Platelet-derived growth factor in idiopathic pulmonary fibrosis

Abnormal re-epithelialization and lung remodeling in idiopathic pulmonary fibrosis: the role of deltaN-p63

Products of the p63 gene, a recently described member of the p53 family, are constitutively expressed in the basal cells of human bronchi and bronchioli. The truncated isoforms of the p63 gene (deltaN-p63 proteins) counteract the apoptotic and cell cycle inhibitory functions of p53 after DNA damage, and this property is likely to be central in the cell renewal strategy of stratified epithelial tissues. To investigate the dysfunctional repair processes that characterize idiopathic pulmonary fibrosis/usual interstitial pneumonia (IPF/UIP), we immunohistochemically analyzed the expression of the transactivating and dominant-negative isoforms of the p63 gene on 16 tissue samples obtained from patients suffering from this disorder. In most IPF cases herein investigated, epithelial cells expressing deltaN-p63 were observed at sites of abnormal proliferation at the bronchiolo-alveolar junctions, characterized by epithelial hyperplasia, squamous metaplasia, bronchiolization, and abnormal p53 nuclear accumulation. Similar features were not observed in normal lung and in samples taken from other pulmonary diseases used as controls, including acute interstitial pneumonia, idiopathic bronchiolitis obliterans organizing pneumonia, nonspecific interstitial pneumonia, and desquamative interstitial pneumonia. On the basis of these findings, we can hypothesize a new model for UIP pathogenesis, involving a deregulated development of mesenchymal-epithelial interactions and abnormal proliferation of epithelial cells at the bronchiolo-alveolar junction after cell injury. In our view, the progressive loss of alveolar tissue and lung remodeling after injury in IPF/UIP is concomitantly produced by pneumocyte loss and alveolar collapse on one hand and by progressive bronchiolar proliferation and architectural distortion on the other.

Titration of non-replicating adenovirus as a vector for transducing active TGF-beta1 gene expression causing inflammation and fibrogenesis in the lungs of C57BL/6 mice

Investigators have shown that interstitial pulmonary fibrosis (IPF) can be induced in rats by overexpressing transforming growth factor beta1 (TGF-beta1) through a replication-deficient recombinant adenovirus vector instilled into the lungs (Sime et al. 1997). We have shown that this vector induces IPF in fibrogenic-resistant tumour necrosis factor alpha-receptor knockout (TNF-alphaRKO) mice (Liu et al. 2001). The object of our studies is to understand how peptide growth factors, such as TGF-beta1, mediate interstitial lung disease (ILD). To do so, we must be able to manipulate the dose of the factor and sort out its effects on multiple other mediators in the lung parenchyma. As a step in this complex process, in the studies reported here, we have determined the concentrations of the recombinant adenovirus vector carrying the gene for porcine active TGF-beta1 (AVTGFbeta1) that have little apparent effect, cause clear induction of disease, or severe disease. The disease largely resolves by 28 days in all cases, thus providing a valuable model to understand the mechanisms of the IPF that is mediated, at least in part, by TGF-beta1. The findings here show that 10(6) plaque-forming units (pfu) of AVTGFbeta1, provide essentially a 'no-effect' dose, but even this amount of TGF-beta1 causes a significant increase in whole-lung collagen by day 28 after treatment. In contrast, 10(8) and 10(9) pfu cause severe IPF in 4 days, whereas 10(7) and 5 x 10(7) are intermediate for all parameters studied, i.e. TGF-beta protein, inflammatory cells, cell proliferation, pro-alpha 1(I) collagen gene expression and whole-lung collagen accumulation, and expression of growth factors such as TGF-beta1, TNF-alpha and PDGF-A and -B. Interestingly enough, TGF-beta1, as a potent blocker of epithelial cell proliferation, appears to suppress airway epithelial cell growth that would be expected during the inflammatory phase of IPF. Thus, this model system helps us to understand some quantitative aspects of TGF-beta1 biological activity and allows us to manipulate this potent factor as a mediator of interstitial fibrogenesis.

Fibroblast mitogenic activity of lung lavage fluid from infants with chronic lung disease of prematurity

BACKGROUND

Lung fibrosis is thought to be important in chronic lung disease of prematurity (CLD).

METHODS

Fibroblast proliferative activity was assessed in 207 bronchoalveolar lavage fluid (BALF) samples from 43 infants. Sixteen developed CLD (birth weight 765 g (630-1230), gestation 26.5 weeks (23-29)), 18 developed respiratory distress syndrome (RDS) (birth weight 1415 g (430-4160), gestation 31 weeks (23-39)), and nine control infants (birth weight 2110 g (900-3720), gestation 32 weeks (26-41)) received mechanical ventilation for non-pulmonary reasons.

RESULTS

The fibroblast proliferative activity relative to 10% fetal calf serum was 64-75% in infants with CLD, 55-86% in the RDS group, and 42-68% in control infants during the first 5 weeks of life. Only at day 3 was there a difference between the groups (CLD 72% v control 42%, p < 0.01; RDS 63% v control 42%, p < 0.05). With the use of neutralising antibodies, platelet derived growth factor BB (PDGF-BB) and epidermal growth factor were undetectable, and insulin-like growth factor I (IGF-I) accounted for 14% (p < 0.05) and 11% (p < 0.005) of BALF mitogenic activity from the RDS and CLD groups respectively.

CONCLUSIONS

The mitogenic activity of BALF was similar in the three groups studied and was only partially accounted for by IGF-I. Growth factors other than PDGF-BB and IGF-I contribute significantly to this process.

Idiopathic pulmonary fibrosis: an epithelial/fibroblastic cross-talk disorder

Idiopathic pulmonary fibrosis is a chronic and usually progressive lung disorder of unknown etiology. A growing body of evidence suggests that, in contrast to other interstitial lung diseases, IPF is a distinct entity in which inflammation is a secondary and non-relevant pathogenic partner. Evidence includes the presence of similar mild/moderate inflammation either in early or late disease, and the lack of response to potent anti-inflammatory therapy. Additionally, it is clear from experimental models and some human diseases that it is possible to have fibrosis without inflammation. An evolving hypothesis proposes that IPF may result from epithelial micro-injuries and abnormal wound healing.

DNA sequence variants of the platelet-derived growth factor A-chain gene

BACKGROUND

Platelet-derived growth factor A-chain (PDGF-A) is a potent connective tissue mitogen implicated in lung growth and development. PDGF-A may have a role in asthma through effects on fibroblasts and bronchial smooth muscle cells.

OBJECTIVE

To test the hypothesis that there exist variations in the PDGF-A gene associated with the asthma phenotype.

METHODS

We screened genomic DNA from normal and asthmatic subjects using single-stranded conformational polymorphism (SSCP) for mutations in the promoter and all seven exons of the gene.

RESULTS

Four transition polymorphisms (three novel) were identified: one each in exons 3 and 4 (overall population allele frequencies 0.18 and 0.02, respectively) which did not alter the protein sequence, one in exon 4 (frequency 0.005) which resulted in a valine to isoleucine substitution, and one in intron 5 (frequency 0.5). The intron 5-sequence variant is close to the 3' end of exon 5 but does not appear to affect alternative splicing of PDGF-A exon 6 RNA. The frequencies of the polymorphisms in exons 3 and intron 5 did not differ between the asthmatic and non-asthmatic subjects, but there was a significant frequency difference between Caucasian and African-American subjects for each of these polymorphisms (P = 0.03 and 0.003, respectively).

CONCLUSION

No association was found between the sequence variants in the PDGF-A gene and the development of asthma. However, the allele frequency of some of the sequence variants differed between the Caucasian and African-American subjects.

Upregulation of tenascin and TGFbeta production in a type II alveolar epithelial cell line by antibody against a pulmonary auto-antigen

Type II alveolar epithelial cells express a 70-90 kDa antigen to which circulating auto-antibodies have been previously identified in patients with cryptogenic fibrosing alveolitis (CFA). In vitro experiments have been conducted with a rabbit polyclonal antibody raised to this auto-antigen, and the type II epithelial cell line A549. This study examined possible effects that interaction of this antibody with type II epithelial cells might have on the production of cytokines and extracellular matrix components that may be important in the pathogenesis of CFA. There was a significant increase in TGFbeta and tenascin, but not IL4, production by the A549 cells after culture with the immune serum. Further experiments showed that after 72 hours in culture, the antibody decreased A549 cell number in a complement-dependent process, which appeared to be cytostatic rather than cytolytic. These results indicate in vitro biological activity for this antibody and suggest a possible in vivo role for auto-antibody to type II epithelial cells in the pathogenesis of CFA.

