Transgenerational response to nutrition, early life circumstances and longevity

Influence of intergenerational in utero parental energy and nutrient restriction on offspring growth in rural Gambia

The prenatal environment can alter an individual’s developmental trajectory with long-lasting effects on health. Animal models demonstrate that the impact of the early life environment extends to subsequent generations, but there is a paucity of data from human populations on intergenerational transmission of environmentally induced phenotypes. Here we investigated the association of parental exposure to energy and nutrient restriction in utero on their children’s growth in rural Gambia. In a Gambian cohort with infants born between 1972 and 2011, we used multiple regression to test whether parental season of birth predicted offspring birth weight (n = 2097) or length (n = 1172), height-for-age z score (HAZ), weight-for-height z score (WHZ), and weight-for-age z score (WAZ) at 2 yr of age (n = 923). We found that maternal exposure to seasonal energy restriction in utero was associated with reduced offspring birth length (crude:−4.2 mm, P = 0.005; adjusted: −4.0 mm, P = 0.02). In contrast, paternal birth season predicted offspring HAZ at 24 mo (crude: −0.21, P = 0.005; adjusted: −0.22, P = 0.004) but had no discernible impact at birth. Our results indicate that periods of nutritional restriction in a parent’s fetal life can have intergenerational consequences in human populations. Fetal growth appears to be under matriline influence, and postnatal growth appears to be under patriline intergenerational influences.—Eriksen, K. G., Radford, E. J., Silver, M. J., Fulford, A. J. C., Wegmüller, R., Prentice, A. M. Influence of intergenerational in utero parental energy and nutrient restriction on offspring growth in rural Gambia.

Multigenerational cohorts in patients with asthma and allergy

Recent observations that disease risk can be transmitted across generations without the need for direct exposure of the child to the index environmental insult has sparked interest in transgenerational inheritance. Epigenetics describes processes that modify gene expression without a change in the nucleotide sequence. Epigenetic processes can be induced in response to environmental exposures, can influence disease risk, and might explain these multigenerational effects. In experimental models a number of epigenetic mechanisms have been identified that could mediate vertical transmission of epigenetic inheritance. However, relevance of these findings to human disease is not yet clear. An alternative model is one in which transgenerational inheritance of disease risk requires the presence of exposure-related diseases in the mother during pregnancy (termed induced epigenetic transmission model). A number of cross-sectional studies have investigated multigenerational effects in allergy and asthma. However, given the early-life origins of asthma and allergy, birth cohort studies are ideal to investigate the effect of genetic predisposition, epigenetics, and environmental exposures, avoiding pitfalls, such as recall bias and confounding by ongoing exposures, disease, and treatment. The well-characterized 3 generations of the Isle of Wight cohort include 2 consecutive birth cohorts, providing longitudinal data that can be studied for epigenetic transfer of information, such as the effect of grand parental smoking or exposure to other toxic compounds. Further large multigenerational birth cohorts are needed to establish the clinical relevance of this phenomenon and differentiate between vertical and induced transmission models, which might influence future preventive strategies.

Non-genomic transmission of longevity between generations: potential mechanisms and evidence across species

Accumulating animal and human data indicate that environmental exposures experienced during sensitive developmental periods may strongly influence risk of adult disease. Moreover, the effects triggered by developmental environmental cues can be transgenerationally transmitted, potentially affecting offspring health outcomes. Increasing evidence suggests a central role of epigenetic mechanisms (heritable alterations in gene expression occurring without changes in underlying DNA sequence) in mediating these effects. This review summarizes the findings from animal models, including worms, insects, and rodents, and also from human studies, indicating that lifespan and longevity-associated characteristics can be transmitted across generations via non-genetic factors.

Transgenerational paternal transmission of acquired traits: Stress-induced modification of the sperm regulatory transcriptome and offspring phenotypes

In recent years, it has become evident that pre-conceptual exposure of males to various environmental factors induces epigenetic changes in sperm, which can mediate the transmission of acquired traits in their offspring. The most thoroughly examined paternal exposures involve stress and elevated corticosterone, which have been shown to modulate offspring phenotypes in a manner that is relevant to predisposition to brain disorders, and psychiatric illness in particular. Recent seminal studies have demonstrated that key epigenetic information transmitted via the paternal germline involves small non-coding (snc) RNA transcripts such as microRNAs. Following fertilisation, these sncRNAs appear to regulate development so as to modify the phenotype of the offspring. Understanding the mechanisms involved in such transgenerational effects may facilitate future screening of human sperm for 'epigenetic health' and the tailoring of therapeutic interventions according to genetic and epigenetic contributions to illness.

Gene expression and epigenetic aberrations in F1-placentas fathered by obese males

Gene expression and/or epigenetic deregulation may have consequences for sperm and blastocysts, as well as for the placenta, together potentially contributing to problems observed in offspring. We previously demonstrated specific perturbations of fertilization, blastocyst formation, implantation, as well as aberrant glucose metabolism and adiposity in offspring using a mouse model of paternal obesity. The current investigation analyzed gene expression and methylation of specific CpG residues in F1 placentas of pregnancies fathered by obese and normal-weight male mice, using real-time PCR and bisulfite pyrosequencing. Our aim was to determine if paternal obesity deregulated placental gene expression and DNA methylation when compared to normal-weight males. Gene methylation of sperm DNA was analyzed and compared to placentas to address epigenetic transmission. Of the 10 paternally expressed genes (Pegs), 11 genes important for development and transport of nutrients, and the long-terminal repeat Intracisternal A particle (IAP) elements, derived from a member of the class II endogenous retroviral gene family, we observed a significant effect of paternal diet-induced obesity on deregulated expression of Peg3, Peg9, Peg10, and the nutrient transporter gene Slc38a2, and aberrant DNA methylation of the Peg9 promoter in F1 placental tissue. Epigenetic changes in Peg9 were also found in sperm from obese fathers. We therefore propose that paternal obesity renders changes in gene expression and/or methylation throughout the placental genome, which could contribute to the reproductive problems related to fertility and to the metabolic, long-term health impact on offspring.

