OXIDIZED LOW-DENSITY-LIPOPROTEIN INDUCES APOPTOSIS OF HUMAN ENDOTHELIAL-CELLS BY ACTIVATION OF CPP32-LIKE PROTEASES - A MECHANISTIC CLUE TOTHE RESPONSE TO INJURY HYPOTHESIS

Background Oxidized LDL (oxLDL) is believed to play a key role as a tr iggering molecule that causes injury to the endothelium as an early ev ent in atherogenesis, However, the mechanisms by which oxLDL injures e ndothelial cells are entirely unknown. We speculate that oxLDL may act ivate a cellular suicide pathway that leads to apoptosis. Methods and Results Human umbilical venous endothelial cells (HUVEC) were incubate d with increasing doses of native or oxLDL for 18 hours. Apoptosis of HUVEC was measured with an ELISA specific for histone-associated DNA f ragments and confirmed with DNA laddering. Native LDL had no effect, b ut incubation with oxLDL dose-dependently induced apoptosis of HUVEC. Induction of apoptosis by oxLDL was associated with increased CPP32-li ke protease activity, which is the major enzyme that initiates the pro teolytical cascade leading to cell death. Specific inhibition of CPP32 activity completely abrogated oxLDL-induced apoptosis. The antioxidan ts N-acetylcysteine and the combination of vitamins C and E prevented oxLDL-induced apoptosis, abrogated the enhancement of CPP32-like prote ase activity, and inhibited the proteolytic cleavage of CPP32 into its active subunit p17. Conclusions oxLDL activates the suicide pathway l eading to apoptosis of endothelial cells by enhancing CPP32-like prote ase activity. The oxLDL-mediated activation of CPP32 appears to involv e the elaboration of reactive oxygen species. Activation of the cell d eath effector CPP32 by oxLDL mag provide a mechanistic clue to the ''r esponse-to-injury'' hypothesis of atherogenesis.