Posttraumatic stress disorder-like induction elevates β-amyloid levels, which directly activates corticotropin-releasing factor neurons to exacerbate stress responses

Multi-omics delineate growth factor network underlying exercise effects in an Alzheimer's mouse model

Physical exercise represents a primary defense against age-related cognitive decline and neurodegenerative disorders like Alzheimer's disease (AD). To impartially investigate the underlying mechanisms, we conducted single-nucleus transcriptomic and chromatin accessibility analyses (snRNA-seq and ATAC-seq) on the hippocampus of mice carrying AD-linked NL-G-F mutations in the amyloid precursor protein gene (APPNL-G-F) following prolonged voluntary wheel-running exercise. Our study reveals that exercise mitigates amyloid-induced changes in both transcriptomic expression and chromatin accessibility through cell type-specific transcriptional regulatory networks. These networks converge on the activation of growth factor signaling pathways, particularly the epidermal growth factor receptor (EGFR) and insulin signaling, correlating with an increased proportion of immature dentate granule cells and oligodendrocytes. Notably, the beneficial effects of exercise on neurocognitive functions can be blocked by pharmacological inhibition of EGFR and the downstream phosphoinositide 3-kinases (PI3K). Furthermore, exercise leads to elevated levels of heparin-binding EGF (HB-EGF) in the blood, and intranasal administration of HB-EGF enhances memory function in sedentary APPNL-G-F mice. These findings offer a panoramic delineation of cell type-specific hippocampal transcriptional networks activated by exercise and suggest EGF-related growth factor signaling as a druggable contributor to exercise-induced memory enhancement, thereby suggesting therapeutic avenues for combatting AD-related cognitive decline.

Potential Therapeutic Effects of Bifidobacterium breve MCC1274 on Alzheimer's Disease Pathologies in AppNL-G-F Mice

We previously demonstrated that orally supplemented Bifidobacterium breve MCC1274 (B. breve MCC1274) mitigated Alzheimer's disease (AD) pathologies in both 7-month-old AppNL-G-F mice and wild-type mice; thus, B. breve MCC1274 supplementation might potentially prevent the progression of AD. However, the possibility of using this probiotic as a treatment for AD remains unclear. Thus, we investigated the potential therapeutic effects of this probiotic on AD using 17-month-old AppNL-G-F mice with memory deficits and amyloid beta saturation in the brain. B. breve MCC1274 supplementation ameliorated memory impairment via an amyloid-cascade-independent pathway. It reduced hippocampal and cortical levels of phosphorylated extracellular signal-regulated kinase and c-Jun N-terminal kinase as well as heat shock protein 90, which might have suppressed tau hyperphosphorylation and chronic stress. Moreover, B. breve MCC1274 supplementation increased hippocampal synaptic protein levels and upregulated neuronal activity. Thus, B. breve MCC1274 supplementation may alleviate cognitive dysfunction by reducing chronic stress and tau hyperphosphorylation, thereby enhancing both synaptic density and neuronal activity in 17-month-old AppNL-G-F mice. Overall, this study suggests that B. breve MCC1274 has anti-AD effects and can be used as a potential treatment for AD.

Traumatic Brain Injury and Post-Traumatic Stress Disorder and Their Influence on Development and Pattern of Alzheimer's Disease Pathology in Later Life

Background

Traumatic brain injury (TBI) and posttraumatic stress disorder (PTSD) are potential risk factors for the development of dementia including Alzheimer's disease (AD) in later life. The findings of studies investigating this question are inconsistent though.

Objective

To investigate if these inconsistencies are caused by the existence of subgroups with different vulnerability for AD pathology and if these subgroups are characterized by atypical tau load/atrophy pattern.

Methods

The MRI and PET data of 89 subjects with or without previous TBI and/or PTSD from the DoD ADNI database were used to calculate an age-corrected gray matter tau mismatch metric (ageN-T mismatch-score and matrix) for each subject. This metric provides a measure to what degree regional tau accumulation drives regional gray matter atrophy (matrix) and can be used to calculate a summary score (score) reflecting the severity of AD pathology in an individual.

Results

The ageN-T mismatch summary score was positively correlated with whole brain beta-amyloid load and general cognitive function but not with PTSD or TBI severity. Hierarchical cluster analysis identified five different spatial patterns of tau-gray matter interactions. These clusters reflected the different stages of the typical AD tau progression pattern. None was exclusively associated with PTSD and/or TBI.

Conclusions

These findings suggest that a) although subsets of patients with PTSD and/or TBI develop AD-pathology, a history of TBI or PTSD alone or both is not associated with a significantly higher risk to develop AD pathology in later life. b) remote TBI or PTSD do not modify the typical AD pathology distribution pattern.

Interplay of G-proteins and Serotonin in the Neuroimmunoinflammatory Model of Chronic Stress and Depression: A Narrative Review

INTRODUCTION

This narrative review addresses the clinical challenges in stress-related disorders such as depression, focusing on the interplay between neuron-specific and pro-inflammatory mechanisms at the cellular, cerebral, and systemic levels.

OBJECTIVE

We aim to elucidate the molecular mechanisms linking chronic psychological stress with low-grade neuroinflammation in key brain regions, particularly focusing on the roles of G proteins and serotonin (5-HT) receptors.

METHODS

This comprehensive review of the literature employs systematic, narrative, and scoping review methodologies, combined with systemic approaches to general pathology. It synthesizes current research on shared signaling pathways involved in stress responses and neuroinflammation, including calcium-dependent mechanisms, mitogen-activated protein kinases, and key transcription factors like NF-κB and p53. The review also focuses on the role of G protein-coupled neurotransmitter receptors (GPCRs) in immune and pro-inflammatory responses, with a detailed analysis of how 13 of 14 types of human 5-HT receptors contribute to depression and neuroinflammation.

RESULTS

The review reveals a complex interaction between neurotransmitter signals and immunoinflammatory responses in stress-related pathologies. It highlights the role of GPCRs and canonical inflammatory mediators in influencing both pathological and physiological processes in nervous tissue.

CONCLUSION

The proposed Neuroimmunoinflammatory Stress Model (NIIS Model) suggests that proinflammatory signaling pathways, mediated by metabotropic and ionotropic neurotransmitter receptors, are crucial for maintaining neuronal homeostasis. Chronic mental stress can disrupt this balance, leading to increased pro-inflammatory states in the brain and contributing to neuropsychiatric and psychosomatic disorders, including depression. This model integrates traditional theories on depression pathogenesis, offering a comprehensive understanding of the multifaceted nature of the condition.

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.

