Chronic stress exacerbates tau pathology, neurodegeneration, and cognitive performance through a corticotropin-releasing factor receptor-dependent mechanism in a transgenic mouse model of tauopathy

Alpha-synuclein-induced stress sensitivity renders the Parkinson's disease brain susceptible to neurodegeneration

A link between chronic stress and Parkinson's disease (PD) pathogenesis is emerging. Ample evidence demonstrates that the presynaptic neuronal protein alpha-synuclein (asyn) is closely tied to PD pathogenesis. However, it is not known whether stress system dysfunction is present in PD, if asyn is involved, and if, together, they contribute to neurodegeneration. To address these questions, we assess stress axis function in transgenic rats overexpressing full-length wildtype human asyn (asyn BAC rats) and perform multi-level stress and PD phenotyping following chronic corticosterone administration. Stress signaling, namely corticotropin-releasing factor, glucocorticoid and mineralocorticoid receptor gene expression, is also examined in post-mortem PD patient brains. Overexpression of human wildtype asyn leads to HPA axis dysregulation in rats, while chronic corticosterone administration significantly aggravates nigrostriatal degeneration, serine129 phosphorylated asyn (pS129) expression and neuroinflammation, leading to phenoconversion from a prodromal to an overt motor PD phenotype. Interestingly, chronic corticosterone in asyn BAC rats induces a robust, twofold increase in pS129 expression in the hypothalamus, the master regulator of the stress response, while the hippocampus, both a regulator and a target of the stress response, also demonstrates elevated pS129 asyn levels and altered markers of stress signalling. Finally, defective hippocampal stress signalling is mirrored in human PD brains and correlates with asyn expression levels. Taken together, our results link brain stress system dysregulation with asyn and provide evidence that elevated circulating glucocorticoids can contribute to asyn-induced neurodegeneration, ultimately triggering phenoconversion from prodromal to overt PD.

Experimental laboratory models as tools for understanding modifiable dementia risk

Experimental laboratory research has an important role to play in dementia prevention. Mechanisms underlying modifiable risk factors for dementia are promising targets for dementia prevention but are difficult to investigate in human populations due to technological constraints and confounds. Therefore, controlled laboratory experiments in models such as transgenic rodents, invertebrates and in vitro cultured cells are increasingly used to investigate dementia risk factors and test strategies which target them to prevent dementia. This review provides an overview of experimental research into 15 established and putative modifiable dementia risk factors: less early-life education, hearing loss, depression, social isolation, life stress, hypertension, obesity, diabetes, physical inactivity, heavy alcohol use, smoking, air pollution, anesthetic exposure, traumatic brain injury, and disordered sleep. It explores how experimental models have been, and can be, used to address questions about modifiable dementia risk and prevention that cannot readily be addressed in human studies. HIGHLIGHTS: Modifiable dementia risk factors are promising targets for dementia prevention. Interrogation of mechanisms underlying dementia risk is difficult in human populations. Studies using diverse experimental models are revealing modifiable dementia risk mechanisms. We review experimental research into 15 modifiable dementia risk factors. Laboratory science can contribute uniquely to dementia prevention.

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.

Chronic stress induces Alzheimer's disease-like pathologies through DNA damage-Chk1-CIP2A signaling

Stress is an important initiating factor in promoting Alzheimer's disease (AD) pathogenesis. However, the mechanism by which stress induces AD-like cognitive impairment remains to be clarified. Here, we demonstrate that DNA damage is increased in stress hormone Corticotropin-releasing factor (CRF)-treated cells and in brains of mice exposed to chronic restraint stress. Accumulation of DNA damage drives activation of cell cycle checkpoint protein kinase 1 (Chk1), upregulation of cancerous inhibitor of PP2A (CIP2A), tau hyperphosphorylation, and Aβ overproduction, eventually resulting in synaptic impairment and cognitive deficits. Pharmacological intervention targeting Chk1 by specific inhibitor and DNA damage by vitamin C, suppress DNA damage-Chk1-CIP2A signaling pathway in chronic stress animal model, which in turn attenuate AD-like pathologies, synaptic impairments and cognitive deficits. Our study uncovers a novel molecular mechanism of stress-induced AD-like pathologies and provides effective preventive and therapeutic strategies targeting this signaling pathway.

Serotonergic dysfunction may mediate the relationship between alcohol consumption and Alzheimer's disease

The impact of Alzheimer's disease (AD) and its related dementias is rapidly expanding, and its mitigation remains an urgent social and technical challenge. To date there are no effective treatments or interventions for AD, but recent studies suggest that alcohol consumption is correlated with the risk of developing dementia. In this review, we synthesize data from preclinical, clinical, and epidemiological models to evaluate the combined role of alcohol consumption and serotonergic dysfunction in AD, underscoring the need for further research on this topic. We first discuss the limitations inherent to current data-collection methods, and how neuropsychiatric symptoms common among AD, alcohol use disorder, and serotonergic dysfunction may mask their co-occurrence. We additionally describe how excess alcohol consumption may accelerate the development of AD via direct effects on serotonergic function, and we explore the roles of neuroinflammation and proteostasis in mediating the relationship between serotonin, alcohol consumption, and AD. Lastly, we argue for a shift in current research to disentangle the pathogenic effects of alcohol on early-affected brainstem structures in AD.

Anorexigenic neuropeptides as anti-obesity and neuroprotective agents: exploring the neuroprotective effects of anorexigenic neuropeptides

Since 1975, the incidence of obesity has increased to epidemic proportions, and the number of patients with obesity has quadrupled. Obesity is a major risk factor for developing other serious diseases, such as type 2 diabetes mellitus, hypertension, and cardiovascular diseases. Recent epidemiologic studies have defined obesity as a risk factor for the development of neurodegenerative diseases, such as Alzheimer's disease (AD) and other types of dementia. Despite all these serious comorbidities associated with obesity, there is still a lack of effective antiobesity treatment. Promising candidates for the treatment of obesity are anorexigenic neuropeptides, which are peptides produced by neurons in brain areas implicated in food intake regulation, such as the hypothalamus or the brainstem. These peptides efficiently reduce food intake and body weight. Moreover, because of the proven interconnection between obesity and the risk of developing AD, the potential neuroprotective effects of these two agents in animal models of neurodegeneration have been examined. The objective of this review was to explore anorexigenic neuropeptides produced and acting within the brain, emphasizing their potential not only for the treatment of obesity but also for the treatment of neurodegenerative disorders.

