Muscle fiber atrophy and regeneration coexist in collagen VI-deficient human muscle: role of calpain-3 and nuclear factor-κB signaling

Type VI Collagen Deficiency Causes Enhanced Periodontal Tissue Destruction

The periodontal ligament (PDL) is a fibrillar connective tissue that lies between the alveolar bone and the tooth and is composed of highly specialized extracellular matrix (ECM) molecules and a heterogeneous population of cells that are responsible for collagen formation, immune response, bone formation, and chewing force sensation. Type VI collagen (COL6), a widely distributed ECM molecule, plays a critical role in the structural integrity and mechanical properties of various tissues including muscle, tendon, bone, cartilage, and skin. However, its role in the PDL remains largely unknown. Our study shows that deficiency of COL6 impairs PDL fibrillogenesis and exacerbates tissue destruction in ligature-induced periodontitis (LIP). We found that COL6-deficient mice exhibited increased bone loss and degraded PDL in LIP and that fibroblasts expressing high levels of Col6α2 are pivotal in ECM organization and cell-ECM interactions. Moreover, COL6 deficiency in the PDL led to an increased number of fibroblasts geared toward the inflammatory response. We also observed that cultured COL6-deficient fibroblasts from the PDL exhibited decreased expression of genes related to collagen fiber turnover and ECM organization as well as migration and proliferation. Our findings suggest that COL6 plays a crucial role in the PDL, influencing fibroblast function in fibrillogenesis and affecting the immune response in periodontitis. These insights advance our understanding of the molecular mechanisms underlying PDL maturation and periodontal disease.

Personalized in vitro Extracellular Matrix Models of Collagen VI-Related Muscular Dystrophies

Collagen VI-related dystrophies (COL6-RDs) are a group of rare congenital neuromuscular dystrophies that represent a continuum of overlapping clinical phenotypes that go from the milder Bethlem myopathy (BM) to the severe Ullrich congenital muscular dystrophy, for which there is no effective treatment. Mutations in one of the three Collagen VI genes alter the incorporation of this protein into the extracellular matrix (ECM), affecting the assembly and the structural integrity of the whole fibrillar network. Clinical hallmarks of COL6-RDs are secondary to the ECM disruption and include muscle weakness, proximal joint contractures, and distal hyperlaxity. Although some traits have been identified in patients’ ECMs, a correlation between the ECM features and the clinical phenotype has not been established, mainly due to the lack of predictive and reliable models of the pathology. Herein, we engineered a new personalized pre-clinical model of COL6-RDs using cell-derived matrices (CDMs) technology to better recapitulate the complexity of the native scenario. We found that CDMs from COL6-RD patients presented alterations in ECM structure and composition, showing a significantly decreased Collagen VI secretion, especially in the more severe phenotypes, and a decrease in Fibrillin-1 inclusion. Next, we examined the Collagen VI-mediated deposition of Fibronectin in the ECM, finding a higher alignment, length, width, and straightness than in patients with COL6-RDs. Overall, these results indicate that CDMs models are promising tools to explore the alterations that arise in the composition and fibrillar architecture due to mutations in Collagen VI genes, especially in early stages of matrix organization. Ultimately, CDMs derived from COL6-RD patients may become relevant pre-clinical models, which may help identifying novel biomarkers to be employed in the clinics and to investigate novel therapeutic targets and treatments.

Defining and identifying satellite cell-opathies within muscular dystrophies and myopathies

Muscular dystrophies and congenital myopathies arise from specific genetic mutations causing skeletal muscle weakness that reduces quality of life. Muscle health relies on resident muscle stem cells called satellite cells, which enable life-course muscle growth, maintenance, repair and regeneration. Such tuned plasticity gradually diminishes in muscle diseases, suggesting compromised satellite cell function. A central issue however, is whether the pathogenic mutation perturbs satellite cell function directly and/or indirectly via an increasingly hostile microenvironment as disease progresses. Here, we explore the effects on satellite cell function of pathogenic mutations in genes (myopathogenes) that associate with muscle disorders, to evaluate clinical and muscle pathological hallmarks that define dysfunctional satellite cells. We deploy transcriptomic analysis and comparison between muscular dystrophies and myopathies to determine the contribution of satellite cell dysfunction using literature, expression dynamics of myopathogenes and their response to the satellite cell regulator PAX7. Our multimodal approach extends current pathological classifications to define Satellite Cell-opathies: muscle disorders in which satellite cell dysfunction contributes to pathology. Primary Satellite Cell-opathies are conditions where mutations in a myopathogene directly affect satellite cell function, such as in Progressive Congenital Myopathy with Scoliosis (MYOSCO) and Carey-Fineman-Ziter Syndrome (CFZS). Primary satellite cell-opathies are generally characterised as being congenital with general hypotonia, and specific involvement of respiratory, trunk and facial muscles, although serum CK levels are usually within the normal range. Secondary Satellite Cell-opathies have mutations in myopathogenes that affect both satellite cells and muscle fibres. Such classification aids diagnosis and predicting probable disease course, as well as informing on treatment and therapeutic development.

