Abstract-Understanding molecular mechanisms regulating angiogenesis may lead to novel therapies for ischemic disorders. Hypoxia-inducible factor 1 (HIF-1) activates vascular endothelial growth factor (VEGF) gene expression in hypoxic/ischemic tissue. In this study we demonstrate that exposure of primary cultures of cardiac and vascular cells to hypoxia or AdCA5, an adenovirus encoding a constitutively active form of HIF-1␣, modulates the expression of genes encoding the angiogenic factors angiopoietin-1 (ANGPT1), ANGPT2, placental growth factor, and platelet-derived growth factor-B. Loss-of-function effects were also observed in HIF-1␣-null embryonic stem cells. Depending on the cell type, expression of ANGPT1 and ANGPT2 was either activated or repressed in response to hypoxia or AdCA5. In all cases, there was complete concordance between the effects of hypoxia and AdCA5. Injection of AdCA5 into mouse eyes induced neovascularization in multiple capillary beds, including those not responsive to VEGF alone. Analysis of gene expression revealed increased expression of ANGPT1, ANGPT2, platelet-derived growth factor-B, placental growth factor, and VEGF mRNA in AdCA5-injected eyes. These results indicate that HIF-1 functions as a master regulator of angiogenesis by controlling the expression of multiple angiogenic growth factors and that adenovirusmediated expression of a constitutively active form of HIF-1␣ is sufficient to induce angiogenesis in nonischemic tissue of an adult animal.

Background-Preconditioning phenomena provide evidence for adaptive responses to ischemia that have important implications for treatment/prevention of myocardial infarction. Hypoxia-inducible factor 1 (HIF-1) mediates adaptive transcriptional responses to hypoxia/ischemia. Methods and Results-Exposure of wild-type mice to intermittent hypoxia resulted in protection of isolated hearts against ischemia-reperfusion injury 24 hours later. Cardiac protection induced by intermittent hypoxia was lost in Hif1a ϩ/Ϫ mice heterozygous for a knockout allele at the locus encoding HIF-1␣. Erythropoietin (EPO) mRNA expression was induced in kidneys of wild-type mice subjected to intermittent hypoxia, resulting in increased plasma EPO levels. EPO mRNA expression was not induced in Hif1a ϩ/Ϫ mice. EPO administration to rats increased functional recovery and decreased apoptosis in isolated hearts subjected to ischemia-reperfusion 24 hours later. Conclusions-Hearts isolated from rodents subjected to intermittent hypoxia or EPO administration are protected against postischemic injury. Cardiac protection induced by intermittent hypoxia is critically dependent on Hif1a gene dosage. Our data suggest that additional studies to evaluate therapeutic applications of EPO administration are warranted.

HIF-1 alpha is required for IPC-induced mitochondrial ROS production and myocardial protection against ischaemia-reperfusion injury.

Both preclinical and clinical studies suggest that brief cycles of ischemia and reperfusion in the arm or leg may protect the heart against injury following prolonged coronary artery occlusion and reperfusion, a phenomenon known as remote ischemic preconditioning. Recent studies in mice indicate that increased plasma interleukin-10 (IL-10) levels play an important role in remote ischemic preconditioning induced by clamping the femoral artery for 5 min followed by 5 min of reperfusion for a total of three cycles. In this study, we demonstrate that remote ischemic preconditioning increases plasma IL-10 levels and decreases myocardial infarct size in wild-type mice but not in littermates that are heterozygous for a knockout allele at the locus encoding hypoxia-inducible factor (HIF) 1α. Injection of a recombinant adenovirus encoding a constitutively active form of HIF-1α into mouse hind limb muscle was sufficient to increase plasma IL-10 levels and decrease myocardial infarct size. Exposure of C2C12 mouse myocytes to cyclic hypoxia and reoxygenation rapidly increased levels of IL-10 mRNA, which was blocked by administration of the HIF-1 inhibitor acriflavine or by expression of short hairpin RNA targeting HIF-1α or HIF-1β. Chromatin immunoprecipitation assays demonstrated that binding of HIF-1 to the Il10 gene was induced when myocytes were subjected to cyclic hypoxia and reoxygenation. Taken together, these data indicate that HIF-1 activates Il10 gene transcription and is required for remote ischemic preconditioning.cardiac surgery | cardioprotection | coronary heart disease | myocardial infarction C oronary heart disease (CHD) is the leading cause of mortality in the US population, accounting for one in every six deaths, at a rate of one death from CHD every minute (1). Coronary artery stenosis due to atherosclerotic plaques results in reduced perfusion and myocardial ischemia. Plaque rupture results in complete arterial occlusion and the death of cardiac cells (myocardial infarction; MI) due to oxygen deprivation (2). Rapid reperfusion by thrombolytic therapy or percutaneous coronary intervention is the most important clinical factor to limit infarct size (IS), while at the same time reperfusion contributes to tissue injury by increasing intracellular reactive oxygen species and Ca 2+ levels (3, 4). Exposure of the heart to short (5-min) episodes of ischemia (I 5 ) and reperfusion (R 5 ) protects the heart against injury caused by a subsequent prolonged episode of ischemia and reperfusion (IR), a phenomenon known as ischemic preconditioning (IPC) (5).Although IPC was shown to have a powerful protective effect in animal models, the obvious difficulties involved in subjecting the heart to direct IPC restrict its potential clinical applications. However, the discovery that an IPC stimulus applied to the circumflex coronary artery reduced the size of an MI arising from sustained occlusion of the left anterior descending artery (6) was subsequently extended by the demonstration that the heart could be protected by su...

