Hypoxia, leukocytes, and the pulmonary circulation

Changes in pulmonary arterial pressure in term-infants with hypoxic-ischemic encephalopathy

BACKGROUND

Hypoxic-ischemic encephalopathy (HIE) is an important complication that results from birth asphyxia or some other adverse conditions and has a high risk of neonatal morbidity and mortality. It is unclear, however, whether the elevated pulmonary arterial pressure (PAP) can aggravate the condition and prognosis of HIE. The purpose of the present study was to investigate the relationship between the changes of PAP and HIE in term infants after birth asphyxia.

METHODS

The left/right ventricle pre-ejection phase (LPEP/RPEP), left/right ventricle ejection time (LVET/RVET) and the ratios of LPEP/LVET and RPET/RVET were evaluated in 40 term infants with HIE and 40 healthy controls on days 1, 3, 7, and 12-14 after birth using echocardiogram. PAP such as pulmonary arterial diastolic pressure (PADP, mmHg), pulmonary arterial resistance (PAR, mmHg), and pulmonary arterial resistance/systemic resistance ratio (PAR/RS) was calculated using these indexes. Patient mortality was also evaluated.

RESULTS

PADP, PAR, and PAR/RS were significantly higher in HIE patients than in healthy controls during the first week after birth, particularly in severe-degree HIE patients. And until the end of the first week of life, these indexes may return to the levels of healthy controls. Persistent fetal circulation (PFC) was found in nine patients (7/16 severe, 2/12 moderate HIE patients), and non-PFC was found in mild HIE patients. Two patients with PFC died. No patients without PFC died. The course of HIE was longer in patients with pulmonary hypertension than in those without.

CONCLUSION

Increased PAP is an important pathophysiological process that may influence the course and prognoses of HIE in infants after birth asphyxia, particular in severe HIE patients who often have PFC. Thus it is important to assess changes in PAP using echocardiography.

Cyclooxygenase-2 inhibition and hypoxia-induced pulmonary hypertension: effects on pulmonary vascular remodeling and contractility

Pulmonary arterial hypertension (PAH) is a significant disease process characterized by elevated pulmonary vascular resistance leading to increased right ventricular afterload and ultimately progressing to right ventricular dysfunction and often death. Irreversible remodeling of the pulmonary vasculature is the hallmark of pulmonary hypertension and frequently leads to progressive functional decline in patients with PAH despite treatment with currently available therapies. Metabolites of the arachidonic acid cascade play an important homeostatic role in the pulmonary vasculature, and dysregulation of pathways downstream of arachidonic acid plays a central role in the pathobiology of PAH. Cyclooxygenase-2 (COX-2) is up-regulated in pulmonary artery smooth muscle cells (PASMC) and inflammatory cells during hypoxia and plays a protective role in the lung's response to hypoxia. We recently demonstrated that absence of COX-2 was detrimental in a mouse model of hypoxia-induced pulmonary hypertension. Exposure of COX-2 null mice to hypoxia resulted in severe pulmonary hypertension characterized by enhanced pulmonary vascular remodeling and significant up-regulation of the endothelin-1 receptor ET(A)R in the lung after hypoxia. Absence of COX-2 in vitro led to enhanced contractility of PASMC after exposure to hypoxia, which could be attenuated by iloprost, a prostaglandin I(2) analog. These findings suggest that selective inhibition of COX-2 may have detrimental pulmonary vascular consequences in patients with preexisting pulmonary hypertension or underlying hypoxemic lung diseases. Here, we discuss our recent data demonstrating the adverse consequences of COX-2 inhibition on pulmonary vascular remodeling and PASMC contractility.

ROS production and angiogenic regulation by macrophages in response to heat therapy

PURPOSE

It has been well established that inadequate blood supply combined with high metabolic rates of oxygen consumption results in areas of low oxygen tension (<1%) within malignant tumours and that elevating tumour temperatures above 39 degrees Celsius results in significant improvement in tumour oxygenation. Macrophages play a dual role in tumour initiation and progression having both pro-tumour and anti-tumour effects. However, the response of macrophages to heat within a hypoxic environment has not yet been clearly defined.

METHODS

Raw 264.7 murine macrophages were incubated under normoxia and chronic hypoxia at temperatures ranging from 37-43 degrees Celsius. Under normoxia at 41 degrees Celsius, macrophages start to release significant levels of superoxide. The combination of heat with hypoxia constitutes an additional stimulus leading to increased respiratory burst of macrophages.

RESULTS

The high levels of superoxide were found to be associated with changes in macrophage production of pro-angiogenic cytokines. While hypoxia alone (37 degrees Celsius) increased levels of hypoxia inducible factor-1alpha (HIF-1alpha) in macrophages, the combination of hypoxia and mild hyperthermia (39-41 degrees Celsius) induced a strong reduction in HIF-1alpha expression. The HIF-regulated vascular endothelial growth factor (VEGF) decreased simultaneously, revealing that heat inhibits both HIF-1alpha stabilization and transcriptional activity.

CONCLUSION

The data suggest that temperatures which are readily achievable in the clinic (39-41 degrees Celsius) might be optimal for maximizing hyperthermic response. At higher temperatures, these effects are reversed, thereby limiting the therapeutic benefits of more severe hyperthermic exposure.

