Treatment targets for M2 microglia polarization in ischemic stroke

Microglia Phenotype and Intracerebral Hemorrhage: A Balance of Yin and Yang

Intracerebral hemorrhage (ICH) features extremely high rates of morbidity and mortality, with no specific and effective therapy. And local inflammation caused by the over-activated immune cells seriously damages the recovery of neurological function after ICH. Fortunately, immune intervention to microglia has provided new methods and ideas for ICH treatment. Microglia, as the resident immune cells in the brain, play vital roles in both tissue damage and repair processes after ICH. The perihematomal activated microglia not only arouse acute inflammatory responses, oxidative stress, excitotoxicity, and cytotoxicity to cause neuron death, but also show another phenotype that inhibit inflammation, clear hematoma and promote tissue regeneration. The proportion of microglia phenotypes determines the progression of brain tissue damage or repair after ICH. Therefore, microglia may be a promising and imperative therapeutic target for ICH. In this review, we discuss the dual functions of microglia in the brain after an ICH from immunological perspective, elaborate on the activation mechanism of perihematomal microglia, and summarize related therapeutic drugs researches.

Baicalein ameliorates ischemic brain damage through suppressing proinflammatory microglia polarization via inhibiting the TLR4/NF-κB and STAT1 pathway

Microglial polarization mediated neuroinflammation plays an important role in the pathological process of stroke. The aim of this study is to determine whether baicalein indirectly ameliorates neuronal injury through modulating microglial polarization after stroke and if so, then by what mechanism. The effects of baicalein on microglial polarization were revealed through the middle cerebral artery occlusion mouse model (MCAO, n = 6), the lipopolysaccharide (LPS) + interferon-γ (IFN-γ) and oxygen-glucose deprivation (OGD) induced neuroinflammatory microglia model (BV2, n = 3), respectively. Mice were treated with baicalein (100 mg/kg, i.g.) after reperfusion, and followed by daily administrations for 3 days. Results showed that the infarct volumes at 3 d in vehicle and baicalein-treated MCAO mice were 91.18 ± 4.02% and 55.36 ± 4.10%. Baicalein improved sensorimotor functions (p < 0.01) after MCAO. Real-time PCR revealed that baicalein decreased proinflammatory markers expression (p < 0.05), while elevated the anti-inflammatory markers (p < 0.05) in vivo and in vitro. Both western blot and immunofluorescent staining further confirmed that baicalein reduced proinflammatory marker CD16 levels (p < 0.01) and enhanced anti-inflammatory marker CD206 or Arg-1 levels (p < 0.05). Notably, baicalein suppressed the release of proinflammatory cytokines (p < 0.05) and nitric oxide (NO, p < 0.001). Mechanistically, baicalein prevented increases in TLR4 protein levels (p < 0.001), the phosphorylation of IKBα and p65 (p < 0.01), and the nuclear translocation of NF-κB p65 (p < 0.05). The NF-κB inhibitor, BAY 11-7085, enhanced the inhibitory effect of baicalein on the proinflammatory microglial polarization. Baicalein also inhibited the phosphorylation of signal transducer and activator of transcription 1 (STAT1, p < 0.001). A microglia-neuron co-culture system revealed that baicalein driven neuroprotection against OGD induced neuronal damage through modulating microglial polarization (p < 0.05). Baicalein indirectly ameliorates neuronal injury after stroke by polarizing microglia toward the anti-inflammatory phenotype via inhibition of the TLR4/NF-κB pathway and down-regulation of phosphorylated STAT1, suggesting that baicalein might serve a potential therapy for stroke.

Ephedrine ameliorates cerebral ischemia injury via inhibiting NOD-like receptor pyrin domain 3 inflammasome activation through the Akt/GSK3β/NRF2 pathway

Ischemic stroke is a leading cause of death and long-term disability worldwide. The aim of this study is to explore the potential function of ephedrine in ischemic stroke and the underlying molecular mechanism. A middle cerebral artery occlusion (MCAO) rat model was established. The potential effects of ephedrine on MCAO rats and LPS-stimulated BV2 microglial cells were evaluated. Ephedrine reduced the infarct volume, cell apoptosis, brain water content, neurological score, and proinflammatory cytokines (TNF-α and IL-1β) production in MCAO rats. Ephedrine treatment also suppressed TNF-α and IL-1β production and NOD-like receptor pyrin domain 3 (NLRP3) inflammasome activation in BV2 microglial cells. The expression of NLRP3, caspase-1, and IL-1β was suppressed by ephedrine. Moreover, ephedrine treatment increased the phosphorylation of Akt and GSK3β and nuclear NRF2 levels in LPS-treated BV2 microglial cells. Meanwhile, LY294002 attenuated the inhibitory effects of ephedrine on NLRP3 inflammasome activation and TNF-α and IL-1β production. In addition, the level of pAkt was increased, while NLRP3, caspase-1, and IL-1β were decreased by ephedrine treatment in MCAO rats. In conclusion, ephedrine ameliorated cerebral ischemia injury via inhibiting NLRP3 inflammasome activation through the Akt/GSK3β/NRF2 pathway. Our results revealed a potential role of ephedrine in ischemic stroke treatment.

LncRNA SNHG8 sponges miR-449c-5p and regulates the SIRT1/FoxO1 pathway to affect microglia activation and blood-brain barrier permeability in ischemic stroke

Ischemic stroke (IS) can cause disability and death, and microglia as the immune component of the CNS can release inflammatory factors and participate in blood-brain barrier (BBB) dysfunction. This study aimed to investigate the effects of long noncoding RNA (lncRNA) SNHG8 on microglia activation and BBB permeability in IS. A rat model of permanent middle cerebral artery occlusion (p-MCAO) and a cell model of oxygen and glucose deprivation (OGD) in microglia were established, followed by evaluation of neurobehavioral function, BBB permeability, brain edema, and pathologic changes of microglia in brain tissue. The activation status of microglia and expressions of inflammatory factors were detected. Cell viability and integrity of microglia membrane were assessed. The downstream microRNA (miR), gene, and pathway of SNHG8 were analyzed. LncRNA SNHG8 was down-regulated in MCAO rats. Overexpression of SNHG8 improved the neural function defect, reduced brain water content, BBB permeability, brain tissue damage and inflammation, and inhibited microglia activation. In OGD-induced microglia, overexpression of SNHG8 or miR-449c-5p down-regulation increased cell viability and decreased lactate dehydrogenase activity. Moreover, SNHG8 sponged miR-449c-5p to regulate SIRT1. Overexpression of SNHG8 increased the expression of SIRT1 and FoxO1. MiR-449c-5p mimic could annul the effect of SNHG8 overexpression on ischemic microglia. Collectively, SNHG8 inhibits microglia activation and BBB permeability via the miR-449c-5p/SIRT1/FoxO1 pathway, thus eliciting protective effects on ischemic brain injury.

Brain Immune Interactions-Novel Emerging Options to Treat Acute Ischemic Brain Injury

Ischemic stroke is still among the leading causes of mortality and morbidity worldwide. Despite intensive advancements in medical sciences, the clinical options to treat ischemic stroke are limited to thrombectomy and thrombolysis using tissue plasminogen activator within a narrow time window after stroke. Current state of the art knowledge reveals the critical role of local and systemic inflammation after stroke that can be triggered by interactions taking place at the brain and immune system interface. Here, we discuss different cellular and molecular mechanisms through which brain–immune interactions can take place. Moreover, we discuss the evidence how the brain influence immune system through the release of brain derived antigens, damage-associated molecular patterns (DAMPs), cytokines, chemokines, upregulated adhesion molecules, through infiltration, activation and polarization of immune cells in the CNS. Furthermore, the emerging concept of stemness-induced cellular immunity in the context of neurodevelopment and brain disease, focusing on ischemic implications, is discussed. Finally, we discuss current evidence on brain–immune system interaction through the autonomic nervous system after ischemic stroke. All of these mechanisms represent potential pharmacological targets and promising future research directions for clinically relevant discoveries.

Effects of lead exposure on the activation of microglia in mice fed with high-fat diets

Lead (Pb) exposure can cause central nervous system (CNS) damage. The process of Pb neurotoxicity is accompanied by the microglia activation. In addition, microglia activation was observed under the intervention of high-fat diets (HFD). This study was designed to investigate the effect of Pb on the cognitive function of mice with HFD, with focus on the microglia activation in brain. Male C57BL/6J mice, 8 weeks of age, were randomly divided into control, HFD, Pb, and HFD + Pb groups. The results showed that HFD following Pb exposure could exacerbate the learning and memory impairment in mice. Pb exposure could promote microglia activation and increase the expression of M1 microglia marker and decrease the expression of M2 microglia marker in the hippocampus of mice with HFD. Our finding suggested that Pb exposure may aggravate CNS damage by promoting M1 polarization and inhibiting M2 polarization of hippocampal microglia in HFD mice.

