Maternal obesity and diabetes may cause DNA methylation alteration in the spermatozoa of offspring in mice

Sperm epigenetics and sperm RNAs as drivers of male infertility: truth or myth?

Male infertility represents a complex clinical condition that often challenges the ability of reproductive specialists to find its etiology and then propose an adequate treatment. The unexplained decline in sperm count, as well as the association between male infertility and mortality, morbidity, and cancer, has prompted researchers toward an urgent need to better understand the causes of male infertility. Therefore, molecular biologists are increasingly trying to study whether sperm epigenetic alterations may be involved in male infertility and embryo developmental abnormalities. In this context, research is also trying to uncover the hidden role of sperm RNAs, both coding and non-coding. This narrative review aims to thoroughly and comprehensively present the relationship between sperm epigenetics, sperm RNAs, and human fertility. We first focused on the technological aspects of studying sperm epigenetics and RNAs, relating to the complex role(s) played in sperm maturation, fertilization, and embryo development. Then, we examined the intricate connections between epigenetics and RNAs with fertility measures, namely sperm concentration, embryo growth and development, and live birth rate, in both animal and human studies. A better understanding of the molecular mechanisms involved in sperm epigenetic regulation, as well as the impact of RNA players, will help to tackle infertility.

Impact of diet-induced maternal obesity on the reproductive capacity of F1 female offspring and the early development of the second generation

The aim of this study was to examine the impact of maternal obesity on the reproductive capacity of the female offspring (F1) and on the early development of the second generation (F2). To this end, rats were fed either standard (SD) or cafeteria (CD) diet. CD rats and their offspring were divided into 2 groups: rats with 18% and ≥25% overweight (CD18 and CD25, respectively) and offspring from CD18 and CD25 rats (OCD18 and OCD25, respectively). Both OCD groups achieved greater weight gain than controls, without changes in the serum levels of glucose, cholesterol or triglycerides. However, they showed increased gonadal cholesterol concentration and fat content compared to controls. Female OCD groups showed a slight prolongation of the estrous cycle and different pattern of changes in the weight gain during pregnancy. The OCD25 group displayed an increased fertility index and preimplantation losses, and changes in some fetal measurements. Some OCD25 dams gave birth to a larger litter of pups and displayed a lower viability index and lactation rate than controls. OCD25 dams also showed an increase in estradiol and a decrease in testosterone and anti-Müllerian hormone. OCD25 rats showed increased mRNA levels of steroidogenenic enzymes. The offspring from OCD25 females (F2OCD25 offspring) showed early vaginal opening and higher ovulation rate in females, and lower ano-genital distances in males, compared to controls. In conclusion, these results reflect that maternal obesity impacts on the reproductive health of successive generations, probably as a result of epigenetic changes in different systems, including germ cells.

Maternal Obesity Induces the Meiotic Defects and Epigenetic Alterations During Fetal Oocyte Development

It has been widely reported that obesity adversely impacts reproductive performance of females. However, the effects of maternal obesity on fetal germ cells remain poorly understood. In the present study, by employing a high-fat diet (HFD)-based mouse model, it is discovered that maternal obesity disrupts the chromosomal synapsis and homologous recombination during fetal oogenesis. Moreover, transcriptomic profiling reveales the potential molecular network controlling this process. Of note, the global hypermethylation of genomic DNA in fetal oocytes from obese mouse is detected. Importantly, time-restricted feeding (TRF) of obese mice not only ameliorate the meiotic defects, but also partly restore the epigenetic remodeling in fetal oocytes. In sum, the evidence are provided showing the deficit fetal oogenesis in obese mother, implicating a mechanism underlying the intergenerational effects of environmental insults. TRF may represent a potentially effective approach for mitigating fertility issues in obese patients.

Paternal programming of fetoplacental and offspring metabolic disorders

The alarming increase in the prevalence of metabolic pathologies is of worldwide concern and has been linked not only to genetic factors but also to a large number of non-genetic factors. In recent years, there has been increasing interest in the study of the programming of metabolic diseases, such as type 2 diabetes mellitus (T2DM) and obesity, by paternal exposure, a paradigm termed "Paternal Origins of Health and Disease" (POHaD). This term derives from the better known "Developmental Origins of Health and Disease" (DOHaD), which focuses on the involvement of the maternal intrauterine environment and complications during pregnancy associated with the health and disease of the offspring. Studies on paternal programming have documented environmentally induced epigenetic modifications in the male germline and in seminal plasma, which lead to intergenerational and transgenerational phenotypes, evident already during fetoplacental development. Studies with animal models at both ends of the nutritional spectrum (undernutrition or overnutrition) have been performed to understand the possible mechanisms and signaling pathways leading to the programming of metabolic disorders by exploring epigenetic changes throughout the life of the offspring. The aim of this review was to address the evidence of the programming of fetoplacental developmental alterations and metabolic pathologies in the offspring of males with metabolic disorders and unhealthy exposures, highlighting the mechanisms involved in such programming and looking for paternal interventions to reduce negative health outcomes in the offspring.

A comprehensive approach to modeling maternal immune activation in rodents

Prenatal brain development is a highly orchestrated process, making it a very vulnerable window to perturbations. Maternal stress and subsequent inflammation during pregnancy leads to a state referred to as, maternal immune activation (MIA). If persistent, MIA can pose as a significant risk factor for the manifestation of neurodevelopmental disorders (NDDs) such as autism spectrum disorder and schizophrenia. To further elucidate this association between MIA and NDD risk, rodent models have been used extensively across laboratories for many years. However, there are few uniform approaches for rodent MIA models which make not only comparisons between studies difficult, but some established approaches come with limitations that can affect experimental outcomes. Here, we provide researchers with a comprehensive review of common experimental variables and potential limitations that should be considered when designing an MIA study based in a rodent model. Experimental variables discussed include: innate immune stimulation using poly I:C and LPS, environmental gestational stress paradigms, rodent diet composition and sterilization, rodent strain, neonatal handling, and the inclusion of sex-specific MIA offspring analyses. We discuss how some aspects of these variables have potential to make a profound impact on MIA data interpretation and reproducibility.

