Paternal diet-induced obesity retards early mouse embryo development, mitochondrial activity and pregnancy health

The impact of mitochondrial impairments on sperm function and male fertility: a systematic review

BACKGROUND

Besides adenine triphosphate (ATP) production for sustaining motility, the mitochondria of sperm also host other critical cellular functions during germ cell development and fertilization including calcium homeostasis, generation of reactive oxygen species (ROS), apoptosis, and in some cases steroid hormone biosynthesis. Normal mitochondrial membrane potential with optimal mitochondrial performance is essential for sperm motility, capacitation, acrosome reaction, and DNA integrity.

RESULTS

Defects in the sperm mitochondrial function can severely harm the fertility potential of males. The role of sperm mitochondria in fertilization and its final fate after fertilization is still controversial. Here, we review the current knowledge on human sperm mitochondria characteristics and their physiological and pathological conditions, paying special attention to improvements in assistant reproductive technology and available treatments to ameliorate male infertility.

CONCLUSION

Although mitochondrial variants associated with male infertility have potential clinical use, research is limited. Further understanding is needed to determine how these characteristics lead to adverse pregnancy outcomes and affect male fertility potential.

Epigenetic inheritance of diet-induced and sperm-borne mitochondrial RNAs

Spermatozoa harbour a complex and environment-sensitive pool of small non-coding RNAs (sncRNAs)1, which influences offspring development and adult phenotypes1-7. Whether spermatozoa in the epididymis are directly susceptible to environmental cues is not fully understood8. Here we used two distinct paradigms of preconception acute high-fat diet to dissect epididymal versus testicular contributions to the sperm sncRNA pool and offspring health. We show that epididymal spermatozoa, but not developing germ cells, are sensitive to the environment and identify mitochondrial tRNAs (mt-tRNAs) and their fragments (mt-tsRNAs) as sperm-borne factors. In humans, mt-tsRNAs in spermatozoa correlate with body mass index, and paternal overweight at conception doubles offspring obesity risk and compromises metabolic health. Sperm sncRNA sequencing of mice mutant for genes involved in mitochondrial function, and metabolic phenotyping of their wild-type offspring, suggest that the upregulation of mt-tsRNAs is downstream of mitochondrial dysfunction. Single-embryo transcriptomics of genetically hybrid two-cell embryos demonstrated sperm-to-oocyte transfer of mt-tRNAs at fertilization and suggested their involvement in the control of early-embryo transcription. Our study supports the importance of paternal health at conception for offspring metabolism, shows that mt-tRNAs are diet-induced and sperm-borne and demonstrates, in a physiological setting, father-to-offspring transfer of sperm mitochondrial RNAs at fertilization.

The "Bad Father": Paternal Role in Biology of Pregnancy and in Birth Outcome

Pregnancy is generally studied as a biological interaction between a mother and a fetus; however, the father, with his characteristics, lifestyle, genetics, and living environment, is by no means unrelated to the outcome of pregnancy. The half of the fetal genetic heritage of paternal derivation can be decisive in cases of inherited chromosomal disorders, and can be the result of de novo genetic alterations. In addition to the strictly pathological aspects, paternal genetics may transmit thrombophilic traits that affect the implantation and vascular construction of the feto-placental unit, lead to placenta-mediated diseases such as pre-eclampsia and fetal growth retardation, and contribute to the multifactorial genesis of preterm delivery. Biological aspects of immunological tolerance to paternal antigens also appear to be crucial for these pathologies. Finally, this review describes the biological findings by which the environment, exposure to pathogens, lifestyle, and nutritional style of the father affect fetal pathophysiological and epigenetic definition.

Paternal high-fat diet altered H3K36me3 pattern of pre-implantation embryos

The global transition towards diets high in calories has contributed to 2.1 billion people becoming overweight, or obese, which damages male reproduction and harms offspring. Recently, more and more studies have shown that paternal exposure to stress closely affects the health of offspring in an intergenerational and transgenerational way. SET Domain Containing 2 (SETD2), a key epigenetic gene, is highly conserved among species, is a crucial methyltransferase for converting histone 3 lysine 36 dimethylation (H3K36me2) into histone 3 lysine 36 trimethylation (H3K36me3), and plays an important regulator in the response to stress. In this study, we compared patterns of SETD2 expression and the H3K36me3 pattern in pre-implantation embryos derived from normal or obese mice induced by high diet. The results showed that SETD2 mRNA was significantly higher in the high-fat diet (HFD) group than the control diet (CD) group at the 2-cell, 4-cell, 8-cell, and 16-cell stages, and at the morula and blastocyst stages. The relative levels of H3K36me3 in the HFD group at the 2-cell, 4-cell, 8-cell, 16-cell, morula stage, and blastocyst stage were significantly higher than in the CD group. These results indicated that dietary changes in parental generation (F0) male mice fed a HFD were traceable in SETD2/H3K36me3 in embryos, and that a paternal high-fat diet brings about adverse effects for offspring that might be related to SETD2/H3K36me3, which throws new light on the effect of paternal obesity on offspring from an epigenetic perspective.

Sperm DNA damage: The possible link between obesity and male infertility, an update of the current literature

Obesity prevalence worldwide is increasing significantly. Whilst maternal obesity has clear detrimental impacts on fertility, pregnancy and foetal outcomes, more recently there has been an increasing focus on the role of paternal obesity in human fertility. Recent meta-analyses have indicated that obesity in men negatively affects basic sperm parameters such as sperm count, concentration and motility, increases the incidence of infertility and reduces the chances of conception. Sperm DNA damage, typically characterised by DNA strand breaks and oxidation of DNA nucleotides, is a specialised marker of sperm quality that has been independently associated with recurrent miscarriage, reduced assisted reproduction success and increased mutational loads in subsequent offspring. Whilst, there are still conflicting data in humans as to the association of obesity in men with sperm DNA damage, evidence from rodent models is clear, indicating that male obesity increases sperm DNA damage. Human data are often conflicting because of the large heterogeneity amongst studies, the use of body mass index as the indicator of obesity and the methods used for detection of sperm DNA damage. Furthermore, comorbidities of obesity (i.e., heat stress, adipokines, insulin resistance, changes in lipids, hypogonadism and obstructive sleep apnoea) are also independently associated with increased sperm DNA damage that is not always modified in men with obesity, and as such may provide a causative link to the discrepancies amongst human studies. In this review, we provide an update on the literature regarding the associations between obesity in men and fertility, basic sperm parameters and sperm DNA damage. We further discuss potential reasons for the discrepancies in the literature and outline possible direct and indirect mechanisms of increased sperm DNA damage resulting from obesity. Finally, we summarise intergenerational obesity through the paternal linage and how sperm DNA damage may contribute to the transmission.

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.

Paternal obesity induces epigenetic aberrations and gene expression changes in placenta and fetus

Paternal epigenome regulates placental and fetal growth. However, the effect of paternal obesity on placenta and its subsequent effect on the fetus via sperm remains unknown. We previously discovered abnormal methylation of imprinted genes involved in placental and fetal development in the spermatozoa of obese rats. In the present study, elaborate epigenetic characterization of sperm, placenta, and fetus was performed. For 16 weeks, male rats were fed either control or a high-fat diet. Following mating studies, sperm, placenta, and fetal tissue were collected. Significant changes were observed in placental weights, morphology, and cell populations. Methylation status of imprinted genes-Igf2, Peg3, Cdkn1c, and Gnas in spermatozoa, correlated with their expression in the placenta and fetus. Placental DNA methylating enzymes and 5-methylCytosine levels increased. Furthermore, in spermatozoa, DNA methylation of a few genes involved in pathways associated with placental endocrine function-gonadotropin-releasing hormone, prolactin, estrogen, and vascular endothelial growth factor, correlated with their expression in placenta and fetus. Changes in histone-modifying enzymes were also observed in the placenta. Histone marks H3K4me3, H3K9me3, and H4ac were downregulated, while H3K27me3 and H3ac were upregulated in placentas derived from obese male rats. This study shows that obesity-related changes in sperm methylome translate into abnormal expression in the F1-placenta fathered by the obese male, presumably affecting placental and fetal development.

