Alterations in sperm-inherited noncoding RNAs associate with late-term fetal growth restriction induced by preconception paternal alcohol use

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.

Alterations in sperm RNAs persist after alcohol cessation and correlate with epididymal mitochondrial dysfunction

BACKGROUND

Chronic preconception paternal alcohol use adversely modifies the sperm epigenome, inducing fetoplacental and craniofacial growth defects in the offspring of exposed males. A crucial outstanding question in the field of paternal epigenetic inheritance concerns the resilience of the male germline and its capacity to recover and correct sperm-inherited epigenetic errors after stressor withdrawal.

OBJECTIVES

We set out to determine if measures of the sperm-inherited epigenetic program revert to match the control treatment 1 month after withdrawing the daily alcohol treatments.

MATERIALS AND METHODS

Using a voluntary access model, we exposed C57BL/6J males to 6% or 10% alcohol for 10 weeks, withdrew the alcohol treatments for 4 weeks, and used RNA sequencing to examine gene expression patterns in the caput section of the epididymis. We then compared the abundance of sperm small RNA species between treatments.

RESULTS

In the caput section of the epididymis, chronic alcohol exposure induced changes in the transcriptional control of genetic pathways related to the mitochondrial function, oxidative phosphorylation, and the generalized stress response (EIF2 signaling). Subsequent analysis identified region-specific, alcohol-induced changes in mitochondrial DNA copy number across the epididymis, which correlated with increases in the mitochondrial DNA content of alcohol-exposed sperm. Notably, in the corpus section of the epididymis, increases in mitochondrial DNA copy number persisted 1 month after alcohol cessation. Analysis of sperm noncoding RNAs between control and alcohol-exposed males 1 month after alcohol withdrawal revealed a ∼100-fold increase in mir-196a, a microRNA induced as part of the nuclear factor erythroid 2-related factor 2 (Nrf2)-driven cellular antioxidant response.

DISCUSSION AND CONCLUSION

Our data reveal that alcohol-induced epididymal mitochondrial dysfunction and differences in sperm noncoding RNA content persist after alcohol withdrawal. Further, differences in mir-196a and sperm mitochondrial DNA copy number may serve as viable biomarkers of adverse alterations in the sperm-inherited epigenetic program.

Maternal 129S1/SvImJ background attenuates the placental phenotypes induced by chronic paternal alcohol exposure

Paternal alcohol use is emerging as a plausible driver of alcohol-related growth and patterning defects. Studies from our lab using an inbred C57Bl/6 J mouse model suggest that these paternally-inherited phenotypes result from paternally programmed deficits in the formation and function of the placenta. The 129S1/SvImJ genetic background is typically more susceptible to fetoplacental growth defects due to strain-specific differences in placental morphology. We hypothesized that these placental differences would sensitize 129S1/SvImJ-C57Bl/6 J hybrid offspring to paternally-inherited fetoplacental growth phenotypes induced by paternal alcohol exposure. Using a limited access model, we exposed C57Bl/6 J males to alcohol and bred them to naïve 129S1/SvImJ dams. We then assayed F1 hybrid offspring for alterations in fetoplacental growth and used micro-CT imaging to contrast placental histological patterning between the preconception treatments. F1 hybrid placentae exhibit larger placental weights than pure C57Bl/6 J offspring but display a proportionally smaller junctional zone with increased glycogen content. The male F1 hybrid offspring of alcohol-exposed sires exhibit modest placental hyperplasia but, unlike pure C57Bl/6 J offspring, do not display observable changes in placental histology, glycogen content, or measurable impacts on fetal growth. Although F1 hybrid female offspring do not exhibit any measurable alterations in fetoplacental growth, RT-qPCR analysis of placental gene expression reveals increased expression of genes participating in the antioxidant response. The reduced placental junctional zone but increased glycogen stores of 129S1/SvImJ-C57Bl/6 J F1 hybrid placentae ostensibly attenuate the previously observed placental patterning defects and fetal growth restriction induced by paternal alcohol use in the C57Bl/6 J strain.

Inter- and trans-generational impacts of environmental exposures on the germline resolved at the single-cell level

Reproduction is a remarkably intricate process involving the interaction of multiple cell types and organ systems unfolding over long periods of time and that culminates with the production of gametes. The initiation of germ cell development takes place during embryogenesis but only completes decades later in humans. The complexity inherent to reproduction and its study has long hampered our ability to decipher how environmental agents disrupt this process. Single-cell approaches provide an opportunity for a deeper understanding of the action of toxicants on germline function and analyze how the response to their exposure is differentially distributed across tissues and cell types. In addition to single-cell RNA sequencing, other single-cell or nucleus level approaches such as ATAC-sequencing and multi-omics have expanded the strategies that can be implemented in reproductive toxicological studies to include epigenomic and the nuclear transcriptomic data. Here we will discuss the current state of single-cell technologies and how they can best be utilized to advance reproductive toxicological studies. We will then discuss case studies in two model organisms (Caenorhabditis elegans and mouse) studying different environmental exposures (alcohol and e-cigarettes respectively) to highlight the value of single-cell and single-nucleus approaches for reproductive biology and reproductive toxicology.

