Mechanisms contributing to cerebral infarct size after stroke: gender, reperfusion, T lymphocytes, and Nox2-derived superoxide

Microglial heterogeneity in the ischemic stroke mouse brain of both sexes

BACKGROUND

Ischemic stroke elicits a complex and sustained immune response in the brain. Immunomodulatory treatments have long held promise for improving stroke outcomes, yet none have succeeded in the clinical setting. This lack of success is largely due to our incomplete understanding of how immune cells respond to stroke. The objective of the current study was to dissect the effect of permanent stroke on microglia, the resident immune cells within the brain parenchyma.

METHODS

A permanent middle cerebral artery occlusion (pMCAO) model was used to induce ischemic stroke in young male and female mice. Microglia were sorted from fluorescence reporter mice after pMCAO or sham surgery and then subjected to single-cell RNA sequencing analysis. Various methods, including flow cytometry, RNA in situ hybridization, immunohistochemistry, whole-brain imaging, and bone marrow transplantation, were also employed to dissect the microglial response to stroke. Stroke outcomes were evaluated by infarct size and behavioral tests.

RESULTS

First, we showed the morphologic and spatial changes in microglia after stroke. We then performed single-cell RNA sequencing analysis on microglia isolated from sham and stroke mice of both sexes. The data indicate no major sexual dimorphism in the microglial response to permanent stroke. Notably, we identified seven potential stroke-associated microglial clusters, including four major clusters characterized by a disease-associated microglia-like signature, a highly proliferative state, a macrophage-like profile, and an interferon (IFN) response signature, respectively. Importantly, we provided evidence that the macrophage-like cluster may represent the long-sought stroke-induced microglia subpopulation with increased CD45 expression. Lastly, given that the IFN-responsive subset constitutes the most prominent microglial population in the stroke brain, we used fludarabine to pharmacologically target STAT1 signaling and found that fludarabine treatment improved long-term stroke outcome.

CONCLUSIONS

Our findings shed new light on microglia heterogeneity in stroke pathology and underscore the potential of targeting specific microglial populations for effective stroke therapies.

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

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

Sex differences in the inflammatory response to stroke

Ischemic stroke is a leading cause of morbidity and mortality and disproportionally affects women, in part due to their higher longevity. Older women have poorer outcomes after stroke with high rates of cognitive deficits, depression, and reduced quality of life. Post-stroke inflammatory responses are also sexually dimorphic and drive differences in infarct size and recovery. Factors that influence sex-specific immune responses can be both intrinsic and extrinsic. Differences in gonadal hormone exposure, sex chromosome compliment, and environmental/social factors can drive changes in transcriptional and metabolic profiles. In addition, how these variables interact, changes across the lifespan. After the onset of ischemic injury, necrosis and apoptosis occur, which activate microglia and other glial cells within the central nervous system, promoting the release of cytokines and chemokines and neuroinflammation. Cells involved in innate and adaptive immune responses also have dual functions after stroke as they can enhance inflammation acutely, but also contribute to suppression of the inflammatory cascade and later repair. In this review, we provide an overview of the current literature on sex-specific inflammatory responses to ischemic stroke. Understanding these differences is critical to identifying therapeutic options for both men and women.

The critical role of KLF4 in regulating the activation of A1/A2 reactive astrocytes following ischemic stroke

BACKGROUND

We have previously demonstrated that the expression of kruppel-like transcription factor-4 (KLF-4) is upregulated in astrocytes following acute ischemic stroke (AIS) and found that KLF4 confers vascular protection against cerebral ischemic injury. However, the functional role of KLF4 in astrocyte after AIS is far from clear.

METHODS

The intrinsic relationship between KLF4 and A1/A2 reactive astrocytes and the impact of astrocytic KLF4 on the activation of A1/A2 subtype astrocytes were evaluated in middle cerebral artery occlusion (MCAO) mice and oxygen-glucose deprivation and restoration (OGD/R) astrocytes.

RESULTS

Our results demonstrated that astrocytic KLF4 expression and complement C3-positive A1 and S100 calcium binding protein A10 (S100A10)-positive A2 astrocytes were induced in the ischemic penumbra following focal cerebral ischemia, and the time course of upregulation of astrocytic KLF4 correlated closely with the activation of A2 astrocytes. The dual immunofluorescent studies displayed that in the ischemic hemisphere, where the high levels of KLF4 were expressed, there were relatively low levels of C3 expressed in the reactive astrocytes and vice versa, but KLF4 was always co-stained well with S100A10. Mechanistic analyses revealed that astrocytic KLF4 inhibited the activation of A1 astrocyte but promoted A2 astrocyte polarization after OGD/R by modulating expressions of nuclear factor-kB.

