The effect of stress on the expression of the amyloid precursor protein in rat brain

Chronic Social and Psychological Stress Impact Select Neuropathologies in the PS19 Mouse Model of Tauopathy

OBJECTIVE

Despite advances toward understanding the etiology of Alzheimer's disease (AD), it remains unclear which aspects of this disease are affected by environmental factors. Chronic life stress increases the risk of aging-related diseases including AD. The impact of stress on tauopathies remains understudied. We examined the effects of stress elicited by social (chronic subordination stress [CSS]) or psychological/physical (chronic restraint stress [CRS]) factors on the PS19 mouse model of tauopathy.

METHODS

Male PS19 mice (average age, 6.3 months) were randomized to receive CSS or CRS, or to remain as singly housed controls. Behavioral tests were used to assess anxiety-like behaviors and cognitive functions. Immunofluorescence staining and Western blotting analysis were used to measure levels of astrogliosis, microgliosis, and tau burden. Immunohistochemistry was used to assess glucocorticoid receptor expression.

RESULTS

PS19 mice exhibit neuroinflammation (glial fibrillary acidic protein, t tests: p = .0297; allograft inflammatory factor 1, t tests: p = .006) and tau hyperphosphorylation ( t test, p = .0446) in the hippocampus, reduced anxiety (post hoc, p = .046), and cognitive deficits, when compared with wild-type mice. Surprisingly, CRS reduced hippocampal levels of both total tau and phospho-tau S404 ( t test, p = .0116), and attenuated some aspects of both astrogliosis and microgliosis in PS19 mice ( t tests, p = .068-.0003); however, this was not associated with significant changes in neurodegeneration or cognitive function. Anxiety-like behaviors were increased by CRS (post hoc, p = .046). Conversely, CSS impaired spatial learning in Barnes maze without impacting tau phosphorylation or neurodegeneration and having a minimal impact on gliosis.

CONCLUSIONS

Our results demonstrate that social or psychological stress can differentially impact anxiety-like behavior, select cognitive functions, and some aspects of tau-dependent pathology in PS19 male mice, providing entry points for the development of experimental approaches designed to slow AD progression.

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.

The temporal balance between self-renewal and differentiation of human neural stem cells requires the amyloid precursor protein

Neurogenesis in the developing human cerebral cortex occurs at a particularly slow rate owing in part to cortical neural progenitors preserving their progenitor state for a relatively long time, while generating neurons. How this balance between the progenitor and neurogenic state is regulated, and whether it contributes to species-specific brain temporal patterning, is poorly understood. Here, we show that the characteristic potential of human neural progenitor cells (NPCs) to remain in a progenitor state as they generate neurons for a prolonged amount of time requires the amyloid precursor protein (APP). In contrast, APP is dispensable in mouse NPCs, which undergo neurogenesis at a much faster rate. Mechanistically, APP cell-autonomously contributes to protracted neurogenesis through suppression of the proneurogenic activator protein-1 transcription factor and facilitation of canonical WNT signaling. We propose that the fine balance between self-renewal and differentiation is homeostatically regulated by APP, which may contribute to human-specific temporal patterns of neurogenesis.

Endoplasmic reticulum stress induces Alzheimer's disease-like phenotypes in the neuron derived from the induced pluripotent stem cell with D678H mutation on amyloid precursor protein

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is mainly caused by the interaction of genetic and environmental factors. The impact of environmental factors on the genetic mutation in the amyloid precursor protein (APP) is not well characterized. We hypothesized that Endoplasmic Reticulum (ER) stress would promote disease for the patient carrying the APP D678H mutation. Therefore, we analyzed the impact of a familial AD mutation on amyloid precursor protein (APP D678H) under ER stress. Induced pluripotent stem cell (iPSC) from APP D678H mutant carrier was differentiated into neurons, which were then analyzed for AD-like changes. Immunocytochemistry and whole-cell patch-clamp recording revealed that the derived neurons on day 28 after differentiation showed neuronal markers and electrophysiological properties similar to those of mature neurons. However, the APP D678H mutant neurons did not have significant alterations in the levels of amyloid-β (Aβ) and phosphorylated tau (pTau) compared to its isogenic wild-type neuron. Only under ER stress, the neurons with the APP D678H mutation had more Aβ and pTau via immune detection assays. The higher level of Aβ in the APP D678H mutant neurons was probably due to the increased level of β-site APP cleaving enzyme (BACE1) and decreased level of Aβ degrading enzymes under ER stress. Increased Aβ and pTau under ER stress reduced the N-methyl-D-aspartate receptor (NMDAR) in Western blot analysis and altered electrophysiological properties in the mutant neurons. Our study provides evidence that the interaction between genetic mutation and ER stress would induce AD-like changes.