Early Morphological Changes of the Rectus Femoris Muscle and Deep Fascia in Ullrich Congenital Muscular Dystrophy

Ullrich congenital muscular dystrophy (UCMD) is a severe form of muscular dystrophy caused by the loss of function of collagen VI, a critical component of the muscle-tendon matrix. Magnetic resonance imaging of UCMD patients’ muscles shows a peculiar rim of abnormal signal at the periphery of each muscle, and a relative sparing of the internal part. The mechanism/s involved in the early fat substitution of muscle fiber at the periphery of muscles remain elusive. We studied a muscle biopsy of the rectus femoris/deep fascia (DF) of a 3-year-old UCMD patient, with a homozygous mutation in the COL6A2 gene. By immunohistochemical and ultrastructural analysis, we found a marked fatty infiltration at the interface of the muscle with the epimysium/DF and an atrophic phenotype, primarily in fast-twitch fibers, which has never been reported before. An unexpected finding was the widespread increase of interstitial cells with long cytoplasmic processes, consistent with the telocyte phenotype. Our study documents for the first time in a muscle biopsy the peculiar pattern of outside-in muscle degeneration followed by fat substitution as already shown by muscle imaging, and an increase of telocytes in the interstitium of the deep fascia, which highlights a potential involvement of this structure in the pathogenesis of UCMD.

Systemic Supplementation of Collagen VI by Neonatal Transplantation of iPSC-Derived MSCs Improves Histological Phenotype and Function of Col6-Deficient Model Mice

Collagen VI is distributed in the interstitium and is secreted mainly by mesenchymal stromal cells (MSCs) in skeletal muscle. Mutations in COL6A1-3 genes cause a spectrum of COL6-related myopathies. In this study, we performed a systemic transplantation study of human-induced pluripotent stem cell (iPSC)-derived MSCs (iMSCs) into neonatal immunodeficient COL6-related myopathy model (Col6a1^KO/NSG) mice to validate the therapeutic potential. Engraftment of the donor cells and the resulting rescued collagen VI were observed at the quadriceps and diaphragm after intraperitoneal iMSC transplantation. Transplanted mice showed improvement in pathophysiological characteristics compared with untreated Col6a1^KO/NSG mice. In detail, higher muscle regeneration in the transplanted mice resulted in increased muscle weight and enlarged myofibers. Eight-week-old mice showed increased muscle force and performed better in the grip and rotarod tests. Overall, these findings support the concept that systemic iMSC transplantation can be a therapeutic option for COL6-related myopathies.

CAPN3: A muscle‑specific calpain with an important role in the pathogenesis of diseases (Review)

Calpains are a family of Ca²⁺‑dependent cysteine proteases that participate in various cellular processes. Calpain 3 (CAPN3) is a classical calpain with unique N‑terminus and insertion sequence 1 and 2 domains that confer characteristics such as rapid autolysis, Ca²⁺‑independent activation and Na⁺ activation of the protease. CAPN3 is the only muscle‑specific calpain that has important roles in the promotion of calcium release from skeletal muscle fibers, calcium uptake of sarcoplasmic reticulum, muscle formation and muscle remodeling. Studies have indicated that recessive mutations in CAPN3 cause limb‑girdle muscular dystrophy (MD) type 2A and other types of MD; eosinophilic myositis, melanoma and epilepsy are also closely related to CAPN3. In the present review, the characteristics of CAPN3, its biological functions and roles in the pathogenesis of a number of disorders are discussed.