The Impact of Oxidative Stress on the Epigenetics of Fetal Alcohol Spectrum Disorders

Fetal alcohol spectrum disorders (FASD) represent a continuum of lifelong impairments resulting from prenatal exposure to alcohol, with significant global impact. The "spectrum" of disorders includes a continuum of physical, cognitive, behavioral, and developmental impairments which can have profound and lasting effects on individuals throughout their lives, impacting their health, social interactions, psychological well-being, and every aspect of their lives. This narrative paper explores the intricate relationship between oxidative stress and epigenetics in FASD pathogenesis and its therapeutic implications. Oxidative stress, induced by alcohol metabolism, disrupts cellular components, particularly in the vulnerable fetal brain, leading to aberrant development. Furthermore, oxidative stress is implicated in epigenetic changes, including alterations in DNA methylation, histone modifications, and microRNA expression, which influence gene regulation in FASD patients. Moreover, mitochondrial dysfunction and neuroinflammation contribute to epigenetic changes associated with FASD. Understanding these mechanisms holds promise for targeted therapeutic interventions. This includes antioxidant supplementation and lifestyle modifications to mitigate FASD-related impairments. While preclinical studies show promise, further clinical trials are needed to validate these interventions' efficacy in improving clinical outcomes for individuals affected by FASD. This comprehensive understanding of the role of oxidative stress in epigenetics in FASD underscores the importance of multidisciplinary approaches for diagnosis, management, and prevention strategies. Continued research in this field is crucial for advancing our knowledge and developing effective interventions to address this significant public health concern.

Inter- and transgenerational heritability of preconception chronic stress or alcohol exposure: Translational outcomes in brain and behavior

Chronic stress and alcohol (ethanol) use are highly interrelated and can change an individual's behavior through molecular adaptations that do not change the DNA sequence, but instead change gene expression. A recent wealth of research has found that these nongenomic changes can be transmitted across generations, which could partially account for the "missing heritability" observed in genome-wide association studies of alcohol use disorder and other stress-related neuropsychiatric disorders. In this review, we summarize the molecular and behavioral outcomes of nongenomic inheritance of chronic stress and ethanol exposure and the germline mechanisms that could give rise to this heritability. In doing so, we outline the need for further research to: (1) Investigate individual germline mechanisms of paternal, maternal, and biparental nongenomic chronic stress- and ethanol-related inheritance; (2) Synthesize and dissect cross-generational chronic stress and ethanol exposure; (3) Determine cross-generational molecular outcomes of preconception ethanol exposure that contribute to alcohol-related disease risk, using cancer as an example. A detailed understanding of the cross-generational nongenomic effects of stress and/or ethanol will yield novel insight into the impact of ancestral perturbations on disease risk across generations and uncover actionable targets to improve human health.

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.

Pregabalin alters reproductive performance in male mice and causes congenital anomalies in offspring

CONTEXT

Pregabalin is an anticonvulsant drug with analgesic activity for the treatment of neuropathic pain.

AIMS

To valuate the toxicity of pregabalin in reproductive parameters, spermatogenesis, and teratogenicity in the offspring of mice.

METHODS

Twenty male mice were randomly distributed into two groups: PGB group and group C (n =10 per group). The animals in the PGB group received, via gavage, 200mg/kg of pregabalin diluted in distilled water daily, for a period of 45days. Group C received distilled water under the same experimental design.

KEY RESULTS

In the paternal parameters of the PGB group, there was a significant increase in the size of the testicles, morphological alterations in the spermatozoa, a decrease in the Johnsen score, an increase in the Leydig cells, and a decrease in the serum level of testosterone. In the intrauterine development parameters of females mated with males from the PGB group, a significant decrease in placental weight, weight and length of fetuses, and fetal viability rate was observed. There was a significant increase in the number of resorptions and post-implantation losses. The significant anomalies observed in the offspring were alteration in the size of the kidneys, absent metacarpals and phalanges, alteration in the sternum, and supernumerary thoracic vertebrae.

CONCLUSION

Results suggest that pregabalin had toxic effects on the reproductive function of male mice and teratogenic potential.

IMPLICATIONS

The findings of this study may provide new hypotheses, taking into account the risk-benefit ratio for male reproduction and offspring health.

