Characterization of astrocytes throughout life in wildtype and APP/PS1 mice after early-life stress exposure.

BACKGROUND: Early-life stress (ES) is an emerging risk factor for later life development of Alzheimer's disease (AD). We have previously shown that ES modulates amyloid-beta pathology and the microglial response to it in the APPswe/PS1dE9 mouse model. Because astrocytes are key players in the pathogenesis of AD, we studied here if and how ES affects astrocytes in wildtype (WT) and APP/PS1 mice and how these relate to the previously reported amyloid pathology and microglial profile. METHODS: We induced ES by limiting nesting and bedding material from postnatal days (P) 2-9. We studied in WT mice (at P9, P30, and 6 months) and in APP/PS1 mice (at 4 and 10 months) (i) GFAP coverage, cell density, and complexity in hippocampus (HPC) and entorhinal cortex (EC); (ii) hippocampal gene expression of astrocyte markers; and (iii) the relationship between astrocyte, microglia, and amyloid markers. RESULTS: In WT mice, ES increased GFAP coverage in HPC subregions at P9 and decreased it at 10 months. APP/PS1 mice at 10 months exhibited both individual cell as well as clustered GFAP signals. APP/PS1 mice when compared to WT exhibited reduced total GFAP coverage in HPC, which is increased in the EC, while coverage of the clustered GFAP signal in the HPC was increased and accompanied by increased expression of several astrocytic genes. While measured astrocytic parameters in APP/PS1 mice appear not be further modulated by ES, analyzing these in the context of ES-induced alterations to amyloid pathology and microglial shows alterations at both 4 and 10 months of age. CONCLUSIONS: Our data suggest that ES leads to alterations to the astrocytic response to amyloid-ß pathology.

Increasing availability of ω-3 fatty acid in the early-life diet prevents the early-life stress-induced cognitive impairments without affecting metabolic alterations.

Exposure to early-life stress (ES) is associated with cognitive and metabolic deficits in adulthood. The role of early nutrition in programming these long-term effects is largely unknown. We focused on essential ω-3 and ω-6 long-chain polyunsaturated fatty acids (LCPUFA) and investigated whether ES affects central and peripheral FA profiles, as well as if and how an early diet with increased availability of ω-3 LCPUFA ( via lowering ω-6/ω-3 ratio) protects against ES-induced impairments. ES exposure [limited nesting and bedding paradigm from postnatal day (P)2 to P9] altered central and peripheral FA profiles in mice. An early diet with low ω-6/ω-3 ratio from P2 to P42 notably prevented the ES-induced cognitive impairments, and the alterations in hippocampal newborn cell survival and in CD68+ microglia, without affecting the ES-induced metabolic alterations. Other markers for hippocampal plasticity, apoptosis, and maternal care were unaffected by ES or diet. Our findings highlight the importance of early dietary lipid quality for later cognition in ES-exposed populations.-Yam, K.-Y., Schipper, L., Reemst, K., Ruigrok, S. R., Abbink, M. R., Hoeijmakers, L., Naninck, E. F. G., Zarekiani, P., Oosting, A., Van der Beek, E. M., Lucassen, P. J., Korosi, A. Increasing availability of ω-3 fatty acid in the early-life diet prevents the early-life stress-induced cognitive impairments without affecting metabolic alterations.

Early-life stress lastingly alters the neuroinflammatory response to amyloid pathology in an Alzheimer's disease mouse model.

