The collagen VI-related myopathies: muscle meets its matrix

Optimized allele-specific silencing of the dominant-negative COL6A1 G293R substitution causing collagen VI-related dystrophy

Collagen VI-related dystrophies (COL6-RDs) are a group of severe, congenital-onset muscular dystrophies for which there is no effective causative treatment. Dominant-negative mutations are common in COL6A1, COL6A2, and COL6A3 genes, encoding the collagen α1, α2, and α3 (VI) chains. They act by incorporating into the hierarchical assembly of the three α (VI) chains and consequently produce a dysfunctional collagen VI extracellular matrix, while haploinsufficiency for any of the COL6 genes is not associated with disease. Hence, allele-specific transcript inactivation is a valid therapeutic strategy, although selectively targeting a pathogenic single nucleotide variant is challenging. Here, we develop a small interfering RNA (siRNA) that robustly, and in an allele-specific manner, silences a common glycine substitution (G293R) caused by a single nucleotide change in COL6A1 gene. By intentionally introducing an additional mismatch into the siRNA design, we achieved enhanced specificity toward the mutant allele. Treatment of patient-derived fibroblasts effectively reduced the levels of mutant transcripts while maintaining unaltered wild-type transcript levels, rescuing the secretion and assembly of collagen VI matrix by reducing the dominant-negative effect of mutant chains. Our findings establish a promising treatment approach for patients with the recurrent dominantly negative acting G293R glycine substitution.

Identification of novel variations in three cases with rare inherited neuromuscular disorder

Inherited neuromuscular disorder (IND) is a broad-spectrum, clinically diverse group of diseases that are caused due to defects in the neurosystem, muscles and related tissue. Since IND may originate from mutations in hundreds of different genes, the resulting heterogeneity of IND is a great challenge for accurate diagnosis and subsequent management. Three pediatric cases with IND were enrolled in the present study and subjected to a thorough clinical examination. Next, a genetic investigation was conducted using whole-exome sequencing (WES). The suspected variants were validated through Sanger sequencing or quantitative fluorescence PCR assay. A new missense variant of the Spastin (SPAST) gene was found and analyzed at the structural level using molecular dynamics (MD) simulations. All three cases presented with respective specific clinical manifestations, which reflected the diversity of IND. WES detected the diagnostic variants in all 3 cases: A compound variation comprising collagen type VI α3 chain (COL6A3) (NM_004369; exon19):c.6322G>T(p.E1208*) and a one-copy loss of COL6A3:exon19 in Case 1, which are being reported for the first time; a de novo SPAST (NM_014946; exon8):c.1166C>A(p.T389K) variant in Case 2; and a de novo Duchenne muscular dystrophy (NM_004006; exon11):c.1150-17_1160delACTTCCTTCTTTGTCAGGGGTACATGATinsC variant in Case 3. The structural and MD analyses revealed that the detected novel SPAST: c.1166C>A(p.T389K) variant mainly altered the intramolecular hydrogen bonding status and the protein segment's secondary structure. In conclusion, the present study expanded the IND mutation spectrum. The study not only detailed the precise diagnoses of these cases but also furnished substantial grounds for informed consultations. The approach involving the genetic evaluation strategy using WES for variation screening followed by validation using appropriate methods is beneficial due to the considerable heterogeneity of IND.

Anaesthesia management of a patient with Bethlem Myopathy for elective tonsillectomy: a case report

BACKGROUND

Bethlem Myopathy is a collagen VI-related myopathy presenting as a rare hereditary muscular disorder with progressive muscular weakness and joint contractures. Despite its milder clinical course relative to other myopathies, anaesthetic management can be challenging. High arched palates and fixed flexion deformities may contribute to a difficult airway. A progressive decline in pulmonary function can present later into adulthood. This respiratory decline can carry secondary cardiovascular consequences due to the progressive nature of restrictive lung disease, including right sided heart disease and pulmonary hypertension. We describe a case of a male patient with Bethlem Myopathy undergoing anaesthesia, to contribute to the limited body of literature on this condition and enhance awareness and guidance amongst anaesthesiologists on approaching patients with this condition. This is the first case report within the literature of its kind.

CASE PRESENTATION

This case details a 33-year-old male with Bethlem Myopathy undergoing tonsillectomy. Diagnosed in childhood following developmental delays, the patient had no prior anaesthetic exposure and no family history of anaesthetic complications. Anaesthetic induction was achieved without complications, avoiding depolarizing muscle relaxants and careful airway management. Extreme care was taken in patient positioning to prevent complications. The surgery proceeded without incident and muscle paralysis was reversed with Suggammadex, resulting in no adverse post-operative respiratory complications. The patient was discharged on the first post-operative day without any respiratory or cardiovascular compromise.

CONCLUSIONS

Bethlem Myopathy, while often exhibiting a mild clinical course, can present anaesthetic challenges. Awareness of potential complications including a difficult airway, cardiovascular and respiratory implications as well as the need for specialised monitoring and positioning is crucial to ensure a safe peri-operative course.

Mustn1 is a smooth muscle cell-secreted microprotein that modulates skeletal muscle extracellular matrix composition

OBJECTIVE

Skeletal muscle plasticity and remodeling are critical for adapting tissue function to use, disuse, and regeneration. The aim of this study was to identify genes and molecular pathways that regulate the transition from atrophy to compensatory hypertrophy or recovery from injury. Here, we have used a mouse model of hindlimb unloading and reloading, which causes skeletal muscle atrophy, and compensatory regeneration and hypertrophy, respectively.

METHODS

We analyzed mouse skeletal muscle at the transition from hindlimb unloading to reloading for changes in transcriptome and extracellular fluid proteome. We then used qRT-PCR, immunohistochemistry, and bulk and single-cell RNA sequencing data to determine Mustn1 gene and protein expression, including changes in gene expression in mouse and human skeletal muscle with different challenges such as exercise and muscle injury. We generated Mustn1-deficient genetic mouse models and characterized them in vivo and ex vivo with regard to muscle function and whole-body metabolism. We isolated smooth muscle cells and functionally characterized them, and performed transcriptomics and proteomics analysis of skeletal muscle and aorta of Mustn1-deficient mice.

RESULTS

We show that Mustn1 (Musculoskeletal embryonic nuclear protein 1, also known as Mustang) is highly expressed in skeletal muscle during the early stages of hindlimb reloading. Mustn1 expression is transiently elevated in mouse and human skeletal muscle in response to intense exercise, resistance exercise, or injury. We find that Mustn1 expression is highest in smooth muscle-rich tissues, followed by skeletal muscle fibers. Muscle from heterozygous Mustn1-deficient mice exhibit differences in gene expression related to extracellular matrix and cell adhesion, compared to wild-type littermates. Mustn1-deficient mice have normal muscle and aorta function and whole-body glucose metabolism. We show that Mustn1 is secreted from smooth muscle cells, and that it is present in arterioles of the muscle microvasculature and in muscle extracellular fluid, particularly during the hindlimb reloading phase. Proteomics analysis of muscle from Mustn1-deficient mice confirms differences in extracellular matrix composition, and female mice display higher collagen content after chemically induced muscle injury compared to wild-type littermates.

CONCLUSIONS

We show that, in addition to its previously reported intracellular localization, Mustn1 is a microprotein secreted from smooth muscle cells into the muscle extracellular space. We explore its role in muscle ECM deposition and remodeling in homeostasis and upon muscle injury. The role of Mustn1 in fibrosis and immune infiltration upon muscle injury and dystrophies remains to be investigated, as does its potential for therapeutic interventions.

Exome sequencing in extreme altitude mountaineers identifies pathogenic variants in RTEL1 and COL6A1 previously associated with respiratory failure

Adaptation of humans to challenging environmental conditions, such as extreme temperature, malnutrition, or hypoxia, is an interesting phenomenon for both basic and applied research. Identification of the genetic factors contributing to human adaptation to these conditions enhances our understanding of the underlying molecular and physiological mechanisms. In our study, we analyzed the exomes of 22 high altitude mountaineers to uncover genetic variants contributing to hypoxic adaptation. To our surprise, we identified two putative loss-of-function variants, rs1385101139 in RTEL1 and rs1002726737 in COL6A1 in two extremely high altitude (personal record of more than 8500 m) professional climbers. Both variants can be interpreted as pathogenic according to medical geneticists' guidelines, and are linked to inherited conditions involving respiratory failure (late-onset pulmonary fibrosis and severe Ullrich muscular dystrophy for rs1385101139 and rs1002726737, respectively). Our results suggest that a loss of gene function may act as an important factor of human adaptation, which is corroborated by previous reports in other human subjects.

