The Local and Peripheral Immune Responses to Stroke: Implications for Therapeutic Development

Peripheral inflammation and trajectories of depressive symptomology after ischemic stroke: A prospective cohort study

BACKGROUND

Understanding the association of peripheral inflammation and post-stroke depressive symptomology (PSDS) might provide further insights into the complex etiological mechanism of organic depression. However, studies focusing on the longitudinal patterns of PSDS were limited and it remained unclear whether peripheral inflammation influences the occurrence and development of PSDS.

METHODS

A total of 427 prospectively enrolled and followed ischemic stroke patients were included in the analytical sample. Depressive symptomology was assessed on four occasions during 1 year after ischemic stroke. Peripheral inflammatory proteins on admission and repeated measures of peripheral immune markers in three stages were collected. Latent class growth analysis (LCGA) was employed to delineate group-based trajectories of peripheral immune markers and PSDS. Multinomial regression was performed to investigate the association of peripheral inflammation with PSDS trajectories.

RESULTS

Four distinct trajectories of PSDS were identified: stable-low (n = 237, 55.5 %), high-remitting (n = 120, 28.1 %), late-onset (n = 44, 10.3 %), and high-persistent (n = 26, 6.1 %) PSDS trajectories. The elevation of peripheral fibrinogen on admission increased the risk of high-persistent PSDS in patients with early high PSDS. Additionally, chronic elevation of innate immune levels might not only increase the risk of high-persistent PSDS in patients with early high PSDS but also increase the risk of late-onset PSDS in patients without early high PSDS. The elevation of adaptive immune levels in the convalescence of ischemic stroke may contribute to the remission of early high PSDS.

CONCLUSIONS

Peripheral immunity could influence the development of PSDS, and this influence might have temporal heterogeneity. These results might provide vital clues for the inflammation hypothesis of PSD.

Stem cell therapies for neurological disorders: current progress, challenges, and future perspectives

Stem cell-based therapies have emerged as a promising approach for treating various neurological disorders by harnessing the regenerative potential of stem cells to restore damaged neural tissue and circuitry. This comprehensive review provides an in-depth analysis of the current state of stem cell applications in primary neurological conditions, including Parkinson's disease (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), stroke, spinal cord injury (SCI), and other related disorders. The review begins with a detailed introduction to stem cell biology, discussing the types, sources, and mechanisms of action of stem cells in neurological therapies. It then critically examines the preclinical evidence from animal models and early human trials investigating the safety, feasibility, and efficacy of different stem cell types, such as embryonic stem cells (ESCs), mesenchymal stem cells (MSCs), neural stem cells (NSCs), and induced pluripotent stem cells (iPSCs). While ESCs have been studied extensively in preclinical models, clinical trials have primarily focused on adult stem cells such as MSCs and NSCs, as well as iPSCs and their derivatives. We critically assess the current state of research for each cell type, highlighting their potential applications and limitations in different neurological conditions. The review synthesizes key findings from recent, high-quality studies for each neurological condition, discussing cell manufacturing, delivery methods, and therapeutic outcomes. While the potential of stem cells to replace lost neurons and directly reconstruct neural circuits is highlighted, the review emphasizes the critical role of paracrine and immunomodulatory mechanisms in mediating the therapeutic effects of stem cells in most neurological disorders. The article also explores the challenges and limitations associated with translating stem cell therapies into clinical practice, including issues related to cell sourcing, scalability, safety, and regulatory considerations. Furthermore, it discusses future directions and opportunities for advancing stem cell-based treatments, such as gene editing, biomaterials, personalized iPSC-derived therapies, and novel delivery strategies. The review concludes by emphasizing the transformative potential of stem cell therapies in revolutionizing the treatment of neurological disorders while acknowledging the need for rigorous clinical trials, standardized protocols, and multidisciplinary collaboration to realize their full therapeutic promise.

Low serum alanine aminotransferase (ALT) levels are associated with poor outcomes in acute ischemic stroke patients regardless of age

Studies have indicated that reduced serum ALT levels are commonly linked to aging and are known to predict poor outcomes in many clinical conditions as potential frailty indicators. There are close connections between the brain and peripheral organs, particularly the liver. In patients with acute ischemic stroke (AIS), the interactive effects may change ALT levels, which in turn influence stroke outcomes. Whether ALT has potential neuroprotective effects or is an indicator of frailty in AIS patients remains unknown. This retrospective analysis examined 572 AIS patients in Beijing Luhe Hospital between August 2020 and June 2021. Patient demographics and laboratory results were assembled. The National Institutes of Health Stroke Scale (NIHSS) was used to analyze stroke severity. Modified Rankin Score (mRS) determined stroke outcome 3 months after AIS, with mRS≤2 indicating a favorable outcome. Based on serum ALT measurements, patients were classified into three tertiles (T1-T3). Binary logistic regression analysis evaluated the correlation between ALT tertiles and AIS outcomes. Of the patients, 66 exhibited unfavorable outcomes. The median ALT level in this group was 13 (IQR: 11-18.25), which was lower than in the favorable outcomes cohort (16; IQR: 11-22). A decline in ALT corresponded with a higher incidence of poor outcomes at 3 months (T1, 15.5 %; T2, 11.4 %; T3, 7.0 %; p = 0.03). The lowest ALT tertile (T1) was independently linked to an adverse 3-month outcome (OR 2.50 95 %CI 1.24-5.07, p = 0.038) compared to the highest tertile. ALT levels demonstrated no correlation with age (T1, 62.59 ± 12.64; T2, 64.01 ± 11.47; T3, 65.12 ± 11.27; p > 0.05). Regardless of age, lower serum ALT levels are independently associated with poorer outcomes in AIS patients. This finding suggests the potential pivotal part of the liver in AIS outcomes, highlighting the need to consider both neurological and liver functions post-stroke.

Development and validation of a novel nomogram model predicting the unfavorable outcome based on NAR and collaterals status for patients with AIS

INTRODUCTION

Stroke is a leading cause of disability and mortality globally. This study aimed to develop a prognostic nomogram based on neutrophil-to-albumin ratio (NAR) and collateral status in acute ischemic stroke (AIS) patients with anterior large vessel occlusion (LVO).

MATERIAL & METHOD

590 AIS patients with LVO assessed for regional leptomeningeal collateral (rLMC) were retrospectively enrolled, and randomly divided into a training set (n = 414) and a testing set (n = 176). Unfavorable functional outcome was defined as a modified Rankin scale (mRS) score of 3 to 6 at 3 months. We assessed the accuracy and clinical utility of the nomogram using calibration plots, area under the curve (AUC), decision curve analysis (DCA), net reclassification index (NRI), and integrated discrimination improvement (IDI).

RESULTS

Both NAR and rLMC were independently associated with unfavorable outcome at 3 months (OR=8.96, p=0.0341; OR=0.89, p=0.0002, respectively). The developed nomogram (akaike information criterion (AIC)=398.77), which included NAR, rLMC and other factors, showed good performance (the AUC for the development and validation cohorts was 0.848 and 0.840 respectively) and improved the predictive value compared to a model without NAR and rLMC, according to an overall NRI of 3.27% (p=0.2401), overall IDI of 3.27% (p=0.2414), and a higher AUC (0.848 vs 0.831).

CONCLUSIONS

NAR can serve as an independent predictor in AIS patients with anterior LVO, and the nomogram incorporating NAR and rLMC is reliable in predicting unfavorable outcome. Further studies with larger sample sizes are needed to validate and extend these findings.

MMP-3 Knockout Induces Global Transcriptional Changes and Reduces Cerebral Infarction in Both Male and Female Models of Ischemic Stroke

Ischemic stroke followed by reperfusion (IR) leads to extensive cerebrovascular injury characterized by neuroinflammation and brain cell death. Inhibition of matrix metalloproteinase-3 (MMP-3) emerges as a promising therapeutic approach to mitigate IR-induced stroke injury. We employed middle cerebral artery occlusion with subsequent reperfusion (MCAO/R) to model ischemic stroke in adult mice. Specifically, we investigated the impact of MMP-3 knockout (KO) on stroke pathophysiology using RNA sequencing (RNA-seq) of stroke brains harvested 48 h post-MCAO. MMP-3 KO significantly reduced brain infarct size following stroke. Notably, RNA-seq analysis showed that MMP-3 KO altered expression of 333 genes (252 downregulated) in male stroke brains and 3768 genes (889 downregulated) in female stroke brains. Functional pathway analysis revealed that inflammation, integrin cell surface signaling, endothelial- and epithelial-mesenchymal transition (EndMT/EMT), and apoptosis gene signatures were decreased in MMP-3 KO stroke brains. Intriguingly, MMP-3 KO downregulated gene signatures more profoundly in females than in males, as indicated by greater negative enrichment scores. Our study underscores MMP-3 inhibition as a promising therapeutic strategy, impacting multiple cellular pathways following stroke.

