote inflammation by releasing pro-inflammatory cytokines and compounds, including myeloperoxidase (MPO) and neutrophil elastase (NE), that lead to oxidative stress and are thought to have a role in prolonging inflammation in DMD. In this review, we provide an overview of the roles of the innate immune response, with particular focus on mechanisms used by neutrophils to exacerbate muscle damage and impair regeneration in DMD.

Complexity of skeletal muscle degeneration: multi-systems pathophysiology and organ crosstalk in dystrophinopathy

Duchenne muscular dystrophy is a highly progressive muscle wasting disorder due to primary abnormalities in one of the largest genes in the human genome, the DMD gene, which encodes various tissue-specific isoforms of the protein dystrophin. Although dystrophinopathies are classified as primary neuromuscular disorders, the body-wide abnormalities that are associated with this disorder and the occurrence of organ crosstalk suggest that a multi-systems pathophysiological view should be taken for a better overall understanding of the complex aetiology of X-linked muscular dystrophy. This article reviews the molecular and cellular effects of deficiency in dystrophin isoforms in relation to voluntary striated muscles, the cardio-respiratory system, the kidney, the liver, the gastrointestinal tract, the nervous system and the immune system. Based on the establishment of comprehensive biomarker signatures of X-linked muscular dystrophy using large-scale screening of both patient specimens and genetic animal models, this article also discusses the potential usefulness of novel disease markers for more inclusive approaches to differential diagnosis, prognosis and therapy monitoring that also take into account multi-systems aspects of dystrophinopathy. Current therapeutic approaches to combat muscular dystrophy are summarised.

Validation of Chemokine Biomarkers in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a progressive muscle disease involving complex skeletal muscle pathogenesis. The pathogenesis is triggered by sarcolemma instability due to the lack of dystrophin protein expression, leading to Ca²⁺ influx, muscle fiber apoptosis, inflammation, muscle necrosis, and fibrosis. Our lab recently used two high-throughput multiplexing techniques (e.g., SomaScan^® aptamer assay and tandem mass tag-(TMT) approach) and identified a series of serum protein biomarkers tied to different pathobiochemical pathways. In this study, we focused on validating the circulating levels of three proinflammatory chemokines (CCL2, CXCL10, and CCL18) that are believed to be involved in an early stage of muscle pathogenesis. We used highly specific and reproducible MSD ELISA assays and examined the association of these chemokines with DMD pathogenesis, age, disease severity, and response to glucocorticoid treatment. As expected, we confirmed that these three chemokines were significantly elevated in serum and muscle samples of DMD patients relative to age-matched healthy controls (p-value < 0.05, CCL18 was not significantly altered in muscle samples). These three chemokines were not significantly elevated in Becker muscular dystrophy (BMD) patients, a milder form of dystrophinopathy, when compared in a one-way ANOVA to a control group but remained significantly elevated in the age-matched DMD group (p < 0.05). CCL2 and CCL18 but not CXCL10 declined with age in DMD patients, whereas all three chemokines remained unchanged with age in BMD and controls. Only CCL2 showed significant association with time to climb four steps in the DMD group (r = 0.48, p = 0.038) and neared significant association with patients' reported outcome in the BMD group (r = 0.39, p = 0.058). Furthermore, CCL2 was found to be elevated in a serum of the mdx mouse model of DMD, relative to wild-type mouse model. This study suggests that CCL2 might be a suitable candidate biomarker for follow-up studies to demonstrate its physiological significance and clinical utility in DMD.

Met and Cxcr4 cooperate to protect skeletal muscle stem cells against inflammation-induced damage during regeneration

Acute skeletal muscle injury is followed by an inflammatory response, removal of damaged tissue, and the generation of new muscle fibers by resident muscle stem cells, a process well characterized in murine injury models. Inflammatory cells are needed to remove the debris at the site of injury and provide signals that are beneficial for repair. However, they also release chemokines, reactive oxygen species, as well as enzymes for clearance of damaged cells and fibers, which muscle stem cells have to withstand in order to regenerate the muscle. We show here that MET and CXCR4 cooperate to protect muscle stem cells against the adverse environment encountered during muscle repair. This powerful cyto-protective role was revealed by the genetic ablation of Met and Cxcr4 in muscle stem cells of mice, which resulted in severe apoptosis during early stages of regeneration. TNFα neutralizing antibodies rescued the apoptosis, indicating that TNFα provides crucial cell-death signals during muscle repair that are counteracted by MET and CXCR4. We conclude that muscle stem cells require MET and CXCR4 to protect them against the harsh inflammatory environment encountered in an acute muscle injury.

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.

