APOE gene polymorphism: The impact of APOE4 allele on systemic inflammation and its role in the pathogenesis of Alzheimer's disease

Abstract

ApoE is a member of lipoprotein family. It is the most common lipoprotein in the central nervous system (CNS), secreted by astrocytes, microglia, neurons and immunocompetent cells, including lymphocytes, monocytes and macrophages. According to recent data, it has endotheliotropic and immunomodulatory functions, regulating inflammatory activation of mononuclear phagocytes and antigen-induced lymphocyte proliferation. APOE4 allele is a major genetic risk factor of Alzheimer's disease, with prevalence 3-12 times higher in those who have this allele. Mechanisms that predispose carriers of the allele to earlier clinical presentation of neurodegeneration include changes in lipid metabolism in the CNS, in the buildup of neurotoxic amyloid-beta oligomers, in the clearance of amyloid-beta peptides from the CNS and in regulation of immune response. In this review the functions of ApoE protein in central nervous and immune system and changes in functional activity of the protein in APOE4 carriers are discussed. The impact of APOE4 allele on monocyte phenotype and inflammatory activation of monocytes, on specific cell-mediated immune response to amyloid-beta antigens and on effectiveness of immunomodulatory therapy in patients with Alzheimer's disease summarized, as well as the possible role of changes in the immune response characteristic for APOE4 carriers in the increased risk of Alzheimer's disease.