development of novel conservative therapies for joint disease under controlled HSP expression-usage of HSP-inducing agents and thermotherapy-

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Heat stimulation was applied to the knee joints of Japanese white rabbits for 20 min using a microwave (MW) applicator (2.45-GHz, 0-80 W). After 8-72 hrs, the articular cartilage was removed from the knee joints and proteins and total RNA were extracted. As controls, the knee joints without heat stimulation were analyzed. Expression of heat shock protein (HSP) 70 was confirmed by real-time PCR and Western blotting. Expression of proteoglycan core protein (PG) and type II collagen (Col II) were quantified using real-time PCR to assess cartilage matrix metabolism. Compared to controls, HSP70 expression was higher with more than 40 W of heat stimulation. The expression of PG and Col II mRNA were higher with more than 20 W of heat stimulation and peaked with 40 W. The highest expression of HSP70, PG, and Col II mRNA were observed 8hrs, 48hrs, and 72hrs after heat stimulation, respectively. On the other hand, the highest HSP70 protein expression was observed 24 h after heat stimulation. When quercetin was used to inhibit the induction of HSP70 expression, PG mRNA expression did not increase. The present study demonstrated that appropriate heat stimulation increased the expressions of extracellular matrix gene, which might be partially mediated by HSP70. These findings showed that controlling HSP70 expression in the cartilage using thermotherapy might offer a novel strategy for suppressing cartilage degeneration in osteoarthritis.