Transient induction of TGF-alpha disrupts lung morphogenesis, causing pulmonary disease in adulthood

Clinical studies have associated increased transforming growth factor (TGF)-alpha and EGF receptor with lung remodeling in diseases including bronchopulmonary dysplasia (BPD). BPD is characterized by disrupted alveolar and vascular morphogenesis, inflammation, and remodeling. To determine whether transient increases in TGF-alpha are sufficient to disrupt postnatal lung morphogenesis, we utilized neonatal transgenic mice conditionally expressing TGF-alpha. Expression of TGF-alpha from postnatal days 3 to 5 disrupted postnatal alveologenesis, causing permanent enlargement of distal air spaces in neonatal and adult mice. Lung volume-to-body weight ratios and lung compliance were increased in adult TGF-alpha transgenic mice, whereas tissue and airway elastance were reduced. Elastin fibers in the alveolar septae were fragmented and disorganized. Pulmonary vascular morphogenesis was abnormal in TGF-alpha mice, with attenuated and occasionally tortuous arterial branching. The ratios of right ventricle weight to left ventricle plus septal weight were increased in TGF-alpha mice, indicating pulmonary hypertension. Electron microscopy showed gaps in the capillary endothelium and extravasation of erythrocytes into the alveolar space of TGF-alpha mice. Hemorrhage and inflammatory cells were seen in distal air spaces at 1 mo of age. In adult TGF-alpha mice, alveolar remodeling, nodules, proteinaceous deposits, and inflammatory cells were seen. Immunostaining for pro-surfactant protein C showed that type II cells were abundant in the nodules, as well as neutrophils and macrophages. Trichrome staining showed that pulmonary fibrosis was minimal, apart from areas of nodular remodeling in adult TGF-alpha mice. Transient induction of TGF-alpha during early alveologenesis permanently disrupted lung structure and function and caused chronic lung disease.     

Spatial distribution of collagen and elastin fibers in the lungs

Surface tension forces acting on the thin-wall alveolar septa and the collagen-elastin fiber network are major factors in lung parenchymal micromechanics. Quantitative serial section analysis and morphometric evaluations of planar sections were used to determine the spatial location of collagen and elastin fibers in Sprague-Dawley rat and normal human lung samples. A large concentration of connective tissue fibers was located in the alveolar duct wall in both species. For rats, the tissue densities of collagen and elastin fibers located within 10 microns of an alveolar duct were 13 and 9%, respectively. In human lung samples, the tissue densities of collagen and elastin fibers within 20 microns of an alveolar duct were 18 and 16%, respectively. In both species, bands of elastin fibers formed a continuous ring around each alveolar mouth. In human lungs, elastin fibers were found to penetrate significantly deeper into alveolar septal walls than they did in rat lungs. The concentration of connective tissue elements in the alveolar duct walls of both species is consistent with their proposed roles as the principal load-bearing elements of the lung parenchyma.     

Gene transfer of hepatocyte growth factor by electroporation reduces bleomycin-induced lung fibrosis

Abnormal alveolar wound repair contributes to the development of pulmonary fibrosis after lung injury. Hepatocyte growth factor (HGF) is a potent mitogenic factor for alveolar epithelial cells and may therefore improve alveolar epithelial repair in vitro and in vivo. We hypothesized that HGF could increase alveolar epithelial repair in vitro and improve pulmonary fibrosis in vivo. Alveolar wound repair in vitro was determined using an epithelial wound repair model with HGF-transfected A549 alveolar epithelial cells. Electroporation-mediated, nonviral gene transfer of HGF in vivo was performed 7 days after bleomycin-induced lung injury in the rat. Alveolar epithelial repair in vitro was increased after transfection of wounded epithelial monolayers with a plasmid encoding human HGF, pCikhHGF [human HGF (hHGF) gene expressed from the cytomegalovirus (CMV) immediate-early promoter and enhancer] compared with medium control. Electroporation-mediated in vivo HGF gene transfer using pCikhHGF 7 days after intratracheal bleomycin reduced pulmonary fibrosis as assessed by histology and hydroxyproline determination 14 days after bleomycin compared with controls treated with the same vector not containing the HGF sequence (pCik). Lung epithelial cell proliferation was increased and apoptosis reduced in hHGF-treated lungs compared with controls, suggesting increased alveolar epithelial repair in vivo. In addition, profibrotic transforming growth factor-beta1 (TGF-beta1) was decreased in hHGF-treated lungs, indicating an involvement of TGF-beta1 in hHGF-induced reduction of lung fibrosis. In conclusion, electroporation-mediated gene transfer of hHGF decreases bleomycin-induced pulmonary fibrosis, possibly by increasing alveolar epithelial cell proliferation and reducing apoptosis, resulting in improved alveolar wound repair.     

