Applying human in vitro models to understand the link between trauma and tau pathology

点击翻译按钮获取中文摘要

Traumatic brain injury (TBI) is the most important environmental risk factor for Alzheimer’s disease and Alzheimer’s disease related dementias (AD/ADRD). The TBI event may occur years before the emergence of AD/ADRD so there is time to apply treatments. Unfortunately, no appropriate treatments exist because the connection between TBI and AD/ADRD is poorly understood. Changes in tau proteins play an important role in AD/ADRD. Calcium overload drives changes in tau. Calcium overload is also a consequence of TBI. This proposal hypothesizes that TBI causes calcium overload that leads to tau changes and this sequence helps explain why TBI increases the risk of AD/ADRD. Piezo1 is a calcium channel that opens when cells deform. Therefore, it could be opened by trauma. This proposal will test this hypothesis in cortical astrocytes, cortical neurons, and endothelial cells. These cells will be generated from human induced pluripotent stem cells. The first Aim will measure how vulnerable each cell type is to trauma. The cells will be deformed in the same way they are during a TBI event and resulting cell death and cell damage will be measured. Calcium overload and inflammatory signaling will also be quantified. In patient brains, tau changes accumulate around blood vessels after TBI but it is not clear if this pattern reflects the toxic influence of blood or the endothelial cells that line blood vessels. Therefore, the influence of endothelial cells on neighboring astrocytes and neurons will be measured with experiments that either mix cells in culture or transfer cell culture media between cell cultures. Experiments with trauma-sensitive outcomes will be repeated after Piezo1 has been eliminated from the cells to determine if Piezo1 is required for a trauma response. In addition, the same outcomes will be measured in experiments that activate Piezo1 chemically without trauma. The second Aim will employ brain organoids. These are clusters of brain cells that are approximately round and about 1 millimeter wide. They contain cortical neurons and astrocytes and, in some cases, endothelial cells will be added to them. These organoids can reproduce the calcium overload-dependent tau changes that are hypothesized to drive disease in post-TBI AD/ADRD. They will be mechanically deformed in the same way they would be deformed during a TBI event. Resulting cell death and cell damage will be quantified. Secretion of proteins known to indicate brain damage and changes in spontaneous electrical activity will also be measured. In addition, total tau protein and phosphorylated tau protein will be quantified after trauma. Microscopic imaging will determine if tau changes accumulate around endothelial cells when they are present. As before, experiments that show sensitivity to trauma will be repeated after Piezo1 has been eliminated from the cells. Then, they will be repeated when Piezo1 has been activated chemically without trauma. In combination, these experiments will reproduce the progression from mechanical trauma to tau changes that drive AD/ADRD and reveal the role of Piezo1 in that process. These results will be an important step toward treating these patients to interrupt this progression.