The amyloidogenic potential and behavioral correlates of stress

Exploring the Significance of Microglial Phenotypes and Morphological Diversity in Neuroinflammation and Neurodegenerative Diseases: From Mechanisms to Potential Therapeutic Targets

Studying various microglial phenotypes and their functions in neurodegenerative diseases is crucial due to the intricate nature of their phenomics and their vital immunological role. Microglia undergo substantial phenomic changes, encompassing morphological, transcriptional, and functional aspects, resulting in distinct cell types with diverse structures, functions, properties, and implications. The traditional classification of microglia as ramified, M1 (proinflammatory), or M2 (anti-inflammatory) phenotypes is overly simplistic, failing to capture the wide range of recently identified microglial phenotypes in various brain regions affected by neurodegenerative diseases. Altered and activated microglial phenotypes deviating from the typical ramified structure are significant features of many neurodegenerative conditions. Understanding the precise role of each microglial phenotype is intricate and sometimes contradictory. This review specifically focuses on elucidating recent modifications in microglial phenotypes within neurodegenerative diseases. Recognizing the heterogeneity of microglial phenotypes in diseased states can unveil novel therapeutic strategies for targeting microglia in neurodegenerative diseases. Moreover, the exploration of the use of healthy isolated microglia to mitigate disease progression has provided an innovative perspective. In conclusion, this review discusses the dynamic landscape of mysterious microglial phenotypes, emphasizing the need for a nuanced understanding to pave the way for innovative therapeutic strategies for neurodegenerative diseases.

Transcutaneous vagus nerve stimulation: a new strategy for Alzheimer's disease intervention through the brain-gut-microbiota axis?

Transcutaneous vagus nerve stimulation (tVNS) is an emerging non-invasive technique designed to stimulate branches of the vagus nerve distributed over the body surface. Studies suggest a correlation between the brain-gut-microbiota (BGM) axis and the pathogenesis of Alzheimer's disease (AD). The BGM axis represents a complex bidirectional communication system, with the vagus nerve being a crucial component. Therefore, non-invasive electrical stimulation of the vagus nerve might have the potential to modify-most of the time probably in a non-physiological way-the signal transmission within the BGM axis, potentially influencing the progression or symptoms of AD. This review explores the interaction between percutaneous vagus nerve stimulation and the BGM axis, emphasizing its potential effects on AD. It examines various aspects, such as specific brain regions, gut microbiota composition, maintenance of intestinal environmental homeostasis, inflammatory responses, brain plasticity, and hypothalamic-pituitary-adrenal (HPA) axis regulation. The review suggests that tVNS could serve as an effective strategy to modulate the BGM axis and potentially intervene in the progression or treatment of Alzheimer's disease in the future.

Effects of early tooth loss on chronic stress and progression of neuropathogenesis of Alzheimer's disease in adult Alzheimer's model AppNL-G-F mice

Introduction

Alzheimer's disease (AD), the most common neurodegenerative disease, is characterized by accumulated amyloid-β (Aβ) plaques, aggregated phosphorylated tau protein, gliosis-associated neuroinflammation, synaptic dysfunction, and cognitive impairment. Many cohort studies indicate that tooth loss is a risk factor for AD. The detailed mechanisms underlying the association between AD and tooth loss, however, are not yet fully understood.

Methods

We explored the involvement of early tooth loss in the neuropathogenesis of the adult AppNL-G-F mouse AD model. The maxillary molars were extracted bilaterally in 1-month-old male mice soon after tooth eruption.

Results

Plasma corticosterone levels were increased and spatial learning memory was impaired in these mice at 6 months of age. The cerebral cortex and hippocampus of AD mice with extracted teeth showed an increased accumulation of Aβ plaques and phosphorylated tau proteins, and increased secretion of the proinflammatory cytokines, including interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α), accompanied by an increased number of microglia and astrocytes, and decreased synaptophysin expression. AD mice with extracted teeth also had a shorter lifespan than the control mice.

Discussion

These findings revealed that long-term tooth loss is a chronic stressor, activating the recruitment of microglia and astrocytes; exacerbating neuroinflammation, Aβ deposition, phosphorylated tau accumulation, and synaptic dysfunction; and leading to spatial learning and memory impairments in AD model mice.

Sex Differences in Stress Response: Classical Mechanisms and Beyond

Neuropsychiatric disorders, which are associated with stress hormone dysregulation, occur at different rates in men and women. Moreover, nowadays, preclinical and clinical evidence demonstrates that sex and gender can lead to differences in stress responses that predispose males and females to different expressions of similar pathologies. In this curated review, we focus on what is known about sex differences in classic mechanisms of stress response, such as glucocorticoid hormones and corticotrophin-releasing factor (CRF), which are components of the hypothalamicpituitary- adrenal (HPA) axis. Then, we present sex differences in neurotransmitter levels, such as serotonin, dopamine, glutamate and GABA, as well as indices of neurodegeneration, such as amyloid β and Tau. Gonadal hormone effects, such as estrogens and testosterone, are also discussed throughout the review. We also review in detail preclinical data investigating sex differences caused by recentlyrecognized regulators of stress and disease, such as the immune system, genetic and epigenetic mechanisms, as well neurosteroids. Finally, we discuss how understanding sex differences in stress responses, as well as in pharmacology, can be leveraged into novel, more efficacious therapeutics for all. Based on the supporting evidence, it is obvious that incorporating sex as a biological variable into preclinical research is imperative for the understanding and treatment of stress-related neuropsychiatric disorders, such as depression, anxiety and Alzheimer's disease.

The Role of Insulin-like Growth Factor I in Mechanisms of Resilience and Vulnerability to Sporadic Alzheimer's Disease

Despite decades of intense research, disease-modifying therapeutic approaches for Alzheimer's disease (AD) are still very much needed. Apart from the extensively analyzed tau and amyloid pathological cascades, two promising avenues of research that may eventually identify new druggable targets for AD are based on a better understanding of the mechanisms of resilience and vulnerability to this condition. We argue that insulin-like growth factor I (IGF-I) activity in the brain provides a common substrate for the mechanisms of resilience and vulnerability to AD. We postulate that preserved brain IGF-I activity contributes to resilience to AD pathology as this growth factor intervenes in all the major pathological cascades considered to be involved in AD, including metabolic impairment, altered proteostasis, and inflammation, to name the three that are considered to be the most important ones. Conversely, disturbed IGF-I activity is found in many AD risk factors, such as old age, type 2 diabetes, imbalanced diet, sedentary life, sociality, stroke, stress, and low education, whereas the Apolipoprotein (Apo) E4 genotype and traumatic brain injury may also be influenced by brain IGF-I activity. Accordingly, IGF-I activity should be taken into consideration when analyzing these processes, while its preservation will predictably help prevent the progress of AD pathology. Thus, we need to define IGF-I activity in all these conditions and develop a means to preserve it. However, defining brain IGF-I activity cannot be solely based on humoral or tissue levels of this neurotrophic factor, and new functionally based assessments need to be developed.

