Ullrich Congenital Muscular Dystrophy Patients Research Articles

Collagen VI Deficiency Impairs Tendon Fibroblasts Mechanoresponse in Ullrich Congenital Muscular Dystrophy.

The pericellular matrix (PCM) is a specialized extracellular matrix that surrounds cells. Interactions with the PCM enable the cells to sense and respond to mechanical signals, triggering a proper adaptive response. Collagen VI is a component of muscle and tendon PCM. Mutations in collagen VI genes cause a distinctive group of inherited skeletal muscle diseases, and Ullrich congenital muscular dystrophy (UCMD) is the most severe form. In addition to muscle weakness, UCMD patients show structural and functional changes of the tendon PCM. In this study, we investigated whether PCM alterations due to collagen VI mutations affect the response of tendon fibroblasts to mechanical stimulation. By taking advantage of human tendon cultures obtained from unaffected donors and from UCMD patients, we analyzed the morphological and functional properties of cellular mechanosensors. We found that the length of the primary cilia of UCMD cells was longer than that of controls. Unlike controls, in UCMD cells, both cilia prevalence and length were not recovered after mechanical stimulation. Accordingly, under the same experimental conditions, the activation of the Hedgehog signaling pathway, which is related to cilia activity, was impaired in UCMD cells. Finally, UCMD tendon cells exposed to mechanical stimuli showed altered focal adhesions, as well as impaired activation of Akt, ERK1/2, p38MAPK, and mechanoresponsive genes downstream of YAP. By exploring the response to mechanical stimulation, for the first time, our findings uncover novel unreported mechanistic aspects of the physiopathology of UCMD-derived tendon fibroblasts and point at a role for collagen VI in the modulation of mechanotransduction in tendons.

Evaluation of clinico-pathological and genetic spectrum of Ullrich congenital muscular dystrophy patients from Indian cohort

Evaluation of clinico-pathological and genetic spectrum of Ullrich congenital muscular dystrophy patients from Indian cohort

The UCMD-Causing COL6A1 ( c . 930 + 189 C > T ) Intron Mutation Leads to the Secretion and Aggregation of Single Mutated Collagen VI α1 Chains

Collagen VI is a unique member of the collagen family. Its assembly is a complex multistep process and the vulnerability of the process is manifested in muscular diseases. Mutations in COL6A1, COL6A2, and COL6A3 lead to the severe Ullrich Congenital Muscular Dystrophy (UCMD) and a spectrum of disease of varying severity including the milder Bethlem muscular dystrophy. The recently identified dominant intronic mutation in COL6A1 ( c . 930 + 189 C > T ) leads to the partial in-frame insertion of a pseudoexon between exon 11 and exon 12. The pseudoexon is translated into 24 amino acid residues in the N-terminal region of the triple helix and results in the interruption of the typical G-X-Y motif. This recurrent de novo mutation leads to UCMD with a severe progression within the first decade of life. Here, we demonstrate that a mutation-specific antibody detects the mutant chain colocalizing with wild type collagen VI in the endomysium in patient muscle. Surprisingly, in the cell culture of patient dermal fibroblasts, the mutant chain is secreted as a single α chain, while in parallel, normal collagen VI tetramers are assembled with the wild-type α1 chain. The mutant chain cannot be incorporated into collagen VI tetramers but forms large aggregates in the extracellular matrix that may retain the ability to interact with collagen VI and potentially with other molecules. Also, α1 chain-deficient WI-26 VA4 cells transfected with the mutant α1 chain do not assemble collagen VI tetramers but, instead, form aggregates. Interestingly, both the wild type and the mutant single α1 chains form amorphous aggregates when expressed in HEK293 cells in the absence of α2 and α3 chains. The detection of aggregated, assembly incompetent, mutant collagen VI α1 chains provides novel insights into the disease pathophysiology of UCMD patients with the COL6A1 ( c . 930 + 189 C > T ) mutation.

