biostudies-literatureVan Raemdonck KBLRD VANIAID NIH HHSNIAMS NIH HHS2003-2014https://www.ebi.ac.uk/biostudies/studies/S-EPMC8568622biostudies-literatureUnknown73(11)<h4>Objective</h4>In rheumatoid arthritis (RA), elevated serum interleukin-34 (IL-34) levels are linked with increased disease severity. IL-34 binds to 2 receptors, macrophage colony-stimulating factor receptor (M-CSFR) and syndecan 1, which are coexpressed in RA macrophages. Expression of both IL-34 and syndecan 1 is strikingly elevated in the RA synovium, yet their mechanisms of action remain undefined. This study was undertaken to investigate the mechanism of action of IL-34 in RA.<h4>Methods</h4>To characterize the significance of IL-34 in immunometabolism, its mechanism of action was elucidated in joint macrophages, fibroblasts, and T effector cells using RA and preclinical models.<h4>Results</h4>Intriguingly, syndecan 1 activated IL-34-induced M-CSFR phosphorylation and reprogrammed RA naive cells into distinctive CD14+CD86+GLUT1+ M34 macrophages that expressed elevated levels of IL-1β, CXCL8, and CCL2. In murine M34 macrophages, the inflammatory phenotype was accompanied by potentiated glycolytic activity, exhibited by transcriptional up-regulation of GLUT1, c-Myc, and hypoxia-inducible factor 1α (HIF-1α) and amplified pyruvate and l-lactate secretion. Local expression of IL-34 provoked arthritis by expanding the glycolytic F4/80-positive, inducible nitric oxide synthase (iNOS)-positive macrophage population, which in turn attracted fibroblasts and polarized Th1/Th17 cells. The cross-talk between murine M34 macrophages and Th1/Th17 cells broadened the inflammatory and metabolic phenotypes, resulting in the expansion of IL-34 pathogenicity. Consequently, IL-34-instigated joint inflammation was alleviated in RAG^-/- mice compared to wild-type mice. Syndecan 1 deficiency attenuated IL-34-induced arthritis by interfering with joint glycolytic M34 macrophage and osteoclast remodeling. Similarly, inhibition of glycolysis by 2-deoxy-d-glucose reversed the joint swelling and metabolic rewiring triggered by IL-34 via HIF-1α and c-Myc induction.<h4>Conclusion</h4>IL-34 is a novel endogenous factor that remodels hypermetabolic M34 macrophages and facilitates their cross-regulation with T effector cells to advance inflammatory bone destruction in RA.Arthritis & rheumatology (Hoboken, N.J.)Interleukin-34 Reprograms Glycolytic and Osteoclastic Rheumatoid Arthritis Macrophages via Syndecan 1 and Macrophage Colony-Stimulating Factor Receptor.PMC8568622I01 BX002286R41 AI147697R03 AR065778R03 AR056099R01 AI167155Umar SShahrara SSweiss NVan Raemdonck KAhmed AZomorrodi RKPalasiewicz KRomay BAmin MAElshabrawy HATetali CVolin MVfalseInterleukin-34 Reprograms Glycolytic and Osteoclastic Rheumatoid Arthritis Macrophages via Syndecan 1 and Macrophage Colony-Stimulating Factor Receptor.<h4>Objective</h4>In rheumatoid arthritis (RA), elevated serum interleukin-34 (IL-34) levels are linked with increased disease severity. IL-34 binds to 2 receptors, macrophage colony-stimulating factor receptor (M-CSFR) and syndecan 1, which are coexpressed in RA macrophages. Expression of both IL-34 and syndecan 1 is strikingly elevated in the RA synovium, yet their mechanisms of action remain undefined. This study was undertaken to investigate the mechanism of action of IL-34 in RA.<h4>Methods</h4>To characterize the significance of IL-34 in immunometabolism, its mechanism of action was elucidated in joint macrophages, fibroblasts, and T effector cells using RA and preclinical models.<h4>Results</h4>Intriguingly, syndecan 1 activated IL-34-induced M-CSFR phosphorylation and reprogrammed RA naive cells into distinctive CD14+CD86+GLUT1+ M34 macrophages that expressed elevated levels of IL-1β, CXCL8, and CCL2. In murine M34 macrophages, the inflammatory phenotype was accompanied by potentiated glycolytic activity, exhibited by transcriptional up-regulation of GLUT1, c-Myc, and hypoxia-inducible factor 1α (HIF-1α) and amplified pyruvate and l-lactate secretion. Local expression of IL-34 provoked arthritis by expanding the glycolytic F4/80-positive, inducible nitric oxide synthase (iNOS)-positive macrophage population, which in turn attracted fibroblasts and polarized Th1/Th17 cells. The cross-talk between murine M34 macrophages and Th1/Th17 cells broadened the inflammatory and metabolic phenotypes, resulting in the expansion of IL-34 pathogenicity. Consequently, IL-34-instigated joint inflammation was alleviated in RAG^-/- mice compared to wild-type mice. Syndecan 1 deficiency attenuated IL-34-induced arthritis by interfering with joint glycolytic M34 macrophage and osteoclast remodeling. Similarly, inhibition of glycolysis by 2-deoxy-d-glucose reversed the joint swelling and metabolic rewiring triggered by IL-34 via HIF-1α and c-Myc induction.<h4>Conclusion</h4>IL-34 is a novel endogenous factor that remodels hypermetabolic M34 macrophages and facilitates their cross-regulation with T effector cells to advance inflammatory bone destruction in RA.2021-01-01T00:00:00Z2021 Nov2025-04-03T22:45:15.808Z2025-02-19T01:30:41.527ZS-EPMC85686223398289510.1002/art.41792