CONCLUSIONS

Astrocyte-derived KLF4 has a critical role in regulating the activation of A1/A2 reactive astrocytes following AIS.

Neuroprotective Effect of Angiopoietin2 Is Associated with Angiogenesis in Mouse Brain Following Ischemic Stroke

Angiogenic factors play an important role in protecting, repairing, and reconstructing vessels after ischemic stroke. In the brains of transient focal cerebral ischemic mice, we observed a reduction in infarct volume after the administration of Angiopoietin 2 (Angpt2), but whether this process is promoted by Angpt2-induced angiogenesis has not been fully elaborated. Therefore, this study explored the angiogenic activities, in reference to CD34 which is a marker of activated ECs and blood vessels, of cultured ECs in vitro and in ischemic damaged cerebral area in mice following Angpt2 administration. Our results demonstrate that Angpt2 administration (100 ng/mL) is neuroprotective by significantly increasing the CD34 expression in in vitro-cultured ECs, reducing the infarct volume and mitigating neuronal loss, as well as enhancing CD34⁺ vascular length and area. In conclusion, these results indicate that Angpt2 promotes repair and attenuates ischemic injury, and that the mechanism of this is closely associated with angiogenesis in the brain after stroke.

Sexual dimorphism in immune cell responses following stroke

Recent bodies of work in regard to stroke have revealed significant sex differences in terms of risk and outcome. While differences in sex hormones have been the focus of earlier research, the reasons for these differences are much more complex and require further identification. This review covers differences in sex related immune responses with a focus on differences in immune cell composition and function. While females are more susceptible to immune related diseases, they seem to have better outcomes from stroke at the experimental level with reduced pro-inflammatory responses. However, at the clinical level, the picture is much more complex with worse neurological outcomes from stroke. While the use of exogenous sex steroids can replicate some of these findings, it is apparent that many other factors are involved in the modulation of immune responses. As a result, more research is needed to better understand these differences and identify appropriate interventions and risk modification.

Inhibition of Γδ T Cells Alleviates Brain Ischemic Injury in Cardiopulmonary-Cerebral Resuscitation Mice

BACKGROUND

A half-million people in the United States suffer from cardiac arrest (CA) requiring cardiopulmonary resuscitation (CPR). An inflammatory mechanism is associated with neuronal injury in the presence of cerebral ischemia. T lymphocytes are identified as crucial regulators of inflammation. Therefore, we investigated the relationship between CA/CPR-induced ischemia injury and T lymphocytes.

METHODS

C57BL/6 mice were subjected to CA through injection of KCl (30 μL of 0.5 mol/L) and cessation of mechanical ventilation followed by CPR. The survival rate and neurologic deficit scores were assessed. Terminal deoxynucleotidyl transferase dUTP nick end labeling staining was carried out to detect neuronal death. Histologic changes were observed by hematoxylin-eosin staining. The levels of Trgv4, Trgv5 and Trgv7 were quantified by RT-qPCR. Inflammatory responses were identified by measurement of IL-1β, IL-6 and IL-17.

RESULTS

Downregulated γδ T cells improved survival and neurologic outcomes and inhibits neuronal apoptosis. γδ T inhibition protected brains from CA/CPR-mediated tissue damage. UC7-13D5 treatment inhibited the levels of γδ T markers. Knockdown of γδ T cells ameliorated neuroinflammation.

CONCLUSIONS

Inhibition of γδ T cells ameliorates ischemic injury in mice with CA/CPR by attenuating inflammation and neuronal apoptosis.

Inflammatory Responses After Ischemic Stroke

Ischemic stroke generates an immune response that contributes to neuronal loss as well as tissue repair. This is a complex process involving a range of cell types and effector molecules and impacts tissues outside of the CNS. Recent reviews address specific aspects of this response, but several years have passed and important advances have been made since a high-level review has summarized the overall state of the field. The present review examines the initiation of the inflammatory response after ischemic stroke, the complex impacts of leukocytes on patient outcome, and the potential of basic science discoveries to impact the development of therapeutics. The information summarized here is derived from broad PubMed searches and aims to reflect recent research advances in an unbiased manner. We highlight valuable recent discoveries and identify gaps in knowledge that have the potential to advance our understanding of this disease and therapies to improve patient outcomes.