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.

Role and characteristics of hippocampal region microglial activation in poststroke depression

AIMS

To study the role and characteristics of activated microglia in poststroke depression (PSD) .

METHODS

Twenty-four male Wistar rats were randomly divided into three groups: the poststroke (PS) group, PSD group, and Sham group. Neurobehavioral testing was performed 24 h postoperation. The body weights of the rats were regularly recorded, and behavioral testing was regularly performed at 1, 2 and 3 weeks postmodeling. Immunofluorescent staining was used to detect the microglial marker OX42. Real-time PCR was used to analyze the relative gene expression of microglial activation markers (TNF-a, IL-10, IL-1, TGF-β, CD86, iNOS, CD206, IL-1β, and Arg1) .

RESULTS

The relative gene expression of proinflammatory markers (IL-1, TNF-a, iNOS, and IL1β) and anti-inflammatory markers (CD206 and Arg1) significantly increased in the hippocampal region compared with that in the right cerebral and left cerebral hemispheres in the PSD group. The relative gene expression of proinflammatory markers (TNF-a, IL-1, iNOS, and CD86) in the hippocampal region was significantly increased in the PSD group compared with that in the Sham and PS groups. The anti-inflammatory markers (TGF-β and CD206) in the hippocampal region were significantly increased in the PSD group compared with that in the Sham group, and the M2 marker Arg1 was significantly increased in the PSD group compared with that in the PS group. Correlation analysis showed that IL-1 was strongly negatively correlated with PSD .

CONCLUSIONS

Most microglia in the hippocampal region of PSD had a proinflammatory status and an anti-inflammatory status. IL-1 showed a strong negative correlation with PSD.

BK Channel-Mediated Microglial Phagocytosis Alleviates Neurological Deficit After Ischemic Stroke

Microglial phagocytosis benefits neurological recovery after stroke. Large-conductance Ca2⁺-activated K⁺ currents are expressed in activated microglia, and BK channel knockout aggravates cerebral ischemic injury. However, the effect of BK channels on microglial phagocytosis after ischemic stroke remains unknown. Here, we explored whether BK channel activation is beneficial for neurological outcomes through microglial phagocytosis after ischemic stroke. ICR mice after transient middle cerebral artery occlusion (tMCAO) were treated with dimethyl sulfoxide (DMSO), BK channel activator NS19504, and inhibitor Paxilline. The results showed a decrease in BK channel expression after tMCAO. BK channel activator NS19504 alleviates neurological deficit after experimental modeling of tMCAO in mice compared to the control. Furthermore, we treated primary microglia with DMSO, NS19504, and Paxilline after oxygen glucose deprivation (OGD). NS19504 promoted primary microglial phagocytosing fluorescent beads and neuronal debris, which reduced neuronal apoptosis after stroke. These effects could be reversed by BK channel inhibitor Paxilline. Finally, NS19504 increased relative phosphorylated extracellular signal-regulated kinase 1/2 expression compared to the Paxilline group at the third day after stroke. Our findings indicate that microglial BK channels are a potential target for acute stage of ischemic stroke therapy.

Extracellular vesicles derived from M2 microglia reduce ischemic brain injury through microRNA-135a-5p/TXNIP/NLRP3 axis

Accumulating evidences have suggested that extracellular vesicles (EVs) are crucial players in the pathogenesis of ischemic brain injury. This study was designed to explore the specific functions of M2 phenotype microglia-derived EVs in ischemic brain injury progression. The expression of microRNA-135a-5p (miR-135a-5p) in M2 microglia-derived EVs was determined by reverse transcription-quantitative polymerase chain reaction (RT-qPCR), followed by the identification of expression relationship among miR-135a-5p, thioredoxin-interacting protein (TXNIP), and nod-like receptor protein 3 (NLRP3) by dual luciferase reporter gene assay. After construction of an oxygen-glucose deprivation/reperfusion (OGD/R) cell model, the effects of miR-135a-5p on the biological characteristics of HT-22 cells were assessed by cell counting kit 8 (CCK-8) assay and flow cytometry. Finally, a mouse model of transient middle cerebral artery occlusion (tMCAO) was established and cerebral infarction volume was determined by triphenyltetrazolium chloride (TTC) staining and the expression of IL-18 and IL-1β in the brain tissue was determined by enzyme-linked immunosorbent assay (ELISA). We found that M2 microglia-derived EVs had high expression of miR-135a-5p, and that miR-135a-5p in M2 microglia-derived EVs negatively regulated the expression of NLRP3 via TXNIP. Overexpression of miR-135a-5p promoted the proliferation but inhibited the apoptosis of neuronal cells, and inhibited the expression of autophagy-related proteins. M2 microglia-derived EVs delivered miR-135a-5p into neuronal cells to inhibit TXNIP expression, which further inhibited the activation of NLRP3 inflammasome, thereby reducing neuronal autophagy and ischemic brain injury. Hence, M2 microglia-derived EVs are novel therapeutic targets for ischemic brain injury treatment.

Effects of Microglial Activation and Polarization on Brain Injury After Stroke

Stroke is one of the most common causes of death worldwide. The subsequent development of neuroinflammation and brain edema dramatically increases the risks associated with stroke, leading to a substantial increase in mortality. Although considerable progress has been made in improving cerebral perfusion in the acute phase of stroke, effective treatment options for the subacute and chronic phases associated with cerebral infarction are limited. Microglia, the innate immune cells of the central nervous system (CNS), can be activated and polarized to take on different phenotypes in response to stimulations associated with stroke, including pro-inflammatory and anti-inflammatory phenotypes, which affect the prognosis of stroke. Therefore, investigation of the activation and polarizing mechanisms of microglia plays a critical role in treating stroke. The aim of this article was to investigate the significance of microglial phenotype regulation in stroke treatment by summarizing the activation, polarizing mechanisms, and general microglia characteristics.

Multi-scale modeling for systematically understanding the key roles of microglia in AD development

Alzheimer's disease (AD) is the leading cause of age-related dementia, affecting over 5 million people in the United States. Unfortunately, current therapies are largely palliative and several potential drug candidates have failed in late-stage clinical trials. Studies suggest that microglia-mediated neuroinflammation might be responsible for the failures of various therapies. Microglia contribute to Aβ clearance in the early stage of neurodegeneration and may contribute to AD development at the late stage by releasing pro-inflammatory cytokines. However, the activation profile and phenotypic changes of microglia during the development of AD are poorly understood. To systematically understand the key role of microglia in AD progression and predict the optimal therapeutic strategy in silico, we developed a 3D multi-scale model of AD (MSMAD) by integrating multi-level experimental data, to manipulate the neurodegeneration in a simulated system. Based on our analysis, we revealed that how TREM2-related signal transduction leads to an imbalance in the activation of different microglia phenotypes, thereby promoting AD development. Our MSMAD model also provides an optimal therapeutic strategy for improving the outcome of AD treatment.

miR-24 protects against ischemia-induced brain damage in rats via regulating microglia polarization by targeting Clcn3

Microglia and macrophages play important roles in ischemic brain injury. Changes in their M1/M2 polarization phenotypes significantly impact disease progression. The M2 microglia/macrophages are anti-inflammatory and have a protective effect against ischemic injury. The microRNA 24 (miR-24) promotes M2 macrophage polarization and suppresses inflammation. We tested the hypothesis that miR-24 is protective in ischemic brain injury by regulating microglia polarization. We treated rats with miR-24 inhibitor or mimic and subsequently subjected the rats to middle cerebral artery occlusion (MCAO) to induce ischemic brain injury. Neurological deficit and infarct volume were analyzed. Microglia and macrophages were assessed by fluorescence-activated cell sorting. Microglia polarization was determined by genes specific for M1 and M2 both in vivo and in BV-2 cells. The effect of miR-24 target Clcn3 on microglia polarization was examined. We found that miR-24 inhibition aggravated MCAO induced damage, while miR-24 overexpression alleviated brain injury by suppressing microglia/macrophage infiltration. miR-24 suppressed M1 and promoted M2 microglia polarization both in vivo and in vitro. Finally, we showed that miR-24 targeted Clcn3 to regulate microglia polarization. Our study indicates that miR-24 plays a neuroprotective role by promoting anti-proinflammatory microglia polarization during ischemic brain injury.