Rat alveolar type II cells inhibit lung fibroblast proliferation in vitro

Fibroblasts stimulate alveolar type II epithelial cell differentiation and proliferation in vitro and during lung development. However, little is known about the effects of adult type II cells on fibroblasts. We investigated the effect of adult rat type II cells on proliferation of adult human lung fibroblasts. Fibroblasts were suspended within rat tail collagen which was gelled on a floating polycarbonate filter, and type II cells were cultured on Matrigel. In this coculture system, alveolar type II cells inhibited fibroblast proliferation and indomethacin blocked the inhibitory effect on fibroblast growth. Prostaglandin (PG) E2, the major PG secreted by type II cells, inhibited fibroblast proliferation and was increased during the period of inhibition of fibroblast proliferation. Incubation with arachidonate showed that most of the PGE2 in the coculture system was produced by the fibroblasts. In addition, we found that rat type II cells also inhibited rat fibroblasts and that inhibition of fibroblast growth by type II cells could be stimulated by keratinocyte growth factor. We conclude that in this coculture system, type II cells inhibit fibroblast proliferation by secreting a factor(s) that stimulates PGE2 production by fibroblasts, and that PGE2 directly inhibits fibroblast proliferation.

Peplomycin, a bleomycin derivative, induces myofibroblasts in pulmonary fibrosis

To analyse the mechanism by which a bleomycin derivative, peplomycin (PLM) induces pulmonary fibrosis, we investigated differentiation of rat pulmonary fibroblasts to myofibroblasts (MF). In intraperitoneally PLM (5 mg/kg/day)-injected rats, the peripheries of lungs adjacent to the pleura revealed advanced fibrosis with a small number of alpha-smooth muscle actin (alpha-SMA)-positive MF, which ultrastructurally possessed abundant microfilaments and cellular organelles. In the fibrotic tissue, the expression of alpha-SMA-mRNA was detected by in situ reverse transcription-polymerase (RT-PCR). The message was strong just after a 2-week administration of PLM then decreased thereafter, although fibrosis advanced. When pulmonary fibroblasts were separated from saline-injected rats (N-Fib) and cultivated for 7 days in the presence of 5 mg/mL PLM, alpha-SMA protein was weakly expressed, while the majority of pulmonary fibroblasts separated from PLM-injected rats (P-Fib) became positive for alpha-SMA in 7-day cultivation and the expression of alpha-SMA in P-Fib was strongly increased by cultivation in the presence of PLM and transforming growth factor-beta (TGF-beta), but not basic fibroblast growth factor (bFGF) or platelet-derived growth factor (PDGF), although the cell proliferation was most strongly enhanced by bFGF and only slightly by PLM and TGF-beta. The alpha-SMA-positive cells expressed vimentin, but only weakly expressed desmin. Additionally, P-Fib generated larger amounts of TGF-beta and bFGF than were generated by N-Fib. These results indicate that PLM induces pulmonary fibrosis by differentiating fibroblasts to alpha-SMA-positive MF, and that bFGF and TGF-beta play each critical role in the different phases of PLM-induced pulmonary fibrosis by inducing fibroblast proliferation and transformation, respectively.

Type II alveolar epithelial cells and interstitial fibroblasts express connective tissue growth factor in IPF

Connective tissue growth factor (CTGF) is a growth and chemotactic factor for fibroblasts encoded by an immediate early gene that is transcriptionally activated by transforming growth factor-beta. Previous studies have shown that both CTGF messenger ribonuclear acid (mRNA) and protein are expressed in renal fibrosis and bleomycin-induced pulmonary fibrosis in mice. The aim of the present study was to investigate the localization of CTGF protein and its mRNA expression in the fibrotic lung tissue of patients with idiopathic pulmonary fibrosis (IPF). Using human fibrotic lung tissue obtained from eight autopsy cases and four biopsy cases with IPF, immunohistochemical staining, in situ hybridization, and reverse transcription-polymerase chain reaction (RT-PCR) were performed. The cellular immunoreactivity for CTGF was markedly increased in the lung tissue of patients with IPF, compared to normal lungs. The immunolocalization of CTGF was confined predominantly to proliferating type II alveolar epithelial cells and activated fibroblasts. In the normal lung, type II alveolar epithelial cells stained for CTGF were sparsely distributed. CTGF mRNA was localized in proliferating type II alveolar epithelial cells and activated fibroblasts in the interstitium of fibrotic lung tissues. RT-PCR analysis showed that CTGF mRNA was expressed at a higher level in fibrotic lungs than in normal lungs. In both an autocrine and a paracrine manner, type II alveolar epithelial cells and activated fibroblasts may play a critical role in pulmonary fibrosis by producing connective tissue growth factor which modulates fibroblast proliferation and extracellular matrix production.

Involvement of platelet-derived growth factor in disease: development of specific antagonists

Platelet-derived growth factor (PDGF) is a family of dimeric isoforms that stimulates, e.g., growth, chemotaxis and cell shape changes of various connective tissue cell types and certain other cells. The cellular effects of PDGF isoforms are exerted through binding to two structurally related tyrosine kinase receptors. Ligand binding induces receptor dimerization and autophosphorylation. This enables a number of SH2 domain containing signal transduction molecules to bind to the receptors, thereby initiating various signaling pathways. PDGF isoforms have important roles during the embryonic development, particularly in the formation of connective tissue in various organs. In the adult, PDGF stimulates wound healing. Overactivity of PDGF has been implicated in certain disorders, including fibrotic conditions, atherosclerosis, and malignancies. Different kinds of PDGF antagonists are currently being developed and evaluated in different animal disease models, as well as in clinical trials.

Role of osteopontin in the pathogenesis of bleomycin-induced pulmonary fibrosis

Pulmonary fibrosis is initiated by migration, adhesion, and proliferation of fibroblasts. Osteopontin (OPN) is one of the cytokines produced by activated macrophages and mediates various functions, including cell attachment and migration, by interacting with alphav integrin. In this study, we have investigated the role of OPN in the pathogenesis of pulmonary fibrosis. We developed a mouse model for pulmonary fibrosis by intratracheal instillation of bleomycin (BLM). OPN was strongly expressed in alveolar macrophages accumulating in the fibrotic area of the lung. OPN messenger RNA (mRNA) in the lung was notably induced by BLM instillation, and the development of the fibrotic process was associated with an increase in the expression of OPN mRNA and protein. In vitro, recombinant OPN enhanced migration, adhesion, and platelet-derived growth factor (PDGF)-mediated DNA synthesis of murine fibroblast cell line NIH3T3. These effects of OPN on fibroblasts were significantly suppressed by addition of antimouse alphav integrin monoclonal antibody (RMV-7). Furthermore, treatment of mice with RMV-7 repressed the extent of pulmonary fibrosis in this model. Conclusively, these data suggest that OPN produced by alveolar macrophages functions as a fibrogenic cytokine that promotes migration, adhesion, and proliferation of fibroblasts in the development of BLM-induced pulmonary fibrosis.

Gene transfer and expression of platelet-derived growth factors modulate periodontal cellular activity

Platelet-derived growth factor (PDGF) is a potent stimulator of wound healing. PDGF gene therapy may promote greater periodontal regeneration than local protein application, due to sustained growth factor delivery to the target tissue. This investigation tested the ability of recombinant adenoviruses (rAds) encoding PDGF-A or PDGF-1308 (a PDGF-A dominant-negative mutant that disrupts endogenous PDGF bioactivity) to affect cells derived from the periodontium. Osteoblasts, periodontal ligament fibroblasts, and gingival fibroblasts were transduced with rAds, and gene expression, DNA synthesis, and cell proliferation were evaluated. The results revealed strong message for the PDGF-A gene for 7 days following gene delivery. Ad2/PDGF-A enhanced the mitogenic and proliferative response in all cell types, while Ad2/PDGF-1308 potently inhibited mitogenesis and proliferation. In conclusion, Ad2/PDGF can effectively transduce cells derived from the periodontium and promote biological activity equivalent to PDGF-AA. These studies support the potential use of gene therapy for sustained PDGF release in periodontal tissues.

Idiopathic pneumonia syndrome following myeloablative chemotherapy and autologous transplantation

OBJECTIVE

To report the outcome as well as the clinical, radiographic, and pathologic features of idiopathic pneumonia syndrome (IPS) following autologous peripheral blood stem cell transplantation (aPBSCT).

CLINICAL FINDINGS

A total of 271 patients with a variety of underlying malignancies received busulfan-containing myeloablative chemotherapy prior to aPBSCT; none of these patients received total body irradiation. Ten individuals developed IPS, with a median time of onset of 102 days after stem cell infusion. The major clinical and radiographic findings included an acute or subacute onset of dyspnea, cough, hypoxemia, and bilateral or unilateral infiltrates with or without pleural effusion. Pathologic findings consisted mainly of diffuse interstitial pneumonitis, organizing alveolitis, and cellular atypia. Nine patients diagnosed with IPS were treated with high doses of glucocorticoids parenterally. Despite heroic measures, eight patients died of IPS. The two remaining individuals recovered without experiencing significant long-term pulmonary sequelae.

