Alpha 7 integrin preserves the function of the extensor digitorum longus muscle in dystrophin-null mice

The Role of the MYL4 Gene in Porcine Muscle Development and Its Molecular Regulatory Mechanisms

Muscle growth stands as a pivotal economic trait within pig production, governed by a complex interplay of multiple genes, each playing a role in its quantitative manifestation. Understanding the intricate regulatory mechanisms of porcine muscle development is crucial for enhancing both pork yield and quality. This study used the GSE99749 dataset downloaded from the GEO database, conducting a detailed analysis of the RNA-seq results from the longissimus dorsi muscle (LD) of Tibetan pigs (TP), Wujin pigs (WJ) and large white pigs (LW) at 60 days of gestation, representing diverse body sizes and growth rates. Comparative analyses between TPvsWJ and TPvsLW, along with differential gene expression (DEG) analysis, functional enrichment analysis, and protein-protein interaction (PPI) network analysis, revealed 1048 and 1157 significantly differentially expressed genes (p < 0.001) in TPvsWJ and TPvsLW, respectively. With stricter screening criteria, 37 DEGs were found to overlap between the 2 groups. PPI analysis identified MYL5, MYL4, and ACTC1 as the three core genes. This article focuses on exploring the MYL4 gene. Molecular-level experimental validation, through overexpression and interference of the MYL4 gene combined with EDU staining experiments, demonstrated that overexpression of MYL4 significantly promoted the proliferation of porcine skeletal muscle satellite cells (PSMSC), while interference with MYL4 inhibited their proliferation. Furthermore, by examining the effects of overexpressing and interfering with the MYL4 gene on the muscle hypertrophy marker Fst gene and the muscle degradation marker FOXO3 gene, the pivotal role of the MYL4 gene in promoting muscle growth and preventing muscle degradation was further confirmed. These findings offer a new perspective on the molecular mechanisms behind porcine muscle growth and development, furnishing valuable data and insights for muscle biology research.

RNA sequencing and immunofluorescence of the myotendinous junction of mature horses and humans

The myotendinous junction (MTJ) is a specialized interface for transmitting high forces between the muscle and tendon and yet the MTJ is a common site of strain injury with a high recurrence rate. The aim of this study was to identify previously unknown MTJ components in mature animals and humans. Samples were obtained from the superficial digital flexor (SDF) muscle-tendon interface of 20 horses, and the tissue was separated through a sequential cryosectioning approach into muscle, MTJ (muscle tissue enriched in myofiber tips attached to the tendon), and tendon fractions. RT-PCR was performed for genes known to be expressed in the three tissue fractions and t-distributed stochastic neighbor embedding (t-SNE) plots were used to select the muscle, MTJ, and tendon samples from five horses for RNA sequencing. The expression of previously known and unknown genes identified through RNA sequencing was studied by immunofluorescence on human hamstring MTJ tissue. The main finding was that RNA sequencing identified the expression of a panel of 61 genes enriched at the MTJ. Of these, 48 genes were novel for the MTJ and 13 genes had been reported to be associated with the MTJ in earlier studies. The expression of known [COL22A1 (collagen XXII), NCAM (neural cell adhesion molecule), POSTN (periostin), NES (nestin), OSTN (musclin/osteocrin)] and previously undescribed [MNS1 (meiosis-specific nuclear structural protein 1), and LCT (lactase)] MTJ genes was confirmed at the protein level by immunofluorescence on tissue sections of human MTJ. In conclusion, in muscle-tendon interface tissue enriched with myofiber tips, we identified the expression of previously unknown MTJ genes representing diverse biological processes, which may be important in the maintenance of the specialized MTJ.

Extracellular matrix: an important regulator of cell functions and skeletal muscle development

Extracellular matrix (ECM) is a kind of connective tissue in the cell microenvironment, which is of great significance to tissue development. ECM in muscle fiber niche consists of three layers: the epimysium, the perimysium, and the endomysium (basal lamina). These three layers of connective tissue structure can not only maintain the morphology of skeletal muscle, but also play an important role in the physiological functions of muscle cells, such as the transmission of mechanical force, the regeneration of muscle fiber, and the formation of neuromuscular junction. In this paper, detailed discussions are made for the structure and key components of ECM in skeletal muscle tissue, the role of ECM in skeletal muscle development, and the application of ECM in biomedical engineering. This review will provide the reader with a comprehensive overview of ECM, as well as a comprehensive understanding of the structure, physiological function, and application of ECM in skeletal muscle tissue.

