Lower concentration of pulmonary hepatocyte growth factor is associated with more severe lung disease in preterm infants

Epigenetic scores derived in saliva are associated with gestational age at birth

BACKGROUND

Epigenetic scores (EpiScores), reflecting DNA methylation (DNAm)-based surrogates for complex traits, have been developed for multiple circulating proteins. EpiScores for pro-inflammatory proteins, such as C-reactive protein (DNAm CRP), are associated with brain health and cognition in adults and with inflammatory comorbidities of preterm birth in neonates. Social disadvantage can become embedded in child development through inflammation, and deprivation is overrepresented in preterm infants. We tested the hypotheses that preterm birth and socioeconomic status (SES) are associated with alterations in a set of EpiScores enriched for inflammation-associated proteins.

RESULTS

In total, 104 protein EpiScores were derived from saliva samples of 332 neonates born at gestational age (GA) 22.14 to 42.14 weeks. Saliva sampling was between 36.57 and 47.14 weeks. Forty-three (41%) EpiScores were associated with low GA at birth (standardised estimates |0.14 to 0.88|, Bonferroni-adjusted p-value < 8.3 × 10-3). These included EpiScores for chemokines, growth factors, proteins involved in neurogenesis and vascular development, cell membrane proteins and receptors, and other immune proteins. Three EpiScores were associated with SES, or the interaction between birth GA and SES: afamin, intercellular adhesion molecule 5, and hepatocyte growth factor-like protein (standardised estimates |0.06 to 0.13|, Bonferroni-adjusted p-value < 8.3 × 10-3). In a preterm subgroup (n = 217, median [range] GA 29.29 weeks [22.14 to 33.0 weeks]), SES-EpiScore associations did not remain statistically significant after adjustment for sepsis, bronchopulmonary dysplasia, necrotising enterocolitis, and histological chorioamnionitis.

CONCLUSIONS

Low birth GA is substantially associated with a set of EpiScores. The set was enriched for inflammatory proteins, providing new insights into immune dysregulation in preterm infants. SES had fewer associations with EpiScores; these tended to have small effect sizes and were not statistically significant after adjusting for inflammatory comorbidities. This suggests that inflammation is unlikely to be the primary axis through which SES becomes embedded in the development of preterm infants in the neonatal period.

Hedgehog-responsive PDGFRa(+) fibroblasts maintain a unique pool of alveolar epithelial progenitor cells during alveologenesis

The lung alveolus is lined with alveolar type 1 (AT1) and type 2 (AT2) epithelial cells. During alveologenesis, increasing demand associated with expanding alveolar numbers is met by proliferating progenitor AT2s (pAT2). Little information exists regarding the identity of this population and their niche microenvironment. We show that during alveologenesis, Hedgehog-responsive PDGFRa(+) progenitors (also known as SCMFs) are a source of secreted trophic molecules that maintain a unique pAT2 population. SCMFs are in turn maintained by TGFβ signaling. Compound inactivation of Alk5 TβR2 in SCMFs reduced their numbers and depleted the pAT2 pool without impacting differentiation of daughter cells. In lungs of preterm infants who died with bronchopulmonary dysplasia, PDGFRa is reduced and the number of proliferative AT2s is diminished, indicating that an evolutionarily conserved mechanism governs pAT2 behavior during alveologenesis. SCMFs are a transient cell population, active only during alveologenesis, making them a unique stage-specific niche mesodermal cell type in mammalian organs.

Patho-mechanisms of the origins of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) continues to be one of the most common complications of prematurity, despite significant advancement in neonatology over the last couple of decades. The new BPD is characterized histopathologically by impaired lung alveolarization and dysregulated vascularization. With the increased survival of extremely preterm infants, the risk for the development of BPD remains high, emphasizing the continued need to understand the patho-mechanisms that play a role in the development of this disease. This brief review summarizes recent advances in our understanding of the maldevelopment of the premature lung, highlighting recent research in pathways of oxidative stress-related lung injury, the role of placental insufficiency, growth factor signaling, the extracellular matrix, and microRNAs.

