Fig. 2

Osteogenic differentiation of bone marrow-derived mesenchymal stem cells (MSCs) in coculture with nucleus pulposus cells (NPCs) and annulus fibrosus cells (AFCs). a Alizarin red staining. Macroscopic (top row) and microscopic images (bottom row, ×10 magnification) showed reduced alizarin staining of MSCs in coculture with NPCs or AFCs compared with the positive control. Scale bar 100 μm. b Alkaline phosphatase (ALP) activity of MSCs after 21 days (n = 5) showed an increase under all osteogenic conditions compared with the negative control. ALP activity was reduced in cocultures of MSCs with NPCs and similar levels were found between cocultures of MSCs with AFCs and the positive control. c Relative gene expression of osteogenic markers (ALP, RUNX2 and OPN) in MSCs in response to the presence of intervertebral disc (IVD) cells in alginate beads (n = 5). Cocultures with IVD cells showed reduced gene expression of these osteogenic markers compared with the positive control. Furthermore, a significant increase in gene expression of NOG was observed under the osteogenic condition: *p <0.05, **p <0.01, ***p <0.001, and ^# p <0.0001