CATHEPSIN-K ANTISENSE OLIGODEOXYNUCLEOTIDE INHIBITS OSTEOCLASTIC BONE-RESORPTION

Cathepsin K is a recently identified cysteine protease which is abunda ntly and selectively expressed in osteoclasts, To evaluate the contrib ution of cathepsin K to bone resorption processes, we investigated the effect of cathepsin K antisense phosphothiorate oligodeoxynucleotide (S-ODN) on the bone-resorbing activity of osteoclasts. Rabbit osteocla sts were cultured on dentine slices for 24 h in the presence or absenc e of antisense S-ODN in a medium containing 100 nM Tfx(TM)-50, polycat ionic liposome, as a carrier of the S-ODN, Uptake of the S-ODN by oste oclasts was confirmed microscopically using fluorescein-labeled S-ODN, The treatment with antisense significantly decreased the amount of ca thepsin K protein in osteoclasts. The antisense inhibited the osteocla stic pit formation in a concentration-dependent fashion, At 10 mu M th e antisense reduced the total pit number and area and average pit dept h by 46, 52, and 30%, respectively, The sense and mismatch S-ODNs, whi ch were used as negative controls, had no effect on either the catheps in K protein level or the pit formation. A nonspecific cysteine protea se inhibitor, E-64, also reduced pit formation in a concentration-depe ndent manner with maximum reductions at 1 mu M of 46, 48, and 35% in t he above pit parameters, The inhibitory effect of the antisense almost equal to that of E-64 demonstrates that cathepsin K is a cysteine pro tease playing a crucial role in osteoclastic bone resorption.