Emerging Alzheimer's disease therapeutics: promising insights from lipid metabolism and microglia-focused interventions

More than 55 million people suffer from dementia, with this number projected to double every 20 years. In the United States, 1 in 3 aged individuals dies from Alzheimer's disease (AD) or another type of dementia and AD kills more individuals than breast cancer and prostate cancer combined. AD is a complex and multifactorial disease involving amyloid plaque and neurofibrillary tangle formation, glial cell dysfunction, and lipid droplet accumulation (among other pathologies), ultimately leading to neurodegeneration and neuronal death. Unfortunately, the current FDA-approved therapeutics do not reverse nor halt AD. While recently approved amyloid-targeting antibodies can slow AD progression to improve outcomes for some patients, they are associated with adverse side effects, may have a narrow therapeutic window, and are expensive. In this review, we evaluate current and emerging AD therapeutics in preclinical and clinical development and provide insight into emerging strategies that target brain lipid metabolism and microglial function - an approach that may synergistically target multiple mechanisms that drive AD neuropathogenesis. Overall, we evaluate whether these disease-modifying emerging therapeutics hold promise as interventions that may be able to reverse or halt AD progression.

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

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

Amyloid β-based therapy for Alzheimer's disease: challenges, successes and future

Amyloid β protein (Aβ) is the main component of neuritic plaques in Alzheimer's disease (AD), and its accumulation has been considered as the molecular driver of Alzheimer's pathogenesis and progression. Aβ has been the prime target for the development of AD therapy. However, the repeated failures of Aβ-targeted clinical trials have cast considerable doubt on the amyloid cascade hypothesis and whether the development of Alzheimer's drug has followed the correct course. However, the recent successes of Aβ targeted trials have assuaged those doubts. In this review, we discussed the evolution of the amyloid cascade hypothesis over the last 30 years and summarized its application in Alzheimer's diagnosis and modification. In particular, we extensively discussed the pitfalls, promises and important unanswered questions regarding the current anti-Aβ therapy, as well as strategies for further study and development of more feasible Aβ-targeted approaches in the optimization of AD prevention and treatment.

Posttraumatic stress symptom severity predicts cognitive decline beyond the effect of Alzheimer's disease biomarkers in Veterans

Chronic stress is a risk factor for dementia but whether it explains unique variance in cognitive decline in older adults above Alzheimer's disease (AD) biomarkers is unknown. In a preclinical cohort of Vietnam Veterans, we examined the relationship between posttraumatic stress disorder (PTSD) symptom severity, AD biomarkers of beta-amyloid (Aβ) and tau, and change in cognitive performance on two widely-used screeners, the Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA). Analyses indicated that PTSD symptom severity was associated with a greater decline on the MMSE (p < 0.04) and MoCA (p < 0.024) after adjusting for biomarkers of AD, notably on the attention scale of the MoCA and the memory index of the MMSE. These analyses survived multiple comparison corrections. Taken together, PTSD symptom severity is associated with accelerated cognitive decline. Treating PTSD should be considered instrumental to maintaining cognitive function as adults age.

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.

Transcriptional Regulation, Signaling Pathways, and Subcellular Localization of Corticotropin-Releasing Factor Receptors in the Central Nervous System

Corticotropin-releasing factor (CRF) receptors CRF-R1 and CRF-R2 are differentially distributed in body tissues, and although they respond differentially to stimuli due to their association with different signaling pathways, both receptors have a fundamental role in the response and adaptation to stressful stimuli. Here, we summarize the reported data on different forms of CRF-R1 and CRF-R2 regulation as well as on their subcellular localization. Although the presence of R1 has been described at pre- and postsynaptic sites, R2 is mainly associated with postsynaptic densities. Different studies have provided valuable information on how these receptors regulate responses at a central level, elucidating different and sometimes synergistic roles in response to stress, but despite their high sequence identity, both receptors have been described to be differentially regulated both by their ligands and by transcriptional factors. To date, and from the point of view of their promoter sequences, it has not yet been reported how the different consensus sites identified in silico could be modulating the transcriptional regulation and expression of the receptors under different conditions, which strongly limits the full understanding of their differential functions, providing a wide field to increase and expand the study of the regulation and role of CRF receptors in the CRF system. SIGNIFICANCE STATEMENT: A large number of physiological functions related to the organization of the stress response in different body tissues are associated with the corticotropin-releasing factor system. This system also plays a relevant role in depression and anxiety disorders, as well as being a direct connection between stress and addiction. A better understanding of how the receptors of this system are regulated would help to expand the understanding of how these receptors respond differently to both drugs and stressful stimuli.

Influence of Cortisol on the Fibril Formation Kinetics of Aβ42 Peptide: A Multi-Technical Approach

Amyloid-β peptide (Aβ) aggregates are known to be correlated with pathological neurodegenerative diseases. The fibril formation process of such peptides in solution is influenced by several factors, such as the ionic strength of the buffer, concentration, pH, and presence of other molecules, just to mention a few. In this paper, we report a detailed analysis of in vitro Aβ42 fibril formation in the presence of cortisol at different relative concentrations. The thioflavin T fluorescence assay allowed us to monitor the fibril formation kinetics, while a morphological characterization of the aggregates was obtained by atomic force microscopy. Moreover, infrared absorption spectroscopy was exploited to investigate the secondary structure changes along the fibril formation path. Molecular dynamics calculations allowed us to understand the intermolecular interactions with cortisol. The combined results demonstrated the influence of cortisol on the fibril formation process: indeed, at cortisol-Aβ42 concentration ratio (ρ) close to 0.1 a faster organization of Aβ42 fragments into fibrils is promoted, while for ρ = 1 the formation of fibrils is completely inhibited.

Inescapable footshocks induce molecular changes in the prefrontal cortex of rats in an amyloid-beta-42 model of Alzheimer's disease

Alzheimer's disease (AD) affects several brain areas, including the prefrontal cortex (PFC) involved in execution, working memory, and fear extinction. Despite these critical roles, the PFC is understudied in AD pathology. People with post-traumatic stress disorder (PTSD) have twice the risk of developing AD, and the underlying mechanisms linking these two diseases are less understood. Here, we investigated the effect of footshock stress on behavioural vis-a-vis molecular changes in the PFC of an amyloid-beta (Aβ)-42 lesion rat model of AD. Trauma-like conditions were induced by exposing the animals to several footshocks. AD-like condition was induced via intra-hippocampal injection of Aβ-42 peptide. Following Aβ-42 injections, animals were tested for behavioural changes using the Open Field Test (OFT) and Y-maze test. The PFC was later harvested for neurochemical analyses. Our results showed an interactive effect of footshocks and Aβ-42 lesion on: reduced percentage alternation in the Y-maze test, suggesting memory impairment; reduced number of line crosses and time spent in the centre square of the OFT, indicating anxiogenic responses. Similarly, there was an interactive effect of footshocks and Aβ-42 lesion on: increased FK506 binding protein 51 (FKBP5) expression, which can be associated with stress-induced anxiogenic behaviours; and increased neuronal apoptosis in the PFC of the animals. In addition, footshocks, as well as Aβ-42 lesion, reduced superoxide dismutase levels and Bridging Integrator-1 (BIN1) expression in the PFC of the animals, which can be linked to the observed memory impairment. In conclusion, our findings indicate that footshocks exaggerate PFC-associated behavioural and molecular changes induced by an AD-like pathology.

