Demonstration of mitochondrial oestrogen receptor beta and oestrogen-induced attenuation of cytochrome c oxidase subunit I expression in human periodontal ligament cells.

Objective: Periodontal ligament (PDL) cells express oestrogen receptor beta (ERbeta) protein, but cellular functions regulated by ERbeta in these cells have not been identified. In this study we determine if ERbeta 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 ERbeta was determined by confocal microscopy of cells co-stained with ERbeta 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 17beta-oestradiol.

Results: ERbeta immunoreactivity was observed both in the nuclei and the cytoplasm. MitoTracker-labelling was observed in the cytoplasm, especially in the perinuclear region, but not in the nuclei. Co-localisation of ERbeta and MitoTracker was observed in cells derived from both male and female subjects. Mitochondrial localisation of ERbeta was confirmed by immunogold electron microscopy. Cells treated with or without 17beta-oestradiol (100 nM) displayed an identical pattern of staining for mitochondria. Treatment with 100 nM 17beta-oestradiol attenuated cytochrome c oxidase subunit I expression by about 30%, while combined treatment with 17beta-oestradiol and the ER blocker ICI 182780 (10 microM) had no effect.

Conclusion: This study demonstrates mitochondrial localisation of ERbeta and oestrogen-induced decrease in the expression of cytochrome c oxidase subunit I in human PDL cells, suggesting that oestrogen probably via ERbeta influences mitochondrial function and PDL cell energy metabolism.