Stage-specific regulation of respiratory epithelial cell differentiation by Foxa1.

Foxa1 is a member of the winged helix family of transcription factors that is expressed in epithelial cells of the conducting airways and in alveolar type II cells of the lung. To determine the role of Foxa1 during lung morphogenesis, histology and gene expression were assessed in lungs from Foxa1-/- gene-targeted mice from embryonic day (E) 16.5 to postnatal day (PN) 13. Deletion of Foxa1 perturbed maturation of the respiratory epithelium at precise times during lung morphogenesis. While dilatation of peripheral lung saccules was delayed in Foxa1-/- mice at E16.5, sacculation was unperturbed later in development (E17.5-E18.5). At PN5, alveolarization was markedly delayed in Foxa1-/- mice; however, by PN13 lung histology was comparable to wild-type controls. Clara cell secretory protein (CCSP), prosurfactant protein (SP)-C, and SP-B protein content and immunostaining were decreased in Foxa1-/- mice between E16.5 and E18.5 but normalized after birth. Timing and sites of expression of thyroid transcription factor-1, Foxj1, and beta-tubulin were unaltered in lungs of Foxa1-/- mice. In vitro, Foxa1 regulated the activity of CCSP and SP-A, SP-B, SP-C, and SP-D promoters as assessed by luciferase reporter assays in HeLa, H441, and MLE15 cells. Although Foxa1 regulates respiratory epithelial differentiation and structural maturation of the lung at precise developmental periods, the delay in maturation is subsequently compensated at times to enable respiratory function and restore normal lung structure after birth.

Aquaporin 5-deficient mouse lungs are hyperresponsive to cholinergic stimulation.

Although aquaporin 5 (AQP5) is the major water channel expressed in alveolar type I cells in the lung, its actual role in the lung is a matter of considerable speculation. By using immunohistochemical staining, we show that AQP5 expression in mouse lung is not restricted to type I cells, but is also detected in alveolar type II cells, and in tracheal and bronchial epithelium. Aqp5 knockout (Aqp5(-/-)) mice were used to analyze AQP5 function in pulmonary physiology. Compared with Aqp5(+/+) mice, Aqp5(-/-) mice show a significantly increased concentration-dependent bronchoconstriction to intravenously administered Ach, as shown by an increase in total lung resistance and a decrease in dynamic lung compliance (P < 0.05). Likewise, Penh, a measure of bronchoconstriction, was significantly enhanced in Aqp5(-/-) mice challenged with aerosolized methacholine (P < 0.05). The hyperreactivity to bronchoconstriction observed in the Aqp5(-/-) mice was not due to differences in tracheal smooth muscle contractility in isolated preparations or to altered levels of surfactant protein B. These data suggest a novel pathway by which AQP5 influences bronchoconstriction. This observation is of special interest because studies to identify genetic loci involved in airway hyperresponsiveness associated with asthma bracket genetic intervals on human chromosome 12q and mouse chromosome 15, which contain the Aqp5 gene.

Immunolocalization of sonic hedgehog (Shh) in developing mouse lung.

Expression of sonic hedgehog (Shh) is required for normal development of the lung during embryogenesis. Loss of Shh expression in mice results in tracheoesophageal fistula, lung hypoplasia, and abnormal lung lobulation. To determine whether Shh may play a role later in lung morphogenesis, immunostaining for Shh was performed in mouse lung from embryonic day (E) 10.5 to postnatal day (PD) 24. Shh was detected in the distal epithelium of the developing mouse lung from E10.5 to E16.5. From E16.5 until PD15, Shh was present in epithelial cells in both the peripheral and conducting airways. Although all cells of the developing epithelium uniformly expressed Shh at E10.5, Shh expression was restricted to subsets of epithelial cells by E16.5. Between E16.5 and PD15, non-uniform Shh staining of epithelial cells was observed in the conducting airways in a pattern consistent with the distribution of non-ciliated bronchiolar cells (i.e., Clara cells) and the Clara cell marker CCSP. Shh did not co-localize with hepatocyte nuclear factor/forkhead homologue-4 (HFH-4), beta-tubulin, or with the presence of cilia. These results support the concept that Shh plays a distinct regulatory role in the lung later in morphogenesis, when it may influence formation or cytodifferentiation of the conducting airways.

