Frequent and mild scrotal heat stress in mice epigenetically alters glucose metabolism in the male offspring

Paternal age, de novo mutations, and offspring health? New directions for an ageing problem

This Directions article examines the mechanisms by which a father's age impacts the health and wellbeing of his children. Such impacts are significant and include adverse birth outcomes, dominant genetic conditions, neuropsychiatric disorders, and a variety of congenital developmental defects. As well as age, a wide variety of environmental and lifestyle factors are also known to impact offspring health via changes mediated by the male germ line. This picture of a dynamic germ line responsive to a wide range of intrinsic and extrinsic factors contrasts with the results of trio studies indicating that the incidence of mutations in the male germ line is low and exhibits a linear, monotonic increase with paternal age (∼two new mutations per year). While the traditional explanation for this pattern of mutation has been the metronomic plod of replication errors, an alternative model pivots around the 'faulty male' hypothesis. According to this concept, the genetic integrity of the male germ line can be dynamically impacted by age and a variety of other factors, and it is the aberrant repair of such damage that drives mutagenesis. Fortunately, DNA proofreading during spermatogenesis is extremely effective and these mutant cells are either repaired or deleted by apoptosis/ferroptosis. There appear to be only two mechanisms by which mutant germ cells can escape this apoptotic fate: (i) if the germ cells acquire a mutation that by enhancing proliferation or suppressing apoptosis, permits their clonal expansion (selfish selection hypothesis) or (ii) if a genetically damaged spermatozoon manages to fertilize an oocyte, which then fixes the damage as a mutation (or epimutation) as a result of defective DNA repair (oocyte collusion hypothesis). Exploration of these proposed mechanisms should not only help us better understand the aetiology of paternal age effects but also inform potential avenues of remediation.

Melatonin increases AKT and SOD gene and protein expressions in diabetic rats

Diabetes mellitus (DM) is a chronic metabolic disease marked by hyperglycemia due to insulin deficiency or insulin resistance leading to many chronic complications. It is thus important to manage diabetes effectively in order to prevent and or delay these complications. Melatonin is produced by the pineal gland and regulates the wake-sleep circadian rhythm. Existing evidence suggests that melatonin may be effective in the management of DM. However, the evidence on the mechanism of the beneficial effect melatonin as a treatment for DM is limited. In this study, we investigated the effect of melatonin treatment on blood glucose, insulin (INS), AKT and superoxide dismutase (SOD) gene levels in diabetic rats. Non-diabetic and diabetic rats were treated orally for 4 weeks with either 25 mg or 50 mg/kg body weight of melatonin. At the end of the study, pancreatic and liver tissues morphology, glucose homeostasis, serum insulin and SOD levels, hepatic gene and protein expression of SOD as protecting antioxidant enzyme and AKT as central element involved in PI3K/AKT insulin signaling pathway were estimated. Melatonin treated diabetic rats showed reduced hyperglycemia, and increased serum insulin and SOD levels. In addition, melatonin induced an increased gene and protein expression of SOD and AKT. In conclusion, melatonin may play a role in treating diabetic rats via stimulation of insulin secretion, insulin signaling and reduction in oxidative stress.

The effects of heat stress on intrauterine development, reproductive function, and ovarian gene expression of F1 female mice as well as gene expression of F2 embryos†

Exposure to heat stress (HS) in utero was postulated to trigger an adaptive molecular response that can be transmitted to the next generation. Hence, this study assessed the impact of HS exposure at different stages of the gestational period of mice on the female F1 population and their offspring. Heat stress exposure (41°C and 65% relative humidity-RH) occurred during the first half (FP), the second half (SP), or the entire pregnancy (TP). A control group (C) was maintained in normothermic conditions (25°C, 45% RH) throughout the experiment. Heat stress had a significant negative effect on intrauterine development, mainly when HS exposure occurred in the first half of pregnancy (FP and TP groups). Postnatal growth of FP and TP mice was hindered until 4 weeks of age. The total number of follicles per ovary did not vary (P > 0.05) between the control and HS-exposed groups. Mean numbers of primordial follicles were lower (P < 0.05) in the sexually mature FP than those in SP and TP F1 females. However, the mean number of viable embryos after superovulation was lower (P < 0.05) in TP compared with C group. The expression of genes associated with physiological and cellular response to HS, autophagy, and apoptosis was significantly affected in the ovarian tissue of F1 females and F2 in vivo-derived blastocysts in all HS-exposed groups. In conclusion, exposure to HS during pregnancy compromised somatic development and reproductive parameters as well as altered gene expression profile that was then transmitted to the next generation of mice.

