Clara cell differentiation in the mouse: ultrastructural morphology and cytochemistry for surfactant protein A and Clara cell 10 kD protein

Postnatal development of the bronchiolar club cells of distal airways in the mouse lung: stereological and molecular biological studies

Club (Clara) cells are nonciliated secretory epithelial cells present in bronchioles of distal pulmonary airways. So far, no information is available on the postnatal differentiation of club cells by a combination of molecular biological, biochemical, and stereological approaches in the murine lung. Therefore, the present study was designed to investigate the changes in the club cell secretory proteins (CC10, surfactant proteins A, B and D) and club cell abundance within the epithelium of bronchioles of distal airways during the postnatal development of the mouse lung. Perfusion-fixed murine lungs of three developmental stages (newborn, 15-day-old and adult) were used. Frozen, unfixed lungs were used for cryosectioning and subsequent laser-assisted microdissection of bronchiolar epithelial cells and RT-PCR analyses. High resolution analyses of the three-dimensional structures and composition of lung airways were obtained by scanning electron microscopy. Finally, using design-based stereology, the total and average club cell volume and the volume of secretory granules were quantified by light and transmission electron microscopy. Our results reveal that murine club cells are immature at birth and differentiate postnatally. Further, increase of the club cell volume and number of intracellular granules are closely correlated to the total lung volume enlargement. However, secretory granule density was only increased within the first 15 days of postnatal development. The differentiation is accompanied by a decrease in glycogen content, and a close positive relationship between CC10 expression and secretory granule abundance. Taken together, our data are consistent with the concept that the morphological and functional differentiation of club cells is a postnatal phenomenon.

Analysis of a lung defect in autophagy-deficient mouse strains

Yeast Atg1 initiates autophagy in response to nutrient limitation. The Ulk gene family encompasses the mammalian orthologs of yeast ATG1. We created mice deficient for both Ulk1 and Ulk2 and found that the mice die within 24 h of birth. When found alive, pups exhibited signs of respiratory distress. Histological sections of lungs of the Ulk1/2 DKO pups showed reduced airspaces with thickened septae. A similar defect was seen in Atg5-deficient pups as both Ulk1/2 DKO and Atg5 KO lungs show numerous glycogen-laden alveolar type II cells by electron microscopy, PAS staining, and increased levels of glycogen in lung homogenates. No abnormalities were noted in expression of genes encoding surfactant proteins but the ability to incorporate exogenous choline into phosphatidylcholine, the major phospholipid component of surfactant, was increased in comparison to controls. Despite this, there was a trend for total phospholipid levels in lung tissue to be lower in Ulk1/2 DKO and Atg5 KO compared with controls. Autophagy was abundant in lung epithelial cells from wild-type mice, but lacking in Atg5 KO and Ulk1/2 DKO mice at P1. Analysis of the autophagy signaling pathway showed the existence of a negative feedback loop between the ULK1 and 2 and MTORC1 and 2, in lung tissue. In the absence of autophagy, alveolar epithelial cells are unable to mobilize internal glycogen stores independently of surfactant maturation. Together, the data suggested that autophagy plays a vital role in lung structural maturation in support of perinatal adaptation to air breathing.

Molecular staging of epithelial maturation using secretory cell-specific genes as markers

Bronchiolar Clara cells undergo phenotypic changes during development and in disease. These changes are poorly described due to a paucity of molecular markers. We used chemical and transgenic approaches to ablate Clara cells, allowing identification of their unique gene expression profile. Flavin monooxygenase 3 (Fmo3), paraoxonase 1 (Pon1), aldehyde oxidase 3 (Aox3), and claudin 10 (Cldn10) were identified as novel Clara cell markers. New and existing Clara cell marker genes were categorized into three classes based on their unique developmental expression pattern. Cldn10 was uniformly expressed in the epithelium at Embryonic Day (E)14.5 and became restricted to secretory cells at E18.5. This transition was defined by induction of CCSP. Maturation of secretory cells was associated with progressive increases in the expression of Fmo3, Pon1, Aox3, and Cyp2f2 between late embryonic and postnatal periods. Messenger RNA abundance of all categories of genes was dramatically decreased after naphthalene-induced airway injury, and displayed a sequence of temporal induction during repair that suggested sequential secretory cell maturation. We have defined a broader repertoire of Clara cell-specific genes that allows staging of epithelial maturation during development and repair.

