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The defense mechanisms of endothelial cells (EC) against reactive oxygen species (ROS) are insufficiently characterized. We have addressed the hypothesis that vascular endothelial growth factor (VEGF) and its receptors are relevant elements in this response. Cell viability, VEGF and VEGF receptor (VEGFR1 and VEGFR2) expression, and transcription factor activation were studied on transient exposure of monolayer EC to H2O2. Wild-type and mutant inhibitors of κBα (IκBα) constructions were used to further assess the role of NF-κB in the induction of VEGFR2 expression. A concentration of H2O2 ≥60 μM elicited clear-cut damaging effects on EC, whereas lower concentrations (2–4 μM) were cytoprotective. The cytoprotective effect was shifted to an EC-damaging pattern by means of specific VEGF blockade, therefore revealing a major role of autologous VEGF. Exposure to H2O2 increased VEGF and VEGFR2 mRNA and protein in EC, without affecting VEGFRI expression. Also, H2O2 challenge was accompanied by increased NF-κB, activator protein-1, and specific protein-1 nuclear binding. A role of NF-κB as the mediator of the H2O2 induction of VEGFR2 mRNA expression was supported by inhibition by the ROS scavenger pyrrolidine dithiocarbamate and by the blocking effect of transfected IκBα. Exposure to exogenous VEGF also increased VEGFR2 and induced NF-κB in EC. In summary, autologous VEGF is instrumental for EC protection induced by low concentrations of ROS. ROS induce expression not only of VEGF but also of VEGFR2. VEGFR2 increase by ROS is mainly driven through a NF-κB-dependent pathway. [ABSTRACT FROM AUTHOR]

The defense mechanisms of endothelial cells (EC) against reactive oxygen species (ROS) are insufficiently characterized. We have addressed the hypothesis that vascular endothelial growth factor (VEGF) and its receptors are relevant elements in this response. Cell viability, VEGF and VEGF receptor (VEGFR1 and VEGFR2) expression, and transcription factor activation were studied on transient exposure of monolayer EC to H2O2. Wild-type and mutant inhibitors of κBα (IκBα) constructions were used to further assess the role of NF-κB in the induction of VEGFR2 expression. A concentration of H2O2 ≥60 μM elicited clear-cut damaging effects on EC, whereas lower concentrations (2–4 μM) were cytoprotective. The cytoprotective effect was shifted to an EC-damaging pattern by means of specific VEGF blockade, therefore revealing a major role of autologous VEGF. Exposure to H2O2 increased VEGF and VEGFR2 mRNA and protein in EC, without affecting VEGFRI expression. Also, H2O2 challenge was accompanied by increased NF-κB, activator protein-1, and specific protein-1 nuclear binding. A role of NF-κB as the mediator of the H2O2 induction of VEGFR2 mRNA expression was supported by inhibition by the ROS scavenger pyrrolidine dithiocarbamate and by the blocking effect of transfected IκBα. Exposure to exogenous VEGF also increased VEGFR2 and induced NF-κB in EC. In summary, autologous VEGF is instrumental for EC protection induced by low concentrations of ROS. ROS induce expression not only of VEGF but also of VEGFR2. VEGFR2 increase by ROS is mainly driven through a NF-κB-dependent pathway. [ABSTRACT FROM AUTHOR]

Cyclosporin A is an immunosuppressant drug widely used in solid organ transplantation, but it has nephrotoxic properties that promote oxidative stress. The JAK2/STAT pathway has been implicated in both cell protection and cell injury; therefore, we determined a role of JAK2 in oxidative stress-mediated renal cell injury using pathophysiologically relevant oxidative challenges. The AG490 JAK2 inhibitor and overexpression of a dominant negative JAK2 protein protected endothelial and renal epithelial cells in culture against peroxide, superoxide anion and cyclosporin A induced cell death while reducing intracellular oxidation in cells challenged with peroxide and cyclosporin A. The decrease in Bcl2 expression and caspase 3 activation, induced by oxidative stress, was prevented by AG490. In mouse models of ischemia/reperfusion and cyclosporin A nephrotoxicity, AG490 decreased peritubular capillary and tubular cell injury. Our study shows that JAK2 inhibition is a promising renoprotective strategy defending endothelial and tubular cells from cyclosporin A- and oxidative stress-induced death.Kidney International (2009) 75, 227–234; doi:10.1038/ki.2008.487; published online 24 September 2008 [ABSTRACT FROM AUTHOR]

In the adult hippocampus, neuroprogenitor cells in the subgranular zone (SGZ) of the dentate gyrus give rise to newborn neuroblasts. However, only a small subset of these cells integrates into the hippocampal circuitry as mature neurons at the end of a 4 week period. Here, we show that the majority of the newborn cells undergo death by apoptosis in the first 1 to 4 days of their life, during the transition from amplifying neuroprogenitors to neuroblasts. These apoptotic newborn cells are rapidly cleared out through phagocytosis by unchallenged microglia present in the adult SGZ niche. Phagocytosis by the microglia is efficient and undeterred by increased age or inflammatory challenge. Our results suggest that the main critical period of newborn cell survival occurs within a few days of birth and reveal a new role for microglia in maintaining the homeostasis of the baseline neurogenic cascade., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Inhibition of the JAK2/STAT pathway has been implicated recently in cytoprotective mechanisms in both vascular smooth muscle cells and astrocytes. The advent of JAK2-specific inhibitors provides a practical tool for the study of this pathway in different cellular types. An interest in finding methods to improve endothelial cell (EC) resistance to injury led us to examine the effect of JAK2/STAT inhibition on EC protection. Furthermore, the signaling pathways involved in JAK2/STAT inhibition-related actions were examined. Our results reveal, for the first time, that blockade of JAK2 with the tyrosine kinase inhibitor AG490 strongly protects cultured EC against cell detachment-dependent death and serum deprivation and increases reseeding efficiency. Confirmation of the specificity of the effects of JAK2 inhibition was attained by finding protective effects on transfection with a dominant negative JAK2. Furthermore, AG490 blocked serum deprivation-induced phosphorylation of JAK2. In terms of mechanism, treatment with AG490 induces several relevant responses, both in monolayer and detached cells. These mechanisms include the following: 1) Increase and nuclear translocation of the active, dephosphorylated form of beta-catenin. In functional terms, this translocation is transcriptionally active, and its protective effect is further supported by the stimulation of EC cytoprotection by transfectionally induced excess of beta-catenin. 2) Increase of platelet endothelial cell adhesion molecule (PECAM)/CD31 levels. 3) Increase in total and phosphorylated AKT. 4) Increase in phosphorylated glycogen synthase kinase (GSK)3alpha/beta. The present findings imply potential practical applications of JAK2 inhibition on EC. These applications affect not only EC in the monolayer but also circulating detached cells and involve mechanistic interactions not previously described.