Chronic stress as a risk factor for Alzheimer's disease

The Interrelation of Neurological and Psychological Symptoms of COVID-19: Risks and Remedies

COVID-19 has catastrophically affected the world's panoramic view of human well-being in terms of healthcare and management. With the increase in the number of cases worldwide, neurological symptoms and psychological illnesses from COVID-19 have increasingly upsurged. Mental health illness and affective disorders, including depression, obsessive-compulsive disorder, anxiety, phobia, and panic disorders, are highly impacted due to social distress. The COVID-19 pandemic not only affected people with pre-existing mental and affective illnesses, but also healthy individuals with anxiety, worrying, and panic symptoms, and fear conditioning. In addditon, the novel coronavirus is known to impact the central nervous system in the brain, resulting in severe and certain long-lasting neurological issues. Owing to the significance of neurological and psychological events, the present perspective has been an attempt to disseminate the impact of COVID-19 on neural injury through inflammation, and its interrelation with psychological symptoms. In this current review, we synthesize the literature to highlight the critical associations between SARS-CoV-2 infection and the nervous system, and mental health illness, and discuss potential mechanisms of neural injury through psycho-neuroimmunity.

On the Etiopathogenesis and Pathophysiology of Alzheimer's Disease: A Comprehensive Theoretical Review

Alzheimers' disease (AD) is the most common cause of dementia, with an estimated 5 million new cases occurring annually. Among the elderly, AD shortens life expectancy, results in disability, decreases quality of life, and ultimately, leads to institutionalization. Despite extensive research in the last few decades, its heterogeneous pathophysiology and etiopathogenesis have made it difficult to develop an effective treatment and prevention strategy. Aging is the biggest risk factor for AD and evidence suggest that the total number of older people in the population is going to increase astronomically in the next decades. Also, there is evidence that air pollution and increasing income inequality may result in higher incidence and prevalence of AD. This makes the need for a comprehensive understanding of the etiopathogenesis and pathophysiology of the disease extremely critical. In this paper, a quintuple framework of thyroid dysfunction, vitamin D deficiency, sex hormones, and mitochondria dysfunction and oxidative stress are used to provide a comprehensive description of AD etiopathogenesis and pathophysiology. The individual role of each factor, their synergistic and genetic interactions, as well as the limitations of the framework are discussed.

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.

Mitophagy and iron: two actors sharing the stage in age-associated neuronal pathologies

Aging is characterized by the deterioration of different cellular and organismal structures and functions. A typical hallmark of the aging process is the accumulation of dysfunctional mitochondria and excess iron, leading to a vicious cycle that promotes cell and tissue damage, which ultimately contribute to organismal aging. Accordingly, altered mitochondrial quality control pathways such as mitochondrial autophagy (mitophagy) as well as altered iron homeostasis, with consequent iron overload, can accelerate the aging process and the development and progression of different age-associated disorders. In this review we first briefly introduce the aging process and summarize molecular mechanisms regulating mitophagy and iron homeostasis. We then provide an overview on how dysfunction of these two processes impact on aging and age-associated neurodegenerative disorders with a focus on Alzheimer's disease, Parkinson's disease and Amyotrophic Lateral Sclerosis. Finally, we summarize some recent evidence showing mechanistic links between iron metabolism and mitophagy and speculate on how regulating the crosstalk between the two processes may provide protective effects against aging and age-associated neuronal pathologies.

Effectiveness of a Cognitive Behavioral Coaching Program Delivered via Video in Real World Settings

Background: Many employees experience high levels of stress in the workplace, which negatively impact their productivity and well-being. Effective stress management interventions exist, but are inaccessible due to insufficient numbers of mental health providers, long waiting times to initiate care, high out-of-pocket cost of care, and stigma related to receiving psychotherapy.

Introduction: The purpose of this study was to test the efficacy, in real-world circumstances, of a structured, cognitive behavioral coaching (CBC) program delivered through video or telephone.

Materials and Methods: Retrospective data on 289 subjects who had sought support for emotional health through a behavioral health benefit offered through employers were examined. Changes in perceived stress and well-being over the course of the program were measured using the Perceived Stress Scale (PSS) and Warwick–Edinburgh Mental Well-being Scale (WEMWBS), respectively. Rates of reliable change and satisfaction with the coaching program were also assessed.

Results: Scores on both the PSS and WEMWBS improved between baseline and follow-up. Approximately 61.9% (n = 289) of participants demonstrated reliable improvement on either measure.

Discussion: CBC is a promising intervention that has the potential to significantly expand access to effective and more affordable interventions for emotional health care.

Conclusions: Coaching, when delivered by accredited professionals trained in cognitive behavioral theory and interventions and working in real-world settings, can be efficacious in decreasing perceived stress and increasing well-being when delivered through video or telephone.

Astragaloside IV Supplementation Promotes A Neuroprotective Effect in Experimental Models of Neurological Disorders: A Systematic Review

Background:

Neurological disorders constitute a growing worldwide concern due to the progressive aging of the population and the risky behavior they represent. Herbal medicines have scientific relevance in the treatment of these pathol-ogies. One of these substances, Astragaloside IV (AS-IV), is the main active compound present in the root of Astragalus membranaceus (Fisch.) Bge, a Chinese medicinal herb with neuroprotective properties.

Objective:

In the present study we performed a systematic review that sought to comprehend the neuroprotective effect pre-sented by AS-IV in experimental models of neurological disorders.

Method:

This study is a systematic review, where an electronic search in United States National Library of Medicine (Pub-Med), Science Direct, Cochrane Library, Scientific Electronic Library Online (SciELO), Scopus, Web of Science, Medline via Proquest and Periodicos Capes databases covering the years between 2007 and 2017, using “Astragaloside IV” and “Neurodegenerative diseases”; “Astragaloside IV” and “ Neurological disorders” as reference terms was made.

Results:

A total of 16 articles were identified, in which the efficacy of AS-IV was described in experimental models of Par-kinson’s disease, Alzheimer’s disease, cerebral ischemia and autoimmune encephalomyelitis, by improving motor deficits and/or neurochemical activity, especially antioxidant systems, reducing inflammation and oxidative stress.

