Epigenetics in reproductive medicine

Epigenetics and the role of nutraceuticals in health and disease

In the post-genomic era, the data provided by complete genome sequencing could not answer several fundamental questions about the causes of many noninfectious diseases, diagnostic biomarkers, and novel therapeutic approaches. The rapidly expanding understanding of epigenetic mechanisms, as well as widespread acceptance of their hypothesized role in disease induction, facilitated the development of a number of novel diagnostic markers and therapeutic concepts. Epigenetic aberrations are reversible in nature, which enables the treatment of serious incurable diseases. Therefore, the interest in epigenetic modulatory effects has increased over the last decade, so about 60,000 publications discussing the expression of epigenetics could be detected in the PubMed database. Out of these, 58,442 were published alone in the last 10 years, including 17,672 reviews (69 historical articles), 314 clinical trials, 202 case reports, 197 meta-analyses, 156 letters to the editor, 108 randomized controlled trials, 87 observation studies, 40 book chapters, 22 published lectures, and 2 clinical trial protocols. The remaining publications are either miscellaneous or a mixture of the previously mentioned items. According to the species and gender, the publications included 44,589 human studies (17,106 females, 14,509 males, and the gender is not mentioned in the remaining papers) and 30,253 animal studies. In the present work, the role of epigenetic modulations in health and disease and the influencing factors in epigenetics are discussed.

Altered GNAS imprinting due to folic acid deficiency contributes to poor embryo development and may lead to neural tube defects

Disturbed epigenetic modifications have been linked to the pathogenesis of Neural Tube Defects (NTDs) in those with folate deficiency during pregnancy. However, evidence is lacking to delineate the critical region in epigenome regulated by parental folic acid and mechanisms by which folate deficiency affects normal embryogenesis. Our data from clinical samples revealed the presence of aberrant DNA methylation in GNAS imprinting cluster in NTD samples with low folate concentrations. Results from mouse models indicated that the establishment of GNAS imprinting was influenced by both maternal and paternal folate-deficient diets. Such aberrant GNAS imprinting was present prior to the gametogenesis period. Imprinting in Exon1A/GNAS gDMR was abolished in both spermatozoa and oocytes upon treating with a parental folate-deficient diet (3.6% in spermatozoa, 9.8% in oocytes). Interestingly, loss of imprinting in the GNAS gene cluster altered chromatin structure to an overwhelmingly open structure (58.48% in the folate-free medium group vs. 39.51% in the folate-normal medium group; P < 0.05), and led to a disturbed expression of genes in this region. Furthermore, an elevated cyclic AMP levels was observed in folate acid deficiency group. Our results imply that GNAS imprinting plays major roles in folic acid metabolism regulation during embryogenesis. Aberrant GNAS imprinting is an attribute to NTDs, providing a new perspective for explaining the molecular mechanisms by which folate supplementation in human pregnancy provides protection from NTDs.

Correlation of hypertensive disorders in pregnancy with procedures of in vitro fertilization and pregnancy outcomes