The recurrent deep intronic pseudoexon-inducing variant COL6A1 c.930+189C>T results in a consistently severe phenotype of COL6-related dystrophy: Towards clinical trial readiness for splice-modulating therapy

Collagen VI-related dystrophies (COL6-RDs) manifest with a spectrum of clinical phenotypes, ranging from Ullrich congenital muscular dystrophy (UCMD), presenting with prominent congenital symptoms and characterised by progressive muscle weakness, joint contractures and respiratory insufficiency, to Bethlem muscular dystrophy, with milder symptoms typically recognised later and at times resembling a limb girdle muscular dystrophy, and intermediate phenotypes falling between UCMD and Bethlem muscular dystrophy. Despite clinical and immunohistochemical features highly suggestive of COL6-RD, some patients had remained without an identified causative variant in COL6A1, COL6A2 or COL6A3. With combined muscle RNA-sequencing and whole-genome sequencing we uncovered a recurrent, de novo deep intronic variant in intron 11 of COL6A1 (c.930+189C>T) that leads to a dominantly acting in-frame pseudoexon insertion. We subsequently identified and have characterised an international cohort of forty-four patients with this COL6A1 intron 11 causative variant, one of the most common recurrent causative variants in the collagen VI genes. Patients manifest a consistently severe phenotype characterised by a paucity of early symptoms followed by an accelerated progression to a severe form of UCMD, except for one patient with somatic mosaicism for this COL6A1 intron 11 variant who manifests a milder phenotype consistent with Bethlem muscular dystrophy. Characterisation of this individual provides a robust validation for the development of our pseudoexon skipping therapy. We have previously shown that splice-modulating antisense oligomers applied in vitro effectively decreased the abundance of the mutant pseudoexon-containing COL6A1 transcripts to levels comparable to the in vivo scenario of the somatic mosaicism shown here, indicating that this therapeutic approach carries significant translational promise for ameliorating the severe form of UCMD caused by this common recurrent COL6A1 causative variant to a Bethlem muscular dystrophy phenotype.

The coordinated activities of collagen VI and XII in maintenance of tissue structure, function and repair: evidence for a physical interaction

Collagen VI and collagen XII are structurally complex collagens of the extracellular matrix (ECM). Like all collagens, type VI and XII both possess triple-helical components that facilitate participation in the ECM network, but collagen VI and XII are distinct from the more abundant fibrillar collagens in that they also possess arrays of structurally globular modules with the capacity to propagate signaling to attached cells. Cell attachment to collagen VI and XII is known to regulate protective, proliferative or developmental processes through a variety of mechanisms, but a growing body of genetic and biochemical evidence suggests that at least some of these phenomena may be potentiated through mechanisms that require coordinated interaction between the two collagens. For example, genetic studies in humans have identified forms of myopathic Ehlers-Danlos syndrome with overlapping phenotypes that result from mutations in either collagen VI or XII, and biochemical and cell-based studies have identified accessory molecules that could form bridging interactions between the two collagens. However, the demonstration of a direct or ternary structural interaction between collagen VI or XII has not yet been reported. This Hypothesis and Theory review article examines the evidence that supports the existence of a functional complex between type VI and XII collagen in the ECM and discusses potential biological implications.

A humanized knock-in Col6a1 mouse recapitulates a deep-intronic splice-activating variant

Antisense therapeutics such as splice-modulating antisense oligonucleotides (ASOs) are promising tools to treat diseases caused by splice-altering intronic variants. However, their testing in animal models is hampered by the generally poor sequence conservation of the intervening sequences between human and other species. Here we aimed to model in the mouse a recurrent, deep-intronic, splice-activating, COL6A1 variant, associated with a severe form of Collagen VI-related muscular dystrophies (COL6-RDs), for the purpose of testing human-ready antisense therapeutics in vivo. The variant, c.930+189C>T, creates a donor splice site and inserts a 72-nt-long pseudoexon, which, when translated, acts in a dominant-negative manner, but which can be skipped with ASOs. We created a unique humanized mouse allele (designated as "h"), in which a 1.9 kb of the mouse genomic region encoding the amino-terminus (N-) of the triple helical (TH) domain of collagen a1(VI) was swapped for the human orthologous sequence. In addition, we also created an allele that carries the c.930+189C>T variant on the same humanized knock-in sequence (designated as "h+189T"). We show that in both models, the human exons are spliced seamlessly with the mouse exons to generate a chimeric mouse-human collagen a1(VI) protein. In homozygous Col6a1 h+189T/h+189T mice, the pseudoexon is expressed at levels comparable to those observed in heterozygous patients' muscle biopsies. While Col6a1h/h mice do not show any phenotype compared to wildtype animals, Col6a1 h/h+189T and Col6a1 h+189T/h+189T mice have smaller muscle masses and display grip strength deficits detectable as early as 4 weeks of age. The pathogenic h+189T humanized knock-in mouse allele thus recapitulates the pathogenic splicing defects seen in patients' biopsies and allows testing of human-ready precision antisense therapeutics aimed at skipping the pseudoexon. Given that the COL6A1 N-TH region is a hot-spot for COL6-RD variants, the humanized knock-in mouse model can be utilized as a template to introduce other COL6A1 pathogenic variants. This unique humanized mouse model thus represents a valuable tool for the development of antisense therapeutics for COL6-RDs.

Allele-specific CRISPR/Cas9 editing inactivates a single nucleotide variant associated with collagen VI muscular dystrophy

The application of allele-specific gene editing tools can expand the therapeutic options for dominant genetic conditions, either via gene correction or via allelic gene inactivation in situations where haploinsufficiency is tolerated. Here, we used allele-targeted CRISPR/Cas9 guide RNAs (gRNAs) to introduce inactivating frameshifting indels at a single nucleotide variant in the COL6A1 gene (c.868G>A; G290R), a variant that acts as dominant negative and that is associated with a severe form of congenital muscular dystrophy. We expressed spCas9 along with allele-targeted gRNAs, without providing a repair template, in primary fibroblasts derived from four patients and one control subject. Amplicon deep-sequencing for two gRNAs tested showed that single nucleotide deletions accounted for the majority of indels introduced. While activity of the two gRNAs was greater at the G290R allele, both gRNAs were also active at the wild-type allele. To enhance allele-selectivity, we introduced deliberate additional mismatches to one gRNA. One of these optimized gRNAs showed minimal activity at the WT allele, while generating productive edits and improving collagen VI matrix in cultured patient fibroblasts. This study strengthens the potential of gene editing to treat dominant-negative disorders, but also underscores the challenges in achieving allele selectivity with gRNAs.

Native collagen VI delays early muscle stem cell differentiation

Adult muscle stem cells (MuSCs) are critical for muscle homeostasis and regeneration, and their behavior relies on a finely regulated niche made of specific extracellular matrix (ECM) components and soluble factors. Among ECM proteins, collagen VI (Col6) influences the mechanical properties of the niche and, in turn, MuSC self-renewal capabilities. Here, we investigated whether Col6 can exert a direct function as a biochemical signal for regulating the stemness and differentiation of murine MuSCs and myoblasts. Native Col6, but not its pepsin-resistant fragment, counteracts the early differentiation of myogenic cells by reducing the expression of differentiation marker genes and preserving stemness features, with inhibition of the canonical Wnt pathway. Our data indicate that extracellular Col6 acts as a soluble ligand in delaying early myogenic differentiation by regulating intracellular signals involved in adult myogenesis.

Retrospective clinical and genetic analysis of COL6-RD patients with a long-term follow-up at a single French center

Collagen type VI-related dystrophies (COL6-RD) are rare diseases with a wide phenotypic spectrum ranging from severe Ullrich's congenital muscular dystrophy Ullrich congenital muscular dystrophy to much milder Bethlem myopathy Both dominant and recessive forms of COL6-RD are caused by pathogenic variants in three collagen VI genes (COL6A1, COL6A2 and COL6A3). The prognosis of these diseases is variable and difficult to predict during early disease stages, especially since the genotype-phenotype correlation is not always clear. For this reason, studies with long-term follow-up of patients with genetically confirmed COL6-RD are still needed. In this study, we present phenotypic and genetic data from 25 patients (22 families) diagnosed with COL6-RD and followed at a single French center, in both adult and pediatric neurology departments. We describe three novel pathogenic variants and identify COL6A2:c.1970-9G>A as the most frequent variant in our series (29%). We also observe an accelerated progression of the disease in a subgroup of patients. This large series of rare disease patients provides essential information on phenotypic variability of COL6-RD patients as well as on frequency of pathogenic COL6A gene variants in Southern France, thus contributing to the phenotypic and genetic description of Collagen type VI-related dystrophies.

