Altered chromatin condensation of heat-stressed spermatozoa perturbs the dynamics of DNA methylation reprogramming in the paternal genome after in vitro fertilisation in cattle

Heat shock affects the Ca2+/calmodulin-dependent protein kinase II dynamic during bovine sperm capacitation and acrosome reaction

Background

Heat shock during sperm capacitation affects the spermatozoa quality, resulting in increased early acrosome reaction and consequently decreasing their fertilizing capacity. Although the mechanisms involved in the regulation of sperm capacitation and acrosome reaction are not fully understood, it has been reported that Ca2+/calmodulin-dependent protein kinase II (CaMKII) is an important regulator of these processes. Thus, the present aimed to evaluate the effect of heat shock in the CaMKII signaling during the bovine sperm capacitation and acrosome.

Methods

Bovine spermatozoa were in vitro capacitated for 4 hours. The acrosome reaction was induced by exposure to heparin and calcium ionophore A23187 for 1 hour. Heat shock was applied by incubating spermatozoa at 41 °C with 7% CO2, while the control group was maintained at 38.5 °C with 5% CO2. At the end of each treatment, the localization of total CaMKII and phosphorylated CaMKII (pCaMKII), as well as acrosomal membrane integrity, were evaluated by immunofluorescence.

Results

It was observed that CaMKII and not phosphorylated CaMKII (pCaMKII) localization at the acrosome region was affected by sperm capacitation. In contrast, the localization of both, CaMKII and its phosphorylated form was affected by the acrosome reaction (p < 0.05). The acrosome membrane integrity, as well as the pCamKII localization in bovine spermatozoa, was affected by incubation time. This effect of incubation time was stronger in heated shock sperm, although it was observed only after 2 h of incubation. Heat shock also affected the acrosomal localization of pCaMKII in the acrosomal region of spermatozoa with intact acrosome.

Discussion

Taken together, the data present here show that CaMKII and pCaMKII localization is dynamic during bovine sperm capacitation and acrosome reaction and that this pattern of localization is affected by heat shock, suggesting that failure in CaMKII signaling is probably involved in the early acrosome reaction observed in heated-shock spermatozoa.

Heat stress: a major threat to ruminant reproduction and mitigating strategies

Stress is an external event or condition that puts pressure on a biological system. Heat stress is defined as the combination of internal and external factors acting on an animal to cause an increase in body temperature and elicit a physiological response. Heat stress is a set of conditions caused by overexposure to or overexertion at excess ambient temperature and leads to the inability of animals to dissipate enough heat to sustain homeostasis. Heat exhaustion, heat stroke, and cramps are among the symptoms. For the majority of mammalian species, including ruminants, heat stress has a negative impact on physiological, reproductive, and nutritional requirements. Reproductive functions, including the male and female reproductive systems, are negatively affected by heat stress. It decreases libido and spermatogenic activity in males and negatively affects follicle development, oogenesis, oocyte maturation, fertilization, implantation, and embryo-fetal development in females. These effects lead to a decrease in the rate of reproduction and financial losses for the livestock industry. Understanding the impact of heat stress on reproductive tissues will aid in the development of strategies for preventing heat stress and improving reproductive functions. Modification of the microenvironment, nutritional control, genetic development of heat-tolerant breeds, hormonal treatment, estrous synchronization, timed artificial insemination, and embryo transfer are among the strategies used to reduce the detrimental effects of heat stress on reproduction. These strategies may also increase the likelihood of establishing pregnancy in farm animals.

Summer heat during spermatogenesis reduces in vitro blastocyst rates and affects sperm quality of next generation bulls

BACKGROUND

Due to global warming seasonal heat stress is an increasing problem in temperate zones. Heat stress not only decreases fertility in females, but can also be detrimental to male fertility.

OBJECTIVES

We studied the effects of natural summer heat stress during spermatogenesis in Holstein bulls on semen quality parameters and on fertilization performance in vitro and possible intergenerational transmission of effects on the next male generation.

MATERIALS AND METHODS

Semen samples from young Holstein breeding bulls, referred to as F0 founders during this study, were collected during summer (F0 "summer" semen) and the following winter (F0 "winter" semen). Parameters such as ejaculate volume, sperm density, motility, thermoresistance, and in vitro blastocyst rates from these F0 semen samples were determined. In addition, after generation of offspring by artificial insemination, semen samples from F1 male offspring were collected and tested for the same quality and performance parameters to capture intergenerational effects. F1 bulls were raised together under identical conditions and semen was collected at about 1 year after birth.

