Morphological and functional analyses of skeletal muscles from an immunodeficient animal model of limb-girdle muscular dystrophy type 2E

MEK-inhibitors decrease Nfix in muscular dystrophy but induce unexpected calcifications, partially rescued with Cyanidin diet

Muscular dystrophies (MDs) are incurable genetic myopathies characterized by progressive degeneration of skeletal muscles. Dystrophic mice lacking the transcription factor Nfix display morphological and functional improvements of the disease. Recently, we demonstrated that MAPK signaling pathway positively regulates Nfix in muscle development and that Cyanidin, a natural antioxidant molecule, strongly ameliorates the pathology. To explore a synergistic approach aimed at treating MDs, we administered Trametinib, a clinically approved MEK inhibitor, alone or combined with Cyanidin to adult Sgca null mice. We observed that chronic treatment with Trametinib and Cyanidin reduced Nfix in myogenic cells but, unexpectedly, caused ectopic calcifications exclusively in dystrophic muscles. The combined treatment with Cyanidin resulted in histological improvements by preventing Trametinib-induced calcifications in Diaphragm and Soleus. Collectively, this first pilot study revealed that Nfix is modulated by the MAPK pathway in MDs, and that Cyanidin partly rescued the unexpected ectopic calcifications caused by MEK inhibition.

Extracellular vesicle-derived miRNAs improve stem cell-based therapeutic approaches in muscle wasting conditions

Skeletal muscle holds an intrinsic capability of growth and regeneration both in physiological conditions and in case of injury. Chronic muscle illnesses, generally caused by genetic and acquired factors, lead to deconditioning of the skeletal muscle structure and function, and are associated with a significant loss in muscle mass. At the same time, progressive muscle wasting is a hallmark of aging. Given the paracrine properties of myogenic stem cells, extracellular vesicle-derived signals have been studied for their potential implication in both the pathogenesis of degenerative neuromuscular diseases and as a possible therapeutic target. In this study, we screened the content of extracellular vesicles from animal models of muscle hypertrophy and muscle wasting associated with chronic disease and aging. Analysis of the transcriptome, protein cargo, and microRNAs (miRNAs) allowed us to identify a hypertrophic miRNA signature amenable for targeting muscle wasting, consisting of miR-1 and miR-208a. We tested this signature among others in vitro on mesoangioblasts (MABs), vessel-associated adult stem cells, and we observed an increase in the efficiency of myogenic differentiation. Furthermore, injections of miRNA-treated MABs in aged mice resulted in an improvement in skeletal muscle features, such as muscle weight, strength, cross-sectional area, and fibrosis compared to controls. Overall, we provide evidence that the extracellular vesicle-derived miRNA signature we identified enhances the myogenic potential of myogenic stem cells.

Preying dangerously: black widow spider venom resistance in sympatric lizards

Lizards and spiders are natural adversaries, yet little is known of adaptations that lizards might possess for dealing with the venomous defences of spider prey. In the Western USA, two lizard species (Elgaria multicarinata and Sceloporus occidentalis) are sympatric with and predate western black widow spiders (Latrodectus hesperus). The consequences of black widow spider venom (BWSV) can be severe, and are well understood for mammals but unknown for reptiles. We evaluated potential resistance to BWSV in the lizards that consume black widows, and a potentially susceptible species (Uta stansburiana) known as prey of widows. We investigated BWSV effects on whole-animal performance (sprint) and muscle tissue at two venom doses compared with control injections. Sprint speed was not significantly decreased in E. multicarinata or S. occidentalis in any treatment, while U. stansburiana suffered significant performance reductions in response to BWSV. Furthermore, E. multicarinata showed minimal tissue damage and immune response, while S. occidentalis and U. stansburiana exhibited increased muscle damage and immune system infiltration in response to BWSV. Our data suggest predator-prey relationships between lizards and spiders are complex, possibly leading to physiological and molecular adaptations that allow some lizards to tolerate or overcome the dangerous defences of their arachnid prey.

Intramuscular adipocyte and fatty acid differences between high-fat and control rabbit groups subject to a restricted diet

Fatty acids of intramuscular fat (IMF) in rabbits can influence meat quality, but it is unclear which fatty acids benefit to human health. A rabbit model of weight gain and weight loss was constructed using two rabbit groups and two growth stages. Stage 1 included control group1 fed a commercial diet(CG1) and experimental group1 fed a high fat diet (EG1). Stage 2 include control group2(CG2) and experimental group2 (EG2) both fed a restricted commercial diet. We detected differences in blood biochemical indicators as well as changes in intramuscular adipose cells and intramuscular fatty acid content in control and experiment groups at two stages. High fat induction can make rabbits become obese, have higher concentrations of glucose (GLU), total cholesterol (TC), triglyceride (TG), low density lipoprotein-cholesterol (LDL-C) and free fatty acid (FFA), and lower concentrations of insulin (INS). In addition, a high-fat diet promotes hypertrophy of precursor adipocytes in femoral muscles. Conversely, a restricted diet causes weight loss, decreases the concentration of TG, FFA, and INS in CG2 and EG2, and increases the deposition of unsaturated fatty acids in the femoral muscle. The content of monounsaturated trans oleic acid (C18:1n-9T) in EG2 was significantly higher than in CG2, whereas oleic acid (C18:1n-9C) was significantly lower in EG2 than in CG2. The polyunsaturated fatty acids Linolenate (C18:3 n-3) and cis-5,8,11,14,17-Eicosapentaenoate (C20:5 n-3) increased in CG2 and EG2. The content of Linoleate (C18:2 n-6) and γ-Linolenic acid (C18:3 n-6) significantly increased in CG2. The content of cis-11,14-Eicosatrienoic acid (C20:2) decreased significantly in CG2, but increased significantly in EG2.Thus, a high-fat diet can increase the formation of unhealthy fatty acids. Conversely, weight loss due to a restricted diet leads to an increase in unsaturated fatty acids in the femoral muscle, indicating that it reduces obesity symptoms and it may improve meat quality in rabbit.

