Microglia states and nomenclature: A field at its crossroads

Ageing-related changes in the regulation of microglia and their interaction with neurons

Ageing is one of the most important risk factors for chronic health conditions, including neurodegenerative diseases. Inflammation is a feature of ageing, as well as a key pathophysiological mechanism for degenerative diseases. Microglia play multiple roles in the central nervous system; their states entail a complex assemblage of responses reflecting the multiplicity of functions they fulfil both under homeostatic basal conditions and in response to stimuli. Whereas glial cells can promote neuronal homeostasis and limit neurodegeneration, age-related inflammation (i.e. inflammaging) leads to the functional impairment of microglia and astrocytes, exacerbating their response to stimuli. Thus, microglia are key mediators for age-dependent changes of the nervous system, participating in the generation of a less supportive or even hostile environment for neurons. Whereas multiple changes of ageing microglia have been described, here we will focus on the neuron-microglia regulatory crosstalk through fractalkine (CX3CL1) and CD200, and the regulatory cytokine Transforming Growth Factor β1 (TGFβ1), which is involved in immunomodulation and neuroprotection. Ageing results in a dysregulated activation of microglia, affecting neuronal survival, and function. The apparent unresponsiveness of aged microglia to regulatory signals could reflect a restriction in the mechanisms underlying their homeostatic and reactive states. The spectrum of functions, required to respond to life-long needs for brain maintenance and in response to disease, would progressively narrow, preventing microglia from maintaining their protective functions. This article is part of the Special Issue on "Microglia".

Fatty acid amide hydrolase gene inactivation induces hetero-cellular potentiation of microglial function in the 5xFAD mouse model of Alzheimer's disease

Neuroinflammation has recently emerged as a crucial factor in Alzheimer's disease (AD) etiopathogenesis. Microglial cells play an important function in the inflammatory response; specifically, the emergence of disease-associated microglia (DAM) has offered new insights into the conflicting perspectives on the detrimental or beneficial roles of microglia. We previously showed that modulating the endocannabinoid tone by fatty acid amide hydrolase (FAAH) inactivation renders beneficial effects in an amyloidosis context, paradoxically accompanied by an exacerbated neuroinflammatory response and the enrichment of DAM population. Here, we aim to elucidate the role of microglial cells in FAAH-lacking mice in the 5xFAD mouse model of AD by using RNA-sequencing analysis, molecular determinations, and morphological studies by using in vivo multiphoton microscopy. FAAH-lacking AD mice displayed upregulated inflammatory genes and exhibited a DAM genetic profile. Conversely, genes linked to AD were downregulated. Depleting microglia using PLX5622 revealed that plaque-associated microglia in FAAH-deficient AD mice had a more stable, ramified morphology and increased Aβ uptake, leading to reduced plaque growth compared to control mice. Importantly, FAAH expression was negligible in microglial cells, thus suggesting a role for FAAH in the cellular interplay in the central nervous system. Our findings show that Faah gene inactivation triggers a hetero-cellular enhancement of microglial function that was paradoxically paralleled by an exacerbated inflammatory response. Taken together, the present data highlight FAAH as a potential therapeutic target in AD.

A bottom-up approach identifies the antipsychotic and antineoplastic trifluoperazine and the ribose derivative deoxytubercidin as novel microglial phagocytosis inhibitors

Phagocytosis is an indispensable function of microglia, the brain professional phagocytes. Microglia is particularly efficient phagocytosing cells that undergo programmed cell death (apoptosis) in physiological conditions. However, mounting evidence suggests microglial phagocytosis dysfunction in multiple brain disorders. These observations prompted us to search for phagocytosis modulators (enhancers or inhibitors) with therapeutic potential. We used a bottom-up strategy that consisted on the identification of phagocytosis modulators using phenotypic high throughput screenings (HTSs) in cell culture and validation in organotypic cultures and in vivo. We performed two complementary HTS campagnes: at Achucarro, we used primary cultures of mouse microglia and compounds of the Prestwick Chemical Library; at Roche, we used human iPSC derived macrophage-like cells and a proprietary chemo-genomic library with 2200 compounds with known mechanism-of-action. Next, we validated the more robust compounds using hippocampal organotypic cultures and identified two phagocytosis inhibitors: trifluoperazine, a dopaminergic and adrenergic antagonist used as an antipsychotic and antineoplastic; and deoxytubercidin, a ribose derivative. Finally, we tested whether these compounds were able to modulate phagocytosis of apoptotic newborn cells in the adult hippocampal neurogenic niche in vivo by administering them into the mouse hippocampus using osmotic minipumps. We confirmed that both trifluoperazine and deoxytubercidin have anti-phagocytic activity in vivo, and validated our bottom-up strategy to identify novel phagocytosis modulators. These results show that chemical libraries with annotated mechanism of action are an starting point for the pharmacological modulation of microglia in drug discovery projects aiming at the therapeutic manipulation of phagocytosis in brain diseases.

Transcranial focused ultrasound stimulation alleviates NLRP3-related neuroinflammation induced by ischemic stroke via regulation of the Nespas/miR-383-3p/SHP2 pathway

Transcranial focused ultrasound stimulation (tFUS) has emerged as a promising therapeutic strategy for mitigating brain injury in animal models. In this study, the effects and mechanisms of tFUS on ischemic stroke were explored in a transient middle cerebral artery occlusion (MCAO) rat model. Low-intensity tFUS was administered to the ischemic hemisphere 24 h post-MCAO for seven consecutive days. Neurological function was evaluated through neurobehavioral assessments following tFUS treatment. Western blotting, immunofluorescence staining, and quantitative real-time PCR were performed to examine the impact of tFUS on NLRP3-related neuroinflammation using brain tissues from MCAO rats and BV2 cells subjected to oxygen glucose deprivation/reperfusion (OGD/R). Additionally, RNA sequencing and cell transient transfection were employed to elucidate the underlying mechanisms. The findings revealed that tFUS improved neurobehavioral performance, reduced infarct size, and suppressed NLRP3 inflammasome activation seven days post-MCAO. Notably, Nespas expression was significantly elevated in tFUS-treated rats, whereas Nespas silencing exacerbated neurological deficits and enhanced NLRP3 activation. Moreover, Nespas positively regulated src homology 2 domain-containing tyrosine phosphatase-2 (SHP2), and SHP2 inhibition significantly amplified NLRP3 activation. Mechanistic in vitro studies further demonstrated that Nespas attenuated microglial NLRP3 activation via the Nespas/miR-383-3p/SHP2 pathway. These results suggest that the neuroprotective effects of tFUS are likely mediated through the upregulation of Nespas and suppression of NLRP3 via the Nespas/miR-383-3p/SHP2 axis, offering new insights into the molecular mechanisms supporting tFUS as a potential therapeutic approach for stroke-induced brain injury.

18 kDa TSPO targeting drives polarized human microglia towards a protective and restorative neurosteroidome profile

An aberrant pro-inflammatory microglia response has been associated with most neurodegenerative disorders. Identifying microglia druggable checkpoints to restore their physiological functions is an emerging challenge. Recent data have shown that microglia produce de novo neurosteroids, endogenous molecules exerting potent anti-inflammatory activity. Here, the role of neurosteroidogenesis in the modulation of microgliosis was explored in human microglia cells. In particular, CYP11A1 inhibition or TSPO pharmacological stimulation, crucial proteins involved in the rate limiting step of the neurosteroidogenic cascade, were employed. CYP11A1 inhibition led microglia to acquire a dysfunctional and hyperreactive phenotype, while selective TSPO ligands promoted the establishment of an anti-inflammatory one. Analysis of specific neurosteroid levels (neurosteroidome) identified allopregnanolone/pregnanolone as crucial metabolites allowing controlled activation of microglia. Importantly, the neurosteroid shift towards a greater androgenic/estrogenic profile supported the transition from pro-inflammatory to neuroprotective microglia, suggesting the therapeutic potential of de novo microglial neurosteroidogenesis stimulation for neuroinflammatory-related disorders.

