Hypoxia-inducible factor-dependent induction of netrin-1 dampens inflammation caused by hypoxia

Repression of the equilibrative nucleoside transporters dampens inflammatory lung injury

Acute lung injury (ALI) is a devastating disorder of the lung that is characterized by hypoxemia, overwhelming pulmonary inflammation, and a high mortality in the critically ill. Adenosine has been implicated as an anti-inflammatory signaling molecule, and previous studies showed that extracellular adenosine concentrations are increased in inflamed tissues. Adenosine signaling is terminated by the uptake of adenosine from the extracellular into the intracellular compartment via equilibrative nucleoside transporters (ENTs). However, their role in controlling adenosine signaling during pulmonary inflammation remains unknown. After inflammatory in vitro experiments, we observed a repression of ENT1 and ENT2 that was associated with an attenuation of extracellular adenosine uptake. Experiments using short, interfering RNA silencing confirmed a significant contribution of ENT repression in elevating extracellular adenosine concentrations during inflammation. Furthermore, an examination of the ENT2 promoter implicated NF-κB as a key regulator for the observed ENT repression. Additional in vivo experiments using a murine model of inflammatory lung injury showed that the pharmacological inhibition of ENT1 and ENT2 resulted in improved pulmonary barrier function and reduced signs of acute inflammation of the lung. Whereas experiments on Ent1(-/-) or Ent2(-/-) mice revealed lung protection in LPS-induced lung injury, an examination of bone marrow chimeras for ENTs pointed to the nonhematopoetic expression of ENTs as the underlying cause of dampened pulmonary inflammation during ALI. Taken together, these findings reveal the transcriptional repression of ENTs as an innate protective response during acute pulmonary inflammation. The inhibition of ENTs could be pursued as a therapeutic option to ameliorate inflammatory lung injury.

HIF1A reduces acute lung injury by optimizing carbohydrate metabolism in the alveolar epithelium

BACKGROUND

While acute lung injury (ALI) contributes significantly to critical illness, it resolves spontaneously in many instances. The majority of patients experiencing ALI require mechanical ventilation. Therefore, we hypothesized that mechanical ventilation and concomitant stretch-exposure of pulmonary epithelia could activate endogenous pathways important in lung protection.

METHODS AND FINDINGS

To examine transcriptional responses during ALI, we exposed pulmonary epithelia to cyclic mechanical stretch conditions--an in vitro model resembling mechanical ventilation. A genome-wide screen revealed a transcriptional response similar to hypoxia signaling. Surprisingly, we found that stabilization of hypoxia-inducible factor 1A (HIF1A) during stretch conditions in vitro or during ventilator-induced ALI in vivo occurs under normoxic conditions. Extension of these findings identified a functional role for stretch-induced inhibition of succinate dehydrogenase (SDH) in mediating normoxic HIF1A stabilization, concomitant increases in glycolytic capacity, and improved tricarboxylic acid (TCA) cycle function. Pharmacologic studies with HIF activator or inhibitor treatment implicated HIF1A-stabilization in attenuating pulmonary edema and lung inflammation during ALI in vivo. Systematic deletion of HIF1A in the lungs, endothelia, myeloid cells, or pulmonary epithelia linked these findings to alveolar-epithelial HIF1A. In vivo analysis of ¹³C-glucose metabolites utilizing liquid-chromatography tandem mass-spectrometry demonstrated that increases in glycolytic capacity, improvement of mitochondrial respiration, and concomitant attenuation of lung inflammation during ALI were specific for alveolar-epithelial expressed HIF1A.

CONCLUSIONS

These studies reveal a surprising role for HIF1A in lung protection during ALI, where normoxic HIF1A stabilization and HIF-dependent control of alveolar-epithelial glucose metabolism function as an endogenous feedback loop to dampen lung inflammation.

The inflammatory tissue microenvironment in IBD

A current view of the inflammatory bowel diseases (IBDs) includes the luminal triggering of innate immune disease in a genetically susceptible host. Given the unique anatomy and complex environment of the intestine, local microenvironmental cues likely contribute significantly to both disease progression and resolution in IBD. Compartmentalized tissue and microbe populations within the intestine result in significant metabolic shifts within these tissue microenvironments. During active inflammatory disease, metabolic demands often exceed supply, resulting in localized areas of metabolic stress and diminished oxygen delivery (hypoxia). There is much recent interest in harnessing these microenvironmental changes to the benefit of the tissue, including targeting these pathways for therapy of IBD. Here, we review the current understanding of metabolic microenvironments within the intestine in IBD, with discussion of the advantages and disadvantages of targeting these pathways to treat patients with IBD.

Stimulation of A2B adenosine receptors protects against trauma-hemorrhagic shock-induced lung injury

Inflammation is responsible for secondary organ failure after trauma and hemorrhagic shock (T/HS). Adenosine, acting through four G protein-coupled cell surface receptors, A1, A2A, A2B, and A3, exerts a number of tissue protective and anti-inflammatory effects. The goal of the present study was to test the effect of A2B adenosine receptor stimulation on T/HS-induced organ injury and inflammation in rats. Rats after T/HS were resuscitated with Ringer's lactate containing the A2B receptor agonist BAY 60-6583 or its vehicle. We found that BAY 60-6583 decreased T/HS-induced lung permeability and plasma creatine kinase levels but failed to affect T/HS-induced lung neutrophil infiltration and IκBα expression and plasma alanine aminotransferase levels. Thus, we conclude that stimulation of A2B receptors protects against T/HS-induced lung and muscle injury.

Cobalt Chloride-induced Hypoxia Ameliorates NLRP3-Mediated Caspase-1 Activation in Mixed Glial Cultures

Hypoxia has been shown to promote inflammation, including the release of proinflammatory cytokines, but it is poorly investigated how hypoxia directly affects inflammasome signaling pathways. To explore whether hypoxic stress modulates inflammasome activity, we examined the effect of cobalt chloride (CoCl₂)-induced hypoxia on caspase-1 activation in primary mixed glial cultures of the neonatal mouse brain. Unexpectedly, hypoxia induced by oxygen-glucose deprivation or CoCl₂ treatment failed to activate caspase-1 in microglial BV-2 cells and primary mixed glial cultures. Of particular interest, CoCl₂-induced hypoxic condition considerably inhibited NLRP3-dependent caspase-1 activation in mixed glial cells, but not in bone marrow-derived macrophages. CoCl₂-mediated inhibition of NLRP3 inflammasome activity was also observed in the isolated brain microglial cells, but CoCl₂ did not affect poly dA:dT-triggered AIM2 inflammasome activity in mixed glial cells. Our results collectively demonstrate that CoCl₂-induced hypoxia may negatively regulate NLRP3 inflammasome signaling in brain glial cells, but its physiological significance remains to be determined.