Hemoglobin disorders and endothelial cell interactions

Endothelial damage and inflammation make a significant contribution to the pathophysiology of sickle cell disease (SCD) and the beta-thalassemia syndromes. Endothelial dysfunction and ensuing vasculopathy are implicated in pulmonary hypertension in the hemoglobinopathies and endothelial activation and endothelial-blood cell adhesion, accompanied by inflammatory processes and oxidative stress, are imperative to the vaso-occlusive process in SCD. Herein, we discuss the role that the endothelium plays in all of these processes and the effect that genetic modifiers and hydroxyurea therapy may have upon endothelial interactions. Therapies targeting the endothelium and endothelial interactions may represent a promising approach for treating these diseases.

IL-4 is proangiogenic in the lung under hypoxic conditions

IL-4-mediated proangiogenic and proinflammatory vascular responses have been implicated in the pathogenesis of chronic lung diseases such as asthma. Although it is well known that hypoxia induces pulmonary angiogenesis and vascular alterations, the underlying mechanism of IL-4 on the pulmonary vasculature under hypoxic conditions remains unknown. In this context, we designed the present study to determine the functional importance of IL-4 for pulmonary angiogenesis under hypoxic conditions using IL-4 knockout (KO) animals. Our results show that hypoxia significantly increased IL-4R alpha expression in wild-type (WT) control lungs. Even though hypoxia significantly up-regulated vascular endothelial growth factor (VEGF) receptor expression in the lungs of both genotypes, hypoxia-induced VEGF, VCAM-1, HIF-1alpha, and ERK phosphorylation were significantly diminished in IL-4 KO lungs as compared with WT control lungs. In addition, hypoxia-induced pulmonary angiogenesis and proliferating activities in the airway and pulmonary artery were significantly suppressed in IL-4 KO lungs as compared with WT control lungs. We also isolated primary lung fibroblasts from these genotypes and stimulated these cells with hypoxia. Hypoxia-induced VEGF production was significantly suppressed in lung fibroblasts from IL-4 KO mice. These in vitro results are in accordance with the in vivo data. Furthermore, we observed a significant increase of hypoxia-induced pulmonary angiogenesis in STAT6 KO mice similar to that in WT controls. In conclusion, IL-4 has proangiogenic properties in the lung under hypoxic conditions via the VEGF pathway, and this is independent of the STAT6 pathway.

Sustained hypoxia promotes the development of a pulmonary artery-specific chronic inflammatory microenvironment

Recent studies demonstrate that sustained hypoxia induces the robust accumulation of leukocytes and mesenchymal progenitor cells in pulmonary arteries (PAs). Since the factors orchestrating hypoxia-induced vascular inflammation are not well-defined, the goal of this study was to identify mediators potentially responsible for recruitment to and retention and differentiation of circulating cells within the hypoxic PA. We analyzed mRNA expression of 44 different chemokine/chemokine receptor, cytokine, adhesion, and growth and differentiation genes in PAs obtained via laser capture microdissection in adjacent lung parenchyma and in systemic arteries by RT-PCR at several time points of hypoxic exposure (1, 7, and 28 days) in Wistar-Kyoto rats. Analysis of inflammatory cell accumulation and protein expression of selected genes was concomitantly assessed by immunochemistry. We found that hypoxia induced progressive accumulation of monocytes and dendritic cells in the vessel wall with few T cells and no B cells or neutrophils. Upregulation of stromal cell-derived factor-1 (SDF-1), VEGF, growth-related oncogene protein-alpha (GRO-alpha), C5, ICAM-1, osteopontin (OPN), and transforming growth factor-beta (TGF-beta) preceded mononuclear cell influx. With time, a more complex pattern of gene expression developed with persistent upregulation of adhesion molecules (ICAM-1, VCAM-1, and OPN) and monocyte/fibrocyte growth and differentiation factors (TGF-beta, endothelin-1, and 5-lipoxygenase). On return to normoxia, expression of many genes (including SDF-1, monocyte chemoattractant protein-1, C5, ICAM-1, and TGF-beta) rapidly returned to control levels, changes that preceded the disappearance of monocytes and reversal of vascular remodeling. In conclusion, sustained hypoxia leads to the development of a complex, PA-specific, proinflammatory microenvironment capable of promoting recruitment, retention, and differentiation of circulating monocytic cell populations that contribute to vascular remodeling.

Newer aspects of the pathophysiology of sickle cell disease vaso-occlusion

Sickle cell disease is an inherited disorder of hemoglobin (Hb) synthesis, caused by a single nucleotide substitution (GTG>GAG) at the sixth codon of the beta-globin gene, leading to the production of a defective form of Hb, Hb S. When deoxygenated, Hb S polymerizes, damaging the sickle erythrocyte and it is this polymerization that is the primary indispensable event in the molecular pathogenesis of sickle cell disease. Hb S polymerization results in a series of cellular alterations in red cell morphology and function that shorten the red cell life span and leads to vascular occlusion. Sickle cell disease vaso-occlusion is now known to constitute a complex multifactorial process characterized by recurrent vaso-occlusion, ischemia-reperfusion injury, and oxidative stress with consequent vascular endothelial cell activation that induces a chronic inflammatory state in sickle cell disease individual and is propagated by elevated levels of circulating inflammatory cytokines. Activation of the endothelium results in the induction of endothelial adhesion molecule expression that mediates red and white cell adhesion to the vessel wall and the formation of heterocellular aggregates, followed by secondary red cell trapping, all of which contribute to reduced blood flow and eventually obstruction of the micro-circulation. Reduced nitric oxide bioavailability, caused principally by its consumption by cell-free Hb, liberated during intravascular hemolysis, contributes to this process by facilitating vasoconstriction and adhesion molecule activity.

