Person:

Klagsbrun, Michael

Neuropilin-1 (NRP1) is a receptor for vascular endothelial growth factor (VEGF). A soluble isoform of Nrp1 (sNrp1) has not been described in the mouse. Our goal was to examine the expression of mouse sNrp1 during liver development and regeneration. sNrp1 was cloned from mouse liver. The expression of sNrp1 and VEGF was examined in mouse liver during postnatal development and regeneration using northern blot, western blot, in situ hybridization, and immunohistochemical analyses. HGF/NRP1 binding was examined in vitro. A novel 588-amino acid sNrp1 isoform was found to contain the ligand binding regions of Nrp1. The adult liver expressed more sNrp1 than full-length Nrp1. In vivo, hepatocytes constitutively expressed VEGF and sNrp1 in the quiescent state. sNrp1 was highly upregulated at P20, a time point coinciding with a plateau in liver and body weights. Following hepatectomy, endogenous levels of sNrp1 decreased during the rapid growth phase; and VEGF levels were highest just prior to and during the angiogenic phase. sNrp1 levels again rose 5-10 days post-hepatectomy, presumably to control regeneration. HGF protein bound NRP1 and binding was competed with sNRP1. We cloned a novel mouse sNrp1 isoform from liver and provide evidence that this endogenous angiogenesis inhibitor may regulate VEGF or HGF bioavailability during normal physiological growth and development as well as during liver regeneration.

Bovine retina and hypothalamus contain anionic endothelial cell mitogens that display unusual affinities for the negatively charged glycosaminoglycan heparin. Both growth factor activities are acidic polypeptides (pl's of 5.0) as determined by isoelectric focusing and DEAE-affinity chromatography. In spite of their anionic nature, the factors bound to heparin-Sepharose columns with high affinity and could be eluted only at high salt concentrations (0.9-1.1 M NaCl). The affinity of the retina-derived growth factor (RDGF) for heparin permitted a 15,000-fold purification of the mitogen in two steps: heparin-affinity chromatography and size exclusion high-performance liquid chromatography. RDGF and the anionic hypothalamus-derived factor (aHDGF) exhibit three major biochemical similarities including isoelectric point, (pl's of 5.0), heparin affinity (elution at 0.9-1.1 M NaCl) and molecular weight (18,000). Additionally, the two factors display similar biological activities, stimulating the proliferation of capillary and human umbilical vein endothelial and 3T3 cells but not vascular smooth muscle cells. We suggest that RDGF and aHDGF are related if not identical growth factor molecules.