The objectives of this proposal are to identify the structural features of lipoprotein lipase (LPL) required for binding to GPIHBP1 and to define mechanisms by which LPL is transported across endothelial cells. We discovered that GPIHBP1, an endothelial cell protein, binds LPL and is absolutely required for the lipolytic processing of triglyceride-rich lipoproteins. We showed that an absence of GPIHBP1 in mice causes severe hypertriglyceridemia (chylomicronemia) and that humans with GPIHBP1 mutations exhibit the same phenotype. Initially, we proposed that GPIHBP1 was a binding site for LPL in capillaries, but we recently found that GPIHBP1 has a second role-transporting LPL from the extracellular spaces into the capillary lumen. The identification of GPIHBP1 as the LPL transporter solved a longstanding mystery of plasma lipid metabolism, posing many new questions for investigation. Among these are: What amino acid sequences within LPL are important for binding to GPIHBP1? Do certain LPL mutations cause disease by abolishing LPL's ability to bind to GPIHBP1? Do other mutations enhance LPL transport? What is the efficiency of LPL transport across endothelial cells? Is LPL movement across capillaries bidirectional? Is LPL transported across capillaries in transcytotic vesicles? We have begun to investigate each of these issues. We have identified amino acid substitutions within the carboxyl terminus of LPL that abolish its ability to bind to GPIHBP1. These mutations have provided important clues regarding the location of LPL's GPIHBP1-binding domain, but many more studies are required to fully understand LPL-GPIHBP1 interactions. We have made great progress in understanding mechanisms of LPL transport, both in vitro and in vivo. Our studies have taken advantage of a host of new antibody reagents and expertise with both confocal and electron microscopy. We have two specific aims, each designed to better understand lipolysis in health and disease.
In Aim 1, we will test the hypothesis that the carboxyl terminus of LPL is crucial for binding GPIHBP1 and examine LPL mutations that interfere with GPIHBP1 binding and transport across endothelial cells.
In Aim 2, we will test the hypothesis that LPL is transported across endothelial cells by caveolar-mediated transcytosis. We are excited by these aims, and are poised-with all of the necessary expertise, reagents, and experimental techniques-to carry out the proposed studies.
LPL has a major influence on plasma lipid levels and on the delivery of lipid nutrients to vital tissues. Our goals are to understand LPL mutations that cause hypertriglyceridemia and to understand mechanisms for LPL transport into capillaries (so that lipolysis can proceed). Our topic is highly relevant to human fuel metabolism and to the pathogenesis of hyperlipidemias in humans.
|Kristensen, Kristian K; Midtgaard, Søren Roi; Mysling, Simon et al. (2018) A disordered acidic domain in GPIHBP1 harboring a sulfated tyrosine regulates lipoprotein lipase. Proc Natl Acad Sci U S A 115:E6020-E6029|
|Miyashita, Kazuya; Fukamachi, Isamu; Nagao, Manabu et al. (2018) An enzyme-linked immunosorbent assay for measuring GPIHBP1 levels in human plasma or serum. J Clin Lipidol 12:203-210.e1|
|He, Cuiwen; Weston, Thomas A; Jung, Rachel S et al. (2018) NanoSIMS Analysis of Intravascular Lipolysis and Lipid Movement across Capillaries and into Cardiomyocytes. Cell Metab 27:1055-1066.e3|
|Larsson, Mikael; Allan, Christopher M; Heizer, Patrick J et al. (2018) Impaired thermogenesis and sharp increases in plasma triglyceride levels in GPIHBP1-deficient mice during cold exposure. J Lipid Res 59:706-713|
|He, Cuiwen; Hu, Xuchen; Weston, Thomas A et al. (2018) Macrophages release plasma membrane-derived particles rich in accessible cholesterol. Proc Natl Acad Sci U S A 115:E8499-E8508|
|Hu, Xuchen; Dallinga-Thie, Geesje M; Hovingh, G Kees et al. (2017) GPIHBP1 autoantibodies in a patient with unexplained chylomicronemia. J Clin Lipidol 11:964-971|
|Allan, Christopher M; Jung, Cris J; Larsson, Mikael et al. (2017) Mutating a conserved cysteine in GPIHBP1 reduces amounts of GPIHBP1 in capillaries and abolishes LPL binding. J Lipid Res 58:1453-1461|
|He, Cuiwen; Hu, Xuchen; Jung, Rachel S et al. (2017) Lipoprotein lipase reaches the capillary lumen in chickens despite an apparent absence of GPIHBP1. JCI Insight 2:|
|Beigneux, Anne P; Miyashita, Kazuya; Ploug, Michael et al. (2017) Autoantibodies against GPIHBP1 as a Cause of Hypertriglyceridemia. N Engl J Med 376:1647-1658|
|Hu, Xuchen; Sleeman, Mark W; Miyashita, Kazuya et al. (2017) Monoclonal antibodies that bind to the Ly6 domain of GPIHBP1 abolish the binding of LPL. J Lipid Res 58:208-215|
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