Dynamic roles of neutrophils in post-stroke neuroinflammation

St3gal5-mediated sialylation of glyco-CD177 on neutrophils restricts neuroinflammation following CNS injury

Neutrophils are the most abundant circulating leukocyte population that play critical roles in neuroinflammation following central nervous system (CNS) injury. CD177, a glycoprotein on neutrophils, is emerging as an important immune regulator which can fundamentally affect multiple human inflammatory diseases. However, the role and regulatory mechanism of CD177 glycobiology of neutrophils in neuroinflammation remain elusive. Here, we show that CD177+ neutrophils expand significantly and infiltrate the injured brain following CNS injury both in the human and mouse. Using single-cell RNA sequencing and genetic approaches, we find CD177+ neutrophils as an anti-inflammatory subset that is critical for modulating neuroinflammation after CNS injury. We further identify St3gal5, a sialyltransferase (ST), that can mediate the sialylation and cell surface presentation of glyco-CD177 on neutrophils. Glycoproteomics reveal downregulated sialylation levels in St3gal5-deficient neutrophils. Neutrophil-specific depletion of St3gal5 prevents the cell surface presentation of CD177 on brain-infiltrated neutrophils and exacerbates neuroinflammation. Administration of the FDA-approved anticonvulsant valproic acid (VPA), an St3gal5 upregulator, promotes the glycosylation of neutrophils and attenuates neuroinflammation following CNS injury. Our study reveals a glycoimmuno-regulatory effect of neutrophils and suggests VPA as a neutrophil glycobiology targeting approach to combat neuroinflammation following CNS injury.

Remote Organ Damage Induced by Stroke: Molecular Mechanisms and Comprehensive Interventions

Significance: Damage after stroke is not only limited to the brain but also often occurs in remote organs, including the heart, lung, liver, kidney, digestive tract, and spleen, which are frequently affected by complex pathophysiological changes. The organs in the human body are closely connected, and signals transmitted through various molecular substances could regulate the pathophysiological changes of remote organs. Recent Advances: The latest studies have shown that inflammatory response plays an important role in remote organ damage after stroke, and can aggravate remote organ damage by activating oxidative stress, sympathetic axis, and hypothalamic axis, and disturbing immunological homeostasis. Remote organ damage can also cause damage to the brain, aggravating inflammatory response and oxidative damage. Critical Issues: Therefore, an in-depth exploration of inflammatory and oxidative mechanisms and adopting corresponding comprehensive intervention strategies have become necessary to reduce damage to remote organs and promote brain protection. Future Directions: The comprehensive intervention strategy involves multifaceted treatment methods such as inflammation regulation, antioxidants, and neural stem cell differentiation. It provides a promising treatment alternative for the comprehensive recovery of stroke patients and an inspiration for future research and treatment. The various organs of the human body are interconnected at the molecular level. Only through comprehensive intervention at the molecular and organ levels can we save remote organ damage and protect the brain after stroke to the greatest extent. Antioxid. Redox Signal. 00, 000-000.

Targeting HPK1 inhibits neutrophil responses to mitigate post-stroke lung and cerebral injuries

Circulating neutrophils are responsible for poor neurological outcomes and have been implicated in respiratory morbidity after acute ischemic stroke (AIS). However, the molecular mechanisms regulating neutrophil responses and their pathological relevance in post-stroke complications remain unclear. In this study, we investigated the involvement of hematopoietic progenitor kinase 1 (HPK1) in neutrophil responses and mobilization, as well as subsequent lung and cerebral injuries following AIS. We found that lipopolysaccharide treatment triggered neutrophil activation in an HPK1-dependent manner. HPK1 enhanced intrinsic NF-κB/STAT3/p38-MAPK pathways and gasdermin D cleavage, leading to neutrophil hyperactivation. Following AIS, HPK1 promoted the mobilization of CXCR2high bone marrow neutrophils. HPK1 loss inhibited peripheral neutrophil hyperactivation, neutrophil infiltration, and aggregation of neutrophil extracellular traps, progressively alleviating systemic inflammation and impairments in mouse pulmonary and neurological functions. Furthermore, HPK1 pharmacological inhibition attenuated post-stroke pulmonary and neurological impairments in mice. Our findings revealed that HPK1 upregulates neutrophil mobilization and various responses, promoting post-stroke systemic inflammation and tissue injury. This study highlights HPK1 as a therapeutic target for improving pulmonary and neurological functions after AIS.

Mechanism of inflammatory response and therapeutic effects of stem cells in ischemic stroke: current evidence and future perspectives

Ischemic stroke is a leading cause of death and disability worldwide, with an increasing trend and tendency for onset at a younger age. China, in particular, bears a high burden of stroke cases. In recent years, the inflammatory response after stroke has become a research hotspot: understanding the role of inflammatory response in tissue damage and repair following ischemic stroke is an important direction for its treatment. This review summarizes several major cells involved in the inflammatory response following ischemic stroke, including microglia, neutrophils, monocytes, lymphocytes, and astrocytes. Additionally, we have also highlighted the recent progress in various treatments for ischemic stroke, particularly in the field of stem cell therapy. Overall, understanding the complex interactions between inflammation and ischemic stroke can provide valuable insights for developing treatment strategies and improving patient outcomes. Stem cell therapy may potentially become an important component of ischemic stroke treatment.

