Microglia and Monocyte-Derived Macrophages in Stroke

Advancements in Single-Cell RNA Sequencing Research for Neurological Diseases

Neurological diseases are a major cause of the global burden of disease. Although the mechanisms of the occurrence and development of neurological diseases are not fully clear, most of them are associated with cells mediating neuroinflammation. Yet medications and other therapeutic options to improve treatment are still very limited. Single-cell RNA sequencing (scRNA-seq), as a delightfully potent breakthrough technology, not only identifies various cell types and response states but also uncovers cell-specific gene expression changes, gene regulatory networks, intercellular communication, and cellular movement trajectories, among others, in different cell types. In this review, we describe the technology of scRNA-seq in detail and discuss and summarize the application of scRNA-seq in exploring neurological diseases, elaborating the corresponding specific mechanisms of the diseases as well as providing a reliable basis for new therapeutic approaches. Finally, we affirm that scRNA-seq promotes the development of the neuroscience field and enables us to have a deeper cellular understanding of neurological diseases in the future, which provides strong support for the treatment of neurological diseases and the improvement of patients' prognosis.

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.

Neuroprotection of Human Umbilical Cord-Derived Mesenchymal Stem Cells (hUC-MSCs) in Alleviating Ischemic Stroke-Induced Brain Injury by Regulating Inflammation and Oxidative Stress

Brain injury caused by stroke has a high rate of mortality and remains a major medical challenge worldwide. In recent years, there has been significant attention given to the use of human Umbilical cord-derived Mesenchymal Stem Cells (hUC-MSCs) for the treatment of stroke in different adult and neonate animal models of stroke. However, using hUC-MSCs by systemic administration to treat ischemic stroke has not been investigated sufficiently. In this study, we conducted various experiments to explore the neuroprotection of hUC-MSCs in rats. Our findings demonstrate that an intravenous injection of a high dose of hUC-MSCs at 2 × 10^7 cells/kg markedly ameliorated brain injury resulting from ischemic stroke. This improvement was observed one day after inducing transient middle cerebral artery occlusion (MCAO) and subsequent reperfusion in rats. Notably, the efficacy of this single administration of hUC-MSCs surpassed that of edaravone, even when the latter was used continuously over three days. Mechanistically, secretory factors derived from hUC-MSCs, such as HGF, BDNF, and TNFR1, ameliorated the levels of MDA and T-SOD to regulate oxidative stress. In particular, TNFR1 also improved the expression of NQO-1 and HO-1, important proteins associated with oxidative stress. More importantly, TNFR1 played a significant role in reducing inflammation by modulating IL-6 levels in the blood. Furthermore, TNFR1 was observed to influence the permeability of the blood-brain barrier (BBB) as demonstrated in the evan's blue experiment and protein expression of ZO-1. This study represented a breakthrough in traditional methods and provided a novel strategy for clinical medication and trials.

Immune Cells Promote BDNF Expression by Infiltrated Macrophages via Interleukin 4 in the Cerebral Ischemia of Male Rats

We reported that infiltrated Ly6C+ macrophages express brain-derived neurotrophic factor (BDNF) only at the cerebral cortex infarct in a rat dMCAO model. However, the changein neuron-expressed BDNF, the niche components that induce the Ly6C+ cells to express BDNF, and the cellular sources of these components, remain unclear. In this study, immunofluorescence double staining was performed to label BDNF and Ly6C on brain sections at 3, 24, and 48 h following distal middle cerebral artery occlusion (dMCAO) of male rats, and to stain BDNF with Ly6C, IL-4R, and IL-10R. A neutralizing anti-IL-4 antibody was injected into the infarct, and the IL-4 and BDNF concentrations in the subareas of the infarct were determined using enzyme-linked immunosorbent assay. To find out the cellular sources of IL-4, the markers for microglia, T cells, and neurons were co-stained with IL-4 separately. In certain infarct subareas, the main BDNF-expressing cells shifted quickly from NeuN+ neurons to Ly6C+ cells during 24-48 h post-stroke, and the Ly6C+/BDNF+ cells mostly expressed IL-4 receptor. Following IL-4 neutralizing antibody injection, the BDNF, IL-4 protein levels, and BDNF+/Ly6C+ cells decreased significantly. The main IL-4-expressing cell type in this infarct subarea is not neuron either, but immune cells, including microglia, monocyte, macrophages, and T cells. The neurons, maintained BDNF and IL-4 expression in the peri-infarct area. In conclusion, in a specific cerebral subarea of the rat dMCAO model, IL-4 secreted by immune cells is one of the main inducers for Ly6C+ cells to express BDNF.

Dissecting glial scar formation by spatial point pattern and topological data analysis

Glial scar formation represents a fundamental response to central nervous system (CNS) injuries. It is mainly characterized by a well-defined spatial rearrangement of reactive astrocytes and microglia. The mechanisms underlying glial scar formation have been extensively studied, yet quantitative descriptors of the spatial arrangement of reactive glial cells remain limited. Here, we present a novel approach using point pattern analysis (PPA) and topological data analysis (TDA) to quantify spatial patterns of reactive glial cells after experimental ischemic stroke in mice. We provide open and reproducible tools using R and Julia to quantify spatial intensity, cell covariance and conditional distribution, cell-to-cell interactions, and short/long-scale arrangement, which collectively disentangle the arrangement patterns of the glial scar. This approach unravels a substantial divergence in the distribution of GFAP+ and IBA1+ cells after injury that conventional analysis methods cannot fully characterize. PPA and TDA are valuable tools for studying the complex spatial arrangement of reactive glia and other nervous cells following CNS injuries and have potential applications for evaluating glial-targeted restorative therapies.

Unraveling dynamic immunological landscapes in intracerebral hemorrhage: insights from single-cell and spatial transcriptomic profiling

Intracerebral hemorrhage (ICH) poses a formidable challenge in stroke management, with limited therapeutic options, particularly in the realm of immune-targeted interventions. Clinical trials targeting immune responses post-ICH have encountered setbacks, potentially attributable to the substantial cellular heterogeneity and intricate intercellular networks within the brain. Here, we present a pioneering investigation utilizing single-cell RNA sequencing and spatial transcriptome profiling at hyperacute (1 h), acute (24 h), and subacute (7 days) intervals post-ICH, aimed at unraveling the dynamic immunological landscape and spatial distributions within the cerebral tissue. Our comprehensive analysis revealed distinct cell differentiation patterns among myeloid and lymphocyte populations, along with delineated spatial distributions across various brain regions. Notably, we identified a subset of lymphocytes characterized by the expression of Spp1 and Lyz2, termed macrophage-associated lymphocytes, which exhibited close interactions with myeloid cells. Specifically, we observed prominent interactions between Lgmn+Macro-T cells and microglia through the spp1-cd44 pathway during the acute phase post-ICH in the choroid plexus. These findings represent a significant advancement in our understanding of immune cell dynamics at single-cell resolution across distinct post-ICH time points, thereby laying the groundwork for exploring critical temporal windows and informing the development of targeted therapeutic strategies.

Role of microglia in stroke

Microglia play key roles in the post-ischemic inflammatory response and damaged tissue removal reacting rapidly to the disturbances caused by ischemia and working to restore the lost homeostasis. However, the modified environment, encompassing ionic imbalances, disruption of crucial neuron-microglia interactions, spreading depolarization, and generation of danger signals from necrotic neurons, induce morphological and phenotypic shifts in microglia. This leads them to adopt a proinflammatory profile and heighten their phagocytic activity. From day three post-ischemia, macrophages infiltrate the necrotic core while microglia amass at the periphery. Further, inflammation prompts a metabolic shift favoring glycolysis, the pentose-phosphate shunt, and lipid synthesis. These shifts, combined with phagocytic lipid intake, drive lipid droplet biogenesis, fuel anabolism, and enable microglia proliferation. Proliferating microglia release trophic factors contributing to protection and repair. However, some microglia accumulate lipids persistently and transform into dysfunctional and potentially harmful foam cells. Studies also showed microglia that either display impaired apoptotic cell clearance, or eliminate synapses, viable neurons, or endothelial cells. Yet, it will be essential to elucidate the viability of engulfed cells, the features of the local environment, the extent of tissue damage, and the temporal sequence. Ischemia provides a rich variety of region- and injury-dependent stimuli for microglia, evolving with time and generating distinct microglia phenotypes including those exhibiting proinflammatory or dysfunctional traits and others showing pro-repair features. Accurate profiling of microglia phenotypes, alongside with a more precise understanding of the associated post-ischemic tissue conditions, is a necessary step to serve as the potential foundation for focused interventions in human stroke.

