Expression of hypoxia-inducible factors in normal human lung development

Hypoxia-inducible factor and cellular senescence in pulmonary aging and disease

Cellular senescence and hypoxia-inducible factor (HIF) signaling are crucial in pulmonary aging and age-related lung diseases such as chronic obstructive pulmonary disease idiopathic pulmonary fibrosis and lung cancer. HIF plays a pivotal role in cellular adaptation to hypoxia, regulating processes like angiogenesis, metabolism, and inflammation. Meanwhile, cellular senescence leads to irreversible cell cycle arrest, triggering the senescence-associated secretory phenotype which contributes to chronic inflammation, tissue remodeling, and fibrosis. Dysregulation of these pathways accelerates lung aging and disease progression by promoting oxidative stress, mitochondrial dysfunction, and epigenetic alterations. Recent studies indicate that HIF and senescence interact at multiple levels, where HIF can both induce and suppress senescence, depending on cellular conditions. While transient HIF activation supports tissue repair and stress resistance, chronic dysregulation exacerbates pulmonary pathologies. Furthermore, emerging evidence suggests that targeting HIF and senescence pathways could offer new therapeutic strategies to mitigate age-related lung diseases. This review explores the intricate crosstalk between these mechanisms, shedding light on how their interplay influences pulmonary aging and disease progression. Additionally, we discuss potential interventions, including senolytic therapies and HIF modulators, that could enhance lung health and longevity.

Opposing Effects of TGFβ and BMP in the Pulmonary Vasculature in Congenital Diaphragmatic Hernia

Background: Pulmonary hypertension is the major cause of morbidity and mortality in congenital diaphragmatic hernia (CDH). Mutations in several genes that encode signaling molecules of the transforming growth factor β (TGFβ) and bone morphogenetic protein (BMP) pathways have previously been associated with CDH. Since studies on the activation of these pathways in CDH are scarce, and have yielded inconsistent conclusions, the downstream activity of both pathways was assessed in the nitrofen-CDH rat model.

Methods and Results: Pregnant Sprague-Dawley rats were treated with nitrofen at embryonic day (E) 9.5 to induce CDH in offspring. At E21, lungs were screened for the expression of key factors of both signaling pathways, at both the mRNA transcript and protein levels. Subsequently, paying particular attention to the pulmonary vasculature, increased phosphorylation of SMAD2, and decreased phosphorylation of Smad5 was noted in the muscular walls of small pulmonary vessels, by immunohistochemistry. This was accompanied by increased proliferation of constituent cells of the smooth muscle layer of these vessels.

Conclusions: Increased activation of the TGFβ pathway and decreased activation of the BMP pathway in the pulmonary vasculature of rats with experimentally-induced CDH, suggesting that the deregulated of these important signaling pathways may underlie the development of pulmonary hypertension in CDH.

Myopericytoma arising from myopericytosis-a hitherto unrecognized entity within the lung

Two cases of myopericytosis combined with pericytoma originating within the lung are reported. These are rare pulmonary tumors. The differential diagnosis for hemangiopericytoma and pericytic tumors with glomus elements is discussed. Both myopericytic lesions mimic other lesions, which are more commonly seen in the lung. Based on the expression of vascular growth factor receptors 2 and 3, an antiangiogenic therapy was suggested for the patient with the myopericytoma. A treatment with an angiogenesis inhibitor resulted in a regression of the tumor, but not the precursor lesion. Probably a more specific therapy using tyrosine kinase inhibitors for VEGFR2/3 might better control these myopericytic proliferations.

Bioengineering of Pulmonary Epithelium With Preservation of the Vascular Niche

The shortage of transplantable donor organs directly affects patients with end-stage lung disease, for which transplantation remains the only definitive treatment. With the current acceptance rate of donor lungs of only 20%, rescuing even one half of the rejected donor lungs would increase the number of transplantable lungs threefold, to 60%. We review recent advances in lung bioengineering that have potential to repair the epithelial and vascular compartments of the lung. Our focus is on the long-term support and recovery of the lung ex vivo, and the replacement of defective epithelium with healthy therapeutic cells. To this end, we first review the roles of the lung epithelium and vasculature, with focus on the alveolar-capillary membrane, and then discuss the available and emerging technologies for ex vivo bioengineering of the lung by decellularization and recellularization. While there have been many meritorious advances in these technologies for recovering marginal quality lungs to the levels needed to meet the standards for transplantation – many challenges remain, motivating further studies of the extended ex vivo support and interventions in the lung. We propose that the repair of injured epithelium with preservation of quiescent vasculature will be critical for the immediate blood supply to the lung and the lung survival and function following transplantation.

An EGLN1 mutation may regulate hypoxic response in cyanotic congenital heart disease through the PHD2/HIF-1A pathway

Cyanotic congenital heart disease (CCHD), a term describing the most severe congenital heart diseases are characterized by the anatomic malformation of a right to left shunt. Although the incidence of CCHD are far less than the that of congenital heart diseases (CHD), patients with CCHD always present severe clinical features such as hypoxia, dyspnea, and heart failure. Chronic hypoxia induces hypoxemia that significantly contributes to poor prognosis in CCHD. Current studies have demonstrated that the prolyl-4-hydroxylase2 (PHD2, encoded by EGLN1)/hypoxia-inducible factor-1A (HIF-1A) pathway is a key regulator of hypoxic response. Thus, we aim to assess the associations of single polymorphisms (SNPs) of the EGLN1 gene and hypoxic response in CCHD. A missense variant of EGLN1 c.380G>C (rs1209790) was found in 46 patients (46/126), with lower hypoxia incidence and higher rate of collateral vessel formation, compared with the wild type (P < 0.05). In vitro experiments, during hypoxia, EGLN1 mutation reduced EGLN1 expression compared with the wild type, with higher HIF-1A, VEGF and EPO expression levels in the mutant. No difference in HK1 expression was observed between the mutant and wild type. CCHD patients with c.380G>C showed improved response to hypoxia compared with the wild-type counterparts. The EGLN1 c.380G>C mutation improves hypoxic response through the PHD2/HIF-1A pathway, which may provide a molecular mechanism for hypoxic response in CCHD. The effects of the EGLN1 c.380G>C mutation on CCHD prognosis deserve further investigation.