Effect of hyperglycemia on microglial polarization after cerebral ischemia-reperfusion injury in rats

Hyperglycemia has been shown to aggravate ischemic brain damage, in which the inflammatory reaction induced by hyperglycemia is involved in the worsening of cerebral ischemia-reperfusion injury. However, the role of microglial polarization in hyperglycemia-aggravating cerebral ischemia-reperfusion injury remains unknown. The present study investigated whether diabetic hyperglycemia inhibited or activated microglia, as well as microglial subtypes 1 and 2. Rats were used to establish the diabetic hyperglycemia and middle cerebral artery occlusion (MCAO) model. The markers CD11b, CD16, CD32, CD86, CD206, and Arg1 were used to show M1 or M2 microglia. The results revealed increased neurological deficits, infarct volume, and neural apoptosis in rats with hyperglycemia subjected to MCAO for 30 min and reperfused at 1, 3, and 7 days compared with the normoglycemic rats. Microglia and astrocyte activation and proliferation were inhibited in hyperglycemic rats. Furthermore, M1 microglia polarization was promoted, while that of M2 microglia was inhibited in hyperglycemic rats. These findings suggested that the polarization of M1 and M2 microglia is activated and inhibited, respectively, in hyperglycemic rats and may be involved in the aggravated brain damage caused by ischemia-reperfusion in diabetic hyperglycemia.

New insights into targeting mitochondria in ischemic injury

Stroke is the leading cause of adult disability and death worldwide. Mitochondrial dysfunction has been recognized as a marker of neuronal death during ischemic stroke. Maintaining the function of mitochondria is important for improving the survival of neurons and maintaining neuronal function. Damaged mitochondria induce neuronal cell apoptosis by releasing reactive oxygen species (ROS) and pro-apoptotic factors. Mitochondrial fission and fusion processes and mitophagy are of great importance to mitochondrial quality control. This paper reviews the dynamic changes in mitochondria, the roles of mitochondria in different cell types, and related signaling pathways in ischemic stroke. This review describes in detail the role of mitochondria in the process of neuronal injury and protection in cerebral ischemia, and integrates neuroprotective drugs targeting mitochondria in recent years, which may provide a theoretical basis for the progress of treatment of ischemic stroke. The potential of mitochondrial-targeted therapy is also emphasized, which provides valuable insights for clinical research.

Microglial Polarization: Novel Therapeutic Strategy against Ischemic Stroke

Ischemic stroke, which is the second highest cause of death and the leading cause of disability, represents ~71% of all strokes globally. Some studies have found that the key elements of the pathobiology of stroke is immunity and inflammation. Microglia are the first line of defense in the nervous system. After stroke, the activated microglia become a double-edged sword, with distinct phenotypic changes to the deleterious M1 types and neuroprotective M2 types. Therefore, ways to promote microglial polarization toward M2 phenotype after stroke have become the focus of attention in recent years. In this review, we discuss the process of microglial polarization, summarize the alternation of signaling pathways and epigenetic regulation that control microglial polarization in ischemic stroke, aiming to find the potential mechanisms by which microglia can be transformed into the M2 polarized phenotype.

Minocycline promotes functional recovery in ischemic stroke by modulating microglia polarization through STAT1/STAT6 pathways

BACKGROUND

Increasing evidence suggests that microglia experience two distinct phenotypes after acute ischemic stroke (AIS): a deleterious M1 phenotype and a neuroprotective M2 phenotype. Promoting the phenotype shift of M1 microglia to M2 microglia is thought to improve functional recovery after AIS. Minocycline, a tetracycline antibiotic, can improve functional recovery after cerebral ischemia in pre-clinical and clinical research. However, the role and mechanisms of minocycline in microglia polarization is unclear.

METHODS

Using the transient middle cerebral artery occlusion - reperfusion (MCAO/R) model, we treated mice with saline or different minocycline concentration (10, 25, or 50 mg/kg, i.p., daily for 2 wk) at 24 h after reperfusion. Neurobehavioral evaluation, rotarod test, and corner turning test were carried out on day 14 after reperfusion. Then, neuronal injury, reactive gliosis, and microglia polarization were performed on day 7 following MCAO/R. Finally, we treated primary microglial cultures with LPS (Lipopolysaccharide; 100 ng/mL) plus IFN-γ (20 ng/mL) 24 h to induce M1 phenotype and observed the effects of minocycline on the M1/M2-related mRNAs and the STAT1/STAT6 pathway.

RESULTS

We found that a 14-day treatment with minocycline increased the survival rate and promoted functional outcomes evaluated with neurobehavioral evaluation, rotarod test, and corner turning test. Meanwhile, minocycline reduced the brain infarct volume, alleviated neuronal injury, and suppressed reactive gliosis on day 7 following MCAO/R. Moreover, we observed an additive effect of minocycline on microglia polarization to the M1 and M2 phenotypes in vivo and in vitro. In the primary microglia, we further found that minocycline prevented neurons from OGD/R-induced cell death in neuron-microglia co-cultures via regulating M1/M2 microglia polarization through the STAT1/STAT6 pathway.

CONCLUSION

Minocycline promoted microglial M2 polarization and inhibited M1 polarization, leading to neuronal survival and neurological functional recovery. The findings deepen our understanding of the mechanisms underlying minocycline-mediated neuroprotection in AIS.

Long Non-coding RNAs as Promising Therapeutic Approach in Ischemic Stroke: a Comprehensive Review

In recent years, ischemic stroke (IS) has been one of the major causes of disability and mortality worldwide. The general mechanism of IS is based on reduced blood supply to neuronal tissue, resulting in neuronal cell damage by various pathological reactions. One of the main techniques for acute IS treatment entails advanced surgical approaches for restoration of cerebral blood supply but this is often associated with secondary brain injury, also known as ischemic reperfusion injury (I/R injury). Many researches have come to emphasize the significant role of long non-coding RNAs (lncRNAs) in IS, especially in I/R injury and their potential as therapeutic approaches. LncRNAs are non-protein transcripts that are able to regulate cellular processes and gene expression. Further, lncRNAs have been shown to be involved in neuronal signaling pathways. Several lncRNAs are recognized as key factors in the physiological and pathological processes of IS. In this review, we discuss the role of lncRNAs in neuronal injury mechanisms and their association with brain neuroprotection. Moreover, we identify the lncRNAs that show the greatest potential as novel therapeutic approaches in IS, which therefore merit further investigation in preclinical research. Graphical Abstract.

PSD-93 mediates the crosstalk between neuron and microglia and facilitates acute ischemic stroke injury by binding to CX3CL1

Post-synaptic density 93 (PSD-93) mediates glutamate excitotoxicity induced by ischemic brain injury, which then induces microglial inflammatory response. However, the underlying mechanisms of how PSD-93 mediates the crosstalk between neurons and microglia in the post-synaptic dense region remain elusive. CX3 chemokine ligand 1 (CX3CL1) is a chemokine specifically expressed in neurons while its receptor CX3CR1 is highly expressed in microglia. In this study, we examined the interaction of PSD-93 and CX3CL1 in the crosstalk between neurons and microglia in acute ischemic stroke. We utilized male C57BL/6 mice to establish the middle cerebral artery occlusion model (MCAO) and designed a fusion small peptide Tat-CX3CL1 (357-395aa) to inhibit PSD-93 and CX3CL1 interaction. The combination peaks of PSD-93 and CX3CL1 at 6 hr after I/R were observed. The binding sites were located at the 420-535 amino acid sequence of PSD-93 and 357-395 amino acid sequence of CX3CL1. Tat-CX3CL1 (357-395aa) could inhibit the interaction of PSD-93 and CX3CL1 and inhibited the pro-inflammatory cytokine IL-1β and TNF-α expression and provided neuroprotection following reperfusion. Together, these data suggest that PSD-93 binds CX3CL1 to activate microglia and initiate neuroinflammation. Specific blockade of PSD-93-CX3CL1 interaction reduces I/R induced neuronal cell death, and provides a new therapeutic target for ischemic stroke.

Dynamical Simulation of Effective Stem Cell Transplantation for Modulation of Microglia Responses in Stroke Treatment

Stem cell transplantation therapy may inhibit inflammation during stroke and increase the presence of healthy cells in the brain. The novelty of this work, is to introduce a new mathematical model of stem cells transplanted to treat stroke. This manuscript studies the stability of the mathematical model by using the current biological information on stem cell therapy as a possible treatment for inflammation from microglia during stroke. The model is proposed to represent the dynamics of various immune brain cells (resting microglia, pro-inflammation microglia, and anti-inflammation microglia), brain tissue damage and stem cells transplanted. This model is based on a set of five ordinary differential equations and explores the beneficial effects of stem cells transplanted at early stages of inflammation during stroke. The Runge–Kutta method is used to discuss the model analytically and solve it numerically. The results of our simulations are qualitatively consistent with those observed in experiments in vivo, suggesting that the transplanted stem cells could contribute to the increase in the rate of ant-inflammatory microglia and decrease the damage from pro-inflammatory microglia. It is found from the analysis and simulation results that stem cell transplantation can help stroke patients by modulation of the immune response during a stroke and decrease the damage on the brain. In conclusion, this approach may increase the contributions of stem cells transplanted during inflammation therapy in stroke and help to study various therapeutic strategies for stem cells to reduce stroke damage at the early stages.