Deletion of Slc9a1 in Cx3cr1+ cells stimulated microglial subcluster CREB1 signaling and microglia-oligodendrocyte crosstalk

Microglial Na/H exchanger-1 (NHE1) protein, encoded by Slc9a1, plays a role in white matter demyelination of ischemic stroke brains. To explore underlying mechanisms, we conducted single cell RNA-seq transcriptome analysis in conditional Slc9a1 knockout (cKO) and wild-type (WT) mouse white matter tissues at 3 days post-stroke. Compared to WT, Nhe1 cKO brains expanded a microglial subgroup with elevated transcription of white matter myelination genes including Spp1, Lgals3, Gpnmb, and Fabp5. This subgroup also exhibited more acidic pHi and significantly upregulated CREB signaling detected by ingenuity pathway analysis and flow cytometry. Moreover, the Nhe1 cKO white matter tissues showed enrichment of a corresponding oligodendrocyte subgroup, with pro-phagocytosis and lactate shuffling gene expression, where activated CREB signaling is a likely upstream regulator. These findings demonstrate that attenuation of NHE1-mediated H+ extrusion acidifies microglia/macrophage and may underlie the stimulation of CREB1 signaling, giving rise to restorative microglia-oligodendrocyte interactions for remyelination.

Neuronal ablation of GHSR mitigates diet-induced depression and memory impairment via AMPK-autophagy signaling-mediated inflammation

Obesity is associated with chronic inflammation in the central nervous system (CNS), and neuroinflammation has been shown to have detrimental effects on mood and cognition. The growth hormone secretagogue receptor (GHSR), the biologically relevant receptor of the orexigenic hormone ghrelin, is primarily expressed in the brain. Our previous study showed that neuronal GHSR deletion prevents high-fat diet-induced obesity (DIO). Here, we investigated the effect of neuronal GHSR deletion on emotional and cognitive functions in DIO. The neuron-specific GHSR-deficient mice exhibited reduced depression and improved spatial memory compared to littermate controls under DIO. We further examined the cortex and hippocampus, the major regions regulating cognitive and emotional behaviors, and found that the neuronal deletion of GHSR reduced DIO-induced neuroinflammation by suppressing proinflammatory chemokines/cytokines and decreasing microglial activation. Furthermore, our data showed that neuronal GHSR deletion suppresses neuroinflammation by downregulating AMPK-autophagy signaling in neurons. In conclusion, our data reveal that neuronal GHSR inhibition protects against DIO-induced depressive-like behavior and spatial cognitive dysfunction, at least in part, through AMPK-autophagy signaling-mediated neuroinflammation.

Eriocalyxin B alleviated ischemic cerebral injury by limiting microglia-mediated excessive neuroinflammation in mice

Excessive neuroinflammation mediated by microglia has a detrimental effect on the progression of ischemic stroke. Eriocalyxin B (EriB) was found with a neuroprotective effect in mice with Parkinson's disease via the suppression of microglial overactivation. This study aimed to investigate the roles of EriB in permanent middle cerebral artery occlusion (pMCAO) mice. The pMCAO was induced in the internal carotid artery of the mice by the intraluminal filament method, and EriB (10 mg/kg) was administered immediately after surgery by intraperitoneal injection. The behavior score, 2,3,5-triphenyltetrazole chloride staining, Nissl staining, TUNEL, immunohistochemistry, immunofluorescence, PCR, ELISA, and immunoblotting revealed that EriB administration reduced brain infarct and neuron death and ameliorated neuroinflammation and microglia overactivation in pMCAO mice, manifested by alterations of TUNEL-positive cell numbers, ionized calcium binding adaptor molecule 1 (Iba-1)-positive cell numbers, and expression of tumor necrosis factor-α, interleukin 6, IL-1β, inducible nitric oxide synthase, and arginase 1. In addition, EriB suppressed ischemia-induced activation of nuclear factor kappa B (NF-κB) signaling in the brain penumbra, suggesting the involvement of NF-κB in EriB function. In conclusion, EriB exerted anti-inflammatory effects in ischemia stroke by regulating the NF-κB signaling pathway, and this may provide insights into the neuroprotective effect of EriB in the treatment of ischemic stroke.

Ocimum sanctum [Tulsi] as a Potential Immunomodulator for the Treatment of Ischemic Injury in the Brain

Stroke causes brain damage and is one of the main reasons for death. Most survivors of stroke face long-term physical disabilities and cognitive dysfunctions. In addition, they also have persistent emotional and behavioral changes. The two main treatments that are effective are reperfusion with recombinant tissue plasminogen activator and recanalization of penumbra using mechanical thrombectomy. However, these treatments are suitable only for a few patients due to limitations such as susceptibility to hemorrhage and the requirement for administering tissue plasminogen activators within the short therapeutic window during the early hours following a stroke. The paucity of interventions and treatments could be because of the multiple pathological mechanisms induced in the brain by stroke. The ongoing immune response following stroke has been attributed to the worsening brain injury. Hence, novel compounds with immunomodulatory properties that could improve the outcome of stroke patients are required. Natural compounds and medicinal herbs with anti-inflammatory activities and having minimal or no adverse systemic effect could be beneficial in treating stroke. Ocimum sanctum is a medicinal herb that can be considered an effective therapeutic option for ischemic brain injury. Ocimum sanctum, commonly known as holy basil or "Tulsi," is mentioned as the "Elixir of Life" for its healing powers. Since antiquity, Tulsi has been used in the Ayurvedic and Siddha medical systems to treat several diseases. It possesses immuno-modulatory activity, which can alter cellular and humoral immune responses. Tulsi can be considered a potential option as an immuno-modulator for treating various diseases, including brain stroke. In this review, we will focus on the immunomodulatory properties of Tulsi, specifically its effect on both innate and adaptive immunity, as well as its antioxidant and antiinflammatory properties, which could potentially be effective in treating ongoing immune reactions following ischemic brain injury.

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.

The role and mechanisms of mesenchymal stem cells regulating macrophage plasticity in spinal cord injury

Spinal Cord Injury (SCI) is a devastating neurological disorder comprising primary mechanical injury and secondary inflammatory response-mediated injury for which an effective treatment is still unavailable. It is well known that secondary inflammatory responses are a significant cause of difficulties in neurological recovery. An immune imbalance between M1/M2 macrophages at the sites of injury is involved in developing and progressing the secondary inflammatory response. Recently, Mesenchymal Stem Cells (MSCs) have shown significant therapeutic potential in tissue engineering and regenerative medicine due to their potential multidirectional differentiation and immunomodulatory properties. Accumulating evidence shows that MSCs can regulate the balance of M1/M2 macrophage polarization, suppress downstream inflammatory responses, facilitate tissue repair and regeneration, and improve the prognosis of SCI. This article briefly overviews the impact of macrophages and MSCs on SCI and repair. It discusses the mechanisms by which MSCs regulate macrophage plasticity, including paracrine action, release of exosomes and apoptotic bodies, and metabolic reprogramming. Additionally, the article summarizes the relevant signaling pathways of MSCs that regulate macrophage polarization.

Targeting Nrf2 signaling pathway by quercetin in the prevention and treatment of neurological disorders: An overview and update on new developments

BACKGROUND

Neurological disorders (NLDs) are widely acknowledged as a significant public health concern worldwide. Stroke, Alzheimer's disease (AD), and traumatic brain injury (TBI) are three of these disorders that have sparked major study attention. Neurological dysfunction, protein buildup, oxidation and neuronal injury, and aberrant mitochondria are all prevalent neuropathological hallmarks of these disorders. The signaling cascade of nuclear factor erythroid 2 related factor 2 (Nrf2) shares all of them as a common target. Several studies have found that overexpression of Nrf2 is a promising treatment method in NLDs. Effective treatment of these disorders continues to be a universal concern regardless of various medicines. In order to treat a variety of neurological problems, organic remedies may provide an alternative treatment. It has been demonstrated that polyphenols like quercetin (Que) offer considerable capabilities for treating NLDs. One of Que's greatest key targets, Nrf2, has the capacity to control the production of a number of cytoprotective enzymes that exhibit neuroprotective, detoxifying, and antioxidative effects. Additionally, Que enhanced the expression of Nrf2 and inhibited alterations in the shape and death of neurons in the hippocampus.

