Spermatogenic dysfunction is one of the major secondary complications of diabetes; however, the underlying mechanisms remain ill-defined, and there is no available drug or strategy for the radical treatment of diabetic spermatogenic dysfunction. Therefore, the objective of this study is to investigate the protective effects of nicotinamide mononucleotide (NMN) on testicular spermatogenic function in streptozotocin (STZ)-induced diabetic mice. The results show that oral administration of NMN significantly increases the body and testis weight and the number of sperms. Moreover, the abnormal sperm count and the rate of sperm malformation are significantly decreased compared with the saline-treated diabetic mice. Histological analysis reveals that NMN treatment significantly increases the area and diameter of seminiferous tubules, accompanied by an increased number of spermatogenic cells and sperms. Immunohistochemistry and qRT-PCR results show that NMN increases Bcl-2 expression and decreases Bax expression in the testis. NMN also increases the protein expression of Vimentin and the mRNA expressions of WT1 and GATA4. In addition, qRT-PCR, western blot analysis and immunohistochemistry results also show that NMN increases the expressions of glycolysis-related rate-limiting enzymes including HK2, PKM2, and LDHA. In summary, this study demonstrates the protective effects of NMN on the testis in an STZ-induced diabetic mice model. NMN exerts its protective effects via reducing spermatogenic cell apoptosis by regulating glycolysis of Sertoli cells in diabetic mice. This study provides an experimental basis for the future clinical application of NMN in diabetes-induced spermatogenic dysfunction.

Epigenetics is the discipline that studies the mechanisms that allow for a phenotype modification without any change in DNA sequence. This phenotypic modification can be induced by the environment. It can be reversible but also transmissible from generation to generation. The mechanisms involved are multiple and are not yet all known. The methylation of certain DNA cytosines as well as the methylation and acetylation of histones play a major role. Other less well-known mechanisms, such as specific changes in chromatin structure and the intervention of various noncoding RNA, short such as miRNAs or microRNAs, and long noncoding RNAs, lncRNAs, or events involving biochemical or regulatory phenomena, also play an important role. Epigenetic modifications can be the cause of pathologies of practically all fields of Medicine, from chronic diseases to microbial infections. Progress in epigenetics allowed to explain some observations such as phenotypic mismatches in monozygotic twins, which share the same genetic heritage, or the transmission to offspring of pathologies such as obesity or cardiovascular diseases. (C) 2021 l'Academie nationale de medecine. Published by Elsevier Masson SAS. All rights reserved.

L’épigénétique est la discipline qui étudie les mécanismes permettant une modification du phénotype sans aucune modification de la séquence de l’ADN. Cette modification phénotypique est notamment induite par l’environnement. Elle peut être réversible mais aussi transmissible de génération en génération. Les mécanismes impliqués sont multiples et ne sont pas encore tous connus. La méthylation de certaines cytosines de l’ADN ainsi que les méthylations et les acétylations des histones jouent un rôle majeur. D’autres mécanismes moins bien connus, comme les modifications de la structure de la chromatine et l’intervention de divers ARN non codants courts, comme les miARN ou microARN, et long, comme les lncARN ou long ARN non codant, ou encore des événements impliquant des phénomènes biochimiques ou de régulation jouent aussi un rôle important. Les modifications épigénétiques peuvent être à l’origine de pathologies et pratiquement tous les domaines de la Médecine peuvent être concernés, des maladies chroniques aux infections microbiennes. Les progrès dans le domaine de l’épigénétique ont permis d’apporter une explication à des observations telles que certaines discordances du phénotype chez les jumeaux monozygotes, qui partagent pourtant le même patrimoine génétique, ou la transmission à la descendance d’une obésité ou de maladies cardiovasculaires.

According to the “developmental origins of health and disease” (DOHaD) concept, maternal obesity predisposes the offspring to non-communicable diseases in adulthood. While a preconceptional weight loss (WL) is recommended for obese women, its benefits on the offspring have been poorly addressed. We evaluated whether preconceptional WL was able to reverse the adverse effects of maternal obesity in a mouse model, exhibiting a modification of foetal growth and of the expression of genes encoding epigenetic modifiers in liver and placenta. We tracked metabolic and olfactory behavioural trajectories of offspring born to control, obese or WL mothers. After weaning, the offspring were either put on a control diet (CD) or a high-fat (HFD). After only few weeks of HFD, the offspring developed obesity, metabolic alterations and olfactory impairments, independently of maternal context. However, male offspring born to obese mother gained even more weight under HFD than their counterparts born to lean mothers. Preconceptional WL normalized the offspring metabolic phenotypes but had unexpected effects on olfactory performance: a reduction in olfactory sensitivity, along with a lack of fasting-induced, olfactory-based motivation. Our results confirm the benefits of maternal preconceptional WL for male offspring metabolic health but highlight some possible adverse outcomes on olfactory-based behaviours.