Oxidative Stress, Inflammation, and Autophagy: Potential Targets of Mesenchymal Stem Cells-Based Therapies in Ischemic Stroke

Ischemic stroke is a leading cause of death worldwide; currently available treatment approaches for ischemic stroke are to restore blood flow, which reduce disability but are time limited. The interruption of blood flow in ischemic stroke contributes to intricate pathophysiological processes. Oxidative stress and inflammatory activity are two early events in the cascade of cerebral ischemic injury. These two factors are reciprocal causation and directly trigger the development of autophagy. Appropriate autophagy activity contributes to brain recovery by reducing oxidative stress and inflammatory activity, while autophagy dysfunction aggravates cerebral injury. Abundant evidence demonstrates the beneficial impact of mesenchymal stem cells (MSCs) and secretome on cerebral ischemic injury. MSCs reduce oxidative stress through suppressing reactive oxygen species (ROS) and reactive nitrogen species (RNS) generation and transferring healthy mitochondria to damaged cells. Meanwhile, MSCs exert anti-inflammation properties by the production of cytokines and extracellular vesicles, inhibiting proinflammatory cytokines and inflammatory cells activation, suppressing pyroptosis, and alleviating blood–brain barrier leakage. Additionally, MSCs regulation of autophagy imbalances gives rise to neuroprotection against cerebral ischemic injury. Altogether, MSCs have been a promising candidate for the treatment of ischemic stroke due to their pleiotropic effect.

Crosstalk between gut microbiome and immunology in the management of ischemic brain injury

Ischemic brain injury is a serious neurological complication, which accrues an immense activation of neuroinflammatory responses. Several lines of research suggested the interconnection of gut microbiota perturbation with the activation of proinflammatory mediators. Intestinal microbial communities also interchange information with the brain through various afferent and efferent channels and microbial by-products. Herein, we discuss the different microelements of gut microbiota and its connection with the host immune system and how change in immune-microbial signatures correlates with the stroke incidence and post-injury neurological sequelae. The activated inflammatory cells increase the production of proinflammatory cytokines, chemokines, proteases and adhesive proteins that are involved in the systemic inflammation, blood brain barrier disruption, gut dysbiosis and aggravation of ischemic brain injury. We suggest that fine-tuning of commensal gut microbiota (eubiosis) may regulate the activation of CNS resident cells like microglial, astrocytes, mast cells and natural killer cells.

Activation of MC1R with BMS-470539 attenuates neuroinflammation via cAMP/PKA/Nurr1 pathway after neonatal hypoxic-ischemic brain injury in rats

Background

Microglia-mediated neuroinflammation plays a crucial role in the pathogenesis of hypoxic-ischemic (HI)-induced brain injury. Activation of melanocortin-1 receptor (MC1R) has been shown to exert anti-inflammatory and neuroprotective effects in several neurological diseases. In the present study, we have explored the role of MC1R activation on neuroinflammation and the potential underlying mechanisms after neonatal hypoxic-ischemic brain injury in rats.

Methods

A total of 169 post-natal day 10 unsexed rat pups were used. HI was induced by right common carotid artery ligation followed by 2.5 h of hypoxia. BMS-470539, a specific selective MC1R agonist, was administered intranasally at 1 h after HI induction. To elucidate the potential underlying mechanism, MC1R CRISPR KO plasmid or Nurr1 CRISPR KO plasmid was administered via intracerebroventricular injection at 48 h before HI induction. Percent brain infarct area, short- and long-term neurobehavioral tests, Nissl staining, immunofluorescence staining, and Western blot were conducted.

Results

The expression levels of MC1R and Nurr1 increased over time post-HI. MC1R and Nurr1 were expressed on microglia at 48 h post-HI. Activation of MC1R with BMS-470539 significantly reduced the percent infarct area, brain atrophy, and inflammation, and improved short- and long-term neurological deficits at 48 h and 28 days post-HI. MC1R activation increased the expression of CD206 (a microglial M2 marker) and reduced the expression of MPO. Moreover, activation of MC1R with BMS-470539 significantly increased the expression levels of MC1R, cAMP, p-PKA, and Nurr1, while downregulating the expression of pro-inflammatory cytokines (TNFα, IL-6, and IL-1β) at 48 h post-HI. However, knockout of MC1R or Nurr1 by specific CRISPR reversed the neuroprotective effects of MC1R activation post-HI.

Conclusions

Our study demonstrated that activation of MC1R with BMS-470539 attenuated neuroinflammation, and improved neurological deficits after neonatal hypoxic-ischemic brain injury in rats. Such anti-inflammatory and neuroprotective effects were mediated, at least in part, via the cAMP/PKA/Nurr1 signaling pathway. Therefore, MC1R activation might be a promising therapeutic target for infants with hypoxic-ischemic encephalopathy (HIE).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02078-2.

Astragaloside IV promotes microglia/macrophages M2 polarization and enhances neurogenesis and angiogenesis through PPARγ pathway after cerebral ischemia/reperfusion injury in rats

Microglia/macrophages play a dual role in brain injury and repair following cerebral ischemia/reperfusion. Promoting microglia/macrophage polarization from pro-inflammatory M1 to anti-inflammatory M2 phenotype has been considered as a potential treatment for ischemic stroke. Astragaloside IV (AS-IV) is a primary active ingredient of Chinese herb Radix Astragali, which protects against acute cerebral ischemic/reperfusion injury through its antioxidant, anti-inflammatory, and anti-apoptotic properties. However, it remains unknown whether AS-IV improves ischemic brain tissue repair and its underlying mechanism. A transient middle cerebral artery occlusion (tMCAO) rat model was used in this study. The results showed that AS-IV significantly improved long-term brain injury, reduced the expression of M1 microglia/macrophage markers and increased the expression of M2 microglia/macrophage markers 14 days after cerebral ischemia/reperfusion. AS-IV also increased peroxisome proliferator-activated receptor γ (PPARγ) mRNA and protein expression. Moreover, AS-IV promoted neurogenesis and angiogenesis, and increased the protein expression of brain-derived growth factor (BDNF), insulin-like growth factor-1 (IGF-1) and vascular endothelial growth factor (VEGF). However, these beneficial effects were greatly blocked by PPARγ antagonist T0070907. These results together suggest that AS-IV could enhance neurogenesis, angiogenesis and neurological functional recovery, which may be partially through transforming microglia/macrophage from M1 to M2 phenotype in a PPARγ-dependent manner after cerebral ischemia/reperfusion injury. Therefore, AS-IV can be considered as a promising therapeutic agent for ischemic stroke.

Neuroinflammation in Ischemic Stroke: Focus on MicroRNA-mediated Polarization of Microglia

Ischemic stroke is one of the most common causes of death and disability worldwide. Neuroinflammation is a major pathological event involved in the process of ischemic injury and repair. In particular, microglia play a dual role in neuroinflammation. During the acute phase of stroke onset, M2 microglia are the dominant phenotype and exert protective effects on neuronal cells, whereas permanent M1 microglia contribute to prolonged inflammation and are detrimental to brain tissue. Emerging evidence indicates that microRNAs (miRNAs) may have regulatory effects on microglia-associated inflammation. Thus, we briefly reviewed the dynamic response of microglia after a stroke and assessed how specific miRNAs affect the behavior of reactive microglia. We concluded that miRNAs may be useful novel therapeutic targets to improve stroke outcomes and modulate neuroinflammation.

Peripheral inflammation and blood-brain barrier disruption: effects and mechanisms

The blood-brain barrier (BBB) is an important physiological barrier that separates the central nervous system (CNS) from the peripheral circulation, which contains inflammatory mediators and immune cells. The BBB regulates cellular and molecular exchange between the blood vessels and brain parenchyma. Normal functioning of the BBB is crucial for the homeostasis and proper function of the brain. It has been demonstrated that peripheral inflammation can disrupt the BBB by various pathways, resulting in different CNS diseases. Recently, clinical research also showed CNS complications following SARS-CoV-2 infection and chimeric antigen receptor (CAR)-T cell therapy, which both lead to a cytokine storm in the circulation. Therefore, elucidation of the mechanisms underlying the BBB disruption induced by peripheral inflammation will provide an important basis for protecting the CNS in the context of exacerbated peripheral inflammatory diseases. In the present review, we first summarize the physiological properties of the BBB that makes the CNS an immune-privileged organ. We then discuss the relevance of peripheral inflammation-induced BBB disruption to various CNS diseases. Finally, we elaborate various factors and mechanisms of peripheral inflammation that disrupt the BBB.

