Tissue Specific Control of Cholesterol Metabolism

胆固醇代谢的改变通常与慢性衰老疾病有关，包括心血管疾病、二型糖尿病、非酒精性脂肪性肝炎、多发性硬化症和阿尔茨海默病。虽然胆固醇升高与许多慢性疾病有关，但在大多数情况下，驱动功能病理变化的胆固醇依赖性途径尚未得到很好的描述。细胞结合使用负反馈和正前馈控制来协调维持胆固醇稳态。当细胞内胆固醇增加时，通过抑制转录因子甾醇调节元件结合蛋白 2 (SREBP2) 的蛋白水解激活，抑制胆固醇合成所需酶的基因表达（负反馈）。相反，升高的胆固醇通过增加肝脏 X 受体 (LXR) 的转录活性，诱导编码参与胆固醇排泄的蛋白质的基因表达（正前馈）。 LXR 是配体激活转录因子核激素受体超家族的成员，该转录因子可响应胆固醇衍生物的直接结合而调节基因表达。我们建议，阐明胆固醇在慢性疾病中的作用的独特方法是以细胞类型特异性方式可逆地破坏胆固醇稳态。为此，我们建议培育一种小鼠品系，该小鼠品系允许组织特异性表达 LXRα，并将色氨酸 441 突变为苯丙氨酸 (W441F)。 W441F 破坏内源性胆固醇衍生的 LXR 配体的结合，同时仍然允许通过有效的合成激动剂进行转录激活，提供一种独特的工具，阻止 LXRα 感知胆固醇水平变化的能力，同时仍然允许药理学控制。我们的初步数据表明 LXRα W441F 作为显性失活发挥作用，关闭 LXR 转录活性并促进细胞内胆固醇积累。重要的是，用合成 LXR 激动剂处理表达 LXRα W441F 的细胞可以恢复 LXR 活性。因此，我们建议开发一种新型小鼠模型，通过在 Cre 重组酶控制下表达 LXRα W441F 来实现胆固醇稳态的时间和空间调节。

Alterations in cholesterol metabolism are often associated with chronic diseases of aging including cardiovascular disease, type II diabetes, non-alcoholic steatohepatitis, multiple sclerosis, and Alzheimer’s disease. While elevated cholesterol is linked to many chronic diseases, in most cases the cholesterol-dependent pathways that drive pathological changes in function have not been well described. Cells use a combination of negative feedback and positive feed forward control to coordinately maintain cholesterol homeostasis. When intracellular cholesterol increases, expression of genes encoding enzymes required for cholesterol synthesis is repressed (negative feedback) by inhibiting the proteolytic activation of the transcription factor sterol regulatory element binding protein 2 (SREBP2). In contrast, elevated cholesterol induces expression of genes encoding proteins involved in cholesterol excretion (positive feed forward) by increasing the transcriptional activity of the liver x receptors (LXRs). The LXRs are members of the nuclear hormone receptor superfamily of ligand activated transcription factors that regulate gene expression in response to the direct binding of cholesterol derivatives. We suggest that a unique approach to unraveling the roles of cholesterol in chronic diseases will be to reversibly disrupt cholesterol homeostasis in a cell type specific manner. To this end we propose to generate a mouse line that allows tissue specific expression of LXRα with a mutation of tryptophan 441 to phenylalanine (W441F). W441F disrupts binding of endogenous cholesterol-derived LXR ligands while still allowing transcription activation by potent synthetic agonists providing a unique tool that blocks the ability of LXRα to sense changes in cholesterol levels while still allowing pharmacological control. Our preliminary data indicates that LXRα W441F functions as a dominant negative that shuts down LXR transcriptional activity and promotes intracellular cholesterol accumulation. Importantly, LXR activity can be restored by treating cells expressing LXRα W441F with synthetic LXR agonists. Therefore, we propose to develop a novel mouse model that allows temporal and spatial regulation of cholesterol homeostasis by expressing LXRα W441F under Cre recombinase control.