Redox regulation of lung development and perinatal lung epithelial function

Selenium Deficiency Exacerbates Hyperoxia-Induced Lung Injury in Newborn C3H/HeN Mice

Extremely preterm infants are often treated with supraphysiological oxygen, which contributes to the development of bronchopulmonary dysplasia (BPD). These same infants exhibit compromised antioxidant capacities due in part to selenium (Se) deficiency. Se is essential for basal and inducible antioxidant responses. The present study utilized a perinatal Se deficiency (SeD) mouse model to identify the combined effects of newborn hyperoxia exposure and SeD on alveolarization and antioxidant responses, including the identification of affected developmental pathways. Se-sufficient (SeS) and SeD C3H/HeN breeding pairs were generated, and pups were exposed to room air or 85% O2 from birth to 14 d. Survival, antioxidant protein expression, and RNA seq analyses were performed. Greater than 40% mortality was observed in hyperoxia-exposed SeD pups. Surviving SeD pups had greater lung growth deficits than hyperoxia-exposed SeS pups. Gpx2 and 4 protein and Gpx activity were significantly decreased in SeD pups. Nrf2-regulated proteins, Nqo1 and Gclc were increased in SeD pups exposed to hyperoxia. RNA seq revealed significant decreases in the Wnt/β-catenin and Notch pathways. Se is a biologically relevant modulator of perinatal lung development and antioxidant responses, especially in the context of hyperoxia exposure. The RNA seq analyses suggest pathways essential for normal lung development are dysregulated by Se deficiency.

Wildfire smoke exposure and early childhood respiratory health: a study of prescription claims data

Wildfire smoke is associated with short-term respiratory outcomes including asthma exacerbation in children. As investigations into developmental wildfire smoke exposure on children's longer-term respiratory health are sparse, we investigated associations between developmental wildfire smoke exposure and first use of respiratory medications. Prescription claims from IBM MarketScan Commercial Claims and Encounters database were linked with wildfire smoke plume data from NASA satellites based on Metropolitan Statistical Area (MSA). A retrospective cohort of live infants (2010-2016) born into MSAs in six western states (U.S.A.), having prescription insurance, and whose birthdate was estimable from claims data was constructed (N = 184,703); of these, gestational age was estimated for 113,154 infants. The residential MSA, gestational age, and birthdate were used to estimate average weekly smoke exposure days (smoke-day) for each developmental period: three trimesters, and two sequential 12-week periods post-birth. Medications treating respiratory tract inflammation were classified using active ingredient and mode of administration into three categories:: 'upper respiratory', 'lower respiratory', 'systemic anti-inflammatory'. To evaluate associations between wildfire smoke exposure and medication usage, Cox models associating smoke-days with first observed prescription of each medication category were adjusted for infant sex, birth-season, and birthyear with a random intercept for MSA. Smoke exposure during postnatal periods was associated with earlier first use of upper respiratory medications (1-12 weeks: hazard ratio (HR) = 1.094 per 1-day increase in average weekly smoke-day, 95%CI: (1.005,1.191); 13-24 weeks: HR = 1.108, 95%CI: (1.016,1.209)). Protective associations were observed during gestational windows for both lower respiratory and systemic anti-inflammatory medications; it is possible that these associations may be a consequence of live-birth bias. These findings suggest wildfire smoke exposure during early postnatal developmental periods impact subsequent early life respiratory health.

Pre-natal exposure to NO2 and PM2.5 and newborn lung function: An approach based on repeated personal exposure measurements

CONTEXT

While strong evidence supports adverse effects of pre-natal air pollution on child's lung function, previous studies rarely considered fine particulate matter (PM_2.5) or the potential role of offspring sex and no study examined the effects of pre-natal PM_2.5 on the lung function of the newborn.

AIM

We examined overall and sex-specific associations of personal pre-natal exposure to PM_2.5 and nitrogen (NO₂) with newborn lung function measurements.

METHODS

This study relied on 391 mother-child pairs from the French SEPAGES cohort. PM_2.5 and NO₂ exposure was estimated by the average concentration of pollutants measured by sensors carried by the pregnant women during repeated periods of one week. Lung function was assessed with tidal breathing analysis (TBFVL) and nitrogen multiple breath washout (N₂MBW) test, performed at 7 weeks. Associations between pre-natal exposure to air pollutants and lung function indicators were estimated by linear regression models adjusted for potential confounders, and then stratified by sex.

RESULTS

Mean exposure to NO₂ and PM_2.5 during pregnancy was 20.2 μg/m³ and 14.3 μg/m³, respectively. A 10 μg/m³ increase in PM_2.5 maternal personal exposure during pregnancy was associated with an adjusted 2.5 ml (2.3%) decrease in the functional residual capacity of the newborn (p-value = 0.11). In females, functional residual capacity was decreased by 5.2 ml (5.0%) (p = 0.02) and tidal volume by 1.6 ml (p = 0.08) for each 10 μg/m³ increase in PM_2.5. No association was found between maternal NO₂ exposure and newborns lung function.

CONCLUSIONS

Personal pre-natal PM_2.5 exposure was associated with lower lung volumes in female newborns, but not in males. Our results provide evidence that pulmonary effects of air pollution exposure can be initiated in utero. These findings have long term implications for respiratory health and may provide insights into the underlying mechanisms of PM_2.5 effects.

