Myeloid IRF4 Deficiency Attenuates Peritoneal Fibrosis by Suppressing Macrophage Migration

Background: Interferon regulatory factor 4 (IRF4) is a transcription factor involved in the regulation of immune responses, but its role in peritoneal inflammation and fibrosis remains poorly understood. This study aimed to elucidate the impact of myeloid-specific IRF4 deficiency on peritoneal fibrosis and macrophage function and polarization. Methods: We utilized LysM-Cre IRF4fl/fl mice (MφIRF4-KO) and induced peritoneal fibrosis using methylglyoxal (MGO), a well-established agent for modeling peritoneal injury. Inflammatory and fibrotic changes in the peritoneum were compared between MφIRF4-KO and control mice. Transwell assays were performed to evaluate macrophage migratory capacity, and in vitro stimulation was conducted using advanced glycation end-products (AGEs) and the chemokine CCL2. CCR2 expression and AKT phosphorylation were assessed via flow cytometry, immunofluorescence, and immunoblotting. Results: MφIRF4-KO mice demonstrated reduced macrophage infiltration in peritoneal tissues, along with attenuated inflammation and fibrosis, resulting in improved peritoneal function. Histological analysis showed decreased thickening of the submesothelial compact zone and reduced fibrotic change, as confirmed by HE and Masson's trichrome staining. Expression of pro-fibrotic markers such as collagen1 was significantly downregulated in the peritoneum of MφIRF4-KO mice. Migration assays revealed impaired motility of peritoneal macrophages in MφIRF4-KO mice. These macrophages exhibited reduced responsiveness to chemotactic stimuli, suggesting a defect in migration. Mechanistically, these macrophages showed diminished AKT phosphorylation and significantly downregulated expression of the chemokine receptor CCR2. Flow cytometry confirmed a reduced CCR2 positive macrophage population in MφIRF4-KO mice, indicating that IRF4 influence macrophage migratory capacity. Conclusion: Myeloid-specific IRF4 deficiency suppresses macrophage migration by downregulating CCR2 expression and AKT signaling, thereby mitigating peritoneal inflammation and fibrosis. IRF4 may serve as a novel therapeutic target for the treatment of peritoneal fibrosis.