Hyperoxia-induced bronchopulmonary dysplasia: better models for better therapies

Bronchopulmonary dysplasia (BPD) is a chronic lung disease caused by exposure to high levels of oxygen (hyperoxia) and is the most common complication that affects preterm newborns. At present, there is no cure for BPD. Infants can recover from BPD; however, they will suffer from significant morbidity into adulthood in the form of neurodevelopmental impairment, asthma and emphysematous changes of the lung. The development of hyperoxia-induced lung injury models in small and large animals to test potential treatments for BPD has shown some success, yet a lack of standardization in approaches and methods makes clinical translation difficult. In vitro models have also been developed to investigate the molecular pathways altered during BPD and to address the pitfalls associated with animal models. Preclinical studies have investigated the efficacy of stem cell-based therapies to improve lung morphology after damage. However, variability regarding the type of animal model and duration of hyperoxia to elicit damage exists in the literature. These models should be further developed and standardized, to cover the degree and duration of hyperoxia, type of animal model, and lung injury endpoint, to improve their translational relevance. The purpose of this Review is to highlight concerns associated with current animal models of hyperoxia-induced BPD and to show the potential of in vitro models to complement in vivo studies in the significant improvement to our understanding of BPD pathogenesis and treatment. The status of current stem cell therapies for treatment of BPD is also discussed. We offer suggestions to optimize models and therapeutic modalities for treatment of hyperoxia-induced lung damage in order to advance the standardization of procedures for clinical translation.

Placental and Fetal Effects of Onartuzumab, a Met/HGF Signaling Antagonist, When Administered to Pregnant Cynomolgus Monkeys

Onartuzumab is an engineered single arm, monovalent monoclonal antibody that targets the MET receptor and prevents hepatocyte growth factor (HGF) signaling. Knockout mice have clearly demonstrated that HGF/MET signaling is developmentally critical. A pre- and postnatal development study (enhanced design) was conducted in cynomolgus monkeys to evaluate the potential developmental consequences following onartuzumab administration. Control or onartuzumab, at loading/maintenance doses of 75/50 mg/kg (low) or 100/100 mg/kg (high), was administered intravenously once weekly to 12 confirmed pregnant female cynomolgus monkeys per group from gestation day (GD) 20 through GD 174. Onartuzumab administration resulted in decreased gestation length, decreased birth weight, and increased fetal and perinatal mortality. A GD147 C-section was conducted for a subset of Control and High Dose monkeys, and identified placental infarcts with hemorrhage in the chorionic plate, chorionic villus and/or decidual plate. These findings were limited to placentas from onartuzumab-treated animals. In addition, decreased cellularity of the hepatocytes with dilated hepatic sinusoids was inconsistently observed in the liver of a few fetal or infant monkeys that died in the perinatal period. Surviving offspring had some evidence of developmental delay compared with controls, but no overt teratogenicity. Overall, effects on the perinatal fetuses were consistent with those reported in knockout mice, but not as severe. Onartuzumab concentrations were low or below the level of detection in most offspring, with cord blood concentrations only 1%-2% of maternal levels on GD 147. Malperfusion secondary to onartuzumab-induced placental injury could explain the adverse pregnancy outcomes, fetal growth restriction and relatively low fetal exposures.

Pulmonary pericytes regulate lung morphogenesis

Blood vessels are essential for blood circulation but also control organ growth, homeostasis, and regeneration, which has been attributed to the release of paracrine signals by endothelial cells. Endothelial tubules are associated with specialised mesenchymal cells, termed pericytes, which help to maintain vessel wall integrity. Here we identify pericytes as regulators of epithelial and endothelial morphogenesis in postnatal lung. Mice lacking expression of the Hippo pathway components YAP and TAZ in pericytes show defective alveologenesis. Mutant pericytes are present in normal numbers but display strongly reduced expression of hepatocyte growth factor leading to impaired activation of the c-Met receptor, which is expressed by alveolar epithelial cells. YAP and TAZ are also required for expression of angiopoietin-1 by pulmonary pericytes, which also controls hepatocyte growth factor expression and thereby alveologenesis in an autocrine fashion. These findings establish that pericytes have important, organ-specific signalling properties and coordinate the behavior of epithelial and vascular cells during lung morphogenesis.

Pericytes surround endothelial tubules and help maintain the integrity of blood vessels. Here the authors show that pericytes regulate lung morphogenesis via paracrine signalling controlled by components of the Hippo pathway.

