In utero effects. In utero undernourishment perturbs the adult sperm methylome and intergenerational metabolism

Pre-eclamptic foetal programming predisposes offspring to hepatic steatosis via DNA methylation

OBJECTIVES

Gamete and embryo-foetal origins of adult diseases hypothesis proposes that adulthood chronic disorders are associated with adverse foetal and early life traits. Our study aimed to characterise developmental changes and underlying mechanisms of metabolic disorders in offspring of pre-eclampsia (PE) programmed pregnancy.

METHODS

Nω-Nitro-l-arginine methyl ester hydrochloride (L-NAME) induced pre-eclampsia-like C57BL/6J mouse model was used. Lipid profiling, histological morphology, indirect calorimetry, mRNA sequencing, and pyrosequencing were performed on PE offspring of both young and elderly ages.

RESULTS

PE offspring exhibited increased postnatal weight gain, hepatic lipid accumulation, enlarged adipocytes, and impaired energy balance that continued to adulthood. Integrated RNA sequencing of foetal and 52-week-old livers revealed that the differentially expressed genes were mainly enriched in lipid metabolism, including glycerol-3-phosphate acyl-transferase 3 (Gpat3), a key enzyme for de novo synthesis of triglycerides (TG), and carnitine palmitoyltransferase-1a (Cpt1a), a key transmembrane enzyme that mediates fatty acid degradation. Pyrosequencing of livers from PE offspring identified hypomethylated and hypermethylated regions in Gpat3 and Cpt1a promoters, which were associated with upregulated and downregulated expressions of Gpat3 and Cpt1a, respectively. These epigenetic alterations are persistent and consistent from the foetal stage to adulthood in PE offspring.

CONCLUSION

These findings suggest a methylation-mediated epigenetic mechanism for PE-induced intergenerational lipid accumulation, impaired energy balance and obesity in offspring, and indicate the potential benefits of early interventions in offspring exposed to maternal PE to reduce their susceptibility to metabolic disorder in their later life.

Trans-generational effects of parental exposure to drugs of abuse on offspring memory functions

Recent evidence reported that parental-derived phenotypes can be passed on to the next generations. Within the inheritance of epigenetic characteristics allowing the transmission of information related to the ancestral environment to the offspring, the specific case of the trans-generational effects of parental drug addiction has been extensively studied. Drug addiction is a chronic disorder resulting from complex interactions among environmental, genetic, and drug-related factors. Repeated exposures to drugs induce epigenetic changes in the reward circuitry that in turn mediate enduring changes in brain function. Addictive drugs can exert their effects trans-generally and influence the offspring of addicted parents. Although there is growing evidence that shows a wide range of behavioral, physiological, and molecular phenotypes in inter-, multi-, and trans-generational studies, transmitted phenotypes often vary widely even within similar protocols. Given the breadth of literature findings, in the present review, we restricted our investigation to learning and memory performances, as examples of the offspring's complex behavioral outcomes following parental exposure to drugs of abuse, including morphine, cocaine, cannabinoids, nicotine, heroin, and alcohol.

The transgenerational effects of maternal low-protein diet during lactation on offspring

Environmental factors such as diet and lifestyle can influence the health of both mothers and offspring. However, its transgenerational transmission and underlying mechanisms remain largely unknown. Here, using a maternal lactation-period low-protein diet (LPD) mouse model, we show that maternal LPD during lactation causes decreased survival and stunted growth, significantly reduces ovulation and litter size, and alters the gut microbiome in the female LPD-F1 offspring. The transcriptome of LPD-F1 metaphase II (MII) oocytes shows that differentially expressed genes are enriched in female pregnancy and multiple metabolic processes. Moreover, maternal LPD causes early stunted growth and impairs metabolic health, which is transmitted over two generations. The methylome alteration of LPD-F1 oocytes can be partly transmitted to the F2 oocytes. Together, our results reveal that LPD during lactation transgenerationally affects offspring health, probably via oocyte epigenetic changes.

Paternal dietary macronutrient balance and energy intake drive metabolic and behavioral differences among offspring

Paternal diet can influence the phenotype of the next generation, yet, the dietary components inducing specific responses in the offspring are not identified. Here, we use the Nutritional Geometry Framework to determine the effects of pre-conception paternal dietary macronutrient balance on offspring metabolic and behavioral traits in mice. Ten isocaloric diets varying in the relative proportion of protein, fats, and carbohydrates are fed to male mice prior to mating. Dams and offspring are fed standard chow and never exposed to treatment diets. Body fat in female offspring is positively associated with the paternal consumption of fat, while in male offspring, an anxiety-like phenotype is associated to paternal diets low in protein and high in carbohydrates. Our study uncovers that the nature and the magnitude of paternal effects are driven by interactions between macronutrient balance and energy intake and are not solely the result of over- or undernutrition.

Is developmental plasticity triggered by DNA methylation changes in the invasive cane toad (Rhinella marina)?

Many organisms can adjust their development according to environmental conditions, including the presence of conspecifics. Although this developmental plasticity is common in amphibians, its underlying molecular mechanisms remain largely unknown. Exposure during development to either 'cannibal cues' from older conspecifics, or 'alarm cues' from injured conspecifics, causes reduced growth and survival in cane toad (Rhinella marina) tadpoles. Epigenetic modifications, such as changes in DNA methylation patterns, are a plausible mechanism underlying these developmental plastic responses. Here we tested this hypothesis, and asked whether cannibal cues and alarm cues trigger the same DNA methylation changes in developing cane toads. We found that exposure to both cannibal cues and alarm cues was associated with local changes in DNA methylation patterns. These DNA methylation changes affected genes putatively involved in developmental processes, but in different genomic regions for different conspecific-derived cues. Genetic background explains most of the epigenetic variation among individuals. Overall, the molecular mechanisms triggered by exposure to cannibal cues seem to differ from those triggered by alarm cues. Studies linking epigenetic modifications to transcriptional activity are needed to clarify the proximate mechanisms that regulate developmental plasticity in cane toads.

Intrauterine developmental origin, programming mechanism, and prevention strategy of fetal-originated hypercholesterolemia

There is increasing evidence that hypercholesterolemia has an intrauterine developmental origin. However, the pathogenesis of fetal-originated is still lacking in a theoretical system, which makes its clinical early prevention and treatment difficult. It has been found that an adverse environment during pregnancy (e.g., xenobiotic exposure) may lead to changes in fetal blood cholesterol levels through changing maternal cholesterol metabolic function and/or placental cholesterol transport function and may also directly affect the liver cholesterol metabolic function of the offspring in utero and continue after birth. Adverse environmental conditions during pregnancy may also raise maternal glucocorticoid levels and promote the placental glucocorticoid barrier opening, leading to fetal overexposure to maternal glucocorticoids. Intrauterine high-glucocorticoid exposure can alter the liver cholesterol metabolism of offspring, resulting in an increased susceptibility to hypercholesterolemia after birth. Abnormal epigenetic modifications are involved in the intrauterine programming mechanism of fetal-originated hypercholesterolemia. Some interventions targeted at pregnant mothers or offspring in early life have been proposed to effectively prevent and treat the development of fetal-originated hypercholesterolemia. In this paper, the recent research progress on fetal-originated hypercholesterolemia was reviewed, with emphasis on intrauterine maternal glucocorticoid programming mechanisms, in order to provide a theoretical basis for its early clinical warning, prevention, and treatment.

