title: Angiopoietin-1 opposes VEGF-induced increase in endothelial permeability by inhibiting TRPC1-dependent Ca2 influx.
abstract: Angiopoietin-1 (Ang1) exerts a vascular endothelial barrier protective effect by blocking the action of permeability-increasing mediators such as vascular endothelial growth factor (VEGF) through unclear mechanisms. Because VEGF may signal endothelial hyperpermeability through the phospholipase C (PLC)-IP3 pathway that activates extracellular Ca2+ entry via the plasmalemmal store-operated channel transient receptor potential canonical-1 (TRPC1), we addressed the possibility that Ang1 acts by inhibiting this Ca2+ entry mechanism in endothelial cells. Studies in endothelial cell monolayers demonstrated that Ang1 inhibited the VEGF-induced Ca2+ influx and increase in endothelial permeability in a concentration-dependent manner. Inhibitors of the PLC-IP3 Ca2+ signaling pathway prevented the VEGF-induced Ca2+ influx and hyperpermeability similar to the inhibitory effects seen with Ang1. Ang1 had no effect on PLC phosphorylation and IP3 production, thus its permeability-decreasing effect could not be ascribed to inhibition of PLC activation. However, Ang1 interfered with downstream IP3-dependent plasmalemmal Ca2+ entry without affecting the release of intracellular Ca2+ stores. Anti-TRPC1 antibody inhibited the VEGF-induced Ca2+ entry and the increased endothelial permeability. TRPC1 overexpression in endothelial cells augmented the VEGF-induced Ca2+ entry, and application of Ang1 opposed this effect. In immunoprecipitation studies, Ang1 inhibited the association of IP3 receptor (IP3R) and TRPC1, consistent with the coupling hypothesis of Ca2+ entry. These results demonstrate that Ang1 blocks the TRPC1-dependent Ca2+ influx induced by VEGF by interfering with the interaction of IP3R with TRPC1, and thereby abrogates the increase in endothelial permeability.
authors.affiliation: Department of Pharmacology and The Center of Lung and Vascular Biology, The University of Illinois, Chicago, IL 60612, USA.
authors.forename: David
authors.initials: D
authors.lastname: Jho
authors.forename: Dolly
authors.initials: D
authors.lastname: Mehta
authors.forename: Gias
authors.initials: G
authors.lastname: Ahmmed
authors.forename: Xiao-Pei
authors.initials: XP
authors.lastname: Gao
authors.forename: Chinnaswamy
authors.initials: C
authors.lastname: Tiruppathi
authors.forename: Michael
authors.initials: M
authors.lastname: Broman
authors.forename: Asrar B
authors.initials: AB
authors.lastname: Malik
mesh_terms: D042683:Angiopoietin-1 / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D002199:Capillary Permeability / Q000187:drug effects*; D042783:Endothelial Cells / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D051966:Phospholipase C gamma; D050052:TRPC Cation Channels; D010738:Type C Phospholipases / Q000502:physiology; D042461:Vascular Endothelial Growth Factor A / Q000037:antagonists & inhibitors*
chemical_list: D042683:Angiopoietin-1; D015220:Calcium Channels; D050052:TRPC Cation Channels; D042461:Vascular Endothelial Growth Factor A; C096351:transient receptor potential cation channel, subfamily C, member 1; D015544:Inositol 1,4,5-Trisphosphate; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D002118:Calcium