We investigated the correlation of hypertensive disorders in pregnancy with different procedures of in vitro fertilization, and analyzed pregnancy outcomes of patients with hypertensive disorders in pregnancy. A retrospective analysis was performed on the medical records of 658 maternity patients who conceived through in vitro fertilization in Maternal and Child Health Hospital of Wuxi. Patients were divided into two groups according to different fertilization procedures: i) the routine in vitro fertilization-embryo transfer group (IVF-ET group, 377 cases) and ii) intra-cytoplasmic sperm injection-embryo transfer group (ICSI-ET group, 281 cases). Consequently, patients were further divided into two groups according to different embryo transfer cycles: the fresh embryo transfer group (F-ET group, 446 cases) and the frozen-thawed embryo transfer group (T-ET group, 212 cases). Characteristics of patients in each group were evaluated, and incidence of hypertensive disorders in pregnancy resulting from different assisted reproductive technology was compared. Among patients who conceived through IVF, there were 56 cases of hypertensive disorders in pregnancy, including 21 cases of gestational hypertension, 34 cases of pre-eclampsia and 1 case of eclampsia. The odds ratio (OR) of gestational hypertension in the comparison between the ICSI-ET and IVF-ET groups was 2.01 (0.81-4.74), and was reduced to 1.69 (0.70-4.02) after correction. The difference of OR in twin-birth patients of the two groups was statistically significant, but the difference in single-birth patients was not statistically significant. The odds ratio (OR) of gestational hypertension in the comparison between the F-ET and T-ET groups was 0.44 (0.13-1.34), and became 0.49 (0.15-1.51) after correction. The odds ratio of pre-eclampsia in the comparison between the ICSI-ET and IVF-ET groups was 1.36 (0.42-4.18), and was reduced to 1.17 (0.36-3.62) after correction. The odds ratio of pre-eclampsia in the comparison between the F-ET and T-ET groups was 0.93 (0.42-1.96), and became 0.98 (0.44-2.12) after correction. The differences were not statistically significant. The risk of onset of hypertensive disorders in pregnancy has a certain correlation with the ICSI fertilization technology, but has no apparent correlation with embryo transfer cycles.

DNA methylation in spermatogenesis and male infertility

Infertility is a significant problem for human reproduction, with males and females equally affected. However, the molecular mechanisms underlying male infertility remain unclear. Spermatogenesis is a highly complex process involving mitotic cell division, meiosis cell division and spermiogenesis; during this period, unique and extensive chromatin and epigenetic modifications occur to bring about specific epigenetic profiles in spermatozoa. It has recently been suggested that the dysregulation of epigenetic modifications, in particular the methylation of sperm genomic DNA, may serve an important role in the development of numerous diseases. The present study is a comprehensive review on the topic of male infertility, aiming to elucidate the association between sperm genomic DNA methylation and poor semen quality in male infertility. In addition, the current status of the genetic and epigenetic determinants of spermatogenesis in humans is discussed.

Effects of different oocyte retrieval and in vitro maturation systems on bovine embryo development and quality

Cyclic adenosine monophosphate (cAMP) modulators have been used to avoid spontaneous oocyte maturation and concomitantly improve oocyte developmental competence. The current work evaluated the effects of the addition of cAMP modulators forskolin, 3-isobutyl-1-methylxanthine (IBMX) and cilostamide during in vitro maturation on the quality and yields of blastocysts. The following experimental groups were evaluated: (i) slicing or (ii) aspiration and maturation in tissue culture medium (TCM)199 for 24 h (TCM24slicing and TCM24aspiration, respectively), (iii) aspiration and maturation in the presence of cAMP modulators for 30 h (cAMP30aspiration) and in vivo-produced blastocysts. In vitro-matured oocytes were fertilized and presumptive zygotes were cultured in vitro to assess embryo development. Cleavage, blastocyst formation, blastocyst cell number, mRNA abundance of selected genes and global methylation profiles were evaluated. Blastocyst rate/zygotes for the TCM24aspiration protocol was improved (32.2 ± 2.1%) compared with TCM24slicing and cAMP30aspiration (23.4 ± 1.2% and 23.3 ± 2.0%, respectively, P<0.05). No statistical differences were found for blastocyst cell numbers. The mRNA expression for the EGR1 gene was down-regulated eight-fold in blastocysts that had been produced in vitro compared with their in vivo counterparts. Gene expression profiles for IGF2R, SLC2A8, COX2, DNMT3B and PCK2 did not differ among experimental groups. Bovine testis satellite I and Bos taurus alpha satellite methylation profiles from cAMP30aspiration protocol-derived blastocysts were similar to patterns that were observed in their in vivo equivalents (P > 0.05), while those from the other groups were significantly elevated. It is concluded that retrieval, collection systems and addition of cAMP modulators can affect oocyte developmental competence, which is reflected not only in blastocyst rates but also in global DNA methylation and gene expression patterns.

