IL-17 triggers the onset of cognitive and synaptic deficits in early stages of Alzheimer's disease

The interaction between KIF21A and KANK1 regulates dendritic morphology and synapse plasticity in neurons

JOURNAL/nrgr/04.03/01300535-202501000-00029/figure1/v/2024-05-14T021156Z/r/image-tiff Morphological alterations in dendritic spines have been linked to changes in functional communication between neurons that affect learning and memory. Kinesin-4 KIF21A helps organize the microtubule-actin network at the cell cortex by interacting with KANK1; however, whether KIF21A modulates dendritic structure and function in neurons remains unknown. In this study, we found that KIF21A was distributed in a subset of dendritic spines, and that these KIF21A-positive spines were larger and more structurally plastic than KIF21A-negative spines. Furthermore, the interaction between KIF21A and KANK1 was found to be critical for dendritic spine morphogenesis and synaptic plasticity. Knockdown of either KIF21A or KANK1 inhibited dendritic spine morphogenesis and dendritic branching, and these deficits were fully rescued by coexpressing full-length KIF21A or KANK1, but not by proteins with mutations disrupting direct binding between KIF21A and KANK1 or binding between KANK1 and talin1. Knocking down KIF21A in the hippocampus of rats inhibited the amplitudes of long-term potentiation induced by high-frequency stimulation and negatively impacted the animals' cognitive abilities. Taken together, our findings demonstrate the function of KIF21A in modulating spine morphology and provide insight into its role in synaptic function.

Nanoligomers targeting NF-κB and NLRP3 reduce neuroinflammation and improve cognitive function with aging and tauopathy

Neuroinflammation contributes to impaired cognitive function in brain aging and neurodegenerative disorders like Alzheimer's disease, which is characterized by the aggregation of pathological tau. One major driver of both age- and tau-associated neuroinflammation is the NF-κB and NLRP3 signaling axis. However, current treatments targeting NF-κB or NLRP3 may have adverse/systemic effects, and most have not been clinically translatable. In this study, we tested the efficacy of a novel, nucleic acid therapeutic (Nanoligomer) cocktail specifically targeting both NF-κB and NLRP3 in the brain for reducing neuroinflammation and improving cognitive function in old (aged 19 months) wildtype mice, and in rTg4510 tau pathology mice (aged 2 months). We found that 4 weeks of NF-κB/NLRP3-targeting Nanoligomer treatment strongly reduced neuro-inflammatory cytokine profiles in the brain and improved cognitive-behavioral function in both old and rTg4510 mice. These effects of NF-κB/NLRP3-targeting Nanoligomers were also associated with reduced glial cell activation and pathology, favorable changes in transcriptome signatures of glia-associated inflammation (reduced) and neuronal health (increased), and positive systemic effects. Collectively, our results provide a basis for future translational studies targeting both NF-κB and NLRP3 in the brain, perhaps using Nanoligomers, to inhibit neuroinflammation and improve cognitive function with aging and neurodegeneration.

The Anti-Neuroinflammatory Effect of Extra-Virgin Olive Oil in the Triple Transgenic Mouse Model of Alzheimer's Disease

Background

Chronic intake of extra virgin olive oil is beneficial for brain health and protects from age-related cognitive decline and dementia, whose most common clinical manifestation is Alzheimer's disease. Besides the classical pathologic deposits of amyloid beta peptides and phosphorylated tau proteins, another frequent feature of the Alzheimer's brain is neuroinflammation.

Objective

In the current study, we assessed the effect that extra virgin olive oil has on neuroinflammation when administered to a mouse model of the disease.

Methods

Triple transgenic mice were randomized to receive a diet enriched with extra virgin olive oil or regular diet for 8 weeks. At the end of this treatment period the expression level of several inflammatory biomarkers was assessed in the central nervous system.

Results

Among the 79 biomarkers measured, compared with the control group, mice receiving the extra virgin olive oil had a significant reduction in MIP-2, IL-17E, IL-23, and IL-12p70, but an increase in IL-5. To validate these results, specific ELISA kits were used for each of them. Confirmatory results were obtained for MIP-2, IL-17E, IL-23, and IL-12-p70. No significant differences between the two groups were observed for IL-5.

Conclusions

Our results demonstrate that chronic administration of extra virgin olive oil has a potent anti-neuroinflammatory action in a model of Alzheimer's disease. They provide additional pre-clinical support and novel mechanistic insights for the beneficial effect that this dietary intervention has on brain health and dementia.

The microbiome shapes immunity in a sex-specific manner in mouse models of Alzheimer's disease

INTRODUCTION

Preclinical studies reveal that the microbiome broadly affects immune responses and the deposition and/or clearance of amyloid-beta (Aβ) in mouse models of Alzheimer's disease (AD). Whether the microbiome shapes central and peripheral immune profiles in AD models remains unknown.

METHODS

We examined adaptive immune responses in two mouse models containing AD-related genetic predispositions (3xTg and 5xFAD) in the presence or absence of the microbiome.

RESULTS

T and B cells were altered in brain-associated and systemic immune tissues between genetic models and wildtype mice, with earlier signs if inflammation in female mice. Systemic immune responses were modulated by the microbiome and differed by sex. Further, the absence of a microbiome in germ-free mice resulted in reduced cognitive deficits, primarily in female mice.

DISCUSSION

These data reveal sexual dimorphism in early signs of inflammation and the effects of the microbiome, and highlight a previously unrecognized interaction between sex and the microbiome in mouse models of AD.

Research in Context

Systemic review: We reviewed the literature related to Alzheimer's disease (AD), inflammation, and the microbiome using PubMed. We cite several studies that demonstrate the influence of the microbiome on inflammation and cognitive performance in both animal models and humans. However, the mechanisms linking immunity to AD are not well understood. Interpretation: Using two well-established mouse models of AD, we found that the microbiome does not strongly influence the onset of inflammation in brain-draining lymph nodes; rather, it largely modulates systemic immune responses, local cytokine production, and cognitive performance. Notably, the inflammatory state in mice was affected by sex, and this sex effect differed between local and systemic tissues and mice with or without a microbiome. Future directions: Our work identified a sex- and microbiome-mediated effect on inflammation and cognitive performance. Future studies may focus on microbiome-dependent mechanisms that intersect with sex hormone and immune responses to determine peripheral effects on AD outcomes.

Highlights

Adaptive immunity is activated at early ages and differentially by sex in mouse models of AD.Inflammation in 5xFAD mice is characterized by increased IL-17A-producing T cells.Inflammation in 3xTg mice is characterized by increased cytokine responses in males, but attenuated cytokine responses in female mice.Longitudinal immune responses differ between 3xTg mice and 5xFAD mice.Both 3xTg and 5xFAD female mice show improved learning and cognition in the absence of a microbiome.

Increased levels and activation of the IL-17 receptor in microglia contribute to enhanced neuroinflammation in cerebellum of hyperammonemic rats

BACKGROUND

Patients with liver cirrhosis may show minimal hepatic encephalopathy (MHE) with mild cognitive impairment and motor incoordination. Rats with chronic hyperammonemia reproduce these alterations. Motor incoordination in hyperammonemic rats is due to increased GABAergic neurotransmission in cerebellum, induced by neuroinflammation, which enhances TNFα-TNFR1-S1PR2-CCL2-BDNF-TrkB pathway activation. The initial events by which hyperammonemia triggers activation of this pathway remain unclear. MHE in cirrhotic patients is triggered by a shift in inflammation with increased IL-17. The aims of this work were: (1) assess if hyperammonemia increases IL-17 content and membrane expression of its receptor in cerebellum of hyperammonemic rats; (2) identify the cell types in which IL-17 receptor is expressed and IL-17 increases in hyperammonemia; (3) assess if blocking IL-17 signaling with anti-IL-17 ex-vivo reverses activation of glia and of the TNFα-TNFR1-S1PR2-CCL2-BDNF-TrkB pathway.

RESULTS

IL-17 levels and membrane expression of the IL-17 receptor are increased in cerebellum of rats with hyperammonemia and MHE, leading to increased activation of IL-17 receptor in microglia, which triggers activation of STAT3 and NF-kB, increasing IL-17 and TNFα levels, respectively. TNFα released from microglia activates TNFR1 in Purkinje neurons, leading to activation of NF-kB and increased IL-17 and TNFα also in these cells. Enhanced TNFR1 activation also enhances activation of the TNFR1-S1PR2-CCL2-BDNF-TrkB pathway which mediates microglia and astrocytes activation.