A paradoxical method to enhance compensatory lung growth: Utilizing a VEGF inhibitor

Exogenous vascular endothelial growth factor (VEGF) accelerates compensatory lung growth (CLG) in mice after unilateral pneumonectomy. In this study, we unexpectedly discovered a method to enhance CLG with a VEGF inhibitor, soluble VEGFR1. Eight-week-old C57BL/6 male mice underwent left pneumonectomy, followed by daily intraperitoneal (ip) injection of either saline (control) or 20 μg/kg of VEGFR1-Fc. On post-operative day (POD) 4, mice underwent pulmonary function tests (PFT) and lungs were harvested for volume measurement and analyses of the VEGF signaling pathway. To investigate the role of hypoxia in mediating the effects of VEGFR1, experiments were repeated with concurrent administration of PT-2385, an inhibitor of hypoxia-induced factor (HIF)2α, via orogastric gavage at 10 mg/kg every 12 hours for 4 days. We found that VEGFR1-treated mice had increased total lung capacity (P = 0.006), pulmonary compliance (P = 0.03), and post-euthanasia lung volume (P = 0.049) compared to control mice. VEGFR1 treatment increased pulmonary levels of VEGF (P = 0.008) and VEGFR2 (P = 0.01). It also stimulated endothelial proliferation (P < 0.0001) and enhanced pulmonary surfactant production (P = 0.03). The addition of PT-2385 abolished the increase in lung volume and endothelial proliferation in response to VEGFR1. By paradoxically stimulating angiogenesis and enhancing lung growth, VEGFR1 could represent a new treatment strategy for neonatal lung diseases characterized by dysfunction of the HIF-VEGF pathway.

Hypoxia inducible factor 2α (HIF2α/EPAS1) is associated with development of pulmonary hypertension in severe congenital diaphragmatic hernia patients

We show that hypoxia inducible factor 2α (HIF2α) is highly expressed in patients with pulmonary hypertension (PH). HIF2α is expressed in every patient with congenital diaphragmatic hernia, while only half of the controls express HIF2α. Our data suggest that HIF2α is a link between hypoxia and the development of PH.

Treatment of rat congenital diaphragmatic hernia with sildenafil and NS-304, selexipag's active compound, at the pseudoglandular stage improves lung vasculature

Patients with congenital diaphragmatic hernia (CDH) often suffer from severe pulmonary hypertension, and the choice of current vasodilator therapy is mostly based on trial and error. Because pulmonary vascular abnormalities are already present early during development, we performed a study to modulate these pulmonary vascular changes at an early stage during gestation. Pregnant Sprague-Dawley rats were treated with nitrofen at day 9.5 of gestation (E9.5) to induce CDH in the offspring, and subsequently, the phosphodiesterase-5 inhibitor sildenafil and/or the novel prostaglandin-I receptor agonist selexipag (active compound NS-304) were administered from E17.5 until E20.5. The clinical relevant start of the treatment corresponds to week 20 of gestation in humans, when CDH is usually detected by ultrasound. CDH pups showed increased density of air saccules that was reverted after the use of only sildenafil. The pulmonary vascular wall was thickened, and right ventricular hypertrophy was present in the CDH group and improved both after single treatment with sildenafil or selexipag, whereas the combination therapy with both compounds did not have additive value. In conclusion, antenatal treatment with sildenafil improved airway morphogenesis and pulmonary vascular development, whereas selexipag only acted positively on pulmonary vascular development. The combination of both compounds did not act synergistically, probably because of a decreased efficiency of both compounds caused by cytochrome- P450 3A4 interaction and induction. These new insights create important possibilities for future treatment of pulmonary vascular abnormalities in CDH patients already in the antenatal period of life.

The BPD trio? Interaction of dysregulated PDGF, VEGF, and TGF signaling in neonatal chronic lung disease

The development of neonatal chronic lung disease (nCLD), i.e., bronchopulmonary dysplasia (BPD) in preterm infants, significantly determines long-term outcome in this patient population. Risk factors include mechanical ventilation and oxygen toxicity impacting on the immature lung resulting in impaired alveolarization and vascularization. Disease development is characterized by inflammation, extracellular matrix remodeling, and apoptosis, closely intertwined with the dysregulation of growth factor signaling. This review focuses on the causes and consequences of altered signaling in central pathways like transforming growth factor (TGF), platelet-derived growth factor (PDGF), and vascular endothelial growth factor (VEGF) driving these above indicated processes, i.e., inflammation, matrix remodeling, and vascular development. We emphasize the shared and distinct role of these pathways as well as their interconnection in disease initiation and progression, generating important knowledge for the development of future treatment strategies.

Changes in vasoactive pathways in congenital diaphragmatic hernia associated pulmonary hypertension explain unresponsiveness to pharmacotherapy

BACKGROUND

Patients with congenital diaphragmatic hernia (CDH) have structural and functional different pulmonary vessels, leading to pulmonary hypertension. They often fail to respond to standard vasodilator therapy targeting the major vasoactive pathways, causing a high morbidity and mortality. We analyzed whether the expression of crucial members of these vasoactive pathways could explain the lack of responsiveness to therapy in CDH patients.

METHODS

The expression of direct targets of current vasodilator therapy in the endothelin and prostacyclin pathway was analyzed in human lung specimens of control and CDH patients.

RESULTS

CDH lungs showed increased expression of both ETA and ETB endothelin receptors and the rate-limiting Endothelin Converting Enzyme (ECE-1), and a decreased expression of the prostaglandin-I₂ receptor (PTGIR). These data were supported by increased expression of both endothelin receptors and ECE-1, endothelial nitric oxide synthase and PTGIR in the well-established nitrofen-CDH rodent model.

CONCLUSIONS

Together, these data demonstrate aberrant expression of targeted receptors in the endothelin and prostacyclin pathway in CDH already early during development. The analysis of this unique patient material may explain why a significant number of patients do not respond to vasodilator therapy. This knowledge could have important implications for the choice of drugs and the design of future clinical trials internationally.

Postnatal growth restriction augments oxygen-induced pulmonary hypertension in a neonatal rat model of bronchopulmonary dysplasia

BACKGROUND

Prematurity and fetal growth restriction are risk factors for pulmonary hypertension (PH) in infants with bronchopulmonary dysplasia (BPD). Neonatal rats develop PH and vascular remodeling when exposed to hyperoxia. We hypothesize that postnatal growth restriction (PNGR) due to under-nutrition increases the severity of PH induced by hyperoxia in neonatal rats.

METHODS

Pups were randomized at birth to litters maintained in room air or 75% oxygen (hyperoxia), together with litters of normal milk intake (10 pups) or PNGR (17 pups). After 14 d, right ventricular hypertrophy (RVH) was assessed by Fulton's index (right ventricular weight/left ventricular plus septal weight) and PH by echocardiography. Lungs were analyzed by immunohistochemistry, morphometrics, western blotting, and metabolomics.

