Fraxinellone-mediated targeting of cathepsin B leakage from lysosomes induces ferroptosis in fibroblasts to inhibit hypertrophic scar formation.

backgroundHypertrophic scar (HS) is a common fibrotic skin disorder characterized by the excessive deposition of extracellular matrix (ECM). Fibroblasts are the most important effector cells involved in HS formation. Currently no satisfactory treatment has been developed.

methodsThe impact of fraxinellone (FRA) on the proliferation and migration capacity of human hypertrophic scar-derived fibroblasts (HSFs) was assessed by EdU proliferation, wound healing and transwell assays. Quantitative real-time PCR (qRT‒PCR), Western blot (WB), immunofluorescence staining and collagen gel contraction assays were performed to evaluate the collagen production and activation capacity of HSFs. Oxford Nanopore Technologies long-read RNA sequencing (ONT long-read RNA-seq) revealed the occurrence of ferroptosis in HSF and ferroptosis executioner-cathepsin B (CTSB). The mechanisms underlying FRA-induced HSF ferroptosis were examined through fluorescence staining, qRT‒PCR, WB and molecular docking study. The therapeutic efficacy of FRA was further validated in vivo using a rabbit ear scar model.

resultsFRA treatment significantly suppressed the proliferation, migration, collagen production and activation capacity of HSFs. ONT long-read RNA-seq discovered that FRA modulated the expression of transcripts related to ferroptosis and lysosomes. Mechanistically, FRA treatment reduced the protein expression level of glutathione peroxidase 4 (GPX4) and induced the release of CTSB from lysosomes into the cytoplasm. CTSB further induced ferroptosis via spermidine/spermine-N1-acetyltransferase (SAT1)-mediated lipid peroxidation, mitochondrial damage and mitogen-activated protein kinase (MAPK) signalling pathway activation, eventually affecting the function of HSFs. Moreover, FRA treatment attenuated the formation of HS in rabbit ears via CTSB-mediated ferroptosis. The antifibrotic effects of FRA were abrogated by pretreatment with a CTSB inhibitor (CA-074-me).

conclusionsThis study reveals that FRA ameliorates HS by inducing CTSB leakage from lysosomes, causing SAT1-mediated lipid peroxidation, mitochondrial damage and MAPK signalling pathway activation, thus mediating HSF ferroptosis. Therefore, FRA could be a promising therapeutic agent for treating HS.