Early-life stress induces cognitive disorder in middle-aged mice

Molecular underpinnings of programming by early-life stress and the protective effects of early dietary ω6/ω3 ratio, basally and in response to LPS: Integrated mRNA-miRNAs approach

Early-life stress (ELS) exposure increases the risk for mental disorders, including cognitive impairments later in life. We have previously demonstrated that an early diet with low ω6/ω3 polyunsaturated fatty acid (PUFA) ratio protects against ELS-induced cognitive impairments. Several studies have implicated the neuroimmune system in the ELS and diet mediated effects, but currently the molecular pathways via which ELS and early diet exert their long-term impact are not yet fully understood. Here we study the effects of ELS and dietary PUFA ratio on hippocampal mRNA and miRNA expression in adulthood, both under basal as well as inflammatory conditions. Male mice were exposed to chronic ELS by the limiting bedding and nesting material paradigm from postnatal day(P)2 to P9, and provided with a diet containing a standard (high (15:1.1)) or protective (low (1.1:1)) ω6 linoleic acid to ω3 alpha-linolenic acid ratio from P2 to P42. At P120, memory was assessed using the object location task. Subsequently, a single lipopolysaccharide (LPS) injection was given and 24 h later hippocampal genome-wide mRNA and microRNA (miRNA) expression was measured using microarray. Spatial learning deficits induced by ELS in mice fed the standard (high ω6/ω3) diet were reversed by the early-life protective (low ω6/ω3) diet. An integrated miRNA - mRNA analysis revealed that ELS and early diet induced miRNA driven mRNA expression changes into adulthood. Under basal conditions both ELS and the diet affected molecular pathways related to hippocampal plasticity, with the protective (low ω6/ω3 ratio) diet leading to activation of molecular pathways associated with improved hippocampal plasticity and learning and memory in mice previously exposed to ELS (e.g., CREB signaling and endocannabinoid neuronal synapse pathway). LPS induced miRNA and mRNA expression was strongly dependent on both ELS and early diet. In mice fed the standard (high ω6/ω3) diet, LPS increased miRNA expression leading to activation of inflammatory pathways. In contrast, in mice fed the protective diet, LPS reduced miRNA expression and altered target mRNA expression inhibiting inflammatory signaling pathways and pathways associated with hippocampal plasticity, which was especially apparent in mice previously exposed to ELS. This data provides molecular insights into how the protective (low ω6/ω3) diet during development could exert its long-lasting beneficial effects on hippocampal plasticity and learning and memory especially in a vulnerable population exposed to stress early in life, providing the basis for the development of intervention strategies.

Epigenetic regulation in major depression and other stress-related disorders: molecular mechanisms, clinical relevance and therapeutic potential

Major depressive disorder (MDD) is a chronic, generally episodic and debilitating disease that affects an estimated 300 million people worldwide, but its pathogenesis is poorly understood. The heritability estimate of MDD is 30-40%, suggesting that genetics alone do not account for most of the risk of major depression. Another factor known to associate with MDD involves environmental stressors such as childhood adversity and recent life stress. Recent studies have emerged to show that the biological impact of environmental factors in MDD and other stress-related disorders is mediated by a variety of epigenetic modifications. These epigenetic modification alterations contribute to abnormal neuroendocrine responses, neuroplasticity impairment, neurotransmission and neuroglia dysfunction, which are involved in the pathophysiology of MDD. Furthermore, epigenetic marks have been associated with the diagnosis and treatment of MDD. The evaluation of epigenetic modifications holds promise for further understanding of the heterogeneous etiology and complex phenotypes of MDD, and may identify new therapeutic targets. Here, we review preclinical and clinical epigenetic findings, including DNA methylation, histone modification, noncoding RNA, RNA modification, and chromatin remodeling factor in MDD. In addition, we elaborate on the contribution of these epigenetic mechanisms to the pathological trait variability in depression and discuss how such mechanisms can be exploited for therapeutic purposes.

Repetitive and compulsive behavior after Early-Life-Pain associated with reduced long-chain sphingolipid species

BACKGROUND

Pain in early life may impact on development and risk of chronic pain. We developed an optogenetic Cre/loxP mouse model of "early-life-pain" (ELP) using mice with transgenic expression of channelrhodopsin-2 (ChR2) under control of the Advillin (Avil) promoter, which drives expression of transgenes predominantly in isolectin B4 positive non-peptidergic nociceptors in postnatal mice. Avil-ChR2 (Cre +) and ChR2-flfl control mice were exposed to blue light in a chamber once daily from P1-P5 together with their Cre-negative mother.