DNA methylation reprogramming mediates transgenerational diabetogenic effect induced by early-life p,p'-DDE exposure

Increasing evidence shows that an adverse environment during the early fetal development can affect the epigenetic modifications on a wide range of diabetes-related genes, leading to an increased diabetic susceptibility in adulthood or even in subsequent generations. p,p'-Dichlorodiphenoxydichloroethylene (p,p'-DDE) is a break-down product of the pesticide dichlorodiphenyltrichloroethane (DDT). p,p'-DDE has been associated with various health concerns, such as diabetogenic effect. However, the precise molecular mechanism remains unclear. In this study, p,p'-DDE was given by gavage to pregnant rat dams from gestational day (GD) 8 to GD15 to generate male germline to investiagate the transgenerational effects. We found that early-life p,p'-DDE exposure increased the transgenerational diabetic susceptibility through male germline inheritance. In utero exposure to p,p'-DDE altered the sperm DNA methylome in F1 progeny, and a significant number of those differentially methylated genes could be inherited by F2 progeny. Furthermore, early-life p,p'-DDE exposure altered DNA methylation in glucose metabolic genes Gck and G6pc in sperm and the methylation modification were also found in liver of the next generation. Our study demonstrate that DNA methylation plays a critical role in mediating transgenerational diabetogenic effect induced by early-life p,p'-DDE exposure.

Paternal p,p'-DDE exposure and pre-pubertal high-fat diet increases the susceptibility to fertility impairment and sperm Igf2 DMR2 hypo-methylation in male offspring

The hypothesis of paternal origins of health and disease (POHaD) indicates that paternal exposure to adverse environment could alter the epigenetic modification in germ line, increasing the disease susceptibility in offspring or even in subsequent generations. p,p'-Dichlorodiphenyldichloroethylene (p,p'-DDE) is an anti-androgenic chemical and male reproductive toxicant. Gestational p,p'-DDE exposure could impair reproductive development and fertility in male offspring. However, the effect of paternal p,p'-DDE exposure on fertility in male offspring remains uncovered. From postnatal day (PND) 35 to 119, male rats (F0) were given 10 mg/body weight (b.w.) p,p'-DDE or corn oil by gavage. Male rats were then mated with the control females to generate male offspring. On PND35, the male offspring were divided into 4 groups according whether to be given the high-fat diet (HF): corn oil treatment with control diet (C-C), p,p'-DDE treatment with control diet (DDE-C), corn oil treatment with high-fat diet (C-HF) or p,p'-DDE treatment with high-fat diet (DDE-HF) for 35 days. Our results indicated that paternal p,p'-DDE exposure did not affect the male fertility of male offspring directly, but decreased sperm quality and induced testicular apoptosis after the high-fat diet treatment. Further analysis demonstrated that paternal exposure to p,p'-DDE and pre-pubertal high-fat diet decreased sperm Igf2 DMR2 methylation and gene expression in male offspring. Hence, paternal exposure to p,p'-DDE and pre-pubertal high-fat diet increases the susceptibility to male fertility impairment and sperm Igf2 DMR2 hypo-methylation in male offspring, posing a significant implication in the disease etiology.

Frequency, morbidity and equity - the case for increased research on male fertility

Currently, most men with infertility cannot be given an aetiology, which reflects a lack of knowledge around gamete production and how it is affected by genetics and the environment. A failure to recognize the burden of male infertility and its potential as a biomarker for systemic illness exists. The absence of such knowledge results in patients generally being treated as a uniform group, for whom the strategy is to bypass the causality using medically assisted reproduction (MAR) techniques. In doing so, opportunities to prevent co-morbidity are missed and the burden of MAR is shifted to the woman. To advance understanding of men's reproductive health, longitudinal and multi-national centres for data and sample collection are essential. Such programmes must enable an integrated view of the consequences of genetics, epigenetics and environmental factors on fertility and offspring health. Definition and possible amelioration of the consequences of MAR for conceived children are needed. Inherent in this statement is the necessity to promote fertility restoration and/or use the least invasive MAR strategy available. To achieve this aim, protocols must be rigorously tested and the move towards personalized medicine encouraged. Equally, education of the public, governments and clinicians on the frequency and consequences of infertility is needed. Health options, including male contraceptives, must be expanded, and the opportunities encompassed in such investment understood. The pressing questions related to male reproductive health, spanning the spectrum of andrology are identified in the Expert Recommendation.

The Emerging Function and Promise of tRNA-Derived Small RNAs in Cancer

Fragments derived from tRNA, called tRNA-derived small RNAs (tsRNAs), have attracted widespread attention in the past decade. tsRNAs are widespread in prokaryotic and eukaryotic transcriptome, which contains two main types, tRNA-derived fragments (tRFs) and tRNA-derived stress-inducing RNA (tiRNAs), derived from the precursor tRNAs or mature tRNAs. According to differences in the cleavage position, tRFs can be divided into tRF-1, tRF-2, tRF-3, tRF-5, and i-tRF, whereas tiRNAs can be divided into 5'-tiRNA and 3'-tiRNA. Studies have found that tRFs and tiRNAs are abnormally expressed in a variety of human malignant tumors, promote or inhibit the proliferation and apoptosis of cancer cells by regulating the expression of oncogene, and play an important role in the aggressive metastasis and progression of tumors. This article reviews the biological origins of various tsRNAs, introduces their functions and new concepts of related mechanisms, and focuses on the molecular mechanisms of tsRNAs in cancer, including breast cancer, prostate cancer, colorectal cancer, lung cancer, b-cell lymphoma, and chronic lymphoma cell leukemia. Lastly, this article puts forward some unresolved problems and future research prospects.

The Association between Long-Term DDT or DDE Exposures and an Altered Sperm Epigenome-a Cross-Sectional Study of Greenlandic Inuit and South African VhaVenda Men

BACKGROUND

The organochlorine dichlorodiphenyltrichloroethane (DDT) is banned worldwide owing to its negative health effects. It is exceptionally used as an insecticide for malaria control. Exposure occurs in regions where DDT is applied, as well as in the Arctic, where its endocrine disrupting metabolite, p , p ' -dichlorodiphenyldichloroethylene (p , p ' -DDE) accumulates in marine mammals and fish. DDT and p , p ' -DDE exposures are linked to birth defects, infertility, cancer, and neurodevelopmental delays. Of particular concern is the potential of DDT use to impact the health of generations to come via the heritable sperm epigenome.

OBJECTIVES

The objective of this study was to assess the sperm epigenome in relation to p , p ' -DDE serum levels between geographically diverse populations.

METHODS

In the Limpopo Province of South Africa, we recruited 247 VhaVenda South African men and selected 50 paired blood serum and semen samples, and 47 Greenlandic Inuit blood and semen paired samples were selected from a total of 193 samples from the biobank of the INUENDO cohort, an EU Fifth Framework Programme Research and Development project. Sample selection was based on obtaining a range of p , p ' -DDE serum levels (mean = 870.734 ± 134.030  ng / mL ). We assessed the sperm epigenome in relation to serum p , p ' -DDE levels using MethylC-Capture-sequencing (MCC-seq) and chromatin immunoprecipitation followed by sequencing (ChIP-seq). We identified genomic regions with altered DNA methylation (DNAme) and differential enrichment of histone H3 lysine 4 trimethylation (H3K4me3) in sperm.

RESULTS

Differences in DNAme and H3K4me3 enrichment were identified at transposable elements and regulatory regions involved in fertility, disease, development, and neurofunction. A subset of regions with sperm DNAme and H3K4me3 that differed between exposure groups was predicted to persist in the preimplantation embryo and to be associated with embryonic gene expression.

DISCUSSION

These findings suggest that DDT and p , p ' -DDE exposure impacts the sperm epigenome in a dose-response-like manner and may negatively impact the health of future generations through epigenetic mechanisms. Confounding factors, such as other environmental exposures, genetic diversity, and selection bias, cannot be ruled out. https://doi.org/10.1289/EHP12013.

Maternal obstructive sleep apnea aggravates metabolic dysfunction-associated fatty liver disease via HMGB1-TLR4 signaling-mediated endoplasmic reticulum stress in male offspring rats

AIMS/HYPOTHESIS

Maternal obstructive sleep apnea (MOSA) may inflict long-term metabolic effects on offspring. We hypothesize that MOSA increases the propensity for metabolic dysregulation in offspring and thus facilitates the development of metabolic dysfunction-associated fatty liver disease (MAFLD). This study aims to test the hypothesis and explore the underlying mechanism.

