The ontogeny and distribution of surfactant protein B in human fetuses and newborns

Human decidua-derived mesenchymal stem cells differentiate into functional alveolar type II-like cells that synthesize and secrete pulmonary surfactant complexes

Lung alveolar type II (ATII) cells are specialized in the synthesis and secretion of pulmonary surfactant, a lipid-protein complex that reduces surface tension to minimize the work of breathing. Surfactant synthesis, assembly and secretion are closely regulated and its impairment is associated with severe respiratory disorders. At present, well-established ATII cell culture models are not available. In this work, Decidua-derived Mesenchymal Stem Cells (DMSCs) have been differentiated into Alveolar Type II- Like Cells (ATII-LCs), which display membranous cytoplasmic organelles resembling lamellar bodies, the organelles involved in surfactant storage and secretion by native ATII cells, and accumulate disaturated phospholipid species, a surfactant hallmark. Expression of characteristic ATII cells markers was demonstrated in ATII-LCs at gene and protein level. Mimicking the response of ATII cells to secretagogues, ATII-LCs were able to exocytose lipid-rich assemblies, which displayed highly surface active capabilities, including faster interfacial adsorption kinetics than standard native surfactant, even in the presence of inhibitory agents. ATII-LCs could constitute a highly useful ex vivo model for the study of surfactant biogenesis and the mechanisms involved in protein processing and lipid trafficking, as well as the packing and storage of surfactant complexes.

Napsin A Is Differentially Expressed in Sclerosing Hemangiomas of the Lung

Context.—Sclerosing hemangiomas (SH) are lung tumors characterized by surface cuboidal cells and round stromal cells. The cell of origin remains controversial, though immunohistochemical and ultrastructural studies suggest primitive respiratory epithelium. Napsin A, a human aspartic proteinase found primarily in type II pneumocytes and alveolar macrophages, is emerging as a helpful immunohistochemical marker in characterizing the origin of lung neoplasms, and may be of use in evaluating SH.

Objective.—To evaluate napsin A immunohistochemical staining in SH to further characterize the cell of origin.

Design.—Six cases of SH were stained for napsin A, as well as thyroid transcription factor 1 and cytokeratin in selected cases.

Results.—Surface and round cells were positive for thyroid transcription factor 1 in all cases stained with this marker. Cytokeratins were positive in surface cells in all cases stained with this marker; 2 cases had focal cytokeratin staining in round cells. Round cells had focal napsin A staining in 1 case (17%); surface cells were napsin positive in all cases.

Conclusions.—The observation of thyroid transcription factor 1 positivity in both surface and round cells in all SH suggests primitive respiratory epithelium as the cell of origin of SH. Our napsin A findings support this, with positivity in surface cells of all tumors (100%), and focal round cell staining in only 1 (17%). In fact, surface cells may represent entrapped type II pneumocytes, which normally express napsin A in a granular cytoplasmic pattern, similar to surface cells. The coexpression of thyroid transcription factor 1 and napsin A also introduces a caveat in differentiating primary pulmonary adenocarcinomas from SH in small biopsy specimens.

Genetic disorders of surfactant dysfunction

Mutations in the genes encoding the surfactant proteins B and C (SP-B and SP-C) and the phospholipid transporter, ABCA3, are associated with respiratory distress and interstitial lung disease in the pediatric population. Expression of these proteins is regulated developmentally, increasing with gestational age, and is critical for pulmonary surfactant function at birth. Pulmonary surfactant is a unique mixture of lipids and proteins that reduces surface tension at the air-liquid interface, preventing collapse of the lung at the end of expiration. SP-B and ABCA3 are required for the normal organization and packaging of surfactant phospholipids into specialized secretory organelles, known as lamellar bodies, while both SP-B and SP-C are important for adsorption of secreted surfactant phospholipids to the alveolar surface. In general, mutations in the SP-B gene SFTPB are associated with fatal respiratory distress in the neonatal period, and mutations in the SP-C gene SFTPC are more commonly associated with interstitial lung disease in older infants, children, and adults. Mutations in the ABCA3 gene are associated with both phenotypes. Despite this general classification, there is considerable overlap in the clinical and histologic characteristics of these genetic disorders. In this review, similarities and differences in the presentation of these disorders with an emphasis on their histochemical and ultrastructural features will be described, along with a brief discussion of surfactant metabolism. Mechanisms involved in the pathogenesis of lung disease caused by mutations in these genes will also be discussed.

