Mechanism of Fatty Acid Uptake by CD36

点击翻译按钮获取中文摘要

The overall objective of my research program is to understand the mechanism and impact of CD36 mediated transport of fatty acids (FA) across cell membranes, starting from the most basic question: how does the physical structure of CD36 facilitate FA uptake?, all the way to physiological and pathophysiological changes in vivo. Although more widely accepted today, protein mediated FA uptake remains controversial because un-ionized FA can rapidly flip/flop across membranes. Flip/flop, however, does not lead to productive incorporation of FA into cellular pools of triacylglycerides and phospholipids. In contrast, when CD36 is present on membranes, more than 90% of FA are subsequently found in cellular derivatives of FA. CD36-deficient mice and humans have phenotypic changes that could be explained by a defect in FA-uptake. The recently published model structure of CD36 provides important new information that allows rational and strategic structure:function interrogation of CD36 and perhaps a final answer to the FA uptake controversy. We hypothesize that, based on the structural model, a CD36 channel sequesters FA through to the membrane, where they flip/flop over. CD36 is localized in specific domains, lipid rafts, detergent resistant domains and caveolin, which may act as transport hubs. Other proteins which assist CD36 may interact physically, or may simply be enriched. Thus we imagine CD36 channels FA to cytoplasmic fatty acid binding proteins (FABP) and fatty acyl-CoA synthetase allowing for seemingly unidirectional FA flow and incorporation into cellular pools. It is the structure of CD36, however, that we hypothesize is intrinsic to the outcome. The objectives of this research proposal are 1. To create mutants of CD36 in the FA channel, such that they are FA-uptake dead, but otherwise competent, and expressed correctly on the cell surface, 2. To test the impact of this (these) mutant(s) on macrophage function and 3. To test an alternative hypothesis that CD36 affects FA esterification through signaling. These Aims complement and support other work in the lab in which we study CD36 co-localization with cytoplasmic FABPs and fatty acyl-CoA synthetase and the impact of endothelial cell CD36 on systemic FA uptake, obesity, insulin resistance and atherosclerosis using mouse models. The projects also synergize in that reagents and techniques created for one project can be incorporated into others, and knowledge gained from one informs the others. Understanding the fundamentals of FA uptake into cells increases our scientific knowledge and has the potential to effect strategies for obesity, insulin resistance/diabetes and cardiovascular diseases.