Functional Significance of Estrogen Receptors in Periodontal Ligament Cells

Objectives: Several studies have addressed the association between changes in estrogen and progesterone levels and changes in parameters of periodontitis. The purpose of this project is to investigate how estrogen affects the properties of periodontal ligament cells (PDL cells) and thereby the structure and function of the periodontal ligament. Methods: PDL cells were obtained from teeth extracted for orthodontic reasons. The cells were cultured from periodontal tissue explants and used in passages 3-5. Estrogen (ER) expression was investigated by immunocytochemistry. Subcellular distribution of ERb was determined using co-staining with ERb antibody and the mitochondrion selective probe MitoTracker. Expression of mitochondrial proteins was investigated using Western blotting. DNA and collagen synthesis was measured using incorporation of radioactive thymidine and proline, respectively. Cytokine expression was investigated using ELISA. Results: ERb but not ERa immunoreactivity was observed in the PDL cells. Preliminary results show that ERb is distributed not only in the nucleus but also in the mitochondria. Estrogen increased DNA synthesis in human breast cancer cells but had no effect on PDL cell DNA or collagen synthesis. Conclusion: Human PDL cells express ERb suggesting that estrogen affects PDL cellular function via this ER subtype. Estrogen has no effect on DNA and collagen synthesis, showing that estrogen has no beneficial effect on the periodontium via this mechanism. Instead estrogen via ERb acts on the periodontium via another still unknown mechanism, perhaps via regulation of mitochondrial function or cytokine production.