Classification of Microglial Morphological Phenotypes Using Machine Learning

Microglia in retinal diseases: From pathogenesis towards therapeutic strategies

Microglia, a widely dispersed cohort of immune cells in the retina, are intricately involved in a diverse range of pivotal biological processes, including inflammation, vascular development, complement activation, antigen presentation, and phagocytosis. Within the retinal milieu, microglia are crucial for the clearance of dead cells and cellular debris, release of anti-inflammatory agents, and orchestration of vascular network remodeling to maintain homeostasis. In addition, microglia are key mediators of neuroinflammation. Triggered by oxidative stress, elevated intraocular pressure, genetic anomalies, and immune dysregulation, microglia release numerous inflammatory cytokines, contributing to the pathogenesis of various retinal disorders. Recent studies on the ontogeny and broad functions of microglia in the retina have elucidated their characteristics during retinal development, homeostasis, and disease. Furthermore, therapeutic strategies that target microglia and their effector cytokines have been developed and shown positive results for some retinal diseases. Therefore, we systematically review the microglial ontogeny in the retina, elucidate their dual roles in retinal homeostasis and disease pathogenesis, and demonstrate microglia-based targeted therapeutic strategies for retinal diseases.

ROS exhaustion reverses the effects of hyperbaric oxygen on hemorrhagic transformation through reactivating microglia in post-stroke hyperglycemic mice

Acute ischemic stroke (AIS) is a major global health concern due to its high mortality and disability rates. Hemorrhagic transformation, a common complication of AIS, leads to poor prognosis yet lacks effective treatments. Preclinical studies indicate that hyperbaric oxygen (HBO) treatment within 12 h of AIS onset alleviates ischemia/reperfusion injuries, including hemorrhagic transformation. However, clinical trials have yielded conflicting results, suggesting some underlying mechanisms remain unclear. In this study, we confirmed that HBO treatments beginning within 1 h post reperfusion significantly alleviated the haemorrhage and neurological deficits in hyperglycemic transient middle cerebral arterial occlusion (tMCAO) mice, partly due to the inhibition of the NLRP3 inflammasome-mediated pro-inflammatory response in microglia. Notably, reactive oxygen species (ROS) mediate the anti-inflammatory and protective effect of early HBO treatment, as edaravone and N-Acetyl-L-Cysteine (NAC), two commonly used antioxidants, reversed the suppressive effect of HBO treatment on NLRP3 inflammasome-mediated inflammation in microglia. Furthermore, NAC countered the protective effect of early HBO treatment in tMCAO mice with hyperglycemia. These findings support that early HBO treatment is a promising intervention for AIS, however, caution is warranted when combining antioxidants with HBO treatment. Further assessments are needed to clarify the role of antioxidants in HBO therapy for AIS.

Maternal Minocycline as Fetal Therapy in a Rat Model of Myelomeningocele

INTRODUCTION

This study aimed to investigate whether the maternal administration of minocycline, a tetracycline antibiotic known to have anti-inflammatory and neuroprotective properties in models of neural injury, reduces inflammation and neural cell death in a fetal rat model of myelomeningocele (MMC).

METHODS

E10 pregnant rats were gavaged with olive oil or olive oil + retinoic acid to induce fetal MMC. At E12, the dams were exposed to regular drinking water or water containing minocycline (range, 40-140 mg/kg/day). At E21, fetal lumbosacral spinal cords were isolated for immunohistochemistry and quantitative gene expression studies focused on microglia activity, inflammation, and apoptosis (P < 0.05).

RESULTS

There was a trend toward decreased activated Iba1+ microglial cells within the dorsal spinal cord of MMC pups following minocycline exposure when compared to water (H2O) alone (P = 0.052). Prenatal minocycline exposure was correlated with significantly reduced expression of the proinflammatory cytokine, IL-6 (minocycline: 1.75 versus H2O: 3.52, P = 0.04) and apoptosis gene, Bax (minocycline: 0.71 versus H2O: 1.04, P < 0.001) among MMC pups.

CONCLUSIONS

This study found evidence that the maternal administration of minocycline reduces selected markers of inflammation and apoptosis within the exposed dorsal spinal cords of fetal MMC rats. Further study of minocycline as a novel prenatal treatment strategy to mitigate spinal cord damage in MMC is warranted.

Switch to phagocytic microglia by CSFR1 inhibition drives amyloid-beta clearance from glutamatergic terminals rescuing LTP in acute hippocampal slices

Microglia, traditionally regarded as innate immune cells in the brain, drive neuroinflammation and synaptic dysfunctions in the early phases of Alzheimer disease (AD), acting upstream to Aβ accumulation. Colony stimulating factor 1-receptor (CSF-1R) is predominantly expressed on microglia and its levels are significantly increased in neurodegenerative diseases, possibly contributing to the chronic inflammatory microglial response. On the other hand, CSF-1R inhibitors confer neuroprotection in preclinical models of neurodegenerative diseases. Here, we determined the effects of the CSF-1R inhibitor PLX3397 on the Aβ-mediated synaptic alterations in ex vivo hippocampal slices. Electrophysiological findings show that PLX3397 rescues LTP impairment and neurotransmission changes induced by Aβ. In addition, using confocal imaging experiments, we demonstrate that PLX3397 stimulates a microglial transition toward a phagocytic phenotype, which in turn promotes the clearance of Aβ from glutamatergic terminals. We believe that the selective pruning of Aβ-loaded synaptic terminals might contribute to the restoration of LTP and excitatory transmission alterations observed upon acute PLX3397 treatment. This result is in accordance with the mechanism proposed for CSF1R inhibitors, that is to eliminate responsive microglia and replace it with newly generated, homeostatic microglia, capable of promoting brain repair. Overall, our findings identify a connection between the rapid microglia adjustments and the early synaptic alterations observed in AD, possibly highlighting a novel disease-modifying target.

Repeated seizure-induced brainstem neuroinflammation contributes to post-ictal ventilatory control dysfunction

Patients with epilepsy face heightened risk of post-ictal cardiorespiratory suppression and sudden unexpected death in epilepsy (SUDEP). Studies have shown that neuroinflammation, mediated by the activation of microglia and astrocytes, may be a cause or consequence of seizure disorders. Kcnj16 (Kir5.1) knockout rats (SS kcnj16-/- ) are susceptible to repeated audiogenic seizures and recapitulate features of human SUDEP, including post-ictal ventilatory suppression, which worsens with repeated seizures and seizure-induced mortality. In this study, we tested the hypothesis that repeated seizures cause neuroinflammation within key brainstem regions that contribute to the control of breathing. Audiogenic seizures were elicited once/day for up to 10 days in groups of adult male SS kcnj16-/- rats, from which frozen brainstem biopsies of the pre-Bötzinger complex/nucleus ambiguus (preBötC/NA), Bötzinger complex (BötC), and raphe magnus (RMg) regions were subjected to a cytokine array. Several cytokines/chemokines, including IL-1α and IL-1ß, were increased selectively in preBötC/NA after 3 or 5 days of seizures with fewer changes in other regions tested. In additional groups of male SS kcnj16-/- rats that underwent repeated seizures, we quantified microglial (IBA-1+) cell counts and morphology, specifically within the preBötC/NA region, and showed increased microglial cell counts, area, and volume consistent with microglial activation. To further test the role of inflammation in physiological responses to seizures and seizure-related mortality, additional groups of SS kcnj16-/- rats were treated with anakinra (IL-1R antagonist), ketoprofen (non-selective COX inhibitor), or saline for 3 days before and up to 10 days of seizures (1/day), and breathing was measured before, during, and after each seizure. Remarkably, IL-1R antagonism mitigated changes in post-ictal ventilatory suppression on days 7-10 but failed to prevent seizure-related mortality, whereas ketoprofen treatment exacerbated post-ictal ventilatory suppression compared to other treatment groups but prevented seizure-related mortality. These data demonstrate neuroinflammation and microglial activation within the key brainstem region of respiratory control following repeated seizures, which may functionally but differentially contribute to the pathophysiological consequences of repeated seizures.