RESULTS

Hyperoxia and PNGR each significantly increased pulmonary arterial pressure, RVH and pulmonary arterial medial wall thickness, and significantly decreased pulmonary vessel number. These changes were significantly augmented in pups exposed to both insults. Hyperoxia and PNGR both significantly decreased expression of proteins involved in lung development and vasodilation.

CONCLUSION

PNGR induces right ventricular and pulmonary vascular remodeling and augments the effects of oxygen in neonatal rats. This may be a powerful tool to investigate the mechanisms that induce PH in low-birth-weight preterm infants with BPD.

Clinically relevant timing of antenatal sildenafil treatment reduces pulmonary vascular remodeling in congenital diaphragmatic hernia

Patients with congenital diaphragmatic hernia (CDH) suffer from severe pulmonary hypertension attributable to altered development of the pulmonary vasculature, which is often resistant to vasodilator therapy. Present treatment starts postnatally even though significant differences in the pulmonary vasculature are already present early during pregnancy. We examined the effects of prenatal treatment with the phosphodiesterase-5 inhibitor sildenafil on pulmonary vascular development in experimental CDH starting at a clinically relevant time. The well-established, nitrofen-induced CDH rodent model was treated daily with 100 mg/kg sildenafil from day 17.5 until day 20.5 of gestation (E17.5–20.5). Importantly, this timing perfectly corresponds to the developmental stage of the lung at 20 wk of human gestation, when CDH is detectable by 2D-ultrasonography and/or MRI. At E21.5 pups were delivered by caesarean section and euthanized by lethal injection of pentobarbital. The lungs were isolated and subsequently analyzed using immunostaining, real-time PCR, and volume measurements. Prenatal treatment with sildenafil improved lung morphology and attenuated vascular remodeling with reduced muscularization of the smaller vessels. Pulmonary vascular volume was not affected by sildenafil treatment. We show that prenatal treatment with sildenafil within a clinically relevant period improves pulmonary vascular development in an experimental CDH model. This may have important implications for the management of this disease and related pulmonary vascular diseases in human.

Loss of Hif-2α Rescues the Hif-1α Deletion Phenotype of Neonatal Respiratory Distress In Mice

Hypoxia is a state of decreased oxygen reaching the tissues of the body. During prenatal development, the fetus experiences localized occurrences of hypoxia that are essential for proper organogenesis and survival. The response to decreased oxygen availability is primarily regulated by hypoxia-inducible factors (HIFs), a family of transcription factors that modulate the expression of key genes involved in glycolysis, angiogenesis, and erythropoiesis. HIF-1α and HIF-2α, two key isoforms, are important in embryonic development, and likely are involved in lung morphogenesis. We have recently shown that the inducible loss of Hif-1α in lung epithelium starting at E4.5 leads to death within an hour of parturition, with symptoms similar to neonatal respiratory distress syndrome (RDS). In addition to Hif-1α, Hif-2α is also expressed in the developing lung, although the overlapping roles of Hif-1α and Hif-2α in this context are not fully understood. To further investigate the independent role of Hif-2α in lung epithelium and its ability to alter Hif-1α-mediated lung maturation, we generated two additional lung-specific inducible Hif-α knockout models (Hif-2α and Hif-1α+Hif-2α). The intrauterine loss of Hif-2α in the lungs does not lead to decreased viability or observable phenotypic changes in the lung. More interestingly, survivability observed after the loss of both Hif-1α and Hif-2α suggests that the loss of Hif-2α is capable of rescuing the neonatal RDS phenotype seen in Hif-1α-deficient pups. Microarray analyses of lung tissue from these three genotypes identified several factors, such as Scd1, Retlnγ, and Il-1r2, which are differentially regulated by the two HIF-α isoforms. Moreover, network analysis suggests that modulation of hormone-mediated, NF-κB, C/EBPα, and c-MYC signaling are central to HIF-mediated changes in lung development.

Regulation of lung development and regeneration by the vascular system

Blood vessels have been described a long time ago as passive circuits providing sufficient blood supply to ensure proper distribution of oxygen and nutrition. Blood vessels are mainly formed during embryonic development and in the early postnatal period. In the adult, blood vessels are quiescent, but can be activated and subsequently induced under pathophysiological conditions, such as ischemia and tumor growth. Surprisingly, recent data have suggested an active function for blood vessels, named angiocrine signaling, releasing trophogens which regulate organ development and organ regeneration including in the pancreas, lung, tumor cells, liver and bone. Lung development is driven by hypoxia as well as an intense endothelial-epithelial interaction, and important mechanisms contributing to these processes have recently been identified. This review aims to summarize recent developments and concepts about embryonic pulmonary vascular development and lung regeneration. We discuss hypoxia-inducible factor HIF-2α and vascular endothelial growth factor VEGF as important mediators in lung development and focus on endothelial-epithelial interactions and angiocrine signaling mechanisms.

The thioredoxin system in neonatal lung disease

SIGNIFICANCE

Fetal lung development takes place in hypoxia meaning that premature birth is hyperoxia for the prematurely born infant. The most common respiratory morbidity afflicting premature infants is bronchopulmonary dysplasia (BPD). Pathophysiologically, BPD represents the impact of injury, including O2 toxicity, to the immature developing lung that causes arrested lung development.

RECENT ADVANCES

The thioredoxin (Trx) system, which is predominantly expressed in pulmonary epithelia in the newborn lung, acts as an antioxidant system; however, it is increasingly recognized as a key redox regulator of signal transduction and gene expression via thiol-disulfide exchange reactions.

CRITICAL ISSUES

This review focuses on the contribution of Trx family proteins toward normal and aberrant lung development, in particular, the roles of the Trx system in hyperoxic responses of alveolar epithelial cells, aberrant lung development in animal models of BPD, O2-dependent signaling processes, and possible therapeutic efficacy in preventing O2-mediated lung injury.

FUTURE DIRECTIONS

The significant contribution of the Trx system toward redox regulation of key developmental pathways necessary for proper lung development suggests that therapeutic strategies focused on preserving pulmonary Trx function could significantly improve the outcomes of prematurely born human infants.

Role of reactive oxygen species in neonatal pulmonary vascular disease

SIGNIFICANCE

Abnormal lung development in the perinatal period can result in severe neonatal complications, including persistent pulmonary hypertension (PH) of the newborn and bronchopulmonary dysplasia. Reactive oxygen species (ROS) play a substantive role in the development of PH associated with these diseases. ROS impair the normal pulmonary artery (PA) relaxation in response to vasodilators, and ROS are also implicated in pulmonary arterial remodeling, both of which can increase the severity of PH.

