Lung connective tissue

The receptor for advanced glycation end-products supports lung tissue biomechanics

The receptor for advanced glycation end-products (RAGE) and its soluble forms are predominantly expressed in lung but its physiological importance in this organ is not yet fully understood. Since RAGE acts as a cell adhesion molecule, we postulated its physiological importance in the respiratory mechanics. Respiratory function in a buffer-perfused isolated lung system and biochemical parameters of the lung were studied in young, adult, and old RAGE knockout (RAGE-KO) mice and wild-type (WT) mice. Lungs from RAGE-KO mice showed a significant increase in the dynamic lung compliance and a decrease in the maximal expiratory air flow independent of age-related changes. We also determined lower mRNA and protein levels of elastin in lung tissue of RAGE-KO mice. RAGE deficiency did not influence the collagen protein level, lung capillary permeability, and inflammatory parameters (TNF-α, high-mobility group box protein 1) in lung. Overexpressing RAGE as well as soluble RAGE in lung fibroblasts or cocultured lung epithelial cells increased the mRNA expression of elastin. Moreover, immunoprecipitation studies indicated a trans interaction of RAGE in lung epithelial cells. Our findings suggest the physiological importance of RAGE and its soluble forms in supporting the respiratory mechanics in which RAGE trans interactions and the influence on elastin expression might play an important role.

Identification of Ata, a multifunctional trimeric autotransporter of Acinetobacter baumannii

Acinetobacter baumannii has recently emerged as a highly troublesome nosocomial pathogen, especially in patients in intensive care units and in those undergoing mechanical ventilation. We have identified a surface protein adhesin of A. baumannii, designated the Acinetobacter trimeric autotransporter (Ata), that contains all of the typical features of trimeric autotransporters (TA), including a long signal peptide followed by an N-terminal, surface-exposed passenger domain and a C-terminal domain encoding 4 β-strands. To demonstrate that Ata encoded a TA, we created a fusion protein in which we replaced the entire passenger domain of Ata with the epitope tag V5, which can be tracked with specific monoclonal antibodies, and demonstrated that the C-terminal 101 amino acids of Ata were capable of exporting the heterologous V5 tag to the surface of A. baumannii in a trimeric form. We found that Ata played a role in biofilm formation and bound to various extracellular matrix/basal membrane (ECM/BM) components, including collagen types I, III, IV, and V and laminin. Moreover, Ata mediated the adhesion of whole A. baumannii cells to immobilized collagen type IV and played a role in the survival of A. baumannii in a lethal model of systemic infection in immunocompetent mice. Taken together, these results reveal that Ata is a TA of A. baumannii involved in virulence, including biofilm formation, binding to ECM/BM proteins, mediating the adhesion of A. baumannii cells to collagen type IV, and contributing to the survival of A. baumannii in a mouse model of lethal infection.

Elastin gene expression is upregulated during pulmonary fibrosis

Elastin is a chief component of lung interstitium, and it is central to lung morphology and function. Efforts to understand the pathogenesis of pulmonary fibrosis have focused primarily upon collagen turnover in the lung; few studies have focused on elastin. In this study, we examined steady-state elastin mRNA levels after lung injury in the mouse induced by (1) butylated hydroxytoluene (BHT) which causes acute lung injury with recovery, (2) BHT + 70% O2 (fibrosis), or (3) 70% O2. Total lung elastin mRNA increased 70-80-fold on d10-14 after BHT/O2, but was unchanged after BHT or O2 alone. In situ hybridization studies localized elastin mRNA to cells in the muscularis of conducting airways and to scattered interstitial cells in fibrotic foci. Elastic fiber morphology was markedly distorted after BHT/O2. Thus, marked upregulation of elastin gene expression is correlated with the histopathology of fibrotic lung disease.

Altered insulin-like growth factor I mRNA expression in human hypoplastic lung in congenital diaphragmatic hernia

BACKGROUND/PURPOSE

Insulin-like growth factor I (IGF-I) is a peptide growth factor that is synthesized in many organs during human development and plays a role in the growth and differentiation of tissue. IGF-I has been shown to be produced in rat and human fetal lung and to be an important mitogen involved in lung growth and development. The cells responsible for the synthesis of IGF-I in lung in vivo have been demonstrated to be type II pneumocytes, alveolar macrophages, and mesenchymal cells. Recent studies have shown that IGF-I mRNA expression in the lung is predominant during fetal life and decreases before birth, becoming barely detectable in the neonatal lung. The aim of this study was to investigate IGF-I mRNA expression in CDH lung to understand the basis of pulmonary hypoplasia in newborns with CDH.

METHODS

Lung tissue samples were obtained during autopsy from 13 patients with CDH. Nine were full-term newborns (mean age, 3.8 days), and four were stillborns. Normal lung tissue from eight sudden infant death syndrome infants (mean age, 15.3 days) acted as controls. In situ hybridization was performed on frozen sections using IGF-I-specific and digoxigenin-labeled oligonucleotide probe and visualized by nitro blue tetrazolium staining.

RESULTS

In control lung, IGF-I mRNA expression was absent or weak in type II pneumocytes and alveolar macrophages. In contrast, there was strong IGF-I mRNA expression in type II pneumocytes and alveolar macrophages in hypoplastic CDH lung in newborns as well as stillborns.

CONCLUSION

The findings of strong IGF-I mRNA expression in the hypoplastic lung suggest that lung hypoplasia in CDH is a persistence of fetal stage of lung development.