Differential effects of chronic stress on anxiety-like behavior and contextual fear conditioning in the TgF344-AD rat model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative brain disorder that leads to severe cognitive and functional impairments. Many AD patients also exhibit neuropsychiatric symptoms, such as anxiety and depression, prior to the clinical diagnosis of dementia. Chronic stress is associated with numerous adverse health consequences and disease states, and AD patients exhibit altered stress systems. Thus, stress may represent a causal link between neuropsychiatric symptoms and AD. To address this possibility, we examined the effects of chronic stress in the TgF344-AD rat model that co-expresses the mutant human amyloid precursor protein (APPsw) and presenilin 1 (PS1ΔE9) genes. Adult male transgenic (Tg+) and wild-type (WT) rats (6-7.5 months of age), with and without a history of chronic restraint stress, were tested for footshock-induced conditioned fear and for anxiety-like behavior in the elevated plus-maze. We found that non-stressed Tg+ rats showed increased anxiety-like behavior compared to non-stressed WT rats. In contrast, Tg+ and WT rats did not differ in levels of freezing immediately following footshock or during contextual re-exposure. Additionally, stressed Tg+ rats were not significantly different from stressed WT rats on any measures of anxiety or fear. Thus, while stress has been linked as a risk factor for AD-related pathology, it appears from the present findings that two weeks of daily restraint stress did not further enhance anxiety- or fear-like behaviors in TgF344-AD rats.

Cognitive impairment and World Trade Centre-related exposures

On 11 September 2001 the World Trade Center (WTC) in New York was attacked by terrorists, causing the collapse of multiple buildings including the iconic 110-story 'Twin Towers'. Thousands of people died that day from the collapse of the buildings, fires, falling from the buildings, falling debris, or other related accidents. Survivors of the attacks, those who worked in search and rescue during and after the buildings collapsed, and those working in recovery and clean-up operations were exposed to severe psychological stressors. Concurrently, these 'WTC-affected' individuals breathed and ingested a mixture of organic and particulate neurotoxins and pro-inflammogens generated as a result of the attack and building collapse. Twenty years later, researchers have documented neurocognitive and motor dysfunctions that resemble the typical features of neurodegenerative disease in some WTC responders at midlife. Cortical atrophy, which usually manifests later in life, has also been observed in this population. Evidence indicates that neurocognitive symptoms and corresponding brain atrophy are associated with both physical exposures at the WTC and chronic post-traumatic stress disorder, including regularly re-experiencing traumatic memories of the events while awake or during sleep. Despite these findings, little is understood about the long-term effects of these physical and mental exposures on the brain health of WTC-affected individuals, and the potential for neurocognitive disorders. Here, we review the existing evidence concerning neurological outcomes in WTC-affected individuals, with the aim of contextualizing this research for policymakers, researchers and clinicians and educating WTC-affected individuals and their friends and families. We conclude by providing a rationale and recommendations for monitoring the neurological health of WTC-affected individuals.

Neurobiological mechanisms underlying delayed expression of posttraumatic stress disorder: A scoping review

BACKGROUND

The capacity of posttraumatic stress disorder (PTSD) to occur with delayed onset has been documented in several systematic reviews and meta-analyses. Neurobiological models of PTSD may provide insight into the mechanisms underlying the progressive increase in PTSD symptoms over time as well as into occasional occurrences of long-delayed PTSD with few prodromal symptoms.

AIM

To obtain an overview of key concepts explaining and types of evidence supporting neurobiological underpinnings of delayed PTSD.

METHODS

A scoping review of studies reporting neurobiological findings relevant to delayed PTSD was performed, which included 38 studies in the qualitative synthesis.

RESULTS

Neurobiological mechanisms underlying PTSD symptoms, onset, and course involve several interconnected systems. Neural mechanisms involve the neurocircuitry of fear, comprising several structures, such as the hippocampus, amygdala, and prefrontal cortex, that are amenable to time-dependent increases in activity through sensitization and kindling. Neural network models explain generalization of the fear response. Neuroendocrine mechanisms consist of autonomic nervous system and hypothalamic-pituitary-adrenocortical axis responses, both of which may be involved in sensitization to stress. Neuroinflammatory mechanisms are characterized by immune activation, which is sometimes due to the effects of traumatic brain injury. Finally, neurobehavioral/contextual mechanisms involve the effects of intervening stressors and mental and physical disorder comorbidities, and these may be particularly relevant in cases of long-delayed PTSD.

CONCLUSION

Thus, delayed PTSD may result from multiple underlying neurobiological mechanisms that may influence the likelihood of developing prodromal symptoms preceding the onset of full-blown PTSD.

Risk of Dementia in Posttraumatic Stress Disorder

Several studies have investigated the risk of dementia in posttraumatic stress disorder (PTSD) using a varying methodology. Epidemiological studies have found an increased risk of dementia with PTSD in Vietnam veterans as well as the general population. Laboratory studies reported the accelerated formation of β-amyloid and tau, which represent the primary pathology of Alzheimer's dementia in animal models of PTSD. These investigations were conducted against a background of cognitive impairment and atrophy of the hippocampus and certain cortical areas in patients with PTSD. Very few studies have investigated the pathological basis in humans for the reported association of PTSD with dementia. This important gap in the literature has recently been partly addressed by very few studies that estimated the burden of β-amyloid and tau. The PET studies did not show an association between PTSD and the specific pathology of Alzheimer's disease or signs of neurodegenerative diseases underlying other dementia syndromes. Another study demonstrated decreased plasma β-amyloid load and increased plasma β-amyloid 42/40 ratio in PTSD without PET evaluation. While PTSD is associated with an increased risk of dementia syndrome in general, there is no convincing evidence that it causes or accelerates the pathology of Alzheimer's disease, which causes the most common type of dementia. Factors that may account for the association between PTSD and a clinical diagnosis of dementia are discussed in this review.

Altered stress hormone levels affect in vivo vascular function in the hAPP23+/- overexpressing mouse model of Alzheimer's disease

Alzheimer's disease (AD) has long been considered a brain-specific dementia syndrome. However, in recent decades, the occurrence of cardiovascular (CV) disease in the progression of AD has been confirmed by increasing epidemiological evidence. In this study, we conducted an in-depth cardiovascular characterization of a humanized amyloid precursor protein (APP) overexpressing mouse model (hAPP23+/-), which overexpresses the Swedish mutation (KM670/671NL). At the age of 6 mo, hAPP23+/- mice had a lower survival, lower body weight, and increased corticosterone and VMA levels compared with C57BL/6 littermates. Systolic blood pressure was increased in hAPP23+/- animals compared with C57BL/6 littermates, but diastolic blood pressure was not statistically different. Pulse pressure remained unchanged but abdominal and carotid pulse-wave velocity (aPWV and cPWV) were increased in hAPP23+/- compared with C57BL/6 mice. Echocardiography showed no differences in systolic or diastolic cardiac function. Ex vivo evaluation of vascular function showed decreased adreno receptor dependent vasoconstriction of hAPP23+/- aortic segments, although the isobaric biomechanics of the aortic wall were similar to C57BL/6 aortic segments. In conclusion, hAPP23+/- mice exhibited high serum corticosterone levels, elevated systolic blood pressure, and increased arterial stiffness in vivo. However, ex vivo aortic stiffness of hAPP23+/- aortic segments was not changed and vascular reactivity to α1-adrenoceptor stimulation was attenuated. These findings highlight the need for more frequent assessment of circulating stress hormone levels and PWV measurements in daily clinical practice for people at risk of AD.NEW & NOTEWORTHY We showed that male amyloid precursor protein (APP) transgenic mice have higher circulating stress hormone levels. As a result, higher systolic blood pressure and pulse-wave velocity were measured in vivo in addition to a smaller α-adrenergic receptor-dependent contraction upon ex vivo stimulation with phenylephrine. Our findings highlight the need for more frequent assessment of circulating stress hormone levels and PWV measurements in daily clinical practice for people at risk of Alzheimer's disease.

