ApoE4 inhibition of VMAT2 in the locus coeruleus exacerbates Tau pathology in Alzheimer's disease

Spatiotemporal Imaging of Catechol Aldehydes in Neural Tissue

Catechol aldehydes (CAs), particularly 3,4-dihydroxyphenylacetaldehyde (DOPAL) and 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL), are potently cytotoxic and have been implicated in pathogenesis of neurodegenerative disorders. Understanding the dynamics of CAs in the brain is crucial for elucidating neurodegenerative pathways. Herein, we present an innovative fluorescent sensor system designed for the selective imaging of CAs within cells and neural tissues. This system employs a dual-reaction trigger, utilizing o-phenylenediamine's selectivity for aldehydes and phenylboronic acid for catechols, generating a specific Förster Resonance Energy Transfer (FRET) signal for CAs. Importantly, we have integrated fluorescence lifetime imaging microscopy (FLIM) with FRET (FLIM-FRET) to enhance detection accuracy while mitigating issues like spectral crosstalk and photobleaching. This dual-reaction FLIM-FRET system allows for the precise visualization of endogenous CAs in the substantia nigra and locus coeruleus of mice, the primary sites of CA production. Notably, this method represents a significant advancement in our ability to study these critical brain regions, as it uniquely enables the tracking of CAs spread across different parts of the brain, addressing a critical gap in the field, as no existing methods allow for such detailed localization of CAs across different brain regions. By enabling precise visualization of CAs within neural tissues, our method enhances understanding of their roles in disease progression.

Serum proteomics reveals early biomarkers of Alzheimer's disease: The dual role of APOE-ε4

Alzheimer's disease (AD), the leading cause of dementia, significantly impacts global public health, with cases expected to exceed 150 million by 2050. Late-onset Alzheimer's disease (LOAD), predominantly influenced by the APOE-ε4 allele, exhibits complex pathogenesis involving amyloid-β (Aβ) plaques, neurofibrillary tangles (NFTs), neuroinflammation, and blood-brain barrier (BBB) disruption. Proteomics has emerged as a pivotal technology in uncovering molecular mechanisms and identifying biomarkers for early diagnosis and intervention in AD. This paper reviews the genetic and molecular roles of APOE-ε4 in the pathology of AD, including its effects on Aβ aggregation, tau phosphorylation, neuroinflammation, and BBB integrity. Additionally, it highlights recent advances in serum proteomics, revealing APOE-ε4-dependent and independent protein signatures with potential as early biomarkers for AD. Despite technological progress, challenges such as population diversity, standardization, and distinguishing AD-specific biomarkers remain. Directions for future research emphasize multicenter longitudinal studies, multi-omics integration, and the clinical translation of proteomic findings to enable early detection of AD and personalized treatment strategies. Proteomics advances in AD research hold the promise of improving patient outcomes and reducing the global disease burden.

ApoE3 R136S binds to Tau and blocks its propagation, suppressing neurodegeneration in mice with Alzheimer's disease

PSEN1 E280A carrier for the APOE3 Christchurch variant (R136S) is protected against Alzheimer's disease (AD) symptoms with a distinct anatomical pattern of Tau pathology. However, the molecular mechanism accounting for this protective effect remains incompletely understood. Here, we show that the ApoE3 R136S mutant strongly binds to Tau and reduces its uptake into neurons and microglia compared with ApoE3 wild type (WT), diminishing Tau fragmentation by asparagine endopeptidase (AEP), proinflammatory cytokines by Tau pre-formed fibrils (PFFs) or β-amyloid (Aβ), and neurotoxicity. Further, ApoE3 R136S demonstrates more robust effects in attenuating AEP activation and Tau PFF spreading in the brains of both 5xFAD and Tau P301S mice than in ApoE3 WT, leading to improved cognitive functions. Thus, our findings support the idea that ApoE3 R136S strongly binds Tau and decreases its cellular uptake, abrogating Tau pathology propagation in AD brains.

Fading Blue: Exploring the Causes of Locus Coeruleus Damage Across the Lifespan

Locus Coeruleus (LC) is a brain nucleus that is involved in a variety of key functions (ranging from attention modulation to sleep-wake cycle regulation, to memory encoding); its proper function is necessary both during brain development and for brain integrity maintenance, and both at the microscale and macroscale level. Due to their specific intrinsic and extrinsic features, LC cells are considered particularly susceptible to damage concerning a variety of insults. This explains LC involvement in degenerative diseases not only in adults (in the context of neurodegenerative disease, mainly), but also in children (in relation to early hypoxic damage and Down's Syndrome, among others). In this narrative review, we dissect the potential mechanisms through which LC is affected in different diseases, with a special emphasis on the high rate of activity it is subjected to and the oxidative stress associated with it. Further research aimed at deepening our understanding of these mechanisms is needed to enable the development of potential strategies in the future that could slow down LC degeneration in subjects predisposed to specific brain disorders.