Sex-Associated Differences in Neurovascular Dysfunction During Ischemic Stroke

Neurovascular units (NVUs) are basic functional units in the central nervous system and include neurons, astrocytes and vascular compartments. Ischemic stroke triggers not only neuronal damage, but also dissonance of intercellular crosstalk within the NVU. Stroke is sexually dimorphic, but the sex-associated differences involved in stroke-induced neurovascular dysfunction are studied in a limited extend. Preclinical studies have found that in rodent models of stroke, females have less neuronal loss, stronger repairing potential of astrocytes and more stable vascular conjunction; these properties are highly related to the cerebroprotective effects of female hormones. However, in humans, these research findings may be applicable only to premenopausal stroke patients. Women who have had a stroke usually have poorer outcomes compared to men, and because stoke is age-related, hormone replacement therapy for postmenopausal women may exacerbate stroke symptoms, which contradicts the findings of most preclinical studies. This stark contrast between clinical and laboratory findings suggests that understanding of neurovascular differences between the sexes is limited. Actually, apart from gonadal hormones, differences in neuroinflammation as well as genetics and epigenetics promote the sexual dimorphism of NVU functions. In this review, we summarize the confirmed sex-associated differences in NVUs during ischemic stroke and the possible contributing mechanisms. We also describe the gap between clinical and preclinical studies in terms of sexual dimorphism.

Bim Deletion Reduces Functional Deficits Following Ischemic Stroke in Association with Modulation of Apoptosis and Inflammation

Cellular apoptosis is a key pathological mechanism contributing to neuronal death following ischemic stroke. The pro-apoptotic Bcl-2 family protein, Bim, is an important regulator of apoptosis. In this study we investigated the effect of Bim expression on post-stroke functional outcomes, brain injury and inflammatory mechanisms. Wild type (WT) and Bim-deficient mice underwent 1-h middle cerebral artery occlusion (MCAO) followed by 23 h of reperfusion. At 24-h post-stroke, we assessed functional deficit, infarct volume, immune cell death, as well as the number of infiltrating immune cells in the brain and circulating immune cells. Bim deficiency did not affect infarct volume (P > 0.05), but resulted in less motor impairment (~ threefold greater latency to fall in hanging grip strength test, P < 0.05) and a lower median clinical score than WT mice (P < 0.05). Additionally following MCAO, Bim-deficient mice exhibited fewer myeloid cells (particularly neutrophils) in the ischemic brain hemisphere and less apoptosis of CD3⁺ T cells in the spleen and thymus compared with WT (all P < 0.05). After MCAO, Bim-deficient mice also tended to have more M2-polarised macrophages in the brain than WT mice. In sham-operated mice, we found that Bim deficiency resulted in greater numbers of circulating total CD45⁺ leukocytes, Ly6C^lo+ monocytes and CD3⁺ T cells, although MCAO did not affect the number of circulating cells at 24 h in either genotype. Our findings suggest that Bim deficiency modulates post-stroke outcomes, including reductions in motor impairment, brain inflammation and systemic post-stroke leukocyte apoptosis. Bim could therefore serve as a potential therapeutic target for stroke.

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

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

Genetic Modulators of Traumatic Brain Injury in Animal Models and the Impact of Sex-Dependent Effects

Traumatic brain injury (TBI) is a major health problem causing disability and death worldwide. There is no effective treatment, due in part to the complexity of the injury pathology and factors affecting its outcome. The extent of brain injury depends on the type of insult, age, sex, lifestyle, genetic risk factors, socioeconomic status, other co-injuries, and underlying health problems. This review discusses the genes that have been directly tested in TBI models, and whether their effects are known to be sex-dependent. Sex differences can affect the incidence, symptom onset, pathology, and clinical outcomes following injury. Adult males are more susceptible at the acute phase and females show greater injury in the chronic phase. TBI is not restricted to a single sex; despite variations in the degree of symptom onset and severity, it is important to consider both female and male animals in TBI pre-clinical research studies.