Impact of Oxidative Stress on Embryogenesis and Fetal Development

Multiple cellular processes are regulated by oxygen radicals or reactive oxygen species (ROS) where they play crucial roles as primary or secondary messengers, particularly during cell proliferation, differentiation, and apoptosis. Embryogenesis and organogenesis encompass all these processes; therefore, their role during these crucial life events cannot be ignored, more so when there is an imbalance in redox homeostasis. Perturbed redox homeostasis is responsible for damaging the biomolecules such as lipids, proteins, and nucleic acids resulting in leaky membrane, altered protein, enzyme function, and DNA damage which have adverse impact on the embryo and fetal development. In this article, we attempt to summarize the available data in literature for an in-depth understanding of redox regulation during development that may help in optimizing the pregnancy outcome both under natural and assisted conditions.

Calcium-Sensing Receptor Contributes to Hyperoxia Effects on Human Fetal Airway Smooth Muscle

Supplemental O₂ (hyperoxia), necessary for maintenance of oxygenation in premature infants, contributes to neonatal and pediatric airway diseases including asthma. Airway smooth muscle (ASM) is a key resident cell type, responding to hyperoxia with increased contractility and remodeling [proliferation, extracellular matrix (ECM) production], making the mechanisms underlying hyperoxia effects on ASM significant. Recognizing that fetal lungs experience a higher extracellular Ca²⁺ ([Ca²⁺]_o) environment, we previously reported that the calcium sensing receptor (CaSR) is expressed and functional in human fetal ASM (fASM). In this study, using fASM cells from 18 to 22 week human fetal lungs, we tested the hypothesis that CaSR contributes to hyperoxia effects on developing ASM. Moderate hyperoxia (50% O₂) increased fASM CaSR expression. Fluorescence [Ca²⁺]_i imaging showed hyperoxia increased [Ca²⁺]_i responses to histamine that was more sensitive to altered [Ca²⁺]_o, and promoted IP₃ induced intracellular Ca²⁺ release and store-operated Ca²⁺ entry: effects blunted by the calcilytic NPS2143. Hyperoxia did not significantly increase mitochondrial calcium which was regulated by CaSR irrespective of oxygen levels. Separately, fASM cell proliferation and ECM deposition (collagens but not fibronectin) showed sensitivity to [Ca²⁺]_o that was enhanced by hyperoxia, but blunted by NPS2143. Effects of hyperoxia involved p42/44 ERK via CaSR and HIF1α. These results demonstrate functional CaSR in developing ASM that contributes to hyperoxia-induced contractility and remodeling that may be relevant to perinatal airway disease.

P311 regulates distal lung development via its interaction with several binding proteins

Little is known about the molecular mechanisms underlying alveolar development. P311, a putative neuronal protein originally identified for its high expression during neuronal development, has once been reported to play a potential role in distal lung generation. However, the function of this protein has been poorly understood so far. Hence, we carried out a yeast two-hybrid screen, combining with other protein-protein interaction experiments, to isolate several binding partners of P311 during lung development, which may help us explore its function. We report 7 proteins here, including Gal-1, Loxl-1 and SPARC, etc, that can interact with it. Most of them have similar spatio-temporal expression patterns to P311. In addition, it was also found that P311 could stimulate their expression indirectly in L929 mouse fibroblast. Besides, computational methods were applied to construct a P311 centered protein-protein interaction network during alveolarization, using the 7 binding partners and their protein interaction information provided by public data resources. By analyzing the structure and function of this network, the effects of P311 on lung development were further clarified and all of the bioinformatic predictions from the network could be validated by real experiments. We have found here that P311 can control lung redox events, extracellular matrix and cell cycle progression, which are all crucial to pulmonary morphogenesis. This gives us a novel thought to explore the mechanisms controlling alveolarization.

Biochemical basis and metabolic interplay of redox regulation

Accumulated evidence strongly indicates that oxidative stress, characterized by an imbalance between reactive oxygen species (ROS) production and antioxidants in favor of oxidants, plays an important role in disease pathogenesis. However, ROS can act as signaling molecules and fulfill essential physiological functions at basal levels. Each ROS would be different in the extent to stimulate and contribute to different pathophysiological effects. Importantly, multiple ROS generators can be activated either concomitantly or sequentially by relevant signaling molecules for redox biological functions. Here, we summarized the current knowledge related to chemical and biochemical features of primary ROS species and corresponding antioxidants. Metabolic pathways of five major ROS generators and five ROS clearance systems were described, including their ROS products, specific ROS enriched tissue, cell and organelle, and relevant functional implications. We provided an overview of ROS generation and induction at different levels of metabolism. We classified 11 ROS species into three types based on their reactivity and target selectivity and presented ROS homeostasis and functional implications in pathological and physiological status. This article intensively reviewed and refined biochemical basis, metabolic signaling and regulation, functional insights, and provided guidance for the identification of novel therapeutic targets.

Calcium sensing receptor in developing human airway smooth muscle

Airway smooth muscle (ASM) regulation of airway structure and contractility is critical in fetal/neonatal physiology in health and disease. Fetal lungs experience higher Ca²⁺ environment that may impact extracellular Ca²⁺ ([Ca²⁺ ]_o ) sensing receptor (CaSR). Well-known in the parathyroid gland, CaSR is also expressed in late embryonic lung mesenchyme. Using cells from 18-22 week human fetal lungs, we tested the hypothesis that CaSR regulates intracellular Ca²⁺ ([Ca²⁺ ]_i ) in fetal ASM (fASM). Compared with adult ASM, CaSR expression was higher in fASM, while fluorescence Ca²⁺ imaging showed that [Ca²⁺ ]_i was more sensitive to altered [Ca²⁺ ]_o . The fASM [Ca²⁺ ]_i responses to histamine were also more sensitive to [Ca²⁺ ]_o (0-2 mM) compared with an adult, enhanced by calcimimetic R568 but blunted by calcilytic NPS2143. [Ca²⁺ ]_i was enhanced by endogenous CaSR agonist spermine (again higher sensitivity compared with adult). Inhibition of phospholipase C (U73122; siRNA) or inositol 1,4,5-triphosphate receptor (Xestospongin C) blunted [Ca²⁺ ]_o sensitivity and R568 effects. NPS2143 potentiated U73122 effects. Store-operated Ca²⁺ entry was potentiated by R568. Traction force microscopy showed responsiveness of fASM cellular contractility to [Ca²⁺ ]_o and NPS2143. Separately, fASM proliferation showed sensitivity to [Ca²⁺ ]_o and NPS2143. These results demonstrate functional CaSR in developing ASM that modulates airway contractility and proliferation.