Microglial type I interferon signaling mediates chronic stress-induced synapse loss and social behavior deficits

Inflammation and synapse loss have been associated with deficits in social behavior and are involved in pathophysiology of many neuropsychiatric disorders. Synapse loss, characterized by reduction in dendritic spines can significantly disrupt synaptic connectivity and neural circuitry underlying social behavior. Chronic stress is known to induce loss of spines and dendrites in the prefrontal cortex (PFC), a brain region implicated in social behavior. However, the underlying mechanisms are not well understood. In the present study, we investigated the role of type I Interferon (IFN-I) signaling in chronic unpredictable stress (CUS)-induced synapse loss and behavior deficits in mice. We found increased expression of type I IFN receptor (IFNAR) in microglia following CUS. Conditional knockout of microglial IFNAR in adult mice rescued CUS-induced social behavior deficits and synapse loss. Bulk RNA sequencing data show that microglial IFNAR deletion attenuated CUS-mediated changes in the expression of genes such as Keratin 20 (Krt20), Claudin-5 (Cldn5) and Nuclear Receptor Subfamily 4 Group A Member 1 (Nr4a1) in the PFC. Cldn5 and Nr4a1 are known for their roles in synaptic plasticity. Krt20 is an intermediate filament protein responsible for the structural integrity of epithelial cells. The reduction in Krt20 following CUS presents a novel insight into the potential contribution of cytokeratin in stress-induced alterations in neuroplasticity. Overall, these results suggest that microglial IFNAR plays a critical role in regulating synaptic plasticity and social behavior deficits associated with chronic stress conditions.

Opposing effects of the purinergic P2X7 receptor on seizures in neurons and microglia in male mice

BACKGROUND

The purinergic ATP-gated P2X7 receptor (P2X7R) is increasingly recognized to contribute to pathological neuroinflammation and brain hyperexcitability. P2X7R expression has been shown to be increased in the brain, including both microglia and neurons, in experimental models of epilepsy and patients. To date, the cell type-specific downstream effects of P2X7Rs during seizures remain, however, incompletely understood.

METHODS

Effects of P2X7R signaling on seizures and epilepsy were analyzed in induced seizure models using male mice including the kainic acid model of status epilepticus and pentylenetetrazole model and in male and female mice in a genetic model of Dravet syndrome. RNA sequencing was used to analyze P2X7R downstream signaling during seizures. To investigate the cell type-specific role of the P2X7R during seizures and epilepsy, we generated mice lacking exon 2 of the P2rx7 gene in either microglia (P2rx7:Cx3cr1-Cre) or neurons (P2rx7:Thy-1-Cre). To investigate the protective potential of overexpressing P2X7R in GABAergic interneurons, P2X7Rs were overexpressed using adeno-associated virus transduction under the mDlx promoter.

RESULTS

RNA sequencing of hippocampal tissue from wild-type and P2X7R knock-out mice identified both glial and neuronal genes, in particular genes involved in GABAergic signaling, under the control of the P2X7R following seizures. Mice with deleted P2rx7 in microglia displayed less severe acute seizures and developed a milder form of epilepsy, and microglia displayed an anti-inflammatory molecular profile. In contrast, mice lacking P2rx7 in neurons showed a more severe seizure phenotype when compared to epileptic wild-type mice. Analysis of single-cell expression data revealed that human P2RX7 expression is elevated in the hippocampus of patients with temporal lobe epilepsy in excitatory and inhibitory neurons. Functional studies determined that GABAergic interneurons display increased responses to P2X7R activation in experimental epilepsy. Finally, we show that viral transduction of P2X7R in GABAergic interneurons protects against evoked and spontaneous seizures in experimental temporal lobe epilepsy and in mice lacking Scn1a, a model of Dravet syndrome.

CONCLUSIONS

Our results suggest a dual and opposing action of P2X7R in epilepsy and suggest P2X7R overexpression in GABAergic interneurons as a novel therapeutic strategy for acquired and, possibly, genetic forms of epilepsy.

Targeted therapy and deep learning insights into microglia modulation for spinal cord injury

Spinal cord injury (SCI) is a devastating condition that can cause significant motor and sensory impairment. Microglia, the central nervous system's immune sentinels, are known to be promising therapeutic targets in both SCI and neurodegenerative diseases. The most effective way to deliver medications and control microglial inflammation is through nanovectors; however, because of the variability in microglial morphology and the lack of standardized techniques, it is still difficult to precisely measure their activation in preclinical models. This problem is especially important in SCI, where the intricacy of the glia response following traumatic events necessitates the use of a sophisticated method to automatically discern between various microglial cell activation states that vary over time and space as the secondary injury progresses. We address this issue by proposing a deep learning-based technique for quantifying microglial activation following drug-loaded nanovector treatment in a preclinical SCI model. Our method uses a convolutional neural network to segment and classify microglia based on morphological characteristics. Our approach's accuracy and efficiency are demonstrated through evaluation on a collection of histology pictures from injured and intact spinal cords. This robust computational technique has potential for analyzing microglial activation across various neuropathologies and demonstrating the usefulness of nanovectors in modifying microglia in SCI and other neurological disorders. It has the ability to speed development in this crucial sector by providing a standardized and objective way to compare therapeutic options.

Chronic activation of a negative engram induces behavioral and cellular abnormalities

Negative memories engage a brain and body-wide stress response in humans that can alter cognition and behavior. Prolonged stress responses induce maladaptive cellular, circuit, and systems-level changes that can lead to pathological brain states and corresponding disorders in which mood and memory are affected. However, it is unclear if repeated activation of cells processing negative memories induces similar phenotypes in mice. In this study, we used an activity-dependent tagging method to access neuronal ensembles and assess their molecular characteristics. Sequencing memory engrams in mice revealed that positive (male-to-female exposure) and negative (foot shock) cells upregulated genes linked to anti- and pro-inflammatory responses, respectively. To investigate the impact of persistent activation of negative engrams, we chemogenetically activated them in the ventral hippocampus over 3 months and conducted anxiety and memory-related tests. Negative engram activation increased anxiety behaviors in both 6- and 14-month-old mice, reduced spatial working memory in older mice, impaired fear extinction in younger mice, and heightened fear generalization in both age groups. Immunohistochemistry revealed changes in microglial and astrocytic structure and number in the hippocampus. In summary, repeated activation of negative memories induces lasting cellular and behavioral abnormalities in mice, offering insights into the negative effects of chronic negative thinking-like behaviors on human health.

Development of a High-Throughput Pipeline to Characterize Microglia Morphological States at a Single-Cell Resolution

As rapid responders to their environments, microglia engage in functions that are mirrored by their cellular morphology. Microglia are classically thought to exhibit a ramified morphology under homeostatic conditions which switches to an ameboid form during inflammatory conditions. However, microglia display a wide spectrum of morphologies outside of this dichotomy, including rod-like, ramified, ameboid, and hypertrophic states, which have been observed across brain regions, neurodevelopmental timepoints, and various pathological contexts. We applied dimensionality reduction and clustering to consider contributions of multiple morphology measures together to define a spectrum of microglial morphological states in a mouse dataset that we used to demonstrate the utility of our toolset. Using ImageJ, we first developed a semiautomated approach to characterize 27 morphology features from hundreds to thousands of individual microglial cells in a brain region-specific manner. Within this pool of features, we defined distinct sets of highly correlated features that describe different aspects of morphology, including branch length, branching complexity, territory span, and circularity. When considered together, these sets of features drove different morphological clusters. Our tools captured morphological states similarly and robustly when applied to independent datasets and using different immunofluorescent markers for microglia. We have compiled our morphology analysis pipeline into an accessible, easy-to-use, and fully open-source ImageJ macro and R package that the neuroscience community can expand upon and directly apply to their own analyses. Outcomes from this work will supply the field with new tools to systematically evaluate the heterogeneity of microglia morphological states across various experimental models and research questions.

Maternal SARS-CoV-2 impacts fetal placental macrophage programs and placenta-derived microglial models of neurodevelopment

BACKGROUND

The SARS-CoV-2 virus activates maternal and placental immune responses. Such activation in the setting of other infections during pregnancy is known to impact fetal brain development. The effects of maternal immune activation on neurodevelopment are mediated at least in part by fetal brain microglia. However, microglia are inaccessible for direct analysis, and there are no validated non-invasive surrogate models to evaluate in utero microglial priming and function. We have previously demonstrated shared transcriptional programs between microglia and Hofbauer cells (HBCs, or fetal placental macrophages) in mouse models.

METHODS AND RESULTS

We assessed the impact of maternal SARS-CoV-2 on HBCs isolated from 24 term placentas (N = 10 SARS-CoV-2 positive cases, 14 negative controls). Using single-cell RNA-sequencing, we demonstrated that HBC subpopulations exhibit distinct cellular programs, with specific subpopulations differentially impacted by SARS-CoV-2. Assessment of differentially expressed genes implied impaired phagocytosis, a key function of both HBCs and microglia, in some subclusters. Leveraging previously validated models of microglial synaptic pruning, we showed that HBCs isolated from placentas of SARS-CoV-2 positive pregnancies can be transdifferentiated into microglia-like cells (HBC-iMGs), with impaired synaptic pruning behavior compared to HBC models from negative controls.

