Parathyroid Hormone 1-34 Inhibits Terminal Differentiation of Human Articular Chondrocytes and Osteoarthritis Progression in Rats

Objective. Parathyroid hormone 1-34 (PTH[1-34]), a parathyroid hormone analog, shares the same receptor, PTH receptor 1, with parathyroid hormone-related peptide (PTHrP). This study was undertaken to address the hypothesis that PTH(1-34) inhibits terminal differentiation of articular chondrocytes and in turn suppresses the progression of osteoarthritis (OA). Methods. We studied the effect of PTH(1-34) on human articular chondrocytes with azacytidine (azaC)-induced terminal differentiation in vitro and on papain-induced OA in the knee joints of rats. In the in vitro study, we measured the levels of messenger RNA for SOX9, aggrecan, type II collagen, type X collagen, alkaline phosphatase (AP), Indian hedgehog (IHH), Bcl-2, and Bax by real-time polymerase chain reaction, levels of glycosaminoglycan (GAG) by dimethylmethylene blue assay, and rate of apoptosis by TUNEL staining. In the in vivo study, we evaluated the histologic changes in GAG, type II collagen, type X collagen, and chondrocyte apoptosis in the articular cartilage of rat knees. Results. AzaC induced terminal differentiation of human chondrocytes, including down-regulation of aggrecan, type II collagen, and GAG and up-regulation of type X collagen, alkaline phosphatase, and IHH. Apoptosis was reversed by 3-10 days of treatment with 10 nM PTH(1-34). SOX9 expression was not changed by either azaC or PTH(1-34) treatment. Bcl-2 and Bax were up-regulated on day 10 and day 14, respectively, after azaC induction of terminal differentiation, but PTH(1-34) treatment did not reverse this effect. Furthermore, PTH(1-34) treatment reversed papain-induced OA changes (decreasing GAG and type II collagen, and increasing type X collagen and chondrocyte apoptosis) in the knee joints of rats. Conclusion. Our findings indicate that PTH(1-34) inhibits the terminal differentiation of human articular chondrocytes in vitro and inhibits progression of OA in rats in vivo, and may be used to treat OA.