Chronic stress as a risk factor for Alzheimer's disease: Roles of microglia-mediated synaptic remodeling, inflammation, and oxidative stress

Association of Posttraumatic Stress Disorder With Accelerated Cognitive Decline in Middle-aged Women

IMPORTANCE

Posttraumatic stress disorder (PTSD) has been hypothesized to lead to impaired cognitive function. However, no large-scale studies have assessed whether PTSD is prospectively associated with cognitive decline in middle-aged adults.

OBJECTIVE

To assess the association between PTSD and decline in cognitive function over time.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study included participants from the Nurses' Health Study II, an ongoing longitudinal cohort study involving community-dwelling middle-aged female nurses residing in the US who had at least a 2-year nursing degree at the time of enrollment in 1989. The present study included 12 270 trauma-exposed women who were enrolled in the PTSD substudy of the Nurses' Health Study II and completed 1 to 5 cognitive assessments. Data were collected from March 1, 2008, to July 30, 2019.

EXPOSURES

Lifetime PTSD symptoms, assessed using a validated questionnaire between March 1, 2008, and February 28, 2010.

MAIN OUTCOMES AND MEASURES

The main outcome was evaluated using the Cogstate Brief Battery, a self-administered online cognitive battery. Cognitive function was measured by a psychomotor speed and attention composite score and a learning and working memory composite score. Women completed the Cogstate Brief Battery every 6 or 12 months (up to 24 months) from October 3, 2014, to July 30, 2019. Linear mixed-effects models were used to evaluate the association of PTSD symptoms with the rate of change in cognition over follow-up, considering a broad range of relevant covariates, including the presence of depression symptoms and history of clinician-diagnosed depression. The rate of cognitive change was adjusted for potential practice effects (ie, potential changes in test results that occur when a test is taken more than once) by including indicators for the number of previous tests taken.

RESULTS

Among 12 270 women, the mean (SD) age at the baseline cognitive assessment was 61.1 (4.6) years; 125 women (1.0%) were Asian, 75 (0.6%) were Black, 156 (1.3%) were Hispanic, 11 767 (95.9%) were non-Hispanic White, and 147 (1.2%) were of other race and/or ethnicity. A higher number of PTSD symptoms was associated with worse cognitive trajectories. Compared with women with no PTSD symptoms, women with the highest symptom level (6-7 symptoms) had a significantly worse rate of change in both learning and working memory (β = -0.08 SD/y; 95% CI, -0.11 to -0.04 SD/y; P < .001) and psychomotor speed and attention (β = -0.05 SD/y; 95% CI, -0.09 to -0.01 SD/y; P = .02), adjusted for demographic characteristics. Associations were unchanged when additionally adjusted for behavioral factors (eg, 6-7 symptoms in the analysis of learning and working memory: β = -0.08 SD/y; 95% CI, -0.11 to -0.04 SD/y; P < .001) and health conditions (eg, 6-7 symptoms in the analysis of learning and working memory: β = -0.08 SD/y; 95% CI, -0.11 to -0.04 SD/y; P < .001) and were partially attenuated but still evident when further adjusted for practice effects (eg, 6-7 symptoms in the analysis of learning and working memory: β = -0.07 SD/y; 95% CI, -0.10 to -0.03 SD/y; P < .001) and comorbid depression (eg, 6-7 symptoms in the analysis of learning and working memory: β = -0.07 SD/y; 95% CI, -0.11 to -0.03 SD/y; P < .001).

CONCLUSIONS AND RELEVANCE

In this large-scale prospective cohort study, PTSD was associated with accelerated cognitive decline in middle-aged women, suggesting that earlier cognitive screening among women with PTSD may be warranted. Given that cognitive decline is strongly associated with subsequent Alzheimer disease and related dementias, better understanding of this association may be important to promote healthy aging.

An Overview of Oxidative Stress, Neuroinflammation, and Neurodegenerative Diseases

Oxidative stress has been linked with a variety of diseases, being involved in the debut and/or progress of several neurodegenerative disorders. This review intends to summarize some of the findings that correlate the overproduction of reactive oxygen species with the pathophysiology of Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, and amyotrophic lateral sclerosis. Oxidative stress was also noted to modify the inflammatory response. Even though oxidative stress and neuroinflammation are two totally different pathological events, they are linked and affect one another. Nonetheless, there are still several mechanisms that need to be understood regarding the onset and the progress of neurodegenerative diseases in order to develop efficient therapies. As antioxidants are a means to alter oxidative stress and slow down the symptoms of these neurodegenerative diseases, the most common antioxidants, enzymatic as well as non-enzymatic, have been mentioned in this paper as therapeutic options for the discussed disorders.

Effects of acute and chronic oxidative stress on the blood-brain barrier in 2D and 3D in vitro models

Oxidative stress is a shared pathology of neurodegenerative disease and brain injuries, and is derived from perturbations to normal cell processes by aging or environmental factors such as UV exposure and air pollution. As oxidative cues are often present in systemic circulation, the blood-brain barrier (BBB) plays a key role in mediating the effect of these cues on brain dysfunction. Therefore, oxidative damage and disruption of the BBB is an emergent focus of neurodegenerative disease etiology and progression. We assessed barrier dysfunction in response to chronic and acute oxidative stress in 2D and 3D in vitro models of the BBB with human iPSC-derived brain microvascular endothelial-like cells (iBMECs). We first established doses of hydrogen peroxide to induce chronic damage (modeling aging and neurodegenerative disease) and acute damage (modeling the response to traumatic brain injury) by assessing barrier function via transendothelial electrical resistance in 2D iBMEC monolayers and permeability and monolayer integrity in 3D tissue-engineered iBMEC microvessels. Following application of these chronic and acute doses in our in vitro models, we found local, discrete structural changes were the most prevalent responses (rather than global barrier loss). Additionally, we validated unique functional changes in response to oxidative stress, including dysfunctional cell turnover dynamics and immune cell adhesion that were consistent with changes in gene expression.

The Association of Stress, Metabolic Syndrome, and Systemic Inflammation With Neurocognitive Function in the Hispanic Community Health Study/Study of Latinos and Its Sociocultural Ancillary Study

OBJECTIVES

Identifying sociocultural correlates of neurocognitive dysfunction among Hispanics/Latinos, and their underlying biological pathways, is crucial for understanding disparities in Alzheimer's disease and related dementias. We examined cross-sectional associations between stress and neurocognition, and the role that metabolic syndrome (MetS) and systemic inflammation might play in these associations.

METHOD

Participants included 3,045 adults aged 45-75 (56% female, education 0-20+ years, 86% Spanish-speaking, 23% U.S.-born), enrolled in the Hispanic Community Health Study/Study of Latinos and its Sociocultural Ancillary Study. Global neurocognition was the primary outcome and operationalized as the average of the z scores of measures of learning and memory, word fluency, and processing speed. Stress measures included self-report assessments of stress appraisal (perceived and acculturative stress) and exposure to chronic and traumatic stressors. MetS was defined via established criteria including waist circumference, high blood pressure, elevated triglycerides, fasting plasma glucose, and high levels of high-density lipoprotein cholesterol. Systemic inflammation was represented by high-sensitivity C-reactive protein (hs-CRP).

RESULTS

Separate survey multivariable linear regression models adjusting for covariates showed that higher perceived (b = -0.004, SE = 0.002, p < .05) and acculturative stress (b = -0.004, SE = 0.001, p < .0001) were significantly associated with worse global neurocognition, while lifetime exposure to traumatic stressors was associated with better global neurocognition (b = 0.034, SE = 0.009, p < .001). Neither MetS nor hs-CRP were notable pathways in the association between stress and neurocognition; rather, they were both independently associated with worse neurocognition in models including stress measures (ps < .05).