Neuroprotective action of Cortexin, Cerebrolysin and Actovegin in acute or chronic brain ischemia in rats

This study was the first to compare the neuroprotective activity of Cerebrolysin®, Actovegin® and Cortexin® in rodent models of acute and chronic brain ischemia. The neuroprotective action was evaluated in animals with acute (middle cerebral artery occlusion) or chronic (common carotid artery stenosis) brain ischemia models in male rats. Cortexin® (1 or 3 mg/kg/day), Cerebrolysin® (538 or 1614 mg/kg/day) and Actovegin® (200 mg/kg/day) were administered for 10 days. To assess the neurological and motor impairments, open field test, adhesive removal test, rotarod performance test and Morris water maze test were performed. Brain damage was assessed macro- and microscopically, and antioxidant system activity was measured in brain homogenates. In separate experiments in vitro binding of Cortexin® to a wide panel of receptors was assessed, and blood-brain barrier permeability of Cortexin® was assessed in mice in vivo. Cortexin® or Cerebrolysin® and, to a lesser extent, Actovegin® improved the recovery of neurological functions, reduced the severity of sensorimotor and cognitive impairments in rats. Cortexin® reduced the size of necrosis of brain tissue in acute ischemia, improved functioning of the antioxidant system and prevented the development of severe neurodegenerative changes in chronic ischemia model. Radioactively labeled Cortexin® crossed the blood-brain barrier in mice in vivo with concentrations equal to 6-8% of concentrations found in whole blood. During in vitro binding assay Cortexin® (10 μg/ml) demonstrated high or moderate binding to AMPA-receptors (80.1%), kainate receptors (73.5%), mGluR1 (49.0%), GABAA1 (44.0%) and mGluR5 (39.7%), which means that effects observed in vivo could be related on the glutamatergic and GABAergic actions of Cortexin®. Thus, Cortexin, 1 or 3 mg/kg, or Cerebrolysin®, 538 or 1614 mg/kg, were effective in models acute and chronic brain ischemia in rats. Cortexin® contains compounds acting on AMPA, kainate, mGluR1, GABAA1 and mGluR5 receptors in vitro, and readily crosses the blood-brain barrier in mice.

Longitudinal hippocampal volumetric changes in mice following brain infarction

Hippocampal atrophy is increasingly described in many neurodegenerative syndromes in humans, including stroke and vascular cognitive impairment. However, the progression of brain volume changes after stroke in rodent models is poorly characterized. We aimed to monitor hippocampal atrophy occurring in mice up to 48-weeks post-stroke. Male C57BL/6J mice were subjected to an intraluminal filament-induced middle cerebral artery occlusion (MCAO). At baseline, 3-days, and 1-, 4-, 12-, 24-, 36- and 48-weeks post-surgery, we measured sensorimotor behavior and hippocampal volumes from T₂-weighted MRI scans. Hippocampal volume-both ipsilateral and contralateral-increased over the life-span of sham-operated mice. In MCAO-subjected mice, different trajectories of ipsilateral hippocampal volume change were observed dependent on whether the hippocampus contained direct infarction, with a decrease in directly infarcted tissue and an increase in non-infarcted tissue. To further investigate these volume changes, neuronal and glial cell densities were assessed in histological brain sections from the subset of MCAO mice lacking hippocampal infarction. Our findings demonstrate previously uncharacterized changes in hippocampal volume and potentially brain parenchymal cell density up to 48-weeks in both sham- and MCAO-operated mice.

[The role of the inflammatory process in the development of post-stroke cognitive impairment]

Post-stroke cognitive impairment (PCI) is a common complication of stroke. PCI in most cases is associated with an increased risk of progression to dementia, with a progression rate of 8-15% per year. When post-stroke cognitive impairment reaches dementia, patients lose independence, professional and social maladjustment occurs, which, in turn, significantly worsen the quality of life and reduce the rehabilitation potential. According to many experimental and clinical studies, the inflammatory process has an important role in the development of PCI. Several previous studies have looked at the association between inflammatory markers and PCI, with some results conflicting with specific biomarkers. Based on the results of studies, inflammatory markers such as IL-8, IL-12 and ESR were closely associated with PCI, high ESR values are associated with worse cognitive impairment, especially memory. The relationship was not confirmed between the markers IFN-gamma, TNF-α and PCI. With regard to IL-1β, IL-6, IL-10, CRP, the results obtained are not unambiguous. Thus, the inflammatory process in the development of PCI has an important role, including a series of complex reactions, the combined effect of which induces neuronal damage and loss of synapses that ultimately leads to cognitive impairment.

Pathophysiology and Therapeutic Potential of NADPH Oxidases in Ischemic Stroke-Induced Oxidative Stress

Stroke is a leading cause of death and disability in humans. The excessive production of reactive oxygen species (ROS) is an important contributor to oxidative stress and secondary brain damage after stroke. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, an enzyme complex consisting of membrane subunits and cytoplasmic subunits, regulates neuronal maturation and cerebrovascular homeostasis. However, NADPH oxidase overproduction contributes to neurotoxicity and cerebrovascular disease. NADPH oxidase has been implicated as the principal source of ROS in the brain, and numerous studies have shown that the knockout of NADPH exerts a protective effect in the model of ischemic stroke. In this review, we summarize the mechanism of activation of the NADPH oxidase family members, the pathophysiological effects of NADPH oxidase isoforms in ischemic stroke, and the studies of NADPH oxidase inhibitors to explore potential clinical applications.