The amyloid precursor protein: a converging point in Alzheimer's disease

The decades of evidence that showcase the role of amyloid precursor protein (APP), and its fragment amyloidβ (Aβ), in Alzheimer's disease (AD) pathogenesis are irrefutable. However, the absolute focus on the single APP metabolite Aβ as the cause for AD has resulted in APP and its other fragments that possess toxic propensity, to be overlooked as targets for treatment. The complexity of its processing and its association with systematic metabolism suggests that, if misregulated, APP has the potential to provoke an array of metabolic dysfunctions. This review discusses APP and several of its cleaved products with a particular focus on their toxicity and ability to disrupt healthy cellular function, in relation to AD development. We subsequently argue that the reduction of APP, which would result in a concurrent decrease in Aβ as well as all other toxic APP metabolites, would alleviate the toxic environment associated with AD and slow disease progression. A discussion of those drug-like compounds already identified to possess this capacity is also included.

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.

Lifelong chronic psychosocial stress induces a proteomic signature of Alzheimer's disease in wildtype mice

Late onset, sporadic Alzheimer's disease (AD) accounts for the vast majority of cases. Unlike familial AD, the factors that drive the onset of sporadic AD are poorly understood, although aging and stress play a role. The early onset/severity of neuropathology observed in most genetic mouse models of AD hampers the study of the role of aging and environmental factors; thus alternate strategies are necessary to understand the contributions of these factors to sporadic AD. We demonstrate that mice acquiring a low social status (subordinate) in a lifelong chronic psychosocial stress (CPS) model, accrue widespread proteomic changes in the frontal/temporal cortex during aging. To better understand the significance of these stress-induced changes, we compared the differentially expressed proteins (DEPs) of subordinate mice to those of patients at varying stages of dementia. Sixteen and fifteen DEPs upregulated in subordinate mice were also upregulated in patients with mild cognitive impairment (MCI) and AD, respectively. Six of those upregulated proteins (CPE, ERC2, GRIN2B, SLC6A1, SYN1, WFS1) were shared by subordinate mice and patients with MCI or AD. Finally, comparison with a spatially detailed transcriptomic database revealed that the superior frontal gyrus and hippocampus had the greatest overlap between mice subjected to lifelong CPS and AD patients. Overall, most of the overlapping proteins were functionally associated with enhanced NMDA receptor mediated glutamatergic signaling, an excitotoxicity mechanism known to affect neurodegeneration. These findings support the association between stress and AD progression and provide valuable insight into potential early biomarkers and protein mediators of this relationship.

Amyloid-β Precursor Protein APP Down-Regulation Alters Actin Cytoskeleton-Interacting Proteins in Endothelial Cells

The amyloid-β precursor protein (APP) is a ubiquitous membrane protein often associated with Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA). Despite its role in the development of the pathogenesis, APP exerts several physiological roles that have been mainly investigated in neuronal tissue. To date, the role of APP in vasculature and endothelial cells has not been fully elucidated. In this study, we used molecular and proteomic approaches to identify and investigate major cellular targets of APP down-regulation in endothelial cells. We found that APP is necessary for endothelial cells proliferation, migration and adhesion. The loss of APP alters focal adhesion stability and cell-cell junctions' expression. Moreover, APP is necessary to mediate endothelial response to the VEGF-A growth factor. Finally, we document that APP propagates exogenous stimuli and mediates cellular response in endothelial cells by modulating the Scr/FAK signaling pathway. Thus, the intact expression and processing of APP is required for normal endothelial function. The identification of molecular mechanisms responsible for vasoprotective properties of endothelial APP may have an impact on clinical efforts to preserve and protect healthy vasculature in patients at risk of the development of cerebrovascular disease and dementia including AD and CAA.

Stress and Alzheimer's disease: A senescence link?

