Both Dickkopf-1 (DKK1) and sclerostin (SOST) are downregulated in proteoglycan-induced spondylitis (PGISp)-affected mouse spines. (A) At week 12 and 24 both SOST and DKK1 expression are significantly downregulated in PGISp-affected spines, as shown by qPCR. Data are shown as Sost (vertical bars) or Dkk1 (diagonal bars) expression normalised to β-actin and expressed as the ratio of PGISp/Control. The dashed red line represents a ratio of 1, that is, no change in expression. Downregulation of SOST at the protein level was confirmed by immunohistochemistry. (B) The percentage of SOST-positive osteocytes is significantly reduced in the PGISp spine and pelvis. (C-F) Representative images demonstrating numbers of SOST+ve osteocytes in PGISp spines. Osteocyte-containing lacunae staining positive for SOST (D) are common in control bone but less evident in PGISp-affected samples (F). Isotype stained controls are also included (C,E). *P < 0.05, ** P < 0.01, PGISp vs. control.