Beneficial effects of curtailing immune susceptibility in an Alzheimer's disease model

Differential roles of regulatory T cells in Alzheimer's disease

Regulatory T (Treg) cells interact with a variety of resident cells and infiltrated immune cells in the central nervous system (CNS) to modulate neuroinflammation and neurodegeneration. Extracellular amyloid-β (Aβ) peptide deposition and secondary persistent inflammation due to activation of microglia, astrocytes, and infiltrated immune cells contribute to Alzheimer's disease (AD)-related neurodegeneration. The majority of evidence supports the neuroprotective effects of Treg cells in AD. In the early stages of AD, appropriate Treg cell activity is required for the induction of microglia and astrocyte phagocytic activity in order to clear A deposits and prevent neuroinflammation. Such neuroprotective impacts were in part attributed to the ability of Treg cells to suppress deleterious and/or boost beneficial functions of microglia/astrocytes. In the later stages of AD, an effective Treg cell activity needs to prevent neurotoxicity and neurodegeneration. Treg cells can exert preventive effects on Th1-, and Th17 cell-related pathologic responses, whilst potentiating Th2-mediated protective activity. The impaired Treg cell-related immunomodulatory mechanisms have been described in AD patients and in related animal models which can contribute to the onset and progression of AD. This review aimed to provide a comprehensive figure regarding the role of Treg cells in AD while highlighting potential therapeutic approaches.

N-acetylneuraminic acid links immune exhaustion and accelerated memory deficit in diet-induced obese Alzheimer's disease mouse model

Systemic immunity supports lifelong brain function. Obesity posits a chronic burden on systemic immunity. Independently, obesity was shown as a risk factor for Alzheimer's disease (AD). Here we show that high-fat obesogenic diet accelerated recognition-memory impairment in an AD mouse model (5xFAD). In obese 5xFAD mice, hippocampal cells displayed only minor diet-related transcriptional changes, whereas the splenic immune landscape exhibited aging-like CD4+ T-cell deregulation. Following plasma metabolite profiling, we identified free N-acetylneuraminic acid (NANA), the predominant sialic acid, as the metabolite linking recognition-memory impairment to increased splenic immune-suppressive cells in mice. Single-nucleus RNA-sequencing revealed mouse visceral adipose macrophages as a potential source of NANA. In vitro, NANA reduced CD4+ T-cell proliferation, tested in both mouse and human. In vivo, NANA administration to standard diet-fed mice recapitulated high-fat diet effects on CD4+ T cells and accelerated recognition-memory impairment in 5xFAD mice. We suggest that obesity accelerates disease manifestation in a mouse model of AD via systemic immune exhaustion.

Sex-dependent worsening of NMDA-induced responses, anxiety, hypercortisolemia, and organometry of early peripheral immunoendocrine impairment in adult 3xTg-AD mice and their long-lasting ontogenic modulation by neonatal handling

The neuroimmunomodulation hypothesis for Alzheimer's disease (AD) postulates that alterations in the innate immune system triggered by damage signals result in adverse effects on neuronal functions. The peripheral immune system and neuroimmunoendocrine communication are also impaired. Here we provide further evidence using a longitudinal design that also studied the long-lasting effects of an early life sensorial intervention (neonatal handling, from postnatal day 1-21) in 6-month-old (early stages of the disease) male and female 3xTg-AD mice compared to age- and sex-matched non-transgenic (NTg) mice with normal aging. The behavioral patterns elicited by the direct exposure to an open field, and the motor depression response evoked by NMDA (25 mg/kg, i.p) were found correlated to the organometry of peripheral immune-endocrine organs (thymus involution, splenomegaly, and adrenal glands' hypertrophy) and increased corticosterone levels, suggesting their potential value for diagnostic and biomonitoring.The NMDA-induced immediate and depressant motor activity and endocrine (corticosterone) responses were sensitive to sex and AD-genotype, suggesting worse endogenous susceptibility/neuroprotective response to glutamatergic excitotoxicity in males and in the AD-genotype. 3xTg-AD females showed a reduced immediate response, whereas the NTg showed higher responsiveness to subsequent NMDA-induced depressant effect than their male counterparts. The long-lasting ontogenic modulation by handling was shown as a potentiation of NMDA-depressant effect in NTg males and females, while sex × treatment effects were found in 3xTg-AD mice. Finally, NMDA-induced corticosterone showed sex, genotype and interaction effects with sexual dimorphism enhanced in the AD-genotype, suggesting different endogenous vulnerability/neuroprotective capacities and modulation of the neuroimmunoendocrine system.

