HIF-dependent regulation of AKAP12 (gravin) in the control of human vascular endothelial function.

Hypoxia has been widely implicated in many pathological conditions, including those associated with inflammation and tumorigenesis. A number of recent studies have implicated hypoxia in the control of vasculogenesis and permeability, the basis for which is not fully understood. Here we examine the transcriptional regulation of angiogenesis and permeability by hypoxia in endothelial cells. Guided by a global profiling approach in cultured endothelial cells, these studies revealed the selective induction of human gravin (protein kinase A anchoring protein 12) by hypoxia. Analysis of the cloned gravin promoter identified a functional hypoxia-responsive region including 2 binding sites for hypoxia-inducible factor (HIF). Site-directed mutagenesis identified the most distal HIF-binding site as essential for the induction of gravin by hypoxia. Further studies examining gravin gain and loss of function confirmed strong dependence of gravin in control of microvascular endothelial tube formation, wherein gravin functions as a "braking" system for angiogenesis. Additional studies in confluent endothelia revealed that gravin functionally couples to control endothelial barrier function in response to protein kinase A (PKA) agonists. Taken together, these results demonstrate transcriptional coordination of gravin by HIF-1α and amplified PKA-dependent endothelial responses. These findings provide an important link between hypoxia and metabolic conditions associated with inflammation and angiogenesis.

Phosphorylation of vasodilator-stimulated phosphoprotein prevents platelet-neutrophil complex formation and dampens myocardial ischemia-reperfusion injury.

BACKGROUND: Recent work has suggested that the formation of platelet-neutrophil complexes (PNCs) aggravates the severity of inflammatory tissue injury. Given the importance of vasodilator-stimulated phosphoprotein (VASP) for platelet function, we pursued the role of VASP on the formation of PNCs and its impact on the extent of myocardial ischemia-reperfusion (IR) injury. METHODS AND RESULTS: In initial in vitro studies we found that neutrophils facilitated the movement of platelets across endothelial monolayers. Phosphorylation of VASP reduced the formation of PNCs and transendothelial movement of PNCs. During myocardial IR injury, VASP(-/-) animals demonstrated reduced intravascular formation of PNCs and reduced presence of PNCs within the ischemic myocardial tissue. This was associated with reduced IR injury. Studies using platelet transfer and bone marrow chimeric animals showed that hematopoietic VASP expression was crucial for the intravascular formation of PNCs the presence of PNCs within ischemic myocardial tissue and the extent of myocardial IR injury. Furthermore, phosphorylation of VASP on Ser153 or Ser235 reduced intravascular PNC formation and presence of PNCs within ischemic myocardial tissue. This finding was associated with reduced myocardial IR injury. CONCLUSION: Previously unappreciated, the phosphorylation of VASP performs a key function for the formation of PNCs that is crucially important for the extent of myocardial IR injury.

PMNs facilitate translocation of platelets across human and mouse epithelium and together alter fluid homeostasis via epithelial cell-expressed ecto-NTPDases.

Mucosal diseases are often characterized by an inflammatory infiltrate that includes polymorphonuclear leukocytes (PMNs), monocytes, lymphocytes, and platelets. A number of studies have suggested that the interaction of platelets with leukocytes has an essential proinflammatory role. Here, we examined whether platelets migrate across mucosal epithelium, as PMNs are known to do, and whether platelets influence epithelial cell function. Initial studies revealed that human platelets did not efficiently transmigrate across human epithelial cell monolayers. However, in the presence of human PMNs, platelet movement across the epithelium was proportional to the extent of PMN transmigration, and strategies that blocked PMN transmigration diminished platelet movement. Furthermore, platelet-PMN comigration was observed in intestinal tissue derived from human patients with inflammatory bowel disease (IBD). The translocated platelets were found to release large quantities of ATP, which was metabolized to adenosine via a 2-step enzymatic reaction mediated by ecto-nucleotidases, including CD73 and ecto-nucleoside triphosphate diphosphohydrolases (ecto-NTPDases), expressed on the apical membrane of the intestinal epithelial cells. In vitro studies and a mouse model of intestinal inflammation were employed to define a mechanism involving adenosine-mediated induction of electrogenic chloride secretion, with concomitant water movement into the intestinal lumen. These studies demonstrate that ecto-NTPDases are expressed on the apical membrane of epithelial cells and are involved in what we believe to be a previously unappreciated function for platelets in the inflamed intestine, which might promote bacterial clearance under inflammatory conditions.

Identification of vasodilator-stimulated phosphoprotein (VASP) as an HIF-regulated tissue permeability factor during hypoxia.

