Effect of Baricitinib on the epithelial-mesenchymal transition of alveolar epithelial cells induced by IL-6

• Serum IL-6 was significantly increased in patients with ASS-ILD. • The level of serum IL-6 was related to the improvement and deterioration of ILD. • Baricitinib can inhibit the occurrence and development of ILD by inhibiting EMT of alveolar epithelial cells induced by IL-6. Interstitial lung disease (ILD) is one of the common complications of Connective tissue disease (CTD). Epithelial-mesenchymal transition (EMT) is one of the main pathological mechanisms of ILD. IL-6 may induce ILD through the JAK/STAT pathway. Therefore, exploring the mechanism of IL-6 on the EMT of alveolar epithelial cells and inhibition JAK/STAT pathway with Baricitinib on the EMT of alveolar epithelial cells is helpful in revealing the pathogenesis of CTD-ILD and guiding treatment. Electrochemiluminescence was applied to detect the changes in serum IL-6 levels before and after treatment in 37 patients with anti-synthetase syndrome-associated ILD; A549 cells (a human AEC cell line) were incubated with IL-6, Baricitinib, or both IL-6 and Baricitinib, and changes in EMT-related markers levels were measured using real-time PCR, western blotting and fluorescence microscopy. The related proteins in the JAK/STAT signaling pathways were examined by western blot. The level of Connective tissue growth factor (CTGF) and Hydroxyproline (Hyp) in cell supernatants was measured by ELISA. Serum IL-6 level in patients with anti-synthetase syndrome-associated ILD was significantly higher than that in health (6.78(4.19, 16.14)pg/ml vs. 2.10(1.43, 5.18)pg/ml, p < 0.01). The level of IL-6 in the improvement group of ASS-ILD was considerably decreased than that before treatment(before(7.48(4.54, 22.76) pg/mL vs. 5.00(3.46, 11.32)pg/mL, p < 0.01), p < 0.01), and the level of IL-6 in the progressive group of ASS-ILD was significantly higher than that before treatment(before(7.49(6.77, 35.80) pg/mL vs. 30.02(8.01, 82.98) pg/mL, p < 0.05). IL-6 increased the expression of epithelial phenotypic marker E-cadherin and inhibited mesenchymal phenotypic markers, including vimentin and N-cadherin in A549 cells. Moreover, IL-6-induced EMT was attenuated by Baricitinib. Furthermore, we found that IL-6 activated the phosphorylation of JAK1/2, STAT3, and Baricitinib, partially inhibiting these changes in this process. Baricitinib reduced the secretion of CTGF and Hyp in A549 cells. The significant higher level of IL-6 in patients with anti-synthase syndrome-associated ILD may be related to disease activity and recurrence. Our results suggest that Baricitinib attenuates epithelial-mesenchymal transition in alveolar epithelial cells in the presence of IL-6 through the JAK/STAT signaling pathway.