Exposure to stress during the sensitive period of early-life increases the risk to develop cognitive impairments and psychopathology later in life. In addition, early-life stress (ES) exposure, next to genetic causes, has been proposed to modulate the development and progression of Alzheimer's disease (AD), however evidence for this hypothesis is currently lacking. We here tested whether ES modulates progression of AD-related neuropathology and assessed the possible contribution of neuroinflammatory factors in this. We subjected wild-type (WT) and transgenic APP/PS1 mice, as a model for amyloid neuropathology, to chronic ES from postnatal day (P)2 to P9. We next studied how ES exposure affected; 1) amyloid ß (Aß) pathology at an early (4month old) and at a more advanced pathological (10month old) stage, 2) neuroinflammatory mediators immediately after ES exposure as well as in adult WT mice, and 3) the neuroinflammatory response in relation to Aß neuropathology. ES exposure resulted in a reduction of cell-associated amyloid in 4month old APP/PS1 mice, but in an exacerbation of Aß plaque load at 10months of age, demonstrating that ES affects Aß load in the hippocampus in an age-dependent manner. Interestingly, ES modulated various neuroinflammatory mediators in the hippocampus of WT mice as well as in response to Aß neuropathology. In WT mice, immediately following ES exposure (P9), Iba1-immunopositive microglia exhibited reduced complexity and hippocampal interleukin (IL)-1ß expression was increased. In contrast, microglial Iba1 and CD68 were increased and hippocampal IL-6 expression was decreased at 4months, while these changes resolved by 10months of age. Finally, Aß neuropathology triggered a neuroinflammatory response in APP/PS1 mice that was altered after ES exposure. APP/PS1 mice exhibited increased CD68 expression at 4months, which was further enhanced by ES, whereas the microglial response to Aß neuropathology, as measured by Iba1 and CD11b, was less prominent after ES at 10months of age. Finally, the hippocampus appears to be more vulnerable for these ES-induced effects, since ES did not affect Aß neuropathology and neuroinflammation in the entorhinal cortex of adult ES exposed mice. Overall, our results demonstrate that ES exposure has both immediate and lasting effects on the neuroinflammatory response. In the context of AD, such alterations in neuroinflammation might contribute to aggravated neuropathology in ES exposed mice, hence altering disease progression. This indicates that, at least in a genetic context, ES could aggravate AD pathology.

Pharmacological Inhibition of the Psychiatric Risk Factor FKBP51 Has Anxiolytic Properties.

Anxiety-related psychiatric disorders represent one of the largest health burdens worldwide. Single nucleotide polymorphisms of the FK506 binding protein 51 (FKBP51) gene have been repeatedly associated with anxiety-related disorders and stress sensitivity. Given the intimate relationship of stress and anxiety, we hypothesized that amygdala FKBP51 may mediate anxiety-related behaviors. Mimicking the stress effect by specifically overexpressing FKBP51 in the basolateral amygdala (BLA) or central amygdala resulted in increased anxiety-related behavior, respectively. In contrast, application of a highly selective FKBP51 point mutant antagonist, following FKBP51(mut) BLA-overexpression, reduced the anxiogenic phenotype. We subsequently tested a novel FKBP51 antagonist, SAFit2, in wild-type mice via BLA microinjections, which reduced anxiety-related behavior. Remarkably, the same effect was observed following peripheral administration of SAFit2. To our knowledge, this is the first in vivo study using a specific FKBP51 antagonist, thereby unraveling the role of FKBP51 and its potential as a novel drug target for the improved treatment of anxiety-related disorders.

Epigenetic imprinting during assisted reproductive technologies: The effect of temporal and cumulative fluctuations in methionine cycling on the DNA methylation state.

Assisted reproductive technology (ART) exposes gametes and embryos to an artificial environment that does not resemble the conditions of natural conception, and therefore might change epigenetic regulation of genes that are imprinted during development. In the present review, we discuss the relationship between susceptibility of specific genes to receive an altered epigenetic composition during ART processes, possibly via alterations in the biochemical folate and methionine cycle. We provide a comprehensive view of the current state of epigenetic patterning in ART-conceived healthy children and in Angelman syndrome (AS) and Beckwith-Wiedemann syndrome (BWS) patients. We illustrate that similar genes--that is, MEST, KCNQ1OT1, and IGF2--possess an altered DNA methylation profile in animal models, ART-conceived healthy children, and AS and BWS patients. The developmental stage at which these genes receive their epigenetic imprint appears to coincide with the specific moment that ART takes place. We highlight that ART procedures affect physiological levels of enzymes and substrates involved in the folate and methionine cycle thereby altering the DNA methylation state. Moreover, although the DNA methylation rate appears to be robust: (i) temporal imbalances coinciding with defined moments of epigenetic imprinting of specific genes affect the eventual DNA methylation state of those genes and (ii) cumulative ART effects on methionine and folate cycling can alter DNA methylation rates. These observations underscore the necessity to further investigate consequences of ART treatments on the epigenetic profile.

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.

Early-life stress does not alter spatial memory performance, hippocampal neurogenesis, neuroinflammation, or telomere length in 20-month-old male mice.

