[The effects and mechanisms of PAD2 inhibitor AFM-30a attenuates pulmonary fibrosis in silicotic mice].

Objective: To observe the effects of peptidylarginine deiminase 2 (PAD2) inhibitor AFM-30a on silicotic mice and its possible mechanisms. Methods: In May 2022, 40 SPF male C57BL/6J mice were randomly divided into control group, AFM-30a group, silicosis model group and AFM-30a treatment group, with 10 mice in each group. Silicosis model group and AFM-30a treatment group were perfused with silicon dioxide (SiO(2)) suspension (10 mg/piece, 50 μl), and the other groups were perfused with an equal amount of sodium chloride solution. After 2 weeks, AFM-30a group and AFM-30a treatment group were intraperitoneally injected AFM-30a (20 mg/kg, 100 μl) daily, and mice of other groups were injected with equal amounts of sodium chloride solution for 4 weeks. Mouse RAW264.7 monocytes/macrophages were cultured in vitro and divided into blank control group, AFM-30a group (5 μmol/L), SiO(2) group (200 μg/ml), and SiO(2)+AFM-30a group (200 μg/ml SiO(2) induction for 12 h, followed by 5 μmol/L AFM-30a treatment for 12 h). As well as blank control group, vimentin (Vim) group (2 μg/ml), citrullinated vimentin (Cit-Vim) group (2 μg/ml), and Cit-Vim+TLR4-C34 group (10 μmol/L TLR4-C34 treatment for 1 h, followed by 2 μg/ml Cit-Vim induction for 24 h). Hematoxylin Eosin (HE) and Masson staining were used to observe the pathological morphology of lung. The lung fieldclarity and lung texture of each group was observed by micro-CT. The number of positive cells was detected by tartrate resistant acid phosphatase (TRAP) staining. The localization and expression levels of PAD2, Cit-Vim, toll-like receptor 4 (TLR4) signaling and receptor activator of nuclear factor-κB ligand (RANKL) signaling proteins were measured by Immunofluorescence staining and Western blotting in vitro and in vivo. The experimental data were all presented as Mean±SD. A completely random design of one-way analysis of variance was used among the groups. The pduo comparison was performed using LSD test for homogeneity of variance and Tamhane's test for inconsistency. Results: Compared with the control group, the silicosis model group showed the formation of silicon nodules accompanied by collagen deposition, the silicosis model group showed thickened, and several high-density shadows of varying sizes in the lung field, and the number of TRAP positive cells in silicosis model group were increased significantly, the expression levels of PAD2, Cit-Vim, TLR4 and RANKL signal-related proteins were also significantly increased in silicosis groupmodel (P<0.05). Compared with the silicosis model group, the AFM-30a treatment group reduced deposition of collagen in lung, and the number of TRAP positive cells was decreased in AFM-30a treatment group. The expression levels of PAD2, Cit-Vim, TLR4 and RANKL signaling related proteins were significantly decreased in AFM-30a treatment group (P<0.05). In vitro, compared with the blank control group, the number of TRAP positive cells and the expression levels of PAD2, Cit-Vim, TLR4 and RANKL signaling related proteins in the SiO(2) group were significantly increased (P<0.05). Compared with the SiO(2) group, the number of TRAP positive cells and the expression levels of PAD2, Cit-Vim, TLR4 and RANKL signaling related proteins in the SiO(2)+AFM-30a group were significantly decreased (P<0.05). Compared with the blank control group, the expression levels of TLR4 and RANKL signaling related proteins in the Cit-Vim group were significantly increased (P<0.05). Compared with the Cit-Vim group, the expression levels of TLR4 and RANKL signaling related proteins in the Cit-Vim+TLR4-C34 group were significantly decreased (P<0.05) . Conclusion: PAD2 inhibitor AFM-30a may play an antagonisticrole in silicotic fibrosis in mice by potentialregulating TLR4 and RANKL signaling pathways.