T cells modulate the microglial response to brain ischemia

Targeting CD74 in microglia to modulate experimental cerebral ischemia and reperfusion injury: insights from Single-Cell and bulk transcriptomics

Ischemic stroke remains a leading cause of mortality and long-term disability, with reperfusion injury contributing significantly to poor clinical outcomes. Microglia, the primary immune cells of the central nervous system, play a dual role in ischemic stroke by both exacerbating injury through neuroinflammation and supporting recovery through neuroprotection. This study aimed to explore the role of CD74, a gene upregulated in microglia following ischemia-reperfusion injury. Using single-cell RNA sequencing and bulk RNA sequencing, we identified CD74 as a potential target involved in microglial-mediated neuroinflammation. We observed a significant increase in CD74 expression in microglia following middle cerebral artery occlusion/reperfusion (MCAO/R), which correlated with pro-inflammatory cytokine production and neuroinflammation. Targeted knockdown of CD74 in microglia using CX3CR1Cre/ERT2 mice led to a reduction in infarct volume, inflammatory cytokine levels, and long-term neurological deficits. Behavioral tests showed improved motor coordination, sensory function, and exploratory behavior in CD74 knockdown mice. These results suggest that CD74 is a critical mediator of microglia-driven neuroinflammation, and targeting CD74 may represent a promising therapeutic strategy for reducing ischemic brain injury and promoting recovery after stroke.

T cell interactions with microglia in immune-inflammatory processes of ischemic stroke

The primary mechanism of secondary injury after cerebral ischemia may be the brain inflammation that emerges after an ischemic stroke, which promotes neuronal death and inhibits nerve tissue regeneration. As the first immune cells to be activated after an ischemic stroke, microglia play an important immunomodulatory role in the progression of the condition. After an ischemic stroke, peripheral blood immune cells (mainly T cells) are recruited to the central nervous system by chemokines secreted by immune cells in the brain, where they interact with central nervous system cells (mainly microglia) to trigger a secondary neuroimmune response. This review summarizes the interactions between T cells and microglia in the immune-inflammatory processes of ischemic stroke. We found that, during ischemic stroke, T cells and microglia demonstrate a more pronounced synergistic effect. Th1, Th17, and M1 microglia can co-secrete pro-inflammatory factors, such as interferon-γ, tumor necrosis factor-α, and interleukin-1β, to promote neuroinflammation and exacerbate brain injury. Th2, Treg, and M2 microglia jointly secrete anti-inflammatory factors, such as interleukin-4, interleukin-10, and transforming growth factor-β, to inhibit the progression of neuroinflammation, as well as growth factors such as brain-derived neurotrophic factor to promote nerve regeneration and repair brain injury. Immune interactions between microglia and T cells influence the direction of the subsequent neuroinflammation, which in turn determines the prognosis of ischemic stroke patients. Clinical trials have been conducted on the ways to modulate the interactions between T cells and microglia toward anti-inflammatory communication using the immunosuppressant fingolimod or overdosing with Treg cells to promote neural tissue repair and reduce the damage caused by ischemic stroke. However, such studies have been relatively infrequent, and clinical experience is still insufficient. In summary, in ischemic stroke, T cell subsets and activated microglia act synergistically to regulate inflammatory progression, mainly by secreting inflammatory factors. In the future, a key research direction for ischemic stroke treatment could be rooted in the enhancement of anti-inflammatory factor secretion by promoting the generation of Th2 and Treg cells, along with the activation of M2-type microglia. These approaches may alleviate neuroinflammation and facilitate the repair of neural tissues.

Neuroinflammation and acute ischemic stroke: impact on translational research and clinical care

Background

Stroke, encompassing both ischemic and hemorrhagic subtypes, is a leading cause of mortality and disability globally and current treatments remain limited. Neuroinflammation plays a crucial role in the pathophysiology of stroke, influencing both acute injury and long-term recovery.

Objective

This review aims to provide a comprehensive overview of neuroinflammation in stroke, detailing the mechanisms, clinical implications, and potential therapeutic strategies.

Methods

A detailed literature review was conducted, focusing on recent advancements in understanding the neuroinflammatory processes in stroke, including the roles of thromboinflammation, blood-brain barrier (BBB) disruption, and the immune response.

Results

The initial ischemic insult triggers an inflammatory cascade involving both innate and adaptive immune responses. BBB disruption allows peripheral immune cells and neurotoxic substances to infiltrate the brain, exacerbating neuronal damage and increasing the risk of infections such as pneumonia and urinary tract infections. Thromboinflammation, characterized by platelet activation and immune cell interactions, further complicates the ischemic environment. Proteomic studies have identified key biomarkers that offer insights into neuroinflammatory mechanisms and potential therapeutic targets. Advances in imaging techniques, such as PET and MRI, enable real-time monitoring of neuroinflammation, facilitating personalized treatment approaches.

