Aberrant SP-B mRNA in lung tissue of patients with congenital alveolar proteinosis (CAP)

SNP–SNP Interactions of Surfactant Protein Genes in Persistent Respiratory Morbidity Susceptibility in Previously Healthy Children

We studied associations of persistent respiratory morbidity (PRM) at 6 and 12 months after acute respiratory failure (ARF) in previously healthy children with single-nucleotide polymorphisms (SNPs) of surfactant protein (SP) genes. Of the 250 enrolled subjects, 155 and 127 were followed at 6 and 12 months after an ARF episode, respectively. Logistic regression analysis and SNP–SNP interaction models were used. We found that 1) in the multivariate analysis, an increased risk at 6 and 12 months was associated with rs1124_A and rs4715_A of SFTPC, respectively; 2) in a single SNP model, increased and decreased risks of PRM at both timepoints were associated with rs1124 of SFTPC and rs721917 of SFTPD, respectively; an increased risk at 6 months was associated with rs1130866 of SFTPB and rs4715 of SFTPC, and increased and decreased risks at 12 months were associated with rs17886395 of SFTPA2 and rs2243639 of SFTPD, respectively; 3) in a two-SNP model, PRM susceptibility at both timepoints was associated with a number of intergenic interactions between SNPs of the studied SP genes. An increased risk at 12 months was associated with one intragenic (rs1965708 and rs113645 of SFTPA2) interaction; 4) in a three-SNP model, decreased and increased risks at 6 and 12 months, respectively, were associated with an interaction among rs1130866 of SFTPB, rs721917 of SFTPD, and rs1059046 of SFTPA2. A decreased risk at 6 months was associated with an interaction among the same SNPs of SFTPB and SFTPD and the rs1136450 of SFTPA1. The findings revealed that SNPs of all SFTPs appear to play a role in long-term outcomes of ARF survivors and may serve as markers for disease susceptibility.

SNP and Haplotype Interaction Models Reveal Association of Surfactant Protein Gene Polymorphisms With Hypersensitivity Pneumonitis of Mexican Population

Background: Hypersensitivity pneumonitis (HP) is an interstitial lung disease caused by inhalation of common environmental organic particles. Surfactant proteins (SPs) play a role in innate immunity and surfactant function. We hypothesized that single nucleotide polymorphisms (SNPs) or haplotypes of the SP genes associate with HP. Methods: Seventy-five HP patients caused by avian antigen and 258 controls, asymptomatic antigen exposed and non-exposed were enrolled. SNP association was performed using logistic regression analysis and SNP-SNP interaction models. Results: Based on odds ratio, regression analyses showed association of (a) rs7316_G, 1A3 (protective) compared to antigen exposed; (b) male sex, smoking, rs721917_T and rs1130866_T (protective) compared to non-exposed controls with HP; (c) compared to antigen exposed, 25 interactions associated with HP in a three-SNP model; (d) compared to non-exposed, (i) rs1136451 associated with increased, whereas rs1136450 and rs1130866 associated with lower HP risk, (ii) 97 interactions associated with HP in a three-SNP model. The majority of SNP-SNP interactions associated with increased HP risk involved SNPs of the hydrophilic SPs, whereas, the majority of interactions associated with lower HP risk involved SNPs of both hydrophilic and hydrophobic SPs; (e) haplotypes of SP genes associated with HP risk. Conclusions: The complexity of SNPs interactions of the SFTP genes observed indicate that the lung inflammatory response to avian antigens is modulated by a complex gene interplay rather than by single SNPs.

Single Nucleotide Polymorphisms Interactions of the Surfactant Protein Genes Associated With Respiratory Distress Syndrome Susceptibility in Preterm Infants

