Apolipoprotein E activates Akt pathway in neuro-2a in an isoform-specific manner.

Apolipoprotein E (apoE) is a ligand for members of the low density lipoprotein (LDL) receptor family, receptors highly expressed in neurons. A study of one of the mechanisms by which apoE might affect neuronal cell metabolism is reported herein. ApoE can induce Akt/protein kinase B phosphorylation in Neuro-2a via two different pathways. Both pathways are mediated by phosphatidylinositol 3-kinase and cAMP-dependent protein kinase. The first pathway is stimulated by apoE3 and E4, but not by E2, after a 1-h incubation. The process requires the binding of apoE to the heparan sulfate proteoglycan/LDL receptor-related protein complex. The second pathway is activated after a 2-h incubation of the cells, in another isoform-dependent manner (E2 = E3 dbl greater-than sign E4) and is mediated by calcium. Our results suggest that apoE might affect cell metabolism and survival in neurons in an isoform-specific manner by inducing novel signaling pathways.