Ancestral Exposure to Stress Generates New Behavioral Traits and a Functional Hemispheric Dominance Shift

In a continuously stressful environment, the effects of recurrent prenatal stress (PS) accumulate across generations and generate new behavioral traits in the absence of genetic variation. Here, we investigated if PS or multigenerational PS across 4 generations differentially affect behavioral traits, laterality, and hemispheric dominance in male and female rats. Using skilled reaching and skilled walking tasks, 3 findings support the formation of new behavioral traits and shifted laterality by multigenerational stress. First, while PS in the F1 generation did not alter paw preference, multigenerational stress in the F4 generation shifted paw preference to favor left-handedness only in males. Second, multigenerational stress impaired skilled reaching and skilled walking movement abilities in males, while improving these abilities in females beyond the levels of controls. Third, the shift toward left-handedness in multigenerationally stressed males was accompanied by increased dendritic complexity and greater spine density in the right parietal cortex. Thus, cumulative multigenerational stress generates sexually dimorphic left-handedness and dominance shift toward the right hemisphere in males. These findings explain the origins of apparently heritable behavioral traits and handedness in the absence of DNA sequence variations while proposing epigenetic mechanisms.

Tertiary Epimutations - A Novel Aspect of Epigenetic Transgenerational Inheritance Promoting Genome Instability

Exposure to environmental factors can induce the epigenetic transgenerational inheritance of disease. Alterations to the epigenome termed “epimutations” include “primary epimutations” which are epigenetic alterations in the absence of genetic change and “secondary epimutations” which form following an initial genetic change. To determine if secondary epimutations contribute to transgenerational transmission of disease following in utero exposure to the endocrine disruptor vinclozolin, we exposed pregnant female rats carrying the lacI mutation-reporter transgene to vinclozolin and assessed the frequency of mutations in kidney tissue and sperm recovered from F1 and F3 generation progeny. Our results confirm that vinclozolin induces primary epimutations rather than secondary epimutations, but also suggest that some primary epimutations can predispose a subsequent accelerated accumulation of genetic mutations in F3 generation descendants that have the potential to contribute to transgenerational phenotypes. We therefore propose the existence of “tertiary epimutations” which are initial primary epimutations that promote genome instability leading to an accelerated accumulation of genetic mutations.

Transgenerational effects of childhood conditions on third generation health and education outcomes

This paper examines the extent to which pre-puberty nutritional conditions in one generation affect productivity-related outcomes in later generations. Recent findings from the biological literature suggest that the so-called slow growth period around age 9 is a sensitive period for male germ cell development. We build on this evidence and investigate whether undernutrition at those ages transmits to children and grandchildren. Our findings indicate that third generation males (females) tend to have higher mental health scores if their paternal grandfather (maternal grandmother) was exposed to a famine during the slow growth period. These effects appear to reflect biological responses to adaptive expectations about scarcity in the environment, and as such they can be seen as an economic correctional mechanism in evolution, with marked socio-economic implications for the offspring.

Behavioral epigenetics

Why do we grow up to have the traits we do? Most 20th century scientists answered this question by referring only to our genes and our environments. But recent discoveries in the emerging field of behavioral epigenetics have revealed factors at the interface between genes and environments that also play crucial roles in development. These factors affect how genes work; scientists now know that what matters as much as which genes you have (and what environments you encounter) is how your genes are affected by their contexts. The discovery that what our genes do depends in part on our experiences has shed light on how Nature and Nurture interact at the molecular level inside of our bodies. Data emerging from the world's behavioral epigenetics laboratories support the idea that a person's genes alone cannot determine if, for example, he or she will end up shy, suffering from cardiovascular disease, or extremely smart. Among the environmental factors that can influence genetic activity are parenting styles, diets, and social statuses. In addition to influencing how doctors treat diseases, discoveries about behavioral epigenetics are likely to alter how biologists think about evolution, because some epigenetic effects of experience appear to be transmissible from generation to generation. This domain of research will likely change how we think about the origins of human nature. WIREs Syst Biol Med 2017, 9:e1333. doi: 10.1002/wsbm.1333 For further resources related to this article, please visit the WIREs website.

Epigenetic legacy of parental experiences: Dynamic and interactive pathways to inheritance

The quality of the environment experienced by an individual across his or her lifespan can result in a unique developmental trajectory with consequences for adult phenotype and reproductive success. However, it is also evident that these experiences can impact the development of offspring with continued effect on subsequent generations. Epigenetic mechanisms have been proposed as a mediator of both these within- and across-generation effects, and there is increasing evidence to support the role of environmentally induced changes in DNA methylation, posttranslational histone modifications, and noncoding RNAs in predicting these outcomes. Advances in our understanding of these molecular modifications contribute to increasingly nuanced perspectives on plasticity and transmission of phenotypes across generations. A challenge that emerges from this research is in how we integrate these "new" perspectives with traditional views of development, reproduction, and inheritance. This paper will highlight evidence suggestive of an epigenetic impact of the environment on mothers, fathers, and their offspring, and illustrate the importance of considering the dynamic nature of reproduction and development and inclusive views of inheritance within the evolving field of behavioral and environmental epigenetics.