Krill oil treatment ameliorates lipid metabolism imbalance in chronic unpredicted mild stress-induced depression-like behavior in mice

The pathology of depression involves various factors including the interaction between genes and the environment. The deficiency of n-3 polyunsaturated fatty acids (n-3 PUFAs) in the brain and depressive symptoms are closely related. Krill oil contains abundant amounts of n-3 PUFAs incorporated in phosphatidylcholine. However, the effect of krill oil treatment on depression-like behaviors induced by chronic stress and its molecular mechanism in the brain remain poorly understood. Here, we used a chronic unpredictable mild stress (CUMS) model to evaluate the effect of krill oil on depression-like behaviors and explored its molecular mechanism through lipid metabolomics and mRNA profiles in the whole brain. We observed that CUMS-induced depression-like behaviors were ameliorated by krill oil supplementation in mice. The metabolism of glycerophospholipids and sphingolipids was disrupted by CUMS treatment, which were ameliorated after krill oil supplementation. Further analysis found that differently expressed genes after krill oil supplementation were mainly enriched in the membrane structures and neuroactive ligand-receptor interaction pathway, which may be responsible for the amelioration of CUMS-induced depression-like behaviors. Altogether, our results uncovered the relationship between lipid metabolism and CUMS, and provided new strategies for the prevention and treatment of depression.

Chronic Stress, Depression, and Alzheimer's Disease: The Triangle of Oblivion

Chronic stress and high levels of the main stress hormones, and glucocorticoids (GC), are implicated in susceptibility to brain pathologies such as depression and Alzheimer's disease (AD), as they promote neural plasticity damage and glial reactivity, which can lead to dendritic/synaptic loss, reduced neurogenesis, mood deficits, and impaired cognition. Moreover, depression is implicated in the development of AD with chronic stress being a potential link between both disorders via common neurobiological underpinnings. Hereby, we summarize and discuss the clinical and preclinical evidence related to the detrimental effect of chronic stress as a precipitator of AD through the activation of pathological mechanisms leading to the accumulation of amyloid β (Aβ) and Tau protein. Given that the modern lifestyle increasingly exposes individuals to high stress loads, it is clear that understanding the mechanistic link(s) between chronic stress, depression, and AD pathogenesis may facilitate the treatment of AD and other stress-related disorders.

Posttraumatic Stress and Traumatic Brain Injury: Cognition, Behavior, and Neuroimaging Markers in Vietnam Veterans

BACKGROUND

Posttraumatic stress disorder (PTSD) and traumatic brain injury (TBI) are common in Veterans and linked to behavioral disturbances, increased risk of cognitive decline, and Alzheimer's disease.

OBJECTIVE

We studied the synergistic effects of PTSD and TBI on behavioral, cognitive, and neuroimaging measures in Vietnam war Veterans.

METHODS

Data were acquired at baseline and after about one-year from male Veterans categorized into: PTSD, TBI, PTSD+TBI, and Veteran controls without PTSD or TBI. We applied manual tractography to examine white matter microstructure of three fiber tracts: uncinate fasciculus (N = 91), cingulum (N = 87), and inferior longitudinal fasciculus (N = 95). ANCOVAs were used to compare Veterans' baseline behavioral and cognitive functioning (N = 285), white matter microstructure, amyloid-β (N = 230), and tau PET (N = 120). Additional ANCOVAs examined scores' differences from baseline to follow-up.

RESULTS

Veterans with PTSD and PTSD+TBI, but not Veterans with TBI only, exhibited poorer behavioral and cognitive functioning at baseline than controls. The groups did not differ in baseline white matter, amyloid-β, or tau, nor in behavioral and cognitive functioning, and tau accumulation change. Progression of white matter abnormalities of the uncinate fasciculus in Veterans with PTSD compared to controls was observed; analyses in TBI and PTSD+TBI were not run due to insufficient sample size.

CONCLUSIONS

PTSD and PTSD+TBI negatively affect behavioral and cognitive functioning, while TBI does not contribute independently. Whether progressive decline in uncinate fasciculus microstructure in Veterans with PTSD might account for cognitive decline should be further studied. Findings did not support an association between PTSD, TBI, and Alzheimer's disease pathology based on amyloid and tau PET.

Association Between Psychological Distress and Incident Dementia in a Population-Based Cohort in Finland

IMPORTANCE

Symptoms of psychological distress have shown association with subsequent dementia, but the nature of association remains unclear.

OBJECTIVE

To examine the association of psychological distress with etiological risk of dementia and incidence of dementia in presence of competing risk of death.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study consisted of population-based cross-sectional National FINRISK Study surveys collected in 1972, 1977, 1982, 1987, 1992, 1997, 2002, and 2007 in Finland with register-based follow-up; and the cohort was linked to Finnish Health Register data for dementia and mortality for each participant until December 31, 2017. Participants included individuals without dementia who had complete exposure data. Data were analyzed from May 2019 to April 2022.

EXPOSURES

Self-reported symptoms of psychological distress: stress (more than other people), depressive mood, exhaustion, and nervousness (often, sometimes, never).

MAIN OUTCOMES AND MEASURES

Incident all-cause dementia, ascertained through linkage to national health registers. Poisson cause-specific hazard model (emphasizing etiological risk) and Fine-Gray subdistribution hazard model (emphasizing effect on incidence) considering dementia and death without dementia as competing risks. Covariates of age, sex, baseline year, follow-up time, educational level, body mass index, smoking, diabetes, systolic blood pressure, cholesterol, and physical activity. Sensitivity analysis was performed to reduce reverse causation bias by excluding individuals with follow-up less than 10 years.

RESULTS

Among 67 688 participants (34 968 [51.7%] women; age range, 25 to 74 years; mean [SD] age, 45.4 years), 7935 received a diagnosis of dementia over a mean follow-up of 25.4 years (range, 10 to 45 years). Psychological distress was significantly associated with all-cause dementia in a multivariable Poisson model, with incidence rate ratios from 1.17 (95% CI, 1.08-1.26) for exhaustion to 1.24 (95% CI, 1.11-1.38) for stress, and remained significant in sensitivity analyses. A Fine-Gray model showed significant associations (with hazard ratios from 1.08 [95% CI, 1.01-1.17] for exhaustion to 1.12 [95% CI, 1.00-1.25] for stress) for symptoms other than depressive mood (hazard ratio, 1.08 [95% CI, 0.98-1.20]). All the symptoms showed significant associations with competing risk of death in both models.

CONCLUSIONS AND RELEVANCE

In this cohort study, psychological distress symptoms were significantly associated with increased risk of all-cause dementia in the model emphasizing etiological risk. Associations with real incidence of dementia were diminished by the competing risk of death.

Targeting the cannabinoid system to counteract the deleterious effects of stress in Alzheimer’s disease

Alzheimer’s disease is a progressive neurodegenerative disorder characterized histologically in postmortem human brains by the presence of dense protein accumulations known as amyloid plaques and tau tangles. Plaques and tangles develop over decades of aberrant protein processing, post-translational modification, and misfolding throughout an individual’s lifetime. We present a foundation of evidence from the literature that suggests chronic stress is associated with increased disease severity in Alzheimer’s patient populations. Taken together with preclinical evidence that chronic stress signaling can precipitate cellular distress, we argue that chronic psychological stress renders select circuits more vulnerable to amyloid- and tau- related abnormalities. We discuss the ongoing investigation of systemic and cellular processes that maintain the integrity of protein homeostasis in health and in degenerative conditions such as Alzheimer’s disease that have revealed multiple potential therapeutic avenues. For example, the endogenous cannabinoid system traverses the central and peripheral neural systems while simultaneously exerting anti-inflammatory influence over the immune response in the brain and throughout the body. Moreover, the cannabinoid system converges on several stress-integrative neuronal circuits and critical regions of the hypothalamic-pituitary-adrenal axis, with the capacity to dampen responses to psychological and cellular stress. Targeting the cannabinoid system by influencing endogenous processes or exogenously stimulating cannabinoid receptors with natural or synthetic cannabis compounds has been identified as a promising route for Alzheimer’s Disease intervention. We build on our foundational framework focusing on the significance of chronic psychological and cellular stress on the development of Alzheimer’s neuropathology by integrating literature on cannabinoid function and dysfunction within Alzheimer’s Disease and conclude with remarks on optimal strategies for treatment potential.