Developmental and genetic regulation of human surfactant protein B in vivo

BACKGROUND

Genetic and developmental disruption of surfactant protein B (SP-B) expression causes neonatal respiratory distress syndrome (RDS).

OBJECTIVES

To assess developmental and genetic regulation of SP-B expression in vivo.

METHODS

To evaluate in vivo developmental regulation of SP-B, we used immunoblotting to compare frequency of detection of mature and pro-SP-B peptides in developmentally distinct cohorts: 24 amniotic fluid samples, unfractionated tracheal aspirates from 101 infants >or=34 weeks' gestation with (75) and without (26) neonatal RDS, and 6 nonsmoking adults. To examine genetic regulation, we used univariate and logistic regression analyses to detect associations between common SP-B (SFTPB) genotypes and SP-B peptides in the neonatal RDS cohort.

RESULTS

We found pro-SP-B peptides in 24/24 amniotic fluid samples and in 100/101 tracheal aspirates from newborn infants but none in bronchoalveolar lavage from normal adults (0/6) (p < 0.001). We detected an association (p = 0.0011) between pro-SP-B peptides (M(r) 40 and 42 kDa) and genotype of a nonsynonymous single nucleotide polymorphism at genomic position 1580 that regulates amino-terminus glycosylation.

CONCLUSIONS

Pro-SP-B peptides are more common in developmentally less mature humans. Association of genotype at genomic position 1580 with pro-SP-B peptides (M(r) 40 and 42 kDa) suggests genetic regulation of amino terminus glycosylation in vivo.

The concentration of surfactant protein-A in amniotic fluid decreases in spontaneous human parturition at term

OBJECTIVE

The fetus is thought to play a central role in the onset of labor. Pulmonary surfactant protein (SP)-A, secreted by the maturing fetal lung, has been implicated in the mechanisms initiating parturition in mice. The present study was conducted to determine whether amniotic fluid concentrations of SP-A and SP-B change during human parturition.

STUDY DESIGN

Amniotic fluid SP-A and SP-B concentrations were measured with a sensitive and specific ELISA in the following groups of pregnant women: (1) mid-trimester of pregnancy, between 15 and 18 weeks of gestation (n = 29), (2) term pregnancy not in labor (n = 28), and (3) term pregnancy in spontaneous labor (n = 26). Non-parametric statistics were used for analysis.

RESULTS

SP-A was detected in all amniotic fluid samples. SP-B was detected in 24.1% (7/29) of mid-trimester samples and in all samples at term. The median amniotic fluid concentrations of SP-A and SP-B were significantly higher in women at term than in women in the mid-trimester (SP-A term no labor: median 5.6 microg/mL, range 2.2-15.2 microg/mL vs. mid-trimester: median 1.64 microg/mL, range 0.1-4.7 microg/mL, and SP-B term no labor: median 0.54 microg/mL, range 0.17-1.99 microg/mL vs. mid-trimester: median 0 microg/mL, range 0-0.35 microg/mL; both p < 0.001). The median amniotic fluid SP-A concentration in women at term in labor was significantly lower than that in women at term not in labor (term in labor: median 2.7 microg/mL, range 1.2-10.1 microg/mL vs. term no labor: median 5.6 microg/mL, range 2.2-15.2 microg/mL; p < 0.001). There was no significant difference in the median amniotic fluid SP-B concentrations between women in labor and those not in labor (term in labor: median 0.47 microg/mL, range 0.04-1.32 microg/mL vs. term no labor: median 0.54 microg/mL, range 0.17-1.99 microg/mL; p = 0.2).

CONCLUSION

The amniotic fluid concentration of SP-A decreases in spontaneous human parturition at term.