Conclusion

Neuroinflammation significantly impacts stroke outcomes, presenting both challenges and opportunities for treatment. Current immunologic therapeutic strategies are limited. Future research should aim to further elucidate the complex immune interactions in stroke, refine imaging biomarkers for clinical use, and develop effective interventions to mitigate neuroinflammation.

Transcriptomics, single-cell sequencing and spatial sequencing-based studies of cerebral ischemia

With high disability and mortality rate as well as highly complex pathogenesis, cerebral ischemia is highly morbid, prone to recurrence. To comprehensively understand the pathophysiological process of cerebral ischemia and to find new therapeutic strategies, a new approach to cerebral ischemia transcriptomics has emerged in recent years. By integrating data from multiple levels of transcriptomics, such as transcriptomics, single-cell transcriptomics, and spatial transcriptomics, this new approach can provide powerful help in revealing the molecular mechanisms of cerebral ischemia occurrence and development. Key findings highlight the critical roles of inflammation, blood-brain barrier dysfunction, and mitochondrial dysregulation in cerebral ischemia, offering potential biomarkers and therapeutic targets for early diagnosis and personalized treatment. A review of the research progress of cerebral ischemic injury mechanism under the analysis of the comprehensive transcriptomics research method was presented in this article, aiming to study the potential mechanism to provide new, innovative therapeutic strategies for this disease.

Heart-brain axis in health and disease: role of innate and adaptive immunity

The importance of the brain-heart interaction has been increasingly recognized as a critical physiological axis that is altered in disease. In this review, we explore the intricate relationship between the central nervous system and cardiovascular health, focusing particularly on immunological mechanisms that influence the course of both neurological and cardiovascular diseases. While previous studies have established a key role of the autonomic nervous system (ANS) in linking brain and the heart, more recent studies have expanded our understanding of the multifaceted inter-organ interactions. As such, circulating mediators include immune cells of the adaptive and innate immune system and their secreted immunogenic factors have come into the focus as mediators along this bidirectional communication. Hence, in this review we briefly discuss the contribution of the ANS and then focus on innate and adaptive immune mechanisms along the heart-to-brain and brain-to-heart axes, illustrating how cardiovascular diseases affect cognitive functions and how brain pathologies lead to cardiac complications.

Profiling X chromosome genes expression relevant to sex dimorphism in stroke: insights from transcriptomics landscape analysis

Introduction

Although age is the most important non-modifiable risk factor for cerebral stroke, it is also apparent that females commonly exhibit longer lifespan and better outcome after stroke compared to the age-matched males. A critical event after stroke is the peripheral infiltration of immune cells across damaged blood-brain barrier, which induces inflammatory and immune responses within the brain parenchyma and consequently worsen brain injury. These events are also dependent on age and display a sex different pattern. Theoretically, X chromosome-encoded differential expression genes (DEGs) may explain differences between the sexes. However, the expression and regulation of these DEGs after stroke have not been studied in detail.

Methods

We conducted three datasets of human blood cells, mice brain, mice microglia and T cells that were previously published, and analyzed the contribution of gender, age and stroke insult on the X chromosome-encoded DEGs.

Results

The main findings were (i) compared to age, the stroke/hypoxia was a more potent factor in eliciting the DEGs. Particularly, older stroke patients exhibited more changes compared to young stroke group. (ii) After a stroke, the DEGs was diversely influenced by sex, age and cell types being studied. Particularly, either aging or gender led to more striking changes in brain-infiltrating T cells than in the resident immune cells.

Discussion

These findings highlight the complex interplay between sex, age, and immune responses in mediating stroke incidence and outcome. Investigation of the identified X chromosome-encoded genes in brain-infiltrating T cells deserves high priority, as they may play more important roles in explaining gender-related differences in stroke and brain injury.

Absence of T-box transcription factor 21 limits neuromuscular junction recovery after nerve injury in T-bet-knockout mice

Introduction

Terminal Schwann cells (tSCs), at the neuromuscular junction (NMJ), play critical roles in the repair of motor axon terminals at muscle, and rebuild neuronal signaling following nerve injury. Knowledge of mediators impacting tSCs post-nerve injury and in disease may guide beneficial therapies to improve motor outcomes. We previously found T-box transcription factor 21 (TBX21/TBET), classically associated with T-helper1 cells and immune cell recruitment, is expressed in tSCs at the mouse NMJ. The purpose of this study was to examine effects of Tbx21 absence during NMJ regeneration following peripheral nerve injury.

