Genetic disorders of neonatal respiratory function

Postnatal hypoxic preconditioning attenuates lung damage from hyperoxia in newborn mice

BACKGROUND

Preterm infants frequently require oxygen supplementation at birth. However, preterm lung is especially sensible to structural and functional damage caused by oxygen free radicals.

METHODS

The adaptive mechanisms implied in the fetal-neonatal transition from a lower to a higher oxygen environment were evaluated in a murine model using a custom-designed oxy-chamber. Pregnant mice were randomly assigned to deliver in 14% (hypoxic preconditioning group) or 21% (normoxic group) oxygen environment. Eight hours after birth FiO2 was increased to 100% for 60 min and then switched to 21% in both groups. A control group remained in 21% oxygen throughout the study.

RESULTS

Mice in the normoxic group exhibited thinning of the alveolar septa, increased cell death, increased vascular damage, and decreased synthesis of pulmonary surfactant. However, lung histology, lamellar bodies microstructure, and surfactant integrity were preserved in the hypoxic preconditioning group after the hyperoxic insult.

CONCLUSION

Postnatal hyperoxia has detrimental effects on lung structure and function when preceded by normoxia compared to controls. However, postnatal hypoxic preconditioning mitigates lung damage caused by a hyperoxic insult.

IMPACT

Hypoxic preconditioning, implemented shortly after birth mitigates lung damage caused by postnatal supplemental oxygenation. The study introduces an experimental mice model to investigate the effects of hypoxic preconditioning and its effects on lung development. This model enables researchers to delve into the intricate processes involved in postnatal lung maturation. Our findings suggest that hypoxic preconditioning may reduce lung parenchymal damage and increase pulmonary surfactant synthesis in reoxygenation strategies during postnatal care.

Association of Fetal Lung Development Disorders with Adult Diseases: A Comprehensive Review

Fetal lung development is a crucial and complex process that lays the groundwork for postnatal respiratory health. However, disruptions in this delicate developmental journey can lead to fetal lung development disorders, impacting neonatal outcomes and potentially influencing health outcomes well into adulthood. Recent research has shed light on the intriguing association between fetal lung development disorders and the development of adult diseases. Understanding these links can provide valuable insights into the developmental origins of health and disease, paving the way for targeted preventive measures and clinical interventions. This review article aims to comprehensively explore the association of fetal lung development disorders with adult diseases. We delve into the stages of fetal lung development, examining key factors influencing fetal lung maturation. Subsequently, we investigate specific fetal lung development disorders, such as respiratory distress syndrome (RDS), bronchopulmonary dysplasia (BPD), congenital diaphragmatic hernia (CDH), and other abnormalities. Furthermore, we explore the potential mechanisms underlying these associations, considering the role of epigenetic modifications, transgenerational effects, and intrauterine environmental factors. Additionally, we examine the epidemiological evidence and clinical findings linking fetal lung development disorders to adult respiratory diseases, including asthma, chronic obstructive pulmonary disease (COPD), and other respiratory ailments. This review provides valuable insights for healthcare professionals and researchers, guiding future investigations and shaping strategies for preventive interventions and long-term care.

Natural Versus Synthetic Surfactant Therapy in Respiratory Distress Syndrome of Prematurity

OBJECTIVES

To compare the clinical efficacy and the cost of treatment between the newborns who received either a natural or a protein-free synthetic surfactant for respiratory distress syndrome (RDS) of prematurity.

METHODS

This is a retrospective analytical study incorporating comparisons of clinical parameters and cost in newborns having RDS of prematurity who received either Survanta (bovine lung extract), a natural surfactant or Surfact (protein-free colfosceril palmitate), a synthetic surfactant.

RESULTS

There were 100 newborns who received either of the natural (n = 52) or synthetic (n = 48) surfactant with mean (SD) gestational age and mean (SD) birth weight of 31.5 (2.6) wk, 1425 (461) g and 32.2 (2.2) wk, 1519 (413) g, respectively. Majority of the newborns (> 90%) received endotracheal surfactant within the first 24 h of life and had similar baseline characteristics in either group. No differences were noted in ventilator settings on admission and 24 h after surfactant/admission. Oxygen requirement, extubation age, complications, hospital stay, and mortality were similar across groups, except that the necrotizing enterocolitis was noted only in natural surfactant group. There was a significant pharmacy cost savings in synthetic surfactant group.

CONCLUSION

Synthetic surfactant was comparable to natural surfactant with regard to outcomes, like ventilator settings, hospital stay, and mortality. Pharmacy cost was less in synthetic surfactant group.

The utility of pregnancy associated plasma protein-A MoM values in prediction of term respiratory distress syndrome

This study aimed to investigate if the pregnancy associated plasma Protein-A (PAPP-A) multiples of median (MoM) levels could be used as a marker for the early prediction of RDS. The present study was designed with data gathered from 1773 patients who were referred to our institution for first trimester fetal chromosomal anomaly screening. First trimester PAPP-A MoM values and postnatal RDS occurrences in these pregnancies were retrospectively analysed. Of the 1773 neonates that were included in the study, 28 were delivered at or beyond 37 weeks, and 42 were delivered less than 37 weeks of gestation. In the group of neonates at or beyond 37 weeks, the cut-off value for RDS prediction was determined as 1.02. For this cut-off value, sensitivity was 72.41% and specificity was 91.84%. The area under curve (AUC) was determined to be statistically significant (p < .01). In conclusion, it was determined that in neonates that were delivered at or beyond 37 weeks of gestation, RDS occurrence could be predicted at a significant rate by utilising PAPP-A MoM values.IMPACT STATEMENTWhat is already known on this subject? Respiratory distress syndrome (RDS) is one of the major global healthcare problems, and continues to effect newborns despite the improvements in diagnosis and treatments of the disease. Studies have shown that pregnancy associated plasma protein-A (PAPP-A) has a critical role in cellular proliferation and differentiation, and it is closely associated with many physiological and pathological processes via regulation of local insulin like growth factor (IGF) concentrations. In majority of the past studies in the literature regarding PAPP-A values in pregnancies, the association between low values of PAPP-A MoM and maternal-fetal complications were investigated.What do the results of this study add? This study retrospectively examines the PAPP-A MoM levels and the occurence of RDS. In neonates that were delivered at or beyond 37 weeks of gestation, RDS occurrence could be predicted at a significant rate by utilising PAPP-A MoM values which was measured at the first trimester fetal anomaly screening test.What are the implications of these findings for clinical practice and/or further research? In the light of these findings, in order to reduce RDS related neonatal morbidity and mortality, pregnancies with PAPP-A MoM values greater than 1.02 at the first trimester fetal anomaly screening should be more closely followed up and a higher rate of suspicion should be kept for RDS occurrence.

