Microglial immune checkpoint mechanisms

The role of macrophage plasticity in neurodegenerative diseases

Tissue-resident macrophages and recruited macrophages play pivotal roles in innate immunity and the maintenance of brain homeostasis. Investigating the involvement of these macrophage populations in eliciting pathological changes associated with neurodegenerative diseases has been a focal point of research. Dysregulated states of macrophages can compromise clearance mechanisms for pathological proteins such as amyloid-β (Aβ) in Alzheimer's disease (AD) and TDP-43 in Amyotrophic lateral sclerosis (ALS). Additionally, recent evidence suggests that abnormalities in the peripheral clearance of pathological proteins are implicated in the pathogenesis and progression of neurodegenerative diseases. Furthermore, numerous genome-wide association studies have linked genetic risk factors, which alter the functionality of various immune cells, to the accumulation of pathological proteins. This review aims to unravel the intricacies of macrophage biology in both homeostatic conditions and neurodegenerative disorders. To this end, we initially provide an overview of the modifications in receptor and gene expression observed in diverse macrophage subsets throughout development. Subsequently, we outlined the roles of resident macrophages and recruited macrophages in neurodegenerative diseases and the progress of targeted therapy. Finally, we describe the latest advances in macrophage imaging methods and measurement of inflammation, which may provide information and related treatment strategies that hold promise for informing the design of future investigations and therapeutic interventions.

Microglia signaling in health and disease - Implications in sex-specific brain development and plasticity

Microglia, the intrinsic neuroimmune cells residing in the central nervous system (CNS), exert a pivotal influence on brain development, homeostasis, and functionality, encompassing critical roles during both aging and pathological states. Recent advancements in comprehending brain plasticity and functions have spotlighted conspicuous variances between male and female brains, notably in neurogenesis, neuronal myelination, axon fasciculation, and synaptogenesis. Nevertheless, the precise impact of microglia on sex-specific brain cell plasticity, sculpting diverse neural network architectures and circuits, remains largely unexplored. This article seeks to unravel the present understanding of microglial involvement in brain development, plasticity, and function, with a specific emphasis on microglial signaling in brain sex polymorphism. Commencing with an overview of microglia in the CNS and their associated signaling cascades, we subsequently probe recent revelations regarding molecular signaling by microglia in sex-dependent brain developmental plasticity, functions, and diseases. Notably, C-X3-C motif chemokine receptor 1 (CX3CR1), triggering receptors expressed on myeloid cells 2 (TREM2), calcium (Ca2+), and apolipoprotein E (APOE) emerge as molecular candidates significantly contributing to sex-dependent brain development and plasticity. In conclusion, we address burgeoning inquiries surrounding microglia's pivotal role in the functional diversity of developing and aging brains, contemplating their potential implications for gender-tailored therapeutic strategies in neurodegenerative diseases.

Medulla oblongata and NCCs are central defenders against Streptococcus agalactiae infection of the tilapia brain

Various types of professional immune cells first emerge in fish and likely represent the primordial form and functions. Recent advancements revealed the direct connection between the central nervous system and the immune system in the mammalian brain. However, the specifics of brain-immune networks in the fish and the underlying mechanisms of teleost's brain against pathogen infection have not been fully elucidated. In this study, we investigated the distribution of markers representing cerebral cells associated with protection and professional lymphocytes in the seven major components of the Nile tilapia brain through RNA-Seq assay and observed the most dominant abundance in the medulla oblongata. The subsequent challenge test revealed the non-specific cytotoxic cells (NCCs) exhibited the strongest response against streptococcal infection of the brain. The presence of NCCs in the brain was then confirmed using immunofluorescence and the cytotoxic effects usually induced by NCCs under infection were determined as well. Collectively, these findings contribute significantly to comprehending the mechanism of fish neuroimmune interaction and enhancing our understanding of its evolutionary development.

Exploring the gut microbiome-Postoperative Cognitive Dysfunction connection: Mechanisms, clinical implications, and future directions

Postoperative Cognitive Dysfunction (POCD) is a common yet poorly understood complication of surgery that can lead to long-term cognitive decline. The gut-brain axis, a bidirectional communication system between the central nervous system and the gut microbiota, plays a significant role in maintaining cognitive health. The potential for anesthetic agents and perioperative medications to modulate the gut microbiota and influence the trajectory of POCD suggests the need for a more integrated approach in perioperative care. Perioperative medications, including opioids and antibiotics, further compound these disruptions, leading to dysbiosis and consequent systemic and neuroinflammation implicated in cognitive impairment. Understanding how surgical interventions and associated treatments affect this relationship is crucial for developing strategies to reduce the incidence of POCD. Strategies to preserve and promote a healthy gut microbiome may mitigate the risk and severity of POCD. Future research should aim to clarify the mechanisms linking gut flora alterations to cognitive outcomes and explore targeted interventions, such as probiotic supplementation and microbiota-friendly prescription practices, to safeguard cognitive function postoperatively.

Chronically activated microglia in ALS gradually lose their immune functions and develop unconventional proteome

Neuroinflammation and chronic activation of microglial cells are the prominent features of amyotrophic lateral sclerosis (ALS) pathology. While alterations in the mRNA profile of diseased microglia have been well documented, the actual microglia proteome remains poorly characterized. Here we performed a functional characterization together with proteome analyses of microglial cells at different stages of disease in the SOD1-G93A model of ALS. Functional analyses of microglia derived from the lumbar spinal cord of symptomatic mice revealed: (i) remarkably high mitotic index (close to 100% cells are Ki67+) (ii) significant decrease in phagocytic capacity when compared to age-matched control microglia, and (iii) diminished response to innate immune challenges in vitro and in vivo. Proteome analysis revealed a development of two distinct molecular signatures at early and advanced stages of disease. While at early stages of disease, we identified several proteins implicated in microglia immune functions such as GPNMB, HMBOX1, at advanced stages of disease microglia signature at protein level was characterized with a robust upregulation of several unconventional proteins including rootletin, major vaults proteins and STK38. Upregulation of GPNMB and rootletin has been also found in the spinal cord samples of sporadic ALS. Remarkably, the top biological functions of microglia, in particular in the advanced disease, were not related to immunity/immune response, but were highly enriched in terms linked to RNA metabolism. Together, our results suggest that, over the course of disease, chronically activated microglia develop unconventional protein signatures and gradually lose their immune identity ultimately turning into functionally inefficient immune cells.

Enhanced innate responses in microglia derived from retinoblastoma patient-specific iPSCs

RB1 deficiency leads to retinoblastoma (Rb), the most prevalent intraocular malignancy. Tumor-associated macrophages (TAMs) are related to local inflammation disorder, particularly by increasing cytokines and immune escape. Microglia, the unique resident macrophages for retinal homeostasis, are the most important immune cells of Rb. However, whether RB1 deficiency affects microglial function remain unknown. In this study, microglia were successfully differentiated from Rb patient- derived human induced pluripotent stem cells (hiPSCs) and human embryonic stem cells (hESCs), and then we investigated the function of RB1 in microglia by live imaging phagocytosis assay, immunofluorescence, RNA-seq, qRT-PCR, ELISA and retina organoids/microglia co-culturing. RB1 was abundantly expressed in microglia and predominantly located in the nucleus. We then examined the phagocytosis ability and secretion function of iMGs in vitro. We found that RB1 deficiency did not affect the expression of microglia-specific markers or the phagocytic abilities of these cells by live-imaging. Upon LPS stimulation, RB1-deficient microglia displayed enhanced innate immune responses, as evidenced by activated MAPK signaling pathway and elevated expression of IL-6 and TNF-α at both mRNA and protein levels, compared to wildtype microglia. Furthermore, retinal structure disruption was observed when retinal organoids were co-cultured with RB1-deficient microglia, highlighting the potential contribution of microglia to Rb development and potential therapeutic strategies for retinoblastoma.

