CH25H mediates microglial neuroinflammation and tau toxicities in AD

About This Grant

Project Summary Apolipoprotein E4 (E4) is the predominant genetic risk factor for Alzheimer’s disease (AD). Recent studies demonstrate that E4 contributing to tau-induced neurodegeneration. However, the mechanisms by which E4 contributes to tau toxicity remain poorly understood. The GAS-STING-Interferon (IFN) signaling pathway is known to exacerbate the immuno-inflammatory response, worsening the procession neurodegenerative diseases. In AD, pathogenic tau can induce cGAS-STING-IFN signaling in microglia. Importantly, inflammatory responses, such as IFN, are heightened in microglia expressing E4, suggesting a potential mechanistic association between E4 and IFN pathway. Cholesterol 25-hydroxylase (CH25H) is an interferon inducible gene (ISG) predominantly expressed in disease associated microglia, where it produces 25-hydroxycholesterol (25- HC), a bioactive lipid involved in immune regulation. We previously showed that 25-HC exacerbates, while deletion of Ch25h suppresses, microglial inflammatory response. Notably, E4 promotes a stronger 25-HC- dependent IL1b/a cleavage compared to E3 or E2. Our preliminary studies suggest that Ch25h deletion mitigates tau pathology, reduces neurodegeneration, and improves cognitive function in tauopathy mouse models. These protective effects are linked to suppressed microglial inflammatory signaling and reduced STING expression in vivo and in vitro. These results suggest that 25-HC may regulate cGAS-STING signaling, a pathway implicated in tauopathy in our previous studies. Based on these observations on 25-HC and APOE, we hypothesize that CH25H acts with APOE4 to activate microglial STING-IFN signaling and promote Tau toxicity and neurodegeneration in AD. Aim 1 will investigate how 25-HC promotes cGAS-STING-Inflammasome signaling in microglia, by characterize the dose-dependent effects of exogeneous 25-HC in cGAS-STING-IFN activation, investigating whether 25-HC activates the STING-inflammasome pathway and exploring alternative mechanisms involving cytosolic dsDNA accumulation using unbiased multi-omics approaches. Aim 2 will determine if E4 activates cGAS-STING-IFN via an CH25H-dependent mechanism by characterizing the effects of E4 on tau- induced IFN responses in microglia and assess if E4 activates cGAS-STING signaling at baseline and under tau fibrils stimulation, investigating whether CH25H mediates E4-induced IFN response in microglia, and determining if intracellular cholesterol dysregulation is the convergent mechanism for Ch25h and E4. Aim 3 will investigate if CH25H enzymatic activity is required for E4-induced toxicity in tauopathy mice and assess the therapeutic potential of CH25H inhibition using antisense oligonucleotides (ASOs) by leveraging newly established mouse models with enzyme-active and enzyme-inactive CH25H overexpression to examine the role of 25-HC in tauopathy mice expressing E4 (TE4). We have assembled a highly complementary and collaborative research team to address these aims. We anticipate that our study will identify novel cellular mechanisms, uncover innovative pathways, and provide new models that have therapeutic implications.