Role of stem cell factor and bone marrow-derived fibroblasts in airway remodeling

Recent evidence suggests that bone marrow-derived fibroblasts are involved in airway remodeling in asthma, but the role and mechanism of recruitment of these fibroblasts remains unclear. Stem cell factor (SCF), a key factor in the propagation of hematopoietic stem cells, is important in the process of airway remodeling as well. To test the hypothesis that SCF is involved in the recruitment and differentiation of bone marrow-derived progenitor cells, GFP-bone marrow chimeric mice were created. These mice were then sensitized and chronically challenged with cockroach antigen to induce chronic airway disease. Fluorescence microscopy revealed an influx of significant numbers of GFP-expressing fibroblasts in the airways of these mice, which was confirmed by flow cytometric analysis of cells co-expressing both GFP and collagen I. These cells preferentially expressed c-kit, interleukin-31 receptor, and telomerase reverse transcriptase when compared with control lung-derived fibroblasts. Interestingly, SCF stimulated interleukin-31 receptor expression in bone marrow cells, whereas interleukin-31 strongly induced telomerase reverse transcriptase expression in fibroblasts. Treatment with neutralizing antibodies to SCF significantly reduced airway remodeling and suppressed the recruitment of these bone marrow-derived cells to the lung. Thus SCF in conjunction with interleukin-31 may play a significant role in airway remodeling by promoting the recruitment of bone marrow-derived fibroblast precursors into the lung with the capacity to promote lung myofibroblast differentiation.

Pathobiology of pulmonary hypertension

A variety of conditions can lead to the development of pulmonary arterial hypertension (PAH). Current treatments can improve symptoms and reduce the severity of the hemodynamic abnormality, but most patients remain quite limited, and deterioration in their condition necessitates a lung transplant. This review discusses current experimental and clinical studies that investigate the pathobiology of PAH. An emerging theme is the consideration of ways in which one might reverse the advanced occlusive structural changes in the pulmonary circulation causing PAH. The current debate concerning the role of regeneration through stem cells is presented. This review also highlights investigations in a number of laboratories relating the pathobiology of PAH to mutations causing loss of function of bone morphogenetic protein receptor II in patients with familial PAH, as well as sporadic cases.

Using laboratory measurements to predict in-flight desaturation in respiratory patients: are current guidelines appropriate?

In an attempt to guide physicians asked by respiratory patients for advice on flight fitness, the British Thoracic Society (BTS) have published guidelines on fitness to fly. The main potential hazard is hypobaric hypoxia, and efforts have focused on the prediction of hypoxia in individuals. The present study examines 10 years' experience of hypoxic challenge (HC) of respiratory patients to evaluate if the guidelines recommended by the BTS are appropriate. One hundred and eighteen patients (67 female, mean age 65.6+/-11.4 (SD) years) were referred for assessment. Patients underwent HC using a 40% Venturi mask supplied with 100% N(2) which lowered the F(i)O(2) to 15.1%. A further 13 patients on long-term oxygen therapy also underwent HC whilst receiving supplemental oxygen. In agreement with the BTS guidelines, all patients with a sea level SpO(2) of over 95% maintained their SpO(2) > or = 90% during HC. One third of patients with sea level SpO(2) of 92-95%, but no other risk factor (as defined by the guidelines) also desaturated below 90% during HC. Thirty-two patients were assessed as fit to fly with supplemental oxygen. Our results support the BTS guidelines for patients with a sea level SpO(2) > 95% but suggest that some revision is required for patients with a sea level SpO(2) of 92-95%. It was not possible to predict from either initial SpO(2) or spirometry which individuals were at risk of desaturation below 90% during hypoxic challenge.

Role of hypoxia in inflammatory upper airway disease

PURPOSE OF REVIEW

Hypoxia is a potent stimulus for inflammation and remodeling. Hypoxia develops in chronic sinusitis as shown via tissue oxygen concentrations and colonization with obligate anaerobes. This hypoxia reflects occlusion of the sinus ostia and thereby failure of transepithelial oxygenation, nonvascularized exudates, and the tendency of inflammatory hyperplasia to exceed neovascularization.

RECENT FINDINGS

Hypoxia-induced transcription factors are responsible for transcription of numerous inflammatory cytokines and growth factors, including vascular endothelial growth factor, CXCL8, CCL11, transforming growth factor-beta, inducible nitric oxide synthase, as well as matrix remodeling proteins such as procollagen and matrix metalloproteinases.

