Contribution of microglia/macrophages to expansion of infarction and response of oligodendrocytes after focal cerebral ischemia in rats

Role of microglia in stroke

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

Modulating monocyte-derived macrophage polarization in cerebral ischemic injury with hyperglycemia

Ischemic stroke (IS), characterized by high mortality rate, occurs owing to diminished or blocked blood flow to the brain. Hyperglycemia (HG) is a major contributor to the risk of IS. HG induces augmented oxidative stress and Blood-Brain Barrier breakdown, which increases the influx of blood-derived myeloid cells into the brain parenchyma. In cerebral ischemia, infiltrating monocytes undergo differentiation into pro-inflammatory or anti-inflammatory macrophages, having a large effect on outcomes of ischemic stroke. In addition, interleukin-4 (IL-4) and interleukin-13 (IL-13) engage in post-ischemia repair by polarizing the infiltrating monocytes into an anti-inflammatory phenotype. In this study, we aimed to determine the effect of phenotypic polarization of monocyte-derived macrophages on the prognosis of IS with HG (HG-IS). We first established a hyperglycemic mouse model using streptozotocin (150 mg/kg) and induced transient middle cerebral artery occlusion. We observed that blood-brain barrier permeability increased in HG-IS mice, as per two-photon live imaging and Evans blue staining. We also confirmed the increased infiltration of monocyte-derived macrophages and the downregulation of anti-inflammatory macrophages related to tissue remodeling after inflammation in HG-IS mice through immunohistochemistry, western blotting, and flow cytometry. We observed phenotypic changes in monocyte-derived macrophages, alleviated infarct volume, and improved motor function in HG-IS mice treated with IL-4 and IL-13. These findings suggest that the modulation of phenotypic changes in monocyte-derived macrophages following IS in hyperglycemic mice may influence ischemic recovery.

Unveiling the role of HIST2H2AC in stroke through single-cell and transcriptome analysis

Stroke is a leading cause of death and disability, and genetic risk factors play a significant role in its development. Unfortunately, effective therapies for stroke are currently limited. Early detection and diagnosis are critical for improving outcomes and developing new treatment strategies. In this study, we aimed to identify potential biomarkers and effective prevention and treatment strategies for stroke by conducting transcriptome and single-cell analyses. Our analysis included screening for biomarkers, functional enrichment analysis, immune infiltration, cell-cell communication, and single-cell metabolism. Through differential expression analysis, enrichment analysis, and protein-protein interaction (PPI) network construction, we identified HIST2H2AC as a potential biomarker for stroke. Our study also highlighted the diagnostic role of HIST2H2AC in stroke, its relationship with immune cells in the stroke environment, and our improved understanding of metabolic pathways after stroke. Overall, our research provided important insights into the pathogenesis of stroke, including potential biomarkers and treatment strategies that can be explored further to improve outcomes for stroke patients.

Out of the core: the impact of focal ischemia in regions beyond the penumbra

The changes in the necrotic core and the penumbra following induction of focal ischemia have been the focus of attention for some time. However, evidence shows, that ischemic injury is not confined to the primarily affected structures and may influence the remote areas as well. Yet many studies fail to probe into the structures beyond the penumbra, and possibly do not even find any significant results due to their short-term design, as secondary damage occurs later. This slower reaction can be perceived as a therapeutic opportunity, in contrast to the ischemic core defined as irreversibly damaged tissue, where the window for salvation is comparatively short. The pathologies in remote structures occur relatively frequently and are clearly linked to the post-stroke neurological outcome. In order to develop efficient therapies, a deeper understanding of what exactly happens in the exo-focal regions is necessary. The mechanisms of glia contribution to the ischemic damage in core/penumbra are relatively well described and include impaired ion homeostasis, excessive cell swelling, glutamate excitotoxic mechanism, release of pro-inflammatory cytokines and phagocytosis or damage propagation via astrocytic syncytia. However, little is known about glia involvement in post-ischemic processes in remote areas. In this literature review, we discuss the definitions of the terms "ischemic core", "penumbra" and "remote areas." Furthermore, we present evidence showing the array of structural and functional changes in the more remote regions from the primary site of focal ischemia, with a special focus on glia and the extracellular matrix. The collected information is compared with the processes commonly occurring in the ischemic core or in the penumbra. Moreover, the possible causes of this phenomenon and the approaches for investigation are described, and finally, we evaluate the efficacy of therapies, which have been studied for their anti-ischemic effect in remote areas in recent years.

Glial Populations in the Human Brain Following Ischemic Injury

There is a growing interest in glial cells in the central nervous system due to their important role in maintaining brain homeostasis under physiological conditions and after injury. A significant amount of evidence has been accumulated regarding their capacity to exert either pro-inflammatory or anti-inflammatory effects under different pathological conditions. In combination with their proliferative potential, they contribute not only to the limitation of brain damage and tissue remodeling but also to neuronal repair and synaptic recovery. Moreover, reactive glial cells can modulate the processes of neurogenesis, neuronal differentiation, and migration of neurons in the existing neural circuits in the adult brain. By discovering precise signals within specific niches, the regulation of sequential processes in adult neurogenesis holds the potential to unlock strategies that can stimulate the generation of functional neurons, whether in response to injury or as a means of addressing degenerative neurological conditions. Cerebral ischemic stroke, a condition falling within the realm of acute vascular disorders affecting the circulation in the brain, stands as a prominent global cause of disability and mortality. Extensive investigations into glial plasticity and their intricate interactions with other cells in the central nervous system have predominantly relied on studies conducted on experimental animals, including rodents and primates. However, valuable insights have also been gleaned from in vivo studies involving poststroke patients, utilizing highly specialized imaging techniques. Following the attempts to map brain cells, the role of various transcription factors in modulating gene expression in response to cerebral ischemia is gaining increasing popularity. Although the results obtained thus far remain incomplete and occasionally ambiguous, they serve as a solid foundation for the development of strategies aimed at influencing the recovery process after ischemic brain injury.

Regeneration of the cerebral cortex by direct chemical reprogramming of macrophages into neuronal cells in acute ischemic stroke

Theoretically, direct chemical reprogramming of somatic cells into neurons in the infarct area represents a promising regenerative therapy for ischemic stroke. Previous studies have reported that human fibroblasts and astrocytes transdifferentiate into neuronal cells in the presence of small molecules without introducing ectopic transgenes. However, the optimal combination of small molecules for the transdifferentiation of macrophages into neurons has not yet been determined. The authors hypothesized that a combination of small molecules could induce the transdifferentiation of monocyte-derived macrophages into neurons and that the administration of this combination may be a regenerative therapy for ischemic stroke because monocytes and macrophages are directly involved in the ischemic area. Transcriptomes and morphologies of the cells were compared before and after stimulation using RNA sequencing and immunofluorescence staining. Microscopic analyses were also performed to identify cell markers and evaluate functional recovery by blinded examination following the administration of small molecules after ischemic stroke in CB-17 mice. In this study, an essential combination of six small molecules [CHIR99021, Dorsomorphin, Forskolin, isoxazole-9 (ISX-9), Y27632, and DB2313] that transdifferentiated monocyte-derived macrophages into neurons in vitro was identified. Moreover, administration of six small molecules after cerebral ischemia in model animals generated a new neuronal layer in the infarct cortex by converting macrophages into neuronal cells, ultimately improving neurological function. These results suggest that altering the transdifferentiation of monocyte-derived macrophages by the small molecules to adjust their adaptive response will facilitate the development of regenerative therapies for ischemic stroke.

Regulation of microglia polarization after cerebral ischemia

Stroke ranks second as a leading cause of death and permanent disability globally. Microglia, innate immune cells in the brain, respond rapidly to ischemic injury, triggering a robust and persistent neuroinflammatory reaction throughout the disease's progression. Neuroinflammation plays a critical role in the mechanism of secondary injury in ischemic stroke and is a significant controllable factor. Microglia activation takes on two general phenotypes: the pro-inflammatory M1 type and the anti-inflammatory M2 type, although the reality is more complex. The regulation of microglia phenotype is crucial to controlling the neuroinflammatory response. This review summarized the key molecules and mechanisms of microglia polarization, function, and phenotypic transformation following cerebral ischemia, with a focus on the influence of autophagy on microglia polarization. The goal is to provide a reference for the development of new targets for the treatment for ischemic stroke treatment based on the regulation of microglia polarization.

