CCR2 deficiency alters activation of microglia subsets in traumatic brain injury

Identifying microglia-derived NFKBIA as a potential contributor to the pathogenesis of Alzheimer's disease and age-related macular degeneration

BackgroundAlzheimer's disease (AD) and age-related macular degeneration (AMD) place considerable health burden on affected individuals and significant economic burden on society.ObjectiveThis study aims to explore the shared cellular and molecular mechanisms underlying the pathogenesis of AD and AMD.MethodsThe investigation in this study is conducted via single-cell and bulk tissue transcriptomic analysis. Transcriptomic datasets of AD and AMD were obtained from the GEO database. The shared differentially expressed genes (DEGs) in control and AD- and AMD-affected samples were identified. Functional enrichment analysis for DEGs was subsequently performed. Then, the protein-protein interaction (PPI) network of these DEGs was established via the STRING database and hub genes of this network were identified by Cytoscape software. Single-cell transcriptomic analysis was performed using Seurat R package to explore their expression in different cell types.ResultsDifferential analysis identified 127 shared DEGs of the two diseases, including 71 upregulated and 56 downregulated genes. Upregulated DEGs were enriched in inflammation, gliogenesis, cell apoptosis, and response to bacterial and viral infection and downregulated DEGs were enriched in mitochondrial function and energy production. PPI network and Cytoscape determined 10 hub genes, of which the NFKBIA gene was associated with the severity of both AD and AMD. Moreover, single-cell transcriptomic analysis showed that NFKBIA was highly expressed in microglia from disease-affected tissues.ConclusionsThe findings indicated that microglia with high NFKBIA expression were important contributors to the progression of both AD and AMD. Microglia-derived NFKBIA might serve as a potential therapeutic target for AD and AMD.

Single cell RNA sequencing after moderate traumatic brain injury: effects of therapeutic hypothermia

Traumatic brain injury (TBI) initiates a cascade of cellular and molecular events that promote acute and long-term patterns of neuronal, glial, vascular, and synaptic vulnerability leading to lasting neurological deficits. These complex responses lead to patterns of programmed cell death, diffuse axonal injury, increased blood-brain barrier disruption, neuroinflammation, and reactive gliosis, each a potential target for therapeutic interventions. Posttraumatic therapeutic hypothermia (TH) has been reported to be highly protective after brain and spinal cord injury and studies have investigated molecular mechanisms underlying mild hypothermic protection while commonly assessing heterogenous cell populations. In this study we conducted single-cell RNA sequencing (scRNA-seq) on cerebral cortical tissues after experimental TBI followed by a period of normothermia or hypothermia to comprehensively assess multiple cell type-specific transcriptional responses. C57BL/6 mice underwent moderate controlled cortical impact (CCI) injury or sham surgery and then placed under sustained normothermia (37⁰C) or hypothermia (33⁰C) for 2 h. After 24 h, cortical tissues including peri-contused regions were processed for scRNA-seq. Unbiased clustering revealed cellular heterogeneity among glial and immune cells at this subacute posttraumatic time point. The analysis also revealed vascular and immune subtypes associated with neovascularization and debris clearance, respectively. Compared to normothermic conditions, TH treatment altered the abundance of specific cell subtypes and induced reactive astrocyte-specific modulation of neurotropic factor gene expression. In addition, an increase in the proportion of endothelial tip cells in the hypothermic TBI group was documented compared to normothermia. These data emphasize the importance of early temperature-sensitive glial and vascular cell processes in producing potentially neuroprotective downstream signaling cascades in a cell-type-dependent manner. The use of scRNA-seq to address cell type-specific mechanisms underlying therapeutic treatments provides a valuable resource for identifying targetable biological pathways for the development of neuroprotective and reparative interventions.

A central role for CCR2 in monocyte recruitment and blood-brain barrier disruption during Usutu virus encephalitis

Usutu virus (USUV) is an emerging neurotropic flavivirus capable of causing encephalitis in humans. Here, our main goal was to characterize the innate immune response in the brain during USUV encephalitis and to identify strategies to control disease severity. Using an immunocompetent mouse model of USUV encephalitis, we showed that microglia activation, blood-brain barrier (BBB) disruption and inflammatory monocyte recruitment are hallmarks of disease 6 days post infection. Activated microglia were in close association to USUV-infected cells, concomitantly with elevated levels of IL-6, IFN-γ, CCL2, CCL5, CXCL10 and CXCL1 in the brain. Monocyte recruitment was CCR2-dependent and driven by IFN-γ and CCL2 production beneath the brain vasculature. Moreover, CCR2 deficiency inhibited microglia activation and BBB disruption, showing the central role of CCR2 in USUV encephalitis. Accordingly, treatment with dexamethasone prevented pro-inflammatory mediator production and reduced leukocyte recruitment significantly, restraining encephalitis severity. Concluding, USUV encephalitis is driven by CCR2-mediated monocyte recruitment and BBB disruption, and blocked therapeutically by glucocorticoids.

Infiltration by monocytes of the central nervous system and its role in multiple sclerosis: reflections on therapeutic strategies

Mononuclear macrophage infiltration in the central nervous system is a prominent feature of neuroinflammation. Recent studies on the pathogenesis and progression of multiple sclerosis have highlighted the multiple roles of mononuclear macrophages in the neuroinflammatory process. Monocytes play a significant role in neuroinflammation, and managing neuroinflammation by manipulating peripheral monocytes stands out as an effective strategy for the treatment of multiple sclerosis, leading to improved patient outcomes. This review outlines the steps involved in the entry of myeloid monocytes into the central nervous system that are targets for effective intervention: the activation of bone marrow hematopoiesis, migration of monocytes in the blood, and penetration of the blood-brain barrier by monocytes. Finally, we summarize the different monocyte subpopulations and their effects on the central nervous system based on phenotypic differences. As activated microglia resemble monocyte-derived macrophages, it is important to accurately identify the role of monocyte-derived macrophages in disease. Depending on the roles played by monocyte-derived macrophages at different stages of the disease, several of these processes can be interrupted to limit neuroinflammation and improve patient prognosis. Here, we discuss possible strategies to target monocytes in neurological diseases, focusing on three key aspects of monocyte infiltration into the central nervous system, to provide new ideas for the treatment of neurodegenerative diseases.

Chronic traumatic brain injury induces neurodegeneration, neuroinflammation, and cognitive deficits in a T cell-dependent manner

Traumatic brain injury (TBI) can lead to chronic neuroinflammation, and neurodegeneration associated with long-term cognitive deficits. Following TBI, the acute neuroinflammatory response involves microglial activation and the release of proinflammatory cytokines and chemokines which induce the recruitment of peripheral immune cells such as monocytes and ultimately T cells. Persistent innate and adaptive immune cell responses can lead to chronic neurodegeneration and functional deficits. Therefore, understanding the dynamic interaction between chronic immune responses and TBI-related pathogenesis and progression of the disease is crucial. We hypothesized that T cells have an essential role in TBI severity and recovery. We used generic T cell deletion mice (TCRβ-/-δ-/-) vs Wild-type mice that underwent controlled cortical impact assessing behavioral, histological, and immune system response outcomes at 3 months post-TBI. The absence of T cells reduced neurodegeneration and was associated with improved neurological outcomes 3 months post-injury. Furthermore, the absence of T cells enhanced an anti-inflammatory phenotype in peripheral myeloid cells in the injured brain. Collectively, these data indicate that T cells promote persistent neuropathology and functional impairments chronically after TBI.