Exposure to footshock stress downregulates antioxidant genes and increases neuronal apoptosis in an Aβ(1-42) rat model of Alzheimer's disease

Post-traumatic stress disorder (PTSD) is a neuropsychiatric disorder that develops from exposure to trauma, mostly when normal psychological mechanisms fail. Studies have shown that people who have PTSD are susceptible to developing dementia, mostly Alzheimer's disease (AD), suggesting common underlying risk factors in the comorbidity. However, data elucidating links between these conditions is scarce. Here we show that footshock stress exacerbates AD-like pathology. To induce a trauma-like condition, the rats were exposed to multiple intense footshocks followed by a single reminder. This was followed by bilateral intrahippocampal lesions with amyloid-beta (Aβ) (1-42), to model AD-like pathology. We found that footshocks increased anxiety behavior and impaired fear memory extinction in Aβ(1-42) lesioned rats. We also found a reduced expression of nuclear factor erythroid 2-related factor 2 (Nrf2), NAD (P) H: quinone oxidoreductase 1 (NQO1), heme oxygenase-1 (HO-1), and an increased expression of Kelch-like ECH-associated protein 1 (Keap1) in the amygdala and hippocampus. Furthermore, oxidative stress level was sustained, which was associated with increased apoptosis in the amygdala and hippocampus. Our finding suggests that AD-like pathology can induce oxidative changes in the amygdala and hippocampus, which can be exaggerated by footshock stress.

Quantitative Proteomics Analysis of Susceptibility and Resilience to Stress in a Rat model of PTSD

Posttraumatic stress disorder (PTSD) is a prevalent psychiatric disorder and sometimes deadly consequence of exposure to severe psychological trauma. However, there has been little known about the definitive molecular changes involved in determining vulnerability to PTSD. In the current study, we used proteomics to quantify protein changes in the hippocampus of foot shocks rats. A total of 6151 proteins were quantified and 97 proteins were significantly differentially expressed. The protein-protein interaction (PPI) analysis showed that oxidation-reduction process and glutathione homeostasis may be the potential key progress of being vulnerable to PTSD. The Gene Ontology analysis revealed enriched GO terms in the protein groups of Susceptible group vs Control group rats for glutathione binding,oligopeptide binding,modified amino acid binding,and glutathione transferase activity for their molecular functions (MF) and in the process of cellular response to toxic substance,xenobiotic metabolic process, urea metabolic process, and response to drug for the biological process (BP).SIGNIFICANCE:In recent years, there has been a growing interest in mental illness associated with trauma exposure. We found that stress susceptibility was associated with increased expression of arginase 1 indicated as a potential treatment target. Our results also proposed that carbonic anhydrases 3 could be a biomarker for the development of PTSD. This research helps to explain the potential molecular mechanism in PTSD and supply a new method for ameliorating PTSD.

Current Views on the Role of Stress in the Pathogenesis of Chronic Neurodegenerative Diseases

The review summarizes the results of studies on the cellular and molecular mechanisms mediating the impact of stress on the pathogenesis of neurodegenerative brain pathologies (Alzheimer's disease, Parkinson's disease, etc.) and presents current information on the role of stress in the hyperphosphorylation of tau protein, aggregation of beta-amyloid, and hyperactivation of the hypothalamic-pituitary-adrenal axis involved in the hyperproduction of factors that contribute to the pathogenetic role of stress in neurodegeneration. The data on the participation of microglia in the effects of stress on the pathogenesis of neurodegenerative diseases are presented.

Serum Corticosterone and Insulin Resistance as Early Biomarkers in the hAPP23 Overexpressing Mouse Model of Alzheimer's Disease

Increasing epidemiological evidence highlights the association between systemic insulin resistance and Alzheimer’s disease (AD). As insulin resistance can be caused by high-stress hormone levels and since hypercortisolism appears to be an important risk factor of AD, we aimed to investigate the systemic insulin functionality and circulating stress hormone levels in a mutant humanized amyloid precursor protein (APP) overexpressing (hAPP23+/−) AD mouse model. Memory and spatial learning of male hAPP23+/− and C57BL/6 (wild type, WT) mice were assessed by a Morris Water Maze (MWM) test at the age of 4 and 12 months. The systemic metabolism was examined by intraperitoneal glucose and insulin tolerance tests (GTT, ITT). Insulin and corticosterone levels were determined in serum. In the hippocampus, parietal and occipital cortex of hAPP23+/− brains, amyloid-beta (Aβ) deposits were present at 12 months of age. MWM demonstrated a cognitive decline in hAPP23+/− mice at 12 but not at 4 months, evidenced by increasing total path lengths and deteriorating probe trials compared to WT mice. hAPP23+/− animals presented increased serum corticosterone levels compared to WT mice at both 4 and 12 months. hAPP23+/− mice exhibited peripheral insulin resistance compared to WT mice at 4 months, which stabilized at 12 months of age. Serum insulin levels were similar between genotypes at 4 months of age but were significantly higher in hAPP23+/− mice at 12 months of age. Peripheral glucose homeostasis remained unchanged. These results indicate that peripheral insulin resistance combined with elevated circulating stress hormone levels could be potential biomarkers of the pre-symptomatic phase of AD.

Chronic stress and Alzheimer's disease

Stress is a key factor in the development and progress of diseases. In neurodegenerative conditions, stress management can play an important role in maintaining the quality of life and the capacity to improve. Neurodegenerative diseases, including Alzheimer's disease, cause the motor and cognitive malfunctions that are spontaneously stressful and also can disturb the neural circuits that promote stress responses. The interruption of those circuits leads to aggressive and inappropriate behavior. In addition, stress contributes to illness and may exacerbate symptoms. In this review, we present stress-activated neural pathways involved in Alzheimer's disease from a clinical and experimental point of view, as well as supportive drugs and therapies.

Posttraumatic Stress Disorder in the Elderly

Posttraumatic stress disorder (PTSD) can occur at any point in the life span and can last for decades. Chronic PTSD can affect quality of life and have a negative impact on physical function and health in the elderly and may be associated with premature aging and dementia. It is critical that clinicians screen for trauma-based symptoms and to treat as appropriate.

