Adrenergic induction of bimodal myocardial protection: signal transduction and cardiac gene reprogramming

α1A-Adrenergic receptor prevents cardiac ischemic damage through PKCδ/GLUT1/4-mediated glucose uptake

While α(1)-adrenergic receptors (ARs) have been previously shown to limit ischemic cardiac damage, the mechanisms remain unclear. Most previous studies utilized low oxygen conditions in addition to ischemic buffers with glucose deficiencies, but we discovered profound differences if the two conditions are separated. We assessed both mouse neonatal and adult myocytes and HL-1 cells in a series of assays assessing ischemic damage under hypoxic or low glucose conditions. We found that α(1)-AR stimulation protected against increased lactate dehydrogenase release or Annexin V(+) apoptosis under conditions that were due to low glucose concentration not to hypoxia. The α(1)-AR antagonist prazosin or nonselective protein kinase C (PKC) inhibitors blocked the protective effect. α(1)-AR stimulation increased (3)H-deoxyglucose uptake that was blocked with either an inhibitor to glucose transporter 1 or 4 (GLUT1 or GLUT4) or small interfering RNA (siRNA) against PKCδ. GLUT1/4 inhibition also blocked α(1)-AR-mediated protection from apoptosis. The PKC inhibitor rottlerin or siRNA against PKCδ blocked α(1)-AR stimulated GLUT1 or GLUT4 plasma membrane translocation. α(1)-AR stimulation increased plasma membrane concentration of either GLUT1 or GLUT4 in a time-dependent fashion. Transgenic mice overexpressing the α(1A)-AR but not α(1B)-AR mice displayed increased glucose uptake and increased GLUT1 and GLUT4 plasma membrane translocation in the adult heart while α(1A)-AR but not α(1B)-AR knockout mice displayed lowered glucose uptake and GLUT translocation. Our results suggest that α(1)-AR activation is anti-apoptotic and protective during cardiac ischemia due to glucose deprivation and not hypoxia by enhancing glucose uptake into the heart via PKCδ-mediated GLUT translocation that may be specific to the α(1A)-AR subtype.

Cardiac alpha1-adrenergic receptors: novel aspects of expression, signaling mechanisms, physiologic function, and clinical importance

Adrenergic receptors (AR) are G-protein-coupled receptors (GPCRs) that have a crucial role in cardiac physiology in health and disease. Alpha1-ARs signal through Gαq, and signaling through Gq, for example, by endothelin and angiotensin receptors, is thought to be detrimental to the heart. In contrast, cardiac alpha1-ARs mediate important protective and adaptive functions in the heart, although alpha1-ARs are only a minor fraction of total cardiac ARs. Cardiac alpha1-ARs activate pleiotropic downstream signaling to prevent pathologic remodeling in heart failure. Mechanisms defined in animal and cell models include activation of adaptive hypertrophy, prevention of cardiac myocyte death, augmentation of contractility, and induction of ischemic preconditioning. Surprisingly, at the molecular level, alpha1-ARs localize to and signal at the nucleus in cardiac myocytes, and, unlike most GPCRs, activate "inside-out" signaling to cause cardioprotection. Contrary to past opinion, human cardiac alpha1-AR expression is similar to that in the mouse, where alpha1-AR effects are seen most convincingly in knockout models. Human clinical studies show that alpha1-blockade worsens heart failure in hypertension and does not improve outcomes in heart failure, implying a cardioprotective role for human alpha1-ARs. In summary, these findings identify novel functional and mechanistic aspects of cardiac alpha1-AR function and suggest that activation of cardiac alpha1-AR might be a viable therapeutic strategy in heart failure.

Alpha-1-adrenergic receptors: targets for agonist drugs to treat heart failure

Evidence from cell, animal, and human studies demonstrates that α1-adrenergic receptors mediate adaptive and protective effects in the heart. These effects may be particularly important in chronic heart failure, when catecholamine levels are elevated and β-adrenergic receptors are down-regulated and dysfunctional. This review summarizes these data and proposes that selectively activating α1-adrenergic receptors in the heart might represent a novel and effective way to treat heart failure. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure."

Inhibition of endogenous hedgehog signaling protects against acute liver injury after ischemia reperfusion

PURPOSE

Although Hedgehog (Hh) signaling is required for endodermal commitment and hepatogenesis, the possibility that it regulates liver injury after ischemia reperfusion (I/R) has not been considered. Therefore, we determined the expression pattern of Hh signaling and its role in liver injury following I/R using Hh antagonist cyclopamine (CYA).

