Insulin-like growth factor I and pulmonary hypertension induced by continuous air embolization in sheep

Dynamic Regulation of GH-IGF1 Signaling in Injury and Recovery in Hyperoxia-Induced Neonatal Lung Injury

Prematurely born infants often require supplemental oxygen that impairs lung growth and results in arrest of alveolarization and bronchopulmonary dysplasia (BPD). The growth hormone (GH)- and insulin-like growth factor (IGF)1 systems regulate cell homeostasis and organ development. Since IGF1 is decreased in preterm infants, we investigated the GH- and IGF1 signaling (1) in newborn mice with acute and prolonged exposure to hyperoxia as well as after recovery in room air; and (2) in cultured murine lung epithelial cells (MLE-12) and primary neonatal lung fibroblasts (pLFs) after treatment with GH, IGF1, and IGF1-receptor (IGF1-R) inhibitor or silencing of GH-receptor (Ghr) and Igf1r using the siRNA technique. We found that (1) early postnatal hyperoxia caused an arrest of alveolarization that persisted until adulthood. Both short-term and prolonged hyperoxia reduced GH-receptor expression and STAT5 signaling, whereas Igf1 mRNA and pAKT signaling were increased. These findings were related to a loss of epithelial cell markers (SFTPC, AQP5) and proliferation of myofibroblasts (αSMA+ cells). After recovery, GH-R-expression and STAT5 signaling were activated, Igf1r mRNA reduced, and SFTPC protein significantly increased. Cell culture studies showed that IGF1 induced expression of mesenchymal (e.g., Col1a1, Col4a4) and alveolar epithelial cell type I (Hopx, Igfbp2) markers, whereas inhibition of IGF1 increased SFTPC and reduced AQP5 in MLE-12. GH increased Il6 mRNA and reduced proliferation of pLFs, whereas IGF1 exhibited the opposite effect. In summary, our data demonstrate an opposite regulation of GH- and IGF1- signaling during short-term/prolonged hyperoxia-induced lung injury and recovery, affecting alveolar epithelial cell differentiation, inflammatory activation of fibroblasts, and a possible uncoupling of the GH-IGF1 axis in lungs after hyperoxia.

rhIGF-1/BP3 Preserves Lung Growth and Prevents Pulmonary Hypertension in Experimental Bronchopulmonary Dysplasia

Rationale: Antenatal factors, such as chorioamnionitis, preeclampsia, and postnatal injury, are associated with an increased risk for bronchopulmonary dysplasia (BPD) and pulmonary hypertension (PH) after preterm birth. IGF-1 (insulin-like growth factor-1) is markedly decreased in normal preterm infants, but whether IGF-1 treatment can prevent BPD or PH is unknown.Objectives: To evaluate whether postnatal treatment with rhIGF-1 (recombinant human IGF-1)/BP3 (binding peptide 3) improves lung growth and prevents PH in two antenatal models of BPD induced by intraamniotic exposure to endotoxin (ETX) or sFlt-1 (soluble fms-like tyrosine kinase 1), and in a postnatal model due to prolonged hyperoxia.Methods: ETX or sFlt-1 were administered into the amniotic sac of pregnant rats at Embryonic Day 20 to simulate antenatal models of chorioamnionitis and preeclampsia, respectively. Pups were delivered by cesarean section at Embryonic Day 22 and treated with rhIGF-1/BP3 (0.02-20 mg/kg/d intraperitoneal) or buffer for 2 weeks. Study endpoints included radial alveolar counts (RACs), vessel density, and right ventricular hypertrophy (RVH). Direct effects of rhIGF-1/BP3 (250 ng/ml) on fetal lung endothelial cell proliferation and tube formation and alveolar type 2 cell proliferation were studied by standard methods in vitro.Measurements and Main Results: Antenatal ETX and antenatal sFlt-1 reduced RAC and decreased RVH in infant rats. In both models, postnatal rhIGF-1/BP3 treatment restored RAC and RVH to normal values when compared with placebo injections. rhIGF-1/BP3 treatment also preserved lung structure and prevented RVH after postnatal hyperoxia. In vitro studies showed that rhIGF-1/BP3 treatment increased lung endothelial cell and alveolar type 2 cell proliferation.Conclusions: Postnatal rhIGF-1/BP3 treatment preserved lung structure and prevented RVH in antenatal and postnatal BPD models. rhIGF-1/BP3 treatment may provide a novel strategy for the prevention of BPD in preterm infants.