Familial resemblances in blood leukocyte DNA methylation levels

Epigenetic factors such as DNA methylation are DNA alterations affecting gene expression that can convey environmental information through generations. Only a few studies have demonstrated epigenetic inheritance in humans. Our objective is to quantify genetic and common environmental determinants of familial resemblances in DNA methylation levels, using a family based sample. DNA methylation was measured in 48 French Canadians from 16 families as part of the GENERATION Study. We used the Illumina HumanMethylation450 BeadChip array to measure DNA methylation levels in blood leukocytes on 485,577 CpG sites. Heritability was assessed using the variance components method implemented in the QTDT software, which partitions the variance into polygenic (G), common environmental (C), and non-shared environmental (E) effects. We computed maximal heritability, genetic heritability, and common environmental effect for all probes (12.7%, 8.2%, and 4.5%, respectively) and for statistically significant probes (81.8%, 26.9%, and 54.9%, respectively). Higher maximal heritability was observed in the Major Histocompatibility Complex region on chromosome 6. In conclusion, familial resemblances in DNA methylation levels are mainly attributable to genetic factors when considering the average across the genome, but common environmental effect plays an important role when considering statistically significant probes. Further epigenome-wide studies on larger samples combined with genome-wide genotyping studies are needed to better understand the underlying mechanisms of DNA methylation heritability.

Epigenetics in male reproduction: effect of paternal diet on sperm quality and offspring health

Epigenetic inheritance and its underlying molecular mechanisms are among the most intriguing areas of current biological and medical research. To date, studies have shown that both female and male germline development follow distinct paths of epigenetic events and both oocyte and sperm possess their own unique epigenomes. Fertilizing male and female germ cells deliver not only their haploid genomes but also their epigenomes, which contain the code for preimplantation and postimplantation reprogramming and embryonal development. For example, in spermatozoa, DNA methylation profile, DNA-associated proteins, protamine 1:protamine 2 ratio, nucleosome distribution pattern, histone modifications and other properties make up a unique epigenetic landscape. However, epigenetic factors and mechanisms possess certain plasticity and are affected by environmental conditions. Paternal and maternal lifestyle, including physical activity, nutrition and exposure to hazardous substances, can alter the epigenome and, moreover, can affect the health of their children. In male reproductive health, data are emerging on epigenetically mediated effects of a man's diet on sperm quality, for example through phytochemicals, minerals and vitamins, and nutritional support for subfertile men is already being used. In addition, studies in animal models and human epidemiological data point toward a transgenerational effect of the paternally contributed sperm epigenome on offspring health.

High-fat diet disrupts metabolism in two generations of rats in a parent-of-origin specific manner

Experimental and epidemiological evidence demonstrate that ancestral diet might contribute towards offspring health. This suggests that nutrition may be able to modify genetic or epigenetic information carried by germ cells (GCs). To examine if a parental high fat diet (HFD) influences metabolic health in two generations of offspring, GC-eGFP Sprague Dawley rats were weaned onto HFD (45% fat) or Control Diet (CD; 10% fat). At 19 weeks, founders (F0) were bred with controls, establishing the F1 generation. HFD resulted in 9.7% and 14.7% increased weight gain in male and female F0 respectively. F1 offspring of HFD mothers and F1 daughters of HFD-fed fathers had increased weight gain compared to controls. F1 rats were bred with controls at 19 weeks to generate F2 offspring. F2 male offspring derived from HFD-fed maternal grandfathers exhibited increased adiposity, plasma leptin and luteinising hormone to testosterone ratio. Despite transmission via the founding male germline, we did not find significant changes in the F0 intra-testicular GC transcriptome. Thus, HFD consumption by maternal grandfathers results in a disrupted metabolic and reproductive hormone phenotype in grandsons in the absence of detectable changes in the intra-testicular GC transcriptome.

Enzyme Changes in the Offspring of Female Rats due to Long-Term Administration of Cyclic AMP and Insulin before Pregnancy

We studied the effects of insulin and cAMP on the offspring of female rats after daily treatment with these substances over 4 weeks. In adult offspring from cAMP-treated females, activities of pyruvate kinase and glucose-6-phosphate dehydrogenase decreased in the liver and brain and activities of NADP-dependent malate dehydrogenase and 6-phosphogluconate dehydrogenase decreased in the liver. In the offspring of insulin-treated females, we observed only activation of glucose-6-phosphate dehydrogenase and malate dehydrogenase in the liver and only in females. Enzyme activity probably correlates with their content, as no changes in their kinetic properties were observed under these conditions. Long-term hormone treatment before pregnancy can affect the expression of genes for some enzymes in the offspring due to transmission of epigenetic signals by the ovum. However, further studies are required to confirm this mechanism.

Transgenerational transmission of pregestational and prenatal experience: maternal adversity, enrichment, and underlying epigenetic and environmental mechanisms

Transgenerational transmission refers to positive and negative adaptations in brain function and behavior that affect following generations. In this paper, empirical findings regarding the transgenerational transmission of maternal adversity during three critical periods - childhood, pregestational adulthood and pregnancy - will be reviewed in terms of pregnancy outcomes, maternal care, offspring behavior and development, and physiological functioning. Research on the transgenerational transmission of enrichment and the implications for interventions to ameliorate the consequences of adversity will also be presented. In the final section, underlying epigenetic and environmental mechanisms that have been proposed to explain how experience is transferred across generations through transgenerational transmission will be reviewed. Directions for future research are suggested throughout.

Paternal overweight is associated with increased breast cancer risk in daughters in a mouse model

While many studies have shown that maternal weight and nutrition in pregnancy affects offspring's breast cancer risk, no studies have investigated the impact of paternal body weight on daughters' risk of this disease. Here, we show that diet-induced paternal overweight around the time of conception can epigenetically reprogram father's germ-line and modulate their daughters' birth weight and likelihood of developing breast cancer, using a mouse model. Increased body weight was associated with changes in the miRNA expression profile in paternal sperm. Daughters of overweight fathers had higher rates of carcinogen-induced mammary tumors which were associated with delayed mammary gland development and alterations in mammary miRNA expression. The hypoxia signaling pathway, targeted by miRNAs down-regulated in daughters of overweight fathers, was activated in their mammary tissues and tumors. This study provides evidence that paternal peri-conceptional body weight may affect daughters' mammary development and breast cancer risk and warrants further studies in other animal models and humans.