The phenotype of an individual is the result of complex interactions between genotype and current, past and ancestral environment leading to a lifelong remodelling of our epigenomes. The vast majority of common diseases, including atherosclerosis, diabetes, osteoporosis, asthma, neuropsychological and autoimmune diseases, which often take root in early development, display some degree of sex bias, very marked in some cases. This bias could be explained by the role of sex chromosomes, the different regulatory pathways underlying sexual development of most organs and finally, lifelong fluctuating impact of sex hormones. A substantial proportion of dimorphic genes expression might be under the control of sex-specific epigenetic marks. Environmental factors such as social behaviour, nutrition or chemical compounds can influence, in a gender-related manner, these flexible epigenetic marks during particular spatiotemporal windows of life. Thus, finely tuned developmental program aspects, for each sex, may be more sensitive to specific environmental challenges, particularly during developmental programming and gametogenesis, but also throughout the individual's life under the influence of sex steroid hormones and/or sex chromosomes. An unfavourable programming could thus lead to various defects and different susceptibility to diseases between males and females. Recent studies suggest that this epigenetic programming could be sometimes transmitted to subsequent generations in a sex specific manner and lead to transgenerational effects (TGEs). This review summarizes the current understanding in the field of epigenetic programming and highlights the importance of studying both sexes in epidemiological protocols or dietary interventions both in humans and in experimental animal models.

The concept of the developmental origins of and (DOHaD) alters our understanding of what constitutes health or disease intended as chronic, non-communicable diseases, which develop over the life course in high income and emerging countries. It implies a change in paradigm forming a basis for prevention policies across the globe. It also impacts psychological, social, economic, ethical and legal sciences. In line with the unanticipated underpinning epigenetic mechanisms are also the social issues (including public policies) that could be produced by the knowledge related to DOHaD that opens a wide field of inquiry. The information unveiled by epigenetics coupled with information on lifestyle including during the development phase, is of unforeseen nature, raising issues of different nature. Therefore it requires specific attention and research, and a specific support by a pluridisciplinary reflection since the very beginning of its production, to anticipate the questions that might be raised in the future.

The Developmental Origins of Health and Disease (DOHaD) paradigm is one of the most rapidly expanding areas of biomedical research. Environmental stressors that can impact on DOHaD encompass a variety of environmental and occupational hazards as well as deficiency and oversupply of nutrients and energy. They can disrupt early developmental processes and lead to increased susceptibility to disease/dysfunctions later in life. Presentations at the fourth Conference on Prenatal Programming and Toxicity in Boston, in October 2014, provided important insights and led to new recommendations for research and public health action. The conference highlighted vulnerable exposure windows that can occur as early as the preconception period and epigenetics as a major mechanism than can lead to disadvantageous "reprogramming" of the genome, thereby potentially resulting in transgenerational effects. Stem cells can also be targets of environmental stressors, thus paving another way for effects that may last a lifetime. Current testing paradigms do not allow proper characterization of risk factors and their interactions. Thus, relevant exposure levels and combinations for testing must be identified from human exposure situations and outcome assessments. Testing of potential underpinning mechanisms and biomarker development require laboratory animal models and in vitro approaches. Only few large-scale birth cohorts exist, and collaboration between birth cohorts on a global scale should be facilitated. DOHaD-based research has a crucial role in establishing factors leading to detrimental outcomes and developing early preventative/remediation strategies to combat these risks.

Genetic variants in the FTO (fat mass- and obesity-associated) gene have the highest association of all obesity-associated genes. Its placental expression was shown to relate to birth weight, suggesting that it may participate in the control of fetal weight gain. To gain more insight into the implication of FTO in fetal growth, we measured its placental expression in samples including extremes of abnormal fetal growth, such as after intrauterine growth restriction (IUGR) or macrosomia in both rats and humans. In rats, fetal growth was modulated by maternal nutritional modifications. In humans, placental villi were collected from pathological pregnancies (i.e. with IUGR or fetal macrosomia). Placental FTO mRNA expression was reduced by IUGR but was not significantly affected by macrosomia in either rats or humans. Our data suggest that placental FTO may participate in interactions between the in utero environment and the control of fetal growth under IUGR conditions by modulating epigenetic processes.

