Collagen VI is an essential component of the extracellular matrix (ECM) composed by α1, α2 and α3 chains and encoded by COL6A1, COL6A2 and COL6A3 genes. Dominant negative pathogenic variants in COL6A genes result in defects in collagen VI protein and are implicated in the pathogenesis of muscular diseases, including Ullrich congenital muscular dystrophy (UCMD). Here, we designed a CRISPR genome editing strategy to tackle a dominant heterozygous deletion c.824_838del in exon 9 of the COL6A1 gene, causing a lack of secreted collagen VI in a patient’s dermal fibroblasts. The evaluation of efficiency and specificity of gene editing in treating patient’s fibroblasts revealed the 32% efficiency of editing the mutated allele but negligible editing of the wild-type allele. CRISPR-treated UCMD skin fibroblasts rescued the secretion of collagen VI in the ECM, which restored the ultrastructure of the collagen VI microfibril network. By using normal melanocytes as surrogates of muscle cells, we found that collagen VI secreted by the corrected patient’s skin fibroblasts recovered the anchorage to the cell surface, pointing to a functional improvement of the protein properties. These results support the application of the CRISPR editing approach to knock out COL6A1 mutated alleles and rescue the UCMD phenotype in patient-derived fibroblasts.

Emery–Dreifuss muscular dystrophy (EDMD) is caused by mutations in EMD, LMNA, SYNE1, SYNE2, and other related genes. The disease is characterized by joint contractures, muscle weakening and wasting, and heart conduction defects associated with dilated cardiomyopathy. Previous studies demonstrated the activation of fibrogenic molecules such as TGFbeta 2 and CTGF in preclinical models of EDMD2 and increased secretion of TGFbeta 2 in patient serum. A wide screening of patient cells suggested fibrosis, metabolism, and myogenic signaling as the most affected pathways in various EDMD forms. In this study, we show that alpha-smooth muscle actin-positive myofibroblasts are overrepresented in patient fibroblast cultures carrying EMD, LMNA, or SYNE2 mutations, and profibrotic miRNA-21 is upregulated. Upon CRISPR/Cas correction of the mutated EMD or LMNA sequence in EDMD1 or EDMD2 fibroblasts, respectively, we observe a reduced expression of fibrogenic molecules. However, in patient myoblasts, neither fibrogenic proteins nor miRNA-21 were upregulated; instead, miRNA-21-5p was downregulated along with muscle-specific miRNA-133b and miRNA-206, which have a crucial role in muscle cell homeostasis. These observations suggest that the conversion of laminopathic fibroblasts into a profibrotic phenotype is a determinant of EDMD-associated muscle fibrosis, while miRNA-206-dependent defects of laminopathic myoblasts, including altered regulation of VEGF levels, contribute to muscle cell deterioration. Notably, our study provides a proof-of-principle for the application of gene correction to EDMD1 and EDMD2 and presents EDMD1 isogenic cells that exhibit an almost complete rescue of a disease-specific miRNA signature. These cells can be used as experimental models for studying muscular laminopathies.