Epigenetic Modifications in Obesity and Type 2 Diabetes

Obesity is a chronic condition that is also a risk factor of several other chronic conditions including type 2 diabetes. The effects of maternal obesity and type 2 diabetes on fetal development and offspring health are mediated through the transmission of epigenetic modifications in addition to the possible permanent changes of the organs caused by the intrauterine environment hypothesized by the Developmental Origins of Health and Disease (DOHaD) theory. Epigenetic modifications can be altered by environmental factors including dietary and lifestyle factors. The current priorities include identification and confirmation of the specific epigenetic biomarkers associated with obesity and type 2 diabetes in human subjects and identification of the dietary and lifestyle factors that contribute to each of the identified specific epigenetic biomarkers.

Deep Insight of the Pathophysiology of Gestational Diabetes Mellitus

Diabetes mellitus is a severe metabolic disorder, which consistently requires medical care and self-management to restrict complications, such as obesity, kidney damage and cardiovascular diseases. The subtype gestational diabetes mellitus (GDM) occurs during pregnancy, which severely affects both the mother and the growing foetus. Obesity, uncontrolled weight gain and advanced gestational age are the prominent risk factors for GDM, which lead to high rate of perinatal mortality and morbidity. In-depth understanding of the molecular mechanism involved in GDM will help researchers to design drugs for the optimal management of the condition without affecting the mother and foetus. This review article is focused on the molecular mechanism involved in the pathophysiology of GDM and the probable biomarkers, which can be helpful for the early diagnosis of the condition. The early diagnosis of the metabolic disorder, most preferably in first trimester of pregnancy, will lead to its effective long-term management, reducing foetal developmental complications and mortality along with safety measures for the mother.

Influence of maternal obesity on the multi-omics profiles of the maternal body, gestational tissue, and offspring

Epidemiological studies show that obesity during pregnancy affects more than half of the pregnancies in the developed countries and is associated with obstetric problems and poor outcomes. Obesity tends to increase the incidence of complications. Furthermore, the resulting offspring are also adversely affected. However, the molecular mechanisms of obesity leading to poor pregnancy outcomes remain unclear. Omics methods are used for genetic diagnosis and marker discovery. The aim of this review was to summarize the maternal and fetal pathophysiological alterations induced by gestational obesity,identified using multi-omics detection techniques, and to generalize the biological functions and potential mechanisms of the differentially expressed molecules.

Tea polyphenols alleviate the adverse effects of diabetes on oocyte quality

Maternal diabetes mellitus reduces oocyte quality, such as abnormalities of spindle assembly and chromosome segregation, mitochondrial dysfunction, decrease of fertilization rate, increase of ROS, and so on. So, it is important to research how to restore the decreased oocyte quality induced by maternal diabetes mellitus. Polyphenols are the most abundant bioactive components of green tea. It is reported that tea polyphenols have many health functions, for instance anti-oxidation, anti-inflammation, anti-obesity, and anti-diabetes. Thus, we hypothesize that tea polyphenols may play a crucial role in alleviating adverse effects of diabetes on oocyte quality. In the present study, we researched the effects of tea polyphenols on diabetic oocyte maturation in vitro. Compared with the control, oocytes from diabetic mice displayed a lower maturation rate and a higher frequency of spindle defects and chromosome misalignment. However, tea polyphenols significantly increased the oocyte maturation rate, and reduced the incidence of abnormal spindle assembly and chromosome segregation. Tea polyphenols also obviously decreased the reactive oxygen species (ROS) levels in diabetic oocytes, and increased the expression of antioxidant genes (Sod1 and Sod2). Abnormal mitochondrial membrane potential was also alleviated in diabetic oocytes, and the expression of genes regulating mitochondrial fusion (Opa1, Mfn1 and Mfn2) and fission (Drp1) was significantly increased while tea polyphenols were added. Meanwhile, tea polyphenols reduced DNA damage in diabetic oocytes which may be mediated by the increased expression of Rad51, related to DNA damage repair. Our results suggest that tea polyphenols would, at least partially, restore the adverse effects of diabetes mellitus on oocyte quality.

Looking at the Future Through the Mother's Womb: Gestational Diabetes and Offspring Fertility

Altered nutrition or intrauterine exposure to various adverse conditions during fetal development or earlier in a mother's life can lead to epigenetic changes in fetal tissues, predisposing those tissues to diseases that manifest when offspring become adults. An example is a maternal obesity associated with gestational diabetes (GDM), where fetal exposure to a hyperglycemic, hyperinsulinemic, and/or hyperlipidemic gestational environment can provoke epigenetic changes that predispose offspring to various diseased conditions later in life. While it is now well established that offspring exposed to GDM have an increased risk of developing obesity, metabolic disorders, and/or cardiovascular disease in adult life, there are limited studies assessing the reproductive health of these offspring. This mini-review discusses the long-term effect of in utero exposure to GDM-associated adverse prenatal environment on the reproductive health of the offspring. Moreover, using evidence from various animal models and human epidemiological studies, this review offers molecular insight and understanding of how epigenetic reprogramming of genes culminates in reproductive dysfunction and the development of subfertility or infertility later in adult life.

Epigenetics of Male Infertility: The Role of DNA Methylation

In recent years, a number of studies focused on the role of epigenetics, including DNA methylation, in spermatogenesis and male infertility. We aimed to provide an overview of the knowledge concerning the gene and genome methylation and its regulation during spermatogenesis, specifically in the context of male infertility etiopathogenesis. Overall, the findings support the hypothesis that sperm DNA methylation is associated with sperm alterations and infertility. Several genes have been found to be differentially methylated in relation to impaired spermatogenesis and/or reproductive dysfunction. Particularly, DNA methylation defects of MEST and H19 within imprinted genes and MTHFR within non-imprinted genes have been repeatedly linked with male infertility. A deep knowledge of sperm DNA methylation status in association with reduced reproductive potential could improve the development of novel diagnostic tools for this disease. Further studies are needed to better elucidate the mechanisms affecting methylation in sperm and their impact on male infertility.