METHODS

Sprague-Dawley rats were randomly divided into three groups. Sham group underwent a sham operation with no liver I/R. Vehicle or CYA preconditioned I/R groups underwent liver ischemia for 90 min followed by reperfusion for 1 h. Liver tissue and blood were analyzed for gene expression, histological and biochemical evaluation.

RESULTS

Hedgehog ligands were upregulated after reperfusion injury. Serum levels of aspartate transaminase and alanine transaminase, inflammatory cytokines, neutrophil infiltration, and tissue damage were significantly less in CYA-pretreated rats compared with vehicle-pretreated rats. CYA also decreased the phosphorylated form of JNK and ERK.

CONCLUSIONS

This study provides evidence that endogenous Hh signaling is an early mediator of liver injury and inflammation after I/R. CYA abrogates normothermic I/R injury in rats by inhibiting the MAPK pathway and decreasing the acute inflammatory response. This novel strategy of preconditioning livers with Hh antagonist may have effective therapeutic potential in preventing acute liver injury.

Pharmacological and ischemic preconditioning of the human myocardium: mitoK(ATP) channels are upstream and p38MAPK is downstream of PKC

BACKGROUND

These studies investigate the role of mitoK(ATP) channels, protein kinase C (PKC) and Mitogen activated protein kinase (p38MAPK) on the cardioprotection of ischemic (IP) and pharmacological preconditioning (PP) of the human myocardium and their sequence of activation.

RESULTS

Right atrial appendages from patients undergoing elective cardiac surgery were equilibrated for 30 min and then subjected to 90 min of simulated ischemia followed by 120 min reoxygenation. At the end of each protocol creatinine kinase leakage (CK U/g wet wt) and the reduction of MTT to formazan dye (mM/g wet wt) were measured. Similar protection was obtained with alpha1 agonist phenylephrine, adenosine and IP and their combination did not afford additional cardioprotection. Blockade of mitoK(ATP) channels with 5-hydroxydecanoate, PKC with chelerythrine, or p38MAPK with SB203580 abolished the protection of IP and of PP. In additional studies, the stimulation of mitoK(ATP) channels with diazoxide or activation of PKC with PMA or p38MAPK with anisomycin induced identical protection to that of IP and PP. The protection induced by diazoxide was abolished by blockade of PKC and by blockade of p38MAPK. Furthermore, the protection induced by PMA was abolished by SB203580 but not by 5-hydroxydecanoate, whereas the protection induced by anisomycin was unaffected by either 5-hydroxydecanoate or chelerythrine.

CONCLUSIONS

Opening of mitoK(ATP) channels and activation of PKC and p38MAPK are obligatory steps in the signal transduction cascade of IP and PP of the human myocardium with PKC activation being downstream of the opening of mitoK(ATP) channels and upstream of p38MAPK activation.

Exercise directly enhances myocardial tolerance to ischaemia-reperfusion injury in the rat through a protein kinase C mediated mechanism

OBJECTIVE

To determine whether exercise is capable of protecting the myocardium from experimental infarction and to explore the involvement of protein kinase C, a key signalling protein, in the development of any protection observed.

METHODS

Rats were exercised on a treadmill for 30 minutes at 23-27 m/min. Sham treated animals were placed on the stationary treadmill but not exercised. Twenty four hours later, hearts were Langendorff perfused and subjected to 35 minute left main coronary artery occlusion followed by 120 minute reperfusion. Infarct size was determined by tetrazolium staining and expressed as a percentage of the risk zone (I/R%). To examine the potential signalling pathway, animals were treated with either the selective protein kinase C inhibitor chelerythrine, 5 mg/kg intraperitoneally, or with vehicle 10 minutes before the exercise or sham treadmill period.

RESULTS

In the non-exercised group, mean (SEM) I/R was 48.4 (3.0)%. In the exercised group, infarct size was reduced to 17.3 (3.0)% (p < 0.01). Infarct size limitation induced by exercise was abolished by chelerythrine (I/R 45.0 (6.0)%). Chelerythrine pretreatment alone did not have any effect on infarct size (I/R 51.1 (3.9)%). Differences in infarct size were independent of risk zone size and myocardial contractile function during ischaemia-reperfusion.

CONCLUSIONS

Experimental moderate exercise induces protection against myocardial infarction 24 hours later. Protein kinase C activation during exercise appears to be an important signal mediator of this protective response.