Localization of leucine-rich repeat-containing G-protein-coupled receptor 5- and Ki67-positive periodontal cells expressing runt-related transcription factor 2 during tooth movement

Abstract

Purpose

Mechanical stimuli induce the proliferation and osteogenic differentiation of periodontal ligament (PDL) progenitor cells. However, the localization of formative and proliferative cells in response to orthodontic force in the PDL is unknown. We aimed to elucidate the expression patterns and localization of the cell proliferation- and osteogenesis-associated markers in the PDL during tooth movement.

Materials and methods

Five-week-old male Sprague–Dawley rats had their right maxillary first molars (rM1s) moved mesially using a 10-gf titanium-nickel alloy closed-coil spring. Left maxillary first molars (lM1s) served as controls. Immunohistochemical analyses of leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5), Ki67, and runt-related transcription factor 2 (RUNX2) were performed in the periapical region of M1. mRNA levels of Ki67, Runx2, and β-catenin were quantified by real-time reverse transcription polymerase chain reaction (qRT-PCR). In vitro human PDL stem cells (hPDLSCs) were cyclically stretched for 24 h, and MTT assay and western blot analysis of LGR5 were performed.

Results

Immunohistochemistry showed that LGR5 and Ki67 were partially co-expressed with RUNX2 in the periapical PDL. Immunoreactivities of LGR5, Ki67, and RUNX2 were significantly greater in the PDL of the rM1 than in that of the lM1 on day 3. qRT-PCR showed that Ki67 and Runx2 mRNA levels, but not β-catenin levels, increased on the mesial side of the periapical PDL on day 3. Western blot analysis revealed that 24 h of cyclic strain stimulated LGR5 expression in hPDLSCs.

Conclusion

Our findings suggested that orthodontic force induced LGR-5- and Ki67-positive cells expressing RUNX2 in the PDL during tooth movement.