Metabolomics reveals critical adrenergic regulatory checkpoints in glycolysis and pentose-phosphate pathways in embryonic heart

Cardiac energy demands during early embryonic periods are sufficiently met through glycolysis, but as development proceeds, the oxidative phosphorylation in mitochondria becomes increasingly vital. Adrenergic hormones are known to stimulate metabolism in adult mammals and are essential for embryonic development, but relatively little is known about their effects on metabolism in the embryonic heart. Here, we show that embryos lacking adrenergic stimulation have ∼10-fold less cardiac ATP compared with littermate controls. Despite this deficit in steady-state ATP, neither the rates of ATP formation nor degradation was affected in adrenergic hormone-deficient hearts, suggesting that ATP synthesis and hydrolysis mechanisms were fully operational. We thus hypothesized that adrenergic hormones stimulate metabolism of glucose to provide chemical substrates for oxidation in mitochondria. To test this hypothesis, we employed a metabolomics-based approach using LC/MS. Our results showed glucose 1-phosphate and glucose 6-phosphate concentrations were not significantly altered, but several downstream metabolites in both glycolytic and pentose-phosphate pathways were significantly lower compared with controls. Furthermore, we identified glyceraldehyde-3-phosphate dehydrogenase and glucose-6-phosphate dehydrogenase as key enzymes in those respective metabolic pathways whose activity was significantly (p < 0.05) and substantially (80 and 40%, respectively) lower in adrenergic hormone-deficient hearts. Addition of pyruvate and to a lesser extent ribose led to significant recovery of steady-state ATP concentrations. These results demonstrate that without adrenergic stimulation, glucose metabolism in the embryonic heart is severely impaired in multiple pathways, ultimately leading to insufficient metabolic substrate availability for successful transition to aerobic respiration needed for survival.

High post-natal mortality associated with defects in lung maturation and reduced adiposity in mice with gestational exposure to high fat and N-acetylcysteine

Studies have demonstrated that maternal consumption of a high fat diet (HFD) increases offspring susceptibility to metabolic disease. This study was initiated to identify the mechanistic contribution of oxidative stress on this phenomenon. Two weeks prior to mating, dams were fed either HFD or Control diet with or without supplementation with the anti-oxidant N-acetylcysteine (NAC). Pups born to HFD dams had reduced crown rump length (CRL) at birth and higher neonatal mortality compared to pups from Control dams. Supplementation with NAC normalized CRL in pups from HFD dams, but notably increased mortality. Histological examination of the lungs postnatally and prenatally, revealed normal branching morphogenesis but delayed alveolarization in pups from dams fed HFD+NAC. Discontinuation of NAC at ED17.5 with re-introduction at PD3 improved offspring survival and lung maturation. Additionally, interscapular brown adipose tissue (BAT) was reduced in ED18.5 embryos from HFD dams. These findings suggest that increased mortality in offspring from dams fed HFD+NAC during pregnancy may in part be the result of delayed pulmonary alveolarization and decreased BAT.

Lung extracellular matrix and redox regulation

Pulmonary fibrosis affects millions worldwide and, even though there has been a significant investment in understanding the processes involved in wound healing and maladaptive repair, a complete understanding of the mechanisms responsible for lung fibrogenesis eludes us, and interventions capable of reversing or halting disease progression are not available. Pulmonary fibrosis is characterized by the excessive expression and uncontrolled deposition of extracellular matrix (ECM) proteins resulting in erosion of the tissue structure. Initially considered an 'end-stage' process elicited after injury, these events are now considered pathogenic and are believed to contribute to the course of the disease. By interacting with integrins capable of signal transduction and by influencing tissue mechanics, ECM proteins modulate processes ranging from cell adhesion and migration to differentiation and growth factor expression. In doing so, ECM proteins help orchestrate complex developmental processes and maintain tissue homeostasis. However, poorly controlled deposition of ECM proteins promotes inflammation, fibroproliferation, and aberrant differentiation of cells, and has been implicated in the pathogenesis of pulmonary fibrosis, atherosclerosis and cancer. Considering their vital functions, ECM proteins are the target of investigation, and oxidation-reduction (redox) reactions have emerged as important regulators of the ECM. Oxidative stress invariably accompanies lung disease and promotes ECM expression directly or through the overproduction of pro-fibrotic growth factors, while affecting integrin binding and activation. In vitro and in vivo investigations point to redox reactions as targets for intervention in pulmonary fibrosis and related disorders, but studies in humans have been disappointing probably due to the narrow impact of the interventions tested, and our poor understanding of the factors that regulate these complex reactions. This review is not meant to provide a comprehensive review of this field, but rather to highlight what has been learned and to raise interest in this area in need of much attention.