DISCUSSION

These cross-sectional analyses suggest that stress appraisal, MetS, and systemic inflammation may be targets to reduce neurocognitive dysfunction among Hispanics/Latinos.

Induction of Accelerated Aging in a Mouse Model

With the global increase of the elderly population, the improvement of the treatment for various aging-related diseases and the extension of a healthy lifespan have become some of the most important current medical issues. In order to understand the developmental mechanisms of aging and aging-related disorders, animal models are essential to conduct relevant studies. Among them, mice have become one of the most prevalently used model animals for aging-related studies due to their high similarity to humans in terms of genetic background and physiological structure, as well as their short lifespan and ease of reproduction. This review will discuss some of the common and emerging mouse models of accelerated aging and related chronic diseases in recent years, with the aim of serving as a reference for future application in fundamental and translational research.

Corticosterone potentiates ochratoxin A-induced microglial activation

Microglial activation in the central nervous system (CNS) has been associated with brain damage and neurodegenerative disorders. Ochratoxin A (OTA) is a mycotoxin that occurs naturally in food and feed and has been associated with neurotoxicity, while corticosteroids are CNS’ physiological function modulators. This study examined how OTA affected microglia activation and how corticosteroids influenced microglial neuroinflammation. Murine microglial cells (BV-2) were stimulated by OTA, and the potentiation effects on OTA-induced inflammation were determined by corticosterone pre-treatment. Expressions of pro-inflammatory mediators including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), and inducible nitric oxide synthase (iNOS) were determined. Phosphorylation of mitogen-activated protein kinases (MAPKs) was analyzed by western blotting. OTA significantly increased the mRNA expression of IL-6, TNF-α, IL-1β, and iNOS and also elevated IL-6 and NO levels. Corticosterone pre-treatment enhanced the neuroinflammatory response to OTA in a mineralocorticoid receptor (MR)-dependent mechanism, which is associated with increases in extracellular signal-regulated kinase (ERK) and p38 MAPK activation. In response to OTA, microglial cells produced pro-inflammatory cytokines and NO, while corticosterone increased OTA-induced ERK and p38 MAPK phosphorylation via MR. Findings indicated the direct role of OTA in microglia activation and neuroinflammatory response and suggested that low corticosterone concentrations in the brain exacerbated neurodegeneration.

Magnetic resonance elastography to study the effect of amyloid plaque accumulation in a mouse model

BACKGROUND AND PURPOSE

Biomechanical changes in the brain have not been fully elucidated in Alzheimer's disease (AD). We aimed to investigate the effect of β-amyloid accumulation on mouse brain viscoelasticity.

METHODS

Magnetic resonance elastography was used to calculate magnitude of the viscoelastic modulus (|G*|), elasticity (G_d ), and viscosity (G_l ) in the whole brain parenchyma (WB) and bilateral hippocampi of 9 transgenic J20 (AD) mice (5 males/4 females) and 10 wild-type (WT) C57BL/6 mice (5 males/5 females) at 11 and 14 months of age.

RESULTS

Cross-sectional analyses showed no significant difference between AD and WT mice at either timepoints. No sex-specific differences were observed at 11 months of age, but AD females showed significantly higher hippocampal |G*| and G_l and WB |G*|, G_d , and G_l compared to both AD and WT males at 14 months of age. Similar trending differences were found between female AD and female WT animals but did not reach significance. Longitudinal analyses showed significant increases in hippocampal |G*|, G_d , and G_l , and significant decreases in WB |G*|, G_d , and G_l between 11 and 14 months in both AD and WT mice. Each subgroup showed significant increases in all hippocampal and significant decreases in all WB measures, with the exception of AD females, which showed no significant changes in WB |G*|, G_d , or G_l .

CONCLUSION

Aging had region-specific effects on cerebral viscoelasticity, namely, WB softening and hippocampal stiffening. Amyloid plaque deposition may have sex-specific effects, which require further scrutiny.

Zika virus infection accelerates Alzheimer’s disease phenotypes in brain organoids

Alzheimer’s disease (AD) is one of the progressive neurodegenerative diseases characterized by β-amyloid (Aβ) production and Phosphorylated-Tau (p-Tau) protein in the cerebral cortex. The precise mechanisms of the cause, responsible for disease pathology and progression, are not well understood because there are multiple risk factors associated with the disease. Viral infection is one of the risk factors for AD, and we demonstrated that Zika virus (ZIKV) infection in brain organoids could trigger AD pathological features, including Aβ and p-Tau expression. AD-related phenotypes in brain organoids were upregulated via endoplasmic reticulum (ER) stress and unfolded protein response (UPR) after ZIKV infection in brain organoids. Under persistent ER stress, activated-double stranded RNA-dependent protein kinase-like ER-resident (PERK) triggered the phosphorylation of Eukaryotic initiation factor 2 (eIF2α) and then BACE, and GSK3α/β related to AD. Furthermore, we demonstrated that pharmacological inhibitors of PERK attenuated Aβ and p-Tau in brain organoids after ZIKV infection.

Astrocytes in Post-traumatic Stress Disorder

Although posttraumatic stress disorder (PTSD) is on the rise, traumatic events and their consequences are often hidden or minimized by patients for reasons linked to PTSD itself. Traumatic experiences can be broadly classified into mental stress (MS) and traumatic brain injury (TBI), but the cellular mechanisms of MS- or TBI-induced PTSD remain unknown. Recent evidence has shown that the morphological remodeling of astrocytes accompanies and arguably contributes to fearful memories and stress-related disorders. In this review, we summarize the roles of astrocytes in the pathogenesis of MS-PTSD and TBI-PTSD. Astrocytes synthesize and secrete neurotrophic, pro- and anti-inflammatory factors and regulate the microenvironment of the nervous tissue through metabolic pathways, ionostatic control, and homeostatic clearance of neurotransmitters. Stress or trauma-associated impairment of these vital astrocytic functions contribute to the pathophysiological evolution of PTSD and may present therapeutic targets.

Chronic Stress Induces Hippocampal Mitochondrial Damage in APPPS1 Model Mice and Wildtype Littermates

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder and the most common cause of dementia worldwide. Despite decades of investigation, the etiology of AD is not fully understood, although emerging evidence suggest that chronic environmental and psychological stress plays a role in the mechanisms and contributes to the risk of developing AD. Thus, dissecting the impact of stress on the brain could improve our understanding of the pathological mechanisms.

OBJECTIVE

We aimed to study the effect of chronic stress on the hippocampal proteome in male APPPS1 transgenic mice and wildtype (WT) littermates.

METHODS

APPPS1 and WT mice were subjected to 4 weeks of chronic stress followed by 3 weeks of continued diurnal disruption. Hippocampal tissue was used for proteomics analysis using label-free quantitative DIA based LC-MS/MS analysis.

RESULTS

We identified significantly up- and downregulated proteins in both APPPS1 and WT mice exposed to chronic stress compared to the control groups. Via interaction network mapping, significant proteins could be annotated to specific pathways of mitochondrial function (oxidative phosphorylation and TCA cycle), metabolic pathways, AD pathway and synaptic functions (long term potentiation). In WT mice, chronic stress showed the highest impact on complex I of the oxidative phosphorylation pathway, while in APPPS1 mice this pathway was compromised broadly by chronic stress.