RESULTS

The data showed that in vitro blastocyst rates of F0 "summer" semen samples were lower compared with "winter" semen, whereas blastocyst rates of F1 semen samples did not show significant differences. However, whereas F0 semen samples did not indicate significantly different quality parameters we found that motility of F1 semen samples showed significant differences with higher values when collected from bulls generated with F0 "winter" semen.

DISCUSSION AND CONCLUSION

From our data, we conclude that (i) natural summer heat stress during spermatogenesis can affect in vitro fertility parameters and (ii) the observed effects on sperm motility of F1 semen samples suggest intergenerational paternal transmission.

Genome-wide 5'-C-phosphate-G-3' methylation patterns reveal the effect of heat stress on the altered semen quality in Bubalus bubalis

Semen production and quality are closely correlated with different environmental factors in bovines, particularly for the buffalo (Bubalus bubalis) bulls reared under tropical and sub-tropical conditions. Factors including DNA methylation patterns, an intricate process in sperm cells, have an impact on the production of quality semen in buffalo bulls under abiotic stress conditions. The present study was conducted to identify DNA methylome signatures for semen quality in Murrah buffalo bulls, acclaimed as a major dairy breed globally, under summer heat stress. Based on semen quality parameters that significantly varied between the two groups over the seasons, the breeding bulls were classified into seasonally affected (SA = 6) and seasonally non-affected (SNA = 6) categories. DNA was isolated from purified sperm cells and sequenced using the RRBS (Reduced Representation Bisulfite Sequencing) technique for genome-wide methylome data generation. During the hot summer months, the physiological parameters such as scrotal surface temperature, rectal temperature, and respiration rate for both the SA and SNA bulls were significantly higher in the afternoon than in the morning. Whereas, the global CpG% of SA bulls was positively correlated with the afternoon's scrotal surface and rectal temperature. The RRBS results conveyed differentially methylated cytosines in the promoter region of the genes encoding the channels responsible for Ca2+ exchange, NPTN, Ca2+ activated chloride channels, ANO1, and a few structure-related units such as septins (SEPT4 and SEPT6), SPATA, etc. Additionally, the hypermethylated set of genes in SA was significantly enriched for pathways such as the FOXO signaling pathway and oocyte meiosis. The methylation patterns suggest promoter methylation in the genes regulating the sperm structure as well as surface transporters, which could contribute to the reduced semen quality in the Murrah buffalo bulls during the season-related heat stress.

Impact of bull age, sperm processing, and microclimatic conditions on the viability and DNA integrity of cryopreserved bovine sperm

Context Seasonal microclimatic fluctuations can cause changes in sperm quality even in dairy bulls bred under temperate climate. These changes can vary between sires of different age and affect sperm freezability. Aims We aimed to evaluate the modulating effect of bull age and equilibration time before freezing on the seasonal pattern of sperm viability and DNA integrity post-thaw. Methods In the frame of systematic sperm quality control, we assessed the integrity of sperm plasma membrane and acrosome (PMAI) in 15,496 cryopreserved bovine batches, and the percentage of sperm with high DNA fragmentation index (%DFI) after 0h and 3h incubation at 38°C post-thaw (3h) in 3422 batches. Semen was equilibrated for 24h before freezing if collected on Monday or Wednesday and 72h if produced on Friday. We investigated the effect of season, bull age, equilibration, and temperature-humidity index (THI) on the day of semen collection on sperm traits using mixed-effects linear models. Key results PMAI and %DFI (0h and 3h) deteriorated with increasing THI. The effect of THI on %DFI was detected with a 30-day time lag. Seasonal fluctuations of sperm quality were similar between young, mature, and older sires. Prolonged equilibration did not affect PMAI but was linked to elevated %DFI (3h) in summer. Conclusions Extending equilibration from 24 to 72h is compatible with commercial standards of bovine sperm quality post-thaw; however, it could interfere with the seasonal pattern of the latter. Implications Systematic monitoring of bovine sperm quality enables the prompt detection of stress factors related to microclimate and semen processing.