SP-D and GM-CSF regulate surfactant homeostasis via distinct mechanisms.

Both surfactant protein (SP) D and granulocyte-macrophage colony-stimulating factor (GM-CSF) influence pulmonary surfactant homeostasis, with the deficiency of either protein causing marked accumulation of surfactant phospholipids in lung tissues and in the alveoli. To assess whether the effects of each gene were mediated by distinct or shared mechanisms, surfactant homeostasis and lung morphology were assessed in 1) double-transgenic mice in which both SP-D and GM-CSF genes were ablated [SP-D(-/-),GM(-/-)] and 2) transgenic mice deficient in both SP-D and GM-CSF in which the expression of GM-CSF was increased in the lung. Saturated phosphatidylcholine (Sat PC) pool sizes were markedly increased in SP-D(-/-),GM(-/-) mice, with the effects of each gene deletion on surfactant Sat PC pool sizes being approximately additive. Expression of GM-CSF in lungs of SP-D(-/-),GM(-/-) mice corrected GM-CSF-dependent abnormalities in surfactant catabolism but did not correct lung pathology characteristic of SP-D deletion. In contrast to findings in GM(-/-) mice, degradation of [(3)H]dipalmitoylphosphatidylcholine by alveolar macrophages from the SP-D(-/-) mice was normal. The emphysema and foamy macrophage infiltrates characteristic of SP-D(-/-) mice were similar in the presence or absence of GM-CSF. Taken together, these findings demonstrate the distinct roles of SP-D and GM-CSF in the regulation of surfactant homeostasis and lung structure.

Surfactant protein deficiency in familial interstitial lung disease.

OBJECTIVE: To determine the contribution of surfactant protein abnormalities to the development of chronic lung injury in a familial form of interstitial lung disease. STUDY DESIGN: An 11-year-old girl, her sister, and their mother who were diagnosed with chronic interstitial lung disease underwent laboratory investigation of surfactant protein expression in bronchoalveolar lavage fluid and lung biopsy specimens. Nineteen patients with idiopathic pulmonary fibrosis and 9 patients who were investigated for pulmonary malignancy but who did not have interstitial lung disease served as control subjects. RESULTS: The 3 family members were found to have absent surfactant protein C (SP-C) and decreased levels of SP-A and SP-B in bronchoalveolar lavage fluid (BALF). Immunostaining for pulmonary surfactant proteins in lung biopsy specimens obtained from both children demonstrated a marked decrease of pro-SP-C in the alveolar epithelial cells but strong staining for pro-SP-B, SP-B, SP-A, and SP-D. No deviations from published surfactant protein B or C coding sequences were identified by DNA sequence analysis. All control subjects had a detectable level of SP-C in the BALF. CONCLUSION: The apparent absence of SP-C and a decrease in the levels of SP-A and SP-B are associated with familial interstitial lung disease.

Expression of thyroid transcription factor-1, surfactant proteins, type I cell-associated antigen, and Clara cell secretory protein in pulmonary hypoplasia.

Pulmonary hypoplasia (PH) is a developmental abnormality characterized by diminished distal lung parenchyma. Recent studies have demonstrated that thyroid transcription factor 1 (TTF-1), a member of NKx2 family of homeodomain transcription factors, plays an important role in lung organogenesis and lung epithelial gene expression. In order to evaluate whether abnormal expression of TTF-1 contributes to the pathophysiology of PH, we studied the expression of TTF-1, as well as that of the surfactant proteins (SPs), Clara cell secretory protein (CCSP), and type I cell-associated antigen (T1 cell-Ag), in PH. Immunolocalization patterns of these proteins were evaluated in 15 cases of PH with different associated diseases and compared with those of 14 matched controls. Our study demonstrated that the concentration gradient of TTF-1 along the proximal-distal axis in normal fetal lung is disrupted in PH after 24 weeks gestational age, while the expression of the SPs, CCSP, and T1 cell-Ag seemed to be preserved. We conclude that a normal TTF-1 expression pattern might be crucial in the control of distal lung development. Failure to switch off expression of TTF-1 in PH of more than 24 weeks gestational age may be a final common pathway leading to PH associated with the disease processes investigated in this study.