Distribution of intracellular and secreted surfactant during postnatal rat lung development

Pulmonary surfactant prevents alveolar collapse via reduction of surface tension. In contrast to human neonates, rats are born with saccular lungs. Therefore, rat lungs serve as a model for investigation of the surfactant system during postnatal alveolar formation. We hypothesized that this process is associated with characteristic structural and biochemical surfactant alterations. We aimed to discriminate changes related to alveolarization from those being either invariable or follow continuous patterns of postnatal changes. Secreted active (mainly tubular myelin (tm)) and inactive (unilamellar vesicles (ulv)) surfactant subtypes as well as intracellular surfactant (lamellar bodies (lb)) in type II pneumocytes (PNII) were quantified before (day (d) 1), during (d 7), at the end of alveolarization (d 14), and after completion of lung maturation (d 42) using electron microscopic methods supplemented by biochemical analyses (phospholipid quantification, immunoblotting for SP-A). Immunoelectron microscopy determined the localization of surfactant protein A (SP-A). (1) At d 1 secreted surfactant was increased relative to d 7-42 and then decreased significantly. (2) Air spaces of neonatal lungs comprised lower fractions of tm and increased ulv, which correlated with low SP-A concentrations in lung lavage fluid (LLF) and increased respiratory rates, respectively. (3) Alveolarization (d 7-14) was associated with decreasing PNII size although volume and sizes of Lb continuously increased. (4) The volume fractions of Lb correlated well with the pool sizes of phospholipids in lavaged lungs. Our study emphasizes differential patterns of developmental changes of the surfactant system relative to postnatal alveolarization.

Expression of ABCA3 in developing lung and other tissues

ABCA3 is a member of the ATP-binding cassette (ABC) family of transport proteins and is required for perinatal respiratory adaptation. Monoclonal and polyclonal antibodies were generated against a recombinant human ABCA3 peptide and used to assess its expression in the developing lung and adult tissues. Immunostaining for ABCA3 was detected at highest levels in type II epithelial cells of the lung but was also noted in other organs including liver, stomach, kidney, adrenal, pancreas, trachea, and brain. In the fetal lung, ABCA3 staining and mRNA increased prior to birth. Like other surfactant protein genes, ABCA3 expression was induced by thyroid transcription factor-1 in vitro. ABCA3 was coexpressed with SP-B and proSP-C in type II epithelial cells. ABCA3 staining was detected surrounding large, intracellular organelles consistent with its association with lamellar bodies. In the human fetal lung, ABCA3 staining was not detected prior to 22-23 weeks of gestation, except in the presence of pulmonary inflammation. ABCA3 was detected in type II epithelial cells of the human lung from 28 weeks of gestation and thereafter. Postnatally, intense ABCA3 staining was observed in hyperplastic epithelial cells relining injured airways in infants with chronic lung disease. Localization and regulation of ABCA3 in the respiratory epithelium is consistent with its proposed role in surfactant homeostasis. The role of ABCA3 in extrapulmonary tissues and organs remains to be elucidated. This manuscript contains online supplemental material at (www.jhc.org). Please visit this article online to view these materials.

Distribution of surfactant proteins in type II pneumocytes of newborn, 14-day old, and adult rats: an immunoelectron microscopic and stereological study

Surfactant proteins (SP) have an important impact on the function of the pulmonary surfactant. In contrast to humans, rat lungs are immature at birth. Alveolarization starts on postnatal day 4. Little is known about the distribution of SP during postnatal alveolarization. By immunoelectron microscopy, we studied the distribution of SP-A, SP-D, SP-B, and precursors of SP-C in type II pneumocytes before, near the end and after alveolarization and in mature lungs. We determined the subcellular volume fractions and the relative labeling index to obtain information about preferential labeling of compartments and non-randomness of labeling. Independently of alveolarization, the overall cellular distribution of SP was non-random. A preferential labeling for SP-A and SP-D was found in small vesicles and multivesicular bodies (mvb). SP-B and precursors of SP-C were localized in mvb and lamellar bodies (lb). There are no postnatal changes in labeling for all three SP in these compartments. Labeling intensity for SP-B in lb increased in close correlation with a significant increase in the volume fractions of lb during alveolarization. Our results support the concept that postnatal alveolarization in rat lungs is associated with significant increases in the SP-B content in lb and volume fraction of lb in type II pneumocytes. The postnatal compartment-specific distribution of SP-A, precursors of SP-C and SP-D does not change.

