IFN-gamma priming of adipose-derived stromal cells at "physiological" hypoxia

Multipotent mesenchymal stromal cells (MSCs) are considered cue regulators of tissue remodeling. Their activity is strongly governed by local milieu, where O₂ level is most important. The elevation of inflammatory mediators and acute O₂ lowering may additionally modulate MSC activity. In present paper the priming effects of IFN-gamma on adipose tissue-derived MSCs (ASCs) at tissue-related O₂ level (5%) and acute hypoxic stress (0.1% O₂ ) were assessed as alterations of ASCs' CFU-F, proliferation, migration, osteo-commitment. IFN-gamma priming provoked ROS elevation, cell growth slowdown, attenuation of both spontaneous and induced osteodifferentiation of tissue O₂ -adapted ASCs. The prominent changes in ASC cytoskeleton-related gene transcription was detected. IFN-gamma exposure shifted the ASC paracrine profile, suppressing the production of VEGF and IL-8, while MCP-1 and IL-6 were stimulated. Conditioned medium of IFN-gamma-primed ASCs did not activate vessel growth in the CAM assay, but induced endothelial cell migration in "wound closure." Short-term hypoxia suppressed CFU-F number, IFN-gamma-induced elevation of IL-6 and endothelial cell migration, while it abolished IFN-gamma-provoked VEGF inhibition. After N-acetyl cysteine treatment ROS level was partly abolished providing additional enhancement of IL-6 and suppression of IL-8 and VEGF production. These findings demonstrated that paracrine activity of ASCs in part may be governed by ROS level. Thus, this study first demonstrated that IFN-gamma priming itself and in combination with acute O₂ deprivation could supply dual effects on ASC functions providing both stimulatory and hampering effects. The equilibrium of these factors is a substantial requirement for the execution of MSC remodeling functions.