Apolipoproteins E and AV mediate lipoprotein clearance by hepatic proteoglycans

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Abstract

The heparan sulfate proteoglycan (HSPG) syndecan-1 (SDC1) acts as a major receptor for triglyceride-rich lipoprotein (TRL) clearance in the liver. We sought to identify the relevant apolipoproteins on TRLs that mediate binding to SDC1 and determine their clinical relevance. Evidence supporting ApoE as a major determinant arose from its enrichment in TRLs from mice defective in hepatic heparan sulfate (Ndst1^f/fAlbCre⁺ mice), decreased binding of ApoE-deficient TRLs to HSPGs on human hepatoma cells, and decreased clearance of ApoE-deficient [³H]TRLs in vivo. Evidence for a second ligand was suggested by the faster clearance of ApoE-deficient TRLs after injection into WT Ndst1^f/fAlbCre^– versus mutant Ndst1^f/fAlbCre⁺ mice and elevated fasting and postprandial plasma triglycerides in compound Apoe^–/–Ndst1^f/fAlbCre⁺ mice compared with either single mutant. ApoAV emerged as a candidate based on 6-fold enrichment of ApoAV in TRLs accumulating in Ndst1^f/fAlbCre⁺ mice, decreased binding of TRLs to proteoglycans after depletion of ApoAV or addition of anti-ApoAV mAb, and decreased heparan sulfate–dependent binding of ApoAV-deficient particles to hepatocytes. Importantly, disruption of hepatic heparan sulfate–mediated clearance increased atherosclerosis. We conclude that clearance of TRLs by hepatic HSPGs is atheroprotective and mediated by multivalent binding to ApoE and ApoAV.

Authors

Jon C. Gonzales, Philip L.S.M. Gordts, Erin M. Foley, Jeffrey D. Esko