Monocyte-Derived Macrophages Contribute to Spontaneous Long-Term Functional Recovery after Stroke in Mice

NLR and LMR could powerfully predict unfavorable outcomes in patients with acute anterior circulation large vessel occlusion stroke (ALVOS) who underwent mechanical thrombectomy

INTRODUCTION

To investigate the predictive value of Neutrophil to lymphocyte ratio (NLR) and Lymphocyte to monocyte ratio (LMR) on unfavorable outcomes of acute anterior circulation large vessel occlusion stroke (ALVOS) in patients who underwent mechanical thrombectomy (MT).

MATERIAL & METHOD

We retrospectively recruited 96 cases with ALVOS who underwent MT. These cases were divided into two groups including the favorable outcome group (3-month modified Rankin Scale scores (mRS) of 0-2) and the unfavorable outcome group (3-month mRS of 3-6). Logistic regression analysis was used to examine the independent risk factors of the 3-month unfavorable outcome of ALVOS. Moreover, we conducted a receiver operating characteristic curve (ROC) to estimate the valuable predictor of NLR, LMR, and the combination of NLR and LMR on unfavorable outcomes of ALVOS after MT.

RESULTS

46.9 % (45/96) cases had an unfavorable outcome and 53.1 % (51/96) cases had a favorable outcome. In the univariate regression analysis, baseline NIHSS score, symptomatic intracranial hemorrhage, and fasting glucose were included in the multi-factor binary logistic regression, and this revealed that NLR (OR 3.776, 95 %CI 1.067-13.363, p = 0.039) and LMR (OR 0.092, 95 %CI 0.017-0.0506, p = 0.006) were independent predictors of unfavorable outcomes (mRS score 3-6) at 3-month. Higher NLR (> 2.984) and lower LMR (< 3.775) were independently associated with unfavorable outcomes, and the combined predictive levels of both NLR and LMR (AUC = 0.941) were higher than single indicators (NLR, AUC = 0.876; LMR, AUC = 0.934).

CONCLUSIONS

The combination of NLR and LMR was a more powerful predictor of unfavorable outcomes of ALVOS after MT than NLR alone.

Advancements in research on the thrombo-inflammation mechanisms mediated by factor XII in ischemic stroke

Ischemic stroke (IS) is a major cause of mortality and disability, with thrombo-inflammation constituting a core pathophysiological mechanism. This process is closely linked to coagulation cascade activation, endothelial injury, immune cell infiltration, and neuronal damage. Coagulation factor XII (FXII), a key mediator of the contact activation pathway, has emerged as a promising therapeutic target due to its dual role in pathological thrombosis and immune regulation, without compromising physiological hemostasis. However, the clinical translation of FXII-targeted therapies is hindered by paradoxical observations. Recent studies highlight that FXII's functional complexity stems from its structural and spatial heterogeneity: full-length FXII derived from the liver and short FXII mRNA isoforms expressed in neurons mediate distinct biological effects. While FXII contributes to neuroinflammation and vascular injury via endothelial-platelet-neutrophil interactions, neuron-derived FXII exhibits neuroprotective effects through HGF-mediated signaling pathways. Additionally, circulating FXIIa promotes vascular remodeling by enhancing endothelial growth factor (VEGF) release. This review summarizes the multifaceted regulatory mechanisms of FXII in IS, focusing on its structure, distribution, preclinical-clinical paradox, and current therapeutic strategies. Special emphasis is placed on its domain-specific functions and the neuroprotective effects of FXII.

Type I collagen secreted in white matter lesions inhibits remyelination and functional recovery

White matter injury is caused by cerebral blood flow disturbances associated with stroke and demyelinating diseases such as multiple sclerosis. Remyelination is induced spontaneously after white matter injury, but progressive multiple sclerosis and white matter stroke are usually characterised by remyelination failure. However, the mechanisms underlying impaired remyelination in lesions caused by demyelination and stroke remain unclear. In the current study, we demonstrated that collagen fibres accumulated in the demyelinated lesions of multiple sclerosis patients (age range 23-80 years) and white matter lesions of stroke patients (age range 80-87 years), suggesting that the accumulation of collagen fibres correlates with remyelination failure in these lesions. To investigate the function of collagen fibres in the white matter lesions, we generated two types of white matter injury in mice. We induced focal demyelination by lysolecithin (LPC) injection and ischemic stroke by endothelin 1 (ET1) injection into the internal capsule. We found that type I collagen fibres were secreted in ET1-induced lesions with impaired white matter regeneration in the chronic phase of disease. We also showed that monocyte-derived macrophages that infiltrated into lesions from the peripheral blood produced type I collagen after white matter injury, and that type I collagen also exacerbated microglial activation, astrogliosis, and axonal injury. Finally, we demonstrated that oligodendrocyte differentiation and remyelination were inhibited in the presence of type I collagen after LPC-induced demyelination. These results suggest that type I collagen secreted by monocyte-derived macrophages inhibited white matter regeneration, and therefore, the modulation of type I collagen metabolism might be a novel therapeutic target for white matter injury.

Central Nervous System Macrophages in Health and Disease

The central nervous system (CNS) has a unique set of macrophages that seed the tissue early during embryonic development. Microglia reside in the parenchyma, and border-associated macrophages are present in border regions, including the meninges, perivascular spaces, and choroid plexus. CNS-resident macrophages support brain homeostasis during development and steady state. In the diseased brain, however, the immune landscape is altered, with phenotypic and transcriptional changes in resident macrophages and the invasion of blood-borne monocytes, which differentiate into monocyte-derived macrophages upon entering the CNS. In this review, we focus on the fate and function of the macrophage compartment in health, neurodegenerative conditions such as amyloidosis, and neuroinflammation as observed in multiple sclerosis and infection. We discuss our current understanding that monocyte-derived macrophages contribute to neuropathology whereas native macrophages play a neuroprotective role in disease.

Emerging Insights into Brain Inflammation: Stem-Cell-Based Approaches for Regenerative Medicine

Neuroinflammation is a complex immune response triggered by brain injury or pathological stimuli, and is highly exacerbated in neurodegenerative diseases. It plays a dual role in the central nervous system, promoting repair in acute stages while aggravating disease progression by contributing to neuronal loss, synaptic dysfunction, and glial dysregulation in chronic phases. Inflammatory responses are mainly orchestrated by microglia and infiltrated monocytes, which, when dysregulated, not only harm existing neurons, but also impair the survival and differentiation of neural stem and progenitor cells in the affected brain regions. Modulating neuroinflammation is crucial for harnessing its protective functions while minimizing its detrimental effects. Current therapeutic strategies focus on fine-tuning inflammatory responses through pharmacological agents, bioactive molecules, and stem cell-based therapies. These approaches aim to restore immune homeostasis, support neuroprotection, and promote regeneration in various neurological disorders. However, animal models sometimes fail to reproduce human-specific inflammatory responses in the brain. In this context, stem-cell-derived models provide a powerful tool to study neuroinflammatory mechanisms in a patient-specific and physiologically relevant context. These models facilitate high-throughput screening, personalized medicine, and the development of targeted therapies while addressing the limitations of traditional animal models, paving the way for more targeted and effective treatments.

Therapeutic mitochondria treatment amplifies macrophage-mediated phagocytosis and recycling exocytosis

Therapeutic administration of mitochondria has been increasingly explored. However, how these administered mitochondria impact immune response remains to be fully addressed. In this proof-of-concept study, we show that extracellularly added mitochondria to cultured peritoneal macrophages increase phagocytosis and recycling exocytosis that amplifies neuroplasticity mediated by recycled mitochondria transfer. Macrophage activation markers such as Nos2, Arg1, and Cd163 were unchanged at 3 h post-treatment with mitochondria, but whole mitochondria or delivery of mRNAs extracted from whole mitochondria appeared to increase SQSTM1 protein and activate Nrf2-mediated phagocytosis in macrophages, whereas mitochondria treatment did not change the ability of phagocytosis in cultured microglia or astrocytes. Notably, the once engulfed mitochondria in macrophages appear to be released via Rab27a-mediated recycling pathway that were favorably incorporated in mechanically damaged neurons compared with healthy neurons, resulting in accelerating neurite extension in damaged neurons in a direct co-culture model. Altogether, these findings uncover unappreciated mechanisms that mitochondria-treated macrophages upregulate phagocytosis and recycling exocytosis, implicating that engineering mitochondria delivery to macrophages is a new therapeutic intervention to promote neurorecovery in CNS disorders.

