E.F.G. Naninck

Early-life stress mediated modulation of adult neurogenesis and behavior

Early life is a period of unique sensitivity during which experience can confer enduring effects on brain structure and function. During early perinatal life the quality of the surrounding environment and experiences, in particular the parent-child relationship, is associated with emotional and cognitive development later in life. For instance, adverse early-life experience is correlated with an increased vulnerability to develop psychopathologies and aging-related cognitive decline. These are thought to be mediated by acute and long-lasting effects on the, at that time still developing, stress-neuroendocrine and cognitive systems. Adult hippocampal neurogenesis is involved in learning and memory while both regulation of the stress response as well as early-life stress is known to permanently reduce neurogenesis, and to be implicated in these functional deficits. In order to increase our understanding of the influence of the perinatal environment on the long-lasting programming of neurogenesis, we here discuss immediate and lasting effects of various adverse early-life experiences on hippocampal neurogenesis and the associated behavioral alterations. Considering the persistence of these effects, the underlying molecular mechanisms, with focus on the potential epigenetic mechanisms will be discussed as well. Finally, special attention will be paid to the prominent sex differences in early-life stress-induced alterations in neurogenesis.

Perinatal programming of adult hippocampal structure and function; emerging roles of stress, nutrition and epigenetics

Early-life stress lastingly affects adult cognition and increases vulnerability to psychopathology, but the underlying mechanisms remain elusive. In this Opinion article, we propose that early nutritional input together with stress hormones and sensory stimuli from the mother during the perinatal period act synergistically to program the adult brain, possibly via epigenetic mechanisms. We hypothesize that stress during gestation or lactation affects the intake of macro- and micronutrients, including dietary methyl donors, and/or impairs the dams metabolism, thereby altering nutrient composition and intake by the offspring. In turn, this may persistently modulate gene expression via epigenetic programming, thus altering hippocampal structure and cognition. Understanding how the combination of stress, nutrition, and epigenetics shapes the adult brain is essential for effective therapies.

Chronic Early Life Stress Alters Developmental and Adult Neurogenesis and Impairs Cognitive Function in Mice

Early life stress (ES) increases vulnerability to psychopathology and impairs cognition in adulthood. These ES‐induced deficits are associated with lasting changes in hippocampal plasticity. Detailed information on the neurobiological basis, the onset, and progression of such changes and their sex‐specificity is currently lacking but is required to tailor specific intervention strategies. Here, we use a chronic ES mouse model based on limited nesting and bedding material from postnatal day (P) 2–9 to investigate; (1) if ES leads to impairments in hippocampus‐dependent cognitive function in adulthood and (2) if these alterations are paralleled by changes in developmental and/or adult hippocampal neurogenesis. ES increased developmental neurogenesis (proliferation and differentiation) in the dentate gyrus (DG) at P9, and the number of immature (NeurD1+) cells migrating postnatally from the secondary dentate matrix, indicating prompt changes in DG structure in both sexes. ES lastingly reduced DG volume and the long‐term survival of developmentally born neurons in both sexes at P150. In adult male mice only, ES reduced survival of adult‐born neurons (BrdU/NeuN+ cells), while proliferation (Ki67+) and differentiation (DCX+) were unaffected. These changes correlated with impaired performance in all learning and memory tasks used here. In contrast, in female mice, despite early alterations in developmental neurogenesis, no lasting changes were present in adult neurogenesis after ES and the cognitive impairments were less prominent and only apparent in some cognitive tasks. We further show that, although neurogenesis and cognition correlate positively, only the hippocampus‐dependent functions depend on changes in neurogenesis, whereas cognitive functions that are not exclusively hippocampus‐dependent do not. This study indicates that chronic ES has lasting consequences on hippocampal structure and function in mice and suggests that male mice are more susceptible to ES than females. Unraveling the mechanisms that underlie the persistent ES‐induced effects may have clinical implications for treatments to counteract ES‐induced deficits.

Sex differences in adolescent depression: do sex hormones determine vulnerability?

Depression is one of the most common, costly and severe psychopathologies worldwide. Its incidence, however, differs significantly between the sexes, and depression rates in women are twice those of men. Interestingly, this sex difference emerges during adolescence. Although the adolescent period is characterised by major physical and behavioural transformations, it is unclear why the incidence of depression increases so dramatically in girls during this otherwise generally healthy developmental period. Although psychological and environmental factors are also involved, we discuss the neuroendocrinological factors determining adolescent vulnerability to depression. In particular, we address the role of sex steroids in mood regulation, hypothalamic‐pituitary‐adrenal axis maturation and sexual differentiation of the brain, with a focus on hippocampal plasticity.