CONCLUSIONS

All these steps are triggered by enhanced activation of IL-17 receptor in microglia and are prevented by ex-vivo treatment with anti-IL-17. IL-17 and IL-17 receptor in microglia would be therapeutic targets to treat neurological impairment in patients with MHE.

CD4+ T-Cell Senescence in Neurodegenerative Disease: Pathogenesis and Potential Therapeutic Targets

With the increasing proportion of the aging population, neurodegenerative diseases have become one of the major health issues in society. Neurodegenerative diseases (NDs), including multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS), are characterized by progressive neurodegeneration associated with aging, leading to a gradual decline in cognitive, emotional, and motor functions in patients. The process of aging is a normal physiological process in human life and is accompanied by the aging of the immune system, which is known as immunosenescence. T-cells are an important part of the immune system, and their senescence is the main feature of immunosenescence. The appearance of senescent T-cells has been shown to potentially lead to chronic inflammation and tissue damage, with some studies indicating a direct link between T-cell senescence, inflammation, and neuronal damage. The role of these subsets with different functions in NDs is still under debate. A growing body of evidence suggests that in people with a ND, there is a prevalence of CD4+ T-cell subsets exhibiting characteristics that are linked to senescence. This underscores the significance of CD4+ T-cells in NDs. In this review, we summarize the classification and function of CD4+ T-cell subpopulations, the characteristics of CD4+ T-cell senescence, the potential roles of these cells in animal models and human studies of NDs, and therapeutic strategies targeting CD4+ T-cell senescence.

The immune system in neurological diseases: What innate-like T cells have to say

The immune system classically consists of 2 lines of defense, innate and adaptive, both of which interact with one another effectively to protect us against any pathogenic threats. Importantly, there is a diverse subset of cells known as innate-like T cells that act as a bridge between the innate and adaptive immune systems and are pivotal players in eliciting inflammatory immune responses. A growing body of evidence has demonstrated the regulatory impact of these innate-like T cells in central nervous system (CNS) diseases and that such immune cells can traffic into the brain in multiple pathological conditions, which can be typically attributed to the breakdown of the blood-brain barrier. However, until now, it has been poorly understood whether innate-like T cells have direct protective or causative properties, particularly in CNS diseases. Therefore, in this review, our attention is focused on discussing the critical roles of 3 unique subsets of unconventional T cells, namely, natural killer T cells, γδ T cells, and mucosal-associated invariant T cells, in the context of CNS diseases, disorders, and injuries and how the interplay of these immune cells modulates CNS pathology, in an attempt to gain a better understanding of their complex functions.

The role of T-lymphocytes in central nervous system diseases

The central nervous system (CNS) has been considered an immunologically privileged site. In the past few decades, research on inflammation in CNS diseases has mostly focused on microglia, innate immune cells that respond rapidly to injury and infection to maintain CNS homeostasis. Discoveries of lymphatic vessels within the dura mater and peripheral immune cells in the meningeal layer indicate that the peripheral immune system can monitor and intervene in the CNS. This review summarizes recent advances in the involvement of T lymphocytes in multiple CNS diseases, including brain injury, neurodegenerative diseases, and psychiatric disorders. It emphasizes that a deep understanding of the pathogenesis of CNS diseases requires intimate knowledge of T lymphocytes. Aiming to promote a better understanding of the relationship between the immune system and CNS and facilitate the development of therapeutic strategies targeting T lymphocytes in neurological diseases.

Antineoplastics for treating Alzheimer's disease and dementia: Evidence from preclinical and observational studies

As the world population ages, there will be an increasing need for effective therapies for aging-associated neurodegenerative disorders, which remain untreatable. Dementia due to Alzheimer's disease (AD) is one of the leading neurological diseases in the aging population. Current therapeutic approaches to treat this disorder are solely symptomatic, making the need for new molecular entities acting on the causes of the disease extremely urgent. One of the potential solutions is to use compounds that are already in the market. The structures have known pharmacokinetics, pharmacodynamics, toxicity profiles, and patient data available in several countries. Several drugs have been used successfully to treat diseases different from their original purposes, such as autoimmunity and peripheral inflammation. Herein, we divulge the repurposing of drugs in the area of neurodegenerative diseases, focusing on the therapeutic potential of antineoplastics to treat dementia due to AD and dementia. We briefly touch upon the shared pathological mechanism between AD and cancer and drug repurposing strategies, with a focus on artificial intelligence. Next, we bring out the current status of research on the development of drugs, provide supporting evidence from retrospective, clinical, and preclinical studies on antineoplastic use, and bring in new areas, such as repurposing drugs for the prion-like spreading of pathologies in treating AD.

IL-17A deficiency alleviates cerebral ischemia-reperfusion injury via activating ERK/MAPK pathway in hippocampal CA1 region

Cognitive impairment is a major complication of cerebral ischemia-reperfusion (CIR) injury and has an important impact on the quality of life of patients. However, the precise mechanisms underlying cognitive impairment after CIR injury remain elusive. In the current study, we investigated the role of interleukin 17 A (IL-17A) on CIR injury-induced cognitive impairment in wild-type and IL-17A knockout mice using RNA sequencing analysis, neurological assessments, Golgi-Cox staining, dendritic spine analysis, immunofluorescence assay, and western blot analysis. RNA sequencing identified 195 CIR-induced differentially expressed genes (83 upregulated and 112 downregulated), highlighting several enriched biological processes (negative regulation of phosphorylation, transcription regulator complex, and receptor ligand activity) and signaling pathways (mitogen-activated protein kinase [MAPK], tumor necrosis factor, and IL-17 signaling pathways). We also injected adeno-associated virus into the bilateral hippocampal CA1 regions of CIR mice to upregulate or downregulate cyclic AMP response element-binding protein. IL-17A knockout activated the extracellular signal-regulated kinase (ERK)/MAPK signaling pathway and further improved synaptic plasticity, structure, and function in CIR mice. Together, our findings suggest that IL-17A deficiency alleviates CIR injury by activating the ERK/MAPK signaling pathway and enhancing hippocampal synaptic plasticity.

Nutritional strategies modulating the gut microbiome as a preventative and therapeutic approach in normal and pathological age-related cognitive decline: a systematic review of preclinical and clinical findings

CONTEXT

The proportion of the elderly population is on the rise across the globe, and with it the prevalence of age-related neurodegenerative diseases. The gut microbiota, whose composition is highly regulated by dietary intake, has emerged as an exciting research field in neurology due to its pivotal role in modulating brain functions via the gut-brain axis.

OBJECTIVES

We aimed at conducting a systematic review of preclinical and clinical studies investigating the effects of dietary interventions on cognitive ageing in conjunction with changes in gut microbiota composition and functionality.

METHODS

PubMed and Scopus were searched using terms related to ageing, cognition, gut microbiota and dietary interventions. Studies were screened, selected based on previously determined inclusion and exclusion criteria, and evaluated for methodological quality using recommended risk of bias assessment tools.

RESULTS

A total of 32 studies (18 preclinical and 14 clinical) were selected for inclusion. We found that most of the animal studies showed significant positive intervention effects on cognitive behavior, while outcomes on cognition, microbiome features, and health parameters in humans were less pronounced. The effectiveness of dietary interventions depended markedly on the age, gender, degree of cognitive decline and baseline microbiome composition of participants.

CONCLUSION

To harness the full potential of microbiome-inspired nutrition for cognitive health, one of the main challenges remains to better understand the interplay between host, his microbiome, dietary exposures, whilst also taking into account environmental influences. Future research should aim toward making use of host-specific microbiome data to guide the development of personalized therapies.