Unravelling the impact of QRICH1 modulation on endoplasmic reticulum stress and neuronal apoptosis in traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is a major public health concern with high morbidity and mortality rates. Secondary brain injury, marked by inflammatory responses and apoptosis, worsens TBI outcomes. The endoplasmic reticulum stress (ERS) response has been implicated in secondary brain injury, with Glutamine Rich 1 Gene (QRICH1) emerging as a potential mediator. However, the precise role of QRICH1 in TBI pathogenesis and its therapeutic implications remain unclear.

METHODS

Controlled cortical impact mouse and Lipopolysaccharide-stimulated primary neuron models were used. Behavioral assessments, including the modified Garcia score, Y-maze test, and open-field test, were used to evaluate postoperative recovery in mice. QRICH1 neuron conditional knockout (cKO) mice were used to assess QRICH1 function, whereas adeno-associated virus (AAV)-mediated gene manipulation was used to modulate QRICH1 expression in cortical neurons.

RESULTS

QRICH1 expression was upregulated in the brain tissue of TBI mice, particularly 24 h post-injury, as shown by western blot analysis and immunofluorescence staining. QRICH1 is localized within neuronal nuclei, suggesting a role in cellular stress responses. QRICH1 cKO improved behavioral outcomes post-TBI, whereas AAV-mediated QRICH1 overexpression exacerbated secondary brain injury, characterized by increased ERS-related protein expression and neuronal death. Conversely, AAV-mediated QRICH1 knockdown reduced secondary brain injury as evidenced by decreased ERS-related protein expression and neuronal death.

CONCLUSION

QRICH1 plays a critical role in exacerbating ERS and apoptosis, and influences neuronal fate in secondary brain injury. Its involvement in the ERS pathway and in the induction of neuronal apoptosis post-TBI highlights QRICH1 as a potential therapeutic target for TBI treatment.

High-altitude hypoxia aggravated neurological deficits in mice induced by traumatic brain injury via BACH1 mediating astrocytic ferroptosis

Traumatic brain injury (TBI) is one of the leading causes of disability and mortality, which was classified as low-altitude TBI and high-altitude TBI. A large amount of literature shows that high-altitude TBI is associated with more severe neurological impairments and higher mortality rates compared to low-altitude TBI, due to the special environment of high-altitude hypoxia. However, the role of high-altitude hypoxia in the pathogenesis of TBI remains unclear. In order to deeply investigate this scientific issue, we constructed a high-altitude hypoxic TBI model at different altitudes and used animal behavioral assessments (Modified neurological severity score, rotarod test, elevated plus maze test) as well as histopathological analyses (brain gross specimens, brain water content, Evans blue content, hypoxia inducible factor-1α, Hematoxylin-Eosin staining and ROS detection) to reveal its underlying principles and characteristics. We found that with higher altitude, TBI-induced neurological deficits were more severe and the associated histopathological changes were more significant. Single-nuclear RNA sequencing was subsequently employed to further reveal differential gene expression profiles in high-altitude TBI. We found a significant increase in ferroptosis of astrocytes in cases of high-altitude TBI compared to those at low-altitude TBI. Analyzing transcription factors in depth, we found that Bach1 plays a crucial role in regulating key molecules that induce ferroptosis in astrocytes following high-altitude TBI. Down-regulation of Bach1 can effectively alleviate high-altitude TBI-induced neurological deficits and histopathological changes in mice. In conclusion, high-altitude hypoxia may significantly enhance the ferroptosis of astrocytes and aggravate TBI by up-regulating Bach1 expression. Our study provides a theoretical foundation for further understanding of the mechanism of high-altitude hypoxic TBI and targeted intervention therapy.

Single-cell RNA sequencing in stroke and traumatic brain injury: Current achievements, challenges, and future perspectives on transcriptomic profiling

Single-cell RNA sequencing (scRNA-seq) is a high-throughput transcriptomic approach with the power to identify rare cells, discover new cellular subclusters, and describe novel genes. scRNA-seq can simultaneously reveal dynamic shifts in cellular phenotypes and heterogeneities in cellular subtypes. Since the publication of the first protocol on scRNA-seq in 2009, this evolving technology has continued to improve, through the use of cell-specific barcodes, adoption of droplet-based systems, and development of advanced computational methods. Despite induction of the cellular stress response during the tissue dissociation process, scRNA-seq remains a popular technology, and commercially available scRNA-seq methods have been applied to the brain. Recent advances in spatial transcriptomics now allow the researcher to capture the positional context of transcriptional activity, strengthening our knowledge of cellular organization and cell-cell interactions in spatially intact tissues. A combination of spatial transcriptomic data with proteomic, metabolomic, or chromatin accessibility data is a promising direction for future research. Herein, we provide an overview of the workflow, data analyses methods, and pros and cons of scRNA-seq technology. We also summarize the latest achievements of scRNA-seq in stroke and acute traumatic brain injury, and describe future applications of scRNA-seq and spatial transcriptomics.

Severe traumatic brain injury temporally affects cerebral blood flow, endothelial cell phenotype, and cilia

Background

Previous clinical work suggested that altered cerebral blood flow (CBF) in severe traumatic brain injury (sTBI) correlates with poor executive function and clinical outcome. However, the molecular consequences of altered CBF on endothelial cells (ECs) and their blood flow-sensor organelle called cilia are not known.

Methods

We performed laser speckle contrast imaging, single cell isolation, and single cell RNA sequencing (scRNAseq) after sTBI in a closed skull, linear impact mouse model. Validation of select ciliary target protein changes was performed using flow cytometry. Additionally, in vitro experiments modeled the post-injury hypoxic environment to evaluate the effect on cilia protein ARL13B in human brain microvascular ECs.

Results

We detected immediate reductions in CBF that were sustained for at least 100 minutes in both impacted and non-impacted sides of the brain. Our scRNAseq data detected heterogeneity in the brain cortex-derived EC cluster and demonstrated that two of five unique EC sub-clusters changed their relative proportions post-sTBI. Consistent with flow changes, we identified multiple genes associated with the fluid shear stress pathway that were significantly differentially expressed in brain ECs post-injury. Also, ECs displayed activation of ischemic pathway as early as day 1 post-injury, and enrichment of hypoxia pathway at day 7 and 28 post- injury. Arl13b ciliary gene expression was lost on day 1 in ECs cluster and remained lost for the entire course of the injury. We validated the loss of cilia protein ARL13B specifically from brain ECs as early as day 1 post-injury and detected the protein in the peripheral blood of the injured mice. We also determined that hypoxia could induce loss of ARL13B protein from cultured ECs.

Conclusions

In severe TBI, blood flow is disrupted in both impacted and non-impacted regions of the brain, creating a hypoxic environment that may influence ciliary gene and protein expression on ECs.

The FGFR inhibitor Rogaratinib reduces microglia reactivity and synaptic loss in TBI

Background

Traumatic brain injury (TBI) induces an acute reactive state of microglia, which contribute to secondary injury processes through phagocytic activity and release of cytokines. Several receptor tyrosine kinases (RTK) are activated in microglia upon TBI, and their blockade may reduce the acute inflammation and decrease the secondary loss of neurons; thus, RTKs are potential therapeutic targets. We have previously demonstrated that several members of the Fibroblast Growth Factor Receptor (FGFR) family are transiently phosporylated upon TBI; the availability for drug repurposing of FGFR inhibitors makes worthwhile the elucidation of the role of FGFR in the acute phases of the response to TBI and the effect of FGFR inhibition.

