Microglial responses after ischemic stroke and intracerebral hemorrhage. Clin Dev Immunol. 2013;2013:746068. [PMID: 24223607 PMCID: PMC3810327 DOI: 10.1155/2013/746068]

Encouraging an excitable brain state: mechanisms of brain repair in stroke

Stroke induces a plastic state in the brain. This period of enhanced plasticity leads to the sprouting of new axons, the formation of new synapses and the remapping of sensory-motor functions, and is associated with motor recovery. This is a remarkable process in the adult brain, which is normally constrained in its levels of neuronal plasticity and connectional change. Recent evidence indicates that these changes are driven by molecular systems that underlie learning and memory, such as changes in cellular excitability during memory formation. This Review examines circuit changes after stroke, the shared mechanisms between memory formation and brain repair, the changes in neuronal excitability that underlie stroke recovery, and the molecular and pharmacological interventions that follow from these findings to promote motor recovery in animal models. From these findings, a framework emerges for understanding recovery after stroke, central to which is the concept of neuronal allocation to damaged circuits. The translation of the concepts discussed here to recovery in humans is underway in clinical trials for stroke recovery drugs.

Neuroinflammation in hemorrhagic transformation after tissue plasminogen activator thrombolysis: Potential mechanisms, targets, therapeutic drugs and biomarkers

Hemorrhagic transformation (HT) is a common and serious complication following ischemic stroke, especially after tissue plasminogen activator (t-PA) thrombolysis, which is associated with increased mortality and disability. Due to the unknown mechanisms and targets of HT, there are no effective therapeutic drugs to decrease the incidence of HT. In recent years, many studies have found that neuroinflammation is closely related to the occurrence and development of HT after t-PA thrombolysis, including glial cell activation in the brain, peripheral inflammatory cell infiltration and the release of inflammatory factors, involving inflammation-related targets such as NF-κB, MAPK, HMGB1, TLR4 and NLRP3. Some drugs with anti-inflammatory activity have been shown to protect the BBB and reduce the risk of HT in preclinical experiments and clinical trials, including minocycline, fingolimod, tacrolimus, statins and some natural products. In addition, the changes in MMP-9, VAP-1, NLR, sICAM-1 and other inflammatory factors are closely related to the occurrence of HT, which may be potential biomarkers for the diagnosis and prognosis of HT. In this review, we summarize the potential inflammation-related mechanisms, targets, therapeutic drugs, and biomarkers associated with HT after t-PA thrombolysis and discuss the relationship between neuroinflammation and HT, which provides a reference for research on the mechanisms, prevention and treatment drugs, diagnosis and prognosis of HT.

The Stroke-Induced Blood-Brain Barrier Disruption: Current Progress of Inspection Technique, Mechanism, and Therapeutic Target

Stroke is one of the leading causes of mortality and morbidity worldwide. The blood-brain barrier (BBB) is a characteristic structure of microvessel within the brain. Under normal physiological conditions, the BBB plays a role in the prevention of harmful substances entering into the brain parenchyma within the central nervous system. However, stroke stimuli induce the breakdown of BBB leading to the influx of cytotoxic substances, vasogenic brain edema, and hemorrhagic transformation. Therefore, BBB disruption is a major complication, which needs to be addressed in order to improve clinical outcomes in stroke. In this review, we first discuss the structure and function of the BBB. Next, we discuss the progress of the techniques utilized to study BBB breakdown in in-vitro and in-vivo studies, along with biomarkers and imaging techniques in clinical settings. Lastly, we highlight the mechanisms of stroke-induced neuroinflammation and apoptotic process of endothelial cells causing BBB breakdown, and the potential therapeutic targets to protect BBB integrity after stroke. Secondary products arising from stroke-induced tissue damage provide transformation of myeloid cells such as microglia and macrophages to pro-inflammatory phenotype followed by further BBB disruption via neuroinflammation and apoptosis of endothelial cells. In contrast, these myeloid cells are also polarized to anti-inflammatory phenotype, repairing compromised BBB. Therefore, therapeutic strategies to induce anti-inflammatory phenotypes of the myeloid cells may protect BBB in order to improve clinical outcomes of stroke patients.

The Dual Role of Microglia in Blood-Brain Barrier Dysfunction after Stroke

It is well-known that stroke is one of the leading causes of death and disability all over the world. After a stroke, the blood-brain barrier subsequently breaks down. The BBB consists of endothelial cells surrounded by astrocytes. Microglia, considered the long-living resident immune cells of the brain, play a vital role in BBB function. M1 microglia worsen BBB disruption, while M2 microglia assist in repairing BBB damage. Microglia can also directly interact with endothelial cells and affect BBB permeability. In this review, we are going to discuss the mechanisms responsible for the dual role of microglia in BBB dysfunction after stroke.

Longitudinal monitoring of microglial/macrophage activation in ischemic rat brain using Iba-1-specific nanoparticle-enhanced magnetic resonance imaging

Microglial/macrophage activation plays a dual role in response to brain injury after a stroke, promoting early neuroinflammation and benefit for neurovascular recovery. Therefore, the dynamics of stroke-induced cerebral microglial/macrophage activation are of substantial interest. This study used novel anti-Iba-1-targeted superparamagnetic iron-platinum (FePt) nanoparticles in conjunction with magnetic resonance imaging (MRI) to measure the spatiotemporal changes of the microglial/macrophage activation in living rat brain for four weeks post-stroke. Ischemic lesion areas were identified and measured using T₂-weighted MR images. After injection of the FePt-nanoparticles, T₂*-weighted MR images showed that the nanoparticles were seen solely in brain regions that coincided with areas of active microglia/macrophages detected by post-mortem immunohistochemistry. Good agreement in morphological and distributive dynamic changes was also observed between the Fe⁺-cells and the Iba-1⁺-microglia/macrophages. The spatiotemporal changes of nanoparticle detected by T₂*-weighted images paralleled the changes of microglial/macrophage activation and phenotypes measured by post-mortem immunohistochemistry over the four weeks post-stroke. Maximum microglial/macrophage activation occurred seven days post-stroke for both measures, and the diminished activation found after two weeks continued to four weeks. Our results suggest that nanoparticle-enhanced MRI may constitute a novel approach for monitoring the dynamic development of neuroinflammation in living animals during the progression and treatment of stroke.

Angiogenesis and Blood-Brain Barrier Permeability in Vascular Remodeling after Stroke

Angiogenesis, the growth of new blood vessels, is a natural defense mechanism helping to restore oxygen and nutrient supply to the affected brain tissue following an ischemic stroke. By stimulating vessel growth, angiogenesis may stabilize brain perfusion, thereby promoting neuronal survival, brain plasticity, and neurologic recovery. However, therapeutic angiogenesis after stroke faces challenges: new angiogenesis-induced vessels have a higher than normal permeability, and treatment to promote angiogenesis may exacerbate outcomes in stroke patients. The development of therapies requires elucidation of the precise cellular and molecular basis of the disease. Microenvironment homeostasis of the central nervous system is essential for its normal function and is maintained by the blood-brain barrier (BBB). Tight junction proteins (TJP) form the tight junction (TJ) between vascular endothelial cells (ECs) and play a key role in regulating the BBB permeability. We demonstrated that after stroke, new angiogenesis-induced vessels in peri-infarct areas have abnormally high BBB permeability due to a lack of major TJPs in ECs. Therefore, promoting TJ formation and BBB integrity in the new vessels coupled with speedy angiogenesis will provide a promising and safer treatment strategy for improving recovery from stroke. Pericyte is a central neurovascular unite component in vascular barriergenesis and are vital to BBB integrity. We found that pericytes also play a key role in stroke-induced angiogenesis and TJ formation in the newly formed vessels. Based on these findings, in this article, we focus on regulation aspects of the BBB functions and describe cellular and molecular special features of TJ formation with an emphasis on role of pericytes in BBB integrity during angiogenesis after stroke.

