Heterogeneity of CNS myeloid cells and their roles in neurodegeneration

Role of microglia in stroke

Microglia play key roles in the post-ischemic inflammatory response and damaged tissue removal reacting rapidly to the disturbances caused by ischemia and working to restore the lost homeostasis. However, the modified environment, encompassing ionic imbalances, disruption of crucial neuron-microglia interactions, spreading depolarization, and generation of danger signals from necrotic neurons, induce morphological and phenotypic shifts in microglia. This leads them to adopt a proinflammatory profile and heighten their phagocytic activity. From day three post-ischemia, macrophages infiltrate the necrotic core while microglia amass at the periphery. Further, inflammation prompts a metabolic shift favoring glycolysis, the pentose-phosphate shunt, and lipid synthesis. These shifts, combined with phagocytic lipid intake, drive lipid droplet biogenesis, fuel anabolism, and enable microglia proliferation. Proliferating microglia release trophic factors contributing to protection and repair. However, some microglia accumulate lipids persistently and transform into dysfunctional and potentially harmful foam cells. Studies also showed microglia that either display impaired apoptotic cell clearance, or eliminate synapses, viable neurons, or endothelial cells. Yet, it will be essential to elucidate the viability of engulfed cells, the features of the local environment, the extent of tissue damage, and the temporal sequence. Ischemia provides a rich variety of region- and injury-dependent stimuli for microglia, evolving with time and generating distinct microglia phenotypes including those exhibiting proinflammatory or dysfunctional traits and others showing pro-repair features. Accurate profiling of microglia phenotypes, alongside with a more precise understanding of the associated post-ischemic tissue conditions, is a necessary step to serve as the potential foundation for focused interventions in human stroke.

Unraveling the Endocannabinoid System: Exploring Its Therapeutic Potential in Autism Spectrum Disorder

The salient features of autism spectrum disorder (ASD) encompass persistent difficulties in social communication, as well as the presence of restricted and repetitive facets of behavior, hobbies, or pursuits, which are often accompanied with cognitive limitations. Over the past few decades, a sizable number of studies have been conducted to enhance our understanding of the pathophysiology of ASD. Preclinical rat models have proven to be extremely valuable in simulating and analyzing the roles of a wide range of established environmental and genetic factors. Recent research has also demonstrated the significant involvement of the endocannabinoid system (ECS) in the pathogenesis of several neuropsychiatric diseases, including ASD. In fact, the ECS has the potential to regulate a multitude of metabolic and cellular pathways associated with autism, including the immune system. Moreover, the ECS has emerged as a promising target for intervention with high predictive validity. Particularly noteworthy are resent preclinical studies in rodents, which describe the onset of ASD-like symptoms after various genetic or pharmacological interventions targeting the ECS, providing encouraging evidence for further exploration in this area.

Hiding in plain sight: Do recruited dendritic cells surround amyloid plaques in Alzheimer's disease?

Over the past decade, human genome-wide association and expression studies have strongly implicated dysregulation of the innate immune system in the pathogenesis of Alzheimer's disease (AD). Single cell mRNA sequencing studies have identified innate immune cell subtypes that are minimally present in normal healthy brain, but whose numbers greatly increase in association with AD pathology. These AD pathology-associated immune cells are putatively the locus for the immune-related AD risk. While the prevailing view is that these immune cells arise from transformation of resident brain microglia, studies across several decades and using multiple techniques and strategies suggest instead that the pathology-associated immune cells are bone-marrow derived hematopoietic cells that are recruited into brain. We critically review this translational literature, emphasizing the strengths and limitations of techniques used to address recruitment and the experimental designs employed. We conclude that the aggregate evidence points toward recruitment into brain of innate immune cells of the myeloid dendritic cell lineage. Recruitment of dendritic cells and their role in AD pathogenesis has broad implications for our understanding of the etiology and pathobiology of AD that impact the strategies to develop new, immune system-targeted therapeutics for this devastating disease.

LRRK2 regulates ferroptosis through the system Xc-GSH-GPX4 pathway in the neuroinflammatory mechanism of Parkinson's disease

Parkinson's disease (PD) is the most prevalent neurodegenerative disorder. Neuroinflammation mediated by activated microglia and apoptosis of dopaminergic (DA) neurons in the midbrain are its primary pathological manifestations. Leucine-rich repeat protein kinase 2 (LRRK2) kinase has been observed to increase expression during neuroinflammation, however, the effect of LRRK2 on microglia activation remains poorly understood. In this study, we have established lipopolysaccharide (LPS) treated BV2 cells and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) models for both in vivo and in vitro investigation. Our data in vivo reveal that LRRK2 can promote microglia activation by regulating ferroptosis and activating nuclear factor-κB. Inhibition of LRRK2 expression effectively suppressed the LPS-induced pro-inflammatory cytokines and facilitated the secretion of neuroprotective factors. Importantly, by co-overexpressing LRRK2 and glutathione peroxidase 4 (GPX4), we identified the system Xc-GSH-GPX4 pathway as a crucial component in LRRK2-mediated microglial ferroptosis and inflammatory responses. Using a microglial culture supernatant (MCS) transfer model, we found that inhibiting LRRK2 or downregulating ferroptosis in BV2 cells prevented SH-SY5Y cell apoptosis. Additionally, we observed abundant expression of LRRK2 and P-P65 in the midbrain, which was elevated in the MPTP-induced PD model, along with microglia activation. LRRK2 and P-P65 expression inhibition with PF-06447475 attenuated microglia activation in the nigrostriatal dense part of MPTP-treated mice. Based on our findings, it is evident that LRRK2 plays a critical role in promoting the neuroinflammatory response during the pathogenesis of PD by regulating the system Xc-GSH-GPX4 pathway. Taken together, our data highlights the potential research and therapeutic value of targeting LRRK2 to regulate neuroinflammatory response in PD through ferroptosis.

Role of NLRP3 in Parkinson's disease: Specific activation especially in dopaminergic neurons

Parkinson's disease (PD) is a neurodegenerative disorder with motor symptoms like bradykinesia, tremors, and balance issues. The pathology is recognized by progressively degenerative nigrostriatal dopaminergic neurons (DANs) loss. Its exact pathogenesis is unclear. Numerous studies have shown that nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) contributes to the pathogenesis of PD. Previous studies have demonstrated that the over-activation of NLRP3 inflammasome in microglia indirectly leads to the loss of DANs, which can worsen PD. In recent years, autopsy analyses of PD patients and studies in PD models have revealed upregulation of NLRP3 expression within DANs and demonstrated that activation of NLRP3 inflammasome in neurons is sufficient to drive neuronal loss, whereas microglial activation occurs after neuronal death, and that inhibition of intraneuronal NLRP3 inflammasome prevents degeneration of DANs. In this review, we provide research evidence related to NLRP3 inflammasome in DANs in PD as well as focus on possible mechanisms of NLRP3 inflammasome activation in neurons, aiming to provide a new way of thinking about the pathogenesis and prevention of PD.

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.

Border-associated macrophages in the central nervous system

Tissue-resident macrophages play an important role in the local maintenance of homeostasis and immune surveillance. In the central nervous system (CNS), brain macrophages are anatomically divided into parenchymal microglia and non-parenchymal border-associated macrophages (BAMs). Among these immune cell populations, microglia have been well-studied for their roles during development as well as in health and disease. BAMs, mostly located in the choroid plexus, meningeal and perivascular spaces, are now gaining increased attention due to advancements in multi-omics technologies and genetic methodologies. Research on BAMs over the past decade has focused on their ontogeny, immunophenotypes, involvement in various CNS diseases, and potential as therapeutic targets. Unlike microglia, BAMs display mixed origins and distinct self-renewal capacity. BAMs are believed to regulate neuroimmune responses associated with brain barriers and contribute to immune-mediated neuropathology. Notably, BAMs have been observed to function in diverse cerebral pathologies, including Alzheimer's disease, Parkinson's disease, multiple sclerosis, ischemic stroke, and gliomas. The elucidation of the heterogeneity and diverse functions of BAMs during homeostasis and neuroinflammation is mesmerizing, since it may shed light on the precision medicine that emphasizes deep insights into programming cues in the unique brain immune microenvironment. In this review, we delve into the latest findings on BAMs, covering aspects like their origins, self-renewal capacity, adaptability, and implications in different brain disorders.

Myeloid cells in vascular dementia and Alzheimer's disease: Possible therapeutic targets?

