Apolipoprotein E in sporadic Alzheimer's disease: allelic variation and receptor interactions.

An increased prevalence of apolipoprotein E (ApoE) epsilon 4 allele exists in late onset familial Alzheimer's disease. We found, in sporadic Alzheimer's disease, that 62% of patients possessed an ApoE-epsilon 4 allele, compared with 20% of controls. ApoE-epsilon 4/4 patients had more senile plaques (SPs) than epsilon 3/3 patients. ApoE immunoreactivity of SPs was equivalent in both groups. Two receptors bind ApoE complexes, the low density lipoprotein (LDL) receptor and the LDL receptor-related protein (LRP). In normal brain, anti-LRP antibodies strongly stained neurons and lightly stained astrocytes; anti-LDL receptor antibodies stained only the neuropil and astrocytes. In Alzheimer's disease, SPs and reactive astrocytes were also strongly LRP immunoreactive. Colocalization of ApoE and LRP to SPs implies that these molecules may be involved in metabolism of components of SPs.