Recent Advances in the Development of Nanodelivery Systems Targeting the TRAIL Death Receptor Pathway

The TRAIL (TNF-related apoptosis-inducing ligand) apoptotic pathway is extensively exploited in the development of targeted antitumor therapy due to TRAIL specificity towards its cognate receptors, namely death receptors DR4 and DR5. Although therapies targeting the TRAIL pathway have encountered many obstacles in attempts at clinical implementation for cancer treatment, the unique features of the TRAIL signaling pathway continue to attract the attention of researchers. Special attention is paid to the design of novel nanoscaled delivery systems, primarily aimed at increasing the valency of the ligand for improved death receptor clustering that enhances apoptotic signaling. Optionally, complex nanoformulations can allow the encapsulation of several therapeutic molecules for a combined synergistic effect, for example, chemotherapeutic agents or photosensitizers. Scaffolds for the developed nanodelivery systems are fabricated by a wide range of conventional clinically approved materials and innovative ones, including metals, carbon, lipids, polymers, nanogels, protein nanocages, virus-based nanoparticles, dendrimers, DNA origami nanostructures, and their complex combinations. Most nanotherapeutics targeting the TRAIL pathway are aimed at tumor therapy and theranostics. However, given the wide spectrum of action of TRAIL due to its natural role in immune system homeostasis, other therapeutic areas are also involved, such as liver fibrosis, rheumatoid arthritis, Alzheimer's disease, and inflammatory diseases caused by bacterial infections. This review summarizes the recent innovative developments in the design of nanodelivery systems modified with TRAIL pathway-targeting ligands.

Acupuncture regulates the Th17/Treg balance and improves cognitive deficits in a rat model of vascular dementia

Objective

The present study was developed to explore the impact of acupuncture on the Th17/Treg balance in the brain and the periphery and associated changes in cognitive deficits in a rat model of vascular dementia (VD).

Methods

Male Wistar rats (8 weeks old) were randomly assigned to sham-operated (Gs, n = 10), and operation (n = 30) groups. A VD model was established for all rats in the operation group via the permanent bilateral occlusion of the common carotid artery. Behavioral screening of these rats was conducted via a hidden platform trial at 2 months post-operation. These operation group rats were then further subdivided into impaired (Gi) and acupuncture (Ga) groups (n = 10/group). Acupuncture was performed over a 21-day period for rats in the Ga group. A Morris water maze (MWM) test was used to assess cognitive function for rats in all groups. Flow cytometry and fluorescent staining were used to detect Th17 and Treg cells in samples from these animals based on IL-17/FoxP3 or CD4⁺FoxP3⁺/CD4⁺RORγt⁺ staining profiles.

Results

Relative to the Gs group, escape latency values for rats in the Gi group were significantly increased. Following treatment, rats in the Ga group exhibited significant reductions in escape latency values as compared to rats in the Gi group (P < 0.05). The relative Treg proportion in the peripheral blood and spleen additionally trended upwards in these Ga rats as compared to those in the Gi group (P > 0.05), whereas the frequency of Th17 cells in the peripheral blood and spleen of Ga group rats trended downward relative to the Gi group (P > 0.05). Significantly fewer CD4⁺RORγt⁺ and RORγt⁺ cells were detected in the Ga group relative to the Gi group, whereas CD4⁺FoxP3⁺ and FoxP3⁺ cell counts were increased (P < 0.01).

Conclusion

In summary, VD model rats exhibited dysregulated Th17/Treg homeostasis. Acupuncture treatment was sufficient to reduce the frequency and numbers of Th17 cells in these animals while increasing Treg cell levels, thereby alleviating cognitive deficits with respect to both spatial learning and memory impairment. Consequently, the therapeutic benefits of such acupuncture treatment may be attributable to the regulation of the Th17/Treg balance and associated improvements in cognitive function.

Elevated Expression of Two Pore Potassium Channel THIK-1 in Alzheimer's Disease: An Inflammatory Mechanism

INTRODUCTION

Tandem pore domain halothane-inhibited K+ channel 1 (THIK-1, coded by KCNK13) provides an upstream regulation of the activation of the NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome, which has been suggested as one of the key mechanisms of the pathological process in neurodegeneration mainly from in vitro and in vivo model systems studies. However, unequivocal evidence from neurodegenerative disorders has been lacking.

OBJECTIVE

To investigate the involvement of the THIK-1/NLRP3 pathway in the pathological process of Alzheimer's disease (AD) and Parkinson's disease (PD).

