Fig. 6

Maintenance of NPPC (Tie2+) phenotype. Primary NPPC were stimulated with various growth factors (growth and differentiation factor 5 (GDF5), GDF6, transforming growth factor β1 (TGFβ1), fibroblast growth factor 2 (FGF2), epidermal growth factor (EGF), and vascular endothelial growth factor (VEGF)), cocultured with IVD tissue or subjected to hypoxic conditions for 7 days, and the transcript levels of Tie2 were measured: endothelial tyrosine kinase (TEK) (a), collagen type 2 (COL2) (b), aggrecan (ACAN) (c), and hypoxia-inducible factor 1 alpha (HIF1α) (d). Values are mean ± SD (N = 5). *p < 0.05 compared with Tie2– of primary NPC. Protein level of Tie2 was monitored by flow cytometry in NPPC that were subjected to hypoxic conditions and/or FGF2 (e). Values are mean ± SD (N = 3). *p < 0.05 compared with normoxic conditions. #p < 0.05 compared with FGF2 + hypoxic conditions. IVD intervertebral disc, Tie2 angiopoietin-1 receptor