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

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

Paternal preconceptional diet enriched with n-3 polyunsaturated fatty acids affects offspring brain function in mice

Recent studies demonstrate that paternal nutrition prior to conception may determine offspring development and health through epigenetic modification. This study aims to investigate the effects of paternal supplementation of n-3 polyunsaturated fatty acids (n-3 PUFAs) on the brain development and function, and associated gene imprinting in the offspring. Three to four-week-old male C57BL/6J mice (founder) were fed with an n-3 PUFA-deficient diet (n-3 D), and two n-3 PUFA supplementation diets – a normal n-3 PUFA content diet (n-3 N) and a high n-3 PUFA content diet (n-3 H) for 12 weeks. Then they were mated to 10-week-old virgin female C57BL/6J mice to generate the offspring. The results showed that paternal n-3 PUFA supplementation in preconception reduced the anxiety- and depressive-like behavior, and improved sociability, learning and memory in the offspring, along with increased synaptic number, upregulated expressions of neuron specific enolase, myelin basic protein, glial fibrillary acidic protein, brain-derived neurotrophic factor in the hippocampus and cerebral cortex, and altered expressions of genes associated with mitochondria biogenesis, fusion, fission and autophagy. Furthermore, with paternal n-3 PUFA supplementation, the expression of imprinted gene Snrpn was downregulated both in testes of the founder mice and their offspring, but upregulated in the cerebral cortex and hippocampus, with altered DNA methylation in its differentially methylated region. The data suggest that higher paternal intake of n-3 PUFAs in preconception may help to maintain optimal brain development and function in the offspring, and further raise the possibility of paternal nutritional intervention for mental health issues in subsequent generations.

Parental obesity-induced changes in developmental programming

Many studies support the link between parental obesity and the predisposition to develop adult-onset metabolic syndromes that include obesity, high blood pressure, dyslipidemia, insulin resistance, and diabetes in the offspring. As the prevalence of obesity increases in persons of childbearing age, so does metabolic syndrome in their descendants. Understanding how parental obesity alters metabolic programs in the progeny, predisposing them to adult-onset metabolic syndrome, is key to breaking this cycle. This review explores the basis for altered metabolism of offspring exposed to overnutrition by focusing on critical developmental processes influenced by parental obesity. We draw from human and animal model studies, highlighting the adaptations in metabolism that occur during normal pregnancy that become maladaptive with obesity. We describe essential phases of development impacted by parental obesity that contribute to long-term alterations in metabolism in the offspring. These encompass gamete formation, placentation, adipogenesis, pancreas development, and development of brain appetite control circuits. Parental obesity alters the developmental programming of these organs in part by inducing epigenetic changes with long-term consequences on metabolism. While exposure to parental obesity during any of these phases is sufficient to alter long-term metabolism, offspring often experience multiple exposures throughout their development. These insults accumulate to increase further the susceptibility of the offspring to the obesogenic environments of modern society.

Parental Programming of Offspring Health: The Intricate Interplay between Diet, Environment, Reproduction and Development

As adults, our health can be influenced by a range of lifestyle and environmental factors, increasing the risk for developing a series of non-communicable diseases such as type 2 diabetes, heart disease and obesity. Over the past few decades, our understanding of how our adult health can be shaped by events occurring before birth has developed into a well-supported concept, the Developmental Origins of Health and Disease (DOHaD). Supported by epidemiological data and experimental studies, specific mechanisms have been defined linking environmental perturbations, disrupted fetal and neonatal development and adult ill-health. Originally, such studies focused on the significance of poor maternal health during pregnancy. However, the role of the father in directing the development and well-being of his offspring has come into recent focus. Whereas these studies identify the individual role of each parent in shaping the long-term health of their offspring, few studies have explored the combined influences of both parents on offspring well-being. Such understanding is necessary as parental influences on offspring development extend beyond the direct genetic contributions from the sperm and oocyte. This article reviews our current understanding of the parental contribution to offspring health, exploring some of the mechanisms linking parental well-being with gamete quality, embryo development and offspring health.

The effects of metformin and forskolin on sperm quality parameters and sexual hormones in type II diabetic male rats

This study aimed to investigate the effects of metformin and forskolin independently and in combinations on the sperm quality parameters and sexual hormones of diabetic male rats. Fifty adult male rats were divided randomly into five identical groups, and diabetes mellitus was induced to the rats, except for the rats in the control group, using a high-fat diet and injection of Streptozotocin. Daily administration of metformin and forskolin independently and in combinations were performed for 8 weeks in different groups. Sperm quality parameters (including sperm count, morphology, sperm motility and Johnson score), testosterone, blood sugar level, Bax to Bcl-2 ratio mRNA expression level and oxidative stress levels were measured and compared between the investigated groups. Treating diabetic rats with metformin and forskolin resulted in significant improvement in sperm quality parameters, increased testosterone levels, reduced oxidative stress in blood and testicular tissue, and decreased blood sugar, and Bax to Bcl-2 ratio level. Although the combination of metformin with forskolin had a higher effect in some parameters such as testosterone levels compared to treatment with metformin or forskolin alone, this combination had not shown a synergistic effect in all the sperm quality parameters. Metformin and forskolin are effective anti-diabetic agents, which significantly improve the sperm quality and sexual hormone levels in diabetic rats. Combining metformin and gorskolin resulted in significantly better testosterone level and antioxidant activity in blood serum without significant effect on sperm quality of diabetic rats.

Paternal obesity induces placental hypoxia and sex-specific impairments in placental vascularization and offspring metabolism

Paternal obesity predisposes offspring to metabolic dysfunction, but the underlying mechanisms remain unclear. We investigated whether this metabolic dysfunction is associated with changes in placental vascular development and is fueled by endoplasmic reticulum (ER) stress-mediated changes in fetal hepatic development. We also determined whether paternal obesity indirectly affects the in utero environment by disrupting maternal metabolic adaptations to pregnancy. Male mice fed a standard chow or high fat diet (60%kcal fat) for 8–10 weeks were time-mated with female mice to generate pregnancies and offspring. Glucose tolerance was evaluated in dams at mid-gestation (embryonic day (E) 14.5) and late gestation (E18.5). Hypoxia, angiogenesis, endocrine function, macronutrient transport, and ER stress markers were evaluated in E14.5 and E18.5 placentae and/or fetal livers. Maternal glucose tolerance was assessed at E14.5 and E18.5. Metabolic parameters were assessed in offspring at ~60 days of age. Paternal obesity did not alter maternal glucose tolerance but induced placental hypoxia and altered placental angiogenic markers, with the most pronounced effects in female placentae. Paternal obesity increased ER stress-related protein levels (ATF6 and PERK) in the fetal liver and altered hepatic expression of gluconeogenic factors at E18.5. Offspring of obese fathers were glucose intolerant and had impaired whole-body energy metabolism, with more pronounced effects in female offspring. Metabolic deficits in offspring due to paternal obesity may be mediated by sex-specific changes in placental vessel structure and integrity that contribute to placental hypoxia and may lead to poor fetal oxygenation and impairments in fetal metabolic signaling pathways in the liver.

Using publicly available transcriptomic data to identify mechanistic and diagnostic biomarkers in azoospermia and overall male infertility

Azoospermia, which is the absence of spermatozoa in an ejaculate occurring due to defects in sperm production, or the obstruction of the reproductive tract, affects about 1% of all men and is prevalent in up to 10–15% of infertile males. Conventional semen analysis remains the gold standard for diagnosing and treating male infertility; however, advances in molecular biology and bioinformatics now highlight the insufficiency thereof. Hence, the need to widen the scope of investigating the aetiology of male infertility stands pertinent. The current study aimed to identify common differentially expressed genes (DEGs) that might serve as potential biomarkers for non-obstructive azoospermia (NOA) and overall male infertility. DEGs across different datasets of transcriptomic profiling of testis from human patients with different causes of infertility/ impaired spermatogenesis and/or azoospermia were explored using the gene expression omnibus (GEO) database. Following the search using the GEOquery, 30 datasets were available, with 5 meeting the inclusion criteria. The DEGs for datasets were identified using limma R packages through the GEO2R tool. The annotated genes of the probes in each dataset were intersected with DEGs from all other datasets. Enriched Ontology Clustering for the identified genes was performed using Metascape to explore the possible connection or interaction between the genes. Twenty-five DEGs were shared between most of the datasets, which might indicate their role in the pathogenesis of male infertility. Of the 25 DEGs, eight genes (THEG, SPATA20, ROPN1L, GSTF1, TSSK1B, CABS1, ADAD1, RIMBP3) are either involved in the overall spermatogenic processes or at specific phases of spermatogenesis. We hypothesize that alteration in the expression of these genes leads to impaired spermatogenesis and, ultimately, male infertility. Thus, these genes can be used as potential biomarkers for the early detection of NOA.

