Haploinsufficiency of Dll4, a vascular-specific Notch ligand, has shown that it is essential for embryonic vascular development and arteriogenesis. Mechanistically, it is unclear how the Dll4-mediated Notch pathway contributes to complex vascular processes that demand meticulous coordination of multiple signalling pathways. Here we show that Dll4-mediated Notch signalling has a unique role in regulating endothelial cell proliferation and differentiation. Neutralizing Dll4 with a Dll4-selective antibody rendered endothelial cells hyperproliferative, and caused defective cell fate specification or differentiation both in vitro and in vivo. In addition, blocking Dll4 inhibited tumour growth in several tumour models. Remarkably, antibodies against Dll4 and antibodies against vascular endothelial growth factor (VEGF) had paradoxically distinct effects on tumour vasculature. Our data also indicate that Dll4-mediated Notch signalling is crucial during active vascularization, but less important for normal vessel maintenance. Furthermore, unlike blocking Notch signalling globally, neutralizing Dll4 had no discernable impact on intestinal goblet cell differentiation, supporting the idea that Dll4-mediated Notch signalling is largely restricted to the vascular compartment. Therefore, targeting Dll4 might represent a broadly efficacious and well-tolerated approach for the treatment of solid tumours.

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. Gpihbp1-deficient mice exhibit a striking accumulation of chylomicrons in the plasma, even on a low-fat diet, resulting in milky plasma and plasma triglyceride levels as high as 5000 mg/dl. Normally, Gpihbp1 is expressed highly in heart and adipose tissue, the same tissues that express high levels of LpL. In these tissues, GPIHBP1 is located on the luminal face of the capillary endothelium. Expression of GPIHBP1 in cultured cells confers the ability to bind both LpL and chylomicrons. These studies strongly suggest that GPIHBP1 is an important platform for the LpL-mediated processing of chylomicrons in capillaries.

Although previous studies have investigated the role of IL-27/WSX-1 interactions in the regulation of Th1 responses, little is known about their role in regulating Th2-type responses. Studies presented in this work identify a direct role for IL-27/WSX-1 interactions in the negative regulation of type 2 responses independent of effects on type 1 cytokines. WSX-1−/− mice infected with the gastrointestinal helminth Trichuris muris displayed accelerated expulsion of parasites and the development of exaggerated goblet cell hyperplasia and mastocytosis in the gut due to increased production of Th2 cytokines. Enhanced mast cell activity in the absence of WSX-1 was consistent with the ability of wild-type mast cells to express this receptor. In addition, IL-27 directly suppressed CD4+ T cell proliferation and Th2 cytokine production. Together, these studies identify a novel role for IL-27/WSX-1 in limiting innate and adaptive components of type 2 immunity at mucosal sites.

Glial-cell-line-derived neurotrophic factor (GDNF), neurturin and persephin are structurally related, secreted proteins that are widely expressed in the nervous system and other tissues and promote the survival of a variety of neurons during development. GDNF and neurturin signal through multicomponent receptors that consist of the Ret receptor tyrosine kinase and one of two structurally related glycosyl-phosphatidylinositol (GPI)-linked ligand-binding subunits: GFR alpha-1 is the preferred ligand-binding subunit for GDNF, and GFR alpha-2 is the preferred ligand-binding subunit for neurturin. Two additional members of the GFR alpha family of GPI-linked proteins have recently been cloned: GFR alpha-3 and GFR alpha-4. We have shown that persephin binds efficiently only to GFR alpha-4, and labelled persephin is effectively displaced from cells expressing GFR alpha-4 by persephin but not by GDNF or neurturin. Using microinjection to introduce expression plasmids into cultured neurons, we have also shown that coexpression of Ret with GFR alpha-4, confers a marked survival response to persephin but not to GDNF or neurturin. These results demonstrate that GFR alpha-4 is the ligand-binding subunit for persephin and that persephin, like GDNF and neurturin, also requires Ret for signalling.

No abstract