Comparison of rat and mouse pulmonary tissue mechanical properties and histology.

The present study compares the dynamic mechanical properties and the contents of collagen and elastic fibers (oxytalan + elaunin + fully developed elastic fibers) of mice and rat lung strips. Resistance, elastance (E), and hysteresivity (eta) were obtained during sinusoidal oscillations. The relative amounts of blood vessel, bronchial, and alveolar walls, as well as the mean alveolar diameter were determined. In both species, resistance had a negative and E a positive dependence on frequency, whereas eta remained unchanged. Mice showed higher E and lower eta than rats. Although collagen and elastic fiber contents were similar in both groups, mice had more oxytalan and less elaunin and fully developed elastic fibers than rats. Rats showed less alveolar and more blood vessel walls and higher mean alveolar diameter than mice. In conclusion, mice and rats present distinct tissue mechanical properties, which are accompanied by specific extracellular fiber composition.     

Altered bleomycin-induced lung fibrosis in osteopontin-deficient mice

Osteopontin is a multifunctional matricellular protein abundantly expressed during inflammation and repair. Osteopontin deficiency is associated with abnormal wound repair characterized by aberrant collagen fibrillogenesis in the heart and skin. Recent gene microarray studies found that osteopontin is abundantly expressed in both human and mouse lung fibrosis. Macrophages and T cells are known to be major sources of osteopontin. During lung fibrosis, however, osteopontin expression continues to increase when inflammation has receded, suggesting alternative sources of ostepontin during this response. In this study, we demonstrate immunoreactivity for osteopontin in lung epithelial and inflammatory cells in human usual interstitial pneumonitis and murine bleomycin-induced lung fibrosis. After treatment with bleomycin, osteopontin-null mice develop lung fibrosis characterized by dilated distal air spaces and reduced type I collagen expression compared with wild-type controls. There is also a significant decrease in levels of active transforming growth factor-beta(1) and matrix metalloproteinase-2 in osteopontin null mice. Type III collagen expression and total collagenase activity are similar in both groups. These results demonstrate that osteopontin expression is associated with important fibrogenic signals in the lung and that the epithelium may be an important source of osteopontin during lung fibrosis.     

Histochemistry of the lung of the Australian snake-necked tortoise chelodina longicollis

The innervation and structure of the lung of the Australian snake-necked tortoise, Chelodina longicollis, was examined by using light microscopy including fluorescence histochemical techniques. The anterior lung was divided into a number of compartments with numerous alveolar spaces. The posterior lung was simpler and saclike in structure and alveolar spaces were absent. Smooth muscle fibers occurred in discrete muscle bands and in the walls of the septal bands. Ganglion cells occurred along nerve trunks throughout the lung but were more numerous in the posterior lung. Smooth muscle bands, the extrinsic pulmonary artery, and the arteries within the lung were sparsely innervated by adrenergic fibers. Substance P-containing sensory fibers were not demonstrated. The innervation and structure of the lung are compared to published work on other reptiles.     

HGF Expressing Stem Cells in Usual Interstitial Pneumonia Originate from the Bone Marrow and Are Antifibrotic

Background

Pulmonary fibrosis may result from abnormal alveolar wound repair after injury. Hepatocyte growth factor (HGF) improves alveolar epithelial wound repair in the lung. Stem cells were shown to play a major role in lung injury, repair and fibrosis. We studied the presence, origin and antifibrotic properties of HGF-expressing stem cells in usual interstitial pneumonia.