The miR-25802/KLF4/NF-κB signaling axis regulates microglia-mediated neuroinflammation in Alzheimer's disease

Microglia-mediated neuroinflammation plays a critical role in the occurrence and progression of Alzheimer's disease (AD). In recent years, studies have increasingly explored microRNAs as biomarkers and treatment interventions for AD. This study identified a novel microRNA termed miR-25802 from our high-throughput sequencing dataset of an AD model and explored its role and the underlying mechanism. The results confirmed the miRNA properties of miR-25802 based on bioinformatics and experimental verification. Expression of miR-25802 was increased in the plasma of AD patients and in the hippocampus of APP/PS1 and 5 × FAD mice carrying two and five familial AD gene mutations. Functional studies suggested that overexpression or inhibition of miR-25802 respectively aggravated or ameliorated AD-related pathology, including cognitive disability, Aβ deposition, microglial pro-inflammatory phenotype activation, and neuroinflammation, in 5 × FAD mice and homeostatic or LPS/IFN-γ-stimulated EOC20 microglia. Mechanistically, miR-25802 negatively regulates KLF4 by directly binding to KLF4 mRNA, thus stimulating microglia polarization toward the pro-inflammatory M1 phenotype by promoting the NF-κB-mediated inflammatory response. The results also showed that inhibition of miR-25802 increased microglial anti-inflammatory M2 phenotype activity and suppressed NF-κB-mediated inflammatory reactions in the brains of 5 × FAD mice, while overexpression of miR-25802 exacerbated microglial pro-inflammatory M1 activity by enhancing NF-κB pathways. Of note, AD-associated manifestations induced by inhibition or overexpression of miR-25802 via the NF-κB signaling pathway were reversed by KLF4 silencing or upregulation. Collectively, these results provide the first evidence that miR-25802 is a regulator of microglial activity and establish the role of miR-25802/KLF4/NF-κB signaling in microglia-mediated neuroinflammation, suggesting potential therapeutic targets for AD.

Exploring the common mechanism of vascular dementia and inflammatory bowel disease: a bioinformatics-based study

Objective

Emerging evidence has shown that gut diseases can regulate the development and function of the immune, metabolic, and nervous systems through dynamic bidirectional communication on the brain-gut axis. However, the specific mechanism of intestinal diseases and vascular dementia (VD) remains unclear. We designed this study especially, to further clarify the connection between VD and inflammatory bowel disease (IBD) from bioinformatics analyses.

Methods

We downloaded Gene expression profiles for VD (GSE122063) and IBD (GSE47908, GSE179285) from the Gene Expression Omnibus (GEO) database. Then individual Gene Set Enrichment Analysis (GSEA) was used to confirm the connection between the two diseases respectively. The common differentially expressed genes (coDEGs) were identified, and the STRING database together with Cytoscape software were used to construct protein-protein interaction (PPI) network and core functional modules. We identified the hub genes by using the Cytohubba plugin. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were applied to identify pathways of coDEGs and hub genes. Subsequently, receiver operating characteristic (ROC) analysis was used to identify the diagnostic ability of these hub genes, and a training dataset was used to verify the expression levels of the hub genes. An alternative single-sample gene set enrichment (ssGSEA) algorithm was used to analyze immune cell infiltration between coDEGs and immune cells. Finally, the correlation between hub genes and immune cells was analyzed.

Results

We screened 167 coDEGs. The main articles of coDEGs enrichment analysis focused on immune function. 8 shared hub genes were identified, including PTPRC, ITGB2, CYBB, IL1B, TLR2, CASP1, IL10RA, and BTK. The functional categories of hub genes enrichment analysis were mainly involved in the regulation of immune function and neuroinflammatory response. Compared to the healthy controls, abnormal infiltration of immune cells was found in VD and IBD. We also found the correlation between 8 shared hub genes and immune cells.

Conclusions

This study suggests that IBD may be a new risk factor for VD. The 8 hub genes may predict the IBD complicated with VD. Immune-related coDEGS may be related to their association, which requires further research to prove.

Blood-brain barrier biomarkers

The blood-brain barrier (BBB) is a dynamic interface that regulates the exchange of molecules and cells between the brain parenchyma and the peripheral blood. The BBB is mainly composed of endothelial cells, astrocytes and pericytes. The integrity of this structure is essential for maintaining brain and spinal cord homeostasis and protection from injury or disease. However, in various neurological disorders, such as traumatic brain injury, Alzheimer's disease, and multiple sclerosis, the BBB can become compromised thus allowing passage of molecules and cells in and out of the central nervous system parenchyma. These agents, however, can serve as biomarkers of BBB permeability and neuronal damage, and provide valuable information for diagnosis, prognosis and treatment. Herein, we provide an overview of the BBB and changes due to aging, and summarize current knowledge on biomarkers of BBB disruption and neurodegeneration, including permeability, cellular, molecular and imaging biomarkers. We also discuss the challenges and opportunities for developing a biomarker toolkit that can reliably assess the BBB in physiologic and pathophysiologic states.

The neurotransmitter puzzle of Alzheimer's: Dissecting mechanisms and exploring therapeutic horizons

Alzheimer's Disease (AD) represents a complex interplay of neurological pathways and molecular mechanisms, with significant impacts on patients' lives. This review synthesizes the latest developments in AD research, focusing on both the scientific advancements and their clinical implications. We examine the role of microglia in AD, highlighting their contribution to the disease's inflammatory aspects. The cholinergic hypothesis, a cornerstone of AD research, is re-evaluated, including the role of Alpha-7 Nicotinic Acetylcholine Receptors in disease progression. This review places particular emphasis on the neurotransmission systems, exploring the therapeutic potential of GABAergic neurotransmitters and the role of NMDA inhibitors in the context of glutamatergic neurotransmission. By analyzing the interactions and implications of neurotransmitter pathways in AD, we aim to shed light on emerging therapeutic strategies. In addition to molecular insights, the review addresses the clinical and personal aspects of AD, underscoring the need for patient-centered approaches in treatment and care. The final section looks at the future directions of AD research and treatment, discussing the integration of scientific innovation with patient care. This review aims to provide a comprehensive update on AD, merging scientific insights with practical considerations, suitable for both specialists and those new to the field.

A P2RY12 deficiency results in sex-specific cellular perturbations and sexually dimorphic behavioral anomalies

Microglia are sexually dimorphic, yet, this critical aspect is often overlooked in neuroscientific studies. Decades of research have revealed the dynamic nature of microglial-neuronal interactions, but seldom consider how this dynamism varies with microglial sex differences, leaving a significant gap in our knowledge. This study focuses on P2RY12, a highly expressed microglial signature gene that mediates microglial-neuronal interactions, we show that adult females have a significantly higher expression of the receptor than adult male microglia. We further demonstrate that a genetic deletion of P2RY12 induces sex-specific cellular perturbations with microglia and neurons in females more significantly affected. Correspondingly, female mice lacking P2RY12 exhibit unique behavioral anomalies not observed in male counterparts. These findings underscore the critical, sex-specific roles of P2RY12 in microglial-neuronal interactions, offering new insights into basal interactions and potential implications for CNS disease mechanisms.