Chronic stress has been shown to promote numerous aging-related diseases, and to accelerate the aging process itself. Of particular interest is the impact of stress on Alzheimer's disease (AD), the most prevalent form of dementia. The vast majority of AD cases have no known genetic cause, making it vital to identify the environmental factors involved in the onset and progression of the disease. Age is the greatest risk factor for AD, and measures of biological aging such as shorter telomere length, significantly increase likelihood for developing AD. Stress is also considered a crucial contributor to AD, as indicated by a formidable body of research, although the mechanisms underlying this association remain unclear. Here we review human and animal literature on the impact of stress on AD and discuss the mechanisms implicated in the interaction. In particular we will focus on the burgeoning body of research demonstrating that senescent cells, which accumulate with age and actively drive a number of aging-related diseases, may be a key mechanism through which stress drives 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.

French maritime pine bark treatment decelerates plaque development and improves spatial memory in Alzheimer's disease mice

BACKGROUND

Plant extracts are increasingly investigated as potential drugs against Alzheimer's disease (AD) and dementia in general. Pycnogenol is an extract from the bark of the French maritime pine (Pinus pinaster Aiton subsp. atlantica) with known anti-oxidative and neuroprotective effects.

HYPOTHESIS/PURPOSE

Pycnogenol is thought to improve cognitive functions in elderly. We wanted to investigate and quantify these effects in a model system of cerebral ß-amyloidosis/AD.

STUDY DESIGN/METHODS

This study experimentally assessed the effects of Pycnogenol on AD-related pathology in a ß-amyloidosis mouse model. APP-transgenic mice and controls were treated orally in a pre-onset and post-onset treatment paradigm. The effects of Pycnogenol were characterized by analysing ß-amyloid (Aß) plaques, number of neurons, glia coverage, myelination pattern, and cortical coverage with axons using immunohistochemistry. Aß levels were quantified using ELISA and gene expression levels of APP-processing enzymes ADAM10, BACE1 and IDE protein levels were determined by Western blot. Behavioural changes in circadian rhythm were monitored and spatial memory / cognition was assessed using a water maze test.

RESULTS

Pycnogenol significantly decreased the number of plaques in both treatment paradigms but did not alter levels of soluble Aß or the gene expression of APP-processing enzymes. The morphological analyses revealed no changes in the number of neurons, astrocytes, microglia, the myelination pattern, or the morphology of axons. Behavioural testing revealed an improvement of the spatial memory in the pre-onset treatment paradigm only.

CONCLUSION

Our results suggest to evaluate clinically a potential use of Pycnogenol in the prevention or in early stages of mild cognitive impairment (MCI) and AD.

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.

Genetic variants associated with development of TMD and its intermediate phenotypes: the genetic architecture of TMD in the OPPERA prospective cohort study

Genetic risk factors are believed to combine with environmental exposures and contribute to the risk of developing temporomandibular disorder (TMD). In this prospective cohort study, 2,737 people without TMD were assessed for common genetic variation in 358 genes known to contribute to nociceptive pathways, inflammation, and affective distress. During a median follow-up period of 2.8 years, 260 people developed first-onset TMD. Hazard ratios were computed as measures of association between 2,924 single-nucleotide polymorphisms and TMD incidence. After correction for multiple testing, no single single-nucleotide polymorphism was significantly associated with risk of onset TMD. However, several single-nucleotide polymorphisms exceeded Bonferroni correction for multiple comparison or false discovery rate thresholds (.05, .1, or .2) for association with intermediate phenotypes shown to be predictive of TMD onset. Nonspecific orofacial symptoms were associated with voltage-gated sodium channel, type I, alpha subunit (SCN1A, rs6432860, P = 2.77 × 10(-5)) and angiotensin I-converting enzyme 2 (ACE2, rs1514280, P = 4.86 × 10(-5)); global psychological symptoms with prostaglandin-endoperoxide synthase 1 (PTGS1, rs3842803, P = 2.79 × 10(-6)); stress and negative affectivity with amyloid-β (A4) precursor protein (APP, rs466448, P = 4.29 × 10(-5)); and heat pain temporal summation with multiple PDZ domain protein (MPDZ, rs10809907, P = 3.05 × 10(-5)). The use of intermediate phenotypes for complex pain diseases revealed new genetic pathways influencing risk of TMD.

