Die weltweite Zunahme der Prävalenz von Übergewicht und Adipositas und den damit verbundenen medizinischen und sozioökonomischen Herausforderungen stellt eine der wesentlichen Herausforderungen der modernen medizinischen Versorgung dar. Im Mittelpunkt stehen dabei insbesondere die Auswirkungen von Übergewicht und Adipositas auf das kardiovaskuläre System und den damit verbundenen funktionellen und strukturellen Veränderungen der kardiovaskulären Funktion. Als Mediatoren dieser funktionellen und strukturellen Veränderungen stehen dabei zunehmend Adipozytokine im Interesse wissenschaftlicher Arbeiten. Unter Adipozytokinen versteht man in diesem Zusammenhang einen Sammelbegriff für von Adipozyten und anderen Fettgewebszellen sezernierten autokrin-, endokrin- und parakrin wirkenden bioaktiven Molekülen. Insbesondere bei Übergewicht und Adipositas kommt es zu einer charakteristischen Veränderung im Sekretionsmuster dieser Adipozytokine. Die Wirkung einzelner Adipozytokine auf die kardiovaskuläre Funktion wurde in den letzten Jahren intensiv untersucht, über die Wirkung ganzer Adipozytokinprofile ist bisher jedoch nur wenig bekannt. Ziel der vorliegenden Arbeit war es zu klären, welchen Einfluss eine 24-stündige Behandlung von neonatalen ventrikulären Kardiomyozyten mit einem physiologischen Adipozytokin-Profil auf Hypertrophie-assoziierte Signalwege und Zellproteine hat.

Die weltweite Zunahme der Prävalenz von Übergewicht und Adipositas und den damit verbundenen medizinischen und sozioökonomischen Herausforderungen stellt eine der wesentlichen Herausforderungen der modernen medizinischen Versorgung dar. Im Mittelpunkt stehen dabei insbesondere die Auswirkungen von Übergewicht und Adipositas auf das kardiovaskuläre System und den damit verbundenen funktionellen und strukturellen Veränderungen der kardiovaskulären Funktion. Als Mediatoren dieser funktionellen und strukturellen Veränderungen stehen dabei zunehmend Adipozytokine im Interesse wissenschaftlicher Arbeiten. Unter Adipozytokinen versteht man in diesem Zusammenhang einen Sammelbegriff für von Adipozyten und anderen Fettgewebszellen sezernierten autokrin-, endokrin- und parakrin wirkenden bioaktiven Molekülen. Insbesondere bei Übergewicht und Adipositas kommt es zu einer charakteristischen Veränderung im Sekretionsmuster dieser Adipozytokine. Die Wirkung einzelner Adipozytokine auf die kardiovaskuläre Funktion wurde in den letzten Jahren intensiv untersucht, über die Wirkung ganzer Adipozytokinprofile ist bisher jedoch nur wenig bekannt. Ziel der vorliegenden Arbeit war es zu klären, welchen Einfluss eine 24-stündige Behandlung von neonatalen ventrikulären Kardiomyozyten mit einem physiologischen Adipozytokin-Profil auf Hypertrophie-assoziierte Signalwege und Zellproteine hat.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