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.

Glucocorticoid stress hormones stimulate vesicle-free Tau secretion and spreading in the brain

Chronic stress and elevated levels of glucocorticoids (GCs), the main stress hormones, accelerate Alzheimer's disease (AD) onset and progression. A major driver of AD progression is the spreading of pathogenic Tau protein between brain regions, precipitated by neuronal Tau secretion. While stress and high GC levels are known to induce intraneuronal Tau pathology (i.e. hyperphosphorylation, oligomerization) in animal models, their role in trans-neuronal Tau spreading is unexplored. Here, we find that GCs promote secretion of full-length, primarily vesicle-free, phosphorylated Tau from murine hippocampal neurons and ex vivo brain slices. This process requires neuronal activity and the kinase GSK3β. GCs also dramatically enhance trans-neuronal Tau spreading in vivo, and this effect is blocked by an inhibitor of Tau oligomerization and type 1 unconventional protein secretion. These findings uncover a potential mechanism by which stress/GCs stimulate Tau propagation in AD.

Effects of Intranasal Dantrolene Nanoparticles on Brain Concentration and Behavior in PS19 Tau Transgenic Mice

Background

Repurposing dantrolene to treat Alzheimer's disease has been shown to be effective in amyloid transgenic mouse models but has not been examined in a model of tauopathy.

Objective

The effects of a nanoparticle intranasal formulation, the Eagle Research Formulation of Ryanodex (ERFR), in young adult and aged wild type and PS19 tau transgenic mice was investigated.

Methods

The bioavailability of intranasal ERFR was measured in 2 and 9-11-month-old C57BL/6J mice. Blood and brain samples were collected 20 minutes after a single ERFR dose, and the plasma and brain concentrations were analyzed. Baseline behavior was assessed in untreated PS19 tau transgenic mice at 6 and 9 months of age. PS19 mice were treated with intranasal ERFR, with or without acrolein (to potentiate cognitive dysfunction), for 3 months, beginning at 2 months of age. Animal behavior was examined, including cognition (cued and contextual fear conditioning, y-maze), motor function (rotarod), and olfaction (buried food test).

Results

The dantrolene concentration in the blood and brain decreased with age, with the decrease greater in the blood resulting in a higher brain to blood concentration ratio. The behavioral assays showed no significant changes in cognition, olfaction, or motor function in the PS19 mice compared to controls after chronic treatment with intranasal ERFR, even with acrolein.

Conclusions

Our studies suggest the intranasal administration of ERFR has higher concentrations in the brain than the blood in aged mice and has no serious systemic side effects with chronic use in PS19 mice.

Early Benefits with Potential Long-Term Risks of a Comprehensive Intervention on Serum Cortisol Levels and Cognitive Performance in Patients with Alzheimer's Disease

Background

Elevated cortisol levels represent a risk factor for Alzheimer's disease (AD), prompting treatments to lower hormone concentrations for preventive or therapeutic purposes.

Objective

To assess the efficacy of a comprehensive intervention (CI) in modulating serum cortisol levels in patients with AD.

Methods

CI consisted in a 2-month protocol involving cognitive stimulation, psychological support, lifestyle guidance, leisure activities, and socialization. AD subjects were randomly assigned to experimental (EG, n = 45) and control (CG, n = 45) groups. A wide range of sociodemographic, cognitive, psychosocial, and functional conditions were evaluated before, at the conclusion, and 24 months after CI. Data about lifestyle and drug prescription were also recorded.

Results

Baseline evaluations revealed that higher cortisol levels correlated with worse cognitive status (higher CDR and ADAS-Cog values and lower MMSE scores), increased depressive symptoms, and reduced physical and social engagement. Following CI, EG exhibited reduced cortisol levels, improved overall cognitive status, and enhanced verbal working memory and executive functions compared to CG. However, at the 24-month follow-up, EG displayed a rebound effect, characterized by elevated cortisol levels and cognitive decline compared to CG.

Conclusions

These findings strengthen the adverse relationship between excessive cortisol and deficits in cognition/behavior in AD, demonstrate the short-term benefits of CI, and emphasize the potential long-term risks, which may be attributed to the fragile nature of the AD brain. Comprehensive interventions can yield positive results, but careful calibration of type and duration is necessary, considering disease progression and the potential need for re-administration.

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.

Stress, depression, and risk of dementia - a cohort study in the total population between 18 and 65 years old in Region Stockholm

BACKGROUND

Chronic stress and depression are potential risk factors for mild cognitive impairment and dementia, including Alzheimer disease. The aim was to investigate whether any such risk is additive.

METHODS

Cohort study including 1 362 548 people (665 997 women, 696 551 men) with records in the Region Stockholm administrative healthcare database (VAL). Exposure was a recorded ICD-10 diagnosis of chronic stress, depression, or both, recorded in 2012 or 2013. Outcome was a diagnosis of Alzheimer disease, other dementia, or mild cognitive impairment recorded from 2014 through 2022. Odds ratios with 99% confidence intervals (CI) adjusted for age, sex, neighborhood socioeconomic status, diabetes, and cardiovascular disorders were calculated.

RESULTS

During the exposure period, 4 346 patients were diagnosed with chronic stress, 40 101 with depression, and 1 898 with both. The average age at baseline was around 40 years in all groups. In the fully adjusted model, the odds ratio of Alzheimer disease was 2.45 (99% CI 1.22-4.91) in patients with chronic stress, 2.32 (99% CI 1.85-2.90) in patients with depression, and 4.00 (99% CI 1.67-9.58) in patients with chronic stress and depression. The odds ratio of mild cognitive impairment was 1.87 (99% CI 1.20-2.91) in patients with chronic stress, 2.85 (99% CI 2.53-3.22) in patients with depression, and 3.87 (99% CI 2.39-6.27) in patients with both. When other dementia was analyzed, the odds ratio was significant only in patients with depression, 2.39 (99% CI 1.92-2.96).