Surfactant proteins and cell markers in the respiratory epithelium of the amphibian, Ambystoma mexicanum.

The respiratory tract is lined by diverse epithelial cell types whose morphology, gene expression and functions are highly specialized along the cephalo-caudal axis of the lung. Pulmonary gas exchange, surface tension reduction, host defense, fluid and electrolyte transport are functions shared by various vertebrate species, each organism facing similar requirements for adaptation to air breathing. Consistent with this concept, we have identified distinct respiratory epithelial cell populations in the amphibian, Ambystoma mexicanum, using morphologic, histochemical and immunochemical techniques. Thyroid transcription factor-1 (TTF-1), a homeodomain nuclear transcription factor critical to lung formation, and surfactant protein B (SP-B), an amphipathic polypeptide required for surfactant function, were detected in the peripheral respiratory epithelial cells of the axolotl lung, in cells with characteristics of Type II alveolar epithelial cells in mammals. beta-Tubulin and carbohydrate staining identified distinct subsets of ciliated and goblet cells. SP-D, a member of the collectin family of innate host defense proteins, was also detected in peripheral epithelial cells of the axolotl lung. Pulmonary surfactant and host defense proteins are shared across diverse phyla supporting the concept that pulmonary structure and function have evolved from common ancestors.

FGF-10 disrupts lung morphogenesis and causes pulmonary adenomas in vivo.

Transgenic mice in which fibroblast growth factor (FGF)-10 was expressed in the lungs of fetal and postnatal mice were generated with a doxycycline-inducible system controlled by surfactant protein (SP) C or Clara cell secretory protein (CCSP) promoter elements. Expression of FGF-10 mRNA in the fetal lung caused adenomatous malformations, perturbed branching morphogenesis, and caused respiratory failure at birth. When expressed after birth, FGF-10 caused multifocal pulmonary tumors. FGF-10-induced tumors were highly differentiated papillary and lepidic pulmonary adenomas. Epithelial cells lining the tumors stained intensely for thyroid transcription factor (TTF)-1 and SP-C but not CCSP, indicating that FGF-10 enhanced differentiation of cells to a peripheral alveolar type II cell phenotype. Withdrawal from doxycycline caused rapid regression of the tumors associated with rapid loss of the differentiation markers TTF-1, SP-B, and proSP-C. FGF-10 disrupted lung morphogenesis and induced multifocal pulmonary tumors in vivo and caused reversible type II cell differentiation of the respiratory epithelium.

Role of cystic fibrosis transmembrane conductance regulator in pulmonary clearance of Pseudomonas aeruginosa in vivo.

Cystic fibrosis (CF)2 is a fatal genetic disease caused by mutations in the CF transmembrane conductance regulator (CFTR) that is commonly associated with chronic pulmonary infections with mucoid Pseudomonas aeruginosa (PA). To test the hypothesis that CFTR plays a direct role in PA adhesion and clearance, we have used mouse lines expressing varying levels of human (h) or mouse (m) CFTR. A subacute intratracheal dose of 3 x 10(6) bacteria was cleared with similar kinetics in control wild-type (WT) and transgenic mice overexpressing hCFTR in the lung from the surfactant protein C (SP-C) promoter (SP-C-hCFTR+/-). In a second series of experiments, the clearance of an acute intratracheal dose of 1.5 x 10(7) PA bacteria was also similar in WT, hemizygous SP-C-hCFTR+/-, and bitransgenic gut-corrected FABP-hCFTR+/+-mCFTR-/-, the latter lacking expression of mCFTR in the lung. However, a small but significant decrease in bacterial killing was observed in lungs of homozygote SP-C-hCFTR+/+ mice. Lung pathology in both WT and SP-C-hCFTR+/+ mice was marked by neutrophilic inflammation and bacterial invasion of perivascular and subepithelial compartments. Bacteria were associated primarily with leukocytes and were not associated with alveolar type II or bronchiolar epithelial cells, the cellular sites of SP-C-hCFTR+/+ transgene expression. The results indicate that there is no direct correlation between levels of CFTR expression and bacterial clearance or association of bacteria with epithelial cells in vivo.