Conclusion:

The findings of the present study indicate that the administration of AS-IV can improve behavioral and neuro-chemical deficits largely due to its antioxidant, antiapoptotic and anti-inflammatory properties, emerging as an alternative therapeutic approach for the treatment of neurological disorders.

Baseline Results: The Association Between Cardiovascular Risk and Preclinical Alzheimer's Disease Pathology (ASCEND) Study

BACKGROUND

The rate of AD for African Americans (AAs) is 64% higher than for non-Hispanic White Americans (Whites). It is hypothesized that poor peripheral vascular function, in combination with genetics, stress, and inflammation may directly contribute to the accumulation of AD pathologic biomarkers. These risk factors may disproportionately affect AAs.

OBJECTIVE

Our objective was to determine if in a healthy middle-aged cohort at risk for AD (1) AD biomarkers in CSF differ by race, (2) peripheral vascular dysfunction and cognition are related to a higher burden of CSF AD biomarkers, and (3) these relationships differ by race.

METHODS

We enrolled 82 cognitively normal, middle-aged (45 and older) adults including AAs and Whites at high risk for AD due to parental history. Study procedures included lumbar puncture, vascular ultrasound, and cognitive testing.

RESULTS

While participants were in overall good health, AAs exhibited poorer indices of preclinical vascular health, including higher central SBP, central MAP, and EndoPAT AI, a marker of arterial stiffness. AAs also had significantly less cerebrospinal fluid tau burden than Whites. After polynomial regression analysis, adjusted for age, gender, education, and ApoE4 status, race significantly modified the relationship between total tau, phospho-tau, and Trails B, a marker of executive function. Small differences in tau correlated with poorer cognition in AAs.

CONCLUSION

In a healthy middle-aged cohort at risk for AD, AAs had worse peripheral vascular health and worse cognition than Whites. Despite lower tau burden overall, race modified the relationship between tau and cognition, such that small differences in tau between AAs was related to worse cognition when compared to Whites.

GABA-A receptor modulating steroids in acute and chronic stress; relevance for cognition and dementia?

Cognitive dysfunction, dementia and Alzheimer's disease (AD) are increasing as the population worldwide ages. Therapeutics for these conditions is an unmet need. This review focuses on the role of the positive GABA-A receptor modulating steroid allopregnanolone (APα), it's role in underlying mechanisms for impaired cognition and of AD, and to determine options for therapy of AD. On one hand, APα given intermittently promotes neurogenesis, decreases AD-related pathology and improves cognition. On the other, continuous exposure of APα impairs cognition and deteriorates AD pathology. The disparity between these two outcomes led our groups to analyze the mechanisms underlying the difference. We conclude that the effects of APα depend on administration pattern and that chronic slightly increased APα exposure is harmful to cognitive function and worsens AD pathology whereas single administrations with longer intervals improve cognition and decrease AD pathology. These collaborative assessments provide insights for the therapeutic development of APα and APα antagonists for AD and provide a model for cross laboratory collaborations aimed at generating translatable data for human clinical trials.

Psychological distress as a risk factor for dementia after the 2004 Niigata-Chuetsu earthquake in Japan

BACKGROUND

A large earthquake can cause extreme stress and may adversely affect cognitive function in humans. We aimed to examine a possible association between psychological distress and incident dementia after the 2004 Niigata-Chuetsu earthquake in Japan.

METHODS

This is a retrospective cohort study followed participants for 10-12 years. Subjects were 6,012 residents in 2005, 5,424 in 2006, and 5,687 in 2007 (age ≥40 years) living in Ojiya city who participated in the annual health check examinations after the 2004 Niigata-Chuetsu earthquake. Psychological distress was assessed using the Kessler Psychological Distress Scale (K10), and individuals with a K10 score ≥10 were considered to have psychological distress. Incident dementia cases were identified from a long-term care insurance database of the local government during the follow-up period. We evaluated hazard ratios (HRs) of psychological distress for incident dementia in each year, unadjusted and adjusted for covariates, including sex, age, occupation, BMI, and property damage of residential area.

RESULTS

The average age of the subjects was 64.6 years in 2005, 64.6 in 2006, and 65.2 in 2007. Adjusted HRs were significantly higher (HR = 1.20-1.66) in the psychological distress group than in the reference group in each year. In particular, adjusted HR was high (HR = 2.89) in those with psychological distress in all three years (2005-2007).

CONCLUSION

Psychological distress, especially persistent distress, is a risk factor for incident dementia in victims of large disasters.

Exercise, diet and stress as modulators of gut microbiota: Implications for neurodegenerative diseases

The last decade has witnessed an exponentially growing interest in gut microbiota and the gut-brain axis in health and disease. Accumulating evidence from preclinical and clinical research indicate that gut microbiota, and their associated microbiomes, may influence pathogenic processes and thus the onset and progression of various diseases, including neurological and psychiatric disorders. In fact, gut dysbiosis (microbiota dysregulation) has been associated with a range of neurodegenerative diseases, including Alzheimer's, Parkinson's, Huntington's and motor neuron disease, as well as multiple sclerosis. The gut microbiota constitutes a dynamic microbial system constantly challenged by many biological variables, including environmental factors. Since the gut microbiota constitute a changeable and experience-dependent ecosystem, they provide potential therapeutic targets that can be modulated as new interventions for dysbiosis-related disorders, including neurodegenerative diseases. This article reviews the evidence for environmental modulation of gut microbiota and its relevance to brain disorders, exploring in particular the implications for neurodegenerative diseases. We will focus on three major environmental factors that are known to influence the onset and progression of those diseases, namely exercise, diet and stress. Further exploration of environmental modulation, acting via both peripheral (e.g. gut microbiota and associated metabolic dysfunction or 'metabolopathy') and central (e.g. direct effects on CNS neurons and glia) mechanisms, may lead to the development of novel therapeutic approaches, such as enviromimetics, for a wide range of neurological and psychiatric disorders.

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.

