transforming-growth-factor-beta and Asbestosis

Pleural fibrosis resembles fibrosis in other tissues and can be defined as an excessive deposition of matrix components that results in the destruction of normal pleural tissue architecture and compromised function. Pleural fibrosis may be the consequence of an organised haemorrhagic effusion, tuberculous effusion, empyema or asbestos-related pleurisy and can manifest itself as discrete localised lesions (pleural plaques) or diffuse pleural thickening and fibrosis. Although the pathogenesis is unknown, it is likely that the complex interactions between resident and inflammatory cells, profibrotic mediators and coagulation, and fibrinolytic pathways are integral to pleural remodelling and fibrosis. It is generally considered that the primary target cell for pleural fibrosis is the subpleural fibroblast. However, increasing evidence suggests that mesothelial cells may also play a significant role in the pathogenesis of this condition, both by initiating inflammatory responses and producing matrix components. A greater understanding of the interactions between pleural and inflammatory cells, cytokines and growth factors, and blood derived proteins is required before adequate therapies can be developed to prevent pleural fibrosis from occurring.

Topics: Asbestosis; Epithelium; Fibrinolysis; Fibrosis; Humans; Platelet-Derived Growth Factor; Pleura; Pleural Diseases; Pleurisy; Thromboplastin; Transforming Growth Factor beta

Various growth factors, including platelet-derived growth factor (PDGF) and transforming growth factor (TGF)-beta, have been implicated in the pathogenesis of asbestos-induced disease. PDGF and TGF-beta levels were determined by enzyme-linked immunosorbent assays in the banked serum samples of a cohort of workers with asbestosis, and the relationships of the growth factor levels to the subsequent development of cancer and to the radiographic severity and progression of asbestosis in the cohort were examined. Serum levels of PDGF and TGF-beta were found to be unrelated to the development of cancer, and serum levels of PDGF were found to be unrelated to the severity and progression of asbestosis. However, serum levels of TGF-beta were found to be statistically significantly related to disease severity (p = 0.01), increasing approximately 2.4-fold from ILO radiographic category 0 to category 3, and they were marginally related to disease progression (p = 0.07), in multivariate analysis controlling for other contributory factors including cumulative asbestos exposure. This suggests that serum TGF-beta may be a useful biomarker for asbestos-induced fibrotic disease.

Topics: Asbestosis; Cohort Studies; Enzyme-Linked Immunosorbent Assay; Humans; Platelet-Derived Growth Factor; Transforming Growth Factor beta

The genes that mediate fibroproliferative lung disease remain to be defined. Prior studies from our laboratory showed by in situ hybridization and immunohistochemistry that the genes coding for tumour necrosis factor alpha, transforming growth factor beta, the platelet-derived growth factor A and B isoforms, and alpha-1 pro-collagen are expressed in fibroproliferative lesions that develop quickly after asbestos inhalation. These five genes, along with matrix metalloproteinase 9, a collagenase found to be increased in several lung diseases, are known to control matrix production and cell proliferation in humans and animals. Here we show by laser capture microdissection that (i) The six genes are expressed at significantly higher levels in the asbestos-exposed mice when comparing the same anatomic regions 'captured' in unexposed mice. (ii) The bronchiolar-alveolar duct (BAD) junctions, where the greatest number of fibres initially deposit, were always significantly higher than the other anatomic regions for each gene. The first alveolar duct bifurcation (ADB) generally was higher than the second ADB, the ADBs were always significantly higher than the airway walls and pleura, and the airway walls and pleura were generally higher than the unexposed tissues. (iii) Animals exposed for 3 days always exhibited significantly higher levels of gene expression at the BAD junctions and ADBs than animals exposed for 2 days. To our knowledge, this is the first demonstration of a dose-response to a toxic particle in situ, and this response appears to be dependent on the number of fibres that deposits at the individual anatomic site.