METHODS

This study investigated gene expression of markers in the THIK-1/NLRP3 pathway in an animal model representing AD as well as in human postmortem brains of AD and PD by quantitative real-time PCR. THIK-1 protein expression was determined using automated capillary electrophoresis immunoblotting. Furthermore, DNA methylation of KCNK13 was analysed in AD cohort by pyrosequencing.

RESULTS

A substantial upregulation of KCNK13, glial activation markers, NLRP3 inflammasome components, and IL1B was observed in the animal study. Increased expression of KCNK13 support an inflammatory glial cell activation in both advanced AD and PD. The increase in KCNK13 expression was also supported by downregulation in DNA methylation of KCNK13 in AD.

CONCLUSIONS

The association between THIK-1 K+ channels expression and pathology changes indicates a THIK-1-induced activation of this glial subtype in AD and PD. Therefore, specific blocks of the microglial THIK-1 K+ channels at the early stage of AD and PD may be beneficial for the patients.

TRAIL-R Deficient Mice Are Protected from Neurotoxic Effects of Amyloid-β

TRAIL, a member of TNF superfamily, is a potent inducer of neuronal death. Neurotoxic effects of TRAIL appear mediated by its death receptor TRAIL-R2/DR5. To assess the role of TRAIL/TRAIL-R2 pathway in AD-related neurodegeneration, we studied the impact of the treatment with amyloid-β (Aβ) upon cell viability and inflammation in TRAIL-R-deficient mice (TRAIL-R^−/−). Here, we demonstrate that the lack of TRAIL-R2 protects from death cultured TRAIL-R^−/− mouse embryonic hippocampal cells after treatment with either Aβ1-42 or TRAIL. Consistently, stereotaxic injection of Aβ1-42 resulted in blunted caspase activation, as well as in reduction of JNK phosphorylation and increased AKT phosphorylation in TRAIL-R^−/− mice. Moreover, the lack of TRAIL-R2 was associated with blunted constitutive p53 expression in mice that have undergone Aβ1-42 treatment, as well as in decrease of phosphorylated forms of tau and GSK3β proteins. Likewise, TRAIL-R2 appears essential to both TRAIL and Aβ-mediated neurotoxicity and inflammation. Indeed, hippocampi of TRAIL-R^−/− mice challenged with Aβ1-42, showed a slight expression of microglial (Iba-1) and astrocytic (GFAP) markers along with attenuated levels of IL-1β, TNF-α, NOS2 and COX2. In conclusion, the bulk of these results demonstrate that the constitutive lack of TRAIL-R2 is associated with a substantial reduction of noxious effects of Aβ1-42, providing further evidence on the prominent role played by TRAIL in course of Aβ-related neurodegeneration and confirming that the TRAIL system represents a potential target for innovative AD therapy.

Intranasal Administration of a TRAIL Neutralizing Monoclonal Antibody Adsorbed in PLGA Nanoparticles and NLC Nanosystems: An In Vivo Study on a Mouse Model of Alzheimer’s Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder that progressively compromises cognitive functions. Tumor necrosis factor (TNF)-Related Apoptosis Inducing Ligand (TRAIL), a proinflammatory cytokine belonging to the TNF superfamily, appears to be a key player in the inflammatory/immune orchestra of the AD brain. Despite the ability of an anti-TRAIL monoclonal antibody to reach the brain producing beneficial effects in AD mice, we attempted to develop such a TRAIL-neutralizing monoclonal antibody adsorbed on lipid and polymeric nanocarriers, for intranasal administration, in a valid approach to overcome issues related to both high dose and drug transport across the blood–brain barrier. The two types of nanomedicines produced showed physico-chemical characteristics appropriate for intranasal administration. As confirmed by enzyme-linked immunosorbent assay (ELISA), both nanomedicines were able to form a complex with the antibody with an encapsulation efficiency of ≈99%. After testing in vitro the immunoneutralizing properties of the nanomedicines, the latter were intranasally administered in AD mice. The antibody–nanocarrier complexes were detectable in the brain in substantial amounts at concentrations significantly higher compared to the free form of the anti-TRAIL antibody. These data support the use of nanomedicine as an optimal method for the delivery of the TRAIL neutralizing antibody to the brain through the nose-to-brain route, aiming to improve the biological attributes of anti-TRAIL-based therapy for AD treatment.

