Laminin-211 in skeletal muscle function

Glycations on Decellularized Muscle Matrix Reduce Muscle Regeneration and Increase Inflammation

Volumetric muscle loss (VML) due to traumatic injury results in the abrupt loss of contractile units, stem cells, and connective tissue, leading to long-term muscle dysfunction and reduced regenerative potential. Muscle connective tissue contains a proregenerative extracellular matrix (ECM), and our lab harnesses the regenerative capacity of decellularized muscle matrix (DMM) to treat VML, a condition with limited treatment options. However, a major limitation is that muscle often comes from aged donors. Previous work from our lab showed that aged donor muscle contains higher levels of advanced glycation end-product (AGE) cross-links compared to muscle from younger donors. This study aimed to determine whether increased AGE cross-links reduce the regenerative capacity of DMM. To test this, we first generated AGEs in DMM with direct D-ribose incubation. We then removed ∼35% of the gastrocnemius muscle in a model and treated it with either AGE-DMM or standard DMM (no AGEs), comparing results to controls. Although muscle force results remained unchanged between AGE-DMM and DMM, AGEs led to reduced muscle mass in histological sections, fewer fibers, and smaller fiber diameters. AGEs also increased collagen levels in histology, but protein assays showed reduced collagen production. We investigated the canonical receptor for AGEs, the receptor for AGEs (RAGE), and found elevated levels in AGE-treated VML compared to DMM alone, along with increased levels of the noncanonical receptor galectin-3. Both RAGE and galectin-3 are associated with inflammation, and proteomics revealed higher inflammatory markers in AGE-treated muscle than in DMM alone. In conclusion, our data suggest that AGEs impair the regenerative potential of DMM, highlighting the importance of considering donor age when sourcing muscle for DMM therapies. Impact Statement This study investigates advanced glycation end-product cross-links in skeletal muscle extracellular matrix (ECM) as a way to model its deleterious effects on muscle regeneration in vivo. We demonstrate here that ECM glycations reduce muscle regeneration, enhance inflammatory markers, reduce ECM protein production, and proteomic analysis identified unique targets that could be explored in future research endeavors.

Hidden pathway: the role of extracellular matrix in type 2 diabetes mellitus-related sarcopenia

Type 2 diabetes mellitus-related sarcopenia (T2DMRS) is a common complication in elderly and advanced diabetes patients that affects long-term prognosis and quality of life. Skeletal muscle is the main unit of glucose metabolism, and it is surrounded by extracellular matrix (ECM), which is a microenvironment that acts as an efficient highway system. The ECM is essential for cellular communication and nutrient transport and supports muscle cell growth and repair. When this "ECM highway" fails to function effectively because of damage or blockage, the development of T2DMRS can be triggered or exacerbated. In recent years, the ECM has been widely demonstrated to play a critical role in insulin resistance and skeletal muscle regeneration. However, how the remodeling of skeletal muscle ECM components specifically affects the T2DMRS mechanism of action has not been scientifically described in detail. In this review, we comprehensively summarize the T2DMRS-related mechanisms of ECM remodeling, suggesting that collagen and integrins may be potential therapeutic targets.

Targeting Galectin-3 to modulate inflammation in LAMA2-deficient congenital muscular dystrophy

LAMA2-deficient congenital muscular dystrophy (LAMA2-CMD) is a severe neuromuscular disorder characterized by muscle degeneration, chronic inflammation, and fibrosis. While inflammation is one the hallmarks of LAMA2-CMD, the immune cell composition in laminin-deficient muscles remains understudied. Consequently, targeted pharmacological intervention to reduce inflammation remains underexplored. Here, we characterized the immune landscape in the dyW mouse model of LAMA2-CMD using RNA sequencing and flow cytometry. Transcriptomic analysis of dyW quadriceps femoris muscle identified 2,143 differentially expressed genes, with most upregulated genes linked to immune-related pathways. Lgals3 (Galectin-3) was significantly upregulated and identified as a key upstream regulator of the immune-related pathways. Flow cytometry revealed elevated leukocyte (CD45⁺) infiltration, with macrophages as the predominant population. Pro-inflammatory (M1) macrophages were increased, whereas anti-inflammatory (M2) macrophages remained low, indicating persistent and unresolved inflammation. Notably, Galectin-3 + macrophages were significantly enriched, suggesting that Galectin-3 drives inflammation in LAMA2-CMD. Treatment of dyW mice with TD-139, a Galectin-3 inhibitor, reduced leukocyte infiltration, decreased Galectin-3 + macrophages, and shifted macrophage polarization toward an M2 anti-inflammatory profile. RNA sequencing of TD-139-treated dyW muscles showed upregulation of muscle contraction pathways and downregulation of fibrosis-related genes. These findings highlight Galectin-3 + macrophages as key contributors to LAMA2-CMD pathophysiology and support further exploration of TD-139 as a potential therapeutic strategy for LAMA2-CMD and other dystrophic conditions driven by chronic inflammation.

Decellularized Extracellular Matrix-Derived Hydrogels: a Powerful Class of Biomaterials for Skeletal Muscle Regenerative Engineering Applications

Purpose

The extracellular matrix (ECM) is a complicated milieu consisting of structural and functional molecules secreted by the resident cells that provides an optimal microenvironmental niche for enhanced cell adhesion, growth, differentiation, and tissue formation and maturation. For decades, ECM bio-scaffolds prepared from decellularized tissues have been used to promote skeletal muscle regeneration; however, it was recently discovered that these decellularized ECM (dECM) materials can be further processed into hydrogels, thus expanding the potential applications of dECM materials in skeletal muscle regenerative engineerisng (SMRE). This review article highlights the recent advances in dECM-derived hydrogels toward skeletal muscle regeneration and repair.

Method

We screened articles in PubMed and bibliographic search using a combination of keywords. Relevant and high-cited articles were chosen for inclusion in this narrative review.

Results

Here, we discuss the skeletal muscle ECM's structure, function, and biochemical composition with emphasis on the role of the ECM during skeletal muscle embryogenesis, growth, development, and repair. Furthermore, we review various hydrogels used to promote skeletal muscle regeneration. We also review the current applications of dECM-derived hydrogels toward SMRE. Finally, we discuss the clinical translation potential of dECM-derived hydrogels for skeletal muscle regeneration and repair and their potential clinical considerations in the future.

Conclusion

Although much progress has been made in the field of dECM-derived hydrogels toward SMRE, it is still in its nascent stage. We believe improving and standardizing the methods of decellularization, lowering the immunogenicity of dECMs, and carrying out in vivo investigations in large animal models would advance their future clinical applications.

Lay Summary

Researchers have discovered an effective way to turn tissue materials into jelly-like substances known as extracellular matrix (ECM)-derived hydrogels. These ECM-derived hydrogels can help muscles heal better after serious injuries. They can be injected into gaps or used to guide muscle growth in the lab or body. This review article explains how these ECM-derived hydrogels are made and how they can be used to improve muscle healing. It also discusses their possible use in clinics and what needs to be considered before using them for medical treatments.

Extracellular matrix: Dystroglycan interactions-Roles for the dystrophin-associated glycoprotein complex in skeletal tissue dynamics

Contributions made by the dystrophin-associated glycoprotein complex (DGC) to cell-cell and cell-extracellular matrix (ECM) interactions are vital in development, homeostasis and pathobiology. This review explores how DGC functions may extend to skeletal pathophysiology by appraising the known roles of its major ECM ligands, and likely associated DGC signalling pathways, in regulating cartilage and bone cell behaviour and emergent skeletal phenotypes. These considerations will be contextualised by highlighting the potential of studies into the role of the DGC in isolated chondrocytes, osteoblasts and osteoclasts, and by fuller deliberation of skeletal phenotypes that may emerge in very young mice lacking vital, yet diverse core elements of the DGC. Our review points to roles for individual DGC components-including the glycosylation of dystroglycan itself-beyond the establishment of membrane stability which clearly accounts for severe muscle phenotypes in muscular dystrophy. It implies that the short stature, low bone mineral density, poor bone health and greater fracture risk in these patients, which has been attributed due to primary deficiencies in muscle-evoked skeletal loading, may instead arise due to primary roles for the DGC in controlling skeletal tissue (re)modelling.

