Hypoxia induces cell-specific changes in gene expression in vascular wall cells: implications for pulmonary hypertension

Three rare presentations of high-altitude pulmonary edema at a high-altitude clinic in the Everest region (4371 m): A case series

Diagnosis of HAPE can be challenging when the presentation deviates from usual natural history. Point of care ultrasonography serves as a great diagnostic tool in such settings. An umbrella treatment could be beneficial during such scenarios.

Melatonin Decreases Pulmonary Vascular Remodeling and Oxygen Sensitivity in Pulmonary Hypertensive Newborn Lambs

Background: Chronic hypoxia and oxidative stress during gestation lead to pulmonary hypertension of the neonate (PHN), a condition characterized by abnormal pulmonary arterial reactivity and remodeling. Melatonin has strong antioxidant properties and improves pulmonary vascular function. Here, we aimed to study the effects of melatonin on the function and structure of pulmonary arteries from PHN lambs.

Methods: Twelve lambs (Ovis aries) gestated and born at highlands (3,600 m) were instrumented with systemic and pulmonary catheters. Six of them were assigned to the control group (CN, oral vehicle) and 6 were treated with melatonin (MN, 1 mg.kg⁻¹.d⁻¹) during 10 days. At the end of treatment, we performed a graded oxygenation protocol to assess cardiopulmonary responses to inspired oxygen variations. Further, we obtained lung and pulmonary trunk samples for histology, molecular biology, and immunohistochemistry determinations.

Results: Melatonin reduced the in vivo pulmonary pressor response to oxygenation changes. In addition, melatonin decreased cellular density of the media and diminished the proliferation marker KI67 in resistance vessels and pulmonary trunk (p < 0.05). This was associated with a decreased in the remodeling markers α-actin (CN 1.28 ± 0.18 vs. MN 0.77 ± 0.04, p < 0.05) and smoothelin-B (CN 2.13 ± 0.31 vs. MN 0.88 ± 0.27, p < 0.05). Further, melatonin increased vascular density by 134% and vascular luminal surface by 173% (p < 0.05). Finally, melatonin decreased nitrotyrosine, an oxidative stress marker, in small pulmonary vessels (CN 5.12 ± 0.84 vs. MN 1.14 ± 0.34, p < 0.05).

Conclusion: Postnatal administration of melatonin blunts the cardiopulmonary response to hypoxia, reduces the pathological vascular remodeling, and increases angiogenesis in pulmonary hypertensive neonatal lambs.These effects improve the pulmonary vascular structure and function in the neonatal period under chronic hypoxia.

High Altitude Pulmonary Edema Without Appropriate Action Progresses to Right Ventricular Strain: A Case Study

Mills, Logan, Chris Harper, Sophie Rozwadowski, and Chris Imray. High altitude pulmonary edema without appropriate action progresses to right ventricular strain: A case study. High Alt Med Biol. 17:228-232, 2016.-A 24-year-old male developed high altitude pulmonary edema (HAPE) after three ascents to 4061 m over 3 days, sleeping each night at 2735 m. He complained of exertional dyspnea, dry cough, chest pain, fever, nausea, vertigo, and a severe frontal headache. Inappropriate continuation of ascent despite symptoms led to functional impairment and forced a return to the valley, but dyspnea persisted in addition to new orthopnea. Hospital admission showed hypoxemia, resting tachycardia, and systemic hypertension. ECG revealed right ventricular strain and a chest X-ray revealed right lower zone infiltrates. This case demonstrates that HAPE can develop in previously unaffected individuals given certain precipitating factors, and that in the presence of HAPE, prolonged exposure to altitude with exercise (or exertion) does not confer acclimatization with protective adaptations and that rest and descent are the appropriate actions. The case additionally demonstrates well-characterized right ventricular involvement.

Thromboxane promotes smooth muscle phenotype commitment but not remodeling of hypoxic neonatal pulmonary artery

Background

Persistent pulmonary hypertension of the newborn (PPHN) is characterized by vasoconstriction and pulmonary vascular remodeling. Remodeling is believed to be a response to physical or chemical stimuli including pro-mitotic inflammatory mediators such as thromboxane. Our objective was to examine the effects of hypoxia and thromboxane signaling ex vivo and in vitro on phenotype commitment, cell cycle entry, and proliferation of PPHN and control neonatal pulmonary artery (PA) myocytes in tissue culture.