The uncoordinated-5 homolog B (UNC5B) receptor increases myocardial ischemia-reperfusion injury

The UNC5 receptor family are chemorepulsive neuronal guidance receptors with additional functions outside the central nervous system. Previous studies have implicated that the UNC5B receptor influences the migration of leukocytes into sites of tissue inflammation. Given that this process is a critical step during the pathophysiology of myocardial ischemia followed by reperfusion (IR) we investigated the role of UNC5B during myocardial IR. In initial in-vitro experiments, the functional inhibition of UNC5B resulted in a significant reduction of chemotactic migration of neutrophils. In-vivo, using a model of acute myocardial ischemia in UNC5B^+/− and wild type (WT) animals, we found a significant reduction of infarct sizes in UNC5B^+/− animals. This was associated with significantly reduced levels of troponin-I and IL-6 in UNC5B^+/− mice. The repression of UNC5B using siRNA and the functional inhibition of UNC5B significantly dampened the extent of myocardial IR injury. Following depletion of neutrophils, we were not able to observe any further reduction in infarct size through functional inhibition of UNC5B in WT and UNC5B^+/− mice. In summary our studies demonstrate an important role for UNC5B during myocardial IR injury, and that UNC5B might be a potential therapeutic target to control reperfusion injury in the future.

Hypoxia-inducible factor and target gene expression are decreased in patients with sepsis: prospective observational clinical and cellular studies

BACKGROUND

Hypoxia-inducible factor-1 (HIF-1) is a molecular key player in response to hypoxemic/inflammatory conditions prevailing in sepsis. In a prospective observational study, we tested the hypotheses that sepsis affects HIF-1α messenger ribonucleic acid (mRNA) expression (primary hypothesis) and also (secondary hypotheses) the expression of the HIF-1α target genes adrenomedullin and β2-integrins. Furthermore, we tested that lipopolysaccharide administration increases HIF-1α mRNA and protein in naive and endotoxin-tolerant monocytes.

METHODS

In 99 patients with sepsis and 48 healthy volunteers, leukocyte HIF-1α mRNA expression (real-time polymerase chain reaction), cytokine concentrations (enzymelinked immunosorbent assay), and intracellular distribution of HIF-1α protein (immunofluorescence staining) were assessed. In vitro, HIF-1α mRNA expression and protein were measured in naive or endotoxin-tolerant (48 h; 0.05 ng/ml lipopolysaccharide) monocytes, with/without additional lipopolysaccharide (6h; 1 μg/ml).

RESULTS

In comparison to healthy volunteers, HIF-1α mRNA expression (-67%; P = 0.0001) and HIF-1α protein positive cells (-66.7%; P = 0.01) were decreased in sepsis. mRNA expression of adrenomedullin (-75%), CD11a (-85%), and CD11b (-86%; all P = 0.0001) was also decreased. In contrast, interleukin 6 (P = 0.0001), interleukin 10 (P = 0.0001), and tumor necrosis factor-α (P = 0.0002) concentrations were increased. Of note, HIF-1α mRNA expression was inversely associated with illness severity (Simplified Acute Physiology Score II; r = -0.29; P = 0.0001). In vitro, acute lipopolysaccharide administration of naive monocytic cells increased HIF-1α mRNA expression, whereas HIF-1α mRNA and protein (-60%; P = 0.001) were decreased in endotoxin-tolerant cells, which still up regulated cytokines.

CONCLUSIONS

In sepsis, HIF-1α mRNA expression was suppressed and inversely associated with illness severity. While acute lipopolysaccharide administration increased HIF-1α mRNA expression, prolonged stimulation suppressed HIF-1α expression. The clinical implications of decreased HIF-1α may include maladaption to tissue hypoxia or depressed immune function.

Detrimental role of the airway mucin Muc5ac during ventilator-induced lung injury

Acute lung injury (ALI) is associated with high morbidity and mortality in critically ill patients. At present, the functional contribution of airway mucins to ALI is unknown. We hypothesized that excessive mucus production could be detrimental during lung injury. Initial transcriptional profiling of airway mucins revealed a selective and robust induction of MUC5AC upon cyclic mechanical stretch exposure of pulmonary epithelia (Calu-3). Additional studies confirmed time- and stretch-dose-dependent induction of MUC5AC transcript or protein during cyclic mechanical stretch exposure in vitro or during ventilator-induced lung injury in vivo. Patients suffering from ALI showed a 58-fold increase in MUC5AC protein in their bronchoalveolar lavage. Studies of the MUC5AC promoter implicated nuclear factor κB in Muc5ac induction during ALI. Moreover, mice with gene-targeted deletion of Muc5ac⁻/⁻ experience attenuated lung inflammation and pulmonary edema during injurious ventilation. We observed that neutrophil trafficking into the lungs of Muc5ac⁻/⁻ mice was selectively attenuated. This implicates that endogenous Muc5ac production enhances pulmonary neutrophil trafficking during lung injury. Together, these studies reveal a detrimental role for endogenous Muc5ac production during ALI and suggest pharmacological strategies to dampen mucin production in the treatment of lung injury.

Signaling through hepatocellular A2B adenosine receptors dampens ischemia and reperfusion injury of the liver

Ischemia and reperfusion significantly contributes to the morbidity and mortality of liver surgery and transplantation. Based on studies showing a critical role for adenosine signaling in mediating tissue adaptation during hypoxia, we hypothesized that signaling events through adenosine receptors (ADORA1, ADORA2A, ADORA2B, or ADORA3) attenuates hepatic ischemia and reperfusion injury. Initial screening studies of human liver biopsies obtained during hepatic transplantation demonstrated a selective and robust induction of ADORA2B transcript and protein following ischemia and reperfusion. Subsequent exposure of gene-targeted mice for each individual adenosine receptor to liver ischemia and reperfusion revealed a selective role for the Adora2b in liver protection. Moreover, treatment of wild-type mice with an Adora2b-selective antagonist resulted in enhanced liver injury, whereas Adora2b-agonist treatment was associated with attenuated hepatic injury in wild-type, but not in Adora2b(-/-) mice. Subsequent studies in mice with Adora2b deletion in different tissues--including vascular endothelia, myeloid cells, and hepatocytes--revealed a surprising role for hepatocellular-specific Adora2b signaling in attenuating nuclear factor NF-κB activation and thereby mediating liver protection from ischemia and reperfusion injury. These studies provide a unique role for hepatocellular-specific Adora2b signaling in liver protection during ischemia and reperfusion injury.

CD73+ regulatory T cells contribute to adenosine-mediated resolution of acute lung injury

Acute lung injury (ALI) is characterized by alveolar injury and uncontrolled inflammation. Since most cases of ALI resolve spontaneously, understanding the endogenous mechanisms that promote ALI resolution is important to developing effective therapies. Previous studies have implicated extracellular adenosine signaling in tissue adaptation and wound healing. Therefore, we hypothesized a functional contribution for the endogenous production of adenosine during ALI resolution. As a model, we administered intratracheal LPS and observed peak lung injury at 3 d, with resolution by d 14. Treatment with pegylated adenosine-deaminase to enhance extracellular adenosine breakdown revealed impaired ALI resolution. Similarly, genetic deletion of cd73, the pacemaker for extracellular adenosine generation, was associated with increased mortality (0% wild-type and 40% in cd73(-/-) mice; P<0.05) and failure to resolve ALI adequately. Studies of inflammatory cell trafficking into the lungs during ALI resolution revealed that regulatory T cells (Tregs) express the highest levels of CD73. While Treg numbers in cd73(-/-) mice were similar to controls, cd73-deficient Tregs had attenuated immunosuppressive functions. Moreover, adoptive transfer of cd73-deficient Tregs into Rag(-/-) mice emulated the observed phenotype in cd73(-/-) mice, while transfer of wild-type Tregs was associated with normal ALI resolution. Together, these studies implicate CD73-dependent adenosine generation in Tregs in promoting ALI resolution.