Prenatal Particulate Air Pollution and Asthma Onset in Urban Children. Identifying Sensitive Windows and Sex Differences

RATIONALE

The influence of particulate air pollution on respiratory health starts in utero. Fetal lung growth and structural development occurs in stages; thus, effects on postnatal respiratory disorders may differ based on timing of exposure.

OBJECTIVES

We implemented an innovative method to identify sensitive windows for effects of prenatal exposure to particulate matter with a diameter less than or equal to 2.5 μm (PM2.5) on children's asthma development in an urban pregnancy cohort.

METHODS

Analyses included 736 full-term (≥37 wk) children. Each mother's daily PM2.5 exposure was estimated over gestation using a validated satellite-based spatiotemporal resolved model. Using distributed lag models, we examined associations between weekly averaged PM2.5 levels over pregnancy and physician-diagnosed asthma in children by age 6 years. Effect modification by sex was also examined.

MEASUREMENTS AND MAIN RESULTS

Most mothers were ethnic minorities (54% Hispanic, 30% black), had 12 or fewer years of education (66%), and did not smoke in pregnancy (80%). In the sample as a whole, distributed lag models adjusting for child age, sex, and maternal factors (education, race and ethnicity, smoking, stress, atopy, prepregnancy obesity) showed that increased PM2.5 exposure levels at 16-25 weeks gestation were significantly associated with early childhood asthma development. An interaction between PM2.5 and sex was significant (P = 0.01) with sex-stratified analyses showing that the association exists only for boys.

CONCLUSIONS

Higher prenatal PM2.5 exposure at midgestation was associated with asthma development by age 6 years in boys. Methods to better characterize vulnerable windows may provide insight into underlying 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.

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.

Storage at -80°C preserves the antioxidant capacity of preterm human milk

BACKGROUND AND OBJECTIVE

It is essential to establish optimum parameters for maintaining the quality of stored milk until the moment of consumption with minimal deterioration of its properties. The aim of the study was to evaluate total antioxidant capacity (TAC) and total oxidation status (TOS) of fresh and freeze-stored samples (at -80°C) of preterm human milk (HM).

METHODS

Samples of colostrum were collected from 98 healthy women within the first 4 days after delivery. The total milk volume collected (6 ml) was divided in two aliquot parts: 3 ml for the fresh analysis which was done immediately after the extraction and 3 ml for storage under freezing conditions at -80°C for three months. The antioxidant status and oxidative stress of the fresh and stored breast milk were assessed via determination of TAC and TOS levels.

RESULTS

The mean gestational age and the birth weight of the infants were 31.26 ± 2.93 weeks and 1620 ± 581.91 g; respectively. There were no significant correlations between maternal age, route of delivery and milk oxidative stress. There was no significant difference between the levels of TAC, TOS and the oxidative stress index in fresh and freeze-stored samples of colostrum in preterm HM (p > 0.05).

CONCLUSION

Freeze storage of preterm HM at -80°C for three months preserves the antioxidant capacity without changing oxidative status of HM, which could be noteworthy for the preterm infant nutrition.

Transcription factor Klf4, induced in the lung by oxygen at birth, regulates perinatal fibroblast and myofibroblast differentiation

The fluid-filled lung exists in relative hypoxia in utero (∼25 mm Hg), but at birth fills with ambient air where the partial pressure of oxygen is ∼150 mm Hg. The impact of this change was studied in mouse lung with microarrays to analyze gene expression one day before, and 2, 6, 12 and 24 hours after birth into room air or 10% O₂. The expression levels of >150 genes, representing transcriptional regulation, structure, apoptosis and antioxidants were altered 2 hrs after birth in room air but blunted or absent with birth in 10% O₂. Kruppel-like factor 4 (Klf4), a regulator of cell growth arrest and differentiation, was the most significantly altered lung gene at birth. Its protein product was expressed in fibroblasts and airway epithelial cells. Klf4 mRNA was induced in lung fibroblasts exposed to hyperoxia and constitutive expression of Klf4 mRNA in Klf4-null fibroblasts induced mRNAs for p21^cip1/Waf1, smooth muscle actin, type 1 collagen, fibronectin and tenascin C. In Klf4 perinatal null lung, p21^cip1/Waf1mRNA expression was deficient prior to birth and associated with ongoing cell proliferation after birth; connective tissue gene expression was deficient around birth and smooth muscle actin protein expression was absent from myofibroblasts at tips of developing alveoli; p53, p21^cip1/Waf1 and caspase-3 protein expression were widespread at birth suggesting excess apoptosis compared to normal lung. We propose that the changing oxygen environment at birth acts as a physiologic signal to induce lung Klf4 mRNA expression, which then regulates proliferation and apoptosis in fibroblasts and airway epithelial cells, and connective tissue gene expression and myofibroblast differentiation at the tips of developing alveoli.

Mitochondrial DNA damage mediates hyperoxic dysmorphogenesis in rat fetal lung explants

BACKGROUND

Numerous studies in cultured cells indicate that damage to mitochondrial DNA (mtDNA) dictates cellular responses to oxidant stress, yet the consequences of mtDNA damage have not been studied directly in the preterm lung.

OBJECTIVE

We sought to determine whether hyperoxia-induced fetal lung dysmorphogenesis is linked to mtDNA damage and establish mtDNA repair as a potential therapeutic approach for treating lung dysplasia in the preterm neonate.

METHODS

Hyperoxia-induced mtDNA damage was assessed by quantitative alkaline gel electrophoresis in normoxic (3% O2) and hyperoxic (21% O2) fetal rat lung explants. A fusion protein construct targeting the DNA repair enzyme endonuclease III (Endo III) to the mitochondria was used to augment mtDNA repair. Fetal lung branching and surfactant protein C (SFPTC) were assessed in these tissues.