Therapeutic aspects of cell signaling and communication in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a devastating chromosome X-linked disease that manifests predominantly in progressive skeletal muscle wasting and dysfunctions in the heart and diaphragm. Approximately 1/5000 boys and 1/50,000,000 girls suffer from DMD, and to date, the disease is incurable and leads to premature death. This phenotypic severity is due to mutations in the DMD gene, which result in the absence of functional dystrophin protein. Initially, dystrophin was thought to be a force transducer; however, it is now considered an essential component of the dystrophin-associated protein complex (DAPC), viewed as a multicomponent mechanical scaffold and a signal transduction hub. Modulating signal pathway activation or gene expression through epigenetic modifications has emerged at the forefront of therapeutic approaches as either an adjunct or stand-alone strategy. In this review, we propose a broader perspective by considering DMD to be a disease that affects myofibers and muscle stem (satellite) cells, as well as a disorder in which abrogated communication between different cell types occurs. We believe that by taking this systemic view, we can achieve safe and holistic treatments that can restore correct signal transmission and gene expression in diseased DMD tissues.

Beneficial Role of Exercise in the Modulation of mdx Muscle Plastic Remodeling and Oxidative Stress

Duchenne muscular dystrophy (DMD) is an X-linked recessive progressive lethal disorder caused by the lack of dystrophin, which determines myofibers mechanical instability, oxidative stress, inflammation, and susceptibility to contraction-induced injuries. Unfortunately, at present, there is no efficient therapy for DMD. Beyond several promising gene- and stem cells-based strategies under investigation, physical activity may represent a valid noninvasive therapeutic approach to slow down the progression of the pathology. However, ethical issues, the limited number of studies in humans and the lack of consistency of the investigated training interventions generate loss of consensus regarding their efficacy, leaving exercise prescription still questionable. By an accurate analysis of data about the effects of different protocol of exercise on muscles of mdx mice, the most widely-used pre-clinical model for DMD research, we found that low intensity exercise, especially in the form of low speed treadmill running, likely represents the most suitable exercise modality associated to beneficial effects on mdx muscle. This protocol of training reduces muscle oxidative stress, inflammation, and fibrosis process, and enhances muscle functionality, muscle regeneration, and hypertrophy. These conclusions can guide the design of appropriate studies on human, thereby providing new insights to translational therapeutic application of exercise to DMD patients.

Proteomic profiling of the interface between the stomach wall and the pancreas in dystrophinopathy

The neuromuscular disorder Duchenne muscular dystrophy is a multi-systemic disease that is caused by a primary abnormality in the X-chromosomal Dmd gene. Although progressive skeletal muscle wasting and cardio-respiratory complications are the most serious symptoms that are directly linked to the almost complete loss of the membrane cytoskeletal protein dystrophin, dystrophic patients also suffer from gastrointestinal dysfunction. In order to determine whether proteome-wide changes potentially occur in the gastrointestinal system due to dystrophin deficiency, total tissue extracts from the interface between the stomach wall and the pancreas of the mdx-4cv model of dystrophinopathy were analysed by mass spectrometry. Following the proteomic establishment of both smooth muscle markers of the gastrointestinal system and key enzymes of the pancreas, core members of the dystrophin-glycoprotein complex, including dystrophin, dystroglycans, sarcoglycans, dystrobrevins and syntrophins were identified in this tissue preparation. Comparative proteomics revealed a drastic reduction in dystrophin, sarcoglycan, dystroglycan, laminin, titin and filamin suggesting loss of cytoskeletal integrity in mdx-4cv smooth muscles. A concomitant increase in various mitochondrial enzymes is indicative of metabolic disturbances. These findings agree with abnormal gastrointestinal function in dystrophinopathy.

The linkage between inflammation and fibrosis in muscular dystrophies: The axis autotaxin-lysophosphatidic acid as a new therapeutic target?

Muscular dystrophies (MDs) are a diverse group of severe disorders characterized by increased skeletal muscle feebleness. In many cases, respiratory and cardiac muscles are also compromised. Skeletal muscle inflammation and fibrosis are hallmarks of several skeletal muscle diseases, including MDs. Until now, several keys signaling pathways and factors that regulate inflammation and fibrosis have been identified. However, no curative treatments are available. Therefore, it is necessary to find new therapeutic targets to fight these diseases and improve muscle performance. Lysophosphatidic acid (LPA) is an active glycerophospholipid mainly synthesized by the secreted enzyme autotaxin (ATX), which activates six different G protein-coupled receptors named LPA₁ to LPA₆ (LPARs). In conjunction, they are part of the ATX/LPA/LPARs axis, involved in the inflammatory and fibrotic response in several organs-tissues. This review recapitulates the most relevant aspects of inflammation and fibrosis in MDs. It analyzes experimental evidence of the effects of the ATX/LPA/LPARs axis on inflammatory and fibrotic responses. Finally, we speculate about its potential role as a new therapeutic pharmacological target to treat these diseases.