CONCLUSION

These findings suggest that HBCs isolated at birth can be used to create personalized cellular models of offspring microglial programming.

Characterizing Cellular Physiological States with Three-Dimensional Shape Descriptors for Cell Membranes

The shape of a cell as defined by its membrane can be closely associated with its physiological state. For example, the irregular shapes of cancerous cells and elongated shapes of neuron cells often reflect specific functions, such as cell motility and cell communication. However, it remains unclear whether and which cell shape descriptors can characterize different cellular physiological states. In this study, 12 geometric shape descriptors for a three-dimensional (3D) object were collected from the previous literature and tested with a public dataset of ~400,000 independent 3D cell regions segmented based on fluorescent labeling of the cell membranes in Caenorhabditis elegans embryos. It is revealed that those shape descriptors can faithfully characterize cellular physiological states, including (1) cell division (cytokinesis), along with an abrupt increase in the elongation ratio; (2) a negative correlation of cell migration speed with cell sphericity; (3) cell lineage specification with symmetrically patterned cell shape changes; and (4) cell fate specification with differential gene expression and differential cell shapes. The descriptors established may be used to identify and predict the diverse physiological states in numerous cells, which could be used for not only studying developmental morphogenesis but also diagnosing human disease (e.g., the rapid detection of abnormal cells).

Role of microglia in stroke

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

Investigation of microglial diversity in a LRRK2 G2019S mouse model of Parkinson's disease

Microglia contribute to the outcomes of various pathological conditions including Parkinson's disease (PD). Microglia are heterogenous, with a variety of states recently identified in aging and neurodegenerative disease models. Here, we delved into the diversity of microglia in a preclinical PD model featuring the G2019S mutation in LRRK2, a known pathological mutation associated with PD. Specifically, we investigated the 'dark microglia' (DM) and the 'disease-associated microglia' (DAM) which present a selective enrichment of CLEC7A expression. In the dorsal striatum - a region affected by PD pathology - extensive ultrastructural features of cellular stress as well as reduced direct cellular contacts, were observed for microglia from old LRRK2 G2019S mice versus controls. In addition, DM were more prevalent while CLEC7A-positive microglia had extensive phagocytic ultrastructural characteristics in the LRRK2 G2019S mice. Furthermore, our findings revealed a higher proportion of DM in LRRK2 G2019S mice, and an increased number of CLEC7A-positive cells with age, exacerbated by the pathological mutation. These CLEC7A-positive cells exhibited a selective enrichment of ameboid morphology and tended to cluster in the affected animals. In summary, we provide novel insights into the occurrence and features of recently defined microglial states, CLEC7A-positive cells and DM, in the context of LRRK2 G2019S PD pathology.

Neuroinflammation: A Critical Factor in Neurodegenerative Disorders

This review offers a comprehensive review of the signals and the paramount role neuroinflammation plays in neurodegenerative diseases such as Alzheimer's, Parkinson's, Huntington's, and amyotrophic lateral sclerosis. The study explores the sophisticated interactions between microglial, astrocytic, and dendritic cells and how neuroinflammation affects long-term neuronal damage and dysfunction. There are specific pathways related to the mentioned inflammatory processes, including Janus kinases/signal transducer and activator of transcriptions, nuclear factor-κB, and mitogen-activated protein kinases pathways. Neuroinflammation is argued to be a double-edged sword, being not only a protective agent that prevents further neuron damage but also the causative factor in more cell injury development. This concept of contrasting inflammation with neuroprotection advocates for the use of therapeutic techniques that seek to modulate neuroinflammatory responses as part of the neurodegeneration treatment. The recent research findings are integrated with the established knowledge to help present a comprehensive image of neuroinflammation's impact on neurodegenerative diseases and its implications for future therapy.

Metabolic disorders exacerbate the formation of glial scar after stroke

Metabolic disorders are risk factors for stroke exacerbating subsequent complications. Rapidly after brain injury, a glial scar forms, preventing excessive inflammation and limiting axonal regeneration. Despite the growing interest in wound healing following brain injury, the formation of a glial scar in the context of metabolic disorders is poorly documented. In this study, we used db/db mice to investigate the impact of metabolic perturbations on brain repair mechanisms, with a focus on glial scarring. First, we confirmed the development of obesity, poor glucose regulation, hyperglycaemia and liver steatosis in these mice. Then, we observed that 3 days after a 30-min middle cerebral artery occlusion (MCAO), db/db mice had larger infarct area compared with their control counterparts. We next investigated reactive gliosis and glial scar formation in db/+ and db/db mice. We demonstrated that astrogliosis and microgliosis were exacerbated 3 days after stroke in db/db mice. Furthermore, we also showed that the synthesis of extracellular matrix (ECM) proteins (i.e., chondroitin sulphate proteoglycan, collagen IV and tenascin C) was increased in db/db mice. Consequently, we demonstrated for the first time that metabolic disorders impair reactive gliosis post-stroke and increase ECM deposition. Given that the damage size is known to influence glial scar, this study now raises the question of the direct impact of hyperglycaemia/obesity on reactive gliosis and glia scar. It paves the way to promote the development of new therapies targeting glial scar formation to improve functional recovery after stroke in the context of metabolic disorders.

Role of Glial Cells in Neuronal Function, Mood Disorders, and Drug Addiction

Mood disorders and substance use disorder (SUD) are of immense medical and social concern. Although significant progress on neuronal involvement in mood and reward circuitries has been achieved, it is only relatively recently that the role of glia in these disorders has attracted attention. Detailed understanding of the glial functions in these devastating diseases could offer novel interventions. Here, following a brief review of circuitries involved in mood regulation and reward perception, the specific contributions of neurotrophic factors, neuroinflammation, and gut microbiota to these diseases are highlighted. In this context, the role of specific glial cells (e.g., microglia, astroglia, oligodendrocytes, and synantocytes) on phenotypic manifestation of mood disorders or SUD are emphasized. In addition, use of this knowledge in the potential development of novel therapeutics is touched upon.

Quantifying microglial morphology: an insight into function

Microglia are specialized immune cells unique to the central nervous system (CNS). Microglia have a highly plastic morphology that changes rapidly in response to injury or infection. Qualitative and quantitative measurements of ever-changing microglial morphology are considered a cornerstone of many microglia-centric research studies. The distinctive morphological variations seen in microglia are a useful marker of inflammation and severity of tissue damage. Although a wide array of damage-associated microglial morphologies has been documented, the exact functions of these distinct morphologies are not fully understood. In this review, we discuss how microglia morphology is not synonymous with microglia function, however, morphological outcomes can be used to make inferences about microglial function. For a comprehensive examination of the reactive status of a microglial cell, both histological and genetic approaches should be combined. However, the importance of quality immunohistochemistry-based analyses should not be overlooked as they can succinctly answer many research questions.

Neurotoxic effects of polystyrene nanoplastics on memory and microglial activation: Insights from in vivo and in vitro studies

Nanoplastics, arising from the fragmentation of plastics into environmental pollutants and specialized commercial applications, such as cosmetics, have elicited concerns due to their potential toxicity. Evidence suggests that the oral ingestion of nanoplastics smaller than 100 nm may penetrate the brain and induce neurotoxicity. However, comprehensive research in this area has been hampered by technical challenges associated with the detection and synthesis of nanoplastics. This study aimed to bridge this research gap by successfully synthesizing fluorescent polystyrene nanoplastics (PSNPs, 30-50 nm) through the incorporation of IR-813 and validating them using various analytical techniques. We administered PSNPs orally (10 and 20 mg/kg/day) to mice and observed that they reached brain tissues and induced cognitive dysfunction, as measured by spatial and fear memory tests, while locomotor and social behaviors remained unaffected. In vitro studies (200 μg/mL) demonstrated a predominant uptake of PSNPs by microglia over astrocytes or neurons, leading to microglial activation, as evidenced by immunostaining of cellular markers and morphological analysis. Transcriptomic analysis indicated that PSNPs altered gene expression in microglia, highlighting neuroinflammatory responses that may contribute to cognitive deficits. To further explore the neurotoxic effects of PSNPs mediated by microglial activation, we measured endogenous neuronal activity using a multi-electrode array in cultured hippocampal neurons. The application of conditioned media from microglia exposed to PSNPs suppressed neuronal activity, which was reversed by inhibitors of microglial activation. Our findings offer detailed insights into the mechanisms by which nanoplastics damage the brain, particularly emphasizing the potential environmental risk factors that contribute to cognitive impairment in neurodegenerative diseases.