MicroRNA Dysregulation in Pulmonary Arteries from Chronic Obstructive Pulmonary Disease. Relationships with Vascular Remodeling

Pulmonary vascular remodeling is an angiogenic-related process involving changes in smooth muscle cell (SMC) homeostasis, which is frequently observed in chronic obstructive pulmonary disease (COPD). MicroRNAs (miRNAs) are small, noncoding RNAs that regulate mRNA expression levels of many genes, leading to the manifestation of cell identity and specific cellular phenotypes. Here, we evaluate the miRNA expression profiles of pulmonary arteries (PAs) of patients with COPD and its relationship with the regulation of SMC phenotypic change. miRNA expression profiles from PAs of 12 patients with COPD, 9 smokers with normal lung function (SK), and 7 nonsmokers (NS) were analyzed using TaqMan Low-Density Arrays. In patients with COPD, expression levels of miR-98, miR-139-5p, miR-146b-5p, and miR-451 were upregulated, as compared with NS. In contrast, miR-197, miR-204, miR-485-3p, and miR-627 were downregulated. miRNA-197 expression correlated with both airflow obstruction and PA intimal enlargement. In an in vitro model of SMC differentiation, miR-197 expression was associated with an SMC contractile phenotype. miR-197 inhibition blocked the acquisition of contractile markers in SMCs and promoted a proliferative/migratory phenotype measured by both cell cycle analysis and wound-healing assay. Using luciferase assays, Western blot, and quantitative PCR, we confirmed that miR-197 targets the transcription factor E2F1. In PAs from patients with COPD, levels of E2F1 were increased as compared with NS. In PAs of patients with COPD, remodeling of the vessel wall is associated with downregulation of miR-197, which regulates SMC phenotype. The effect of miR-197 on PAs might be mediated, at least in part, by the key proproliferative factor, E2F1.

Identifying Involvement of H19-miR-675-3p-IGF1R and H19-miR-200a-PDCD4 in Treating Pulmonary Hypertension with Melatonin

Non-coding RNAs play an important role in the pathogenesis of pulmonary arterial hypertension (PAH). The aim of this study was to characterize the therapeutic role of melatonin as well as the underlying molecular mechanism (its effects on the expression of H19 and its downstream signaling pathways) in the treatment of PAH. Real-time PCR and western blot analysis were performed to evaluate the expression of H19, miR-200a, miR-675, insulin-like growth factor-1 receptor (IGF1R), and programmed cell death 4 (PDCD4). The value of systolic pulmonary artery pressure (SPAP) and the ratio of medial thickening in the monocrotaline (MCT) group were increased, whereas the melatonin treatment could decrease these values to some extent. The weights of RV (right ventricle), LV (left ventricle) + IVS (interventricular septal), and RV/(LV + IVS) in the MCT group were much higher than those in the MCT + melatonin and control groups. In addition, the expression of H19, miR-675, IGF1R mRNA, and IGF1R protein in the MCT group was the highest, whereas their expression in the control group was the lowest. The expression of miR-200, PDCD4 mRNA, and PDCD4 protein in the MCT group was the lowest, whereas their expression in the control group was the highest. Furthermore, H19 directly suppressed the expression of miR-200a, whereas miR-675-3p and miR-200a directly inhibited the expression of IGF1R and PDCD4, respectively. Finally, melatonin treatment inhibited cell proliferation; upregulated the expression of H19, miR-675-3p, and PDCD4; and downregulated the expression of miR-200a and IGF1R. This study demonstrated the role of H19-miR-675-3p-IGF1R- and H19-miR-200a-PDCD4-signaling pathways in the melatonin treatment of PAH.

The Role of Nicotinamide Adenine Dinucleotide Phosphate Oxidases in Lung Architecture Remodeling

Chronic lung disorders, such as pulmonary artery hypertension (PAH), chronic obstructive pulmonary disease (COPD), asthma and neonatal bronchopulmonary dysplasia (BPD), are characterized by airway and/or vascular remodeling. Despite differences in the pathology, reactive oxygen species (ROS) have been highlighted as a critical contributor to the initiation and development of airway and vascular remodeling. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (Nox) appear to play a pivotal role in lung signaling, leading to marked changes in pulmonary airway and vascular cell phenotypes, including proliferation, hypertrophy and apoptosis. In this review, we summarized the current literature regarding the role of Nox in the airway and vascular remodeling.

Smooth Muscle Insulin-Like Growth Factor-1 Mediates Hypoxia-Induced Pulmonary Hypertension in Neonatal Mice

Insulin-like growth factor (IGF)-1 is a potent mitogen of vascular smooth muscle cells (SMCs), but its role in pulmonary vascular remodeling associated with pulmonary hypertension (PH) is not clear. In an earlier study, we implicated IGF-1 in the pathogenesis of hypoxia-induced PH in neonatal mice. In this study, we hypothesized that hypoxia-induced up-regulation of IGF-1 in vascular smooth muscle is directly responsible for pulmonary vascular remodeling and PH. We studied neonatal and adult mice with smooth muscle-specific deletion of IGF-1 and also used an inhibitor of IGF-1 receptor (IGF-1R), OSI-906, in neonatal mice. We found that, in neonatal mice, SMC-specific deletion of IGF-1 or IGF-1R inhibition with OSI-906 attenuated hypoxia-induced pulmonary vascular remodeling in small arteries, right ventricular hypertrophy, and right ventricular systolic pressure. Pulmonary arterial SMCs from IGF-1-deleted mice or after OSI-906 treatment exhibited reduced proliferative potential. However, in adult mice, smooth muscle-specific deletion of IGF-1 had no effect on hypoxia-induced PH. Our data suggest that vascular smooth muscle-derived IGF-1 plays a critical role in hypoxia-induced PH in neonatal mice but not in adult mice. We speculate that the IGF-1/IGF-1R axis is important in pathogenesis of PH in the developing lung and may be amenable to therapeutic manipulation in this age group.