Methods

To examine concurrent effects of hypoxia and thromboxane on myocyte growth, serum-fed first-passage newborn porcine PA myocytes were randomized into normoxic (21 % O₂) or hypoxic (10 % O₂) culture for 3 days, with daily addition of thromboxane mimetic U46619 (10⁻⁹ to 10⁻⁵ M) or diluent. Cell survival was detected by MTT assay. To determine the effect of chronic thromboxane exposure (versus whole serum) on activation of arterial remodeling, PPHN was induced in newborn piglets by a 3-day hypoxic exposure (FiO₂ 0.10); controls were 3 day-old normoxic and day 0 piglets. Third-generation PA were segmented and cultured for 3 days in physiologic buffer, Ham’s F-12 media (in the presence or absence of 10 % fetal calf serum), or media with 10⁻⁶ M U46619. DNA synthesis was measured by ³H-thymidine uptake, protein synthesis by ³H-leucine uptake, and proliferation by immunostaining for Ki67. Cell cycle entry was studied by laser scanning cytometry of nuclei in arterial tunica media after propidium iodide staining. Phenotype commitment was determined by immunostaining tunica media for myosin heavy chain and desmin, quantified by laser scanning cytometry.

Results

Contractile and synthetic myocyte subpopulations had differing responses to thromboxane challenge. U46619 decreased proliferation of synthetic and contractile myocytes. PPHN arteries exhibited decreased protein synthesis under all culture conditions. Serum-supplemented PA treated with U46619 had decreased G1/G0 phase myocytes and an increase in S and G2/M. When serum-deprived, PPHN PA incubated with U46619 showed arrested cell cycle entry (increased G0/G1, decreased S and G2/M) and increased abundance of contractile phenotype markers.

Conclusions

We conclude that thromboxane does not initiate phenotypic dedifferentiation and proliferative activation in PPHN PA. Exposure to thromboxane triggers cell cycle exit and myocyte commitment to contractile phenotype.

Hypoxia-induced endothelial CX3CL1 triggers lung smooth muscle cell phenotypic switching and proliferative expansion

Distal arterioles with limited smooth muscles help maintain the high blood flow and low pressure in the lung circulation. Chronic hypoxia induces lung distal vessel muscularization. However, the molecular events that trigger alveolar hypoxia-induced peripheral endothelium modulation of vessel wall smooth muscle cell (SMC) proliferation and filling of nonmuscular areas are unclear. Here, we investigated the role of CX3CL1/CX3CR1 system in endothelial-SMC cross talk in response to hypoxia. Human lung microvascular endothelial cells responded to alveolar oxygen deficiency by overproduction of the chemokine CX3CL1. The CX3CL1 receptor CX3CR1 is expressed by SMCs that are adjacent to the distal endothelium. Hypoxic release of endothelial CX3CL1 induced SMC phenotypic switching from the contractile to the proliferative state. Inhibition of CX3CR1 prevented CX3CL1 stimulation of SMC proliferation and monolayer expansion. Furthermore, CX3CR1 deficiency attenuated spiral muscle expansion, distal vessel muscularization, and pressure elevation in response to hypoxia. Our findings indicate that the capillary endothelium relies on the CX3CL1-CX3CR1 axis to sense alveolar hypoxia and promote peripheral vessel muscularization. These results have clinical significance in the development of novel therapeutics that target mechanisms of distal arterial remodeling associated with pulmonary hypertension induced by oxygen deficiency that is present in people living at high altitudes and patients with obstructive lung diseases.

Persistent pulmonary hypertension results in reduced tetralinoleoyl-cardiolipin and mitochondrial complex II + III during the development of right ventricular hypertrophy in the neonatal pig heart