Knockdown of miR-130a-3p alleviates spinal cord injury induced neuropathic pain by activating IGF-1/IGF-1R pathway

BACKGROUND

Recent studies have elucidated the instrumental role of microRNAs (miRNAs) in neuropathic pain (NP) progression. As one member of miRNAs, miR-130a-3p has been proved as a mediator in inflammation and neuronal maturation. The present study attempted to elucidate what effect miR-130a-3p exerts on NP.

MATERIALS AND METHODS

The miR-130a-3p expression in the spinal cord tissues of rat with spinal cord compression injury (SCI) and LPS-induced BV2 microglia was determined with RT-PCR, which was further applied to analyze the clinical relevance between miR-130a-3p and neuropathic pain. Besides, the expression of IGF-1, IL-1β, IL-6, and TNF-α in the spinal cord tissues of rats was measured using RT-PCR and ELISA after intrathecal injection of miR-130a-3p inhibitors and tail vein injection of IGF-1 low-expression lentivirus (Lv-shIGF-1). Further, neuronal apoptosis (labeled by Caspase3) and microglial activation (labeled by Iba1) were examined by immunohistochemistry (IHC), and the levels of IGF-1, IGF-1R, NF-κB were determined by western blot. Additionally, bioinformatic was employed to analyze the potential target genes of miR-130a-3p. Furthermore, the dual luciferase activity assay and RNA immunoprecipitation assay were conducted to further substantiate whether miR-130a-3p targets IGF-1.

RESULTS

In comparison with the sham group, the miR-130a-3p expression was remarkably up-regulated in the spinal cord lesions of SCI rats. The ELISA results showed that inhibiting the miR-130a-3p significantly reduced NP symptoms of SCI rats, mitigated neuronal apoptosis, microglial activation, repressed NF-κB phosphorylation and the IL-1β, IL-6 and TNF-α expressions in SCI rats. Contrarily, downregulation of miR-130a-3p increased IGF-1 and IGF-1R expression. What's more, we observed the same effects in BV2 microglia. In addition, the bioinformatics analysis showed that miR-130-3p targeted at the 3'-untranslated region of IGF-1 and inhibiting its expression. However, abolishing IGF-1 not only promoted the inflammatory responses in the SCI lesions, but also aggravated NP of SCI rats, while those effects were attenuated by the downregulation of miR-130a-3p.

CONCLUSION

The inhibition of miR-130a-3p expression up-regulates the IGF-1/IGF-1R signaling pathway, thus reducing neuropathic pain caused by spinal cord injury.

Fingolimod suppressed the chronic unpredictable mild stress-induced depressive-like behaviors via affecting microglial and NLRP3 inflammasome activation

Depression is a common aspect of the modern lifestyle, and most patients are recalcitrant to the current antidepressants. Fingolimod (FTY720), a sphingosine analogue approved for the treatment of multiple sclerosis, has a significant neuroprotective effect on the central nervous system. The aim of this study was to determine the potential therapeutic effect of FTY720 on the behavior and cognitive function of rats exposed daily to chronic unpredictable mild stress (CUMS), and elucidate the underlying mechanisms. The 42-day CUMS modeling induced depression-like behavior as indicated by the scores of sugar water preference, forced swimming, open field and Morris water maze tests. Mechanistically, CUMS caused significant damage to the hippocampal neurons, increased inflammation and oxidative stress, activated the NF-κB/NLRP3 axis, and skewed microglial polarization to the M1 phenotype. FTY720 not only alleviated neuronal damage and oxidative stress, but also improved the depression-like behavior and cognitive function of the rats. It also inhibited NF-κB activation and blocked NLRP3 inflammasome assembly by down-regulating NLRP3, ACS and caspase-1. Furthermore, FTY720 inhibited the microglial M1 polarization markers iNOS and CD16, and promoted the M2 markers Arg-1 and CD206. This in turn reduced the levels of TNF-α, IL-6 and IL-1β, and increased that of IL-10 in the hippocampus. In conclusion, FTY720 protects hippocampal neurons from stress-induced damage and alleviates depressive symptoms by inhibiting neuroinflammation. Our study provides a theoretical basis for S1P receptor modulation in treating depression.

Microglia and Macrophages in the Pathological Central and Peripheral Nervous Systems

Microglia, the immunocompetent cells in the central nervous system (CNS), have long been studied as pathologically deteriorating players in various CNS diseases. However, microglia exert ameliorating neuroprotective effects, which prompted us to reconsider their roles in CNS and peripheral nervous system (PNS) pathophysiology. Moreover, recent findings showed that microglia play critical roles even in the healthy CNS. The microglial functions that normally contribute to the maintenance of homeostasis in the CNS are modified by other cells, such as astrocytes and infiltrated myeloid cells; thus, the microglial actions on neurons are extremely complex. For a deeper understanding of the pathophysiology of various diseases, including those of the PNS, it is important to understand microglial functioning. In this review, we discuss both the favorable and unfavorable roles of microglia in neuronal survival in various CNS and PNS disorders. We also discuss the roles of blood-borne macrophages in the pathogenesis of CNS and PNS injuries because they cooperatively modify the pathological processes of resident microglia. Finally, metabolic changes in glycolysis and oxidative phosphorylation, with special reference to the pro-/anti-inflammatory activation of microglia, are intensively addressed, because they are profoundly correlated with the generation of reactive oxygen species and changes in pro-/anti-inflammatory phenotypes.

DHCR24 overexpression modulates microglia polarization and inflammatory response via Akt/GSK3β signaling in Aβ25-35 treated BV-2 cells

Microglial phenotypic polarization, divided into pro-inflammatory "M1" phenotype and anti-inflammatory "M2" phenotype, played a crucial role in the pathogenesis of Alzheimer's disease (AD). Facilitating microglial polarization from M1 to M2 phenotype was shown to alleviate AD-associate pathologic damage, and modulator of the microglial phenotype has become a promising therapeutic approach for the treatment of AD. Previous little evidence showed that DHCR24 (3-β-hydroxysteroid-Δ-24-reductase), also known as seladin-1 (selective Alzheimer's disease indicator-1), exerted potential anti-inflammatory property, however, the link between DHCR24 and microglial polarization has never been reported. Thus, the role of DHCR24 in microglial polarization in amyloid-beta 25-35 (Aβ_25-35) treated BV-2 cells was evaluated in this study. Our results demonstrated that Aβ_25-35 aggravated inflammatory response and facilitated the transition of microglia phenotype from M2 to M1 in BV-2 cells, by upregulating M1 marker (i-NOS, IL-1β and TNF-α) and downregulating M2 marker (arginase-1, IL-4 and TGF-β). DHCR24 overexpression by lentivirus transfection could significantly reverse these effects, meanwhile, activated Akt/GSK3β signaling pathway via increasing the protein expression of P-Akt and P-GSK3β. Furthermore, when co-treated with Akt inhibitor MK2206, the effect of DHCR24 was obviously reversed. The study exhibited the neuroprotective function of DHCR24 in AD-related inflammatory injury and provided a novel therapeutic target for AD in the future.

Tomentosin inhibit cerebral ischemia/reperfusion induced inflammatory response via TLR4/ NLRP3 signalling pathway - in vivo and in vitro studies

Stoke is a global threat, leading to 50 % of deaths worldwide and it causes permanent disability to about 5 million individuals globally each year. In this study, we assessed the potency of tomentosin to inhibit the neuroinflammation in in vivo and in vitro models. The Sprague Dawley rats were pretreated with 25 mg/kg bodyweight (b.wt) and 50 mg/kg b.wt of tomentosin for seven days followed by induction of cerebral ischemic reperfusion. The brain edema and cerebral infractions were analyzed. The levels of antioxidants and the interleukins were measured by standard methods. The NLRP3 signaling proteins expression was evaluated using qPCR analysis. In vitro studies were performed in SH-SY5Y-cells pretreated with tomentosin and subjected to OGD-R treatment. Our results depicts tomentosin scavenges the free radicals, enhances antioxidant system, inhibits the NLRP3 signaling. In vitro results substantiates with in vivo results. To conclude, our in vivo and in vitro results confirm tomentosin may be potent alternative for existing antistroke drugs.

Identifying the pattern of immune related cells and genes in the peripheral blood of ischemic stroke

Background

Ischemic stroke (IS) is the second leading cause of death worldwide which is a serious hazard to human health. Evidence suggests that the immune system plays a key role in the pathophysiology of IS. However, the precisely immune related mechanisms were still not been systematically understood.

Methods

In this study, we aim to identify the immune related modules and genes that might play vital role in the occurrence and development of IS by using the weighted gene co-expression network analysis (WGCNA). Meanwhile, we applied a kind of deconvolution algorithm to reveal the proportions of 22 subsets of immune cells in the blood samples.

