IL-22 Effects on Osteoblast Mineralization and Metabolic Profile

Abstract Ankylosing spondylitis (AS) is an immune-mediated inflammatory disease characterized by persistent entheseal inflammation and aberrant bone formation that can lead to vertebral fusion. The Type 17 cytokine IL-17 and IL-10 family member IL-22 are involved in pathogenesis. Moreover, IL-22 has been implicated in aberrant bone formation, but its precise role remains unclear. Mesenchymal stem cells (MSCs) differentiate into osteoblasts (OBs) and are believed to reside near entheseal tissues and contribute to the observed bone formation. They express the IL-22 receptor after commitment to the OB lineage. The objective of this study was to determine how IL-22 affects OB development and mineralization in vitro. MSCs were placed in osteogenic media and then treated with IL-22 for up to 21 days after pre-conditioning with IFNg, TNF, or IFNg+TNF (I+T) for 72 hours. Mineralization was measured with Alizarin red staining, gene expression with Nanostring or RNA-seq. IL-22 significantly increases mineralization in cells pre-conditioned with I+T, compared to I+T alone or IL-22 alone, which has no effect. There was no significant acute effect of IL-22 on expression of osteogenic genes during early osteoblast differentiation in I+T treated cells. In contrast, we found that IL-22 induces a glycolytic shift within 24 hours in pre-conditioned early osteoblasts using Seahorse analysis. Given the recently recognized role of metabolic change in osteogenesis, these results suggest a novel effect of IL-22 on osteogenesis and mineralization that may be mediated by increased glycolysis. Further studies are aimed at investigating mechanisms that facilitate these effects and linking the increased matrix deposition with the metabolic shift caused by IL-22.