Small RNAs: An expanding world with therapeutic promises

Small non-coding RNAs (sncRNAs), such as microRNAs (miRNAs), small interfering RNAs (siRNAs), PIWI-interacting RNAs (piRNAs), and transfer RNA (tRNA)-derived small RNAs (tsRNAs), play essential roles in regulating various cellular and developmental processes. Over the past three decades, researchers have identified novel sncRNA species from various organisms. These molecules demonstrate dynamic expression and diverse functions, and they are subject to intricate regulation through RNA modifications in both healthy and diseased states. Notably, certain sncRNAs in gametes, particularly sperm, respond to environmental stimuli and facilitate epigenetic inheritance. Collectively, the in-depth understanding of sncRNA functions and mechanisms has accelerated the development of small RNA-based therapeutics. In this review, we present the recent advances in the field, including new sncRNA species and the regulatory influences of RNA modifications. We also discuss the current limitations and challenges associated with using small RNAs as either biomarkers or therapeutic drugs.

Developmental origins of health and disease: Impact of paternal nutrition and lifestyle

Most epidemiological and experimental studies have focused on maternal influences on offspring's health. The impact of maternal undernutrition, overnutrition, hypoxia, and stress is linked to adverse offspring outcomes across a range of systems including cardiometabolic, respiratory, endocrine, and reproduction among others. During the past decade, it has become evident that paternal environmental factors are also linked to the development of diseases in offspring. In this article, we aim to outline the current understanding of the impact of male health and environmental exposure on offspring development, health, and disease and explore the mechanisms underlying the paternal programming of offspring health. The available evidence suggests that poor paternal pre-conceptional nutrition and lifestyle, and advanced age can increase the risk of negative outcomes in offspring, via both direct (genetic/epigenetic) and indirect (maternal uterine environment) effects. Beginning at preconception, and during utero and the early life after birth, cells acquire an epigenetic memory of the early exposure which can be influential across the entire lifespan and program a child's health. Potentially not only mothers but also fathers should be advised that maintaining a healthy diet and lifestyle is important to improve offspring health as well as the parental health status. However, the evidence is mostly based on animal studies, and well-designed human studies are urgently needed to verify findings from animal data.

Preconception paternal alcohol exposure decreases IVF embryo survival and pregnancy success rates in a mouse model

Increasingly, couples struggling with fertility turn to assisted reproductive techniques, including IVF, to have children. Despite the demonstrated influence of periconception male health and lifestyle choices on offspring development, studies examining IVF success rates and child health outcomes remain exclusively focused on maternal factors. Using a physiologically relevant mouse model, we tested the hypothesis that chronic paternal preconception alcohol intake adversely affects IVF success and negatively impacts IVF offspring fetoplacental growth. Using a voluntary, binge-like mouse model, we exposed sexually mature C57BL/6J males to three preconception treatments (0% (Control), 6% EtOH or 10% EtOH) for 6 weeks, isolated and cryopreserved caudal sperm from treated males, and then used these samples to fertilize oocytes before assessing IVF embryo developmental outcomes. We found that preconception paternal alcohol use reduced IVF embryo survival and pregnancy success rates in a dose-dependent manner, with the pregnancy success rate of the 10% EtOH treatment falling to half those of the Controls. Mechanistically, we found that preconception paternal alcohol exposure disrupts embryonic gene expression, including Fgf4 and Egfr, two critical regulators of trophectoderm stem cell growth and placental patterning, with lasting impacts on the histological organization of the late-term placenta. The changes in placental histoarchitecture were accompanied by altered regulation of pathways controlling mitochondrial function, oxidative phosphorylation and some imprinted genes. Our studies indicate that male alcohol use may significantly impede IVF success rates, increasing the couple's financial burden and emotional stress, and highlights the need to expand prepregnancy messaging to emphasize the reproductive dangers of alcohol use by both parents.

The Sperm Small RNA Transcriptome: Implications beyond Reproductive Disorder

Apart from the paternal half of the genetic material, the male gamete carries assorted epigenetic marks for optimal fertilization and the developmental trajectory for the early embryo. Recent works showed dynamic changes in small noncoding RNA (sncRNA) in spermatozoa as they transit through the testicular environment to the epididymal segments. Studies demonstrated the changes to be mediated by epididymosomes during the transit through the adluminal duct in the epididymis, and the changes in sperm sncRNA content stemmed from environmental insults significantly altering the early embryo development and predisposing the offspring to metabolic disorders. Here, we review the current knowledge on the establishment of the sperm sncRNA transcriptome and their role in male-factor infertility, evidence of altered offspring health in response to the paternal life experiences through sperm sncRNA species and, finally, their implications in assisted reproductive technology in terms of epigenetic inheritance.

Paternal alcohol exposure has task- and sex-dependent behavioral effect in offspring

BACKGROUND

Endophenotypes for alcohol use disorder are well known and may reflect paternal exposure effects passed down to offspring via epigenetic mechanisms. Previously, we showed that paternal alcohol exposure prior to conception attenuates the acquisition of operant alcohol self-administration. We now test whether paternal alcohol exposure alters their offsprings' behavioral responses to alcohol (endophenotypes) and global DNA methylation levels in reward-related brain regions.

