Abstract 1746: Insulin Like Growth Factor Binding Protein-3 (IGFBP-3) Mediates Vascular Repair By HDL Receptor Activation And Sphingosine Kinase (SK-1)/Sphingosine 1-Phosphate (S1P) Dependent Nitric Oxide (NO) Generation
Purpose: We demonstrated that IGFBP-3 stimulates hematopoietic stem cells (HSC) to differentiate into endothelial cells, form capillaries, and stabilize the vasculature (Chang, et al, PNAS 2007). Local IGFBP- 3 production is increased by hypoxia and facilitates the homing of HSC to areas of injury. In the circulation, IGFBP-3 is bound to HDL. In this study, we investigated the signaling pathways responsible for the robust migratory effects of IGFBP-3.
Methods: The effects of IGFBP-3 on NO generation in human vascular precursors (CD 34+, CD14−), human lung microvascular endothelial cells, and human umbilical vein endothelial cells were examined using DAF-FM fluorescence. Western analysis was use for detection of eNOS and vasodilator-stimulated phosphoprotein (VASP), which redistributes to lamellipodia forming an active motor complex that supports motility and is phosphorylated in response to NO. Localization of VASP was performed by immunohistochemistry. SK-1 was assessed following IGFBP-3 stimulation.
Results: In CD34+ cells and endothelial cells, IGFBP-3 stimulated eNOS phosphorylation at Ser1177 (102 ± 1.8%, P = 0.0002) and increased NO generation (275 ± 50%, P = 0.05) by increasing SK-1 and S1P generation. IGFBP-3 was bound and internalized by the HDL receptor, scavenger receptor 1B (SR1B). NO generation following IGFBP-3 exposure was reduced by SK inhibitors or SR-1B blocking antibody pretreatment (35 ± 5%, P < 0.02). IGFBP-3 generated NO increased phosphorylation of VASP at Ser239 and promoted the redistribution of VASP to lamellipodia.
Conclusions: IGFBP-3 effects on cell migration are NO dependent and mediated in part by activation of the HDL receptor SR1B suggesting that some of the beneficial effects of HDL are mediated by the association of IGFBP-3.