Regenerating Locus Coeruleus-Norepinephrine (LC-NE) Function: A Novel Approach for Neurodegenerative Diseases

Pathological changes in the locus coeruleus-norepinephrine (LC-NE) neurons, the major source of norepinephrine (NE, also known as noradrenaline) in the brain, are evident during the early stages of neurodegenerative diseases (ND). Research on both human and animal models have highlighted the therapeutic potential of targeting the LC-NE system to mitigate the progression of ND and alleviate associated psychiatric symptoms. However, the early and widespread degeneration of the LC-NE system presents a significant challenge for direct intervention in ND. Recent advances in regenerative cell therapy offer promising new strategies for ND treatment. The regeneration of LC-NE from pluripotent stem cells (PSCs) could significantly broaden the scope of LC-NE-based therapies for ND. In this review, we delve into the fundamental background and physiological functions of LC-NE. Additionally, we systematically examine the evidence and role of the LC-NE system in the neuropathology of ND and psychiatric diseases over recent years. Notably, we focus on the significance of PSCs-derived LC-NE and its potential impact on ND therapy. A deeper understanding and further investigation into the regeneration of LC-NE function could pave the way for practical and effective treatments for ND.

The Neuroanatomy of Induced Pluripotent Stem Cells: In Vitro Models of Subcortical Nuclei in Neurodegenerative Disorders

Neuromodulatory subcortical systems (NSSs) are monoaminergic and cholinergic neuronal groups that are markedly and precociously involved in the pathogenesis of many neurodegenerative disorders (NDDs), including Parkinson's and Alzheimer's diseases. In humans, although many tools have been developed to infer information on these nuclei, encompassing neuroimaging and neurophysiological methods, a detailed and specific direct evaluation of their cellular features in vivo has been difficult to obtain until recent years. The development of induced pluripotent stem cell (iPSC) models has allowed research to deeply delve into the cellular and molecular biology of NSS neurons. In fact, iPSCs can be produced easily and non-invasively from patients' fibroblasts or circulating blood monocytes, by de-differentiating those cells using specific protocols, and then be re-differentiated towards neural phenotypes, which may reproduce the specific features of the correspondent brain neurons (including NSS ones) from the same patient. In this review, we summarized findings obtained in the field of NDDs using iPSCs, with the aim to understand how reliably these might represent in vitro models of NSS. We found that most of the current literature in the field of iPSCs and NSSs in NDDs has focused on midbrain dopaminergic neurons in Parkinson's disease, providing interesting results on cellular pathophysiology and even leading to the first human autologous transplantation. Differentiation protocols for noradrenergic, cholinergic, and serotoninergic neurons have also been recently defined and published. Thus, it might be expected that in the near future, this approach could extend to other NSSs and other NDDs.

Mechanistic Approach to Immunity and Immunotherapy of Alzheimer's Disease: A Review

Alzheimer's disease (AD) is a debilitating neurodegenerative condition characterized by progressive cognitive decline and memory loss, affecting millions of people worldwide. Traditional treatments, such as cholinesterase inhibitors and NMDA receptor antagonists, offer limited symptomatic relief without addressing the underlying disease mechanisms. These limitations have driven the development of more potent and effective therapies. Recent advances in immunotherapy present promising avenues for AD treatment. Immunotherapy strategies, including both active and passive approaches, harness the immune system to target and mitigate AD-related pathology. Active immunotherapy stimulates the patient's immune response to produce antibodies against AD-specific antigens, while passive immunotherapy involves administering preformed antibodies or immune cells that specifically target amyloid-β (Aβ) or tau proteins. Monoclonal antibodies, such as aducanumab and lecanemab, have shown potential in reducing Aβ plaques and slowing cognitive decline in clinical trials, despite challenges related to adverse immune responses and the need for precise targeting. This comprehensive review explores the role of the immune system in AD, evaluates the current successes and limitations of immunotherapeutic approaches, and discusses future directions for enhancing the treatment efficacy.

Behavioral and histological analyses of the mouse Bassoon p.P3882A mutation corresponding to the human BSN p.P3866A mutation

Tauopathy is known to be a major pathognomonic finding in important neurodegenerative diseases such as progressive supranuclear palsy (PSP) and corticobasal degeneration. However, the mechanism by which tauopathy is triggered remains to be elucidated. We previously identified the point mutation c.11596C > G, p.Pro3866Ala in the Bassoon gene (BSN) in a Japanese family with PSP-like syndrome. We showed that mutated BSN may have been involved in its own insolubilization and tau accumulation. Furthermore, BSN mutations have also been related to various neurological diseases. In order to further investigate the pathophysiology of BSN mutation in detail, it is essential to study it in mouse models. We generated a mouse model with the mouse Bassoon p.P3882A mutation, which corresponds to the human BSN p.P3866A mutation, knock-in (KI) and we performed systematic behavioral and histological analyses. Behavioral analyses revealed impaired working memory in a Y-maze test at 3 months of age and decreased locomotor activity in the home cage at 3 and 12 months of age in KI mice compared to those in wild-type mice. Although no obvious structural abnormalities were observed at 3 months of age, immunohistochemical studies showed elevation of Bsn immunoreactivity in the hippocampus and neuronal loss without tau accumulation in the substantia nigra at 12 months of age in KI mice. Although our mice model did not show progressive cognitive dysfunction and locomotor disorder like PSP-like syndrome, dopaminergic neuronal loss was observed in the substantia nigra in 12-month-old KI mice. It is possible that BSN mutation may result in dopaminergic neuronal loss without locomotor symptoms due to the early disease stage. Thus, further clinical course can induce cognitive dysfunction and locomotor symptoms.

