From the article:
Severe damage to vascular cells called pericytes was linked to more severe cognitive problems in APOE4 carriers. APOE4 seems to speed up breakdown of the blood-brain barrier by activating an inflammatory pathway in blood vessels, which is associated with pericyte injury."
[…]
Zlokovic’s previous research shows that people who develop early memory problems also experience the most leakage in their brain’s blood vessels – independent of amyloid plaque or tau, two common contributors to Alzheimer’s. The leakage starts when cells called pericytes, which line the walls of blood vessels in the brain and maintain blood-brain barrier integrity, are damaged.
[…]
In participants who had the APOE4 gene, researchers found damaged capillaries in the brain’s memory center, the hippocampus and medial temporal lobe. The damage correlated with increased levels of a protein that causes inflammation, cyclophilin A – an early sign of the disease in people already at higher risk of developing Alzheimer’s.