Rheumatoid cachexia: the underappreciated role of myoblast, macrophage and fibroblast interplay in the skeletal muscle niche

Although rheumatoid arthritis affects 1% of the global population, the role of rheumatoid cachexia, which occurs in up to a third of patients, is relatively neglected as research focus, despite its significant contribution to decreased quality of life in patients. A better understanding of the cellular and molecular processes involved in rheumatoid cachexia, as well as its potential treatment, is dependent on elucidation of the intricate interactions of the cells involved, such as myoblasts, fibroblasts and macrophages. Persistent RA-associated inflammation results in a relative depletion of the capacity for regeneration and repair in the satellite cell niche. The repair that does proceed is suboptimal due to dysregulated communication from the other cellular role players in this multi-cellular environment. This includes the incomplete switch in macrophage phenotype resulting in a lingering pro-inflammatory state within the tissues, as well as fibroblast-associated dysregulation of the dynamic control of the extracellular matrix. Additional to this endogenous dysregulation, some treatment strategies for RA may exacerbate muscle wasting and no multi-cell investigation has been done in this context. This review summarizes the most recent literature characterising clinical RA cachexia and links these features to the roles of and complex communication between multiple cellular contributors in the muscle niche, highlighting the importance of a targeted approach to therapeutic intervention.

Nanomedicine for Gene Delivery and Drug Repurposing in the Treatment of Muscular Dystrophies

Muscular Dystrophies (MDs) are a group of rare inherited genetic muscular pathologies encompassing a variety of clinical phenotypes, gene mutations and mechanisms of disease. MDs undergo progressive skeletal muscle degeneration causing severe health problems that lead to poor life quality, disability and premature death. There are no available therapies to counteract the causes of these diseases and conventional treatments are administered only to mitigate symptoms. Recent understanding on the pathogenetic mechanisms allowed the development of novel therapeutic strategies based on gene therapy, genome editing CRISPR/Cas9 and drug repurposing approaches. Despite the therapeutic potential of these treatments, once the actives are administered, their instability, susceptibility to degradation and toxicity limit their applications. In this frame, the design of delivery strategies based on nanomedicines holds great promise for MD treatments. This review focuses on nanomedicine approaches able to encapsulate therapeutic agents such as small chemical molecules and oligonucleotides to target the most common MDs such as Duchenne Muscular Dystrophy and the Myotonic Dystrophies. The challenge related to in vitro and in vivo testing of nanosystems in appropriate animal models is also addressed. Finally, the most promising nanomedicine-based strategies are highlighted and a critical view in future developments of nanomedicine for neuromuscular diseases is provided.

Duchenne muscular dystrophy

Duchenne muscular dystrophy is a severe, progressive, muscle-wasting disease that leads to difficulties with movement and, eventually, to the need for assisted ventilation and premature death. The disease is caused by mutations in DMD (encoding dystrophin) that abolish the production of dystrophin in muscle. Muscles without dystrophin are more sensitive to damage, resulting in progressive loss of muscle tissue and function, in addition to cardiomyopathy. Recent studies have greatly deepened our understanding of the primary and secondary pathogenetic mechanisms. Guidelines for the multidisciplinary care for Duchenne muscular dystrophy that address obtaining a genetic diagnosis and managing the various aspects of the disease have been established. In addition, a number of therapies that aim to restore the missing dystrophin protein or address secondary pathology have received regulatory approval and many others are in clinical development.

Proteomic profiling of the interface between the stomach wall and the pancreas in dystrophinopathy

The neuromuscular disorder Duchenne muscular dystrophy is a multi-systemic disease that is caused by a primary abnormality in the X-chromosomal Dmd gene. Although progressive skeletal muscle wasting and cardio-respiratory complications are the most serious symptoms that are directly linked to the almost complete loss of the membrane cytoskeletal protein dystrophin, dystrophic patients also suffer from gastrointestinal dysfunction. In order to determine whether proteome-wide changes potentially occur in the gastrointestinal system due to dystrophin deficiency, total tissue extracts from the interface between the stomach wall and the pancreas of the mdx-4cv model of dystrophinopathy were analysed by mass spectrometry. Following the proteomic establishment of both smooth muscle markers of the gastrointestinal system and key enzymes of the pancreas, core members of the dystrophin-glycoprotein complex, including dystrophin, dystroglycans, sarcoglycans, dystrobrevins and syntrophins were identified in this tissue preparation. Comparative proteomics revealed a drastic reduction in dystrophin, sarcoglycan, dystroglycan, laminin, titin and filamin suggesting loss of cytoskeletal integrity in mdx-4cv smooth muscles. A concomitant increase in various mitochondrial enzymes is indicative of metabolic disturbances. These findings agree with abnormal gastrointestinal function in dystrophinopathy.

The Dystrophin Node as Integrator of Cytoskeletal Organization, Lateral Force Transmission, Fiber Stability and Cellular Signaling in Skeletal Muscle

The systematic bioanalytical characterization of the protein product of the DMD gene, which is defective in the pediatric disorder Duchenne muscular dystrophy, led to the discovery of the membrane cytoskeletal protein dystrophin. Its full-length muscle isoform Dp427-M is tightly linked to a sarcolemma-associated complex consisting of dystroglycans, sarcoglyans, sarcospan, dystrobrevins and syntrophins. Besides these core members of the dystrophin-glycoprotein complex, the wider dystrophin-associated network includes key proteins belonging to the intracellular cytoskeleton and microtubular assembly, the basal lamina and extracellular matrix, various plasma membrane proteins and cytosolic components. Here, we review the central role of the dystrophin complex as a master node in muscle fibers that integrates cytoskeletal organization and cellular signaling at the muscle periphery, as well as providing sarcolemmal stabilization and contractile force transmission to the extracellular region. The combination of optimized tissue extraction, subcellular fractionation, advanced protein co-purification strategies, immunoprecipitation, liquid chromatography and two-dimensional gel electrophoresis with modern mass spectrometry-based proteomics has confirmed the composition of the core dystrophin complex at the sarcolemma membrane. Importantly, these biochemical and mass spectrometric surveys have identified additional members of the wider dystrophin network including biglycan, cavin, synemin, desmoglein, tubulin, plakoglobin, cytokeratin and a variety of signaling proteins and ion channels.