RESULTS

Hyperoxia induced mtDNA damage in lung explants and was accompanied by impaired branching morphogenesis and decreased SFPTC mRNA expression. Treatment of lung explants with Endo III fusion protein prevented hyperoxia-induced mtDNA damage and restored normal branching morphogenesis and SFPTC mRNA expression.

CONCLUSION

These findings support the concept that mtDNA governs cellular responses to oxidant stress in the fetal lung and suggest that modulation of mtDNA repair is a potential pharmacologic strategy in the prevention of hyperoxic lung injury.

Abnormal platelet-derived growth factor signaling accounting for lung hypoplasia in experimental congenital diaphragmatic hernia

PURPOSE

The pathogenesis of pulmonary hypoplasia in congenital diaphragmatic hernia (CDH) is not fully understood. Platelet-derived growth factor A (PDGFA) and platelet-derived growth factor receptor α (PDGFRα) play a crucial role in lung development. It has been reported that PDGF induces H(2)O(2)-production and that oxidative stress may be an important mechanism for the impaired lung development in the nitrofen rat model. We hypothesized that pulmonary expression of PDGFA and PDGFRα is altered in the nitrofen induced CDH model.

MATERIALS AND METHODS

Pregnant rats received 100 mg nitrofen or vehicle on gestational day 9 (D9) and were sacrificed on D15, D18 or D21. RNA was extracted from fetal left lungs and mRNA levels of PDGFA and PDGFRα were determined using real-time polymerase chain reaction. Immunohistochemistry for protein expression of PDGFA and PDGFRα was performed. Pulmonary H(2)O(2) was measured colorimetrically.

RESULTS

mRNA levels of PDGFRα at D15 (4.50 ± 0.87) and PDGFA at D18 (2.90 ± 1.38) were increased in the nitrofen group (P < .05). Immunohistochemistry revealed increased pulmonary expression of PDGFRα and PDGFA. H(2)O(2) content was significantly higher in the nitrofen group.

CONCLUSIONS

Increased expression of PDGFA and PDGFRα suggests that pulmonary hypoplasia in the nitrofen CDH model may be owing to PDGF-induced oxidative stress during lung development.

Moderate postnatal hyperoxia accelerates lung growth and attenuates pulmonary hypertension in infant rats after exposure to intra-amniotic endotoxin

To determine the separate and interactive effects of fetal inflammation and neonatal hyperoxia on the developing lung, we hypothesized that: 1) antenatal endotoxin (ETX) causes sustained abnormalities of infant lung structure; and 2) postnatal hyperoxia augments the adverse effects of antenatal ETX on infant lung growth. Escherichia coli ETX or saline (SA) was injected into amniotic sacs in pregnant Sprague-Dawley rats at 20 days of gestation. Pups were delivered 2 days later and raised in room air (RA) or moderate hyperoxia (O₂, 80% O₂ at Denver's altitude, ∼65% O₂ at sea level) from birth through 14 days of age. Heart and lung tissues were harvested for measurements. Intra-amniotic ETX caused right ventricular hypertrophy (RVH) and decreased lung vascular endothelial growth factor (VEGF) and VEGF receptor-2 (VEGFR-2) protein contents at birth. In ETX-exposed rats (ETX-RA), alveolarization and vessel density were decreased, pulmonary vascular wall thickness percentage was increased, and RVH was persistent throughout the study period compared with controls (SA-RA). After antenatal ETX, moderate hyperoxia increased lung VEGF and VEGFR-2 protein contents in ETX-O₂ rats and improved their alveolar and vascular structure and RVH compared with ETX-RA rats. In contrast, severe hyperoxia (≥95% O₂ at Denver's altitude) further reduced lung vessel density after intra-amniotic ETX exposure. We conclude that intra-amniotic ETX induces fetal pulmonary hypertension and causes persistent abnormalities of lung structure with sustained pulmonary hypertension in infant rats. Moreover, moderate postnatal hyperoxia after antenatal ETX restores lung growth and prevents pulmonary hypertension during infancy.

Redox control of the cell cycle in health and disease

The cellular oxidation and reduction (redox) environment is influenced by the production and removal of reactive oxygen species (ROS). In recent years, several reports support the hypothesis that cellular ROS levels could function as ''second messengers'' regulating numerous cellular processes, including proliferation. Periodic oscillations in the cellular redox environment, a redox cycle, regulate cell-cycle progression from quiescence (G(0)) to proliferation (G(1), S, G(2), and M) and back to quiescence. A loss in the redox control of the cell cycle could lead to aberrant proliferation, a hallmark of various human pathologies. This review discusses the literature that supports the concept of a redox cycle controlling the mammalian cell cycle, with an emphasis on how this control relates to proliferative disorders including cancer, wound healing, fibrosis, cardiovascular diseases, diabetes, and neurodegenerative diseases. We hypothesize that reestablishing the redox control of the cell cycle by manipulating the cellular redox environment could improve many aspects of the proliferative disorders.