Methods

Immunohistochemistry was performed in lung tissue sections and primary alveolar epithelial cells obtained from patients with usual interstitial pneumonia (UIP, n = 7). Bone marrow derived stromal cells (BMSC) from adult male rats were transfected with HGF, instilled intratracheally into bleomycin injured rat lungs and analyzed 7 and 14 days later.

Results

In UIP, HGF was expressed in specific cells mainly located in fibrotic areas close to the hyperplastic alveolar epithelium. HGF-positive cells showed strong co-staining for the mesenchymal stem cell markers CD44, CD29, CD105 and CD90, indicating stem cell origin. HGF-positive cells also co-stained for CXCR4 (HGF+/CXCR4+) indicating that they originate from the bone marrow. The stem cell characteristics were confirmed in HGF secreting cells isolated from UIP lung biopsies. In vivo experiments showed that HGF-expressing BMSC attenuated bleomycin induced pulmonary fibrosis in the rat, indicating a beneficial role of bone marrow derived, HGF secreting stem cells in lung fibrosis.

Conclusions

HGF-positive stem cells are present in human fibrotic lung tissue (UIP) and originate from the bone marrow. Since HGF-transfected BMSC reduce bleomycin induced lung fibrosis in the bleomycin lung injury and fibrosis model, we assume that HGF-expressing, bone-marrow derived stem cells in UIP have antifibrotic properties.     

Overexpression of tumor necrosis factor-alpha produces an increase in lung volumes and pulmonary hypertension

Tumor necrosis factor (TNF)-alpha is a key proinflammatory cytokine that is thought to be important in the development of pulmonary fibrosis, whereas its role in pulmonary emphysema has not been as thoroughly documented. In the present study, TNF-alpha was overexpressed in alveolar type II cells under the control of the human surfactant protein C promoter. In this report, we further characterized the pulmonary abnormalities and provided a physiological assessment of these mice. Histopathology of the lungs revealed chronic inflammation, severe alveolar air space enlargement and septal destruction, and bronchiolitis. However, pulmonary fibrosis was very limited and only seen in the subpleural, peribronchiolar, and perivascular regions. Physiological assessment showed an increase in lung volumes and a decrease in elastic recoil characteristic of emphysema; there was no evidence of restrictive lung disease characteristic of pulmonary fibrosis. In addition, the mice raised in ambient conditions in Denver developed pulmonary hypertension. Gelatinase activity was increased in the lavage fluid from these lungs. These results suggest that in these mice TNF-alpha contributed to the development of pulmonary emphysema through chronic lung inflammation and activation of the elastolytic enzymes but by itself was unable to produce significant pulmonary fibrosis.     

Structural changes in elastic fibers after pancreatic elastase administration in hamsters.

Ultrastructural changes in lung parenchymal elastic fibers were studied morphometrically 1, 4, and 12 wk after a single 12-unit dose of pancreatic elastase and in a saline-instilled control group. The mean linear intercept of the parenchymal air spaces was increased in the 1-, 4-, and 12-wk post-elastase instillation groups compared with age-matched controls. The volume of alveolar connective tissue fibers predominantly composed of elastin (elastic fibers) was decreased by 35% 1 wk after the instillation of elastase but returned to control levels by 4 wk. Although the total volume of elastic fibers was normal 12 wk after instillation of elastase, the volume of elastic fibers in alveolar entrance rings remained significantly reduced. In serial sections of elastic fibers, numerous gaps or separations in the normally continuous band of elastic fibers that encircle each alveolus were identified 1 wk after elastase instillation. There were 169 +/- 8 (SE), 62 +/- 32, and 12 +/- 6 gaps per millimeter of alveolar entrance ring circumference at 1, 4, and 12 wk, respectively, in the elastase-treated groups. The number of gaps at 12 wk was equivalent to two gaps or discontinuities in the elastic fibers of every alveolar entrance ring. No gaps or separations in elastic fibers were detected at 1, 4, or 12 wk in the control groups. These defects occur in concordance with the progression of air space enlargement and presumably contribute to the progression of air space enlargement that occurs after the elastin content of the tissue has returned to normal.     