Sperm Histone H3 Lysine 4 tri-methylation serves as a metabolic sensor of paternal obesity and is associated with the inheritance of metabolic dysfunction

Objective

Parental environmental exposures can strongly influence descendant risks for adult disease. How paternal obesity changes the sperm chromatin leading to the acquisition of metabolic disease in offspring remains controversial and ill-defined. The objective of this study was to assess (1) whether obesity induced by a high-fat diet alters sperm histone methylation; (2) whether paternal obesity can induce metabolic disturbances across generations; (3) whether there could be cumulative damage to the sperm epigenome leading to enhanced metabolic dysfunction in descendants; and (4) whether obesity-sensitive regions associate with embryonic epigenetic and transcriptomic profiles. Using a genetic mouse model of epigenetic inheritance, we investigated the role of histone H3 lysine 4 methylation (H3K4me3) in the paternal transmission of metabolic dysfunction. This transgenic mouse overexpresses the histone demethylase enzyme KDM1A in the developing germline and has an altered sperm epigenome at the level of histone H3K4 methylation. We hypothesized that challenging transgenic sires with a high-fat diet would further erode the sperm epigenome and lead to enhanced metabolic disturbances in the next generations.

Methods

To assess whether paternal obesity can have inter- or transgenerational impacts, and if so to identify potential mechanisms of this non-genetic inheritance, we used wild-type C57BL/6NCrl and transgenic males with a pre-existing altered sperm epigenome. To induce obesity, sires were fed either a control or high-fat diet (10% or 60% kcal fat, respectively) for 10–12 weeks, then bred to wild-type C57BL/6NCrl females fed a regular diet. F₁ and F₂ descendants were characterized for metabolic phenotypes by examining the effects of paternal obesity by sex, on body weight, fat mass distribution, the liver transcriptome, intraperitoneal glucose, and insulin tolerance tests. To determine whether obesity altered the F₀ sperm chromatin, native chromatin immunoprecipitation-sequencing targeting H3K4me3 was performed. To gain insight into mechanisms of paternal transmission, we compared our sperm H3K4me3 profiles with embryonic and placental chromatin states, histone modification, and gene expression profiles.

Results

Obesity-induced alterations in H3K4me3 occurred in genes implicated in metabolic, inflammatory, and developmental processes. These processes were associated with offspring metabolic dysfunction and corresponded to genes enriched for H3K4me3 in embryos and overlapped embryonic and placenta gene expression profiles. Transgenerational susceptibility to metabolic disease was only observed when obese F₀ had a pre-existing modified sperm epigenome. This coincided with increased H3K4me3 alterations in sperm and more severe phenotypes affecting their offspring.

Conclusions

Our data suggest sperm H3K4me3 might serve as a metabolic sensor that connects paternal diet with offspring phenotypes via the placenta. This non-DNA-based knowledge of inheritance has the potential to improve our understanding of how environment shapes heritability and may lead to novel routes for the prevention of disease. This study highlights the need to further study the connection between the sperm epigenome, placental development, and children's health.

Summary sentence

Paternal obesity impacts sperm H3K4me3 and is associated with placenta, embryonic and metabolic outcomes in descendants.

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Sperm H3K4me3 serves as a metabolic sensor of HFD-induced obesity.

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Obesity-altered sperm H3K4me3 corresponds to embryonic transcription and chromatin profiles.

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HFD- and KDM1A-induced cumulative sperm epimutations enhanced F₁ metabolic dysfunction.

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Sperm epimutations may influence placenta function inducing F₁ metabolic phenotypes.

Effects of paternal overnutrition and interventions on future generations

In the last two decades, evidence from human and animal studies suggests that paternal obesity around the time of conception can have adverse effects on offspring health through developmental programming. This may make significant contributions to the current epidemic of obesity and related metabolic and reproductive complications like diabetes, cardiovascular disease, and subfertility/infertility. To date, changes in seminal fluid composition, sperm DNA methylation, histone composition, small non-coding RNAs, and sperm DNA damage have been proposed as potential underpinning mechanism to program offspring health. In this review, we discuss current human and rodent evidence on the impact of paternal obesity/overnutrition on offspring health, followed by the proposed mechanisms, with a focus on sperm DNA damage underpinning paternal programming. We also summarize the different intervention strategies implemented to minimize effects of paternal obesity. Upon critical review of literature, we find that obesity-induced altered sperm quality in father is linked with compromised offspring health. Paternal exercise intervention before conception has been shown to improve metabolic health. Further work to explore the mechanisms underlying benefits of paternal exercise on offspring are warranted. Conversion to healthy diets and micronutrient supplementation during pre-conception have shown some positive impacts towards minimizing the impact of paternal obesity on offspring. Pharmacological approaches e.g., metformin are also being applied. Thus, interventions in the obese father may ameliorate the potential detrimental impacts of paternal obesity on offspring.

Restoring Impaired Fertility Through Diet: Observations of Switching From High-Fat Diet During Puberty to Normal Diet in Adulthood Among Obese Male Mice

BACKGROUND

Obesity is associated with a decrease in testicular function, yet the effects and mechanisms relative to different stages of sexual development remain unclear. The aim of this study is to determine whether high-fat diet-induced obesity impairs male fertility during puberty and in adulthood, and to ascertain its underlying mechanisms. This study aims to further reveal whether restoring to a normal diet can improve impaired fertility.

METHODS

Male mice were divided into 6 groups: the group N and H exposed to a normal diet or high-fat diet during puberty. The group NN or NH were further maintained a normal diet or exposed to high-fat diet in adulthood, the group HH or HN were further maintained high-fat diet or switched to normal diet in adulthood. Metabolic parameters, fertility parameters, testicular function parameters, TUNEL staining and testicular function-related proteins were evaluated, respectively.

RESULTS

The fertility of the mice in the high-fat diet group was impaired, which validated by declines in pregnancy rates and litter weight loss. Further analysis demonstrated the increased level of oxidative stress, the increased number of spermatogenic cell apoptosis and decreased number of sperm and decreased acrosome integrity. The expression of steroidogenic acute regulatory (StAR) and spermatogenesis related proteins (WT-1) decreased. Fertility among the HN group recovered, accompanied by the recovery of metabolism, fertility and testicular function parameters, StAR and WT-1 expression.

CONCLUSIONS

The findings suggest that high-fat diet-induced obesity impairs male fertility during puberty and in adulthood. The loss of acrosome integrity, the increase of oxidative stress, the increase of cells apoptosis and the down-regulation of StAR and WT-1 may be the underlying mechanisms. Switching from high-fat diets during puberty to normal diets in adulthood can improve male fertility.

Effects of Paternal Obesity on Fetal Development and Pregnancy Complications: A Prospective Clinical Cohort Study

OBJECTIVES

To evaluate the association between paternal obesity and fetal development and pregnancy complications.

STUDY DESIGN

This prospective cohort clinical trial analyzed data from 7683 women with singleton pregnancies. All study subjects were sequentially divided into four groups based on paternal BMI. We compared the differences in fetal growth and pregnancy complications between different paternal BMI groups by univariate logistic regression and independent t-test. Finally, the independent predictors of SGA and macrosomia were determined.

RESULTS

The incidences of preeclampsia, cesarean section, SGA, macrosomia, and postpartum hemorrhage in the paternal obesity group were significantly higher than the normal BMI group. With the increase of paternal BMI, fetal ultrasound measurement parameter, neonatal and placental weight showed an increasing trend (trend P < 0.05). However, these differences disappeared in the obese group. The test for interaction showed the effect of paternal obesity on SGA and macrosomia was significantly affected by maternal obesity. We also found paternal obesity was an independent predictor of both SGA and macrosomia. Based on the above results, we plotted the Nomograms for clinical prediction.