Genetic risk factors associated with respiratory distress syndrome

Respiratory distress syndrome (RDS) among preterm infants is typically due to a quantitative deficiency of pulmonary surfactant. Aside from the degree of prematurity, diverse environmental and genetic factors can affect the development of RDS. The variance of the risk of RDS in various races/ethnicities or monozygotic/dizygotic twins has suggested genetic influences on this disorder. So far, several specific mutations in genes encoding surfactant-associated molecules have confirmed this. Specific genetic variants contributing to the regulation of pulmonary development, its structure and function, or the inflammatory response could be candidate risk factors for the development of RDS. This review summarizes the background that suggests the genetic predisposition of RDS, the identified mutations, and candidate genetic polymorphisms of pulmonary surfactant proteins associated with RDS.

Lucinactant for the prevention of respiratory distress syndrome in premature infants

Respiratory distress syndrome (RDS) is the leading cause of neonatal morbidity and mortality in premature infants. It is caused by surfactant deficiency and lung immaturity. Lucinactant is a synthetic surfactant containing sinapultide, a bioengineered peptide mimic of surfactant-associated protein B. A meta-analysis of clinical trials demonstrates that lucinactant is as effective as animal-derived surfactants in preventing RDS in premature neonates, and in vitro studies suggest it is more resistant to oxidative and protein-induced inactivation. Its synthetic origin confers lower infection and inflammation risks as well other potential benefits, which may make lucinactant an advantageous alternative to its animal-derived counterparts, which are presently the standard treatment for RDS.

Interstitial lung disease in two brothers with novel compound heterozygous ABCA3 mutations

Mutations in genes critical for surfactant metabolism, including surfactant protein C (SP-C) and ABCA3, are well-recognized causes of interstitial lung disease. Recessive mutations in ABCA3 were first attributed to fatal respiratory failure in full-term neonates, but they are also increasingly being recognized as a cause of respiratory disorders with less severe phenotypes in older children and also adults. Here, we report a 20-month-old boy with interstitial lung disease caused by two distinct ABCA3 mutations. Initial treatment with methylprednisolone was unsuccessful, but the additional administration of hydroxychloroquine was effective. The family history revealed that the patient's older brother had died of idiopathic interstitial lung disease at 6 months of age, suggesting a genetic etiology of the disease. Sequence analyses of SP-C and ABCA3 genes were performed using DNA samples from the patient himself, his parents, and his brother. These analyses revealed novel compound heterozygous mutations in the coding exons of ABCA3 in both the patient and his brother: c.2741A > G, of paternal origin, and c.3715_3716insGGGGGG, of maternal origin. Conclusion Since ABCA3 mutations seem to be a heterogeneous entity with various phenotypes, we recommend genetic testing for mutations in SP-C and ABCA3 genes to be considered in children with unexplained interstitial lung disease.

Disruption of sorting nexin 5 causes respiratory failure associated with undifferentiated alveolar epithelial type I cells in mice

Sorting nexin 5 (Snx5) has been posited to regulate the degradation of epidermal growth factor receptor and the retrograde trafficking of cation-independent mannose 6-phosphate receptor/insulin-like growth factor II receptor. Snx5 has also been suggested to interact with Mind bomb-1, an E3 ubiquitin ligase that regulates the activation of Notch signaling. However, the in vivo functions of Snx5 are largely unknown. Here, we report that disruption of the Snx5 gene in mice (Snx5^-/- mice) resulted in partial perinatal lethality; 40% of Snx5^-/- mice died shortly after birth due to cyanosis, reduced air space in the lungs, and respiratory failure. Histological analysis revealed that Snx5^-/- mice exhibited thickened alveolar walls associated with undifferentiated alveolar epithelial type I cells. In contrast, alveolar epithelial type II cells were intact, exhibiting normal surfactant synthesis and secretion. Although the expression levels of surfactant proteins and saturated phosphatidylcholine in the lungs of Snx5^-/- mice were comparable to those of Snx5^+/+ mice, the expression levels of T1α, Aqp5, and Rage, markers for distal alveolar epithelial type I cells, were significantly decreased in Snx5^-/- mice. These results demonstrate that Snx5 is necessary for the differentiation of alveolar epithelial type I cells, which may underlie the adaptation to air breathing at birth.

A pharmacoeconomic analysis of in-hospital costs resulting from reintubation in preterm infants treated with lucinactant, beractant, or poractant alfa

OBJECTIVES

Reintubation and subsequent mechanical ventilation (MV) in preterm infants after surfactant replacement therapy are associated with excess morbidity and mortality and likely increase in-hospital costs. Specific surfactant therapy selection for prevention of respiratory distress syndrome (RDS) in preterm infants receiving conventional MV may impact not only clinical outcomes but also pharmacoeconomic outcomes.

METHODS

We conducted a pharmacoeconomic analysis of the impact of surfactant selection and reintubation and subsequent MV of preterm infants on health care resource utilization. Rates of reintubation and duration of MV after reintubation were determined from 1546 preterm infants enrolled in two surfactant trials comparing lucinactant to beractant and poractant alfa. Hospital costs were obtained from a 2010 US database from 1564 preterm infants with RDS, with a direct cost of $2637 per day for MV in the neonatal intensive care unit. Cost of reintubation by study and treatment was estimated as the incidence of reintubation multiplied by days on MV therapy after reintubation multiplied by cost per day for direct MV costs, standardized per 100 surfactant-treated infants.

RESULTS

There were no differences between studies or treatment groups in the overall extubation rate. Average MV duration following reintubation was similar between groups in both trials; however, reintubation rates were significantly lower (p<0 05) for infants treated with lucinactant than for those receiving beractant or poractant alfa. The observed differences in reintubation rates resulted in a projected cost saving of $160,013 to $252,203 per 100 infants treated with lucinactant versus animal-derived surfactants.

CONCLUSIONS

In this analysis, higher reintubation rates following successful extubation in preterm infants receiving animal-derived surfactant preparations significantly increased estimated in-hospital costs, primarily due to excess costs associated with MV. This analysis suggests that surfactant selection may have a significant pharmacoeconomic impact on cost of patient care. Additional cost assessment of potential reduction in reintubation-associated morbidity is warranted.

A pilot, randomized, controlled clinical trial of lucinactant, a peptide-containing synthetic surfactant, in infants with acute hypoxemic respiratory failure

OBJECTIVE

Inhibition of surfactant function and abnormal surfactant synthesis lead to surfactant dysfunction in children with acute hypoxemic respiratory failure. We evaluated whether intratracheal lucinactant, a synthetic, peptide-containing surfactant, was safe and well-tolerated in infants with acute hypoxemic respiratory failure, and assessed its effects on clinical outcomes.