Partial hydatidiform mole diagnosis in a cat: a case report

A case of a stillborn Norwegian Forest kitten characterised in the course of anatomopathological and genetic examination is reported. The hydatidiform mole was diagnosed by delayed development, low birth weight of the kitten and abnormal placental development. Anatomopathological diagnosis was confirmed in genetic tests based on the amplification of highly heterozygous microsatellite sequences located on the X (FCA311) and autosomal chromosomes (FCA506, FCA532 and FCA178), as well as the sex-specific Sry and amelogenin (Amel) genes. The presence of two microsatellite alleles of paternal origin and one allele of maternal origin was observed in all analysed tissues (kidney, liver, brain, heart and spleen) of the stillborn kitten. The kitten's sex was diagnosed by the presence of the paternal Sry gene, and maternal and paternal products of Amel, as well as one maternal and one paternal X chromosome FCA311 microsatellite allele. The results thus confirmed that the haploid egg was fertilised by two sperm, yielding a triploid karyotype. In summary, the successful application of genetic markers in postnatal diagnosis of this condition in the cat confirms considerable usefulness of these techniques, especially in cases where cytogenetic diagnosis is insufficient or impossible.

Cytoplasmic inheritance redux

Since the early twentieth century, inheritance was seen as the inheritance of genes. Concurrent with the acceptance of the genetic theory of inheritance was the rejection of the idea that the cytoplasm of the oocyte could also play a role in inheritance and a corresponding devaluation of embryology as a discipline critical for understanding human development. Development, and variation in development, came to be viewed solely as matters of genetic inheritance and genetic variation. We now know that inheritance is a matter of both genetic and cytoplasmic inheritance. A growing awareness of the centrality of the cytoplasm in explaining both human development and phenotypic variation has been promoted by two contemporaneous developments: the continuing elaboration of the molecular mechanisms of epigenetics and the global rise of artificial reproductive technologies. I review recent developments in the ongoing elaboration of the role of the cytoplasm in human inheritance and development.

Ovarian function is restored after grafting of cryopreserved immature ovary in ewes

As a result of advances in medical treatment, almost 80% of children who are diagnosed with cancer survive long-term. The adverse consequences of cancer treatments include impaired puberty and fertility. In prepubertal girls, the only therapeutic option is the cryopreservation of an ovary. To date, a dozen births have been reported after reimplantation of cryopreserved mature ovaries. To analyze ovarian function after immature grafts, we performed ovarian grafting in a ewe model. Fresh or cryopreserved ovaries from immature ewes were autografted in prepubertal or adult ewes. Cyclic hormonal activity was recovered 3 mo after grafting. Histological analysis demonstrated the presence of all follicle populations and corpora lutea not affected by cryopreservation. After 3 reproductive seasons, births had been observed in all groups, and the follicle-stimulating hormone status was under the limit, which indicated an exhausted ovary. As an indicator of potential imprinting default, the methylation status of the Igf2r gene was analyzed and did not show significant alteration compared with that of nonmanipulated animals. Taken together, these results demonstrate that immature ovarian grafting is able to restore spontaneous puberty and fertility and could guide the reimplantation of immature cortex in women.

Application of a NotI subtraction and methylation‑specific genome subtractive hybridization technique in the detection of genomic DNA methylation differences between hydatidiform moles and villi

Previous studies indicate that epigenetic modifications play an important role in transcriptional regulation and contribute to the pathogenesis of gestational trophoblastic disease, including complete hydatidiform moles (CHMs). However, the underlying mechanisms and the critical genes have not been clearly identified. In the present study, we developed a novel technique, NotI subtraction and methylation-specific genome subtractive hybridization (MS-G-SH), as a method of screening for methylation changes between hydatidiform moles and villi. Following NotI subtraction and hybridization, three different positive DNA clones were found in 110 random clones of DNA samples. Most importantly, two DNA clones having long CpG islands and high homology with exons of insulin-like growth factor 2 (IGF2) and transforming growth factor-β (TGF-β) were identified using bioinformatic tools. After bisulfite treatment and methylation-specific PCR, the specific methylation of certain exons of IGF2 and TGF-β was identified. In addition, the mRNA expression levels of these two genes were markedly different. In conclusion, this novel MS-G-SH technique is an alternative and effective approach for the detection of specific DNA methylation.