Bridging Lung Development with Chronic Obstructive Pulmonary Disease. Relevance of Developmental Pathways in Chronic Obstructive Pulmonary Disease Pathogenesis

Chronic obstructive pulmonary disease (COPD) is characterized by chronic airflow limitation. This generic term encompasses emphysema and chronic bronchitis, two common conditions, each having distinct but also overlapping features. Recent epidemiological and experimental studies have challenged the traditional view that COPD is exclusively an adult disease occurring after years of inhalational insults to the lungs, pinpointing abnormalities or disruption of the pathways that control lung development as an important susceptibility factor for adult COPD. In addition, there is growing evidence that emphysema is not solely a destructive process because it is also characterized by a failure in cell and molecular maintenance programs necessary for proper lung development. This leads to the concept that tissue regeneration required stimulation of signaling pathways that normally operate during development. We undertook a review of the literature to outline the contribution of developmental insults and genes in the occurrence and pathogenesis of COPD, respectively.

Hepatocyte growth factor as a downstream mediator of vascular endothelial growth factor-dependent preservation of growth in the developing lung

Impaired vascular endothelial growth factor (VEGF) signaling contributes to the pathogenesis of bronchopulmonary dysplasia (BPD). We hypothesized that the effects of VEGF on lung structure during development may be mediated through its downstream effects on both endothelial nitric oxide synthase (eNOS) and hepatocyte growth factor (HGF) activity, and that, in the absence of eNOS, trophic effects of VEGF would be mediated through HGF signaling. To test this hypothesis, we performed an integrative series of in vitro (fetal rat lung explants and isolated fetal alveolar and endothelial cells) and in vivo studies with normal rat pups and eNOS(-/-) mice. Compared with controls, fetal lung explants from eNOS(-/-) mice had decreased terminal lung bud formation, which was restored with recombinant human VEGF (rhVEGF) treatment. Neonatal eNOS(-/-) mice were more susceptible to hyperoxia-induced inhibition of lung growth than controls, which was prevented with rhVEGF treatment. Fetal alveolar type II (AT2) cell proliferation was increased with rhVEGF treatment only with mesenchymal cell (MC) coculture, and these effects were attenuated with anti-HGF antibody treatment. Unlike VEGF, HGF directly stimulated isolated AT2 cells even without MC coculture. HGF directly stimulates fetal pulmonary artery endothelial cell growth and tube formation, which is attenuated by treatment with JNJ-38877605, a c-Met inhibitor. rHGF treatment preserves alveolar and vascular growth after postnatal exposure to SU-5416, a VEGF receptor inhibitor. We conclude that the effects of VEGF on AT2 and endothelial cells during lung development are partly mediated through HGF-c-Met signaling and speculate that reciprocal VEGF-HGF signaling between epithelia and endothelia is disrupted in infants who develop BPD.

Hepatocyte growth factor, a determinant of airspace homeostasis in the murine lung

The alveolar compartment, the fundamental gas exchange unit in the lung, is critical for tissue oxygenation and viability. We explored hepatocyte growth factor (HGF), a pleiotrophic cytokine that promotes epithelial proliferation, morphogenesis, migration, and resistance to apoptosis, as a candidate mediator of alveolar formation and regeneration. Mice deficient in the expression of the HGF receptor Met in lung epithelial cells demonstrated impaired airspace formation marked by a reduction in alveolar epithelial cell abundance and survival, truncation of the pulmonary vascular bed, and enhanced oxidative stress. Administration of recombinant HGF to tight-skin mice, an established genetic emphysema model, attenuated airspace enlargement and reduced oxidative stress. Repair in the TSK/+ mouse was punctuated by enhanced akt and stat3 activation. HGF treatment of an alveolar epithelial cell line not only induced proliferation and scattering of the cells but also conferred protection against staurosporine-induced apoptosis, properties critical for alveolar septation. HGF promoted cell survival was attenuated by akt inhibition. Primary alveolar epithelial cells treated with HGF showed improved survival and enhanced antioxidant production. In conclusion, using both loss-of-function and gain-of-function maneuvers, we show that HGF signaling is necessary for alveolar homeostasis in the developing lung and that augmentation of HGF signaling can improve airspace morphology in murine emphysema. Our studies converge on prosurvival signaling and antioxidant protection as critical pathways in HGF–mediated airspace maintenance or repair. These findings support the exploration of HGF signaling enhancement for diseases of the airspace.