METHODS AND MAIN RESULTS

Infants ≤ 2 yrs of age with acute hypoxemic respiratory failure were enrolled in a phase II, double-blind, multinational, placebo-controlled randomized trial across 36 pediatric intensive care units. Infants requiring mechanical ventilation with persistent hypoxemia meeting acute lung injury criteria were randomized to receive intratracheal lucinactant (175 mg/kg) or air placebo. One retreatment was allowed 12-24 hrs after initial dosing if hypoxemia persisted. Peri-dosing tolerability of intratracheal lucinactant and adverse experiences were assessed. Mechanical ventilation duration was analyzed using analysis of variance. The Cochran-Mantel-Haenszel test was used for categorical variables.We enrolled 165 infants (84 lucinactant; 81 placebo) with acute hypoxemic respiratory failure. There were no significant differences in baseline subject characteristics, with the exception of a lower positive end-expiratory pressure and higher tidal volume in placebo subjects. The incidence of transient peri-dosing bradycardia and desaturation was significantly higher in the lucinactant treatment group. There were no statistical differences between groups for other adverse events or mortality. Oxygenation improved in infants randomized to receive lucinactant as indicated by fewer second treatments (67% lucinactant vs. 81% placebo, p = .02) and a trend in improvement in partial pressure of oxygen in arterial blood to fraction of inspired oxygen from eligibility to 48 hrs after dose (p = .06). There was no significant reduction in duration of mechanical ventilation with lucinactant (geometric least square means: 4.0 days lucinactant vs. 4.5 days placebo; p = .254). In a subset of infants (n = 22), the duration of mechanical ventilation in children with acute lung injury (partial pressure of oxygen in arterial blood to fraction of inspired oxygen >200) was significantly shorter with lucinactant (least square means: 2.4 days lucinactant vs. 4.3 days placebo; p = .006).

CONCLUSIONS

In mechanically ventilated infants with acute hypoxemic respiratory failure, treatment with intratracheal lucinactant appeared to be generally safe. An improvement in oxygenation and a significantly reduced requirement for retreatment suggests that lucinactant might improve lung function in infants with acute hypoxemic respiratory failure.

Surfactant protein C gene (SFTPC) mutation-associated lung disease: high-resolution computed tomography (HRCT) findings and its relation to histological analysis

AIM OF THE STUDY

Determine high-resolution tomography (HRCT) scan characteristics in children with SFTPC mutation and correlate them to histological findings.

PATIENTS AND METHODS

This retrospective multicenter study included 15 children (7 females and 8 males) with SFTPC mutations. HRCT scans have been performed in all the children and lung biopsies in 8 children.

RESULTS

From all signs assessed on initial HRCT scans, ground-glass opacities (n =14, 93%) and lung cysts (n = 6, 40%) were predominant. Interlobular septal thickening (n = 1, 7%), air space consolidation (n = 1, 7%), paraseptal emphysema (n = 2, 13%), and pulmonary nodules (n = 1, 7%) were also found. Histological analysis revealed accumulation of macrophages in the alveolar lumen, type II pneumocyte hyperplasia, and alveolar septal thickening. Dilatation of the respiratory bronchiole and alveolar duct associated with muscular hyperplasia were also described. Interestingly, lung cysts on HRCT scans were associated with dilatation of terminal bronchioli and alveolar duct in lung biopsies.

CONCLUSION

In children with SFTPC mutations, HRCT scan finding was highly correlated to the histological findings and, as such, represent a useful tool to identify patients that may require SFTPC gene sequencing.

Clinical and genetic aspects of primary ciliary dyskinesia/Kartagener syndrome

Primary ciliary dyskinesia is a genetically heterogeneous disorder of motile cilia. Most of the disease-causing mutations identified to date involve the heavy (dynein axonemal heavy chain 5) or intermediate(dynein axonemal intermediate chain 1) chain dynein genes in ciliary outer dynein arms, although a few mutations have been noted in other genes. Clinical molecular genetic testing for primary ciliary dyskinesia is available for the most common mutations. The respiratory manifestations of primary ciliary dyskinesia (chronic bronchitis leading to bronchiectasis, chronic rhino-sinusitis, and chronic otitis media)reflect impaired mucociliary clearance owing to defective axonemal structure. Ciliary ultrastructural analysis in most patients (>80%) reveals defective dynein arms, although defects in other axonemal components have also been observed. Approximately 50% of patients with primary ciliary dyskinesia have laterality defects (including situs inversus totalis and, less commonly, heterotaxy, and congenital heart disease),reflecting dysfunction of embryological nodal cilia. Male infertility is common and reflects defects in sperm tail axonemes. Most patients with primary ciliary dyskinesia have a history of neonatal respiratory distress, suggesting that motile cilia play a role in fluid clearance during the transition from a fetal to neonatal lung. Ciliopathies involving sensory cilia, including autosomal dominant or recessive polycystic kidney disease, Bardet-Biedl syndrome, and Alstrom syndrome, may have chronic respiratory symptoms and even bronchiectasis suggesting clinical overlap with primary ciliary dyskinesia.

Interpreting neonatal lethal phenotypes in mouse mutants: insights into gene function and human diseases

The mouse represents the model of choice to study the biological function of mammalian genes through mutation of its genome. However, the biggest challenge of mouse geneticists remains the phenotypic analysis of mouse mutants. A survey of mouse mutant databases reveals a surprisingly high number of gene mutations leading to neonatal death. These genetically modified mouse mutants have been instrumental in elucidating gene function and have become important models of congenital human diseases. The main complication when phenotyping mutant mice dying during the neonatal period is the large spectrum of physiological systems whose defects can challenge neonatal survival. Here, we present a comprehensive review of gene mutations leading to neonatal lethality and discuss the impact of these mutations on the major physiological processes critical to mouse newborn survival: parturition, breathing, suckling, and homeostasis. Selected examples of mouse mutants are highlighted to illustrate how the precise identification of the timing and cause of death associated with these physiological processes allows for a more profound understanding of the underlying cellular and molecular defects. This review provides a guide for the analysis of neonatal lethal phenotypes in mutant mice that will be helpful for dissecting out the function of specific genes during mouse development.

Review: Surfactant respiratory therapy using Surfaxin/sinapultide

Respiratory distress syndrome (RDS) is a leading cause of mortality and morbidity in preterm infants. Surfactant replacement therapy has been widely used to prevent and treat RDS in these newborns and has now become a standard of care. First-generation synthetic surfactants such as Exosurf did not contain any surfactant protein. This disadvantage was overcome with animal-derived surfactant preparations which contain specific proteins but has the limitation of being derived from animal sources. This has led to development of newer synthetic surfactants such as lucinactant (Surfaxin, Discovery Laboratories, Philadelphia) which contains the protein B mimic synthetic peptide, sinapultide. Recent phase 3 clinical trials with Surfaxin show promising results with similar efficacy as animal derived surfactants and yet avoiding the disadvantage associated with animal products. The purpose of this paper is to summarise results of recent clinical trials of Surfaxin use in newborns with RDS.