Activation of adenosine A3 receptor reduces early brain injury by alleviating neuroinflammation after subarachnoid hemorrhage in elderly rats

The incidence of subarachnoid hemorrhage (SAH) and hazard ratio of death increase with age. Overactivation of microglia contributes to brain damage. This study aimed to investigate the effects of A3 adenosine receptors (A3R) activation on neurofunction and microglial phenotype polarization in the context of SAH in aged rats. The A3R agonist (CI-IB-MECA) and antagonist (MRS1523) were used in the SAH model. Microglia were cultured to mimic SAH in the presence or absence of CI-IB-MECA and/or siRNA for A3R. The neurofunction and status of the microglial phenotype were evaluated. The P38 inhibitor SB202190 and the STAT6 inhibitor AS1517499 were used to explore the signaling pathway. The results showed that SAH induced microglia to polarize to the M(LPS) phenotype both in vivo and in vitro. CI-IB-MECA distinctly skewed microglia towards the M(IL-4) phenotype and ameliorated neurological dysfunction, along with the downregulation of inflammatory cytokines. Knockdown of A3R or inhibition of P38 and/or STAT6 weakened the effects of CI-IB-MECA on microglial phenotypic shifting. Collectively, our findings suggest that activation of A3R exerted anti-inflammatory and neuroprotective effects by regulating microglial phenotype polarization through P38/STAT6 pathway and indicated that A3R agonists may be a promising therapeutic options for the treatment of brain injury after SAH.

Brain injury and repair after intracerebral hemorrhage: The role of microglia and brain-infiltrating macrophages

Intracerebral hemorrhage (ICH) is a major public health problem characterized by cerebral bleeding. Despite recent advances in preclinical studies, there is no effective treatment for ICH making it the deadliest subtype of stroke. The lack of effective treatment options partly attributes to the complexity as well as poorly defined pathophysiology of ICH. The emerging evidence indicates the potential of targeting secondary brain damage and hematoma resolution for improving neurological outcomes after ICH. Herein, we provide an overview of our understanding of the functional roles of activated microglia and brain-infiltrating monocyte-derived macrophages in brain injury and repair after ICH. The clinical and preclinical aspects that we discuss in this manuscript are related to ICH that occurs in adults, but not in infants. Also, we attempt to identify the knowledge gap in the field for future functional studies given the potential of targeting microglia and brain-infiltrating macrophages for therapeutic intervention after ICH.

The Role of ADF/Cofilin in Synaptic Physiology and Alzheimer's Disease

Actin-depolymerization factor (ADF)/cofilin, a family of actin-binding proteins, are critical for the regulation of actin reorganization in response to various signals. Accumulating evidence indicates that ADF/cofilin also play important roles in neuronal structure and function, including long-term potentiation and depression. These are the most extensively studied forms of long-lasting synaptic plasticity and are widely regarded as cellular mechanisms underlying learning and memory. ADF/cofilin regulate synaptic function through their effects on dendritic spines and the trafficking of glutamate receptors, the principal mediator of excitatory synaptic transmission in vertebrates. Regulation of ADF/cofilin involves various signaling pathways converging on LIM domain kinases and slingshot phosphatases, which phosphorylate/inactivate and dephosphorylate/activate ADF/cofilin, respectively. Actin-depolymerization factor/cofilin activity is also regulated by other actin-binding proteins, activity-dependent subcellular distribution and protein translation. Abnormalities in ADF/cofilin have been associated with several neurodegenerative disorders such as Alzheimer’s disease. Therefore, investigating the roles of ADF/cofilin in the brain is not only important for understanding the fundamental processes governing neuronal structure and function, but also may provide potential therapeutic strategies to treat brain disorders.

Intracerebroventricular Administration of hNSCs Improves Neurological Recovery after Cardiac Arrest in Rats

Irreversible brain injury and neurological dysfunction induced by cardiac arrest (CA) have long been a clinical challenge due to lack of effective therapeutic interventions to reverse neuronal loss and prevent secondary reperfusion injury. The neuronal regenerative potential of neural stem cells (NSCs) provides a possible solution to this clinical deficit. We investigated the neuronal recovery potential of human neural stem cells (hNSCs) via intracerebroventricular (ICV) xenotransplantation after CA in rats and the effects of transplanted NSCs on the proliferation and migration of endogenous NSCs. Outcome measures included neurological functional recovery measured by neurological deficit score (NDS), electrophysiologic analysis of EEG, and assessment of proliferation and migration at the cellular level and the Wnt/β-catenin pathway at the molecular level. Neurological functional assessment based on aggregate neurological deficit score (NDS) showed better recovery of function after hNSCs therapy (P < 0.05). Tracking of stem cells' proliferation with Ki67 antibody suggested that the NSCs group had more prominent proliferation compared to control group (number of Ki67+ cells, Control VS. NSC: 89.0 ± 31.6 VS. 352.7 ± 97.3, P < 0.05). In addition, cell migration tracked by Dcx antibody showed more Dcx + cells migrated to the far distance zone from SVZ in the treatment group (P < 0.05). Further immunofluorescence staining confirmed that the expression of the Wnt signaling pathway protein (β-catenin) was upregulated in the NSC group (P < 0.05). ICV delivery of hNSCs promotes endogenous NSC proliferation and migration and ultimately enhances neuronal survival and neurological functional recovery. Wnt/β-catenin pathway may be involved in the initiation and maintenance of this enhancement.Graphical abstract.

The protective effects of prolactin on brain injury

AIMS

Brain injuries based on their causes are divided into two categories, TBI and NTBI. TBI is caused by damages such as head injury, but non-physical injury causes NTBI. Prolactin is one of the blood factors that increase during brain injury. It has been assumed to play a regenerative role in post-injury recovery.

MATERIALS AND METHODS

In this review, various valid papers from electronic sources (including Web of Science, Scopus, PubMed, SID, Google Scholar, and ISI databases) used, which in them the protective effect of prolactin on brain injury investigated.

KEY FINDINGS

Inflammation following brain injury with the production of pro-inflammatory cytokines in the affected area can even lead to excitotoxicity and cell death in the damaged area. Medical brain damage treatments are long-term, and can have several side effects. Therefore, it is better to consider medication treatments that have fewer side effects and greater efficacy. Research suggests that prolactin has numerous regenerative effects on brain injury, and prevents cell death. Prolactin is one of the hormones produced in the body; therefore it has fewer side effects and may be more effective because it increases during brain injury.

SIGNIFICANCE

Prolactin can be used peripherally and centrally, and exerts its neuro regenerative effects against further damage post-TBI and NTBI.

Sphingosine 1-Phosphate Receptors in Cerebral Ischemia

Sphingosine 1-phosphate (S1P) is an important lipid biomolecule that exerts pleiotropic cellular actions as it binds to and activates its five G-protein-coupled receptors, S1P_1-5. Through these receptors, S1P can mediate diverse biological activities in both healthy and diseased conditions. S1P is produced by S1P-producing enzymes, sphingosine kinases (SphK1 and SphK2), and is abundantly present in different organs, including the brain. The medically important roles of receptor-mediated S1P signaling are well characterized in multiple sclerosis because FTY720 (Gilenya™, Novartis), a non-selective S1P receptor modulator, is currently used as a treatment for this disease. In cerebral ischemia, its role is also notable because of FTY720's efficacy in both rodent models and human patients with cerebral ischemia. In particular, some of the S1P receptors, including S1P₁, S1P₂, and S1P₃, have been identified as pathogenic players in cerebral ischemia. Other than these receptors, S1P itself and S1P-producing enzymes have been shown to play certain roles in cerebral ischemia. This review aims to compile the current updates and overviews about the roles of S1P signaling, along with a focus on S1P receptors in cerebral ischemia, based on recent studies that used in vivo rodent models of cerebral ischemia.

Neuroinflammatory Mechanisms in Ischemic Stroke: Focus on Cardioembolic Stroke, Background, and Therapeutic Approaches

One of the most important causes of neurological morbidity and mortality in the world is ischemic stroke. It can be a result of multiple events such as embolism with a cardiac origin, occlusion of small vessels in the brain, and atherosclerosis affecting the cerebral circulation. Increasing evidence shows the intricate function played by the immune system in the pathophysiological variations that take place after cerebral ischemic injury. Following the ischemic cerebral harm, we can observe consequent neuroinflammation that causes additional damage provoking the death of the cells; on the other hand, it also plays a beneficial role in stimulating remedial action. Immune mediators are the origin of signals with a proinflammatory position that can boost the cells in the brain and promote the penetration of numerous inflammatory cytotypes (various subtypes of T cells, monocytes/macrophages, neutrophils, and different inflammatory cells) within the area affected by ischemia; this process is responsible for further ischemic damage of the brain. This inflammatory process seems to involve both the cerebral tissue and the whole organism in cardioembolic stroke, the stroke subtype that is associated with more severe brain damage and a consequent worse outcome (more disability, higher mortality). In this review, the authors want to present an overview of the present learning of the mechanisms of inflammation that takes place in the cerebral tissue and the role of the immune system involved in ischemic stroke, focusing on cardioembolic stroke and its potential treatment strategies.