Electroacupuncture promotes macrophage/microglial M2 polarization and suppresses inflammatory pain through AMPK

Inflammatory pain, the most prevalent disease globally, remains challenging to manage. Electroacupuncture emerges as an effective therapy, yet its underlying mechanisms are not fully understood. This study investigates whether adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK)-regulated silent information regulator 1 (SIRT1) contributes to electroacupuncture's antinociceptive effects by modulating macrophage/microglial polarization in the spinal dorsal horn of a mouse model of inflammatory pain. In this study, mice, introduced to inflammatory pain through subcutaneous injections of complete freund's adjuvant (CFA) in the plantar area, underwent electroacupuncture therapy every alternate day for 30-min sessions. The assessment of mechanical allodynia and thermal hyperalgesia in these subjects was carried out using paw withdrawal frequency and paw withdrawal latency measurements, respectively. Western blot analysis measured levels of AMPK, phosphorylation-adenosine 5'-monophosphate (AMP)-activated protein kinase, SIRT1, inducible nitric oxide synthase, cluster of differentiation 86, arginase 1, and interleukin 10. In contrast to the group treated solely with CFA, the cohort receiving both CFA and electroacupuncture demonstrated notable decreases in both thermal hyperalgesia and mechanical allodynia. This was accompanied by a marked enhancement in AMPK phosphorylation levels. AMPK knockdown reversed electroacupuncture's analgesic effects and reduced M2 macrophage/microglial polarization enhancement. Additionally, AMPK knockdown significantly weakened electroacupuncture-induced SIRT1 upregulation, and EX-527 injection attenuated electroacupuncture's facilitation of M2 macrophage/microglial polarization without affecting AMPK phosphorylation levels. Furthermore, combining electroacupuncture with SRT1720 enhanced the analgesic effect of SRT1720. Our findings suggest that AMPK regulation of SIRT1 plays a critical role in electroacupuncture's antinociceptive effect through the promotion of M2 macrophage/microglial polarization.

Investigating the causal relationship between immune cell and Alzheimer's disease: a mendelian randomization analysis

BACKGROUND

Complex interactions between the immune system and the brain may affect neural development, survival, and function, with etiological and therapeutic implications for neurodegenerative diseases. However, previous studies investigating the association between immune inflammation and Alzheimer's disease (AD) have yielded inconsistent results.

METHODS

We applied Mendelian randomization (MR) to examine the causal relationship between immune cell traits and AD risk using genetic variants as instrumental variables. MR is an epidemiological study design based on genetic information that reduces the effects of confounding and reverse causation. We analyzed the causal associations between 731 immune cell traits and AD risk based on publicly available genetic data.

RESULTS

We observed that 5 immune cell traits conferred protection against AD, while 7 immune cell traits increased the risk of AD. These immune cell traits mainly involved T cell regulation, monocyte activation and B cell differentiation. Our findings suggest that immune regulation may influence the development of AD and provide new insights into potential targets for AD prevention and treatment. We also conducted various sensitivity analyses to test the validity and robustness of our results, which revealed no evidence of pleiotropy or heterogeneity.

CONCLUSION

Our research shows that immune regulation is important for AD and provides new information on potential targets for AD prevention and treatment. However, this study has limitations, including the possibility of reverse causality, lack of validation in independent cohorts, and potential confounding by population stratification. Further research is needed to validate and amplify these results and to elucidate the potential mechanisms of the immune cell-AD association.

Microbiota-gut-brain axis and its therapeutic applications in neurodegenerative diseases

The human gastrointestinal tract is populated with a diverse microbial community. The vast genetic and metabolic potential of the gut microbiome underpins its ubiquity in nearly every aspect of human biology, including health maintenance, development, aging, and disease. The advent of new sequencing technologies and culture-independent methods has allowed researchers to move beyond correlative studies toward mechanistic explorations to shed light on microbiome-host interactions. Evidence has unveiled the bidirectional communication between the gut microbiome and the central nervous system, referred to as the "microbiota-gut-brain axis". The microbiota-gut-brain axis represents an important regulator of glial functions, making it an actionable target to ameliorate the development and progression of neurodegenerative diseases. In this review, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases. As the gut microbiome provides essential cues to microglia, astrocytes, and oligodendrocytes, we examine the communications between gut microbiota and these glial cells during healthy states and neurodegenerative diseases. Subsequently, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases using a metabolite-centric approach, while also examining the role of gut microbiota-related neurotransmitters and gut hormones. Next, we examine the potential of targeting the intestinal barrier, blood-brain barrier, meninges, and peripheral immune system to counteract glial dysfunction in neurodegeneration. Finally, we conclude by assessing the pre-clinical and clinical evidence of probiotics, prebiotics, and fecal microbiota transplantation in neurodegenerative diseases. A thorough comprehension of the microbiota-gut-brain axis will foster the development of effective therapeutic interventions for the management of neurodegenerative diseases.

Troxerutin dampened hypothalamic neuroinflammation via microglial IL-22/IL-22R1/IRF3 activation in dihydrotestosterone-induced polycystic ovary syndrome rats

BACKGROUND

Polycystic ovary syndrome (PCOS) is the most common reproductive-endocrine condition in premenopausal women. Troxerutin, a common clinical anti-coagulant agent, was shown to work as a strong IL-22 boosting agent counteracting the hyperactivated gonadotrophin releasing hormone (GnRH) neurons and heightened GnRH release, the neuroendocrine origin of PCOS with unknown mechanism in rats. Exploring the off-label use of troxerutin medication for PCOS is thus sorely needed.

METHODS

Serum IL-22 content and hypothalamic IL-22 protein were detected. Inflammatory factor levels in hypothalamo-pituitary were evaluated. Immunofluorescence staining was employed to determine the activation and M1/M2-prone polarization of microglia in arcuate hypothalamus and median eminence. RNA-sequencing and transcriptome analysis were applied to explore the potential driver of microglia M2-polarization in response to IL-22 bolstering effect. The function of microglial IL-22/IL-22R1/IRF3 system was further verified using in vivo knockdown of IL-22R1 and a potent IRF3 inhibitor in BV2 microglial cell lines in vitro.

RESULTS

Troxerutin augmented serum IL-22 content, and its consequent spillover into the hypothalamus led to the direct activation of IL-22R1/IRF3 system on microglia, thereby promoted microglia M2 polarization in arcuate hypothalamus and median eminence, dampened hypothalamic neuroinflammation, inhibited hyperactive GnRH and rescued a breadth of PCOS-like traits in dihydrotestosterone (DHT) rats. The salutary effects of troxerutin treatment on hypothalamic neuroinflammation, microglial M1/2 polarization, GnRH secretion and numerous PCOS-like features were blocked by in vivo knockdown of IL-22R1. Moreover, evidence in vitro illustrated that IL-22 supplement to BV-2 microglia cell lines promoted M2 polarization, overproduction of anti-inflammatory marker and limitation of pro-inflammatory factors, whereas these IL-22 effects were blunted by geldanamycin, a potent IRF3 inhibitor.

CONCLUSION

Here, the present study reported the potential off-label use of troxerutin medication, a common clinical anti-coagulant agent and an endogenous IL-22 enhancer, for multiple purposes in PCOS. The rational underlying the application of troxerutin as a therapeutic choice in PCOS derived from its activity as an IL-22 memetic agent targeting the neuro-endocrine origin of PCOS, and its promotive impact on microglia M2 polarization via activating microglial IL-22R1/IRF3 system in the arcuate hypothalamus and median eminence of DHT female rats.

SerpinA1 levels in amyotrophic lateral sclerosis patients: An exploratory study

BACKGROUND

SerpinA1, a serine protease inhibitor, is involved in the modulation of microglial-mediated inflammation in neurodegenerative diseases. We explored SerpinA1 levels in cerebrospinal fluid (CSF) and serum of amyotrophic lateral sclerosis (ALS) patients to understand its potential role in the pathogenesis of the disease.

METHODS

SerpinA1, neurofilament light (NfL) and heavy (NfH) chain, and chitinase-3-like protein-1 (CHI3L1) were determined in CSF and serum of ALS patients (n = 110) and healthy controls (n = 10) (automated next-generation ELISA), and correlated with clinical parameters, after identifying three classes of progressors (fast, intermediate, slow). Biomarker levels were analyzed for diagnostic power and association with progression and survival.

