Figure 4.

Immunohistochemical of staining for the bone morphogenic protein (BMP) inhibitors chordin, gremlin, and noggin. Human osteoarthritic cartilage was used as a positive control for chordin and gremlin (A and B, respectively) and bovine cartilage for noggin (C). Images D-G show positive gremlin staining in human degenerative explant tissues cultured in standard medium (D), osteogenic medium (E and F) and osteogenic with VitD₃ and BMP2 (G). (D and E) and (F and G) are from the same intervertebral disc (IVD) explants with the sample in (E) being positive for calcification (NP10 from Fig. 3A ). Scale bar = 50 micron.