Exosomes derived from bone marrow mesenchymal stem cells harvested from type two diabetes rats promotes neurorestorative effects after stroke in type two diabetes rats

BACKGROUND AND PURPOSE

Diabetes elevates the risk of stroke, promotes inflammation, and exacerbates vascular and white matter damage post stroke, thereby hindering long term functional recovery. Here, we investigated the neurorestorative effects and the underlying therapeutic mechanisms of treatment of stroke in type 2 diabetic rats (T2DM) using exosomes harvested from bone marrow stromal cells obtained from T2DM rats (T2DM-MSC-Exo).

METHODS

T2DM was induced in adult male Wistar rats using a combination of high fat diet and Streptozotocin. Rats were subjected to transient 2 h middle cerebral artery occlusion (MCAo) and 3 days later randomized to one of the following treatment groups: 1) phosphate-buffered-saline (PBS, i.v), 2) T2DM-MSC-Exo, (3 × 10¹¹, i.v), 3) T2DM-MSC-Exo with miR-9 over expression (miR9+/+-T2DM-MSC-Exo, 3 × 10¹¹, i.v) or 4) MSC-Exo derived from normoglycemic rats (Nor-MSC-Exo) (3 × 10¹¹, i.v). T2DM sham control group is included as reference. Rats were sacrificed 28 days after MCAo.

RESULTS

T2DM-MSC-Exo treatment does not alter blood glucose, lipid levels, or lesion volume, but significantly improves neurological function and attenuates post-stroke weight loss compared to PBS treated as well as Nor-MSC-Exo treated T2DM-stroke rats. Compared to PBS treatment, T2DM-MSC-Exo treatment of T2DM-stroke rats significantly 1) increases tight junction protein ZO-1 and improves blood brain barrier (BBB) integrity; 2) promotes white matter remodeling indicated by increased axon and myelin density, and increases oligodendrocytes and oligodendrocyte progenitor cell numbers in the ischemic border zone as well as increases primary cortical neuronal axonal outgrowth; 3) decreases activated microglia, M1 macrophages, and inflammatory factors MMP-9 (matrix mettaloproteinase-9) and MCP-1 (monocyte chemoattractant protein-1) expression in the ischemic brain; and 4) decreases miR-9 expression in serum, and increases miR-9 target ABCA1 (ATP-binding cassette transporter 1) and IGFR1 (Insulin-like growth factor 1 receptor) expression in the brain. MiR9+/+-T2DM-MSC-Exo treatment significantly increases serum miR-9 expression compared to PBS treated and T2DM-MSC-Exo treated T2DM stroke rats. Treatment of T2DM stroke with miR9+/+-T2DM-MSC-Exo fails to improve functional outcome and attenuates T2DM-MSC-Exo treatment induced white matter remodeling and anti-inflammatory effects in T2DM stroke rats.

CONCLUSIONS

T2DM-MSC-Exo treatment for stroke in T2DM rats promotes neurorestorative effects and improves functional outcome. Down regulation of miR-9 expression and increasing its target ABCA1 pathway may contribute partially to T2DM-MSC-Exo treatment induced white matter remodeling and anti-inflammatory responses.

Insulin-Like Growth Factor 2 (IGF-2) Regulates Neuronal Density and IGF-2 Distribution Following Hippocampal Intracerebral Hemorrhage

BACKGROUND

The insulin-like growth factor 2 (IGF-2) is a growth factor and anti-inflammatory cytokine that plays a crucial role in memory consolidation. However, the precise role of this factor in acute brain damage is still unclear. The present study aimed to evaluate the variations in hippocampal IGF-2 distribution on different days and investigate the effect of recombinant IGF-2 on memory cell density, and IGF-2 distribution following acute hippocampal damage resulting from intracerebral hemorrhage (ICH).

METHODS

ICH was induced by injection of 100 μL of autologous blood into the left hippocampus of 72 male Sprague-Dawley rats. Recombinant IGF-2 was injected into the damaged hippocampus 30 min post-induction of ICH in the ICH-IGF-2 group. Then, on postoperative days 1, 3, 7, and 14, samples of brain tissue were collected to perform histopathological and immunohistochemical examinations.

RESULTS

The stereological study indicated that the volume of the hippocampus and the number of neurons had a significant reduction, and the infarct volume had a significant increase following ICH. Following the injection of IGF-2, a significant improvement was observed in stereological studies. Immunohistochemical data showed that IGF-2 distribution increased in the hippocampus on different days after ICH, and IGF-2 injection led to a dramatic reduction in this distribution.

CONCLUSIONS

In summary, the gradual increase of endogenous IGF-2 as growth and anti-inflammatory factor following hemorrhagic stroke reveals a critical role of this factor in brain recovery after injury. Moreover, the injection of IGF-2 can prevent cell death and alleviate the damage caused by the hemorrhagic stroke.

Microglia and Their Promising Role in Ischemic Brain Injuries: An Update

Ischemic brain injuries are common diseases with high morbidity, disability, and mortality rates, which have significant impacts on human health and life. Microglia are resident cells of the central nervous system (CNS). The inflammatory responses mediated by microglia play an important role in the occurrence and development of ischemic brain injuries. This article summarizes the activation, polarization, depletion, and repopulation of microglia after ischemic brain injuries, proposing new treatment strategies for such injuries through the modulation of microglial function.

miR-183-5p alleviates early injury after intracerebral hemorrhage by inhibiting heme oxygenase-1 expression

Differences in microRNA (miRNA) expression after intracerebral hemorrhage (ICH) have been reported in human and animal models, and miRNAs are being investigated as a new treatment for inflammation and oxidative stress after ICH. In this study, we found that microRNA-183-5p expression was decreased in the mouse brain after ICH. To investigate the effect of miRNA-183-5p on injury and repair of brain tissue after ICH, saline, miRNA-183-5p agomir, or miRNA-183-5p antagomir were injected into the lateral ventricles of 8-week-old mice with collagenase-induced ICH. Three days after ICH, mice treated with exogenous miRNA-183-5p showed less brain edema, neurobehavioral defects, inflammation, oxidative stress, and ferrous deposition than control mice. In addition, by alternately treating mice with a heme oxygenase-1 (HO-1) inducer, a HO-1 inhibitor, a nuclear factor erythroid 2-related factor (Nrf2) activator, and Nrf2 knockout, we demonstrated an indirect, HO-1-dependent regulatory relationship between miRNA-183-5p and Nrf2. Our results indicate that miRNA-183-5p and HO-1 are promising therapeutic targets for controlling inflammation and oxidative damage after hemorrhagic stroke.

L-3-n-butylphthalide attenuates inflammation response and brain edema in rat intracerebral hemorrhage model

L-3-n-butylphthalide(NBP), a compound found in Apium graveolens Linn seed extracts, has a therapeutic effect on acute ischemic stroke. The pathological inflammatory pathways and consequent brain edema in intracerebral hemorrhage (ICH) share some similar characteristics with ischemic stroke. We hypothesized that NBP has anti-inflammatory and therapeutic effects on rats with ICH. ICH was induced by an infusion of bacterial collagenase type IV into the unilateral striatum of anesthetized rats. The therapeutic effect of NBP was measured by assessing neurological function, brain water content, blood-brain barrier permeability, and expression of tumor necrosis factor-alpha (TNF-α) and matrix metalloproteinase-9 (MMP-9) around the hematoma 48 hours after surgery. Magnetic resonance imaging was performed 4 and 48 hours after ICH induction, and ICH-induced injured area volumes were measured using T2-weighted images. The NBP treatment group performed better in the neurological function test than the vehicle group. Moreover, in comparison with the vehicle group, NBP group showed a lower expanded hematoma volume, brain water content, blood-brain barrier permeability, and TNF-α/ MMP-9 expression level. Our results indicate that NBP attenuates inflammation and brain edema in rat ICH model. Therefore, our findings also provide a potential therapeutic strategy for the treatment of ICH with NBP.

