7-ketocholesterol contributes to microglia-driven increases in astrocyte reactive oxygen species in a mouse model of Alzheimer’s disease

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Oxidative stress is a prominent feature of Alzheimer’s disease (AD). Within this context, cholesterol undergoes oxidation, producing the pro-inflammatory product 7-ketocholesterol (7-KC). In this study, we observe elevated levels of 7-KC in the brains of the 3xTg mouse model of AD. To further understand the contribution of 7-KC on the oxidative environment, we developed a method to express a genetically encoded fluorescent hydrogen peroxide (H 2 O 2 ) sensor in astrocytes, the primary source of cholesterol in the brain. With this sensor, we showed that 7-KC increases H 2 O 2 levels in astrocytes in vivo, but not when directly applied to astrocytes in vitro. When 7-KC was applied to a microglia cell line alone or mixed astrocyte and microglia cultures, it resulted in microglia activation and increased oxidative stress in astrocytes. Depletion of microglia from 3xTg mice resulted in reduced 7-KC and reduced reactive oxygen species in astrocytes. Taken together, these findings suggest that 7-KC, via microglia activation, contributes to increased astrocyte oxidative stress in the 3xTg mouse model of AD. This study contributes to understanding one of the drivers of the vicious cycle of oxidative stress seen in mouse models of AD whereby increased reactive oxygen species drive cholesterol oxidation, resulting in additional oxidative stress.