Background-Parenteral administration of recombinant human erythropoietin (rhEPO) to rats induces protection against myocardial ischemia/reperfusion injury 24 hours later. However, the mechanisms by which rhEPO mediates protection have not been determined. Methods and Results-rhEPO was perfused into isolated rat hearts over 15 minutes immediately before 30 minutes of no-flow ischemia and 45 minutes of reperfusion. Compared with saline-perfused control hearts, recovery of left ventricular developed pressure was increased in rhEPO-perfused hearts. rhEPO also increased AKT activity and decreased apoptosis. All of these effects were blocked when the phosphatidylinositol-3-kinase inhibitor wortmannin was infused with rhEPO. Conclusions-rhEPO provides immediate protection against ischemia/reperfusion injury in the isolated perfused rat heart that is mediated by the phosphatidylinositol-3-kinase pathway. Key Words: erythropoietin Ⅲ ischemia Ⅲ reperfusion Ⅲ myocardial infarction N ovel therapies are needed to reduce cardiac cell dysfunction and death in patients presenting with acute myocardial ischemia. 1,2 Administration of recombinant human erythropoietin (rhEPO) to rats has a dramatic protective effect against cardiac injury when administered 24 hours before global ischemia/reperfusion, as measured by improved recovery of left ventricular developed pressure (LVDP), reduced numbers of apoptotic cells, and reduced activation of caspase 3 in the hearts of treated animals. 3 Treatment with rhEPO also reduces apoptosis and increases functional recovery after in vivo coronary artery occlusion/reperfusion. 4 -6 These initial studies did not define the molecular mechanisms underlying the observed protective effects of rhEPO in the heart. The present study was designed to determine whether rhEPO has an immediate protective effect on the isolated perfused heart and whether protection mediated by rhEPO is dependent on signaling via phosphatidylinositol-3-kinase. Methods Rat Heart PerfusionHearts isolated from male Sprague-Dawley rats (Harlan, Indianapolis, Ind) were perfused in Langendorff mode with KrebsHenseleit buffer at 37°C at a constant pressure of 100 cm H 2 O. 3 A latex balloon was inserted into the left ventricle (LV) and inflated to an initial LV end-diastolic pressure (LVEDP) of 4 to 8 mm Hg. Saline or rhEPO was infused through an aortic cannula by syringe pump at a rate of 2 mL/h for 15 minutes. Hearts were subjected to 30 minutes of no-flow ischemia followed by 45 minutes of reperfusion in buffer alone. LVEDP, LVDP (LV systolic pressureϪLVEDP), and coronary flow rate (CFR) were monitored continuously (PowerLab, AD Instruments). A third group of hearts was infused with rhEPO and 1 mol/L wortmannin (Sigma Chemical Co) before ischemia, and wortmannin was included in the buffer during reperfusion. Statistical analyses were performed by ANOVA. Immunoblot AssaysHearts were lysed in 50 mmol/L Tris-HCl (pH 7.4), 1% NP-40, 0.25% sodium deoxycholate, 150 mmol/L NaCl, and 1 mmol/L EGTA, and aliquots were subjected to immunob...

Remote ischemic preconditioning (RIPC) induces a prolonged late phase of multi-organ protection against ischemia-reperfusion (IR) injury. In the present study, we tested the hypothesis that RIPC confers late protection against myocardial IR injury by upregulating expression of interleukin (IL)-10. Mice were exposed to lower limb RIPC or sham ischemia. After 24 h, mice with RIPC demonstrated decreased myocardial infarct size and improved cardiac contractility following 30-min ischemia and 120-min reperfusion (I-30/R-120). These effects of RIPC were completely blocked by anti-IL-10 receptor antibodies. In IL-10 knockout mice, RIPC cardioprotection was lost, but it was mimicked by exogenous IL-10. Administration of IL-10 to isolated perfused hearts increased phosphory-lation of the protein kinase Akt and limited infarct size after I-30/R-120. In wild-type mice, RIPC increased plasma and cardiac IL-10 protein levels and caused activation of Akt and endothelial nitric oxide synthase in the heart at 24 h, which was also blocked by anti-IL-10 receptor antibodies. In the gastrocnemius muscle, RIPC resulted in immediate inactivation of the phosphatase PTEN and activation of Stat3, with increased IL-10 expression 24 h later. Myocyte-specific PTEN inactivation led to increased Stat3 phosphorylation and IL-10 protein expression in the gastrocnemius muscle. Taken together, these results suggest that RIPC induces late protection against myocardial IR injury by increasing expression of IL-10 in the remote muscle, followed by release of IL-10 into the circulation, and activation of protective signaling pathways in the heart. This study provides a scientific basis for the use of RIPC to confer systemic protection against IR injury.

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Recent evidence suggests that nitric oxide (NO) within the inner medullary collecting duct (IMCD) functions to regulate sodium and water reabsorption. Because fluid shear stress has been shown to increase NO production in endothelial and vascular smooth muscle cells, experiments were designed to determine whether a similar mechanism exists in IMCD cells. Cultured IMCD-3 cells derived from murine IMCD were subjected to 60 min of pulsatile shear stress. Nitrite production (2,3-diaminonaphthalene fluorometric assay) increased 12-, 16-, and 23-fold at 3.3, 10, and 30 dyn/cm(2), respectively, compared with static control cultures. Preincubation with the non-isoform-specific NO synthase inhibitor nitro-L-arginine methyl ester reduced nitrite production by 83% in response to 30 dyn/cm(2). Western blotting and immunofluorescence analysis of static IMCD-3 cell cultures revealed the expression of all three NO synthase isoforms (NOS-1 or neuronal NOS, NOS-2 or inducible NOS, and NOS-3 or endothelial NOS) in IMCD-3 cultures. These results indicate that NO production is modulated by shear stress in IMCD-3 cells and that fluid shear stress within the renal tubular system may play a role in the regulation of sodium and water excretion by control of NO production in the IMCD.