Transgenerational effects of paternal alcohol exposure in mouse offspring

Paternal Preconceptional Alcohol Use Disorder With the Offspring's Mortality Risk

INTRODUCTION

Paternal preconceptional alcohol use may contribute to early pregnancy loss. However, the link between paternal preconceptional alcohol use disorder and long-term offspring's mortality risk remains unclear. This study examined the association of paternal preconceptional alcohol use disorder and recency of diagnosis with offspring's mortality and further stratified the mortality after the first year of birth by age.

METHODS

This is a nationwide cohort study with 1,973,174 Danish births (1980-2012), with follow-up from birth until death; emigration; or December 31, 2016. Paternal conceptional alcohol use disorder was identified from Danish National Patient Register and Prescription Registry, categorizing recency of diagnosis into <1 year, 1 to <4 years, 4 to <8 years, and ≥8 years. Logistic regression estimated the ORs and 95% CIs for offspring mortality risk. All data were analyzed in 2023.

RESULTS

Paternal preconceptional alcohol use disorder was associated with a 28% increased mortality after 1 year of birth (95% CI=1.09, 1.51), 23% increased infant mortality (95% CI=1.07, 1.42), and 23% increased odds of stillbirth (95% CI=1.06, 1.43). Paternal alcohol use disorder diagnosed <1 year before conception was associated with an 85%-111% increased risk of mortality in offspring aged 15-40 years. More recent alcohol use disorder diagnosis (i.e., 1 year before conception) had a higher risks of death from infectious and circulatory diseases in offsprings.

CONCLUSIONS

Offspring of fathers with alcohol use disorder before conception had higher mortality risk from birth to early adulthood, especially when alcohol use disorder diagnosis is close to conception. Current awareness regarding paternal preconceptional alcohol dependence use is insufficient. Promoting alcohol dependence avoidance, including educating men on the impact of alcohol on child health during prepregnancy examination, may help reduce or prevent long-term offspring mortality.

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.

Transgenerational Abnormalities Induced by Paternal Preconceptual Alcohol Drinking: Findings from Humans and Animal Models

Alcohol consumption during pregnancy and lactation is a widespread preventable cause of neurodevelopmental impairment in newborns. While the harmful effects of gestational alcohol use have been well documented, only recently, the role of paternal preconceptual alcohol consumption (PPAC) prior to copulating has drawn specific epigenetic considerations. Data from human and animal models have demonstrated that PPAC may affect sperm function, eliciting oxidative stress. In newborns, PPAC may induce changes in behavior, cognitive functions, and emotional responses. Furthermore, PPAC may elicit neurobiological disruptions, visuospatial impairments, hyperactivity disorders, motor skill disruptions, hearing loss, endocrine, and immune alterations, reduced physical growth, placental disruptions, and metabolic alterations. Neurobiological studies on PPAC have also disclosed changes in brain function and structure by disrupting the growth factors pathways. In particular, as shown in animal model studies, PPAC alters brain nerve growth factor (NGF) and brainderived neurotrophic factor (BDNF) synthesis and release. This review shows that the crucial topic of lifelong disabilities induced by PPAC and/or gestational alcohol drinking is quite challenging at the individual, societal, and familial levels. Since a nontoxic drinking behavior before pregnancy (for both men and women), during pregnancy, and lactation cannot be established, the only suggestion for couples planning pregnancies is to completely avoid the consumption of alcoholic beverages.

An indigenous framework of the cycle of fetal alcohol spectrum disorder risk and prevention across the generations: historical trauma, harm and healing

Objective: To build on Evans-Campbell's [2008. "Historical Trauma in American Indian/Native Alaska Communities: A Multilevel Framework for Exploring Impacts on Individuals, Families, and Communities." Journal of Interpersonal Violence 23 (3): 316-338. doi:10.1177/0886260507312290.] multilevel framework of historical trauma and health by focusing on the cycle of fetal alcohol spectrum disorders (FASD) in the socio-cultural, historical, and interpersonal context of trauma shared by American Indian and Alaska Native (AI/AN) peoples.Methods: We analyzed qualitative data from focus groups with seventy four urban AI/ANs who were 15 years of age and older. Community-based participatory research methods were used for data collection and analysis. Our study explored knowledge and attitudes about FASD, perspectives on FASD risk factors, and culturally relevant approaches to FASD prevention and healthcare.Results: According to our study's participants, efforts to address FASD among urban AI/ANs should align with and emerge from community values, promote healing, consider the broader context that influences behaviors, and reflect the community's understanding that FASD risk behaviors are inextricably linked with historical and contemporary trauma.Conclusion: Effective, multiple-level FASD prevention approaches for AI/ANs may include prioritizing Indigenous culture, supporting intergenerational cohesion, focusing on non-stigmatic healing of traumas, and authentically engaging community knowledge. This work draws on community and cultural strengths in an effort to reduce the occurrence of substance-exposed pregnancies, and encourages transformational changes in systems that serve AI/AN peoples to promote a healthy and thriving community and future generations.