The airspace compartment of the mammalian lung, comprised of spherical sacs termed alveoli, harbors the architecture, cellular composition, and molecular armamentarium to perform the critical function of gas exchange or oxygen uptake. Despite the necessity of this alveolar compartment for organismal viability, the mechanism by which alveoli are formed and maintained is obscure. Furthermore, no treatments are currently available that can regenerate the airspace once damaged. In this manuscript, we sought to determine whether hepatocyte growth factor, a cytokine with a functional armamentarium that subserves the critical events of alveolar formation (epithelial proliferation, migration, resistance from apoptosis and angiogenesis), could be an important mediator of alveolar formation and airspace maintenance. Our simple paradigm was that critical homeostatic pathways for the lung should operate both in lung formation and in lung maintenance/regeneration. Using an informative battery of mouse models and cell lines, we show that hepatocyte growth factor is a determinant of alveolar formation and that the enhancement of hepatocyte growth factor signaling can both protect and repair the airspace from pathologic airspace enlargement or emphysema.

Inhibition of apoptosis by 60% oxygen: a novel pathway contributing to lung injury in neonatal rats

During early postnatal alveolar formation, the lung tissue of rat pups undergoes a physiological remodeling involving apoptosis of distal lung cells. Exposure of neonatal rats to severe hyperoxia (≥95% O2) both arrests lung growth and results in increased lung cell apoptosis. In contrast, exposure to moderate hyperoxia (60% O2) for 14 days does not completely arrest lung cell proliferation and is associated with parenchymal thickening. On the basis of similarities in lung architecture observed following either exposure to 60% O2, or pharmacological inhibition of physiological apoptosis, we hypothesized that exposure to 60% O2 would result in an inhibition of physiological lung cell apoptosis. Consistent with this hypothesis, we observed that the parenchymal thickening induced by exposure to 60% O2 was associated with decreased numbers of apoptotic cells, increased expressions of the antiapoptotic regulator Bcl-xL, and the putative antiapoptotic protein survivin, and decreased expressions of the proapoptotic cleaved caspases-3 and -7. In summary, exposure of the neonatal rat lung to moderate hyperoxia results in an inhibition of physiological apoptosis, which contributes to the parenchymal thickening observed in the resultant lung injury.

Dexamethasone and betamethasone for prenatal lung maturation: differences in vascular endothelial growth factor expression and alveolarization in rats

BACKGROUND

Fetal and postnatal lung development is regulated by glucocorticoids. The use of antenatal corticosteroids is reported to produce effects on vascular endothelial growth factor (VEGF), which plays a crucial role in pulmonary development.

OBJECTIVES

The purpose of this study was to compare pulmonary VEGF expression in newborn rats that were exposed to antenatal betamethasone versus dexamethasone and to evaluate its impact on the alveolarization period of rats (0-14 days of life).

METHODS

Betamethasone, dexamethasone or equivalent saline solution (control group) was administered to pregnant rats on 20th and 21st days of gestation. Pulmonary VEGF mRNA, VEGF protein expression, and alveolarization changes were evaluated at birth and at 14 days of life.

RESULTS

Betamethasone and dexamethasone were observed to have different actions on VEGF expression with a correlation with alveolarization on both days of study. Antenatal dexamethasone decreased VEGF expression, betamethasone tended to produce the induction of the expression of VEGF, and moreover, betamethasone did not produce a decrease in alveolarization as seen in the animals that received dexamethasone.

CONCLUSIONS

Our results support the notion that betamethasone could be a better choice than dexamethasone for antenatal lung maturation.

