Delayed cardioprotection is associated with the sub-cellular relocalisation of ventricular protein kinase C epsilon, but not p42/44MAPK

PRKCE gene encoding protein kinase C-epsilon-Dual roles at sarcomeres and mitochondria in cardiomyocytes

Protein kinase C-epsilon (PKCε) is an isoform of a large PKC family of enzymes that has a variety of functions in different cell types. Here we discuss two major roles of PKCε in cardiac muscle cells; specifically, its role in regulating cardiac muscle contraction via targeting the sarcomeric proteins, as well as modulating cardiac cell energy production and metabolism by targeting cardiac mitochondria. The importance of PKCε action is described within the context of intracellular localization, as substrate selectivity and specificity is achieved through spatiotemporal targeting of PKCε. Accordingly, the role of PKCε in regulating myocardial function in physiological and pathological states has been documented in both cardioprotection and cardiac hypertrophy.

Hypercholesterolemia abrogates an increased resistance of diabetic rat hearts to ischemia-reperfusion injury

Both, diabetes mellitus (DM) and hypercholesterolemia (HCH) are known as risk factors of ischemic heart disease, however, the effects of experimental DM, as well as of HCH alone, on ischemia/reperfusion-induced myocardial injury are not unequivocal. We have previously demonstrated an enhanced resistance to ischemia-induced arrhythmias in rat hearts in the acute phase of DM. Our objectives were thus to extend our knowledge on how DM in combination with HCH, a model that is relevant to diabetic patients with altered lipid metabolism, may affect the size of myocardial infarction and susceptibility to arrhythmias. A combination of streptozotocin (STZ; 80 mg/kg, i.p.) and the fat-cholesterol diet (1% cholesterol, 1% coconut oil; FCHD) was used as a double-disease model mimicking DM and HCH simultaneosly occurring in humans. Following 5 days after STZ injection and FCHD leading to increased blood glucose and cholesterol levels, anesthetized open-chest diabetic, diabetic-hypercholesterolemic (DM-HCH) and age-matched control rats were subjected to 6-min ischemia (occlusion of LAD coronary artery) followed by 10 reperfusion to test susceptibility to ventricular arrhythmias in the in vivo experiments and to 30-min ischemia and subsequent 2-h reperfusion for the evaluation of the infarct size (IS) in the Langendorff-perfused hearts. The incidence of the most life-threatening ventricular arrhythmia, ventricular fibrillation, was significantly increased in the DM-HCH rats as compared with non-diabetic control animals (100% vs. 50%; p<0.05). Likewise, arrhythmia severity score (AS) was significantly higher in the DM-HCH rats than in the controls (4.9+/-0.2 vs. 3.5+/-0.5; p<0.05), but was not increased in the diabetic animals (AS 3.7+/-0.9; p>0.05 vs. controls). Diabetic hearts exhibited a reduced IS (15.1+/-3.0% of the area at risk vs. 37.6+/-2.8% in the control hearts; p<0.05), however, a combination of DM and HCH increased the size of myocardial infarction to that observed in the controls. In conclusion, HCH abrogates enhanced resistance to ischemia-reperfusion injury in the diabetic rat heart.

New insight into the signalling pathways of heat stress-induced myocardial preconditioning: protein kinase Cepsilon translocation and heat shock protein 27 phosphorylation