The Role of Aging in Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is the cerebrovascular disease with the highest disability and mortality rates, causing severe damage to the health of patients and imposing a significant socioeconomic burden. Aging stands as a foremost risk factor for ICH, with a significant escalation in ICH incidence within the elderly demographic, highlighting a close association between ICH and aging. In recent years, with the acceleration of the "aging society" trend, exploring the intricate relationship between aging and ICH has become increasingly urgent and worthy of in-depth attention. We have summarized the characteristics of ICH in the elderly, reviewing how aging influences the onset and development of ICH by examining its etiology and the mechanisms of damage via ICH. Additionally, we explored the potential impacts of ICH on accelerated aging, including its effects on cognitive abilities, quality of life, and lifespan. This review aims to reveal the connection between aging and ICH, providing new ideas and insights for future ICH research.

Inhibition of Notch1 signal promotes brain recovery by modulating glial activity after stroke

BACKGROUND

Notch1 signaling inhibiton with N-[N-(3,5-difluorophenacetyl)-1-alanyl]-S-phenylglycine t-butylester] (DAPT) treatment could promote brain recovery and the intervention effect is different between striatum (STR) and cortex (CTX), which might be accounted for different changes of glial activities, but the in-depth mechanism is still unknown. The purpose of this study was to identify whether DAPT could modulate microglial subtype shifts and astroglial-endfeet aquaporin-4 (AQP4) mediated waste solute drainage.

METHODS

Sprague-Dawley rats (n=10) were subjected to 90min of middle cerebral artery occlusion (MCAO) and were treated with DAPT (n=5) or act as control with no treatment (n=5). Two groups of rats underwent MRI scans at 24h and 4 week, and sacrificed at 4 week after stroke for immunofluorescence (IF).

RESULTS

Compared with control rats, MRI data showed structural recovery in ipsilateral STR but not CTX. And IF showed decreased pro-inflammatory M1 microglia and increased anti-inflammatory M2 microglia in striatal lesion core and peri-lesions of STR, CTX. Meanwhile, IF showed decreased AQP4 polarity in ischemic brain tissue, however, AQP4 polarity in striatal peri-lesions of DAPT treated rats was higher than that in control rats but shows no difference in cortical peri-lesions between control and treated rats.

CONCLUSIONS

The present study indicated that DAPT could promote protective microglia subtype shift and striatal astrocyte mediated waste solute drainage, that the later might be the major contributor of waste solute metabolism and one of the accounts for discrepant recovery of STR and CTX.

Repurposing the KCa3.1 Blocker Senicapoc for Ischemic Stroke

Senicapoc, a small molecule inhibitor of the calcium-activated potassium channel KCa3.1, was safe and well-tolerated in clinical trials for sickle cell anemia. We previously reported proof-of-concept data suggesting that both pharmacological inhibition and genetic deletion of KCa3.1 reduces infarction and improves neurologic recovery in rodents by attenuating neuroinflammation. Here we evaluated the potential of repurposing senicapoc for ischemic stroke. In cultured microglia, senicapoc inhibited KCa3.1 currents with an IC50 of 7 nM, reduced Ca2+ signaling induced by the purinergic agonist ATP, suppressed expression of pro-inflammatory cytokines and enzymes (iNOS and COX-2), and prevented induction of the inflammasome component NLRP3. When transient middle cerebral artery occlusion (tMCAO, 60 min) was induced in male C57BL/6 J mice, twice daily administration of senicapoc at 10 and 40 mg/kg starting 12 h after reperfusion dose-dependently reduced infarct area determined by T2-weighted magnetic resonance imaging (MRI) and improved neurological deficit on day 8. Ultra-high-performance liquid chromatography/mass spectrometry analysis of total and free brain concentrations demonstrated sufficient KCa3.1 target engagement. Senicapoc treatment significantly reduced microglia/macrophage and T cell infiltration and activation and attenuated neuronal death. A different treatment paradigm with senicapoc started at 3 h and MRI on day 3 and day 8 revealed that senicapoc reduces secondary infarct growth and suppresses expression of inflammation markers, including T cell cytokines in the brain. Lastly, we demonstrated that senicapoc does not impair the proteolytic activity of tissue plasminogen activator (tPA) in vitro. We suggest that senicapoc could be repurposed as an adjunctive immunocytoprotective agent for combination with reperfusion therapy for ischemic stroke.

Human monocyte subtype expression of neuroinflammation and regeneration-related genes is linked to age and sex

Stroke is a leading cause of disability and the third cause of death. The immune system plays an essential role in post-stroke recovery. After an ischemic stroke, monocytes infiltrate the injured brain tissue and can exacerbate or mitigate the damage. Ischemic stroke is more prevalent in the aged population, and the aging brain exhibits an altered immune response. There are also sex disparities in ischemic stroke incidence, outcomes, and recovery, and these differences may be hormone-driven and determined by genetic and epigenetic factors. Here, we studied whether human peripheral blood monocyte subtype (classical, intermediate, and non-classical) expression of neuronal inflammation- and regeneration-related genes depends on age and sex. A FACS analysis of blood samples from 44 volunteers (male and female, aged 28 to 98) showed that in contrast to other immune cells, the proportion of natural killer cells increased in females. The proportion of B-cells decreased in both sexes with age, and subtypes of monocytes were not linked to age or sex. Gene expression analysis by qPCR identified several genes differentially correlating with age and sex within different monocyte subtypes. Interestingly, ANXA1 and CD36 showed a consistent increase with aging in all monocytes, specifically in intermediate (CD36) and intermediate and non-classical (ANXA1) subtypes. Other genes (IL-1β, S100A8, TNFα, CD64, CD33, TGFβ1, TLR8, CD91) were differentially changed in monocyte subtypes with increased aging. Most age-dependent gene changes were differentially expressed in female monocytes. Our data shed light on the nuanced interplay of age and sex in shaping the expression of inflammation- and regeneration-related genes within distinct monocyte subtypes. Understanding these dynamics could pave the way for targeted interventions and personalized approaches in post-stroke care, particularly for the aging population and individuals of different sexes.

Immune regulation of the gut-brain axis and lung-brain axis involved in ischemic stroke

Local ischemia often causes a series of inflammatory reactions when both brain immune cells and the peripheral immune response are activated. In the human body, the gut and lung are regarded as the key reactional targets that are initiated by brain ischemic attacks. Mucosal microorganisms play an important role in immune regulation and metabolism and affect blood-brain barrier permeability. In addition to the relationship between peripheral organs and central areas and the intestine and lung also interact among each other. Here, we review the molecular and cellular immune mechanisms involved in the pathways of inflammation across the gut-brain axis and lung-brain axis. We found that abnormal intestinal flora, the intestinal microenvironment, lung infection, chronic diseases, and mechanical ventilation can worsen the outcome of ischemic stroke. This review also introduces the influence of the brain on the gut and lungs after stroke, highlighting the bidirectional feedback effect among the gut, lungs, and brain.

Intruders or protectors - the multifaceted role of B cells in CNS disorders

B lymphocytes are immune cells studied predominantly in the context of peripheral humoral immune responses against pathogens. Evidence has been accumulating in recent years on the diversity of immunomodulatory functions that B cells undertake, with particular relevance for pathologies of the central nervous system (CNS). This review summarizes current knowledge on B cell populations, localization, infiltration mechanisms, and function in the CNS and associated tissues. Acute and chronic neurodegenerative pathologies are examined in order to explore the complex, and sometimes conflicting, effects that B cells can have in each context, with implications for disease progression and treatment outcomes. Additional factors such as aging modulate the proportions and function of B cell subpopulations over time and are also discussed in the context of neuroinflammatory response and disease susceptibility. A better understanding of the multifactorial role of B cell populations in the CNS may ultimately lead to innovative therapeutic strategies for a variety of neurological conditions.