Dysplasia: a review

Bronchopulmonary dysplasia (BPD) is a common perinatal complication of very low birth weight preterm infants with a significant risk of long-term disability and morbidity. While clinical conditions such as prematurity and mechanical ventilation are its major risk factors, studies suggest that there is an individual susceptibility to BPD. This comprehensive review summarizes data collected about the implication of genetic polymorphisms in BPD and in its risk factors. Some studies have directly related the risk of BPD to genotype. Indeed, carrier states of genetic variants of cytokines (IFNgamma T+874A), adhesion molecules (L-selectin-Pro213Ser), elements of renin-angiotensin system (ACE-I/D), antioxidant enzymes (GST-P1 Val105Ile), and surfactant proteins (SPA1, SPB intron 4) has been identified as risk factors to BPD. Other studies investigated the role of genotype in BPD risk factors. Premature birth has been linked to carrier states of genetic variants with an impact on immune status (such as IL-6 G(-174)C, MBL2 54G/A, VEGF G+405C, HSP72 A+1267G genes) and matrix metalloproteases. Fetal inflammatory response syndrome, a major determinant of BPD is also affected by genotype (including LTalpha A+250G). Disturbed intrauterine lung development and vascularization may also contribute to BPD; these processes may be impaired in the presence of some rare genetic mutations. Furthermore, there is also a genetic component in the susceptibility to other perinatal adaptational disturbances such as respiratory distress syndrome that are associated with an increased need for mechanical ventilation, and, hence, with lung damage. The genetic variants presented in this article may help to identify infants at risk for BPD.

Comparison of surfactant protein B polymorphisms of healthy term newborns with preterm newborns having respiratory distress syndrome

Polymorphisms and mutations in the surfactant protein B (SP-B) gene have been associated with the pathogenesis of respiratory distress syndrome (RDS). The objective of the present study was to compare the frequencies of SP-B gene polymorphisms between preterm babies with RDS and healthy term newborns. We studied 50 preterm babies with RDS (inclusion criteria - newborns with RDS and gestational age between 28 and 33 weeks and 6 days), and 100 healthy term newborns. Four SP-B gene polymorphisms were analyzed: A/C at nucleotide -18, C/T at nucleotide 1580, A/G at nucleotide 9306, and G/C at nucleotide 8714, by PCR amplification of genomic DNA and genotyping by cRFLP. The healthy newborns comprised 42 female and 58 male neonates; 39 were white and 61 non-white. The RDS group comprised 21 female and 29 male preterm neonates; 28 were white and 22 non-white. Weight ranged from 640 to 2080 g (mean: 1273 g); mean gestational age was 31 weeks and 2 days (range: 28-33 weeks and 6 days). When white children were analyzed separately, a statistically significant difference in the G/C polymorphism at 8714 was observed between groups (P = 0.028). All other genotype frequencies were similar for both groups when sex and race were analyzed together. Analysis of the SP-B polymorphism G/C at nucleotide 8714 showed that among white neonates the GG genotype was found only in the RDS group at a frequency of 17% and the GC genotype was more frequently found in healthy term newborns. These data demonstrate an association of GG genotype with RDS.

The importance of surfactant on the development of neonatal pulmonary diseases

Pulmonary surfactant is a substance composed of a lipoprotein complex that is essential to pulmonary function. Pulmonary surfactant proteins play an important role in the structure, function, and metabolism of surfactant; 4 specific surfactant proteins have been identified: surfactant proteins-A, surfactant proteins-B, surfactant proteins-C, and surfactant proteins-D. Clinical, epidemiological, and biochemical evidence suggests that the etiology of respiratory distress syndrome is multifactorial with a significant genetic component. There are reports about polymorphisms and mutations on the surfactant protein genes, especially surfactant proteins-B, that may be associated with respiratory distress syndrome, acute respiratory distress syndrome, and congenital alveolar proteinosis. Individual differences regarding respiratory distress syndrome and acute respiratory distress syndrome as well as patient response to therapy might reflect phenotypic diversity due to genetic variation, in part. The study of the differences between the allelic variants of the surfactant protein genes can contribute to the understanding of individual susceptibility to the development of several pulmonary diseases. The identification of the polymorphisms and mutations that are indeed important for the pathogenesis of the diseases related to surfactant protein dysfunction, leading to the possibility of genotyping individuals at increased risk, constitutes a new research field. In the future, findings in these endeavors may enable more effective genetic counseling as well as the development of prophylactic and therapeutic strategies that would provide a real impact on the management of newborns with respiratory distress syndrome and other pulmonary diseases.

Genetic disorders of surfactant proteins

Inherited disorders of pulmonary surfactant-associated proteins are rare but provide important insights into unique mechanisms of surfactant dysfunction. Recessive loss-of-function mutations in the surfactant protein-B and the ATP-binding cassette family member A3 (ABCA3) genes present as lethal surfactant deficiency in the newborn, whereas other recessive mutations in ABCA3 and dominant mutations in the surfactant protein-C gene result in interstitial lung disease in older infants and children. The molecular basis and the genetic and tissue-based approaches to the evaluation of children suspected of having one of these disorders are discussed.

Inherited surfactant protein-B deficiency and surfactant protein-C associated disease: clinical features and evaluation

The pulmonary surfactant is a mixture of phospholipids and proteins synthesized, packaged, and secreted by alveolar type II cells that lowers surface tension and prevents atelectasis at end-expiration. A tightly regulated, complex metabolic cycle involves all components of the pulmonary surfactant. Disorders of surfactant metabolism that have a genetic basis are rare, but causes of respiratory dysfunction in infants and children emerge. Recessive loss of function mutations in surfactant protein-B (SP-B) gene lead to respiratory failure that is lethal in the newborn period while single allelic mutations in the surfactant protein-C (SP-C) gene cause interstitial lung disease of varying severity and age of onset. The genetic basis, mechanisms, clinical presentation and outcome, diagnostic approach and limited therapeutic options for disease due to mutations the SP-B and SP-C genes will be described in detail in this article. These disorders provide insights into some of the distinct mechanisms that disrupt the surfactant metabolic cycle and cause respiratory disease in infants and children.

Primary ciliary dyskinesia and newborn respiratory distress

Primary ciliary dyskinesia is an autosomal recessive genetic disease that results in impaired mucociliary clearance causing progressive involvement of the upper and lower respiratory tract, characterized by airway obstruction and recurrent infections of the lungs, middle ear and paranasal sinuses. Other clinical manifestations include situs inversus totalis and male infertility. Recently, neonatal respiratory distress has been found to be a common clinical presentation of patients with primary ciliary dyskinesia, indicating that this is an important symptom complex in early life for this condition. The diagnosis requires a high index of suspicion, but primary ciliary dyskinesia must be considered in any term neonate who develops respiratory distress or persistent hypoxemia and has situs inversus or an affected sibling. Moreover, further evaluation is warranted in children who had transient respiratory distress in newborn period and subsequently develop persistent cough or chronic otitis media.