Decrease of the surface fraction of surfactant proteins containing clara cells and type II pneumocytes in a rat asthma model

In asthma surfactant proteins (SP) might differ in distribution and composition and thus play a role in pathophysiology of this disease. Therefore, the well-established animal model of ovalbumin sensitized and challenged rats were used to study the distribution of surfactant proteins in Clara cells and type II pneumocytes. Serial sections of paraffin embedded lung tissue were sequentially immunostained by the avidin-biotin-peroxidase complex (ABC) technique. Antisera against SP-A, SP-B and Clara cell specific protein (CC10) were used. We determined stereologically' the surface fraction of immunolabelled cells and semiquantitatively the percentage of test fields containing labelled alveolar macrophages. In allergen sensitized and provocated rat lungs: (1) the surface fraction of SP-A and SP-B positive Clara cells was significantly reduced, (2) the surface fraction of Clara cells stained with CC10 was coincided with controls, (3) the surface fraction of SP-A and not of SP-B possitive type II pneumocytes decreased significantly, (4) a significantly higher percentage of test fields with SP-A labelled alveolar macrophages was evaluated. Thus, in this animal model of asthma the inflammatory process after allergen challenge is accompanied by alterations in the distribution patterns of SP in Clara cells and type II pneumocytes.

Expression of epithelial sodium channel α-subunit mRNAs with alternative 5′-untranslated regions in the developing human lung

In preparation for birth, lung epithelia must switch from net fluid secretion, required for lung development, to net absorption, which prepares the lungs for postnatal gas exchange. The apical membrane amiloride-sensitive epithelial Na channel (ENaC) is the rate-limiting step for Na+ and fluid absorption. Expression of α-ENaC mRNA has been detected in human lung as early as the embryonic stage of development. However, humans express multiple transcripts for α-ENaC, containing differing 5′-untranslated regions (UTR) with unknown effects on protein translation, and different ontogenies for individual transcripts could provide a novel mechanism for developmental regulation of ENaC function. To assess the relative expression of the two most abundant α-ENaC transcripts (α-ENaC1 and α-ENaC2) during lung development, we performed nonradioactive in situ hybridization using probes specific to the alternative 5′-UTRs. Both transcripts were expressed throughout intrauterine lung development (8 to 40 wk gestation), and expression was localized to the surface epithelial cells of the conductive and respiratory airways in both ciliated cells and nonciliated Clara cells. α-ENaC mRNA expression was also identified in the serous cells of the submucosal glands surrounding the proximal airways. In the mature prenatal lung, subsets of alveolar type II (ATII) cells expressed one or both of the α-ENaC transcripts. Our observations demonstrate that a developmentally regulated switch between α-ENaC 5′-UTR variants is not the trigger by which the developing human lung becomes a fluid-absorbing organ at birth, that individual ATII cells express neither, one, or both of the α-ENaC transcripts, and that the overall expression is linked to epithelial cell differentiation and lung maturation.

Circadian rhythm of surfactant protein A, B and C mRNA in rats

BACKGROUND

All organisms have developed an internal timing system capable of reacting to and anticipating environmental stimuli with a program of appropriately timed metabolic, physiologic and behavioral events. The alveolar epithelial type II cell of the mammalian lung synthesizes, stores, and secretes a lipoprotein pulmonary surfactant, which functions to stabilize alveoli at low lung volumes.

METHODS

The authors investigated the diurnal variation of surfactant protein A, B and C mRNA accumulation. The diunal variation on gene expression of surfactant protein A, B and C was analysed using filter hybridization at 9 a.m., 4 p.m. and 11 p.m. Lung SP-A protein content was determined by double sandwich ELISA assay using a polyclonal antiserum raised in rabbits against purified rat SP-A.

RESULTS

1. The accumulation of SP-A mRNA at 4 p.m. was significantly decreased by 23.5% compared to the value at 9 a.m. (p < 0.05). 2. The accumulation of SP-B mRNA at 4 p.m. and 11 p.m. was decreased by 15.1% and 5.7%, respectively, compared to the value at 9 a.m. (p = 0.07, p = 0.69). 3. The accumulation of SP-C mRNA at 4 p.m. and 11 p.m. was decreased by 6.8% and 7.7%, respectively, compared to the value at 9 a.m. (p = 0.38, p = 0.57). 4. Total lung SP-A content at 4 p.m. and 11 p.m. was increased by 5.3% and 15.9%, respectively, compared to the value at 9 a.m. (p = 0.64, p = 0.47).