Extracellular matrix and lung inflammation

Lung injury triggers an acute inflammatory response characterized by increased expression and deposition of extracellular matrix (ECM) components such as fibronectin and collagen. Although the function of newly deposited matrices in injured lungs is unknown, their ability to affect the migration, proliferation, differentiation, and activation state of cells in vitro suggests an important role in the initiation and maintenance of the inflammatory response in vivo. Interactions between immune and nonimmune cells with the lung ECM are mediated via cell surface receptors of the integrin family which link the ECM with intracellular molecules involved in signal transduction. Activation of integrin-mediated intracellular signals may promote inflammation by facilitating leukocyte recruitment and cytokine expression.

Interleukin-4 and interferon-gamma discordantly regulate collagen biosynthesis by functionally distinct lung fibroblast subsets

Pulmonary fibrosis is a potentially fatal consequence of treatments for malignancy and is an increasing problem in bone marrow transplant patients and in cases of allogenic lung transplant. The fibrotic response is characterized by increases in lung fibroblast number and collagen synthesis. This laboratory previously isolated stable, functionally distinct, murine lung fibroblast subsets (Thy-1+ and Thy-1-) to study the contribution of fibroblast subpopulations in lung fibrosis. The fibroblast fibrotic response may be induced by cytokines secreted by infiltrating cells such as T lymphocytes and mast cells. In the current study two key regulatory cytokines, interferon-gamma (IFN-gamma) and interleukin-4 (IL-4), were investigated for their effects on the collagen synthesis of murine lung fibroblast subsets. IL-4 and IFN-gamma are putatively characterized as fibrogenic and anti-fibrogenic cytokines, respectively, and are found in repairing lung tissue. Stimulation with recombinant IL-4 induced a100% increase in total collagen production only by Thy-1+ fibroblasts. Types I and III collagen mRNA were increased in the Thy-1+ fibroblasts, unlike the Thy-1- subset. In contrast, IFN-gamma decreased constitutive collagen production by more than 50% in Thy-1+ and Thy-1- fibroblasts. Interestingly, the two subsets utilized their collagen production machinery (collagenase, tissue inhibitors of metalloproteinases) differently to further regulate collagen turnover in response to IL-4 and IFN-gamma. Overall, our data support the hypothesis that IL-4 is fibrogenic and IFN-gamma is anti-fibrogenic. Moreover, selective expansion of IL-4 responsive fibroblasts (e.g., Thy-1+) may be important in the transition from repair to chronic fibrosis. In addition, these data suggest that an inflammatory response dominated by IL-4-producing Th2 lymphocytes and/or mast cells will promote fibrosis development.

Immunoquantification of type I, III, IV and V collagen in small samples of human lung parenchyma

The involvement of collagen in pathological conditions underscores the need for sensitive, collagen type-specific assays. A method for the quantification of different types of collagen in lung has been developed. Human lung parenchyma is digested with cyanogen bromide which results in almost complete solubilization of collagen to type-specific collagen peptides. The peptides are quantified using inhibition enzyme immunoassays with type-specific antibodies. The 50% inhibition value for the type I collagen assay is 1 microgram type I collagen peptides, for the type III collagen assay 350 ng type III collagen peptides, for the type IV collagen 200 ng type IV collagen peptides, and for the type V collagen assay 50 ng type V collagen peptides. Using less than 1 mg lyophilized human parenchymal lung tissue it was established that the amount of collagen/mg dry tissue (+/- SD, n = 10) is 84.6 +/- 16.1 micrograms for type I collagen, 26.6 +/- 10.3 micrograms for type III collagen, 9.6 +/- 2.0 micrograms for type IV collagen and 1.8 +/- 0.3 micrograms for type V collagen. The procedure is useful for the quantification of different types of collagen, including minor collagens, and requires only minimal sample preparation.

Mechanism of antifibrotic effect of taurine and niacin in the multidose bleomycin-hamster model of lung fibrosis: inhibition of lysyl oxidase and collagenase

In the multiple-dose bleomycin-hamster model of pulmonary fibrosis, combined treatment with taurine and niacin blocks the increase in lung collagen deposition. We investigated the effects of taurine and niacin on lung lysyl oxidase and type I collagenase activities in this model. Hamsters were intratracheally instilled with three weekly doses of saline or bleomycin sulfate. Animals were fed either a diet containing 2.5% niacin and 2.5% taurine, or a control diet throughout the experiment. The four groups were saline-instilled with the control diet (BCD), bleomycin-instilled with the diet containing taurine and niacin (BTN), and saline-instilled with the diet containing taurine and niacin (STN). Animals were sacrificed at 1, 4, and 8 weeks after the last bleomycin instillation. Hydroxyproline per lung in the BCD group was significantly elevated by 38, 56, and 60% over the SCD group at 1, 4, and 8 weeks, respectively. Lysyl oxidase activity per lung in the BCD group was significantly elevated by 57.5 and 91.4% over the SCD controls at 1 and 4 week time periods, respectively. Type I collagenase activity per lung in the BCD group was significantly elevated by 65 and 80% over the SCD controls at 1 and 4 weeks, respectively. The combined treatment with taurine and niacin abolished the bleomycin-induced increases in the lung hydroxyproline content and lysyl oxidase and collagenase activities. It was postulated that one of the mechanisms for the antifibrotic effect of taurine and niacin may be the blockage of bleomycin-induced increases in the lung lysyl oxidase and collagenase activities.