Defects in surfactant synthesis: clinical implications

Since the original description of deficiency of the pulmonary surfactant in premature newborn infants by Avery and Mead in 1959, respiratory distress syndrome has most commonly been attributed to developmental immaturity of surfactant production. Studies of different ethnic groups, gender, targeted gene ablation in murine lineages, and recent clinical reports of monogenic causes of neonatal respiratory distress syndrome have demonstrated that genetic defects disrupt pulmonary surfactant metabolism and cause respiratory distress syndrome, especially in term or near-term infants and in older infants, children, and adults. In contrast to developmental causes of respiratory distress, which may improve as infants and children mature, genetic causes result in both acute and chronic (and potentially irreversible) respiratory failure.

Surfactant protein D levels in umbilical cord blood and capillary blood of premature infants. The influence of perinatal factors

Surfactant protein D (SP-D) is a collectin that plays an important role in the innate immune system and takes part in the surfactant homeostasis by regulating the surfactant pool size. The aims of this study were to investigate the values of SP-D in umbilical cord blood and capillary blood of premature infants and to relate the levels to perinatal conditions. A total of 254 premature infants were enrolled in the present study. Umbilical cord blood was drawn at the time of birth and capillary blood at regular intervals throughout the admission. The concentration of SP-D in umbilical cord blood and capillary blood was measured using ELISA technique. The median concentration of SP-D in umbilical cord blood was twice as high as in mature infants, 769 ng/mL (range 140-2,551), with lowest values in infants with intrauterine growth retardation (IUGR) and rupture of membranes (ROM). The median concentration of SP-D in capillary blood day 1 was 1,466 ng/mL (range 410-5,051 ng/mL), with lowest values in infants born with ROM and delivered vaginally. High SP-D levels in umbilical cord blood and capillary blood on day 1 were found to be more likely in infants in need for respiratory support or surfactant treatment and susceptibility to infections. We conclude that SP-D concentrations in umbilical cord blood and capillary blood in premature infants are twice as high as in mature infants and depend on several perinatal conditions. High SP-D levels in umbilical cord blood and capillary blood on day 1 were found to be related to increased risk of RDS and infections.

Single nucleotide polymorphism in 5'-flanking region reduces transcription of surfactant protein B gene in H441 cells

Surfactant protein (SP)-B is expressed in a cell-specific manner and is essential for surfactant function and survival. Abnormal surfactant function occurs in humans and genetically engineered mice with SP-B levels well below 50% of normal. SP-B mRNA levels vary in fetal lung explants among individuals, possibly due to genetic variety. Polymorphisms within the SP-B gene have been described extensively; however, some of their functional relevance remains unclear. Mutations within the SP-B gene may affect mRNA content, but altered gene transcription or mRNA-stability has not been clearly demonstrated. We characterized a single nucleotide polymorphism (SNP) found in the upstream enhancer of SP-B, consisting of a single base pair change in the consensus sequence of the most downstream-located thyroid transcription factor 1 binding element in the upstream enhancer of the SP-B 5'-flanking region and located at position 384 upstream of the transcriptional start site of the SP-B gene. In a small patient population (n = 53) we found 70% were homozygous for the wild type (WT), one individual (2%) was homozygous for the polymorphism (Pm), and 28% were heterozygous. To further elucidate possible functions we performed electromobility shift assays with extracts from H441 cells that showed a reduced binding affinity of the mutated sequence compared with WT. In reporter gene assays the Pm caused a reduction of 53% in transcriptional activity compared with WT in transfected H441 cells. Stimulation of these constructs with retinoic acid resulted in enhanced reporter gene activity of both constructs. After stimulation the Pm still exhibited a reduced activity compared with the WT sequence. We conclude that the described SNP causes differences in SP-B transcriptional activity and thus may contribute to individually different SP-B mRNA levels.

ABCA3 mutations associated with pediatric interstitial lung disease

RATIONALE

ABCA3 is a member of the ATP-binding cassette family of proteins that mediate the translocation of a wide variety of substrates, including lipids, across cellular membranes. Mutations in the gene encoding ABCA3 were recently identified in full-term neonates with fatal surfactant deficiency.

OBJECTIVE

To test the hypothesis that ABCA3 mutations are not always associated with fatal neonatal lung disease but are a cause of pediatric interstitial lung disease.

METHODS

DNA samples were obtained from 195 children with chronic lung disease of unknown etiology. The 30 coding exons of the ABCA3 gene were sequenced in four unrelated children with a referring diagnosis of desquamative interstitial pneumonitis and who were older than 10 years at the time of enrollment.

RESULTS

Three of four patients (ages 16, 23, and 11 years) with desquamative interstitial pneumonitis had ABCA3 mutations identified on both alleles. All three had the same missense mutation (E292V) and a second unique mutation. The E292V mutation was not found on 200 control alleles from adults without lung disease, but seven additional patients of the remaining study patients had the E292V mutation on one allele. Immunohistochemical analysis of surfactant protein expression in three patients revealed a specific staining pattern for surfactant protein-B, which was the same pattern observed in several infants with fatal lung disease due to ABCA3 mutations.

CONCLUSION

ABCA3 mutations cause some types of interstitial lung disease in pediatric patients.

l7Rn6 encodes a novel protein required for clara cell function in mouse lung development

The highly secretory Clara cells play a pivotal role in protecting the lung against inflammation and oxidative stress. This study reports the positional cloning of a novel protein required for Clara cell physiology in mouse lung development. The perinatal lethal N-ethyl-N-nitrosourea-induced l7Rn6(4234SB) allele contained a nonsense mutation in the previously hypothetical gene NM_026304 on chromosome 7. Whereas l7Rn6 mRNA levels were indistinguishable from wild type, l7Rn6(4234SB) homozygotes exhibited decreased expression of the truncated protein, suggesting protein instability. During late gestation, l7Rn6 was widely expressed in the cytoplasm of lung epithelial cells, whereas perinatal expression was restricted to the bronchiolar epithelium. Homozygosity for the l7Rn6(4234SB) allele did not affect early steps in lung patterning, growth, or cellular differentiation. Rather, mutant lungs demonstrated severe emphysematous enlargement of the distal respiratory sacs at birth. Clara cell pathophysiology was evident from decreased cytoplasmic CCSP and SP-B protein levels, enlargement and disorganization of the Golgi complex, and formation of aberrant vesicular structures. Additional support for a role in the secretory pathway derived from l7Rn6 localization to the endoplasmic reticulum. Thus, l7Rn6 represents a novel protein required for organization and/or function of the secretory apparatus in Clara cells in mouse lung.