CONCLUSION

These findings represent the diurnal variation of surfactant proteins mRNA expression in vivo. These results indicated that the diurnal variation of significant gene expression is observed in hydrophilic surfactant protein rather than in hydrophobic surfactant proteins.

Different expression of surfactant protein B mature peptide and proprotein at 21 weeks' gestation in human fetal pulmonary epithelial cells

AIM

The aim of this study is to evaluate the maturation of pulmonary epithelial cells in human fetal lungs at 21 weeks' gestation.

METHODS

Eight fetuses at 21 weeks' gestation were evaluated. The maturation of pulmonary epithelial cells was assessed by immunohistochemical examination for surfactant proteins and by electron microscopy.

RESULTS

Surfactant protein B mature peptide was detected slightly in the epithelial lining of the bronchioles, but was totally absent in the terminal airways. Surfactant protein B proprotein was clearly detected in the epithelial lining of both bronchioles and terminal airways. Transmission electron microscopy of terminal airway cells showed abundant glycogen granules and few intracellular organelles.

CONCLUSIONS

The production of mature surfactant protein B in terminal airways is scarce at 21 weeks' gestation, which is associated with the immature mechanism of proprotein processing in the cytoplasm.

Human surfactant protein B promoter in transgenic mice: temporal, spatial, and stimulus-responsive regulation

Surfactant protein B (SP-B) is a developmentally and hormonally regulated lung protein that is required for normal surfactant function. We generated transgenic mice carrying the human SP-B promoter (-1,039/+431 bp) linked to chloramphenicol acetyltransferase (CAT). CAT activity was high in lung and immunoreactive protein localized to alveolar type II and bronchiolar epithelial cells. In addition, thyroid, trachea, and intestine demonstrated CAT activity, and each of these tissues also expressed low levels of SP-B mRNA. Developmental expression of CAT activity and SP-B mRNA in fetal lung were similar and both increased during explant culture. SP-B mRNA but not CAT activity decreased during culture of adult lung, and both were reduced by transforming growth factor (TGF)-beta(1). Treatment of adult mice with intratracheal bleomycin caused similar time-dependent decreases in lung SP-B mRNA and CAT activity. These findings indicate that the human SP-B promoter fragment directs tissue- and lung cell-specific transgene expression and contains cis-acting elements involved in regulated expression during development, fetal lung explant culture, and responsiveness to TGF-beta and bleomycin-induced lung injury.

Pulmonary epithelial cell maturation in hyperplastic lungs associated with fetal tracheal agenesis

BACKGROUND/PURPOSE

Cellular differentiation of pulmonary hyperplasia has not been reported in human cases. The authors studied surfactant protein expression and ultrastructure of pulmonary epithelial cells in fetal hyperplastic lungs associated with congenital tracheal agenesis.

METHODS

The maturation of pulmonary epithelial cells was assessed by immunohistochemical examination for surfactant proteins (SP-A, mature SP-B, proSP-B, proSP-C, and SP-D) and transmission electron microscopy. As controls normal lung portions of 8 fetuses born at 21 weeks gestation were used.

RESULTS

Mature SP-B and SP-D was detected in terminal airways in this case, but not in controls. In electron microscopy, lamellar bodies were recognized, and glycogen granules were less abundant in terminal airway cells.

CONCLUSION

The differentiation of pulmonary epithelial cells appeared to be more advanced for the gestational age in pulmonary hyperplasia with congenital tracheal agenesis. J Pediatr Surg 36:1845-1848.

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.

A clinicopathologic study of 100 cases of pulmonary sclerosing hemangioma with immunohistochemical studies: TTF-1 is expressed in both round and surface cells, suggesting an origin from primitive respiratory epithelium

