Chronic pain causes Tau-mediated hippocampal pathology and memory deficits.

Persistent pain has been recently suggested as a risk factor for dementia. Indeed, chronic pain is frequently accompanied by maladaptive brain plasticity and cognitive deficits whose molecular underpinnings are poorly understood. Despite the emerging role of Tau as a key regulator of neuronal plasticity and pathology in diverse brain disorders, the role of Tau has never been studied in the context of chronic pain. Using a peripheral (sciatic) neuropathy to model chronic pain in mice-spared nerve injury (SNI) for 4 months-in wildtype as well as P301L-Tau transgenic mice, we hereby demonstrate that SNI triggers AD-related neuropathology characterized by Tau hyperphosphorylation, accumulation, and aggregation in hippocampus followed by neuronal atrophy and memory deficits. Molecular analysis suggests that SNI inhibits autophagy and reduces levels of the Rab35, a regulator of Tau degradation while overexpression of Rab35 or treatment with the analgesic drug gabapentin reverted the above molecular changes leading to neurostructural and memory recovery. Interestingly, genetic ablation of Tau blocks the establishment of SNI-induced hippocampal morphofunctional deficits supporting the mediating role of Tau in SNI-evoked hippocampal pathology and memory impairment. These findings reveal that exposure to chronic pain triggers Tau-related neuropathology and may be relevant for understanding how chronic pain precipitates memory loss leading to dementia.

A novel isolation method for spontaneously released extracellular vesicles from brain tissue and its implications for stress-driven brain pathology.

BACKGROUND: Extracellular vesicles (EVs), including small EVs (sEVs) such as exosomes, exhibit great potential for the diagnosis and treatment of brain disorders, representing a valuable tool for precision medicine. The latter demands high-quality human biospecimens, especially in complex disorders in which pathological and specimen heterogeneity, as well as diverse individual clinical profile, often complicate the development of precision therapeutic schemes and patient-tailored treatments. Thus, the collection and characterization of physiologically relevant sEVs are of the utmost importance. However, standard brain EV isolation approaches rely on tissue dissociation, which can contaminate EV fractions with intracellular vesicles. METHODS: Based on multiscale analytical platforms such as cryo-EM, label-free proteomics, advanced flow cytometry, and ExoView analyses, we compared and characterized the EV fraction isolated with this novel method with a classical digestion-based EV isolation procedure. Moreover, EV biogenesis was pharmacologically manipulated with either GW4869 or picrotoxin to assess the validity of the spontaneous-release method, while the injection of labelled-EVs into the mouse brain further supported the integrity of the isolated vesicles. RESULTS: We hereby present an efficient purification method that captures a sEV-enriched population spontaneously released by mouse and human brain tissue. In addition, we tested the significance of the release method under conditions where biogenesis/secretion of sEVs was pharmacologically manipulated, as well as under animals' exposure to chronic stress, a clinically relevant precipitant of brain pathologies, such as depression and Alzheimer's disease. Our findings show that the released method monitors the drug-evoked inhibition or enhancement of sEVs secretion while chronic stress induces the secretion of brain exosomes accompanied by memory loss and mood deficits suggesting a potential role of sEVs in the brain response to stress and related stress-driven brain pathology. CONCLUSIONS: Overall, the spontaneous release method of sEV yield may contribute to the characterization and biomarker profile of physiologically relevant brain-derived sEVs in brain function and pathology. Video Abstract.

Chronic Stress, Depression, and Alzheimer's Disease: The Triangle of Oblivion.

Chronic stress and high levels of the main stress hormones, and glucocorticoids (GC), are implicated in susceptibility to brain pathologies such as depression and Alzheimer's disease (AD), as they promote neural plasticity damage and glial reactivity, which can lead to dendritic/synaptic loss, reduced neurogenesis, mood deficits, and impaired cognition. Moreover, depression is implicated in the development of AD with chronic stress being a potential link between both disorders via common neurobiological underpinnings. Hereby, we summarize and discuss the clinical and preclinical evidence related to the detrimental effect of chronic stress as a precipitator of AD through the activation of pathological mechanisms leading to the accumulation of amyloid ß (Aß) and Tau protein. Given that the modern lifestyle increasingly exposes individuals to high stress loads, it is clear that understanding the mechanistic link(s) between chronic stress, depression, and AD pathogenesis may facilitate the treatment of AD and other stress-related disorders.