Monocyte-derived macrophages act as reinforcements when microglia fall short in Alzheimer's disease

The central nervous system (CNS) is endowed with its own resident innate immune cells, the microglia. They constitute approximately 10% of the total cells within the CNS parenchyma and act as 'sentinels', sensing and mitigating any deviation from homeostasis. Nevertheless, under severe acute or chronic neurological injury or disease, microglia are unable to contain the damage, and the reparative activity of monocyte-derived macrophages (MDMs) is required. The failure of the microglia under such conditions could be an outcome of their prolonged exposure to hostile stimuli, leading to their exhaustion or senescence. Here, we describe the conditions under which the microglia fall short, focusing mainly on the context of Alzheimer's disease, and shed light on the functions performed by MDMs. We discuss whether and how MDMs engage in cross-talk with the microglia, why their recruitment is often inadequate, and potential ways to augment their homing to the brain in a well-controlled manner.

Ischemic Conditioning Promotes Transneuronal Survival and Stroke Recovery via CD36-Mediated Efferocytosis

BACKGROUND

Remote ischemic conditioning (RIC) has been implicated in cross-organ protection in cerebrovascular disease, including stroke. However, the lack of a consensus protocol and controversy over the clinical therapeutic outcomes of RIC suggest an inadequate mechanistic understanding of RIC. The current study identifies RIC-induced molecular and cellular events in the blood, which enhance long-term functional recovery in experimental cerebral ischemia.

METHODS

Naive mice or mice subjected to transient ischemic stroke were randomly selected to receive sham conditioning or RIC in the hindlimb at 2 hours post-stroke. At 3 days post-stroke, monocyte composition in the blood was analyzed, and brain tissue was examined for monocyte-derived macrophage (Mφ), levels of efferocytosis, and CD36 expression. Mouse with a specific deletion of CD36 in monocytes/Mφs was used to establish the role of CD36 in RIC-mediated modulation of efferocytosis, transneuronal degeneration, and recovery following stroke.

RESULTS

RIC applied 2 hours after stroke increased the entry of monocytes into the injured brain. In the postischemic brain, Mφ had increased levels of CD36 expression and efferocytosis. These changes in brain Mφ were derived from RIC-induced changes in circulating monocytes. In the blood, RIC increased CD36 expression in circulating monocytes and shifted monocytes to a proinflammatory Lymphocyte antigen 6 complex (LY6C)High state. Conditional deletion of CD36 in Mφ abrogated the RIC-induced monocyte shift in the blood and efferocytosis in the brain. During the recovery phase of stroke, RIC rescued the loss of the volume and of tyrosine hydroxylase+ neurons in substantia nigra and behavioral deficits in wild-type mice but not in mice with a specific deletion of CD36 in monocytes/Mφs.

CONCLUSIONS

RIC induces a shift in monocytes to a proinflammatory state with elevated CD36 levels, and this is associated with CD36-dependent efferocytosis in Mφs that rescues delayed transneuronal degeneration in the postischemic brain and promotes stroke recovery. Together, these findings provide novel insight into our mechanistic understanding of how RIC improves poststroke recovery.

A specific and adaptable approach to track CD206+ macrophages by molecular MRI and fluorescence imaging

Rationale: The mannose receptor (CD206, expressed by the gene Mrc1) is a surface marker overexpressed by anti-inflammatory and pro-tumoral macrophages. As such, CD206+ macrophages play key roles in the immune response to different pathophysiological conditions and represent a promising diagnostic and therapeutic target. However, methods to specifically target these cells remain challenging. In this study, we describe a multi-mannose approach to develop CD206-targeting fluorescent and MRI agents that specifically and sensitively detect and monitor CD206+ macrophage immune response in different disease conditions. Methods: We designed and synthesized fluorescent agents MR1-cy5 and MR2-cy5, and MRI agents Mann2-DTPA-Gd and MannGdFish. Cellular assays using pro-inflammatory and anti-inflammatory macrophages differentiated from RAW 264.7 cells were performed, and signals were detected by fluorescence microscopy and inductively coupled plasma mass spectrometry (ICP-MS) to validate specificity in vitro. In vivo specificity and efficacy of the agents were evaluated by MRI in a subcutaneous wound healing model and experimental glioma with Mrc1 +/+ without and with D-mannose treatment, Mrc1 +/-, and Mrc1 -/- mice, and in stroke. One-way ANOVA and two-way ANOVA tests were used for data analysis. P < 0.05 was considered statistically different. Results: Both in vitro fluorescence imaging with MR2-cy5, ICP-MS with Mann2-DTPA-Gd, and in vivo MRI in Mrc1 -/- mice confirmed the specificity of our approach. Mann2-DTPA-Gd MRI can track the changes of CD206+ macrophages at different stages of wound healing, correlating well with flow cytometry data using another anti-inflammatory macrophage marker (arginase-1). The specificity and efficacy of Mann2-DPTA-Gd were further validated in experimental glioma, in which Mann2-DTPA-Gd imaging detected CD206+ tumor-associated macrophages (TAMs), demonstrated significantly decreased signals in Mrc1 +/- mice and Mrc1 -/- mice, and tracked treatment changes in D-mannose-treated Mrc1 +/+ mice. Furthermore, Mann2-DTPA-Gd can report microglia/macrophages and correlate with histology in stroke. The more Gd-stable agent MannGdFish demonstrated similar efficacy as Mann2-DTPA-Gd in vivo with favorable biodistribution and pharmacokinetics. Conclusion: We have developed a fluorescent agent (MR2-cy5) and MRI agents (Mann2-DTPA-Gd and MannGdFish) with two mannose moieties that are highly specific to CD206 and can track CD206+ macrophages in disease models of wound healing, tumor, and neurological disease. Importantly, MannGdFish, with its high specificity, stability, favorable biodistribution, and pharmacokinetics, is a promising translational candidate to noninvasively monitor CD206+ macrophages in repair/regeneration and tumors in patients. In addition, with the specific binding motif to CD206, other imaging modalities and therapeutic agents could also be introduced for theranostic applications.

Tet2-mediated clonal hematopoiesis modestly improves neurological deficits and is associated with inflammation resolution in the subacute phase of experimental stroke

Introduction

Recent work has revealed that clonal hematopoiesis (CH) is associated with a higher risk of numerous age-related diseases, including ischemic stroke, however little is known about whether it influences stroke outcome independent of its widespread effects on cardiovascular disease. Studies suggest that leukocytes carrying CH driver mutations have an enhanced inflammatory profile, which could conceivably exacerbate brain injury after a stroke.

Methods

Using a competitive bone marrow transplant model of Tet2-mediated CH, we tested the hypothesis that CH would lead to a poorer outcome after ischemic stroke by augmenting brain inflammation. Stroke was induced in mice by middle cerebral artery occlusion and neurological outcome was assessed at acute (24 h) and subacute (14 d) timepoints. Brains were collected at both time points for histological, immunofluorescence and gene expression assays.

Results

Unexpectedly, Tet2-mediated CH had no effect on acute stroke outcome but led to a reduction in neurological deficits during the subacute phase. This improved neurological outcome was associated with lower levels of brain inflammation as evidenced by lower transcript levels of various inflammatory molecules alongside reduced astrogliosis.

Discussion

These findings suggest that Tet2-mediated CH may have beneficial effects on outcome after stroke, contrasting with the conventional understanding of CH whereby leukocytes with driver mutations promote disease by exacerbating inflammation.

Uncovering the dual roles of peripheral immune cells and their connections to brain cells in stroke and post-stroke stages through single-cell sequencing

Ischemic stroke is a cerebrovascular disease that affects the blood vessels and the blood supply to the brain, making it the second leading cause of death worldwide. Studies suggest that immune cells play a dual role during the inflammatory and recovery phases of stroke. However, in-depth investigations of specific cell subtypes and their differentiation trajectories remain to be elucidated. In this review, we highlight the application of single-cell RNA sequencing (scRNA-seq) for the unbiased identification of cell heterogeneity in brain and peripheral blood mononuclear cells (PBMCs) during and after a stroke. Our goal is to explore the phenotypic landscape of cells with different roles in this context. Specifically, we provide an overview of the roles, cell surface markers, immune cell-released cytokines, and intercellular interactions identified in major immune cells during and after stroke, as identified by different technologies. Additionally, we summarize the connection between immune cells in peripheral blood and the brain via their differentiation trajectories. By synthesizing the application of scRNA-seq in the combined analysis of PBMCs and brain tissue at higher sampling frequencies, we aim to unveil the dual role of peripheral immune cells, which could facilitate the development of new treatment strategies for ischemic stroke.

