Transcriptional repression of the Ahr gene by LHCGR signaling in preovulatory granulosa cells is controlled by chromatin accessibility

Endoplasmic Reticulum Stress: A New Research Direction for Polycystic Ovary Syndrome?

Polycystic ovary syndrome (PCOS) is one of the most common gynecological endocrine disorders, with sporadic ovulation, excessive androgens, and polycystic ovarian changes as the main clinical manifestations. Due to the high heterogeneity of its clinical manifestations, the discussion on its pathogenesis has not been unified. Current research has found that genetic factors, hyperandrogenism, chronic inflammation and oxidative stress, insulin resistance, and obesity are strongly associated with PCOS. Recently, when studying the specific mechanisms of the abovementioned factors in PCOS, the biological response process of endoplasmic reticulum stress (ERS) has gradually come to researchers' attention, and several studies have confirmed the involvement of ERS in the pathogenesis of PCOS and the improvement of a series of pathological manifestations of PCOS after the application of ERS inhibitors, which may be a new entry point for the treatment of PCOS. In this article, we review the relationship between ERS and various pathogenic factors of PCOS.

Induction of aryl hydrocarbon receptor in granulosa cells by endoplasmic reticulum stress contributes to pathology of polycystic ovary syndrome

Recent studies have uncovered the critical role of aryl hydrocarbon receptor (AHR) in various diseases, including obesity and cancer progression, independent of its previously identified role as a receptor for endocrine-disrupting chemicals (EDCs). We previously showed that endoplasmic reticulum (ER) stress, a newly recognized local factor in the follicular microenvironment, is activated in granulosa cells from patients with polycystic ovary syndrome (PCOS) and a mouse model of the disease. By affecting diverse functions of granulosa cells, ER stress contributes to PCOS pathology. We hypothesized that expression of AHR and activation of its downstream signaling were upregulated by ER stress in granulosa cells, irrespective of the presence of EDCs, thereby promoting PCOS pathogenesis. In this study, we found that AHR, AHR nuclear translocator (ARNT), and AHR target gene cytochrome P450 1B1 (CYP1B1) were upregulated in the granulosa cells of PCOS patients and model mice. We examined CYP1B1 as a representative AHR target gene. AHR and ARNT were upregulated by ER stress in human granulosa-lutein cells (GLCs), resulting in an increase in the expression and activity of CYP1B1. Administration of the AHR antagonist CH223191 to PCOS mice restored estrous cycling and decreased the number of atretic antral follicles, concomitant with downregulation of AHR and CYP1B1 in granulosa cells. Taken together, our findings indicate that AHR activated by ER stress in the follicular microenvironment contributes to PCOS pathology, and that AHR represents a novel therapeutic target for PCOS.

Kynurenine promotes the cytotoxicity of NK cells through aryl hydrocarbon receptor in early pregnancy

During early pregnancy, decidual NK (dNK) cells play indispensable roles in many processes including the decidualization, the implantation, and the maintenance of immune tolerance. Abnormal cytotoxic activity of NK cells can cause recurrent spontaneous abortion (RSA), while the regulatory mechanism of NK cytotoxicity remains to be unclear. In this study, we found that kynurenine in decidua and villus was in a comparable level between patients with RSA and normal pregnancy women. However, the aryl hydrocarbon receptor (AhR) in decidual NK cells was significantly increased in RSA. Compared with AhR^- NK cells, cytotoxic activity-related molecules (NKP30, NKP46, NKG2D, perforin, granzyme B and IFN-γ) was highly expressed in both AhR⁺ peripheral and decidual NK cells, and kynurenine stimulation promoted the expression of killer receptors and the cytoplasmic granules in an AhR-dependent manner. Stimulation with TNF-α, IL-β and LPS upregulated the AhR expression in dNK cells in vitro. These results indicate that kyn/AhR signal enhances the cytotoxicity of NK cells, and increased expression of AhR may be an induction factor of RSA.