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

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

Allosteric modulation of AMPA receptors counteracts Tau-related excitotoxic synaptic signaling and memory deficits in stress- and Aß-evoked hippocampal pathology.

Despite considerable progress in the understanding of its neuropathology, Alzheimer's disease (AD) remains a complex disorder with no effective treatment that counteracts the memory deficits and the underlying synaptic malfunction triggered by the accumulation of amyloid beta (Aß) and Tau protein. Mounting evidence supports a precipitating role for chronic environmental stress and glutamatergic excitotoxicity in AD, suggesting that targeting of glutamate receptor signaling may be a promising approach against both stress and AD pathologies. In light of the limited cognitive benefit of the direct antagonism of NMDA receptors in AD, we here focus on an alternative way to modify glutamatergic signaling through positive allosteric modulation of AMPA receptors, by the use of a PAM-AMPA compound. Using non-transgenic animal model of Aß oligomer injection as well as the combined stress and Aß i.c.v. infusion, we demonstrate that positive allosteric modulation of AMPA receptors by PAM-AMPA treatment reverted memory, but not mood, deficits. Furthermore, PAM-AMPA treatment reverted stress/Aß-driven synaptic missorting of Tau and associated Fyn/GluN2B-driven excitotoxic synaptic signaling accompanied by recovery of neurotransmitter levels in the hippocampus. Our findings suggest that positive allosteric modulation of AMPA receptors restores synaptic integrity and cognitive performance in stress- and Aß-evoked hippocampal pathology. As the prevalence of AD is increasing at an alarming rate, novel therapeutic targeting of glutamatergic signaling should be further explored against the early stages of AD synaptic malfunction with the goal of attenuating further synaptic damage before it becomes irreversible.

Correction: Nucleus accumbens medium spiny neurons subtypes signal both reward and aversion.

A correction to this paper has been published and can be accessed via a link at the top of the paper.

Nucleus accumbens medium spiny neurons subtypes signal both reward and aversion.

Deficits in decoding rewarding (and aversive) signals are present in several neuropsychiatric conditions such as depression and addiction, emphasising the importance of studying the underlying neural circuits in detail. One of the key regions of the reward circuit is the nucleus accumbens (NAc). The classical view on the field postulates that NAc dopamine receptor D1-expressing medium spiny neurons (D1-MSNs) convey reward signals, while dopamine receptor D2-expressing MSNs (D2-MSNs) encode aversion. Here, we show that both MSN subpopulations can drive reward and aversion, depending on their neuronal stimulation pattern. Brief D1- or D2-MSN optogenetic stimulation elicited positive reinforcement and enhanced cocaine conditioning. Conversely, prolonged activation induced aversion, and in the case of D2-MSNs, decreased cocaine conditioning. Brief stimulation was associated with increased ventral tegmenta area (VTA) dopaminergic tone either directly (for D1-MSNs) or indirectly via ventral pallidum (VP) (for D1- and D2-MSNs). Importantly, prolonged stimulation of either MSN subpopulation induced remarkably distinct electrophysiological effects in these target regions. We further show that blocking κ-opioid receptors in the VTA (but not in VP) abolishes the behavioral effects induced by D1-MSN prolonged stimulation. In turn, blocking δ-opioid receptors in the VP (but not in VTA) blocks the behavioral effects elicited by D2-MSN prolonged stimulation. Our findings demonstrate that D1- and D2-MSNs can bidirectionally control reward and aversion, explaining the existence of controversial studies in the field, and highlights that the proposed striatal functional opposition needs to be reconsidered.

