Global Gene Expression in Mouse Vaginae Exposed to Diethylstilbestrol at Different Ages

New frontiers of developmental endocrinology opened by researchers connecting irreversible effects of sex hormones on developing organs

In the early 1960's, at Professor Bern's laboratory, University of California, Berkeley) in the US, Takasugi discovered ovary-independent, persistent vaginal changes in mice exposed neonatally to estrogen, which resulted in vaginal cancer later in life. Reproductive abnormalities in rodents were reported as a result of perinatal exposure to various estrogenic chemicals. Ten years later, vaginal cancers were reported in young women exposed in utero to the synthetic estrogen diethylstilbestrol (DES) and this has been called the "DES syndrome". The developing organism is particularly sensitive to developmental exposure to estrogens inducing long-term changes in various organs including the reproductive organs. The molecular mechanism underlying the persistent vaginal changes induced by perinatal estrogen exposure was partly demonstrated. Persistent phosphorylation and sustained expression of EGF-like growth factors, lead to estrogen receptor α (ESR1) activation, and then persistent vaginal epithelial cell proliferation. Agents which are weakly estrogenic by postnatal criteria may have major developmental effects, especially during a critical perinatal period. The present review outlines various studies conducted by four generations of investigators all under the influence of Prof. Bern. The studies include reports of persistent changes induced by neonatal androgen exposure, analyses of estrogen responsive genes, factors determining epithelial differentiation in the Müllerian duct, ESR and growth factor signaling, and polyovular follicles in mammals. This review is then expanded to the studies on the effects of environmental estrogens on wildlife and endocrine disruption in Daphnids.

Physiological and pathological implications of retinoid action in the endometrium

Retinol (vitamin A) and its derivatives, collectively known as retinoids, are required for maintaining vision, immunity, barrier function, reproduction, embryogenesis and cell proliferation and differentiation. Despite the fact that most events in the endometrium are predominantly regulated by steroid hormones (estrogens and progesterone), accumulating evidence shows that retinoid signaling is also involved in the development and maintenance of the endometrium, stromal decidualization and blastocyst implantation. Moreover, aberrant retinoid metabolism seems to be a critical factor in the development of endometriosis, a common gynecological disease, which affects up to 10% of reproductive age women and is characterized by the ectopic localization of endometrial-like tissue in the pelvic cavity. This review summarizes recent advances in research on the mechanisms and molecular actions of retinoids in normal endometrial development and physiological function. The potential roles of abnormal retinoid signaling in endometriosis are also discussed. The objectives are to identify limitations in current knowledge regarding the molecular actions of retinoids in endometrial biology and to stimulate new investigations toward the development potential therapeutics to ameliorate or prevent endometriosis symptoms.

Retinoic acid signaling determines the fate of uterine stroma in the mouse Müllerian duct

The Müllerian duct develops into the oviduct, uterus, and vagina, all of which are quite distinct in their morphology and function. The epithelial fate of these female reproductive organs in developing mice is determined by factors secreted from the stroma; however, how stromal differentiation occurs in the female reproductive organs derived from the Müllerian duct is still unclear. In the present study, roles of retinoic acid (RA) signaling in developing female reproductive tracts were investigated. Retinol dehydrogenase 10 (RDH10) and aldehyde dehydrogenase family 1 subfamily A2 (ALDH1A2) mRNAs and proteins and transactivation activity of endogenous RA were found in the stroma of proximal Müllerian ducts and gradually decreased from the proximal to caudal regions in fetal mice. In organ-cultured Müllerian ducts, retinaldehyde or RA treatment induced uterine epithelial differentiation, defined as a layer of columnar epithelial cells negative for oviductal and vaginal epithelial markers. In contrast, inhibition of RA receptor (RAR) signaling induced vaginal epithelial differentiation, characterized as vaginal epithelial marker genes-positive stratified epithelium. Grafting experiments of the organ-cultured Müllerian duct revealed irreversible epithelial fate determination. Although RAR did not directly bind to the homeobox A10 (Hoxa10) promoter region, RA-RAR signaling stimulated Hoxa10 expression. Thus, RA-RAR signaling in the Müllerian duct determines the fate of stroma to form the future uterus and vagina.

Immune maintenance of self in morphostasis of distinct tissues, tumour growth and regenerative medicine

Morphostasis (tissue homeostasis) is a complex process consisting of three circumstances: (1) tissue renewal from stem cells, (2) preservation of tissue cells in a proper differentiated state and (3) maintenance of tissue quantity. This can be executed by a tissue control system (TCS) consisting of vascular pericytes, immune system-related components--monocyte-derived cells (MDC), T cells and immunoglobulins and autonomic innervation. Morphostasis is established epigenetically, during the critical developmental period corresponding to the morphogenetic immune adaptation. Subsequently, the tissues are maintained in a state of differentiation reached during the adaptation by a 'stop effect' of MDC influencing markers of differentiating tissue cells and presenting self-antigens to T cells. Retardation or acceleration of certain tissue differentiation during adaptation results in its persistent functional immaturity or premature ageing. The tissues being absent during adaptation, like ovarian corpus luteum, are handled as a 'graft.' Morphostasis is altered with age advancement, because of the degenerative changes of the immune system. That is why the ageing of individuals and increased incidence of neoplasia and degenerative diseases occur. Hybridization of tumour stem cells with normal tissue cells causes an augmentation of neoplasia by host pericytes and MDC stimulating a 'regeneration' of depleted functional cells. Degenerative diseases are associated with apoptosis. If we are able to change morphostasis in particular tissue, we may disrupt apoptotic process of the cell. An ability to manage the 'stop effect' of MDC may provide treatment for early post-natal tissue disorders, improve regenerative medicine and delay physical, mental and hormonal ageing.