Hot Spots for the Use of Intranasal Insulin: Cerebral Ischemia, Brain Injury, Diabetes Mellitus, Endocrine Disorders and Postoperative Delirium

A decrease in the activity of the insulin signaling system of the brain, due to both central insulin resistance and insulin deficiency, leads to neurodegeneration and impaired regulation of appetite, metabolism, endocrine functions. This is due to the neuroprotective properties of brain insulin and its leading role in maintaining glucose homeostasis in the brain, as well as in the regulation of the brain signaling network responsible for the functioning of the nervous, endocrine, and other systems. One of the approaches to restore the activity of the insulin system of the brain is the use of intranasally administered insulin (INI). Currently, INI is being considered as a promising drug to treat Alzheimer's disease and mild cognitive impairment. The clinical application of INI is being developed for the treatment of other neurodegenerative diseases and improve cognitive abilities in stress, overwork, and depression. At the same time, much attention has recently been paid to the prospects of using INI for the treatment of cerebral ischemia, traumatic brain injuries, and postoperative delirium (after anesthesia), as well as diabetes mellitus and its complications, including dysfunctions in the gonadal and thyroid axes. This review is devoted to the prospects and current trends in the use of INI for the treatment of these diseases, which, although differing in etiology and pathogenesis, are characterized by impaired insulin signaling in the brain.

Stroke: Molecular mechanisms and therapies: Update on recent developments

Stroke, a neurological disease, is one of the leading causes of death worldwide, resulting in long-term disability in most survivors. Annual stroke costs in the United States alone were estimated at $46 billion recently. Stroke pathophysiology is complex, involving multiple causal factors, among which atherosclerosis, thrombus, and embolus are prevalent. The molecular mechanisms involved in the pathophysiology are essential to understanding targeted drug development. Some common mechanisms are excitotoxicity and calcium overload, oxidative stress, and neuroinflammation. In addition, various modifiable and non-modifiable risk factors increase the chances of stroke manifolds. Once a patient encounters a stroke, complete restoration of motor ability and cognitive skills is often rare. Therefore, shaping therapeutic strategies is paramount for finding a viable therapeutic agent. Apart from tPA, an FDA-approved therapy that is applied in most stroke cases, many other therapeutic strategies have been met with limited success. Stroke therapies often involve a combination of multiple strategies to restore the patient's normal function. Certain drugs like Gamma-aminobutyric receptor agonists (GABA), Glutamate Receptor inhibitors, Sodium, and Calcium channel blockers, and fibrinogen-depleting agents have shown promise in stroke treatment. Recently, a drug, DM199, a recombinant (synthetic) form of a naturally occurring protein called human tissue kallikrein-1 (KLK1), has shown great potential in treating stroke with fewer side effects. Furthermore, DM199 has been found to overcome the limitations presented when using tPA and/or mechanical thrombectomy. Cell-based therapies like Neural Stem Cells, Hematopoietic stem cells (HSCs), and Human umbilical cord blood-derived mesenchymal stem cells (HUCB-MSCs) are also being explored as a treatment of choice for stroke. These therapeutic agents come with merits and demerits, but continuous research and efforts are being made to develop the best therapeutic strategies to minimize the damage post-stroke and restore complete neurological function in stroke patients.

Blocking postsynaptic density-93 binding to C-X3-C motif chemokine ligand 1 promotes microglial phenotypic transformation during acute ischemic stroke

We previously reported that postsynaptic density-93 mediates neuron-microglia crosstalk by interacting with amino acids 357-395 of C X3 C motif chemokine ligand 1 (CX3CL1) to induce microglia polarization. More importantly, the peptide Tat-CX3CL1 (comprising amino acids 357-395 of CX3CL1) disrupts the interaction between postsynaptic density-93 and CX3CL1, reducing neurological impairment and exerting a protective effect in the context of acute ischemic stroke. However, the mechanism underlying these effects remains unclear. In the current study, we found that the pro-inflammatory M1 phenotype increased and the anti-inflammatory M2 phenotype decreased at different time points. The M1 phenotype increased at 6 hours after stroke and peaked at 24 hours after perfusion, whereas the M2 phenotype decreased at 6 and 24 hours following reperfusion. We found that the peptide Tat-CX3CL1 (357-395aa) facilitates microglial polarization from M1 to M2 by reducing the production of soluble CX3CL1. Furthermore, the a disintegrin and metalloprotease domain 17 (ADAM17) inhibitor GW280264x, which inhibits metalloprotease activity and prevents CX3CL1 from being sheared into its soluble form, facilitated microglial polarization from M1 to M2 by inhibiting soluble CX3CL1 formation. Additionally, Tat-CX3CL1 (357-395aa) attenuated long-term cognitive deficits and improved white matter integrity as determined by the Morris water maze test at 31-34 days following surgery and immunofluorescence staining at 35 days after stroke, respectively. In conclusion, Tat-CX3CL1 (357-395aa) facilitates functional recovery after ischemic stroke by promoting microglial polarization from M1 to M2. Therefore, the Tat-CX3CL1 (357-395aa) is a potential therapeutic agent for ischemic stroke.

Expression pattern and clinical value of Key RNA methylation modification regulators in ischemic stroke

Ischemic stroke (IS) is one of the major causes of death and disability worldwide, and effective diagnosis and treatment methods are lacking. RNA methylation, a common epigenetic modification, plays an important role in disease progression. However, little is known about the role of RNA methylation modification in the regulation of IS. The aim of this study was to investigate RNA methylation modification patterns and immune infiltration characteristics in IS through bioinformatics analysis. We downloaded gene expression profiles of control and IS model rat brain tissues from the Gene Expression Omnibus database. IS profiles were divided into two subtypes based on RNA methylation regulators, and functional enrichment analyses were conducted to determine the differentially expressed genes (DEGs) between the subtypes. Weighted gene co-expression network analysis was used to explore co-expression modules and genes based on DEGs. The IS clinical diagnosis model was successfully constructed and four IS characteristic genes (GFAP, GPNMB, FKBP9, and CHMP5) were identified, which were significantly upregulated in IS samples. Characteristic genes were verified by receiver operating characteristic curve and real-time quantitative PCR analyses. The correlation between characteristic genes and infiltrating immune cells was determined by correlation analysis. Furthermore, GPNMB was screened using the protein-protein interaction network, and its regulatory network and the potential therapeutic drug chloroquine were predicted. Our finding describes the expression pattern and clinical value of key RNA methylation modification regulators in IS and novel diagnostic and therapeutic targets of IS from a new perspective.

Non-invasive brain stimulation for osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease, the prevalence of OA is increasing, and the elderly are the most common in patients with OA. OA has a severe impact on the daily life of patients, this increases the demand for treatment of OA. In recent years, the application of non-invasive brain stimulation (NIBS) has attracted extensive attention. It has been confirmed that NIBS plays an important role in regulating cortical excitability and oscillatory rhythm in specific brain regions. In this review, we summarized the therapeutic effects and mechanisms of different NIBS techniques in OA, clarified the potential of NIBS as a treatment choice for OA, and provided prospects for further research in the future.

Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) in Patients after Acute Stroke: Relation to Stroke Severity, Myocardial Injury, and Impact on Prognosis

Background: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is known to be associated with poor prognosis after cardiovascular events. We aimed to assess the dynamic changes in TRAIL levels and the relation of TRAIL level to stroke severity, its impact on the short-term outcomes, and its association with markers of cardiac injury in patients after acute stroke. Methods: Between August 2020 and August 2021, 120 consecutive patients, 104 after acute ischemic stroke (AIS), 76 receiving reperfusion therapy, and 16 patients after intracerebral hemorrhage (ICH) were enrolled in our study. Blood samples were obtained from patients at the time of admission, 24 h later, and 48 h later to determine the plasma level of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), N-terminal prohormone of brain natriuretic peptide (NT-proBNP), and high-sensitive Troponin I (hs-TnI). Twelve-lead ECGs were obtained at the time of admission, 24 h later, 48 h later, and at the release of the patients. Evaluations were performed using the National Institutes of Health Stroke Scale (NIHSS) at the time of admission and using the modified Rankin Scale (mRS) 90 days following the patient’s discharge from the hospital. Results: We observed a connection between lower TRAIL levels and stroke severity evaluated using the NIHSS (p = 0.044) on the first day. Lower TRAIL showed an association with severe disability and death as evaluated using the mRS at 90 days, both after 24 (p = 0.0022) and 48 h (p = 0.044) of hospitalization. Moreover, we observed an association between lower TRAIL and NT-proBNP elevation at the time of admission (p = 0.039), after 24 (p = 0.043), and after 48 h (p = 0.023) of hospitalization. In the ECG analysis, lower TRAIL levels were associated with the occurrence of premature ventricular extrasystoles (p = 0.043), and there was an association with prolonged QTc interval (p = 0.052). Conclusions: The results show that lower TRAIL is associated with stroke severity, unfavorable functional outcome, and short-term mortality in patients after acute ischemic stroke. Moreover, we described the association with markers of cardiac injury and ECG changes.

Is Immune Suppression Involved in the Ischemic Stroke? A Study Based on Computational Biology

Objective

To identify the genetic mechanisms of immunosuppression-related genes implicated in ischemic stroke.

Background

A better understanding of immune-related genes (IGs) involved in the pathophysiology of ischemic stroke may help identify drug targets beneficial for immunomodulatory approaches and reducing stroke-induced immunosuppression complications.

Methods

Two datasets related to ischemic stroke were downloaded from the GEO database. Immunosuppression-associated genes were obtained from three databases (i.e., DisGeNET, HisgAtlas, and Drugbank). The CIBERSORT algorithm was used to calculate the mean proportions of 22 immune-infiltrating cells in the stroke samples. Differential gene expression analysis was performed to identify the differentially expressed genes (DEGs) involved in stroke. Immunosuppression-related crosstalk genes were identified as the overlapping genes between ischemic stroke-DEGs and IGs. Feature selection was performed using the Boruta algorithm and a classifier model was constructed to evaluate the prediction accuracy of the obtained immunosuppression-related crosstalk genes. Functional enrichment analysis, gene-transcriptional factor and gene-drug interaction networks were constructed.

Results

Twenty two immune cell subsets were identified in stroke, where resting CD4 T memory cells were significantly downregulated while M0 macrophages were significantly upregulated. By overlapping the 54 crosstalk genes obtained by feature selection with ischemic stroke-related genes obtained from the DisGenet database, 17 potentially most valuable immunosuppression-related crosstalk genes were obtained, ARG1, CD36, FCN1, GRN, IL7R, JAK2, MAFB, MMP9, PTEN, STAT3, STAT5A, THBS1, TLR2, TLR4, TLR7, TNFSF10, and VASP. Regulatory transcriptional factors targeting key immunosuppression-related crosstalk genes in stroke included STAT3, SPI1, CEPBD, SP1, TP53, NFIL3, STAT1, HIF1A, and JUN. In addition, signaling pathways enriched by the crosstalk genes, including PD-L1 expression and PD-1 checkpoint pathway, NF-kappa B signaling, IL-17 signaling, TNF signaling, and NOD-like receptor signaling, were also identified.

Conclusion

Putative crosstalk genes that link immunosuppression and ischemic stroke were identified using bioinformatics analysis and machine learning approaches. These may be regarded as potential therapeutic targets for ischemic stroke.

Impact of systemic inflammatory response syndrome on acute ischemic stroke patients treated with mechanical thrombectomy

AIM

Systemic inflammatory response syndrome (SIRS) has been associated with poor outcomes after acute ischemic stroke (AIS). The primary goal of this study was to determine whether SIRS status on admission correlated with functional outcomes in AIS treated with mechanical thrombectomy (MT).

METHODS

Consecutive patients from September 2015 to April 2019 were retrospectively reviewed for SIRS on admission. SIRS was defined as the presence of ≥2 of the following: temperature < 36 °C or > 38 °C, heart rate > 90, respiratory rate > 20, and white blood cell count <4000/mm or > 12,000 mm.

RESULTS

Of 202 patients, 188 met inclusion criteria. 49 patients (26%) had evidence of SIRS. Neither basic patient demographics nor standard stroke risk factors predicted the development of SIRS. However, presentation with SIRS was correlated with higher rates of death (odds ratio [OR], 2.6; 95% confidence interval [CI], 1.2-5.5) as well as lower rates of favorable functional outcomes at discharge (OR, 0.09; 95% CI, 0.02-0.40) and 3-month follow up (OR 0.12; 95% CI 0.03-0.43). These results remained significant even after adjustment for age, sex, baseline NIHSS, recanalization status, and prior co-morbidities.

CONCLUSION

In our sample population, SIRS was associated with worse outcomes and higher rates of mortality in AIS patients treated with MT. Recognition of key risk factors can provide better prognostication and possible future therapeutic targets.

Extracellular vesicles from hypoxia-preconditioned microglia promote angiogenesis and repress apoptosis in stroke mice via the TGF-β/Smad2/3 pathway

Systemic transplantation of oxygen-glucose deprivation (OGD)-preconditioned primary microglia enhances neurological recovery in rodent stroke models, albeit the underlying mechanisms have not been sufficiently addressed. Herein, we analyzed whether or not extracellular vesicles (EVs) derived from such microglia are the biological mediators of these observations and which signaling pathways are involved in the process. Exposing bEnd.3 endothelial cells (ECs) and primary cortical neurons to OGD, the impact of EVs from OGD-preconditioned microglia on angiogenesis and neuronal apoptosis by the tube formation assay and TUNEL staining was assessed. Under these conditions, EV treatment stimulated both angiogenesis and tube formation in ECs and repressed neuronal cell injury. Characterizing microglia EVs by means of Western blot analysis and other techniques revealed these EVs to be rich in TGF-β1. The latter turned out to be a key compound for the therapeutic potential of microglia EVs, affecting the Smad2/3 pathway in both ECs and neurons. EV infusion in stroke mice confirmed the aforementioned in vitro results, demonstrating an activation of the TGF-β/Smad2/3 signaling pathway within the ischemic brain. Furthermore, enriched TGF-β1 in EVs secreted from OGD-preconditioned microglia stimulated M2 polarization of residing microglia within the ischemic cerebral environment, which may contribute to a regulation of an early inflammatory response in postischemic hemispheres. These observations are not only interesting from the mechanistic point of view but have an immediate therapeutic implication as well, since stroke mice treated with such EVs displayed a better functional recovery in the behavioral test analyses. Hence, the present findings suggest a new way of action of EVs derived from OGD-preconditioned microglia by regulating the TGF-β/Smad2/3 pathway in order to promote tissue regeneration and neurological recovery in stroke mice.

Systemic macrophage depletion attenuates infarct size in an experimental mouse model of stroke

Objective

Macrophages have been shown to play important roles in various pathophysiological processes of the central nervous system via neuroinflammation, leading to an increased interest in macrophage biology. Circulating blood monocytes are among the first cells to infiltrate the brain after ischemic stroke; however, the role of innate immune cells such as monocytes and macrophages remains to be elucidated. Here, we investigated the association between blood monocytes and infarct size following ischemic stroke.

Methods

We induced stroke using a focal ischemia mouse model through middle cerebral artery suture occlusion. To deplete circulating blood monocytes, clodronate was injected intraperitoneally 24 h before the surgery. Animals were sacrificed at specified time points, and the infarct size and mRNA expression were then measured.

Results

The clodronate-injected mice showed significantly smaller infarct size than the control mice. Immunohistochemical staining revealed that monocyte depletion significantly blocked the infiltration of macrophages and microglia. The mRNA expression levels of macrophage and microglia markers were higher in the left infarcted brain than in the right non-infarcted brain.

Conclusions

In summary, monocyte depletion reduced the infarct size and mitigated neurological deficits in mice following ischemic stroke, likely by blocking the infiltration of inflammatory cells such as macrophages and microglia.