Transgenerational transmission of environmental effects in livestock in the age of global warming

Recent decades provide mounting evidence for the continual increase in global temperatures, now termed "global warming," to the point of drastic worldwide change in the climate. Climatic change is a long-term shift in temperatures and weather patterns, including increased frequency and intensity of extreme environmental events such as heat waves accompanied by extreme temperatures and high humidity. Climate change and global warming put several challenges to the livestock industry by directly affecting the animal's production, reproduction, health, and welfare. The broad impact of global warming, and in particular heat stress, on-farm animals' performance has been comprehensively studied. It has been estimated that the US livestock industry's loss caused by heat stress is up to $2.4 billion annually. However, the long-term intergenerational and transgenerational effects of climatic change and global warming on farm animals are sparse. Transgenerational effects, which are mediated by epigenetic mechanisms, can affect the animal's performance regardless of its immediate environment by altering its phenotypic expression to fit its ancestors' environment. In many animal species, environmental effects are epigenetically encoded within a narrow time interval during the organism's gametogenesis, and these epigenetic modifications can then be intergenerationally transmitted. Several epigenetic mechanisms mediate intergenerational transmission of environmental effects, typically in a parent-dependent manner. Therefore, exposure of the animal to an extreme climatic event and other environmental stressors during gametogenesis can undergo epigenetic stabilization in the germline and be passed to the offspring. As a result, the offspring might express a phenotype adjusted to fit the stressors experienced by their ancestors, regardless of their direct environment. The purpose of this perspective is to review current evidence for intergenerational and transgenerational transmission of environmental stress effects, specifically in the context of global warming and climate change, and to offer viewpoints on the possible impacts on the livestock industry.

Sperm RNA Payload: Implications for Intergenerational Epigenetic Inheritance

There is mounting evidence that ancestral life experiences and environment can influence phenotypes in descendants. The parental environment regulates offspring phenotypes potentially via modulating epigenetic marks in the gametes. Here, we review examples of across-generational inheritance of paternal environmental effects and the current understanding of the role of small RNAs in such inheritance. We discuss recent advances in revealing the small RNA payload of sperm and how environmental conditions modulate sperm small RNAs. Further, we discuss the potential mechanism of inheritance of paternal environmental effects by focusing on sperm small RNA-mediated regulation of early embryonic gene expression and its role in influencing offspring phenotypes.

Evolutionary Implications of Environmental Toxicant Exposure

Homo sapiens have been exposed to various toxins and harmful compounds that change according to various phases of human evolution. Population genetics studies showed that such exposures lead to adaptive genetic changes; while observing present exposures to different toxicants, the first molecular mechanism that confers plasticity is epigenetic remodeling and, in particular, DNA methylation variation, a molecular mechanism proposed for medium-term adaptation. A large amount of scientific literature from clinical and medical studies revealed the high impact of such exposure on human biology; thus, in this review, we examine and infer the impact that different environmental toxicants may have in shaping human evolution. We first describe how environmental toxicants shape natural human variation in terms of genetic and epigenetic diversity, and then we describe how DNA methylation may influence mutation rate and, thus, genetic variability. We describe the impact of these substances on biological fitness in terms of reproduction and survival, and in conclusion, we focus on their effect on brain evolution and physiology.

sncRNAs in Epididymosomes: The Contribution to Embryonic Development and Offspring Health

Much progress has been made in determining that paternal environmental exposures can remodel their spermatozoa small noncoding RNAs (sncRANs) and, in turn, affect the phenotypes of their offspring. Studies have shown that changes in the spermatozoa sncRNAs profile occur during passing through the epididymis. Due to the absence of transcription and translation in the epididymis, spermatozoa remodel their sncRNAs profile through communication with the epididymal microenvironment. Since epididymosomes contribute to the process of spermatozoa maturation by mediating the crosstalk between the epididymis and the passing spermatozoa, they are considered to be the leading candidate to mediate these changes. Previous studies and reviews on the role of epididymal transfer proteins in sperm maturation and function are myriad. This review focuses on the role and mechanisms of epididymosome-mediated transfer of sncRNAs cargoes onembryonic development and offspring health.

