Subset of the periodontal ligament expressed leptin receptor contributes to part of hard tissue-forming cells

The lineage of periodontal ligament (PDL) stem cells contributes to alveolar bone (AB) and cementum formation, which are essential for tooth-jawbone attachment. Leptin receptor (LepR), a skeletal stem cell marker, is expressed in PDL; however, the stem cell capacity of LepR(+) PDL cells remains unclear. We used a Cre/LoxP-based approach and detected LepR-cre-labeled cells in the perivascular around the root apex; their number increased with age. In the juvenile stage, LepR(+) PDL cells differentiated into AB-embedded osteocytes rather than cementocytes, but their contribution to both increased with age. The frequency of LepR(+) PDL cell-derived lineages in hard tissue was < 20% per total cells at 1-year-old. Similarly, LepR(+) PDL cells differentiated into osteocytes following tooth extraction, but their frequency was < 9%. Additionally, both LepR(+) and LepR(−) PDL cells demonstrated spheroid-forming capacity, which is an indicator of self-renewal. These results indicate that both LepR(+) and LepR(−) PDL populations contributed to hard tissue formation. LepR(−) PDL cells increased the expression of LepR during spheroid formation, suggesting that the LepR(−) PDL cells may hierarchically sit upstream of LepR(+) PDL cells. Collectively, the origin of hard tissue-forming cells in the PDL is heterogeneous, some of which express LepR.