Achaete-scute homolog-1 linked to remodeling and preneoplasia of pulmonary epithelium

The basic helix-loop-helix protein achaete-scute homolog-1 (ASH1) is involved in lung neuroendocrine (NE) differentiation and tumor promotion in SV40 transgenic mice. Constitutive expression of human ASH-1 (hASH1) in mouse lung results in hyperplasia and remodeling that mimics bronchiolization of alveoli (BOA), a potentially premalignant lesion of human lung carcinomas. We now show that this is due to sustained cellular proliferation in terminal bronchioles and resistance to apoptosis. Throughout the airway epithelium the expression of anti-apoptotic Bcl-2 and c-Myb was increased and Akt/mTOR pathway activated. Moreover, the expression of matrix metalloproteases (MMPs) including MMP7 was specifically enhanced at the bronchiolo-alveolar duct junction and BOA suggesting that MMPs play a key role in this microenvironment during remodeling. We also detected MMP7 in 70% of human BOA lesions. Knockdown of hASH1 gene in human lung cancer cells in vitro suppressed growth by increasing apoptosis. We also show that forced expression of hASH1 in immortalized human bronchial epithelial cells decreases apoptosis. We conclude that the impact of hASH1 is not limited to cells with NE phenotype. Rather, constitutive expression of hASH1 in lung epithelium promotes remodeling through multiple pathways that are commonly activated during lung carcinogenesis. The collective results suggest a novel model of BOA formation via hASH1-induced suppression of the apoptotic pathway. Our study yields a promising new preclinical tool for chemoprevention of peripheral lung carcinomas.

Budesonide effects on Clara cell under normal and allergic inflammatory condition

Clara cells are nonciliated secretory cells implicated in lung homeostasis by the synthesis of immunomodulatory and host defense products, being one of the most important the CC16 protein. In this study, we compared the effects of budesonide (BUD), an inhaled corticoid, on Clara cell biology and its ability to reverse morphofunctional changes induced in an allergic airway hyper-responsiveness mouse model. In normal mice, exposure to BUD induced morphological changes compatible with a state of maximal differentiation on CC16 positive cells which developed a prominent cupola filled up with numerous mitochondria rich in CYP2E1, a member of the cytochrome P450 family. Consequently, CYP2E1 expression raised significantly. Exposure to OVA provoked hypertrophy of Clara cells and an increment in their number per millimeter of basal membrane. These cells acquired a mucous cell phenotype characterized by a notorious expansion of the secretory granular content. Synthesis of CC16 was greatly up-regulated concurrent to the finding of MUC5AC expression and the increment of epidermal growth factor receptor (EGFR). Mitochondrial content decreased significantly with a consequent reduction in CYP2E1 expression. After BUD treatment of OVA-challenged animals, the majority of Clara cells regained their normal morphology and functional characteristics; CYP2E1 levels raised when compared to the OVA exposed group. The BUD potential to differentiate Clara cells appeared to be important for the regression of the profound changes generated by the allergic injury. These results demonstrated the wide range of stimuli that can modify different aspects of Clara cell biology, and highlighted the effects of budesonide as a modulator of P450 enzymes, which probably contributes to a complementary antiinflamatory activity.

Proliferation during early phases of bronchiolar repair in neonatal rabbits following lung injury by 4-ipomeanol

Nonciliated bronchiolar (Clara cells) are progenitor cells during development. During differentiation, they are more susceptible to injury by environmental toxicants metabolized by the cytochrome P450 monooxygenase system, and injury results in altered bronchiolar repair and development. Squamous cells and abnormal cuboidal epithelium persist into early adulthood. The hypothesis tested in this study was that the failure of bronchiolar epithelium to repair normally in neonates following injury is due to an inhibition of proliferation. A model of differential repair in rabbit kits was used. Proliferation was followed for 1 week post injury in rabbit kits treated with a single dose of the P450-mediated cytotoxicant 4-ipomeanol (IPO) at 7 days old (repair abnormal) and compared to rabbits treated with a single dose of IPO at 21 days old (repair normal). Proliferation was measured by the nuclear incorporation of 5-chloro-2'-deoxyuridine (CldU) within epithelium at the target site (terminal bronchiole). The repair pattern between the two age groups was histologically defined. There was no difference in the CldU labeling index during the week of repair between the two age groups, even though the bronchiolar epithelium did not return to normal in the animals treated at 7 days old. In summary, proliferation (through S-phase) is not inhibited during repair in neonatal rabbits treated with IPO at 7 days old compared to animals treated at 21 days old, and we conclude that other factors may be responsible for the altered repair in the young neonates injured by a P450-mediated cytotoxicant.