RECENT ADVANCES

PA ROS levels are elevated when endogenous ROS-generating enzymes are activated and/or when endogenous ROS scavengers are inactivated. Animal models have provided valuable insights into ROS generators and scavengers that are dysregulated in different forms of neonatal PH, thus identifying potential therapeutic targets.

CRITICAL ISSUES

General antioxidant therapy has proved ineffective in reversing PH, suggesting that it is necessary to target specific signaling pathways for successful therapy.

FUTURE DIRECTIONS

Development of novel selective pharmacologic inhibitors along with nonantioxidant therapies may improve the treatment outcomes of patients with PH, while further investigation of the underlying mechanisms may enable earlier detection of the disease.

Kelch-like ECT2-interacting protein KLEIP regulates late-stage pulmonary maturation via Hif-2α in mice

Respiratory distress syndrome (RDS) caused by preterm delivery is a major clinical problem with limited mechanistic insight. Late-stage embryonic lung development is driven by hypoxia and the hypoxia-inducible transcription factors Hif-1α and Hif-2α, which act as important regulators for lung development. Expression of the BTB-and kelch-domain-containing (BTB-kelch) protein KLEIP (Kelch-like ECT2-interacting protein; also named Klhl20) is controlled by two hypoxia response elements, and KLEIP regulates stabilization and transcriptional activation of Hif-2α. Based on the available data, we hypothesized an essential role for KLEIP in murine lung development and function. Therefore, we have performed a functional, histological, mechanistic and interventional study in embryonic and neonatal KLEIP^−/− mice. Here, we show that about half of the KLEIP^−/− neonates die due to respiratory failure that is caused by insufficient aeration, reduced septal thinning, reduced glycogenolysis, type II pneumocyte immaturity and reduced surfactant production. Expression analyses in embryonic day (E) 18.5 lungs identified KLEIP in lung capillaries, and showed strongly reduced mRNA and protein levels for Hif-2α and VEGF; such reduced levels are associated with embryonic endothelial cell apoptosis and lung bleedings. Betamethasone injection in pregnant females prevented respiratory failure in KLEIP^−/− neonates, normalized lung maturation, vascularization, aeration and function, and increased neonatal Hif-2α expression. Thus, the experimental study shows that respiratory failure in KLEIP^−/− neonates is determined by insufficient angiocrine Hif-2α–VEGF signaling and that betamethasone activates this newly identified signaling cascade in late-stage embryonic lung development.

Antenatal hypoxia and pulmonary vascular function and remodeling

This review provides evidence that antenatal hypoxia, which represents a significant and worldwide problem, causes prenatal programming of the lung. A general overview of lung development is provided along with some background regarding transcriptional and signaling systems of the lung. The review illustrates that antenatal hypoxic stress can induce a continuum of responses depending on the species examined. Fetuses and newborns of certain species and specific human populations are well acclimated to antenatal hypoxia. However, antenatal hypoxia causes pulmonary vascular disease in fetuses and newborns of most mammalian species and humans. Disease can range from mild pulmonary hypertension, to severe vascular remodeling and dangerous elevations in pressure. The timing, length, and magnitude of the intrauterine hypoxic stress are important to disease development, however there is also a genetic-environmental relationship that is not yet completely understood. Determining the origins of pulmonary vascular remodeling and pulmonary hypertension and their associated effects is a challenging task, but is necessary in order to develop targeted therapies for pulmonary hypertension in the newborn due to antenatal hypoxia that can both treat the symptoms and curtail or reverse disease progression.

Hypoxia-inducible factors promote alveolar development and regeneration

Understanding how alveoli and the underlying capillary network develop and how these mechanisms are disrupted in disease states is critical for developing effective therapies for lung regeneration. Recent evidence suggests that lung angiogenesis promotes lung development and repair. Vascular endothelial growth factor (VEGF) preserves lung angiogenesis and alveolarization in experimental O2-induced arrested alveolar growth in newborn rats, but combined VEGF+angiopoietin 1 treatment is necessary to correct VEGF-induced vessel leakiness. Hypoxia-inducible factors (HIFs) are transcription factors that activate multiple O2-sensitive genes, including those encoding for angiogenic growth factors, but their role during postnatal lung growth is incompletely understood. By inducing the expression of a range of angiogenic factors in a coordinated fashion, HIF may orchestrate efficient and safe angiogenesis superior to VEGF. We hypothesized that HIF inhibition impairs alveolarization and that HIF activation regenerates irreversible O2-induced arrested alveolar growth. HIF inhibition by intratracheal dominant-negative adenovirus (dnHIF-1α)-mediated gene transfer or chetomin decreased lung HIF-1α, HIF-2α, and VEGF expression and led to air space enlargement and arrested lung vascular growth. In experimental O2-induced arrested alveolar growth in newborn rats, the characteristic features of air space enlargement and loss of lung capillaries were associated with decreased lung HIF-1α and HIF-2α expression. Intratracheal administration of Ad.HIF-1α restored HIF-1α, endothelial nitric oxide synthase, VEGF, VEGFR2, and Tie2 expression and preserved and rescued alveolar growth and lung capillary formation in this model. HIFs promote normal alveolar development and may be useful targets for alveolar regeneration.

Alveolar type II cells maintain bioenergetic homeostasis in hypoxia through metabolic and molecular adaptation

Although many lung diseases are associated with hypoxia, alveolar type II epithelial (ATII) cell impairment, and pulmonary surfactant dysfunction, the effects of O(2) limitation on metabolic pathways necessary to maintain cellular energy in ATII cells have not been studied extensively. This report presents results of targeted assays aimed at identifying specific metabolic processes that contribute to energy homeostasis using primary ATII cells and a model ATII cell line, mouse lung epithelial 15 (MLE-15), cultured in normoxic and hypoxic conditions. MLEs cultured in normoxia demonstrated a robust O(2) consumption rate (OCR) coupled to ATP generation and limited extracellular lactate production, indicating reliance on oxidative phosphorylation for ATP production. Pharmacological uncoupling of respiration increased OCR in normoxic cultures to 175% of basal levels, indicating significant spare respiratory capacity. However, when exposed to hypoxia for 20 h, basal O(2) consumption fell to 60% of normoxic rates, and cells maintained only ∼50% of normoxic spare respiratory capacity, indicating suppression of mitochondrial function, although intracellular ATP levels remained at near normoxic levels. Moreover, while hypoxic exposure stimulated glycogen synthesis and storage in MLE-15, glycolytic rate (as measured by lactate generation) was not significantly increased in the cells, despite enhanced expression of several enzymes related to glycolysis. These results were largely recapitulated in murine primary ATII, demonstrating MLE-15 suitability for modeling ATII metabolism. The ability of ATII cells to maintain ATP levels in hypoxia without enhancing glycolysis suggests that these cells are exceptionally efficient at conserving ATP to maintain bioenergetic homeostasis under O(2) limitation.

