Evidence to suggest that cathepsin K degrades articular cartilage in naturally occurring equine osteoarthritis  T. Vinardell, D.V.M., I.P.S.A.V., M.Sc., V. Dejica, M.D., A.R. Poole, Ph.D., J.S. Mort, Ph.D., H. Richard, S. Laverty, M.V.B., M.R.C.V.S., Dipl. A.C.V.S., Dipl. E.C.V.S.  Osteoarthritis and Cartilage  Volume 17, Issue 3, Pages 375-383 (March 2009) DOI: 10.1016/j.joca.2008.07.017 Copyright © 2008 Osteoarthritis Research Society International Terms and Conditions

Fig. 1 Representative OA lesion on the distal metacarpus illustrating 3 sites from which cartilage was harvested postmortem: L=lesion, PL=adjacent to the lesion, and R=remote from the lesion. Osteoarthritis and Cartilage 2009 17, 375-383DOI: (10.1016/j.joca.2008.07.017) Copyright © 2008 Osteoarthritis Research Society International Terms and Conditions

Fig. 2 C2K immunohistochemically stained sections with corresponding controls of articular cartilage from 3 sites within OA joints (remote (R), peri-lesion (PL) and lesion (L)). Preabsorption of the primary antibody with the immunizing peptide was performed on the control sections. A marked increase in stain is observed in the R, PL & L sites when compared to controls (original magnification ×50, bar=100μm). Osteoarthritis and Cartilage 2009 17, 375-383DOI: (10.1016/j.joca.2008.07.017) Copyright © 2008 Osteoarthritis Research Society International Terms and Conditions

Fig. 3 Immunohistochemically stained representative sections of articular cartilage from 3 sites within OA joints (remote (R), peri-lesion (PL) and lesion (L)). For C2K immunolocalization (CK collagen cleavage) and C2C immunolocalization (MMPs collagen cleavage) we observed an increase in stain in OA sections and the depth of the staining increased with the severity of OA. CK immunolocalization was situated in chondrocyte lacunae and surrounding matrix. Brown colour represents positive staining (original magnification ×50, bar=100μm). Osteoarthritis and Cartilage 2009 17, 375-383DOI: (10.1016/j.joca.2008.07.017) Copyright © 2008 Osteoarthritis Research Society International Terms and Conditions

Fig. 4 Representative cartilage histologic sections from 3 sites in OA joints: remote (R), peri-lesion (PL) and lesion (L). A, Safranin O-Fast Green (SOFG) (stains proteoglycan) stained sections showed a reduction of the staining, hypocellularity and loss of cartilage thickness with the progression of OA. B, Picrosirius red staining (stains collagen) illustrated non-aligned fibers and heterogeneous staining with the progression of the disease from the surface to the deeper zones of cartilage (original magnification ×50, bar=100μm). Osteoarthritis and Cartilage 2009 17, 375-383DOI: (10.1016/j.joca.2008.07.017) Copyright © 2008 Osteoarthritis Research Society International Terms and Conditions

Fig. 5 Vertical scatter plot illustrating comparisons between the histological and immunohistochemical assessments of cartilage sections from healthy (H) and OA joints: remote cartilage (R), peri-lesion (PL) and in the lesion (L). Horizontal bar indicates mean score.*P<0.05 vs N; § P<0.05 vs R; ¶P<0.05 vs PL. Osteoarthritis and Cartilage 2009 17, 375-383DOI: (10.1016/j.joca.2008.07.017) Copyright © 2008 Osteoarthritis Research Society International Terms and Conditions

Fig. 6 Representative patterns of staining with CK at higher magnification. There is an absence of staining in cartilage sections from healthy joints (H) and from remote sites in OA (R): a progressive increase of CK staining was observed in chondrocyte lacunae and surrounding matrix with increasing severity of the disease. PL illustrates a peri-lesion and L a lesion sample (original magnification ×50, bar=100μm). Osteoarthritis and Cartilage 2009 17, 375-383DOI: (10.1016/j.joca.2008.07.017) Copyright © 2008 Osteoarthritis Research Society International Terms and Conditions