Microglial activation resulting from CD40-CD40L interaction after beta-amyloid stimulation

Platelets and inter-cellular communication in immune responses: Dialogue with both professional and non-professional immune cells

Platelets, derived from bone marrow megakaryocytes, are essential for vascular integrity and play multifaceted roles in both physiological and pathological processes within the vasculature. Despite their small size and absence of a nucleus, platelets are increasingly recognized for their diverse immune functions. Recent research highlights their pivotal role in interactions with various immune cells, including professional cells like macrophages, dendritic cells, natural killer cells, T cells, and B cells, influencing host immune responses. Platelets also engage with non-professional immune cells, contributing to immune responses and structural maintenance, particularly in conditions like inflammation and atherosclerosis. This review underscores the emerging significance of platelets as potent immune cells, elucidating their interactions with the immune system. We explore the mechanisms of platelet activation, leading to diverse functions, such as aggregation, immunity, activation of other immune cells, and pathogen clearance. Platelets have become the predominant immune cells in circulation, involved in chronic inflammation, responses to infections, and autoimmune disorders. Their immunological attributes, including bioactive granule molecules and immune receptors, contribute to their role in immune responses. Unlike professional antigen-presenting cells, platelets process and present antigens through an MHC-I-dependent pathway, initiating T-cell immune responses. This review illuminates the unique features of platelets and their central role in modulating host immune responses in health and disease.

Inhibition of P2X4 and P2X7 receptors improves histological and behavioral outcomes after experimental traumatic brain injury in rats

Release of large amounts of adenosine triphosphate (ATP), a gliotransmitter, into the extracellular space by traumatic brain injury (TBI) is considered to activate the microglia followed by release of inflammatory cytokines resulting in excessive inflammatory response that induces secondary brain injury. The present study investigated whether antagonists of ATP receptors (P2X4 and/or P2X7) on microglia are beneficial for reducing the post-injury inflammatory response that leads to secondary injury, a prognostic aggravation factor of TBI. Adult male Sprague-Dawley rats were subjected to cortical contusion injury (CCI) and randomly assigned to injury and drug treatment conditions, as follows: i) No surgical intervention (naïve group); ii) dimethyl sulfoxide treatment after CCI (CCI-control group); iii) 5-BDBD (antagonist of P2X4 receptor) treatment after CCI (CCI-5-BDBD group); iv) CCI-AZ11645373 (antagonist of P2X7 receptor) treatment after CCI (CCI-AZ11645373 group); v) or 5-BDBD and AZ11645373 treatment after CCI (CCI-5-BDBD + AZ11645373 group). In the CCI-5-BDBD, CCI-AZ11645373, and CCI-5-BDBD + AZ11645373 groups, expression of activated microglia was suppressed in the ipsilateral cortex and hippocampus 3 days after the CCI. Western blotting with ionized calcium-binding adaptor molecule 1 antibody revealed that administration of CCI-5-BDBD and/or CCI-AZ11645373 suppressed expression of microglia and reduced expression of inflammatory cytokine mRNA 3 days after the CCI. Furthermore, the plus maze test, which reflects the spatial memory function and involves the hippocampal function, showed improvement 28 days after secondary injury to the hippocampus. These findings confirmed that blocking the P2X4 and P2X7 receptors, which are ATP receptors central in gliotransmission, suppresses microglial activation and subsequent cytokine expression after brain injury, and demonstrates the potential as an effective treatment for reducing secondary brain injury.

Eugenol relieves the pathological manifestations of Alzheimer's disease in 5×FAD mice

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by the accumulation of amyloid-β (Aβ) and excessive neuroinflammation, resulting in neuronal cell death and cognitive impairments. Eugenol, a phenylpropene, is the main component of Syzygium aromaticum L. (Myrtaceae) and has multiple therapeutic effects, including neuroprotective and anti-inflammatory effects, through multimodal mechanisms.

PURPOSE

We aimed to investigate the effect of eugenol on AD pathologies using a 5× familiar AD (5×FAD) mouse model.

METHODS

Eight-month-old 5×FAD and wild-type mice were administered with eugenol (10 or 30 mg/kg/day, p.o) for 2 months. Y-maze and Morris water maze tests were performed to assess the cognitive function of mice. After the behavioral test, molecular analysis was conducted to investigate the therapeutic mechanism of eugenol.

RESULTS

Our findings indicate that eugenol treatment effectively mitigated cognitive impairments in 5×FAD mice. This beneficial effect was associated with a decrease in AD pathologies, including neuronal cell loss and Aβ deposition. Specifically, eugenol inhibited necroptosis activation and increased microglial phagocytosis, which were the underlying mechanisms for the observed reductions in neuronal cell loss and Aβ deposition, respectively.

CONCLUSION

Overall, our data suggest that eugenol would be a potential therapeutic candidate for AD.

A Function of Amyloid-β in Mediating Activity-Dependent Axon/Synapse Competition May Unify Its Roles in Brain Physiology and Pathology

Amyloid-β protein precursor (AβPP) gives rise to amyloid-β (Aβ), a peptide at the center of Alzheimer's disease (AD). AβPP, however, is also an ancient molecule dating back in evolution to some of the earliest forms of metazoans. This suggests a possible ancestral function that may have been obscured by those that evolve later. Based on literature from the functions of Aβ/AβPP in nervous system development, plasticity, and disease, to those of anti-microbial peptides (AMPs) in bacterial competition as well as mechanisms of cell competition uncovered first by Drosophila genetics, I propose that Aβ/AβPP may be part of an ancient mechanism employed in cell competition, which is subsequently co-opted during evolution for the regulation of activity-dependent neural circuit development and plasticity. This hypothesis is supported by foremost the high similarities of Aβ to AMPs, both of which possess unique, opposite (i.e., trophic versus toxic) activities as monomers and oligomers. A large body of data further suggests that the different Aβ oligomeric isoforms may serve as the protective and punishment signals long predicted to mediate activity-dependent axonal/synaptic competition in the developing nervous system and that the imbalance in their opposite regulation of innate immune and glial cells in the brain may ultimately underpin AD pathogenesis. This hypothesis can not only explain the diverse roles observed of Aβ and AβPP family molecules, but also provide a conceptual framework that can unify current hypotheses on AD. Furthermore, it may explain major clinical observations not accounted for and identify approaches for overcoming shortfalls in AD animal modeling.

Lack of Cathepsin D in the central nervous system results in microglia and astrocyte activation and the accumulation of proteinopathy-related proteins

Neuronal ceroid lipofuscinosis is one of many neurodegenerative storage diseases characterized by excessive accumulation of lipofuscins. CLN10 disease, an early infantile neuronal ceroid lipofuscinosis, is associated with a gene that encodes cathepsin D (CtsD), one of the major lysosomal proteases. Whole body CtsD-knockout mice show neurodegenerative phenotypes with the accumulation of lipofuscins in the brain and also show defects in other tissues including intestinal necrosis. To clarify the precise role of CtsD in the central nervous system (CNS), we generated a CNS-specific CtsD-knockout mouse (CtsD-CKO). CtsD-CKO mice were born normally but developed seizures and their growth stunted at around postnatal day 23 ± 1. CtsD-CKO did not exhibit apparent intestinal symptoms as those observed in whole body knockout. Histologically, autofluorescent materials were detected in several areas of the CtsD-CKO mouse's brain, including: thalamus, cerebral cortex, hippocampus, and cerebellum. Expression of ubiquitin and autophagy-associated proteins was also increased, suggesting that the autophagy-lysosome system was impaired. Microglia and astrocytes were activated in the CtsD-CKO thalamus, and inducible nitric oxide synthase (iNOS), an inflammation marker, was increased in the microglia. Interestingly, deposits of proteinopathy-related proteins, phosphorylated α-synuclein, and Tau protein were also increased in the thalamus of CtsD-CKO infant mice. Considering these results, we propose thatt the CtsD-CKO mouse is a useful mouse model to investigate the contribution of cathepsin D to the early phases of neurodegenerative diseases in relation to lipofuscins, proteinopathy-related proteins and activation of microglia and astrocytes.