Sleep in pediatric neuromuscular disorders

Sleep disordered breathing (SDB) is prevalent among children with neuromuscular disorders (NMD). The combination of respiratory muscle weakness, altered drive, and chest wall distortion due to scoliosis make sleep a stressful state in this population. Symptomatology can range from absent to snoring, nocturnal awakenings, morning headaches, and excessive daytime sleepiness. Sequelae of untreated SDB includes cardiovascular effects, metabolic derangements, and neurocognitive concerns which can be compounded by those innate to the NMD. The clinician should have a low threshold for obtaining polysomnography and recognize the nuances of individual disorders due to disproportionately impacted muscle groups such as hypoventilation in ambulating patients from diaphragm weakness. Non-invasive or invasive ventilation are the mainstay of treatment. In this review we explore the diagnosis and treatment of SDB in children with various NMD.

Human skeletal muscle organoids model fetal myogenesis and sustain uncommitted PAX7 myogenic progenitors

In vitro culture systems that structurally model human myogenesis and promote PAX7+ myogenic progenitor maturation have not been established. Here we report that human skeletal muscle organoids can be differentiated from induced pluripotent stem cell lines to contain paraxial mesoderm and neuromesodermal progenitors and develop into organized structures reassembling neural plate border and dermomyotome. Culture conditions instigate neural lineage arrest and promote fetal hypaxial myogenesis toward limb axial anatomical identity, with generation of sustainable uncommitted PAX7 myogenic progenitors and fibroadipogenic (PDGFRa+) progenitor populations equivalent to those from the second trimester of human gestation. Single-cell comparison to human fetal and adult myogenic progenitor /satellite cells reveals distinct molecular signatures for non-dividing myogenic progenitors in activated (CD44High/CD98+/MYOD1+) and dormant (PAX7High/FBN1High/SPRY1High) states. Our approach provides a robust 3D in vitro developmental system for investigating muscle tissue morphogenesis and homeostasis.

Novel COL6A3 frameshift variant in American Staffordshire Terrier dogs with Ullrich-like congenital muscular dystrophy

Two (male and female) 10-month-old American Staffordshire Terrier littermates presented for progressive weakness, joint contracture, and distal limb joint hyperlaxity beginning around 6 months of age. Neurological examination, serum creatine kinase activity, infectious disease titers, cerebrospinal fluid analysis, and electrodiagnostic testing were performed. Muscle biopsies were collected for histopathology and immunofluorescence staining for localization of dystrophy associated proteins. Whole-genome sequencing (WGS) was performed on 1 affected dog. Variants were compared to a database of 671 unaffected dogs of multiple breeds. Histopathology confirmed a dystrophic phenotype and immunofluorescence staining of muscle cryosections revealed an absence of staining for collagen-6. WGS identified a homozygous 1 bp deletion in the COL6A3 gene, unique to the first affected dog. Sanger sequencing confirmed the homozygous presence of the frameshift variant in both affected dogs. This report describes the clinical features and most likely genetic basis of an Ullrich-like recessively inherited form of congenital muscular dystrophy in American Staffordshire Terriers.

Contextual fear memory impairment in Angelman syndrome model mice is associated with altered transcriptional responses

Angelman syndrome (AS) is a rare neurogenetic disorder caused by UBE3A deficiency and characterized by severe developmental delay, cognitive impairment, and motor dysfunction. In the present study, we performed RNA-seq on hippocampal samples from both wildtype (WT) and AS male mice, with or without contextual fear memory recall. There were 281 recall-associated differentially expressed genes (DEGs) in WT mice and 268 DEGs in AS mice, with 129 shared by the two genotypes. Gene ontology analysis showed that extracellular matrix and stimulation-induced response genes were prominently enriched in recall-associated DEGs in WT mice, while nuclear acid metabolism and tissue development genes were highly enriched in those from AS mice. Further analyses showed that the 129 shared DEGs belonged to nuclear acid metabolism and tissue development genes. Unique recall DEGs in WT mice were enriched in biological processes critical for synaptic plasticity and learning and memory, including the extracellular matrix network clustered around fibronectin 1 and collagens. In contrast, AS-specific DEGs were not enriched in any known pathways. These results suggest that memory recall in AS mice, while altering the transcriptome, fails to recruit memory-associated transcriptional programs, which could be responsible for the memory impairment in AS mice.

The molecular mechanism underlying dermatomyositis related interstitial lung disease: evidence from bioinformatic analysis and in vivo validation

Background

Dermatomyositis (DM) is an autoimmune and inflammatory disease that can affect the lungs, causing interstitial lung diseases (ILD). However, the exact pathophysiological mechanisms underlying DM-ILD are unknown. Idiopathic pulmonary fibrosis (IPF) belongs to the broader spectrum of ILD and evidence shows that common pathologic pathways might lie between IPF and DM-ILD.

Methods

We retrieved gene expression profiles of DM and IPF from the Gene Expression Omnibus (GEO) and utilized weighted gene co-expression network analysis (WGCNA) to reveal their co-expression modules. We then performed a differentially expressed gene (DEG) analysis to identify common DEGs. Enrichment analyses were employed to uncover the hidden biological pathways. Additionally, we conducted protein-protein interaction (PPI) networks analysis, cluster analysis, and successfully found the hub genes, whose levels were further validated in DM-ILD patients. We also examined the relationship between hub genes and immune cell abundance in DM and IPF. Finally, we conducted a common transcription factors (TFs)-genes network by NetworkAnalyst.

Results

WGCNA revealed 258 intersecting genes, while DEG analysis identified 66 shared genes in DM and IPF. All of these genes were closely related to extracellular matrix and structure, cell-substrate adhesion, and collagen metabolism. Four hub genes (POSTN, THBS2, COL6A1, and LOXL1) were derived through intersecting the top 30 genes of the WGCNA and DEG sets. They were validated as active transcripts and showed diagnostic values for DM and IPF. However, ssGSEA revealed distinct infiltration patterns in DM and IPF. These four genes all showed a positive correlation with immune cells abundance in DM, but not in IPF. Finally, we identified one possible key transcription factor, MYC, that interact with all four hub genes.

Conclusion

Through bioinformatics analysis, we identified common hub genes and shared molecular pathways underlying DM and IPF, which provides valuable insights into the intricate mechanisms of these diseases and offers potential targets for diagnostic and therapeutic interventions.

Collagen type VI regulates TGFβ bioavailability in skeletal muscle

Collagen VI-related disorders (COL6-RDs) are a group of rare muscular dystrophies caused by pathogenic variants in collagen VI genes (COL6A1, COL6A2, and COL6A3). Collagen type VI is a heterotrimeric, microfibrillar component of the muscle extracellular matrix (ECM), predominantly secreted by resident fibroadipogenic precursor cells in skeletal muscle. The absence or mislocalizatoion of collagen VI in the ECM underlies the non-cell autonomous dysfunction and dystrophic changes in skeletal muscle with an as of yet elusive direct mechanistic link between the ECM and myofiber dysfunction. Here, we conduct a comprehensive natural history and outcome study in a novel mouse model of COL6-RDs (Col6a2-/- mice) using standardized (Treat-NMD) functional, histological, and physiologic parameter. Notably, we identify a conspicuous dysregulation of the TGFβ pathway early in the disease process and propose that the collagen VI deficient matrix is not capable of regulating the dynamic TGFβ bioavailability at baseline and also in response to muscle injury. Thus, we propose a new mechanism for pathogenesis of the disease that links the ECM regulation of TGFβ with downstream skeletal muscle abnormalities, paving the way for developing and validating therapeutics that target this pathway.

