Loss of beta-catenin causes cementum hypoplasia by hampering cementogenic differentiation of Axin2-expressing cells

Background and Objective: Although cementum plays an essential role in tooth attachment and adaptation to occlusal force, the regulatory mechanisms of cementogenesis remain largely unknown. We have previously reported that Axin2-expressing (Axin2(+)) mesenchymal cells in periodontal ligament (PDL) are the main cell source for cementum growth, and constitutive activation of Wnt/beta-catenin signaling in Axin2(+) cells results in hypercementosis. Therefore, the aim of the present study was to further evaluate the effects of beta-catenin deletion in Axin2(+) cells on cementogenesis. Materials and Methods: We generated triple transgenic mice to conditionally delete beta-catenin in Axin2-lineage cells by crossing Axin2(CreERT2/+); R26R(tdTomato/+) mice with beta-catenin(flox/flox) mice. Multiple approaches, including X-ray analysis, micro-CT, histological stainings, and immunostaining assays, were used to analyze cementum phenotypes and molecular mechanisms. Results: Our data revealed that loss of beta-catenin in Axin2(+) cells led to a cementum hypoplasia phenotype characterized by a sharp reduction in the formation of both acellular and cellular cementum. Mechanistically, we found that conditional removal of beta-catenin in Axin2(+) cells severely impaired the secretion of cementum matrix proteins, for example, bone sialoprotein (BSP), dentin matrix protein 1 (DMP1) and osteopontin (OPN), and markedly inhibited the differentiation of Axin2(+) mesenchymal cells into osterix(+) cementoblasts. Conclusions: Our findings confirm the vital role of Axin2(+) mesenchymal PDL cells in cementum growth and demonstrate that Wnt/beta-catenin signaling shows a positive correlation with cementogenic differentiation of Axin2(+) cells.