Growing evidence supports the suggestion that the peripheral immune system plays a role in different pathologies associated with cognitive impairment, such as vascular dementia (VD) or Alzheimer's disease (AD). The aim of this review is to summarize, within the peripheral immune system, the implications of different types of myeloid cells in AD and VD, with a special focus on post-stroke cognitive impairment and dementia (PSCID). We will review the contributions of the myeloid lineage, from peripheral cells (neutrophils, platelets, monocytes and monocyte-derived macrophages) to central nervous system (CNS)-associated cells (perivascular macrophages and microglia). Finally, we will evaluate different potential strategies for pharmacological modulation of pathological processes mediated by myeloid cell subsets, with an emphasis on neutrophils, their interaction with platelets and the process of immunothrombosis that triggers neutrophil-dependent capillary stall and hypoperfusion, as possible effector mechanisms that may pave the way to novel therapeutic avenues to stop dementia, the epidemic of our time. LINKED ARTICLES: This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

Serum amyloid A and mitochondrial DNA in extracellular vesicles are novel markers for detecting traumatic brain injury in a mouse model

This study investigates the potential use of circulating extracellular vesicles' (EVs) DNA and protein content as biomarkers for traumatic brain injury (TBI) in a mouse model. Despite an overall decrease in EVs count during the acute phase, there was an increased presence of exosomes (CD63+ EVs) during acute and an increase in microvesicles derived from microglia/macrophages (CD11b+ EVs) and astrocytes (ACSA-2+ EVs) in post-acute TBI phases, respectively. Notably, mtDNA exhibited an immediate elevation post-injury. Neuronal (NFL) and microglial (Iba1) markers increased in the acute, while the astrocyte marker (GFAP) increased in post-acute TBI phases. Novel protein biomarkers (SAA, Hp, VWF, CFD, CBG) specific to different TBI phases were also identified. Biostatistical modeling and machine learning identified mtDNA and SAA as decisive markers for TBI detection. These findings emphasize the importance of profiling EVs' content and their dynamic release as an innovative diagnostic approach for TBI in liquid biopsies.

The niche matters: origin, function and fate of CNS-associated macrophages during health and disease

There are several cellular and acellular structural barriers associated with the brain interfaces, which include the dura, the leptomeninges, the perivascular space and the choroid plexus epithelium. Each structure is enriched by distinct myeloid populations, which mainly originate from erythromyeloid precursors (EMP) in the embryonic yolk sac and seed the CNS during embryogenesis. However, depending on the precise microanatomical environment, resident myeloid cells differ in their marker profile, turnover and the extent to which they can be replenished by blood-derived cells. While some EMP-derived cells seed the parenchyma to become microglia, others engraft the meninges and become CNS-associated macrophages (CAMs), also referred to as border-associated macrophages (BAMs), e.g., leptomeningeal macrophages (MnMΦ). Recent data revealed that MnMΦ migrate into perivascular spaces postnatally where they differentiate into perivascular macrophages (PvMΦ). Under homeostatic conditions in pathogen-free mice, there is virtually no contribution of bone marrow-derived cells to MnMΦ and PvMΦ, but rather to macrophages of the choroid plexus and dura. In neuropathological conditions in which the blood-brain barrier is compromised, however, an influx of bone marrow-derived cells into the CNS can occur, potentially contributing to the pool of CNS myeloid cells. Simultaneously, resident CAMs may also proliferate and undergo transcriptional and proteomic changes, thereby, contributing to the disease outcome. Thus, both resident and infiltrating myeloid cells together act within their microenvironmental niche, but both populations play crucial roles in the overall disease course. Here, we summarize the current understanding of the sources and fates of resident CAMs in health and disease, and the role of the microenvironment in influencing their maintenance and function.

The synergistic effect of nanocurcumin and donepezil on Alzheimer's via PI3K/AKT/GSK-3β pathway modulating

Alzheimer's disease (AD) hallmarks include amyloid-βeta (Aβ) and tau proteins aggregates, neurite degeneration, microglial activation with cognitive impairment. Phosphatidylinositol-3-kinase/protein kinase B/Glycogen synthase kinase-3-beta (PI3K/AKT/GSK-3) pathway is essential for neuroprotection, cell survival and proliferation by blocking apoptosis. This study aimed to assess protective role of nanocurcumin (NCMN) as strong antioxidant and anti-inflammatory agent with elucidating its synergistic effects with Donepezil as acetylcholinesterase inhibitor on AD in rats via modulating PI3K/AKT/GSK-3β pathway. The experiment was performed on 70 male Wistar albino rats divided into seven groups (control, NCMN, Donepezil, AD-model, Donepezil co-treatment, NCMN only co-treatment, and NCMN+Donepezil combined treatment). Behavioral and biochemical investigations as cholinesterase activity, oxidative stress (malondialdehyde, reduced glutathione, nitric oxide, superoxidedismutase, and catalase), tumor necrosis factor-alpha, Tau, β-site amyloid precursor protein cleaving enzyme-1 (BACE-1), Phosphatase and tensin homolog (Pten), mitogen-activated protein kinase-1 (MAPK-1), Glycogen synthase kinase-3-beta (GSK-3β) and toll-like receptor-4 were evaluated. Treatment with NCMN improved memory, locomotion, neuronal differentiation by activating PI3K/AKT/GSK-3β pathway. These results were confirmed by histological studies in hippocampus.

Modulation of Microglial Function by ATP-Gated P2X7 Receptors: Studies in Rat, Mice and Human

P2X receptors are a family of seven ATP-gated ion channels that trigger physiological and pathophysiological responses in a variety of cells. Five of the family members are sensitive to low concentrations of extracellular ATP, while the P2X6 receptor has an unknown affinity. The last subtype, the P2X7 receptor, is unique in requiring millimolar concentrations to fully activate in humans. This low sensitivity imparts the agonist with the ability to act as a damage-associated molecular pattern that triggers the innate immune response in response to the elevated levels of extracellular ATP that accompany inflammation and tissue damage. In this review, we focus on microglia because they are the primary immune cells of the central nervous system, and they activate in response to ATP or its synthetic analog, BzATP. We start by introducing purinergic receptors and then briefly consider the roles that microglia play in neurodevelopment and disease by referencing both original works and relevant reviews. Next, we move to the role of extracellular ATP and P2X receptors in initiating and/or modulating innate immunity in the central nervous system. While most of the data that we review involve work on mice and rats, we highlight human studies of P2X7R whenever possible.

Relation between microRNA-155 and inflammatory mediators in multiple sclerosis

Multiple sclerosis (MS) is a complex autoimmune condition affecting the central nervous system characterized by axonal damage, demyelination, and chronic inflammation. Multiple molecular and cellular components mediate neuroinflammation in MS. In human macrophages and microglia, miRNA-155 is an essential proinflammatory noncoding RNA that regulates phenotypic and functional polarization properties. This study was conducted to detect the plasma level of miRNA-155 in RRMS and assess its relationship with inflammatory and anti-inflammatory mediators. The study included 60 MS patients and 30 healthy controls. Real-time quantitative polymerase chain reaction was utilized to detect miRNA-155, iNOS, and SMAD2, whereas ELISA was used to determine TNF-α, IFN-ɣ, TGF-β, and IL-10 levels. There was no significant difference in miRNA-155, SMAD2, and iNOS expression in MS patients compared to control subjects. In addition, there was a statistically significant increase in TNF-α, INF-ɣ, and TGF-β levels. IL-10 levels did not differ significantly between MS patients and healthy controls. There was a positive correlation between miRNA-155 and TNF-α (p < 0.000, r = 0.922), INF-ɣ (p < 0.000, r = 0.81), and iNOS (p < 0.000, r = 0.916) and inverse correlation between miRNA-155 and IL-10 (p < 0.000, r = -0.928), TGF-β (p < 0.000, r = -0.904) and SMAD2 (p < 0.000, r = -0.848). We conclude that expression of miRNA-155 in MS may modulate macrophage/microglia polarization by increasing the secretion of TNF-α, IFN-ɣ & iNOS and decreasing anti-inflammatory mediators IL10 and TGF-β.

