Alzheimer’s Disease and Reelin

Alzheimer’s disease (AD) is the most common cause of dementia among elderly people and is characterized by loss of memory and cognitive functions. The pathological hallmarks include extensive synaptic and neuronal loss, astrogliosis, and accumulation of fibrillar deposits. The amyloid plaques are extracellular deposits mainly composed of a small insoluble protein called β-amyloid protein or Aβ that is derived from the β-amyloid precursor protein (APP) (Masters et al., 1985). The neurofibrillary tangles are composed of intracellular paired helical filaments containing an abnormally phosphorylated form of the tau protein (Grundke-Iqbal et al., 1986). Specific genetic factors are also linked closely to AD. Thus, despite the occurrence of missense mutations in APP, the most common mutations in AD to date are in presenilin (PS1 and PS2) genes, membrane proteins which play a critical role in the γ-secretase processing of APP (Selkoe, 2001). Whereas these mutations are quite infrequent causes of AD, the major known genetic risk factor for the disorder in the typical late-onset period is the ε4 allele of apolipoprotein E (ApoE) (Strittmatter et al., 1993). The purposes of this chapter are to review the links between Reelin and elements of its signaling pathway with the main hallmarks of AD pathology and summarize our recent findings, including the first evidence of altered Reelin expression in the AD brain.