title: Enhanced expression of the Flt-1 and Flk-1 receptor tyrosine kinases in a newborn piglet model of ischemic tolerance.
abstract: Vascular endothelial growth factor (VEGF), an angiogenic factor induced by hypoxia, also exerts direct effects on neural tissues. VEGF up-regulation after hypoxia coincides with expression of its two tyrosine kinase receptors Flt-1(VEGFR-1) and Flk-1 (KDR/VEGFR-2), which are the key mediators of physiological angiogenesis. We have recently shown that hypoxic-preconditioning (PC) leading to tolerance to hypoxia-ischemia in neonatal piglet brain resulted in increased expression of VEGF. In this study, we used a hypoxic-preconditioning model of ischemic tolerance to analyze the expression and cellular distribution of VEGF receptors and phosphorylation of cAMP-response element-binding protein (CREB) in newborn piglet brain. The response of Flt-1 and Flk-1 mRNA to PC alone was biphasic with peaks early (6 h) and late (1 week) after PC. The mRNA expression of Flt-1 and Flk-1 in piglets preconditioned 24 h prior to hypoxia-ischemia was significantly higher than non-preconditioned piglets and remained up-regulated up to 7 days. Furthermore, PC prior to hypoxia-ischemia significantly increased the protein levels of Flt-1 and Flk-1 compared with hypoxia-ischemia in a time-dependent manner. Double-immunolabeling indicated that both Flt-1 and Flk-1 are expressed in neurons and endothelial cells with a similar time course of expression following PC and that PC leads to the growth of new vessels. Finally, our data demonstrate that PC significantly phosphorylated and activated cAMP-response element-binding protein in nucleus. These results suggest that mechanism(s) initiated by PC can induce VEGF receptor up-regulation in newborn brain and that VEGF-VEGF receptor-coupled signal transduction pathways could contribute to the establishment of tolerance following hypoxia-ischemia.
authors.affiliation: Department of Pediatrics, Drexel University College of Medicine and Saint Christopher's Hospital for Children, Philadelphia, PA 19102, USA. jahan.ara@drexelmed.edu
authors.forename: Jahan
authors.initials: J
authors.lastname: Ara
authors.forename: Panchanan
authors.initials: P
authors.lastname: Shukla
authors.forename: Melissa
authors.initials: M
authors.lastname: Frank
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western; D050882:CREB-Binding Protein / Q000378:metabolism; D020925:Hypoxia-Ischemia, Brain / Q000201:enzymology*; D007150:Immunohistochemistry; D019194:Ischemic Preconditioning; D010766:Phosphorylation; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D013552:Swine; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000378:metabolism*; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism*
chemical_list: D050882:CREB-Binding Protein; D040281:Vascular Endothelial Growth Factor Receptor-1; D040301:Vascular Endothelial Growth Factor Receptor-2