Maresin-like 1 Ameliorates Neuropathology of Alzheimer's Disease in Brains of a Transgenic Mouse Model

(1) Background: Impeded resolution of inflammation contributes substantially to the pathogenesis of Alzheimer's disease (AD); consequently, resolving inflammation is pivotal to the amelioration of AD pathology. This can potentially be achieved by the treatment with specialized pro-resolving lipid mediators (SPMs), which should resolve neuroinflammation in brains. (2) Methods: Here, we report the histological effects of long-term treatment with an SPM, maresin-like 1 (MarL1), on AD pathogenesis in a transgenic 5xFAD mouse model. (3) Results: MarL1 treatment reduced Aβ overload, curbed the loss of neurons in brains especially cholinergic neurons associated with cleaved-caspase-3-associated apoptotic degeneration, reduced microgliosis and the pro-inflammatory M1 polarization of microglia, curbed the AD-associated decline in anti-inflammatory Iba1+Arg-1+-M2 microglia, inhibited phenotypic switching to pro-inflammatory N1 neutrophils, promoted the blood-brain barrier-associated tight-junction protein claudin-5 and decreased neutrophil leakage in 5xFAD brains, and induced the switch of neutrophils toward the inflammation-resolving N2 phenotype. (4) Conclusions: Long-term administration of MarL1 mitigates AD-related neuropathogenesis in brains by curbing neuroinflammation and neurodegeneration, based on the histological results. These findings provide preclinical leads and mechanistic insights for the development of MarL1 into an effective modality to ameliorate AD pathogenesis.

CKLF1 in cardiovascular and cerebrovascular diseases

Chemokine like factor 1 (CKLF1) is a novel atypical chemokine, playing a crucial role in cardiovascular and cerebrovascular diseases (CCVDs) demonstrated by a growing body of works. In cardiovascular diseases including atherosclerosis and myocardial infarction, meanwhile in cerebrovascular diseases such as ischemic stroke and hemorrhagic stroke, the expression levels of CKLF1 change markedly, which triggers downstream signaling pathways by binding with its functional receptors, and then exerts multiple effects to participate in the occurrence and development of these CCVDs. The functional roles of CKLF1 are dynamic and CKLF1 may act as a double-edged sword. The CCVDs-promoting role is related to recruiting inflammatory cells, enhancing the proliferation of vascular smooth muscle cells and endothelial cells, while the CCVDs-suppressing role may correlate with migration of nerve cells and promotion of hematopoietic stem cell proliferation which contributes to disease recovery. Based on this, the paper intends to review expression shifts, potential roles, and molecular mechanisms of CKLF1 in CCVDs, and the current status of CKLF1 targeted therapeutic strategies is also included. We hope this review may provide a valuable reference for using CKLF1 as a diagnostic and prognostic biomarker for CCVDs or developing novel treatments.

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.

Toxoplasma infection induces an aged neutrophil population in the CNS that is associated with neuronal protection

BACKGROUND

Infection with the protozoan parasite Toxoplasma gondii leads to the formation of lifelong cysts in neurons that can have devastating consequences in the immunocompromised. In the immunocompetent individual, anti-parasitic effector mechanisms and a balanced immune response characterized by pro- and anti-inflammatory cytokine production establishes an asymptomatic infection that rarely leads to neurological symptoms. Several mechanisms are known to play a role in this successful immune response in the brain including T cell production of IFNγ and IL-10 and the involvement of CNS resident cells. This limitation of clinical neuropathology during chronic infection suggests a balance between immune response and neuroprotective mechanisms that collectively prevent clinical manifestations of disease. However, how these two vital mechanisms of protection interact during chronic Toxoplasma infection remains poorly understood.

MAIN TEXT

This study demonstrates a previously undescribed connection between innate neutrophils found chronically in the brain, termed "chronic brain neutrophils" (CBNeuts), and neuroprotective mechanisms during Toxoplasma infection. Lack of CBNeuts during chronic infection, accomplished via systemic neutrophil depletion, led to enhanced infection and deleterious effects on neuronal regeneration and repair mechanisms in the brain. Phenotypic and transcriptomic analysis of CBNeuts identified them as distinct from peripheral neutrophils and revealed two main subsets of CBNeuts that display heterogeneity towards both classical effector and neuroprotective functions in an age-dependent manner. Further phenotypic profiling defined expression of the neuroprotective molecules NRG-1 andErbB4 by these cells, and the importance of this signaling pathway during chronic infection was demonstrated via NRG-1 treatment studies.

CONCLUSIONS

In conclusion, this work identifies CBNeuts as a heterogenous population geared towards both classical immune responses and neuroprotection during chronic Toxoplasma infection and provides the foundation for future mechanistic studies of these cells.

Bacteria extracellular vesicle as nanopharmaceuticals for versatile biomedical potential

Bacteria extracellular vesicles (BEVs), characterized as the lipid bilayer membrane-surrounded nanoparticles filled with molecular cargo from parent cells, play fundamental roles in the bacteria growth and pathogenesis, as well as facilitating essential interaction between bacteria and host systems. Notably, benefiting from their unique biological functions, BEVs hold great promise as novel nanopharmaceuticals for diverse biomedical potential, attracting significant interest from both industry and academia. Typically, BEVs are evaluated as promising drug delivery platforms, on account of their intrinsic cell-targeting capability, ease of versatile cargo engineering, and capability to penetrate physiological barriers. Moreover, attributing to considerable intrinsic immunogenicity, BEVs are able to interact with the host immune system to boost immunotherapy as the novel nanovaccine against a wide range of diseases. Towards these significant directions, in this review, we elucidate the nature of BEVs and their role in activating host immune response for a better understanding of BEV-based nanopharmaceuticals' development. Additionally, we also systematically summarize recent advances in BEVs for achieving the target delivery of genetic material, therapeutic agents, and functional materials. Furthermore, vaccination strategies using BEVs are carefully covered, illustrating their flexible therapeutic potential in combating bacterial infections, viral infections, and cancer. Finally, the current hurdles and further outlook of these BEV-based nanopharmaceuticals will also be provided.

