Tacrolimus ameliorates bleomycin-induced pulmonary fibrosis by inhibiting M2 macrophage polarization via JAK2/STAT3 signaling.

Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic lung disease of unknown cause and characterized by excessive proliferation of fibroblasts and the irregular remodeling of extracellular matrix (ECM), which ultimately cause the severe distortion of the alveolar architecture. The median survival of IPF patients is 2-5 years. IPF patients are predominantly infiltrated by M2 macrophages during the course of disease development and progression. Predominantly accumulation of M2 macrophages accelerates fibrosis progression by secreting multiple cytokines that promote fibroblast to myofibroblast transition. In the process of M2 macrophage polarization, JAK2/STAT3 signaling plays a key role, thus, targeting activated macrophages to inhibit the pro-fibrotic phenotype is considered as an approach to the potential treatment of IPF. Tacrolimus is a macrolide antibiotic that as a specific inhibitor of T-lymphocyte function and has been used widely as an immunosuppressant in human organ transplantation. In this study we explored the potential effect and mechanism of tacrolimus on pulmonary fibrosis in vivo and vitro. Here, we found that tacrolimus is capable of suppressing M2 macrophages polarization by inhibiting pro-fibrotic factors secreted by M2 macrophages. This effect further alleviates M2-induced myofibroblast activation, thus resulting in a decline of collagen deposition, pro-fibrotic cytokines secretion, recovering of lung function, ultimately relieving the progression of fibrosis in vivo. Mechanistically, we found that tacrolimus can inhibit the activation of JAK2/STAT3 signaling by targeting JAK2. Our findings indicate a potential anti-fibrotic effect of tacrolimus by regulating macrophage polarization and might be meaningful in clinical settings.