Alopecia in Patients with Collagen VI-Related Myopathies: A Novel/Unrecognized Scalp Phenotype

Collagen VI-related myopathies are characterized by severe muscle involvement and skin involvement (keratosis pilaris and impaired healing with the development of abnormal scars, especially keloids). Scalp involvement and hair loss have not been reported among cutaneous changes associated with collagen VI mutations. The aim of this study is to describe the clinical, trichoscopic, and histological findings of the scalp changes in patients affected by COL VI mutations and to estimate their prevalence. Patients with Ullrich congenital muscular dystrophy were enrolled and underwent clinical and trichoscopic examinations and a scalp biopsy for histopathology. Five patients were enrolled, and all complained of hair loss and scalp itching. One patient showed yellow interfollicular scales with erythema and dilated, branched vessels, and the histological findings were suggestive of scalp psoriasis. Two patients presented with scarring alopecia patches on the vertex area, and they were histologically diagnosed with folliculitis decalvans. The last two patients presented with scaling and hair thinning, but they were both diagnosed with folliculitis and perifolliculitis. Ten more patients answered to a "scalp involvement questionnaire", and six of them confirmed to have or have had scalp disorders and/or itching. Scalp involvement can be associated with COL VI mutations and should be investigated.

Extracellular Matrix Disorganization and Sarcolemmal Alterations in COL6-Related Myopathy Patients with New Variants of COL6 Genes

Collagen VI is a heterotrimeric protein expressed in several tissues and involved in the maintenance of cell integrity. It localizes at the cell surface, creating a microfilamentous network that links the cytoskeleton to the extracellular matrix. The heterotrimer consists of three chains encoded by COL6A1, COL6A2 and COL6A3 genes. Recessive and dominant molecular defects cause two main disorders, the severe Ullrich congenital muscular dystrophy and the relatively mild and slowly progressive Bethlem myopathy. We analyzed the clinical aspects, pathological features and mutational spectrum of 15 COL6-mutated patients belonging to our cohort of muscular dystrophy probands. Patients presented a heterogeneous phenotype ranging from severe forms to mild adult-onset presentations. Molecular analysis by NGS detected 14 different pathogenic variants, three of them so far unreported. Two changes, localized in the triple-helical domain of COL6A1, were associated with a more severe phenotype. Histological, immunological and ultrastructural techniques were employed for the validation of the genetic variants; they documented the high variability in COL6 distribution and the extracellular matrix disorganization, highlighting the clinical heterogeneity of our cohort. The combined use of these different technologies is pivotal in the diagnosis of COL6 patients.

Collagen VI in the Musculoskeletal System

Collagen VI exerts several functions in the tissues in which it is expressed, including mechanical roles, cytoprotective functions with the inhibition of apoptosis and oxidative damage, and the promotion of tumor growth and progression by the regulation of cell differentiation and autophagic mechanisms. Mutations in the genes encoding collagen VI main chains, COL6A1, COL6A2 and COL6A3, are responsible for a spectrum of congenital muscular disorders, namely Ullrich congenital muscular dystrophy (UCMD), Bethlem myopathy (BM) and myosclerosis myopathy (MM), which show a variable combination of muscle wasting and weakness, joint contractures, distal laxity, and respiratory compromise. No effective therapeutic strategy is available so far for these diseases; moreover, the effects of collagen VI mutations on other tissues is poorly investigated. The aim of this review is to outline the role of collagen VI in the musculoskeletal system and to give an update about the tissue-specific functions revealed by studies on animal models and from patients' derived samples in order to fill the knowledge gap between scientists and the clinicians who daily manage patients affected by collagen VI-related myopathies.

Transcriptome profiling of skeletal muscles from Korean patients with Bethlem myopathy

Bethlem myopathy is one of the collagens VI-related muscular dystrophies caused by mutations in the collagen VI genes. The study was designed to analyze the gene expression profiles in the skeletal muscle of patients with Bethlem myopathy. Six skeletal muscle samples from 3 patients with Bethlem myopathy and 3 control subjects were analyzed by RNA-sequencing. 187 transcripts were significantly differentially expressed, with 157 upregulated and 30 downregulated transcripts in the Bethlem group. Particularly, 1 (microRNA-133b) was considerably upregulated, and 4 long intergenic non-protein coding RNAs, LINC01854, MBNL1-AS1, LINC02609, and LOC728975, were significantly downregulated. We categorized differentially expressed gene using Gene Ontology and showed that Bethlem myopathy is strongly associated with the organization of extracellular matrix (ECM). Kyoto Encyclopedia of Genes and Genomes pathway enrichment reflected themes with significant enrichment of the ECM-receptor interaction (hsa04512), complement and coagulation cascades (hsa04610), and focal adhesion (hsa04510). We confirmed that Bethlem myopathy is strongly associated with the organization of ECM and the wound healing process. Our results demonstrate transcriptome profiling of Bethlem myopathy, and provide new insights into the path mechanism of Bethlem myopathy associated with non-protein coding RNAs.

Lack of COL6/collagen VI causes megakaryocyte dysfunction by impairing autophagy and inducing apoptosis

Endoplasmic reticulum stress is an emerging significant player in the molecular pathology of connective tissue disorders. In response to endoplasmic reticulum stress, cells can upregulate macroautophagy/autophagy, a fundamental cellular homeostatic process used by cells to degrade and recycle proteins or remove damaged organelles. In these scenarios, autophagy activation can support cell survival. Here we demonstrated by in vitro and in vivo approaches that megakaryocytes derived from col6a1^-⁄- (collagen, type VI, alpha 1) null mice display increased intracellular retention of COL6 polypeptides, endoplasmic reticulum stress and apoptosis. The unfolded protein response is activated in col6a1^-⁄- megakaryocytes, as evidenced by the upregulation of molecular chaperones, by the increased splicing of Xbp1 mRNA and by the higher level of the pro-apoptotic regulator DDIT3/CHOP. Despite the endoplasmic reticulum stress, basal autophagy is impaired in col6a1^-⁄- megakaryocytes, which show lower BECN1 levels and reduced autophagosome maturation. Starvation and rapamycin treatment rescue the autophagic flux in col6a1^-⁄- megakaryocytes, leading to a decrease in intracellular COL6 polypeptide retention, endoplasmic reticulum stress and apoptosis. Furthermore, megakaryocytes cultured from peripheral blood hematopoietic progenitors of patients affected by Bethlem myopathy and Ullrich congenital muscular dystrophy, two COL6-related disorders, displayed increased apoptosis, endoplasmic reticulum stress and impaired autophagy. These data demonstrate that genetic disorders of collagens, endoplasmic reticulum stress and autophagy regulation in megakaryocytes may be interrelated.Abbreviations: 7-AAD: 7-amino-actinomycin D; ATF: activating transcriptional factor; BAX: BCL2 associated X protein; BCL2: B cell leukemia/lymphoma 2; BCL2L1/Bcl-xL: BCL2-like 1; BM: bone marrow; COL6: collagen, type VI; col6a1^-⁄-: mice that are null for Col6a1; DDIT3/CHOP/GADD153: DNA-damage inducible transcript 3; EGFP: enhanced green fluorescent protein; ER: endoplasmic reticulum; reticulophagy: endoplasmic reticulum-selective autophagy; HSPA5/Bip: heat shock protein 5; HSP90B1/GRP94: heat shock protein 90, beta (Grp94), member 1; LAMP2: lysosomal associated membrane protein 2; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; Mk: megakaryocytes; MTOR: mechanistic target of rapamycin kinase; NIMV: noninvasive mechanical ventilation; PI3K: phosphoinositide 3-kinase; PPP1R15A/GADD34: protein phosphatase 1, regulatory subunit 15A; RT-qPCR: reverse transcription-quantitative real-time PCR; ROS: reactive oxygen species; SERPINH1/HSP47: serine (or cysteine) peptidase inhibitor, clade H, member 1; sh-RNA: short hairpin RNA; SOCE: store operated calcium entry; UCMD: Ullrich congenital muscular dystrophy; UPR: unfolded protein response; WIPI2: WD repeat domain, phosphoinositide-interacting 2; WT: wild type; XBP1: X-box binding protein 1.