Hippocampal NG2+ pericytes in chronically stressed rats and depressed patients: a quantitative study.

OBJECTIVE: The suggested link between major depression disorder (MDD) and blood-brain barrier (BBB) alterations supports an impact on the neurovascular unit in this disease condition. Here we investigate how pericytes, a major component in the neurovascular unit, respond to stress, stress hormones, proinflammatory cytokine and depression. METHOD: Hippocampal sections of chronic unpredictable stressed (CMS) rats, MDD patients and respective controls were immuno-stained against NG2, where the number of NG2+ pericytes in the molecular layer was counted. Proliferation of cultured pericytes after treatment with cortisol and IL-1ß was analyzed using radioactive-labeled thymidine. FINDINGS: The number of NG2+ pericytes was significantly higher in CMS animals than controls. Higher number of NG2+ pericytes was also detected in MDD patients, but the increase did not reach significance. IL-1ß, but not cortisol, induced a significant increase in proliferation of cultured pericytes. CONCLUSION: Our results indicate that exposure to stressful conditions affects the hippocampal pericyte population. These findings add to our knowledge about the impact of stress on the neurovascular unit, which might be relevant for understanding the alterations in BBB found in MDD patients.

Stress and the Etiopathogenesis of Alzheimer's Disease and Depression.

Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder with a complex physiopathology whose initiators are poorly defined. Accumulating clinical and experimental evidence suggests a causal role of lifetime stress in AD. This chapter summarizes current knowledge about how chronic stress and its accompanying high levels of glucocorticoid (GC) secretion, trigger the two main pathomechanisms of AD: (i) misprocessing of amyloid precursor protein (APP) and the generation of amyloid beta (Aß) and (ii) Tau hyperphosphorylation and aggregation. Given that depression is a well-known stress-related illness, and the evidence that depression may precede AD, this chapter also explores neurobiological mechanisms that may be common to depressive and AD pathologies. This review also discusses emerging insights into the role of Tau and its malfunction in disrupting neuronal cascades and neuroplasticity and, thus triggering brain pathology.

Tau protein is essential for stress-induced brain pathology.

Exposure to chronic stress is frequently accompanied by cognitive and affective disorders in association with neurostructural adaptations. Chronic stress was previously shown to trigger Alzheimer's-like neuropathology, which is characterized by Tau hyperphosphorylation and missorting into dendritic spines followed by memory deficits. Here, we demonstrate that stress-driven hippocampal deficits in wild-type mice are accompanied by synaptic missorting of Tau and enhanced Fyn/GluN2B-driven synaptic signaling. In contrast, mice lacking Tau [Tau knockout (Tau-KO) mice] do not exhibit stress-induced pathological behaviors and atrophy of hippocampal dendrites or deficits of hippocampal connectivity. These findings implicate Tau as an essential mediator of the adverse effects of stress on brain structure and function.

Acetyl Cholinesterase Inhibitors and Cell-Derived Peripheral Inflammatory Cytokines in Early Stages of Alzheimer's Disease.

BACKGROUND: Clinical and preclinical studies firmly support the involvement of the inflammation in the pathogenesis of Alzheimer's disease (AD). Despite acetylcholinesterase inhibitors (AChEI) being widely used in AD patients, there is no conclusive evidence about their impact on the inflammatory response. METHODS: This study investigates peripheral proinflammatory cytokines (interferon gamma [IFN-γ], tumor necrosis factor alpha [TNF-α], and interleukins 1ß [IL-1ß] and 6 [IL-6]) by firstly comparing peripheral blood mononuclear cell (PBMC)-derived secretion in drug-naïve and AChEI-treated AD patients versus healthy controls. A subset of those drug-naïve AD patients, who were prescribed the AChEI donepezil, was followed-up for 6 months to investigate if donepezil suppresses proinflammatory cell-derived cytokine secretion. RESULTS: Patients with AD showed higher levels of PBMC-derived proinflammatory cytokines (IFN-γ, TNF-α, IL-1ß, and IL-6) in comparison with healthy controls. On reexamination, previously drug-naïve AD patients who received donepezil treatment for 6 months displayed a decrease in cell-derived IFN-γ, TNF-α, IL-1ß, and IL-6. CONCLUSIONS: Proinflammatory PBMC-derived cytokines were increased in patients with AD in comparison with healthy controls and donepezil-reduced proinflammatory cytokines when examining drug-naïve AD patients before and after AChEI treatment.