Expression profile of mitochondrial voltage-dependent anion channel-1 (VDAC1) influenced genes is associated with pulmonary hypertension

Several human diseases have been associated with mitochondrial voltage-dependent anion channel-1 (VDAC1) due to its role in calcium ion transportation and apoptosis. Recent studies suggest that VDAC1 may interact with endothelium-dependent nitric oxide synthase (eNOS). Decreased VDAC1 expression may limit the physical interaction between VDAC1 and eNOS and thus impair nitric oxide production, leading to cardiovascular diseases, including pulmonary arterial hypertension (PAH). In this report, we conducted meta-analysis of genome-wide expression data to identify VDAC1 influenced genes implicated in PAH pathobiology. First, we identified the genes differentially expressed between wild-type and Vdac1 knockout mouse embryonic fibroblasts in hypoxic conditions. These genes were deemed to be influenced by VDAC1 deficiency. Gene ontology analysis indicates that the VDAC1 influenced genes are significantly associated with PAH pathobiology. Second, a molecular signature derived from the VDAC1 influenced genes was developed. We suggest that, VDAC1 has a protective role in PAH and the gene expression signature of VDAC1 influenced genes can be used to i) predict severity of pulmonary hypertension secondary to pulmonary diseases, ii) differentiate idiopathic pulmonary artery hypertension (IPAH) patients from controls, and iii) differentiate IPAH from connective tissue disease associated PAH.

Reactive oxygen species in pulmonary vascular remodeling

The pathogenesis of pulmonary hypertension is a complex multifactorial process that involves the remodeling of pulmonary arteries. This remodeling process encompasses concentric medial thickening of small arterioles, neomuscularization of previously nonmuscular capillary-like vessels, and structural wall changes in larger pulmonary arteries. The pulmonary arterial muscularization is characterized by vascular smooth muscle cell hyperplasia and hypertrophy. In addition, in uncontrolled pulmonary hypertension, the clonal expansion of apoptosis-resistant endothelial cells leads to the formation of plexiform lesions. Based upon a large number of studies in animal models, the three major stimuli that drive the vascular remodeling process are inflammation, shear stress, and hypoxia. Although, the precise mechanisms by which these stimuli impair pulmonary vascular function and structure are unknown, reactive oxygen species (ROS)-mediated oxidative damage appears to play an important role. ROS are highly reactive due to their unpaired valence shell electron. Oxidative damage occurs when the production of ROS exceeds the quenching capacity of the antioxidant mechanisms of the cell. ROS can be produced from complexes in the cell membrane (nicotinamide adenine dinucleotide phosphate-oxidase), cellular organelles (peroxisomes and mitochondria), and in the cytoplasm (xanthine oxidase). Furthermore, low levels of tetrahydrobiopterin (BH4) and L-arginine the rate limiting cofactor and substrate for endothelial nitric oxide synthase (eNOS), can cause the uncoupling of eNOS, resulting in decreased NO production and increased ROS production. This review will focus on the ROS generation systems, scavenger antioxidants, and oxidative stress associated alterations in vascular remodeling in pulmonary hypertension.

Simulation of Eisenmenger syndrome with ventricular septal defect using equivalent electronic system

BACKGROUND

In this study, we aim to investigate the simulation of the cardiovascular system using an electronic circuit model under normal and pathological conditions, especially the Eisenmenger syndrome.

METHODS AND RESULTS

The Eisenmenger syndrome includes a congenital communication between the systemic and pulmonary circulation, with resultant pulmonary arterial hypertension and right-to-left reversal of flow through the defect. When pulmonary vascular resistance exceeds systemic vascular resistance, it results in hypoxaemia and cyanosis. The Westkessel model including Resistor-Inductance-Capacitance pi-segments was chosen in order to simulate both systemic and pulmonary circulation. The left and right heart are represented by trapezoidal shape stiffness for better simulation results. The Eisenmenger syndrome is simulated using a resistance (septal resistance) connected between the left ventricle and right ventricle points of the model. Matlab® is used for the model implementation. In this model, although there is a remarkable increase in the pulmonary artery pressure and right ventricle pressure, left ventricle pressure, aortic pressure, aortic flow, and pulmonary compliance decrease in the Eisenmenger syndrome. In addition, left-to-right septal flow reversed in these diseases.