1. Heat stress (HS) is known to induce delayed preconditioning against myocardial infarction 24 h later, but the exact signalling pathway of this response remains to be elucidated. In previous studies, we have shown evidence for the implication of protein kinase C (PKC) and p38 mitogen-activated protein kinase (MAPK) in the HS-induced reduction in infarct size. Furthermore, in their phosphorylated state, small heat shock proteins (Hsp27) seem to confer cytoskeletal protection. In the present study, we sought to determine the effect of HS on the subcellular distribution of PKC isoforms and on Hsp27 phosphorylation. 2. Rats were subjected to either HS (42 degrees C for 15 min; HS group) or sham anaesthesia (sham group) before their hearts were excised. Myocardial tissue extracts obtained 20 min or 24 h after HS were processed for western blot analysis. 3. In the HS group, PKCepsilon translocated from the cytosolic to the particulate fraction (4426 +/- 128 vs 6258 +/- 316 arbitrary units; P = 0.002). Chelerythrine (5 mg/kg, i.p.), a PKC inhibitor, abolished this translocation. Western blot analysis of Hsp27 24 h after HS showed a marked increase in protein expression and phosphorylation in the particulate fraction. 4. In the present study, we have shown that HS induces the translocation of PKCepsilon from the cytosolic to the particulate fraction. Along with our previous observation that PKC is a trigger of HS-induced myocardial preconditioning, the results of the present study suggest an important role of the epsilon isoform of PKC in this cardioprotective mechanism. Furthermore, we have also demonstrated that the cytoprotective protein Hsp27 is phosphorylated following HS. Therefore, we can conclude that PKC and MAPK/Hsp27 are involved in the signalling pathway of HS-induced cardioprotection.

Preconditioning the Myocardium: From Cellular Physiology to Clinical Cardiology

Yellon, Derek M., and James M. Downey. Preconditioning the Myocardium: From Cellular Physiology to Clinical Cardiology. Physiol Rev 83: 1113-1151, 2003; 10.1152/physrev.00009.2003.—The phenomenon of ischemic preconditioning, in which a period of sublethal ischemia can profoundly protect the cell from infarction during a subsequent ischemic insult, has been responsible for an enormous amount of research over the last 15 years. Ischemic preconditioning is associated with two forms of protection: a classical form lasting ∼2 h after the preconditioning ischemia followed a day later by a second window of protection lasting ∼3 days. Both types of preconditioning share similarities in that the preconditioning ischemia provokes the release of several autacoids that trigger protection by occupying cell surface receptors. Receptor occupancy activates complex signaling cascades which during the lethal ischemia converge on one or more end-effectors to mediate the protection. The end-effectors so far have eluded identification, although a number have been proposed. A range of different pharmacological agents that activate the signaling cascades at the various levels can mimic ischemic preconditioning leading to the hope that specific therapeutic agents can be designed to exploit the profound protection seen with ischemic preconditioning. This review examines, in detail, the complex mechanisms associated with both forms of preconditioning as well as discusses the possibility to exploit this phenomenon in the clinical setting. As our understanding of the mechanisms associated with preconditioning are unravelled, we believe we can look forward to the development of new therapeutic agents with novel mechanisms of action that can supplement current treatment options for patients threatened with acute myocardial infarction.

Mitogen-activated protein kinases: a new therapeutic target in cardiac pathology

Eukaryotic cells respond to different external stimuli by activation of mechanisms of cell signaling. One of the major systems participating in the transduction of signal from the cell membrane to nuclear and other intracellular targets is the highly conserved mitogen-activated protein kinase (MAPK) superfamily. The members of MAPK family are involved in the regulation of a large variety of cellular processes such as cell growth, differentiation, development, cell cycle, death and survival. Several MAPK subfamilies, each with apparently unique signaling pathway, have been identified in the mammalian myocardium. These cascades differ in their upstream activation sequence and in downstream substrate specifity. Each pathway follows the same conserved three-kinase module consisting of MAPK, MAPK kinase (MAPKK, MKK or MEK), and MAPK kinase kinase (MAPKKK, MEKK). The major groups of MAPKs found in cardiac tissue include the extracellular signal-regulated kinases (ERKs), the stress-activated/c-Jun NH2-terminal kinases (SAPK/JNKs), p38-MAPK, and ERK5/big MAPK 1 (BMK1). The ERKs are strongly activated by mitogenic and growth factors and by physical stress, whereas SAPK/JNKs and p38-MAPK can be activated by various cell stresses, such as hyperosmotic shock, metabolic stress or protein synthesis inhibitors, UV radiation, heat shock, cytokines, and ischemia. Activation of MAPKs family plays a key role in the pathogenesis of various processes in the heart, e.g. myocardial hypertrophy and its transition to heart failure, in ischemic and reperfusion injury, as well in the cardioprotection conferred by ischemia- or pharmacologically-induced preconditioning. The following approaches are currently utilized to elucidate the role of MAPKs in the myocardium: (i) studies of the effects of myocardial processes on the activity of these kinases; (ii) pharmacological modulations of MAPKs activity and evaluation of their impact on the (patho)physiological processes in the heart; (iii) gene targeting or expression of constitutively active and dominant-negative forms of enzymes (adenovirus-mediated gene transfer). This review is focused on the regulatory role of MAPKs in the myocardium, with particular regard to their involvement in pathophysiological processes, such as myocardial hypertrophy and heart failure, ischemia/reperfusion injury, as well as in the mechanisms of cardioprotection. In addition, it summarizes current information on pharmacological modulations of MAPKs activity and their impact on the cardiac response to pathophysiological processes.