Chronic restraint stress exacerbates neurological deficits and disrupts the remodeling of the neurovascular unit in a mouse intracerebral hemorrhage model

Growing evidences have shown that patients recovering from stroke experience high and unremitting stress. Chronic restraint stress (CRS) has been found to exacerbate neurological impairments in an experimental focal cortical ischemia model. However, there have been no studies reporting the effect and mechanism of CRS on intracerebral hemorrhage (ICH). This study aimed to evaluate the effect of CRS on a mouse ICH model. Adult male C57BL mice were subjected to infusion of collagenase IV (to induce ICH) or saline (for sham) into the left striatum. After ICH, animals were stressed with application of CRS protocol for 21 days. Our results showed that CRS significantly exacerbated neurological deficits (Garcia test, corner turn test, and wire grip test) and the ipsilateral brain atrophy and reduced body weight gain after ICH. Immunofluorescence staining indicated that CRS exerted significant suppressive effects on neuron, astrocyte, vascular endothelial cell and pericyte and excessively activated microglia post ICH. All of the key cellular components mentioned above are involved in the neurovascular unit (NVU) remodeling in the peri-hemorrhagic region after ICH. Western blot results showed that matrix metalloproteinase (MMP)-9 and tight junction (TJ) proteins including zonula occludens-1, occludin and claudin-5 were increased after ICH, but MMP-9 protein was further up-regulated and TJ-related proteins were down-regulated by CRS. In addition, ICH-induced activation of endoplasmic reticulum stress and apoptosis were further strengthened by CRS. Collectively, CRS exacerbates neurological deficits and disrupts the remodeling of the peri-hemorrhagic NVU after ICH, which may be associated with TJ proteins degradation and excessive activation of MMP-9 and endoplasmic reticulum stress-apoptosis.LAY SUMMARYCRS exacerbates neurological deficits and disrupts the remodeling of the NVU in the recovery stage after ICH, which suggest that monitoring chronic stress levels in patients recovering from ICH may merit consideration in the future.

Blood Vitronectin Induces Detrimental Brain Interleukin-6 and Correlates With Outcomes After Stroke Only in Female Mice

Background and Purpose- Women have worse stroke outcomes than men, especially after menopause. Few studies have focused on female-specific mechanisms, other than hormones. We investigated the role of the blood protein VTN (vitronectin) after ischemic stroke in mice. Methods- Adult male and female VTN knockout and wild-type littermates and C57BL/6 mice received a middle cerebral artery occlusion and the injured brain tissue analyzed 24 hours to 3 weeks later for cell loss and inflammation, as well as neurological function. Blood VTN levels were measured before and after stroke. Results- Intravenously injected VTN leaked extensively from bloodstream into brain infarct and penumbra by 24 hours after stroke. Strikingly, VTN was detrimental in female, but not male, mice, as shown by reduced brain injury (26.2±2.6% versus 13.4±3.8%; P=0.018; n=6 and 5) and forelimb dysfunction in female VTN knockout mice. Stroke increased plasma VTN 2- to 8-fold at 24 hours in females (36±4 versus 145±24 μg/mL; P<0.0001; n=10 and 7), but not males (62±8 versus 68±6; P>0.99; n=10 and 7), and returned to control levels by 7 days. Individually variable VTN levels at 24 hours correlated with stroke-induced brain injury at 7 days only in females. VTN promoted stroke-induced microglia/macrophage activation and leukocyte infiltration in females. Proinflammatory IL (interleukin)-6 greatly increased in the striatum at 24 hours in wild-type mice but was increased ≈60% less in female (739±159 versus 268±111; P=0.02; n=7 and 6), but not male (889±178 versus 1179±295; P=0.73; n=10 and 11), knockout mice. In individual wild-type females, plasma VTN levels correlated with striatal IL-6 expression at 24 hours. The female-specific effect of VTN-induced IL-6 expression following stroke was not due to gonadal hormones, as shown by ovariectomy and castration. Lastly, intrastriatal injection of IL-6 in female mice immediately before stroke reversed the VTN knockout phenotypes of reduced brain injury and microglia/macrophage activation. Conclusions- VTN plays a novel sexually dimorphic detrimental pathophysiological role in females and might ultimately be a therapeutic target to improve stroke outcomes in women.

Neurovascular protection by peroxisome proliferator-activated receptor α in ischemic stroke

Ischemic stroke is a leading cause of death and disability worldwide. Currently, the only pharmacological therapy for ischemic stroke is thrombolysis with tissue plasminogen activator that has a narrow therapeutic window and increases the risk of intracerebral hemorrhage. New pharmacological treatments for ischemic stroke are desperately needed, but no neuroprotective drugs have successfully made it through clinical trials. Beneficial effects of peroxisome proliferator-activated receptor alpha (PPARα) activation on vascular integrity and function have been reported, and PPARα agonists have clinically been used for many years to manage cardiovascular disease. Thus, PPARα has gained interest in recent years as a target for neurovascular disease such as ischemic stroke. Accumulating preclinical evidence suggests that PPARα activation modulates several pathophysiological hallmarks of stroke such as oxidative stress, blood-brain barrier (BBB) dysfunction, and neuroinflammation to improve functional recovery. Therefore, this review summarizes the various actions PPARα exerts in neurovascular health and disease and the potential of employing exogenous PPARα agonists for future pharmacological treatment of ischemic stroke.

Normobaric intermittent hypoxic training regulates microglia phenotype and enhances phagocytic activity

IMPACT STATEMENT

The effects of intermittent hypoxic training or conditioning on many pathological conditions have been widely investigated. One of the pathological conditions dealt with intermittent hypoxic training is ischemic stroke. Well-known mechanisms of intermittent hypoxia-induced protection are related to increased energy metabolism and the enhanced antioxidant effects. In the last decades, the role of microglia in the progress of ischemic stroke-related brain damage has been focused. The dual-edge function of microglia indicates that the microglia-mediated inflammatory response is definitely beneficial in the early stage of ischemic stroke, but long-term activation of microglia is rather detrimental during the recovery process. The effect of IHT on microglia polarization is not investigated. This study focused on whether IHT regulates the polarization of microglia without dampening its classic phagocytic function. This study will provide pivotal information regarding the effects of IHT on the long-term effects on the recovery process from ischemic stroke.

The Cerebral Thrombin System Is Activated after Intracerebral Hemorrhage and Contributes to Secondary Lesion Growth and Poor Neurological Outcome in C57Bl/6 Mice

With increasing evidence for the existence of a cerebral thrombin system, coagulation factor IIa (thrombin) is suspected to influence the pathogenesis of secondary injury progression after intracerebral hemorrhage (ICH). We hypothesized that mechanisms associated with local volume expansion after ICH, rather than blood constituents, activate the cerebral thrombin system and are responsible for detrimental neurological outcome. To test this hypothesis, we examine the local thrombin expression after ICH in a C57BL/6N mouse model in the presence and absence of blood constituents. ICH was established using stereotaxic orthotopic injection of utologous blood (n = 10) or silicone oil as inert volume substance (n = 10) into the striatum. Intracranial pressure (ICP), cerebral blood flow (CBF), and mean arterial blood pressure (MAP) were monitored during and 30 min after the procedure. No significant differences between ICP, CBF, and MAP were found between both groups. Prothrombin messenger RNA expression was upregulated early after ICH. Immunohistochemistry showed an increase of perilesional thrombin in both groups (blood, 4.24-fold; silicone, 3.10-fold), whereas prothrombin fragment (F1.2) was elevated only in the absence of whole blood. Thrombin expression is colocalized with neuronal antigen expression. After 24 h, lesion size and neuronal loss were similar. Perihematomal thrombin correlated with increased neuronal loss and detrimental neurological outcome in vivo. In our study, we demonstrate, for the first time, that the local cerebral thrombin system is activated after ICH and that this activation is independent of the presence of whole-blood constituents. In our study, neuronal damage is driven by local thrombin expression and leads to an adverse clinical outcome.

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.