Results

There were total 128 IS patients and 67 healthy control samples in the three Gene Expression Omnibus (GEO) datasets. Under the screening criteria, 1082 DEGs (894 up-regulated and 188 down-regulated) were chosen for further analysis. A total of 11 clinically significant modules were identified, from which immune-related hub modules and hub genes were further explored. Finally, 16 genes were selected as real hub genes for further validation analysis. Furthermore, these CIBERSORT results suggest that detailed analysis of the immune subtype distribution pattern has the potential to enhance clinical prediction and to identify candidates for immunotherapy. More specifically, we identified that neutrophil emerge as a promising target for IS therapies.

Conclusions

In the present study, we investigated the immune related gene expression modules, in which the SLAMF1, IL7R and NCF4 may be novel therapeutic targets to promote functional and histological recovery after ischemic stroke. Furthermore, these hub genes and neutrophils may become important biological targets in the drug screening and drug designing.

A novel compound DBZ ameliorates neuroinflammation in LPS-stimulated microglia and ischemic stroke rats: Role of Akt(Ser473)/GSK3β(Ser9)-mediated Nrf2 activation

Microglia-mediated neuroinflammation plays a crucial role in the pathophysiological process of multiple neurological disorders such as ischemic stroke, yet lacks effective therapeutic agents. Previously, we discovered one novel synthetic compound, tanshinol borneol ester (DBZ), possesses anti-inflammatory and anti-atherosclerotic activities, whereas little is known about its effects in CNS. Therefore, the present study aims to explore the effects and potential mechanism of DBZ on neuroinflammation and microglial function. Our studies revealed that DBZ significantly inhibited NF-κB activity, suppressed the production of pro-inflammatory mediators meanwhile promoted M2 mediators expression in LPS-stimulated BV2 cells and mouse primary microglia cells. DBZ also exhibited antioxidant activity by enhancing Nrf2 nuclear accumulation and transcriptional activity, increasing HO-1 and NQO1 expression, and inhibiting LPS-induced ROS generation in BV2 cells. Importantly, the anti-neuroinflammatory and antioxidant effects of DBZ above were reversed by Nrf2 knockdown. Additionally, DBZ ameliorated sickness behaviors of neuroinflammatory mice induced by systemic LPS administration, and significantly reduced infract volume, improved sensorimotor and cognitive function in rats subjected to transient middle cerebral artery occlusion (tMCAO); besides, DBZ restored microglia morphological alterations and shifted the M1/M2 polarization in both murine models. Mechanistically, DBZ-induced Nrf2 nuclear accumulation and antioxidant enzymes expression were accompanied by increased level of p-Akt(Ser473) (activation) and p-GSK3β(Ser9) (inactivation), and decreased nuclear level of Fyn both in vitro and in vivo. Pharmacologically inhibiting PI3K or activating GSK3β markedly increased nuclear density of Fyn in microglia cells, which blocked the promoting effect of DBZ on Nrf2 nuclear accumulation and its antioxidant and anti-neuroinflammatory activities. Collectively, these results indicated the effects of DBZ on microglia-mediated neuroinflammation were strongly associated with the nuclear accumulation and stabilization of Nrf2 via the Akt(Ser473)/GSK3β(Ser9)/Fyn pathway. With anti-neuroinflammatory and antioxidant properties, DBZ could be a promising new drug candidate for prevention and/or treatment of cerebral ischemia and other neuroinflammatory disorders.

Modulators of microglia activation and polarization in ischemic stroke (Review)

Ischemic stroke is one of the leading causes of mortality and disability worldwide. However, there is a current lack of effective therapies available. As the resident macrophages of the brain, microglia can monitor the microenvironment and initiate immune responses. In response to various brain injuries, such as ischemic stroke, microglia are activated and polarized into the proinflammatory M1 phenotype or the anti‑inflammatory M2 phenotype. The immunomodulatory molecules, such as cytokines and chemokines, generated by these microglia are closely associated with secondary brain damage or repair, respectively, following ischemic stroke. It has been shown that M1 microglia promote secondary brain damage, whilst M2 microglia facilitate recovery following stroke. In addition, autophagy is also reportedly involved in the pathology of ischemic stroke through regulating the activation and function of microglia. Therefore, this review aimed to provide a comprehensive overview of microglia activation, their functions and changes, and the modulators of these processes, including transcription factors, membrane receptors, ion channel proteins and genes, in ischemic stroke. The effects of autophagy on microglia polarization in ischemic stroke were also reviewed. Finally, future research areas of ischemic stroke and the implications of the current knowledge for the development of novel therapeutics for ischemic stroke were identified.

Biomaterials to Neuroprotect the Stroke Brain: A Large Opportunity for Narrow Time Windows

Ischemic stroke represents one of the most prevalent pathologies in humans and is a leading cause of death and disability. Anti-thrombolytic therapy with tissue plasminogen activator (t-PA) and surgical thrombectomy are the primary treatments to recanalize occluded vessels and normalize the blood flow in ischemic and peri-ischemic regions. A large majority of stroke patients are refractory to treatment or are not eligible due to the narrow time window of therapeutic efficacy. In recent decades, we have significantly increased our knowledge of the molecular and cellular mechanisms that inexorably lead to progressive damage in infarcted and peri-lesional brain areas. As a result, promising neuroprotective targets have been identified and exploited in several stroke models. However, these considerable advances have been unsuccessful in clinical contexts. This lack of clinical translatability and the emerging use of biomaterials in different biomedical disciplines have contributed to developing a new class of biomaterial-based systems for the better control of drug delivery in cerebral disorders. These systems are based on specific polymer formulations structured in nanoparticles and hydrogels that can be administered through different routes and, in general, bring the concentrations of drugs to therapeutic levels for prolonged times. In this review, we first provide the general context of the molecular and cellular mechanisms impaired by cerebral ischemia, highlighting the role of excitotoxicity, inflammation, oxidative stress, and depolarization waves as the main pathways and targets to promote neuroprotection avoiding neuronal dysfunction. In the second part, we discuss the versatile role played by distinct biomaterials and formats to support the sustained administration of particular compounds to neuroprotect the cerebral tissue at risk of damage.

Arginine is neuroprotective through suppressing HIF-1α/LDHA-mediated inflammatory response after cerebral ischemia/reperfusion injury

Neuroinflammation is a secondary response following ischemia stroke. Arginine is a non-essential amino acid that has been shown to inhibit acute inflammatory reaction. In this study we show that arginine treatment decreases neuronal death after rat cerebral ischemia/reperfusion (I/R) injury and improves functional recovery of stroke animals. We also show that arginine suppresses inflammatory response in the ischemic brain tissue and in the cultured microglia after OGD insult. We further provide evidence that the levels of HIF-1α and LDHA are increased after rat I/R injury and that arginine treatment prevents the elevation of HIF-1α and LDHA after I/R injury. Arginine inhibits inflammatory response through suppression of HIF-1α and LDHA in the rat ischemic brain tissue and in the cultured microglia following OGD insult, and protects against ischemic neuron death after rat I/R injury by attenuating HIF-1α/LDHA-mediated inflammatory response. Together, these results indicate a possibility that arginine-induced neuroprotective effect may be through the suppression of HIF-1α/LDHA-mediated inflammatory response in microglia after cerebral ischemia injury.

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

The immune response to stroke is an exciting target for future stroke therapies. Stroke is a leading cause of morbidity and mortality worldwide, and clot removal (mechanical or pharmacological) to achieve tissue reperfusion is the only therapy currently approved for patient use. Due to a short therapeutic window and incomplete effectiveness, however, many patients are left with infarcted tissue that stimulates inflammation. Although this is critical to promote repair, it can also damage surrounding healthy brain tissue. In addition, acute immunodepression and subsequent infections are common and are associated with worse patient outcomes. Thus, the acute immune response is a major focus of researchers attempting to identify ways to amplify its benefits and suppress its negative effects to improve short-term recovery of patients. Here we review what is known about this powerful process. This includes the role of brain resident cells such as microglia, peripherally activated cells such as macrophages and neutrophils, and activated endothelium. The role of systemic immune activation and subsequent immunodepression in the days after stroke is also discussed, as is the chronic immune responses and its effects on cognitive function. The biphasic role of inflammation, as well as complex timelines of cell production, differentiation, and trafficking, suggests that the relationship between the acute and chronic phases of stroke recovery is complex. Gaining a more complete understanding of this intricate process by which inflammation is initiated, propagated, and terminated may potentially lead to therapeutics that can treat a larger population of stroke patients than what is currently available. The immune response plays a critical role in patient recovery in both the acute and chronic phases after stroke. In patients, the immune response can be beneficial by promoting repair and recovery, and also detrimental by propagating a pro-inflammatory microenvironment. Thus, it is critical to understand the mechanisms of immune activation following stroke in order to successfully design therapeutics.