Background: Neonatal respiratory distress syndrome (RDS), due to surfactant deficiency in preterm infants, is the most common cause of respiratory morbidity. The surfactant proteins (SFTP) genetic variants have been well-studied in association with RDS; however, the impact of SNP-SNP (single nucleotide polymorphism) interactions on RDS has not been addressed. Therefore, this study utilizes a newer statistical model to determine the association of SFTP single SNP model and SNP-SNP interactions in a two and a three SNP interaction model with RDS susceptibility. Methods: This study used available genotype and clinical data in the Floros biobank at Penn State University. The patients consisted of 848 preterm infants, born <36 weeks of gestation, with 477 infants with RDS and 458 infants without RDS. Seventeen well-studied SFTPA1, SFTPA2, SFTPB, SFTPC, and SFTPD SNPs were investigated. Wang's statistical model was employed to test and identify significant associations in a case-control study. Results: Only the rs17886395 (C allele) of the SFTPA2 was associated with protection for RDS in a single-SNP model (Odd's Ratio 0.16, 95% CI 0.06-0.43, adjusted p = 0.03). The highest number of interactions (n = 27) in the three SNP interactions were among SFTPA1 and SFTPA2. The three SNP models showed intergenic and intragenic interactions among all SFTP SNPs except SFTPC. Conclusion: The single SNP model and SNP interactions using the two and three SNP interactions models identified SFTP-SNP associations with RDS. However, the large number of significant associations containing SFTPA1 and/or SFTPA2 SNPs point to the importance of SFTPA1 and SFTPA2 in RDS susceptibility.

Association of SNP-SNP Interactions of Surfactant Protein Genes with Pediatric Acute Respiratory Failure

The hallmarks of pediatric acute respiratory failure (ARF) are dysregulated inflammation and surfactant dysfunction. The objective is to study association of surfactant protein (SP) genes’ single nucleotide polymorphisms (SNPs) with ARF and its morbidity: pulmonary dysfunction at discharge (PDAD), employing a single-, two-, and three-SNP interaction model. We enrolled 468 newborn controls and 248 children aged ≤ 24 months with ARF; 86 developed PDAD. Using quantitative genetic principles, we tested the association of SP genes SNPs with ARF and PDAD. We observed a dominant effect of rs4715 of the SFTPC on ARF risk. In a three-SNP model, we found (a) 34 significant interactions among SNPs of SFTPA1, SFTPA2, and SFTPC associated with ARF (p = 0.000000002–0.05); 15 and 19 of those interactions were associated with increased and decreased risk for ARF, respectively; (b) intergenic SNP–SNP interactions of both hydrophobic and hydrophilic SP genes associated with PDAD (p = 0.00002–0.03). The majority of intra- and intergenic interactions associated with ARF involve the SFTPA2 SNPs, whereas most of the intra- and intergenic interactions associated with PDAD are of SFTPA1 SNPs. We also observed a dominant effect of haplotypes GG of SFTPA1 associated with increased and AA of SFTPC associated with decreased ARF risk (p = 0.02). To the best of our knowledge, this is the first study showing an association of complex interactions of SP genes with ARF and PDAD. Our data indicate that SP genes polymorphisms may contribute to ARF pathogenesis and subsequent PDAD and/or may serve as markers for disease susceptibility in healthy children.

Genetic Association of Pulmonary Surfactant Protein Genes, SFTPA1, SFTPA2, SFTPB, SFTPC, and SFTPD With Cystic Fibrosis

Surfactant proteins (SP) are involved in surfactant function and innate immunity in the human lung. Both lung function and innate immunity are altered in CF, and altered SP levels and genetic association are observed in Cystic Fibrosis (CF). We hypothesized that single nucleotide polymorphisms (SNPs) within the SP genes associate with CF or severity subgroups, either through single SNP or via SNP-SNP interactions between two SNPs of a given gene (intragenic) and/or between two genes (intergenic). We genotyped a total of 17 SP SNPs from 72 case-trio pedigree (SFTPA1 (5), SFTPA2 (4), SFTPB (4), SFTPC (2), and SFTPD (2)), and identified SP SNP associations by applying quantitative genetic principles. The results showed (a) Two SNPs, SFTPB rs7316 (p = 0.0083) and SFTPC rs1124 (p = 0.0154), each associated with CF. (b) Three intragenic SNP-SNP interactions, SFTPB (rs2077079, rs3024798), and SFTPA1 (rs1136451, rs1059057 and rs4253527), associated with CF. (c) A total of 34 intergenic SNP-SNP interactions among the 4 SP genes to be associated with CF. (d) No SNP-SNP interaction was observed between SFTPA1 or SFTPA2 and SFTPD. (e) Equal number of SNP-SNP interactions were observed between SFTPB and SFTPA1/SFTPA2 (n = 7) and SP-B and SFTPD (n = 7). (f) SFTPC exhibited significant SNP-SNP interactions with SFTPA1/SFTPA2 (n = 11), SFTPB (n = 4) and SFTPD (n = 3). (g) A single SFTPB SNP was associated with mild CF after Bonferroni correction, and several intergenic interactions that are associated (p < 0.01) with either mild or moderate/severe CF were observed. These collectively indicate that complex SNP-SNP interactions of the SP genes may contribute to the pulmonary disease in CF patients. We speculate that SPs may serve as modifiers for the varied progression of pulmonary disease in CF and/or its severity.

