New approaches for understanding lipid movement in health and disease

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PPG Title: New Approaches for Understanding Lipid Movement in Health and Disease SUMMARY/ABSTRACT Our Program Project Grant (PPG) focuses on lipid metabolism and transport, with the goal of defining mechanisms for metabolic and cardiovascular disease. Our PPG team has made seminal discoveries in lipid metabolism and transport. We discovered an endothelial cell protein, GPIHBP1, that transports lipoprotein lipase (LPL) to the capillary lumen and stabilizes the structure of LPL. Recently, we defined the structure of the GPIHBP1–LPL complex, providing fresh insights into mutations causing hypertriglyceridemia and opening the door to understanding mechanisms that regulate intravascular lipolysis. In the realm of cholesterol metabolism, our PPG discovered that macrophages release, by plasma membrane (PM) budding, particles that are enriched in cholesterol. Our PPG uncovered a link between inflammatory signaling and cholesterol metabolism in macrophages, and we identified a new protein, Aster-B, that is critical for cholesterol movement between the PM and the endoplasmic reticulum (ER). A deficiency of Aster-B impairs cholesterol movement to the ER, causing a striking upregulation of lipid biosynthetic genes. These discoveries, all relevant to the pathogenesis of atherosclerosis, were utterly dependent on collaborations between our PPG leaders and the advanced molecular, biochemical, and imaging capabilities in their laboratories. As we look to the future, we will dig deeper into the molecules and mechanisms that we have uncovered. In project 1, Drs. Young and his PPG colleagues will use biochemical and biophysical tools to elucidate the functions of the LPL–GPIHBP1 complex, including the role of GPIHBP1’s acidic domain in stabilizing LPL activity and capturing LPL within the subendothelial spaces. They will also study, with electron microscopy and NanoSIMS imaging, the budding of cholesterol-rich particles from the macrophage PM. They will define the composition of the particles and explore their relevance to reverse cholesterol transport. In project 2, Dr. Bensinger and coworkers will determine how inflammatory signals modulate the lipidome of macrophages. They will also define mechanisms by which alterations in cholesterol homeostasis affect STING signaling and the impact of the STING pathway on dyslipidemia, inflammation, and atherogenesis. In Project 3, Dr. Tontonoz and his PPG coworkers will explore the role of Aster-B in cholesterol transport, efflux, and esterification and elucidate the function of Aster-B in sterol transport in vivo. They will also assess the contribution of the “macrophage Aster pathway” to atherosclerosis and screen for additional proteins required for the nonvesicular transport of cholesterol within cells. The three component projects will be supported by a single scientific core, led by Dr. Loren Fong and colleagues. They will produce recombinant proteins, provide advanced microscopy services, including NanoSIMS imaging of lipids. They will also work with Dr. Keriann Backus to provide chemical proteomics for investigating lipid metabolism. Our PPG is confident in success because we have exciting hypotheses and we work as a team at both scientific and technical levels.