Rab35 and glucocorticoids regulate APP and BACE1 trafficking to modulate Aβ production

Chronic stress and elevated glucocorticoids (GCs), the major stress hormones, are risk factors for Alzheimer’s disease (AD) and promote AD pathomechanisms, including overproduction of toxic amyloid-β (Aβ) peptides and intraneuronal accumulation of hyperphosphorylated Tau protein. The latter is linked to downregulation of the small GTPase Rab35, which mediates Tau degradation via the endolysosomal pathway. Whether Rab35 is also involved in Aβ overproduction remains an open question. Here, we find that hippocampal Rab35 levels are decreased not only by stress/GC but also by aging, another AD risk factor. Moreover, we show that Rab35 negatively regulates Aβ production by sorting amyloid precursor protein (APP) and β-secretase (BACE1) out of the endosomal network, where they interact to produce Aβ. Interestingly, Rab35 coordinates distinct intracellular trafficking steps for BACE1 and APP, mediated by its effectors OCRL and ACAP2, respectively. Finally, we demonstrate that Rab35 overexpression prevents the amyloidogenic trafficking of APP and BACE1 induced by high GC levels. These studies identify Rab35 as a key regulator of APP processing and suggest that its downregulation may contribute to stress-related and AD-related amyloidogenesis.

Hesperidin Preserves Cognitive Functions and Hippocampus Histological Architecture in Albino Wistar Rats Subjected to Stress Through Enhancement of Brain-Derived Neurotrophic Factor

Hesperidin (HSD) is a natural compound with antioxidant potential. On the other hand, chronic stress had been linked to impaired cognitive functions as it affects many neurotransmitters and brain regions such as the hippocampus. The current study was conducted to examine the effect of HSD on learning and memory after chronic mild stress. Albino Wistar rats were subjected to chronic mild stress with HSD administered as supplements. HSD was found to decrease hippocampal amyloid beta and malondialdehyde levels, in addition, to preserve cognitive functions together with preserving hippocampus histological architecture. In conclusion, the present study sheds the light on the potential of HSD to ameliorate the deleterious effects of chronic mild stress on cognitive functions through brain-derived neurotrophic factor enhancement and reduction in Aβ formation in addition to activation of the antioxidant pathway.

Inhibition of 11β-HSD1 Ameliorates Cognition and Molecular Detrimental Changes after Chronic Mild Stress in SAMP8 Mice

Impaired glucocorticoid (GC) signaling is a significant factor in aging, stress, and neurodegenerative diseases such as Alzheimer's disease. Therefore, the study of GC-mediated stress responses to chronic moderately stressful situations, which occur in daily life, is of huge interest for the design of pharmacological strategies toward the prevention of neurodegeneration. To address this issue, SAMP8 mice were exposed to the chronic mild stress (CMS) paradigm for 4 weeks and treated with RL-118, an 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) inhibitor. The inhibition of this enzyme is linked with a reduction in GC levels and cognitive improvement, while CMS exposure has been associated with reduced cognitive performance. The aim of this project was to assess whether RL-118 treatment could reverse the deleterious effects of CMS on cognition and behavioral abilities and to evaluate the molecular mechanisms that compromise healthy aging in SAMP8 mice. First, we confirmed the target engagement between RL-118 and 11β-HSD1. Additionally, we showed that DNA methylation, hydroxymethylation, and histone phosphorylation were decreased by CMS induction, and increased by RL-118 treatment. In addition, CMS exposure caused the accumulation of reactive oxygen species (ROS)-induced damage and increased pro-oxidant enzymes-as well as pro-inflammatory mediators-through the NF-κB pathway and astrogliosis markers, such as GFAP. Of note, these modifications were reversed by 11β-HSD1 inhibition. Remarkably, although CMS altered mTORC1 signaling, autophagy was increased in the SAMP8 RL-118-treated mice. We also showed an increase in amyloidogenic processes and a decrease in synaptic plasticity and neuronal remodeling markers in mice under CMS, which were consequently modified by RL-118 treatment. In conclusion, 11β-HSD1 inhibition through RL-118 ameliorated the detrimental effects induced by CMS, including epigenetic and cognitive disturbances, indicating that GC-excess attenuation shows potential as a therapeutic strategy for age-related cognitive decline and AD.

Allosteric modulation of AMPA receptors counteracts Tau-related excitotoxic synaptic signaling and memory deficits in stress- and Aβ-evoked hippocampal pathology

Despite considerable progress in the understanding of its neuropathology, Alzheimer's disease (AD) remains a complex disorder with no effective treatment that counteracts the memory deficits and the underlying synaptic malfunction triggered by the accumulation of amyloid beta (Aβ) and Tau protein. Mounting evidence supports a precipitating role for chronic environmental stress and glutamatergic excitotoxicity in AD, suggesting that targeting of glutamate receptor signaling may be a promising approach against both stress and AD pathologies. In light of the limited cognitive benefit of the direct antagonism of NMDA receptors in AD, we here focus on an alternative way to modify glutamatergic signaling through positive allosteric modulation of AMPA receptors, by the use of a PAM-AMPA compound. Using non-transgenic animal model of Aβ oligomer injection as well as the combined stress and Aβ i.c.v. infusion, we demonstrate that positive allosteric modulation of AMPA receptors by PAM-AMPA treatment reverted memory, but not mood, deficits. Furthermore, PAM-AMPA treatment reverted stress/Aβ-driven synaptic missorting of Tau and associated Fyn/GluN2B-driven excitotoxic synaptic signaling accompanied by recovery of neurotransmitter levels in the hippocampus. Our findings suggest that positive allosteric modulation of AMPA receptors restores synaptic integrity and cognitive performance in stress- and Aβ-evoked hippocampal pathology. As the prevalence of AD is increasing at an alarming rate, novel therapeutic targeting of glutamatergic signaling should be further explored against the early stages of AD synaptic malfunction with the goal of attenuating further synaptic damage before it becomes irreversible.

Vitamin D3 administration prevents memory deficit and alteration of biochemical parameters induced by unpredictable chronic mild stress in rats

The present study aimed to investigate the effects of vitamin D3 (Vit D) administration on memory function, hippocampal level of amyloid-beta (Aβ), brain-derived neurotrophic factor (BDNF) and oxidative stress status in a rat model of unpredictable chronic mild stress (UCMS). Vit D was intraperitoneally administered at doses of 100, 1000, and 10,000 IU/kg. Animals were subjected to UCMS for a total period of 4 weeks. Memory function was assessed using morris water maze (MWM) and passive avoidance (PA) tests. Biochemical markers were measured to reveal the status of oxidative stress and antioxidant defense system. In addition, the levels of Aβ and BDNF were measured in hippocampal region. In the UCMS group, latency to find the platform was greater and the time spent in target quadrant (MWM test) as well as the latency to enter the dark compartment (PA test), were less than the vehicle group. Hippocampal malondialdehyde (MDA) and Aβ concentrations in the UCMS group were higher than the vehicle group. Hippocampal level of thiol and BDNF plus the activities of catalase and superoxide dismutase (SOD) were reduced in UCMS group compared to the control subjects (i.e. vehicle group). Interestingly, Vit D treatment supplementation reversed the mentioned effects of UCMS. Our findings indicated that Vit D administration improves UCMS-induced impairment of learning and memory through prevention of adverse effects on Aβ, BDNF and oxidative stress parameters.