METHODS

Adult male rats were exposed to alcohol vapors or air for 6 weeks and mated with alcohol-naïve females 8 weeks later. Adult male and female offspring of the alcohol- and control-sired litters were tested on three behaviors 30 m after gavage with water or alcohol (1.5 g/kg): open field, elevated plus maze, and accelerating rotarod. Global DNA methylation levels in sperm, nucleus accumbens, and prefrontal cortex were examined in male sires and in another group of offspring.

RESULTS

Alcohol-sired males showed less anxiety-like behavior in the elevated plus maze that was not affected by alcohol administration. By contrast, alcohol had anxiolytic effects in the open field in male offspring only with no paternal alcohol effect. Neither paternal alcohol exposure nor alcohol administration altered locomotor activity in either sex. Sex-specific effects of paternal alcohol exposure were seen in the rotarod test. Alcohol-sired male offspring showed blunted sensitivity to the alcohol's motor-impairing effects, whereas alcohol-sired female offspring showed enhanced sensitivity. Global DNA methylation was altered in the sperm of alcohol-exposed males, but no changes were seen in their offspring.

CONCLUSIONS

Paternal alcohol exposure prior to conception has sex- and task-dependent effects on unconditioned behaviors in their offspring.

Paternal alcohol exposures program intergenerational hormetic effects on offspring fetoplacental growth

Hormesis refers to graded adaptive responses to harmful environmental stimuli where low-level toxicant exposures stimulate tissue growth and responsiveness while, in contrast, higher-level exposures induce toxicity. Although the intergenerational inheritance of programmed hormetic growth responses is described in plants and insects, researchers have yet to observe this phenomenon in mammals. Using a physiologically relevant mouse model, we demonstrate that chronic preconception paternal alcohol exposures program nonlinear, dose-dependent changes in offspring fetoplacental growth. Our studies identify an inverse j-shaped curve with a threshold of 2.4 g/Kg per day; below this threshold, paternal ethanol exposures induce programmed increases in placental growth, while doses exceeding this point yield comparative decreases in placental growth. In male offspring, higher paternal exposures induce dose-dependent increases in the placental labyrinth layer but do not impact fetal growth. In contrast, the placental hypertrophy induced by low-level paternal ethanol exposures associate with increased offspring crown-rump length, particularly in male offspring. Finally, alterations in placental physiology correlate with disruptions in both mitochondrial-encoded and imprinted gene expression. Understanding the influence of ethanol on the paternally-inherited epigenetic program and downstream hormetic responses in offspring growth may help explain the enormous variation observed in fetal alcohol spectrum disorder (FASD) phenotypes and incidence.

Establishment of a male fertility prediction model with sperm RNA markers in pigs as a translational animal model

BACKGROUND

Male infertility is an important issue that causes low production in the animal industry. To solve the male fertility crisis in the animal industry, the prediction of sperm quality is the most important step. Sperm RNA is the potential marker for male fertility prediction. We hypothesized that the expression of functional genes related to fertilization will be the best target for male fertility prediction markers. To investigate optimum male fertility prediction marker, we compared target genes expression level and a wide range of field data acquired from artificial insemination of boar semen.

RESULTS

Among the genes related to acrosomal vesicle exocytosis and sperm-oocyte fusion, equatorin (EQTN), zona pellucida sperm-binding protein 4 (ZP4), and sperm acrosome membrane-associated protein 3 exhibited high accuracy (70%, 90%, and 70%, respectively) as markers to evaluate male fertility. Combinations of EQTN-ZP4, ZP4-protein unc-13 homolog B, and ZP4-regulating synaptic membrane exocytosis protein 1 (RIMS1) showed the highest prediction value, and all these markers are involved in the acrosome reaction.

CONCLUSION

The EQTN-ZP4 model was efficient in clustering the high-fertility group and may be useful for selection of animal that has superior fertility in the livestock industry. Compared to the EQTN-ZP4 model, the ZP4-RIMS1 model was more efficient in clustering the low-fertility group and may be useful in the diagnosis of male infertility in humans and other animals. The appointed translational animal model and established biomarker combination can be widely used in various scientific fields such as biomedical science.