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Glucocorticoids (GCs) are endogenous steroid hormones that regulate a number of critical physiological processes. Psychological stress increases the level of GCs in the circulating system. The biological effect of elevated GCs on the heart is not well understood. We found that GCs induced Cyclooxygenase-1 (COX-1) and COX-2 gene expression in cardiomyocytes. COX-1 or COX-2 encodes the rate-limiting enzyme in the biosynthesis of prostanoids, which modulate crucial physiological and pathophysiological responses. The present studies aim to elucidate the signaling transduction pathway and the mechanism underlying GC induced COX expression.Our data demonstrate that GCs activate COX-1 gene expression through transcriptional regulation. COX-1 gene promoter studies support a role of Sp binding site in CT induced COX-1 gene expression. The nuclear protein binding to this site appears to be Sp3 transcription factor. Co-immunoprecipitation assays indicated a physical interaction between GR and Sp3 protein. Silencing of Sp3 transcription factor with small interfering RNA suppressed CT-induced COX-1 promoter activation. These data suggest that the activated GR interacts with Sp3 transcription factor that binds to COX-1 promoter to up-regulate COX-1 gene expression in cardiomyocytes.We also found that administration of GC in adult mice increased the level of COX-2 in the ventricles. With isolated neonatal cardiomyocytes, corticosterone (CT) induces the transcription of COX-2 gene. This response appears to be cardiomyocyte cell type specific and GC receptor (GR)-dependent. CT causes activation of p38 MAPK and subsequently CREB phosphorylation that mediates COX-2 gene expression. Mifepristone, a GR antagonist, failed to inhibit p38 and CREB activation and p38 inhibition failed to prevent activation of GR. These data suggest that two parallel signaling pathways, GR and p38 MAPK, act in concert to regulate the expression of COX-2 gene in cardiomyocytes.In addition to the investigation of mechanism and signaling transduction pathway, I have explored pharmacological agents that modulate COX expression. LY294002, a commonly used PI3K inhibitor, inhibited COX-2 gene expression via a PI3K-independent mechanism. Whereas GSK-3 inhibitors, such as lithium chloride, upregulated COX-2 gene expression, but suppressed GC-induced COX-1 expression. These data have paved the foundation for pharmacological manipulation of COX-1 and COX-2 gene expression in the heart.

Introduction: Therapeutic agents like doxorubicin, an anthracycline antibiotic drug, are widely used in cancer chemotherapy. The use of doxorubicin is limited however by an increased risk of cardiac damage as a side effect, and an increased cancer cell drug resistance mediated by efflux drug transporters. Strategies are needed to protect the heart and still allow the benefits of drug treatment. “Basic” fibroblast growth factor-2 (FGF-2) is a multi-functional protein. It is angiogenic and cardioprotective against ischemia-reperfusion injury. FGF-2 can also regulate cancer cell drug resistance or sensitivity, however, so far, there is no evidence that FGF-2 protects against doxorubicin-induced cardiac damage through effects on efflux drug transporter levels or function. Aims: To investigate whether: (1) FGF-2 can increase resistance to doxorubicin-induced neonatal rat cardiac myocyte damage; and if so whether (2) an effect on efflux drug transporters might contribute to this cardioprotection by FGF-2. Methods: Neonatal rat cardiac myocyte cultures were treated with doxorubicin in the absence or presence of pre-treatment with FGF-2. To assess cell damage: (i) culture medium was tested for lactate dehydrogenase (LDH) activity as an indication of plasma membrane disruption; (ii) cells were stained with fluorescent apoptosis and necrosis biomarkers as well as (iii) terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and acridine orange to assess DNA fragmentation or compaction. The role of FGF receptor (FGFR) or protein kinase C (PKC) was addressed through use of inhibitors including SU5402, or chelerythrine as well as bisindomaleimide. Multidrug resistance gene 1a and 1b (MDR1a, 1b), multidrug resistance gene 2 (MDR2) and multidrug resistance-related protein 1 (MRP1) gene expression, as well as the function of MDRs and MRPs protein products were assessed by real-time reverse transcriptase-polymerase chain reaction (qPCR), as well as retention/extrusion of (fluorescent) doxorubicin/calcein in cardiac myocytes, respectively. Efflux drug transporter inhibitors, including 20 µM cyclosporine A (CsA), 2 µM verapamil and 1 µM Tariquidar (XR9576) were used to asssess for a direct effect of FGF-2 on transporter function. Fluorescence-activated cell sorting (FACS) was used to measure fluorescent doxorubicin/calcein levels inside treated cardiac myocytes. Results: Doxorubicin increased the incidence of programmed cell death, DNA damage, and lysosome and LDH activity, while decreasing cell number at 24 hours. FGF-2 prevented the detrimental effects of doxorubicin. In turn, the protective effects of FGF-2 were blocked in the presence of FGFR or PKC inhibitors. FGF-2 treatment significantly increased MDR1a, MDR1b, MDR2, MRP1 RNA levels by qPCR, and protein levels as assessed by function, and specifically extrusion of doxorubicin/calcein, in the presence of doxorubicin when compared to doxorubicin treatment alone. Furthermore, inhibition of efflux drug transporters with CsA and Tariquidar (XR9576) significantly reduced the ability of FGF-2 to protect against doxorubicin-induced damage; the beneficial effect of FGF-2 was completely blocked by pretreatment with verapamil. Conclusion(s): These data indicate for the first time that exogenous FGF-2 can increase resistance to doxorubicin-induced neonatal rat cardiac myocyte damage, and implicate PKC and regulation of efflux transporter protein levels and/or function in the mechanism.

