THE ACTIVATION AND FUNCTION OF HOST MATRIX METALLOPROTEINASES IN DENTIN MATRIX BREAKDOWN IN CARIES LESIONS

Matrix metalloproteinases (MMPs) are a family of enzymes which, in con cert, are capable of degrading collagen. We investigated whether human MMPs could participate in the degradation of dentin organic matrix af ter demineralization. We performed Western blot analyses using MMP-spe cific antibodies to identify MMPs in human dental caries lesions. Enzy mography and functional activity assays, with I-125-labeled gelatin as substrate or quantitating the degradation of type I collagen, were us ed to determine the activity of purified and salivary gelatinolytic (M MP-2 and MMP-9) and collagenolytic (MMP-8) enzymes with and without ac id-activation in pi-Is relevant to caries. Respective analyses were do ne with caries-related bacteria. We performed electron microscope anal yses to assess the degradative activity of sterilized salivary host MM Ps on demineralized human dentin. Human MMP-2, MMP-8, and MMP-9 were i dentified in demineralized dentinal lesions. The latent purified forms of these enzymes were activated at low pH (4.5), followed by neutrali zation, mimicking the conditions during caries progression. Incubation of human saliva at low pH followed by neutralization resulted in a fo ur-fold increase in the gelatinolytic activity. No gelatinolytic or co llagenolytic activity was observed in bacterial samples. The activated enzymes in saliva degraded demineralized dentin organic matrix in vit ro. These results demonstrate the pH-dependent activation mechanism of MMPs, which may have a distinct role in different physiological and p athological conditions. They further demonstrate that host MMPs, activ ated by bacterial acids, have a crucial role in the destruction of den tin by caries.