Transforming growth factor β suppresses glutamate–cysteine ligase gene expression and induces oxidative stress in a lung fibrosis model

Abstract

The concentration of glutathione (GSH), the most abundant intracellular free thiol and an important antioxidant, is decreased in the lung in both fibrotic diseases and experimental fibrosis models. The underlying mechanisms and biological significance of GSH depletion, however, remain unclear. Transforming growth factor beta (TGF-β) is the most potent and ubiquitous profibrogenic cytokine and its expression is increased in almost all fibrotic diseases. In this study, we show that increasing TGF-β1 expression in mouse lung to a level comparable to those found in lung fibrotic diseases by intranasal instillation of AdTGF-β1223/225, an adenovirus expressing constitutively active TGF-β1, suppressed the expression of both catalytic and modifier subunits of glutamate cysteine ligase (GCL), the rate-limiting enzyme in de novo GSH synthesis, decreased GSH concentration, and increased protein and lipid peroxidation in mouse lung. Furthermore, we show that increasing TGF-β1 expression activated JNK and induced activating transcription factor 3 (ATF3), a transcriptional repressor involved in the regulation of the catalytic subunit of GCL (GCLC), in mouse lung. Control virus (AdDL70-3) had no significant effect on any of these parameters, compared to saline treated control. Concurrent with GSH depletion, TGF-β1 induced lung epithelial apoptosis and robust pulmonary fibrosis. Importantly, lung GSH levels returned to the normal whereas fibrosis persisted at least 21 days after TGF-β1 instillation. Together, the data suggest that increased TGF-β1 expression may contribute to the GSH depletion observed in pulmonary fibrosis diseases and that GSH depletion may be an early event in, rather than a consequence of, fibrosis development.

Combined effects of maternal inflammation and neonatal hyperoxia on lung fibrosis and RAGE expression in newborn rats

“…including lung fibrosis and idiopathic pulmonary fibrosis. The activation of TGF-β1 expression induces fibroblasts to synthesize and contract the extracellular matrix (29,30). We found that maternal LPS treatment and/or postnatal hyperoxia increased total collagen content and the level of TGF-β1 expression in lung tissues, compared with those of the control pups.…”

Glycolytic Reprogramming in Myofibroblast Differentiation and Lung Fibrosis

“…To further confirm that the augmented glycolysis does occur during lung fibrosis, we used another wellrecognized model in that mice were intratracheally administered adenovirus that express constitutively active TGF-b1 (Ad-TGF-b1 223/225 ) (19). As shown in Figure 1I, there were significantly greater levels of lactate in the lungs of mice that received TGF-b1-expressing adenovirus.…”

“…The bleomycin and TGF-b1-induced lung fibrosis models were described previously (19,20) and detailed in the online supplement METHODS. The animal protocol was approved by the University of Alabama Birmingham Institutional Animal Care and Use Committee.…”

“…To further test the therapeutic value of glycolytic suppression by the PFKFB3 inhibitor 3PO in treating this disease, we performed a similar experiment with the TGF-b1-induced pulmonary fibrosis model (19). 3PO was given 1 week after the administration of TGF-b1-expressing adenovirus for a total of seven times ( Figure 8A).…”

Reactive oxygen species and fibrosis: further evidence of a significant liaison

“…Of these two subunits, TGF-β1 has been shown to down-regulate the expression of gamma-GCSh in the fibrotic areas of interstitial pneumonia (Tiitto et al 2004) and in human lung alveolar epithelial cells (Liu et al 2012). The reduction of gamma-GCSh expression and GSH generation in response to TGF-β1 is also in agreement with the increased protein oxidation and lipid peroxidation in mice with lung fibrosis (Liu et al 2012). All in all, TGF-β1-mediated reduction in GSH production might contribute to oxidative stress during the fibrotic process.…”