Pb induces the release of CXCL10 and CCL2 chemokines via mtROS/NF-κB activation in BV-2 cells

Lead (Pb), a well-known environmental pollutant, could cause damage of microglia, the resident macrophages vitally regulating inflammation in brain. Previous studies have found that Pb exposure induces typical pro-inflammatory factors release, such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), but what effects of Pb treatment below the dose causing these factors release are unknown. Thus, cytokines assay was performed to identify the factors released from Pb-treated BV-2 cells at 2.5 μM, causing no effects on TNF-α, IL-1β, and IL-6 release and cell death. Cytokines assay identified low doses of Pb exposure mainly induce an increase in specific chemokines, including CXCL10, CCL2, and CXCL2, which were confirmed by ELISA. Subsequent assessment found Pb could damage mitochondria function and generate mitochondrial reactive oxygen species (mtROS), and Mito TEMPO, a specific inhibitor of mtROS, suppressed Pb-caused upregulation of CXCL10 and CCL2, but not CXCL2. Finally, we determined that mtROS mediated Pb-induced activation of NF-κB pathway, as Mito TEMPO treatment inhibited P-p65/p65 escalation during Pb treatment. Inhibition of NF-κB pathway by Bay11-7821 suppressed the release of CXCL10 and CCL2. Collectively, low dose of Pb induces the release of CXCL10 and CCL2 chemokines, but not TNF-α and IL-1β, via mtROS/NF-κB activation in BV-2 cells.

Alzheimer's disease: The role of T lymphocytes in neuroinflammation and neurodegeneration

Alzheimer's disease, the leading cause of progressive cognitive decline globally, has been reported to be enhanced by neuroinflammation. Brain-resident innate immune cells and adaptive immune cells work together to produce neuroinflammation. Studies over the past decade have established the neuroimmune axis present in Alzheimer's disease; the crosstalk between adaptive and innate immune cells within and outside the brain is crucial to the onset and progression of Alzheimer's disease. Although the role of the adaptive immune system in Alzheimer's disease is not fully understood, it has been hypothesized that the brain's immune homeostasis is significantly disrupted, which greatly contributes to neuroinflammation. Brain-infiltrating T cells possess proinflammatory phenotypes and activities that directly contribute to neuroinflammation. The pro-inflammatory activities of the adaptive immune system in Alzheimer's disease are characterized by the upregulation of effector T cell activities and the downregulation of regulatory T cell activities in the brain, blood, and cerebrospinal fluid. In this review, we discuss the major impact of T lymphocytes on the pathogenesis and progression of Alzheimer's disease. Understanding the role and mechanism of action of T cells in Alzheimer's disease would significantly contribute to the identification of novel biomarkers for diagnosing and monitoring the progression of the disease. This knowledge could also be crucial to the development of immunotherapies for Alzheimer's disease.

Long-term exercise training inhibits inflammation by suppressing hippocampal NLRP3 in APP/PS1 mice

Behavioral experiments have demonstrated that long-term physical exercise can be beneficial for learning and memory dysfunction caused by neuroinflammation in Alzheimer's disease (AD). However, the molecular mechanism remains poorly understood due to a lack of sufficient pertinent biochemical evidence. We investigated the potential effect of long-term physical exercise on cognition and hippocampal gene and protein expression changes in a transgenic AD mouse model. Following twenty weeks of treadmill exercise, transgenic AD mice showed improvement in cognitive functions and downregulation of Nod-like receptor protein 3 (NLRP3) (p ​< ​0.01), interleukin-1beta (IL-1β) (p ​< ​0.05), and amyloid-β1-42 (Aβ1-42) (p ​< ​0.05) expression levels. In addition, we observed significant reductions of microglial activation and hippocampal neuronal damage in the exercised AD mice (p ​< ​0.01), which might be a result of the downregulation of NLRP3-mediated signaling and neuro-inflammatory responses. As neuronal damage due to inflammation might be a likely cause of AD-associated cognitive dysfunction. Our results suggested that the anti-inflammatory effects of exercise training involved downregulating the expression of key inflammatory factors and might play an important role in protecting hippocampal neurons against damage during the course of AD.

The role of microglial activation on ischemic stroke: Modulation by fibroblast growth factors

Stroke is one of the devastating clinical conditions that causes death and permanent disability. Its occurrence causes the reduction of oxygen and glucose supply, resulting in events such as inflammatory response, oxidative stress, and apoptosis in the brain. Microglia are brain-resident immune cells in the central nervous system (CNS) that exert diverse roles and respond to pathological process after an ischemic insult. The discovery of fibroblast growth factors (FGFs) in mammals, resulted to the findings that they can treat experimental models of stroke in animals effectively. FGFs function as homeostatic factors that control cells and hormones involved in metabolism, and they also regulate the secretion of proinflammatory (M1) and anti-inflammatory (M2) cytokines after stroke. In this review, we outline current evidence of microglia activation in experimental models of stroke focusing on its ability to exacerbate damage or repair tissue. Also, our review sheds light on the pharmacological actions of FGFs on multiple targets to regulate microglial modulation and highlighted their theoretical molecular mechanisms to provide possible therapeutic targets, as well as their limitations for the treatment of stroke. DATA AVAILABILITY: Not applicable.

The Neuroimmune System and the Cerebellum

The recognition that there is an innate immune system of the brain, referred to as the neuroimmune system, that preforms many functions comparable to that of the peripheral immune system is a relatively new concept and much is yet to be learned. The main cellular components of the neuroimmune system are the glial cells of the brain, primarily microglia and astrocytes. These cell types preform many functions through secretion of signaling factors initially known as immune factors but referred to as neuroimmune factors when produced by cells of the brain. The immune functions of glial cells play critical roles in the healthy brain to maintain homeostasis that is essential for normal brain function, to establish cytoarchitecture of the brain during development, and, in pathological conditions, to minimize the detrimental effects of disease and injury and promote repair of brain structure and function. However, dysregulation of this system can occur resulting in actions that exacerbate or perpetuate the detrimental effects of disease or injury. The neuroimmune system extends throughout all brain regions, but attention to the cerebellar system has lagged that of other brain regions and information is limited on this topic. This article is meant to provide a brief introduction to the cellular and molecular components of the brain immune system, its functions, and what is known about its role in the cerebellum. The majority of this information comes from studies of animal models and pathological conditions, where upregulation of the system facilitates investigation of its actions.

Brain macrophage development, diversity and dysregulation in health and disease

Brain macrophages include microglia in the parenchyma, border-associated macrophages in the meningeal-choroid plexus-perivascular space, and monocyte-derived macrophages that infiltrate the brain under various disease conditions. The vast heterogeneity of these cells has been elucidated over the last decade using revolutionary multiomics technologies. As such, we can now start to define these various macrophage populations according to their ontogeny and their diverse functional programs during brain development, homeostasis and disease pathogenesis. In this review, we first outline the critical roles played by brain macrophages during development and healthy aging. We then discuss how brain macrophages might undergo reprogramming and contribute to neurodegenerative disorders, autoimmune diseases, and glioma. Finally, we speculate about the most recent and ongoing discoveries that are prompting translational attempts to leverage brain macrophages as prognostic markers or therapeutic targets for diseases that affect the brain.

Galectin-1 as a marker for microglia activation in the aging brain

Microglia cells, the immune cells residing in the brain, express immune regulatory molecules that have a central role in the manifestation of age-related brain characteristics. Our hypothesis suggests that galectin-1, an anti-inflammatory member of the beta-galactoside-binding lectin family, regulates microglia and neuroinflammation in the aging brain. Through our in-silico analysis, we discovered a subcluster of microglia in the aged mouse brain that exhibited increased expression of galectin-1 mRNA. In our Western blotting experiments, we observed a decrease in galectin-1 protein content in our rat primary cortical cultures over time. Additionally, we found that the presence of lipopolysaccharide, an immune activator, significantly increased the expression of galectin-1 protein in microglial cells. Utilizing flow cytometry, we determined that a portion of the galectin-1 protein was localized on the surface of the microglial cells. As cultivation time increased, we observed a decrease in the expression of activation-coupled molecules in microglial cells, indicating cellular exhaustion. In our mixed rat primary cortical cell cultures, we noted a transition of amoeboid microglial cells labeled with OX42(CD11b/c) to a ramified, branched phenotype during extended cultivation, accompanied by a complete disappearance of galectin-1 expression. By analyzing the transcriptome of a distinct microglial subpopulation in an animal model of aging, we established a correlation between chronological aging and galectin-1 expression. Furthermore, our in vitro study demonstrated that galectin-1 expression is associated with the functional activation state of microglial cells exhibiting specific amoeboid morphological characteristics. Based on our findings, we identify galectin-1 as a marker for microglia activation in the context of aging.