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.

Collagen-VI supplementation by cell transplantation improves muscle regeneration in Ullrich congenital muscular dystrophy model mice

BackgroundMesenchymal stromal cells (MSCs) function as supportive cells on skeletal muscle homeostasis through several secretory factors including type 6 collagen (COL6). Several mutations of COL6A1, 2, and 3 genes cause Ullrich congenital muscular dystrophy (UCMD). Skeletal muscle regeneration deficiency has been reported as a characteristic phenotype in muscle biopsy samples of human UCMD patients and UCMD model mice. However, little is known about the COL6-dependent mechanism for the occurrence and progression of the deficiency. The purpose of this study was to clarify the pathological mechanism of UCMD by supplementing COL6 through cell transplantation.MethodsTo test whether COL6 supplementation has a therapeutic effect for UCMD, in vivo and in vitro experiments were conducted using four types of MSCs: (1) healthy donors derived-primary MSCs (pMSCs), (2) MSCs derived from healthy donor induced pluripotent stem cell (iMSCs), (3) COL6-knockout iMSCs (COL6KO-iMSCs), and (4) UCMD patient-derived iMSCs (UCMD-iMSCs).ResultsAll four MSC types could engraft for at least 12 weeks when transplanted into the tibialis anterior muscles of immunodeficient UCMD model (Col6a1KO) mice. COL6 protein was restored by the MSC transplantation if the MSCs were not COL6-deficient (types 1 and 2). Moreover, muscle regeneration and maturation in Col6a1KO mice were promoted with the transplantation of the COL6-producing MSCs only in the region supplemented with COL6. Skeletal muscle satellite cells derived from UCMD model mice (Col6a1KO-MuSCs) co-cultured with type 1 or 2 MSCs showed improved proliferation, differentiation, and maturation, whereas those co-cultured with type 3 or 4 MSCs did not.ConclusionsThese findings indicate that COL6 supplementation improves muscle regeneration and maturation in UCMD model mice.

Surgical treatment of scoliosis in Ullrich Congenital Muscular Dystrophy: a case series of 3 patients.

Scoliosis in Ullrich Congenital Muscular Dystrophy (UCMD) is very common, with a reported incidence of more than 50%, and it is rapidly progressive. There are no previous studies which specifically focus on scoliosis surgery in UCMD patients. This article reports three cases of scoliosis surgery in UCMD, focusing on operative course, clinical and radiological results achieved, fusion area and complications, with a 2-year follow-up. The surgical technique adopted for vertebral arthrodesis included: high-density pedicle screw systems, asymmetric rods contouring and direct vertebral rotation. The summary results shown a significative correction of the coronal deformity, with a reduction of the mean Cobb angle from 49° to 25° post-operatively. Mean pelvic tilt remained stable, while L5-tilt showed a decrease from 10° to 6°. Mean screw density was 1.92. None of the patients required extended fixation to S2. No major complications were reported, and patients maintained their pre-operative walking ability. All the patients reported a subjective improvement in quality of life, with a better sitting comfort. In conclusion, posterior spinal fusion with high-density pedicle screw systems and direct vertebral rotation may be safe and effective in surgical correction of scoliosis in UCMD. If pelvic obliquity and L5-tilt are less than 15°, could be possible to achieve an optimal spinal and pelvic balance even without sacral or pelvic fixation.

Tendon Extracellular Matrix Remodeling and Defective Cell Polarization in the Presence of Collagen VI Mutations.