Persistent pulmonary hypertension of the newborn (PPHN) results in right ventricular (RV) hypertrophy followed by right heart failure and an associated mitochondrial dysfunction. The phospholipid cardiolipin plays a key role in maintaining mitochondrial respiratory and cardiac function via modulation of the activities of enzymes involved in oxidative phosphorylation. In this study, changes in cardiolipin and cardiolipin metabolism were investigated during the development of right heart failure. Newborn piglets (<24 h old) were exposed to a hypoxic (10% O(2)) environment for 3 days, resulting in the induction of PPHN. Two sets of control piglets were used: 1) newborn or 2) exposed to a normoxic (21% O(2)) environment for 3 days. Cardiolipin biosynthetic and remodeling enzymes, mitochondrial complex II + III activity, incorporation of [1-(14)C]linoleoyl-CoA into cardiolipin precursors, and the tetralinoleoyl-cardiolipin pool size were determined in both the RV and left ventricle (LV). PPHN resulted in an increased heart-to-body weight ratio, RV-to-LV plus septum weight ratio, and expression of brain naturetic peptide in RV. In addition, PPHN reduced cardiolipin biosynthesis and remodeling in the RV and LV, which resulted in decreased tetralinoleoyl-cardiolipin levels and reduced complex II + III activity and protein levels of mitochondrial complexes II, III, and IV in the RV. This is the first study to examine the pattern of cardiolipin metabolism during the early development of both the RV and LV of the newborn piglet and to demonstrate that PPHN-induced alterations in cardiolipin biosynthetic and remodeling enzymes contribute to reduced tetralinoleoyl-cardiolipin and mitochondrial respiratory chain function during the development of RV hypertrophy. These defects in cardiolipin may play an important role in the rapid development of RV dysfunction and right heart failure in PPHN.

Heterogeneity of hypoxia-mediated decrease in I(K(V)) and increase in [Ca2+](cyt) in pulmonary artery smooth muscle cells

Hypoxic pulmonary vasoconstriction is caused by a rise in cytosolic Ca(2+) ([Ca(2+)](cyt)) in pulmonary artery smooth muscle cells (PASMC) via multiple mechanisms. PASMC consist of heterogeneous phenotypes defined by contractility, proliferation, and apoptosis as well as by differences in expression and function of various genes. In rat PASMC, hypoxia-mediated decrease in voltage-gated K(+) (Kv) currents (I(K(V))) and increase in [Ca(2+)](cyt) were not uniformly distributed in all PASMC tested. Acute hypoxia decreased I(K(V)) and increased [Ca(2+)](cyt) in approximately 46% and approximately 53% of PASMC, respectively. Using combined techniques of single-cell RT-PCR and patch clamp, we show here that mRNA expression level of Kv1.5 in hypoxia-sensitive PASMC (in which hypoxia reduced I(K(V))) was much greater than in hypoxia-insensitive cells (in which hypoxia negligibly affected I(K(V))). These results demonstrate that 1) different PASMC express different Kv channel alpha- and beta-subunits, and 2) the sensitivity of a PASMC to acute hypoxia partially depends on the expression level of Kv1.5 channels; hypoxia reduces whole-cell I(K(V)) only in PASMC that express high level of Kv1.5. In addition, the acute hypoxia-mediated changes in [Ca(2+)](cyt) also vary in different PASMC. Hypoxia increases [Ca(2+)](cyt) only in 34% of cells tested, and the different sensitivity of [Ca(2+)](cyt) to hypoxia was not related to the resting [Ca(2+)](cyt). An intrinsic mechanism within each individual cell may be involved in the heterogeneity of hypoxia-mediated effect on [Ca(2+)](cyt) in PASMC. These data suggest that the heterogeneity of PASMC may partially be related to different expression levels and functional sensitivity of Kv channels to hypoxia and to differences in intrinsic mechanisms involved in regulating [Ca(2+)](cyt).

Hypoxia-driven proliferation of human pulmonary artery fibroblasts: cross-talk between HIF-1alpha and an autocrine angiotensin system

Pulmonary artery adventitial fibroblasts (FBPA) may play a central role in lung vascular remodeling under conditions of hypoxia and inflammation, the result being pulmonary hypertension and cor pulmonale. In cultured human FBPA, both angiotensin II (Ang II) and hypoxia promoted cell cycle progression and cell proliferation and suppressed apoptosis. These effects were further enhanced when both stimuli were applied simultaneously. Hypoxia elevated the expression of hypoxia-inducible factor 1alpha (HIF-1alpha) and increased the expression of genes regulated by the hypoxia-responsive element (HRE). Up-regulation of both angiotensin-converting enzyme (ACE) and Ang II receptor type 1 (AT1) was also observed. Exogenous Ang II further increased HIF/HRE-dependent signaling in FBPA, whereas suppression of the autocrine ACE-Ang II-AT1 loop with inhibitors of ACE, AT1, and phosphatidylinositol 3-kinase (PI3K) reduced the proliferative response to both hypoxia and exogenous Ang II. Overexpression of HIF-1alpha by transient transfection caused the same proliferative effect and up-regulation of AT1 expression that were observed under hypoxic conditions. In contrast, small interfering RNA targeting HIF-1alpha inhibited hypoxia-induced ACE and AT1 expression. Our studies indicate that the ACE-Ang II-AT1 system serves as a positive feedback loop and fosters FBPA proliferation under hypoxic conditions, with the PI3K-HIF-HRE axis as the central effector pathway. This pathway may thus facilitate vascular remodeling under hypoxic conditions.