Heat Stress as a Barrier to Successful Reproduction and Potential Alleviation Strategies in Cattle

In recent decades, the adverse effects of global warming on all living beings have been unanimously recognized across the world. A high environmental temperature that increases the respiration and rectal temperature of cattle is called heat stress (HS), and it can affect both male and female reproductive functions. For successful reproduction and fertilization, mature and healthy oocytes are crucial; however, HS reduces the developmental competence of oocytes, which compromises reproduction. HS disturbs the hormonal balance that plays a crucial role in successful reproduction, particularly in reducing the luteinizing hormone and progesterone levels, which leads to severe problems such as poor follicle development with a poor-quality oocyte and problems related to maturity, silent estrus, abnormal or weak embryo development, and pregnancy loss, resulting in a declining reproduction rate and losses for the cattle industry. Lactating cattle are particularly susceptible to HS and, hence, their reproduction rate is substantially reduced. Additionally, bulls are also affected by HS; during summer, semen quality and sperm motility decline, leading to compromised reproduction. In summer, the conception rate is reduced by 20-30% worldwide. Although various techniques, such as the provision of water sprinklers, shade, and air conditioning, are used during summer, these methods are insufficient to recover the normal reproduction rate and, therefore, special attention is needed to improve reproductive efficiency and minimize the detrimental effect of HS on cattle during summer. The application of advanced reproductive technologies such as the production of embryos in vitro, cryopreservation during the hot season, embryo transfer, and timed artificial insemination may minimize the detrimental effects of HS on livestock reproduction and recover the losses in the cattle industry.

Developmental Programming of Fertility in Cattle-Is It a Cause for Concern?

Cattle fertility remains sub-optimal despite recent improvements in genetic selection. The extent to which an individual heifer fulfils her genetic potential can be influenced by fetal programming during pregnancy. This paper reviews the evidence that a dam's age, milk yield, health, nutrition and environment during pregnancy may programme permanent structural and physiological modifications in the fetus. These can alter the morphology and body composition of the calf, postnatal growth rates, organ structure, metabolic function, endocrine function and immunity. Potentially important organs which can be affected include the ovaries, liver, pancreas, lungs, spleen and thymus. Insulin/glucose homeostasis, the somatotropic axis and the hypothalamo-pituitary-adrenal axis can all be permanently reprogrammed by the pre-natal environment. These changes may act directly at the level of the ovary to influence fertility, but most actions are indirect. For example, calf health, the timing of puberty, the age and body structure at first calving, and the ability to balance milk production with metabolic health and fertility after calving can all have an impact on reproductive potential. Definitive experiments to quantify the extent to which any of these effects do alter fertility are particularly challenging in cattle, as individual animals and their management are both very variable and lifetime fertility takes many years to assess. Nevertheless, the evidence is compelling that the fertility of some animals is compromised by events happening before they are born. Calf phenotype at birth and their conception data as a nulliparous heifer should therefore both be assessed to avoid such animals being used as herd replacements.

Association of occupations with decreased semen quality in eastern China: a cross-sectional study of 12 301 semen donors

OBJECTIVES

This study aims to examine the association between occupational factors and semen quality in semen donors in eastern China.

METHODS

We recruited 12 301 semen donors from 2006 to 2020 as the studying population. A self-designed questionnaire was applied for collecting lifestyle and work style information. Semen samples were analysed according to WHO guidelines. A crude and adjusted linear regression model was used to analyse the association between occupational factors and semen quality.

RESULTS

College students accounted for 36.2% of all semen donors. The majority (81.3%) of semen donors were between 18 year and 30 years. Soldiers or the police had the highest semen volume (the median value=3.8 mL), however, they had the lowest sperm concentration (53.6×10⁶/ml) and sperm motility (45.5%). Workers in finance or insurance had an elevated risk of low semen volume, sperm concentration and total sperm count (OR=1.43, 1.57 and 1.98, respectively). Unemployed men had a high risk of low sperm concentration and low total sperm count (OR=1.84 and 1.58, respectively). Working in the information technology industry had a deleterious effect on the progressive motility of sperm (OR=1.27, 95% CI 1.03 to 1.57).

CONCLUSION

Our study indicated that sedentary work style and intensive sports in certain professions might be associated with decreased semen quality. We reported evidence of becoming unemployed on the damage to semen quality. Hence, we advocate a healthy work style to improve semen quality in eastern China.