DISCUSSION

Chronic low-dose busulfan therapy results in lung injury in 4-6% of patients after several years of treatment and once the cumulative dosage begins to approach 3g. High-dose, short-course busulfan (16 mg/kg)-containing conditioning chemotherapy prior to aPBSCT can also be complicated by IPS. IPS differs from lung damage due to chronic busulfan therapy by its earlier onset, an acute or subacute rather than indolent presentation, characteristic clinical and radiographic features, and lack of multinucleated giant cells on pathologic review. The pathophysiology of IPS secondary to high-dose busulfan-containing myeloablative regimens is not known, but cell-mediated immune reactions and release of cytokines may contribute to the lung injury. Mortality is high (80%) despite the use of heroic measures, including mechanical ventilation. Some patients, however, can respond to high doses of parenteral corticosteroid therapy.

CONCLUSIONS

IPS following high-dose, short-course busulfan-containing regimens exhibits unique clinical, radiographic, and pathologic features that differ from lung damage characteristic of chronic, low-dose busulfan therapy. Mortality from this complication is 80%, but some patients survive without long-term pulmonary sequelae following early treatment with glucocorticoids.

Alveolar epithelial type II cell: defender of the alveolus revisited

In 1977, Mason and Williams developed the concept of the alveolar epithelial type II (AE2) cell as a defender of the alveolus. It is well known that AE2 cells synthesise, secrete, and recycle all components of the surfactant that regulates alveolar surface tension in mammalian lungs. AE2 cells influence extracellular surfactant transformation by regulating, for example, pH and [Ca2+] of the hypophase. AE2 cells play various roles in alveolar fluid balance, coagulation/fibrinolysis, and host defence. AE2 cells proliferate, differentiate into AE1 cells, and remove apoptotic AE2 cells by phagocytosis, thus contributing to epithelial repair. AE2 cells may act as immunoregulatory cells. AE2 cells interact with resident and mobile cells, either directly by membrane contact or indirectly via cytokines/growth factors and their receptors, thus representing an integrative unit within the alveolus. Although most data support the concept, the controversy about the character of hyperplastic AE2 cells, reported to synthesise profibrotic factors, proscribes drawing a definite conclusion today.

Surfactant components modulate fibroblast apoptosis and type I collagen and collagenase-1 expression

During lung injury, fibroblasts migrate into the alveolar spaces where they can be exposed to pulmonary surfactant. We examined the effects of Survanta and surfactant protein A (SP-A) on fibroblast growth and apoptosis and on type I collagen, collagenase-1, and tissue inhibitor of metalloproteinase (TIMP)-1 expression. Lung fibroblasts were treated with 100, 500, and 1,000 microg/ml of Survanta; 10, 50, and 100 microg/ml of SP-A; and 500 microg/ml of Survanta plus 50 microg/ml of SP-A. Growth rate was evaluated by a formazan-based chromogenic assay, apoptosis was evaluated by DNA end labeling and ELISA, and collagen, collagenase-1, and TIMP-1 were evaluated by Northern blotting. Survanta provoked fibroblast apoptosis, induced collagenase-1 expression, and decreased type I collagen affecting mRNA stability approximately 10-fold as assessed with the use of actinomycin D. Collagen synthesis and collagenase activity paralleled the gene expression results. SP-A increased collagen expression approximately 2-fold and had no effect on collagenase-1, TIMP-1, or growth rate. When fibroblasts were exposed to a combination of Survanta plus SP-A, the effects of Survanta were partially reversed. These findings suggest that surfactant lipids may protect against intraluminal fibrogenesis by inducing fibroblast apoptosis and decreasing collagen accumulation.

Expression of transforming growth factor-beta type I and type II receptors is altered in rat lungs undergoing bleomycin-induced pulmonary fibrosis

Transforming growth factor-beta (TGF-beta) is a family of autocrine/paracrine/endocrine cytokines involved in controlling cell growth and extracellular matrix metabolism. TGF-beta exerts its biological effects via binding to type I (TbetaRI) and type II (TbetaRII) receptors. To gain insight into the possible role of TGF-beta receptors in the pathogenesis of pulmonary fibrosis, we investigated the expression of TGF-beta receptors and their ligands in a bleomycin-induced model of pulmonary fibrosis. We found that the expression of both TbetaRI and TbetaRII was altered in rat lungs during pulmonary fibrosis induced by bleomycin. The increase in TbetaRI mRNA level was evident after 3 days of bleomycin administration, and TbetaRI mRNA continually increased for over 12 days after bleomycin instillation, whereas TbetaRII mRNA declined at day 3 post bleomycin instillation and then increased during the reparative phase of lung injury (days 8 and 12). The immunoreactivity for both TbetaRI and TbetaRII was detected in the cells of the interstitium, the epithelium, and the blood vessels of normal rat lungs. In bleomycin-induced pulmonary fibrosis, an extensive immunostaining for TbetaRI and TbetaRII was present in the cells at the sites of injury and active fibrosis. These results demonstrate that the expression of TGF-beta type I and type II receptors was altered during pulmonary fibrosis, suggesting that the TGF-beta signal transduction pathway may be involved in the pathogenesis of lung fibrosis.

Interstitial fibrosis and growth factors

Interstitial pulmonary fibrosis (IPF) is scarring of the lung caused by a variety of inhaled agents including mineral particles, organic dusts, and oxidant gases. The disease afflicts millions of individuals worldwide, and there are no effective therapeutic approaches. A major reason for this lack of useful treatments is that few of the molecular mechanisms of disease have been defined sufficiently to design appropriate targets for therapy. Our laboratory has focused on the molecular mechanisms through which three selected peptide growth factors could play a role in the development of IPF. Hundreds of growth factors and cytokines could be involved in the complex disease process. We are studying platelet-derived growth factor because it is the most potent mesenchymal cell mitogen yet described, transforming growth factor beta because it is a powerful inducer of extracellular matrix (scar tissue) components by mesenchymal cells, and tumor necrosis factor alpha because it is a pleiotropic cytokine that we and others have shown is essential for the development of IPF in animal models. This review describes some of the evidence from studies in humans, in animal models, and in vitro, that supports the growth factor hypothesis. The use of modern molecular and transgenic technologies could elucidate those targets that will allow effective therapeutic approaches.

Differential regulation of metalloproteinase production, proliferation and chemotaxis of human lung fibroblasts by PDGF, interleukin-1beta and TNF-alpha

Fibroblast migration, proliferation, extracellular matrix protein synthesis and degradation, all of which play important roles in inflammation, are themselves induced by various growth factors and cytokines. Less is known about the interaction of these substances on lung fibroblast function in pulmonary fibrosis. The goal of this study was to investigate the effects of PDGF alone and in combination with IL-1beta and TNF-alpha on the production of human lung fibroblast matrix metalloproteinases, proliferation, and the chemotactic response. The assay for MMPs activity against FITC labeled type I and IV collagen was based on the specificity of the enzyme cleavage of collagen. Caseinolytis and gelatinolytic activities of secreted proteinases were analyzed by zymography. Fibronectin in conditioned media was measured using human lung fibronectin enzyme immunoassay. Cell proliferation was measured by 3H-Thymidine incorporation assay. Cell culture supernatants were tested for PGE2 content by ELISA. Chemotactic activity was measured using the modified Boyden chamber. Matrix metalloproteinase assay indicated that IL-1beta, TNF-alpha and PDGF induced intestitial collagenase (MMP-1) production. MMP assay also indicated that IL-1beta and TNF-alpha had inhibitory effects on MMP-2,9(gelatinaseA,B) production. Casein zymography confirmed that IL-1beta stimulated stromlysin (matrix metalloproteinase 3; MMP-3) and gelatin zymography demonstrated that TNF-alpha induced MMP-9 production in human lung fibroblast, whereas PDGF alone did not. PDGF in combination with IL-1beta and TNF-alpha induced MMP-3 and MMP-9 activity, as demonstrated by zymography. PDGF stimulated lung fibroblast proliferation in a concentration-dependent manner, whereas IL-1beta and TNF-alpha alone had no effect. In contrast, the proliferation of human lung fibroblasts by PDGF was inhibited in the presence of IL-1beta and TNF-alpha, and this inhibition was not a consequence of any elevation of PGE2. PDGF stimulated fibroblast chemotaxis in a concentration-dependent manner, and this stimulation was augmented by combining PDGF with IL-1beta and TNF-alpha. These findings suggested that PDGF differentially regulated MMPs production in combination with cytokines, and further that MMP assay and zymography had differential sensitivity for detecting MMPs. The presence of cytokines with PDGF appears to modulate the proliferation and chemotaxis of human lung fibroblasts.