Transcriptomic Profile of Blood–Brain Barrier Remodeling in Cerebral Amyloid Angiopathy

Cerebral amyloid angiopathy (CAA) is a small vessel disease characterized by amyloid β (Aβ) peptide deposition within the walls of medium to small-caliber blood vessels, cerebral microhemorrhage, and blood–brain barrier (BBB) leakage. It is commonly associated with late-stage Alzheimer’s disease. BBB dysfunction is indicated as a pathological substrate for CAA progression with hyperpermeability, enhancing the extravasation of plasma components and inducing neuroinflammation, further worsening BBB injury and contributing to cognitive decline. Although significant effort has been made in defining the gene mutations and risk factors involved in microvascular alterations with vascular dementia and Alzheimer’s disease, the intra- and intercellular pathogenic mechanisms responsible for vascular hyperpermeability are still largely unknown. The present study aimed to elucidate the transcriptional profile of the cerebral microvessels (BBB) in a murine model with CAA vasculopathy to define potential causes and underlying mechanisms of BBB injury. A comprehensive RNA sequencing analysis was performed of CAA vasculopathy in Tg-SwDI mice at 6 and 18 months in comparison to age-matched wildtype controls to examine how age and amyloid accumulation impact the transcriptional signature of the BBB. Results indicate that Aβ has a critical role in triggering brain endothelial cell and BBB dysfunction in CAA vasculopathy, causing an intense proinflammatory response, impairing oxidative metabolism, altering the coagulation status of brain endothelial cells, and remodeling barrier properties. The proinflammatory response includes both adaptive and innate immunity, with pronounced induction of genes that regulate macrophage/microglial activation and chemokines/adhesion molecules that support T and B cell transmigration. Age has an important impact on the effects of Aβ, increasing the BBB injury in CAA vasculopathy. However, early inflammation, particularly microglia/macrophage activation and the mediators of B lymphocytes’ activities are underlying processes of BBB hyperpermeability and cerebral microbleeds in the early stage of CAA vasculopathy. These findings reveal a specific profile of the CAA-associated BBB injury that leads to a full progression of CAA.

Innate Immune Cell Death in Neuroinflammation and Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder molecularly characterized by the formation of amyloid β (Aβ) plaques and type 2 microtubule-associated protein (Tau) abnormalities. Multiple studies have shown that many of the brain’s immunological cells, specifically microglia and astrocytes, are involved in AD pathogenesis. Cells of the innate immune system play an essential role in eliminating pathogens but also regulate brain homeostasis and AD. When activated, innate immune cells can cause programmed cell death through multiple pathways, including pyroptosis, apoptosis, necroptosis, and PANoptosis. The cell death often results in the release of proinflammatory cytokines that propagate the innate immune response and can eliminate Aβ plaques and aggregated Tau proteins. However, chronic neuroinflammation, which can result from cell death, has been linked to neurodegenerative diseases and can worsen AD. Therefore, the innate immune response must be tightly balanced to appropriately clear these AD-related structural abnormalities without inducing chronic neuroinflammation. In this review, we discuss neuroinflammation, innate immune responses, inflammatory cell death pathways, and cytokine secretion as they relate to AD. Therapeutic strategies targeting these innate immune cell death mechanisms will be critical to consider for future preventive or palliative treatments for AD.

Early metabolic impairment as a contributor to neurodegenerative disease: Mechanisms and potential pharmacological intervention

The metabolic syndrome comprises a family of clinical and laboratory findings, including insulin resistance, hyperglycemia, hypertriglyceridemia, low high-density lipoprotein cholesterol levels, and hypertension, in addition to central obesity. The syndrome confers a high risk of cardiovascular mortality. Indeed, metabolic dysfunction has been shown to cause a direct insult to smooth muscle and endothelial components of the vasculature, which leads to vascular dysfunction and hyperreactivity. This, in turn, causes cerebral vasoconstriction and hypoperfusion, eventually contributing to cognitive deficits. Moreover, the metabolic syndrome disrupts key homeostatic processes in the brain, including apoptosis, autophagy, and neurogenesis. Impairment of such processes in the context of metabolic dysfunction has been implicated in the pathogenesis of neurodegenerative diseases, including Alzheimer, Parkinson, and Huntington diseases. The aim of this review is to elucidate the role that the metabolic syndrome plays in the pathogenesis of the latter disorders, with a focus on the role of perivascular adipose inflammation in the peripheral-to-central transduction of the inflammatory insult. This review delineates common signaling pathways that contribute to these pathologies. Moreover, the role of therapeutic agents aimed at treating the metabolic syndrome, as well as their risk factors that interfere with the aforementioned pathways, are discussed as potential interventions for neurodegenerative diseases.

Microglia Polarization in Alzheimer's Disease: Mechanisms and a Potential Therapeutic Target

Neuroinflammation regulated by microglia is one of the important factors involved in the pathogenesis of Alzheimer’s disease (AD). Activated microglia exhibited phenotypes termed as M1 and M2 phenotypes separately. M1 microglia contribute to the development of inflammation via upregulating pro-inflammatory cytokines, while M2 microglia exert anti-inflammation effects through enhancing the expression of anti-inflammation factors. Moreover, M1 and M2 microglia could be mutually transformed under various conditions. Both M1 and M2 microglia are implicated in AD. Amyloid-β (Aβ) and hyperphosphorylated tau are two major components of AD pathological hallmarks, neuritic plaques, and neurofibrillary tangles. Both Aβ and hyperphosphorylated tau were involved in microglial activation and subsequent inflammation, which further contribute to neuronal and synaptic loss in AD. In this review, we summarized the roles of M1 and M2 microglia in AD and underlying mechanisms, which will provide an insight into the role of microglia in the pathogenesis of AD and highlight the therapeutic potential of modulating microglia.

Dementia-associated changes of immune cell composition within the cerebrospinal fluid

Inflammation and alterations in essential protein structures in the brain might also change the cellular distribution in the cerebrospinal fluid (CSF).

Using flow cytometry, we analyzed cell populations of the innate and adaptive immune system associated with the most frequent forms of dementias. We included patients with mild cognitive impairment (MCI; N ​= ​33), Alzheimer’s disease (AD; N ​= ​90), vascular dementia (VD; N ​= ​35) and frontotemporal dementia (FTD; N ​= ​17) at the time of diagnosis, before onset of treatment and 11 elderly non-demented individuals. Dependent on the form of dementia, an increased frequency of CD14⁺ monocytes, NK cells and NKT cells was measured. Within the T cell population, a dementia-associated shift from central memory towards (late-stage) effector cells was detected. T cells and NKT cells were correlated with MMSE, NK and NKT cells were correlated with ptau, CD14⁺ monocytes and NK cells were correlated with Amyloid-β 1–40.

Our data suggest that each investigated immune cell type is involved in dementia-associated alterations within the CSF, possibly having distinct functions in their pathogenesis.

Downregulation of CD40L-CD40 attenuates seizure susceptibility and severity of seizures

Unregulated neuro-inflammation mediates seizures in temporal lobe epilepsy (TLE). Our aim was to determine the effect of CD40-CD40L activation in experimental seizures. CD40 deficient mice (CD40KO) and control mice (wild type, WT) received pentenyltetrazole (PTZ) or pilocarpine to evaluate seizures and status epilepticus (SE) respectively. In mice, anti-CD40L antibody was administered intranasally before PTZ. Brain samples from human TLE and post-seizure mice were processed to determine CD40-CD40L expression using histological and molecular techniques. CD40 expression was higher in hippocampus from human TLE and in cortical neurons and hippocampal neural terminals after experimental seizures. CD40-CD40L levels increased after seizures in the hippocampus and in the cortex. After SE, CD40L/CD40 levels increased in cortex and showed an upward trend in the hippocampus. CD40KO mice demonstrated reduction in seizure severity and in latency compared to WT mice. Anti-CD40L antibody limited seizure susceptibility and seizure severity. CD40L-CD40 interaction can serve as a target for an immuno-therapy for TLE.

Microarray Analysis Revealed Inflammatory Transcriptomic Changes after LSL60101 Treatment in 5XFAD Mice Model

I2-IR have been found dysregulated in patients with neurodegenerative diseases, such as Alzheimer’s disease (AD), in which the importance of neuroinflammation in the establishment and maintenance of cognitive decline is well-documented. To research the implication of I2-IR in neuroinflammatory pathways altered in AD, we determined the expression profile of genes associated with inflammation in the 5XFAD model treated with LSL60101, a well-established I2-IR ligand. Thus, we performed a qPCR array containing 84 inflammation-related genes. Hierarchical clustering analysis revealed three gene clusters, suggesting that treatment with LSL60101 affects the gene expression associated with inflammation in the 5XFAD model. Furthermore, we evaluated the functions of the three clusters; thereby performing a pathway enrichment analysis using the GO database. As we expected, clusters 2 and 3 showed alterations in the inflammatory response, chemotaxis and the chemokine-mediated signaling pathway, among others. To validate previous results from the gene profiling analysis, the expression levels of a representative subset of mRNAs were selected according to the intensity of the observed changes and their biological relevance. Interestingly, changes induced by LSL60101 in the 5XFAD model were validated for several genes. These results suggest that treatment with LSL60101 in the 5XFAD model reverses the inflammatory process during the development of AD.