CONCLUSION

Our model is effective and available for simulating normal cardiac conditions and cardiovascular diseases, especially the Eisenmenger syndrome.

Reduction of reactive oxygen species prevents hypoxia-induced CREB depletion in pulmonary artery smooth muscle cells

Hypoxia-induced pulmonary arterial hypertension (PAH) is a deadly disease characterized by progressive remodeling and persistent vasoconstriction of the pulmonary arterial system. Remodeling of the pulmonary artery (PA) involves smooth muscle cell (SMC) proliferation, hypertrophy, migration, and elevated extracellular matrix (ECM) production elicited by mitogens and oxidants produced in response to hypoxic insult. We previously reported that the transcription factor cAMP response element binding protein (CREB) is depleted in medial PA SMCs in remodeled, hypertensive vessels in rats or calves exposed to chronic hypoxia. In culture, CREB loss can be induced in PA SMCs by exogenous oxidants or platelet-derived growth factor. Forced depletion of CREB with small interfering RNA (siRNA) in PA SMCs is sufficient to induce their proliferation, hypertrophy, migration, dedifferentiation, and ECM production. This suggests that oxidant and/or mitogen-induced loss of CREB in medial SMCs is, in part, responsible for PA thickening. Here, we tested whether oxidant scavengers could prevent the loss of CREB in PA SMCs and inhibit SMC proliferation, migration, and ECM production using in vitro and in vivo models. Exposure of PA SMCs to hypoxia induced hydrogen peroxide (H2O2) production and loss of CREB. Treatment of SMCs with exogenous H2O2 or a second oxidant, Sin-1, elicited CREB depletion under normoxic conditions. Exogenous H2O2 also induced SMC proliferation, migration, and increased elastin levels as did forced depletion of CREB. In vivo, hypoxia-induced thickening of the PA wall was suppressed by the superoxide dismutase mimetic, Tempol, which also prevented the loss of CREB in medial SMCs. Tempol also reduced hypoxia-induced SMC proliferation and elastin deposition in the PA. The data indicate that CREB levels in the arterial wall are regulated in part by oxidants produced in response to hypoxia and that CREB plays a crucial role in regulating SMC phenotype and PA remodeling.

Platelet-derived growth factor BB induces nuclear export and proteasomal degradation of CREB via phosphatidylinositol 3-kinase/Akt signaling in pulmonary artery smooth muscle cells

Cyclic AMP response element binding protein (CREB) content is diminished in smooth muscle cells (SMCs) in remodeled pulmonary arteries from animals with pulmonary hypertension and in the SMC layers of atherogenic systemic arteries and cardiomyocytes from hypertensive individuals. Loss of CREB can be induced in cultured SMCs by chronic exposure to hypoxia or platelet-derived growth factor BB (PDGF-BB). Here we investigated the signaling pathways and mechanisms by which PDGF elicits depletion of SMC CREB. Chronic PDGF treatment increased CREB ubiquitination in SMCs, while treatment of SMCs with the proteasome inhibitor lactacystin prevented decreases in CREB content. The nuclear export inhibitor leptomycin B also prevented depletion of SMC CREB alone or in combination with lactacystin. Subsequent studies showed that PDGF activated extracellular signal-regulated kinase, Jun N-terminal protein kinase, and phosphatidylinositol 3 (PI3)-kinase pathways in SMCs. Inhibition of these pathways blocked SMC proliferation in response to PDGF, but only inhibition of PI3-kinase or its effector, Akt, blocked PDGF-induced CREB loss. Finally, chimeric proteins containing enhanced cyan fluorescent protein linked to wild-type CREB or CREB molecules with mutations in several recognized phosphorylation sites were introduced into SMCs. PDGF treatment reduced the levels of each of these chimeric proteins except for one containing mutations in adjacent serine residues (serines 103 and 107), suggesting that CREB loss was dependent on CREB phosphorylation at these sites. We conclude that PDGF stimulates nuclear export and proteasomal degradation of CREB in SMCs via PI3-kinase/Akt signaling. These results indicate that in addition to direct phosphorylation, proteolysis and intracellular localization are key mechanisms regulating CREB content and activity in SMCs.

Eisenmenger syndrome: medical prevention and management strategies

The original definition of Eisenmenger syndrome refers to an unrestrictive post-tricuspid valve congenital systemic-to-pulmonary shunt. When the pulmonary arterial systolic pressure becomes equal to the systemic arterial systolic pressure, the direction of the shunt becomes pulmonary-to-systemic. The latter leads to progressive cyanosis, and exercise intolerance is initially proportional to the degree of hypoxaemia. Later, congestive heart failure may occur . The management principle is to avoid any factors that destabilise this delicately balanced physiology. Until recently, this could only be achieved by symptomatic therapy; however, when patients are severely incapacitated, transplantation is needed. At present, new drugs, which are more selective pulmonary vasodilators, are available to interfere with the ongoing disease process to improve functional capacity and delay the decision for transplantation.