Spatiotemporal patterns of locus coeruleus integrity predict cortical tau and cognition

Autopsy studies indicated that the locus coeruleus (LC) accumulates hyperphosphorylated tau before allocortical regions in Alzheimer's disease. By combining in vivo longitudinal magnetic resonance imaging measures of LC integrity, tau positron emission tomography imaging and cognition with autopsy data and transcriptomic information, we examined whether LC changes precede allocortical tau deposition and whether specific genetic features underlie LC's selective vulnerability to tau. We found that LC integrity changes preceded medial temporal lobe tau accumulation, and together these processes were associated with lower cognitive performance. Common gene expression profiles between LC-medial temporal lobe-limbic regions map to biological functions in protein transport regulation. These findings advance our understanding of the spatiotemporal patterns of initial tau spreading from the LC and LC's selective vulnerability to Alzheimer's disease pathology. LC integrity measures can be a promising indicator for identifying the time window when individuals are at risk of disease progression and underscore the importance of interventions mitigating initial tau spread.

C/EBPβ: A transcription factor associated with the irreversible progression of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder distinguished by a swift cognitive deterioration accompanied by distinctive pathological hallmarks such as extracellular Aβ (β-amyloid) peptides, neuronal neurofibrillary tangles (NFTs), sustained neuroinflammation, and synaptic degeneration. The elevated frequency of AD cases and its proclivity to manifest at a younger age present a pressing challenge in the quest for novel therapeutic interventions. Numerous investigations have substantiated the involvement of C/EBPβ in the progression of AD pathology, thus indicating its potential as a therapeutic target for AD treatment.

AIMS

Several studies have demonstrated an elevation in the expression level of C/EBPβ among individuals afflicted with AD. Consequently, this review predominantly delves into the association between C/EBPβ expression and the pathological progression of Alzheimer's disease, elucidating its underlying molecular mechanism, and pointing out the possibility that C/EBPβ can be a new therapeutic target for AD.

METHODS

A systematic literature search was performed across multiple databases, including PubMed, Google Scholar, and so on, utilizing predetermined keywords and MeSH terms, without temporal constraints. The inclusion criteria encompassed diverse study designs, such as experimental, case-control, and cohort studies, restricted to publications in the English language, while conference abstracts and unpublished sources were excluded.

RESULTS

Overexpression of C/EBPβ exacerbates the pathological features of AD, primarily by promoting neuroinflammation and mediating the transcriptional regulation of key molecular pathways, including δ-secretase, apolipoprotein E4 (APOE4), acidic leucine-rich nuclear phosphoprotein-32A (ANP32A), transient receptor potential channel 1 (TRPC1), and Forkhead BoxO (FOXO).

DISCUSSION

The correlation between overexpression of C/EBPβ and the pathological development of AD, along with its molecular mechanisms, is evident. Investigating the pathways through which C/EBPβ regulates the development of AD reveals numerous multiple vicious cycle pathways exacerbating the pathological progression of the disease. Furthermore, the exacerbation of pathological progression due to C/EBPβ overexpression and its molecular mechanism is not limited to AD but also extends to other neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), and multiple sclerosis (MS).

CONCLUSION

The overexpression of C/EBPβ accelerates the irreversible progression of AD pathophysiology. Additionally, C/EBPβ plays a crucial role in mediating multiple pathways linked to AD pathology, some of which engender vicious cycles, leading to the establishment of feedback mechanisms. To sum up, targeting C/EBPβ could hold promise as a therapeutic strategy not only for AD but also for other degenerative diseases.