Effects of chronic L-NAME treatment lung tissue mechanics, eosinophilic and extracellular matrix responses induced by chronic pulmonary inflammation

The importance of lung tissue in asthma pathophysiology has been recently recognized. Although nitric oxide mediates smooth muscle tonus control in airways, its effects on lung tissue responsiveness have not been investigated previously. We hypothesized that chronic nitric oxide synthase (NOS) inhibition by N(omega)-nitro-L-arginine methyl ester (L-NAME) may modulate lung tissue mechanics and eosinophil and extracellular matrix remodeling in guinea pigs with chronic pulmonary inflammation. Animals were submitted to seven saline or ovalbumin exposures with increasing doses (1 approximately 5 mg/ml for 4 wk) and treated or not with L-NAME in drinking water. After the seventh inhalation (72 h), animals were anesthetized and exsanguinated, and oscillatory mechanics of lung tissue strips were performed in baseline condition and after ovalbumin challenge (0.1%). Using morphometry, we assessed the density of eosinophils, neuronal NOS (nNOS)- and inducible NOS (iNOS)-positive distal lung cells, smooth muscle cells, as well as collagen and elastic fibers in lung tissue. Ovalbumin-exposed animals had an increase in baseline and maximal tissue resistance and elastance, eosinophil density, nNOS- and iNOS-positive cells, the amount of collagen and elastic fibers, and isoprostane-8-PGF(2alpha) expression in the alveolar septa compared with controls (P<0.05). L-NAME treatment in ovalbumin-exposed animals attenuated lung tissue mechanical responses (P<0.01), nNOS- and iNOS-positive cells, elastic fiber content (P<0.001), and isoprostane-8-PGF(2alpha) in the alveolar septa (P<0.001). However, this treatment did not affect the total number of eosinophils and collagen deposition. These data suggest that NO contributes to distal lung parenchyma constriction and to elastic fiber deposition in this model. One possibility may be related to the effects of NO activating the oxidative stress pathway.     

Distal air space epithelial fluid clearance in near-term rat fetuses is fast and requires endogenous catecholamines

Knowledge about the conversion of the epithelium in the distal air spaces of the lung from secretion to absorption is imperative to the understanding of postnatal lung development; little such information is available in rats. Distal air space fluid clearance was therefore measured in 21- to 22-day gestation rat fetuses and newborn (40 h) rats. Distal air space fluid clearance was measured from the increase in (131)I-albumin concentration in an isosmolar, physiological solution instilled into the developing lungs. There was no net fluid movement across the distal air space epithelium in the lungs of 21-day gestation fetuses. Twenty-four hours later, distal air space fluid was cleared at a rapid rate in the 22-day gestation fetuses. Within the first 40 h after birth, the rate rapidly declined to adult levels. The high distal air space fluid clearance at 22 days gestation and at 40 h after birth was mediated by beta-adrenergic receptors as demonstrated by elevated plasma epinephrine levels and inhibition by propranolol. Interestingly, the elevated distal air space fluid clearance in the 22-day gestation fetuses was only minimally amiloride sensitive; however, amiloride sensitivity increased over the first 40 h after birth. In conclusion, these studies demonstrate that 1) rapid rates of net alveolar fluid clearance occur late in gestation in the rat and 2) this clearance is driven by elevations of endogenous epinephrine.     

Analysis of stress distribution in the alveolar septa of normal and simulated emphysematic lungs.