Obesogens: an emerging threat to public health

Endocrine disrupting chemicals (EDCs) are defined as exogenous chemicals, or mixtures of chemicals, that can interfere with any aspect of hormone action. The field of endocrine disruption is historically rooted in wildlife biology and reproductive endocrinology where EDCs are demonstrated contributors to infertility, premature puberty, endometriosis, and other disorders. Recently, EDCs have been implicated in metabolic syndrome and obesity. Adipose tissue is a true endocrine organ and, therefore, an organ that is highly susceptible to disturbance by EDCs. A subset of EDCs, called "obesogens," promote adiposity by altering programming of fat cell development, increasing energy storage in fat tissue, and interfering with neuroendocrine control of appetite and satiety. Obesity adds more than $200 billion to US healthcare costs and the number of obese individuals continues to increase. Hence, there is an urgent, unmet need to understand the mechanisms underlying how exposures to certain EDCs may predispose our population to be obese. In this review, we discuss the history of obesogen discovery from its origins in reproductive biology to its latest role in the transgenerational inheritance of obesity in mice. We discuss the development of adipose tissue in an embryo, maintenance of adipocyte number in adults, how EDC disruption programs stem cells to preferentially make more adipocytes, the mechanisms by which chemicals can permanently alter the germline epigenome, and whether there are barriers to EDCs in the gametes.

Placental, Matrilineal, and Epigenetic Mechanisms Promoting Environmentally Adaptive Development of the Mammalian Brain

The evolution of intrauterine development, vivipary, and placentation in eutherian mammals has introduced new possibilities and constraints in the regulation of neural plasticity and development which promote neural function that is adaptive to the environment that a developing brain is likely to encounter in the future. A range of evolutionary adaptations associated with placentation transfers disproportionate control of this process to the matriline, a period unique in mammalian development in that there are three matrilineal genomes interacting in the same organism at the same time (maternal, foetal, and postmeiotic oocytes). The interactions between the maternal and developing foetal hypothalamus and placenta can provide a template by which a mother can transmit potentially adaptive information concerning potential future environmental conditions to the developing brain. In conjunction with genomic imprinting, it also provides a template to integrate epigenetic information from both maternal and paternal lineages. Placentation also hands ultimate control of genomic imprinting and intergenerational epigenetic information transfer to the matriline as epigenetic markers undergo erasure and reprogramming in the developing oocyte. These developments, in conjunction with an expanded neocortex, provide a unique evolutionary template by which matrilineal transfer of maternal care, resources, and culture can be used to promote brain development and infant survival.

Obesity and Bariatric Surgery Drive Epigenetic Variation of Spermatozoa in Humans

Obesity is a heritable disorder, with children of obese fathers at higher risk of developing obesity. Environmental factors epigenetically influence somatic tissues, but the contribution of these factors to the establishment of epigenetic patterns in human gametes is unknown. Here, we hypothesized that weight loss remodels the epigenetic signature of spermatozoa in human obesity. Comprehensive profiling of the epigenome of sperm from lean and obese men showed similar histone positioning, but small non-coding RNA expression and DNA methylation patterns were markedly different. In a separate cohort of morbidly obese men, surgery-induced weight loss was associated with a dramatic remodeling of sperm DNA methylation, notably at genetic locations implicated in the central control of appetite. Our data provide evidence that the epigenome of human spermatozoa dynamically changes under environmental pressure and offers insight into how obesity may propagate metabolic dysfunction to the next generation.

Obesogens: an emerging threat to public health

Endocrine disrupting chemicals (EDCs) are defined as exogenous chemicals, or mixtures of chemicals, that can interfere with any aspect of hormone action. The field of endocrine disruption is historically rooted in wildlife biology and reproductive endocrinology where EDCs are demonstrated contributors to infertility, premature puberty, endometriosis, and other disorders. Recently, EDCs have been implicated in metabolic syndrome and obesity. Adipose tissue is a true endocrine organ and, therefore, an organ that is highly susceptible to disturbance by EDCs. A subset of EDCs, called "obesogens," promote adiposity by altering programming of fat cell development, increasing energy storage in fat tissue, and interfering with neuroendocrine control of appetite and satiety. Obesity adds more than $200 billion to US healthcare costs and the number of obese individuals continues to increase. Hence, there is an urgent, unmet need to understand the mechanisms underlying how exposures to certain EDCs may predispose our population to be obese. In this review, we discuss the history of obesogen discovery from its origins in reproductive biology to its latest role in the transgenerational inheritance of obesity in mice. We discuss the development of adipose tissue in an embryo, maintenance of adipocyte number in adults, how EDC disruption programs stem cells to preferentially make more adipocytes, the mechanisms by which chemicals can permanently alter the germline epigenome, and whether there are barriers to EDCs in the gametes.

The Role of the Epigenome in Translating Neighborhood Disadvantage Into Health Disparities

The possible causal role of the environment in health disparities is not well understood, even though it has been a national priority for many years. Progress to investigate the relationship between genetics, environmental exposures, and health outcomes has been hampered by the lack of analytical tools to quantify the combined or cumulative effect of multiple chemical and non-chemical stressors on gene expression. The studies cited here provide a strong rationale for using epigenomic analysis to assess cumulative risk from multiple environmental exposures over the life course. The environment-specific "imprints" on the genome, coupled with transcriptomics and metabolomics, can be used to advance our understanding of the relationship between neighborhood disadvantage and health disparities.