The Contributions of the Endolysosomal Compartment and Autophagy to APOEɛ4 Allele-Mediated Increase in Alzheimer's Disease Risk

Apolipoprotein E4 (APOE4), although yet-to-be fully understood, increases the risk and lowers the age of onset of Alzheimer's disease (AD), which is the major cause of dementia among elderly individuals. The endosome-lysosome and autophagy pathways, which are necessary for homeostasis in both neurons and glia, are dysregulated even in early AD. Nonetheless, the contributory roles of these pathways to developing AD-related pathologies in APOE4 individuals and models are unclear. Therefore, this review summarizes the dysregulations in the endosome-lysosome and autophagy pathways in APOE4 individuals and non-human models, and how these anomalies contribute to developing AD-relevant pathologies. The available literature suggests that APOE4 causes endosomal enlargement, increases endosomal acidification, impairs endosomal recycling, and downregulates exosome production. APOE4 impairs autophagy initiation and inhibits basal autophagy and autophagy flux. APOE4 promotes lysosome formation and trafficking and causes ApoE to accumulate in lysosomes. APOE4-mediated changes in the endosome, autophagosome and lysosome could promote AD-related features including Aβ accumulation, tau hyperphosphorylation, glial dysfunction, lipid dyshomeostasis, and synaptic defects. ApoE4 protein could mediate APOE4-mediated endosome-lysosome-autophagy changes. ApoE4 impairs vesicle recycling and endosome trafficking, impairs the synthesis of autophagy genes, resists being dissociated from its receptors and degradation, and forms a stable folding intermediate that could disrupt lysosome structure. Drugs such as molecular correctors that target ApoE4 molecular structure and enhance autophagy may ameliorate the endosome-lysosome-autophagy-mediated increase in AD risk in APOE4 individuals.

Impact of Apolipoprotein E4 on the Locus Coeruleus Functional Connectivity in Preclinical Alzheimer's Disease

Background

Recent interest has surged in the locus coeruleus (LC) for its early involvement in Alzheimer's disease (AD), notably concerning the apolipoprotein ɛ4 allele (APOE4).

Objective

This study aimed to discern LC functional connectivity (FC) variations in preclinical AD subjects, dissecting the roles of APOE4 carrier status and amyloid-β (Aβ) deposition.

Methods

A cohort of 112 cognitively intact individuals, all Aβ-positive, split into 70 APOE4 noncarriers and 42 carriers, underwent functional MRI scans, neuropsychological assessments, and APOE genotyping. The research utilized seed to voxel analysis for illustrating LC rsFC discrepancies between APOE4 statuses and employed a general linear model to examine the interactive influence of APOE4 carrier status and Aβ deposition on LC FC values.

Results

The investigation revealed no significant differences in sex, age, or SUVR between APOE4 carriers and noncarriers. It found diminished LC FC with the occipital cortex in APOE4 carriers and identified a significant interaction between APOE4 carrier status and temporal lobe SUVR in LC FC with the occipital cortex. This interaction suggested a proportional increase in LC FC for APOE4 carriers. Additional notable interactions were observed affecting LC FC with various brain regions, indicating a proportional decrease in LC FC for APOE4 carriers.

Conclusions

These findings confirm that APOE4 carrier status significantly influences LC FC in preclinical AD, showcasing an intricate relationship with regional Aβ deposition. This underscores the critical role of genetic and pathological factors in early AD pathophysiology, offering insights into potential biomarkers for early detection and intervention strategies.

Roles of ApoE4 on the Pathogenesis in Alzheimer's Disease and the Potential Therapeutic Approaches

The Apolipoprotein E ε4 (ApoE ε4) allele, encoding ApoE4, is the strongest genetic risk factor for late-onset Alzheimer's disease (LOAD). Emerging epidemiological evidence indicated that ApoE4 contributes to AD through influencing β-amyloid (Aβ) deposition and clearance. However, the molecular mechanisms of ApoE4 involved in AD pathogenesis remains unclear. Here, we introduced the structure and functions of ApoE isoforms, and then we reviewed the potential mechanisms of ApoE4 in the AD pathogenesis, including the effect of ApoE4 on Aβ pathology, and tau phosphorylation, oxidative stress; synaptic function, cholesterol transport, and mitochondrial dysfunction; sleep disturbances and cerebrovascular integrity in the AD brains. Furthermore, we discussed the available strategies for AD treatments that target to ApoE4. In general, this review overviews the potential roles of ApoE4 in the AD development and suggests some therapeutic approaches for AD. ApoE4 is genetic risk of AD. ApoE4 is involved in the AD pathogenesis. Aβ deposition, NFT, oxidative stress, abnormal cholesterol, mitochondrial dysfunction and neuroinflammation could be observed in the brains with ApoE4. Targeting the interaction of ApoE4 with the AD pathology is available strategy for AD treatments.

Noradrenergic neuromodulation in ageing and disease

The locus coeruleus (LC) is a small brainstem structure located in the lower pons and is the main source of noradrenaline (NA) in the brain. Via its phasic and tonic firing, it modulates cognition and autonomic functions and is involved in the brain's immune response. The extent of degeneration to the LC in healthy ageing remains unclear, however, noradrenergic dysfunction may contribute to the pathogenesis of Alzheimer's (AD) and Parkinson's disease (PD). Despite their differences in progression at later disease stages, the early involvement of the LC may lead to comparable behavioural symptoms such as preclinical sleep problems and neuropsychiatric symptoms as a result of AD and PD pathology. In this review, we draw attention to the mechanisms that underlie LC degeneration in ageing, AD and PD. We aim to motivate future research to investigate how early degeneration of the noradrenergic system may play a pivotal role in the pathogenesis of AD and PD which may also be relevant to other neurodegenerative diseases.