Glial Cells as Therapeutic Approaches in Brain Ischemia-Reperfusion Injury

Ischemic stroke is the second cause of mortality and the first cause of long-term disability constituting a serious socioeconomic burden worldwide. Approved treatments include thrombectomy and rtPA intravenous administration, which, despite their efficacy in some cases, are not suitable for a great proportion of patients. Glial cell-related therapies are progressively overcoming inefficient neuron-centered approaches in the preclinical phase. Exploiting the ability of microglia to naturally switch between detrimental and protective phenotypes represents a promising therapeutic treatment, in a similar way to what happens with astrocytes. However, the duality present in many of the roles of these cells upon ischemia poses a notorious difficulty in disentangling the precise pathways to target. Still, promoting M2/A2 microglia/astrocyte protective phenotypes and inhibiting M1/A1 neurotoxic profiles is globally rendering promising results in different in vivo models of stroke. On the other hand, described oligodendrogenesis after brain ischemia seems to be strictly beneficial, although these cells are the less studied players in the stroke paradigm and negative effects could be described for oligodendrocytes in the next years. Here, we review recent advances in understanding the precise role of mentioned glial cell types in the main pathological events of ischemic stroke, including inflammation, blood brain barrier integrity, excitotoxicity, reactive oxygen species management, metabolic support, and neurogenesis, among others, with a special attention to tested therapeutic approaches.

Pharmacologic neuroprotection in ischemic brain injury after cardiac arrest

Cardiac arrest has many implications for morbidity and mortality. Few interventions have been shown to improve return of spontaneous circulation (ROSC) and long-term outcomes after cardiac arrest. Ischemic-reperfusion injury upon achieving ROSC creates an imbalance between oxygen supply and demand. Multiple events occur in the postcardiac arrest period, including excitotoxicity, mitochondrial dysfunction, and oxidative stress and inflammation, all of which contribute to ongoing brain injury and cellular death. Given that complex pathophysiology underlies global brain hypoxic ischemia, neuroprotective strategies targeting multiple stages of the neuropathologic cascade should be considered as a means of mitigating secondary neuronal injury and improving neurologic outcomes and survival in cardiac arrest victims. In this review article, we discuss a number of different pharmacologic agents that may have a potential role in targeting these injurious pathways following cardiac arrest. Pharmacologic therapies most relevant for discussion currently include memantine, perampanel, magnesium, propofol, thiamine, methylene blue, vitamin C, vitamin E, coenzyme Q₁₀ , minocycline, steroids, and aspirin.

Regulation of post-ischemic inflammatory response: A novel function of the neuronal tyrosine phosphatase STEP

The neuron-specific tyrosine phosphatase STEP is emerging as a key neuroprotectant against acute ischemic stroke. However, it remains unclear how STEP impacts the outcome of stroke. We find that the exacerbation of ischemic brain injury in STEP deficient mice involves an early onset and sustained activation of neuronal p38 mitogen activated protein kinase, a substrate of STEP. This leads to rapid increase in the expression of neuronal cyclooxygenase-2 and synthesis of prostaglandin E₂, causing change in microglial morphology to an amoeboid activated state, activation of matrix metalloproteinase-9, cleavage of tight junction proteins and extravasation of IgG into the ischemic brain. Restoration of STEP signaling with intravenous administration of a STEP-derived peptide mimetic reduces the post-ischemic inflammatory response and attenuates brain injury. The findings identify a unique role of STEP in regulating post-ischemic neuroinflammation and further emphasizes the therapeutic potential of the STEP-mimetic in neurological disorders where inflammation contributes to brain damage.

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.

Induced mRNA expression of matrix metalloproteinases Mmp-3, Mmp-12, and Mmp-13 in the infarct cerebral cortex of photothrombosis model mice

A strong therapeutic target of ischemic stroke is controlling brain inflammation. Recent studies have implicated the critical role of C-C chemokine receptor 5 (CCR5) in neuroinflammation during ischemic stroke. It has been reported that the expression of the matrix metalloproteinases, MMP-3, MMP-12, and MMP-13, is controlled by CCR5; however, their expressional regulation in the infarct brain has not been clearly understood. This study investigated the mRNA expression of Mmp-3, -12, and -13 in the ischemic cerebral cortex of photothrombosis mouse model. The three Mmps were highly upregulated in the early stages of ischemic stroke and were expressed in different types of cells. Mmp-3 and Mmp-13 were expressed in blood vessel endothelial cells after ischemia-induction, whereas Mmp-12 was expressed in activated microglia. The expression of Mmp-13 in resting microglia and in neurons of uninjured cerebral cortex was lost in the infarct region. Therefore, the MMPs responding to CCR5 are differentially regulated during ischemic stroke.

Activated microglia-derived macrophage-like cells exacerbate brain edema after ischemic stroke correlate with astrocytic expression of aquaporin-4 and interleukin-1 alpha release

Brain edema following brain infarction affects mobility and mortality. The mechanisms underlying this process remain to be elucidated. Animal studies have shown that aquaporin-4 (AQP4) expression in astrocytes increases after stroke, and its deletion significantly reduces brain swelling. Recently, two kinds of cells, resident microglia-derived macrophage-like cells (MG-MΦ) and bone marrow-derived macrophages (BM-MΦ), have been reported to accumulate in the ischemic core and stimulate adjacent astrocytes. Therefore, we hypothesized that these cells play crucial roles in the expression of AQP4 and ultimately lead to exacerbated brain edema. To verify this hypothesis, we investigated the role of MG- or BM-MΦ in brain edema using a rat model of transient middle cerebral artery occlusion and rat astrocyte primary cultures. AQP4 expression significantly increased in the peri-infarct tissue at 3-7 days post-reperfusion (dpr) and in the core tissue at 5 and 7 dpr, which synchronized with the expression of Iba1, Il1a, Tnf, and C1qa mRNA. Interleukin (IL)-1α treatment or coculture with MG- and BM-MΦ increased AQP4 expression in astrocytes, while an IL-1 receptor type I antagonist reduced these effects. Furthermore, aggravated animals exhibited high expression of Aqp4 and Il1a mRNA in the ischemic core at 7 dpr, which led to the exacerbation of brain edema. MG-MΦ signature genes were highly expressed in the ischemic core in aggravated rats, while BM-MΦ signature genes were weakly expressed. These findings suggest that IL-1α produced by MG-MΦ induces astrocytic AQP4 expression in the peri-infarct and ischemic core tissues, thereby exacerbating brain edema. Therefore, the regulation of MG-MΦ may prevent the exacerbation of brain edema.

Insight into the divergent role of TRAIL in non-neoplastic neurological diseases

Tumour necrosis factor–related apoptosis‐inducing ligand (TRAIL) is a member of the tumour necrosis factor (TNF) superfamily which mainly induces apoptosis of tumour cells and transformed cell lines with no systemic toxicity, whereas they share high sequence homology with TNF and CD95L. These unique effects of TRAIL have made it an important molecule in oncology research. However, the research on TRAIL‐related antineoplastic agents has lagged behind and has been limited by the extensive drug resistance in cancer cells. Given the several findings showing that TRAIL is involved in immune regulation and other pleiotropic biological effects in non‐malignant cells, TRAIL and its receptors have attracted widespread attention from researchers. In the central nervous system (CNS), TRAIL is highly correlated with malignant tumours such as glioma and other non‐neoplastic disorders such as acute brain injury, CNS infection and neurodegenerative disease. Many clinical and animal studies have revealed the dual roles of TRAIL in which it causes damage by inducing cell apoptosis, and confers protection by enhancing both pro‐ and non‐apoptosis effects in different neurological disorders and at different sites or stages. Its pro‐apoptotic effect produces a pro‐survival effect that cannot be underestimated. This review extensively covers in vitro and in vivo experiments and clinical studies investigating TRAIL. It also provides a summary of the current knowledge on the TRAIL signalling pathway and its involvement in pathogenesis, diagnosis and therapeutics of CNS disorders as a basis for future research.

