Suppression of Endothelial Cell Apoptosis by High Density Lipoproteins (HDL) and HDL-associated Lysosphingolipids

Abstract

Apoptotic cell death following injury of vascular endothelium is assumed to play an important role in the pathogenesis of atherosclerosis. In this report, we demonstrate that high density lipoproteins (HDL), a major anti-atherogenic lipoprotein fraction, protect endothelial cells against growth factor deprivation-induced apoptosis. HDL blocked the mitochondrial pathway of apoptosis by inhibiting dissipation of mitochondrial potential (⌬ m ), generation of reactive oxygen species, and release of cytochrome c into the cytoplasm. As a consequence, HDL prevented activation of caspases 9 and 3 and apoptotic alterations of the plasma membrane such as increase of permeability and translocation of phosphatidylserine. Treatment of endothelial cells with HDL induced activation of the protein kinase Akt, an ubiquitous transducer of anti-apoptotic signals, and led to phosphorylation of BAD, a major Akt substrate. Suppression of Akt activity both by wortmannin and LY-294002 or by a dominant negative Akt mutant abolished the anti-apoptotic effect of HDL. Two bioactive lysosphingolipids present in HDL particles, sphingosylphosphorylcholine and lysosulfatide, fully mimicked the survival effect of HDL by blocking the mitochondrial pathway of apoptosis and potently activating Akt. In conclusion, the present study identifies HDL as a carrier of endogenous endothelial survival factors and suggests that inhibition of endothelial apoptosis by HDLassociated lysosphingolipids may represent an important and novel aspect of the anti-atherogenic activity of HDL.

Involvement of Cdc42 Signaling in ApoA-I-induced Cholesterol Efflux

“…SDS-PAGE and Western Blotting-SDS-PAGE and Western blotting were performed exactly as described previously (14). For each blot with anti-phosphospecific antibodies loading controls were performed using an antibody against a ubiquitously expressed protein (␣-actin).…”

“…HDL was shown previously to induce a variety of cellular signals, none of which, with the exception of protein kinase C, could be unequivocally shown to be associated with removal of cellular cholesterol (8 -16). Moreover, most of these responses could not be mimicked by apoA-I, thus precluding their direct involvement in the specific cholesterol efflux (11,14,16). The goal of the present study was to specifically investigate the apoA-I-induced signal transduction and its relationship to cholesterol efflux.…”

Modification of High Density Lipoprotein by Myeloperoxidase Generates a Pro-inflammatory Particle

“…HUVECs undergo apoptosis upon serum deprivation, and previous studies have shown that isolated human HDL, but not low density lipoprotein, inhibits serum starvation-induced endothelial cell apoptosis (40). In cells that were serum-deprived for 6 h, the level of apoptosis as measured by both annexin staining ( Fig.…”

Insulin-secreting β-Cell Dysfunction Induced by Human Lipoproteins

“…In the endocrine pancreas, Akt1 has been shown to regulate ␤-cell growth and survival (21). In endothelial cells, Akt is a mediator of the antiapoptotic effects of HDL (22).…”