Binding of β-VLDL to Heparan Sulfate Proteoglycans Requires Lipoprotein Lipase, Whereas ApoE Only Modulates Binding Affinity

Abstract

Abstract —The binding of β-VLDL to heparan sulfate proteoglycans (HSPG) has been reported to be stimulated by both apoE and lipoprotein lipase (LPL). In the present study we investigated the effect of the isoform and the amount of apoE per particle, as well as the role of LPL on the binding of β-VLDL to HSPG. Therefore, we isolated β-VLDL from transgenic mice, expressing either APOE*2(Arg158→Cys) or APOE*3-Leiden (E2-VLDL and E3Leiden-VLDL, respectively), as well as from apoE-deficient mice containing no apoE at all (Enull-VLDL). In the absence of LPL, the binding affinity and maximal binding capacity of all β-VLDL samples for HSPG-coated microtiter plates was very low. Addition of LPL to this cell-free system resulted in a 12- to 55-fold increase in the binding affinity and a 7- to 15-fold increase in the maximal binding capacity ( B max ). In the presence of LPL, the association constant ( K a ) tended to increase in the order Enull-VLDL<E2-VLDL<E3Leiden-VLDL, whereas B max increased in the reverse order: E3Leiden-VLDL≈E2-VLDL<Enull-VLDL. Addition of LPL resulted in a marked stimulation of both K a and B max for binding of β-VLDL samples to J774 cells similar to that found for the binding to HSPG-LPL complexes. Our results indicate that both K a and B max for binding of β-VLDL to HSPG are increased more than 1 order of magnitude on addition of LPL. In addition, for the binding of β-VLDL to HSPG-LPL complexes, the presence of apoE is not a prerequisite, but results in an increased binding affinity, depending on the apoE isoform used.