OBJECTIVE

In this review, we have focused on Que's medicinal prospects as a neuroprotective drug.

METHODS

PubMed, Scopus, Science Direct, and Google Scholar were used to search articles for this study.

RESULTS

The findings of this research demonstrate that (1) Que protected the blood-brain barrier via stimulating Nrf2 in animal stroke, which alleviated ischemic reperfusion and motor dysfunction. (2) By triggering the Nrf2 pathway, Que reduced the neuroinflammation and oxidative damage brought on by TBI in the cortex. (3) In an experimental model of AD, Que enhanced cognitive function by decreasing A1-4, antioxidant activity, and Nrf2 levels in the brain.

CONCLUSION

We discuss recent research on Que-mediated Nrf2 expression in the management of several NLDs in this paper.

Magnetic Resonance Perfusion-Weighted Imaging in Predicting Hemorrhagic Transformation of Acute Ischemic Stroke: A Retrospective Study

Hemorrhagic transformation (HT) is one of the common complications in patients with acute ischemic stroke (AIS). This study aims to investigate the value of different thresholds of Tmax generated from perfusion-weighted MR imaging (PWI) and the apparent diffusion coefficient (ADC) value in the prediction of HT in AIS. A total of 156 AIS patients were enrolled in this study, with 55 patients in the HT group and 101 patients in non-HT group. The clinical baseline data and multi-parametric MRI findings were compared between HT and non-HT groups to identify indicators related to HT. The optimal parameters for predicting HT and the corresponding cutoff values were obtained using the receiver operating characteristic curve analysis of the volumes of ADC < 620 × 10-6 mm2/s and Tmax > 6 s, 8 s, and 10 s. The results showed that the volumes of ADC < 620 × 10-6 mm2/s and Tmax > 6 s, 8 s, and 10 s in the HT group were all significantly larger than that in the non-HT group and were all independent risk factors for HT. Early measurement of the volume of Tmax > 10 s had the highest value, with a cutoff lesion volume of 10.5 mL.

The interaction between intestinal microenvironment and stroke

BACKGROUND

Stroke is not only a major cause of disability but also the third leading cause of death, following heart disease and cancer. It has been established that stroke causes permanent disability in 80% of survivors. However, current treatment options for this patient population are limited. Inflammation and immune response are major features that are well-recognized to occur after a stroke. The gastrointestinal tract hosts complex microbial communities, the largest pool of immune cells, and forms a bidirectional regulation brain-gut axis with the brain. Recent experimental and clinical studies have highlighted the importance of the relationship between the intestinal microenvironment and stroke. Over the years, the influence of the intestine on stroke has emerged as an important and dynamic research direction in biology and medicine.

AIMS

In this review, we describe the structure and function of the intestinal microenvironment and highlight its cross-talk relationship with stroke. In addition, we discuss potential strategies aiming to target the intestinal microenvironment during stroke treatment.

CONCLUSION

The structure and function of the intestinal environment can influence neurological function and cerebral ischemic outcome. Improving the intestinal microenvironment by targeting the gut microbiota may be a new direction in treating stroke.

Multi-omics and network pharmacology study reveals the effects of Dengzhan Shengmai capsule against neuroinflammatory injury and thrombosis induced by ischemic stroke

ETHNOPHARMACOLOGICAL RELEVANCE

Dengzhan Shengmai capsule (DZSM) is a traditional herb medicine used by Dai, an ethnic-minority community living in Xishuang banna tropical rainforest in Southwest of China. It was originally intended to treat disorders caused by insufficient brain function, characterized by gibberish, unresponsiveness, or confusion. Accumulating clinical evidences exhibited that it is effective on treating ischemic stroke (IS). However, the action of DZSM against IS needs to be further elucidated.

AIM OF THE STUDY

To investigate the effect of DZSM and its active components against IS and the way of its action by multi-omics and network pharmacology.

MATERIALS AND METHODS

A middle cerebral artery occlusion/reperfusion (MCAO/R) rat model was established to investigate the effect of DZSM on the focal cerebral ischemia/reperfusion injury. An integrated strategy combining metabolomics, network pharmacology and transcriptomics was performed to systematically clarify the underlying mechanism of action of DZSM against IS. AutoDock Vina was applied to conduct molecular docking simulation for the binding between the potential active compounds and targets. Arachidonic acid (AA) induced platelet aggregation and lipopolysaccharide (LPS) stimulated microglial cells BV2 inflammation models were applied for the in vitro validation of effects of DZSM and its potential active compounds.

RESULTS

In MCAO/R rats, DZSM could significantly reduce the infarct volume. Putative target prediction and functional enrichment analysis based on network pharmacological indicated that the key targets and the potential active compounds played important roles in DZSM's treatment to IS. The targets included four common genes (PTGS1, PTGS2, NFKB1 and NR1I2) and five key TFs (NFKB1, RELA, HIF1A, ESR1 and HDAC1), whilst 22 potential active compounds were identified. Molecular docking indicated that good binding affinity have been seen between those compounds and NR1I2, NFKB1, and RELA. Multi-omics study revealed that DZSM could regulate glutamate by influencing citrate cycle and glutamate involved pathways, and have showed neuroprotection activity and anti-inflammation activity by inhibiting NF-κB pathway. Neuroprotective effects of DZSM was validated by regulating of NF-κB signaling pathway and its downstream NO, TNF-α and IL-6 cytokines contributed to the activity of DZSM and its active compounds of scutellarin, quercetin 3-O-glucuronide, ginsenoside Rb1, schizandrol A and 3, 5-diCQA, whilst the antithrombotic activity of DZSM and its active compounds of schisanhenol, apigenin and schisantherin B were screened out by anti-platelet aggregation experiment.

CONCLUSION

DZSM could against IS via regulating its downstream NO, TNF-α and IL-6 cytokines through NF-κB signaling pathway and alleviating thrombosis.

Strategies for Manipulating Microglia to Determine Their Role in the Healthy and Diseased Brain

Microglia are the specialized macrophages of the central nervous system and play an important role in neural circuit development, modulating neurotransmission, and maintaining brain homeostasis. Microglia in normal brain is quiescent and show ramified morphology with numerous branching processes. They constantly survey their surrounding microenvironment through the extension and retraction of their processes and interact with neurons, astrocytes, and blood vessels using these processes. Microglia respond quickly to any pathological event in the brain by assuming ameboid morphology devoid of branching processes and restore homeostasis. However, when there is chronic inflammation, microglia may lose their homeostatic functions and secrete various proinflammatory cytokines and mediators that initiate neural dysfunction and neurodegeneration. In this article, we review the role of microglia in the normal brain and in various pathological brain conditions, such as Alzheimer's disease and multiple sclerosis. We describe strategies to manipulate microglia, focusing on depletion, repopulation, and replacement, and we discuss their therapeutic potential.

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.

Effects of magnetically targeted iron oxide@polydopamine-labeled human umbilical cord mesenchymal stem cells in cerebral infarction in mice

Mesenchymal stem cells are a potential therapeutic candidate for cerebral infarction due to their anti-inflammatory proprieties. However, ensuring the engraftment of sufficient cells into the affected brain area remains a challenge. Herein, magnetic targeting techniques were used for the transplantation of a large number of cells noninvasively. Mice subjected to pMCAO surgery were administered MSCs labeled or not with iron oxide@polydopamine nanoparticles by tail vein injection. Iron oxide@polydopamine particles were characterized by transmission electron microscopy, and labeled MSCs were characterized by flow cytometry and their differentiation potential was assessed in vitro. Following the systemic injection of iron oxide@polydopamine-labeled MSCs into pMCAO-induced mices, magnetic navigation increased the MSCs localization to the brain lesion site and reduced the lesion volume. Treatment with iron oxide@polydopamine-labeled MSCs also significantly inhibited M1 microglia polarization and increased M2 microglia cell infiltration. Furthermore, western blotting and immunohistochemical analysis demonstrated that microtubule-associated protein 2 and NeuN levels were upregulated the brain tissue of mice treated with iron oxide@polydopamine-labeled MSCs. Thus, iron oxide@polydopamine-labeled MSCs attenuated brain injury and protected neurons by preventing pro-inflammatory microglia activation. Overall, the proposed iron oxide@polydopamine-labeled MSCs approach may overcome the major drawback of the conventional MSCs therapy for the treatment of cerebral infarction.

