The role of signal transducer and activator of transcription-3 (STAT-3) in ischaemic and pharmacological postconditioning

Includes abstract. Includes bibliographical references (leaves 131-147)

The PGE2-Stat3 interaction in doxorubicin-induced myocardial apoptosis

Aims Both cyclooxygenase-2 (COX-2) and the transcription factor signal transducer and activator of transcription 3 (Stat3) are involved in adaptive growth and survival of cardiomyocytes. In ventricular cardiomyocytes, prostaglandin E2 (PGE2), a major COX-2 product, leads to adaptive growth via Stat3 activation, but whether this transcription factor acts as a signalling molecule in PGE2-induced cell survival is unknown. Therefore, the purpose of this study was to determine whether PGE2 counteracts cardiac apoptosis induced by doxorubicin (DOX), and if so, whether Stat3 plays a critical role in this cardioprotective effect. Methods and results Neonatal rat ventricular cardiomyocytes were incubated with DOX (0.5 µM) and/or PGE2 (1 µM). Apoptosis was assessed by determining caspase3 activation and apoptotic DNA fragmentation. The role of Stat3 was evaluated in vitro and in vivo by transfecting cardiomyocytes with siRNA targeting rat Stat3 and by using cardiomyocyte-restricted Stat3 knockout (Stat3 KO) mice, respectively. Incubation of ventricular cardiomyocytes with PGE2 led to a time-dependent decrease in the DOX-induced caspase3 activation, reaching a maximal inhibition of 70 ± 5% after 4 h. Similarly, PGE2 inhibited DOX-induced DNA fragmentation by 58 ± 5% after 24 h. This antiapoptotic action of PGE2 was strongly reduced by the ERK1/2 inhibitor, U0126, whereas the p38 MAP kinase inhibitor, SB203580, had no effect. Depleting Stat3 expression by 50-60% in isolated ventricular cardiomyocytes markedly reduced the protective effect of PGE2 on DOX-induced caspase3 activation and DNA fragmentation. Likewise, the stable PGE2 analogue, 16,16-dimethyl-PGE2, was unable to counteract cardiac apoptosis induced by DOX in Stat3 KO mice. Conclusion Our results demonstrate that PGE2 prevents myocardial apoptosis induced by DOX. This protection requires the activation of the prosurvival pathways of Stat3 and ERK1/

Ethanolamine is a novel STAT-3 dependent cardioprotective agent

Ethanolamine is a biogenic amine found naturally in the body as part of membrane lipids and as a metabolite of the cardioprotective substances, sphingosine-1-phosphate (S1P) and anandamide. In the brain, ethanolamine, formed from the breakdown of anandamide protects against ischaemic apoptosis. However, the effects of ethanolamine in the heart are unknown. Signal transducer and activator of transcription 3 (STAT-3) is a critical prosurvival factor in ischaemia/reperfusion (I/R) injury. Therefore, we investigated whether ethanolamine protects the heart via activation of STAT-3. Isolated hearts from wildtype or cardiomyocyte specific STAT-3 knockout (K/O) mice were pre-treated with ethanolamine (Etn) (0.3 mmol/L) before I/R insult. In vivo rat hearts were subjected to 30 min ischaemia/2 h reperfusion in the presence or absence of 5 mg/kg S1P and/or the FAAH inhibitor, URB597. Infarct size was measured at the end of each protocol by triphenyltetrazolium chloride staining. Pre-treatment with ethanolamine decreased infarct size in isolated mouse or rat hearts subjected to I/R but this infarct sparing effect was lost in cardiomyocyte specific STAT-3 deficient mice. Pre-treatment with ethanolamine increased nuclear phosphorylated STAT-3 [control 0.75 ± 0.08 vs. Etn 1.50 ± 0.09 arbitrary units; P < 0.05]. Our findings suggest a novel cardioprotective role for ethanolamine against I/R injury via activation of STAT-3

Role of nuclear factors kappa-B in TNFα-induced cytoprotection

Includes bibliographical references (leaves 67-81)

TNFα-induced cardioprotection is independent of the activation of the prosurvival kinase Erk