Attenuation of Acute Intracerebral Hemorrhage-Induced Microglial Activation and Neuronal Death Mediated by the Blockade of Metabotropic Glutamate Receptor 5 In Vivo

The activation of microglia in response to intracerebral hemorrhagic stroke is one of the principal components of the progression of this disease. It results in the formation of pro-inflammatory cytokines that lead to neuronal death, a structural deterioration that, in turn interferes with functional recovery. Metabotropic glutamate receptor 5 (mGluR5) is highly expressed in reactive microglia and is involved in the pathological processes of brain disorders, but its role in intracerebral hemorrhage (ICH) remains unknown. We hypothesized that mGluR5 regulates microglial activation and ICH maintenance. In this study, collagenase-induced ICH mice received a single intraperitoneal injection of the mGluR5 antagonist-, MTEP, or vehicle 2 h after injury. We found that acute ICH upregulated mGluR5 and microglial activation. mGluR5 was highly localized in reactive microglia in the peri-hematomal cortex and striatum on days 3 and 7 post-ICH. The MTEP-mediated pharmacological inhibition of mGluR5 in vivo resulted in the substantial attenuation of acute microglial activation and IL-6, and TNF-α release. We also showed that the blockade of mGluR5 markedly reduced cell apoptosis, and neurodegeneration and markedly elevated neuroprotection. Furthermore, the MTEP-mediated inhibition of mGluR5 significantly reduced the lesion volume and improved functional recovery. Taken together, our results demonstrate that ICH injury enhances mGluR5 expression in the acute and subacute stages and that mGluR5 is highly localized in reactive microglia. The blockade of mGluR5 reduces ICH-induced acute microglial activation, provides neuroprotection and promotes neurofunctional recovery after ICH. The inhibition of mGluR5 may be a relevant therapeutic target for intracerebral hemorrhagic stroke.

Ischemic stroke and mitochondria: mechanisms and targets

Stroke is one of the main causes of mortality and disability in most countries of the world. The only way of managing patients with ischemic stroke is the use of intravenous tissue plasminogen activator and endovascular thrombectomy. However, very few patients receive these treatments as the therapeutic time window is narrow after an ischemic stroke. The paucity of stroke management approaches can only be addressed by identifying new possible therapeutic targets. Mitochondria have been a rare target in the clinical management of stroke. Previous studies have only investigated the bioenergetics and apoptotic roles of this organelle; however, the mitochondrion is now considered as a key organelle that participates in many cellular and molecular functions. This review discusses the mitochondrial mechanisms in cerebral ischemia such as its role in reactive oxygen species (ROS) generation, apoptosis, and electron transport chain dysfunction. Understanding the mechanisms of mitochondria in neural cell death during ischemic stroke might help to design new therapeutic targets for ischemic stroke as well as other neurological diseases.

Neuroinflammation after Intracerebral Hemorrhage and Potential Therapeutic Targets

Spontaneous intracerebral hemorrhage (ICH) is a catastrophic illness causing significant morbidity and mortality. Despite advances in surgical technique addressing primary brain injury caused by ICH, little progress has been made treating the subsequent inflammatory cascade. Pre-clinical studies have made advancements identifying components of neuroinflammation, including microglia, astrocytes, and T lymphocytes. After cerebral insult, inflammation is initially driven by the M1 microglia, secreting cytokines (e.g., interleukin-1β [IL-1β] and tumor necrosis factor-α) that are involved in the breakdown of the extracellular matrix, cellular integrity, and the blood brain barrier. Additionally, inflammatory factors recruit and induce differentiation of A1 reactive astrocytes and T helper 1 (Th1) cells, which contribute to the secretion of inflammatory cytokines, augmenting M1 polarization and potentiating inflammation. Within 7 days of ICH ictus, the M1 phenotype coverts to a M2 phenotype, key for hematoma removal, tissue healing, and overall resolution of inflammation. The secretion of anti-inflammatory cytokines (e.g., IL-4, IL-10) can drive Th2 cell differentiation. M2 polarization is maintained by the secretion of additional anti-inflammatory cytokines by the Th2 cells, suppressing M1 and Th1 phenotypes. Elucidating the timing and trigger of the anti-inflammatory phenotype may be integral in improving clinical outcomes. A challenge in current translational research is the absence of an equivalent disease animal model mirroring the patient population and comorbid pathophysiologic state. We review existing data and describe potential therapeutic targets around which we are creating a bench to bedside translational research model that better reflects the pathophysiology of ICH patients.

Crosstalk between stressed brain cells: direct and indirect effects of ischemia and aglycemia on microglia

Background

In cerebral ischemia, microglia have a dichotomous role in keeping the balance between pro- and anti-inflammatory mediators to avoid deleterious chronic inflammation and to leverage repair processes.

Methods

We examined functional and inflammatory markers in primary rat microglia in vitro after oxygen-glucose deprivation (OGD) or glucose deprivation (aglycemia). We then investigated the preconditioning effect of OGD or aglycemia upon a subsequent strong inflammatory stimulus, here lipopolysaccharides (LPS). Moreover, an “in vitro brain model” of neurons and glia, differentiated from primary rat neural stem cells, was exposed to OGD or aglycemia. Conditioned medium (CM) of this neuronal/glial co-culture was then used to condition microglia, followed by LPS as a “second hit.”

Results

OGD or aglycemia at sublethal doses did not significantly affect microglia function, including the expression of inflammatory markers. However, preconditioning with either OGD or aglycemia led to a decreased pro-inflammatory response to a subsequent stimulus with LPS. Interestingly, the anti-inflammatory markers IGF-1 and IL-10 were additionally reduced after such preconditioning, while expression of CD206 remained unaffected. Treatment with CM from the neuronal/glial co-culture alone did not affect the expression of inflammatory markers in microglia. In contrast, treatment with CM increased the expression of both pro- and anti-inflammatory markers in microglia upon a second hit with LPS. Interestingly, this effect could be attenuated in microglia treated with CM from neuronal/glia co-cultures preconditioned with OGD or aglycemia.

Conclusions

Data suggest specific and distinct microglia signatures in response to metabolic stress. While metabolic stress directly and indirectly applied to microglia did not mitigate their subsequent response to inflammation, preconditioning with metabolic stress factors such as OGD and aglycemia elicited a decreased inflammatory response to a subsequent inflammation stimulus.

Neuroprotective effects of minocycline on focal cerebral ischemia injury: a systematic review

To review the neuroprotective effects of minocycline in focal cerebral ischemia in animal models. By searching in the databases of PubMed, ScienceDirect, and Scopus, and considering the inclusion and exclusion criteria of the study. Studies were included if focal cerebral ischemia model was performed in mammals and including a control group that has been compared with a minocycline group. Written in languages other than English; duplicate data; in vitro studies and combination of minocycline with other neuroprotective agents were excluded. Neurological function of patients was assessed by National Institute of Health Stroke Scale, modified Rankin Scale, and modified Barthel Index. Neuroprotective effects were assessed by detecting the expression of inflammatory cytokines. We examined 35 papers concerning the protective effects of minocycline in focal cerebral ischemia in animal models and 6 clinical trials which had evaluated the neuroprotective effects of minocycline in ischemic stroke. These studies revealed that minocycline increases the viability of neurons and decreases the infarct volume following cerebral ischemia. The mechanisms that were reported in these studies included anti-inflammatory, antioxidant, as well as anti-apoptotic effects. Minocycline also increases the neuronal regeneration following cerebral ischemia. Minocycline has considerable neuroprotective effects against cerebral ischemia-induced neuronal damages. However, larger clinical trials may be required before using minocycline as a neuroprotective drug in ischemic stroke.

Microglial IRF5-IRF4 regulatory axis regulates neuroinflammation after cerebral ischemia and impacts stroke outcomes

Microglial activation plays a central role in poststroke inflammation and causes secondary neuronal damage; however, it also contributes in debris clearance and chronic recovery. Microglial pro- and antiinflammatory responses (or so-called M1-M2 phenotypes) coexist and antagonize each other throughout the disease progress. As a result of this balance, poststroke immune responses alter stroke outcomes. Our previous study found microglial expression of interferon regulatory factor 5 (IRF5) and IRF4 was related to pro- and antiinflammatory responses, respectively. In the present study, we genetically modified the IRF5 and IRF4 signaling to explore their roles in stroke. Both in vitro and in vivo assays were utilized; IRF5 or IRF4 small interfering RNA (siRNA), lentivirus, and conditional knockout (CKO) techniques were employed to modulate IRF5 or IRF4 expression in microglia. We used a transient middle cerebral artery occlusion model to induce stroke and examined both acute and chronic stroke outcomes. Poststroke inflammation was evaluated with flow cytometry, RT-PCR, MultiPlex, and immunofluorescence staining. An oscillating pattern of the IRF5-IRF4 regulatory axis function was revealed. Down-regulation of IRF5 signaling by siRNA or CKO resulted in increased IRF4 expression, enhanced M2 activation, quenched proinflammatory responses, and improved stroke outcomes, whereas down-regulation of IRF4 led to increased IRF5 expression, enhanced M1 activation, exacerbated proinflammatory responses, and worse functional recovery. Up-regulation of IRF4 or IRF5 by lentivirus induced similar results. We conclude that the IRF5-IRF4 regulatory axis is a key determinant in microglial activation. The IRF5-IRF4 regulatory axis is a potential therapeutic target for neuroinflammation and ischemic stroke.