Apolipoprotein E e4 is associated with worse self-reported neurobehavioral symptoms following uncomplicated mild traumatic brain injury in U.S. military service members

Past research has found a relationship between the apolipoprotein E (APOE) e4 allele and worse neurobehavioral functioning following mild traumatic brain injury (MTBI) in civilian populations. The purpose of this study was to examine this relationship in service members and veterans (SMVs) following MTBI. Participants were 151 SMVs (103 uncomplicated MTBI; 48 Injured Controls [IC]) prospectively enrolled in the DVBIC-TBICoE 15-Year Longitudinal TBI Study. Participants completed a battery of self-reported neurobehavioral symptom measures on average 76.2 months post-injury (SD = 31.8). APOE genotyping was undertaken using non-fasting blood samples. Participants were classified into four subgroups based on injury (MTBI vs. IC) and APOE e4 allele status (e4 present/absent). In the IC group, there were no significant differences across APOE e4 status subgroups for all measures. In the MTBI group, participants with the APOE e4 allele had significantly worse scores on measures of depression, pain, anxiety, grief, positive well-being, social participation, and resilience compared to those without the e4 allele (d = .44 to d = .69). When comparing the number of 'clinically elevated' neurobehavioral measures simultaneously, the MTBI/e4 present subgroup consistently had a higher number of elevated measures compared to the MTBI/e4 absent, IC/e4 present, and IC/e4 absent subgroups. The APOE e4 allele was associated with poorer neurobehavioral outcome in SMVs in the chronic phase of recovery following MTBI. APOE e4 could be incorporated into screening tools to predict SMVs at risk for poor long-term neurobehavioral outcome in an effort to provide early intervention to improve long-term clinical outcome.

Natural antioxidants enhance the power of physical and mental activities versus risk factors inducing progression of Alzheimer's disease in rats

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disease that is exacerbated by social isolation (SI) and protein malnutrition (PM). Antioxidants, physical and mental activities (Ph&M) can maintain cognitive functions and protect against dementia.

OBJECTIVE

To investigate the impact of Epigallocatechin-3-gallate (EGCG), Vitamin E (VE), Vitamin C (VC), and Selenium (Se), in enhancing the potential effect of Ph&M versus SI&PM as risk factors in the progression of AD in rats.

METHODS

Aluminum chloride (70 mg/kg, I.P for 5 weeks) was used to induce AD in rats that either normally fed or socially isolated and protein malnourished (SI&PM). Simultaneously, rats were weekly exposed to Ph&M either alone or in combination with EGCG (10 mg/kg, I.P), VC (400 mg/kg, P.O), VE (100 mg/kg, P.O), and Se (1 mg/kg, P.O).

RESULTS

The combination protocol of EGCG, VE, VC, and Se together with Ph&M significantly increased brain monoamines, superoxide dismutase (SOD), total antioxidant capacity (TAC) and brain-derived neurotrophic factor (BDNF) in AD, SI&PM and SI&PM/AD groups. Additionally, this regimen significantly mitigated brain acetylcholine esterase (ACHE), β-amyloid (Aβ), Tau protein, β-secretase, malondialdehyde (MDA), tumor necrosis factor-alpha (TNF-α), and Interleukin 1β (IL-1β) as well as DNA fragmentation. These biochemical findings were supported by the histopathological examinations of brain tissue.

CONCLUSION

The combination protocol of antioxidants with Ph&M activities mitigated SI&PM-induced progressive risk of AD.

Deciphering the links between psychological stress, depression, and neurocognitive decline in patients with Down syndrome

The relationships between psychological stress and cognitive functions are still to be defined despite some recent progress. Clinically, we noticed that patients with Down syndrome (DS) may develop rapid neurocognitive decline and Alzheimer's disease (AD) earlier than expected, often shortly after a traumatic life event (bereavement over the leave of a primary caregiver, an assault, modification of lifestyle, or the loss of parents). Of course, individuals with DS are naturally prone to develop AD, given the triplication of chromosome 21. However, the relatively weak intensity of the stressful event and the rapid pace of cognitive decline after stress in these patients have to be noticed. It seems DS patients react to stress in a similar manner normal persons react to a very intense stress, and thereafter develop a state very much alike post-traumatic stress disorders. Unfortunately, only a few studies have studied stress-induced regression in patients with DS. Thus, we reviewed the biochemical events involved in psychological stress and found some possible links with cognitive impairment and AD. Interestingly, these links could probably be also applied to non-DS persons submitted to an intense stress. We believe these links should be further explored as a better understanding of the relationships between stress and cognition could help in many situations including individuals of the general population.

Amyloid toxicity in a Drosophila Alzheimer's model is ameliorated by autophagy activation

Alzheimer's disease (AD) is the prevailing form of dementia. Protein degradation and antioxidant pathways have a critical role in preventing the accumulation of protein aggregation; thus, failure of proteostasis in neurons along with redox imbalance mark AD. Herein, we exploited an AD Drosophila model expressing human amyloid precursor (hAPP) and beta-secretase 1 (hBACE1) proteins, to better understand the role of proteostatic or antioxidant pathways in AD. Ubiquitous expression of hAPP, hBACE1 in flies caused more severe degenerative phenotypes versus neuronal targeted expression; it also, suppressed proteasome activity, increased oxidative stress and significantly enhanced stress-sensitivity. Overexpression of Prosβ5 proteasomal subunit or Nrf2 transcription factor in AD Drosophila flies partially restored proteasomal activity but did not rescue hAPP, hBACE1 induced neurodegeneration. On the other hand, expression of autophagy-related Atg8a in AD flies decelerated neurodegeneration, increased stress-resistance, and improved flies' health-/lifespan. Overall, our data suggest that the noxious effects of amyloid-beta aggregates can be alleviated by enhanced autophagy, thus dietary or pharmacological interventions that target autophagy should be considered in AD therapeutic approaches.

Therapeutic implications of hypothalamic-pituitaryadrenal-axis modulation in Alzheimer's disease: A narrative review of pharmacological and lifestyle interventions

With disease-modifying treatments for Alzheimer's disease (AD) still elusive, the search for alternative intervention strategies has intensified. Growing evidence suggests that dysfunction in hypothalamic-pituitaryadrenal-axis (HPAA) activity may contribute to the development of AD pathology. The HPAA, may therefore offer a novel target for therapeutic action. This review summarises and critically evaluates animal and human studies investigating the effects of pharmacological and non-pharmacological intervention on HPAA modulation alongside cognitive performance. The interventions discussed include glucocorticoid receptor antagonists and 11β-hydroxysteroid dehydrogenase inhibitors as well as lifestyle treatments such as physical activity, diet, sleep and contemplative practices. Pharmacological HPAA modulators improve pathology and cognitive deficit in animal AD models, but human pharmacological trials are yet to provide definitive support for such benefits. Lifestyle interventions may offer promising strategies for HPAA modification and cognitive health, but several methodological caveats across these studies were identified. Directions for future research in AD studies are proposed.

Gut Microbiota and Dysbiosis in Alzheimer's Disease: Implications for Pathogenesis and Treatment

Understanding how gut flora influences gut-brain communications has been the subject of significant research over the past decade. The broadening of the term “microbiota-gut-brain axis” from “gut-brain axis” underscores a bidirectional communication system between the gut and the brain. The microbiota-gut-brain axis involves metabolic, endocrine, neural, and immune pathways which are crucial for the maintenance of brain homeostasis. Alterations in the composition of gut microbiota are associated with multiple neuropsychiatric disorders. Although a causal relationship between gut dysbiosis and neural dysfunction remains elusive, emerging evidence indicates that gut dysbiosis may promote amyloid-beta aggregation, neuroinflammation, oxidative stress, and insulin resistance in the pathogenesis of Alzheimer’s disease (AD). Illustration of the mechanisms underlying the regulation by gut microbiota may pave the way for developing novel therapeutic strategies for AD. In this narrative review, we provide an overview of gut microbiota and their dysregulation in the pathogenesis of AD. Novel insights into the modification of gut microbiota composition as a preventive or therapeutic approach for AD are highlighted.