Methods

Wildtype (WT) and Tbet-knockout (Tbet-KO) mice underwent sciatic nerve transection and immediate repair. Functional muscle recovery assessment was performed with muscle force testing on mice at 2-, 3-, 4-, and 6-week (wks) and 6 months after nerve injury repair. Morphometric analyses of NMJ reinnervation, tSC number, and tSC processes were evaluated. Full NMJ reinnervation was defined as ≥75% coverage of endplates by axons. A minimum of three mice were evaluated in each group, and 50-100 NMJs were evaluated per mouse.

Results

Tbet-KO mice had significantly diminished muscle function compared to WT mice at every time point beyond 3 weeks. Tbet-KO mice showed just over half of the muscle force generated by WT mice at 4 weeks and 6 weeks post-injury and repair. By 6 months, Tbet-KO mice generated only 84.1% the muscle force of WT mice. Tbet-KO mice showed significantly decreased levels of fully reinnervated NMJs compared to WT mice at each time point tested. Tbet-KO mice also showed a lower number of tSCs with reduced cytoplasmic processes beyond NMJ area and lower number of immune cells during process of NMJ regeneration.

Discussion

Our findings show that the Tbx21 transcription factor promotes NMJ reinnervation to regain muscle function following nerve injury.

Umbilical mesenchymal stem cells mitigate T-cell compartments shift and Th17/Treg imbalance in acute ischemic stroke via mitochondrial transfer

BACKGROUND

Acute ischemic stroke (AIS) initiates secondary injuries that worsen neurological damage and hinder recovery. While peripheral immune responses play a key role in stroke outcomes, clinical results from immunotherapy have been suboptimal, with limited focus on T-cell dynamics. Umbilical mesenchymal stem cells (UMSCs) offer therapeutic potential due to their immunomodulatory properties. They can regulate immune responses and reduce neuroinflammation, potentially enhancing recovery by fostering a pro-regenerative peripheral immune environment. However, the effect of UMSCs on T-cell dynamics in AIS remains underexplored. This study investigates T-cell dynamics following AIS and examines how UMSCs may mitigate immune dysregulation to develop better treatment strategies.

METHODS

AIS patients (NIHSS scores 0-15) were recruited within 72 h of stroke onset, with peripheral blood samples collected on Day 0 (enrollment) and Day 7. T-cell compartments were identified by flow cytometry, and plasma cytokine levels were quantified using a cytometric bead array (CBA). Mitochondria in UMSCs were labeled with MitoTracker. Peripheral blood mononuclear cells from patients were isolated, treated with lipopolysaccharide (LPS), and cocultured with UMSCs in both direct contact and Transwell systems. Flow cytometry, CBA, RT-qPCR, and immunofluorescence assays were used to detect T-cell compartments, gene expression markers for helper T (Th) cell differentiation, cytokine profiles, mitochondrial transfer, reactive oxygen species (ROS) production, and mitochondrial membrane potential. Additionally, mitochondrial DNA in UMSCs was depleted. The effects of UMSCs and mitochondria-depleted UMSCs on ischemic stroke mice were compared through behavioral assessments and analysis of the peripheral immune microenvironment.

RESULTS

In AIS, T-cell compartments underwent a phenotypic shift from naïve to effector or memory states, with a specific increase in Th17 cells and a decrease in regulatory T cells, leading to alterations in T-cell-mediated immune functions. In an ex vivo co-culture system, LPS stimulation further amplified these disparities, inducing mitochondrial dysfunction and oxidative stress in T cells. Notably, UMSCs restored mitochondrial function and reversed the shift in T-cell compartments through mitochondrial transfer. Critically, UMSC treatment significantly improved both neurological deficits and peripheral immune disorders in ischemic stroke mice, whereas mitochondria-depleted UMSCs failed to produce this effect.

CONCLUSIONS

Our comprehensive insights into the key attributes of T-cell compartments in acute ischemic stroke and the immune regulatory mechanisms of UMSCs provide a crucial theoretical foundation for understanding peripheral immune disorders in ischemic stroke and the therapeutic potential of UMSC treatment.