RESULTS

ELP caused cortical hyperexcitability at P8-9 as assessed via multi-electrode array recordings that coincided with reduced expression of synaptic genes (RNAseq) including Grin2b, neurexins, piccolo and voltage gated calcium and sodium channels. Young adult (8-16 wks) Avil-ChR2 mice presented with nociceptive hypersensitivity upon heat or mechanical stimulation, which did not resolve up until one year of age. The persistent hypersensitivy to nociceptive stimuli was reflected by increased calcium fluxes in primary sensory neurons of aged mice (1 year) upon capsaicin stimulation. Avil-ChR2 mice behaved like controls in maze tests of anxiety, social interaction, and spatial memory but IntelliCage behavioral studies revealed repetitive nosepokes and corner visits and compulsive lickings. Compulsiveness at the behavioral level was associated with a reduction of sphingomyelin species in brain and plasma lipidomic studies. Behavioral studies were done with female mice.

CONCLUSION

The results suggest that ELP may predispose to chronic "pain" and compulsive psychopathology in part mediated by alterations of sphingolipid metabolism, which have been previously described in the context of addiction and psychiatric diseases.

Early life adversity as a risk factor for cognitive impairment and Alzheimer's disease

Neurological conditions, including cognitive impairment and Alzheimer's disease (AD), impose a huge burden on society, affecting millions of people globally. In addition to genetic factors, recent studies indicate that environmental and experiential factors may contribute to the pathogenesis of these diseases. Early life adversity (ELA) has a profound impact on brain function and health later in life. In rodent models, exposure to ELA results in specific cognitive deficits and aggravated AD pathology. Extensive concerns have been raised regarding the higher risk of developing cognitive impairments in people with a history of ELA. In this review, we scrutinize findings from human and animal studies focusing on the connection of ELA with cognitive impairment and AD. These discoveries suggest that ELA, especially at early postnatal stages, increases susceptibility to cognitive impairment and AD later in life. In terms of mechanisms, ELA could lead to dysregulation of the hypothalamus-pituitary-adrenal axis, altered gut microbiome, persistent inflammation, oligodendrocyte dysfunction, hypomyelination, and aberrant adult hippocampal neurogenesis. Crosstalks among these events may synergistically contribute to cognitive impairment later in life. Additionally, we discuss several interventions that may alleviate adverse consequences of ELA. Further investigation into this crucial area will help improve ELA management and reduce the burden of related neurological conditions.

Early Adversity and Accelerated Brain Aging: A Mini-Review

Early adversity is an important risk factor that influences brain aging. Diverse animal models of early adversity, including gestational stress and postnatal paradigms disrupting dam-pup interactions evoke not only persistent neuroendocrine dysfunction and anxio-depressive behaviors, but also perturb the trajectory of healthy brain aging. The process of brain aging is thought to involve hallmark features such as mitochondrial dysfunction and oxidative stress, evoking impairments in neuronal bioenergetics. Furthermore, brain aging is associated with disrupted proteostasis, progressively defective epigenetic and DNA repair mechanisms, the build-up of neuroinflammatory states, thus cumulatively driving cellular senescence, neuronal and cognitive decline. Early adversity is hypothesized to evoke an “allostatic load” via an influence on several of the key physiological processes that define the trajectory of healthy brain aging. In this review we discuss the evidence that animal models of early adversity impinge on fundamental mechanisms of brain aging, setting up a substratum that can accelerate and compromise the time-line and nature of brain aging, and increase risk for aging-associated neuropathologies.

Effects of early life adversity on immediate early gene expression: Systematic review and 3-level meta-analysis of rodent studies

Early-life adversity (ELA) causes long-lasting structural and functional changes to the brain, rendering affected individuals vulnerable to the development of psychopathologies later in life. Immediate-early genes (IEGs) provide a potential marker for the observed alterations, bridging the gap between activity-regulated transcription and long-lasting effects on brain structure and function. Several heterogeneous studies have used IEGs to identify differences in cellular activity after ELA; systematically investigating the literature is therefore crucial for comprehensive conclusions. Here, we performed a systematic review on 39 pre-clinical studies in rodents to study the effects of ELA (alteration of maternal care) on IEG expression. Females and IEGs other than cFos were investigated in only a handful of publications. We meta-analyzed publications investigating specifically cFos expression. ELA increased cFos expression after an acute stressor only if the animals (control and ELA) had experienced additional hits. At rest, ELA increased cFos expression irrespective of other life events, suggesting that ELA creates a phenotype similar to naïve, acutely stressed animals. We present a conceptual theoretical framework to interpret the unexpected results. Overall, ELA likely alters IEG expression across the brain, especially in interaction with other negative life events. The present review highlights current knowledge gaps and provides guidance to aid the design of future studies.

