Neuronal apoptosis by apolipoprotein E4 through low-density lipoprotein receptor-related protein and heterotrimeric GTPases

The epsilon4 genotype of apolipoprotein E (apoE4) is the most established p redisposing factor in Alzheimer's disease (AD); however, it remains unclear how apoE4 contributes to the pathophysiology. Here, we report that the apo E4 protein (ApoE4) evokes apoptosis in neuronal cells through the low-densi ty lipoprotein receptor-related protein (LRP) and heterotrimeric GTPases. W e examined neuron/neuroblastoma hybrid F11 cells and found that these cells were killed by 30 mug/ml ApoE4, but not by 30 mg/ml ApoE3. ApoE4-induced d eath occurred with typical features for apoptosis in time- and dose-depende nt manners, and was observed in SH-SY5Y neuroblastomas, but not in glioblas tomas or non-neuronal Chinese hamster ovary cells. Activated, but not nativ e, alpha2-macroglobulin suppressed this ApoE4 toxicity. Suppression by the antisense oligonucleotide to LRP and inhibition by low nanomolar concentrat ions of LRP-associated protein RAP provided evidence for the involvement of LRP. The involvement of heterotrimeric GTPases was demonstrated by the fin dings that (1) ApoE4-induced death was suppressed by pertussis toxin (PTX), but not by heat-inactivated PTX; and (2) transfection with PTX-resistant m utant cDNAs of G alpha (i) restored the toxicity of ApoE4 restricted by PTX . We thus conclude that one of the neurotoxic mechanisms triggered by ApoE4 is to activate a cell type-specific apoptogenic program involving LRP and the Gi class of GTPases and that the apoE4 gene may play a direct role in t he pathogenesis of AD and other forms of dementia.