Sirt1 regulates microglial activation and inflammation following oxygen-glucose deprivation/reoxygenation injury by targeting the Shh/Gli-1 signaling pathway

BACKGROUND

Cerebral ischemic injury leads to over-activation of microglia, which release pro-inflammatory factors that deteriorate neurological function during the acute phase of stroke. Thus, inhibiting microglial over-activation is crucial for reducing ischemic injury. Sirtuin 1 (Sirt1) has been shown to play a critical role in stroke, neurodegenerative diseases and aging. However, the effect of Sirt1 on the regulation of microglial activation following cerebral ischemic injury, as well as the underlying mechanism, remain unknown. Therefore, the purpose of the present study is to mainly investigate the effect of Sirt1 on oxygen-glucose deprivation/reoxygenation (OGD/R)-treated N9 microglia following treatment with the Sirt1 agonists resveratrol and SRT1720 and the Sirt1 antagonist sirtinol.

METHODS

Cell viability, Apoptosis, activation and inflammatory responses of microglia, expressions and activity of Shh signaling pathway proteins were detected by Cell Counting Kit 8, Flow Cytometry, immunocytochemistry, ELISA, and Western blotting, respectively.

RESULTS

The results demonstrated that treatment with resveratrol or SRT1720 could inhibit the activation of microglia and inflammation during OGD/R. Moreover, these treatments also led to the translocation of the GLI family zinc finger-1 (Gli-1) protein from the cytoplasm to the nucleus and upregulated the expression of Sonic hedgehog (Shh), Patched homolog-1 (Ptc-1), smoothened frizzled class receptor and Gli-1. By contrast, the inhibition of Sirt1 using sirtinol had the opposite effect.

CONCLUSION

These findings suggested that Sirt1 may regulate microglial activation and inflammation by targeting the Shh/Gli-1 signaling pathway following OGD/R injury. Schematic representation of Sirt1 regulating the microglial activation and inflammation following oxygen-glucose deprivation/reoxygenation injury via mediation of Shh/Gli-1 signaling pathway.

Resveratrol Inhibits Activation of Microglia after Stroke through Triggering Translocation of Smo to Primary Cilia

Activated microglia act as a double-edged sword for stroke. In the acute phase of stroke, activated microglia might deteriorate neurological function. Therefore, it is of great clinical transforming potential to explore drugs or methods that can inhibit abnormal activation of microglia in the acute phase of stroke to improve neurological function after stroke. Resveratrol has a potential effect of regulating microglial activation and anti-inflammation. However, the molecular mechanism of resveratrol-inhibiting microglial activation has not been fully clarified. Smoothened (Smo) belongs to the Hedgehog (Hh) signaling pathway. Smo activation is the critical step that transmits the Hh signal across the primary cilia to the cytoplasm. Moreover, activated Smo can improve neurological function via regulating oxidative stress, inflammation, apoptosis, neurogenesis, oligodendrogenesis, axonal remodeling, and so on. More studies have indicated that resveratrol can activate Smo. However, it is currently unknown whether resveratrol inhibits microglial activation via Smo. Therefore, in this study, N9 microglia in vitro and mice in vivo were used to investigate whether resveratrol inhibited microglial activation after oxygen-glucose deprivation/reoxygenation (OGD/R) or middle cerebral artery occlusion/reperfusion (MCAO/R) injury and improved functional outcome via triggering translocation of Smo in primary cilia. We definitively found that microglia had primary cilia; resveratrol partially inhibited activation and inflammation of microglia, improved functional outcome after OGD/R and MCAO/R injury, and triggered translocation of Smo to primary cilia. On the contrary, Smo antagonist cyclopamine canceled the above effects of resveratrol. The study suggested that Smo receptor might be a therapeutic target of resveratrol for contributing to inhibit microglial activation in the acute phase of stroke.

Utilizing the codon adaptation index to evaluate the susceptibility to HIV-1 and SARS-CoV-2 related coronaviruses in possible target cells in humans

Comprehensive identification of possible target cells for viruses is crucial for understanding the pathological mechanism of virosis. The susceptibility of cells to viruses depends on many factors. Besides the existence of receptors at the cell surface, effective expression of viral genes is also pivotal for viral infection. The regulation of viral gene expression is a multilevel process including transcription, translational initiation and translational elongation. At the translational elongation level, the translational efficiency of viral mRNAs mainly depends on the match between their codon composition and cellular translational machinery (usually referred to as codon adaptation). Thus, codon adaptation for viral ORFs in different cell types may be related to their susceptibility to viruses. In this study, we selected the codon adaptation index (CAI) which is a common codon adaptation-based indicator for assessing the translational efficiency at the translational elongation level to evaluate the susceptibility to two-pandemic viruses (HIV-1 and SARS-CoV-2) of different human cell types. Compared with previous studies that evaluated the infectivity of viruses based on codon adaptation, the main advantage of our study is that our analysis is refined to the cell-type level. At first, we verified the positive correlation between CAI and translational efficiency and strengthened the rationality of our research method. Then we calculated CAI for ORFs of two viruses in various human cell types. We found that compared to high-expression endogenous genes, the CAIs of viral ORFs are relatively low. This phenomenon implied that two kinds of viruses have not been well adapted to translational regulatory machinery in human cells. Also, we indicated that presumptive susceptibility to viruses according to CAI is usually consistent with the results of experimental research. However, there are still some exceptions. Finally, we found that two viruses have different effects on cellular translational mechanisms. HIV-1 decouples CAI and translational efficiency of endogenous genes in host cells and SARS-CoV-2 exhibits increased CAI for its ORFs in infected cells. Our results implied that at least in cases of HIV-1 and SARS-CoV-2, CAI can be regarded as an auxiliary index to assess cells' susceptibility to viruses but cannot be used as the only evidence to identify viral target cells.

Modulatory effects of mesenchymal stem cells on microglia in ischemic stroke

Ischemic stroke accounts for 70-80% of all stroke cases. Immunity plays an important role in the pathophysiology of ischemic stroke. Microglia are the first line of defense in the central nervous system. Microglial functions are largely dependent on their pro-inflammatory (M1-like) or anti-inflammatory (M2-like) phenotype. Modulating neuroinflammation via targeting microglia polarization toward anti-inflammatory phenotype might be a novel treatment for ischemic stroke. Mesenchymal stem cells (MSC) and MSC-derived extracellular vesicles (MSC-EVs) have been demonstrated to modulate microglia activation and phenotype polarization. In this review, we summarize the physiological characteristics and functions of microglia in the healthy brain, the activation and polarization of microglia in stroke brain, the effects of MSC/MSC-EVs on the activation of MSC in vitro and in vivo, and possible underlying mechanisms, providing evidence for a possible novel therapeutics for the treatment of ischemic stroke.

Neutrophil Heterogeneity and its Roles in the Inflammatory Network after Ischemic Stroke

As the first peripheral immune cells to enter the brain after ischemic stroke, neutrophils are important participants in stroke-related neuroinflammation. Neutrophils are quickly mobilized from the periphery in response to a stroke episode and cross the blood-brain barrier to reach the ischemic brain parenchyma. This process involves the mobilization and activation of neutrophils from peripheral immune organs (including the bone marrow and spleen), their chemotaxis in the peripheral blood, and their infiltration into the brain parenchyma (including disruption of the blood-brain barrier, inflammatory effects on brain tissue, and interactions with other immune cell types). In the past, it was believed that neutrophils aggravated brain injuries through the massive release of proteases, reactive oxygen species, pro-inflammatory factors, and extracellular structures known as neutrophil extracellular traps (NETs). With the failure of early clinical trials targeting neutrophils and uncovering their underlying heterogeneity, our view of their role in ischemic stroke has become more complex and multifaceted. As neutrophils can be divided into N1 and N2 phenotypes in tumors, neutrophils have also been found to have similar phenotypes after ischemic stroke, and play different roles in the development and prognosis of ischemic stroke. N1 neutrophils are dominant during the acute phase of stroke (within three days) and are responsible for the damage to neural structures via the aforementioned mechanisms. However, the proportion of N2 neutrophils gradually increases in later phases, and this has a beneficial effect through the release of anti-inflammatory factors and other neuroprotective mediators. Moreover, the N1 and N2 phenotypes are highly plastic and can be transformed into each other under certain conditions. The pronounced differences in their function and their high degree of plasticity make these neutrophil subpopulations promising targets for the treatment of ischemic stroke.

