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

Identifying Hub Genes and Metabolic Pathways in Collagen VI-Related Dystrophies: A Roadmap to Therapeutic Intervention

Collagen VI-related dystrophies (COL6RD) are a group of rare muscle disorders caused by mutations in specific genes responsible for type VI collagen production. It affects muscles, joints, and connective tissues, leading to weakness, joint problems, and structural issues. Currently, there is no effective treatment for COL6RD; its management typically addresses symptoms and complications. Therefore, it is essential to decipher the disease's molecular mechanisms, identify drug targets, and develop effective treatment strategies to treat COL6RD. In this study, we employed differential gene expression analysis, weighted gene co-expression network analysis, and genome-scale metabolic modeling to investigate gene expression patterns in COL6RD patients, uncovering key genes, significant metabolites, and disease-related pathophysiological pathways. First, we performed differential gene expression and weighted gene co-expression network analyses, which led to the identification of 12 genes (CHCHD10, MRPS24, TRIP10, RNF123, MRPS15, NDUFB4, COX10, FUNDC2, MDH2, RPL3L, NDUFB11, PARVB) as potential hub genes involved in the disease. Second, we utilized a drug repurposing strategy to identify pharmaceutical candidates that could potentially modulate these genes and be effective in the treatment. Next, we utilized context-specific genome-scale metabolic models to compare metabolic variations between healthy individuals and COL6RD patients. Finally, we conducted reporter metabolite analysis to identify reporter metabolites (e.g., phosphatidates, nicotinate ribonucleotide, ubiquinol, ferricytochrome C). In summary, our analysis revealed critical genes and pathways associated with COL6RD and identified potential targets, reporter metabolites, and candidate drugs for therapeutic interventions.

Endotrophin, a Key Marker and Driver for Fibroinflammatory Disease

Our overview covers several key areas related to recent results obtained for collagen type VI and endotrophin (ETP). (1) An introduction to the history of ETP, including how it was identified, how it is released, and its function and potential receptors. (2) An introduction to the collagen family, with a focus on what differentiates collagen type VI from an evolutionary standpoint. (3) An overview of collagen type VI, the 6 individual chains (COL6A1, A2, A3, A4, A5, and A6), their differences and similarities, as well as their expression profiles and function. (4) A detailed analysis of COL6A3, including the cleaved product endotrophin, and what separates it from the other 5 collagen 6 molecules, including its suggested function based on insights gained from knockout and gain of function mouse models. (5) The pathology of ETP. What leads to its presence and release and what are the consequences thereof? (6) Functional implications of circulating ETP. Here we review the data with the functional roles of ETP in mind. (7) We propose that ETP is a mediator for fibrotic (or fibroinflammatory) disorders. Based on what we know about ETP, we have to consider it as a target for the treatment of fibrotic (or fibroinflammatory) disorders. What segment(s) of the patient population would most dramatically respond to an ETP-targeted intervention? How can we find the population that would profit most from an intervention? We aim to present a broad overview over the ETP field at large, providing an assessment of where the future research efforts need to be placed to tap into the vast potential of ETP, both as a marker and as a target in different diseases.

The UCMD-Causing COL6A1 (c.930 + 189C > 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 + 189C > 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 + 189C > T) mutation.

Anästhesie bei einer thoraxchirurgischen Patientin mit kongenitaler Muskeldystrophie Typ Ullrich

Die kongenitale Muskeldystrophie Typ Ullrich (UCMD) ist eine seltene Erkrankung. Weltweit wurden bislang 50 Fälle genetisch gesichert. Autosomal-dominante und rezessive Mutationen des COL6A1/COL6A2 im Chromosom 21q22.3 oder des COL6A3 im Chromosom 2q37.3 führen zu einem Mangel an Kollagen VI. Typische Merkmale der UCMD sind Muskelschwäche von Körperstamm und Extremitäten, Hyperflexibilität der distalen und Kontrakturen der proximalen Gelenke, Rollstuhlpflichtigkeit im Alter von 9 bis 11 Jahren, Versteifung und Skoliose der Wirbelsäule und eine progrediente restriktive Ventilationsstörung. Etwa 50 % der Kinder benötigen im Alter von 11 bis 12 Jahren eine nichtinvasive Ventilation (NIV), wozu auch eine gestörte Funktion des Diaphragmas beiträgt. Es wird über die Narkose bei einer 21-jährigen Patientin mit einer UCMD berichtet, die seit dem 6. Lebensjahr rollstuhlpflichtig war und bei der seit 2018 eine lebenserhaltene NIV erfolgte. Wegen einer subpleuralen Einblutung in den linken Lungenunterlappen nach Entlastung eines Pneumothorax wurde eine videoassistierte thorakoskopische Chirurgie (VATS) vorgenommen. Die spezifischen Anforderungen durch die UCMD, das Atemwegsmanagement für die Einlungenventilation sowie Aspekte zur Auswahl der Anästhetika werden diskutiert. Nach erfolgreicher VATS konnte die Patientin am 7. postoperativen Tag in die Häuslichkeit entlassen werden.

Oxidative Stress, Inflammation and Connexin Hemichannels in Muscular Dystrophies

Muscular dystrophies (MDs) are a heterogeneous group of congenital neuromuscular disorders whose clinical signs include myalgia, skeletal muscle weakness, hypotonia, and atrophy that leads to progressive muscle disability and loss of ambulation. MDs can also affect cardiac and respiratory muscles, impairing life-expectancy. MDs in clude Duchenne muscular dystrophy, Emery-Dreifuss muscular dystrophy, facioscapulohumeral muscular dystrophy and limb-girdle muscular dystrophy. These and other MDs are caused by mutations in genes that encode proteins responsible for the structure and function of skeletal muscles, such as components of the dystrophin-glycoprotein-complex that connect the sarcomeric-actin with the extracellular matrix, allowing contractile force transmission and providing stability during muscle contraction. Consequently, in dystrophic conditions in which such proteins are affected, muscle integrity is disrupted, leading to local inflammatory responses, oxidative stress, Ca²⁺-dyshomeostasis and muscle degeneration. In this scenario, dysregulation of connexin hemichannels seem to be an early disruptor of the homeostasis that further plays a relevant role in these processes. The interaction between all these elements constitutes a positive feedback loop that contributes to the worsening of the diseases. Thus, we discuss here the interplay between inflammation, oxidative stress and connexin hemichannels in the progression of MDs and their potential as therapeutic targets.