Protective role for netrin-1 during diabetic nephropathy

Recent studies implicate neuronal guidance molecules in the orchestration of inflammatory events. For example, previous studies demonstrate a functional role for netrin-1 in attenuating acute kidney injury. Here, we hypothesized a kidney-protective role for netrin-1 during chronic kidney disease, such as occurs during diabetic nephropathy. To study the role of netrin-1 during diabetic nephropathy, we induced diabetes in mice at the age of 8 weeks by streptocotozin (STZ) treatment. Sixteen weeks after STZ treatment, we examined the kidneys. Initial studies in wild-type mice demonstrated robust induction of renal, urinary, and plasma netrin-1 protein levels during diabetic nephropathy. Subsequent genetic studies in mice with partial netrin-1 deficiency (Ntrn1(+/-) mice) revealed a more severe degree of diabetic nephropathy, including more severe loss of kidney function (albuminuria, glomerular filtration rate, histology). We subsequently performed pharmacologic studies with recombinant netrin-1 treatment given continuously via osmotic pump. Indeed, netrin-1 treatment was associated with attenuated albuminuria and improved histologic scores for diabetic nephropathy compared to controls. Consistent with previous studies implicating purinergic signaling in netrin-1-elicited tissue protection, mice deficient in the Adora2b adenosine receptor were not protected. Taken together, these studies demonstrate a functional role for endogenous netrin-1 in attenuating diabetic kidney disease.

Myeloid hypoxia-inducible factor 1α prevents airway allergy in mice through macrophage-mediated immunoregulation

Hypoxia-inducible factor (HIF) has important roles in promoting pro-inflammatory and bactericidal functions in myeloid cells. Conditional genetic ablation of its major subunit Hif1α in the myeloid lineage consequently results in decreased inflammatory responses in classical models of acute inflammation in mice. By contrast, we report here that mice conditionally deficient for Hif1α in myeloid cells display enhanced sensitivity to the development of airway allergy to experimental allergens and house-dust mite antigens. We support that upon allergen exposure, MyD88-dependent upregulation of Hif1α boosts the expression of the immunosuppressive cytokine interleukin (IL)-10 by lung interstitial macrophages (IMs). Hif1α-dependent IL-10 secretion is required for IMs to block allergen-induced dendritic cell activation and consequently for preventing the development of allergen-specific T-helper cell responses upon allergen exposure. Thus, this study supports that, in addition to its known pro-inflammatory activities, myeloid Hif1α possesses immunoregulatory functions implicated in the prevention of airway allergy.

Crosstalk between the equilibrative nucleoside transporter ENT2 and alveolar Adora2b adenosine receptors dampens acute lung injury

The signaling molecule adenosine has been implicated in attenuating acute lung injury (ALI). Adenosine signaling is terminated by its uptake through equilibrative nucleoside transporters (ENTs). We hypothesized that ENT-dependent adenosine uptake could be targeted to enhance adenosine-mediated lung protection. To address this hypothesis, we exposed mice to high-pressure mechanical ventilation to induce ALI. Initial studies demonstrated time-dependent repression of ENT1 and ENT2 transcript and protein levels during ALI. To examine the contention that ENT repression represents an endogenous adaptive response, we performed functional studies with the ENT inhibitor dipyridamole. Dipyridamole treatment (1 mg/kg; EC50=10 μM) was associated with significant increases in ALI survival time (277 vs. 395 min; P<0.05). Subsequent studies in gene-targeted mice for Ent1 or Ent2 revealed a selective phenotype in Ent2(-/-) mice, including attenuated pulmonary edema and improved gas exchange during ALI in conjunction with elevated adenosine levels in the bronchoalveolar fluid. Furthermore, studies in genetic models for adenosine receptors implicated the A2B adenosine receptor (Adora2b) in mediating ENT-dependent lung protection. Notably, dipyridamole-dependent attenuation of lung inflammation was abolished in mice with alveolar epithelial Adora2b gene deletion. Our newly identified crosstalk pathway between ENT2 and alveolar epithelial Adora2b in lung protection during ALI opens possibilities for combined therapies targeted to this protein set.

Hypoxia induces netrin-1 and Unc5b in atherosclerotic plaques: mechanism for macrophage retention and survival

OBJECTIVE

Hypoxia is intimately linked to atherosclerosis and has become recognized as a primary impetus of inflammation. We recently demonstrated that the neuroimmune guidance cue netrin-1 (Ntn1) inhibits macrophage emigration from atherosclerotic plaques, thereby fostering chronic inflammation. However, the mechanisms governing netrin-1 expression in atherosclerosis are not well understood. In this study, we investigate the role of hypoxia in regulating expression of netrin-1 and its receptor uncoordinated-5-B receptor (Unc5b) in plaque macrophages and its functional consequences on these immune cells.

APPROACH AND RESULTS

We show by immunostaining that netrin-1 and Unc5b are expressed in macrophages in hypoxia-rich regions of human and mouse plaques. In vitro, Ntn1 and Unc5b mRNA are upregulated in macrophages treated with oxidized low-density lipoprotein or inducers of oxidative stress (CoCl2, dimethyloxalylglycine, 1% O2). These responses are abrogated by inhibiting hypoxia-inducible transcription factor (HIF)-1α, indicating a causal role for this transcription factor in regulating Ntn1 and Unc5b expression in macrophages. Indeed, using promoter-luciferase reporter genes, we show that Ntn1- and Unc5b-promoter activities are induced by oxidized low-density lipoprotein and require HIF-1α. Correspondingly, J774 macrophages overexpressing active HIF-1α show increased netrin-1 and Unc5b expression and reduced migratory capacity compared with control cells, which was restored by blocking the effects of netrin-1. Finally, we show that netrin-1 protects macrophages from apoptosis under hypoxic conditions in a HIF-1α-dependent manner.

CONCLUSIONS

These findings provide a molecular mechanism by which netrin-1 and its receptor Unc5b are expressed in atherosclerotic plaques and implicate hypoxia and HIF-1α-induced netrin-1/Unc5b in sustaining inflammation by inhibiting the emigration and promoting the survival of lesional macrophages.

Neutrophil recruitment and function in health and inflammation

Neutrophils have traditionally been thought of as simple foot soldiers of the innate immune system with a restricted set of pro-inflammatory functions. More recently, it has become apparent that neutrophils are, in fact, complex cells capable of a vast array of specialized functions. Although neutrophils are undoubtedly major effectors of acute inflammation, several lines of evidence indicate that they also contribute to chronic inflammatory conditions and adaptive immune responses. Here, we discuss the key features of the life of a neutrophil, from its release from bone marrow to its death. We discuss the possible existence of different neutrophil subsets and their putative anti-inflammatory roles. We focus on how neutrophils are recruited to infected or injured tissues and describe differences in neutrophil recruitment between different tissues. Finally, we explain the mechanisms that are used by neutrophils to promote protective or pathological immune responses at different sites.