Influence of low molecular mass heparin on the kinetics of neutrophil elastase inhibition by mucus proteinase inhibitor

Commercial low molecular mass heparin accelerates the inhibition of neutrophil elastase by mucus proteinase inhibitor, the predominant antielastase of lung secretions (Faller, B., Mély, Y., Gérard, D., and Bieth, J.G. (1992) Biochemistry 31, 8285-8290). To study the kinetic mechanism of this rate enhancement, we have isolated a 4.5-kDa heparin fragment from commercial heparin. This compound is fairly monodisperse as shown by analytical ultracentrifugation. It binds elastase and inhibitor with a 1:1 stoichiometry and an equilibrium dissociation constant of 3 and 210 nM, respectively. It also forms a tight complex with EI. Flow calorimetry shows that the inhibitor-heparin interaction is characterized by a large negative enthalpy change (delta H0 = -45.2 kJ mol-1) and a small entropy change (delta S = -23.7 J K-1 mol-1). Stopped-flow kinetics run under pseudo-first-order conditions ([Io] >> [Eo]) show that in the absence of heparin the inhibition conforms to a simple bimolecular reaction, [formula: see text] where, ka = 3.1 x 10(6) M-1 s-1, kd = 10(-4) s-1, and Ki = 33 pM, whereas in the presence of heparin, E and I react via a two-step mechanism, [formula: see text] where Ki* = 86 nM, k2 = 2.2 s-1, k-2 = 10(-3) s-1, and Ki = 37 pM. Thus, heparin increases both the rate of inhibition by promoting the formation of a high affinity EI* intermediate and the rate of EI dissociation. Since the dissociation is negligible in bronchial secretions where the inhibitor concentration is much higher than Ki, it may be concluded that heparin significantly potentiates the inhibitor's antielastase potential in vivo.

Amelioration of bleomycin-induced lung fibrosis by treatment with the platelet activating factor receptor antagonist WEB 2086 in hamsters

Therapeutic use of bleomycin, an antineoplastic drug, is complicated by the development of a dose-dependent lung toxicity leading to fibrosis. This study tested the effectiveness of a platelet activating factor (PAF) receptor antagonist, WEB 2086, against bleomycin (BLEO)-induced lung fibrosis in hamsters. The animals were assigned to four groups: (1) saline (SA) + SA, (2) WEB 2086 (WEB) + SA, (3) SA + BLEO, and (4) WEB + BLEO. Sterile isotonic saline or WEB 2086 (10 mg/kg IP) was administered daily for the duration of the study starting 2 days prior to intratracheal (IT) instillation of saline or bleomycin (2.5, 2.0, and 1.5 units/kg 5 mL-1) in three consecutive doses at weekly intervals. The animals were killed at 21 days after the last IT instillation and their lungs were processed for various studies. The lung hydroxyproline levels in SA + SA, WEB + SA, SA + BLEO, and WEB + BLEO groups were 932 +/- 31, 943 +/- 48, 1302 +/- 72, and 964 +/- 63 micrograms/lung, respectively. The lung myeloperoxidase (MPO) activity and malondialdehyde equivalent, an index of lipid peroxidation, in the corresponding groups were 10 +/- 2, 8 +/- 2, 14 +/- 3, and 5 +/- 1 units/lung and 93 +/- 7, 77 +/- 5, 102 +/- 8, and 75 +/- 6 nmol/lung, respectively. The lung prolyl hydroxylase activity in the WEB + SA, SA + BLEO, and WEB + BLEO groups was 130.1 +/- 7.7, 236.2 +/- 12.8, and 138.1 +/- 7.0% of the SA + SA control group (8.3 x 10(4) dpm/lung 30 min-1), respectively. Daily treatment with WEB 2086 caused significant (p < or = .05) reductions in the BLEO-induced increases in the lung hydroxyproline content, prolyl hydroxylase and MPO activities, lipid peroxidation, and acid phosphatase activity of the BALF supernatant. Although daily treatment with WEB 2086 reduced the bleomycin-induced increases in the BALF total and neutrophil cell counts, BALF supernatant protein, and morphometric estimates of the lesions, these parameters were not significantly different from those of the SA-BLEO group. Histopathologic studies revealed that there were no lesions of alveolar consolidation and fibrosis in the lungs of WEB + BLEO group as compared with the SA + BLEO group. The results suggest that PAF is involved in the BLEO-induced lung fibrosis and that PAF-receptor antagonist may therefore be potentially useful in the attenuation of lung fibrosis caused by bleomycin.

Leukotriene C4 upregulates collagenase expression and synthesis in human lung fibroblasts

Leukotriene C4 (LTC4), a mediator generated by a variety of inflammatory cells, participates in several physiological and pathological processes. It has been shown that LTC4 stimulates collagen synthesis by fibroblasts, suggesting a role in collagen turnover. However, the possible effect of this mediator on collagen degradation has not been examined. In this study we explored the role of LTC4 in the modulation of fibroblast interstitial collagenase and TIMP-1. Confluent cultures of three human normal lung fibroblast cell lines, and one derived from idiopathic pulmonary fibrosis (IPF) were exposed to LTC4 0.1, 1 and 10 nM, and to IL-1 beta as positive control. Collagenase and TIMP mRNAs expression were analyzed by Northern blot followed by densitometric scanning. Immunoreactive procollagenase was detected by immunoblot, and collagenase activity was measured using [3H]collagen. Our results showed that LTC4 enhanced several-fold collagenase mRNA expression in collagenase-producing fibroblasts, and induced the expression of the enzyme mRNA in collagenase-nonproducing fibroblasts, both in normal and IPF derived cell lines. LTC4 1 nM induced the highest response. Collagenolytic activity and immunoreactive collagenase paralleled collagenase mRNA expression. Interestingly, simultaneous exposure of fibroblasts to LTC4 plus IL-1 failed to show additive effects. Moreover, in two cell lines the combination resulted in a decrease of collagenase mRNA expression compared with both mediators separately. TIMP mRNA levels were not significantly modified by LTC4, nor IL1 beta. Our findings suggest that LTC4 plays a role in the modulation of fibroblast collagenase, and it may participate in extracellular matrix remodeling during lung inflammation.