Differences in Immune-Related Genes Underlie Temporal and Regional Pathological Progression in 3xTg-AD Mice

The prevalence of Alzheimer’s disease (AD), the most common cause of age-associated dementia, is estimated to increase over the next decades. Evidence suggests neuro-immune signaling deregulation and risk genes beyond the amyloid-β (Aβ) deposition in AD pathology. We examined the temporal profile of inflammatory mediators and microglia deactivation/activation in the brain cortex and hippocampus of 3xTg-AD mice at 3- and 9-month-old. We found upregulated APP processing, decreased expression of CD11b, CX3CR1, MFG-E8, TNF-α, IL-1β, MHC-II and C/EBP-α and increased miR-146a in both brain regions in 3-month-old 3xTG-AD mice, suggestive of a restrictive regulation. Enhanced TNF-α, IL-1β, IL-6, iNOS, SOCS1 and Arginase 1 were only present in the hippocampus of 9-month-old animals, though elevation of HMGB1 and reduction of miR-146a and miR-124 were common features in the hippocampus and cortex regions. miR-155 increased early in the cortex and later in both regions, supporting its potential as a biomarker. Candidate downregulated target genes by cortical miR-155 included Foxo3, Runx2 and CEBPβ at 3 months and Foxo3, Runx2 and Socs1 at 9 months, which are implicated in cell survival, but also in Aβ pathology and microglia/astrocyte dysfunction. Data provide new insights across AD state trajectory, with divergent microglia phenotypes and inflammatory-associated features, and identify critical targets for drug discovery and combinatorial therapies.

Physiological clearance of Aβ by spleen and splenectomy aggravates Alzheimer-type pathogenesis

Background

A previous study demonstrated that nearly 40%–60% of brain Aβ flows out into the peripheral system for clearance. However, where and how circulating Aβ is cleared in the periphery remains unclear. The spleen acts as a blood filter and an immune organ. The aim of the present study was to investigate the role of the spleen in the clearance of Aβ in the periphery.

Methods

We investigated the physiological clearance of Aβ by the spleen and established a mouse model of AD and spleen excision by removing the spleens of APP/PS1 mice to investigate the effect of splenectomy on AD mice.

Results

We found that Aβ levels in the splenic artery were higher than those in the splenic vein, suggesting that circulating Aβ is cleared when blood flows through the spleen. Next, we found that splenic monocytes/macrophages could take up Aβ directly in vivo and in vitro. Splenectomy aggravated behaviour deficits, brain Aβ burden and AD‐related pathologies in AD mice.

Conclusion

Our study reveals for the first time that the spleen exerts a physiological function of clearing circulating Aβ in the periphery. Our study also suggests that splenectomy, which is a routine treatment for splenic rupture and hypersplenism, might accelerate the development of AD.

Targeting the miRNA-155/TNFSF10 network restrains inflammatory response in the retina in a mouse model of Alzheimer's disease

Age-related disorders, such as Alzheimer’s disease (AD) and age-related macular degeneration (AMD) share common features such as amyloid-β (Aβ) protein accumulation. Retinal deposition of Aβ aggregates in AMD patients has suggested a potential link between AMD and AD. In the present study, we analyzed the expression pattern of a focused set of miRNAs, previously found to be involved in both AD and AMD, in the retina of a triple transgenic mouse model of AD (3xTg-AD) at different time-points. Several miRNAs were differentially expressed in the retina of 3xTg-AD mice, compared to the retina of age-matched wild-type (WT) mice. In particular, bioinformatic analysis revealed that miR-155 had a central role in miRNA-gene network stability, regulating several pathways, including apoptotic and inflammatory signaling pathways modulated by TNF-related apoptosis-inducing ligand (TNFSF10). We showed that chronic treatment of 3xTg-AD mice with an anti-TNFSF10 monoclonal antibody was able to inhibit the retinal expression of miR-155, which inversely correlated with the expression of its molecular target SOCS-1. Moreover, the fine-tuned mechanism related to TNFSF10 immunoneutralization was tightly linked to modulation of TNFSF10 itself and its death receptor TNFRSF10B, along with cytokine production by microglia, reactive gliosis, and specific AD-related neuropathological hallmarks (i.e., Aβ deposition and Tau phosphorylation) in the retina of 3xTg-AD mice. In conclusion, immunoneutralization of TNFSF10 significantly preserved the retinal tissue in 3xTg-AD mice, suggesting its potential therapeutic application in retinal degenerative disorders.

