Dynamics of the Complement, Cytokine, and Chemokine Systems in the Regulation of Synaptic Function and Dysfunction Relevant to Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia affecting nearly 45 million people worldwide. However, the etiology of AD is still unclear. Accumulations of amyloid-β plaques and tau tangles, neuroinflammation, and synaptic and neuronal loss are the major neuropathological hallmarks of AD, with synaptic loss being the strongest correlating factor with memory and cognitive impairment in AD. Many of these pathological hallmarks influence each other during the onset and progression of the disease. Recent genetic evidence suggests the possibility of a causal link between altered immune pathways and synaptic dysfunction in AD. Emerging studies also suggest that immune system-mediated synaptic pruning could initiate early-stage pathogenesis of AD. This comprehensive review is toward understanding the crosstalk of neuron-microglia-astrocyte and dynamics of complement, cytokine, and chemokine systems in the regulation of synaptic function and dysfunction relevant to AD. We start with summarizing several immune pathways, involving complements, MHC-I and CX3CL1, which mediate synaptic elimination during development and in AD. We then will discuss the potential of targeting these molecules as therapeutic interventions or as biomarkers for AD.