CONCLUSIONS

Documented chronic stress increased the risk of mild cognitive impairment and Alzheimer disease. The same was seen with depression. The novel finding is the potential additive effect of chronic stress to depression, on risk of MCI and AD.

Long-term social isolation stress exacerbates sex-specific neurodegeneration markers in a natural model of Alzheimer's disease

Social interactions have a significant impact on health in humans and animal models. Social isolation initiates a cascade of stress-related physiological disorders and stands as a significant risk factor for a wide spectrum of morbidity and mortality. Indeed, social isolation stress (SIS) is indicative of cognitive decline and risk to neurodegenerative conditions, including Alzheimer's disease (AD). This study aimed to evaluate the impact of chronic, long-term SIS on the propensity to develop hallmarks of AD in young degus (Octodon degus), a long-lived animal model that mimics sporadic AD naturally. We examined inflammatory factors, bioenergetic status, reactive oxygen species (ROS), oxidative stress, antioxidants, abnormal proteins, tau protein, and amyloid-β (Aβ) levels in the hippocampus of female and male degus that were socially isolated from post-natal and post-weaning until adulthood. Additionally, we explored the effect of re-socialization following chronic isolation on these protein profiles. Our results showed that SIS promotes a pro-inflammatory scenario more severe in males, a response that was partially mitigated by a period of re-socialization. In addition, ATP levels, ROS, and markers of oxidative stress are severely affected in female degus, where a period of re-socialization fails to restore them as it does in males. In females, these effects might be linked to antioxidant enzymes like catalase, which experience a decline across all SIS treatments without recovery during re-socialization. Although in males, a previous enzyme in antioxidant pathway diminishes in all treatments, catalase rebounds during re-socialization. Notably, males have less mature neurons after chronic isolation, whereas phosphorylated tau and all detectable forms of Aβ increased in both sexes, persisting even post re-socialization. Collectively, these findings suggest that long-term SIS may render males more susceptible to inflammatory states, while females are predisposed to oxidative states. In both scenarios, the accumulation of tau and Aβ proteins increase the individual susceptibility to early-onset neurodegenerative conditions such as AD.

Glucocorticoid stress hormones stimulate vesicle-free Tau secretion and spreading in the brain

Chronic stress and elevated levels of glucocorticoids (GCs), the main stress hormones, accelerate Alzheimer's disease (AD) onset and progression. A major driver of AD progression is the spreading of pathogenic Tau protein between brain regions, precipitated by neuronal Tau secretion. While stress and high GC levels are known to induce intraneuronal Tau pathology (i.e. hyperphosphorylation, oligomerization) in animal models, their role in trans-neuronal Tau spreading is unexplored. Here, we find that GCs promote secretion of full-length, vesicle-free, phosphorylated Tau from murine hippocampal neurons and ex vivo brain slices. This process occurs via type 1 unconventional protein secretion (UPS) and requires neuronal activity and the kinase GSK3b. GCs also dramatically enhance trans-neuronal Tau spreading in vivo, and this effect is blocked by an inhibitor of Tau oligomerization and type 1 UPS. These findings uncover a potential mechanism by which stress/GCs stimulate Tau propagation in AD.

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

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

Glucocorticoid stress hormones stimulate vesicle-free Tau secretion and spreading in the brain

Chronic stress and elevated levels of glucocorticoids (GCs), the main stress hormones, accelerate Alzheimer's disease (AD) onset and progression. A major driver of AD progression is the spreading of pathogenic Tau protein between brain regions, precipitated by neuronal Tau secretion. While stress and high GC levels are known to induce intraneuronal Tau pathology ( i.e. hyperphosphorylation, oligomerization) in animal models, their role in trans-neuronal Tau spreading is unexplored. Here, we find that GCs promote secretion of full-length, vesicle-free, phosphorylated Tau from murine hippocampal neurons and ex vivo brain slices. This process occurs via type 1 unconventional protein secretion (UPS) and requires neuronal activity and the kinase GSK3β. GCs also dramatically enhance trans-neuronal Tau spreading in vivo , and this effect is blocked by an inhibitor of Tau oligomerization and type 1 UPS. These findings uncover a potential mechanism by which stress/GCs stimulate Tau propagation in AD.

Sex-dependent effects of acute stress on amyloid-β in male and female mice

The risk of developing Alzheimer's disease is mediated by a combination of genetics and environmental factors, such as stress, sleep abnormalities and traumatic brain injury. Women are at a higher risk of developing Alzheimer's disease than men, even when controlling for differences in lifespan. Women are also more likely to report high levels of stress than men. Sex differences in response to stress may play a role in the increased risk of Alzheimer's disease in women. In this study, we use in vivo microdialysis to measure levels of Aβ in response to acute stress in male and female mice. We show that Aβ levels are altered differently between female and male mice (APP/PS1 and wild-type) in response to stress, with females showing significantly increased levels of Aβ while most males do not show a significant change. This response is mediated through β-arrestin involvement in Corticotrophin Releasing Factor receptor signalling pathway differences in male and female mice as male mice lacking β-arrestin show increase in Aβ in response to stress similar to females.

Effects of intranasal dantrolene nanoparticles on brain concentration and behavior in PS19 tau transgenic mice

Background

Repurposing dantrolene as a potential disease-modifying treatment for Alzheimer's disease has been shown to be effective in amyloid transgenic mouse models but has not been examined in a model of tauopathy.

Objective

The effects of a nanoparticle intranasal formulation, the Eagle Research Formulation of Ryanodex (ERFR), in young adult and aged wild type and PS19 tau transgenic mice was investigated.

Methods

The bioavailability of intranasal ERFR was measured in 2 months and 9-12 month old C57BL/6J male mice. Mice received a single intranasal dose of ERFR and, after 20 min, blood and brain samples were collected. Dantrolene concentrations in the plasma and brain were analyzed by High Performance Liquid Chromatography. Animal behavior was examined in PS19 tau transgenic mice, with/without acrolein treatment to exacerbate cognitive deficits. Behavioral tests included cognition (cued and contextual fear conditioning, y-maze), motor function (rotarod), and olfaction (buried food test).

