BACKGROUND:Acute respiratory distress syndrome (ARDS) is a devastating complication of numerous underlying conditions, most notably sepsis. Although pathologic vascular leak has been implicated in the pathogenesis of ARDS and sepsis-associated lung injury, the mechanisms promoting leak are incompletely understood. Angiopoietin-2 (Ang-2), a known antagonist of the endothelial Tie-2 receptor, was originally described as a naturally occurring disruptor of normal embryonic vascular development otherwise mediated by the Tie-2 agonist angiopoietin-1 (Ang-1). We hypothesized that Ang-2 contributes to endothelial barrier disruption in sepsis-associated lung injury, a condition involving the mature vasculature.METHODS AND FINDINGS:We describe complementary human, murine, and in vitro investigations that implicate Ang-2 as a mediator of this process. We show that circulating Ang-2 is significantly elevated in humans with sepsis who have impaired oxygenation. We then show that serum from these patients disrupts endothelial architecture. This effect of sepsis serum from humans correlates with measured Ang-2, abates with clinical improvement, and is reversed by Ang-1. Next, we found that endothelial barrier disruption can be provoked by Ang-2 alone. This signal is transduced through myosin light chain phosphorylation. Last, we show that excess systemic Ang-2 provokes pulmonary leak and congestion in otherwise healthy adult mice.CONCLUSIONS:Our results identify a critical role for Ang-2 in disrupting normal pulmonary endothelial function.

Background —The coronary artery collateral circulation may be beneficial in protecting against myocardial ischemia and necrosis. However, there is a tremendous interindividual variability in the degree of new collateral formation in patients with coronary artery disease. The basis for this interindividual heterogeneity is not understood. In this study we test the hypothesis that failure to generate collateral vessels is associated with a failure to appropriately induce with hypoxia or ischemia the angiogenic factor, vascular endothelial growth factor (VEGF). Methods and Results —We correlated the VEGF response to hypoxia in the monocytes harvested from patients with coronary artery disease with the presence of collaterals visualized during routine angiography. We found that there was a highly significant difference in the hypoxic induction of VEGF in patients with no collaterals compared with patients with some collaterals (mean fold induction 1.9±0.2 versus 3.2±0.3 , P <0.0001). After subjecting the data to ANCOVA, using as covariates a number of factors that might influence the amount of collateral formation (ie, age, sex, diabetes, smoking, hypercholesterolemia), patients with no collaterals still have a significantly lower hypoxic induction of VEGF than patients with collaterals. Conclusions —This study provides evidence in support of the hypothesis that the ability to respond to progressive coronary artery stenosis is strongly associated with the ability to induce VEGF in response to hypoxia. The observed interindividual heterogeneity in this response may be due to environmental, epigenetic, or genetic causes. This interindividual heterogeneity may also help to explain the variable angiogenic responses seen in other conditions such as diabetic retinopathy and solid tumors.

BACKGROUND The coronary artery collateral circulation may be beneficial in protecting against myocardial ischemia and necrosis. However, there is a tremendous interindividual variability in the degree of new collateral formation in patients with coronary artery disease. The basis for this interindividual heterogeneity is not understood. In this study we test the hypothesis that failure to generate collateral vessels is associated with a failure to appropriately induce with hypoxia or ischemia the angiogenic factor, vascular endothelial growth factor (VEGF). METHODS AND RESULTS We correlated the VEGF response to hypoxia in the monocytes harvested from patients with coronary artery disease with the presence of collaterals visualized during routine angiography. We found that there was a highly significant difference in the hypoxic induction of VEGF in patients with no collaterals compared with patients with some collaterals (mean fold induction 1.9+/-0.2 versus 3.2+/-0.3, P<0.0001). After subjecting the data to ANCOVA, using as covariates a number of factors that might influence the amount of collateral formation (ie, age, sex, diabetes, smoking, hypercholesterolemia), patients with no collaterals still have a significantly lower hypoxic induction of VEGF than patients with collaterals. CONCLUSIONS This study provides evidence in support of the hypothesis that the ability to respond to progressive coronary artery stenosis is strongly associated with the ability to induce VEGF in response to hypoxia. The observed interindividual heterogeneity in this response may be due to environmental, epigenetic, or genetic causes. This interindividual heterogeneity may also help to explain the variable angiogenic responses seen in other conditions such as diabetic retinopathy and solid tumors.