Regulation of Adult Neurogenesis and Plasticity by (Early) Stress, Glucocorticoids, and Inflammation

Exposure to stress is one of the best-known negative regulators of adult neurogenesis (AN). We discuss changes in neurogenesis in relation to exposure to stress, glucocorticoid hormones, and inflammation, with a particular focus on early development and on lasting effects of stress. Although the effects of acute and mild stress on AN are generally brief and can be quickly overcome, chronic exposure or more severe forms of stress can induce longer lasting reductions in neurogenesis that can, however, in part, be overcome by subsequent exposure to exercise, drugs targeting the stress system, and some antidepressants. Exposure to stress, particularly during the sensitive period of early life, may (re)program brain plasticity, in particular, in the hippocampus. This may increase the risk to develop cognitive or anxiety symptoms, common to brain diseases like dementia and depression in which plasticity changes occur, and a normalization of neurogenesis may be required for a successful treatment response and recovery.

Early-life adversity programs emotional functions and the neuroendocrine stress system: the contribution of nutrition, metabolic hormones and epigenetic mechanisms

Abstract Clinical and pre-clinical studies have shown that early-life adversities, such as abuse or neglect, can increase the vulnerability to develop psychopathologies and cognitive decline later in life. Remarkably, the lasting consequences of stress during this sensitive period on the hypothalamic–pituitary–adrenal axis and emotional function closely resemble the long-term effects of early malnutrition and suggest a possible common pathway mediating these effects. During early-life, brain development is affected by both exogenous factors, like nutrition and maternal care as well as by endogenous modulators including stress hormones. These elements, while mostly considered for their independent actions, clearly do not act alone but rather in a synergistic manner. In order to better understand how the programming by early-life stress takes place, it is important to gain further insight into the exact interplay of these key elements, the possible common pathways as well as the underlying molecular mechanisms that mediate their effects. We here review evidence that exposure to both early-life stress and early-life under-/malnutrition similarly lead to life-long alterations on the neuroendocrine stress system and modify emotional functions. We further discuss how the different key elements of the early-life environment interact and affect one another and next suggest a possible role for the early-life adversity induced alterations in metabolic hormones and nutrient availability in shaping later stress responses and emotional function throughout life, possibly via epigenetic mechanisms. Such knowledge will help to develop intervention strategies, which gives the advantage of viewing the synergistic action of a more complete set of changes induced by early-life adversity.

Exposure to chronic early-life stress lastingly alters the adipose tissue, the leptin system and changes the vulnerability to western-style diet later in life in mice

Early-life stress (ES) increases the vulnerability to develop psychopathologies and cognitive decline in adulthood. Interestingly, this is often comorbid with metabolic disorders, such as obesity. However, it is unclear whether ES leads to lasting metabolic changes and to what extent this is associated with the ES-induced cognitive impairments. Here, we used an established chronic ES mouse model (from postnatal day (P) 2 to P9) to investigate the short- and long-term effects of ES exposure on parameters of the adipose tissue and the leptin system (i.e. circulating levels and gene expression of leptin and its receptor) in both sexes. Immediately following ES, the offspring exhibited reductions in white adipose tissue (WAT) mass, plasma leptin levels and in leptin mRNA expression in WAT. Furthermore, ES exposure led to increased brown adipose tissue and browning of WAT, which was evident by a drastic increase in uncoupling protein 1 mRNA expression in the inguinal WAT at P9. Notably, the ES-induced reductions in WAT mass, plasma leptin and leptin expression in WAT were sustained into adulthood and were accompanied by changes in body fat distribution, such as a higher ratio between mesenteric WAT and other WATs. Interestingly, while ES exposure increased leptin receptor mRNA expression in the choroid plexus, it was unaltered in the hippocampus. This suggests an adaptation to maintain central leptin homeostasis following ES exposure. In addition, chronic ES exposure resulted in the well-established cognitive impairment in object recognition performance during adulthood, which correlated positively with reductions in WAT mass observed in male, but not in female mice. Finally, to assess if ES leads to a different metabolic phenotype in a moderate obesogenic environment, we measured body fat accumulation of control and ES-exposed mice in response to a moderate western-style diet (WSD) that was provided during adulthood. ES-exposed mice subjected to WSD exhibit a higher increase in adiposity when compared to controls, suggesting that ES exposure might result in a higher vulnerability to develop obesity in a moderate obesogenic environment. To conclude, chronic ES exposure alters parameters of the adipose tissue, leads to central adaptations in leptin regulation and results in higher fat accumulations when exposed to a WSD challenge later in life. A better understanding of these metabolic effects induced by ES might open up new avenues for therapeutic (e.g. nutritional) interventions.

