APOE Lipoprotein Particles: Pathophysiology, Therapy, and the Crosstalk in Alzheimer’s Disease and Cardiovascular Disease

The APOE4 variant was the strongest genetic risk factor for sporadic Alzheimer's disease (AD). Individuals with APOE4 have an increased risk of developing the disease at an early age of onset. Similarly, APOE4 carriers are predisposed to high cholesterol levels and tend to have an increased risk of cardiovascular disease (CVD). The global allele frequency of APOE4 was 13.7%, underlining its widespread impact on global human health. Conversely, the relatively rare APOE2 allele was a genetic protective factor against AD and CVD. However, the mechanisms underlying this association remain to be elucidated. The apolipoprotein E (APOE) protein coats lipoprotein particles and mediates lipid transport and metabolism in the peripheral circulation and central nervous system (CNS). Although initial studies causally linked APOE lipoprotein particles (APOE particles) with lipid homeostasis, our understanding of the physiological and pathological effects of APOE particles has extended to amyloid-β (Aβ) accumulation, tau hyperphosphorylation and spread, as well as neuroinflammation in AD initiation and progression. Moreover, the most examined functions of APOE particles are reverse cholesterol transport, anti-inflammatory, anti-oxidation, and improvement of endothelial dysfunction in atherosclerotic CVD. This review outlines what is known about the structure and functions of APOE particles, emphasizing their involvement in AD and CVD pathogenesis, while also considering the crosstalk between the peripheral circulation and CNS. In addition, we discuss how these APOE particles act as therapeutic targets.