Increased tissue permeability is commonly associated with hypoxia of many origins. Since hypoxia-inducible factor (HIF) represents a predominant hypoxia signaling mechanism, we compared hypoxia-elicited changes in tissue barrier function in mice conditionally lacking intestinal epithelial hypoxia-inducible factor-1alpha (hif1a). Somewhat surprisingly, these studies revealed that mutant hif1a mice were protected from hypoxia-induced increases in intestinal permeability in vivo. Guided by microarray analysis of tissues derived from these mutant hif1a mice, we identified HIF-1-dependent repression of vasodilator-stimulated phosphoprotein (VASP), a molecule known to be important in the control of cytoskeletal dynamics, including barrier function. Studies at the mRNA and protein level confirmed hypoxia-elicited repression of VASP in murine tissue, cultured epithelia and endothelia, as well as human saphenous vein ex vivo. Targeted repression of VASP by siRNA recapitulated our findings with hypoxia and directed overexpression of VASP abolished hypoxia-induced barrier dysfunction. Studies in the cloned human VASP promoter revealed hypoxia-dependent transcriptional repression, and functional studies by chromatin immunoprecipitation (ChIP) and site-directed mutagenesis revealed hypoxia-dependent binding of HIF-1alpha to the human VASP promoter. These studies identify HIF-1-dependent repression of VASP as a control point for hypoxia-regulated barrier dysfunction.

ATP release from activated neutrophils occurs via connexin 43 and modulates adenosine-dependent endothelial cell function.

Extracellular ATP liberated during hypoxia and inflammation can either signal directly on purinergic receptors or can activate adenosine receptors following phosphohydrolysis to adenosine. Given the association of polymorphonuclear leukocytes (PMNs) with adenine-nucleotide/nucleoside signaling in the inflammatory milieu, we hypothesized that PMNs are a source of extracellular ATP. Initial studies using high-performance liquid chromatography and luminometric ATP detection assays revealed that PMNs release ATP through activation-dependent pathways. In vitro models of endothelial barrier function and neutrophil/endothelial adhesion indicated that PMN-derived ATP signals through endothelial adenosine receptors, thereby promoting endothelial barrier function and attenuating PMN/endothelial adhesion. Metabolism of extracellular ATP to adenosine required PMNs, and studies addressing these metabolic steps revealed that PMN express surface ecto-apyrase (CD39). In fact, studies with PMNs derived from cd39(-/-) mice showed significantly increased levels of extracellular ATP and lack of ATP dissipation from their supernatants. After excluding lytic ATP release, we used pharmacological strategies to reveal a potential mechanism involved in PMN-dependent ATP release (eg, verapamil, dipyridamole, brefeldin A, 18-alpha-glycyrrhetinic acid, connexin-mimetic peptides). These studies showed that PMN ATP release occurs through connexin 43 (Cx43) hemichannels in a protein/phosphatase-A-dependent manner. Findings in human PMNs were confirmed in PMNs derived from induced Cx43(-/-) mice, whereby activated PMNs release less than 15% of ATP relative to littermate controls, whereas Cx43 heterozygote PMNs were intermediate in their capacity for ATP release (P<0.01). Taken together, our results identify a previously unappreciated role for Cx43 in activated PMN ATP release, therein contributing to the innate metabolic control of the inflammatory milieu.

Nucleotide metabolism and cell-cell interactions.

Interactions between the vascular endothelium and polymorphonuclear leukocytes (PMNs) are central to PMN emigration into inflamed tissues, and to neutrophil-endothelial crosstalk pathways that modulate inflammatory responses and vascular barrier function. For example, during episodes of inflammation, the transendothelial migration (TEM) of PMNs potentially disturbs vascular barrier and gives rise to intravascular fluid extravasation and edema. However, because of the close special relationship between PMNs and the vascular endothelium, TEM creates an ideal situation for neutrophil-endothelial crosstalk. While investigating innate mechanisms to dampen intravascular fluid loss and edema occurring during TEM, we observed that PMNs release adenine nucleotides after activation (adenosine triphosphate [ATP] and adenosine monophosphate [AMP]). ATP and AMP are metabolized by endothelial cell-surface enzymes, the ecto-apyrase (CD39, metabolizes ATP to AMP) and the 5'-ecto-nucleotidase (CD73, metabolizes AMP to adenosine). Adenosine generated in this fashion can activate endothelial adenosine receptors, leading to increases in intracellular cyclic AMP and resealing of the endothelial junctions, thereby promoting vascular barrier function. This crosstalk pathway provides an endogenous mechanism to dampen vascular leak syndrome during neutrophil-endothelial interaction. In other words, during TEM, neutrophils close the door behind them.

Acute hemodynamic collapse after induction of general anesthesia for emergent pulmonary embolectomy.

Patients undergoing pulmonary embolectomy often experience hemodynamic deterioration during induction of general anesthesia (GA). Therefore, we studied the incidence and possible risk factors for hemodynamic deterioration during GA induction. Fifty-two consecutive patients undergoing emergent pulmonary embolectomy at our institution were included. Hemodynamic collapse after GA induction was defined as hypotension refractory to vasopressor, inotrope, or fluid administration, requiring cardiopulmonary resuscitation followed by urgent institution of cardiopulmonary bypass (CPB). Demographic variables, comorbidities, specific location of thromboemboli, preoperative inotropic support, and anesthetic drugs used for GA induction were evaluated as possible risk factors. After GA induction, hemodynamic collapse occurred in 19% of patients (n = 10). However, the occurrence of hemodynamic instability was not predicted by any of the evaluated risk factors. In addition, the incidence of in-hospital mortality did not differ between hemodynamically stable or unstable patients (10%; 4 of 42 versus 10%; 1 of 10 patients, respectively). In conclusion, hemodynamic deterioration after GA induction develops frequently during emergent pulmonary embolectomy. On the basis of our experience from this study and the unpredictable nature of hemodynamic deterioration, we suggest that patients undergoing pulmonary embolectomy should be prepared and draped before GA induction, and a cardiac surgical team should immediately be available for emergent institution of cardiopulmonary bypass.