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

Aging profoundly affects the immune system leading to an increased propensity for inflammation. Age-related dysregulation of immune cells is implicated in the development and progression of numerous age-related diseases such as: cardiovascular diseases, neurodegenerative disorders, and metabolic syndromes. Monocytes and monocyte-derived macrophages, being important players in the inflammatory response, significantly influence the aging process and the associated increase in inflammatory disease risk. Ischemic stroke is among age-related diseases where inflammation, particularly monocyte-derived macrophages, plays an important deteriorating role but could also strongly promote post-stroke recovery. Also, biological sex influences the incidence, presentation, and outcomes of ischemic stroke, reflecting both biological differences between men and women. Here, we studied whether human peripheral blood monocyte subtype (classical, intermediate, and non-classical) expression of genes implicated in stroke-related inflammation and post-stroke tissue regeneration depends on age and sex. A flow cytometry analysis of blood samples from 44 healthy volunteers (male and female, aged 28 to 98) showed that in contrast to other immune cells, the proportion of NK-cells increased in females. The proportion of B-cells decreased in both sexes with age. 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 increasing age. 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.

Soluble Epoxide Hydrolase Inhibitor Ameliorates Olfactory Dysfunction, Modulates Microglia Polarization, and Attenuates Neuroinflammation after Ischemic Brain Injury

Olfactory bulb (OB) microglia activation and inflammation can lead to olfactory dysfunction, which often occurs after an ischemic stroke. Inhibition of soluble epoxide hydrolase (sEH) attenuates neuroinflammation in brain injuries by reducing the degradation of anti-inflammatory epoxyeicosatrienoic acids. However, whether sEH inhibitors can ameliorate olfactory dysfunction after an ischemic stroke remains unknown. Ischemic brain injury and olfactory dysfunction were induced by middle cerebral artery occlusion (MCAO) in Wistar Kyoto rats. The rats were administered 12-(3-adamantan-1-yl-ureido)-dodecanoic acid (AUDA), a selective sEH inhibitor. Olfactory function, cerebral infarct volume, and the degree of degeneration, microglial polarization and neuroinflammation in OB were evaluated. Following treatment with AUDA, rats subjected to MCAO displayed mild cerebral infarction and OB degeneration, as well as better olfactory performance. In OB, AUDA triggered a modulation of microglial polarization toward the M2 anti-inflammatory type, reduction in proinflammatory mediators, and enhancement of the antioxidant process. The effectiveness of AUDA in terms of anti-inflammatory, neuroprotection and anti-oxidative properties suggests that it may have clinical therapeutic implication for ischemic stroke related olfactory dysfunction.

Dipeptidyl peptidase 4 deficiency improves survival after focal cerebral ischemia in mice and ameliorates microglia activation and specific inflammatory markers

Dipeptidyl peptidase 4 (DPP4; CD26) is involved in the regulation of various metabolic, immunological, and neurobiological processes in healthy individuals. Observations based on epidemiological data indicate that DPP4 inhibition by gliptins, typically used in patients with diabetes, may reduce the risk for cerebral ischemia and may also improve related outcomes. However, as DPP4 inhibitor application is neither complete nor specific for suppression of DPP4 enzymatic activity and DPP4 has non-enzymatic functions as well, the variety of consequences is a matter of debate. Therefore, we here used DPP4 knock-out (KO) mice to analyze the specific contribution of DPP4 to cellular, immunological, and functional consequences of experimental focal cerebral ischemia. We observed a significantly higher survival rate of DPP4 KO mice after ischemia, which was accompanied by a lower abundance of the pro-inflammatory chemokine CCL2 and reduced activation of Iba1-positive microglia cells in brain tissue of DPP4 KO mice. In addition, after ischemia for 24 h to 72 h, decreased concentrations of CCL5 and CCL12 in plasma and of CCL17 in brain tissue of DPP4 KO mice were observed when compared to wild type mice. Other aspects analyzed, such as the functional Menzies score, astrocyte activation and chemokine levels in plasma and brain tissue were affected by ischemia but appeared to be unaffected by the DPP4 KO genotype. Taken together, experimental ablation of DPP4 functions in mice improves survival and ameliorates aspects of cellular and molecular inflammation after focal cerebral ischemia.

Characteristics of two different immune infiltrating pyroptosis subtypes in ischemic stroke

Background

Ischemic stroke (IS) is a serious health hazard and identified as the second leading cause of mortality around the world. However, the role of pyroptosis in the immune microenvironment regulation in IS is still unclear. Here, our study aims to elucidate the effect of pyroptosis on immune microenvironment in IS.

Methods

The regulation mode of pyroptosis in IS was systematically evaluated, and its effects on immune microenvironment were explored, including infiltration of immune cells, immune response gene sets, and human leukocyte antigen (HLA) gene. The genes and drugs related to pyroptosis phenotype were also identified. An MCAO rat model was constructed, and the mRNA expression levels in the classifier model were validated by qRT-PCR.

Results

The separator is composed of 11 pyroptosis genes, out of which 10 genes could distinguish between ischemic stroke and control samples. CHMP2A, CHMP4A, and NAIP genes are significantly related to immune infiltrating cells, immune response gene sets, and HLA. However, two different pyroptosis subtypes mediated by 10 pyroptosis genes were identified, which were different in immune cell abundance, HLA genes, and immune response gene sets. Furthermore, 199 genes associated with pyroptosis phenotype was identified along with the analysis of biological functions.

Conclusion

These findings reveal the potential mechanism of pyroptosis in the immune microenvironment of IS, indicating that pyroptosis functions as a vital component in the complexity and diversity of the immune microenvironment in patients with IS.

Integrated Strategies for Targeting Arteriogenesis and Angiogenesis After Stroke

The interdependence between arteriogenesis and angiogenesis is crucial for enhancing perfusion by synchronously improving leptomeningeal collaterals (LMCs) and microvascular networks after stroke. However, current approaches often focus on promoting arteriogenesis and angiogenesis separately, neglecting the potential synergistic benefits of targeting both processes simultaneously. Therefore, it is imperative to consider both arteriogenesis and angiogenesis as integral and complementary strategies for post-stroke revascularization. To gain a deeper understanding of their relationships after stroke and to facilitate the development of targeted revascularization strategies, we compared them based on their timescale, space, and pathophysiology. The temporal differences in the occurrence of arteriogenesis and angiogenesis allow them to restore blood flow at different stages after stroke. The spatial differences in the effects of arteriogenesis and angiogenesis enable them to specifically target the ischemic penumbra and core infarct region. Additionally, the endothelial cell, as the primary effector cell in their pathophysiological processes, is promising target for enhancing both. Therefore, we provide an overview of key signals that regulate endothelium-mediated arteriogenesis and angiogenesis. Finally, we summarize current therapeutic strategies that involve these signals to promote both processes after stroke, with the aim of inspiring future therapeutic advances in revascularization.

Focal Cerebral Ischemia Induces Expression of Glutaminyl Cyclase along with Downstream Molecular and Cellular Inflammatory Responses

Glutaminyl cyclase (QC) and its isoenzyme (isoQC) catalyze the formation of N-terminal pyroglutamate (pGlu) from glutamine on a number of neuropeptides, peptide hormones and chemokines. Chemokines of the C-C ligand (CCL) motif family are known to contribute to inflammation in neurodegenerative conditions. Here, we used a model of transient focal cerebral ischemia to explore functional, cellular and molecular responses to ischemia in mice lacking genes for QC, isoQC and their substrate CCL2. Mice of the different genotypes were evaluated for functional consequences of stroke, infarct volume, activation of glia cells, and for QC, isoQC and CCL2 expression. The number of QC-immunoreactive, but not of isoQC-immunoreactive, neurons increased robustly in the infarct area at 24 and 72 h after ischemia. In parallel, immunohistochemical signals for the QC substrate CCL2 increased from 24 to 72 h after ischemia induction without differences between genotypes analyzed. The increase in CCL2 was accompanied by morphological activation of Iba1-immunoreactive microglia and recruitment of MHC-II-positive cells at 72 h after ischemia. Among other chemokines quantified in the brain tissue, CCL17 showed higher concentrations at 72 h compared to 24 h after ischemia. Collectively, these data suggest a critical role for QC in inflammatory processes in the stroke-affected brain.