The alveolar septum consists of a skeleton of fine collagen and elastin fibers, which are interlaced with a capillary network. Its mechanical characteristics play an important role in the overall performance of the lung. An alveolar sac model was developed for numerical analysis of the internal stress distribution and septal displacements within the alveoli of both normal and emphysematic saline-filled lungs. A scanning electron micrograph of the parenchyma was digitized to yield a geometric replica of a typical two-dimensional alveolar sac. The stress-strain relationship of the alveolar tissue was adopted from experimental data. The model was solved by using commercial finite-element software for quasi-static loading of alveolar pressure. Investigation of the state of stresses and displacements in a healthy lung simulation yielded values that compared well with experimentally reported data. Alteration of the mechanical characteristics of the alveolar septa to simulate elastin destruction in the emphysematic model induced significant stress concentrations (e.g., at a lung volume of 60% total capacity, tensions at certain parts in an emphysematic lung were up to 6 times higher than those in a normal lung). The combination of highly elevated stress sites together with the cyclic loading of breathing may explain the observed progressive damage to elastin fibers in emphysematic patients.     

Neuraminidase-1 is required for the normal assembly of elastic fibers

The assembly of elastic fibers in tissues that undergo repeated cycles of extension and recoil, such as the lungs and blood vessels, is dependent on the proper interaction and alignment of tropoelastin with a microfibrillar scaffold. Here, we describe in vivo histopathological effects of neuraminidase-1 (Neu1) deficiency on elastin assembly in the lungs and aorta of mice. These mice exhibited a tight-skin phenotype very similar to the Tsk mouse. Normal septation of Neu1-null mice did not occur in neonatal mice, resulting in enlarged alveoli that were maintained in adults. The abnormal development of elastic fibers was remarkable under electron microscopy and confirmed by the overlapping distribution of elastin, fibrillin-1, fibrillin-2, and fibulin-5 (Fib-5) by the light microscopy immunostainings. Fib-5 fibers appeared diffuse and unorganized around the alveolar walls and the apex of developing secondary septal crests. Fibrillin-2 deposition was also abnormal in neonatal and adult lungs. Dispersion of myofibroblasts appeared abnormal in developing lungs of Neu1-null mice, with a random distribution of myofibroblast around the alveolar walls, rather than concentrating at sites of elastin synthesis. The elastic lamellae in the aorta of the Neu1-null mice were thinner and separated by hypertrophic smooth muscle cells that were surrounded by an excess of the sialic acid-containing moieties. The concentration of elastin, as measure by desmosine levels, was significantly reduced in the aorta of Neu1-null mice. Message levels for tropoelastin and Fib-5 were normal, suggesting the elastic fiber defects in Neu1-null mice result from impaired extracellular assembly.     

Fatal pneumonia with terminal emaciation in nude mice caused by pneumonia virus of mice

Athymic nude mice used as sentinel animals in a mouse holding room died of pneumonia 17 to 32 weeks after being placed in the room. Lesions in the pulmonary parenchyma consisted of monocytic exudate, epithelial cell necrosis, hemorrhage, fibrin deposition and interstitial fibrosis. Septal edema, septal cell necrosis and septal capillary stasis were common, but there was limited sloughing of bronchial lining epithelium. Indirect fluorescence microscopy (IFA) of lung sections using pneumonia virus of mice (PVM) antibody was positive. The pneumonia and IFA results were reproduced in euthymic mice inoculated experimentally with lung suspension from naturally infected mice or with tissue culture fluid from cultures infected with American Type Culture Collection PVM. The lungs of a naturally infected nude mouse were studied by transmission electron microscopy. Virus growth was found on Type II alveolar epithelium and on poorly differentiated replacement alveolar epithelium. Virus particles appeared as long exophytic filaments containing one to six linearly arranged nucleocapsids. Inclusion bodies and intracellular virus structures were not observed.     

