The PPAR-gamma agonist rosiglitazone facilitates Akt rephosphorylation and inhibits apoptosis in cardiomyocytes during hypoxia/reoxygenation.

BACKGROUND AND AIM

Results on the cardiovascular effects of PPAR-gamma agonists are conflicting. On one hand, it was suggested that the PPAR-gamma agonist rosiglitazone may increase the risk of cardiovascular events. On the other hand, PPAR-gamma agonists reduce myocardial infarct size and improve myocardial function during ischemia/reperfusion in animal studies in vivo. However, the mechanism of this effect is unclear, and it is open if PPAR-gamma agonists have a direct effect on cardiac myocyte survival in ischemia/reperfusion. The aim of this study was to determine the effect of the PPAR-gamma agonist rosiglitazone on hypoxia/reoxygenation-induced apoptosis of isolated cardiomyocytes.

METHODS

Isolated rat cardiac myocytes were pretreated with rosiglitazone or vehicle for 30 min before they were subjected to hypoxia for 4 h followed by different times of reoxygenation (5 min to 12 h). Apoptosis was determined by in situ hybridization for DNA fragmentation (TUNEL) as well as detection of cytoplasmic accumulation of histone-associated DNA fragments by enzyme-linked immunosorbent assay (ELISA). Activation of apoptosis regulating intracellular signalling pathways was studied by immunoblotting using phosphospecific antibodies.

RESULTS

Rosiglitazone significantly reduced apoptosis of isolated cardiomyocytes subjected to hypoxia/reoxygenation, independently determined with two methods. After 4 h of hypoxia and 12 h of reoxygenation, 34 +/- 3.6% of the vehicle treated cardiac myocytes stained positive for DNA fragmentation in the TUNEL staining. Rosiglitazone treatment reduced this effect by 23% (p < 0.01). Even more pronounced, cytoplasmic accumulation of histone-associated DNA fragments detected by ELISA was reduced by 35% (p < 0.05) in the presence of rosiglitazone. This inhibition of hypoxia/reoxygenation-induced apoptosis was associated with an increased reoxygenation-induced rephosphorylation of the protein kinase Akt, a crucial mediator of cardiomyocyte survival in ischemia/reperfusion of the heart. This effect was reversed by GW-9662, an irreversible PPAR-gamma antagonist. However, rosiglitazone did not alter phosphorylation of the MAP kinases ERK1/2 and c-Jun N-terminal kinase (JNK).

CONCLUSION

It can be concluded that cardiac myocytes are direct targets of PPAR-gamma agonists promoting its survival in ischemia/reperfusion, at least in part by facilitating Akt rephosphorylation. This effect may be of clinical relevance inhibiting the reperfusion-induced injury in patients suffering from myocardial infarction or undergoing cardiac surgery.