RESULTS

SerpinA1serum was significantly decreased in ALS (median: 1032 μg/mL) compared with controls (1343 μg/mL) (p = 0.02). SerpinA1CSF was elevated only in fast progressors (8.6 μg/mL) compared with slow (4.43 μg/mL, p = 0.01) and intermediate (4.42 μg/mL, p = 0.03) progressors. Moreover, SerpinA1CSF correlated with neurofilament and CHI3L1 levels in CSF. Contrarily to SerpinA1CSF , neurofilament and CHI3L1 concentrations in CSF correlated with measures of disease progression in ALS, while SerpinA1serum mildly related with time to generalization (rho = 0.20, p = 0.04). In multivariate analysis, the ratio between serum and CSF SerpinA1 (SerpinA1 ratio) and NfHCSF were independently associated with survival.

CONCLUSIONS

Higher SerpinA1CSF levels are found in fast progressors, suggesting SerpinA1 is a component of the neuroinflammatory mechanisms acting upon fast-progressing forms of ALS. Both neurofilaments or CHI3L1CSF levels outperformed SerpinA1 at predicting disease progression rate in our cohort, and so the prognostic value of SerpinA1 alone as a measure remains inconclusive.

New insight on microglia activation in neurodegenerative diseases and therapeutics

Microglia are immune cells within the central nervous system (CNS) closely linked to brain health and neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. In response to changes in the surrounding environment, microglia activate and change their state and function. Several factors, example for circadian rhythm disruption and the development of neurodegenerative diseases, influence microglia activation. In this review, we explore microglia's function and the associated neural mechanisms. We elucidate that circadian rhythms are essential factors influencing microglia activation and function. Circadian rhythm disruption affects microglia activation and, consequently, neurodegenerative diseases. In addition, we found that abnormal microglia activation is a common feature of neurodegenerative diseases and an essential factor of disease development. Here we highlight the importance of microglia activation in neurodegenerative diseases. Targeting microglia for neurodegenerative disease treatment is a promising direction. We introduce the progress of methods targeting microglia for the treatment of neurodegenerative diseases and summarize the progress of drugs developed with microglia as targets, hoping to provide new ideas for treating neurodegenerative diseases.

Single-Cell Sequencing Technology and Its Application in the Study of Central Nervous System Diseases

The mammalian central nervous system consists of a large number of cells, which contain not only different types of neurons, but also a large number of glial cells, such as astrocytes, oligodendrocytes, and microglia. These cells are capable of performing highly refined electrophysiological activities and providing the brain with functions such as nutritional support, information transmission and pathogen defense. The diversity of cell types and individual differences between cells have brought inspiration to the study of the mechanism of central nervous system diseases. In order to explore the role of different cells, a new technology, single-cell sequencing technology has emerged to perform specific analysis of high-throughput cell populations, and has been continuously developed. Single-cell sequencing technology can accurately analyze single-cell expression in mixed-cell populations and collect cells from different spatial locations, time stages and types. By using single-cell sequencing technology to compare gene expression profiles of normal and diseased cells, it is possible to discover cell subsets associated with specific diseases and their associated genes. Therefore, scientists can understand the development process, related functions and disease state of the nervous system from an unprecedented depth. In conclusion, single-cell sequencing technology provides a powerful technology for the discovery of novel therapeutic targets for central nervous system diseases.

Oral nano-antioxidants improve sleep by restoring intestinal barrier integrity and preventing systemic inflammation

Sleep deprivation (SD) is a severe public health threat that can cause systemic inflammation and nerve damage. Few effective and side-effect-free drugs are available to address SD. However, the bidirectional communications between the brain and gut provide new strategies for anti-SD therapeutics. Here we explored oral delivery of fullerene nano-antioxidants (FNAO) in the SD model to improve sleep by regulating abnormal intestinal barrier and systemic inflammation via the brain-gut axis. SD caused excessive reactive oxygen species (ROS) production and hyperactive inflammatory responses in the intestines of zebrafish and mouse models, leading to disturbed sleep patterns and reduced brain nerve activity. Of note, based on the property of the conjugated π bond of the C60 structure to absorb unpaired electrons, oral FNAO efficiently reduced the excessive ROS in the intestines, maintained redox homeostasis and intestinal barrier integrity, and ameliorated intestinal and systemic inflammation, resulting in superior sleep improvement. Our findings suggest that maintaining intestinal homeostasis may be a promising avenue for SD-related nerve injury therapy.

Anti-inflammatory reprogramming of microglia cells by metabolic modulators to counteract neurodegeneration; a new role for Ranolazine

Microglia chronic activation is a hallmark of several neurodegenerative diseases, including the retinal ones, possibly contributing to their etiopathogenesis. However, some microglia sub-populations have anti-inflammatory and neuroprotective functions, thus making arduous deciphering the role of these cells in neurodegeneration. Since it has been proposed that functionally different microglia subsets also rely on different metabolic routes, we hypothesized that modulating microglia metabolism might be a tool to enhance their anti-inflammatory features. This would have a preventive and therapeutic potential in counteracting neurodegenerative diseases. For this purpose, we tested various molecules known to act on cell metabolism, and we revealed the anti-inflammatory effect of the FDA-approved piperazine derivative Ranolazine on microglia cells, while confirming the one of the flavonoids Quercetin and Naringenin, both in vitro and in vivo. We also demonstrated the synergistic anti-inflammatory effect of Quercetin and Idebenone, and the ability of Ranolazine, Quercetin and Naringenin to counteract the neurotoxic effect of LPS-activated microglia on 661W neuronal cells. Overall, these data suggest that using the selected molecules -also in combination therapies- might represent a valuable approach to reduce inflammation and neurodegeneration while avoiding long term side effects of corticosteroids.

Microglia preserve visual function loss in the aging retina by supporting retinal pigment epithelial health

BACKGROUND

Increased age is a risk factor for the development and progression of retinal diseases including age-related macular degeneration (AMD). Understanding the changes that occur in the eye due to aging is important in enhancing our understanding of AMD pathogenesis and the development of novel AMD therapies. Microglia, the resident brain and retinal immune cells are associated with both maintaining homeostasis and protection of neurons and loss of microglia homeostasis could be a significant player in age related neurodegeneration. One important characteristic of retinal aging is the migration of microglia from the inner to outer retina where they reside in the subretinal space (SRS) in contact with the retinal pigment epithelial (RPE) cells. The role of aged subretinal microglia is unknown. Here, we depleted microglia in aged C57/BL6 mice fed for 6 weeks with a chow containing PLX5622, a small molecule inhibitor of colony-stimulating factor-1 receptor (Csf1r) required for microglial survival.

RESULTS

The subretinal P2RY12 + microglia in aged mice displayed a highly amoeboid and activated morphology and were filled with autofluorescence droplets reminiscent of lipofuscin. TEM indicates that subretinal microglia actively phagocytize shed photoreceptor outer segments, one of the main functions of retinal pigmented epithelial cells. PLX5622 treatment depleted up to 90% of the retinal microglia and was associated with significant loss in visual function. Mice on the microglia depletion diet showed reduced contrast sensitivity and significantly lower electroretinogram for the c-wave, a measurement of RPE functionality, compared to age-matched controls. The loss of c-wave coincided with a loss of RPE cells and increased RPE swelling in the absence of microglia.

CONCLUSIONS

We conclude that microglia preserve visual function in aged mice and support RPE cell function, by phagocytosing shed photoreceptor outer segments and lipids, therefore compensating for the known age-related decline of RPE phagocytosis.