Urinary prostaglandin D2 and E2 metabolites are elevated with disease severity in patients with Fukuyama congenital muscular dystrophy

Treatment approaches are lacking for Fukuyama congenital muscular dystrophy (FCMD), the second most common type of pediatric muscular dystrophy after Duchenne muscular dystrophy (DMD) in the Japanese population. Recent studies demonstrating the involvement of prostaglandin (PG) D2 in DMD progression has led to the development of novel inhibitors targeting hematopoietic PGD2 synthase. This study aimed to determine the role of PGD2 in FCMD etiology in 42 patients with FCMD and 77 healthy age-matched individuals. Concentrations of tetranor-PGDM and tetranor-PGEM, the metabolites of PGD2 and PGE2, respectively, and creatinine were measured in spot urine samples. Mean tetranor-PGDM/creatinine and tetranor-PGEM/creatinine concentrations and tetranor-PGEM/tetranor-PGDM ratio were significantly higher in patients with FCMD than the healthy controls (5.3 ± 2.1 and 30.9 ± 52.3 ng/mg creatinine and 6.8 ± 2.0 vs. 3.4 ± 0.3 and 9.5 ± 0.9 ng/mg creatinine and 3.2 ± 0.3, respectively; p = 0.0011, p < 0.0001 and p < 0.0001, respectively). These metabolites were increased in patients with typical and severe FCMD phenotypes than in those with the mild FCMD phenotype, indicating their correlation with disease severity. These results implicate that PGD2 and PGE2 play important roles in FCMD pathogenesis and that novel hematopoietic PGD2 synthase inhibitors and steroids used in DMD may also have therapeutic utility in FCMD.

Systemic inhibition of bone morphogenetic protein 1.3 as a possible treatment for laminin-related congenital muscular dystrophy

Congenital muscular dystrophy (CMD) is a group of rare neuromuscular disorders typically characterized by the onset of symptoms at birth or within the first two years of life. CMDs are relatively rare, but extremely severe pathological conditions currently without a safe and effective therapeutic solution. Merosin-deficient congenital muscular dystrophy type 1A (MDC1A) is among the most frequent CMDs and it is caused by mutations in the LAMA2 gene that encodes for the α2 chain of laminin-211 (merosin). Laminin-211 is a crucial constituent of the basement membrane that provides muscle fibre stability and signal transduction. Bone morphogenetic protein 1.3 (BMP1.3) is evolutionarily conserved and structurally related to mammalian Tolloid-like metalloproteinase (mTld) that is involved in the processing of procollagens, non-collagenous extracellular matrix proteins, and growth factor-related proteins. Recently, it has been shown that BMP1.3 is present in circulation and its levels are elevated in patients with chronic kidney failure, hepatic fibrosis, and acute myocardial infarction. It has been demonstrated that administering the BMP1.3 antibody ameliorated kidney, liver, and heart function in animal disease models. Furthermore, we observed highly enhanced BMP1.3 gene expression in the skeletal muscles of mice with congenital muscular dystrophy. Therefore, we hypothesize that BMP1.3 inhibition represents a novel therapeutic strategy for reversing the progression of CMD. The development of an anti-BMP1.3 therapy might lead to groundbreaking changes in CMD treatment and provide relief to numerous patients suffering from this disabling disease.

External Scaffold for Strengthening the Pulmonary Autograft in the Ross Procedure

Despite offering several potential benefits over standard prosthetic aortic valve replacement, the use of the pulmonary autograft has been limited to date due to concerns over the risk of pulmonary autograft expansion and the need for reintervention. Several techniques using materials with biomimetic potential have been developed to reduce this complication. The incidence, risk factors, and pathophysiology of pulmonary autograft dilatation are discussed in this article. This seminar will provide an overview of the techniques of external pulmonary autograft support and their advantages and limitations. It also considers future directions for further investigation and future clinical applications of external pulmonary autograft support. Dilatation of the autograft is more likely to occur in patients with aortic regurgitation and a dilated aortic annulus. External scaffolding may prevent autograft stretching and expansion in these specific cases. However, from a biomimetic point of view, any permanent scaffold potentially restricts the movement of the autograft root. This reduces some of the benefits associated with the use of autologous tissue, which is the priority of the Ross procedure. To address this issue, several bioresorbable matrices could be used to support the root during its initial adaptive phase. Control of blood pressure with aggressive therapy is the first line to avoid this problem in the first year after pulmonary autograft implantation, together with support of the annular and sinotubular junction in some selected cases. This is the best way to maintain stable autograft root dimensions while preserving root dynamics. However, to determine the efficacy of this combined external support and best medical management, it is important to perform regular imaging and clinical follow-up.

Dominantly inherited muscle disorders: understanding their complexity and exploring therapeutic approaches

Treatments for disabling and life-threatening hereditary muscle disorders are finally close to becoming a reality. Research has thus far focused primarily on recessive forms of muscle disease. The gene replacement strategies that are commonly employed for recessive, loss-of-function disorders are not readily translatable to most dominant myopathies owing to the presence of a normal chromosome in each nucleus, hindering the development of novel treatments for these dominant disorders. This is largely due to their complex, heterogeneous disease mechanisms that require unique therapeutic approaches. However, as viral and RNA interference-based therapies enter clinical use, key tools are now in place to develop treatments for dominantly inherited disorders of muscle. This article will review what is known about dominantly inherited disorders of muscle, specifically their genetic basis, how mutations lead to disease, and the pathomechanistic implications for therapeutic approaches.

Mechanism underlying the role of integrin α3β1 in adhesive dysfunction between thyroid cells induced by diesel engine exhaust particles

The role and mechanisms of DEP exposure on thyroid injury are not yet clear. This study explores thyroid damage induced by in vivo DEP exposure using a mouse model. This study has observed alterations in thyroid follicular architecture, including rupture, colloid overflow, and the formation of voids. Additionally, there was a significant decrease in the expression levels of proteins involved in thyroid hormone synthesis, such as thyroid peroxidase and thyroglobulin, their trend of change is consistent with the damage to the thyroid structure. Serum levels of triiodothyronine and tetraiodothyronine were raise. However, the decrease in TSH expression suggests that the function of the HPT axis is unaffected. To delve deeper into the intrinsic mechanisms of thyroid injury, we performed KEGG pathway enrichment analysis, which revealed notable alterations in the cell adhesion signaling pathway. Our immunofluorescence results show that DEP exposure impairs thyroid adhesion, and integrin α3β1 plays an important role. CD151 binds to α3β1, promoting multimolecular complex formation and activating adhesion-dependent small GTPases. Our in vitro model has confirmed the pivotal role of integrin α3β1 in thyroid cell adhesion, which may be mediated by the CD151/α3β1/Rac1 pathway. In summary, exposure to DEP disrupts the structure and function of the thyroid, a process that likely involves the regulation of cell adhesion through the CD151/α3β1/Rac1 pathway, leading to glandular damage.

Thrombospondin-4 deletion does not exacerbate muscular dystrophy in β-sarcoglycan-deficient and laminin α2 chain-deficient mice

Muscular dystrophy is a group of genetic disorders that lead to muscle wasting and loss of muscle function. Identifying genetic modifiers that alleviate symptoms or enhance the severity of a primary disease helps to understand mechanisms behind disease pathology and facilitates discovery of molecular targets for therapy. Several muscular dystrophies are caused by genetic defects in the components of the dystrophin-glycoprotein adhesion complex (DGC). Thrombospondin-4 overexpression has been shown to mitigate dystrophic disease in mouse models for Duchenne muscular dystrophy (dystrophin deficiency) and limb-girdle muscular dystrophy type 2F (LGMD2F, δ-sarcoglycan deficiency), while deletion of the thrombospondin-4 gene exacerbated the diseases. Hence, thrombospondin-4 has been considered a candidate molecule for therapy of muscular dystrophies involving the DGC. We have investigated whether thrombospondin-4 could act as a genetic modifier for other DGC-associated diseases: limb-girdle muscular dystrophy type 2E (LGMD2E, β-sarcoglycan deficiency) and laminin α2 chain-deficient muscular dystrophy (LAMA2-RD). Deletion of the thrombospondin-4 gene in mouse models for LGMD2E and LAMA2-RD, respectively, did not result in worsening of the dystrophic phenotype. Loss of thrombospondin-4 did not enhance sarcolemma damage and did not impair trafficking of transmembrane receptors integrin α7β1 and dystroglycan in double knockout muscles. Our results suggest that thrombospondin-4 might not be a relevant therapeutic target for all muscular dystrophies involving the DGC. This data also demonstrates that molecular pathology between very similar diseases like LGMD2E and 2F can differ significantly.

Fatal Case of Exercise Collapse Associated with Sickle Cell Trait with Novel Underlying LAMA2 Mutation

ABSTRACT

Sickle cell trait is typically thought to be an asymptomatic carrier state, but it is rarely associated with exertional rhabdomyolysis in cases termed Exercise Collapse Associated with Sickle Cell Trait (ECAST). In a subset of these cases, underlying disease contributes to the development and/or severity of the ensuing medical complications. We describe the first ever case of ECAST reported in a previously asymptomatic, multiply deployed, highly physically active service member with an underlying heterozygous LAMA2 mutation. Moreover, the mutation identified via whole exome sequencing is a novel, likely pathogenic variant that has yet to be described in the literature.

