Salt-inducible kinase 2 (SIK2) inhibitor ARN-3236 attenuates bleomycin-induced pulmonary fibrosis in mice

BACKGROUND: Pulmonary fibrosis is a fatal lung disease with complex pathogenesis and limited effective therapies. Salt-inducible kinase 2 (SIK2) is a kinase that phosphorylates CRTCs and regulates many physiological processes. However, the role of SIK2 on pulmonary fibrosis remains unclear, and whether SIK2 inhibitor can attenuate pulmonary fibrosis is unknown. METHOD: We subjected human fetal lung fibroblasts (HFLs) to transforming growth factor-β1 (5 ng/mL) for 12 h, and examined the expression of SIK2, CRTCs and pCRTCs in fibroblasts by western-blot. To address the roles of SIK2 and CRTCs involved in the progression of pulmonary fibrosis, HFLs were treated with a small-molecule inhibitor ARN-3236 or by siRNA-mediated knockdown of SIK2 expression. Pulmonary fibrosis model was established with mice by exposing to bleomycin, and assessed by H&E and Masson’s trichrome staining. COL1A and α-SMA distributions were detected in lung tissues by immunohistochemical staining. RESULTS: We discovered that SIK2 and phosphorylated-CRTC2 were expressed at a low basal level in normal lung tissues and quiescent fibroblasts, but increased in fibrotic lung tissues and activated fibroblasts. Inhibition of SIK2 by ARN-3236 prevented the fibroblasts differentiation and extracellular matrix expression in HFLs and attenuated bleomycin-induced pulmonary fibrosis in mice. Mechanistically, inactivation of SIK2 resulted in the dephosphorylation and nuclear translocation of CRTC2. Within the nucleus, CRTC2 binds to CREB, promoting CREB-dependent anti-fibrotic actions. CONCLUSION: In conclusion, our results elucidated a previously unexplored role of SIK2 in pulmonary fibrosis, and identified SIK2 as a new target for anti-fibrosis medicines.