Alcohol induced increases in sperm Histone H3 lysine 4 trimethylation correlate with increased placental CTCF occupancy and altered developmental programming

Using a mouse model, studies by our group reveal that paternal preconception alcohol intake affects offspring fetal-placental growth, with long-lasting consequences on adult metabolism. Here, we tested the hypothesis that chronic preconception male alcohol exposure impacts histone enrichment in sperm and that these changes are associated with altered developmental programming in the placenta. Using chromatin immunoprecipitation, we find alcohol-induced increases in sperm histone H3 lysine 4 trimethylation (H3K4me3) that map to promoters and presumptive enhancer regions enriched in genes driving neurogenesis and craniofacial development. Given the colocalization of H3K4me3 with the chromatin binding factor CTCF across both sperm and embryos, we next examined CTCF localization in the placenta. We find global changes in CTCF binding within placentae derived from the male offspring of alcohol-exposed sires. Furthermore, altered CTCF localization correlates with dysregulated gene expression across multiple gene clusters; however, these transcriptional changes only occur in male offspring. Finally, we identified a correlation between genomic regions exhibiting alcohol-induced increases in sperm H3K4me3 and increased CTCF binding in male placentae. Collectively, our analysis demonstrates that the chromatin landscape of sperm is sensitive to chronic alcohol exposure and that a subset of these affected regions exhibits increased placental CTCF enrichment.

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.

Paternal alcohol consumption has intergenerational consequences in male offspring

PURPOSE

Alcoholism is a heterogeneous set of disorders caused by ethanol intake. Harmful effects of paternal consumption on the offspring are poorly explored and not fully understood. We analyzed the effect of paternal alcohol consumption on both their own reproductive capacity and that of their male offspring.

METHODS

We used a model of ethanol consumption (15% v/v in drinking water) for 12 days in adult CF-1 male mice. DNA integrity and post-translational modifications of histones were assessed in sperm; testicular weight, histology, and DNA fragmentation were analyzed. Treated or untreated male mice were mated with non-treated females to obtain two cell embryos that were cultured for 7 days; morphology and embryonic cell death were evaluated. Males of both groups were mated with non-treated females. Adult male offspring was euthanized, and sperm and testicular parameters determined.

RESULTS

Paternal ethanol consumption caused histological and epigenetic changes, as well as damage in DNA integrity in the testicular germline and sperm. These alterations gave rise to deleterious effects on embryonic development and to testicular and spermatic changes in the offspring.

CONCLUSION

This study provides critical information on reproductive disturbances brought about by paternal alcohol consumption and the profound impact these could have on the male progeny. The need to explore the effects of paternal alcohol consumption in detail and warn about the importance of controlling alcohol intake for the well-being of future generations should not be underscored.

Impact of Alcohol Consumption on Male Fertility Potential: A Narrative Review

Alcohol abuse disorder is a serious condition, implicating more than 15 million people aged 12 years and older in 2019 in the United States. Ethanol (or ethyl alcohol) is mainly oxidized in the liver, resulting in the synthesis of acetaldehyde and acetate, which are toxic and carcinogenic metabolites, as well as in the generation of a reductive cellular environment. Moreover, ethanol can interact with lipids, generating fatty acid ethyl esters and phosphatidylethanol, which interfere with physiological cellular pathways. This narrative review summarizes the impact of excessive alcohol consumption on male fertility by describing its metabolism and how ethanol consumption may induce cellular damage. Furthermore, the impact of alcohol consumption on hormonal regulation, semen quality, and genetic and epigenetic regulations is discussed based on evidence from animal and human studies, focusing on the consequences on the offspring. Finally, the limitations of the current evidence are discussed. Our review highlights the association between chronic alcohol consumption and poor semen quality, mainly due to the development of oxidative stress, as well as its genotoxic impact on hormonal regulation and DNA integrity, affecting the offspring’s health. New landscapes of investigation are proposed for the identification of molecular markers for alcohol-associated infertility, with a focus on advanced OMICS-based approaches applied to the analysis of semen samples.

Small Noncoding RNAs in Reproduction and Infertility

Infertility has been reported as one of the most common reproductive impairments, affecting nearly one in six couples worldwide. A large proportion of infertility cases are diagnosed as idiopathic, signifying a deficit in information surrounding the pathology of infertility and necessity of medical intervention such as assisted reproductive therapy. Small noncoding RNAs (sncRNAs) are well-established regulators of mammalian reproduction. Advanced technologies have revealed the dynamic expression and diverse functions of sncRNAs during mammalian germ cell development. Mounting evidence indicates sncRNAs in sperm, especially microRNAs (miRNAs) and transfer RNA (tRNA)-derived small RNAs (tsRNAs), are sensitive to environmental changes and mediate the inheritance of paternally acquired metabolic and mental traits. Here, we review the critical roles of sncRNAs in mammalian germ cell development. Furthermore, we highlight the functions of sperm-borne sncRNAs in epigenetic inheritance. We also discuss evidence supporting sncRNAs as promising biomarkers for fertility and embryo quality in addition to the present limitations of using sncRNAs for infertility diagnosis and treatment.