Ginkgo biloba extract promotes Treg differentiation to ameliorate ischemic stroke via inhibition of HIF-1α/HK2 pathway

The ischemic brain can dialogue with peripheral tissues through the immune system. Ginkgo biloba extract (EGb) was used to regulate various neurological disorders; however, the impact of EGb on ischemic stroke is still unclear. Here, we aimed to investigate whether immunomodulation has participated in the beneficial effects of EGb on ischemia/reperfusion (I/R) brain injury. Mice were orally administered with EGb once daily for 7 days before the induction of I/R. Neurobehavioral scores, infarct volume, and brain inflammation were determined. The proportion of CD4+ T cells was detected by flow cytometry. EGb significantly lowered neurobehavioral scores, infarct volume, and the level of inflammatory cytokines in I/R mice. Interestingly, EGb altered the proportion of CD4+ T cells, particularly increasing the proportion of Treg cells. Depletion of Treg cells weakened the neuroprotective effects of EGb on ischemic stroke; furthermore, EGb decreased the expression of HIF-1α and HK2 and promoted the differentiation of Treg cells in vitro. EGb suppressed the HIF-1α/HK2 signaling pathway to promote the differentiation of Treg cells and ameliorate ischemic stroke in mice. The expansion effect of EGb on Treg cells could be exploited as part of future stroke therapy.

Effects of admission systemic inflammatory indicators on clinical outcomes in patients with vertebrobasilar artery occlusion: insight from the PERSIST registry

BACKGROUND

Few studies have focused on the effect of systemic inflammation in vertebrobasilar artery occlusion (VBAO). The aim of this study was to investigate the relationship between inflammatory indicators and the prognosis of VBAO patients receiving endovascular treatment (EVT).

METHOD

Patients with VBAO who were treated with EVT within 24 hours of the estimated occlusion time were included in this study. Multivariate logistic regression and elastic net regularization were performed to analyze the effects of inflammatory indicators on the prognosis of patients with VBAO. The primary outcome was unfavorable outcome (a modified Rankin Scale score of 4-6) at 90 days. Secondary outcomes included symptomatic intracranial hemorrhage, in-hospital mortality, 90 day mortality, 1 year unfavorable outcome, and mortality.

RESULTS

560 patients were included in the study. Multivariate analysis showed that white blood cells (W), neutrophils (N), neutrophil to lymphocyte ratio (NLR), platelet to neutrophil ratio, platelet to white blood cell ratio, and NLR to platelet ratio were associated with the primary outcome. Elastic net regularization indicated that W, N, and NLR were the major inflammatory predictors of unfavorable outcome at 90 days. For long term prognosis, we found that the inflammatory indicators that predicted 1 year outcomes were consistent with those that predicted 90 day outcomes.

CONCLUSION

Inflammatory indicators, especially W, N, and NLR, were associated with moderate and long term prognosis of patients with VBAO treated with EVT.

RIPK1 and RIPK3 inhibitors: potential weapons against inflammation to treat diabetic complications

Diabetes mellitus is a metabolic disease that is characterized by chronic hyperglycemia due to a variety of etiological factors. Long-term metabolic stress induces harmful inflammation leading to chronic complications, mainly diabetic ophthalmopathy, diabetic cardiovascular complications and diabetic nephropathy. With diabetes complications being one of the leading causes of disability and death, the use of anti-inflammatories in combination therapy for diabetes is increasing. There has been increasing interest in targeting significant regulators of the inflammatory pathway, notably receptor-interacting serine/threonine-kinase-1 (RIPK1) and receptor-interacting serine/threonine-kinase-3 (RIPK3), as drug targets for managing inflammation in treating diabetes complications. In this review, we aim to provide an up-to-date summary of current research on the mechanism of action and drug development of RIPK1 and RIPK3, which are pivotal in chronic inflammation and immunity, in relation to diabetic complications which may be benefit for explicating the potential of selective RIPK1 and RIPK3 inhibitors as anti-inflammatory therapeutic agents for diabetic complications.

Clinical Potential of Immunotherapies in Subarachnoid Hemorrhage Treatment: Mechanistic Dissection of Innate and Adaptive Immune Responses

Subarachnoid hemorrhage (SAH), classified as a medical emergency, is a devastating and severe subtype of stroke. SAH induces an immune response, which further triggers brain injury; however, the underlying mechanisms need to be further elucidated. The current research is predominantly focused on the production of specific subtypes of immune cells, especially innate immune cells, post-SAH onset. Increasing evidence suggests the critical role of immune responses in SAH pathophysiology; however, studies on the role and clinical significance of adaptive immunity post-SAH are limited. In this present study, we briefly review the mechanistic dissection of innate and adaptive immune responses post-SAH. Additionally, we summarized the experimental studies and clinical trials of immunotherapies for SAH treatment, which may form the basis for the development of improved therapeutic approaches for the clinical management of SAH in the future.

Smart Liposomal Nanocarrier Enhanced the Treatment of Ischemic Stroke through Neutrophil Extracellular Traps and Cyclic Guanosine Monophosphate-Adenosine Monophosphate Synthase-Stimulator of Interferon Genes (cGAS-STING) Pathway Inhibition of Ischemic Penumbra

Brain inflammation is regarded as one of the leading causes that aggravates secondary brain injury and hinders the prognosis of ischemic stroke. After ischemic stroke, high quantities of peripheral neutrophils are recruited to brain lesions and release neutrophil extracellular traps (NETs), leading to the aggravation of blood-brain barrier (BBB) damage, activation of microglia, and ultimate neuronal death. Herein, a smart multifunctional delivery system has been developed to regulate immune disorders in the ischemic brain. Briefly, Cl-amidine, an inhibitor of peptidylarginine deiminase 4 (PAD4), is encapsulated into self-assembled liposomal nanocarriers (C-Lipo/CA) that are modified by reactive oxygen species (ROS)-responsive polymers and fibrin-binding peptide to achieve targeting ischemic lesions and stimuli-responsive release of a drug. In the mouse model of cerebral artery occlusion/reperfusion (MCAO), C-Lipo/CA can suppress the NETs release process (NETosis) and further inhibit the cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon genes (cGAS-STING) pathway in an ischemic brain. In addition, MCAO mice treated with C-Lipo/CA significantly mitigated ischemic and reperfusion injury, with a reduction in the area of cerebral infarction to 12.1%, compared with the saline group of about 46.7%. These results demonstrated that C-Lipo/CA, which integrated microglia regulation, BBB protection, and neuron survival, exerts a potential therapy strategy to maximize ameliorating the mortality of ischemic stroke.

Neuroimmune Support of Neuronal Regeneration and Neuroplasticity following Cerebral Ischemia in Juvenile Mice

Ischemic damage to the brain and loss of neurons contribute to functional disabilities in many stroke survivors. Recovery of neuroplasticity is critical to restoration of function and improved quality of life. Stroke and neurological deficits occur in both adults and children, and yet it is well documented that the developing brain has remarkable plasticity which promotes increased post-ischemic functional recovery compared with adults. However, the mechanisms underlying post-stroke recovery in the young brain have not been fully explored. We observed opposing responses to experimental cerebral ischemia in juvenile and adult mice, with substantial neural regeneration and enhanced neuroplasticity detected in the juvenile brain that was not found in adults. We demonstrate strikingly different stroke-induced neuroimmune responses that are deleterious in adults and protective in juveniles, supporting neural regeneration and plasticity. Understanding age-related differences in neuronal repair and regeneration, restoration of neural network function, and neuroimmune signaling in the stroke-injured brain may offer new insights for the development of novel therapeutic strategies for stroke rehabilitation.

Therapeutic application of regeneration-associated cells: a novel source of regenerative medicine

Chronic diseases with comorbidities or associated risk factors may impair the function of regenerative cells and the regenerative microenvironment. Following this consideration, the vasculogenic conditioning culture (VCC) method was developed to boost the regenerative microenvironment to achieve regeneration-associated cells (RACs), which contain vasculogenic endothelial progenitor cells (EPCs) and anti-inflammatory/anti-immunity cells. Preclinical and clinical studies demonstrate that RAC transplantation is a safe and convenient cell population for promoting ischemic tissue recovery based on its strong vasculogenicity and functionality. The outputs of the scientific reports reviewed in the present study shed light on the fact that RAC transplantation is efficient in curing various diseases. Here, we compactly highlight the universal features of RACs and the latest progress in their translation toward clinics.

Preceding transient ischemic attack was associated with functional outcome after stroke thrombectomy: A propensity score matching study

Whether preceding transient ischemic attack (TIA) can provide neuroprotective benefits in subsequent acute ischemic stroke (AIS) caused by large vessel occlusion remains unclarified. This study aimed to investigate the association between preceding TIA and functional outcomes in AIS patients with endovascular therapy (EVT). Eligible patients were divided into TIA and non-TIA groups according to whether they experienced TIA within 96 hours prior to stroke. Two groups were balanced using propensity score matching (PSM) analysis at a 1:3 ratio. Onset stroke severity and 3-month functional independence were evaluated. A total of 887 patients were included. After PSM, 73 patients with and 217 patients without preceding TIA were well matched. Onset stroke severity was not different between the groups (p > 0.05). However, the TIA group had a lower systemic immune-inflammation index (SII) (median, 1091 versus 1358, p < 0.05). Preceding TIA was significantly associated with 3-month functional independence (adjusted odds ratio, 2.852; 95% confidence interval [CI], 1.481-5.495; adjusted p < 0.01). The effects of preceding TIA on functional independence were partially mediated by SII (average causal mediation effects 0.02; 95% CI, 0.001-0.06, p < 0.05). In AIS patients treated by EVT, preceding TIA within 96 hours was associated with three-month functional independence but not with reduced onset stroke severity.