The Tumor Stroma of Squamous Cell Carcinoma: A Complex Environment That Fuels Cancer Progression

The tumor microenvironment (TME), a complex assembly of cellular and extracellular matrix (ECM) components, plays a crucial role in driving tumor progression, shaping treatment responses, and influencing metastasis. This narrative review focuses on the cutaneous squamous cell carcinoma (cSCC) tumor stroma, highlighting its key constituents and their dynamic contributions. We examine how significant changes within the cSCC ECM-specifically, alterations in fibronectin, hyaluronic acid, laminins, proteoglycans, and collagens-promote cancer progression, metastasis, and drug resistance. The cellular composition of the cSCC TME is also explored, detailing the intricate interplay of cancer-associated fibroblasts (CAFs), mesenchymal stem cells (MSCs), endothelial cells, pericytes, adipocytes, and various immune cell populations. These diverse players modulate tumor development, angiogenesis, and immune responses. Finally, we emphasize the TME's potential as a therapeutic target. Emerging strategies discussed in this review include harnessing the immune system (adoptive cell transfer, checkpoint blockade), hindering tumor angiogenesis, disrupting CAF activity, and manipulating ECM components. These approaches underscore the vital role that deciphering TME interactions plays in advancing cSCC therapy. Further research illuminating these complex relationships will uncover new avenues for developing more effective treatments for cSCC.

Current Research, Industrialization Status, and Future Perspective of Cultured Meat

Expectations for the industrialization of cultured meat are growing due to the increasing support from various sectors, such as the food industry, animal welfare organizations, and consumers, particularly vegetarians, but the progress of industrialization is slower than initially reported. This review analyzes the main issues concerning the industrialization of cultured meat, examines research and media reports on the development of cultured meat to date, and presents the current technology, industrialization level, and prospects for cultured meat. Currently, over 30 countries have companies industrializing cultured meat, and around 200 companies that are developing or industrializing cultured meat have been surveyed globally. By country, the United States has over 50 companies, accounting for more than 20% of the total. Acquiring animal cells, developing cell lines, improving cell proliferation, improving the efficiency of cell differentiation and muscle production, or developing cell culture media, including serum-free media, are the major research themes related to the development of cultured meat. In contrast, the development of devices, such as bioreactors, which are crucial in enabling large-scale production, is relatively understudied, and few of the many companies invested in the development of cultured meat have presented products for sale other than prototypes. In addition, because most information on key technologies is not publicly available, it is not possible to determine the level of technology in the companies, and it is surmised that the technology of cultured meat-related startups is not high. Therefore, further research and development are needed to promote the full-scale industrialization of cultured meat.

The extracellular matrix niche of muscle stem cells

Preserving the potency of stem cells in adult tissues is very demanding and relies on the concerted action of various cellular and non-cellular elements in a precise stoichiometry. This balanced microenvironment is found in specific anatomical "pockets" within the tissue, known as the stem cell niche. In this review, we explore the interplay between stem cells and their niches, with a primary focus on skeletal muscle stem cells and the extracellular matrix (ECM). Quiescent muscle stem cells, known as satellite cells are active producers of a diverse array of ECM molecules, encompassing major constituents like collagens, laminins, and integrins, some of which are explored in this review. The conventional perception of ECM as merely a structural scaffold is evolving. Collagens can directly interact as ligands with receptors on satellite cells, while other ECM proteins have the capacity to sequester growth factors and regulate their release, especially relevant during satellite cell turnover in homeostasis or activation upon injury. Additionally, we explore an evolutionary perspective on the ECM across a range of multicellular organisms and discuss a model wherein satellite cells are self-sustained by generating their own niche. Considering the prevalence of ECM proteins in the connective tissue of various organs it is not surprising that mutations in ECM genes have pathological implications, including in muscle, where they can lead to myopathies. However, the particular role of certain disease-related ECM proteins in stem cell maintenance highlights the potential contribution of stem cell deregulation to the progression of these disorders.

Therapeutic applications of ginseng for skeletal muscle-related disorder management

Skeletal muscle (SM) is the largest organ of the body and is largely responsible for the metabolism required to maintain body functions. Furthermore, the maintenance of SM is dependent on the activation of muscle satellite (stem) cells (MSCs) and the subsequent proliferation and fusion of differentiating myoblasts into mature myofibers (myogenesis). Natural compounds are being used as therapeutic options to promote SM regeneration during aging, muscle atrophy, sarcopenia, cachexia, or obesity. In particular, ginseng-derived compounds have been utilized in these contexts, though ginsenoside Rg1 is mostly used for SM mass management. These compounds primarily function by activating the Akt/mTOR signaling pathway, upregulating myogenin and MyoD to induce muscle hypertrophy, downregulating atrophic factors (atrogin1, muscle ring-finger protein-1, myostatin, and mitochondrial reactive oxygen species production), and suppressing the expressions of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in cachexia. Ginsenoside compounds are also used for obesity management, and their anti-obesity effects are attributed to peroxisome proliferator activated receptor gamma (PPARγ) inhibition, AMPK activation, glucose transporter type 4 (GLUT4) translocation, and increased phosphorylations of insulin resistance (IR), insulin receptor substrate-1 (IRS-1), and Akt. This review was undertaken to provide an overview of the use of ginseng-related compounds for the management of SM-related disorders.

Extracellular Matrix Proteomics: The mdx-4cv Mouse Diaphragm as a Surrogate for Studying Myofibrosis in Dystrophinopathy

The progressive degeneration of the skeletal musculature in Duchenne muscular dystrophy is accompanied by reactive myofibrosis, fat substitution, and chronic inflammation. Fibrotic changes and reduced tissue elasticity correlate with the loss in motor function in this X-chromosomal disorder. Thus, although dystrophinopathies are due to primary abnormalities in the DMD gene causing the almost-complete absence of the cytoskeletal Dp427-M isoform of dystrophin in voluntary muscles, the excessive accumulation of extracellular matrix proteins presents a key histopathological hallmark of muscular dystrophy. Animal model research has been instrumental in the characterization of dystrophic muscles and has contributed to a better understanding of the complex pathogenesis of dystrophinopathies, the discovery of new disease biomarkers, and the testing of novel therapeutic strategies. In this article, we review how mass-spectrometry-based proteomics can be used to study changes in key components of the endomysium, perimysium, and epimysium, such as collagens, proteoglycans, matricellular proteins, and adhesion receptors. The mdx-4cv mouse diaphragm displays severe myofibrosis, making it an ideal model system for large-scale surveys of systematic alterations in the matrisome of dystrophic fibers. Novel biomarkers of myofibrosis can now be tested for their appropriateness in the preclinical and clinical setting as diagnostic, pharmacodynamic, prognostic, and/or therapeutic monitoring indicators.

Super-Resolution Imaging Reveals the Nanoscale Distributions of Dystroglycan and Integrin Itga7 in Zebrafish Muscle Fibers

Cell signaling is determined partially by the localization and abundance of proteins. Dystroglycan and integrin are both transmembrane receptors that connect the cytoskeleton inside muscle cells to the extracellular matrix outside muscle cells, maintaining proper adhesion and function of muscle. The position and abundance of Dystroglycan relative to integrins is thought to be important for muscle adhesion and function. The subcellular localization and quantification of these receptor proteins can be determined at the nanometer scale by FPALM super-resolution microscopy. We used FPALM to determine localizations of Dystroglycan and integrin proteins in muscle fibers of intact zebrafish (Danio rerio). Results were consistent with confocal imaging data, but illuminate further details at the nanoscale and show the feasibility of using FPALM to quantify interactions of two proteins in a whole organism.