PERSPECTIVE

This article reports the findings of a large candidate gene association study of first-onset TMD and related intermediate phenotypes in the OPPERA Study. Although no genetic markers predicted TMD onset, several genetic risk factors for clinical, psychological, and sensory phenotypes associated with TMD onset were observed.

3xTgAD mice exhibit altered behavior and elevated Aβ after chronic mild social stress

Chronic stress may be a risk factor for developing Alzheimer's disease (AD), but most studies of the effects of stress in models of AD utilize acute adverse stressors of questionable clinical relevance. The goal of this work was to determine how chronic psychosocial stress affects behavioral and pathological outcomes in an animal model of AD, and to elucidate underlying mechanisms. A triple-transgenic mouse model of AD (3xTgAD mice) and nontransgenic control mice were used to test for an affect of chronic mild social stress on blood glucose, plasma glucocorticoids, plasma insulin, anxiety, and hippocampal amyloid β-particle (Aβ), phosphorylated tau (ptau), and brain-derived neurotrophic factor (BDNF) levels. Despite the fact that both control and 3xTgAD mice experienced rises in corticosterone during episodes of mild social stress, at the end of the 6-week stress period 3xTgAD mice displayed increased anxiety, elevated levels of Aβ oligomers and intraneuronal Aβ, and decreased brain-derived neurotrophic factor levels, whereas control mice did not. Findings suggest 3xTgAD mice are more vulnerable than control mice to chronic psychosocial stress, and that such chronic stress exacerbates Aβ accumulation and impairs neurotrophic signaling.

The transcriptional response to chronic stress and glucocorticoid receptor blockade in the hippocampal dentate gyrus

The dentate gyrus (DG) of the hippocampus plays a crucial role in learning and memory. This subregion is unique in its ability to generate new neurons throughout life and integrate these new neurons into the hippocampal circuitry. Neurogenesis has further been implicated in hippocampal plasticity and depression. Exposure to chronic stress affects DG function and morphology and suppresses neurogenesis and long-term potentiation (LTP) with consequences for cognition. Previous studies demonstrated that glucocorticoid receptor (GR) blockade by a brief treatment with the GR antagonist mifepristone (RU486) rapidly reverses the stress and glucocorticoid effects on neurogenesis. The molecular pathways underlying both the stress-induced effects and the RU486 effects on the DG are, however, largely unknown. The aim of this study was therefore (1) to investigate by microarray analysis which genes and pathways in the DG are sensitive to chronic stress and (2) to investigate to what extent blockade of GR can normalize these stress-induced effects on DG gene expression. Chronic stress exposure affected the expression of 90 genes in the DG (P < 0.01), with an overrepresentation of genes involved in brain development and morphogenesis and synaptic transmission. RU486 treatment of stressed animals affected expression of 107 genes; however, mostly different genes than those responding to stress. Interestingly, we found CREBBP to be normalized by RU486 treatment to levels observed in control animals, suggesting that CREB-signaling may play a central role in mediating the chronic stress effects on neurogenesis, LTP and calcium currents. The identified genetic pathways provide insight into the stress-induced adaptive plasticity of the hippocampal DG that is so central in learning and memory and will direct future studies on the functional outcome and modulation of these stress effects.

Adverse stress, hippocampal networks, and Alzheimer's disease

Recent clinical data have implicated chronic adverse stress as a potential risk factor in the development of Alzheimer's disease (AD) and data also suggest that normal, physiological stress responses may be impaired in AD. It is possible that pathology associated with AD causes aberrant responses to chronic stress, due to potential alterations in the hypothalamic-pituitary-adrenal (HPA) axis. Recent study in rodent models of AD suggests that chronic adverse stress exacerbates the cognitive deficits and hippocampal pathology that are present in the AD brain. This review summarizes recent findings obtained in experimental AD models regarding the influence of chronic adverse stress on the underlying cellular and molecular disease processes including the potential role of glucocorticoids. Emerging findings suggest that both AD and chronic adverse stress affect hippocampal neural networks in a similar fashion. We describe alterations in hippocampal plasticity, which occur in both chronic stress and AD including dendritic remodeling, neurogenesis, and long-term potentiation. Finally, we outline potential roles for oxidative stress and neurotrophic factor signaling as the key determinants of the impact of chronic stress on the plasticity of neural networks and AD pathogenesis.