Matrix Metalloproteinase-2 (MMP-2) Localization and Activity in Carious Dentine

Introduction: The progression of the carious dentine occurs by demineralization of inorganic matrices. This is effected by bacterial acids and leads to the exposure of collagen. At present, there is no clear evidence to support the hypothesis that bacterial proteases can directly degrade collagen. Host-derived matrix metalloproteinases (MMPs) play a significant role in the turnover of extracellular matrix components. MMPs are secreted in an inactive form. Many mechanisms have been proposed for the subsequent activation of MMPs. Any imbalance in the control of MMPs can lead to excessive degradation of collagen.

Objectives: The aim of this study is to clarify the role of MMP-2 in the progression of dental caries. 

Methods: 22 molar teeth with carious lesions and 10 healthy teeth were used for the study. After extraction, teeth were vertically split. The tooth half containing the pulp was fixed and embedded in resin. Sections of 2-μm thickness were used for fluorescence in-situ hybridization (FISH) and immunohistochemistry (IHC) for MMP-2.The other half was used for pH measurements and gelatinase assays. RT-PCR was used to measure the amount of mRNA for the protein of interest.

Results: The pH of carious samples was significantly lower than for healthy samples while gelatinase activity was significantly increased in disease samples. Overlay of FISH and IHC for MMP-2 demonstrated co-localisation of bacteria and MMP-2 in carious samples. RT-PCR demonstrated up-regulation of mRNA for MMP-2 during disease.

Conclusions: The pH decrease during disease could activate MMPs. This correlated to the increase of gelatinase activity in carious samples. According to the co-localisation of bacteria and MMP-2, it is possible that bacteria have the capacity to bind and activate MMP-2. MMP-2 up-regulated during disease might play other roles rather than being destructive, e.g., essential processing of components required for reactionary dentine which prevents the invasion of bacteria.