Astragaloside IV against Alzheimer's disease via microglia-mediated neuroinflammation using network pharmacology and experimental validation

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases in the world. The effective therapeutic methods and drugs are still not clear. Astragaloside IV (AS-IV), a triterpenoid saponin isolated from the root of Huangqi, has a beneficial effect in the treatment of AD. However, whether AS-IV alters microglia in the inflammation of AD is still ambiguous. In our study, 99 common targets were collected between AS-IV and AD. BCL2 apoptosis regulator (Bcl-2), pro-apoptotic BCL-2 protein BAX, epidermal growth factor receptor (EGFR), and receptor tyrosine phosphatase type C (PTPRC) were screened for inflammation and microglia in the above targets by network pharmacology. Interleukin-1β (IL-1β) and EGFR both interact with signal transducer and activator of transcription 3 (STAT3) by a protein interaction network, and IL-1β had a higher affinity for AS-IV based on molecular docking. Enrichment revealed targets involved in the regulation of neuronal cell bodies, growth factor receptor binding, EGFR tyrosine kinase inhibitor resistance., etc. Besides, AS-IV alleviated the reduced cell proliferation in amyloid-beta (Aβ)-treated microglial BV2 cells. AS-IV affected BV2 cell morphological changes and decreased cluster of differentiation 11b (CD11b) gene, IL-1β, and EGFR mRNA levels increment during lipopolysaccharide (LPS) injury in BV2 cell activation. Therefore, AS-IV may regulate microglial activation and inflammation via EGFR-dependent pathways in AD. EGFR and IL-1β are vital targets that may relate to each other to coregulate downstream molecular functions in the cure of AD. Our study provides a candidate drug and disease target for the treatment of neurodegenerative diseases in the clinic.

Time-dependent dual effect of microglia in ischemic stroke

Stroke, the third leading cause of death and disability worldwide, is classified into ischemic or hemorrhagic, in which approximately 85% of strokes are ischemic. Ischemic stroke occurs as a result of arterial occlusion due to embolus or thrombus, with ischemia in the perfusion territory supplied by the occluded artery. The traditional concept that ischemic stroke is solely a vascular occlusion disorder has been expanded to include the dynamic interaction between microglia, astrocytes, neurons, vascular cells, and matrix components forming the "neurovascular unit." Acute ischemic stroke triggers a wide spectrum of neurovascular disturbances, glial activation, and secondary neuroinflammation that promotes further injury, ultimately resulting in neuronal death. Microglia, as the resident macrophages in the central nervous system, is one of the first responders to ischemic injury and plays a significant role in post-ischemic neuroinflammation. In this review, we reviewed the mechanisms of microglia in multiple stages of post-ischemic neuroinflammation development, including acute, sub-acute and chronic phases of stroke. A comprehensive understanding of the dynamic variation and the time-dependent role of microglia in post-stroke neuroinflammation could aid in the search for more effective therapeutics and diagnostic strategies for ischemic stroke.

Cellular and molecular mechanisms in vascular repair after traumatic brain injury: a narrative review

Traumatic brain injury (TBI) disrupts normal brain function and is associated with high morbidity and fatality rates. TBI is characterized as mild, moderate or severe depending on its severity. The damage may be transient and limited to the dura matter, with only subtle changes in cerebral parenchyma, or life-threatening with obvious focal contusions, hematomas and edema. Blood vessels are often injured in TBI. Even in mild TBI, dysfunctional cerebral vascular repair may result in prolonged symptoms and poor outcomes. Various distinct types of cells participate in vascular repair after TBI. A better understanding of the cellular response and function in vascular repair can facilitate the development of new therapeutic strategies. In this review, we analyzed the mechanism of cerebrovascular impairment and the repercussions following various forms of TBI. We then discussed the role of distinct cell types in the repair of meningeal and parenchyma vasculature following TBI, including endothelial cells, endothelial progenitor cells, pericytes, glial cells (astrocytes and microglia), neurons, myeloid cells (macrophages and monocytes) and meningeal lymphatic endothelial cells. Finally, possible treatment techniques targeting these unique cell types for vascular repair after TBI are discussed.

Cell competition for neuron-derived trophic factor controls the turnover and lifespan of microglia

Microglia are brain-resident macrophages capable of long-term maintenance through self-renewal. Yet the mechanism governing the turnover and lifespan of microglia remains unknown. In zebrafish, microglia arise from two sources, rostral blood island (RBI) and aorta-gonad-mesonephros (AGM). The RBI-derived microglia are born early but have a short lifespan and diminish in adulthood, while the AGM-derived microglia emerge later and are capable of long-term maintenance in adulthood. Here, we show that the attenuation of RBI microglia is due to their less competitiveness for neuron-derived interleukin-34 (Il34) caused by age-dependent decline of colony-stimulating factor-1 receptor a (csf1ra). Alterations of Il34/Csf1ra levels and removal of AGM microglia revamp the proportion and lifespan of RBI microglia. The csf1ra/CSF1R expression in zebrafish AGM-derived microglia and murine adult microglia also undergo age-dependent decline, leading to the elimination of aged microglia. Our study reveals cell competition as a general mechanism controlling the turnover and lifespan of microglia.

Ovalbumin-specific CD4+ and CD8+ T cells contribute to different susceptibility for Theiler's murine encephalomyelitis virus persistence

Theiler's murine encephalomyelitis virus (TMEV) is the causative agent of TMEV-induced demyelinating disease (TMEV-IDD); a well-established animal model for the chronic progressive form of human multiple sclerosis (MS). In susceptible mice with an inadequate immune response, TMEV-IDD is triggered by virus persistence and maintained by a T cell mediated immunopathology. OT-mice are bred on a TMEV-resistant C57BL/6 background and own predominantly chicken ovalbumin (OVA)-specific populations of CD8⁺ T cells (OT-I) or CD4⁺ T cells (OT-II), respectively. It is hypothesized that the lack of antigen specific T cell populations increases susceptibility for a TMEV-infection in OT-mice on a TMEV-resistant C57BL/6 background. OT-I, OT-II, and C57BL/6 control mice were infected intracerebrally with the TMEV-BeAn strain. Mice were scored weekly for clinical disease and after necropsy, histological and immunohistochemical evaluation was performed. OT-I mice started to develop progressive motor dysfunction between 7 and 21 days post infection (dpi), leading up to hind limb paresis and critical weight loss, which resulted in euthanasia for humane reasons between 14 and 35 dpi. OT-I mice displayed a high cerebral virus load, an almost complete absence of CD8⁺ T cells from the central nervous system (CNS) and a significantly diminished CD4⁺ T cell response. Contrarily, only 60% (12 of 20) of infected OT-II mice developed clinical disease characterized by mild ataxia. 25% of clinically affected OT-II mice (3 of 12) made a full recovery. 5 of 12 OT-II mice with clinical disease developed severe motor dysfunction similar to OT-I mice and were euthanized for humane reasons between 13 and 37 dpi. OT-II mice displayed only low virus-immunoreactivity, but clinical disease correlated well with severely reduced infiltration of CD8⁺ T cells and the increased presence of CD4⁺ T cells in the brains of OT-II mice. Though further studies are needed to reveal the underlying pathomechanisms following TMEV infection in OT mice, findings indicate an immunopathological process as a main contributor to clinical disease in OT-II mice, while a direct virus-associated pathology may be the main contributor to clinical disease in TMEV-infected OT-I mice.

A novel ex vivo assay to define charge-balanced electrical stimulation parameters for neural precursor cell activation in vivo

Endogenous neural stem cells and their progeny (together termed neural precursor cells (NPCs)) are promising candidates to facilitate neuroregeneration. Charge-balanced biphasic monopolar stimulation (BPMP) is a clinically relevant approach that can activate NPCs both in vitro and in vivo. Herein, we established a novel ex vivo stimulation system to optimize the efficacy of BPMP electric field (EF) application in activating endogenous NPCs. Using the ex vivo system, we discerned that cathodal amplitude of 200 μA resulted in the greatest NPC pool expansion and enhanced cathodal migration. Application of the same stimulation parameters in vivo resulted in the same NPC activation in the mouse brain. The design and implementation of the novel ex vivo model bridges the gap between in vitro and in vivo systems, enabling a moderate throughput stimulation system to explore and optimize EF parameters that can be applied to clinically relevant brain injury/disease models.