Effect of heparin and related glycosaminoglycan on PDGF-induced lung fibroblast proliferation, chemotactic response and matrix metalloproteinases activity

Fibroblast migration, proliferation, extracellular matrix protein synthesis and degradation are the key events in various biological and pathological processes in pulmonary fibrosis. In addition, biopsy specimens from the lungs of patients with pulmonary fibrosis show increased numbers of mast cells which have metachromatic granules containing heparin, histamine and proteases. Little is known about how these products influence pulmonary fibrosis. In the present study, we investigated the effect of heparin and related glycosaminoglycans on PDGF-induced lung fibroblast proliferation and chemotactic response in vitro. In addition, we examined the effect of heparin on both the induction of matrix metalloproteinases (MMPs) and MMPs activity in lung fibroblasts in vitro. Heparin, de-N-sulphated heparin but not heparan sulphate inhibited PDGF-induced lung fibroblast proliferation. In contrast, only heparin inhibited PDGF-stimulated human lung fibroblast chemotaxis. Negatively charged poly-L-glutamic acid had no effect on either fibroblast proliferation or chemotaxis. Thus the negative charge alone cannot account for the ant-proliferative and anti-chemotactic effects of heparin. Furthermore, heparin and heparan sulphate also had no inhibitory effect on induction of MMPS, including MMP-1 (interstitial collagenase), MMP-2 (gelatinase A) and MMP-9 (gelatinase B). Only heparin inhibited both MMP-1 and MMP-2/MMP-9 activity. Additionally, tissue inhibitor of metalloproteinase type 1 (TIMP-1) and type 2 (TIMP-2) inhibited PDGF-stimulated human lung fibroblast chemotaxis. The ability of heparin to inhibit fibroblast chemotaxis may account for the inhibitory effect of heparin on MMP activity. The above results suggested that heparin and related glycosaminoglycans differentially regulate PDGF-induced lung fibroblast proliferation, chemotaxis and MMPs activity and further that these effects may have a key role in extracellular matrix remodeling in inflammatory lung disease.

Human lung myofibroblast-derived inducers of alveolar epithelial apoptosis identified as angiotensin peptides

Earlier work from this laboratory found that fibroblasts isolated from fibrotic human lung [human interstitial pulmonary fibrosis (HIPF)] secrete a soluble inducer(s) of apoptosis in alveolar epithelial cells (AECs) in vitro [B. D. Uhal, I. Joshi, A. True, S. Mundle, A. Raza, A. Pardo, and M. Selman. Am. J. Physiol. 269 (Lung Cell. Mol. Physiol. 13): L819-L828, 1995]. The cultured human fibroblast strains most active in producing the apoptotic activity contained high numbers of stellate cells expressing alpha-smooth muscle actin, a myofibroblast marker. The apoptotic activity eluted from gel-filtration columns only in fractions corresponding to proteins. Western blotting of the protein fraction identified immunoreactive angiotensinogen (ANGEN), and two-step RT-PCR revealed expression of ANGEN by HIPF fibroblasts but not by normal human lung fibroblasts. Specific ELISA detected angiotensin II (ANG II) at concentrations sixfold higher in HIPF-conditioned medium than in normal fibroblast-conditioned medium. Pretreatment of the concentrated medium with purified renin plus purified angiotensin-converting enzyme (ACE) further increased the ELISA-detectable ANG II eightfold. Apoptosis of AECs in response to HIPF-conditioned medium was completely abrogated by the ANG II receptor antagonist saralasin (50 microg/ml) or anti-ANG II antibodies. These results identify the protein inducers of AEC apoptosis produced by HIPF fibroblasts as ANGEN and its derivative ANG II. They also suggest a mechanism for AEC death adjacent to HIPF myofibroblasts [B. D. Uhal, I. Joshi, C. Ramos, A. Pardo, and M. Selman. Am. J. Physiol. 275 (Lung Cell. Mol. Physiol. 19): L1192-L1199, 1998].

In vivo gene transfer of an extracellular domain of platelet-derived growth factor beta receptor by the HVJ-liposome method ameliorates bleomycin-induced pulmonary fibrosis

A number of investigators have reported augmented expression of PDGF in lungs with idiopathic pulmonary fibrosis (IPF) or with other types of pulmonary fibrosis. To accomplish such a regulation of PDGF activity, we constructed an expression plasmid of the extracellular domain of PDGF receptor beta chain (XR), which lacks intracellular tyrosine kinase domain and transmembrane portions, and estimated the therapeutic effects of XR gene transfer through the trachea on bleomycin-induced lung fibrosis of C57BL/6 mice using the hemagglutinating virus of Japan(HVJ)-liposome method. The XR gene transfer ameliorated the increases in the wet weight and hydroxyproline content and the histopathologic changes of the lung induced by bleomycin. These findings suggest that PDGF plays a crucial role in the pathogenesis of pulmonary fibrosis, and that XR gene transfer using the HVJ-liposome method may limit the progression of pulmonary fibrosis.

Mechanism of action and in vivo role of platelet-derived growth factor

Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells and certain other cell types. It is a dimeric molecule consisting of disulfide-bonded, structurally similar A- and B-polypeptide chains, which combine to homo- and heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors, denoted the alpha-receptor and the beta-receptor. Activation of PDGF receptors leads to stimulation of cell growth, but also to changes in cell shape and motility; PDGF induces reorganization of the actin filament system and stimulates chemotaxis, i.e., a directed cell movement toward a gradient of PDGF. In vivo, PDGF has important roles during the embryonic development as well as during wound healing. Moreover, overactivity of PDGF has been implicated in several pathological conditions. The sis oncogene of simian sarcoma virus (SSV) is related to the B-chain of PDGF, and SSV transformation involves autocrine stimulation by a PDGF-like molecule. Similarly, overproduction of PDGF may be involved in autocrine and paracrine growth stimulation of human tumors. Overactivity of PDGF has, in addition, been implicated in nonmalignant conditions characterized by an increased cell proliferation, such as atherosclerosis and fibrotic conditions. This review discusses structural and functional properties of PDGF and PDGF receptors, the mechanism whereby PDGF exerts its cellular effects, and the role of PDGF in normal and diseased tissues.

Role of platelet-derived growth factor in obliterative bronchiolitis (chronic rejection) in the rat

The role of platelet-derived growth factor (PDGF) in the development of obliterative bronchiolitis (OB) as a manifestation of chronic rejection was investigated in the heterotopic rat tracheal allograft model. An increase in intragraft PDGF-Ralpha and -Rbeta mRNA expression, and in PDGF-AA and -Ralpha immunoreactivity, was demonstrated during the progressive loss of respiratory epithelium and airway occlusion in nontreated allografts compared with syngeneic grafts. Treatment with CGP 53716, a protein-tyrosine kinase inhibitor selective for PDGF receptor, alone and in combination with suboptimal doses of cyclosporin A, significantly reduced myofibroproliferation and the degree of OB by more than 50%. CGP 53716 did not affect airway wall inflammatory cell proliferation, the number of graft-infiltrating CD4(+) or CD8(+) T cells, ED3(+) macrophages, or the level of immune activation determined as IL-2R and MHC class II expression. This study suggests a regulatory role for PDGF, especially for PDGF-AA and -Ralpha, in the development of obliterative bronchiolitis in this model, and demonstrates that inhibition of PDGF receptor protein-tyrosine kinase activation prevents these obliterative changes. Thus, receptor protein-tyrosine kinase inhibitors may provide a novel therapeutic strategy for the prevention of chronic rejection.

Specific inhibitors of platelet-derived growth factor or epidermal growth factor receptor tyrosine kinase reduce pulmonary fibrosis in rats

The proliferation of myofibroblasts is a central feature of pulmonary fibrosis. In this study we have used tyrosine kinase inhibitors of the tyrphostin class to specifically block autophosphorylation of the platelet-derived growth factor receptor (PDGF-R) or epidermal growth factor receptor (EGF-R). AG1296 specifically inhibited autophosphorylation of PDGF-R and blocked PDGF-stimulated [3H]thymidine uptake by rat lung myofibroblasts in vitro. AG1478 was demonstrated as a selective blocker of EGF-R autophosphorylation and inhibited EGF-stimulated DNA synthesis in vitro. In a rat model of pulmonary fibrosis caused by intratracheal instillation of vanadium pentoxide (V2O5), intraperitoneal delivery of 50 mg/kg AG1296 or AG1478 in dimethylsulfoxide 1 hour before V2O5 instillation and again 2 days after instillation reduced the number of epithelial and mesenchymal cells incorporating bromodeoxyuridine (Brdu) by approximately 50% at 3 and 6 days after instillation. V2O5 instillation increased lung hydroxyproline fivefold 15 days after instillation, and AG1296 was more than 90% effective in preventing the increase in hydroxyproline, whereas AG1478 caused a 50% to 60% decrease in V2O5-stimulated hydroxyproline accumulation. These data provide evidence that PDGF and EGF receptor ligands are potent mitogens for collagen-producing mesenchymal cells during pulmonary fibrogenesis, and targeting tyrosine kinase receptors could offer a strategy for the treatment of fibrotic lung diseases.