The Role of Bacteria in Central Nervous System Tumors: Opportunities and Challenges

Tumors of the central nervous system (CNS) are severe and refractory diseases with poor prognosis, especially for patients with malignant glioblastoma and brain metastases. Currently, numerous studies have explored the potential role of bacteria and intestinal flora in tumor development and treatment. Bacteria can penetrate the blood-brain barrier (BBB), targeting the hypoxic microenvironment at the core of tumors, thereby eliminating tumors and activating both the innate and adaptive immune responses, rendering them promising therapeutic agents for CNS tumors. In addition, engineered bacteria and derivatives, such as bacterial membrane proteins and bacterial spores, can also be used as good candidate carriers for targeted drug delivery. Moreover, the intestinal flora can regulate CNS tumor metabolism and influence the immune microenvironment through the "gut-brain axis". Therefore, bacterial anti-tumor therapy, engineered bacterial targeted drug delivery, and intervention of the intestinal flora provide therapeutic modalities for the treatment of CNS tumors. In this paper, we performed a comprehensive review of the mechanisms and therapeutic practices of bacterial therapy for CNS tumors and discussed potential future research directions in this field.

Diving head-first into brain intravital microscopy

Tissue microenvironments during physiology and pathology are highly complex, meaning dynamic cellular activities and their interactions cannot be accurately modelled ex vivo or in vitro. In particular, tissue-specific resident cells which may function and behave differently after isolation and the heterogenous vascular beds in various organs highlight the importance of observing such processes in real-time in vivo. This challenge gave rise to intravital microscopy (IVM), which was discovered over two centuries ago. From the very early techniques of low-optical resolution brightfield microscopy, limited to transparent tissues, IVM techniques have significantly evolved in recent years. Combined with improved animal surgical preparations, modern IVM technologies have achieved significantly higher speed of image acquisition and enhanced image resolution which allow for the visualisation of biological activities within a wider variety of tissue beds. These advancements have dramatically expanded our understanding in cell migration and function, especially in organs which are not easily accessible, such as the brain. In this review, we will discuss the application of rodent IVM in neurobiology in health and disease. In particular, we will outline the capability and limitations of emerging technologies, including photoacoustic, two- and three-photon imaging for brain IVM. In addition, we will discuss the use of these technologies in the context of neuroinflammation.

The immunomodulatory mechanism of acupuncture treatment for ischemic stroke: research progress, prospects, and future direction

Ischemic stroke (IS) is one of the leading causes of death and disability. Complicated mechanisms are involved in the pathogenesis of IS. Immunomodulatory mechanisms are crucial to IS. Acupuncture is a traditional non-drug treatment that has been extensively used to treat IS. The exploration of neuroimmune modulation will broaden the understanding of the mechanisms underlying acupuncture treatment. This review summarizes the immune response of immune cells, immune cytokines, and immune organs after an IS. The immunomodulatory mechanisms of acupuncture treatment on the central nervous system and peripheral immunity, as well as the factors that influence the effects of acupuncture treatment, were summarized. We suggest prospects and future directions for research on immunomodulatory mechanisms of acupuncture treatment for IS based on current progress, and we hope that these will provide inspiration for researchers. Additionally, acupuncture has shown favorable outcomes in the treatment of immune-based nervous system diseases, generating new directions for research on possible targets and treatments for immune-based nervous system diseases.

Th17 Cells and IL-17A in Ischemic Stroke

The neurological injury and repair mechanisms after ischemic stroke are complex. The inflammatory response is present throughout stroke onset and functional recovery, in which CD4 + T helper(Th) cells play a non-negligible role. Th17 cells, differentiated from CD4 + Th cells, are regulated by various extracellular signals, transcription factors, RNA, and post-translational modifications. Th17 cells specifically produce interleukin-17A(IL-17A), which has been reported to have pro-inflammatory effects in many studies. Recently, experimental researches showed that Th17 cells and IL-17A play an important role in promoting stroke pathogenesis (atherosclerosis), inducing secondary damage after stroke, and regulating post-stroke repair. This makes Th17 and IL-17A a possible target for the treatment of stroke. In this paper, we review the mechanism of action of Th17 cells and IL-17A in ischemic stroke and the progress of research on targeted therapy.

