Association of Increased Ubiquitinated Proteins with Cardiac Apoptosis

ABSTRACT Intracellular proteases play an important role in the regulation of apoptosis. A study was performed to determine whether inhibition of the cardiac ATP-dependent ubiquitin 26S protease complex affects cardiomyocyte apoptosis. Isolated rat hearts were perfused for up to 80 min with Krebs-Henseleit buffer ± the 26S-proteasome inhibitor, MG132 (Z-leu-leu-leucinal). TUNEL-staining of hearts perfused with 25 μM MG132 for 50 min revealed a significant increase (p < 0.05) in the apoptotic index from 1.1% to 15.5% when compared with control hearts perfused with buffer only. Histology of adjacent myocardial sections revealed no signs of necrotic or late apoptotic (nuclear condensation) changes, indicating that the TUNEL-positive nuclei were in the early stages of apoptosis. This early stage of apoptosis was associated with a significant (p < 0.05) reduction in cardiac function. There was a 63% decrease in the rate · pressure product in hearts perfused with 25 μM MG132 as compared with a 35% decrease in co...