Early-life stress (ES) increases the risk for psychopathology and cognitive decline later in life. Because the neurobiological substrates affected by ES (i.e., cognition, neuroplasticity, and neuroinflammation) are also altered in aging, we set out to investigate if and how ES in the first week of life affects these domains at an advanced age, and how ES modulates the aging trajectory per se. We subjected C57BL/6j mice to an established ES mouse model from postnatal days 2-9. Mice underwent behavioral testing at 19 months of age and were sacrificed at 20 months to investigate their physiology, hippocampal neuroplasticity, neuroinflammation, and telomere length. ES mice, as a group, did not perform differently from controls in the open field or Morris water maze (MWM). Hippocampal neurogenesis and synaptic marker gene expression were not different in ES mice at this age. While we find aging-associated alterations to neuroinflammatory gene expression and telomere length, these were unaffected by ES. When integrating the current data with those from our previously reported 4- and 10-month-old cohorts, we conclude that ES leads to a 'premature' shift in the aging trajectory, consisting of early changes that do not further worsen at the advanced age of 20 months. This could be explained e.g. by a 'floor' effect in ES-induced impairments, and/or age-induced impairments in control mice. Future studies should help understand how exactly ES affects the overall aging trajectory.

Early-Life Stress Does Not Aggravate Spatial Memory or the Process of Hippocampal Neurogenesis in Adult and Middle-Aged APP/PS1 Mice.

Life-time experiences are thought to influence the risk to develop the neurodegenerative disorder Alzheimer's disease (AD). In particular, early-life stress (ES) may modulate the onset and progression of AD. There is recent evidence by our group and others that AD-related neuropathological progression and the associated neuroimmune responses are modulated by ES in the classic APPswe/PS1dE9 mouse model for AD. We here extend our previous study on ES mediated modulation of neuropathology and neuroinflammation and address in the same cohort of mice whether ES accelerates and/or aggravates AD-induced cognitive decline and alterations in the process of adult hippocampal neurogenesis (AHN), a form of brain plasticity. Chronic ES was induced by limiting bedding and nesting material during the first postnatal week and is known to induce cognitive deficits by 4 months in wild type (WT) mice. The onset of cognitive decline in APP/PS1 mice generally starts around 6 months of age. We here tested mice at ages 2-4 months to study acceleration and at ages 8-10 months for aggravation of the APP/PS1 phenotype. ES-exposed WT and APP/PS1 mice were able to perform the object recognition (ORT) and location tasks (OLT) at 2 months of age. Interestingly, at 3 months, ES induced impairments in the performance of the OLT in WT, but not in APP/PS1 mice. APP/PS1 mice exhibited alterations in hippocampal cell proliferation and differentiation, but ES exposure did not further change this. At 9 months, APP/PS1 mice exhibited impaired performance in the Morris Water Maze (MWM) task, as well as reductions in markers of the AHN process, which were not further modulated by ES exposure. In addition, we observed a so far unreported hyperactivity in ES-exposed mice at 8 months of age, which hampered assessment of cognitive functions in the ORT and OLT. In conclusion, while ES has been reported to modulate AD neuropathology and neuroinflammation before, it failed to accelerate or aggravate the decline in cognition or the process of AHN in APP/PS1 mice at ages 2-4 and 8-10 months. Future studies are needed to unravel how ES might affect the vulnerability to develop AD.

A preclinical perspective on the enhanced vulnerability to Alzheimer's disease after early-life stress.

Stress experienced early in life (ES), in the form of childhood maltreatment, maternal neglect or trauma, enhances the risk for cognitive decline in later life. Several epidemiological studies have now shown that environmental and adult life style factors influence AD incidence or age-of-onset and early-life environmental conditions have attracted attention in this respect. There is now emerging interest in understanding whether ES impacts the risk to develop age-related neurodegenerative disorders, and their severity, such as in Alzheimer's disease (AD), which is characterized by cognitive decline and extensive (hippocampal) neuropathology. While this might be relevant for the identification of individuals at risk and preventive strategies, this topic and its possible underlying mechanisms have been poorly studied to date. In this review, we discuss the role of ES in modulating AD risk and progression, primarily from a preclinical perspective. We focus on the possible involvement of stress-related, neuro-inflammatory and metabolic factors in mediating ES-induced effects on later neuropathology and the associated impairments in neuroplasticity. The available studies suggest that the age of onset and progression of AD-related neuropathology and cognitive decline can be affected by ES, and may aggravate the progression of AD neuropathology. These relevant changes in AD pathology after ES exposure in animal models call for future clinical studies to elucidate whether stress exposure during the early-life period in humans modulates later vulnerability for AD.

Vulnerability and resilience to Alzheimer's disease: early life conditions modulate neuropathology and determine cognitive reserve.