METHODS

The MOSA rat model of upper airway obstruction was established and fecundated. The postweaning male offspring (n = 171) from both the control group and MOSA group were randomly fed the normal chow diet (NCD, n = 89) or high-fat diet (HFD, n = 82) for the next 5 months. Liver function, lipid profile, glucose, and insulin levels were measured. Expression levels of fibrosis-related proteins and endoplasmic reticulum (ER) stress-related proteins in liver tissues were assessed using immunohistochemistry and western blotting.

RESULTS

MOSA increased body and liver weight in male offspring, along with augmented liver organ coefficient. Serum levels of aminotransferases, low-density lipoprotein, high-density lipoprotein, triglycerides, total cholesterol, total bile acid, fasting glucose, and insulin increased significantly. MOSA exacerbated HFD-induced hepatic steatosis and fibrosis. These effects were driven by the overactivated double-stranded RNA-activated protein kinase (PKR)-like eukaryotic initiation factor 2(PERK)-activating transcription factor (ATF)4-C/EBP homologous protein (CHOP) signaling pathway-induced ER stress, and hyperacetylation and release of high mobility group box-1(HMGB1) elicited above signaling in a TLR4-dependent manner.

CONCLUSIONS

These findings indicate that MOSA can exert prolonged adverse effects manifested as metabolic dysfunction in male offspring. Therefore, surveillance and management of OSA during pregnancy may be necessary to prevent and alleviate MAFLD in offspring.

Metastable epialleles in humans

First identified in isogenic mice, metastable epialleles (MEs) are loci where the extent of DNA methylation (DNAm) is variable between individuals but correlates across tissues derived from different germ layers within a given individual. This property, termed systemic interindividual variation (SIV), is attributed to stochastic methylation establishment before germ layer differentiation. Evidence suggests that some putative human MEs are sensitive to environmental exposures in early development. In this review we introduce key concepts pertaining to human MEs, describe methods used to identify MEs in humans, and review their genomic features. We also highlight studies linking DNAm at putative human MEs to early environmental exposures and postnatal (including disease) phenotypes.

Legacies of salient environmental experiences-insights from chemosensation

Evidence for parental environments profoundly influencing the physiology, biology, and neurobiology of future generations has been accumulating in the literature. Recent efforts to understand this phenomenon and its underlying mechanisms have sought to use species like rodents and insects to model multi-generational legacies of parental experiences like stress and nutritional exposures. From these studies, we have come to appreciate that parental exposure to salient environmental experiences impacts the cadence of brain development, hormonal responses to stress, and the expression of genes that govern cellular responses to stress in offspring. Recent studies using chemosensory exposure have emerged as a powerful tool to shed new light on how future generations come to be influenced by environments to which parents are exposed. With a specific focus on studies that have leveraged such use of salient chemosensory experiences, this review synthesizes our current understanding of the concept, causes, and consequences of the inheritance of chemosensory legacies by future generations and how this field of inquiry informs the larger picture of how parental experiences can influence offspring biology.

Higher incidence of embryonic defects in mouse offspring conceived with assisted reproduction from fathers with sperm epimutations

Assisted reproductive technologies (ART) account for 1-6% of births in developed countries. While most children conceived are healthy, increases in birth and genomic imprinting defects have been reported; such abnormal outcomes have been attributed to underlying parental infertility and/or the ART used. Here, we assessed whether paternal genetic and lifestyle factors, that are associated with male infertility and affect the sperm epigenome, can influence ART outcomes. We examined how paternal factors, haploinsufficiency for Dnmt3L, an important co-factor for DNA methylation reactions, and/or diet-induced obesity, in combination with ART (superovulation, in vitro fertilization, embryo culture and embryo transfer), could adversely influence embryo development and DNA methylation patterning in mice. While male mice fed high-fat diets (HFD) gained weight and showed perturbed metabolic health, their sperm DNA methylation was minimally affected by the diet. In contrast, Dnmt3L haploinsufficiency induced a marked loss of DNA methylation in sperm; notably, regions affected were associated with neurodevelopmental pathways and enriched in young retrotransposons, sequences that can have functional consequences in the next generation. Following ART, placental imprinted gene methylation and growth parameters were impacted by one or both paternal factors. For embryos conceived by natural conception, abnormality rates were similar for WT and Dnmt3L+/- fathers. In contrast, paternal Dnmt3L+/- genotype, as compared to WT fathers, resulted in a 3-fold increase in the incidence of morphological abnormalities in embryos generated by ART. Together, the results indicate that embryonic morphological and epigenetic defects associated with ART may be exacerbated in offspring conceived by fathers with sperm epimutations.

Sperm chromatin accessibility's involvement in the intergenerational effects of stress hormone receptor activation

Dexamethasone is a stress hormone receptor agonist used widely in clinics. We and others previously showed that paternal administration of dexamethasone in mice affects the phenotype of their offspring. The substrate of intergenerational transmission of environmentally induced effects often involves changes in sperm RNA, yet other epigenetic modifications in the germline can be affected and are also plausible candidates. First, we tested the involvement of altered sperm RNAs in the transmission of dexamethasone induced phenotypes across generations. We did this by injecting sperm RNA into naïve fertilized oocytes, before performing metabolic and behavioral phenotyping of the offspring. We observed phenotypic changes in discordance with those found in offspring generated by in vitro fertilization using sperm from dexamethasone exposed males. Second, we investigated the effect of dexamethasone on chromatin accessibility using ATAC sequencing and found significant changes at specific genomic features and gene regulatory loci. Employing q-RT-PCR, we show altered expression of a gene in the tissue of offspring affected by accessibility changes in sperm. Third, we establish a correlation between specific DNA modifications and stress hormone receptor activity as a likely contributing factor influencing sperm accessibility. Finally, we independently investigated this dependency by genetically reducing thymine-DNA glycosylase levels and observing concomitant changes at the level of chromatin accessibility and stress hormone receptor activity.

Revisiting Carl Jung's archetype theory a psychobiological approach

This paper delves into the concept of archetypes, universal patterns of behavior and cognition, and proposes a novel tripartite model distinguishing between structural, regulatory, and representational archetypes. Drawing on insights from code biology, neuroscience, genetics, and epigenetics, the model provides a nuanced framework for understanding archetypes and their role in shaping cognition and behavior. The paper also explores the interplay between these elements to express representational archetypes. Furthermore, it addresses the informational capacity of the genome and its influence on post-natal development and the psyche. The paper concludes by discussing the future trajectory of psychology, emphasizing the need for an integrative approach that combines our understanding of social constructs with insights into our inherent organizational propensities or archetypes. This exploration holds the potential to advance our understanding of the human condition.

Thermoneutral Housing Enables Studies of Vertical Transmission of Obesogenic Diet-Driven Metabolic Diseases

Vertical transmission of obesity is a critical contributor to the unabated obesity pandemic and the associated surge in metabolic diseases. Existing experimental models insufficiently recapitulate "human-like" obesity phenotypes, limiting the discovery of how severe obesity in pregnancy instructs vertical transmission of obesity. Here, via utility of thermoneutral housing and obesogenic diet feeding coupled to syngeneic mating of WT obese female and lean male mice on a C57BL/6 background, we present a tractable, more "human-like" approach to specifically investigate how maternal obesity contributes to offspring health. Using this model, we found that maternal obesity decreased neonatal survival, increased offspring adiposity, and accelerated offspring predisposition to obesity and metabolic disease. We also show that severe maternal obesity was sufficient to skew offspring microbiome and create a proinflammatory gestational environment that correlated with inflammatory changes in the offspring in utero and adulthood. Analysis of a human birth cohort study of mothers with and without obesity and their infants was consistent with mouse study findings of maternal inflammation and offspring weight gain propensity. Together, our results show that dietary induction of obesity in female mice coupled to thermoneutral housing can be used for future mechanistic interrogations of obesity and metabolic disease in pregnancy and vertical transmission of pathogenic traits.

