Effect of lipoprotein lipase on binding of chylomicrons to LDL receptor-deficient Chinese hamster ovary cells

Abstract

SUMMARY. The authors investigated the binding of human plasma125 I-labelled chylomicrons to Chinese hamster ovary (CHO) cells, i.e. native CHO cells are mutant ldl-A7 cells lacking the low-density lipoproteins receptor, in the absence and presence of exogenous bovine milk lipoprotein lipase (LPL) in the culture medium. Only a small amount of binding to either cell was observed in the absence of added LPL. Exogenously added LPL increased the speci®c binding of chylomicrons to ldl-A7 cells, as well as to native CHO cells. The enhanced binding of chylomicrons to ldl-A7 cells or native CHO cells by LPL was inhibited by heparinase and a monoclonal antibody against LPL (5D2) which recognizes the carboxyl terminal of LPL. However, the enhanced binding was not inhibited by 1 M NaCl, which abolishes the enzymatic activity of LPL in either ldl-A7 cell or native CHO cells. These results suggest that LPL enhances the binding of chylomicrons to heparan sulphate proteoglycans of CHO cells, and that it is the carboxyl terminal of LPL but not the enzymatic activity of LPL that is essential for LPL to mediate the binding of chylomicrons to CHO cells.Lipoprotein lipase (LPL) is a lipolytic enzyme which catalyses the hydrolysis of triglycerides in triglyceride-rich lipoproteins (TRLP), such as very low-density lipoprotein (VLDL) and chylomicrons. This hydrolysis requires TRLP binding to LPL, which is anchored to the endothelial cell by heparan sulphate proteoglycans (HSPG).LPL is known to mediate the binding of all classes of lipoproteins, such as chylomicrons, VLDL, low-density lipoproteins (LDL) and high-density lipoproteins (HDL), to a variety of cells, such as Hep G2 cells, ®broblasts and macrophages, 1±7 and it is speculated that this process does not depend on the hydrolytic function of the enzyme. LPL has high binding af®nity for HSPG, and several studies 3±5,8,9 suggest that these cell-surface molecules may be involved in the LPL-mediated enhanced binding of lipoproteins to cultured cells. It was reported that the binding of apolipoprotein E liposomes to the a 2 -macroglobulin/LDL receptor-related protein (LRP) is increased in the presence of LPL.3 Moreover, several studies 10,11 have demonstrated that the carboxyl terminal domain of LPL binds to the LDL receptor. However, the molecular mechanisms of LPLmediated lipoproteins binding to cells are still controversial. The availability of the ldl-A7 cells or the LDL receptor-de®cient Chinese hamster ovary (CHO) cells gave us a unique opportunity to investigate the effect of LPL on the binding of lipoproteins to cells. In this study we investigated the effects of LPL on the binding of chylomicrons to the cell surface and its possible mechanisms, using a series of CHO cells, namely, native CHO cells and ldl-A7 cells. MATERIALS AND METHODSMutant CHO cells lacking the LDL receptor (ldl-A7) 12 were kindly provided by Dr Monty Krieger (Massachusetts Institute of Technology).CHO cells were grown in HAM-F12 medium with 10% foetal calf serum, and the medium was changed to HAM-F12 ...

Effect of the APOC3 Sst I SNP on fasting triglyceride levels in men heterozygous for the LPL P207L deficiency

“…In heterozygous, we can speculate that (1) VLDL particles enriched in apoC-III would remain longer in the blood compartment, increasing their ability to interact with other circulating lipoproteins and favoring apolipoprotein and lipid exchanges mediated by the CETP activity, (2) the elevated apoC-III concentrations in VLDL subclass of the APOC3 S2 allele carriers 10 is believed to be particularly atherogenic since it would delay the clearance of these particles by inhibiting LPL activity and reducing the clearance of remnants lipoproteins via LDL and VLDL receptors (for review), 5 (3) finally, additive effects may occur as the LPL binding activity (responsible for the TG-rich lipoprotein internalization by LDL and VLDL receptors via the LPL-mediated binding of particles to heparin sulfate proteoglycans) is altered in LPL-deficient heterozygotes since they lack the carboxyl-terminal part of the LPL protein (at least in half of the protein) that is essential for the binding activity. 34 As observed in the present association analysis, the relative risk of having an atherogenic VLDL profile is considerably increased in patients bearing the S2 allele since they exhibited a greater number of small VLDL particles. Furthermore, correlation data provided us with some evidence that the concentrations of VLDL-TG are strongly correlated with the waist circumference only in carriers of APOC3 Sst I SNP in LPL-deficient patients C Garenc et al the APOC3 S2 allele.…”

Catalytically Inactive Lipoprotein Lipase Overexpression Increases Insulin Sensitivity in Mice

“…The nonhydrolytic functions of enzyme accelerate incorporation of these lipoproteins into cells through specific receptors and/or by unclarified pathways. We have shown that LPL induces the chylomicrons uptake using LDL receptor-deficient cultured cells [11]. LPL can bridge between lipoproteins and cell-surface heparan sulfate proteoglycans [5], which does not depend on the hydrolyzing function of the enzyme [11,12].…”

“…Therefore, in the presence of systemic insulin resistance, transcriptionally and post-transcriptionally reduced LPL activity could contribute to the development of hypertriglyceridemia [8]. In addition to the hydrolytic activity, LPL mediates the binding of all classes of lipoproteins to a variety of cells, such as Hep G2 cells, fibroblast and macrophages [9][10][11]. The nonhydrolytic functions of enzyme accelerate incorporation of these lipoproteins into cells through specific receptors and/or by unclarified pathways.…”