Oestrogen receptor β (ERβ) regulates osteogenic differentiation of human dental pulp cells

Estradiol (E-2) has many important actions in the tissues of the oral cavity. Disruption of E-2 metabolism or alterations in systemic E-2 concentrations have been associated with compromised periodontal health. In many instances such changes occur secondarily to the well characterised effects of E-2 on bone physiology - especially maintenance of bone mineral density (BMD). Despite these important epidemiological findings, little is known about the mechanism of action of E-2 in oral tissues or the expression and function of oestrogen receptor (ER) isoforms in these tissues. We have isolated human dental pulp cells (hDPCs), which are able to differentiate towards an osteogenic lineage under appropriate culture conditions. We show that hDPCs express ER alpha, ER beta 1, ER beta 2 and the cell membrane associated G protein-coupled ER (GPR30). Following osteogenic differentiation of hDPCs, ER beta 1 and ER beta 2 were up regulated approximately 50-fold while ERa and GPR30 were down regulated, but to a much lesser degree (approximately 2-fold). ER beta was characterised as a 59 kDa protein following Western blot analysis with validated antibodies and ER beta was detected in both nuclear and cytoplasmic cell compartments following immunofluorescence (IF) and immunohistochemical (IHC) analysis of cultured cells. Furthermore isoform specific antibodies detected both ER beta 1 and ER beta 2 in DPC cultures and in situ analysis of ER beta expression in decalcified tooth/pulp sections identified the odontoblast layer of pulp cells juxtaposed to the tooth enamel as strongly reactive for both ER beta isoforms. Finally the use of isoform specific agonists identified ER beta as the main receptor responsible for the pro-osteogenic effect of oestrogenic hormones in this tissue. Our data suggest that Oestrogens stimulated osteogenic differentiation in hDPCs and that this action is mediated principally through the ER beta isoform. These findings may have important consequences for the investigation and treatment of oral and periodontal pathologies which are associated with imbalances in oestrogen concentrations and action.