Figure 1.

Dedifferentiation of chondrocytes in a monolayer culture was associated with a change in cell and nucleus phenotype as well as changes in extracellular matrix-related gene expression. (a) PD0 (corresponding to passage 0) and PD16 (corresponding to passage 4) chondrocytes were stained for actin (phalloidin-GFP) and DNA (DAPI) to visualize cells and nuclei respectively using confocal microscopy at two different magnifications. Culture conditions included type I collagen-treated membranes and TCP (tissue culture plate). Irrespective of culture condition, the PD0 chondrocytes were smaller, rounder, and displayed fewer F-actin stress fibers than the PD16 chondrocytes. (b) Several biophysical features were used to quantify the cell morphological changes between the PD0 and PD16. From PD0 to PD16, the cell and nuclear area increased, and the nuclear dimensions increased compared with the cell dimensions. Cells lost their round shape and approached a more irregular shape, while nuclei maintained their round shape compared with cells. ^∗p < 0.01, number of cells analyzed >60 from three biological replicates. (c) Chondrocyte dedifferentiation from PD0 to PD16 was associated with an increase in the fibroblast-specific extracellular matrix markers, and decrease in chondrocyte-specific extracellular matrix markers. Except THY1, all other gene expression changes were significant with p < 0.01, ns = not significant, number of samples = 4. Error bars represent SD about mean.