Meningeal interleukin-17-producing T cells mediate cognitive impairment in a mouse model of salt-sensitive hypertension

Hypertension (HTN), a disease afflicting over one billion individuals worldwide, is a leading cause of cognitive impairment, the mechanisms of which remain poorly understood. In the present study, in a mouse model of HTN, we find that the neurovascular and cognitive dysfunction depends on interleukin (IL)-17, a cytokine elevated in individuals with HTN. However, neither circulating IL-17 nor brain angiotensin signaling can account for the dysfunction. Rather, IL-17 produced by T cells in the dura mater is the mediator released in the cerebrospinal fluid and activating IL-17 receptors on border-associated macrophages (BAMs). Accordingly, depleting BAMs, deleting IL-17 receptor A in brain macrophages or suppressing meningeal T cells rescues cognitive function without attenuating blood pressure elevation, circulating IL-17 or brain angiotensin signaling. Our data unveil a critical role of meningeal T cells and macrophage IL-17 signaling in the neurovascular and cognitive dysfunction in a mouse model of HTN.

Physiological roles of human interleukin-17 family

Interleukin-17 s (IL-17s) are well-known proinflammatory cytokines, and their antagonists perform excellently in the treatment of inflammatory skin diseases such as psoriasis. However, their physiological functions have not been given sufficient attention by clinicians. IL-17s can protect the host from extracellular pathogens, maintain epithelial integrity, regulate cognitive processes and modulate adipocyte activity through distinct mechanisms. Here, we present a systematic review concerning the physiological functions of IL-17s. Our goal is not to negate the therapeutic effect of IL-17 antagonists, but to ensure their safe use and reasonably explain the possible adverse events that may occur in their application.

Comparing HD knockin pigs and mice reveals the pathological role of IL-17

Our previous work has established a knockin (KI) pig model of Huntington's disease (HD) that can replicate the typical pathological features of HD, including selective striatal neuronal loss, reactive gliosis, and axonal degeneration. However, HD KI mice exhibit milder neuropathological phenotypes and lack overt neurodegeneration. By performing RNA sequencing to compare the gene expression profiles between HD KI pigs and mice, we find that genes related to interleukin-17 (IL-17) signaling are upregulated in the HD pig brains compared to the mouse brains. Delivery of IL-17 into the brain striatum of HD KI mice causes greater reactive gliosis and synaptic deficiency compared to HD KI mice that received PBS. These findings suggest that the upregulation of genes related to IL-17 signaling in HD pig brains contributes to severe glial pathology in HD and identify this as a potential therapeutic target for treating HD.

27-hydroxycholesterol causes cognitive deficits by disturbing Th17/Treg balance and the related immune responses in mild cognitive impairment patients and C57BL/6J mice

BACKGROUND

Cognitive impairment is associated with dysregulated immune responses. Emerging evidence indicates that Th17 cells and their characteristic cytokine-IL-17 are receiving growing interest in the pathogenesis of cognitive decline. Here, we focus on the involvement of Th17 cells in mild cognitive impairment (MCI) and the possible mechanism of cholesterol metabolite-27-hydroxycholesterol (27-OHC).

METHODS

100 individuals were recruited into the nested case-control study who completed cognition assessment and the detection of oxysterols and Th17-related cytokines in serum. In addition, mice were treated with 27-OHC and inhibitors of RORγt and Foxp3 (Th17 and Treg transcription factors), and the factors involved in Th17/Treg balance and amyloidosis were detected.

RESULTS

Our results showed there was enhanced 27-OHC level in serum of MCI individuals. The Th17-related cytokines homeostasis was altered, manifested as increased IL-17A, IL-12p70, IL-23, GM-CSF, MIP-3α and TNF-α but decreased IL-13, IL-28A and TGF-β1. Further, in vivo experiments showed that 27-OHC induced higher immunogenicity, which increased Th17 proportion but decreased Treg cells in peripheral blood mononuclear cells (PBMCs); Th17 proportions in hippocampus, and IL-17A level in serum and brain were also higher than control mice. The fluorescence intensity of amyloid-β (Aβ) and the precursor of amyloid A amyloidosis-serum amyloid A (SAA) was increased in the brain of 27-OHC-treated mice, and worse learning and memory performance was supported by water maze test results. While by inhibiting RORγt in 27-OHC-loaded mice, Th17 proportions in both PBMCs and hippocampus were reduced, and expressions of IL-17A and TGF-β1 were down- and up-regulated, respectively, along with a decreased amyloidosis in brain and improved learning and memory decline.

CONCLUSIONS

Altogether, our results demonstrate that excessive 27-OHC aggravates the amyloidosis and leads to cognitive deficits by regulating RORγt and disturbing Th17/Treg balance.

IL-17A promotes the progression of Alzheimer's disease in APP/PS1 mice

BACKGROUND

Alzheimer's disease (AD), which is the most common cause of dementia in elderly individuals, is a progressive neurodegenerative disorder. Neuroinflammation, which is an immune response that is activated by glial cells in the central nervous system, plays an important role in neurodegenerative diseases. Many studies have shown that interleukin-17A (IL-17A) plays an important role in AD, but research on the pathological effects of IL-17A on AD is limited.

METHODS

We report the effect of IL-17A on AD progression in APPswe/PS1dE9 (APP/PS1) mice, which are the most widely used AD model mice. The BV2 cell line, which is a microglial cell line derived from C57/BL6 mice, was used to establish a cell model to verify the role of IL-17A in neuroinflammation at the cellular level. The HT22 hippocampal neuronal cell line was used to investigate the relationship between IL-17A and Aβ deposition.

RESULTS

In this research, we found that IL-17A promotes the progression of AD in the APP/PS1 mouse model. The role of IL-17A in neuroinflammation is related to tumour necrosis factor (TNF)-α. Circulating IL-17A stimulates the secretion of TNF-α by microglia through the Toll-like receptor 4 (TLR4)/nuclear factor (NF)-κB signalling pathway, thus exacerbating neuroinflammation. In addition, intraperitoneal injection of IL-17A antibody (IL17Ab) significantly improved the cognitive function of APP/PS1 mice.

CONCLUSIONS

IL-17A increased TNF-α levels in the brain and exacerbated neuroinflammation through the TLR4/NF-κB signalling pathway and microglial activation in APP/PS1 mice. Moreover, IL-17A promoted the progression of AD by enhancing neuroinflammation, inhibiting microglial phagocytosis, and promoting the deposition of β-amyloid 42 in AD model mice.

Gut dysbiosis aggravates cognitive deficits, amyloid pathology and lipid metabolism dysregulation in a transgenic mouse model of Alzheimer's disease

Gut dysbiosis, a well-known risk factor to triggers the progression of Alzheimer's disease (AD), is strongly associated with metabolic disturbance. Trimethylamine N-oxide (TMAO), produced in the dietary choline metabolism, has been found to accelerate neurodegeneration in AD pathology. In this study, the cognitive function and gut microbiota of TgCRND8 (Tg) mice of different ages were evaluated by Morris water maze task (MWMT) and 16S rRNA sequencing, respectively. Young pseudo germ-free (PGF) Tg mice that received faecal microbiota transplants from aged Tg mice and wild-type (WT) mice were selected to determine the role of the gut microbiota in the process of neuropathology. Excessive choline treatment for Tg mice was used to investigate the role of abnormal choline metabolism on the cognitive functions. Our results showed that gut dysbiosis, neuroinflammation response, Aβ deposition, tau hyperphosphorylation, TMAO overproduction and cyclin-dependent kinase 5 (CDK5)/transcription 3 (STAT3) activation occurred in Tg mice age-dependently. Disordered microbiota of aged Tg mice accelerated AD pathology in young Tg mice, with the activation of CDK5/STAT3 signaling in the brains. On the contrary, faecal microbiota transplantation from WT mice alleviated the cognitive deficits, attenuated neuroinflammation, Aβ deposition, tau hyperphosphorylation, TMAO overproduction and suppressed CDK5/STAT3 pathway activation in Tg mice. Moreover, excessive choline treatment was also shown to aggravate the cognitive deficits, Aβ deposition, neuroinflammation and CDK5/STAT3 pathway activation. These findings provide a novel insight into the interaction between gut dysbiosis and AD progression, clarifying the important roles of gut microbiota-derived substances such as TMAO in AD neuropathology.