Lower Extremity Muscle Involvement in the Intermediate and Bethlem Myopathy Forms of COL6-Related Dystrophy and Duchenne Muscular Dystrophy: A Cross-Sectional Study

Collagen VI-related dystrophies (COL6-RDs) and Duchenne muscular dystrophy (DMD) cause progressive muscle weakness and disability. COL6-RDs are caused by mutations in the COL6 genes (COL6A1, COL6A2 and COL6A3) encoding the extracellular matrix protein collagen VI, and DMD is caused by mutations in the DMD gene encoding the cytoplasmic protein dystrophin. Both COL6-RDs and DMD are characterized by infiltration of the muscles by fatty and fibrotic tissue. This study examined the effect of disease pathology on skeletal muscles in lower extremity muscles of COL6-RDs using timed functional tests, strength measures and qualitative/ quantitative magnetic resonance imaging/spectroscopy measures (MRI/MRS) in comparison to unaffected (control) individuals. Patients with COL6-RD were also compared to age and gender matched patients with DMD.Patients with COL6-RD presented with a typical pattern of fatty infiltration of the muscle giving rise to an apparent halo effect around the muscle, while patients with DMD had evidence of fatty infiltration throughout the muscle areas imaged. Quantitatively, fat fraction, and transverse relaxation time (T2) were elevated in both COL6-RD and DMD patients compared to unaffected (control) individuals. Patients with COL6-RD had widespread muscle atrophy, likely contributing to weakness. In contrast, patients with DMD revealed force deficits even in muscle groups with increased contractile areas.

Protein homeostasis in LGMDR9 (LGMD2I) - The role of ubiquitin-proteasome and autophagy-lysosomal system

AIMS

Limb-girdle muscular dystrophy R9 (LGMDR9) is an autosomal recessive disorder caused by mutations in the fukutin-related protein gene (FKRP), encoding a glycosyltransferase involved in α-dystroglycan modification. Muscle atrophy, a significant feature of LGMDR9, occurs by a change in the normal balance between protein synthesis and protein degradation. The ubiquitin-proteasome system (UPS) and autophagy-lysosomal system play a key role in protein degradation in skeletal muscle cells, but their involvement in the pathology of LGMDR9 is still largely unknown. We have aimed at clarifying whether proteolysis through the UPS and the autophagy-lysosomal pathway is dysregulated in LGMDR9 patients.

METHODS

Vastus lateralis biopsies from 8 normal controls and 12 LGMDR9 patients harbouring the c.826C>A/c.826C>A FKRP genotype were assessed for protein markers related to UPS, the autophagy-lysosomal system and endoplasmic reticulum (ER) stress/unfolded protein response (UPR), followed by ultrastructural analysis by transmission electron microscopy (TEM).

RESULTS

Protein levels of E3 ubiquitin ligases Atrogin-1 and MuRF1 showed a pattern similar to normal controls. Elevation of the autophagy markers Atg7, LC3B-II, decreased level of p62 as well as downregulation of the negative autophagy regulator mTORC1, indicated an activation of autophagy in LGMDR9. Mitophagy markers Bnip3 and Parkin were decreased. TEM analysis demonstrated accumulation of autophagosome-like structures in LGMDR9 muscle. There was also an increase in the expression of ER stress/UPR markers PDI, peIF2α and CHOP and a decrease in IRE1α. However, GRP94, Bip and Calnexin remained unchanged.

CONCLUSION

Our findings indicate that autophagy and ER stress are induced in LGMDR9 muscle.

Transcriptome profiling identifies regulators of pathogenesis in collagen VI related muscular dystrophy

Objectives

The collagen VI related muscular dystrophies (COL6-RD), Ullrich congenital muscular dystrophy (UCMD) and Bethlem myopathy (BM) are among the most common congenital muscular dystrophies and are characterized by distal joint laxity and a combination of distal and proximal joint contractures. Inheritance can be dominant negative (DN) or recessive depending on the type and location of the mutation. DN mutations allow incorporation of abnormal chains into secreted tetramers and are the most commonly identified mutation type in COL6-RD. Null alleles (nonsense, frameshift, and large deletions) do not allow incorporation of abnormal chains and act recessively. To better define the pathways disrupted by mutations in collagen VI, we have used a transcriptional profiling approach with RNA-Seq to identify differentially expressed genes in COL6-RD individuals from controls.