Impact of AHR Ligand TCDD on Human Embryonic Stem Cells and Early Differentiation

Aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor, which mediates the effects of a variety of environmental stimuli in multiple tissues. Recent advances in AHR biology have underlined its importance in cells with high developmental potency, including pluripotent stem cells. Nonetheless, there is little data on AHR expression and its role during the initial stages of stem cell differentiation. The purpose of this study was to investigate the temporal pattern of AHR expression during directed differentiation of human embryonic stem cells (hESC) into neural progenitor, early mesoderm and definitive endoderm cells. Additionally, we investigated the effect of the AHR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the gene expression profile in hESCs and differentiated cells by RNA-seq, accompanied by identification of AHR binding sites by ChIP-seq and epigenetic landscape analysis by ATAC-seq. We showed that AHR is differentially regulated in distinct lineages. We provided evidence that TCDD alters gene expression patterns in hESCs and during early differentiation. Additionally, we identified novel potential AHR target genes, which expand our understanding on the role of this protein in different cell types.

Age-dependent vulnerability of the ovary to AhR-mediated TCDD action before puberty: Evidence from mouse models

In female mammals, puberty and fertility are regulated by the synthesis of estradiol (E2) by the ovaries at the infantile stage and at the approach of puberty, a process which may be affected by endocrine disrupting chemicals (EDC)s acting through the Aryl hydrocarbon receptor (AhR). However, there is no information on AhR-mediated regulation of ovarian estrogenic activity during these developmental periods. Here, we assessed in mouse models, the intrinsic and exogenous ligand-induced AhR action on E2 synthesis at the infantile stage (14 days postnatal (dpn)) and at the approach of puberty (28 dpn). Intrinsic AhR pathway became activated in the ovary at the approach of puberty, as suggested by the decreased intra-ovarian expression in prototypical and steroidogenesis-related AhR targets and E2 contents in Ahr knockout (Ahr^-/-) mice versus Ahr^+/+ mice exclusively at 28 dpn. Accordingly, AhR nuclear localization in granulosa cells, reflecting its activity in cells responsible for E2 synthesis, was much lower at 14 dpn than at 28 dpn in C57BL/6 mice. However, AhR signaling could be activated by exogenous ligands at both ages, as revealed by FICZ- and TCDD-induced Ahrr and Cyp1a1 expression in C57BL/6 mice. Nevertheless, TCDD impacted ovarian estrogenic activity only at 28 dpn. This age-related AhR action may be ligand-dependent, since FICZ had no effect on E2 synthesis at 28 dpn. In conclusion, AhR would not regulate ovarian estrogenic activity before the approach of puberty. Its activation by EDCs may be more detrimental to reproductive health at this stage than during infancy.

Global analysis of FSH-regulated gene expression and histone modification in mouse granulosa cells

Follicle-stimulating hormone (FSH) regulates ovarian follicular development through a specific gene expression program. We analyzed FSH-regulated transcriptome and histone modification in granulosa cells during follicular development. We used super-stimulated immature mice and collected granulosa cells before and 48 h after stimulation with equine chorionic gonadotropin (eCG). We profiled the transcriptome using RNA-sequencing (N = 3/time-point) and genome-wide trimethylation of lysine 4 of histone H3 (H3K4me3; an active transcription marker) using chromatin immunoprecipitation and sequencing (ChIP-Seq; N = 2/time-point). Across the mouse genome, 14,583 genes had an associated H3K4me3 peak and 63-66% of these peaks were observed within ≤1 kb promoter region. There were 72 genes with differential H3K4me3 modification at 48 h eCG (absolute log fold change > 1; false discovery rate [FDR] < 0.05) relative to 0 h eCG. Transcriptome data analysis showed 1463 differentially expressed genes at 48 h eCG (absolute log fold change > 1; FDR < 0.05). Among the 20 genes with differential expression and altered H3K4me3 modification, Lhcgr had higher H3K4me3 abundance and expression, while Nrip2 had lower H3K4me3 abundance and expression. Using ChIP-qPCR, we showed that FSH-regulated expression of Lhcgr, Cyp19a1, Nppc, and Nrip2 through regulation of H3K4me3 at their respective promoters. Transcript isoform analysis using Kallisto-Sleuth tool revealed 875 differentially expressed transcripts at 48 h eCG (b > 1; FDR < 0.05). Pathway analysis of RNA-seq data demonstrated that TGF-β signaling and steroidogenic pathways were regulated at 48 h eCG. Thus, FSH regulates gene expression in granulosa cells through multiple mechanisms namely altered H3K4me3 modification and inducing specific transcripts. These data form the basis for further studies investigating how these specific mechanisms regulate granulosa cell functions.