Pulmonary sclerosing hemangioma (SH) is a lung neoplasm of uncertain histogenesis that is composed of two major cell types: surface and round cells. The authors studied 100 cases of pulmonary SH that presented as a peripheral (95%), solitary (96%) mass of less than 3 cm in diameter (74%) in asymptomatic patients who were mostly women (83%) with a mean age of 46.2 years. Immunohistochemistry of multiple epithelial, mesothelial, pneumocyte, neuroendocrine, and mesenchymal markers was performed on 47 cases to investigate the histogenesis of this neoplasm. Both surface and round cells stained with epithelial membrane antigen (EMA) and thyroid transcription factor-1 (TTF-1) in more than 90% of cases; however, the round cells were uniformly negative for pancytokeratin and positive for cytokeratin-7 and CAM 5.2 in only 31% and 17% of cases, respectively. Surfactant proteins A and B as well as Clara cell antigen were positive in varying numbers of surface cells but they were negative in the round cells. Neuroendocrine cells either as isolated scattered cells or as a tumorlet within the center of SH were detected (chromogranin, Leu-7, synaptophysin positive) in three cases. The expression of TTF-1 in the absence of surfactant proteins A and B and Clara cell antigens in the round cells of SH suggests that they are derived from primitive respiratory epithelium. The alveolar pneumocytes and neuroendocrine cells may either represent phenotypic differentiation of a primitive respiratory epithelial component or they may correspond to non-neoplastic entrapped or hyperplastic elements. The concomitant positivity of both cell types in SH for TTF-1 and EMA, and the negativity of round cells for pancytokeratin and neuroendocrine markers, provide useful clues not only for histogenesis but also for the diagnosis of this lung neoplasm.

HNF-3/forkhead homologue-4 influences lung morphogenesis and respiratory epithelial cell differentiation in vivo

HNF-3/forkhead homologue 4 (HFH-4), a transcription factor of the winged helix/forkhead family, is expressed in various tissues including lung, brain, oviduct, testis, and embryonic kidney. In order to test whether the temporospatial expression of HFH-4 influences lung morphogenesis, HFH-4 was expressed in lungs of transgenic mice under control of the surfactant protein C (SP-C) promoter. The morphology of the lungs from SP-C/HFH-4 embryos (day 18 postconception) was distinctly abnormal, and the severity of the alterations correlated with the level of transgene expression as detected by in situ hybridization. At high levels of expression, HFH-4 altered epithelial cell differentiation and inhibited branching morphogenesis. Atypical cuboidal or columnar cells lined the lung periphery of SP-C/HFH-4 transgenic mice. The atypical epithelial cells seen in the SP-C/HFH-4 mice expressed thyroid transcription factor-1 and hepatocyte nuclear factor 3beta (HNF-3beta). However, surfactant proteins SP-B, SP-C, and Clara cell secretory protein, normally produced by nonciliated epithelial cells in lung parenchyma were lacking. beta-Tubulin IV, a marker of ciliated cells, stained the atypical columnar cells produced by expression of high levels of the SP-C/HFH-4 transgene. Ectopic expression of HFH-4 in developing mouse lung altered epithelial cell differentiation and morphology, restricting the expression of markers typical of nonciliated cells of the distal lung parenchyma.

Congenital cystic adenomatoid malformation of the lung (CCAM): evaluation of the cellular components

Congenital cystic adenomatoid malformation of the lung (CCAM) is a rare congenital lesion whose pathogenesis is not well defined. It is generally accepted that the various types of CCAMs originate at different levels of the tracheobronchial tree. To further define the pathogenesis of CCAM, we evaluated the cellular composition of different CCAM types by immunohistochemistry. Twenty-two CCAMs (17 CCAM type 1, two type 2, one type 3, and two type 4) were collected. The cellular composition was determined using immunohistochemical stains for type I cell-associated antigen (T1 cell-Ag), surfactant proteins and surfactant protein precursors (SP-A, SP-B, proSP-B, and proSP-C), neuroendocrine cells (GRP), Clara cells (UP-1), and the adhesion molecule CD44v6, a glycoprotein thought to be involved in cell-matrix and cell-cell interactions. Eleven fetal lungs also were analyzed to compare cytodifferentiation of the epithelial-lined cysts of the different types of CCAM with the stages of normal lung development. Our results indicate that CCAM is caused by an arrest in lung development, and, on the basis of cytodifferentiation, two major subtypes can be distinguished. One subtype consisting of CCAM types 1, 2, and 3 that shows a bronchiolar type of epithelium and a second subtype, consisting of CCAM type 4, that has an acinar-alveolar type of epithelium. Our findings also suggest that these two subtypes may arise at different stages of the branching of the bronchopulmonary tree, the first at the pseudoglandular stage and the second at the saccular stage.

