Early-life stress induces the development of Alzheimer's disease pathology via angiopathy

Anethole via increase in the gene expression of PI3K/AKT/mTOR mitigates the autistic-like behaviors induced by maternal separation stress in mice

Autism spectrum disorder (ASD) is a neurodegenerative disease with increasing incidence in the world. The maternal separation (MS) stress at early life with its own neuroendocrine and neurostructural changes can provide the basis for development of ASD. Previously it has been reported neuroprotective characteristics for anethole. The PI3K/AKT/mTOR signaling pathway has pivotal role in the function of central nervous system (CNS). This study aimed to evaluate the possible effects of anethole on the autistic-like behaviors in the maternally separated (MS) mice focusing on the potential role of the PI3K/AKT/mTOR pathway. Forty male Naval Medical Research Institute (NMRI) mice were assigned to five groups (n = 8) comprising a control group (treated with normal saline) and four groups subjected to MS and treated with normal saline and or anethole at doses of 31.25, 62.5 and 125 mg/kg, respectively. All gents were administrated via intraperitoneal (i.p.) route for 14 constant days. Behavioral tests were conducted, including the three-chamber test, shuttle box and resident-intruder test. The gene expression of the PI3K, AKT and mTOR assessed in the hippocampus by qRT-PCR. Findings indicated that MS is associated with autistic-like behaviors. Anethole increased the sociability and social preference indexes in the three-chamber test, increased duration of secondary latency in the shuttle box test and decreased aggressive behaviors in the resident-intruder test. Also, anethole increased the gene expression of PI3K, AKT and mTOR in the hippocampus of MS mice. We concluded that anethole through increase in the gene expression of PI3K/ AKT/mTOR mitigated autistic-like behaviors induced by MS in mice.

Protective effects of rosmarinic acid against autistic-like behaviors in a mouse model of maternal separation stress: behavioral and molecular amendments

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with worldwide increasing incidence. Maternal separation (MS) stress at the beginning of life with its own neuroendocrine changes can provide the basis for development of ASD. Rosmarinic acid (RA) is a phenolic compound with a protective effect in neurodegenerative diseases. The aim of this study was to determine the effect of RA on autistic-like behaviors in maternally separated mice focusing on its possible effects on neuroimmune response and nitrite levels in the hippocampus. In this study, 40 mice were randomly divided into five groups of control (received normal saline (1 ml/kg)) and MS that were treated with normal saline (1 ml/kg) or doses of 1, 2, and 4 mg/kg RA, respectively, for 14 days. Three-chamber sociability, shuttle box, and marble burying tests were used to investigate autistic-like behaviors. Nitrite level and gene expression of inflammatory cytokines including TNF-α, IL-1β, TLR4, and iNOS were assessed in the hippocampus. The results showed that RA significantly increased the social preference and social novelty indexes, as well as attenuated impaired passive avoidance memory and the occurrence of repetitive and obsessive behaviors in the MS mice. RA reduced the nitrite level and gene expression of inflammatory cytokines in the hippocampus. RA, probably via attenuation of the nitrite level as well as of the neuroimmune response in the hippocampus, mitigated autistic-like behaviors in maternally separated mice.

Maternal separation stress through triggering of the neuro-immune response in the hippocampus induces autistic-like behaviors in male mice

Autism spectrum disorder (ASD) is the fastest-growing neurodevelopmental disease throughout the world. Neuro-immune responses from prenatal to adulthood stages of life induce developmental defects in synaptic signaling, neurotransmitter imbalance, and even structural changes in the brain. In this study, we aimed to focus on the possible role of neuroinflammatory response in the hippocampus in development of the autistic-like behaviors following maternal separation (MS) stress in mice. To do this, mice neonates daily separated from their mothers from postnatal day (PND) 2 to PND 14 for 3 h. During PND45-60, behavioral tests related to autistic-like behaviors including three-chamber sociability, Morris water maze (MWM), shuttle box, resident-intruder, and marble burying tests were performed. Then, hippocampi were dissected out, and the gene expression of inflammatory mediators including TNF-α, IL-1β, TLR4, HMGB1, and NLRP3 was assessed in the hippocampus using RT-PCR. Results showed that MS mice exerted impaired sociability preference, repetitive behaviors, impaired passive avoidance, and spatial memories. The gene expression of inflammatory mediators significantly increased in the hippocampi of MS mice. We concluded that MS stress probably via activating of the HMGB1/TLR4 signaling cascade in the hippocampus induced autistic-like behaviors in mice.