Effects of pharmacological preconditioning with U50488H on calcium homeostasis in rat ventricular myocytes subjected to metabolic inhibition and anoxia

1. The effects of pharmacological preconditioning with U50488H (U(50)), a selective kappa-opioid receptor agonist, on Ca(2+) homeostasis in rat ventricular myocytes subjected for 9 min to metabolic inhibition (MI) and anoxia (A), consequences of ischaemia, were studied and compared with those of preconditioning with brief periods of MI/A. 2. Precondition with 30 micro M of U(50) for three cycles of 1 min each cycle separated by 3 min of recovery (UP) significantly increased the percentage of non-blue cells following MI/A. The effect of UP is the same as that of preconditioning with an inhibitor of glycolysis and an oxygen scavenger for three 1-min cycles separated by three-minute recovery (MI/AP). The results indicate that like MI/AP, UP also confers cardioprotection. 3. MI/A increased intracellular Ca(2+) ([Ca(2+)](i)) and reduced the amplitude of caffeine-induced [Ca(2+)](i) transients, an indication of Ca(2+) content in the sarcoplasmic reticulum (SR). MI/A also reduced the electrically-induced [Ca(2+)](i) transient, that indicates Ca(2+)-release during excitation-contraction coupling, and Ca(2+) sparks in unstimulated myocytes, that indicates spontaneous Ca(2+)-release from SR. It also prolonged the decline of the electrically-induced [Ca(2+)](i) transient and slowed down the recovery of the electrically-induced [Ca(2+)](i) transient after administration of caffeine. In addition, MI/A prolonged the decline of caffeine induced [Ca(2+)](i) transient, an indication of Na(+)-Ca(2+) exchange activity, and UP prevented it. So UP, that confers cardioprotection, prevented the changes induced by MI/A. With the exception of Ca(2+)-spark, which was not studied, the effects of MI/AP are the same as those of UP. 4. It is concluded that pharmacological preconditioning with U(50), that confers immediate cardioprotection, prevents changes of Ca(2+) homeostasis altered by MI/A in the rat heart. This may be responsible, at least partly, for the cardioprotective action. 5. The study also provided evidence that MI/A causes mobilization of Ca(2+) from SR to cytoplasm causing Ca(2+)-overload which may be due to reduced Ca(2+)-uptake by SR. MI/A also reduces spontaneous and electrically induced Ca(2+) release from SR.

Adenosine A(1) receptor mediates late preconditioning via activation of PKC-delta signaling pathway