C/EBP transcription factors in the lung epithelium

During recent years, the biological roles of CCAAT/enhancer binding proteins (C/EBPs) in the lung have started to be uncovered. C/EBPs form a family within the basic region-leucine zipper class of transcription factors. In the lung epithelium C/EBPalpha, -beta, and -delta are expressed. Lung-specific target genes for these transcription factors include the surfactant proteins A and D, the Clara cell secretory protein, and the P450 enzyme CYP2B1. As more information is gathered, a picture is emerging in which C/EBPalpha has a role in regulating proliferation as well as differentiation-dependent gene expression, whereas C/EBPbeta and -delta, in addition to a partly overlapping role in regulating expression of differentiation markers, also seem to be involved in responses to injury and hormones.

Synergistic transactivation of the differentiation-dependent lung gene Clara cell secretory protein (secretoglobin 1a1) by the basic region leucine zipper factor CCAAT/enhancer-binding protein alpha and the homeodomain factor Nkx2.1/thyroid transcription factor-1

The basic region-leucine zipper transcription factor CCAAT/enhancer-binding protein alpha (C/EBPalpha) and the homeodomain transcription factor Nkx2.1/thyroid transcription factor-1 are essential for normal lung morphogenesis. Nkx2.1 is expressed from the onset of lung development, whereas C/EBPalpha expression is turned on at later stages. The expression of C/EBPalpha correlates to the appearance of lung-specific proteins with differentiation-dependent expression patterns, such as the Clara cell secretory protein (secretoglobin 1a1 (Scgb1a1), CCSP). In this study, we demonstrate synergistic transactivation by C/EBPalpha and Nkx2.1 in the regulation of the CCSP gene. We show that the synergistic activity of C/EBPalpha and Nkx2.1 originates from cis-acting elements in the proximal promoter of CCSP and that the synergism is dependent on NH(2)-terminal transactivation domains of C/EBPalpha and Nkx2.1. Our results suggest that the cooperation of C/EBPalpha and Nkx2.1 is a major determinant for the high level, lung epithelial-specific expression of CCSP during the later stages of lung development and in the adult lung.

Amniotic fluid Clara cell protein concentration in normal pregnancy, a marker of fetal airway growth or fetal lung maturation?

OBJECTIVE

To evaluate the relationship of Clara cell protein (CCP) in amniotic fluid (AF) with the lecithin/sphingomyelin (L/S) ratio, and the concentrations of saturated phosphatidylcholine (Sat PC) and surfactant protein A (SP-A).

STUDY DESIGN

AF samples were obtained by amniocentesis from 98 pregnancies without conditions known to influence fetal lung maturation between 25 and 41 weeks of gestation. These samples were used for determinations of CCP, L/S ratio, Sat PC, and SP-A. Simple and multiple linear regressions were used to analyze the data.

RESULTS

CCP in AF increased logarithmically with gestational age (R(2)=0.51, p=0.006). The L/S ratio (R(2)=0.41, p<0.001), and the concentrations of Sat PC (R(2)=0.26, p<0.001) and SP-A (R(2)=0.52, p<0.001) also increased with advancing gestation. Weak correlations of CCP with the L/S ratio (R(2)=0.22, p=0.009) and Sat PC (R(2)=0.12, p=0.004), but not with SP-A (R(2)=0.07, p=0.10), were found. Using multiple linear regressions, gestational age was the only predictor of CCP (F=10.9, R(2)=0.13, p=0.015). Conversely, gestational age, Sat PC, and SP-A accounted for most of the variation of the L/S ratio (F=34.7, R(2)=0.61, p=0.0001).

CONCLUSION

CCP correlated very poorly with known and widely accepted indices of fetal lung maturation. The increasing concentration of CCP in AF throughout gestation probably reflects growth and development of the fetal airways.