Microglial Responses to Alzheimer's Disease Pathology: Insights From "Omics" Studies

Human genetics studies lent firm evidence that microglia are key to Alzheimer's disease (AD) pathogenesis over a decade ago following the identification of AD-associated genes that are expressed in a microglia-specific manner. However, while alterations in microglial morphology and gene expression are observed in human postmortem brain tissue, the mechanisms by which microglia drive and contribute to AD pathology remain ill-defined. Numerous mouse models have been developed to facilitate the disambiguation of the biological mechanisms underlying AD, incorporating amyloidosis, phosphorylated tau, or both. Over time, the use of multiple technologies including bulk tissue and single cell transcriptomics, epigenomics, spatial transcriptomics, proteomics, lipidomics, and metabolomics have shed light on the heterogeneity of microglial phenotypes and molecular patterns altered in AD mouse models. Each of these 'omics technologies provide unique information and biological insight. Here, we review the literature on the approaches and findings of these methods and provide a synthesis of the knowledge generated by applying these technologies to mouse models of AD.

Targeting common disease pathomechanisms to treat amyotrophic lateral sclerosis

The motor neuron disease amyotrophic lateral sclerosis (ALS) is a devastating condition with limited treatment options. The past few years have witnessed a ramping up of translational ALS research, offering the prospect of disease-modifying therapies. Although breakthroughs using gene-targeted approaches have shown potential to treat patients with specific disease-causing mutations, the applicability of such therapies remains restricted to a minority of individuals. Therapies targeting more general mechanisms that underlie motor neuron pathology in ALS are therefore of considerable interest. ALS pathology is associated with disruption to a complex array of key cellular pathways, including RNA processing, proteostasis, metabolism and inflammation. This Review details attempts to restore cellular homeostasis by targeting these pathways in order to develop effective, broadly-applicable ALS therapeutics.

PTPN2 dephosphorylates STAT3 to ameliorate anesthesia-induced cognitive decline in aged rats by altering the microglial phenotype and inhibiting inflammation

Perioperative neurocognitive disorders (PNDs) are common neurological complications after anesthesia in the elderly. Protein tyrosine phosphatase non-receptor type 2 (PTPN2) regulates signal transducer and activator of transcription protein 3 (STAT3) signaling to control inflammation in certain organs, but its role in PNDs remains unknown. Herein, we constructed a PND model in 18-month-old rats by treating them with sevoflurane. PND rats developed neuroinflammation, along with a significant decrease in PTPN2 expression and a rise in STAT3 phosphorylation in the hippocampus. Ptpn2 overexpression alleviated the behavioral disorders of PND rats, ameliorated neuronal injury, inhibited neuroinflammation, inflammasome activation, microglial activation, and microglial phenotype switching. Similar results were observed in sevoflurane-treated HMC3 microglia with PTPN2 overexpression, while PTPN2 silencing showed the opposite results. Additionally, PTPN2 seems to be a target of T-box transcription factor 2 (TBX2). These results contribute to the evidence supporting the idea that PTPN2 is a regulatory factor in PND progression.

Running exercise decreases microglial activation in the medial prefrontal cortex in an animal model of depression

BACKGROUND

Running exercise effectively ameliorates depressive symptoms in humans and depression-like behaviors in animals, but the underlying mechanisms remain unclear. Microglia-mediated neuroinflammation plays a major role in the development of depression. The medial prefrontal cortex (mPFC) is a key brain region involved in depression and is sensitive to physical activity. Whether the antidepressant effect of running exercise involves changes in mPFC microglia is not understood.

METHODS

The animals were subjected to chronic unpredictable stress (CUS) intervention followed by treadmill running. The sucrose preference test and elevated plus maze test or tail suspension test were used for behavioral assessment of the animals. The number of microglia in the mPFC was quantified by immunohistochemistry and stereology. The density and morphology of microglia were analyzed via immunofluorescence staining combined with three-dimensional laser scanning techniques. The mRNA expressions of inflammatory cytokines in the mPFC were examined via quantitative real-time PCR.

RESULTS

Running exercise effectively alleviated depressive-like behaviors in depression model animals. Running exercise reversed the increase in the number of microglia and the density of activated microglia in the mPFC of CUS animals. Running exercise effectively reversed the changes in microglia (reduced cell body area, total branch length and branch complexity) in the mPFC of CUS animals. Furthermore, running exercise regulated the gene expressions of pro-/antiinflammatory cytokines in the mPFC of CUS animals.

CONCLUSIONS

Our results suggested that the antidepressant effects of running exercise may involve decreasing the number of activated microglia, reversing morphological changes in microglia in the mPFC, and reducing inflammatory responses.

Protein kinase R induced by type I interferons is a main regulator of reactive microglia in Zika virus infection

Microglial cells are the phagocytic cells of the brain that under physiological conditions participate in brain homeostasis and surveillance. Under pathogenic states, microglia undergoes strong morphological and transcriptional changes potentially leading to sustained neuroinflammation, brain damage, and cognitive disorders. Postnatal and adult Zika virus (ZIKV) brain infection is characterized by the induction of reactive microglia associated with brain inflammation, synapse loss and neuropathogenesis. Contrary to neurons, microglial cells are not infected by ZIKV thus raising the question of the mechanism governing ZIKV-induced microglia's reactivity. In this work, we have questioned the role of exogenous, neuronal type I interferons (IFNs-I) in regulating ZIKV-induced microglia's reactivity. Primary cultured microglial cells were either treated with conditioned media from ZIKV-infected mature neurons or co-cultured with ZIKV-infected neurons. Using either an antibody directed against the IFNAR receptor that neutralizes the IFNs-I response or Ifnar-/-microglial cells, we demonstrate that IFNs-I produced by ZIKV-infected neurons are the main regulators of the phagocytic capacity and the pro-inflammatory gene expression profile of reactive, non-infected microglial cells. We identify protein kinase R (PKR), whose expression is activated by IFNs-I, as a major regulator of the phagocytic capacity, pro-inflammatory response, and morphological changes of microglia induced by IFNs-I while up-regulating STAT1 phosphorylation and IRF1 expression. Results obtained herein in vitro with primary cultured cells and in vivo in ZIKV-infected adult immunocompetent mice, unravel a role for IFNs-I and PKR in directly regulating microglia's reactivity that could be at work in other infectious and non-infectious brain pathologies.

Fundamental Neurochemistry Review: Lipids across microglial states

The capacity of immune cells to alter their function based on their metabolism is the basis of the emerging field of immunometabolism. Microglia are the resident innate immune cells of the central nervous system, and it is a current focus of the field to investigate how alterations in their metabolism impact these cells. Microglia have the ability to utilize lipids, such as fatty acids, as energy sources, but also alterations in lipids can impact microglial form and function. Recent studies highlighting different microglial states and transcriptional signatures have highlighted modifications in lipid processing as defining these states. This review highlights these recent studies and uses these altered pathways to discuss the current understanding of lipid biology in microglia. The studies highlighted here review how lipids may alter microglial phagocytic functioning or alter their pro- and anti-inflammatory balance. These studies provide a foundation by which lipid supplementation or diet alterations could influence microglial states and function. Furthermore, targets modulating microglial lipid metabolism may provide new treatment avenues.

(Re)building the nervous system: A review of neuron-glia interactions from development to disease

Neuron-glia interactions are fundamental to the development and function of the nervous system. During development, glia, including astrocytes, microglia, and oligodendrocytes, influence neuronal differentiation and migration, synapse formation and refinement, and myelination. In the mature brain, glia are crucial for maintaining neural homeostasis, modulating synaptic activity, and supporting metabolic functions. Neurons, inherently vulnerable to various stressors, rely on glia for protection and repair. However, glia, in their reactive state, can also promote neuronal damage, which contributes to neurodegenerative and neuropsychiatric diseases. Understanding the dual role of glia-as both protectors and potential aggressors-sheds light on their complex contributions to disease etiology and pathology. By appropriately modulating glial activity, it may be possible to mitigate neurodegeneration and restore neuronal function. In this review, which originated from the International Society for Neurochemistry (ISN) Advanced School in 2019 held in Montreal, Canada, we first describe the critical importance of glia in the development and maintenance of a healthy nervous system as well as their contributions to neuronal damage and neurological disorders. We then discuss potential strategies to modulate glial activity during disease to protect and promote a properly functioning nervous system. We propose that targeting glial cells presents a promising therapeutic avenue for rebuilding the nervous system.