An immune cell atlas reveals the dynamics of human macrophage specification during prenatal development

Macrophages are heterogeneous and play critical roles in development and disease, but their diversity, function, and specification remain inadequately understood during human development. We generated a single-cell RNA sequencing map of the dynamics of human macrophage specification from PCW 4-26 across 19 tissues. We identified a microglia-like population and a proangiogenic population in 15 macrophage subtypes. Microglia-like cells, molecularly and morphologically similar to microglia in the CNS, are present in the fetal epidermis, testicle, and heart. They are the major immune population in the early epidermis, exhibit a polarized distribution along the dorsal-lateral-ventral axis, and interact with neural crest cells, modulating their differentiation along the melanocyte lineage. Through spatial and differentiation trajectory analysis, we also showed that proangiogenic macrophages are perivascular across fetal organs and likely yolk-sac-derived as microglia. Our study provides a comprehensive map of the heterogeneity and developmental dynamics of human macrophages and unravels their diverse functions during development.

Cortisol and cytokines in schizophrenia: A scoping review

Background

With a complex etiology and chronic, disabling evolution, schizophrenia continues to represent a challenge for patients, clinicians, and researchers alike. Recent emphasis in research on finding practical blood-based biomarkers for diagnosis improvement, disease development prediction, and therapeutic response monitoring in schizophrenia, led to studies aiming at elucidating a connection between stress and inflammation markers.

Methods

We set here to explore recent literature aiming to understand the connection between cytokines and cortisol level changes in individuals with schizophrenia and their potential relevance as markers of clinical improvement under treatment. A search was completed in Pubmed, Embase, Web of Science, and APAPsycInfo databases with search terms: (cytokines) AND (cortisol) AND (schizophrenia). This provided 43 results from Pubmed, 82 results from Embase, 52 results from Web of Science, and 9 results from APA PsycInfo. After removing articles not fitting the criteria, 13 articles were selected.

Results

While all studies included assess cortisol levels in individuals with schizophrenia, most of them included a healthy control group for comparisons there is diversity in the inflammation markers assessed - the most frequent being the IL-2, IL-4, IL-6, IL-8, and TNF-α. Eleven of the 13 studies compare stress and inflammatory markers in individuals with schizophrenia to healthy controls, one study compares two subgroups of patients with schizophrenia, and one study compares pre- and post-measures in the same group of individuals with schizophrenia.

Conclusions

The focus of the studies within the topic is diverse. Many of the selected studies found correlations between cortisol and inflammation markers, however, the direction of correlation and inflammatory markers included differed. A variety of mechanisms behind cortisol and immunological changes associated with schizophrenia were considered. Evidence was found in these studies to suggest that biological immune and stress markers may be associated with clinical improvement in participants with schizophrenia, however, the exact mechanisms remain to be determined.

Role of NCKAP1 in the Defective Phagocytic Function of Microglia-Like Cells Derived from Rapidly Progressing Sporadic ALS

Microglia plays a key role in determining the progression of amyotrophic lateral sclerosis (ALS), yet their precise role in ALS has not been identified in humans. This study aimed to identify a key factor related to the functional characteristics of microglia in rapidly progressing sporadic ALS patients using the induced microglia model, although it is not identical to brain resident microglia. After confirming that microglia-like cells (iMGs) induced by human monocytes could recapitulate the main signatures of brain microglia, step-by-step comparative studies were conducted to delineate functional differences using iMGs from patients with slowly progressive ALS [ALS(S), n = 14] versus rapidly progressive ALS [ALS(R), n = 15]. Despite an absence of significant differences in the expression of microglial homeostatic genes, ALS(R)-iMGs preferentially showed defective phagocytosis and an exaggerated pro-inflammatory response to LPS stimuli compared to ALS(S)-iMGs. Transcriptome analysis revealed that the perturbed phagocytosis seen in ALS(R)-iMGs was closely associated with decreased NCKAP1 (NCK-associated protein 1)-mediated abnormal actin polymerization. NCKAP1 overexpression was sufficient to rescue impaired phagocytosis in ALS(R)-iMGs. Post-hoc analysis indicated that decreased NCKAP1 expression in iMGs was correlated with the progression of ALS. Our data suggest that microglial NCKAP1 may be an alternative therapeutic target in rapidly progressive sporadic ALS.

Microglial crosstalk with astrocytes and immune cells in amyotrophic lateral sclerosis

In recent years, biomedical research efforts aimed to unravel the mechanisms involved in motor neuron death that occurs in amyotrophic lateral sclerosis (ALS). While the main causes of disease progression were first sought in the motor neurons, more recent studies highlight the gliocentric theory demonstrating the pivotal role of microglia and astrocyte, but also of infiltrating immune cells, in the pathological processes that take place in the central nervous system microenvironment. From this point of view, microglia-astrocytes-lymphocytes crosstalk is fundamental to shape the microenvironment toward a pro-inflammatory one, enhancing neuronal damage. In this review, we dissect the current state-of-the-art knowledge of the microglial dialogue with other cell populations as one of the principal hallmarks of ALS progression. Particularly, we deeply investigate the microglia crosstalk with astrocytes and immune cells reporting in vitro and in vivo studies related to ALS mouse models and human patients. At last, we highlight the current experimental therapeutic approaches that aim to modulate microglial phenotype to revert the microenvironment, thus counteracting ALS progression.

Microglia NLRP3 Inflammasome and Neuroimmune Signaling in Substance Use Disorders

During the last decade, substance use disorders (SUDs) have been increasingly recognized as neuroinflammation-related brain diseases. Various types of abused drugs (cocaine, methamphetamine, alcohol, opiate-like drugs, marijuana, etc.) can modulate the activation status of microglia and neuroinflammation levels which are involved in the pathogenesis of SUDs. Several neuroimmune signaling pathways, including TLR/NF-кB, reactive oxygen species, mitochondria dysfunction, as well as autophagy defection, etc., have been implicated in promoting SUDs. Recently, inflammasome-mediated signaling has been identified as playing critical roles in the microglia activation induced by abused drugs. Among the family of inflammasomes, NOD-, LRR-, and pyrin-domain-containing protein 3 (NLRP3) serves the primary research target due to its abundant expression in microglia. NLRP3 has the capability of integrating multiple external and internal inputs and coordinately determining the intensity of microglia activation under various pathological conditions. Here, we summarize the effects of abused drugs on NLRP3 inflammasomes, as well as others, if any. The research on this topic is still at an infant stage; however, the readily available findings suggest that NLRP3 inflammasome could be a common downstream effector stimulated by various types of abused drugs and play critical roles in determining abused-drug-mediated biological effects through enhancing glia-neuron communications. NLRP3 inflammasome might serve as a novel target for ameliorating the development of SUDs.

Degeneracy in epilepsy: multiple routes to hyperexcitable brain circuits and their repair

Due to its complex and multifaceted nature, developing effective treatments for epilepsy is still a major challenge. To deal with this complexity we introduce the concept of degeneracy to the field of epilepsy research: the ability of disparate elements to cause an analogous function or malfunction. Here, we review examples of epilepsy-related degeneracy at multiple levels of brain organisation, ranging from the cellular to the network and systems level. Based on these insights, we outline new multiscale and population modelling approaches to disentangle the complex web of interactions underlying epilepsy and to design personalised multitarget therapies.

Transforming the understanding of brain immunity

Contemporary studies have completely changed the view of brain immunity from envisioning the brain as isolated and inaccessible to peripheral immune cells to an organ in close physical and functional communication with the immune system for its maintenance, function, and repair. Circulating immune cells reside in special niches in the brain's borders, the choroid plexus, meninges, and perivascular spaces, from which they patrol and sense the brain in a remote manner. These niches, together with the meningeal lymphatic system and skull microchannels, provide multiple routes of interaction between the brain and the immune system, in addition to the blood vasculature. In this Review, we describe current ideas about brain immunity and their implications for brain aging, diseases, and immune-based therapeutic approaches.