Results

Dantrolene concentration in the blood and brain decreased with age, though the decrease was greater in the blood resulting in a higher brain to blood concentration ratio. The behavioral assays showed no significant changes in cognition, olfaction or motor function in the PS19 mice compared to controls after chronic ERFR treatment even with acrolein treatment.

Conclusion

Our studies suggest that while we did not find PS19 mice to be a reliable Alzheimer animal model to test the therapeutic efficacy of dantrolene, the results suggest a potential for ERFR to be an effective chronic therapy for Alzheimer's disease and that further studies are indicated.

The involvement of NLRP3 inflammasome in CUMS-induced AD-like pathological changes and related cognitive decline in mice

BACKGROUND

Numerous studies have found that inhibiting the expression of NLRP3 inflammasome can significantly improve depressive-like behaviors in mice, but the research on its effect on cognitive decline in depression and its mechanism is still lacking. This study aimed to elucidate the role of NLRP3 inflammasome in cognitive decline in depression and explore the common neuro-immunological mechanisms of depression and Alzheimer's disease (AD).

METHODS

Male C57BL/6 mice were subjected to chronic unpredictable mild stress (CUMS) for 5 weeks, treatment group was administered with the NLRP3 inhibitor MCC950 (10 mg/kg, i.p.), fluoxetine served as positive control. Then, the mice were assessed for cognitive behaviors and depression-like behaviors, and changes of microglia and neurons in hippocampus and levels of Aβ metabolic pathway and tau protein were measured. To explore the mechanism of NLRP3 activation on neurons, we performed in vitro studies using BV2 microglia and mouse primary neurons. Furthermore, we focused on the role of NLRP3 inflammasome in the function of neurons and the expression of AD pathological indicators.

RESULTS

CUMS induced depressive-like behaviors and cognitive decline in mice, which could be reversed by inhibiting NLRP3 inflammasome. MCC950, a specific NLRP3 inhibitor, alleviated CUMS-induced neuron injury and AD-like pathological changes, including the abnormal expression of Aβ metabolic pathway and the hyper-phosphorylation of tau protein. LPS (1 μg/mL) + ATP (1 mM) treatment activated the expression of NLRP3 inflammasome and IL-1β in vitro. In vitro experiment also proved that inhibiting the expression of NLRP3 inflammasome in microglia can restore the Aβ metabolic pathway to normal, decrease neuronal tau protein phosphorylation and protect neurons.

CONCLUSIONS

Inhibition of NLRP3 inflammasome effectively alleviated CUMS-induced depressive-like behaviors and cognitive decline in mice, and inhibited the activation of AD physiological indicators.

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.

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

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

Common Neuropsychiatric S ymptoms in Alzheimer's Disease, Mild Cognitive Impairment, and Subjective Memory Complaints: A Unified Framework

The Alzheimer's disease (AD) continuum is a unique spectrum of cognitive impairment that typically involves the stages of subjective memory complaints (SMC), mild cognitive impairment (MCI), and AD dementia. Neuropsychiatric symptoms (NPS), such as apathy, anxiety, stress, and depression, are highly common throughout the AD continuum. However, there is a dearth of research on how these NPS vary across the AD continuum, especially SMC. There is also disagreement on the effects of specific NPS on each stage of the AD continuum due to their collinearity with other NPS, cognitive decline, and environmental factors (e.g., stress). In this article, we conduct a novel perspective review of the scientific literature to understand the presence of NPS across the AD continuum. Specifically, we review the effects of apathy, depression, anxiety, and stress in AD, MCI, and SMC. We then build on this knowledge by proposing two theories of NPS' occurrence across the AD continuum. Consequently, we highlight the current landscape, limitations (e.g., differing operationalization), and contentions surrounding the NPS literature. We also outline theories that could clear up contention and inspire future NPS research.

Early Chronic Stress Induced Changes within the Locus Coeruleus in Sporadic Alzheimer's Disease

Chronic exposure to stress throughout the lifespan has been the focus of many studies on Alzheimer's disease (AD) because of the similarities between the biological mechanisms involved in chronic stress and the pathophysiology of AD. In fact, the earliest abnormality associated with the disease is the presence of phosphorylated tau protein in locus coeruleus neurons, a brain structure highly responsive to stress and perceived threat. Here, we introduce allostatic load as a useful concept for understanding many of the complex, interacting neuropathological changes involved in the AD degenerative process. In response to chronic stress, aberrant tau proteins that begin to accumulate within the locus coeruleus decades prior to symptom onset appear to represent a primary pathological event in the AD cascade, triggering a wide range of interacting brain changes involving neuronal excitotoxicity, endocrine alterations, inflammation, oxidative stress, and amyloid plaque exacerbation. While it is acknowledged that stress will not necessarily be the major precipitating factor in all cases, early tau-induced changes within the locus coeruleus-norepinephrine pathway suggests that a therapeutic window might exist for preventative measures aimed at managing stress and restoring balance within the HPA axis.

Research Progress on the Etiology and Pathogenesis of Alzheimer's Disease from the Perspective of Chronic Stress

Due to its extremely complex pathogenesis, no effective drugs to prevent, delay progression, or cure Alzheimer's disease (AD) exist at present. The main pathological features of AD are senile plaques composed of β-amyloid, neurofibrillary tangles formed by hyperphosphorylation of the tau protein, and degeneration or loss of neurons in the brain. Many risk factors associated with the onset of AD, including gene mutations, aging, traumatic brain injury, endocrine and cardiovascular diseases, education level, and obesity. Growing evidence points to chronic stress as one of the major risk factors for AD, as it can promote the onset and development of AD-related pathologies via a mechanism that is not well known. The use of murine stress models, including restraint, social isolation, noise, and unpredictable stress, has contributed to improving our understanding of the relationship between chronic stress and AD. This review summarizes the evidence derived from murine models on the pathological features associated with AD and the related molecular mechanisms induced by chronic stress. These results not only provide a retrospective interpretation for understanding the pathogenesis of AD, but also provide a window of opportunity for more effective preventive and identifying therapeutic strategies for stress-induced AD.