An evaluation of the amyloid cascade model using in vivo positron emission tomographic imaging

AIM

The amyloid cascade hypothesis posits that the accumulation of amyloid β (Aβ) is the triggering factor for Alzheimer's disease, which consecutively induces aggregation of tau, synaptic loss, and cell death. Most experimental and clinical evidence supports this model, but the available data are largely qualitative. Here, we tested the amyloid cascade hypothesis by using in vivo evaluation of positron emission tomography and magnetic resonance imaging.

METHODS

Path analysis was used to estimate the relationships among Aβ accumulation (PiB standardized uptake value ratio (SUVR)), tau aggregation and its related neuroinflammation (THK5351 SUVR), grey matter atrophy in the medial temporal region, and memory function in Aβ-positive subjects. We also performed additional regression analyses to evaluate the effect of Aβ on the toxicity of tau aggregation/neuroinflammation.

RESULTS

Path analysis supported our hypothesized model: Aβ accumulation affected tau aggregation/neuroinflammation in the medial temporal region, and these pathological changes caused of the grey matter atrophy and memory dysfunction. In separate regression analyses, THK5351 SUVR had a significant effect on grey matter atrophy only in PiB-positive subjects. The analysis of the interaction effect showed that the effects of THK5351 SUVR on grey matter atrophy were significantly different between PiB-positive and PiB-negative groups. When we included the effect of being an apolipoprotein E ε4 carrier as a covariate, the interaction effect remained significant.

CONCLUSION

Our in vivo evaluation of positron emission tomographic and magnetic resonance imaging data supported the amyloid cascade hypothesis. In addition, it indicated that Aβ not only accelerates tau aggregation/neuroinflammation but promotes its toxicity. Our findings showed the importance of understanding the role and therapeutic potential of the interaction between amyloid and tau aggregation/neuroinflammation in Alzheimer's disease.

Platelets as Mediators of Neuroinflammation and Thrombosis

Beyond platelets function in hemostasis, there is emerging evidence to suggest that platelets contribute crucially to inflammation and immune responses. Therefore, considering the detrimental role of inflammatory conditions in severe neurological disorders such as multiple sclerosis or stroke, this review outlines platelets involvement in neuroinflammation. For this, distinct mechanisms of platelet-mediated thrombosis and inflammation are portrayed, focusing on the interaction of platelet receptors with other immune cells as well as brain endothelial cells. Furthermore, we draw attention to the intimate interplay between platelets and the complement system as well as between platelets and plasmatic coagulation factors in the course of neuroinflammation. Following the thorough exposition of preclinical approaches which aim at ameliorating disease severity after inducing experimental autoimmune encephalomyelitis (a counterpart of multiple sclerosis in mice) or brain ischemia-reperfusion injury, the clinical relevance of platelet-mediated neuroinflammation is addressed. Thus, current as well as future propitious translational and clinical strategies for the treatment of neuro-inflammatory diseases by affecting platelet function are illustrated, emphasizing that targeting platelet-mediated neuroinflammation could become an efficient adjunct therapy to mitigate disease severity of multiple sclerosis or stroke associated brain injury.

Prevention of brain damage after traumatic brain injury by pharmacological enhancement of KCNQ (Kv7, "M-type") K+ currents in neurons

Nearly three million people in the USA suffer traumatic brain injury (TBI) yearly; however, there are no pre- or post-TBI treatment options available. KCNQ2-5 voltage-gated K⁺ channels underlie the neuronal "M current", which plays a dominant role in the regulation of neuronal excitability. Our strategy towards prevention of TBI-induced brain damage is predicated on the suggested hyper-excitability of neurons induced by TBIs, and the decrease in neuronal excitation upon pharmacological augmentation of M/KCNQ K⁺ currents. Seizures are very common after a TBI, making further seizures and development of epilepsy disease more likely. Our hypothesis is that TBI-induced hyperexcitability and ischemia/hypoxia lead to metabolic stress, cell death and a maladaptive inflammatory response that causes further downstream morbidity. Using the mouse controlled closed-cortical impact blunt TBI model, we found that systemic administration of the prototype M-channel "opener", retigabine (RTG), 30 min after TBI, reduces the post-TBI cascade of events, including spontaneous seizures, enhanced susceptibility to chemo-convulsants, metabolic stress, inflammatory responses, blood-brain barrier breakdown, and cell death. This work suggests that acutely reducing neuronal excitability and energy demand via M-current enhancement may be a novel model of therapeutic intervention against post-TBI brain damage and dysfunction.

Is Alzheimer's disease an inflammasomopathy?

Alzheimer's disease (AD) is the most common form of dementia in the elderly and, despite the tremendous efforts researchers have put into AD research, there are no effective options for prevention and treatment of the disease. The best way to reach this goal is to clarify the mechanisms involved in the onset and progression of AD. In the last few years the views about the drivers of AD have been changing and nowadays it is believed that neuroinflammation takes center stage in disease pathogenesis. Herein, we provide an overview about the role of neuroinflammation in AD describing the role of microglia and astroglia is this process. Then, we will debate the NLRP3 inflammasome putting the focus on its activation through the canonical, non-canonical and alternative pathways and the triggers involved herein namely endoplasmic reticulum stress, mitochondrial dysfunction, reactive oxygen species and amyloid β peptide. Data supporting the hypothesis that inflammasome-mediated peripheral inflammation may contribute to AD pathology will be presented. Finally, a brief discussion about the therapeutic potential of NLRP3 inflammasome modulation is also provided.

Pharmacological Treatment of Depression in Alzheimer's Disease: A Challenging Task

Besides the memory impairment, Alzheimer’s disease (AD) is often complicated by neuropsychiatric symptoms also known as behavioral and psychological symptoms of dementia, which occur in one-third of patients at an early stage of the disease. Although the relationship between depressive disorders and AD is debated, the question if depression is a prodromal symptom preceding cognitive deficits or an independent risk factor for AD is still unclear. Moreover, there is growing evidence reporting that conventional antidepressants are not effective in depression associated with AD and, therefore, there is an urgent need to understand the neurobiological mechanism underlying the resistance to the antidepressants. Another important question that remains to be addressed is whether the antidepressant treatment is able to modulate the levels of amyloid-β peptide (Aβ), which is a key pathological hallmark in AD. The present review summarizes the present knowledge on the link between depression and AD with a focus on the resistance of antidepressant therapies in AD patients. Finally, we have briefly outlined the preclinical and clinical evidences behind the possible mechanisms by which antidepressants modulate Aβ pathology. To our opinion, understanding the cellular processes that regulate Aβ levels may provide greater insight into the disease pathogenesis and might be helpful in designing novel selective and effective therapy against depression in AD.

Hypothesis: cerebrospinal fluid protein markers suggest a pathway toward symptomatic resilience to AD pathology

INTRODUCTION

We sought biological pathways that explained discordance between Alzheimer's disease (AD) pathology and symptoms.

METHODS

In 306 Alzheimer's Disease Neuroimaging Initiative (ADNI)-1 participants across the AD clinical spectrum, we investigated association between cognitive outcomes and 23 cerebrospinal fluid (CSF) analytes associated with abnormalities in the AD biomarkers amyloid β_1-42 and total-tau. In a 200-person "training" set, Least Absolute Shrinkage and Selection Operator regression estimated model weights for the 23 proteins, and for the AD biomarkers themselves, as predictors of ADAS-Cog₁₁ scores. In the remaining 106 participants ("validation" set), fully adjusted regression models then tested the Least Absolute Shrinkage and Selection Operator-derived models and a related protein marker summary score as predictors of ADAS-Cog₁₁, ADNI diagnostic category, and longitudinal cognitive trajectory.

RESULTS

AD biomarkers alone explained 26% of the variance in validation set cognitive scores. Surprisingly, the 23 AD-related proteins explained 31% of this variance. The biomarkers and protein markers appeared independent in this respect, jointly explaining 42% of test score variance. The composite protein marker score also predicted ADNI diagnosis and subsequent cognitive trajectory. Cognitive outcome prediction redounded principally to ten markers related to lipid or vascular functions or to microglial activation or chemotaxis. In each analysis, apoE protein and four markers in the latter immune-activation group portended better outcomes.

DISCUSSION

CSF markers of vascular, lipid-metabolic and immune-related functions may explain much of the disjunction between AD biomarker abnormality and symptom severity. In particular, our results suggest the hypothesis that innate immune activation improves cognitive outcomes in persons with AD pathology. This hypothesis should be tested by further study of cognitive outcomes related to CSF markers of innate immune activation.