Emphysematous lesions, inflammation, and fibrosis in the lungs of transgenic mice overexpressing platelet-derived growth factor

Because of its expression pattern and its potent effects on mesenchymal cells, platelet-derived growth factor (PDGF) has been implicated as an important factor in epithelial-mesenchymal cell interactions during normal lung development and in the pathogenesis of fibrotic lung disease. To further explore the role of PDGF in these processes, we have developed transgenic mice that express the PDGF-B gene from the lung-specific surfactant protein C (SPC) promoter. Adult SPC-PDGFB transgenic mice exhibited lung pathology characterized by enlarged airspaces, inflammation, and fibrosis. Emphysematous changes frequently occurred throughout the lung, but inflammation and fibrotic lesions were usually confined to focal areas. The severity of this phenotype varied significantly among individual mice within the same SPC-PDGFB transgenic lineage. A pathology similar to that observed in adult mice was noted in lungs from transgenic mice as young as 1 week of age. Neonatal transgenic mice exhibited enlarged saccules and thickened primary septa. Results of these studies indicated that overexpression of PDGF-B induced distinct abnormalities in the developing and adult lung and led to a complex phenotype that encompassed aspects of both emphysema and fibrotic lung disease.

Prostaglandin-E2 counteracts interleukin-1beta-stimulated upregulation of platelet-derived growth factor alpha-receptor on rat pulmonary myofibroblasts

The platelet-derived growth factor (PDGF) alpha-receptor (PDGF-Ralpha) is upregulated during lung fibrogenesis, and induction of PDGF-Ralpha on cultured lung myofibroblasts by interleukin (IL)-1beta results in an increased mitogenic response to PDGF. Because IL-1beta stimulates prostaglandin (PG) E2 production, we investigated whether IL-1beta could upregulate PDGF-Ralpha via a PGE2-dependent mechanism. IL-1beta increased the production of PGE2 by rat lung myofibroblasts and the cyclooxygenase (COX) inhibitor indomethacin blocked IL-1beta-induced PGE2 production. However, indomethacin did not inhibit IL-1beta-stimulated upregulation of [125I]PDGF-AA binding sites, indicating that PDGF-Ralpha induction does not require PGE2 synthesis. Instead, PGE2 downregulated PDGF-Ralpha protein and messenger RNA expression, and counteracted the IL-1beta-stimulated increase in [125I]PDGF-AA binding. Pretreatment of cells with indomethacin or the COX-2 specific inhibitor NS-398 attenuated the suppressive effect of exogenous PGE2 on PDGF-Ralpha, indicating that endogenous PGE2 released by IL-1beta treatment also contributed to downregulation of PDGF-Ralpha. PDGF-Rbeta expression was not altered by IL-1beta or PGE2. Pretreatment of myofibroblasts with IL-lbeta increased PDGF-stimulated mitogenesis, and this effect was blocked by coincubation with PGE2. In contrast, PGE2 enhanced epidermal growth factor- or basic fibroblast growth factor-2-stimulated cell proliferation approximately 50%. Because IL-1beta upregulates both PGE2 production and PDGF-Ralpha expression, these data suggest that PGE2 functions in a negative feedback loop to limit expression of PDGF-Ralpha and suppress PDGF-stimulated myofibroblast proliferation.

Immunoreactive interleukin 4 and interferon-gamma expression by type II alveolar epithelial cells in interstitial lung disease

Cryptogenic fibrosing alveolitis (CFA), extrinsic allergic alveolitis (EAA), and sarcoid are all immunologically mediated forms of interstitial lung disease. In contrast to most patients with EAA and sarcoid, patients with CFA show relentless pulmonary fibrosis which is unresponsive to immunosuppressive therapy. Previous studies have indicated a possible role for epithelial-derived cytokines in the regulation of immunological and fibrotic responses in the lung. This study has examined lung biopsy specimens from patients with CFA, EAA, and sarcoid for immunoreactive interleukin 4 (IL4) and interferon-gamma (INFgamma) expression by type II alveolar epithelial cells, as these cytokines have been suggested to have in vitro stimulatory and inhibitory effects on fibroblast function. In addition, mRNA in situ hybridization was performed on the CFA lung biopsies to confirm transcription of these cytokine genes within the cells. The results show that type II epithelial cells in EAA and sarcoid show up-regulation of immunoreactivity for both IL4 and INF-gamma, but that in CFA only IL4 is detectable. The mRNA in situ hybridization results indicate that this may represent post-transcriptional regulation of INFgamma expression in CFA. These results are consistent with previous observations of a paucity of INFgamma and a predominantly type II (Th2-like) pattern of immune response in patients with CFA and suggest a possible imbalance of pro-fibrogenic cytokines in the distal lung of patients with this condition, compared with those with EAA or sarcoid.

In vitro reconstitution of the tracheal epithelium

We have developed a unique in vitro reconstitution system for tracheal epithelia of guinea pigs. In the system, a human amnion membrane was used as a basement membrane and the tracheal epithelial cells were cultured on the epithelial side of the membrane. Three weeks later, the tracheal fibroblasts were co-cultured on the serosal side of the amnion membrane and the culturing was continued for an additional 10 d. The morphology of the cultured epithelial cells consisted of a pseudostratified columnar ciliated epithelium from cuboidal ciliated epithelium during the last 10 d of the culture period. Epithelial cells included both goblet-like and basal cells. In addition, the frequency of each type of differentiated cells was almost identical to that of in vivo tracheas. Interestingly, the same results were obtained when the conditioned medium of the tracheal fibroblasts was used instead of the fibroblasts themselves. These results suggest that epithelial-mesenchymal interaction is likely involved in growth and differentiation of epithelial cells in vivo in a soluble factor(s)-mediated manner. As well as the epithelial cells, the fibroblasts also formed a multilayer during the last 10 d of co-culturing. This indicates that in vitro reconstitution of tracheal epithelia is achieved without addition of any exogenous growth or differentiation factors. The reconstitution system is shown to be useful for investigating the cellular and molecular interaction of epithelial and mesenchymal cells. Possible applications of the culture system and possible factors involved in growth and differentiation of epithelial cells are discussed.

Pirfenidone inhibits PDGF isoforms in bleomycin hamster model of lung fibrosis at the translational level

Pirfenidone (PD) is known for its antifibrotic effects in the bleomycin (BL) hamster model of lung fibrosis. We evaluated whether pretreatment of hamsters with PD could influence the effects of BL-induced overexpression of platelet-derived growth factor (PDGF)-A and PDGF-B genes and proteins in the same model of lung fibrosis. We demonstrate elevated levels of PDGF-A and PDGF-B mRNAs in bronchoalveolar lavage (BAL) cells from lungs of BL-treated compared with saline control hamsters by RT-PCR analysis. However, these levels were not altered in BAL cells obtained from BL-treated hamsters on diets containing 0.5% PD. Western blot analysis of BAL fluid for PDGF isoforms demonstrated that PD treatment inhibited the synthesis of both PDGF-A and PDGF-B isoforms. PD treatment also decreased the mitogenic activity in the BAL fluid from BL-treated hamster lungs. Taken together, these data provide evidence that the protective effects of PD against BL-induced lung fibrosis may be mediated by a reduction in PDGF isoforms produced by lung macrophages.

