Expression of cathepsin K mRNA during experimental tooth movement in rat as revealed by in situ hybridization

The expression of cathepsin K, a novel collagenolytic enzyme specifically e xpressed in osteoclasts, was investigated in the rat maxillary dentoalveola r unit during experimental tooth movement by in situ hybridization histoche mistry with a non-radioisotopic cRNA probe for rat cathepsin K. Orthodontic elastics were inserted into the interproximal space between the maxillary first and second molars of 7-week-old male SD rats according to Waldo's met hod and sections prepared from tissues obtained at 12 hr, 1, 2, 3, 4, 7, an d 12 days after orthodontic force application. Cathepsin K mRNA expression was detected in the mono- and multinuclear osteoclasts on the pressure side of the alveolar bone at 12 hr after force application, and the distributio n and number of cathepsin K mRNA-positive osteoclasts increased time-depend ently on the pressure side. At 3-4 days, a marked increase in cathepsin K m RNA-positive osteoclasts was found not only on the pressure side but also o n the tension side of the alveolar bone in response to tooth movement. At 7 -12 days, the cathepsin K mRNA-positive osteoclasts on both sides had disap peared. These findings suggest that the recruitment of osteoclasts on the p ressure side begins during the initial stage of orthodontic tooth movement and the site-specific early induction of cathepsin K mRNA may cause an imba lance in the relative resorption activities on the pressure and tension sid e incident to such movement. (C). 2000 Elsevier Science Ltd. All rights res erved.