CONCLUSION

Paternal obesity can affect fetal growth parameters and placental development, which has an adverse impact on pregnancy outcomes. Optimizing the paternal BMI will help improve the health of the next generation.

Effects of paternal diet and antioxidant addition to the semen extender on bovine semen characteristics and on the phenotype of the resulting embryo

The aim of this study was to examine the effects of long-term dietary supplementation of young Nellore bulls with rumen-protected polyunsaturated fatty acids (PUFAs) and of the inclusion of catalase in the semen extender on semen quality, in vitro sperm fertilizing ability, and intracytoplasmic lipid content in the resulting embryos. Twelve Nellore bulls were supplemented with rumen-protected PUFAs or with a basal diet from 14 to 24 months of age. The semen was collected at the end of supplementation. For cryopreservation, the ejaculate was divided into two equal volumes and catalase was added to the extender in one of the fractions. Thus, the experimental design consisted of a 2 × 2 factorial scheme with two diets (control and PUFA) and two extenders (Cat+ and Cat-). Total motility and the percentage of rapid cells in fresh semen were negatively affected by dietary supplementation with PUFAs (P < 0.05), but these effects did not persist after freezing. The frozen/thawed semen of animals fed PUFAs exhibited an increase in the percentages of damaged plasma and acrosomal membranes, as well as an increase in the proportion of lipids ions at m/z 578 and m/z 757 detected by MALDI-MS. Nevertheless, there was no effect of the treatments on in vitro embryo development. However, embryos derived from bulls supplemented with PUFAs exhibited higher lipid accumulation compared to control (P < 0.05). In conclusion, PUFA supplementation promoted worsening of semen quality without affecting the in vitro sperm fertilizing ability; however, the paternal diet affected the intracytoplasmic lipid content in the resulting embryos.

Paternal high protein diet modulates body composition, insulin sensitivity, epigenetics, and gut microbiota intergenerationally in rats

Mounting evidence demonstrates that paternal diet programs offspring metabolism. However, the contribution of a pre-conception paternal high protein (HP) diet to offspring metabolism, gut microbiota, and epigenetic changes remains unclear. Here we show that paternal HP intake in Sprague Dawley rats programs protective metabolic outcomes in offspring. Compared to paternal high fat/sucrose (HF/S), HP diet improved body composition and insulin sensitivity and improved circulating satiety hormones and cecal short-chain fatty acids compared to HF/S and control diet (P < .05). Further, using 16S rRNA gene sequencing to assess gut microbial composition, we observed increased alpha diversity, distinct bacterial clustering, and increased abundance of Bifidobacterium, Akkermansia, Bacteroides, and Marvinbryantia in HP fathers and/or male and female adult offspring. At the epigenetic level, DNMT1and 3b expression was altered intergenerationally. Our study identifies paternal HP diet as a modulator of gut microbial composition, epigenetic markers, and metabolic function intergenerationally.

Consequences of Paternal Nutrition on Offspring Health and Disease

It is well established that the maternal diet during the periconceptional period affects the progeny’s health. A growing body of evidence suggests that the paternal diet also influences disease onset in offspring. For many years, sperm was considered only to contribute half of the progeny’s genome. It now appears that it also plays a crucial role in health and disease in offspring’s adult life. The nutritional status and environmental exposure of fathers during their childhood and/or the periconceptional period have significant transgenerational consequences. This review aims to describe the effects of various human and rodent paternal feeding patterns on progeny’s metabolism and health, including fasting or intermittent fasting, low-protein and folic acid deficient food, and overnutrition in high-fat and high-sugar diets. The impact on pregnancy outcome, metabolic pathways, and chronic disease onset will be described. The biological and epigenetic mechanisms underlying the transmission from fathers to their progeny will be discussed. All these data provide evidence of the impact of paternal nutrition on progeny health which could lead to preventive diet recommendations for future fathers.

The Role of the 3Rs for Understanding and Modeling the Human Placenta

Modeling the physiology of the human placenta is still a challenge, despite the great number of scientific advancements made in the field. Animal models cannot fully replicate the structure and function of the human placenta and pose ethical and financial hurdles. In addition, increasingly stricter animal welfare legislation worldwide is incentivizing the use of 3R (reduction, refinement, replacement) practices. What efforts have been made to develop alternative models for the placenta so far? How effective are they? How can we improve them to make them more predictive of human pathophysiology? To address these questions, this review aims at presenting and discussing the current models used to study phenomena at the placenta level: in vivo, ex vivo, in vitro and in silico. We describe the main achievements and opportunities for improvement of each type of model and critically assess their individual and collective impact on the pursuit of predictive studies of the placenta in line with the 3Rs and European legislation.

Probing morphological, genetic and metabolomic changes of in vitro embryo development in a microfluidic device

Assisted reproduction technologies for clinical and research purposes rely on a brief in vitro embryo culture which, despite decades of progress, remain suboptimal in comparison to the physiological environment. One promising tool to improve this technique is the development of bespoke microfluidic chambers. Here we present and validate a new microfluidic device in polydimethylsiloxane (PDMS) for the culture of early mouse embryos. Device material and design resulted embryo compatible and elicit minimal stress. Blastocyst formation, hatching, attachment and outgrowth formation on fibronectin-coated devices were similar to traditional microdrop methods. Total blastocyst cell number and allocation to the trophectoderm and inner cell mass lineages were unaffected. The devices were designed for culture of 10-12 embryos. Development rates, mitochondrial polarization and metabolic turnover of key energy substrates glucose, pyruvate and lactate were consistent with groups of 10 embryos in microdrop controls. Increasing group size to 40 embryos per device was associated with increased variation in development rates and altered metabolism. Device culture did not perturb blastocyst gene expression but did elicit changes in embryo metabolome, which can be ascribed to substrate leaching from PDMS and warrant further investigation.

Of rodents and ruminants: a comparison of small noncoding RNA requirements in mouse and bovine reproduction

Ruminants are major producers of meat and milk, thus managing their reproductive potential is a key element in cost-effective, safe, and efficient food production. Of particular concern, defects in male germ cells and female germ cells may lead to significantly reduced live births relative to fertilization. However, the underlying molecular drivers of these defects are unclear. Small noncoding RNAs, such as piRNAs and miRNAs, are known to be important regulators of germ-cell physiology in mouse (the best-studied mammalian model organism) and emerging evidence suggests that this is also the case in a range of ruminant species, in particular bovine. Similarities exist between mouse and bovids, especially in the case of meiotic and postmeiotic male germ cells. However, fundamental differences in small RNA abundance and metabolism between these species have been observed in the female germ cell, differences that likely have profound impacts on their physiology. Further, parentally derived small noncoding RNAs are known to influence early embryos and significant species-specific differences in germ-cell born small noncoding RNAs have been observed. These findings demonstrate the mouse to be an imperfect model for understanding germ-cell small noncoding RNA biology in ruminants and highlight the need to increase research efforts in this underappreciated aspect of animal reproduction.

A genome-wide transcriptomic analysis of embryos fathered by obese males in a murine model of diet-induced obesity

Paternal obesity is known to have a negative impact on the male’s reproductive health as well as the health of his offspring. Although epigenetic mechanisms have been implicated in the non-genetic transmission of acquired traits, the effect of paternal obesity on gene expression in the preimplantation embryo has not been fully studied. To this end, we investigated whether paternal obesity is associated with gene expression changes in eight-cell stage embryos fathered by males on a high-fat diet. We used single embryo RNA-seq to compare the gene expression profile of embryos generated by males on a high fat (HFD) versus control (CD) diet. This analysis revealed significant upregulation of the Samd4b and Gata6 gene in embryos in response to a paternal HFD. Furthermore, we could show a significant increase in expression of both Gata6 and Samd4b during differentiation of stromal vascular cells into mature adipocytes. These findings suggest that paternal obesity may induce changes in the male germ cells which are associated with the gene expression changes in the resulting preimplantation embryos.