Islet Epigenetic Impacts on β-Cell Identity and Function

The development and maintenance of differentiation is vital to the function of mature cells. Terminal differentiation is achieved by locking in the expression of genes essential for the function of those cells. Gene expression and its memory through generations of cell division is controlled by transcription factors and a host of epigenetic marks. In type 2 diabetes, β cells have altered gene expression compared to controls, accompanied by altered chromatin marks. Mutations, diet, and environment can all disrupt the implementation and preservation of the distinctive β-cell transcriptional signature. Understanding of the full complement of genomic control in β cells is still nascent. This article describes the known effects of histone marks and variants, DNA methylation, how they are regulated in the β cell, and how they affect cell-fate specification, maintenance, and lineage propagation. © 2021 American Physiological Society. Compr Physiol 11:1-18, 2021.

Early-life nutrition and metabolic disorders in later life: a new perspective on energy metabolism

Type 2 diabetes mellitus and metabolic disorders have become an epidemic globally. However, the pathogenesis remains largely unclear and the prevention and treatment are still limited. In addition to environmental factors during adulthood, early life is the critical developmental window with high tissue plasticity, which might be modified by external environmental cues. Substantial evidence has demonstrated the vital role of early-life nutrition in programming the metabolic disorders in later life. In this review, we aim to overview the concepts of fetal programming and investigate the effects of early-life nutrition on energy metabolism in later life and the potential epigenetic mechanism. The related studies published on PubMed database up to March 2020 were included. The results showed that both maternal overnutrition and undernutrition increased the riskes of metabolic disorders in offspring and epigenetic modifications, including DNA methylation, miRNAs, and histone modification, might be the vital mediators. The beneficial effects of early-life lifestyle modifications as well as dietary and nutritional interventions on these deleterious metabolic remolding were initially observed. Overall, characterizing the early-life malnutrition that reshapes metabolic disease trajectories may yield novel targets for early prevention and intervention and provide a new point of view to the energy metabolism.

Paternal multigenerational exposure to an obesogenic diet drives epigenetic predisposition to metabolic diseases in mice

Obesity is a growing societal scourge. Recent studies have uncovered that paternal excessive weight induced by an unbalanced diet affects the metabolic health of offspring. These reports mainly employed single-generation male exposure. However, the consequences of multigenerational unbalanced diet feeding on the metabolic health of progeny remain largely unknown. Here, we show that maintaining paternal Western diet feeding for five consecutive generations in mice induces an enhancement in fat mass and related metabolic diseases over generations. Strikingly, chow-diet-fed progenies from these multigenerational Western-diet-fed males develop a 'healthy' overweight phenotype characterized by normal glucose metabolism and without fatty liver that persists for four subsequent generations. Mechanistically, sperm RNA microinjection experiments into zygotes suggest that sperm RNAs are sufficient for establishment but not for long-term maintenance of epigenetic inheritance of metabolic pathologies. Progressive and permanent metabolic deregulation induced by successive paternal Western-diet-fed generations may contribute to the worldwide epidemic of metabolic diseases.

Single-cell transcriptome analysis reveals that maternal obesity affects DNA repair, histone methylation, and autophagy level in mouse embryos

Obesity causes many reproductive dysfunctions such as reduced conception, infertility, and early pregnancy loss, and this is largely due to the negative effects of obesity on oocyte and embryo quality. In the present study, we employed single-cell RNA transcriptome sequencing to investigate the potential causes for the maternal obesity effects on mouse embryos. Our results showed that the 4-cell and morula/blastocyst rates were all significantly decreased during embryo development in obese mice. Genome-wide analysis indicated that obesity altered the expression of more than 1100 genes in 2-cell embryos, including the genes which were related to the p53 signaling pathway and apoptosis. Further analysis showed that the expression of 47 genes related to DNA damage was changed, and a positive γH2A signal and the altered expression of Rad51 and Tex15 were observed in the obese embryos. Obesity also affected histone methylation, shown by the decrease of the H3K4-me2 level. Besides this, we observed the occurrence of autophagy and apoptosis in the embryos of obese mice. There were 42 genes that were related to autophagy/apoptosis that showed aberrant expression, and the positive LC3 signal and the decrease of Clec16a, Rraga, and Atg10 level were also observed. In summary, our study suggested that obesity affected early embryonic development by inducing DNA damage, aberrant histone methylation, and autophagy levels in mice.

The Roles of H19 in Regulating Inflammation and Aging

Accumulating evidence suggests that long non-coding RNA H19 correlates with several aging processes. However, the role of H19 in aging remains unclear. Many studies have elucidated a close connection between H19 and inflammatory genes. Chronic systemic inflammation is an established factor associated with various diseases during aging. Thus, H19 might participate in the development of age-related diseases by interplay with inflammation and therefore provide a protective function against age-related diseases. We investigated the inflammatory gene network of H19 to understand its regulatory mechanisms. H19 usually controls gene expression by acting as a microRNA sponge, or through mir-675, or by leading various protein complexes to genes at the chromosome level. The regulatory gene network has been intensively studied, whereas the biogenesis of H19 remains largely unknown. This literature review found that the epithelial-mesenchymal transition (EMT) and an imprinting gene network (IGN) might link H19 with inflammation. Evidence indicates that EMT and IGN are also tightly controlled by environmental stress. We propose that H19 is a stress-induced long non-coding RNA. Because environmental stress is a recognized age-related factor, inflammation and H19 might serve as a therapeutic axis to fight against age-related diseases.