Early Inflammation in Muscular Dystrophy Differs between Limb and Respiratory Muscles and Increases with Dystrophic Severity

Duchenne muscular dystrophy (DMD) is a genetic, degenerative, striated muscle disease exacerbated by chronic inflammation. Mdx mice in the genotypic DMD model poorly represent immune-mediated pathology observed in patients. Improved understanding of innate immunity in dystrophic muscles is required to develop specific anti-inflammatory treatments. Here, inflammation in mdx mice and the more fibrotic utrn^+/-;mdx Het model was comprehensively investigated. Unbiased analysis showed that mdx and Het mice contain increased levels of numerous chemokines and cytokines, with further increased in Het mice. Chemokine and chemokine receptor gene expression levels were dramatically increased in 4-week-old dystrophic quadriceps muscles, and to a lesser extent in diaphragm during the early injury phase, and had a small but consistent increase at 8 and 20 weeks. An optimized direct immune cell isolation method prevented loss of up to 90% of macrophages with density-dependent centrifugation previously used for mdx flow cytometry. Het quadriceps contain higher proportions of neutrophils and infiltrating monocytes than mdx, and higher percentages of F4/80^Hi, but lower percentages of F4/80^Lo cells and patrolling monocytes compared with Het diaphragms. These differences may restrict regenerative potential of dystrophic diaphragms, increasing pathologic severity. Fibrotic and inflammatory gene expression levels are higher in myeloid cells isolated from Het compared with mdx quadriceps, supporting Het mice may represent an improved model for testing therapeutic manipulation of inflammation in DMD.

Oxidative damage to urinary proteins from the GRMD dog and mdx mouse as biomarkers of dystropathology in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a lethal, X-chromosome linked muscle-wasting disease affecting about 1 in 3500–6000 boys worldwide. Myofibre necrosis and subsequent loss of muscle mass are due to several molecular sequelae, such as inflammation and oxidative stress. We have recently shown increased neutrophils, highly reactive oxidant hypochlorous acid (HOCl) generation by myeloperoxidase (MPO), and associated oxidative stress in muscle from the GRMD dog and mdx mouse models for DMD. These findings have led us to hypothesise that generation of HOCl by myeloperoxidase released from neutrophils has a significant role in dystropathology. Since access to muscle from DMD patients is limited, the aim of this study was to develop methods to study this pathway in urine. Using immunoblotting to measure markers of protein oxidation, we show increased labelling of proteins with antibodies to dinitrophenylhydrazine (DNP, oxidative damage) and DiBrY (halogenation by reactive oxidants from myeloperoxidase) in GRMD and mdx urine. A strong positive correlation was observed between DiBrY labelling in dog urine and muscle. A strong positive correlation was also observed when comparing DNP and DiBrY labelling (in muscle and urine) to markers of dystropathology (plasma creatine kinase) and neutrophil presence (muscle MPO). Our results indicate the presence of neutrophil mediated oxidative stress in both models, and suggest that urine is a suitable bio-fluid for the measurement of such biomarkers. These methods could be employed in future studies into the role of neutrophil mediated oxidative stress in DMD and other inflammatory pathologies.

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.

eATP/P2X7R Axis: An Orchestrated Pathway Triggering Inflammasome Activation in Muscle Diseases

In muscle ATP is primarily known for its function as an energy source and as a mediator of the "excitation-transcription" process, which guarantees muscle plasticity in response to environmental stimuli. When quickly released in massive concentrations in the extracellular space as in presence of muscle membrane damage, ATP acts as a damage-associated molecular pattern molecule (DAMP). In experimental murine models of muscular dystrophies characterized by membrane instability, blockade of eATP/P2X7 receptor (R) purinergic signaling delayed the progression of the dystrophic phenotype dampening the local inflammatory response and inducing Foxp3⁺ T Regulatory lymphocytes. These discoveries highlighted the relevance of ATP as a harbinger of immune-tissue damage in muscular genetic diseases. Given the interactions between the immune system and muscle regeneration, the comprehension of ATP/purinerigic pathway articulated organization in muscle cells has become of extreme interest. This review explores ATP release, metabolism, feedback control and cross-talk with members of muscle inflammasome in the context of muscular dystrophies.