Riddles in the dark: Decoding the relationship between neuromelanin and neurodegeneration in locus coeruleus neurons

The noradrenergic locus coeruleus (LC) is among the first regions of the brain affected by pathology in both Alzheimer's disease (AD) and Parkinson's disease (PD), but the reasons for this selective vulnerability are not completely understood. Several features of LC neurons have been proposed as contributing factors to this dysfunction and degeneration, and this review will focus on the presence of neuromelanin (NM). NM is a dark pigment unique to catecholaminergic cells that is formed of norepinephrine (NE) and dopamine (DA) metabolites, heavy metals, protein aggregates, and oxidated lipids. We cover what is currently known about NM and the limitations of historical approaches, then discuss the new human tyrosinase (hTyr) model of NM production in rodent catecholamine cells in vivo that offers unique opportunities for studying its neurobiology, neurotoxicity, and potential of NM-based therapeutics for treating neurodegenerative disease.

ApoE4-mediated Blood-Brain Barrier Damage in Alzheimer's Disease: Progress and Prospects

Late-onset Alzheimer's disease (AD), a neurodegenerative disease, is expected in the elderly population and adversely affects families and society. The extensive debate on the deposition of amyloid (Aβ), abnormal phosphorylation of Tau protein, and neuroinflammation hypothesis in the pathogenesis of AD has been recognized by many scholars. The blood-brain barrier (BBB) is an essential physical barrier that protects the brain from external material interference, and its integrity affects the process of AD. Apolipoprotein E4 (ApoE4) has shown a critical regulatory role in many studies and is a crucial protein that affects AD. Numerous current studies on ApoE4 are based on complementary hypotheses to the three hypotheses above, ignoring the effect of ApoE4 on BBB constitutive cells and the role of the BBB in AD. In this review, we summarize the findings of the role of ApoE4 in the composition of the BBB and the value of ApoE4 for maintaining BBB integrity, which may play an essential role in changing the progression of the disease.

Fast-Specific Fluorescent Probes to Visualize Norepinephrine Signaling Pathways and Its Flux in the Epileptic Mice Brain

Norepinephrine (NE) is synthesized in the locus coeruleus and widely projected throughout the brain and spinal cord. It regulates various actions and consciousness linked to a variety of neurological diseases. A "hunting-shooting" strategy was proposed in this work to improve the specificity and response rate of an NE fluorescent probe: 2-(cyclohex-2-en-1-ylidene)malononitrile derivatives were chosen as a fluorophore. To create a dual-site probe, an aldehyde group was added to the ortho of the ester group (or benzene sulfonate). Because of its excellent electrophilic activity, the aldehyde group could rapidly "hunt" the amino group and then form an intramolecular five-membered ring via the nucleophilic reaction with the β-hydroxyl group. The -NH- in the five-membered ring "shoots" the adjacent ester group, releasing the fluorophore and allowing for rapid and specific NE detection. The NE release and reuptake ″emetic″-″swallow″ transient process is captured and visualized under the action of the primary NE receptor drug. Furthermore, by introducing halogen into the fluorophore to lengthen the absorption wavelength, improve lipid solubility, and adjust the pK_a appropriately, the probe successfully penetrated the blood-brain barrier (BBB). In situ synchronous probe imaging was used to detect the NE level in the brains of epileptic and normal mice, and abnormal expression of NE in the brain was discovered during epilepsy. Brain anatomy was used to examine the distribution and level changes of NE in various brain regions before and after epilepsy. This research provides useful tools and a theoretical foundation for diagnosing and treating central nervous system diseases early.

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

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

Mitochondrial Dysfunction Links to Impaired Hippocampal Serotonin Release in a Mouse Model of Alzheimer's Disease

BACKGROUND

Deprivation of extracellular serotonin has been linked to cognitive decline and neuropsychiatric disturbances in Alzheimer's disease (AD). However, despite degeneration of serotonin-producing neurons, whether serotonin release is affected in AD-sensitive brain regions is unknown.

OBJECTIVE

This study investigated the impact of mitochondrial dysfunction in decreased hippocampal serotonin release in AD amyloidosis mouse model 5xFAD mice.

METHODS

Electrochemical assays were applied to examine hippocampal serotonin release. We also employed multidisciplinary techniques to determine the role of oligomeric amyloid-β (Aβ) in hippocampal mitochondrial deficits and serotonin release deficiency.