The composition of pulmonary surfactant from diving mammals

Maintaining a functional pulmonary surfactant system at depth is critical for diving mammals to ensure that inspiration is possible upon re-emergence. The lipid and protein composition of lavage extracts from three pinniped species (California sea lion, Northern elephant seal and Ringed seal) were compared to several terrestrial species. Lavage samples were purified using a NaBr discontinuous gradient. Concentrations of phospholipid classes and molecular species were measured using electrospray ionisation mass spectrometry, cholesterol was measured using high-performance liquid chromatography, surfactant protein A (SP-A) and SP-B were measured using enzyme-linked immunosorbent assays. There were small differences in phospholipid classes, with a lower level of anionic surfactant phospholipids, PG and PI, between diving and terrestrial mammals. There were no differences in PL saturation or SP-A levels between species. PC16:0/14:0, PC16:0/16:1, PC16:0/16:0, long chain PI species and the total concentrations of alkyl-acyl species of PC and PG as a ratio of diacyl species were increased in diving mammals, whereas concentrations of PC16:0/18:1, PG16:0/16:0 and PG16:0/18:1 were decreased. Cholesterol levels were very variable between species and SP-B was very low in diving mammals. These differences may explain the very poor surface activity of pinniped surfactant that we have previously described [Miller, N.J., Daniels, C.B., Schürch, S., Schoel, W.M., Orgeig, S., 2005. The surface activity of pulmonary surfactant from diving mammals. Respir. Physiol. Neurobiol. 150 (2006) 220-232], supporting the hypothesis that pinniped surfactant has primarily an anti-adhesive function to meet the challenges of regularly collapsing lungs.

A multicenter, randomized, masked, comparison trial of lucinactant, colfosceril palmitate, and beractant for the prevention of respiratory distress syndrome among very preterm infants

BACKGROUND AND OBJECTIVE

Evidence suggests that synthetic surfactants consisting solely of phospholipids can be improved through the addition of peptides, such as sinapultide, that mimic the action of human surfactant protein-B (SP-B). A synthetic surfactant containing a mimic of SP-B may also reduce the potential risks associated with the use of animal-derived products. Our objective was to compare the efficacy and safety of a novel synthetic surfactant containing a functional SP-B mimic (lucinactant; Discovery Laboratories, Doylestown, PA) with those of a non-protein-containing synthetic surfactant (colfosceril palmitate; GlaxoSmithKline, Brentford, United Kingdom) and a bovine-derived surfactant (beractant; Abbott Laboratories, Abbott Park, IL) in the prevention of neonatal respiratory distress syndrome (RDS) and RDS-related death.

METHODS

We assigned randomly (double-masked) 1294 very preterm infants, weighing 600 to 1250 g and of < or =32 weeks gestational age, to receive colfosceril palmitate (n = 509), lucinactant (n = 527), or beractant (n = 258) within 20 to 30 minutes after birth. Primary outcome measures were the rates of RDS at 24 hours and the rates of death related to RDS during the first 14 days after birth. All-cause mortality rates, bronchopulmonary dysplasia (BPD) rates, and rates of other complications of prematurity were prespecified secondary outcomes. Primary outcomes, air leaks, and causes of death were assigned by an independent, masked, adjudication committee with prespecified definitions. The study was monitored by an independent data safety monitoring board.

RESULTS

Lucinactant reduced significantly the incidence of RDS at 24 hours, compared with colfosceril (39.1% vs 47.2%; odds ratio [OR]: 0.68; 95% confidence interval [CI]: 0.52-0.89). There was no significant difference in comparison with beractant (33.3%). However, lucinactant reduced significantly RDS-related mortality rates by 14 days of life, compared with both colfosceril (4.7% vs 9.4%; OR: 0.43; 95% CI: 0.25-0.73) and beractant (10.5%; OR: 0.35; 95% CI: 0.18-0.66). In addition, BPD at 36 weeks postmenstrual age was significantly less common with lucinactant than with colfosceril (40.2% vs 45.0%; OR: 0.75; 95% CI: 0.56-0.99), and the all-cause mortality rate at 36 weeks postmenstrual age was lower with lucinactant than with beractant (21% vs 26%; OR: 0.67; 95% CI: 0.45-1.00).

CONCLUSIONS

Lucinactant is a more effective surfactant preparation than colfosceril palmitate for the prevention of RDS. In addition, lucinactant reduces the incidence of BPD, compared with colfosceril palmitate, and decreases RDS-related mortality rates, compared with beractant. Therefore, we conclude that lucinactant, the first of a new class of surfactants containing a functional protein analog of SP-B, is an effective therapeutic option for preterm infants at risk for RDS.

A multicenter, randomized, controlled trial of lucinactant versus poractant alfa among very premature infants at high risk for respiratory distress syndrome

BACKGROUND

Available therapeutic surfactants are either animal-derived or non-protein-containing synthetic products. Animal-derived surfactants contain variable amounts of surfactant apoproteins, whereas the older-generation synthetic products contain only phospholipids and lack surfactant proteins (SPs). Both decrease morbidity and mortality rates associated with respiratory distress syndrome (RDS) among preterm infants, compared with placebo. However, excess mortality rates have been observed with non-protein-containing synthetic surfactants, compared with the animal-derived products. Evidence suggests that synthetic surfactants consisting solely of phospholipids can be improved with the addition of peptides that are functional analogs of SPs. Lucinactant is a new synthetic peptide-containing surfactant that contains sinapultide, a novel, 21-amino acid peptide (leucine and lysine repeating units, KL4 peptide) designed to mimic human SP-B. It is completely devoid of animal-derived components.

OBJECTIVE

We hypothesized that the outcomes for premature infants treated with lucinactant and poractant alfa would be similar. Therefore, we compared lucinactant (Surfaxin; Discovery Laboratories, Doylestown, PA) with porcine-derived, poractant alfa (Curosurf; Chiesi Farmaceutici, Parma, Italy) in a trial to test for noninferiority.

METHODS

A total of 252 infants born between 24 and 28 weeks of completed gestation, with birth weights between 600 and 1250 g, were assigned randomly in a multicenter, multinational, noninferiority, randomized, controlled study to receive either lucinactant (n = 124) or poractant alfa (n = 128) within 30 minutes of life. The primary outcome was the incidence of being alive without bronchopulmonary dysplasia (BPD) through 28 days of age. Key secondary outcomes included death at day 28 and 36 weeks postmenstrual age (PMA), air leaks, neuroimaging abnormalities, and other complications related to either prematurity or RDS. An independent, international, data and safety monitoring committee monitored the trial.