B355252 Suppresses LPS-Induced Neuroinflammation in the Mouse Brain

B355252 is a small molecular compound known for potentiating neural growth factor and protecting against neuronal cell death induced by glutamate in vitro and cerebral ischemia in vivo. However, its other biological functions remain unclear. This study aims to investigate whether B355252 suppresses neuroinflammatory responses and cell death in the brain. C57BL/6j mice were intraperitoneally injected with a single dosage of lipopolysaccharide (LPS, 1 mg/kg) to induce inflammation. B355252 (1 mg/kg) intervention was started two days prior to the LPS injection. The animal behavioral changes were assessed pre- and post-LPS injections. The animal brains were harvested at 4 and 24 h post-LPS injection, and histological, biochemical, and cytokine array outcomes were examined. Results showed that B355252 improved LPS-induced behavioral deterioration, mitigated brain tissue damage, and suppressed the activation of microglial and astrocytes. Furthermore, B355252 reduced the protein levels of key pyroptotic markers TLR4, NLRP3, and caspase-1 and inhibited the LPS-induced increases in IL-1β, IL-18, and cytokines. In conclusion, B355252 demonstrates a potent anti-neuroinflammatory effect in vivo, suggesting that its potential therapeutic value warrants further investigation.

Vagus nerve stimulation enhances remyelination and decreases innate neuroinflammation in lysolecithin-induced demyelination

BACKGROUND

Current treatments for Multiple Sclerosis (MS) poorly address chronic innate neuroinflammation nor do they offer effective remyelination. The vagus nerve has a strong regulatory role in inflammation and Vagus Nerve Stimulation (VNS) has potential to affect both neuroinflammation and remyelination in MS.

OBJECTIVE

This study investigated the effects of VNS on demyelination and innate neuroinflammation in a validated MS rodent model.

METHODS

Lysolecithin (LPC) was injected in the corpus callosum (CC) of 46 Lewis rats, inducing a demyelinated lesion. 33/46 rats received continuously-cycled VNS (cVNS) or one-minute per day VNS (1minVNS) or sham VNS from 2 days before LPC-injection until perfusion at 3 days post-injection (dpi) (corresponding with a demyelinated lesion with peak inflammation). 13/46 rats received cVNS or sham from 2 days before LPC-injection until perfusion at 11 dpi (corresponding with a partial remyelinated lesion). Immunohistochemistry and proteomics analyses were performed to investigate the extend of demyelination and inflammation.

RESULTS

Immunohistochemistry showed that cVNS significantly reduced microglial and astrocytic activation in the lesion and lesion border, and significantly reduced the Olig2+ cell count at 3 dpi. Furthermore, cVNS significantly improved remyelination with 57.4 % versus sham at 11 dpi. Proteomic gene set enrichment analyses showed increased activation of (glutamatergic) synapse pathways in cVNS versus sham, most pronounced at 3 dpi.

CONCLUSION

cVNS improved remyelination of an LPC-induced lesion. Possible mechanisms might include modulation of microglia and astrocyte activity, increased (glutamatergic) synapses and enhanced oligodendrocyte clearance after initial injury.

The medulla oblongata shows a sex-specific inflammatory response to systemic neonatal lipopolysaccharide

Early life inflammation has been linked to long-term modulation of behavioural outcomes due to the central nervous system, but it is now becoming apparent it is also linked to dysfunction of visceral physiology. The medulla oblongata contains a number of nuclei critical for homeostasis, therefore we utilised the well-established model of neonatal lipopolysaccharide (LPS) exposure to examine the immediate and long-term impacts of systemic inflammation on the medulla oblongata. Wistar rats were injected with LPS or saline on postnatal days 3 and 5, with tissues collected on postnatal days 7 or 90 in order to assess expression of inflammatory mediators and microglial morphology in autonomic regions of the medulla oblongata. We observed a distinct sex-specific response of all measured inflammatory mediators at both ages, as well as significant neonatal sex differences in inflammatory mediators within saline groups. At both ages, microglial morphology had significant changes in branch length and soma size in a sex-specific manner in response to LPS exposure. This data not only highlights the strong sex-specific response of neonates to LPS administration, but also the significant life-long impact on the medulla oblongata and the potential altered control of visceral organs.

Pharmacological inhibition of mTORC1 reduces neural death and damage volume after MCAO by modulating microglial reactivity

Ischemic stroke is a sudden and acute disease characterized by neuronal death, increment of reactive gliosis (reactive microglia and astrocytes), and a severe inflammatory process. Neuroinflammation is an early event after cerebral ischemia, with microglia playing a leading role. Reactive microglia involve functional and morphological changes that drive a wide variety of phenotypes. In this context, deciphering the molecular mechanisms underlying such reactive microglial is essential to devise strategies to protect neurons and maintain certain brain functions affected by early neuroinflammation after ischemia. Here, we studied the role of mammalian target of rapamycin (mTOR) activity in the microglial response using a murine model of cerebral ischemia in the acute phase. We also determined the therapeutic relevance of the pharmacological administration of rapamycin, a mTOR inhibitor, before and after ischemic injury. Our data show that rapamycin, administered before or after brain ischemia induction, reduced the volume of brain damage and neuronal loss by attenuating the microglial response. Therefore, our findings indicate that the pharmacological inhibition of mTORC1 in the acute phase of ischemia may provide an alternative strategy to reduce neuronal damage through attenuation of the associated neuroinflammation.

The effects of urolithin A on poly I:C-induced microglial activation

Neuroinflammation can be triggered by various stimuli, including viral infections. Viruses can directly invade the brain and infect neuronal cells or indirectly trigger a "cytokine storm" in the periphery that eventually leads to microglial activation in the brain. While this initial activation of microglial cells is important for viral clearance, chronic activation leads to excessive inflammation and oxidative stress, which can be neurotoxic. Remarkebly, recent studies have shown that certain viruses such as influenza A virus, coronavirus, herpes virus and Epstein-Barr virus may be involved in the development of neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, and multiple sclerosis. Therefore, it is important to find therapeutic strategies against chronic neuroinflammation triggered by viral infections. Here, we investigated the effects of urolithin A (UA) on microglial activation in vitro induced by a viral mimetic, poly I:C, in a triple co-culture system of neurons, astrocytes and microglial cells. Immunocytochemistry was used to perform a comprehensive single-cell analysis of the morphological changes of microglia as an indicator of their reactive state. Treatment with UA significantly prevented the poly I:C-induced reactive state of microglia, which was characterized by increased expression of the microglial activation markers CD68 and IBA-1. UA restored the poly I:C-induced morphology by restoring microglial ramification. In addition, UA was able to reduce the release of the pro-inflammatory mediators CCL2, TNF-α, and IL-1β and showed a trend toward attenuation of cellular ROS production in poly I:C-treated cultures. Overall, this study suggests that UA as a component of a healthy diet may help prevent virus-induced neuroinflammation and may have therapeutic potential for future studies to prevent or treat neurodegenerative diseases by targeting the associated neuroinflammatory processes.

Nicotinic Acetylcholine Receptors in Glial Cells as Molecular Target for Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by resting tremor, bradykinesia, rigidity, and postural instability that also includes non-motor symptoms such as mood dysregulation. Dopamine (DA) is the primary neurotransmitter involved in this disease, but cholinergic imbalance has also been implicated. Current intervention in PD is focused on replenishing central DA, which provides remarkable temporary symptomatic relief but does not address neuronal loss and the progression of the disease. It has been well established that neuronal nicotinic cholinergic receptors (nAChRs) can regulate DA release and that nicotine itself may have neuroprotective effects. Recent studies identified nAChRs in nonneuronal cell types, including glial cells, where they may regulate inflammatory responses. Given the crucial role of neuroinflammation in dopaminergic degeneration and the involvement of microglia and astrocytes in this response, glial nAChRs may provide a novel therapeutic target in the prevention and/or treatment of PD. In this review, following a brief discussion of PD, we focus on the role of glial cells and, specifically, their nAChRs in PD pathology and/or treatment.

Radiotherapy induces persistent innate immune reprogramming of microglia into a primed state

Over half of patients with brain tumors experience debilitating and often progressive cognitive decline after radiotherapy treatment. Microglia, the resident macrophages in the brain, have been implicated in this decline. In response to various insults, microglia can develop innate immune memory (IIM), which can either enhance (priming or training) or repress (tolerance) the response to subsequent inflammatory challenges. Here, we investigate whether radiation affects the IIM of microglia by irradiating the brains of rats and later exposing them to a secondary inflammatory stimulus. Comparative transcriptomic profiling and protein validation of microglia isolated from irradiated rats show a stronger immune response to a secondary inflammatory insult, demonstrating that radiation can lead to long-lasting molecular reprogramming of microglia. Transcriptomic analysis of postmortem normal-appearing non-tumor brain tissue of patients with glioblastoma indicates that radiation-induced microglial priming is likely conserved in humans. Targeting microglial priming or avoiding further inflammatory insults could decrease radiotherapy-induced neurotoxicity.

