Macrophage-to-myofibroblast transition promotes pulmonary fibrosis occurred in LPS-induced acute lung injury of mouse models

Objective To explore the impact of macrophage-to-myofibroblast transition (MMT) on pulmonary fibrosis induced by acute lung injury by LPS. Methods Totally 21 male mice were randomly classified into 7 groups: control group, model group (LPS-PF) at different time points and intervention group of clodronate-liposomes (CL-LIP)treatement at different time points(n=3). Pulmonary fibrosis was identified by HE and Masson staining microscopy. The immuno-fluorescence technology was used for the evaluation of numbers of macrophage- to- myofibroblast transition cells (MMT cell which co-expressed CD68 and α-SMA). Bone marrow-derived macrophages (BMDMs) were randomly classified into two group: control (Ctrl) group and TGF-β1-treated group induced by transforming growthfactor-β1. α-SMA, FN and Col1 were detected by RT-qPCR. The expression of α-SMA, Smad3 and p-Smad3 protein was evaluated by Western blot. Results At day 7, the Ashcroft score of lung tissue in LPS-PF mouse model was significantly increased when compared with the Ctrl group (P＜0.01); While the score significantly declined when the model was pretreated with CL-LIP (P＜0.05). As detected by immuno-fluorescence staining, in CL-LIP group the number of CD68-positive cells co-labeled with α-SMA was obviously less then that of LPS-PF group of the corresponding time point(P＜0.01). When the BMDMs were stimulated by TGF-β1 at 24 h, 48 h and 96 h respectively, a higher expression of α-SMA,FN,Col1, were found in TGF-β1-treated group than that in Ctrl group at the corresponding time point (P＜0.01). The expression of Smad3, p-Smad3 significantly higher in LPS-PF group (at both day 7 and day 10) and TGF-β1-treated group (at both 48 h and 96 h) as compared to corresponding control group (P＜0.01). Conclusions MMT promotes pulmonary fibrosis induced by ALI via LPS. Smad3 is proved to be involved in the MMT process.