Effect of an Intracerebroventricular Injection of Aggregated Beta-amyloid (1-42) on Daily Rhythms of Oxidative Stress Parameters in the Prefrontal Cortex

Accumulation of amyloid peptides in the brain plays a key role in the pathogenesis of Alzheimer's disease (AD). Aggregated beta-amyloid (Aβ) peptide increases intracellular reactive oxygen species associated to a deficient antioxidant defense system. Prefrontal cortex plays a key role in memory and learning and is especially susceptible to oxidative stress. The objective of this work was to investigate the effects of an intracerebroventricular (i.c.v.) injection of Aβ (1-42) on 24 h patterns of oxidative stress parameters and antioxidant defenses in the rat prefrontal cortex. Four-month-old male Holtzman rats were divided into two groups defined as: control (CO) and Aβ-injected (Aβ). Rats were maintained under12 h-light:12 h-dark conditions and received water and food ad libitum. Tissues samples were isolated every 6 h during a 24 h period. Interestingly, we found that an i.c.v. injection of Aβ(1-42) increased lipid peroxidation, reduced total antioxidant capacity level, phase-shifted the daily peak of reduced glutathione, and had a differential effect on the oscillating catalase and glutathione peroxidase specific activity. Thus, elevated levels of Aβ aggregates-a pathogenic hallmark of AD, caused altered temporal patterns of the cellular redox state in prefrontal cortex rat. These findings might contribute, at least in part, to the understanding of the molecular and biochemical basis of redox changes caused by circadian rhythms alterations observed in AD patients.

Association of IL1R2 rs34043159 with sporadic Alzheimer's disease in southern Han Chinese

BACKGROUND AND PURPOSE

The objective of the study was to investigate the relationship between IL1R2 rs34043159 and Alzheimer's disease (AD) in the Chinese population.

METHODS

A total of 500 AD patients and 500 healthy controls were recruited. The SNaPshot technique was used to detect IL1R2 rs34043159.

RESULTS

The dominant and recessive models of IL1R2 rs34043159 were associated with AD with or without adjustment of age, gender and education [dominant model, P = 0.019, odds ratio (OR) 1.42, 95% confidence interval (CI) 1.06-1.89, adjusted; recessive model, P = 0.011, OR 0.69, 95% CI 0.51-0.92, adjusted]. The recessive model of IL1R2 rs34043159 was associated with early-onset AD (EOAD) with or without adjustment of age, gender and education (recessive model, P = 0.038, OR 0.60, 95% CI 0.37-0.97, adjusted). The additive model was associated with late-onset AD (LOAD) (P = 0.041). The dominant model of IL1R2 rs34043159 was associated with LOAD with or without adjustment of age, gender and education (dominant model, P = 0.005, OR 1.68, 95% CI 1.17-2.44, adjusted).

CONCLUSION

An association between the dominant and recessive model of IL1R2 rs34043159 and AD was found. The recessive model of IL1R2 rs34043159 was associated with EOAD. The additive and dominant models of IL1R2 rs34043159 were associated with LOAD.

Sex Hormone Depletion Augments Glucocorticoid Induction of Tau Hyperphosphorylation in Male Rat Brain

Steroid hormones secreted by the gonads (sex steroids) and adrenal glands (glucocorticoids, GC) are known to influence brain structure and function. While levels of sex steroids wane in late adulthood, corticosteroid levels tend to rise in many individuals due to age-related impairments in their feedback on central mechanisms regulating adrenal function. These fluctuations in sex and adrenal steroid secretion may be relevant to age-related neurodegenerative disorders such as Alzheimer's disease (AD) in which hyperphosphorylation of Tau protein is a key pathological event. We here report that both, long-term GC deprivation (by adrenalectomy) and exogenous GC administration with natural or synthetic glucocorticoid receptor ligands (corticosterone and dexamethasone, respectively) induce Tau hyperphosphorylation in the hippocampus and frontocortical regions at epitopes associated with disruption of cytoskeletal and synaptic function. Interestingly, we observed that the changes in Tau induced by manipulation of the GC milieu of male rats were exacerbated by testosterone depletion (by orchiectomy). While this finding supports previous suggestions of a neuroprotective role of male sex hormones, this is the first study to address interactions between adrenal and sex steroids on Tau hyperphosphorylation and accumulation that are known to endanger neuronal function and plasticity. These results are particularly important for understanding the mechanisms that can precipitate AD because, besides being modulated by age, GC are elevated by stress, a phenomenon now established as a trigger of deficits in neural plasticity and survival, cognitive behaviour and AD-like Tau pathology.

Microglia, Lifestyle Stress, and Neurodegeneration

Recent years have witnessed a revolution in our understanding of microglia biology, including their major role in the etiology and pathogenesis of neurodegenerative diseases. Technological advances have enabled the identification of microglial signatures in health and disease, including the development of new models to investigate and manipulate human microglia in vivo in the context of disease. In parallel, genetic association studies have identified several gene risk factors associated with Alzheimer's disease that are specifically or highly expressed by microglia in the central nervous system (CNS). Here, we discuss evidence for the effect of stress, diet, sleep patterns, physical activity, and microbiota composition on microglia biology and consider how lifestyle might influence an individual's predisposition to neurodegenerative diseases. We discuss how different lifestyles and environmental factors might regulate microglia, potentially leading to increased susceptibility to neurodegenerative disease, and we highlight the need to investigate the contribution of modern environmental factors on microglia modulation in neurodegeneration.

Sex Differences in the Phosphoproteomic Profiles of APP/PS1 Mice after Chronic Unpredictable Mild Stress

Approximately two-thirds of those suffering with Alzheimer's disease (AD) are women, however, the biological mechanisms underlying this sex divergence of AD prevalence remain unknown. Previous research has shown sex-specific biochemical differences that bias female mice toward pro-AD signaling on the phosphoproteomic level via corticotropin releasing factor (CRF) receptor 1 activation after CRF overexpression. Here we aimed to determine if chronic stress would induce a similar response in AD mouse models. We stressed 4-month-old APP/PS1 mice using a chronic unpredictable mild stress (CUMS) paradigm for up to 1 month. Following CUMS and behavioral assessments, we quantified whole protein and phosphoprotein levels in the cortex of stressed and non-stressed APP/PS1 mice using mass spectrometry-based proteomics. While there were no statistically significant differences at the total protein and peptide abundance levels, we found 909 and 841 statistically significant phosphopeptides between stressed and unstressed females and males, respectively, using a false discovery rate of 5%. Of these significant phosphopeptides, only 301 were the same in males and females. These results indicate that while both males and females undergo protein phosphorylation changes following stress, the peptides that are phosphorylated differ between sexes. We then used Metacore analysis to determine which biological pathways were affected. We found that several pathways were changed differently between male and female mice including NMDA receptor trafficking, cytoskeleton organization, and tau pathology. The differing biological pathways affected between males and females in response to chronic stress may help us to better understand why women are at a higher risk of AD.