Improving stroke outcomes in hyperglycemic mice by modulating tPA/NMDAR signaling to reduce inflammation and hemorrhages

ABSTRACT

The pharmacological intervention for ischemic stroke hinges on intravenous administration of the recombinant tissue-type plasminogen activator (rtPA, Alteplase/Actilyse) either as a standalone treatment or in conjunction with thrombectomy. However, despite its clinical significance, broader use of rtPA is constrained because of the risk of hemorrhagic transformations (HTs). Furthermore, the presence of diabetes or chronic hyperglycemia is associated with an elevated risk of HT subsequent to thrombolysis. This detrimental impact of tPA on the neurovascular unit in patients with hyperglycemia has been ascribed to its capacity to induce endothelial N-methyl-D-aspartate receptor (NMDAR) signaling, contributing to compromised blood-brain barrier integrity and neuroinflammatory processes. In a mouse model of thromboembolic stroke with chronic hyperglycemia, we assessed the effectiveness of rtPA and N-acetylcysteine (NAC) as thrombolytic agents. We also tested the effect of blocking tPA/NMDAR signaling using a monoclonal antibody, Glunomab. Magnetic resonance imaging, speckle contrast imaging, flow cytometry, and behavioral tasks were used to evaluate stroke outcomes. In hyperglycemic animals, treatment with rtPA resulted in lower recanalization rates and increased HTs. Conversely, NAC treatment reduced lesion sizes while mitigating HTs. After a single administration, either in standalone or combined with rtPA-induced thrombolysis, Glunomab reduced brain lesion volumes, HTs, and neuroinflammation after stroke, translating into improved neurological outcomes. Additionally, we demonstrated the therapeutic efficacy of Glunomab in combination with NAC or as a standalone strategy in chronic hyperglycemic animals. Counteracting tPA-dependent endothelial NMDAR signaling limits ischemic damages induced by both endogenous and exogenous tPA, including HTs and inflammatory processes after ischemic stroke in hyperglycemic animals.

Brain Maturation as a Fundamental Factor in Immune-Neurovascular Interactions in Stroke

Injuries in the developing brain cause significant long-term neurological deficits. Emerging clinical and preclinical data have demonstrated that the pathophysiology of neonatal and childhood stroke share similar mechanisms that regulate brain damage, but also have distinct molecular signatures and cellular pathways. The focus of this review is on two different diseases-neonatal and childhood stroke-with emphasis on similarities and distinctions identified thus far in rodent models of these diseases. This includes the susceptibility of distinct cell types to brain injury with particular emphasis on the role of resident and peripheral immune populations in modulating stroke outcome. Furthermore, we discuss some of the most recent and relevant findings in relation to the immune-neurovascular crosstalk and how the influence of inflammatory mediators is dependent on specific brain maturation stages. Finally, we comment on the current state of treatments geared toward inducing neuroprotection and promoting brain repair after injury and highlight that future prophylactic and therapeutic strategies for stroke should be age-specific and consider gender differences in order to achieve optimal translational success.

Neutrophil-to-albumin Ratio as a Prognostic Factor in Patients with Acute Ischemic Stroke

BACKGROUND

Neutrophil-To-Albumin Ratio (NAR) is a novel inflammatory biomarker. However, the potential prognostic value of NAR in acute ischemic stroke (AIS) remains unclear. This study aimed to evaluate whether NAR levels correlated with the 3-month modified Rankin scale (mRS) in patients with AIS.

METHODS

AIS patients were included in this retrospective study. NAR was calculated as the ratio of absolute neutrophil count to serum albumin level. Logistic regression analyses were used to investigate the effect of NAR on 3-month mRS of AIS. The predictive values of NAR, albumin level, and neutrophil count were compared utilizing receiver operating characteristic (ROC) curves. Moreover, subgroup analyses and interaction tests were conducted to evaluate the consistency of NAR's effect on AIS prognosis.

RESULTS

Of the 780 patients included, 403 (51.67%) had a poor clinical outcome (mRS 3-6) at 3 months. NAR was independently correlated to 3-month poor functional outcome after adjusting for confounders (Odds ratios (OR), 9.34; 95% confidence intervals (CI), 1.09 to 80.13; p =0.0417). Subgroup analysis showed a relative effect consistent with the overall population results, and no statistical interactions were found in the subgroups (all p for interaction > 0.05). The ROC curve showed that the prognosis-related cutoff value for NAR was 0.123, with corresponding specificity and sensitivity of 53.55% and 63.94%, respectively. When comparing the predictive power, NAR (0.590; 95%CI 0.549-0.630) exhibited the highest area under the curve (AUC) of ROC compared to neutrophils (0.584; 95%CI 0.543-0.624) and albumin (0.540; 95%CI 0.500-0.581).

CONCLUSION

There is a positive relationship between NAR levels and 3-month poor functional outcomes in AIS patients, supporting the potential of NAR as a readily available and economic serum biomarker for the early identification of AIS prognosis. Further studies are required to validate the prognostic value and clinical utility of the NAR.

"No-reflow" phenomenon in acute ischemic stroke

Acute ischemic stroke (AIS) afflicts millions of individuals worldwide. Despite the advancements in thrombolysis and thrombectomy facilitating proximal large artery recanalization, the resultant distal hypoperfusion, referred to "no-reflow" phenomenon, often impedes the neurological function restoration in patients. Over half a century of scientific inquiry has validated the existence of cerebral "no-reflow" in both animal models and human subjects. Furthermore, the correlation between "no-reflow" and adverse clinical outcomes underscores the necessity to address this phenomenon as a pivotal strategy for enhancing AIS prognoses. The underlying mechanisms of "no-reflow" are multifaceted, encompassing the formation of microemboli, microvascular compression and contraction. Moreover, a myriad of complex mechanisms warrant further investigation. Insights gleaned from mechanistic exploration have prompted advancements in "no-reflow" treatment, including microthrombosis therapy, which has demonstrated clinical efficacy in improving patient prognoses. The stagnation in current "no-reflow" diagnostic methods imposes limitations on the timely application of combined therapy on "no-reflow" post-recanalization. This narrative review will traverse the historical journey of the "no-reflow" phenomenon, delve into its underpinnings in AIS, and elucidate potential therapeutic and diagnostic strategies. Our aim is to equip readers with a swift comprehension of the "no-reflow" phenomenon and highlight critical points for future research endeavors.