Paternal transgenerational nutritional epigenetic effect: A new insight into nutritional manipulation to reduce the use of antibiotics in animal feeding

The use of antibiotics in animal feeding has been banned in many countries because of increasing concerns about the development of bacterial resistance to antibiotics and potential issues on food safety. Searching for antibiotic substitutes is essential. Applying transgenerational epigenetic technology to animal production could be an alternative. Some environmental changes can be transferred to memory-like responses in the offspring through epigenetic mechanisms without changing the DNA sequence. In this paper, we reviewed those nutrients and non-nutritional additives that have transgenerational epigenetic effects, including some amino acids, vitamins, and polysaccharides. The paternal transgenerational nutritional epigenetic regulation was particularly focused on mechanism of the substantial contribution of male stud animals to the animal industries. We illustrated the effects of paternal transgenerational epigenetics on the metabolism and immunity in farming animals and proposed strategies to modulate male breeding livestock or poultry.

Impact of Heat Stress on Bovine Sperm Quality and Competence

Global warming has negatively influenced animal production performance, in addition to animal well-being and welfare, consequently impairing the economic sustainability of the livestock industry. Heat stress impact on male fertility is complex and multifactorial, with the fertilizing ability of spermatozoa affected by several pathways. Among the most significative changes are the increase in and accumulation of reactive oxygen species (ROS) causing lipid peroxidation and motility impairment. The exposure of DNA during the cell division of spermatogenesis makes it vulnerable to both ROS and apoptotic enzymes, while the subsequent post-meiotic DNA condensation makes restoration impossible, harming later embryonic development. Mitochondria are also susceptible to the loss of membrane potential and electron leakage during oxidative phosphorylation, lowering their energy production capacity under heat stress. Although cells are equipped with defense mechanisms against heat stress, heat insults that are too intense lead to cell death. Heat shock proteins (HSP) belong to a thermostable and stress-induced protein family, which eliminate protein clusters and are essential to proteostasis under heat stress. This review focuses on effects of heat stress on sperm quality and on the mechanisms leading to defective sperm under heat stress.

Identification of key Genes and Pathways Associated With Thermal Stress in Peripheral Blood Mononuclear Cells of Holstein Dairy Cattle

The objectives of the present study were to identify key genes and biological pathways associated with thermal stress in Chinese Holstein dairy cattle. Hence, we constructed a cell-model, applied various molecular biology experimental techniques and bioinformatics analysis. A total of 55 candidate genes were screened from published literature and the IPA database to examine its regulation under cold (25°C) or heat (42°C) stress in PBMCs. We identified 29 (3 up-regulated and 26 down-regulated) and 41 (15 up-regulated and 26 down-regulated) significantly differentially expressed genes (DEGs) (fold change ≥ 1.2-fold and P < 0.05) after cold and heat stress treatments, respectively. Furthermore, bioinformatics analyses confirmed that major biological processes and pathways associated with thermal stress include protein folding and refolding, protein phosphorylation, transcription factor binding, immune effector process, negative regulation of cell proliferation, autophagy, apoptosis, protein processing in endoplasmic reticulum, estrogen signaling pathway, pathways related to cancer, PI3K- Akt signaling pathway, and MAPK signaling pathway. Based on validation at the cellular and individual levels, the mRNA expression of the HIF1A gene showed upregulation during cold stress and the EIF2A, HSPA1A, HSP90AA1, and HSF1 genes showed downregulation after heat exposure. The RT-qPCR and western blot results revealed that the HIF1A after cold stress and the EIF2A, HSPA1A, HSP90AA1, and HSF1 after heat stress had consistent trend changes at the cellular transcription and translation levels, suggesting as key genes associated with thermal stress response in Holstein dairy cattle. The cellular model established in this study with PBMCs provides a suitable platform to improve our understanding of thermal stress in dairy cattle. Moreover, this study provides an opportunity to develop simultaneously both high-yielding and thermotolerant Chinese Holstein cattle through marker-assisted selection.

Parental Effects on Epigenetic Programming in Gametes and Embryos of Dairy Cows

The bovine represents an important agriculture species and dairy breeds have experienced intense genetic selection over the last decades. The selection of breeders focused initially on milk production, but now includes feed efficiency, health, and fertility, although these traits show lower heritability. The non-genetic paternal and maternal effects on the next generation represent a new research topic that is part of epigenetics. The evidence for embryo programming from both parents is increasing. Both oocytes and spermatozoa carry methylation marks, histones modifications, small RNAs, and chromatin state variations. These epigenetic modifications may remain active in the early zygote and influence the embryonic period and beyond. In this paper, we review parental non-genetic effects retained in gametes on early embryo development of dairy cows, with emphasis on parental age (around puberty), the metabolism of the mother at the time of conception and in vitro culture (IVC) conditions. In our recent findings, transcriptomic signatures and DNA methylation patterns of blastocysts and gametes originating from various parental and IVC conditions revealed surprisingly similar results. Embryos from all these experiments displayed a metabolic signature that could be described as an "economy" mode where protein synthesis is reduced, mitochondria are considered less functional. In the absence of any significant phenotype, these results indicated a possible similar adaptation of the embryo to younger parental age, post-partum metabolic status and IVC conditions mediated by epigenetic factors.

