Caveolin-1 expression in the course of early intervertebral disc degeneration. (A) Caveolin-1 gene expression and (B) proportion of the NP surface area that stained for Caveolin-1, and mean gray value for Caveolin-1 protein expression in the notochordal cell (NC)-rich, mixed, and chondrocyte-like cell (CLC)-rich nucleus pulposus (NP) from non-chondrodystrophic (NCD) and chondrodystrophic (CD) dogs. *Significant difference between degeneration stages; §significant difference between NCD and CD dogs. The proportion of the NP surface area that stained for caveolin-1 was not divided into NCD and CD dogs because no significant differences were found between breed types. (C) Typical examples of NP samples stained for Caveolin-1, showing the NC-rich NP, mixed cell population NP with NCs and CLCs, and the CLC-rich NP. In the NC-rich and mixed groups, membranous (arrow) and cytoplasmic (arrowhead) staining can be observed. Note that Caveolin-1 staining is not observed in CLCs. (D) Immunofluorescent staining of the NC-rich NP for the proteins Caveolin-1 (green) and β-catenin (red), and for DNA (blue). Region of interest (ROI) lines drawn across cell bodies were used to generate profile intensity plots (right) for the signal intensity of the Caveolin-1 (green), β-catenin (red), and Topro-3 (blue). The signal intensity peaks for Caveolin-1 correspond with the signal peaks of β-catenin at the cell membrane (located at the same distance of the ROI line), indicating colocalization of these proteins. Also, the central β-catenin signal peaks correspond with the Topro-3 signal peaks, indicating nuclear localization of β-catenin.