Maternal background alters the penetrance of growth phenotypes and sex-specific placental adaptation of offspring sired by alcohol-exposed males

Epigenetic mechanisms of paternal inheritance are an emerging area of interest in our efforts to understand fetal alcohol spectrum disorders. In rodent models examining maternal alcohol exposures, different maternal genetic backgrounds protect or sensitize offspring to alcohol‐induced teratogenesis. However, whether maternal background can mitigate sperm‐inherited alterations in developmental programming and modify the penetrance of growth defects induced by preconception paternal alcohol exposures remains unaddressed. In our previous studies examining pure C57Bl/6J crosses, the offspring of alcohol‐exposed sires exhibited fetal growth restriction, enlarged placentas, and decreased placental efficiency. Here, we find that in contrast to our previous studies, the F1 offspring of alcohol‐exposed C57Bl/6J sires and CD‐1 dams do not exhibit fetal growth restriction, with male fetuses developing smaller placentas and increased placental efficiencies. However, in these hybrid offspring, preconception paternal alcohol exposure induces sex‐specific changes in placental morphology. Specifically, the female offspring of alcohol‐exposed sires displayed structural changes in the junctional and labyrinth zones, along with increased placental glycogen content. These changes in placental organization are accompanied by female‐specific alterations in the expression of imprinted genes Cdkn1c and H19. Although male placentae do not display overt changes in placental histology, using RNA‐sequencing, we identified programmed alterations in genes regulating oxidative phosphorylation, mitochondrial function, and Sirtuin signaling. Collectively, our data reveal that preconception paternal alcohol exposure transmits a stressor to developing offspring, that males and females exhibit distinct patterns of placental adaptation, and that maternal genetic background can modulate the effects of paternal alcohol exposure.

Pre-implantation alcohol exposure induces lasting sex-specific DNA methylation programming errors in the developing forebrain

Background

Prenatal alcohol exposure is recognized for altering DNA methylation profiles of brain cells during development, and to be part of the molecular basis underpinning Fetal Alcohol Spectrum Disorder (FASD) etiology.  However, we have negligible information on the effects of alcohol exposure during pre-implantation, the early embryonic window marked with dynamic DNA methylation reprogramming, and on how this may rewire the brain developmental program.

Results

Using a pre-clinical in vivo mouse model, we show that a binge-like alcohol exposure during pre-implantation at the 8-cell stage leads to surge in morphological brain defects and adverse developmental outcomes during fetal life. Genome-wide DNA methylation analyses of fetal forebrains uncovered sex-specific alterations, including partial loss of DNA methylation maintenance at imprinting control regions, and abnormal de novo DNA methylation profiles in various biological pathways (e.g., neural/brain development).

Conclusion

These findings support that alcohol-induced DNA methylation programming deviations during pre-implantation could contribute to the manifestation of neurodevelopmental phenotypes associated with FASD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13148-021-01151-0.

Paternal and/or maternal preconception-induced neurobehavioral teratogenicity in animal and human models

Prenatal insult exposure effects on the offspring, have and are still considered the main interest of most teratological studies, while paternal and maternal preconception effects have received relatively little interest. Once thought to be a myth, paternal exposure to insults leading to numerous detrimental effects in the offspring, has been confirmed on several occasions and is gaining increased attention. These effects could be demonstrated molecularly, biochemically and/or behaviorally. Different epigenetic mechanisms have been proposed for these effects to occur, including DNA methylation, histone modification and sperm RNA transmission. Paternal insult exposure has been shown to cause several neurobehavioral and developmental defects in the offspring. Findings on parental insult exposure effects on the progeny will be discussed in this review, with the main focus being on neurobehavioral effects after parental preconceptional exposure. The exposure to the insults induced long-lasting, mostly marked, defects. A few pioneering, prevention and reversal studies were published. Interestingly, most studies were conducted on paternal exposure and, at the present state of this field, on animal models. Clinical translation remains the subsequent challenge.

Exposure to drugs of abuse induce effects that persist across generations

Substance use disorders are highly prevalent and continue to be one of the leading causes of disability in the world. Notably, not all people who use addictive drugs develop a substance use disorder. Although substance use disorders are highly heritable, patterns of inheritance cannot be explained purely by Mendelian genetic mechanisms. Vulnerability to developing drug addiction depends on the interplay between genetics and environment. Additionally, evidence from the past decade has pointed to the role of epigenetic inheritance in drug addiction. This emerging field focuses on how environmental perturbations, including exposure to addictive drugs, induce epigenetic modifications that are transmitted to the embryo at fertilization and modify developmental gene expression programs to ultimately impact subsequent generations. This chapter highlights intergenerational and transgenerational phenotypes in offspring following a history of parental drug exposure. Special attention is paid to parental preconception exposure studies of five drugs of abuse (alcohol, cocaine, nicotine, cannabinoids, and opiates) and associated behavioral and physiological outcomes in offspring. The highlighted studies demonstrate that parental exposure to drugs of abuse has enduring effects that persist into subsequent generations. Understanding the contribution of epigenetic inheritance in drug addiction may provide clues for better treatments and therapies for substance use disorders.

