Proteoglycan (PG) content of osteoarthritits (OA) cartilage in STR/ort mice. STR/ort mice (4 weeks old) were injected intra-articularly with Ad-transforming growth factor-β (TGF-β) combined with Ad-Smad7 or Ad-luciferase and injected again 2 weeks later. Four weeks after the first injection, knee joints were isolated and the effect of TGF-β overexpression on PG content was assessed. TGF-β exposure resulted in a significantly higher PG content of cartilage than luciferase-injected controls (p < 0.05). Co-expression with Smad7 had no effect on the PG content. Error bars display standard error.