Childhood outcomes of assisted reproductive technology

There is a large population of children conceived via assisted reproductive technology (ART), which continues to increase worldwide, without a clear understanding of associated long-term outcomes. ART children are more likely to be the result of multiple pregnancies, and thus to be born prematurely or low birthweight. There is growing evidence that ART children are phenotypically and biochemically different from naturally conceived children, but the mechanism(s) leading to these changes have not been elucidated. There is a possible increased risk of rare imprinted gene disorders in these children. However, it remains unclear whether more subtle changes in DNA methylation occur commonly, leading to differences in gene expression and phenotype in ART children. Although an increased risk of cancer among ART children has been reported, the role of ART in the development of cancer has not been demonstrated. Further research and ongoing surveillance of ART children is essential to better understand the possible effects of ART on the long-term health of this population.

Is it the patient or the IVF? Beckwith-Wiedemann syndrome in both spontaneous and assisted reproductive conceptions

OBJECTIVE

To describe two children diagnosed with Beckwith-Wiedemann Syndrome (BWS) arising from a spontaneous conception and an assisted reproductive technology (ART) cycle from one patient with a long-standing history of subfertility.

DESIGN

Case report.

SETTING

Academic medical center.

PATIENT(S)

Two children with the morphologic features of BWS as a result of a spontaneous conception and an ART cycle from the same patient.

INTERVENTION(S)

Assisted reproductive technology.

MAIN OUTCOME MEASURE(S)

Neonatal and pediatric morphologic evaluation by geneticists.

RESULT(S)

Two children with the morphologic features consistent with the criteria for the diagnosis of BWS.

CONCLUSION(S)

Patients with subfertility may be carriers for genetic disorders that can be passed to a child with or without the use of assisted reproductive technologies (ART). The use of ART may bypass natural selection mechanisms.

DNA methylation: an introduction to the biology and the disease-associated changes of a promising biomarker

DNA methylation occurring on the 5 position of the pyrimidine ring of cytosines in the context of the dinucleotide sequence CpG forms one of the multiple layers of epigenetic mechanisms controlling and modulating gene expression through chromatin structure. It closely interacts with histone modifications and chromatin remodeling complexes to form the genomic chromatin landscape. DNA methylation is essential for proper mammalian development, crucial for imprinting and plays a role in maintaining genomic stability as well as in dosage compensation. DNA methylation patterns are susceptible to change in response to environmental stimuli such as diet or toxins, whereby the epigenome seems to be most vulnerable during early in utero development. Aberrant DNA methylation changes have been detected in several diseases, particularly cancer where genome-wide hypomethylation coincides with genespecific hypermethylation. DNA methylation patterns can be used to detect cancer at very early stages, to classify tumors as well as predict and monitor the response to antineoplastic treatment. As a stable nucleic-acid-based modification with limited dynamic range that is technically easy to handle, DNA methylation is a promising biomarker for many applications.