Microglial and neuronal fates following inhibition of CSF-1R in synucleinopathy mouse model

Synucleinopathies are age-related neurological disorders characterized by the abnormal accumulation of α-synuclein (α-syn) in neuronal and non-neuronal cells. It has been proposed that microglial cells play an important role in synucleinopathy neuroinflammation, as well as homeostatically, such as in the clearance of α-syn aggregates in the brain. Here, we examined the effects of microglia on the pathogenesis of synucleinopathies by cell depletion in a mouse model of synucleinopathies. For this purpose, we treated non-transgenic (Non-tg) and α-synuclein transgenic (α-syn-tg) mice with pexidartinib (PLX3397), a tyrosine kinase inhibitor of colony-stimulating factor 1 receptor (CSF-1R). Neuropathological and immunoblot analysis confirmed that Iba-1 immunoreactive microglial cells were decreased by 95% following PLX3397 treatment in Non-tg and α-syn-tg mice. The level of total α-syn in the Triton X-insoluble fraction of brain homogenate was significantly decreased by microglial depletion in the α-syn-tg mice, while the level of Triton X-soluble human α-syn was not affected. Furthermore, the number of p-α-syn immunoreactive inclusions was reduced in α-syn-tg mice treated with PLX3397. Microglial depletion also ameliorated neuronal and synaptic degeneration in α-syn-tg mice, thereby resulted partially improving the motor behavioral deficit in α-syn-tg mice. Moreover, we demonstrated that microglia that survived post-PLX3397 treatment (PLX-resistant microglia) have lower expressions of CSF-1R, and microglial transcriptome analysis further elucidated that PLX-resistant microglia have unique morphology and transcriptomic signatures relative to vehicle-treated microglia of both genotypes; these include differences in definitive microglial functions such as their immune response, cell mobility, cell-cell communications, and regulation of neural homeostasis. Therefore, we suggest that microglia play a critical role in the pathogenesis of synucleinopathies, and that modulation of microglial status might be an effective therapeutic strategy for synucleinopathies.

Bindarit Attenuates Neuroinflammation After Subarachnoid Hemorrhage by Regulating the CCL2/CCR2/NF-κB Pathway

BACKGROUND AND PURPOSE

The poor prognosis of subarachnoid hemorrhage (SAH) is closely linked to neuroinflammation and neuronal apoptosis. The CCL2/CCR2 signaling axis, a cytoplasmic pathway responsible for recruiting immune cells, plays a significant role in regulating neuroinflammation in neurological diseases. Bindarit, an inhibitor of chemokine CC motif ligand 2(CCL2), has been shown to demonstrate neuroprotective effects in various central nervous system diseases. This study aimed to investigate the anti-inflammatory effects of Bindarit after SAH.

METHODS

Pre-processed RNA-seq transcriptome datasets GSE79416 from the Gene Expression Omnibus (GEO) database were analyzed to identify genes differentially expressed between mice with SAH and control mice using bioinformatics methods. Bindarit, a CCL2 inhibitor, was administered intraperitoneally one hour after SAH. Recombinant CCL2 protein was administered via the lateral ventricle one hour before SAH induction. HT22 cells were cultured and stimulated by oxyhemoglobin to establish an in vitro model of SAH.

RESULTS

Analysis of GSE79416 datasets revealed upregulation of CCL2 expression, identifying it as a hub gene in SAH. Following SAH, CCL2 expression increased in rat brain tissue, reaching the highest level 24hours after SAH. Bindarit improved the short-term and long-term neurological deficits after SAH and also exhibited the anti-inflammatory effects following SAH. Conversely, administration of recombinant CCL2 protein attenuated the protective effects of Bindarit. In vitro, Bindarit significantly reduced neuronal inflammation.

CONCLUSION

Endogenous CCL2 expression was upregulated in the rat SAH model. Bindarit improved neurological functions and reduced neuroinflammation by regulating the CCL2/CCR2/NF-κB pathway in early brain injury after SAH.

Brain macrophages in vascular health and dysfunction

Diverse macrophage populations inhabit the rodent and human central nervous system (CNS), including microglia in the parenchyma and border-associated macrophages (BAMs) in the meninges, choroid plexus, and perivascular spaces. These innate immune phagocytes are essential in brain development and maintaining homeostasis, but they also play diverse roles in neurological diseases. In this review, we highlight the emerging roles of CNS macrophages in regulating vascular function in health and disease. We discuss that, in addition to microglia, BAMs, including perivascular macrophages, play roles in supporting vascular integrity and maintaining blood flow. We highlight recent advancements in understanding how these macrophages are implicated in protecting against vascular dysfunction and modulating the progression of cerebrovascular diseases, as seen in vessel-associated neurodegeneration.

Human pluripotent stem cell-derived microglia shape neuronal morphology and enhance network activity in vitro

BACKGROUND

Microglia, the resident immune cells of the central nervous system, play a critical role in maintaining neuronal health, but are often overlooked in traditional neuron-focused in vitro models.

NEW METHOD

In this study, we developed a novel co-culture system of human pluripotent stem cell (hPSC)-derived microglia and neurons to investigate how hPSC-derived microglia influence neuronal morphology and network activity. Using high-content morphological analysis and multi-electrode arrays (MEA), we demonstrate that these microglia successfully incorporate into neuronal networks and modulate key aspects of neuronal function.

RESULTS

hPSC-derived microglia significantly reduced cellular debris and altered neuronal morphology by decreasing axonal and dendritic segments and reducing synapse density. Interestingly, despite the decrease in synapse density, neuronal network activity increased.

CONCLUSION

Our findings underscore the importance of including hPSC-derived microglia in in vitro models to better simulate in vivo neuroglial interactions and provide a platform for investigating neuron-glia dynamics in health and disease.

Microglial Depletion, a New Tool in Neuroinflammatory Disorders: Comparison of Pharmacological Inhibitors of the CSF-1R

A growing body of evidence highlights the importance of microglia, the resident immune cells of the CNS, and their pro-inflammatory activation in the onset of many neurological diseases. Microglial proliferation, differentiation, and survival are highly dependent on the CSF-1 signaling pathway, which can be pharmacologically modulated by inhibiting its receptor, CSF-1R. Pharmacological inhibition of CSF-1R leads to an almost complete microglial depletion whereas treatment arrest allows for subsequent repopulation. Microglial depletion has shown promising results in many animal models of neurodegenerative diseases (Alzheimer's disease (AD), Parkinson's disease, or multiple sclerosis) where transitory microglial depletion reduced neuroinflammation and improved behavioral test results. In this review, we will focus on the comparison of three different pharmacological CSF-1R inhibitors (PLX3397, PLX5622, and GW2580) regarding microglial depletion. We will also highlight the promising results obtained by microglial depletion strategies in adult models of neurological disorders and argue they could also prove promising in neurodevelopmental diseases associated with microglial activation and neuroinflammation. Finally, we will discuss the lack of knowledge about the effects of these strategies on neurons, astrocytes, and oligodendrocytes in adults and during neurodevelopment.

Multiple Sclerosis: Glial Cell Diversity in Time and Space

Multiple sclerosis (MS) is the most prevalent human inflammatory disease of the central nervous system with demyelination and glial scar formation as pathological hallmarks. Glial cells are key drivers of lesion progression in MS with roles in both tissue damage and repair depending on the surrounding microenvironment and the functional state of the individual glial subtype. In this review, we describe recent developments in the context of glial cell diversity in MS summarizing key findings with respect to pathological and maladaptive functions related to disease-associated glial subtypes. A particular focus is on the spatial and temporal dynamics of glial cells including subtypes of microglia, oligodendrocytes, and astrocytes. We contextualize recent high-dimensional findings suggesting that glial cells dynamically change with respect to epigenomic, transcriptomic, and metabolic features across the inflamed rim and during the progression of MS lesions. In summary, detailed knowledge of spatially restricted glial subtype functions is critical for a better understanding of MS pathology and its pathogenesis as well as the development of novel MS therapies targeting specific glial cell types.

