Yoshihiro Morita

Resveratrol promotes expression of SIRT1 and StAR in rat ovarian granulosa cells: An implicative role of SIRT1 in the ovary

BackgroundResveratrol is a natural polyphenolic compound known for its beneficial effects on energy homeostasis, and it also has multiple properties, including anti-oxidant, anti-inflammatory, and anti-tumor activities. Recently, silent information regulator genes (Sirtuins) have been identified as targets of resveratrol. Sirtuin 1 (SIRT1), originally found as an NAD+-dependent histone deacetylase, is a principal modulator of pathways downstream of calorie restriction, and the activation of SIRT1 ameliorates glucose homeostasis and insulin sensitivity. To date, the presence and physiological role of SIRT1 in the ovary are not known. Here we found that SIRT1 was localized in granulosa cells of the human ovary.MethodsThe physiological roles of resveratrol and SIRT1 in the ovary were analyzed. Immunohistochemistry was performed to localize the SIRT1 expression. SIRT1 protein expression of cultured cells and luteinized human granulosa cells was investigated by Western blot. Rat granulosa cells were obtained from diethylstilbestrol treated rats. The cells were treated with increasing doses of resveratrol, and subsequently harvested to determine mRNA levels and protein levels. Cell viability was tested by MTS assay. Cellular apoptosis was analyzed by caspase 3/7 activity test and Hoechst 33342 staining.ResultsSIRT1 protein was expressed in the human ovarian tissues and human luteinized granulosa cells. We demonstrated that resveratrol exhibited a potent concentration-dependent inhibition of rat granulosa cells viability. However, resveratrol-induced inhibition of rat granulosa cells viability is independent of apoptosis signal. Resveratrol increased mRNA levels of SIRT1, LH receptor, StAR, and P450 aromatase, while mRNA levels of FSH receptor remained unchanged. Western blot analysis was consistent with the results of quantitative real-time RT-PCR assay. In addition, progesterone secretion was induced by the treatment of resveratrol.ConclusionsThese results suggest a novel mechanism that resveratrol could enhance progesterone secretion and expression of luteinization-related genes in the ovary, and thus provide important implications to understand the mechanism of luteal phase deficiency.

SIRT3 positively regulates the expression of folliculogenesis- and luteinization-related genes and progesterone secretion by manipulating oxidative stress in human luteinized granulosa cells.

SIRT3 is a member of the sirtuin family and has recently emerged as a vital molecule in controlling the generation of reactive oxygen species (ROS) in oocytes. Appropriate levels of ROS play pivotal roles in human reproductive medicine. The aim of the present study was to investigate SIRT3 expression and analyze the SIRT3-mediated oxidative response in human luteinized granulosa cells (GCs). Human ovarian tissues were subjected to immunohistochemical analysis to localize SIRT3 expression. Hydrogen peroxide and human chorionic gonadotropin were used to analyze the relationship between ROS and SIRT3 by quantitative RT-PCR and Western blotting. Intracellular levels of ROS were investigated by fluorescence after small interfering RNA-mediated knockdown of SIRT3 in human GCs. To uncover the role of SIRT3 in folliculogenesis and luteinization, mRNA levels of related genes and the progesterone concentration were analyzed by quantitative RT-PCR and immunoassays, respectively. We detected the expression of SIRT3 in the GCs of the human ovary. The mRNA levels of SIRT3, catalase, and superoxide dismutase 1 were up-regulated by hydrogen peroxide in both COV434 cells and human GCs and down-regulated by human chorionic gonadotropin. Knockdown of SIRT3 markedly elevated ROS generation in human GCs. In addition, SIRT3 depletion resulted in decreased mRNA expression of aromatase, 17β-hydroxysteroid dehydrogenase 1, steroidogenic acute regulatory protein, cholesterol side-chain cleavage enzyme, and 3β-hydroxysteroid dehydrogenase in GCs and thus resulted in decreased progesterone secretion. These results have the important clinical implication that SIRT3 might play a positive role in the folliculogenesis and luteinization processes in GCs, possibly by sensing and regulating the generation of ROS. Activation of SIRT3 function might help to sustain human reproduction by maintaining GCs as well as oocytes.

CCAR2 negatively regulates nuclear receptor LXRα by competing with SIRT1 deacetylase.