Recurrent familial neonatal deaths: hereditary surfactant protein B deficiency.

Hereditary surfactant protein B (SP-B) deficiency is an uncommon autosomal recessive lung disorder that causes hypoxemic respiratory failure in mature, morphologically normal infants. Recognition and diagnosis of this condition is of paramount importance, as it has significant implications for future pregnancies with a recurrence risk of 25%. In a family with three neonatal deaths over 20 years, SP-B deficiency was diagnosed following the death of the fourth affected infant. Previous deaths were mistakenly attributed to hyaline membrane disease (HMD), congenital Mycoplasma hominis infection, and pulmonary hypertension, however, following the diagnosis in the proposita, SP-B deficiency was also confirmed in her deceased siblings by immunohistochemical staining of autopsy specimens. This case highlights the presentation, postnatal course, diagnosis, and therapeutic options of SP-B deficiency in addition to the mode of inheritance and the possibility of antenatal diagnosis. Genetic consultation is imperative in the investigations of recurrent neonatal deaths, especially in cases of remote events. The recent enormous advances in human genetics have shown that many conditions previously ascribed to environmental agents have a genetic basis.

Prolonged survival in hereditary surfactant protein B (SP-B) deficiency associated with a novel splicing mutation.

Hereditary surfactant protein B (SP-B) deficiency has been lethal in the first year of life without lung transplantation. We tested the hypothesis that SP-B gene mutations may result in milder phenotypes by investigating the mechanisms for lung disease in two children with less severe symptoms than have been previously observed in SP-B deficiency. Immunostaining patterns for pulmonary surfactant proteins were consistent with SP-B deficiency in both children. DNA sequence analysis indicated that both children were homozygous for a mutation in exon 5 that created an alternative splice site. Reverse transcriptase PCR and sequence analysis confirmed use of this splice site, which resulted in a frameshift and a premature termination codon in exon 7. The predominant reverse transcriptase PCR product, however, lacked exon 7, which restored the reading frame but would not allow translation of the exons that encode mature SP-B. Western blot analysis detected reduced amounts of mature SP-B as well as an aberrant SP-B proprotein that corresponded to the size expected from translation of the abnormal transcript. We conclude that a novel splicing mutation was the cause of lung disease in these children and that hereditary SP-B deficiency can be the cause of lung disease in older children.

Expression of thyroid transcription factor-1 in congenital cystic adenomatoid malformation of the lung.

Congenital cystic adenomatoid malformation (CCAM) is an abnormality of branching morphogenesis of the lung. CCAM types 1, 2, and 3 exhibit a cellular composition that is different from that of CCAM type 4 when evaluated with bronchiolar and alveolar cell markers. Thyroid transcription factor 1 (TTF-1) regulates early lung development. To evaluate the potential role of TTF-1 in the development of CCAM, TTF-1 expression in CCAM was compared to that of fetal lungs at varying gestational ages. Twenty-three CCAM cases (17 type 1, two type 2, two type 3, and two type 4) and 11 fetal lungs (3 pseudoglandular, 4 canalicular, and 4 terminal sac stages) were analyzed using a rabbit polyclonal antiserum to rat TTF-1. Nuclear staining for TTF-1 was observed in ciliated and nonciliated cells of the bronchial and bronchiolar epithelia and in cells lining the distal air spaces by 12 weeks gestational age. By mid-gestation, proximal bronchial cells were TTF-1 negative, except for the basal cells, while TTF-1 staining was maintained in distal bronchiolar and alveolar cells. TTF-1 expression decreased in both bronchial, bronchiolar, and alveolar epithelia with advancing gestational age and cytodifferentiation. At term, TTF-1 expression persisted in a few bronchial and bronchiolar basal cells and in all alveolar type II cells, whereas type I cells were negative. In CCAM, TTF-1 was detected in the nuclei of epithelial cells lining the cysts. TTF-1 was expressed in a majority of the bronchiolar-like epithelial cells of the cysts in CCAM types 1, 2, and 3, where almost 100% of the cells were TTF-1 positive. In contrast, TTF-1 expression in the alveolar-like epithelium of CCAM type 4 cysts was restricted to type II cells and only 30%-60% of the lining cells were TTF-1 positive. These results support the hypothesis that CCAM types 1, 2, and 3 reflect abnormalities in lung morphogenesis and differentiation that are distinct from those for CCAM type 4. The role played by TTF-1 in the development of CCAM, if any, is not clear.