Protein kinase C (PKC) plays a central role in both early and late preconditioning (PC) but its association with inducible nitric oxide synthase (iNOS) is not clear in late PC. This study investigates the PKC signaling pathway in the late PC induced by activation of adenosine A(1) receptor (A(1)R) with adenosine agonist 2-chloro-N(6)-cyclopentyladenosine (CCPA) and the effect on iNOS upregulation. Adult male mice were pretreated with saline or CCPA (100 microg/kg iv) or CCPA (100 microg/kg iv) with PKC-delta inhibitor rottlerin (50 microg/kg ip). Twenty-four hours later, the hearts were isolated and perfused in the Langendorff mode. Hearts were subjected to 40 min of ischemia, followed by 30 min reperfusion. After ischemia, the left ventricular end-diastolic pressure (LVEDP) was significantly improved and the rate-pressure product (RPP) was significantly higher in the CCPA group compared with the ischemia-reperfusion (I/R) control group. Creatine kinase release and infarct size were significantly lower in the CCPA group compared with the I/R control group. These salutary effects of CCPA were abolished in hearts pretreated with rottlerin. Immunoblotting of PKC showed that PKC-delta was upregulated (150.0 +/- 11.4% of control group) whereas other PKC isoforms remained unchanged, and iNOS was also significantly increased (146.2 +/- 9.0%, P < 0.05 vs. control group) after 24 h of treatment with CCPA. The data show that PKC is an important component of PC with adenosine agonist. It is concluded that activation of A(1)R induces late PC via PKC-delta and iNOS signaling pathways.

Streptozotocin diabetes protects against arrhythmias in rat isolated hearts: role of hypothyroidism

We examined the contribution of hypothyroidism to streptozotocin diabetes-induced alterations in the arrhythmia susceptibility of ex vivo hearts to regional zero-flow ischaemia. Diabetic rats received either protamine zinc insulin (10 IU/kg/day, s.c.) or triiodothyronine (10 microg/kg/day, s.c.) for 8 weeks commencing 72 h after injection of streptozotocin (60 mg/kg, i.p.). Arrhythmias were determined in ex vivo Langendorff-perfused hearts, subjected to a 30-min main left coronary artery occlusion, followed by 30-min reperfusion. Serum free thyroxine concentrations, rectal temperature and ex vivo heart rate were significantly decreased in the 8-week diabetic group (P<0.001). These changes were prevented by administration of triiodothyronine or insulin. Ventricular fibrillation during reperfusion was abolished in hearts from diabetic rats. This protection was prevented by treatment with either triiodothyronine or insulin. Hearts from methimazole-hypothyroid rats also showed no ventricular fibrillation during reperfusion. The protection against ischaemia-reperfusion-arrhythmias observed in hearts from streptozotocin-diabetic rats may be due to diabetes-induced hypothyroidism.

Ischemic preconditioning: from adenosine receptor to KATP channel

Ischemic preconditioning is a phenomenon whereby exposure of the myocardium to a brief episode of ischemia and reperfusion markedly reduces tissue necrosis induced by a subsequent prolonged ischemia. It is hoped that elucidation of the mechanism for preconditioning will yield therapeutic strategies capable of reducing myocardial infarction. In the rabbit, the brief period of preconditioning ischemia and reperfusion releases adenosine, bradykinin, opioids, and oxygen radicals. The combined effect of the release of these substances on G proteins and the cell's phospholipases induces the translocation and activation of the epsilon isozyme of protein kinase C. Protein kinase C appears to be the first element of a complex kinase cascade that is activated during the prolonged ischemia in preconditioned hearts. Current evidence indicates that this cascade contains at least one tyrosine kinase and ultimately leads to the activation of p38 mitogen-activated protein kinase. p38 Mitogen-activated protein kinase phosphorylates mitogen-activated protein kinase-activated protein kinase 2. Mitogen-activated protein kinase-activated protein kinase 2 phosphorylates HSP27, a 27-kDa heat shock protein that controls actin filament polymerization, and, therefore, affects the integrity of the cytoskeleton. Finally, mitochondrial adenosine 5'-triphosphate-sensitive K+ channels open, and the latter may be the final mediator of protection for ischemic preconditioning. The protective pathway has many built-in redundancies, perhaps creating a safety factor. These redundancies may also explain some of the species-related differences seen in ischemic preconditioning in which one redundant pathway may predominate over another.