The central role of peripheral inflammation in ischemic stroke

Stroke pathology and its treatments conventionally focus on the brain. Probing inflammation, a critical secondary cell death mechanism in stroke, has been largely relegated to the brain. To this end, peripheral inflammation has emerged as an equally potent contributor to the onset and progression of stroke secondary cell death. Here, we review novel concepts on peripheral organs displaying robust inflammatory response to stroke. These inflammation-plagued organs include the spleen, cervical lymph nodes, thymus, bone marrow, gastrointestinal system, and adrenal glands, likely converging their inflammatory effects through B and T-cells. Recognizing the significant impact of this systemic inflammation, we also discuss innovative stroke therapeutics directed at sequestration of peripheral inflammation. This review paper challenges the paradigm of a brain-centered disease pathology and treatment and offers a peripheral approach to our stroke understanding.

Inflammation and immunomodulation in central nervous system injury - B cells as a novel therapeutic opportunity

Acute injury to the central nervous system (CNS) remains a complex and challenging clinical need. CNS injury initiates a dynamic neuroinflammatory response, mediated by both resident and infiltrating immune cells. Following the primary injury, dysregulated inflammatory cascades have been implicated in sustaining a pro-inflammatory microenvironment, driving secondary neurodegeneration and the development of lasting neurological dysfunction. Due to the multifaceted nature of CNS injury, clinically effective therapies for conditions such as traumatic brain injury (TBI), spinal cord injury (SCI), and stroke have proven challenging to develop. No therapeutics that adequately address the chronic inflammatory component of secondary CNS injury are currently available. Recently, B lymphocytes have gained increasing appreciation for their role in maintaining immune homeostasis and regulating inflammatory responses in the context of tissue injury. Here we review the neuroinflammatory response to CNS injury with particular focus on the underexplored role of B cells and summarize recent results on the use of purified B lymphocytes as a novel immunomodulatory therapeutic for tissue injury, particularly in the CNS.

The bidirectional lung brain-axis of amyloid-β pathology: ozone dysregulates the peri-plaque microenvironment

The mechanisms underlying how urban air pollution affects Alzheimer's disease (AD) are largely unknown. Ozone (O3) is a reactive gas component of air pollution linked to increased AD risk, but is confined to the respiratory tract after inhalation, implicating the peripheral immune response to air pollution in AD neuropathology. Here, we demonstrate that O3 exposure impaired the ability of microglia, the brain's parenchymal immune cells, to associate with and form a protective barrier around Aβ plaques, leading to augmented dystrophic neurites and increased Aβ plaque load. Spatial proteomic profiling analysis of peri-plaque proteins revealed a microenvironment-specific signature of dysregulated disease-associated microglia protein expression and increased pathogenic molecule levels with O3 exposure. Unexpectedly, 5xFAD mice exhibited an augmented pulmonary cell and humoral immune response to O3, supporting that ongoing neuropathology may regulate the peripheral O3 response. Circulating HMGB1 was one factor upregulated in only 5xFAD mice, and peripheral HMGB1 was separately shown to regulate brain Trem2 mRNA expression. These findings demonstrate a bidirectional lung-brain axis regulating the central and peripheral AD immune response and highlight this interaction as a potential novel therapeutic target in AD.

Monocyte, neutrophil, and whole blood transcriptome dynamics following ischemic stroke

BACKGROUND

After ischemic stroke (IS), peripheral leukocytes infiltrate the damaged region and modulate the response to injury. Peripheral blood cells display distinctive gene expression signatures post-IS and these transcriptional programs reflect changes in immune responses to IS. Dissecting the temporal dynamics of gene expression after IS improves our understanding of immune and clotting responses at the molecular and cellular level that are involved in acute brain injury and may assist with time-targeted, cell-specific therapy.

METHODS

The transcriptomic profiles from peripheral monocytes, neutrophils, and whole blood from 38 ischemic stroke patients and 18 controls were analyzed with RNA-seq as a function of time and etiology after stroke. Differential expression analyses were performed at 0-24 h, 24-48 h, and >48 h following stroke.

RESULTS

Unique patterns of temporal gene expression and pathways were distinguished for monocytes, neutrophils, and whole blood with enrichment of interleukin signaling pathways for different time points and stroke etiologies. Compared to control subjects, gene expression was generally upregulated in neutrophils and generally downregulated in monocytes over all times for cardioembolic, large vessel, and small vessel strokes. Self-organizing maps identified gene clusters with similar trajectories of gene expression over time for different stroke causes and sample types. Weighted Gene Co-expression Network Analyses identified modules of co-expressed genes that significantly varied with time after stroke and included hub genes of immunoglobulin genes in whole blood.

CONCLUSIONS

Altogether, the identified genes and pathways are critical for understanding how the immune and clotting systems change over time after stroke. This study identifies potential time- and cell-specific biomarkers and treatment targets.

Clinical experience: Outcomes of mesenchymal stem cell transplantation in five stroke patients

Stem cell therapy, which has promising results in acute disorders such as stroke, supports treatment by providing rehabilitation in the chronic stage patients. In acute stroke, thrombolytic medical treatment protocols are clearly defined in neurologic emergencies, but in neurologic patients who miss the "thrombolytic treatment intervention window," or in cases of hypoxic-ischemic encephalopathy, our hands are tied, and we are still unfortunately faced with hopeless clinical implementations. We consider mesenchymal stem cell therapy a viable option in these cases. In recent years, novel research has focused on neuro-stimulants and supportive and combined therapies for stroke. Currently, available treatment options are limited, and only certain patients are eligible for acute treatment. In the scope of our experience, five stroke patients were evaluated in this study, who was treated with a single dose of 1-2 × 10⁶ cells/kg allogenic umbilical cord-mesenchymal stem cells (UC-MSCs) with the official confirmation of the Turkish Ministry of Health Stem Cell Commission. The patients were followed up for 12 months, and clinical outcomes are recorded. NIH Stroke Scale/Scores (NIHSS) decreased significantly (p = 0.0310), and the Rivermead Assessment Scale (RMA) increased significantly (p = 0.0234) for all patients at the end of the follow-up. All the patients were followed up for 1 year within a rehabilitation program. Major clinical outcome improvements were observed in the overall clinical conditions of the UC-MSC treatment patients. We observed improvement in the patients' upper extremity and muscle strength, spasticity, and fine motor functions. Considering recent studies in the literature together with our results, allogenic stem cell therapies are introduced as promising novel therapies in terms of their encouraging effects on physiological motor outcomes.

Integrated bioinformatics and machine-learning screening for immune-related genes in diagnosing non-alcoholic fatty liver disease with ischemic stroke and RRS1 pan-cancer analysis

Background

The occurrence of ischemic stroke (IS) is associated with nonalcoholic fatty liver disease (NAFLD). The cancer burden of NAFLD complicated by IS also warrants attention. This study aimed to identify candidate immune biomarkers linked to NAFLD and IS and analyze their association with cancer.

Methods

Two of each of the NAFLD and IS datasets were downloaded, differentially expressed genes (DEGs) were identified, and module genes were screened via weighted gene coexpression network analysis (WGCNA). Subsequently, utilizing machine learning (least absolute shrinkage and selection operator regression, random forest and support vector machine-recursive feature elimination) and immune cell infiltration analysis, immune-related candidate biomarkers for NAFLD with IS were determined. Simultaneously, a nomogram was established, the diagnostic efficacy was assessed, and the role of candidate biomarkers in cancer was ascertained through pan-cancer analyses.

Results

In this study, 117 and 98 DEGs were identified from the combined NAFLD and IS datasets, respectively, and 279 genes were obtained from the most significant modules of NAFLD. NAFLD module genes and IS DEGs were intersected to obtain nine genes, which were enriched in the inflammatory response and immune regulation. After overlapping the results of the three machine learning algorithms, six candidate genes were obtained, based on which a nomogram was constructed. The calibration curve demonstrated good accuracy, and the candidate genes had high diagnostic values. The genes were found to be related to the immune dysregulation of stroke, and RRS1 was strongly associated with the prognosis, immune cell infiltration, microsatellite instability (MSI), and tumor mutation burden (TMB).