Genetic Analysis of HIBM Myopathy-Specific GNE V727M Hotspot Mutation Identifies a Novel COL6A3 Allied Gene Signature That Is Also Deregulated in Multiple Neuromuscular Diseases and Myopathies

The GNE-associated V727M mutation is one of the most prevalent ethnic founder mutations in the Asian HIBM cohort; however, its role in inducing disease phenotype remains largely elusive. In this study, the function of this hotspot mutation was profoundly investigated. For this, V727M mutation-specific altered expression profile and potential networks were explored. The relevant muscular disorder-specific in vivo studies and patient data were further analyzed, and the key altered molecular pathways were identified. Our study found that the GNEV727M mutation resulted in a deregulated lincRNA profile, the majority of which (91%) were associated with a down-regulation trend. Further, in silico analysis of associated targets showed their active role in regulating Wnt, TGF-β, and apoptotic signaling. Interestingly, COL6a3 was found as a key target of these lincRNAs. Further, GSEA analysis showed HIBM patients with variable COL6A3 transcript levels have significant alteration in many critical pathways, including epithelial-mesenchymal-transition, myogenesis, and apoptotic signaling. Interestingly, 12 of the COL6A3 coexpressed genes also showed a similar altered expression profile in HIBM. A similar altered trend in COL6A3 and coexpressed genes were found in in vivo HIBM disease models as well as in multiple other skeletal disorders. Thus, the COL6A3-specific 13 gene signature seems to be altered in multiple muscular disorders. Such deregulation could play a pivotal role in regulating many critical processes such as extracellular matrix organization, cell adhesion, and skeletal muscle development. Thus, investigating this novel COL6A3-specific 13 gene signature provides valuable information for understanding the molecular cause of HIBM and may also pave the way for better diagnosis and effective therapeutic strategies for many muscular disorders.

Dry synovitis, a rare entity distinct from juvenile idiopathic arthritis

BACKGROUND

Dry synovitis (DS) is a rare entity as only a few cases have been reported to date. We describe the clinical features, radiological manifestations and course of DS in comparison with rheumatoid factor negative polyarticular juvenile idiopathic arthritis (RFneg-polyJIA).

METHODS

We performed a multicenter retrospective collection of data of DS patients who presented with progressive joint limitations without palpable synovitis, absence of elevated acute phase reactants, negative ANA and RF, and imaging showing joint and/or osteochondral involvement. For comparative purposes, we included a cohort of RF neg-polyJIA patients.

RESULTS

Twelve DS patients, 8F/4 M, with mean age at onset of 6.1 years, were included. Presenting signs comprised delayed motor development, functional limitations and/or progressive stiffness. Clinical examination showed symmetric polyarticular involvement with variable muscular atrophy. MRI showed mild, diffuse synovial involvement, without effusion. With time, signs of progressive osteochondral damage became evident, despite treatment. All patients were treated with low-dose corticosteroids and methotrexate. Anti-TNF agents were prescribed in five. The response was variable with limited joint mobility in 11/12, and need of joint replacement in 2. In comparison with a cohort of RFneg-polyJIA, DS patients presented higher number of joint involved (p = 0.0001) and contractures (p = 0.0001), less swelling (p = 0.0001) and prolonged diagnostic delay (p = 0.0001).

CONCLUSION

DS represents a unique juvenile-onset arthropathy, distinct from polyarticular JIA. Awareness among pediatricians is essential for early recognition and proper treatment. Further studies, including synovial pathology, immunology and genetics may contribute to a better understanding of this rare disorder of childhood.

Childhood muscular dystrophies

Infancy- and childhood-onset muscular dystrophies are associated with a characteristic distribution and progression of motor dysfunction. The underlying causes of progressive childhood muscular dystrophies are heterogeneous involving diverse genetic pathways and genes that encode proteins of the plasma membrane, extracellular matrix, sarcomere, and nuclear membrane components. The prototypical clinicopathological features in an affected child may be adequate to fully distinguish it from other likely diagnoses based on four common features: (1) weakness and wasting of pelvic-femoral and scapular muscles with involvement of heart muscle; (2) elevation of serum muscle enzymes in particular serum creatine kinase; (3) necrosis and regeneration of myofibers; and (4) molecular neurogenetic assessment particularly utilizing next-generation sequencing of the genome of the likeliest candidates genes in an index case or family proband. A number of different animal models of therapeutic strategies have been developed for gene transfer therapy, but so far these techniques have not yet entered clinical practice. Treatment remains for the most part symptomatic with the goal of ameliorating locomotor and cardiorespiratory manifestations of the disease.

CONVENTIONAL APPROACHES TO THE THERAPY OF HEREDITARY MYOPATHIES

The aim of the work was to analyze the available therapeutic options for the conventional therapy of hereditary myopathies.

Materials and methods. When searching for the material for writing a review article, such abstract databases as PubMed and Google Scholar were used. The search was carried out on the publications during the period from 1980 to September 2022. The following words and their combinations were selected as parameters for the literature selection: “myopathy”, “Duchenne”, “myodystrophy”, “metabolic”, “mitochondrial”, “congenital”, “symptoms”, “replacement”, “recombinant”, “corticosteroids”, “vitamins”, “tirasemtiv”, “therapy”, “treatment”, “evidence”, “clinical trials”, “patients”, “dichloracetate”.

Results. Congenital myopathies are a heterogeneous group of pathologies that are caused by atrophy and degeneration of muscle fibers due to mutations in genes. Based on a number of clinical and pathogenetic features, hereditary myopathies are divided into: 1) congenital myopathies; 2) muscular dystrophy; 3) mitochondrial and 4) metabolic myopathies. At the same time, treatment approaches vary significantly depending on the type of myopathy and can be based on 1) substitution of the mutant protein; 2) an increase in its expression; 3) stimulation of the internal compensatory pathways expression; 4) restoration of the compounds balance associated with the mutant protein function (for enzymes); 5) impact on the mitochondrial function (with metabolic and mitochondrial myopathies); 6) reduction of inflammation and fibrosis (with muscular dystrophies); as well as 7) an increase in muscle mass and strength. The current review presents current data on each of the listed approaches, as well as specific pharmacological agents with a description of their action mechanisms.

Conclusion. Currently, the following pharmacological groups are used or undergoing clinical trials for the treatment of various myopathies types: inotropic, anti-inflammatory and antifibrotic drugs, antimyostatin therapy and the drugs that promote translation through stop codons (applicable for nonsense mutations). In addition, metabolic drugs, metabolic enzyme cofactors, mitochondrial biogenesis stimulators, and antioxidants can be used to treat myopathies. Finally, the recombinant drugs alglucosidase and avalglucosidase have been clinically approved for the replacement therapy of metabolic myopathies (Pompe’s disease).

Genetic-Based Treatment Strategies for Muscular Dystrophy and Congenital Myopathies

PURPOSE OF REVIEW

This article discusses the foundational concepts of genetic treatment strategies employed in neuromuscular medicine, as well as the importance of genetic testing as a requirement for applying gene-based therapy.

RECENT FINDINGS

Gene therapies have become a reality for several neuromuscular disorders. Exon-skipping and (in Europe) ribosomal read-through approaches are currently available to a subset of patients with Duchenne muscular dystrophy. Microdystrophin gene replacement has shown promise and is nearing the final stages of clinical trials. Numerous gene-based therapies for other muscular dystrophies and congenital myopathies are progressing toward approval as well.

SUMMARY

Muscular dystrophies and congenital myopathies are a heterogenous group of hereditary muscle disorders. Confirming a diagnosis with genetic testing is not only critical for guiding management, but also an actual prerequisite for current and future gene therapies. Recessive loss-of-function or dominant haploinsufficiency disorders may be treated with gene replacement strategies, whereas dominant negative and toxic gain-of-function disorders are best addressed with a variety of knockdown approaches. It is important to recognize that many therapeutics are mutation specific and will only benefit a subset of individuals with a specific disease.

Kyphoscoliotic Ehlers-Danlos syndrome caused by pathogenic variants in FKBP14: Further insights into the phenotypic spectrum and pathogenic mechanisms

The Ehlers-Danlos syndromes (EDS) are a heterogeneous group of heritable connective tissue diseases. The autosomal recessive kyphoscoliotic EDS results from deficiency of either lysyl hydroxylase 1 (encoded by PLOD1), crucial for collagen cross-linking; or the peptidyl-prolyl cis-trans isomerase family FK506-binding protein 22 kDa (FKBP22 encoded by FKBP14), a molecular chaperone of types III, IV, VI, and X collagen. This study reports the clinical manifestations of three probands with homozygous pathogenic FKBP14 variants, including the previously reported c.362dupC; p.(Glu122Argfs*7) variant, a novel missense variant (c.587A>G; p.(Asp196Gly)) and a start codon variant (c.2T>G; p.?). Consistent clinical features in the hitherto reported individuals (n = 40) are kyphoscoliosis, generalized joint hypermobility and congenital muscle hypotonia. Severe vascular complications have been observed in 12.5%. A previously unreported feature is microcornea observed in two probands reported here. Both the c.587A>G and the c.362dupC variant cause complete loss of FKBP22. With immunocytochemistry on dermal fibroblasts, we provide the first evidence for intracellular retention of types III and VI collagen in EDS-FKBP14. Scratch wound assays were largely normal. Western blot of proteins involved in the unfolded protein response and autophagy did not reveal significant upregulation in dermal fibroblasts.