P2X4 signalling contributes to hyperactivity but not pain sensitization comorbidity in a mouse model of attention deficit/hyperactivity disorder

Introduction: Attention deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder characterized by hyperactivity, inattention, and impulsivity that often persist until adulthood. Frequent comorbid disorders accompany ADHD and two thirds of children diagnosed with ADHD also suffer from behavioural disorders and from alteration of sensory processing. We recently characterized the comorbidity between ADHD-like symptoms and pain sensitisation in a pharmacological mouse model of ADHD, and we demonstrated the implication of the anterior cingulate cortex and posterior insula. However, few studies have explored the causal mechanisms underlying the interactions between ADHD and pain. The implication of inflammatory mechanisms has been suggested but the signalling pathways involved have not been explored. Methods: We investigated the roles of purinergic signalling, at the crossroad of pain and neuroinflammatory pathways, by using a transgenic mouse line that carries a total deletion of the P2X4 receptor. Results: We demonstrated that P2X4 deletion prevents hyperactivity in the mouse model of ADHD. In contrast, the absence of P2X4 lowered thermal pain thresholds in sham conditions and did not affect pain sensitization in ADHD-like conditions. We further analysed microglia reactivity and the expression of inflammatory markers in wild type and P2X4KO mice. Our results revealed that P2X4 deletion limits microglia reactivity but at the same time exerts proinflammatory effects in the anterior cingulate cortex and posterior insula. Conclusion: This dual role of P2X4 could be responsible for the differential effects noted on ADHD-like symptoms and pain sensitization and calls for further studies to investigate the therapeutic benefit of targeting the P2X4 receptor in ADHD patients.

iPSC-derived PSEN2 (N141I) astrocytes and microglia exhibit a primed inflammatory phenotype

BACKGROUND

Widescale evidence points to the involvement of glia and immune pathways in the progression of Alzheimer's disease (AD). AD-associated iPSC-derived glial cells show a diverse range of AD-related phenotypic states encompassing cytokine/chemokine release, phagocytosis and morphological profiles, but to date studies are limited to cells derived from PSEN1, APOE and APP mutations or sporadic patients. The aim of the current study was to successfully differentiate iPSC-derived microglia and astrocytes from patients harbouring an AD-causative PSEN2 (N141I) mutation and characterise the inflammatory and morphological profile of these cells.

METHODS

iPSCs from three healthy control individuals and three familial AD patients harbouring a heterozygous PSEN2 (N141I) mutation were used to derive astrocytes and microglia-like cells and cell identity and morphology were characterised through immunofluorescent microscopy. Cellular characterisation involved the stimulation of these cells by LPS and Aβ42 and analysis of cytokine/chemokine release was conducted through ELISAs and multi-cytokine arrays. The phagocytic capacity of these cells was then indexed by the uptake of fluorescently-labelled fibrillar Aβ42.

RESULTS

AD-derived astrocytes and microglia-like cells exhibited an atrophied and less complex morphological appearance than healthy controls. AD-derived astrocytes showed increased basal expression of GFAP, S100β and increased secretion and phagocytosis of Aβ42 while AD-derived microglia-like cells showed decreased IL-8 secretion compared to healthy controls. Upon immunological challenge AD-derived astrocytes and microglia-like cells showed exaggerated secretion of the pro-inflammatory IL-6, CXCL1, ICAM-1 and IL-8 from astrocytes and IL-18 and MIF from microglia.

CONCLUSION

Our study showed, for the first time, the differentiation and characterisation of iPSC-derived astrocytes and microglia-like cells harbouring a PSEN2 (N141I) mutation. PSEN2 (N141I)-mutant astrocytes and microglia-like cells presented with a 'primed' phenotype characterised by reduced morphological complexity, exaggerated pro-inflammatory cytokine secretion and altered Aβ42 production and phagocytosis.

Contribution of circulating monocytes in maintaining homeostasis of resident macrophages in postnatal and young adult mouse cochlea

The percentage of macrophage subpopulations based on their origins in the adult cochlea remains unclear. This study aimed to elucidate the origins of cochlear macrophages during the onset phase and development of auditory function. We used three types of mice: wildtype ICR mice, colony-stimulating factor 1 receptor (Csf1r)-deficient mice, and Ms4a3Cre-Rosa tdTomato (Ms4a3tdT) transgenic mice. Macrophages were labeled with ionized calcium-binding adapter molecule 1 (Iba1), which is specific to more mature macrophages, and CD11b, which is specific to monocyte lineage. We investigated the spatial and temporal distribution patterns of resident macrophages in the cochlea during the postnatal and early adult stages. During the adult stages, the rate of monocytes recruited from the systemic circulation increased; moreover, Iba1+/CD11b- cochlear macrophages gradually decreased with age. Fate mapping of monocytes using Ms4a3tdT transgenic mice revealed an increased proportion of bone marrow-derived cochlear macrophages in the adult stage. Contrastingly, the proportion of yolk sac- and fetal liver-derived tissue-resident macrophages decreased steadily with age. This heterogeneity could be attributed to differences in environmental niches within the tissue or at the sub-tissue levels. Future studies should investigate the role of cochlear macrophages in homeostasis, inflammation, and other diseases, including infection, autoimmune, and metabolic diseases.

Cortical microglia dynamics are conserved during voluntary wheel running

We present the first demonstration of chronic in vivo imaging of microglia in mice undergoing voluntary wheel running. We find that healthy mice undergoing voluntary wheel running have similar microglia dynamics, morphologies, and responses to injury when compared to sedentary mice. This suggests that exercise over a period of 1 mo does not grossly alter cortical microglial phenotypes and that exercise may exert its beneficial effects on the brain through other mechanisms. Future work examining how microglia dynamics may be altered during exercise in disease or injury models could provide further insights into the therapeutic benefit of exercise.NEW & NOTEWORTHY We demonstrate the first use of chronic in vivo imaging of microglia over time during physical exercise. We found that microglia movement, morphology, and process motility were remarkably stable during voluntary wheel running (VWR). Additionally, microglia in running mice respond similarly to laser ablation injury compared to sedentary mice. These findings indicate that VWR does not induce changes in microglia dynamics in healthy adults. Exercise may elicit positive effects on the brain through other mechanisms.

Maternal SARS-CoV-2 impacts fetal placental macrophage programs and placenta-derived microglial models of neurodevelopment

The SARS-CoV-2 virus activates maternal and placental immune responses, which in the setting of other infections occurring during pregnancy are known to impact fetal brain development. The effects of maternal immune activation on neurodevelopment are mediated at least in part by fetal brain microglia. However, microglia are inaccessible for direct analysis, and there are no validated non-invasive surrogate models to evaluate in utero microglial priming and function. We have previously demonstrated shared transcriptional programs between microglia and Hofbauer cells (HBCs, or fetal placental macrophages) in mouse models. Here, we assessed the impact of maternal SARS-CoV-2 on HBCs isolated from term placentas using single-cell RNA-sequencing. We demonstrated that HBC subpopulations exhibit distinct cellular programs, with specific subpopulations differentially impacted by SARS-CoV-2. Assessment of differentially expressed genes implied impaired phagocytosis, a key function of both HBCs and microglia, in some subclusters. Leveraging previously validated models of microglial synaptic pruning, we showed that HBCs isolated from placentas of SARS-CoV-2 positive pregnancies can be transdifferentiated into microglia-like cells, with altered morphology and impaired synaptic pruning behavior compared to HBC models from negative controls. These findings suggest that HBCs isolated at birth can be used to create personalized cellular models of offspring microglial programming.

Challenges and opportunities to computationally deconvolve heterogeneous tissue with varying cell sizes using single-cell RNA-sequencing datasets

Deconvolution of cell mixtures in "bulk" transcriptomic samples from homogenate human tissue is important for understanding disease pathologies. However, several experimental and computational challenges impede transcriptomics-based deconvolution approaches using single-cell/nucleus RNA-seq reference atlases. Cells from the brain and blood have substantially different sizes, total mRNA, and transcriptional activities, and existing approaches may quantify total mRNA instead of cell type proportions. Further, standards are lacking for the use of cell reference atlases and integrative analyses of single-cell and spatial transcriptomics data. We discuss how to approach these key challenges with orthogonal "gold standard" datasets for evaluating deconvolution methods.