Impact of HIF‐1α and HIF‐2α on proliferation and migration of human pulmonary artery fibroblasts in hypoxia

Proliferation of adventitial fibroblasts of small intrapulmonary arteries (FBPA) has been disclosed as an early event in the development of pulmonary hypertension and cor pulmonale in response to hypoxia. We investigated the role of hypoxia-inducible transcription factors (HIF) in human FBPA exposed to hypoxia. Primary cultures of FBPA displayed a strong mitogenic response to 24 h hypoxia, whereas the rate of apoptosis was significantly suppressed. In addition, the migration of FBPA was strongly increased under hypoxic conditions but not the expression of alpha-smooth muscle actin. Hypoxia induced a marked up-regulation (protein level) of both HIF-1alpha and HIF-2alpha, alongside with nuclear translocation of these transcription factors. Specific inhibition of either HIF-1alpha or HIF-2alpha was achieved by RNA interference technology, as proven by HIF-1alpha and HIF-2alpha mRNA and protein analysis and expression analysis of HIF downstream target genes. With the use of this approach, the hypoxia-induced proliferative response of the FBPA was found to be solely HIF-2alpha dependent, whereas the migratory response was significantly reduced by both HIF-1alpha and HIF-2alpha interference. In conclusion, HIF up-regulation is essential for hypoxic cellular responses in human pulmonary artery adventitial fibroblasts such as proliferation and migration, mimicking the pulmonary hypertensive phenotype in vivo. Differential HIF subtype dependency was noted, with HIF-2alpha playing a predominant role, which may offer future intervention strategies.

Molecular and cellular basis of pulmonary vascular remodeling in pulmonary hypertension

Clinical pulmonary hypertension is characterized by a sustained elevation in pulmonary arterial pressure. Pulmonary vascular remodeling involves structural changes in the normal architecture of the walls of pulmonary arteries. The process of vascular remodeling can occur as a primary response to injury, or stimulus such as hypoxia, within the resistance vessels of the lung. Alternatively, the changes seen in more proximal vessels may arise secondary to a sustained increase in intravascular pressure. To withstand the chronic increase in intraluminal pressure, the vessel wall becomes thickened and stronger. This "armouring" of the vessel wall with extra-smooth muscle and extracellular matrix leads to a decrease in lumen diameter and reduced capacity for vasodilatation. This maladaptive response results in increased pulmonary vascular resistance and consequently, sustained pulmonary hypertension. The process of pulmonary vascular remodeling involves all layers of the vessel wall and is complicated by the finding that cellular heterogeneity exists within the traditional compartments of the vascular wall: intima, media, and adventitia. In addition, the developmental stage of the organism greatly modifies the response of the pulmonary circulation to injury. This review focuses on the latest advances in our knowledge of these processes as they relate to specific forms of pulmonary hypertension and particularly in the light of recent genetic studies that have identified specific pathways involved in the pathogenesis of severe pulmonary hypertension.

Hypoxic pulmonary artery fibroblasts trigger proliferation of vascular smooth muscle cells: role of hypoxia-inducible transcription factors

Chronic lung hypoxia causes vascular remodeling with pulmonary artery smooth muscle cell (SMCPA) hyperplasia, resulting in pulmonary hypertension and cor pulmonale. We investigated SMCPA and pulmonary artery adventitial fibroblasts (FBPA) for their proliferative response to hypoxia. Strong SMCPA growth occurred under hypoxic conditions in SMCPA/FBPA co-cultures, but not in SMCPA monocultures. SMCPA growth was fully reproduced by transferring serum-free supernatant from hypoxic cultured FBPA to normoxic SMCPA. Hypoxia-inducible-transcription-factor subtypes (HIF-1alpha, HIF-2alpha, HIF-3alpha) and its dependent target genes, carrying the hypoxia-responsive-element as regulatory component, were strongly activated in both hypoxic FBPA and SMCPA. HIF-transcription-factor decoy technique, employed to FBPA during hypoxic culturing, blocked the mitogenic activity of FBPA conditioned medium on SMCPA. The data suggest that hypoxia-driven gene regulation in pulmonary artery fibroblasts results in a mitogenic stimulus on adjacent pulmonary artery smooth muscle cells, and HIF-transcription-decoy may offer a new therapeutic approach to suppress these events.