Vascular and epithelial damage in the lung of the mouse after X rays or neutrons

The response of the lung was studied in CFLP mice after exposure of the whole thorax to X rays (250 kVp) or cyclotron neutrons (16 MeV deuterons on Be, mean energy 7.5 MeV). To measure blood volume and leakage of plasma proteins, 51Cr-labeled red blood cells and 125I-albumin were injected intravenously and 24 h later lungs were lavaged via the trachea. Radioactivities in lung tissue and lavage fluid were determined to estimate the accumulation of albumin in the interstitial and alveolar spaces indicating damage to blood vessels and alveolar epithelium respectively. Function of type II pneumonocytes was assessed by the amounts of surfactant (assayed as lipid phosphorous) released into the lavage fluid. During the first 6 weeks, lavage protein and surfactant were increased, the neutron relative biological effectiveness (RBE) being unity. During pneumonitis at 12-24 weeks, surfactant levels were normal, blood volume was decreased, and both interstitial and alveolar albumin were increased. Albumin levels then decreased. At late times after exposure (42-64 weeks) alveolar albumin returned to normal but interstitial albumin was still slightly elevated. Values of RBE for changes in blood volume and interstitial and alveolar albumin at 15 weeks and for changes in blood volume and interstitial albumin at 46 weeks were 1.4, comparable with that for animal survival at 180 days. The results indicate that surfactant production is not critical for animal survival. They suggest that changes in blood vessels and alveolar epithelium occur during acute pneumonitis; epithelial repair follows but some vascular damage may persist. The time course of the changes in albumin levels did not correlate with increases in collagen biosynthesis which have been observed as early as 1 month after exposure and persist for up to 1 year. Furthermore, a dose which had no effect on leakage caused a marked increase in collagen biosynthesis. Thus the present results do not support a causal relationship between exudation of vascular protein during pneumonitis and the later development of fibrosis.     

Immunolocalization of CC10 in Clara cells in mouse and human lung

Two antisera, denoted R41 and R42, were raised against a synthetic peptide from the murine Clara cell-specific protein CC10, and one antiserum, denoted R40, was raised against human recombinant uteroglobin, the human homolog of murine CC10. Purified antigen-specific antisera, denoted R40AP, R41AP, and R42AP were prepared using peptide columns. The purified antisera were characterized by dot blots, immunohistochemistry, and immunoblots. Immunohistochemistry of mouse lung showed specific labeling of Clara cells in distal bronchioles by all three antisera. In human lung, the antiuteroglobin antiserum specifically labeled Clara cells, while the anti-mouse peptide antisera had weak crossreactivity and higher background staining. Electron microscopy revealed immunogold labeling of CC10 granules in Clara cells of mouse lung with all antisera. All antisera also labeled a 5-kDa protein on immunoblots of mouse lung homogenates. The surface epithelium of the alveolar air spaces around the distal bronchioles were CC10 positive suggesting a functional activity for CC10 in the lung parenchyma distal to Clara cells. R40AP immunohistochemical staining of sections of normal human lungs and lungs from patients with surfactant protein B deficiency, bronchopneumonia, and idiopathic alveolar proteinosis illustrate the utility of the anti-human CC10 antibody for diagnostic pathology.     

Lung and alveolar wall elastic and hysteretic behavior in rats: effects of in vivo elastase treatment.

We investigated the relationship between the microscopic elastic and hysteretic behavior of the alveolar walls and the macroscopic mechanical properties of the whole lung in an in vivo elastase-treated rat model of emphysema. We measured the input impedance of isolated lungs at three levels of transpulmonary pressure (Ptp) and used a linear model to estimate the dynamic elastance and hysteresivity of the lungs. The elastance of the normal lungs increased steeply with Ptp, whereas this dependence diminished in the treated lungs. Hysteresivity decreased significantly with Ptp in the normal lungs, but this dependence disappeared in the treated lungs. To investigate the microscopic origins of these changes, the alveolar walls were immunofluorescently labeled in small tissue strips. By using a fluorescent microscope, the lengths and angular orientations of individual alveolar walls were followed during cyclic uniaxial stretching of the tissue strips. The microstrains (relative change in segment length) and changes in angle of the alveolar walls showed considerable heterogeneity, which was interpreted in terms of a network model. In the normal strips, the alveolar walls showed larger angular changes compared with the treated tissue, whereas the alveolar walls of the treated tissue tended to be more extensible. Hysteresis in the average angle change was also larger in the treated tissue than in the normal tissue. We conclude that the decreased Ptp dependence of elastance and the constant hysteresivity in the treated lungs are related to microstructural remodeling and network phenomena at the level of the alveolar walls.     

