Lung fibrosis is a characteristic feature and terminal stage of many lung diseases with no efficacious treatment. The concentration of glutathione (GSH), the most abundant intracellular free thiol and an important antioxidant, is decreased in both experimental fibrosis and human fibrotic diseases. Importantly, aerosol or oral administration of GSH or N-acetylcysteine (NAC), a precursor of GSH, attenuates lung fibrosis in experimental fibrosis models and slows the deterioration of lung functions in patients with lung fibrotic diseases, indicating a potential therapeutic value of GSH/NAC for pulmonary fibrotic diseases. Nonetheless, the efficacy and mechanism underlying the therapeutic effects of GSH/NAC remains equivocal. Specifically, it is unclear whether GSH/NAC exerts its therapeutic effects by suppressing early-stage inflammatory response or whether it has direct antifibrotic activity and therefore can also block the progression of fibrosis in later stages of the disease. TGF-( is a most potent and ubiquitous profibrogenic cytokine. Our previous studies showed that TGF-( decreased GSH and increased reactive oxygen species (ROS) production in fibroblasts and in a lung fibrosis model while GSH/NAC supplementation inhibited TGF-(-stimulated collagen accumulation by blocking the expression of plasminogen activator inhibitor 1 (PAI-1), a protease inhibitor, and thus stimulating collagen degradation. Increasing GSH in lung ELF in tetracycline inducible lung specific glutamate cysteine ligase (GCL) transgenic mice also inhibits TGF-(-induced PAI-1 expression and lung fibrosis. Preliminary studies further show that TGF-( induces protein thiol modifications and inhibits the activity of JNK-directed phosphatases, associated with a stimulation of JNK/p38 phosphorylation while GSH blocks TGF-( activation of JNK and p38 MAPKs, which mediate TGF-( induction of PAI-1 expression. Therefore, we hypothesize that GSH/NAC can block fibrosis progression by attenuating TGF-('s fibrotic signaling and stimulating collagen degradation.
Three specific aims are proposed that couple cell and animal models with pharmacologic and genetic approaches to elucidate the molecular mechanisms whereby GSH/NAC antagonizes TGF-(-induced lung fibrosis.
Aim 1 will determine whether GSH/NAC can block the progression of late stage lung fibrosis induced by constitutively active TGF-( in GCL transgenic mice or NAC treated wild type mice.
Aim 2 will determine whether GSH/NAC stimulates collagen degradation as well as the expression/activities of plasmin and the collagenases in TGF-( treated wild type and PAI-1 knockout mice. The bleomycin-induced lung fibrosis model will be used to further test our hypothesis.
Aim 3 will focus on the molecular mechanisms whereby GSH/NAC antagonizes TGF-( fibrogenesis using mouse and primary human lung fibroblasts. Effect of GSH/NAC on TGF-(-induced thiol modifications and the activity of JNK/p38 directed phosphatases as well as the relationship between inhibition of the phosphatases and JNK/p38 activation/PAI-1 induction will be studied systematically. The results from these studies will provide new insight into the molecular mechanisms underlying TGF-('s fibrogenesis and GSH/NAC antifibrogenic effects, which will enable the design of more efficacious strategies for prevention and treatment of these fibroproliferative disorders. PROJECT NARRATIVE: Lung fibrosis is a characteristic feature and terminal stage of many lung diseases with no efficacious treatment. This project will test a novel hypothesis that glutathione, the most abundant intracellular free thiol and an important antioxidant, and N-acetyl cysteine (NAC), a precursor of GSH, can block fibrosis progression by attenuating the fibrogenic signals of TGF-(, a most potent and ubiquitous profibrogenic cytokine, and stimulating collagen degradation. The results from these studies will provide new insight into the molecular mechanisms underlying TGF-('s fibrogenesis and GSH/NAC antifibrogenic effects, which will enable the design of more efficacious strategies for prevention and treatment of these fibroproliferative disorders.
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