JP1, a polypeptide specifically targeting integrin αVβ3, ameliorates choroidal neovascularization and diabetic retinopathy in mice

Anti-vascular endothelial growth factor (VEGF) drugs have revolutionized the treatment of neovascular eye diseases, but responses are incomplete in some patients. Recent evidence shows that integrins are involved in the pathogenesis of neovascular age-related macular degeneration and diabetic retinopathy. JP1, derived from an optimized seven-amino-acid fragment of JWA protein, is a polypeptide specifically targeting integrin αVβ3. In this study we evaluated the efficacy of JP1 on laser-induced choroidal neovascularization (CNV) and retinal vascular leakage. CNV mice received a single intravitreal (IVT) injection of JP1 (10, 20, 40 µg) or ranibizumab (RBZ, 10 µg). We showed that JP1 injection dose-dependently inhibited laser-induced CNV; the effect of RBZ was comparable to that of 20 µg JP1; a combined IVT injection of JP1 (20 μg) and RBZ (5 μg) exerted a synergistic effect on CNV. In the 3rd month after streptozotocin injection, diabetic mice receiving IVT injection of JP1 (40 µg) or RBZ (10 µg) once a week for 4 weeks showed significantly suppressed retinal vascular leakage. In both in vivo and in vitro experiments, JP1 counteracted oxidative stress and inflammation via inhibiting ROS/NF-κB signaling in microglial cells, and angiogenesis via modulating MEK1/2-SP1-integrin αVβ3 and TRIM25-SP1-MMP2 axes in vascular endothelial cells. In addition, intraperitoneal injection of JP1 (1, 5 or 10 mg) once every other day for 3 times also dose-dependently inhibited CNV. After intraperitoneal injection of FITC-labeled JP1 (FITC-JP1) or FITC in laser-induced CNV mice, the fluorescence intensity in the CNV lesion was markedly increased in FITC-JP1 group, compared with that in FITC group, confirming that JP1 could penetrate the blood-retinal barrier to target CNV lesion. We conclude that JP1 can be used to design novel CNV-targeting therapeutic agents that may replace current invasive intraocular injections.

Microglial IL-1RA ameliorates brain injury after ischemic stroke by inhibiting astrocytic CXCL1-mediated neutrophil recruitment and microvessel occlusion

Acute ischemic stroke (AIS), one of the leading causes of mortality worldwide, is characterized by a rapid inflammatory cascade resulting in exacerbation of ischemic brain injury. Microglia are the first immune responders. However, the role of postischemic microglial activity in ischemic brain injury remains far from being fully understood. Here, using the transgenic mouse line CX₃ CR1^creER :R26^iDTR to genetically ablate microglia, we showed that microglial deletion exaggerated ischemic brain injury. Associated with this worse outcome, there were increased neutrophil recruitment, microvessel blockade and blood flow stagnation in the acute phase, accompanied by transcriptional upregulation of chemokine (C-X-C motif) ligand 1 (CXCL1). Our study showed that microglial interleukin-1 receptor antagonist (IL-1RA) suppressed astrocytic CXCL1 expression induced by oxygen and glucose deprivation and inhibited neutrophil migration. Furthermore, neutralizing antibody therapy against CXCL1 or the administration of recombinant IL-1RA protein reduced brain infarct volume and improved motor coordination performance of mice after ischemic stroke. Our study suggests that microglia protect against acute ischemic brain injury by secreting IL-1RA to inhibit astrocytic CXCL1 expression, which reduces neutrophil recruitment and neutrophil-derived microvessel occlusion.

Neurodegeneration cell per cell

The clinical definition of neurodegenerative diseases is based on symptoms that reflect terminal damage of specific brain regions. This is misleading as it tells little about the initial disease processes. Circuitry failures that underlie the clinical symptomatology are themselves preceded by clinically mostly silent, slowly progressing multicellular processes that trigger or are triggered by the accumulation of abnormally folded proteins such as Aβ, Tau, TDP-43, and α-synuclein, among others. Methodological advances in single-cell omics, combined with complex genetics and novel ways to model complex cellular interactions using induced pluripotent stem (iPS) cells, make it possible to analyze the early cellular phase of neurodegenerative disorders. This will revolutionize the way we study those diseases and will translate into novel diagnostics and cell-specific therapeutic targets, stopping these disorders in their early track before they cause difficult-to-reverse damage to the brain.

Suicide in bipolar disorder patients is associated with hippocampal microglia activation and reduction of lymphocytes-activation gene 3 (LAG3) microglial checkpoint expression

BACKGROUND

Bipolar disorder (BD) is associated with marked functional impairments along with increased rate of suicide. Although there is ample evidence for the involvement of inflammatory processes and microglia activation in the pathophysiology of BD, the mechanisms that regulate these cells in BD patients, and particularly the role of microglia checkpoints, is still unclear.

METHODS

Immunohistochemical analyses of hippocampal sections from post-mortem brains of 15 BD patients and 12 control subjects were used to assess microglia density, by staining the microglia-specific receptor P2RY12, and microglia activation, by staining the activation marker MHC II. Given recent findings on the involvement of LAG3, which interacts with MHC II and serves as a negative microglia checkpoint, in depression and electroconvulsive therapy, we assessed the levels of LAG3 expression and their correlations with microglia density and activation.

RESULTS

There were no overall differences between BD patients and controls, but BD patients who committed suicide (N = 9) displayed a significant elevation in the overall microglia density and the density of MHC II-labeled microglia (but not other MHC II-labeled cells), compared with no suicide BD patients (N = 6) and controls. Furthermore, the percent of microglia expressing LAG3 was significantly reduced only in suicidal BD patients, with significant negative correlations between microglial LAG3 expression levels and the density of microglia, in general, and activated microglia, in particular.

CONCLUSION

Suicidal BD patients exhibit microglia activation, which is possibly mediated by reduced LAG3 checkpoint expression, suggesting that anti-microglial therapeutics, including LAG3 modulators, may be beneficial for this subgroup of patients.

LilrB3 is a putative cell surface receptor of APOE4

The three isoforms of apolipoprotein E (APOE2, APOE3, and APOE4) only differ in two amino acid positions but exert quite different immunomodulatory effects. The underlying mechanism of such APOE isoform dependence remains enigmatic. Here we demonstrate that APOE4, but not APOE2, specifically interacts with the leukocyte immunoglobulin-like receptor B3 (LilrB3). Two discrete immunoglobin-like domains of the LilrB3 extracellular domain (ECD) recognize a positively charged surface patch on the N-terminal domain (NTD) of APOE4. The atomic structure reveals how two APOE4 molecules specifically engage two LilrB3 molecules, bringing their intracellular signaling motifs into close proximity through formation of a hetero-tetrameric complex. Consistent with our biochemical and structural analyses, APOE4, but not APOE2, activates human microglia cells (HMC3) into a pro-inflammatory state in a LilrB3-dependent manner. Together, our study identifies LilrB3 as a putative immune cell surface receptor for APOE4, but not APOE2, and may have implications for understanding the biological functions as well as disease relevance of the APOE isoforms.

Fibroblast-Conditioned Media Enhance the Yield of Microglia Isolated from Mixed Glial Cultures

Microglia are the main immune cells of the central nervous system (CNS) and comprise various model systems used to investigate inflammatory mechanisms in CNS disorders. Currently, shaking and mild trypsinization are widely used microglial culture methods; however, the problems with culturing microglia include low yield and a time-consuming process. In this study, we replaced normal culture media (NM) with media containing 25% fibroblast-conditioned media (F-CM) to culture mixed glia and compared microglia obtained by these two methods. We found that F-CM significantly improved the yield and purity of microglia and reduced the total culture time of mixed glia. The microglia obtained from the F-CM group showed longer ramified morphology than those from the NM group, but no difference was observed in cell size. Microglia from the two groups had similar phagocytic function and baseline phenotype markers. Both methods yielded microglia were responsive to various stimuli such as lipopolysaccharide (LPS), interferon-γ (IFN-γ), and interleukin-4 (IL-4). The current results suggest that F-CM affect the growth of primary microglia in mixed glia culture. This method can produce a high yield of primary microglia within a short time and may be a convenient method for researchers to investigate inflammatory mechanisms and some CNS disorders.