Effect of acute heat shock on stress gene expression and DNA methylation in zebu (Bos indicus) and crossbred (Bos indicus × Bos taurus) dairy cattle

Environmental temperature is one of the major factors to affect health and productivity of dairy cattle. Gene expression networks within the cells and tissues coordinate stress response, metabolism, and milk production in dairy cattle. Epigenetic DNA methylations were found to mediate the effect of environment by regulating gene expression patterns. In the present study, we compared three Indian native zebu cattle, Bos indicus (Sahiwal, Tharparkar, and Hariana) and one crossbred Bos indicus × Bos taurus (Vrindavani) for stress gene expression and differences in the DNA methylation patterns. The results indicated acute heat shock to cultured PBMC affected their proliferation, stress gene expression, and DNA methylation. Interestingly, expressions of HSP70, HSP90, and STIP1 were found more pronounced in zebu cattle than the crossbred cattle. However, no significant changes were observed in global DNA methylation due to acute heat shock, even though variations were observed in the expression patterns of DNA methyltransferases (DNMT1, DNMT3a) and demethylases (TET1, TET2, and TET3) genes. The treatment 5-AzaC (5-azacitidine) that inhibit DNA methylation in proliferating PBMC caused significant increase in heat shock-induced HSP70 and STIP1 expression indicating that hypomethylation facilitated stress gene expression. Further targeted analysis DNA methylation in the promoter regions revealed no significant differences for HSP70, HSP90, and STIP1. However, there was a significant hypomethylation for BDNF in both zebu and crossbred cattle. Similarly, NR3C1 promoter region showed hypomethylation alone in crossbred cattle. Overall, the results indicated that tropically adapted zebu cattle had comparatively higher expression of stress genes than the crossbred cattle. Furthermore, DNA methylation may play a role in regulating expression of certain genes involved in stress response pathways.

Thermal regime during parental sexual maturation, but not during offspring rearing, modulates DNA methylation in brook charr (Salvelinus fontinalis)

Epigenetic inheritance can result in plastic responses to changing environments being faithfully transmitted to offspring. However, it remains unclear how epigenetic mechanisms such as DNA methylation can contribute to multigenerational acclimation and adaptation to environmental stressors. Brook charr (Salvelinus fontinalis), an economically important salmonid, is highly sensitive to thermal stress and is of conservation concern in the context of climate change. We studied the effects of temperature during parental sexual maturation and offspring rearing on whole-genome DNA methylation in brook charr juveniles (fry). Parents were split between warm and cold temperatures during sexual maturation, mated in controlled breeding designs, then offspring from each family were split between warm (8°C) and cold (5°C) rearing environments. Using whole-genome bisulfite sequencing, we found 188 differentially methylated regions (DMRs) due to parental maturation temperature after controlling for family structure. By contrast, offspring rearing temperature had a negligible effect on offspring methylation. Stable intergenerational inheritance of DNA methylation and minimal plasticity in progeny could result in the transmission of acclimatory epigenetic states to offspring, priming them for a warming environment. Our findings have implications pertaining to the role of intergenerational epigenetic inheritance in response to ongoing climate change.

Harnessing the power of multi-omics data for predicting climate change response

Predicting how species will respond to future climate change is of central importance in the midst of the global biodiversity crisis, and recent work has demonstrated the utility of population genomics for improving these predictions. Here, we suggest a broadening of the approach to include other types of genomic variants that play an important role in adaptation, like structural (e.g. copy number variants) and epigenetic variants (e.g. DNA methylation). These data could provide additional power for forecasting response, especially in weakly structured or panmictic species. Incorporating structural and epigenetic variation into estimates of climate change vulnerability, or maladaptation, may not only improve prediction power but also provide insight into the molecular mechanisms underpinning species' response to climate change.

Shade availability on pasture does not affect semen characteristics of Brahman bulls (Bos taurus indicus)

Testicular degeneration by heat is the leading cause of infertility in bulls. Beef cattle are generally farmed under hot and humid conditions, and consequently, the thermotolerance of each breed must be considered in their natural environment. This study aimed to evaluate the reproductive characteristics of Brahman bulls maintained in the grazing system, with or without shadow availability. Ten Brahman bulls aging between 24 and 30 months were allocated in two different paddocks, with or without shadow availability. The heat tolerance test was performed on three non-consecutive typical summer days. The semen samples were collected at four times points in a 14 days interval. The climate conditions were monitored throughout the experiment; and clinical evaluation, testicular consistence and scrotal circumference were measured before every semen collection. In addition, semen was evaluated regarding volume, aspect, turbulence, motility, straight movement, sperm concentration, and morphological exam. The studied Brahman bulls showed a high thermolysis capacity, high heat tolerance, and no differences in semen quality were observed between groups.