Liver X receptors (LXRs) monitor endogenous sterol levels to maintain whole-body cholesterol levels and regulate inflammatory responses. Recent studies have demonstrated that LXRs may inhibit cellular proliferation, but the underlying mechanism remains unclear. Cell cycle and apoptosis regulator 2 (CCAR2), previously known as DBC1/KIAA1967, is a transcriptional regulator that regulates cellular proliferation and energy metabolism by inhibiting sirtuin 1 (SIRT1) deacetylase. Based on the findings that CCAR2 regulates several nuclear receptors, including the estrogen receptors and androgen receptor, we aimed to identify the underlying mechanism of CCAR2 regulation of LXRα. We found that CCAR2 formed a complex with LXRα in a ligand-independent manner in HepG2 cells, and in vitro pull-down assays, it revealed a direct interaction between the amino terminus of CCAR2 and the AF-2 domain of LXRα. Thereby, CCAR2 attenuates the ligand-dependent transcriptional activation function of LXRα. RNA interference-mediated depletion of endogenous CCAR2 potentiated the expression of the LXRα target genes ATP-binding cassette transporter A1 and G1, and the abrogation of CCAR2 resulted in decreased cellular proliferation. Moreover, competitive immunoprecipitation studies revealed that the LXRα downregulation involves the inhibition of SIRT1-LXRα complex formation. Therefore, these results clearly indicate a novel mechanism in which CCAR2 may regulate the transcriptional activation function of LXRα due to its specific inhibition of SIRT1 and serve to regulate cellular proliferation.

The Emerging Role of FOXL2 in Regulating the Transcriptional Activation Function of Estrogen Receptor β: An Insight Into Ovarian Folliculogenesis.

Germline mutations of the fork-head transcriptional factor forkhead box L2 (FOXL2) predispose embryos to autosomal-dominant blepharophimosis–ptosis–epicanthus inversus syndrome with primary ovarian insufficiency in female patients, but the mechanisms of FOXL2 in ovarian follicular development remain elusive. Estrogens produced by ovarian granulosa cells and estrogen receptor (ER) α and ERβ play fundamental roles in ovarian pathophysiology, and a previous study revealed that ERα and ERβ physically interact with FOXL2. However, the underlying functions of these interactions have not been investigated. Herein, we report an ERβ-specific repressive function of FOXL2. Histological examination demonstrated that FOXL2 expression tends to be intense during early follicular development. Immunoprecipitation revealed that ERβ and FOXL2 interact in a ligand-independent manner. In vitro pull-down assays revealed a direct interaction between FOXL2 and the activation function (AF)-1/2 domain of ERβ. The expression of FOXL2 represses the ligand-dependent transcriptional activation of ERβ, but FOXL2 does not influence the ligand-dependent transcriptional activation of ERα. Consistent with these results, RNA interference-mediated depletion of FOXL2 stimulates the expression of the ERβ-downstream gene p450 aromatase. The convergence between FOXL2 functions and ERβ-mediated transcription in the ovary suggests the putative mechanism of FOXL2 in early-phase follicular development, which may be partially attributed to the regulation of ERβ-dependent gene expression.

HAND2‑mediated proteolysis negatively regulates the function of estrogen receptor α

A previous study demonstrated that the progesterone‑inducible HAND2 gene product is a basic helix‑loop‑helix transcription factor and prevents mitogenic effects of estrogen receptor α (ERα) by inhibiting fibroblast growth factor signalling in mouse uteri. However, whether HAND2 directly affects the transcriptional activation function of ERα remains to be elucidated. In the present study, the physical interaction between HAND2 and ERα was investigating by performing an immunoprecipitation assay and an in vitro pull‑down assay. The results demonstrated that HAND2 and ERα interacted in a ligand‑independent manner. The in vitro pull‑down assays revealed a direct interaction between HAND2 and the amino‑terminus of ERα, termed the activation function‑1 domain. To determine the physiological significance of this interaction, the role of HAND2 as a cofactor of ERα was investigated, which revealed that HAND2 inhibited the ligand‑dependent transcriptional activation function of ERα. This result was further confirmed and the mRNA expression of vascular endothelial growth factor, an ERα‑downstream factor, was decreased by the overexpression of HAND2. This inhibition of ligand‑dependent transcriptional activation function of ERα was possibly attributed to the proteasomic degradation of ERα by HAND2. These results indicate a novel anti‑tumorigenic function of HAND2 in regulating ERα‑dependent gene expression. Considering that HAND2 is commonly hypermethylated and silenced in endometrial cancer, it is hypothesized that HAND2 may serve as a possible tumor suppressor, particularly in uterine tissue.