Small, dense HDL 3 particles attenuate apoptosis in endothelial cells: pivotal role of apolipoprotein A‐I

Abstract

Plasma high-density lipoproteins (HDLs) protect endothelial cells against apoptosis induced by oxidized low-density lipoprotein (oxLDL). The specific component(s) of HDLs implicated in such cytoprotection remain(s) to be identified. Human microvascular endothelial cells (HMEC-1) were incubated with mildly oxLDL in the presence or absence of each of five physicochemically distinct HDL subpopulations fractionated from normolipidemic human plasma (n= 7) by isopycnic density gradient ultracentrifugation. All HDL subfractions protected HMEC-1 against oxLDL-induced primary apoptosis as revealed by nucleic acid staining, annexin V binding, quantitative DNA fragmentation, inhibition of caspase-3 activity and reduction of cytoplasmic release of cytochrome c and apoptosis-inducing factor. Small, dense HDL 3c displayed twofold superior intrinsic cytoprotective activity (as determined by mitochondrial dehydrogenase activity) relative to large, light HDL 2b on a per particle basis (P < 0.05). Equally, all HDL subfractions attenuated intracellular generation of reactive oxygen species (ROS); such anti-oxidative activity diminished from HDL 3c to HDL 2b. The HDL protein moiety, in which apolipoprotein A-I (apoA-I) predominated, accounted for ∼70% of HDL anti-apoptotic activity. Furthermore, HDL reconstituted with apoA-I, cholesterol and phospholipid potently protected HMEC-1 from apoptosis. By contrast, modification of the content of sphingosine-1-phosphate in HDL did not significantly alter cytoprotection. We conclude that small, dense, lipid-poor HDL 3 potently protects endothelial cells from primary apoptosis and intracellular ROS generation induced by mildly oxLDL, and that apoA-I is pivotal to such protection.

Dysfunctional HDL: From Structure-Function-Relationships to Biomarkers

“…In a more detailed study, HDL subpopulations enriched with apoA-I account for approximately 70 % of the antiapoptotic activity of HDL in a cell culture model with human microvascular endothelial cells that were treated with mildly oxidized LDL. Using rHDL consisting of apoA-I, cholesterol and phospholipids potently inhibited oxLDLinduced apoptosis in these cells (de Souza et al 2010). This suggests that apoA-I plays an important role for the antiapoptotic capacity of HDL in oxLDL-stimulated endothelial cells.…”

“…In the aorta the capacity of HDL to quench endothelial cell apoptosis may therefore represent an antiatherogenic property of HDL (de Souza et al 2010;Nofer et al 2001;Suc et al 1997;Sugano et al 2000). HDL has been shown to attenuate endothelial cell apoptosis induced by different stimuli such as TNF-α, oxLDL, and growth factor deprivation (de Souza et al 2010;Nofer et al 2001;Suc et al 1997;Sugano et al 2000). It has been suggested that HDL may inhibit both death-receptor and mitochondrial-mediated apoptotic pathways.…”

“…The situation is completely different in atherosclerotic plaques, in a high oxidative stress environment where macrophages produce high amounts of nitric oxide or peroxynitrite that could induce apoptotic cell death (Kockx and Herman 2000). In the aorta the capacity of HDL to quench endothelial cell apoptosis may therefore represent an antiatherogenic property of HDL (de Souza et al 2010;Nofer et al 2001;Suc et al 1997;Sugano et al 2000). HDL has been shown to attenuate endothelial cell apoptosis induced by different stimuli such as TNF-α, oxLDL, and growth factor deprivation (de Souza et al 2010;Nofer et al 2001;Suc et al 1997;Sugano et al 2000).…”

Dysfunctional high-density lipoproteins in coronary heart disease: implications for diagnostics and therapy

“…[16][17][18][19] Furthermore, HDL functions as a protective factor for the vascular endothelium by mechanisms that involve interactions with signaling receptors and hence go beyond the regulation of cholesterol homoeostasis or the inhibition of oxidation ( Figure 1). HDL induces endothelium-dependent vascular relaxation via increased endothelial nitric oxide synthase (eNOS) phosphorylation and nitric oxide production, 20 and maintains endothelial barrier stability by promoting endothelial cell survival, 21,22 stimulating endothelial junction closure via HDL-bound sphingosine-1-phosphate (S1P), 23,24 and accelerating endothelial cell migration and re-endothelialization of injured arteries. 25,26 Moreover, antiinflammatory activities of HDL in atherosclerosis have been documented.…”

Lipidomics of Plasma High-Density Lipoprotein: Insights into Anti-Atherogenic Function

“…HDL particles feature a high level of structural, compositional and functional heterogeneity, differing in physical (shape, size, density, electrophoretic mobility) and biological properties. Interestingly, small, dense HDL3, which feature distinct structure [16,17] and are enriched in several bioactive lipids and proteins [10,18] display enhanced capacity to efflux cellular cholesterol via the ATP-binding cassette transporter A1 (ABCA1) [19,20], to reduce apoptosis in endothelial cells [21] and to protect low-density lipoprotein (LDL) from oxidative stress [22]. The content of major lipid classes per HDL particle typically diminishes with progressive increase in HDL density, reflecting depletion of total lipid relative to protein components [10].…”