A tandem repeat of a fragment of Listeria monocytogenes internalin B protein induces cell survival and proliferation

Hepatocyte growth factor (HGF) is critical for tissue homeostasis and repair in many organs including the lung, heart, kidney, liver, nervous system, and skin. HGF is a heterodimeric protein containing 20 disulfide bonds distributed among an amino-terminal hairpin, four kringle domains, and a serine protease-like domain. Due to its complex structure, recombinant production of HGF in prokaryotes requires denaturation and refolding, processes that are impractical for large-scale manufacture. Thus, pharmaceutical quantities of HGF are not available despite its potential applications. A fragment of the Listeria monocytogenes internalin B protein from amino acids 36-321 (InlB₃₆₋₃₂₁) was demonstrated to bind to and partially activate the HGF receptor Met. InlB₃₆₋₃₂₁ has a stable β-sheet structure and is easily produced in its native conformation by Escherichia coli. We cloned InlB₃₆₋₃₂₁ (1×InlB₃₆₋₃₂₁) and engineered a head-to-tail repeat of InlB₃₆₋₃₂₁ with a linker peptide (2×InlB₃₆₋₃₂₁); 1×InlB₃₆₋₃₂₁ and 2×InlB₃₆₋₃₂₁ were purified from E. coli. Both 1× and 2×InlB₃₆₋₃₂₁ activated the Met tyrosine kinase. We subsequently compared signal transduction of the two proteins in primary lung endothelial cells. 2×InlB₃₆₋₃₂₁ activated ERK1/2, STAT3, and phosphatidylinositol 3-kinase/Akt pathways, whereas 1×InlB₃₆₋₃₂₁ activated only STAT3 and ERK1/2. The 2×InlB₃₆₋₃₂₁ promoted improved motility compared with 1×InlB₃₆₋₃₂₁ and additionally stimulated proliferation equivalent to full-length HGF. Both the 1× and 2×InlB₃₆₋₃₂₁ prevented apoptosis by the profibrotic peptide angiotensin II in cell culture and ex vivo lung slice cultures. The ease of large-scale production and capacity of 2×InlB₃₆₋₃₂₁ to mimic HGF make it a potential candidate as a pharmaceutical agent for tissue repair.

High-mobility group box-1 protein in tracheal aspirates from premature infants: relationship with bronchopulmonary dysplasia and steroid therapy

OBJECTIVE

High-mobility group box-1 (HMGB1) is a potent inflammatory mediator and contributes to acute lung injury in adults. The role of HMGB1 in neonatal lung injury and the development of bronchopulmonary dysplasia (BPD) is unknown. We studied the association between HMGB1 levels in tracheal aspirates (TAs) and adverse outcomes (BPD/death) in ventilated premature infants (VPIs) and modulation of HMGB1 levels with dexamethasone (Dex) use.

STUDY DESIGN

Infants born before 32 weeks gestation and requiring mechanical ventilation were enrolled. Serial TA samples were collected on days 1, 3, 5 and 7 and HMGB1 levels were measured. HMGB1 levels in TA samples were compared between infants with no BPD and infants who developed BPD or died. HMGB1 TA levels were also compared before and after using Dex.

RESULT

In all, 24 infants (gestational age 26.4+/-1.9 weeks, birth weight 859+/-200 g) had no BPD, 60 infants (gestational age 25.4+/-1.8 weeks, birth weight 749+/-156 g) developed BPD or died before 36 weeks postmenstrual age. Mean HMGB1 level in first week of life was significantly lower in infants with no BPD (27.3+/-16.5 ng mg(-1)) compared with those who developed BPD or died (45.1+/-30.9 ng mg(-1), P=0.004). In total, 29 VPIs received Dex. There was no significant change in HMGB1 levels with steroid therapy (before 47.0+/-43.9, after 60.1.5+/-58.8, P=0.3).

CONCLUSION

Our data suggest that higher HMGB1 levels in TA are associated with the development of BPD or death in VPI. Dex use had no effect on HMGB1 levels.

Hyperoxia-derived lung damage in preterm infants

Hyperoxia-induced lung injury is characterized by an influx of inflammatory cells, increased pulmonary permeability, endothelial and epithelial cell death. This review highlights the mechanistic aspects of inflammation, vascular leak and cell death. The focus will be on agents that contribute to hyperoxia-induced lung injury in developmentally appropriate animal models, and those that have been detected in human premature neonates.