SUMMARY

Many diseases, such as asthma, share the tendency to afflict respiratory epithelium of the lower (bronchi) and upper (sinus) airway. Although the histopathology and inflammation of asthma and its associated sinusitis share many features, aggressive fibrosis, polyp formation and intense hyperplasia are not features of asthma, a disease seldom associated with significant chronic hypoxia. In contrast, fibrosis is a cardinal feature of hypoxic diseases of the lungs such as interstitial lung diseases and primary pulmonary hypertension. Arguably, chronic sinusitis can be viewed as reflecting both 'asthma' and 'primary pulmonary hypertension' of the upper airway.

Immunolocalization of VEGF, VEGFR-1 and VEGFR-2 in lung tissues after acute hemorrhage in rats

In treatment of hypovolemia it is important to reestablish normal tissue hemodynamics after fluid resuscitation. Vascular endothelial growth factor (VEGF) and VEGF receptors (VEGFR) have been identified as important in many physiological and pathological processes. In this study, we aimed to investigate the histo-physiological effects of VEGF, VEGFR-1 (flt-1) and VEGFR-2 (KDR/flk-1) in resuscitation with different plasma substitutes on lung tissues after acute hemorrhage in rats. Male Sprague-Dawley rats (n=25) were used in this study. The left femoral vein and artery were cannulated for the administration of volume expanders and for direct measurement of mean arterial blood pressure (MAP) (Power-Lab) and heart rate (HR). Fifteen rats were bled (5 ml/10 min) and infused (5 ml/5 min) with one of three randomly selected fluids: (a) dextran-70 (Macrodex); (b) gelatin (Gelofusine); or (c) physiological saline (PS, 0.9% isotonic saline) solutions. Five rats were bled and none were infused (hypovolemia group) and five rats were untreated as the control group. At the end of the experiment, rats were sacrificed and lung tissues were removed for routine processing and paraffin wax embedding. Sections of tissue were stained with hematoxylin and eosin (H&E) and selected blocks were then prepared for indirect immunohistochemical labeling for anti-VEGF, anti-VEGFR-1 and anti-VEGFR-2 primary antibodies. It was observed that both MAP and HR decreased parallel to blood withdrawn in this time interval. The MAP and HR were restored in the following periods. In the control rats, positive immunoreactivity of VEGF and its receptors (VEGFR-1 and VEGFR-2) were detected in respiratory epithelial cells, respiratory and vascular smooth muscle cells, alveolar cells and endothelial cells. While strong immunoreactivities of VEGF and VEGFR-1 were observed in the hypovolemia group, only moderate immunoreactivity of VEGFR-2 was seen in this group. Moderately strong immunolabeling of VEGF and VEGFR-1 were observed in the dextran-70, gelatin and PS resuscitated groups, whereas only weak immunolabeling of VEGFR-2 was observed in these groups. In summary, the vascular protecting effects of these factors were observed with fluid resuscitation, contributing to the pathophysiological changes seen in hypovolemia.

Reactivation of γHV68 induces neointimal lesions in pulmonary arteries of S100A4/Mts1-overexpressing mice in association with degradation of elastin

S100A4/Mts-overexpressing mice have thick elastic laminae and mild pulmonary arterial hypertension (PAH), and the occasional older mouse develops occlusive neointimal lesions and perivascular inflammation. We hypothesized that a vasculotropic virus could induce neointimal lesions in the S100A4/Mts1 mouse by facilitating breakdown of elastin and migration and proliferation of smooth muscle cells. To test this hypothesis, we infected S100A4/Mts1 mice with gammaherpesvirus 68 (γHV68). We observed, 6 mo after γHV68 [4 × 103 plaque-forming units (PFU)], perivascular inflammation in 10/15 S100A4/Mts1 mice and occlusive neointimal formation in 3/10 mice, accompanied by striking degradation of elastin. We then compared the early response after high-dose γHV68 (4 × 106 PFU) in C57Bl/6 and S100A4/Mts1 mice. In S100A4/Mts1 mice only, significant PAH, muscularization of distal vessels, and elastase activity were observed 6 wk after γHV68. These features resolved by 3 mo without neointimal formation. We therefore infected mice with the M1-γHV68 strain that reactivates from latency with higher efficiency and observed neointimal lesions at 3 mo in 2/5 C57Bl/6 (5–9% of vessels) and in 5/5 S100A4/Mts1 mice (13–40% of vessels) accompanied by mild PAH, heightened lung elastase activity, and intravascular viral expression. This suggested that enhanced generation of elastin peptides in S100A4/Mts1 mice may promote increased viral entry in the vessel wall. Using S100A4/Mts1 PA organ culture, we showed, in response to elastase activity, heightened production of elastin peptides associated with invasion of inflammatory cells and intravascular viral antigen. We therefore propose that early viral access to the vessel wall may be a critical determinant of the extent of vascular pathology following reactivation.

