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Browsing by Subject "transkriptiotekijät"

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  • Pohjolainen, Lotta (2017)
    Left ventricular hypertrophy (LVH) is defined as an increase in left ventricular mass. It is initially a coping mechanism by which the heart tries to compensate for the increase in load caused by, for example, hypertension, but it will eventually lead to heart failure. LVH is the result of primarily an increase in cardiac myocyte size, in addition to increased apoptosis and necrosis of cardiac myocytes and fibrosis. Current treatment of LVH is based on a treatment of suspected cause, generally hypertension. Antihypertensive medication has been found to have beneficial effects on LVH. However, antihypertensive drugs can not cure LVH completely, hence other treatment options are needed. To identify new possible drug targets, it is important to increase the inadequate knowledge of the mechanisms and signal transduction pathways mediating LVH. The most relevant stimuli causing hypertrophy are considered to be mechanical stretch, as well as some humoral mediators such as angiotensin II and endothelin 1 (ET-1), to which cardiomyocytes respond through activation of several intracellular signal transduction pathways. As a result, cardiomyocyte gene expression and protein synthesis increase and sarcomeres grow and rearrange, resulting in an increase in cell size. In addition, regulation of calcium, contractile function and energy metabolism of cardiac myocytes change. Numerous intracellular signal mediators interact with each other and can compensate for each other, making it difficult to investigate the significance of individual factors. As important signal mediators are considered to include protein kinase C (PKC) and cardiac transcription factors GATA4 and NKX2-5. In vitro studies of cardiac hypertrophy are usually performed with primary cardiac myocytes isolated from the ventricles of neonatal rats. The H9c2 continuous cell line has been used in some studies as an alternative cell model to reduce the use of laboratory animals. In the experimental part of this thesis, the suitability of H9c2 cells for hypertrophy studies was examined by comparing them to primary cardiac myocytes. In addition, experimental compounds targeted to cardiac transcription factors and PKC were studied by exploring their effects on viability and hypertrophic responses of H9c2 cells and primary cardiac myocytes. The toxicity of the compounds and the effects on cell viability were studied using the lactate dehydrogenase (LDH) assay and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The hypertrophy responses to cyclic mechanical stretch and ET-1 were primarily assessed by measuring the surface area of cells from fluorescence microscopy images. In addition, the relative expression levels of Nppa and Nppb genes in ET-1 stimulated primary cardiac myocytes were studied by quantitative polymerase chain reaction (qPCR). Both stretching and ET-1 caused an increase in the cell surface area in primary cardiac myocytes but not in H9c2 cells. On this basis, the H9c2 cells respond differently to hypertrophic stimuli than primary cardiac myocytes, and the suitability of H9c2 cell line to hypertrophy studies can therefore be questioned. The compounds targeted to cardiac transcription factors were not cytotoxic at 1-30 µM concentrations, but they also had no significant effect on the hypertrophic responses. In contrast, the PKC compound HMI-1a3 at 30 µM was toxic to primary cardiac myocytes and HMI-1b11 at 30 µM was toxic to H9c2 cells. HMI-1b11 and bryostatin-1 also induced changes in the hypertrophic responses of primary cardiac myocytes, but the significance of these results requires further investigation.