CONCLUSION

Our data shows that chronic stress and amyloidosis additively contribute to mitochondrial damage in hippocampus. Although these results do not explain all effects of chronic stress in AD, they add to the scientific knowledge on the topic.

The Gut Microbiota-Brain Axis: A New Frontier on Neuropsychiatric Disorders

Alzheimer's disease (AD) is a progressive and incurable neurodegenerative disorder of integrative areas of the brain, characterized by cognitive decline and disability resulting in negative impacts on the family of the patients and the health care services worldwide. AD involves oxidative stress, neuroinflammation and accelerated apoptosis, accompanied by deposition of amyloid-β peptide plaques and tau protein-based neurofibrillary tangles in the central nervous system. Among the multiple factors that contribute to the onset and evolution of this disease, aging stands out. That is why the prevalence of this disease has increased due to the constant increase in life expectancy. In the hope of finding new, more effective methods to slow the progression of this disease, over the last two decades, researchers have promoted "omics"-based approaches that include the gut microbiota and their reciprocal interactions with different targets in the body. This scientific advance has also led to a better understanding of brain compartments and the mechanisms that affect the integrity of the blood-brain barrier. This review aims to discuss recent advances related to the gut-brain-microbiota axis in AD. Furthermore, considering that AD involves psychiatric symptoms, this review also focuses on the psychiatric factors that interact with this axis (an issue that has not yet been sufficiently addressed in the literature).

Lyl-1 regulates primitive macrophages and microglia development

During ontogeny, macrophage populations emerge in the Yolk Sac (YS) via two distinct progenitor waves, prior to hematopoietic stem cell development. Macrophage progenitors from the primitive/"early EMP" and transient-definitive/"late EMP" waves both contribute to various resident primitive macrophage populations in the developing embryonic organs. Identifying factors that modulates early stages of macrophage progenitor development may lead to a better understanding of defective function of specific resident macrophage subsets. Here we show that YS primitive macrophage progenitors express Lyl-1, a bHLH transcription factor related to SCL/Tal-1. Transcriptomic analysis of YS macrophage progenitors indicate that primitive macrophage progenitors present at embryonic day 9 are clearly distinct from those present at later stages. Disruption of Lyl-1 basic helix-loop-helix domain leads initially to an increased emergence of primitive macrophage progenitors, and later to their defective differentiation. These defects are associated with a disrupted expression of gene sets related to embryonic patterning and neurodevelopment. Lyl-1-deficiency also induce a reduced production of mature macrophages/microglia in the early brain, as well as a transient reduction of the microglia pool at midgestation and in the newborn. We thus identify Lyl-1 as a critical regulator of primitive macrophages and microglia development, which disruption may impair resident-macrophage function during organogenesis.

The potential roles of excitatory-inhibitory imbalances and the repressor element-1 silencing transcription factor in aging and aging-associated diseases

Disruptions to the central excitatory-inhibitory (E/I) balance are thought to be related to aging and underlie a host of neural pathologies, including Alzheimer's disease. Aging may induce an increase in excitatory signaling, causing an E/I imbalance, which has been linked to shorter lifespans in mice, flies, and worms. In humans, extended longevity correlates to greater repression of genes involved in excitatory neurotransmission. The repressor element-1 silencing transcription factor (REST) is a master regulator in neural cells and is believed to be upregulated with senescent stimuli, whereupon it counters hyperexcitability, insulin/insulin-like signaling pathway activity, oxidative stress, and neurodegeneration. This review examines the putative mechanisms that distort the E/I balance with aging and neurodegeneration, and the putative roles of REST in maintaining neuronal homeostasis.

Chronic MC-LR exposure promoted Aβ and p-tau accumulation via regulating Akt/GSK-3β signal pathway

It has been reported that microcystin-leucine-arginine (MC-LR) can enter into the brain and demonstrate neurotoxicity resulting in learning and memory deficits. While, there is still a lack of clear understanding of the related molecular mechanisms. In this study, we observed β-amyloid (Aβ) accumulation and tau hyperphosphorylation (p-tau) at sites of Ser396 and Thr205 in mouse hippocampus and cortex, Alzheimer's disease (AD) like changes, after chronic exposure to MC-LR at different concentrations (1, 7.5, 15 and 30 μg/L) for 180 days. The hallmarks of AD are characterized by senile plaques and neurofibrillary tangles (NFT), with associated loss of neurons, resulting in cognitive impairment and dementia. Similarly, the production of Aβ and tau hyperphosphorylation was also detected in HT-22 cells treated with MC-LR. In addition, MC-LR promoted increased expressions of BACE1 and PS1, but reduced mRNA expressions of ADAM family members both in vivo and in vitro, promoting the Aβ production. Moreover, we identified Akt/GSK-3β signal pathway mediated the Aβ and p-tau accumulation, bringing about Alzheimer's disease-like changes. Furthermore, microglial cells were activated in those mice exposed to MC-LR. Inflammatory cytokines were also found being activated to release in vitro. In conclusion, this study could provide a clue for MC-LR-induced neurotoxicity, which gave insights into the environmental risks of Alzheimer's disease.

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

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

Microglial functional alteration and increased diversity in the challenged brain: Insights into novel targets for intervention

Microglia are the resident immune cells of the central nervous system (CNS) parenchyma, which perform beneficial physiological roles across life. These immune cells actively maintain CNS health by clearing toxic debris and removing dysfunctional or degenerating cells. They also modify the wiring of neuronal circuits, by acting on the formation, modification, and elimination of synapses-the connections between neurons. Microglia furthermore recently emerged as highly diverse cells comprising several structural and functional states, indicating a far more critical involvement in orchestrating brain development, plasticity, behaviour, and cognition. Various environmental factors, together with the individual genetic predispositions, confer an increased risk for neurodevelopmental and neuropsychiatric disorders, as well as neurodegenerative diseases that include autism spectrum disorders, schizophrenia, major depressive disorder, and Alzheimer's disease, across life. Microglia are highly sensitive to chronic psychological stress, inadequate diet, viral/bacterial infection, pollution, and insufficient or altered sleep, especially during critical developmental periods, but also throughout life. These environmental challenges can compromise microglial physiological functions, resulting notably in defective neuronal circuit wiring, altered brain functional connectivity, and the onset of behavioral deficits into adolescence, adulthood, and aging. This short review provides a historical and technical perspective, notably focused on my contribution to the field, on how environmental challenges affect microglia, particularly their physiological functions, and increase their diversity, which provides novel targets for intervention.

Microglia and BDNF at the crossroads of stressor related disorders: Towards a unique trophic phenotype

Stressors ranging from psychogenic/social to neurogenic/injury to systemic/microbial can impact microglial inflammatory processes, but less is known regarding their effects on trophic properties of microglia. Recent studies do suggest that microglia can modulate neuronal plasticity, possibly through brain derived neurotrophic factor (BDNF). This is particularly important given the link between BDNF and neuropsychiatric and neurodegenerative pathology. We posit that certain activated states of microglia play a role in maintaining the delicate balance of BDNF release onto neuronal synapses. This focused review will address how different "activators" influence the expression and release of microglial BDNF and address the question of tropomyosin receptor kinase B (TrkB) expression on microglia. We will then assess sex-based differences in microglial function and BDNF expression, and how microglia are involved in the stress response and related disorders such as depression. Drawing on research from a variety of other disorders, we will highlight challenges and opportunities for modulators that can shift microglia to a "trophic" phenotype with a view to potential therapeutics relevant for stressor-related disorders.