Immunothrombosis in neurovascular disease

A State of the Art lecture titled "Immunothrombosis in Neurovascular Diseases" was presented at the International Society on Thrombosis and Haemostasis Congress in 2023. Despite significant clinical advancements in stroke therapy, stroke remains a prominent contributor to both mortality and disability worldwide. Brain injury resulting from an ischemic stroke is a dynamic process that unfolds over time. Initially, an infarct core forms due to the abrupt and substantial blockage of blood flow. In the subsequent hours to days, the surrounding tissue undergoes gradual deterioration, primarily driven by sustained hypoperfusion, programmed cell death, and inflammation. While anti-inflammatory strategies have proven highly effective in experimental models of stroke, their successful translation to clinical use has proven challenging. To overcome this translational hurdle, a better understanding of the distinct immune response driving ischemic stroke brain injury is needed. In this review article, we give an overview of current knowledge regarding the immune response in ischemic stroke and the contribution of immunothrombosis to this process. We discuss therapeutic approaches to overcome detrimental immunothrombosis in ischemic stroke and how these can be extrapolated to other neurovascular diseases, such as Alzheimer's disease and multiple sclerosis. Finally, we summarize relevant new data on this topic presented during the 2023 International Society on Thrombosis and Haemostasis Congress.

Human neutrophil-like cells demonstrate antimicrobial responses to the chronic cyst form of Toxoplasma gondii

The protozoan parasite Toxoplasma gondii infects approximately 2.5 billion people worldwide. Infection induces a rapid dissemination of parasites throughout the body followed by the formation of lifelong cysts within neurons of the host brain. Both stages require a dynamic immune response comprised of both innate and adaptive cells. Neutrophils are a primary responding cell to acute infection and have been observed in the brain during murine chronic infection. Previous studies investigating human neutrophils found that invasion by Toxoplasma tachyzoites inhibits apoptosis of neutrophils, prolonging their survival under inflammatory conditions. Here, we demonstrate the differentiation of two distinct subsets following exposure of human neutrophil-like-cells (HNLC) to Toxoplasma cysts. In vitro stimulation and imaging studies show cyst-specific induction of cytokines and cyst clearance by HNLCs. Further testing demonstrates that aged HNLCs perform less phagocytosis of cysts compared to non-aged HNLCs. In conclusion, this study identifies a novel response of HNLCs to Toxoplasma cysts and may indicate a role for neutrophils in the clearance of cysts during human infection with Toxoplasma.

Bacteria-Derived Outer-Membrane Vesicles Hitchhike Neutrophils to Enhance Ischemic Stroke Therapy

The treatment of reperfusion injury after ischemic stroke remains unsatisfactory since the blood-brain barrier (BBB) prevents most neuroprotective agents from entering the brain. Here, a strategy is proposed based on bacteria-derived outer-membrane vesicle (OMV) hitchhiking on the neutrophils for enhanced brain delivery of pioglitazone (PGZ) to treat ischemic stroke. By encapsulating PGZ into OMV, the resulting OMV@PGZ nanoparticles inherit the functions associated with the bacterial outer membrane, making them ideal decoys for neutrophil uptake. The results show that OMV@PGZ simultaneously inhibits the activation of nucleotide oligomerization-like receptor protein 3 (NLRP3) inflammasomes and ferroptosis and reduces the reperfusion injury to exert a neuroprotective effect. Notably, the transcription factors Pou2f1 and Nrf1 of oligodendrocytes are identified for the first time to be involved in this process and promoted neural repair by single-nucleus RNA sequencing (snRNA-seq).

Neutrophil-Lymphocyte Ratio as a Predictor of Cerebral Small Vessel Disease in a Geriatric Community: The I-Lan Longitudinal Aging Study

Cerebral Small Vessel Disease (CSVD) frequently affects the elderly, with inflammation playing a crucial role in related health complications, including dementia, stroke, and SVD. Studies, including animal experiments, indicate a strong link between inflammation and SVD progression. The Neutrophil-Lymphocyte Ratio (NLR) serves as a possible biomarker for ongoing inflammatory risks. A total of 720 adults aged 50 years or older from the community-based I-Lan Longitudinal Aging Study were included in this study. General linear regression and ordinally logistic regression analyses were performed to evaluate the association between NLR and CSVD. We further examined the presence of lacune, microbleed, and white matter hyperintensity (WMH) on brain MRI, which were used to construct a combined CSVD score. The NLR was positively associated with WMH (adjusted r = 0.109, p = 0.003), microbleed (adjusted r = 0.102, p = 0.006), and lacune (adjusted r = 0.100, p = 0.008). After adjustments for smoking, drinking, and physical activity in the ordinal logistic regression analysis, age, gender, brachial Systolic Blood Pressure (SBP), fasting glucose, LDL-cholesterol, and Hs-CRP were compared among subjects with low tertile (T1), medium tertile (T2) and high tertile (T3) NLR. The results showed that T2 vs. T1 had an odds ratio of 1.23 (0.86-1.77); and T3 vs. T1 had an odds ratio of 1.87 (1.29-2.71) of CSVD scores in four groups (zero (reference group), one, two, and three or more). NLR could be used to assess the state of inflammation in cerebral vessels. A significant and positive correlation between NLR and CSVD was verified in this study. However, the practical clinical application of NLR in CSVD patients and prognosis prediction should be validated through more scientific attempts.

