CX3CR1 deficiency alters microglial activation and reduces beta-amyloid deposition in two Alzheimer's disease mouse models.

摘要

Microglia, the primary immune effector cells in the brain, continually monitor the tissue parenchyma for pathological alterations and become activated in Alzheimer's disease. Loss of signaling between neurons and microglia via deletion of the microglial receptor, CX3CR1, worsens phenotypes in various models of neurodegenerative diseases. In contrast, CX3CR1 deficiency ameliorates pathology in murine stroke models. To examine the role of CX3CR1 in Alzheimer's disease-related beta-amyloid pathology, we generated APPPS1 and R1.40 transgenic mouse models of Alzheimer's disease deficient for CX3CR1. Surprisingly, CX3CR1 deficiency resulted in a gene dose-dependent reduction in beta-amyloid deposition in both the APPPS1 and R1.40 mouse models of AD. Immunohistochemical analysis revealed reduced staining for CD68, a marker of microglial activation. Furthermore, quantitative immunohistochemical analysis revealed reduced numbers of microglia surrounding beta-amyloid deposits in the CX3CR1-deficient APPPS1 animals. The reduced beta-amyloid pathology correlated with reduced levels of TNFalpha and CCL2 mRNAs, but elevated IL1beta mRNA levels, suggesting an altered neuroinflammatory milieu. Finally, to account for these seemingly disparate results, both in vitro and in vivo studies provided evidence that CX3CL1/CX3CR1 signaling alters the phagocytic capacity of microglia, including the uptake of Abeta fibrils. Taken together, these results demonstrate that loss of neuron-microglial fractalkine signaling leads to reduced beta-amyloid deposition in mouse models of AD that is potentially mediated by altered activation and phagocytic capability of CX3CR1-deficient microglia.