Effects of insulin-like growth factor on weight gain in chronic hypoxic rats

Chronic hypoxemia has been suggested as the cause of weight loss in malnourished patients with chronic obstructive pulmonary disease. Insulin-like growth factor I (IGF-I) is believed to improve nitrogen balance and have anabolic effects, and it has been proposed as one of the mediators of vascular smooth muscle proliferation. The aim of this study was to assess the effects of IGF-I administration on the nutritional status and pulmonary vasculature in normoxic and chronic hypoxic rats. Twenty rats were randomly assigned to the normoxic (n = 10) and chronic hypoxic groups (n = 10). They received daily subcutaneous injections of either 3.2 mg/kg of recombinant human IGF-I (rhIGF-I) or isotonic saline (control group) for 3 weeks. Body weight was greater in IGF-I-treated rats compared with vehicle-treated rats, especially during the early and late stages of chronic hypoxic exposure, whereas similar weight gain was observed between IGF-I- and vehicle-treated normoxic rats. In addition, IGF-I treatment increased serum total protein and albumin at the end of hypoxic exposure. However, IGF-I had no additive effects on the degree of pulmonary hypertension. These results indicated that IGF-I promoted anabolism under chronic exposure to hypoxia, whereas no adverse effect was observed in the development of pulmonary hypertension.

Pulmonary vascular remodeling: a target for therapeutic intervention in pulmonary hypertension

Pulmonary vascular remodelling is an important pathological feature of pulmonary hypertension, leading to increased pulmonary vascular resistance and reduced compliance. It involves thickening of all three layers of the blood vessel wall (due to hypertrophy and/or hyperplasia of the predominant cell type within each layer), as well as extracellular matrix deposition. Neomuscularisation of non-muscular arteries and formation of plexiform and neointimal lesions also occur. Stimuli responsible for remodelling involve transmural pressure, stretch, shear stress, hypoxia, various mediators [angiotensin II, endothelin (ET)-1, 5-hydroxytryptamine, growth factors, and inflammatory cytokines], increased serine elastase activity, and tenascin-C. In addition, there are reductions in the endothelium-derived antimitogenic substances, nitric oxide, and prostacyclin. Intracellular signalling mechanisms involved in pulmonary vascular remodelling include elevations in intracellular Ca2+ and activation of the phosphatidylinositol pathway, protein kinase C, and mitogen-activated protein kinase. In animal models of pulmonary hypertension, various drugs have been shown to attenuate pulmonary vascular remodelling. These include angiotensin-converting enzyme inhibitors, angiotensin receptor antagonists, ET receptor antagonists, ET-converting enzyme inhibitors, nitric oxide, phosphodiesterase 5 inhibitors, prostacyclin, Ca2+ -channel antagonists, heparin, and serine elastase inhibitors. Inhibition of remodelling is generally accompanied by reductions in pulmonary artery pressure. The efficacy of some of the drugs varies, depending on the animal model of the disease. In view of the complexity of the remodelling process and the diverse aetiology of pulmonary hypertension in humans, it is to be anticipated that successful anti-remodelling therapy in the clinic will require a range of different drug options.

The pathology of pulmonary artery hypertension

The pathologic features of primary pulmonary hypertension (PPH) are well known but its pathogenesis remains uncertain. In the first section, this chapter outlines the characteristic structural changes of PPH. The second section deals with the pathogenesis of these changes drawing on animal models of chronic pulmonary hypertension. The third section deals with phenotypic alterations in cells from the wall of the pulmonary artery of hypertensive animals. The recent identification of a germlike mutation in the BMPR2 gene in patients with PPH provides a novel opportunity to further our understanding of the pathogenesis of this disease.

Regional variability in preproEndothelin-1 gene expression in sheep pulmonary artery and lung during the onset of air-induced chronic pulmonary hypertension. Participation Of arterial smooth muscle cells

We investigated preproendothelin-1 (ppET-1) gene expression in the main and midregion pulmonary artery, and peripheral lung from control sheep and from animals during the development of the structural and functional changes of air-induced chronic pulmonary hypertension (CPH). Measurement of ET-1 in lung lymph (n = 7) at 1, 4, 8, and 12 d of continuous air embolization (CAE) showed a significant increase from day 4 compared with controls (n = 4). A semiquantitative reverse transcription PCR for ppET-1 gene expression was developed using ovine-specific primers. Control sheep showed strikingly fewer ppET-1 transcripts in the midregion (22.9+/-2.3 ng cDNA equivalents) than in the main pulmonary artery and lung (736.0+/-263.7 and 705.5+/-125.7, respectively). Smooth muscle cells (SMC) isolated from the main and midregion artery of control sheep confirmed these findings and showed higher levels of intracellular ET-1 synthesis in the main versus the midregion artery. Differences in gene expression persisted during CAE. In main pulmonary artery and lung, ppET-1 transcripts fell to < 1% of controls. However, transcripts in the midregion artery showed a gradual increase. Coincubation of SMC from the midregion with ET-1 plus TGF-beta resulted in an increase in intracellular big ET-1 and a decrease in SMC from the main artery. We conclude that SMC from the main and midregion pulmonary artery are phenotypically different and suggest that local synthesis of ET-1 and TGF-beta, and increased levels of ET-1 in lung lymph, regulate ppET-1 gene expression and synthesis in arterial SMC during the development of air-induced CPH.