Reduction of human Alzheimer's disease risk and reversal of mouse model cognitive deficit with nucleoside analog use

Innate immune signaling through the NLRP3 inflammasome has been implicated in the pathogenesis of Alzheimer's disease (AD), the most prevalent form of dementia. We previously demonstrated that nucleoside reverse transcriptase inhibitors (NRTIs), drugs approved to treat HIV and hepatitis B infections, also inhibit inflammasome activation. Here we report that in humans, NRTI exposure was associated with a significantly lower incidence of AD in two of the largest health insurance databases in the United States. Treatment of aged 5xFAD mice (a mouse model of amyloid-β deposition that expresses five mutations found in familial AD) with Kamuvudine-9 (K-9), an NRTI-derivative with enhanced safety profile, reduced Aβ deposition and reversed their cognitive deficit by improving their spatial memory and learning performance to that of young wild-type mice. These findings support the concept that inflammasome inhibition could benefit AD and provide a rationale for prospective clinical testing of NRTIs or K-9 in AD.

Leflunomide abrogates neuroinflammatory changes in a rat model of Alzheimer's disease: the role of TNF-α/NF-κB/IL-1β axis inhibition

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases and is associated with disrupted cognition and behavior. Neuroinflammatory pathogenesis is the main component that contributes to AD initiation and progression through microglial activation and neuronal damage. Thus, targeting inflammatory pathways may help manage AD. In this study, for the first time, the potential prophylactic and therapeutic effects of leflunomide were investigated either alone or in combination with rivastigmine in aluminum chloride (AlCl₃)-induced AD-like rats using behavioral, biochemical, and histological approaches. Thirty-six adult male albino rats were divided into two protocols: the treatment protocol, subdivided into five groups (n = 6)-(1) control group, (2) AlCl₃ (50, 70, 100 mg/kg/I.P) group, (3) reference group (rivastigmine 2 mg/kg/P.O.), (4) experimental group (leflunomide 10 mg/kg/P.O.), and (5) combination group (rivastigmine + leflunomide); and the prophylactic protocol (leflunomide 10 mg/kg/P.O.), which started 2 weeks before AlCl₃ induction. The results showed that AlCl₃ disrupted learning and memory parameters in rats and increased amyloid-β plaque deposition and neurofibrillary tangle aggregation. Moreover, AlCl₃ administration markedly elevated acetylcholinesterase activity, nuclear factor-kappa β, tumor necrosis factor-α, and interleukin-1 beta, and marked degenerative changes in the pyramidal neurons. However, administration of leflunomide alone or with rivastigmine in AlCl₃-induced AD rats restored most of the behavioral, biochemical, and histological parameters triggered by AlCl₃ in rats. Our findings suggest that leflunomide can potentially restore most of the neuronal damage in the hippocampal tissues of AlCl₃-induced AD rats. However, these preclinical findings still need to be confirmed in clinical trials.

Microglia-mediated T cell infiltration drives neurodegeneration in tauopathy

Extracellular deposition of amyloid-β as neuritic plaques and intracellular accumulation of hyperphosphorylated, aggregated tau as neurofibrillary tangles are two of the characteristic hallmarks of Alzheimer's disease1,2. The regional progression of brain atrophy in Alzheimer's disease highly correlates with tau accumulation but not amyloid deposition3-5, and the mechanisms of tau-mediated neurodegeneration remain elusive. Innate immune responses represent a common pathway for the initiation and progression of some neurodegenerative diseases. So far, little is known about the extent or role of the adaptive immune response and its interaction with the innate immune response in the presence of amyloid-β or tau pathology6. Here we systematically compared the immunological milieux in the brain of mice with amyloid deposition or tau aggregation and neurodegeneration. We found that mice with tauopathy but not those with amyloid deposition developed a unique innate and adaptive immune response and that depletion of microglia or T cells blocked tau-mediated neurodegeneration. Numbers of T cells, especially those of cytotoxic T cells, were markedly increased in areas with tau pathology in mice with tauopathy and in the Alzheimer's disease brain. T cell numbers correlated with the extent of neuronal loss, and the cells dynamically transformed their cellular characteristics from activated to exhausted states along with unique TCR clonal expansion. Inhibition of interferon-γ and PDCD1 signalling both significantly ameliorated brain atrophy. Our results thus reveal a tauopathy- and neurodegeneration-related immune hub involving activated microglia and T cell responses, which could serve as therapeutic targets for preventing neurodegeneration in Alzheimer's disease and primary tauopathies.

How Does Vitamin D Affect Immune Cells Crosstalk in Autoimmune Diseases?

Vitamin D is a secosteroid hormone that is highly involved in bone health. Mounting evidence revealed that, in addition to the regulation of mineral metabolism, vitamin D is implicated in cell proliferation and differentiation, vascular and muscular functions, and metabolic health. Since the discovery of vitamin D receptors in T cells, local production of active vitamin D was demonstrated in most immune cells, addressing the interest in the clinical implications of vitamin D status in immune surveillance against infections and autoimmune/inflammatory diseases. T cells, together with B cells, are seen as the main immune cells involved in autoimmune diseases; however, growing interest is currently focused on immune cells of the innate compartment, such as monocytes, macrophages, dendritic cells, and natural killer cells in the initiation phases of autoimmunity. Here we reviewed recent advances in the onset and regulation of Graves' and Hashimoto's thyroiditis, vitiligo, and multiple sclerosis in relation to the role of innate immune cells and their crosstalk with vitamin D and acquired immune cells.

Novel image analysis tool for rapid screening of cell morphology in preclinical animal models of disease

The field of cell biology has seen major advances in both cellular imaging modalities and the development of automated image analysis platforms that increase rigor, reproducibility, and throughput for large imaging data sets. However, there remains a need for tools that provide accurate morphometric analysis of single cells with complex, dynamic cytoarchitecture in a high-throughput and unbiased manner. We developed a fully automated image-analysis algorithm to rapidly detect and quantify changes in cellular morphology using microglia cells, an innate immune cell within the central nervous system, as representative of cells that exhibit dynamic and complex cytoarchitectural changes. We used two preclinical animal models that exhibit robust changes in microglia morphology: (1) a rat model of acute organophosphate intoxication, which was used to generate fluorescently labeled images for algorithm development; and (2) a rat model of traumatic brain injury, which was used to validate the algorithm using cells labeled using chromogenic detection methods. All ex vivo brain sections were immunolabeled for IBA-1 using fluorescence or diaminobenzidine (DAB) labeling, images were acquired using a high content imaging system and analyzed using a custom-built algorithm. The exploratory data set revealed eight statistically significant and quantitative morphometric parameters that distinguished between phenotypically distinct groups of microglia. Manual validation of single-cell morphology was strongly correlated with the automated analysis and was further supported by a comparison with traditional stereology methods. Existing image analysis pipelines rely on high-resolution images of individual cells, which limits sample size and is subject to selection bias. However, our fully automated method integrates quantification of morphology and fluorescent/chromogenic signals in images from multiple brain regions acquired using high-content imaging. In summary, our free, customizable image analysis tool provides a high-throughput, unbiased method for accurately detecting and quantifying morphological changes in cells with complex morphologies.

The Vascular-Immune Hypothesis of Alzheimer's Disease

Alzheimer's disease (AD) is a devastating and irreversible neurodegenerative disorder with unknown etiology. While its cause is unclear, a number of theories have been proposed to explain the pathogenesis of AD. In large part, these have centered around potential causes for intracerebral accumulation of beta-amyloid (βA) and tau aggregates. Yet, persons with AD dementia often exhibit autopsy evidence of mixed brain pathologies including a myriad of vascular changes, vascular brain injuries, complex brain inflammation, and mixed protein inclusions in addition to hallmark neuropathologic lesions of AD, namely insoluble βA plaques and neurofibrillary tangles (NFTs). Epidemiological data demonstrate that overlapping lesions diminish the βA plaque and NFT threshold necessary to precipitate clinical dementia. Moreover, a subset of persons who exhibit AD pathology remain resilient to disease while other persons with clinically-defined AD dementia do not exhibit AD-defining neuropathologic lesions. It is increasingly recognized that AD is a pathologically heterogeneous and biologically multifactorial disease with uncharacterized biologic phenomena involved in its genesis and progression. Here, we review the literature with regard to neuropathologic criteria and incipient AD changes, and discuss converging concepts regarding vascular and immune factors in AD.

