Inhibition of myocardial apoptosis by ischaemic and beta-adrenergic preconditioning is dependent on p38 MAPK.

INTRODUCTION

Apoptosis occurring during ischaemia /reperfusion contributes independently to tissue damage, and involves activation of the stress-kinase, p38 MAPK during reperfusion. Ischaemic preconditioning (IPC) protects against ischaemia/reperfusion mediated necrosis and apoptosis. The role of p38 MAPK in the protective effect of preconditioning against apoptosis is unknown. Pharmacologic preconditioning with isoproterenol (beta-PC) also protects against necrosis, but it is not known whether it protects against apoptosis.

AIM

The aim of the study was to investigate whether the protective effect of IPC against apoptosis is related to activation of p38 MAPK and whether beta-PC also protects against apoptosis.

MATERIALS AND METHODS

Isolated perfused rat hearts were used to study the effect of ischaemia and reperfusion on apoptosis and infarct size. Ischaemic preconditioning was elicited by 3 x 5 min global ischaemia, and beta-PC by 5 min isoproterenol 10(-7) M. For infarct size hearts were subjected to regional ischaemia for 35 min followed by 120 min reperfusion. Infarct size was determined by the tetrazolium staining technique, and expressed as percentage of area at risk. For markers of apoptosis hearts were subjected to global ischaemia of 25 min plus 30 min reperfusion. Apoptosis was determined by Western blot using antibodies against caspase-3 and PARP. p38 MAPK activation was inhibited by SB203580 (1 microM) administration 10 min prior to commencing ischaemia, and bracketing the IPC and beta-PC preconditioning protocols. p38 MAPK was activated by administration of anisomycin (5 microM) 10 min prior to index ischaemia in one protocol, and 10 min during reperfusion in non-preconditioned as well as IPC and beta-PC hearts. Results were analysed using ANOVA and a Newman-Keuls post-hoc test.

RESULTS

In the apoptosis model using global ischaemia, IPC and beta-PC both resulted in a significant decrease in p38 MAPK activation at the end of reperfusion when compared to non-preconditioned hearts. This was accompanied by a significant decrease in apoptosis as measured with both caspase-3 activation and PARP cleavage. Inhibiting p38 MAPK by administration of SB203580 10 min prior to ischaemia resulted in a significant reduction in both markers of apoptosis. Bracketing the triggering phase of either IPC or beta-PC with SB203580 resulted in attenuated p38 MAPK activation during reperfusion and did not abolish the protective effect of IPC or beta-PC against apoptosis. Activating p38 MAPK with anisomycin prior to ischaemia resulted in a reduction of markers of apoptosis, whereas activation of p38 MAPK with anisomycin during reperfusion did not exacerbate apoptosis in any groups, exept for an increase in PARP cleavage in IPC hearts. In the model of regional ischaemia, IPC and beta-PC reduced infarct size significantly, and to the same extent as inhibition of p38 MAPK by administration of SB203580 10 min prior to ischaemia. Bracketing the triggering phase of either IPC or beta-PC did not abolish the reduction in infarct size. Activating p38 MAPK during reperfusion was accompanied by an increase in infarct size only in IPC hearts, but not in beta-PC hearts.

CONCLUSION

These results indicate that (1) Both IPC and beta-PC elicit protection against apoptosis and necrosis, (2) activation of p38 MAPK is not a trigger of preconditioning against apoptosis and necrosis and (3) activation of p38 MAPK during reperfusion increases necrosis only if ischaemia is used to precondition hearts, but not with pharmacologic preconditioning with isoproterenol.