Chain-specificity of laminin α1-5 LG45 modules in the recognition of carbohydrate-linked receptors and intramolecular binding

Laminins are a family of heterotrimers composed of α-, β-, and γ-chains in the basement membrane. Five α chains contain laminin globular (LG) domain consisting of five tandem modules (LG1-5 modules) at their C-terminus. Each LG45 modules is connected to a compact cloverleaf-shaped structure of LG1-3 through a flexible linker. Although the accumulated studies of the LG45 modules have suggested differences in each α chain regarding the binding of carbohydrate chain and intramolecular interaction, this remains unclear. In this study, to characterize their functions comparatively, we produced recombinant proteins of LG45 modules of human laminin α1-5 chains. Dystroglycan (DG) modified with matriglycan readily bound to the LG45 modules of α1 and α2 chains but not to the other α chains. In contrast, heparin bound to the LG45 modules of the α chains, except for α2. The binding of heparan sulfate/heparin-linked syndecans (SDCs) to LG45 modules was influenced by their core proteins. Furthermore, the α1 and α4LG45 modules bound to SDCs in a pH-dependent manner. A cell adhesion assay showed that HEK293 cells could readily adhere to the LG45 modules of α3-5 chains through a combination of SDCs and integrins. Moreover, α5LG45 modules bound to the E8 fragment, which includes the C-terminus of the laminin coiled-coil (LCC) domain and LG1-3 modules, but α2LG45 modules did not. The results suggested that although α5LG45 modules was fixed within the LG domain, α2LG45 modules was freely placed in the vicinity of LG1-3. Our findings provide information for investigation of the structural and functional diversity of basement membranes.

Case report: Novel frameshift mutation in LAMA2 gene causing congenital muscular dystrophy type 1A

Congenital muscular dystrophy type 1A (CMD1A) is a rare autosomal recessive disorder caused by mutations in the LAMA2 gene. CMD1A is characterized by peripheral hypotonia and muscle weakness from the first months of life, cerebral white matter abnormalities, and elevated creatine phosphokinase (CPK) levels. We describe an 8-year-old girl from Colombia with clinical features compatible with CMD1A, severe scoliosis corrected with surgery, and feeding difficulty corrected with a gastrostomy. Whole-exome sequencing identified two heterozygous variants: a reported nonsense variant (LAMA2 NM_000426.3:c.4198C>T) and a novel likely pathogenic variant (LAMA2 NM_000426.3:c.9227_9243dup). This is the first genetically confirmed case of CMD1A in Colombia and the first report of the c.9227_9243dup variant causing CMD1A.

Merosin-deficient congenital muscular dystrophy type 1a: detection of LAMA2 variants in Vietnamese patients

Background: Merosin-deficient congenital muscular dystrophy type 1A (MDC1A), also known as laminin-α2 chain-deficient congenital muscular dystrophy (LAMA2-MD), is an autosomal recessive disease caused by biallelic variants in the LAMA2 gene. In MDC1A, laminin- α2 chain expression is absent or significantly reduced, leading to some early-onset clinical symptoms including severe hypotonia, muscle weakness, skeletal deformity, non-ambulation, and respiratory insufficiency. Methods: Six patients from five unrelated Vietnamese families presenting with congenital muscular dystrophy were investigated. Targeted sequencing was performed in the five probands. Sanger sequencing was carried out in their families. Multiplex ligation-dependent probe amplification was performed in one family to examine an exon deletion. Results: Seven variants of the LAMA2 (NM_000426) gene were identified and classified as pathogenic/likely pathogenic variants using American College of Medical Genetics and Genomics criteria. Two of these variants were not reported in the literature, including c.7156-5_7157delinsT and c.8974_8975insTGAT. Sanger sequencing indicated their parents as carriers. The mothers of family 4 and family 5 were pregnant and a prenatal testing was performed. The results showed that the fetus of the family 4 only carries c.4717 + 5G>A in the heterozygous form, while the fetus of the family 5 carries compound heterozygous variants, including a deletion of exon 3 and c.4644C>A. Conclusion: Our findings not only identified the underlying genetic etiology for the patients, but also provided genetic counseling for the parents whenever they have an offspring.

Link between insulin resistance and skeletal muscle extracellular matrix remodeling

Skeletal muscle is the main metabolic tissue responsible for glucose homeostasis in the body. It is surrounded by the extracellular matrix (ECM) consisting of three layers: epimysium, perimysium, and endomysium. ECM plays an important role in the muscle, as it provides integrity and scaffolding cells. The observed disturbances in this structure are related to the abnormal remodeling of the ECM (through an increase in the concentration of its components). ECM rearrangement may impair insulin action by increasing the physical barrier to insulin transport and reducing insulin transport into muscle cells as well as by directly inhibiting insulin action through integrin signaling. Thus, improper ECM remodeling may contribute to the development of insulin resistance (IR) and related comorbidities. In turn, IR-associated conditions may further aggravate disturbances of ECM in skeletal muscle. This review describes the major components of the ECM that are necessary for its proper function. Particular attention was also paid to receptors (integrins) involved in the signaling of metabolic pathways. Finally, changes in ECM components in the context of clinical and animal studies are discussed. This article will help the reader to systematize knowledge related to the ECM and to better understand the relationship between ECM remodeling and IR, and its role in the pathogenesis of T2DM. The information in this article presents the concept of the role of ECM and its remodeling in the pathogenesis of IR, which may contribute to developing new therapeutic solutions.

CRISPRa-induced upregulation of human LAMA1 compensates for LAMA2-deficiency in Merosin-deficient congenital muscular dystrophy

Merosin-deficient congenital muscular dystrophy (MDC1A) is an autosomal recessive disorder caused by mutations in the LAMA2 gene, resulting in a defective form of the extracellular matrix protein laminin-α2 (LAMA2). Individuals diagnosed with MDC1A exhibit progressive muscle wasting and declining neuromuscular functions. No treatments for this disorder are currently available. We previously showed that postnatal Lama1 upregulation, achieved through CRISPR activation (CRISPRa), compensates for Lama2 deficiency and prevents neuromuscular pathophysiology in a mouse model of MDC1A. In this study, we assessed the feasibility of upregulating human LAMA1 as a potential therapeutic strategy for individuals with MDC1A, regardless of their mutations. We hypothesized that CRISPRa-mediated upregulation of human LAMA1 would compensate for the lack of LAMA2 and rescue cellular abnormalities in MDC1A fibroblasts. Global transcriptomic and pathway enrichment analyses of fibroblasts collected from individuals carrying pathogenic LAMA2 mutations, compared with healthy controls, indicated higher expression of transcripts encoding proteins that contribute to wound healing, including Transforming Growth Factor-β (TGF-β) and Fibroblast Growth Factor (FGF). These findings were supported by wound-healing assays indicating that MDC1A fibroblasts migrated significantly more rapidly than the controls. Subsequently, we treated the MDC1A fibroblasts with SadCas9-2XVP64 and sgRNAs targeting the LAMA1 promoter. We observed robust LAMA1 expression, which was accompanied by significant decreases in cell migration and expression of FGFR2, TGF-β2, and ACTA2, which are involved in the wound-healing mechanism in MDC1A fibroblasts. Collectively, our data suggest that CRISPRa-mediated LAMA1 upregulation may be a feasible mutation-independent therapeutic approach for MDC1A. This strategy might be adapted to address other neuromuscular diseases and inherited conditions in which strong compensatory mechanisms have been identified.

Histological Methods to Assess Skeletal Muscle Degeneration and Regeneration in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a progressive disease caused by the loss of function of the protein dystrophin. This protein contributes to the stabilisation of striated cells during contraction, as it anchors the cytoskeleton with components of the extracellular matrix through the dystrophin-associated protein complex (DAPC). Moreover, absence of the functional protein affects the expression and function of proteins within the DAPC, leading to molecular events responsible for myofibre damage, muscle weakening, disability and, eventually, premature death. Presently, there is no cure for DMD, but different treatments help manage some of the symptoms. Advances in genetic and exon-skipping therapies are the most promising intervention, the safety and efficiency of which are tested in animal models. In addition to in vivo functional tests, ex vivo molecular evaluation aids assess to what extent the therapy has contributed to the regenerative process. In this regard, the later advances in microscopy and image acquisition systems and the current expansion of antibodies for immunohistological evaluation together with the development of different spectrum fluorescent dyes have made histology a crucial tool. Nevertheless, the complexity of the molecular events that take place in dystrophic muscles, together with the rise of a multitude of markers for each of the phases of the process, makes the histological assessment a challenging task. Therefore, here, we summarise and explain the rationale behind different histological techniques used in the literature to assess degeneration and regeneration in the field of dystrophinopathies, focusing especially on those related to DMD.

Extracellular matrix: Brick and mortar in the skeletal muscle stem cell niche

The extracellular matrix (ECM) is an interconnected macromolecular scaffold occupying the space between cells. Amongst other functions, the ECM provides structural support to tissues and serves as a microenvironmental niche that conveys regulatory signals to cells. Cell-matrix adhesions, which link the ECM to the cytoskeleton, are dynamic multi-protein complexes containing surface receptors and intracellular effectors that control various downstream pathways. In skeletal muscle, the most abundant tissue of the body, each individual muscle fiber and its associated muscle stem cells (MuSCs) are surrounded by a layer of ECM referred to as the basal lamina. The core scaffold of the basal lamina consists of self-assembling polymeric laminins and a network of collagens that tether proteoglycans, which provide lateral crosslinking, establish collateral associations with cell surface receptors, and serve as a sink and reservoir for growth factors. Skeletal muscle also contains the fibrillar collagenous interstitial ECM that plays an important role in determining tissue elasticity, connects the basal laminae to each other, and contains matrix secreting mesenchymal fibroblast-like cell types and blood vessels. During skeletal muscle regeneration fibroblast-like cell populations expand and contribute to the transitional fibronectin-rich regenerative matrix that instructs angiogenesis and MuSC function. Here, we provide a comprehensive overview of the role of the skeletal muscle ECM in health and disease and outline its role in orchestrating tissue regeneration and MuSC function.