Mutations in collagen VI genes cause two major clinical myopathies, Bethlem myopathy (BM) and Ullrich congenital muscular dystrophy (UCMD), and the rarer myosclerosis myopathy. In addition to congenital muscle weakness, patients affected by collagen VI-related myopathies show axial and proximal joint contractures, and distal joint hypermobility, which suggest the involvement of tendon function. To gain further insight into the role of collagen VI in human tendon structure and function, we performed ultrastructural, biochemical, and RT-PCR analysis on tendon biopsies and on cell cultures derived from two patients affected with BM and UCMD. In vitro studies revealed striking alterations in the collagen VI network, associated with disruption of the collagen VI-NG2 (Collagen VI-neural/glial antigen 2) axis and defects in cell polarization and migration. The organization of extracellular matrix (ECM) components, as regards collagens I and XII, was also affected, along with an increase in the active form of metalloproteinase 2 (MMP2). In agreement with the in vitro alterations, tendon biopsies from collagen VI-related myopathy patients displayed striking changes in collagen fibril morphology and cell death. These data point to a critical role of collagen VI in tendon matrix organization and cell behavior. The remodeling of the tendon matrix may contribute to the muscle dysfunction observed in BM and UCMD patients.

Gapmer Antisense Oligonucleotides to Selectively Suppress the Mutant Allele in COL6A Genes in Dominant Ullrich Congenital Muscular Dystrophy.

Allele-specific gene silencing by antisense oligonucleotide (ASO) or small interference RNA (siRNA) has been used as a therapeutic approach for conditions caused by dominant gain-of-function mutations. We here present an antisense approach using gapmer ASO to diminish the dominant-negative effect in Ullrich congenital muscular dystrophy (UCMD) caused by dominant mutation in one of the COL6A genes. We provide the details of methods that our lab has used. The methods comprise the design of gapmer ASOs and the in vitro evaluation of gapmer ASOs on the specific silencing of the mutant allele at mRNA levels, and functional assessment at protein levels. A fibroblast cell line cultured from a UCMD patient carrying a dominant mutation in one of the COL6A genes is used as a cellular model.

Overexpression of miR-29 Leads to Myopathy that Resemble Pathology of Ullrich Congenital Muscular Dystrophy.

Ullrich congenital muscular dystrophy (UCMD) bring heavy burden to patients’ families and society. Because the incidence of this disease is very low, studies in patients are extremely limited. Animal models of this disease are indispensable. UCMD belongs to extracellular matrix-related diseases. However, the disease models constructed by knocking out some pathogenic genes of human, such as the Col6a1, Col6a2, or Col6a3 gene, of mice could not mimic UCMD. The purpose of this study is to construct a mouse model which can resemble the pathology of UCMD. miR-29 is closely related to extracellular matrix deposition of tissues and organs. To address this issue, we developed a mouse model for overexpression miR-29 using Tet-on system. In the muscle-specific miR-29ab1 cluster transgenic mice model, we found that mice exhibited dyskinesia, dyspnea, and spinal anomaly. The skeletal muscle was damaged and regenerated. At the same time, we clarify the molecular mechanism of the role of miR-29 in this process. Different from human, Col4a1 and Col4a2, target genes of miR-29, are the key pathogenic genes associating with these phenotypes. This mouse model simulates the human clinical and pathological characteristics of UCMD patients and is helpful for the subsequent research and treatment of UCMD.

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.

Gapmer Antisense Oligonucleotides Suppress the Mutant Allele of COL6A3 and Restore Functional Protein in Ullrich Muscular Dystrophy.

Dominant-negative mutations in the genes that encode the three major α chains of collagen type VI, COL6A1, COL6A2, and COL6A3, account for more than 50% of Ullrich congenital muscular dystrophy patients and nearly all Bethlem myopathy patients. Gapmer antisense oligonucleotides (AONs) are usually used for gene silencing by stimulating RNA cleavage through the recruitment of an endogenous endonuclease known as RNase H to cleave the RNA strand of a DNA-RNA duplex. In this study, we exploited the application of the allele-specific silencing approach by gapmer AON as a potential therapy for Collagen-VI-related congenital muscular dystrophy (COL6-CMD). A series of AONs were designed to selectively target an 18-nt heterozygous genomic deletion in exon 15 of COL6A3 at the mRNA and pre-mRNA level. We showed that gapmer AONs can selectively suppress the expression of mutant transcripts at both pre-mRNA and mRNA levels, and that the latter strategy had a far stronger efficiency than the former. More importantly, we found that silencing of the mutant transcripts by gapmer AONs increased the deposition of collagen VI protein into the extracellular matrix, thus restoring functional protein production. Our findings provide a clear proof of concept for AON allele-specific silencing as a therapeutic approach for COL6-CMD.