Comparative Transcriptome Analysis of the Expression of Antioxidant and Immunity Genes in the Spleen of a Cyanidin 3-O-Glucoside-Treated Alzheimer's Mouse Model

Cyanidin 3-O-glucoside (C3G) is a well-known antioxidant found as a dietary anthocyanin in different fruits and vegetables. It has protective and therapeutic effects on various diseases. It can reduce neuronal death from amyloid-beta (Aβ)-induced toxicity and promote the inhibition of Aβ fibrillization. Antioxidant and immune modulation might play a critical role in the properties of C3G against Alzheimer's disease (AD) and other diseases. However, limited studies have been performed on the mechanism involved in the effect of C3G through transcriptome analysis. Thus, the objective of this study was to perform comparative transcriptome analysis of the spleen to determine gene expression profiles of wild-type mice (C57BL/6J Jms), an Alzheimer's mouse model (APPswe/PS1dE9 mice), and a C3G-treated Alzheimer's mouse model. Differentially expressed antioxidant, immune-related, and AD pathways genes were identified in the treated group. The validation of gene expression data via RT-PCR studies further supported the current findings. Six important antioxidant genes (S100a8, S100a9, Prdx2, Hp, Mpst, and Prxl2a) and a high number of immune-related genes were found to be upregulated in the treatment groups, suggesting the possible antioxidant and immunomodulatory mechanisms of C3G, respectively. Further studies are strongly recommended to elucidate the precise role of these essential genes and optimize the therapeutic function of C3G in AD and other disease conditions.

IntelliCage Automated Behavioral Phenotyping Reveals Behavior Deficits in the 3xTg-AD Mouse Model of Alzheimer's Disease Associated With Brain Weight

Transgenic rodent models of Alzheimer’s disease (AD) were designed to study mechanisms of pathogenesis and connect these mechanisms with cognitive decline. Measurements of cognition in rodents can be confounded, however, by human handling and interaction; the IntelliCage was created to circumvent these issues while measuring various facets of cognition in a social environment with water consumption as the primary motivator for task completion. Here, for the first time, we examined the behavioral performance of 3xTg-AD mice in the IntelliCage. Seven- to 9-month-old female 3xTg-AD and non-transgenic (NonTg) mice were tested for 29 days in the IntelliCage to measure prefrontal cortical and hippocampal function. We found that a higher percentage of NonTg mice (86.96%) were able to successfully complete the training (adaptation) phases compared to their 3xTg-AD (57.14%) counterparts. Furthermore, the 3xTg-AD mice showed impairments in attention and working memory. Interestingly, we found that differences in body and brain weight between NonTg and 3xTg-AD mice were associated with whether mice were able to complete the IntelliCage tasks. 3xTg-AD mice that completed IntelliCage tasks had lower cortical insoluble amyloid-β₄₀ fractions than their 3xTg-AD counterparts who failed to complete the tasks. Collectively, these results demonstrate deficits in cognition in the 3xTg-AD mouse and inform scientists of important factors to consider when testing this transgenic model in the IntelliCage.

Repurposing Immunomodulatory Imide Drugs (IMiDs) in Neuropsychiatric and Neurodegenerative Disorders

Neuroinflammation represents a common trait in the pathology and progression of the major psychiatric and neurodegenerative disorders. Neuropsychiatric disorders have emerged as a global crisis, affecting 1 in 4 people, while neurological disorders are the second leading cause of death in the elderly population worldwide (WHO, 2001; GBD 2016 Neurology Collaborators, 2019). However, there remains an immense deficit in availability of effective drug treatments for most neurological disorders. In fact, for disorders such as depression, placebos and behavioral therapies have equal effectiveness as antidepressants. For neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease, drugs that can prevent, slow, or cure the disease have yet to be found. Several non-traditional avenues of drug target identification have emerged with ongoing neurological disease research to meet the need for novel and efficacious treatments. Of these novel avenues is that of neuroinflammation, which has been found to be involved in the progression and pathology of many of the leading neurological disorders. Neuroinflammation is characterized by glial inflammatory factors in certain stages of neurological disorders. Although the meta-analyses have provided evidence of genetic/proteomic upregulation of inflammatory factors in certain stages of neurological disorders. Although the mechanisms underpinning the connections between neuroinflammation and neurological disorders are unclear, and meta-analysis results have shown high sensitivity to factors such as disorder severity and sample type, there is significant evidence of neuroinflammation associations across neurological disorders. In this review, we summarize the role of neuroinflammation in psychiatric disorders such as major depressive disorder, generalized anxiety disorder, post-traumatic stress disorder, and bipolar disorder, as well as in neurodegenerative disorders, such as Parkinson's disease and Alzheimer's disease, and introduce current research on the potential of immunomodulatory imide drugs (IMiDs) as a new treatment strategy for these disorders.