Adenosine receptors as drug targets--what are the challenges?

Adenosine signalling has long been a target for drug development, with adenosine itself or its derivatives being used clinically since the 1940s. In addition, methylxanthines such as caffeine have profound biological effects as antagonists at adenosine receptors. Moreover, drugs such as dipyridamole and methotrexate act by enhancing the activation of adenosine receptors. There is strong evidence that adenosine has a functional role in many diseases, and several pharmacological compounds specifically targeting individual adenosine receptors--either directly or indirectly--have now entered the clinic. However, only one adenosine receptor-specific agent--the adenosine A2A receptor agonist regadenoson (Lexiscan; Astellas Pharma)--has so far gained approval from the US Food and Drug Administration (FDA). Here, we focus on the biology of adenosine signalling to identify hurdles in the development of additional pharmacological compounds targeting adenosine receptors and discuss strategies to overcome these challenges.

Attenuating myocardial ischemia by targeting A2B adenosine receptors

Myocardial ischemia is associated with profound tissue hypoxia due to an imbalance in oxygen supply and demand, and studies of hypoxia-elicited adaptive responses during myocardial ischemia revealed a cardioprotective role for the signaling molecule adenosine. In ischemic human hearts, the A2B adenosine receptor (ADORA2B) is selectively induced. Functional studies in genetic models show that ADORA2B signaling attenuates myocardial infarction by adapting metabolism towards more oxygen efficient utilization of carbohydrates. This adenosine-mediated cardio-adaptive response involves the transcription factor hypoxia-inducible factor HIF1α and the circadian rhythm protein PER2. In this article, we discuss advances in the understanding of adenosine-elicited cardioprotection with particular emphasis on ADORA2B, its downstream targets, and the implications for novel strategies to prevent or treat myocardial ischemia.

Neuronal ER stress impedes myeloid-cell-induced vascular regeneration through IRE1α degradation of netrin-1

In stroke and proliferative retinopathy, despite hypoxia driven angiogenesis, delayed revascularization of ischemic tissue aggravates the loss of neuronal function. What hinders vascular regrowth in the ischemic central nervous system remains largely unknown. Using the ischemic retina as a model of neurovascular interaction in the CNS, we provide evidence that the failure of reparative angiogenesis is temporally and spatially associated with endoplasmic reticulum (ER) stress. The canonical ER stress pathways of protein kinase RNA-like ER kinase (PERK) and inositol-requiring enzyme-1α (IRE1α) are activated within hypoxic/ischemic retinal ganglion neurons, initiating a cascade that results in angiostatic signals. Our findings demonstrate that the endoribonuclease IRE1α degrades the classical guidance cue netrin-1. This neuron-derived cue triggers a critical reparative-angiogenic switch in neural macrophage/microglial cells. Degradation of netrin-1, by persistent neuronal ER stress, thereby hinders vascular regeneration. These data identify a neuronal-immune mechanism that directly regulates reparative angiogenesis.

Netrin-1 regulates colon-kidney cross talk through suppression of IL-6 function in a mouse model of DSS-colitis

Organ cross talk is increasingly appreciated in human disease, and inflammatory mediators are shown to mediate distant organ injury in many disease models. Colitis and intestinal injury are known to be mediated by infiltrating immune cells and their secreted cytokines. However, its effect on other organs, such as the kidney, has never been studied. In the current study, we examined the effect of dextran sulfate sodium (DSS)-colitis on kidney injury and inflammation. In addition, we hypothesized that netrin-1 could modulate colon-kidney cross talk through regulation of inflammation and apoptosis. Consistent with our hypothesis, DSS-colitis induced acute kidney injury in mice. Epithelial-specific overexpression of netrin-1 suppressed both colitis and colitis-induced acute kidney injury, which was associated with reduced weight loss, neutrophil infiltration into colon mucosa, intestinal permeability, epithelial cell apoptosis, and cytokine and chemokine production in netrin-1 transgenic mice colon and kidney. To determine whether netrin-1-protective effects were mediated through suppression of IL-6, IL-6 knockout mice were treated with DSS and acute kidney injury was determined. IL-6 knockout was resistant to colitis and acute kidney injury. Moreover, administration of IL-6 to netrin-1 transgenic mice did not affect the netrin-1-protective effects on the colon and kidney, suggesting that netrin-1 may reduce both IL-6 production and its activity. The present study identifies previously unrecognized cross talk between the colon and kidney, and netrin-1 may limit distant organ injury by suppressing inflammatory mediators and apoptosis.

Netrin-1 regulates the inflammatory response of neutrophils and macrophages, and suppresses ischemic acute kidney injury by inhibiting COX-2-mediated PGE2 production

Netrin-1 regulates inflammation but the mechanism by which this occurs is unknown. Here we explore the role of netrin-1 in regulating the production of the prostanoid metabolite PGE2 from neutrophils in in vitro and in vivo disease models. Ischemia reperfusion in wild-type and RAG-1 knockout mice induced severe kidney injury that was associated with a large increase in neutrophil infiltration and COX-2 expression in the infiltrating leukocytes. Administration of netrin-1 suppressed COX-2 expression, PGE2 and thromboxane production, and neutrophil infiltration into the kidney. This was associated with reduced apoptosis, inflammatory cytokine and chemokine expression, and improved kidney function. Treatment with the PGE2 receptor EP4 agonist enhanced neutrophil infiltration and renal injury which was not inhibited by netrin-1. Consistent with in vivo data, both LPS and IFNγ-induced inflammatory cytokine production in macrophages and IL-17-induced IFNγ production in neutrophils were suppressed by netrin-1 in vitro by suppression of COX-2 expression. Moreover, netrin-1 regulates COX-2 expression at the transcriptional level through the regulation of NFκB activation. Thus, netrin-1 regulates the inflammatory response of neutrophils and macrophages through suppression of COX-2 mediated PGE2 production. This could be a potential drug for treating many inflammatory immune disorders.

Endothelial expression of guidance cues in vessel wall homeostasis dysregulation under proatherosclerotic conditions

OBJECTIVE

Emerging evidence suggests that neuronal guidance cues, typically expressed during development, are involved in both physiological and pathological immune responses. We hypothesized that endothelial expression of such guidance cues may regulate leukocyte trafficking into the vascular wall during atherogenesis.

APPROACH AND RESULTS

We demonstrate that members of the netrin, semaphorin, and ephrin family of guidance molecules are differentially regulated under conditions that promote or protect from atherosclerosis. Netrin-1 and semaphorin3A are expressed by coronary artery endothelial cells and potently inhibit chemokine-directed migration of human monocytes. Endothelial expression of these negative guidance cues is downregulated by proatherogenic factors, including oscillatory shear stress and proinflammatory cytokines associated with monocyte entry into the vessel wall. Furthermore, we show using intravital microscopy that inhibition of netrin-1 or semaphorin3A using blocking peptides increases leukocyte adhesion to the endothelium. Unlike netrin-1 and semaphorin3A, the guidance cue ephrinB2 is upregulated under proatherosclerotic flow conditions and functions as a chemoattractant, increasing leukocyte migration in the absence of additional chemokines.