Corticotropin-Releasing Hormone: Biology and Therapeutic Opportunities

In 1981, Wylie Vale, Joachim Spiess, Catherine Rivier, and Jean Rivier reported on the characterization of a 41-amino-acid peptide from ovine hypothalamic extracts with high potency and intrinsic activity stimulating the secretion of adrenocorticotropic hormone and β-endorphin by cultured anterior pituitary cells. With its sequence known, this neuropeptide was determined to be a hormone and consequently named corticotropin-releasing hormone (CRH), although the term corticotropin-releasing factor (CRF) is still used and preferred in some circumstances. Several decades have passed since this seminal contribution that opened a new research era, expanding the understanding of the coding of stress-related processes. The characterization of CRH receptors, the availability of CRH agonists and antagonists, and advanced immunocytochemical staining techniques have provided evidence that CRH plays a role in the regulation of several biological systems. The purpose of this review is to summarize the present knowledge of this 41-amino-acid peptide.

Spouse bereavement and brain pathologies: A propensity score matching study

AIM

Spouse bereavement is one of life's greatest stresses and has been suggested to trigger or accelerate cognitive decline and dementia. However, little information is available about the potential brain pathologies underlying the association between spouse bereavement and cognitive decline. We aimed to investigate that lifetime spouse bereavement is associated with in vivo human brain pathologies underlying cognitive decline.

METHODS

A total of 319 ever-married older adults between the ages of 61 and 90 years underwent comprehensive clinical assessments and multimodal brain imaging including [¹¹ C] Pittsburgh compound B-positron emission tomography (PET), AV-1451 PET, [¹⁸ F] fluorodeoxyglucose-PET, and magnetic resonance imaging. Participants were classified as experiencing no spouse bereavement or spouse bereavement, and comparisons using propensity score matching (59 cases and 59 controls) were performed.

RESULTS

Spouse bereavement was significantly associated with higher cerebral white matter hyperintensity (WMH) volume compared with no spouse bereavement. Interaction and subsequent subgroup analyses showed that spouse bereavement was significantly associated with higher WMH in the older (>75 years) subgroup and among those with no- or low-skill occupations. In addition, spouse bereavement at 60 years or older affects WMH volume compared with no spouse bereavement, whereas spouse bereavement at younger than 60 years did not. No group differences were observed in other brain pathologies between spouse bereavement categories.

CONCLUSIONS

The findings suggest that the spouse bereavement may contribute to dementia or cognitive decline by increasing cerebrovascular injury, particularly in older individuals and those with no- or low-skill occupations.

The gut microbiome and Alzheimer's disease: Complex and bidirectional interactions

Structural and functional alterations to the gut microbiome, referred to as gut dysbiosis, have emerged as potential key mediators of neurodegeneration and Alzheimer disease (AD) pathogenesis through the "gut -brain" axis. Emerging data from animal and clinical studies support an important role for gut dysbiosis in mediating neuroinflammation, central and peripheral immune dysregulation, abnormal brain protein aggregation, and impaired intestinal and brain barrier permeability, leading to neuronal loss and cognitive impairment. Gut dysbiosis has also been shown to directly influence various mechanisms involved in neuronal growth and repair, synaptic plasticity, and memory and learning functions. Aging and lifestyle factors including diet, exercise, sleep, and stress influence AD risk through gut dysbiosis. Furthermore, AD is associated with characteristic gut microbial signatures which offer value as potential markers of disease severity and progression. Together, these findings suggest the presence of a complex bidirectional relationship between AD and the gut microbiome and highlight the utility of gut modulation strategies as potential preventative or therapeutic strategies in AD. We here review the current literature regarding the role of the gut-brain axis in AD pathogenesis and its potential role as a future therapeutic target in AD treatment and/or prevention.

Glial Cell-Mediated Neuroinflammation in Alzheimer’s Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder; it is the most common cause of dementia and has no treatment. It is characterized by two pathological hallmarks, the extracellular deposits of amyloid beta (Aβ) and the intraneuronal deposits of Neurofibrillary tangles (NFTs). Yet, those two hallmarks do not explain the full pathology seen with AD, suggesting the involvement of other mechanisms. Neuroinflammation could offer another explanation for the progression of the disease. This review provides an overview of recent advances on the role of the immune cells’ microglia and astrocytes in neuroinflammation. In AD, microglia and astrocytes become reactive by several mechanisms leading to the release of proinflammatory cytokines that cause further neuronal damage. We then provide updates on neuroinflammation diagnostic markers and investigational therapeutics currently in clinical trials to target neuroinflammation.

Combination of Stem Cells with Chinese Herbs for Secondary Depression in Neurodegenerative Diseases Based on Traditional Chinese Medicine Theories

Depression is a common secondary symptom in neurodegenerative diseases (NDs) caused by the loss of neurons and glial cells. Recent research focuses on stem cell therapy to replace dead nerve cells, but the low efficiency of stem cell differentiation and short survival time are obstacles limiting the therapy's effectiveness. Clinically, patients with different diseases cannot obtain the same effect by using the same cell therapy. However, traditional Chinese medicine (TCM) often uses syndrome differentiation to determine the treatment plan for NDs. Based on TCM syndrome differentiation and treatment, this article summarizes the advantages of Chinese herbal medicine combined with stem cell therapy, mainly for the effects of various herbs on diseases and stem cells, including prolonging the survival time of stem cells, resisting inflammation, and antidepressant-like effects. In particular, it analyzes the unique pathways of the influence of drugs and acupuncture on different therapies, seeking to clarify the scientific TCM system. This review mainly elaborates on the treatment of secondary depression in TCM and the advantages of a herbal combined stem cell therapy in various methods. We believe it can provide a new clinical concept for secondary depression to obtain good clinical effects and reduce the risks borne by patients.