Egr-1 antisense oligonucleotides inhibit hypoxia-induced proliferation of pulmonary artery adventitial fibroblasts

In most mammalian species, chronic exposure to hypoxia leads to pulmonary hypertension and vascular remodeling. The adventitial fibroblast, because of its ability to proliferate in response to hypoxia, is thought to be a critical cell in the remodeling process. However, the transcription factors driving hypoxia-induced fibroblast proliferation have yet to be elucidated. The early growth response-1 (Egr-1) transcription factor has been shown to be upregulated by hypoxia in pulmonary artery adventitial fibroblasts. We therefore hypothesized that Egr-1 is directly involved in hypoxia-induced adventitial fibroblast proliferation. Immunohistochemical analysis of in vivo lung tissue from animals exposed to chronic hypoxia revealed increased expression of Egr-1 in the pulmonary artery fibroblasts vs. expression shown in normoxic controls. In fibroblasts cultured from chronically hypoxic animals, exposure to 1% oxygen upregulated Egr-1 protein and cell proliferation. To evaluate the role of Egr-1 in hypoxia-induced proliferation, we employed an Egr-1 antisense strategy. Addition of antisense Egr-1 oligonucleotides, but not sense oligonucleotides, attenuated the hypoxia-induced upregulation of Egr-1 protein and reduced hypoxia-induced DNA synthesis by 50%. Cell proliferation was also significantly inhibited by the addition of antisense Egr-1 oligonucleotides but not the sense oligonucleotides. In addition, hypoxia-induced upregulations of cyclin D and epidermal growth factor receptor were attenuated by Egr-1 antisense oligonucleotides. We conclude that Egr-1 protein expression is very sensitive to upregulation by hypoxia in pulmonary artery adventitial fibroblasts and that it plays an important role in the autonomous growth phenotype induced by hypoxia in these cells.

Effects of hypoxia on rat airway smooth muscle cell proliferation

Although it is well known that hypoxemia induces pulmonary vasoconstriction and vascular remodeling, due to the proliferation of both vascular smooth muscle cells and fibroblasts, the effects of hypoxemia on airway smooth muscle cells are not well characterized. The present study was designed to assess the in vitro effects of hypoxia (1 or 3% O(2)) on rat airway smooth muscle cell growth and response to mitogens (PDGF and 5-HT). Cell growth was assessed by cell counting and cell cycle analysis. Compared with normoxia (21% O(2)), there was a 42.2% increase in the rate of proliferation of cells exposed to 3% O(2) (72 h, P = 0.006), as well as an enhanced response to PDGF (13.9% increase; P = 0.023) and to 5-HT (17.2% increase; P = 0.039). Exposure to 1% O(2) (72 h) decreased cell proliferation by 21.0% (P = 0.017) and reduced the increase in cell proliferation induced by PGDF and 5-HT by 16.2 and 15.7%, respectively (P = 0.019 and P = 0.011). A significant inhibition in hypoxia-induced cell proliferation was observed after the administration of bisindolylmaleimide GF-109203X (a specific PKC inhibitor) or downregulation of PKC with PMA. Pretreatment with GF-109203X decreased proliferation by 21.5% (P = 0.004) and PMA by 31.5% (P = 0.005). These results show that hypoxia induces airway smooth muscle cell proliferation, which is at least partially dependent on PKC activation. They suggest that hypoxia could contribute to airway remodeling in patients suffering from chronic, severe respiratory diseases.

