Fig. 2

Isolation and identification of human nucleus pulposus mesenchymal stem cells (NPMSCs). a Flow diagram of the separation and purification of NPMSCs from human nucleus pulposus (NP) tissue. The harvested NPMSCs at passage 3 displayed a spindle shape in spiral or parallel arrangement. b Identification of the stem cell surface molecular profile indicated that the harvested cells were negative for HLA-DR, CD34, and CD45 expression, but positive for CD73, CD90, and CD105 expression. Osteogenic differentiation of NPMSCs (c) and control cells (f) stained with alizarin red after 3 weeks. Adipogenic differentiation of NPMSCs (d) and control cells (g) stained with oil red O after 3 weeks. Chondrogenic differentiation of NPMSCs (e) and control cells (h) stained with Alcian blue after 3 weeks. Identification of chondrogenic microspheres by alcian blue (i) and toluidine blue (j) staining, respectively. Higher mRNA expression of collagen IIα1 and aggrecan was observed in NPMSCs after a 4-week induction (k). Quantitative mRNA analysis of the expression of markers of the three lineages in both induced and control cells showed higher mRNA expression levels of all osteogenic (k), adipogenic (l), and chondrogenic (m) differentiation-related gene expression