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.

Does finasteride treatment for benign prostatic hyperplasia influence sperm DNA integrity in dogs?

BACKGROUND

Benign prostatic hyperplasia (BPH) is one of the most common reproductive disorders in both male dogs and men. Finasteride, a synthetic inhibitor of the enzyme 5α-reductase, is widely used as medical treatment. Although sperm can be affected by both BPH and finasteride treatment, the direct influence on DNA integrity remains unclear. Thus, the aim of this study was to verify the direct effect of BPH and/or finasteride treatment on DNA integrity of dog spermatozoa. A 2 × 2 factorial experiment was designed with 20 male dogs assigned to 4 experimental groups: BPH Group (n = 5), BPH-Finasteride Group (n = 5), Non-BPH Finasteride-Treated Group (n = 5) and Non-BPH Untreated Group (n = 5). Sperm evaluation was performed monthly for 60 days after the start of finasteride therapy or BPH diagnosis (D0, D30 and D60). Sperm DNA integrity was analyzed through fragmentation susceptibility (toluidine blue staining and Sperm Chromatic Structure Assay - SCSA), direct evaluation of DNA fragmentation (Sperm Chromatin Dispersion Assay - SCDA) and sperm protamination (chromomycin A3).

RESULTS

Sperm DNA integrity was not affected by finasteride treatment. However, BPH dogs had higher susceptibility to sperm DNA acid denaturation (SCSA) compared to dogs not presenting BPH, as well as lower percentage of sperm with DNA integrity (toluidine blue staining).

CONCLUSION

In conclusion, benign prostatic hyperplasia causes post-testicular sperm DNA damage, albeit finasteride treatment itself does not directly influence sperm DNA integrity.

Exposing dairy bulls to high temperature-humidity index during spermatogenesis compromises subsequent embryo development in vitro

The possible impact of natural heat stress on animal fertility is currently a major concern for breeding companies. Here, we aimed to address this concern by determining the effects of natural heat stress on the fertility of Holstein bulls located in the Netherlands. Semen samples were collected from six bulls at two locations in March 2016 (low temperature-humidity index (THI) group; maximum THI of 51.8 and 55 at their respective locations) or August (high THI group; maximum THI of 77.9 and 80.5 during meiotic and spermiogenic stages of spermatogenesis, 42 to 14 days prior to semen collection). The effect of heat stress on semen quality was assessed by sperm morphology, motility, reactive oxygen species production, lipid peroxidation, viability, and DNA fragmentation. Moreover, we evaluated the development of embryos generated in vitro by low and high THI semen, and determined inner cell mass/trophectoderm ratio, apoptotic cell ratio, and embryonic gene expression in day-8 blastocysts. An increase in cell death (propidium iodide-positive cells; P = 0.039) was observed in the high THI group (31.5%) compared to the low THI group (27.6%). Moreover, a decrease (P < 0.001) was observed in the total blastocyst rates at day 7 post-insemination (15.3 vs 20.9%) and day 8 (23.2 vs 29.6%) in the high THI compared to the low THI group, respectively. There were no differences in the relative abundance of candidate transcripts examined. In conclusion, sperm samples from dairy bulls obtained during a period with higher THI had reduced viability and led to a decrease in blastocyst development and delayed hatching, compared to semen collected during a period with low THI.

Epigenetic Transgenerational Inheritance

Epigenetic information refers to heritable changes in gene expression that occur without modifications at the DNA sequence level. These changes are orchestrated by different epigenetic mechanisms such as DNA methylation, posttranslational modifications of histones, and the presence of noncoding RNAs. Epigenetic information regulates chromatin structure to confer cell-specific gene expression.The sperm epigenome is the result of three periods of global resetting during men's life. Germ cell epigenome reprogramming is designed to allow cell totipotency and to prevent the transmission of epimutations via spermatozoa. At the end of these reprogramming events, the sperm epigenome has a very specific epigenetic pattern that is a footprint of past reprogramming events and has an influence on embryo development.Several data demonstrate that not all regions of the epigenome are erased during the reprogramming periods, suggesting the transmission of epigenetic information from fathers to offspring via spermatozoa. Moreover, it is becoming increasingly clear that the sperm epigenome is sensitive to environmental factors during the process of gamete differentiation, suggesting the plasticity of the sperm epigenetic signature according to the circumstances of the individual's life.In this chapter, we provided strong evidences about the association between variations of the sperm epigenome and the exposure to environmental factors. Moreover, we will present data about how epigenetic mechanisms are candidates for transferring paternal environmental information to offspring.

