Expression and biological activity of a novel protein species from cementum

Cementum is a specialized mineralized connective tissue with singular histological and functional characteristics. Proteins isolated from human cementum appear to regulate periodontal ligament stem cells differentiation, help to maintain homeostasis and appear to control some of the molecular events required for periodontium formation, therefore emerging as novel therapeutic candidates for periodontal regeneration. The possibility that there might be cementum components, so far not described, was explored in these studies. This study reports the expression and biological activity of a novel human species from cementum termed cementogenin (CMGN). This molecule encodes a 195 aminoacid protein species with a predicted molecular mass of 20.2 kDa. Polyclonal antibodies against a GMGN's selected peptide sequence were produced to identify the protein. Expression of CMGN in cells of the periodontium was examined by Western blot and immunofluorescence using histological sections of the periodontium. These studies revealed that CMGN is expressed by cementoblasts and cells of the periodontal ligament. Expression of CMGN's mRNA and its protein in different periodontium cell types was determined by RT-qPCR and Western blot, respectively. CMGN mRNA and gene product levels were highly expressed by cementoblasts and osteoblasts cells. The CMGN protein was expressed in E. coli for functional studies using in vitro cell-free system. Assays revealed that hrCMGN promotes the nucleation of hydroxyapatite crystals. The human recombinant CMGN (hrCMGN) promoted cell proliferation, cell attachment, and differentiation by human periodontal ligament cells to a mineralized phenotype. Overall, our findings reveal that CMGN represents a new species isolated from cementum and might provide the basis for future studies that will allow further characterization of the structural features of CMGN and a better understanding of its functional properties. This new protein might be highly relevant in future periodontal therapeutics.