Effect of hydroxyethyl starch on vascular leak syndrome and neutrophil accumulation during hypoxia.

OBJECTIVE: Several studies have suggested that intravenous hydroxyethyl starch treatment may dampen acute inflammatory responses. It is well documented that limited oxygen delivery to tissues (hypoxia) is common in acute inflammation, and numerous parallels exist between acute responses to hypoxia and to inflammation, including the observation that both are associated with increased vascular leakage and neutrophil infiltration of tissues. Therefore, we compared functional influences of hydroxyethyl starch on normoxic or posthypoxic endothelia. DESIGN: Laboratory study. SETTING: University hospital. SUBJECTS: Cultured human microvascular endothelial cells and mice (C57BL/6/129 svj). INTERVENTIONS: We measured functional influences of hydroxyethyl starch on normoxic or posthypoxic endothelia. MEASUREMENTS AND MAIN RESULTS: Studies to assess endothelial barrier function in vitro indicated that the addition of hydroxyethyl starch promotes endothelial barrier in a dose-dependent fashion and hydroxyethyl starch-barrier effects are increased following endothelial hypoxia exposure (human microvascular endothelial cells, 48 hrs, 2% oxygen). Treatment of human microvascular endothelial cells with hydroxyethyl starch resulted in a dose-dependent increase in 157-phosphorylated vasodilator-stimulated phosphoprotein, a protein responsible for controlling the geometry of actin-filaments. Neutrophil adhesion was decreased in the presence of physiologically relevant concentrations of hydroxyethyl starch in vitro, particularly after endothelial hypoxia exposure. Using a murine model of normobaric hypoxia, increases in vascular leakage and pulmonary edema associated with hypoxia exposure (4 hrs at 8% oxygen) were decreased in animals treated with intravenous hydroxyethyl starch. Increases of tissue neutrophil accumulation following hypoxia exposure were dampened in hydroxyethyl starch-treated mice. CONCLUSIONS: Taken together, these results indicate that hypoxia-induced increases in vascular leakage and acute inflammation are attenuated by hydroxyethyl starch treatment.

Dynamic purine signaling and metabolism during neutrophil-endothelial interactions.

During episodes of hypoxia and inflammation, polymorphonuclear leukocytes (PMN) move into underlying tissues by initially passing between endothelial cells that line the inner surface of blood vessels (transendothelial migration, TEM). TEM creates the potential for disturbances in vascular barrier and concomitant loss of extravascular fluid and resultant edema. Recent studies have demonstrated a crucial role for nucleotide metabolism and nucleoside signaling during inflammation. These studies have implicated multiple adenine nucleotides as endogenous tissue protective mechanisms invivo. Here, we review the functional components of vascular barrier, identify strategies for increasing nucleotide generation and nucleoside signaling, and discuss potential therapeutic targets to regulate the vascular barrier during inflammation.

Decreased proopiomelanocortin mRNA in lymphocytes of chronic alcoholics after intravenous human corticotropin releasing factor injection.

BACKGROUND: Alcohol abuse may involve an altered neuroendocrine response that mediates lymphocyte-derived proopiomelanocortin (POMC) production and inflammation. We investigated POMC messenger RNA (mRNA) expression in human lymphocytes ex vivo and their relation to plasma ACTH and immunoreactive beta-endorphin (IR-beta-EP) after intravenous injection of human corticotropin releasing factor (hCRF) in chronic alcoholics (n = 12) and nonalcoholics (n = 12) before surgery. Lipopolysaccharide-stimulated interleukin (IL)-1 receptor antagonist (IL-1 Ra) as a marker for chronic inflammation was determined. METHODS: Chronic alcohol abuse was diagnosed according to DSM-IV criteria and alcohol consumption >60 g/day. A reverse transcription-polymerase chain reaction method with total RNA and subsequent solid phase minisequencing was used to quantify lymphocytic POMC mRNA after intravenous hCRF injection. Plasma ACTH, cortisol, and lipopolysaccharide-stimulated IL-1 Ra of monocytes were measured by enzyme-linked immunosorbent assay, and plasma IR-beta-EP was measured by using radioimmunoassay. RESULTS: Baseline values of POMC mRNA content in lymphocytes and IL-1 Ra of chronic alcoholics were significantly increased compared with nonalcoholics (p < 0.01). Thirty minutes after intravenous hCRF injection, a significant increase of lymphocytic POMC mRNA was measured (p < 0.05) in nonalcoholics, whereas in chronic alcoholics a significant decrease was observed (p < 0.05). CONCLUSIONS: Chronic alcoholic patients had an altered neuroendocrine immune axis before intravenous hCRF administration and were not able to adjust to intravenous CRF injection by increasing lymphocytic POMC mRNA expression.