Topics: Animals; Asbestos; Asbestosis; Collagen Type I; Collagen Type I, alpha 1 Chain; Gene Expression Regulation; Genes, APC; Lung; Male; Matrix Metalloproteinase 9; Mice; Mice, Inbred C57BL; Microdissection; Microscopy, Electron, Scanning; Platelet-Derived Growth Factor; Proto-Oncogene Proteins c-sis; Reverse Transcriptase Polymerase Chain Reaction; Transforming Growth Factor beta; Tumor Necrosis Factor-alpha

Inhalation of numerous fibrogenic agents causes interstitial pulmonary fibrosis (IPF) in humans and in a number of animal models. Several of these models provide evidence that certain peptide growth factors (GF) are playing a role in the disease process. Transforming growth factor beta 1 (TGF-beta1) is a potent inducer of extracellular matrix production by mesenchymal cells, and we have shown that this peptide is produced in the lung after asbestos exposure. We used in situ hybridization to demonstrate that the mRNA for TGF-beta1 is rapidly expressed post-exposure at sites of initial asbestos-induced lung injury in both rats and mice. The TGF-beta1 is expressed by bronchiolar-alveolar epithelial cells as well as by mesenchymal cells and lung macrophages in exposed animals. Normal rats and mice express little TGF-beta1, as we have demonstrated previously for PDGF-A and -B, TGF-alpha, and TNF-alpha. TGF-beta1 expression is accompanied by collagen and fibronectin production in asbestos-exposed animals. Most interesting, TGF-beta1 expression is largely absent in the lungs of TNF-alpha receptor knockout mice that fail to develop asbestos-induced IPE We have shown previously that the mRNAs and cognate peptides of PDGF-A and -B and TGF-alpha, but not TNF-alpha, are reduced in the fibrosis-resistant knockout mice. In this article, we show that TGF-beta1 is included in this group of cytokines, supporting the postulate that TNF-alpha is necessary for the expression of other, more downstream growth factors, and the consequent development of idiopathic pulmonary fibrosis (IPF).

Topics: Administration, Inhalation; Animals; Asbestos; Asbestosis; Collagen; Fibronectins; Immunoenzyme Techniques; In Situ Hybridization; Lung; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Pulmonary Fibrosis; Rats; Rats, Sprague-Dawley; Receptors, Tumor Necrosis Factor; RNA, Messenger; Transforming Growth Factor beta; Transforming Growth Factor beta1

Asbestosis is characterized by increased collagen deposition along the walls of terminal respiratory bronchioles that extends into the alveolar ducts and septae. Alveolar macrophages are activated and release growth factors that stimulate mesenchymal cell proliferation and enhanced formation of extracellular matrix. Both insulin-like growth factor-I (IGF-I), and transforming growth factor beta (TGF-beta) regulate cellular growth and promote matrix accumulation and are hypothesized to play important roles in asbestosis. We performed immunohistochemistry using polyclonal antibodies to specific synthetic peptides of the three mammalian isoforms of TGF-beta (TGF-beta 1, -beta 2, -beta 3) and to IGF-I on lungs of sheep treated intratracheally with chrysotile asbestos. All three TGF-beta isoforms were found in bronchial and bronchiolar epithelium, macrophages, and bronchial and vascular smooth muscle in control lungs. The distribution of TGF-beta was increased in these lung constituents as fibrotic lesions developed. Fibrotic lesions additionally demonstrated intense immunostaining of all three TGF-beta isoforms that localized to the extracellular matrix zones with little staining of interstitial cells. In the control sheep lungs, IGF-I staining was detected in bronchial and bronchiolar epithelium, bronchial glands, bronchial and vascular smooth muscle, endothelium, and macrophages. IGF-I immunostaining was detected in macrophages in peribronchial fibrosis and in fibroblasts along the periphery of and within lesions, but not in the extracellular matrix. Metaplastic proliferating epithelium and macrophages were strongly immunoreactive for IGF-I in advanced lesions. Our data demonstrate different immunostaining patterns for IGF-I and TGF-beta in asbestosis, with IGF-I in the cellular periphery and TGF-beta in the extracellular matrix consistent with a complementary role in stimulating interstitial fibroblast proliferation and new collagen deposition in areas of active fibrosis.