Activation of Swell1 in microglia suppresses neuroinflammation and reduces brain damage in ischemic stroke

Cl^- movement and Cl^--sensitive signal pathways contributes to the survival and switch of inflammatory phenotype of microglia and are believed to play a key role in the inflammatory brain injury after ischemic stroke. Here, we demonstrated an important role of Cl^- transmembrane transporter Swell1, in the survival and M2-like polarization of microglia in ischemic stroke. Knockdown or overexpression of Swell1 in cultured microglia inhibited or increased hypotonic-activated Cl^- currents, respectively, and these changes were completely blocked by the volume-regulated anion channels (VRACs) inhibitor DCPIB. Swell1 conditional knock-in mice promoted microglia survival in ischemic brain region and resulted in significant reductions in neural cell death, infarction volume and neurological deficits following transient middle cerebral artery occlusion (tMCAO). Using gene manipulating technique and pharmacological inhibitors, we further revealed that Swell1 opening led to SGK1 (a Cl^--sensitive kinase)-mediated activation of FOXO3a/CREB as well as WNK1 (another Cl^--sensitive kinase)-mediated SPAK/OSR1-CCCs activation, which promoted microglia survival and M2-like polarization, thereby attenuating neuroinflammation and ischemic brain injury. Taken together, our results demonstrated that Swell1 is an essential component of microglia VRACs and its activation protects against ischemic brain injury through promoting microglia survival and M2-like polarization.

Research progress of mechanisms for tight junction damage on blood-brain barrier inflammation

Inflammation in the central nervous system (CNS) contributes to disease pathologies by disrupting the integrity of the blood-brain barrier (BBB). Tight junctions (TJ) are a key component of the BBB. Following hypoxic-ischaemic or mechanical injury to the brain, inflammatory mediators are released such as cytokines, chemokines, and growth factors. Simultaneously, matrix metalloproteinases (MMPs) are released which can degrade TJ proteins. Subsequently, the function and morphology of the BBB are disrupted, which allows immune cells an opportunity to enter into the brain parenchyma. This review summarises the information on the role of TJ protein families in the BBB and provides a comprehensive summary of the mechanisms whereby inflammation breaks down the BBB by increasing degradation of TJ proteins.

PET/CT imaging of CSF1R in a mouse model of tuberculosis

PURPOSE

Macrophages represent an essential means of sequestration and immune evasion for Mycobacterium tuberculosis. Pulmonary tuberculosis (TB) is characterized by dense collections of tissue-specific and recruited macrophages, both of which abundantly express CSF1R on their outer surface. 4-Cyano-N-(5-(1-(dimethylglycyl)piperidin-4-yl)-2',3',4',5'-tetrahydro-[1,1'-biphenyl]-2-yl)-1H-imidazole-2-carboxamide (JNJ-28312141) is a reported high affinity, CSF1R-selective antagonist. We report the radiosynthesis of 4-cyano-N-(5-(1-(N-methyl-N-([11C]methyl)glycyl)piperidin-4-yl)-2',3',4',5'-tetrahydro-[1,1'-biphenyl]-2-yl)-1H-imidazole-2-carboxamide ([11C]JNJ-28312141) and non-invasive detection of granulomatous and diffuse lesions in a mouse model of TB using positron emission tomography (PET).

METHODS

Nor-methyl-JNJ-28312141 precursor was radiolabeled with [11C]iodomethane to produce [11C]JNJ-28312141. PET/CT imaging was performed in the C3HeB/FeJ murine model of chronic pulmonary TB to co-localize radiotracer uptake with granulomatous lesions observed on CT. Additionally, CSF1R, Iba1 fluorescence immunohistochemistry was performed to co-localize CSF1R target with reactive macrophages in infected and healthy mice.

RESULTS

Radiosynthesis of [11C]JNJ-28312141 averaged a non-decay-corrected yield of 18.7 ± 2.1%, radiochemical purity of 99%, and specific activity averaging 658 ± 141 GBq/µmol at the end-of-synthesis. PET/CT imaging in healthy mice showed hepatobiliary [13.39-25.34% ID/g, percentage of injected dose per gram of tissue (ID/g)] and kidney uptake (12.35% ID/g) at 40-50 min post-injection. Infected mice showed focal pulmonary lesion uptake (5.58-12.49% ID/g), hepatobiliary uptake (15.30-40.50% ID/g), cervical node uptake, and renal uptake (11.66-29.33% ID/g). The ratio of infected lesioned lung/healthy lung uptake is 5.91:1, while the ratio of lesion uptake to adjacent infected radiolucent lung is 2.8:1. Pre-administration of 1 mg/kg of unlabeled JNJ-28312141 with [11C]JNJ-28312141 in infected animals resulted in substantial blockade. Fluorescence microscopy of infected and uninfected whole lung sections exclusively co-localized CSF1R staining with abundant Iba1 + macrophages. Healthy lung exhibited no CSF1R staining and very few Iba1 + macrophages.

CONCLUSION

[11C]JNJ-28312141 binds specifically to CSF1R + macrophages and delineates granulomatous foci of disease in a murine model of pulmonary TB.

The dual function of microglial polarization and its treatment targets in ischemic stroke

Stroke is the leading cause of disability and death worldwide, with ischemic stroke occurring in ~5% of the global population every year. Recently, many studies have been conducted on the inflammatory response after stroke. Microglial/macrophage polarization has a dual function and is critical to the pathology of ischemic stroke. Microglial/macrophage activation is important in reducing neuronal apoptosis, enhancing neurogenesis, and promoting functional recovery after ischemic stroke. In this review, we investigate the physiological characteristics and functions of microglia in the brain, the activation and phenotypic polarization of microglia and macrophages after stroke, the signaling mechanisms of polarization states, and the contribution of microglia to brain pathology and repair. We summarize recent advances in stroke-related microglia research, highlighting breakthroughs in therapeutic strategies for microglial responses after stroke, thereby providing new ideas for the treatment of ischemic stroke.

Changes in macrophage-like cells characterized by en face optical coherence tomography after retinal stroke

Purpose

The retina could serve as a window of neuroinflammation, but the in vivo changes in macrophage-like cell (MLC), such as microglia, in acute ischemic retinal stroke remain unclear. Thus, the current study aimed to investigate the in vivo changes in MLC characterized by en face optical coherence tomography (OCT) after acute ischemic retinal stroke.

Methods

Twenty patients with unilateral acute nonarteritic reperfused central retinal artery occlusion (CRAO) were participated in this study, and their contralateral eyes served as control group. A 3 μm en face OCT slab on the inner limiting membrane of the optic nerve head (ONH) region or macular region was used to visualize and binarize the MLCs. The MLCs were binarized and quantified using a semiautomated method. OCT angiography was used to evaluate the reperfusion status and obtain the structural data of the inner retina in the ONH and macula. The thickness of the ganglion cell complex in the macular region was measured. The optical intensity and optical intensity ratio of the inner retina were calculated to evaluate the ischemia severity.

Results

In the ONH region, decreased vessel densities of radial peripapillary capillaries accompanied by increased thickness of the retinal nerve fiber layer were found in the CRAO eyes in comparison to the unaffected eyes (p=0.001, p=0.009, respectively). In the macular region, significantly lower vessel densities in both the superficial and deep capillary plexus and increased thickness of the ganglion cell complex were also found in the CRAO eyes (all p ≤ 0.001). The ONH and macular MLC quantities and densities in CRAO eyes were significantly higher than those in the unaffected eyes (both p<0.001). Larger and plumper MLCs were observed in the CRAO eyes compared with their unaffected eyes. ONH and macular MLC densities were positively associated with the disease duration in the acute phase and the optical intensity ratio of inner retina.