Methods

A closed, blunt, weight-drop mild TBI protocol was employed. The pan-FGFR inhibitor Rogaratinib was administered to mice 30min after the TBI and daily up to 7 days post injury. Phosphor-RTK Arrays and proteomic antibody arrays were used to determine target engagement and large-scale impact of the FGFR inhibitor. pFGFR1 and pFGFR3 immunostaining were employed for validation. As outcome parameters of the TBI injury immunostainings for NeuN, VGLUT1, VGAT at 7dpi were considered.

Results

Inhibition of FGFR during TBI restricted phosphorylation of FGFR1, FGFR3, FGFR4 and ErbB4. Phosphorylation of FGFR1 and FGFR3 during TBI was traced back to Iba1+ microglia. Rogaratinib substantially dowregulated the proteomic signature of the neuroimmunological response to trauma, including the expression of CD40L, CXCR3, CCL4, CCR4, ILR6, MMP3 and OPG. Prolonged Rogaratinib treatment reduced neuronal loss upon TBI and prevented the loss of excitatory (vGLUT+) synapses.

Conclusion

The FGFR family is involved in the early induction of reactive microglia in TBI. FGFR inhibition selectively prevented FGFR phosphorylation in the microglia, dampened the overall neuroimmunological response and enhanced the preservation of neuronal and synaptic integrity. Thus, FGFR inhibitors may be relevant targets for drug repurposing aimed at modulating microglial reactivity in TBI.

Dynamics of synaptic damage in severe traumatic brain injury revealed by cerebrospinal fluid SNAP-25 and VILIP-1

BACKGROUND

Biomarkers of neuronal, glial cells and inflammation in traumatic brain injury (TBI) are available but they do not specifically reflect the damage to synapses, which represent the bulk volume of the brain. Experimental models have demonstrated extensive involvement of synapses in acute TBI, but biomarkers of synaptic damage in human patients have not been explored.

METHODS

Single-molecule array assays were used to measure synaptosomal-associated protein-25 (SNAP-25) and visinin-like protein 1 (VILIP-1) (along with neurofilament light chain (NFL), ubiquitin carboxy-terminal hydrolase L1 (UCH-L1), glial fibrillar acidic protein (GFAP), interleukin-6 (IL-6) and interleukin-8 (IL-8)) in ventricular cerebrospinal fluid (CSF) samples longitudinally acquired during the intensive care unit (ICU) stay of 42 patients with severe TBI or 22 uninjured controls.

RESULTS

CSF levels of SNAP-25 and VILIP-1 are strongly elevated early after severe TBI and decline in the first few days. SNAP-25 and VILIP-1 correlate with inflammatory markers at two distinct timepoints (around D1 and then again at D5) in follow-up. SNAP-25 and VILIP-1 on the day-of-injury have better sensitivity and specificity for unfavourable outcome at 6 months than NFL, UCH-L1 or GFAP. Later elevation of SNAP-25 was associated with poorer outcome.

CONCLUSION

Synaptic damage markers are acutely elevated in severe TBI and predict long-term outcomes, as well as, or better than, markers of neuroaxonal injury. Synaptic damage correlates with initial injury and with a later phase of secondary inflammatory injury.

Monocyte Invasion into the Retina Restricts the Regeneration of Neurons from Müller Glia

Endogenous reprogramming of glia into neurogenic progenitors holds great promise for neuron restoration therapies. Using lessons from regenerative species, we have developed strategies to stimulate mammalian Müller glia to regenerate neurons in vivo in the adult retina. We have demonstrated that the transcription factor Ascl1 can stimulate Müller glia neurogenesis. However, Ascl1 is only able to reprogram a subset of Müller glia into neurons. We have reported that neuroinflammation from microglia inhibits neurogenesis from Müller glia. Here we found that the peripheral immune response is a barrier to CNS regeneration. We show that monocytes from the peripheral immune system infiltrate the injured retina and negatively influence neurogenesis from Müller glia. Using CCR2 knock-out mice of both sexes, we found that preventing monocyte infiltration improves the neurogenic and proliferative capacity of Müller glia stimulated by Ascl1. Using scRNA-seq analysis, we identified a signaling axis wherein Osteopontin, a cytokine highly expressed by infiltrating immune cells is sufficient to suppress mammalian neurogenesis. This work implicates the response of the peripheral immune system as a barrier to regenerative strategies of the retina.

Ethanol-activated microglial exosomes induce MCP1 signaling mediated death of stress-regulatory proopiomelanocortin neurons in the developing hypothalamus

BACKGROUND

Microglia, a type of resident immune cells within the central nervous system, have been implicated in ethanol-activated neuronal death of the stress regulatory proopiomelanocortin (POMC) neuron-producing β-endorphin peptides in the hypothalamus in a postnatal rat model of fetal alcohol spectrum disorders. We determined if microglial extracellular vesicles (exosomes) are involved in the ethanol-induced neuronal death of the β-endorphin neuron via secreting elevated levels of the chemokine monocyte chemoattractant protein 1 (MCP1), a key regulator of neuroinflammation.

METHODS

We employed an in vitro model, consisting of primary culture of hypothalamic microglia prepared from postnatal day 2 (PND2) rat hypothalami and treated with or without 50 mM ethanol for 24 h, and an in vivo animal model in which microglia were obtained from hypothalami of PND6 rats fed daily with 2.5 mg/kg ethanol or control milk formula for five days prior to use. Exosomes were extracted and characterized with nanosight tracking analysis (NTA), transmission electron microscopy and western blot. Chemokine multiplex immunoassay and ELISA were used for quantitative estimation of MCP1 level. Neurotoxic ability of exosome was tested using primary cultures of β-endorphin neurons and employing nucleosome assay and immunocytochemistry. Elevated plus maze, open field and restraint tests were used to assess anxiety-related behaviors.

RESULTS

Ethanol elevated MCP1 levels in microglial exosomes both in vitro and in vivo models. Ethanol-activated microglial exosomes when introduced into primary cultures of β-endorphin neurons, increased cellular levels of MCP1 and the chemokine receptor CCR2 related signaling molecules including inflammatory cytokines and apoptotic genes as well as apoptotic death of β-endorphin neurons. These effects of microglial exosomes on β-endorphin neurons were suppressed by a CCR2 antagonist RS504393. Furthermore, RS504393 when injected in postnatal rats prior to feeding with ethanol it reduced alcohol-induced β-endorphin neuronal death in the hypothalamus. RS504393 also suppressed corticosterone response to stress and anxiety-like behaviors in postnatally alcohol-fed rats during adult period.

CONCLUSION

These data suggest that alcohol exposures during the developmental period elevates MCP1 levels in microglial exosomes that promote MCP1/CCR2 signaling to increase the apoptosis of β-endorphin neurons and resulting in hormonal and behavioral stress responses.

Ccr2-dependent monocytes exacerbate intestinal inflammation and modulate gut serotonergic signaling following traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) leads to acute gastrointestinal dysfunction and mucosal damage, resulting in feeding intolerance. C-C motif chemokine receptor 2 (Ccr2 + ) monocytes are crucial immune cells that regulate the gut's inflammatory response via the brain-gut axis. Using Ccr2 ko mice, we investigated the intricate interplay between these cells to better elucidate the role of systemic inflammation after TBI.

METHODS

A murine-controlled cortical impact model was used, and results were analyzed on postinjury days 1 and 3. The experimental groups included (1) sham C57Bl/6 wild type (WT), (2) TBI WT, (3) sham Ccr2 ko , and (4) TBI Ccr2 ko . Mice were euthanized on postinjury days 1 and 3 to harvest the ileum and study intestinal dysfunction and serotonergic signaling using a combination of quantitative real-time polymerase chain reaction, immunohistochemistry, fluorescein isothiocyanate-dextran motility assays, and flow cytometry. Student's t test and one-way analysis of variance were used for statistical analysis, with significance achieved when p < 0.05.