Near-infrared-IIb emitting single-atom catalyst for imaging-guided therapy of blood-brain barrier breakdown after traumatic brain injury

The blood-brain barrier breakdown, as a prominent feature after traumatic brain injury, always triggers a cascade of biochemical events like inflammatory response and free radical-mediated oxidative damage, leading to neurological dysfunction. The dynamic monitoring the status of blood-brain barrier will provide potent guidance for adopting appropriate clinical intervention. Here, we engineer a near-infrared-IIb Ag₂Te quantum dot-based Mn single-atom catalyst for imaging-guided therapy of blood-brain barrier breakdown of mice after traumatic brain injury. The dynamic change of blood-brain barrier, including the transient cerebral hypoperfusion and cerebrovascular damage, could be resolved with high spatiotemporal resolution (150 ms and ~ 9.6 µm). Notably, the isolated single Mn atoms on the surface of Ag₂Te exhibited excellent catalytic activity for scavenging reactive oxygen species to alleviate neuroinflammation in brains. The timely injection of Mn single-atom catalyst guided by imaging significantly promoted the reconstruction of blood-brain barrier and recovery of neurological function after traumatic brain injury.

The Relationship of Astrocytes and Microglia with Different Stages of Ischemic Stroke

Ischemic stroke is the predominant cause of severe morbidity and mortality worldwide. Post-stroke neuroinflammation has recently received increasing attention with the aim of providing a new effective treatment strategy for ischemic stroke. Microglia and astrocytes are major components of the innate immune system of the central nervous system. They can be involved in all phases of ischemic stroke, from the early stage, contributing to the first wave of neuronal cell death, to the late stage involving phagocytosis and repair. In the early stage of ischemic stroke, a vicious cycle exists between the activation of microglia and astrocytes (through astrocytic connexin 43 hemichannels), aggravating neuroinflammatory injury post-stroke. However, in the late stage of ischemic stroke, repeatedly activated microglia can induce the formation of glial scars by triggering reactive astrogliosis in the peri-infarct regions, which may limit the movement of activated microglia in reverse and restrict the diffusion of inflammation to healthy brain tissues, alleviating the neuroinflammatory injury poststroke. In this review, we elucidated the various roles of astrocytes and microglia and summarized their relationship with neuroinflammation. We also examined how astrocytes and microglia influence each other at different stages of ischemic stroke. Several potential therapeutic approaches targeting astrocytes and microglia in ischemic stroke have been reviewed. Understanding the details of astrocytemicroglia interaction processes will contribute to a better understanding of the mechanisms underlying ischemic stroke, contributing to the identification of new therapeutic interventions.

The BET inhibitor apabetalone decreases neuroendothelial proinflammatory activation in vitro and in a mouse model of systemic inflammation

Brain vascular inflammation is characterized by endothelial activation and immune cell recruitment to the blood vessel wall, potentially causing a breach in the blood - brain barrier, brain parenchyma inflammation, and a decline of cognitive function. The clinical-stage small molecule, apabetalone, reduces circulating vascular endothelial inflammation markers and improves cognitive scores in elderly patients by targeting epigenetic regulators of gene transcription, bromodomain and extraterminal proteins. However, the effect of apabetalone on cytokine-activated brain vascular endothelial cells (BMVECs) is unknown. Here, we show that apabetalone treatment of BMVECs reduces hallmarks of in vitro endothelial activation, including monocyte chemoattractant protein-1 (MCP-1) and RANTES chemokine secretion, cell surface expression of endothelial cell adhesion molecule VCAM-1, as well as endothelial capture of THP-1 monocytes in static and shear stress conditions. Apabetalone pretreatment of THP-1 downregulates cell surface expression of chemokine receptors CCR1, CCR2, and CCR5, and of the VCAM-1 cognate receptor, integrin α4. Consequently, apabetalone reduces THP-1 chemoattraction towards soluble CCR ligands MCP-1 and RANTES, and THP-1 adhesion to activated BMVECs. In a mouse model of brain inflammation, apabetalone counters lipopolysaccharide-induced transcription of endothelial and myeloid cell markers, consistent with decreased neuroendothelial inflammation. In conclusion, apabetalone decreases proinflammatory activation of brain endothelial cells and monocytes in vitro and in the mouse brain during systemic inflammation.

Trends in perivascular macrophages research from 1997 to 2021: A bibliometric analysis

INTRODUCTION

Perivascular macrophages (PVMs) play pivotal roles in maintaining the physiological function of the brain. Dysfunction of PVMs is emerging as an important mechanism in various disease conditions in the brain.

METHODS

In this work, we analyzed recent research advances in PVMs, especially in the brain, from the Web of Science (WoS) core database using bibliometric analysis based on the search terms "perivascular macrophages" and "perivascular macrophage" on October 27, 2021. Visualization and collaboration analysis were performed by Citespace (5.8 R3 mac).

RESULTS

We found 2384 articles published between 1997 and 2021 in the field of PVMs, which were selected for analysis. PVMs were involved in several physio-pathological fields, in which Neurosciences and Neurology, Neuroscience, Immunology, Pathology, and Cardiovascular System and Cardiology were most reported. The research focuses on PVMs mainly in the central nervous system (CNS), inflammation, macrophage or T-cell, and disease, and highlights the related basic research regarding its activation, oxidative stress, angiotensin II, and insulin resistance. Tumor-associated macrophage, obesity, myeloid cell, and inflammation were relatively recent highlight keywords that attracted increasing attention in recent years. Harvard Univ, Vrije Univ Amsterdam, occupied important positions in the research field of PVMs. Meanwhile, PVM research in China (Peking Univ, Sun Yat Sen Univ, Shanghai Jiao Tong Univ, and Shandong Univ) is on the rise. Cluster co-citation analysis revealed that the mechanisms of CNS PVMs and related brain diseases are major specialties associated with PVMs, while PVMs in perivascular adipose tissue and vascular diseases or obesity are another big category of PVMs hotspots.

CONCLUSION

In conclusion, the research on PVMs continues to deepen, and the hotspots are constantly changing. Future studies of PVMs could have multiple disciplines intersecting.

Emerging roles of innate and adaptive immunity in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease, with characteristic extracellular amyloid-β (Aβ) deposition and intracellular accumulation of hyperphosphorylated, aggregated tau. Several key regulators of innate immune pathways are genetic risk factors for AD. While these genetic risk factors as well as in vivo data point to key roles for microglia, emerging evidence also points to a role of the adaptive immune response in disease pathogenesis. We review the roles of innate and adaptive immunity, their niches, their communication, and their contributions to AD development and progression. We also summarize the cellular compositions and physiological functions of immune cells in the parenchyma, together with those in the brain border structures that form a dynamic disease-related immune niche. We propose that both innate and adaptive immune responses in brain parenchyma and border structures could serve as important therapeutic targets for treating both the pre-symptomatic and the symptomatic stages of AD.

Marine Natural Products from the Russian Pacific as Sources of Drugs for Neurodegenerative Diseases

Neurodegenerative diseases are growing to become one of humanity's biggest health problems, given the number of individuals affected by them. They cause enough mortalities and severe economic impact to rival cancers and infections. With the current diversity of pathophysiological mechanisms involved in neurodegenerative diseases, on the one hand, and scarcity of efficient prevention and treatment strategies, on the other, all possible sources for novel drug discovery must be employed. Marine pharmacology represents a relatively uncharted territory to seek promising compounds, despite the enormous chemodiversity it offers. The current work discusses one vast marine region-the Northwestern or Russian Pacific-as the treasure chest for marine-based drug discovery targeting neurodegenerative diseases. We overview the natural products of neurological properties already discovered from its waters and survey the existing molecular and cellular targets for pharmacological modulation of the disease. We further provide a general assessment of the drug discovery potential of the Russian Pacific in case of its systematic development to tackle neurodegenerative diseases.