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.

Current Strategies of Muscular Dystrophy Therapeutics: An Overview

Muscular dystrophies are a group of genetic disorders characterized by varying degrees of progressive muscle weakness and degeneration. They are clinically and genetically heterogeneous but share the common histological features of dystrophic muscle. There is currently no cure for muscular dystrophies, which is of particular concern for the more disabling and/or lethal forms of the disease. Through the years, several therapies have encouragingly been developed for muscular dystrophies and include genetic, cellular, and pharmacological approaches. In this chapter, we undertake a comprehensive exploration of muscular dystrophy therapeutics under current development. Our review includes antisense therapy, CRISPR, gene replacement, cell therapy, nonsense suppression, and disease-modifying small molecule compounds.

Exon-Skipping for a Pathogenic COL6A1 Variant in Ullrich Congenital Muscular Dystrophy

Single nucleotide variants that alter splice sites or splicing regulatory elements can lead to the skipping of exons, retention of introns, or insertion of pseudo-exons (PE) into the mature mRNA transcripts. When translated, these changes can disrupt the function of the synthesized protein. Splice-switching antisense oligonucleotides (ASOs) are synthetic, modified nucleic acids that can correct these aberrant splicing events. They are currently in active clinical development for a number of conditions and have been approved by regulatory agencies for the treatment of neuromuscular disorders such as Duchenne muscular dystrophy and spinal muscular atrophy. We have previously reported that splice-switching ASOs effectively skip a pathogenic PE that causes Ullrich congenital muscular dystrophy (UCMD). This erroneous PE insertion is caused by a deep-intronic variant located within intron 11 of COL6A1 (c.930+189 C>T). Here, we describe the detailed protocols and workflow that our labs have used to assess the efficacy of ASOs to skip this PE in vitro. The protocols include designing ASOs; isolating, culturing, and transfecting fibroblasts; extracting RNA and protein; and validating splicing correction at the mRNA and protein levels using quantitative reverse transcription PCR (qRT-PCR) and western blot assays, respectively.

The Role of Type VI Collagen in Alveolar Bone

Many studies have been conducted to elucidate the role of Type VI collagen in muscle and tendon, however, its role in oral tissues remains unclear. In this study, an α2(VI) deficient mouse (Col6α2-KO) model was used to examine the role of Type VI collagen in oral tissues. Tissue volume and mineral density were measured in oral tissues by µCT. Proteome analysis was performed using protein extracted from alveolar bone. In addition, alveolar bone was evaluated with a periodontitis induced model. µCT analysis showed the Col6α2-KO mice had less volume of alveolar bone, dentin and dental pulp, while the width of periodontal ligament (PDL) was greater than WT. The mineral density in alveolar bone and dentin were elevated in Col6α2-KO mice compared with WT. Our proteome analysis showed significant changes in proteins related to ECM organization and elevation of proteins associated with biomineralization in the Col6α2-KO mice. In induced periodontitis, Col6α2-KO mice had greater alveolar bone loss compared with WT. In conclusion, Type VI collagen has a role in controlling biomineralization in alveolar bone and that changes in the ECM of alveolar bone could be associated with greater bone loss due to periodontitis.

Lack of evidence for a role of anthrax toxin receptors as surface receptors for collagen VI and for its cleaved-off C5 domain/endotrophin

The microfibril-forming collagen VI is proteolytically cleaved and it was proposed that the released C-terminal Kunitz domain (C5) of the α3 chain is an adipokine important for tumor progression and fibrosis. Designated “endotrophin,” C5 is a potent biomarker for fibroinflammatory diseases. However, the biochemical mechanisms behind endotrophin activity were not investigated. Earlier, anthrax toxin receptor 1 was found to bind C5, but this potential interaction was not further studied. Given the proposed physiological role of endotrophin, we aimed to determine how the signal is transmitted. Surprisingly, we could not detect any interaction between endotrophin and anthrax toxin receptor 1 or its close relative, anthrax toxin receptor 2. Moreover, we detect no binding of fully assembled collagen VI to either receptor. We also studied the collagen VI receptor NG2 (CSPG4) and confirmed that NG2 binds assembled collagen VI, but not cleaved C5/endotrophin. A cellular receptor for C5/endotrophin, therefore, still remains elusive.

•

ANTXR1 does not support collagen VI or C5/endotrophin binding to the cell surface

•

ANTXR2 does not support collagen VI or C5/endotrophin binding to the cell surface

•

NG2/CSPG4 supports collagen VI, but not C5/endotrophin binding to the cell surface

Collagen VI ablation in zebrafish causes neuromuscular defects during developmental and adult stages

Collagen VI (COL6) is an extracellular matrix protein exerting multiple functions in different tissues. In humans, mutations of COL6 genes cause rare inherited congenital disorders, primarily affecting skeletal muscles and collectively known as COL6-related myopathies, for which no cure is available yet. In order to get insights into the pathogenic mechanisms underlying COL6-related diseases, diverse animal models were produced. However, the roles exerted by COL6 during embryogenesis remain largely unknown. Here, we generated the first zebrafish COL6 knockout line through CRISPR/Cas9 site-specific mutagenesis of the col6a1 gene. Phenotypic characterization during embryonic and larval development revealed that lack of COL6 leads to neuromuscular defects and motor dysfunctions, together with distinctive alterations in the three-dimensional architecture of craniofacial cartilages. These phenotypic features were maintained in adult col6a1 null fish, which displayed defective muscle organization and impaired swimming capabilities. Moreover, col6a1 null fish showed autophagy defects and organelle abnormalities at both embryonic and adult stages, thus recapitulating the main features of patients affected by COL6-related myopathies. Mechanistically, lack of COL6 led to increased BMP signaling, and direct inhibition of BMP activity ameliorated the locomotor col6a1 null embryos. Finally performance of, treatment with salbutamol, a  β₂-adrenergic receptor agonist, elicited a significant amelioration of the neuromuscular and motility defects of col6a1 null fish embryos. Altogether, these findings indicate that this newly generated zebrafish col6a1 null line is a valuable in vivo tool to model COL6-related myopathies and suitable for drug screenings aimed at addressing the quest for effective therapeutic strategies for these disorders.

Tissue mechanics coevolves with fibrillar matrisomes in healthy and fibrotic tissues

Fibrillar proteins are principal components of extracellular matrix (ECM) that confer mechanical properties to tissues. Fibrosis can result from wound repair in nearly every tissue in adults, and it associates with increased ECM density and crosslinking as well as increased tissue stiffness. Such fibrotic tissues are a major biomedical challenge, and an emerging view posits that the altered mechanical environment supports both synthetic and contractile myofibroblasts in a state of persistent activation. Here, we review the matrisome in several fibrotic diseases, as well as normal tissues, with a focus on physicochemical properties. Stiffness generally increases with the abundance of fibrillar collagens, the major constituent of ECM, with similar mathematical trends for fibrosis as well as adult tissues from soft brain to stiff bone and heart development. Changes in expression of other core matrisome and matrisome-associated proteins or proteoglycans contribute to tissue stiffening in fibrosis by organizing collagen, crosslinking ECM, and facilitating adhesion of myofibroblasts. Understanding how ECM composition and mechanics coevolve during fibrosis can lead to better models and help with antifibrotic therapies.

