Equivalent binding of wild-type lipoprotein lipase (LPL) and S447X-LPL to GPIHBP1, the endothelial cell LPL transporter.

The S447X polymorphism in lipoprotein lipase (LPL), which shortens LPL by two amino acids, is associated with low plasma triglyceride levels and reduced risk for coronary heart disease. S447X carriers have higher LPL levels in the pre- and post-heparin plasma, raising the possibility that the S447X polymorphism leads to higher LPL levels within capillaries. One potential explanation for increased amounts of LPL in capillaries would be more avid binding of S447X-LPL to GPIHBP1 (the protein that binds LPL dimers and shuttles them to the capillary lumen). This explanation seems plausible because sequences within the carboxyl terminus of LPL are known to mediate LPL binding to GPIHBP1. To assess the impact of the S447X polymorphism on LPL binding to GPIHBP1, we compared the ability of internally tagged versions of wild-type LPL (WT-LPL) and S447X-LPL to bind to GPIHBP1 in both cell-based and cell-free binding assays. In the cell-based assay, we compared the binding of WT-LPL and S447X-LPL to GPIHBP1 on the surface of cultured cells. This assay revealed no differences in the binding of WT-LPL and S447X-LPL to GPIHBP1. In the cell-free assay, we compared the binding of internally tagged WT-LPL and S447X-LPL to soluble GPIHBP1 immobilized on agarose beads. Again, no differences in the binding of WT-LPL and S447X-LPL to GPIHBP1 were observed. We conclude that increased binding of S447X-LPL to GPIHBP1 is unlikely to be the explanation for more efficient lipolysis and lower plasma triglyceride levels in S447X carriers.

A new monoclonal antibody, 4-1a, that binds to the amino terminus of human lipoprotein lipase.

Lipoprotein lipase (LPL) has been highly conserved through vertebrate evolution, making it challenging to generate useful antibodies. Some polyclonal antibodies against LPL have turned out to be nonspecific, and the available monoclonal antibodies (Mabs) against LPL, all of which bind to LPL's carboxyl terminus, have drawbacks for some purposes. We report a new LPL-specific monoclonal antibody, Mab 4-1a, which binds to the amino terminus of LPL (residues 5-25). Mab 4-1a binds human and bovine LPL avidly; it does not inhibit LPL catalytic activity nor does it interfere with the binding of LPL to heparin. Mab 4-1a does not bind to human hepatic lipase. Mab 4-1a binds to GPIHBP1-bound LPL and does not interfere with the ability of the LPL-GPIHBP1 complex to bind triglyceride-rich lipoproteins. Mab 4-1a will be a useful reagent for both biochemists and clinical laboratories.

IL-16/miR-125a axis controls neutrophil recruitment in pristane-induced lung inflammation.

Severe lung inflammation and alveolar hemorrhage can be life-threatening in systemic lupus erythematosus (SLE) patients if not treated early and aggressively. Neutrophil influx is the driver key of this pathology, but little is known regarding the molecular events regulating this recruitment. Here, we uncover a role for IL-16/mir-125a in this pathology and show not only that IL-16 is a target for miR-125a but that reduced miR-125a expression in SLE patients associates with lung involvement. Furthermore, in the pristane model of acute "SLE-like" lung inflammation and alveolar hemorrhage, we observed reduced pulmonary miR-125a and enhanced IL-16 expression. Neutrophil infiltration was markedly reduced in the peritoneal lavage of pristane-treated IL-16-deficient mice and elevated following i.n. delivery of IL-16. Moreover, a miR-125a mimic reduced pristane-induced IL-16 expression and neutrophil recruitment and rescued lung pathology. Mechanistically, IL-16 acts directly on the pulmonary epithelium and markedly enhances neutrophil chemoattractant expression both in vitro and in vivo, while the miR-125a mimic can prevent this. Our results reveal a role for miR-125a/IL-16 in regulating lung inflammation and suggest this axis may be a therapeutic target for management of acute lung injury in SLE.