RESULTS

Traumatic brain injury resulted in severe dysfunction and dysmotility of the small intestine in WT mice as established by significant upregulation of inflammatory cytokines iNOS , Lcn2 , TNFα , and IL1β and the innate immunity receptor toll-like receptor 4 ( Tlr4 ). This was accompanied by disruption of genes related to serotonin synthesis and degradation. Notably, Ccr2 ko mice subjected to TBI showed substantial improvements in intestinal pathology. Traumatic brain injury Ccr2 ko groups demonstrated reduced expression of inflammatory mediators ( iNOS , Lcn2 , IL1β , and Tlr4 ) and improvement in serotonin synthesis genes, including tryptophan hydroxylase 1 ( Tph1 ) and dopa decarboxylase ( Ddc ).

CONCLUSION

Our study reveals a critical role for Ccr2 + monocytes in modulating intestinal homeostasis after TBI. Ccr2 + monocytes aggravate intestinal inflammation and alter gut-derived serotonergic signaling. Therefore, targeting Ccr2 + monocyte-dependent responses could provide a better understanding of TBI-induced gut inflammation. Further studies are required to elucidate the impact of these changes on brain neuroinflammation and cognitive outcomes.

Engineered Extracellular Vesicle-Based Nanoformulations That Coordinate Neuroinflammation and Immune Homeostasis, Enhancing Parkinson's Disease Therapy

Although conventional intervention to microglia can mitigate neuroinflammation in the short term, immune disorders by peripheral inflammatory cells can infiltrate continuously, resulting in an overactivated immune microenvironment of Parkinson's disease (PD). Here, we design engineered extracellular vesicle-based nanoformulations (EVNs) to address multiple factors for the management of PD. Specifically, EVN is developed by coating CCR2-enriched mesenchymal stem cell-derived extracellular vesicles (MSCCCR2 EVs) onto a dihydrotanshinone I-loaded nanocarrier (MSeN-DT). The MSCCCR2 EVs (the shell of EVN) can actively show homing to specific chemokines CCL2 in the substantia nigra, which enables them to block the infiltration of peripheral inflammatory cells. Interestingly, MSeN-DT (the core of EVN) can promote the Nrf2-GPX4 pathway for the suppression of the source of inflammation by inhibiting ferroptosis in microglia. In the PD model mice, a satisfactory therapeutic effect is achieved, with inhibition of peripheral inflammatory cell infiltration, precise regulation of inflammatory microglia in the substantia nigra, as well as promotion of behavioral improvement and repairing damaged neurons. In this way, the combinatorial code of alleviation of inflammation and modulation of immune homeostasis can reshape the immune microenvironment in PD, which bridges internal anti-inflammatory and external immunity. This finding reveals a comprehensive therapeutic paradigm for PD that breaks the vicious cycle of immune overactivation.

Anti-CCL2 therapy reduces oxygen toxicity to the immature lung

Oxygen toxicity constitutes a key contributor to bronchopulmonary dysplasia (BPD). Critical step in the pathogenesis of BPD is the inflammatory response in the immature lung with the release of pro-inflammatory cytokines and the influx of innate immune cells. Identification of efficient therapies to alleviate the inflammatory response remains an unmet research priority. First, we studied macrophage and neutrophil profiles in tracheal aspirates of n = 103 preterm infants <29 weeks´ gestation requiring mechanical ventilation. While no differences were present at birth, a higher fraction of macrophages, the predominance of the CD14+CD16+ subtype on day 5 of life was associated with moderate/severe BPD. Newborn CCL-2-/- mice insufficient in pulmonary macrophage recruitment had a reduced influx of neutrophils, lower apoptosis induction in the pulmonary tissue and better-preserved lung morphometry with higher counts of type II cells, mesenchymal stem cells and vascular endothelial cells when exposed to hyperoxia for 7 days. To study the benefit of a targeted approach to prevent the pulmonary influx of macrophages, wildtype mice were repeatedly treated with CCL-2 blocking antibodies while exposed to hyperoxia for 7 days. Congruent with the results in CCL-2-/- animals, the therapeutic intervention reduced the pulmonary inflammatory response, attenuated cell death in the lung tissue and better-preserved lung morphometry. Overall, our preclinical and clinical datasets document the predominant role of macrophage recruitment to the pathogenesis of BPD and establish the abrogation of CCL-2 function as novel approach to protect the immature lung from hyperoxic injury.

The contribution of the meningeal immune interface to neuroinflammation in traumatic brain injury

Traumatic brain injury (TBI) is a major cause of disability and mortality worldwide, particularly among the elderly, yet our mechanistic understanding of what renders the post-traumatic brain vulnerable to poor outcomes, and susceptible to neurological disease, is incomplete. It is well established that dysregulated and sustained immune responses elicit negative consequences after TBI; however, our understanding of the neuroimmune interface that facilitates crosstalk between central and peripheral immune reservoirs is in its infancy. The meninges serve as the interface between the brain and the immune system, facilitating important bi-directional roles in both healthy and disease settings. It has been previously shown that disruption of this system exacerbates neuroinflammation in age-related neurodegenerative disorders such as Alzheimer's disease; however, we have an incomplete understanding of how the meningeal compartment influences immune responses after TBI. In this manuscript, we will offer a detailed overview of the holistic nature of neuroinflammatory responses in TBI, including hallmark features observed across clinical and animal models. We will highlight the structure and function of the meningeal lymphatic system, including its role in immuno-surveillance and immune responses within the meninges and the brain. We will provide a comprehensive update on our current knowledge of meningeal-derived responses across the spectrum of TBI, and identify new avenues for neuroimmune modulation within the neurotrauma field.

Fibrin promotes oxidative stress and neuronal loss in traumatic brain injury via innate immune activation

BACKGROUND

Traumatic brain injury (TBI) causes significant blood-brain barrier (BBB) breakdown, resulting in the extravasation of blood proteins into the brain. The impact of blood proteins, especially fibrinogen, on inflammation and neurodegeneration post-TBI is not fully understood, highlighting a critical gap in our comprehension of TBI pathology and its connection to innate immune activation.

METHODS

We combined vascular casting with 3D imaging of solvent-cleared organs (uDISCO) to study the spatial distribution of the blood coagulation protein fibrinogen in large, intact brain volumes and assessed the temporal regulation of the fibrin(ogen) deposition by immunohistochemistry in a murine model of TBI. Fibrin(ogen) deposition and innate immune cell markers were co-localized by immunohistochemistry in mouse and human brains after TBI. We assessed the role of fibrinogen in TBI using unbiased transcriptomics, flow cytometry and immunohistochemistry for innate immune and neuronal markers in Fggγ390-396A knock-in mice, which express a mutant fibrinogen that retains normal clotting function, but lacks the γ390-396 binding motif to CD11b/CD18 integrin receptor.

RESULTS

We show that cerebral fibrinogen deposits were associated with activated innate immune cells in both human and murine TBI. Genetic elimination of fibrin-CD11b interaction reduced peripheral monocyte recruitment and the activation of inflammatory and reactive oxygen species (ROS) gene pathways in microglia and macrophages after TBI. Blockade of the fibrin-CD11b interaction was also protective from oxidative stress damage and cortical loss after TBI.

