Cathepsin K and glycosaminoglycans differentially regulate matrix metalloproteinase activity in dentin under various...

This study examined the pH-dependent (3, 5, and 7) regulation of matrix metalloproteinase (MMP) activity by cathepsin K (catK) and glycosaminoglycans (GAGs) using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), fluorescence assays, and human dentin slice experiments. The direct effects of catK were evaluated in the catK-active, catK-deficient, and odanacatib (ODN)-inhibited groups, whereas indirect GAG/tissue inhibitor of metalloproteinase (TIMP)-mediated regulation was assessed in the catK-active, ODN-inhibited, and chondroitin sulfate (CS)-treated groups through dimethylmethylene blue (DMMB) assays, in situ zymography, and immunofluorescence staining. CatK directly activated MMP-2 (62 kDa) and MMP-9 (82 kDa) at all pH values, with no activation observed in the ODN-inhibited or catK-deficient groups. MMP activity was significantly higher at pH 5/7 than at pH 3. ODN treatment reduced the amount of liberated GAGs, particularly at pH 5. A comparative analysis revealed a consistent activity gradient of ODN-inhibited < catK-active < CS-treated for gelatinase activity across all pH values, and significantly lower collagenase intensity in the ODN group than in the catK/CS groups at pH 5. TIMP-1 and TIMP-2 levels were increased in ODN-inhibited slices at pH 3 and 5 respectively, compared with those in controls. These results demonstrate the dual regulatory mechanism of catK involving direct MMP activation and GAG-mediated TIMP modulation, which is strongly pH dependent. The increased efficacy of ODN under acidic conditions suggests its therapeutic potential for preventing dentin erosion when it is applied following acidic challenges.