β-Asarone regulates microglia polarization to alleviate TBI-induced nerve damage via Fas/FasL signaling axis

Acute injury and secondary injury caused by traumatic brain injury (TBI) seriously threaten the health of patients. The purpose of this study was to investigate the role of β-Asarone in TBI-induced neuroinflammation and injury. In this work, the effects of β-Asarone on nerve injury and neuronal apoptosis were investigated in mice with TBI by controlled cortical impingement. The results of this research implied that β-Asarone dose-dependently decreased the mNSS score, brain water content and neuronal apoptosis, but increased the levels of the axonal markers Nrp-1 and Tau in TBI mice. In addition, β-Asarone caused a decrease in the levels of Fas, FasL, and inflammatory factors in cerebrospinal fluid and serum of TBI mice. Therefore, β-Asarone inhibited neuroinflammation and promoted axon regeneration in TBI mice. Besides, β-Asarone treatment inhibited M1 phenotype polarization but promoted M2 phenotype polarization in microglia of TBI mice. Overexpression of Fas and FasL reversed the above effects of β-Asarone. Thus, β-Asarone regulated microglial M1/M2 polarization balance in TBI mice by suppressing Fas/FasL signaling axis. In conclusion, β-Asarone inhibited Fas/FasL signaling pathway to promote the M1/M2 polarization balance of microglia toward M2 polarization, thus alleviating TBI-induced nerve injury.

Embryonic exposure to acetamiprid insecticide induces CD68-positive microglia and Purkinje cell arrangement abnormalities in the cerebellum of neonatal rats

Concerns have been raised regarding acetamiprid (ACE), a neonicotinoid insecticide, due to its potential neurodevelopmental toxicity. ACE, which is structurally similar to nicotine, acts as an agonist of nicotinic acetylcholine receptors (nAChRs) and resists degradation by acetylcholinesterase. Furthermore, ACE has been reported to disrupt neuronal transmission and induce developmental neurotoxicity and ataxia in animal models. However, the prenatal ACE exposure and its pathological changes, including impacts on motor control, remains unclear. In this study, we investigated the effects of ACE exposure, focusing on the development of cerebellar neurons and glia, which are linked to motor impairment. ACE at doses of 20, 40-, and 60 mg/kg body weight was administered to Pregnant Wistar rats via feed on gestational day (G) 15. The developing cerebellum of the pups was examined on postnatal days (P) 7, 14, and 18, corresponding to the critical periods of cerebellar maturation in rodents. Our data revealed that ACE exposure at 40 and 60 mg/kg induced abnormal neuronal alignment on P14, and neuronal cell loss on P18. Additionally, ACE altered microglial behavior, with an increase in the number of CD68-positive microglia, suggesting that the exposure results in an increase in phagocytic microglia in response to neuronal abnormalities, ultimately leading to neuronal cell loss. Pups exposed to 60 mg/kg ACE exhibited hindlimb clasping during the hindlimb suspension test, indicating motor impairment. These findings suggest that ACE exposure causes neuronal cell loss of developing Purkinje cells and promotes a phase shift to the activate mode of microglia. This study further highlights the crucial role of neuron-glia interactions in ACE-induced motor impairment, thus contributing to our understanding of the potential risks associated with prenatal ACE exposure.

Glial-immune interactions in barrier organs

Neuro-immune interactions within barrier organs, such as lung, gut, and skin, are crucial in regulating tissue homeostasis, inflammatory responses, and host defence. Our rapidly advancing understanding of peripheral neuroimmunology is transforming the field of barrier tissue immunology, offering a fresh perspective for developing therapies for complex chronic inflammatory disorders affecting barrier organs. However, most studies have primarily examined interactions between the peripheral nervous system and the immune system from a neuron-focused perspective, while glial cells, the nonneuronal cells of the nervous system, have received less attention. Glial cells were long considered as mere bystanders, only supporting their neuronal neighbours, but recent discoveries mainly on enteric glial cells in the intestine have implicated these cells in immune-regulation and inflammatory disease pathogenesis. In this review, we will highlight the bi-directional interactions between peripheral glial cells and the immune system and discuss the emerging immune regulatory functions of glial cells in barrier organs.

CXCL4 deficiency limits M4 macrophage infiltration and attenuates hyperoxia-induced lung injury

BACKGROUND

Bronchopulmonary dysplasia (BPD), a chronic lung disease prevalent among premature infants, significantly impacts lifelong respiratory health. Macrophages, as key components of the innate immune system, play a role in lung tissue inflammation and injury, exhibiting diverse and dynamic functionalities. The M4 macrophage, a distinctive subtype primarily triggered by chemokine (C-X-C motif) ligand 4 (CXCL4), has been implicated in pulmonary inflammatory and fibrotic processes. Nonetheless, its contribution to the pathophysiology of BPD remains uncertain.

OBJECTIVE

This study aimed to elucidate the involvement of CXCL4 in hyperoxia-induced neonatal lung injury and fibrosis, with a particular focus on its influence on M4 macrophages.

METHODS

A BPD model in neonatal mice was established through continuous exposure to 95% O2 for 7 days. Comparative analyses of lung damage and subsequent regeneration were conducted between wild-type (WT) and CXCL4 knockout (KO) mice. Lung tissue inflammation and fibrosis were assessed using histological and immunofluorescence staining, enzyme-linked immunosorbent assay, Western blot, and real-time quantitative polymerase chain reaction. Differentiation of M0 and M4 macrophages was performed in vitro using macrophage colony-stimulating factor and CXCL4, while expressions of S100A8 and MMP7, along with migration assays, were evaluated.

RESULTS

Elevated CXCL4 levels and M4 macrophage activation were identified in the lung tissue of BPD model mice. CXCL4 deficiency conferred protection to alveolar type 2 epithelial cells, reduced sphingosine-1-phosphate metabolic activity, mitigated pulmonary fibrosis, and limited M4 macrophage progression. This deletion further enhanced lung matrix remodeling during recovery. In vitro, CXCL4 promoted M4 macrophage differentiation and increased macrophage migration via chemokine (C-C motif) receptor 1.

CONCLUSION

CXCL4 contributes to hyperoxia-induced lung injury and fibrosis through modulation of cytokine release, alveolar cell proliferation, lipid metabolism, and the regulation of macrophage phenotype and function.

Multimodal single-cell profiling reveals neuronal vulnerability and pathological cell states in focal cortical dysplasia

Focal cortical dysplasia (FCD) is a neurodevelopmental condition characterized by malformations of the cerebral cortex that often cause drug-resistant epilepsy. In this study, we performed multi-omics single-nuclei profiling to map the chromatin accessibility and transcriptome landscapes of FCD type II, generating a comprehensive multimodal single-nuclei dataset comprising 61,525 cells from 11 clinical samples of lesions and controls. Our findings revealed profound chromatin, transcriptomic, and cellular alterations affecting neuronal and glial cells in FCD lesions, including the selective loss of upper-layer excitatory neurons, significant expansion of oligodendrocytes and immature astrocytic populations, and a distinct neuronal subpopulation harboring dysmorphic neurons. Furthermore, we uncovered activated microglia subsets, particularly in FCD IIb cases. This comprehensive study unveils neuronal and glial cell states driving FCD development and epileptogenicity, enhancing our understanding of FCD and offering directions for targeted therapy development.

snRNA-seq stratifies multiple sclerosis patients into distinct white matter glial responses

Poor understanding of the cellular and molecular basis of clinical and genetic heterogeneity in progressive multiple sclerosis (MS) has hindered the search for new effective therapies. To address this gap, we analyzed 632,000 single-nucleus RNA sequencing profiles from 156 brain tissue samples of MS and control donors to examine inter- and intra-donor heterogeneity. We found distinct cell type-specific gene expression changes between MS gray and white matter, highlighting clear pathology differences. MS lesion subtypes had different cellular compositions but surprisingly similar cell-type gene expression patterns both within and across patients, suggesting global changes. Most gene expression variability was instead explained by patient effects, allowing us to stratify patients and describe the different pathological processes occurring between patient subgroups. Future mapping of these brain molecular profiles with blood and/or CSF profiles from living MS patients will allow precision medicine approaches anchored in patient-specific pathological processes.