Conclusion

Six common candidate immune-related genes (PTGS2, FCGR1A, MMP9, VNN3, S100A12, and RRS1) of NAFLD and IS were identified, and a nomogram for diagnosing NAFLD with IS was established. RRS1 may serve as a candidate gene for predicting the prognosis of patients with cancer who have NAFLD complicated by IS, which could aid in their diagnosis and treatment.

Immunologic Implications for Stroke Recovery: Unveiling the Role of the Immune System in Pathogenesis, Neurorepair, and Rehabilitation

Stroke is a debilitating neurologic condition characterized by an interruption or complete blockage of blood flow to certain areas of the brain. While the primary injury occurs at the time of the initial ischemic event or hemorrhage, secondary injury mechanisms contribute to neuroinflammation, disruption of the blood-brain barrier (BBB), excitotoxicity, and cerebral edema in the days and hours after stroke. Of these secondary mechanisms of injury, significant dysregulation of various immune populations within the body plays a crucial role in exacerbating brain damage after stroke. Pathological activity of glial cells, infiltrating leukocytes, and the adaptive immune system promote neuroinflammation, BBB damage, and neuronal death. Chronic immune activation can additionally encourage the development of neurologic deficits, immunosuppression, and dysregulation of the gut microbiome. As such, immunotherapy has emerged as a promising strategy for the clinical management of stroke in a highly patient-specific manner. These strategies include regulatory T cells (Tregs), cell adhesion molecules, cytokines, and monoclonal antibodies. However, the use of immunotherapy for stroke remains largely in the early stages, highlighting the need for continued research efforts before widespread clinical use.

Serum Bilirubin Associated with Stroke Severity and Prognosis: Preliminary Findings on Liver Function after Acute Ischemic Stroke

OBJECTIVE

This study investigates relationships between serum bilirubin, stroke severity, and prognosis of patients with acute ischemic stroke (AIS) to elucidate the roles of the liver in AIS.

METHODS

This retrospective study collected data from 527 patients diagnosed with AIS within 24 hours after their symptom onset. Stroke severity was assessed using the National Institutes of Health Stroke Scale (NIHSS). Mild stroke was defined as NIHSS≤5. Prognosis was assessed with modified Rankin Scale (mRS) on 90 days after AIS and good prognosis was defined as mRS≤2. The patients were divided based on their total bilirubin (Tbil) and direct bilirubin (Dbil) levels to study these serum markers' association with the severity of stroke. Tbil levels were measured and compared with mRS on 90 days to analyze prognosis of mild stroke patients.

RESULTS

Both Tbil abnormal (NIHSS = 6.8 ± 5.3) and Dbil abnormal groups (NIHSS = 7.3 ± 5.7) had higher NIHSS scores on admission than the normal groups (p< 0.05 or p< 0.01, respectively). Severity of stroke at discharge was similar between these groups (p = 0.025 and 0.019, respectively). Serum bilirubin levels were independently associated with stroke severity on admission and discharge after risk factors were adjusted (p< 0.001 and p< 0.05, respectively; β (95%CI) were 0.116 (0.064-0.167) and 0.058 (0.012-0.103), respectively). The average Tbil levels of mild stroke with good prognosis was 15.1 ± 6.4umol/l versus 11.8 ± 3.1umol/l with poor prognosis; this difference was statistically significant (p = 0.003). The same difference was observed with Dtil levels but it did not reach a significant level.

CONCLUSION

High Tbil and Dbil level within 48 hours of symptom onset could be an independent marker of severity of stroke on admission and discharge for all AIS patients. For patient with mild stroke, elevation of bilirubin after AIS suggests a good prognosis. These findings imply that the liver play the key roles in the mechanism of AIS.

Low Lymphocyte-to-Monocyte Ratio as a Possible Predictor of an Unfavourable Clinical Outcome in Patients with Acute Ischemic Stroke after Mechanical Thrombectomy

Background. Although considerable progress has been made in the treatment of acute ischemic stroke (AIS), the clinical outcome of patients is still significantly influenced by the inflammatory response that follows stroke-induced brain injury. The aim of this study was to evaluate the potential use of complete blood count parameters, including indices and ratios, for predicting the clinical outcome in AIS patients undergoing mechanical thrombectomy (MT). Methods. This single-centre retrospective study is consisted of 179 patients. Patient data including demographic characteristics, risk factors, clinical data, laboratory parameters on admission, and clinical outcome were collected. Based on the clinical outcome assessed at 3 months after MT by the modified Rankin Scale (mRS), patients were divided into two groups: the favourable group (mRS 0–2) and unfavourable group (mRS 3–6). Stepwise multivariate logistic regression analysis was used to detect an independent predictor of the unfavourable clinical outcome. Results. An unfavourable clinical outcome was detected after 3 months in 101 patients (54.4%). Multivariate logistic regression analysis confirmed that the lymphocyte-to-monocyte ratio (LMR) was an independent predictor of unfavourable clinical outcome at 3 months ( $\text{odds}\text{ratio}=0.761$ , 95% confidence interval 0.625–0.928, and $P=0.007$ ). The value of 3.27 was chosen to be the optimal cut-off value of LMR. This value could predict the unfavourable clinical outcome with a 74.0% sensitivity and a 54.4% specificity. Conclusion. The LMR at the time of hospital admission is a predictor of an unfavourable clinical outcome at 3 months in AIS patients after MT.

Expression pattern and clinical value of Key RNA methylation modification regulators in ischemic stroke

Ischemic stroke (IS) is one of the major causes of death and disability worldwide, and effective diagnosis and treatment methods are lacking. RNA methylation, a common epigenetic modification, plays an important role in disease progression. However, little is known about the role of RNA methylation modification in the regulation of IS. The aim of this study was to investigate RNA methylation modification patterns and immune infiltration characteristics in IS through bioinformatics analysis. We downloaded gene expression profiles of control and IS model rat brain tissues from the Gene Expression Omnibus database. IS profiles were divided into two subtypes based on RNA methylation regulators, and functional enrichment analyses were conducted to determine the differentially expressed genes (DEGs) between the subtypes. Weighted gene co-expression network analysis was used to explore co-expression modules and genes based on DEGs. The IS clinical diagnosis model was successfully constructed and four IS characteristic genes (GFAP, GPNMB, FKBP9, and CHMP5) were identified, which were significantly upregulated in IS samples. Characteristic genes were verified by receiver operating characteristic curve and real-time quantitative PCR analyses. The correlation between characteristic genes and infiltrating immune cells was determined by correlation analysis. Furthermore, GPNMB was screened using the protein-protein interaction network, and its regulatory network and the potential therapeutic drug chloroquine were predicted. Our finding describes the expression pattern and clinical value of key RNA methylation modification regulators in IS and novel diagnostic and therapeutic targets of IS from a new perspective.

Role of alarmins in poststroke inflammation and neuronal repair

Severe loss of cerebral blood flow causes hypoxia and glucose deprivation in the brain tissue, resulting in necrotic cell death in the ischemic brain. Several endogenous molecules, called alarmins or damage-associated molecular patterns (DAMPs), are extracellularly released from the dead cells to activate pattern recognition receptors (PRRs) in immune cells that infiltrate into ischemic brain tissue following the disruption of the blood-brain barrier (BBB) after stroke onset. The activated immune cells produce various inflammatory cytokines and chemokines, triggering sterile cerebral inflammation in the ischemic brain that causes further neuronal cell death. Poststroke inflammation is resolved within several days after stroke onset, and neurological functions are restored to some extent as neural repair occurs around peri-infarct neurons. Clearance of DAMPs from the injured brain is necessary for the resolution of poststroke inflammation. Neurons and glial cells also express PRRs and receive DAMP signaling. Although the role of PRRs in neural cells in the ischemic brain has not yet been clarified, the signaling pathway is likely to be contribute to stroke pathology and neural repair after ischemic stroke. This review describes the molecular dynamics, signaling pathways, and functions of DAMPs in poststroke inflammation and its resolution.