Glutaminase C Regulates Microglial Activation and Pro-inflammatory Exosome Release: Relevance to the Pathogenesis of Alzheimer's Disease

Microglial activation is a key pathogenic process at the onset of Alzheimer’s disease (AD). Identifying regulators of microglial activation bears great potential in elucidating causes and mechanisms of AD and determining candidates for early intervention. Previous studies demonstrate abnormal elevation of glutaminase C (GAC) in HIV-infected or immune-activated microglia. However, whether GAC elevation causes microglial activation remains unknown. In this study, we found heightened expression levels of GAC in early AD mouse brain tissues compared with those in control littermates. Investigations on an in vitro neuroinflammation model revealed that GAC is increased in primary mouse microglia following pro-inflammatory stimulation. To model GAC elevation we overexpressed GAC by plasmid transfection and observed that GAC-overexpression shift the microglial phenotype to a pro-inflammatory state. Treatment with BPTES, a glutaminase inhibitor, reversed LPS-induced microglial activation and inflammation. Furthermore, we discovered that GAC overexpression in mouse microglia increased exosome release and changed exosome content, which includes specific packaging of pro-inflammatory miRNAs that activate microglia. Together, our results demonstrate a causal effect of GAC elevation on microglial activation and exosome release, both of which promote the establishment of a pro-inflammatory microenvironment. Therefore, GAC may have important relevance to the pathogenesis of AD.

Bi-directional Association of Cerebrospinal Fluid Immune Markers with Stage of Alzheimer's Disease Pathogenesis

Immune mechanisms may be important in the pathogenesis of Alzheimer’s disease (AD). Yet, studies comparing cerebrospinal fluid (CSF) and plasma immune marker levels of healthy and demented individuals have yielded conflicting results. We analyzed CSF from 101 members of the parental history-positive PREVENT-AD cohort of healthy aging adults, and 237 participants without dementia from the initial cohort of the Alzheimer’s Disease Neuroimaging Initiative (ADNI-1). Following recent practice, we used the biomarkers total-tau and amyloid-β_1-42 to allocate participants from each study into four stages of AD pathogenesis: Stage 0 (no abnormality), Stage 1 (reduced amyloid-β_1-42), Stage 2 (reduced amyloid-β_1-42 and increased total-tau), or “Suspected Non-Alzheimer Pathology” (elevated total-tau only). Investigating the PREVENT-AD participants’ CSF assay results for 19 immune/inflammatory markers, we found six that showed a distinct bi-directional relationship with pathogenetic stage. Relative to Stage 0, these were diminished at Stage 1 but strongly increased at Stage 2. Among the ADNI participants (90 healthy controls and 147 with mild cognitive impairment), we found that 23 of 83 available CSF markers also showed this distinct pattern. These results support recent observations that immune activation may become apparent only after the onset of both amyloid and tau pathologies. Unexpectedly, they also suggest that immune marker activity may diminish along with earliest appearance of amyloid-β plaque pathology. These findings may explain discordant results from past studies, and suggest the importance of characterizing the extent of AD pathology when comparing clinical groups.

Ultrastructural evidence of microglial heterogeneity in Alzheimer's disease amyloid pathology

BACKGROUND

Alzheimer's disease (AD) is the most common neurodegenerative disease, characterized by the deposition of extracellular fibrillar amyloid β (fΑβ) and the intracellular accumulation of neurofibrillary tangles. As AD progresses, Aβ drives a robust and prolonged inflammatory response via its recognition by microglia, the brain's immune cells. Microglial reactivity to fAβ plaques may impair their normal surveillance duties, facilitating synaptic loss and neuronal death, as well as cognitive decline in AD.

METHODS

In the current study, we performed correlative light, transmission, and scanning electron microscopy to provide insights into microglial structural and functional heterogeneity. We analyzed microglial cell bodies and processes in areas containing fAβ plaques and neuronal dystrophy, dystrophy only, or appearing healthy, among the hippocampus CA1 of 14-month-old APPSwe-PS1Δe9 mice versus wild-type littermates.

RESULTS

Our quantitative analysis revealed that microglial cell bodies in the AD model mice were larger and displayed ultrastructural signs of cellular stress, especially nearby plaques. Microglial cell bodies and processes were overall less phagocytic in AD model mice. However, they contained increased fibrillar materials and non-empty inclusions proximal to plaques. Microglial cell bodies and processes in AD model mice also displayed reduced association with extracellular space pockets that contained debris. In addition, microglial processes in healthy subregions of AD model mice encircled synaptic elements more often compared with plaque-associated processes. These observations in mice were qualitatively replicated in post-mortem hippocampal samples from two patients with AD (Braak stage 5).

CONCLUSION

Together, our findings identify at the ultrastructural level distinct microglial transformations common to mouse and human in association with amyloid pathology.

Chronic Microglial Activation in the GFAP-IL6 Mouse Contributes to Age-Dependent Cerebellar Volume Loss and Impairment in Motor Function

Chronic microglial activation is a prominent feature of many chronic neurodegenerative diseases, including Parkinson’s and Alzheimer’s disease. To investigate the effects of chronic microglial activation on cerebellar structure and motor function throughout the lifespan, the transgenic GFAP-IL6 mouse model was used. The aim of the study was to examine inflammatory markers and neuronal degeneration while simultaneously characterizing the motor performance of GFAP-IL6 mice at 3, 6, 14, and 24 months of age in comparison to WT (C57BL/6) mice. In respect to markers of neuroinflammation in the cerebellum, increased numbers of Iba1⁺ microglia were observed as early as at 3 months of age. In addition, TNF-α levels proved to be significantly higher in the GFAP-IL6 compared to WT mice at all time points. A difference in cerebellar volume between the GFAP-IL6 and WT mice was observed later in life, starting at 6 months and increasing to a loss of about 50% in aged (24 months old) GFAP-IL6 mice. Synaptic deficits were also assessed by using pre- (synaptophysin) and post-synaptic (PSD95) markers. While synaptophysin levels remained unchanged, PSD95 levels decreased in the aging GFAP-IL6 mice compared to their WT littermates from 14 months onward. To assess the effect of microglia activation and neurodegeneration on behavior, a variety of motor function tests, semi-quantitative cerebellar ataxia score, accelerod, beam walking, and open field tests were performed. An age-dependent difference between the genotypes was observed in many of the motor function tests. For example, reduced performance on the accelerod and higher ataxia scores were observed at 6 months of age, followed by the beam walking test showing differences at 14 months of age. In summary, this study constitutes a comprehensive, age-dependent examination of inflammatory, synaptic and neurodegenerative changes in the brains of GFAP-IL6 mice leading to a deterioration in motor performance. The results also indicate that early chronic microglia activation in the GFAP-IL6 mouse leads to observable cerebellar volume loss and motor deficits later in life.

Regional hypometabolism in the 3xTg mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive age-related neurodegenerative disease. Although neurofibrillary tangles and amyloid beta are classic hallmarks of AD, the earliest deficits in AD progression may be caused by unknown factors. One suspected factor has to do with brain energy metabolism. To investigate this factor, brain metabolic activity in 3xTg-AD mice and age-matched controls were measured with FDG-PET. Significant hypometabolic changes (p < .01) in brain metabolism were detected in the cortical piriform and insular regions of AD brains relative to controls. These regions are associated with olfaction, which is a potential clinical marker for AD progression as well as neurogenesis. The activity of the terminal component of the mitochondrial respiratory chain (complex IV) and the expression of complex I-V were significantly decreased (p < .05), suggesting that impaired metabolic activity coupled with impaired oxidative phosphorylation leads to decreased mitochondrial bioenergetics and subsequent Neurodegeneration. Although there is an association between neuroinflammatory pathological markers (microglial) and hypometabolism in AD, there was no association found between neuropathological (Aβ, tau, and astrocytes) and functional changes in AD sensitive brain regions, also suggesting that brain hypometabolism occurs prior to AD pathology. Therefore, targeting metabolic mechanisms in cortical piriform and insular regions at early stages may be a promising approach for preventing, slowing, and/or blocking the onset of AD and preserving neurogenesis.

HEWL interacts with dissipated oleic acid micelles, and decreases oleic acid cytotoxicity

Senile plaques are well-known hallmarks of Alzheimer's Diseases (AD). However, drugs targeting tangles of the protein tau and plaques of β-amyloid have no significant effect on disease progression, and the studies on the underlying mechanism of AD remain in high demand. Growing evidence supports the protective role of senile plaques in local inflammation driven by S100A9. We herein demonstrate that oleic acid (OA) micelles interact with hen egg white lysozyme (HEWL) and promote its amyloid formation. Consequently, SH-SY5Y cell line and mouse neural stem cells are rescued from OA toxicity by co-aggregation of OA and HEWL. Using atomic force microscopy in combination with fluorescence microscopy, we revealed that HEWL forms round-shaped aggregates in the presence of OA micelles instead of protofibrils of HEWL alone. These HEWL amyloids act as a sink for toxic OA micelles and their co-aggregate form large clumps, suggesting a protective function in amyloid and OA cytotoxicity.