CONCLUSIONS

These data suggest that fibrinogen is a regulator of innate immune activation and neurodegeneration in TBI. Abrogating post-injury neuroinflammation by selective blockade of fibrin's inflammatory functions may have implications for long-term neurologic recovery following brain trauma.

CC Chemokine Family Members' Modulation as a Novel Approach for Treating Central Nervous System and Peripheral Nervous System Injury-A Review of Clinical and Experimental Findings

Despite significant progress in modern medicine and pharmacology, damage to the nervous system with various etiologies still poses a challenge to doctors and scientists. Injuries lead to neuroimmunological changes in the central nervous system (CNS), which may result in both secondary damage and the development of tactile and thermal hypersensitivity. In our review, based on the analysis of many experimental and clinical studies, we indicate that the mechanisms occurring both at the level of the brain after direct damage and at the level of the spinal cord after peripheral nerve damage have a common immunological basis. This suggests that there are opportunities for similar pharmacological therapeutic interventions in the damage of various etiologies. Experimental data indicate that after CNS/PNS damage, the levels of 16 among the 28 CC-family chemokines, i.e., CCL1, CCL2, CCL3, CCL4, CCL5, CCL6, CCL7, CCL8, CCL9, CCL11, CCL12, CCL17, CCL19, CCL20, CCL21, and CCL22, increase in the brain and/or spinal cord and have strong proinflammatory and/or pronociceptive effects. According to the available literature data, further investigation is still needed for understanding the role of the remaining chemokines, especially six of them which were found in humans but not in mice/rats, i.e., CCL13, CCL14, CCL15, CCL16, CCL18, and CCL23. Over the past several years, the results of studies in which available pharmacological tools were used indicated that blocking individual receptors, e.g., CCR1 (J113863 and BX513), CCR2 (RS504393, CCX872, INCB3344, and AZ889), CCR3 (SB328437), CCR4 (C021 and AZD-2098), and CCR5 (maraviroc, AZD-5672, and TAK-220), has beneficial effects after damage to both the CNS and PNS. Recently, experimental data have proved that blockades exerted by double antagonists CCR1/3 (UCB 35625) and CCR2/5 (cenicriviroc) have very good anti-inflammatory and antinociceptive effects. In addition, both single (J113863, RS504393, SB328437, C021, and maraviroc) and dual (cenicriviroc) chemokine receptor antagonists enhanced the analgesic effect of opioid drugs. This review will display the evidence that a multidirectional strategy based on the modulation of neuronal-glial-immune interactions can significantly improve the health of patients after CNS and PNS damage by changing the activity of chemokines belonging to the CC family. Moreover, in the case of pain, the combined administration of such antagonists with opioid drugs could reduce therapeutic doses and minimize the risk of complications.

STING-Dependent Signaling in Microglia or Peripheral Immune Cells Orchestrates the Early Inflammatory Response and Influences Brain Injury Outcome

While originally identified as an antiviral pathway, recent work has implicated that cyclic GMP-AMP-synthase-Stimulator of Interferon Genes (cGAS-STING) signaling is playing a critical role in the neuroinflammatory response to traumatic brain injury (TBI). STING activation results in a robust inflammatory response characterized by the production of inflammatory cytokines called interferons, as well as hundreds of interferon stimulated genes (ISGs). Global knock-out (KO) mice inhibiting this pathway display neuroprotection with evidence that this pathway is active days after injury; yet, the early neuroinflammatory events stimulated by STING signaling remain understudied. Furthermore, the source of STING signaling during brain injury is unknown. Using a murine controlled cortical impact (CCI) model of TBI, we investigated the peripheral immune and microglial response to injury utilizing male chimeric and conditional STING KO animals, respectively. We demonstrate that peripheral and microglial STING signaling contribute to negative outcomes in cortical lesion volume, cell death, and functional outcomes postinjury. A reduction in overall peripheral immune cell and neutrophil infiltration at the injury site is STING dependent in these models at 24 h. Transcriptomic analysis at 2 h, when STING is active, reveals that microglia drive an early, distinct transcriptional program to elicit proinflammatory genes including interleukin 1-β (IL-1β), which is lost in conditional knock-out mice. The upregulation of alternative innate immune pathways also occurs after injury in these animals, which supports a complex relationship between brain-resident and peripheral immune cells to coordinate the proinflammatory response and immune cell influx to damaged tissue after injury.

Genetic Contributions to Recovery following Brain Trauma: A Narrative Review

Traumatic brain injury (TBI) is a frequently encountered form of injury that can have lifelong implications. Despite advances in prevention, diagnosis, monitoring, and treatment, the degree of recovery can vary widely between patients. Much of this is explained by differences in severity of impact and patient-specific comorbidities; however, even among nearly identical patients, stark disparities can arise. Researchers have looked to genetics in recent years as a means of explaining this phenomenon. It has been hypothesized that individual genetic factors can influence initial inflammatory responses, recovery mechanisms, and overall prognoses. In this review, we focus on cytokine polymorphisms, mitochondrial DNA (mtDNA) haplotypes, immune cells, and gene therapy given their associated influx of novel research and magnitude of potential. This discussion is prefaced by a thorough background on TBI pathophysiology to better understand where each mechanism fits within the disease process. Cytokine polymorphisms causing unfavorable regulation of genes encoding IL-1β, IL-RA, and TNF-α have been linked to poor TBI outcomes like disability and death. mtDNA haplotype H has been correlated with deleterious effects on TBI recovery time, whereas haplotypes K, T, and J have been depicted as protective with faster recovery times. Immune cell genetics such as microglial differentially expressed genes (DEGs), monocyte receptor genes, and regulatory factors can be both detrimental and beneficial to TBI recovery. Gene therapy in the form of gene modification, inactivation, and editing show promise in improving post-TBI memory, cognition, and neuromotor function. Limitations of this study include a large proportion of cited literature being focused on pre-clinical murine models. Nevertheless, favorable evidence on the role of genetics in TBI recovery continues to grow. We aim for this work to inform interested parties on the current landscape of research, highlight promising targets for gene therapy, and galvanize translation of findings into clinical trials.

Engineered Macrophage Membrane-Coated Nanoparticles with Enhanced CCR2 Expression Promote Spinal Cord Injury Repair by Suppressing Neuroinflammation and Neuronal death

Spinal cord injury (SCI) is a severe neurological disorder characterized by significant disability and limited treatment options. Mitigating the secondary inflammatory response following the initial injury is the primary focus of current research in the treatment of SCI. CCL2 (C─C motif chemokine ligand 2) serves as the primary regulator responsible for inflammatory chemotaxis of the majority of peripheral immune cells, blocking the CCL2-CCR2 (C─C chemokine receptor type 2) axis has shown considerable therapeutic potential for inflammatory diseases, including SCI. In this study, it presents a multifunctional biomimetic nanoplatform (CCR2-MM@PLGA/Cur) specifically designed to target the CCL2-CCR2 axis, which consisted of an engineered macrophage membrane (MM) coating with enhanced CCR2 expression and a PLGA (poly (lactic-co-glycolic acid)) nanoparticle that encapsulated therapeutic drugs. CCR2 overexpression on MM not only enhanced drug-targeted delivery to the injury site, but also attenuated macrophage infiltration, microglia pro-inflammatory polarization, and neuronal apoptosis by trapping CCL2. Consequently, it facilitated neural regeneration and motor function recovery in SCI mice, enabling a comprehensive treatment approach for SCI. The feasibility and efficacy of this platform are confirmed through a series of in vitro and in vivo assays, offering new insights and potential avenues for further exploration in the treatment of SCI.