Shikonin improve sepsis-induced lung injury via regulation of miRNA-140-5p/TLR4-a vitro and vivo study

Shikonin is an anti-inflammatory agent extracted from natural herbs. The aim of this study is to explain the treatment effects and mechanism of Shikonin in acute lung injury induced by sepsis. In this study, first, we evaluate different Shikonin concentrations for the anti-inflammation of acute lung injury induced by sepsis in an in vivo study. On the basis of the results, we confirm that 50.0 mg/kg was the best therapeutic Shikonin concentration. As a second step, we discuss the mechanism of Shikonin by a vitro cell experiment. Finaly, we validate that Shikonin has effective treatment effects on acute lung injury via regulation of microRNA-140-5p/toll-like receptor 4 (miRNA-140-5p/TLR4) in the in vivo study. The results of vitro and vivo study showed that Shikonin could improve acute lung injury induced by sepsis. The mechanism might be correlation miRNA-140-5p expression increasing, and regulated targeted gene TLR4, with TLR4 expression depressing, the downstream myeloid differentiation protein 88 and nuclear factor κB proteins expression were suppressed. In conclusion, Shikonin improved sepsis induced lung injury by regulation miRNA-140-5p/TLR4.

Cysteinyl Leukotriene Receptor 2 is Involved in Inflammation and Neuronal Damage by Mediating Microglia M1/M2 Polarization through NF-κB Pathway

Microglia activation plays a key role in regulating inflammatory and immune reaction during cerebral ischemia and it exerts pro-inflammatory or anti-inflammatory effect depending on M₁/M₂ polarization phenotype. Cysteinyl leukotriene 2 receptor (CysLT₂R) is a potent inflammatory mediator receptor, and involved in cerebral ischemic injury, but the mechanism of CysLT₂R regulating inflammation and neuron damage remains unclear. Here, we found that LPS and CysLT₂R agonist NMLTC₄ significantly increased microglia proliferation and phagocytosis, up-regulated the mRNA expression of M₁ polarization markers (IL-1β, TNF-α, IFN-γ, CD86 and iNOS), down-regulated the expression of M₂ polarization markers (Arg-1, CD206, TGF-β, IL-10, Ym-1) and increased the release of IL-1β and TNF-α. CysLT₂R selective antagonist HAMI3379 could antagonize these effects. IL-4 significantly up-regulated the mRNA expression of M₂ polarization markers, and HAMI3379 further increased IL-4-induced up-regulation of M₂ polarization markers expression. Additionally, LPS and NMLTC₄ stimulated NF-κB p50 and p65 proteins expression, and promoted p50 transfer to the nucleus. Pre-treatment with HAMI3379 and NF-κB signaling inhibitor Bay 11-7082 could reverse the up-regulation of p50 and p65 proteins expression, and inhibited p50 transfer to the nucleus. The conditional medium of BV-2 cells contained HAMI3379 could inhibit SH-SY5Y cells apoptosis induced by LPS and NMLTC₄. These results were further confirmed in primary microglia. The findings indicate that CysLT₂R was involved in inflammation and neuronal damage by inducing the activation of microglia M1 polarization and NF-κB pathway, inhibiting microglia M1 polarization and promoting microglia polarization toward M2 phenotype which may exerts neuroprotective effects, and targeting CysLT₂R may be a new therapeutic strategy against cerebral ischemia stroke.

Experimental ischemic stroke induces long-term T cell activation in the brain

Mounting evidence has demonstrated that both innate and adaptive immune cells infiltrate into the brain after ischemic stroke. T cell invasion has been found in the ischemic region up to one month post experimental ischemic stroke and has been shown to persist for years in stroke patients. However, the function and phenotypic characteristics of the brain invading T cells after ischemic stroke have not been investigated. In the current study, we determined the function of brain invading T cells in the acute and chronic phase following experimental ischemic stroke induced by transient middle cerebral artery occlusion. We observed a significant increase of CD4⁺ and CD8⁺ T cells presented in the peri-infarct area at up to one month after experimental ischemic stroke. The brain invading T cells after ischemic stroke demonstrated close interaction with active astrocytes and a progressive proinflammatory phenotype as evidenced by the increased expression of T cell activation markers CD44 and CD25, proinflammatory cytokines INF-γ, IL-17, IL-10, TNF-α, and perforin, with corresponding transcriptional factors T-bet and RORc. Our results indicated a prolonged activation of brain invading CD4⁺ and CD8⁺ T cells after ischemic stroke which may play a role in the neural repair process after stroke.

Vitronectin mitigates stroke-increased neurogenesis only in female mice and through FAK-regulated IL-6

Vitronectin (VTN) is a blood protein produced mainly by the liver. We show that VTN leaks from the bloodstream into the injury site and neighboring subventricular zone (SVZ) following ischemic stroke (middle cerebral artery occlusion, MCAO) in adult mice. MCAO is known to increase neurogenesis after stroke. VTN inhibits this response in females, but not in males, as shown by ~70% more stroke-induced SVZ neurogenesis in female VTN-/- mice at 14 d. In female VTN-/- mice, stroke-induced expression of interleukin-6 (IL-6) at 24 h was reduced in the SVZ. The closely related leukemia inhibitory factor (LIF) or pro-neurogenic ciliary neurotrophic factor (CNTF) were not affected. The female-specific effect of VTN on IL-6 expression was not due to sex hormones, as shown by ovariectomy and castration. IL-6 injection next to the SVZ reversed the MCAO-induced increase in neurogenesis seen in VTN-/- mice. Our in vitro and vivo data suggest that plasma VTN activates focal adhesion kinase (FAK) in the SVZ following MCAO, which reduces IL-6 expression in astrocytes but increases it in other cells such as microglia/macrophages. Inducible conditional astrocytic FAK deletion increased MCAO-induced IL-6 expression in females at 24 h and blocked MCAO-induced neurogenesis at 14 d, confirming a key detrimental role of IL-6. Collectively, these data suggest that leakage of VTN into the SVZ reduces the neurogenic response to stroke in female mice by promoting IL-6 expression. Reducing VTN or VTN signaling may be an approach to promote neurogenesis for neuroprotection and cell replacement after stroke in females.

Interferon regulatory factor 4/5 signaling impacts on microglial activation after ischemic stroke in mice

Microglial activation is a key element in initiating and perpetuating inflammatory responses to stroke. Interferon regulatory factor 5 (IRF5) and IRF4 signaling have been found critical in mediating macrophage pro‐inflammatory (M1) and anti‐inflammatory (M2) phenotypes, respectively, in peripheral inflammation. We hypothesize that the IRF5/4 regulatory axis also mediates microglial activation after stroke. C57BL6 mice of 8–12 weeks were subject to a 90‐min middle cerebral artery occlusion, and the brains evaluated at 24 h, 3, 10 and 30 days after reperfusion. Flow cytometry was utilized to examine microglial activation and cytokine expression. RT‐PCR was performed for mRNA levels of IRF5/4 in sorted microglia. Microglial expression of IRF5/4 was examined by immunohistochemistry, and brain cytokine levels were determined by ELISA. Our results revealed that the IRF5 mRNA level in sorted microglia increased at 3 days of stroke; whereas IRF4 mRNA level exhibited biphasic increases, with a transient rise at 24 h and a peak at 10 days. The same pattern was seen in IRF5/4 protein colocalization with Iba‐1⁺ cells by IHC. Intracellular levels of TNF‐α and IL‐1β in microglia peaked at 3 days of stroke, and IL‐4⁺IL‐10⁺ double‐positive microglia significantly increased at day 10. Brain levels of these cytokines were consistent with microglial cytokine changes. Worse behavior test results were seen at 3 days vs. 10 days of stroke. We conclude that microglia phenotypes are dynamic to ischemic stroke, and IRF5/4 signaling may regulate microglial M1/M2 activation and impact on stroke outcomes.