Human monocyte-derived microglia-like cell models: A review of the benefits, limitations and recommendations

In the last few decades, mounting evidence has highlighted that microglia have crucial roles in both health and disease. This has led to a growing interest in studying human microglia in disease-relevant models. However, current models present limitations that can make them unsuitable for moderate throughput studies in human cohorts. Primary human microglia are ethically and technically difficult to obtain and only allow low throughput studies; immortalized cell lines have been shown to differ too greatly from primary human microglia; and induced pluripotent stem cell-derived microglia, although physiologically relevant in most contexts, have limited potential for use in large cohorts of people or for personalised drug screening. In this review, we discuss monocyte-derived microglia-like (MDMi) cells, a model that has been developed and increasingly used in the last decade, using human monocytes isolated from blood samples. We describe the variety of protocols that have been used to develop MDMi cell models and highlight a need for standardization across protocols. We then summarize data that validate MDMi cells as an appropriate model to study human microglia in health and disease. We also present the benefits and limitations of using this approach to study human microglia compared with other microglial models, when used in combination with the relevant downstream applications and with cross-validation of findings in other systems. Finally, we summarize the paradigms in which MDMi models have been used to advance research on microglia in immune-related disease. This review is an important reference for scientists who seek to establish MDMi cells as a microglial model for the advancement of our understanding of microglia in human health and disease.

Innate Immunity in Cardiovascular Diseases-Identification of Novel Molecular Players and Targets

During the past few years, unexpected developments have driven studies in the field of clinical immunology. One driver of immense impact was the outbreak of a pandemic caused by the novel virus SARS-CoV-2. Excellent recent reviews address diverse aspects of immunological re-search into cardiovascular diseases. Here, we specifically focus on selected studies taking advantage of advanced state-of-the-art molecular genetic methods ranging from genome-wide epi/transcriptome mapping and variant scanning to optogenetics and chemogenetics. First, we discuss the emerging clinical relevance of advanced diagnostics for cardiovascular diseases, including those associated with COVID-19-with a focus on the role of inflammation in cardiomyopathies and arrhythmias. Second, we consider newly identified immunological interactions at organ and system levels which affect cardiovascular pathogenesis. Thus, studies into immune influences arising from the intestinal system are moving towards therapeutic exploitation. Further, powerful new research tools have enabled novel insight into brain-immune system interactions at unprecedented resolution. This latter line of investigation emphasizes the strength of influence of emotional stress-acting through defined brain regions-upon viral and cardiovascular disorders. Several challenges need to be overcome before the full impact of these far-reaching new findings will hit the clinical arena.

Advanced therapeutic strategies targeting microglia: beyond neuroinflammation

For a long time, microglia have been recognized as the main culprits of neuroinflammatory responses because they are primary phagocytes present in the parenchyma of the central nervous system (CNS). However, with the evolving concept of microglial biology, advanced and precise approaches, rather than the global inhibition of activated microglia, have been proposed in the management of neurological disorders. Yolk sac-derived resident microglia have heterogeneous composition according to brain region, sex, and diseases. They play a key role in the maintenance of CNS homeostasis and as primary phagocytes. The perturbation of microglia development can induce neurodevelopmental disorders. Microglia aggravate or alleviate neuroinflammation according to microenvironment and their spatiotemporal dynamics. They are long-lived cells and repopulate via their proliferation or external monocyte engraft. Based on this evolving concept, understanding advanced therapeutic strategies targeting microglia can give us an opportunity to discover novel therapies for neurological disorders.

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

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

Therapeutic targets and biomarkers of tumor immunotherapy: response versus non-response

Cancers are highly complex diseases that are characterized by not only the overgrowth of malignant cells but also an altered immune response. The inhibition and reprogramming of the immune system play critical roles in tumor initiation and progression. Immunotherapy aims to reactivate antitumor immune cells and overcome the immune escape mechanisms of tumors. Represented by immune checkpoint blockade and adoptive cell transfer, tumor immunotherapy has seen tremendous success in the clinic, with the capability to induce long-term regression of some tumors that are refractory to all other treatments. Among them, immune checkpoint blocking therapy, represented by PD-1/PD-L1 inhibitors (nivolumab) and CTLA-4 inhibitors (ipilimumab), has shown encouraging therapeutic effects in the treatment of various malignant tumors, such as non-small cell lung cancer (NSCLC) and melanoma. In addition, with the advent of CAR-T, CAR-M and other novel immunotherapy methods, immunotherapy has entered a new era. At present, evidence indicates that the combination of multiple immunotherapy methods may be one way to improve the therapeutic effect. However, the overall clinical response rate of tumor immunotherapy still needs improvement, which warrants the development of novel therapeutic designs as well as the discovery of biomarkers that can guide the prescription of these agents. Learning from the past success and failure of both clinical and basic research is critical for the rational design of studies in the future. In this article, we describe the efforts to manipulate the immune system against cancer and discuss different targets and cell types that can be exploited to promote the antitumor immune response.

Microbial and immune factors regulate brain maintenance and aging

Tissue aging can be viewed as a loss of normal maintenance; in advanced age, the mechanisms which keep the tissue healthy on daily bases fail to manage the accumulating "wear and tear", leading to gradual loss of function. In the brain, maintenance is provided primarily by three components: the blood-brain barrier, which allows the influx of certain molecules into the brain while excluding others, the circulation of the cerebrospinal fluid, and the phagocytic function of microglia. Indeed, failure of these systems is associated with cognitive loss and other hallmarks of brain aging. Interestingly, all three mechanisms are regulated not only by internal conditions within the aging brain, but remain highly sensitive to the peripheral signals, such as cytokines or microbiome-derived molecules, present in the systemic circulation. In this article, we discuss the contribution of such peripheral factors to brain maintenance and its loss in aging.

Recent Advances in Microglia Modelling to Address Translational Outcomes in Neurodegenerative Diseases

Neurodegenerative diseases are deteriorating conditions of the nervous system that are rapidly increasing in the aging population. Increasing evidence suggests that neuroinflammation, largely mediated by microglia, the resident immune cells of the brain, contributes to the onset and progression of neurodegenerative diseases. Hence, microglia are considered a major therapeutic target that could potentially yield effective disease-modifying treatments for neurodegenerative diseases. Despite the interest in studying microglia as drug targets, the availability of cost-effective, flexible, and patient-specific microglia cellular models is limited. Importantly, the current model systems do not accurately recapitulate important pathological features or disease processes, leading to the failure of many therapeutic drugs. Here, we review the key roles of microglia in neurodegenerative diseases and provide an update on the current microglia platforms utilised in neurodegenerative diseases, with a focus on human microglia-like cells derived from peripheral blood mononuclear cells as well as human-induced pluripotent stem cells. The described microglial platforms can serve as tools for investigating disease biomarkers and improving the clinical translatability of the drug development process in neurodegenerative diseases.