Anxiety and Alzheimer's disease: Behavioral analysis and neural basis in rodent models of Alzheimer's-related neuropathology

Alzheimer's disease (AD) pathology is commonly associated with cognitive decline but is also composed of neuropsychiatric symptoms including psychological distress and alterations in mood, including anxiety and depression. Emotional dysfunction in AD is frequently modeled using tests of anxiety-like behavior in transgenic rodents. These tests often include the elevated plus-maze, light/dark test and open field test. In this review, we describe prototypical behavioral paradigms used to examine emotional dysfunction in transgenic models of AD, specifically anxiety-like behavior. Next, we summarize the results of studies examining anxiety-like behavior in transgenic rodents, noting that the behavioral outcomes using these paradigms have produced inconsistent results. We suggest that future research will benefit from using a battery of tests to examine emotional behavior in transgenic AD models. We conclude by discussing putative, overlapping neurobiological mechanisms underlying AD-related neuropathology, stress and anxiety-like behavior reported in AD models.

COVID-19 and Alzheimer's disease: how one crisis worsens the other

Alzheimer’s disease (AD) has emerged as a key comorbidity of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). The morbidity and mortality of COVID-19 are elevated in AD due to multiple pathological changes in AD patients such as the excessive expression of viral receptor angiotensin converting enzyme 2 and pro-inflammatory molecules, various AD complications including diabetes, lifestyle alterations in AD, and drug-drug interactions. Meanwhile, COVID-19 has also been reported to cause various neurologic symptoms including cognitive impairment that may ultimately result in AD, probably through the invasion of SARS-CoV-2 into the central nervous system, COVID-19-induced inflammation, long-term hospitalization and delirium, and post-COVID-19 syndrome. In addition, the COVID-19 crisis also worsens behavioral symptoms in uninfected AD patients and poses new challenges for AD prevention. In this review, we first introduce the symptoms and pathogenesis of COVID-19 and AD. Next, we provide a comprehensive discussion on the aggravating effects of AD on COVID-19 and the underlying mechanisms from molecular to social levels. We also highlight the influence of COVID-19 on cognitive function, and propose possible routes of viral invasion into the brain and potential mechanisms underlying the COVID-19-induced cognitive impairment. Last, we summarize the negative impacts of COVID-19 pandemic on uninfected AD patients and dementia prevention.

Sleep Deprivation, a Link Between Post-Traumatic Stress Disorder and Alzheimer's Disease

An estimated 5 million Americans are living with Alzheimer's disease (AD), and there is also a significant impact on caregivers, with an additional 16 million Americans providing unpaid care for individuals with AD and other dementias. These numbers are projected to increase in the coming years. While AD is still without a cure, continued research efforts have led to better understanding of pathology and potential risk factors that could be exploited to slow disease progression. A bidirectional relationship between sleep deprivation and AD has been suggested and is well supported by both human and animal studies. Even brief episodes of inadequate sleep have been shown to cause an increase in amyloidβ and tau proteins, both well-established contributors toAD pathology. Sleep deprivation is also the most common consequence of post-traumatic stress disorder (PTSD). Patients with PTSD frequently present with sleep disturbances and also develop dementia at twice the rate of the general population accounting for a disproportionate representation of AD among U.S. Veterans. The goal of this review is to highlight the relationship triad between sleep deprivation, AD, and PTSD as well as their impact on molecular mechanisms driving AD pathology.

The Immunopathogenesis of Alzheimer's Disease Is Related to the Composition of Gut Microbiota

The microbiota-gut-brain axis plays an important role in the development of neurodegenerative diseases. Commensal and pathogenic enteric bacteria can influence brain and immune system function by the production of lipopolysaccharides and amyloid. Dysbiosis of the intestinal microbiome induces local and consecutively systemic immune-mediated inflammation. Proinflammatory cytokines then trigger neuroinflammation and finally neurodegeneration. Immune-mediated oxidative stress can lead to a deficiency of vitamins and essential micronutrients. Furthermore, the wrong composition of gut microbiota might impair the intake and metabolization of nutrients. In patients with Alzheimer's disease (AD) significant alterations of the gut microbiota have been demonstrated. Standard Western diet, infections, decreased physical activity and chronic stress impact the composition and diversity of gut microbiota. A higher abundancy of "pro-inflammatory" gut microbiota goes along with enhanced systemic inflammation and neuroinflammatory processes. Thus, AD beginning in the gut is closely related to the imbalance of gut microbiota. Modulation of gut microbiota by Mediterranean diet, probiotics and curcumin can slow down cognitive decline and alter the gut microbiome significantly. A multi-domain intervention approach addressing underlying causes of AD (inflammation, infections, metabolic alterations like insulin resistance and nutrient deficiency, stress) appears very promising to reduce or even reverse cognitive decline by exerting positive effects on the gut microbiota.

Posttraumatic stress symptom persistence across 24 years: association with brain structures

Posttraumatic stress disorder (PTSD) is known to persist, eliciting early medical co-morbidity, and accelerated aging. Although PTSD diagnosis has been found to be associated with smaller volume in multiple brain regions, posttraumatic stress (PTS) symptoms and their associations with brain morphometry are rarely assessed over long periods of time. We predicted that persistent PTS symptoms across ~24 years would be inversely associated with hippocampal, amygdala, anterior cingulate volumes, and hippocampal occupancy (HOC = hippocampal volume/[hippocampal volume + inferior lateral ventricle volume]) in late middle age. Exploratory analyses examined prefrontal regions. We assessed PTS symptoms in 247 men at average ages 38 (time 1) and 62 (time 2). All were trauma-exposed prior to time 1. Brain volumes were assessed at time 2 using 3 T structural magnetic resonance imaging. Symptoms were correlated over time (r = 0.46 p < .0001). Higher PTS symptoms averaged over time and symptoms at time 1 were both associated with lower hippocampal, amygdala, rostral middle frontal gyrus (MFG), and medial orbitofrontal cortex (OFC) volumes, and a lower HOC ratio at time 2. Increased PTS symptomatology from time 1 to time 2 was associated with smaller hippocampal volume. Results for hippocampal, rostral MFG and medial OFC remained significant after omitting individuals above the threshold for PTSD diagnosis. Even at sub-diagnostic threshold levels, PTS symptoms were present decades after trauma exposure in parallel with highly correlated structural deficits in brain regions regulating stress responsivity and adaptation.

Psychological Stress-Induced Immune Response and Risk of Alzheimer's Disease in Veterans from Operation Enduring Freedom and Operation Iraqi Freedom

PURPOSE

Psychological stress is a significant health problem in veterans and their family members. Traumatic brain injury (TBI) and stress lead to the onset, progression, and worsening of several inflammatory and neurodegenerative diseases in veterans and civilians. Alzheimer's disease (AD) is a progressive, irreversible neuroinflammatory disease that causes problems with memory, thinking, and behavior. TBIs and chronic psychological stress cause and accelerate the pathology of neuroinflammatory diseases such as AD. However, the precise molecular and cellular mechanisms governing neuroinflammation and neurodegeneration are currently unknown, especially in veterans. The purpose of this review article was to advance the hypothesis that stress and TBI-mediated immune response substantially contribute and accelerate the pathogenesis of AD in veterans and their close family members and civilians.