Effect of antibody to transforming growth factor beta on bleomycin induced accumulation of lung collagen in mice

BACKGROUND

Increased production of transforming growth factor beta (TGF-beta) seems to have an important role in the pathophysiology of bleomycin induced lung fibrosis. This is attributed to the ability of TGF-beta to stimulate infiltration of inflammatory cells and promote synthesis of connective tissue, leading to collagen deposition.

METHODS

The study was designed to evaluate the antifibrotic potential of TGF-beta antibody in mice treated with bleomycin, which is a model of lung fibrosis. Under methoxyflurane anaesthesia, each mouse received intratracheally either 50 microliters sterile isotonic saline or 0.125 units bleomycin in 50 microliters. Within five minutes after the instillation, mice received into the tail vein 100 microliters non-immune rabbit IgG, TGF-beta 2 antibody, or a combination of TGF-beta 2 and TGF-beta 1 antibodies at various dose regimens. Mice were killed 14 days after the instillation and their lungs processed for morphological and biochemical studies.

RESULTS

Administration of 250 micrograms of TGF-beta 2 antibody after instillation of bleomycin followed by 100 micrograms on day 5 and 100 micrograms on day 9 significantly reduced the bleomycin induced increases in the accumulation of lung collagen from 445.8 (42.3) micrograms/lung to 336.7 (56.6) micrograms/lung at 14 days. Similarly, the combined treatment with 250 micrograms TGF-beta 2 antibody and 250 micrograms TGF-beta 1 antibody after bleomycin instillation followed by 100 micrograms of each antibody on day 5 also caused a significant reduction in bleomycin induced increases in lung collagen accumulation and myeloperoxidase activity at 14 days.

CONCLUSIONS

These results suggest that TGF-beta has an important role in the aetiology of bleomycin induced lung fibrosis; the neutralisation of TGF-beta by systemic treatment with its antibodies offers a new mode of pharmacological intervention which may be useful in treating lung fibrosis.

Biochemical characterization and quantitation of the collagenous components of urethral stricture tissue

The collagenous composition of normal and strictured human urethral tissue was analyzed qualitatively by immunohistochemistry and quantitatively by 2-dimensional gel electrophoresis of cyanogen bromide digested tissue. Histological comparison of the normal and strictured urethral tissue showed that the normal urethral spongiosum was replaced by densely packed connective tissue fibers interspersed with fibroblasts in the strictured tissue. The immunohistochemical analysis of urethral tissue identified the presence of types I and III collagen fibers in normal spongiosum and in the connective tissue scar of strictured tissue. Estimation of the collagen type III:I ratio using scanning densitometry revealed a CB5:CB8 peptide ratio of 0.357 +/- 0.058 in the normal tissue, while the urethral stricture tissue had a CB5:CB8 ratio of 0.203 +/- 0.079 (p = 0.010). Total collagen content, as determined by hydroxyproline analysis, revealed no statistically significant differences between control and strictured tissue. Therefore, the normal urethral spongiosum was comprised of 75.1% type I collagen and 24.9% type III collagen. In contrast, the type I collagen in urethral stricture tissue was increased (83.9%), with a corresponding decrease in type III collagen (16.1%). This alteration in the ratio of collagen type III:I may explain the fibrotic noncompliant nature of urethral stricture scar tissue.

Increased fibronectin mRNA in alveolar macrophages following in vivo hyperoxia

Oxygen-mediated lung injury can stimulate a fibroproliferative response resulting in the alteration of the pulmonary extracellular matrix and subsequent scarring of parenchymal tissue. Fibronectin (FN), a component of the extracellular matrix, appears in increased quantities in fibrotic lung disease. Alveolar macrophages (AMs) are a potential source of this molecule. Using quantitative in situ hybridization, we demonstrated that AMs from rabbits acutely exposed to 100% oxygen (hyperoxia) for up to 64 h have 20-fold greater levels of FN mRNA relative to cells from control animals. When animals were allowed to recover in room air for up to 72 h after maximal oxygen exposure, AM FN mRNA abundance approached baseline levels. Furthermore, in oxygen-exposed animals, the fraction of lavaged cells expressing FN mRNA was increased 10-fold relative to controls. Although there was marked cell-to-cell variation, we conclude that the AM is a potential source of FN in the events leading to hyperoxia-induced pulmonary fibrosis.

