Microglial Activation in Alzheimer Disease: Association with APOE Genotype

Authors

  • Rupert Egensperger,

    1. Molecular Neuropathology Laboratory, Institute of Neuropathology, Hannover Medical School, Hannover, Germany
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  • Siegfried Kösel,

    1. Molecular Neuropathology Laboratory, Institute of Neuropathology, Ludwig Maximilians University, Munich, Germany
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  • Ulrich von Eitzen,

    1. Molecular Neuropathology Laboratory, Institute of Neuropathology, Ludwig Maximilians University, Munich, Germany
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  • Manuel B. Graeber

    Corresponding author
    1. Molecular Neuropathology Laboratory, Department of Neuromorphology, Max Planck Institute of Neurobiology (formerly Max Planck Institute of Psychiatry, Basic Sciences Institute), Martinsried, Germany
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Corresponding author: Manuel B. Graeber, M.D., Molecular Neuropathology Laboratory, Department of Neuromorphology, Max Planck Institute of Neurobiology, Am Klopferspitz 18a, 82152 Martinsried, Germany; Tel.: +49 89 8578 3666; Fax: +49 89 8995 0077; E-mail: neuropat@neuro.mpg.de

Abstract

Microglial cells are considered to play an important role in the pathogenesis of Alzheimer disease. Apart from producing the Alzheimer amyloid precursor (APP) as an acute phase protein, microglial cells seem to be involved in the deposition of its amyloidogenic cleavage product, the amyloid-β peptide (Aβ). Aβ is bound by apolipoprotein E (APOE) in an isoform-specific manner, and it has been demonstrated that inheritance of the AD susceptibility allele, APOE ε4, is associated with increased deposition of Aβ in the cerebral cortex. However, the relationship between APOE ε4 gene dose and microglial activation is unknown. Using microglial expression of major histocompatibility complex class II molecules as a marker, we have performed a quantitative genotype-phenotype analysis on microglial activation in frontal and temporal cortices of 20 APOE genotyped AD brains. The number of activated microglia and the tissue area occupied by these cells increased significantly with APOE ε4 gene dose. When a model of multiple linear regression was used to compare the relative influence of APOE genotype, sex, disease duration, age at death, diffuse and neuritic plaques as well as neurofibrillary tangles on microglial activation, only APOE genotype was found to have a significant effect. Thus, the APOE gene product represents an important determinant of microglial activity in AD. Since microglial activation by APP has been shown to be modulated by apoE in vitro, a direct role of microglia in AD pathogenesis is conceivable.

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