Juglanin alleviates bleomycin-induced lung injury by suppressing inflammation and fibrosis via targeting sting signaling

Idiopathic pulmonary fibrosis (IPF), characterized by excessive collagen deposition, is a progressive and typically fatal lung disease without effective therapeutic strategies. Juglanin, as a natural product mainly isolated from green walnut husks of Juglans mandshuric, has various bioactivities, including anti-oxidative, anti-inflammatory and anti-fibrotic effects. Stimulator of interferon genes (STING) is a signaling molecule and plays an essential role in meditating fibrosis. However, the effects of Jug and STING on pulmonary fibrosis are not fully understood. In this study, we investigated the role of Jug in bleomycin (BLM)-induced inflammation and fibrosis mouse model, as well as the underlying molecular mechanism. The results here indicated that Jug-treated mice exhibited a definitively improved survival rate than that of the BLM-challenged mice. Jug administration significantly alleviated neutrophil alveolar infiltration, lung vascular permeability and pro-inflammatory response in BLM mice. Subsequently, the pulmonary fibrosis induced by BLM was markedly attenuated by Jug through reducing the expression of fibrotic hallmarks, including transforming growth factor-β1 (TGF-β1), fibronectin, matrix metallo-proteinase-9 (MMP-9), α-smooth muscle actin (α-SMA) and collagen I. Importantly, we found that BLM mice showed higher expression levels of STING in lung tissues, which were notably restrained by Jug treatment. The role of Jug in suppressing STING was confirmed in TGF-β-incubated cells. Notably, the in vitro analysis further showed that STING knockdown could ameliorate TGF-β-triggered collagen accumulation. In contrast, TGF-β-induced fibrosis was accelerated by STING over-expression. Therefore, BLM may induce lung fibrosis through activating STING signaling, and Jug could be used therapeutically to improve tissue repair and attenuate the intractable disease.