Nasal anti-CD3 monoclonal antibody ameliorates traumatic brain injury, enhances microglial phagocytosis and reduces neuroinflammation via IL-10-dependent Treg-microglia crosstalk

Neuroinflammation plays a crucial role in traumatic brain injury (TBI), contributing to both damage and recovery, yet no effective therapy exists to mitigate central nervous system (CNS) injury and promote recovery after TBI. In the present study, we found that nasal administration of an anti-CD3 monoclonal antibody ameliorated CNS damage and behavioral deficits in a mouse model of contusional TBI. Nasal anti-CD3 induced a population of interleukin (IL)-10-producing regulatory T cells (Treg cells) that migrated to the brain and closely contacted microglia. Treg cells directly reduced chronic microglia inflammation and regulated their phagocytic function in an IL-10-dependent manner. Blocking the IL-10 receptor globally or specifically on microglia in vivo abrogated the beneficial effects of nasal anti-CD3. However, the adoptive transfer of IL-10-producing Treg cells to TBI-injured mice restored these beneficial effects by enhancing microglial phagocytic capacity and reducing microglia-induced neuroinflammation. These findings suggest that nasal anti-CD3 represents a promising new therapeutic approach for treating TBI and potentially other forms of acute brain injury.

Progress of research on short-chain fatty acids, metabolites of gut microbiota, and acute ischemic stroke

Acute ischemic stroke (AIS) significantly impacts the well-being and quality of life of individuals within our population. Short-chain fatty acids (SCFAs), metabolites produced by the intestinal microbiota, are integral to the bidirectional regulatory pathway linking the gut and the brain. SCFAs may significantly influence the risk, prognosis, recurrence, and management of complications associated with AIS. Potential mechanisms underlying these effects include the facilitation of brain-gut barrier repair, the mitigation of oxidative stress, the reduction of neuroinflammatory responses, and the inhibition of autophagy and apoptosis. Consequently, SCFAs hold promise as a prospective target for AIS intervention, with the potential to significantly impact AIS prevention and treatment strategies.

Mechanisms Underlying Vascular Inflammaging: Current Insights and Potential Treatment Approaches

Inflammaging refers to chronic, low-grade inflammation that becomes more common with age and plays a central role in the pathophysiology of various vascular diseases. Key inflammatory mediators involved in inflammaging contribute to endothelial dysfunction and accelerate the progression of atherosclerosis. In addition, specific pathological mechanisms and the role of inflammasomes have emerged as critical drivers of immune responses within the vasculature. A comprehensive understanding of these processes may lead to innovative treatment strategies that could significantly improve the management of age-related vascular diseases. Emerging therapeutic approaches, including cytokine inhibitors, senolytics, and specialized pro-resolving mediators, aim to counteract inflammaging and restore vascular health. This review seeks to provide an in-depth exploration of the molecular pathways underlying vascular inflammaging and highlight potential therapeutic interventions.

Regulatory T Cells for Stroke Recovery: A Promising Immune Therapeutic Strategy

BACKGROUND

Stroke remains a leading cause of mortality and disability among adults. Given the restricted therapeutic window for intravascular interventions and neuroprotection during the acute phase, there has been a growing focus on tissue repair and functional recovery in the subacute and chronic phases after stroke. The pro-inflammatory microglial polarization occurs in subacute and chronic phases after stroke and may represent therapeutic targets for stroke recovery. CD4+ regulatory T cells (Tregs), a subtype of T cells with immunosuppressive effects, have been shown to be important in stroke. Tregs infiltrate into the brain primarily during the subacute and chronic phases following a stroke. Infiltrating Tregs play a critical role in mitigating pro-inflammatory microglial responses, modulating the immune microenvironment, and promoting the functional restoration of the damaged brain following a stroke.

METHODS

A systematic literature search was conducted in PubMed, Scopus, and Web of Science and then conduct a comprehensive analysis of the searched literature.

RESULTS

This review provides a comprehensive summary of recent preclinical research advances on the role of Tregs in stroke, with a particular focus on their reparative functions during the subacute and chronic phases. It discusses changes in peripheral and brain infiltrating Tregs post-stroke, their functions and underlying mechanisms, and therapeutic strategies involving Tregs. Additionally, this review explores the potential and challenges associated with the clinical application of Tregs in ischemic stroke.

CONCLUSION

Treg cell-related therapy represents a promising immune-therapeutic strategy for stroke recovery. However, there are several critical issues that must be resolved before its advancement to clinical application.