Cytokines, synaptic plasticity and network dynamics: a matter of balance

The modern view of the immune system as a sensitizing and modulating machinery of the central nervous system is now well recognized. However, the specific mechanisms underlying this fine crosstalk have yet to be fully disentangled. To control cognitive function and behavior, the two systems are engaged in a subtle interacting act. In this scenario, a dual action of pro-inflammatory cytokines in the modulation of brain network connections is emerging. Pro-inflammatory cytokines are indeed required to express physiological plasticity in the hippocampal network while being detrimental when over-expressed during uncontrolled inflammatory processes. In this dynamic equilibrium, synaptic functioning and the performance of neural networks are ensured by maintaining an appropriate balance between pro- and anti-inflammatory molecules in the central nervous system microenvironment.

Inhibition of γδ T Cells Alleviates Blood-Brain Barrier in Cardiac Arrest and Cardiopulmonary Resuscitation in Mice

Ischemia/reperfusion (I/R) injury is the leading cause of death following cardiac arrest (CA) and cardiopulmonary resuscitation (CPR). γδT cells are suggested to aggravate blood-brain barrier (BBB) injury in various pathological processes. We herein investigate the effects of γδT cells inhibitor (UC7-13D5) against I/R injury post-CA/CPR. C57BL/6 mice were subjected to CA through injection of KCL (70 μL of 0.5 mol/L) and cessation of mechanical ventilation followed by CPR. Flow cytometry was performed to measure the proportion of CD3-positive cells after intraperitoneal injection of 200 μg UC7-13D5 at 6 h, 24 h, and 48 h post-resuscitation into mice. Neurological scores and modified neurological severity scores were assessed to examine neurological functions. Brain edema was estimated via brain water content measurements. Immunohistochemistry of caspase-3 and immunofluorescence staining of claudin-1, ZO-1 and CD31 were performed to detect neuronal apoptosis, BBB integrity and angiogenesis. Microvascular morphology in the cortical area was assessed via H&E staining. Oxidative stress was determined by measuring malondialdehyde, myeloperoxidase, xanthine oxidase, superoxide dismutase, and glutathione peroxidase activities. Western blotting was performed to measure the protein levels of Nuclear factor-E2-related factor 2 (Nrf2) and Heme oxygenase-1 (HO-1). UC7-13D5 effectively depleted γδT cells. Inhibition of γδT cells improved neurological deficits and reduced brain edema post-CA/CPR. γδT cells depletion attenuated neuronal apoptosis, BBB disruption and oxidative stress and promoted angiogenesis following CA/CPR. Inhibition of γδT cells facilitated the activation of the Nrf2/HO-1 pathway in CA/CPR-induced mice. Inhibition of γδT cells alleviates neurological deficits and cerebral edema in mice with CA/CPR by inhibiting neuronal apoptosis, BBB disruption and oxidative stress, and promoting angiogenesis via activation of the Nrf2/HO-1 pathway.

Advances in the study of IL-17 in neurological diseases and mental disorders

Interleukin-17 (IL-17), a cytokine characteristically secreted by T helper 17 (Th17) cells, has attracted increasing attention in recent years because of its importance in the pathogenesis of many autoimmune or chronic inflammatory diseases. Recent studies have shown that neurological diseases and mental disorders are closely related to immune function, and varying degrees of immune dysregulation may disrupt normal expression of immune molecules at critical stages of neural development. Starting from relevant mechanisms affecting immune regulation, this article reviews the research progress of IL-17 in a selected group of neurological diseases and mental disorders (autism spectrum disorder, Alzheimer's disease, epilepsy, and depression) from the perspective of neuroinflammation and the microbiota-gut-brain axis, summarizes the commonalities, and provides a prospective outlook of target application in disease treatment.

Interleukin-1β and TNF-α are elevated in the amygdala of adult rats prenatally exposed to ethanol

Affective disorders, including anxiety and depression, developed in adult offspring of the mothers who consumed alcohol during pregnancy could be associated with an imbalance in neuroimmune factors in the amygdala (corpus amygdaloideum) resulted in impaired emotional stimulus processing. The aim of this study was to compare the content of cytokines TNF-α, IL-1α, IL-1β, IL-10, and IL-17 in the amygdala of adult female rats exposed to alcohol in utero and control rats. Cytokine levels were evaluated using a multiplex immunoassay system; mRNA expression was investigated using a real-time reverse transcription-polymerase chain reaction (RT-qPCR) assay. Prenatal alcohol exposure led to the increase in the content of TNF-α and IL-1β without significant changes in the mRNA expression level. Our data suggest that ethanol exposure to the fetus during pregnancy can result in long-term alterations in the content of the key neuroinflammatory factors in the amygdala, which in turn can be a risk factor for affective disorders in the adulthood.

Exosomes Derived from M2 Microglial Cells Modulated by 1070-nm Light Improve Cognition in an Alzheimer's Disease Mouse Model

Near-infrared photobiomodulation has been identified as a potential strategy for Alzheimer's disease (AD). However, the mechanisms underlying this therapeutic effect remain poorly characterize. Herein, it is illustrate that 1070-nm light induces the morphological alteration of microglia from an M1 to M2 phenotype that secretes exosomes, which alleviates the β-amyloid burden to improve cognitive function by ameliorating neuroinflammation and promoting neuronal dendritic spine plasticity. The results show that 4 J cm-2 1070-nm light at a 10-Hz frequency prompts microglia with an M1 inflammatory type to switch to an M2 anti-inflammatory type. This induces secretion of M2 microglial-derived exosomes containing miR-7670-3p, which targets activating transcription factor 6 (ATF6) during endoplasmic reticulum (ER) stress. Moreover, it is found that miR-7670-3p reduces ATF6 expression to further ameliorate ER stress, thus attenuating the inflammatory response and protecting dendritic spine integrity of neurons in the cortex and hippocampus of 5xFAD mice, ultimately leading to improvements in cognitive function. This study highlights the critical role of exosomes derive from 1070-nm light-modulated microglia in treating AD mice, which may provide a theoretical basis for the treatment of AD with the use of near-infrared photobiomodulation.

Unconventional T cells in brain homeostasis, injury and neurodegeneration

The interaction between peripheral immune cells and the brain is an important component of the neuroimmune axis. Unconventional T cells, which include natural killer T (NKT) cells, mucosal-associated invariant T (MAIT) cells, γδ T cells, and other poorly defined subsets, are a special group of T lymphocytes that recognize a wide range of nonpolymorphic ligands and are the connection between adaptive and innate immunity. Recently, an increasing number of complex functions of these unconventional T cells in brain homeostasis and various brain disorders have been revealed. In this review, we describe the classification and effector function of unconventional T cells, review the evidence for the involvement of unconventional T cells in the regulation of brain homeostasis, summarize the roles and mechanisms of unconventional T cells in the regulation of brain injury and neurodegeneration, and discuss immunotherapeutic potential as well as future research goals. Insight of these processes can shed light on the regulation of T cell immunity on brain homeostasis and diseases and provide new clues for therapeutic approaches targeting brain injury and neurodegeneration.

Aging unconventionally: γδ T cells, iNKT cells, and MAIT cells in aging

Unconventional T cells include γδ T cells, invariant Natural Killer T cells (iNKT) cells and Mucosal Associated Invariant T (MAIT) cells, which are distinguished from conventional T cells by their recognition of non-peptide ligands presented by non-polymorphic antigen presenting molecules and rapid effector functions that are pre-programmed during their development. Here we review current knowledge of the effect of age on unconventional T cells, from early life to old age, in both mice and humans. We then discuss the role of unconventional T cells in age-associated diseases and infections, highlighting the similarities between members of the unconventional T cell family in the context of aging.

Immune senescence in aged APP/PS1 mice

Objectives

To evaluate the linkage between age and deficits in innate and adaptive immunity which heralds both Alzheimer's disease (AD) onset and progression. The pathobiological events which underlie and tie these outcomes remain not fully understood.

Methods

To investigate age-dependent immunity in AD, we evaluated innate and adaptive immunity in coordinate studies of regulatory T cell (Treg) function, T cell frequencies, and microglial integrity. These were assessed in blood, peripheral lymphoid tissues, and the hippocampus of transgenic (Tg) amyloid precursor protein/presenilin 1 (APP/PS1) against non-Tg mice. Additionally, immune arrays of hippocampal tissue were performed at 4, 6, 12, and 20 months of age.