Inhibition of double-strand DNA-sensing cGAS ameliorates brain injury after ischemic stroke

Cytosolic double‐stranded DNA (dsDNA) is a danger signal that is tightly monitored and sensed by nucleic acid‐sensing pattern recognition receptors. We study the inflammatory cascade on dsDNA recognition and investigate the neuroprotective effect of cyclic GMP‐AMP (cGAMP) synthase (cGAS) antagonist A151 and its mechanisms of neuroprotection in a mouse model of experimental stroke. Here, we found that cerebral ischemia promoted the release of dsDNA into the cytosol, where it initiated inflammatory responses by activating the cGAS. A151 effectively reduced the expression of cGAS, absent in melanoma 2 (AIM2) inflammasome, and pyroptosis‐related molecules, including caspase‐1, gasdermin D, IL‐1β, and IL‐18. Furthermore, mice treated with A151 showed a dampened immune response to stroke, with reduced counts of neutrophils, microglia, and microglial production of IL‐6 and TNF‐α after MCAO. Moreover, A151 administration significantly reduced infarct volume, attenuated neurodeficits, and diminished cell death. Notably, the protective effect of A151 was blocked in a microglia‐specific cGAS knockout mouse. These findings offer unique perspectives on stroke pathogenesis and indicate that inhibition of cGAS could attenuate brain inflammatory burden, representing a potential therapeutic opportunity for stroke.

Cerebral ischemia-reperfusion aggravated cerebral infarction injury and possible differential genes identified by RNA-Seq in rats

Numerous studies have shown that local excessive inflammatory response in brain tissue was an important pathogenesis of secondary injury following cerebral ischemia-reperfusion (I/R). However, the inflammatory-related targets and pathways after cerebral I/R injury are still unclear. This study was to investigate possible targets and mechanisms after cerebral I/R injury. Rats were subjected to transient or permanent middle cerebral artery occlusion (MCAO). Neurological deficit scores test was used to evaluate neurological function. Cerebral infarction was evaluated by MRI, TTC staining and Nissl staining. Microglia activation was detected by immunofluorescence using Iba-1 antibody. Inflammatory factors were detected by ELISA assay. RNA-sequencing transcriptome analysis was processed and the differential genes were verified by real-time quantitative PCR (qPCR) and western blotting. The results showed that neurological function of rats in I/R group was more severe than that in I group on the 7^th after cerebral I/R. Therefore, the differences between cerebral ischemia and cerebral I/R for 7 days were studied in further study. The results showed that the levels of pro-inflammatory factors in I/R group were higher and the levels of anti-inflammatory factors were lower than those in I group. KEGG pathway and gene network enrichment analysis revealed that some common differential up- and down-regulated genes were involved in most of significant pathways. These common differential up-regulated genes belonged to TLR4/MYD88 inflammatory signaling pathway and common differential down-regulated genes belonged to HRAS/RAF1 neurotrophic signaling pathway. Interestingly, according to the genetic interaction analysis of string database, these up-regulated differential genes might promote the development of inflammation, while the down-regulated differential genes might inhibit the development of inflammation. Furthermore, qPCR and WB results verified that these pro-inflammatory genes in the I/R group were higher than those in the I group, while possible anti-inflammatory genes in the I/R group were lower than those in the I group. It is concluded that TLR4/MYD88 inflammatory signaling pathway and HRAS/RAF1 neurotrophic signaling pathway may play different roles after cerebral I or I/R and may be therapeutic targets for stroke recovery.

Developmental analyses of mouse embryos and adults using a non-overlapping tracing system for all three germ layers

Genetic lineage-tracing techniques are powerful tools for studying specific cell populations in development and pathogenesis. Previous techniques have mainly involved systems for tracing a single gene, which are limited in their ability to facilitate direct comparisons of the contributions of different cell lineages. We have developed a new combinatorial system for tracing all three germ layers using self-cleaving 2A peptides and multiple site-specific recombinases (SSRs). In the resulting TRiCK (TRiple Coloured germ layer Knock-in) mice, the three germ layers are conditionally and simultaneously labelled with distinct fluorescent proteins via embryogenesis. We show that previously reported ectopic expressions of lineage markers are the outcome of secondary gene expression. The results presented here also indicate that the commitment of caudal axial stem cells to neural or mesodermal fate proceeds without lineage fluctuations, contrary to the notion of their bi-potency. Moreover, we developed IMES, an optimized tissue clearing method that is highly compatible with a variety of fluorescent proteins and immunostaining, and the combined use of TRiCK mice and IMES can facilitate comprehensive analyses of dynamic contributions of all three germ layers.

Angiogenesis in the ischemic core: A potential treatment target?

The ischemic penumbra is both a concept in understanding the evolution of cerebral tissue injury outcome of focal ischemia and a potential therapeutic target for ischemic stroke. In this review, we examine the evidence that angiogenesis can contribute to beneficial outcomes following focal ischemia in model systems. Several studies have shown that, following cerebral ischemia, endothelial proliferation and subsequent angiogenesis can be detected beginning four days after cerebral ischemia in the border of the ischemic core, or in the ischemic periphery, in rodent and non-human primate models, although initial signals appear within hours of ischemia onset. Components of the neurovascular unit, its participation in new vessel formation, and the nature of the core and penumbra responses to experimental focal cerebral ischemia, are considered here. The potential co-localization of vascular remodeling and axonal outgrowth following focal cerebral ischemia based on the definition of tissue remodeling and the processes that follow ischemic stroke are also considered. The region of angiogenesis in the ischemic core and its surrounding tissue (ischemic periphery) may be a novel target for treatment. We summarize issues that are relevant to model studies of focal cerebral ischemia looking ahead to potential treatments.

NEMO-binding domain peptides alleviate perihematomal inflammation injury after experimental intracerebral hemorrhage

Inflammation aggravates the lethal consequences of intracerebral hemorrhage. Recently, many studies have found that nuclear factor-κB (NF-κB) is a crucial transcription factor that initiates inflammation in the perihematomal region of ICH. NF-κB essential modulator (NEMO)-binding domain (NBD) peptide, a cell-permeable peptide spanning the NBD of IKKα or IKKβ, functions as a highly specific inhibitor of NF-κB. This peptide can negatively regulate the NF-κB pathway. The present study aimed to explore the effects and underlying pathomechanisms of NBD peptides after ICH. Striatum infusion of whole blood or saline was performed on C57BL/6 mice (n = 198). Experimental animals were administered NBD or control (mutated) peptides 2 h before or after ICH by intracerebroventricular injection (icv.). NBD peptides significantly inhibited edema formation, ameliorated the neurological deficits, markedly reduced IκBα and p65 phosphorylation, blocked nuclear translocation of p65, and upregulated IκBα expression by NF-κB after ICH induction. Using an in vitro hemin toxicity model, we investigated the effects of NBD peptides on microglial inflammation. We found that NBD peptides suppressed microglia inflammation and lowered the expression of TNF-α and IL-1β in both in vivo and in vitro experiments. Further experiments were performed in mice and cultured microglia, which treated with NBD peptides in the presence of p65 siRNA confirmed that the specificity of NBD peptides inhibit ICH-induced NF-κB activation. This study demonstrated that NBD peptides exert a neuroprotective role after ICH and might be a potential candidate for a novel therapeutic strategy for ICH.

Propagermanium, a CCR2 inhibitor, attenuates cerebral ischemia/reperfusion injury through inhibiting inflammatory response induced by microglia

CCR2 could recruit immune cells migrating into brain after ischemic stroke. It is unclear whether and why Propagermanium (PG, a CCR2 inhibitor) is able to protect against ischemic injury. Middle cerebral artery occlusion (MCAO) and reperfusion injury in C57BL/6 J male mice were performed in vivo to mimic ischemic stroke. Cultured BV2 microglia exposed to oxygen and glucose deprivation (OGD)/reoxygenation injury, LPS or IL-4 incubation were served in vitro. TTC staining, neurological score, brain water content, and MRI scan were performed to evaluate stroke outcome. Real time PCR, ELISA, and immunofluorescence were used to estimate inflammatory cytokines expression and releasing. Western blot was utilized to detect pSTAT1/STAT1 expression. Compared with MCAO mice, PG treatment significantly reduced infarction size and brain edema, improved neurological behavior at 72 h after MCAO. For inflammatory response, PG treatment inhibited inflammatory cytokines releasing, such as TNF-α, IFN-γ, IL-1β, IL-6, IL-12, IL-17, and IL-23. Further studies indicated that PG treatment downregulated mRNA expression of pro-inflammatory iNOS and CD86, and inhibited CD16 expressed in microglia. In vitro, PG incubation inhibited BV2 polarized to pro-inflammatory phenotype through STAT1 downregulation, while had no obvious effect on anti-inflammatory phenotype. Our observations suggest that CCR2 inhibitor PG downregulated pro-inflammatory microglia polarization for decreasing pro-inflammatory microglia phenotype marker, and thereafter inhibited inflammatory responses after MCAO in a STAT1-dependent manner.