Temperature induces brain-intake shift of recombinant high-density lipoprotein after traumatic brain injury

Traumatic brain injury (TBI) is one of the leading public health concerns in the world. Therapeutic hypothermia is routinely used in severe TBI, and pathophysiological hyperthermia, frequently observed in TBI patients, has an unclear impact on drug transport in the injured brain due to a lack of study on its effects. We investigated the effect of post-traumatic therapeutic hypothermia at 33°C and pathophysiological hyperthermia at 39°C on brain transport and cell uptake of neuroprotectants after TBI. Recombinant high-density lipoprotein (rHDL), which possesses anti-inflammatory, antioxidant activity, and blood-brain barrier (BBB) permeability, was chosen as the model drug. First, we found that mild hypothermia and hyperthermia impaired rHDL transport to the brain and lesion targeting in controlled cortical impact mice. Second, we investigated the temperature-induced rHDL uptake shift by various brain cell types. Mild hypothermia impeded the uptake of rHDL by endothelial cells, neurons, microglia, and astrocytes. Hyperthermia impeded the uptake of rHDL by endothelial cells and neurons while promoting its uptake by microglia and astrocytes. In an attempt to understand the mechanisms behind the above phenomena, it was found that temperature induced brain-intake shift of rHDL through the regulation of low-density lipoprotein receptor (LDLR) and LDLR-related protein 1 (LRP1) stability in brain cells. We therefore reported the full view of the temperature-induced brain-intake shift of rHDL after TBI for the first time. It would be of help in coordinating pharmacotherapy with temperature management in individualization and precision medicine.

Effective Nose-to-Brain Delivery of Blood-Brain Barrier Impermeant Anti-IL-1β Antibody via the Minimally Invasive Nasal Depot (MIND) Technique

Treatment of neuroinflammation and neurodegenerative diseases using biologic therapies is limited due to the blood-brain barrier (BBB). This study explores a clinically validated approach to bypass the BBB for the purposes of direct central nervous system (CNS) delivery of antibodies using the Minimally Invasive Nasal Depot (MIND) technique. Using a lipopolysaccharide (LPS)-induced mouse model of neuroinflammation, we evaluated the efficacy of MIND in delivering a BBB impermeant full-length anti-IL-1β antibody. The results demonstrated that MIND delivery resulted in a significant reduction in IL-1β levels and microglial activation in relevant brain regions, notably outperforming conventional intravenous (IV) administration. These results underscore the ability of the MIND approach to transform the treatment landscape for a range of neurodegenerative diseases by enabling the targeted delivery of otherwise BBB impermeant therapeutics.

Microglia in the aged brain develop a hypoactive molecular phenotype after surgery

BACKGROUND

Microglia, the resident immune cells of the brain, play a crucial role in maintaining homeostasis in the central nervous system (CNS). However, they can also contribute to neurodegeneration through their pro-inflammatory properties and phagocytic functions. Acute post-operative cognitive deficits have been associated with inflammation, and microglia have been implicated primarily based on morphological changes. We investigated the impact of surgery on the microglial transcriptome to test the hypothesis that surgery produces an age-dependent pro-inflammatory phenotype in these cells.

METHODS

Three-to-five and 20-to-22-month-old C57BL/6 mice were anesthetized with isoflurane for an abdominal laparotomy, followed by sacrifice either 6 or 48 h post-surgery. Age-matched controls were exposed to carrier gas. Cytokine concentrations in plasma and brain tissue were evaluated using enzyme-linked immunosorbent assays (ELISA). Iba1+ cell density and morphology were determined by immunohistochemistry. Microglia from both surgically treated mice and age-matched controls were isolated by a well-established fluorescence-activated cell sorting (FACS) protocol. The microglial transcriptome was then analyzed using quantitative polymerase chain reaction (qPCR) and RNA sequencing (RNAseq).

RESULTS

Surgery induced an elevation in plasma cytokines in both age groups. Notably, increased CCL2 was observed in the brain post-surgery, with a greater change in old compared to young mice. Age, rather than the surgical procedure, increased Iba1 immunoreactivity and the number of Iba1+ cells in the hippocampus. Both qPCR and RNAseq analysis demonstrated suppression of neuroinflammation at 6 h after surgery in microglia isolated from aged mice. A comparative analysis of differentially expressed genes (DEGs) with previously published neurodegenerative microglia phenotype (MGnD), also referred to disease-associated microglia (DAM), revealed that surgery upregulates genes typically downregulated in the context of neurodegenerative diseases. These surgery-induced changes resolved by 48 h post-surgery and only a few DEGs were detected at that time point, indicating that the hypoactive phenotype of microglia is transient.

CONCLUSIONS

While anesthesia and surgery induce pro-inflammatory changes in the plasma and brain of mice, microglia adopt a homeostatic molecular phenotype following surgery. This effect seems to be more pronounced in aged mice and is transient. These results challenge the prevailing assumption that surgery activates microglia in the aged brain.

The role of microglia in Neuroinflammation associated with cardiopulmonary bypass

Cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA) are indispensable core techniques in cardiac surgery. Numerous studies have shown that cardiopulmonary bypass and deep hypothermic circulatory arrest are associated with the occurrence of neuroinflammation, accompanied by the activation of microglia. Microglia, as macrophages in the central nervous system, play an irreplaceable role in neuroinflammation. Current research on neuroinflammation induced by microglia activation mainly focuses on neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, neuropathic pain, acquired brain injury, and others. However, there is relatively limited research on microglia and neuroinflammation under conditions of cardiopulmonary bypass and deep hypothermic circulatory arrest. The close relationship between cardiopulmonary bypass, deep hypothermic circulatory arrest, and cardiac surgery underscores the importance of identifying targets for intervening in neuroinflammation through microglia. This could greatly benefit cardiac surgery patients during cardiopulmonary bypass and the perioperative period, significantly improving patient prognosis. This review article provides the first comprehensive discussion on the signaling pathways associated with neuroinflammation triggered by microglia activation, the impact of cardiopulmonary bypass on microglia, as well as the current status and advancements in cardiopulmonary bypass animal models. It provides new insights and methods for the treatment of neuroinflammation related to cardiopulmonary bypass and deep hypothermic circulatory arrest, holding significant importance for clinical treatment by cardiac surgeons, management strategies by cardiopulmonary bypass physicians, and the development of neurologically related medications.

Immune mechanisms and shared immune targets in neurodegenerative diseases

The immune system plays a major part in neurodegenerative diseases. In some, such as multiple sclerosis, it is the primary driver of the disease. In others, such as Alzheimer disease, amyotrophic lateral sclerosis and Parkinson disease, it has an amplifying role. Immunotherapeutic approaches that target the adaptive and innate immune systems are being explored for the treatment of almost all neurological diseases, and the targets and approaches are often common across diseases. Microglia are the primary immune cells in the brain that contribute to disease pathogenesis, and are consequently a common immune target for therapy. Other therapeutic approaches target components of the peripheral immune system, such as regulatory T cells and monocytes, which in turn act within the CNS. This Review considers in detail how microglia, monocytes and T cells contribute to the pathogenesis of multiple sclerosis, Alzheimer disease, amyotrophic lateral sclerosis and Parkinson disease, and their potential as shared therapeutic targets across these diseases. The microbiome is also highlighted as an emerging therapeutic target that indirectly modulates the immune system. Therapeutic approaches being developed to target immune function in neurodegenerative diseases are discussed, highlighting how immune-based approaches developed to treat one disease could be applicable to multiple other neurological diseases.

Minocycline inhibits microglial activation in the CA1 hippocampal region and prevents long-term cognitive sequel after experimental cerebral malaria

Cerebral malaria is the worst complication of malaria infection, has a high mortality rate, and may cause different neurodysfunctions, including cognitive decline. Neuroinflammation is an important cause of cognitive damage in neurodegenerative diseases, and microglial cells can be activated in a disease-associated profile leading to tissue damage and neuronal death. Here, we demonstrated that treatment with minocycline reduced blood-brain barrier breakdown and modulated ICAM1 mRNA expression; reduced proinflammatory cytokines, such as TNF-α, IL-1β, IFN-γ, and IL-6; and prevented long-term cognitive decline in contextual and aversive memory tasks. Taken together, our data suggest that microglial cells are activated during experimental cerebral malaria, leading to neuroinflammatory events that end up in cognitive damage. In addition, pharmacological modulation of microglial activation, by drugs such as minocycline may be an important therapeutic strategy in the prevention of long-term memory impairment.