Results

APP/PS1 mice showed progressive impairment of Treg immunosuppressive function with age. There was partial restoration of Treg function in 20-month-old mice. Ingenuity pathway analyses of hippocampal tissues were enriched in inflammatory, oxidative, and cellular activation pathways that paralleled advancing age and AD-pathobiology. Operative genes in those pathways included, but were not limited to triggering receptor on myeloid cells 1 (TREM1), T helper type 1 (Th1), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathways. Interleukin-17 (IL-17), nitric oxide, acute phase, and T cell receptor signaling pathways were also perturbed. Significant inflammation was observed at 6- and 12-months. However, at 20-months, age associated partial restoration of Treg function reduced inflammatory phenotype.

Conclusions

Impaired Treg function, inflammation and oxidative stress were associated with AD pathology. Age associated partial restoration of Treg function in old mice reduced the hippocampal inflammatory phenotype. Restoring Treg suppressive function can be a therapeutic modality for AD.

As a Potential Therapeutic Target, C1q Induces Synapse Loss Via Inflammasome-activating Apoptotic and Mitochondria Impairment Mechanisms in Alzheimer's Disease

C1q, the initiator of the classical pathway of the complement system, is activated during Alzheimer's disease (AD) development and progression and is especially associated with the production and deposition of β-amyloid protein (Aβ) and phosphorylated tau in β-amyloid plaques (APs) and neurofibrillary tangles (NFTs). Activation of C1q is responsible for induction of synapse loss, leading to neurodegeneration in AD. Mechanistically, C1q could activate glial cells, which results in the loss of synapses via regulation of synapse pruning and phagocytosis in AD. In addition, C1q induces neuroinflammation by inducing proinflammatory cytokine secretion, which is partially mediated by inflammasome activation. Activation of inflammasomes might mediate the effects of C1q on induction of synapse apoptosis. On the other hand, activation of C1q impairs mitochondria, which hinders the renovation and regeneration of synapses. All these actions of C1q contribute to the loss of synapses during neurodegeneration in AD. Therefore, pharmacological, or genetic interventions targeting C1q may provide potential therapeutic strategies for combating AD.

IL-17: Balancing Protective Immunity and Pathogenesis

The biological role of interleukin 17 (IL-17) has been explored during recent decades and identified as a pivotal player in coordinating innate and adaptive immune responses. Notably, IL-17 functions as a double-edged sword with both destructive and protective immunological roles. While substantial progress has implicated unrestrained IL-17 in a variety of infectious diseases or autoimmune conditions, IL-17 plays an important role in protecting the host against pathogens and maintaining physiological homeostasis. In this review, we describe canonical IL-17 signaling mechanisms promoting neutrophils recruitment, antimicrobial peptide production, and maintaining the epithelium barrier integrity, as well as some noncanonical mechanisms involving IL-17 that elicit protective immunity.

Using Stems to Bear Fruit: Deciphering the Role of Alzheimer's Disease Risk Loci in Human-Induced Pluripotent Stem Cell-Derived Microglia

Alzheimer's disease (AD) is the most common neurodegenerative disorder globally. In people aged 65 and older, it is estimated that 1 in 9 currently live with the disease. With aging being the greatest risk factor for disease onset, the physiological, social and economic burden continues to rise. Thus, AD remains a public health priority. Since 2007, genome-wide association studies (GWAS) have identified over 80 genomic loci with variants associated with increased AD risk. Although some variants are beginning to be characterized, the effects of many risk loci remain to be elucidated. One advancement which may help provide a patient-focused approach to tackle this issue is the application of gene editing technology and human-induced pluripotent stem cells (hiPSCs). The relatively non-invasive acquisition of cells from patients with known AD risk loci may provide important insights into the pathological role of these risk variants. Of the risk genes identified, many have been associated with the immune system, including ABCA7, CLU, MEF2C, PICALM and TREM2-genes known to be highly expressed in microglia. This review will detail the potential of using hiPSC-derived microglia to help clarify the role of immune-associated genetic risk variants in AD.

Sex-based differences in effector cells of the adaptive immune system during Alzheimer's disease and related dementias

Neurological conditions such as Alzheimer's disease (AD) and related dementias (ADRD) present with many challenges due to the heterogeneity of the related disease(s), making it difficult to develop effective treatments. Additionally, the progression of ADRD-related pathologies presents differently between men and women. With two-thirds of the population affected with ADRD being women, ADRD has presented itself with a bias toward the female population. However, studies of ADRD generally do not incorporate sex-based differences in investigating the development and progression of the disease, which is detrimental to understanding and treating dementia. Additionally, recent implications for the adaptive immune system in the development of ADRD bring in new factors to be considered as part of the disease, including sex-based differences in immune response(s) during ADRD development. Here, we review the sex-based differences of pathological hallmarks of ADRD presentation and progression, sex-based differences in the adaptive immune system and how it changes with ADRD, and the importance of precision medicine in the development of a more targeted and personalized treatment for this devastating and prevalent neurodegenerative condition.

Potential active compounds and common mechanisms of Evodia rutaecarpa for Alzheimer's disease comorbid pain by network pharmacology analysis

Evodia rutaecarpa (Evodia) is a Chinese herbal medicine with analgesic and anti-neurodegenerative properties. However, whether Evodia compounds can be applied for the comorbid pain of Alzheimer's disease (AD) and the underlying mechanisms remain unclear. Herein, 137 common targets of Evodia between AD and pain were predicted from drug and disease target databases. Subsequently, protein-protein interaction (PPI) network, protein function module construction, and bioinformatics analyses were used to analyze the potential relationship among targets, pathways, and diseases. Evodia could simultaneously treat AD comorbid pain through multi-target, multi-component, and multi-pathway mechanisms, and inflammation was an important common phenotype of AD and pain. The relationship between important transcription factors such as RELA, NF-κB1, SP1, STAT3, and JUN on IL-17, TNF, and MAPK signaling pathways might be potential mechanisms of Evodia. Additionally, 10 candidate compounds were predicted, and evodiamine might be the effective active ingredient of Evodia in treating AD or pain. In summary, this study provided a reference for subsequent research and a novel understanding and direction for the clinical use of evodiamine to treat AD patients with comorbid pain.

Proteomics identifies lipocalin-2 in neonatal inflammation associated with cerebrovascular alteration in mice and preterm infants

Staphylococcus (S.) epidermidis is the most common nosocomial coagulase-negative staphylococci infection in preterm infants. Clinical signs of infection are often unspecific and novel markers to complement diagnosis are needed. We investigated proteomic alterations in mouse brain after S. epidermidis infection and in preterm infant blood. We identified lipocalin-2 (LCN2) as a crucial protein associated with cerebrovascular changes and astrocyte reactivity in mice. We further proved that LCN2 protein expression was associated with endothelial cells but not astrocyte reactivity. By combining network analysis and differential expression approaches, we identified LCN2 linked to blood C-reactive protein levels in preterm infants born <28 weeks of gestation. Blood LCN2 levels were associated with similar alterations of cytokines and chemokines in both infected mice and human preterm infants with increased levels of C-reactive protein. This experimental and clinical study suggests that LCN2 may be a marker of preterm infection/inflammation associated with cerebrovascular changes and neuroinflammation.

Development of a novel immune infiltration-related diagnostic model for Alzheimer's disease using bioinformatic strategies

Background

The pathogenesis of Alzheimer's disease (AD) is complex and multi-factorial. Increasing evidence has shown the important role of immune infiltration in AD. Thus the current study was designed to identify immune infiltration-related genes and to explore their diagnostic value in AD.

Methods

The expression data of AD patients were downloaded from the GEO database. The limma R package identified differentially expressed genes (DEGs) between AD and controls. The CIBERSORT algorithm identified differentially infiltrated immune cells (DIICs) between AD and controls. DIIC-correlated DEGs were obtained by Pearson correlation analysis. WGCNA was employed to identify DIIC-related modules. Next, LASSO, RFE, and RF machine learning methods were applied to screen robust DIIC-related gene signatures in AD, followed by the construction and validation of a diagnostic nomogram. Detection of the expression of related genes in the peripheral blood of Alzheimer's disease and healthy volunteers by RT-PCR. In addition, the CTD database predicted chemicals targeting DIIC-related gene signatures in the treatment of AD.