Cerebroprotection by progesterone following ischemic stroke: Multiple effects and role of the neural progesterone receptors

Treatment with progesterone limits brain damage after stroke. However, the cellular bases of the cerebroprotective effects of progesterone are not well documented. The aims of this study were to determine neural cells and functions that are affected by progesterone treatment and the role of neural progesterone receptors (PR) after stroke. Adult male PR^NesCre mice, selectively lacking PR in the central nervous system, and their control PR^loxP/loxP littermates were subjected to transient ischemia by middle cerebral artery occlusion (MCAO) for 30 min. Mice received either progesterone (8 mg/kg) or vehicle at 1-, 6- and 24- hrs post-MCAO and outcomes were analyzed at 48 h post-MCAO. In PR^loxP/loxP mice, progesterone exerted multiple effects on different neural cell types, improved motor functional outcomes and reduced total infarct volumes. In the peri-infarct, progesterone increased the density of neurons (NeuN⁺ cells), of cells of the oligodendroglial lineage (Olig2⁺ cells) and of oligodendrocyte progenitors (OP, NG2⁺ cells). Progesterone decreased the density of activated astrocytes (GFAP⁺ cells) and reactive microglia (Iba1⁺ cells) coexpressing the mannose receptor type 1 CD206 marker. Progesterone also reduced the expression of aquaporin 4 (AQP4), the water channel involved in both edema formation and resorption. The beneficial effects of progesterone were not observed in PR^NesCre mice. Our findings show that progesterone treatment exerts beneficial effects on neurons, oligodendroglial cells and neuroinflammatory responses via PR. These findings demonstrate that progesterone is a pleiotropic cerebroprotective agent and that neural PR represent a therapeutic target for stroke cerebroprotection.

Glia-immune interactions post-ischemic stroke and potential therapies

IMPACT STATEMENT

This article reviews glial cell interactions with the immune system post-ischemic stroke. Research has shown that glial cells in the brain play a role in altering phenotypes of other glial cells and have downstream immune cell targets ultimately regulating a neuroinflammatory response. These interactions may play a deleterious as well as beneficial role in stroke recovery. Furthermore, they may provide a novel way to approach potential therapies, since current stroke drug therapy is limited to only one Food and Drug Administration-approved drug complicated by a narrow therapeutic window. Until this point, most research has emphasized neuroimmune interactions, but little focus has been on bidirectional communication of glial-immune interactions in the ischemic brain. By expanding our understanding of these interactions through a compilation of glial cell effects, we may be able to pinpoint major modulating factors in brain homeostasis to maintain or discover ways to suppress irreversible ischemic damage and improve brain repair.

Intravenous Transplantation of Mesenchymal Stem Cells Reduces the Number of Infiltrated Ly6C+ Cells but Enhances the Proportions Positive for BDNF, TNF-1α, and IL-1β in the Infarct Cortices of dMCAO Rats

The resident microglial and infiltrating cells from peripheral circulation are involved in the pathological processes of ischemia stroke and may be regulated by mesenchymal stem/stromal cell (MSC) transplantation. The present study is aimed at differentiating the neurotrophic and inflammatory roles played by microglial vs. infiltrating circulation-derived cells in the acute phase in rat ischemic brains and explore the influences of intravenously infused allogeneic MSCs. The ischemic brain injury was induced by distal middle cerebral artery occlusion (dMCAO) in SD rats, with or without MSC infusion in the same day following dMCAO. Circulation-derived infiltrating cells in the brain were identified by Ly6C, a majority of which were monocytes/macrophages. Without MSC transplantation, among the infiltrated Ly6C⁺ cells, some were positive for BDNF, IL-1β, or TNF-α. Following MSC infusion, the overall number of Ly6C⁺ infiltrated cells was reduced by 50%. In contrast, the proportions of infiltrated Ly6C⁺ cells coexpressing BDNF, IL-1β, or TNF-α were significantly enhanced. Interestingly, Ly6C⁺ cells in the infarct area could produce either neurotrophic factor BDNF or inflammatory cytokines (IL-1β or TNF-α), but not both. This suggests that the Ly6C⁺ cells may constitute heterogeneous populations which react differentially to the microenvironments in the infarct area. The changes in cellular composition in the infarct area may have contributed to the beneficial effect of MSC transplantation.

Docosanoids and elovanoids from omega-3 fatty acids are pro-homeostatic modulators of inflammatory responses, cell damage and neuroprotection

The functional significance of the selective enrichment of the omega-3 essential fatty acid docosahexaenoic acid (DHA; 22C and 6 double bonds) in cellular membrane phospholipids of the nervous system is being clarified by defining its specific roles on membrane protein function and by the uncovering of the bioactive mediators, docosanoids and elovanoids (ELVs). Here, we describe the preferential uptake and DHA metabolism in photoreceptors and brain as well as the significance of the Adiponectin receptor 1 in DHA retention and photoreceptor cell (PRC) survival. We now know that this integral membrane protein is engaged in DHA retention as a necessary event for the function of PRCs and retinal pigment epithelial (RPE) cells. We present an overview of how a) NPD1 selectively mediates preconditioning rescue of RPE and PR cells; b) NPD1 restores aberrant neuronal networks in experimental epileptogenesis; c) the decreased ability to biosynthesize NPD1 in memory hippocampal areas of early stages of Alzheimer's disease takes place; d) NPD1 protection of dopaminergic circuits in an in vitro model using neurotoxins; and e) bioactivity elicited by DHA and NPD1 activate a neuroprotective gene-expression program that includes the expression of Bcl-2 family members affected by Aβ42, DHA, or NPD1. In addition, we highlight ELOVL4 (ELOngation of Very Long chain fatty acids-4), specifically the neurological and ophthalmological consequences of its mutations, and their role in providing precursors for the biosynthesis of ELVs. Then we outline evidence of ELVs ability to protect RPE cells, which sustain PRC integrity. In the last section, we present a summary of the protective bioactivity of docosanoids and ELVs in experimental ischemic stroke. The identification of early mechanisms of neural cell survival mediated by DHA-synthesized ELVs and docosanoids contributes to the understanding of cell function, pro-homeostatic cellular modulation, inflammatory responses, and innate immunity, opening avenues for prevention and therapeutic applications in neurotrauma, stroke and neurodegenerative diseases.

Neuroprotective and therapeutic effect of Cordyceps militaris on ischemia-induced neuronal death and cognitive impairments

Cordyceps militaris is a type of fungus consumed by people all over the world and renowned for their nutritional benefits and herbal formulas to promote health and longevity. In the present study investigation was carried out to explore the therapeutic properties and neuroprotective effect of the C. militaris on ischemic brain neuronal injury, impairment of memory and learning in experimental rats induced by a global cerebral ischemia-reperfusion injury in WISTAR rats. Vascular Dementia with transient global brain injuries induced by a four-vessel occlusion (4-VO) in WISTAR rats. Further, donepezil (5 mg/kg) and C. militaris was (100 and 300 mg/kg, p.o.) were orally administered for 7 days in 4-VO WISTAR rats. C. militaris has the ability to improve memory impairments due to global cerebral ischemia and scopolamine-induced memory deterioration. Our present findings suggest that C. militaris may be a potential candidate for the neuroprotection of hippocampus and the recovery of various vascular dementia or neuroinflammatory disorders.