Pulmonary veins and bronchial vessels undergo remodeling in sustained pulmonary hypertension induced by continuous air embolization into sheep

While it is well known that chronic pulmonary hypertension is accompanied by characteristic structural changes in the pulmonary arteries, it is becoming increasingly apparent that the remodeling process also involves the venous side of the circulation. The present paper utilizes a sheep model of sustained pulmonary hypertension induced by continuous air embolization (CAE) into the pulmonary arterial circulation to examine the structure of the pulmonary veins and bronchial vasculature. Morphometric techniques were applied to the pulmonary veins and bronchial vessels following distension of the venous circulation with a barium-sulfate gelatin mixture; this route of filling also resulted in distension of the bronchial vessels. Four and 12 days of CAE resulted in a significant increase in the proportion of muscular pulmonary veins (e.g., percent muscular veins < 75 microns following 12 days CAE = 17.7 +/- 6.9; controls = 0), an approximate doubling in percent venous medial thickness, and a 50% reduction in number of barium-filled peripheral vessels. Examination of the bronchial circulation revealed a striking increase in volume due both to a 50% increase in vessel diameter and a threefold increase in number of small vessels (p < .05). The authors conclude that CAE-induced chronic pulmonary hypertension is associated with remodeling of both the pulmonary veins and bronchial circulation as well as the pulmonary arteries. The mechanisms for these structural alterations are not certain, but may include local release of vasoactive and inflammatory mediators and an increase in bronchopulmonary anastomoses.

Cellular and molecular mechanisms of pulmonary vascular remodeling

In many organs and tissues, the cellular response to injury is associated with a reiteration of specific developmental processes. Studies have shown that, in response to injury, vascular wall cells in adult organisms express genes or gene products characteristic of earlier developmental states. Other genes, expressed preferentially in adult cells in vivo, are down-regulated following injurious stimuli. Complicating matters, however, are recent observations demonstrating that the vascular wall is comprised of phenotypically heterogeneous subpopulations of endothelial cells, smooth muscle cells, and fibroblasts. It is unclear how specific subsets of cells respond to injury and thus contribute to the vascular remodeling that characterizes chronic pulmonary hypertension. This review discusses vascular development in the lung and the cellular responses occurring in pulmonary hypertension; special attention is given to heterogeneity of responses within cell populations and reiteration of developmental processes.

In vivo adenovirus-mediated gene transfer via the pulmonary artery of rats

Gene transfer into the pulmonary vasculature has the potential to be a powerful technique for both investigation of pulmonary pathophysiology and development of genetic therapies for pulmonary vascular disease. To evaluate the potential for in vivo pulmonary arterial gene transfer, we infused adenoviral vectors into the left pulmonary artery of Sprague-Dawley and cotton rats. Access to the left pulmonary artery was obtained by a percutaneous transcatheter approach or through thoracotomy and pulmonary arteriotomy. With the thoracotomy approach, both pulmonary arterial inflow and pulmonary venous outflow were occluded during vector influsion and throughout a subsequent 20-minute dwell period. The success of gene transfer was assessed by staining for evidence of recombinant gene expression in lungs excised at time points ranging from 48 to 72 hours after virus infusion. With the thoracotomy technique, pulmonary gene transfer was successful in 15% of surviving Sprague-Dawley rats and 30% of surviving cotton rats. Percutaneous catheter-based pulmonary gene transfer was not successful. In rats with pulmonary gene transfer, 1% to 8% of total left lung cells expressed the recombinant gene. Recombinant gene expression was found in endothelial cells (0.2% to 18% of total transduced cells), smooth muscle cells (0% to 3%), macrophages (1% to 7%), airway epithelial cells (2% to 50%), and alveolar epithelial cells (38% to 94%). Investigation of the low rate of successful gene transfer in individual animals suggested that insufficient physical contact between the virions and pulmonary cells was the most likely cause. In vivo gene transfer into the rat pulmonary vasculature can be accomplished with adenovirus vectors.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced growth capacity of neonatal pulmonary artery smooth muscle cells in vitro: dependence on cell size, time from birth, insulin-like growth factor I, and auto-activation of protein kinase C