Opposing Epigenetic Signatures in Human Sperm by Intake of Fast Food Versus Healthy Food

Animal experiments have demonstrated that diets high in fats create a harmful environment for developing sperm cells, contributing to impaired reproductive health and induced risk for chronic diseases in the next generation. Changes at the level of the epigenome have been suggested to underlie these observations. Human data are limited to verify this hypothesis. While we earlier demonstrated a link between male obesity and DNA methylation changes at imprinted genes in mature sperm cells and newborns, it is currently unknown if -or how- a paternal eating pattern (related to obesity) is related to indices for epigenetic inheritance. We here aim to examine a yet unexplored link between consumption of healthy (rich in vitamins and fibers) or unhealthy ("fast") foods and methylation at imprint regulatory regions in DNA of sperm. We obtained semen and data from 67 men, as part of a North Carolina-based study: The Influence of the Environment on Gametic Epigenetic Reprogramming (TIEGER) study. Dietary data included intake of fruits/nuts, vegetables/soups, whole grain bread, meat, seafood/fish, and fatty or processed food items. Multiple regression models were used to explore the association between dietary habits and clinical sperm parameters as well as DNA methylation levels, quantified using bisulfite pyrosequencing at 12 differentially methylated regions (DMRs) of the following imprinted genes: GRB10, IGF2, H19, MEG3, NDN, NNAT, PEG1/MEST, PEG3, PLAGL1, SNRPN, and SGCE/PEG10. After adjusting for age, obesity status and recruitment method, we found that Total Motile Count (TMC) was significantly higher if men consumed fruits/nuts (β=+6.9, SE=1.9, p=0.0005) and vegetables (β=+5.4, SE=1.9, p=0.006), whereas consumption of fries was associated with lower TMC (β=-20.2, SE=8.7, p=0.024). Semen volume was also higher if vegetables or fruits/nuts were frequently consumed (β=+0.06, SE=0.03, p=0.03). Similarly, our sperm epigenetic analyses showed opposing associations for healthy versus fast food items. Frequent consumption of fries was related to a higher chance of sperm being methylated at the MEG3-IG CpG4 site (OR=1.073, 95%CI: 1.035-1.112), and high consumption of vegetables was associated with a lower risk of DNA methylation at the NNAT CpG3 site (OR=0.941, 95%CI: 0.914-0.968). These results remained significant after adjusting for multiple testing. We conclude that dietary habits are linked to sperm epigenetic outcomes. If carried into the next generation paternal unhealthy dietary patterns may result in adverse metabolic conditions and increased risk for chronic diseases in offspring.

Paternal programming of offspring health

In recent years, a new focus of the Developmental Origins of Health and Disease hypothesis has emerged examining the potential role that paternal health may play in embryo development, fetal growth and long-term offspring health. While the association between male health and sperm quality has been studied in detail, our understanding of the long-term paternal effects on offspring health remains limited. As with studies aimed at understanding maternal programming, animal models are an essential tool with which to define the underlying mechanisms linking paternal health to post-fertilisation development and offspring well-being. Here, new insights into the genetic and epigenetic nature of the sperm, as well as the role seminal plasma plays in modulating the maternal reproductive environment, are demonstrating the significant role a father's wellbeing at the time of conception has for programming the health of his offspring. In this article we will outline the current understanding of the impact of male health on semen quality, reproductive fitness and post-fertilisation offspring development and explore the mechanisms underlying the paternal programming of offspring health.

Paternal low protein diet and the supplementation of methyl-donors impact fetal growth and placental development in mice

Introduction

Paternal low-protein diet can alter sperm methylation status, fetal growth and program offspring ill-health, however its impact on the placenta remains poorly defined. Here we examine the influence paternal low-protein diet has on fetal and placental development and the additional impact of supplementary methyl-donors on fetoplacental physiology.

Methods

Male C57BL/6J mice were fed a control normal protein diet (NPD; 18% protein), a low-protein diet (LPD; 9% protein) or LPD with methyl-donor supplementation (MD-LPD; choline chloride, betaine, methionine, folic acid, vitamin B12) for a minimum of 8 weeks. Males were mated with 8–11 week old female C57BL/6J mice and fetal and placental tissue collected on embryonic day 17.5.

Results

Paternal LPD was associated with increased fetal weights compared to NPD and MD-LPD with 22% fetuses being above the 90th centile for fetal weight. However, LPD and MD-LPD placental weights were reduced when compared to NPD. Placentas from LPD fathers demonstrated a reduced junctional zone area and reduced free-fatty acid content. MD-LPD placentas did not mirror these finding, demonstrating an increased chorion area, a reduction in junctional-specific glycogen staining and reduced placental Dnmt3bexpression, none of which were apparent in either NPD or LPD placentas.

Discussion

A sub-optimal paternal diet can influence fetal growth and placental development, and dietary methyl-donor supplementation alters placental morphology and gene expression differentially to that observed with LPD alone. Understanding how paternal diet and micro-nutrient supplementation influence placental development is crucial for determining connections between paternal well-being and future offspring health.

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Paternal low protein diet (LPD) increased late gestation fetal weight.

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Supplementing the LPD with methyl donors (MD-LPD) normalised fetal weight.

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Placental weight and morphology are altered by both LPD and MD-LPD.

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Placental metabolite content and gene expression were perturbed by paternal LPD and MD-LPD.

Effects of maternal and paternal exercise on offspring metabolism

Maternal and paternal obesity and type 2 diabetes are recognized risk factors for the development of metabolic dysfunction in offspring, even when the offspring follow a healthful lifestyle. Multiple studies have demonstrated that regular physical activity in mothers and fathers has striking beneficial effects on offspring health, including preventing the development of metabolic disease in rodent offspring as they age. Here, we review the benefits of maternal and paternal exercise in combating the development of metabolic dysfunction in adult offspring, focusing on offspring glucose homeostasis and adaptations to metabolic tissues. We discuss recent findings regarding the roles of the placenta and sperm in mediating the effects of parental exercise on offspring metabolic health, as well as the mechanisms hypothesized to underlie these beneficial changes. Given the worldwide epidemics of obesity and type 2 diabetes, if these findings translate to humans, regular exercise during the reproductive years might limit the vicious cycles in which increased metabolic risk propagates across generations.

Defining the male contribution to embryo quality and offspring health in assisted reproduction in farm animals

Assisted reproductive technologies such as artificial insemination have delivered significant benefits for farm animal reproduction. However, as with humans, assisted reproduction in livestock requires the manipulation of the gametes and preimplantation embryo. The significance of this ‘periconception’ period is that it represents the transition from parental genome regulation to that of the newly formed embryo. Environmental perturbations during these early developmental stages can result in persistent changes in embryonic gene expression, fetal organ development and ultimately the long-term health of the offspring. While associations between maternal health and offspring wellbeing are well-defined, the significance of paternal health for the quality of his semen and the post-conception development of his offspring have largely been overlooked. Human and animal model studies have identified sperm epigenetic status (DNA methylation levels, histone modifications and RNA profiles) and seminal plasma-mediated maternal uterine immunological, inflammatory and vascular responses as the two central mechanisms capable of linking paternal health and post-fertilisation development. However, there is a significant knowledge gap about the father’s contribution to the long-term health of his offspring, especially with regard to farm animals. Such insights are essential to ensure the safety of widely used assisted reproductive practices and to gain better understanding of the role of paternal health for the well-being of his offspring. In this article, we will outline the impact of male health on semen quality (both sperm and seminal plasma), reproductive fitness and post-fertilisation offspring development and explore the mechanisms underlying the paternal programming of offspring health in farm animals.

Obesity significantly alters the human sperm proteome, with potential implications for fertility

PURPOSE

In men, obesity may lead to poor semen parameters and reduced fertility. However, the causative links between obesity and male infertility are not totally clear, particularly on a molecular level. As such, we investigated how obesity modifies the human sperm proteome, to elucidate any important implications for fertility.

METHODS

Sperm protein lysates from 5 men per treatment, classified as a healthy weight (body mass index (BMI) ≤ 25 kg/m2) or obese (BMI ≥ 30 kg/m2), were FASP digested, submitted to liquid chromatography tandem mass spectrometry, and compared by label-free quantification. Findings were confirmed for several proteins by qualitative immunofluorescence and a quantitative protein immunoassay.