Loss of hypoxia-inducible factor 2 alpha in the lung alveolar epithelium of mice leads to enhanced eosinophilic inflammation in cobalt-induced lung injury

Hard metal lung disease (HMLD) is an occupational lung disease specific to inhalation of cobalt-containing particles whose mechanism is largely unknown. Cobalt is a known hypoxia mimic and stabilizer of the alpha subunits of hypoxia-inducible factors (HIFs). Previous work revealed that though HIF1α contrib utes to cobalt toxicity in vitro, loss of HIF1α in the alveolar epithelial cells does not provide in vivo protection from cobalt-induced lung inflammation. HIF1α and HIF2α show unique tissue expression profiles, and HIF2α is known to be the predominant HIF mRNA isoform in the adult lung. Thus, if HIF2α activation by cobalt contributes to pathophysiology of HMLD, we hypothesized that loss of HIF2α in lung epithelium would provide protection from cobalt-induced inflammation. Mice with HIF2α-deficiency in Club and alveolar type II epithelial cells (ATIIs) (HIF2α(Δ/Δ)) were exposed to cobalt (60 µg/day) or saline using a subacute occupational exposure model. Bronchoalveolar lavage cellularity, cytokines, qRT-PCR, and histopathology were analyzed. Results show that loss of HIF2α leads to enhanced eosinophilic inflammation and increased goblet cell metaplasia. Additionally, control mice demonstrated a mild recovery from cobalt-induced lung injury compared with HIF2α(Δ/Δ) mice, suggesting a role for epithelial HIF2α in repair mechanisms. The expression of important cytokines, such as interleukin (IL)-5 and IL-10, displayed significant differences following cobalt exposure when HIF2α(Δ/Δ) and control mice were compared. In summary, our data suggest that although loss of HIF2α does not afford protection from cobalt-induced lung inflammation, epithelial HIF2α signaling does play an important role in modulating the inflammatory and repair response in the lung.

Hypoxia inducible factor 3α plays a critical role in alveolarization and distal epithelial cell differentiation during mouse lung development

Lung development occurs under relative hypoxia and the most important oxygen-sensitive response pathway is driven by Hypoxia Inducible Factors (HIF). HIFs are heterodimeric transcription factors of an oxygen-sensitive subunit, HIFα, and a constitutively expressed subunit, HIF1β. HIF1α and HIF2α, encoded by two separate genes, contribute to the activation of hypoxia inducible genes. A third HIFα gene, HIF3α, is subject to alternative promoter usage and splicing, leading to three major isoforms, HIF3α, NEPAS and IPAS. HIF3α gene products add to the complexity of the hypoxia response as they function as dominant negative inhibitors (IPAS) or weak transcriptional activators (HIF3α/NEPAS). Previously, we and others have shown the importance of the Hif1α and Hif2α factors in lung development, and here we investigated the role of Hif3α during pulmonary development. Therefore, HIF3α was conditionally expressed in airway epithelial cells during gestation and although HIF3α transgenic mice were born alive and appeared normal, their lungs showed clear abnormalities, including a post-pseudoglandular branching defect and a decreased number of alveoli. The HIF3α expressing lungs displayed reduced numbers of Clara cells, alveolar epithelial type I and type II cells. As a result of HIF3α expression, the level of Hif2α was reduced, but that of Hif1α was not affected. Two regulatory genes, Rarβ, involved in alveologenesis, and Foxp2, a transcriptional repressor of the Clara cell specific Ccsp gene, were significantly upregulated in the HIF3α expressing lungs. In addition, aberrant basal cells were observed distally as determined by the expression of Sox2 and p63. We show that Hif3α binds a conserved HRE site in the Sox2 promoter and weakly transactivated a reporter construct containing the Sox2 promoter region. Moreover, Hif3α affected the expression of genes not typically involved in the hypoxia response, providing evidence for a novel function of Hif3α beyond the hypoxia response.

Toll-like receptor levels and caffeine responsiveness in rat pups during perinatal period

Infants born prematurely are prone to bronchopulmonary dysplasia which is a devastating form of chronic lung disease that develops in very low birth weight infants. Toll-like receptors (TLRs) are pattern recognition receptors that initiate innate immune responses. We tested TLR2, 4, and 9 levels in the lungs of rat pups given caffeine at the first days of postnatal life. Twenty-four rat pups equally divided into three groups. The study group received caffeine immediately after birth for ten days. The levels of TLR9 were found significantly higher in study group than control groups. We conclude that the beneficial and anti-inflammatory effects of caffeine in the lungs of newborn rats may be due to increased TLR9 levels.

Premature differentiation of vascular smooth muscle cells in human congenital diaphragmatic hernia

BACKGROUND

Congenital diaphragmatic hernia (CDH) is a rare congenital anomaly characterized by the herniation of abdominal organs into the chest cavity. The high mortality and morbidity of CDH patients are primarily caused by the associated pulmonary hypertension (PH), characterized by the thickening of the vascular media and adventitia. The media consist of heterogeneous populations of vascular smooth muscle cells (VSMC), ranging from synthetic to the characteristic contractile cells. VSMCs are influenced by developmental and environmental cues and may play a role in the development of the structural changes observed in CDH patients. Therefore, we hypothesized that the distribution of the VSMC populations may already be different at the origin of CDH development.

METHODOLOGY

We analyzed the protein expression of specific markers associated with synthetic and contractile VSMC phenotypes in human lungs at different developmental stages. Next, we compared lungs of premature and term CDH patients, as well as patients with lung hypoplasia due to renal agenesis or PROM, with age-matched controls.

RESULTS

Synthetic and contractile VSMCs are distributed in a temporal and spatial specific pattern along the proximodistal axis of the lung. CDH patients have more abundant contractile VSMCs which are also more distally distributed. This different distribution pattern is already observed from 19 weeks of gestation onwards.

CONCLUSION

Our data suggest that the more extensive distribution of contractile VSMCs is associated with an early maturation of the pulmonary vasculature, contrasting the concept that CDH might be the result of delayed maturation of the epithelium.