Walnut peptide WEKPPVSH in alleviating oxidative stress and inflammation in lipopolysaccharide-activated BV-2 microglia via the Nrf2/HO-1 and NF-κB/p38 MAPK pathways

The peptide WEKPPVSH from walnut protein hydrolyzate was used to evaluate the antioxidant and anti-inflammatory protective effect on lipopolysaccharide (LPS)-activated BV-2 microglia and its possible mechanism. The results indicated that WEKPPVSH significantly decreased nitric oxide (NO) and reactive oxygen species (ROS) generation in a dose-dependent manner, and significantly up-regulated superoxide dismutase and catalase activities (P < 0.01). Results of enzyme-linked immunosorbent assay (ELISA) showed that WEKPPVSH significantly mitigated the secretion of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) (P < 0.01). Immunofluorescence analysis exhibited that WEKPPVSH down-regulated p65 translocation to the cell nucleus. Western blotting showed that WEKPPVSH up-regulated the expression of nuclear factor erythroid 2-related factor (Nrf2) and heme oxygenase-1 (HO-1), and down-regulated the expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), p-IκB/IκB, p-p65/p65 and p-p38/p38. In summary, WEKPPVSH might protect against oxidative stress and inflammation in LPS-stimulated BV-2 microglia by enhancing the Nrf2/HO-1 signaling pathway and blocking the nuclear factor-κB/p38 mitogen - activated protein kinase (NF-κB/p38 MAPK) signaling pathway. The results provided an experimental basis for the research and development of walnut peptide products.

Air Pollution and Alzheimer's Disease: A Systematic Review and Meta-Analysis

BACKGROUND

Ambient air pollution has been associated with Alzheimer's disease (AD) in the elderly. However, its effects on AD have not been meta-analyzed comprehensively.

OBJECTIVE

We conducted a systematic review and meta-analysis to assess the associations between air pollution and AD incidence.

METHODS

We searched PubMed and Web of Science for indexed publications up to March 2020. Odds risk (OR) and confidence intervals (CI) were estimated for particulate matter (PM)10 (PM10), PM2.5, ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO). The subgroup analysis was conducted based on the pollution levels.

RESULTS

Nine studies were included in the meta-analysis and review. The OR per 10μg/m3 increase of PM2.5 was 1.95 (95% CI: 0.88-4.30). The corresponding values per 10μg/m3 increment of other pollutants were 1.03 (95% CI: 0.68-1.57) for O3, 1.00 (95% CI: 0.89-1.13) for NO2, and 0.95 (95% CI: 0.91-0.99) for PM10 (only one study), respectively. Overall OR of the five air pollutants above with AD was 1.32 (95% CI: 1.09-1.61), suggesting a positive association between ambient air pollution and AD incidence. The sub-analysis indicated that the OR (2.20) in heavily polluted regions was notably higher than that in lightly polluted regions (1.06). Although AD risk rate data related to SO2 or CO exposure are still limited, the epidemiologic and toxicological evidence indicated that higher concentration of SO2 or CO exposure increased risks of dementia, implying that SO2 or CO might have a potential impact on AD.

CONCLUSION

Air pollution exposure may exacerbate AD development.

Sevoflurane inhalation has a cognitive impairing effect of aging rats involving the regulation of AChE and ChAT

Background

Acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) are closely related to the regulation of learning and memory. Nevertheless, whether sevoflurane has influence on cognition through regulating the expression of AChE and ChAT remains unclear.

Methods

Aging rat model was established by subcutaneously injection of D-galactose for 6 consecutive weeks. To determine the role of AChE and ChAT in sevoflurane-induced cognitive impairment, the Morris water maze (MWM) was used to assess the cognitive and memory function after sevoflurane exposure. Then, the variations of AChE and ChAT was detected by western blotting analysis and quantitative real-time polymerase chain reaction (qRT-PCR) respectively.

Results

Our result indicated that aging model rats had showed cognition decline at 2 hours and 1week after exposure to sevoflurane. Moreover, the expression of AChE and ChAT enhanced in rats that had inhaled sevoflurane. Interestingly, our study also found that the increase of oxygen concentration had a positive impact on the gene expression of ChAT.

Conclusion

We have identified that the overexpression of AChE and ChAT improved significantly cognitive function after sevoflurane exposure.

Effect of chronically electric foot shock stress on spatial memory and hippocampal blood brain barrier permeability

Maintaining blood-brain barrier (BBB) contributes critically to preserving normal brain functions. According to the available evidence, intense or chronic exposure to stress would potentially affect different brain structures, such as the hippocampus, negatively. The purpose of this study was to define the relationship between the BBB permeability of the hippocampus and the performance of spatial learning and memory under chronically electric foot shock stress. Sixteen rats were divided into the control and stress groups equally. Animals in the stress group were exposed to foot shock (1 mA, 1 Hz) for 10-s duration every 60 s (1 h/day) for 10 consecutive days. The anxiety-related behavior, spatial learning, and memory were assessed by an Open Field (OF) and the Morris Water Maze (MWM) respectively. The hippocampal BBB permeability was determined by Evans blue penetration assay. Our results demonstrated that the stress model not only increased locomotor activities in the OF test but reduced spatial learning and memory in MWM. Moreover, these effects coincided with a significant increase in hippocampal BBB permeability. In sum, the stress model can be used in future studies focusing on the relationship between stress and BBB permeability of the hippocampus.

Age-Related Cognitive Decline May Be Moderated by Frequency of Specific Food Products Consumption

Our study aimed to evaluate whether the type of food products and the frequency of their consumption are associated with cognitive functioning in younger and older adults. The impact of diets that are high in added sugars and saturated fat on cognitive functioning, especially on memory, was at the center of our interest. Participants in the study were 204 healthy adults (aged 20-55) who performed a multitasking cognitive test and completed dietary and psychological questionnaires. Stepwise regression analysis with age and food consumption patterns as predictors, and the cognitive task performance as a dependent variable, revealed that cognitive task performance worsened with age. However, we found that the frequency of consuming different types of foods (healthy versus unhealthy dietary patterns) moderates the effects of age on cognitive functioning. Red meat and animal fat consumption were negatively correlated with cognitive performance, and this relation was dependent on the age of our participants. Conversely, white meat and fish consumption were positively related to memory. Different indices of dietary patterns (both positive and negative) were stronger predictors of cognitive performance in the older adult group. We interpret our results as evidence that diet may be a protective (or worsening) factor in age-related cognitive decline.

Differential Impact of Acute and Chronic Stress on CA1 Spatial Coding and Gamma Oscillations

Chronic and acute stress differentially affect behavior as well as the structural integrity of the hippocampus, a key brain region involved in cognition and memory. However, it remains unclear if and how the facilitatory effects of acute stress on hippocampal information coding are disrupted as the stress becomes chronic. To examine this, we compared the impact of acute and chronic stress on neural activity in the CA1 subregion of male mice subjected to a chronic immobilization stress (CIS) paradigm. We observed that following first exposure to stress (acute stress), the spatial information encoded in the hippocampus sharpened, and the neurons became increasingly tuned to the underlying theta oscillations in the local field potential (LFP). However, following repeated exposure to the same stress (chronic stress), spatial tuning was poorer and the power of both the slow-gamma (30–50 Hz) and fast-gamma (55–90 Hz) oscillations, which correlate with excitatory inputs into the region, decreased. These results support the idea that acute and chronic stress differentially affect neural computations carried out by hippocampal circuits and suggest that acute stress may improve cognitive processing.