Reduced oxygen concentration during in vitro oocyte maturation alters global DNA methylation in the maternal pronucleus of subsequent zygotes in cattle

Preimplantation epigenetic reprogramming is sensitive to the environment of the gametes and the embryo. In vitro maturation (IVM) of bovine oocytes is a critical step of embryo in vitro production procedures and several factors influence its efficiency, including atmospheric oxygen tension. The possibility that the IVM environment can alter this process is tested by determining whether the global DNA methylation pattern (measured via immunofluorescent labeling of 5-methylcytosine [5meC]) in the parental pronuclei of bovine zygotes produced from cumulus-oocyte complexes matured under low (5%) and atmospheric (~20%) oxygen tension. Normalized 5meC signals differed significantly between maternal and paternal pronuclei of oocytes matured in vitro at 5% oxygen (p ≤ 0.05). There was a significant difference of 5meC between maternal pronuclei of oocytes matured at 5% oxygen and 20% oxygen ( p ≤ 0.05). The relative methylation level (normalized fluorescence intensity of paternal pronucleus divided by the normalized fluorescence intensity of maternal pronucleus) subsequent to maturation in vitro at 5% and 20% oxygen was also significantly altered ( p ≤ 0.05). Our results show that the pattern of global DNA methylation in the maternal pronucleus of bovine zygotes is affected by maturing the oocytes under low oxygen tension which may have an impact on early embryonic development. These data may contribute to the understanding of possible effects of IVM conditions on pronucleus reprogramming.

Review: Epigenetics, developmental programming and nutrition in herbivores

Epidemiological studies in humans and animal models (including ruminants and horses) have highlighted the critical role of nutrition on developmental programming. Indeed, it has been demonstrated that the nutritional environment during the periconceptional period and foetal development can altered the postnatal performance of the resultant offspring. This nutritional programming can be exerted by maternal and paternal lineages and can affect offspring beyond the F1 generation. Alterations in epigenetic mechanisms have been proposed as the causative link behind the programming trajectories observed in the offspring. Although a clear cause-effect relationship between epigenetic modifications during early development and later offspring phenotype has not been demonstrated in livestock species, strong associations have been reported for some epigenetic marks (e.g. messenger RNA) that are worth exploring as possible predictors of future offspring phenotype. In this review, we shortly describe the main epigenetic mechanisms studied so far in mammals (i.e. mainly in the mouse) thought to be associated with developmental programming, and discuss the few studies available in mammalian herbivores (e.g. cattle) showing the effect of nutrition on epigenetic marks and the associated phenotype. Clearly, there is a need to develop research on nutritional strategies capable of modulating the epigenetic machinery with positive influence on the phenotype of livestock herbivores. This type of research is needed to alleviate the challenges currently faced by the livestock industry (e.g. impaired fertility of high-yielding dairy cows). This in turn will have a positive influence on animal welfare and productivity of livestock enterprises.

Transcriptome analysis and identification of significantly differentially expressed genes in Holstein calves subjected to severe thermal stress

RNA-Seq analysis was used to characterize transcriptome response of Holstein calves to thermal stress. A total of eight animals aged between 2 and 3 months were randomly selected and subjected to thermal stress corresponding to a temperature humidity index of 95 in an environmentally controlled house for 12 h consecutively for 3 days. A set of 15,787 unigenes were found to be expressed and after a threshold of threefold change, and a Q value <0.05; 502, 394, and 376 genes were found to be differentially expressed on days 1, 2, and 3 out of which 343, 261 and 256 genes were upregulated and 159, 133, and 120 genes were downregulated. Only 356 genes out of these were expressed on all 3 days, and only they were considered as significantly differentially expressed. KEGG pathway analysis revealed that ten pathways were significantly enriched; the top two among them were protein processing in endoplasmic reticulum and MAPK signaling pathways. These results suggest that thermal stress triggered a complex response in Holstein calves and the animals adjusted their physiological and metabolic processes to survive. Many of the genes identified in this study have not been previously reported to be involved in thermal stress response. The results of this study extend our understanding of the animal's response to thermal stress and some of the identified genes may prove useful in the efforts to breed Holstein cattle with superior thermotolerance, which might help in minimizing production loss due to thermal stress.