Unearthing the roles of imprinted genes in the placenta

Mammalian fetal survival and growth are dependent on a well-established and functional placenta. Although transient, the placenta is the first organ to be formed during pregnancy and is responsible for important functions during development, such as the control of metabolism and fetal nutrition, gas and metabolite exchange, and endocrine control. Epigenetic marks and gene expression patterns in early development play an essential role in embryo and fetal development. Specifically, the epigenetic phenomenon known as genomic imprinting, represented by the non-equivalence of the paternal and maternal genome, may be one of the most important regulatory pathways involved in the development and function of the placenta in eutherian mammals. A lack of pattern or an imprecise pattern of genomic imprinting can lead to either embryonic losses or a disruption in fetal and placental development. Genetically modified animals present a powerful approach for revealing the interplay between gene expression and placental function in vivo and allow a single gene disruption to be analyzed, particularly focusing on its role in placenta function. In this paper, we review the recent transgenic strategies that have been successfully created in order to provide a better understanding of the epigenetic patterns of the placenta, with a special focus on imprinted genes. We summarize a number of phenotypes derived from the genetic manipulation of imprinted genes and other epigenetic modulators in an attempt to demonstrate that gene-targeting studies have contributed considerably to the knowledge of placentation and conceptus development.

Genetic and epigenetic characteristics of ICSI children

The outcome of pregnancy and the developmental wellbeing of children conceived from 12,866 consecutive intracytoplasmic sperm injection (ICSI) cycles was assessed. A total of 3277 couples delivered 5891 neonates. There was a higher than normal incidence of de-novo chromosomal abnormalities in a small sample of ICSI offspring. Controlling for maternal age showed that the incidence of low birth weight and gestational length were comparable with the naturally conceived counterpart. Rates of malformation in ICSI offspring ranged from 3.5 to 6.2%. At 3 years of age (n = 811), the proportion of children at risk for developmental delays was 10.4% in ICSI and 10.7% in IVF singletons. However, high order gestations were characterized by 19.4% of the children having compromised development. Epigenetic analysis of assisted reproductive technique conceptuses found minor imprinted gene expression imbalances. ICSI offspring presented with genetic defects that were inherited or arose de novo. Obstetric and neonatal outcomes of singleton pregnancies appeared to be dependent upon maternal age. ICSI and IVF appeared to exert a negative effect on the wellbeing of offspring mainly because of the association with multiple gestations. All assisted reproduction procedures should be monitored for the eventual effect of environmental aggressors on offspring epigenesis.

DNA methylation: an introduction to the biology and the disease-associated changes of a promising biomarker

DNA methylation occurring on the 5 position of the pyrimidine ring of cytosines in the context of the dinucleotide sequence CpG forms one of the multiple layers of epigenetic mechanisms controlling and modulating gene expression through chromatin structure. It closely interacts with histone modifications and chromatin-remodeling complexes to form the genomic chromatin landscape. DNA methylation is essential for proper mammalian development, crucial for imprinting, and plays a role in maintaining genomic stability as well as in dosage compensation. DNA methylation patterns are susceptible to change in response to environmental stimuli such as diet or toxins whereby the epigenome seems to be most vulnerable during early in utero development. Aberrant DNA methylation changes have been detected in several diseases, particularly cancer where genome-wide hypomethylation coincides with gene-specific hypermethylation. DNA methylation patterns can be used to detect cancer at very early stages, to classify tumors as well as predict and monitor the response to antineoplastic treatment. As a stable nucleic acid-based modification with limited dynamic range that is technically easy to handle, DNA methylation is a promising biomarker for many applications.

Genetic and epigenetic contributions to human nutrition and health: managing genome-diet interactions

The Institute of Medicine recently convened a workshop to review the state of the various domains of nutritional genomics research and policy and to provide guidance for further development and translation of this knowledge into nutrition practice and policy. Nutritional genomics holds the promise to revolutionize both clinical and public health nutrition practice and facilitate the establishment of (a) genome-informed nutrient and food-based dietary guidelines for disease prevention and healthful aging, (b) individualized medical nutrition therapy for disease management, and (c) better targeted public health nutrition interventions (including micronutrient fortification and supplementation) that maximize benefit and minimize adverse outcomes within genetically diverse human populations. As the field of nutritional genomics matures, which will include filling fundamental gaps in knowledge of nutrient-genome interactions in health and disease and demonstrating the potential benefits of customizing nutrition prescriptions based on genetics, registered dietitians will be faced with the opportunity of making genetically driven dietary recommendations aimed at improving human health.