Therapeutic potential of stem cells in lung disease: progress and pitfalls

There has been increasing excitement over the last few years with the suggestion that exogenous stem cells may offer new treatment options for a wide range of diseases. Within respiratory medicine, these cells have been shown to have the ability to differentiate and function as both airway and lung parenchyma epithelial cells in both in vitro and increasingly in vivo experiments. The hypothesis is that these cells may actively seek out damaged tissue to assist in the local repair, and the hope is that their use will open up new cellular and genetic treatment modalities. Such is the promise of these cells that they are being rushed from the benchside to the bedside with the commencement of early clinical trials. However, important questions over their use remain and the field is presently littered with controversy and uncertainty. This review evaluates the progress made and the pitfalls encountered to date, and critically assesses the evidence for the use of stem cells in lung disease.

Predicting Risk of Radiation-Induced Lung Injury

Radiation-induced lung injury (RILI) is the most common, dose-limiting complication of thoracic radio- and radiochemotherapy. Unfortunately, predicting which patients will suffer from this complication is extremely difficult. Ideally, individual phenotype- and genotype-based risk profiles should be able to identify patients who are resistant to RILI and who could benefit from dose escalation in chemoradiotherapy. This could result in better local control and overall survival. We review the risk predictors that are currently in clinical use--dosimetric parameters of radiotherapy such as normal tissue complication probability, mean lung dose, V20 and V30--as well as biomarkers that might individualize risk profiles. These biomarkers comprise a variety of proinflammatory and profibrotic cytokines and molecules including transforming growth factor beta1 that are implicated in development and persistence of RILI. Dosimetric parameters of radiotherapy show a low negative predictive value of 60% to 80%. Depending on the studied molecule, negative predictive value of biomarkers is approximately 50%. The predictive power of biomarkers might be increased if they are coupled with radiogenomics, e.g., genotyping analysis of single nucleotide polymorphisms in transforming growth factor beta1, transforming growth factor beta1 pathway genes, and other cytokines. Genetic variability and the complexity of RILI and its underlying molecular mechanisms make identification of biological risk predictors challenging. Further investigations are needed to develop more effective risk predictors of RILI.

Role for cAMP-protein kinase A signalling in augmented neutrophil adhesion and chemotaxis in sickle cell disease

The significance of the leukocyte in sickle cell disease (SCD) pathophysiology is becoming increasingly recognised; we sought to examine whether the chemotactic properties of neutrophils of SCD individuals may be altered and, further, to better understand the signalling events that mediate altered SCD neutrophil function. Adhesion to immobilised fibronectin (FN) and chemotaxis of control and SCD neutrophils were assessed using in vitro static adhesion assays and 96-well chemotaxis chamber assays. Adhesion assays confirmed a significantly higher basal adhesion of SCD neutrophils to FN, compared with control neutrophils. Chemotaxis assays established, for the first time, that SCD neutrophils demonstrate greater spontaneous migration and, also, augmented migration in response to IL-8, when compared with control neutrophils. Co-incubation of SCD neutrophils with KT5720 (an inhibitor of PKA) abrogated increased basal SCD neutrophil adhesion, spontaneous chemotaxis and IL-8-stimulated chemotaxis. Stimulation of SCD neutrophils with IL-8 also significantly augmented SCD neutrophil adhesion to FN with a concomitant increase in cAMP levels and this increase in adhesion was abolished by KT5720. Interestingly, the adhesive properties of neutrophils from SCD individuals on hydroxyurea therapy were not significantly altered and results indicate that a reduction in intracellular cAMP may contribute to lower the adhesive properties of these cells. Data indicate that up-regulated cAMP signalling plays a significant role in the altered adhesive and migratory properties in SCD neutrophils. Such alterations may have important implications for the pathophysiology of the disease and the cAMP-PKA pathway may represent a therapeutic target for the abrogation of altered leukocyte function.

A recurrent stop-codon mutation in succinate dehydrogenase subunit B gene in normal peripheral blood and childhood T-cell acute leukemia

BACKGROUND

Somatic cytidine mutations in normal mammalian nuclear genes occur during antibody diversification in B lymphocytes and generate an isoform of apolipoprotein B in intestinal cells by RNA editing. Here, I describe that succinate dehydrogenase (SDH; mitochondrial complex II) subunit B gene (SDHB) is somatically mutated at a cytidine residue in normal peripheral blood mononuclear cells (PBMCs) and T-cell acute leukemia. Germ line mutations in the SDHB, SDHC or SDHD genes cause hereditary paraganglioma (PGL) tumors which show constitutive activation of homeostatic mechanisms induced by oxygen deprivation (hypoxia).

PRINCIPAL FINDINGS

To determine the prevalence of a mutation identified in the SDHB mRNA, 180 samples are tested. An SDHB stop-codon mutation c.136C>T (R46X) is present in a significant fraction (average = 5.8%, range = less than 1 to 30%, n = 52) of the mRNAs obtained from PBMCs. In contrast, the R46X mutation is present in the genomic DNA of PBMCs at very low levels. Examination of the PBMC cell-type subsets identifies monocytes and natural killer (NK) cells as primary sources of the mutant transcript, although lesser contributions also come from B and T lymphocytes. Transcript sequence analyses in leukemic cell lines derived from monocyte, NK, T and B cells indicate that the mutational mechanism targeting SDHB is operational in T-cell acute leukemia. Accordingly, substantial levels (more than 3%) of the mutant SDHB transcripts are detected in five of 20 primary childhood T-cell acute lymphoblastic leukemia (T-ALL) bone marrow samples, but in none of 20 B-ALL samples. In addition, distinct heterozygous SDHB missense DNA mutations are identified in Jurkat and TALL-104 cell lines which are derived from T-ALLs.

