ERβ compensates for the absence of ERα function to promote osteoblast viability by inhibition of SOST signaling

Gonadal Hormones and Bone

In both sexes, estrogen is one of the most essential hormones for maintaining bone integrity. Also, especially in men, androgen has beneficial effects on bone independent of estrogen. However, estrogen replacement therapy for postmenopausal women increases the risk of developing breast cancer and endometrial cancer, and androgen replacement therapy for partial androgen deficiency of the aging male increases the risk of developing prostate cancer. Various mechanisms have been proposed on the effects of gonadal hormones on bone, such as effects through cytokines including IL-6 and effects on the OPG/RANKL ratio. In addition, large amounts of new information deriving from high-throughput gene expression analysis raise the possibility of multiple other effects on bone cells. Both estrogen and androgen exert their effects via the estrogen receptor (ER) or the androgen receptor (AR), which belongs to the nuclear receptor superfamily. Compounds such as selective estrogen receptor modulators (SERMs) and selective androgen receptor modulators (SARMs) also bind ER and AR, respectively. However, SERMs and SARMs alter the ER or AR structure differently from estrogen or androgen, resulting in other downstream gene responses. As a result they can exert favorable effects on bone while suppressing the undesirable actions of estrogen and androgen. Elucidation of ER and AR ligand-specific and tissue-specific gene regulation mechanisms will also provide information on the signal transduction mechanisms of other nuclear receptors and will be valuable for the development of new therapeutic agents.

Effects of 17β-Estradiol on Activity, Gene and Protein Expression of Superoxide Dismutases in Primary Cultured Human Lens Epithelial Cells

PURPOSE

Protective effects of estradiol against H₂O₂-induced oxidative stress have been demonstrated in lens epithelial cells. The purpose of this study was to investigate the effects of 17β-estradiol (E2) on the different superoxide dismutase (SOD) isoenzymes, SOD-1, SOD-2, and SOD-3, as well as estrogen receptors (ERs), ERα and ERβ, in primary cultured human lens epithelial cells (HLECs).

MATERIALS AND METHODS

HLECs were exposed to 0.1 µM or 1 µM E2 for 1.5 h and 24 h after which the effects were studied. Protein expression and immunolocalization of SOD-1, SOD-2, ERα, and ERβ were studied with Western blot and immunocytochemistry. Total SOD activity was measured, and gene expression analyses were performed for SOD1, SOD2, and SOD3.

RESULTS

Increased SOD activity was seen after 1.5 h exposure to both 0.1 µM and 1 µM E2. There were no significant changes in protein or gene expression of the different SODs. Immunolabeling of SOD-1 was evident in the cytosol and nucleus; whereas, SOD-2 was localized in the mitochondria. Both ERα and ERβ were immunolocalized to the nucleus, and mitochondrial localization of ERβ was evident by colocalization with MitoTracker. Both ERα and ERβ showed altered protein expression levels after exposure to E2.

CONCLUSIONS

The observed increase in SOD activity after exposure to E2 without accompanying increase in gene or protein expression supports a role for E2 in protection against oxidative stress mediated through non-genomic mechanisms.