Molecular mechanisms in Alzheimer's disease and the impact of physical exercise with advancements in therapeutic approaches

Alzheimer's disease (AD) is one of the most common, severe neurodegenerative brain disorder characterized by the accumulation of amyloid-beta plaques, neurofibrillary tangles in the brain causing neural disintegration, synaptic dysfunction, and neuronal death leading to dementia. Although many US-FDA-approved drugs like Donepezil, Rivastigmine, Galantamine are available in the market, their consumption reduces only the symptoms of the disease but fails in potency to cure the disease. This disease affects many individuals with aging. Combating the disease tends to be very expensive. This review focuses on biochemical mechanisms in the neuron both at normal and AD state with relevance to the tau hypothesis, amyloid hypothesis, the risk factors influencing dementia, oxidative stress, and neuroinflammation altogether integrated with neurodegeneration. A brief survey is carried out on available biomarkers in the diagnosis of the disease, drugs used for the treatment, and the challenges in approaching therapeutic targets in inhibiting the disease pathologies. This review conjointly assesses the demerits with the inefficiency of drugs to reach targets, their side effects, and toxicity. Optimistically, this review directs on the advantageous strategies in using nanotechnology-based drug delivery systems to cross the blood-brain barrier for improving the efficacy of drugs combined with a novel neuronal stem cell therapy approach. Determinately, this review aims at the natural, non-therapeutic healing impact of physical exercise on different model organisms and the effect of safe neuromodulation treatments using repetitive Transcranial Magnetic Stimulation (rTMS), transcranial Electrical Stimulation (tES) in humans to control the disease pathologies prominent in enhancing the synaptic function.

TRAIL Mediates Neuronal Death in AUD: A Link between Neuroinflammation and Neurodegeneration

Although the cause of progressive neurodegeneration is often unclear, neuronal death can occur through several mechanisms. In conditions such as Alzheimer’s or alcohol use disorder (AUD), Toll-like receptor (TLR) induction is observed with neurodegeneration. However, links between TLR activation and neurodegeneration are lacking. We report a role of apoptotic neuronal death in AUD through TLR7-mediated induction of death receptor signaling. In postmortem human cortex, a two-fold increase in apoptotic terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining in neurons was found in AUD versus controls. This occurred with the increased expression of TLR7 and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) death receptors. Binge ethanol treatment in C57BL/6 mice increased TLR7 and induced neuronal apoptosis in cortical regions that was blocked by TLR7 antagonism. Mechanistic studies in primary organotypic brain slice culture (OBSC) found that the inhibition of TLR7 and its endogenous ligand let-7b blocked ethanol-induced neuronal cell death. Both IMQ and ethanol induced the expression of TRAIL and its death receptor. In addition, TRAIL-neutralizing monoclonal antibodies blocked both imiquimod (IMQ) and ethanol induced neuronal death. These findings implicate TRAIL as a mediator of neuronal apoptosis downstream of TLR7 activation. TLR7 and neuronal apoptosis are implicated in other neurodegenerative diseases, including Alzheimer’s disease. Therefore, TRAIL may represent a therapeutic target to slow neurodegeneration in multiple diseases.

Parvalbumin interneuron-mediated neural disruption in an animal model of postintensive care syndrome: prevention by fluoxetine

Postintensive care syndrome (PICS) is defined as a new or worsening impairment in cognition, mental health, and physical function after critical illness and persisting beyond hospitalization, which is associated with reduced quality of life and increased mortality. Recently, we have developed a clinically relevant animal model of PICS based on two-hit hypothesis. However, the underlying mechanism remains unclear. Accumulating evidence has demonstrated that hippocampal GABAergic interneuron dysfunction is implicated in various mood disorders induced by stress. Thus, this study investigated the role of hippocampal GABAergic interneurons and relevant neural activities in an animal model of PICS. In addition, we tested whether fluoxetine treatment early following combined stress can prevent these anatomical and behavioral pathologies. In the present study, we confirmed our previous study that this PICS model displayed reproducible anxiety- and depression like behavior and cognitive impairments, which resembles clinical features of human PICS. This behavioral state is accompanied by hippocampal neuroinflammation, reduced parvalbumin (PV) expression, and decreased theta and gamma power. Importantly, chronic fluoxetine treatment reversed most of these abnormities. In summary, our study provides additional evidence that PV interneuron-mediated hippocampal network activity disruption might play a key role in the pathology of PICS, while fluoxetine offers protection via modulation of the hippocampal PV interneuron and relevant network activities.