Glucocorticoid receptors signaling impairment potentiates amyloid-β oligomers-induced pathology in an acute model of Alzheimer's disease

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis occurs early in Alzheimer's disease (AD), associated with elevated circulating glucocorticoids (GC) and glucocorticoid receptors (GR) signaling impairment. However, the precise role of GR in the pathophysiology of AD remains unclear. Using an acute model of AD induced by the intracerebroventricular injection of amyloid-β oligomers (oAβ), we analyzed cellular and behavioral hallmarks of AD, GR signaling pathways, processing of amyloid precursor protein, and enzymes involved in Tau phosphorylation. We focused on the prefrontal cortex (PFC), particularly rich in GR, early altered in AD and involved in HPA axis control and cognitive functions. We found that oAβ impaired cognitive and emotional behaviors, increased plasma GC levels, synaptic deficits, apoptosis and neuroinflammatory processes. Moreover, oAβ potentiated the amyloidogenic pathway and enzymes involved both in Tau hyperphosphorylation and GR activation. Treatment with a selective GR modulator (sGRm) normalized plasma GC levels and all behavioral and biochemical parameters analyzed. GR seems to occupy a central position in the pathophysiology of AD. Deregulation of the HPA axis and a feed-forward effect on PFC GR sensitivity could participate in the etiology of AD, in perturbing Aβ and Tau homeostasis. These results also reinforce the therapeutic potential of sGRm in AD.

Neuroendocrine Disturbances in Neurodegenerative Disorders: A Scoping Review

BACKGROUND

Neurodegenerative diseases cause progressive irreversible neuronal loss that has broad downstream effects. The neuroendocrine system regulates homeostasis of circuits that control critical functions such as the stress response, metabolism, reproduction, fluid balance, and glucose control. These systems are frequently disrupted in neurodegenerative disorders yet often overlooked in clinical practice.

OBJECTIVE

This review aims to gather the available data regarding these disturbances in Alzheimer's disease, Parkinson's disease, frontotemporal dementia, amyotrophic lateral sclerosis, and Huntington's disease and also to demonstrate the volume of literature in these individual arenas.

METHODS

Using the scoping review framework, a literature search was performed in PubMed to identify relevant articles published within the past 30 years (January 1988 to November 2018). The search criteria produced a total of 2022 articles, 328 of which were identified as relevant to this review.

RESULTS

Several major themes emerged from this review. These neuroendocrine disturbances may be a precursor to the illness, a part of the primary pathophysiology, or a direct consequence of the disease or independent of it. They have the potential to further understanding of the disease, exacerbate the underlying pathology, or provide therapeutic benefit.

CONCLUSIONS

By synthesizing the data from a systems' perspective, we aim to broaden how clinicians think about these illnesses and provide care.

Psychosocial stress associated with memory performance in older South African adults

Older adults with past or current chronic stress exposure perform poorly on memory assessments and are at higher risk for Alzheimer's disease (AD). In low- or middle-income countries, many older adults are, or have been, exposed to stress-provoking events. Few published studies examine such populations, however, and few take multiple measures of stress. In a sample of South African older adults with mild-to-moderate AD (n = 65) and healthy controls (n = 69), we assessed relations between stress (psychosocial and physiological), memory performance, and patient status. Participants, all aged > 60, were administered the Perceived Stress Scale (a questionnaire assessing subjective psychosocial stress) and the Cambridge Cognitive Examination-Revised (CAMCOG-R; a test battery measuring performance across several cognitive domains). We measured their salivary cortisol concentrations as a proxy for physiological stress. Patients reported significantly higher levels of psychosocial stress than controls, p = .008. Logistic regression showed that psychosocial stress, but not cortisol, predicted AD patient status. CAMCOG-R Memory subscale scores were significantly associated with psychosocial stress, r = -.18, p = .040, but not with cortisol levels. These findings are the first on the topic to emerge from a low-or middle-income country. We replicated findings from previous studies conducted in high-income countries, with data supporting predictions derived from the glucocorticoid cascade/neurotoxicity hypothesis. The results suggest that clinical interventions focused on increasing resilience of older adults to effects of chronic stress may help protect against declining memory performance and reduce the risk for AD.

Concurrent Mild Traumatic Brain Injury and Posttraumatic Stress Disorder Is Associated With Elevated Tau Concentrations in Peripheral Blood Plasma

Concurrent mild traumatic brain injury (mTBI) and posttraumatic stress disorder (PTSD) are common in U.S. military service members and veterans. Tau and amyloid-beta-42 (Aβ42) are proteins that have been linked to cognitive impairment, neurological hallmarks of Alzheimer's disease, and may also relate to recovery from mTBI. However, the role of these proteins in the maintenance or resolution of chronic symptoms has not yet been determined. Participants in the current study were 102 service members and veterans who had sustained an mTBI (n = 84) or injured controls (IC) without TBI (n = 18). They were categorized into three groups based on the presence or absence of mTBI and PTSD: IC/PTSD-Absent (n = 18), mTBI/PTSD-Absent (n = 63), and mTBI/PTSD-Present (n = 21). Concentrations of tau and Aβ42 in peripheral blood plasma were measured using Simoa^TM , an ultrasensitive technology, and compared across groups. Tau concentrations were highest in the mTBI/PTSD-Present group, F(2, 99) = 4.33, p = .016, compared to the other two groups. Linear multiple regression was conducted to determine the independent effects of PTSD and mTBI on tau concentrations, controlling for gender and sleep medication. PTSD was a significant and independent predictor of tau concentrations, β = .25, p = .009, η_p ² = .26. Aβ42 concentrations did not differ between the groups. The results indicated that PTSD was associated with an elevation of tau in peripheral blood and suggest that there may be increased biological effects of PTSD in this young cohort of service members and veterans following mTBI.

The Arctic/Swedish APP mutation alters the impact of chronic stress on cognition in mice

Chronic stress is a major risk factor for developing Alzheimer's disease (AD) and promotes the processing of amyloid precursor protein (APP) to β-amyloid (Aβ). However, the precise relationship of stress and disease-typical cognitive decline is presently not well understood. The aim of this study was to investigate how early life stress may affect cognition in adult mice with and without soluble Aβ pathology typical for the early stages of the disease. We focussed on sustained attention and response control, aspects of cognition mediated by the prefrontal cortex that are consistently impaired both in early AD and after chronic stress exposure. Young wild-type mice as well as transgenic arcAβ mice overexpressing the hAPParc/swe transgene were exposed to a chronic unpredictable stress paradigm (age 3-8 weeks). At 15 weeks, these mice were tested on the 5-choice serial reaction time task, a test of sustained attention and executive control. We found that, expectedly, chronic stress increased impulsive choices and impaired sustained attention in wild-type mice. However, the same treatment reduced impulsivity and did not interfere with sustained attention in arcAβ mice. These findings suggest an unexpected interaction between chronic stress and Aβ whereby Aβ-pathology caused by the hAPParc/swe mutation prevented and/or reversed stress-induced cognitive changes through mechanisms that deserve further investigation. They also indicate that Aβ, in modest amounts, may have a beneficial role for cognitive stability, for example by protecting neural networks from the impact of further physiological or behavioural stress.