Effect of dexamethasone therapy on fibronectin and albumin levels in lung secretions of infants with bronchopulmonary dysplasia

The influence of dexamethasone on levels of total fibronectin (tFn), cellular fibronectin (cFn), plasma fibronectin (pFn), and albumin in lung secretions was determined in tracheal aspirate samples collected from 45 infants with bronchopulmonary dysplasia during a 6-week course of dexamethasone therapy. Secretory component for IgA (SC) was used as a reference protein. Thirty-seven infants (82%) survived and had their endotracheal tubes successfully removed. Corticosteroid therapy was associated with a significant decrease in the cFn/SC ratio. There was also a significant decrease in albumin/SC and pFn/SC ratios, suggesting decreased capillary permeability with corticosteroid therapy. Four of the remaining infants did not improve while receiving corticosteroids and died of respiratory failure at 3 to 8 weeks of age. In these "no response" infants, tFn/SC, cFn/SC, pFn/SC, and albumin/SC ratios when corticosteroid therapy was initiated were threefold to fourfold greater (p < 0.01) than ratios in survivors. Another group of four infants initially responded to corticosteroids but subsequently died with severe pulmonary cystic degeneration at 4 to 6 months of age; in these infants, tracheal aspirate tFn/SC, cFn/SC, and albumin/SC ratios were significantly lower than in survivors and remained unchanged during corticosteroid therapy. The decrease in the concentrations of plasma fibronectin and albumin in tracheal aspirate samples from the survivors suggests that the rapid clinical improvement seen in infants with bronchopulmonary dysplasia after the initiation of dexamethasone therapy is due in part to improvement in the integrity of the alveolar-capillary barrier. In addition, the decrease in the aspirate levels of cFn suggests the potential for corticosteroids to limit pulmonary fibrosis in the surviving infants. The depressed levels of fibronectin observed in the infants with severe cystic lung disease may represent an impaired healing response to lung injury.

Heparin-induced conformational change and activation of mucus proteinase inhibitor

Low molecular mass heparin (5.1 kDa) forms a tight complex with mucus proteinase inhibitor, the physiologic neutrophil elastase inhibitor of the upper respiratory tract. This binding strongly enhances the intrinsic fluorescence of the inhibitor and the rate of neutrophil elastase inhibitor association. One mole of this heparin fragment binds 1 mol of inhibitor with a Kd of 50 nM. From the variation of Kd with ionic strength, it is inferred that (i) 85% of the heparin--inhibitor binding energy i due to electrostatic interactions, (ii) about seven ionic interactions are involved in heparin--inhibitor binding. strength, it is inferred that (i) 85% of the heparin--inhibitor binding energy is due to electrostatic interactions, (ii) about seven ionic interactions are involved in heparin--inhibitor binding. and (iii), about one-third of low quantum yield of Trp30, the single tryptophan residue of the inhibitor, blue-shifts its maximum emission wavelength by 6 nm, decreases the acrylamide quenching rate constant by a factor of 4, and increases the mean intensity weighted lifetime by a factor of 2.5. These important spectroscopic changes evidence a heparin--induced conformational change of the inhibitor which buries Trp30 in a very hydrophobic environment. Heparin accelerates the inhibition of elastase in a concentration-dependent manner. When both enzyme and inhibitor are saturated by the polymer, the second-order association rate constant is 7.7 x 10(7) M-1 s-1, a value that is 27-fold higher than that measured with the free partners. This finding may have important physiologic and therapeutic bearing.

Dynamic changes in the functional characteristics of the interstitial fibroblast during lung repair

To evaluate the mechanisms involved in the regulation of fibroblast function during the repair of fibrotic lung injury, we isolated lung fibroblasts from adult male Fischer-344 rats before the induction of severe unilateral paraquat lung injury, as well as 1 and 14 days later. Fibroblasts were utilized at an early generation time to avoid senescence. In general, fibroblasts of injured lungs displayed significant increases in proliferative and matrix synthesis properties, with more pronounced increases detected early after the induction of injury. This was true of DNA synthesis, which increased by 3- and 1.4-fold on days 1 and 14, respectively; tyrosine kinase activity, which increased by 4- and 3.5-fold; fibronectin synthesis, 14- and 8-fold, respectively; and glycosaminoglycans synthesis, 4.4- and 3-fold, respectively. The increase in function of fibroblasts isolated from the immediate influence of extrinsic growth factors suggests that fibroblast function during repair may be under intrinsic as well as extrinsic control. In the early phases of repair, intrinsic changes may be more dominant and may result in autoregulation of fibroblast function. In the later phases of repair, despite some reduction in intrinsic fibroblast activation, exposure to extrinsic growth factors may result in maintaining the state of activation and in sustaining the repair process.

Elevation of fibronectin levels in lung secretions of infants with respiratory distress syndrome and development of bronchopulmonary dysplasia

To determine whether the level of fibronectin in lung secretions correlates with the severity of lung injury or with the development of bronchopulmonary dysplasia, or both, serial tracheal aspirate samples were collected from 32 preterm infants with severe respiratory distress syndrome. Levels of total fibronectin, cellular fibronectin, plasma fibronectin, albumin, and secretory component of IgA (SC) were determined for the first 1 to 2 weeks of life in the 14 infants who recovered without pulmonary sequelae, and for weeks 1 to 4 in the 18 infants in whom bronchopulmonary dysplasia developed. Secretory component was chosen as the reference protein because its concentration in lung secretions is minimally influenced by capillary leak and does not vary with gestational or postnatal age. Albumin/SC and plasma fibronectin/SC ratios in tracheal aspirates were significantly higher (p less than 0.05) during the first 2 weeks of life in infants in whom bronchopulmonary dysplasia developed, suggesting greater capillary permeability in these infants. Cellular fibronectin/SC ratios in aspirates from infants with bronchopulmonary dysplasia were also significantly higher in the first 2 weeks, 9.0 +/- 1.7 and 7.4 +/- 2.0 micrograms/microgram SC in weeks 1 and 2, respectively, in comparison with values from infants without bronchopulmonary dysplasia, 1.6 +/- 0.4 and 1.1 +/- 0.8 micrograms/microgram SC (p less than 0.01), suggesting increased synthesis of fibronectin in the lungs of infants with subsequent bronchopulmonary dysplasia. Elevated levels of both plasma and cellular fibronectin in tracheal aspirate samples may provide an early index of the severity of lung injury in infants with severe respiratory distress syndrome.