Association of SP-B gene 9306 A/G polymorphism (rs7316) and risk of RDS

BACKGROUND

Respiratory distress syndrome (RDS) is a severe pulmonary disease predominantly affects preterm newborns. Polymorphisms of surfactant-protein genes have been mostly evaluated as the candidate contributors in genetics of RDS. However the results are divers in different studies. We aimed at investigating the association of surfactant protein B (SPB) gene 9306 A/G polymorphism (rs7316) with RDS development.

METHOD

Three hundred and eighty newborns with gestational age of less than 34 weeks were included in a multicenter case-control study. Respiratory distress (RD) was scored according to Downes' scoring system. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was used for genotyping.

RESULT

One hundred and eighty-four neonates showed RDS and 196 did not. Gestational age (GA) was significantly lower in the RDS group compared with the controls. AA genotype and A allele were found more frequently in the RDS group than the controls (96.2% versus 63.8% and 98.1% versus 80.6%, respectively) (p =.0001).

CONCLUSIONS

This is the first report of association of SFTPB rs7316 polymorphism with RDS development in Iranian newborns. The current study suggests that GA <28-weeks is the most important factor in predisposition to RDS. Genetic background in terms of SP-B gene might be involved in predisposition to RDS in premature neonates.

Human Surfactant Proteins A2 (SP-A2) and B (SP-B) Genes as Determinants of Respiratory Distress Syndrome

OBJECTIVE

To study the relationship between SP-A2 and SP-B gene polymorphisms and respiratory distress syndrome in preterm neonates.

DESIGN

Cross-sectional.

SETTING

Neonatal intensive care unit and the Molecular Biology unit of the Chemical Pathology Department, Kasr Alainy hospital, Cairo University.

PARTICIPANTS

Sixty-five preterm infants with respiratory distress syndrome and 50 controls. The genomic DNA was isolated using DNA extraction kits. SYBR Green-based real-time PCR was used to determine the variant genotypes of SP-A2 c.751 G>A and SP-B c.8714 G>C single nucleotide polymorphisms.

RESULTS

Homozygosity of SP-A (OR 46, 95% CI 14-151) and SP-B (OR 5.2, 95% CI 2.3-11.4) alleles increased the risk of respiratory distress syndrome. The logistic regression model showed that genotypes SP-A2 (OR 164) and SP-B (OR 18) were directly related to the occurrence of respiratory distress syndrome, whereas gestational age (OR 0.57) and 5-minute Apgar score (OR 0.19) were inversely related to its occurrence.

CONCLUSIONS

There is a possible involvement of SP-A2 and SP-B genes polymorphisms in the genetic predisposition to respiratory distress syndrome.

Association of surfactant protein B gene polymorphisms (C/A-18, C/T1580, intron 4 and A/G9306) and haplotypes with bronchopulmonary dysplasia in chinese han population