Methods

RNA-Seq allows precise detection of all expressed transcripts in a sample and provides a tool for quantification of expression data on a genomic scale. We have used RNA-Seq to identify differentially expressed genes in cultured dermal fibroblasts from 13 COL6-RD individuals (8 dominant negative and 5 null) and 6 controls. To better assess the transcriptional changes induced by abnormal collagen VI in the extracellular matrix (ECM); we compared transcriptional profiles from subjects with DN mutations and subjects with null mutations to transcriptional profiles from controls.

Results

Differentially expressed transcripts between COL6-RD and control fibroblasts include upregulation of ECM components and downregulation of factors controlling matrix remodeling and repair. DN and null samples are differentiated by downregulation of genes involved with DNA replication and repair in null samples.

Conclusions

Differentially expressed genes identified here may help identify new targets for development of therapies and biomarkers to assess the efficacy of treatments.

Differences in Adipose Tissue and Lean Mass Distribution in Patients with Collagen VI Related Myopathies Are Associated with Disease Severity and Physical Ability

Mutations in human collagen VI genes cause a spectrum of musculoskeletal conditions in children and adults collectively termed collagen VI-related myopathies (COL6-RM) characterized by a varying degree of muscle weakness and joint contractures and which include Ullrich Congenital Muscular Dystrophy (UCMD) and Bethlem Myopathy (BM). Given that collagen VI is one of the most abundant extracellular matrix proteins in adipose tissue and its emerging role in energy metabolism we hypothesized that collagen VI deficiency might be associated with alterations in adipose tissue distribution and adipokines serum profile. We analyzed body composition by means of dual-energy X-ray absorptiometry in 30 pediatric and adult COL6-RM myopathy patients representing a range of severities (UCMD, intermediate-COL6-RM, and BM). We found a distinctive pattern of regional adipose tissue accumulation which was more evident in children at the most severe end of the spectrum. In particular, the accumulation of fat in the android region was a distinguishing feature of UCMD patients. In parallel, there was a decrease in lean mass compatible with a state of sarcopenia, particularly in ambulant children with an intermediate phenotype. All children and adult patients that were sarcopenic were also obese. These changes were significantly more pronounced in children with collagen VI deficiency than in children with Duchenne Muscular Dystrophy of the same ambulatory status. High molecular weight adiponectin and leptin were significantly increased in sera from children in the intermediate and BM group. Correlation analysis showed that the parameters of fat mass were negatively associated with motor function according to several validated outcome measures. In contrast, lean mass parameters correlated positively with physical performance and quality of life. Leptin and adiponectin circulating levels correlated positively with fat mass parameters and negatively with lean mass and thus may be relevant to the disease pathogenesis and as circulating markers. Taken together our results indicate that COL6-RM are characterized by specific changes in total fat mass and distribution which associate with disease severity, motor function, and quality of life and which are clinically meaningful and thus should be taken into consideration in the management of these patients.

Calpain-14 and its association with eosinophilic esophagitis

Calpains are a family of intracellular, calcium-dependent cysteine proteases involved in a variety of regulatory processes, including cytoskeletal dynamics, cell-cycle progression, signal transduction, gene expression, and apoptosis. These enzymes have been implicated in a number of disease processes, notably for this review involving eosinophilic tissue inflammation, such as eosinophilic esophagitis (EoE), a chronic inflammatory disorder triggered by allergic hypersensitivity to food and associated with genetic variants in calpain 14 (CAPN14). Herein we review the genetic, structural, and biochemical properties of CAPN14 and its gene product CAPN14, and its emerging role in patients with EoE. The CAPN14 gene is localized at chromosome 2p23.1-p21 and is most homologous to CAPN13 (36% sequence identity), which is located 365 kb downstream of CAPN14. Structurally, CAPN14 has classical calpain motifs, including a cysteine protease core. In comparison with other human calpains, CAPN14 has a unique expression pattern, with the highest levels in the upper gastrointestinal tract, particularly in the squamous epithelium of the esophagus. The CAPN14 gene is positioned in an epigenetic hotspot regulated by IL-13, a T_H2 cytokine with increased levels in patients with EoE that has been shown to be a mediator of the disease. CAPN14 induces disruptive effects on the esophageal epithelium by impairing epithelial barrier function in association with loss of desmoglein-1 expression and has a regulatory role in repairing epithelial changes induced by IL-13. Thus CAPN14 is a unique protease with distinct tissue-specific expression and function in patients with EoE and is a potential therapeutic target for EoE and related eosinophilic and allergic diseases.