METHODS

The information in this article was collected and interpreted from published articles in PubMed between 1985 and 2020 using the key words stress, psychological stress, Afghanistan war, Operation Enduring Freedom (OEF), Iraq War, Operation Iraqi Freedom (OIF), Operation New Dawn (OND), traumatic brain injury, mast cell and stress, stress and neuroimmune response, stress and Alzheimer's disease, traumatic brain injury, and Alzheimer's disease.

FINDINGS

Chronic psychological stress and brain injury induce the generation and accumulation of beta-amyloid peptide, amyloid plaques, neurofibrillary tangles, and phosphorylation of tau in the brain, thereby contributing to AD pathogenesis. Active military personnel and veterans are under enormous psychological stress due to various war-related activities, including TBIs, disabilities, fear, new environmental conditions, lack of normal life activities, insufficient communications, explosions, military-related noise, and health hazards. Brain injury, stress, mast cell, and other immune cell activation can induce headache, migraine, dementia, and upregulate neuroinflammation and neurodegeneration in veterans of Operation Enduring Freedom, Operation Iraqi Freedom, and Operation New Dawn. TBIs, posttraumatic stress disorder, psychological stress, pain, glial activation, and dementia in active military personnel, veterans, or their family members can cause AD several years later in their lives. We suggest that there are increasing numbers of veterans with TBIs and stress and that these veterans may develop AD late in life if no appropriate therapeutic intervention is available.

IMPLICATIONS

Per these published reports, the fact that TBIs and psychological stress can accelerate the pathogenesis of AD should be recognized. Active military personnel, veterans, and their close family members should be evaluated regularly for stress symptoms to prevent the pathogenesis of neurodegenerative diseases, including AD.

Neuroprotection of Tropical Fruit Juice Mixture via the Reduction of iNOS Expression and CRH Level in β-Amyloid-Induced Rats Model of Alzheimer's Disease

This study aimed to determine the effects of tropical fruit juice mixture (pomegranate, white guava, and Roselle) on biochemical, behavioral, and histopathological changes of β-amyloid- (Aβ-) induced rats. Formulation 8 (F8) of tropical fruit juice mixture was chosen for this present study due to its high phenolic content and antioxidant capacity. Forty Wistar male rats were divided into five groups: dPBS (sham-operated control), dAβ (Aβ control), JPBS (F8 and PBS), JAβ (F8 and Aβ), and IBFAβ (ibuprofen and Aβ). F8 (5 ml/kg BW), and ibuprofen (10 ml/kg BW) was given orally daily for four weeks before the intracerebroventricular infusion of Aβ for two weeks. Histological analysis and neuronal count of hippocampus tissue in the Cornu Ammonis (CA1) region showed that supplementation with F8 was able to prevent Aβ-induced tissue damage and neuronal shrinkage. However, no significant difference in locomotor activity and novel object recognition (NOR) percentage was detected among different groups at day 7 and day 14 following Aβ infusion. Only effect of time differences (main effect of day) was observed at day 7 as compared to day 14, where reduction in locomotor activity and NOR percentage was observed in all groups, with F (1, 7) = 6.940, p < 0.05 and F (1, 7) = 7.152, p < 0.05, respectively. Besides, the MDA level of the JAβ group was significantly lower (p < 0.01) than that of the dPBS group. However, no significant changes in SOD activity were detected among different groups. Significant reduction in plasma CRH level (p < 0.05) and iNOS expression (p < 0.01) in the brain was detected in the JAβ group as compared to the dAβ group. Hence, our current findings suggest that the tropical fruit juice mixture (F8) has the potential to protect the rats from Aβ-induced neurotoxicity in brain hippocampus tissue possibly via its antioxidant properties and the suppression of iNOS expression and CRH production.

Can mouse models mimic sporadic Alzheimer's disease?

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia worldwide. As age is the main risk factor, > 97% of all AD cases are of sporadic origin, potentiated by various risk factors associated with life style and starting at an age > 60 years. Only < 3% of AD cases are of genetic origin caused by mutations in the amyloid precursor protein or Presenilins 1 or 2, and symptoms already start at an age < 30 years. In order to study progression of AD, as well as therapeutic strategies, mouse models are state-of-the-art. So far many transgenic mouse models have been developed and used, with mutations in the APP or presenilin or combinations (3×Tg, 5×Tg). However, such transgenic mouse models more likely mimic the genetic form of AD and no information can be given how sporadic forms develop. Several risk genes, such as Apolipoprotein E4 and TREM-2 enhance the risk of sporadic AD, but also many risk factors associated with life style (e.g., diabetes, hypercholesterolemia, stress) may play a role. In this review we discuss the current situation regarding AD mouse models, and the problems to develop a sporadic mouse model of AD.

Stress-Induced Neurodegeneration: The Potential for Coping as Neuroprotective Therapy

Stress responses are essential for survival, but become detrimental to health and cognition with chronic activation. Chronic hypothalamic-pituitary-adrenal axis release of glucocorticoids induces hypothalamic-pituitary-adrenal axis dysfunction and neuronal loss, decreases learning and memory, and modifies glucocorticoid receptor/mineralocorticoid receptor expression. Elderly who report increased stress are nearly 3 times more likely to develop Alzheimer's disease, have decreased global cognition and faster cognitive decline than those reporting no stress. Patients with mild cognitive impairment are more sensitive to stress compared to healthy elderly and those with Alzheimer's disease. Stress may also transduce neurodegeneration via the gut microbiome. Coping styles determine hippocampal mineralocorticoid receptor expression in mice, indicating that coping modifies cortisol's effect on the brain. Identifying neuroprotective coping strategies that lessen the burden of stress may prevent or slow cognitive decline. Treatments and education designed to reduce stress should be recognized as neuroprotective.

The selenium-containing compound 3-((4-chlorophenyl)selanyl)-1-methyl-1H-indole reverses depressive-like behavior induced by acute restraint stress in mice: modulation of oxido-nitrosative stress and inflammatory pathway

RATIONALE AND OBJECTIVES

Stress-induced alterations in oxidative and inflammatory parameters have been implicated in the pathophysiology of mood disorders. Based on the antioxidant and anti-inflammatory properties of the selenium-containing compound 3-((4-chlorophenyl)selanyl)-1-methyl-1H-indole (CMI), we assessed its ability to reverse depression-like behavioral alterations, neuroinflammation, and oxidative imbalance induced by acute restraint stress.

METHODS

Mice submitted to restraint for 240 min received CMI (1 or 10 mg/kg, orally) 10 min after the end of the stress induction. Behavioral and biochemical tests were carried out after further 30 min.

RESULTS

Restraint-induced depression-like behavior in the tail suspension test (TST), splash test, and new object exploration test was reversed by CMI. None of the treatments evoked locomotor alteration. In addition, CMI abrogated restraint-induced increases in plasma levels of corticosterone and in markers of oxidative stress and impaired superoxide dismutase and catalase activity in the prefrontal cortex (PFC) and hippocampus (HC). CMI also blocked stress-induced downregulation of mRNA levels of glucocorticoid receptor and brain-derived neurotrophic factor and upregulation of nuclear factor kappa B, inducible nitric oxide synthase, tumor necrosis alpha, indoelamine-2,3-dioxygenase, and glycogen synthase kinase 3 beta in PFC and HC.

