Résumé :
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Muscle responds to a wide variety of stressors by hypertrophic growth of myocytes. In various muscular disorders, this hypertrophic response may temporarily serve a compensatory role but becomes detrimental when prohypertrophic stimulation persists. As such, cardiac hypertrophy has been identified as a risk factor for impaired cardiac function, future heart failure and life threatening arrhythmias.Recently, several microRNAs (miRNAs) have been implicated in muscle disorders and in particularly in cardiac hypertrophy and failure. MiRNAs interact specifically with mRNAs by repressing their translation or inducing their degradation. They are thus, by their impact on gene expression, key factors in the development and maintenance of tissue, both in health and disease states. The majority of experiments have focussed on miRNAs whose cellular levels change under disease-causing conditions, based on the assumption that disease relevance and deregulation are tightly linked. In particular, hypertrophied cardiac cells or tissue have repeatedly been used as a source for microarray analyses and led to the identification of several miRNAs as potential disease modulators. A few of these miRNAs have been further characterized by experimentally induced alteration of their cellular concentration, and were thereby shown to either elicit or to prevent disease. We have identified miR-21 as the strongest upregulated microRNA in myocardial disease. We show that miR-21 regulates the ERKMAPkinase signalling pathway in cardiac fibroblasts, which impacts on global cardiac structure and function.However, focussing on the most strongly expressed and de-regulated miRNAs risks to neglect other disease-relevant miRNAs. This may be one reason why only few of the hundreds of miRNAs have so far been functionally characterized in the cardiovascular system. Taking these arguments into account, assays are highly desired that allow for a direct correlation of miRNAs with cellular effects, at best in an automated set-up that screens multiple miRNAs in parallel. A HCS technique designed to screen miRNA libraries for cellular effects has hitherto not been established in primary cells of the cardiovascular system. We have established a high content screening assay in neonatal rat cardiomyocytes (NRCM) and used this approach to identify hypertrophy-inducing miRNAs.
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