A novel phenotype of B cells associated with enhanced phagocytic capability and chemotactic function after ischemic stroke

Accumulating evidence has demonstrated the involvement of B cells in neuroinflammation and neuroregeneration. However, the role of B cells in ischemic stroke remains unclear. In this study, we identified a novel phenotype of macrophage-like B cells in brain-infiltrating immune cells expressing a high level of CD45. Macrophage-like B cells characterized by co-expression of B-cell and macrophage markers, showed stronger phagocytic and chemotactic functions compared with other B cells and showed upregulated expression of phagocytosis-related genes. Gene Ontology analysis found that the expression of genes associated with phagocytosis, including phagosome- and lysosome-related genes, was upregulated in macrophage-like B cells. The phagocytic activity of macrophage-like B cells was verified by immunostaining and three-dimensional reconstruction, in which TREM2-labeled macrophage-like B cells enwrapped and internalized myelin debris after cerebral ischemia. Cell-cell interaction analysis revealed that macrophage-like B cells released multiple chemokines to recruit peripheral immune cells mainly via CCL pathways. Single-cell RNA sequencing showed that the transdifferentiation to macrophage-like B cells may be induced by specific upregulation of the transcription factor CEBP family to the myeloid lineage and/or by downregulation of the transcription factor Pax5 to the lymphoid lineage. Furthermore, this distinct B cell phenotype was detected in brain tissues from mice or patients with traumatic brain injury, Alzheimer's disease, and glioblastoma. Overall, these results provide a new perspective on the phagocytic capability and chemotactic function of B cells in the ischemic brain. These cells may serve as an immunotherapeutic target for regulating the immune response of ischemic stroke.

Single-nucleus transcriptomic mapping uncovers targets for traumatic brain injury

The subventricular zone (SVZ) is a neurogenic niche that contributes to homeostasis and repair after brain injury. However, the effects of mild traumatic brain injury (mTBI) on the divergence of the regulatory DNA landscape within the SVZ and its link to functional alterations remain unexplored. In this study, we mapped the transcriptome atlas of murine SVZ and its responses to mTBI at the single-cell level. We observed cell-specific gene expression changes following mTBI and unveiled diverse cell-to-cell interaction networks that influence a wide array of cellular processes. Moreover, we report novel neurogenesis lineage trajectories and related key transcription factors, which we validate through loss-of-function experiments. Specifically, we validate the role of Tcf7l1, a cell cycle gene regulator, in promoting neural stem cell differentiation toward the neuronal lineage after mTBI, providing a potential target for regenerative medicine. Overall, our study profiles an SVZ transcriptome reference map, which underlies the differential cellular behavior in response to mTBI. The identified key genes and pathways that may ameliorate brain damage or facilitate neural repair serve as a comprehensive resource for drug discovery in the context of mTBI.

Infiltrating anti-inflammatory monocytes modulate microglial activation through toll-like receptor 4/interferon-dependent pathways following traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is the leading cause of morbidity and mortality in the pediatric population. Microglia and infiltrating monocyte-derived macrophages are crucial immune cells that modulate the neuroinflammatory response following TBI. Using C34, a novel pharmacologic toll-like receptor 4 inhibitor, we investigated the intricate interactions between these cells in a murine TBI model.

METHODS

A murine controlled cortical impact model was used, and the results were analyzed on postinjury days 1, 7, 28, and 35. The experimental groups are as follows: (1) sham C57BL/6 wild-type (WT), (2) TBI WT, (3) sham WT + C34, and (4) TBI WT + C34. Quantitative real-time polymerase chain reaction was used to quantify gene expression associated with microglial activation, apoptotic pathways, and type 1 interferon pathway. Flow cytometry was used to isolate microglia and infiltrating monocytes. Brain lesion volumes were assessed using magnetic resonance imaging. Last, neurocognitive outcomes were evaluated using the Morris Water Maze test. Student's t test and one-way analysis of variance were used for statistical analysis with significance achieved when p < 0.05.

RESULTS

Toll-like receptor 4 inhibition leads to improved neurological sequela post-TBI, possibly because of an increase in infiltrating anti-inflammatory monocytes and a decrease in IFN regulatory factor 7 during acute inflammation, followed by a reduction in apoptosis and M2 microglial expression during chronic inflammation.

CONCLUSION

Toll-like receptor 4 inhibition with C34 skews infiltrating monocytes toward an anti-inflammatory phenotype, leading to enhanced neurocognitive outcomes. Moreover, although M2 microglia have been consistently shown as inducers of neuroprotection, our results clearly demonstrate their detrimental role during the chronic phases of healing post-TBI.

Selective neuroimmune modulation by type I interferon drives neuropathology and neurologic dysfunction following traumatic brain injury

Accumulating evidence suggests that type I interferon (IFN-I) signaling is a key contributor to immune cell-mediated neuropathology in neurodegenerative diseases. Recently, we demonstrated a robust upregulation of type I interferon-stimulated genes in microglia and astrocytes following experimental traumatic brain injury (TBI). The specific molecular and cellular mechanisms by which IFN-I signaling impacts the neuroimmune response and neuropathology following TBI remains unknown. Using the lateral fluid percussion injury model (FPI) in adult male mice, we demonstrated that IFN α/β receptor (IFNAR) deficiency resulted in selective and sustained blockade of type I interferon-stimulated genes following TBI as well as decreased microgliosis and monocyte infiltration. Molecular alteration of reactive microglia also occurred with diminished expression of genes needed for MHC class I antigen processing and presentation following TBI. This was associated with decreased accumulation of cytotoxic T cells in the brain. The IFNAR-dependent modulation of the neuroimmune response was accompanied by protection from secondary neuronal death, white matter disruption, and neurobehavioral dysfunction. These data support further efforts to leverage the IFN-I pathway for novel, targeted therapy of TBI.

Prospects for Nerve Regeneration and Gene Therapy in the Treatment of Traumatic Brain Injury

Traumatic brain injury (TBI) is a prevalent neurological disorder and a leading cause of death and disability worldwide. The high mortality rates result in a tremendous burden on society and families in terms of public health and economic costs. Despite advances in biomedical research, treatment options for TBI still remain limited, and there is no effective therapy to restore the structure and function of the injured brain. Regrettably, due to the excessive heterogeneity of TBI and the lack of objective and reliable efficacy evaluation indicators, no proven therapeutic drugs or drugs with clear benefits on functional outcomes have been successfully developed to date. Therefore, it is urgent to explore new therapeutic approaches to protect or regenerate the injured brain from different perspectives. In this review, we first provide a brief overview of the causes and current status of TBI and then summarize the preclinical and clinical research status of cutting-edge treatment methods, including nerve regeneration therapy and gene therapy, with the aim of providing valuable references for effective therapeutic strategies for TBI.