Inheritance of environment-induced phenotypic changes through epigenetic mechanisms

Growing evidence suggests that epigenetic changes through various parental environmental factors alter the phenotypes of descendants in various organisms. Environmental factors, including exposure to chemicals, stress and abnormal nutrition, affect the epigenome in parental germ cells by different epigenetic mechanisms, such as DNA methylation, histone modification as well as small RNAs via metabolites. Some current remaining questions are the causal relationship between environment-induced epigenetic changes in germ cells and altered phenotypes of descendants, and the molecular basis of how the abnormal epigenetic changes escape reprogramming in germ cells. In this review, we introduce representative examples of intergenerational and transgenerational inheritance of phenotypic changes through parental environmental factors and the accompanied epigenetic and metabolic changes, with a focus on animal species. We also discuss the molecular mechanisms of epigenomic inheritance and their possible biological significance.

Teratogenesis and the epigenetic programming of congenital defects: Why paternal exposures matter

Until recently, clinicians and researchers did not realize paternal exposures could impact child developmental outcomes. Indeed, although there is growing recognition that sperm carry a large amount of non-genomic information and that paternal stressors influence the health of the next generation, toxicologists are only now beginning to explore the role paternal exposures have in dysgenesis and the incidence of congenital malformations. In this commentary, I will briefly summarize the few studies describing congenital malformations resulting from preconception paternal stressors, argue for the theoretical expansion of teratogenic perspectives into the male preconception period, and discuss some of the challenges in this newly emerging branch of toxicology. I argue that we must consider gametes the same as any other malleable precursor cell type and recognize that environmentally-induced epigenetic changes acquired during the formation of the sperm and oocyte hold equal teratogenic potential as exposures during early development. Here, I propose the term epiteratogen to reference agents acting outside of pregnancy that, through epigenetic mechanisms, induce congenital malformations. Understanding the interactions between the environment, the essential epigenetic processes intrinsic to spermatogenesis, and their cumulative influences on embryo patterning is essential to addressing a significant blind spot in the field of developmental toxicology.

A systematic scientometric review of paternal inheritance of acquired metabolic traits

BACKGROUND

The concept of the inheritance of acquired traits, a foundational principle of Lamarck's evolutionary theory, has garnered renewed attention in recent years. Evidence for this phenomenon remained limited for decades but gained prominence with the Överkalix cohort study in 2002. This study revealed a link between cardiovascular disease incidence and the food availability experienced by individuals' grandparents during their slow growth periods, reigniting interest in the inheritance of acquired traits, particularly in the context of non-communicable diseases. This scientometric analysis and systematic review comprehensively explores the current landscape of paternally transmitted acquired metabolic traits.

RESULTS

Utilizing Scopus Advanced search and meticulous screening, we included mammalian studies that document the inheritance or modification of metabolic traits in subsequent generations of unexposed descendants. Our inclusive criteria encompass intergenerational and transgenerational studies, as well as multigenerational exposures. Predominantly, this field has been driven by a select group of researchers, potentially shaping the design and focus of existing studies. Consequently, the literature primarily comprises transgenerational rodent investigations into the effects of ancestral exposure to environmental pollutants on sperm DNA methylation. The complexity and volume of data often lead to multiple or redundant publications. This practice, while understandable, may obscure the true extent of the impact of ancestral exposures on the health of non-exposed descendants. In addition to DNA methylation, studies have illuminated the role of sperm RNAs and histone marks in paternally acquired metabolic disorders, expanding our understanding of the mechanisms underlying epigenetic inheritance.

CONCLUSIONS

This review serves as a comprehensive resource, shedding light on the current state of research in this critical area of science, and underscores the need for continued exploration to uncover the full spectrum of paternally mediated metabolic inheritance.

Maternal restricted- and over- feeding during gestation perturb offspring sperm epigenome in sheep

In brief

Inadequate maternal nutrition during gestation can have immediate and lifelong effects on offspring. This study shows that maternal restricted - and over- nutrition during gestation do not affect semen characteristics in F1 male offspring but alters offspring sperm sncRNA profiles and DNA methylome in sheep.

Abstract

There is a growing body of evidence that inadequate maternal nutrition during gestation can have immediate and lifelong effects on offspring. However, little is known about the effects of maternal nutrition during gestation on male offspring reproduction. Here, using a sheep model of maternal restricted - and over - nutrition (60 or 140% of the National Research Council requirements) during gestation, we found that maternal restricted - and over - nutrition do not affect semen characteristics (i.e. volume, sperm concentration, pH, sperm motility, sperm morphology) or scrotal circumference in male F1 offspring. However, using small RNA sequencing analysis, we demonstrated that both restricted - and over - nutrition during gestation induced marked changes in composition and expression of sperm small noncoding RNAs (sncRNAs) subpopulations including in male F1 offspring. Whole-genome bisulfite sequencing analysis further identified specific genomic loci where poor maternal nutrition resulted in alterations in DNA methylation. These findings indicate that maternal restricted - and over - nutrition during gestation induce epigenetic modifications in sperm of F1 offspring sperm in sheep, which may contribute to environmentally influenced phenotypes in ruminants.

Transgenerational inheritance of adrenal steroidogenesis inhibition induced by prenatal dexamethasone exposure and its intrauterine mechanism

BACKGROUND

Adrenal gland is the synthesis and secretion organ of glucocorticoid, which is crucial to fetal development and postnatal fate. Recently, we found that prenatal dexamethasone exposure (PDE) could cause adrenal dysfunction in offspring rats, but its multigenerational genetic effects and related mechanisms have not been reported.

METHODS

The PDE rat model was established, and female filial generation 1 (F1) rats mate with wild males to produce the F2, the same way for the F3. Three generation rats were sacrificed for the related detection. SW-13 cells were used to clarify the epigenetic molecular mechanism.

RESULTS

This study confirmed that PDE could activate fetal adrenal glucocorticoid receptor (GR). The activated GR, on the one hand, up-regulated Let-7b (in human cells) to inhibit steroidogenic acute regulatory protein (StAR) expression directly; on the other hand, down-regulated CCCTC binding factor (CTCF) and up-regulated DNA methyltransferase 3a/3b (Dnmt3a/3b), resulting in H19 hypermethylation and low expression. The decreased interaction of H19 and let-7 can further inhibit adrenal steroidogenesis. Additionally, oocytes transmitted the expression change of H19/let-7c axis to the next generation rats. Due to its genetic stability, F2 generation oocytes indirectly exposed to dexamethasone also inhibited H19 expression, which could be inherited to the F3 generation.

CONCLUSIONS

This cascade effect of CTCF/H19/Let-7c ultimately resulted in the transgenerational inheritance of adrenal steroidogenesis inhibition of PDE offspring. This study deepens the understanding of the intrauterine origin of adrenal developmental toxicity, and it will provide evidence for the systematic analysis of the transgenerational inheritance effect of acquired traits induced by PDE. Video Abstract.

Unaltered hepatic wound healing response in male rats with ancestral liver injury

The possibility that ancestral environmental exposure could result in adaptive inherited effects in mammals has been long debated. Numerous rodent models of transgenerational responses to various environmental factors have been published but due to technical, operational and resource burden, most still await independent confirmation. A previous study reported multigenerational epigenetic adaptation of the hepatic wound healing response upon exposure to the hepatotoxicant carbon tetrachloride (CCl4) in male rats. Here, we comprehensively investigate the transgenerational effects by repeating the original CCl4 multigenerational study with increased power, pedigree tracing, F2 dose-response and suitable randomization schemes. Detailed pathology evaluations do not support adaptive phenotypic suppression of the hepatic wound healing response or a greater fitness of F2 animals with ancestral liver injury exposure. However, transcriptomic analyses identified genes whose expression correlates with ancestral liver injury, although the biological relevance of this apparent transgenerational transmission at the molecular level remains to be determined. This work overall highlights the need for independent evaluation of transgenerational epigenetic inheritance paradigms in mammals.

