Grant: Discovery Grants Program - Individual

Homeostasis, or the maintenance of a steady-state internal environment by living systems, is a core principal of life. Cholesterol homeostasis is a conserved and essential eukaryotic process. Within mammalian cells, intracellular membrane cholesterol levels are tightly regulated, with complex cellular mechanisms in place to maintain proper cholesterol concentrations at distinct intracellular sites. For this, both vesicular and non-vesicular cholesterol trafficking pathways are required for cholesterol movement between cell compartments. Despite extensive study of these pathways, many questions remain about the mechanisms of cholesterol transfer between different cell compartments and how these processes are regulated. Oxysterol-binding (OSBP)-related proteins (ORPs) are a family of lipid transfer proteins (LTPs) implicated in many cellular processes related with oxysterols, inter-organelle contact, lipid metabolism and non-vesicular sterol transport. The goal of my NSERC research program is to investigate the role of LTPs in the maintenance of cellular and whole-body cholesterol homeostasis. Oxysterol-binding protein-Related Protein 6 (ORP6), a poorly characterized member of the ORP family, has recently emerged as a novel regulator of intracellular cholesterol levels. We previously showed that ORP6 regulates cholesterol trafficking between cell compartments (endosomes and the ER) and the plasma membrane for efflux. Yet, how ORP6 regulates these pathways, and its function in the brain where it is most highly expressed, are unknown. Gene and protein expression data provide evidence that ORP6 expression is enriched in the brain relative to other tissues, and more specifically in astrocytes and neurons relative to other cells of the central nervous system (CNS). To investigate how ORP6 regulates cholesterol transport and to define its physiological role in whole-body cholesterol homeostasis, we propose to: I.Investigate the role of ORP6 in neuronal and glial cholesterol homeostasis. II.Identify mechanisms of ORP6-mediated cholesterol trafficking. III.Determine the physiological role of ORP6 in cholesterol homeostasis. The current proposal combines my unique expertise on oxysterol-binding proteins, cholesterol trafficking, and lipid metabolism. We will employ a combination of techniques established in the lab to test the hypothesis that ORP6 regulates cholesterol homeostasis in the CNS. Because lipoproteins that shuttle lipid to supply tissues of the body cannot cross the blood-brain barrier, the brain constitutes a particularly interesting microenvironment to study lipid homeostasis as it must be more tightly controlled. With functional biological tools in-hand to study ORP6, we are poised to dissect the fundamental mechanisms of action of this unique ORP family member in cellular cholesterol homeostasis and shed light on fundamental mechanisms of lipid transport in the CNS and mammalian cells.