Polyphyllin VII ameliorates neuroinflammation and brain injury via modulating Treg/Th17 balance in a mouse model of cerebral ischemia-reperfusion injury

Dysregulation of Th17 and Treg cells contributes to the pathophysiology of cerebral ischemia. Metabolic changes of peripheral CD4+ T cells lead to the imbalance of Treg/Th17 polarization, which represents a promising strategy for post-stroke therapy. Polyphyllin VII (PVII), a steroidal saponin extracted from traditional Chinese herb Rhizoma Paridis, has multiple bioactivities, but the potential function of PVII in cerebral ischemia-reperfusion injury is not elucidated yet. In our study, a mouse transient middle cerebral artery occlusion (MCAO) model was constructed. TTC staining, H&E staining, TUNEL staining, ELISA assay, flow cytometry, western blot, RT-qPCR, Open-field test, Morris water maze test, hanging wire test, rotarod test and foot-fault test were performed to evaluate the potential function of PVII in MCAO mice. We found that PVII showed protective effects on cerebral ischemia-reperfusion injury by reducing infarct volume, ameliorating brain injury and neuroinflammation, and improving long-term functional recovery of MCAO mice. PVII promoted Treg infiltration and suppressed infiltration of Th1/Th17 cells in ischemic brain in vivo. Moreover, PVII impaired peripheral CD4+ T cell activation and modulated Treg/Th17 differentiation in vitro. Mechanistically, PVII suppressed mTORC1 activation to influence glycolytic metabolism and ROS generation of T cells, thus leads to the imbalance of Treg/Th17 polarization towards Treg skewed. Furthermore, reactivation of mTORC1 by MHY1485 abolished the influence of PVII on brain injury and neuroinflammation in MCAO mice. Our data provided a novel role of PVII in cerebral ischemia-reperfusion injury via manipulating Treg/Th17 imbalance.

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.

Emerging roles of astrocytes as immune effectors in the central nervous system

The astrocyte, a major glial cell type in the central nervous system (CNS), is widely regarded as a functionally diverse mediator of homeostasis. During development and throughout adulthood, astrocytes have essential roles, such as providing neuron metabolic support, modulating synaptic function, and maintaining the blood-brain barrier (BBB). Recent evidence continues to underscore their functional heterogeneity and importance for CNS maintenance, as well as how these cells ensure optimal CNS and immune responses to disease, acute trauma, and infection. Advances in our understanding of neuroimmune interactions complement our knowledge of astrocyte functional heterogeneity, where astrocytes are now regarded as key effectors and propagators of immune signaling. This shift in perspective highlights the role of astrocytes not merely as support cells, but as active participants in CNS immune responses.

Central nervous system-associated macrophages modulate the immune response following stroke in aged mice

Age is a major nonmodifiable risk factor for ischemic stroke. Central nervous system-associated macrophages (CAMs) are resident immune cells located along the brain vasculature at the interface between the blood circulation and the parenchyma. By using a clinically relevant thromboembolic stroke model in young and aged male mice and corresponding human tissue samples, we show that during aging, CAMs acquire a central role in orchestrating immune cell trafficking after stroke through the specific modulation of adhesion molecules by endothelial cells. The absence of CAMs provokes increased leukocyte infiltration (neutrophils and CD4+ and CD8+ T lymphocytes) and neurological dysfunction after stroke exclusively in aged mice. Major histocompatibility complex class II, overexpressed by CAMs during aging, plays a significant role in the modulation of immune responses to stroke. We demonstrate that during aging, CAMs become central coordinators of the neuroimmune response that ensure a long-term fine-tuning of the immune responses triggered by stroke.

Changes in Neuroimmunological Synapses During Cerebral Ischemia

The direct interplay between the immune and nervous systems is now well established. Within the brain, these interactions take place between neurons and resident glial cells, i.e., microglia and astrocytes, or infiltrating immune cells, influenced by systemic factors. A special form of physical cell-cell interactions is the so-called "neuroimmunological (NI) synapse." There is compelling evidence that the same signaling pathways that regulate inflammatory responses to injury or ischemia also play potent roles in brain development, plasticity, and function. Proper synaptic wiring is as important during development as it is during disease states, as it is necessary for activity-dependent refinement of neuronal circuits. Since the process of forming synaptic connections in the brain is highly dynamic, with constant changes in strength and connectivity, the immune component is perfectly suited for the regulatory task as it is in constant turnover. Many cellular and molecular players in this interaction remain to be uncovered, especially in pathological states. In this review, we discuss and propose possible communication hubs between components of the adaptive and innate immune systems and the synaptic element in ischemic stroke pathology.

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.