Between Scylla and Charybdis: renegotiating resolution of the 'obstetric dilemma' in response to ecological change

Hominin evolution saw the emergence of two traits-bipedality and encephalization-that are fundamentally linked because the fetal head must pass through the maternal pelvis at birth, a scenario termed the 'obstetric dilemma'. While adaptive explanations for bipedality and large brains address adult phenotype, it is brain and pelvic growth that are subject to the obstetric dilemma. Many contemporary populations experience substantial maternal and perinatal morbidity/mortality from obstructed labour, yet there is increasing recognition that the obstetric dilemma is not fixed and is affected by ecological change. Ecological trends may affect growth of the pelvis and offspring brain to different extents, while the two traits also differ by a generation in the timing of their exposure. Two key questions arise: how can the fit between the maternal pelvis and the offspring brain be 'renegotiated' as the environment changes, and what nutritional signals regulate this process? I argue that the potential for maternal size to change across generations precludes birthweight being under strong genetic influence. Instead, fetal growth tracks maternal phenotype, which buffers short-term ecological perturbations. Nevertheless, rapid changes in nutritional supply between generations can generate antagonistic influences on maternal and offspring traits, increasing the risk of obstructed labour.

Neighborhood and Family Environment of Expectant Mothers May Influence Prenatal Programming of Adult Cancer Risk: Discussion and an Illustrative DNA Methylation Example

Childhood stressors including physical abuse predict adult cancer risk. Prior research portrays this finding as an indirect mechanism that operates through coping behaviors, including adult smoking, or through increased toxic exposures during childhood. Little is known about potential direct causal mechanisms between early-life stressors and adult cancer. Because prenatal conditions can affect gene expression by altering DNA methylation, with implications for adult health, we hypothesize that maternal stress may program methylation of cancer-linked genes during gametogenesis. To illustrate this hypothesis, we related maternal social resources to methylation at the imprinted MEG3 differentially methylated regulatory region, which has been linked to multiple cancer types. Mothers (n = 489) from a diverse birth cohort (Durham, North Carolina) provided newborns' cord blood and completed a questionnaire. Newborns of currently married mothers showed lower (-0.321 SD, p < .05) methylation compared to newborns of never-married mothers, who did not differ from newborns whose mothers were cohabiting and others (adjusted for demographics). MEG3 DNA methylation levels were also lower when maternal grandmothers co-resided before pregnancy (-0.314 SD, p < .05). A 1-SD increase in prenatal neighborhood disadvantage also predicted higher methylation (-0.137 SD, p < .05). In conclusion, we found that maternal social resources may result in differential methylation of MEG3, which demonstrates a potential partial mechanism priming socially disadvantaged newborns for later risk of some cancers.

Models of Intergenerational and Transgenerational Transmission of Risk for Psychopathology in Mice

Trajectories toward risk or resilience in psychiatric disorders are influenced by acquired and inherited factors. More recently, evidence from rodent studies suggest that acquired risk factors can be transmitted through non-genomic, epigenetic mechanisms to subsequent generations, potentially contributing to a cycle of disease and disease risk. Here, we review examples of transmission of environmental factors across generations and illustrate the difference between behavioral transmission and epigenetic inheritance. We highlight essential definitions of intergenerational and transgenerational transmission of disease risk with corresponding examples. We then explore how these phenomena may influence our understanding of psychiatric disorders leading toward new prevention and therapeutic approaches.

RNA-mediated paternal heredity of diet-induced obesity and metabolic disorders

The paternal heredity of obesity and diabetes induced by a high-fat and/or high-sugar diet (Western-like diet) has been demonstrated through epidemiological analysis of human cohorts and experimental analysis, but the nature of the hereditary vector inducing this newly acquired phenotype is not yet well defined. Here, we show that microinjection of either testis or sperm RNA of male mice fed a Western-like diet into naive one-cell embryos leads to the establishment of the Western-like diet-induced metabolic phenotype in the resulting progenies, whereas RNAs prepared from healthy controls did not. Among multiple sequence differences between the testis transcriptomes of the sick and healthy fathers, we noted that several microRNAs had increased expression, which was of interest because this class of noncoding RNA is known to be involved in epigenetic control of gene expression. When microinjected into naive one-cell embryos, one of these small RNA, i.e., the microRNA miR19b, induced metabolic alterations that are similar to the diet-induced phenotype. Furthermore, this pathological phenotype was inherited by the offspring after crosses with healthy partners. Our results indicate that acquired food-induced trait inheritance might be enacted by RNA signalling.

Transgenerational epigenetic inheritance of diabetes risk as a consequence of early nutritional imbalances

In today's world, there is an unprecedented rise in the prevalence of chronic metabolic diseases, including obesity, insulin resistance and type 2 diabetes (T2D). The pathogenesis of T2D includes both genetic and environmental factors, such as excessive energy intake and physical inactivity. It has recently been suggested that environmental factors experienced during early stages of development, including the intrauterine and neonatal periods, might play a major role in predisposing individuals to T2D. Furthermore, several studies have shown that such early environmental conditions might even contribute to disease risk in further generations. In this review, we summarise recent data describing how parental nutrition during development increases the risk of diabetes in the offspring. We also discuss the potential mechanisms underlying transgenerational inheritance of metabolic disease, with particular emphasis on epigenetic mechanisms.

Epigenetics and male reproduction: the consequences of paternal lifestyle on fertility, embryo development, and children lifetime health

The correlation between epigenetics and human reproduction represents a very interesting field of study, mainly due to the possible transgenerational effects related to epigenetic modifications of male and female gametes. In the present review, we focused our attention to the role played by epigenetics on male reproduction, evidencing at least four different levels at which sperm epigenetic modifications could affect reproduction: (1) spermatogenesis failure; (2) embryo development; (3) outcome of assisted reproduction technique (ART) protocols, mainly as concerning genomic imprinting; and (4) long-term effects during the offspring lifetime. The environmental agents responsible for epigenetic modifications are also examined, suggesting that the control of paternal lifestyle prior to conception could represent in the next future a novel hot topic in the management of human reproduction.