"Target" and "Sandwich" Signs in Thigh Muscles have High Diagnostic Values for Collagen VI-related Myopathies.

Background:Collagen VI-related myopathies are autosomal dominant and recessive hereditary myopathies, mainly including Ullrich congenital muscular dystrophy (UCMD) and Bethlem myopathy (BM). Muscle magnetic resonance imaging (MRI) has been widely used to diagnosis muscular disorders. The purpose of this study was to evaluate the diagnostic value of thigh muscles MRI for collagen VI-related myopathies.Methods:Eleven patients with collagen VI gene mutation-related myopathies were enrolled in this study. MRI of the thigh muscles was performed in all patients with collagen VI gene mutation-related myopathies and in 361 patients with other neuromuscular disorders (disease controls). T1-weighted images were used to assess fatty infiltration of the muscles using a modified Mercuri's scale. We assessed the sensitivity and specificity of the MRI features of collagen VI-related myopathies. The relationship between fatty infiltration of muscles and specific collagen VI gene mutations was also investigated.Results:Eleven patients with collagen VI gene mutation-related myopathies included six UCMD patients and five BM patients. There was no significant difference between UCMD and BM patients in the fatty infiltration of each thigh muscle except sartorius (P = 0.033); therefore, we combined the UCMD and BM data. Mean fatty infiltration scores were 3.1 and 3.0 in adductor magnus and gluteus maximus, while the scores were 1.3, 1.3, and 1.5 in gracilis, adductor longus, and sartorius, respectively. A “target” sign in rectus femoris (RF) was present in seven cases, and a “sandwich” sign in vastus lateralis (VL) was present in ten cases. The “target” and “sandwich” signs had sensitivities of 63.6% and 90.9% and specificities of 97.3% and 96.9% for the diagnosis of collagen VI-related myopathies, respectively. Fatty infiltration scores were 2.0–3.0 in seven patients with mutations in the triple-helical domain, and 1.0–1.5 in three of four patients with mutations in the N- or C-domain of the collagen VI genes.Conclusions:The “target” sign in RF and “sandwich” sign in VL are common MRI features and are useful for the diagnosis of collagen VI-related myopathies. The severity of fatty infiltration of muscles may have a relationship with the mutation location of collagen VI gene.

Collagen VI–NG2 axis in human tendon fibroblasts under conditions mimicking injury response

In response to injury, tendon fibroblasts are activated, migrate to the wound, and contribute to tissue repair by producing and organizing the extracellular matrix. Collagen VI is a microfibrillar collagen enriched in the pericellular matrix of tendon fibroblasts with a potential regulatory role in tendon repair mechanism. We investigated the molecular basis of the interaction between collagen VI and the cell membrane both in tissue sections and fibroblast cultures of human tendon, and analyzed the deposition of collagen VI during migration and myofibroblast trans-differentiation, two crucial events for tendon repair. Tendon fibroblast displayed a collagen VI microfibrillar network closely associated with the cell surface. Binding of collagen VI with the cell membrane was mediated by NG2 proteoglycan, as demonstrated by in vitro perturbation of collagen VI–NG2 interaction with a NG2-blocking antibody.Cultures subjected to wound healing scratch assay displayed collagen VI–NG2 complexes at the trailing edge of migrating cells, suggesting a potential role in cell migration. In fact, the addition of a NG2-blocking antibody led to an impairment of cell polarization and delay of wound closure. Similar results were obtained after in vitro perturbation of collagen VI extracellular assembly with the 3C4 anti-collagen VI antibody and in collagen VI-deficient tendon cultures of a Ullrich congenital muscular dystrophy patient carrying mutations in COL6A2 gene.Moreover, in vitro treatment with transforming growth factor β1 (TGFβ1) induced a dramatic reduction of NG2 expression, both at protein and mRNA transcript level, and the impairment of collagen VI association with the cell membrane. Instead, collagen VI was still detectable in the extracellular matrix in association with ED-A fibronectin and collagen I, which were strongly induced by TGFβ1 treatment.Our findings reveal a critical role of the NG2 proteoglycan for the binding of collagen VI to the surface of tendon fibroblasts. By interacting with NG2 proteoglycan and other extracellular matrix proteins, collagen VI regulates fibroblasts behavior and the assembly of tendon matrix, thereby playing a crucial role in tendon repair.