Conclusions

The increased density and morphological changes of MLCs may indicate the aggregation and activation of MLCs following acute reperfused CRAO. The aggregation of MLCs may be more pronounced in CRAO eyes with longer disease duration and more severe ischemia. MLCs characterized by en face OCT may serve as an in vivo visual tool to investigate neuroinflammation in the ischemic-reperfusion process of stroke.

The Role of the Monocyte-to-Lymphocyte Ratio in Acute Ischemic Stroke Patients with Acute Kidney Injury

Objective

The objective of the study was to determine if acute kidney injury (AKI) in patients with acute ischemic stroke was associated with the monocyte-to-lymphocyte ratio (MLR) assessed upon admission to the neurology intensive care unit (NICU) (AIS). We also looked into the MLR's function in predicting hospital mortality in AIS patients.

Methods

This retrospective analysis included 595 adult patients with AIS who were hospitalized to the NICU of the First Affiliated Hospital of South China between January 2017 and December 2019. Clinical signs and imaging studies were used to diagnose AIS. KDIGO criteria were used to define AKI. The ratio of monocytes to lymphocytes was used to compute MLR, the ratio of neutrophils to lymphocytes was used to calculate NLR, and the ratio of platelets to lymphocytes was used to calculate PLR.

Result

361 males and 234 women between the ages of 66.27 ± 12.05 years took part in the study. The individuals' MLR was 0.4729 ± 0.3461 and their neutrophil-to-lymphocyte ratio (NLR) was 8.18 ± 5.45. There were notable disparities in MLR and NLR between the AKI and non-AKI groups (p < 0.001). The link between MLR and AKI development risk was enhanced after adjustment, with respective cutoff values of 0.4581 and 9.26. For the MLR-based prediction of AKI incidence, the areas under the receiver-operating characteristic curves (AUCs) were 0.711 (95% CI: 0.663-0.758). And NLR-based prediction of AKI incidence the AUCs was (95% CI: 0.742-0826). Additionally, MLR was associated with a higher rate of in-hospital mortality (2.825, 95% confidence interval: 1.058, 7.545), whereas NLR was associated with a risk of in-hospital mortality of 1.085. (95 percent CI: 1.022, 1.151). An AUC of 0.745 (95% CI: 0.601-0.889, p = 0.026) was obtained for in-hospital mortality based on the MLR, whereas an AUC of 0.724 (95% CI: 0.531-0.916, p = 0.042) was obtained for in-hospital mortality based on the NLR.

Conclusion

MLR and neutrophil-to-lymphocyte ratio (NLR) were associated with a higher risk of AKI and in-hospital death in AIS patients.

Cerebral edema after ischemic stroke: Pathophysiology and underlying mechanisms

Ischemic stroke is associated with increasing morbidity and has become the main cause of death and disability worldwide. Cerebral edema is a serious complication arising from ischemic stroke. It causes an increase in intracranial pressure, rapid deterioration of neurological symptoms, and formation of cerebral hernia, and is an important risk factor for adverse outcomes after stroke. To date, the detailed mechanism of cerebral edema after stroke remains unclear. This limits advances in prevention and treatment strategies as well as drug development. This review discusses the classification and pathological characteristics of cerebral edema, the possible relationship of the development of cerebral edema after ischemic stroke with aquaporin 4, the SUR1-TRPM4 channel, matrix metalloproteinase 9, microRNA, cerebral venous reflux, inflammatory reactions, and cerebral ischemia/reperfusion injury. It also summarizes research on new therapeutic drugs for post-stroke cerebral edema. Thus, this review provides a reference for further studies and for clinical treatment of cerebral edema after ischemic stroke.

High ratio of monocytes to high-density lipoprotein is associated with hemorrhagic transformation in acute ischemic stroke patients on intravenous thrombolysis

Background

Hemorrhagic transformation (HT) is a frequent, serious complication in acute ischemic stroke patients on intravenous thrombolysis. Here we investigated whether risk of HT is associated with the ratio of monocyte count to high-density lipoprotein level (MHR).

Materials and methods

Medical records were retrospectively examined for consecutive patients with acute ischemic stroke who received thrombolytic therapy. HT was diagnosed by computed tomography at 24–36 h after therapy. Potential association between MHR and HT was examined using logistic regression.

Results

A total of 340 patients were analyzed, and their median MHR was 0.44 (0.31–0.59). MHR was higher in the 51 patients (15.0%) with HT than in those who did not suffer HT (0.53 vs. 0.42, P = 0.001). Multivariate logistic regression showed that, after adjusting for potential confounders, MHR was an independent risk factor for HT (OR 7.50, 95% CI 1.64 to 34.35, P = 0.009). Risk of HT was significantly higher among patients whose MHR fell in the third quartile (0.42–0.53) and the fourth quartile (&gt; 0.53) than among those with MHR in the first quartile (&lt; 0.31; OR 3.53, 95% CI 1.11 to 11.20, P = 0.032; OR 4.79, 95% CI 1.49 to 15.42, P = 0.009).

Conclusion

High MHR may be independently associated with higher risk of HT in patients with acute ischemic stroke on intravenous thrombolysis.

The Role of Concomitant Nrf2 Targeting and Stem Cell Therapy in Cerebrovascular Disease

Despite the reality that a death from cerebrovascular accident occurs every 3.5 min in the United States, there are few therapeutic options which are typically limited to a narrow window of opportunity in time for damage mitigation and recovery. Novel therapies have targeted pathological processes secondary to the initial insult, such as oxidative damage and peripheral inflammation. One of the greatest challenges to therapy is the frequently permanent damage within the CNS, attributed to a lack of sufficient neurogenesis. Thus, recent use of cell-based therapies for stroke have shown promising results. Unfortunately, stroke-induced inflammatory and oxidative damage limit the therapeutic potential of these stem cells. Nuclear factor erythroid 2-related factor 2 (Nrf2) has been implicated in endogenous antioxidant and anti-inflammatory activity, thus presenting an attractive target for novel therapeutics to enhance stem cell therapy and promote neurogenesis. This review assesses the current literature on the concomitant use of stem cell therapy and Nrf2 targeting via pharmaceutical and natural agents, highlighting the need to elucidate both upstream and downstream pathways in optimizing Nrf2 treatments in the setting of cerebrovascular disease.

Hypothermia Protects against Ischemic Stroke through Peroxisome-Proliferator-Activated-Receptor Gamma

Ischemic stroke (IS) remains a global public health burden and requires novel strategies. Hypothermia plays a beneficial role in central nervous system diseases. However, the role of hypothermia in IS has not yet been elucidated. In this study, we determined the role of hypothermia in IS and explored its underlying mechanisms. The IS phenotype was detected based on infarct size, infarct volume, and brain edema in mice. Neuroinflammation was evaluated by the activation of microglial cells and the expression of inflammatory genes after ischemia/reperfusion (I/R) and oxygen-glucose deprivation/reperfusion (OGD/R). Neuronal cell apoptosis, cleaved caspase-3 and Bax/Bcl-2 expressions, cell viability, and lactate dehydrogenase (LDH) release were detected after I/R and OGD/R. Blood–brain barrier (BBB) permeability was calculated based on Evans blue extravasation, tight junction protein expression, cell viability, and LDH release after I/R and OGD/R. The expression of peroxisome proliferator-activated receptor gamma (PPARγ) was assessed after OGD/R. Our results suggested that hypothermia significantly reduced infarct size, brain edema, and neuroinflammation after I/R. Hypothermia increased PPARγ expression in microglial cells after OGD/R. Mechanistic studies revealed that hypothermia was a protectant against IS, including attenuated apoptosis of neuronal cells and BBB disruption after I/R and OGD/R, by upregulating PPARγ expression. The hypothermic effect was reversed by GW9662, a PPARγ inhibitor. Our data showed that hypothermia may reduce microglial cell-mediated neuroinflammation by upregulating PPARγ expression in microglial cells. Targeting hypothermia may be a feasible approach for IS treatment.