Characterization of genes and pathways that respond to heat stress in Holstein calves through transcriptome analysis

This study aimed to investigate the genes and pathways that respond to heat stress in Holstein bull calves exposed to severe ranges of temperature and humidity. A total of ten animals from 4 to 6 months of age were subjected to heat stress at 37 °C and 90 % humidity for 12 h. Skin and rectal temperatures were measured before and after heat stress; while no correlation was found between them before heat stress, a moderate correlation was detected after heat stress, confirming rectal temperature to be a better barometer for monitoring heat stress. RNAseq analysis identified 8567 genes to be differentially regulated, out of which 465 genes were significantly upregulated (≥2-fold, P < 0.05) and 49 genes were significantly downregulated (≤2-fold, P < 0.05) in response to heat stress. Significant terms and pathways enriched in response to heat stress included chaperones, cochaperones, cellular response to heat stress, phosphorylation, kinase activation, immune response, apoptosis, Toll-like receptor signaling pathway, Pi3K/AKT activation, protein processing in endoplasmic reticulum, interferon signaling, pathways in cancer, estrogen signaling pathway, and MAPK signaling pathway. The differentially expressed genes were validated by quantitative real-time PCR analysis, which confirmed the tendency of the expression. The genes and pathways identified in this analysis extend our understanding of transcriptional response to heat stress and their likely functioning in adapting the animal to hyperthermic stress. The identified genes could be used as candidate genes for association studies to select and breed animals with improved heat tolerance.

Decreased activity of superoxide dismutase in the seminal plasma of infertile men correlates with increased sperm deoxyribonucleic acid fragmentation during the first hours after sperm donation

Sperm DNA fragmentation varies between individuals and is more pronounced with increased patient age and time after sperm donation. The intensification of DNA fragmentation depends on the balance of the oxidoreductive system, which is regulated mainly by two enzymes - superoxide dismutase (SOD) and catalase. The objective of this study was to determine the relationship between sperm DNA fragmentation dynamics, fertility and seminal SOD and catalase activity. The study was conducted in 2013 and 2014 at the Non-Public Health Care Unit 'Ovum Reproduction and Andrology' in Lublin, Lublin, Poland, and covered 218 men aged 25-35 (85 fertile and 133 patients treated for infertility). Percentage of fragmented DNA was measured in a modified chromatin dispersion test at four time points after sperm donation (t = 0, 3, 6, 12 h). SOD and catalase activities were determined spectrophotometrically. We confirmed that the activity of SOD in the seminal plasma of men with reproductive disorders was lower compared with fertile men. Conversely, no significant correlations were found between fertility and catalase activity. Sperm DNA of infertile males was initially more fragmented than fertile male sperm DNA. SOD and catalase activity did not correlate with the degree of DNA fragmentation in fertile men. In men with reproductive disorders, the rate of DNA fragmentation was slow within first 3 h after sperm donation and then increased between 6 and 12 h. In this group of infertile men, those with higher SOD activity had a lower DNA fragmentation index (DFI) after 12 h, and a reduced rate of intensity of fragmentation from 6 to 12 h. Alternatively, higher catalase activity among men treated for infertility was accompanied by higher initial DFI and higher rate of DNA fragmentation from 6 to 12 h. These results highlight the importance of determining a proper time window between sperm donation and procedures of assisted reproductive technology.

Obesity-related DNA methylation at imprinted genes in human sperm: Results from the TIEGER study

BACKGROUND

Epigenetic reprogramming in mammalian gametes resets methylation marks that regulate monoallelic expression of imprinted genes. In males, this involves erasure of the maternal methylation marks and establishment of paternal-specific methylation to appropriately guide normal development. The degree to which exogenous factors influence the fidelity of methylation reprogramming is unknown. We previously found an association between paternal obesity and altered DNA methylation in umbilical cord blood, suggesting that the father's endocrine, nutritional, or lifestyle status could potentiate intergenerational heritable epigenetic abnormalities. In these analyses, we examine the relationship between male overweight/obesity and DNA methylation status of imprinted gene regulatory regions in the gametes.

