Researchers identify molecular cause of age-related cognitive decline

A research team from University Hospitals, Case Western Reserve University and the Louis Stokes Cleveland VA Medical Center has identified a critical molecular cause of age-related cognitive decline, potentially paving the way for new treatments to protect brain health as we age.

Their research, led by the Pieper Laboratory, published recently in Proceedings of the National Academy of Sciences.

The study centers on a protective structure called the blood-brain barrier (BBB). Within this structure, the endothelial cells lining the blood vessels are tightly packed through an energetically demanding process that keeps harmful substances and pathogens in the bloodstream from entering the brain, removes some waste products that accumulate during normal brain activity, and dynamically adjusts blood flow to whichever areas of the brain are most active at any given moment.

Breakdown of these critical functions of the BBB has long been observed in the aging brain, but whether this is sufficient to cause cognitive decline in aging has not been previously established. Furthermore, the underlying molecular causes of aging-related BBB degradation have remained unclear, limiting the development of targeted treatments.

"At the center of our findings is a protein called KLF4, which is produced by the endothelial cells that line the blood-brain barrier. As people age, endothelial cells lose their ability to generate KLF4. We found that accelerating the loss of KLF4 in endothelial cells also accelerated aging-related BBB degradation and cognitive decline," said Andrew A. Pieper, MD, PhD, senior author of the study, University Hospitals Morley-Mather Chair of Neuropsychiatry, and Rebecca E. Barchas, MD, DLFAPA, Case Western Reserve University Professor of Translational Psychiatry."

Using advanced two-photon microscopy to monitor brain and blood vessel activity in living mice at multiple points across their lifespan, the team observed that loss of KLF4 caused the BBB to leak, reduced the abundance of small blood vessels in the brain, and disrupted the BBB's ability to match blood supply to neuronal activity. Even in middle-aged mice, these changes triggered oxidative brain damage, neuroinflammation, nerve cell damage, anxiety, and cognitive decline, conditions normally seen only in much older animals.

"Loss of endothelial cell KLF4 accelerated every key aspect of brain aging that we measured. This suggests that therapies designed to preserve or restore KLF4 function in endothelial cells may help prevent age-related deterioration of the blood-brain barrier and the cognitive decline that follows," added Dr. Pieper, who also serves as director of the Brain Health Medicines Center at Harrington Discovery Institute at UH, and psychiatrist and investigator in the Louis Stokes VA Geriatric Research Education and Clinical Center.

Further analysis using single-cell RNA sequencing showed that loss of KLF4 disrupted gene programs tied to immune response and BBB integrity, helping explain its central role in maintaining brain health.

The identification of a major culprit in age-related cognitive decline has opened important new lines of investigation required for developing neuroprotective therapeutics. Next steps in this research involve utilizing the findings to open new avenues for future studies and drug development focused on why KLF4 declines with age and how its activity can be safely enhanced to protect the brain.