Impacts of obesity, maternal obesity and nicotinamide mononucleotide supplementation on sperm quality in mice

Male fertility and sperm quality are negatively impacted by obesity. Furthermore, recent evidence has shown that male offspring from obese rat mothers also have reduced sperm quality and fertility. Here, we extend work in this area by comparing the effects of both maternal obesity and offspring post-weaning diet-induced obesity, as well as their combination, on sperm quality in mice. We additionally tested whether administration of the NAD⁺-booster nicotinamide mononucleotide (NMN) can ameliorate the negative effects of obesity and maternal obesity on sperm quality. We previously showed that intraperitoneal (i.p.) injection of NMN can reduce the metabolic deficits induced by maternal obesity or post-weaning dietary obesity in mice. In this study, female mice were fed a high-fat diet (HFD) for 6 weeks until they were 18% heavier than a control diet group. Thereafter, HFD and control female mice were mated with control diet males, and male offspring were weaned into groups receiving control or HFD. At 30 weeks of age, mice received 500 mg/kg body weight NMN or vehicle PBS i.p. for 21 days. As expected, adiposity was increased by both maternal and post-weaning HFD but reduced by NMN supplementation. Post-weaning HFD reduced sperm count and motility, while maternal HFD increased offspring sperm DNA fragmentation and levels of aberrant sperm chromatin. There was no evidence that the combination of post-weaning and maternal HFD exacerbated the impacts in sperm quality suggesting that they impact spermatogenesis through different mechanisms. Surprisingly NMN reduced sperm count, vitality and increased sperm oxidative DNA damage, which was associated with increased NAD⁺ in testes. A subsequent experiment using oral NMN at 400 mg/kg body weight was not associated with reduced sperm viability, oxidative stress, mitochondrial dysfunction or increased NAD⁺ in testes, suggesting that the negative impacts on sperm could be dependent on dose or mode of administration.

Maternal Obesity Programs Offspring Development and Resveratrol Potentially Reprograms the Effects of Maternal Obesity

Maternal obesity during pregnancy is a now a public health burden that may be the culprit underlying the ever-increasing rates of adult obesity worldwide. Understanding the association between maternal obesity and adult offspring’s obesity would inform policy and practice regarding offspring health through available resources and interventions. This review first summarizes the programming effects of maternal obesity and discusses the possible underlying mechanisms. We then summarize the current evidence suggesting that maternal consumption of resveratrol is helpful in maternal obesity and alleviates its consequences. In conclusion, maternal obesity can program offspring development in an adverse way. Maternal resveratrol could be considered as a potential regimen in reprogramming adverse outcomes in the context of maternal obesity.

In Vivo and In Vitro Models of Diabetes: A Focus on Pregnancy

Diabetes in pregnancy is associated with an increased risk of poor outcomes, both for the mother and her offspring. Although clinical and epidemiological studies are invaluable to assess these outcomes and the effectiveness of potential treatments, there are certain ethical and practical limitations to what can be assessed in human studies.Thus, both in vivo and in vitro models can aid us in the understanding of the mechanisms behind these complications and, in the long run, towards their prevention and treatment. This review summarizes the existing animal and cell models used to mimic diabetes, with a specific focus on the intrauterine environment. Summary of this review.

Insights into the Role of DNA Methylation and Protein Misfolding in Diabetes Mellitus

Background:

Diabetes mellitus is a metabolic disorder that is characterized by impaired glucose tolerance resulting from defects in insulin secretion, insulin action, or both. Epigenetic modifications, which are defined as inherited changes in gene expression that occur without changes in gene sequence, are involved in the etiology of diabetes.

Methods:

In this review, we focused on the role of DNA methylation and protein misfolding and their contribution to the development of both type 1 and type 2 diabetes mellitus.

Results:

Changes in DNA methylation in particular are highly associated with the development of diabetes. Protein function is dependent on their proper folding in the endoplasmic reticulum. Defective protein folding and consequently their functions have also been reported to play a role. Early treatment of diabetes has proven to be of great benefit, as even transient hyperglycemia may lead to pathological effects and complications later on. This has been explained by the theory of the development of a metabolic memory in diabetes. The basis for this metabolic memory was attributed to oxidative stress, chronic inflammation, non-enzymatic glycation of proteins and importantly, epigenetic changes. This highlights the importance of linking new therapeutics targeting epigenetic mechanisms with traditional antidiabetic drugs.

Conclusion:

Although new data is evolving on the relation between DNA methylation, protein misfolding, and the etiology of diabetes, more studies are required for developing new relevant diagnostics and therapeutics.

Epigenetic Transgenerational Inheritance

Epigenetic information refers to heritable changes in gene expression that occur without modifications at the DNA sequence level. These changes are orchestrated by different epigenetic mechanisms such as DNA methylation, posttranslational modifications of histones, and the presence of noncoding RNAs. Epigenetic information regulates chromatin structure to confer cell-specific gene expression.The sperm epigenome is the result of three periods of global resetting during men's life. Germ cell epigenome reprogramming is designed to allow cell totipotency and to prevent the transmission of epimutations via spermatozoa. At the end of these reprogramming events, the sperm epigenome has a very specific epigenetic pattern that is a footprint of past reprogramming events and has an influence on embryo development.Several data demonstrate that not all regions of the epigenome are erased during the reprogramming periods, suggesting the transmission of epigenetic information from fathers to offspring via spermatozoa. Moreover, it is becoming increasingly clear that the sperm epigenome is sensitive to environmental factors during the process of gamete differentiation, suggesting the plasticity of the sperm epigenetic signature according to the circumstances of the individual's life.In this chapter, we provided strong evidences about the association between variations of the sperm epigenome and the exposure to environmental factors. Moreover, we will present data about how epigenetic mechanisms are candidates for transferring paternal environmental information to offspring.

In utero programming and early detection of cardiovascular disease in the offspring of mothers with obesity

The offspring of women with obesity during their pregnancy are exposed to an altered intra-uterine environment. A subsequent influence on the cardiovascular development during fetal life is assumed. In the present thematic review, we report on the current knowledge about this early development of cardiovascular disease from fetal life until adolescence. Based on animal studies, different contributing mechanisms have been hypothesized that still need confirmation in human subjects. Insulin resistance, increased levels of leptin, chronic inflammatory state, perturbation of sympathetic tone and epigenetic modifications contribute to a suboptimal nutrient environment and changed hemodynamics. The ensuing aberrant cardiomyocyte development, impaired endothelial cell relaxation and atherogenic lipid profile put these children at risk for the development of endothelial cell dysfunction. Increasing possibilities for early detection of this preliminary stage of atherosclerotic disease offer new insights into future prevention and treatment strategies. Future research should focus on further unraveling the effect of moderate intense, aerobic exercise. Since it is used to treat the condition in children and adolescents with good results, it might be a contributor to tackling endothelial cell dysfunction at its cradle when applied in early pregnancy.