Neuronal loss and gliosis in the rat striatum subjected to 15 and 30 minutes of middle cerebral artery occlusion

Selective neuronal death or loss in certain brain regions has been well characterized in animal models of transient global cerebral ischemia. However, selective neuronal death in transient focal cerebral ischemia needs more investigation. Therefore, in this study, we studied selective neuronal death in the striatum (caudate putamen) of rats subjected to 15 or 30 min middle cerebral artery occlusion (MCAO). Neuronal death occurred in the dorsolateral field, not in the medial field in 30 min, not 15 min, MCAO-operated rats 5 days after MCAO using neuronal nuclear antigen immunohistochemistry and Fluoro-Jade B histofluorescence staining. In this group, immunoreactivity of glial fibrillary acidic protein in astrocytes was hardly shown in the dorsolateral field, although the immunoreactivity increased in the medial field. In addition, immunoreactivity of ionized calcium binding adapter molecule 1 in microglia was dramatically increased in the dorsolateral, not in the medial, field only in 30 min MCAO-operated rats. Briefly, these results show that at least 30 min of MCAO can evoke selective neuronal death, astrocytic dysfunction and microglial activation in the dorsolateral field of the rat striatum and suggest that a rat model of 30 min MCAO can be used to investigate mechanisms of neuronal death and gliosis following brief transient focal cerebral ischemic events for acute transient ischemic attack.

Atomoxetine, a selective norepinephrine reuptake inhibitor, improves short-term histological outcomes after hypoxic-ischemic brain injury in the neonatal male rat

BACKGROUND

Despite the recent progress of perinatal medicine, perinatal hypoxic-ischemic (HI) insult remains an important cause of brain injury in neonates, and is pathologically characterized by neuronal loss and the presence of microglia. Neurotransmitters, such as norepinephrine (NE) and glutamate, are involved in the pathogenesis of hypoxic-ischemic encephalopathy via the interaction between neurons and microglia. Although it is well known that the monoamine neurotransmitter NE acts as an anti-inflammatory agent in the brain under pathological conditions, its effects on perinatal HI insult remains elusive. Atomoxetine, a selective NE reuptake inhibitor, has been used clinically for the treatment of attention-deficit hyperactivity disorder in children. Here, we investigated whether the enhancement of endogenous NE by administration of atomoxetine could protect neonates against HI insult by using the neonatal male rat model. We also examined the involvement of microglia in this process.

METHODS

Unilateral HI brain injury was induced by the combination of left carotid artery dissection followed by ligation and hypoxia (8% O₂, 2 h) in postnatal day 7 (P7) male rat pups. The pups were randomized into three groups: the atomoxetine treatment immediately after HI insult, the atomoxetine treatment at 3 h after HI insult, or the vehicle treatment group. The pups were euthanized on P8 and P14, and the brain regions including the cortex, striatum, hippocampus, and thalamus were evaluated by immunohistochemistry.

RESULTS

HI insult resulted in severe brain damage in the ipsilateral hemisphere at P14. Atomoxetine treatment immediately after HI insult significantly increased NE levels in the ipsilateral hemisphere at 1 h after HI insult and reduced the neuronal damage via the increased phosphorylation of cAMP response element-binding protein (pCREB) in all brain regions examined. In addition, the number of microglia was maintained under atomoxetine treatment compared with that of the vehicle treatment group. To determine the involvement of microglia in the process of neuronal loss by HI insult, we further examined the influence of hypoxia on rat primary cultured microglia by the quantitative real-time polymerase chain reaction. Hypoxia did not cause the upregulation of interleukin-1beta (IL-1β) mRNA expression, but decreased the microglial intrinsic nitric oxide synthase (iNOS)/arginase1 mRNA expression ratio. NE treatment further decreased the microglial iNOS/arginase1 mRNA expression ratio. In contrast, no significant neuroprotective effect was observed at P14 when atomoxetine was administered at 3 h after HI insult.

CONCLUSIONS

These findings suggested that the enhancement of intrinsic neurotransmitter NE signaling by a selective NE reuptake inhibitor, atomoxetine, reduced the perinatal HI insult brain injury. In addition, atomoxetine treatment was associated with changes of TUNEL, pCREB, and BDNF expression levels, and microglial numbers, morphology, and responses.

Microglia and Monocytes/Macrophages Polarization Reveal Novel Therapeutic Mechanism against Stroke

Stroke is a leading cause of morbidity and mortality worldwide, and consists of two types, ischemic and hemorrhagic. Currently, there is no effective treatment to increase the survival rate or improve the quality of life after ischemic and hemorrhagic stroke in the subacute to chronic phases. Therefore, it is necessary to establish therapeutic strategies to facilitate functional recovery in patients with stroke during both phases. Cell-based therapies, using microglia and monocytes/macrophages preconditioned by optimal stimuli and/or any therapies targeting these cells, might be an ideal therapeutic strategy for managing stroke. Microglia and monocytes/macrophages polarize to the classic pro-inflammatory type (M1-like) or alternative protective type (M2-like) by optimal condition. Cell-based therapies using M2-like microglia and monocytes/macrophages might be protective therapeutic strategies against stroke for three reasons. First, M2-like microglia and monocytes/monocytes secrete protective remodeling factors, thus prompting neuronal network recovery via tissue (including neuronal) and vascular remodeling. Second, these cells could migrate to the injured hemisphere through the blood–brain barrier or choroid–plexus. Third, these cells could mitigate the extent of inflammation-induced injuries by suitable timing of therapeutic intervention. Although future translational studies are required, M2-like microglia and monocytes/macrophages therapies are attractive for managing stroke based on their protective functions.

Osteopontin Augments M2 Microglia Response and Separates M1- and M2-Polarized Microglial Activation in Permanent Focal Cerebral Ischemia

Background

Focal cerebral ischemia induces distinct neuroinflammatory processes. We recently reported the extracellular phosphor-glyco-protein osteopontin (OPN) to directly affect primary microglia in vitro, promoting survival while shifting their inflammatory profile towards a more neutral phenotype. We here assessed the effects of OPN on microglia after stroke in vivo, with focus on infarct demarcation.

Methods

Animals underwent focal photothrombotic stroke and were injected intracerebroventricularly with 500 μg OPN or vehicle. Immunohistochemistry assessed neuronal damage and infarct volume, neovascularisation, glial scar formation, microglial activation, and M1 and M2 polarisation.

Results

After photothrombotic stroke, areas covered by M1 and M2 microglia substantially overlapped. OPN treatment reduced that overlap, with microglia appearing more spread out and additionally covering the infarct core. OPN additionally modulated the quantity of microglia subpopulations, reducing iNOS+ M1 cells while increasing M2 microglia, shifting the M1/M2 balance towards an M2 phenotype. Moreover, OPN polarized astrocytes towards the infarct.

Conclusion

Microglial activation and M1 and M2 polarization have distinct but overlapping spatial patterns in permanent focal ischemia. Data suggest that OPN is involved in separating M1 and M2 subpopulations, as well as in shifting microglia polarization towards the M2 phenotype modulating beneficially inflammatory responses after focal infarction.

Timing of Cord Blood Treatment after Experimental Stroke Determines Therapeutic Efficacy

Embolic stroke is thought to cause irreparable damage in the brain immediately adjacent to the region of reduced blood perfusion. Therefore, much of the current research focuses on treatments such as anti-inflammatory, neuroprotective, and cell replacement strategies to minimize behavioral and physiological consequences. In the present study, intravenous delivery of human umbilical cord blood cells (HUCBC) 48 h after a middle cerebral artery occlusion (MCAo) in a rat resulted in both behavioral and physiological recovery. Nissl and TUNEL staining demonstrated that many of the neurons in the core were rescued, indicating that while both necrotic and apoptotic cell death occur in ischemia, it is clear that apoptosis plays a larger role than first anticipated. Further, immunohistochemical and histochemical analysis showed a diminished and/or lack of granulocyte and monocyte infiltration and astrocytic and microglial activation in the parenchyma in animals treated with HUCBC 48 h poststroke. Successful treatment at this time point should offer encouragement to clinicians that a therapy with a broader window of efficacy may soon be available to treat stroke.