Differential effects of chronic immunosuppression on behavioral, epigenetic, and Alzheimer's disease-associated markers in 3xTg-AD mice

BACKGROUND

Circulating autoantibodies and sex-dependent discrepancy in prevalence are unexplained phenomena of Alzheimer's disease (AD). Using the 3xTg-AD mouse model, we reported that adult males show early manifestations of systemic autoimmunity, increased emotional reactivity, enhanced expression of the histone variant macroH2A1 in the cerebral cortex, and loss of plaque/tangle pathology. Conversely, adult females display less severe autoimmunity and retain their AD-like phenotype. This study examines the link between immunity and other traits of the current 3xTg-AD model.

METHODS

Young 3xTg-AD and wild-type mice drank a sucrose-laced 0.4 mg/ml solution of the immunosuppressant cyclophosphamide on weekends for 5 months. After behavioral phenotyping at 2 and 6 months of age, we assessed organ mass, serologic markers of autoimmunity, molecular markers of early AD pathology, and expression of genes associated with neurodegeneration.

RESULTS

Chronic immunosuppression prevented hematocrit drop and reduced soluble Aβ in 3xTg-AD males while normalizing the expression of histone variant macroH2A1 in 3xTg-AD females. This treatment also reduced hepatosplenomegaly, lowered autoantibody levels, and increased the effector T cell population while decreasing the proportion of regulatory T cells in both sexes. Exposure to cyclophosphamide, however, neither prevented reduced brain mass and BDNF expression nor normalized increased tau and anxiety-related behaviors.

CONCLUSION

The results suggest that systemic autoimmunity increases soluble Aβ production and affects transcriptional regulation of macroH2A1 in a sex-related manner. Despite the complexity of multisystem interactions, 3xTg-AD mice can be a useful in vivo model for exploring the regulatory role of autoimmunity in the etiology of AD-like neurodegenerative disorders.

Repositioning of Immunomodulators: A Ray of Hope for Alzheimer's Disease?

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder characterized by cognitive decline and by the presence of amyloid β plaques and neurofibrillary tangles in the brain. Despite recent advances in understanding its pathophysiological mechanisms, to date, there are no disease-modifying therapeutic options, to slow or halt the evolution of neurodegenerative processes in AD. Current pharmacological treatments only transiently mitigate the severity of symptoms, with modest or null overall improvement. Emerging evidence supports the concept that AD is affected by the impaired ability of the immune system to restrain the brain's pathology. Deep understanding of the relationship between the nervous and the immune system may provide a novel arena to develop effective and safe drugs for AD treatment. Considering the crucial role of inflammatory/immune pathways in AD, here we discuss the current status of the immuno-oncological, immunomodulatory and anti-TNF-α drugs which are being used in preclinical studies or in ongoing clinical trials by means of the drug-repositioning approach.

Hypoperfusion is a potential inducer of immunosuppressive network in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease which causes a non-reversible cognitive impairment and dementia. The primary cause of late-onset AD remains unknown although its pathology was discovered over a century ago. Recently, the vascular hypothesis of AD has received backing from evidence emerging from neuroimaging studies which have revealed the presence of a significant hypoperfusion in the brain regions vulnerable to AD pathology. In fact, hypoxia can explain many of the pathological changes evident in AD pathology, e.g. the deposition of β-amyloid plaques and chronic low-grade inflammation. Hypoxia-inducible factor-1α (HIF-1α) stimulates inflammatory responses and modulates both innate and adaptive immunity. It is known that hypoxia-induced inflammation evokes compensatory anti-inflammatory response involving tissue-resident microglia/macrophages and infiltrated immune cells. Hypoxia/HIF-1α induce immunosuppression by (i) increasing the expression of immunosuppressive genes, (ii) stimulating adenosinergic signaling, (iii) enhancing aerobic glycolysis, i.e. lactate production, and (iv) augmenting the secretion of immunosuppressive exosomes. Interestingly, it seems that these common mechanisms are also involved in the pathogenesis of AD. In AD pathology, an enhanced immunosuppression appears, e.g. as a shift in microglia/macrophage phenotypes towards the anti-inflammatory M2 phenotype and an increase in the numbers of regulatory T cells (Treg). The augmented anti-inflammatory capacity promotes the resolution of acute inflammation but persistent inflammation has crucial effects not only on immune cells but also harmful responses to the homeostasis of AD brain. I will examine in detail the mechanisms of the hypoperfusion/hypoxia-induced immunosuppressive state in general and especially, in its association with AD pathogenesis. These immunological observations support the vascular hypothesis of AD pathology.