The immune response of T cells and therapeutic targets related to regulating the levels of T helper cells after ischaemic stroke

Through considerable effort in research and clinical studies, the immune system has been identified as a participant in the onset and progression of brain injury after ischaemic stroke. Due to the involvement of all types of immune cells, the roles of the immune system in stroke pathology and associated effects are complicated. Past research concentrated on the functions of monocytes and neutrophils in the pathogenesis of ischaemic stroke and tried to demonstrate the mechanisms of tissue injury and protection involving these immune cells. Within the past several years, an increasing number of studies have elucidated the vital functions of T cells in the innate and adaptive immune responses in both the acute and chronic phases of ischaemic stroke. Recently, the phenotypes of T cells with proinflammatory or anti-inflammatory function have been demonstrated in detail. T cells with distinctive phenotypes can also influence cerebral inflammation through various pathways, such as regulating the immune response, interacting with brain-resident immune cells and modulating neurogenesis and angiogenesis during different phases following stroke. In view of the limited treatment options available following stroke other than tissue plasminogen activator therapy, understanding the function of immune responses, especially T cell responses, in the post-stroke recovery period can provide a new therapeutic direction. Here, we discuss the different functions and temporal evolution of T cells with different phenotypes during the acute and chronic phases of ischaemic stroke. We suggest that modulating the balance between the proinflammatory and anti-inflammatory functions of T cells with distinct phenotypes may become a potential therapeutic approach that reduces the mortality and improves the functional outcomes and prognosis of patients suffering from ischaemic stroke.

Neutrophil to Lymphocyte Ratio Predicts Outcome of Stroke by Cervicocranial Arterial Dissection

Background and Purpose: Neutrophil to lymphocyte ratio (NLR) is positively associated with poor prognosis in patients with cerebral infarction. The goal of this prospective study is to explore the predictive value of NLR in patients with acute ischemic stroke (AIS) caused by cervicocranial arterial dissection (CCAD).

Methods: Ninety-nine patients with AIS caused by CCAD met criteria for inclusion and exclusion were selected for this study. We collected baseline data on the admission including NLR. The primary poor outcome was major disability (modified Rankin Scale score ≥ 3) or death at 3 months after AIS.

Results: A total of 20 (20.2%) patients had a poor outcome at 3 months after AIS. According to the 3-month outcome, the patients were divided into two groups and univariate and multivariable analyses were conducted. Among the risk factors, elevated NLR levels were independently associated with 3-month poor outcomes. Further, we made the ROC curve to evaluate the predictive value of NLR level on prognosis. The area under the curve was 0.79 and a cut-off value of NLR was 2.97 for differentiating the poor outcome. We divided patients into groups according to the cut-off value. Patients with high NLR have a higher risk of poor outcome than those with low NLR (P < 0.05).

Conclusion: As an inflammatory marker, elevated NLR levels were associated with 3-month poor outcome in AIS caused by CCAD.

Deletion of NoxO1 limits atherosclerosis development in female mice

OBJECTIVE

Oxidative stress is a risk factor for atherosclerosis. NADPH oxidases of the Nox family produce ROS but their contribution to atherosclerosis development is less clear. Nox2 promotes and Nox4 rather limits atherosclerosis. Although Nox1 with its cytosolic co-factors are largely expressed in epithelial cells, a role for Nox1 for atherosclerosis development was suggested. To further define the role of this homologue, the role of its essential cytosolic cofactor, NoxO1, was determined for atherosclerosis development with the aid of knockout mice.

METHODS AND RESULTS

Wildtype (WT) and NoxO1 knockout mice were treated with high fat diet and adeno-associated virus (AAV) overexpressing pro-protein convertase subtilisin/kexin type 9 (PCSK9) to induce hepatic low-density lipoprotein (LDL) receptor loss. As a result, massive hypercholesterolemia was induced and spontaneous atherosclerosis developed within three month. Deletion of NoxO1 reduced atherosclerosis formation in brachiocephalic artery and aortic arch in female but not male NoxO1-/- mice as compared to WT littermates. This was associated with a reduced pro-inflammatory cytokine signature in the plasma of female but not male NoxO1-/- mice. MACE-RNAseq of the vessel did not reveal this signature and the expression of the Nox1/NoxO1 system was low to not detectable.