In Utero and Postnatal Exposure to High Fat, High Sucrose Diet Suppressed Testis Apoptosis and Reduced Sperm Count

Obesity affects male fertility and maternal diabetes affects the offspring sperm epigenome. However, the effects of in utero exposure to maternal glucose intolerance in combination with postnatal high fat, high sucrose (HFHS) diet consumption on offspring spermatogenesis is not clear. The present study was designed to test these effects. One week before and during pregnancy, dams were fed either control or HFHS diet to induce gestational glucose intolerance, and returned to standard diet during lactation. Male offspring from each maternal group were split into control and HFHS-fed groups for eight weeks prior to sacrifice at 11, 19 or 31 weeks of age, and reproductive tissues were harvested for analysis of testicular germ cell apoptosis and sperm output. Postnatal HFHS diet suppressed spermatogonia apoptosis in all age groups and maternal HFHS diet reduced testosterone levels at 11 weeks. At 31 weeks of age, the postnatal HFHS diet increased body weight, and reduced epididymis weight and sperm count. The combination of in utero and postnatal exposure impacted sperm counts most significantly. In summary, HFHS diet during pregnancy puts male offspring at greater risk of infertility, particularly when combined with postnatal high fat diet feeding.

Effect of gestational diabetes mellitus on testis and pancreatic tissues of male offspring

The purpose of this study was to determine the effect of gestational diabetes mellitus (GDM) on some reproductive characteristics, testicular and pancreatic oxidative status and pancreatic endocrine receptor densities of male offspring at post-pubertal stage. A total of 36 1-day-old Wistar Albino male offspring including 12 pups of nontreated mothers (control group), 14 pups of 40 mg/kg STZ-injected mothers (STZ-40 group) and 10 pups of 60 mg/kg STZ-injected mothers (STZ-60 group) were used. The offspring were euthanised on post-natal day 60, their blood, reproductive organs and pancreatic tissues were obtained and examined. When compared with the control group, there was a significant decrease in body and absolute reproductive organ weights, serum testosterone level, testicular and pancreatic catalase activities, pancreatic glutathione level, epididymal sperm concentration of both STZ-40 and STZ-60 groups as well as in testicular glutathione level of only STZ-60 group. Significant increases were determined in testicular and pancreatic malondialdehyde level and glutathione peroxidase activity in both groups and in fasting serum glucose of only STZ-60 group in comparison with the control group. Although some histopathological damages were observed in testes of both STZ-40 and STZ-60 groups, there were no detectable differences between the groups in density of insulin, glucagon and somatostatin receptors in pancreas. In conclusion, GDM has negative effects on reproductive efficiency and testicular-pancreatic tissue oxidant/antioxidant balance of male offspring at post-pubertal stage.

Long non-coding RNA H19 induces hippocampal neuronal apoptosis via Wnt signaling in a streptozotocin-induced rat model of diabetes mellitus

Defects in hippocampal synaptic plasticity and disorders of memory and learning are the central nervous system complications of diabetes mellitus (DM). Here, we used a streptozotocin-induced rat DM model to investigate the effects of long non-coding RNA H19 (lncRNA H19) on learning and memory and apoptosis of hippocampal neurons, and the involvement of the Wnt signaling. Our data demonstrate that lncRNA H19 is highly expressed in rats with DM. Over-expression of lncRNA H19 increased positioning navigation latency in DM rats and decreased duration of space exploration. lncRNA H19 over-expression also increased hippocampal neuronal apoptosis and expression of Wnt3, β-catenin, TCF-1, Bax, caspase-8 and caspase-3. By contrast, expression of GSK-3β and Bcl-2 was suppressed in DM rats over-expressing lncRNA H19. These results suggest that lncRNA H19 induces hippocampal neuronal apoptosis via Wnt signaling, and that inhibition of lncRNA H19 may serve as a promising novel target for the treatment of cognitive decline in patients with DM.

Epigenetic signatures of gestational diabetes mellitus on cord blood methylation

Background

Intrauterine exposure to gestational diabetes mellitus (GDM) confers a lifelong increased risk for metabolic and other complex disorders to the offspring. GDM-induced epigenetic modifications modulating gene regulation and persisting into later life are generally assumed to mediate these elevated disease susceptibilities. To identify candidate genes for fetal programming, we compared genome-wide methylation patterns of fetal cord bloods (FCBs) from GDM and control pregnancies.

Methods and results

Using Illumina’s 450K methylation arrays and following correction for multiple testing, 65 CpG sites (52 associated with genes) displayed significant methylation differences between GDM and control samples. Four candidate genes, ATP5A1, MFAP4, PRKCH, and SLC17A4, from our methylation screen and one, HIF3A, from the literature were validated by bisulfite pyrosequencing. The effects remained significant after adjustment for the confounding factors maternal BMI, gestational week, and fetal sex in a multivariate regression model. In general, GDM effects on FCB methylation were more pronounced in women with insulin-dependent GDM who had a more severe metabolic phenotype than women with dietetically treated GDM.

Conclusions

Our study supports an association between maternal GDM and the epigenetic status of the exposed offspring. Consistent with a multifactorial disease model, the observed FCB methylation changes are of small effect size but affect multiple genes/loci. The identified genes are primary candidates for transmitting GDM effects to the next generation. They also may provide useful biomarkers for the diagnosis, prognosis, and treatment of adverse prenatal exposures.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-017-0329-3) contains supplementary material, which is available to authorized users.

Obesity: epigenetic aspects

Epigenetics, defined as inheritable and reversible phenomena that affect gene expression without altering the underlying base pair sequence has been shown to play an important role in the etiopathogenesis of obesity. Obesity is associated with extensive gene expression changes in tissues throughout the body. Epigenetics is emerging as perhaps the most important mechanism through which the lifestyle-choices we make can directly influence the genome. Considerable epidemiological, experimental and clinical data have been amassed showing that the risk of developing disease in later life is dependent on early life conditions, mainly operating within the normative range of developmental exposures. In addition to the 'maternal' interactions, there has been increasing interest in the epigenetic mechanisms through which 'paternal' influences on offspring development can be achieved. Nutrition, among many other environmental factors, is a key player that can induce epigenetic changes not only in the directly exposed organisms but also in subsequent generations through the transgenerational inheritance of epigenetic traits. Overall, significant progress has been made in the field of epigenetics and obesity and the first potential epigenetic markers for obesity that could be detected at birth have been identified. Fortunately, epigenetic phenomena are dynamic and rather quickly reversible with intensive lifestyle changes. This is a very promising and sustainable resolution to the obesity pandemic.