Glucocorticoid-mediated repression of REDD1 mRNA expression in rat fetal distal lung epithelial cells

REDD1 (Regulated in Development and DNA Damage-1) is a stress-response gene that represses mammalian target of rapamycin (mTOR) thus decreasing protein synthesis. In contrast to studies using cell lines and adult alveolar type II (ATII) cells, we find that REDD1 mRNA levels did not increase in rat fetal distal lung epithelia (FDLE) or fetal lung fibroblasts grown in primary cultures and then exposed to 3% O2. REDD1 mRNA expression was repressed by dexamethasone (DEX) in FDLE and ATII, but induced by DEX in fibroblasts. Lung epithelial cell lines, A549 and MLE-15, showed increases in REDD1 mRNA in response to hypoxia and DEX. The effect of DEX on REDD1 mRNA and protein in FDLE and fibroblasts was dose- and time-dependent. Inhibitor studies support repression of REDD1 mRNA by DEX in FDLE was mediated via glucocorticoid receptor and not by nongenomic effects of glucocorticoids via MAPK pathways. The half-life of REDD1 mRNA was shorter in DEX-exposed FDLE compared with hormone-free media suggesting that DEX reduced REDD1 mRNA stability in FDLE. These studies indicate that REDD1 expression in response to hypoxia and DEX is cell-type specific and that physiologically appropriate levels of PO2 should be used when investigating fetal lung development.

Mechanisms of macrophage migration inhibitory factor (MIF)-dependent tumor microenvironmental adaptation

Since its activity was first reported in the mid-1960s, macrophage migration inhibitory factor (MIF) has gone from a cytokine activity modulating monocyte motility to a pleiotropic regulator of a vast array of cellular and biological processes. Studies in recent years suggest that MIF contributes to malignant disease progression on several different levels. Both circulating and intracellular MIF protein levels are elevated in cancer patients and MIF expression reportedly correlates with stage, metastatic spread and disease-free survival. Additionally, MIF expression positively correlates with angiogenic growth factor expression, microvessel density and tumor-associated neovascularization. Not coincidentally, MIF has recently been shown to contribute to tumoral hypoxic adaptation by promoting hypoxia-induced HIF-1alpha stabilization. Intriguingly, hypoxia is a strong regulator of MIF expression and secretion, suggesting that hypoxia-induced MIF acts as an amplifying factor for both hypoxia and normoxia-associated angiogenic growth factor expression in human malignancies. Combined, these findings suggest that MIF overexpression contributes to tumoral hypoxic adaptation and, by extension, therapeutic responsiveness and disease prognosis. This review summarizes recent literature on the contributions of MIF to tumor-associated angiogenic growth factor expression, neovascularization and hypoxic adaptation. We also will review recent efforts aimed at identifying and employing small-molecule antagonists of MIF as a novel approach to cancer therapeutics.

Human milk enhances antioxidant defenses against hydroxyl radical aggression in preterm infants

BACKGROUND

Preterm infants endowed with an immature antioxidant defense system are prone to oxidative stress. Hydroxyl radicals are very aggressive reactive oxygen species that lack specific antioxidants. These radicals cannot be measured directly, but oxidation byproducts of DNA or phenylalanine in urine are reliable markers of their activity. Human milk has a higher antioxidant capacity than formula.

OBJECTIVE

We hypothesized that oxidative stress associated with prematurity could be diminished by feeding human milk.

DESIGN

We recruited a cohort of stable preterm infants who lacked perinatal conditions associated with oxidative stress; were not receiving prooxidant or antioxidant drugs, vitamins, or minerals before recruitment; and were fed exclusively human milk (HM group) or preterm formula (PTF group). Collected urine was analyzed for oxidative bases of DNA [8-hydroxy-2'-deoxyguanosine (8-oxodG)/2'-deoxyguanosine (2dG) ratio] and oxidative derivatives of phenylalanine [ortho-tyrosine (o-Tyr)/Phe ratio] by HPLC coupled to tandem mass spectrometry. Healthy term newborn infants served as control subjects.

RESULTS

Both preterm groups eliminated greater amounts of metabolites than did the control group. However, the PTF group eliminated significantly (P < 0.02) higher amounts of 8-oxodG (8-oxodG/2dG ratio: 10.46 +/- 3.26) than did the HM group (8-oxodG/2dG ratio: 9.05 +/- 2.19) and significantly (P < 0.01) higher amounts of o-Tyr (o-Tyr/Phe ratio: 14.90 +/- 3.75) than did the HM group (o-Tyr/Phe ratio: 12.53 +/- 3.49). When data were lumped together independently of the type of feeding received, a significant correlation was established between the 8-oxodG/2dG and o-Tyr/Phe ratios in urine, dependent on gestational age and birth weight.

CONCLUSION

Prematurity is associated with protracted oxidative stress, and human milk is partially protective.

Global and gene-specific translational regulation in rat lung development

During the peripartum period, the lung must respond to dramatic changes in circulating hormones, nutritional factors, and physiologic signals during its transition to becoming the organ of gas exchange. Protein synthesis consumes a significant proportion of metabolic resources and is inhibited by many environmental stresses. We hypothesized that translational control mechanisms play a role in the perinatal lung. Immunoblots of late-gestation (Fetal Day [FD] 17-22) rat lung extracts revealed gradual decreases in phosphorylated forms of the mammalian target of rapamycin effectors, eukaryotic initiation factor (eIF) 4E-binding protein, p70 S6 kinase, and ribosomal protein S6, followed by sharp increases on Postnatal Day 1 (P1). Immunohistochemistry showed phospho-S6 staining was most prominent in epithelial cells of the large and small airways. m(7)GTP-sepharose pulldown experiments showed a decrease in association of translation initiation factor, eIF4E, with its inhibitor, eIF4E-binding protein, and a concomitant increase in eIF4E association with eIF4G immediately after birth, and polysome profiles confirmed a decrease in abundance of large polysomes between FD19 and FD22, which was reversed on P1. Microarray analysis of polysomal versus total RNA from FD19, FD22, and P1 lungs was used to identify specific genes, the association of which with large polysomes changed either pre- or postnatally. RT-PCR and Northern blotting were used to confirm translational changes in selected candidate genes, including a prenatal increase in IL-18 and a postnatal decrease in regulatory subunit 2 of protein phosphatase 1. Translational regulation of IL-18 and protein phosphatase 1 regulatory (inhibitor) subunit 2 is gene-specific, as these changes contrast with the corresponding global changes in polysome abundance.