RESULTS

The treatment difference between lucinactant and poractant alfa for survival without BPD through 28 days was 4.75% (95% confidence interval [CI]: -7.3% to 16.8%) in favor of lucinactant, with the lower boundary of the 95% CI for the difference, ie, -7.3%, being greater than the prespecified noninferiority margin of -14.5%. At 28 days, 45 of 119 infants given lucinactant were alive without BPD (37.8%; 95% CI: 29.1-46.5%), compared with 41 of 124 given poractant alfa (33.1%; 95% CI: 24.8-41.3%); at 36 weeks PMA, the rates were 64.7% and 66.9%, respectively. The corresponding mortality rate through day 28 for the lucinactant group was lower than that for the poractant alfa group (11.8% [95% CI: 6.0-17.6%] vs 16.1% [95% CI: 9.7-22.6%]), as was the rate at 36 weeks PMA (16% and 18.5%, respectively). There were no differences in major dosing complications. In addition, no significant differences were observed in the incidences of common complications of prematurity, including intraventricular hemorrhage (grades 3 and 4) and cystic periventricular leukomalacia (lucinactant: 14.3%; poractant alfa: 16.9%).

CONCLUSIONS

Lucinactant and poractant alfa were similar in terms of efficacy and safety when used for the prevention and treatment of RDS among preterm infants. The ability to enhance the performance of a synthetic surfactant with the addition of a peptide that mimics the action of SP-B, such as sinapultide, brings potential advantages to exogenous surfactant therapy.

Delayed clearance of fetal lung liquid and sodium transport--genetic predisposition not evident yet

The epithelial Na+ channel (ENaC) contributes to the clearance of fetal lung liquid. In premature infants, low ENaC activity and low expression level of alpha-ENaC have been associated with respiratory failure. The polymorphism in the alpha-ENaC gene remains to be studied as a factor explaining the variation in the incidence of transient tachypnoea or respiratory distress syndrome in the newborn.

CONCLUSION

The study of genetic predisposition to common multifactorial diseases requires analyses of large, well-defined cohorts for representative variants of relevant candidate genes.

A common mutation in the surfactant protein C gene associated with lung disease

OBJECTIVE

To determine the contribution of the surfactant protein C (SP-C) I73T mutation to lung disease.

STUDY DESIGN

Genomic DNA was obtained from 116 children with interstitial lung disease (ILD) or chronic lung disease of unclear cause and from 166 control subjects and was screened for the I73T mutation using an allele-specific polymerase chain reaction assay.

RESULTS

The I73T mutation was found on 7 of 232 SP-C alleles from 7 unrelated children with ILD but was not found on 332 control SP-C alleles ( P < .01, Fisher exact test). The I73T mutation segregated with lung disease in one kindred with familial ILD. The I73T mutation was found in an asymptomatic parent from two different families with affected children consistent with variable penetrance, but it was not found in either asymptomatic parent of two other unrelated affected children consistent with a de novo mutation. Analysis of single nucleotide polymorphisms indicated diverse genetic backgrounds of the I73T alleles. Immunohistochemical analysis of lung tissue from an infant with the I73T mutation demonstrated normal staining patterns for proSP-B, SP-B, and proSP-C.

CONCLUSIONS

These findings support the hypothesis that the I73T mutation predisposes to or causes lung disease.

Randomized trial comparing two natural surfactants (Survanta vs. bLES) for treatment of neonatal respiratory distress syndrome

Exogenous surfactants have been used as an effective treatment of neonatal respiratory distress syndrome (RDS). Different preparations of surfactant carry different biophysical and clinical properties. To study the response pattern and treatment outcome of two natural surfactants (bLES and Survanta) for the treatment of RDS, we conducted a randomized clinical trial at the neonatal unit of a university teaching hospital. Premature babies with birth weight between 500-1,800 g who developed RDS requiring mechanical ventilation with an oxygen requirement of more than 30% within 6 hr of life were randomized into two treatment groups. Oxygenation indices (OIs) within 12 hr of treatment were compared as primary outcomes, while neonatal complications were analyzed as secondary outcomes of the study. Sixty babies were recruited, with 29 in the bLES and 31 in the Survanta treatment group. Both groups had significant and sustained improvements in OI after surfactant replacement therapy (SRT), while the bLES group was associated with a significantly lower OI throughout the initial 12 hr after treatment compared with the Survanta group. There was no difference in secondary outcomes including mortality, ventilator days, and occurrence of chronic lung disease. We conclude that infants with RDS respond favorably to both types of surfactant replacement, and that bLES achieved a faster clinical response in terms of improvement in OI than Survanta.

Evidence for a conserved function in synapse formation reveals Phr1 as a candidate gene for respiratory failure in newborn mice

Genetic studies using a set of overlapping deletions centered at the piebald locus on distal mouse chromosome 14 have defined a genomic region associated with respiratory distress and lethality at birth. We have isolated and characterized the candidate gene Phr1 that is located within the respiratory distress critical genomic interval. Phr1 is the ortholog of the human Protein Associated with Myc as well as Drosophila highwire and Caenorhabditis elegans regulator of presynaptic morphology 1. Phr1 is expressed in the embryonic and postnatal nervous system. In mice lacking Phr1, the phrenic nerve failed to completely innervate the diaphragm. In addition, nerve terminal morphology was severely disrupted, comparable with the synaptic defects seen in the Drosophila hiw and C. elegans rpm-1 mutants. Although intercostal muscles were completely innervated, they also showed dysmorphic nerve terminals. In addition, sensory neuron terminals in the diaphragm were abnormal. The neuromuscular junctions showed excessive sprouting of nerve terminals, consistent with inadequate presynaptic stimulation of the muscle. On the basis of the abnormal neuronal morphology seen in mice, Drosophila, and C. elegans, we propose that Phr1 plays a conserved role in synaptic development and is a candidate gene for respiratory distress and ventilatory disorders that arise from defective neuronal control of breathing.

Surfactant protein B deficiency in infants with respiratory failure

Surfactant Protein B (SP-B) deficiency has been recently identified as an uncommon, autosomal recessive lung disorder in term infants. This inability to produce SP-B leads to progressive, lethal, hypoxemic respiratory failure in the first year of life. A frameshift mutation (121 ins 2) is the predominant but not exclusive cause. The clue to diagnosis is to have a high suspicion of SP-B deficiency in any term infant with severe respiratory distress without any apparent cause. SP-B deficiency can be diagnosed prenatally or postnatally. The only current treatment options available include lung transplantation or compassionate care. Current developments in gene therapy offer hope for future treatment.

Exogenous surfactant therapy: newer developments

There are numerous pulmonary conditions in which qualitative or quantitative anomalies of the surfactant system have been demonstrated. In premature newborns with immature lungs, a functional deficit in surfactant is the main physiopathologic mechanism of the neonatal respiratory distress syndrome (RDS). Since the landmark pilot study of Fujiwara, published more than 20 years ago, the efficacy of exogenous surfactant for the treatment of neonatal RDS has been established by numerous controlled studies and meta-analyses. Promising results have also been reported in infants suffering from other lung disorders in which endogenous surfactant function is compromised. Enlightened by a growing insight into both the structure and function of the different surfactant components, a new generation of synthetic surfactants has been developed. Various complementary approaches have confirmed the fundamental role of the two hydrophobic proteins, SP-B and SP-C, in the surfactant system, thus opening the way to the design of analogues, either by chemical synthesis or expression in a prokaryotic system. These peptide-containing synthetic surfactant preparations are presently undergoing clinical trials, and may eventually replace the animal-derived surfactants currently used for the treatment of RDS.