Telomere dynamics may link stress exposure and ageing across generations

Although exposure to stressors is known to increase disease susceptibility and accelerate ageing, evidence is accumulating that these effects can span more than one generation. Stressors experienced by parents have been reported to negatively influence the longevity of their offspring and even grand offspring. The mechanisms underlying these long-term, cross-generational effects are still poorly understood, but we argue here that telomere dynamics are likely to play an important role. In this review, we begin by surveying the current connections between stress and telomere dynamics. We then lay out the evidence that exposure to stressors in the parental generation influences telomere dynamics in offspring and potentially subsequent generations. We focus on evidence in mammalian and avian studies and highlight several promising areas where our understanding is incomplete and future investigations are critically needed. Understanding the mechanisms that link stress exposure across generations requires interdisciplinary studies and is essential to both the biomedical community seeking to understand how early adversity impacts health span and evolutionary ecologists interested in how changing environmental conditions are likely to influence age-structured population dynamics.

Constitutional epimutation as a mechanism for cancer causality and heritability?

Constitutional epimutation, which is an aberration in gene expression due to an altered epigenotype that is widely distributed in normal tissues (albeit frequently mosaic), provides an alternative mechanism to genetic mutation for cancer predisposition. Observational studies in cancer-affected families have revealed intergenerational inheritance of constitutional epimutation, providing unique insights into the heritability of epigenetic traits in humans. In this Opinion article, the potential contribution of constitutional epimutation to the 'missing' causality and heritability of cancer is explored.

Molecular insights into transgenerational non-genetic inheritance of acquired behaviours

Behavioural traits in mammals are influenced by environmental factors, which can interact with the genome and modulate its activity by complex molecular interplay. Environmental experiences can modify social, emotional and cognitive behaviours during an individual's lifetime, and result in acquired behavioural traits that can be transmitted to subsequent generations. This Review discusses the concept of, and experimental support for, non-genetic transgenerational inheritance of acquired traits involving the germ line in mammals. Possible mechanisms of induction and maintenance during development and adulthood are considered along with an interpretation of recent findings showing the involvement of epigenetic modifications and non-coding RNAs in male germ cells.

From paramutation to human disease: RNA-mediated heredity

Epigenetic variation, a stable alteration in gene expression, occurs at multiple moments during development. Several instances of non-Mendelian transmission to the progenies modes are very intriguing. Studies of the mode of hereditary transmission revealed in a series of such cases a role of noncoding RNA molecules as inducers. While still an enigmatic mechanism, emerging models pinpoint to a more general roles of these variations, initiated as a response to genetic and environmental variation. Here we compare the known modes of transgenerational epigenetic variation in mice and humans.

Sex-Differences in the Metabolic Health of Offspring of Parents with Diabetes: A Record-Linkage Study

Maternal diabetes in pregnancy affects offspring health. The impact of parental diabetes on offspring health is unclear. We investigated the impact of parental diabetes on the metabolic-health of adult-offspring who did not themselves have diabetes. Data from the Generation Scotland: Scottish Family Health Study, a population-based family cohort, were record-linked to subjects’ own diabetes medical records. From F₀-parents, we identified F₁-offspring of: mothers with diabetes (OMD, n = 409), fathers with diabetes (OFD, n = 468), no parent with diabetes (ONoPD, n = 2489). Metabolic syndrome, body, biochemical measurements and blood-pressures were compared between F₁-offspring groups by sex. A higher proportion of female OMD had metabolic syndrome than female OFD or ONoPD (P<0.0001). In female offspring, predictors of metabolic syndrome were: having a mother with diabetes (OR = 1.78, CI 1.03–3.07, [reference ONoPD]), body mass index (BMI, OR = 1.21, CI 1.13–1.30) and age (OR = 1.03, CI 1.01–1.06). In male offspring, predictors of metabolic syndrome were: BMI (OR = 1.18, CI 1.09–1.29) and percent body-fat (OR = 1.12, CI 1.05–1.19). In both sexes, OMD had higher blood-pressures than OFD (P<0.0001). In females, OMD had higher glucose (P<0.0001) and percent body-fat (P<0.0001) compared with OFD or ONoPD. OMD and OFD both had increased waist-measurements (P<0.0001), BMI (P<0.0001) and percent body-fat (P<0.0001) compared with ONoPD. Female OMD and OFD had lower HDL-cholesterol levels (P<0.0001) than female ONoPD. Parental diabetes is associated with higher offspring-BMI and body-fat. In female offspring, maternal diabetes increased the odds of metabolic syndrome, even after adjusting for BMI. Further investigations are required to determine the mechanisms involved.

Paternal early experiences influence infant development through non-social mechanisms in Rhesus Macaques

BACKGROUND

Early experiences influence the developing organism, with lifelong and potentially adaptive consequences. It has recently become clear that the effects of early experiences are not limited to the exposed generation, but can influence physiological and behavioral traits in the next generation. Mechanisms of transgenerational effects of parental early experiences on offspring development are often attributed to prenatal or postnatal parental influence, but recent data suggest that germ-line plasticity may also play a role in the transgenerational effects of early experiences. These non-genetic transgenerational effects are a potentially important developmental and evolutionary force, but the effects of parental experiences on behavior and physiology are not well understood in socially complex primates. In the non-human primate, the rhesus macaque, nursery rearing (NR) is an early life manipulation used for colony management purposes, and involves separating infants from parents early in life. We examined the effects of maternal and paternal early NR on infant rhesus macaque immunity, physiology, and behavior.

RESULTS

We theorized that differences in behavior or physiology in the absence of parent-offspring social contact would point to biological and perhaps germ-line, rather than social, mechanisms of effect. Thus, all subjects were themselves NR. Male and female infant rhesus macaques (N= 206) were separated from parents and social groups in the first four days of life to undergo NR. These infants differed only in their degree of NR ancestry - whether their dams or sires were themselves NR. At 3-4 months of age, infants underwent a standardized biobehavioral assessment. Factors describing immunity, plasma cortisol, and emotion regulation were generated from these data using factor analysis. Paternal, but not maternal, NR was associated with greater emotionality and higher plasma cortisol, compared with infants born to CONTROL reared fathers.

CONCLUSIONS

These data suggest that macaque biobehavioral makeup is strongly influenced by paternal experiences, and via non-social mechanisms.

