Evidence indicates dysregulation. of the immunoregulatory molecule CD45 occurs in Alzheimers disease (AD). Transgenic mice overproducing amyloid-β peptide (Aβ) and deficient in CD45 (PSAPP/CD45−/−) recapitulate AD neuropathology. Increased cerebral intracellular and extracellular soluble oligomeric and insoluble Aβ, decreased plasma soluble Aβ increased microglial neurotoxic cytokines TNF-α and IL-1β, and neuronal loss were found in PSAPP/CD45−/− mice compared with CD45-sufficient PSAPP littermates. After CD45 ablation, in vitro and in vivo studies demonstrate a microglial phenotype whereby microglia phagocytose less Aβ but display proinflammatory properties. This microglial activation occurs with elevated Aβ oligomers and neural injury and loss as determined by decreased ratio of anti-apoptotic Bcl-xL to proapoptotic Bax, increased activated caspase-3, mitochondrial dysfunction, and loss of cortical neurons in PSAPP/CD45−/− mice. These data show that deficiency in CD45 activity leads to brain accumulation of neurotoxic Aβ oligomers and validate CD45-mediated microglial clearance of oligomeric Aβ as a novel AD therapeutic target.