Paternal effects on fetal programming

Paternal programming is the concept that the environmental signals from the sire's experiences leading up to mating can alter semen and ultimately affect the phenotype of resulting offspring. Potential mechanisms carrying the paternal effects to offspring can be associated with epigenetic signatures (DNA methylation, histone modification and non-coding RNAs), oxidative stress, cytokines, and the seminal microbiome. Several opportunities exist for sperm/semen to be influenced during development; these opportunities are within the testicle, the epididymis, or accessory sex glands. Epigenetic signatures of sperm can be impacted during the pre-natal and pre-pubertal periods, during sexual maturity and with advancing sire age. Sperm are susceptible to alterations as dictated by their developmental stage at the time of the perturbation, and sperm and seminal plasma likely have both dependent and independent effects on offspring. Research using rodent models has revealed that many factors including over/under nutrition, dietary fat, protein, and ingredient composition (e.g., macro- or micronutrients), stress, exercise, and exposure to drugs, alcohol, and endocrine disruptors all elicit paternal programming responses that are evident in offspring phenotype. Research using livestock species has also revealed that sire age, fertility level, plane of nutrition, and heat stress can induce alterations in the epigenetic, oxidative stress, cytokine, and microbiome profiles of sperm and/or seminal plasma. In addition, recent findings in pigs, sheep, and cattle have indicated programming effects in blastocysts post-fertilization with some continuing into post-natal life of the offspring. Our research group is focused on understanding the effects of common management scenarios of plane of nutrition and growth rates in bulls and rams on mechanisms resulting in paternal programming and subsequent offspring outcomes. Understanding the implication of paternal programming is imperative as short-term feeding and management decisions have the potential to impact productivity and profitability of our herds for generations to come.

Developmental origins of diabetes mellitus: Environmental epigenomics and emerging patterns

Mounting epidemiological evidence indicates that environmental exposures in early life have roles in diabetes susceptibility in later life. Additionally, environmentally induced diabetic susceptibility could be transmitted to subsequent generations. Epigenetic modifications provide a potential association with the environmental factors and altered gene expression that might cause disease phenotypes. Here, we bring the increasing evidence that environmental exposures early in development are linked to diabetes through epigenetic modifications. This review first summarizes the epigenetic targets, including metastable epialleles and imprinting genes, by which the environmental factors can modify the epigenome. Then we review the epigenetics changes in response to environmental challenge during critical developmental windows, gametogenesis, embryogenesis, and fetal and postnatal period, with the specific example of diabetic susceptibility. Although the mechanisms are still largely unknown, especially in humans, the new research methods are now gradually available, and the animal models can provide more in-depth study of mechanisms. These have implications for investigating the link of the phenomena to human diabetes, providing a new perspective on environmentally triggered diabetes risk.

Sex-specific effects of chronic paternal stress on offspring development are partially mediated via mothers

Paternal stress exposure is known to impact the development of stress-related behaviors in offspring. Previous work has highlighted the importance of sperm mediated factors, such as RNAs, in transmitting the effects of parental stress. However, a key unanswered question is whether mothers behavior could drive or modulate the transmission of paternal stress effects on offspring development. Here we investigate how chronic variable stress in Balb/C mice influences the sex-specific development of anxiety- and depression-like neural and behavioral development in offspring. Moreover, we examined how stressed fathers influenced mate maternal investment towards their offspring and how this may modulate the transmission of paternal stress effects on offspring. We show that paternal stress leads to sex-specific effects on offspring behavior. Males that are chronically stressed sire female offspring that show increased anxiety and depression-like behaviors. However, male offspring of stressed fathers show reductions in anxiety- and depression-behaviors and are generally more exploratory. Moreover, we show that females mated with stressed males gain less weight during pregnancy and provide less care towards their offspring which additionally influenced offspring development. These data indicate that paternal stress can influence offspring development both directly and indirectly via changes in mothers, with implications for sex-specific offspring development.

Emerging evidence that the mammalian sperm epigenome serves as a template for embryo development

Although more studies are demonstrating that a father's environment can influence child health and disease, the molecular mechanisms underlying non-genetic inheritance remain unclear. It was previously thought that sperm exclusively contributed its genome to the egg. More recently, association studies have shown that various environmental exposures including poor diet, toxicants, and stress, perturbed epigenetic marks in sperm at important reproductive and developmental loci that were associated with offspring phenotypes. The molecular and cellular routes that underlie how epigenetic marks are transmitted at fertilization, to resist epigenetic reprogramming in the embryo, and drive phenotypic changes are only now beginning to be unraveled. Here, we provide an overview of the state of the field of intergenerational paternal epigenetic inheritance in mammals and present new insights into the relationship between embryo development and the three pillars of epigenetic inheritance: chromatin, DNA methylation, and non-coding RNAs. We evaluate compelling evidence of sperm-mediated transmission and retention of paternal epigenetic marks in the embryo. Using landmark examples, we discuss how sperm-inherited regions may escape reprogramming to impact development via mechanisms that implicate transcription factors, chromatin organization, and transposable elements. Finally, we link paternally transmitted epigenetic marks to functional changes in the pre- and post-implantation embryo. Understanding how sperm-inherited epigenetic factors influence embryo development will permit a greater understanding related to the developmental origins of health and disease.

Parental exposure to famine in early life and child overweight in offspring in Chinese populations

BACKGROUND

Little is known about the transgenerational effect of nutrition deficiency in early life. This study aimed to evaluate the associations of fetal and childhood exposure to famine of parents with their offspring's risk of overweight during childhood.

METHODS

This analysis included a total of 3734 participants of the China Health and Nutrition Survey aged 1-17 years whose fathers and/or mothers were born in 1955-1966. These children were classified into subgroups according to parental famine exposure status (unexposed and exposed) and timing (fetal-exposed and childhood-exposed). Random effects models were applied to evaluate the associations of parental famine exposure with body mass index (BMI) and overweight of offspring. Fractional polynomial functions were adopted to describe trajectories of BMI against age.

RESULTS

Compared with children of unexposed parents, there was a lower risk of overweight among offspring of childhood-exposed fathers [OR (95%CI): 0.80 (0.61, 1.04)] or exposed parents [0.84 (0.68, 1.04)], particularly among male offspring, but not among those with exposed mothers only [0.98 (0.65, 1.47)]. For BMI, children with exposed mothers only had a slightly higher BMI [β(95%CI): 0.17 (-0.15, 0.49)], while those with exposed fathers only had no difference [-0.02 (-0.23, 0.19)] or exposed parents had a slightly lower BMI [-0.17 (-0.33, 0.00)] (p < 0.05 for interaction between maternal and paternal exposures). Stratified analysis showed little heterogeneity between male and female offspring, but the association between paternal childhood exposure to famine and lower overweight risk in offspring was more evident in high (vs low) paternal education group (p for interaction< 0.05).

CONCLUSIONS

The transgenerational associations of early-life exposure to famine with lower risks of child overweight may be via the paternal line and differ by the educational levels of parents. Further studies are warranted to confirm the results and reveal the biological mechanisms underlying.