The aim of this study was to investigate the effect of exposure to a 900-MHz electromagnetic field (EMF) in the prenatal term on the 21-old-day rat testicle. Pregnant rats were divided into control (CG) and EMF (EMFG) groups. EMFG was exposed to 900-MHz EMF during days 13–21 of pregnancy. Newborn CG rats were obtained from the CG and newborn EMFG (NEMFG) rats from the EMFG. Testicles were extracted at postnatal day 21. Lipid peroxidation and DNA oxidation levels, apoptotic index and histopathological damage scores were compared. NEMFG rats exhibited irregularities in seminiferous tubule basal membrane and epithelium, immature germ cells in the lumen, and a decreased diameter in seminiferous tubules and thickness of epithelium. Apoptotic index, lipid peroxidation and DNA oxidation were higher in NEMFG rats than in NCG. 21-day-old rat testicles exposed to 900-MHz EMF in the prenatal term may be adversely affected, and this effect persists after birth.

Epigenetics is the study of heritable changes in gene expression or cellular phenotype caused by mechanisms other than changes in the underlying DNA sequence. Epigenetics is one of the major mechanisms explaining the "Developmental Origin of Health and Diseases" (DOHaD). Besides genetic background inherited from parents, which confers susceptibility to certain pathologies, epigenetic changes constitute the memory of previous events, either positive or negative, along the life cycle, including at the in utero stage. The later exposition to hostile environment may reveal such susceptibility, with the development of various pathologies, among them numerous chronic complex diseases. The demonstration of such a sequence of events has been shown for metabolic diseases as obesity, metabolic syndrome and type 2 diabetes, cardiovascular disease and cancer. In contrast to genetic predisposition, which is irreversible, epigenetic changes are potentially reversible, thus giving targets not only for prevention, but possibly also for the treatment of certain complex diseases.

Le 6 octobre 2011, le Fond français alimentation et santé a organisé un colloque sur les déterminants précoces de la santé future de l’enfant. Il discutait de la relation qui existe entre l’alimentation et l’épigénétique. Voici ci-après une brève présentation des idées abordées.

Metabolic programming and metabolic imprinting describe early life events, which impact upon on later physiological outcomes. Despite the increasing numbers of papers and studies, the distinction between metabolic programming and metabolic imprinting remains confusing. The former can be defined as a dynamic process whose effects are dependent upon a critical window(s) while the latter can be more strictly associated with imprinting at the genomic level. The clinical end points associated with these phenomena can sometimes be mechanistically explicable in terms of gene expression mediated by epigenetics. The predictivity of outcomes depends on determining if there is causality or association in the context of both early dietary exposure and future health parameters. The use of biomarkers is a key aspect of determining the predictability of later outcome, and the strengths of particular types of biomarkers need to be determined. It has become clear that several important health endpoints are impacted upon by metabolic programming/imprinting. These include the link between perinatal nutrition, nutritional epigenetics and programming at an early developmental stage and its link to a range of future health risks such as CVD and diabetes. In some cases, the evidence base remains patchy and associative, while in others, a more direct causality between early nutrition and later health is clear. In addition, it is also essential to acknowledge the communication to consumers, industry, health care providers, policy-making bodies as well as to the scientific community. In this way, both programming and, eventually, reprogramming can become effective tools to improve health through dietary intervention at specific developmental points.

The brain-derived neurotrophic factor (BDNF) has been shown to exert an important role during implantation, placental development, and fetal growth control in mice. Its expression is closely related to the nutritional status in several tissues such as in the nervous system. In a previous study, we demonstrated that maternal undernutrition (MU), during the perinatal life, modified both the BDNF and its functional receptor, the tyrosine kinase receptor B (TrkB) gene expression in the brain of growth-restricted rat offspring during sensitive developmental windows, suggesting that these early modifications may have long-lasting consequences. In the present study, we measured BDNF/TrkB mRNA and protein levels in rat placentas from mothers submitted to a 50% food restriction during gestation, and in human placentas from pregnancies with fetal growth restriction or fetal macrosomia. In the rat, two subtypes of placental TrkB receptors have been identified: the TrkB-FL and TrkB-T1 receptors. We found that MU induced intrauterine growth restriction (IUGR) of fetuses at term and decreased the placental BDNF mRNA and protein levels. Placentae from undernourished mothers exhibited an increased mRNA expression of TrkB-FL whereas both TrkB-FL and TrkB-T1 receptors proteins levels were not modified. In human IUGR placentas, both BDNF and TrkB receptor mRNA expressions were up-regulated. Finally, although neither BDNF nor TrkB mRNA levels were altered by fetal macrosomia alone, BDNF mRNA levels were decreased when macrosomia was associated with maternal type 1 diabetes. These results show that the placental BDNF/TrkB system is modulated in rats and humans during pregnancies with fetal growth perturbations and is affected by the maternal energetic status. These data suggest that this system may exert an important role for the feto-placental unit development and that it may also be implicated in the etiology of pathologies related to placental and fetal growth disturbances.