Microglia-Dependent and Independent Brain Cytoprotective Effects of Mycophenolate Mofetil During Neuronal Damage

Acute lesions of the central nervous system often lead to permanent limiting deficits. In addition to the initial primary damage, accompanying neuroinflammation is responsible for progression of damage. Mycophenolate mofetil (MMF) as a selective inhibitor of inosine 5-monophosphate dehydrogenase (IMPDH) was shown to modulate the inflammatory response and promote neuronal survival when applied in specific time windows after neuronal injury. The application of brain cytoprotective therapeutics early after neuronal damage is a fundamental requirement for a successful immunomodulation approach. This study was designed to evaluate whether MMF can still mediate brain cytoprotection when applied in predefined short time intervals following CNS injury. Furthermore, the role of microglia and changes in IMPDH2 protein expression were assessed. Organotypic hippocampal slice cultures (OHSC) were used as an in vitro model and excitotoxically lesioned with N-methyl-aspartate (NMDA). Clodronate (Clo) was used to deplete microglia and analyze MMF mediated microglia independent effects. The temporal expression of IMPDH2 was studied in primary glial cell cultures treated with lipopolysaccharide (LPS). In excitotoxically lesioned OHSC a significant brain cytoprotective effect was observed between 8 and 36 h but not within 8 and 24 h after the NMDA damage. MMF mediated effects were mainly microglia dependent at 24, 36, 48 h after injury. However, further targets like astrocytes seem to be involved in protective effects 72 h post-injury. IMPDH2 expression was detected in primary microglia and astrocyte cell cultures. Our data indicate that MMF treatment in OHSC should still be started no later than 8–12 h after injury and should continue at least until 36 h post-injury. Microglia seem to be an essential mediator of the observed brain cytoprotective effects. However, a microglia-independent effect was also found, indicating involvement of astrocytes.

Periodontal microorganisms and Alzheimer disease - A causative relationship?

In the initiation or exacerbation of Alzheimer disease, the dissemination of oral microorganisms into the brain tissue or the low‐level systemic inflammation have been speculated to play a role. However, the impact of oral microorganisms, such as Porphyromonas gingivalis, on the pathogenesis of Alzheimer disease and the potential causative relationship is still unclear. The present review has critically reviewed the literature by examining the following aspects: (a) the oral microbiome and the immune response in the elderly population, (b) human studies on the association between periodontal and gut microorganisms and Alzheimer disease, (c) animal and in vitro studies on microorganisms and Alzheimer disease, and (d) preventive and therapeutic approaches. Factors contributing to microbial dysbiosis seem to be aging, local inflammation, systemic diseases, wearing of dentures, living in nursing homes and no access to adequate oral hygiene measures. Porphyromonas gingivalis was detectable in post‐mortem brain samples. Microbiome analyses of saliva samples or oral biofilms showed a decreased microbial diversity and a different composition in Alzheimer disease compared to cognitively healthy subjects. Many in‐vitro and animal studies underline the potential of P gingivalis to induce Alzheimer disease‐related alterations. In animal models, recurring applications of P gingivalis or its components increased pro‐inflammatory mediators and β‐amyloid in the brain and deteriorated the animals' cognitive performance. Since periodontitis is the result of a disturbed microbial homoeostasis, an effect of periodontal therapy on the oral microbiome and host response related to cognitive parameters may be suggested and should be elucidated in further clinical trials.

Neuron–Microglia Contacts Govern the PGE2 Tolerance through TLR4-Mediated de Novo Protein Synthesis

Cellular and molecular mechanisms of the peripheral immune system (e.g., macrophage and monocyte) in programming endotoxin tolerance (ET) have been well studied. However, regulatory mechanism in development of brain immune tolerance remains unclear. The inducible COX-2/PGE₂ axis in microglia, the primary innate immune cells of the brain, is a pivotal feature in causing inflammation and neuronal injury, both in acute excitotoxic insults and chronic neurodegenerative diseases. This present study investigated the regulatory mechanism of PGE₂ tolerance in microglia. Multiple reconstituted primary brain cells cultures, including neuron–glial (NG), mixed glial (MG), neuron-enriched, and microglia-enriched cultures, were performed and consequently applied to a treatment regimen for ET induction. Our results revealed that the levels of COX-2 mRNA and supernatant PGE₂ in NG cultures, but not in microglia-enriched and MG cultures, were drastically reduced in response to the ET challenge, suggesting that the presence of neurons, rather than astroglia, is required for PGE₂ tolerance in microglia. Furthermore, our data showed that neural contact, instead of its soluble factors, is sufficient for developing microglial PGE₂ tolerance. Simultaneously, this finding determined how neurons regulated microglial PGE₂ tolerance. Moreover, by inhibiting TLR4 activation and de novo protein synthesis by LPS-binding protein (LBP) manipulation and cycloheximide, our data showed that the TLR4 signal and de novo protein synthesis are necessary for microglia to develop PGE₂ tolerance in NG cells under the ET challenge. Altogether, our findings demonstrated that neuron–microglia contacts are indispensable in emerging PGE₂ tolerance through the regulation of TLR4-mediated de novo protein synthesis.

Microglia and their LAG3 checkpoint underlie the antidepressant and neurogenesis-enhancing effects of electroconvulsive stimulation

Despite evidence implicating microglia in the etiology and pathophysiology of major depression, there is paucity of information regarding the contribution of microglia-dependent molecular pathways to antidepressant procedures. In this study, we investigated the role of microglia in a mouse model of depression (chronic unpredictable stress-CUS) and its reversal by electroconvulsive stimulation (ECS), by examining the effects of microglia depletion with the colony stimulating factor-1 antagonist PLX5622. Microglia depletion did not change basal behavioral measures or the responsiveness to CUS, but it completely abrogated the therapeutic effects of ECS on depressive-like behavior and neurogenesis impairment. Treatment with the microglia inhibitor minocycline concurrently with ECS also diminished the antidepressant and pro-neurogenesis effects of ECS. Hippocampal RNA-Seq analysis revealed that ECS significantly increased the expression of genes related to neurogenesis and dopamine signaling, while reducing the expression of several immune checkpoint genes, particularly lymphocyte-activating gene-3 (Lag3), which was the only microglial transcript significantly altered by ECS. None of these molecular changes occurred in microglia-depleted mice. Immunohistochemical analyses showed that ECS reversed the CUS-induced changes in microglial morphology and elevation in microglial LAG3 receptor expression. Consistently, either acute or chronic systemic administration of a LAG3 monoclonal antibody, which readily penetrated into the brain parenchyma and was found to serve as a direct checkpoint blocker in BV2 microglia cultures, rapidly rescued the CUS-induced microglial alterations, depressive-like symptoms, and neurogenesis impairment. These findings suggest that brain microglial LAG3 represents a promising target for novel antidepressant therapeutics.

Persistent Acidic Environment Induces Impaired Phagocytosis via ERK in Microglia

Acidic environment evoked by stroke, traumatic brain injury, and Alzheimer's disease may change the functional properties of microglia. Nevertheless, the underlying mechanisms of functional changes in microglia remain unclear. In this study, we found that acidic stimuli (pH 6.8) increased rapidly interleukin (IL)-1β and IL-6 mRNA levels and subsequently reduced IL-10, transforming growth factor (TGF)-β1, Cx3cr1, and P2ry12 as the exposure time to acidic environment increase in BV2 cells. In addition, persistent acidic environment (pH 6.8 for 6 h) induced impaired phagocytic function in BV2 cells. Short-term acidic exposure (pH 6.8 for 30 min) increased cyclic AMP (cAMP) and phospho-protein kinase A (PKA) but inhibited phospho-extracellular signal-regulated kinase (p-ERK). However, under persistent acidic environment (pH 6.8 for 6 h), cyclic AMP and PKA were normalized and p-ERK was increased with TDAG8 (T cell death associated gene 8; GPR65) reduction. FR 180,204, an ERK inhibitor, rescued the persistent acidic environment-induced functional changes in BV2 cells and its effect was recapitulated in primary neonatal microglia. Thus, we propose that ERK targeting may be an alternative strategy to restore microglial dysfunction in the central nervous system (CNS) acidic environment in various neurological disorders.