Cholesterol 25-hydroxylase mediates neuroinflammation and neurodegeneration in a mouse model of tauopathy

Alzheimer's disease (AD) is characterized by amyloid plaques and neurofibrillary tangles in addition to neuroinflammation and changes in brain lipid metabolism. Recent findings have demonstrated that microglia are key drivers of neurodegeneration in tauopathy mouse models. A subset of microglia referred to as disease-associated microglia (DAM) display gene signatures signifying changes in proinflammatory signaling and lipid metabolism in mouse models of amyloid and tau pathology. Ch25h is a DAM gene encoding cholesterol 25- hydroxylase that produces 25-hydroxycholesterol (25HC), a known modulator of inflammation as well as lipid metabolism. However, whether Ch25h influences tau-mediated neuroinflammation and neurodegeneration is unknown. Here, we show that in the absence of Ch25h and the resultant reduction in 25HC there is strikingly reduced age-dependent neurodegeneration and neuroinflammation in the hippocampus and entorhinal/piriform cortex of PS19 mice, which express the P301S mutant human tau transgene. Transcriptomic analyses of bulk hippocampal tissue and single nuclei revealed that Ch25h deficiency in PS19 mice strongly suppressed proinflammatory cytokine and chemokine signaling in microglia and restored sterol synthesis. Our results suggest a key role for Ch25h/25HC in potentiating proinflammatory signaling to promote tau-mediated neurodegeneration. Ch25h may represent a novel therapeutic target for primary tauopathies, AD, and other neuroinflammatory diseases. The PS19 transgenic mouse model overexpresses 1N4R human microtubule-associated protein tau (MAPT) driven by the PrP promoter, containing the P301S mutation that causes a familial form of frontotemporal dementia. The PS19 (T) mice were crossed to the Ch25h knockout (CKO) mice to generate wild type (WT), Ch25h KO (CKO), T and TCKO mice. Animals were perfused with PBS. Left hemisphere was fixed in 4% paraformaldehyde for immunostaining. Hippocampus from the right hemisphere was flash frozen and stored at -80 degrees C until RNA isolation using Zymo Research Quick-RNA MiniPrep Plus kit (Cat. #: R1058).阿尔茨海默病（Alzheimer's disease, AD）的病理特征除神经炎症与脑脂质代谢改变外，还包括淀粉样斑块与神经原纤维缠结。近期研究证实，小胶质细胞是tau蛋白病小鼠模型中神经退行性变的关键驱动因素。一类被称为疾病相关小胶质细胞（disease-associated microglia, DAM）的小胶质细胞亚群，在淀粉样蛋白与tau病理的小鼠模型中，呈现出与促炎信号通路及脂质代谢改变相关的基因表达特征。Ch25h作为一种DAM基因，编码胆固醇25-羟化酶，可合成25-羟胆固醇（25-hydroxycholesterol, 25HC）——后者是已知的炎症与脂质代谢调节剂。然而目前尚不清楚Ch25h是否会影响tau介导的神经炎症与神经退行性变。 本研究结果显示，在表达P301S突变型人tau转基因的PS19小鼠中，敲除Ch25h并由此导致25HC水平降低后，其海马体与内嗅/梨状皮层的年龄依赖性神经退行性变与神经炎症均显著减轻。对大块海马组织与单细胞核的转录组分析表明，PS19小鼠中Ch25h缺陷可强烈抑制小胶质细胞的促炎细胞因子与趋化因子信号通路，并恢复固醇合成通路。本研究结果提示，Ch25h/25HC在增强促炎信号通路以促进tau介导的神经退行性变过程中发挥关键作用。Ch25h或可成为原发性tau蛋白病、阿尔茨海默病及其他神经炎症性疾病的新型治疗靶点。 PS19转基因小鼠模型在PrP启动子驱动下过表达1N4R型人微管相关蛋白tau（microtubule-associated protein tau, MAPT），携带可导致家族性额颞叶痴呆的P301S突变。研究中将PS19（T）小鼠与Ch25h敲除（CKO）小鼠杂交，获得野生型（WT）、Ch25h敲除（CKO）、T及TCKO四种小鼠。对所有动物进行PBS灌流处理：左侧大脑半球经4%多聚甲醛固定以用于免疫染色；右侧大脑半球的海马体经快速冷冻后保存于-80℃冰箱，直至使用Zymo Research Quick-RNA MiniPrep Plus试剂盒（Cat. #: R1058）完成RNA提取。