GPR55 Inactivation Diminishes Splenic Responses and Improves Neurological Outcomes in the Mouse Ischemia/Reperfusion Stroke Model

Although strokes are frequent and severe, treatment options are scarce. Plasminogen activators, the only FDA-approved agents for clot treatment (tissue plasminogen activators (tPAs)), are used in a limited patient group. Moreover, there are few approaches for handling the brain's inflammatory reactions to a stroke. The orphan G protein-coupled receptor 55 (GPR55)'s connection to inflammatory processes has been recently reported; however, its role in stroke remains to be discovered. Post-stroke neuroinflammation involves the central nervous system (CNS)'s resident microglia activation and the infiltration of leukocytes from circulation into the brain. Additionally, splenic responses have been shown to be detrimental to stroke recovery. While lymphocytes enter the brain in small numbers, they regularly emerge as a very influential leukocyte subset that causes secondary inflammatory cerebral damage. However, an understanding of how this limited lymphocyte presence profoundly impacts stroke outcomes remains largely unclear. In this study, a mouse model for transient middle cerebral artery occlusion (tMCAO) was used to mimic ischemia followed by a reperfusion (IS/R) stroke. GPR55 inactivation, with a potent GPR55-specific antagonist, ML-193, starting 6 h after tMCAO or the absence of the GPR55 in mice (GPR55 knock out (GPR55ko)) resulted in a reduced infarction volume, improved neurological outcomes, and decreased splenic responses. The inhibition of GPR55 with ML-193 diminished CD4+T-cell spleen egress and attenuated CD4+T-cell brain infiltration. Additionally, ML-193 treatment resulted in an augmented number of regulatory T cells (Tregs) in the brain post-tMCAO. Our report offers documentation and the functional evaluation of GPR55 in the brain-spleen axis and lays the foundation for refining therapeutics for patients after ischemic attacks.

siRNA lipid nanoparticles for CXCL12 silencing modulate brain immune response during Zika infection

CXCL12 is a key chemokine implicated in neuroinflammation, particularly during Zika virus (ZIKV) infection. Specifically, CXCL12 is upregulated in circulating cells of ZIKV infected patients. Here, we developed a lipid nanoparticle (LNP) to deliver siRNA in vivo to assess the impact of CXCL12 silencing in the context of ZIKV infection. The biodistribution of the LNP was assessed in vivo after intravenous injection using fluorescently tagged siRNA. Next, we investigated the ability of the developed LNP to silence CXCL12 in vivo and assessed the resulting effects in a murine model of ZIKV infection. The LNP encapsulating siRNA significantly inhibited CXCL12 levels in the spleen and induced microglial activation in the brain during ZIKV infection. This activation was evidenced by the enhanced expression of iNOS, TNF-α, and CD206 within microglial cells. Moreover, T cell subsets exhibited reduced secretion of IFN-ɣ and IL-17 following LNP treatment. Despite no observable alteration in viral load, CXCL12 silencing led to a significant reduction in type-I interferon production compared to both ZIKV-infected and uninfected groups. Furthermore, we found grip strength deficits in the group treated with siRNA-LNP compared to the other groups. Our data suggest a correlation between the upregulated pro-inflammatory cytokines and the observed decrease in strength. Collectively, our results provide evidence that CXCL12 silencing exerts a regulatory influence on the immune response in the brain during ZIKV infection. In addition, the modulation of T-cell activation following CXCL12 silencing provides valuable insights into potential protective mechanisms against ZIKV, offering novel perspectives for combating this infection.

Integrative Analysis of Machine Learning and Molecule Docking Simulations for Ischemic Stroke Diagnosis and Therapy

Due to the narrow therapeutic window and high mortality of ischemic stroke, it is of great significance to investigate its diagnosis and therapy. We employed weighted gene coexpression network analysis (WGCNA) to ascertain gene modules related to stroke and used the maSigPro R package to seek the time-dependent genes in the progression of stroke. Three machine learning algorithms were further employed to identify the feature genes of stroke. A nomogram model was built and applied to evaluate the stroke patients. We analyzed single-cell RNA sequencing (scRNA-seq) data to discern microglia subclusters in ischemic stroke. The RNA velocity, pseudo time, and gene set enrichment analysis (GSEA) were performed to investigate the relationship of microglia subclusters. Connectivity map (CMap) analysis and molecule docking were used to screen a therapeutic agent for stroke. A nomogram model based on the feature genes showed a clinical net benefit and enabled an accurate evaluation of stroke patients. The RNA velocity and pseudo time analysis showed that microglia subcluster 0 would develop toward subcluster 2 within 24 h from stroke onset. The GSEA showed that the function of microglia subcluster 0 was opposite to that of subcluster 2. AZ_628, which screened from CMap analysis, was found to have lower binding energy with Mmp12, Lgals3, Fam20c, Capg, Pkm2, Sdc4, and Itga5 in microglia subcluster 2 and maybe a therapeutic agent for the poor development of microglia subcluster 2 after stroke. Our study presents a nomogram model for stroke diagnosis and provides a potential molecule agent for stroke therapy.