Introduction: Tumour Necrosis Factor alpha (TNFα) contributes to cardiac dysfunction following ischaemia-reperfusion. Nonetheless, brief exposure to exogenous low doses of TNFα can mimic ischaemic preconditioning and thus be cardio-protective. The extracellular signal-regulated kinase (Erk) has been implicated in the protection against ischaemia-reperfusion and is known to be activated by TNFα. However, whether Erk activation contributes to TNFα-induced cardio-protection remains unknown. Methods: PD 98059 (10μM), an Erk inhibitor, was used to evaluate the role of this prosurvival kinase with respect to infarct size (expressed as a percentage of the area at risk) in isolated rat hearts subjected to ischaemic preconditioning (IPC) or TNFα preconditioning (TNFαP). Western blot analyses were used to determine the degree of Erk phosphorylation after the application of the preconditioning stimulus. Results: Pre-treatment of the hearts with 0.5ng/ml of TNFα (for 7min) or 2 cycles of 5min ischaemia-reperfusion prior to 30min regional index ischaemia and 2h of reperfusion reduced the infarct size by 76% and 88%, respectively, versus control. Western blot analysis of isolated rat hearts revealed that IPC but not TNFαP activated phosphorylation of Erk (+54% for IPC vs. control). Coadministration of PD 98059 during the preconditioning stimulus did not influence the infarct size.Conclusion: These findings confirm that activation of TNFα may be considered as a novel therapeutic approach against ischaemic heart disease and that its effect is independent of the activation of the classic prosurvival factor Erk

Interplay between SAFE and RISK pathways in sphingosine-1-phosphate-induced cardioprotection

We studied the role of two powerful molecular signalling mechanisms involved in the cardioprotective effect of sphingosine-1-phosphate (S1P), a major component of high density lipoprotein (HDL) against myocardial ischaemic-reperfusion injury, namely the RISK pathway (Akt/Erk), including its downstream target FOXO-1 and, the SAFE pathway (TNF/STAT-3)

The PGE2-Stat3 interaction in doxorubicin-induced myocardial apoptosis

AIMS: Both cyclooxygenase-2 (COX-2) and the transcription factor signal transducer and activator of transcription 3 (Stat3) are involved in adaptive growth and survival of cardiomyocytes. In ventricular cardiomyocytes, prostaglandin E(2) (PGE(2)), a major COX-2 product, leads to adaptive growth via Stat3 activation, but whether this transcription factor acts as a signalling molecule in PGE(2)-induced cell survival is unknown. Therefore, the purpose of this study was to determine whether PGE(2) counteracts cardiac apoptosis induced by doxorubicin (DOX), and if so, whether Stat3 plays a critical role in this cardioprotective effect. METHODS AND RESULTS: Neonatal rat ventricular cardiomyocytes were incubated with DOX (0.5 microM) and/or PGE(2) (1 microM). Apoptosis was assessed by determining caspase3 activation and apoptotic DNA fragmentation. The role of Stat3 was evaluated in vitro and in vivo by transfecting cardiomyocytes with siRNA targeting rat Stat3 and by using cardiomyocyte-restricted Stat3 knockout (Stat3 KO) mice, respectively. Incubation of ventricular cardiomyocytes with PGE(2) led to a time-dependent decrease in the DOX-induced caspase3 activation, reaching a maximal inhibition of 70 +/- 5% after 4 h. Similarly, PGE(2) inhibited DOX-induced DNA fragmentation by 58 +/- 5% after 24 h. This antiapoptotic action of PGE(2) was strongly reduced by the ERK1/2 inhibitor, U0126, whereas the p38 MAP kinase inhibitor, SB203580, had no effect. Depleting Stat3 expression by 50-60% in isolated ventricular cardiomyocytes markedly reduced the protective effect of PGE(2) on DOX-induced caspase3 activation and DNA fragmentation. Likewise, the stable PGE(2) analogue, 16,16-dimethyl-PGE(2), was unable to counteract cardiac apoptosis induced by DOX in Stat3 KO mice. CONCLUSION: Our results demonstrate that PGE(2) prevents myocardial apoptosis induced by DOX. This protection requires the activation of the prosurvival pathways of Stat3 and ERK1/2

HDL protects against ischemia reperfusion injury by preserving mitochondrial integrity

High density lipoproteins (HDL) protect against ischemia reperfusion injury (IRI). However the precise mechanisms are not clearly understood. The novel intrinsic prosurvival signaling pathway named survivor activating factor enhancement (SAFE) path involves the activation of tumor necrosis factor (TNF) alpha and signal transducer and activator of transcription 3 (STAT3). SAFE plays a crucial role in cardioprotection against IRI. We propose that HDL protect against IRI via activation of the SAFE pathway and modulation of the mitochondrial permeability transition pore (mPTP) opening