Central IRF4/5 Signaling Are Critical for Microglial Activation and Impact on Stroke Outcomes

Microglia and monocytes play a critical role in immune responses to cerebral ischemia. Previous studies have demonstrated that interferon regulatory factor 4 (IRF4) and IRF5 direct microglial polarization after stroke and impact outcomes. However, IRF4/5 are expressed by both microglia and monocytes, and it is not clear if it is the microglial (central) or monocytic (peripheral) IRF4-IRF5 regulatory axis that functions in stroke. In this work, young (8-12 weeks) male pep boy (PB), IRF4 or IRF5 flox, and IRF4 or IRF5 conditional knockout (CKO) mice were used to generate 8 types of bone marrow chimeras, to differentiate the role of central (PB-to-IRF CKO) vs. peripheral (IRF CKO-to-PB) phagocytic IRF4-IRF5 axis in stroke. Chimeras generated from PB and flox mice were used as controls. All chimeras were subjected to 60-min middle cerebral artery occlusion (MCAO) model. Three days after the stroke, outcomes and inflammatory responses were analyzed. We found that PB-to-IRF4 CKO chimeras had more robust microglial pro-inflammatory responses than IRF4 CKO-to-PB chimeras, while ameliorated microglial response was seen in PB-to-IRF5 CKO vs. IRF5 CKO-to-PB chimeras. PB-to-IRF4 or IRF5 CKO chimeras had worse or better stroke outcomes respectively than their controls, whereas IRF4 or 5 CKO-to-PB chimeras had similar outcomes compared to controls. We conclude that the central IRF4/5 signaling is responsible for microglial activation and mediates stroke outcomes.

Bone marrow-derived myeloid cells transiently colonize the brain during postnatal development and interact with glutamatergic synapses

Although the roles of embryonic yolk sac-derived, resident microglia in neurodevelopment were extensively studied, the possible involvement of bone marrow-derived cells remains elusive. In this work, we used a fate-mapping strategy to selectively label bone marrow-derived cells and their progeny in the brain (FLT3+IBA1+). FLT3+IBA1+ cells were confirmed to be transiently present in the healthy brain during early postnatal development. FLT3+IBA1+ cells have a distinct morphology index at postnatal day(P)0, P7, and P14 compared with neighboring microglia. FLT3+IBA1+ cells also express the microglial markers P2RY12 and TMEM119 and interact with VGLUT1 synapses at P14. Scanning electron microscopy indeed showed that FLT3+ cells contact and engulf pre-synaptic elements. Our findings suggest FLT3+IBA1+ cells might assist microglia in their physiological functions in the developing brain including synaptic pruning which is performed using their purinergic sensors. Our findings stimulate further investigation on the involvement of peripheral macrophages during homeostatic and pathological development.

Blocking cGAS-STING pathway promotes post-stroke functional recovery in an extended treatment window via facilitating remyelination

BACKGROUND

Ischemic stroke is a major cause of worldwide death and disability, with recombinant tissue plasminogen activator being the sole effective treatment, albeit with a limited treatment window. The cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING) pathway is emerging as the major DNA-sensing pathway to invoke immune responses in neuroinflammatory disorders.

METHODS

By performing a series of neurobehavioral assessments, electrophysiological analysis, high-throughput sequencing, and cell-based assays based on the transient middle cerebral artery occlusion (tMCAO) mouse stroke model, we examined the effects and underlying mechanisms of genetic and pharmacological inhibition of the cGAS-STING pathway on long-term post-stroke neurological functional outcomes.

FINDINGS

Blocking the cGAS-STING pathway, even 3 days after tMCAO, significantly promoted functional recovery in terms of white matter structural and functional integrity as well as sensorimotor and cognitive functions. Mechanistically, the neuroprotective effects via inhibiting the cGAS-STING pathway were contributed not only by inflammation repression at the early stage of tMCAO but also by modifying the cell state of phagocytes to facilitate remyelination at the sub-acute phase. The activation of the cGAS-STING pathway significantly impeded post-stroke remyelination through restraining myelin debris uptake and degradation and hindering oligodendrocyte differentiation and maturation.

CONCLUSIONS

Manipulating the cGAS-STING pathway has an extended treatment window in promoting long-term post-stroke functional recovery via facilitating remyelination in a mouse stroke model. Our results highlight the roles of the cGAS-STING pathway in aggregating stroke pathology and propose a new way for improving functional recovery after ischemic stroke.

FUNDING

This work was primarily funded by the National Key R&D Program of China.

Mechanisms of inflammation after ischemic stroke in brain-peripheral crosstalk

Stroke is a devastating disease with high morbidity, disability, and mortality, among which ischemic stroke is more common. However, there is still a lack of effective methods to improve the prognosis and reduce the incidence of its complications. At present, there is evidence that peripheral organs are involved in the inflammatory response after stroke. Moreover, the interaction between central and peripheral inflammation includes the activation of resident and peripheral immune cells, as well as the activation of inflammation-related signaling pathways, which all play an important role in the pathophysiology of stroke. In this review, we discuss the mechanisms of inflammatory response after ischemic stroke, as well as the interactions through circulatory pathways between peripheral organs (such as the gut, heart, lung and spleen) and the brain to mediate and regulate inflammation after ischemic stroke. We also propose the potential role of meningeal lymphatic vessels (MLVs)-cervical lymph nodes (CLNs) as a brain-peripheral crosstalk lymphatic pathway in ischemic stroke. In addition, we also summarize the mechanisms of anti-inflammatory drugs in the treatment of ischemic stroke.

Molecular Pathogenesis of Ischemic and Hemorrhagic Strokes: Background and Therapeutic Approaches

Stroke represents one of the neurological diseases most responsible for death and permanent disability in the world. Different factors, such as thrombus, emboli and atherosclerosis, take part in the intricate pathophysiology of stroke. Comprehending the molecular processes involved in this mechanism is crucial to developing new, specific and efficient treatments. Some common mechanisms are excitotoxicity and calcium overload, oxidative stress and neuroinflammation. Furthermore, non-coding RNAs (ncRNAs) are critical in pathophysiology and recovery after cerebral ischemia. ncRNAs, particularly microRNAs, and long non-coding RNAs (lncRNAs) are essential for angiogenesis and neuroprotection, and they have been suggested to be therapeutic, diagnostic and prognostic tools in cerebrovascular diseases, including stroke. This review summarizes the intricate molecular mechanisms underlying ischemic and hemorrhagic stroke and delves into the function of miRNAs in the development of brain damage. Furthermore, we will analyze new perspectives on treatment based on molecular mechanisms in addition to traditional stroke therapies.

Establishment of a high-content compatible platform to assess effects of monocyte-derived factors on neural stem cell proliferation and differentiation

During neuroinflammation, monocytes that infiltrate the central nervous system (CNS) may contribute to regenerative processes depending on their activation status. However, the extent and mechanisms of monocyte-induced CNS repair in patients with neuroinflammatory diseases remain largely unknown, partly due to the lack of a fully human assay platform that can recapitulate monocyte-neural stem cell interactions within the CNS microenvironment. We therefore developed a human model system to assess the impact of monocytic factors on neural stem cells, establishing a high-content compatible assay for screening monocyte-induced neural stem cell proliferation and differentiation. The model combined monocytes isolated from healthy donors and human embryonic stem cell derived neural stem cells and integrated both cell-intrinsic and -extrinsic properties. We identified CNS-mimicking culture media options that induced a monocytic phenotype resembling CNS infiltrating monocytes, while allowing adequate monocyte survival. Monocyte-induced proliferation, gliogenic fate and neurogenic fate of neural stem cells were affected by the conditions of monocytic priming and basal neural stem cell culture as extrinsic factors as well as the neural stem cell passage number as an intrinsic neural stem cell property. We developed a high-content compatible human in vitro assay for the integrated analysis of monocyte-derived factors on CNS repair.