Human laminin-111 and laminin-211 protein therapy prevents muscle disease progression in an immunodeficient mouse model of LAMA2-CMD

BACKGROUND

Laminin-α2-related congenital muscular dystrophy (LAMA2-CMD) is a devastating genetic disease caused by mutations in the LAMA2 gene. These mutations result in progressive muscle wasting and inflammation leading to delayed milestones, and reduced lifespan in affected patients. There is currently no cure or treatment for LAMA2-CMD. Preclinical studies have demonstrated that mouse laminin-111 can serve as an effective protein replacement therapy in a mouse model of LAMA2-CMD.

METHODS

In this study, we generated a novel immunocompromised dyW mouse model of LAMA2-CMD to study the role the immune system plays in muscle disease progression. We used this immune-deficient dyW mouse model to test the therapeutic benefits of recombinant human laminin-111 and laminin-211 protein therapy on laminin-α2-deficient muscle disease progression.

RESULTS

We show that immunodeficient laminin-α2 null mice demonstrate subtle differences in muscle regeneration compared to immunocompetent animals during early disease stages but overall exhibit a comparable muscle disease progression. We found human laminin-111 and laminin-211 could serve as effective protein replacement strategies with mice showing improvements in muscle pathology and function. We observed that human laminin-111 and laminin-211 exhibit differences on satellite and myoblast cell populations and differentially affect muscle repair.

CONCLUSIONS

This study describes the generation of a novel immunodeficient mouse model that allows investigation of the role the immune system plays in LAMA2-CMD. This model can be used to assess the therapeutic potential of heterologous therapies that would elicit an immune response. Using this model, we show that recombinant human laminin-111 can serve as effective protein replacement therapy for the treatment of LAMA2-CMD.

Co-Transplantation of Bone Marrow-MSCs and Myogenic Stem/Progenitor Cells from Adult Donors Improves Muscle Function of Patients with Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a genetic disorder associated with a progressive deficiency of dystrophin that leads to skeletal muscle degeneration. In this study, we tested the hypothesis that a co-transplantation of two stem/progenitor cell populations, namely bone marrow-derived mesenchymal stem cells (BM-MSCs) and skeletal muscle-derived stem/progenitor cells (SM-SPCs), directly into the dystrophic muscle can improve the skeletal muscle function of DMD patients. Three patients diagnosed with DMD, confirmed by the dystrophin gene mutation, were enrolled into a study approved by the local Bioethics Committee (no. 79/2015). Stem/progenitor cells collected from bone marrow and skeletal muscles of related healthy donors, based on HLA matched antigens, were expanded in a closed MC3 cell culture system. A simultaneous co‑transplantation of BM-MSCs and SM-SPCs was performed directly into the biceps brachii (two patients) and gastrocnemius (one patient). During a six‑month follow‑up, the patients were examined with electromyography (EMG) and monitored for blood kinase creatine level. Muscle biopsies were examined with histology and assessed for dystrophin at the mRNA and protein level. A panel of 27 cytokines was analysed with multiplex ELISA. We did not observe any adverse effects after the intramuscular administration of cells. The efficacy of BM‑MSC and SM‑SPC application was confirmed through an EMG assessment by an increase in motor unit parameters, especially in terms of duration, amplitude range, area, and size index. The beneficial effect of cellular therapy was confirmed by a decrease in creatine kinase levels and a normalised profile of pro-inflammatory cytokines. BM-MSCs may support the pro-regenerative potential of SM-SPCs thanks to their trophic, paracrine, and immunomodulatory activity. Both applied cell populations may fuse with degenerating skeletal muscle fibres in situ, facilitating skeletal muscle recovery. However, further studies are required to optimise the dose and timing of stem/progenitor cell delivery.

Identification of marker proteins of muscular dystrophy in the urine proteome from the mdx-4cv model of dystrophinopathy

Since the protein constituents of urine present a dynamic proteome that can reflect a variety of disease-related alterations in the body, the mass spectrometric survey of proteome-wide changes in urine promises new insights into pathogenic mechanisms. Urine can be investigated in a completely non-invasive way and provides valuable biomedical information on body-wide changes. In this report, we have focused on the urine proteome in X-linked muscular dystrophy using the established mdx-4cv mouse model of dystrophinopathy. In order to avoid potential artefacts due to the manipulation of the biofluid proteome prior to mass spectrometry, crude urine specimens were analyzed without the prior usage of centrifugation steps or concentration procedures. Comparative proteomics revealed 21 increased and 8 decreased proteins out of 870 identified urinary proteoforms using 50 μl of biofluid per investigated sample, i.e. 14 wild type versus 14 mdx-4cv specimens. Promising marker proteins that were almost exclusively found in mdx-4cv urine included nidogen, parvalbumin and titin. Interestingly, the mass spectrometric identification of urine-associated titin revealed a wide spread of peptides over the sequence of this giant muscle protein. The newly established urinomic signature of dystrophinopathy might be helpful for the design of non-invasive assays to improve diagnosis, prognosis, therapy-monitoring and evaluation of potential harmful side effects of novel treatments in the field of muscular dystrophy research.