Induction of unilateral pulmonary fibrosis in the rat by cadmium chloride

Intralobar instillation of cadmium chloride (CdCl2) into the left lungs of rats initiated a sequence of events that culminated in massive unilateral intraluminal fibrosis. Early events (days 1 and 2) after CdCl2 administration included infiltration of the treated lung with polymorphonuclear leukocytes, an increase in the number of alveolar macrophages, activation of the macrophages as assessed by the induction of cathepsin L mRNA, and the induction in liver of mRNA for the acute-phase response protein, alpha 1-acid glycoprotein. By days 5 to 7 in the treated lungs, mRNA for procollagen alpha 1(I) increased 20- to 60-fold, and mRNA for procollagen alpha 1(III) increased 4- to 14-fold. These increases were correlated with the almost complete filling of the alveolar spaces with fibroblasts and collagen. The contralateral lung exhibited no significant change in histology but showed a similar induction of collagen gene expression. These increases were tissue-specific, as the livers of these animals showed no change from the control levels of collagen gene expression. Procollagen messages in the treated and contralateral lungs were equally competent for translation into pro-alpha 1(I) and pro-alpha 2(I) polypeptides. Both the treated and contralateral lungs increased hydroxyproline content about 1.5- to 2-fold over 14 days. The contralateral lung, but not the treated lung, showed a 2-fold increase in lung volume. As a result, the collagen density (mg collagen/ml lung volume) doubled in the treated lung but remained constant in the contralateral lung. These data indicate that CdCl2 caused a rapid induction of pulmonary fibrosis in the treated lungs of rats and stimulated histologically normal growth of the contralateral lung.

Elastin metabolism during recovery from impaired crosslink formation

Accelerated proteolysis of tropoelastin and elastin occurs in the arteries of chicks rendered nutritionally copper-deficient. The process results in part from decreased elastin crosslinking. Repletion of copper-deficient chicks with copper causes a deposition of elastin that is proteinase resistant. Resistance to proteolysis is conferred within 48 h of dietary copper repletion. Deposition of aorta elastin to near normal values occurs after 3-4 days in copper-repleted chicks. Moreover, elastolysis was enhanced when the content of dehydrolysinonorleucine in elastin was abnormally low. The chemical modification of lysyl residue in elastin by citroconylation, however, did not influence the rate of elastolysis. We have shown previously that tropoelastin messenger RNA activity and synthesis are not influenced by dietary copper deprivation (1986, Biochem. J. 236, 17-23). Rather, as demonstrated herein, the decrease in elastin content in arteries of copper-deficient birds appears to be more the result of enhanced degradation. Restoration of normal crosslinking restores deposition and imparts resistance to elastolysis. Moreover, serum appears to be a good source of elastolytic proteinases when the elastin substrate is partially or abnormally crosslinked.

Coordinate regulation of transforming growth factor beta gene expression and cell proliferation in hamster lungs undergoing bleomycin-induced pulmonary fibrosis

The number of mesenchymal cells, as well as their ability to synthesize extracellular matrix (ECM) components, greatly increase in the interstitium of fibrotic lungs. We have previously shown that the transcription of type I procollagen and fibronectin genes in the lungs is preferentially elevated during the early stages of bleomycin-induced pulmonary fibrosis (Raghow, R., S. Lurie, J. M. Seyer, and A. H. Kang. 1985, J. Clin. Invest. 76:1734-1739. Since a cytokine-like transforming growth factor beta (TGF beta) that is capable of enhancing mesenchymal cell proliferation and ECM synthesis could be potentially involved in this process, we investigated the temporal relationship between the regulation of TGF beta gene transcription and cellular proliferation in the bleomycin-treated hamster lungs. We observed a transient 5-7-fold increase in the accumulation of TGF beta transcripts, a concomitant 3-4-fold elevation in the cellular proliferation, and 8-10-fold stimulation of DNA synthesis in these lungs; all three parameters peaked around day 10 after bleomycin administration. Based on these results, we conclude that regulation of TGF beta gene expression may contribute significantly to the early events that lead to bleomycin-induced pulmonary fibrosis.

Effects of interferon-gamma on expression of cell surface receptors for collagen and deposition of newly synthesized collagen by cultured human lung fibroblasts

We used cultured human diploid lung fibroblasts as a model system to examine the effects of recombinant IFN-gamma on synthesis of collagen, matrix deposition of newly synthesized collagen, and the expression of cell surface receptors for collagen. Using [3H]proline-labeled cells we found that IFN-gamma resulted in dose-dependent inhibition of fibroblast collagen synthesis. Pulse-chase experiments to analyze compartmentalization of newly synthesized collagen showed that the decrease in collagen synthesis was confined to the soluble pool of procollagen in the medium, while extracellular matrix associated collagen was not changed, indicating that a larger proportion of newly synthesized collagen was deposited into the matrix in IFN-gamma exposed fibroblasts (34.2 vs. 25.3%). This increase in the efficiency of collagen matrix deposition was associated with enhanced expression of a cell surface receptor for collagen as detected by indirect immunofluorescence labeling and analysis by flow cytometry. Fibroblasts (IMR-90) cultured in the presence of IFN-gamma (1,000 U/ml) exhibited a twofold increase in mean linear fluorescence intensity compared with cells cultured under control conditions. The distribution of log fluorescence intensity in both control and IFN-gamma exposed cells was normally distributed about the mean, indicating that discrete subpopulations with respect to receptor expression were not present. Increased fluorescence intensity and log normal distribution of fluorescence intensity also were identified in IFN-gamma-treated lung fibroblasts from a normal adult individual and two strains obtained from patients with pulmonary fibrosis. These results indicate that IFN-gamma modulates fibroblast collagen matrix deposition as well as collagen synthesis. The associated increase in collagen receptors suggests that cytokine-mediated modulation of the cell surface maybe a contributing factor in regulation of fibroblast collagen accumulation in the extracellular matrix or in cellular interaction with collagen-containing matrix. Such an effect could modulate the interaction of fibroblasts with extracellular matrix at sites of inflammation and play an important role in the remodeling of matrix during repair from tissue injury.