Microglial phagocytosis and regulatory mechanisms after stroke

Stroke, including ischemic stroke and hemorrhagic stroke can cause massive neuronal death and disruption of brain structure, which is followed by secondary inflammatory injury initiated by pro-inflammatory molecules and cellular debris. Phagocytic clearance of cellular debris by microglia, the brain's scavenger cells, is pivotal for neuroinflammation resolution and neurorestoration. However, microglia can also exacerbate neuronal loss by phagocytosing stressed-but-viable neurons in the penumbra, thereby expanding the injury area and hindering neurofunctional recovery. Microglia constantly patrol the central nervous system using their processes to scour the cellular environment and start or cease the phagocytosis progress depending on the "eat me" or "don't eat me'' signals on cellular surface. An optimal immune response requires a delicate balance between different phenotypic states to regulate neuro-inflammation and facilitate reconstruction after stroke. Here, we examine the literature and discuss the molecular mechanisms and cellular pathways regulating microglial phagocytosis, their resulting effects in brain injury and neural regeneration, as well as the potential therapeutic targets that might modulate microglial phagocytic activity to improve neurological function after stroke.

Experimental verification and validation of immune biomarkers based on chromatin regulators in ischemic stroke

Ischemic stroke (IS) is a disease characterized by rapid progression and high mortality and disability rates. Its pathophysiological process is inseparable from immune dysfunction. Recently, chromatin regulators (CRs) have been described as a class of enzymes that can recognize, form, and maintain the epigenetic state of an organism, and are closely associated with immune regulation. Nevertheless, the role of CR-related genes in IS has not been fully elucidated. In this study, seven CR-related immune biomarkers in the GSE58294 and GSE22255 datasets were identified by combining differential gene expression analysis, weighted correlation network analysis, and single sample gene set enrichment analysis. After experimental validation using quantitative polymerase chain reaction, four genes (DPF2, LMNB1, MLLT3, and JAK2) were screened as candidate immune biomarkers. These four biomarkers demonstrated good predictive power in the clinical risk model (area under the curve, 0.775). Molecular docking simulations revealed that mevastatin, WP1066, cladribine, trichostatin A, mequitazine, and zuclomiphene may be potential immunomodulatory drugs for IS. Overall, the results of this study contribute to the identification of CR-related immune therapeutics target in IS and provide an important reference for further research.

MicroRNA-193a-5p Rescues Ischemic Cerebral Injury by Restoring N2-Like Neutrophil Subsets

Circulating neutrophils are activated shortly after stroke and in turn affect the fate of ischemic brain tissue, and microRNAs (miRNA) participate in regulating neuroinflammation. We probed the role of neutrophilic miRNA in ischemic stroke. miR-193a-5p was decreased in circulating neutrophils of acute ischemic stroke (AIS) patients and healthy controls. In another set of AIS patients treated with recombinant tissue plasminogen activator, higher neutrophilic miR-193a-5p levels were associated with favorable outcomes at 3 months and non-symptomatic intracerebral hemorrhage. An experimental stroke model and human neutrophil-like HL-60 cells were further transfected with agomiR-193a-5p/antagomiR-193a-5p or ubiquitin-conjugating enzyme V2 (UBE2V2)-siRNA prior to model induction for in vivo and in vitro studies. Results of 2,3,5-triphenyl tetrazolium chloride staining and neurological function evaluations at post-experimental stroke showed that intravenous agomiR-193a-5p transfusion protected against ischemic cerebral injury in the acute stage and promoted neurological recovery in the subacute stage. This protective role was suggested to correlate with neutrophil N2 transformation based on the N2-like neutrophil proportions in the bone marrow, peripheral blood, and spleen of the experimental stroke model and the measurement of neutrophil phenotype-associated molecule levels. Mechanistically, analyses indicated that UBE2V2 might be a target of miR-193a-5p. Cerebral injury and neuroinflammation aggravated by miR-193a-5p inhibition were reversed by UBE2V2 silencing. In conclusion, miR-193a-5p protects against cerebral ischemic injury by restoring neutrophil N2 phenotype-associated neuroinflammation suppression, likely, in part, via UBE2V2 induction.

Interactions between the Autonomic Nervous System and the Immune System after Stroke

Acute stroke is one of the leading causes of morbidity and mortality worldwide. Stroke-induced immune-inflammatory response occurs in the perilesion areas and the periphery. Although stroke-induced immunosuppression may alleviate brain injury, it hinders brain repair as the immune-inflammatory response plays a bidirectional role after acute stroke. Furthermore, suppression of the systemic immune-inflammatory response increases the risk of life-threatening systemic bacterial infections after acute stroke. Therefore, it is essential to explore the mechanisms that underlie the stroke-induced immune-inflammatory response. Autonomic nervous system (ANS) activation is critical for regulating the local and systemic immune-inflammatory responses and may influence the prognosis of acute stroke. We review the changes in the sympathetic and parasympathetic nervous systems and their influence on the immune-inflammatory response after stroke. Importantly, this article summarizes the mechanisms on how ANS regulates the immune-inflammatory response through neurotransmitters and their receptors in immunocytes and immune organs after stroke. To facilitate translational research, we also discuss the promising therapeutic approaches modulating the activation of the ANS or the immune-inflammatory response to promote neurologic recovery after stroke. © 2022 American Physiological Society. Compr Physiol 12:3665-3704, 2022.

Phagocytic microglia and macrophages in brain injury and repair

AIMS

Phagocytosis is the cellular digestion of extracellular particles, such as pathogens and dying cells, and is a key element in the evolution of central nervous system (CNS) disorders. Microglia and macrophages are the professional phagocytes of the CNS. By clearing toxic cellular debris and reshaping the extracellular matrix, microglia/macrophages help pilot the brain repair and functional recovery process. However, CNS resident and invading immune cells can also magnify tissue damage by igniting runaway inflammation and phagocytosing stressed-but viable-neurons.

DISCUSSION

Microglia/macrophages help mediate intercellular communication and react quickly to the "find-me" signals expressed by dead/dying neurons. The activated microglia/macrophages then migrate to the injury site to initiate the phagocytic process upon encountering "eat-me" signals on the surfaces of endangered cells. Thus, healthy cells attempt to avoid inappropriate engulfment by expressing "do not-eat-me" signals. Microglia/macrophages also have the capacity to phagocytose immune cells that invade the injured brain (e.g., neutrophils) and to regulate their pro-inflammatory properties. During brain recovery, microglia/macrophages engulf myelin debris, initiate synaptogenesis and neurogenesis, and sculpt a favorable extracellular matrix to support network rewiring, among other favorable roles. Here, we review the multilayered nature of phagocytotic microglia/macrophages, including the molecular and cellular mechanisms that govern microglia/macrophage-induced phagocytosis in acute brain injury, and discuss strategies that tap into the therapeutic potential of this engulfment process.

CONCLUSION

Identification of biological targets that can temper neuroinflammation after brain injury without hindering the essential phagocytic functions of microglia/macrophages will expedite better medical management of the stroke recovery stage.

Immune Pathways in Etiology, Acute Phase, and Chronic Sequelae of Ischemic Stroke

Inflammation and immune mechanisms are crucially involved in the pathophysiology of the development, acute damage cascades, and chronic course after ischemic stroke. Atherosclerosis is an inflammatory disease, and, in addition to classical risk factors, maladaptive immune mechanisms lead to an increased risk of stroke. Accordingly, individuals with signs of inflammation or corresponding biomarkers have an increased risk of stroke. Anti-inflammatory drugs, such as IL (interleukin)-1β blockers, methotrexate, or colchicine, represent attractive treatment strategies to prevent vascular events and stroke. Lately, the COVID-19 pandemic shows a clear association between SARS-CoV2 infections and increased risk of cerebrovascular events. Furthermore, mechanisms of both innate and adaptive immune systems influence cerebral damage cascades after ischemic stroke. Neutrophils, monocytes, and microglia, as well as T and B lymphocytes each play complex interdependent roles that synergize to remove dead tissue but also can cause bystander injury to intact brain cells and generate maladaptive chronic inflammation. Chronic systemic inflammation and comorbid infections may unfavorably influence both outcome after stroke and recurrence risk for further stroke. In addition, stroke triggers specific immune depression, which in turn can promote infections. Recent research is now increasingly addressing the question of the extent to which immune mechanisms may influence long-term outcome after stroke and, in particular, cause specific complications such as poststroke dementia or even poststroke depression.

Single-cell transcriptomic analysis of the immune cell landscape in the aged mouse brain after ischemic stroke

Background

Ischemic stroke is a medical emergency that primarily affects the elderly. A complex immune response in the post-stroke brain constitutes a key component of stroke pathophysiology. This study aimed to determine how stroke affects immune cell populations in the aged brain based on molecular profiles of individual cells.

Methods

Single-cell RNA sequencing and a new transient ischemic stroke mouse model with late reperfusion were used.