Inflammatory Disequilibrium in Stroke

Over the past several decades, there have been substantial advances in our knowledge of the pathophysiology of stroke. Understanding the benefits of timely reperfusion has led to the development of thrombolytic therapy as the cornerstone of current management of ischemic stroke, but there remains much to be learned about mechanisms of neuronal ischemic and reperfusion injury and associated inflammation. For ischemic stroke, novel therapeutic targets have continued to remain elusive. When considering modern molecular biological techniques, advanced translational stroke models, and clinical studies, a consistent pattern emerges, implicating perturbation of the immune equilibrium by stroke in both central nervous system injury and repair responses. Stroke triggers activation of the neuroimmune axis, comprised of multiple cellular constituents of the immune system resident within the parenchyma of the brain, leptomeninges, and vascular beds, as well as through secretion of biological response modifiers and recruitment of immune effector cells. This neuroimmune activation can directly impact the initiation, propagation, and resolution phases of ischemic brain injury. To leverage a potential opportunity to modulate local and systemic immune responses to favorably affect the stroke disease curve, it is necessary to expand our mechanistic understanding of the neuroimmune axis in ischemic stroke. This review explores the frontiers of current knowledge of innate and adaptive immune responses in the brain and how these responses together shape the course of ischemic stroke.

Effect of PPAR-β/δ agonist GW0742 treatment in the acute phase response and blood-brain barrier permeability following brain injury

The systemic response to ischemic stroke is associated with the hepatic acute phase response (APR) that modulates leukocytes recruitment to the injured brain. The inappropriate recruitment of leukocytes to the brain parenchyma can result in blood-brain barrier (BBB) breakdown. Emerging data suggest that peroxisome proliferator-activated receptor beta/delta (PPAR-β/δ) activation has a potential neuroprotective role in ischemic stroke. However, mechanisms of PPAR-β/δ mediated protection in ischemic insults remain unclear. In the present study, we determined for the first time, the effects of GW0742, a PPAR-β/δ agonist on the APR following brain injury and assessed the effects on BBB permeability and tight junction integrity via claudin-5, occludin, and zona occludens-1 expression. C57/BL6 mice were exposed to 1 hour of ischemia and received 10 minutes before reperfusion either a vehicle solution or GW0742. Hepatic expression of chemokines (C-X-C motif ligand: CXCL1, CXCL2, and CXCL10), serum amyloid A-1, tumor necrosis factor alpha, interleukin-1β, and interleukin-6 was measured, and the extent of brain and hepatic neutrophil infiltration was determined. The results showed that GW0742 treatment decreased infarct volume and edema, reactant production and neutrophil recruitment to the brain and liver, which is a hallmark of the APR. GW0742 significantly reduced BBB leakage and metalloproteinase 9 expression and upregulated the expression of tight junction proteins. These findings may help to guide the experimental and clinical therapeutic use of PPAR-β/δ agonists against brain injury.

Regulation of microglial activation in stroke

When ischemic stroke occurs, oxygen and energy depletion triggers a cascade of events, including inflammatory responses, glutamate excitotoxicity, oxidative stress, and apoptosis that result in a profound brain injury. The inflammatory response contributes to secondary neuronal damage, which exerts a substantial impact on both acute ischemic injury and the chronic recovery of the brain function. Microglia are the resident immune cells in the brain that constantly monitor brain microenvironment under normal conditions. Once ischemia occurs, microglia are activated to produce both detrimental and neuroprotective mediators, and the balance of the two counteracting mediators determines the fate of injured neurons. The activation of microglia is defined as either classic (M1) or alternative (M2): M1 microglia secrete pro-inflammatory cytokines (TNFα, IL-23, IL-1β, IL-12, etc) and exacerbate neuronal injury, whereas the M2 phenotype promotes anti-inflammatory responses that are reparative. It has important translational value to regulate M1/M2 microglial activation to minimize the detrimental effects and/or maximize the protective role. Here, we discuss various regulators of microglia/macrophage activation and the interaction between microglia and neurons in the context of ischemic stroke.

Therapeutic Strategies to Attenuate Hemorrhagic Transformation After Tissue Plasminogen Activator Treatment for Acute Ischemic Stroke

This review focuses on the mechanisms and emerging concepts of stroke and therapeutic strategies for attenuating hemorrhagic transformation (HT) after tissue plasminogen activator (tPA) treatment for acute ischemic stroke (AIS). The therapeutic time window for tPA treatment has been extended. However, the patients who are eligible for tPA treatment are still ＜5% of all patients with AIS. The risk of serious or fatal symptomatic hemorrhage increases with delayed initiation of treatment. HT is thought to be caused by 1) ischemia/reperfusion injury; 2) the toxicity of tPA itself; 3) inflammation; and/or 4) remodeling factor-mediated effects. Modulation of these pathophysiologies is the basis of direct therapeutic strategies to attenuate HT after tPA treatment. Several studies have revealed that matrix metalloproteinases and free radicals are potential therapeutic targets. In addition, we have demonstrated that the inhibition of the vascular endothelial growth factor-signaling pathway and supplemental treatment with a recombinant angiopoietin-1 protein might be a promising therapeutic strategy for attenuating HT after tPA treatment through vascular protection. Moreover, single-target therapies could be insufficient for attenuating HT after tPA treatment and improving the therapeutic outcome of patients with AIS. We recently identified progranulin, which is a growth factor and a novel target molecule with multiple therapeutic effects. Progranulin might be a therapeutic target that protects the brain through suppression of vascular remodeling (vascular protection), neuroinflammation, and/or neuronal death (neuroprotection). Clinical trials which evaluate the effects of anti-VEGF drugs or PGRN-based treatment with tPA will be might worthwhile.

New insights into coupling and uncoupling of cerebral blood flow and metabolism in the brain

The brain has high metabolic and energy needs and requires continuous cerebral blood flow (CBF), which is facilitated by a tight coupling between neuronal activity, CBF, and metabolism. Upon neuronal activation, there is an increase in energy demand, which is then met by a hemodynamic response that increases CBF. Such regional CBF increase in response to neuronal activation is observed using neuroimaging techniques such as functional magnetic resonance imaging and positron emission tomography. The mechanisms and mediators (eg, nitric oxide, astrocytes, and ion channels) that regulate CBF-metabolism coupling have been extensively studied. The neurovascular unit is a conceptual model encompassing the anatomical and metabolic interactions between the neurons, vascular components, and glial cells in the brain. It is compromised under disease states such as stroke, diabetes, hypertension, dementias, and with aging, all of which trigger a cascade of inflammatory responses that exacerbate brain damage. Hence, tight regulation and maintenance of neurovascular coupling is central for brain homeostasis. This review article also discusses the waste clearance pathways in the brain such as the glymphatic system. The glymphatic system is a functional waste clearance pathway that removes metabolic wastes and neurotoxins from the brain along paravascular channels. Disruption of the glymphatic system burdens the brain with accumulating waste and has been reported in aging as well as several neurological diseases.

Microglia preconditioned by oxygen-glucose deprivation promote functional recovery in ischemic rats

Cell-therapies that invoke pleiotropic mechanisms may facilitate functional recovery in stroke patients. We hypothesized that a cell therapy using microglia preconditioned by optimal oxygen-glucose deprivation (OGD) is a therapeutic strategy for ischemic stroke because optimal ischemia induces anti-inflammatory M2 microglia. We first delineated changes in angiogenesis and axonal outgrowth in the ischemic cortex using rats. We found that slight angiogenesis without axonal outgrowth were activated at the border area within the ischemic core from 7 to 14 days after ischemia. Next, we demonstrated that administration of primary microglia preconditioned by 18 hours of OGD at 7 days prompted functional recovery at 28 days after focal cerebral ischemia compared to control therapies by marked secretion of remodelling factors such as vascular endothelial growth factor, matrix metalloproteinase-9, and transforming growth factor-β polarized to M2 microglia in vitro/vivo. In conclusion, intravascular administration of M2 microglia preconditioned by optimal OGD may be a novel therapeutic strategy against ischemic stroke.