Effects of Paternal Preconception Vapor Alcohol Exposure Paradigms on Behavioral Responses in Offspring

We and others previously reported that paternal preconception chronic ethanol exposure leads to molecular, physiological, and behavioral changes in offspring including reduced ethanol consumption and preference relative to controls. The goal of the present study was to further explore the impact of paternal ethanol exposure on a wide variety of basal and drug-induced behavioral responses in first generation offspring. Adult male mice were exposed to chronic intermittent vapor ethanol or control conditions for 5-6 weeks before being mated with ethanol-naïve females to produce ethanol (E)- and control (C)-sired offspring. E-sired male offspring showed stress hyporesponsivity in a stress-induced hyperthermia assay and E-sired female offspring had reduced binge-like ethanol consumption in a drinking in the dark assay compared to C-sired offspring. E-sired offspring also showed altered sensitivity to a sedative/hypnotic dose of the GABAergic drug midazolam, but not ketamine or ethanol, in a loss of the righting response assay. E-sired offspring did not differ from controls in marble burying, novel object location, novel object recognition, social interaction, bottle-brush, novelty suppressed feeding, prepulse inhibition, every-other-day ethanol drinking, or home cage activity assays. This study adds to a growing body of literature suggesting that like in utero alcohol exposure, paternal preconception alcohol exposure can also have effects that persist and impact behavior of offspring.

Coincubation of sperm with epididymal extracellular vesicle preparations from chronic intermittent ethanol-treated mice is sufficient to impart anxiety-like and ethanol-induced behaviors to adult progeny

We previously reported that paternal preconception chronic ethanol exposure in mice imparts adult male offspring with reduced ethanol drinking preference and consumption, increased ethanol sensitivity, and attenuated stress responsivity. That same chronic ethanol exposure paradigm was later revealed to affect the sperm epigenome by altering the abundance of several small noncoding RNAs, a mechanism that mediates the intergenerational effects of numerous paternal environmental exposures. Although recent studies have revealed that the unique RNA signature of sperm is shaped during maturation in the epididymis via extracellular vesicles (EVs), formal demonstration that EVs mediate the effects of paternal preconception perturbations is lacking. Therefore, in the current study we tested the hypothesis that epididymal EV preparations are sufficient to induce intergenerational effects of paternal preconception ethanol exposure on offspring. To test this hypothesis, sperm from ethanol-naïve donors were incubated with epididymal EV preparations from chronic ethanol (Ethanol EV-donor) or control-treated (Control EV-donor) mice prior to in vitro fertilization (IVF) and embryo transfer. Progeny were examined for ethanol- and stress-related behaviors in adulthood. Ethanol EV-donors imparted reduced body weight at weaning and imparted modestly increased limited access ethanol intake to male offspring. Ethanol-EV donors also imparted increased basal anxiety-like behavior and reduced sensitivity to ethanol-induced anxiolysis to female offspring. Although Ethanol EV-donor treatment did not recapitulate the ethanol- or stress-related intergenerational effects of paternal ethanol following natural mating, these results demonstrate that coincubation of sperm with epididymal EV preparations is sufficient to impart intergenerational effects of ethanol through the male germline. This mechanism may generalize to the intergenerational effects of a wide variety of paternal preconception perturbations.

An interaction between fetal sex and placental weight and efficiency predicts intrauterine growth in response to maternal protein insufficiency and gestational exposure window in a mouse model of FASD

BACKGROUND

Individuals exposed to gestational stressors such as alcohol exhibit a spectrum of growth patterns, suggesting individualized responses to the stressors. We hypothesized that intrauterine growth responses to gestational alcohol are modified not only by the stressor's severity but by fetal sex and the placenta's adaptive capacity.

METHODS

Pregnant C57BL/6J mice were assigned to one of three groups. Group 1 consumed a normal protein diet (18% protein by weight) and received 4.5 g alcohol/kg body weight (NP-Alc-8) or isocaloric maltodextrin (NP-MD-8) daily from embryonic day (E) 8.5-E17.5. Group 2 consumed the same diet but received alcohol (NP-Alc-13) or maltodextrin (NP-MD-13) daily from E13.5-E17.5. Group 3 consumed the same diet but containing a lower protein content (12% protein by weight) from E0.5 and also received alcohol (LP-Alc-8) or maltodextrin (LP-MD-8) daily from E8.5-E17.5. Maternal, placental, and fetal outcomes were assessed on E17.5 using 2-way ANOVA or mixed linear model.