BACKGROUND: Alzheimer's disease (AD) is a progressive neurodegenerative disorder with a high prevalence among the elderly and a huge personal and societal impact. Recent epidemiological studies have indicated that the incidence and age of onset of sporadic AD can be modified by lifestyle factors such as education, exercise, and (early) stress exposure. Early life adversity is known to promote cognitive decline at a later age and to accelerate aging, which are both primary risk factors for AD. In rodent models, exposure to 'negative' or 'positive' early life experiences was recently found to modulate various measures of AD neuropathology, such as amyloid-beta levels and cognition at later ages. Although there is emerging interest in understanding whether experiences during early postnatal life also modulate AD risk in humans, the mechanisms and possible substrates underlying these long-lasting effects remain elusive. METHODS: We review literature and discuss the role of early life experiences in determining later age and AD-related processes from a brain and cognitive 'reserve' perspective. We focus on rodent studies and the identification of possible early determinants of later AD vulnerability or resilience in relation to early life adversity/enrichment. RESULTS: Potential substrates and mediators of early life experiences that may influence the development of AD pathology and cognitive decline are: programming of the hypothalamic-pituitary-adrenal axis, priming of the neuroinflammatory response, dendritic and synaptic complexity and function, overall brain plasticity, and proteins such as early growth response protein 1 (EGR1), activity regulated cytoskeleton-associated protein (Arc), and repressor element-1 silencing transcription factor (REST). CONCLUSIONS: We conclude from these rodent studies that the early postnatal period is an important and sensitive phase that influences the vulnerability to develop AD pathology. Yet translational studies are required to investigate whether early life experiences also modify AD development in human studies, and whether similar molecular mediators can be identified in the sensitivity to develop AD in humans.

The age-related slow increase in amyloid pathology in APP.V717I mice activates microglia, but does not alter hippocampal neurogenesis.

In Alzheimer's disease, the hippocampus is characterized by abundant deposition of amyloid peptides (amyloid ß [Aß]) and neuroinflammation. Adult hippocampal neurogenesis (AHN) is a form of plasticity that contributes to cognition and can be influenced by either or both pathology and neuroinflammation. Their interaction has been studied before in rapidly progressing transgenic mouse models with strong overexpression of amyloid precursor protein (APP) and/or presenilin 1. So far, changes in AHN and neuroinflammation remain poorly characterized in slower progressing models at advanced age, which approach more closely sporadic Alzheimer's disease. Here, we analyzed 10- to 26-month-old APP.V717I mice for possible correlations between Aß pathology, microglia, and AHN. The age-related increase in amyloid pathology was closely paralleled by microglial CD68 upregulation, which was largely absent in age-matched wild-type littermates. Notably, aging reduced the AHN marker doublecortin, but not calretinin, to a similar extent in wild-type and APP.V717I mice between 10 and 26 months. This demonstrates that AHN is influenced by advanced age in the APP.V717I mouse model, but not by Aß and microglial activation.

Microglial Priming and Alzheimer's Disease: A Possible Role for (Early) Immune Challenges and Epigenetics?

Neuroinflammation is thought to contribute to Alzheimer's disease (AD) pathogenesis that is, to a large extent, mediated by microglia. Given the tight interaction between the immune system and the brain, peripheral immune challenges can profoundly affect brain function. Indeed, both preclinical and clinical studies have indicated that an aberrant inflammatory response can elicit behavioral impairments and cognitive deficits, especially when the brain is in a vulnerable state, e.g., during early development, as a result of aging, or under disease conditions like AD. However, how exactly peripheral immune challenges affect brain function and whether this is mediated by aberrant microglial functioning remains largely elusive. In this review, we hypothesize that: (1) systemic immune challenges occurring during vulnerable periods of life can increase the propensity to induce later cognitive dysfunction and accelerate AD pathology; and (2) that "priming" of microglial cells is instrumental in mediating this vulnerability. We highlight how microglia can be primed by both neonatal infections as well as by aging, two periods of life during which microglial activity is known to be specifically upregulated. Lasting changes in (the ratios of) specific microglial phenotypes can result in an exaggerated pro-inflammatory cytokine response to subsequent inflammatory challenges. While the resulting changes in brain function are initially transient, a continued and/or excess release of such pro-inflammatory cytokines can activate various downstream cellular cascades known to be relevant for AD. Finally, we discuss microglial priming and the aberrant microglial response as potential target for treatment strategies for AD.

Chaperoning epigenetics: FKBP51 decreases the activity of DNMT1 and mediates epigenetic effects of the antidepressant paroxetine.