Aberrant Mitochondria in a Bethlem Myopathy Patient with a Homozygous Amino Acid Substitution That Destabilizes the Collagen VI α2(VI) Chain

Bethlem myopathy and Ullrich congenital muscular dystrophy (UCMD) sit at opposite ends of a clinical spectrum caused by mutations in the extracellular matrix protein collagen VI. Bethlem myopathy is relatively mild, and patients remain ambulant in adulthood while many UCMD patients lose ambulation by their teenage years and require respiratory interventions. Dominant and recessive mutations are found across the entire clinical spectrum; however, recessive Bethlem myopathy is rare, and our understanding of the molecular pathology is limited. We studied a patient with Bethlem myopathy. Electron microscopy of his muscle biopsy revealed abnormal mitochondria. We identified a homozygous COL6A2 p.D871N amino acid substitution in the C-terminal C2 A-domain. Mutant α2(VI) chains are unable to associate with α1(VI) and α3(VI) and are degraded by the proteasomal pathway. Some collagen VI is assembled, albeit more slowly than normal, and is secreted. These molecules contain the minor α2(VI) C2a splice form that has an alternative C terminus that does include the mutation. Collagen VI tetramers containing the α2(VI) C2a chain do not assemble efficiently into microfibrils and there is a severe collagen VI deficiency in the extracellular matrix. We expressed wild-type and mutant α2(VI) C2 domains in mammalian cells and showed that while wild-type C2 domains are efficiently secreted, the mutant p.D871N domain is retained in the cell. These studies shed new light on the protein domains important for intracellular and extracellular collagen VI assembly and emphasize the importance of molecular investigations for families with collagen VI disorders to ensure accurate diagnosis and genetic counseling.

Nutritional status evaluation in patients affected by bethlem myopathy and ullrich congenital muscular dystrophy.

Collagen VI mutations lead to disabling myopathies like Bethlem myopathy (BM) and Ullrich congenital muscular dystrophy (UCMD). We have investigated the nutritional and metabolic status of one UCMD and seven BM patients (five female, three male, mean age 31 ± 9 years) in order to find a potential metabolic target for nutritional intervention. For this study, we used standard anthropometric tools, such as BMI evaluation and body circumference measurements. All results were compared to dual-energy X-ray absorptiometry (DXA), considered the “gold standard” method. Energy intake of each patient was evaluated through longitudinal methods (7-day food diary) while resting energy expenditure (REE) was predicted using specific equations and measured by indirect calorimetry. Clinical evaluation included general and nutritional blood and urine laboratory analyses and quantitative muscle strength measurement by hand-held dynamometry. BM and UCMD patients showed an altered body composition, characterized by low free fat mass (FFM) and high fat mass (FM), allowing us to classify them as sarcopenic, and all but one as sarcopenic-obese. Another main result was the negative correlation between REE/FFM ratio (basal energy expenditure per kilograms of fat-free mass) and the severity of the disease, as defined by the muscle megascore (correlation coefficient −0.955, P-value <0.001). We postulate that the increase of the REE/FFM ratio in relation to the severity of the disease may be due to an altered and pathophysiological loss of energetic efficiency at the expense of skeletal muscle. We show that a specific metabolic disequilibrium is related to the severity of the disease, which may represent a target for a nutritional intervention in these patients.

