Human periapical granulation tissue contains osteogenic cells

Bone defects caused by periapical inflammation can be treated and improved by endodontic therapy. However, the mechanism for osseous healing of periapical lesions after root canal treatment is unclear. In this study we examined whether fibroblastic cells from human periapical granulation tissue could produce calcified matrix in vitro. Periapical lesions from three patients were dissected in endodontic surgery, and fibroblastic cells (HFC) migrating from these lesions in vitro were used in this study. The HFC were cultured with or without beta-glycerophosphate (β-GP) and ascorbic acid (AA), and the expression of human runt-related transcription factor-2 (Runx2), osterix (Osx), osteopontin (Opn), and osteocalcin (Ocn) mRNA, and alkaline phosphatase (ALPase) was examined by reverse transcriptase-polymerase chain reaction (RT-PCR) or by an enzyme-cytochemical technique. Furthermore, calcification in the cells was investigated by von Kossa staining. At the beginning of the culture, HFC expressed Runx2 mRNA faintly, but neither Opn mRNA nor ALPase activity. Immunocytochemical study also showed HFC expressed Runx2 more weakly, compared to SaOS2. However, the expression levels of ALPase, and Runx2, Osx, and Opn mRNA, were stimulated by 2 mM β-GP and 50 μg/ml AA. After 4 weeks of culture with 2 mM β-GP and 50 μg/ ml AA, HFC formed von Kossa staining-positive calcified deposits on culture dishes, and also expressed Ocn mRNA. These results suggest that inflamed periapical granulation tissue contains osteogenic cells that have the potential to differentiate into mature osteoblastic or cementoblastic cells, and that such cells might contribute to osseous healing after root canal treatment.