Association of CSF CD40 levels and synaptic degeneration across the Alzheimer's disease spectrum

The CD40 pathway has been implicated in microglial activation, which is considered as a key factor in the pathogenesis of Alzheimer's disease (AD). However, the association of CSF CD40 and synaptic degeneration in living human is not clear. A total of 294 subjects with different severities of cognitive impairments were included in this study: 84 participants with normal cognition, 143 patients with mild cognitive impairment (MCI) and 67 patients with mild AD. Levels of CD40 in CSF were compared among the three groups. Further, several linear regression models were conducted to explore the associations of CSF CD40 and neurogranin levels (reflecting synaptic degeneration) when controlling for age, gender, educational attainment, APOE4 genotype, clinical diagnosis, CSF Aβ42 and tau proteins. We found that CSF CD40 levels were significantly decreased in patients with mild AD compared with healthy controls and MCI patients (control vs. AD, p = 0.0026; MCI vs. AD, p = 0.0268). However, there were no significant differences in CSF CD40 levels between controls and patients with MCI (p = 0.37). In addition, CSF CD40 levels were associated with neurogranin in the pooled sample when controlling for age, gender, educational attainment, APOE4 genotype and diagnosis. In summary, our findings support the notion that the CD40 pathway may contribute to an important mechanism underlying synaptic degeneration in AD.

Calcium Signaling Deficits in Glia and Autophagic Pathways Contributing to Neurodegenerative Disease

SIGNIFICANCE

Numerous cellular processes and signaling mechanisms have been identified that contribute to Alzheimer's disease (AD) pathology; however, a comprehensive or unifying pathway that binds together the major disease features remains elusive. As an upstream mechanism, altered calcium (Ca²⁺) signaling is a common driving force for many pathophysiological events that emerge during normal aging and development of neurodegenerative disease. Recent Advances: Over the previous three decades, accumulated evidence has validated the concept that intracellular Ca²⁺ dysregulation is centrally involved in AD pathogenesis, including the aggregation of pathogenic β-amyloid (Aβ) and phospho-τ species, synapse loss and dysfunction, cognitive impairment, and neurotoxicity.

CRITICAL ISSUES

Although neuronal Ca²⁺ signaling within the cytosol and endoplasmic reticulum (ER) has been well studied, other critical central nervous system-resident cell types affected by aberrant Ca²⁺ signaling, such as astrocytes and microglia, have not been considered as thoroughly. In addition, certain intracellular Ca²⁺-harboring organelles have been well studied, such as the ER and mitochondria; however other critical Ca²⁺-regulated organelles, such as lysosomes and autophagosomes, have only more recently been investigated. In this review, we examine Ca²⁺ dysregulation in microglia and astrocytes, as well as key intracellular organelles important for cellular maintenance and protein handling. Ca²⁺ dysregulation within these non-neuronal cells and organelles is hypothesized to disrupt the effective clearance of misaggregated proteins and cellular signaling pathways needed for memory networks.

FUTURE DIRECTIONS

Overall, we aim to explore how these disrupted mechanisms could be involved in AD pathology and consider their role as potential therapeutic targets. Antioxid. Redox Signal. 29, 1158-1175.

Alterations in the Peripheral Immune System in Dementia

Alterations in the immune response that result in inflammation might play a role in the pathology of dementias. In order to analyze changes of the peripheral immune system associated with different types of dementias, we determined several innate and adaptive cell populations in whole blood using flow cytometry. We included patients with Alzheimer's disease (AD; n = 60), vascular dementia (VaD; n = 20), and frontotemporal dementia (FTD; n = 12) at the time point of diagnosis and 24 age-matched neuropsychiatric healthy persons. Monocytes and NK cells were diminished in VaD, but not in AD and FTD. B cell and T cell numbers were decreased in all investigated forms of dementia. Changes in the contribution of naïve/memory T cells were only present in AD. Correlation and regression analyses revealed associations between altered immune cell populations and Q Albumin as marker for the integrity of the blood-cerebrospinal fluid-barrier, Mini-Mental State Examination values, and age. The peripheral immune system is altered in AD, VaD, and FTD. However, each disorder presents unique changes in the investigated cell types indicating different mechanisms underlying the pathology.

Protective effects of evodiamine in experimental paradigm of Alzheimer's disease

Evodiamine, a major component of Evodia rutaecarpa, has been reported to possess various pharmacological activities, including anti-inflammatory, antioxidative stress, and neuroprotective effects. Our previous study has shown that the potential effects of evodiamine on the learning and memory impairments in the transgenic mouse model of Alzheimer's disease (AD). The present study was designed to investigate neuroprotective mechanism and therapeutic potential of evodiamine against intracerebroventricular streptozotocin (ICV-STZ)-induced experimental sporadic Alzheimer's disease in mice. STZ was injected twice intracerebroventrically (3 mg/kg ICV) on alternate days (day 1 and day 3) in mice. Daily oral administration with evodiamine (50 or 100 mg/kg per day) starting from the first dose of STZ for 21 days showed an improvement in STZ induced cognitive deficits as assessed by novel object recognition and Morris water maze test. Evodiamine significantly decreased STZ induced elevation in acetylcholinesterase activity and malondialdehyde level, and significantly increased STZ induced reduction in glutathione activities and superoxide dismutase activities in the hippocampus compared to control. Furthermore, evodiamine inhibited significantly glial cell activation and neuroinflammation (TNF-α, IL-1β, and IL-6 levels) in the hippocampus. Moreover, evodiamine increased the activity of AKT/GSK-3β signalling pathway and inhibited the activity of nuclear factor κB. In summary, our study suggests that evodiamine can be a novel therapeutic agent for the management of sporadic AD.

Multifunctional neuroprotective effect of Withanone, a compound from Withania somnifera roots in alleviating cognitive dysfunction

Alzheimer's disease (AD) is a chronic disorder that slowly worsens and impairs the person's memory, learning, reasoning, judgment, communication and familiar tasks with loss of orientation. AD is characterized clinically by cognitive deficit and pathologically by the deposition of β amyloid plaques, neurofibrillary tangles, associated with degeneration of the cholinergic forebrain. Withanone (WS-2), a compound isolated from root extract of Withania somnifera at doses administered orally/day to wistar rats for duration of 21 days showed significant improvement in the cognitive skill by inhibiting amyloid β-42 and attenuated the elevated levels of pro-inflammatory cytokines like TNF alpha, IL-1 beta, IL-6, MCP-1, Nitric oxide, lipid peroxidation and both β- and γ- secretase enzymatic activity. Administration of WS-2 also significantly reversed the decline in acetyl choline and Glutathione (GSH) activity. None of the treatments that are available today alter the underlying causes of this terminal disease. Few preliminary clinical treatments have demonstrated that some plant medicines do ameliorate and improve memory and learning in patients with mild-to-moderate AD. WS-2 showed promise in AD treatment because of cognitive benefits and more importantly, mechanisms of action with respect to the fundamental pathophysiology of the disease, not limited to the inhibition of AChE, but also include the modification of Aβ processing, protection against oxidative stress and anti-inflammatory effects.

M344 promotes nonamyloidogenic amyloid precursor protein processing while normalizing Alzheimer's disease genes and improving memory

Hundreds of failed clinical trials with Alzheimer’s disease (AD) patients over the last fifteen years demonstrate that the one-target–one-disease approach is not effective in AD. In silico, structure-based, multitarget drug design approaches to treat multifactorial diseases have not been successful in the context of AD either. Here, we show that M344, an inhibitor of class I and IIB histone deacetylases, affects multiple AD-related genes, including those related to both early- and late-onset AD. We also show that M344 improves memory in the 3xTg AD mouse model. This work endorses a shift to a multitargeted approach to the treatment of AD, supporting the therapeutic potential of a single small molecule with an epigenetic mechanism of action.

Alzheimer’s disease (AD) comprises multifactorial ailments for which current therapeutic strategies remain insufficient to broadly address the underlying pathophysiology. Epigenetic gene regulation relies upon multifactorial processes that regulate multiple gene and protein pathways, including those involved in AD. We therefore took an epigenetic approach where a single drug would simultaneously affect the expression of a number of defined AD-related targets. We show that the small-molecule histone deacetylase inhibitor M344 reduces beta-amyloid (Aβ), reduces tau Ser³⁹⁶ phosphorylation, and decreases both β-secretase (BACE) and APOEε4 gene expression. M344 increases the expression of AD-relevant genes: BDNF, α-secretase (ADAM10), MINT2, FE65, REST, SIRT1, BIN1, and ABCA7, among others. M344 increases sAPPα and CTFα APP metabolite production, both cleavage products of ADAM10, concordant with increased ADAM10 gene expression. M344 also increases levels of immature APP, supporting an effect on APP trafficking, concurrent with the observed increase in MINT2 and FE65, both shown to increase immature APP in the early secretory pathway. Chronic i.p. treatment of the triple transgenic (APP_sw/PS1_M146V/Tau_P301L) mice with M344, at doses as low as 3 mg/kg, significantly prevented cognitive decline evaluated by Y-maze spontaneous alternation, novel object recognition, and Barnes maze spatial memory tests. M344 displays short brain exposure, indicating that brief pulses of daily drug treatment may be sufficient for long-term efficacy. Together, these data show that M344 normalizes several disparate pathogenic pathways related to AD. M344 therefore serves as an example of how a multitargeting compound could be used to address the polygenic nature of multifactorial diseases.

