Prolactin receptor and osteogenic induction of prolactin in human periodontal ligament fibroblasts.

Prolactin is an important hormone involved in the interaction between maternal, extraembryonic, and fetal tissues that remains in high levels during the entire duration of pregnancy. Although many systemic alterations occur during pregnancy, such as hormonal changes, that are known to be associated with periodontitis and tooth loss, PRL function in human periodontal ligament fibroblasts (HPDLF) had never been studied. Herein, we investigated the role of PRL in the regulation of HPDLF proliferation and differentiation. HPDLF were cultured in differentiating medium with various concentrations of PRL. The present study demonstrated that HPDLF and primary human PDL cells that were extracted for orthodontic purpose expressed both short and long isoforms of PRLR mRNA and its proteins. An incubation with of high concentration of PRL (600 and 1,000 ng/mL) modestly decreased the HPDLF number. In contrast, PRL at a non-reproductive level (10 ng/mL) and pregnant level (100 ng/mL) significantly upregulated the markers of osteogenesis, such as RUNX2, BMP2, and POSTN, but not SOX9. Mineral nodule formation was induced, whereas proteoglycan accumulation was reduced by PRL suggesting that HPDLF were undergoing differentiation into preosteoblastic cells. In conclusion, the presence of hPRLR in human PDL together with PRL-induced upregulation of osteogenic markers strongly suggested a direct regulatory role of PRL in PDL and periodontal tissue development.