Immunosenescence and Aging: Neuroinflammation Is a Prominent Feature of Alzheimer's Disease and Is a Likely Contributor to Neurodegenerative Disease Pathogenesis

Alzheimer's disease (AD) is a chronic multifactorial and complex neuro-degenerative disorder characterized by memory impairment and the loss of cognitive ability, which is a problem affecting the elderly. The pathological intracellular accumulation of abnormally phosphorylated Tau proteins, forming neurofibrillary tangles, and extracellular amyloid-beta (Aβ) deposition, forming senile plaques, as well as neural disconnection, neural death and synaptic dysfunction in the brain, are hallmark pathologies that characterize AD. The prevalence of the disease continues to increase globally due to the increase in longevity, quality of life, and medical treatment for chronic diseases that decreases the mortality and enhance the survival of elderly. Medical awareness and the accurate diagnosis of the disease also contribute to the high prevalence observed globally. Unfortunately, no definitive treatment exists that can be used to modify the course of AD, and no available treatment is capable of mitigating the cognitive decline or reversing the pathology of the disease as of yet. A plethora of hypotheses, ranging from the cholinergic theory and dominant Aβ cascade hypothesis to the abnormally excessive phosphorylated Tau protein hypothesis, have been reported. Various explanations for the pathogenesis of AD, such as the abnormal excitation of the glutamate system and mitochondrial dysfunction, have also been suggested. Despite the continuous efforts to deliver significant benefits and an effective treatment for this distressing, globally attested aging illness, multipronged approaches and strategies for ameliorating the disease course based on knowledge of the underpinnings of the pathogenesis of AD are urgently needed. Immunosenescence is an immune deficit process that appears with age (inflammaging process) and encompasses the remodeling of the lymphoid organs, leading to alterations in the immune function and neuroinflammation during advanced aging, which is closely linked to the outgrowth of infections, autoimmune diseases, and malignant cancers. It is well known that long-standing inflammation negatively influences the brain over the course of a lifetime due to the senescence of the immune system. Herein, we aim to trace the role of the immune system in the pathogenesis of AD. Thus, we explore alternative avenues, such as neuroimmune involvement in the pathogenesis of AD. We determine the initial triggers of neuroinflammation, which is an early episode in the pre-symptomatic stages of AD and contributes to the advancement of the disease, and the underlying key mechanisms of brain damage that might aid in the development of therapeutic strategies that can be used to combat this devastating disease. In addition, we aim to outline the ways in which different aspects of the immune system, both in the brain and peripherally, behave and thus to contribute to AD.

Genome integrity and inflammation in the nervous system

Preservation of genomic integrity is crucial for nervous system development and function. DNA repair deficiency results in several human diseases that are characterized by both neurodegeneration and neuroinflammation. Recent research has highlighted a role for compromised genomic integrity as a key factor driving neuropathology and triggering innate immune signaling to cause inflammation. Here we review the mechanisms by which DNA damage engages innate immune signaling and how this may promote neurological disease. We also consider the contributions of different neural cell types towards DNA damage-driven neuroinflammation. A deeper knowledge of genome maintenance mechanisms that prevent aberrant immune activation in neural cells will guide future therapies to ameliorate neurological disease.

Promoted CD4+ T cell-derived IFN-γ/IL-10 by photobiomodulation therapy modulates neurogenesis to ameliorate cognitive deficits in APP/PS1 and 3xTg-AD mice

Background

The immune system has been implicated in synaptic plasticity, inflammation, and the progression of Alzheimer's disease (AD). However, there were few studies on improving the niche microenvironment of neural stem cells (NSCs) in the brain of AD to promote adult hippocampal neurogenesis (AHN) by regulating the function of non-parenchymal immune cells.

Methods

The lymph nodes of amyloid precursor protein/presenilin 1 (APP/PS1) and 3xTg (APP/PS1/tau) mouse models of AD were treated with photobiomodulation therapy (PBMT) for 10 J/cm² per day for 1 month (10 min for each day), T lymphocytes isolated from these two AD models were treated with PBMT for 2 J/cm² (5 min for each time). The NSCs isolated from hippocampus of these two AD models at E14, and the cells were co-cultivated with PBMT-treated T lymphocyte conditioned medium for NSCs differentiation.

Results

Our results showed that PBMT treatment could promote AHN and reverse cognitive deficits in AD mouse model. The expression of interferon-γ (IFN-γ) and interleukin-10 (IL-10) was upregulated in the brain of these two AD models after PBMT treated, which was induced by the activation of Janus kinase 2 (JAK2)-mediated signal transducer and activator of transcription 4 (STAT4)/STAT5 signaling pathway in CD4⁺ T cells. In addition, elevated CD4⁺ T cell levels and upregulated transforming growth factor-β1 (TGFβ1)/insulin-like growth factors-1 (IGF-1)/brain-derived neurotrophic factor (BDNF) protein expression levels were also detected in the brain. More importantly, co-cultivated the PBMT-treated T lymphocyte conditioned medium with NSCs derived from these two AD models was shown to promote NSCs differentiation, which was reflected in the upregulation of both neuronal class-III β-tubulin (Tuj1) and postsynaptic density protein 95 (PSD95), but the effects of PBMT was blocked by reactive oxygen species (ROS) scavenger or JAK2 inhibitor.

Conclusion

Our research suggests that PBMT exerts a beneficial neurogenesis modulatory effect through activating the JAK2/STAT4/STAT5 signaling pathway to promote the expression of IFN-γ/IL-10 in non-parenchymal CD4⁺ T cells, induction of improvement of brain microenvironmental conditions and alleviation of cognitive deficits in APP/PS1 and 3xTg-AD mouse models.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02617-5.

Magnetic labeling of primary murine monocytes using very small superparamagnetic iron oxide nanoparticles

Due to their very small size, nanoparticles can interact with all cells in the central nervous system. One of the most promising nanoparticle subgroups are very small superparamagnetic iron oxide nanoparticles (VSOP) that are citrate coated for electrostatic stabilization. To determine their influence on murine blood-derived monocytes, which easily enter the injured central nervous system, we applied VSOP and carboxydextran-coated superparamagnetic iron oxide nanoparticles (Resovist). We assessed their impact on the viability, cytokine, and chemokine secretion, as well as iron uptake of murine blood-derived monocytes. We found that (1) the monocytes accumulated VSOP and Resovist, (2) this uptake seemed to be nanoparticle- and time-dependent, (3) the decrease of monocytes viability was treatment-related, (4) VSOP and Resovist incubation did not alter cytokine homeostasis, and (5) overall a 6-hour treatment with 0.75 mM VSOP-R1 was probably sufficient to effectively label monocytes for future experiments. Since homeostasis is not altered, it is safe to label blood-derived monocles with VSOP. VSOP labeled monocytes can be used to study injured central nervous system sites further, for example with drug-carrying VSOP.

Normalization of Neuroinflammation: A New Strategy for Treatment of Persistent Pain and Memory/Emotional Deficits in Chronic Pain

Chronic pain, which affects around 1/3 of the world population and is often comorbid with memory deficit and mood depression, is a leading source of suffering and disability. Studies in past decades have shown that hyperexcitability of primary sensory neurons resulting from abnormal expression of ion channels and central sensitization mediated pathological synaptic plasticity, such as long-term potentiation in spinal dorsal horn, underlie the persistent pain. The memory/emotional deficits are associated with impaired synaptic connectivity in hippocampus. Dysregulation of numerous endogenous proteins including receptors and intracellular signaling molecules is involved in the pathological processes. However, increasing knowledge contributes little to clinical treatment. Emerging evidence has demonstrated that the neuroinflammation, characterized by overproduction of pro-inflammatory cytokines and glial activation, is reliably detected in humans and animals with chronic pain, and is sufficient to induce persistent pain and memory/emotional deficits. The abnormal expression of ion channels and pathological synaptic plasticity in spinal dorsal horn and in hippocampus are resulting from neuroinflammation. The neuroinflammation is initiated and maintained by the interactions of circulating monocytes, glial cells and neurons. Obviously, unlike infectious diseases and cancer, which are caused by pathogens or malignant cells, chronic pain is resulting from alterations of cells and molecules which have numerous physiological functions. Therefore, normalization (counterbalance) but not simple inhibition of the neuroinflammation is the right strategy for treating neuronal disorders. Currently, no such agent is available in clinic. While experimental studies have demonstrated that intracellular Mg²⁺ deficiency is a common feature of chronic pain in animal models and supplement Mg²⁺ are capable of normalizing the neuroinflammation, activation of upregulated proteins that promote recovery, such as translocator protein (18k Da) or liver X receptors, has a similar effect. In this article, relevant experimental and clinical evidence is reviewed and discussed.