Pitfalls, problems, and progress in bronchopulmonary dysplasia

Bronchopulmonary dysplasia is a chronic lung disease associated with premature birth and characterized by early lung injury. In this review we discuss some pitfalls, problems, and progress in this condition over the last decade, focusing mainly on the last 5 years, limited to studies in human neonates. Changes in the definition, pathogenesis, genetic susceptibility, and recent biomarkers associated with bronchopulmonary dysplasia will be discussed. Progress in current management strategies, along with novel approaches/therapies, will be critically appraised. Finally, recent data on long-term pulmonary and neurodevelopmental outcomes of infants with bronchopulmonary dysplasia will be summarized.

Pulmonary Biomarkers of Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia, or BPD, is a chronic pulmonary disorder of premature infants, commonly defined as having an oxygen requirement at 36 weeks postmenstrual age. It is an important source of morbidity and mortality in premature neonates. Its' etiology appears to be multifactorial with the most common associations being prematurity, need for mechanical ventilation, and oxygen exposure. Implied in the pathogenesis of BPD is the role of cytokines which are immune mediators produced by most cell types. This is evidenced by studies in which there exist alterations in the levels of "pro-inflammatory" and "anti-inflammatory" cytokines. The imbalance of these cytokines have either heralded the onset or predicted the presence of BPD, or indicated a decreased propensity to developing this chronic respiratory disorder of preterm infants. Many other pulmonary markers have been shown to be altered in patients with BPD. These include markers indicative of altered lung repair processes, decreased endothelial integrity, oxidative damage and abnormal fibrinolytic activity, all of which are thought to be mechanisms contributing to the development of BPD.In this review, we will discuss the physiologic role of specific biomarkers in the pulmonary tract of the human premature neonate, the perturbations that enable them to be deranged, and their proposed association with BPD.

Angiopoietin 2 concentrations in infants developing bronchopulmonary dysplasia: attenuation by dexamethasone

OBJECTIVES

To study the association between angiopoietin 2 (Ang2) concentrations in tracheal aspirates (TAs) and adverse outcome (bronchopulmonary dysplasia (BPD)/death) in ventilated premature infants (VPIs) and modulation of Ang2 concentrations with dexamethasone (Dex) use.

STUDY DESIGN

Serial TA samples were collected on days 1, 3, 5 and 7, and Ang2 concentrations were measured. Ang2 TA concentrations were compared prior to and after 48 to 72 h of using Dex.

RESULT

A total of 151 TA samples were collected from 60 VPIs. BPD was defined as the oxygen requirement at 36 weeks postmenstrual age (PMA). Twelve infants (mean+/-s.d.) (gestational age (GA) 26.5+/-2.1 weeks, birth weight (BW) 913+/-230 g) had no BPD, 32 infants (GA 25.8+/-1.4 weeks, BW 768+/-157 g) developed BPD and 16 infants (GA 24.5+/-1.1 weeks, BW 710+/-143 g) died before 36 weeks PMA. Ang2 concentrations were significantly lower in infants with no BPD (median, 25th and 75th percentile) (157, 16 and 218 pg mg(-1)) compared with those who developed BPD (234, 138 and 338 pg mg(-1), P=0.03) or BPD and/or death (234, 157 and 347 pg mg(-1), P=0.017), in the first week of life. Twenty-six VPIs (BW 719+/-136 g, GA 25.1+/-1.3 weeks) received 27 courses of Dex. Ang2 concentrations before starting Dex were 202, 137 and 278 pg mg(-1) and significantly decreased to 144, 0 and 224 pg mg(-1) after therapy (P=0.007).

CONCLUSIONS

Higher Ang2 concentrations in TAs are associated with the development of BPD or death in VPIs. Dex use suppressed Ang2 concentrations.

Inflammation and bronchopulmonary dysplasia: a continuing story

Increasing evidence indicates that bronchopulmonary dysplasia (BPD) results, at least in part, from an imbalance between pro-inflammatory and anti-inflammatory mechanisms, with a persistent imbalance that favours pro-inflammatory mechanisms. The inflammatory response is characterised by an accumulation of neutrophils and macrophages in the airways and pulmonary tissue of preterm infants and, moreover, by an arsenal of pro-inflammatory mediators which affect the alveolar capillary unit and tissue integrity. As well as pro-inflammatory cytokines and toxic oxygen radicals, various lipid mediators as well as potent proteases may be responsible for acute lung injury. During the last decade it has become evident that multiple pre- and postnatal events contribute to the development of BPD in preterm infants. Chorioamnionitis and cytokine exposure in utero, plus sequential lung injury caused by postnatal resuscitation, oxygen toxicity, volu-, barotrauma and infection all lead to a pulmonary inflammatory response which is most probably associated with aberrant wound healing and an inhibition of alveolarisation as well as vascular development in the immature lungs of very preterm infants, causing the 'new BPD'.

