The objective of Project 1 (""""""""Function of GPIHBPI in Triglyceride Metabolism"""""""") in our Program Project Grant (PPG) is to define the function of GPIHBPI, a member of the Ly6 family of proteins, in plasma triglyceride metabolism and in the delivery of lipid nutrients to adipose tissue and muscle. This objective is closely aligned with the theme of our PPGto understand new molecules and mechanisms underlying triglyceride delivery to parenchymal tissues, triglyceride synthesis, and adipogenesis. Over the past 5 years, our PPG team showed that GPIHBPI transports lipoprotein lipase (LPL) from the interstitial spaces (where it is secreted by adipocytes and myocytes) to its site of action within the capillary lumen. This discovery solved a longstanding mystery in plasma lipid metabolism but simultaneously highlighted other lingering mysteries within the field. For example, no one has yet defined the mechanisms by which triglyceride-rich lipoproteins (TRLs) marginate within capillaries, so that lipolysis can proceed. Other mysteries include the mechanism by which TRL-derived lipids move across endothelial cells and the precise structures governing LPL-GPIHBP1 interactions and interactions of TRLs with the LPL-GPIHBP1 complex. Also, it is unclear whether other members of the Ly6 protein family, aside from GPIHBP1, contribute to metabolism and obesity. Recently, Project 1 investigators have shown that knockouts of several Ly6 genes near Gpihbp1 are associated with protection from obesity and lower plasma lipid levels. For the next 5 years. Project 1 investigators will pursue three Specific Aims.
Specific Aim 1 is to define mechanisms for the margination of TRLs in capillaries. As part of this aim, we will investigate the functional relevance of a newly discovered endothelial cell organelle, nanovilli, in TRL margination and in the transport of LPL across endothelial cells.
Specific Aim 2 is to better define interactions between GPIHBP1 and LPL and to further elucidate the features of the LPL-GPIHBP1 complex required for interactions with TRLs.
Specific Aim 3 is to investigate how the inactivation of a cluster of Ly6 genes (Slurpl, Slurp2, Lypd2) near Gpihbp1 affects energy balance in mice and protects against adiposity.

Public Health Relevance

Hypertriglyceridemia (high levels of triglycerides in the blood) is a common clinical problem and is associated with both pancreatitis and coronary disease. Triglycerides are cleared from the bloodstream along the surface of capillaries, mainly in adipose tissue and muscle. We seek to understand the mechanisms of triglyceride clearance from the blood and to find new treatments for hypertriglyceridemia.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Program Projects (P01)
Project #
2P01HL090553-06A1
Application #
8608033
Study Section
Special Emphasis Panel (ZHL1-PPG-R (O1))
Project Start
Project End
Budget Start
2013-12-15
Budget End
2014-11-30
Support Year
6
Fiscal Year
2014
Total Cost
$665,343
Indirect Cost
$175,265
Name
University of California Los Angeles
Department
Type
DUNS #
092530369
City
Los Angeles
State
CA
Country
United States
Zip Code
90095
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
Gao, Jie; Marosi, Mate; Choi, Jinkuk et al. (2017) The E3 ubiquitin ligase IDOL regulates synaptic ApoER2 levels and is important for plasticity and learning. Elife 6:
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
Allan, Christopher M; Larsson, Mikael; Jung, Rachel S et al. (2017) Mobility of ""HSPG-bound"" LPL explains how LPL is able to reach GPIHBP1 on capillaries. J Lipid Res 58:216-225
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
Zhang, Li; Rajbhandari, Prashant; Priest, Christina et al. (2017) Inhibition of cholesterol biosynthesis through RNF145-dependent ubiquitination of SCAP. Elife 6:
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:
Allan, Christopher M; Tran, Deanna; Tu, Yiping et al. (2017) A hypomorphic Egfr allele does not ameliorate the palmoplantar keratoderma caused by SLURP1 deficiency. Exp Dermatol 26:1134-1136
Wang, Jiexin; Rajbhandari, Prashant; Damianov, Andrey et al. (2017) RNA-binding protein PSPC1 promotes the differentiation-dependent nuclear export of adipocyte RNAs. J Clin Invest 127:987-1004
Wang, Huan; Airola, Michael V; Reue, Karen (2017) How lipid droplets ""TAG"" along: Glycerolipid synthetic enzymes and lipid storage. Biochim Biophys Acta 1862:1131-1145

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