Mechanism of PGC-1α-mediated mitochondrial biogenesis in cerebral ischemia-reperfusion injury

Cerebral ischemia-reperfusion injury (CIRI) is a series of cascade reactions that occur after blood flow recanalization in the ischemic zone in patients with cerebral infarction, causing an imbalance in intracellular homeostasis through multiple pathologies such as increased oxygen free radicals, inflammatory response, calcium overload, and impaired energy metabolism, leading to mitochondrial dysfunction and ultimately apoptosis. Rescue of reversibly damaged neurons in the ischemic hemispheric zone is the key to saving brain infarction and reducing neurological deficits. Complex and active neurological functions are highly dependent on an adequate energy supply from mitochondria. Mitochondrial biogenesis (MB), a process that generates new functional mitochondria and restores normal mitochondrial function by replacing damaged mitochondria, is a major mechanism for maintaining intra-mitochondrial homeostasis and is involved in mitochondrial quality control to ameliorate mitochondrial dysfunction and thus protects against CIRI. The main regulator of MB is peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), which improves mitochondrial function to protect against CIRI by activating its downstream nuclear respiratory factor 1 (NRF1) and mitochondrial transcription factor A (TFAM) to promote mitochondrial genome replication and transcription. This paper provides a theoretical reference for the treatment of neurological impairment caused by CIRI by discussing the mechanisms of mitochondrial biogenesis during cerebral ischemia-reperfusion injury.

Resolvin D1 reprograms energy metabolism to promote microglia to phagocytize neutrophils after ischemic stroke

Neutrophil aggregation and clearance are important factors affecting neuroinflammatory injury during acute ischemic stroke. Emerging evidence suggests that energy metabolism is essential for microglial functions, especially microglial phagocytosis, which determines the degree of brain injury. Here, we demonstrate that Resolvin D1 (RvD1), a lipid mediator derived from docosahexaenic acid (DHA), promotes the phagocytosis of neutrophils by microglia, thereby reducing neutrophil accumulation in the brain and alleviating neuroinflammation in the ischemic brain. Further studies reveal that RvD1 reprograms energy metabolism from glycolysis to oxidative phosphorylation (OXPHOS), providing sufficient energy for microglial phagocytosis. Moreover, RvD1 enhances microglial glutamine uptake and stimulates glutaminolysis to support OXPHOS to boost ATP production depending on adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) activation. Overall, our results reveal that RvD1 reprograms energy metabolism to promote the microglial phagocytosis of neutrophils after ischemic stroke. These findings may guide perspectives for stroke therapy from modulating microglial immunometabolism.

A Brief Overview of Neutrophils in Neurological Diseases

Neutrophils are the most abundant leukocyte in circulation and are the first line of defense after an infection or injury. Neutrophils have a broad spectrum of functions, including phagocytosis of microorganisms, the release of pro-inflammatory cytokines and chemokines, oxidative burst, and the formation of neutrophil extracellular traps. Traditionally, neutrophils were thought to be most important for acute inflammatory responses, with a short half-life and a more static response to infections and injury. However, this view has changed in recent years showing neutrophil heterogeneity and dynamics, indicating a much more regulated and flexible response. Here we will discuss the role of neutrophils in aging and neurological disorders; specifically, we focus on recent data indicating the impact of neutrophils in chronic inflammatory processes and their contribution to neurological diseases. Lastly, we aim to conclude that reactive neutrophils directly contribute to increased vascular inflammation and age-related diseases.

Prognostic value of inflammation biomarkers for 30-day mortality in critically ill patients with stroke

Objective

To explore the values of neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR), neutrophil to albumin ratio (NAR), prognostic nutritional index (PNI), systemic immune inflammatory index (SII) and red cell distribution width to albumin ratio (RA) for evaluating the risk of 30-day mortality of ischemic stroke or hemorrhagic stroke patients.

Methods

In this cohort study, the data of 1,601 patients diagnosed with stroke were extracted from the Medical Information Mart for Intensive Care III (MIMIC-III) database. Among them, 908 were hemorrhagic stroke patients and 693 were ischemic stroke patients. Demographic and clinical variables of patients were collected. Univariate and multivariable Cox regression were performed to evaluate the predictive values of NLR, PLR, SII, NAR, RA, and PNI for 30-day mortality in hemorrhagic stroke or ischemic stroke patients. The receiver operator characteristic (ROC) curves were plotted to assess the predictive values of NLR, NAR, and RA for 30-day mortality of hemorrhagic stroke patients.

Results

At the end of follow-up, 226 hemorrhagic stroke patients and 216 ischemic stroke patients died. The elevated NLR level was associated with increased risk of 30-day mortality in hemorrhagic stroke [hazard ratio (HR) = 1.17, 95% confidence interval (CI): 1.06-1.29]. The increased NAR level was associated with elevated risk of 30-day mortality in hemorrhagic stroke (HR = 1.16, 95% CI: 1.02-1.30). The high RA level was linked with increased risk of 30-day mortality (HR = 1.44, 95% CI: 1.23-1.69). No significant correlation was observed in these inflammation biomarkers with the risk of 30-day mortality in ischemic stroke patients. The area under the curves (AUCs) of NLR, RA, and NAR for evaluating the risk of 30-day mortality of hemorrhagic stroke patients were 0.552 (95% CI: 0.503-0.601), 0.644 (95% CI: 0.590-0.699) and 0.541 (95% CI: 0.490-0.592).