RESULTS

We found that intrauterine growth differed in the alcohol-exposed fetuses depending on sex and insult severity. Both NP-Alc-8 (vs. NP-MD-8) males and females had lower body weight and asymmetrical growth, but only NP-Alc-8 females had lower placental weight (P < 0.05). NP-Alc-13 (vs. NP-MD-13) females, but not their male littermates, had lower body weight (P = 0.019). Alcohol exposure beginning from E8.5 (vs. E13.5) decreased the ratio of fetal liver-to-body weight and increased the ratio of fetal brain-to-liver weight in both sexes (P < 0.05). LP-Alc-8 (vs. NP-MD-8) group had smaller litter size (P = 0.048), but the survivors had normal placental and body weight at E17.5. Nevertheless, LP-Alc-8 fetuses still showed asymmetrical growth. Correlation analyses reveal a relationship between litter size and placental outcomes, which were related to fetal outcomes in a sex-dependent manner, suggesting that the placenta may mediate the consequence of LP-Alc-altered litter size on fetal development.

CONCLUSIONS

Our data indicate that the placenta is strongly involved in the fetal stress response and adapts in a sex-dependent fashion to support fetal development under the alcohol stressor. These variables may further influence the spectrum of intrauterine growth outcomes observed in those diagnosed with fetal alcohol spectrum disorder.

Fetal alcohol spectrum disorders: Genetic and epigenetic mechanisms

Fetal alcohol spectrum disorders (FASD) are a consequence of prenatal alcohol exposure (PAE). The etiology of the complex FASD phenotype with growth deficit, birth defects, and neurodevelopmental impairments is under extensive research. Both genetic and environmental factors contribute to the wide phenotype: chromosomal rearrangements, risk and protective alleles, environmental-induced epigenetic alterations as well as gene-environment interactions are all involved. Understanding the molecular mechanisms of PAE can provide tools for prevention or intervention of the alcohol-induced developmental disorders in the future. By revealing the alcohol-induced genetic and epigenetic alterations which associate with the variable FASD phenotypes, it is possible to identify biomarkers for the disorder. This would enable early diagnoses and personalized support for development of the affected child.

Gestational exposure to particulate air pollution exacerbates the growth phenotypes induced by preconception paternal alcohol use: a multiplex model of exposure

It is now clear that parental histories of drug use, toxicant exposure, and social stress all have a significant influence on the health and development of the next generation. However, the ability of epigenetic parental life memories to interact with subsequent gestational exposures and cumulatively modify the developmental trajectory of the offspring remains an unexplored perspective in toxicology. Studies from our laboratory have identified male-specific postnatal growth restriction in a mouse model of chronic, preconception paternal alcohol exposure. The goal of the current study was to determine if paternal alcohol use, before conception, could modify the susceptibility of the offspring to a completely separate exposure encountered by the mother during pregnancy. In independent experiments, we previously identified altered developmental programming and increased markers of severe asthma induced by gestational exposure to particulate air pollution. In this study, male mice were exposed to either the control or alcohol preconception treatments, then mated to naive females, which we subsequently exposed to an ultrafine mixture of particulate matter via inhalation. Individually, neither preconception paternal drinking nor gestational exposures to particulate air pollution impacted the postnatal growth of female offspring. However, when both exposures were combined, females displayed a 30% reduction in weight gain. Unexpectedly, this exposure paradigm resulted in a dramatic postnatal increase in litter loss due to maternal cannibalism, which prevented additional measures of offspring health. These preliminary studies provide evidence of a complex interplay between preconception life history and intrauterine environmental factors in the control of postnatal growth.

Programmed increases in LXRα induced by paternal alcohol use enhance offspring metabolic adaptation to high-fat diet induced obesity

Objectives

Paternally inherited alterations in epigenetic programming are emerging as relevant factors in numerous disease states, including the growth and metabolic defects observed in fetal alcohol spectrum disorders. In rodents, chronic paternal alcohol use induces fetal growth restriction, as well as sex-specific alterations in insulin signaling and lipid homeostasis in the offspring. Based on previous studies, we hypothesized that the observed metabolic irregularities are the consequence of paternally inherited alterations liver x receptor (LXR) activity.

Methods

Male offspring of alcohol-exposed sires were challenged with a high-fat diet and the molecular pathways controlling glucose and lipid homeostasis assayed for LXR-induced alterations.

Results

Similar to findings in studies employing LXR agonists we found that the male offspring of alcohol-exposed sires display resistance to diet-induced obesity and improved glucose homeostasis when challenged with a high-fat diet. This improved metabolic adaptation is mediated by LXRα trans-repression of inflammatory cytokines, releasing IKKβ inhibition of the insulin signaling pathway. Interestingly, paternally programmed increases in LXRα expression are liver-specific and do not manifest in the pancreas or visceral fat.

Conclusions

These studies identify LXRα as a key mediator of the long-term metabolic alterations induced by preconception paternal alcohol use.

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Chronic paternal alcohol use induces up-regulation of LXRα in the male offspring.

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Male offspring of alcohol-exposed fathers are protected from diet-induced obesity.

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Paternally-inherited up-regulation of LXRα only manifests in the liver.

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Improved metabolic adaptation is linked to LXRα suppression of cytokine production.

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Male offspring exhibit the same phenotypes observed in studies of LXR agonists.