Understanding the chemical properties of macerals and minerals in coal and its potential application for occupational lung disease prevention

Recent increases in oil price further strengthen the argument that coal and coal products will play an increasingly important role in fulfilling the energy needs of our society. Coal is an aggregate of heterogeneous substances composed of organic (macerals) and inorganic (minerals) materials. The objective of this review was to assess whether some chemical parameters in coal play a role in producing environmental health problems. Basic properties of coal--such as chemical forms of the organic materials, structure, compositions of minerals--vary from one coal mine region to another as well as from coals of different ranks. Most importantly, changes in chemical properties of coals due to exposure to air and humidity after mining--a dynamic process--significantly affect toxicity attributed to coal and environmental fate. Although coal is an extremely complex and heterogeneous material, the fundamental properties of coal responsible for environmental and adverse health problems are probably related to the same inducing components of coal. For instance, oxidation of pyrite (FeS2) in the coal forms iron sulfate and sulfuric acid, which produces occupational lung diseases (e.g., pneumoconiosis) and other environmental problems (e.g., acid mine drainage and acid rain). Calcite (CaCO3) contained in certain coals alters the end products of pyrite oxidation, which may make these coals less toxic to human inhalation and less hazardous to environmental pollution. Finally, knowledge gained on understanding of the chemical properties of coals is illustrated to apply for prediction of toxicity due to coal possibly before large-scale mining and prevention of occupational lung disease during mining.

Effects of oxidative stress on embryonic development

Oxygen radicals, or reactive oxygen species (ROS) act as primary or secondary messengers to promote cell growth or death. Many instances demonstrate an important direct role of ROS in development because redox status regulates key transcription factors that influence cell signaling pathways involved in proliferation, differentiation, and apoptosis. Therefore, oxidative stress can alter many important reactions that affect embryonic development both positively and negatively. During particular periods in development, the embryo is more or less susceptible to oxidative stress, and teratogens, which can modify redox status, such as thalidomide, phenytoin, and ethanol, will disrupt fetal development. Various events in pregnancy such as diabetes also alter the redox state. Fortunately, antioxidants can obviate these effects through modification of gene expression, transcription factor signaling, and cell cycle alterations. A better understanding of ROS-mediated reactions and their impact on embryonic development is important to ensure optimal outcomes.

Current concepts of redox signaling in the lungs

In the intracellular redox state (GSH/GSSG) the cell plays a key role in the regulation and potentiation of the inflammatory response in lung cells. Glutathione and thioredoxin are the important protective antioxidants in the lungs. Regulation of intracellular redox glutathione and thioredoxin levels in response to reactive oxygen/nitrogen species and in inflammation should have critical effects on different lung cells on the activation of redox sensor/signal transduction pathways and various transcription factors. Possibly via the modification of cysteine residues, oxidative stress activates multiple stress kinase pathways and transcription factors nuclear factor-kappaB and activator protein-1, which differentially regulate the genes for proinflammatory cytokines as well as the protective antioxidant genes. Emerging data suggest that protein-S-thiolation, protein-S-nitrosation, and oxidation of protein-SH (formation of sulfenic, sulfinic, and sulfonic acids) are critical in redox signaling during normal physiology and under oxidative stress in controlling the cellular processes. In this review, we discuss the recent findings in the context of redox signaling during inflammation, pathology, and the role of redox modulating agents/dietary interventions either to inhibit abnormal signaling or induce/boost the endogenous antioxidant systems. Furthermore, this also provides information as to how antioxidants are involved in redox signaling to control inflammatory and oxidative stress in the lung.

Growth hormone (GH) receptor knockout mice reveal actions of GH in lung development

The presence of growth hormone (GH) and GH receptors (GHRs) in the lung suggests it is an autocrine/paracrine target site for pulmonary GH action and/or an endocrine site of pituitary GH action. Roles for GH in lung growth or pulmonary function are, however, uncertain. The possibility that pituitary and/or pulmonary GH have physiological roles in lung development has therefore been investigated in GHR knockout (KO or -/-) mice, using a proteomics approach to determine if an absence of GH-signaling affects the proteome of the developing lung. More than 600 proteins were detected by 2-DE in the lungs of control [GHR (+/+)] and GHR (-/-) mice at the end of the alveolarization period (at day 14 postnatally). Of these, 39 differed significantly in protein content at the p>0.05 level [6 were of higher abundance in the GHR (-/-) group, 33 were of lower abundance] and 17 differed at the p>0.02 level [5 of higher abundance in the GHR (-/-) group, 12 of lower abundance] and 7 were definitively identified by MS. Vimentin, a protein involved in cellular proliferation, was reduced in content by approximately 75% in the lungs of the GHR (-/-) mice. Three proteins involved in oxidative protection [SH3 domain-binding glutamic acid-rich-like protein, peroxiredoxin 6 (Prdx6), and isocitrate dehydrogenase 1] were also of lower content in the GHR (-/-) lungs (by approximately 88%, 81% and 70%, respectively). Prdx6 is also involved in lipid and surfactant metabolism, as is apolipoprotein A-IV, the lung content of which was reduced by approximately 73% in these mice. Proteasome 26S ATPase subunit 4, a protein involved in the non-lysosomal degradation of intracellular proteins, and electron flavoprotein alpha subunit , involved in intracellular metabolism, were also reduced in content in the lungs of the GHR (-/-) mice (by approximately 70% and 49%, respectively). These results therefore suggest that these proteins are normally dependent upon GH signaling, and that GH is normally involved in early lung growth, oxidative protection, lipid and energy metabolism and in proteasomal activity. These roles may reflect endocrine actions of pituitary GH and/or local autocrine/paracrine actions of GH produced within the lung.