Feasibility of a Yoga Intervention for Individuals with Mild Cognitive Impairment: A Randomized Controlled Trial

Background: Yoga is a potentially low risk intervention for cognitive impairment that combines mental and physical practice and includes instruction on breathing, stress reduction, and mindfulness meditation. Previous research documents that yoga can target modifiable risk factors for mild cognitive impairment (MCI) progression. The authors describe a randomized feasibility trial of yoga for individuals with MCI. Methods: Participants were 37 individuals with amnestic MCI who were randomly assigned to receive 12 weeks of twice-weekly yoga intervention (YI) or healthy living education (HLE) classes. Acceptability and feasibility were assessed by tracking adverse events, class attendance, and participant satisfaction. Participants completed neuropsychological and mood measures as well as measures of potential intervention mechanisms at baseline and immediately postintervention. Results: Participants in both conditions reported high levels of satisfaction and reasonable class attendance rates. Home practice rates were low. There were no adverse events deemed related to the YI. Results showed a medium effect size in favor of the YI in visuospatial skills. The yoga group also showed a large effect size indicating decline in perceived stress compared with the HLE group, whereas HLE resulted in greater reductions in depressive symptoms after the intervention (large effect size). Conclusions: Study findings indicated that the YI was safe, modestly feasible, and acceptable to older adults with MCI. The authors found preliminary evidence that yoga may improve visuospatial functioning in individuals with MCI. Results support stress reduction as a possible mechanism for the YI. Future studies should address a YI in a larger sample and include strategies to enhance engagement and home practice.

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.

Accumulation of C-terminal cleaved tau is distinctly associated with cognitive deficits, synaptic plasticity impairment, and neurodegeneration in aged mice

C-terminal cleaved tau at D421 (∆D421-tau) accumulates in the brains of Alzheimer's disease (AD) patients. However, it is unclear how tau truncation, an understudied tau post-translational modification, contributes to AD pathology and progression. Utilizing an adeno-associated virus (AAV) gene delivery-based approach, we overexpressed full-length tau (FL-tau) and ∆D421-tau in 4- and 12-month-old mice for 4 months to study the neuropathological impact of accumulation in young adult (8-month) and middle-aged (16-month) mice. Overall, we show that independent of the tau species, age was an important factor facilitating tau phosphorylation, oligomer formation, and deposition into silver-positive tangles. However, mice overexpressing ∆D421-tau exhibited a distinct phosphorylation profile to those overexpressing FL-tau and increased tau oligomerization in the middle-age group. Importantly, overexpression of ∆D421-tau, but not FL-tau in middle-aged mice, resulted in pronounced cognitive impairments and hippocampal long-term potentiation deficits. While both FL-tau and ∆D421-tau induced neuronal loss in mice with age, ∆D421-tau led to significant neuronal loss in the CA3 area of the hippocampus and medial entorhinal cortex compared to FL-tau. Based on our data, we conclude that age increases the susceptibility to neuronal degeneration associated with ΔD421-tau accumulation. Our findings suggest that ΔD421-tau accumulation contributes to synaptic plasticity and cognitive deficits, thus representing a potential target for tau-associated pathologies.

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

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

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.

Mechanisms Involved in Microglial-Interceded Alzheimer's Disease and Nanocarrier-Based Treatment Approaches

Alzheimer's disease (AD) is a common neurodegenerative disorder accountable for dementia and cognitive dysfunction. The etiology of AD is complex and multifactorial in origin. The formation and deposition of amyloid-beta (Aβ), hyperphosphorylated tau protein, neuroinflammation, persistent oxidative stress, and alteration in signaling pathways have been extensively explored among the various etiological hallmarks. However, more recently, the immunogenic regulation of AD has been identified, and macroglial activation is considered a limiting factor in its etiological cascade. Macroglial activation causes neuroinflammation via modulation of the NLRP3/NF-kB/p38 MAPKs pathway and is also involved in tau pathology via modulation of the GSK-3β/p38 MAPK pathways. Additionally, microglial activation contributes to the discrete release of neurotransmitters and an altered neuronal synaptic plasticity. Therefore, activated microglial cells appear to be an emerging target for managing and treating AD. This review article discussed the pathology of microglial activation in AD and the role of various nanocarrier-based anti-Alzeihmenr's therapeutic approaches that can either reverse or inhibit this activation. Thus, as a targeted drug delivery system, nanocarrier approaches could emerge as a novel means to overcome existing AD therapy limitations.

Excess tau PET ligand retention in elderly patients with major depressive disorder

Depression is one of the common psychiatric disorders in old age. Major depressive disorder (MDD) has been identified as a risk factor or prodrome for neurodegenerative dementias, suggesting neuropathological overlaps and a continuum between MDD and neurodegenerative disorders. In this study, we examined tau and amyloid-β (Aβ) accumulations in the brains of MDD and healthy controls using positron emission tomography (PET) to explore pathological substrates of this illness. Twenty MDD and twenty age-matched, healthy controls were examined by PET with a tau radioligand, [¹¹C]PBB3, and an Aβ radioligand, [¹¹C]PiB. Radioligand retentions were quantified as a standardized uptake value ratio (SUVR). We also assessed clinical manifestations of the patients using the 17-item Hamilton Depression Scale, the Geriatric Depression Scale, and psychotic symptoms. Mean cortical [¹¹C]PBB3 SUVRs in MDD patients were significantly higher than those of healthy controls. These values were higher in MDD patients with psychotic symptoms than in those without any. The present findings indicate that tau depositions may underlie MDD, and especially in patients with psychotic symptoms. PET detection of tau accumulations may provide mechanistic insights into neuronal dysfunctions in these cases and could serve as predictions of their clinical consequences.

Perceived Stress is Associated with Alzheimer's Disease Cerebrospinal Fluid Biomarkers in African Americans with Mild Cognitive Impairment

BACKGROUND

African Americans (AA) have a higher Alzheimer's disease (AD) prevalence and report more perceived stress than White Americans. The biological basis of the stress-AD link is unclear. This study investigates the connection between stress and AD biomarkers in a biracial cohort.

OBJECTIVE

Establish biomarker evidence for the observed association between stress and AD, especially in AA.

METHODS

A cross-sectional study (n = 364, 41.8% AA) administering cognitive tests and the perceived stress scale (PSS) questionnaire. A subset (n = 309) provided cerebrospinal fluid for measurement of Aβ42, Tau, Ptau, Tau/Aβ42 (TAR), and Ptau/Aβ42 (PTAR). Multivariate linear regression, including factors that confound racial differences in AD, was performed.