Time course of lung parenchyma remodeling in pulmonary and extrapulmonary acute lung injury.

The aim of this study is to test the hypothesis that the early changes in lung mechanics and the amount of type III collagen fiber do not predict the evolution of lung parenchyma remodeling in pulmonary and extrapulmonary acute lung injury (ALI). For this purpose, we analyzed the time course of lung parenchyma remodeling in murine models of pulmonary and extrapulmonary ALI with similar degrees of mechanical compromise at the early phase of ALI. Lung histology (light and electron microscopy), the amount of elastic and collagen fibers in the alveolar septa, the expression of matrix metalloproteinase-9, and mechanical parameters (lung-resistive and viscoelastic pressures, and static elastance) were analyzed 24 h, 1, 3, and 8 wk after the induction of lung injury. In control (C) pulmonary (p) and extrapulmonary (exp) groups, saline was intratracheally (it; 0.05 ml) instilled and intraperitoneally (ip; 0.5 ml) injected, respectively. In ALIp and ALIexp groups, mice received Escherichia coli lipopolysaccharide (10 microg it and 125 microg ip, respectively). At 24 h, all mechanical and morphometrical parameters, as well as type III collagen fiber content, increased similarly in ALIp and ALIexp groups. In ALIexp, all mechanical and histological data returned to control values at 1 wk. However, in ALIp, static elastance returned to control values at 3 wk, whereas resistive and viscoelastic pressures, as well as type III collagen fibers and elastin, remained elevated until week 8. ALIp showed higher expression of matrix metalloproteinase-9 than ALIexp. In conclusion, insult in pulmonary epithelium yielded fibroelastogenesis, whereas mice with ALI induced by endothelial lesion developed only fibrosis that was repaired early in the course of lung injury. Furthermore, early functional and morphological changes did not predict lung parenchyma remodeling.     

Human insulin-like growth factor-IA expression in transgenic mice promotes adenomatous hyperplasia but not pulmonary fibrosis

Insulin-like growth factor-I (IGF-I) has been implicated in postnatal alveolar development, pulmonary fibrosis, and non-small cell lung cancer. To further investigate the role of IGF-I, we created a line of transgenic mice in which alveolar type II epithelial cells express human IGF-IA under the control of the surfactant protein C promoter. We determined the effect of pulmonary overexpression of human IGF-IA on 1) pulmonary inflammation and fibrosis in response to intratracheal instillation of bleomycin, 2) premalignant pulmonary adenomatous hyperplasia, and 3) adenoma formation. Transgenic expression of human IGF-IA had no effect on baseline gross lung pathology, cellularity of bronchoalveolar lavage, or total lung collagen content. In addition, there were no significant differences between transgenic mice and nontransgenic littermate controls in the development of pulmonary inflammation or pulmonary fibrosis in response to intratracheal bleomycin instillation. However, pulmonary expression of human IGF-IA in older mice (>12 mo) significantly increased the incidence of premalignant adenomatous hyperplastic lesions compared with littermate controls without affecting adenoma formation. These findings suggest that increased expression of human IGF-IA in alveolar air spaces does not affect the development of pulmonary fibrosis but promotes premalignant changes in the alveolar epithelium.     

Alveolar septal folding and lung inflation history.

On the basis of microscopic appearance of excised lungs, it has been thought that alveolar septa may fold and unfold during deflation and inflation. We suspected that this appearance might depend heavily on the inflation history of the lung preparation. We therefore studied, by light and electron microscopy, dog, rabbit, and rat lungs fixed over a range of inflation pressures and after a variety of inflation histories. Septal folding, as suggested by the configurations of the air spaces, by the placement of the fine and coarse connective tissue elements, and by the pattern of infolding of alveolar epithelium, was readily seen with some inflation protocols but was absent with others. Pressure at fixation was not as important as events before fixation; deflation to 3 cmH2O did not induce folding, and inflation to 16 cmH2O did not undo the folds. This range corresponds with concepts of critical opening and closing pressures. We suggest that folds form de novo during experimental preparation; one need not postulate that septal folding was present in vivo.