The phenotype of an individual is the result of complex interactions between genome, epigenome and current, past and ancestral environment leading to a lifelong remodelling of the epigenomes. The genetic information expression contained in the genome is controlled by labile chromatin-associated epigenetic marks. Epigenetic misprogramming during development is widely thought to have a persistent effect on the health of the offspring and may even be transmitted to the next generation. The epigenome serves as an interface between the environment and the genome. Dietary factors, including folate involved in C1 metabolism, and other social and lifestyle exposures have a profound effect on many aspects of health including ageing and do so, at least partly, through interactions with the genome, which result in altered gene expression with consequences for cell function and health throughout the life course. Depending on the nature and intensity of the environmental insult, the critical spatiotemporal windows and developmental or lifelong processes involved, epigenetic alterations can lead to permanent changes in tissue and organ structure and function or to phenotypic changes that can (or cannot) be reversed using appropriate epigenetic tools. Moreover, the flexibility of epigenetic marks may make it possible for environmental, nutritional and hormonal factors or endocrine disruptors to alter, during a particular spatiotemporal window in a sex-specific manner, the sex-specific methylation or demethylation of specific CpG and/or histone modifications underlying sex-specific expression of a substantial proportion of genes. Moreover, genetic factors, the environment and stochastic events change the epigenetic landscape during the lifetime of an individual. Epigenetic alterations leading to gene expression dysregulation accumulate during ageing and are important in tumorigenesis and age-related diseases. Several encouraging trials suggest that prevention and therapy of age- and lifestyle-related diseases by individualised tailoring to optimal epigenetic diets or drugs are conceivable. However, these interventions will require intense efforts to unravel the complexity of these epigenetic, genetic and environment interactions and to evaluate their potential reversibility with minimal side effects.

The phenotype of an individual is the result of complex interactions between genotype and current, past and ancestral environment leading to a lifelong remodelling of our epigenomes. The vast majority of common diseases, including atherosclerosis, diabetes, osteoporosis, asthma, neuropsychological and autoimmune diseases, which often take root in early development, display some degree of sex bias, very marked in some cases. This bias could be explained by the role of sex chromosomes, the different regulatory pathways underlying sexual development of most organs and finally, lifelong fluctuating impact of sex hormones. A substantial proportion of dimorphic genes expression might be under the control of sex-specific epigenetic marks. Environmental factors such as social behaviour, nutrition or chemical compounds can influence, in a gender-related manner, these flexible epigenetic marks during particular spatiotemporal windows of life. Thus, finely tuned developmental program aspects, for each sex, may be more sensitive to specific environmental challenges, particularly during developmental programming and gametogenesis, but also throughout the individual's life under the influence of sex steroid hormones and/or sex chromosomes. An unfavourable programming could thus lead to various defects and different susceptibility to diseases between males and females. Recent studies suggest that this epigenetic programming could be sometimes transmitted to subsequent generations in a sex-specific manner and lead to transgenerational effects (TGEs). This review summarizes the current understanding in the field of epigenetic programming and highlights the importance of studying both sexes in epidemiological protocols or dietary interventions both in humans and in experimental animal models.

Au cours du développement, à l’héritage génétique inscrit dans les gènes, vient s’ajouter une programmation par des processus épigénétiques – qui modulent de manière définitive ou transitoire l’expression spatiotemporelle des gènes sans modifier leur séquence. De manière concomittante, une multitude de facteurs environnementaux comme l’environnement intrautérin, aux effets délétères mais aussi protecteurs, interfèrent avec les processus épigénétiques, eux-mêmes en interaction permanente avec le fond génétique, le dimorphisme sexuel et les rythmes circadiens. Ainsi, au cours du développement puis au cours de la vie l’environnement, dans toute sa diversité, devient l’indispensable « révélateur » d’une « vulnérabilité » latente à la fois innée et acquise.