Severe murine limb-girdle muscular dystrophy type 2C pathology is diminished by FTY720 treatment

The Role of P2X7 Purinoceptors in the Pathogenesis and Treatment of Muscular Dystrophies

Muscular dystrophies are inherited neuromuscular diseases, resulting in progressive disability and often affecting life expectancy. The most severe, common types are Duchenne muscular dystrophy (DMD) and Limb-girdle sarcoglycanopathy, which cause advancing muscle weakness and wasting. These diseases share a common pathomechanism where, due to the loss of the anchoring dystrophin (DMD, dystrophinopathy) or due to mutations in sarcoglycan-encoding genes (LGMDR3 to LGMDR6), the α-sarcoglycan ecto-ATPase activity is lost. This disturbs important purinergic signaling: An acute muscle injury causes the release of large quantities of ATP, which acts as a damage-associated molecular pattern (DAMP). DAMPs trigger inflammation that clears dead tissues and initiates regeneration that eventually restores normal muscle function. However, in DMD and LGMD, the loss of ecto-ATPase activity, that normally curtails this extracellular ATP (eATP)-evoked stimulation, causes exceedingly high eATP levels. Thus, in dystrophic muscles, the acute inflammation becomes chronic and damaging. The very high eATP over-activates P2X7 purinoceptors, not only maintaining the inflammation but also tuning the potentially compensatory P2X7 up-regulation in dystrophic muscle cells into a cell-damaging mechanism exacerbating the pathology. Thus, the P2X7 receptor in dystrophic muscles is a specific therapeutic target. Accordingly, the P2X7 blockade alleviated dystrophic damage in mouse models of dystrophinopathy and sarcoglycanopathy. Therefore, the existing P2X7 blockers should be considered for the treatment of these highly debilitating diseases. This review aims to present the current understanding of the eATP-P2X7 purinoceptor axis in the pathogenesis and treatment of muscular dystrophies.

The P2X7 purinoceptor in pathogenesis and treatment of dystrophino- and sarcoglycanopathies

Dystrophinopathy and sarcoglycanopathies are incurable diseases caused by mutations in the genes encoding dystrophin or members of the dystrophin associated protein complex (DAPC). Restoration of the missing dystrophin or sarcoglycans via genetic approaches is complicated by the downsides of personalised medicines and immune responses against re-expressed proteins. Thus, the targeting of disease mechanisms downstream from the mutant protein has a strong translational potential. Acute muscle damage causes release of large quantities of ATP, which activates P2X7 purinoceptors, resulting in inflammation that clears dead tissues and triggers regeneration. However, in dystrophic muscles, loss of α-sarcoglycan ecto-ATPase activity further elevates extracellular ATP (eATP) levels, exacerbating the pathology. Moreover, seemingly compensatory P2X7 upregulation in dystrophic muscle cells, combined with high eATP leads to further damage. Accordingly, P2X7 blockade alleviated dystrophic damage in mouse models of both dystrophinopathy and sarcoglycanopathy. Existing P2X7 blockers could be re-purposed for the treatment of these highly debilitating diseases.

Microbiota dysbiosis influences immune system and muscle pathophysiology of dystrophin-deficient mice

Duchenne muscular dystrophy (DMD) is a progressive severe muscle-wasting disease caused by mutations in DMD, encoding dystrophin, that leads to loss of muscle function with cardiac/respiratory failure and premature death. Since dystrophic muscles are sensed by infiltrating inflammatory cells and gut microbial communities can cause immune dysregulation and metabolic syndrome, we sought to investigate whether intestinal bacteria support the muscle immune response in mdx dystrophic murine model. We highlighted a strong correlation between DMD disease features and the relative abundance of Prevotella. Furthermore, the absence of gut microbes through the generation of mdx germ-free animal model, as well as modulation of the microbial community structure by antibiotic treatment, influenced muscle immunity and fibrosis. Intestinal colonization of mdx mice with eubiotic microbiota was sufficient to reduce inflammation and improve muscle pathology and function. This work identifies a potential role for the gut microbiota in the pathogenesis of DMD.