Functional overexpression of wild-type p53 correlates with alveolar cell differentiation in the developing human lung

At 15 weeks after conception (a.c.), the human pulmonary acinus is lined by distal low-columnar and more proximal cuboidal cells that are successive stages in alveolar type II cell differentiation (pseudoglandular period of lung development). From 16 weeks a.c. onward, there are also 'flatter' cells that are intermediate stages in the differentiation of cuboidal type II cells into squamous type I cells (canalicular period). We investigated the role of wild-type p53 protein and the proliferation marker Ki-67 in the differentiation of type II and type I cells in these two periods. Serial sections from fetal lungs (n = 30) were immunoincubated with antibodies against p53 and Ki-67. The presence of prospective type II and type I cells was confirmed using immunohistochemistry for surfactant protein SP-A as a differentiation marker and light and electron microscopy. The p53 and Ki-67 positive nuclei were quantified per alveolar cell phenotype (i.e., low-columnar; cuboidal; flatter). The occurrence of cell apoptosis was studied using propidium iodide (PI) and 4',6'-diamino-2-phenylindol dihydrochloride (DAPI) staining. The combined increase in p53 expression and decrease in Ki-67 expression during alveolar epithelial cell differentiation suggests that wild-type p53 protein plays a role in the differentiation of alveolar type II and type I cells in the human lung, and that this function is mediated through cell cycle arrest. The rare incidence of apoptotic nuclei in alveolar type II cells, together with their absence in alveolar type I cells, supports the view that p53 is involved in the differentiation, rather than the death, of alveolar epithelial cells.

Conditional clara cell ablation reveals a self-renewing progenitor function of pulmonary neuroendocrine cells

The neuroepithelial body (NEB) is a highly dynamic structure that responds to chronic airway injury through hyperplasia of associated pulmonary neuroendocrine (PNE) cells. Although NEB dysplasia is correlated with preneoplastic conditions and PNE cells are thought to serve as a precursor for development of small cell lung carcinoma, mechanisms regulating expansion of the PNE cell population are not well understood. Based on studies performed in animal models, it has been suggested that NEB-associated progenitor cells that are phenotypically distinct from PNE cells contribute to PNE cell hyperplasia. We have previously used a Clara cell-specific toxicant, naphthalene, to induce airway injury in mice and have demonstrated that naphthalene-resistant Clara cells, characterized by their expression of Clara cell secretory protein (CCSP), and PNE cells contribute to airway repair and associated hyperplasia of NEBs. This study was conducted to define the contribution of NEB-associated CCSP-expressing progenitor cells to PNE cell hyperplasia after Clara cell ablation. Transgenic (CCtk) mice were generated in which herpes simplex virus thymidine kinase was expressed within all CCSP-expressing cells of the conducting airway epithelium through the use of transcriptional regulatory elements from the mouse CCSP promoter. Chronic administration of ganciclovir (GCV) to CCtk transgenic mice resulted in selective ablation of CCSP-expressing cells within conducting airways. Proliferation and hyperplasia of PNE cells occurred in the absence of detectable proliferation among any other residual airway epithelial cell populations. These results demonstrate that PNE cells function as a self-renewing progenitor population and that NEB-associated Clara cells are not necessary for PNE cell hyperplasia.

Comparative ultrastructure of Clara cells in neonatal and older cattle

Calf lungs were fixed with glutaraldehyde and examined by scanning (SEM) and transmission (TEM) electron microscopy to compare the ultrastructure of Clara cells in terminal bronchioles of neonatal calves and older cattle. In the neonatal calf, SEM revealed numerous smooth-surfaced Clara cells protruding above a similar number of ciliated cells, whereas in older animals the surface of Clara cells was lobulated. Thin sections examined by TEM revealed numerous cuboidal to columnar Clara cells with indented nuclei and a pale cytoplasm filled with faintly granular glycogen in the neonatal calf. Some cells were characterized by apical dense and/or pale membrane-bound granules or secretory droplets. Many cells had an apical tubular network of cisternae that were partly smooth and partly decorated with ribosomes. Ultrastructural comparison of Clara cells in a 2-day-old calf with those of 14- and 19-day-old, 4- and 5. 5-month-old, and 3.5-year-old cattle revealed a striking reduction in the amount of glycogen per cell after 14 days. The number of cells with apical granules was small at all ages, and the density of the secretory granules varied greatly in different cells. A variable amount of smooth endoplasmic reticulum (SER) was present but was less prominent than cisternae of ribosomal endoplasmic reticulum (RER). In older cattle, the limited amount of SER compared to the RER and secretory granules suggests that bovine Clara cells are more likely to be secretory than detoxifying.