Absence of lamellar bodies with accumulation of dense bodies characterizes a novel form of congenital surfactant defect.

Two female sibling full-term newborns developed respiratory distress shortly after birth, which progressed to respiratory failure. Tracheal lavage demonstrated presence of surfactant protein A (SP-A), but little surfactant protein B (SP-B), without aberrant surfactant protein C (SP-C). On a lung biopsy performed in both infants, prominent type II pneumocyte hyperplasia was evident. Through ultrastructural examination an absence of normally formed lamellar bodies was determined, with numerous irregular electron dense bodies within the type II pneumocytes. These electron dense bodies could also be identified in the alveolar spaces and alveolar macrophages. No alveolar tubular myelin was present. Abnormally high immunoreactivity for surfactant proteins SP-A, proSP-B, SP-B, and proSP-C was demonstrated by light microscopy. Presence of incompletely processed immunopositive proSP-B, but not proSP-C was observed in the alveolar lumina. No mutations in either the SP-B or SP-C gene were identified by sequence analysis of amplified cDNA. We conclude that these siblings exhibit an inherited surfactant deficiency characterized by abnormal accumulations of surfactant proteins within the pneumocytes. This abnormal accumulation may be due to a primary secretory defect, a defect in surfactant phospholipids, or an abnormal interaction between the phospholipids and surfactant proteins.

Increased metalloproteinase activity, oxidant production, and emphysema in surfactant protein D gene-inactivated mice.

Targeted ablation of the surfactant protein D (SP-D) gene caused chronic inflammation, emphysema, and fibrosis in the lungs of SP-D (-/-) mice. Although lung morphology was unperturbed during the first 2 weeks of life, airspace enlargement was observed by 3 weeks and progressed with advancing age. Inflammation consisted of hypertrophic alveolar macrophages and peribronchiolar-perivascular monocytic infiltrates. These abnormalities were associated with increased activity of the matrix metalloproteinases, MMP2 and MMP9, and immunostaining for MMP9 and MMP12 in alveolar macrophages. Hydrogen peroxide production by isolated alveolar macrophages also was increased significantly (10-fold). SP-D plays a critical role in the suppression of alveolar macrophage activation, which may contribute to the pathogenesis of chronic inflammation and emphysema.

Allelic heterogeneity in hereditary surfactant protein B (SP-B) deficiency.

Inability to produce surfactant protein B (SP-B) causes fatal neonatal respiratory disease. A frame-shift mutation (121ins2) is the predominant but not exclusive cause of disease. To determine the range of mechanisms responsible for SP-B deficiency, both alleles from 32 affected infants were characterized. Sixteen infants were homozygous for the 121ins2 mutation, 10 infants were heterozygous for the 121ins2 and another mutation, and six infants were homozygous for other mutations. Thirteen novel SP-B gene mutations were identified, which were not found in a control population. One novel mutation was found in two unrelated families. Surfactant protein expression was evaluated by immunohistochemistry and/or protein blotting. Absence of proSP-B and mature SP-B was associated with nonsense and frame-shift mutations. In contrast, proSP-B expression was associated with missense mutations, or mutations causing in-frame deletions or insertions, and low levels of mature SP-B expression were associated with four mutations. Extracellular staining for proSP-C and/or aberrantly processed SP-C was observed in lungs of all infants with SP-B gene mutations. Hereditary SP-B deficiency is caused by a variety of distinct mutations in the SP-B gene and may be associated with reduced, as well as absent, levels of mature SP-B, likely caused by impaired processing of proSP-B.

Deficiency of lamellar bodies in alveolar type II cells associated with fatal respiratory disease in a full-term infant.

