The Heparin-Binding Proteins Apolipoprotein E and Lipoprotein Lipase Enhance Cellular Proteoglycan Production

Abstract—Apolipoprotein E (apoE) and lipoprotein lipase (LPL), key proteins in the regulation of lipoprotein metabolism, bind with high affinity to heparin and cell-surface heparan sulfate proteoglycan (HSPG). In the present study, we tested whether the expression of apoE or LPL would modulate proteoglycan (PG) metabolism in cells. Two apoE-expressing cells, macrophages and fibroblasts, and LPL-expressing Chinese hamster ovary (CHO) cells were used to study the effect of apoE and LPL on PG production. Cellular PGs were metabolically labeled with 35[S]sulfate for 20 hours, and medium, pericellular PGs, and intracellular PGs were assessed. In all transfected cells, PG levels in the 3 pools increased 1.6- to 3-fold when compared with control cells. Initial PG production was assessed from the time of addition of radiolabeled sulfate; at 1 hour, there was no difference in PG synthesis by apoE-expressing cells when compared with control cells. After 1 hour, apoE-expressing cells had significantly greater produc...