Entropic elastic processes in protein mechanisms. II. Simple (passive) and coupled (active) development of elastic forces

The first part of this review on entropic elastic processes in protein mechanisms (Urry, 1988) demonstrated with the polypentapeptide of elastin (Val1-Pro2-Gly3-Val4-Gly5)n that elastic structure develops as the result of an inverse temperature transition and that entropic elasticity is due to internal chain dynamics in a regular nonrandom structure. This demonstration is contrary to the pervasive perspective of entropic protein elasticity of the past three decades wherein a network of random chains has been considered the necessary structural consequence of the occurrence of dominantly entropic elastomeric force. That this is not the case provides a new opportunity for understanding the occurrence and role of entropic elastic processes in protein mechanisms. Entropic elastic processes are considered in two classes: passive and active. The development of elastomeric force on deformation is class I (passive) and the development of elastomeric force as the result of a chemical process shifting the temperature of a transition is class II (active). Examples of class I are elastin, the elastic filament of muscle, elastic force changes in enzyme catalysis resulting from binding processes and resulting in the straining of a scissile bond, and in the turning on and off of channels due to changes in transmembrane potential. Demonstration of the consequences of elastomeric force developing as the result of an inverse temperature transition are seen in elastin, where elastic recoil is lost on oxidation, i.e., on decreasing the hydrophobicity of the chain and shifting the temperature for the development of elastomeric force to temperatures greater than physiological. This is relevant in general to loss of elasticity on aging and more specifically to the development of pulmonary emphysema. Since random chain networks are not the products of inverse temperature transitions and the temperature at which an inverse temperature transition occurs depends on the hydrophobicity of the polypeptide chain, it now becomes possible to consider chemical processes for turning elastomeric force on and off by reversibly changing the hydrophobicity of the polypeptide chain. This is herein called mechanochemical coupling of the first kind; this is the chemical modulation of the temperature for the transition from a less-ordered less elastic state to a more-ordered more elastic state. In the usual considerations to date, development of elastomeric force is the result of a standard transition from a more-ordered less elastic state to a less-ordered more elastic state.(ABSTRACT TRUNCATED AT 400 WORDS)

Matrix deposition and extracellular processing of newly synthesized collagens in the isolated perfused rat lung

We have examined the matrix deposition and proteolytic processing of newly synthesized interstitial and basement membrane collagens in the isolated perfused adult rat lung. Isolated, perfused, and ventilated lungs were labeled for up to 4 h with radiolabeled proline. Collagens were partially purified from homogenates by salt fractionation and ion exchange chromatography and examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The major collagenous species were identified as types I, III, and IV collagen by peptide mapping and indirect immunoprecipitation assays. Whereas extraction with neutral salts recovered radiolabeled types I and III collagen, extraction of the neutral salt residue with 2 M guanidine-HCl preferentially recovered types III and IV collagen. Reextraction of the guanidine-HCl residue in the presence of dithiothreitol selectively recovered type IV procollagen (PC) and covalently cross-linked aggregates of type IV chains. In pulse-chase experiments we observed extensive conversion of type I PC to collagen during a 4-h chase. Although type III PC was efficiently converted to p-collagen, only small amounts of fully processed chains were identified. Type IV PC did not undergo detectable proteolytic processing. The isolated perfused rat lung should prove useful for further studies of lung collagen metabolism.

Malotilate reduces collagen synthesis and cell migration activity of fibroblasts in vitro

Diisopropyl-1,3-dithiol-2-ylidenemalonate (malotilate) was studied for and compared with cyanidanol, hydrocortisone and colchicin on its impact on fibroblast cultures. Under in vitro conditions, malotilate specifically reduces collagen synthesis of fibroblasts. In addition, malotilate is an efficient inhibitor of fibroblast migration as tested by a chemotaxis assay in a modified Boyden chamber. Our data may support the notion that malotilate is of potential interest for interfering with fibrotic processes.