Mapping the tumor microenvironment in clear cell renal carcinoma by single-cell transcriptome analysis

Introduction: Clear cell renal cell carcinoma (ccRCC) is associated with unfavorable clinical outcomes. To identify viable therapeutic targets, a comprehensive understanding of intratumoral heterogeneity is crucial. In this study, we conducted bioinformatic analysis to scrutinize single-cell RNA sequencing data of ccRCC tumor and para-tumor samples, aiming to elucidate the intratumoral heterogeneity in the ccRCC tumor microenvironment (TME). Methods: A total of 51,780 single cells from seven ccRCC tumors and five para-tumor samples were identified and grouped into 11 cell lineages using bioinformatic analysis. These lineages included tumor cells, myeloid cells, T-cells, fibroblasts, and endothelial cells, indicating a high degree of heterogeneity in the TME. Copy number variation (CNV) analysis was performed to compare CNV frequencies between tumor and normal cells. The myeloid cell population was further re-clustered into three major subgroups: monocytes, macrophages, and dendritic cells. Differential expression analysis, gene ontology, and gene set enrichment analysis were employed to assess inter-cluster and intra-cluster functional heterogeneity within the ccRCC TME. Results: Our findings revealed that immune cells in the TME predominantly adopted an inflammatory suppression state, promoting tumor cell growth and immune evasion. Additionally, tumor cells exhibited higher CNV frequencies compared to normal cells. The myeloid cell subgroups demonstrated distinct functional properties, with monocytes, macrophages, and dendritic cells displaying diverse roles in the TME. Certain immune cells exhibited pro-tumor and immunosuppressive effects, while others demonstrated antitumor and immunostimulatory properties. Conclusion: This study contributes to the understanding of intratumoral heterogeneity in the ccRCC TME and provides potential therapeutic targets for ccRCC treatment. The findings emphasize the importance of considering the diverse functional roles of immune cells in the TME for effective therapeutic interventions.

The role of signaling crosstalk of microglia in hippocampus on progression of ageing and Alzheimer's disease

Based on single-cell sequencing of the hippocampi of 5× familiar Alzheimer's disease (5× FAD) and wild type mice at 2-, 12-, and 24-month of age, we found an increased percentage of microglia in aging and Alzheimer's disease (AD) mice. Blood brain barrier injury may also have contributed to this increase. Immune regulation by microglia plays a major role in the progression of aging and AD, according to the functions of 41 intersecting differentially expressed genes in microglia. Signaling crosstalk between C-C motif chemokine ligand (CCL) and major histocompatibility complex-1 bridges intercellular communication in the hippocampus during aging and AD. The amyloid precursor protein (APP) and colony stimulating factor (CSF) signals drive 5× FAD to deviate from aging track to AD occurrence among intercellular communication in hippocampus. Microglia are involved in the progression of aging and AD can be divided into 10 functional types. The strength of the interaction among microglial subtypes weakened with aging, and the CCL and CSF signaling pathways were the fundamental bridge of communication among microglial subtypes.

Selective neuroimmune modulation by type I interferon drives neuropathology and neurologic dysfunction following traumatic brain injury

Accumulating evidence suggests that type I interferon (IFN-I) signaling is a key contributor to immune cell-mediated neuropathology in neurodegenerative diseases. Recently, we demonstrated a robust upregulation of type I interferon-stimulated genes in microglia and astrocytes following experimental traumatic brain injury (TBI). The specific molecular and cellular mechanisms by which IFN-I signaling impacts the neuroimmune response and neuropathology following TBI remains unknown. Using the lateral fluid percussion injury model (FPI) in adult male mice, we demonstrated that IFN α/β receptor (IFNAR) deficiency resulted in selective and sustained blockade of type I interferon-stimulated genes following TBI as well as decreased microgliosis and monocyte infiltration. Phenotypic alteration of reactive microglia also occurred with diminished expression of molecules needed for MHC class I antigen processing and presentation following TBI. This was associated with decreased accumulation of cytotoxic T cells in the brain. The IFNAR-dependent modulation of the neuroimmune response was accompanied by protection from secondary neuronal death, white matter disruption, and neurobehavioral dysfunction. These data support further efforts to leverage the IFN-I pathway for novel, targeted therapy of TBI.

The interplay between monocytes, α-synuclein and LRRK2 in Parkinson's disease

The accumulation of aggregated α-synuclein in susceptible neurons in the brain, together with robust activation of nearby myeloid cells, are pathological hallmarks of Parkinson's disease (PD). While microglia represent the dominant type of myeloid cell in the brain, recent genetic and whole-transcriptomic studies have implicated another type of myeloid cell, bone-marrow derived monocytes, in disease risk and progression. Monocytes in circulation harbor high concentrations of the PD-linked enzyme leucine-rich repeat kinase 2 (LRRK2) and respond to both intracellular and extracellular aggregated α-synuclein with a variety of strong pro-inflammatory responses. This review highlights recent findings from studies that functionally characterize monocytes in PD patients, monocytes that infiltrate into cerebrospinal fluid, and emerging analyses of whole myeloid cell populations in the PD-affected brain that include monocyte populations. Central controversies discussed include the relative contribution of monocytes acting in the periphery from those that might engraft in the brain to modify disease risk and progression. We conclude that further investigation into monocyte pathways and responses in PD, especially the discovery of additional markers, transcriptomic signatures, and functional classifications, that better distinguish monocyte lineages and responses in the brain from other types of myeloid cells may reveal points for therapeutic intervention, as well as a better understanding of ongoing inflammation associated with PD.

Transforming the understanding of brain immunity

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

Brain and blood single-cell transcriptomics in acute and subacute phases after experimental stroke

Cerebral ischemia triggers a powerful inflammatory reaction involving both peripheral leukocytes and brain resident cells. Recent evidence indicates that their differentiation into a variety of functional phenotypes contributes to both tissue injury and repair. However, the temporal dynamics and diversity of post-stroke immune cell subsets remain poorly understood. To address these limitations, we performed a longitudinal single-cell transcriptomic study of both brain and mouse blood to obtain a composite picture of brain-infiltrating leukocytes, circulating leukocytes, microglia and endothelium diversity over the ischemic/reperfusion time. Brain cells and blood leukocytes isolated from mice 2 or 14 days after transient middle cerebral artery occlusion or sham surgery were purified by FACS sorting and processed for droplet-based single-cell transcriptomics. The analysis revealed a strong divergence of post-ischemic microglia, macrophages, and neutrophils over time, while such diversity was less evident in dendritic cells, B, T and NK cells. Conversely, brain endothelial cells and brain associated-macrophages showed altered transcriptomic signatures at 2 days post-stroke, but low divergence from sham at day 14. Pseudotime trajectory inference predicted the in-situ longitudinal progression of monocyte-derived macrophages from their blood precursors into day 2 and day 14 phenotypes, while microglia phenotypes at these two time points were not connected. In contrast to monocyte-derived macrophages, neutrophils were predicted to be continuously de-novo recruited from the blood. Brain single-cell transcriptomics from both female and male aged mice did not show major changes in respect to young mice, but aged and young brains differed in their immune cell composition. Furthermore, blood leukocyte analysis also revealed altered transcriptomes after stroke. However, brain-infiltrating leukocytes displayed higher transcriptomic divergence than their circulating counterparts, indicating that phenotypic diversification into cellular subsets occurs within the brain in the early and the recovery phase of ischemic stroke. In addition, this resource report contains a searchable database https://anratherlab.shinyapps.io/strokevis/ to allow user-friendly access to our data. The StrokeVis tool constitutes a comprehensive gene expression atlas that can be interrogated at the gene and cell type level to explore the transcriptional changes of endothelial and immune cell subsets from mouse brain and blood after stroke.

