Two transcription associated estrogen receptor (ER) subtypes have been identified and named ERalpha and ERbeta. In the present study we investigate the expression of these ER subtypes in cultured human periodontal ligament (PDL) cells by immunocytochemistry. ERbeta immunoreactivity was observed in the nuclei of about 40% of the PDL cells, while no ERalpha immunoreactivity was detected. In human breast cancer MCF-7 cells, serving as positive controls, both ERalpha and ERbeta immunoreactivities were demonstrated. No immunoreactivity was observed after omission of the primary antibodies. This study suggests that estrogen acts on gene transcription preferentially via ERbeta in human PDL cells.

Objective: Periodontal ligament (PDL) cells express oestrogen receptor b (ERb) protein, but cellular functions regulated by ERb in these cells have not been identified. In this study we determine if ERb is localised to mitochondria and if oestrogen regulates mitochondrial function in human PDL cells obtained from teeth extracted for orthodontic reasons. Design: Subcellular distribution of ERb was determined by confocal microscopy of cells costained with ERb antibody and the mitochondrion-selective probe MitoTracker and by immunogold electron microscopy. Expression of the mitochondrial enzyme cytochrome c oxidase subunit I, involved in oxidative phosphorylation, was determined by Western blotting in cells treated with or without physiological concentrations of the endogenous oestrogen 17b-oestradiol. Results: ERb immunoreactivity was observed both in the nuclei and the cytoplasm. Mito- Tracker-labelling was observed in the cytoplasm, especially in the perinuclear region, but not in the nuclei. Co-localisation of ERb and MitoTracker was observed in cells derived from both male and female subjects. Mitochondrial localisation of ERb was confirmed by immunogold electron microscopy. Cells treated with or without 17b-oestradiol (100 nM) displayed an identical pattern of staining for mitochondria. Treatment with 100 nM 17b-oestradiol attenuated cytochrome c oxidase subunit I expression by about 30%, while combined treatment with 17b-oestradiol and the ER blocker ICI 182780 (10 mM) had no effect. Conclusion: This study demonstrates mitochondrial localisation of ERb and oestrogeninduced decrease in the expression of cytochrome c oxidase subunit I in human PDL cells, suggesting that oestrogen probably via ERb influences mitochondrial function and PDL cell energy metabolism.

Background:  It is important to clarify the biological function of the female sex hormones estrogen and progesterone in periodontal ligament cells, as these hormones may affect periodontal health. We have previously shown that human periodontal ligament cells express estrogen receptor β (ERβ) but not ERα, whereas human breast cancer cells (MCF7) express both ERα and ERβ. Data on progesterone receptor (PgR) expression in human periodontal ligament cells have not been reported.

Objectives:  Determine PgR expression in human periodontal ligament and MCF7 cells and to investigate how estrogen affects DNA and collagen synthesis in these two cell types showing different pattern of expression for ERα and β.

Methods:  Periodontal ligament cells were obtained from the periodontal ligament of premolars extracted for orthodontic reasons and MCF7 cells from the American Type Culture Collection (ATCC). PgR expression was determined by immunocytochemistry. DNA and collagen synthesis was determined by [ 3 H]thymidine and l ‐[ 3 H]proline incorporation, respectively.

Results:  PgR immunoreactivity was observed in nuclei of MCF7 but not periodontal ligament cells. Treatment with estrogen (17β‐estradiol, E 2 ) at physiological concentrations for 24 h stimulated DNA synthesis by more than two times in MCF7 cells, whereas there was no effect on periodontal ligament cell DNA synthesis. The ER blocker ICI 182780 fully reversed the stimulatory effect of E 2 . Not only short‐term (24 h) but also long‐term (5 days) treatment with E 2 lacked effect on DNA synthesis in periodontal ligament cells. Neither periodontal ligament cell viability nor collagen synthesis was affected by E 2 treatment. Identical results were observed in periodontal ligament cells from male and female subjects.

Conclusions:  Human MCF7 but not periodontal ligament cells express PgR, suggesting that progesterone via PgR affects MCF7 but not periodontal ligament cells. Further, estrogen stimulates breast cancer MCF7 cell proliferation, whereas it has no effect on proliferation of periodontal ligament cells, probably reflecting cell type specific ER expression pattern in these two cell types.