RESULTS

5xFAD mice exhibited serotonin release decrease and relatively moderate downregulation of serotonergic fiber density as well as serotonin content in the hippocampal region. Further experiments showed an inhibitory effect of oligomeric amyloid-β (Aβ) on hippocampal serotonin release without affecting the density of serotonergic fibers. Pharmaceutical uncoupling of mitochondrial oxidative phosphorylation (OXPHOS) disrupted hippocampal serotonin release in an ex vivo setting. This echoes the mitochondrial defects in serotonergic fibers in 5xFAD mice and oligomeric Aβ-challenged primary serotonergic neuron cultures and implicates a link between mitochondrial dysfunction and serotonin transmission defects in AD-relevant pathological settings.

CONCLUSION

The most parsimonious interpretation of our findings is that mitochondrial dysfunction is a phenotypic change of serotonergic neurons, which potentially plays a role in the development of serotonergic failure in AD-related conditions.

APOE in the bullseye of neurodegenerative diseases: impact of the APOE genotype in Alzheimer's disease pathology and brain diseases

ApoE is the major lipid and cholesterol carrier in the CNS. There are three major human polymorphisms, apoE2, apoE3, and apoE4, and the genetic expression of APOE4 is one of the most influential risk factors for the development of late-onset Alzheimer's disease (AD). Neuroinflammation has become the third hallmark of AD, together with Amyloid-β plaques and neurofibrillary tangles of hyperphosphorylated aggregated tau protein. This review aims to broadly and extensively describe the differential aspects concerning apoE. Starting from the evolution of apoE to how APOE's single-nucleotide polymorphisms affect its structure, function, and involvement during health and disease. This review reflects on how APOE's polymorphisms impact critical aspects of AD pathology, such as the neuroinflammatory response, particularly the effect of APOE on astrocytic and microglial function and microglial dynamics, synaptic function, amyloid-β load, tau pathology, autophagy, and cell-cell communication. We discuss influential factors affecting AD pathology combined with the APOE genotype, such as sex, age, diet, physical exercise, current therapies and clinical trials in the AD field. The impact of the APOE genotype in other neurodegenerative diseases characterized by overt inflammation, e.g., alpha- synucleinopathies and Parkinson's disease, traumatic brain injury, stroke, amyotrophic lateral sclerosis, and multiple sclerosis, is also addressed. Therefore, this review gathers the most relevant findings related to the APOE genotype up to date and its implications on AD and CNS pathologies to provide a deeper understanding of the knowledge in the APOE field.

Losartan Mitigates Oxidative Stress in the Brains of Aged and Inflamed IL-10-/- Mice

Chronic inflammation, oxidative stress, and dysregulation of the renin-angiotensin system are closely linked, and their crosstalk commonly contributes to age-related physical and cognitive decline. The primary dementia-protective benefits of Angiotensin II type 1 receptor (AT1R) blockers are believed to arise from systemic effects on blood pressure. However, there is an independently regulated brain-specific renin-angiotensin system. Here, we examined the impact of 4 weeks of oral Losartan treatment on the brains of aged (100 weeks old) IL-10-/- mice, an animal model of chronic inflammation and frailty. Our data show that aged IL-10-/- mice have higher AT1R and Nitrotyrosine (oxidative stress marker) levels in their frontal cortex tissue but not in cerebellar or hippocampal tissue compared to age- and sex-matched wild type mice. Losartan treatment for 4 weeks is associated with lower AT1R protein level, Nitrotyrosine, and Tau protein in the frontal cortex of aged IL-10-/- mice. Our results highlight the impact of Losartan, an AT1R blocker commonly prescribed for treating high blood pressure, on the brain-specific angiotensin system and AT1R-linked downstream effects such as brain oxidative stress damage and Tau burden in a frailty mouse model.

Cognitive and neuropsychiatric effects of noradrenergic treatment in Alzheimer's disease: systematic review and meta-analysis

BACKGROUND

Dysfunction of the locus coeruleus-noradrenergic system occurs early in Alzheimer's disease, contributing to cognitive and neuropsychiatric symptoms in some patients. This system offers a potential therapeutic target, although noradrenergic treatments are not currently used in clinical practice.

OBJECTIVE

To assess the efficacy of drugs with principally noradrenergic action in improving cognitive and neuropsychiatric symptoms in Alzheimer's disease.

METHODS

The MEDLINE, Embase and ClinicalTrials.gov databases were searched from 1980 to December 2021. We generated pooled estimates using random effects meta-analyses.

RESULTS

We included 19 randomised controlled trials (1811 patients), of which six were judged as 'good' quality, seven as 'fair' and six 'poor'. Meta-analysis of 10 of these studies (1300 patients) showed a significant small positive effect of noradrenergic drugs on global cognition, measured using the Mini-Mental State Examination or Alzheimer's Disease Assessment Scale-Cognitive Subscale (standardised mean difference (SMD): 0.14, 95% CI: 0.03 to 0.25, p=0.01; I2=0%). No significant effect was seen on measures of attention (SMD: 0.01, 95% CI: -0.17 to 0.19, p=0.91; I2=0). The apathy meta-analysis included eight trials (425 patients) and detected a large positive effect of noradrenergic drugs (SMD: 0.45, 95% CI: 0.16 to 0.73, p=0.002; I2=58%). This positive effect was still present following removal of outliers to account for heterogeneity across studies.