A tale of two cells: Regulatory T cell-microglia cross-talk in the ischemic brain

Regulatory T cells exert a beneficial immunomodulatory effect on poststroke neuroinflammation that is amplified by microglial cells.

Evolving Clinical-Translational Investigations of Cerebroprotection in Ischemic Stroke

Ischemic stroke is a highly morbid disease, with over 50% of large vessel stroke (middle cerebral artery or internal carotid artery terminus occlusion) patients suffering disability despite maximal acute reperfusion therapy with thrombolysis and thrombectomy. The discovery of the ischemic penumbra in the 1980s laid the foundation for a salvageable territory in ischemic stroke. Since then, the concept of neuroprotection has been a focus of post-stroke care to (1) minimize the conversion from penumbra to core irreversible infarct, (2) limit secondary damage from ischemia-reperfusion injury, inflammation, and excitotoxicity and (3) to encourage tissue repair. However, despite multiple studies, the preclinical-clinical research enterprise has not yet created an agent that mitigates post-stroke outcomes beyond thrombolysis and mechanical clot retrieval. These translational gaps have not deterred the scientific community as agents are under continuous investigation. The NIH has recently promoted the concept of cerebroprotection to consider the whole brain post-stroke rather than just the neurons. This review will briefly outline the translational science of past, current, and emerging breakthroughs in cerebroprotection and use of these foundational ideas to develop a novel paradigm for optimizing stroke outcomes.

Microglial MHC-I induction with aging and Alzheimer's is conserved in mouse models and humans

Major histocompatibility complex I (MHC-I) CNS cellular localization and function is still being determined after previously being thought to be absent from the brain. MHC-I expression has been reported to increase with brain aging in mouse, rat, and human whole tissue analyses, but the cellular localization was undetermined. Neuronal MHC-I is proposed to regulate developmental synapse elimination and tau pathology in Alzheimer's disease (AD). Here, we report that across newly generated and publicly available ribosomal profiling, cell sorting, and single-cell data, microglia are the primary source of classical and non-classical MHC-I in mice and humans. Translating ribosome affinity purification-qPCR analysis of 3-6- and 18-22-month-old (m.o.) mice revealed significant age-related microglial induction of MHC-I pathway genes B2m, H2-D1, H2-K1, H2-M3, H2-Q6, and Tap1 but not in astrocytes and neurons. Across a timecourse (12-23 m.o.), microglial MHC-I gradually increased until 21 m.o. and then accelerated. MHC-I protein was enriched in microglia and increased with aging. Microglial expression, and absence in astrocytes and neurons, of MHC-I-binding leukocyte immunoglobulin-like (Lilrs) and paired immunoglobin-like type 2 (Pilrs) receptor families could enable cell -autonomous MHC-I signaling and increased with aging in mice and humans. Increased microglial MHC-I, Lilrs, and Pilrs were observed in multiple AD mouse models and human AD data across methods and studies. MHC-I expression correlated with p16INK4A, suggesting an association with cellular senescence. Conserved induction of MHC-I, Lilrs, and Pilrs with aging and AD opens the possibility of cell-autonomous MHC-I signaling to regulate microglial reactivation with aging and neurodegeneration.

Assessing the role of T cells in response to retinal injury to uncover new therapeutic targets for the treatment of retinal degeneration

BACKGROUND

Retinal degeneration is a disease affecting the eye, which is an immune-privileged site because of its anatomical and physiological properties. Alterations in retinal homeostasis-because of injury, disease, or aging-initiate inflammatory cascades, where peripheral leukocytes (PL) infiltrate the parenchyma, leading to retinal degeneration. So far, research on PL's role in retinal degeneration was limited to observing a few cell types at specific times or sectioning the tissue. This restricted our understanding of immune cell interactions and response duration.

METHODS

In vivo microscopy in preclinical mouse models can overcome these limitations enabling the spatio-temporal characterization of PL dynamics. Through in vivo imaging, we assessed structural and fluorescence changes in response to a focal injury at a defined location over time. We also utilized minimally invasive techniques, pharmacological interventions, and knockout (KO) mice to determine the role of PL in local inflammation. Furthermore, we investigated PL abundance and localization during retinal degeneration in human eyes by histological analysis to assess to which extent our preclinical study translates to human retinal degeneration.