RESULTS

A total of 2034 proteins were confidently identified, with 24 proteins being significantly (p < 0.05) less abundant (fold change < 0.05) in the spermatozoa of obese men and 3 being more abundant (fold change > 1.5) compared with healthy weight controls. Proteins with altered abundance were involved in a variety of biological processes, including oxidative stress (GSS, NDUFS2, JAGN1, USP14, ADH5), inflammation (SUGT1, LTA4H), translation (EIF3F, EIF4A2, CSNK1G1), DNA damage repair (UBEA4), and sperm function (NAPA, RNPEP, BANF2).

CONCLUSION

These results suggest that oxidative stress and inflammation are closely tied to reproductive dysfunction in obese men. These processes likely impact protein translation and folding during spermatogenesis, leading to poor sperm function and subfertility. The observation of these changes in obese men with no overt andrological diagnosis further suggests that traditional clinical semen assessments fail to detect important biochemical changes in spermatozoa which may compromise fertility.

Paternal high-fat diet and exercise regulate sperm miRNA and histone methylation to modify placental inflammation, nutrient transporter mRNA expression and fetal weight in a sex-dependent manner

We previously have shown that male offspring (F1) of fathers (F0) fed a high-fat (HF) diet and that exercised had greater skeletal muscle insulin signaling and reduced type 2 diabetes mellitus (T2DM) risk compared to fathers fed HF diet and that remained sedentary. The current study extends this work by hypothesizing that F0 HF diet and exercise regulate F1 T2DM risk by alterations in placental tissue growth via changes in sperm miRNA expression. To test these hypotheses, 3-week-old male C57BL/6 mice were fed a normal-fat diet (16% fat) or an HF diet (45% fat) and assigned to either voluntary wheel running exercise or cage activity for 3 months. Results showed that F0 sperm miRNA 193b expression was decreased while miRNA 204 was increased by paternal exercise. Protein expression of dimethylated histone 3 lysine 9 was decreased with F0 HF diet. Placental and fetal tissue weights were decreased by F0 HF diet in F1 males. Placental interleukin-1β and tumor necrosis factor (TNF)-α mRNA expression was reduced by paternal exercise, while nutrient transporter mRNA expression was decreased by paternal HF diet only in the placentae of F1 females. Treatment of primary placental cell with miRNA 193b inhibited TNF-α mRNA expression, and treatment of TNF-α decreased SLC38a2 mRNA expression. Moreover, paternal exercise increased body weight at weaning in a female offspring. These results demonstrate that placental tissue weight, placental nutrient transporter gene expression and fetal weights are altered by paternal exercise, while placental inflammatory gene expression is influenced by paternal exercise in offspring in a sex-specific manner.

Metformin treatment of high-fat diet-fed obese male mice restores sperm function and fetal growth, without requiring weight loss

Male obesity is associated with subfertility and increased disease risk of offspring. It is unknown if effects can be reversed through pharmacological interventions. Five- to 6-week-old C57BL6 male mice were fed control diet (n = 10, CD) or high-fat diet (n = 20, HFD) for 16 weeks. Animals fed with a HFD were then allocated to continuation of HFD (n = 8) or HFD with metformin 28 mg kg⁻¹ day⁻¹ (n = 8) for 6 weeks. Animals fed with CD continued on a CD (n = 9). Males were mated with fertile C57BL6 females for the assessment of pregnancy and fetal growth. Sperm motility, spermatozoa and testicular morphology, sperm-zona pellucida binding, sperm reactive oxygen species (ROS) (intracellular [DCFDA], superoxide [MSR], and oxidative DNA lesions [8OHdG]), and mitochondrial membrane potential (JC1) were assessed. Metformin treatment of HFD males improved glucose tolerance (+12%, P < 0.05) and reduced Homeostatic Model Assessment of Insulin Resistance (HOMA-IR; −36%, P < 0.05). This occurred in the absence of a change in body weight or adiposity. Metformin treatment of HFD-fed males restored testicular morphology (+33%, P < 0.05), sperm motility (+66%, P < 0.05), sperm–zona pellucida binding (+25%, P < 0.05), sperm intracellular ROS concentrations (−32%, P < 0.05), and oxidative DNA lesions (−45%, P < 0.05) to the levels of the CD males. Metformin treatment of HFD fathers increased fetal weights and lengths compared with those born to HFD fathers (+8%, P < 0.05), with fetal lengths restored to those of fetuses of CD males. Short-term metformin treatment in men who are obese could be a potential intervention for the treatment of subfertility, without the need for a reduction in body weight/adiposity.

The age of the bull influences the transcriptome and epigenome of blastocysts produced by IVF

Genetic selection for the best suited offspring drives the dairy industry to use young genitors and assisted reproductive technologies (ART) to reduce generation intervals. However, sperm samples collected from peri-pubertal bulls have lower counts and quality compared to samples from adult bulls. Moreover, our previous study identified differentially methylated regions (DMRs) in sperms from early-, peri- and post-pubertal bulls. The aim of this study was to further investigate the impacts of paternal age on early embryos. To achieve this, we evaluated the transcriptome and the epigenome of bovine blastocysts generated from spermatozoa of bulls at 10, 12, and 16 months of age and used in vitro fertilization (IVF) of oocytes recovered from the same adult cows. A total of 259 probes were differentially expressed and 6953 probes were differentially methylated in the 10- vs 16-month and the 12- vs 16-month groups. Ingenuity Pathway Analysis (IPA) of transcriptomic data demonstrated that energy-related pathways such as oxidative phosphorylation, EIF2 signaling, and mitochondrial dysfunction were affected the most by the age of the bull. Meanwhile, IPA analysis of the epigenome revealed that protein kinase A signaling, RAR activation, and other pathways were influenced by paternal age. Overall, we showed that the bull's age mainly influenced metabolism-related pathways in blastocysts, and this could therefore impact subsequent development.

Dietary Micronutrient Supplementation for 12 Days in Obese Male Mice Restores Sperm Oxidative Stress

Male obesity, which often co-presents with micronutrient deficiencies, is associated with sub-fertility. Here we investigate whether short-term dietary supplementation of micronutrients (zinc, selenium, lycopene, vitamins E and C, folic acid, and green tea extract) to obese mice for 12 days (designed to span the epididymal transit) could improve sperm quality and fetal outcomes. Five-week-old C57BL6 males were fed a control diet (CD, n = 24) or high fat diet (HFD, n = 24) for 10 weeks before allocation to the 12-day intervention of maintaining their original diets (CD, n = 12, HFD n = 12) or with micronutrient supplementation (CD + S, n = 12, HFD + S, n = 12). Measures of sperm quality (motility, morphology, capacitation, binding), sperm oxidative stress (DCFDA, MSR, and 8OHdG), early embryo development (2-cell cleavage, 8OHdG), and fetal outcomes were assessed. HFD + S males had reduced sperm intracellular reactive oxygen species (ROS) concentrations and 8OHdG lesions, which resulted in reduced 8OHdG lesions in the male pronucleus, increased 2-cell cleavage rates, and partial restoration of fetal weight similar to controls. Sub-fertility associated with male obesity may be restored with very short-term micronutrient supplementation that targets the timing of the transit of sperm through the epididymis, which is the developmental window where sperm are the most susceptible to oxidative damage.

Transgenerational effect of parental obesity and chronic parental bisphenol A exposure on hormonal profile and reproductive organs of preadolescent Wistar rats of F1 generation: A one-generation study

There is a global concern about adverse health effects of endocrine-disrupting chemicals (EDCs). Bisphenol A (BPA), an estrogenic and obesogenic compound, used in the plastic and medical industry has a dominant position among EDCs as far as human health and regulatory scenario are concerned. Due to its omnipresence across the biosphere, population of all age groups and health status is unavoidably exposed to BPA. Transgenerational exposure to BPA and its effects have also been recognized. However, there is no report on the transgenerational effect of BPA on metabolically disordered parents, such as obese ones. We studied effect of BPA exposure in F0 generation and its impact on F1 generation and factored parental obesity in transgenerational effect of concurrent exposure to low dose BPA (10 ppm × 180 days) in Wistar rats in a one-generation study protocol. The exposed F0 generation animals were crossed and F1 generation was analyzed 35 days after birth for indications of reproductive toxicity. We observed changes in hormone levels and disturbance in glucose and lipid homeostasis. Animals showed increased serum cholesterol and triglycerides along with higher birth weight and rapid weight gain. Histopathological evidence confirmed the presence of regressive and inflammatory changes in the ovary and testis. The test group showed metabolic disturbances in comparison to control group. Our study showed the additive effect of parental obesity in transgenerational reproductive toxicity of BPA. Female animals of F1 generation of BPA-treated obese parents showed more insulin resistance than males with similar exposure scenario. Our study highlights the confounding role of metabolic disorders such as obesity in the transgenerational toxicity of BPA, which otherwise itself is implicated in the aetiology of such metabolic disorders, directly or indirectly.

