Bone Morphogenetic Protein 2 Induces the Expression of Cementum Attachment Protein in Human Periodontal Ligament Clones

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Abstract
Cementum is continuously formed during the lifetime of a tooth. The paravascular zones in the adult periodontal ligament (PL) comprise the progenitors for the fibroblastic (Fb) lineage and mineralized tissue-forming (MTF) cell lineages--the osteoblastic (Ob) and cementoblastic (Cb) lineages. Recent studies indicate that cementum attachment protein (CAP) is related to the differentiation of the Cb lineage and is instrumental in differentiating between the three periodontal cell lineages. The purpose of this study was to assess the effect of bone morphogenetic protein 2 (BMP2) on the expression of cementum attachment protein (CAP) and on the differentiation of cloned PL progenitors. The effect of BMP2 on CAP expression and on the differentiation of cloned Fb and MTF progenitors was tested by assessing the expression of alkaline phosphatase (ALP), CAP, and bone sialoprotein (BSP) by immunochemistry and by determining the CAP-binding capacity of these clones. Untreated Fb clones were negative for all tested markers and had low CAP-binding capacity. Untreated MTF clones had a high CAP-binding capacity and were positive for the three markers. BMP2 enhanced the CAP-binding potential of both Fb and MTF clones. BMP2 induced the expression of CAP, ALP, and BSP in the Fb clones and enhanced the expression of CAP and BSP in the MTF clones. These results indicate for the first time that BMP2 can recruit progenitors to the Cb lineage and regulate the differentiation of the Cb lineage by inducing and enhancing the expression of CAP, a cell lineage-specific regulator. Furthermore, the results suggest that the MTF and Fb lineages may originate from a common early progenitor cell.