Handling stress impairs learning through a mechanism involving caspase-1 activation and adenosine signaling

Acute stressors can induce fear and physiologic responses that prepare the body to protect from danger. A key component of this response is immune system readiness. In particular, inflammasome activation appears critical to linking stress to the immune system. Here, we show that a novel combination of handling procedures used regularly in mouse research impairs novel object recognition (NOR) and activates caspase-1 in the amygdala. In male mice, this handling-stress paradigm combined weighing, scruffing and sham abdominal injection once per hr. While one round of weigh/scruff/needle-stick had no impact on NOR, two rounds compromised NOR without impacting location memory or anxiety-like behaviors. Caspase-1 knockout (KO), IL-1 receptor 1 (IL-1R1) KO and IL-1 receptor antagonist (IL-RA)-administered mice were resistant to handling stress-induced loss of NOR. In addition, examination of the brain showed that handling stress increased caspase-1 activity 85% in the amygdala without impacting hippocampal caspase-1 activity. To delineate danger signals relevant to handling stress, caffeine-administered and adenosine 2A receptor (A2AR) KO mice were tested and found resistant to impaired learning and caspase-1 activation. Finally, mice treated with the β-adrenergic receptor antagonist, propranolol, were resistant to handling stress-induced loss of NOR and caspase-1 activation. Taken together, these results indicate that handling stress-induced impairment of object learning is reliant on a pathway requiring A2AR-dependent activation of caspase-1 in the amygdala that appears contingent on β-adrenergic receptor functionality.

Early life stress amplifies fear responses and hippocampal synaptic potentiation in the APPswe/PS1dE9 Alzheimer mouse model

Cognitive deficits and alterations in emotional behaviour are typical features of Alzheimer's disease (AD). Moreover, exposure to stress or adversity during the early life period has been associated with an acceleration of cognitive deficits and increased AD pathology in transgenic AD mouse models. Whether and how early life adversity affects fear memory in AD mice remains elusive. We therefore investigated whether exposure to early life stress (ELS) alters fear learning in APPswe/PS1dE9 mice, a classic mouse model for AD, and whether this is accompanied by alterations in hippocampal synaptic potentiation, an important cellular substrate for learning and memory. Transgenic APPswe/PS1dE9 mice were subjected to ELS by housing the dams and her pups with limited nesting and bedding material from postnatal days 2-9. Following a fear conditioning paradigm, 12-month-old ELS-exposed APPswe/PS1dE9 mice displayed enhanced contextual freezing behaviour, both in the conditioning context and in a novel context. ELS-exposed APPswe/PS1dE9 mice also displayed enhanced hippocampal synaptic potentiation, even in the presence of the GluN2B antagonist Ro25-6981 (which prevented synaptic potentiation in control mice). No differences in the level of PSD-95 or synaptophysin were observed between the groups. We conclude that in APPswe/PS1dE9 mice, ELS increases fear memory in the conditioning context as well as a novel context, which is accompanied by aberrant hippocampal synaptic potentiation. These results may help to understand how individual differences in the vulnerability to develop AD arise and emphasise the importance of the early postnatal time window in these differences. This article is part of Special Issue entitled: Lifestyle and Brain Metaplasticity.

Pathological Effects of Cortisol on Intervertebral Disc Cells and Mesenchymal Stem Cells from Lower Back Pain Patients

In western countries, lower back pain (LBP) is one of the most common disorders, experienced by more than 80% of the population. Chronic LBP due to disc degeneration has been linked to ongoing inflammatory processes in the disc and endplates. Pain effects the body in different ways, inducing a general stress response in which the body responds by releasing the stress hormone cortisol. Little is known about the impact of pain-induced stress on the progression of disc degeneration. Thus, the effects of cortisol on disc cells (DCs) and human mesenchymal stem cells (hMSCs) were explored in vitro with the objective of investigating the repercussions of cortisol on these cell types involved in de- and regenerative mechanisms of the disc. DC and hMSC pellet cultures were exposed to cortisol at two concentrations (150 and 300 ng/mL) for 28 days to simulate pain-induced stress. Cell viability, histological staining, and GAG DNA, along with apo-ptotic assays were conducted. Detection of OCT4, SOX9, IL-1R, and CXCR2 expressions was performed by immunohistochemistry. With cortisol treatment, restricted cell proliferation and less GAG production in both DCs and hMSCs were observed. Suppression of the differentiation and immunomodulatory efficacy of hMSCs was also detected. Moreover, elevated expressions of IL-1R and CXCR2 were detected in both cell types. To conclude, constant exposure to cortisol even at a physiological level enhanced pathological cellular processes in both DCs and hMSCs, which further jeopardized chondrogenesis. This suggests that cortisol resulting from pain-induced stress is a contributing component of intervertebral disc degeneration and may negatively affect regenerative attempts of the disc.

The cerebellum under stress

Stress-related psychiatric conditions are one of the main causes of disability in developed countries. They account for a large portion of resource investment in stress-related disorders, become chronic, and remain difficult to treat. Research on the neurobehavioral effects of stress reveals how changes in certain brain areas, mediated by a number of neurochemical messengers, markedly alter behavior. The cerebellum is connected with stress-related brain areas and expresses the machinery required to process stress-related neurochemical mediators. Surprisingly, it is not regarded as a substrate of stress-related behavioral alterations, despite numerous studies that show cerebellar responsivity to stress. Therefore, this review compiles those studies and proposes a hypothesis for cerebellar function in stressful conditions, relating it to stress-induced psychopathologies. It aims to provide a clearer picture of stress-related neural circuitry and stimulate cerebellum-stress research. Consequently, it might contribute to the development of improved treatment strategies for stress-related disorders.

Childhood Lead Exposure and Adult Neurodegenerative Disease

Millions of Americans now entering midlife and old age were exposed to high levels of lead, a neurotoxin, as children. Evidence from animal-model and human observational studies suggest that childhood lead exposure may raise the risk of adult neurodegenerative disease, particularly dementia, through a variety of possible mechanisms including epigenetic modification, delayed cardiovascular and kidney disease, direct degenerative CNS injury from lead remobilized from bone, and lowered neural and cognitive reserve. Within the next ten years, the generation of children with the highest historical lead exposures, those born in the 1960s, 1970s, and 1980s, will begin to enter the age at which dementia symptoms tend to emerge. Many will also enter the age in which lead stored in the skeleton may be remobilized at greater rates, particularly for women entering menopause and men and women experiencing osteoporosis. Should childhood lead exposure prove pro-degenerative, the next twenty years will provide the last opportunities for possible early intervention to forestall greater degenerative disease burden across the aging lead-exposed population. More evidence is needed now to characterize the nature and magnitude of the degenerative risks facing adults exposed to lead as children and to identify interventions to limit long-term harm.

