SULF1 expression is increased and promotes fibrosis through the TGF-β1/SMAD pathway in idiopathic pulmonary fibrosis.

Background: Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive interstitial lung disease of unknown etiology. Despite the increasing global incidence and poor prognosis, the exact pathogenic mechanisms remain elusive. Currently, effective therapeutic targets and treatment methods for this disease are still lacking. This study tried to explore the pathogenic mechanisms of IPF. We found elevated expression of SULF1 in lung tissues of IPF patients compared to normal control lung tissues. SULF1 is an enzyme that modifies heparan sulfate chains of heparan sulfate proteoglycans, playing a critical role in biological regulation. However, the effect of SULF1 in pulmonary fibrosis remains incompletely understood. Our study aimed to investigate the impact and mechanisms of SULF1 in fibrosis.

Methods: We collected lung specimens from IPF patients for transcriptome sequencing. Validation of SULF1 expression in IPF patients was performed using Western blotting and RT-qPCR on lung tissues. ELISA experiments were employed to detect SULF1 concentrations in IPF patient plasma and TGF-β1 levels in cell culture supernatants. We used lentiviral delivery of SULF1 shRNA to knock down SULF1 in HFL1 cells, evaluating its effects on fibroblast secretion, activation, proliferation, migration, and invasion capabilities. Furthermore, we employed Co-Immunoprecipitation (Co-IP) to investigate the regulatory mechanisms involved.

Results: Through bioinformatic analysis of IPF transcriptomic sequencing data (HTIPF) and datasets GSE24206, and GSE53845, we identified SULF1 may potentially play a crucial role in IPF. Subsequently, we verified that SULF1 was upregulated in IPF and predominantly increased in fibroblasts. Furthermore, SULF1 expression was induced in HFL1 cells following exposure to TGF-β1. Knockdown of SULF1 suppressed fibroblast secretion, activation, proliferation, migration, and invasion under both TGF-β1-driven and non-TGF-β1-driven conditions. We found that SULF1 catalyzes the release of TGF-β1 bound to TGFβRIII, thereby activating the TGF-β1/SMAD pathway to promote fibrosis. Additionally, TGF-β1 induces SULF1 expression through the TGF-β1/SMAD pathway, suggesting a potential positive feedback loop between SULF1 and the TGF-β1/SMAD pathway.

Conclusions: Our findings reveal that SULF1 promotes fibrosis through the TGF-β1/SMAD pathway in pulmonary fibrosis. Targeting SULF1 may offer a promising therapeutic strategy against IPF.