Activated PPARγ Abrogates Misprocessing of Amyloid Precursor Protein, Tau Missorting and Synaptotoxicity

Type 2 diabetes increases the risk for dementia, including Alzheimer’s disease (AD). Pioglitazone (Pio), a pharmacological agonist of the peroxisome proliferator-activated receptor γ (PPARγ), improves insulin sensitivity and has been suggested to have potential in the management of AD symptoms, albeit through mostly unknown mechanisms. We here investigated the potential of Pio to counter synaptic malfunction and loss, a characteristic of AD pathology and its accompanying cognitive deficits. Results from experiments on primary mouse neuronal cultures and a human neural cell line (SH-SY5Y) show that Pio treatment attenuates amyloid β (Aβ)-triggered the pathological (mis-) processing of amyloid precursor protein (APP) and inhibits Aβ-induced accumulation and hyperphosphorylation of Tau. These events are accompanied by increased glutamatergic receptor 2B subunit (GluN2B) levels that are causally linked with neuronal death. Further, Pio treatment blocks Aβ-triggered missorting of hyperphosphorylated Tau to synapses and the subsequent loss of PSD95-positive synapses. These latter effects of Pio are PPARγ-mediated since they are blocked in the presence of GW9662, a selective PPARγ inhibitor. Collectively, these data show that activated PPARγ buffer neurons against APP misprocessing, Tau hyperphosphorylation and its missorting to synapses and subsequently, synaptic loss. These first insights into the mechanisms through which PPARγ influences synaptic loss make a case for further exploration of the potential usefulness of PPARγ agonists in the prevention and treatment of synaptic pathology in AD.

Past to Future: What Animal Models Have Taught Us About Alzheimer's Disease

Alzheimer's disease (AD) impairs memory and causes significant cognitive deficits. The disease course is prolonged, with a poor prognosis, and thus exacts an enormous economic and social burden. Over the past two decades, genetically engineered mouse models have proven indispensable for understanding AD pathogenesis, as well as for discovering new therapeutic targets. Here we highlight significant studies from our laboratory that have helped advance the AD field by elucidating key pathogenic processes operative in AD and exploring a variety of aspects of the disease which may yield novel therapeutic strategies for combatting this burdensome disease.

Exposure to a single immobilization or lipopolysaccharide challenge increases expression of genes implicated in the development of Alzheimer's disease in the mice brain cortex

OBJECTIVES

Despite extensive research efforts, mechanisms participating on development of Alzheimer's disease (AD) are covered only partially. Data from the last decades indicate that various stressors, as etiological factors, may play a role of in the AD. Therefore, we investigated the effect of two acute stressors, immobilization (IMO) and lipopolysaccharide (LPS), on the AD-related neuropathology.

METHODS

Adult C57BL/6J mice males were exposed to a single IMO stress or a single intraperitoneal injection of LPS (250 µg/kg body weight). After terminating the experiments, the brains were removed and their cortices isolated. Gene expression of pro-inflammatory cytokines, as well as expression of genes implicated in the AD neuropathology were determined. In addition, mediators related to the activation of the microglia, monocytes, and perivascular macrophages were determined in brain cortices, as well.

RESULTS

In comparison with the control animals, we found increased gene expression of proinflammatory mediators in mice brain cortex in both IMO and LPS groups. In stressed animals, we also showed an increased expression of genes related to the AD neuropathology, as well as positive correlations between genes implicated in AD development and associated neuroinflammation.

CONCLUSIONS

Our data indicate that acute exposure to a strong IMO stressor, composed of the combined physical and psychological challenges, induces similar inflammatory and other ADrelated neuropathological changes as the immune LPS treatment. Our data also indicate that cytokines are most likely released from the peripheral immune cells, as we detected myeloid cells activity, without any microglia response. We hypothesize that stress induces innate immune response in the brain that consequently potentiate the expression of genes implicated in the AD-related neuropathology.

Icariin Attenuates M1 Activation of Microglia and Aβ Plaque Accumulation in the Hippocampus and Prefrontal Cortex by Up-Regulating PPARγ in Restraint/Isolation-Stressed APP/PS1 Mice

Background

Studies have shown that psychosocial stress is involved in Alzheimer's disease (AD) pathogenesis; it induces M1 microglia polarization and production of pro-inflammatory cytokines, leading to neurotoxic outcomes and decreased β-amyloid (Aβ) clearance. Icariin has been proven to be an effective anti-inflammatory agent and to activate peroxisome proliferator-activated receptors gamma (PPARγ) which induces the M2 phenotype in the microglia. However, whether restraint/isolation stress reduces the clearance ability of microglia by priming and polarizing microglia to the M1 phenotype, and the effects of icariin in attenuating the inflammatory response and relieving the pathological changes of AD are still unclear.

Methods

APP/PS1 mice (male, aged 3 months) were randomly divided into a control group, a restraint/isolation stress group, and a restraint/isolation stress + icariin group. The restraint/isolation stress group was subjected to a paradigm to build a depressive animal model. Sucrose preference, open field, elevated plus maze, and Y maze test were used to assess the stress paradigm. The Morris water maze test was performed to evaluate spatial reference learning and memory. Enzyme-linked immunosorbent assay and immunohistochemistry were used to identify the microglia phenotype and Aβ accumulation. Western blotting was used to detect the expression of PPARγ in the hippocampus and prefrontal cortex (PFC).

Results

Restraint/isolation stress induced significant depressive-like behaviors in APP/PS1 mice at 4 months of age and memory impairment at 10 months of age, while 6 months of icariin administration relieved the memory damage. Restraint/isolation stressed mice had elevated pro-inflammatory cytokines, decreased anti-inflammatory cytokines, increased Aβ plaque accumulation and more M1 phenotype microglia in the hippocampus and PFC at 10 months of age, while 6 months of icariin administration relieved these changes. Moreover, restraint/isolation stressed mice had down-regulated PPARγ expression in the hippocampus and PFC at 10 months of age, while 6 months of icariin administration reversed the alteration, especially in the hippocampus.

Conclusion

Restraint/isolation stress induced depressive-like behaviors and spatial memory damage, over-expression of M1 microglia markers and more severe Aβ accumulation by suppressing PPARγ in APP/PS1 mice. Icariin can be considered a new treatment option as it induces the switch of the microglia phenotype by activating PPARγ.

Alzheimer's Disease and Cancer: When Two Monsters Cannot Be Together

Alzheimer's disease (AD) and cancer are among the leading causes of human death around the world. While neurodegeneration is the main feature of AD, the most important characteristic of malignant tumors is cell proliferation, placing these two diseases in opposite sides of cell division spectrum. Interestingly, AD and cancer's pathologies consist of a remarkable common feature and that is the presence of active cell cycle in both conditions. In an in vitro model of primary adult neuronal culture, we previously showed that treating cell with beta amyloid forced neurons to start a cell cycle. Instead of cell division, however, neuronal cell cycle was aborted and a massive neurodegeneration was left behind as the consequence. A high level of cell cycle entry, which is a requirement for cancer pathogenesis, was reported in clinically diagnosed cases of AD, leading to neurodegeneration. The diverse clinical manifestation of a similar etiology, have puzzled researchers for many years. In fact, the evidence showed an inverse association between AD and cancer prevalence, suggesting that switching pathogenesis toward AD protects patients against cancer and vice versa. In this mini review, we discussed the possibility of involvement of cell proliferation and survival dysregulation as the underlying mechanism of neurodegeneration in AD, and the leading event to develop both disorders' pathology. As examples, the role of phosphoinositide 3 kinase/Akt/ mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pathway in cell cycle re-entry and blocking autophagy are discussed as potential common intracellular components between AD and cancer pathogenesis, with diverse clinical diagnosis.

How stress mediators can cumulatively contribute to Alzheimer's disease An allostatic load approach

Allostatic load is defined as the frequent activation of the neuroendocrine, immunological, metabolic and cardiovascular systems, which makes individuals more susceptible to stress-related health problems. According to this model, physiological dysregulations start to emerge decades before diseases manifest. Consequently, stress research has shifted its attention to anticipating the degree of this dysregulation to better understand the impact of stress hormones and other biomarkers on disease progression. In view of the growing number of studies that demonstrate the influence of modifiable risk factors on cognitive decline, in addition to the effects of chronic stress mediators, the objective of the present review was to present an overview of the development of cognitive changes based on studies on stress and its mediators.