Maternal medical conditions during pregnancy and gross motor development up to age 24 months in the Upstate KIDS study

AIM

We examined whether children of mothers with a medical condition diagnosed before or during pregnancy took longer to achieve gross motor milestones up to age 24 months.

METHOD

We obtained information on medical conditions using self-reports, birth certificates, and hospital records in 4909 mothers participating in Upstate KIDS, a population-based birth cohort. Mothers reported on their children's motor milestone achievement at 4, 8, 12, 18, and 24 months of age.

RESULTS

After adjustment for covariates (including pre-pregnancy body mass index), children of mothers with gestational diabetes took longer to achieve sitting without support (hazard ratio [HR]=0.84, 95% confidence interval [CI] 0.75-0.93), walking with assistance (HR=0.88, 95% CI 0.77-0.98), and walking alone (HR=0.88, 95% CI 0.77-0.99) than children of females with no gestational diabetes. Similar findings emerged for maternal diabetes. Gestational hypertension was associated with a longer time to achieve walking with assistance. These associations did not change after adjustment for gestational age or birthweight. Severe hypertensive disorders of pregnancy were related to a longer time to achieve milestones, but not after adjustment for perinatal factors.

INTERPRETATION

Children exposed to maternal diabetes, gestational or pre-gestational, may take longer to achieve motor milestones than non-exposed children, independent of maternal obesity.

Environmental Susceptibility of the Sperm Epigenome During Windows of Male Germ Cell Development

Male germ cells require multiple epigenetic reprogramming events during their lifespan to achieve reproductive capacity. An emerging body of compelling data demonstrates that environmental exposures can be embodied within the developing male germ cell as epigenetic marks. In turn, these epigenetic marks can impart information at fertilization to affect the trajectory of offspring health and development. While it is recognized that in utero epigenetic reprogramming of male germ cells is a particularly susceptible window to environmental exposures, other such windows exist during germ cell development. The objective of this review is to discuss epigenetic reprogramming events during male germ cell development and to provide supporting evidence from animal and human studies that during specific periods of development, germ cells are susceptible to environmentally induced epigenetic errors. Moving forward, the nascent field of sperm epigenetics research is likely to advance our understanding of paternal environmental determinants of offspring health and development.

Obesity-related DNA methylation at imprinted genes in human sperm: Results from the TIEGER study

BACKGROUND

Epigenetic reprogramming in mammalian gametes resets methylation marks that regulate monoallelic expression of imprinted genes. In males, this involves erasure of the maternal methylation marks and establishment of paternal-specific methylation to appropriately guide normal development. The degree to which exogenous factors influence the fidelity of methylation reprogramming is unknown. We previously found an association between paternal obesity and altered DNA methylation in umbilical cord blood, suggesting that the father's endocrine, nutritional, or lifestyle status could potentiate intergenerational heritable epigenetic abnormalities. In these analyses, we examine the relationship between male overweight/obesity and DNA methylation status of imprinted gene regulatory regions in the gametes.

METHODS

Linear regression models were used to compare sperm DNA methylation percentages, quantified by bisulfite pyrosequencing, at 12 differentially methylated regions (DMRs) from 23 overweight/obese and 44 normal weight men. Our study population included 69 volunteers from The Influence of the Environment on Gametic Epigenetic Reprogramming (TIEGER) study, based in NC, USA.

RESULTS

After adjusting for age and fertility patient status, semen from overweight or obese men had significantly lower methylation percentages at the MEG3 (β = -1.99; SE = 0.84; p = 0.02), NDN (β = -1.10; SE = 0.47; p = 0.02), SNRPN (β = -0.65; SE = 0.27; p = 0.02), and SGCE/PEG10 (β = -2.5; SE = 1.01; p = 0.01) DMRs. Our data further suggest a slight increase in DNA methylation at the MEG3-IG DMR (β = +1.22; SE = 0.59; p = 0.04) and H19 DMR (β = +1.37; SE = 0.62; p = 0.03) in sperm of overweight/obese men.

CONCLUSIONS

Our data support that male overweight/obesity status is traceable in the sperm epigenome. Further research is needed to understand the effect of such changes and the point of origin of DNA methylation differences between lean and overweight/obese men. Together with our earlier reports on paternal obesity and epigenetic shifts in the offspring, our studies set the groundwork for future studies investigating male gametic methylation aberrations due to paternal lifestyle factors such as obesity.

Genetics of Type 2 Diabetes: It Matters From Which Parent We Inherit the Risk

Type 2 diabetes (T2D) results from a co-occurrence of genes and environmental factors. There are more than 120 genetic loci suggested to be associated with T2D, or with glucose and insulin levels in European and multi-ethnic populations. Risk of T2D is higher in the offspring if the mother rather than the father has T2D. Genetically, this can be associated with a unique parent-of-origin (PoO) transmission of risk alleles, and it relates to genetic programming during the intrauterine period, resulting in the inability to increase insulin secretion in response to increased demands imposed by insulin resistance later in life. Such PoO transmission is seen for variants in the KLF14, KCNQ1, GRB10, TCF7L2, THADA, and PEG3 genes. Here we describe T2D susceptibility genes associated with defects in insulin secretion, and thereby risk of overt T2D. This review emphasizes the need to consider distorted parental transmission of risk alleles by exploring the genetic risk of T2D.

Obesity: epigenetic regulation – recent observations

Genetic and environmental factors, especially nutrition and lifestyle, have been discussed in the literature for their relevance to epidemic obesity. Gene-environment interactions may need to be understood for an improved understanding of the causes of obesity, and epigenetic mechanisms are of special importance. Consequences of epigenetic mechanisms seem to be particularly important during certain periods of life: prenatal, postnatal and intergenerational, transgenerational inheritance are discussed with relevance to obesity. This review focuses on nutrients, diet and habits influencing intergenerational, transgenerational, prenatal and postnatal epigenetics; on evidence of epigenetic modifiers in adulthood; and on animal models for the study of obesity.