A Comprehensive View of the Structural and Functional Alterations of Extracellular Matrix by Snake Venom Metalloproteinases (SVMPs): Novel Perspectives on the Pathophysiology of Envenoming

Snake venom metalloproteinases (SVMPs) affect the extracellular matrix (ECM) in multiple and complex ways. Previously, the combination of various methodological platforms, including electron microscopy, histochemistry, immunohistochemistry, and Western blot, has allowed a partial understanding of such complex pathology. In recent years, the proteomics analysis of exudates collected in the vicinity of tissues affected by SVMPs has provided novel and exciting information on SVMP-induced ECM alterations. The presence of fragments of an array of ECM proteins, including those of the basement membrane, has revealed a complex pathological scenario caused by the direct action of SVMPs. In addition, the time-course analysis of these changes has underscored that degradation of some fibrillar collagens is likely to depend on the action of endogenous proteinases, such as matrix metalloproteinases (MMPs), synthesized as a consequence of the inflammatory process. The action of SVMPs on the ECM also results in the release of ECM-derived biologically-active peptides that exert diverse actions in the tissue, some of which might be associated with reparative events or with further tissue damage. The study of the effects of SVMP on the ECM is an open field of research which may bring a renewed understanding of snake venom-induced pathology.

Transcriptome Analysis of Ullrich Congenital Muscular Dystrophy Fibroblasts Reveals a Disease Extracellular Matrix Signature and Key Molecular Regulators

Background

Collagen VI related myopathies encompass a range of phenotypes with involvement of skeletal muscle, skin and other connective tissues. They represent a severe and relatively common form of congenital disease for which there is no treatment. Collagen VI in skeletal muscle and skin is produced by fibroblasts.

Aims & Methods

In order to gain insight into the consequences of collagen VI mutations and identify key disease pathways we performed global gene expression analysis of dermal fibroblasts from patients with Ullrich Congenital Muscular Dystrophy with and without vitamin C treatment. The expression data were integrated using a range of systems biology tools. Results were validated by real-time PCR, western blotting and functional assays.

Findings

We found significant changes in the expression levels of almost 600 genes between collagen VI deficient and control fibroblasts. Highly regulated genes included extracellular matrix components and surface receptors, including integrins, indicating a shift in the interaction between the cell and its environment. This was accompanied by a significant increase in fibroblasts adhesion to laminin. The observed changes in gene expression profiling may be under the control of two miRNAs, miR-30c and miR-181a, which we found elevated in tissue and serum from patients and which could represent novel biomarkers for muscular dystrophy. Finally, the response to vitamin C of collagen VI mutated fibroblasts significantly differed from healthy fibroblasts. Vitamin C treatment was able to revert the expression of some key genes to levels found in control cells raising the possibility of a beneficial effect of vitamin C as a modulator of some of the pathological aspects of collagen VI related diseases.

A muscle stem cell for every muscle: variability of satellite cell biology among different muscle groups

The human body contains approximately 640 individual skeletal muscles. Despite the fact that all of these muscles are composed of striated muscle tissue, the biology of these muscles and their associated muscle stem cell populations are quite diverse. Skeletal muscles are affected differentially by various muscular dystrophies (MDs), such that certain genetic mutations specifically alter muscle function in only a subset of muscles. Additionally, defective muscle stem cells have been implicated in the pathology of some MDs. The biology of muscle stem cells varies depending on the muscles with which they are associated. Here we review the biology of skeletal muscle stem cell populations of eight different muscle groups. Understanding the biological variation of skeletal muscles and their resident stem cells could provide valuable insight into mechanisms underlying the susceptibility of certain muscles to myopathic disease.