Results

NK cells, M0 macrophages, activated myeloid dendritic cells, resting mast cells, CD8+ T cells, resting memory CD4+ T cells, gamma delta T cells, and M2 macrophages were differentially infiltrated between AD and controls. Pearson analysis identified a total of 277 DIIC-correlated DEGs between AD and controls. Thereafter, 177 DIIC-related genes were further obtained by WGCNA analysis. By LASSO, RFE and RF algorithms, CMTM2, DDIT4, LDHB, NDUFA1, NDUFB2, NDUFS5, RPL17, RPL21, RPL26 and NDUFAF2 were identified as robust gene signature in AD. The results of RT-PCR detection of peripheral blood samples from Alzheimer's disease and healthy volunteers showed that the expression trend of ten genes screened was consistent with the detection results; among them, the expression levels of CMTM2, DDIT4, LDHB, NDUFS5, and RPL21 are significantly different among groups. Thus, a diagnostic nomogram based on a DIIC-related signature was constructed and validated. Moreover, candidate chemicals targeting those biomarkers in the treatment of AD, such as 4-hydroxy-2-nonenal, rosiglitazone, and resveratrol, were identified in the CTD database.

Conclusion

For the first time, we identified 10 immune infiltration-related biomarkers in AD, which may be helpful for the diagnosis of AD and provide guidance in the treatment of AD.

Clonal CD8 T cells in the leptomeninges are locally controlled and influence microglia in human neurodegeneration

Recent murine studies have highlighted a crucial role for the meninges in surveilling the central nervous system (CNS) and influencing CNS inflammation. However, how meningeal immunity is altered in human neurodegeneration and its potential effects on neuroinflammation is understudied. In the present study, we performed single-cell analysis of the transcriptomes and T cell receptor repertoire of 72,576 immune cells from 36 postmortem human brain and leptomeninges tissues from donors with neurodegenerative diseases including amyotrophic lateral sclerosis, Alzheimer's disease, and Parkinson's disease. We identified the meninges as an important site of antigen presentation and CD8 T cell activation and clonal expansion and found that T cell activation in the meninges is a requirement for infiltration into the CNS. We further found that natural killer cells have the potential to negatively regulate T cell activation locally in the meninges through direct killing and are one of many regulatory mechanisms that work to control excessive neuroinflammation.

Interleukin-17 as a key player in neuroimmunometabolism

In mammals, interleukin (IL)-17 cytokines are produced by innate and adaptive lymphocytes. However, the IL-17 family has widespread expression throughout evolution, dating as far back as cnidaria, molluscs and worms, which predate lymphocytes. The evolutionary conservation of IL-17 suggests that it is involved in innate defence strategies, but also that this cytokine family has a fundamental role beyond typical host defence. Throughout evolution, IL-17 seems to have a major function in homeostatic maintenance at barrier sites. Most recently, a pivotal role has been identified for IL-17 in regulating cellular metabolism, neuroimmunology and tissue physiology, particularly in adipose tissue. Here we review the emerging role of IL-17 signalling in regulating metabolic processes, which may shine a light on the evolutionary role of IL-17 beyond typical immune responses. We propose that IL-17 helps to coordinate the cross-talk among the nervous, endocrine and immune systems for whole-body energy homeostasis as a key player in neuroimmunometabolism.

Increased Interleukin-17-Producing γδT Cells in the Brain Exacerbate the Pathogenesis of Sepsis-Associated Encephalopathy and Sepsis-Induced Anxiety in Mice

Overactivated microglia play a key role in sepsis-associated encephalopathy (SAE), although the involvement of T cells is unclear. γδT cells in the brain and meninges regulate normal fear responses via interleukin (IL)-17 in healthy mice. In our sepsis model, the mice showed exacerbated anxious behavior at 10 days post-induction (dpi). At 8 dpi, IL-17 mRNA was significantly upregulated in the brains of septic mice compared with those of control mice. Simultaneously, the number of γδT cells increased in the brains of septic mice in a severity-dependent manner. Additionally, IL-17-producing γδT cells, expressing both the C-X-C motif receptor (CXCR) 6 and the C-C motif receptor (CCR) 6, increased in mice brains, dependent on the severity of sepsis. The frequency of γδT cells in the meninges fluctuated similarly to that in the brain, peaking at 8 dpi of sepsis. Behavioral tests were performed on septic mice after the continuous administration of anti-γδTCR (α-γδTCR) or anti-IL-17A (α-IL-17A) antibodies to deplete the γδT cells and IL-17A, respectively. Compared with IgG-treated septic mice, α-γδTCR- and α-IL-17A-treated septic mice showed suppressed microglial activation and improvements in anxious behavior. These results suggested that CCR6⁺CXCR6⁺ IL-17-producing γδT cells in the brain and meninges promote the exacerbation of SAE and sepsis-induced psychological disorders in mice.

Adolescent swimming exercise following maternal valproic acid treatment improves cognition and reduces stress-related symptoms in offspring mice: Role of sex and brain cytokines

Valproic acid (VPA) treatment during pregnancy is a risk factor for developing autism spectrum disorder, cognitive deficits, and stress-related disorders in children. No effective therapeutic strategies are currently approved to treat or manage core symptoms of autism. Active lifestyles and physical activity are closely associated with health and quality of life during childhood and adulthood. This study aimed to evaluate whether swimming exercise during adolescence can prevent the development of cognitive dysfunction and stress-related disorders in prenatally VPA-exposed mice offspring. Pregnant mice received VPA, afterwards, offspring were subjected to swimming exercise. We assessed neurobehavioral performances and inflammatory cytokines (interleukin-(IL)6, tumor-necrosis-factor-(TNF)α, interferon-(IFN)γ, and IL-17A) in the hippocampus and prefrontal cortex of offspring. Prenatal VPA treatment increased anxiety-and anhedonia-like behavior and decreased social behavior in male and female offspring. Prenatal VPA exposure also increased behavioral despair and reduced working and recognition memory in male offspring. Although prenatal VPA increased hippocampal IL-6 and IFN-γ, and prefrontal IFN-γ and IL-17 in males, it only increased hippocampal TNF-α and IFN-γ in female offspring. Adolescent exercise made VPA-treated male and female offspring resistant to anxiety-and anhedonia-like behavior in adulthood, whereas it only made VPA-exposed male offspring resistant to behavioral despair, social and cognitive deficits in adulthood. Exercise reduced hippocampal IL-6, TNF-α, IFN-γ, and IL-17, and prefrontal IFN-γ and IL-17 in VPA-treated male offspring, whereas it reduced hippocampal TNF-α and IFN-γ in VPA-treated female offspring. This study suggests that adolescent exercise may prevents the development of stress-related symptoms, cognitive deficits, and neuroinflammation in prenatally VPA-exposed offspring mice.

Cytokines as emerging regulators of central nervous system synapses

Cytokines are key messengers by which immune cells communicate, and they drive many physiological processes, including immune and inflammatory responses. Early discoveries demonstrated that cytokines, such as the interleukin family members and TNF-α, regulate synaptic scaling and plasticity. Still, we continue to learn more about how these traditional immune system cytokines affect neuronal structure and function. Different cytokines shape synaptic function on multiple levels ranging from fine-tuning neurotransmission, to regulating synapse number, to impacting global neuronal networks and complex behavior. These recent findings have cultivated an exciting and growing field centered on the importance of immune system cytokines for regulating synapse and neural network structure and function. Here, we highlight the latest findings related to cytokines in the central nervous system and their regulation of synapse structure and function. Moreover, we explore how these mechanisms are becoming increasingly important to consider in diseases-especially those with a large neuroinflammatory component.

Ginsenoside Rg1 in neurological diseases: From bench to bedside

Ginseng has been used in China as a superior medicinal material for thousands of years that can nourish the five internal organs, calm the mind and benefit wisdom. Due to its anti-inflammatory, antioxidant and neuroprotective activities, one of the active components of ginseng, ginsenoside Rg1, has been extensively investigated in the remedy of brain disorders, especially dementia and depression. In this review, we summarized the research progress on the action mechanisms of Rg1 ameliorating depression-like behaviors, including inhibition of hyperfunction of hypothalamic-pituitary-adrenal (HPA) axis, regulation of synaptic plasticity and gut flora. Rg1 may alleviate Alzheimer's disease in the early phase, as well as in the middle-late phases through repairing dendrite, axon and microglia- and astrocyte-related inflammations. We also proposed that Rg1 could regulate memory state (the imbalance of working and aversive memory) caused by distinct stimuli. These laboratory studies would further the clinical trials on Rg1. From the prospective of drug development, we discussed the limitations of the present investigations and proposed our ideas to increase permeability and bioavailability of Rg1. Taken together, Rg1 has the potential to treat neuropsychiatric disorders, but a future in-depth investigation of the mechanisms is still required. In addition, drug development will benefit from the clinical trials in one specific neuropsychiatric disorder.

