Effects of antisense mediated inhibition of cathepsin K on human osteoclasts obtained from peripheral blood

Cathepsin K is a cystein protease that displays a proteolytic activity against Type I collagen and is abundantly and selectively expressed in osteoclasts where it plays a critical role in bone degradation. Its direct role in bone tissue has been defined by knock‐out mice studies and inhibiting strategies in animals models. However, direct proof of cathepsin K function in human osteoclast model in vitro is lacking. The aim of this study is to analyze cathepsin K expression and localization in human osteoclasts obtained from peripheral blood and to examine cathepsin K function in these cells by antisense oligodeoxynucleotide (AS‐ODN) strategy. AS‐ODN was added to the culture of osteoclast precursors induced to differentiate by RANKL and M‐CSF. AS‐ODN treatment produced a significant down‐regulation of cathepsin K mRNA (>80%) and protein expression, as verified respectively by Real‐time PCR and by immunocytochemistry or Western blot. The cathepsin K inhibition caused an impairment of resorption activity as evaluated by a pit formation assay ( p = 0.045) and by electron microscopy, while the acidification process was unaffected. We demonstrated that antisense strategies against cathepsin K are selectively effective to inhibit resorption activity in human osteoclasts, like in animal models. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 24:1699–1708, 2006