Ullrich congenital muscular dystrophy: clinicopathological features, natural history and pathomechanism(s)

Collagen VI is widely distributed throughout extracellular matrices (ECMs) in various tissues. In skeletal muscle, collagen VI is particularly concentrated in and adjacent to basement membranes of myofibers. Ullrich congenital muscular dystrophy (UCMD) is caused by mutations in either COL6A1, COL6A2 or COL6A3 gene, thereby leading to collagen VI deficiency in the ECM. It is known to occur through either recessive or dominant genetic mechanism, the latter most typically by de novo mutations. UCMD is well defined by the clinicopathological hallmarks including distal hyperlaxity, proximal joint contractures, protruding calcanei, scoliosis and respiratory insufficiency. Recent reports have depicted the robust natural history of UCMD; that is, loss of ambulation by early teenage years, rapid decline in respiratory function by 10 years of age and early-onset, rapidly progressive scoliosis. Muscle pathology is characterised by prominent interstitial fibrosis disproportionate to the relative paucity of necrotic and regenerating fibres. To date, treatment for patients is supportive for symptoms such as joint contractures, respiratory failure and scoliosis. There have been clinical trials based on the theory of mitochondrion-mediated myofiber apoptosis or impaired autophagy. Furthermore, the fact that collagen VI producing cells in skeletal muscle are interstitial mesenchymal cells can support proof of concept for stem cell-based therapy.

The intriguing regulators of muscle mass in sarcopenia and muscular dystrophy

Recent advances in our understanding of the biology of muscle have led to new interest in the pharmacological treatment of muscle wasting. Loss of muscle mass and increased intramuscular fibrosis occur in both sarcopenia and muscular dystrophy. Several regulators (mammalian target of rapamycin, serum response factor, atrogin-1, myostatin, etc.) seem to modulate protein synthesis and degradation or transcription of muscle-specific genes during both sarcopenia and muscular dystrophy. This review provides an overview of the adaptive changes in several regulators of muscle mass in both sarcopenia and muscular dystrophy.

Transcriptomic profiling of TK2 deficient human skeletal muscle suggests a role for the p53 signalling pathway and identifies growth and differentiation factor-15 as a potential novel biomarker for mitochondrial myopathies

Background

Mutations in the gene encoding thymidine kinase 2 (TK2) result in the myopathic form of mitochondrial DNA depletion syndrome which is a mitochondrial encephalomyopathy presenting in children. In order to unveil some of the mechanisms involved in this pathology and to identify potential biomarkers and therapeutic targets we have investigated the gene expression profile of human skeletal muscle deficient for TK2 using cDNA microarrays.

Results

We have analysed the whole transcriptome of skeletal muscle from patients with TK2 mutations and compared it to normal muscle and to muscle from patients with other mitochondrial myopathies. We have identified a set of over 700 genes which are differentially expressed in TK2 deficient muscle. Bioinformatics analysis reveals important changes in muscle metabolism, in particular, in glucose and glycogen utilisation, and activation of the starvation response which affects aminoacid and lipid metabolism. We have identified those transcriptional regulators which are likely to be responsible for the observed changes in gene expression.

Conclusion

Our data point towards the tumor suppressor p53 as the regulator at the centre of a network of genes which are responsible for a coordinated response to TK2 mutations which involves inflammation, activation of muscle cell death by apoptosis and induction of growth and differentiation factor 15 (GDF-15) in muscle and serum. We propose that GDF-15 may represent a potential novel biomarker for mitochondrial dysfunction although further studies are required.

Dystromirs as serum biomarkers for monitoring the disease severity in Duchenne muscular Dystrophy

Duchenne muscular Dystrophy (DMD) is an inherited disease caused by mutations in the dystrophin gene that disrupt the open reading frame, while in frame mutations result in Becker muscular dystrophy (BMD). Ullrich congenital muscular dystrophy (UCMD) is due to mutations affecting collagen VI genes. Specific muscle miRNAs (dystromirs) are potential non-invasive biomarkers for monitoring the outcome of therapeutic interventions and disease progression. We quantified miR-1, miR-133a,b, miR-206 and miR-31 in serum from patients with DMD, BMD, UCMD and healthy controls. MiR-1, miR-133a,b and miR-206 were upregulated in DMD, but unchanged in UCMD compared to controls. Milder DMD patients had higher levels of dystromirs than more severely affected patients. Patients with low forced vital capacity (FVC) values, indicating respiratory muscle weakness, had low levels of serum miR-1 and miR-133b. There was no significant difference in the level of the dystromirs in BMD compared to controls.