Phenotypic and spatial heterogeneity of brain myeloid cells after stroke is associated with cell ontogeny, tissue damage, and brain connectivity

Acute stroke triggers extensive changes to myeloid immune cell populations in the brain that may be targets for limiting brain damage and enhancing repair. Immunomodulatory approaches will be most effective with precise manipulation of discrete myeloid cell phenotypes in time and space. Here, we investigate how stroke alters mononuclear myeloid cell composition and phenotypes at single-cell resolution and key spatial patterns. Our results show that multiple reactive microglial states and monocyte-derived populations contribute to an extensive myeloid cell repertoire in post-stroke brains. We identify important overlaps and distinctions among different cell types/states that involve ontogeny- and spatial-related properties. Notably, brain connectivity with infarcted tissue underpins the pattern of local and remote altered cell accumulation and reactivity. Our discoveries suggest a global but anatomically governed brain myeloid cell response to stroke that comprises diverse phenotypes arising through intrinsic cell ontogeny factors interacting with exposure to spatially organized brain damage and neuro-axonal cues.

Advances in Engineered Nanoparticles for the Treatment of Ischemic Stroke by Enhancing Angiogenesis

Angiogenesis, or the formation of new blood vessels, is a natural defensive mechanism that aids in the restoration of oxygen and nutrition delivery to injured brain tissue after an ischemic stroke. Angiogenesis, by increasing vessel development, may maintain brain perfusion, enabling neuronal survival, brain plasticity, and neurologic recovery. Induction of angiogenesis and the formation of new vessels aid in neurorepair processes such as neurogenesis and synaptogenesis. Advanced nano drug delivery systems hold promise for treatment stroke by facilitating efficient transportation across the the blood-brain barrier and maintaining optimal drug concentrations. Nanoparticle has recently been shown to greatly boost angiogenesis and decrease vascular permeability, as well as improve neuroplasticity and neurological recovery after ischemic stroke. We describe current breakthroughs in the development of nanoparticle-based treatments for better angiogenesis therapy for ischemic stroke employing polymeric nanoparticles, liposomes, inorganic nanoparticles, and biomimetic nanoparticles in this study. We outline new nanoparticles in detail, review the hurdles and strategies for conveying nanoparticle to lesions, and demonstrate the most recent advances in nanoparticle in angiogenesis for stroke treatment.

Obesity-induced Ly6CHigh and Ly6CLow monocyte subset changes abolish post-ischemic limb conditioning benefits in stroke recovery

Remote limb conditioning (RLC), performed by intermittent interruption of blood flow to a limb, triggers endogenous tolerance mechanisms and improves stroke outcomes. The underlying mechanism for the protective effect involves a shift of circulating monocytes to a Ly6CHigh proinflammatory subset in normal metabolic conditions. The current study investigates the effect of RLC on stroke outcomes in subjects with obesity, a vascular comorbidity. Compared to lean mice, obese stroke mice displayed significantly higher circulating monocytes (monocytosis), increased CD45High monocytes/macrophages infiltration to the injured brain, worse acute outcomes, and delayed recovery. Unlike lean mice, obese mice with RLC at 2 hours post-stroke failed to shift circulating monocytes to pro-inflammatory status and nullified RLC-induced functional benefit. The absence of the monocyte shift was also observed in splenocytes incubated with RLC serum from obese mice, while the shift was observed in the cultures with RLC serum from lean mice. These results showed that the alteration of monocytosis and subsets underlies negating RLC benefits in obese mice and suggest careful considerations of comorbidities at the time of RLC application for stroke therapy.

CCR2+ monocytes replenish border-associated macrophages in the diseased mouse brain

Border-associated macrophages (BAMs) are tissue-resident macrophages that reside at the border of the central nervous system (CNS). Since BAMs originate from yolk sac progenitors that do not persist after birth, the means by which this population of cells is maintained is not well understood. Using two-photon microscopy and multiple lineage-tracing strategies, we determine that CCR2+ monocytes are significant contributors to BAM populations following disruptions of CNS homeostasis in adult mice. After BAM depletion, while the residual BAMs possess partial self-repopulation capability, the CCR2+ monocytes are a critical source of the repopulated BAMs. In addition, we demonstrate the existence of CCR2+ monocyte-derived long-lived BAMs in a brain compression model and in a sepsis model after the initial disruption of homeostasis. Our study reveals that the short-lived CCR2+ monocytes transform into long-lived BAM-like cells at the CNS border and subsequently contribute to BAM populations.

Targeting brain-peripheral immune responses for secondary brain injury after ischemic and hemorrhagic stroke

The notion that the central nervous system is an immunologically immune-exempt organ has changed over the past two decades, with increasing evidence of strong links and interactions between the central nervous system and the peripheral immune system, both in the healthy state and after ischemic and hemorrhagic stroke. Although primary injury after stroke is certainly important, the limited therapeutic efficacy, poor neurological prognosis and high mortality have led researchers to realize that secondary injury and damage may also play important roles in influencing long-term neurological prognosis and mortality and that the neuroinflammatory process in secondary injury is one of the most important influences on disease progression. Here, we summarize the interactions of the central nervous system with the peripheral immune system after ischemic and hemorrhagic stroke, in particular, how the central nervous system activates and recruits peripheral immune components, and we review recent advances in corresponding therapeutic approaches and clinical studies, emphasizing the importance of the role of the peripheral immune system in ischemic and hemorrhagic stroke.

The systemic inflammation score is a prognostic factor for patients with ischemic stroke who have not undergone intravenous thrombolysis or endovascular thrombectomy therapy

BACKGROUND

The systemic inflammation score (SIS) has been utilised as a representative biomarker for evaluating nutritional and inflammation status. However, the predictive value of SIS has not been reported in patients with acute ischemic stroke (AIS). We aimed to evaluate whether SIS is associated with prognosis in stroke.

METHODS

A total of 4801 patients with AIS were included in the study. The primary outcome was a modified Rankin Scale score>2 at the 3-month follow-up. A total of 4801 patients were randomly allocated into training (n=3361) and validation cohorts (n=1440) at a ratio of 7:3. Model performance was validated using the receiver operating characteristic (ROC) curve and calibration curve. Additionally, a comparison was made between the nomogram and the THRIVE score in regards to their respective predictive capabilities.

RESULTS

Overall, 1091(32.5%) patients in the training cohort and 446 (31.0%) patients in the validation cohort experienced an unfavorable outcome. The multivariate logistic regression analysis revealed that a high SIS, age, NIHSS, diabetes and prior stroke were associated with unfavorable outcome. Our nomogram was developed based on the variables mentioned above. The area under the curve (AUC) of the training set and the validation set are 0.702 and 0.708, respectively, indicating that the model has modest agreement and discrimination. The results of AUC, net reclassification improvement (NRI) and integrated discrimination improvement (IDI) showed that nomogram had significantly higher predictive value than THRIVE scores (all P<0.001). However, unlike the THRIVE publication, all patients who had undergone intravenous thrombolysis or endovascular thrombectomy therapy were excluded in our study. In consequence, our derived THRIVE scores cannot be compared to those in the original THRIVE study.

CONCLUSION

The SIS exhibits potential as a simple prognostic biomarker, and the nomogram, which utilizes the SIS, may serve as a valuable tool for clinicians in the early identification of patients at heightened risk for unfavorable outcomes.

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.