CONCLUSIONS

The identification of a recurrent, inactivating stop-codon mutation in the SDHB gene in normal blood cells suggests that SDHB is targeted by a cytidine deaminase enzyme. The SDHB mutations in normal PBMCs and leukemic T cells might play a role in cellular pre-adaptation to hypoxia.

Hypoxia stimulates inflammatory and fibrotic responses from nasal-polyp derived fibroblasts

OBJECTIVES/HYPOTHESIS

Chronic sinusitis is primarily an inflammatory disorder characterized by hyperplasia of immune cells and sinus tissue. Nasal mucosal swelling or polyps can occlude the sinus ostia, decreasing the level of oxygen available to the sinus tissue. Hypoxia in many diseases results in increased recruitment of inflammatory cells and release of cytokines. The role of hypoxia in chronic sinusitis is unknown. We hypothesized that hypoxia induces production of mediators that recruit cells into the sinus tissue and are involved in remodeling of the nasal mucosa.

METHODS

We compared data from unstimulated nasal-polyp derived fibroblasts with those cultured in hypoxic (10% O2) and anoxic (0% O2) environments. Changes in mRNA expression and protein levels of cytokines and chemokines were measured along with changes in cellular proliferation.

RESULTS

Hypoxic conditions did not change the proliferative capacity of fibroblasts, whereas anoxia led to a 40% reduction in cellular proliferation (P < .05). Hypoxia led to increases in secretion of many cytokines including vascular endothelial growth factor and CCL11. As a marker of remodeling, procollagen and fibronectin production were significantly increased under hypoxic conditions.

CONCLUSIONS

Hypoxic conditions present in the sinus tissue could increase production of proinflammatory and remodeling cytokines that contribute to the inflammation observed in sinusitis. Surgical intervention may help decrease inflammation by allowing reoxygenation of the sinus cavity and decrease the hypoxic induction of cytokines and remodeling factors.

Molecular effects of loss of BMPR2 signaling in smooth muscle in a transgenic mouse model of PAH

Idiopathic pulmonary arterial hypertension (IPAH) in human patients is associated with mutations in type 2 receptor for the bone morphogenic protein pathway (BMPR2). Mice expressing an inducible dominant negative form of BMPR2 in smooth muscle develop elevated right ventricular pressures when the transgene is activated. We hypothesized that transcriptional changes in these mice may allow insight into the early molecular events leading to IPAH. Microarray analysis was used to examine the transcriptional changes induced in whole lung by loss of normal smooth muscle cell (SMC) BMPR2 signaling in adult male or female mice (12 wk at time of death) expressing the transgene for either 1 or 8 wk. Our key results include a decrease in markers of smooth muscle differentiation, an increase in cytokines and markers of immune response, particularly in female mice, and a decrease in angiogenesis-related genes. These broad patterns of gene expression appear as early as 1 wk and are well established by 8 wk. Results were confirmed by quantitative RT-PCR to RNA from individual mice. Primary pulmonary artery SMC cultures transfected with small interfering RNA to BMPR2 also show loss of SMC markers myosin heavy chain 11 and calponin by quantitative RT-PCR and Western blot. These studies show classes of genes differentially regulated in response to loss of BMPR2 in SMC in vivo with clear relevance to the IPAH disease process, suggesting that the relevance of BMPR2 dysregulation may extend beyond proliferation.

Prostacyclin analogs inhibit fibroblast contraction of collagen gels through the cAMP-PKA pathway

Prostacyclin is an arachidonic acid metabolite that modulates vascular tone within the lung. The current study evaluated the hypothesis that prostacyclin can also modulate tissue remodeling by affecting fibroblast-mediated contraction of extracellular matrix. To accomplish this, fibroblasts were cultured in three-dimensional native type I collagen gels in the presence of prostacyclin analogs: carbaprostacyclin, iloprost, and beraprost. All three analogs significantly inhibited contraction of the three-dimensional collagen gels mediated by three different fibroblasts. All three analogs significantly inhibited fibronectin release and reduced fibroblast fibronectin mRNA expression. Addition of exogenous fibronectin restored the contractile activity to fibroblasts incubated in the presence of all three analogs. Iloprost and beraprost significantly activated cAMP-dependent protein kinase-A (PKA), and an action through this pathway was confirmed by blockade of the inhibitory effect on contraction and fibronectin release with the PKA inhibitor KT-5720. In contrast, carbaprostacyclin, which is not as selective for the prostacyclin (IP) receptor, did not activate PKA, and its effects on contraction and fibronectin release were not fully blocked by KT-5720. Finally, the cAMP analogs N(6)-Benzoyl- (6-Bnz-) cAMP and dibutyryl-cAMP inhibited contraction, and this contrasted with the activity of an Epac selective agonist 8-pCPT-2'-O-Me-cAMP, which had no effect. Taken together, these results indicate that prostacyclin, acting through the IP receptor and by activating PKA, can lead to inhibition of fibronectin release and can subsequently inhibit fibroblast-mediated collagen gel contraction. The ability of prostacyclin to modulate fibroblast function suggests that prostacyclin can contribute to tissue remodeling.