The interrelationship between cerebral ischemic stroke and glioma: a comprehensive study of recent reports

Glioma and cerebral ischemic stroke are two major events that lead to patient death worldwide. Although these conditions have different physiological incidences, ~10% of ischemic stroke patients develop cerebral cancer, especially glioma, in the postischemic stages. Additionally, the high proliferation, venous thrombosis and hypercoagulability of the glioma mass increase the significant risk of thromboembolism, including ischemic stroke. Surprisingly, these events share several common pathways, viz. hypoxia, cerebral inflammation, angiogenesis, etc., but the proper mechanism behind this co-occurrence has yet to be discovered. The hypercoagulability and presence of the D-dimer level in stroke are different in cancer patients than in the noncancerous population. Other factors such as atherosclerosis and coagulopathy involved in the pathogenesis of stroke are partially responsible for cancer, and the reverse is also partially true. Based on clinical and neurosurgical experience, the neuronal structures and functions in the brain and spine are observed to change after a progressive attack of ischemia that leads to hypoxia and atrophy. The major population of cancer cells cannot survive in an adverse ischemic environment that excludes cancer stem cells (CSCs). Cancer cells in stroke patients have already metastasized, but early-stage cancer patients also suffer stroke for multiple reasons. Therefore, stroke is an early manifestation of cancer. Stroke and cancer share many factors that result in an increased risk of stroke in cancer patients, and vice-versa. The intricate mechanisms for stroke with and without cancer are different. This review summarizes the current clinical reports, pathophysiology, probable causes of co-occurrence, prognoses, and treatment possibilities.

Bone marrow-mesenchymal stem cells modulate microglial activation in the peri-infarct area in rats during the acute phase of stroke

AIM

Bone marrow-mesenchymal stem cells (BM-MSCs) possess immunomodulatory properties in the brain. However, it remains unclear whether intravenously transplanted BM-MSCs have a neuromodulator effect on the activation of microglias after ischemic stroke. This study aimed to investigate the immunomodulatory effect of BM-MSCs on the regulation of brain microglial inactivation during the acute phase of stroke.

METHODS

A rat model of middle cerebral artery occlusion (MCAO) was established. Rat BM-MSCs were transplanted through the tail vein at 12 h after MCAO. CD200 Receptor 1 (CD200R1) antibody was injected into the peri-infarct area of the rat brain at 3 h prior to BM- MSCs transplantation. Protein expression was determined by immunofluorescence staining and Western blot. The volume of the infarct area was determined by TTC (2,3,5-triphenyltetrazolium hydrochloride) staining. Neuron apoptosis was determined by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining.

RESULTS

In vitro study showed that co-culture with BM-MSCs significantly decreased LPS-induced iNOS expression in the microglial cells. Immunofluorescence and Western blot consistently revealed that BM-MSC transplantation significantly reduced the IBA-expressing microglial cells and IBA protein levels in the peri-infarct area. The inhibitory effect of BM-MSC on IBA expression was significantly attenuated by pretreatment of CD200R1 neutralizing antibody in the peri-infarct zone. BM-MSC transplantation significantly reduced the infarct volume, protected neuron apoptosis, and increased neuronal CD200 expression in the peri-infarct area.

CONCLUSION

The transplanted BM-MSCs exerted immunomodulatory effect by inactivating the microglias in the peri-infarct area, at least partially, via the CD200-CD200R1 signaling.

Peripheral Administration of IL-13 Induces Anti-inflammatory Microglial/Macrophage Responses and Provides Neuroprotection in Ischemic Stroke

Neuroinflammation is strongly induced by cerebral ischemia. The early phase after the onset of ischemic stroke is characterized by acute neuronal injury, microglial activation, and subsequent infiltration of blood-derived inflammatory cells, including macrophages. Therefore, modulation of the microglial/macrophage responses has increasingly gained interest as a potential therapeutic approach for the ischemic stroke. In our study, we investigated the effects of peripherally administered interleukin 13 (IL-13) in a mouse model of permanent middle cerebral artery occlusion (pMCAo). Systemic administration of IL-13 immediately after the ischemic insult significantly reduced the lesion volume, alleviated the infiltration of CD45+ leukocytes, and promoted the microglia/macrophage alternative activation within the ischemic region, as determined by arginase 1 (Arg1) immunoreactivity at 3 days post-ischemia (dpi). Moreover, IL-13 enhanced the expression of M2a alternative activation markers Arg1 and Ym1 in the peri-ischemic (PI) area, as well as increased plasma IL-6 and IL-10 levels at 3 dpi. Furthermore, IL-13 treatment ameliorated gait disturbances at day 7 and 14 and sensorimotor deficits at day 14 post-ischemia, as analyzed by the CatWalk gait analysis system and adhesive removal test, respectively. Finally, IL-13 treatment decreased neuronal cell death in a coculture model of neuroinflammation with RAW 264.7 macrophages. Taken together, delivery of IL-13 enhances microglial/macrophage anti-inflammatory responses in vivo and in vitro, decreases ischemia-induced brain cell death, and improves sensory and motor functions in the pMCAo mouse model of cerebral ischemia.

Intravenous Immunoglobulin (IVIg) Induce a Protective Phenotype in Microglia Preventing Neuronal Cell Death in Ischaemic Stroke

Targeting the immune system and thereby modulating the inflammatory response in ischemic stroke has shown promising therapeutic potential in various preclinical trials. Among those, intravenous immunoglobulins (IVIg) have moved into the focus of attention. In a murine model of experimental stroke, we explored the therapeutic potential of IVIg on the neurological outcome and the inflammatory response. Further, we used an in vitro system to assess effects of IVIg-stimulated microglia on neuronal survival. Treatment with IVIg resulted in decreased lesion sizes, without significant effects on the infiltration and activation pattern of peripheral immune cells. However, in microglia IVIg induced a switch towards an upregulation of protective polarization markers, and the ablation of microglia led to the loss of neuroprotective IVIg effects. Functionally, IVIg stimulated microglia ameliorated neuronal cell death elicited by oxygen and glucose deprivation in vitro. Notably, application of IVIg in vivo led to a comparable decrease of apoptotic neurons in the penumbra area. Although neuroprotective effects of IVIg in vivo and in vitro have been established in previous studies, we were able to show for the first time, that IVIg modulates the polarization of microglia during the pathogenesis of stroke.

Fractalkine Modulates Microglia Metabolism in Brain Ischemia

In the CNS, the chemokine CX3CL1 (fractalkine) is expressed on neurons while its specific receptor CX3CR1 is expressed on microglia and macrophages. Microglia play an important role in health and disease through CX3CL1/CX3CR1 signaling, and in many neurodegenerative disorders, microglia dysregulation has been associated with neuro-inflammation. We have previously shown that CX3CL1 has neuroprotective effects against cerebral ischemia injury. Here, we investigated the involvement of CX3CL1 in the modulation of microglia phenotype and the underlying neuroprotective effect on ischemia injury. The expression profiles of anti- and pro-inflammatory genes showed that CX3CL1 markedly inhibited microglial activation both in vitro and in vivo after permanent middle cerebral artery occlusion (pMCAO), accompanied by an increase in the expression of anti-inflammatory genes. Moreover, CX3CL1 induces a metabolic switch in microglial cells with an increase in the expression of genes related to the oxidative pathway and a reduction in those related to the glycolytic pathway, which is the metabolic state associated to the pro-inflammatory phenotype for energy production. The data reported in this paper suggest that CX3CL1 protects against cerebral ischemia modulating the activation state of microglia and its metabolism in order to restrain inflammation and organize a neuroprotective response against the ischemic insult.

Application of Meridian Electrical Conductance in the Setting of Acute Ischemic Stroke: A Cross-Sectional Study

Acupuncture is widely used for improving poststroke care. Knowing the condition of meridian can help traditional Chinese medicine (TCM) doctors make a tailored choice of acupoints for every patient. The establishment of an objective meridian energy measurement for acute ischemic stroke that can be used for future acupuncture treatment and research is an important area in stroke-assisted therapy. In this study, a total of 102 subjects diagnosed with acute ischemic stroke within 7 days of onset were recruited, and the meridian energy analysis device (MEAD) was used to record the meridian electrical conductance (MEC) values of twelve meridians on unaffected and affected limbs. We found that the MEC value of the twelve meridians on the affected limbs was significantly higher than that on the unaffected limbs (P=0.001). Compared with the unaffected limbs, there was a higher value of MEC on the affected limbs of the lung meridian, heart meridian, pericardium meridian, and small intestine meridian, with significant differences (P < 0.05, P < 0.001, P < 0.001, and P < 0.05, respectively). Further analysis revealed that the MEC values of both Yin and Yang meridians of the affected limbs were significantly higher than those of the unaffected limbs (P=0.001 and P < 0.05, respectively). Meanwhile, the mean of the index of sympathovagal balance in patients with acute ischemic stroke (5.49 ± 4.21) was higher than the normal range (1–1.5), indicating autonomic imbalance. The results of this study are consistent with TCM theory as well as clinical observation and pathological mechanisms, suggesting that the measurement of MEC values may be used as a supplementary diagnostic method for acupuncture in patients with acute ischemic stroke.