Tripchlorolide attenuates β-amyloid generation by inducing NEP activity in N2a/APP695 cells

Background and purpose

Alzheimer’s disease (AD) is a neurodegeneration disease. The previous work from our research group demonstrated the neuroprotective effects of tripchlorolide (T4) in AD animal models.

Materials and methods

Neprilysin (NEP) is known as an important physiological amyloid-β protein (Aβ) peptide-degrading enzyme in the brain due to its apparent rate-limiting function. In this study, we explored the effect of NEP on AD model N2a/APP695 cells. Western blots and enzyme-linked immunosorbent assays were performed to assess the expression of proteins, while quantitative real-time polymerase chain reaction assays were used to evaluate RNA levels. Cell vitality was detected by the MTT assay, and reactive oxygen species (ROS) levels were assessed using a ROS activity assay kit.

Results

We discovered that T4 was able to enhance the enzyme activity of NEP. T4 administration decreased the protein levels of the soluble amyloid precursor protein. In further experiments, we found that by using thiorphan the secretion of Aβ, oxidative stress, nitrosative stress, and inflammatory factors, which were suppressed by T4, were reversed. Due to its ability to attenuate Aβ generation and to protect neurons against the neurotoxicity of Aβ, T4 may be a potential therapy in the regulation of Aβ-related pathology in AD by affecting NEP activity.

Conclusion

Tripchlorolide attenuates Aβ generation by inducing NEP activity in N2a/APP695 cells.

Design and optimization of curcumin loaded nano lipid carrier system using Box-Behnken design

Herbal antioxidant like curcumin holds great potential to treat neurodegenerative disease like Alzheimer's disease. However, its therapeutic potency is obstructed due to rapid metabolism, poor solubility, GI susceptibility, enzymatic degradation and lower bioavailability. Thus, the present work aimed to design and optimize curcumin-loaded NLC (CNL) with higher drug entrapment, prolonged release and better stability. CNL was prepared by modified melt emulsification method followed by ultrasonication. The formulation was optimized by 3 factor 3 level Box-Behnken design using solid: liquid lipid, surfactant concentration and ultrasonication time as independent variable while particle size, entrapment efficiency and % drug release as dependant variable. The design suggested 3.092 solid:liquid lipid, 2.131% surfactant and 4.757 min ultrasonication fit best to get the optimized formulation. The size of the optimized CNL was noted 124.37 ± 55.81 nm, which is in the acceptable range for brain delivery. SEM results also comply with this size range (near 150 nm) and demonstrated almost spherical and uniform particles with porous and uneven surface structures. PDI, zeta potential, entrapment efficiency and % drug release were observed as 0.201 ± 0.00, - 17.2 ± 2.35 mV, 93.62 ± 0.68% and 92.73 ± 0.06%, respectively. The NLC demonstrated initial burst release with subsequent prolonged release of drug for 48 h. Weibull kinetic equation with 0.9958 R², minimum AIC and maximum MSC value was found best fit to explain the release behavior. The β exponent and diffusional coefficient (n) indicated combined release mechanism with Fickian diffusion as drug release mechanism. Formulation was also found stable at different storage condition.

Effect of Global Brain Ischemia on Amyloid Precursor Protein Metabolism and Expression of Amyloid-Degrading Enzymes in Rat Cortex: Role in Pathogenesis of Alzheimer's Disease

The incidence of Alzheimer's disease (AD) increases significantly following chronic stress and brain ischemia which, over the years, cause accumulation of toxic amyloid species and brain damage. The effects of global 15-min ischemia and 120-min reperfusion on the levels of expression of the amyloid precursor protein (APP) and its processing were investigated in the brain cortex (Cx) of male Wistar rats. Additionally, the levels of expression of the amyloid-degrading enzymes neprilysin (NEP), endothelin-converting enzyme-1 (ECE-1), and insulin-degrading enzyme (IDE), as well as of some markers of oxidative damage were assessed. It was shown that the APP mRNA and protein levels in the rat Cx were significantly increased after the ischemic insult. Protein levels of the soluble APP fragments, especially of sAPPβ produced by β-secretase, (BACE-1) and the levels of BACE-1 mRNA and protein expression itself were also increased after ischemia. The protein levels of APP and BACE-1 in the Cx returned to the control values after 120-min reperfusion. The levels of NEP and ECE-1 mRNA also decreased after ischemia, which correlated with the decreased protein levels of these enzymes. However, we have not observed any changes in the protein levels of insulin-degrading enzyme. Contents of the markers of oxidative damage (di-tyrosine and lysine conjugates with lipid peroxidation products) were also increased after ischemia. The obtained data suggest that ischemia shifts APP processing towards the amyloidogenic β-secretase pathway and accumulation of the neurotoxic Aβ peptide as well as triggers oxidative stress in the cells. These results are discussed in the context of the role of stress and ischemia in initiation and progression of AD.

Experimental evidence and mechanism of action of some popular neuro-nutraceutical herbs

Brain and neuronal circuits constitute the most complex organ networks in human body. They not only control and coordinate functions of all other organs, but also represent one of the most-affected systems with stress, lifestyle and age. With global increase in aging populations, these neuropathologies have emerged as major concern for maintaining quality of life. Recent era has witnessed a surge in nutritional remediation of brain dysfunctions primarily by "nutraceuticals" that refer to functional foods and supplements with pharmacological potential. Specific dietary patterns with a balanced intake of carbohydrates, fatty acids, vitamins and micronutrients have also been ascertained to promote brain health. Dietary herbs and their phytochemicals with wide range of biological and pharmacological activities and minimal adverse effects have gained remarkable attention as neuro-nutraceuticals. Neuro-nutraceutical potentials of herbs are often expressed as effects on cognitive response, circadian rhythm, neuromodulatory, antioxidant and anti-inflammatory activities that are mediated by effects on gene expression, epigenetics, protein synthesis along with their turnover and metabolic pathways. Epidemiological and experimental evidence have implicated enormous applications of herbal supplementation in neurodegenerative and psychiatric disorders. The present review highlights the identification, experimental evidence and applications of some herbs including Bacopa monniera, Withania somnifera, Curcuma longa, Helicteres angustifolia, Undaria pinnatifida, Haematococcus pluvialis, and Vitis vinifera, as neuro-nutraceuticals.

Profiling DNA break sites and transcriptional changes in response to contextual fear learning

Neuronal activity generates DNA double-strand breaks (DSBs) at specific loci in vitro and this facilitates the rapid transcriptional induction of early response genes (ERGs). Physiological neuronal activity, including exposure of mice to learning behaviors, also cause the formation of DSBs, yet the distribution of these breaks and their relation to brain function remains unclear. Here, following contextual fear conditioning (CFC) in mice, we profiled the locations of DSBs genome-wide in the medial prefrontal cortex and hippocampus using γH2AX ChIP-Seq. Remarkably, we found that DSB formation is widespread in the brain compared to cultured primary neurons and they are predominately involved in synaptic processes. We observed increased DNA breaks at genes induced by CFC in neuronal and non-neuronal nuclei. Activity-regulated and proteostasis-related transcription factors appear to govern some of these gene expression changes across cell types. Finally, we find that glia but not neurons have a robust transcriptional response to glucocorticoids, and many of these genes are sites of DSBs. Our results indicate that learning behaviors cause widespread DSB formation in the brain that are associated with experience-driven transcriptional changes across both neuronal and glial cells.

The piperine derivative HJ105 inhibits Aβ1-42-induced neuroinflammation and oxidative damage via the Keap1-Nrf2-TXNIP axis

BACKGROUND

Piperine is a great lead compound, as a phytopharmaceutical with reported neuroprotective effects in neurodegenerative diseases. HJ105, a piperine derivative with high affinity to Keap1 receptor, attracts increasing attention in Alzheimer's disease (AD) treatment.