Are Dietary Patterns of Mothers during Pregnancy Related to Children's Weight Status? Evidence from the Lifeways Cross- Generational Cohort Study

Children's diet patterns are likely to be influenced by their mothers' diet pattern. The primary objective of this study was to examine whether children's adiposity could be influenced by diet patterns of mothers during pregnancy. A secondary objective was to study the relative influence of fathers' and children's dietary patterns on childhood adiposity. The design was a prospective cross-generational cohort study initiated with 1,124 mothers recruited during pregnancy. Self-reported questionnaires included a food frequency instrument (FFQ) to assess parental intakes during the perinatal period. Child body mass index (BMI) was measured at 5 years and an age-appropriate FFQ was administered. Dietary patterns for each group were identified by principal components analysis. Pearson's correlation and logistic regression were used to test for associations. Dietary patterns were described for n = 1,042 mothers during pregnancy and n = 331 fathers during the perinatal period. Dietary patterns and BMI data were available for n = 443 children at age 5 years. The diet patterns identified for mothers correlated with the corresponding diet patterns for fathers. The children's "pasta & vegetable" pattern was positively correlated with "healthy patterns" in mothers (r = 0.195, p < 0.01) and fathers (r = 0.250, p < 0.01). The children's "junk" food pattern was correlated with the "processed" pattern in mothers (r = 0.245, p < 0.01) and fathers (r = 0.257, p < 0.01). In multivariate logistic regression analysis the upper tertiles of children's "cereal and juice" [Tertile 2 (T2): OR 0.44, 95% CI (0.22-0.90); T3: 0.41, (0.19-0.85)] and the middle tertile of the "pasta and veg" patterns [T3: 0.37, (0.18-0.75)] were negatively associated with overweight and obesity. The mothers' processed pattern during pregnancy was positively associated with offspring overweight and obesity [T2: 2.64, (1.28-5.45); T3: 2.03, (0.87-4.73)]. No significant associations were observed for the paternal diet patterns. This analysis shows that the influence of maternal diet pattern on child obesity is apparent early in the lifecourse.

Early-life influences on obesity: from preconception to adolescence

The double burden of under- and overnutrition profoundly affects human health globally. According to the World Health Organization, obesity and diabetes rates have almost doubled worldwide since 1980, and, in 2011, more than 40 million children under 5 years of age were overweight. Ecologic factors, parental genetics and fitness, and the intrauterine environment significantly influence the likelihood of offspring developing the dysmetabolic diathesis of obesity. This report examines the effects of these factors, including preconception, intrauterine and postnatal energy balance affecting programming of transgenerational transmission, and development of chronic diseases later in life-in particular, diabesity and its comorbidities.

Inter- and transgenerational epigenetic inheritance: evidence in asthma and COPD?

Evidence is now emerging that early life environment can have lifelong effects on metabolic, cardiovascular, and pulmonary function in offspring, a concept also known as fetal or developmental programming. In mammals, developmental programming is thought to occur mainly via epigenetic mechanisms, which include DNA methylation, histone modifications, and expression of non-coding RNAs. The effects of developmental programming can be induced by the intrauterine environment, leading to intergenerational epigenetic effects from one generation to the next. Transgenerational epigenetic inheritance may be considered when developmental programming is transmitted across generations that were not exposed to the initial environment which triggered the change. So far, inter- and transgenerational programming has been mainly described for cardiovascular and metabolic disease risk. In this review, we discuss available evidence that epigenetic inheritance also occurs in respiratory diseases, using asthma and chronic obstructive pulmonary disease (COPD) as examples. While multiple epidemiological as well as animal studies demonstrate effects of 'toxic' intrauterine exposure on various asthma-related phenotypes in the offspring, only few studies link epigenetic marks to the observed phenotypes. As epigenetic marks may distinguish individuals most at risk of later disease at early age, it will enable early intervention strategies to reduce such risks. To achieve this goal further, well designed experimental and human studies are needed.

Elements of the cellular metabolic structure

A large number of studies have demonstrated the existence of metabolic covalent modifications in different molecular structures, which are able to store biochemical information that is not encoded by DNA. Some of these covalent mark patterns can be transmitted across generations (epigenetic changes). Recently, the emergence of Hopfield-like attractor dynamics has been observed in self-organized enzymatic networks, which have the capacity to store functional catalytic patterns that can be correctly recovered by specific input stimuli. Hopfield-like metabolic dynamics are stable and can be maintained as a long-term biochemical memory. In addition, specific molecular information can be transferred from the functional dynamics of the metabolic networks to the enzymatic activity involved in covalent post-translational modulation, so that determined functional memory can be embedded in multiple stable molecular marks. The metabolic dynamics governed by Hopfield-type attractors (functional processes), as well as the enzymatic covalent modifications of specific molecules (structural dynamic processes) seem to represent the two stages of the dynamical memory of cellular metabolism (metabolic memory). Epigenetic processes appear to be the structural manifestation of this cellular metabolic memory. Here, a new framework for molecular information storage in the cell is presented, which is characterized by two functionally and molecularly interrelated systems: a dynamic, flexible and adaptive system (metabolic memory) and an essentially conservative system (genetic memory). The molecular information of both systems seems to coordinate the physiological development of the whole cell.