The Myotendinous Junction-A Vulnerable Companion in Sports. A Narrative Review

The incidence of strain injuries continues to be high in many popular sports, especially hamstring strain injuries in football, despite a documented important effect of eccentric exercise to prevent strains. Studies investigating the anatomical properties of these injuries in humans are sparse. The majority of strains are seen at the interface between muscle fibers and tendon: the myotendinous junction (MTJ). It has a unique morphology with a highly folded muscle membrane filled with invaginations of collagen fibrils from the tendon, establishing an increased area of force transmission between muscle and tendon. There is a very high rate of remodeling of the muscle cells approaching the MTJ, but little is known about how the tissue adapts to exercise and which structural changes heavy eccentric exercise may introduce. This review summarizes the current knowledge about the anatomy, composition and adaptability of the MTJ, and discusses reasons why strain injuries can be prevented by eccentric exercise.

Sunitinib promotes myogenic regeneration and mitigates disease progression in the mdx mouse model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a lethal, muscle degenerative disease causing premature death of affected children. DMD is characterized by mutations in the dystrophin gene that result in a loss of the dystrophin protein. Loss of dystrophin causes an associated reduction in proteins of the dystrophin glycoprotein complex, leading to contraction-induced sarcolemmal weakening, muscle tearing, fibrotic infiltration and rounds of degeneration and failed regeneration affecting satellite cell populations. The α7β1 integrin has been implicated in increasing myogenic capacity of satellite cells, therefore restoring muscle viability, increasing muscle force and preserving muscle function in dystrophic mouse models. In this study, we show that a Food and Drug Administration (FDA)-approved small molecule, Sunitinib, is a potent α7 integrin enhancer capable of promoting myogenic regeneration by stimulating satellite cell activation and increasing myofiber fusion. Sunitinib exerts its regenerative effects via transient inhibition of SHP-2 and subsequent activation of the STAT3 pathway. Treatment of mdx mice with Sunitinib demonstrated decreased membrane leakiness and damage owing to myofiber regeneration and enhanced support at the extracellular matrix. The decreased myofiber damage translated into a significant increase in muscle force production. This study identifies an already FDA-approved compound, Sunitinib, as a possible DMD therapeutic with the potential to treat other muscular dystrophies in which there is defective muscle repair.

Laminin-111 protein therapy enhances muscle regeneration and repair in the GRMD dog model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a devastating X-linked disease affecting ~1 in 5000 males. DMD patients exhibit progressive muscle degeneration and weakness, leading to loss of ambulation and premature death from cardiopulmonary failure. We previously reported that mouse Laminin-111 (msLam-111) protein could reduce muscle pathology and improve muscle function in the mdx mouse model for DMD. In this study, we examined the ability of msLam-111 to prevent muscle disease progression in the golden retriever muscular dystrophy (GRMD) dog model of DMD. The msLam-111 protein was injected into the cranial tibial muscle compartment of GRMD dogs and muscle strength and pathology were assessed. The results showed that msLam-111 treatment increased muscle fiber regeneration and repair with improved muscle strength and reduced muscle fibrosis in the GRMD model. Together, these findings support the idea that Laminin-111 could serve as a novel protein therapy for the treatment of DMD.

Regional regulation of focal adhesion kinase after concentric and eccentric loading is related to remodelling of human skeletal muscle

AIMS

We assessed focal adhesion kinase (FAK) response to concentric (CON) vs eccentric (ECC) resistance training (RT) at two vastus lateralis (VL) sites, and the relationships between FAK, muscle protein synthesis (MPS) and morphological remodelling.

METHODS

Six young males trained both legs unilaterally 3 times/week for 8 weeks; one leg performed CON RT, the contralateral performed ECC RT. Muscle biopsies were collected after training from VL mid-belly (MID) and distal (distal) sites at 0, 4, 8 weeks. Focal adhesion kinase content and activation were evaluated by immunoblotting. MPS was assessed by deuterium oxide tracer; morphological adaptations were evaluated by ultrasound and DXA.