DISCUSSION

Repurposing of established noradrenergic drugs is most likely to offer effective treatment in Alzheimer's disease for general cognition and apathy. However, several factors should be considered before designing future clinical trials. These include targeting of appropriate patient subgroups and understanding the dose effects of individual drugs and their interactions with other treatments to minimise risks and maximise therapeutic effects.

PROSPERO REGISTERATION NUMBER

CRD42021277500.

The synapse as a treatment avenue for Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder with devastating symptoms, including memory impairments and cognitive deficits. Hallmarks of AD pathology are amyloid-beta (Aβ) deposition forming neuritic plaques and neurofibrillary tangles (NFTs). For many years, AD drug development has mainly focused on directly targeting the Aβ aggregation or the formation of tau tangles, but this disease has no cure so far. Other common characteristics of AD are synaptic abnormalities and dysfunctions such as synaptic damage, synaptic loss, and structural changes in the synapse. Those anomalies happen in the early stages of the disease before behavioural symptoms have occurred. Therefore, better understanding the mechanisms underlying the synaptic dysfunction found in AD and targeting the synapse, especially using early treatment windows, can lead to finding novel and more effective treatments that could improve the lives of AD patients. Researchers have recently started developing different disease-modifying treatments targeting the synapse to rescue and prevent synaptic dysfunction in AD. The main objectives of these new strategies are to halt synaptic loss, strengthen synaptic connections, and improve synaptic density, potentially leading to the rescue or prevention of cognitive impairments. This article aims to address the mechanisms of synaptic degeneration in AD and discuss current strategies that focus on the synapse for AD therapy. Alzheimer's disease (AD) is a neurodegenerative disorder that significantly impairs memory and causes cognitive and behavioural deficits. Scientists worldwide have tried to find a treatment that can reverse or rescue AD symptoms, but there is no cure so far. One prominent characteristic of AD is the brain atrophy caused by significant synaptic loss and overall neuronal damage, which starts at the early stages of the disease before other AD hallmarks such as neuritic plaques and NFTs. The present review addresses the underlying mechanisms behind synaptic loss and dysfunction in AD and discusses potential strategies that target the synapse.

Noradrenaline in Alzheimer's Disease: A New Potential Therapeutic Target

A growing body of evidence demonstrates the important role of the noradrenergic system in the pathogenesis of many neurodegenerative processes, especially Alzheimer’s disease, due to its ability to control glial activation and chemokine production resulting in anti-inflammatory and neuroprotective effects. Noradrenaline involvement in this disease was first proposed after finding deficits of noradrenergic neurons in the locus coeruleus from Alzheimer’s disease patients. Based on this, it has been hypothesized that the early loss of noradrenergic projections and the subsequent reduction of noradrenaline brain levels contribute to cognitive dysfunctions and the progression of neurodegeneration. Several studies have focused on analyzing the role of noradrenaline in the development and progression of Alzheimer’s disease. In this review we summarize some of the most relevant data describing the alterations of the noradrenergic system normally occurring in Alzheimer’s disease as well as experimental studies in which noradrenaline concentration was modified in order to further analyze how these alterations affect the behavior and viability of different nervous cells. The combination of the different studies here presented suggests that the maintenance of adequate noradrenaline levels in the central nervous system constitutes a key factor of the endogenous defense systems that help prevent or delay the development of Alzheimer’s disease. For this reason, the use of noradrenaline modulating drugs is proposed as an interesting alternative therapeutic option for Alzheimer’s disease.

The role of the locus coeruleus/norepinephrine system in the pathogenesis of neurodegenerative disorders: An update

PURPOSE OF REVIEW

The aim of this review was to provide an update on current and emerging knowledge of the neuropathological processes affecting the locus coeruleus/norepinephrine (LC/NE) system, their effect on Alzheimer's disease and Parkinson's disease symptomatology, including efforts to translate these notions into therapeutic actions targeting the noradrenergic system.

RECENT FINDINGS

Over the past 2 years, work from multiple groups has contributed to support an early role of locus coeruleus degeneration and/or hyperactivation in the neurodegenerative process, including a trigger of neuroinflammation. Imaging advances are allowing the quantification of locus coeruleus structural features in vivo, which is critical in the early stages of disease. Nonmotor and noncognitive symptoms, often secondary to the involvement of the LC/NE system, are becoming more important in the definition of these diseases and their treatment.

SUMMARY

The diverse symptomatology of Parkinson's disease and Alzheimer's disease, which is not limited to cardinal motor and cognitive abnormalities, strongly suggests a multisystem neurodegenerative process. In this context, it is increasingly clear how the LC/NE system plays a key role in the initiation and maintenance of the neurodegenerative process.

