Components of the canonical WNT pathway in adult human articular cartilage. (a,b) Time course of the differential expression of FRZB mRNA in injured versus uninjured explants in (a) the presence or (b) the absence of fetal bovine serum (FBS) in the culture medium. Values were calculated using a standard curve, normalized for the housekeeping β actin gene and expressed as fold change of gene expression in the injured explants from paired uninjured controls. Diamonds indicate samples from preserved areas from joints affected by osteoarthritis; open squares indicate sample pairs from healthy cartilage. (c-f) Immunohistochemical staining for FRZB protein (red) in (c) uninjured and (d) injured explants at the day 1 time point. Haematoxylin was used as a nuclear counterstain. (e,f) Larger magnifications of the boxed areas in (c) and (d), respectively. (g) Percentage of FRZB-positive cells in injured explants and in the paired uninjured controls from 3 independent donors as evaluated by immunohistochemistry. (h) Haematoxylin-eosin and (i) safranin O stainings of an explant with a relatively high degree of osteoarthritis (modified Mankin score 5). (j-m) Immunostaining for β catenin in parallel, non-consecutive sections of (h) and (i). (j-l) Indirect immunofluorescence stainings for β catenin from a parallel section in the area of (h) boxed with the dashed line (top). (k) β catenin (green). (l) DAPI counterstain of the same section (blue). (j) The superimposition of (k) and (l). In this tissue, which is commonly called pannus, there were cells with a nuclear localization of β catenin. (m) Immunohistochemistry showing the cytoplasmic localization of β catenin in chondrocytes of the basal layer (area in (h) boxed with a solid line). *p < 0.05; **p < 0.01. D, day(s); H, hours; SF, serum free Medium.