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.

Mast Cells in Neurodegenerative Disease

Neurodegenerative diseases affect millions of people worldwide, yet there are currently no effective treatments. Because risk of neurodegenerative disease substantially increases with age, greater life expectancy with a concomitant aging population means more individuals will be affected in the coming decades. Thus, there is an urgent need for understanding the mechanisms driving neurodegenerative diseases in order to develop improved treatment strategies. Inflammation in the nervous system, termed “neuroinflammation,” has become increasingly recognized as being associated with neurodegenerative diseases. Early attention focused primarily on morphological changes in astrocytes and microglia; however, brain and CNS resident mast cells are now receiving attention as a result of being “first responders” to injury. Mast cells also exert profound effects on their microenvironment and neighboring cells including behavior and/or activation of astrocytes, microglia, and neurons, which, in turn, are implicated in neuroinflammation, neurogenesis and neurodegeneration. Mast cells also affect disruption/permeability of the blood brain barrier enabling toxin and immune cell entry exacerbating an inflammatory microenvironment. Here, we discuss the roles of mast cells in neuroinflammation and neurodegeneration with a focus on development and progression of four prominent neurodegenerative diseases: Alzheimer’s Disease, Parkinson’s Disease, Amyotrophic Lateral Sclerosis, and Huntington’s Disease.

Hybrid Resiliency-Stressor Conceptual Framework for Informing Decision Support Tools and Addressing Environmental Injustice and Health Inequities

While structural factors may drive health inequities, certain health-promoting attributes of one's "place" known as salutogens may further moderate the cumulative impacts of exposures to socio-environmental stressors that behave as pathogens. Understanding the synergistic relationship between socio-environmental stressors and resilience factors is a critical component in reducing health inequities; however, the catalyst for this concept relies on community-engaged research approaches to ultimately strengthen resiliency and promote health. Furthermore, this concept has not been fully integrated into environmental justice and cumulative risk assessment screening tools designed to identify geospatial variability in environmental factors that may be associated with health inequities. As a result, we propose a hybrid resiliency-stressor conceptual framework to inform the development of environmental justice and cumulative risk assessment screening tools that can detect environmental inequities and opportunities for resilience in vulnerable populations. We explore the relationship between actual exposures to socio-environmental stressors, perceptions of stressors, and one's physiological and psychological stress response to environmental stimuli, which collectively may perpetuate health inequities by increasing allostatic load and initiating disease onset. This comprehensive framework expands the scope of existing screening tools to inform action-based solutions that rely on community-engaged research efforts to increase resiliency and promote positive health outcomes.

On the central role of mitochondria dysfunction and oxidative stress in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is the commonest cause of dementia, with approximately 5 million new cases occurring annually. Despite decades of research, its complex pathophysiology and etiopathogenesis presents a major hindrance to the development of an effective treatment and prevention strategy. Aging is the biggest risk factor for the development of AD, and the total number of older people in the population is going to significantly increase in the next decades, suggesting that AD incidence and prevalence is likely to increase in the future. This makes the need for a better understanding of the disease to be extremely urgent.

METHODS

A search was done by accessing PubMed/Medline, EBSCO, and PsycINFO databases. The search string used was "(dementia* OR Alzheimer's) AND (pathophysiology* OR pathogenesis)". New key terms were identified (new term included "vitamin D, thyroid hormone, mitochondria dysfunction, oxidative stress, testosterone, estrogen, melatonin, progesterone, luteinizing hormone, amyloid-β (Aβ), and hyperphosphorylated tau"). The electronic databases were searched for titles or abstracts containing these terms in all published articles between January 1, 1965, and January 31, 2019. The search was limited to studies published in English and other languages involving both animal and human subjects.

RESULTS

Mitochondria dysfunction and oxidative stress play a critical role in AD etiopathogenesis and pathophysiology.

CONCLUSION

AD treatment and prevention strategies must be geared towards improving mitochondrial function and attenuating oxidative stress.

Inflammatory mechanisms in neurodegeneration

This review discusses the profound connection between microglia, neuroinflammation, and Alzheimer's disease (AD). Theories have been postulated, tested, and modified over several decades. The findings have further bolstered the belief that microglia-mediated inflammation is both a product and contributor to AD pathology and progression. Distinct microglia phenotypes and their function, microglial recognition and response to protein aggregates in AD, and the overall role of microglia in AD are areas that have received considerable research attention and yielded significant results. The following article provides a historical perspective of microglia, a detailed discussion of multiple microglia phenotypes including dark microglia, and a review of a number of areas where microglia intersect with AD and other pathological neurological processes. The overall breadth of important discoveries achieved in these areas significantly strengthens the hypothesis that neuroinflammation plays a key role in AD. Future determination of the exact mechanisms by which microglia respond to, and attempt to mitigate, protein aggregation in AD may lead to new therapeutic strategies.

Treatment with a brain-selective prodrug of 17β-estradiol improves cognitive function in Alzheimer's disease mice by regulating klf5-NF-κB pathway

10β,17β-dihydroxyestra-1,4-dien-3-one (DHED) which is a brain-selective prodrug of 17β-estradiol has been reported to improve the cognitive function in Alzheimer’s disease (AD) mice model. However, little is known about the potential mechanism for cognitive improvement. In the present study, we used AD mice to investigate the effects and mechanisms of DHED treatment. Female Tg2576 transgenic AD mice were ovariectomized and then treated by implanting Alzet osmotic minipumps containing DHED or vehicle subcutaneously for 8 weeks. Consistent with previous report, DHED treatment ameliorated cognitive function of AD mice with decreasing Aβ levels in the hippocampus. Besides, we also found DHED treatment could reduce oxidative and inflammatory stress and the level of p-tau. The mechanisms underlying the cognitive function improvement may be linked with estrogen receptor (ER)-klf5-NF-κB pathway, demonstrated by decreased expression of klf5 and the secretion of inflammatory cytokines. However, the effects of DHED treatment could be reversed when ERα was inhibited by ICI182780. Taken together, our findings uncovered a new mechanism for DHED to improve the cognitive function of AD mice and may provide a viable therapy to treat AD.

