Cardiovascular disease is the principal cause of death in patients with diabetes. In spite of ample epidemiological data linking diabetes and cardiovascular disease, the molecular mechanisms that underlie how hyperglycemia promotes atherosclerosis, remain poorly understood. The Liver X Receptors (LXRs) are transcription factors activated by oxidized forms of cholesterol (oxysterols) that serve as sensors of excessive intracellular cholesterol accumulation. In addition to their role in regulation of cholesterol and lipid homeostasis, the LXRs also modulate expression of key genes in glucose metabolism. We recently reported the surprising observation that glucose can bind the LXRs and activate LXR target genes in vivo. Their ability to bind both glucose and oxysterols hints that LXRs may represent a molecular connection between the diabetic hyperglycemic state and atherosclerosis. The proposed research will test the idea that LXRs act as dual oxysterol-glucose sensors in vivo. Elucidation of such a role is expected to enhance our understanding of the transcriptional mechanisms that link diabetes and atherosclerosis. Evaluation of the role of LXR as a dual oxysterol-glucose sensor will be facilitated by the identification of mutants that respond differentially to these two physiological ligands.
Specific Aim 1 is to use modeling to isolate and characterize in cell-based and biochemical assays LXR mutants with altered ligand responses. To understand how LXR integrates metabolic signals from two nutrients, and to enable guided design of LXR mutants, in Specific Aim 2 we will elucidate the structural basis of the LXR-glucose-oxysterol interaction.
In Specific Aim 3, the ability of LXR mutants with dissociated ligand responses to regulate endogenous LXR targets will be tested in cultured hepatocytes and selected mutants will be used to systematically profile the impact of LXR signaling on metabolic pathways.
In Specific Aim 4, LXR mutants with altered ligand responses will be used to create using gene targeting animal models to dissect the role of LXR in glucose and cholesterol metabolism in vivo. The ultimate goal of these studies is to use animals with engineered mutations to test the role of LXRs as glucose-oxysterol sensors in vivo. Future studies with mice expressing mutant LXRs will test the in vivo significance of LXR as a link between diabetes and atherosclerosis. We expect this work to enhance our understanding of how diabetes accelerates atherosclerosis, and to suggest novel therapeutic approaches to treat these conditions. Cardiovascular disease is a major complication of diabetes that accounts for more than 70% of all deaths in patients with diabetes. The risk of cardiovascular mortality is four times higher in individuals with diabetes than in nondiabetic individuals with similar levels of serum cholesterol. The long term goal of the proposed research is to advance our understanding of the cellular and molecular mechanisms that link diabetes and cardiovascular disease.
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