RESULTS

pY397-FAK 8 weeks levels were ~4-fold greater after ECC at the distal site compared to CON (P < .05); pY397FAK to total FAK ratio was greater in ECC vs CON at 4 (~2.2-fold, P < .05) and 8 weeks (~9-fold, P < .001) at the distal site. Meta-vinculin was found transiently increased at 4 weeks at the distal site only after ECC RT. ECC presented greater fascicle length (Lf) increases (10.5% vs 4%), whereas CON showed greater in pennation angle (PA) changes (12.3% vs 2.1%). MPS did not differ between exercise types or muscle sites at all time points. distal pY397-FAK and pY397-FAK/FAK values correlated to changes in Lf at 8 weeks (r = .76, P < .01 and r = .66, P < .05 respectively).

CONCLUSION

Focal adhesion kinase phosphorylation was greater at 8 weeks after ECC RT and was muscle region-specific. FAK activity correlated to contraction-dependent architectural remodelling, suggesting a potential role of FAK in orienting muscle structural changes in response to distinct mechanical stimuli.

Modified forelimb grip strength test detects aging-associated physiological decline in skeletal muscle function in male mice

The conventional forelimb grip strength test is a widely used method to assess skeletal muscle function in rodents; in this study, we modified this method to improve its variability and consistency. The modified test had lower variability among trials and days than the conventional test in young C57BL6 mice, especially by improving the variabilities in male. The modified test was more sensitive than the conventional test to detect a difference in motor function between female and male mice, or between young and old male mice. When the modified test was performed on male mice during the aging process, reduction of grip strength manifested between 18 and 24 months of age at the group level and at the individual level. The modified test was similar to the conventional test in detecting skeletal muscle dysfunction in young male dystrophic mice. Thus, the modified forelimb grip strength test, with its improved validity and reliability may be an ideal substitute for the conventional method.

Loss of niche-satellite cell interactions in syndecan-3 null mice alters muscle progenitor cell homeostasis improving muscle regeneration

Background

The skeletal muscle stem cell niche provides an environment that maintains quiescent satellite cells, required for skeletal muscle homeostasis and regeneration. Syndecan-3, a transmembrane proteoglycan expressed in satellite cells, supports communication with the niche, providing cell interactions and signals to maintain quiescent satellite cells.

Results

Syndecan-3 ablation unexpectedly improves regeneration in repeatedly injured muscle and in dystrophic mice, accompanied by the persistence of sublaminar and interstitial, proliferating myoblasts. Additionally, muscle aging is improved in syndecan-3 null mice. Since syndecan-3 null myofiber-associated satellite cells downregulate Pax7 and migrate away from the niche more readily than wild type cells, syxndecan-3 appears to regulate satellite cell homeostasis and satellite cell homing to the niche.

Conclusions

Manipulating syndecan-3 provides a promising target for development of therapies to enhance muscle regeneration in muscular dystrophies and in aged muscle.

Electronic supplementary material

The online version of this article (doi:10.1186/s13395-016-0104-8) contains supplementary material, which is available to authorized users.

Pathoproteomic profiling of the skeletal muscle matrisome in dystrophinopathy associated myofibrosis

The gradual accumulation of collagen and associated proteins of the extracellular matrix is a crucial myopathological parameter of many neuromuscular disorders. Progressive tissue damage and fibrosis play a key pathobiochemical role in the dysregulation of contractile functions and often correlates with poor motor outcome in muscular dystrophies. Following a brief introduction into the role of the extracellular matrix in skeletal muscles, we review here the proteomic profiling of myofibrosis and its intrinsic role in X-linked muscular dystrophy. Although Duchenne muscular dystrophy is primarily a disease of the membrane cytoskeleton, one of its most striking histopathological features is a hyperactive connective tissue and tissue scarring. We outline the identification of novel factors involved in the modulation of the extracellular matrix in muscular dystrophy, such as matricellular proteins. The establishment of novel proteomic markers will be helpful in improving the diagnosis, prognosis, and therapy monitoring in relation to fibrotic substitution of contractile tissue. In the future, the prevention of fibrosis will be crucial for providing optimum conditions to apply novel pharmacological treatments, as well as establish cell-based approaches or gene therapeutic interventions. The elimination of secondary abnormalities in the matrisome promises to reduce tissue scarring and the loss of skeletal muscle elasticity.