CONCLUSIONS

The concurrent regulation of negative and positive guidance cues may facilitate leukocyte infiltration of the endothelium through a balance between chemoattraction and chemorepulsion. These data indicate a previously unappreciated role for axonal guidance cues in maintaining the endothelial barrier and regulating leukocyte trafficking during atherogenesis.

Proximal tubule-specific overexpression of netrin-1 suppresses acute kidney injury-induced interstitial fibrosis and glomerulosclerosis through suppression of IL-6/STAT3 signaling

Acute kidney injury-induced organ fibrosis is recognized as a major risk factor for the development of chronic kidney disease, which remains one of the leading causes of death in the developed world. However, knowledge on molecules that may suppress the fibrogenic response after injury is lacking. In ischemic models of acute kidney injury, we demonstrate a new function of netrin-1 in regulating interstitial fibrosis. Acute injury was promptly followed by a rise in serum creatinine in both wild-type and netrin-1 transgenic animals. However, the wild-type showed a slow recovery of kidney function compared with netrin-1 transgenic animals and reached baseline by 3 wk. Histological examination showed increased infiltration of interstitial macrophages, extensive fibrosis, reduction of capillary density, and glomerulosclerosis. Collagen IV and α-smooth muscle actin expression was absent in sham-operated kidneys; however, their expression was significantly increased at 2 wk and peaked at 3 wk after reperfusion. These changes were reduced in the transgenic mouse kidney, which overexpresses netrin-1 in proximal tubular epithelial cells. Fibrosis was associated with increased expression of IL-6 and extensive and chronic activation of STAT3. Administration of IL-6 exacerbated fibrosis in vivo in wild-type, but not in netrin-1 transgenic mice kidney and increased collagen I expression and STAT3 activation in vitro in renal epithelial cells subjected to hypoxia-reoxygenation, which was suppressed by netrin-1. Our data suggest that proximal tubular epithelial cells may play a prominent role in interstitial fibrosis and that netrin-1 could be a useful therapeutic agent for treating kidney fibrosis.

Death by a thousand cuts in Alzheimer's disease: hypoxia--the prodrome

A wide range of clinical consequences may be associated with obstructive sleep apnea (OSA) including systemic hypertension, cardiovascular disease, pulmonary hypertension, congestive heart failure, cerebrovascular disease, glucose intolerance, impotence, gastroesophageal reflux, and obesity, to name a few. Despite this, 82 % of men and 93 % of women with OSA remain undiagnosed. OSA affects many body systems, and induces major alterations in metabolic, autonomic, and cerebral functions. Typically, OSA is characterized by recurrent chronic intermittent hypoxia (CIH), hypercapnia, hypoventilation, sleep fragmentation, peripheral and central inflammation, cerebral hypoperfusion, and cerebral glucose hypometabolism. Upregulation of oxidative stress in OSA plays an important pathogenic role in the milieu of hypoxia-induced cerebral and cardiovascular dysfunctions. Strong evidence underscores that cerebral amyloidogenesis and tau phosphorylation--two cardinal features of Alzheimer's disease (AD), are triggered by hypoxia. Mice subjected to hypoxic conditions unambiguously demonstrated upregulation in cerebral amyloid plaque formation and tau phosphorylation, as well as memory deficit. Hypoxia triggers neuronal degeneration and axonal dysfunction in both cortex and brainstem. Consequently, neurocognitive impairment in apneic/hypoxic patients is attributable to a complex interplay between CIH and stimulation of several pathological trajectories. The framework presented here helps delineate the emergence and progression of cognitive decline, and may yield insight into AD neuropathogenesis. The global impact of CIH should provide a strong rationale for treating OSA and snoring clinically, in order to ameliorate neurocognitive impairment in aged/AD patients.

Hypoxia in murine atherosclerotic plaques and its adverse effects on macrophages

Hypoxia has been found in the atherosclerotic plaques of larger mammals, including humans. Whether hypoxia occurs in the plaques of standard mouse models with atherosclerosis has been controversial, given their small size. In this review, we summarize the findings of a recent report demonstrating that direct evidence of hypoxia can indeed be found in the plaques of mice deficient in apolipoprotein E (apoE-/-mice). Furthermore, studies in vitro showed that hypoxia promoted lipid synthesis and reduced cholesterol efflux through the ABCA1 pathway, and that the transcription factor HIF-1α mediated many, but not all, of the effects. These results are discussed in the context of the literature and clinical practice.

Transcriptional control of adenosine signaling by hypoxia-inducible transcription factors during ischemic or inflammatory disease

Inflammatory lesions, ischemic tissues, or solid tumors are characterized by the occurrence of severe tissue hypoxia within the diseased tissue. Subsequent stabilization of hypoxia-inducible transcription factors-particularly of hypoxia-inducible factor 1α (HIF1A)--results in significant alterations of gene expression of resident cells or inflammatory cells that have been recruited into such lesions. Interestingly, studies of hypoxia-induced changes of gene expression identified a transcriptional program that promotes extracellular adenosine signaling. Adenosine is a signaling molecule that functions through the activation of four distinct adenosine receptors--the ADORA1, ADORA2A, ADORA2B, and ADORA3 receptors. Extracellular adenosine is predominantly derived from the phosphohydrolysis of precursor nucleotides, such as adenosine triphosphate or adenosine monophosphate. HIF1A-elicited alterations in gene expression enhance the enzymatic capacity within inflamed tissues to produce extracellular adenosine. Moreover, hypoxia-elicited induction of adenosine receptors--particularly of ADORA2B--results in increased signal transduction. Functional studies in genetic models for HIF1A or adenosine receptors implicate this pathway in an endogenous feedback loop that dampens excessive inflammation and promotes injury resolution, while at the same time enhancing ischemia tolerance. Therefore, pharmacological strategies to enhance HIF-elicited adenosine production or to promote adenosine signaling through adenosine receptors are being investigated for the treatment of acute inflammatory or ischemic diseases characterized by tissue hypoxia.

Role of the nervous system in cancer metastasis

The notion that tumors lack innervation was proposed several years ago. However, nerve fibers are irregulatedly found in some tumor tissues. Their terminals interaction with cancer cells are considered to be neuro-neoplastic synapses. Moreover, neural-related factors, which are important players in the development and activity of the nervous system, have been found in cancer cells. Thus, they establish a direct connection between the nervous system and tumor cells. They modulate the process of metastasis, including degradation of base membranes, cancer cell invasion, migration, extravasation and colonization. Peripheral nerve invasion provides another pathway for the spread of cancer cells when blood and lymphatic metastases are absent, which is based on the interactions between the microenvironments of nerve fibers and tumor cells. The nervous system also modulates angiogenesis, the tumor microenvironment, bone marrow, immune functions and inflammatory pathways to influence metastases. Denervation of the tumor has been reported to enhance cancer metastasis. Stress, social isolation and other emotional factors may increase distant metastasis through releasing hormones from the brain, the hypothalamic-pituitary-adrenal axis and autonomic nervous system. Disruption of circadian rhythms will also promote cancer metastasis through direct and indirect actions of the nervous system. Therefore, the nervous system plays an important role in cancer metastasis.