This study aimed to investigate the association between surfactant protein B (SP-B) polymorphisms and bronchopulmonary dysplasia (BPD) in Chinese Han infants. We performed a casecontrol study including 86 infants with BPD and 156 matched controls. Genotyping was performed by sequence specific primer-polymerase chain reaction (PCR) and haplotypes were reconstructed by the fastPHASE software. The results showed that significant differences were detected in the genotype distribution of C/A-18 and intron 4 polymorphisms of SP-B gene between cases and controls. No significant differences were detected in the genotype distribution of C/T1580 or A/G9306 between the two groups. Haplotype analysis revealed that the frequency of A-del-C-A haplotype was higher in case group (0.12 to 0.05, P=0.003), whereas the frequency of C-inv-C-A haplotype was higher in control group (0.19 to 0.05, P=0.000). In addition, a significant difference was observed in the frequency of C-inv-T-A haplotype between the two groups. It was concluded that the polymorphisms of SP-B intron 4 and C/A-18 could be associated with BPD in Chinese Han infants, and the del allele of intron 4 and A allele of C/A-18 might be used as markers of susceptibility in the disease. Haplotype analysis indicated that the gene-gene interactions would play an important part in determining susceptibility to 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.

ABCA3 deficiency: neonatal respiratory failure and interstitial lung disease

ABCA3 is a member of the ATP Binding Cassette family of proteins, transporters that hydrolyze ATP in order to move substrates across biological membranes. Mutations in the gene encoding ABCA3 have been found in children with severe neonatal respiratory disease and older children with some forms of interstitial lung disease. This review summarizes current knowledge concerning clinical, genetic, and pathologic features of the lung disease associated with mutations in the ABCA3 gene, and also briefly reviews some other forms of childhood interstitial lung diseases that have their antecedents in the neonatal period and may also have a genetic basis.

Deletions within a CA-repeat-rich region of intron 4 of the human SP-B gene affect mRNA splicing

Length variants within a CA-repeat-rich region of intron 4 of the human SP-B (pulmonary surfactant protein-B) gene are associated with several lung diseases. The hypothesis that SP-B intron 4 affects mRNA splicing was studied. SP-B minigenes containing exons 1-6 with a normal-sized intron 4 (pBi4normal) or intron 4 containing deletions (pBi4del) of 193, 211, 264 or 340 bp were expressed in CHO (Chinese hamster ovary) cells by transient transfection. Two forms of SP-B transcripts, normal and incompletely spliced, were detected. With pBi4normal, normal-sized SP-B mRNA was the predominant form and a very low amount of incompletely spliced mRNA was present, whereas with the pBi4del variants the amount of normal SP-B mRNAs was lower and the amount of incompletely spliced mRNA was relatively high. Reverse transcription-PCR results and sequencing data indicated that the incompletely spliced SP-B RNA contained intron 4 sequence, and this incompletely spliced RNA was also observed in normal lung. Lung cancer tissues with intron 4 deletions exhibited a larger amount of abnormally spliced RNAs compared with normal lung tissue or cancerous tissue with normal-sized intron 4. The results indicate that intron 4 length variants affect SP-B mRNA splicing, and that this may contribute to lung disease.

Pulmonary pathology

Common causes of neonatal respiratory distress include meconium aspiration, pneumonia, persistent pulmonary hypertension of the newborn, pneumothorax and cystic adenomatoid malformation. Genomics and proteomics have enabled the recent recognition of several additional disorders that lead to neonatal death from respiratory disease. These are broadly classified as disorders of lung homeostasis and have pathological features of proteinosis, interstitial pneumonitis or lipidosis. These pathological changes result from inherited disorders of surfactant proteins or granulocyte-macrophage colony stimulating factor. Abnormal lung vascular development is the basis for another cause of fatal neonatal respiratory distress, alveolar capillary dysplasia with or without associated misalignment of veins. Diagnosis of these genetically transmitted disorders is important because of the serious implications for future siblings. There is also a critical need for establishing an archival tissue bank to permit future molecular biological studies.

Alterations in SP-B and SP-C expression in neonatal lung disease

The hydrophobic surfactant proteins, SP-B and SP-C, have important roles in surfactant function. The importance of these proteins in normal lung function is highlighted by the lung diseases associated with abnormalities in their expression. Mutations in the gene encoding SP-B result in severe, fatal neonatal lung disease, and mutations in the gene encoding SP-C are associated with chronic interstitial lung diseases in newborns, older children, and adults. This work reviews the current state of knowledge concerning the lung diseases associated with mutations in the SP-B and SP-C genes, and the potential roles of abnormal SP-B and SP-C expression and genetic variation in these genes in other lung diseases.