Maternal obesity enhances oocyte chromosome abnormalities associated with aging

Obesity is increasing globally, and maternal obesity has adverse effects on pregnancy outcomes and the long-term health of offspring. Maternal obesity has been associated with pregnancy failure through impaired oogenesis and embryogenesis. However, whether maternal obesity causes chromosome abnormalities in oocytes has remained unclear. Here we show that chromosome abnormalities are increased in the oocytes of obese mice fed a high-fat diet and identify weakened sister-chromatid cohesion as the likely cause. Numbers of full-grown follicles retrieved from obese mice were the same as controls and the efficiency of in vitro oocyte maturation remained high. However, chromosome abnormalities presenting in both metaphase-I and metaphase-II were elevated, most prominently the premature separation of sister chromatids. Weakened sister-chromatid cohesion in oocytes from obese mice was manifested both as the terminalization of chiasmata in metaphase-I and as increased separation of sister centromeres in metaphase II. Obesity-associated abnormalities were elevated in older mice implying that maternal obesity exacerbates the deterioration of cohesion seen with advancing age.

Total Antioxidant Capacity; A Potential Biomarker for Non-Invasive Sex Prediction in Culture Medium of Preimplantation Human Embryos

Objective

The presence of a sex related metabolic difference in glucose utilization and, on the other hand, different developmental kinetic rates in human preimplantation embryos, has been previously observed, hawever, the correlation between these two events is unknown. Oxidative stress (OS) induced by higher glucose consumption appears to be a possible cause for the delayed development rate in female embryos. We examined the correlation between glucose consumption and total antioxidant capacity (TAC) concentration in individual embryo culture media for both male and female embryos.

Materials and Methods

In this cross-sectional study, we evaluated high quality embryos from 51 patients that underwent intracytoplasmic sperm injection (ICSI) and preimplantation genetic diagnosis (PGD) at the Royan Institute between December 2014 and September 2017. The embryos were individually cultured in G-2TMmedium droplets at days 3-5 or 48 hours post PGD. We analysed the spent culture media following embryo transfer for total antioxidant capacity (TAC) and any remaining glucose concentrations through fluorometric measurement by chemiluminecence system which indirectly was used for measurement of glucose consumed by embryos.

Results

The results showed that female embryos consumed more glucose which was associated with decreased TAC concentration in their culture medium compared to male embryos. The mean of glucose concentration consumed by the female embryos (30.7 ± 4.7 pmol/embryo/hour) was significantly higher than that of the male embryos (25.3 ± 3.3 pmol/embryo/hour) (P<0.001). There were significantly lower levels of TAC in the surrounding culture medium of female embryos (22.60 ± 0.19 nmol/µl) compared with male embryos (24.74 ± 0.27 nmol/µl, P<0.01).

Conclusion

This finding highlighted the utilization of sex dependent metabolic diversity between preimplantation embryos for non-invasive sex diagnosis and suggests the TAC concentration as a potential noninvasive biomarker for prediction of sex.

High-fat diets reduce male reproductive success in animal models: A systematic review and meta-analysis

Sperm counts have shown a progressive decline across the world since the mid-1900s. Global rates of obesity have been climbing at a similarly alarming rate, suggesting that these two factors may be linked. However, studies examining the relationship between body mass index (BMI) and male fertility have produced conflicting results. These discrepancies among studies are commonly attributed to limitations that are inherent in human studies such as correlational data and confounding factors-limitations that are absent from animal studies. Hence, we conducted a systematic review and meta-analysis of animal studies that experimentally induced obesity with a high-fat diet and measured impacts on sperm traits and/or male fertility. Overall, we found strong, consistent evidence in animal studies that high-fat diets are detrimental for male fertility. Compared with controls, males fed a high-fat diet had smaller testes and sex accessory glands relative to body size, reduced semen quality, reduced mating success, and reduced fertilization success. This is the first time that experimental data of high-fat diet effects on male reproduction have been synthesized in a meta-analysis, and thus, our results provide novel insight to the complex question of how dietary-induced obesity affects male fertility. The strong negative effects detected in animal models suggest that the inconsistent results plaguing human studies are an artefact of limitations inherent in correlational studies rather than a true effect.

Periconceptional environment and the developmental origins of disease

The concept emerging from Professor David Barker’s seminal research on the developmental origins of later-life disease has progressed in many directions since it was first published. One critical question being when during gestation might environment alter the developmental programme with such enduring consequences. Here, we review the growing consensus from clinical and animal research that the period around conception, embracing gamete maturation and early embryogenesis might be the most vulnerable period. We focus on four types of environmental exposure shown to modify periconceptional reproduction and offspring development and health: maternal overnutrition and obesity; maternal undernutrition; paternal diet and health; and assisted reproductive technology. These conditions may act through diverse epigenetic, cellular and physiological mechanisms to alter gene expression and cellular signalling and function in the conceptus affecting offspring growth and metabolism leading to increased risk for cardiometabolic and neurological disease in later life.

Adverse effects of paternal obesity on the motile spermatozoa quality

Growing evidence suggests that paternal obesity may decrease male fertility potential. During infertility treatment with intra-cytoplasmic sperm injection (ICSI), a morphologically normal motile spermatozoon is injected into a mature egg, when possible. However, sperm motility and morphology per se do not reflect the sperm molecular composition. In this study, we aimed to assess the quality of motile spermatozoa in the context of obesity by analysing their conventional and molecular characteristics as well as their ability to promote early embryonic development. A prospective study was conducted on 128 infertile men divided into three groups: 40 lean, 42 overweight, and 46 obese men. Conventional sperm parameters (concentration, motility and morphology) and sperm molecular status (chromatin composition and integrity, 5-methycytosine (5-mC) and 5-hydroxycytosine (5-hmC) contents and oxidative stress level) were analysed on raw semen and/or on motile spermatozoa selected by density gradient or swim-up techniques. Morphokinetic analysis of the embryos derived from ICSI was performed using the Embryoviewer software. Our results showed that the motile sperm-enriched fraction from obese men exhibited higher levels of retained histones (p<0.001), elevated percentage of altered chromatin integrity (p<0.001), and decreased contents of 5-hmC (p<0.001), and 5-mC (p<0.05) levels as compared to that from lean men. Importantly, there were no statistically significant correlations between these molecular parameters and the percentages of morphologically normal motile spermatozoa. Regarding embryo morphokinetics, the CC1 (p<0.05) and CC3 (p<0.05) embryonic cell cycles were significantly delayed in the cleavage embryos of the obese group as compared to the embryos of the lean group. Our data is of particular interest because, besides demonstrating the negative impacts of obesity on motile spermatozoa molecular composition, it also highlights the possible risk of disturbing early embryonic cell cycles kinetics in the context of paternal obesity.