Adenosine and gastrointestinal inflammation

Nucleosides such as adenosine (Ado) influence nearly every aspect of physiology and pathophysiology. Extracellular nucleotides liberated at local sites of inflammation are metabolized through regulated phosphohydrolysis by a series of ecto-nucleotidases including ectonucleoside triphosphate diphosphohydrolase-1 (CD39) and ecto-5'-nucleotidase (CD73), found on the surface of a variety of cell types. Once generated, Ado is made available to bind and activate one of four G protein-coupled Ado receptors. Recent in vitro and in vivo studies implicate Ado in a broad array of tissue-protective mechanisms that provide new insight into adenosine actions. Studies in cultured cells and murine tissues have indicated that Ado receptors couple to novel posttranslational protein modifications, including Cullin deneddylation, as a new anti-inflammatory mechanism. Studies in Ado receptor-null mice have been revealing and indicate a particularly important role for the Ado A2B receptor in animal models of intestinal inflammation. Here, we review contributions of Ado to cell and tissue stress responses, with a particular emphasis on the gastrointestinal mucosa.

Netrin-1 attenuates the progression of renal dysfunction by inhibiting peritubular capillary loss and hypoxia in 5/6 nephrectomized rats

BACKGROUND/AIMS

The aim of this study was to investigate the effect of netrin-1 on peritubular capillary (PTC) loss and hypoxia in 5/6 nephrectomized (Nx) rats.

METHODS

Male Sprague-Dawley rats were divided into three groups (n = 10 rats/group): sham-operated rats treated with control adenovirus; 5/6 Nx rats treated with control adenovirus; and 5/6 Nx rats treated with recombinant adenovirus mediated netrin-1 gene (Ad-netrin-1) therapy. Rats were killed 12 weeks after surgery. Blood urea nitrogen (BUN), serum creatinine (Scr) and 24-h urinary albumin excretion rates were measured. Pathological changes in renal tissues were analyzed histologically. The concentration of netrin-1, CD34, and hypoxia-inducible factor-1α (HIF-1α) were analyzed by immunohistochemistry, Western blotting and real-time PCR.

RESULTS

Renal function and histopathological damage were significantly improved in Adnetrin-1 treated 5/6 Nx rats, compared with rats treated with the control adenovirus in the 5/6 Nx group. Furthermore, Ad-netrin-1 treatment induced a significant increase in renal PTC density, accompanied by a significant decrease in HIF-1α expression.

CONCLUSION

Adenovirus mediated netrin-1 treatment attenuates PTC damage, relieves tissues hypoxia and improves renal function, thus alleviating renal pathological changes and interstitial fibrosis in 5/6 Nx rats.

Erythrocytes induce proinflammatory endothelial activation in hypoxia

Although exposure to ambient hypoxia is known to cause proinflammatory vascular responses, the mechanisms initiating these responses are not understood. We tested the hypothesis that in systemic hypoxia, erythrocyte-derived H(2)O(2) induces proinflammatory gene transcription in vascular endothelium. We exposed mice or isolated, perfused murine lungs to 4 hours of hypoxia (8% O(2)). Leukocyte counts increased in the bronchoalveolar lavage. The expression of leukocyte adhesion receptors, reactive oxygen species, and protein tyrosine phosphorylation increased in freshly recovered lung endothelial cells (FLECs). These effects were inhibited by extracellular catalase and by the removal of erythrocytes, indicating that the responses were attributable to erythrocyte-derived H(2)O(2). Concomitant nuclear translocation of the p65 subunit of NF-κB and hypoxia-inducible factor-1α stabilization in FLECs occurred only in the presence of erythrocytes. Hemoglobin binding to the erythrocyte membrane protein, band 3, induced the release of H(2)O(2) from erythrocytes and the p65 translocation in FLECs. These data indicate for the first time, to our knowledge, that erythrocytes are responsible for endothelial transcriptional responses in hypoxia.

Expression of hypoxia-inducible factor-1α (HIF-1α) in infiltrating inflammatory cells is associated with chronic allograft dysfunction and predicts long-term graft survival

BACKGROUND

In chronic kidney failure, a hypoxic state, infiltrating inflammatory cells play a crucial role in the progression to end-stage renal disease. No studies have evaluated the influence of hypoxia and infiltrating inflammatory cells on chronic allograft dysfunction.

METHODS

Renal transplant recipients who underwent renal allograft biopsy with interstitial fibrosis/tubular atrophy (IF/TA) were enrolled and renal allograft tissue sections were processed for immunohistochemical staining including hypoxia-inducible factor-1α (HIF-1α), nitrotyrosine, α-smooth muscle actin and e-cadherin. Patients with total renal tissue HIF score ≥1 were defined as positive for HIF-1α. To assess the phenotype of the infiltrating cells, dual staining of HIF-1α with CD45, CD68 and CD3 was performed. The correlation between HIF-1α score and Banff's score was analysed. Clinical parameters including renal survival among patients with or without an expression of HIF-1α were compared.

RESULTS

Out of 55 patients enrolled, 23 patients (41.8%) had an HIF-1α score ≥1 (Group B). Compared with Group A (total renal HIF score <1), Group B had a significantly higher Banff score of interstitial infiltrates (i) (P = 0.029), vascular fibrous intimal thickening (cv) (P = 0.007) and arteriolar hyaline thickening (ah) (P = 0.026). Clinically, patients with an HIF-1α score were associated with a poor graft survival. Significantly inferior allograft survival was noted in Group B. HIF scores had an adjusted hazard ratio of 3.25 (95% confidence inteval: 1.71-6.16, P = 0.0003) in allograft failure.

CONCLUSIONS

We first demonstrated the expression of HIF-1α protein among infiltrating inflammatory cells in areas with IF/TA in patients with chronic allograft dysfunction.

Netrin-1 protects against L-Arginine-induced acute pancreatitis in mice

Acute pancreatitis (AP) is a common inflammatory disease mediated by damage to acinar cells and subsequent pancreatic inflammation with infiltration of leukocytes. The neuronal guidance protein, netrin-1, has been shown to control leukocyte trafficking and modulate inflammatory responses in several inflammation-based diseases. The present study was aimed toward investigating the effects of netrin-1 in an in vivo model of AP in mice. AP was induced in C57BL/6 mice by administration of two intraperitoneal injections of L-Arginine (4 g/kg). Mice were treated with recombinant mouse netrin-1 at a dose of 1 µg/mouse or vehicle (0.1% BSA) intravenously through the tail vein immediately after the second injection of L-Arginine, and every 24 h thereafter. Mice were sacrificed at several time intervals from 0 to 96 h after the induction of pancreatitis. Blood and tissue samples of pancreas and lung were collected and processed to determine the severity of pancreatitis biochemically and histologically. Immunohistochemical staining demonstrated that netrin-1 was mainly expressed in the islet cells of the normal pancreas and the AP model pancreas, and the pancreatic expression of netrin-1 was down-regulated at both the mRNA and protein levels during the course of AP. Exogenous netrin-1 administration significantly reduced plasma amylase levels, myeloperoxidase activity, pro-inflammatory cytokine production, and pancreas and lung tissue damages. Furthermore, netrin-1 administration did not cause significant inhibition of nuclear factor-kappa B activation in the pancreas of L-Arginine-induced AP. In conclusion, our novel data suggest that netrin-1 is capable of improving damage of pancreas and lung, and exerting anti-inflammatory effects in mice with severe acute pancreatitis. Thus, our results indicate that netrin-1 may constitute a novel target in the management of AP.

