Localization of α-smooth muscle actin in osteoblast differentiation during periodontal development

Abstract α-smooth muscle actin (α-SMA) is an actin isoform commonly found within vascular smooth muscle cells. Moreover, α-SMA-positive cells in the periodontal tissue are speculated to be a marker for mesenchymal stem cells during tooth development. This study demonstrated the fate of α-SMA-positive cells around the tooth germ immunohistochemically. First, α-SMA- and Runx2-positive localization was demonstrated. Second, the distribution of α-SMA-positive cell progeny at the early root (P9) and root (P15) formation stage were revealed using lineage-tracing analysis. α-SMA-positive cells were detected in the upper part of the dental follicle at the early bell stage (P1). The positive reaction of Runx2 was detected around the dental follicle and the positive reaction area of Runx2 was broader than that of α-SMA. At P9 and P15, α-SMA-positive cells in the periodontal ligament (PDL) were detected in the upper and lower parts. The positive reaction of Runx2 was also localized in the PDL. The lineage-tracing analysis demonstrated that the α-SMA/tomato-positive cells expressing Runx2 or Osterix are localized in the PDL at P15. Some of the Runx2- and Osterix-positive cells on the alveolar bone surface and Col1-positive reaction were found in the osteocytes. α-SMA/tomato-positive reactions were also found in the Runx2- and Osterix-positive cells and Col1-positive reaction area. Thus, indicate that the progeny of the α-SMA-positive cells in the PDL during the root formation stage could differentiate into osteoblasts. In conclusion, α-SMA could be a potential marker of progenitor cells that differentiate during alveolar bone ossification.