Select Prenatal Environmental Exposures and Subsequent Alterations of Gene-Specific and Repetitive Element DNA Methylation in Fetal Tissues

Strong evidence implicates maternal environmental exposures in contributing to adverse outcomes during pregnancy and later in life through the developmental origins of health and disease hypothesis. Recent research suggests these effects are mediated through the improper regulation of DNA methylation in offspring tissues, specifically placental tissue, which plays a critical role in fetal development. This article reviews the relevant literature relating DNA methylation in multiple tissues at or near delivery to several prenatal environmental toxicants and stressors, including cigarette smoke, endocrine disruptors, heavy metals, as well as maternal diet. These human studies expand upon previously reported outcomes in animal model interventions and include effects on both imprinted and non-imprinted genes. We have also noted some of the strengths and limitations in the approaches used, and consider the appropriate interpretation of these findings in terms of their effect size and their relationship to differential gene expression and potential health outcomes. The studies suggest an important role of DNA methylation in mediating the effects of the intrauterine environment on children's health and a need for additional research to better clarify the role of this epigenetic mechanism as well as others.

Sodium Fluoride Affects DNA Methylation of Imprinted Genes in Mouse Early Embryos

Fluorine is reported to affect embryonic development, but the underlining mechanism is unclear. The modification of DNA methylation of the H19 and Peg3 genes is important in embryonic development. Therefore, the effect of fluorine on methylation of H19 and Peg3 during early mouse embryos was studied. It was shown that the H19 gene was significantly downmethylated in E2.5, E3.5, and E4.5 embryos from pregnant mice treated with 120 mg/l NaF in drinking water for 48 h. But methylation of both H19 and Peg3 genes was disrupted when the parent male mice were treated with NaF for 35 days. H19 DNA methylation decreased significantly, while Peg3 was almost completely methylated. However, when pregnant mice, mated with NaF-treated male mice, were again treated with NaF for 48 h, either H19 or Peg3 methylation in the embryos decreased significantly. In addition, the mRNA level of H19 considerably increased in E3.5 and E4.5 embryos from NaF-treated pregnant mice. Further, the expression of DNMT1 decreased significantly after NaF treatment. Conclusively, we demonstrated that fluorine may adversely affect early embryonic development by disrupting the methylation of H19 and Peg3 through downregulation of DNMT1.

Experimental diabetes induced by alloxan and streptozotocin: The current state of the art

Diabetes mellitus is a chronic metabolic disorder with a high prevalence worldwide. Animal models of diabetes represent an important tool in diabetes investigation that helps us to avoid unnecessary and ethically challenging studies in human subjects, as well as to obtain a comprehensive scientific viewpoint of this disease. Although there are several methods through which diabetes can be induced, chemical methods of alloxan- and streptozotocin-induced diabetes represent the most important and highly preferable experimental models for this pathological condition. Therefore, the aim of this article was to review the current knowledge related to quoted models of diabetes, including to this point available information about mechanism of action, particular time- and dose-dependent protocols, frequent problems, as well as major limitations linked to laboratory application of alloxan and sterptozotocin in inducing diabetes. Given that diabetes is known to be closely associated with serious health consequences it is of fundamental importance that current animal models for induction of diabetes should be continuously upgraded in order to improve overall prevention, diagnosis and treatment of this pathological condition.

Epigenetic Alterations in Human Liver From Subjects With Type 2 Diabetes in Parallel With Reduced Folate Levels

OBJECTIVE

Epigenetic variation may contribute to the development of complex metabolic diseases such as type 2 diabetes (T2D). Hepatic insulin resistance is a hallmark of T2D. However, it remains unknown whether epigenetic alterations take place in the liver from diabetic subjects. Therefore, we investigated the genome-wide DNA methylation pattern in the liver from subjects with T2D and nondiabetic controls and related epigenetic alterations to gene expression and circulating folate levels.

RESEARCH DESIGN AND METHODS

Liver biopsies were obtained from 35 diabetic and 60 nondiabetic subjects, which are part of the Kuopio Obesity Surgery Study. The genome-wide DNA methylation pattern was analyzed in the liver using the HumanMethylation450 BeadChip. RNA expression was analyzed from a subset of subjects using the HumanHT-12 Expression BeadChip.

RESULTS

After correction for multiple testing, we identified 251 individual CpG sites that exhibit differential DNA methylation in liver obtained from T2D compared with nondiabetic subjects (Q < .05). These include CpG sites annotated to genes that are biologically relevant to the development of T2D such as GRB10, ABCC3, MOGAT1, and PRDM16. The vast majority of the significant CpG sites (94%) displayed decreased DNA methylation in liver from subjects with T2D. The hypomethylation found in liver from diabetic subjects may be explained by reduced folate levels. Indeed, subjects with T2D had significantly reduced erythrocyte folate levels compared with nondiabetic subjects. We further identified 29 genes that displayed both differential DNA methylation and gene expression in human T2D liver including the imprinted gene H19.

CONCLUSIONS

Our study highlights the importance of epigenetic and transcriptional changes in the liver from subjects with T2D. Reduced circulating folate levels may provide an explanation for hypomethylation in the human diabetic liver.