CONCLUSIONS

These preclinical results indicate that administration of selenium-containing compounds might help to treat depression associated with inflammation and oxidative stress. Graphical abstract ᅟ.

GSK-3β and ERK1/2 incongruously act in tau hyperphosphorylation in SPS-induced PTSD rats

Post-traumatic stress disorder (PTSD) manifests in neurocognitive deficits in association with increased tau deposition, which mainly consist of phosphorylated tau in Alzheimer disease (AD) brain. However, the exact mechanism of PTSD inducing tau hyperphosphorylation remains unclear and therefore no effective treatment options are currently available. We here show that employing single prolonged stress (SPS), as a consensus PTSD model, induced a typical anxiety and abnormal hyperphosphorylation of tau at Ser202/Thr205 (AT8) and Ser404 but not at Ser199 and Ser396 in the hippocampus compared to the control rats. Furthermore, there was a decrease in the level of inactivated phosphorylated GSK-3β at Ser9, an increase in the level of activated phosphorylated GSK-3β at Thr216 and an obvious decrease in the level of activated phosphorylated ERK1/2, but no alterations in CaMKII and PP2A in hippocampus of SPS rats. On the other hand, the levels of both phosphorylated AKT and total SGK1, stress- and GSK-3β/ERK1/2-related proteins, were down-regulated. Interestingly, Overexpression of SGK1 increased the level of phosphorylated ERK1/2 and led to tau hyperphosphorylation at Ser199 and Ser396. These findings suggest that SPS exposure results in differential tau phosphorylation at different sites probably due to incongruous action between AKT-related GSK-3β activation and SGK1-related ERK1/2 inactivation, suggesting a link between SPS-induced PTSD and AD-associated tau pathogenic mechanisms.

Alzheimer's disease: risk factors and potentially protective measures

Alzheimer's disease (AD) is the most common type of dementia and typically manifests through a progressive loss of episodic memory and cognitive function, subsequently causing language and visuospatial skills deficiencies, which are often accompanied by behavioral disorders such as apathy, aggressiveness and depression. The presence of extracellular plaques of insoluble β-amyloid peptide (Aβ) and neurofibrillary tangles (NFT) containing hyperphosphorylated tau protein (P-tau) in the neuronal cytoplasm is a remarkable pathophysiological cause in patients' brains. Approximately 70% of the risk of developing AD can be attributed to genetics. However, acquired factors such as cerebrovascular diseases, diabetes, hypertension, obesity and dyslipidemia increase the risk of AD development. The aim of the present minireview was to summarize the pathophysiological mechanism and the main risk factors for AD. As a complement, some protective factors associated with a lower risk of disease incidence, such as cognitive reserve, physical activity and diet will also be addressed.

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.

Intermittent hypoxia improves behavioral and adrenal gland dysfunction induced by posttraumatic stress disorder in rats

Nonpharmacological treatments of stress-induced disorders are promising, since they enhance endogenous stress defense systems, are free of side effects, and have few contraindications. The present study tested the hypothesis that intermittent hypoxia conditioning (IHC) ameliorates behavioral, biochemical, and morphological signs of experimental posttraumatic stress disorder (PTSD) induced in rats with a model of predator stress (10-day exposure to cat urine scent, 15 min daily followed by 14 days of stress-free rest). After the last day of stress exposure, rats were conditioned in an altitude chamber for 14 days at a 1,000-m simulated altitude for 30 min on day 1 with altitude and duration progressively increasing to 4,000 m for 4 h on day 5. PTSD was associated with decreased time spent in open arms and increased time spent in closed arms of the elevated X-maze, increased anxiety index, and increased rate of freezing responses. Functional and structural signs of adrenal cortex degeneration were also observed, including decreased plasma concentration of corticosterone, decreased weight of adrenal glands, reduced thickness of the fasciculate zone, and hydropic degeneration of adrenal gland cells. The thickness of the adrenal fasciculate zone negatively correlated with the anxiety index. IHC alleviated both behavioral signs of PTSD and morphological evidence of adrenal cortex dystrophy. Also, IHC alone exerted an antistress effect, which was evident from the increased time spent in open arms of the elevated X-maze and a lower number of rats displaying freezing responses. Therefore, IHC of rats with experimental PTSD reduced behavioral signs of the condition and damage to the adrenal glands.

NEW & NOTEWORTHY Intermittent hypoxia conditioning (IHC) has been shown to be cardio-, vaso-, and neuroprotective. For the first time, in a model of posttraumatic stress disorder (PTSD), this study showed that IHC alleviated both PTSD-induced behavioral disorders and functional and morphological damage to the adrenal glands. Also, IHC alone exerted an antistress effect. These results suggest that IHC may be a promising complementary treatment for PTSD-associated disorders.

Amyloid pathology fingerprint differentiates post-traumatic stress disorder and traumatic brain injury

Introduction

Traumatic brain injury (TBI) and post-traumatic stress disorder (PTSD) are risk factors for early onset of Alzheimer's disease (AD) and may accelerate the progression rate of AD pathology. As amyloid-beta (Aβ) plaques are a hallmark of AD pathology, we hypothesized that TBI and PTSD might increase Aβ accumulation in the brain.

Methods

We examined PET and neuropsychological data from Vietnam War veterans compiled by the US Department of Defense Alzheimer's Disease Neuroimaging Initiative, to examine the spatial distribution of Aβ in male veterans' who had experienced a TBI and/or developed PTSD. Subjects were classified into controls, TBI only, PTSD only, and TBI with PTSD (TBI_PTSD) groups and data were analyzed using both voxel-based and ROI-based approaches.

Results

Compared to controls, all three clinical groups showed a pattern of mainly increased referenced standard uptake values (SUVR) for the amyloid tracer [18F]-AV45 PET, with rank order PTSD > TBI_PTSD > TBI > Control, and same rank order was seen in the deficits of cognitive functions. SUVR increase was observed in widespread cortical regions of the PTSD group; in white matter of the TBI_PTSD group; and cerebellum and precuneus area of the TBI group, in contrast with controls. The [18F]-AV45 SUVR correlated negatively with cerebrospinal fluid (CSF) amyloid levels and positively with the CSF tau concentrations.

Conclusion

These results suggest that both TBI and PTSD are substantial risk factors for cognition decline and increased Aβ deposition resembling that in AD. In addition, both PTSD and TBI_PTSD have a different pathways of Aβ accumulation.

Posttraumatic Stress Disorder in the Elderly

Posttraumatic stress disorder (PTSD) can occur at any point in the life span and can last for decades. Chronic PTSD can affect quality of life and have a negative impact on physical function and health in the elderly and may be associated with premature aging and dementia. It is critical that clinicians screen for trauma-based symptoms and to treat as appropriate.