Ginsenoside Rg1 ameliorates depressive-like behavior by inhibiting NLRP3 inflammasome activation in mice exposed to chronic stress

Microglia-mediated inflammatory process is recognized as a target in the treatment of depression. Ginsenoside Rg1 (GRg1), the active ingredient of traditional ginseng, regulates microglial phenotypes to resist stress-induced inflammatory responses. Here we used a mouse model of stress-induced depression to investigate the involvement of microglial Nod-like receptor protein 3 (NLRP3) in the antidepressant effects of GRg1. Male C57BL/6J mice were exposed to chronic mild stress (CMS) for three weeks, followed by intraperitoneal injection of GRg1 (20 mg/kg) or the antidepressant imipramine (20 mg/kg) for another three weeks. Depressive-like behaviors were assessed by sucrose preference test, forced swimming test, and tail suspension test. Microglial phenotypes were assessed in terms of morphological features and cytokine profiles; inflammasome activity, in terms of levels of complexes containing NLRP3, apoptosis-associated speck-like protein containing CARD (ASC) and caspase-1; and neurogenesis, in terms of numbers of proliferating, differentiating, and mature neurons identified by immunostaining. GRg1 reduced abnormal animal behaviors caused by CMS, such as anhedonia and desperate behaviors, without affecting locomotor behaviors. GRg1 also reduced the number of ASC-specks, implying inhibition of inflammasome activation, which was associated with weaker activation of pro-inflammatory microglia. At the same time, GRg1 rescued impairment of hippocampal neurogenesis in vivo and in vitro, which correlated with modulation of microglial phenotypes. GRg1 exert antidepressant effects by preventing stress from activating the NLRP3 inflammasome in microglia, promoting a proneurogenic phenotype and allowing adult hippocampal neurogenesis.

Reduced neural progenitor cell count and cortical neurogenesis in guinea pigs congenitally infected with Toxoplasma gondii

Toxoplasma (T.) gondii is an obligate intracellular parasite with a worldwide distribution. Congenital infection can lead to severe pathological alterations in the brain. To examine the effects of toxoplasmosis in the fetal brain, pregnant guinea pigs are infected with T. gondii oocysts on gestation day 23 and dissected 10, 17 and 25 days afterwards. We show the neocortex to represent a target region of T. gondii and the parasite to infect neural progenitor cells (NPCs), neurons and astrocytes in the fetal brain. Importantly, we observe a significant reduction in neuron number at end-neurogenesis and find a marked reduction in NPC count, indicating that impaired neurogenesis underlies the neuronal decrease in infected fetuses. Moreover, we observe focal microglioses to be associated with T. gondii in the fetal brain. Our findings expand the understanding of the pathophysiology of congenital toxoplasmosis, especially contributing to the development of cortical malformations.

Microglia/macrophages are ultrastructurally altered by their proximity to spinal cord injury in adult female mice

Traumatic spinal cord injury can cause immediate physical damage to the spinal cord and result in severe neurological deficits. The primary, mechanical tissue damage triggers a variety of secondary damage mechanisms at the injury site which significantly contribute to a larger lesion size and increased functional damage. Inflammatory mechanisms which directly involve both microglia (MG) and monocyte-derived macrophages (MDM) play important roles in the post-injury processes, including inflammation and debris clearing. In the current study, we investigated changes in the structure and function of MG/MDM in the injured spinal cord of adult female mice, 7 days after a thoracic contusion SCI. With the use of chip mapping scanning electron microscopy, which allows to image large samples at the nanoscale, we performed an ultrastructural comparison of MG/MDM located near the lesion vs adjacent regions to provide novel insights into the mechanisms at play post-injury. We found that MG/MDM located near the lesion had more mitochondria overall, including mitochondria with and without morphological alterations, and had a higher proportion of altered mitochondria. MG/MDM near the lesion also showed an increased number of phagosomes, including phagosomes containing myelin and partiallydigested materials. MG/MDM near the injury interacted differently with the spinal cord parenchyma, as shown by their reduced number of direct contacts with synaptic elements, axon terminals and dendritic spines. In this study, we characterized the ultrastructural changes of MG/MDM in response to spinal cord tissue damage in mice, uncovering changes in phagocytic activity, mitochondrial ultrastructure, and inter-cellular interactions within the spinal cord parenchyma.

ThermoCyte: an inexpensive open-source temperature control system for in vitro live-cell imaging

Live-cell imaging is a common technique in microscopy to investigate dynamic cellular behaviour and permits the accurate and relevant analysis of a wide range of cellular and tissue parameters, such as motility, cell division, wound healing responses and calcium (Ca2+) signalling in cell lines, primary cell cultures and ex vivo preparations. Furthermore, this can occur under many experimental conditions, making live-cell imaging indispensable for biological research. Systems which maintain cells at physiological conditions outside of a CO2 incubator are often bulky, expensive and use proprietary components. Here we present an inexpensive, open-source temperature control system for in vitro live-cell imaging. Our system 'ThermoCyte', which is constructed from standard electronic components, enables precise tuning, control and logging of a temperature 'set point' for imaging cells at physiological temperature. We achieved stable thermal dynamics, with reliable temperature cycling and a standard deviation of 0.42°C over 1 h. Furthermore, the device is modular in nature and is adaptable to the researcher's specific needs. This represents simple, inexpensive and reliable tool for laboratories to carry out custom live-cell imaging protocols, on a standard laboratory bench, at physiological temperature.

Voluntary wheel exercise ameliorates cognitive impairment, hippocampal neurodegeneration and microglial abnormalities preceded by demyelination in a male mouse model of noise-induced hearing loss

Acquired peripheral hearing loss (APHL) in midlife has been identified as the greatest modifiable risk factor for dementia; however, the pathophysiological neural mechanisms linking APHL with an increased risk of dementia remain to be elucidated. Here, in an adult male mouse model of noise-induced hearing loss (NIHL), one of the most common forms of APHL, we demonstrated accelerated age-related cognitive decline and hippocampal neurodegeneration during a 6-month follow-up period, accompanied by progressive hippocampal microglial aberrations preceded by immediate-onset transient elevation in serum glucocorticoids and delayed-onset sustained myelin disruption in the hippocampus. Pretreatment with the glucocorticoid receptor antagonist RU486 before stressful noise exposure partially mitigated the early activation of hippocampal microglia, which were present at 7 days post noise exposure (7DPN), but had no impact on later microglial aberrations, hippocampal neurodegeneration, or cognitive decline exhibited at 1 month post noise exposure (1MPN). One month of voluntary wheel exercise following noise exposure barely affected either the hearing threshold shift or hippocampal myelin changes but effectively countered cognitive impairment and the decline in hippocampal neurogenesis in NIHL mice at 1MPN, paralleled by the normalization of microglial morphology, which coincided with a reduction in microglial myelin inclusions and a restoration of microglial hypoxia-inducible factor-1α (HIF1α) expression. Our results indicated that accelerated cognitive deterioration and hippocampal neuroplastic decline following NIHL are most likely driven by the maladaptive response of hippocampal microglia to myelin damage secondary to hearing loss, and we also demonstrated the potential of voluntary physical exercise as a promising and cost-effective strategy to alleviate the detrimental impact of APHL on cognitive function and thus curtail the high and continuously increasing global burden of dementia. Furthermore, the findings of the present study highlight the contribution of myelin debris overload to microglial malfunction and identify the microglial HIF1α-related pathway as an attractive candidate for future comprehensive investigation to obtain a more definitive picture of the underlying mechanisms linking APHL and dementia.

Polarized microtubule remodeling transforms the morphology of reactive microglia and drives cytokine release

Microglial reactivity is a pathological hallmark in many neurodegenerative diseases. During stimulation, microglia undergo complex morphological changes, including loss of their characteristic ramified morphology, which is routinely used to detect and quantify inflammation in the brain. However, the underlying molecular mechanisms and the relation between microglial morphology and their pathophysiological function are unknown. Here, proteomic profiling of lipopolysaccharide (LPS)-reactive microglia identifies microtubule remodeling pathways as an early factor that drives the morphological change and subsequently controls cytokine responses. We find that LPS-reactive microglia reorganize their microtubules to form a stable and centrosomally-anchored array to facilitate efficient cytokine trafficking and release. We identify cyclin-dependent kinase 1 (Cdk-1) as a critical upstream regulator of microtubule remodeling and morphological change in-vitro and in-situ. Cdk-1 inhibition also rescues tau and amyloid fibril-induced morphology changes. These results demonstrate a critical role for microtubule dynamics and reorganization in microglial reactivity and modulating cytokine-mediated inflammatory responses.