We also assessed the effect of dystrophin restoration on the expression of the five dystromirs in serum of DMD patients treated systemically for 12 weeks with antisense oligomer eteplirsen that induces skipping of exon 51 in the dystrophin gene. The dystromirs were also analysed in muscle biopsies of DMD patients included in a single dose intramuscular eteplirsen clinical trial. Our analysis detected a trend towards normalization of these miRNA between the pre- and post-treatment samples of the systemic trial, which however failed to reach statistical significance. This could possibly be due to the small number of patients and the short duration of these clinical trials.

Although longer term studies are needed to clarify the relationship between dystrophin restoration following therapeutic intervention and the level of circulating miRNAs, our results indicate that miR-1 and miR-133 can be considered as exploratory biomarkers for monitoring the progression of muscle weakness and indirectly the remaining muscle mass in DMD.

Mitochondrial alterations and oxidative stress in an acute transient mouse model of muscle degeneration: implications for muscular dystrophy and related muscle pathologies

Muscular dystrophies (MDs) and inflammatory myopathies (IMs) are debilitating skeletal muscle disorders characterized by common pathological events including myodegeneration and inflammation. However, an experimental model representing both muscle pathologies and displaying most of the distinctive markers has not been characterized. We investigated the cardiotoxin (CTX)-mediated transient acute mouse model of muscle degeneration and compared the cardinal features with human MDs and IMs. The CTX model displayed degeneration, apoptosis, inflammation, loss of sarcolemmal complexes, sarcolemmal disruption, and ultrastructural changes characteristic of human MDs and IMs. Cell death caused by CTX involved calcium influx and mitochondrial damage both in murine C2C12 muscle cells and in mice. Mitochondrial proteomic analysis at the initial phase of degeneration in the model detected lowered expression of 80 mitochondrial proteins including subunits of respiratory complexes, ATP machinery, fatty acid metabolism, and Krebs cycle, which further decreased in expression during the peak degenerative phase. The mass spectrometry (MS) data were supported by enzyme assays, Western blot, and histochemistry. The CTX model also displayed markers of oxidative stress and a lowered glutathione reduced/oxidized ratio (GSH/GSSG) similar to MDs, human myopathies, and neurogenic atrophies. MS analysis identified 6 unique oxidized proteins from Duchenne muscular dystrophy samples (n = 6) (versus controls; n = 6), including two mitochondrial proteins. Interestingly, these mitochondrial proteins were down-regulated in the CTX model thereby linking oxidative stress and mitochondrial dysfunction. We conclude that mitochondrial alterations and oxidative damage significantly contribute to CTX-mediated muscle pathology with implications for human muscle diseases.

Gene expression profiling identifies molecular pathways associated with collagen VI deficiency and provides novel therapeutic targets

Ullrich congenital muscular dystrophy (UCMD), caused by collagen VI deficiency, is a common congenital muscular dystrophy. At present, the role of collagen VI in muscle and the mechanism of disease are not fully understood. To address this we have applied microarrays to analyse the transcriptome of UCMD muscle and compare it to healthy muscle and other muscular dystrophies. We identified 389 genes which are differentially regulated in UCMD relative to controls. In addition, there were 718 genes differentially expressed between UCMD and dystrophin deficient muscle. In contrast, only 29 genes were altered relative to other congenital muscular dystrophies. Changes in gene expression were confirmed by real-time PCR. The set of regulated genes was analysed by Gene Ontology, KEGG pathways and Ingenuity Pathway analysis to reveal the molecular functions and gene networks associated with collagen VI defects. The most significantly regulated pathways were those involved in muscle regeneration, extracellular matrix remodelling and inflammation. We characterised the immune response in UCMD biopsies as being mainly mediated via M2 macrophages and the complement pathway indicating that anti-inflammatory treatment may be beneficial to UCMD as for other dystrophies. We studied the immunolocalisation of ECM components and found that biglycan, a collagen VI interacting proteoglycan, was reduced in the basal lamina of UCMD patients. We propose that biglycan reduction is secondary to collagen VI loss and that it may be contributing towards UCMD pathophysiology. Consequently, strategies aimed at over-expressing biglycan and restore the link between the muscle cell surface and the extracellular matrix should be considered.