Functional analysis reveals that Tinagl1 is required for normal muscle development in mice through the activation of ERK signaling

Tinagl1 (tubulointerstitial nephritis antigen-like 1) is a matricellular protein involved in female infertility and breast cancer tumorigenesis. In this study, we analyzed the function of Tinagl1 in skeletal muscle using knockout mice and cell experiments. Although primary myoblasts isolated from Tinagl1-decifient (Tinagl1^-/-) mice differentiated into normal myotubes, and treatment with recombinant Tinagl1 did not affect the proliferation or differentiation of C2C12 myoblasts, Tinagl1^-/- mice exhibited reduced body mass and calf muscle weights compared to the control group (Tinagl1^flox/flox). Furthermore, Tinagl1^-/- mice showed myofibers with centrally located nuclei, which is a morphological marker of regenerating muscle or myopathy. In addition, the capillary density in the soleus muscle of Tinagl1^-/- mice showed a decreasing trend compared to that of the control group. Importantly, si-RNA-mediated knockdown of TINAGL1 resulted in reduced tube formation in human umbilical vein endothelial cells (HUVECs), whereas treatment with Tinagl1 promoted tube formation. Immunoblot analysis revealed that Tinagl1 activates ERK signaling in both HUVECs and C2C12 myoblasts and myotubes, which are involved in the regulation of myogenic differentiation, proliferation, metabolism, and angiogenesis. Our results demonstrate that Tinagl1 may be required for normal muscle and capillary development through the activation of ERK signaling.

Laminin α5_CD239_Spectrin is a candidate association that compensates the linkage between the basement membrane and cytoskeleton in skeletal muscle fibers

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Laminin α5_CD239_spectrin complex is a candidate linkage in sarcolemma.

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The linkage molecules are expressed in embryonic and regenerative muscle fibers.

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CD239 expression is upregulated by steroid therapy for muscular dystrophy.

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The compensatory linkage may be a therapeutic target for muscular dystrophy.

The linkage between the basement membrane (BM) and cytoskeleton is crucial for muscle fiber stability and signal transduction. Mutations in the linkage molecules can cause various types of muscular dystrophies. The different severities and times of onset suggest that compensatory linkages occur at the sarcolemma. Cluster of differentiation 239 (CD239) binds to the α5 subunit of laminin-511 extracellularly and is connected to spectrin intracellularly, resulting in a linkage between the BM and cytoskeleton. In this study, we explored the linkage of laminin α5_CD239_spectrin in skeletal muscles. Although laminin α5, CD239, and spectrin were present in embryonic skeletal muscles, they disappeared in adult skeletal muscle tissues, except for the soleus and diaphragm. Laminin α5_CD239_spectrin was localized in the skeletal muscle tissues of Duchenne muscular dystrophy and congenital muscular dystrophy mouse models. The experimental regeneration of skeletal muscle increased the CD239-mediated linkage, indicating that it responds to regeneration, but not to genetic influence. Furthermore, in silico analysis showed that laminin α5_CD239_spectrin was upregulated by steroid therapy for muscular dystrophy. Therefore, CD239-mediated linkage may serve as a therapeutic target to prevent the progression of muscular dystrophy.

Myostatin and its Regulation: A Comprehensive Review of Myostatin Inhibiting Strategies

Myostatin (MSTN) is a well-reported negative regulator of muscle growth and a member of the transforming growth factor (TGF) family. MSTN has important functions in skeletal muscle (SM), and its crucial involvement in several disorders has made it an important therapeutic target. Several strategies based on the use of natural compounds to inhibitory peptides are being used to inhibit the activity of MSTN. This review delivers an overview of the current state of knowledge about SM and myogenesis with particular emphasis on the structural characteristics and regulatory functions of MSTN during myogenesis and its involvements in various muscle related disorders. In addition, we review the diverse approaches used to inhibit the activity of MSTN, especially in silico approaches to the screening of natural compounds and the design of novel short peptides derived from proteins that typically interact with MSTN.

Injectable laminin-biofunctionalized gellan gum hydrogels loaded with myoblasts for skeletal muscle regeneration

Moderate muscular injuries that exceed muscular tissue's auto-healing capacity are still a topic of noteworthy concern. Tissue engineering appeared as a promising therapeutic strategy capable of overcoming this unmet clinical need. To attain such goal, herein we propose an in situ-crosslinking gellan gum (GG)-based hydrogel tethered with a skeletal muscle-inspired laminin-derived peptide RKRLQVQLSIRTC(Q) and encapsulated with skeletal muscle cells (SMCs). Pre-hydrogel solutions presented decreasing shear viscosity with increasing shear rate and shear stress, and required low forces for extrusion, validating their injectability. The GGDVS hydrogel was functionalized with Q-peptide with 30% of efficiency. C2C12 were able to adhere to the developed hydrogel, remained living and spreading 7 days post-encapsulation. Q-peptide release studies indicated that 25% of the unbound peptide can be released from the hydrogels up to 7 days, dependent on the hydrogel formulation. Treatment of a chemically-induced muscular lesion in mice with an injection of C2C12-laden hydrogels improved myogenesis, primarily promoted by the C2C12. In accordance, a high density of myoblasts (α-SA⁺ and MYH7⁺) were localized in tissues treated with the C2C12 (alone or encapsulated in the hydrogel). α-SA protein levels were significantly increased 8 weeks post-treatment with C2C12-laden hydrogels and MHC protein levels were increased in all experimental groups 4 weeks post-treatment, in relation to the SHAM. Neovascularization and neoinnervation was also detected in the defects. Altogether, this study indicates that C2C12-laden hydrogels hold great potential for skeletal muscle regeneration. STATEMENT OF SIGNIFICANCE: We developed an injectable gellan gum-based hydrogel for delivering C2C12 into localized myopathic model. The gellan gum was biofunctinalized with laminin-derived peptide to mimic the native muscular ECM. In addition, hydrogel was physically tuned to mimic the mechanical properties of native tissue. To the best of our knowledge, this formula was used for the first time under the context of skeletal muscle tissue regeneration. The injectability of the developed hydrogel provided non-invasive administration method, combined with a reliable microenvironment that can host C2C12 with nominal inflammation, indicated by the survival and adhesion of encapsulated cells post-injection. The treatment of skeletal muscle defect with the cell-laden hydrogel approach significantly enhanced the regeneration of localized muscular trauma.

Lysosomes and the pathogenesis of merosin-deficient congenital muscular dystrophy

Congenital muscular dystrophy type 1A (MDC1A), the most common congenital muscular dystrophy in Western countries, is caused by recessive mutations in LAMA2, the gene encoding laminin alpha 2. Currently, no cure or disease modifying therapy has been successfully developed for MDC1A. Examination of patient muscle biopsies revealed altered distribution of lysosomes. We hypothesized that this redistribution was a novel and potentially druggable aspect of disease pathogenesis. We explored this hypothesis using candyfloss (caf), a zebrafish model of MDC1A. We found that lysosome distribution in caf zebrafish was also abnormal. This altered localization was significantly associated with fiber detachment and could be prevented by blocking myofiber detachment. Overexpression of transcription factor EB, a transcription factor that promotes lysosomal biogenesis, led to increased lysosome content and decreased fiber detachment. We conclude that genetic manipulation of the lysosomal compartment is able to alter the caf zebrafish disease process, suggesting that lysosome function may be a target for disease modification.

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.

Laminin Triggers Neutrophil Extracellular Traps (NETs) and Modulates NET Release Induced by Leishmania amazonensis

Neutrophils are recruited from the blood and transmigrate through the endothelium to reach tissues, where they are prone to respond through different mechanisms, including the release of neutrophil extracellular traps (NETs). These responses occur in close contact with proteins from the basement membrane and extracellular matrix, where laminins are abundant. Thus, we investigated the interactions between neutrophils and different laminin (LM) isoforms and analyzed the induction of NETs. We showed that neutrophils stimulated with LM isoforms 111, 211, 332, 411, 421, and 511 released NETs. The same occurred when neutrophils interacted with polymerized LMs 111, 411, and 511. LM-induced NETs were partially inhibited by pretreatment of neutrophils with an anti-α6 integrin antibody. Furthermore, NETs triggered by laminins were dependent on elastase and peptidylarginine deiminase (PAD)-4, enzymes that participate in chromatin decondensation. We also found that LMs 411 and LM 511 potentiated the NET release promoted by promastigotes of the protozoan parasite Leishmania, and that NETs stimulated by LMs alone display leishmanicidal activity. The ability of LM to induce NET release may have potential implications for the course of inflammation or infection.