Identification of uterine leiomyoma genes developmentally reprogrammed by neonatal exposure to diethylstilbestrol

Environmental exposures during development can alter susceptibility later in life to adult diseases including uterine leiomyoma, a phenomenon termed developmental reprogramming. The goal of this study was to identify genes developmentally reprogrammed by diethylstilbestrol (DES) and aberrantly expressed in leiomyomas. Transcriptional profiling identified 171 genes differentially expressed in leiomyomas relative to normal myometrium, of which 6/18 genes with putative estrogen responsive elements and confirmed to be estrogen-responsive in neonatal uteri were reprogrammed by neonatal DES exposure. Calbindin D9k and Dio2, normally induced by estrogen, exhibited elevated expression in DES-exposed animals during both phases of the estrus cycle. Gdf10, Car8, Gria2, and Mmp3, genes normally repressed by estrogen, exhibited elevated expression in DES-exposed animals during the proliferative phase, when estrogen is highest. These data demonstrate that neonatal DES exposure causes reprogramming of estrogen-responsive genes expressed in uterine leiomyomas, leading to over-expression of these genes in the myometrium of exposed animals prior to the onset of tumorigenesis.

Molecular analysis of the vaginal response to estrogens in the ovariectomized rat and postmenopausal woman

Background

Vaginal atrophy (VA) is the thinning of the vaginal epithelial lining, typically the result of lowered estrogen levels during menopause. Some of the consequences of VA include increased susceptibility to bacterial infection, pain during sexual intercourse, and vaginal burning or itching. Although estrogen treatment is highly effective, alternative therapies are also desired for women who are not candidates for post-menopausal hormone therapy (HT). The ovariectomized (OVX) rat is widely accepted as an appropriate animal model for many estrogen-dependent responses in humans; however, since reproductive biology can vary significantly between mammalian systems, this study examined how well the OVX rat recapitulates human biology.

Methods

We analyzed 19 vaginal biopsies from human subjects pre and post 3-month 17β-estradiol treated by expression profiling. Data were compared to transcriptional profiling generated from vaginal samples obtained from ovariectomized rats treated with 17β-estradiol for 6 hrs, 3 days or 5 days. The level of differential expression between pre- vs. post- estrogen treatment was calculated for each of the human and OVX rat datasets. Probe sets corresponding to orthologous rat and human genes were mapped to each other using NCBI Homologene.

Results

A positive correlation was observed between the rat and human responses to estrogen. Genes belonging to several biological pathways and GO categories were similarly differentially expressed in rat and human. A large number of the coordinately regulated biological processes are already known to be involved in human VA, such as inflammation, epithelial development, and EGF pathway activation.

Conclusion

At the transcriptional level, there is evidence of significant overlap of the effects of estrogen treatment between the OVX rat and human VA samples.

Toxicogenomics and ecotoxicogenomics for studying endocrine disruption and basic biology

Chemicals released into the environment have the potential to disrupt the endocrine system in wild animals, mouse, and humans. To understand molecular mechanisms of chemical toxicity in various species, toxicogenomics/ecotoxicogenomics, describing the integration of genomics (trascriptomics, proteomics and metabolomics) into toxicology/ecotoxicology, needs to be established as a powerful tool for research. Ecotoxicogenomics is defined as the study of gene and protein expression in non-target organisms that is important in responses to environmental toxicant exposures. Estrogen-responsive genes and estrogen response element(s) in genes have been identified in the mouse reproductive tract by application of cDNA microarray technology. Additionally, functional mechanisms of tributyltin action via nuclear receptors such as retinoid X receptor alpha and peroxisome proliferator activated receptor gamma also have been identified using cDNA microarray. A microarray system has been established for Daphnia magna. Toxicogenomics/ecotoxicogenomics provide powerful tools to help us understand not only molecular mechanisms of chemical toxicity but also the basic biology of various animal species.

Immunoneutralization of endometrial monoclonal nonspecific suppressor factor beta (MNSFβ) inhibits mouse embryo implantation in vivo

Successful embryo implantation and pregnancy in mammals depends on the establishment of immune tolerance between the maternal immune system and fetal cells. Monoclonal nonspecific suppressor factor beta (MNSFbeta), a cytokine produced by suppressor T cells in various tissues, possesses an antigen-nonspecific immune-suppressive function, and may be involved in the regulation of the uterine immune response during embryo implantation. In this study, anti-MNSFbeta IgG administered directly into the uterine lumen, significantly inhibited mouse embryo implantation in a dose-dependent manner in vivo, and this effect was reversed by co-administration of recombinant MNSFbeta. The effects of anti-MNSFbeta IgG on the gene pattern profiles in mouse uterine tissues were examined by cDNA microarray and several changes were confirmed by real-time PCR. Anti-MNSFbeta IgG caused up-regulation (> or = 2-fold) of 71 known genes and 17 unknown genes, and decreased expression (> or = 2-fold) of 74 known genes and 43 unknown genes, including several genes previously associated with embryo implantation or fetal development. Most of the known genes are involved in immune regulation, cell cycle/proliferation, cell differentiation/apoptosis, and lipid/glucose metabolism. These results demonstrate that MNSFbeta plays critical roles during the early pregnancy via multiple pathways.