Effect of hypoxia and dexamethasone on inflammation and ion transporter function in pulmonary cells

Dexamethasone has been found to reduce the incidence of high-altitude pulmonary oedema. Mechanisms explaining this effect still remain unclear. We assessed the effect of dexamethasone using established cell lines, including rat alveolar epithelial cells (AEC), pulmonary artery endothelial cells (RPAEC) and alveolar macrophages (MAC), in an environment of low oxygen, simulating a condition of alveolar hypoxia as found at high altitude. Inflammatory mediators and ion transporter expression were quantified. Based on earlier results, we hypothesized that hypoxic conditions trigger inflammation. AEC, RPAEC and MAC, pre-incubated for 1 h with or without dexamethasone (10(-7) mol/l), were subsequently exposed to mild hypoxia (5% O(2), or normoxia as control) for 24 h. mRNA and protein levels of cytokine-induced neutrophil chemoattractant-1, monocyte chemoattractant protein-1 and interleukin-6 were analysed. mRNA expression and functional activity of the apical epithelial sodium channel and basolateral Na(+)/K(+)-ATPase were determined using radioactive marker ions. In all three types of pulmonary cells hypoxic conditions led to an attenuated secretion of inflammatory mediators, which was even more pronounced in dexamethasone pretreated samples. Function of Na(+)/K(+)-ATPase was not significantly influenced by hypoxia or dexamethasone, while activity of epithelial sodium channels was decreased under hypoxic conditions. When pre-incubated with dexamethasone, however, transporter activity was partially maintained. These findings illustrate that long-term hypoxia does not trigger an inflammatory response. The ion transport across apical epithelial sodium channels under hypoxic conditions is ameliorated in cells treated with dexamethasone.

Hypoxia-inducible factor-1 alpha-dependent induction of FoxP3 drives regulatory T-cell abundance and function during inflammatory hypoxia of the mucosa

Recent studies have demonstrated dramatic shifts in metabolic supply-and-demand ratios during inflammation, a process resulting in localized tissue hypoxia within inflammatory lesions ("inflammatory hypoxia"). As part of the adaptive immune response, T cells are recruited to sites of inflammatory hypoxia. Given the profound effects of hypoxia on gene regulation, we hypothesized that T-cell differentiation is controlled by hypoxia. To pursue this hypothesis, we analyzed the transcriptional consequences of ambient hypoxia (1% oxygen) on a broad panel of T-cell differentiation factors. Surprisingly, these studies revealed selective, robust induction of FoxP3, a key transcriptional regulator for regulatory T cells (Tregs). Studies of promoter binding or loss- and gain-of-function implicated hypoxia-inducible factor (HIF)-1α in inducing FoxP3. Similarly, hypoxia enhanced Treg abundance in vitro and in vivo. Finally, Treg-intrinsic HIF-1α was required for optimal Treg function and Hif1a-deficient Tregs failed to control T-cell-mediated colitis. These studies demonstrate that hypoxia is an intrinsic molecular cue that promotes FoxP3 expression, in turn eliciting potent anti-inflammatory mechanisms to limit tissue damage in conditions of reduced oxygen availability.

Guidance for life, cell death, and colorectal neoplasia by netrin dependence receptors

This review is focusing on a critical mediator of embryonic and postnatal development with multiple implications in inflammation, neoplasia, and other pathological situations in brain and peripheral tissues. These morphogenetic guidance and dependence processes are involved in several malignancies targeting the epithelial and immune systems including the progression of human colorectal cancers. We consider the most important findings and their impact on basic, translational, and clinical cancer research. Expected information can bring new cues for innovative, efficient, and safe strategies of personalized medicine based on molecular markers, protagonists, signaling networks, and effectors inherent to the Netrin axis in pathophysiological states.

Adenosine receptor A2b on hematopoietic cells mediates LPS-induced migration of PMNs into the lung interstitium

Uncontrolled transmigration of polymorphonuclear leukocytes (PMNs) into the different compartments of the lungs (intravascular, interstitial, alveolar) is a critical event in the early stage of acute lung injury and acute respiratory distress syndrome. Adenosine receptor A2b is highly expressed in the inflamed lungs and has been suggested to mediate cell trafficking. In a murine model of LPS-induced lung inflammation, we investigated the role of A2b on migration of PMNs into the different compartments of the lung. In A2b−/− mice, LPS-induced accumulation of PMNs was significantly higher in the interstitium, but not in the alveolar space. In addition, pulmonary clearance of PMNs was delayed in A2b−/− mice. Using chimeric mice, we identified A2b on hematopoietic cells as crucial for PMN migration. A2b did not affect the release of relevant chemokines into the alveolar space. LPS-induced microvascular permeability was under the control of A2b on both hematopoietic and nonhematopoietic cells. Activation of A2b on endothelial cells also reduced formation of LPS-induced stress fibers, highlighting its role for endothelial integrity. A specific A2b agonist (BAY 60–6583) was effective in decreasing PMN migration into the lung interstitium and microvascular permeability. In addition, in vitro transmigration of human PMNs through a layer of human endothelial or epithelial cells was A2b dependent. Activation of A2b on human PMNs reduced oxidative burst activity. Together, our results demonstrate anti-inflammatory effects of A2b on two major characteristics of acute lung injury, with a distinct role of hematopoietic A2b for cell trafficking and endothelial A2b for microvascular permeability.

Vasodilator phosphostimulated protein (VASP) protects endothelial barrier function during hypoxia

The endothelial barrier controls the passage of solutes from the vascular space. This is achieved through active reorganization of the actin cytoskeleton. A central cytoskeletal protein involved into this is vasodilator-stimulated phosphoprotein (VASP). However, the functional role of endothelial VASP during hypoxia has not been thoroughly elucidated. We determined endothelial VASP expression through real-time PCR (Rt-PCR), immunhistochemistry, and Western blot analysis during hypoxia. VASP promoter studies were performed using a PGL3 firefly luciferase containing plasmid. Following approval by the local authorities, VASP ( -/- ) mice and littermate controls were subjected to normobaric hypoxia (8% O(2), 92% N(2)) after intravenous injection of Evans blue dye. In in vitro studies, we found significant VASP repression in human microvascular and human umbilical vein endothelial cells through Rt-PCR, immunhistochemistry, and Western blot analysis. The VASP promoter construct demonstrated significant repression in response to hypoxia, which was abolished when the binding of hypoxia-inducible factor 1 alpha was excluded. Exposure of wild-type (WT) and VASP ( -/- ) animals to normobaric hypoxia for 4 h resulted in an increase in Evans blue tissue extravasation that was significantly increased in VASP ( -/- ) animals compared to WT controls. In summary, we demonstrate here that endothelial VASP holds significant importance for endothelial barrier properties during hypoxia.