The therapeutic potential of bone marrow-derived macrophages in neurological diseases

Circulating monocytes are precursors of both tissue macrophages and dendritic cells, and they can infiltrate the central nervous system (CNS) where they transform into bone marrow-derived macrophages (BMDMs). BMDMs play essential roles in various CNS diseases, thus modulating BMDMs might be a way to treat these disorders because there are currently no efficient therapeutic methods available for most of these neurological diseases. Moreover, BMDMs can serve as promising gene delivery vehicles following bone marrow transplantation for otherwise incurable genetic CNS diseases. Understanding the distinct roles that BMDMs play in CNS diseases and their potential as gene delivery vehicles may provide new insights and opportunities for using BMDMs as therapeutic targets or delivery vehicles. This review attempts to comprehensively summarize the neurological diseases that might be treated by modulating BMDMs or by delivering gene therapies via BMDMs after bone marrow transplantation.

IL-37 expression reduces acute and chronic neuroinflammation and rescues cognitive impairment in an Alzheimer's disease mouse model

The anti-inflammatory cytokine interleukin-37 (IL-37) belongs to the IL-1 family but is not expressed in mice. We used a human IL-37 (hIL-37tg) expressing mouse, which has been subjected to various models of local and systemic inflammation as well as immunological challenges. Previous studies reveal an immunomodulatory role of IL-37, which can be characterized as an important suppressor of innate immunity. Here, we examined the functions of IL-37 in the central nervous system and explored the effects of IL-37 on neuronal architecture and function, microglial phenotype, cytokine production and behavior after inflammatory challenge by intraperitoneal LPS-injection. In wild-type mice, decreased spine density, activated microglial phenotype and impaired long-term potentiation (LTP) were observed after LPS injection, whereas hIL-37tg mice showed no impairment. In addition, we crossed the hIL-37tg mouse with an animal model of Alzheimer’s disease (APP/PS1) to investigate the anti-inflammatory properties of IL-37 under chronic neuroinflammatory conditions. Our results show that expression of IL-37 is able to limit inflammation in the brain after acute inflammatory events and prevent loss of cognitive abilities in a mouse model of AD.

Oxytocin and microglia in the development of social behaviour

Oxytocin is a well-established regulator of social behaviour. Microglia, the resident immune cells of the central nervous system, regulate brain development and maintenance in health and disease. Oxytocin and microglia interact: microglia appear to regulate the oxytocin system and are, in turn, regulated by oxytocin, which appears to have anti-inflammatory effects. Both microglia and oxytocin are regulated in sex-specific ways. Oxytocin and microglia may work together to promote experience-dependent circuit refinement through multiple developmental-sensitive periods contributing to individual differences in social behaviour. This article is part of the theme issue 'Interplays between oxytocin and other neuromodulators in shaping complex social behaviours'.

The gut-immune-brain axis in neurodevelopment and neurological disorders

The gut-brain axis is gaining momentum as an interdisciplinary field addressing how intestinal microbes influence the central nervous system (CNS). Studies using powerful tools, including germ-free, antibiotic-fed, and fecal microbiota transplanted mice, demonstrate how gut microbiota perturbations alter the fate of neurodevelopment. Probiotics are also becoming more recognized as potentially effective therapeutic agents in alleviating symptoms of neurological disorders. While gut microbes may directly communicate with the CNS through their effector molecules, including metabolites, their influence on neuroimmune populations, including newly discovered brain-resident T cells, underscore the host immunity as a potent mediator of the gut-brain axis. In this review, we examine the unique immune populations within the brain, the effects of the gut microbiota on the CNS, and the efficacy of specific probiotic strains to propose the novel concept of the gut-immune-brain axis.

The Significance of NLRP Inflammasome in Neuropsychiatric Disorders

The NLRP inflammasome is a multi-protein complex which mainly consists of the nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain. Its activation is linked to microglial-mediated neuroinflammation and partial neuronal degeneration. Many neuropsychiatric illnesses have increased inflammatory responses as both a primary cause and a defining feature. The NLRP inflammasome inhibition delays the progression and alleviates the deteriorating effects of neuroinflammation on several neuropsychiatric disorders. Evidence on the central effects of the NLRP inflammasome potentially provides the scientific base of a promising drug target for the treatment of neuropsychiatric disorders. This review elucidates the classification, composition, and functions of the NLRP inflammasomes. It also explores the underlying mechanisms of NLRP inflammasome activation and its divergent role in neuropsychiatric disorders, including Alzheimer’s disease, Huntington’s disease, Parkinson’s disease, depression, drug use disorders, and anxiety. Furthermore, we explore the treatment potential of the NLRP inflammasome inhibitors against these disorders.

Microglial Engulfment of Spines in the Ventral Zona Incerta Regulates Anxiety-Like Behaviors in a Mouse Model of Acute Pain

Although activation of microglial cells is critical in developing brain disorders, their role in anxiety-like behaviors in pain is still vague. This study indicates that alteration of microglia’s neuronal spine engulfment capacity in ventral zona incerta (ZI_V) leads to significant pain and anxiety-like behaviors in mice 1-day post-injection of Complete Freud’s Adjuvant (CFA1D). Performing whole-cell patch-clamp recordings in GABAergic neurons in the ZI_V (ZI_V^GABA) in brain slices, we observed decreased activity in ZIv^GABA and reduced frequency of the miniature excitatory postsynaptic currents (mEPSCs) in ZI_V^GABA of CFA1D mice compared with the saline1D mice. Besides, chemogenetic activation of ZI_V^GABA significantly relieved pain and anxiety-like behaviors in CFA1D mice. Conversely, in naïve mice, chemogenetic inhibition of ZI_V^GABA induced pain and anxiety-like behaviors. Interestingly, we found changes in the density and morphology of ZI_V^Microglia and increased microglial engulfment of spines in ZI_V of CFA1D mice. Furthermore, pain sensitization and anxiety-like behaviors were reversed when the ZI_V^Microglia of CFA1D-treated mice were chemically inhibited by intra-ZI_V minocycline injection, accompanied by the recovery of decreased ZI_V^GABA excitability. Conclusively, our results provide novel insights that dysregulation of microglial engulfment capacity encodes maladaptation of ZI_V^GABA, thus promoting the development of anxiety-like behaviors in acute pain.

Leukocyte invasion of the brain after peripheral trauma in zebrafish (Danio rerio)

Despite well-known systemic immune reactions in peripheral trauma, little is known about their roles in posttraumatic neurological disorders, such as anxiety, sickness, and cognitive impairment. Leukocyte invasion of the brain, a common denominator of systemic inflammation, is involved in neurological disorders that occur in peripheral inflammatory diseases, whereas the influences of peripheral leukocytes on the brain after peripheral trauma remain largely unclear. In this study, we found that leukocytes, largely macrophages, transiently invaded the brain of zebrafish larvae after peripheral trauma through vasculature-independent migration, which was a part of the systemic inflammation and was mediated by interleukin-1b (il1b). Notably, myeloid cells in the brain that consist of microglia and invading macrophages were implicated in posttraumatic anxiety-like behaviors, such as hyperactivity (restlessness) and thigmotaxis (avoidance), while a reduction in systemic inflammation or myeloid cells can rescue these behaviors. In addition, invading leukocytes together with microglia were found to be responsible for the clearance of apoptotic cells in the brain; however, they also removed the nonapoptotic cells, which suggested that phagocytes have dual roles in the brain after peripheral trauma. More importantly, a category of conserved proteins between zebrafish and humans or rodents that has been featured in systemic inflammation and neurological disorders was determined in the zebrafish brain after peripheral trauma, which supported that zebrafish is a translational model of posttraumatic neurological disorders. These findings depicted leukocyte invasion of the brain during systemic inflammation after peripheral trauma and its influences on the brain through il1b-dependent mechanisms.

Invasion of the brain by white blood cells followed tail amputation in zebrafish, the resulting systemic inflammation producing anxiety-like behaviors. Scientists have long recognised an association between systemic inflammation following peripheral traumatic injury such as limb loss and post-traumatic neurological disorders such as anxiety and depression. Raymond Chuen-Chung Chang at the University of Hong Kong, Alvin Chun-Hang Ma at Hong Kong Polytechnic University, China, and co-workers found that following trauma, white cells, mainly macrophages, flowed from neighboring tissues into the hindbrain, before spreading throughout the brain. This influx of white cells, mediated by the small signaling protein interleukin-1b, triggered anxiety-like behaviors such as hyperactivity and avoidance in the zebrafish. The researchers emphasize that the links between systemic inflammation following peripheral trauma and neurological responses require extensive further research.