Columbia University researchers have pinpointed a biological mechanism that could explain why some carriers of the APOE ε4 Alzheimer’s risk variant stay mentally sharp into their eighties, suggesting a rare FN1 genetic mutation may shield the brain’s blood vessels and protect the blood-brain barrier. The discovery potentially opens a new path toward treatments for a disease that remains a major UK and global health challenge.
The study, published in Nature Aging, builds on prior work linking the APOE ε4 gene variant—widely associated with heightened Alzheimer’s risk—with a rare protective mutation in the fibronectin (FN1) gene. Fibronectin forms part of the tissue-support framework, but in APOE ε4 carriers it can accumulate around brain vessels, potentially compromising the blood-brain barrier. The FN1 mutation appears to limit this buildup and the damage it can cause.
Fibronectin is a protein that helps maintain tissue structure. When excessive amounts accumulate around brain vessels in APOE ε4 carriers, the brain’s protective barrier can be undermined, allowing harmful substances to enter brain tissue more easily.
The research combined analyses of human brain tissue and cerebrospinal fluid with genetic and epigenetic techniques to study DNA and gene activity. It also employed single-cell sequencing, spatial imaging, human stem-cell models, three-dimensional vascular cultures, and experiments in zebrafish and mice.
How excess fibronectin damages the brain’s protective barrier
Across these approaches, the team repeatedly found that APOE ε4 promotes the production and accumulation of fibronectin around brain vessels, correlating with a leakier blood-brain barrier in mice engineered to carry the human gene.
In particular, researchers observed nearly twice as much fibronectin in the brains of APOE ε4 mice compared with those carrying APOE ε3, accompanied by evidence of barrier dysfunction.
One pivotal experiment showed that increasing human fibronectin specifically in astrocytes—cells that help sustain the barrier—was sufficient to disrupt permeability. By contrast, reducing fibronectin improved barrier function, providing experimental evidence that excess fibronectin can directly contribute to vascular damage rather than merely co-occurring with it.
Co-first author Prabesh Bhattarai, an associate research scientist in the Kizil lab, explained: “Increasing fibronectin in these cells was enough to disrupt the barrier, allowing it to become more permeable. Conversely, reducing fibronectin improved the barrier’s ability to function normally.”
Further work traced the molecular cascade: excess fibronectin appears to activate abnormal signals through integrins and an enzyme known as focal adhesion kinase, which disrupts a network of growth factors including VEGF, HBEGF and IGF1. These signals normally help astrocytes and blood vessel cells coordinate barrier maintenance, and their disturbance may weaken the barrier’s integrity.
Single-cell analysis enabled the researchers to observe this pathway across the diverse cells that maintain the brain’s vasculature, with the same pattern seen in experimental models and human Alzheimer’s tissue, lending robustness to the proposed mechanism, according to co-first author Elanur Yilmaz.
Analyses of human brains and cerebrospinal fluid further linked elevated fibronectin with astrocyte inflammation and connected FN1 to vascular disease and changes in VEGFA, a growth factor vital to healthy brain vessels. Taken together, the findings reinforce the idea that excess fibronectin feeds the vascular damage associated with APOE ε4.
Badri Vardarajan, associate professor of neurological science and a collaborator on the FN1 discovery, said: “The convergence of these independent human datasets strengthens the case that fibronectin is part of the APOE ε4-related vascular disease process.”
A rare genetic defence could inspire new Alzheimer’s treatments, the researchers note, given that APOE ε4 is the strongest common genetic risk factor for the disease and about one in five people carry at least one copy.
Potential therapeutic approaches include preventing harmful fibronectin accumulation around brain vessels, blocking the abnormal cellular signals triggered by excess fibronectin, or restoring growth-factor signalling to maintain barrier integrity. However, the researchers warn that fibronectin plays essential roles throughout the body, so any future therapy would need to target the harmful effects without impairing its beneficial functions.
Richard Mayeux, chair of the Department of Neurology and a project collaborator, emphasised the clinical implications: “By showing how fibronectin contributes to early vascular damage, this study gives us new therapeutic targets and potential ways to measure whether treatments are working. Clinically, it connects a major genetic risk factor for Alzheimer’s to an early disease process that may be possible to modify.”
While the potential therapies are still experimental, the work offers a promising new direction in Alzheimer’s research. Rather than focusing solely on damage that develops later in the disease, scientists may eventually harness a natural genetic defence to protect vulnerable brains before significant harm occurs.