Reversal of pulmonary vascular remodeling in pulmonary hypertensive rats

Pulmonary hypertension is responsible for significant mortality and morbidity among newborns and infants. The pathology is characterized by pulmonary vascular remodeling with medial hypertrophy and adventitial thickening, leading to decreased gas exchange. Since it is unknown if these abnormalities are reversible, we analyzed these vascular changes in pulmonary hypertensive rats. Exposure of rats to hypobaric hypoxia for 4 weeks induced clinical signs of pulmonary hypertension, such as increased right ventricular systolic pressure, increased right ventricular weight and considerable pulmonary vascular remodeling. The vascular changes were associated with the expression of Non -Muscle Myosin Heavy Chain B in the pre-acinar vessels and an increased expression of alpha Smooth Muscle Actin, Smooth Muscle Myosin Heavy Chain 2 and Calponin in the intra-acinar vessels. The right ventricular systolic pressure and right ventricular weight gradually decreased after specific periods of recovery in normoxia, although this reversal did not reach baseline levels after six weeks at normoxia. However, the cellular changes in the pulmonary vasculature were completely reversed. Development of pulmonary hypertension is associated with an increase of synthetic perivascular cells in the pre-acinar arteries and an aberrant differentiation of perivascular cells in the smallest intra-acinar arteries. These cellular and structural changes in the pulmonary vasculature are completely reversible after recovery in normoxia.

SOX2 redirects the developmental fate of the intestinal epithelium toward a premature gastric phenotype

Various factors play an essential role in patterning the digestive tract. During development, Sox2 and Cdx2 are exclusively expressed in the anterior and the posterior parts of the primitive gut, respectively. However, it is unclear whether these transcription factors influence each other in determining specification of the naïve gut endoderm. We therefore investigated whether Sox2 redirects the fate of the prospective intestinal part of the primitive gut. Ectopic expression of Sox2 in the posterior region of the primitive gut caused anteriorization of the gut toward a gastric-like phenotype. Sox2 activated the foregut transcriptional program, in spite of sustained co-expression of endogenous Cdx2. However, binding of Cdx2 to its genomic targets and thus its transcriptional activity was strongly reduced. Recent findings indicate that endodermal Cdx2 is required to initiate the intestinal program and to suppress anterior cell fate. Our findings suggest that reduced Cdx2 expression by itself is not sufficient to cause anteriorization, but that Sox2 expression is also required. Moreover, it indicates that the balance between Sox2 and Cdx2 function is essential for proper specification of the primitive gut and that Sox2 may overrule the initial patterning of the primitive gut, emphasizing the plasticity of the primitive gut.

Hypoxia-inducible factor 2α plays a critical role in the formation of alveoli and surfactant

Alveolarization of the developing lung is an important step toward the switch from intrauterine life to breathing oxygen-rich air after birth. The distal airways structurally change to minimize the gas exchange path, and Type II pneumocytes increase the production of surfactants, which are required to reduce surface tension at the air-liquid interface in the alveolus. Hypoxia-inducible factor 2α (Hif2α) is an oxygen-regulated transcription factor expressed in endothelial and Type II cells, and its expression increases toward the end of gestation. We investigated the role of Hif2α in Type II cells by conditionally expressing an oxygen-insensitive mutant of Hif2α in airway epithelial cells during development. Newborn mice expressing the mutant Hif2α were born alive but quickly succumbed to respiratory distress. Subsequent analysis of the lungs revealed dilated alveoli covered with enlarged, aberrant Type II cells and a diminished number of Type I cells. The Type II cells accumulated glycogen in part by increased glucose uptake via the up-regulation of the glucose transporter 1. Furthermore, the cells lacked two crucial enzymes involved in the metabolism of glycogen into surfactant lipids, lysophosphatidylcholine acyltransferase and ATP-binding cassette sub-family A member 3. We conclude that Hif2α is a key regulator in alveolar maturation and the production of phospholipids by Type II cells.

HIF-2α expression is suppressed in SCLC cells, which survive in moderate and severe hypoxia when HIF-1α is repressed

Small cell lung carcinoma (SCLC) is extremely aggressive and frequently metastasizes widely in its early stage. Because tumor hypoxia is related to aggressive tumor behavior and the hypoxic adaptation of SCLC is poorly documented, we stained SCLC tumors arranged in a tissue microarray for hypoxia-inducible factor (HIF)-1α and HIF-2α proteins. We found an overall lack of HIF-2α protein expression, which was confirmed in large tumor sections. HIF-1α protein was strongly expressed in most tumors, frequently adjacent to necrotic regions. In concordance, cultured SCLC but not non-small cell lung carcinoma cells showed no or extremely low levels of HIF-2α mRNA and no HIF-2α protein at hypoxia. HIF-1α was stabilized after 4 hours at hypoxia, and its accumulation increased up to 96 hours. SCLC cells survived well and showed net proliferation and low cell death in modest (1% oxygen) and severe (0.1% oxygen) hypoxia. HIF-1α repression virtually did not influence cell death or viability despite reduced levels of hypoxia-inducible genes, such as BNIP3 and BNIP3L. At 1% oxygen no increased autophagy (LC3B-II activation) or NF-κB signaling were detected, whereas the unfolded protein response was activated at severe hypoxia. Our data indicate that HIFs are not exclusively required for SCLC cell survival at modest or severe hypoxia and that additional, yet uncharacterized, hypoxia-driven adaptation pathways may become activated.

Exposure to ethanol during the last trimester of pregnancy alters the maturation and immunity of the fetal lung

The effects of ethanol exposure on fetal lungs remain under investigation. Previously, we demonstrated that lambs exposed to ethanol during gestation had impaired expression of pulmonary surfactant protein A, a crucial component of lung immunity. In this study, we investigated the effects of in utero exposure to ethanol on maturation and immunity of the fetal lung. Pregnant ewes were surgically implanted with an abomasal cannula and administered 1g ethanol/kg (n=8) or water (n=8) during the last trimester of pregnancy. Lambs were delivered prematurely or naturally. Neonatal lungs were assessed for maturation markers (hypoxia-inducible factor-1α [HIF-1α], HIF-2α, HIF-3α, vascular endothelial growth factor-A [VEGF-A], VEGFR-1, VEGFR-2, glycogen, and lung protein levels) and immunity (cytokines and chemokines). Preterm animals exposed to ethanol had significantly reduced VEGF-A mRNA (P=.066) and protein levels, HIF-1α (P=.055), HIF-2α (P=.019), VEGFR-1 (P=.088), and VEGFR-2 (P=.067) mRNA levels but no changes in HIF-3α mRNA. No significant changes occurred in full-term animals exposed to ethanol. Glycogen levels were significantly higher in preterm animals exposed to ethanol (P=.006) but not in full-term animals. Ethanol exposure was associated with significantly lower lung protein levels in preterm (P=.03) but not full-term animals. Preterm animals exposed to ethanol had significantly reduced TNF-α (P=.05), IL-10 (P=.03), chemokine (C-C motif) ligand 5 (CCL5) (P=.017), and monocyte chemotactic protein-1 (MCP-1) (P=.0004) mRNA. In full-term animals exposed to ethanol, the immune alterations were either sustained (TNF-α, P=.009; IL-10, P=.03) or returned to near baseline levels (CCL5 and MCP-1). The ethanol-mediated alterations in fetal lung maturation and immunity may explain the increased incidence of respiratory infections in neonates exposed to ethanol in utero.