Diagnosis and management of pulmonary hypertension over the past 100 years

Pulmonary hypertension is a rare disease with a poor prognosis. It was first described in the late 19th century as a clinical-pathological syndrome characterised by obstruction of the small pulmonary arteries and right ventricular hypertrophy in patients presenting with severe dyspnoea and cyanosis. After the development of right heart catheterisation in the second half of the 20th century, it was found that many diseases could cause pulmonary hypertension, which is now recognised to be high blood pressure in the arteries that supply the lungs. In the 1960s, an epidemic of pulmonary hypertension caused by appetite suppressants initiated a systematic collection of information on pulmonary hypertension, leading to the first international classification of pulmonary hypertension. Increased understanding of the pathogenesis of the various forms of pulmonary hypertension has led to novel treatments and holds promise for the future.

Airway epithelial stem cells and the pathophysiology of chronic obstructive pulmonary disease

Characteristic pathologic changes in chronic obstructive pulmonary disease (COPD) include an increased fractional volume of bronchiolar epithelial cells, fibrous thickening of the airway wall, and luminal inflammatory mucus exudates, which are positively correlated with airflow limitation and disease severity. The mechanisms driving general epithelial expansion, mucous secretory cell hyperplasia, and mucus accumulation must relate to the effects of initial toxic exposures on patterns of epithelial stem and progenitor cell proliferation and differentiation, eventually resulting in a self-perpetuating, and difficult to reverse, cycle of injury and repair. In this review, current concepts in stem cell biology and progenitor-progeny relationships related to COPD are discussed, focusing on the factors, pathways, and mechanisms leading to mucous secretory cell hyperplasia and mucus accumulation in the airways. A better understanding of alterations in airway epithelial phenotype in COPD will provide a logical basis for novel therapeutic approaches.

Role of reactive oxygen species in chronic hypoxia-induced pulmonary hypertension and vascular remodeling

Pulmonary hypertension is a life-threatening disease process that affects adults and children. Pediatric patients with lung diseases that can be complicated by alveolar hypoxia, such as bronchopulmonary dysplasia (BPD), are at risk for developing pulmonary hypertension, which leads to right heart failure and greatly increases morbidity and mortality. We review the evidence that reactive oxygen species (ROS) are generated by pulmonary vascular wall cells in response to a hypoxic exposure, and that this response contributes to chronic hypoxic pulmonary hypertension. We summarize the accumulating data implicating NADPH oxidase as a major source of O2 responsible for vascular remodeling and hypertension. We also consider the effects of chronic hypoxia on the clearance of O2 by superoxide dismutases, specifically extracellular superoxide dismutase, which is highly expressed in the pulmonary artery. We review the role of the activated vascular adventitial fibroblast in the generation of ROS and in the pathogenesis of vascular remodeling, and provide a rationale to consider the role of the activated fibroblast and ROS in hypoxic pulmonary hypertension using a clinically relevant bovine model of neonatal chronic hypoxic pulmonary hypertension.

Impact of sex and age on bone marrow immune responses in a murine model of trauma-hemorrhage

Although studies have demonstrated that trauma markedly alters the bone marrow immune responses, sex and age are crucial determinants under such conditions and have not been extensively examined. To study this, 21- to 27-day-old (premature), 6- to 8-wk-old (mature), and 20- to 24-mo-old (aged) male and female (proestrus) C3H/HeN mice were sham operated or subjected to trauma (i.e., midline laparotomy) and hemorrhagic shock (30 ± 5 mmHg for 90 min) followed by fluid resuscitation. Twenty-four hours after resuscitation, bone marrow cells were harvested. Trauma-hemorrhage induced an increased number of the early pluripotent stem cell-associated bone marrow cell subsets (Sca1+CD34−CD117+/−lin+/−) in young mice. The CD117+proportion of these cell subsets increased in mature proestrus females, but not in males. Aged males displayed significant lower numbers of Sca1+CD34−CD117+/−lin+/−cells compared with young male mice. Trauma-hemorrhage also increased development of granulocyte/macrophage progenitor cells (CD11b+Gr-1+). Proliferative responses to granulocyte macrophage colony-stimulating factor were maintained in mature and aged proestrus females, but decreased in young mice and mature males. Augmented differentiation into monocyte/macrophage lineage in mature and aged proestrus females was observed and associated with the maintained release of TNF-α and IL-6. Conversely, increased IL-10 and PGE2production was observed in the male trauma-hemorrhage groups. Thus, sex- and age-specific effects in bone marrow differentiation and immune responses after trauma-hemorrhage occur, which are likely to contribute to the sex- and age-related differences in the systemic immune responses under such conditions.