METHODS

Linear regression models were used to compare sperm DNA methylation percentages, quantified by bisulfite pyrosequencing, at 12 differentially methylated regions (DMRs) from 23 overweight/obese and 44 normal weight men. Our study population included 69 volunteers from The Influence of the Environment on Gametic Epigenetic Reprogramming (TIEGER) study, based in NC, USA.

RESULTS

After adjusting for age and fertility patient status, semen from overweight or obese men had significantly lower methylation percentages at the MEG3 (β = -1.99; SE = 0.84; p = 0.02), NDN (β = -1.10; SE = 0.47; p = 0.02), SNRPN (β = -0.65; SE = 0.27; p = 0.02), and SGCE/PEG10 (β = -2.5; SE = 1.01; p = 0.01) DMRs. Our data further suggest a slight increase in DNA methylation at the MEG3-IG DMR (β = +1.22; SE = 0.59; p = 0.04) and H19 DMR (β = +1.37; SE = 0.62; p = 0.03) in sperm of overweight/obese men.

CONCLUSIONS

Our data support that male overweight/obesity status is traceable in the sperm epigenome. Further research is needed to understand the effect of such changes and the point of origin of DNA methylation differences between lean and overweight/obese men. Together with our earlier reports on paternal obesity and epigenetic shifts in the offspring, our studies set the groundwork for future studies investigating male gametic methylation aberrations due to paternal lifestyle factors such as obesity.

Selected sperm traits are simultaneously altered after scrotal heat stress and play specific roles in in vitro fertilization and embryonic development

Improvements in the estimation of male fertility indicators require advances in laboratory tests for sperm assessment. The aims of the present work were (1) to apply a multivariate analysis to examine sperm set of alterations and interactions and (2) to evaluate the importance of sperm parameters on the outcome of standard IVF and embryonic development. Bulls (n = 3) were subjected to scrotal insulation, and ejaculates were collected before (preinsulation = Day 0) and through 56 days (Days 7, 14, 21, 28, 35, 42, 49, and 56) of the experimental period. Sperm head morphometry and chromatin variables were assessed by a computational image analysis, and IVF was performed. Scrotal heat stress induced alterations in all evaluated sperm head features, as well as cleavage and blastocyst rates. A principal component analysis revealed three main components (factors) that represented almost 89% of the cumulative variance. In addition, an association of factor scores with cleavage (factor 1) and blastocyst (factor 3) rates was observed. In conclusion, several sperm traits were simultaneously altered as a result of a thermal insult. These sperm traits likely play specific roles in IVF and embryonic development.

Impact of heat stress on health and performance of dairy animals: A review

Sustainability in livestock production system is largely affected by climate change. An imbalance between metabolic heat production inside the animal body and its dissipation to the surroundings results to heat stress (HS) under high air temperature and humid climates. The foremost reaction of animals under thermal weather is increases in respiration rate, rectal temperature and heart rate. It directly affect feed intake thereby, reduces growth rate, milk yield, reproductive performance, and even death in extreme cases. Dairy breeds are typically more sensitive to HS than meat breeds, and higher producing animals are, furthermore, susceptible since they generates more metabolic heat. HS suppresses the immune and endocrine system thereby enhances susceptibility of an animal to various diseases. Hence, sustainable dairy farming remains a vast challenge in these changing climatic conditions globally.

Relationship between pregnancy, embryo development, and sperm deoxyribonucleic acid fragmentation dynamics

The way the dynamics of DNA fragmentation affects the growth of embryos in real time, and effectiveness of infertility treatment using the ICSI procedure were determined in 148 couples treated with the ICSI technique. The percentage of sperm with fragmented DNA (known as the DNA fragmentation index [DFI]) in semen samples was determined at 3, 6 and 12 h. Embryo culture was assessed continuously during 12 h of observation monitoring.

Statistically significant difference was found in DFI at 12 h and outcome of treatment. For the remaining time intervals, no statistically significant differences were noted. An analysis of relationship between the DFI dynamics over time at individual measurements and achievement of pregnancy, confirmed a statistically significant relationship between the rate measured at 6–12 h of observations of DFI changes (DFI 12 h%/h), and achieving pregnancy. Correlation was observed between DFI (during 0, 3, 6 and 12 h), the growth rate in DFI, and time of embryo development. A statistically significant relationship was found between the rate from the start to the end of observations of the DFI, and outcome of treatment.

Intensity level regarding fragmentation of sperm DNA and its growth rate affected the time of embryo development in the ICSI procedure. The most significant prognostic factor for achieving pregnancy was intensification of sperm DNA fragmentation after 12 h.