Expression of hypoxia-inducible factors, regulators, and target genes in congenital diaphragmatic hernia patients

Congenital diaphragmatic hernia (CDH) is associated with lung hypoplasia and pulmonary hypertension and has high morbidity and mortality rates. The cause and pathophysiology of CDH are not fully understood. However, impaired angiogenesis appears to play an important role in the pathophysiology of CDH. Therefore, we examined different components of an important pathway in angiogenesis: hypoxia-inducible factors (HIFs); HIF regulators von Hippel-Lindau (VHL) and prolyl 3-hydroxylase (PHD3); and HIF target genes vascular endothelial growth factor A ( VEGF-A ) and vascular endothelial growth factor receptor 2 ( VEGFR-2 ). Quantitative polymerase chain reaction of lung tissue showed a significantly decreased expression of VEGF-A mRNA in the alveolar stage of lung development in CDH patients compared with matched control patients. In the canalicular stage, no differences for VEGF-A were seen between the lungs of CDH patients and those of control patients. Other components of angiogenesis (VHL, HIF-1α, HIF-2α, HIF-3α, VEGFR-2 mRNA, PHD3 protein) that were analyzed showed no differences in expression between CDH and control patients, independent of the developmental stage. A lower expression of VEGF mRNA in CDH patients in the alveolar stage, possibly as a result of downregulation of HIF-2α might indicate a role for these factors in the pathophysiology of CDH.

A polymorphism in the macrophage migration inhibitory factor promoter is associated with bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a common adverse outcome of prematurity, causing severe morbidity and mortality. The cytokine macrophage migration inhibitory factor (MIF) has been recently shown to favor murine fetal lung development. In this prospective study, we evaluate the expression of MIF in the lung and in the serum of preterm infants (n = 50) and investigate whether the -173 G/C MIF promoter polymorphism is associated with the risk of BPD (n = 103). MIF was highly expressed in lung tissue from preterm infants. Serum MIF levels were measured by ELISA at d 1 after birth. MIF levels were increased [median (interquartile range), 71.01 (44.9-162.3) ng/mL], particularly in those infants with RDS [110.4 (59.4-239.2) ng/mL] compared with healthy adults [2.4 (1.2-5.0) ng/mL], (p < 0.001). The MIF -173*C allele, which predisposes to higher MIF production, was associated with a lower incidence of BPD (OR, 0.2; 95% CI, 0.04-0.93), independently from mechanical ventilation and oxygen exposure (p = 0.03). In conclusion, these data show that MIF expression is increased in lung and serum of preterm infants and suggest that the high producing MIF -173*C allele may be a protective factor for BPD.

Thioredoxin-interacting protein inhibits hypoxia-inducible factor transcriptional activity

Vascular endothelial growth factor (VEGF) is required for proper lung development and is transcriptionally regulated in alveolar epithelial cells by hypoxia-inducible factor (HIF). Previous findings in a newborn mouse model of bronchopulmonary dysplasia (BPD) suggest that thioredoxin-interacting protein (Txnip) is a novel regulator of VEGF expression. The present studies were designed to test the hypothesis that Txnip negatively regulates VEGF through effects on HIF-mediated gene expression. To test this hypothesis, we first examined the levels of VEGF and Txnip protein in the lungs of 1-day-old newborn mice and E19 embryos and detected a significant inverse correlation. To elucidate the mechanisms underlying this relationship, we studied the effects of Txnip overexpression on HIF-mediated transcription using murine lung epithelial (MLE-12) cells. Overexpression of Txnip inhibited HIF-mediated reporter activity in both hypoxia and room air. Suppression of HIF activity by Txnip seemed to be independent of the ability of Txnip to bind to thioredoxin. Thus, our studies support a model in which Txnip is a potentially critical regulator of HIF-mediated gene transcription in the murine lung. Alterations in Txnip expression could alter lung VEGF expression in prematurely born human infants and contribute to the development of BPD.

Expression of angiogenic and vasculogenic proteins in the lung in alveolar capillary dysplasia/misalignment of pulmonary veins: an immunohistochemical study

Alveolar capillary dysplasia with misalignment of pulmonary veins (ACD/MPV) is a rare, universally fatal developmental disorder of the lung affecting both the parenchyma and the vasculature. Its cause remains incompletely understood; the occurrence of familial cases has suggested a genetic abnormality. While several candidate genes have been studied previously, the affected pathway(s) have not yet been fully defined. The expression patterns of 8 gene products (endothelial nitric oxide synthase-3, fetal liver kinase-1, hypoxia inducible factor 1α, Von Hippel Lindau protein, 3 vascular endothelial growth factors [VEGF147, VEGFC1, and VEGFA20], and activin receptor-like kinase 1), all known to have a role in vascular development in the lung, were studied in 13 ACD/MPV and 17 control lungs by immunohistochemistry to further address the underlying molecular abnormality. Expression was graded with regard to degree and extent for multiple components of the lung parenchyma and pulmonary vasculature for each antibody. Statistical analyses of the data using the Mann-Whitney test revealed only a few significant differences (P ≤ 0.05) in degree of expression between ACD/MPV and control lung samples and do not clearly implicate one of these genes in ACD/MPV.