The jam session between muscle stem cells and the extracellular matrix in the tissue microenvironment

Skeletal muscle requires a highly orchestrated coordination between multiple cell types and their microenvironment to exert its function and to maintain its homeostasis and regenerative capacity. Over the past decades, significant advances, including lineage tracing and single-cell RNA sequencing, have contributed to identifying multiple muscle resident cell populations participating in muscle maintenance and repair. Among these populations, muscle stem cells (MuSC), also known as satellite cells, in response to stress or injury, are able to proliferate, fuse, and form new myofibers to repair the damaged tissue. These cells reside adjacent to the myofiber and are surrounded by a specific and complex microenvironment, the stem cell niche. Major components of the niche are extracellular matrix (ECM) proteins, able to instruct MuSC behavior. However, during aging and muscle-associated diseases, muscle progressively loses its regenerative ability, in part due to a dysregulation of ECM components. This review provides an overview of the composition and importance of the MuSC microenvironment. We discuss relevant ECM proteins and how their mutations or dysregulation impact young and aged muscle tissue or contribute to diseases. Recent discoveries have improved our knowledge about the ECM composition of skeletal muscle, which has helped to mimic the architecture of the stem cell niche and improved the regenerative capacity of MuSC. Further understanding about extrinsic signals from the microenvironment controlling MuSC function and innovative technologies are still required to develop new therapies to improve muscle repair.

A guide to the composition and functions of the extracellular matrix

Extracellular matrix (ECM) is a dynamic 3-dimensional network of macromolecules that provides structural support for the cells and tissues. Accumulated knowledge clearly demonstrated over the last decade that ECM plays key regulatory roles since it orchestrates cell signaling, functions, properties and morphology. Extracellularly secreted as well as cell-bound factors are among the major members of the ECM family. Proteins/glycoproteins, such as collagens, elastin, laminins and tenascins, proteoglycans and glycosaminoglycans, hyaluronan, and their cell receptors such as CD44 and integrins, responsible for cell adhesion, comprise a well-organized functional network with significant roles in health and disease. On the other hand, enzymes such as matrix metalloproteinases and specific glycosidases including heparanase and hyaluronidases contribute to matrix remodeling and affect human health. Several cell processes and functions, among them cell proliferation and survival, migration, differentiation, autophagy, angiogenesis, and immunity regulation are affected by certain matrix components. Structural alterations have been also well associated with disease progression. This guide on the composition and functions of the ECM gives a broad overview of the matrisome, the major ECM macromolecules, and their interaction networks within the ECM and with the cell surface, summarizes their main structural features and their roles in tissue organization and cell functions, and emphasizes the importance of specific ECM constituents in disease development and progression as well as the advances in molecular targeting of ECM to design new therapeutic strategies.

LAMA2 Nonsense Variant in an Italian Greyhound with Congenital Muscular Dystrophy

A 4-month-old, male Italian Greyhound with clinical signs of a neuromuscular disease was investigated. The affected dog presented with an abnormal short-strided gait, generalized muscle atrophy, and poor growth since 2-months of age. Serum biochemistry revealed a marked elevation in creatine kinase activity. Electrodiagnostic testing supported a myopathy. Histopathology of muscle biopsies confirmed a dystrophic phenotype with excessive variability in myofiber size, degenerating fibers, and endomysial fibrosis. A heritable form of congenital muscular dystrophy (CMD) was suspected, and a genetic analysis initiated. We sequenced the genome of the affected dog and compared the data to that of 795 control genomes. This search revealed a private homozygous nonsense variant in LAMA2, XM_022419950.1:c.3285G>A, predicted to truncate 65% of the open reading frame of the wild type laminin α2 protein, XP_022275658.1:p.(Trp1095*). Immunofluorescent staining performed on muscle cryosections from the affected dog confirmed the complete absence of laminin α2 in skeletal muscle. LAMA2 loss of function variants were shown to cause severe laminin α2-related CMD in humans, mouse models, and in one previously described dog. Our data together with current knowledge on other species suggest the LAMA2 nonsense variant as cause for the CMD phenotype in the investigated dog.

Alterations in skeletal muscle repair in young adults with type 1 diabetes mellitus

Though preclinical models of type 1 diabetes (T1D) exhibit impaired muscle regeneration, this has yet to be investigated in humans with T1D. Here, we investigated the impact of damaging exercise (eccentric quadriceps contractions) in 18 physically active young adults with and without T1D. Pre- and postexercise (48 h and 96 h), the participants provided blood samples, vastus lateralis biopsies, and performed maximal voluntary quadriceps contractions (MVCs). Skeletal muscle sarcolemmal integrity, extracellular matrix (ECM) content, and satellite cell (SC) content/proliferation were assessed by immunofluorescence. Transmission electron microscopy was used to quantify ultrastructural damage. MVC was comparable between T1D and controls before exercise. Postexercise, MVC was decreased in both groups, but subjects with T1D exhibited moderately lower strength recovery at both 48 h and 96 h. Serum creatine kinase, an indicator of muscle damage, was moderately higher in participants with T1D at rest and exhibited a small elevation 96 h postexercise. Participants with T1D showed lower SC content at all timepoints and demonstrated a moderate delay in SC proliferation after exercise. A greater number of myofibers exhibited sarcolemmal damage (disrupted dystrophin) and increased ECM (laminin) content in participants with T1D despite no differences between groups in ultrastructural damage as assessed by electron microscopy. Finally, transcriptomic analyses revealed dysregulated gene networks involving RNA translation and mitochondrial respiration, providing potential explanations for previous observations of mitochondrial dysfunction in similar cohorts with T1D. Our findings indicate that skeletal muscle in young adults with moderately controlled T1D is altered after damaging exercise, suggesting that longer recovery times following intense exercise may be necessary.

Fibrin with Laminin-Nidogen Reduces Fibrosis and Improves Soft Palate Regeneration Following Palatal Injury

This study aimed to analyze the effects of fibrin constructs enhanced with laminin-nidogen, implanted in the wounded rat soft palate. Fibrin constructs with and without laminin-nidogen were implanted in 1 mm excisional wounds in the soft palate of 9-week-old rats and compared with the wounded soft palate without implantation. Collagen deposition and myofiber formation were analyzed at days 3, 7, 28 and 56 after wounding by histochemistry. In addition, immune staining was performed for a-smooth muscle actin (a-SMA), myosin heavy chain (MyHC) and paired homeobox protein 7 (Pax7). At day 56, collagen areas were smaller in both implant groups (31.25 ± 7.73% fibrin only and 21.11 ± 6.06% fibrin with laminin-nidogen)) compared to the empty wounds (38.25 ± 8.89%, p < 0.05). Moreover, the collagen area in the fibrin with laminin-nidogen group was smaller than in the fibrin only group (p ˂ 0.05). The areas of myofiber formation in the fibrin only group (31.77 ± 10.81%) and fibrin with laminin-nidogen group (43.13 ± 10.39%) were larger than in the empty wounds (28.10 ± 11.68%, p ˂ 0.05). Fibrin-based constructs with laminin-nidogen reduce fibrosis and improve muscle regeneration in the wounded soft palate. This is a promising strategy to enhance cleft soft palate repair and other severe muscle injuries.

Temporal Proteomic Profiling During Differentiation of Normal and Dystrophin-Deficient Human Muscle Cells

BACKGROUND

Myogenesis is a dynamic process involving temporal changes in the expression of many genes. Lack of dystrophin protein such as in Duchenne muscular dystrophy might alter the natural course of gene expression dynamics during myogenesis.

OBJECTIVE

To gain insight into the dynamic temporal changes in protein expression during differentiation of normal and dystrophin deficient myoblasts to myotubes.

METHOD

A super SILAC spike-in strategy in combination and LC-MS/MS was used for temporal proteome profiling of normal and dystrophin deficient myoblasts during differentiation. The acquired data was analyzed using Proteome Discoverer 2.2. and data clustering using R to define significant temporal changes in protein expression.