Lung tissue tension and glycosaminoglycans

This study tested the hypothesis that the loss of tissue tension which occurs when lung parenchyma is immersed in phosphate buffered saline (PBS) follows a loss of glycosaminoglycans (GAG) and/or protein. Tissue tension decay (TTD) was examined in 30 X 30 X 100 micron strips of rat lung parenchyma immersed in PBS in the presence of agents altering the loss of GAG. GAG were labeled with [35S]sulfate in vitro by tissue culture of lung explants and in vivo by intraperitoneal injection of [35S]sulfate. Labeled GAG were lost from lung explants, lung homogenates, and whole lung immersed in saline. The rate of GAG loss was found to correlate with early TTD. In the presence of agents that markedly reduced the leach rate of GAG from lung parenchyma (Safranin O, Alcian Blue, Acridine Orange) there was no TTD. Cetyl-pyridinium chloride was also effective. Polybrene, however, caused a significantly greater TTD than seen in saline with some reduction in the total amount of GAG leached from the tissue. Greater amounts of heparin sulfate were lost in the presence of polybrene. Human serum, dextran-70, ovalbumin, and gelatin significantly reduced but did not prevent TTD. Dextran-70 was effective in reducing the loss of GAG from tissue explants. Agents that reduced disulfide bonds (dithiothreitol, 2-mercaptoethanol) markedly increased TTD and increased the loss of GAG and protein from lung explants and lung homogenates. These studies provide further evidence that lung tissue tension is a function of the interstitial matrix interacting with the connective tissue network. When the GAG and protein responsible for the swelling pressure of matrix are preserved the tissue tension is stable for one hour or more. Agents that partially preserve the matrix are somewhat effective in reducing TTD while those that increase the loss of GAG and protein increase the loss of tension. From the differential effect of agents that retard and accelerate GAG, heparin sulfate (HS) may be the most important GAG to the tissue properties.

A monoclonal antibody to the carboxyterminal domain of procollagen type I visualizes collagen-synthesizing fibroblasts. Detection of an altered fibroblast phenotype in lungs of patients with pulmonary fibrosis

Excessive collagen deposition plays a critical role in the development of fibrosis, and early or active fibrosis may be more susceptible to therapeutic intervention than later stages of scarring. However, at present there is no simple method for assessing the collagen-synthesizing and secreting activity of fibroblasts in human tissues. Type I procollagen carboxyterminal domains are proteolytically removed during collagen secretion. Thus, antibodies to these domains should stain fibroblasts synthesizing type I collagen but not extracellular collagen fibrils which could mask the signal from the cells. We developed and characterized a monoclonal antibody (Anti-pC) specific for the carboxyterminal propeptide of type I procollagen. To determine the relationship between Anti-pC staining and collagen synthesis, we stained embryonic and adult chicken tendon. Embryonic chick tendon fibroblasts actively synthesizing type I collagen stained heavily with Anti-pC, while quiescent adult tendon fibroblasts did not stain with Anti-pC. Wounded adult tendons developed fibroblasts that stained with Anti-pC at the wound site. Thus, Anti-pC specifically visualized fibroblasts actively synthesizing collagen. Lung biopsies from patients with fibrotic lung disease were stained with Anti-pC. Interstitial and intraalveolar fibroblasts in biopsies from patients with active fibrosis stained intensely with Anti-pC, while normal human lung was unstained. The absence of staining in normal lung supports the hypothesis that fibrosis is associated with an altered collagen-synthesizing phenotype of tissue fibroblasts. Anti-pC may provide a useful clinical tool for assessing fibrogenic activity at sites of tissue injury.

Profiles of steady state levels of messenger RNAs coding for type I procollagen, elastin, and fibronectin in hamster lungs undergoing bleomycin-induced interstitial pulmonary fibrosis

We have characterized the messenger RNAs (mRNAs) coding for procollagen alpha 1(I), elastin, fibronectin, and actin in the lungs of Syrian golden hamsters by Northern blot analyses. While elastin, fibronectin, and beta-actin were each coded for by a single mRNA species of 4.1 kilobases (kb), 9.1 kb, and 2.1 kb in size, respectively, we identified a major (5.4 kb) and a minor (6.5 kb) procollagen alpha 1(I) mRNA species in the hamster lungs. The mRNAs for the three extracellular matrix proteins showed increased accumulation followed by steady decline in the bleomycin-treated lungs. There were significant differences among the three mRNAs in the relative increase and the time of maximum accumulation. After reaching the peak levels between 2-3 wk posttreatment, the levels of procollagen alpha 1(I) and elastin mRNAs declined to near normal values around the fourth week. In contrast, the accumulation of fibronectin mRNA was maximum in the first week after bleomycin treatment. The procollagen alpha 1(I) mRNA accumulated most dramatically (sevenfold above the levels in the untreated animals) compared with a five-fold increase in mRNA coding for fibronectin. Elastin mRNA increased approximately twofold above the control values. Nuclear runoff transcription experiments demonstrated a selective increase in the rates of transcription of genes coding for procollagen alpha 1(I), fibronectin, and elastin; the extent of transcriptional stimulation of procollagen alpha 1(I) and fibronectin genes was significantly greater than that of elastin. Since the amount of actin mRNA, as well as the rate of transcription of actin gene(s), varied only slightly after bleomycin treatment, we conclude that the metabolism of mRNAs coding for extracellular matrix proteins may be preferentially perturbed during pulmonary fibrosis.

Association of hemolytic anemia and early-onset pulmonary emphysema in three siblings

Three of four siblings born to nonconsanguineous parents of Italian origin were affected with severe congenital hemolytic anemia of unknown cause, and early-onset pulmonary emphysema. Two of the three affected siblings died of septic shock after splenectomy, at the ages of 7 and 3 1/2 years, respectively. The remaining affected sibling was shown to have cutis laxa and severe pulmonary emphysema at 15 years of age. Assay of serum components indicated that alpha 1-antitrypsin and alpha 2-macroglobulin levels were normal or slightly elevated. However, there was markedly elevated activity of an elastase-like serum enzyme. The relation of the hemolytic anemia to the pulmonary findings in this family is not clear; pedigree analysis suggests a recessively inherited defect.