Recent developments on the role of epigenetics in obesity and metabolic disease

The increased prevalence of obesity and related comorbidities is a major public health problem. While genetic factors undoubtedly play a role in determining individual susceptibility to weight gain and obesity, the identified genetic variants only explain part of the variation. This has led to growing interest in understanding the potential role of epigenetics as a mediator of gene-environment interactions underlying the development of obesity and its associated comorbidities. Initial evidence in support of a role of epigenetics in obesity and type 2 diabetes mellitus (T2DM) was mainly provided by animal studies, which reported epigenetic changes in key metabolically important tissues following high-fat feeding and epigenetic differences between lean and obese animals and by human studies which showed epigenetic changes in obesity and T2DM candidate genes in obese/diabetic individuals. More recently, advances in epigenetic methodologies and the reduced cost of epigenome-wide association studies (EWAS) have led to a rapid expansion of studies in human populations. These studies have also reported epigenetic differences between obese/T2DM adults and healthy controls and epigenetic changes in association with nutritional, weight loss, and exercise interventions. There is also increasing evidence from both human and animal studies that the relationship between perinatal nutritional exposures and later risk of obesity and T2DM may be mediated by epigenetic changes in the offspring. The aim of this review is to summarize the most recent developments in this rapidly moving field, with a particular focus on human EWAS and studies investigating the impact of nutritional and lifestyle factors (both pre- and postnatal) on the epigenome and their relationship to metabolic health outcomes. The difficulties in distinguishing consequence from causality in these studies and the critical role of animal models for testing causal relationships and providing insight into underlying mechanisms are also addressed. In summary, the area of epigenetics and metabolic health has seen rapid developments in a short space of time. While the outcomes to date are promising, studies are ongoing, and the next decade promises to be a time of productive research into the complex interactions between the genome, epigenome, and environment as they relate to metabolic disease.

Combined parental obesity negatively impacts preimplantation mouse embryo development, kinetics, morphology and metabolism

STUDY QUESTION

Does combined parental obesity, both an obese mother and father, have a greater effect on mouse preimplantation embryo development and quality than single-parent obesity?

SUMMARY ANSWER

Combined parental obesity causes a greater reduction in the blastocyst rate and a greater delay to the timing of key embryonic developmental events than single-parental obesity, as well as altering embryonic characteristics, such as zona pellucida width.

WHAT IS KNOWN ALREADY

Maternal or paternal obesity alone are known to have significant and detrimental impacts on preimplantation embryo development. Furthermore, these early embryonic perturbations can have long-term impacts on both offspring health and further generations. This is one of the first studies to examine the effects of having both an obese mother and an obese father.

STUDY DESIGN, SIZE, DURATION

A cross-sectional control versus treatment mouse study of diet-induced obesity was employed, in which 300 embryos per group were generated and studied from reciprocal matings: (i) control female and control male (Lean Parented Embryos); (ii) control female and obese male (Paternal Obese Parented Embryos); (iii) obese female and control male (Maternal Obese Parented Embryos) and (iv) obese female and obese male (Combined Obese Parented embryos). Assessments of the embryonic development rate, timing of development, morphological characteristics, metabolic gene expression, metabolism and cell lineage allocation were made at selected time points and analysed in relation to parental obesity status.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Three-week-old C57BL6 male and female mice were fed control (7% total fat) or high fat (21% total fat) diets for a minimum of 8 weeks. Females were superovulated, mated, fertilized zygotes recovered and standard mouse in vitro embryo culture performed. Time-lapse monitoring was undertaken to compare developmental timings and morphological characteristics (embryonic area and zona pellucida width) for embryos from all four reciprocal matings. Differential staining identified cell lineage allocation. Real-time quantitative RT-PCR (qRT-PCR) and microfluorescence were used to measure gene expression and metabolism (glucose consumption and lactate production), respectively, in embryos from Lean Parented and Combined Obese Parented matings. This research was completed in a University research laboratory.

MAIN RESULTS AND THE ROLE OF CHANCE

Blastocyst rate was reduced in Combined Obese Parented embryos when compared with both Single Obese (11% decrease for Maternal Obese Parented, P < 0.05; 15% for Paternal Obese Parented, P < 0.05) and Lean Parented embryos (25% decrease, P < 0.01). Time-lapse analysis of developmental kinetics highlighted a delay of 1 h at the 2-3 cell division, extending to 6 h delay by the blastocyst stage for Combined Obese Parented embryos (P < 0.05). A reduction in the total cell number of Combined Obese Parented blastocysts was a further manifestation of this developmental delay (P < 0.05). Zona pellucida width was reduced in Combined Obese Parented embryos (P < 0.05). Glucose consumption was increased in Combined Obese Parented embryos (P < 0.05), which was associated with the up-regulation of Glucose transporter 1 expression (P < 0.05).

LIMITATIONS AND REASON FOR CAUTION

This study was completed in fertile C57BL/6 mice using a well-defined model of diet-induced obesity in which embryos were fertilized in vivo. Human obesity is complex, with many causes and co-morbidities, and therefore, the impact of combined obesity would require further investigation in human settings.

WIDER IMPLICATIONS OF THE FINDINGS

This study demonstrates that combined parental obesity has a detrimental impact on mouse embryo development, a finding consistent with previous studies on individual parent obesity. Of note, the effect of combined parental obesity upon embryo development markers was greater than that of individual parental obesity. Plausibly, human embryos will be similarly impacted. The reduction in the blastocyst rate and delayed time to developmental events confirms that embryos of obese parents differ from those of lean parents. Allowance for this should therefore be incorporated into clinical practice when selecting the best embryo for the transfer of an obese couple.

STUDY FUNDING/COMPETING INTERESTS

Funding was provided by University of Melbourne research monies. M.P.G. currently holds the position of Merck Serono Lecturer of Reproductive Biology. D.K.G. received research funds from Vitrolife AB Sweden. The other authors of this manuscript have nothing to declare and no conflicts of interest.

Epigenetics: an accessible mechanism through which to track and respond to an obesogenic environment

Obesity and its consequences impact everyone. Obesity occurs because of an interaction between an obesogenic environment and genetics. In order to confront obesity, we must understand the contribution of each of these components. Environmental influences on obesity include our extrinsic environment, such as food deserts, as well as our intrinsic environment, like perinatal exposures. Epigenetics provides a biological mechanism to reveal the accumulation of extrinsic and intrinsic environmental exposures from fetal life to adulthood. Human and animal studies demonstrate changes in epigenetic modifications which are associated with an obesogenic environment. Furthermore, evidence exists in humans and animal models that suggest environmental epigenetics may serve as a biomarker or a target for intervention. To successfully target obesity, we must intervene on an environmental as well as genetic level. Combating food deserts for example will help to change the extrinsic environment, while targeting epigenetic modification remains a goal for changing our biology.