Intergenerational Inheritance of Hepatic Steatosis in a Mouse Model of Childhood Obesity: Potential Involvement of Germ-Line microRNAs

Childhood obesity increases the risk of developing metabolic syndrome later in life. Moreover, metabolic dysfunction may be inherited into the following generation through non-genomic mechanisms, with epigenetics as a plausible candidate. The pathways involved in the development of metabolic dysfunction across generations in the context of childhood obesity remain largely unexplored. We have developed a mouse model of early adiposity by reducing litter size at birth (small litter group, SL: 4 pups/dam; control group, C: 8 pups/dam). Mice raised in small litters (SL) developed obesity, insulin resistance and hepatic steatosis with aging. Strikingly, the offspring of SL males (SL-F1) also developed hepatic steatosis. Paternal transmission of an environmentally induced phenotype strongly suggests epigenetic inheritance. We analyzed the hepatic transcriptome in C-F1 and SL-F1 mice to identify pathways involved in the development of hepatic steatosis. We found that the circadian rhythm and lipid metabolic process were the ontologies with highest significance in the liver of SL-F1 mice. We explored whether DNA methylation and small non-coding RNAs might be involved in mediating intergenerational effects. Sperm DNA methylation was largely altered in SL mice. However, these changes did not correlate with the hepatic transcriptome. Next, we analyzed small non-coding RNA content in the testes of mice from the parental generation. Two miRNAs (miR-457 and miR-201) appeared differentially expressed in the testes of SL-F0 mice. They are known to be expressed in mature spermatozoa, but not in oocytes nor early embryos, and they may regulate the transcription of lipogenic genes, but not clock genes, in hepatocytes. Hence, they are strong candidates to mediate the inheritance of adult hepatic steatosis in our murine model. In conclusion, litter size reduction leads to intergenerational effects through non-genomic mechanisms. In our model, DNA methylation does not seem to play a role on the circadian rhythm nor lipid genes. However, at least two paternal miRNAs might influence the expression of a few lipid-related genes in the first-generation offspring, F1.

Inheritance of perturbed methylation and metabolism caused by uterine malnutrition via oocytes

BACKGROUND

Undernourishment in utero has deleterious effects on the metabolism of offspring, but the mechanism of the transgenerational transmission of metabolic disorders is not well known. In the present study, we found that undernourishment in utero resulted in metabolic disorders of female F1 and F2 in mouse model.

RESULTS

Undernutrition in utero induced metabolic disorders of F1 females, which was transmitted to F2 females. The global methylation in oocytes of F1 exposed to undernutrition in utero was decreased compared with the control. KEGG analysis showed that genes with differential methylation regions (DMRs) in promoters were significantly enriched in metabolic pathways. The altered methylation of some DMRs in F1 oocytes located at the promoters of metabolic-related genes were partially observed in F2 tissues, and the expressions of these genes were also changed. Meanwhile, the abnormal DNA methylation of the validated DMRs in F1 oocytes was also observed in F2 oocytes.

CONCLUSIONS

These results indicate that DNA methylation may mediate the transgenerational inheritance of metabolic disorders induced by undernourishment in utero via female germline.

Inheritance of paternal lifestyles and exposures through sperm DNA methylation

Many different lifestyle factors and chemicals present in the environment are a threat to the reproductive tracts of humans. The potential for parental preconception exposure to alter gametes and for these alterations to be passed on to offspring and negatively affect embryo growth and development is of concern. The connection between maternal exposures and offspring health is a frequent focus in epidemiological studies, but paternal preconception exposures are much less frequently considered and are also very important determinants of offspring health. Several environmental and lifestyle factors in men have been found to alter sperm epigenetics, which can regulate gene expression during early embryonic development. Epigenetic information is thought to be a mechanism that evolved for organisms to pass on information about their lived experiences to offspring. DNA methylation is a well-studied epigenetic regulator that is sensitive to environmental exposures in somatic cells and sperm. The continuous production of sperm from spermatogonial stem cells throughout a man's adult life and the presence of spermatogonial stem cells outside of the blood-testis barrier makes them susceptible to environmental insults. Furthermore, altered sperm DNA methylation patterns can be maintained throughout development and ultimately result in impairments, which could predispose offspring to disease. Innovations in human stem cell-based spermatogenic models can be used to elucidate the paternal origins of health and disease.

Multigenerational mistimed feeding drives circadian reprogramming with an impaired unfolded protein response

Mistimed food intake in relation to the day/night cycle disrupts the synchrony of circadian rhythms in peripheral tissues and increases the risk of metabolic diseases. However, the health effects over generations have seldom been explored. Here, we established a 10-generation mouse model that was continuously fed with daytime-restricted feeding (DRF). We performed RNA-seq analysis of mouse liver samples obtained every 4 h over a 24 h period from F2, F5 and F10 generations exposed to DRF. Multigenerational DRF programs the diurnal rhythmic transcriptome through a gain or loss of diurnal rhythmicity over generations. Gene ontology (GO) analysis of the differential rhythmic transcriptome revealed that adaptation to persistent DRF is accompanied by impaired endoplasmic reticulum (ER) stress. Consistently, a substantially higher level of folding-deficient proinsulin was observed in F10 liver tissues than in F2 and F5 liver tissues following tail vein injection. Subsequently, tunicamycin induced more hepatocyte death in F10 samples than in F2 and F5 samples. These data demonstrate that mistimed food intake could produce cumulative effects over generations on ER stress sensitivity in mice.

Transcriptional analyses provide novel insights into the transgenerational effects of Poly (I:C) on chickens

Pathogenic microorganisms that are ubiquitous in the environment threaten human health and food safety. Polyinosinic:polycytidylic acid (Poly (I:C)) is a macromolecule with a double-stranded RNA structure, which is often used to simulate viruses. Our previous study found that Poly (I:C) maternal stimulation could affect the reproduction of laying hens and their offspring, but the underlying mechanism needed to be explored. In the present study, splenic transcriptomes were sequenced and analyzed from two groups (Poly (I:C) treatment as the challenged group and saline treatment as the control) and in three generations (maternal stimulated F0 hens, unchallenged F1 and F2 generations). The results showed that Poly (I:C) maternal stimulation affected gene expression patterns in laying hens and their offspring. A total of 27 differentially expressed genes (DEGs) with the same regulating trend were discovered in the F0 and F1 generations, indicating an influence of the intergenerational transmission effect. Functional enrichment analysis of Gene Ontology (GO) showed that lymphocyte differentiation, positive regulation of leukocyte differentiation, positive regulation of MAPK cascade, and T cell differentiation were the common biological processes between F0 and F1 generations, revealing Poly (I:C) could affect the immunity of the treated F0 hens and the unchallenged subsequent generations. Further study showed that pathways associated with growth, development, biosynthesis, and metabolism of F2 chicks were also affected by Poly (I:C) maternal stimulation. Correlation analysis between DEGs and reproductive traits revealed that PHLDA2 (pleckstrin homology-like domain family A member 2) and PODN (podocan) with inheritable effect were highly correlated with egg-laying rate and egg weight in F1 hens, suggesting their potential long-term role in regulating reproductive traits. ARHGAP40, FGB, HRH4, PHLDA2, PODN, NTSR1, and NMU were supposed to play important roles in regulating chickens' immunity and reproductive traits. This study reveals the far-reaching effect on transcriptome induced by Poly (I:C), reflecting the influence of the mother's living environment on the offspring. It is an important reference for future research into the multi-generational transmission of maternal stimulation and harmful environmental factors.

