Tissue Specific Control of Cholesterol Metabolism

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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.