STABLE EXPRESSION AND SECRETION OF APOLIPOPROTEINS E3 AND E4 IN MOUSENEUROBLASTOMA-CELLS PRODUCES DIFFERENTIAL-EFFECTS ON NEURITE OUTGROWTH

Previously, we demonstrated in cultured dorsal root ganglion neurons t hat, in the presence of beta-migrating very low density lipoproteins ( beta-VLDL), apolipoprotein (apo) E4, but not apoE3, suppresses neurite outgrowth, In the current studies, murine neuroblastoma cells (Neuro- 2a) were stably transfected with human apoE3 or apoE4 eDNA, and the ef fect on neurite outgrowth was examined, The stably transfected cells s ecreted nano gram quantities of apoE (44-89 ng/mg of cell protein in 4 8 h), In the absence of lipoproteins, neurite outgrowth was similar in the apoE3- and apoE4-secreting cells, The apoE4-secreting cells, when incubated with beta-VLDL, VLDL, cerebrospinal fluid lipoproteins (d < 1.21 g/ml), or with triglyceride/phospholipid (2.7:1 (w/w)) emulsions , showed a reduction in the number of neurites/cell, a decrease in neu rite branching, and an inhibition of neurite extension, whereas in the apoE3-secreting cells in the presence of a lipid source, neurite exte nsion was increased, Uptake of beta-VLDL occurred to a similar extent in both the apoE3- and apoE4-secreting cells. With low density lipopro teins or with dimyristoylphosphatidylcholine emulsions, either alone o r complexed with cholesterol, no differential effect on neurite outgro wth was observed, A slight differential effect was observed with apoE- containing high density lipoproteins. The differential effect of apoE3 and apoE4 in the presence of beta-VLDL was blocked by incubation of t he cells with heparinase and chlorate, with lactoferrin, or with recep tor-assocciated protein, all of which prevent the uptake of lipoprotei ns by the low density lipoprotein receptor-related protein (LRP). The data suggest that the secreted and/or cell surface-bound apoE interact with the lipoproteins and facilitate their internalization via the he paran sulfate proteoglycan-LRP pathway, The mechanism by which apoE3 a nd apoE4 exert differential effects on neurite outgrowth remains specu lative, However, the data suggest that apoE4, which has been shown to be associated with late onset familial and sporadic Alzheimer's diseas e, may inhibit neuronal remodeling and contribute to the progression o f the disease.