Measuring chronic stress exposure incorporating the active and healthy ageing (AHA) concept within the cross-sectional Bern cohort study 2014 (BeCS-14)

The aim of the study was to represent chronic stress exposure by a complex generic Active and Healthy (AHA) diagnostic assessment tool incorporating ICF. This is a single-centre, cross-sectional, observational, non-interventional, non-randomized trial in University based women's hospital, division of Gynecological Endocrinology and Reproductive Medicine. All participants followed a standardized, holistic battery of biopsychosocial assessments consisting of bio-functional status (BFS), bio-functional age (BFA) and the questionnaire for chronic stress exposure (TICS). 624 non-pediatric, non-geriatric subjects were recruited in the BeCS-14 cohort. The mean difference between chronological age and BFA was 7.8 ± 8.0 year equivalents. The mean stress level score assessed by SSCS was 13.2 with 45.4% being exposed to above average stress intensity. 22 BFS items (14 objective, 7 subjective) significantly correlated with chronic stress exposure (TICS-SSCS). The constructed sum score composed of SOC_L9 and complaint questionnaire (physical and emotional wellbeing) represented chronic stress exposure best (pearson-correlation value 0.564, p < 0.0001). Higher chronic stress exposure was associated with bio-functional pro-aging (less vitality) in both sexes. In conclusion, chronic stress is accepted as a major risk factor for developing non-communicable diseases (NCD). Our ICF compatible, complex, generic BFS/BFA assessment tool reflects chronic stress exposure and may be applied in various health care settings, e.g., in health promotion and prevention of NCDs.

Sleep and circadian rhythm disruption and stress intersect in Alzheimer's disease

Alzheimer's disease (AD) was discovered and the pathological hallmarks were revealed more than a century ago. Subsequently, many remarkable discoveries and breakthroughs provided us with mechanistic insights into the pathogenesis of AD. The identification of the molecular underpinning of the disease not only provided the framework of AD pathogenesis but also targets for therapeutic inventions. Despite all the initial successes, no effective treatment for AD has emerged yet as all the late stages of clinical trials have failed. Many factors ranging from genetic to environmental factors have been critically appraised as the potential causes of AD. In particular, the role of stress on AD has been intensively studied while the relationship between sleep and circadian rhythm disruption (SCRD) and AD have recently emerged. SCRD has always been thought to be a corollary of AD pathologies until recently, multiple lines of evidence converge on the notion that SCRD might be a contributing factor in AD pathogenesis. More importantly, how stress and SCRD intersect and make their concerted contributions to AD phenotypes has not been reviewed. The goal of this literature review is to examine at multiple levels - molecular, cellular (e.g. microglia, gut microbiota) and holistic - how the interaction between stress and SCRD bi-directionally and synergistically exacerbate AD pathologies and cognitive impairment. AD, in turn, worsens stress and SCRD and forms the vicious cycle that perpetuates and amplifies AD.

The opioid system in stress-induced memory disorders: From basic mechanisms to clinical implications in post-traumatic stress disorder and Alzheimer's disease

Cognitive and emotional impairment are a serious consequence of stress exposure and are core features of neurological and psychiatric conditions that involve memory disorders. Indeed, acute and chronic stress are high-risk factors for the onset of post-traumatic stress disorder (PTSD) and Alzheimer's disease (AD), two devastating brain disorders associated with memory dysfunction. Besides the sympathetic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis, stress response also involves the activation of the opioid system in brain regions associated with stress regulation and memory processing. In this context, it is possible that stress-induced memory disorders may be attributed to alterations in the interaction between the neuroendocrine stress system and the opioid system. In this review, we: (1) describe the effects of acute and chronic stress on memory, and the modulatory role of the opioid system, (2) discuss the contribution of the opioid system to the pathophysiology of PTSD and AD, and (3) present evidence of current and potential therapies that target the opioid receptors to treat PTSD- and AD-associated symptoms.

Anxiety as a risk factor of Alzheimer's disease and vascular dementia

BACKGROUND

The aetiology of dementia is not yet fully understood. Stress can have a damaging effect on brain health. The prognostic effect of anxiety is still unclear regarding Alzheimer's disease as well as vascular dementia.AimsTo explore the association between anxiety and future dementia.

METHOD

Medline, PsycINFO, CINAHL, Web of Science and ALOIS were searched for publications up to 12 January 2018. Longitudinal studies with a follow-up of at least 2 years were included, if the trait or state anxiety had been assessed at baseline. Studies with cognitive impairment at baseline were not included. We used a random effects model to calculate the pooled time to Alzheimer's disease and incidence of vascular dementia.

RESULTS

Anxiety predicts risk of Alzheimer's disease (n = 26 193 out of seven studies, hazard ratio1.53, 95% CI 1.16-2.01, P < 0.01) and vascular dementia (n = 4916 out of two studies, odds ratio1.88, 95% CI 1.05-3.36, P < 0.01). The pooled hazard ratio regarding risk of Alzheimer's disease was still significant when excluding studies with critical risk of bias (n = 14 110 out of six studies, hazard ratio 1.35, 95% CI 1.08-1.70, P < 0.01).

CONCLUSIONS

Anxiety is a risk factor for both types of dementia. The temporal and functional relation between anxiety and dementia needs investigation in future studies. The protective value of treating anxiety should be explored further.Declaration of interestNone.

