The blood-brain barrier consists of specialized cells that line blood vessels passing through the central nervous system, only selectively allowing passage of molecules and cells between the circulation and the brain. Dysfunction of the blood-brain barrier allows unwanted molecules and cells into the brain, where they cause chronic inflammation and become an important contribution to the onset and progression of neurodegenerative conditions. While blood-brain barrier dysfunction appears early in the aging of the brain, and thus seems a good candidate for the position of primary causative mechanism, many studies - such as the one noted here - suggest that other pathologies associated with neurodegenerative conditions can cause blood-brain barrier dysfunction.
Problems with blood vessels in the brain are recognized as some of the earliest changes that can lead to memory loss and other symptoms in Alzheimer's disease and other forms of dementia. These problems generally center around the neurovascular unit - a group of different cell types, including blood vessel cells, support cells, and neurons - that work together to keep the brain healthy. This system helps regulate blood flow in the brain, controls how nutrients and energy are delivered, and helps protect the brain from inflammation and harmful substances.
Until now, scientists did not fully understand what tau protein aggregates were doing at the brain's blood vessels. To uncover the mystery, researchers ran a series of experiments in vitro using a cell model that mimics the brain's protective barrier. When they exposed the cells to protofibrillar tau - a form of tau that appears early in Alzheimer's disease - they discovered that it weakened the barrier, making it more "leaky" and less able to protect the brain. The researchers also found that right after exposure to protofibrillar tau, brain blood vessel cells quickly changed how they make energy. This shift triggered inflammation and weakened the protective barrier, suggesting these damaging changes happen very early in the disease process.
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