Acute injury to differentiating Clara cells in neonatal rabbits results in age-related failure of bronchiolar epithelial repair

Nonciliated bronchiolar (Clara) cells are progenitor cells during lung development. During differentiation, they have a heightened injury susceptibility to environmental toxicants bioactivated by cytochrome P450 monooxygenase. When neonatal rabbits are treated with the P450-mediated cytotoxicant 4-ipomeanol (IPO), abnormal bronchiolar epithelium results. This study establishes the impact of IPO cytotoxicity on 3 stages of rabbit Clara cell differentiation, early (2.5 and 5 days postnatal [DPN]), intermediate (7 and 9 DPN), and late (15 and 21 DPN), and relates the cytotoxicity to the extent of bronchiolar repair. Neonates received a single dose of IPO (5 mg/kg) and were assessed by qualitative pathology 48 hours later for injury or at 4 weeks for repair. IPO injured the 3 stages of Clara cell differentiation to the same degree; epithelium was swollen, exfoliated, and squamated. Epithelial repair differed among the 3 stages. Bronchioles of animals treated during early and intermediate stages had simple squamous and irregularly shaped cuboidal cells. Animals treated during late stages were similar to controls. Thus, differentiating Clara cells are susceptible to injury by the P450-mediated cytotoxicant IPO, but the extent of repair varies based on when the initial injury occurs.

Neuroepithelial bodies of pulmonary airways serve as a reservoir of progenitor cells capable of epithelial regeneration

Remodeling of the conducting airway epithelium is a common finding in the chronically injured lung and has been associated with increased risk for developing lung cancer. Pulmonary neuroendocrine cells and clusters of these cells termed neuroepithelial bodies (NEBs) play a central role in each of these processes. We previously developed an adult mouse model of airway injury and repair in which epithelial regeneration after naphthalene-induced Clara cell ablation occurred preferentially at airway branch points and gave rise to nascent Clara cells. Continued repair was accompanied by NEB hyperplasia. We now provide the following evidence that the NEB microenvironment serves as a source of airway progenitor cells that contribute to focal regeneration of the airway epithelium: 1) nascent Clara cells and NEBs localize to the same spatial domain; 2) within NEB, both Clara cell secretory protein- and calcitonin gene-related peptide-immunopositive cells are proliferative; 3) the NEB microenvironment of both the steady-state and repairing lung includes cells that are dually immunopositive for Clara cell secretory protein and calcitonin gene-related peptide, which were previously identified only within the embryonic lung; and 4) NEBs harbor variant Clara cells deficient in cytochrome P450 2F2-immunoreactive protein. These data suggest that the NEB microenvironment is a reservoir of pollutant-resistant progenitor cells responsive to depletion of an abundant airway progenitor such as the Clara cell.

Expression of surfactant protein mRNA in normal and neoplastic lung of B6C3F1 mice as demonstrated by in situ hybridization

The localization of surfactant protein (SP), A, B, C, and D mRNAs was examined in B6C3F1 mice in the normal lung, and in a range of spontaneous proliferative lung lesions using nonisotopic in situ hybridization (ISH). The aim was to develop diagnostic markers, and if possible, throw further light on the histogenesis of these lesions. Tissues from 21 animals were examined, the lesions studied were: 4 alveolar epithelial hyperplasias, 12 alveolar/bronchiolar (A/B) adenomas, and 5 A/B carcinomas. Lung metastases of hepatocellular carcinoma (HCC) were used as controls. In the nonneoplastic lung, staining for SP A, B, and C mRNA was observed in normal and hyperplastic type II cells but not in the bronchiolar epithelium. SP mRNAs were present in all lung tumors, with SPs A, B, and C being coexpressed in 10/12 (83%) of adenomas and 4/ 5 (80%) of carcinomas in both solid and tubulopapillary areas. No signals for SP D mRNA were noted in normal or neoplastic lung. Additionally, no staining for any SP transcript was observed in the HCC metastases examined. In summary, ISH for SP A, B, or C mRNA was a helpful aid in the diagnosis of proliferative lesions of the murine lung, enabling differentiation from hepatocellular metastases. Furthermore, this work provides strong support for the proposal that spontaneous lung tumors in B6C3F1 mice are of alveolar, not bronchiolar origin, and consistently show type II cell differentiation. We suggest that such tumors should be referred to as alveolar adenomas and carcinomas.