T cell aging and Alzheimer’s disease

The brain has long been considered an immune-privileged organ due to the presence of the blood-brain barrier (BBB). However, recent discoveries have revealed the underestimated role of T cells in the brain through the meningeal lymphatic system. Age is the primary risk factor for Alzheimer’s disease (AD), resulting in marked age-dependent changes in T cells. Manipulating peripheral T cell immune response has been shown to impact AD, but the relationship between T cell aging and AD remains poorly understood. Given the limited success of targeting amyloid beta (Aβ) and the growing evidence of T cells’ involvement in non-lymphoid organ aging, a deeper understanding of the relationship between T cells and AD in the context of aging is crucial for advancing therapeutic progress. In this review, we comprehensively examine existing studies on T cells and AD and offer an integrated perspective on their interconnections in the context of aging. This understanding can inform the development of new interventions to prevent or treat AD.

Interplay between the catecholaminergic enzymatic axis and neurodegeneration/neuroinflammation processes in the Alzheimer's disease continuum

BACKGROUND AND PURPOSE

The locus coeruleus (LC) provides dopamine/noradrenaline (DA/NA) innervation throughout the brain and undergoes early degeneration in Alzheimer's disease (AD). We evaluated catecholaminergic enzyme levels in the cerebrospinal fluid (CSF) of a group of patients biologically defined as within the AD continuum (ADc) and explored their relationship with AD biomarkers and cytokine/growth factor levels to investigate their interplay with neurodegenerative and neuroinflammatory processes.

METHODS

The CSF concentration of DA transporter (DAT), tyrosine-hydroxylase (TH), DOPA-decarboxylase (DDC), and dopamine-β-hydroxylase (DβH), as well as cytokine/growth factor levels, were analyzed in 41 ADc patients stratified according to CSF beta-amyloid (Aβ)_1-42 (A) and p-tau (T) in AD pathological changes (A+ T-) and AD (A+ T+) subgroups, as well as in 15 control subjects (A- T-).

RESULTS

The ADc group had lower CSF levels of DAT and TH but increased DβH levels to compensate for NA synthesis. DDC levels were higher in the A+ T+ subgroup but comparable with controls in the A+ T- subgroup, probably because the DA system is resilient to the degeneration of LC neurons in the absence of tau pathology. Adjusting for age, sex, APOE genotype, and cognitive status, a significant association was found between TH and Aβ_1-42 (R²  = 0.25) and between DDC and p-tau (R²  = 0.33). Finally, TH correlated with interleukin (IL)-10 levels (p = 0.0008) and DβH with IL-1β (p = 0.03), IL-4 (p = 0.02), granulocyte colony-stimulating factor (p = 0.007), and IL-17 (p = 0.01).

CONCLUSIONS

Taken together, these findings suggest that catecholaminergic enzymes, functional markers of the catecholaminergic system, are closely linked to the neurodegenerative and neuroinflammatory processes in AD pathology.

Single-cell multiomic analysis reveals the involvement of Type I interferon-responsive CD8+ T cells in amyloid beta-associated memory loss

Alzheimer's disease (AD) is the leading cause of dementia worldwide, but there are limited therapeutic options and no current cure. While the involvement of microglia in AD has been highly appreciated, the role of other innate and adaptive immune cells remains largely unknown, partly due to their scarcity and heterogeneity. This study aimed to study non-microglial immune cells in wild type and AD-transgenic mouse brains across different ages. Our results uncovered the presence of a unique CD8+ T cell population that were selectively increased in aging AD mouse brains, here referred to as "disease-associated T cells (DATs)". These DATs were found to express an elevated tissue-resident memory and Type I interferon-responsive gene signature. Further analysis of aged AD mouse brains showed that these CD8+ T cells were not present in peripheral or meningeal tissues. Preventing CD8+ T cell development in AD-transgenic mice via genetic deletion of beta-2 microglobulin ( B2m ) led to a reduction of amyloid-β plaque formation in aged mice, and improved memory in AD-transgenic mice as early as four months of age. The integration of transcriptomic and epigenomic profiles at the single-cell level revealed potential transcription factors that reshape the regulomes of CD8+ T cells. These findings highlight a critical role for DATs in the progression of AD and provide a new avenue for treatment.

Control of the temporal development of Alzheimer's disease pathology by the MR1/MAIT cell axis

BACKGROUND

Neuroinflammation is an important feature of Alzheimer's disease (AD). Understanding which aspects of the immune system are important in AD may lead to new therapeutic approaches. We study the major histocompatibility complex class I-related immune molecule, MR1, which is recognized by an innate-like T cell population called mucosal-associated invariant T (MAIT) cells.

METHODS

Having found that MR1 gene expression is elevated in the brain tissue of AD patients by mining the Agora database, we sought to examine the role of the MR1/MAIT cell axis in AD pathology. Brain tissue from AD patients and the 5XFAD mouse model of AD were used to analyze MR1 expression through qPCR, immunofluorescence, and flow cytometry. Furthermore, mice deficient in MR1 and MAIT cells were crossed with the 5XFAD mice to produce a model to study how the loss of this innate immune axis alters AD progression. Moreover, 5XFAD mice were also used to study brain-resident MAIT cells over time.

RESULTS

In tissue samples from AD patients and 5XFAD mice, MR1 expression was substantially elevated in the microglia surrounding plaques vs. those that are further away (human AD: P < 0.05; 5XFAD: P < 0.001). In 5XFAD mice lacking the MR1/MAIT cell axis, the development of amyloid-beta plaque pathology occurred at a significantly slower rate than in those mice with MR1 and MAIT cells. Furthermore, in brain tissue from 5XFAD mice, there was a temporal increase in MAIT cell numbers (P < 0.01) and their activation state, the latter determined by detecting an upregulation of both CD69 (P < 0.05) and the interleukin-2 receptor alpha chain (P < 0.05) via flow cytometry.

CONCLUSIONS

Together, these data reveal a previously unknown role for the MR1/MAIT cell innate immune axis in AD pathology and its potential utility as a novel therapeutic target.

Proinflammatory IL-17 levels in serum/cerebrospinal fluid of patients with neurodegenerative diseases: a meta-analysis study

IL-17 is one of the major proinflammatory cytokine implicated in the pathophysiology of various chronic inflammatory diseases. However, a clear association between the levels of IL-17 and various neurodegenerative diseases is inconclusive due to lack of consistent results reported in several studies. Therefore, we designed and performed a meta-analysis study to assess the levels of IL-17 cytokine in various neurodegenerative diseases. The aim of this meta-analysis study was to assess the level of IL-17 in cerebrospinal fluid/serum of the patients with neurodegenerative diseases such as Alzheimer's disease, Parkinson disease, multiple sclerosis, and amyotrophic lateral sclerosis. An extensive search was performed on electronic databases including PubMed, Cochrane, and Google Scholar to find out the relevant studies for analysis. The quality of selected studies was assessed by Newcastle-Ottawa scale for cohort and case control studies. The standardized mean difference of level of IL-17 in patients with neurodegenerative diseases and control was calculated using RevMan 5 software. A significant increase in the level of serum IL-17 was found to in the patients with neurodegenerative diseases like Alzheimer's disease (p = 0.001) and amyotrophic lateral sclerosis (p = 0.009), whereas IL-17 level in serum of Parkinson's disease (p = 0.22), multiple sclerosis (p = 0.09), and in peripheral blood mononuclear cells of MS patients (p = 0.34) was not found to be significant. IL-17 may be involved in regulation of neuronal inflammation during the pathogenesis of these neurodegenerative disease, and its specific inhibition could be a potential therapeutic target.