Early micronutrient supplementation protects against early stress-induced cognitive impairments

Early‐life stress (ES) impairs cognition later in life. Because ES prevention is problematic, intervention is needed, yet the mechanisms that underlie ES remain largely unknown. So far, the role of early nutrition in brain programming has been largely ignored. Here, we demonstrate that essential 1‐carbon metabolism‐associated micronutrients (1‐CMAMs; i.e., methionine and B vitamins) early in life are crucial in programming later cognition by ES. ES was induced in male C57Bl/6 mice from postnatal d (P)2–9. 1‐CMAM levels were measured centrally and peripherally by using liquid chromatography‐mass spectroscopy. Next, we supplemented the maternal diet with 1‐CMAM only during the ES period and studied cognitive, neuroendocrine, neurogenic, transcriptional, and epigenetic changes in adult offspring. We demonstrate that ES specifically reduces methionine in offspring plasma and brain. Of note, dietary 1‐CMAM enrichment during P2–9 restored methionine levels and rescued ES‐induced adult cognitive impairments. Beneficial effects of this early dietary enrichment were associated with prevention of the ES‐induced rise in corticosterone and adrenal gland hypertrophy did not involve changes in maternal care, hippocampal volume, neurogenesis, or global/Nr3c1‐specific DNA methylation. In summary, nutrition is important in brain programming by ES. A short, early supplementation with essential micronutrients can already prevent lasting effects of ES. This concept opens new avenues for nutritional intervention.—Naninck, E. F. G., Oosterink, J. E., Yam, K.‐Y., de Vries, L. P., Schierbeek, H., van Goudoever, J. B., Verkaik‐Schakel, R.‐N., Plantinga, J. A., Plosch, T., Lucassen, P. J., Korosi, A. Early micronutrient supplementation protects against early stress‐induced cognitive impairments. FASEB J. 31, 505–518 (2017). http://www.fasebj.org

Accurate measurement of the essential micronutrients methionine, homocysteine, vitamins B6, B12, B9 and their metabolites in plasma, brain and maternal milk of mice using LC/MS ion trap analysis

Methionine, homocysteine, vitamins B6, B12, B9, and their metabolites are crucial co-factors and substrates for many basic biological pathways including one-carbon metabolism, and they are particularly important for brain function and development and epigenetic mechanisms. These are essential nutrients that cannot be synthesized endogenously and thus need to be taken in via diet. A novel method was developed that enables simultaneous assessment of the exact concentrations of these essential micronutrients in various matrices, including maternal milk, plasma, and brain of neonatal mice. The protocol for analysis of these components in the various matrices consists of a cleanup step (i.e. lipid extraction followed by protein precipitation) combined with a liquid chromatography mass spectrometry (LC/MS) ion trap method with high sensitivity and selectivity (SRM mode). This novel method enables the measurement of these essential nutrients with good recoveries (69-117%), and high intra-day (<10%) and high intra-day precision (defined as <15% for compounds with an isotopologue and <20% for compounds without an isotopologue as internal standard) in plasma, maternal milk, and brain of mice at low and high levels. In addition, lower limits of quantitation (LOQ) were determined for the various matrices in the range for methionine (700-2000nmol/L), homocysteine (280-460-nmol/L), vitamins B6 (5-230nmol/L), B12 (7-11nmol/L), B9 (20-30nmol/L). Degradation of vitamins and oxidation of homocysteine is limited to a minimum, and only small sample volumes (30μL plasma, 20mg brain and maternal milk) are needed for simultaneous measurement. This method can help to understand how these nutrients are transferred from mother to offspring via maternal milk, as well as how these nutrients are absorbed by the offspring and eventually taken up in various tissues amongst the brain in preclinical and clinical research settings. Therefore the method can help to explore critical periods in lactating mothers and developing offspring.

No role for vitamin D or a moderate fat diet in aging induced cognitive decline and emotional reactivity in C57BL/6 mice

BACKGROUND Epidemiological studies have shown associations between vitamin D, mental health and glucose homeostasis in the elderly. Causal evidence, however, is still lacking. OBJECTIVE The objective of this study was to investigate the importance of vitamin D in the prevention of emotional disturbances and cognitive decline in aging C57BL/6 mice, with pre-diabetes type II as potential effect modifier. METHODS Mice were exposed to one of four diets from 10 months till 24 months of age: low fat vitamin D adequate (LFD), LF vitamin D deficient (LF), moderate fat vitamin D adequate (MFD), and MF vitamin D deficient (MF). The MFD/MF diet was applied to induce a condition resembling pre-diabetes type II. Behavior was assessed twice in the same group of mice at 6-8 and at 22-23 months of age using the Open Field Test (OFT), Elevated Plus Maze (EPM), Object Recognition Test (ORT) and the Morris Water Maze (MWM). RESULTS We successfully induced vitamin D deficiency in the LF/MF mice. Moreover, fasting glucose and fasting insulin levels were significantly higher in MFD/MF mice than in LFD/LF mice. A significant aging effect was observed for most behavioral parameters. A MF(D) diet was shown to delay or prevent the age-related increase in emotional reactivity in the EPM. No effect of vitamin D or vitamin D*fat on behavioral outcomes was measured. CONCLUSION Aging significantly affected emotional reactivity and cognitive performance. Although other studies have shown effects of vitamin D on emotional reactivity and cognitive performance in mice, these findings could not be confirmed in aged C57BL/6 mice in this study.