Cytokines link osteoblasts and inflammation: microarray analysis of interleukin-17- and TNF-α-induced genes in bone cells

The novel cytokine interleukin (IL)‐17 has been implicated in many infectious and autoimmune settings, especially rheumatoid arthritis. Consistent with its proinflammatory effects on bone, osteoblast cells are highly responsive to IL‐17, particularly in combination with other inflammatory cytokines. To better understand the spectrum of activities controlled by IL‐17, we globally profiled genes regulated by IL‐17 and tumor necrosis factor α (TNF‐α) in the preosteoblast cell line MC3T3‐E1. Using Affymetrix microarrays, 80–90 genes were up‐regulated, and 19–50 genes were down‐regulated with IL‐17 and TNF‐α as compared with TNF‐α alone. These included proinflammatory chemokines and cytokines, inflammatory genes, transcriptional regulators, bone‐remodeling genes, signal transducers, cytoskeletal genes, genes involved in apoptosis, and several unknown or unclassified genes. The CXC family chemokines were most dramatically induced by IL‐17 and TNF‐α, confirming the role of IL‐17 as a potent mediator of inflammation and neutrophil recruitment. Several transcription factor‐related genes involved in inflammatory gene expression were also enhanced, including molecule possessing ankyrin repeats induced by lipopolysaccharide/inhibitor of κBζ (MAIL/κBζ), CCAAT/enhancer‐binding protein δ (C/EBPδ), and C/EBPβ. We also identified the acute‐phase gene lipocalin‐2 (LCN2/24p3) as a novel IL‐17 target, which is regulated synergistically by TNF‐α and IL‐17 at the level of its promoter. A similar but not identical pattern of genes was induced by IL‐17 and TNF‐α in ST2 bone marrow stromal cells and murine embryonic fibroblasts. This study provides a profile of genes regulated by IL‐17 and TNF‐α in osteoblasts and suggests that in bone, the major function of IL‐17 is to cooperate and/or synergize with other cytokines to amplify inflammation.