Role of the adventitia in pulmonary vascular remodeling

An increasing volume of experimental data indicates that the adventitial fibroblast, in both the pulmonary and systemic circulations, is a critical regulator of vascular wall function in health and disease. A rapidly emerging concept is that the vascular adventitia acts as biological processing center for the retrieval, integration, storage, and release of key regulators of vessel wall function. In response to stress or injury, resident adventitial cells can be activated and reprogrammed to exhibit different functional and structural behaviors. In fact, under certain conditions, the adventitial compartment may be considered the principal injury-sensing tissue of the vessel wall. In response to vascular stresses such as overdistension and hypoxia, the adventitial fibroblast is activated and undergoes phenotypic changes, which include proliferation, differentiation, upregulation of contractile and extracellular matrix proteins, and release of factors that directly affect medial smooth muscle cell tone and growth and that stimulate recruitment of inflammatory and progenitor cells to the vessel wall. Each of these changes in fibroblast phenotype modulates either directly or indirectly changes in overall vascular function and structure. The purpose of this review is to present the current evidence demonstrating that the adventitial fibroblast acts as a key regulator of pulmonary vascular function and structure from the "outside-in."

Hypoxia-induced mitogenic factor has proangiogenic and proinflammatory effects in the lung via VEGF and VEGF receptor-2

From a mouse model of hypoxia-induced pulmonary hypertension, we previously found a highly upregulated protein in the lung that we named hypoxia-induced mitogenic factor (HIMF), also known as found in inflammatory zone 1 (FIZZ1), and resistin-like molecule alpha (RELMalpha). However, the mechanisms of HIMF in the pulmonary vascular remodeling remain unknown. We now demonstrate that HIMF promoted cell proliferation, migration, and the production of vascular endothelial growth factor (VEGF) and monocyte chemotactic protein-1 (MCP-1) in pulmonary endothelial cells as well as the production of reactive oxygen species in murine monocyte/macrophage cells. HIMF-induced CD31-positive cell infiltrate in in vivo Matrigel plugs was significantly suppressed by VEGF receptor-2 (VEGFR2) blockade. In ex vivo studies, HIMF stimulated the production of VEGF, MCP-1, and stromal cell-derived factor-1 (SDF-1) in the lung resident cells, and VEGFR2 neutralization significantly suppressed HIMF-induced MCP-1 and SDF-1 production. Furthermore, intravenous injection of HIMF showed marked increase of CD68-positive inflammatory cells in the lungs, and these events were attenuated by VEGFR2 neutralization. Intravenous injection of HIMF also downregulated the expression of VEGFR2 in the lung. These results suggest that HIMF plays critical roles in pulmonary inflammation as well as angiogenesis.

Microvascular Regeneration in Established Pulmonary Hypertension by Angiogenic Gene Transfer

Pulmonary arterial hypertension (PAH) is characterized by widespread loss of pulmonary microvasculature. Therefore we hypothesized that angiogenic gene therapy would reverse established PAH, in part restoring the lung microcirculation. Three weeks after monocrotaline (MCT) treatment, Fisher 344 rats were randomized to receive a total of either 1.5 x 10(6) syngeneic fibroblasts (FB) transfected with vascular endothelial growth factor A (VEGF), endothelial NO synthase (eNOS), or null-plasmid transfected FBs. Right ventricular systolic pressure (RVSP) was similarly increased in all MCT-treated groups at the time of gene transfer. Animals receiving the null-vector progressed to severe PAH by Day 35 (P < 0.001). In contrast, eNOS gene transfer significantly reduced RVSP at Day 35 compared with Day 21, whereas VEGF prevented further increases in RVSP over the subsequent 2 wk but did not reverse established PAH. RV hypertrophy was significantly reduced in both the eNOS-treated and VEGF-treated groups compared with the null-transfected controls. Fluorescent microangiography revealed widespread occlusion of the pre-capillary arterioles 21 d after MCT treatment, and animals receiving eNOS gene transfer exhibited the greatest improvement in the arteriolar architecture and capillary perfusion at Day 35. Cell-based eNOS gene transfer was more effective than VEGF in reversing established PAH, associated with evidence of regeneration of pulmonary microcirculation.

p38 MAP kinase isoform activity and cell cycle regulators in the proliferative response of pulmonary and systemic artery fibroblasts to acute hypoxia

Many cardiopulmonary diseases are associated with pulmonary hypertension which adds significant co-morbidity. Pulmonary hypertension is due partly to vasoconstriction but sustained by pulmonary vascular remodelling. If pathological endpoints are to be reversed in patients with pulmonary hypertension, the processes by which vascular remodelling occur need to be determined. Hypoxia provides a good model of pulmonary hypertension. We have previously shown that chronic hypoxia results in increased proliferation of pulmonary artery fibroblasts and stimulation of the mitogen-activated protein kinase (MAPK) family of signalling enzymes. Under the same conditions systemic artery fibroblasts were unaffected. This differential response of pulmonary fibroblasts to hypoxia represents a model to investigate the processes of pulmonary artery remodelling. The current study showed that acute hypoxia was capable of causing enhanced proliferation in pulmonary but not systemic artery fibroblasts and was linked to increased activation of p38 MAP kinase. Second, we have now shown that it is alpha and gamma isoforms of p38 MAP kinase, which are responsible. Third we have shown a link between stimulation of p38 MAP kinase and HIF-1 proportional, variant induction. An increased understanding of the effects of hypoxia on remodelling and proliferation represents a critical step in identifying targets for the treatment of pulmonary hypertension.