Interleukin-22 drives the proliferation, migration and osteogenic differentiation of mesenchymal stem cells: a novel cytokine that could contribute to new bone formation in spondyloarthropathies.

OBJECTIVES.: The SpAs are genetically and therapeutically linked to IL-23, which in turn regulates IL-22, a cytokine that has been implicated in the regulation of new bone formation in experimental models. We hypothesize that IL-22, a master regulator of stem cells in other niches, might also regulate human mesenchymal stem cell (MSC) osteogenesis. METHODS.: The effects of IL-22 on in vitro MSC proliferation, migration and osteogenic differentiation were evaluated in the presence or absence of IFN-γ and TNF (to ascertain IL-22 activity in pro-inflammatory environments). Colorimetric XTT assay, trans-well migration assays, quantitative real-time PCR (qRT-PCR) for MSC lineage markers and osteogenesis assays were used. RESULTS.: Combined treatment of MSC with IL-22, IFN-γ and TNF resulted in increased MSC proliferation ( P = 0.008) and migration ( P = 0.04), an effect that was not seen in cells treated with IL-22 alone and untreated cells. Osteogenic and adipogenic, but not chondrogenic, transcription factors were upregulated by IL-22 alone ( P < 0.05). MSC osteogenesis was enhanced following IL-22 exposure ( P = 0.03, measured by calcium production). The combination of IFN-γ and TNF with or without IL-22 suppressed MSC osteogenesis ( P = 0.03). CONCLUSION.: This work shows that IL-22 is involved in human MSC proliferation/migration in inflammatory environments, with MSC osteogenesis occurring only in the absence of IFN-γ/TNF. These effects of IL-22 on MSC function is a novel pathway for exploring pathological, post-inflammation osteogenesis in human SpA.