RESULTS

sFour major temporal protein clusters that showed sequential dynamic expression profiles during myogenesis of normal myoblasts were identified. Clusters 1 and 2, consisting mainly of proteins involved mRNA splicing and processing expression, were elevated at days 0 and 0.5 of differentiation then gradually decreased by day 7 of differentiation, then remained lower thereafter. Cluster 3 consisted of proteins involved contractile muscle and actomyosin organization. They increased in their expression reaching maximum at day 7 of differentiation then stabilized thereafter. Cluster 4 consisting of proteins involved in skeletal muscle development glucogenesis and extracellular remodeling had a lower expression during myoblast stage then gradually increased in their expression to reach a maximum at days 11-15 of differentiation. Lack of dystrophin expression in DMD muscle myoblast caused major alteration in temporal expression of proteins involved in cell adhesion, cytoskeleton, and organelle organization as well as the ubiquitination machinery.

CONCLUSION

Time series proteome profiling using super SILAC strategy is a powerful method to assess temporal changes in protein expression during myogenesis and to define the downstream consequences of lack of dystrophin on these temporal protein expressions. Key alterations were identified in dystrophin deficient myoblast differentiation compared to normal myoblasts. These alterations could be an attractive therapeutic target.

Identification of a compound heterozygous missense mutation in LAMA2 gene from a patient with merosin-deficient congenital muscular dystrophy type 1A

Background

Merosin‐deficient congenital muscular dystrophy type 1A (MDC1A) is occurred by mutations in LAMA2 gene that encodes the laminin α2 chain (merosin). MDC1A is a predominant subtype of congenital muscular dystrophy. Herein, we identified two missense mutations in LAMA2 gene in compound heterozygous status in an Iranian patient with MDC1A using whole‐exome sequencing (WES).

Methods

In the present study, we evaluated genetic alterations in an Iranian 35‐month‐old boy with MDC1A and his healthy family using WES method. The identified mutations further confirmed by Sanger sequencing method. Finally, in silico analysis was conducted to further evaluation of molecular function of the identified genetic variants.

Results

We identified two potentially pathogenic missense mutations in compound heterozygous state (c.7681G>A p.Gly2561Ser and c.4840A>G p.Asn1614Asp) in LAMA2 gene as contributing to the MDC1A phenotype. The healthy parents of our proband are single heterozygous for identified mutations. These variants were found to be pathogenic by in silico analysis.

Conclusions

In general, we successfully identified LAMA2 gene mutations in an Iranian patient with MDC1A using WES. The identified mutations in LAMA2 gene can be useful in genetic counseling, prenatal diagnosis, and predicting prognosis of MDC1A.

Engineering Musculoskeletal Grafts for Multi-Tissue Unit Repair: Lessons From Developmental Biology and Wound Healing

In the musculoskeletal system, bone, tendon, and skeletal muscle integrate and act coordinately as a single multi-tissue unit to facilitate body movement. The development, integration, and maturation of these essential components and their response to injury are vital for conferring efficient locomotion. The highly integrated nature of these components is evident under disease conditions, where rotator cuff tears at the bone-tendon interface have been reported to be associated with distal pathological alterations such as skeletal muscle degeneration and bone loss. To successfully treat musculoskeletal injuries and diseases, it is important to gain deep understanding of the development, integration and maturation of these musculoskeletal tissues along with their interfaces as well as the impact of inflammation on musculoskeletal healing and graft integration. This review highlights the current knowledge of developmental biology and wound healing in the bone-tendon-muscle multi-tissue unit and perspectives of what can be learnt from these biological and pathological processes within the context of musculoskeletal tissue engineering and regenerative medicine. Integrating these knowledge and perspectives can serve as guiding principles to inform the development and engineering of musculoskeletal grafts and other tissue engineering strategies to address challenging musculoskeletal injuries and diseases.

Laminin-111 protein therapy after disease onset slows muscle disease in a mouse model of laminin-α2 related congenital muscular dystrophy

Laminin-α2 related congenital muscular dystrophy (LAMA2-CMD) is a fatal muscle disease caused by mutations in the LAMA2 gene. Laminin-α2 is critical for the formation of laminin-211 and -221 heterotrimers in the muscle basal lamina. LAMA2-CMD patients exhibit hypotonia from birth and progressive muscle loss that results in developmental delay, confinement to a wheelchair, respiratory insufficiency and premature death. There is currently no cure or effective treatment for LAMA2-CMD. Several studies have shown laminin-111 can serve as an effective protein-replacement therapy for LAMA2-CMD. Studies have demonstrated early treatment with laminin-111 protein results in an increase in life expectancy and improvements in muscle pathology and function. Since LAMA2-CMD patients are often diagnosed after advanced disease, it is unclear if laminin-111 protein therapy at an advanced stage of the disease can have beneficial outcomes. In this study, we tested the efficacy of laminin-111 protein therapy after disease onset in a mouse model of LAMA2-CMD. Our results showed laminin-111 treatment after muscle disease onset increased life expectancy, promoted muscle growth and increased muscle stiffness. Together these studies indicate laminin-111 protein therapy either early or late in the disease process could serve as an effective protein replacement therapy for LAMA2-CMD.

The influence of circular RNAs on autophagy and disease progression

Circular RNAs (circRNAs) are non-coding RNAs that have attracted considerable attention in recent years. Owing to their distinct circular structure, circRNAs are stable in cells. Autophagy is a catabolic process that helps in the degradation and recycling of harmful or inessential biological macromolecules in cells and enables cells to adapt to stress and changes in the internal and external environments. Evidence has shown that circRNAs influence the course of a disease by regulating autophagy, which indicates that autophagy is involved in the onset and development of various diseases and can affect drug resistance (for example, it affects cisplatin resistance in tumors). In this review, we summarized the role of circRNAs in autophagy and their influence on disease onset and progression as well as drug resistance. The review will expand our understanding of tumors as well as cardiovascular and neurological diseases and also suggest novel therapeutic strategies.Abbreviations: ACR: autophagy-related circRNA; ADSCs: adipogenic mesenchymal stem cells; AMPK: AMP-activated protein kinase; ATG: autophagy related; BCL2: BCL2 apoptosis regulator; BECN1: beclin 1; ceRNA: competing endogenous RNA; circRNA: circular RNA; CMA: chaperone-mediated autophagy; EPCs: endothelial progenitor cells; LE/MVBs: late endosomes/multivesicular bodies; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; NSCLC: non-small cell lung cancer; PDLSCs: periodontal ligament stem cells; PE: phosphatidylethanolamine; PtdIns: phosphatidylinositol; PtdIns3K: phosphatidylinositol 3-kinase; PtdIns3P: phosphatidylinositol-3-phosphate 1,2-dipalmitoyl; PTEN: phosphatase and tensin homolog; RBPs: RNA-binding proteins; SiO₂: silicon dioxide; TFEB: transcription factor EB; ULK: unc-51 like autophagy activating kinase 1.

Functions of the extracellular matrix in development: Lessons from Caenorhabditis elegans

Cell-extracellular matrix interactions are crucial for the development of an organism from the earliest stages of embryogenesis. The main constituents of the extracellular matrix are collagens, laminins, proteoglycans and glycosaminoglycans that form a network of interactions. The extracellular matrix and its associated molecules provide developmental cues and structural support from the outside of cells during development. The complex nature of the extracellular matrix and its ability for continuous remodeling poses challenges when investigating extracellular matrix-based signaling during development. One way to address these challenges is to employ invertebrate models such as Caenorhabditis elegans, which are easy to genetically manipulate and have an invariant developmental program. C. elegans also expresses fewer extracellular matrix protein isoforms and exhibits reduced redundancy compared to mammalian models, thus providing a simpler platform for exploring development. This review summarizes our current understanding of how the extracellular matrix controls the development of neurons, muscles and the germline in C. elegans.

Engineering multi-tissue units for regenerative Medicine: Bone-tendon-muscle units of the rotator cuff

Our body systems are comprised of numerous multi-tissue units. For the musculoskeletal system, one of the predominant functional units is comprised of bone, tendon/ligament, and muscle tissues working in tandem to facilitate locomotion. To successfully treat musculoskeletal injuries and diseases, critical consideration and thoughtful integration of clinical, biological, and engineering aspects are necessary to achieve translational bench-to-bedside research. In particular, identifying ideal biomaterial design specifications, understanding prior and recent tissue engineering advances, and judicious application of biomaterial and fabrication technologies will be crucial for addressing current clinical challenges in engineering multi-tissue units. Using rotator cuff tears as an example, insights relevant for engineering a bone-tendon-muscle multi-tissue unit are presented. This review highlights the tissue engineering strategies for musculoskeletal repair and regeneration with implications for other bone-tendon-muscle units, their derivatives, and analogous non-musculoskeletal tissue structures.