We report a case of a full-term female infant who presented with severe respiratory distress shortly after birth and died at 23 d of age with unremitting respiratory failure. Infectious and other known causes of respiratory disease in this clinical setting were excluded. Examination of a lung biopsy showed abnormal lung parenchyma with features reminiscent of desquamative interstitial pneumonitis. Ultrastructural studies revealed that alveolar type II cells lacked cytoplasmic lamellar bodies, while other organelles appeared normal. Histochemical and immunohistochemical investigations indicated normal alveolar type II cell marker expression including surfactant proteins (SP-A, SP-B, pro-SP-B, and pro-SP-C). Mutations in the coding sequences of the SP-B gene were excluded as a cause of disease. This case appears to be a novel congenital defect affecting the pulmonary surfactant system. The cellular abnormality may involve the assembly of cytoplasmic lamellar bodies in alveolar type II cells-the principal storage site of pulmonary surfactant.

Surfactant protein B corrects oxygen-induced pulmonary dysfunction in heterozygous surfactant protein B-deficient mice.

Surfactant protein B (SP-B) is a 79-amino acid hydrophobic surfactant protein that plays a critical role in postnatal lung function. Homozygous SP-B (-/-)-deficient mice die of respiratory failure at birth, associated with severe pulmonary dysfunction and atelectasis. Heterozygous SP-B (+/-)-deficient mice have 50% less SP-B protein, proprotein, and SP-B mRNA compared with control mice and are highly susceptible to oxygen-induced lung injury. In the current study, we tested whether the susceptibility of SP-B (+/-) mice to hyperoxia was restored by intratracheal administration of exogenous SP-B. After exposure to 95% oxygen for 3 d, opening pressures were increased and maximal lung volumes were significantly decreased in SP-B (+/-) mice compared with SP-B (+/+) mice. SP-B (+/-) mice were administered purified bovine SP-B (2%) with DL-alpha dipalmitoyl phosphatidylcholine (DPPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-( -glycerol)] (POPG) phospholipids or DPPC and POPG phospholipids intratracheally and exposed to 95% oxygen. SP-B-treated SP-B (+/-) mice survived longer in 95% oxygen. Although decreased lung function in SP-B (+/-) mice exposed to oxygen was not altered by administration of DPPC and POPG, administration of lipids containing 2% purified bovine SP-B restored lung function when assessed after 3 d in oxygen. Abnormalities in pulmonary function in SP-B (+/-) mice after oxygen exposure were associated with increased alveolar capillary leak, which was corrected by administration of SP-B with DPPC and POPG. Likewise, histologic abnormalities caused by oxygen-induced lung injury were improved by administration of SP-B with DPPC and POPG. Administration of phospholipids with the active SP-B peptide was sufficient to restore pulmonary function and prevent alveolar capillary leak after oxygen exposure, demonstrating the protective role of SP-B during oxygen-induced lung injury.

Surfactant protein-B-deficient mice are susceptible to hyperoxic lung injury.

Surfactant protein-B (SP-B) is a small, hydrophobic peptide that plays a critical role in pulmonary function and surfactant homeostasis. To determine whether SP-B protects mice from oxygen-induced injury, heterozygous SP-B(+/-) gene-targeted mice and wild-type SP-B(+/+) littermates were exposed to hyperoxia (95% oxygen for 3 d) or room air. Although specific lung compliance in room air in SP-B(+/-) mice was slightly reduced as compared with that in SP-B(+/+) mice, it was reduced more markedly during hyperoxia (46% versus 25% decrease, respectively). The larger decrease in lung compliance in SP-B(+/-) mice was associated with increased severity of pulmonary edema, hemorrhage and inflammation, lung permeability and protein leakage into the alveolar space. Hyperoxia increased SP-B messenger RNA (mRNA) and total protein concentrations by 2-fold in SP-B(+/+) and SP-B(+/-) mice, but decreased the abundance of SP-B protein in lavage fluid relative to total protein only in SP-B(+/-) mice. Hyperoxia increased SP-B expression, but apparently not enough to maintain SP-B function and lung compliance in the presence of increased protein leakage in SP-B(+/-) mice. Increased alveolar-capillary leakage and relative deficiency of SP-B may therefore contribute to oxygen-induced pulmonary dysfunction in SP-B(+/-) mice. These data support the concept that SP-B plays an important protective role in the lung.