Consistent Expression of HGF and c-met in the Perinatal Lung

BACKGROUND

Hepatocyte growth factor (HGF), an epithelial cell mitogen, has been shown to participate in normal lung development and in regeneration after lung injury. In human preterm infants, lower pulmonary HGF has been associated with more severe respiratory disease.

OBJECTIVES

We studied the protein expression of HGF and its receptor c-met during the perinatal period in the human lung.

METHODS

Immunohistochemistry for HGF and c-met was performed on lung tissues from autopsies of 4 fetuses, 5 preterm infants, 5 term infants, and 4 infants with bronchopulmonary dysplasia.

RESULTS

Immunohistochemistry for HGF showed staining in all cases in mesenchymal cells (fibroblasts and cartilage cells). Additional staining was found in bronchial and distal airway epithelium. Immunohistochemistry for c-met showed staining in bronchial and distal airway epithelium, and in most cases in neutrophils.

CONCLUSIONS

The consistent expression of HGF and c-met during the perinatal period supports a physiological role for HGF in human lung development.

Pulmonary inflammation and bronchopulmonary dysplasia

Various pre- and postnatal risk factors, which act additively or synergistically induce an injurious inflammatory response in the airways and the pulmonary interstitium of preterm infants with bronchopulmonary dysplasia. This inflammatory response is characterized by an accumulation of neutrophils and macrophages as well as an arsenal of proinflammatory mediators that affect the endothelium and alveolar-capillary integrity. Besides proinflammatory cytokines and toxic oxygen radicals, lipid mediators as well as potent proteases may be responsible for acute lung injury. There is increasing evidence that an imbalance between pro- and anti-inflammatory factors, which should protect the alveoli and lung tissue, are key features in the pathogenesis of bronchopulmonary dysplasia. In addition, a subnormal generation of growth factors may affect alveolarization and vascular development in preterm infants with bronchopulmonary dysplasia. In this condensed review article, the current concepts on the possible role of inflammation in the evolution of bronchopulmonary dysplasia will be summarized.

Hepatocyte growth factor is required for alveologenesis in the neonatal rat

RATIONALE

Our core hypothesis is that growth factors that have dysregulated expression during experimental neonatal lung injury are likely to be involved in normal postnatal lung growth and alveologenesis.

OBJECTIVES

To determine if hepatocyte growth factor (HGF) is upregulated in neonatal lung injury and is essential for postnatal alveologenesis.

METHODS

A neonatal lung injury, in which there were patchy areas of interstitial thickening with a relative increase in the proportion of epithelial cells, was induced in newborn rats by exposing them to 60% oxygen for 14 days. Air-exposed pups had binding of endogenous HGF to its natural receptor, c-Met, inhibited by the intraperitoneal injection of either neutralizing antibody to HGF, or a truncated soluble c-Met receptor.

MEASUREMENTS AND MAIN RESULTS

The 60% oxygen-mediated lung injury was associated with increased lung mRNAs for hepatocyte growth factor and c-Met, relative to air-exposed control lungs, at Day 7 after birth. After exposure to 60% oxygen, immunoreactive HGF was increased at Days 4 and 7, and immunoreactive c-Met was increased at Day 14. In air-exposed pups, intraperitoneal injections of neutralizing antibody to HGF inhibited DNA synthesis in alveoli-forming secondary crests, and reduced the number of alveoli in 6-day-old pups. Intraperitoneal injections of a truncated soluble c-Met receptor inhibited DNA synthesis in secondary crests in 4-day-old air-exposed rat pups.

CONCLUSIONS

HGF and its c-Met receptor are required for normal postnatal alveolar formation from secondary crests, and are upregulated during 60% oxygen-induced neonatal lung injury.