Ischemic preconditioning triggers the activation of MAP kinases and MAPKAP kinase 2 in rat hearts

Inhibition of kinases impairs neutrophil activation and killing of Staphylococcus aureus

Intracellular phosphorylations polymorphonuclear neutrophils are mediated by kinases, including mitogen activated-protein (MAP) kinases and phosphatidylinositol 3-kinase. In the present study we demonstrate their effector functions upon both ligation of cell-surface seven-transmembrane-spanning receptors by bacterial peptide formylmethionyl-leucylphenylalanine as well as in the process of destruction of Staphylococcus aureus. To regulate neutrophil MAP kinases p38 and p44/42, specifically, we made use of their specific inhibitors 10 microM SK&F 86002 (for p38) and PD 098059 (for activating kinase of p44/42). SK&F 86002 was a potent inhibitor (by 70%) of induced antimicrobial oxygen-radical generation compared with PD 098059 (by 20%). SK&F 86002 and PD 098059 inhibited mobilization of a dominant neutrophil adhesion molecule, beta2 integrin, from cytoplasmic granules to the plasma membrane by 40 and 10% respectively, and the combination of the two drugs resulted in a 90% effect. The combined effect of both drugs was moderate inhibition of bacterial destruction, despite the fact that neither compound had detectable effect on bactericidal activity if applied individually. Bacterial destruction was also inhibited by wortmannin (0.1 microM), the specific inhibitor of phosphatidylinositol 3-kinase, which had previously been described to target various other activations of the neutrophil, including oxygen-radical generation. Although the relative contribution of p38 and p44/42 MAP kinases varied, the marked effects of the combined inhibition of the kinases revealed their concerted actions to be critical for normal neutrophil function.

MKK6 activates myocardial cell NF-kappaB and inhibits apoptosis in a p38 mitogen-activated protein kinase-dependent manner

In cardiac myocytes the stimulation of p38 mitogen-activated protein kinase activates a hypertrophic growth program and the induction of the cardiac-specific genes associated with this program. This study focused on determining whether these novel growth-promoting effects are accompanied by the p38-mediated inhibition of apoptosis, and if so, what signaling pathways might be responsible. Primary neonatal rat ventricular myocytes were driven into apoptosis by treatments known to induce apoptosis in other cell types, e.g. incubation with anisomycin or overexpression constitutively active MEKK-1 (MEKK-1COOH), a protein that strongly activates extracellular signal-regulated kinase and N-terminal c-Jun kinase, but not p38. Overexpression of constitutively active MKK6, MKK6 (Glu), which selectively activates p38 in cardiac myocytes, protected cells from either anisomycin- or MEKK-1COOH-induced apoptosis. This protection was blocked by SB 203580, a selective p38 inhibitor. MKK6 (Glu) also activated transcription mediated by NF-kappaB, a factor which protects other cell types from apoptosis. The activation of NF-kappaB and the protection from apoptosis mediated by MKK6 (Glu) were both blocked by SB 203580. Interestingly, overexpression of a mutant form of I-kappaBalpha, which inhibits nuclear translocation of NF-kappaB, completely blocked MKK6 (Glu)-activated NF-kappaB but had little effect on MKK6s anti-apoptotic effects. These findings suggest that, in part, the overexpression of MKK6 (Glu) may foster growth and survival of cardiac myocytes by protecting them from apoptosis in a p38-dependent manner. Additionally, while NF-kappaB is activated in myocardial cells by p38, this does not appear to be the major mechanism by which MKK6 (Glu) exerts its anti-apoptotic effects in this cell type, suggesting a novel pathway for p38-mediated protection from apoptosis.

TAN-67, a delta 1-opioid receptor agonist, reduces infarct size via activation of Gi/o proteins and KATP channels

We have previously shown that delta (delta)-opioid receptors, most notably delta 1, are involved in the cardioprotective effect of ischemic preconditioning (PC) in rats; however, the mechanism by which delta-opioid receptor-induced cardioprotection is mediated remains unknown. Therefore, we hypothesized that several of the known mediators of ischemic PC such as the ATP-sensitive potassium (KATP) channel and Gi/o proteins are involved in the cardioprotective effect produced by delta 1-opioid receptor activation. To address these possibilities, anesthetized, open-chest Wistar rats were randomly assigned to five groups. Control animals were subjected to 30 min of coronary artery occlusion and 2 h of reperfusion. To demonstrate that stimulating delta 1-opioid receptors produces cardioprotection, TAN-67, a new selective delta 1-agonist, was infused for 15 min before the long occlusion and reperfusion periods. In addition, one group received 7-benzylidenenaltrexone (BNTX), a selective delta 1-antagonist, before TAN-67. To study the involvement of KATP channels or Gi/o proteins in delta 1-opioid receptor-induced cardioprotection, glibenclamide (Glib), a KATP channel antagonist, or pertussis toxin (PTX), an inhibitor of Gi/o proteins, was administered before TAN-67. Infarct size (IS) as a percentage of the area at risk (IS/AAR) was determined by tetrazolium stain. TAN-67 significantly reduced IS/AAR as compared with control (56 +/- 2 to 27 +/- 5%, n = 5, P < 0.05). The cardioprotective effect of TAN-67 was completely abolished by BNTX, Glib, and PTX (51 +/- 3, 53 +/- 5, and 61 +/- 4%, n = 6 for each group, respectively). These results are the first to suggest that stimulating the delta 1-opioid receptor elicits a cardioprotective effect that is mediated via Gi/o proteins and KATP channels in the intact rat heart.