A local regulatory network in the testis mediated by laminin and collagen fragments that supports spermatogenesis

It is almost five decades since the discovery of the hypothalamic-pituitary-testicular axis. This refers to the hormonal axis that connects the hypothalamus, pituitary gland and testes, which in turn, regulates the production of spermatozoa through spermatogenesis in the seminiferous tubules, and testosterone through steroidogenesis by Leydig cells in the interstitium, of the testes. Emerging evidence has demonstrated the presence of a regulatory network across the seminiferous epithelium utilizing bioactive molecules produced locally at specific domains of the epithelium. Studies have shown that biologically active fragments are produced from structural laminin and collagen chains in the basement membrane. Additionally, bioactive peptides are also produced locally in non-basement membrane laminin chains at the Sertoli-spermatid interface known as apical ectoplasmic specialization (apical ES, a testis-specific actin-based anchoring junction type). These bioactive peptides are derived from structural laminins and/or collagens at the corresponding sites through proteolytic cleavage by matrix metalloproteinases (MMPs). They in turn serve as autocrine and/or paracrine factors to modulate and coordinate cellular events across the epithelium by linking the apical and basal compartments, the apical and basal ES, the blood-testis barrier (BTB), and the basement membrane of the tunica propria. The cellular events supported by these bioactive peptides/fragments include the release of spermatozoa at spermiation, remodeling of the immunological barrier to facilitate the transport of preleptotene spermatocytes across the BTB, and the transport of haploid spermatids across the epithelium to support spermiogenesis. In this review, we critically evaluate these findings. Our goal is to identify research areas that deserve attentions in future years. The proposed research also provides the much needed understanding on the biology of spermatogenesis supported by a local network of regulatory biomolecules.

Label-free histological imaging of tissues using Brillouin light scattering contrast

Brillouin light scattering offers a unique label-free approach to measure biomechanical properties non-invasively. While this technique is used in biomechanical analysis of cells and tissues, its potential for visualizing structural features of tissues based on the biomechanical contrast has not been much exploited. Here, we present high-resolution Brillouin microscopy images of four basic tissue types: muscular, connective, epithelial, and nervous tissues. The Brillouin contrast distinguishes between muscle fiber cells and endomysium in skeletal muscle and reveals chondrocytes along with spatially varying stiffness of the extracellular matrix in articular cartilage. The hydration-sensitive contrast can visualize the stratum corneum, epidermis, and dermis in the skin epithelium. In brain tissues, the Brillouin images show the mechanical heterogeneity across the cortex and deeper regions. This work demonstrates the versatility of using the Brillouin shift as histological contrast for examining intact tissue substructures via longitudinal modulus without the need for laborious tissue processing steps.

Extracellular matrix at the muscle - tendon interface: functional roles, techniques to explore and implications for regenerative medicine

The muscle-tendon interface is an anatomically specialized region that is involved in the efficient transmission of force from muscle to tendon. Due to constant exposure to loading, the interface is susceptible to injury. Current treatment methods do not meet the socioeconomic demands of reduced recovery time without compromising the risk of reinjury, requiring the need for developing alternative strategies. The extracellular matrix (ECM) present in muscle, tendon, and at the interface of these tissues consists of unique molecules that play significant roles in homeostasis and repair. Better, understanding the function of the ECM during development, injury, and aging has the potential to unearth critical missing information that is essential for accelerating the repair at the muscle-tendon interface. Recently, advanced techniques have emerged to explore the ECM for identifying specific roles in musculoskeletal biology. Simultaneously, there is a tremendous increase in the scope for regenerative medicine strategies to address the current clinical deficiencies. Advancements in ECM research can be coupled with the latest regenerative medicine techniques to develop next generation therapies that harness ECM for treating defects at the muscle-tendon interface. The current work provides a comprehensive review on the role of muscle and tendon ECM to provide insights about the role of ECM in the muscle-tendon interface and discusses the latest research techniques to explore the ECM to gathered information for developing regenerative medicine strategies.

Xenogeneic Decellularized Extracellular Matrix-based Biomaterials For Peripheral Nerve Repair and Regeneration

Peripheral nerve injury could lead to either impairment or a complete loss of function for affected patients, and a variety of nerve repair materials have been developed for surgical approaches to repair it. Although autologous or autologous tissue-derived biomaterials remain preferred treatment for peripheral nerve injury, the lack of donor sources has led biomedical researchers to explore more other biomaterials. As a reliable alternative, xenogeneic decellularized extracellular matrix (dECM)-based biomaterials have been widely employed for surgical nerve repair. The dECM derived from animal donors is an attractive and unlimited source for xenotransplantation. Meanwhile, as an increasingly popular technique, decellularization could retain a variety of bioactive components in native ECM, such as polysaccharides, proteins, and growth factors. The resulting dECM-based biomaterials preserve a tissue's native microenvironment, promote Schwann cells proliferation and differentiation, and provide cues for nerve regeneration. Although the potential of dECM-based biomaterials as a therapeutic agent is rising, there are many limitations of this material restricting its use. Herein, this review discusses the decellularization techniques that have been applied to create dECM-based biomaterials, the main components of nerve ECM, and the recent progress in the utilization of xenogeneic dECM-based biomaterials through applications as a hydrogel, wrap, and guidance conduit in nerve tissue engineering. In the end, the existing bottlenecks of xenogeneic dECM-based biomaterials and developing technologies that could be eliminated to be helpful for utilization in the future have been elaborated.

The impact of skeletal muscle injury on the expression of laminin and its role in regeneration

Background: Laminins are high-molecular-weight proteins in the extracellular matrix; it is a major component of the basal lamina, influencing cell differentiation, migration, and adhesion. Laminin affects cell growth, besides effects in wound healing and embryonic development. Objectives: The present study aims to assess the histological changes taking place during skeletal muscle healing. Methods: The extensor digitorum longus muscle of 45 male rabbits was set as a skeletal muscle injury model and examined 3&6 weeks after initiation of injury. These animals were divided into three groups control (A) group with no injury, group (B) at 3rd post-injury week, group (C) at 6th post-injury week. The muscle tissues were prepared and examined histologically using H&E and immunohistochemically using Laminin antibodies. Aperio image scope software is used to analyze immunohistochemical reactivity quantitatively. The degeneration and regeneration process were overlapping with each other both in time and cellular morphological changes. Early myoblast-like cell appearance and new myotube formation were recorded during the 3rd week. By the end of the 6th-week postoperatively, the muscle histological maturation and muscle fascicles were noticed. Results: Immunohistochemical reactivity of Laminin antibody showed an intense reactivity in the 3rd-week group while a less intense reactivity in the control and 6th-week groups'. A quantitative assessment of Laminin using Aperio soft wear showed that the 3rd-week group has an intensity of 0.724±0.03 pixel, while the 6th week's group was 0. 321±0.02 pixel and the control group was 0.293±0.02 pixel. The differences were statistically significant, P-value ≤0.0001. Conclusion: The process of regeneration is a dynamic type where degeneration and regeneration superimposed each other.

Carbohydrate-Induced Insulin Signaling Activates Focal Adhesion Kinase: A Nutrient and Mechanotransduction Crossroads

Research has suggested that nutrient, exercise, and metabolism-related proteins interact to regulate mammalian target of rapamycin complex one (mTOR) post-exercise and their interactions needs clarification. In a double-blind, cross-over, repeated measures design, ten participants completed four sets to failure at 70% of 1-repitition maximum (1-RM) with 45 s rest on angled leg press with or without pre-exercise maltodextrin (2 g/kg) after a 3 h fast. Vastus lateralis biopsies were collected at baseline before supplementation and 1 h post-exercise to analyze Focal Adhesion Kinase (FAK), ribosomal protein S6 kinase beta-1 (p70S6K), insulin receptor substrate 1 (IRS-1), phosphatidylinositol 3-kinase (PI3K), and 5' AMP-activated protein kinase (AMPK) activation. FAK and IRS-1 activity were only elevated 1 h post-exercise with carbohydrate ingestion (p < 0.05). PI3K and p70S6K activation were both elevated after exercise in both conditions (p < 0.05). However, AMPK activity did not change from baseline in both conditions (p > 0.05). We conclude that FAK does not induce mTOR activation through PI3K crosstalk in response to exercise alone. In addition, FAK may not be regulated by AMPK catalytic activity, but this needs further research. Interestingly, carbohydrate-induced insulin signaling appears to activate FAK at the level of IRS-1 but did not enhance mTOR activity 1 h post-exercise greater than the placebo condition. Future research should investigate these interactions under different conditions and within different time frames to clearly understand the interactions between these signaling molecules.