An In Vitro and Ex Vivo Analysis of the Potential of GelMA Hydrogels as a Therapeutic Platform for Preclinical Spinal Cord Injury

Spinal cord injury (SCI) is a devastating condition with no curative therapy currently available. Immunomodulation can be applied as a therapeutic strategy to drive alternative immune cell activation and promote a proregenerative injury microenvironment. Locally injected hydrogels carrying immunotherapeutic cargo directly to injured tissue offer an encouraging treatment approach from an immunopharmacological perspective. Gelatin methacrylate (GelMA) hydrogels are promising in this regard, however, detailed analysis on the immunogenicity of GelMA in the specific context of the SCI microenvironment is lacking. Here, the immunogenicity of GelMA hydrogels formulated with a translationally relevant photoinitiator is analyzed in vitro and ex vivo. 3% (w/v) GelMA, synthesized from gelatin type-A, is first identified as the optimal hydrogel formulation based on mechanical properties and cytocompatibility. Additionally, 3% GelMA-A does not alter the expression profile of key polarization markers in BV2 microglia or RAW264.7 macrophages after 48 h. Finally, it is shown for the first time that 3% GelMA-A can support the ex vivo culture of primary murine organotypic spinal cord slices for 14 days with no direct effect on glial fibrillary acidic protein (GFAP+ ) astrocyte or ionized calcium-binding adaptor molecule 1 (Iba-1+ ) microglia reactivity. This provides evidence that GelMA hydrogels can act as an immunotherapeutic hydrogel-based platform for preclinical SCI.

Cytoarchitectureal changes in hippocampal subregions of the NZB/W F1 mouse model of lupus

Over 50% of clinical patients affected by the systemic lupus erythematosus disease display impaired neurological cognitive functions and psychiatric disorders, a form called neuropsychiatric systemic lupus erythematosus. Hippocampus is one of the brain structures most sensitive to the cognitive deficits and psychiatric disorders related to neuropsychiatric lupus. The purpose of this study was to compare, layer by layer, neuron morphology in lupus mice model NZB/W F1 versus Wild Type mice. By a morphometric of cells identified on Nissl-stained sections, we evaluated structural alterations between NZB/W F1 and Wild Type mice in seven hippocampal subregions: Molecular dentate gyrus, Granular dentate gyrus, Polymorph dentate gyrus, Oriens layer, Pyramidal layer, Radiatum layer and Lacunosum molecular layer. By principal component analysis we distinguished healthy Wild Type from NZB/W F1 mice. In NZB/W F1 mice hippocampal cytoarchitecture, the neuronal cells resulted larger in size and more regular than those of Wild Type. In NZB/W F1, neurons were usually denser than in WT. The Pyramidal layer neurons were much denser in Wild Type than in NZB/W F1. Application of principal component analysis, allowed to distinguish NZB/W F1 lupus mice from healthy, showing as NZBW subjects presented a scattered distribution and intrasubject variability. Our results show a hypertrophy of the NZB/W F1 hippocampal neurons associated with an increase in perikaryal size within the CA1, CA2, CA3 region and the DG. These results help advance our understanding on hippocampal organization and structure in the NZB/W F1 lupus model, suggesting the hypothesis that the different subregions could be differentially affected in neuropsychiatric systemic lupus erythematosus disease. Leveraging an in-depth analysis of the morphology of neural cells in the hippocampal subregions and applying dimensionality reduction using PCA, we propose an efficient methodology to distinguish pathological NZBW mice from WT mice."

Altered microbiota caused by disordered gut motility leads to an overactivation of intestinal immune system in APC1638T mice

Adenomatous polyposis coli (APC) is recognized as an antioncogene related to familial adenomatous polyposis and colorectal cancers. However, APC is a large protein with multiple binding partners, indicating APC has diverse roles besides as a tumor suppressor. We have ever studied the roles of APC by using APC1638T/1638T (APC1638T) mice. Through those studies, we have noticed stools of APC1638T mice were smaller than those of APC+/+ mice and hypothesized there be a disturbance in fecal formation processes in APC1638T mice. The gut motility was morphologically analyzed by immunohistochemical staining of the Auerbach's plexus. Gut microbiota was analyzed by terminal restriction fragment length polymorphism (T-RFLP). IgA concentration in stools was determined by enzyme-linked immunosorbent assay (ELISA). As results, macroscopic findings suggestive of large intestinal dysmotility and microscopic findings of disorganization and inflammation of the plexus were obtained in APC1638T mice. An alteration of microbiota composition, especially increased Bacteroidetes population was observed. Increases in IgA positive cells and dendritic cells in the ileum with high fecal IgA concentration were also confirmed, suggesting over-activation of gut immunity. Our findings will contribute to our understanding of APC's functions in the gastrointestinal motility, and lead to a development of novel therapies for gut dysmotility-related diseases.

Microglia-specific knock-out of NF-κB/IKK2 increases the accumulation of misfolded α-synuclein through the inhibition of p62/sequestosome-1-dependent autophagy in the rotenone model of Parkinson's disease

Parkinson's disease (PD) is the most common neurodegenerative movement disorder worldwide, with a greater prevalence in men than women. The etiology of PD is largely unknown, although environmental exposures and neuroinflammation are linked to protein misfolding and disease progression. Activated microglia are known to promote neuroinflammation in PD, but how environmental agents interact with specific innate immune signaling pathways in microglia to stimulate conversion to a neurotoxic phenotype is not well understood. To determine how nuclear factor kappa B (NF-κB) signaling dynamics in microglia modulate neuroinflammation and dopaminergic neurodegeneration, we generated mice deficient in NF-κB activation in microglia (CX3CR1-Cre::IKK2fl/fl ) and exposed them to 2.5 mg/kg/day of rotenone for 14 days, followed by a 14-day post-lesioning incubation period. We postulated that inhibition of NF-κB signaling in microglia would reduce overall inflammatory injury in lesioned mice. Subsequent analysis indicated decreased expression of the NF-κB-regulated autophagy gene, sequestosome 1 (p62), in microglia, which is required for targeting ubiquitinated α-synuclein (α-syn) for lysosomal degradation. Knock-out animals had increased accumulation of misfolded α-syn within microglia, despite an overall reduction in neurodegeneration. Interestingly, this occurred more prominently in males. These data suggest that microglia play key biological roles in the degradation and clearance of misfolded α-syn and this process works in concert with the innate immune response associated with neuroinflammation. Importantly, the accumulation of misfolded α-syn protein aggregates alone did not increase neurodegeneration following exposure to rotenone but required the NF-κB-dependent inflammatory response in microglia.

Cortical superficial siderosis is associated with reactive astrogliosis in cerebral amyloid angiopathy

BACKGROUND

Cortical superficial siderosis (cSS) has recently emerged as one of the most important predictors of symptomatic intracerebral hemorrhage and is a risk factor for post-stroke dementia in cerebral amyloid angiopathy (CAA). However, it remains unknown whether cSS is just a marker of severe CAA pathology or may itself contribute to intracerebral hemorrhage risk and cognitive decline. cSS is a chronic manifestation of convexal subarachnoid hemorrhage and is neuropathologically characterized by iron deposits in the superficial cortical layers. We hypothesized that these iron deposits lead to local neuroinflammation, a potentially contributory pathway towards secondary tissue injury.

METHODS

Accordingly, we assessed the distribution of inflammatory markers in relation to cortical iron deposits in post-mortem tissue from CAA cases. Serial sections from the frontal, parietal, temporal, and occipital lobes of nineteen autopsy cases with CAA were stained with Perls' Prussian blue (iron) and underwent immunohistochemistry against glial fibrillary acidic protein (GFAP, reactive astrocytes) and cluster of differentiation 68 (CD68, activated microglia/macrophages). Digitized sections were uploaded to the cloud-based Aiforia® platform, where deep-learning algorithms were utilized to detect tissue, iron deposits, and GFAP-positive and CD68-positive cells.

RESULTS

We observed a strong local relationship between cortical iron deposits and reactive astrocytes. Like cSS-related iron, reactive astrocytes were mainly found in the most superficial layers of the cortex. Although we observed iron within both astrocytes and activated microglia/macrophages on co-stains, there was no clear local relationship between the density of microglia/macrophages and the density of iron deposits.

CONCLUSION

Iron deposition resulting from cSS is associated with local reactive astrogliosis.

Microglial morphometric analysis: so many options, so little consistency

Quantification of microglial activation through morphometric analysis has long been a staple of the neuroimmunologist's toolkit. Microglial morphological phenomics can be conducted through either manual classification or constructing a digital skeleton and extracting morphometric data from it. Multiple open-access and paid software packages are available to generate these skeletons via semi-automated and/or fully automated methods with varying degrees of accuracy. Despite advancements in methods to generate morphometrics (quantitative measures of cellular morphology), there has been limited development of tools to analyze the datasets they generate, in particular those containing parameters from tens of thousands of cells analyzed by fully automated pipelines. In this review, we compare and critique the approaches using cluster analysis and machine learning driven predictive algorithms that have been developed to tackle these large datasets, and propose improvements for these methods. In particular, we highlight the need for a commitment to open science from groups developing these classifiers. Furthermore, we call attention to a need for communication between those with a strong software engineering/computer science background and neuroimmunologists to produce effective analytical tools with simplified operability if we are to see their wide-spread adoption by the glia biology community.