PURPOSE

This work mainly aimed to study HJ105's therapeutic effects on Aβ_1-42-associated AD and the underpinning mechanisms.

METHODS

In the in vivo part, a rat model of AD was established by bilateral intra-hippocampal administration of aggregated Aβ_1-42, followed by a month of intragastric HJ105 or donepezil administration. Spatial and learning memories were detected by the Morris water maze assay, passive avoidance learning as well as Y-maze test. The morphology of hippocampal neurons was assessed by hematoxylin-eosin (H&E) staining. In addition, the amounts of the IL-1β and TNF-α were obtained with specific ELISA kits. More importantly, apoptosis-related proteins and factors involved in Nrf2/TXNIP/NLPR3 pathways were detected by Western blot, while the interaction between Keap1 and Nrf2 was assessed by co-immunoprecipitation. In the in vitro part, human neuroblastoma (SH-SY5Y) cells were applied to evaluate the role of HJ105 on Aβ_1-42-induced neuronal damage.

RESULTS

Treatment of HJ105 not only reversed memory impairment, but also protected neurons in the hippocampus by inhibiting Bax/Bcl2 ratio increase. HJ105 decreased TXNIP expression, suppressing NLRP3 inflammasome activation in the hippocampus, which in turn counteracted the upregulation of IL-1β and TNF-α. Notably, HJ105 exerted an inhibitory effect on Keap1-Nrf2 interaction and upregulated nuclear Nrf2, which conversely increased the expression levels of superoxide dismutase, catalase and glutathione peroxidase and downregulated malondialdehyde. Additionally, neurotoxicity induced by Aβ_1-42 in SH-SY5Y cells was alleviated by HJ105.

CONCLUSION

Overall, HJ105 exerts neuroprotective effects in SH-SY5Y cells induced by Aβ_1-42 as well as in experimental rats with AD by decreasing apoptosis, oxidative stress and neuroinflammation, partly via suppression of Keap1-Nrf2 complex generation. HJ105 might represent a promising compound for AD treatment.

High-throughput rat immunoglobulin G N-glycosylation profiling revealed subclass-specific changes associated with chronic stress

Immunoglobulin G (IgG) glycosylation corresponds well with immune system changes, so it can potentially be used as a biomarker for the consequences of chronic stress such as low-grade inflammation and enhanced immunosenescence in older animals. Here we present a high-throughput glycoproteomic workflow, including IgG enrichment, HILIC glycopeptide purification, and nano-LC-MS analysis of tryptic glycopeptides applied for the analysis of rat IgG. A cohort of 80 animals was exposed to seven stressors in a customized chronic stress protocol with blood and tissue sampling in three timepoints. Young female rats experienced an increase in agalactosylated glycoforms on IgG2a and IgG2c accompanied by a decrease in monogalactosylation. Among old females, increased galactosylation was observed in the IgG2b subclass, pointing to an anti-inflammatory activity of IgG. Additionally, IgG Fc N-glycosylation patterns in Sprague Dawley rats were analyzed, quantified, and reported for the first time. Our findings emphasize age-, sex- and subclass-dependent differences in IgG glycosylation related to chronic stress exposure, confirming the relevance of newly developed methods for further research in glycobiology of rodent immune response. SIGNIFICANCE: In this study, we showed that a high-throughput streamlined methodology based on protein L 96-well monolithic plates for efficient rat IgG immunoaffinity enrichment from blood plasma, paired with appropriate tryptic glycopeptide preparation, HILIC-SPE enrichment, and nano-LC-MS methods was suitable for quick processing of large sample sets. We report a subclass-specific profiling and changes in rat IgG Fc galactosylation and adrenal gland immunohistochemistry of male and female animals exposed to a customized chronic stress protocol.

Altered spontaneous cortical activity in mild glaucoma: A quantitative EEG study

Functional neuroimaging studies have reported alterations in cortical activity indicating glaucoma as a progressive neurodegenerative disease. Hence the current study aimed to assess the cortical activity using high-density EEG in patients with mild glaucoma during resting state. Treatment-naive 37 patients with primary open angle glaucoma (POAG), 34 patients with primary angle closure glaucoma (PACG), and 32 healthy controls were included in the study. Resting state EEG i.e., eyes closed (EC) and eyes open conditions (EO) were acquired using 128-channel for 3 min. After preprocessing, the current density of 6239 voxels of the data was estimated using sLORETA. In comparison to healthy controls, PACG had higher activity at cingulate gyri, medial and superior frontal gyri during EO only. POAG had significantly higher activity at precentral gyrus and middle frontal gyrus during EC, whereas at cingulate gyri, frontal gyri, precentral gyri, paracentral lobule, sub-gyral region, postcentral gyrus, and precuneus during EO. POAG had significantly higher activity at precuneus and cuneus compared to PACG during EO. Intraocular pressure and mean-deviation of visual fields had a positive correlation with cortical activity. Results of the study indicate physiological alterations not only at the level of retina but also at brain even in the early stages of the disease. These alterations in the cortical activity were more in POAG than PACG. Controlling the IOP alone might be insufficient in glaucoma because of widespread alterations in cortical activity. These findings might enhance the current understanding of cortical involvement in glaucoma.

Toll-Like Receptor Signaling Pathways: Novel Therapeutic Targets for Cerebrovascular Disorders

Toll-like receptors (TLRs), a class of pattern recognition proteins, play an integral role in the modulation of systemic inflammatory responses. Cerebrovascular diseases (CVDs) are a group of pathological conditions that temporarily or permanently affect the brain tissue mostly via the decrease of oxygen and glucose supply. TLRs have a critical role in the activation of inflammatory cascades following hypoxic-ischemic events and subsequently contribute to neuroprotective or detrimental effects of CVD-induced neuroinflammation. The TLR signaling pathway and downstream cascades trigger immune responses via the production and release of various inflammatory mediators. The present review describes the modulatory role of the TLR signaling pathway in the inflammatory responses developed following various CVDs and discusses the potential benefits of the modulation of different TLRs in the improvement of functional outcomes after brain ischemia.

Combined exposure of alumina nanoparticles and chronic stress exacerbates hippocampal neuronal ferroptosis via activating IFN-γ/ASK1/JNK signaling pathway in rats

Alumina nanoparticles (AlNPs) exposure causes hippocampal-dependent cognitive dysfunction. However, whether chronic stress exacerbates AlNPs-induced hippocampal lesion and its mechanism remains unclear. This study was aimed to investigate the combined effects and mechanisms of AlNPs and chronic stress on the hippocampal lesion. The behavioral tests demonstrated that combined exposure to AlNPs and chronic restraint stress (CRS) worsened both cognition and depression-like behavior than exposed to AlNPs and CRS alone. Microstructural and ultrastructural observations showed that combined exposure to AlNPs and CRS exacerbated hippocampal damage. Both AlNPs and CRS induced hippocampal neuronal ferroptosis, presenting as iron and glutamate metabolism disorder, GPX4 fluorescence of neurons decrease, LPO and ROS levels increase, and FJB-positive neurons increase. Meanwhile, combined exposure to AlNPs and CRS exacerbated hippocampal neuronal ferroptosis. Mechanism investigation revealed that combined exposure to AlNPs and CRS activated IFN-γ/ASK1/JNK signaling pathway. Furthermore, IFN-γ neutralizing antibody R4-6A2 effectively inhibited the activation of IFN-γ/ASK1/JNK signaling pathway, alleviated hippocampal neuronal ferroptosis and improved cognition ability. ASK1 inhibitor GS-4997 also improved hippocampal neuronal ferroptosis and cognitive dysfunction by inhibiting ASK1/JNK signaling pathway. Together, these results demonstrate that combined exposure to AlNPs and CRS exacerbates hippocampal neuronal ferroptosis via activating IFN-γ/ASK1/JNK signaling pathway.