Conclusion

NLR, NAR, and RA were potential prognostic biomarkers for predicting 30-day mortality of hemorrhagic stroke patients, which might provide clinicians an easy and cheap way to quickly identify patients with high risk of mortality.

Depletion of Arg1-Positive Microglia/Macrophages Exacerbates Cerebral Ischemic Damage by Facilitating the Inflammatory Response

Stroke is a serious worldwide disease that causes death and disability, more than 80% of which is ischemic stroke. The expression of arginase 1 (Arg1), a key player in regulating nitrogen homeostasis, is altered in the peripheral circulation after stroke. Growing evidence indicates that ischemic stroke also induces upregulated Arg1 expression in the central nervous system, especially in activated microglia and macrophages. This implies that Arg1 may affect stroke progression by modulating the cerebral immune response. To investigate the effect of Arg1+ microglia/macrophages on ischemic stroke, we selectively eliminated cerebral Arg1+ microglia/macrophages by mannosylated clodronate liposomes (MCLs) and investigated their effects on behavior, neurological deficits, and inflammatory responses in mice after ischemic stroke. More than half of Arg1+ cells, mainly Arg1+ microglia/macrophages, were depleted after MCLs administration, resulting in a significant deterioration of motility in mice. After the elimination of Arg1+ microglia/macrophages, the infarct volume expanded and neuronal degenerative lesions intensified. Meanwhile, the absence of Arg1+ microglia/macrophages significantly increased the production of pro-inflammatory cytokines and suppressed the expression of anti-inflammatory factors, thus profoundly altering the immune microenvironment at the lesion site. Taken together, our data demonstrate that depletion of Arg1+ microglia/macrophages exacerbates neuronal damage by facilitating the inflammatory response, leading to more severe ischemic injury. These results suggest that Arg1+ microglia/macrophages, as a subpopulation regulating inflammation, is beneficial in controlling the development of ischemia and promoting recovery from injury. Regulation of Arg1 expression on microglia/macrophages at the right time may be a potential target for the treatment of ischemic brain injury.

Roles of peripheral immune cells in the recovery of neurological function after ischemic stroke

Stroke is a leading cause of mortality and long-term disability worldwide, with limited spontaneous repair processes occurring after injury. Immune cells are involved in multiple aspects of ischemic stroke, from early damage processes to late recovery-related events. Compared with the substantial advances that have been made in elucidating how immune cells modulate acute ischemic injury, the understanding of the impact of the immune system on functional recovery is limited. In this review, we summarized the mechanisms of brain repair after ischemic stroke from both the neuronal and non-neuronal perspectives, and we review advances in understanding of the effects on functional recovery after ischemic stroke mediated by infiltrated peripheral innate and adaptive immune cells, immune cell-released cytokines and cell-cell interactions. We also highlight studies that advance our understanding of the mechanisms underlying functional recovery mediated by peripheral immune cells after ischemia. Insights into these processes will shed light on the double-edged role of infiltrated peripheral immune cells in functional recovery after ischemic stroke and provide clues for new therapies for improving neurological function.

Brain‐associated innate leukocytes display diverse inflammatory states following experimental stroke

Previous studies investigating innate leukocyte recruitment into the brain after cerebral ischemia have shown conflicting results. Using distinct cell surface and intracellular markers, the current study evaluated the contributions of innate immune cells to the poststroke brain following 1‐h middle cerebral artery occlusion (tMCAO) or permanent MCAO (pMCAO), and assessed whether these cells ascribed to an inflammatory state. Moreover, we examined whether there is evidence for leukocyte infiltration into the contralateral (CL) hemisphere despite the absence of stroke infarct. We observed the recruitment of peripheral neutrophils, monocytes and macrophages into the hemisphere ipsilateral (IL) to the ischemic brain infarct at 24 and 96 h following both tMCAO and pMCAO. In addition, we found evidence of increased leukocyte recruitment to the CL hemisphere but to a lesser extent than the IL hemisphere after stroke. Robust production of intracellular cytokines in the innate immune cell types examined was most evident at 24 h after pMCAO. Specifically, brain‐associated neutrophils, monocytes and macrophages demonstrated stroke‐induced production of tumor necrosis factor‐α (TNF‐α) and interleukin (IL)‐1β, while only monocytes and macrophages exhibit a significant expression of arginase 1 (Arg1) after stroke. At 96 h after stroke, brain‐resident microglia demonstrated production of TNF‐α and IL‐1β following both tMCAO and pMCAO. At this later timepoint, neutrophils displayed TNF‐α production and brain‐associated macrophages exhibited elevation of IL‐1β and Arg1 after tMCAO. Further, pMCAO induced significant expression of Arg1 and IL‐1β in monocytes and macrophages at 96 h, respectively. These results revealed that brain‐associated innate immune cells display various stroke‐induced inflammatory states that are dependent on the experimental stroke setting.