Neonatal stress disrupts the glymphatic system development and increases the susceptibility to Parkinson's disease in later life

INTRODUCTION

Neonatal stress disrupts brain development and increases the risk of neurological disorders later in life. However, the impact of neonatal stress on the development of the glymphatic system and susceptibility to Parkinson's disease (PD) remains largely unknown.

METHODS

Neonatal maternal deprivation (NMD) was performed on mice for 14 consecutive days to model chronic neonatal stress. Adeno-associated virus expressing A53T-α-synuclein (α-syn) was injected into the substantia nigra to establish PD model mice. Glymphatic activity was determined using in vivo magnetic resonance imaging, ex vivo fluorescence imaging and microplate assay. The transcription and expression of aquaporin-4 (AQP4) and other molecules were evaluated by qPCR, western blotting, and immunofluorescence. Animal's responses to NMD and α-syn overexpression were observed using behavioral tests.

RESULTS

Glymphatic activity was impaired in adult NMD mice. AQP4 polarization and platelet-derived growth factor B (PDGF-B) signaling were reduced in the frontal cortex and hippocampus of both young and adult NMD mice. Furthermore, exogenous α-syn accumulation was increased and PD-like symptoms were aggravated in adult NMD mice.

CONCLUSION

The results demonstrated that NMD could disrupt the development of the glymphatic system through PDGF-B signaling and increase the risk of PD later in life, indicating that alleviating neonatal stress could be beneficial in protecting the glymphatic system and reducing susceptibility to neurodegeneration.

Early life stress lastingly alters the function and AMPA-receptor composition of glutamatergic synapses in the hippocampus of male mice

Early postnatal life is a sensitive period of development that shapes brain structure and function later in life. Exposure to stress during this critical time window can alter brain development and may enhance the susceptibility to psychopathology and neurodegenerative disorders later in life. The developmental effects of early life stress (ELS) on synaptic function are not fully understood, but could provide mechanistic insights into how ELS modifies later brain function and disease risk. We here assessed the effects of ELS on synaptic function and composition in the hippocampus of male mice. Mice were subjected to ELS by housing dams and pups with limited bedding and nesting material from postnatal days (P) 2-9. Synaptic strength was measured in terms of miniature excitatory postsynaptic currents (mEPSCs) in the hippocampal dentate gyrus at three different developmental stages: the early postnatal phase (P9), preadolescence (P21, at weaning) and adulthood at 3 months of age (3MO). Hippocampal synaptosome fractions were isolated from P9 and 3MO tissue and analyzed for protein content to assess postsynaptic composition. Finally, dendritic spine density was assessed in the DG at 3MO. At P9, ELS increased mEPSC frequency and amplitude. In parallel, synaptic composition was altered as PSD-95, GluA3 and GluN2B content were significantly decreased. The increased mEPSC frequency was sustained up to 3MO, at which age, GluA3 content was significantly increased. No differences were found in dendritic spine density. These findings highlight how ELS affects the development of hippocampal synapses, which could provide valuable insight into mechanisms how ELS alters brain function later in life.

Possible role of NO/NMDA pathway in the autistic-like behaviors induced by maternal separation stress in mice

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder. Maternal separation (MS) stress is an established model of early-life stress associated with autistic-like behaviors. Altered glutamatergic and nitrergic neurotransmissions may contribute to the pathophysiology of ASD. However, the specific mechanisms underlying these alterations and their relationship to MS-induced autistic-like behaviors remain unclear. Addressing this knowledge gap, this study aims to elucidate the involvement of the nitric oxide (NO)/ N-methyl-D-aspartate (NMDA) pathway in MS-induced autistic-like behaviors in mice. This knowledge has the potential to guide future research, potentially leading to the development of targeted interventions or treatments aimed at modulating the NO/NMDA pathway to ameliorate ASD symptoms. Ninety male Naval Medical Research Institute (NMRI) mice were assigned to six groups (n = 15) comprising a control group (treated with saline) and five groups subjected to MS and treated with saline, ketamine, NMDA, L-NAME, and L-arginine. Behavioral tests were conducted, including the three-chamber test, shuttle box, elevated plus-maze, and marble burying test. Gene expression of iNOS, nNOS, and NMDA-R subunits (NR2A and NR2B), along with nitrite levels, was evaluated in the hippocampus. The findings demonstrated that MS induced autistic-like behaviors, accompanied by increased gene expression of iNOS, nNOS, NR2B, NR2A, and elevated nitrite levels in the hippocampus. Modulation of the NO/NMDA pathway with activators and inhibitors altered the effects of MS. These results suggest that the NO/NMDA pathway plays a role in mediating the negative effects of MS and potentially contributes to the development of autistic-like behaviors in maternally separated mice.