Results

We generated, for the first time, a composite picture of immune cell populations in the stroke aged brain at single-cell resolution. We discovered at least 6 microglial subsets in the stroke aged brain, including a potentially stroke-specific subtype. Moreover, we identified major cell subpopulations formed by infiltrated myeloid cells after stroke, and revealed their unique molecular profiles.

Conclusions

This study provided the first scRNA-seq data set for immune cells in the stroke aged brain, and offered novel insights into post-stroke immune cell heterogeneity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02447-5.

A Nomogram That Includes Neutrophils and High-Density Lipoprotein Cholesterol Can Predict the Prognosis of Acute Ischaemic Stroke

Lipids are implicated in inflammatory responses affecting acute ischaemic stroke prognosis. Therefore, we aimed to develop a predictive model that considers neutrophils and high-density lipoprotein cholesterol to predict its prognosis. This prospective study enrolled patients with acute ischaemic stroke within 24 h of onset between January 2015 and December 2017. The main outcome was a modified Rankin Scale score ≥3 at the 90th day of follow-up. Patients were divided into training and testing sets. The training set was divided into four states according to the median of neutrophils and high-density lipoprotein cholesterol levels in all patients. Through binary logistic regression analysis, the relationship between factors and prognosis was determined. A nomogram based on the results was developed; its predictive value was evaluated through internal and external validations. Altogether, 1,090 patients were enrolled with 872 (80%) and 218 (20%) in the training and testing sets, respectively. In the training set, the major outcomes occurred in 24 (10.4%), 24 (11.6%), 37 (17.2%), and 49 (22.3%) in states 1–4, respectively (P = 0.002). Validation of calibration and decision curve analyses showed that the nomogram showed better performance. The internal and external testing set receiver operating characteristics verified the predictive value [area under the curve = 0.794 (0.753–0.834), P &lt; 0.001, and area under the curve = 0.973 (0.954–0.992), P &lt; 0.001, respectively]. A nomogram that includes neutrophils and high-density lipoprotein cholesterol can predict the prognosis of acute ischaemic stroke, thus providing us with an effective visualization tool.

TRIM45 causes neuronal damage by aggravating microglia-mediated neuroinflammation upon cerebral ischemia and reperfusion injury

Excessive and unresolved neuroinflammation is a key component of the pathological cascade in brain injuries such as ischemic stroke. Tripartite motif-containing 45 (TRIM45) is a ubiquitin E3 ligase involved in various critical biological processes. However, the role of TRIM45 in cerebral ischemia remains unknown. Here, we found that the TRIM45 protein was highly expressed in the peri-infarct areas of mice subjected to cerebral ischemia and reperfusion injury induced by middle cerebral artery occlusion. This study systemically evaluated the putative role of TRIM45 in the regulation of neuroinflammation during ischemic injury and the potential underlying mechanisms. We found that TRIM45 knockdown significantly decreased proinflammatory cytokine and chemokine production in primary cultured microglia challenged with oxygen-glucose deprivation and reoxygenation (OGD/R) treatment. Mechanistically, we demonstrated that TRIM45 constitutively interacted with TAB2 and consequently facilitated the Lys-63-linked polyubiquitination of TAB2, leading to the formation of the TAB1-TAK1-TAB2 complex and activation of TAK1, which was ultimately followed by activation of the nuclear factor-kappa B (NF-κB) signaling pathway. In an in vitro coculture Transwell system, downregulation of TRIM45 expression also inhibited the OGD/R-induced activation of microglia and alleviated neuronal apoptosis. More importantly, microglia-specific knockdown of TRIM45 in mice significantly reduced the infarct size, mitigated neurological deficit scores, and improved cognitive function after ischemic stroke. Taken together, our study reveals that the TRIM45-TAB2 axis is a crucial checkpoint that controls NF-κB signaling in microglia during cerebral ischemia and reperfusion injury. Therefore, targeting TRIM45 may be an attractive therapeutic strategy.

Comprehensive Landscape of Immune Infiltration and Aberrant Pathway Activation in Ischemic Stroke

Ischemic stroke (IS) is a multifactorial disease caused by the interaction of multiple environmental and genetic risk factors, and it is the most common cause of disability. The immune microenvironment and inflammatory response participate in the whole process of IS occurrence and development. Therefore, the rational use of relevant markers or characteristic pathways in the immune microenvironment will become one of the important therapeutic strategies for the treatment of IS. We collected peripheral blood samples from 10 patients diagnosed with IS at the First Affiliated Hospital of Gannan Medical University and First Affiliated Hospital, Jinan" University, and from 10 normal people. The GSE16561 dataset was downloaded from the Gene Expression Omnibus (GEO) database. xCell, gene set enrichment analysis (GSEA), single-sample GSEA (ssGSEA) and immune-related gene analysis were used to evaluate the differences in the immune microenvironment and characteristic pathways between the IS and control groups of the two datasets. xCell analysis showed that the IS-24h group had significantly reduced central memory CD8+ T cell, effector memory CD8+ T cell, B cell and Th1 cell scores and significantly increased M1 macrophage and macrophage scores. GSEA showed that the IS-24h group had significantly increased inflammation-related pathway activity(myeloid leukocyte activation, positive regulation of tumor necrosis factor biosynthetic process, myeloid leukocyte migration and leukocyte chemotaxis), platelet-related pathway activity(platelet activation, signaling and aggregation; protein polymerization; platelet degranulation; cell-cell contact zone) and pathology-related pathway activity (ERBB signaling pathway, positive regulation of ERK1 and ERK2 cascade, vascular endothelial growth factor receptor signaling pathway, and regulation of MAP kinase activity). Immune-related signature analysis showed that the macrophage signature, antigen presentation-related signature, cytotoxicity-related signature, B cell-related signature and inflammation-related signature were significantly lower in the IS-24h group than in the control group. In this study, we found that there were significant differences in the immune microenvironment between the peripheral blood of IS patients and control patients, as shown by the IS group having significantly reduced CD8+ Tcm, CD8+ Tem, B cell and Th1 cell scores and significantly increased macrophage and M1 macrophage scores. Additionally, inflammation-related, pathological, and platelet-related pathway activities were significantly higher in the IS group than in the control group.

Age-related immune alterations and cerebrovascular inflammation

Aging is associated with chronic systemic inflammation, which contributes to the development of many age-related diseases, including vascular disease. The world's population is aging, leading to an increasing prevalence of both stroke and vascular dementia. The inflammatory response to ischemic stroke is critical to both stroke pathophysiology and recovery. Age is a predictor of poor outcomes after stroke. The immune response to stroke is altered in aged individuals, which contributes to the disparate outcomes between young and aged patients. In this review, we describe the current knowledge of the effects of aging on the immune system and the cerebral vasculature and how these changes alter the immune response to stroke and vascular dementia in animal and human studies. Potential implications of these age-related immune alterations on chronic inflammation in vascular disease outcome are highlighted.

Cell Heterogeneity Uncovered by Single-Cell RNA Sequencing Offers Potential Therapeutic Targets for Ischemic Stroke

Ischemic stroke is a detrimental neurological disease characterized by an irreversible infarct core surrounded by an ischemic penumbra, a salvageable region of brain tissue. Unique roles of distinct brain cell subpopulations within the neurovascular unit and peripheral immune cells during ischemic stroke remain elusive due to the heterogeneity of cells in the brain. Single-cell RNA sequencing (scRNA-seq) allows for an unbiased determination of cellular heterogeneity at high-resolution and identification of cell markers, thereby unveiling the principal brain clusters within the cell-type-specific gene expression patterns as well as cell-specific subclusters and their functions in different pathways underlying ischemic stroke. In this review, we have summarized the changes in differentiation trajectories of distinct cell types and highlighted the specific pathways and genes in brain cells that are impacted by stroke. This review is expected to inspire new research and provide directions for investigating the potential pathological mechanisms and novel treatment strategies for ischemic stroke at the level of a single cell.

Pertussis toxin-induced inflammatory response exacerbates intracerebral haemorrhage and ischaemic stroke in mice

Background

Stroke is a devastating disease, including intracerebral haemorrhage (ICH) and ischaemic stroke. Emerging evidences indicate that systemic inflammatory cascades after stroke contribute to brain damage. However, the direct effects and features of systemic inflammation on brain injury, especially comparing between ischaemic and haemorrhagic stroke, are still obscure.

Methods

Pertussis toxin (PT) was used to build a pro-inflammatory milieu after ICH and ischaemic stroke in mouse model. The neurodeficits, stroke lesion, immune response and blood–brain barrier (BBB) destruction were assessed.