PD-1/PD-L Axis in Neuroinflammation: New Insights

The approval of immune checkpoint inhibitors (ICIs) by the Food and Drug Administration (FDA) led to an improvement in the treatment of several types of cancer. The main targets of these drugs are cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed cell death protein-1/programmed death-ligand 1 pathway (PD-1/PD-L1), which are important inhibitory molecules for the immune system. Besides being generally safer than common chemotherapy, the use of ICIs has been associated with several immune-related adverse effects (irAEs). Although rare, neurological adverse effects are reported within the irAEs in clinical trials, particularly in patients treated with anti-PD-1 antibodies or a combination of both anti-CTLA-4 and PD-1 drugs. The observations obtained from clinical trials suggest that the PD-1 axis may play a remarkable role in the regulation of neuroinflammation. Moreover, numerous studies in preclinical models have demonstrated the involvement of PD-1 in several neurological disorders. However, a comprehensive understanding of these cellular mechanisms remains elusive. Our review aims to summarize the most recent evidence concerning the regulation of neuroinflammation through PD-1/PD-L signaling, focusing on cell populations that are involved in this pathway.

Neutrophil Count Predicts Malignant Cerebellar Edema and Poor Outcome in Acute Basilar Artery Occlusion Receiving Endovascular Treatment: A Nationwide Registry-Based Study

Background

Acute basilar artery occlusion (ABAO) is known to have a poor outcome with a high rate of morbidity and mortality despite endovascular treatment (EVT), highlighting the necessities of exploring factors to limit the efficacy of EVT in these patients. Cerebellar infarctions in ABAO might progress to malignant cerebellar edema (MCE), a life-threatening complication after reperfusion, posing a secondary injury to the brainstem by mass effects. Therefore, the present research aimed to explore the impacts of MCE on a long-term outcome and investigate the prognostic factors for MCE among ABAO after EVT.

Methods

In the national BASILAR registry, a total of 329 ABO patients with cerebellar infarctions treated by EVT met the inclusion criteria. The presence of MCE defined by the Jauss scale ≥4 points, was evaluated on the computed tomography performed 72 h after EVT. The adjusted odds ratio and 95% CI were obtained by logistic regression models. A favorable outcome was defined as a 90-day modified Rankin Scale score of 0-3.

Results

MCE was statistically associated with the decreased incidence of a favorable outcome [adjusted odds ratio, 0.35(95% CI, 0.18-0.68), P=0.002]. The baseline National Institutes of Health Stroke Scale score, collateral circulation, neutrophil count at admission, and recanalization status were predictors for MCE and a favorable functional status at 90 days (all P<0.05). Among all inflammatory factors, the neutrophil count achieved the highest accuracy, sensitivity, and specificity for MCE. Adding the neutrophil count status into the baseline model obviously enhanced its prediction ability for MCE and favorable outcome by increasing the area under curve and achieving both net reclassification and integrated discrimination improvement (all P<0.05). Mediation analysis indicated that MCE mediated the association between the increased neutrophil count and worse functional outcome (P=0.026).

Discussion

MCE acted essential roles in worsening prognosis for ABAO after EVT. A high neutrophil count at admission was linked to MCE and a poor outcome among ABAO patients, which could be further incorporated into the clinical decision-making system and guide immunomodulation therapy.

Role of Semaphorins in Ischemic Stroke

Ischemic stroke is one of the major causes of neurological morbidity and mortality in the world. Although the management of ischemic stroke has been improved significantly, it still imposes a huge burden on the health and property. The integrity of the neurovascular unit (NVU) is closely related with the prognosis of ischemic stroke. Growing evidence has shown that semaphorins, a family of axon guidance cues, play a pivotal role in multiple pathophysiological processes in NVU after ischemia, such as regulating the immune system, angiogenesis, and neuroprotection. Modulating the NVU function via semaphorin signaling has a potential to develop a novel therapeutic strategy for ischemic stroke. We, therefore, review recent progresses on the role of semphorin family members in neurons, glial cells and vasculature after ischemic stroke.

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.

The Predictive Role of Systemic Inflammation Response Index (SIRI) in the Prognosis of Stroke Patients

Purpose

Stroke is a disease associated with high mortality. Many inflammatory indicators such as neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), lymphocyte to monocyte ratio (LMR) and red blood cell distribution width (RDW) have been documented to predict stroke prognosis, their predictive power is limited. A novel inflammatory indicator called systemic inflammatory response index (SIRI) has been advocated to have an essential role in the prognostic assessment of cancer and infectious diseases. In this study, we attempted to assess the prognosis of stroke by SIRI. Moreover, we compared SIRI with other clinical parameters, including NLR, PLR, LMR and RDW.

Methods

This was a retrospective cohort study. We obtained data of 2450 stroke patients from the Multiparametric Intelligent Monitoring in Intensive Care III database. We used the Cox proportional hazards models to evaluate the relationship between SIRI and all-cause mortality and sepsis. Receiver operating curve (ROC) analysis was used to assess the predictive power of SIRI compared to NLR, PLR, LMR and RDW for the prognosis of stroke. We collected data of 180 patients from the First Affiliated Hospital of Wenzhou Medical University, which used the Pearson’s correlation coefficient to assess the relationship between SIRI and the National Institute of Health stroke scale (NIHSS).

Results

After adjusting multiple covariates, we found that SIRI was associated with all-cause mortality in stroke patients. Rising SIRI accompanied by rising mortality. Besides, ROC analysis showed that the area under the curve of SIRI was significantly greater than for NLR, PLR, LMR and RDW. Besides, Pearson’s correlation test confirmed a significant positive correlation between SIRI and NIHSS.

Conclusion

Elevated SIRI was associated with higher risk of mortality and sepsis and higher stroke severity. Therefore, SIRI is a promising low-grade inflammatory factor for predicting stroke prognosis that outperformed NLR, PLR, LMR, and RDW in predictive power.