Tau modification by the norepinephrine metabolite DOPEGAL stimulates its pathology and propagation

The noradrenergic locus ceruleus (LC) is the first site of detectable tau pathology in Alzheimer's disease (AD), but the mechanisms underlying the selective vulnerability of the LC in AD have not been completely identified. In the present study, we show that DOPEGAL, a monoamine oxidase A (MAO-A) metabolite of norepinephrine (NE), reacts directly with the primary amine on the Lys353 residue of tau to stimulate its aggregation and facilitate its propagation. Inhibition of MAO-A or mutation of the Lys353 residue to arginine (Lys353Arg) decreases tau Lys353-DOPEGAL levels and diminishes tau pathology spreading. Wild-type tau preformed fibrils (PFFs) trigger Lys353-DOPEGAL formation, tau pathology propagation and cognitive impairment in MAPT transgenic mice, all of which are attenuated with PFFs made from the Lys353Arg mutant. Thus, the selective vulnerability of LC neurons in AD may be explained, in part, by NE oxidation via MAO-A into DOPEGAL, which covalently modifies tau and accelerates its aggregation, toxicity and propagation.

Insights into T-cell dysfunction in Alzheimer's disease

T cells, the critical immune cells of the adaptive immune system, are often dysfunctional in Alzheimer's disease (AD) and are involved in AD pathology. Reports highlight neuroinflammation as a crucial modulator of AD pathogenesis, and aberrant T cells indirectly contribute to neuroinflammation by secreting proinflammatory mediators via direct crosstalk with glial cells infiltrating the brain. However, the mechanisms underlying T‐cell abnormalities in AD appear multifactorial. Risk factors for AD and pathological hallmarks of AD have been tightly linked with immune responses, implying the potential regulatory effects of these factors on T cells. In this review, we discuss how the risk factors for AD, particularly Apolipoprotein E (ApoE), Aβ, α‐secretase, β‐secretase, γ‐secretase, Tau, and neuroinflammation, modulate T‐cell activation and the association between T cells and pathological AD hallmarks. Understanding these associations is critical to provide a comprehensive view of appropriate therapeutic strategies for AD.

ApoE4 attenuates autophagy via FoxO3a repression in the brain

Apolipoprotein E (ApoE) plays multiple roles in lipid transport, neuronal signaling, glucose metabolism, mitochondrial function, and inflammation in the brain. It is also associated with neurodegenerative diseases, and its influence differs depending on the isoform. In particular, the ε4 allele of APOE is the highest genetic risk factor for developing late-onset Alzheimer's disease (AD). However, the mechanism by which ApoE4 contributes to the pathogenesis of AD remains unclear. We investigated the effect of ApoE4 on autophagy in the human brains of ApoE4 carriers. Compared to non-carriers, the expression of FoxO3a regulating autophagy-related genes was significantly reduced in ApoE4 carriers, and the phosphorylation level of FoxO3a at Ser253 increased in ApoE4 carriers, indicating that FoxO3a is considerably repressed in ApoE4 carriers. As a result, the protein expression of FoxO3a downstream genes, such as Atg12, Beclin-1, BNIP3, and PINK1, was significantly decreased, likely leading to dysfunction of both autophagy and mitophagy in ApoE4 carriers. In addition, phosphorylated tau accumulated more in ApoE4 carriers than in non-carriers. Taken together, our results suggest that ApoE4 might attenuate autophagy via the repression of FoxO3a in AD pathogenesis. The regulation of the ApoE4-FoxO3a axis may provide a novel therapeutic target for the prevention and treatment of AD with the APOE4 allele.

Sex Differences in Locus Coeruleus: A Heuristic Approach That May Explain the Increased Risk of Alzheimer's Disease in Females

This article aims to reevaluate our approach to female vulnerability to Alzheimer's disease (AD) and put forth a new hypothesis considering how sex differences in the locus coeruleus-noradrenaline (LC-NA) structure and function could account for why females are more likely to develop AD. We specifically focus our attention on locus coeruleus (LC) morphology, the paucity of estrogens, neuroinflammation, blood-brain barrier permeability, apolipoprotein ɛ4 polymorphism (APOEɛ4), and cognitive reserve. The role of the LC-NA system and sex differences are two of the most rapidly emerging topics in AD research. Current literature either investigates the LC due to it being one of the first brain areas to develop AD pathology or acknowledges the neuroprotective effects of estrogens and how the loss of these female hormones have the capacity to contribute to the sex differences seen in AD; however, existing research has neglected to concurrently examine these two rationales and therefore leaving our hypothesis undetermined. Collectively, this article should assist in alleviating current challenges surrounding female AD by providing thought-provoking connections into the interrelationship between the disruption of the female LC-NA system, the decline of estrogens, and AD vulnerability. It is therefore likely that treatment for this heterogeneous disease may need to be distinctly developed for females and males separately, and may require a precision medicine approach.