Maternal stress programs a demasculinization of glutamatergic transmission in stress-related brain regions of aged rats

Brain aging may be programmed by early-life stress. Aging affects males and females differently, but how perinatal stress (PRS) affects brain aging between sexes is unknown. We showed behavioral and neurobiological sex differences in non-stressed control rats that were strongly reduced or inverted in PRS rats. In particular, PRS decreased risk-taking behavior, spatial memory, exploratory behavior, and fine motor behavior in male aged rats. In contrast, female aged PRS rats displayed only increased risk-taking behavior and reduced exploratory behavior. PRS induced large reductions in the expression of glutamate receptors in the ventral and dorsal hippocampus and prefrontal cortex only in male rats. PRS also reduced the expression of synaptic vesicle-associated proteins, glucocorticoid receptors (GR), and mineralocorticoid receptors (MR) in the ventral hippocampus of aged male rats. In contrast, in female aged rats, PRS enhanced the expression of MRs and brain-derived neurotrophic factor (BDNF) in the ventral hippocampus and the expression of glial fibrillary acidic protein (GFAP) and BDNF in the prefrontal cortex. A common PRS effect in both sexes was a reduction in exploratory behavior and metabotropic glutamate (mGlu2/3) receptors in the ventral hippocampus and prefrontal cortex. A multidimensional analysis revealed that PRS induced a demasculinization profile in glutamate-related proteins in the ventral and dorsal hippocampus and prefrontal cortex, as well as a demasculinization profile of stress markers only in the dorsal hippocampus. In contrast, defeminization was observed only in the ventral hippocampus. Measurements of testosterone and 17-β-estradiol in the plasma and aromatase in the dorsal hippocampus were consistent with a demasculinizing action of PRS. These findings confirm that the brains of males and females differentially respond to PRS and aging suggesting that females might be more protected against early stress and age-related inflammation and neurodegeneration. Taken together, these results may contribute to understanding how early environmental factors shape vulnerability to brain aging in both sexes and may lay the groundwork for future studies aimed at identifying new treatment strategies to improve the quality of life of older individuals, which is of particular interest given that there is a high growth of aging in populations around the world.

Long-term behavioral and cell-type-specific molecular effects of early life stress are mediated by H3K79me2 dynamics in medium spiny neurons

Animals susceptible to chronic social defeat stress (CSDS) exhibit depression-related behaviors, with aberrant transcription across several limbic brain regions, most notably in the nucleus accumbens (NAc). Early life stress (ELS) promotes susceptibility to CSDS in adulthood, but associated enduring changes in transcriptional control mechanisms in the NAc have not yet been investigated. In this study, we examined long-lasting changes to histone modifications in the NAc of male and female mice exposed to ELS. Dimethylation of lysine 79 of histone H3 (H3K79me2) and the enzymes (DOT1L and KDM2B) that control this modification are enriched in D2-type medium spiny neurons and are shown to be crucial for the expression of ELS-induced stress susceptibility. We mapped the site-specific regulation of this histone mark genome wide to reveal the transcriptional networks it modulates. Finally, systemic delivery of a small molecule inhibitor of DOT1L reversed ELS-induced behavioral deficits, indicating the clinical relevance of this epigenetic mechanism.

