Figure 5.

Elevated rates of cartilage breakdown in SIRT-1^y/y (y/y) mice. A, Immunohistochemical staining of knee sections from 6-month-old y/y and wild-type (WT) mice with antibody against the Coll2-1 breakdown peptide. An average of 6 fields in 3 sections from 3 separate mice per genotype was assessed, and representative fields are shown. Erosion of cartilage surface (arrows) and diffuse brown staining around the defects was observed in the y/y mice, whereas the staining was strongly intracellular in the WT mice. Original magnification × 20. B, Anti-aggrecan antibody staining of knee sections from 6-month-old y/y and WT mice, showing significantly higher cartilage degradation in the y/y mice than in the WT mice, with cartilage defects (arrows), such as erosions of the cartilage surface, deeper clefts, and fibrillations. Thirty-six knee sections from each genotype were examined; representative results are shown. Original magnification × 16. C, Cartilage degradation grade, determined in Safranin O–light green–stained sections, for y/y and WT mice. The scoring system was adapted from the Osteoarthritis Research Society International (OARSI) semiquantitative scoring system for OA severity. A score of 0 indicates no degradation; a score of 5 indicates denuded cartilage surface with sclerotic bone. The mean scores were 3.41 for the y/y mice and 1.2 for the WT mice. Twelve samples for each genotype (2 sections of 2 different knees from 3 different mice per genotype) were scored, showing more severe grades for the y/y knees. Bars show the mean ± SD. * = P < 0.05 versus WT mice.