The Role of Innate and Adaptive Immune Cells in Skeletal Muscle Regeneration

Skeletal muscle regeneration is highly dependent on the inflammatory response. A wide variety of innate and adaptive immune cells orchestrate the complex process of muscle repair. This review provides information about the various types of immune cells and biomolecules that have been shown to mediate muscle regeneration following injury and degenerative diseases. Recently developed cell and drug-based immunomodulatory strategies are highlighted. An improved understanding of the immune response to injured and diseased skeletal muscle will be essential for the development of therapeutic strategies.

Fingolimod inhibits proliferation and epithelial-mesenchymal transition in sacral chordoma by inactivating IL-6/STAT3 signalling

Purpose: To explore the sensitivity of the immunosuppressive agent fingolimod (FTY720) in chordoma and determine whether it can serve as an appropriate alternate treatment for unresectable tumours in patients after incomplete surgery.

Methods: Cell viability assays, colony formation assays and EdU assays were performed to evaluate the sensitivity of chordoma cell lines to FTY720. Transwell invasion assays, wound healing assays, flow cytometry, cell cycle analysis, immunofluorescence analysis, Western blotting analysis and enzyme-linked immunosorbent assays (ELISAs) were performed to evaluate cell invasion, epithelial–mesenchymal transition (EMT) and activation of related pathways after treatment with FTY720. The effect of FTY720 was also evaluated in vivo in a xenograft model.

Results: We found that FTY720 inhibited the proliferation, invasion and metastasis of sacral chordoma cells (P < 0.01). FTY720 also inhibited the proliferation of tumour cells in a xenograft model using sacral chordoma cell lines (P < 0.01). The mechanism was related to the EMT and apoptosis of chordoma cells and inactivation of IL-6/STAT3 signalling in vitro and in vivo.

Conclusions: Our findings indicate that FTY720 may be an effective therapeutic agent against chordoma. These findings suggest that FTY720 is a novel agent that can treat locally advanced and metastatic chordoma.

S1P/S1P Receptor Signaling in Neuromuscolar Disorders

The bioactive sphingolipid metabolite, sphingosine 1-phosphate (S1P), and the signaling pathways triggered by its binding to specific G protein-coupled receptors play a critical regulatory role in many pathophysiological processes, including skeletal muscle and nervous system degeneration. The signaling transduced by S1P binding appears to be much more complex than previously thought, with important implications for clinical applications and for personalized medicine. In particular, the understanding of S1P/S1P receptor signaling functions in specific compartmentalized locations of the cell is worthy of being better investigated, because in various circumstances it might be crucial for the development or/and the progression of neuromuscular diseases, such as Charcot-Marie-Tooth disease, myasthenia gravis, and Duchenne muscular dystrophy.

Immunobiology of Inherited Muscular Dystrophies

The immune response to acute muscle damage is important for normal repair. However, in chronic diseases such as many muscular dystrophies, the immune response can amplify pathology and play a major role in determining disease severity. Muscular dystrophies are inheritable diseases that vary tremendously in severity, but share the progressive loss of muscle mass and function that can be debilitating and lethal. Mutations in diverse genes cause muscular dystrophy, including genes that encode proteins that maintain membrane strength, participate in membrane repair, or are components of the extracellular matrix or the nuclear envelope. In this article, we explore the hypothesis that an important feature of many muscular dystrophies is an immune response adapted to acute, infrequent muscle damage that is misapplied in the context of chronic injury. We discuss the involvement of the immune system in the most common muscular dystrophy, Duchenne muscular dystrophy, and show that the immune system influences muscle death and fibrosis as disease progresses. We then present information on immune cell function in other muscular dystrophies and show that for many muscular dystrophies, release of cytosolic proteins into the extracellular space may provide an initial signal, leading to an immune response that is typically dominated by macrophages, neutrophils, helper T-lymphocytes, and cytotoxic T-lymphocytes. Although those features are similar in many muscular dystrophies, each muscular dystrophy shows distinguishing features in the magnitude and type of inflammatory response. These differences indicate that there are disease-specific immunomodulatory molecules that determine response to muscle cell damage caused by diverse genetic mutations. © 2018 American Physiological Society. Compr Physiol 8:1313-1356, 2018.