Biomarkers for Duchenne muscular dystrophy: myonecrosis, inflammation and oxidative stress

Duchenne muscular dystrophy (DMD) is a lethal, X-linked disease that causes severe loss of muscle mass and function in young children. Promising therapies for DMD are being developed, but the long lead times required when using clinical outcome measures are hindering progress. This progress would be facilitated by robust molecular biomarkers in biofluids, such as blood and urine, which could be used to monitor disease progression and severity, as well as to determine optimal drug dosing before a full clinical trial. Many candidate DMD biomarkers have been identified, but there have been few follow-up studies to validate them. This Review describes the promising biomarkers for dystrophic muscle that have been identified in muscle, mainly using animal models. We strongly focus on myonecrosis and the associated inflammation and oxidative stress in DMD muscle, as the lack of dystrophin causes repeated bouts of myonecrosis, which are the key events that initiate the resultant severe dystropathology. We discuss the early events of intrinsic myonecrosis, along with early regeneration in the context of histological and other measures that are used to quantify its incidence. Molecular biomarkers linked to the closely associated events of inflammation and oxidative damage are discussed, with a focus on research related to protein thiol oxidation and to neutrophils. We summarise data linked to myonecrosis in muscle, blood and urine of dystrophic animal species, and discuss the challenge of translating such biomarkers to the clinic for DMD patients, especially to enhance the success of clinical trials.

Summary: This Review discusses biomarkers in blood and urine linked to myonecrosis, inflammation and oxidative stress, to enhance development of therapies for DMD, and the challenges to be overcome for clinical translation.

Proteomic profiling of fatty acid binding proteins in muscular dystrophy

Introduction: Duchenne muscular dystrophy is a neuromuscular disorder, which is caused by abnormalities in the DMD gene that encodes the membrane cytoskeletal protein dystrophin. Besides progressive skeletal muscle wasting, dystrophinopathy also affects non-skeletal muscle tissues, including cells in the cardio-respiratory system, the central nervous system, the liver and the kidney.Areas covered: This review summarizes the proteomic characterization of a key class of lipid chaperones, the large family of fatty acid binding proteins, and their potential role in muscular dystrophy. Recent proteomic surveys using animal models and patient specimens are reviewed. Pathobiochemical changes in specific proteoforms of fatty acid binding protein in the multi-system pathology of dystrophinopathy are discussed.Expert opinion: The mass spectrometric identification of distinct changes in fatty acid binding proteins in muscle, heart, liver, kidney and serum demonstrates that considerable alterations occur in key steps of metabolite transport and fat metabolism in muscular dystrophy. These new findings might be helpful to further develop a comprehensive biomarker signature of metabolic changes in X-linked muscular dystrophy, which should improve (i) our understanding of complex pathobiochemical changes due to dystrophin deficiency, (ii) the identification of novel therapeutic targets, and (iii) the design of differential diagnostic, prognostic and therapy-monitoring approaches.

Mineralocorticoid receptor antagonists improve membrane integrity independent of muscle force in muscular dystrophy

Mineralocorticoid receptor (MR) drugs have been used clinically for decades to treat cardiovascular diseases. MR antagonists not only show preclinical efficacy for heart in Duchenne muscular dystrophy (DMD) models but also improve skeletal muscle force and muscle membrane integrity. The mechanisms of action of MR antagonists in skeletal muscles are entirely unknown. Since MR are present in many cell types in the muscle microenvironment, it is critical to define cell-intrinsic functions in each cell type to ultimately optimize antagonist efficacy for use in the widest variety of diseases. We generated a new conditional knockout of MR in myofibers and quantified cell-intrinsic mechanistic effects on functional and histological parameters in a DMD mouse model. Skeletal muscle MR deficiency led to improved respiratory muscle force generation and less deleterious fibrosis but did not reproduce MR antagonist efficacy on membrane susceptibility to induced damage. Surprisingly, acute application of MR antagonist to muscles led to improvements in membrane integrity after injury independent of myofiber MR. These data demonstrate that MR antagonists are efficacious to dystrophic skeletal muscles through both myofiber intrinsic effects on muscle force and downstream fibrosis and extrinsic functions on membrane stability. MR antagonists may therefore be applicable for treating more general muscle weakness and possibly other conditions that result from cell injuries.

Proteomic and cell biological profiling of the renal phenotype of the mdx-4cv mouse model of Duchenne muscular dystrophy

The X-linked inherited muscle wasting disease Duchenne muscular dystrophy, which is caused by primary abnormalities in the membrane cytoskeletal protein dystrophin, is a multi-system disorder. Highly progressive forms of dystrophinopathy are associated with a complex secondary pathophysiology, including renal dysfunction. It was therefore of interest to carry out a systematic survey of potential proteome-wide changes in the kidney of the established mdx-4cv mouse model of dystrophinopathy. Of 5878 mass spectrometrically identified kidney proteins, 82 versus 142 proteins were shown to be decreased or increased, respectively, in association with muscular dystrophy. The most decreased versus increased protein species are the ACSM3 isoform of mitochondrial acyl-coenzyme A synthetase and the FABP1 isoform of fatty acid binding protein, respectively. Both proteomic findings were verified by immunofluorescence microscopy and immunoblot analysis. Interestingly, haematoxylin/eosin staining indicated diffuse whitish deposits in the mdx-4cv kidney, and an increased intensity of Sudan Black labelling of kidney cells revealed ectopic fat deposition. Although the proteomic results and cell biological findings do not demonstrate a direct functional link between increased FABP1 and fat accumulation, the results suggest that the up-regulation of FABP1 may be related to abnormal fat metabolism. This makes FABP1 potentially a novel pathobiochemical indicator for studying kidney abnormalities in the mdx-4cv model of dystrophinopathy.

