(A) Immunohistochemistry of Ki-67 on knee synovia from saline control and Wnt inhibitor mice 10 weeks after surgery showed a reduction in proliferation of synovial fibroblasts after treatment with Wnt inhibitor. Original magnification, ×20 (top); ×40 (bottom). (B) Knee synovia were stained by immunofluorescence with periostin (POSTN, green) and PCNA (red), a proliferating cell marker, and counterstained with nuclear DAPI (blue). The joint region used for immunofluorescence is shown by H&E stain. Synovia from saline-treated control mice demonstrated increased levels of periostin- and PCNA-positive cells, when compared with XAV-939–treated synovia. Additional sections from the same joint from the XAV-939–treated mouse were used as the isotype control. Images from the same joint region were used, although they are from separate sections. The H&E image is therefore reused. The representative isotype control shows minimal staining. Original magnification, ×20 (top row); ×80 (bottom 4 rows). (C) Proliferation was assessed by BrdU assay on synovial fibroblasts. Basal proliferation levels were significantly upregulated in OA patient fibroblasts compared with controls. Furthermore, WNT3A treatment of control fibroblasts also significantly upregulated proliferation. Wnt inhibition in OA fibroblasts decreased the proliferation rate. Two-way ANOVA with Tukey’s post-hoc test was performed, *P < 0.05, **P < 0.01, n = 6. For data presented as box-and-whiskers plots, horizontal lines indicate the medians, cross marks indicate the means, boxes indicate the 25th to 75th percentiles, and whiskers indicate the minimum and maximum values of the data set.