Nicotine is an Immunosuppressant: Implications for Women's Health and Disease

A plethora of evidence supports that nicotine, the primary alkaloid in tobacco products that is generally accepted for maintaining use, is immunoregulatory and may function as an immunosuppressant. Women have unique experiences with use of nicotine-containing products and also undergo significant reproductive transitions throughout their lifespan which may be impacted by nicotine use. Within the extant literature, there is conflicting evidence that nicotine may confer beneficial health effects in specific disease states (e.g., in ulcerative colitis). Use prevalence of nicotine-containing products is exceptionally high in individuals presenting with some comorbid disease states that impact immune system health and can be a risk factor for the development of diseases which disproportionately impact women; however, the mechanisms underlying these relationships are largely unclear. Further, little is known regarding the impacts of nicotine's immunosuppressive effects on women's health during the menopausal transition, which is arguably an inflammatory event characterized by a pro-inflammatory peri-menopause period. Given that post-menopausal women are at a higher risk than men for the development of neurodegenerative diseases such as Alzheimer's disease and are also more vulnerable to negative health effects associated with diseases such as HIV-1 infection, it is important to understand how use of nicotine-containing products may impact the immune milieu in women. In this review, we define instances in which nicotine use confers immunosuppressive, anti-inflammatory, or pro-inflammatory effects in the context of comorbid disease states, and focus on how nicotine impacts neuroimmune signaling to maintain use. We posit that regardless of potential health benefits, nicotine use cessation should be a priority in the clinical care of women. The synthesis of this review demonstrates the importance of systematically defining the relationships between volitional nicotine use, immune system function, and comorbid disease states in women to better understand how nicotine impacts women's health and disease.

Mass-Guided Single-Cell MALDI Imaging of Low-Mass Metabolites Reveals Cellular Activation Markers

Single-cell MALDI mass spectrometry imaging (MSI) of lipids and metabolites >200 Da has recently come to the forefront of biomedical research and chemical biology. However, cell-targeting and metabolome-preserving methods for analysis of low mass, hydrophilic metabolites (<200 Da) in large cell populations are lacking. Here, the PRISM-MS (PRescan Imaging for Small Molecule - Mass Spectrometry) mass-guided MSI workflow is presented, which enables space-efficient single cell lipid and metabolite analysis. In conjunction with giant unilamellar vesicles (GUVs) as MSI ground truth for cell-sized objects and Monte Carlo reference-based consensus clustering for data-dependent identification of cell subpopulations, PRISM-MS enables MSI and on-cell MS2-based identification of low-mass metabolites like amino acids or Krebs cycle intermediates involved in stimulus-dependent cell activation. The utility of PRISM-MS is demonstrated through the characterization of complex metabolome changes in lipopolysaccharide (LPS)-stimulated microglial cells and human-induced pluripotent stem cell-derived microglia. Translation of single cell results to endogenous microglia in organotypic hippocampal slice cultures indicates that LPS-activation involves changes of the itaconate-to-taurine ratio and alterations in neuron-to-glia glutamine-glutamate shuttling. The data suggests that PRISM-MS can serve as a standard method in single cell metabolomics, given its capability to characterize larger cell populations and low-mass metabolites.

Evidence of microglial involvement in the childhood abuse-associated increase in perineuronal nets in the ventromedial prefrontal cortex

Microglia, known for their diverse roles in the central nervous system, have recently been recognized for their involvement in degrading the extracellular matrix. Perineuronal nets (PNNs), a specialized form of this matrix, are crucial for stabilizing neuronal connections and constraining plasticity. Our group recently reported increased PNN densities in the ventromedial prefrontal cortex (vmPFC) of depressed individuals that died by suicide in adulthood after experiencing childhood abuse (DS-CA) compared to matched controls. To explore potential underlying mechanisms, we employed a comprehensive approach in similar postmortem vmPFC samples, combining a human matrix metalloproteinase and chemokine array, isolation of CD11b-positive microglia and enzyme-linked immunosorbent assays (ELISA). Our findings indicate a significant downregulation of matrix metalloproteinase (MMP)-9 and tissue inhibitors of metalloproteinases (TIMP)-2 in both whole vmPFC grey matter and isolated microglial cells from DS-CA samples. Furthermore, our experiments reveal that a history of child abuse is associated with diminished levels of microglial CX3CR1 and IL33R in both vmPFC whole lysate and CD11b+ isolated cells. However, levels of the CX3CR1 ligand, CX3CL1 (Fractalkine), did not differ between groups. While these data suggest potential long-lasting alterations in microglial markers in the vmPFC of individuals exposed to severe childhood adversity, direct functional assessments were not conducted. Nonetheless, these findings offer insight into how childhood abuse may contribute to PNN alterations via microglial-related mechanisms.

Microglia as hunters or gatherers of brain synapses

Over a decade ago, it was discovered that microglia, the brain's immune cells, engulf synaptic material in a process named microglial pruning. This term suggests that microglia actively sculpt brain circuits by tagging and phagocytosing unwanted synapses. However, live imaging studies have yet to demonstrate how microglial synapse elimination occurs. To address this issue, we propose a new conceptual framework distinguishing between two potential mechanisms of synapse elimination, culling and scavenging. During culling, microglia may use a contractile ring to sever the neuronal plasma membrane, removing the unwanted synapse. During scavenging, synapse elimination is neuronal-driven, and the neuronal plasma membrane fission machinery sheds off synapses that are later phagocytosed by microglia. We will discuss the current limitations of studying microglial synapse elimination and evaluate evidence supporting either culling or scavenging. Discerning between these mechanisms is essential for determining the therapeutic value of phagocytosis modulators in diseases with altered brain connectivity.

The role of the CCL5-CCR5 axis in microglial activation leading to postoperative cognitive dysfunction

Postoperative cognitive dysfunction (POCD) is a common complication following surgeries involving general anesthesia. Although the CCL5-CCR5 axis is implicated in various neurological conditions, its role in POCD remains unclear. In our POCD model, we observed an increase in CCL5 and CCR5 levels concurrent with microglial activation and significant upregulation of inflammatory cytokines IL-6 and IL-1β. Administration of MVC, a CCR5 antagonist, alleviated neuroinflammation, prevented dendritic spine loss, and improved cognitive deficits by inhibiting the CCR5/CREB/NLRP1 pathway. However, the cognitive benefits of MVC were reversed by the CREB inhibitor 666-15. Our findings highlight the potential of targeting the CCL5-CCR5 axis as a therapeutic strategy for preventing and treating POCD.

Fractionated alpha and mixed beam radiation promote stronger pro-inflammatory effects compared to acute exposure and trigger phagocytosis

Introduction and methods

Aiming to evaluate safety aspects of a recently proposed approach to target Alzheimer's disease, we mimicked a complex boron neutron capture therapy field using a mixed beam consisting of high- and low-linear energy transfer (LET) radiation, 241Am alpha particles (α) and/or X-ray radiation respectively, in human microglial (HMC3) cells.

Results

Acute exposure to 2 Gy X-rays induced the strongest response in the formation of γH2AX foci 30 min post irradiation, while α- and mixed beam-induced damage (α:X-ray = 3:1) sustained longer. Fractionation of the same total dose (0.4 Gy daily) induced a similar number of γH2AX foci as after acute radiation, however, α- or mixed irradiation caused a higher expression of DNA damage response genes CDKN1A and MDM2 24 h after the last fraction, as well as a stronger decrease in cell viability and clonogenic survival compared to acute exposure. Phosphorylation of STING, followed by phosphorylation of NF-κB subunit p65, was rapidly induced (1 or 3 h, respectively) after the last fraction by all radiation qualities. This led to IL-1β secretion into the medium, strongly elevated expression of pro-inflammatory cytokine genes and enhanced phagocytosis after fractionated exposure to α- and mixed beam-irradiation compared to their acute counterparts 24 h post-irradiation. Nevertheless, all inflammatory changes were returning to basal levels or below 10-14 days post irradiation.