4-Ethylguaiacol Modulates Neuroinflammation and Promotes Heme Oxygenase-1 Expression to Ameliorate Brain Injury in Ischemic Stroke

Ischemic stroke is caused by a sudden reduction in cerebral blood flow that subsequently induces a complex cascade of pathophysiological responses, leading to brain inflammation and irreversible infarction. 4-ethylguaiacol (4-EG) is reported to suppress inflammatory immune responses. However, whether 4-EG exerts anti-inflammatory effects in ischemic stroke remains unexplored. We evaluated the therapeutic potential of 4-EG and examined the cellular and molecular mechanisms underlying the protective effects of 4-EG in ischemic stroke. The effect of 4-EG in ischemic stroke was determined by using a transient middle cerebral artery occlusion (MCAO) animal model followed by exploring the infarct size, neurological deficits, microglia activation, inflammatory cytokine production, blood–brain barrier (BBB) disruption, brain endothelial cell adhesion molecule expression, and microglial heme oxygenase-1 (HO-1) expression. Nrf2^-/- and HO-1 inhibitor ZnPP-treated mice were also subjected to MCAO to evaluate the role of the Nrf2/HO-1 pathway in 4-EG-mediated protection in ischemic stroke. We found that 4-EG attenuated infarct size and neurological deficits, and lessened BBB disruption in ischemic stroke. Further investigation revealed that 4-EG suppressed microglial activation, peripheral inflammatory immune cell infiltration, and brain endothelial cell adhesion molecule upregulation in the ischemic brain. Finally, we identified that the protective effect of 4-EG in ischemic stroke was abolished in Nrf2^-/– and ZnPP-treated MCAO mice. Our results identified that 4-EG confers protection against ischemic stroke and reveal that the protective effect of 4-EG in ischemic stroke is mediated through the induction of the Nrf2/HO1 pathway. Thus, our findings suggest that 4-EG could be developed as a novel therapeutic agent for the treatment of ischemic stroke.

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

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

Targeted BRD4 protein degradation by dBET1 ameliorates acute ischemic brain injury and improves functional outcomes associated with reduced neuroinflammation and oxidative stress and preservation of blood-brain barrier integrity

Bromodomain-containing protein 4 (BRD4), a member of the bromodomain and extra-terminal domain (BET) protein family, plays a crucial role in regulating inflammation and oxidative stress that are tightly related to stroke development and progression. Consequently, BRD4 blockade has attracted increasing interest for associated neurological diseases, including stroke. dBET1 is a novel and effective BRD4 degrader through the proteolysis-targeting chimera (PROTAC) strategy. We hypothesized that dBET1 protects against brain damage and neurological deficits in a transient focal ischemic stroke mouse model by reducing inflammation and oxidative stress and preserving the blood–brain barrier (BBB) integrity. Post-ischemic dBET1 treatment starting 4 h after stroke onset significantly ameliorated severe neurological deficits and reduced infarct volume 48 h after stroke. dBET1 markedly reduced inflammation and oxidative stress after stroke, indicated by multiple pro-inflammatory cytokines and chemokines including IL-1β, IL-6, TNF-α, CCL2, CXCL1 and CXCL10, and oxidative damage markers 4-hydroxynonenal (4-HNE) and gp91^phox and antioxidative proteins SOD2 and GPx1. Meanwhile, stroke-induced BBB disruption, increased MMP-9 levels, neutrophil infiltration, and increased ICAM-1 were significantly attenuated by dBET1 treatment. Post-ischemic dBET1 administration also attenuated ischemia-induced reactive gliosis in microglia and astrocytes. Overall, these findings demonstrate that BRD4 degradation by dBET1 improves acute stroke outcomes, which is associated with reduced neuroinflammation and oxidative stress and preservation of BBB integrity. This study identifies a novel role of BET proteins in the mechanisms resulting in ischemic brain damage, which can be leveraged to develop novel therapies.

Cannabinoids as Glial Cell Modulators in Ischemic Stroke: Implications for Neuroprotection

Stroke is the second leading cause of death worldwide following coronary heart disease. Despite significant efforts to find effective treatments to reduce neurological damage, many patients suffer from sequelae that impair their quality of life. For this reason, the search for new therapeutic options for the treatment of these patients is a priority. Glial cells, including microglia, astrocytes and oligodendrocytes, participate in crucial processes that allow the correct functioning of the neural tissue, being actively involved in the pathophysiological mechanisms of ischemic stroke. Although the exact mechanisms by which glial cells contribute in the pathophysiological context of stroke are not yet completely understood, they have emerged as potentially therapeutic targets to improve brain recovery. The endocannabinoid system has interesting immunomodulatory and protective effects in glial cells, and the pharmacological modulation of this signaling pathway has revealed potential neuroprotective effects in different neurological diseases. Therefore, here we recapitulate current findings on the potential promising contribution of the endocannabinoid system pharmacological manipulation in glial cells for the treatment of ischemic stroke.

Peptidomimetic Lipid-Nanoparticle-Mediated Knockdown of TLR4 in CNS Protects against Cerebral Ischemia/Reperfusion Injury in Mice

Ischemic stroke activates toll-like receptor 4 (TLR4) signaling, resulting in proinflammatory polarization of microglia and secondary neuronal damage. Herein, we report a novel lipid-nanoparticle (LNP)-mediated knockdown of TLR4 in microglia and amelioration of neuroinflammation in a mouse model of transient middle cerebral artery occlusion (tMCAO). siRNA against TLR4 (siTLR4) complexed to the novel LNP (siTLR4/DoGo310), which was based on a dioleoyl-conjugated short peptidomimetic (denote DoGo310), was readily internalized by the oxygen–glucose-deprived (OGD) mouse primary microglia, knocked-down TLR4, and polarized the cell to the anti-inflammatory phenotype in vitro. Systemic administration of siTLR4/DoGo310 LNPs in the tMCAO mice model resulted in the accumulation of siRNA mainly in the Iba1 positive cells in the peri-infarct. Analysis of the peri-infarct brain tissue revealed that a single injection of siTLR4/DoGo310 LNPs led to significant knockdown of TLR4 gene expression, reversing the pattern of cytokines expression, and improving the neurological functions in tMCAO model mice. Our data demonstrate that DoGo310 LNPs could be a promising nanocarrier for CNS-targeted siRNA delivery for the treatment of CNS disorders.

Non-mitogenic fibroblast growth factor 1 protects against ischemic stroke by regulating microglia/macrophage polarization through Nrf2 and NF-κB pathways

Microglia are immune cells in the central nervous system (CNS) that participate in response to pathological process after ischemic injury. Non-mitogenic fibroblast growth factor 1 (nmFGF1) is an effective neuroprotective factor that is also known as a metabolic regulator. The present study aimed to investigate the effects and mechanism of the neuroprotective ability of nmFGF1 on microglia in mice after photothrombosis (PT) stroke model, to determine whether it could ameliorate ischemic injury in stroke experiment. We discovered that the intranasal administration of nmFGF1 reduced infarct size and ameliorated neurological deficits in behavioral assessment by regulating the secretion of proinflammatory and anti-inflammatory cytokines. Furthermore, in the in vitro experiments, we found that nmFGF1 regulated the expression levels of proinflammatory and anti-inflammatory cytokines in oxygen-glucose deprivation (OGD) and lipopolysaccharide (LPS) stimulation. Evidence have shown that when nuclear factor erythroid 2-related factor 2 (Nfr2) is activated, it inhibits nuclear factor-kappa B (NF-κB) activation to alleviate inflammation. Interestingly, nmFGF1 treatment in vivo remarkably inhibited NF-κB pathway activation and activated Nrf2 pathway. In addition, nmFGF1 and NF-κB inhibitor (BAY11-7082) inhibited NF-κB pathway in LPS-stimulated BV2 microglia. Moreover, in LPS-stimulated BV2 microglia, the anti-inflammatory effect produced by nmFGF1 was knocked down by Nrf2 siRNA. These results indicate that nmFGF1 promoted functional recovery in experimental stroke by modulating microglia/macrophage-mediated neuroinflammation via Nrf2 and NF-κB signaling pathways, making nmFGF1 a potential agent against ischemic stroke.

Irisin ameliorates neuroinflammation and neuronal apoptosis through integrin αVβ5/AMPK signaling pathway after intracerebral hemorrhage in mice

Background

Neuroinflammation is a crucial factor in the development of secondary brain injury after intracerebral hemorrhage (ICH). Irisin is a newly identified myokine that confers strong neuroprotective effects in experimental ischemic stroke. However, whether this myokine can exert neuroprotection effects after ICH remains unknown. This study aimed to investigate the impact of irisin treatment on neuroinflammation and neuronal apoptosis and the underlying mechanism involving integrin αVβ5/AMPK pathway after ICH.

