Neuregulin‐4 Limits Pro‐Inflammatory Cytokine Production in Macrophages

BackgroundPro‐inflammatory macrophages are critical mediators of intestinal inflammation. Over‐aggressive responses from these cells, including elevated cytokine release and prolonged persistence in tissue, may contribute to inflammatory bowel disease. We have previously found that the ErbB4 receptor tyrosine kinase is induced on macrophages by pro‐inflammatory stimulation, and that treatment with the ErbB4‐specific ligand neuregulin‐4 (NRG4) reduces macrophage numbers through apoptosis and ameliorates colitis. This suggests that macrophage‐expressed ErbB4 limits colonic inflammation, but the impact of NRG4/ErbB4 on cytokine regulation in these cells remains untested. We hypothesized that ErbB4 inhibits pro‐inflammatory cytokine production in macrophages.MethodsTo test the role of ErbB4 in regulating cytokine expression, we generated bone‐marrow derived macrophages from mice lacking ErbB4 in cells of myeloid lineage (LysMCre/ErbB4FF) or sex‐matched littermate controls, and activated with IFN□/LPS (pro‐inflammatory M1) or IL‐4 (anti‐inflammatory M2). To test the role of NRG4, we treated activated cells with recombinant ligand at 100 ng/ml for 24 hours, harvesting cells before the onset of NRG4‐induced apoptosis to compare functional effects on cytokine expression. RNA was collected and analyzed for cytokines by qPCR.ResultsPro‐inflammatory M1 activation of macrophages induced NRG4 expression 11‐fold (p=0.01). M1 macrophages from LysMCre/ErbB4FF mice expressed elevated levels of TNF (32% higher, p=0.02) and CXCL1 (69% higher, p=0.01) versus M1 macrophages from littermate controls. No differences in expression were seen in anti‐inflammatory M2 macrophages. NRG4 treatment led to reduced TNF (31% lower, p=0.005) and IL‐1β (16% lower, p=0.01) in M1 macrophages from wild‐type mice.Summary/ConclusionNRG4 reduces pro‐inflammatory cytokine production in macrophages through its receptor, ErbB4. This work suggests that ErbB4 signaling in macrophages drives an anti‐inflammatory feedback loop to limit colonic inflammation.Support or Funding InformationNIH 2R01DK095004‐06A1 (Frey); Crohn's and Colitis Foundation (Frey and Schumacher)