Treatment with a novel hypoxia-inducible factor hydroxylase inhibitor (TRC160334) ameliorates ischemic acute kidney injury

BACKGROUND

Hypoxia-inducible factor (HIF) transcriptional system plays a central role in cellular adaptation to low oxygen levels. Preconditional activation of HIF and/or expression of its individual target gene products leading to cytoprotection have been well established in hypoxic/ischemic renal injury. Increasing evidence indicate HIF activation is involved in hypoxic/ischemic postconditioning of heart, brain and kidney. Very few studies evaluated the potential benefits of postischemia HIF activation in renal injury employing a pharmacological agent. We hypothesized that postischemia augmentation of HIF activation with a pharmacological agent would protect renal ischemia/reperfusion injury. For this, TRC160334, a novel HIF hydroxylase inhibitor, was used.

METHODS

TRC160334, a novel HIF hydroxylase inhibitor, was synthesized. Ability of TRC160334 for stabilization of HIF-α and consequent HIF activation was evaluated in Hep3B cells. Efficacy of TRC160334 was evaluated in a rat model of ischemia/reperfusion-induced AKI. Two different treatment protocols were employed, one involved treatment with TRC160334 before onset of ischemia, the other involved treatment after the reperfusion of kidneys.

RESULTS

TRC160334 treatment results in stabilization of HIF-α leading to HIF activation in Hep3B cells. Significant reduction in renal injury was observed by both treatment protocols and remarkable reduction in serum creatinine (23 and 71% at 24 and 48 h, respectively, p < 0.01) was observed with TRC160334 treatment applied after reperfusion. Urine output was significantly improved up to 24 h by both treatment protocols.

CONCLUSION

The data presented here provide pharmacologic evidence for postischemia augmentation of HIF activation by TRC160334 as a promising and clinically feasible strategy for the treatment of renal ischemia/reperfusion injury.

Netrin-1 concentrations in patients with advanced gastric cancer and its relation with treatment

CONTEXT

Netrin-1 is found to be elevated and usable as a diagnostic biomarker in many human cancers.

OBJECTIVES

We evaluated serum Netrin-1 concentrations in patients with advanced gastric cancer compared with those in a healthy group.

MATERIAL AND METHODS

Thirty patients with advanced gastric cancer and thirty healthy people were included in the study. Serum netrin-1 concentrations were measured by quantitative ELISA method in both groups.

RESULTS

The mean serum Netrin-1 concentrations were found to be significantly higher in patients with gastric cancer than in healthy controls. The mean serum Netrin-1 concentrations were found to be significantly higher in patients with gastric cancer before the beginning of chemotherapy when compared after the completion of third cycle.

DISCUSSION AND CONCLUSION

Our results indicated that netrin-1 concentrations elevated in advanced gastric cancer compared to a healthy control group and netrin-1 concentrations decreased with chemotherapy.

Endothelial Semaphorin 7A promotes neutrophil migration during hypoxia

Recent studies identified basic biological principles that are shared by the immune and the nervous system. One of these analogies applies to the orchestration of cellular migration where guidance proteins that serve as a stop signal for axonal migration can also serve as a stop signal for the migration of immune-competent cells. The control of leukocyte migration is of key interest during conditions associated with inflammatory tissue changes such as tissue hypoxia or hypoxic inflammation. Semaphorins are members of these axon guidance molecules. Previously unknown, we report here the expression and induction of semaphorin 7A (SEMA7A) on endothelium through hypoxia-inducible factor 1α during hypoxia. This induction of SEMA7A translates into increased transmigration of polymorphonuclear neutrophil granulocytes across endothelial cells. Extension of these findings demonstrated an attenuated extravasation of polymorphonuclear neutrophil granulocytes in Sema7a-deficient mice from the vasculature during hypoxia. Studies using chimeric animals identified the expression of Sema7A on nonhematopoietic tissue to be the underlying cause of the observed results. Taken together, our findings demonstrate that neuronal guidance proteins do not only serve as a stop signal for leukocyte migration but also can propagate the extravasation of leukocytes from the vascular space. Future anti-inflammatory strategies might be based on this finding.

The uncoordinated-5 homolog B receptor affects hepatic ischemia reperfusion injury

Recent evidence has demonstrated additional roles for the neuronal guidance protein receptor UNC5B outside the nervous system. Given the fact that ischemia reperfusion injury (IRI) of the liver is a common source of liver dysfunction and the role of UNC5B during an acute inflammatory response we investigated the role of UNC5B on acute hepatic IRI. We report here that UNC5B(+/-) mice display reduced hepatic IRI and neutrophil (PMN) infiltration compared to WT controls. This correlated with serum levels of lactate dehydrogenase (LDH), aspartate- (AST) and alanine- (ALT) aminotransferase, the presence of PMN within ischemic hepatic tissue, and serum levels of inflammatory cytokines. Moreover, injection of an anti-UNC5B antibody resulted in a significant reduction of hepatic IR injury. This was associated with reduced parameters of liver injury (LDH, ALT, AST) and accumulation of PMN within the injured hepatic tissue. In conclusion our studies demonstrate a significant role for UNC5B in the development of hepatic IRI and identified UNC5B as a potential drug target to prevent liver dysfunction in the future.

Adora2b signaling on bone marrow derived cells dampens myocardial ischemia-reperfusion injury

BACKGROUND

Cardiac ischemia-reperfusion (I-R) injury represents a major cause of cardiac tissue injury. Adenosine signaling dampens inflammation during cardiac I-R. The authors investigated the role of the adenosine A2b-receptor (Adora2b) on inflammatory cells during cardiac I-R.

METHODS

To study Adora2b signaling on inflammatory cells, the authors transplanted wild-type (WT) bone marrow (BM) into Adora2b(-/-) mice or Adora2b(-/-) BM into WT mice. To study the role of polymorphonuclear leukocytes (PMNs), neutrophil-depleted WT mice were treated with an Adora2b agonist. After treatments, mice were exposed to 60 min of myocardial ischemia and 120 min of reperfusion. Infarct sizes and troponin I concentrations were determined by triphenyltetrazolium chloride staining and enzyme-linked immunosorbent assay, respectively.

RESULTS

Transplantation of WT BM into Adora2b(-/-) mice decreased infarct sizes by 19 ± 4% and troponin I by 87.5 ± 25.3 ng/ml (mean ± SD, n = 6). Transplantation of Adora2b(-/-) BM into WT mice increased infarct sizes by 20 ± 3% and troponin I concentrations by 69.7 ± 17.9 ng/ml (mean ± SD, n = 6). Studies on the reperfused myocardium revealed PMNs as the dominant cell type. PMN depletion or Adora2b agonist treatment reduced infarct sizes by 30 ± 11% or 26 ± 13% (mean ± SD, n = 4); however, the combination of both did not produce additional cardioprotection. Cytokine profiling showed significantly higher cardiac tumor necrosis factor α concentrations in Adora2b(-/-) compared with WT mice (39.3 ± 5.3 vs. 7.5 ± 1.0 pg/mg protein, mean ± SD, n = 4). Pharmacologic studies on human-activated PMNs revealed an Adora2b-dependent tumor necrosis factor α release.

CONCLUSION

Adora2b signaling on BM-derived cells such as PMNs represents an endogenous cardioprotective mechanism during cardiac I-R. The authors' findings suggest that Adora2b agonist treatment during cardiac I-R reduces tumor necrosis factor α release of PMNs, thereby dampening tissue injury.