Tau Deletion Prevents Stress-Induced Dendritic Atrophy in Prefrontal Cortex: Role of Synaptic Mitochondria.

Tau protein in dendrites and synapses has been recently implicated in synaptic degeneration and neuronal malfunction. Chronic stress, a well-known inducer of neuronal/synaptic atrophy, triggers hyperphosphorylation of Tau protein and cognitive deficits. However, the cause-effect relationship between these events remains to be established. To test the involvement of Tau in stress-induced impairments of cognition, we investigated the impact of stress on cognitive behavior, neuronal structure, and the synaptic proteome in the prefrontal cortex (PFC) of Tau knock-out (Tau-KO) and wild-type (WT) mice. Whereas exposure to chronic stress resulted in atrophy of apical dendrites and spine loss in PFC neurons as well as significant impairments in working memory in WT mice, such changes were absent in Tau-KO animals. Quantitative proteomic analysis of PFC synaptosomal fractions, combined with transmission electron microscopy analysis, suggested a prominent role for mitochondria in the regulation of the effects of stress. Specifically, chronically stressed animals exhibit Tau-dependent alterations in the levels of proteins involved in mitochondrial transport and oxidative phosphorylation as well as in the synaptic localization of mitochondria in PFC. These findings provide evidence for a causal role of Tau in mediating stress-elicited neuronal atrophy and cognitive impairment and indicate that Tau may exert its effects through synaptic mitochondria.

Chronic Stress and Glucocorticoids: From Neuronal Plasticity to Neurodegeneration.

Stress and stress hormones, glucocorticoids (GCs), exert widespread actions in central nervous system, ranging from the regulation of gene transcription, cellular signaling, modulation of synaptic structure, and transmission and glial function to behavior. Their actions are mediated by glucocorticoid and mineralocorticoid receptors which are nuclear receptors/transcription factors. While GCs primarily act to maintain homeostasis by inducing physiological and behavioral adaptation, prolonged exposure to stress and elevated GC levels may result in neuro- and psychopathology. There is now ample evidence for cause-effect relationships between prolonged stress, elevated GC levels, and cognitive and mood disorders while the evidence for a link between chronic stress/GC and neurodegenerative disorders such as Alzheimer's (AD) and Parkinson's (PD) diseases is growing. This brief review considers some of the cellular mechanisms through which stress and GC may contribute to the pathogenesis of AD and PD.

Tau as the Converging Protein between Chronic Stress and Alzheimer's Disease Synaptic Pathology.

BACKGROUND: Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder with a complex physiopathology and still undefined initiators. Several risk factors have been suggested for AD with recent evidence supporting an etiopathogenic role of chronic environmental stress and glucocorticoids (GCs, stress hormones) in the development of the disease. Indeed, both AD and chronic stress are associated with neuronal atrophy, synaptic loss and cognitive impairment. Our previous studies have demonstrated the aggravating role of stress and GCs on AD pathology, including Tau hyperphosphorylation and aggregation and cognitive deficits in various AD models. In light of the suggested involvement of Tau missorting in AD synaptotoxity and the dual cytoplasmic and synaptic role of Tau, our recent studies focused on the possible role of Tau in the underlying cascades of stress/GC neuronal malfunction/atrophy in wild-type animals by monitoring the intracellular localization of Tau and its phosphorylation status in different cellular compartments. SUMMARY: Biochemical, ultrastructural, behavioral and neurostructural analysis have helped demonstrate that prolonged GC administration leads to dendritic remodeling and spine atrophy and loss in the rat hippocampus triggering Tau missorting at hippocampal synapses with the participation of specific phosphorylated Tau isoforms in this synaptic accumulation. KEY MESSAGES: The above findings suggest that Tau plays an essential role in mediating the neurodegenerative effects of stress and GCs towards the development of AD pathology. In addition, they highlight the involvement of Tau missorting in mechanism(s) of synaptic atrophy, beyond AD adding to our limited knowledge of the mechanisms through which stress causes brain pathology.