Epigenetic processes, such as DNA methylation, and molecular chaperones, including FK506-binding protein 51 (FKBP51), are independently implicated in stress-related mental disorders and antidepressant drug action. FKBP51 associates with cyclin-dependent kinase 5 (CDK5), which is one of several kinases that phosphorylates and activates DNA methyltransferase 1 (DNMT1). We searched for a functional link between FKBP51 (encoded by FKBP5) and DNMT1 in cells from mice and humans, including those from depressed patients, and found that FKBP51 competed with its close homolog FKBP52 for association with CDK5. In human embryonic kidney (HEK) 293 cells, expression of FKBP51 displaced FKBP52 from CDK5, decreased the interaction of CDK5 with DNMT1, reduced the phosphorylation and enzymatic activity of DNMT1, and diminished global DNA methylation. In mouse embryonic fibroblasts and primary mouse astrocytes, FKBP51 mediated several effects of paroxetine, namely, decreased the protein-protein interactions of DNMT1 with CDK5 and FKBP52, reduced phosphorylation of DNMT1, and decreased the methylation and increased the expression of the gene encoding brain-derived neurotrophic factor (Bdnf). In human peripheral blood cells, FKBP5 expression inversely correlated with both global and BDNF methylation. Peripheral blood cells isolated from depressed patients that were then treated ex vivo with paroxetine revealed that the abundance of BDNF positively correlated and phosphorylated DNMT1 inversely correlated with that of FKBP51 in cells and with clinical treatment success in patients, supporting the relevance of this FKBP51-directed pathway that prevents epigenetic suppression of gene expression.

The interplay of early-life stress, nutrition, and immune activation programs adult hippocampal structure and function.

Early-life adversity increases the vulnerability to develop psychopathologies and cognitive decline later in life. This association is supported by clinical and preclinical studies. Remarkably, experiences of stress during this sensitive period, in the form of abuse or neglect but also early malnutrition or an early immune challenge elicit very similar long-term effects on brain structure and function. During early-life, both exogenous factors like nutrition and maternal care, as well as endogenous modulators, including stress hormones and mediator of immunological activity affect brain development. The interplay of these key elements and their underlying molecular mechanisms are not fully understood. We discuss here the hypothesis that exposure to early-life adversity (specifically stress, under/malnutrition and infection) leads to life-long alterations in hippocampal-related cognitive functions, at least partly via changes in hippocampal neurogenesis. We further discuss how these different key elements of the early-life environment interact and affect one another and suggest that it is a synergistic action of these elements that shapes cognition throughout life. Finally, we consider different intervention studies aiming to prevent these early-life adversity induced consequences. The emerging evidence for the intriguing interplay of stress, nutrition, and immune activity in the early-life programming calls for a more in depth understanding of the interaction of these elements and the underlying mechanisms. This knowledge will help to develop intervention strategies that will converge on a more complete set of changes induced by early-life adversity.

Depletion of FKBP51 in female mice shapes HPA axis activity.

Psychiatric disorders such as depressive disorders and posttraumatic stress disorder are a major disease burden worldwide and have a higher incidence in women than in men. However, the underlying mechanism responsible for the sex-dependent differences is not fully understood. Besides environmental factors such as traumatic life events or chronic stress, genetic variants contribute to the development of such diseases. For instance, variations in the gene encoding the FK506 binding protein 51 (FKBP51) have been repeatedly associated with mood and anxiety. FKBP51 is a negative regulator of the glucocorticoid receptor and thereby of the hypothalamic-pituitary-adrenal axis that also interacts with other steroid hormone receptors such as the progesterone and androgen receptors. Thus, the predisposition of women to psychiatric disorders and the interaction of female hormones with FKBP51 and the glucocorticoid receptor implicate a possible difference in the regulation of the hypothalamic-pituitary-adrenal axis in female FKBP51 knockout (51KO) mice. Therefore, we investigated neuroendocrine, behavioural and physiological alterations relevant to mood disorders in female 51KO mice. Female 51KOs and wild type littermates were subjected to various behavioural tests, including the open field, elevated plus maze and forced swim test. The neuroendocrine profile was investigated under basal conditions and in response to an acute stressor. Furthermore, we analysed the mRNA expression levels of the glucocorticoid receptor and corticotrophin release hormone in different brain regions. Overall, female 51KO mice did not display any overt behavioural phenotype under basal conditions, but showed a reduced basal hypothalamic-pituitary-adrenal axis activity, a blunted response to, and an enhanced recovery from, acute stress. These characteristics strongly overlap with previous studies in male 51KO mice indicating that FKBP51 shapes the behavioural and neuroendocrine phenotype independent of the sex of the individual.