Role of the microglial immune-oxysterol 25-hydroxycholesterol in mediating neuroinflammation and neurodegeneration in the P301S tau transgenic mouse model of Alzheimer's disease

PROJECT SUMMARY/ABSTRACT Alzheimer disease (AD) is the most common neurodegenerative disorder characterized by neuroinflammation associated with amyloid plaques and tau-containing neurofibrillary tangles in the brain as well as severe neurodegeneration, neuroinflammation and lipid accumulation. The apolipoprotein E (APOE) genotype is by far the most powerful genetic risk factor for late-onset AD and is thought to play an important role in neuroinflammation and lipid metabolism. Pathological activation of microglia and astrocytes contribute substantially to the loss of neurons and synapses and lipid dysfunction in AD and related dementias (ADRD). Despite an important pathogenic role for microglia in tau-mediated neurodegeneration, the specific microglial mediators of neuroinflammation and neurodegeneration are poorly understood. Our lab has recently demonstrated that the microglial immune-oxysterol 25-hydroxycholesterol (25HC) augments the production of the proinflammatory cytokine, IL-1b, in an APOE-isoform dependent manner (E4>E3). Cholesterol 25- hydroxylase (CH25H), the enzyme that synthesizes 25HC is upregulated in AD and PS19 brain tissue as well as in disease-associated microglia (DAM). We have preliminary evidence that 25HC directly contributes to the age-dependent neurodegeneration observed in PS19 mice and regulates cholesterol metabolism in astrocytes. We hypothesize that 25HC synthesized and secreted by activated microglia drives tau-dependent neuroinflammation and neurodegeneration via its effects in regulating cholesterol metabolism. We will test this hypothesis as follows – In Aim 1, we will determine the importance of Ch25h in mediating tau-dependent neuroinflammation and neurodegeneration. In Aim 2, we will determine the role of Ch25h/25HC in mediating the deleterious effects of APOE4 on tau-dependent neuropathology. In Aim 3, we will determine whether and how 25HC alters cholesterol metabolism to reduce neuronal viability. Successful completion of this project may enable the development of novel therapeutic strategies towards ADRD.