RESULTS

We demonstrate that PL, especially T cells, play a detrimental role during retinal injury response. In mice, we observed the recruitment of helper and cytotoxic T cells in the parenchyma post-injury, and T cells also resided in the macula and peripheral retina in pathological conditions in humans. Additionally, we found that the pharmacological PL reduction and genetic depletion of T-cells reduced injured areas in murine retinas and rescued the blood-retina barrier (BRB) integrity. Both conditions promoted morphological changes of Cx3cr1+ cells, including microglial cells, toward an amoeboid phenotype during injury response. Interestingly, selective depletion of CD8+ T cells accelerated recovery of the BRB compared to broader depletions. After anti-CD8 treatment, the retinal function improved, concomitant to a beneficial immune response.

CONCLUSIONS

Our data provide novel insights into the adaptive immune response to retinal injury in mice and human retinal degeneration. Such information is fundamental to understanding retinal disorders and developing therapeutics to modulate immune responses to retinal degeneration safely.

Age-dependent immune and lymphatic responses after spinal cord injury

Spinal cord injury (SCI) causes lifelong debilitating conditions. Previous works demonstrated the essential role of the immune system in recovery after SCI. Here, we explored the temporal changes of the response after SCI in young and aged mice in order to characterize multiple immune populations within the mammalian spinal cord. We revealed substantial infiltration of myeloid cells to the spinal cord in young animals, accompanied by changes in the activation state of microglia. In contrast, both processes were blunted in aged mice. Interestingly, we discovered the formation of meningeal lymphatic structures above the lesion site, and their role has not been examined after contusive injury. Our transcriptomic data predicted lymphangiogenic signaling between myeloid cells in the spinal cord and lymphatic endothelial cells (LECs) in the meninges after SCI. Together, our findings delineate how aging affects the immune response following SCI and highlight the participation of the spinal cord meninges in supporting vascular repair.

Sex and interferon gamma signaling regulate microglia migration in the adult mouse cortex in vivo

Although microglia possess the unique ability to migrate, whether mobility is evident in all microglia, is sex dependent, and what molecular mechanisms drive this, is not well understood in the adult brain. Using longitudinal in vivo two-photon imaging of sparsely labeled microglia, we find a relatively small population of microglia (~5%) are mobile under normal conditions. Following injury (microbleed), the fraction of mobile microglia increased in a sex-dependent manner, with male microglia migrating significantly greater distances toward the microbleed relative to their female counterparts. To understand the signaling pathways involved, we interrogated the role of interferon gamma (IFNγ). Our data show that in male mice, stimulating microglia with IFNγ promotes migration whereas inhibiting IFNγ receptor 1 signaling inhibits them. By contrast, female microglia were generally unaffected by these manipulations. These findings highlight the diversity of microglia migratory responses to injury, its dependence on sex and the signaling mechanisms that modulate this behavior.

Microglial MHC-I induction with aging and Alzheimer's is conserved in mouse models and humans

Major Histocompatibility Complex I (MHC-I) CNS cellular localization and function is still being determined after previously being thought to be absent from the brain. MHC-I expression has been reported to increase with brain aging in mouse, rat, and human whole tissue analyses but the cellular localization was undetermined. Neuronal MHC-I is proposed to regulate developmental synapse elimination and tau pathology in Alzheimer's disease (AD). Here we report that across newly generated and publicly available ribosomal profiling, cell sorting, and single-cell data, microglia are the primary source of classical and non-classical MHC-I in mice and humans. Translating Ribosome Affinity Purification-qPCR analysis of 3-6 and 18-22 month old (m.o.) mice revealed significant age-related microglial induction of MHC-I pathway genes B2m , H2-D1 , H2-K1 , H2-M3 , H2-Q6 , and Tap1 but not in astrocytes and neurons. Across a timecourse (12-23 m.o.), microglial MHC-I gradually increased until 21 m.o. and then accelerated. MHC-I protein was enriched in microglia and increased with aging. Microglial expression, and absence in astrocytes and neurons, of MHC-I binding Leukocyte Immunoglobulin-like (Lilrs) and Paired immunoglobin-like type 2 (Pilrs) receptor families could enable cell-autonomous MHC-I signaling and increased with aging in mice and humans. Increased microglial MHC-I, Lilrs, and Pilrs were observed in multiple AD mouse models and human AD data across methods and studies. MHC-I expression correlated with p16INK4A , suggesting an association with cellular senescence. Conserved induction of MHC-I, Lilrs, and Pilrs with aging and AD opens the possibility of cell-autonomous MHC-I signaling to regulate microglial reactivation with aging and neurodegeneration.