The Capillary Morphogenesis Gene 2 Triggers the Intracellular Hallmarks of Collagen VI-Related Muscular Dystrophy

Collagen VI-related disorders (COL6-RD) represent a severe form of congenital disease for which there is no treatment. Dominant-negative pathogenic variants in the genes encoding α chains of collagen VI are the main cause of COL6-RD. Here we report that patient-derived fibroblasts carrying a common single nucleotide variant mutation are unable to build the extracellular collagen VI network. This correlates with the intracellular accumulation of endosomes and lysosomes triggered by the increased phosphorylation of the collagen VI receptor CMG2. Notably, using a CRISPR-Cas9 gene-editing tool to silence the dominant-negative mutation in patients’ cells, we rescued the normal extracellular collagen VI network, CMG2 phosphorylation levels, and the accumulation of endosomes and lysosomes. Our findings reveal an unanticipated role of CMG2 in regulating endosomal and lysosomal homeostasis and suggest that mutated collagen VI dysregulates the intracellular environment in fibroblasts in collagen VI-related muscular dystrophy.

Autosomal dominant Ullrich congenital muscular dystrophy due to a de novo mutation in COL6A3 gene. A case report

Mutations in the genes encoding collagen VI cause Bethlem myopathy (MIM 158810), Ullrich congenital muscular dystrophy (MIM 254090), and myosclerosis myopathy (MIM #255600). BM is a dominantly inherited disorder, characterised by proximal muscle weakness and joint contractures mainly involving the elbows, ankles, and fingers, which usually follows a relatively mild course. By contrast, UCMD is a severe muscular dystrophy characterized by early onset, rapidly progressive muscle wasting and weakness, proximal joint contractures and distal joint hyperlaxity. Rapid progression usually leads to early death due to respiratory failure. UCMD is usually inherited as an autosomal recessive trait though dominant de novo heterozygous variants have recently been reported. We describe a further patient with UCMD classical presentation who showed, at the NGS analysis, the de novo variant c.6210+1G > A in the intron 16 of the gene COL6A3, known in the literature as pathogenic (VCV0000949S6.5).

Screening Protein Prognostic Biomarkers for Stomach Adenocarcinoma Based on The Cancer Proteome Atlas

The objective was to construct a prognostic risk model of stomach adenocarcinoma (STAD) based on The Cancer Proteome Atlas (TCPA) to search for prognostic biomarkers. Protein data and clinical data on STAD were downloaded from the TCGA database, and differential expressions of proteins between carcinoma and para-carcinoma tissues were screened using the R package. The STAD data were randomly divided into a training set and a testing set in a 1:1 ratio. Subsequently, a linear prognostic risk model of proteins was constructed using Cox regression analysis based on training set data. Based on the scores of the prognostic model, sampled patients were categorized into two groups: a high-risk group and a low-risk group. Using the testing set and the full sample, ROC curves and K-M survival analysis were conducted to measure the predictive power of the prognostic model. The target genes of proteins in the prognostic model were predicted and their biological functions were analyzed. A total of 34 differentially expressed proteins were screened (19 up-regulated, 15 down-regulated). Based on 176 cases in the training set, a prognostic model consisting of three proteins (COLLAGEN VI, CD20, TIGAR) was constructed, with moderate prediction accuracy (AUC=0.719). As shown by the Kaplan-Meier and survival status charts, the overall survival rate of the low-risk group was better than that of the high-risk group. Moreover, a total of 48 target proteins were identified to have predictive power, and the level of proteins in hsa05200 (Pathways in cancer) was the highest. According to the results of the Univariate and multivariate COX analysis, tri-protein was identified as an independent prognostic factor. Therefore, the tri-protein prognostic risk model can be used to predict the likelihood of STAD and guide clinical treatment.

Single-nucleus cross-tissue molecular reference maps toward understanding disease gene function

Understanding gene function and regulation in homeostasis and disease requires knowledge of the cellular and tissue contexts in which genes are expressed. Here, we applied four single-nucleus RNA sequencing methods to eight diverse, archived, frozen tissue types from 16 donors and 25 samples, generating a cross-tissue atlas of 209,126 nuclei profiles, which we integrated across tissues, donors, and laboratory methods with a conditional variational autoencoder. Using the resulting cross-tissue atlas, we highlight shared and tissue-specific features of tissue-resident cell populations; identify cell types that might contribute to neuromuscular, metabolic, and immune components of monogenic diseases and the biological processes involved in their pathology; and determine cell types and gene modules that might underlie disease mechanisms for complex traits analyzed by genome-wide association studies.

P4HA1 Regulates CD31 via COL6A1 in the Transition of Glioblastoma Stem-Like Cells to Tumor Endothelioid Cells

Glioblastoma multiforme (GBM) is a common intracranial malignancy characterized by abundant and aberrant vasculature. The efficiency of existing antivascular treatments remains unsatisfactory. The transition of glioblastoma stem-like cells (GSCs) into tumor endothelioid cells (ECs) has been thought to cause glioma neovascularization and anti-angiogenesis tolerance, but the mechanisms regulating glioma transdifferentiation remains unclear. Our previous study found that P4HA1 regulates GSCs vascular mimicry in a hypoxic microenvironment, but the detailed molecular mechanism has not been determined. In this study, candidate protein COL6A1 was screened by mass spectrometry. In vitro experiments show that P4HA1 regulates the expression of CD31 via COL6A1, with the levels of expression of P4HA1, COL6A1 and the vascular endothelial molecular markers CD31 showing positive correlations in vivo assay. Altering the expression of P4HA1 in GSCs altered the expression of COL6A1 and CD31, thereby inducing glioma angiogenesis. In conclusion, this study revealed that the P4HA1/COL6A1 axis modulates the transdifferentiation process of GSCs into ECs. Interrupting this signaling axis can inhibit glioma angiogenesis, suggesting that this axis may be a novel target for antivascular therapy in patients with glioma.

CRISPR/Cas9-Mediated Allele-Specific Disruption of a Dominant COL6A1 Pathogenic Variant Improves Collagen VI Network in Patient Fibroblasts

Collagen VI-related disorders are the second most common congenital muscular dystrophies for which no treatments are presently available. They are mostly caused by dominant-negative pathogenic variants in the genes encoding α chains of collagen VI, a heteromeric network forming collagen; for example, the c.877G>A; p.Gly293Arg COL6A1 variant, which alters the proper association of the tetramers to form microfibrils. We tested the potential of CRISPR/Cas9-based genome editing to silence or correct (using a donor template) a mutant allele in the dermal fibroblasts of four individuals bearing the c.877G>A pathogenic variant. Evaluation of gene-edited cells by next-generation sequencing revealed that correction of the mutant allele by homologous-directed repair occurred at a frequency lower than 1%. However, the presence of frameshift variants and others that provoked the silencing of the mutant allele were found in >40% of reads, with no effects on the wild-type allele. This was confirmed by droplet digital PCR with allele-specific probes, which revealed a reduction in the expression of the mutant allele. Finally, immunofluorescence analyses revealed a recovery in the collagen VI extracellular matrix. In summary, we demonstrate that CRISPR/Cas9 gene-edition can specifically reverse the pathogenic effects of a dominant negative variant in COL6A1.

Temporal changes in the muscle extracellular matrix due to volumetric muscle loss injury

PURPOSE/AIM

Volumetric muscle loss (VML) is a devastating orthopedic injury resulting in chronic persistent functional deficits, loss of joint range of motion, pathologic fibrotic deposition and lifelong disability. However, there is only limited mechanistic understanding of VML-induced fibrosis. Herein we examined the temporal changes in the fibrotic deposition at 3, 7, 14, 28, and 48 days post-VML injury.

MATERIALS AND METHODS

Adult male Lewis rats (n = 39) underwent a full thickness ~20% (~85 mg) VML injury to the tibialis anterior (TA) muscle unilaterally, the contralateral TA muscle served as the control group. All TA muscles were harvested for biochemical and histologic evaluation.

RESULTS

The ratio of collagen I/III was decreased at 3, 7, and 14 days post-VML, but significantly increased at 48 days. Decorin content followed an opposite trend, significantly increasing by day 3 before dropping to below control levels by 48 days. Histological evaluation of the defect area indicates a shift from loosely packed collagen at early time points post-VML, to a densely packed fibrotic scar by 48 days.

CONCLUSIONS

The shift from early wound healing efforts to a fibrotic scar with densely packed collagen within the skeletal muscle occurs around 21 days after VML injury through dogmatic synchronous reduction of collagen III and increase in collagen I. Thus, there appears to be an early window for therapeutic intervention to prevent pathologic fibrous tissue formation, potentially by targeting CCN2/CTGF or using decorin as a therapeutic.