Integrating transcriptomic datasets across neurological disease identifies unique myeloid subpopulations driving disease-specific signatures

Microglia and bone marrow-derived monocytes are key elements of central nervous system (CNS) inflammation, both capable of enhancing and dampening immune-mediated pathology. However, the study-specific focus on individual cell types, disease models or experimental approaches has limited our ability to infer common and disease-specific responses. This meta-analysis integrates bulk and single-cell transcriptomic datasets of microglia and monocytes from disease models of autoimmunity, neurodegeneration, sterile injury, and infection to build a comprehensive resource connecting myeloid responses across CNS disease. We demonstrate that the bulk microglial and monocyte program is highly contingent on the disease environment, challenging the notion of a universal microglial disease signature. Integration of six single-cell RNA-sequencing datasets revealed that these disease-specific signatures are likely driven by differing proportions of unique myeloid subpopulations that were individually expanded in different disease settings. These subsets were functionally-defined as neurodegeneration-associated, inflammatory, interferon-responsive, phagocytic, antigen-presenting, and lipopolysaccharide-responsive cellular states, revealing a core set of myeloid responses at the single-cell level that are conserved across CNS pathology. Showcasing the predictive and practical value of this resource, we performed differential expression analysis on microglia and monocytes across disease and identified Cd81 as a new neuroinflammatory-stable gene that accurately identified microglia and distinguished them from monocyte-derived cells across all experimental models at both the bulk and single-cell level. Together, this resource dissects the influence of disease environment on shared immune response programmes to build a unified perspective of myeloid behavior across CNS pathology.

Sodium aescinate inhibits microglia activation through NF-κB pathway and exerts neuroprotective effect

Background: Microglia are resident immune cells of the central nervous system that sense environmental changes and maintain central nervous system homeostasis. Dysfunctional microglia produce toxic mediators that lead to neuronal death. Recent studies suggest that Sodium Aescinate has a neuroprotective effect. However, it is unclear whether Sodium Aescinate exerts neuroprotective effects by inhibiting activation of microglia. Method: Traumatic brain injury and lipopolysaccharide neuroinflammation model were used to evaluate the microglia activation in vivo. BV2 and primary microglia cells were used to assess the microglia activation in vitro. Molecular docking technique was used to predict the binding energy of Sodium Aescinate to NF-κB signaling pathway proteins. Result: Sodium Aescinate inhibited microglial activation in-vivo and in-vitro. Sodium Aescinate inhibited the activation of microglia in Traumatic brain injury and lipopolysaccharide mouse models. Sodium Aescinate also inhibited the expression of inflammatory proteins in BV2 and primary microglia cells. Western blot experiment showed that SA inhibited the activation of NF-κB pathway in BV2 and primary microglia cells. Molecular docking results also showed that Sodium Aescinate had a better affinity with the core protein of the NF-κB pathway. Western blot identified that SA inhibited activation of NF-κB pathway. In Traumatic brain injury model and conditioned medium experiment, Sodium Aescinate pretreatment inhibited inflammation and protected neuron. Conclusion: Our study confirmed that the protection effects of Sodium Aescinate on neurons by inhibiting microglia activation through NF-κB pathway.

Saturated very long-chain fatty acids regulate macrophage plasticity and invasiveness

Saturated very long-chain fatty acids (VLCFA, ≥ C22), enriched in brain myelin and innate immune cells, accumulate in X-linked adrenoleukodystrophy (X-ALD) due to inherited dysfunction of the peroxisomal VLCFA transporter ABCD1. In its severest form, X-ALD causes cerebral myelin destruction with infiltration of pro-inflammatory skewed monocytes/macrophages. How VLCFA levels relate to macrophage activation is unclear. Here, whole transcriptome sequencing of X-ALD macrophages indicated that VLCFAs prime human macrophage membranes for inflammation and increased expression of factors involved in chemotaxis and invasion. When added externally to mimic lipid release in demyelinating X-ALD lesions, VLCFAs did not activate toll-like receptors in primary macrophages. In contrast, VLCFAs provoked pro-inflammatory responses through scavenger receptor CD36-mediated uptake, cumulating in JNK signalling and expression of matrix-degrading enzymes and chemokine release. Following pro-inflammatory LPS activation, VLCFA levels increased also in healthy macrophages. With the onset of the resolution, VLCFAs were rapidly cleared in control macrophages by increased peroxisomal VLCFA degradation through liver-X-receptor mediated upregulation of ABCD1. ABCD1 deficiency impaired VLCFA homeostasis and prolonged pro-inflammatory gene expression upon LPS treatment. Our study uncovers a pivotal role for ABCD1, a protein linked to neuroinflammation, and associated peroxisomal VLCFA degradation in regulating macrophage plasticity.

Transcriptome profiling of osteoclast subsets associated with arthritis: A pathogenic role of CCR2hi osteoclast progenitors

Introduction

The existence of different osteoclast progenitor (OCP) subsets has been confirmed by numerous studies. However, pathological inflammation-induced osteoclastogenesis remains incompletely understood. Detailed characterization of OCP subsets may elucidate the pathophysiology of increased osteoclast activity causing periarticular and systemic bone resorption in arthritis. In our study, we rely on previously defined OCP subsets categorized by the level of CCR2 expression as circulatory-like committed CCR2^hi OCPs, which are substantially expanded in arthritis, and marrow-resident CCR2^lo OCPs of immature phenotype and behavior.

Methods

In order to perform transcriptome characterization of those subsets in the context of collagen-induced arthritis (CIA), we sorted CCR2^hi and CCR2^lo periarticular bone marrow OCPs of control and arthritic mice, and performed next-generation RNA sequencing (n=4 for each group) to evaluate the differential gene expression profile using gene set enrichment analysis with further validation.

Results

A disparity between CCR2^hi and CCR2^lo subset transcriptomes (863 genes) was detected, with the enrichment of pathways for osteoclast differentiation, chemokine and NOD-like receptor signaling in the CCR2^hi OCP subset, and ribosome biogenesis in eukaryotes and ribosome pathways in the CCR2^lo OCP subset. The effect of intervention (CIA) within each subset was greater in CCR2^hi (92 genes) than in CCR2^lo (43 genes) OCPs. Genes associated with the osteoclastogenic pathway (Fcgr1, Socs3), and several genes involved in cell adhesion and migration (F11r, Cd38, Lrg1) identified the CCR2^hi subset and distinguish CIA from control group, as validated by qPCR (n=6 for control mice, n=9 for CIA mice). The latter gene set showed a significant positive correlation with arthritis clinical score and frequency of CCR2^hi OCPs. Protein-level validation by flow cytometry showed increased proportion of OCPs expressing F11r/CD321, CD38 and Lrg1 in CIA, indicating that they could be used as disease markers. Moreover, osteoclast pathway-identifying genes remained similarly expressed (Fcgr1) or even induced by several fold (Socs3) in preosteoclasts differentiated in vitro from CIA mice compared to pre-cultured levels, suggesting their importance for enhanced osteoclastogenesis of the CCR2^hi OCPs in arthritis.

Conclusion

Our approach detected differentially expressed genes that could identify distinct subset of OCPs associated with arthritis as well as indicate possible therapeutic targets aimed to modulate osteoclast activity.

Neuroinflammation Following Traumatic Brain Injury: Take It Seriously or Not

Traumatic brain injury (TBI) is associated with high mortality and disability, with a substantial socioeconomic burden. With the standardization of the treatment process, there is increasing interest in the role that the secondary insult of TBI plays in outcome heterogeneity. The secondary insult is neither detrimental nor beneficial in an absolute sense, among which the inflammatory response was a complex cascade of events and can thus be regarded as a double-edged sword. Therefore, clinicians should take the generation and balance of neuroinflammation following TBI seriously. In this review, we summarize the current human and animal model studies of neuroinflammation and provide a better understanding of the inflammatory response in the different stages of TBI. In particular, advances in neuroinflammation using proteomic and transcriptomic techniques have enabled us to identify a functional specific delineation of the immune cell in TBI patients. Based on recent advances in our understanding of immune cell activation, we present the difference between diffuse axonal injury and focal brain injury. In addition, we give a figurative profiling of the general paradigm in the pre- and post-injury inflammatory settings employing a bow-tie framework.