Site specificity of surfactant protein expression in airways of baboons during gestation

BACKGROUND

There are disparate reports concerning the presence of surfactant proteins in the airways of lung. The recent finding of SP-A in tracheobronchial epithelium and submucosal glands in lungs from second trimester humans has renewed interest in potential new functions of surfactant in lung biology.

METHODS

In situ hybridization studies were done to determine the distribution of SP-A, SP-B, and SP-C in baboon lung specimens from 60, 90, 120, 140, 160, and 180 (term) days of gestation and adults. Lungs from gestation controls were obtained at the time of hysterotomy and adult lungs at necropsy. Riboprobes used for in situ hybridization contained the entire coding regions for human SP-A, SP-B, and SP-C.

RESULTS

At 60 days, SP-C mRNA expression was evident in focal portions of primitive tubular epithelium but not bronchi. This distal pattern of SP-C mRNA expression persisted and was present in some epithelial cells of respiratory bronchioles at term. At 90 days, SP-A mRNA expression was present in the epithelium of trachea and large bronchi. SP-B mRNA expression was found in small bronchi, bronchioles, and distal tubular epithelium at 120 days of gestation. SP-A mRNA bronchiolar localization became evident at 140 days of gestation and alveolar type 2 cellular expression at 160 days of gestation. Abrupt transitions of surfactant protein expression were identified (e.g., SP-A mRNA-positive cells in the epithelium of large bronchi with adjoining SP-B mRNA expression in small bronchi and bronchioles).

CONCLUSIONS

Findings in the baboon indicate that there are well-delineated sites of surfactant protein mRNA expression in bronchial and bronchiolar epithelia. mRNA expressions of SP-A and SP-B are present in both bronchial and bronchiolar epithelium but at different sites, whereas SP-C expression is seen in loci of epithelial cells in respiratory bronchioles.

Targeting type II and Clara cells for adenovirus-mediated gene transfer using the surfactant protein B promoter

We examined the ability of the human surfactant protein B (SP-B) promoter to confer cell specificity of transgene expression in an adenoviral vector. Using similar replication-deficient adenoviruses (rAd), we compared lacZ reporter gene expression driven by the human SP-B promoter (rAd.SPBlacZ) with the ubiquitously expressed Rous sarcoma virus promoter (rAd.RSVlacZ). rAd.SPBlacZ expressed lacZ in H-441 and A549 lung epithelial cell lines and not in HeLa cells whereas rAd.RSVlacZ expressed in all three cell lines. In primary human fetal lung fibroblasts, beta-galactosidase activity from rAd.RSVlacZ transduction increased in a dose-dependent manner whereas activity from rAd.SPBlacZ remained low. In mixed cell cultures prepared from human fetal lung explants that contained fibroblasts and type II cells, X-Gal staining localized rAd.SPBlacZ expression to only type II cells whereas rAd.RSVlacZ expressed in both cell types. In 24-wk gestation human fetal tissue explants infected ex vivo, the RSV promoter directed lacZ expression in lung, trachea, heart, liver, and esophagus, whereas with the SP-B promoter lacZ was expressed only in lung, specifically in air space-lining cells. This specificity was maintained in vivo. lacZ expression was undetectable in lung and other tissues after intravenous administration of rAd.SPBlacZ whereas rAd.RSV-lacZ expressed primarily in liver. After intratracheal instillation of rAd.SPBlacZ into mice, X-Gal staining localized expression to type II and Clara cells. In contrast, rAd.RSVlacZ expressed in all pulmonary epithelial cell types. Our results indicate that the SP-B promoter may be useful in targeting type II and Clara cells for gene therapy of conditions such as inherited deficiency of SP-B.

