IL-22 inhibits bleomycin-induced pulmonary fibrosis in association with inhibition of IL-17A in mice.

BACKGROUND: Interstitial lung disease, a common extra-articular complication of connective tissue disease, is characterized by progressive and irreversible pulmonary inflammation and fibrosis, which causes significant mortality. IL-22 shows a potential in regulating chronic inflammation and possibly plays an anti-fibrotic role by protecting epithelial cells. However, the detailed effects and underlying mechanisms are still unclear. In this study, we explored the impact of IL-22 on pulmonary fibrosis both in vivo and in vitro. METHODS: To induce pulmonary fibrosis, wild-type mice and IL-22 knockout mice were intratracheally injected with bleomycin followed by treatments with recombinant IL-22 or IL-17A neutralizing antibody. We investigated the role of IL-22 on bleomycin-induced pulmonary fibrosis and the mechanism in the possible interaction between IL-22 and IL-17A. Fibrosis-related genes were detected using RT-qPCR, western blot, and immunofluorescence. Inflammatory and fibrotic changes were assessed based on histological features. We also used A549 human alveolar epithelial cells, NIH/3T3 mouse fibroblast cells, and primary mouse lung fibroblasts to study the impact of IL-22 on fibrosis in vitro. RESULTS: IL-22 knockout mice showed aggravated pulmonary fibrosis compared with wild-type mice, and injection of recombinant IL-22 decreased the severe fibrotic manifestations in IL-22 knockout mice. In cell culture assays, IL-22 decreased protein levels of Collagen I in A549 cells, NIH/3T3 cells, and primary mouse lung fibroblasts. IL-22 also reduced the protein level of Collagen I in NIH/3T3 cells which were co-cultured with T cells. Mechanistically, IL-22 reduced the Th17 cell proportion and IL-17A mRNA level in lung tissues, and treatment with an IL-17A neutralizing antibody alleviated the severe pulmonary fibrosis in IL-22 knockout mice. The IL-17A neutralizing antibody also reduced Collagen I expression in NIH/3T3 cells in vitro. Knockdown of IL-17A with siRNAs or administration of IL-22 in NIH/3T3 cells and MLFs decreased expression of Collagen I, an effect blocked by concurrent use of recombinant IL-17A. CONCLUSIONS: IL-22 mediated an anti-fibrogenesis effect in the bleomycin-induced pulmonary fibrosis model and this effect was associated with inhibition of IL-17A.

Iguratimod decreases bleomycin-induced pulmonary fibrosis in association with inhibition of TNF-α in mice.

Severe interstitial lung disease secondary to connective tissue diseases, characterized by pulmonary inflammation and fibrosis, often have very poor prognosis due to lack of effective treatments. Iguratimod (IGU) shows encouraging efficacy in treating connective tissue diseases, however, the underlying mechanism is still to be elucidated. In this study, we investigated the impact of IGU on bleomycin-induced interstitial lung disease and the related tumor necrosis factor-α (TNF-α) signaling pathway in mice and in the alveolar epithelial cell A549. We found IGU decreased pulmonary inflammation and fibrosis and expression of fibrosis-related genes such as Collagen I, α-smooth muscle actin (α-SMA) and matrix metalloproteinase-2 (MMP-2) induced by bleomycin. IGU inhibited epithelial-mesenchymal transition as evidenced by decreased E-cadherin expression but increased vimentin expression. IGU reduced TNF-α production in the pulmonary fibrosis murine model and in the in vitro cultured A549 cells. Furthermore, IGU ameliorated TNF-α-induced severe pulmonary fibrosis and inhibited TNF-α-induced activation of NF-κB. In addition, IGU decreased IL-6 production and phosphorylation of STAT3. In conclusion, the IGU-mediated anti-fibrogenesis effect was associated with the inhibition of TNF-α and NF-κB.