Ischemic preconditioning: from basic mechanisms to clinical applications

When the heart is subjected to a transient nonlethal period of ischemia, it quickly adapts itself to become resistant to infarction from a subsequent ischemic insult. This adaptation is called preconditioning. This cardioprotection has been shown to be mediated by stimulation of receptors linked to protein kinase C (PKC) (adenosine, bradykinin, opioids, etc.), and these receptors protect by activating PKC. PKC appears to be the first element of a complex kinase cascade that is activated during the prolonged ischemia in the preconditioned heart. Recent studies imply that p38 mitogen-activated protein kinase carries the signal from PKC to the mitochondrial K(ATP) channels, causing them to open and thus protect the heart. The cardioprotection of preconditioning occurs in all species tested to date, and possibly also humans. It is expected that as the mechanism of preconditioning is more thoroughly understood, pharmacological preconditioning will become practical for clinical use.

Adenosine A(1) receptor induced delayed preconditioning in rabbits: induction of p38 mitogen-activated protein kinase activation and Hsp27 phosphorylation via a tyrosine kinase- and protein kinase C-dependent mechanism

Transient adenosine A(1) receptor (A(1)R) activation in rabbits induces delayed preconditioning against myocardial infarction 24 to 72 hours later. The cellular mechanisms downstream of A(1)R mediating this delayed cardioprotection have not been elucidated. This study examined the role of protein kinase C (PKC) and tyrosine kinases (TKs) in the signaling cascade mediating A(1)R-induced late preconditioning in rabbits. The small heat shock protein Hsp27 has been shown to confer cytoskeletal protection when in the phosphorylated state. We therefore also evaluated the potential role of the p38 mitogen-activated protein kinase (p38 MAPK) and Hsp27 as distal mediators of A(1)R-induced delayed preconditioning. Pharmacological preconditioning of rabbits with the selective A(1) agonist 2-chloro-N(6)-cyclopentyladenosine (CCPA; 100 microgram/kg) significantly reduced myocardial infarct size compared with control animals, after 30-minute regional ischemia/2-hour reperfusion in vivo 24 hours later (23.7+/-3.1 versus 43.0+/-4.1%; P<0.05). This delayed protection was abrogated by prior inhibition of either PKC with chelerythrine chloride (5 mg/kg) or of TKs with lavendustin A (1.3 mg/kg), suggesting that both PKC and TK are crucial for the development of delayed preconditioning after A(1) receptor activation in the rabbit. Myocardial tissue extracts obtained 24 hours after CCPA treatment were analyzed for p38 MAPK catalytic activity using an in vitro kinase assay. This showed an almost 7-fold increase in p38 MAPK activity in myocardial samples pretreated with CCPA compared with control hearts. Two-dimensional gel electrophoresis revealed an increase in the phosphorylated isoforms of Hsp27 in hearts pretreated with CCPA compared with control hearts. Prior inhibition of either PKC or TK prevented the CCPA-induced increase in p38 MAPK activity and phosphorylation of Hsp27. This study identifies new components of the signaling mechanism of A(1)R-induced delayed preconditioning. Our results suggest an important role for both PKC and TK as mediators of late preconditioning against infarction after A(1)R activation and, although correlative, point to the p38 MAPK/Hsp27 pathway as a potential distal effector of this protection.

Two distinct mechanisms mediate a differential regulation of protein kinase C isozymes in acute and prolonged myocardial ischemia