Inhibiting RIP1 Improves Chronic Stress-Induced Cognitive Impairments in D-Galactose-Induced Aging Mice

Mounting evidence shows that chronic stress can affect both the structure and function of the brain resulting in decreased synaptic plasticity and cognitive dysfunction. Although several studies have indicated that aged brains are more vulnerable to chronic stress, it remains unknown how to prevent stress-induced memory deficits in aged animals. Neuroinflammation plays an important role in the pathogenesis of chronic stress-related brain dysfunction. Receptor-interacting protein 1 (RIP1) is a key molecule that can modulate inflammation, apoptosis, and necroptosis. Here, we investigated whether inhibiting RIP1 using necrostatin-1 during chronic stress could improve chronic stress-related brain dysfunction in D-galactose-induced aging mice. The stressed mice underwent restraint stress for 14 days. Necrostatin-1 (6.25 mg/kg) or vehicle was administered intraperitoneally once every 3 days during the stress period. Locomotor activity was tested using the open field test and cognitive function was assessed using the novel object recognition and Barnes maze tests. The hippocampus was collected to assess neuroinflammation (Iba1, IL-1α, IL-1β, TNF-α, and C1q), necroptosis [RIP1, RIP3, mixed lineage kinase domain-like (MLKL), and NF-κB], neuroplasticity (doublecortin, NR1, NR2A, NR2B, GluA1, and GluA2), and the expression of glucocorticoid and mineralocorticoid receptors. Blood samples were collected to quantify the levels of corticosterone. We found that chronic stress induced obvious memory impairment and neuroinflammation, decreased neurogenesis and GluA2 expression, and increased the expression of RIP1 and NF-κB. Inhibiting RIP1 by necrostatin-1 during chronic stress rescued the memory impairment and alleviated the pathological changes induced by stress. These suggest that inhibiting RIP1 using necrostatin-1 improves chronic stress-related brain dysfunction in D-galactose-induced aging mice. The potential mechanisms include limitation of neuroinflammation and the rescue of neurogenesis and GluA2 expression.

Acute psychosocial stress in mid-aged male rats causes hyperthermia, cognitive decline, and increased deep sleep power, but does not alter deep sleep duration

Aging is associated with altered sleep architecture and worsened hippocampus-dependent cognition, highly prevalent clinical conditions that detract from quality of life for the elderly. Interestingly, exposure to psychosocial stress causes similar responses in young subjects, suggesting that age itself may act as a stressor. In prior work, we demonstrated that young animals show loss of deep sleep, deficits in cognition, and elevated body temperature after acute stress exposure, whereas aged animals are hyporesponsive on these measures. However, it is unclear if these age-altered stress responses occur in parallel over the course of aging. To address this, here we repeated the experiment in mid-aged animals. We hypothesized that mid-aged stress responses would be intermediate between those of young and aged subjects. Sixteen mid-aged (12 months) male F344 rats were implanted with EEG/EMG emitters to monitor sleep architecture and body temperature, and were trained on the Morris water maze for 3 days. On the fourth day, half of the subjects were restrained for 3 hours immediately before the water maze probe trial. Sleep architecture and body temperature were measured during the ensuing inactive period, and on the following day, endpoint measures were taken. Restrained mid-aged animals showed resistance to deep sleep loss, but demonstrated stress-induced water maze probe trial performance deficits as well as postrestraint hyperthermia. Taken in the context of prior work, these data suggest that age-related loss of sleep architecture stress sensitivity may precede both cognitive and body temperature-related stress insensitivity.

Endolysosomal degradation of Tau and its role in glucocorticoid-driven hippocampal malfunction

Emerging studies implicate Tau as an essential mediator of neuronal atrophy and cognitive impairment in Alzheimer's disease (AD), yet the factors that precipitate Tau dysfunction in AD are poorly understood. Chronic environmental stress and elevated glucocorticoids (GC), the major stress hormones, are associated with increased risk of AD and have been shown to trigger intracellular Tau accumulation and downstream Tau-dependent neuronal dysfunction. However, the mechanisms through which stress and GC disrupt Tau clearance and degradation in neurons remain unclear. Here, we demonstrate that Tau undergoes degradation via endolysosomal sorting in a pathway requiring the small GTPase Rab35 and the endosomal sorting complex required for transport (ESCRT) machinery. Furthermore, we find that GC impair Tau degradation by decreasing Rab35 levels, and that AAV-mediated expression of Rab35 in the hippocampus rescues GC-induced Tau accumulation and related neurostructural deficits. These studies indicate that the Rab35/ESCRT pathway is essential for Tau clearance and part of the mechanism through which GC precipitate brain pathology.

Precision medicine and drug development in Alzheimer's disease: the importance of sexual dimorphism and patient stratification

Neurodegenerative diseases (ND) are among the leading causes of disability and mortality. Considerable sex differences exist in the occurrence of the various manifestations leading to cognitive decline. Alzheimer's disease (AD) exhibits substantial sexual dimorphisms and disproportionately affects women. Women have a higher life expectancy compared to men and, consequently, have more lifespan to develop AD. The emerging precision medicine and pharmacology concepts - taking into account the individual genetic and biological variability relevant for disease risk, prevention, detection, diagnosis, and treatment - are expected to substantially enhance our knowledge and management of AD. Stratifying the affected individuals by sex and gender is an important basic step towards personalization of scientific research, drug development, and care. We hypothesize that sex and gender differences, extending from genetic to psychosocial domains, are highly relevant for the understanding of AD pathophysiology, and for the conceptualization of basic/translational research and for clinical therapy trial design.

Memorcise and Alzheimer's disease

Alzheimer's disease (AD) is a debilitating disease influencing a multitude of outcomes, including memory function. Recent work suggests that memory may be influenced by exercise ('memorcise'), even among those with AD. The present narrative review details (1) the underlying mechanisms of AD; (2) whether exercise has a protective effect in preventing AD; (3) the mechanisms through which exercise may help to prevent AD; (4) the mechanisms through which exercise may help attenuate the progression of AD severity among those with existing AD; (5) the effects and mechanisms through which exercise is associated with memory among those with existing AD; and (6) exercise recommendations for those with existing AD. Such an understanding will aid clinicians in their ability to use exercise as a potential behavioral strategy to help prevent and treat AD.