Interplay between stress-related genes may influence Alzheimer's disease development: The results of genetic interaction analyses of human data

Emerging evidence from experimental and clinical research suggests that stress-related genes may play key roles in AD development. The fact that genome-wide association studies were not able to detect a contribution of such genes to AD indicates the possibility that these genes may influence AD non-linearly, through interactions of their products. In this paper, we selected two stress-related genes (GCN2/EIF2AK4 and APP) based on recent findings from experimental studies which suggest that the interplay between these genes might influence AD in humans. To test this hypothesis, we evaluated the effects of interactions between SNPs in these two genes on AD occurrence, using the Health and Retirement Study data on white indidividuals. We found several interacting SNP-pairs whose associations with AD remained statistically significant after correction for multiple testing. These findings emphasize the importance of nonlinear mechanisms of polygenic AD regulation that cannot be detected in traditional association studies. To estimate collective effects of multiple interacting SNP-pairs on AD, we constructed a new composite index, called Interaction Polygenic Risk Score, and showed that its association with AD is highly statistically significant. These results open a new avenue in the analyses of mechanisms of complex multigenic AD regulation.

Physical Training Inhibits the Fibrosis Formation in Alzheimer's Disease Kidney Influencing the TGFβ Signaling Pathways

Background:

Alzheimer’s disease (AD) is a neurodegenerative illness, with several peripheral pathological signs such as accumulation of amyloid-β (Aβ) plaques in the kidney. Alterations of transforming growth factor β (TGFβ) signaling in the kidney can induce fibrosis, thus disturbing the elimination of Aβ.

Objective:

A protective role of increased physical activity has been proven in AD and in kidney fibrosis, but it is not clear whether TGFβ signalization is involved in this effect.

Methods:

The effects of long-term training on fibrosis were investigated in the kidneys of mice representing a model of AD (B6C3-Tg(APPswe,PSEN1dE9)85Dbo/J) by comparing wild type and AD organs. Alterations of canonical and non-canonical TGFβ signaling pathways were followed with PCR, western blot, and immunohistochemistry.

Results:

Accumulation of collagen type I and interstitial fibrosis were reduced in kidneys of AD mice after long-term training. AD induced the activation of canonical and non-canonical TGFβ pathways in non-trained mice, while expression levels of signal molecules of both TGFβ pathways became normalized in trained AD mice. Decreased amounts of phosphoproteins with molecular weight corresponding to that of tau and the cleaved C-terminal of AβPP were detected upon exercising, along with a significant increase of PP2A catalytic subunit expression.

Conclusion:

Our data suggest that physical training has beneficial effects on fibrosis formation in kidneys of AD mice and TGFβ signaling plays a role in this phenomenon.

Sorafenib Modulates the LPS- and Aβ-Induced Neuroinflammatory Response in Cells, Wild-Type Mice, and 5xFAD Mice

Sorafenib is FDA-approved for the treatment of primary kidney or liver cancer, but its ability to inhibit many types of kinases suggests it may have potential for treating other diseases. Here, the effects of sorafenib on neuroinflammatory responses in vitro and in vivo and the underlying mechanisms were assessed. Sorafenib reduced the induction of mRNA levels of the proinflammatory cytokines COX-2 and IL-1β by LPS in BV2 microglial cells, but in primary astrocytes, only COX-2 mRNA levels were altered by sorafenib. Interestingly, sorafenib altered the LPS-mediated neuroinflammatory response in BV2 microglial cells by modulating AKT/P38-linked STAT3/NF-kB signaling pathways. In LPS-stimulated wild-type mice, sorafenib administration suppressed microglial/astroglial kinetics and morphological changes and COX-2 mRNA levels by decreasing AKT phosphorylation in the brain. In 5xFAD mice (an Alzheimer’s disease model), sorafenib treatment daily for 3 days significantly reduced astrogliosis but not microgliosis. Thus, sorafenib may have therapeutic potential for suppressing neuroinflammatory responses in the brain.

Spilanthes acmella Murr. ameliorates chronic stress through improving mitochondrial function in chronic restraint stress rats

Chronic stress is a risk factor for the development of psychiatric illnesses through impairment of the ability to appropriately regulate physiological and behavioral responses, but the molecular events that lead to damage of hippocampal neurons remain unclear. The medicinal herb Spilanthes acmella Murr. has been used as a traditional medicine for various diseases and its extracts exhibit antioxidant activity. The present study explored the molecular signals of mitochondrial dynamics and investigated the beneficial effects of S. acmella Murr. An ethyl acetate extract of this plant was used to assess mitochondrial dynamics in response to chronic restraint stress (CRS) in male Sprague-Dawley rats. The results demonstrated that the S. acmella Murr. extract reduced the expression of mitochondrial fission protein but induced HSP60, MnSOD and ATPsynthase in the hippocampus of the CRS rats. In addition, S. acmella Murr. extract reversed depressive symptoms in the forced swim test. Our findings suggested that S. acmella Murr. extract provides a potential treatment of chronic stress, and that the mechanism is associated with the alleviation of neuronal injury and maintenance of mitochondrial function.

Insulin Resistance as a Common Link Between Current Alzheimer's Disease Hypotheses

Almost 115 years ago, Alois Alzheimer described Alzheimer's disease (AD) for the first time. Since then, many hypotheses have been proposed. However, AD remains a severe health public problem. The current medical approaches for AD are limited to symptomatic interventions and the complexity of this disease has led to a failure rate of approximately 99.6%in AD clinical trials. In fact, no new drug has been approved for AD treatment since 2003. These failures indicate that we are failing in mimicking this disease in experimental models. Although most studies have focused on the amyloid cascade hypothesis of AD, the literature has made clear that AD is rather a multifactorial disorder. Therefore, the persistence in a single theory has resulted in lost opportunities. In this review, we aim to present the striking points of the long scientific path followed since the description of the first AD case and the main AD hypotheses discussed over the last decades. We also propose insulin resistance as a common link between many other hypotheses.

Chewing Behavior Attenuates the Tumor Progression-Enhancing Effects of Psychological Stress in a Breast Cancer Model Mouse

We examined whether chewing behavior affects the tumor progression-enhancing impact of psychological stress. Human breast cancer cell line (MDA-MB-231) cells were inoculated into the mammary fat pads of athymic nude mice. The mice were assigned randomly to control, stress, and stress+chewing groups. Psychological stress was created by keeping mice in a transparent restraint cylinder for 45 min, three times a day, for 35 days after cell inoculation. Animals in the stress+chewing group were provided with a wooden stick for chewing on during the psychological stress period. Chewing behavior remarkably inhibited the tumor growth accelerated by the psychological stress. Immunohistochemical and Western blot findings revealed that chewing behavior during psychological stress markedly suppressed tumor angiogenesis and cell proliferation. In addition, chewing behavior decreased serum glucocorticoid levels and expressions of glucocorticoid and β2-adrenergic receptors in tumors. Chewing behavior decreased expressions of inducible nitric oxide synthase and 4-hydroxynonenal, and increased expression of superoxide dismutase 2 in tumors. Our findings suggest that chewing behavior could ameliorate the enhancing effects of psychological stress on the progression of breast cancer, at least partially, through modulating stress hormones and their receptors, and the subsequent signaling pathways involving reactive oxygen and nitrogen species.