Absence of Thyroid Hormone Induced Delayed Dendritic Arborization in Mouse Primary Hippocampal Neurons Through Insufficient Expression of Brain-Derived Neurotrophic Factor

Thyroid hormone (TH) plays important roles in the developing brain. TH deficiency in early life leads to severe developmental impairment in the hippocampus. However, the mechanisms of TH action in the developing hippocampus are still largely unknown. In this study, we generated 3,5,3'-tri-iodo-l-thyronine (T3)-free neuronal supplement, based on the composition of neuronal supplement 21 (NS21), to examine the effect of TH in the developing hippocampus using primary cultured neurons. Effects of TH on neurons were compared between cultures in this T3-free culture medium (-T3 group) and a medium in which T3 was added (+T3 group). Morphometric analysis and RT-qPCR were performed on 7, 10, and 14 days in vitro (DIV). On 10 DIV, a decreased dendrite arborization in -T3 group was observed. Such difference was not observed on 7 and 14 DIV. Brain-derived neurotrophic factor (Bdnf) mRNA levels also decreased significantly in -T3 group on 10 DIV. We then confirmed protein levels of phosphorylated neurotrophic tyrosine kinase type 2 (NTRK2, TRKB), which is a receptor for BDNF, on 10 DIV by immunocytochemistry and Western blot analysis. Phosphorylated NTRK2 levels significantly decreased in -T3 group compared to +T3 group on 10 DIV. Considering the role of BDNF on neurodevelopment, we examined its involvement by adding BDNF on 8 and 9 DIV. Addition of 10 ng/ml BDNF recovered the suppressed dendrite arborization induced by T3 deficiency on 10 DIV. We show that the lack of TH induces a developmental delay in primary hippocampal neurons, likely caused through a decreased Bdnf expression. Thus, BDNF may play a role in TH-regulated dendritogenesis.

Holocaust exposure and late-life cognitive performance in men with coronary heart disease

BACKGROUND

Holocaust victims experienced extreme physical and mental stress that could lead to prolonged deficits in psychological and physiological well-being. We aimed to examine whether exposure to Holocaust conditions is associated with cognitive function and decline in a sample of old male adults with coronary heart disease (CHD).

METHODS

The sample included 346 individuals with CHD who participated in a clinical trial in 1990-1997 (mean age 56.7 ± 6.5 y). During 2004-2008 (mean age 71.8 ± 6.5 y) and 2011-2013 (mean age 77.1 ± 6.4 y) participants underwent computerized cognitive assessments. Exposure to Holocaust conditions was based on self-report at the second assessment. Linear regression and mixed-effect models were conducted to evaluate the associations between Holocaust survivorship and subsequent cognitive performance and rate of cognitive decline.

RESULTS

Forty-Three participants (12%) survived concentration camps/ghettos, 69 (20%) were Holocaust survivors who escaped concentration camps/ghettos, and 234 (68%) were not Holocaust survivors. After adjustment for potential confounders, concentration camp/ghetto survivors had poorer global cognitive performance and poorer attention (β = -3.90; 95%CI: 7.11;-0.68 and β = -4.11; 95%CI: 7.83;-0.38, respectively) compared to individuals who were not exposed to Holocaust conditions. Additionally, participants who reported being at concentration camps/ghettoes had increased cognitive decline in global performance and executive function (β = -0.19; 95%CI: 0.37;-0.008 and β = -0.29; 95%CI: 0.53;-0.06, respectively) compared to participants who were not Holocaust survivors. Lastly, those who were Holocaust survivors but not in concentration camps/ghettos had greater decline in attention (β = -0.11; 95%CI: 0.21;-0.01).

DISCUSSION

Exposure to Holocaust conditions in early-life may be linked with poorer cognitive function and greater cognitive decline decades later in old-adults with CHD.

Neurotoxic effects of lactational exposure to perfluorooctane sulfonate on learning and memory in adult male mouse

The present study aims to examine the effect of early lactational perfluorooctane sulfonate (PFOS) exposures on learning and memory in male mice and reveal the underlying mechanisms involved. PFOS solution was orally administered to dams from the postpartum days 1-14, so that pups would be exposed through breast milk. At 8-10 weeks of age, we performed object location test (OLT), object recognition test (ORT), and pairwise visual discrimination (VD) task. We also performed in vivo microdialysis, and mRNA and protein analysis of genes responsible for hippocampal development and function. In both OLT and ORT, the performance of mice in the PFOS-exposed group was significantly lower than those in the control group. In the VD task, the PFOS-exposed group learned significantly slower than the control group. Concentrations of glutamate and gamma-aminobutyric acid in the dorsal hippocampus were significantly higher in the PFOS-exposed group than in the control group. No notable differences were shown in our mRNA and protein studies. The present study showed that lactational PFOS exposure has a profound, long-lasting neurotoxic effect in the hippocampus and consequently leads to learning and memory deficits.