Muscle proteomics reveals novel insights into the pathophysiological mechanisms of collagen VI myopathies.

Mutations in the collagen VI genes cause the Ullrich congenital muscular dystrophy (UCMD), with severe phenotype, and Bethlem myopathy (BM) with mild to moderate phenotype. Both, UCMD and BM patients show dystrophic features with degeneration/regeneration and replacement of muscle with fat and fibrous connective tissue. At molecular level, UCMD patients show autophagic impairment and increased PTP opening; these features are less severe in BM. To elucidate the biochemical mechanisms adopted by the muscle to adapt to collagen VI deficiency in BM and UCMD patients, a proteome analysis was carried out on human muscle biopsies. Qualitative and quantitative differences were assessed by 2D-DIGE coupled to MALDI-ToF/ToF MS. Proteomics results, coupled with immunoblotting, indicate changes in UPR, hexosamine pathway, and amino acid and fatty acid metabolism, suggesting an association of ER stress, metabolic dysregulation, autophagic impairment, and alteration in mechanotransduction signaling. Overall, these results indicate that despite the common downregulation of hexosamine pathway in UCMD and BM, in BM the protein quality control system is sustained by a metabolic adaptation supporting energy requirements for the maintenance of autophagy, counteracting ER misfolded protein overload. In UCMD, this multilayered system may be disrupted and worsened by the metabolic rewiring, which leads to lipotoxicity.

G.P.213: Investigating the molecular mechanisms underlying the progression of collagen VI-related muscular dystrophies

Ullrich congenital muscular dystrophy (UCMD) presents at birth or in infancy with progressive muscle weakness, joint contractures and respiratory failure, and is caused by mutations in the three genes coding for collagen VI. Dysfunction of the collagen VI microfibrills in the extracellular matrix perturbs the normal extracellular matrix/muscle interface, leading to yet incompletely characterized downstream effects. Review of muscle biopsies from UCMD patients show that the histological appearance changes with disease progression, suggesting changing disease-driving pathways throughout the progression of the disease. In preparation for a molecular investigation of such pathways, we analyzed 39 UCMD patient muscle biopsies with an automated image analysis algorithm using the degree of atrophy, fibrosis, and regeneration as criteria to group the biopsies. We performed microarray-based expression profiling on the grouped patient biopsies and age-matched controls. Expression profiling results correlated with staging obtained from the automated image analysis algorithm. Further studies will establish the involvement of specific molecules in different stages of UCMD to identify suitable targets for therapeutic intervention. (NIH).

G.P.215: Ullrich congenital muscular dystrophy: A new cellular study on cultured skin fibroblasts

Ullrich congenital muscular dystrophy (UCMD) is a severe congenital dystrophy caused by collagen VI (COL VI) mutations and resulting in absent or aberrant collagen VI secretion in fibroblasts. The link between the mutated collagen VI, and Col VI synthesis, secretion into the ECM, interaction with the cell, mitochondrial defect, cell death, ... is not well characterized. The objective of our study was to provide additional proteomics based insight into the cellular impact of the defective ColVI in cultured skin fibroblasts. To reach this objective, a quantitative iTRAQ based LC-MALDI method was used to compare the proteome in cultured skin fibroblasts from UCMD patients with control fibroblasts. We used western blot as a confirmatory method to assess the dysregulation of proteome identified candidates. The most important findings were the differences in protein expression patterns linked to ER collagen-chaperone functioning and collagen I synthesis (alpha 1 chain, alpha 2 chain) together with fibronectin. A number of proteins involved in the formation of adhesions points that form an important link between the ECM and the intracellular space were found dysregulated. Additionally, Immunofluorescence (IF) for vinculin evaluated by several independent observers showed an increased number of focal adhesions on Col VI deficient fibroblasts. Finally IF collagen V evidenced disturbed extracellular network formation with intracellular retention of the protein. Our findings suggest that the dysregulation of the extracellular network in Col VI deficient fibroblasts possibly leads to intracellular stress and compensatory mechanisms. Proteins involved in molecular pathways such us the mitochondrial defect and the impairment of the autophagocytic flux, implicated in UCMD muscle fibers, were not found as differentially regulated in our proteomics experiment on fibroblasts, suggesting different pathophysiological mechanisms at play in these two important cell types in UCMD.

