Regulation des CREB-Koaktivators TORC durch β-adrenerge Signale in isolierten neonatalen Rattenkardiomyozyten

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TORC (transducers of regulated CREB) describes a family of transcriptional cofactors, which regulates the activation of several transcription factors in dependence on cAMP. TORC is dephosphorylated and thus activated by β-adrenergic-induced increases in cAMP and subsequent PKA and calcineurin activation. Dephosphorylated TORC translocates into the nucleus where it contributes to the CREB-dependent gene transcription. Its function and regulation has so far been demonstrated in different tissue cells. The aim of this thesis was to determine the function, activation and cellular localisation of TORC in the heart and to investigate its involvement on the pathogenesis of cardiac hypertrophy. In order to investigate whether TORC plays a role in the pathogenesis of maladaptive hypertrophy, heart tissue samples from patients with inherited and acquired myocardial heart diseases were compared to the subcellular localization of TORC1 and TORC3 using immunhistochemistry. Investigations of TORC1 and TORC3 on human hypertrophic heart tissue samples showed that TORC1 expression in the cell nucleus and cytosol is relatively stronger in acquired cardiac hypertrophy than in inherited hypertrophy, which indicates that TORC has a relevance for the pathogenesis of pathological cardiac hypertrophy. It is assumed that pathological myocardial hypertrophy is associated with an increased β1-adrenergic receptor stimulation. On the basis of publications showing that TORC is activated by cAMP signals, it was investigated whether TORC1 in cardiomyocytes can also be activated by activation of the β-adrenergic receptor. A model consisting of neonatal rat cardiomyocytes was used for this study. By treating the cardiomyocytes with the β-adrenoceptor agonist isoprenaline, the alteration of the activity state of TORC1 by a cAMP-dependent signaling pathway was investigated. The effect of isoprenaline on phosphorylated TORC1 in relation to the total amount of TORC1 was investigated in concentration-response and time-response curves and compared with the ratio of the untreated control. The state of phosphorylation, and hence the state of activity, of TORC1 was detected in the immunoblot using phosphorylation-specific antibodies. These investigations did not reveal any reproducible changes in the phosphorylation state of the TORC1-P/TORC1 ratio compared to the control, so that it could not be demonstrated that TORC1 is involved in the signal cascade of the β-adrenergic receptor. As a possible target gene of TORC1, the expression of the PGC1α mRNA was investigated using real-time PCR. However, the results of the PGC1α mRNA expression were not correlated with the TORC1 protein data.