Paternal Exercise Improves Glucose Metabolism in Adult Offspring

Poor paternal diet has emerged as a risk factor for metabolic disease in offspring, and alterations in sperm may be a major mechanism mediating these detrimental effects of diet. Although exercise in the general population is known to improve health, the effects of paternal exercise on sperm and offspring metabolic health are largely unknown. Here, we studied 7-week-old C57BL/6 male mice fed a chow or high-fat diet and housed either in static cages (sedentary) or cages with attached running wheels (exercise trained). After 3 weeks, one cohort of males was sacrificed and cauda sperm obtained, while the other cohort was bred with chow-fed sedentary C57BL/6 females. Offspring were chow fed, sedentary, and studied during the first year of life. We found that high-fat feeding of sires impairs glucose tolerance and increases the percentage of fat mass in both male and female offspring at 52 weeks of age. Strikingly, paternal exercise suppresses the effects of paternal high-fat diet on offspring, reversing the observed impairment in glucose tolerance, percentage of fat mass, and glucose uptake in skeletal muscles of the offspring. These changes in offspring phenotype are accompanied by changes in sperm physiology, as, for example, high-fat feeding results in decreased sperm motility, an effect normalized in males subject to exercise training. Deep sequencing of sperm reveals pronounced effects of exercise training on multiple classes of small RNAs, as multiple changes to the sperm RNA payload observed in animals consuming a high-fat diet are suppressed by exercise training. Thus, voluntary exercise training of male mice results in pronounced improvements in the metabolic health of adult male and female offspring. We provide the first in-depth analysis of small RNAs in sperm from exercise-trained males, revealing a marked change in the levels of multiple small RNAs with the potential to alter phenotypes in the next generation.

Epigenetic paternal effects as costly, condition-dependent traits

It is now recognized that post-copulatory traits, such as sperm and ejaculate production can impose metabolic costs, and such traits are therefore expected to exhibit condition-dependent expression, whereby, low condition individuals experience a greater marginal cost of investment compared to high condition individuals. Ejaculates are especially costly in species where males invest in offspring quality through nutrient-rich spermatophores or other seminal nuptial gifts. However, recent evidence shows that, in species where males do not provision females or offspring, males can still influence offspring development through paternal effects mediated by epigenetic factors, such as non-coding RNAs, DNA methylation and chromatin structure. Because such epigenetic paternal effects do not involve the transfer of substantial quantities of resources, such as nutrients, the costs of conferring such effects have not been considered. Here we argue that if selection favours paternal investment in offspring quality through epigenetic factors, then the epigenetic machinery required to bring about such effects may also be expected to evolve strongly condition-dependent expression. We outline indirect evidence suggesting that epigenetic paternal effects could impose substantial metabolic costs, consider the conditions under which selection may act on such effects, and suggest ways to test for differential costs and condition-dependence of these effects. Incorporating epigenetic paternal effects into condition-dependent life history theory will further our understanding of the heritability of fitness and the evolution of paternal investment strategies.

Consumption of a high-fat diet alters the seminal fluid and gut microbiomes in male mice

Our prior work showed that a novel microbiome resides in the seminal vesicles of wild-type and oestrogen receptor α (Esr1) knock-out mice and is impacted by the presence of functional Esr1 genes. The seminal fluid microbiome (SFM) may influence the health and reproductive status of the male, along with that of his partner and offspring. A high-fat diet (HFD) alters metabolites and other factors within seminal fluid and might affect the SFM. Adult (~15 weeks old) male mice were placed for 4 weeks on a control or high-fat diet and seminal fluid and fecal samples were collected, bacterial DNA isolated and subjected to 16s rRNA sequencing. Corynebacterium spp. were elevated in the seminal fluid of HFD males; however, Acinetobacter johnsonii, Streptophyta, Ammoniphilus spp., Bacillus spp. and Propionibacterium acnes were increased in control males. Rikenellaceae was more abundant in the fecal samples from HFD males. However, Bacteroides ovatus and another Bacteroides species, Bilophila, Sutterella spp., Parabacteroides, Bifidobacterium longum, Akkermansia muciniphila and Desulfovibrio spp. were greater in control males. Thus, short-term consumption of a HFD influences the seminal fluid and fecal microbiomes, which may have important health consequence for males and developmental origins of health and disease effects in resulting offspring.

Seminal fluid metabolome and epididymal changes after antibiotic treatment in mice

Paternal environment can induce detrimental developmental origins of health and disease (DOHaD) effects in resulting offspring and even future descendants. Such paternal-induced DOHaD effects might originate from alterations in a possible seminal fluid microbiome (SFM) and composite metabolome. Seminal vesicles secrete a slightly basic product enriched with fructose and other carbohydrates, providing an ideal habitat for microorganisms. Past studies confirm the existence of a SFM that is influenced by genetic and nutritional status. Herein, we sought to determine whether treatment of male mice with a combination of antibiotics designed to target SFM induces metabolic alterations in seminal vesicle gland secretions (seminal fluid) and histopathological changes in testes and epididymides. Adult (10- to 12-week-old) National Institutes of Health (NIH) Swiss males (n = 10 per group) were treated with Clindamycin 0.06 mg/kg day, Unasyn (ampicillin/sulbactam) 40 mg/kg day and Baytril (enrofloxacin) 50 mg/kg day designed to target the primary bacteria within the SFM or saline vehicle alone. Fourteen-day antibiotic treatment of males induced metabolomic changes in seminal vesicles with inosine, xanthine and l-glutamic acid decreased but d-fructose increased in glandular secretions. While spermatogenesis was not affected in treated males, increased number of epididymal tubules showed cribriform growth in this group (7 antibiotic-treated males: 3 saline control males; P = 0.01). Antibiotic-treated males showed more severe cribriform cysts. Current findings suggest antibiotic treatment of male mice results in seminal fluid metabolome and epididymal histopathological alterations. It remains to be determined whether such changes compromise male reproductive function or lead to DOHaD effects in resulting offspring.

Intergenerational Influence of Paternal Obesity on Metabolic and Reproductive Health Parameters of the Offspring: Male-Preferential Impact and Involvement of Kiss1-Mediated Pathways

Obesity and its comorbidities are reaching epidemic proportions worldwide. Maternal obesity is known to predispose the offspring to metabolic disorders, independently of genetic inheritance. This intergenerational transmission has also been suggested for paternal obesity, with a potential negative impact on the metabolic and, eventually, reproductive health of the offspring, likely via epigenetic changes in spermatozoa. However, the neuroendocrine component of such phenomenon and whether paternal obesity sensitizes the offspring to the disturbances induced by high-fat diet (HFD) remain poorly defined. We report in this work the metabolic and reproductive impact of HFD in the offspring from obese fathers, with attention to potential sex differences and alterations of hypothalamic Kiss1 system. Lean and obese male rats were mated with lean virgin female rats; male and female offspring were fed HFD from weaning onward and analyzed at adulthood. The increases in body weight and leptin levels, but not glucose intolerance, induced by HFD were significantly augmented in the male, but not female, offspring from obese fathers. Paternal obesity caused a decrease in luteinizing hormone (LH) levels and exacerbated the drop in circulating testosterone and gene expression of its key biosynthetic enzymes caused by HFD in the male offspring. LH responses to central kisspeptin-10 administration were also suppressed in HFD males from obese fathers. In contrast, paternal obesity did not significantly alter gonadotropin levels in the female offspring fed HFD, although these females displayed reduced LH responses to kisspeptin-10. Our findings suggest that HFD-induced metabolic and reproductive disturbances are exacerbated by paternal obesity preferentially in males, whereas kisspeptin effects are affected in both sexes.

Gamete cryopreservation of Australian 'old endemic' rodents – spermatozoa from the plains mouse (Pseudomys australis) and spinifex hopping mouse (Notomys alexis)

Most of the Australian ‘old endemic’ rodents have greatly reduced distributions with several species now threatened with extinction. Application of assisted reproductive technology has the potential to assist in their conservation programs in at least a few species. Here we describe an attempt to cryopreserve spermatozoa from two of these species – those of the plains mouse (Pseudomys australis) and spinifex hopping mouse (Notomys alexis), which have dramatic differences in sperm morphology. Slow and rapid freezing and three different cryoprotectant media with either raffinose, glycerol and/or skim milk were used and the results compared with those of house mouse sperm, which were used as controls. Sperm morphology, motility, membrane integrity and DNA damage were determined. Prior to cryopreservation there was a higher percentage of morphologically normal, motile, P. australis sperm than in those from N. alexis. Following cryopreservation, regardless of treatment, the percentage of motile sperm was low but it was higher when raffinose with skim milk was used as a cryoprotectant than in raffinose with glycerol albeit that minimal differences in membrane integrity or DNA damage were evident. Raffinose with skim milk should thus be used as a cryoprotectant for storing sperm of these Australian rodents in the future.