Recombinant adenoviral vector disrupts surfactant homeostasis in mouse lung

Although replication-deficient adenoviruses efficiently transfer genes into epithelial cells of the lung, host immune responses limit the extent and duration of gene expression. To define further the role of inflammatory responses to first-generation, recombinant, deltaE1, deltaE3 adenovirus in lung pathology and surfactant protein homeostasis, expression of the surfactant proteins SP-A, SP-B, and proSP-C was determined by immunohistochemistry 2, 7, and 14 days following intratracheal administration of 2 x 10(9) pfu of a recombinant adenovirus, Av1Luc1, to BALB/c nu/nu and BALB/c wild-type mice. Two to 7 days after virus administration, an acute inflammatory response was observed in both mouse strains. Respiratory epithelial cells were sloughed, and extracellular accumulation of SP-A and SP-B was detected in the airways. Diminished immunostaining for SP-A and SP-B was noted in type II cells, and SP-A and SP-B mRNA expression was decreased in focal regions of the lungs from both mouse strains. One week after virus administration, immunostaining for proSP-C was markedly increased in cells lining the regenerating alveolar epithelial surfaces. Two weeks after Av1Luc1 treatment of nu/nu mice, immunostaining for SP-A, SP-B, and proSP-C was similar to those patterns observed prior to adenoviral administration. In immunocompetent wild-type mice, however, immunostaining for surfactant proteins was absent in areas associated with chronic lymphocytic infiltration. The recombinant adenoviral vector, Av1Luc1, caused acute inflammatory responses in the respiratory epithelium with disruption of surfactant protein homeostasis in both wild-type and nu/nu mice. Alterations in surfactant homeostasis persisted in wild-type mice. Thus, both acute and thymic-dependent immune responses limit transgene expression and disrupt surfactant protein gene expression and homeostasis. Because surfactant proteins are critical to host defense and to the maintenance of alveolar stability following injury, these findings raise concerns regarding both acute and chronic toxicity of first-generation recombinant adenoviral vectors for gene transfer.

Immunohistochemical distribution of surfactant apoproteins in hypoplastic lungs of nonimmunologic hydrops fetalis

Forty-three patients with nonimmunologic hydrops fetalis (NIHF), including 32 patients (74%) with hypoplastic lung, were immunohistochemically examined for the expression of surfactant apolipoproteins (SPs), using anti-gamma G immunoglobulins against human SP-A with a molecular weight (MW) of 35 K and SP-B with a MW of 5 K compared with that in 59 patients in a control group and 45 patients with hypoplastic lung induced by causes other than NIHF. In the control group, SP-A was expressed in the lungs from 23 gestational weeks and became more numerous and intense in alveolar type II cells after 31 gestational weeks, whereas SP-B began to be expressed from 20 gestational weeks, and almost all patients showed a diffuse positivity after 26 gestational weeks. In the NIHF group, SP-A expression was generally weak, even after 31 gestation weeks. Moreover, most of the patients showing a weak expression of SP-A were also associated with hypoplastic lung and had a clinical history of persistent intrauterine pleural effusion of more than 2 weeks. Conversely, the immunoreactivity of SP-B was well preserved in NIHF cases either with or without hypoplastic lung. These results suggest that in the NIHF lung, there is a possible delay in the functional maturation or development of SP-A synthesis by alveolar type II cells, and this retardation of the functional maturation in type II cells also participates in the postnatal respiratory insufficiency in NIHF.

Keratinocyte growth factor is a growth factor for type II pneumocytes in vivo

Keratinocyte growth factor (KGF) administered as a single intratracheal injection causes a prominent dose-dependent proliferation of type II alveolar epithelial cells in the lungs of adult rats. The increase in mitotically active alveolar cells histologically appears as a micropapillary epithelial cell hyperplasia after 2 d and peaks after 3 d in the form of monolayers of cuboidal epithelial cells lining alveolar septae. Proliferating cell nuclear antigen immunohistochemistry confirmed the profound proliferative response induced by KGF. The hyperplastic alveolar lining cells contain immunoreactive surfactant protein B and are ultrastructurally noted to contain lamellar inclusions characteristic of surfactant-producing type II pneumocytes. Mild focal bronchiolar epithelial hyperplasia is noted but is much less striking than the proliferation of type II pneumocytes. Large airways are unaffected by KGF. Daily intravenous injection of KGF is also able to cause pneumocyte proliferation. The normal adult rat lung constitutively expresses both KGF and KGF receptor mRNA, suggesting that endogenous KGF may be implicated in the paracrine regulation of the growth of pneumocytes. In conclusion, KGF rapidly and specifically induces proliferation and differentiation of type II pneumocytes in the normal adult lung.