RESULTS

Higher PSS scores were associated with higher Ptau (β= 0.43, p = 0.01) and PTAR (β= 0.005, p = 0.03) in AA with impaired cognition (mild cognitive impairment).

CONCLUSION

Higher PSS scores were associated with Tau-related AD biomarker indices in AA/MCI, suggesting a potential biological connection for stress with AD and its racial disparity.

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.

Reelin changes hippocampal learning in aging and Alzheimer's disease

The hippocampal formation (HF) is a neuroanatomical region essential for learning and memory. As one of the earliest regions to display the histopathological hallmarks of Alzheimer's disease (AD), determining the specific mechanisms of the HF's vulnerability is of capital importance. Reelin, a glycoprotein crucial in cortical lamination during embryonic neurogenesis, has an uncommon expression pattern within the HF and has been implicated in both learning and AD pathogenesis. We hypothesized that Reelin deficiency would expedite behavioral impairments which accompany normal aging. Additionally, we hypothesized that Reelin deficiency in the presence of mutated human microtubule associated protein tau (MAPT) would further impair hippocampal function. To test our hypothesis, we utilized cohorts of aged mice, aged mice with Reelin conditional knockout (RcKO), and adult mice with both RcKO and MAPT in the Barnes maze and Trace fear conditioning. Consistent with prior literature, increased age in wild-type mice was sufficient to reduce spatial searching in the Barnes maze. Increased age both exacerbated spatial impairments and altered context learning in RcKO mice. Lastly, adult mice with both RcKO and the MAPT transgene displayed both the lowest age-of-onset and most severe spatial learning deficits. In conclusion, Reelin deficiency when combined with AD risk-factors produced consistent impairments in spatial memory tasks. Furthermore, our results further implicate Reelin's importance in both HF homeostasis and AD pathogenesis.

Unsupervised Machine Learning to Identify Separable Clinical Alzheimer's Disease Sub-Populations

Heterogeneity among Alzheimer's disease (AD) patients confounds clinical trial patient selection and therapeutic efficacy evaluation. This work defines separable AD clinical sub-populations using unsupervised machine learning. Clustering (t-SNE followed by k-means) of patient features and association rule mining (ARM) was performed on the ADNIMERGE dataset from the Alzheimer's Disease Neuroimaging Initiative (ADNI). Patient sociodemographics, brain imaging, biomarkers, cognitive tests, and medication usage were included for analysis. Four AD clinical sub-populations were identified using between-cluster mean fold changes [cognitive performance, brain volume]: cluster-1 represented least severe disease [+17.3, +13.3]; cluster-0 [-4.6, +3.8] and cluster-3 [+10.8, -4.9] represented mid-severity sub-populations; cluster-2 represented most severe disease [-18.4, -8.4]. ARM assessed frequently occurring pharmacologic substances within the 4 sub-populations. No drug class was associated with the least severe AD (cluster-1), likely due to lesser antecedent disease. Anti-hyperlipidemia drugs associated with cluster-0 (mid-severity, higher volume). Interestingly, antioxidants vitamin C and E associated with cluster-3 (mid-severity, higher cognition). Anti-depressants like Zoloft associated with most severe disease (cluster-2). Vitamin D is protective for AD, but ARM identified significant underutilization across all AD sub-populations. Identification and feature characterization of four distinct AD sub-population "clusters" using standard clinical features enhances future clinical trial selection criteria and cross-study comparative analysis.

Chronic stress and Alzheimer's disease: the interplay between the hypothalamic-pituitary-adrenal axis, genetics and microglia

Chronic psychosocial stress is increasingly being recognised as a risk factor for sporadic Alzheimer's disease (AD). The hypothalamic-pituitary-adrenal axis (HPA axis) is the major stress response pathway in the body and tightly regulates the production of cortisol, a glucocorticoid hormone. Dysregulation of the HPA axis and increased levels of cortisol are commonly found in AD patients and make a major contribution to the disease process. The underlying mechanisms remain poorly understood. In addition, within the general population there are interindividual differences in sensitivities to glucocorticoid and stress responses, which are thought to be due to a combination of genetic and environmental factors. These differences could ultimately impact an individuals' risk of AD. The purpose of this review is first to summarise the literature describing environmental and genetic factors that can impact an individual's HPA axis reactivity and function and ultimately AD risk. Secondly, we propose a mechanism by which genetic factors that influence HPA axis reactivity may also impact inflammation, a key driver of neurodegeneration. We hypothesize that these factors can mediate glucocorticoid priming of the immune cells of the brain, microglia, to become pro-inflammatory and promote a neurotoxic environment resulting in neurodegeneration. Understanding the underlying molecular mechanisms and identifying these genetic factors has implications for evaluating stress-related risk/progression to neurodegeneration, informing the success of interventions based on stress management and potential risks associated with the common use of glucocorticoids.

Protective Effect of Hydroxysafflor Yellow A against Chronic Mild Stress-induced Memory Impairments by Suppressing Tau Phosphorylation in Mice

Chronic stress plays a critical role in the etiology of sporadic Alzheimer's disease (AD). However, there are currently no effective drugs that can target chronic stress to prevent AD. In this study, we explored the neuroprotective effect of hydroxysafflor yellow A (HSYA) against chronic mild stress (CMS)-induced memory impairments in mice and the underlying mechanism. The Morris water maze test showed that HSYA significantly reduced CMS-induced learning and memory impairments in mice. HSYA increased the expression of brain-derived neurotrophic factor (BDNF) and activated downstream tropomyosin-related kinase B (TrkB) and phosphatidylinositol 3-kinase (PI3K)/protein kinase B(Akt)/mammalian target of rapamycin (mTOR) signaling. HSYA decreased the expression of regulator of calcineurin 1-1L (RCAN1-1L) that could promote the activity of glycogen synthase kinase-3β (GSK-3β). HSYA also attenuated tau phosphorylation by inhibiting the activity of GSK-3β and cyclin-dependent kinase-5 (Cdk5). Our data indicated that HSYA has protective effects against CMS-induced BDNF downregulation, tau phosphorylation and memory impairments. HSYA may be a promising therapeutic candidate for AD by targeting chronic stress.

