Two new studies from Mount Sinai, published in Cell and Cell Stem Cell, describe how APOE4 - the strongest known genetic risk factor for Alzheimer's disease - damages blood vessels in the brain and promotes the buildup of the abnormal proteins tied to neurodegeneration. The researchers report that these processes appear to be reversible, and they introduce a human brain tissue platform grown from stem cells that could speed up testing of potential treatments.
The vascular angle matters because it has long sat in an awkward place in Alzheimer's research. Blood vessels in the brain are known to deteriorate as the disease advances, particularly in people carrying APOE4, but it has not been clear whether that deterioration is a cause or simply a downstream consequence. That ambiguity has meant the brain's circulation often gets treated as collateral damage rather than as a driver worth targeting.
For the Cell paper, published September 24, the Mount Sinai team pooled existing datasets to assemble a single-cell transcriptomic atlas of the human brain's blood vessels - essentially a map of which genes are switched on in each of the cell types that build and maintain brain circulation. Using it, they traced APOE4's effect to pericytes, the cells that wrap small vessels, keep them stable, and help maintain the blood brain barrier. In the presence of APOE4, those pericytes shifted into myofibroblast-like cells that churn out scar tissue instead of doing their usual supportive work.
Alzheimer's affects more than 7 million older adults in the United States, and APOE4 carriers are a large, identifiable slice of the at-risk population. If a specific cellular switch - healthy pericyte to scar-producing cell - can be identified and, as the researchers suggest, reversed, it gives drug developers a concrete target rather than a vague association between poor brain blood flow and dementia. The stem cell-derived tissue platform is the practical half of that proposition: a human system in which such interventions could be tried.