Paternal epigenetic influences on placental health and their impacts on offspring development and disease

Our efforts to understand the developmental origins of birth defects and disease have primarily focused on maternal exposures and intrauterine stressors. Recently, research into non-genomic mechanisms of inheritance has led to the recognition that epigenetic factors carried in sperm also significantly impact the health of future generations. However, although researchers have described a range of potential epigenetic signals transmitted through sperm, we have yet to obtain a mechanistic understanding of how these paternally-inherited factors influence offspring development and modify life-long health. In this endeavor, the emerging influence of the paternal epigenetic program on placental development, patterning, and function may help explain how a diverse range of male exposures induce comparable intergenerational effects on offspring health. During pregnancy, the placenta serves as the dynamic interface between mother and fetus, regulating nutrient, oxygen, and waste exchange and coordinating fetal growth and maturation. Studies examining intrauterine maternal stressors routinely describe alterations in placental growth, histological organization, and glycogen content, which correlate with well-described influences on infant health and adult onset of disease. Significantly, the emergence of similar phenotypes in models examining preconception male exposures indicates that paternal stressors transmit an epigenetic memory to their offspring that also negatively impacts placental function. Like maternal models, paternally programmed placental dysfunction exerts life-long consequences on offspring health, particularly metabolic function. Here, focusing primarily on rodent models, we review the literature and discuss the influences of preconception male health and exposure history on placental growth and patterning. We emphasize the emergence of common placental phenotypes shared between models examining preconception male and intrauterine stressors but note that the direction of change frequently differs between maternal and paternal exposures. We posit that alterations in placental growth, histological organization, and glycogen content broadly serve as reliable markers of altered paternal developmental programming, predicting the emergence of structural and metabolic defects in the offspring. Finally, we suggest the existence of an unrecognized developmental axis between the male germline and the extraembryonic lineages that may have evolved to enhance fetal adaptation.

Transgenerational inheritance and its modulation by environmental cues

The epigenome plays an important role in shaping phenotypes. However, whether the environment can alter an organism's phenotype across several generations through epigenetic remodeling in the germline is still a highly debated topic. In this chapter, we briefly review the mechanisms of epigenetic inheritance and their connection with germline development before highlighting specific developmental windows of susceptibility to environmental cues. We further discuss the evidence of transgenerational inheritance to a range of different environmental cues, both epidemiological in humans and experimental in rodent models. Doing so, we pinpoint the current challenges in demonstrating transgenerational inheritance to environmental cues and offer insight in how recent technological advances may help deciphering the epigenetic mechanisms at play. Together, we draw a detailed picture of how our environment can influence our epigenomes, ultimately reshaping our phenotypes, in an extended theory of inheritance.

Maternal inflammation induces spatial learning and memory impairment in the F1 and F2 generations of mice via sex-specific epigenetic mechanisms

Mounting evidence indicates that histone modifications are involved in aging-associated cognitive decline (AACD) and can be transmitted to offspring over multiple generations under conditions of stress. Here, we investigated the effects of maternal sub-chronic inflammation caused by lipopolysaccharide (LPS) on AACD and histone modifications in the F1 and F2 generations of experimental mice as well as the potential sex specificity of intergenerational effects. In brief, F0-generation CD-1 dams were exposed to LPS (50 µg/kg) or saline (CON) during late pregnancy. Subsequently, F1 males and females (at 2 months-of-age) from the LPS treatment group were mated with non-littermates from the LPS group or wild-type mice to produce F2 generations of parental- (F2-LPS₂), paternal- (F2M-LPS₁) and maternal-origin (F2F-LPS₁) mice. Then, CON-F1 males and females were mated with wild-type mice to generate F2 generations of paternal- (F2M-CON₁) and maternal-origin (F2F-CON₁). Next, we evaluated the cognitive ability and levels of hippocampal H4K12ac and H3K9me3 in the F1 and F2 offspring at 3- and 13 months-of-age. Overall, F1 male and female LPS groups presented with elevated corticosterone (P < 0.001, P = 0.036, P = 0.025, 0.012, respectively) and cytokine responses, poorer cognitive performance (all P < 0.05) and H3K9 hypermethylation and H4K12 hypoacetylation in the dorsal hippocampus (all P < 0.05); these issues were carried over to the F2 generation via the parents, predominantly in the paternal lineage. Moreover, the levels of H3K9me3 and H4K12ac were significant correlated with cognitive performance (all P < 0.05), regardless of whether inflammatory insults had been incurred directly or indirectly. These findings indicated that gestational inflammatory insults in the F0 generation accelerated AACD in the F2 generation, along with H3K9 hypermethylation and H4K12 hypoacetylation in the hippocampus, and that these issues were derived from the F1 parents, especially from the F1 fathers.

The Legacy of Parental Obesity: Mechanisms of Non-Genetic Transmission and Reversibility

While a dramatic increase in obesity and related comorbidities is being witnessed, the underlying mechanisms of their spread remain unresolved. Epigenetic and other non-genetic mechanisms tend to be prominent candidates involved in the establishment and transmission of obesity and associated metabolic disorders to offspring. Here, we review recent findings addressing those candidates, in the context of maternal and paternal influences, and discuss the effectiveness of preventive measures.

Uterosomes: The lost ring of telegony?

Telegony refers to the appearance of some characteristics of the female's previously mated male in her subsequent offspring by another male. According to evidence, telegony may occur either through the infiltration of sperm into the somatic tissues of the female genital tract or the presence of fetal genes in the mother's blood. It is highlighted that sperm penetrates into the mucosa of the uterine and possibly alters the genetic structure, affecting the embryo and enduring from one pregnancy to the next, which may be one of the potential mechanisms of telegony. Uterine fluid, uterine gland-derived histotroph, supplies key nutrients for successful embryo implantation and it is important during the first trimester, especially, because of its susceptibility to maternal states. The presence of EVs in uterine fluid (uterosomes) was reported in mice, sheep, and humans, including a wide range of biomolecules, such as proteins, and non-coding RNAs. In this review article, we presented a new idea to explain telegony. Based on our idea, after the previous male sperm entry into the female reproductive system, those sperm which do not participate in fertilization penetrate into the somatic cells of the uterus and store their genetic/epigenetic information there. The sperm of the next partner reaches a location in the female reproductive canal where it exchanges information with the uterosomes and obtains the proteins and non-coding RNAs required for fertilization, development, and implantation.

Paternal hypoxia exposure primes offspring for increased hypoxia resistance

Background

In a time of rapid environmental change, understanding how the challenges experienced by one generation can influence the fitness of future generations is critically needed. Using tolerance assays and transcriptomic and methylome approaches, we use zebrafish as a model to investigate cross-generational acclimation to hypoxia.

Results

We show that short-term paternal exposure to hypoxia endows offspring with greater tolerance to acute hypoxia. We detected two hemoglobin genes that are significantly upregulated by more than 6-fold in the offspring of hypoxia exposed males. Moreover, the offspring which maintained equilibrium the longest showed greatest upregulation in hemoglobin expression. We did not detect differential methylation at any of the differentially expressed genes, suggesting that other epigenetic mechanisms are responsible for alterations in gene expression.

Conclusions

Overall, our findings suggest that an epigenetic memory of past hypoxia exposure is maintained and that this environmentally induced information is transferred to subsequent generations, pre-acclimating progeny to cope with hypoxic conditions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01389-x.

Multigenerational effects of paternal spatial training are lasting in the F1 and F2 male offspring

Recent studies on intergenerational transmission of learning and memory performances demonstrated that parental spatial training before fertilization could facilitate learning and memory in the offspring, but many questions remain unclarified. Essential issues regarding whether and how long the effects of parental training in a task can last in several generations, and whether learning a task repeated in the successive generations can enhance a load of multigenerational effects. In the present study, the spatial performances of F1 and F2 generations of male offspring of fathers or grandfathers spatially trained in the Morris Water Maze were evaluated and compared with the performance of a control sample matched for age and sex. Further, to investigate the memory process in F1 and F2 male offspring, brain-derived neurotrophic factor (BDNF), p-ERK1/2 and acetylated histone 3 lysine 14 (H3K14) expression levels in the hippocampus were analyzed. The findings showed that paternal training reduced escape latencies and increased time spent in the target quadrant by F1 and F2 male offspring. Besides, paternal spatial training repeated in two generations did not enhance the beneficial effects on offspring's spatial performances. These findings were supported by neurobiologic data showing that paternal training increased BDNF and p-ERK1/2 in the hippocampus of F1 and F2 male offspring. Furthermore, the hippocampal level of acetylated H3K14 increased in the offspring of spatially trained fathers, reinforcing the hypothesis that the augmented histone acetylation might play an essential role in the inheritance of spatial competence.

