Expression and localization of MGP in rat tooth cementum

Tooth cementum, a calcified hard tissue covering the root surfaces, is an important component connecting the teeth to the collagenous fibres of the periodontal ligament. Although the overall composition of cementum may closely resemble that of bone, each part has not been fully characterized. Here, the localization of the matrix gamma-carboxyglutamic acid (Gla) protein (MGP), one of the major Gla-containing proteins in the body, in cementum was investigated using immunohistochemistry and in situ hybridization. (1) Strong MGP antigenicity was observed in the acellular cementum, but was only moderate in the cellular cementum; (2) polygonal periodontal ligament cells facing the acellular cementum and the uncalcified cellular cementum expressed MGP mRNA, indicating that these cells produced MGP and deposited it on the cementum; (3) MGP accumulated at the junction between the uncalcified and calcified cellular cementum; and (4) the distribution pattern of MGP antigenicity resembled that of osteopontin. As one function of MGP could be as a negative regulator for mineral apposition, the expression of MGP in the cells adjacent to the cementum may be important to prevent hyperapposition of minerals.