Topics: Animals; Asbestos, Serpentine; Asbestosis; Disease Models, Animal; Immunohistochemistry; Insulin-Like Growth Factor I; Pulmonary Fibrosis; Sheep; Transforming Growth Factor beta

Transforming growth factor beta (TGF-beta), a multifunctional cytokine and growth factor, plays a key role in scarring and fibrotic processes because of its ability to induce extracellular matrix proteins and modulate the growth and immune function of many cell types. These effects are important in inflammatory disorders with fibrosis and cancer. The asbestos-related diseases are characterized by fibrosis in the lower respiratory tract and pleura and increased occurrence of lung cancer and mesothelioma. We performed immunohistochemistry with isoform-specific antibodies to the three TGF-beta isoforms on 16 autopsy lungs from Quebec, Canada, asbestos miners and millers. There was increased immunolocalization of all three TGF-beta isoforms in the fibrotic lesions of asbestosis and pleural fibrosis. The hyperplastic type II pneumocytes contained all three isoforms. By contrast, there was differential spatial immunostaining for the TGF-beta isoforms in malignant mesothelioma, with TGF-beta 1 in the stroma but TGF-beta 2 in the tumor cells. These data are consistent with an important role for TGF-beta in accumulation of extracellular matrix and cell proliferation in asbestos-related diseases.

Topics: Administration, Inhalation; Aged; Asbestos, Serpentine; Asbestosis; Carcinogens; Extracellular Matrix; Humans; Immunohistochemistry; Isomerism; Lung Neoplasms; Mesothelioma; Pleura; Transforming Growth Factor beta

Although it is recognized that three isoforms of transforming growth factor-beta (TGF-beta) exist in mammals, their expression, distribution, and function in injury and repair are not well characterized. Using immunohistochemistry and antibodies to synthetic peptides of TGF-beta 1, TGF-beta 2, and TGF-beta 3, we determined the distribution of TGF-beta isoforms in lung sections with acute and chronic lesions of idiopathic pulmonary fibrosis (IPF), chronic asbestosis and hypersensitivity pneumonitis, as well as non-specific pneumonitis. In lung sections with advanced pulmonary fibrosis and honeycombing, irrespective of the diagnosis, TGF-beta 1 was prominently expressed in epithelial cells and macrophages and was found to be associated with the extracellular matrix. In lungs with early lesions of IPF and only inflammatory changes, TGF-beta 1 was present in alveolar macrophages but TGF-beta 1 was not present in epithelial cells. Small amounts of matrix-associated TGF-beta 1 were present subepithelially in areas of lung sections from patients with IPF with minimal inflammation and no fibrosis. In normal lungs with no evidence of inflammation or fibrosis TGF-beta 1 was not seen in alveolar macrophages, epithelial cells, or extracellularly. TGF-beta 2 and TGF-beta 3 were expressed in alveolar macrophages, epithelial cells, and smooth muscle cells of vessels and bronchi of normal lungs and lungs with both inflammatory and fibrotic changes. Our findings suggest that while TGF-beta 2 and TGF-beta 3 are ubiquitously expressed in the lung, TGF-beta 1 is expressed in epithelial cells of fibrotic lungs where the presence of TGF-beta 1 is not disease-specific but an indication of the chronicity of the injury.

Topics: Adult; Aged; Antibody Specificity; Asbestosis; Biopsy; Cysts; Epithelium; Humans; Immunohistochemistry; Lung; Lung Diseases, Interstitial; Lung Neoplasms; Macrophages; Middle Aged; Muscle, Smooth, Vascular; Pulmonary Fibrosis; Transforming Growth Factor beta