Muscle Diversity, Heterogeneity, and Gradients: Learning from Sarcoglycanopathies

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.

MICAL2 is essential for myogenic lineage commitment

Contractile myofiber units are mainly composed of thick myosin and thin actin (F-actin) filaments. F-Actin interacts with Microtubule Associated Monooxygenase, Calponin And LIM Domain Containing 2 (MICAL2). Indeed, MICAL2 modifies actin subunits and promotes actin filament turnover by severing them and preventing repolymerization. In this study, we found that MICAL2 increases during myogenic differentiation of adult and pluripotent stem cells (PSCs) towards skeletal, smooth and cardiac muscle cells and localizes in the nucleus of acute and chronic regenerating muscle fibers. In vivo delivery of Cas9–Mical2 guide RNA complexes results in muscle actin defects and demonstrates that MICAL2 is essential for skeletal muscle homeostasis and functionality. Conversely, MICAL2 upregulation shows a positive impact on skeletal and cardiac muscle commitments. Taken together these data demonstrate that modulations of MICAL2 have an impact on muscle filament dynamics and its fine-tuned balance is essential for the regeneration of muscle tissues.

Cross-sectional study into age-related pathology of mouse models for limb girdle muscular dystrophy types 2D and 2F

Limb girdle muscular dystrophy (LGMD) types 2D and 2F are caused by mutations in the genes encoding for α- and δ-sarcoglycan, respectively, leading to progressive muscle weakness. Mouse models exist for LGMD2D (Sgca-/-) and 2F (Sgcd-/-). In a previous natural history study, we described the pathology in these mice at 34 weeks of age. However, the development of muscle pathology at younger ages has not been fully characterised yet. We therefore performed a study into age-related changes in muscle function and pathology by examining mice at different ages. From 4 weeks of age onwards, male mice were subjected to functional tests and sacrificed at respectively 8, 16 or 24 weeks of age. Muscle histopathology and expression of genes involved in muscle pathology were analysed for several skeletal muscles, while miRNA levels were assessed in serum. In addition, for Sgcd-/- mice heart pathology was assessed. Muscle function showed a gradual decline in both Sgca-/- and Sgcd-/- mice. Respiratory function was also impaired at all examined timepoints. Already at 8 weeks of age, muscle pathology was prominent, and fibrotic, inflammatory and regenerative markers were elevated, which remained relatively constant with age. In addition, Sgcd-/- mice showed signs of cardiomyopathy from 16 weeks of age onwards. These results indicate that Sgca-/- and Sgcd-/- are relevant disease models for LGMD2D and 2F.

Growth Factor Screening in Dystrophic Muscles Reveals PDGFB/PDGFRB-Mediated Migration of Interstitial Stem Cells

Progressive muscle degeneration followed by dilated cardiomyopathy is a hallmark of muscular dystrophy. Stem cell therapy is suggested to replace diseased myofibers by healthy myofibers, although so far, we are faced by low efficiencies of migration and engraftment of stem cells. Chemokines are signalling proteins guiding cell migration and have been shown to tightly regulate muscle tissue repair. We sought to determine which chemokines are expressed in dystrophic muscles undergoing tissue remodelling. Therefore, we analysed the expression of chemokines and chemokine receptors in skeletal and cardiac muscles from Sarcoglycan-α null, Sarcoglycan-β null and immunodeficient Sgcβ-null mice. We found that several chemokines are dysregulated in dystrophic muscles. We further show that one of these, platelet-derived growth factor-B, promotes interstitial stem cell migration. This finding provides perspective to an approachable mechanism for improving stem cell homing towards dystrophic muscles.

Pericytes in Muscular Dystrophies

The muscular dystrophies are an heterogeneous group of inherited myopathies characterised by the progressive wasting of skeletal muscle tissue. Pericytes have been shown to make muscle in vitro and to contribute to skeletal muscle regeneration in several animal models, although recent data has shown this to be controversial. In fact, some pericyte subpopulations have been shown to contribute to fibrosis and adipose deposition in muscle. In this chapter, we explore the identity and the multifaceted role of pericytes in dystrophic muscle, potential therapeutic applications and the current need to overcome the hurdles of characterisation (both to identify pericyte subpopulations and track cell fate), to prevent deleterious differentiation towards myogenic-inhibiting subpopulations, and to improve cell proliferation and engraftment efficacy.