Mapping the past, present and future research landscape of paternal effects

BACKGROUND

Although in all sexually reproducing organisms an individual has a mother and a father, non-genetic inheritance has been predominantly studied in mothers. Paternal effects have been far less frequently studied, until recently. In the last 5 years, research on environmentally induced paternal effects has grown rapidly in the number of publications and diversity of topics. Here, we provide an overview of this field using synthesis of evidence (systematic map) and influence (bibliometric analyses).

RESULTS

We find that motivations for studies into paternal effects are diverse. For example, from the ecological and evolutionary perspective, paternal effects are of interest as facilitators of response to environmental change and mediators of extended heredity. Medical researchers track how paternal pre-fertilization exposures to factors, such as diet or trauma, influence offspring health. Toxicologists look at the effects of toxins. We compare how these three research guilds design experiments in relation to objects of their studies: fathers, mothers and offspring. We highlight examples of research gaps, which, in turn, lead to future avenues of research.

CONCLUSIONS

The literature on paternal effects is large and disparate. Our study helps in fostering connections between areas of knowledge that develop in parallel, but which could benefit from the lateral transfer of concepts and methods.

The Impact of Paternal Alcohol Consumption on Offspring Brain and Behavioral Development

BACKGROUND

Fetal alcohol spectrum disorders (FASD) describe the wide array of long-lasting developmental abnormalities in offspring due to prenatal alcohol (ethanol [EtOH]) exposure via maternal gestational drinking. Although the teratogenic consequences of prenatal EtOH exposure, are apparent, the effects of preconception paternal EtOH exposure (PatEE) are still unclear. Previous research suggests that PatEE can induce molecular changes and abnormal behavior in the offspring. However, it is not known whether PatEE impacts the development of the neocortex and behavior in offspring as demonstrated in maternal consumption models of FASD (J Neurosci, 33, 2013, 18893).

METHODS

In this study, we utilized a novel mouse model of PatEE where male mice self-administered 25% EtOH for an extended period prior to conception, generating indirect exposure to the offspring through the paternal germline. Following mating, we examined the effects of PatEE on offspring neocortical development at postnatal day (P) 0 and evaluated several aspects of behavior at both P20 and P30 using a battery of behavioral assays.

RESULTS

PatEE resulted in significant impact on neocortical development, including abnormal patterns of gene expression within the neocortex at P0 and subtle alterations in patterns of intraneocortical connections. Additionally, PatEE mice exhibited a sex-specific increase in activity and sensorimotor integration deficits at P20, and decreased balance, coordination, and short-term motor learning at P30. This suggests that PatEE may generate long-lasting, sex-specific effects on offspring behavior.

CONCLUSIONS

These results demonstrate that the developmental impact of preconception PatEE is more harmful than previously thought and provide additional insights into the biological mechanisms that may underlie atypical behavior observed in children of alcoholic fathers.

Genetic Signatures of Drug Response Variability in Drosophila melanogaster

Knowledge of the genetic basis underlying variation in response to environmental exposures or treatments is important in many research areas. For example, knowing the set of causal genetic variants for drug responses could revolutionize personalized medicine. We used Drosophila melanogaster to investigate the genetic signature underlying behavioral variability in response to methylphenidate (MPH), a drug used in the treatment of attention-deficit/hyperactivity disorder. We exposed a wild-type D. melanogaster population to MPH and a control treatment, and observed an increase in locomotor activity in MPH-exposed individuals. Whole-genome transcriptomic analyses revealed that the behavioral response to MPH was associated with abundant gene expression alterations. To confirm these patterns in a different genetic background and to further advance knowledge on the genetic signature of drug response variability, we used a system of inbred lines, the Drosophila Genetic Reference Panel (DGRP). Based on the DGRP, we showed that the behavioral response to MPH was strongly genotype-dependent. Using an integrative genomic approach, we incorporated known gene interactions into the genomic analyses of the DGRP, and identified putative candidate genes for variability in drug response. We successfully validated 71% of the investigated candidate genes by gene expression knockdown. Furthermore, we showed that MPH has cross-generational behavioral and transcriptomic effects. Our findings establish a foundation for understanding the genetic mechanisms driving genotype-specific responses to medical treatment, and highlight the opportunities that integrative genomic approaches have in optimizing medical treatment of complex diseases.