Effects of organ culture on arterial gene expression and hypoxic relaxation: role of the ryanodine receptor

Organ culture specifically inhibits vasorelaxation to acute hypoxia and preferentially decreases specific voltage-dependent K(+) channel expression over other K(+) and Ca(2+) channel subtypes. To isolate further potential oxygen-sensing mechanisms correlated with altered gene expression, we performed differential display analysis on RNA isolated from control and cultured coronary arterial rings. We hypothesize that organ culture results in altered gene expression important for vascular smooth muscle contractility important to the mechanism of hypoxia-induced relaxation. Our results indicate a milieu of changes suggesting both up- and downregulation of several genes. The altered expression pattern of two positive clones was verified by Northern analysis. Subsequent screening of a porcine cDNA library indicated homology to the ryanodine receptor (RyR). RT-PCR using specific primers to the three subtypes of RyR shows an upregulation of RyR2 and RyR3 after organ culture. Additionally, the caffeine- and/or ryanodine-sensitive intracellular Ca(2+) store was significantly more responsive to caffeine activation after organ culture. Our data indicate that organ culture increases expression of specific RyR subtypes and inhibits hypoxic vasorelaxation. Importantly, ryanodine blunted hypoxic relaxation in control coronary arteries, suggesting that upregulated RyR might play a novel role in altered intracellular Ca(2+) handling during hypoxia.

Angiotensin-converting enzyme gene polymorphism and its association with essential hypertension in a Tibetan population

There is strong evidence to support the idea that the renin-angiotensin system (RAS) plays an important role in the pathogenesis of essential hypertension (EH) and its complications. However, existing data about the association of angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism with blood pressure is conflicting, mainly due to racial differences and environmental exposure status. We therefore conducted a case control study to observe the relationship between ACE I/D polymorphism and EH in a Tibetan population who live in relatively isolated areas and are genetically homogeneous. The study was conducted at stable residential communities in the urban district of Lhasa, the capital of the Tibet autonomous region, China, and 106 unrelated EH patients and 135 normotensIve subjects were recruited. PCR, PCR/RFLP and PCR-SSCP were carried out to study the association between RAS genes and EH. Frequencies for the DD, ID and II genotypes were 27, 47 and 29 in hypertensive subjects, and 15, 60 and 48 in normotensive subjects, respectively. Derived allele frequencies for the I and D alleles were 0.51 and 0.49 in hypertensive subjects and 0.64 and 0.36 in normotensive subjects. There were significant differences in genotype distribution and derived allele frequency between these two groups. The genotype and allele frequencies of the ACE gene differed significantly between hypertensive and normotensive females (p>0.05), but there were no differences in males. In females, the DBP and MAP level were significantly higher for the DD than for the ID and II genotype, and SBP was significantly higher for the DD than for the II genotype. But in males, there were no significant differences in blood pressure among ACE genotypes. The results showed a significant association between the D allele of the ACE gene and hypertension in Tibetan women but not in Tibetan men.

Upregulation of collagens detected by gene array in a model of flow-induced pulmonary vascular remodeling

We recently reported localized increased pulmonary arterial resistance, neointimal lesions, and medial thickening induced by aortopulmonary anastomosis in young pigs. This model was used to investigate changes in expression of genes potentially involved in pulmonary vascular remodeling employing a high throughput Atlas Human Cardiovascular Array carrying approximately 600 cardiovascular-related cDNA sequences. Data were confirmed by Northern analysis, Western blots, and histological examination. With the use of lower stringency conditions for hybridization, 56% of the 588 human genes on the array showed visible signal after autoradiography. Approximately 10% of the genes with visible hybridization were altered by shunt-induced high flow. Extracellular matrix and cell adhesion molecules were the most highly represented group of upregulated genes. To our knowledge, our data are the first to demonstrate flow-induced changes in gene expression using a combination of cross species cDNA arrays, homologous hybridization, immunospecific protein, and histology. Our observations expand the list of genes as putative candidates in pulmonary vascular remodeling and support the utility of cross-species microarray analysis in such applications.

Invited review: Physiological and pathophysiological responses to intermittent hypoxia

This mini-review summarizes the physiological adaptations to and pathophysiological consequences of intermittent hypoxia with special emphasis given to the pathophysiology associated with obstructive sleep apnea. Intermittent hypoxia is an effective stimulus for evoking the respiratory, cardiovascular, and metabolic adaptations normally associated with continuous chronic hypoxia. These adaptations are thought by some to be beneficial in that they may provide protection against disease as well as improve exercise performance in athletes. The long-term consequences of chronic intermittent hypoxia may have detrimental effects, including hypertension, cerebral and coronary vascular problems, developmental and neurocognitive deficits, and neurodegeneration due to the cumulative effects of persistent bouts of hypoxia. Emphasis is placed on reviewing the available data on intermittent hypoxia, making extensions from applicable information from acute and chronic hypoxia studies, and pointing out major gaps in information linking the genomic and cellular responses to intermittent hypoxia with physiological or pathophysiological responses.