Expression of cathepsin K mRNA and protein in odontoclasts after experimental tooth movement in the mouse maxilla by in situ hybridization and immunoelectron microscopy

This study demonstrated the simultaneous expression of cathepsin K (CK) mRN A by in situ hybridization and CK protein by immunoelectron microscopy in o dontoclasts in mouse maxillae after experimental tooth movement. On the pre ssure side (the area under pressure during tooth movement), CK mRNA was det ected in odontoclasts in resorption lacunae in the tooth root, in osteoclas ts in bone resorption lacunae, and in fibroblasts in the periodontal ligame nt. Using electron microscopy CK protein was detected at the apex of odonto clasts, intracellularly in vesicles and granules, and extracellularly in ir regularly shaped vacuoles (extracellular spaces), on the plasma membrane of the ruffled border, and on and between typical striated type I collagen fi brils in the lacunae. These vesicles and granules appeared to fuse with irr egular vacuoles containing CK-positive fragmented fibril-like structures cl ose to the ruffled border. Fn the basolateral portion of odontoclasts, smal l amounts of CK-positive rough endoplasmic reticulum (ER) were found. CK-po sitive intracellular vacuoles (not extracellular spaces) also appeared to f use with the vesicles and granules. However, these fused organelles rarely contained fragmented fibril-like structures. They are probably endolysosome s. The distribution of CK in odontoclasts was similar to that previously se en in osteoclasts. Furthermore, CK-positive fibril-like structures were fou nd in the vacuoles of fibroblasts. These results indicated that during toot h movement CK is synthesized in odontoclasts on the pressure side and secre ted into the tooth resorption lacunae. Therefore, CK may take part in the d egradation of the dentin matrix (type I collagen fibrils and non-collagenou s protein) of the tooth root, and in the subsequent intracellular degradati on of endocytosed fragmented fibril-like structures in endolysosomes.