Apolipoprotein E Containing High Density Lipoprotein Stimulates Endothelial Production of Heparan Sulfate Rich in Biologically Active Heparin-like Domains

Abstract

Reduced heparin and heparan sulfate (HS) proteoglycans (PG) have been observed in both inflammation and atherosclerosis. Methods to increase endogenous heparin and heparan sulfate are not known. We found that incubation of endothelial cells with 500 -1,000 g/ml high density lipoprotein (HDL) increased 35 SO 4 incorporation into PG by 1.5-2.5-fold. A major portion of this increase was in HS and was the result of increased synthesis. Total PG core proteins were not altered by HDL; however, the ratio of 35 SO 4 to [ 3 H]glucosamine was increased by HDL, suggesting increased sulfation of glycosaminoglycans. In addition, HDL increased the amount of highly sulfated heparin-like HS in the subendothelial matrix. HS from HDL-treated cells bound 40 ؎ 5% more 125 I-antithrombin III (requires 3-O sulfated HS) and 49 ؎ 3% fewer monocytes. Moreover, the HS isolated from HDL-treated cells inhibited smooth muscle cell proliferation (by 83 ؎ 5%) better than control HS (56 ؎ 6%) and heparin (42 ؎ 6%). HDL isolated from apolipoprotein E (apoE)-null mice did not stimulate HS production unless apoE was added. ApoE also stimulated HS production in the absence of HDL. ApoE did not increase 35 SO 4 incorporation in macrophages and fibroblasts, suggesting that this is an endothelial cell-specific process. Receptor-associated protein inhibited apoEmediated stimulation of HS only at higher (20 g/ml) doses, suggesting the involvement of a receptor-associated protein-sensitive pathway in mediating apoE actions. In summary, our data identify a novel mechanism by which apoE and apoE-containing HDL can be antiatherogenic. Identification of specific apoE peptides that stimulate endothelial heparin/HS production may have important therapeutic applications. Proteoglycans (PG),1 important constituents of vascular cell membranes and extracellular matrix (1, 2), consist of a core protein to which long chains of negatively charged polysaccharides termed glycosaminoglycans (GAG) are attached. The three major PG classes in the vessel wall are heparan sulfate (HS), chondroitin sulfate, and dermatan sulfate. HSPG play an important role in the regulation of various vascular functions. They bind and promote lipoprotein lipase activity, the key enzyme in the hydrolysis of triglyceride-rich lipoproteins (3). Basic fibroblast growth factor, a potent mitogen and angiogenic factor, requires the presence of cell surface HSPG or exogenous heparin to bind to its high affinity cell signaling receptor (4). In addition, HSPG potentiate the thrombin-inhibiting actions of antithrombin (5). A reduction in arterial HS and heparin has been observed under conditions of inflammation and atherosclerosis as well as with increased age (6 -14). The age-dependent decrease in HS is more pronounced in atherosclerotic tissues than in normal tissues (10,11). An inverse correlation between the amount of cholesterol in the lesion and the concentration of HS was observed in human aortas. More importantly, this negative correlation was observed in both normal and atherosclerotic vessels...

Cell-derived Apolipoprotein E (ApoE) Particles Inhibit Vascular Cell Adhesion Molecule-1 (VCAM-1) Expression in Human Endothelial Cells

“…One explanation is that in transfected wells entrapment of secreted apoE by endothelial HSPG (32) may result in high local concentrations at the cell surface and enhanced biological activity. Indeed, HSPG is abundant on the cell-surface of cultured endothelial cells, and its production is rapidly stimulated by apoE (33). Although our transfection studies are not directly relevant to the situation in vivo, as endothelium does not synthesize apoE, they do have implications for gene therapy; transfecting endothelial cells to express apoE may limit endothelial activation.…”

Apolipoprotein E kinetics: influence of insulin resistance and type 2 diabetes

“…Many studies have now demonstrated that HDL apoE plays a crucial anti-atherogenic role. In vitro studies have shown that HDL apoE promotes cholesterol efflux from peripheral cells to the liver, 44 has a direct anti-atherogenic role at the site of atherosclerotic lesion, 45 has antioxidant activity 18 and inhibits platelet aggregation through the nitric oxide pathway. 46 In a previous work, we have also suggested that HDL apoE could play an anti-inflammatory role in vivo in obese adults.…”

Gene Expression Profiling of Mucosal Addressin Cell Adhesion Molecule-1+ High Endothelial Venule Cells (HEV) and Identification of a Leucine-Rich HEV Glycoprotein as a HEV Marker

“…ApoE also seems to be highly expressed in both MECA-367 ϩ HEV cells and MECA-79 ϩ HEV cells, but not in CD31 ϩ flat endothelial cells. Although ApoE is a ligand for several lipoprotein receptors and is known to play a major role in the hepatic clearance of remnant lipoproteins (45), it also stimulates the incorporation of 35 SO 4 and the production of heparan sulfate in endothelial cells (41). Because intensive incorporation of 35 SO 4 and production of heparan sulfate proteoglycans are observed in HEV cells in vivo (3), an increased expression of ApoE may be functionally related to the unique biosynthetic activity of HEV cells.…”

“…(10) and KC (36), an inflammatory cytokine, TAG7 (37), a promiscuous chemokine receptor, DARC (38), and some TGF-␤-responsive molecules, like mac25 (39), transglutaminase (40), and apolipoprotein E (ApoE) (41). Because these molecules are apparently not expressed in CD31…”