Parvalbumin as a sex-specific target in Alzheimer's disease research - A mini-review

Alzheimer's disease (AD) is the most common form of dementia, and both the incidence of this disease and its associated cognitive decline disproportionally effect women. While the etiology of AD is unknown, recent work has demonstrated that the balance of excitatory and inhibitory activity across the brain may serve as a strong predictor of cognitive impairments in AD. Across the cortex, the most prominent source of inhibitory signalling is from a class of parvalbumin-expressing interneurons (PV+). In this mini-review, the impacts of sex- and age-related factors on the function of PV+ neurons are examined within the context of vulnerability to AD pathology. These primary factors of influence include changes in brain metabolism, circulating sex hormone levels, and inflammatory response. In addition to positing the increased vulnerability of PV+ neurons to dysfunction in AD, this mini-review highlights the critical importance of presenting sex stratified data in the study of AD.

Life Experience Matters: Enrichment and Stress Can Influence the Likelihood of Developing Alzheimer's Disease via Gut Microbiome

Alzheimer's disease (AD) is a chronic neurodegenerative disease, characterized by the presence of β-amyloid (Aβ) plaques and neurofibrillary tangles (NFTs) formed from abnormally phosphorylated tau proteins (ptau). To date, there is no cure for AD. Earlier therapeutic efforts have focused on the clinical stages of AD. Despite paramount efforts and costs, pharmaceutical interventions including antibody therapies targeting Aβ have largely failed. This highlights the need to alternate treatment strategies and a shift of focus to early pre-clinical stages. Approximately 25-40% of AD cases can be attributed to environmental factors including chronic stress. Gut dysbiosis has been associated with stress and the pathogenesis of AD and can increase both Aβ and NFTs in animal models of the disease. Both stress and enrichment have been shown to alter AD progression and gut health. Targeting stress-induced gut dysbiosis through probiotic supplementation could provide a promising intervention to delay disease progression. In this review, we discuss the effects of stress, enrichment, and gut dysbiosis in AD models and the promising evidence from probiotic intervention studies.

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.

Understanding the relationships between physiological and psychosocial stress, cortisol and cognition

Stress is viewed as a state of real or perceived threat to homeostasis, the management of which involves the endocrine, nervous, and immune systems. These systems work independently and interactively as part of the stress response. The scientific stress literature, which spans both animal and human studies, contains heterogeneous findings about the effects of stress on the brain and the body. This review seeks to summarise and integrate literature on the relationships between these systems, examining particularly the roles of physiological and psychosocial stress, the stress hormone cortisol, as controlled by the hypothalamic-pituitary-adrenal (HPA) axis, and the effects of stress on cognitive functioning. Health conditions related to impaired HPA axis functioning and their associated neuropsychiatric symptoms will also be considered. Lastly, this review will provide suggestions of clinical applicability for endocrinologists who are uniquely placed to measure outcomes related to endocrine, nervous and immune system functioning and identify areas of intervention.

A Novel Early Life Stress Model Affects Brain Development and Behavior in Mice

Early life stress (ELS) in developing children has been linked to physical and psychological sequelae in adulthood. In the present study, we investigated the effects of ELS on brain and behavioral development by establishing a novel ELS model that combined the maternal separation paradigm and mesh platform condition. We found that the novel ELS model caused anxiety- and depression-like behaviors and induced social deficits and memory impairment in the offspring of mice. In particular, the novel ELS model induced more enhanced depression-like behavior and memory impairment than the maternal separation model, which is the established ELS model. Furthermore, the novel ELS caused upregulation of arginine vasopressin expression and downregulation of GABAergic interneuron markers, such as parvalbumin (PV), vasoactive intestinal peptide, and calbindin-D_28k (CaBP-28k), in the brains of the mice. Finally, the offspring in the novel ELS model showed a decreased number of cortical PV-, CaBP-28k-positive cells and an increased number of cortical ionized calcium-binding adaptors-positive cells in their brains compared to mice in the established ELS model. Collectively, these results indicated that the novel ELS model induced more negative effects on brain and behavioral development than the established ELS model.