Dietary wheat gluten induces astro- and microgliosis in the hypothalamus of male mice

Gluten, which is found in cereals such as wheat, rye and barley, makes up a major dietary component in most western nations, and has been shown to promote body mass gain and peripheral inflammation in mice. In the current study, we investigated the impact of gluten on central inflammation that is typically associated with diet-induced obesity. While we found no effect of gluten when added to a low-fat diet (LFD), male mice fed high fat diet (HFD) enriched with gluten increased body mass and adiposity compared with mice fed HFD without gluten. We furthermore found that gluten, when added to the LFD, increases circulating C-reactive protein levels. Gluten regardless of whether it was added to LFD or HFD led to a profound increase in the number of microglia and astrocytes in the arcuate nucleus of the hypothalamus, as detected by immunohistochemistry for ionised calcium binding adaptor molecule 1 (Iba-1) and glial fibrillary acidic protein (GFAP), respectively. In mice fed LFD, gluten mimicked the immunogenic effects of HFD exposure and when added to HFD led to a further increase in the number of immunoreactive cells. Taken together, our results confirm a moderate obesogenic effect of gluten when fed to mice exposed to HFD and for the first-time report gluten-induced astro- and microgliosis suggesting the development of hypothalamic injury in rodents.

The link between SARS-CoV-2 related microglial reactivity and astrocyte pathology in the inferior olivary nucleus

The pathological involvement of the central nervous system in SARS-CoV2 (COVID-19) patients is established. The burden of pathology is most pronounced in the brain stem including the medulla oblongata. Hypoxic/ischemic damage is the most frequent neuropathologic abnormality. Other neuropathologic features include neuronophagia, microglial nodules, and hallmarks of neurodegenerative diseases: astrogliosis and microglial reactivity. It is still unknown if these pathologies are secondary to hypoxia versus a combination of inflammatory response combined with hypoxia. It is also unknown how astrocytes react to neuroinflammation in COVID-19, especially considering evidence supporting the neurotoxicity of certain astrocytic phenotypes. This study aims to define the link between astrocytic and microglial pathology in COVID-19 victims in the inferior olivary nucleus, which is one of the most severely affected brain regions in COVID-19, and establish whether COVID-19 pathology is driven by hypoxic damage. Here, we conducted neuropathologic assessments and multiplex-immunofluorescence studies on the medulla oblongata of 18 COVID-19, 10 pre-pandemic patients who died of acute respiratory distress syndrome (ARDS), and 7-8 control patients with no ARDS or COVID-19. The comparison of ARDS and COVID-19 allows us to identify whether the pathology in COVID-19 can be explained by hypoxia alone, which is common to both conditions. Our results showed increased olivary astrogliosis in ARDS and COVID-19. However, microglial density and microglial reactivity were increased only in COVID-19, in a region-specific manner. Also, olivary hilar astrocytes increased YKL-40 (CHI3L1) in COVID-19, but to a lesser extent than ARDS astrocytes. COVID-19 astrocytes also showed lower levels of Aquaporin-4 (AQP4), and Metallothionein-3 in subsets of COVID-19 brain regions. Cluster analysis on immunohistochemical attributes of astrocytes and microglia identified ARDS and COVID-19 clusters with correlations to clinical history and disease course. Our results indicate that olivary glial pathology and neuroinflammation in the COVID-19 cannot be explained solely by hypoxia and suggest that failure of astrocytes to upregulate the anti-inflammatory YKL-40 may contribute to the neuroinflammation. Notwithstanding the limitations of retrospective studies in establishing causality, our experimental design cannot adequately control for factors external to our design. Perturbative studies are needed to confirm the role of the above-described astrocytic phenotypes in neuroinflammation.

Regulation of microglia polarization after cerebral ischemia

Stroke ranks second as a leading cause of death and permanent disability globally. Microglia, innate immune cells in the brain, respond rapidly to ischemic injury, triggering a robust and persistent neuroinflammatory reaction throughout the disease's progression. Neuroinflammation plays a critical role in the mechanism of secondary injury in ischemic stroke and is a significant controllable factor. Microglia activation takes on two general phenotypes: the pro-inflammatory M1 type and the anti-inflammatory M2 type, although the reality is more complex. The regulation of microglia phenotype is crucial to controlling the neuroinflammatory response. This review summarized the key molecules and mechanisms of microglia polarization, function, and phenotypic transformation following cerebral ischemia, with a focus on the influence of autophagy on microglia polarization. The goal is to provide a reference for the development of new targets for the treatment for ischemic stroke treatment based on the regulation of microglia polarization.

Challenges and opportunities to computationally deconvolve heterogeneous tissue with varying cell sizes using single cell RNA-sequencing datasets

Deconvolution of cell mixtures in "bulk" transcriptomic samples from homogenate human tissue is important for understanding the pathologies of diseases. However, several experimental and computational challenges remain in developing and implementing transcriptomics-based deconvolution approaches, especially those using a single cell/nuclei RNA-seq reference atlas, which are becoming rapidly available across many tissues. Notably, deconvolution algorithms are frequently developed using samples from tissues with similar cell sizes. However, brain tissue or immune cell populations have cell types with substantially different cell sizes, total mRNA expression, and transcriptional activity. When existing deconvolution approaches are applied to these tissues, these systematic differences in cell sizes and transcriptomic activity confound accurate cell proportion estimates and instead may quantify total mRNA content. Furthermore, there is a lack of standard reference atlases and computational approaches to facilitate integrative analyses, including not only bulk and single cell/nuclei RNA-seq data, but also new data modalities from spatial -omic or imaging approaches. New multi-assay datasets need to be collected with orthogonal data types generated from the same tissue block and the same individual, to serve as a "gold standard" for evaluating new and existing deconvolution methods. Below, we discuss these key challenges and how they can be addressed with the acquisition of new datasets and approaches to analysis.

A comparison of machine learning approaches for the quantification of microglial cells in the brain of mice, rats and non-human primates

Microglial cells are brain-specific macrophages that swiftly react to disruptive events in the brain. Microglial activation leads to specific modifications, including proliferation, morphological changes, migration to the site of insult, and changes in gene expression profiles. A change in inflammatory status has been linked to many neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease. For this reason, the investigation and quantification of microglial cells is essential for better understanding their role in disease progression as well as for evaluating the cytocompatibility of novel therapeutic approaches for such conditions. In the following study we implemented a machine learning-based approach for the fast and automatized quantification of microglial cells; this tool was compared with manual quantification (ground truth), and with alternative free-ware such as the threshold-based ImageJ and the machine learning-based Ilastik. We first trained the algorithms on brain tissue obtained from rats and non-human primate immunohistochemically labelled for microglia. Subsequently we validated the accuracy of the trained algorithms in a preclinical rodent model of Parkinson's disease and demonstrated the robustness of the algorithms on tissue obtained from mice, as well as from images provided by three collaborating laboratories. Our results indicate that machine learning algorithms can detect and quantify microglial cells in all the three mammalian species in a precise manner, equipotent to the one observed following manual counting. Using this tool, we were able to detect and quantify small changes between the hemispheres, suggesting the power and reliability of the algorithm. Such a tool will be very useful for investigation of microglial response in disease development, as well as in the investigation of compatible novel therapeutics targeting the brain. As all network weights and labelled training data are made available, together with our step-by-step user guide, we anticipate that many laboratories will implement machine learning-based quantification of microglial cells in their research.

Complexity of Sex Differences and Their Impact on Alzheimer's Disease

Sex differences are present in brain morphology, sex hormones, aging processes and immune responses. These differences need to be considered for proper modelling of neurological diseases with clear sex differences. This is the case for Alzheimer's disease (AD), a fatal neurodegenerative disorder with two-thirds of cases diagnosed in women. It is becoming clear that there is a complex interplay between the immune system, sex hormones and AD. Microglia are major players in the neuroinflammatory process occurring in AD and have been shown to be directly affected by sex hormones. However, many unanswered questions remain as the importance of including both sexes in research studies has only recently started receiving attention. In this review, we provide a summary of sex differences and their implications in AD, with a focus on microglia action. Furthermore, we discuss current available study models, including emerging complex microfluidic and 3D cellular models and their usefulness for studying hormonal effects in this disease.