Peripheral clearance of amyloid beta peptide by complement C3-dependent adherence to erythrocytes.

Brain deposits of amyloid beta peptide (Abeta) have been a diagnostic hallmark of Alzheimer's disease (AD) for nearly a century. Recent studies have demonstrated that Abeta is also present in peripheral blood. Here, we present evidence that circulating Abeta42 is subject to complement C3b-dependent adherence to complement receptor 1 (CR1) on erythrocytes, a classical set of mechanisms by which pathogens and proteins recognized as foreign are cleared from the bloodstream. Levels of Abeta42 targeted by this pathway differ significantly in AD compared to mild cognitive impairment and nondemented elderly controls.

Brain estrogen deficiency accelerates Abeta plaque formation in an Alzheimer's disease animal model.

Much evidence indicates that women have a higher risk of developing Alzheimer's disease (AD) than do men. The reason for this gender difference is unclear. We hypothesize that estrogen deficiency in the brains of women with AD may be a key risk factor. In rapidly acquired postmortem brains from women with AD, we found greatly reduced estrogen levels compared with those from age- and gender-matched normal control subjects; AD and control subjects had comparably low levels of serum estrogen. We examined the onset and severity of AD pathology associated with estrogen depletion by using a gene-based approach, by crossing the estrogen-synthesizing enzyme aromatase gene knockout mice with APP23 transgenic mice, a mouse model of AD, to produce estrogen-deficient APP23 mice. Compared with APP23 transgenic control mice, estrogen-deficient APP23 mice exhibited greatly reduced brain estrogen and early-onset and increased beta amyloid peptide (Abeta) deposition. These mice also exhibited increased Abeta production, and microglia cultures prepared from the brains of these mice were impaired in Abeta clearance/degradation. In contrast, ovariectomized APP23 mice exhibited plaque pathology similar to that observed in the APP23 transgenic control mice. Our results indicate that estrogen depletion in the brain may be a significant risk factor for developing AD neuropathology.