Identification of a cell type-specific enhancer in the distal 5'-region of the platelet-derived growth factor A-chain gene

Transient transfection analysis of DNA subfragments from the distal 5'-flanking region of the human platelet-derived growth factor A-chain gene (-18.3 to -1.8 kilobase pairs (kb)) revealed enhancer and silencer elements that contribute significantly to transcriptional regulation. Two adjacent regions (-8.2 to -7.5 kb and -7.5 to -7.0 kb) enhanced transcription of both A-chain and heterologous thymidine kinase promoters, whereas repression was observed in two other nearby regions (-9.9 to -8.2 kb and -7.0 to -5. 9 kb). The -7.5 to -7.0-kb fragment, or J, was the strongest enhancer, and its activity was localized to a 66-base pair element (A-chain cell type-specific enhancer (ACE 66)). ACE66 activity was highly cell type-specific, with greatest activity seen in choriocarcinoma cell lines (4-10-fold enhancement). Progressive 5'- and 3'-deletions of the ACE66 revealed distribution of activity across the element, with nucleotides 1-33 being critical for function. Electrophoretic mobility shift assays revealed cell type-specific patterns of high affinity protein binding to the element. Ethylation interference footprinting of JEG-3 extract localized guanine contacts on nucleotides 1-18 of both strands of the ACE element, whereas more extensive contacts were made with the phosphate backbone (nucleotides 1-32). The ACE66 element is a potent transcriptional regulator in placental cells and represents a valuable model of long distance regulation in a growth factor gene.

Novel roles for chemokines and fibroblasts in interstitial fibrosis

BACKGROUND

Regardless of its involvement in either wound healing or excessive fibrosis, the interstitial fibroblast can now be considered an important early participant in inflammatory responses. Although it is recognized that certain immune cells and proinflammatory mediators are intricately linked to fibrotic disease, little is presently known about the manner in which these mediators and cells are orchestrated to a fibrotic finale. Experimental studies have shown that interstitial fibroblasts are capable of participating in an inflammatory response by promoting direct fibroblast-to-immune cell communication and/or modulating the release of soluble mediators that are mutually recognized by both types of cells.

METHODS

Primary cultures of murine fibroblasts were recovered from either normal tissue or tissue undergoing a cell-mediated inflammatory response. These stromal cells were assessed for the expression of various cytokines and chemokines indicative of a type 1 or type 2 response. In addition, the fibroblasts were co-cultured with mononuclear cells to assess the cell-to-cell communication.

RESULTS

Fibroblasts recovered from different cell-mediated inflammatory responses demonstrated a dramatic alteration in their cytokine profile. Fibroblasts recovered from the type 2 immune response produced high levels of monocyte chemotactic protein-1 (MCP-1), as compared to the normal fibroblasts and fibroblasts recovered from the type 1 lesion. Mononuclear cells co-cultured with fibroblasts induced a contact-dependent expression of elevated levels of chemokines, especially the macrophage-derived MIP-1 alpha. Thus, both fibroblasts themselves and fibroblasts co-cultured with immune-inflammatory cells have the ability to participate in the maintenance of an inflammatory response via the expression of chemokines.

CONCLUSIONS

Our laboratory and others have addressed the role of chemotactic cytokines or chemokines in the fibrotic process, and have demonstrated that fibroblasts are capable of modulating the activation of various immune cells that have been implicated in fibrotic disease. In addition, the interstitial fibroblast is capable of regulating its own behavior within the interstitial environment via the expression of chemokines and chemokine receptors. Thus, novel strategies aimed at preventing fibrotic disease will likely need to address the early engagement of inflammatory cells by fibroblasts, and possibly modulate the ability of fibroblasts to generate and/or recognize profibrotic signals supplied by chemokines.

Alveolar epithelial cell death adjacent to underlying myofibroblasts in advanced fibrotic human lung

Earlier work from this laboratory showed that abnormal fibroblast phenotypes isolated from fibrotic human lung produce factor(s) capable of inducing apoptosis and necrosis of alveolar epithelial cells in vitro [B. D. Uhal, I. Joshi, A. True, S. Mundle, A. Raza, A. Pardo, and M. Selman. Am. J. Physiol. 269 (Lung Cell. Mol. Physiol. 13): L819-L828, 1995]. To determine whether epithelial cell death is associated with proximity to abnormal fibroblasts in vivo, the spatial distribution of epithelial cell loss, DNA fragmentation, and myofibroblasts was examined in the same tissue specimens used previously for fibroblast isolation. Paraffin sections of normal and fibrotic human lung were subjected to in situ end labeling (ISEL) of fragmented DNA and simultaneous immunolabeling of alpha-smooth muscle actin (alpha-SMA); replicate samples were subjected to electron microscopy and detection of collagens by the picrosirius red technique. Normal human lung exhibited very little labeling except for positive alpha-SMA immunoreactivity of smooth muscle surrounding bronchi and vessels. In contrast, fibrotic human lung exhibited moderate to heavy ISEL of interstitial, cuboidal epithelial, and free alveolar cells. ISEL of the alveolar epithelium was not distributed uniformly but was most intense immediately adjacent to underlying foci of alpha-SMA-positive fibroblast-like interstitial cells. Both electron microscopy and picrosirius red confirmed epithelial cell apoptosis, necrosis, and cell loss adjacent to foci of collagen accumulation surrounding fibroblast-like cells. These results demonstrate that the cuboidal epithelium of the fibrotic lung contains dying as well as proliferating cells and support the hypothesis that alveolar epithelial cell death is induced by abnormal lung fibroblasts in vivo as it is in vitro.

Expression of platelet-derived growth factor B-chain and platelet-derived growth factor beta-receptor in fibroblasts of scleroderma

Scleroderma is a fibrotic disease occurring in a localized or systemic form. The pathogenesis of scleroderma remains poorly understood. Recent studies revealed that various cytokines and growth factors were involved in the development of scleroderma fibrosis. Platelet-derived growth factor (PDGF) is a potent growth factor for mesenchymal cells, especially fibroblasts. It can promote fibroblasts proliferation, enhance extracellular matrix synthesis. It is also a chemoattractant to fibroblasts. To better understand the role of PDGF in pathogenesis of scleroderma, we performed both in vivo studies on the expression of PDGF beta-receptor protein in scleroderma tissue and in vitro studies on the expression of PDGF B-chain and PDGF beta-receptor mRNA in cultured fibroblasts derived from both lesions of scleroderma and normal skin. Immunohistochemistry staining showed that PDGF beta-receptor expression was greatly elevated in the dermis of scleroderma lesion whereas PDGF beta-receptor were expressed at low levels in normal skin. Northern blot analysis showed that cultured fibroblasts from scleroderma had higher expression of PDGF B-chain and PDGF beta-receptor mRNA than those from normal control. Two PDGF B-chain mRNA transcripts, 2.8 and 4.0 kb, were expressed. The 2.8 kb transcripts which had more efficient translation ability was the more predominantly expressed one. These results indicate that PDGF B-chain/PDGF beta-receptor signal pathway might be involved in the development of fibrosis in scleroderma, and that the 2.8 kb PDGF B-chain mRNA transcript may be the main modulation gene.

Morphometric analysis of insulin-like growth factor-I localization in lung tissues of patients with idiopathic pulmonary fibrosis

Insulin-like growth factor-I (IGF-I) has been implicated in the pathogenesis of idiopathic pulmonary fibrosis (IPF) through its ability to stimulate fibroblast proliferation and collagen synthesis. However, although alveolar macrophages (AM) have been shown to express this growth factor, it is likely to also have other cellular sources. We sought to determine the distribution of cells expressing IGF-I in lung tissues obtained from 10 patients with IPF and 10 control subjects. We evaluated the levels of IGF-I and of a macrophage/monocyte-specific marker, CD68, by immunocytochemistry and quantified by morphometry. In control subjects, IGF-I was localized principally to AM. In contrast, in IPF patients IGF-I was localized to AM, interstitial macrophages, alveolar epithelial cells, and ciliated columnar epithelial cells. The normalized volume density (Vv) of IGF-I-positive (IGF-I+) interstitial macrophages (Vv of IGF-I+ interstitial macrophages/Vv of lung x 100) was increased in patients with IPF as compared with control subjects, and the ratio of Vv of IGF-I+ to CD68(+) interstitial macrophages correlated with: (1) the degree of clinical impairment in patients with IPF as measured by their clinical-radiologic-physiologic (CRP) score; and (2) the degree of collagen deposition in the interstitium. These findings support a role for interstitial macrophages as a source of IGF-I in IPF.

Immunopathogenesis of conjunctival scarring in trachoma

PURPOSE

Trachoma, a chronic follicular conjunctivitis caused by infection with Chlamydia trachomatis, is the leading cause of preventable blindness. The blinding complications are associated with progressive conjunctival scarring that may result from immunologically mediated responses. We studied the processes involved in the regulation of inflammation and fibrosis in trachoma by investigating the expression of fibrogenic cytokines in the conjunctiva.

METHODS

We studied conjunctival biopsy specimens obtained from nine subjects with active trachoma and from four control subjects. We used immunohistochemical techniques and a panel of monoclonal and polyclonal antibodies directed against interleukin-1 alpha (IL-1 alpha), interleukin-1 beta (IL-1 beta), tumour necrosis factor-alpha (TNF-alpha) and platelet-derived growth factor (PDGF). In addition, we characterised the composition of the inflammatory infiltrate by the use of a panel of monoclonal antibodies. Sirius red and Van Gieson stains were used to characterise the extent of fibrous tissue in the substantia propria.