Post-Ischaemic Immunological Response in the Brain: Targeting Microglia in Ischaemic Stroke Therapy

Microglia, the major endogenous immune cells of the central nervous system, mediate critical degenerative and regenerative responses in ischaemic stroke. Microglia become "activated", proliferating, and undergoing changes in morphology, gene and protein expression over days and weeks post-ischaemia, with deleterious and beneficial effects. Pro-inflammatory microglia (commonly referred to as M1) exacerbate secondary neuronal injury through the release of reactive oxygen species, cytokines and proteases. In contrast, microglia may facilitate neuronal recovery via tissue and vascular remodelling, through the secretion of anti-inflammatory cytokines and growth factors (a profile often termed M2). This M1/M2 nomenclature does not fully account for the microglial heterogeneity in the ischaemic brain, with some simultaneous expression of both M1 and M2 markers at the single-cell level. Understanding and regulating microglial activation status, reducing detrimental and promoting repair behaviours, present the potential for therapeutic intervention, and open a longer window of opportunity than offered by acute neuroprotective strategies. Pharmacological modulation of microglial activation status to promote anti-inflammatory gene expression can increase neurogenesis and improve functional recovery post-stroke, based on promising preclinical data. Cell-based therapies, using preconditioned microglia, are of interest as a method of therapeutic modulation of the post-ischaemic inflammatory response. Currently, there are no clinically-approved pharmacological options targeting post-ischaemic inflammation. A major developmental challenge for clinical translation will be the selective suppression of the deleterious effects of microglial activity after stroke whilst retaining (or enhancing) the neurovascular repair and remodelling responses of microglia.

Excess salt intake promotes M1 microglia polarization via a p38/MAPK/AR-dependent pathway after cerebral ischemia in mice

A high salt diet (HSD) is among the most important risk factors for many diseases. One mechanism by which HSD aggravates cerebral ischemic injury is independent of blood pressure changes. The direct role of HSD in inflammation after cerebral ischemia is unclear. In this research, after twenty-one days of being fed a high salt diet, permanent focal ischemia was induced in mice via operation. At 12 h and 1, 3 and 5 days postischemia, the effects of HSD on the lesion volume, microglia polarization, aldose reductase (AR) expression, and inflammatory processes were analyzed. We report that in mice, surplus dietary salt promotes inflammation and increases the activation of classical lipopolysaccharide (LPS)-induced microglia/macrophages (M1). This effect depends on the expression of the AR protein in activated microglia after permanent middle cerebral artery ligation (pMCAL) in HSD mice. The administration of either the AR inhibitor Epalrestat or a p38-neutralizing antibody blocked the polarization of microglia and alleviated stroke injury. In conclusion, HSD promotes polarization in pro-inflammatory M1 microglia by upregulating the expression of the AR protein via p38/MAPK, thereby exacerbating the development of ischemia stroke.

Aspects of the immune system that impact brain function

The conditions required for effective immune responses to viral or bacterial organisms and chemicals of exogenous origin and to intrinsic molecules of abnormal configuration, are briefly outlined. This is followed by a discussion of endocrine and environmental factors that can lead to excessive continuation of immune activity and persistent elevation of inflammatory responses. Such disproportionate activity becomes increasingly pronounced with aging and some possible reasons for this are considered. The specific vulnerability of the nervous system to prolonged immune events is involved in several disorders frequently found in the aging brain. In addition of being a target for inflammation associated with neurodegenerative disease, the nervous system is also seriously impacted by systemically widespread immune disturbances since there are several means by which immune information can access the CNS. The activation of glial cells and cells of non-nervous origin that form the basis of immune responses within the brain, can occur in differing modes resulting in widely differing consequences. The events underlying the relatively frequent occurrence of derangement and hyperreactivity of the immune system are considered, and a few potential ways of addressing this common condition are described.

Integrated analysis of the proteome and transcriptome in a MCAO mouse model revealed the molecular landscape during stroke progression

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DIA proteomics was applied to MCAO mice detection for the first time.

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Proteomics and bioinformatics revealed relationship between stroke process and immunity, especially inflammation.

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C3, Apoa4 and S100a9 were highlighted as a marker or drug targets for stroke.

Strokes usually results in long-term disability and death, and they occur worldwide. Recently, increased research on both on the physiopathological mechanisms and the transcriptome during stroke progression, have highlighted the relationship between stroke progression and immunity, with a special focus on inflammation. Here, we applied proteome analysis to a middle carotid artery occlusion (MCAO) mouse model at 0 h, 6 h, 12 h and 24 h, in which proteome profiling was performed with 23 samples, and 41 differentially expressed proteins (DEPs) were identified. Bioinformatics studies on our data revealed the importance of the immune response and particularly identified the inflammatory response, cytokine- cytokine receptor interactions, the innate immune response and reactive oxygen species (ROS) during stroke progression. In addition, we compared our data with multiple gene expression omnibus (GEO) datasets with and without a time series, in which similar pathways were identified, and three proteins, C3, Apoa4 and S100a9, were highlighted as markers or drug targets for stroke; these three proteins were significantly upregulated in the MCAO model, both in our proteomic data and in the GEO database.

Meisoindigo Protects Against Focal Cerebral Ischemia-Reperfusion Injury by Inhibiting NLRP3 Inflammasome Activation and Regulating Microglia/Macrophage Polarization via TLR4/NF-κB Signaling Pathway

Ischemic stroke is a devastating disease with long-term disability. However, the pathogenesis is unclear and treatments are limited. Meisoindigo, a second-generation derivative of indirubin, has general water solubility and is well-tolerated. Previous studies have shown that meisoindigo reduces inflammation by inhibiting leukocyte chemotaxis and migration. In the present study, we investigated the hypothesis that meisoindigo was also protective against ischemic stroke, then evaluated its underlying mechanisms. In vivo, adult male C57BL/6J wild-type mice were used to produce a middle cerebral artery occlusion (MCAO) stroke model. On day three after reperfusion, obvious improvement in neurological scores, infarct volume reduction and cerebral edema amelioration were observed in meisoindigo treatment. Moreover, immunofluorescence staining and western-blot showed that the expression of NLRP3 inflammasome and its associated proteins in neurons and microglia was inhibited by meisoindigo. The effects of Meisoindigo on NLRP3 inflammasome inactivation and increased the M2 phenotype of microglia/macrophage through shifting from a M1 phenotype, which was possibly mediated by inhibition of TLR4/NF-κB. Furthermore, we verified the inhibitory effect of meisoindigo on TLR4/NF-κB signaling pathway, and found that meisoindigo treatment could significantly suppressed the expression of TLR4/NF-κB pathway-associated proteins in a dose-dependent manner, meanwhile, which resulted in downregulation of HMGB1 and IL-1β. Next, we established an in vitro oxygen glucose deprivation/Reperfusion (OGD/R) model in HT-22 and BV2 cells to simulate ischemic conditions. Cytotoxicity assay showed that meisoindigo substantially improved relative cell vitality and in HT-22 and BV2 cells following OGD/R in vitro. After suffering OGD/R, the TLR4/NF-κB pathway was activated, the expression of NLRP3 inflammasome-associated proteins and M1 microglia/macrophage were increased, but meisoindigo could inhibit above changes in both HT-22 and BV2 cells. Additionally, though lipopolysaccharide stimulated the activation of TLR4 signaling in OGD/R models, meisoindigo co-treatment markedly reversed the upregulation of TLR4 and following activation of NLRP3 inflammasome and polarization of M1 microglia/macrophages mediated by TLR4. Overall, we demonstrate for the first time that meisoindigo post-treatment alleviates brain damage induced by ischemic stroke in vivo and in vitro experiments through blocking activation of the NLRP3 inflammasome and regulating the polarization of microglia/macrophages via inhibition of the TLR4/NF-κB signaling pathway.