Stress and the Etiopathogenesis of Alzheimer's Disease and Depression

Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder with a complex physiopathology whose initiators are poorly defined. Accumulating clinical and experimental evidence suggests a causal role of lifetime stress in AD. This chapter summarizes current knowledge about how chronic stress and its accompanying high levels of glucocorticoid (GC) secretion, trigger the two main pathomechanisms of AD: (i) misprocessing of amyloid precursor protein (APP) and the generation of amyloid beta (Aβ) and (ii) Tau hyperphosphorylation and aggregation. Given that depression is a well-known stress-related illness, and the evidence that depression may precede AD, this chapter also explores neurobiological mechanisms that may be common to depressive and AD pathologies. This review also discusses emerging insights into the role of Tau and its malfunction in disrupting neuronal cascades and neuroplasticity and, thus triggering brain pathology.

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.

A Complex Relationship Between Suicide, Dementia, and Amyloid: A Narrative Review

Background: Suicide rates are high among older adults and many conditions have been related to suicide in this population: chronic illnesses, physical disabilities, cancer, social isolation, mental disorders and neurocognitive disorders.

Objectives: Among neurocognitive disorders, analysis of the relationships between dementia and suicidal behaviors led to conflicting results and some questions are still without answer. Particularly, it is not known whether (i) Alzheimer's disease (AD) increases the risk of suicidal ideation and suicide attempts (SA) or the frequency of death by suicide; (ii) the presence of suicidal ideation or SA in people older than 65 years of age is an early dementia sign; and (iii) amyloid load in frontal areas facilitates SA by modifying the decision-making pathway.

Methods: Therefore, in this narrative review, we searched the PubMed database using the medical subject heading (MeSH) terms (“Suicide” AND “Depression”) OR (“Amyloid” OR “Dementia”) to identify recent (from 2000 to 2017) original studies on the links between suicidal behavior, dementia and brain amyloid load. We also explored the clinical and pathophysiological role of depression in these relationships.

Results and Discussion: The findings from these studies suggest that late stage dementia could protect against suicidal ideation and SA. Conversely, the risk of complete suicide is increased during the early phase of cognitive decline.

Conclusions: Serious cognitive impairment and decline of executive functions could protect against negative thoughts related to cognitive disability awareness and against suicide planning.Several factors, including brain amyloid load, could be involved in the increased suicide rate early after the diagnosis of dementia.

Targeting glucocorticoid receptors prevents the effects of early life stress on amyloid pathology and cognitive performance in APP/PS1 mice

Exposure to chronic stress or elevated glucocorticoid hormone levels in adult life has been associated with cognitive deficits and an increased risk for Alzheimer's disease (AD). Since exposure to stress during early life enhances stress-responsiveness and lastingly affects cognition in adult life, we here investigated; (i) whether chronic early life stress (ELS) affects AD pathology and cognition in middle-aged APPswe/PS1dE9 mice, and (ii) whether it is still possible to rescue these late effects by briefly blocking glucocorticoid receptors (GRs) at a translationally relevant, middle age. Transgenic APPswe/PS1dE9 mice were subjected to ELS by housing dams and pups with limited nesting and bedding material from postnatal days 2-9 only. In 6- and 12-month-old offspring, this resulted in enhanced hippocampal amyloid-β (Aβ)-40 and -42 levels, and in reduced cognitive flexibility, that correlated well with the Aβ42 levels. In parallel, CORT levels and BACE1 levels were significantly elevated. Surprisingly, blocking GRs for only 3 days at 12 months of age reduced CORT levels, reduced hippocampal Aβ40 and -42, and β-site APP-cleaving enzyme 1 (BACE1) levels, and notably rescued the cognitive deficits in 12-month-old APPswe/PS1dE9 mice. These mouse data demonstrate that exposure to stress during the sensitive period early in life influences later amyloid pathology and cognition in genetically predisposed, mutant mice, and as such, may increase AD vulnerability. The fact that a short treatment with a GR antagonist at middle age lastingly reduced Aβ levels and rescued the cognitive deficits after ELS, highlights the therapeutic potential of this drug for reducing amyloid pathology.

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.

Sex differences in chronic stress responses and Alzheimer's disease

Clinical studies indicate that Alzheimer's disease (AD) disproportionately affects women in both disease prevalence and severity, but the mechanisms underlying this sex divergence are unknown. Though some have suggested this difference in risk is a reflection of known differences in longevity between men and women, mounting clinical and preclinical evidence supports women also having intrinsic susceptibilities towards the disease. While a number of potential risk factors have been hypothesized to affect these differences in risks, none have been definitively verified. In this review, we discuss a novel hypothesis whereby women's susceptibility to chronic stress also mediates increased risk for AD. As stress is a risk factor for AD, and women are twice as likely to develop mood disorders where stress is a major etiology, it is possible that sex dimorphisms in stress responses contribute to the increase in women with AD. In line with this, sex divergence in biochemical responses to stress have been noted along the hypothalamic-pituitary-adrenal (HPA) axis and among known molecular effectors of AD, with crosstalk between these processes also being likely. In addition, activation of the cortical corticotrophin-releasing factor receptor 1 (CRF1) signaling pathway leads to distinct female-biased increases in molecules associated with AD pathogenesis. Therefore, the different biochemical responses to stress between women and men may represent an intrinsic, sex-dependent risk factor for AD.

Purported Interactions of Amyloid-β and Glucocorticoids in Cytotoxicity and Genotoxicity: Implications in Alzheimer's Disease

Alzheimer's disease (AD) is a complex neurodegenerative disorder characterized by the presence of aggregates of the amyloid-β peptide (Aβ) that are believed to be neurotoxic. One of the purposed damaging mechanisms of Aβ is oxidative insult, which eventually could damage the cellular genome. Stress and associated increases in glucocorticoids (GCs) have been described as a risk factor for the development of AD, although the purported genotoxic effects of GCs have not been fully characterized. Therefore, it is possible to speculate about purported synergistic effects of GCs on the Aβ-driven genotoxic damage. This in vitro study addresses the single and combined cyto/genotoxic effects of Aβ and GCs in SH-SY5Y cells. Cytotoxicity was determined by the MTT assay, and the genotoxic effects were studied using the comet assay. A comet assay derivation allows for measuring the presence of the FPG-sensitive sites (mainly 8-oxoguanines) in the DNA, apart from the DNA strand breaks. Treatment with Aβ (10 μM, 72 h) induced cytotoxicity (35% decrease in cell viability) and DNA strand breaks, but had no significant effect on oxidative DNA damage (FPG sites). Corticosterone showed no effect on cell viability, genotoxicity, or reparation processes. Corticosterone was unable to neither reverse nor potentiate Aβ driven effects. The present results suggest the existence of alternative mechanisms for the Aβ driven damage, not involving oxidative damage of DNA. In addition, could be suggested that the interaction between Aβ and GCs in AD does not seem to involve DNA damage.

RCAN1 in the inverse association between Alzheimer's disease and cancer

The inverse association between Alzheimer’s disease (AD) and cancer has been reported in several population-based studies although both of them are age-related disorders. However, molecular mechanisms of the inverse association remain elusive. Increased expression of regulator of calcineurin 1 (RCAN1) promotes the pathogenesis of AD, while it suppresses cancer growth and progression in many types of cancer. Moreover, aberrant RCAN1 expression is detected in both AD and various types of cancer. It suggests that RCAN1 may play a key role in the inverse association between AD and cancer. In this article, we aim to review the role of RCAN1 in the inverse association and discuss underlying mechanisms, providing an insight into developing a novel approach to treat AD and cancer.