BackgroundInvestigations into both the pathophysiology and therapeutic targets in muscle dystrophies have been hampered by the limited proliferative capacity of human myoblasts. Isolation of reliable and stable immortalized cell lines from patient biopsies is a powerful tool for investigating pathological mechanisms, including those associated with muscle aging, and for developing innovative gene-based, cell-based or pharmacological biotherapies.MethodsUsing transduction with both telomerase-expressing and cyclin-dependent kinase 4-expressing vectors, we were able to generate a battery of immortalized human muscle stem-cell lines from patients with various neuromuscular disorders.ResultsThe immortalized human cell lines from patients with Duchenne muscular dystrophy, facioscapulohumeral muscular dystrophy, oculopharyngeal muscular dystrophy, congenital muscular dystrophy, and limb-girdle muscular dystrophy type 2B had greatly increased proliferative capacity, and maintained their potential to differentiate both in vitro and in vivo after transplantation into regenerating muscle of immunodeficient mice.ConclusionsDystrophic cellular models are required as a supplement to animal models to assess cellular mechanisms, such as signaling defects, or to perform high-throughput screening for therapeutic molecules. These investigations have been conducted for many years on cells derived from animals, and would greatly benefit from having human cell models with prolonged proliferative capacity. Furthermore, the possibility to assess in vivo the regenerative capacity of these cells extends their potential use. The innovative cellular tools derived from several different neuromuscular diseases as described in this report will allow investigation of the pathophysiology of these disorders and assessment of new therapeutic strategies.
Hypoglycosylation of α-dystroglycan underpins a subgroup of muscular dystrophies ranging from congenital onset of weakness, severe brain malformations and death in the perinatal period to mild weakness in adulthood without brain involvement. Mutations in 6 genes have been identified in a proportion of patients. POMT1, POMT2 and POMGnT1 encode for glycosyltransferases involved in the mannosylation of α-dystroglycan but the function of fukutin, FKRP and LARGE is less clear. The pathological hallmark is reduced immunolabelling of skeletal muscle with antibodies recognising glycosylated epitopes on α-dystroglycan. If the common pathway of these conditions is the hypoglycosyation of α-dystroglycan, one would expect a correlation between clinical severity and the extent of hypoglycosylation. By studying 24 patients with mutations in these genes, we found a good correlation between reduced α-dystroglycan staining and clinical course in patients with mutations in POMT1, POMT2 and POMGnT1. However this was not always the case in patients with defects in fukutin and FKRP, as we identified patients with mild limb girdle phenotypes without brain involvement with profound depletion of α-dystroglycan.
Antisense oligomer induced exon skipping is showing promise as a therapy to reduce the severity of Duchenne Muscular Dystrophy. To date, the focus has been on excluding single exons flanking frame-shifting deletions in the dystrophin gene, however, a third of all Duchenne Muscular Dystrophy causing mutations are more subtle DNA changes. Forty-five dystrophin exons are potentially frame-shifting and mutations in these will require the targeted removal of exon blocks to generate in-frame transcripts. We report that clustered non-deletion mutations in the dystrophin gene respond differently to different antisense oligomer preparations targeting the same dual exon block, the removal of which bypasses the mutation and restores the open reading-frame. The personalized nature of the responses to antisense oligomer application presents additional challenges to the induction of multi-exon skipping with a single oligomer preparation.
Mutations in COL6A1, COL6A2 and COL6A3 genes result in collagen VI myopathies: Ullrich congenital muscular dystrophy (UCMD), Bethlem myopathy (BM) and intermediate phenotypes. At present, none of the existing diagnostic techniques for evaluating collagen VI expression is quantitative, and the detection of subtle changes in collagen VI expression remains challenging.We investigated flow cytometry analysis as a means of quantitatively measuring collagen VI in primary fibroblasts and compared this method with the standard method of fibroblast collagen VI immunohistochemical analysis. Eight UCMD and five BM molecularly confirmed patients were studied and compared to five controls.Flow cytometry analysis consistently detected a reduction of collagen VI of at least 60% in all UCMD cases. In BM cases the levels of collagen VI were variable but on average 20% less than controls.Flow cytometry analysis provides an alternative method for screening for collagen VI deficiency at the protein level in a quantitative, time and cost-effective manner.
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