Stroke and Neurogenesis: Bridging Clinical Observations to New Mechanistic Insights from Animal Models

Stroke was the 2nd leading cause of death and a major cause of morbidity. Unfortunately, there are limited means to promote neurological recovery post-stroke, but research has unearthed potential targets for therapies to encourage post-stroke neurogenesis and neuroplasticity. The occurrence of neurogenesis in adult mammalian brains, including humans, was not widely accepted until the 1990s. Now, adult neurogenesis has been extensively studied in human and mouse neurogenic brain niches, of which the subventricular zone of the lateral ventricles and subgranular zone of the dentate gyrus are best studied. Numerous other niches are under investigation for neurogenic potential. This review offers a basic overview to stroke in the clinical setting, a focused summary of recent and foundational research literature on cortical neurogenesis and post-stroke brain plasticity, and insights regarding how the meninges and choroid plexus have emerged as key players in neurogenesis and neuroplasticity in the context of focal cerebral ischemia disrupting the anterior circulation. The choroid plexus and meninges are vital as they are integral sites for neuroimmune interactions, glymphatic perfusion, and niche signaling pertinent to neural stem cells and neurogenesis. Modulating neuroimmune interactions with a focus on astrocyte activity, potentially through manipulation of the choroid plexus and meningeal niches, may reduce the exacerbation of stroke by inflammatory mediators and create an environment conducive to neurorecovery. Furthermore, addressing impaired glymphatic perfusion after ischemic stroke likely supports a neurogenic environment by clearing out inflammatory mediators, neurotoxic metabolites, and other accumulated waste. The meninges and choroid plexus also contribute more directly to promoting neurogenesis: the meninges are thought to harbor neural stem cells and are a niche amenable to neural stem/progenitor cell migration. Additionally, the choroid plexus has secretory functions that directly influences stem cells through signaling mechanisms and growth factor actions. More research to better understand the functions of the meninges and choroid plexus may lead to novel approaches for stimulating neuronal recovery after ischemic stroke.

Cerebral protective effect of in situ and remote ischemic postconditioning on ischemic stroke rat via the TGFβ1-Smad2/3 signaling pathway

Patients with acute ischemic stroke achieve inadequate benefit due to the short therapeutic window for thrombolysis and the risk of ischemia/reperfusion (IR) injury. Ischemic postconditioning induces endogenous cerebral protection for acute ischemic stroke, although the protective mechanisms associated with ischemic postconditioning haven't been well clarified. In present study, the rat models of ischemic cerebral stroke with in situ and remote ischemic postconditioning (ISP and RIP) were established successfully. The Zea Longa and the modified neurological severity scoring (mNSS) were carried out to evaluate neurological function in the rats, while the open field test was explored to estimate their autonomic athletic ability. The 2,3,5-riphenyltetrazolium chloride (TTC) staining method was used to measure the size of the infarcts. TUNEL and Nissl's staining were used to detect the apoptosis rate of cells in the ischemic penumbra, with the expression of TGFβ1, Smad2, and Smad3 in the ischemic penumbra and serum detected by immunohistochemical staining, qRT-PCR, Western blots, and ELISA analysis. We showed that application of both types of ischemic postconditioning had cerebral protective effects for the ischemic stroke rats, that included effective reduction in the volume of cerebral infarction, alleviation of apoptosis and inflammation in the ischemic penumbra, and promotion of recovery of neurological function. These effects included significantly enriched gene ontology (GO) terms after RIP intervention that were related to TGFβ1, increased protein levels of TGFβ1 and decreased levels of p-Smad2/3 and smad3 following RIP intervention. We showed that the TGFβ1-Smad2/3 signaling pathway was associated with the cerebral protection of ischemic postconditioning.

Mechanisms of immune response and cell death in ischemic stroke and their regulation by natural compounds

Ischemic stroke (IS), which is the third foremost cause of disability and death worldwide, has inflammation and cell death as its main pathological features. IS can lead to neuronal cell death and release factors such as damage-related molecular patterns, stimulating the immune system to release inflammatory mediators, thereby resulting in inflammation and exacerbating brain damage. Currently, there are a limited number of treatment methods for IS, which is a fact necessitating the discovery of new treatment targets. For this review, current research on inflammation and cell death in ischemic stroke was summarized. The complex roles and pathways of the principal immune cells (microglia, astrocyte, neutrophils, T lymphocytes, and monocytes/macrophage) in the immune system after IS in inflammation are discussed. The mechanisms of immune cell interactions and the cytokines involved in these interactions are summarized. Moreover, the cell death mechanisms (pyroptosis, apoptosis, necroptosis, PANoptosis, and ferroptosis) and pathways after IS are explored. Finally, a summary is provided of the mechanism of action of natural pharmacological active ingredients in the treatment of IS. Despite significant recent progress in research on IS, there remain many challenges that need to be overcome.

Locus Coeruleus and Noradrenergic Pharmacology in Neurodegenerative Disease

Adrenoceptors (ARs) throughout the brain are stimulated by noradrenaline originating mostly from neurons of the locus coeruleus, a brainstem nucleus that is ostensibly the earliest to show detectable pathology in neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. The α1-AR, α2-AR, and β-AR subtypes expressed in target brain regions and on a range of cell populations define the physiological responses to noradrenaline, which includes activation of cognitive function in addition to modulation of neurometabolism, cerebral blood flow, and neuroinflammation. As these heterocellular functions are critical for maintaining brain homeostasis and neuronal health, combating the loss of noradrenergic tone from locus coeruleus degeneration may therefore be an effective treatment for both cognitive symptoms and disease modification in neurodegenerative indications. Two pharmacologic approaches are receiving attention in recent clinical studies: preserving noradrenaline levels (e.g., via reuptake inhibition) and direct activation of target adrenoceptors. Here, we review the expression and role of adrenoceptors in the brain, the preclinical studies which demonstrate that adrenergic stimulation can support cognitive function and cerebral health by reversing the effects of noradrenaline depletion, and the human data provided by pharmacoepidemiologic analyses and clinical trials which together identify adrenoceptors as promising targets for the treatment of neurodegenerative disease.

Monocyte-related cytokines/chemokines in cerebral ischemic stroke

AIMS

Ischemic stroke is one of the leading causes of death worldwide and the most common cause of disability in Western countries. Multiple mechanisms contribute to the development and progression of ischemic stroke, and inflammation is one of the most important mechanisms.

DISCUSSION

Ischemia induces the release of adenosine triphosphate/reactive oxygen species, which activates immune cells to produce many proinflammatory cytokines that activate downstream inflammatory cascades to induce fatal immune responses. Research has confirmed that peripheral blood immune cells play a vital role in the immunological cascade after ischemic stroke. The role of monocytes has received much attention among numerous peripheral blood immune cells. Monocytes induce their effects by secreting cytokines or chemokines, including CCL2/CCR2, CCR4, CCR5, CD36, CX3CL1/CX3CR1, CXCL12(SDF-1), LFA-1/ICAM-1, Ly6C, MMP-2/9, NR4A1, P2X4R, P-selectin, CD40L, TLR2/4, and VCAM-1/VLA-4. Those factors play important roles in the process of monocyte recruitment, migration, and differentiation.

CONCLUSION

This review focuses on the function and mechanism of the cytokines secreted by monocytes in the process of ischemic stroke and provides novel targets for treating cerebral ischemic stroke.

Inhibition of insulin-regulated aminopeptidase confers neuroprotection in a conscious model of ischemic stroke

Stroke is a leading cause of mortality and morbidity with a paucity of effective pharmacological treatments. We have previously identified insulin-regulated aminopeptidase (IRAP) as a potential target for the development of a new class of drugs for the treatment of stroke, as global deletion of this gene in mice significantly protected against ischemic damage. In the current study, we demonstrate that small molecular weight IRAP inhibitors reduce infarct volume and improve neurological outcome in a hypertensive animal model of ischemic stroke. The effects of two structurally distinct IRAP inhibitors (HFI419 or SJM164) were investigated in a model of stroke where the middle cerebral artery was transiently occluded with endothelin-1 in the conscious spontaneously hypertensive rat. IRAP inhibitor was administered into the lateral ventricle at 2 or 6 h after stroke, with subsequent doses delivered at 24, 48 and 70 h post-stroke. Functional outcomes were assessed prior to drug treatment, and on day 1 and 3 post-stroke. Histological analyses and neuroinflammatory cytokine profiling were conducted at 72 and 24 h post-stroke respectively. IRAP inhibitor treatment following stroke significantly reduced infarct volume and improved neurological and motor deficits. These protective effects were maintained even when the therapeutic window was extended to 6 h. Examination of the cellular architecture at 72 h post-stroke demonstrated that IRAP expression was upregulated in CD11b positive cells and activated astrocytes. Furthermore, IRAP inhibitor treatment significantly increased gene expression for interleukin 6 and C-C motif chemokine ligand 2 in the ischemic core. This study provides proof-of-principle that selective inhibition of IRAP activity with two structurally distinct IRAP inhibitors reduces infarct volume and improves functional outcome even when the first dose is administered 6 h post-stroke. This is the first direct evidence that IRAP inhibitors are a class of drug with potential use in the treatment of ischemic stroke.

