Human Apolipoprotein E4 Alters the Amyloid-β 40:42 Ratio and Promotes the Formation of Cerebral Amyloid Angiopathy in an Amyloid Precursor Protein Transgenic Model

Mar 18, 2005The Journal of neuroscience : the official journal of the Society for Neuroscience

Human apolipoprotein E4 changes amyloid-beta 40:42 balance and increases blood vessel amyloid buildup in a mouse model

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Abstract

At 15 months of age, human apoE4 expression led to substantial cerebral amyloid angiopathy (CAA) with very few parenchymal plaques.

The expression of human apoE isoforms resulted in a delay in amyloid-beta deposition of several months compared to murine apoE.
Tg2576 mice expressing human apoE4 exhibited substantial CAA, while those expressing human apoE3 showed almost no CAA or parenchymal plaques.
Young apoE4-expressing mice displayed an elevated ratio of amyloid-beta 40:42 in brain extracellular spaces and a lower ratio in cerebrospinal fluid.
These observations suggest that apoE4 may alter the clearance and transport of amyloid-beta species within the brain.

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Alzheimer's disease (AD) is characterized by the aggregation and deposition of the normally soluble amyloid-beta (Abeta) peptide in the extracellular spaces of the brain as parenchymal plaques and in the walls of cerebral vessels as cerebral amyloid angiopathy (CAA). CAA is a common cause of brain hemorrhage and is found in most patients with AD. As in AD, the epsilon4 allele of the apolipoprotein E (apoE) gene (APOE) is a risk factor for CAA. To determine the effect of human apoE on CAA in vivo, we bred human APOE3 and APOE4 "knock-in" mice to a transgenic mouse model (Tg2576) that develops amyloid plaques as well as CAA. The expression of both human apoE isoforms resulted in a delay in Abeta deposition of several months relative to murine apoE. Tg2576 mice expressing the more fibrillogenic murine apoE develop parenchymal amyloid plaques and CAA by 9 months of age. At 15 months of age, the expression of human apoE4 led to substantial CAA with very few parenchymal plaques, whereas the expression of human apoE3 resulted in almost no CAA or parenchymal plaques. Additionally, young apoE4-expressing mice had an elevated ratio of Abeta 40:42 in brain extracellular pools and a lower 40:42 ratio in CSF, suggesting that apoE4 results in altered clearance and transport of Abeta species within different brain compartments. These findings demonstrate that, once Abeta fibrillogenesis occurs, apoE4 favors the formation of CAA over parenchymal plaques and suggest that molecules or treatments that increase the ratio of Abeta 40:42 may favor the formation of CAA versus parenchymal plaques.

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Human Apolipoprotein E4 Alters the Amyloid-β 40:42 Ratio and Promotes the Formation of Cerebral Amyloid Angiopathy in an Amyloid Precursor Protein Transgenic Model

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