ErbB4 regulates interferon signaling in classically activated macrophages

Background Classically activated macrophages drive intestinal inflammation, which is necessary to limit infection. However, over-aggressive responses from these cells, including elevated cytokine release, may contribute to inflammatory bowel disease. Previous studies have implicated the receptor tyrosine kinase ErbB4 and its ligands (neuregulins/NRGs) in regulating macrophage activity and survival. However, the influence of ErbB4 and its specific ligand NRG4 on cytokine expression and downstream signaling pathways in these cells remains untested. We hypothesized that ErbB4 regulates pathways associated with cytokine production in macrophages. Methods We generated bone-marrow derived macrophages from mice lacking ErbB4 in cells of myeloid lineage (LysMCre/ErbB4FF) or sex-matched littermate controls (ErbB4FF), and stimulated pro-inflammatory activation with interferon (IFN)-gamma plus lipopolysaccharide (classical activation). Cells were analyzed by RNA sequencing, and gene-set enrichment analysis (GSEA) was performed using publicly available Hallmark gene-sets. To test the role of NRG4, activated cells were treated with recombinant ligand at 100 ng/ml for 24 hours to determine effects on cytokine expression. RNA was collected and analyzed for cytokines by qPCR. Results Classically activated macrophages from LysMCre/ErbB4FF mice displayed an enhanced pro-inflammatory cytokine profile by GSEA (p<0.05) compared to ErbB4FF mice. We confirmed elevated levels of Tnf (32% higher, p<0.05) and Cxcl1 (69% higher, p<0.05) by qPCR. NRG4 treatment limited Tnf (p<0.05) and Cxcl1 (p<0.05) expression in classically activated macrophages from wild-type mice. GSEA showed a reduced type-I and type-II IFN gene expression signature in cells from LysMCre/ErbB4FF mice versus ErbB4FF mice. Conclusion Loss of ErbB4 in macrophages leads to dysregulated IFN signaling and enhanced pro-inflammatory cytokine production in macrophages. NRG/ErbB4 signaling in macrophages drives an anti-inflammatory feedback loop and may limit aberrant intestinal inflammation.