RESULTS

Trachoma specimens showed greater numbers of inflammatory cells than control specimens. The expression of cytokines was absent in the normal conjunctiva. Cytoplasmic IL-1 alpha and IL-1 beta expression was noted in the conjunctival epithelium in all trachoma specimens. IL-1 alpha, IL-1 beta, TNF-alpha and PDGF were detected in macrophages infiltrating the substantia propria. B lymphocytes predominated over T lymphocytes in six trachoma biopsies with fibrosis confined to the deep substantia propria, whereas T lymphocytes predominated over B lymphocytes in three biopsies with more extensive fibrosis. In all trachoma biopsies helper/inducer T lymphocytes outnumbered suppressor/cytotoxic T lymphocytes.

CONCLUSIONS

The upregulated local production of IL-1 alpha, IL-beta, TNF-alpha and PDGF might contribute to conjunctival damage and scarring in trachoma.

Induction of the lung myofibroblast PDGF receptor system by urban ambient particles from Mexico City

Platelet-derived growth factor (PDGF) and its receptor system regulate mesenchymal cell proliferation. We recently reported that emission-source fly-ash particles and asbestos fibers induce the PDGF alpha-receptor through a macrophage-dependent pathway, and upregulation of this receptor greatly enhances the mitogenic response of lung myofibroblasts to PDGF (Lindroos and colleagues, Am. J. Respir. Cell Mol. Biol. 1997;16:283-292). In the present study we investigated the effect of particulate matter <= 10 micrometers in size (PM10) from the southern, central, and northern regions of Mexico City on PDGF receptor induction and compared these urban, ambient particles with Mt. St. Helen's volcanic ash particles as a negative control. All Mexico City PM10 samples, but not volcanic ash, stimulated rat alveolar macrophages to secrete a soluble, upregulatory factor(s) for the PDGF alpha-receptor on early passage rat lung myofibroblasts. The macrophage-derived upregulatory activity was blocked by the interleukin (IL)-1 receptor antagonist. The ability of PM10 to stimulate IL-1beta release was blocked in part by a recombinant endotoxin neutralizing protein (rENP). Lipopolysaccharide/endotoxin (LPS) and vanadium, both constituents that were present within these PM10 samples, also stimulated macrophages to secrete factor(s) that upregulated PDGF-Ralpha on lung myofibroblasts. Direct exposure of myofibroblasts to PM10 also elicited upregulation of the PDGF alpha-receptor, and this effect was blocked by rENP and mimicked by LPS, but not vanadium. These findings suggest that PM10 particles induce expression of the PDGF receptor system through macrophage-dependent and -independent mechanisms involving endotoxin and metals.

Induction of pulmonary fibrosis in organ-cultured rat lung by cadmium chloride and transforming growth factor-beta1

Cadmium chloride (CdCl2) exposure has been reported to induce pulmonary fibrosis in rats. Accumulating evidence has shown that cytokines play a pivotal role in the excessive production of connective tissue components in pulmonary fibrosis. In this report, rat lung slice cultures were used to study the synergistic involvement of transforming growth factor-beta1 (TGF-beta1) in CdCl2-induced alveolar fibrosis. Rat lung slices were maintained at the interphase of air and medium on a polyester mesh stretched on a plastic scaffold. Treatment of lung slices with 2.5, 5 or 10 microM CdCl2 for 7 days resulted in 85, 40 and 6% respectively for relative survival. Under these culture conditions, CdCl2 alone did not induce alveolar fibrosis in rat lung slices. However, in the presence of 0.5 ng/ml TGF-beta1, CdCl2 at a dose ranging from 1 to 5 microM increased the thickness of alveolar septa. Furthermore, the thickness of alveolar septa in lung slices treated with CdCl2 was dose-dependently increased by the presence of TGF-beta1. The thickened alveolar septa were apparently due to the deposition of excessive extracellular matrix, as revealed by trichrome stain and ultrastructural examination. Our results also show that fibrogenic activity induced by the combined treatment with CdCl2 and TGF-beta1 can be reduced by co-treatment with 200 microg/ml lambda-carrageenan, a TGF-beta1 inhibitor. Therefore, the present results indicate that TGF-beta1 can synergistically stimulate the fibrogenic activity in lung tissue subsequent to CdCl2 injury.

Upregulation of the PDGF-alpha receptor precedes asbestos-induced lung fibrosis in rats

Platelet-derived growth factor-AA (PDGF-AA) and its matching alpha receptor (PDGF-R alpha) are upregulated in rat lung fibroblasts (RLFs) after exposure to chrysotile asbestos fibers in vitro, which results in asbestos-induced RLF proliferation. We now report our in vivo observations, which show an increase in the expression of PDGF-R alpha mRNA, but not PDGF-beta receptor mRNA, in asbestos-exposed rat lungs when compared with RNA from air-exposed (sham) and iron-exposed lungs. Western analysis of membrane preparations confirmed the observations on mRNA expression by demonstrating an increase in PDGF-R alpha peptide expression in the asbestos-exposed rat lungs, compared with that in the air-exposed lungs. Immunohistochemistry for the PDGF-R alpha was performed on air- and asbestos-exposed rat lungs and revealed a clear increase in staining within interstitial and subepithelial compartments in the exposed animals. These observations, along with our previous report demonstrating an increase in the PDGF-AA isoform expression immediately after asbestos-exposure, suggest a scenario in which a potent lung mesenchymal cell mitogen, PDGF-AA, and its alpha-receptor are upregulated prior to the development of a fibroproliferative lung lesion, and thus may play a central role in the pathogenesis of asbestos-induced lung fibrosis.

Indolocarbazoles: potent and selective inhibitors of platelet-derived growth factor receptor autophosphorylation

A quantitative assay for measuring the autophosphorylation of platelet-derived growth factor (PDGF) receptors in intact vascular smooth muscle cells has been developed and used to screen for novel tyrosine kinase (TK) inhibitors. Several novel inhibitors of PDGF receptor autophosphorylation have been identified from the indolocarbazole series, including the 3,9 dimethoxy derivative, 3744W (IC50 = 14.5+/-2 nM). Tested against a panel of tyrosine and serine/threonine kinases, 3744W is at least 1,000 fold selective for the PDGF receptor tyrosine kinase and was found to inhibit autophosphorylation of both the alpha and beta isoforms of the PDGF receptor in human smooth muscle cells. PDGF-BB-stimulated DNA synthesis in quiescent cultures of human smooth muscle cells was blocked in a concentration-dependent manner by 3744W, IC50 = 10 nM. Binding studies showed that 3744W did not block the binding of PDGF-BB to cell surface receptors on human airway smooth muscle cells. Furthermore, inhibition of bone marrow stem cell proliferation by 3744W was only observed at concentrations 100-1,000 times greater than those needed to block PDGF-driven DNA synthesis in human smooth muscle cells. 3744W represents a novel, potent and selective inhibitor of PDGF receptor autophosphorylation and a powerful biochemical probe for investigating PDGF-dependent responses in vitro.

The expression of PDGF-B chain mRNA in lung tissue from rats repeatedly infected with mycoplasma pneumoniae

In order to investigate the role played by platelet derived growth factor-BB (PDGF-BB) in the pathogenesis of pulmonary interstitial fibrosis in rats repeatedly infected with mycoplasma pneumoniae (MP), a rat MP infection model was developed by infecting rats with MP for 9 times during a period of 24 weeks with a technique of ultrasonic nebulizing inhalation. Then in situ hybridization was performed with PDGF-B chain cDNA probe and the results were quantitatively analyzed to measure the changes in PDGF-B chain mRNA expression in the lung tissue. The results showed that: (1) MP polymerase chain reaction (PCR) tests showed positive results in the bronchoalveolar lavage fluid (BALF) from all of the MP-infected rats (n = 4) while they were all negative in BALF from the control animals (n = 4, P < 0.05) and in BALF from those rats both infected with MP and, at the same time, treated with erythromycin (n = 4, P < 0.05). Bacterial cultures of the bronchial and lung tissue were negative in all three groups. The observation under a transmission electron microscope indicated that the interalveolar septa were widened with increased amount of collagen in the MP-infected rats while there were no obvious abnormalities in the other two groups. (2) Strong positive expression of PDGF-B chain mRNA was found in the plasma of monocytes and macrophages located in the locally widened interalveolar septa and alveolar spaces in the lung tissue from the MP-infected animals with the integral optical densities being 37.42 +/- 9.05 (n = 4) which was significantly higher than the values of control group (0.42 +/- 0.08, n = 4, P < 0.01) and of the group with MP-infection plus erythromycin treatment (1.62 +/- 0.40, n = 4, P < 0.01). These results suggest that PDGF-BB may be involved in the process of the development of pulmonary interstitial fibrosis caused by the repeated MP-infection. It may be an important growth factor for mediating the roles of monocytes and macrophages to promote the aggregation and proliferation of fibroblasts which can then secrete collagen in large quantity in the pulmonary interstitium.