CONCLUSIONS

The scaffolding protein NoxO1 plays some role in atherosclerosis development in female mice probably by attenuating the global inflammatory burden.

Gonadal hormones and stroke risk: PCOS as a case study

It is well known that stroke incidence and outcome is sex-dependent and influenced by age and gonadal hormones. In post-menopausal and/or aged females, declining estrogen levels increases stroke risk. However, women who experience early menopause also have an increase in stroke risk. This suggests that, regardless of age, gonadal hormones regulate stroke risk and severity. This review discusses prolonged gonadal hormone dysfunction in a common female endocrine disorder known as polycystic ovarian syndrome, PCOS, and the associated increased risk of stroke due to resulting hyperandrogenism and metabolic comorbidities.

Anti-Pituitary and Anti-Hypothalamus Autoantibody Associations with Inflammation and Persistent Hypogonadotropic Hypogonadism in Men with Traumatic Brain Injury

Traumatic brain injury (TBI) and can lead to persistent hypogonadotropic hypogonadism (PHH) and poor outcomes. We hypothesized that autoimmune and inflammatory mechanisms contribute to PHH pathogenesis. Men with moderate-to-severe TBI (n = 143) were compared with healthy men (n = 39). The TBI group provided blood samples 1-12 months post-injury (n = 1225). TBI and healthy control (n = 39) samples were assayed for testosterone (T) and luteinizing hormone (LH) to adjudicate PHH status. TBI samples 1-6 months post-injury and control samples were assayed for immunoglobulin M (IgM)/immunoglobulin G (IgG) anti-pituitary autoantibodies (APA) and anti-hypothalamus autoantibodies (AHA). Tissue antigen specificity for APA and AHA was confirmed via immunohistochemistry (IHC). IgM and IgG autoantibodies for glial fibrillary acid protein (GFAP) (AGA) were evaluated to gauge APA and AHA production as a generalized autoimmune response to TBI and to evaluate the specificity of APA and AHA to PHH status. An inflammatory marker panel was used to assess relationships to autoantibody profiles and PHH status. Fifty-one men with TBI (36%) had PHH. An age-related decline in T levels by both TBI and PHH status were observed. Injured men had higher APA IgM, APA IgG, AHA IgM, AHA IgG, AGA IgM, and AGA IgG than controls (p < 0.0001 all comparisons). However, only APA IgM (p = 0.03) and AHA IgM (p = 0.03) levels were lower in the PHH than in the non-PHH group in multivariate analysis. There were no differences in IgG levels by PHH status. Multiple inflammatory markers were positively correlated with IgM autoantibody production. PHH was associated with higher soluble tumor-necrosis-factor receptors I/II, (sTNFRI, sTNFRII), regulated on activation, normal T-cell expressed and secreted (RANTES) and soluble interleukin-2-receptor-alpha (sIL-2Rα) levels. Higher IgM APA, and AHA, but not AGA, in the absence of PHH may suggest a beneficial or reparative role for neuroendocrine tissue-specific IgM autoantibody production against PHH development post-TBI.

Radiotherapy, Lymphopenia, and Host Immune Capacity in Glioblastoma: A Potentially Actionable Toxicity Associated With Reduced Efficacy of Radiotherapy

Radiotherapy is cytotoxic to tumor cells and is therefore a critical component of therapy for many malignancies, including glioblastoma (GBM). We now appreciate the value of the immunomodulatory effects of radiation that may be important to overall therapeutic success in some patients with this primary brain tumor. Although potentially beneficial immune-stimulating properties of radiotherapy treatment have been the focus of recent study, this modality is actually at the same time associated with the depletion of lymphocytes, which are crucial to the defense against neoplastic development and progression. In this review, we describe the association of systemic lymphopenia with poor tumor outcome, present evidence that radiotherapy is an important contributing cause of lymphodepletion, describe the systemic immune context of tumor and brain injury that contributes to immunosuppression, describe other contributing factors to lymphopenia including concomitant medications and treatments, and speculate about the role of the normal physiologic response to brain injury in the immunosuppressive dynamics of GBM. Radiotherapy is one significant and potentially actionable iatrogenic suppressor of immune response that may be limiting the success of therapy in GBM and other tumor types. Altered strategies for radiotherapy more permissive of a vigorous antineoplastic immune response may improve outcome for malignancy.