Pulmonary alveolar proteinosis: progress in the first 44 years

Pulmonary alveolar proteinosis is a rare clinical syndrome that was first described in 1958. Subsequently, over 240 case reports and small series have described at least 410 cases in the literature. Characterized by the alveolar accumulation of surfactant components with minimal interstitial inflammation or fibrosis, pulmonary alveolar proteinosis has a variable clinical course ranging from spontaneous resolution to death with pneumonia or respiratory failure. The most effective proven treatment--whole lung lavage--was described soon after the first recognition of this disease. In the last 8 years, there has been rapid progress toward elucidation of the molecular mechanisms underlying both the congenital and acquired forms of pulmonary alveolar proteinosis, following serendipitous discoveries in gene-targeted mice lacking granulocyte-macrophage colony-stimulating factor (GM-CSF). Impairment of surfactant clearance by alveolar macrophages as a result of inhibition of the action of GM-CSF by blocking autoantibodies may underlie many acquired cases, whereas congenital disease is most commonly attributable to mutations in surfactant protein genes but may also be caused by GM-CSF receptor defects. Therapy with GM-CSF has shown promise in approximately half of those acquired cases treated, but it is unsuccessful in congenital forms of the disease, consistent with the known differences in disease pathogenesis.

Surfactant gene polymorphisms and interstitial lung diseases

Pulmonary surfactant is a complex mixture of phospholipids and proteins, which is present in the alveolar lining fluid and is essential for normal lung function. Alterations in surfactant composition have been reported in several interstitial lung diseases (ILDs). Furthermore, a mutation in the surfactant protein C gene that results in complete absence of the protein has been shown to be associated with familial ILD. The role of surfactant in lung disease is therefore drawing increasing attention following the elucidation of the genetic basis underlying its surface expression and the proof of surfactant abnormalities in ILD.

Alveolar epithelial type II cell: defender of the alveolus revisited

In 1977, Mason and Williams developed the concept of the alveolar epithelial type II (AE2) cell as a defender of the alveolus. It is well known that AE2 cells synthesise, secrete, and recycle all components of the surfactant that regulates alveolar surface tension in mammalian lungs. AE2 cells influence extracellular surfactant transformation by regulating, for example, pH and [Ca2+] of the hypophase. AE2 cells play various roles in alveolar fluid balance, coagulation/fibrinolysis, and host defence. AE2 cells proliferate, differentiate into AE1 cells, and remove apoptotic AE2 cells by phagocytosis, thus contributing to epithelial repair. AE2 cells may act as immunoregulatory cells. AE2 cells interact with resident and mobile cells, either directly by membrane contact or indirectly via cytokines/growth factors and their receptors, thus representing an integrative unit within the alveolus. Although most data support the concept, the controversy about the character of hyperplastic AE2 cells, reported to synthesise profibrotic factors, proscribes drawing a definite conclusion today.

Polymorphisms of human SP-A, SP-B, and SP-D genes: association of SP-B Thr131Ile with ARDS

An allele association study of 19 polymorphisms in surfactant proteins SP-A1, SP-A2, SP-B, and SP-D genes in acute respiratory distress syndrome (ARDS) was carried out. Trend-test analysis revealed differences (p < 0.05) in the frequency of alleles for some of the microsatellite markers flanking SP-B, and for one polymorphism (C/T) at nucleotide 1580 [C/T (1580)], within codon 131 (Thr131Ile) of the SP-B gene. The latter determines the presence or absence of a potential N-linked glycosylation site. Multivariate analysis revealed significant differences only for the C/T (1580) polymorphism. When the ARDS population was divided into subgroups, idiopathic (i.e., pneumonia, etc.) or exogenic (i.e., trauma, etc.), significant differences were observed for the C/T (1580), for the idiopathic ARDS group, and the frequency of the C/C genotype was increased in this group. Based on the odds ratio, the C allele may be viewed as a susceptibility factor for ARDS. Although the expression of both C and T alleles occurs in heterozygous individuals, it is currently not known whether these alleles correspond to similar levels of SP-B protein. These data suggest that SP-B or a linked gene contributes to susceptibility to ARDS.