Mineralocorticoid Receptor Signaling Contributes to Normal Muscle Repair After Acute Injury

Acute skeletal muscle injury is followed by a temporal response of immune cells, fibroblasts, and muscle progenitor cells within the muscle microenvironment to restore function. These same cell types are repeatedly activated in muscular dystrophy from chronic muscle injury, but eventually, the regenerative portion of the cycle is disrupted and fibrosis replaces degenerated muscle fibers. Mineralocorticoid receptor (MR) antagonist drugs have been demonstrated to increase skeletal muscle function, decrease fibrosis, and directly improve membrane integrity in muscular dystrophy mice, and therefore are being tested clinically. Conditional knockout of MR from muscle fibers in muscular dystrophy mice also improves skeletal muscle function and decreases fibrosis. The mechanism of efficacy likely results from blocking MR signaling by its endogenous agonist aldosterone, being produced at high local levels in regions of muscle damage by infiltrating myeloid cells. Since chronic and acute injuries share the same cellular processes to regenerate muscle, and MR antagonists are clinically used for a wide variety of conditions, it is crucial to define the role of MR signaling in normal muscle repair after injury. In this study, we performed acute injuries using barium chloride injections into tibialis anterior muscles both in myofiber MR conditional knockout mice on a wild-type background (MRcko) and in MR antagonist-treated wild-type mice. Steps of the muscle regeneration response were analyzed at 1, 4, 7, or 14 days after injury. Presence of the aldosterone synthase enzyme was also assessed during the injury repair process. We show for the first time aldosterone synthase localization in infiltrating immune cells of normal skeletal muscle after acute injury. MRcko mice had an increased muscle area infiltrated by aldosterone synthase positive myeloid cells compared to control injured animals. Both MRcko and MR antagonist treatment stabilized damaged myofibers and increased collagen infiltration or compaction at 4 days post-injury. MR antagonist treatment also led to reduced myofiber size at 7 and 14 days post-injury. These data support that MR signaling contributes to the normal muscle repair process following acute injury. MR antagonist treatment delays muscle fiber growth, so temporary discontinuation of these drugs after a severe muscle injury could be considered.

Emerging proteomic biomarkers of X-linked muscular dystrophy

Introduction: Progressive skeletal muscle wasting is the manifesting symptom of Duchenne muscular dystrophy, an X-linked inherited disorder triggered by primary abnormalities in the DMD gene. The almost complete loss of dystrophin isoform Dp427 causes a multi-system pathology that features in addition to skeletal muscle weakness also late-onset cardio-respiratory deficiencies, impaired metabolism and abnormalities in the central nervous system. Areas covered: This review focuses on the mass spectrometry-based proteomic characterization of X-linked muscular dystrophy with special emphasis on the identification of novel biomarker candidates in skeletal muscle tissues, as well as non-muscle tissues and various biofluids. Individual sections focus on molecular and cellular aspects of the pathogenic changes in dystrophinopathy, proteomic workflows used in biomarker research, the proteomics of the dystrophin-glycoprotein complex and the potential usefulness of newly identified protein markers involved in fibre degeneration, fibrosis and inflammation. Expert opinion: The systematic application of large-scale proteomic surveys has identified a distinct cohort of both tissue- and biofluid-associated protein species with considerable potential for improving diagnostic, prognostic and therapy-monitoring procedures. Novel proteomic markers include components involved in fibre contraction, cellular signalling, ion homeostasis, cellular stress response, energy metabolism and the immune response, as well as maintenance of the cytoskeletal and extracellular matrix.

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

Dysferlin-deficiency has greater impact on function of slow muscles, compared with fast, in aged BLAJ mice

Dysferlinopathies are a form of muscular dystrophy caused by gene mutations resulting in deficiency of the protein dysferlin. Symptoms manifest later in life in a muscle specific manner, although the pathomechanism is not well understood. This study compared the impact of dysferlin-deficiency on in vivo and ex vivo muscle function, and myofibre type composition in slow (soleus) and fast type (extensor digitorum longus; EDL) muscles using male dysferlin-deficient (dysf^-/-) BLAJ mice aged 10 months, compared with wild type (WT) C57Bl/6J mice. There was a striking increase in muscle mass of BLAJ soleus (+25%) (p<0.001), with no strain differences in EDL mass, compared with WT. In vivo measures of forelimb grip strength and wheel running capacity showed no strain differences. Ex vivo measures showed the BLAJ soleus had faster twitch contraction (-21%) and relaxation (-20%) times, and delayed post fatigue recovery (ps<0.05); whereas the BLAJ EDL had a slower relaxation time (+11%) and higher maximum rate of force production (+25%) (ps<0.05). Similar proportions of MHC isoforms were evident in the soleus muscles of both strains (ps>0.05); however, for the BLAJ EDL, there was an increased proportion of type IIx MHC isoform (+5.5%) and decreased type IIb isoform (-5.5%) (ps<0.01). This identification of novel differences in the impact of dysferlin-deficiency on slow and fast twitch muscles emphasises the importance of evaluating myofibre type specific effects to provide crucial insight into the mechanisms responsible for loss of function in dysferlinopathies; this is critical for the development of targeted future clinical therapies.

