CCR5 deficiency induces astrocyte activation, Aβ deposit and impaired memory function

Activation of astrocytes has been known to be associated with amyloid-beta (A beta) deposit and production of pro-inflammatory cytokines and chemokines that lead to neuronal cell death in the pathogenesis of Alzheimer disease (AD). In the present study, we investigated whether the absence of CC chemokine receptor 5 (CCR5) results in activation of astrocytes, A beta deposit and memory dysfunction in CCR5 knock (CCR5(-/-)) out mice. We found that long-term and spatial memory functions were impaired in CCR5(-/-) mice. There was a significant increased expression of glial fibrillary acidic protein (GFAP) in the brain of CCR5(-/-) mice as compared with that of wild type of CCR5 (CCR5+/+) mice. The expression of CCR5 was observed in CCR5(+/+) astrocytes, but was reduced in the CCR5(-/-) astrocytes even though the expression of GFAP was much higher. Paralleling with the activation of astorcytes, the A beta(1-42) level was higher in the brains of CCR5(-/-) mice than that of CCR5(+/+) mice. Expression of beta-secretase (BACE1) and its product C99 was significantly elevated in CCR5(-/-) mice. The activation of CC chemokine receptor 2 (CCR2) causes activation of astrocytes that leads to A beta deposit and memory dysfunction in CCR5(-/-) mice. In CCR5(-/-) mice, CCR2 expression was high and co-localized with GFAP. These findings suggest that the absence of CCR5 increases expression of CCR2, which leads to the activation of astrocytes causing A beta deposit, and thereby impairs memory function. These results suggest that CCR5 may be a critical suppressor of the development and progression of AD pathology. (C) 2009 Elsevier Inc. All rights reserved.