Environmental Influences and Polycystic Ovarian Syndrome

Polycystic ovarian syndrome (PCOS) is a complex endocrine-metabolic disorder whose pathogenesis is not well-understood. While genetic insults have been hypothesized as possible causes, there are a large number of environmental chemicals known to have detrimental effects on the endocrine system and may be irreversible, especially when exposure occurs early in development. Many of these chemicals have been investigated as causes of PCOS by measuring serum and urinary levels of common endocrine disruptors in women and adolescents with PCOS as well as using animal models for PCOS induction with chemical exposures.

FSH/LH-Dependent Upregulation of Ahr in Murine Granulosa Cells Is Controlled by PKA Signaling and Involves Epigenetic Regulation

The aryl hydrocarbon receptor (Ahr) is a ligand-activated transcription factor primarily known for its toxicological functions. Recent studies have established its importance in many physiological processes including female reproduction, although there is limited data about the precise mechanisms how Ahr itself is regulated during ovarian follicle maturation. This study describes the expression of Ahr in ovarian granulosa cells (GCs) of immature mice in a gonadotropin-dependent manner. We show that Ahr upregulation in vivo requires both follicle stimulating hormone (FSH) and luteinizing hormone (LH) activities. FSH alone increased Ahr mRNA, but had no effect on Ahr protein level, implicating a possible LH-dependent post-transcriptional regulation. Also, the increase in Ahr protein is specific to large antral follicles in induced follicle maturation. We show that Ahr expression in GCs of mid-phase follicular maturation is downregulated by protein kinase A (PKA) signaling and activation of Ahr promoter is regulated by chromatin remodeling.

Aryl hydrocarbon receptor and unexplained miscarriage

AIM

The aim of this study was to carry out a preliminary investigation of the expression of aryl hydrocarbon receptor (AhR) in decidua and villus and the relationship between AhR and unexplained miscarriage.

METHODS

The expression of AhR mRNA and protein from decidua and villus were measured using real-time reverse transcription-polymerase chain reaction, western blot and immunohistochemistry in 34 patients with unexplained miscarriage (miscarriage group) and 38 women with normal early pregnancy (control group).

RESULTS

The AhR mRNA and protein expression was increased significantly in the villus in both groups compared with decidua (P < 0.05, P < 0.05). In decidua, AhR mRNA and protein expression in the miscarriage group was increased significantly compared with the control group (P < 0.05, P < 0.05). In villus, AhR mRNA and protein expression in the miscarriage group was increased significantly compared with the control group (P < 0.05, P < 0.05). AhR is expressed mostly in the cytoplasm of syncytiotrophoblasts in villus, and also in the cytoplasm of decidual cells.

CONCLUSIONS

AhR was expressed more in the villus than in the decidua, and the upregulation of AhR mRNA and protein expression is associated with the pathogenesis of unexplained miscarriage.

Are aryl hydrocarbon receptor and G-protein-coupled receptor 30 involved in the regulation of seasonal testis activity in photosensitive rodent-the bank vole (Myodes glareolus)?

