Monocyte-Derived Macrophage Ferroptosis Amplifies Cholangitis in Primary Biliary Cholangitis via a Calpain/ACSL4 Axis

Background: Recruitment and activation of monocyte-derived macrophages (MoMFs) sustain cholangitis in primary biliary cholangitis (PBC), but whether MoMFs amplify inflammation through ferroptosis remains unclear. We defined ferroptotic programs in MoMFs and evaluated the calpain/ACSL4 axis as a regulatory and therapeutic node. Methods: We analysed a public human liver single-cell RNA sequencing (scRNA-seq) dataset and examined MoMF-associated ACSL4 and 4-hydroxynonenal (4-HNE) signals in CD11b+CD68+ cells by multiplex immunofluorescence. We used a 2OA–BSA-induced PBC-like mouse model to assess liver injury, inflammation and ferroptosis-related markers and tested Liproxstatin-1 (Lip-1), rosiglitazone (ROSI) or the calpain inhibitor PD150606. Bone marrow-derived macrophages (BMDMs) from control and PBC mice were profiled and challenged with RSL3, with or without Ferrostatin-1 (Fer-1), ROSI or PD150606. Results: MoMFs were expanded in PBC livers and showed the strongest induction of ferroptosis signatures, centered on ACSL4, with enhanced inflammatory crosstalk with cholangiocytes. Human PBC tissues showed increased CD11b+CD68+ cells positive for ACSL4 or 4-HNE. In PBC-like mice, malondialdehyde (MDA) increased and glutathione (GSH) decreased, and macrophages showed greater colocalization with ferroptosis markers; Lip-1, ROSI or PD150606 improved liver biochemistry, reduced inflammation scores and limited macrophage infiltration. PBC-derived BMDMs upregulated ACSL4 and CAPN1/2 and were more sensitive to RSL3; Fer-1, ROSI or PD150606 attenuated ferroptosis-associated molecular changes. Conclusions: MoMF ferroptosis is prominently engaged in PBC, and our findings implicate a pharmacologically tractable calpain/ACSL4 axis that may contribute to macrophage ferroptotic susceptibility and inflammatory liver injury.