Duchenne muscular dystrophy (DMD) is the most prevalent neuromuscular disorder, caused by mutations in the DMD gene that prevent synthesis of dystrophin. Fibers that lack dystrophin are sensitive... Show moreDuchenne muscular dystrophy (DMD) is the most prevalent neuromuscular disorder, caused by mutations in the DMD gene that prevent synthesis of dystrophin. Fibers that lack dystrophin are sensitive to exercise-induced damage, resulting in progressive muscle wasting, loss of ambulation and premature death. There is no cure, but several therapeutic approaches are clinically tested. At best, these clinical interventions result in the expression of low dystrophin levels. Fortunately, expression of wild type levels is not needed, as both humans and mice expressing ~50% of dystrophin do not show pathology. Detailed studies on which dystrophin levels are needed to prevent pathology and improve muscle function have been performed in this thesis. After the set-up of good outcome measures and serum biomarkers to monitor disease progression, two new innovative mouse models expressing low levels of dystrophin based on skewed X-inactivation were generated. In the mdx-Xist__hs model we observed that <15% dystrophin already improved muscle performance, while histopathology was largely with >15% dystrophin. To protect muscles from exercise-induced damage >22% dystrophin was needed. Dystrophin levels between 3-21% prevent the development of dilated cardiomyopathy in 10 months old mice. Mice lacking both dystrophin and its homologue utrophin, mimic the human phenotype and die before the age of 12 weeks. In these mice, <10% dystrophin improved life expectancy and muscle function while >10% dystrophin was needed to improve histopathology. These findings are encouraging for ongoing and future clinical trails. Show less
Injection of (stem) cells into the damaged heart has a positive effect on cardiac function. In this thesis two strategies for improving myocardial regeneration over classical cell therapy were... Show moreInjection of (stem) cells into the damaged heart has a positive effect on cardiac function. In this thesis two strategies for improving myocardial regeneration over classical cell therapy were investigated. The first is to induce cardiomyogenic differentiation by genetically engineering cells to express the transcription factor myocardin (a regulator of cardiomyocyte differentiation). We found that overexpression of myocardin induces a large part of the cardiac muscle gene expression program in various non-muscle cells. Forced expression of myocardin enables cardiac infarction scar fibroblasts to conduct a cardiac action potential, and injection of myocardin-transduced MSCs resulted in greater preservation of cardiac function and reduced detrimental remodeling compared to untreated MSCs in a mouse model of myocardial infarction. Indicating that overexpression of myocardin endows cells with several beneficial properties of cardiomyocytes. We hypothesized that myocardial regeneration might be enhanced by including novel cell types with supportive functions in cell therapy strategies. We found that the mesothelial cells of the human epicardium, like embryonic epicardium-derived cells (EPDCs) can form fibroblasts and smooth muscle cells. Indicating that EPDCs from human adults recapitulate at least part of the differentiation potential of their embryonic counterparts, which form various essential supportive cell types during heart development. Show less