Activation of the IL-17/TRAF6/NF-κB pathway is implicated in Aβ-induced neurotoxicity

BACKGROUND

Neuroinflammation plays a critical role in Amyloid-β (Aβ) pathophysiology. The cytokine, interleukin-17A (IL-17) is involved in the learning and memory process in the central nervous system and its level was reported to be increased in Alzheimer's disease (AD) brain, while the effect of IL-17 on the course of Aβ has not been well defined.

METHODS

Here, we used APP/PS1 mice to detect the IL-17 expression level. Primary hippocampal neurons were treated with IL-17, and immunofluorescence was used to investigate whether IL-17 induced neuron damage. At the same time, male C57BL/6 mice were injected with Aβ42 to mimic the Aβ model. Then IL-17 neutralizing antibody (IL-17Ab) was used to inject into the lateral ventricle, and the Open field test, Novel Objective Recognition test, Fear condition test were used to detect cognitive function. LTP was used to assess synaptic plasticity, molecular biology technology was used to assess the IL-17/TRAF6/NF-κB pathway, and ELISA was used to detect inflammatory factors.

RESULTS

Altogether, we here found that IL-17 was increased in APP/PS1 mice, and it induced neural damage by the administration to primary hippocampal neurons. Interestingly, Using Aβ42 mice, the results showed that the level of IL-17 was increased in Aβ42 model mice, and IL-17Ab could ameliorate Aβ-induced neurotoxicity and cognitive decline in C57BL/6 mice by downregulation the TRAF6/NF-κB pathway.

CONCLUSION

These findings highlight the pathogenic role of IL-17 in Aβ induced-synaptic dysfunction and cognitive deficits. Inhibition of IL-17 could ameliorate Aβ-induced neurotoxicity and cognitive decline in C57BL/6 mice by downregulation of the TRAF6/NF-κB pathway, which provides new clues for the mechanism of Aβ-induced cognitive impairments, and a basis for therapeutic intervention.

Postoperative delirium, neuroinflammation, and influencing factors of postoperative delirium: A review

Postoperative delirium (POD) is an acute cognitive dysfunction that is mainly characterized by memory impairment and disturbances in consciousness. POD can prolong the hospital stay and increase the 1-month mortality rate of patients. The overall incidence of POD is approximately 23%, and its prevalence can go up to 50% in high-risk surgeries. Neuroinflammation is an important pathogenic mechanism of POD that mediates microglial activation and leads to synaptic remodeling. Neuroinflammation, as an indispensable pathogenesis of POD, can occur due to a variety of factors, including aseptic inflammation caused by surgery, effects of anesthetic drugs, disruption of the blood-brain barrier, and epigenetics. Understanding these factors and avoiding the occurrence of risk factors may help prevent POD in time. This review provides a brief overview of POD and neuroinflammation and summarizes various factors affecting POD development mediated by neuroinflammation, which may serve as future targets for the prevention and treatment of POD.

Relationship between Hypoxic and Immune Pathways Activation in the Progression of Neuroinflammation: Role of HIF-1α and Th17 Cells

Neuroinflammation is a common event in degenerative diseases of the central and peripheral nervous system, triggered by alterations in the immune system or inflammatory cascade. The pathophysiology of these disorders is multifactorial, whereby the therapy available has low clinical efficacy. This review propounds the relationship between the deregulation of T helper cells and hypoxia, mainly Th17 and HIF-1α molecular pathways, events that are involved in the occurrence of the neuroinflammation. The clinical expression of neuroinflammation is included in prevalent pathologies such as multiple sclerosis, Guillain-Barré syndrome, and Alzheimer's disease, among others. In addition, therapeutic targets are analyzed in relation to the pathways that induced neuroinflammation.

Therapeutic potential of targeting IL-17 and its receptor signaling in neuroinflammation

T helper 17 cells are thought to significantly contribute to the neuroinflammation process during neurogenerative diseases via their signature cytokine, interleukin (IL)-17. Recently, an emerging key role of IL-17 and its receptors has been documented in inflammatory and autoimmune diseases. The clinical studies conducted on patients with neurodegenerative disease have also shown an increase in IL-17 levels in serum as well as cerebrospinal fluid samples. Therapeutic targeting of either IL-17 receptors or direct IL-17 neutralizing antibodies has shown a promising preclinical and clinical proof of concept for treating chronic autoimmune neurodegenerative diseases such as multiple sclerosis. Thus, IL-17 and its receptors have a central role in regulation of neuroinflammation and can be considered as one of the major therapeutic targets in chronic neuroinflammatory diseases.

Interleukin-17 Promotes the Infiltration of CD8+ T Cells into the Brain in a Mouse Model for Alzheimer's Disease

BACKGROUND

Interleukin-17 (IL-17) family cytokines play critical roles in inflammation and pathogen resistance. Inflammation in the central nervous system, denoted as neuroinflammation, promotes the onset and progression of Alzheimer's disease (AD). Previous studies showed that IL-17A neutralizing antibody treatment alleviated Amyloid β (Aβ) burden in rodent models of AD, while overexpression of IL-17A in mouse lateral ventricles rescued part of the AD pathology. However, the involvement of IL-17 in AD and its mechanism of action remain largely unknown.

METHODS

To investigate the role of IL-17 in AD, we crossed mice lacking the common receptor of IL-17 signaling (IL-17RA knockout mice) to the APP/PS1 mouse model of AD. We then analyzed the composition of immune cells and cytokines/chemokines during different phases of AD pathology, and interrogated the underlying mechanism by which IL-17 may regulate immune cell infiltration into AD brains.

RESULTS

Ablation of IL-17RA in APP/PS1 mice decreased infiltration of CD8+ T cells and myeloid cells to mouse brain. IL-17 was able to promote the production of myeloid- and T cell-attracting chemokines CXCL1 and CXCL9/10 in primary glial cells. We also observed that IL-17 is upregulated in the late stage of AD development, and ectopic expression of IL-17 via adenoviral infection to the cortex trended towards worsened cognition in APP/PS1 mice, suggesting a pathogenic role of excessive IL-17 in AD.

CONCLUSION

Our data show that IL-17 signaling promotes neuroinflammation in AD by accelerating the infiltration of CD8+ T lymphocytes and Gr1+ CD11b+ myeloid cells.

Neuro-immune crosstalk in depressive symptoms of multiple sclerosis

Depressive disorders can occur in up to 50% of people with multiple sclerosis in their lifetime. If left untreated, comorbid major depressive disorders may not spontaneously remit and is associated with an increased morbidity and mortality. Conversely, epidemiological evidence supports increased psychiatric visit as a significant prodromal event prior to diagnosis of MS. Are there common molecular pathways that contribute to the co-development of MS and psychiatric illnesses? We discuss immune cells that are dysregulated in MS and how such dysregulation can induce or protect against depressive symptoms. This is not meant to be a comprehensive review of all molecular pathways but rather a framework to guide future investigations of immune responses in depressed versus euthymic people with MS. Currently, there is weak evidence supporting the use of antidepressant medication in comorbid MS patients. It is our hope that by better understanding the neuroimmune crosstalk in the context of depression in MS, we can enhance the potential for future therapeutic options.

The neuroimmune axis of Alzheimer's disease

Alzheimer's disease (AD) is a genetically complex and heterogeneous disorder with multifaceted neuropathological features, including β-amyloid plaques, neurofibrillary tangles, and neuroinflammation. Over the past decade, emerging evidence has implicated both beneficial and pathological roles for innate immune genes and immune cells, including peripheral immune cells such as T cells, which can infiltrate the brain and either ameliorate or exacerbate AD neuropathogenesis. These findings support a neuroimmune axis of AD, in which the interplay of adaptive and innate immune systems inside and outside the brain critically impacts the etiology and pathogenesis of AD. In this review, we discuss the complexities of AD neuropathology at the levels of genetics and cellular physiology, highlighting immune signaling pathways and genes associated with AD risk and interactions among both innate and adaptive immune cells in the AD brain. We emphasize the role of peripheral immune cells in AD and the mechanisms by which immune cells, such as T cells and monocytes, influence AD neuropathology, including microglial clearance of amyloid-β peptide, the key component of β-amyloid plaque cores, pro-inflammatory and cytotoxic activity of microglia, astrogliosis, and their interactions with the brain vasculature. Finally, we review the challenges and outlook for establishing immune-based therapies for treating and preventing AD.