Later life depression as risk factor for developing dementia: epidemiological evidence, predictive models, preventive strategies and future trends

Current investigations in pre-symptomatic dementia have suggested that depressive mood, a treatable condition, may play an important role in the development of the disorder. However, whether depression in adulthood constitute a risk factor, or a prodrome of dementia remains unclear. A major implication in such dispute is the analytic framework used to identify putative risk factors. Indeed, if evaluated in the years immediately prior to dementia diagnosis the association between depression and dementia may reflect depressive symptoms as a prodrome of yet-undiagnosed dementia. Unfortunately, long term prospective cohort investigations, reaching back into the preclinical phase of dementia are sparse. Here, we have surveyed high-quality evidence (systematic reviews and meta-analyses) on the association between depressive symptoms and increased odds of dementia. Meta-analytic findings are also presented and discussed regarding depression as a prodromal stage of dementia, or a consequence of underlying neurodegenerative processes. Additionally, the potential confounding effect of several variables on the risk association between depression and dementia, an aspect hardly investigated, is discussed. While early onset late-life depression - defined as starting before 60 years of age - increases the odds of developing dementia in predisposed subjects, late-onset depression appears to be a prodrome and a clear accelerating factor for cognitive deterioration. Since it is increasingly important to consider the potential of preemptive approaches to decrease the impact of dementia, evidence on potentially effective preventive strategies targeting depression as a risk factor, and next steps in further research are presented as concluding remarks.

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.

Longitudinal Assessment of Working Memory Performance in the APPswe/PSEN1dE9 Mouse Model of Alzheimer's Disease Using an Automated Figure-8-Maze

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, with a long preclinical and prodromal phase. To enable the study of disease mechanisms, AD has been modeled in many transgenic animal lines and cognitive functioning has been tested using several widely used behavioral tasks. These tasks, however, are not always suited for repeated longitudinal testing and are often associated with acute stress such as animal transfer, handling, novelty, or stress related to the task itself. This makes it challenging to relate cognitive dysfunction in animal models to cognitive decline observed in AD patients. Here, we designed an automated figure-8-maze (F8M) to test mice in a delayed alternation task (DAT) in a longitudinal manner. Mice were rewarded when they entered alternate sides of the maze on subsequent trials. Automation as well as connection of the F8M set-up with a home cage reduces experimenter interference and minimizes acute stress, thus making it suitable for longitudinal testing and facilitating clinical translation. In the present study, we monitored cognitive functioning of 2-month-old APPswe/PSEN1dE9 (APP/PS1) mice over a period of 4 months. The percentage of correct responses in the DAT did not differ between wild-type and transgenic mice from 2 to 6 months of age. However, 6-month-old mice displayed an increase in the number of consecutive incorrect responses. These results demonstrate the feasibility of longitudinal testing using an automated F8M and suggest that APP/PS1 mice are not impaired at delayed spatial alternation until 6 months of age under the current experimental conditions.

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.

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

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

Senescent accelerated prone 8 (SAMP8) mice as a model of age dependent neuroinflammation

BACKGROUND

Aging and age-related diseases are strong risk factors for the development of neurodegenerative diseases. Neuroinflammation (NIF), as the brain's immune response, plays an important role in aged associated degeneration of central nervous system (CNS). There is a need for well characterized animal models that will allow the scientific community to understand and modulate this process.

METHODS

We have analyzed aging-phenotypical and inflammatory changes of brain myeloid cells (bMyC) in a senescent accelerated prone aged (SAMP8) mouse model, and compared with their senescence resistant control mice (SAMR1). We have performed morphometric methods to evaluate the architecture of cellular prolongations and determined the appearance of Iba1⁺ clustered cells with aging. To analyze specific constant brain areas, we have performed stereology measurements of Iba1⁺ cells in the hippocampal formation. We have isolated bMyC from brain parenchyma (BP) and choroid plexus plus meningeal membranes (m/Ch), and analyzed their response to systemic lipopolysaccharide (LPS)-driven inflammation.

RESULTS

Aged 10 months old SAMP8 mice present many of the hallmarks of aging-dependent neuroinflammation when compared with their SAMR1 control, i.e., increase of protein aggregates, presence of Iba1⁺ clusters, but not an increase in the number of Iba1⁺ cells. We have further observed an increase of main inflammatory mediator IL-1β, and an augment of border MHCII⁺Iba1⁺ cells. Isolated CD45⁺ bMyC from brain parenchyma (BP) and choroid plexus plus meningeal membranes (m/Ch) have been analyzed, showing that there is not a significant increase of CD45⁺ cells from the periphery. Our data support that aged-driven pro-inflammatory cytokine interleukin 1 beta (IL-1β) transcription is enhanced in CD45⁺BP cells. Furthermore, LPS-driven systemic inflammation produces inflammatory cytokines mainly in border bMyC, sensed to a lesser extent by the BP bMyC, showing that IL-1β expression is further augmented in aged SAMP8 compared to control SAMR1.

CONCLUSION

Our data validate the SAMP8 model to study age-associated neuroinflammatory events, but careful controls for age and strain are required. These animals show morphological changes in their bMyC cell repertoires associated to age, corresponding to an increase in the production of pro-inflammatory cytokines such as IL-1β, which predispose the brain to an enhanced inflammatory response after LPS-systemic challenge.

Trait anxiety, a personality risk factor associated with Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease in elderly population and the leading cause of dementia worldwide. While senile plaques and neurofibrillary tangles have been proposed as the principal histopathologic hallmarks of AD, the exact etiology of this disease is still far from being clearly understood. AD has been recognized as pathological consequences of complex interactions among genetic, aging, medical, life style and psychosocial factors. Recently, the roles of neuroticism personality traits in AD incidence and progression have come into focus. More specifically, increasing evidence has further shown that the trait anxiety, one major component of neuroticism predicting the individual vulnerability in response to stress, is a risk factor for AD and may correlated with various AD pathologies. In this review, we summarized recent literature on the association of trait anxiety with AD. We also discussed the possible neuroendocrinological and neurochemical mechanisms of this association, which may provide clinical implications for AD diagnosis and therapy.