Curcumin Mitigates Neuro-Inflammation by Modulating Microglia Polarization Through Inhibiting TLR4 Axis Signaling Pathway Following Experimental Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) elicits destruction of neuronal cells and neurological function, which is exacerbated by neuro-inflammation in EBI, and toll-like receptor 4 (TLR4) plays an important role in inflammatory cascade via modulation microglia polarization. Curcumin (Cur), as a natural phytochemical compound, has the potential characteristics on anti-inflammatory and microglia phenotype transformation. In this study, we verified the hypothesis curcumin promotes M2 polarization to inhibiting neuro-inflammation, which through suppressing TLR4 signaling pathway after SAH. In tlr4^–/– mice and wild type (WT) subjected to prechiasmatic cistern blood injection, Western blotting, brain water content, neurological score, enzyme-linked immunosorbent assay (ELISA) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining were performed to investigate the role of TLR4 on neuro-inflammation response and microglia polarization. Curcumin with three different concentrations (50 mg/kg, 100 mg/kg and 200 mg/kg) were injected intraperitoneally (i.p.) at 15 min after SAH. The levels of TLR4, myeloid differentiation factor 88 (MyD88), nuclear factor- κB (NF-κB), Iba-1, CD86, CD206 and pro/anti-inflammation cytokines were measured by Western blotting and immunofluorescence staining at 24 h after SAH. SAH induction increased the protein levels of TLR4, pro-inflammation cytokines and proportion of M1 phenotype. Curcumin with 100 mg/kg treatment dramatically inhibited the release of pro-inflammatory mediators, and elevated the protein levels of anti-inflammatory cytokines and promoted microglia switch to M2. Meanwhile, curcumin treatment also decreased the expressions of TLR4, Myd88 and NF-κB at 24 h post SAH. TLR4 deficiency ameliorated brain water content, neurological deficit and reduced pro-inflammation cytokines after SAH. Moreover, curcumin treatment in tlr4^–/– mice further induced M2 polarization, while had no statistic difference on brain water content and neurological score at 24 h post SAH. Our results indicated that curcumin treatment alleviated neuro-inflammation response through promoting microglia phenotype shift toward M2, and which might inhibiting TLR4/MyD88/NF-κB signaling pathway after SAH.

β-Caryophyllene protects against ischemic stroke by promoting polarization of microglia toward M2 phenotype via the TLR4 pathway

AIMS

The objective of the study was to determine whether β-caryophyllene (BCP) exerts a neuroprotective effect in cerebral ischemia-reperfusion (I/R) injury by inhibiting microglial activation and modulating their polarization via the TLR4 pathway.

MAIN METHODS

Wild-type (WT) and TLR4 knockout (KO) C57BL/6J mice were subjected to cerebral I/R injury and neurologic dysfunction, cerebral infarct volume, brain edema, microglia activation and polarization, and TLR4 expression were determined. In vitro, primary microglia were stimulated with LPS and IFN-γ or IL-4 to induce polarization of microglia toward M1 or M2 phenotypes.

KEY FINDINGS

BCP reduced cerebral infarct volume, brain edema, and neurologic deficits in WT mice after I/R. The optimal dose of BCP, 72 mg/kg body weight, inhibited microglial activation and reduced the secretion of proinflammatory cytokines interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and IL-6 by microglia of WT mice. BCP inhibited the level of TLR4 in WT mice, and partially reduced neurologic deficits, infarct volume, and brain edema in TLR4 KO mice. Importantly, BCP reduced the number of activated M1-type microglia and increased the number of M2-type microglia in the ipsilateral cortex of both WT and TLR4 KO mice. In vitro, BCP decreased the secretion of proinflammatory cytokines induced by LPS plus IFN-γ, downregulated the level of TLR4 protein, and polarized microglia towards the M2 phenotype.

SIGNIFICANCES

The decrease in TLR4 activity mediated, at least in part, the anti-inflammatory effects of BCP and its ability to shift microglia polarization from the M1 to M2 phenotype.

Long Non-coding RNA TUG1 Sponges Mir-145a-5p to Regulate Microglial Polarization After Oxygen-Glucose Deprivation

Microglia plays a critical role in neuroinflammation after ischemic stroke by releasing diverse inflammatory cytokines. Long non-coding RNA taurine up-regulated gene 1 (lncRNA TUG1) is widely expressed in adult brain and has been reported to participate in multiple biological processes associated with nervous system diseases. However, the role of TUG1 in microglial activation remains unidentified. BV-2 microglial cells were cultured in vitro and TUG1 siRNA was used to knock down its RNA level. Microglial cells were subjected to oxygen-glucose deprivation (OGD) for 4 h following TUG1 siRNA or scramble siRNA transient transfection. After 24 h reoxygenation, TUG1 level and microglial M1/M2 phenotype, as well as releasing inflammatory cytokines and their role to viability of SH-SY5Y neuroblastoma cells were determined by quantitative real-time PCR (qRT-PCR), ELISA, immunofluorescence and western blot. In addition, miR-145a-5p, a putative microRNA to bind with TUG1 by bioinformatics analysis, was simultaneously examined, then the interaction of TUG1 with miR-145a-5p and the potential involvement of NF-κB pathway were further evaluated by RNA-RNA pull-down assay and western blot. The cellular level of TUG1 was transiently up-regulated in microglial cells 24 h after OGD treatment, with an inverse correlation to downregulated miR-145a-5p. TUG1 knockdown drove microglial M1-like to M2-like phenotypic transformation with reduced production of pro-inflammatory cytokines (tumor necrosis factor-α, TNF-α; interleukin-6, IL-6) and incremental release of anti-inflammatory cytokine (interleukin-10, IL-10), as a result, promoted the survival of SH-SY5Y cells. Meanwhile, TUG1 knockdown prevented OGD-induced activation of NF-κB pathway as well, represented by decreased ratios of p-p65/p65 and p-IκBα/IκBα proteins. Furthermore, we found that TUG1 could physically bind to miR-145a-5p while miR-145a-5p inhibitor abolished the protective effects of TUG1 knockdown through activation of NF-κB pathway, suggesting a negative interaction between TUG1 and miR-145a-5p. Our study demonstrated that lncRNA TUG1, sponging miR-145a-5p with negative interaction, could regulate microglial polarization and production of inflammatory cytokines at a relatively early stage after OGD insult, where NF-κB pathway might be involved, possibly providing a promising therapeutic target against inflammatory injury.

Hypoxic preconditioning relieved ischemic cerebral injury by promoting immunomodulation and microglia polarization after middle cerebral artery occlusion in rats

OBJECTIVES

This study was designed to investigate whether immunomodulation and Microglia polarization is involved in the anti-inflammatory and neuroprotective effect induced by hypoxic preconditioning (HPC) in the middle cerebral artery occlusion (MCAO) brain injury model.

METHODS

Longa method, (neurological disability status scale) NDSS method and TTC staining were used to evaluate the degree of cerebral infarction injury under different treatments (Sham, HPC, MCAO and co-treatment with HPC and MCAO). Western blot was used to detect expression profiles of apoptosis and related factors of neurological function. Flow cytometry was performed to analyze changes in the ratio of helper T cells, toxic T cells and NK cells in peripheral immune cells. And immunohistochemistry was used to examine the changes in microglial morphology. ELISA was used to evaluate the levels of nerve growth factors and neurogenesis conditions. Finally, RT-PCR was determined to analyze the transformation of microglia phenotype after HPC and MCAO treatment.

RESULTS

MCAO dramatically induced local formation of cerebral infarction. HPC relieved MCAO-induced cerebral infarction and increased rat cognition. HPC affected activation of microglia without significantly affecting in peripheral immune cell populations. After HPC co-treatment with MCAO, the M1 phenotype of microglia was changed and there was a transformation to M2.

CONCLUSION

The treatment of HPC remarkably affected the polarization of microglia cells in MCAO rats, and reduced the cerebral nerve injury and played a protective role in MCAO model.

Delayed recanalization at 3 days after permanent MCAO attenuates neuronal apoptosis through FGF21/FGFR1/PI3K/Caspase-3 pathway in rats

Reperfusion exceeded time window may induce ischemia/reperfusion injury, increase hemorrhagic transformation, and deteriorate neurological outcomes in ischemic stroke models. However, the increasing clinical evidences supported that reperfusion even within 6-24 h may salvage ischemic tissue and improve neurological outcomes in selected large vessel occlusion patients, without inducing serious ischemia/reperfusion injury and hemorrhagic transformation. The underlying molecular mechanisms are less clear. In present study, we demonstrated that delayed recanalization at 3 days after permanent middle cerebral artery occlusion (MCAO) decreased infarct volumes and improved neurobehavioral deficits in rats, with no increasing animal mortality and intracerebral hemorrhage. Meanwhile, we observed that endogenous neuroprotective agent fibroblast growth factor 21 (FGF21) significantly increased in serum after MCAO, but which did not synchronously increase in penumbra due to permanent MCAO. Recanalization dramatically increased the endogenous FGF21 expression on neurons in penumbra after MCAO. We confirmed that FGF21 activated the FGFR1/PI3K/Caspase-3 signaling pathway, which attenuated neuronal apoptosis in penumbra. Conversely, knockdown of FGFR1 via FGFR1 siRNA abolished the anti-apoptotic effects of FGF21, and in part abrogated beneficial effects of recanalization on neurological outcomes. These findings suggested that delayed recanalization at 3 days after MCAO improved neurological outcomes in rats via increasing endogenous FGF21 expression and activating FGFR1/PI3K/Caspase-3 pathway to attenuate neuronal apoptosis in penumbra. Delayed recanalization at 3 days after ischemic stroke onset may be a promising treatment strategy in selected patients.