Defective collagen VI α6 chain expression in the skeletal muscle of patients with collagen VI-related myopathies

Collagen VI is a non-fibrillar collagen present in the extracellular matrix (ECM) as a complex polymer; the mainly expressed form is composed of α1, α2 and α3 chains; mutations in genes encoding these chains cause myopathies known as Ullrich congenital muscular dystrophy (UCMD), Bethlem myopathy (BM) and myosclerosis myopathy (MM). The collagen VI α6 chain is a recently identified component of the ECM of the human skeletal muscle. Here we report that the α6 chain was dramatically reduced in skeletal muscle and muscle cell cultures of genetically characterized UCMD, BM and MM patients, independently of the clinical phenotype, the gene involved and the effect of the mutation on the expression of the “classical” α1α2α3 heterotrimer. By contrast, the collagen VI α6 chain was normally expressed or increased in the muscle of patients affected by other forms of muscular dystrophy, the overexpression matching with areas of increased fibrosis. In vitro treatment with TGF-β1, a potent collagen inducer, promoted the collagen VI α6 chain deposition in the ECM of normal muscle cells, whereas, in cultures derived from collagen VI-related myopathy patients, the collagen VI α6 chain failed to develop a network outside the cells and accumulated in the endoplasmic reticulum. The defect of the α6 chain points to a contribution to the pathogenesis of collagen VI-related disorders.

NIM811, a cyclophilin inhibitor without immunosuppressive activity, is beneficial in collagen VI congenital muscular dystrophy models

Ullrich congenital muscular dystrophy (UCMD) and Bethlem myopathy (BM) are inherited muscle diseases due to mutations in the genes encoding the extracellular matrix protein collagen (Col) VI. Opening of the cyclosporin A-sensitive mitochondrial permeability transition pore (PTP) is a causative event in disease pathogenesis, and a potential target for therapy. Here, we have tested the effect of N-methyl-4-isoleucine-cyclosporin (NIM811), a non-immunosuppressive cyclophilin inhibitor, in a zebrafish model of ColVI myopathy obtained by deletion of the N-terminal region of the ColVI α1 triple helical domain, a common mutation of UCMD. Treatment with antisense morpholino sequences targeting col6a1 exon 9 at the 1-4 cell stage (within 1 h post fertilization, hpf) caused severe ultrastructural and motor abnormalities as assessed by electron and fluorescence microscopy, birefringence, spontaneous coiling events and touch-evoked responses measured at 24-48 hpf. Structural and functional abnormalities were largely prevented when NIM811--which proved significantly more effective than cyclosporin A--was administered at 21 hpf, while FK506 was ineffective. Beneficial effects of NIM811 were also detected (i) in primary muscle-derived cell cultures from UCMD and BM patients, where the typical mitochondrial alterations and depolarizing response to rotenone and oligomycin were significantly reduced; and (ii) in the Col6a1(-/-) myopathic mouse model, where apoptosis was prevented and muscle strength was increased. Since the PTP of zebrafish shares its key regulatory features with the mammalian pore, our results suggest that early treatment with NIM811 should be tested as a potential therapy for UCMD and BM.