P2X7 purinoceptor as a therapeutic target in muscular dystrophies

Mutations in the dystrophin and sarcoglycans genes result in muscular dystrophies causing severe disability and premature death and where no effective treatment is available. New therapeutic approaches targeting secondary disease mechanisms have a strong translational potential. Dystrophic muscle damage triggers release of ATP whilst loss of ecto-ATPase activity of sarcoglycan further elevates extracellular ATP (eATP) levels. Such a high eATP activates P2X7 purinoceptors on immune cells; these contribute to chronic inflammatory and immune responses that exacerbate the dystrophic pathology. Dystrophin mutations coincide with a significant P2X7 upregulation in Duchenne muscular dystrophy (DMD) muscle and alter receptor signalling in mouse dystrophic myoblasts and myofibers. P2X7 overexpression combined with the eATP-rich environment lead to cell dysfunction and death and ultimately to ineffective regeneration. P2X7 is therefore a therapeutic target for reducing damaging inflammation and supporting the repair of dystrophic muscles. Accordingly, genetic ablation and pharmacological inhibition of the eATP-P2X7 axis alleviated dystrophic phenotypes in mouse models of dystrophinopathy and sarcoglycanopathy. Thus, P2X7 inhibitors are good candidates for rapid re-purposing for the treatment of these highly debilitating diseases. Such a therapy is not constrained by causative mutations, so it would be suitable for all patients. Moreover, it appears effective in alleviating both muscle and non-muscle symptoms.

Proteomic profiling of the mouse diaphragm and refined mass spectrometric analysis of the dystrophic phenotype

The diaphragm is a crucial muscle involved in active inspiration and whole body homeostasis. Previous biochemical, immunochemical and cell biological investigations have established the distribution and fibre type-specific expression of key diaphragm proteins. Building on these findings, it was of interest to establish the entire experimentally assessable diaphragm proteome and verify the presence of specific protein isoforms within this specialized subtype of skeletal muscle. A highly sensitive Orbitrap Fusion Tribrid mass spectrometer was used for the systematic identification of the mouse diaphragm-associated protein population. Proteomics established 2925 proteins by high confidence peptide identification. Bioinformatics was used to determine the distribution of the main protein classes, biological processes and subcellular localization within the diaphragm proteome. Following the establishment of the respiratory muscle proteome with special emphasis on protein isoform expression in the contractile apparatus, the extra-sarcomeric cytoskeleton, the extracellular matrix and the excitation-contraction coupling apparatus, the mass spectrometric analysis of the diaphragm was extended to the refined identification of proteome-wide changes in X-linked muscular dystrophy. The comparative mass spectrometric profiling of the dystrophin-deficient diaphragm from the mdx-4cv mouse model of Duchenne muscular dystrophy identified 289 decreased and 468 increased protein species. Bioinformatics was employed to analyse the clustering of changes in protein classes and potential alterations in interaction patterns of proteins involved in metabolism, the contractile apparatus, proteostasis and the extracellular matrix. The detailed pathoproteomic profiling of the mdx-4cv diaphragm suggests highly complex alterations in a variety of crucial cellular processes due to deficiency in the membrane cytoskeletal protein dystrophin.

Role of autophagy in inherited metabolic and endocrine myopathies

The prevalence of cardiometabolic disease has reached an exponential rate of rise over the last decades owing to high fat/high caloric diet intake and satiety life style. Although the presence of dyslipidemia, insulin resistance, hypertension and obesity mainly contributes to the increased incidence of cardiometabolic diseases, population-based, clinical and genetic studies have revealed a rather important role for inherited myopathies and endocrine disorders in the ever-rising metabolic anomalies. Inherited metabolic and endocrine diseases such as glycogen storage and lysosomal disorders have greatly contributed to the overall prevalence of cardiometabolic diseases. Recent evidence has demonstrated an essential role for proteotoxicity due to autophagy failure and/or dysregulation in the onset of inherited metabolic and endocrine disorders. Given the key role for autophagy in the degradation and removal of long-lived or injured proteins and organelles for the maintenance of cellular and organismal homeostasis, this mini-review will discuss the potential contribution of autophagy dysregulation in the pathogenesis of inherited myopathies and endocrine disorders, which greatly contribute to an overall rise in prevalence of cardiometabolic disorders. Molecular, clinical, and epidemiological aspects will be covered as well as the potential link between autophagy and metabolic anomalies thus target therapy may be engaged for these comorbidities.