An Inflammation-Centric View of Neurological Disease: Beyond the Neuron

Inflammation is a complex biological response fundamental to how the body deals with injury and infection to eliminate the initial cause of cell injury and effect repair. Unlike a normally beneficial acute inflammatory response, chronic inflammation can lead to tissue damage and ultimately its destruction, and often results from an inappropriate immune response. Inflammation in the nervous system (“neuroinflammation”), especially when prolonged, can be particularly injurious. While inflammation per se may not cause disease, it contributes importantly to disease pathogenesis across both the peripheral (neuropathic pain, fibromyalgia) and central [e.g., Alzheimer disease, Parkinson disease, multiple sclerosis, motor neuron disease, ischemia and traumatic brain injury, depression, and autism spectrum disorder] nervous systems. The existence of extensive lines of communication between the nervous system and immune system represents a fundamental principle underlying neuroinflammation. Immune cell-derived inflammatory molecules are critical for regulation of host responses to inflammation. Although these mediators can originate from various non-neuronal cells, important sources in the above neuropathologies appear to be microglia and mast cells, together with astrocytes and possibly also oligodendrocytes. Understanding neuroinflammation also requires an appreciation that non-neuronal cell—cell interactions, between both glia and mast cells and glia themselves, are an integral part of the inflammation process. Within this context the mast cell occupies a key niche in orchestrating the inflammatory process, from initiation to prolongation. This review will describe the current state of knowledge concerning the biology of neuroinflammation, emphasizing mast cell-glia and glia-glia interactions, then conclude with a consideration of how a cell's endogenous mechanisms might be leveraged to provide a therapeutic strategy to target neuroinflammation.

Impact of the Relationship of Stress and the Immune System in the Appearance of Alzheimer's Disease

The understanding of how the immune system works, as well as its relationship with the stress level, seems to be important at the start of the Alzheimer's disease (AD). To analyze this, immunoglobulin A (IgA) and cortisol in saliva were measured using ELISA in patients with mild AD and healthy volunteers, and the production of both biomarkers was compared and correlated. In participants without AD, IgA was higher when cortisol was lower, and the opposite happened in participants with AD, with the quantification in saliva being a suitable method to determine it.

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.

Developing Cognitive Markers of Alzheimer's Disease for Primary Care: Implications for Behavioral and Global Prevention

A comprehensive approach to the prevention of Alzheimer's disease (AD) warrants a synergy across multiple domains and procedures. Whereas the study of biological markers has mobilized major activity in the field, the development of cognitive markers is largely ignored, despite the unique advantages they may offer. Cognitive markers essentially assess the core clinical feature that biological markers intend to predict. In this respect, cognitive markers expand the foundation of preclinical diagnostics and disease staging in a manner that integrates both physiological and psychological factors. In addition, the cost-effective implementation of cognitive markers makes them remarkably conducive to community-wide screenings, and thereby a vital component of any global blueprint for prevention. Specifically, in the primary care setting, cognitive markers may provide effective gate keeping for more invasive, labor intensive, and expensive procedures. From this perspective, cognitive markers may provide the first step for identifying preclinical treatment recipients in general public. Moreover, the detection of preclinical decline via cognitive markers can increase awareness of AD risk and the motivation for making protective lifestyle changes. The behavioral approach might be expedient for prevention in light of the compelling evidence of lifestyle amelioration of AD risk. In an integrative view, incorporating cognitive markers to primary care may facilitate a synergetic development in preventive interventions that carries epidemiological significance. This paper addresses the theoretical, methodological, and pragmatic aspects of this prospect.

The Stress-Induced Transcription Factor NR4A1 Adjusts Mitochondrial Function and Synapse Number in Prefrontal Cortex

The energetic costs of behavioral chronic stress are unlikely to be sustainable without neuronal plasticity. Mitochondria have the capacity to handle synaptic activity up to a limit before energetic depletion occurs. Protective mechanisms driven by the induction of neuronal genes likely evolved to buffer the consequences of chronic stress on excitatory neurons in prefrontal cortex (PFC), as this circuitry is vulnerable to excitotoxic insults. Little is known about the genes involved in mitochondrial adaptation to the buildup of chronic stress. Using combinations of genetic manipulations and stress for analyzing structural, transcriptional, mitochondrial, and behavioral outcomes, we characterized NR4A1 as a stress-inducible modifier of mitochondrial energetic competence and dendritic spine number in PFC. NR4A1 acted as a transcription factor for changing the expression of target genes previously involved in mitochondrial uncoupling, AMP-activated protein kinase activation, and synaptic growth. Maintenance of NR4A1 activity by chronic stress played a critical role in the regressive synaptic organization in PFC of mouse models of stress (male only). Knockdown, dominant-negative approach, and knockout of Nr4a1 in mice and rats (male only) protected pyramidal neurons against the adverse effects of chronic stress. In human PFC tissues of men and women, high levels of the transcriptionally active NR4A1 correlated with measures of synaptic loss and cognitive impairment. In the context of chronic stress, prolonged expression and activity of NR4A1 may lead to responses of mitochondria and synaptic connectivity that do not match environmental demand, resulting in circuit malfunction between PFC and other brain regions, constituting a pathological feature across disorders.

SIGNIFICANCE STATEMENT The bioenergetic cost of chronic stress is too high to be sustainable by pyramidal prefrontal neurons. Cellular checkpoints have evolved to adjust the responses of mitochondria and synapses to the buildup of chronic stress. NR4A1 plays such a role by controlling the energetic competence of mitochondria with respect to synapse number. As an immediate-early gene, Nr4a1 promotes neuronal plasticity, but sustained expression or activity can be detrimental. NR4A1 expression and activity is sustained by chronic stress in animal models and in human studies of neuropathologies sensitive to the buildup of chronic stress. Therefore, antagonism of NR4A1 is a promising avenue for preventing the regressive synaptic reorganization in cortical systems in the context of chronic stress.

Mast Cell Activation in Brain Injury, Stress, and Post-traumatic Stress Disorder and Alzheimer's Disease Pathogenesis