Early-life stress and dietary fatty acids impact the brain lipid/oxylipin profile into adulthood, basally and in response to LPS

Brain lipid dysregulation is a hallmark of depression and Alzheimer's disease, also marked by chronic inflammation. Early-life stress (ELS) and dietary intake of polyunsaturated fatty acids (PUFAs) are risk factors for these pathologies and are known to impact inflammatory processes. However, if these early-life factors alter brain lipid homeostasis on the long-term and thereby contribute to this risk remains to be elucidated. We have recently shown that an early diet enriched in omega(ω)-3 PUFAs protected against the long-term negative effects of ELS on cognition and neuroinflammation. Here, we aim to understand if modulation of brain lipid and oxylipin profiles contributes to the detrimental effects of ELS and the protective ones of the diet. We therefore studied if and how ELS and early dietary PUFAs modulate the brain lipid and oxylipin profile, basally as well as in response to an inflammatory challenge, to unmask possible latent effects. Male mice were exposed to ELS via the limited bedding and nesting paradigm, received an early diet with high or low ω6/ω3 ratio (HRD and LRD) and were injected with saline or lipopolysaccharide (LPS) in adulthood. Twenty-four hours later plasma cytokines (Multiplex) and hypothalamic lipids and oxylipins (liquid chromatography tandem mass spectrometry) were measured. ELS exacerbated the LPS-induced increase in IL-6, CXCL1 and CCL2. Both ELS and diet affected the lipid/oxylipin profile long-term. For example, ELS increased diacylglycerol and LRD reduced triacylglycerol, free fatty acids and ceramides. Importantly, the ELS-induced alterations were strongly influenced by the early diet. For example, the ELS-induced decrease in eicosapentaenoic acid was reversed when fed LRD. Similarly, the majority of the LPS-induced alterations were distinct for control and ELS exposed mice and unique for mice fed with LRD or HRD. LPS decreased ceramides and lysophosphotidylcholine, increased hexosylceramides and prostaglandin E₂, reduced triacylglycerol species and ω6-derived oxylipins only in mice fed LRD and ELS reduced the LPS-induced increase in phosphatidylcholine. These data give further insights into the alterations in brain lipids and oxylipins that might contribute to the detrimental effects of ELS, to the protective ones of LRD and the possible early-origin of brain lipid dyshomeostasis characterizing ELS-related psychopathologies.

Immune-vascular mural cell interactions: consequences for immune cell trafficking, cerebral blood flow, and the blood-brain barrier

Brain barriers are crucial sites for cerebral energy supply, waste removal, immune cell migration, and solute exchange, all of which maintain an appropriate environment for neuronal activity. At the capillary level, where the largest area of brain-vascular interface occurs, pericytes adjust cerebral blood flow (CBF) by regulating capillary diameter and maintain the blood-brain barrier (BBB) by suppressing endothelial cell (EC) transcytosis and inducing tight junction expression between ECs. Pericytes also limit the infiltration of circulating leukocytes into the brain where resident microglia confine brain injury and provide the first line of defence against invading pathogens. Brain "waste" is cleared across the BBB into the blood, phagocytosed by microglia and astrocytes, or removed by the flow of cerebrospinal fluid (CSF) through perivascular routes-a process driven by respiratory motion and the pulsation of the heart, arteriolar smooth muscle, and possibly pericytes. "Dirty" CSF exits the brain and is probably drained around olfactory nerve rootlets and via the dural meningeal lymphatic vessels and possibly the skull bone marrow. The brain is widely regarded as an immune-privileged organ because it is accessible to few antigen-primed leukocytes. Leukocytes enter the brain via the meninges, the BBB, and the blood-CSF barrier. Advances in genetic and imaging tools have revealed that neurological diseases significantly alter immune-brain barrier interactions in at least three ways: (1) the brain's immune-privileged status is compromised when pericytes are lost or lymphatic vessels are dysregulated; (2) immune cells release vasoactive molecules to regulate CBF, modulate arteriole stiffness, and can plug and eliminate capillaries which impairs CBF and possibly waste clearance; and (3) immune-vascular interactions can make the BBB leaky via multiple mechanisms, thus aggravating the influx of undesirable substances and cells. Here, we review developments in these three areas and briefly discuss potential therapeutic avenues for restoring brain barrier functions.

Early-life stress elicits peripheral and brain immune activation differently in wild type and 5xFAD mice in a sex-specific manner

BACKGROUND

The risk of developing Alzheimer's disease (AD) is modulated by genetic and environmental factors. Early-life stress (ELS) exposure during critical periods of brain development can impact later brain function and health, including increasing the risk of developing AD. Microglial dysfunction and neuroinflammation have been implicated as playing a role in AD pathology and may be modulated by ELS. To complicate matters further, sex-specific effects have been noted in response to ELS and in the incidence and progression of AD.

METHODS

Here, we subjected male and female mice with either a wild type or 5xFAD familial AD-model background to maternal separation (MS) from postnatal day 2 to 14 to induce ELS.