Sarcolemmal chloride channels and associated cell volume regulatory pathways have been shown to be important in local ischemic preconditioning (IPC) induced protection against myocardial ischemia/reperfusion injury. Similarities between intracellular pathways in remote (rIPC) and classic IPC suggest that these mechanisms may also play an important role in rIPC. rIPC protected cultured rabbit ventricular cardiomyocytes against necrosis caused by 75 minutes simulated ischemia followed by 60 minutes simulated reperfusion. The protective effect was abolished by chloride channel blockade using 50 μM indanyloxyacetic acid 94 (IAA-94). rIPC also reduced peak cardiomyocyte swelling during exposure to 200 mOsm hypo-osmotic buffer. The reduction in peak swelling was also abolished by IAA-94. These results suggest that the protective effect of rIPC is achieved, at least in part, by enhancing cell volume regulation and that this effect is dependent on the availability of chloride channels in a similar fashion to local IPC.

Sarcolemmal chloride channels and associated cell volume regulatory pathways have been shown to be important in local ischemic preconditioning (IPC) induced protection against myocardial ischemia/reperfusion injury. Similarities between intracellular pathways in remote (rIPC) and classic IPC suggest that these mechanisms may also play an important role in rIPC. rIPC protected cultured rabbit ventricular cardiomyocytes against necrosis caused by 75 minutes simulated ischemia followed by 60 minutes simulated reperfusion. The protective effect was abolished by chloride channel blockade using 50 μM indanyloxyacetic acid 94 (IAA-94). rIPC also reduced peak cardiomyocyte swelling during exposure to 200 mOsm hypo-osmotic buffer. The reduction in peak swelling was also abolished by IAA-94. These results suggest that the protective effect of rIPC is achieved, at least in part, by enhancing cell volume regulation and that this effect is dependent on the availability of chloride channels in a similar fashion to local IPC.

Insulin and cellular stressors both activate p38 MAPK. Insulin protects cardiac tissue in a p38 MAPK-dependent manner. Paradoxically, inhibiting p38 MAPK is also protective. Hsp27 phosphorylation is regulated by p38 MAPK. Insulin was tested in H9c2 cardiomyocytes subjected to media exchange, 6 hours of oxygen-glucose deprivation, and reoxygenation. Insulin suppressed stress-induced phosphorylation of Hsp27 due to media-exchange or oxygen-glucose deprivation. Surprisingly, insulin increased Hsp27 phosphorylation during reoxygenation. Insulin also reduced total p38 MAPK levels. Insulin before oxygen-glucose deprivation prevented both localization of Hsp27 to the nucleus and localization of phospho-p38 MAPK to the cytoplasm. Insulin during oxygen-glucose deprivation caused the localization of phospho-p38 MAPK in the cytoplasm, but did not increase Hsp27 phosphorylation until reoxygenation. In conclusion, insulin may protect before oxygen-glucose deprivation by redirecting phospho-p38 MAPK to the nucleus away from damaging pathways in the cytoplasm and protects during oxygen-glucose deprivation by priming phospho-p38 MAPK to phosphorylate Hsp27. / Insulin was used on a model on H9c2 myotubes to determine the effect of oxygen-glucose deprivation and reoxygenation on the localization and phosphorylation of Hsp27 and p38 MAPK

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