Maternal secretin ameliorates obesity by promoting white adipose tissue browning in offspring

Our knowledge of the coordination of intergenerational inheritance and offspring metabolic reprogramming by gastrointestinal endocrine factors is largely unknown. Here, we showed that secretin (SCT), a brain-gut peptide, is downregulated by overnutrition in pregnant mice and women. More importantly, genetic loss of SCT in the maternal gut results in undesirable phenotypes developed in offspring including enhanced high-fat diet (HFD)-induced obesity and attenuated browning of inguinal white adipose tissue (iWAT). Mechanistically, loss of maternal SCT represses iWAT browning in offspring by a global change in genome methylation pattern through upregulation of DNMT1. SCT functions to facilitate ubiquitination and degradation of DNMT1 by activating AMPKα, which contributes to the observed alteration of DNMT1 in progeny. Lastly, we showed that SCT treatment during pregnancy can reduce the development of obesity and improve glucose tolerance and insulin resistance in offspring of HFD-fed females, suggesting that SCT may serve as a novel biomarker or a strategy for preventing metabolic diseases.

Epigenetic modifications at DMRs of imprinting genes in sperm of type 2 diabetic men

High rates of infertility in type 2 diabetic (T2DM) men have led to attempts to understand the mechanisms involved in this process. This condition can be investigated from at least two aspects, namely sperm quality indices and epigenetic alterations. Epigenetics science encompasses the phenomena that can lead to inherited changes independently of the genetics. This study has been performed to test the hypothesis of the relationship between T2DM and the epigenetic profile of the sperm, as well as sperm quality indices. This research included 42 individuals referred to the infertility clinic of Royan Institute, Iran in 2019–2021. The study subjects were assigned to three groups: normozoospermic non-diabetic (control), normozoospermic diabetic (DN) and non-normozoospermic diabetic (D.Non-N). Sperm DNA fragmentation was evaluated using the sperm chromatin structure assay technique. The global methylation level was examined using 5-methyl cytosine antibody and the methylation status in differentially methylated regions of H19, MEST, and SNRPN was assessed using the methylation-sensitive high-resolution melting technique. The results showed that the sperm global methylation in spermatozoa of D.Non-N group was significantly reduced compared with the other two groups (P < 0.05). The MEST and H19 genes were hypomethylated in the spermatozoa of D.Non-N individuals, but the difference level was not significant for MEST. The SNRPN gene was significantly hypermethylated in these individuals (P < 0.05). The results of this study suggest that T2DM alters the methylation profile and epigenetic programming in spermatozoa of humans and that these methylation changes may ultimately influence the fertility status of men with diabetes.

Short Communication: Maternal undernutrition during peri-conceptional period affects whole genome ovine muscle methylation in adult offspring

Experimental and epidemiological studies suggest that maternal nutritional status during early pregnancy, including the period around the time of conception, may induce long-lasting epigenetic changes in the offspring. However, this remains largely unexplored in livestock. Therefore, the objective of this study was to evaluate if modification of the maternal diet of sheep (CTR: control; UND: 50% undernutrition) during the peri-conceptional period (42 days in total: -14/+28 from mating), would impact CpG methylation in muscle tissue (Longissimus dorsi) of adult offspring (11.5 months old). Reduced Representation Bisulfite Sequencing (RRBS), identified 262 (Edge-R, FDR<0.05) and 686 (Logistic Regression, FDR <0.001) differentially methylated regions (DMRs) between the UND and CTR groups. Gene ontology (GO) analysis identified genes related to development, functions of the muscular system and steroid hormone receptor activity within the DMRs. The data reported here show that nutritional stress during early pregnancy leads to epigenetic modifications in the muscle of the resulting offspring, with possible implications for cardiac dysfunction, muscle physiology and meat production.

Cardiometabolic Effects of Postnatal High-Fat Diet Consumption in Offspring Exposed to Maternal Protein Restriction In Utero

In recent decades, the high incidence of infectious and parasitic diseases has been replaced by a high prevalence of chronic and degenerative diseases. Concomitantly, there have been profound changes in the behavior and eating habits of families around the world, characterizing a “nutritional transition” phenomenon, which refers to a shift in diet in response to modernization, urbanization, or economic development from undernutrition to the excessive consumption of hypercaloric and ultra-processed foods. Protein malnutrition that was a health problem in the first half of the 20th century has now been replaced by high-fat diets, especially diets high in saturated fat, predisposing consumers to overweight and obesity. This panorama points us to the alarming coexistence of both malnutrition and obesity in the same population. In this way, individuals whose mothers were undernourished early in pregnancy and then exposed to postnatal hyperlipidic nutrition have increased risk factors for developing metabolic dysfunction and cardiovascular diseases in adulthood. Thus, our major aim was to review the cardiometabolic effects resulting from postnatal hyperlipidic diets in protein-restricted subjects, as well as to examine the epigenetic repercussions occasioned by the nutritional transition.

Sex differences in the intergenerational inheritance of metabolic traits

Strong evidence suggests that early-life exposures to suboptimal environmental factors, including those in utero, influence our long-term metabolic health. This has been termed developmental programming. Mounting evidence suggests that the growth and metabolism of male and female fetuses differ. Therefore, sexual dimorphism in response to pre-conception or early-life exposures could contribute to known sex differences in susceptibility to poor metabolic health in adulthood. However, until recently, many studies, especially those in animal models, focused on a single sex, or, often in the case of studies performed during intrauterine development, did not report the sex of the animal at all. In this review, we (a) summarize the evidence that male and females respond differently to a suboptimal pre-conceptional or in utero environment, (b) explore the potential biological mechanisms that underlie these differences and (c) review the consequences of these differences for long-term metabolic health, including that of subsequent generations.

Predicting male fertility from the sperm methylome: application to 120 bulls with hundreds of artificial insemination records

BACKGROUND

Conflicting results regarding alterations to sperm DNA methylation in cases of spermatogenesis defects, male infertility and poor developmental outcomes have been reported in humans. Bulls used for artificial insemination represent a relevant model in this field, as the broad dissemination of bull semen considerably alleviates confounding factors and enables the precise assessment of male fertility. This study was therefore designed to assess the potential for sperm DNA methylation to predict bull fertility.

RESULTS

A unique collection of 100 sperm samples was constituted by pooling 2-5 ejaculates per bull from 100 Montbéliarde bulls of comparable ages, assessed as fertile (n = 57) or subfertile (n = 43) based on non-return rates 56 days after insemination. The DNA methylation profiles of these samples were obtained using reduced representation bisulfite sequencing. After excluding putative sequence polymorphisms, 490 fertility-related differentially methylated cytosines (DMCs) were identified, most of which were hypermethylated in subfertile bulls. Interestingly, 46 genes targeted by DMCs are involved in embryonic and fetal development, sperm function and maturation, or have been related to fertility in genome-wide association studies; five of these were further analyzed by pyrosequencing. In order to evaluate the prognostic value of fertility-related DMCs, the sperm samples were split between training (n = 67) and testing (n = 33) sets. Using a Random Forest approach, a predictive model was built from the methylation values obtained on the training set. The predictive accuracy of this model was 72% on the testing set and 72% on individual ejaculates collected from an independent cohort of 20 bulls.

CONCLUSION

This study, conducted on the largest set of bull sperm samples so far examined in epigenetic analyses, demonstrated that the sperm methylome is a valuable source of male fertility biomarkers. The next challenge is to combine these results with other data on the same sperm samples in order to improve the quality of the model and better understand the interplay between DNA methylation and other molecular features in the regulation of fertility. This research may have potential applications in human medicine, where infertility affects the interaction between a male and a female, thus making it difficult to isolate the male factor.