Brain energy metabolism and neuroinflammation in ageing APP/PS1-21 mice using longitudinal 18F-FDG and 18F-DPA-714 PET imaging

Preclinical animal model studies of brain energy metabolism and neuroinflammation in Alzheimer's disease have produced conflicting results, hampering both the elucidation of the underlying disease mechanism and the development of effective Alzheimer's disease therapies. Here, we aimed to quantify the relationship between brain energy metabolism and neuroinflammation in the APP/PS1-21 transgenic mouse model of Alzheimer's disease using longitudinal in vivo¹⁸F-FDG and ¹⁸F-DPA-714) PET imaging and ex vivo brain autoradiography. APP/PS1-21 (TG, n = 9) and wild type control mice (WT, n = 9) were studied longitudinally every third month from age 6 to 15 months with ¹⁸F-FDG and ¹⁸F-DPA-714 with a one-week interval between the scans. Additional TG (n = 52) and WT (n = 29) mice were used for ex vivo studies. In vivo, the ¹⁸F-FDG SUVs were lower and the ¹⁸F-DPA-714 binding ratios relative to the cerebellum were higher in the TG mouse cortex and hippocampus than in WT mice at age 12 to 15 months ( p < 0.05). The ex vivo cerebellum binding ratios supported the results of the in vivo¹⁸F-DPA-714 studies but not the ¹⁸F-FDG studies. This longitudinal PET study demonstrated decreased energy metabolism and increased inflammation in the brains of APP/PS1-21 mice compared to WT mice.

LISPRO mitigates β-amyloid and associated pathologies in Alzheimer's mice

Lithium has been marketed in the United States of America since the 1970s as a treatment for bipolar disorder. More recently, studies have shown that lithium can improve cognitive decline associated with Alzheimer’s disease (AD). However, the current United States Food and Drug Administration-approved lithium pharmaceutics (carbonate and citrate chemical forms) have a narrow therapeutic window and unstable pharmacokinetics that, without careful monitoring, can cause serious adverse effects. Here, we investigated the safety profile, pharmacokinetics, and therapeutic efficacy of LISPRO (ionic co-crystal of lithium salicylate and l-proline), lithium salicylate, and lithium carbonate (Li₂CO₃). We found that LISPRO (8-week oral treatment) reduces β-amyloid plaques and phosphorylation of tau by reducing neuroinflammation and inactivating glycogen synthase kinase 3β in transgenic Tg2576 mice. Specifically, cytokine profiles from the brain, plasma, and splenocytes suggested that 8-week oral treatment with LISPRO downregulates pro-inflammatory cytokines, upregulates anti-inflammatory cytokines, and suppresses renal cyclooxygenase 2 expression in transgenic Tg2576 mice. Pharmacokinetic studies indicated that LISPRO provides significantly higher brain lithium levels and more steady plasma lithium levels in both B6129SF2/J (2-week oral treatment) and transgenic Tg2576 (8-week oral treatment) mice compared with Li₂CO₃. Oral administration of LISPRO for 28 weeks significantly reduced β-amyloid plaques and tau-phosphorylation. In addition, LISPRO significantly elevated pre-synaptic (synaptophysin) and post-synaptic protein (post synaptic density protein 95) expression in brains from transgenic 3XTg-AD mice. Taken together, our data suggest that LISPRO may be a superior form of lithium with improved safety and efficacy as a potential new disease modifying drug for AD.

Bioactive Nutrients and Nutrigenomics in Age-Related Diseases

The increased life expectancy and the expansion of the elderly population are stimulating research into aging. Aging may be viewed as a multifactorial process that results from the interaction of genetic and environmental factors, which include lifestyle. Human molecular processes are influenced by physiological pathways as well as exogenous factors, which include the diet. Dietary components have substantive effects on metabolic health; for instance, bioactive molecules capable of selectively modulating specific metabolic pathways affect the development/progression of cardiovascular and neoplastic disease. As bioactive nutrients are increasingly identified, their clinical and molecular chemopreventive effects are being characterized and systematic analyses encompassing the "omics" technologies (transcriptomics, proteomics and metabolomics) are being conducted to explore their action. The evolving field of molecular pathological epidemiology has unique strength to investigate the effects of dietary and lifestyle exposure on clinical outcomes. The mounting body of knowledge regarding diet-related health status and disease risk is expected to lead in the near future to the development of improved diagnostic procedures and therapeutic strategies targeting processes relevant to nutrition. The state of the art of aging and nutrigenomics research and the molecular mechanisms underlying the beneficial effects of bioactive nutrients on the main aging-related disorders are reviewed herein.

Mechanisms of Melatonin in Alleviating Alzheimer's Disease

Alzheimer's disease (AD) is a chronic, progressive and prevalent neurodegenerative disease characterized by the loss of higher cognitive functions and an associated loss of memory. The thus far "incurable" stigma for AD prevails because of variations in the success rates of different treatment protocols in animal and human studies. Among the classical hypotheses explaining AD pathogenesis, the amyloid hypothesis is currently being targeted for drug development. The underlying concept is to prevent the formation of these neurotoxic peptides which play a central role in AD pathology and trigger a multispectral cascade of neurodegenerative processes post-aggregation. This could possibly be achieved by pharmacological inhibition of β- or γ-secretase or stimulating the nonamyloidogenic α-secretase. Melatonin the pineal hormone is a multifunctioning indoleamine. Production of this amphiphilic molecule diminishes with advancing age and this decrease runs parallel with the progression of AD which itself explains the potential benefits of melatonin in line of development and devastating consequences of the disease progression. Our recent studies have revealed a novel mechanism by which melatonin stimulates the nonamyloidogenic processing and inhibits the amyloidogenic processing of β-amyloid precursor protein (βAPP) by stimulating α -secretases and consequently down regulating both β- and γ-secretases at the transcriptional level. In this review, we discuss and evaluate the neuroprotective functions of melatonin in AD pathogenesis, including its role in the classical hypotheses in cellular and animal models and clinical interventions in AD patients, and suggest that with early detection, melatonin treatment is qualified to be an anti-AD therapy.

Intranasal Insulin Administration Ameliorates Streptozotocin (ICV)-Induced Insulin Receptor Dysfunction, Neuroinflammation, Amyloidogenesis, and Memory Impairment in Rats

Alzheimer's disease (AD) is associated with reduced insulin level and impairment of insulin receptor (IR) signaling in the brain, which correlates to amyloid pathology, neuroinflammation, and synaptic neurotoxicity. Clinical studies show that intranasal insulin improves memory in AD patients without peripheral hypoglycemia. However, neuroprotective molecular mechanism of the beneficial effect of intranasal insulin in AD pathology is unexplored. Therefore, we investigated the role of intranasal insulin on intracerebroventricular (ICV) streptozotocin (STZ)-induced memory impairment in rats as evaluated in the Morris water maze test. STZ (ICV) treated rats had shown memory impairment along with a significant decrease in IR signaling molecules (IR, pIRS-1, pAkt, and pGSK-3α/β expression) and IDE expression in both hippocampus and cerebral cortex. Intranasal insulin delivery prevented these changes. Moreover, intranasal insulin was found to inhibit significantly glial cell activation (GFAP and Iba-1 expression), neuroinflammation (COX-2 expression, NFκB translocation, TNF-α, and IL-10 level) and amyloidogenic protein expression (BACE-1 and Aβ_1-42 expression) in STZ (ICV)-injected rats. STZ (ICV)-induced caspase activation and postsynaptic neurotoxicity were also prevented by treatment with intranasal insulin. Our findings reveal that insulin has the neuroprotective effect and clearly signifies the potential use of intranasal insulin delivery for the treatment of AD. Graphical Abstract Neuroprotective effects of intranasal insulin administration on streptozotocin (ICV)-induced memory impairment in rats.