Direct neuronal conversion of microglia/macrophages reinstates neurological function after stroke

Although generating new neurons in the ischemic injured brain would be an ideal approach to replenish the lost neurons for repairing the damage, the adult mammalian brain retains only limited neurogenic capability. Here, we show that direct conversion of microglia/macrophages into neurons in the brain has great potential as a therapeutic strategy for ischemic brain injury. After transient middle cerebral artery occlusion in adult mice, microglia/macrophages converge at the lesion core of the striatum, where neuronal loss is prominent. Targeted expression of a neurogenic transcription factor, NeuroD1, in microglia/macrophages in the injured striatum enables their conversion into induced neuronal cells that functionally integrate into the existing neuronal circuits. Furthermore, NeuroD1-mediated induced neuronal cell generation significantly improves neurological function in the mouse stroke model, and ablation of these cells abolishes the gained functional recovery. Our findings thus demonstrate that neuronal conversion contributes directly to functional recovery after stroke.

Macrophage and monocyte subsets in response to ischemic stroke

Ischemic stroke is a leading cause of disability and mortality. Despite extensive efforts in stroke research, the only pharmacological treatment currently available is arterial recanalization, which has limited efficacy only in the acute phase of stroke. The neuroinflammatory response to stroke is believed to provide a wider time window than recanalization and has therefore been proposed as an attractive therapeutic target. In this review, we provide an overview of recent advances in the understanding of cellular and molecular responses of distinct macrophage populations following stroke, which may offer potential targets for therapeutic interventions. Specifically, we discuss the role of local responders in neuroinflammation, including the well-studied microglia as well as the emerging players, border-associated macrophages, and macrophages originating from the skull bone marrow. Additionally, we focus on the behavior of monocytes stemming from distant tissues such as the bone marrow and spleen. Finally, we highlight aging as a crucial factor modulating the immune response, which is often neglected in animal studies.

Time-dependent dual effect of microglia in ischemic stroke

Stroke, the third leading cause of death and disability worldwide, is classified into ischemic or hemorrhagic, in which approximately 85% of strokes are ischemic. Ischemic stroke occurs as a result of arterial occlusion due to embolus or thrombus, with ischemia in the perfusion territory supplied by the occluded artery. The traditional concept that ischemic stroke is solely a vascular occlusion disorder has been expanded to include the dynamic interaction between microglia, astrocytes, neurons, vascular cells, and matrix components forming the "neurovascular unit." Acute ischemic stroke triggers a wide spectrum of neurovascular disturbances, glial activation, and secondary neuroinflammation that promotes further injury, ultimately resulting in neuronal death. Microglia, as the resident macrophages in the central nervous system, is one of the first responders to ischemic injury and plays a significant role in post-ischemic neuroinflammation. In this review, we reviewed the mechanisms of microglia in multiple stages of post-ischemic neuroinflammation development, including acute, sub-acute and chronic phases of stroke. A comprehensive understanding of the dynamic variation and the time-dependent role of microglia in post-stroke neuroinflammation could aid in the search for more effective therapeutics and diagnostic strategies for ischemic stroke.

Monocytes in neonatal stroke and hypoxic‐ischemic encephalopathy: Pathophysiological mechanisms and therapeutic possibilities

Neonatal arterial ischemic stroke (NAIS) and neonatal hypoxic‐ischemic encephalopathy (HIE) are common causes of neurological impairments in infants, for which treatment options are very limited. NAIS and HIE induce an innate immune response that involves the recruitment of peripheral immune cells, including monocytes, into the brain. Monocytes and monocyte‐derived cells have the potential to contribute to both harmful and beneficial pathophysiological processes, such as neuroinflammation and brain repair, but their roles in NAIS and HIE remain poorly understood. Furthermore, recent evidence indicates that monocyte‐derived macrophages can persist in the brain for several months following NAIS and HIE in mice, with possible long‐lasting consequences that are still unknown. This review provides a comprehensive overview of the mechanisms of monocyte infiltration and their potential functions in the ischemic brain, focusing on HIE and NAIS. Therapeutic strategies targeting monocytes and the possibility of using monocytes for cell‐based therapies are also discussed.

Imaging increased metabolism in the spinal cord in mice after middle cerebral artery occlusion

Emerging evidence indicates crosstalk between the brain and hematopoietic system following cerebral ischemia. Here, we investigated metabolism and oxygenation in the spleen and spinal cord in a transient middle cerebral artery occlusion (tMCAO) model. Sham-operated and tMCAO mice underwent [18F]fluorodeoxyglucose (FDG)-positron emission tomography (PET) to assess glucose metabolism. Naïve, sham-operated and tMCAO mice underwent multispectral optoacoustic tomography (MSOT) assisted by quantitative model-based reconstruction and unmixing algorithms for accurate mapping of oxygenation patterns in peripheral tissues at 24 h after reperfusion. We found increased [18F]FDG uptake and reduced MSOT oxygen saturation, indicating hypoxia in the thoracic spinal cord of tMCAO mice compared with sham-operated mice but not in the spleen. Reduced spleen size was observed in tMCAO mice compared with sham-operated mice ex vivo. tMCAO led to an increase in the numbers of mature T cells in femoral bone marrow tissues, concomitant with a stark reduction in these cell subsets in the spleen and peripheral blood. The combination of quantitative PET and MSOT thus enabled observation of hypoxia and increased metabolic activity in the spinal cord of tMCAO mice at 24 h after occlusion compared to sham-operated mice.

Monocyte-derived IL-6 programs microglia to rebuild damaged brain vasculature

Cerebrovascular injury (CVI) is a common pathology caused by infections, injury, stroke, neurodegeneration and autoimmune disease. Rapid resolution of a CVI requires a coordinated innate immune response. In the present study, we sought mechanistic insights into how central nervous system-infiltrating monocytes program resident microglia to mediate angiogenesis and cerebrovascular repair after an intracerebral hemorrhage. In the penumbrae of human stroke brain lesions, we identified a subpopulation of microglia that express vascular endothelial growth factor A. These cells, termed 'repair-associated microglia' (RAMs), were also observed in a rodent model of CVI and coexpressed interleukin (IL)-6Ra. Cerebrovascular repair did not occur in IL-6 knockouts or in mice lacking microglial IL-6Ra expression and single-cell transcriptomic analyses revealed faulty RAM programming in the absence of IL-6 signaling. Infiltrating CCR2+ monocytes were the primary source of IL-6 after a CVI and were required to endow microglia with proliferative and proangiogenic properties. Faulty RAM programming in the absence of IL-6 or inflammatory monocytes resulted in poor cerebrovascular repair, neuronal destruction and sustained neurological deficits that were all restored via exogenous IL-6 administration. These data provide a molecular and cellular basis for how monocytes instruct microglia to repair damaged brain vasculature and promote functional recovery after injury.

Dual effect of C-C motif chemokine receptor 5 on ischemic stroke: More harm than benefit?

Ischemic stroke involves a series of complex pathological mechanisms, of which neuroinflammation is currently the most widely recognized. C-C motif chemokine receptor 5 (CCR5) has recently been shown to be upregulated after cerebral ischemia. Notably, CCR5 is not only involved in neuroinflammation, but also in the blood-brain barrier, neural structures, and connections. Accumulating experimental studies indicate that CCR5 has a dual effect on ischemic stroke. In the acute phase after cerebral ischemia, the pro-inflammatory and disruptive effect of CCR5 on the blood-brain barrier predominates. However, in the chronic phase, the effect of CCR5 on the repair of neural structures and connections is thought to be cell-type dependent. Interestingly, clinical evidence has shown that CCR5 might be harmful rather than beneficial. CCR5-Δ32 mutation or CCR5 antagonist exerts a neuroprotective effect in patients with ischemic stroke. Considering CCR5 as an attractive potential target, we introduce the current research progress of the entangled relationships between CCR5 and ischemic stroke. Clinical data are still needed to determine the efficacy of activating or inactivating CCR5 in the treatment of ischemic stroke, especially for potential phase- or cell type-dependent treatments in the future.

