WNT-3A induces chondrocyte proliferation and de-differentiation in vitro. (A and B) 100 ng/ml WNT-3A stimulated proliferation of primary chondrocytes in vitro as evaluated by an [H³]thymidine incorporation assay in porcine articular chondrocytes (A; n = 6) and by up-regulation of the proliferation marker PCNA in primary AHACs by quantitative PCR (Q-PCR) (B; n = 4). (C and D) WNT-3A–induced down-regulation of the differentiation markers COL2A1, Aggrecan, SOX9, and MMP13, as evaluated by Q-PCR (C; n = 6), and reduced the accumulation of highly sulphated GAG in primary AHACs (D; by Alcian blue staining and spectrophotometric quantification; n = 4). Gene expression values are reported as a percentage of up- or down-regulation compared with control (100%, broken line in the graph). Statistical analysis was performed with an unpaired t test. Error bars indicate mean ± SEM. *, P < 0.05; **, P < 0.005; ***, P < 0.0005.