Lysophosphatidic acid receptor 1 (LPA1) plays critical roles in microglial activation and brain damage after transient focal cerebral ischemia

Background

Lysophosphatidic acid receptor 1 (LPA₁) is in the spotlight because its synthetic antagonist has been under clinical trials for lung fibrosis and psoriasis. Targeting LPA₁ might also be a therapeutic strategy for cerebral ischemia because LPA₁ triggers microglial activation, a core pathogenesis in cerebral ischemia. Here, we addressed this possibility using a mouse model of transient middle cerebral artery occlusion (tMCAO).

Methods

To address the role of LPA₁ in the ischemic brain damage, we used AM095, a selective LPA₁ antagonist, as a pharmacological tool and lentivirus bearing a specific LPA₁ shRNA as a genetic tool. Brain injury after tMCAO challenge was accessed by determining brain infarction and neurological deficit score. Role of LPA₁ in tMCAO-induced microglial activation was ascertained by immunohistochemical analysis. Proinflammatory responses in the ischemic brain were determined by qRT-PCR and immunohistochemical analyses, which were validated in vitro using mouse primary microglia. Activation of MAPKs and PI3K/Akt was determined by Western blot analysis.

Results

AM095 administration immediately after reperfusion attenuated brain damage such as brain infarction and neurological deficit at 1 day after tMCAO, which was reaffirmed by LPA₁ shRNA lentivirus. AM095 administration also attenuated brain infarction and neurological deficit at 3 days after tMCAO. LPA₁ antagonism attenuated microglial activation; it reduced numbers and soma size of activated microglia, reversed their morphology into less toxic one, and reduced microglial proliferation. Additionally, LPA₁ antagonism reduced mRNA expression levels of proinflammatory cytokines and suppressed NF-κB activation, demonstrating its regulatory role of proinflammatory responses in the ischemic brain. Particularly, these LPA₁-driven proinflammatory responses appeared to occur in activated microglia because NF-κB activation occurred mainly in activated microglia in the ischemic brain. Regulatory role of LPA₁ in proinflammatory responses of microglia was further supported by in vitro findings using lipopolysaccharide-stimulated cultured microglia, showing that suppressing LPA₁ activity reduced mRNA expression levels of proinflammatory cytokines. In the ischemic brain, LPA₁ influenced PI3K/Akt and MAPKs; suppressing LPA₁ activity decreased MAPK activation and increased Akt phosphorylation.

Conclusion

This study demonstrates that LPA₁ is a new etiological factor for cerebral ischemia, strongly indicating that its modulation can be a potential strategy to reduce ischemic brain damage.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1555-8) contains supplementary material, which is available to authorized users.

Inhibition of activator protein 1 attenuates neuroinflammation and brain injury after experimental intracerebral hemorrhage

Aims

Intracerebral hemorrhage (ICH) is a devastating type of stroke without specific treatment. Activator protein 1 (AP‐1), as a gene regulator, initiates cytokine expression in response to environmental stimuli. In this study, we investigated the relationship between AP‐1 and neuroinflammation‐associated brain injury triggered by ICH.

Methods

Intracerebral hemorrhage mice were developed by autologous blood or collagenase infusion. We measured the dynamics of AP‐1 in mouse brain tissues during neuroinflammation formation after ICH. The effects of the AP‐1 inhibitor SR11302 on brain injury and neuroinflammation as well as the underlying mechanisms were investigated in vivo and in vitro.

Results

AP‐1 was significantly upregulated in mouse brain tissue as early as 6 hours after ICH, accompanied by elevations in proinflammatory factors, including interleukin (IL)‐6, IL‐1β, and tumor necrosis factor (TNF)‐α. Inhibition of AP‐1 using SR11302 reduced neurodeficits and brain edema at day 3 after ICH. SR11302 ablated microglial IL‐6 and TNF‐α production and brain‐infiltrating leukocytes in ICH mice. In addition, SR11302 treatment diminished thrombin‐induced production of IL‐6 and TNF‐α in cultured microglia.

Conclusions

Inhibition of AP‐1 curbs neuroinflammation and reduces brain injury following ICH.

Rapid neuroinflammatory changes in human acute intracerebral hemorrhage

OBJECTIVE

Spontaneous intracerebral hemorrhage (ICH) is the commonest form of hemorrhagic stroke and is associated with a poor prognosis. Neurosurgical removal of intracerebral hematoma has limited benefit and no pharmacotherapies are available. In acute ICH, primary tissue damage is followed by secondary pathology, where the cellular and neuroinflammatory changes are poorly understood.

METHODS

We studied histological changes in postmortem tissue from a cohort of spontaneous supra-tentorial primary ICH cases (n = 27) with survival of 1-12 days, compared to a matched control group (n = 16) examined in corresponding regions. Hematoxylin-eosin and microglial (Iba1) immunolabelled sections were assessed at 0-2, 3-5, and 7-12 days post-ICH.

RESULTS

Peri-hematoma, the observed ICH-related changes include edema, tissue neutrophils and macrophages from day 1. Ischemic neurons and swollen endothelial cells were common at day 1 and universal after day 5, as were intramural erythrocytes within small vessel walls. Activated microglia were evident at day 1 post-ICH. There was a significant increase in Iba1 positive area fraction at 0-2 (threefold), 3-5 (fourfold), and 7-12 days post ICH (ninefold) relative to controls. Giant microglia were detected peri-hematoma from day 5 and consistently 7-12 days post-ICH.

INTERPRETATION

Our data indicate that neuroinflammatory processes commence from day 1 post-ICH with changing microglial size and morphology following ICH and up to day 12. From day 5 some microglia exhibit a novel multiply nucleated morphology, which may be related to changing phagocytic function. Understanding the time course of neuroinflammatory changes, post-ICH may reveal novel targets for therapy and brain restoration.

Neuroinflammation: friend and foe for ischemic stroke

Stroke, the third leading cause of death and disability worldwide, is undergoing a change in perspective with the emergence of new ideas on neurodegeneration. The concept that stroke is a disorder solely of blood vessels has been expanded to include the effects of a detrimental interaction between glia, neurons, vascular cells, and matrix components, which is collectively referred to as the neurovascular unit. Following the acute stroke, the majority of which are ischemic, there is secondary neuroinflammation that both promotes further injury, resulting in cell death, but conversely plays a beneficial role, by promoting recovery. The proinflammatory signals from immune mediators rapidly activate resident cells and influence infiltration of a wide range of inflammatory cells (neutrophils, monocytes/macrophages, different subtypes of T cells, and other inflammatory cells) into the ischemic region exacerbating brain damage. In this review, we discuss how neuroinflammation has both beneficial as well as detrimental roles and recent therapeutic strategies to combat pathological responses. Here, we also focus on time-dependent entry of immune cells to the ischemic area and the impact of other pathological mediators, including oxidative stress, excitotoxicity, matrix metalloproteinases (MMPs), high-mobility group box 1 (HMGB1), arachidonic acid metabolites, mitogen-activated protein kinase (MAPK), and post-translational modifications that could potentially perpetuate ischemic brain damage after the acute injury. Understanding the time-dependent role of inflammatory factors could help in developing new diagnostic, prognostic, and therapeutic neuroprotective strategies for post-stroke inflammation.

Global brain inflammation in stroke

Stroke, including acute ischaemic stroke and intracerebral haemorrhage, results in neuronal cell death and the release of factors such as damage-associated molecular patterns (DAMPs) that elicit localised inflammation in the injured brain region. Such focal brain inflammation aggravates secondary brain injury by exacerbating blood-brain barrier damage, microvascular failure, brain oedema, oxidative stress, and by directly inducing neuronal cell death. In addition to inflammation localised to the injured brain region, a growing body of evidence suggests that inflammatory responses after a stroke occur and persist throughout the entire brain. Global brain inflammation might continuously shape the evolving pathology after a stroke and affect the patients' long-term neurological outcome. Future efforts towards understanding the mechanisms governing the emergence of so-called global brain inflammation would facilitate modulation of this inflammation as a potential therapeutic strategy for stroke.