Thioredoxin and its role in premature newborn biology

Thioredoxin (Trx) is a redox-active protein that has been shown to regulate various cellular processes due to its thiol-disulfide exchange reaction. It has antioxidant properties and also induces the expression of critical antioxidant enzymes such as manganese superoxide dismutase. Trx along with thioredoxin reductase and peroxiredoxins forms a complete system similar to the glutathione system, but with different and divergent functions. This review is a mini-update on key advances in the role of Trx in signal transduction and premature newborn biology. In addition, this mini-update also reviews recently reported prooxidant properties of Trx that relate to anthracycline redox cycling.

Developmental plasticity of the hypoxic ventilatory response after perinatal hyperoxia and hypoxia

Both genetic and environmental factors influence the normal development of the respiratory control system. This review examines the role perinatal O2 plays in the development of normoxic breathing and the hypoxic ventilatory response in mammals. Hyperoxia and hypoxia elicit plasticity in respiratory control that is unique to development and may persist weeks to years after return to normoxia. Specifically, both hyperoxia and hypoxia during early postnatal development attenuate the adult hypoxic ventilatory response, but the underlying mechanisms for this plasticity differ. Hyperoxia attenuates the hypoxic ventilatory response through potentially life-long changes in carotid body function. Neonatal hypoxia appears to have short-term effects on carotid body function, but persistent changes in the hypoxic ventilatory response may instead reflect changes in respiratory mechanics or related neural pathways. Overall, it appears that a relatively narrow range of environmental O2 is consistent with "normal" postnatal respiratory control development, predisposing animals to potentially maladaptive plasticity in the face of disease or atypical environmental conditions.

iNOS initiates and sustains metabolic arrest in hypoxic lung adenocarcinoma cells: mechanism of cell survival in solid tumor core

Nitric oxide (NO) modulates cellular metabolism by competitively inhibiting the reduction of O2 at respiratory complex IV. The aim of this study was to determine whether this effect could enhance cell survival in the hypoxic solid tumor core by inducing a state of metabolic arrest in cancer cells. Mitochondria from human alveolar type II-like adenocarcinoma (A549) cells showed a fourfold increase in NO-sensitive 4-amino-5-methylamino-2',7'-difluorofluorescein (DAF-FM) fluorescence and sixfold increase in Ca2+-insensitive NO synthase (NOS) activity during equilibration from Po2s of 100-->23 mmHg, which was abolished by N(omega)-nitro-L-arginine methyl ester-HCl (L-NAME) and the inducible NOS (iNOS) inhibitor, N6-(1-iminoethyl)-L-lysine dihydrochloride (L-NIL). Similarly, cytosolic and compartmented DAF-FM fluorescence increased in intact cells during a transition between ambient Po2 and 23 mmHg and was abolished by transfection with iNOS antisense oligonucleotides (AS-ODN). In parallel, mitochondrial membrane potential (deltapsi(m)), measured using 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolo-carbocyanine iodide (JC-1), decreased to a lower steady state in hypoxia without change in glycolytic rate, adenylate energy charge, or cell viability. However, L-NAME or iNOS AS-ODN treatment maintained deltapsi(m) at normoxic levels irrespective of hypoxia and caused a marked activation of glycolysis, destabilization energy charge, and cell death. Comparison with other cancer-derived (H441) or native tissue-derived (human bronchial epithelial; alveolar type II) lung epithelial cells revealed that the hypoxic suppression of deltapsi(m) was common to cells that expressed iNOS. The controlled dissipation of deltapsi(m), absence of an overt glycolytic activation, and conservation of viability suggest that A549 cells enter a state of metabolic suppression in hypoxia, which inherently depends on the activation of iNOS as Po2 falls.

Cobalt chloride, a hypoxia-mimicking agent, modulates redox status and functional parameters of cultured swine granulosa cells

Hypoxia occurs physiologically during ovarian follicle growth; this deprivation represents a triggering stimulus for the production of vascular endothelial growth factor (VEGF) by proliferating granulosa cells, which are mostly responsible for the growth of the follicle. Moreover, the steroidogenic activity of these cells ensures a receptive environment for the implantation and development of the early embryo. The present paper reports the adaptive response of swine granulosa cells to cobalt chloride (CoCl2), a chemical hypoxia-mimicking agent. The effects of the treatment were evaluated on cell proliferation, steroidogenesis and VEGF production. In addition, because mithocondrial reactive oxygen species (ROS) are possibly involved in O2 sensing, ROS levels and scavenging enzyme activity were investigated. In the present study, CoCl2 had no effect on progesterone production, although it significantly reduced oestradiol synthesis. The addition of CoCl2 to granulosa cell culture stimulated VEGF production and the generation of hydrogen peroxide. Chemical hypoxia had different effects on scavenger enzyme activities: the activity of superoxide dismutase was enhanced, that of peroxidase reduced and catalase activity was unaffected. The net result is a ‘pro-oxidant’ state, which appears to be possibly involved in the stimulation of VEGF production, thus inducing follicular angiogenesis.