Discussion

In conclusion, we demonstrate strong transient pro-inflammatory induction by daily high-LET radiation in a microglia model, triggering phagocytosis which may aid in clearing amyloid beta, but importantly, from a safety perspective, without long-term alterations.

Microglial lipid phosphatase SHIP1 limits complement-mediated synaptic pruning in the healthy developing hippocampus

The gene inositol polyphosphate-5-phosphatase D (INPP5D), which encodes the lipid phosphatase SH2-containing inositol polyphosphate 5-phosphatase 1 (SHIP1), is associated with the risk of Alzheimer's disease (AD). How it influences microglial function and brain physiology is unclear. Here, we showed that SHIP1 was enriched in early stages of healthy brain development. By combining in vivo loss-of-function approaches and proteomics, we discovered that mice conditionally lacking microglial SHIP1 displayed increased complement and synapse loss in the early postnatal brain. SHIP1-deficient microglia showed altered transcriptional signatures and abnormal synaptic pruning that was dependent on the complement system. Mice exhibited cognitive defects in adulthood only when microglial SHIP1 was depleted early postnatally but not at later stages. Induced pluripotent stem cell (iPSC)-derived microglia lacking SHIP1 also showed increased engulfment of synaptic structures. These findings suggest that SHIP1 is essential for proper microglia-mediated synapse remodeling in the healthy developing brain. Disrupting this process has lasting behavioral effects and may be linked to vulnerability to neurodegeneration.

Mitigating mitochondrial dysfunction and neuroinflammation by hematoma aspiration in a new surgical model for severe intracerebral hemorrhage

BACKGROUND

Intracerebral hemorrhage (ICH) is associated with a large hematoma that causes compression, increased intracranial pressure (IICP), midline shift, and brain herniation, and may ultimately lead to death. Urgent surgical removal of the large hematoma can ameliorate these injuries, which would be life-saving, but has not improved clinical outcome. A suitable animal model that mimics the clinically relevant human severe ICH injury requiring surgical hematoma evacuation is urgently needed. Here, we established a novel model of severe ICH in rats allowing aspiration of the hematoma and studying the effects of mitochondrial dysfunction in ICH.

METHODS

Severe ICH was induced by intra-striatal injection of 0.6 U of collagenase in 3 μL sterile saline over 15 min. Aspiration of approximately 75 % of the total hematoma was performed 6 h after induction of severe ICH. The effects of hematoma aspiration on hematoma volume, mortality, oxidative stress, ATP levels, mitochondrial dysfunction, and neurological function were measured in rats.

RESULTS

Severe ICH induction increased hematoma volume, neurological deficits, and mortality. Hematoma aspiration abolished mortality and significantly reduced hematoma volume, and neurological deficits. In addition, hematoma aspiration ameliorated the pronounced mitochondrial dysfunction responsible for the failure of energy production and excessive oxidative stress associated with severe hemorrhagic injury. Hematoma aspiration also modulated mitochondrial biogenesis and mitophagy, thereby promoting mitochondrial homeostasis. Markers of neuroinflammation, including iNOS, MMP9, and MPO, were elevated in severe ICH but attenuated by hematoma aspiration.

CONCLUSION

This study established an animal model of severe ICH and provides valuable insights into the complex pathogenesis of severe ICH. The results showed that hematoma aspiration effectively ameliorates mitochondrial dysfunction, oxidative stress, and neuroinflammation, highlighting its potential as a therapeutic intervention.

Glia-glia crosstalk via semaphorins: Emerging implications in neurodegeneration

The central nervous system (CNS) is wired by a complex network of integrated glial and neuronal signals, which is critical for its development and homeostasis. In this context, glia-glia communication is a complex and dynamic process that is essential for ensuring optimal CNS function. Semaphorins, which include secreted and transmembrane molecules, and their receptors, mainly found in the plexin and neuropilin families, are expressed in a wide range of cell types, including glia. In the CNS, semaphorin signalling is involved in a spectrum of processes, including neurogenesis, neuronal migration and wiring, and glial cell recruitment. Recently, semaphorins and plexins have attracted intense research aimed at elucidating their roles in instructing glial cell behavior during development or in response to inflammatory stimuli. In this review, we provide an overview of the multifaceted role of semaphorins in glia-glia communication, highlighting recent discoveries about semaphoring-dependent regulation of glia functions in healthy conditions. We also discuss the mechanisms of gliaglia crosstalk mediated by semaphorins under pathological conditions, and how these interactions may provide potential avenues for therapeutic intervention in neuroinflammation-mediated neurodegeneration.

Maternal exposure to 4-tert-octylphenol causes alterations in the morphology and function of microglia in the offspring mouse brain

4-tert-Octylphenol (OP), an endocrine disrupting chemical is widely used in the production of industrial products. Prenatal exposure to endocrine-disrupting chemicals negatively affects the brain. However, the influence of OP exposure during neurodevelopment in adult offspring remains unclear. Thus, in the present study, we investigated the effects of maternal OP exposure on brain development in adult offspring by analyzing primary glial cell cultures and mice. Our findings revealed that OP exposure led to a specific increase in the mRNA expression of the ionized calcium-binding adapter molecule 1 (Iba-1) and the proportion of amoeboid microglia in the primary glial cell culture and adult offspring mice. Exposure to OP increased the transcriptional activation of Iba-1 and estrogen response element, which were counteracted by estrogen receptor antagonists ICI 182,780. Moreover, OP exposure increased the nuclear localization of the estrogen receptor. Remarkably, OP exposure decreased the mRNA expression levels of proinflammatory cytokines and genes associated with immune response in the brains of the offspring. OP exposure upregulated actin filament-related genes and altered cytoskeletal gene expression, as demonstrated by microarray analysis. The morphological changes in microglia did not result in an inflammatory response following lipopolysaccharide treatment. Taken together, the effects of OP exposure during neurodevelopment persist into adulthood, resulting in microglial dysfunction mediated by estrogen receptor signaling pathways in the brains of adult offspring mice.

Plasticity of Human Microglia and Brain Perivascular Macrophages in Aging and Alzheimer's Disease

The complex roles of myeloid cells, including microglia and perivascular macrophages, are central to the neurobiology of Alzheimer's disease (AD), yet they remain incompletely understood. Here, we profiled 832,505 human myeloid cells from the prefrontal cortex of 1,607 unique donors covering the human lifespan and varying degrees of AD neuropathology. We delineated 13 transcriptionally distinct myeloid subtypes organized into 6 subclasses and identified AD-associated adaptive changes in myeloid cells over aging and disease progression. The GPNMB subtype, linked to phagocytosis, increased significantly with AD burden and correlated with polygenic AD risk scores. By organizing AD-risk genes into a regulatory hierarchy, we identified and validated MITF as an upstream transcriptional activator of GPNMB, critical for maintaining phagocytosis. Through cell-to-cell interaction networks, we prioritized APOE-SORL1 and APOE-TREM2 ligand-receptor pairs, associated with AD progression. In both human and mouse models, TREM2 deficiency disrupted GPNMB expansion and reduced phagocytic function, suggesting that GPNMB's role in neuroprotection was TREM2-dependent. Our findings clarify myeloid subtypes implicated in aging and AD, advancing the mechanistic understanding of their role in AD and aiding therapeutic discovery.