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.

Apolipoprotein E gene polymorphism, trauma burden, and posttraumatic stress symptoms in U.S. military veterans: Results from the National Health and Resilience in Veterans Study

BACKGROUND

Previous research examining the association between apolipoprotein E (APOE) gene polymorphism and risk for posttraumatic stress disorder (PTSD) has been inconsistent due to the use of small and select samples. This study examined the relation between APOE genotype and PTSD symptoms in two nationally representative samples of U.S. military veterans. The potential effect of cumulative trauma burden and social support in moderating this association was also evaluated.

METHODS

The main sample consisted of 1,386 trauma-exposed European American (EA) veterans (mean age: 62-63 years) who participated in the National Health and Resilience in Veterans Study (NHRVS) in 2011. The independent replication sample consisted of 509 trauma-exposed EA veterans from the 2013 NHRVS.

RESULTS

APOE ε4 allele carriers reported significantly greater severity of PTSD symptoms than noncarriers in the main, but not the replication, sample. In both samples, the interaction of APOE ε4 carrier status and cumulative trauma burden was associated with greater severity of PTSD symptoms (F range = 2.53-8.09, all P's < .01), particularly re-experiencing/intrusion symptoms (F range = 3.59-4.24, P's < .001). Greater social support was associated with lower severity of PTSD symptoms among APOE ε4 allele carriers with greater cumulative trauma burden (β range -.27 to -.60, P's < .05).

CONCLUSION

U.S. military veterans who are APOE ε4 allele carriers and exposed to a high number of traumas may be at increased risk for developing PTSD symptoms than ε4 noncarriers. Greater social support may moderate this association, thereby highlighting the potential importance of social support promoting interventions in mitigating the effect of ε4 × cumulative trauma burden on PTSD risk.

The relationship between stress and Alzheimer's disease

Stress is critically involved in the development and progression of disease. From the stress of undergoing treatments to facing your own mortality, the physiological processes that stress drives have a serious detrimental effect on the ability to heal, cope and maintain a positive quality of life. This is becoming increasingly clear in the case of neurodegenerative diseases. Neurodegenerative diseases involve the devastating loss of cognitive and motor function which is stressful in itself, but can also disrupt neural circuits that mediate stress responses. Disrupting these circuits produces aberrant emotional and aggressive behavior that causes long-term care to be especially difficult. In addition, added stress drives progression of the disease and can exacerbate symptoms. In this review, I describe how neural and endocrine pathways activated by stress interact with ongoing neurodegenerative disease from both a clinical and experimental perspective.

ATP-sensitive potassium-channel inhibitor glibenclamide attenuates HPA axis hyperactivity, depression- and anxiety-related symptoms in a rat model of Alzheimer's disease

Affective disorders including depression and anxiety are among the most prevalent behavioral abnormalities in patients with Alzheimer's disease (AD), which affect the quality of life and progression of the disease. Dysregulation of the hypothalamic-pituitary-adrenal-(HPA) axis has been reported in affective disorders and AD. Recent studies revealed that current antidepressant drugs are not completely effective for treating anxiety- and depression-related disorders in people with dementia. ATP-sensitive-potassium-(K_ATP) channels are well-known to be involved in AD pathophysiology, HPA axis function and the pathogenesis of depression and anxiety-related behaviors. Thus, targeting of K_ATP channel may be a potential therapeutic strategy in AD. Hence, we investigated the effects of intracerebroventricular injection of Aβ25-35 alone or in combination with glibenclamide, K_ATP channel inhibitor on depression- and anxiety-related behaviors as well as HPA axis response to stress in rats. To do this, non-Aβ25-35- and Aβ25-35-treated rats were orally treated with glibenclamide, then the behavioral consequences were assessed using sucrose preference, forced swim, light-dark box and plus maze tests. Stress-induced corticosterone levels following forced swim and plus maze tests were also evaluated as indicative of abnormal HPA-axis-function. Aβ25-35 induced HPA axis hyperreactivity and increased depression- and anxiety-related symptoms in rats. Our results showed that blockade of K_ATP channels with glibenclamide decreased depression- and anxiety-related behaviors by normalizing HPA axis activity in Aβ25-35-treated rats. This study provides additional evidence that Aβ administration can induce depression- and anxiety-like symptoms in rodents, and suggests that K_ATP channel inhibitors may be a plausible therapeutic strategy for treating affective disorders in AD patients.

Anxiety-like behavior as an early endophenotype in the TgF344-AD rat model of Alzheimer's disease

Alzheimer's disease (AD) is characterized by progressive cognitive decline and the presence of aggregates of amyloid beta (plaques) and hyperphosphorylated tau (tangles). Early diagnosis through neuropsychological testing is difficult due to comorbidity of symptoms between AD and other types of dementia. As a result, there is a need to identify the range of behavioral phenotypes expressed in AD. In the present study, we utilized a transgenic rat (TgF344-AD) model that bears the mutated amyloid precursor protein as well as presenilin-1 genes, resulting in progressive plaque and tangle pathogenesis throughout the cortex. We tested young adult male and female TgF344-AD rats in a spatial memory task in the Morris water maze and for anxiety-like behavior in the elevated plus-maze. Results indicated that regardless of sex, TgF344-AD rats exhibited increased anxiety-like behavior in the elevated plus-maze, which occurred without significant deficits in the spatial memory. Together, these results indicate that enhanced anxiety-like behavior represents an early-stage behavioral marker in the TgF344-AD rat model.

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.

Effects of chronic noise on the corticotropin-releasing factor system in the rat hippocampus: relevance to Alzheimer's disease-like tau hyperphosphorylation

Background

Chronic noise exposure has been associated with tau hyperphosphorylation and Alzheimer’s disease (AD)-like pathological changes, but the underlying mechanism is unknown. In this study, we explored the effects of long-term noise exposure on the corticotropin-releasing factor (CRF) system in the hippocampus and its role in noise-induced tau phosphorylation.

Methods

Sixty-four rats were randomly divided into the noise-exposed group and the control group, and rats in the exposure group were exposed to 95 dB SPL white noise for 30 consecutive days. The levels of CRF, CRFR1, CRFR2, and total tau and phosphorylated tau (p-tau) at Ser396 (S396) and Thr205 (T205) in the hippocampus were measured at different time points after the final noise exposure. The co-localized distribution of CRF and p-tau (T205) in the hippocampus was evaluated using double-labeling immunofluorescence.

Results

Long-term exposure to noise for 30 consecutive days significantly increased the expression of CRF and CRFR1 and their mRNAs levels in the hippocampus, which persisted for 7 days after final exposure. In contrast, CRFR2 was raised for 3–7 days following the last exposure. These alterations were also concomitant with the phosphorylation of tau at S396 and T205. Furthermore, there was co-localization of p-tau and CRF in hippocampal neurons.

Conclusion

Chronic noise leads to long-lasting increases in the hippocampal CRF system and the hyperphosphorylation of tau in the hippocampus. Our results also provide evidence for the involvement of the CRF system in noise-induced AD-like neurodegeneration.