Control of HIF-1{alpha} and vascular signaling in fetal lung involves cross talk between mTORC1 and the FGF-10/FGFR2b/Spry2 airway branching periodicity clock

Lung development requires coordinated signaling between airway and vascular growth, but the link between these processes remains unclear. Mammalian target of rapamycin complex-1 (mTORC1) can amplify hypoxia-inducible factor-1α (HIF-1α) vasculogenic activity through an NH(2)-terminal mTOR binding (TOS) motif. We hypothesized that this mechanism coordinates vasculogenesis with the fibroblast growth factor (FGF)-10/FGF-receptor2b/Spry2 regulator of airway branching. First, we tested if the HIF-1α TOS motif participated in epithelial-mesenchymal vascular signaling. mTORC1 activation by insulin significantly amplified HIF-1α activity at fetal Po(2) (23 mmHg) in human bronchial epithelium (16HBE14o-) and induced vascular traits (Flk1, sprouting) in cocultured human embryonic lung mesenchyme (HEL-12469). This enhanced activation of HIF-1α by mTORC1 was abolished on expression of a HIF-1α (F99A) TOS-mutant and also suppressed vascular differentiation of HEL-12469 cocultures. Next, we determined if vasculogenesis in fetal lung involved regulation of mTORC1 by the FGF-10/FGFR2b/Spry2 pathway. Fetal airway epithelium displayed distinct mTORC1 activity in situ, and its hyperactivation by TSC1(-/-) knockout induced widespread VEGF expression and disaggregation of Tie2-positive vascular bundles. FGF-10-coated beads grafted into fetal lung explants from Tie2-LacZ transgenic mice induced localized vascular differentiation in the peripheral mesenchyme. In rat fetal distal lung epithelial (FDLE) cells cultured at fetal Po(2), FGF-10 induced mTORC1 and amplified HIF-1α activity and VEGF secretion without induction of ERK1/2. This was accompanied by the formation of a complex between Spry2, the cCBL ubiquitin ligase, and the mTOR repressor, TSC2, which abolished GTPase activity directed against Rheb, the G protein inducer of mTORC1. Thus, mTORC1 links HIF-1α-driven vasculogenesis with the FGF-10/FGFR2b/Spry2 airway branching periodicity regulator.

Expression and function of phosphodiesterases in nitrofen-induced congenital diaphragmatic hernia in rats

BACKGROUND

Congenital diaphragmatic hernia (CDH) is an anomaly associated with pulmonary hypoplasia and pulmonary hypertension (PH). The limited efficacy of current approaches to treat PH in CDH, including inhaled nitric oxide (NO), drives the search for other therapies. Phosphodiesterases (PDEs) degrade cyclic nucleotide second messenger cAMP and cGMP downstream of NO thereby limiting the vasodilatory response to NO.

OBJECTIVE

To identify therapeutic targets by cataloguing the expression and function of PDE isoforms in the pulmonary vasculature in nitrofen-induced CDH in fetal rats.

METHODS/RESULTS

Quantitative RT-PCR revealed PDE1-5 and PDE9 mRNA expression in pulmonary arteries (PAs) of control and nitrofen-induced CDH term fetal rats. In this order of potency, the PDE inhibitors Sildenafil (PDE5) > EHNA (PDE2) > Rolipram (PDE4) > Cilostamide (PDE3) all dilated isolated third generation PA after pre-constriction with the thromboxane analog U46619. Hyperoxic pre-incubation of PAs significantly attenuated vasodilatation induced by the PDE5 inhibitor Sildenafil (65% vs. 33%, P < 0.004). CDH PAs dilated significantly less to PDE2 inhibitor EHNA compared to control (51% vs. 72%, P < 0.05). Subsequently PDE2 protein expression was higher in PAs of CDH animals.

CONCLUSION

Most PDE isoforms exist in the PAs of fetal rats and their inhibition causes pulmonary vasodilatation. PDE5 inhibition was the most potent vasodilator, however, there were no differences between groups. PDE5-induced vasodilatation was attenuated by hyperoxic pre-incubation. PDE inhibitors might be considered therapeutic targets in combination with iNO in neonates with CDH.

The role of hypoxia and neurogenic genes (Mash-1 and Prox-1) in the developmental programming and maturation of pulmonary neuroendocrine cells in fetal mouse lung

Pulmonary neuroendocrine cells (PNECs) are the first cell type to differentiate within the primitive airway epithelium, suggesting a possible role in lung development. The differentiation of PNECs in fetal lung is governed by proneural genes such as the mammalian homolog of the achaete-scute complex (Mash-1) and a related transcription factor, hairy and enhancer of split1 (Hes-1). We examined the expression of Mash-1 and a downstream transcription factor Prox-1 in the developing mouse lung of wild-type and respective knockout mouse models. During early stages (embryonic day 12, E12) of development, only some PNECs expressed Mash-1 and Prox-1, but by E15, all PNECs coexpressed both transcription factors. PNECs failed to develop in Mash-1 but not in Prox-1-null mice, indicating that Mash-1 is essential for the initiation of the PNEC phenotype, whereas Prox-1 is associated with the development of this phenotype. As lung develops within a low O(2) environment (fetal euoxia, pO(2) approximately 20 to 30 mm Hg), we examined the effects of hypoxia on PNEC differentiation. Organ cultures of fetal mouse lungs at E12 and E16 were maintained under either 20% O(2) (normoxia, Nox) or 5% O(2) (hypoxia, Hox) and were examined every 24 h for up to 6 days in culture. In E12 explants, Hox enhanced branching morphogenesis and increased cell proliferation, but PNEC numbers and Mash-1 expression were significantly reduced. This effect could be reversed by switching the explants back to Nox. In contrast, Hox had no apparent effect on Hes-1 expression. Similarly, Hox had no effect on airway branching, PNEC numbers, or Mash-1 expression in E16 explants, indicating locked-in developmental programming. We suggest that during early stages of lung development, pO(2) concentration in concert with neurogenic gene expression modulates PNEC phenotype. Thus, disturbances in intrauterine pO(2) homeostasis could alter the functional maturation of the PNEC system and hence be involved in the pathogenesis of various perinatal pulmonary disorders.

Expression of HIF-1 alpha, VEGF and EPO in peripheral blood from patients with two cardiac abnormalities associated with hypoxia

OBJECTIVES

HIF-1 alpha (hypoxia-inducible factor-1 alpha) mediates the responses of mammalian cells to hypoxia/ischemia by inducing the expression of adaptive gene products (e.g., vascular endothelial growth factor (VEGF) and erythropoietin (EPO)). Persistent pulmonary hypertension of the newborn (PPHN) and cyanotic congenital heart disease (CCHD) are common neonatal diseases considered as paradigms of hypoxemia. Since the expression HIF-1 alpha, VEGF and EPO in newborns diagnosed with these diseases has yet to be studied, we set out to define the expression of these genes in peripheral blood from newborn infants diagnosed with PPHN and CCHD.

DESIGN AND METHODS

The mRNA transcripts encoding HIF-1 alpha, VEGF and EPO were measured by RT-PCR in healthy newborn infants and infants diagnosed with PPHN and CCHD.

RESULTS

An important increase in HIF-1 alpha expression was observed in both pathological conditions, accompanied by significant increases in VEGF and EPO expression when compared to healthy infants.

CONCLUSIONS

HIF-1 alpha mRNA expression increases in newborn infants with PPHN or CCHD, as does the expression of its target genes VEGF and EPO.