Equivalent binding of wild-type lipoprotein lipase (LPL) and S447X-LPL to GPIHBP1, the endothelial cell LPL transporter

Abstract

The S447X polymorphism in lipoprotein lipase (LPL), which shortens LPL by two amino acids, is associated with low plasma triglyceride levels and reduced risk for coronary heart disease. S447X carriers have higher LPL levels in the pre- and post-heparin plasma, raising the possibility that the S447X polymorphism leads to higher LPL levels within capillaries. One potential explanation for increased amounts of LPL in capillaries would be more avid binding of S447X-LPL to GPIHBP1 (the protein that binds LPL dimers and shuttles them to the capillary lumen). This explanation seems plausible because sequences within the carboxyl terminus of LPL are known to mediate LPL binding to GPIHBP1. To assess the impact of the S447X polymorphism on LPL binding to GPIHBP1, we compared the ability of internally tagged versions of wild-type LPL (WT-LPL) and S447X-LPL to bind to GPIHBP1 in both cell-based and cell-free binding assays. In the cell-based assay, we compared the binding of WT-LPL and S447X-LPL to GPIHBP1 on the surface of cultured cells. This assay revealed no differences in the binding of WT-LPL and S447X-LPL to GPIHBP1. In the cell-free assay, we compared the binding of internally tagged WT-LPL and S447X-LPL to soluble GPIHBP1 immobilized on agarose beads. Again, no differences in the binding of WT-LPL and S447X-LPL to GPIHBP1 were observed. We conclude that increased binding of S447X-LPL to GPIHBP1 is unlikely to be the explanation for more efficient lipolysis and lower plasma triglyceride levels in S447X carriers.

Biochemical Analysis of the Lipoprotein Lipase Truncation Variant, LPLS447X, Reveals Increased Lipoprotein Uptake

“…Another study showed that ANGPTL4 displaces LPL from GPIHBP1 35 . Although GPIHBP1 bound equivalently to LPL and LPL S447X , it is possible that GPIHBP1 differently protects LPL and LPL S447X from inhibition by ANGPTL4 11 . We therefore tested the protective effect of GPIHBP1 on LPL and LPL S447X inhibition by ANGPTL4.…”

“…Measurements of proteins in tissue culture media showed that LPL S447X had increased 9 , decreased 8, 10 , or no difference 11, 12 in activity. Many of these studies used LPL quantified by ELISA to determine protein mass, whereas others use Western blots.…”

“…Glycosylphosphatidylinositol anchored high-density lipoprotein binding protein 1 (GPIHBP1) 15 and lipoprotein receptor-related protein (LRP) 16 are both known to interact with the C-terminus of LPL, and could thus interact differently with LPL S447X . GPIHBP1 is the protein responsible for translocation of LPL to the capillary lumen, and a recent study showed that its binding affinity for LPL S447X was not altered, which suggests another factor may be the key to the difference 11, 17 . LRP is a receptor for the endocytosis of ApoE-containing lipoproteins, and LPL enhances LRP-mediated lipoprotein uptake 18–20 .…”

GPIHBP1 and Plasma Triglyceride Metabolism

“…To understand the role of LPL in intravascular lipolysis, the field will ultimately need to define the effects of apo-AV, apo-CII, apo-CIII, and ANGPTL4 on GPIHBP1-bound LPL. Similarly, in order to understand the effects of various LPL polymorphisms ( e.g., the S447X polymorphism) on LPL activity, it will be important to study the effect of the polymorphism on GPIHBP1-bound LPL [29]. …”

Interaction of lipoprotein lipase polymorphisms with body mass index and birth weight to modulate lipid profiles in children and adolescents: the CASPIAN-III Study

“…30 A metaanalysis on previous studies among adults showed that S447X polymorphism decreased TG and increased HDL-C, and therefore decreased the CVD risk. 32 The key role of LPL is in postprandial lipid metabolism.…”