The immune system on the TRAIL of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia, characterized by progressive degeneration and loss of neurons in specific regions of the central nervous system. Chronic activation of the immune cells resident in the brain, peripheral immune cell trafficking across the blood-brain barrier, and release of inflammatory and neurotoxic factors, appear critical contributors of the neuroinflammatory response that drives the progression of neurodegenerative processes in AD. As the neuro-immune network is impaired in course of AD, this review is aimed to point out the essential supportive role of innate and adaptive immune response either in normal brain as well as in brain recovery from injury. Since a fine-tuning of the immune response appears crucial to ensure proper nervous system functioning, we focused on the role of the TNF superfamily member, TNF-related apoptosis-inducing ligand (TRAIL), which modulates both the innate and adaptive immune response in the pathogenesis of several immunological disorders and, in particular, in AD-related neuroinflammation. We here summarized mounting evidence of potential involvement of TRAIL signaling in AD pathogenesis, with the aim to provide clearer insights about potential novel therapeutic approaches in AD.

Association of early-onset Alzheimer's disease with germline-generated high affinity self-antigen load

Self-antigen presentation outside the central nervous system has crucial role regarding self-proteins tolerance and autoimmunity, leading to neuroinflammation. Self-antigen with strong-binding affinity is considered to be pathogenic. We aim to investigate whether strong-binding affinity self-antigen load is associated with early/late-onset Alzheimer's disease (AD). A total of 54 AD samples (22 early-onset, 32 late-onset) underwent next-generation sequencing (NGS) for whole-exome sequencing. Genotypes of HLA class I genes and germline mutations were obtained for estimation of the binding affinity and number of self-antigens. For each patient, self-antigen load was estimated by adding up the number of self-antigens with strong-binding affinity. Self-antigen load of early-onset AD was significantly higher than late-onset AD (mean ± SD: 6115 ± 2430 vs 4373 ± 2492; p = 0.011). An appropriate cutoff value 2503 for dichotomizing self-antigen load was obtained by receiver operating characteristic (ROC) curve analysis. Patients were then dichotomized into high or low self-antigen load groups in the binary multivariate logistic regression analysis. Adjusted odds ratio of the high self-antigen load (>2503) was 14.22 (95% CI, 1.22-165.70; p = 0.034) after controlling other covariates including gender, education, ApoE status, and baseline CDR score. This is the first study using NGS to investigate germline mutations generated self-antigen load in AD. As strong-binding affinity self-antigen is considered to be pathogenic in neuroinflammation, our finding indicated that self-antigen load did have a role in the pathogenesis of AD owing to its association with neuroinflammation. This finding may also contribute to further research regarding disease mechanism and development of novel biomarkers or treatment.

ER stress activates immunosuppressive network: implications for aging and Alzheimer's disease

The endoplasmic reticulum (ER) contains stress sensors which recognize the accumulation of unfolded proteins within the lumen of ER, and subsequently these transducers stimulate the unfolded protein response (UPR). The ER sensors include the IRE1, PERK, and ATF6 transducers which activate the UPR in an attempt to restore the quality of protein folding and thus maintain cellular homeostasis. If there is excessive stress, UPR signaling generates alarmins, e.g., chemokines and cytokines, which activate not only tissue-resident immune cells but also recruit myeloid and lymphoid cells into the affected tissues. ER stress is a crucial inducer of inflammation in many pathological conditions. A chronic low-grade inflammation and cellular senescence have been associated with the aging process and many age-related diseases, such as Alzheimer’s disease. Currently, it is known that immune cells can exhibit great plasticity, i.e., they are able to display both pro-inflammatory and anti-inflammatory phenotypes in a context-dependent manner. The microenvironment encountered in chronic inflammatory conditions triggers a compensatory immunosuppression which defends tissues from excessive inflammation. Recent studies have revealed that chronic ER stress augments the suppressive phenotypes of immune cells, e.g., in tumors and other inflammatory disorders. The activation of immunosuppressive network, including myeloid-derived suppressor cells (MDSC) and regulatory T cells (Treg), has been involved in the aging process and Alzheimer’s disease. We will examine in detail whether the ER stress-related changes found in aging tissues and Alzheimer’s disease are associated with the activation of immunosuppressive network, as has been observed in tumors and many chronic inflammatory diseases.