DPEP1 promotes pulmonary fibrosis by regulating arachidonic acid metabolism.

BACKGROUND: Although dipeptidase 1 (DPEP1) is known to be involved in endothelial function and metabolic regulation, its contribution to idiopathic pulmonary fibrosis (IPF) has not been established. This study aimed to investigate the role of DPEP1 in the pathogenesis of IPF and to explore its potential mechanism involving arachidonic acid (ARA) metabolism and endothelial inflammatory responses. METHODS: Public transcriptomic datasets from the Gene Expression Omnibus (GEO) database, including bulk RNA sequencing and single-cell RNA sequencing datasets, were analyzed to evaluate DPEP1 expression and cellular localization in IPF. Correlations between DPEP1 expression and pulmonary function parameters were assessed. Serum samples from IPF patients and healthy controls were collected to validate DPEP1 and ARA levels. A bleomycin (BLM)-induced pulmonary fibrosis mouse model was established to investigate the in vivo role of DPEP1. Histological staining, enzyme-linked immunosorbent assay (ELISA), reverse transcription quantitative polymerase chain reaction (RT-qPCR), immunohistochemistry, immunofluorescence, and Western blotting were performed to evaluate fibrosis, inflammatory responses, and signaling pathway alterations. The therapeutic effects of the DPEP1 inhibitor cilastatin sodium were also examined. RESULTS: DPEP1 expression was significantly elevated in lung tissues and pulmonary vascular endothelial cells of IPF patients and negatively correlated with lung function indices, including forced expiratory volume in the first second percent predicted (FEV1%), diffusing capacity of the lungs for carbon monoxide percent predicted (DLCO%), and forced vital capacity percent predicted (FVC%). Single-cell RNA sequencing identified endothelial cells as the primary source of DPEP1 expression in IPF lungs. Functional enrichment analysis suggested that DPEP1 was closely associated with fatty acid metabolism, particularly ARA metabolism. Serum ARA levels were significantly decreased in IPF patients and negatively correlated with DPEP1 expression. In the BLM-induced mouse model, DPEP1 expression was markedly increased, whereas ARA levels were reduced. Pharmacological inhibition of DPEP1 alleviated pulmonary fibrosis, decreased inflammatory cytokine expression, restored ARA, PGE2, and cAMP levels, and suppressed activation of the TGF-β1/Smad3 signaling pathway. CONCLUSIONS: DPEP1 promotes pulmonary fibrosis by regulating ARA metabolism and endothelial inflammatory responses. Targeting DPEP1 may represent a promising therapeutic strategy for the treatment of IPF.