Interplay Between Microglia and Alzheimer's Disease-Focus on the Most Relevant Risks: APOE Genotype, Sex and Age

As the main immune cells of the central nervous system (CNS), microglia regulates normal development, homeostasis and general brain physiology. These functions put microglia at the forefront of CNS repair and recovery. Uncontrolled activation of microglia is related to the course of neurodegenerative diseases such as Alzheimer’s disease. It is clear that the classic pathologies of amyloid β (Aβ) and Tau are usually accompanied by the activation of microglia, and the activation of microglia also serves as an early event in the pathogenesis of AD. Therefore, during the occurrence and development of AD, the key susceptibility factors for AD—apolipoprotein E (APOE) genotype, sex and age—may further interact with microglia to exacerbate neurodegeneration. In this review, we discuss the role of microglia in the progression of AD related to the three risk factors for AD: APOE genotype, sex and aging. APOE-expressing microglia accumulates around Aβ plaques, and the presence of APOE4 may disrupt the phagocytosis of Aβ aggregates and aggravate neurodegeneration in Tau disease models. In addition, females have a high incidence of AD, and normal female microglia and estrogen have protective effects under normal conditions. However, under the influence of AD, female microglia seem to lose their protective effect and instead accelerate the course of AD. Aging, another major risk factor, may increase the sensitivity of microglia, leading to the exacerbation of microglial dysfunction in elderly AD. Obviously, in the role of microglia in AD, the three main risk factors of APOE, sex, and aging are not independent and have synergistic effects that contribute to the risk of AD. Moreover, new microglia can replace dysfunctional microglia after microglial depletion, which is a new promising strategy for AD treatment.

Stressed mitochondria: A target to intrude alzheimer's disease

Alzheimer's disease (AD) is the inoperable, incapacitating, neuropsychiatric, and degenerative manifestation that drastically affects human life quality. The current medications target extra-neuronal senile plaques, oxidative stress, neuroinflammation, intraneuronal neurofibrillary tangles, cholinergic deficits, and excitotoxicity. Among novel pathways and targets, bioenergetic and resultant mitochondrial dysfunction has been recognized as essential factors that decide the neuronal fate and consequent neurodegeneration in AD. The crucial attributes of mitochondria, including bioenergesis, signaling, sensing, integrating, and transmitting biological signals contribute to optimum networking of neuronal dynamics and make them indispensable for cell survival. In AD, mitochondrial dysfunction and mitophagy are a preliminary and critical event that aggravates the pathological cascade. Stress is known to promote and exaggerate the neuropathological alteration during neurodegeneration and metabolic impairments, especially in the cortico-limbic system, besides adversely affecting the normal physiology and mitochondrial dynamics. Stress involves the allocation of energy resources for neuronal survival. Chronic and aggravated stress response leads to excessive release of glucocorticoids by activation of the hypothalamic-pituitaryadrenal (HPA) axis. By acting through their receptors, glucocorticoids influence adverse mitochondrial changes and alter mtDNA transcription, mtRNA expression, hippocampal mitochondrial network, and ultimately mitochondrial physiology. Chronic stress also affects mitochondrial dynamics by changing metabolic and neuro-endocrinal signalling, aggravating oxidative stress, provoking inflammatory mediators, altering tropic factors, influencing gene expression, and modifying epigenetic pathways. Thus, exploring chronic stress-induced glucocorticoid dysregulation and resultant bio-behavioral and psychosomatic mitochondrial alterations may be a feasible narrative to investigate and unravel the mysterious pathobiology of AD.

Inflammation, Nitro-Oxidative Stress, Impaired Autophagy, and Insulin Resistance as a Mechanistic Convergence Between Arterial Stiffness and Alzheimer's Disease

The average age of the world's elderly population is steadily increasing. This unprecedented rise in the aged world population will increase the prevalence of age-related disorders such as cardiovascular disease (CVD) and neurodegeneration. In recent years, there has been an increased interest in the potential interplay between CVDs and neurodegenerative syndromes, as several vascular risk factors have been associated with Alzheimer's disease (AD). Along these lines, arterial stiffness is an independent risk factor for both CVD and AD. In this review, we discuss several inflammaging-related disease mechanisms including acute tissue-specific inflammation, nitro-oxidative stress, impaired autophagy, and insulin resistance which may contribute to the proposed synergism between arterial stiffness and AD.

Rat dorsal horn neurons primed by stress develop a long-lasting manifest sensitization after a short-lasting nociceptive low back input

Background

A single injection of nerve growth factor (NGF) into a low back muscle induces a latent sensitization of rat dorsal horn neurons (DHNs) that primes for a manifest sensitization by a subsequent second NGF injection. Repeated restraint stress also causes a latent DHN sensitization.

Objective

In this study, we investigated whether repeated restraint stress followed by a single NGF injection causes a manifest sensitization of DHNs.

Methods

Rats were stressed repeatedly in a narrow plastic restrainer (1 hour on 12 consecutive days). Control animals were handled but not restrained. Two days after stress paradigm, behavioral tests and electrophysiological in vivo recordings from single DHNs were performed. Mild nociceptive low back input was induced by a single NGF injection into the lumbar multifidus muscle just before the recording started.

Results

Restraint stress slightly lowered the low back pressure pain threshold (Cohen d = 0.83). Subsequent NGF injection increased the proportion of neurons responsive to deep low back input (control + NGF: 14%, stress + NGF: 39%; P = 0.041), mostly for neurons with input from outside the low back (7% vs 26%; P = 0.081). There was an increased proportion of neurons with resting activity (28% vs 55%; P = 0.039), especially in neurons having deep input (0% vs 26%; P = 0.004).

Conclusions

The results indicate that stress followed by a short-lasting nociceptive input causes manifest sensitization of DHNs to deep input, mainly from tissue outside the low back associated with an increased resting activity. These findings on neuronal mechanisms in our rodent model suggest how stress might predispose to radiating pain in patients.

Stem cell in neurodegenerative disorders; an emerging strategy

Neurodegenerative disorders are a diversity of disorders, surrounding Alzheimer's (AD), Parkinson's (PD), Huntington's diseases (HD), and amyotrophic lateral sclerosis (ALS) accompanied by some other less common diseases generally characterized by either developed deterioration of central or peripheral nervous system structurally or functionally. Today, with the viewpoint of an increasingly aging society, the number of patients with neurodegenerative diseases and sociomedical burdens will spread intensely. During the last decade, stem cell technology has attracted great attention for treating neurodegenerative diseases worldwide because of its unique attributes. As acknowledged, there are several categories of stem cells being able to proliferate and differentiate into various cellular lineages, highlighting their significance in the context of regenerative medicine. In preclinical models, stem cell therapy using mesenchymal stem/stromal cells (MSCs), hematopoietic stem cells (HSCs), and neural progenitor or stem cells (NPCs or NSCs) along with pluripotent stem cells (PSCs)-derived neuronal cells could elicit desired therapeutic effects, enabling functional deficit rescue partially. Regardless of the noteworthy progress in our scientific awareness and understanding of stem cell biology, there still exist various challenges to defeat. In the present review, we provide a summary of the therapeutic potential of stem cells and discuss the current status and prospect of stem cell strategy in neurodegenerative diseases, in particular, AD, PD, ALS, and HD.