Thyroid transcription factor-1, hepatocyte nuclear factor-3beta and surfactant protein A and B in the developing chick lung

Expression of surfactant proteins SP-A, SP-B and the transcription factors TTF-1 and HNF-3beta was identified by immunohistochemistry in the developing chicken. SP-B, a small hydrophobic peptide critical for lung function and surfactant homeostasis in mammals, was detected in the epithelial cells of parabronchi in embryonic chicken lung from the 15th day of incubation, prior to the onset of the breathing movements and was expressed at high levels in the posthatching chicken lung. SP-A, an abundant surfactant protein involved in innate defence of the mammalian lung, was detected in the chick embryo in subsets of epithelial cells in the mesobronchus, starting from d 15 and was detected in the posthatching chicken lung. The transcription factors hepatocyte nuclear factor 3beta (HNF-3beta) and thyroid transcription factor-1 (TTF-1), both regulators epithelial cell differentiation and gene expression in mammalian species, were detected at the onset of lung bud formation (d 4 of incubation) and throughout lung development. Abundant nuclear expression was detected in nuclei of respiratory epithelial cells of developing bronchial tubules for both transcription factors. In contrast to the surfactant proteins, expression of both TTF-1 and HNF-3beta decreased markedly in posthatching chicken lung. The expression of SP-A and SP-B in chick lung demonstrates the conservation of surfactant proteins in vertebrates. The temporospatial pattern of TTF-1 and HNF-3beta overlaps with that of SP-A and SP-B, supporting their potential roles in chick lung development and demonstrating the conservation of regulatory mechanisms contributing to gene expression in respiratory epithelial cells in vertebrates.

Neonatal Clara cell toxicity by 4-ipomeanol alters bronchiolar organization in adult rabbits

Nonciliated bronchiolar (Clara) cells metabolize environmental toxicants, are progenitor cells during development, and differentiate postnatally. Because differentiating Clara cells of neonatal rabbits are injured at lower doses by the cytochrome P-450-activated cytotoxicant 4-ipomeanol than are those of adults, the impact of early injury on the bronchiolar epithelial organization of adults was defined by treating neonates (3-21 days) and examining them at 4-6 wk. Bronchiolar epithelium of 6-wk-old animals treated on day 7 was most altered from that of control animals. Almost 100% of the bronchioles were lined by zones of squamous epithelial cells. Compared with control animals, the distal bronchiolar epithelium of 4-ipomeanol-treated animals had more squamous cells (70-90 vs. 0%) with a reduced overall epithelial thickness (25% of control value), fewer ciliated cells (0 vs. 10-20%), a reduced expression of Clara cell markers of differentiation (cytochrome P-4502B, NADPH reductase, and 10-kDa protein), and undifferentiated nonciliated cuboidal cell ultrastructure. We conclude that early injury to differentiating rabbit Clara cells by a cytochrome P-450-mediated toxicant inhibits bronchiolar epithelial differentiation and greatly affects repair.

Pulmonary cytochrome P450 monooxygenase and Clara cell differentiation in mice

Various studies indicate that cytodifferentiation of Clara cells and development of pulmonary cytochrome P450 (CYP) monooxygenases occur postnatally. The timing of these events is species-specific. Neonatal mice are more susceptible than adult mice are to Clara cell injury by naphthalene, but little is known about the postnatal development of Clara cells and CYP in mice. This study was designed to determine the developmental pattern of Clara cell differentiation and CYP expression in mice. Lungs from mice aged 16 days gestation to 63 days postnatal (DPN) were studied. Clara cell secretory protein (CC10) expression in nonciliated cells was detected earlier in proximal airways than in distal airways, but reached adult levels at 14 DPN in all airway levels. Cilia-associated tubulin expression closely followed the onset of CC10 expression, as did expression of CYP reductase. CYP2B protein expression appeared and differentiated earlier in bronchi than in bronchioles and reached adult levels at 14 and 28 DPN, respectively. CYP2F2 expression appeared earlier in proximal airways, but did not reach adult levels of expression until after 28 DPN. CYP activity, measured by naphthalene metabolism, increased with age and corresponded to CYP2F2 protein expression. We conclude that in the mouse, (1) Clara cell maturation is a postnatal event, (2) Clara cell differentiation is complete at the same age in proximal and distal airways, (3) CYP reductase protein expression occurs at the same time as CC10 expression, but CYP2B and CYP2F2 lag behind, and (4) stereoselective naphthalene monooxygenase activity corresponds with CYP2F2 protein expression.