The fornix provides multiple biomarkers to characterize circuit disruption in a mouse model of Alzheimer's disease

Multivariate biomarkers are needed for detecting Alzheimer's disease (AD), understanding its etiology, and quantifying the effect of therapies. Mouse models provide opportunities to study characteristics of AD in well-controlled environments that can help facilitate development of early interventions. The CVN-AD mouse model replicates multiple AD hallmark pathologies, and we identified multivariate biomarkers characterizing a brain circuit disruption predictive of cognitive decline. In vivo and ex vivo magnetic resonance imaging (MRI) revealed that CVN-AD mice replicate the hippocampal atrophy (6%), characteristic of humans with AD, and also present changes in subcortical areas. The largest effect was in the fornix (23% smaller), which connects the septum, hippocampus, and hypothalamus. In characterizing the fornix with diffusion tensor imaging, fractional anisotropy was most sensitive (20% reduction), followed by radial (15%) and axial diffusivity (2%), in detecting pathological changes. These findings were strengthened by optical microscopy and ultrastructural analyses. Ultrastructual analysis provided estimates of axonal density, diameters, and myelination-through the g-ratio, defined as the ratio between the axonal diameter, and the diameter of the axon plus the myelin sheath. The fornix had reduced axonal density (47% fewer), axonal degeneration (13% larger axons), and abnormal myelination (1.5% smaller g-ratios). CD68 staining showed that white matter pathology could be secondary to neuronal degeneration, or due to direct microglial attack. In conclusion, these findings strengthen the hypothesis that the fornix plays a role in AD, and can be used as a disease biomarker and as a target for therapy.

Microglia in Alzheimer's disease: A multifaceted relationship

Alzheimer's disease (AD) is a progressive neurodegenerative disorder affecting elderly people worldwide, which is mainly characterized by cerebral amyloid-beta (Aβ) plaque deposition and neurofibrillary tangle formation. The interest in microglia arose from the overwhelming experimental evidence that outlined a key role of neuroinflammation in AD pathology. Microglia constitute the powerhouse of the innate immune system in the brain. It is now widely accepted that microglia are myeloid-derived cells that infiltrate the developing brain at the early embryonic stages, and acquire a highly ramified phenotype postnatally. Microglia use these dynamic ramifications as sentinels to sense and detect any occurring alteration in brain homeostasis. Once a danger signal is detected, microglia get activated by acquiring a less ramified phenotype, and mount adequate responses that range from phagocyting cell debris to secreting inflammatory and trophic factors. Earlier reports have demonstrated, unequivocally, that microglia surround Aβ plaques and internalize Aβ microaggregates. However, the implication of these observations in AD pathology, and consequently treatment, is still a matter of debate. Nonetheless, targeting the activity of these cells constituted a convergent point in this debate. Unfortunately, the conflicting experimental findings obtained following the modulation of microglial activity in AD, further fueled the debate. This review aims at providing an overview regarding what we know about the implication of microglia in AD pathology, and treatment. The emerging role of monocytes is also discussed.

Increased tauopathy drives microglia-mediated clearance of beta-amyloid

Alzheimer disease is characterized by the accumulation of β-amyloid (Aβ) plaques and tau-laden neurofibrillary tangles. Emerging studies suggest that in neurodegenerative diseases, aggregation of one protein species can promote other proteinopathies and that inflammation plays an important role in this process. To study the interplay between Aβ deposition, tau pathology, and microgliosis, we established a new AD transgenic mouse model by crossing 5xfAD mice with Thy-Tau22 transgenic mice. The resulting 'T5x' mice exhibit a greater than three-fold increase in misfolded and hyperphosphorylated tau and further substantiates the hypothesis that Aβ accelerates tau pathology. Surprisingly, T5x mice exhibit a 40-50 % reduction in Aβ plaque load and insoluble Aβ species when compared with aged-matched 5xfAD littermates. T5x mice exhibit significant changes in cytokine production, an almost doubling of microglial number, and a dramatic shift in microglia activation state. Furthermore, T5x microglia exhibit increased phagocytic capacity that enhances the clearance of insoluble Aβ and decreasing plaque load. Therefore, our results suggest that strategies to increase the phagocytic ability of microglia can be employed to reduce Aβ and that tau-induced changes in microglial activation state can promote the clearance of Aβ.

Alzheimer's disease: Is this a brain specific diabetic condition?

Alzheimer's disease (AD) and type 2 diabetes (T2DM) are the two major health issues affecting millions of elderly people worldwide, with major impacts in the patient's daily life. Numerous studies have demonstrated that patients with diabetes have an increased risk of developing AD compared with healthy individuals. The principal biological mechanisms that associate with the progression of diabetes and AD are not completely understood. Impaired insulin signaling, uncontrolled glucose metabolism, oxidative stress, abnormal protein processing, and the stimulation of inflammatory pathways are common features to both AD and T2DM. In recent years brain specific abnormalities in insulin and insulin like growth factor (IGF) signaling considered as a major trigger involved in the etiopathogenesis of AD, showing T2DM like milieu. This review summarizes the pathways that might link diabetes and AD and the effect of diminished insulin.

Telmisartan Modulates Glial Activation: In Vitro and In Vivo Studies

The circulating renin-angiotensin system (RAS), including the biologically active angiotensin II, is a fundamental regulatory mechanism of blood pressure conserved through evolution. Angiotensin II components of the RAS have also been identified in the brain. In addition to pro-inflammatory cytokines, neuromodulators, such as angiotensin II can induce (through angiotensin type 1 receptor (AT₁R)) some of the inflammatory actions of brain glial cells and influence brain inflammation. Moreover, in Alzheimer’s disease (AD) models, where neuroinflammation occurs, increased levels of cortical AT₁Rs have been shown. Still, the precise role of RAS in neuroinflammation is not completely clear. The overall aim of the present study was to elucidate the role of RAS in the modulation of glial functions and AD pathology. To reach this goal, the specific aims of the present study were a. to investigate the long term effect of telmisartan (AT₁R blocker) on tumor necrosis factor-α (TNF-α), interleukin 1-β (IL1-β) and nitric oxide (NO) release from glial cells. b. to examine the effect of intranasally administered telmisartan on amyloid burden and microglial activation in 5X familial AD (5XFAD) mice. Telmisartan effects in vivo were compared to those of perindopril (angiotensin converting enzyme inhibitor). Long-term-exposure of BV2 microglia to telmisartan significantly decreased lipopolysaccharide (LPS) -induced NO, inducible NO synthase, TNF-α and IL1-β synthesis. The effect of Telmisartan on NO production in BV2 cells was confirmed also in primary neonatal rat glial cells. Intranasal administration of telmisartan (1 mg/kg/day) for up to two months significantly reduced amyloid burden and CD11b expression (a marker for microglia) both in the cortex and hipoccampus of 5XFAD. Based on the current view of RAS and our data, showing reduced amyloid burden and glial activation in the brains of 5XFAD transgenic mice, one may envision potential intervention with the progression of glial activation and AD by using AT₁R blockers.

Whole Blood Gene Expression Profiling in Preclinical and Clinical Cattle Infected with Atypical Bovine Spongiform Encephalopathy

Prion diseases, such as bovine spongiform encephalopathies (BSE), are transmissible neurodegenerative disorders affecting humans and a wide variety of mammals. Variant Creutzfeldt-Jakob disease (vCJD), a prion disease in humans, has been linked to exposure to BSE prions. This classical BSE (cBSE) is now rapidly disappearing as a result of appropriate measures to control animal feeding. Besides cBSE, two atypical forms (named H- and L-type BSE) have recently been described in Europe, Japan, and North America. Here we describe the first wide-spectrum microarray analysis in whole blood of atypical BSE-infected cattle. Transcriptome changes in infected animals were analyzed prior to and after the onset of clinical signs. The microarray analysis revealed gene expression changes in blood prior to the appearance of the clinical signs and during the progression of the disease. A set of 32 differentially expressed genes was found to be in common between clinical and preclinical stages and showed a very similar expression pattern in the two phases. A 22-gene signature showed an oscillating pattern of expression, being differentially expressed in the preclinical stage and then going back to control levels in the symptomatic phase. One gene, SEL1L3, was downregulated during the progression of the disease. Most of the studies performed up to date utilized various tissues, which are not suitable for a rapid analysis of infected animals and patients. Our findings suggest the intriguing possibility to take advantage of whole blood RNA transcriptional profiling for the preclinical identification of prion infection. Further, this study highlighted several pathways, such as immune response and metabolism that may play an important role in peripheral prion pathogenesis. Finally, the gene expression changes identified in the present study may be further investigated as a fingerprint for monitoring the progression of disease and for developing targeted therapeutic interventions.