Blocking CRH receptors in adults mitigates age-related memory impairments provoked by early-life adversity

In humans, early-life adversity is associated with impairments in learning and memory that may emerge later in life. In rodent models, early-life adversity directly impacts hippocampal neuron structure and connectivity with progressive deficits in long-term potentiation and spatial memory function. Previous work has demonstrated that augmented release and actions of the stress-activated neuropeptide, CRH, contribute to the deleterious effects of early-life adversity on hippocampal dendritic arborization, synapse number and memory-function. Early-life adversity increases hippocampal CRH expression, and blocking hippocampal CRH receptor type-1 (CRHR1) immediately following early-life adversity prevented the consequent memory and LTP defects. Here, we tested if blocking CRHR1 in young adults ameliorates early-life adversity-provoked memory deficits later in life. A weeklong course of a CRHR1 antagonist in 2-month-old male rats prevented early-life adversity-induced deficits in object recognition memory that emerged by 12 months of age. Surprisingly, whereas the intervention did not mitigate early-life adversity-induced spatial memory losses at 4 and 8 months, it restored hippocampus-dependent location memory in 12-month-old rats that experienced early-life adversity. Neither early-life adversity nor CRHR1 blockade in the adult influenced anxiety- or depression-related behaviors. Altogether, these findings suggest that cognitive deficits attributable to adversity during early-life-sensitive periods are at least partially amenable to interventions later in life.

Ceftriaxone modulates the acute corticosterone effects in local field potentials in the primary somatosensory cortex of anesthetized mice

Stress responses are associated with elevations in corticosterone levels and, as a consequence, increases in glutamate in the central nervous system which can lead to neurological impairment. Ceftriaxone promotes glutamate transport and has been used to reduce glutamate toxicity, but so far it is not known whether ceftriaxone is able to reverse the effects of corticosterone administration. Here we describe the separate and combined effects of acute ceftriaxone and acute corticosterone administration in local field potentials (LFPs) recorded from the somatosensory cortex (S1) of anesthetized mice. For this, LFPs were recorded from groups of anesthetized mice injected with saline, corticosterone, ceftriaxone, or both. Comparison of global state maps, and their displacements, as measured by ratios of different frequency bands (Ratio 1: 0.5–20 Hz/0.5–45 Hz; and Ratio 2: 0.5–4.5 Hz/0.5–9 Hz) revealed distinct and opposite effects for corticosterone and for ceftriaxone. Corticosterone specifically increased the displacement in Ratio 2, while ceftriaxone decreased it; in addition, when both corticosterone and ceftriaxone were injected, Ratio 2 displacement values were again similar to those of the control group. The present results suggest that ceftriaxone and corticosterone modulate specific frequency bands in opposite directions and reveal a potential role for ceftriaxone in counteracting the effects of corticosterone.

Effects of Mild Perinatal Hypothyroidism on Cognitive Function of Adult Male Offspring

Mild perinatal hypothyroidism may result from inadequate iodine intake, insufficient treatment of congenital hypothyroidism, or exposure to endocrine-disrupting chemicals. Because thyroid hormones are critical for brain development, severe hypothyroidism that is untreated in infancy causes irreversible cretinism. Milder hypothyroidism may also affect cognitive development; however, the effects of mild and/or moderate hypothyroidism on brain development are not fully understood. In this study, we examined the behavior of adult male mice rendered mildly hypothyroid during the perinatal period using low-dose propylthiouracil (PTU). PTU was administered through drinking water (5 or 50 ppm) from gestational day 14 to postnatal day 21. Cognitive performance, studied by an object in-location test (OLT), was impaired in PTU-treated mice at postnatal week 8. These results suggest that, although the hypothyroidism was mild, it partially impaired cognitive function. We next measured the concentration of neurotransmitters (glutamate, γ-aminobutyric acid, and glycine) in the hippocampus using in vivo microdialysis during OLT. The concentrations of neurotransmitters, particularly glutamate and glycine, decreased in PTU-treated mice. The expression levels of N-methyl-d-aspartate receptor subunits, which are profound regulators of glutamate neurotransmission and memory function, also were decreased in PTU-treated mice. These data indicate that mild perinatal hypothyroidism causes cognitive disorders in adult offspring. Such disorders may be partially induced secondary to decreased concentrations of neurotransmitters and receptor expression.