The toxicology of environmental tobacco smoke

It has by now become obvious that environmental tobacco smoke (ETS) may pose a health risk to nonsmokers. Epidemiological data suggest that exposure to ETS may increase the risk of developing lung cancer, cardiovascular disease, intrauterine growth retardation, predisposition to chronic lung disease, and sudden infant death syndrome. The human populations most at risk from ETS exposure appear to be neonates, young children, and possibly the fetus while in utero. Experimental studies with cigarette sidestream smoke (SS) have successfully duplicated several of these disease conditions in laboratory animals, particularly the effects of SS on fetal growth, lung maturation, and altered airway reactivity. The availability of animal models may open the way to fruitful experimental studies on mechanisms that help us to better understand disease.

Monoclonal antibodies to surfactant protein D: evaluation of immunoreactivity in normal rat lung and in a radiation-induced fibrosis model

This report describes the development of a new panel of monoclonal antibodies established after immunization of mice with purified surfactant protein D of the rat. To enhance the detection of SP-D in formalin- or Schaffer-fixed samples, immunohistochemistry was performed by using microwave pretreatment of paraffin sections. Using these new antibodies that bind to type II epithelial cells, Clara cells, and alveolar macrophages, the responses of lung parenchymal cells were examined in a radiation-induced fibrosis model. Increased accumulation of extracellular SP-D in the alveolar space was found. Double staining with anti-surfactant protein A antibodies revealed different Clara cell populations containing one or both types of surfactant proteins.

Alveolar epithelial composition and architecture of the late fetal pulmonary acinus: an immunocytochemical and morphometric study in a rat model of pulmonary hypoplasia and congenital diaphragmatic hernia

The aim of the present study was to compare the architecture and alveolar epithelial cell composition of the pulmonary acinus in hypoplastic and normal fetal rat lungs. For this purpose, a rat model of pulmonary hypoplasia in association with congenital diaphragmatic hernia (CDH) induced by Nitrofen (100 mg on day 10 of pregnancy) was studied. Sections (5 microns) from lungs of control and Nitrofen-exposed fetal Sprague Dawley rats with or without CDH aged 18-22 days (vaginal plug on day 1, birth on day 23) were stained with hematoxylin and eosin. To identify developing alveolar epithelial cells, sections were incubated with anti-surfactant protein A (SP-A; rabbit anti-mouse) or preimmunization serum (indirect immunofluorescence). On days 18 and 19, control lungs and exposed lungs from fetuses with and without CDH looked similar (pseudoglandular stage of lung development). The prospective pulmonary acinus consisted of acinar tubules with small round lumens, lined by cuboid, fluorescent type II cells. Morphometric analysis on day 19 showed significantly smaller lung volumes and lung tissue volumes after Nitrofen exposure. On day 20 (canalicular stage), some tubules were slightly dilated and lined by cuboid and thinner fluorescent cells; these dilated tubules were less numerous in lungs from exposed fetuses with CDH. On days 21 and 22 (saccular stage), the saccular lining consisted of cuboid to thin fluorescent cells in exposed lungs from fetuses with and without CDH, and fluorescent (low) cuboid cells interspersed with dark zones (type I cell areas) in control lungs. In the exposed lungs from fetuses with CDH, the lumens of all airspaces were frequently slit-like, and the septa were thicker. These phenomena gave the lungs a primitive, compact aspect. Morphometric analysis on day 22 showed smaller lung volumes and lung tissue volumes, smaller airspace/tissue ratios, smaller epithelial surface areas, and more type II cells per surface area in Nitrofen-exposed lungs than in normal control lungs. The results suggest that Nitrofen-exposed, and thus hypoplastic, fetal rat lungs are retarded with respect to the differentiation of cuboid type II cells into squamous type I cells whether or not CDH is present, and with respect to the development of the future airspaces between days 20 and 22 if CDH is present.