Phosphatidylserine receptor is required for clearance of apoptotic cells

Cells undergoing apoptosis during development are removed by phagocytes, but the underlying mechanisms of this process are not fully understood. Phagocytes lacking the phosphatidylserine receptor (PSR) were defective in removing apoptotic cells. Consequently, in PSR-deficient mice, dead cells accumulated in the lung and brain, causing abnormal development and leading to neonatal lethality. A fraction of PSR knockout mice manifested a hyperplasic brain phenotype resembling that of mice deficient in the cell death-associated genes encoding Apaf-1, caspase-3, and caspase-9, which suggests that phagocytes may also be involved in promoting apoptosis. These data demonstrate a critical role for PSR in early stages of mammalian organogenesis and suggest that this receptor may be involved in respiratory distress syndromes and congenital brain malformations.

Genetic influences and neonatal lung disease

Neonatal lung diseases may have a genetic background. The available studies mainly concentrate on surfactant proteins (SP-A, SP-B) and respiratory distress syndrome. Specific alleles of the SP-A and SP-B genes associate interactively with susceptibility to respiratory distress syndrome. This genetic impact on the condition is influenced by environmental, acquired and inherited factors. Other alleles and genotypes of SP-A and SP-D associate with severe respiratory infections in early infancy. Rare mutations causing an absence of the SP-B protein result in progressive respiratory failure. Dominant mutations of SP-C associate with chronic lung disease, with variable manifestations. The first steps towards unraveling the genetic network influencing the susceptibility to neonatal lung diseases are now being taken. Genes encoding multifunctional proteins in the distal lung are prime candidates for causing susceptibility to neonatal lung disease, including bronchopulmonary dysplasia.

Surfactant proteins and genetic predisposition to respiratory distress syndrome

Respiratory distress syndrome (RDS) is caused by surfactant deficiency at birth. The risk of RDS decreases from the gestational age of 24 weeks to full-term. Genetic and acquired factors additionally influence the risk of RDS. Surfactant deficiency in RDS is mainly caused by immaturity and a lack of differentiation of the alveolar epithelial cells involved in surfactant synthesis and secretion. A network of hormones and growth factors regulate perinatal development. Host-related factors, including the levels of expression of surfactant proteins (SP), modulate the responsiveness of growth factors. SP-A has roles in surface activity and regulatory roles particularly in innate immunity; SP-B is essential for the processing of surfactant and for the surface activity; SP-C has roles in surfactant metabolism and function; the regulatory roles of SP-D mainly pertain to innate immunity. The genetic variation of SP-A and SP-B genes and the risk of RDS have been studied. Both SP-A and SP-B associate with susceptibility to RDS. The association between the SP-A allele and genotypes and the risk of RDS is dependent on the SP-B genotype and significantly influenced by the degree of prematurity, antenatal glucocorticoid therapy, multiple birth, and birth order. The alleles/genotypes of SP-A, SP-C, or SP-D also associate with several other inflammatory lung and airway diseases. Rare mutations in SP-B or SP-C cause serious, often fatal lung diseases. Genetic and post-genomic research is likely to eventually result in new diagnostic applications and specific therapies for the prevention of respiratory failure and inflammatory lung diseases.

Transforming growth factor-beta inhibits pulmonary surfactant protein B gene transcription through SMAD3 interactions with NKX2.1 and HNF-3 transcription factors

Transforming growth factor-beta (TGF-beta) represses surfactant protein B (Sp-B) gene transcription through a mechanism that remains unknown. A homeodomain and a forkhead transcription factor, NKX2.1 and HNF-3, respectively, are known activators of Sp-B transcription. Because SMADs are the effectors of TGF-beta-induced gene activation, we examined the possibility that gene repression by TGF-beta may also occur through interactions of SMADs with NKX2.1 and HNF-3. We found that lung epithelial carcinoma H441 cells contain SMAD2/3 and -4, which localize to the nucleus in response to TGF-beta treatment. The activity of a transfected Sp-B promoter/reporter construct was reduced in a dose-dependent manner by TGF-beta. Cotransfection with a mutant, constitutively activated form of the Tgf-beta type I receptor repressed Sp-B promoter activity in the absence of TGF-beta ligand. Dominant negative mutants of Smads blocked the repressor activity of TGF-beta. SMAD3, but not SMAD2, mediated the repressor activity of TGF-beta on the Sp-B promoter. Mutations within a 70-base pair domain that includes binding sites for NKX2.1, hepatocyte nuclear factor 3 (HNF-3), or cAMP response element-binding protein (CREB) eliminated SMAD3-dependent repression of Sp-B transcription. Electrophoretic mobility shift analysis showed no evidence for direct binding of SMAD3 to the Sp-B promoter, and a DNA binding mutant of SMAD3 also repressed Sp-B, suggesting that direct DNA binding of SMAD3 may not be required. Using a mammalian two hybrid assay, we found physical and functional interactions between SMAD3 and both NKX2.1 and HNF-3. Also, a glutathione S-transferase-fused SMAD3 directly binds to in vitro synthesized NKX2.1 or HNF-3, demonstrating protein-protein interactions between SMAD3 and the two transcriptional factors. The DNA binding of NKX2.1 to Sp-B promoter was reduced in response to TGF-beta treatment, although expression of Nkx2.1 was not affected. We conclude that SMAD3 interactions with the positive regulators NKX2.1 and HNF-3 underlie the molecular basis for TGF-beta-induced repression of Sp-B gene transcription.

Surfactant proteins as genetic determinants of multifactorial pulmonary diseases

Surfactant proteins, SP-A, SP-B, SP-C and SP-D, play important roles in pulmonary surfactant function and metabolism. SP-A and SP-D, being members of the collectin family of proteins, also interact with pathogens and are involved in pulmonary host defense. Respiratory diseases are among the most common causes of death worldwide. Several life-threatening lung diseases, such as neonatal respiratory distress syndrome (RDS) and acute ROS (ARDS), are associated with impaired surfactant function. Allelic variations of the SP-A and SP-B genes have been shown to be important genetic determinants in individual susceptibility to RDS, which is a good general model for a multifactorial pulmonary disease resulting from complex interactions between several environmental and genetic factors. Because SP-A and SP-D act directly in the clearance of common lung pathogens, the genes encoding these proteins have been implicated as candidates in a few infectious diseases, including respiratory syncytial virus (RSV) infections and tuberculosis.