Published online before print December 18, 2003, doi: 10.1161/01.RES.0000113782.07824.BE
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© 2004 American Heart Association, Inc.
Cellular Biology |
Role of Caspases in Ox-LDL–Induced Apoptotic Cascade in Human Coronary Artery Endothelial Cells
From the Departments of Internal Medicine and Physiology and Biophysics (J.C., J.L.M., X.J., D.L.), University of Arkansas for Medical Sciences and Central Arkansas Veterans Healthcare System, Little Rock, Ark; and the Department of Medicine (N.H., J.N.), Drexel University, Philadelphia, Pa.
Correspondence to Dayuan Li, MD, PhD, Division of Cardiovascular Medicine, University of Arkansas for Medical Sciences, 4301 W Markham St, Slot 532, Little Rock, AR 72205. E-mail lidayuan{at}uams.edu
Oxidized low-density lipoprotein (ox-LDL) induces apoptosis in endothelial cells. However, steps leading to ox-LDL–induced apoptosis remain unclear. We examined the role of ox-LDL and its newly described receptor LOX-1 in the expression of intracellular pro- and antiapoptotic proteins and caspase pathways in human coronary artery endothelial cells (HCAECs). Cells were cultured and treated with different concentrations (10 to 80 µg/mL) of ox-LDL for different times (2 to 24 hours). Ox-LDL induced apoptosis in HCAECs in a concentration- and time-dependent manner. Ox-LDL also activated caspase-9 and caspase-3, but not caspase-8. After ox-LDL treatment, there was a significant release of activators of caspase-9, including cytochrome c and Smac from mitochondria to cytoplasmic compartment, and their release was not affected by treatment of cells with inhibitors of either caspase-8 or caspase-9. Ox-LDL also decreased expression of antiapoptotic proteins Bcl-2 and c-IAP (inhibitory apoptotic protein)-1, which are involved in the release of cytochrome c and Smac and activation of caspase-9, in a concentration- and time-dependent manner. On the other hand, ox-LDL did not change the expression of Fas-associated death domain-like interleukin-1ß–converting enzyme-inhibitory protein (FLIP) and proapoptotic protein Fas, which are required for the activation of caspase-8. Further, ox-LDL did not cause the truncation of Bid, which implies the activation of caspase-8. In other experiments, pretreatment of HCAECs with the caspase-9 inhibitor z-LEHD-fmk, but not the caspase-8 inhibitor z-IETD-fmk, blocked ox-LDL–induced activation of caspase-3 and apoptosis. As expected, pretreatment with the caspase-3 inhibitor DEVD-CHO inhibited ox-LDL–induced activation of caspase-3 and resultant apoptosis. The proapoptotic effects of ox-LDL were mediated by its receptor LOX-1, because pretreatment of HCAECs with antisense-LOX-1, but not sense-LOX-1, blocked these effects of ox-LDL. These findings suggest that ox-LDL through its receptor LOX-1 decreases the expression of antiapoptotic proteins Bcl-2 and c-IAP-1. This is followed by activation of apoptotic signaling pathway, involving release of cytochrome c and Smac and activation of caspase-9 and then caspase-3.
Key Words: apoptosis • caspases • endothelial cells • LOX-1 • oxidized LDL
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