Genistein, an inhibitor of tyrosine kinase, prevents the antiarrhythmic effects of preconditioning

The possible involvement of tyrosine kinase in the signal transduction processes associated with the antiarrhythmic effects of ischaemic preconditioning was assessed by the administration, prior to the preconditioning stimulus, of the tyrosine kinase inhibitor genistein (5 mg/kg i.v.) to pentobarbitone anaesthetised male rats. The hearts were then removed, perfused by the Langendorff technique and preconditioned by a single brief (3 min) coronary artery occlusion prior to the 30 min test ischaemic insult. Preconditioning reduced ventricular arrhythmias during occlusion (e.g., premature ventricular beats from 333 +/- 60 in controls to 52 +/- 5 in preconditioned hearts; P < 0.05) but this protective effect was not observed in the hearts of rats given genistein (272 +/- 37 premature beats). A similar abolition of the protective effects of preconditioning could be demonstrated in hearts perfused in vitro with genistein (100 microM). This suggests the involvement of tyrosine kinase activation in this powerful form of endogenous cardioprotection.

A role for the p38 mitogen-activated protein kinase pathway in myocardial cell growth, sarcomeric organization, and cardiac-specific gene expression

Three hallmark features of the cardiac hypertrophic growth program are increases in cell size, sarcomeric organization, and the induction of certain cardiac-specific genes. All three features of hypertrophy are induced in cultured myocardial cells by alpha1- adrenergic receptor agonists, such as phenylephrine (PE) and other growth factors that activate mitogen- activated protein kinases (MAPKs). In this study the MAPK family members extracellular signal-regulated kinase (ERK), c-jun NH2-terminal kinase (JNK), and p38 were activated by transfecting cultured cardiac myocytes with constructs encoding the appropriate kinases possessing gain-of-function mutations. Transfected cells were then analyzed for changes in cell size, sarcomeric organization, and induction of the genes for the A- and B-type natriuretic peptides (NPs), as well as the alpha-skeletal actin (alpha-SkA) gene. While activation of JNK and/or ERK with MEKK1COOH or Raf-1 BXB, respectively, augmented cell size and effected relatively modest increases in NP and alpha-SkA promoter activities, neither upstream kinase conferred sarcomeric organization. However, transfection with MKK6 (Glu), which specifically activated p38, augmented cell size, induced NP and alpha-Ska promoter activities by up to 130-fold, and elicited sarcomeric organization in a manner similar to PE. Moreover, all three growth features induced by MKK6 (Glu) or PE were blocked with the p38-specific inhibitor, SB 203580. These results demonstrate novel and potentially central roles for MKK6 and p38 in the regulation of myocardial cell hypertrophy.

Ischemic preconditioning triggers phospholipase D signaling in rat heart

Recent studies have indicated that repeated brief episodes of ischemia and reperfusion render the myocardium more tolerant to subsequent lethal ischemic injury. In view of the previous observations that ischemia-reperfusion potentiates phospholipase D signaling and that such signaling is beneficial for the heart, we investigated whether a similar phospholipase D signaling is responsible for the beneficial effects associated with repeated ischemia and reperfusion. Using an isolated perfused working rat heart model, we demonstrated that four brief episodes of 5 min of ischemia and 10 min of reperfusion reduced the incidence of ventricular arrhythmias, enhanced the postischemic ventricular performance, and decreased the release of creatine kinase from the reperfused heart, with simultaneous activation of phospholipase D generating the second messengers diacylglycerol and phosphatidic acid and leading to the translocation and activation of protein kinase C. The specific antiphospholipase D antibody blocked the activation of phospholipase D and attenuated the generation of diacylglycerol and phosphatidic acid and activation of protein kinase C. In concert, phospholipase D inhibition increased the incidence of ventricular arrhythmias, blocked the beneficial effects of preconditioning on the ventricular performance, and increased the amount of creatine kinase release from the coronary effluent. The results of this study indicate that repeated brief episodes of ischemia and reperfusion exert beneficial effects on the intact rat heart by triggering the activation of a phospholipase D signaling mechanism.

Ischaemic preconditioning of myocardium

Myocardium has the innate potential to adapt to transient sublethal ischaemia so that it becomes more resistant to a subsequent, more severe, ischaemic insult. The response is called ischaemic preconditioning and protection of the myocardium is manifested by a slowing of adenosine triphosphate decline, limitation of ischaemic necrosis and a reduction in dysrhythmia severity. Protection conferred by preconditioning occurs in two distinct temporal phases. An early phase of protection is observed immediately but wanes within two to three hours (classic preconditioning). This is followed many hours later by a second window of protection (delayed preconditioning). The cellular mechanisms underpinning both forms of protection are currently being intensively investigated. There is evidence that human myocardium can be preconditioned ex vivo and also in situ during elective procedures such as angioplasty and coronary artery bypass grafting. Furthermore, evidence points to the possibility that preconditioning occurs naturally in some ischaemic syndromes, particularly warm-up angina and preinfarction angina. Ultimately, investigation of the mechanisms of preconditioning may contribute to the development of rational therapies for protecting the ischaemic myocardium and, perhaps more importantly, enhance our understanding of the molecular basis of ischaemic heart disease.