Chylomicronemia with a mutant GPIHBP1 (Q115P) that cannot bind lipoprotein lipase.

Objective: GPIHBP1 is an endothelial cell protein that binds lipoprotein lipase (LPL) and chylomicrons. Because GPIHBP1 deficiency causes chylomicronemia in mice, we sought to determine whether some cases of chylomicronemia in humans could be attributable to defective GPIHBP1 proteins.

Methods And Results: Patients with severe hypertriglyceridemia (n=60, with plasma triglycerides above the 95th percentile for age and gender) were screened for mutations in GPIHBP1.

Abnormal patterns of lipoprotein lipase release into the plasma in GPIHBP1-deficient mice.

GPIHBP1-deficient mice (Gpihbp1(-/-)) exhibit severe chylomicronemia. GPIHBP1 is located within capillaries of muscle and adipose tissue, and expression of GPIHBP1 in Chinese hamster ovary cells confers upon those cells the ability to bind lipoprotein lipase (LPL). However, there has been absolutely no evidence that GPIHBP1 actually interacts with LPL in vivo.

In vivo arterial lipoprotein lipase expression augments inflammatory responses and impairs vascular dilatation.

Objective: Although epidemiologic data suggest that hypertriglyceridemia and elevated plasma levels of fatty acids are toxic to arteries, in vitro correlates have been inconsistent. To investigate whether increased endothelial cell expression of lipoprotein lipase (LpL), the primary enzyme creating free fatty acids from circulating triglycerides (TG), affects vascular function, we created transgenic mice that express human LpL (hLpL) driven by the promoter and enhancer of the Tie2 receptor.

Methods And Results: Mice expressing this transgene, denoted EC-hLpL and L for low and H for high expression, had decreased plasma TG levels compared with wild-type mice (WT): 106+/-31 in WT, 37+/-17 (line H), and 63+/-31 mg/dL (line L) because of a reduction in VLDL TG; plasma cholesterol and HDL levels were unaltered.

Glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 plays a critical role in the lipolytic processing of chylomicrons.

The triglycerides in chylomicrons are hydrolyzed by lipoprotein lipase (LpL) along the luminal surface of the capillaries. However, the endothelial cell molecule that facilitates chylomicron processing by LpL has not yet been defined. Here, we show that glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPIHBP1) plays a critical role in the lipolytic processing of chylomicrons.

Interaction of lipoprotein lipase and receptor-associated protein.

Receptor-associated protein (RAP) is a recognized chaperone/escort protein for members of the low density lipoprotein receptor family. In this report, we show that RAP binds to lipoprotein lipase (LPL) and may play a role in the maturation of LPL. Binding of highly purified RAP to LPL was demonstrated in vitro by solid phase assays, surface plasmon resonance, and rate zonal centrifugation.

Murine glypican-4 gene structure and expression; Sp1 and Sp3 play a major role in glypican-4 expression in 3T3-F442A cells.

In this report we describe the genomic organization of the mouse glypican-4 (Gpc4), an analysis of its promoter and its transcriptional regulation in the 3T3-F442A adipocyte cell line. The Gpc4 gene consists of nine exons separated by eight introns. A series of deletion mutants and 4391 bp of the 5'-flanking region were cloned into pGL3-BASIC upstream of the luciferase reporter gene and transfected into 3T3-F442A adipocytes.

Mice expressing only covalent dimeric heparin binding-deficient lipoprotein lipase: muscles inefficiently secrete dimeric enzyme.

Lipoprotein lipase (LpL) hydrolyzes triglycerides of circulating lipoproteins while bound as homodimers to endothelial cell surface heparan sulfate proteoglycans. This primarily occurs in the capillary beds of muscle and adipose tissue. By creating a mouse line that expresses covalent dimers of heparin-binding deficient LpL (hLpLHBM-Dimer) in muscle, we confirmed in vivo that linking two LpL monomers in a head to tail configuration creates a functional LpL.