Results

In ICH mouse model, PT-induced systemic inflammation exacerbated neurological deficits, and enlarged haemorrhage lesion and perihaematomal oedema. We also found promoted leucocyte infiltration and inflammatory cytokine release into the brain after PT treatment. Moreover, the integrity of the BBB was further disrupted after receiving PT. Furthermore, we demonstrated that PT enhanced brain inflammation and aggravated stroke severity in middle cerebral artery occlusion mouse model.

Conclusions

Our results suggest that PT increases inflammatory response that exacerbates brain injury after ICH or ischaemic stroke in mouse model.

Prognostic Value of Abnormal Liver Function Tests After Mechanical Thrombectomy for Acute Ischemic Stroke

Objective: To determine the clinical significance of post-procedural abnormal liver function test (ALFT) on the functional outcomes at 90 days in acute ischemic stroke (AIS) treated with mechanical thrombectomy (MT).

Methods: In this retrospective observational study, patients with AIS undergoing MT were enrolled from the Nanjing Stroke Registry Program and the multicenter Captor trial. A favorable outcome was defined as a modified Rankin Scale score 0–2 at 90 days. Predictive models were established by multivariable logistic regression. Improved predictive value of models was assessed by continuous net reclassification improvement (NRI) and integrated discrimination improvement (IDI). In addition, multivariable logistic regression and restricted cubic spline were used to analyze dose–response correlations between the severity of ALFT and prognosis.

Results: Among 420 patients enrolled, 234 (55.7%) patients were diagnosed as post-procedural ALFT after MT. Patients with post-procedural ALFT had higher National Institute of Health Stroke Scale score on admission (median, 18 vs. 15, p < 0.001) and more pneumonia (65.4 vs. 38.2%, p < 0.001) than those without post-procedural ALFT. Post-procedural ALFT, rather than preprocedural ALFT, was independently associated with favorable outcome (adjusted odds ratio, 0.48; 95% CI 0.28–0.81; p = 0.006). The improvement of predictive model after adding post-procedural ALFT was significant [continuous NRI (value, 0.401; p < 0.001), IDI (value, 0.013; p < 0.001)]. However, the restricted cubic spline indicated no evidence of a dose–response relationship between the severity of post-procedural ALFT and prognosis.

Conclusions: In AIS patients treated by MT, post-procedural ALFT was associated with more severe stroke and served as an independent predictor of worse prognosis at 90 days.

T cells direct microglial repair of white matter after stroke

A recent paper by Shi et al. defines the role of regulatory T cells (Tregs) in white matter recovery after ischemic stroke. This study elucidates the mechanisms by which Tregs direct microglia to alter their phenotype to support oligodendrogenesis, thereby improving white matter integrity and functional recovery after stroke in mice.

The Role of the Blood Neutrophil-to-Lymphocyte Ratio in Aneurysmal Subarachnoid Hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is an important type of stroke with the highest rates of mortality and disability. Recent evidence indicates that neuroinflammation plays a critical role in both early brain injury and delayed neural deterioration after aSAH, contributing to unfavorable outcomes. The neutrophil-to-lymphocyte ratio (NLR) is a peripheral biomarker that conveys information about the inflammatory burden in terms of both innate and adaptive immunity. This review summarizes relevant studies that associate the NLR with aSAH to evaluate whether the NLR can predict outcomes and serve as an effective biomarker for clinical management. We found that increased NLR is valuable in predicting the clinical outcome of aSAH patients and is related to the risk of complications such as delayed cerebral ischemia (DCI) or rebleeding. Combined with other indicators, the NLR provides improved accuracy for predicting prognosis to stratify patients into different risk categories. The underlying pathophysiology is highlighted to identify new potential targets for neuroprotection and to develop novel therapeutic strategies.

Downregulation of CD151 restricts VCAM-1 mediated leukocyte infiltration to reduce neurobiological injuries after experimental stroke

Background

Translational failures in anti-adhesion molecule therapies after stroke reveal the necessity of developing new strategies that not only interrupt leukocyte recruitment but also consider the inhibition of endothelial cell inflammation, verification of therapeutic time window, and normal function maintenance of circulating leukocytes. Our study focused on the potential therapeutic value of CD151 downregulation in improving current anti-adhesion molecule therapies.

Methods

Lentivirus intracerebroventricular administration was conducted to inhibit the CD151 expression and observe its functional influence on neurological injuries and outcomes. Then, immunohistochemistry and myeloperoxidase activity assessment were performed to explore the effects of CD151 expression on neutrophil and monocyte recruitment after rat cerebral ischemia. Primary rat brain microvascular endothelial cells were subjected to oxygen glucose deprivation and reoxygenation to elucidate the underlying working mechanisms between CD151 and VCAM-1.

Results

The CD151 downregulation remarkably reduced neurological injuries and improved neurological outcomes, which were accompanied with reduced neutrophil and monocyte infiltration after the CD151 downregulation. The VCAM-1 expression was remarkably decreased among the adhesion molecules on the endothelial cell responsible for neutrophil and monocyte infiltration. The activation of p38 MAPK and NF-κB pathways was restricted after the CD151 downregulation. p38 MAPK and NF-κB inhibitors decreased the VCAM-1 expression, and p38 acted as an upstream regulator of NF-κB. However, CD151 downregulation did not directly influence the neutrophil and monocyte activation.

Conclusions

Overall, CD151 regulated the expression of adhesion molecules. It also played a critical role in suppressing VCAM-1-mediated neutrophil and monocyte infiltration via the p38/NF-κB pathway. This study possibly provided a new basis for improving current anti-adhesion molecule therapies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02171-6.

Embryonic Stem Cell Derived Small Extracellular Vesicles Modulate Regulatory T Cells to Protect against Ischemic Stroke

Stem cell derived small extracellular vesicles (sEVs) have been proved to promote neurological recovery after stroke. Recent studies demonstrate a phenomenal tissue repair ability in embryonic stem cell derived sEVs (ESC-sEVs). However, whether ESC-sEVs could protect against ischemic stroke remains unknown. Immune responses play an essential role in the pathogenesis of ischemic stroke, and modulating post-stroke immune responses ameliorates ischemia-induced brain damage. In this study, we aim to determine the therapeutic function of ESC-sEVs, specifically focusing on their role in immunomodulation after ischemic stroke. ESC-sEVs are intravenously administered after transient middle cerebral artery occlusion. ESC-sEVs significantly decrease leukocyte infiltration, inflammatory cytokine expression, neuronal death, and infarct volume and alleviate long-term neurological deficits and tissue loss after ischemic stroke. Interestingly, ESC-sEVs induce a marked increase in regulatory T cells (Tregs) after stroke. Further, ESC-sEV-afforded immunomodulatory function and neuroprotection against stroke are dependent on Tregs, as the depletion of Tregs almost completely abrogates the protective effects. Mechanistically, proteomic analysis reveals the enrichment of TGF-β, Smad2, and Smad4 proteins in ESC-sEVs, which could be delivered to activate the TGF-β/Smad pathway in CD4⁺ T cells and therefore induce Treg expansion. ESC-sEVs modulate neuroinflammation and protect against ischemic stroke through the expansion of Tregs, a process that is partially dependent on the activation of the TGF-β/Smad signaling pathway by the transfer of TGF-β, Smad2, and Smad4. The results suggest ESC-sEVs might be a candidate for immune modulation.

Role of B cells and the aging brain in stroke recovery and treatment

As mitigation of brain aging continues to be a key public health priority, a wholistic and comprehensive consideration of the aging body has identified immunosenescence as a potential contributor to age-related brain injury and disease. Importantly, the nervous and immune systems engage in bidirectional communication and can exert profound influence on each other. Emerging evidence supports numerous impacts of innate, inflammatory immune responses and adaptive T cell-mediated immunity in neurological function and diseased or injured brain states, such as stroke. Indeed, a growing body of evidence supports key impacts of brain-resident immune cell activation and peripheral immune infiltration in both the post-stroke acute injury phase and the long-term recovery period. As such, modulation of the immune system is an attractive strategy for novel therapeutic interventions for a devastating age-related brain injury for which there are few readily available neuroprotective treatments or neurorestorative approaches. However, the role of B cells in the context of brain function, and specifically in response to stroke, has not been thoroughly elucidated and remains controversial, leaving our understanding of neuroimmune interactions incomplete. Importantly, emerging evidence suggests that B cells are not pathogenic contributors to stroke injury, and in fact may facilitate functional recovery, supporting their potential value as novel therapeutic targets. By summarizing the current knowledge of the role of B cells in stroke pathology and recovery and interpreting their role in the context of their interactions with other immune cells as well as the immunosenescence cascades that alter their function in aged populations, this review supports an increased understanding of the complex interplay between the nervous and immune systems in the context of brain aging, injury, and disease.