Induction of PDGF receptor-alpha in rat myofibroblasts during pulmonary fibrogenesis in vivo

Platelet-derived growth factor (PDGF) is a potent mitogen for mesenchymal cells. Induction of the PDGF receptor-alpha (PDGF-R alpha) in vitro enhances PDGF-induced mitogenesis and chemotaxis. Thus we investigated whether the PDGF-R alpha is induced in vivo during pulmonary fibrogenesis using a vanadium pentoxide (V2O5) model of lung injury. PDGF-R alpha mRNA expression was induced 24 h postinstillation. PDGF-R beta mRNA was constitutively expressed and did not increase. Western blotting showed upregulation of PDGF-R alpha protein by 48 h, and immunohistochemical analysis localized PDGF-R alpha primarily in mesenchymal cells residing within fibrotic lesions. Upregulation of PDGF-R alpha in vivo preceded mesenchymal cell hyperplasia (3-7 days) and collagen deposition by day 15. Supernatants from alveolar macrophages treated with V2O5 in vitro released upregulatory activity for PDGF-R alpha on cultured lung myofibroblasts, and this activity was blocked by the interleukin-1-receptor antagonist. These data suggest that interleukin-1 beta-mediated induction of PDGF-R alpha in vivo is important to lung myofibroblast hyperplasia during fibrogenesis.

A case of lymphoid interstitial pneumonia in a 3-month-old boy not associated with HIV infection: immunohistochemistry of lung biopsy specimens and serum transforming growth factor-beta 1 assay

The case of a 3-month-old boy with lymphoid interstitial pneumonia (LIP) is reported. He had cough and tachypnea, his weight gain was poor and a chest radiograph showed microgranular shadows in almost all lung areas. Histological investigations revealed severe cellular infiltration by a variety of lymphoid and plasma cells with lymphoid follicle formation in the alveolar walls and also around the bronchioles. Foamy macrophages, a few lymphocytes and exudate filled the alveolar spaces. Epithelial cells lining the air spaces expressed human leukocyte antigen (HLA)-DR. Lymphocytes and macrophages in the alveolar spaces expressed transforming growth factor (TGF)-beta strongly. Serum TGF-beta 1 concentrations were measured eight times during the course of his illness. They exceeded the upper end of the normal range in four samples and were within it in the others. These results suggested that dysfunction of the immune system, especially abnormal expression of HLA-DR in non-immune cells and exaggerated production of TGF-beta played important roles in the pathogenesis of LIP in this patient.

KL-6, a human MUC1 mucin, is chemotactic for human fibroblasts

KL-6 in serum and bronchoalveolar lavage fluid has been reported to be a sensitive marker indicating the activity of fibrosing lung diseases. The molecule is clustered in MUC1 mucin according to the findings of immunohistochemical and cytometric studies. To elucidate the pathogenic role of KL-6 in fibrosing lung disease, we characterized its biochemical properties and examined whether purified KL-6 is chemotactic for human fibroblasts in vitro using modified Boyden chambers. Biochemical properties of purified KL-6 were similar to those of other MUC1 mucins previously reported. KL-6 promoted the migration of 5 of 5 human lung fibroblasts and 3 of 4 human skin fibroblasts. Checkerboard analysis revealed that KL-6 was chemotactic as well as chemokinetic. Though platelet-derived growth factor, fibroblast growth factor, or fibronectin were also chemotactic for fibroblasts in the experimental system, only fibronectin augmented KL-6-induced chemotaxis. These observations indicate that KL-6 is one of the chemotactic factors for most fibroblasts and that the increased KL-6 in the epithelial lining fluid in small airways may cause the intra-alveolar fibrosis in fibrosing lung diseases.

Rapid activation of PDGF-A and -B expression at sites of lung injury in asbestos-exposed rats

The development of interstitial pulmonary fibrosis is associated with a variety of inflammatory mediators, including peptide growth factors and cytokines. In the work presented here, we have asked whether or not platelet-derived growth factor (PDGF)-A and -B genes and proteins are expressed in anatomic and temporal patterns consistent with this factor playing a role in the disease process. Using an established rat model of asbestos-induced fibroproliferative lung disease, we demonstrate elevated levels of PDGF-A and -B mRNAs in total lung RNA immediately after a single 5-h exposure to approximately 1,000 fibers/ml of chrysotile asbestos. In situ hybridization revealed the PDGF-A and -B in RNAs primarily in macrophages and bronchiolar-alveolar epithelial cells at sites of initial fiber deposition and lung injury. There was clear evidence of PDGF-A and -B mRNAs in interstitial cells as well. The pattern of in situ hybridization was entirely consistent with the appearance (established by immunohistochemistry) of PDGF-A and -B proteins by 24 h post-exposure in the same cell types. Both mRNAs and proteins remained detectable at the fiber deposition sites for almost 2 wk post-exposures. These findings are consistent with our previous studies showing increased mesenchymal cell proliferation and fibroproliferative lesions that progress at the sites where PDGF-A and -B are expressed. Although it is clear that multiple growth factors are produced simultaneously at sites of initial injury, we suggest that the PDGF isoforms could be playing a central role in the disease process based upon their potent mitogenic effects upon mesenchymal cells.

Tissue factor expression and fibrin deposition in the lungs of patients with idiopathic pulmonary fibrosis and systemic sclerosis

Although abnormalities of alveolar fibrin turnover have been reported to play a role in the development of idiopathic pulmonary fibrosis (IPF), the pathophysiological relevance remains unclear. We therefore investigated the localization of tissue factor (TF) and fibrin deposition in patients with IPF using immunohistochemistry and compared the results with those from patients who had interstitial pneumonia associated with systemic sclerosis (IP-SSc) and idiopathic bronchiolitis obliterans with organizing pneumonia (BOOP). Expression of TF-mRNA was also assessed, using in situ hybridization with a digoxigenin-labeled cRNA probe. In patients with IPF, IP-SSc, and idiopathic BOOP, the TF antigen was positively stained in type II pneumocytes and in some alveolar macrophages. The fibrin antigen was stained in the type II pneumocytes and the adjacent area. Tissue factor-mRNA was expressed in the type II pneumocytes and in some alveolar macrophages. Neither TF antigens nor TF-mRNA were detected in the normal lung. These results indicate that type II pneumocytes are a major source of TF, suggesting that TF production in these cells is closely related to fibrin deposition in the lungs of people with these diseases.

Alterations in cytokeratin expression by the alveolar lining epithelial cells in lung tissues from patients with idiopathic pulmonary fibrosis

It is generally recognized that epithelial cytokeratins (CKs) are expressed in tissue-specific patterns and reflect differentiation, functional specialization, and pathological alterations of the cells. Differential epithelial cell types can thus be distinguished from each other by their selective expression of particular sets of CKs. To determine the characteristics of metaplastic and hyperplastic changes of alveolar-lining epithelial cells in the lungs of idiopathic pulmonary fibrosis (IPF), the expression of individual CKs was studied immunohistochemically using monospecific anti-CK monoclonal antibodies (anti-CKs 7, 8, 10, 13, 14, 16, 17, 18, 19). Biopsy specimens from 17 patients with IPF and normal lung tissues (NL) from seven patients with lung cancer were studied. In the IPF specimens, several kinds of altered epithelial cells were observed, which showed characteristic changes in CK expression compared with NL, especially CKs 8, 14, and 17. Hyperplastic type II cells expressed increased CKs 7, 8, and 19, but not CK 17; flattened or stratified squamous metaplastic cells expressed increased CKs 17 and 14, co-expressed with CKs 7, 8, and 19; bronchiolar metaplastic cells expressed increased CKs 7, 8, and 19, co-expressed with CKs 14 and 17; cuboidal metaplastic cells expressed increased CKs 7, 8, 17, and 19. The quantification of individual CKs in the tissues by enzyme-linked immunosorbent assay revealed increased expression of CKs 8, 14, and 17 in IPF lung tissues compared with NL. These results were consistent with the immunohistochemical observations. The hyperplastic and bronchiolar metaplastic phenotypes were characterized by their increased expression of simple CKs without CK alteration. The squamous metaplastic phenotype showed CK alterations, with the appearance of CKs 17 and 14. Epithelial cells are thus altered not only in shape, but possibly also in differentiation and function, with potential implications for the pathogenesis of IPF.