Extending injury- and disease-resistant CNS phenotypes by repetitive epigenetic conditioning

Significant reductions in the extent of acute injury in the CNS can be achieved by exposure to different preconditioning stimuli, but the duration of the induced protective phenotype is typically short-lasting, and thus is deemed as limiting its clinical applicability. Extending the period over which such adaptive epigenetic changes persist – in effect, expanding conditioning’s “therapeutic window” – would significantly broaden the potential applications of such a treatment approach in patients. The frequency of the conditioning stimulus may hold the key. While transient (1–3 days) protection against CNS ischemic injury is well established preclinically following a single preconditioning stimulus, repetitively presenting preconditioning stimuli extends the duration of ischemic tolerance by many weeks. Moreover, repetitive intermittent postconditioning enhances post-ischemic recovery metrics and improves long-term survival. Intermittent conditioning is also efficacious for preventing or delaying injury in preclinical models of chronic neurodegenerative disease, and for promoting long-lasting functional improvements in a number of other pathologies as well. Although the detailed mechanisms underlying these protracted kinds of neuroplasticity remain largely unstudied, accumulating empirical evidence supports the contention that all of these adaptive phenotypes are epigenetically mediated. Going forward, additional preclinical demonstrations of the ability to induce sustained beneficial phenotypes that reduce the burden of acute and chronic neurodegeneration, and experimental interrogations of the regulatory constructs responsible for these epigenetic responses, will accelerate the identification of not only efficacious but also practical, adaptive epigenetics-based treatments for individuals with neurological disease.

Cardiovascular diseases in grandparents and the risk of congenital heart diseases in grandchildren

Hyperglycemia, dyslipidemia and hyperhomocysteinemia are associated with both adult cardiovascular disease (CVD) and having a child with a congenital heart disease (CHD). We investigated associations between CVD in grandparents and the risk of CHD in grandchildren. In a case-control family study, we obtained detailed questionnaire information on CVD and CHD in 247 families with a CHD child and 203 families without a CHD child. Grandparents with CVD or intermittent claudication (IC) were significantly associated with an increased risk for CHD in grandchildren [OR 1.39 (95% CI 1.03-1.89) and OR 2.77 (95% CI 1.02-7.56), respectively]. The risk of CHD grandchildren was particularly increased in paternal grandfathers with CVD [OR 1.85 (95% CI 1.01-3.37)]. Overall, having a grandparent with CVD increased the risk for CHD in the grandchild by 1.65 (95% CI 1.12-2.41). After adjustment for potential maternal confounders, this risk was 1.44 (95% CI 0.94-2.21). Having two or more grandparents with CVD was associated with an approximately threefold risk for CHD grandchildren [OR adjusted 2.72 (95% CI 1.08-6.89)]. Our data suggest that CVD and IC in grandparents are associated with an increased risk of having a CHD grandchild. These first findings may be explained by shared causality of derangements in metabolic pathways and are in line with the fetal origins of health and disease.

The Sperm Epigenome, Male Aging, and Potential Effects on the Embryo

The effect of paternal aging on fertility, embryo quality, and offspring health is an important area of study that has received far less attention than the age effect in women. This is, in part, due to the fact that in females there are dramatic alterations to fertility and pregnancy outcomes that abruptly occur as a female ages. Such abrupt alterations to pregnancy success and/or embryonic and offspring health are not seen in males. Instead, there are subtle alterations to pregnancy success and offspring phenotypes that occur as a man ages. It is believed that, at least in part, these alterations can be explained by perturbations to the sperm epigenome that occur over time. This chapter will explore the effect of aging on the sperm epigenome and the potential impacts these perturbations may have on embryonic development and ultimately offspring health.

Environmentally induced epigenetic transgenerational inheritance of disease susceptibility

Environmental insults, such as exposure to toxicants or nutritional abnormalities, can lead to epigenetic changes that are in turn related to increased susceptibility to disease. The focus of this review is on the transgenerational inheritance of such epigenetic abnormalities (epimutations), and how it is that these inherited epigenetic abnormalities can lead to increased disease susceptibility, even in the absence of continued environmental insult. Observations of environmental toxicant specificity and exposure-specific disease susceptibility are discussed. How epimutations are transmitted across generations and how epigenetic changes in the germline are translated into an increased disease susceptibility in the adult is reviewed with regard to disease etiology.

Transgenerational occurrence of allergic disease and autoimmunity: general practice-based epidemiological research

Background:

Corresponding with the T helper cell type 1/T helper cell type 2 hypothesis, autoimmune and allergic diseases are considered pathologically distinct and mutually exclusive conditions. Co-occurrence of autoimmune disorders and allergy within patients, however, has been reported. Transgenerational co-occurrence of autoimmune and allergic disease has been less often described and may differ from the intra-patient results.

Aims:

To test the hypothesis that autoimmune disorders in parents are a risk factor for the development of an allergic disease in their offspring.

Methods:

Prospectively registered (by academic general practitioners) International Classifications of Primary Care (ICPC) for diagnoses of autoimmune disorders and allergy within families were evaluated (n=5,604 families) by performing multiple logistic regression analyses.

Results:

The presence of any ICPC-encoded autoimmune disorder in fathers appeared to be associated with an increased risk in their eldest children of developing an allergy (odds ratio (OR) 1.4, 95% CI 1.042 to 1.794). Psoriasis in fathers was particularly shown to be of influence (OR 1.5, 95% CI 1.061 to 2.117) and, although any ICPC-encoded autoimmune disease in mothers was found not to be of significance, the combined international code for registering rheumatoid arthritis/ankylosing spondylitis in mothers was OR 1.7 (95% CI 1.031 to 2.852).

Conclusions:

The occurrence of ICPC-encoded autoimmune disorders in parents, especially psoriasis and rheumatoid arthritis/ankylosing spondylitis, significantly increases the occurrence of allergic disease in their children. After validation in follow-up research in a larger sample, these results may lead to the inclusion of ‘parental autoimmune condition’ as a risk factor in the general practitioner's diagnostics of allergic disease.

Natural RNA interference directs a heritable response to the environment

RNA interference can induce heritable gene silencing, but it remains unexplored whether similar mechanisms play a general role in responses to cues that occur in the wild. We show that transient, mild heat stress in the nematode Caenorhabditis elegans results in changes in messenger RNA levels that last for more than one generation. The affected transcripts are enriched for genes targeted by germline siRNAs downstream of the piRNA pathway, and worms defective for germline RNAi are defective for these heritable effects. Our results demonstrate that a specific siRNA pathway transmits information about variable environmental conditions between generations.