RESULTS

We detected hippocampal neuroinflammatory alterations already at postnatal day 15. By 4 months of age, MS mice presented increased immobility time in the forced swim test and a lower discrimination index in the novel object recognition memory test compared to controls. We found altered Bdnf and Arc expression in the hippocampus and increased microglial activation in the prefrontal cortex due to MS in a sex-dependent manner. In 5xFAD mice specifically, MS exacerbated amyloid-beta deposition, particularly in females. In the periphery, the immune cell population was altered by MS exposure.

CONCLUSION

Overall, our results demonstrate that MS has both short- and long-term effects on brain regions related to memory and on the inflammatory system, both in the brain and periphery. These ELS-related effects that are detectable even in adulthood may exacerbate pathology and increase the risk of developing AD via sex-specific mechanisms.

Early Life Stress and Brain Plasticity: From Alterations of Brain Morphology to Development of Psychopathology

Advances in our understanding of the genetics of mental disorders (MD) have contributed to a better understanding of their pathophysiology. Nonetheless, several questions and doubts remain. Recent research has focused on the role of the environment in developing mental disorders, and the advent of neuroscientific methodologies has opened up new avenues of inquiry. However, the mechanism by which childhood stress affects neurodevelopment via mechanisms, such as gene-environment interactions and epigenetic regulation leading to diseases in adulthood, is unclear. This paper aims to review the evidence on the role of early life stress and parental psychopathology in the pathophysiology and clinical expression of MD. Methodology: The study will conduct a comprehensive systematic review using medical search terms (MeSH). Electronic searches for published studies will be performed using the MEDLINE (PubMed), EMBASE, Scopus, PsychINFO, Web of Science, and Google Scholar databases. We will look for research on the neuroplasticity effects of early life stress on development and review articles that evaluate cognitive functions and the development of psychopathology and MD. Before identifying full-text articles, several studies will be filtered based on titles, abstracts, keywords, and synonyms. Publications to be included in the review will be assessed for quality and consistency before inclusion. Data will be extracted independently and duplicated by two authors from each eligible study to ensure consistency between reviews. All databases will be searched from inception until July 2021 and will be limited to human studies. The search will be limited only to publication in the English language and any publication that can be converted to English. Discussion and Conclusions: The findings of this review will meticulously articulate the effects of childhood adversity, such as ELS and parental psychopathology on cognitive development and neuroplasticity.

Early Life Stress and Metabolic Plasticity of Brain Cells: Impact on Neurogenesis and Angiogenesis

Early life stress (ELS) causes long-lasting changes in brain plasticity induced by the exposure to stress factors acting prenatally or in the early postnatal ontogenesis due to hyperactivation of hypothalamic-pituitary-adrenal axis and sympathetic nervous system, development of neuroinflammation, aberrant neurogenesis and angiogenesis, and significant alterations in brain metabolism that lead to neurological deficits and higher susceptibility to development of brain disorders later in the life. As a key component of complex pathogenesis, ELS-mediated changes in brain metabolism associate with development of mitochondrial dysfunction, loss of appropriate mitochondria quality control and mitochondrial dynamics, deregulation of metabolic reprogramming. These mechanisms are particularly critical for maintaining the pool and development of brain cells within neurogenic and angiogenic niches. In this review, we focus on brain mitochondria and energy metabolism related to tightly coupled neurogenic and angiogenic events in healthy and ELS-affected brain, and new opportunities to develop efficient therapeutic strategies aimed to restore brain metabolism and reduce ELS-induced impairments of brain plasticity.

Alzheimer's Disease Animal Models: Elucidation of Biomarkers and Therapeutic Approaches for Cognitive Impairment

Alzheimer’s disease (AD) is an age-related and progressive neurodegenerative disorder. It is widely accepted that AD is mainly caused by the accumulation of extracellular amyloid β (Aβ) and intracellular neurofibrillary tau tangles. Aβ begins to accumulate years before the onset of cognitive impairment, suggesting that the benefit of currently available interventions would be greater if they were initiated in the early phases of AD. To understand the mechanisms of AD pathogenesis, various transgenic mouse models with an accelerated accumulation of Aβ and tau tangles have been developed. However, none of these models exhibit all pathologies present in human AD. To overcome these undesirable phenotypes, APP knock-in mice, which were presented with touchscreen-based tasks, were developed to better evaluate the efficacy of candidate therapeutics in mouse models of early-stage AD. This review assesses several AD mouse models from the aspect of biomarkers and cognitive impairment and discusses their potential as tools to provide novel AD therapeutic approaches.