Transforming Growth Factor- β₁Overexpression in Tumor Necrosis Factor- α Receptor Knockout Mice Induces Fibroproliferative Lung Disease

Abstract

Tumor necrosis factor-alpha receptor knockout (TNF-alphaRKO) mice have homozygous deletions of the genes that code for both the 55- and 75-kD receptors. The mice are protected from the fibrogenic effects of bleomycin, silica, and inhaled asbestos. The asbestos-exposed animals exhibit reduced expression of other peptide growth factors such as transforming growth factor (TGF)-alpha, platelet-derived growth factors, and TGF-beta. In normal animals, these and other cytokines are elaborated at high levels during the development of fibroproliferative lung disease, but there is little information available that has allowed investigators to establish the role of the individual growth factors in disease pathogenesis. Here, we show that overexpression of TGF-beta(1) by means of a replication-deficient adenovirus vector induces fibrogenesis in the lungs of the fibrogenic-resistant TNF-alphaRKO mice. The fibrogenic lesions developed in both the KO and background controls within 7 d, and both types of animals exhibited similar incorporation of bromodeoxyuridine. Interestingly, airway epithelial cell proliferation appeared to be suppressed, perhaps due to the presence of the TGF-beta(1), a well-known inhibitor of epithelial mitogenesis. Before these experiments, there was no information available that would provide a basis for predicting whether or not TGF-beta(1) expression induces fibroproliferative lung disease in fibrogenic-resistant TNF-alphaRKO mice, an increasingly popular animal model.

Regulation of caveolin-1 expression, nitric oxide production and tissue injury by tumor necrosis factor-α following ozone inhalation

“…TNFα is a multifunctional cytokine implicated in the pathogenesis of a number of pulmonary disorders including acute respiratory distress syndrome and idiopathic pneumonia, as well as tissue injury induced by endotoxin, bleomycin, silica and asbestos (Liu et al, 2001;Pryhuber et al, 2003;Shimabukuro et al, 2003;Bhatia and Moochhala, 2004;Zhao et al, 2004;Shukla et al, 2005;Ke et al, 2006;Mukhopadhyay et al, 2006).…”

Asbestos-derived reactive oxygen species activate TGF-β1

“…10,11 Our laboratory and others have demonstrated that expression of a constitutively active form of TGF-b 1 through an adenovirus vector in the lungs of rats and mice induces fibrogenesis. 15,16,31 This treatment causes scarring even in fibrogenicresistant TNF-a double receptor KO mice. 16 Similar expression of the full latent TGF-b 1 complex fails to initiate this fibrogenic response.…”

“…15,16,31 This treatment causes scarring even in fibrogenicresistant TNF-a double receptor KO mice. 16 Similar expression of the full latent TGF-b 1 complex fails to initiate this fibrogenic response. 15 Because latent TGF-b 1 is constitutively produced in the lung by a number of cell types, including type II epithelial cells 32 and macrophages, 10 it is essential that the mechanisms which free the active TGF-b 1 peptide from its LAP be elucidated to understand the precise biological roles of TGF-b 1 .…”

“…15 The methods for propagation and purification of recombinant adenovirus were previously described. 15,16 Briefly, the adenovector was grown up in 293 cells and the virus was purified by two rounds of CsCl-gradient centrifugation. The CsCl was removed by chromatography of the virus suspension in Econo-Pac 10DG desalting columns (Bio-Rad Laboratories, Hercules, CA, USA).…”

“…15 We have shown, using this same vector, that when active TGF-b 1 is transduced into the lungs of fibrogenic-resistant TNF-a receptor knockout mice, the TGF-b 1 alone is sufficient to induce fibroproliferative lung disease. 16 TGF-b 1 is produced in a latent complex, which consists of TGF-b 1 noncovalently bound to a latentassociated peptide (LAP). 17 It is the removal of the LAP, which allows TGF-b 1 to be biologically active.…”