Methods

Two hundred and eighty-five adult (8-week-old) male C57BL/6 mice were randomly assigned to sham and ICH surgery groups. ICH was induced via intrastriatal injection of autologous blood. Irisin was administered intranasally at 30 min after ICH. To elucidate the underlying mechanism, cilengitide (a selective integrin αVβ5 inhibitor) and dorsomorphin (a selective phosphorylated AMPK inhibitor) were administered before irisin treatment. The short- and long-term neurobehavior tests, brain edema, quantitative-PCR, western blotting, Fluoro-Jade C, TUNEL, and immunofluorescence staining were performed to assess the neurofunctional outcome at the level of molecular, cell, histology, and function.

Results

Endogenous irisin and its receptor, integrin αVβ5, were increased, peaked at 24 h after ICH. irisin post-treatment improved both short- and long-term neurological functions, reduced brain edema after ICH. Interestingly, integrin αVβ5 was mainly located in the microglia after ICH, and irisin post-treatment inhibited microglia/macrophage pro-inflammatory polarization and promoted anti-inflammatory polarization. Moreover, irisin treatment inhibited neutrophil infiltration and suppressed neuronal apoptotic cell death in perihematomal areas after ICH. Mechanistically, irisin post-treatment significantly increased the expression of integrin αVβ5, p-AMPK and Bcl-2, and decreased the expression of IL-1β, TNF-α, MPO, and Bax following ICH. The neuroprotective effects of irisin were abolished by both integrin αVβ5 inhibitor cilengitide and AMPK inhibitor dorsomorphin.

Conclusions

This study demonstrated that irisin post-treatment ameliorated neurological deficits, reduced brain edema, and ameliorated neuroinflammation and neuronal apoptosis, at least in part, through the integrin αVβ5/AMPK signaling pathway after ICH. Thus, irisin post-treatment may provide a promising therapeutic approach for the early management of ICH.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02438-6.

Microglia and Neuroinflammation: Crucial Pathological Mechanisms in Traumatic Brain Injury-Induced Neurodegeneration

Traumatic brain injury (TBI) is one of the most common diseases in the central nervous system (CNS) with high mortality and morbidity. Patients with TBI usually suffer many sequelae in the life time post injury, including neurodegenerative disorders such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). However, the pathological mechanisms connecting these two processes have not yet been fully elucidated. It is important to further investigate the pathophysiological mechanisms underlying TBI and TBI-induced neurodegeneration, which will promote the development of precise treatment target for these notorious neurodegenerative consequences after TBI. A growing body of evidence shows that neuroinflammation is a pivotal pathological process underlying chronic neurodegeneration following TBI. Microglia, as the immune cells in the CNS, play crucial roles in neuroinflammation and many other CNS diseases. Of interest, microglial activation and functional alteration has been proposed as key mediators in the evolution of chronic neurodegenerative pathology following TBI. Here, we review the updated studies involving phenotypical and functional alterations of microglia in neurodegeneration after injury, survey key molecules regulating the activities and functional responses of microglia in TBI pathology, and explore their potential implications to chronic neurodegeneration after injury. The work will give us a comprehensive understanding of mechanisms driving TBI-related neurodegeneration and offer novel ideas of developing corresponding prevention and treatment strategies for this disease.

Nrf2 activation in the human brain after stroke due to supratentorial intracerebral haemorrhage: a case–control study

Aims

Pharmacological activation of the antioxidative transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) improves outcomes in experimental models of intracerebral haemorrhage (ICH). However, the Nrf2 pathway has not been previously studied in humans after ICH. Our study aims to address this gap.

Methods

We selected cases with fatal ICH from a prospective community-based inception cohort study and age-matched and sex-matched controls who died suddenly of non-neurological disease. We used immunohistochemistry to quantify Nrf2 (% total area stained overall and % of nuclei stained) and CD68 expression in controls and perihaematomal, ipsilateral and contralateral brain tissue from cases. We measured downstream haem oxygenase-1 (HMOX1) and NAD(P)H dehydrogenase quinone 1 [NQO1] expression using RNA in situ hybridisation.

Results

26 ICH cases (median age: 82 (IQR 76–86); 13 (50%) male) and eight controls (median age: 79 (IQR 77–80); 3 (37.5%) male) were included. We found no significant differences in overall % of Nrf2 staining between ICH cases and controls. However, the mean % of nuclei staining for Nrf2 seemed higher in perihaematomal compared with contralateral regions, although this was only statistically significant >60 days after ICH (25% (95% CI 17% to 33%) vs 14% (95% CI 11% to 17%), p=0.029). The percentage of perihaematomal tissue staining for CD68 was higher >60 days after ICH (6.75%, 95% CI 2.78% to 10.73%) compared with contralateral tissue (1.45%, 95% CI 0.93% to 1.96%, p=0.027) and controls (1.08%, 95% CI 0.20% to 1.97%, p=0.0008). RNA in situ hybridisation suggested increased abundance of HMOX1 and NQO1 transcripts in perihaematomal versus distant ipsilateral brain tissue obtained <7 days from onset of ICH.

Conclusions

We found evidence of Nrf2 activation in human brain tissue after ICH. Pharmacological augmentation of Nrf2 activation after ICH might be a promising therapeutic approach.

|Therapeutic and preventive effects of apigenin in cerebral ischemia: a review

APG can exert various protective effects against cerebral ischemia. Moreover, APG has shown a highly promising ability to prevent cerebral ischemia in terms of regulating blood glucose, blood pressure, lipids and gut microbes.

ADAM8 Activates NLRP3 Inflammasome to Promote Cerebral Ischemia-Reperfusion Injury

Stroke is the leading cause of death and disability in humans. Strokes are classified as either ischemic or hemorrhagic. Ischemic stroke accounts for 70–80% of the cases. Inflammation is a key factor in ischemic brain injury. Studies have shown that inflammatory response induced by NLRP3 inflammasome is one of the root causes of brain damage in mice with cerebral ischemia. However, its specific mechanism in cerebral ischemia is still unclear. ADAM8 (a disintegrin and metalloproteases 8) is a transmembrane protein with different functions. It plays an important role in tumors and neuroinflammation-related diseases. However, the role and molecular mechanism of ADAM8 in cerebral ischemia injury are still unclear. This study aims to evaluate the role of ADAM8 in cerebral ischemic injury and explore its signal transduction mechanism. This experiment shows that ADAM8 can significantly cause neurological deficits in MCAO mice and can substantially cause ipsilateral cerebral edema and cerebral infarction in MCAO mice. In addition, ADAM8 can significantly induce cortical cell apoptosis in MCAO mice, leading to the loss of neurons and the expression of proinflammatory factors COX2, iNOS, TNFα, and IL-6. Importantly, we confirmed that ADAM8 mediates the inflammatory response by promoting the activation of NLRP3 inflammasome, microglia, and astrocytes. These results indicate that ADAM8 may be a candidate drug target for the prevention and treatment of the cerebral ischemic injury.

Modulating poststroke inflammatory mechanisms: Novel aspects of mesenchymal stem cells, extracellular vesicles and microglia

Inflammation plays an important role in the pathological process of ischemic stroke, and systemic inflammation affects patient prognosis. As resident immune cells in the brain, microglia are significantly involved in immune defense and tissue repair under various pathological conditions, including cerebral ischemia. Although the differentiation of M1 and M2 microglia is certainly oversimplified, changing the activation state of microglia appears to be an intriguing therapeutic strategy for cerebral ischemia. Recent evidence indicates that both mesenchymal stem cells (MSCs) and MSC-derived extracellular vesicles (EVs) regulate inflammation and modify tissue repair under preclinical stroke conditions. However, the precise mechanisms of these signaling pathways, especially in the context of the mutual interaction between MSCs or MSC-derived EVs and resident microglia, have not been sufficiently unveiled. Hence, this review summarizes the state-of-the-art knowledge on MSC- and MSC-EV-mediated regulation of microglial activity under ischemic stroke conditions with respect to various signaling pathways, including cytokines, neurotrophic factors, transcription factors, and microRNAs.