MicroRNA-193b-3p alleviates focal cerebral ischemia and reperfusion-induced injury in rats by inhibiting 5-lipoxygenase expression

AIMS

Ischemic stroke has become one of the main causes of death worldwide. MicroRNAs (miRNAs) have been implicated in cerebral ischemia-reperfusion (I/R) injury and could serve as therapeutic targets. 5-Lipoxygenase (5-LOX) is a key enzyme in the biosynthesis of leukotrienes and has been implicated in inflammatory central nerve system disorders. The objective of this study was to explore the neuroprotective effects of miR-193b-3p against focal cerebral I/R injury in rats by regulating 5-LOX expression.

METHODS AND MATERIALS

Adult male Sprague-Dawley rats were subjected to transient middle cerebral artery occlusion and reperfusion injury. The level of miR-193b-3p expression was observed in the rat cortical peri-infarct region after focal cerebral I/R injury. Bioinformatics analysis was used to predict the binding sites of miR-193b-3p, and a dual-luciferase reporter gene assay was applied to verify the potential interaction between 5-LOX mRNA and miR-193b-3p. Then, rats were injected with a miR-193b-3p agomir (modified and enhanced mimic) or antagomir (modified and enhanced inhibitor) in the right lateral ventricle of the brain. Neurological deficit scores, infarct volumes, neuron damage and 5-LOX enzymatic activity and expression were measured. In an in vitro experiment, cultured PC12 cells were exposed to oxygen-glucose deprivation and reperfusion (OGD/R). OGD/R-induced cells were treated with a miR-193b-3p mimic or inhibitor and 5-LOX siRNA. Cell viability, lactate dehydrogenase release, apoptosis rate and 5-LOX expression were evaluated.

RESULTS

The level of miR-193b-3p expression was increased in the cortical peri-infarct region of rats with cerebral focal I/R injury. The results of the dual-luciferase reporter gene assay showed that a miR-193b-3p binding site was located in the 3' untranslated region (3'UTR) of 5-LOX mRNA. Neurological deficit scores, infarct volumes and neuronal injury were alleviated by miR-193b-3p agomir treatment but aggravated by miR-193b-3p antagomir. Furthermore, leukotriene B4, cysteinyl-leukotrienes and 5-LOX expression in the cortical peri-infarct region of rats with focal cerebral I/R injury were also downregulated by miR-193b-3p agomir treatment but upregulated by miR-193b-3p antagomir. In PC12 cells, miR-193b-3p mimic significantly decreased OGD/R-induced cell death and reduced lactate dehydrogenase release and 5-LOX expression. In contrast, miR-193b-3p inhibitor exacerbated OGD/R-induced injury in PC12 cells. Additionally, the in vitro effects of miR-193b-3p inhibitor on OGD/R-induced cell injury were partially reversed by 5-LOX siRNA treatment.

CONCLUSION

MiR-193b-3p has a potentially neuroprotective effect on focal cerebral I/R-induced injury by inhibiting 5-LOX expression.

Sex-specific and opposite modulatory aspects revealed by PPI network and pathway analysis of ischemic stroke in humans

Background

Ischemic Stroke (IS) is a major disease which greatly threatens human health. Recent studies showed sex-specific outcomes and mechanisms of cerebral ischemic stroke. This study aimed to identify the key changes of gene expression between male and female IS in humans.

Methods

Gene expression dataset GSE22255, including peripheral blood samples, was downloaded from the Gene Expression Omnibus (GEO) dataset. Differentially Expressed Genes (DEGs) with a LogFC>1, and a P-value <0.05 were screened by BioConductor R package and grouped in female, male and overlap DEGs for further bioinformatic analysis. Gene Ontology (GO) functional annotation, Protein-Protein Interaction (PPI) network, “Molecular Complex Detection” (MCODE) modules, CytoNCA (cytoscape network centrality analysis) essential genes and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway interrelation analysis were performed.

Results

In a total of 54,665 genes, 185 (73 ups and 112 downs) DEGs in the female dataset, 461 DEGs (297 ups and 164 downs) in the male dataset, within which 118 DEGs overlapped (7 similar changes in female and male, 111 opposite changes in female and male) were obtained from the GSE22255 dataset. Female, male and overlapping DEGs enriched for similar cellular components and molecular function. Male DEGs enriched for divergent biological processes from female and overlapping DEGs. Sex-specific and overlapping DEGs were put into the PPI network. Overlapping genes such as IL6, presented opposite changes and were mainly involved in cytokine-cytokine receptor interactions, the TNF-signalling pathway, etc.

