Carles Sánchez Riera

Sarcoglycanopathies are heterogeneous proximo-distal diseases presenting severe muscle alterations. Although there are 6 different sarcoglycan isoforms, sarcoglycanopathies are caused exclusively by mutations in genes coding for one of the four sarcoglycan transmembrane proteins (alpha, beta, gamma and delta) forming the sarcoglycan complex (SGC) in skeletal and cardiac muscle. Little is known about the different roles of the SGC beyond the dystrophin glycoprotein complex (DGC) structural role. Here, we show that SGC proteins are enriched at the post-synaptic membrane of neuromuscular junctions (NMJs). Using a mouse model lacking the beta-sarcoglycan subunit, we describe for the first time that the loss of the SGC in the NMJ area results in alterations of pre- and postsynaptic membrane, as well as a significant reduction of membrane potential. Moreover, using different denervated wild-type mouse models, we demonstrate that nerve presence precedes the sarcoglycan enrichment at NMJ, suggesting a nerve-dependent sarcoglycan expression. Altogether, our findings suggest that pathological decline should no longer be understood only in terms of sarcolemma damage but also in terms of sarcoglycans’ participation in the NMJ. Henceforth, our work paves the way for the identification of new mechanisms involving sarcoglycans and new approaches for the treatment of sarcoglycanopathies.

Sarcoglycanopathies are heterogeneous proximo-distal diseases presenting severe muscle alterations. These diseases are caused by mutations in genes coding for one of the four sarcoglycan transmembrane proteins, which form the sarcoglycan complex (SGC). Little is known about the different roles of the SGC beyond the dystrophin glycoprotein complex (DGC) structural role. Here, we show that SGC proteins are enriched at the post-synaptic membrane of neuromuscular junctions (NMJs). Using a mouse model lacking the beta-sarcoglycan subunit, we describe for the first time that the loss of the SGC in the NMJ area results in alterations of pre- and postsynaptic membrane, as well as a significant reduction of membrane potential. Moreover, using different denervated wild-type mouse models, we demonstrate that enrichment of sarcoglycans within the NMJ occurs only after innervation, suggesting a nerve-dependent sarcoglycan expression. Altogether, our findings suggest that pathological decline should no longer be understood only in terms of sarcolemma damage but also in terms of sarcoglycans' participation in the NMJ. Henceforth, our work paves the way for the identification of new mechanisms involving sarcoglycans and new approaches for the treatment of sarcoglycanopathies.

Only in recent years, thanks to a precision medicine-based approach, have treatments tailored to the sex of each patient emerged in clinical trials. In this regard, both striated muscle tissues present significant differences between the two sexes, which may have important consequences for diagnosis and therapy in aging and chronic illness. In fact, preservation of muscle mass in disease conditions correlates with survival; however, sex should be considered when protocols for the maintenance of muscle mass are designed. One obvious difference is that men have more muscle than women. Moreover, the two sexes differ in inflammation parameters, particularly in response to infection and disease. Therefore, unsurprisingly, men and women respond differently to therapies. In this review, we present an up-to-date overview on what is known about sex differences in skeletal muscle physiology and disfunction, such as disuse atrophy, age-related sarcopenia, and cachexia. In addition, we summarize sex differences in inflammation which may underly the aforementioned conditions because pro-inflammatory cytokines deeply affect muscle homeostasis. The comparison of these three conditions and their sex-related bases is interesting because different forms of muscle atrophy share common mechanisms; for instance, those responsible for protein dismantling are similar although differing in terms of kinetics, severity, and regulatory mechanisms. In pre-clinical research, exploring sexual dimorphism in disease conditions could highlight new efficacious treatments or recommend implementation of an existing one. Any protective factors discovered in one sex could be exploited to achieve lower morbidity, reduce the severity of the disease, or avoid mortality in the opposite sex. Thus, the understanding of sex-dependent responses to different forms of muscle atrophy and inflammation is of pivotal importance to design innovative, tailored, and efficient interventions.

SUMMARY: Striated muscle is a highly organized structure composed by well-defined anatomical domains with integrated but distinct assignments. So far, the lack of a direct correlation between tissue architecture and gene expression has limited our understanding of how each unit responds to physio-pathologic contexts. Here, we show how the combined use of spatially resolved transcriptomics and immunofluorescence can bridge this gap by enabling the unbiased identification of such domains and the characterization of their response to external perturbations. Using a spatiotemporal analysis, we followed the changes in the transcriptomics profile of specific domains in muscle in a model of denervation. Furthermore, our approach allowed us to identify the spatial distribution and nerve dependence of atrophic signalling pathway and polyamine metabolism to glycolytic fibers. Indeed, we demonstrate a pronounced alteration of polyamine homeostasis upon denervation. Our dataset will serve as a resource for future studies of the mechanisms underlying skeletal muscle homeostasis and innervation. Graphical

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

Skeletal muscle is a highly responsive tissue, able to remodel its size and metabolism in response to external demand. Muscle fibers can vary from fast glycolytic to slow oxidative, and their frequency in a specific muscle is tightly regulated by fiber maturation, innervation, or external causes. Atrophic conditions, including aging, amyotrophic lateral sclerosis, and cancer-induced cachexia, differ in the causative factors and molecular signaling leading to muscle wasting; nevertheless, all of these conditions are characterized by metabolic remodeling, which contributes to the pathological progression of muscle atrophy. Here, we discuss how changes in muscle metabolism can be used as a therapeutic target and review the evidence in support of nutritional interventions and/or physical exercise as tools for counteracting muscle wasting in atrophic conditions.

Volumetric muscle loss (VML) is the massive wasting of skeletal muscle tissue due to traumatic events or surgical ablation. This pathological condition exceeds the physiological healing process carried out by the muscle itself, which owns remarkable capacity to restore damages but only when limited in dimensions. Upon VML occurring, the affected area is severely compromised, heavily influencing the affected a person’s quality of life. Overall, this condition is often associated with chronic disability, which makes the return to duty of highly specialized professional figures (e.g., military personnel or athletes) almost impossible. The actual treatment for VML is based on surgical conservative treatment followed by physical exercise; nevertheless, the results, in terms of either lost mass and/or functionality recovery, are still poor. On the other hand, the efforts of the scientific community are focusing on reconstructive therapy aiming at muscular tissue void volume replenishment by exploiting biomimetic matrix or artificial tissue implantation. Reconstructing strategies represent a valid option to build new muscular tissue not only to recover damaged muscles, but also to better socket prosthesis in terms of anchorage surfaces and reinnervation substrates for reconstructed mass.

Skeletal muscle, the most abundant tissue in the body, is heterogeneous. This heterogeneity forms the basis of muscle diversity, which is reflected in the specialized functions of muscles in different parts of the body. However, these different parts are not always clearly delimitated, and this often gives rise to gradients within the same muscle and even across the body. During the last decade, several studies on muscular disorders both in mice and in humans have observed particular distribution patterns of muscle weakness during disease, indicating that the same mutation can affect muscles differently. Moreover, these phenotypical differences reveal gradients of severity, existing alongside other architectural gradients. These two factors are especially prominent in sarcoglycanopathies. Nevertheless, very little is known about the mechanism(s) driving the phenotypic diversity of the muscles affected by these diseases. Here, we will review the available literature on sarcoglycanopathies, focusing on phenotypic differences among affected muscles and gradients, characterization techniques, molecular signatures, and cell population heterogeneity, highlighting the possibilities opened up by new technologies. This review aims to revive research interest in the diverse disease phenotype affecting different muscles, in order to pave the way for new therapeutic interventions.