We know that the E4 variant of the APOE gene greatly increases the risk of developing Alzheimer’s disease, but the reason is a little more mysterious. It has been thought that it makes it easier for amyloid plaques to form because it produces a protein that binds to amyloid beta. However, a new study shows that APOE and amyloid beta don’t bind together in cerebrospinal fluid and in fluids present outside cells grown in dishes, making it unlikely that they are binding together in the brain.
Mouse and cell culture experiments suggest instead that the APOE protein may be blocking a pathway that normally helps degrade amyloid beta — both APOE and amyloid beta seem to compete to bind to an astrocyte receptor. Previous work has shown that astrocytes can degrade amyloid beta.
The findings suggest that therapeutic strategies that target APOE need to be redirected.
 . ApoE influences amyloid-β (Aβ) clearance despite minimal apoE/Aβ association in physiological conditions. Proceedings of the National Academy of Sciences [Internet]. 2013 ;110(19):E1807 - E1816. Available from: http://www.pnas.org/content/110/19/E1807