Involvement of scavenging receptor‐B1 in NO release by insulin‐like growth factor binding protein‐3 (IGFBP3) in human endothelial and CD34 cells

Abstract

We recently reported the vascular protective potential of IGFBP3 involving recruitment of circulating endothelial progenitor cells (CD34) to the sites of vascular injury. NO plays an important role in the migration of CD34 cells and therefore, we hypothesized that NO is involved in the effects of IGFBP3. NO release was quantified by DAF‐FM fluorescence in human cord blood‐derived CD34 cells, umbilical vein endothelial cells (HUVECs), pulmonary microvascular endothelial cells (HMVECs) and human retinal ganglionic cells (HRGCs). IGFBP3 (100 ng/ml) increased NO release in all four cell types. Pretreatment with scavenging receptor‐B1 (SRB1) antibody inhibited NO release in endothelial cells but not in HRGCs. HDL induced NO release in endothelial and CD34 cells but not in HRGCs in which mRNA for SRB1 was not detected. Co‐treatment with IGFBP3 and HDL caused a greater release of NO than with either individual treatment. DMS, a sphingosine kinase inhibitor blocked NO release in CD34 cells. IGFBP3 caused eNOS and vasodilator‐stimulated peptide (VASP) phosphorylation and redistribution of VASP in endothelial cells that was inhibited by L‐NAME. IGFBP3 and HDL caused relaxation of phenylephrine‐preconstricted rat mesenteric arterial segments that was inhibited by L‐NAME and combination of L‐NAME and indomethacin, respectively. These results suggest involvement of NO in the vascular protective effect of IGFBP3.