Transcytosis of lipoprotein lipase across cultured endothelial cells requires both heparan sulfate proteoglycans and the very low density lipoproteinreceptor

Lipoprotein lipase (LPL), the major enzyme responsible for the hydrolysis o f circulating lipoprotein triglyceride molecules, is synthesized in myocyte s and adipocytes but functions while bound to heparan sulfate proteoglycans (HSPGs) on the luminal surface of vascular endothelial cells. This require s transfer of LPL from the abluminal side to the luminal side of endothelia l cells. Studies were performed to investigate the mechanisms of LPL transc ytosis using cultured monolayers of bovine aortic endothelial cells. We tes ted whether HSPGs and. members of the low density lipoprotein (LDL) recepto r superfamily were involved in transfer of LPL from the basolateral to the apical side of cultured endothelial cells; Heparinase/heparinitase treatmen t of the basolateral cell surface or addition of heparin to the basolateral medium decreased the movement of LPL, This suggested a:requirement for HSP Gs. To assess the role of receptors, we used either receptor-associated pro tein, the 39-kDa inhibitor of ligand binding to the LDL receptor-related pr otein and the very low density lipoprotein (VLDL) receptor,or specific rece ptor antibodies. Receptor-associated protein reduced I-125-LPL and LPL acti vity transfer across the monolayers, When the basolateral surface of the ce lls was treated with antibodies, only anti=VLDL receptor antibodies inhibit ed transcytosis, Moreover, overexpression of the VLDL receptor using adenov iral-mediated gene transfer increased LPL transcytosis, Thus, movement of a ctive LPL across endothelial cells involves both HSPGs and VLDL receptor.