Sex Differences in Stress Response: Classical Mechanisms and Beyond.

Neuropsychiatric disorders, which are associated with stress hormone dysregulation, occur at different rates in men and women. Moreover, nowadays, preclinical and clinical evidence demonstrates that sex and gender can lead to differences in stress responses that predispose males and females to different expressions of similar pathologies. In this curated review, we focus on what is known about sex differences in classic mechanisms of stress response, such as glucocorticoid hormones and corticotrophin-releasing factor (CRF), which are components of the hypothalamicpituitary- adrenal (HPA) axis. Then, we present sex differences in neurotransmitter levels, such as serotonin, dopamine, glutamate and GABA, as well as indices of neurodegeneration, such as amyloid ß and Tau. Gonadal hormone effects, such as estrogens and testosterone, are also discussed throughout the review. We also review in detail preclinical data investigating sex differences caused by recentlyrecognized regulators of stress and disease, such as the immune system, genetic and epigenetic mechanisms, as well neurosteroids. Finally, we discuss how understanding sex differences in stress responses, as well as in pharmacology, can be leveraged into novel, more efficacious therapeutics for all. Based on the supporting evidence, it is obvious that incorporating sex as a biological variable into preclinical research is imperative for the understanding and treatment of stress-related neuropsychiatric disorders, such as depression, anxiety and Alzheimer's disease.

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 GSK3ß. 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.

Meeting Summary of The NYO3 5th NO-Age/AD Meeting and the 1st Norway-UK Joint Meeting on Aging and Dementia: Recent Progress on the Mechanisms and Interventional Strategies.

Unhealthy aging poses a global challenge with profound healthcare and socioeconomic implications. Slowing down the aging process offers a promising approach to reduce the burden of a number of age-related diseases, such as dementia, and promoting healthy longevity in the old population. In response to the challenge of the aging population and with a view to the future, Norway and the United Kingdom are fostering collaborations, supported by a "Money Follows Cooperation agreement" between the 2 nations. The inaugural Norway-UK joint meeting on aging and dementia gathered leading experts on aging and dementia from the 2 nations to share their latest discoveries in related fields. Since aging is an international challenge, and to foster collaborations, we also invited leading scholars from 11 additional countries to join this event. This report provides a summary of the conference, highlighting recent progress on molecular aging mechanisms, genetic risk factors, DNA damage and repair, mitophagy, autophagy, as well as progress on a series of clinical trials (eg, using NAD+ precursors). The meeting facilitated dialogue among policymakers, administrative leaders, researchers, and clinical experts, aiming to promote international research collaborations and to translate findings into clinical applications and interventions to advance healthy aging.

International Society for Extracellular Vesicles Workshop. QuantitatEVs: multiscale analyses, from bulk to single extracellular vesicle.

The 'QuantitatEVs: multiscale analyses, from bulk to single vesicle' workshop aimed to discuss quantitative strategies and harmonized wet and computational approaches toward the comprehensive analysis of extracellular vesicles (EVs) from bulk to single vesicle analyses with a special focus on emerging technologies. The workshop covered the key issues in the quantitative analysis of different EV-associated molecular components and EV biophysical features, which are considered the core of EV-associated biomarker discovery and validation for their clinical translation. The in-person-only workshop was held in Trento, Italy, from January 31st to February 2nd, 2023, and continued in Milan on February 3rd with "Next Generation EVs", a satellite event dedicated to early career researchers (ECR). This report summarizes the main topics and outcomes of the workshop.

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.