ICU patient-on-a-chip emulating orchestration of mast cells and cerebral organoids in neuroinflammation

Propofol and midazolam are the current standard of care for prolonged sedation in Intensive Care Units (ICUs). However, the effects and mechanism of these sedatives in brain tissue are unclear. Herein, the development of an ICU patient-on-a-chip platform to elucidate those effects is reported. The humanized neural tissue compartment combines mast cells differentiated from human induced pluripotent stem cells (hiPSCs) with cerebral organoids in a three-dimensional (3D) matrix, which is covered with a membrane populated with human cerebral microvascular endothelial cells (hCMEC/D3) that separates the tissue chamber from the vascular lumen, where sedatives were infused for four days to evaluate neurotoxicity and cell-mediated immune responses. Subsequent to propofol administration, gene expressions of CD40 and TNF-α in mast cells, AIF1 in microglia and GFAP/S100B/OLIG2/MBP in macroglia were elevated, as well as NOS2, CD80, CD40, CD68, IL6 and TNF-α mediated proinflammation is noted in cerebral organoids, which resulted in higher expressions of GJB1, GABA-A and NMDAR1 in the tissue construct of the platform. Besides, midazolam administration stimulated expression of CD40 and CD203c+ reactivated mast cell proliferation and compromised BBB permeability and decreased TEER values with higher barrier disruption, whereas increased populations of CD11b+ microglia, higher expressions of GFAP/DLG4/GJB1 and GABA-A-/NMDAR1- identities, as well as glutamate related neurotoxicity and IL1B, IFNG, IFNA1, IL6 genes mediated proinflammation, resulting in increased apoptotic zones are observed in cerebral organoids. These results suggest that different sedatives cause variations in cell type activation that modulate different pathways related to neuroinflammation and neurotoxicity in the ICU patient-on-chip platform.

Combining Acmella oleracea and Boswellia serrata extracts: a novel pharmacological approach in inflammatory vestibulodynia

Vulvodynia is a chronic pain condition that affects the vulvar area, often resulting in significant discomfort and a reduced quality of life. Current treatments for vulvodynia are limited, and there is a need for more effective therapeutic options. Acmella oleracea, known for its spilanthol content, and Boswellia serrata, rich in boswellic acids, have been explored for their potential analgesic properties in pain management. In this study, vulvodynia-like symptoms were induced in female mice using Complete Freund's adjuvant (CFA). After the induction of symptoms, the mice were treated with a combination of Acmella oleracea and Boswellia serrata extracts (AO + BS). Behavioral pain assessments were conducted to monitor the effects of the treatment. Additionally, biochemical and functional evaluations were performed to measure spinal microgliosis and neuronal overexcitation. The combination of Acmella oleracea and Boswellia serrata (AO + BS) resulted in a significant reduction of vulvar hypersensitivity in mice. Besides alleviating pain, AO + BS therapy also reduced spinal microgliosis and neuronal overexcitation in mice with vulvodynia. The findings suggest that the AO + BS combination has the potential to alleviate vulvodynia associated pain through mechanisms involving the reduction of spinal microgliosis and neuronal overexcitation. These results point to the therapeutic promise of these plant extracts for chronic pain conditions like vulvodynia. The combination of Acmella oleracea and Boswellia serrata shows potential as a treatment for vulvodynia. However, further studies are needed to explore the underlying mechanisms and to optimize the dosage for clinical use.

MorphoGlia, an interactive method to identify and map microglia morphologies, demonstrates differences in hippocampal subregions of an Alzheimer's disease mouse model

Microglia are dynamic central nervous system cells crucial for maintaining homeostasis and responding to neuroinflammation, as evidenced by their varied morphologies. Existing morphology analysis often fails to detect subtle variations within the full spectrum of microglial morphologies due to their reliance on predefined categories. Here, we present MorphoGlia, an interactive, user-friendly pipeline that objectively characterizes microglial morphologies. MorphoGlia employs a machine learning ensemble to select relevant morphological features of microglia cells, perform dimensionality reduction, cluster these features, and subsequently map the clustered cells back onto the tissue, providing a spatial context for the identified microglial morphologies. We applied this pipeline to compare the responses between saline solution (SS) and scopolamine (SCOP) groups in a SCOP-induced mouse model of Alzheimer's disease, with a specific focus on the hippocampal subregions CA1 and Hilus. Next, we assessed microglial morphologies across four groups: SS-CA1, SCOP-CA1, SS-Hilus, and SCOP-Hilus. The results demonstrated that MorphoGlia effectively differentiated between SS and SCOP-treated groups, identifying distinct clusters of microglial morphologies commonly associated with pro-inflammatory states in the SCOP groups. Additionally, MorphoGlia enabled spatial mapping of these clusters, identifying the most affected hippocampal layers. This study highlights MorphoGlia's capability to provide unbiased analysis and clustering of microglial morphological states, making it a valuable tool for exploring microglial heterogeneity and its implications for central nervous system pathologies.

Microglial morphology aligns with vigilance stage-specific neuronal oscillations in a brain region-dependent manner

Microglia, the resident immune cells in the brain, dynamically adapt their morphology based on their functional state. This study explored the relationship between microglial morphology and sleep-wake cycles in mice. Using Iba1 immunostaining to identify microglia, we quantified morphological changes in microglia at different timepoints in multiple brain regions (cortex, hippocampus, basal forebrain, hindbrain, and cerebellum) in B6 male mice using semi-automated 3D structural analysis. Simultaneously, in a separate group, we monitored wake and sleep stage-specific brain activity using EEG/EMG recordings. During natural sleep-wake cycles, we observed increased microglial complexity (enlarged volume, territorial coverage, and ramification) during wakefulness, characterized by high-frequency theta (8-12 Hz) and gamma activity (30-80 Hz). Conversely, during NREM sleep, which is dominated by delta activity (0.5-4 Hz), microglia displayed reduced complexity. Notably, this pattern was absent in brain regions lacking direct functional connections to areas generating vigilance stage-dependent thalamocortical oscillations. We then extended wakefulness to decouple circadian influence from sleep-wake-specific neuronal activity. This procedure attenuated the decrease in microglial complexity observed during natural sleep, suggesting a crucial role for neuronal activity. Subsequent recovery sleep restored microglial features, independent of the time of day (zeitgeber time). These findings reveal a dynamic interplay between vigilance stage-specific thalamocortical activity and microglial morphology across various brain regions. This suggests a potential role for microglia in sleep regulation and warrants further investigation to understand the underlying mechanisms.

The effect of a dominant kinase-dead Csf1r mutation associated with adult-onset leukoencephalopathy on brain development and neuropathology

Amino acid substitutions in the kinase domain of the human CSF1R protein are associated with autosomal dominant adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP). To model the human disease, we created a disease-associated mutation (Glu631Lys; E631K) in the mouse Csf1r locus. Previous analysis demonstrated that heterozygous mutation (Csf1rE631K/+) had a dominant inhibitory effect on CSF1R signaling in vitro and in vivo but did not recapitulate human disease pathology. We speculated that leukoencephalopathy in humans requires an environmental trigger and/or epistatic interaction with common neurodegenerative disease-associated alleles. Here we examine the Csf1rE631K/+ mutation impact on microglial phenotype, postnatal brain development, age-related changes in gene expression and on prion disease and experimental autoimmune encephalitis (EAE), two pathologies in which microgliosis is a prominent feature. The Csf1rE631K/+ mutation reduced microglial abundance and the expression of microglial-associated transcripts relative to wild-type controls at 12 and 43 weeks of age. There was no selective effect on homeostatic markers e.g. P2ry12, or age-related changes in gene expression in striatum and hippocampus. An epistatic interaction was demonstrated between Csf1rE631K/+ and Cx3cr1EGFP/+ genotypes leading to dysregulated microglial and neuronal gene expression in hippocampus and striatum. Heterozygous Csf1rE631K mutation reduced the microgliosis associated with both diseases. There was no significant impact on disease severity or progression in prion disease. In EAE, inflammation-associated transcripts in the hippocampus and striatum were suppressed in parallel with microglia-specific transcripts. The results support a dominant inhibitory model of CSF1R-related leukoencephalopathy and likely contributions of an environmental trigger and/or genetic background to neuropathology.

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.

Applying single-cell and single-nucleus genomics to studies of cellular heterogeneity and cell fate transitions in the nervous system

Single-cell and single-nucleus genomic approaches can provide unbiased and multimodal insights. Here, we discuss what constitutes a molecular cell atlas and how to leverage single-cell omics data to generate hypotheses and gain insights into cell transitions in development and disease of the nervous system. We share points of reflection on what to consider during study design and implementation as well as limitations and pitfalls.