Intergenerational Effects of Alcohol: A Review of Paternal Preconception Ethanol Exposure Studies and Epigenetic Mechanisms in the Male Germline

While alcohol use disorder (AUD) is a highly heritable psychiatric disease, efforts to elucidate that heritability by examining genetic variation (e.g., single nucleotide polymorphisms) have been insufficient to fully account for familial AUD risk. Perhaps not coincidently, there has been a burgeoning interest in novel nongenomic mechanisms of inheritance (i.e., epigenetics) that are shaped in the male or female germ cells by significant lifetime experiences such as exposure to chronic stress, malnutrition, or drugs of abuse. While many epidemiological and preclinical studies have long pointed to a role for the parental preconception environment in offspring behavior, over the last decade many studies have implicated a causal relationship between the environmentally sensitive sperm epigenome and intergenerational phenotypes. This critical review will detail the heritable effects of alcohol and the potential role for epigenetics.

Preconception paternal alcohol exposure exerts sex-specific effects on offspring growth and long-term metabolic programming

BACKGROUND

Although clinical data support an association between paternal alcohol use and deficits in child neurocognitive development, the relationship between paternal drinking and alcohol-induced growth phenotypes remains challenging to define. Using an established mouse model of chronic exposure, previous work by our group has linked preconception paternal alcohol use to sex-specific patterns of fetal growth restriction and placental dysfunction. The aim of the present study was to investigate the long-term impact of chronic preconception paternal alcohol use on offspring growth and metabolic programming.

RESULTS

Preconception paternal alcohol exposure induced a prolonged period of fetal gestation and an increased incidence of intrauterine growth restriction, which affected the male offspring to a greater extent than the females. While the female offspring of ethanol-exposed males were able to match the body weights of the controls within the first 2 weeks of postnatal life, male offspring continued to display an 11% reduction in weight at 5 weeks of age and a 6% reduction at 8 weeks of age. The observed growth deficits associated with insulin hypersensitivity in the male offspring, while in contrast, females displayed a modest lag in their glucose tolerance test. These metabolic defects were associated with an up-regulation of genes within the pro-fibrotic TGF-β signaling pathway and increased levels of cellular hydroxyproline within the livers of the male offspring. We observed suppressed cytokine profiles within the liver and pancreas of both the male and female offspring, which correlated with the up-regulation of genes in the LiverX/RetinoidX/FarnesoidX receptor pathways. However, patterns of gene expression were highly variable between the offspring of alcohol-exposed sires. In the adult offspring of alcohol-exposed males, we did not observe any differences in the allelic expression of Igf2 or any other imprinted genes.

CONCLUSIONS

The impact of paternal alcohol use on child development is poorly explored and represents a significant gap in our understanding of the teratogenic effects of ethanol. Our studies implicate paternal exposure history as an additional and important modifier of alcohol-induced growth phenotypes and challenge the current maternal-centric exposure paradigm.

Ethical challenges in FASD prevention: Scientific uncertainty, stigma, and respect for women's autonomy

Fetal alcohol spectrum disorder (FASD) is a leading form of neurodevelopmental delay in Canada, affecting an estimated 3000 babies per year. FASD involves a range of disabilities that entail significant costs to affected individuals, families, and society. Exposure to alcohol in utero is a necessary factor for FASD development, and this has led to FASD being described as "completely preventable". However, there are significant ethical challenges associated with FASD prevention. These challenges revolve around 1) what should be communicated about the risks of alcohol consumption during pregnancy, given some ongoing scientific uncertainty about the effects of prenatal alcohol exposure, and 2) how to communicate these risks, given the potential for stigma against women who give birth to children with FASD as well as against children and adults with FASD. In this paper, we share initial thoughts on how primary care physicians can tackle this complex challenge. First, we recommend honest disclosure of scientific evidence to women and the tailoring of information offered to pregnant women. Second, we propose a contextualized, patient-centred, compassionate approach to ensure that appropriate advice is given to patients in a supportive, non-stigmatizing way.

Drinking beyond a lifetime: New and emerging insights into paternal alcohol exposure on subsequent generations

Alcohol-use disorder (AUD) is prevalent and associated with substantial socioeconomic costs. While heritability estimates of AUD are ∼50%, identifying specific gene variants associated with risk for AUD has proven challenging despite considerable investment. Emerging research into heritability of complex diseases has implicated transmission of epigenetic variants in the development of behavioral phenotypes, including drug preference and drug-induced behavior. Several recent rodent studies have specifically focused on paternal transmission of epigenetic variants, which is especially relevant because sires are not present for offspring rearing and changes to offspring phenotype are assumed to result from modifications to the sperm epigenome. While considerable interest in paternal transmission of epigenetic variants has emerged recently, paternal alcohol exposures have been studied for 30+ years with interesting behavioral and physiologic effects noted on offspring. However, only recently, with improvements in technology to identify epigenetic modifications in germ cells, has it been possible to identify mechanisms by which paternal ethanol exposure alters offspring behavior. This review presents an overview of epigenetic inheritance in the context of paternal ethanol exposure and suggests future studies to identify specific effects of paternal ethanol exposure on offspring behavior and response to ethanol.