The network of blood channels and tissues known as the blood-brain barrier, which nourishes and shields the brain from dangerous chemicals flowing in the blood, is compromised in Alzheimer's disease.

Researchers at the Mayo Clinic and associates have now discovered distinct molecular markers of blood-brain barrier disruption, which may lead to novel approaches to the diagnosis and treatment of the condition. In Nature Communications, their research is published.

"These signatures have high potential to become novel biomarkers that capture brain changes in Alzheimer's disease," said senior author Nilufer Ertekin-Taner, MD, PhD, chair of the Department of Neuroscience at Mayo Clinic and leader of the Genetics of Alzheimer's Disease and Endophenotypes Laboratory at Mayo Clinic in Florida.

To conduct the study, the research team analysed human brain tissue from the Mayo Clinic Brain Bank, as well as published datasets and brain tissue samples from collaborating institutions. The study cohort included brain tissue samples from 12 patients with Alzheimer's disease and 12 healthy patients with no confirmed Alzheimer's disease.

All participants had donated their tissue for science. Using these and external datasets, the team analysed thousands of cells in more than six brain regions, making this one of the most rigorous studies of the blood-brain barrier in Alzheimer's disease to date, according to the researchers.

They focused on brain vascular cells, which make up a small portion of cell types in the brain, to examine molecular changes associated with Alzheimer's disease.

In particular, they looked at two cell types that play an important role in maintaining the blood-brain barrier: pericytes, the gatekeepers of the brain that maintain the integrity of blood vessels, and their support cells known as astrocytes, to determine if and how they interact.

They found Alzheimer's disease patients' samples exhibited altered communication between these cells, mediated by a pair of molecules known as VEGFA, which stimulates the growth of blood vessels, and SMAD3, which plays a key role in cellular responses to the external environment.

Using cellular and experimental models, the researchers validated their finding that increased levels of VEGFA lead to lower levels of SMAD3 in the brain.

The team used stem cells from blood and skin samples of the Alzheimer's disease patient donors and those in the control group. They treated the cells with VEGFA to see how it affected SMAD3 levels and overall vascular health.

The VEGFA treatment caused a decline in SMAD3 levels in brain pericytes, indicating an interaction between these molecules.

Donors with higher blood SMAD3 levels had less vascular damage and better Alzheimer's disease-related outcomes, according to the researchers. The team says more research is needed to determine how SMAD3 levels in the brain impact SMAD3 levels in the blood.