Effects of CX3CR1 and Fractalkine Chemokines in Amyloid Beta Clearance and p-Tau Accumulation in Alzheimer's Disease (AD) Rodent Models: Is Fractalkine a Systemic Biomarker for AD?

摘要

Microglia and astrocytes are the major source of cytokines in Alzheimer,s disease (AD). CX3CR1 is a delta chemokine receptor found in microglia and its neuronal ligand, Fractalkine, has two isoforms: an anchored-membrane isoform, and a soluble isoform. The reduced soluble fractalkine levels found in the brain (cortex/hippocampus) of aged rats, may be a consequence of neuronal loss. This soluble fractalkine maintains microglia in an appropiate state by interacting with CX3CR1. The ablation of the CX3CR1 gene in mice overexpressing human amyloid precursor protein (APP/PS-1) increased cytokine levels, enhanced Tau pathology and worsened behavioural performance in these mice. However, CX3CR1 deficiency resulted in a gene dose-dependent A beta clearance in the brain, and induced microglial activation. In addition, CX3CR1 deficiency can have benefical effects by preventing neuronal loss in the 3xTg model. In fact, CX3CR1 deficiency increases microglial phagocytosome activity by inducing selective protofibrillar amyloid-beta phagocytosis in microglial cells in transgenic AD models.