Abstract 20568: Activation of PKN Mediates Survival of Cardiomyocytes Through Cardiac Proteasome Activation and Alpha B Crystallin in the Heart During Ischemia-Reperfusion
Background: PKN is a serine/threonine kinase, whose catalytic domain is highly homologous to protein kinase C. However, the function of PKN in the heart is poorly understood.
Objective: To elucidate the role of PKN in the heart in regulating myocardial injury during ischemia/reperfusion (I/R) and the underlying signaling mechanism.
Results: In the heart subjected to I/R, PKN was phosphorylated at Thr774, which is essential for PKN activation. We generated cardiac-specific constitutively active PKN (Tg-CAPKN) and dominant negative PKN (Tg-DNPKN) transgenic mice and applied 45 minutes of myocardial ischemia followed by 24 hours of reperfusion. Infarct size/area at risk (MI/AAR) was smaller in Tg-CAPKN hearts than in non-Tg (nTg) hearts (15 ± 5 vs. 38 ± 5%, p<0.01). In contrast, MI/AAR was greater in Tg-DNPKN hearts than in nTg hearts (63 ± 9 vs. 45 ± 8%, p<0.01). In Tg-CAPKN hearts, phosphorylation of alpha B crystallin (BC) at both Ser59 and Ser45 was enhanced compared to nTg hearts. In Tg-DNPKN hearts, the increased phosphorylation of alpha BC at both Ser59 and Ser45 after I/R was markedly inhibited. In neonatal rat cardiomyocytes, adenovirus-harboring (Ad) PKN (Ad.PKN) decreased, whereas Ad.PKN-shRNA enhanced, cell death induced by hydrogen peroxide. Downregulation of alpha BC by Ad.alpha BC-shRNA inhibited the cell protective effect of PKN against hydrogen peroxide-induced cell death, suggesting that alpha BC plays an important role in mediating the protective effect of PKN. Proteasome activity in the heart as evaluated by α-chymotrypsin activity was enhanced in Tg-CAPKN hearts by 50% compared to nTg hearts. In the nTg hearts subjected to I/R, the proteasome activity was decreased, whereas it was maintained in Tg-CAPKN hearts. The decreased proteasome activity after I/R was enhanced in Tg-DNPKN hearts. Furthermore, the infarct reducing effect in Tg-CAPKN mice was significantly reversed by epoxomycin, a proteasome inhibitor, suggesting that increases in the proteasome activity are important for cardioprotection by PKN.
Conclusion: Activation of PKN during I/R mediates survival of cardiomyocytes through increased phosphorylation of alpha BC and proteasome activation in the heart.
- © 2010 by American Heart Association, Inc.