An activation of protein kinase C (PKC) in acute myocardial ischemia has been shown previously using its translocation to the plasma membrane as an indirect parameter. However, whether PKC remains activated or whether other mechanisms such as altered gene expression may mediate an isozyme-specific regulation in prolonged ischemia have not been investigated. In isolated perfused rat hearts, PKC activity and the expression of PKC cardiac isozymes were determined on the protein level using enzyme activities and Western blot analyses and on the mRNA level using reverse transcriptase-polymerase chain reaction after various periods of global ischemia (1 to 60 minutes). As early as 1 minute after the onset of ischemia, PKC activity is translocated from the cytosol to the particulate fraction without change in total cardiac enzyme activity. This translocation involves all major cardiac isozymes of PKC (ie, PKCalpha, PKCdelta, PKCepsilon, and PKCzeta). This rapid, nonselective activation of PKCs is only transient. In contrast, prolonged ischemia (>/=15 minutes) leads to an increased cardiac PKC activity (119+/-7 versus 190+/-8 pmol/min per mg protein) residing in the cytosol. This is associated with an augmented, subtype-selective isozyme expression of PKCdelta and PKCvarepsilon (163% and 199%, respectively). The specific mRNAs for PKCdelta (948+/-83 versus 1501+/-138 ag/ng total RNA, 30 minutes of ischemia) and PKCepsilon (1597+/-166 versus 2611+/-252 ag/ng total RNA) are selectively increased. PKCalpha and PKCzeta remain unaltered. In conclusion, two distinct activation and regulation processes of PKC are characterized in acute myocardial ischemia. The early, but transient, translocation involves all constitutively expressed cardiac isozymes of PKC, whereas in prolonged ischemia an increased total PKC activity is associated with an isozyme-selective induction of PKCepsilon and PKCdelta. Whether these fundamentally different activation processes interact remains to be elucidated.

Signal transduction in ischemic preconditioning: the role of kinases and mitochondrial K(ATP) channels

Ischemic preconditioning is a phenomenon whereby exposure of the myocardium to a brief episode of ischemia and reperfusion markedly reduces tissue necrosis induced by a subsequent prolonged ischemia. Therefore, it is hoped that elucidation of the mechanism of preconditioning will yield therapeutic strategies capable of reducing myocardial infarction. In the rabbit, the brief period of preconditioning ischemia and reperfusion releases adenosine, bradykinin, opioids, and oxygen radicals that summate to induce the translocation and activation of protein kinase C (PKC). PKC appears to be the first element of a complex kinase cascade that is activated during the prolonged ischemia in preconditioned hearts. Current evidence indicates that PKC activates a tyrosine kinase that leads to the activation of p38 mitogen-activated protein (MAP) kinase or JNK, or possibly both. The stimulation of these stress-activated protein kinases ultimately induces the opening of mitochondrial K(ATP) channels that may be the final mediator of protection by ischemic preconditioning.

Role of protein kinase C and 72 kDa heat shock protein in ischemic tolerance following heat stress in the rat heart

Heat stress (HS) and the subsequent expression of 72 kDa heat shock protein (HSP 72) has been shown to enhance post-ischemic functional recovery and reduce infarct size. Because the synthesis of heat shock proteins involves activation of heat shock transcription factors through phosphorylation, we hypothesized that inhibition of protein kinase C (PKC) would block HS mediated protection and expression of HSP 72 in the heart. Five groups of rats were studied (1) Sham anesthetized, (2) HS group--animals were heat shocked by raising the whole body core temperature to 42 degrees C for 15 min, (3) Vehicle group--HS rats treated with 50% DMSO in saline, (4) PKC inhibitor-treated group--specific PKC antagonist, chelerythrine chloride (5 mg/kg, i.p) given 30 min prior to HS and (5) Vehicle treated control--non-HS rats treated with vehicle prior to ischemia/reperfusion. Hearts were subjected to 30 min of regional ischemia and 90 min of reperfusion 24 h after HS. Risk area was delineated by injection of 10% Evan's blue and infarct size determined using computer morphometry of tetrazolium stained sections. Infarct size (% area at risk) reduced significantly from 49.4 +/- 2.3% (n = 7) in sham to 10.0 +/- 2.5% (p < 0.01) and 9.1 +/- 3.0% in HS and vehicle treated HS groups respectively (p < 0.05) Treatment with chelerythrine prior to HS increased infarct size to 49.4 +/- 2.3% (p < 0.05). Infarct size in chelerythrine-treated non-HS ischemic/reperfused heart was 40.7 +/- 5.4%, which did not differ significantly from vehicle-treated sham group. Western blot analysis demonstrated marked increase in HSP 72 in HS groups (with or without vehicle treatment) and pretreatment with chelerythrine chloride failed to inhibit the expression of HSP 72. The results suggest that HS-induced ischemic tolerance is mediated via PKC pathway and this protection does not appear to be directly related to the expression of HSP 72 in rat heart.