A Glance at Biogenesis and Functionality of MicroRNAs and Their Role in the Neuropathogenesis of Parkinson's Disease

MicroRNAs (miRNAs) are short, noncoding RNA transcripts. Mammalian miRNA coding sequences are located in introns and exons of genes encoding various proteins. As the central nervous system is the largest source of miRNA transcripts in living organisms, miRNA molecules are an integral part of the regulation of epigenetic activity in physiological and pathological processes. Their activity depends on many proteins that act as processors, transporters, and chaperones. Many variants of Parkinson's disease have been directly linked to specific gene mutations which in pathological conditions are cumulated resulting in the progression of neurogenerative changes. These mutations can often coexist with specific miRNA dysregulation. Dysregulation of different extracellular miRNAs has been confirmed in many studies on the PD patients. It seems reasonable to conduct further research on the role of miRNAs in the pathogenesis of Parkinson's disease and their potential use in future therapies and diagnosis of the disease. This review presents the current state of knowledge about the biogenesis and functionality of miRNAs in the human genome and their role in the neuropathogenesis of Parkinson's disease (PD)-one of the most common neurodegenerative disorders. The article also describes the process of miRNA formation which can occur in two ways-the canonical and noncanonical one. However, the main focus was on miRNA's use in in vitro and in vivo studies in the context of pathophysiology, diagnosis, and treatment of PD. Some issues, especially those regarding the usefulness of miRNAs in PD's diagnostics and especially its treatment, require further research. More standardization efforts and clinical trials on miRNAs are needed.

Thromboinflammatory challenges in stroke pathophysiology

Despite years of encouraging translational research, ischemic stroke still remains as one of the highest unmet medical needs nowadays, causing a tremendous burden to health care systems worldwide. Following an ischemic insult, a complex signaling pathway emerges leading to highly interconnected thrombotic as well as neuroinflammatory signatures, the so-called thromboinflammatory cascade. Here, we thoroughly review the cell-specific and time-dependent role of different immune cell types, i.e., neutrophils, macrophages, T and B cells, as key thromboinflammatory mediators modulating the neuroinflammatory response upon stroke. Similarly, the relevance of platelets and their tight crosstalk with a variety of immune cells highlights the relevance of this cell-cell interaction during microvascular dysfunction, neovascularization, and cellular adhesion. Ultimately, we provide an up-to-date overview of therapeutic approaches mechanistically targeting thromboinflammation currently under clinical translation, especially focusing on phase I to III clinical trials.

Stimulation of Angiotensin II Type 2 Receptor Modulates Pro-Inflammatory Response in Microglia and Macrophages: Therapeutic Implications for the Treatment of Stroke

BACKGROUND

Sustained microglial activation contributes to the development of post-stroke cognitive impairment (PSCI). Compound 21 (C21), an angiotensin II type 2 receptor agonist, has shown some neurovascular protection after stroke. This study aimed to investigate the direct anti-inflammatory effects of C21 on macrophages, as well as brain innate immune cells.

METHODS

Murine microglial cell line (C8-B4) and RAW 264.7 macrophages were exposed to lipopolysaccharide (LPS) and co-treated with C21. Pro-inflammatory mediators were assessed via RT-qPCR and ELISA. Cellular reactive oxygen species (ROS) were evaluated via CellROXGreen staining, and nitrate production was assessed using Griess assay.

RESULTS

C21 suppressed LPS-induced inflammation and ROS generation in both cells. In microglia, C21 blunted LPS-induced mRNA expression of IL-1β, IL-12b, COX-1, iNOS, and IL-6. A similar pattern was observed in macrophages, where C21 suppressed LPS-induced IL-1β, TNF-α, and CXCL1 expression. These anti-inflammatory effects in microglia and macrophages were associated with increased neuroprotective gene expression, including GDNF and BDNF, in a dose-dependent manner.

CONCLUSIONS

Our findings suggest a protective effect of C21 against the inflammatory response, in both macrophages and microglia, via suppression of the release of pro-inflammatory cytokines/chemokines and the generation of ROS while stimulating the production of neurotrophic factors.

Immune stimulation recruits a subset of pro-regenerative macrophages to the retina that promotes axonal regrowth of injured neurons

The multifaceted nature of neuroinflammation is highlighted by its ability to both aggravate and promote neuronal health. While in mammals retinal ganglion cells (RGCs) are unable to regenerate following injury, acute inflammation can induce axonal regrowth. However, the nature of the cells, cellular states and signalling pathways that drive this inflammation-induced regeneration have remained elusive. Here, we investigated the functional significance of macrophages during RGC de- and regeneration, by characterizing the inflammatory cascade evoked by optic nerve crush (ONC) injury, with or without local inflammatory stimulation in the vitreous. By combining single-cell RNA sequencing and fate mapping approaches, we elucidated the response of retinal microglia and recruited monocyte-derived macrophages (MDMs) to RGC injury. Importantly, inflammatory stimulation recruited large numbers of MDMs to the retina, which exhibited long-term engraftment and promoted axonal regrowth. Ligand-receptor analysis highlighted a subset of recruited macrophages that exhibited expression of pro-regenerative secreted factors, which were able to promote axon regrowth via paracrine signalling. Our work reveals how inflammation may promote CNS regeneration by modulating innate immune responses, providing a rationale for macrophage-centred strategies for driving neuronal repair following injury and disease.

Systemic innate myeloid responses to acute ischaemic and haemorrhagic stroke

Acute ischaemic and haemorrhagic stroke account for significant disability and morbidity burdens worldwide. The myeloid arm of the peripheral innate immune system is critical in the immunological response to acute ischaemic and haemorrhagic stroke. Neutrophils, monocytes, and dendritic cells (DC) contribute to the evolution of pathogenic local and systemic inflammation, whilst maintaining a critical role in ongoing immunity protecting against secondary infections. This review aims to summarise the key alterations to myeloid immunity in acute ischaemic stroke, intracerebral haemorrhage (ICH), and subarachnoid haemorrhage (SAH). By integrating clinical and preclinical research, we discover how myeloid immunity is affected across multiple organ systems including the brain, blood, bone marrow, spleen, and lung, and evaluate how these perturbations associate with real-world outcomes including infection. These findings are placed in the context of the rapidly developing field of human immunology, which offers a wealth of opportunity for further research.

Friends or foes: The mononuclear phagocyte system in ischemic stroke

Ischemic stroke (IS) is a major cause of disability and death in adults, and the immune response plays an indispensable role in its pathological process. After the onset of IS, an inflammatory storm, with the infiltration and mobilization of the mononuclear phagocyte system (MPS), is triggered in the brain. Microglia are rapidly activated in situ, followed by waves of circulating monocytes into the ischemic area. Activated microglia and monocytes/macrophages are mainly distributed in the peri-infarct area. These cells have similar morphology and functions, such as secreting cytokines and phagocytosis. Previously, the presence of the MPS was considered a marker of an exacerbated inflammatory response that contributes to brain damage. However, recent studies have suggested a rather complicated role of the MPS in IS. Here, we reviewed articles focusing on various functions of the MPS among different phases of IS, including recruitment, polarization, phagocytosis, angiogenesis, and interaction with other types of cells. Moreover, due to the characteristics of the MPS, we also noted clinical research addressing alterations in the MPS as potential biomarkers for IS patients for the purposes of predicting prognosis and developing novel therapeutic strategies.

Ischemic brain edema: Emerging cellular mechanisms and therapeutic approaches

Brain edema is one of the most devastating consequences of ischemic stroke. Malignant cerebral edema is the main reason accounting for the high mortality rate of large hemispheric strokes. Despite decades of tremendous efforts to elucidate mechanisms underlying the formation of ischemic brain edema and search for therapeutic targets, current treatments for ischemic brain edema remain largely symptom-relieving rather than aiming to stop the formation and progression of edema. Recent preclinical research reveals novel cellular mechanisms underlying edema formation after brain ischemia and reperfusion. Advancement in neuroimaging techniques also offers opportunities for early diagnosis and prediction of malignant brain edema in stroke patients to rapidly adopt life-saving surgical interventions. As reperfusion therapies become increasingly used in clinical practice, understanding how therapeutic reperfusion influences the formation of cerebral edema after ischemic stroke is critical for decision-making and post-reperfusion management. In this review, we summarize these research advances in the past decade on the cellular mechanisms, and evaluation, prediction, and intervention of ischemic brain edema in clinical settings, aiming to provide insight into future preclinical and clinical research on the diagnosis and treatment of brain edema after stroke.