Mast cells are localized throughout the body and mediate allergic, immune, and inflammatory reactions. They are heterogeneous, tissue-resident, long-lived, and granulated cells. Mast cells increase their numbers in specific site in the body by proliferation, increased recruitment, increased survival, and increased rate of maturation from its progenitors. Mast cells are implicated in brain injuries, neuropsychiatric disorders, stress, neuroinflammation, and neurodegeneration. Brain mast cells are the first responders before microglia in the brain injuries since mast cells can release prestored mediators. Mast cells also can detect amyloid plaque formation during Alzheimer's disease (AD) pathogenesis. Stress conditions activate mast cells to release prestored and newly synthesized inflammatory mediators and induce increased blood-brain barrier permeability, recruitment of immune and inflammatory cells into the brain and neuroinflammation. Stress induces the release of corticotropin-releasing hormone (CRH) from paraventricular nucleus of hypothalamus and mast cells. CRH activates glial cells and mast cells through CRH receptors and releases neuroinflammatory mediators. Stress also increases proinflammatory mediator release in the peripheral systems that can induce and augment neuroinflammation. Post-traumatic stress disorder (PTSD) is a traumatic-chronic stress related mental dysfunction. Currently there is no specific therapy to treat PTSD since its disease mechanisms are not yet clearly understood. Moreover, recent reports indicate that PTSD could induce and augment neuroinflammation and neurodegeneration in the pathogenesis of neurodegenerative diseases. Mast cells play a crucial role in the peripheral inflammation as well as in neuroinflammation due to brain injuries, stress, depression, and PTSD. Therefore, mast cells activation in brain injury, stress, and PTSD may accelerate the pathogenesis of neuroinflammatory and neurodegenerative diseases including AD. This review focusses on how mast cells in brain injuries, stress, and PTSD may promote the pathogenesis of AD. We suggest that inhibition of mast cells activation and brain cells associated inflammatory pathways in the brain injuries, stress, and PTSD can be explored as a new therapeutic target to delay or prevent the pathogenesis and severity of AD.

A roadmap for investigating the role of the prion protein in depression associated with neurodegenerative disease

The physiological properties of the native, endogenous prion protein (PrP(C)) is a matter of concern, due to its pleiotropic functions and links to neurodegenerative disorders and cancer. In line with our hypothesis that the basic function of PrP(C) is to serve as a cell surface scaffold for the assembly of signaling modules, multiple interactions have been identified of PrP(C) with signaling molecules, including neurotransmitter receptors. We recently reported evidence that PrP(C) may modulate monoaminergic neurotransmission, as well as depressive-like behavior in mice. Here, we discuss how those results, together with a number of other studies, including our previous demonstration that both inflammatory and behavioral stress modulate PrP(C) content in neutrophils, suggest a distributed role of PrP(C) in clinical depression and inflammation associated with neurodegenerative diseases. An overarching understanding of the multiple interventions of PrP(C) upon physiological events may both shed light on the pathogenesis of, as well as help the identification of novel therapeutic targets for clinical depression, Prion and Alzheimer's Diseases.

Microglia under psychosocial stressors along the aging trajectory: Consequences on neuronal circuits, behavior, and brain diseases

Mounting evidence indicates the importance of microglia for proper brain development and function, as well as in complex stress-related neuropsychiatric disorders and cognitive decline along the aging trajectory. Considering that microglia are resident immune cells of the brain, a homeostatic maintenance of their effector functions that impact neuronal circuitry, such as phagocytosis and secretion of inflammatory factors, is critical to prevent the onset and progression of these pathological conditions. However, the molecular mechanisms by which microglial functions can be properly regulated under healthy and pathological conditions are still largely unknown. We aim to summarize recent progress regarding the effects of psychosocial stress and oxidative stress on microglial phenotypes, leading to neuroinflammation and impaired microglia-synapse interactions, notably through our own studies of inbred mouse strains, and most importantly, to discuss about promising therapeutic strategies that take advantage of microglial functions to tackle such brain disorders in the context of adult psychosocial stress or aging-induced oxidative stress.

Socially Housed Female Macaques: a Translational Model for the Interaction of Chronic Stress and Estrogen in Aging

PURPOSE OF REVIEW

Estrogen's role in cognitive aging remains unclear. Despite evidence implicating stress in pathological aging, the interaction of stress with estrogen on cognition in older women has received little attention, and few animal models exist with which to examine this interaction.

RECENT FINDINGS

We present evidence that aging socially subordinate female macaques that experience chronic psychosocial stress constitute a suitable model to investigate this. First, we review studies showing that estrogen modulates cognition in animal models, as well as studies demonstrating that estrogen's action on certain types of cognition is impaired by stress. Next, we discuss data showing that middle-aged socially subordinate female macaques exhibit distinct stress-induced phenotypes, and review our investigations indicating that estrogen modulates behavior and physiology differently in subordinate female monkeys. We conclude that socially housed female macaques represent a translational animal model for investigating the interplay of chronic stress and estrogen on cognitive aging in women.

Enkephalins: Endogenous Analgesics with an Emerging Role in Stress Resilience

Psychological stress is a state of mental or emotional strain or tension that results from adverse or demanding circumstances. Chronic stress is well known to induce anxiety disorders and major depression; it is also considered a risk factor for Alzheimer's disease. Stress resilience is a positive outcome that is associated with preserved cognition and healthy aging. Resilience presents psychological and biological characteristics intrinsic to an individual conferring protection against the development of psychopathologies in the face of adversity. How can we promote or improve resilience to chronic stress? Numerous studies have proposed mechanisms that could trigger this desirable process. The roles of enkephalin transmission in the control of pain, physiological functions, like respiration, and affective disorders have been studied for more than 30 years. However, their role in the resilience to chronic stress has received much less attention. This review presents the evidence for an emerging involvement of enkephalin signaling through its two associated opioid receptors, μ opioid peptide receptor and δ opioid peptide receptor, in the natural adaptation to stressful lifestyles.

Brain Under Stress and Alzheimer's Disease

Modern society is characterized by the ubiquity of stressors that affect every individual to different extents. Furthermore, experimental, clinical, and epidemiological data have shown that chronic activation of the stress response may participate in the development of various somatic as well as neuropsychiatric diseases. Surprisingly, the role that stress plays in the etiopathogenesis of Alzheimer's disease (AD) has not yet been studied in detail and is therefore not well understood. However, accumulated data have shown that neuroendocrine and behavioral changes accompanying the stress response affect neuronal homeostasis and compromise several key neuronal processes. Mediators of the neuroendocrine stress response, if elevated repeatedly or chronically, exert direct detrimental effects on the brain by impairing neuronal metabolism, plasticity, and survival. Stress-induced hormonal and behavioral reactions may also participate in the development of hypertension, atherosclerosis, insulin resistance, and other peripheral disturbances that may indirectly induce neuropathological processes participating in the development and progression of AD. Importantly, stress-induced detrimental effects as etiological factors of AD are attractive because they can be reduced by several approaches including behavioral and pharmacological interventions. These interventions may therefore represent an important strategy for prevention or attenuation of the progression of AD.