CD40 Negatively Regulates ATP-TLR4-Activated Inflammasome in Microglia

During acute brain injury and/or sterile inflammation, release of danger-associated molecular patterns (DAMPs) activates pattern recognition receptors (PRRs). Microglial toll-like receptor (TLR)-4 activated by DAMPs potentiates neuroinflammation through inflammasome-induced IL-1β and pathogenic Th17 polarization which critically influences brain injury. TLR4 activation accompanies increased CD40, a cognate costimulatory molecule, involved in microglia-mediated immune responses in the brain. During brain injury, excessive release of extracellular ATP (DAMPs) is involved in promoting the damage. However, the regulatory role of CD40 in microglia during ATP-TLR4-mediated inflammasome activation has never been explored. We report that CD40, in the absence of ATP, synergizes TLR4-induced proinflammatory cytokines but not IL-1β, suggesting that the response is independent of inflammasome. The presence of ATP during TLR4 activation leads to NLRP3 inflammasome activation and caspase-1-mediated IL-1β secretion which was inhibited during CD40 activation, accompanied with inhibition of ERK1/2 and reactive oxygen species (ROS), and elevation in p38 MAPK phosphorylation. Experiments using selective inhibitors prove indispensability of ERK 1/2 and ROS for inflammasome activation. The ATP-TLR4-primed macrophages polarize the immune response toward pathogenic Th17 cells, whereas CD40 activation mediates Th1 response. Exogenous supplementation of IFN-γ (a Th1 cytokine and CD40 inducer) results in decreased IL-1β, suggesting possible feedback loop mechanism of inflammasome inhibition, whereby IFN-γ-mediated increase in CD40 expression and activation suppress neurotoxic inflammasome activation required for Th17 response. Collectively, the findings indicate that CD40 is a novel negative regulator of ATP-TLR4-mediated inflammasome activation in microglia, thus providing a checkpoint to regulate excessive inflammasome activation and Th17 response during DAMP-mediated brain injury.

Temporal-logic analysis of microglial phenotypic conversion with exposure to amyloid-β

Alzheimer Disease (AD) remains a leading killer with no adequate treatment. Ongoing research increasingly implicates the brain's immune system as a critical contributor to AD pathogenesis, but the complexity of the immune contribution poses a barrier to understanding. Here I use temporal logic to analyze a computational specification of the immune component of AD. Temporal logic is an extension of logic to propositions expressed in terms of time. It has traditionally been used to analyze computational specifications of complex engineered systems but applications to complex biological systems are now appearing. The inflammatory component of AD involves the responses of microglia to the peptide amyloid-β (Aβ), which is an inflammatory stimulus and a likely causative AD agent. Temporal-logic analysis of the model provides explanations for the puzzling findings that Aβ induces an anti-inflammatory and well as a pro-inflammatory response, and that Aβ is phagocytized by microglia in young but not in old animals. To potentially explain the first puzzle, the model suggests that interferon-γ acts as an "autocrine bridge" over which an Aβ-induced increase in pro-inflammatory cytokines leads to an increase in anti-inflammatory mediators also. To potentially explain the second puzzle, the model identifies a potential instability in signaling via insulin-like growth factor 1 that could explain the failure of old microglia to phagocytize Aβ. The model predicts that augmentation of insulin-like growth factor 1 signaling, and activation of protein kinase C in particular, could move old microglia from a neurotoxic back toward a more neuroprotective and phagocytic phenotype.

Shengmai Formula Ameliorates Pathological Characteristics in AD C. elegans

Shengmai (SM) formula, a classical traditional Chinese medicine formula, is composed of Panax ginseng (Pg), Ophiopogon japonicus (Oj), and Schisandra Chinesis (Sc). SM has been clinically used to treat heart failure and ischemic heart disease. Although SM formula has been reported to be potential for fighting against Alzheimer's disease (AD) by previous works, there are many gaps in our knowledge on its usage in AD treatment on an organism level and will then need to be further clarified. In this study, transgenic Caenorhabditis elegans expressing human Aβ_1-42 are used to evaluate SM formula efficacy to treat AD phenotype and to investigate its underlying mechanism. The results showed that SM formula ameliorated AD pathological characteristics of paralysis behavior and chemotaxis defect in transgenic C. elegans. With SM treatment, the number of Aβ deposits decreased, the levels of gene expressions of hsp16-2, hsp16-41, ace-1, ace-2, and TNFA1P1 homolog genes were down-regulated. Our results also showed that Oj exhibited more stronger effect on delaying paralysis in worms than Pg and Sc did, and synergistic action was observed between Pg and Oj, and Sc further enhanced the activity of Pg/Oj combination on delaying paralysis behavior. Further, SM with herbs of Pg, Oj, and Sc at a dose proportion of 9:9:6 exhibited superior therapeutic efficacy in comparison with herbs at other dose proportions. After SM formula extracted by ethanol, it delayed AD symptoms on a wider dose from 0.2 to 10.0 mg/mL with no toxic effect. These results provided more evidence for SM formula being potential to be used to treat AD.

Pro-Resolving Lipid Mediators Improve Neuronal Survival and Increase Aβ42 Phagocytosis

Inflammation in the brain is a prominent feature in Alzheimer's disease (AD). Recent studies suggest that chronic inflammation can be a consequence of failure to resolve the inflammation. Resolution of inflammation is mediated by a family of lipid mediators (LMs), and the levels of these specialized pro-resolving mediators (SPMs) are reduced in the hippocampus of those with AD. In the present study, we combined analysis of LMs in the entorhinal cortex (ENT) from AD patients with in vitro analysis of their direct effects on neurons and microglia. We probed ENT, an area affected early in AD pathogenesis, by liquid chromatography-tandem mass spectrometry (LC-MS-MS), and found that the levels of the SPMs maresin 1 (MaR1), protectin D1 (PD1), and resolvin (Rv) D5, were lower in ENT of AD patients as compared to age-matched controls, while levels of the pro-inflammatory prostaglandin D2 (PGD2) were higher in AD. In vitro studies showed that lipoxin A4 (LXA4), MaR1, resolvin D1 (RvD1), and protectin DX (PDX) exerted neuroprotective activity, and that MaR1 and RvD1 down-regulated β-amyloid (Aβ)42-induced inflammation in human microglia. MaR1 exerted a stimulatory effect on microglial uptake of Aβ42. Our findings give further evidence for a disturbance of the resolution pathway in AD, and indicate that stimulating this pathway is a promising treatment strategy for AD.

Immune attack: the role of inflammation in Alzheimer disease. Nat Rev Neurosci. 2015;16:358-372. [PMID: 25991443 DOI: 10.1038/nrn3880]

The past two decades of research into the pathogenesis of Alzheimer disease (AD) have been driven largely by the amyloid hypothesis; the neuroinflammation that is associated with AD has been assumed to be merely a response to pathophysiological events. However, new data from preclinical and clinical studies have established that immune system-mediated actions in fact contribute to and drive AD pathogenesis. These insights have suggested both novel and well-defined potential therapeutic targets for AD, including microglia and several cytokines. In addition, as inflammation in AD primarily concerns the innate immune system - unlike in 'typical' neuroinflammatory diseases such as multiple sclerosis and encephalitides - the concept of neuroinflammation in AD may need refinement.

A fresh perspective from immunologists and vaccine researchers: active vaccination strategies to prevent and reverse Alzheimer's disease

Traditional vaccination against infectious diseases relies on generation of cellular and humoral immune responses that act to protect the host from overt disease even though they do not induce sterilizing immunity. More recently, attempts have been made with mixed success to generate therapeutic vaccines against a wide range of noninfectious diseases including neurodegenerative disorders. After the exciting first report of successful vaccine prevention of progression of an Alzheimer's disease (AD) animal model in 1999, various epitope-based vaccines targeting amyloid beta (Aβ) have proceeded to human clinical trials, with varied results. More recently, AD vaccines based on tau protein have advanced into clinical testing too. This review seeks to put perspective to the mixed results obtained so far in clinical trials of AD vaccines and discusses the many pitfalls and misconceptions encountered on the path to a successful AD vaccine, including better standardization of immunologic efficacy measures of antibodies, immunogenicity of platform/carrier and adjuvants.

Neuroinflammation in Alzheimer's disease

Increasing evidence suggests that Alzheimer's disease pathogenesis is not restricted to the neuronal compartment, but includes strong interactions with immunological mechanisms in the brain. Misfolded and aggregated proteins bind to pattern recognition receptors on microglia and astroglia, and trigger an innate immune response characterised by release of inflammatory mediators, which contribute to disease progression and severity. Genome-wide analysis suggests that several genes that increase the risk for sporadic Alzheimer's disease encode factors that regulate glial clearance of misfolded proteins and the inflammatory reaction. External factors, including systemic inflammation and obesity, are likely to interfere with immunological processes of the brain and further promote disease progression. Modulation of risk factors and targeting of these immune mechanisms could lead to future therapeutic or preventive strategies for Alzheimer's disease.