The precursor of eicosanoids is arachidonic acid, which emanates from the cleavage of the sn-2 position of phospholipids by phospholipase A 2 (PLA 2 ). Eicosanoids have diverse physiological and pathophysiological effects in the kidney. The regulation of phospholipase A 2 has important implications for kidney function. In the current communication we focus our attention on mesangial cell cytosolic PLA 2 (cPLA 2 ) and its regulation at the post-translational and post-transcriptional level. At the post-translational level, using site directed mutagenesis of cPLA 2 and a dominant negative ras , we have demonstrated that cPLA 2 can be phosphorylated by mitogen activated protein (MAP-2) kinase leading to increased cPLA 2 enzymatic activity. At the post-transcriptional level we show that the half-life of cPLA 2 mRNA in mesangial cells is significantly increased when mesangial cells are stimulated by mitogens. We further demonstrate the presence of three ATTTA motifs in the 3′ untranslated region (3′ UTR) of the cPLA 2 cDNA. Using chimeric constructs bearing the 3′ UTR from rat cPLA 2 fused downstream of the luciferase reporter, we demonstrate that this region exerts a destabilizing effect on cPLA 2 . We have isolated and mapped genomic DNA and polymorphic markers for cPLA 2 in the human and rat.

1. The precursor of eicosanoids is arachidonic acid, which emanates from the cleavage of the sn-2 position of phospholipids by phospholipase A2 (PLA2). Eicosanoids have diverse physiological and pathophysiological effects in the kidney. The regulation of phospholipase A2 has important implications for kidney function. 2. In the current communication we focus our attention on mesangial cell cytosolic PLA2 (cPLA2) and its regulation at the post-translational and post-transcriptional level. 3. At the post-translational level, using site directed mutagenesis of cPLA2 and a dominant negative ras, we have demonstrated that cPLA2 can be phosphorylated by mitogen activated protein (MAP-2) kinase leading to increased cPLA2 enzymatic activity. 4. At the post-transcriptional level we show that the half-life of cPLA2 mRNA in mesangial cells is significantly increased when mesangial cells are stimulated by mitogens. We further demonstrate the presence of three ATTTA motifs in the 3' untranslated region (3' UTR) of the cPLA2 cDNA. 5. Using chimeric constructs bearing the 3' UTR from rat cPLA2 fused downstream of the luciferase reporter, we demonstrate that this region exerts a destabilizing effect on cPLA2. 6. We have isolated and mapped genomic DNA and polymorphic markers for cPLA2 in the human and rat.

Transmembrane signal transduction is the process whereby a ligand binds to the external surface of the cell membrane and elicits a physiological response specific for that ligand and cell type. It is now appreciated that numerous disease states represent disturbances in normal transmembrane signaling mechanisms. In the current paper, we focus our attention on the mesangial cell of the glomerular microcirculation as a prototypical model system for understanding normal and abnormal transmembrane signaling processes. Among the major receptor and effector mechanisms for transmembrane signal transduction in the mesangial cell, this paper emphasizes the phospholipase effector response to growth factors and vasoactive hormones. The post-translational and transcriptional pathways for regulation of phospholipase C and phospholipase A2 are described, including consideration of perturbations in these systems that characterize two disease models, namely: acute cyclosporine nephrotoxicity and early diabetic glomerulopathy.

Covalent dimers ofalamethicin formconducting structures withgating properties thatpermit measurement of current-voltage (/-V) relationships during thelifetime ofa single channel. TheseI-Vcurvesdemonstrate thatthealamethicin channel isa rectifier that passescurrent preferentially, withvoltages ofthesame signas thatofthevoltage thatinduced opening ofthechannel. Thedegreeofrectification depends on thesaltconcentration; single-channel I-Vrelationships becomealmost linear in3M potassium chloride. Theseproperties may bequalitatively understood byusing Poisson-Nernst- Planck theory anda modeled structure ofthealamethicin pore.