Within the reproductive system both aryl hydrocarbon receptor (AHR) and G-protein-coupled receptor 30 (GPR30) contribute to estrogen signaling and controlling of reproductive physiology. The specific question is whether and how AHR and GPR30 are involved in regulation of testis function in seasonally breeding rodents. Bank vole testes were obtained from animals reared under 18 hours light:6 hours dark (LD) and 6 hours light:18 hours dark (SD) conditions. Aryl hydrocarbon receptor and GPR30 expression were analyzed by quantitative reverse transcriptase-polymerase chain reaction, Western blot, and immunohistochemistry and/or immunofluorescent staining. In addition, the activity of enzymes involved in the intracellular signal transduction; extracellular signal-regulated kinase (ERK), protein kinase (PKA), matrix metalloproteinase 9 (MMP 9) and the concentrations of cyclic adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP), and calcium (Ca(2+)) were examined by immunohistochemical, immunoenzymatic, and colorimetric assays, respectively. Aryl hydrocarbon receptor and GPR30 were expressed in testes of actively reproducing voles and regressed ones although their expression at the messenger RNA and AHR also at protein level appeared to be photoperiod-dependent. A specific cellular localization and expression of AHR and GPR30 correlated with the expression of ERK, PKA, and MMP 9. Moreover, we found robust differences in the levels of cAMP, cGMP, and Ca(2+) in testicular homogenates between LD and SD voles. In the testes of LD voles, the levels of second messengers were always higher compared to SD. In vole testis, AHR and GPR30 can induce signaling pathways that involve ERK, PKA, MMP 9 and cAMP, cGMP, Ca(2+). In addition, in AHR, signaling the engagement of both photoperiod and estrogens, whereas in GPR30, signaling only estrogens is reported. It is likely that in vole, because of a differential activity of signaling molecules, signal transduction via AHR rather than through GPR30 plays a role in regulation of seasonal changes of testis physiology.

Association of serum levels of typical organic pollutants with polycystic ovary syndrome (PCOS): a case-control study

STUDY QUESTION

Is polycystic ovary syndrome (PCOS) associated with increased serum levels of typical organic pollutants?

SUMMARY ANSWER

PCOS in Han females from Northern China was significantly associated with elevated serum levels of pollutants, including polychlorinated biphenyls (PCBs), organochlorine pesticides and polycyclic aromatic hydrocarbons (PAHs).

WHAT IS KNOWN ALREADY

PCOS is arguably the most common endocrinopathy in females of reproductive age. The etiology of PCOS is thought to be multifactorial.

STUDY DESIGN, SIZE, DURATION

This was a preliminary case-control study undertaken at the Division of Reproductive Center, Peking University Third Hospital. Fifty participants affected by PCOS and 30 normal controls were recruited between August and October 2012 from Northern China. All participants were Han women.

PARTICIPANTS/MATERIALS, SETTING, METHODS

PCOS participants were diagnosed according to the 2003 Rotterdam criteria. The control participants were non-pregnant females unable to conceive solely due to male azoospermia. Serum levels of a wide range of organic pollutants, including PCBs, organochlorine pesticides, PAHs and more than 20 phenolic pollutants, were analyzed using gas chromatographic mass spectrometry.

MAIN RESULTS AND THE ROLE OF CHANCE

Serum levels of PCBs, pesticides and PAHs were significantly higher in the PCOS group than the control group. Concentrations of PCBs, p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) and PAHs in serum above median levels were associated with PCOS with odds ratios of 3.81 [95% confidence interval (CI), 1.45-10.0], 4.89 (95% CI, 1.81-13.2) and 2.39 (95% CI, 0.94-6.05), respectively. Partial least-squares-discriminant analysis (PLS-DA) confirmed that serum levels of organic pollutants were associated with PCOS, especially for p,p'-DDE and PCBs.

LIMITATIONS, REASONS FOR CAUTION

Some other possible covariates (e.g. dietary and income) were missed in this study, although education and occupation have been considered as an indicator of personal income. The PLS-DA model allowed a quasi-exposome analysis with over 60 kinds of typical organic pollutants; however, the possibility of other pollutants involved in the PCOS still could not be excluded.

WIDER IMPLICATIONS OF THE FINDINGS

Our study identified that bodily retention of environmental organic pollutants-including PCBs, pesticides (especially p,p'-DDE) and PAHs-was associated with PCOS.

STUDY FUNDING/COMPETING INTERESTS

This research was supported by the Ministry of Science and Technology of China Grants (973 program; 2014CB943203 and 2015CB553401), National Natural Science Foundation of China (21322705, 21190051, 41121004 and 81170538), National Key Technology R&D Program in the Twelve Five-Year Plan (2012BAI32B01) and the Collaborative Innovation Center for Regional Environmental Quality. There are no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

None. This is not a clinical trial.