Deficiency of HtrA3 Attenuates Bleomycin-Induced Pulmonary Fibrosis Via TGF-β1/Smad Signaling Pathway

Purpose Idiopathic pulmonary fibrosis (IPF) is a chronic progressive interstitial lung disease characterized by excessive extracellular matrix deposition. No effective treatments are currently available for IPF. High-temperature requirement A3 (HtrA3) suppresses tumor development by antagonizing transforming growth factor beta (TGF-beta) signaling; however, little is known about the role of HtrA3 in IPF. This study investigated the role of HtrA3 in IPF and underlying mechanisms.Methods Lung tissues were collected from patients with IPF and mice with bleomycin (BLM)-induced pulmonary fibrosis, and HtrA3 expression was measured in tissue samples. Then, HtrA3 gene knockout mice were treated with BLM to induce pulmonary fibrosis and explore the effects and underlying mechanism of HtrA3 on pulmonary fibrosis.Results HtrA3 was up-regulated in the lung tissues of patients with IPF and the pulmonary fibrotic mouse model compared to corresponding control groups. HtrA3 knockout decreased pulmonary fibrosis-related protein expression, alleviated the symptoms of pulmonary fibrosis, and inhibited epithelial-mesenchymal transition (EMT) in BLM-induced lung tissue com-pared with BLM-induced wild-type mice. The TGF-beta 1/Smad signaling pathway was activated in fibrotic lung tissue, whereas HtrA3 knockout inhibited this pathway.Conclusion The expression level of HtrA3 is increased in fibrotic lungs. HtrA3 knockout alleviates the symptoms of pul-monar y fibrosis probably via the TGF-beta 1/Smad signaling pathway. Therefore, HtrA3 inhibition is a potential therapeutic target for pulmonary fibrosis.