Atypical keratosis pilaris-like lesions in a patient with Bethlem myopathy

Bethlem myopathy is a collagen VI-related myopathy. Collagen VI is primarily not only associated with the extracellular matrix of skeletal muscle, but is also found in the skin, blood vessels, and other organs. Dermatologic findings described for Bethlem myopathy include follicular hyperkeratosis and abnormal scar formation, although clinical and histopathologic photographs remain elusive in the literature. We present a case of atypical keratosis pilaris-like follicular lesions in a patient with Bethlem myopathy and provide histopathologic correlation to better characterize the development of skin lesions in this rare neuromuscular disease.

Clinical manifestations and prenatal diagnosis of Ullrich congenital muscular dystrophy: A case report

BACKGROUND

Ullrich congenital muscular dystrophy (UCMD) is one of the collagen-VI-related myopathies caused by mutations of COL6A1, COL6A2, and COL6A3 genes. Affected individuals are characterized by muscle weakness, proximal joint contracture, distal joint hyperlaxity, and progressive respiratory failure. There is currently no cure for UCMD. Here, we report the clinical manifestations and prenatal diagnosis of compound heterozygous mutations of the COL6A2 gene in a Chinese family with UCMD.

CASE SUMMARY

A 3-year-old boy, his 4-year-old brother, their parents, and a 20-wk-old fetus in the mother’s womb were included in the study. The brothers had the typical manifestations of the early-severe subtype: A delayed motor milestone (never walking independently), torticollis, scoliosis, proximal joint contracture, distal joint hyperextension, right hip joint dislocation, and calcaneal protuberance. Both brothers were found by whole-exome sequencing and Sanger sequencing to carry two mutations of the COL6A2 gene (c.1353_c.1354insC, p.Arg453ProfsTer42/c.2105G>A, p.Trp702Ter). The absence of collagen VI staining in the younger brother’s muscle was identified accurately. Genetic counseling and prenatal diagnosis were crucial for the family, as the autosomal recessive genetic disease affected a quarter of the patient’s siblings. The fetus of the mother’s third child underwent prenatal diagnosis and carried the same two mutations of COL6A2, confirmed in the amniotic fluid by multiplex ligation-dependent probe amplification and short tandem repeats. After a painful psychological struggle, the parents finally decided to terminate the pregnancy.

CONCLUSION

We report a Chinese family suffering from UCMD. By clarifying the COL6A2 mutations in the probands, the parents had the opportunity to opt for voluntary interruption of the third UCMD pregnancy.

[JAG2-related muscular dystrophy: When differential diagnosis matters]

JAG2 has recently been involved in autosomal recessive forms of muscular dystrophy as illustrated in this clinical vignette. In many ways, this disease can mimick a COL6-related retractile myopathy including at the imaging level.

Collagen VI Muscle Disorders: Mutation Types, Pathogenic Mechanisms and Approaches to Therapy

Mutations in the genes encoding the major collagen VI isoform, COL6A1, COL6A2 and COL6A3, are responsible for the muscle disorders Bethlem myopathy and Ullrich congenital muscular dystrophy. These disorders form a disease spectrum from mild to severe. Dominant and recessive mutations are found along the entire spectrum and the clinical phenotype is strongly influenced by the way mutations impede collagen VI protein assembly. Most mutations are in the triple helical domain, towards the N-terminus and they compromise microfibril assembly. Some mutations are found outside the helix in the C- and N-terminal globular domains, but because these regions are highly polymorphic it is difficult to discriminate mutations from rare benign changes without detailed structural and functional studies. Collagen VI deficiency leads to mitochondrial dysfunction, deficient autophagy and increased apoptosis. Therapies that target these consequences have been tested in mouse models and some have shown modest efficacy in small human trials. Antisense therapies for a common mutation that introduces a pseudoexon show promise in cell culture but haven't yet been tested in an animal model. Future therapeutic approaches await new research into how collagen VI deficiency signals downstream consequences.

Transcriptome analysis of collagen VI-related muscular dystrophy muscle biopsies

Objective

To define the transcriptomic changes responsible for the histologic alterations in skeletal muscle and their progression in collagen VI‐related muscular dystrophy (COL6‐RD).

Methods

COL6‐RD patient muscle biopsies were stratified into three groups based on the overall level of pathologic severity considering degrees of fibrosis, muscle fiber atrophy, and fatty replacement of muscle tissue. Using microarray and RNA‐Seq, we then performed global gene expression profiling on the same muscle biopsies and compared their transcriptome with age‐ and sex‐matched controls.

Results

COL6‐RD muscle biopsy transcriptomes as a group revealed prominent upregulation of muscle extracellular matrix component genes and the downregulation of skeletal muscle and mitochondrion‐specific genes. Upregulation of the TGFβ pathway was the most conspicuous change across all biopsies and was fully evident even in the mildest/earliest histological group. There was no difference in the overall transcriptional signature between the different histologic groups but polyserial analysis identified relative changes along with COL6‐RD histological severity.

Interpretation

Overall, our study establishes the prominent dysregulation of extracellular matrix genes, TGFβ signaling, and its downstream cellular pathways at the transcriptomic level in COL6‐RD muscle.

Ablation of Collagen VI leads to the release of platelets with altered function

Megakaryocytes express collagen VI that regulates the release of functional platelets.

Collagen VI–null megakaryocytes and platelets display increased mTOR signaling and store-operated calcium entry.

Hemostatic abnormalities and impaired platelet function have been described in patients affected by connective tissue disorders. We observed a moderate bleeding tendency in patients affected by collagen VI–related disorders and investigated the defects in platelet functionality, whose mechanisms are unknown. We demonstrated that megakaryocytes express collagen VI that is involved in the regulation of functional platelet production. By exploiting a collagen VI–null mouse model (Col6a1^−/−), we found that collagen VI–null platelets display significantly increased susceptibility to activation and intracellular calcium signaling. Col6a1^−/− megakaryocytes and platelets showed increased expression of stromal interaction molecule 1 (STIM1) and ORAI1, the components of store-operated calcium entry (SOCE), and activation of the mammalian target of rapamycin (mTOR) signaling pathway. In vivo mTOR inhibition by rapamycin reduced STIM1 and ORAI1 expression and calcium flows, resulting in a normalization of platelet susceptibility to activation. These defects were cell autonomous, because transplantation of lineage-negative bone marrow cells from Col6a1^−/− mice into lethally irradiated wild-type animals showed the same alteration in SOCE and platelet activation seen in Col6a1^−/− mice. Peripheral blood platelets of patients affected by collagen VI–related diseases, Bethlem myopathy and Ullrich congenital muscular dystrophy, displayed increased expression of STIM1 and ORAI1 and were more prone to activation. Altogether, these data demonstrate the importance of collagen VI in the production of functional platelets by megakaryocytes in mouse models and in collagen VI–related diseases.

Alpha-single chains of collagen type VI inhibit the fibrogenic effects of triple helical collagen VI in hepatic stellate cells

The interaction of extracellular matrix (ECM) components with hepatic stellate cells (HSCs) is thought to perpetuate fibrosis by stimulating signaling pathways that drive HSC activation, survival and proliferation. Consequently, disrupting the interaction between ECM and HSCs is considered a therapeutical avenue although respective targets and underlying mechanisms remain to be established. Here we have interrogated the interaction between type VI collagen (CVI) and HSCs based on the observation that CVI is 10-fold upregulated during fibrosis, closely associates with HSCs in vivo and promotes cell proliferation and cell survival in cancer cell lines. We exposed primary rat HSCs and a rat hepatic stellate cell line (CFSC) to soluble CVI and determined the rate of proliferation, apoptosis and fibrogenesis in the absence of any additional growth factors. We find that CVI in nanomolar concentrations prevents serum starvation-induced apoptosis. This potent anti-apoptotic effect is accompanied by induction of proliferation and acquisition of a pronounced pro-fibrogenic phenotype characterized by increased α-smooth muscle actin, TGF-β, collagen type I and TIMP-1 expression and diminished proteolytic MMP-13 expression. The CVI-HSC interaction can be disrupted with the monomeric α2(VI) and α3(VI) chains and abrogates the activating CVI effects. Further, functional relevant α3(VI)—derived 30 amino acid peptides lead to near-complete inhibition of the CVI effect. In conclusion, CVI serves as a potent mitogen and activating factor for HSCs. The antagonistic effects of the CVI monomeric chains and peptides point to linear peptide sequences that prevent activation of CVI receptors which may allow a targeted antifibrotic therapy.