Skeletal Muscle Metabolism in Duchenne and Becker Muscular Dystrophy-Implications for Therapies

The interactions between nutrition and metabolism and skeletal muscle have long been known. Muscle is the major metabolic organ&mdash;it consumes more calories than other organs&mdash;and therefore, there is a clear need to discuss these interactions and provide some direction for future research areas regarding muscle pathologies. In addition, new experiments and manuscripts continually reveal additional highly intricate, reciprocal interactions between metabolism and muscle. These reciprocal interactions include exercise, age, sex, diet, and pathologies including atrophy, hypoxia, obesity, diabetes, and muscle myopathies. Central to this review are the metabolic changes that occur in the skeletal muscle cells of muscular dystrophy patients and mouse models. Many of these metabolic changes are pathogenic (inappropriate body mass changes, mitochondrial dysfunction, reduced adenosine triphosphate (ATP) levels, and increased Ca²⁺) and others are compensatory (increased phosphorylated AMP activated protein kinase (pAMPK), increased slow fiber numbers, and increased utrophin). Therefore, reversing or enhancing these changes with therapies will aid the patients. The multiple therapeutic targets to reverse or enhance the metabolic pathways will be discussed. Among the therapeutic targets are increasing pAMPK, utrophin, mitochondrial number and slow fiber characteristics, and inhibiting reactive oxygen species. Because new data reveals many additional intricate levels of interactions, new questions are rapidly arising. How does muscular dystrophy alter metabolism, and are the changes compensatory or pathogenic? How does metabolism affect muscular dystrophy? Of course, the most profound question is whether clinicians can therapeutically target nutrition and metabolism for muscular dystrophy patient benefit? Obtaining the answers to these questions will greatly aid patients with muscular dystrophy.

Tackling muscle fibrosis: From molecular mechanisms to next generation engineered models to predict drug delivery

Muscle fibrosis represents the end stage consequence of different diseases, among which muscular dystrophies, leading to severe impairment of muscle functions. Muscle fibrosis involves the production of several growth factors, cytokines and proteolytic enzymes and is strictly associated to inflammatory processes. Moreover, fibrosis causes profound changes in tissue properties, including increased stiffness and density, lower pH and oxygenation. Up to now, there is no therapeutic approach able to counteract the fibrotic process and treatments directed against muscle pathologies are severely impaired by the harsh conditions of the fibrotic environment. The design of new therapeutics thus need innovative tools mimicking the obstacles posed by the fibrotic environment to their delivery. This review will critically discuss the role of in vivo and 3D in vitro models in this context and the characteristics that an ideal model should possess to help the translation from bench to bedside of new candidate anti-fibrotic agents.

Treadmill Training with HAL Exoskeleton-A Novel Approach for Symptomatic Therapy in Patients with Limb-Girdle Muscular Dystrophy-Preliminary Study

Purpose: Exoskeletons have been developed for rehabilitation of patients with walking impairment due to neurological disorders. Recent studies have shown that the voluntary-driven exoskeleton HAL® (hybrid assistive limb) can improve walking functions in spinal cord injury and stroke. The aim of this study was to assess safety and effects on walking function of HAL® supported treadmill therapy in patients with limb-girdle muscular dystrophy (LGMD).

Materials and Methods: Three LGMD patients received 8 weeks of treadmill training with HAL® 3 times a week. Outcome parameters were 10-meter walk test (10 MWT), 6-minute walk test, and timed-up-and-go test (TUG). Parameters were assessed pre and post training and 6 weeks later (follow-up).

Results: All patients completed the therapy without adverse reactions and reported about improvement in endurance. Improvements in outcome parameters after 8 weeks could be demonstrated. Persisting effects were observed after 6 weeks for the 10 MWT and TUG test (follow-up).

Conclusions: HAL® treadmill training in LGMD patients can be performed safely and enables an intensive highly repetitive locomotor training. All patients benefitted from this innovative method. Upcoming controlled studies with larger cohorts should prove its effects in different types of LGMD and other myopathies.