Based on the unique susceptibility of the neonatal pulmonary circulation to hypoxia-induced structural alteration in vivo, we hypothesized that pulmonary artery (PA) smooth muscle cells (SMC) from the neonate would demonstrate enhanced growth capacity in vitro compared to adult cells. To test this hypothesis, matched neonatal and adult bovine SMC were tested for differences in size, serum-stimulated proliferation, susceptibility to senescence, resistance to serum withdrawal, autocrine growth capacity, and responsiveness to a locally important growth factor (insulin-like growth factor I; IGF-I) and an activator of protein kinase C (PKC) (phorbol 12-myristate 13-acetate; PMA). Neonatal PA SMC were smaller, grew faster, reached a higher plateau density, and were less susceptible to senescence. They were more resistant to serum withdrawal, had spontaneous autocrine growth capacity, and were more responsive to IGF-I, PMA, and the combination. Acquisition of increased growth factor responsiveness occurred between d5 and d14 after birth. Increased neonatal growth to IGF-I was associated with reduced IGF-I binding activity, implicating a post-receptor mechanism in enhanced responsiveness. Increased membrane-bound PKC catalytic activity was found in serum-deprived neonatal SMC. This basal increase was equal to that stimulated by 1 nM PMA in adult SMC, a pretreatment that caused these cells to become as responsive to IGF-I as untreated neonatal ones. We conclude that neonatal bovine PA SMC have marked enhancement of growth capacity in vitro, the acquisition of which is dependent on time from birth and is associated with auto-activation of PKC, These increased growth properties detected in vitro may contribute to the striking hyperplasia of neonatal PA SMC found in vivo following hypoxic exposure.

The endogenous vascular elastase that governs development and progression of monocrotaline-induced pulmonary hypertension in rats is a novel enzyme related to the serine proteinase adipsin

We showed previously a cause and effect relationship between increased activity of an endogenous vascular elastase (EVE) and experimentally induced pulmonary hypertension in rats. We now report the isolation and characterization of EVE. Degenerate oligonucleotides synthesized to homologous sequences in serine elastases were used in a PCR with rat pulmonary artery (PA) cDNA. The PCR product hybridized to a 1.2-kb mRNA and the intensity of hybridization was threefold increased in RNA from rat hypertensive PA at a timepoint when EVE activity was increased. The PCR product was used to screen a cDNA library and sequences obtained encoded rat adipsin. We then used immunoaffinity to purify EVE. An antibody to the elastin-binding protein was used to remove this competitor of elastase from the PA extract and the elastolytic activity increased 100-fold. The enzyme was purified using an antibody that recognizes NH2-terminal sequences of serine proteinases and the eluate was further purified using an antibody raised against recombinant adipsin. A single band at 20 kD immunoreactive with the adipsin antibody was resolved as an active enzyme on an elastin substrate gel. Immunogold labeling with an antibody to an adipsin peptide sequence localized EVE to PA smooth muscle cells. This is the first isolation of EVE; it appears to be a novel enzyme related to the serine proteinase adipsin originally found in adipose tissue.

Serum-induced vascular smooth muscle cell elastolytic activity through tyrosine kinase intracellular signalling

In previous studies, we related increased elastolytic activity in pulmonary arteries (PA) with endothelial injury to the later development of PA hypertension in rats. As the mechanism causing the increased PA elastase was unknown, we hypothesized that serum factors which are accessible to vascular smooth muscle cells (SMC) following endothelial injury stimulate their elastolytic activity. To test this, we developed an in vitro assay in which we added [3H]-elastin to cultured vascular SMC after 24 h serum starvation and monitored elastolysis following a further 24 h incubation with fetal bovine serum (FBS). We observed that serum induced increased elastolytic activity in both PA and aorta-derived SMC but not in endothelial cells or SMC with low basal levels of elastolytic activity. Maximum stimulation of SMC elastolytic activity occurred with a concentration as low as 1% FBS and despite elastase inhibitors in serum, suggesting that the activity is confined to the immediate pericellular region where enzyme concentration is high. Serum-stimulated elastolytic activity was not reproduced by growth factors or cytokines known to be associated with vascular disease or to induce release of elastases in other cells. The serum inducing elastolytic activity was heat and acid labile. It was associated with increased elastin adhesion to the 67 kD elastin binding protein on SMC surfaces and was prevented by tyrosine kinase inhibitors but not protein kinase C or A inhibitors. Our studies therefore suggest a mechanism whereby serum induction of SMC elastase requires signalling through the elastin binding protein and activation of tyrosine kinase.

Structure function correlates in the pulmonary vasculature during acute lung injury and chronic pulmonary hypertension

Arteries, veins, and capillaries comprise the pulmonary vasculature. Three structural types of artery and vein are identified, the most muscular vessels being the largest. For example, arteries that accompany the preacinar arteries are muscular in structure while those within the acinus may be either, muscular, partially muscular or non-muscular. These small intra-acinar arteries contribute much to the hemodynamic behavior of the lung. Pulmonary edema results from damage to the capillary endothelium while chronic pulmonary hypertension is characterized by structural alterations in the pulmonary arteries. Correlation of the structural and functional changes of chronic pulmonary hypertension suggest that the increases in medial and adventitial thickness of the muscular preacinar arteries are secondary to the onset of this disease, while the changes in the peripheral arteries--appearance of muscle in smaller intra-acinar arteries than normal and reduction in arterial volume--contribute to the rise in pulmonary artery pressure and pulmonary vascular resistance. Such correlations of structure and hemodynamic measurements demand that the lung be fixed in a simple and standardized manner. Available methodology to evaluate the structural changes that occur during the development of pulmonary edema and chronic pulmonary hypertension are described.