Conclusion

The analysis of sex-specific DEGs from GEO human blood samples showed that not only specific but also opposite DEG alterations in the female and male stroke genome wide dataset. The results provided an overview of sex-specific mechanisms, which might provide insight into stroke and its biomarkers and lead to sex-specific prognosis and treatment strategies in future clinical practice.

Therapeutic Potential of Human Amniotic Epithelial Cells on Injuries and Disorders in the Central Nervous System

Despite recent advances in neurosurgery and pharmaceuticals, contemporary treatments are ineffective in restoring lost neurological functions in patients with injuries and disorders of the central nervous system (CNS). Therefore, novel and effective therapies are urgently needed. Recent studies have indicated that stem cells, including embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and mesenchymal stem cells (MSCs), could repair/replace damaged or degenerative neurons and improve functional recovery in both preclinical and clinical trials. However, there are many unanswered questions and unsolved issues regarding stem cell therapy in terms of potency, stability, oncogenicity, immune response, cell sources, and ethics. Currently, human amniotic epithelial cells (hAECs) derived from the amnion exhibit considerable advantages over other stem cells and have drawn much attention from researchers. hAECs are readily available, pose no ethical concerns, and have little risk of tumorigenicity and immunogenicity. Mounting evidence has shown that hAECs can promote neural cell survival and regeneration, repair affected neurons, and reestablish damaged neural connections. It is suggested that hAECs may be the most promising candidate for cell-based therapy of neurological diseases. In this review, we mainly focus on recent advances and potential applications of hAECs for treating various CNS injuries and neurodegenerative disorders. We also discuss current hurdles and challenges regarding hAEC therapies.

CD69 Plays a Beneficial Role in Ischemic Stroke by Dampening Endothelial Activation

RATIONALE

CD69 is an immunomodulatory molecule induced during lymphocyte activation. Following stroke, T-lymphocytes upregulate CD69 but its function is unknown.

OBJECTIVE

We investigated whether CD69 was involved in brain damage following an ischemic stroke.

METHODS AND RESULTS

We used adult male mice on the C57BL/6 or BALB/c backgrounds, including wild-type mice and CD69^-/- mice, and CD69^+/+ and CD69^-/- lymphocyte-deficient Rag2^-/- mice, and generated chimeric mice. We induced ischemia by transient or permanent middle cerebral artery occlusion. We measured infarct volume, assessed neurological function, and studied CD69 expression, as well as platelet function, fibrin(ogen) deposition, and VWF (von Willebrand factor) expression in brain vessels and VWF content and activity in plasma, and performed the tail-vein bleeding test and the carotid artery ferric chloride-induced thrombosis model. We also performed primary glial cell cultures and sorted brain CD45^-CD11b^-CD31⁺ endothelial cells for mRNA expression studies. We blocked VWF by intravenous administration of anti-VWF antibodies. CD69^-/- mice showed larger infarct volumes and worse neurological deficits than the wild-type mice after ischemia. This worsening effect was not attributable to lymphocytes or other hematopoietic cells. CD69 deficiency lowered the time to thrombosis in the carotid artery despite platelet function not being affected. Ischemia upregulated Cd69 mRNA expression in brain endothelial cells. CD69-deficiency increased fibrin(ogen) accumulation in the ischemic tissue, and plasma VWF content and activity, and VWF expression in brain vessels. Blocking VWF reduced infarct volume and reverted the detrimental effect of CD69^-/- deficiency.

CONCLUSIONS

CD69 deficiency promotes a prothrombotic phenotype characterized by increased VWF and worse brain damage after ischemic stroke. The results suggest that CD69 acts as a downregulator of endothelial activation.

The Delta-Subunit Selective GABA A Receptor Modulator, DS2, Improves Stroke Recovery via an Anti-inflammatory Mechanism

Inflammatory processes are known to contribute to tissue damage in the central nervous system (CNS) across a broad range of neurological conditions, including stroke. Gamma amino butyric acid (GABA), the main inhibitory neurotransmitter in the CNS, has been implicated in modulating peripheral immune responses by acting on GABA _A receptors on antigen-presenting cells and lymphocytes. Here, we investigated the effects and mechanism of action of the delta-selective compound, DS2, to improve stroke recovery and modulate inflammation. We report a decrease in nuclear factor (NF)-κB activation in innate immune cells over a concentration range in vitro. Following a photochemically induced motor cortex stroke, treatment with DS2 at 0.1 mg/kg from 1 h post-stroke significantly decreased circulating tumor necrosis factor (TNF)-α, interleukin (IL)-17, and IL-6 levels, reduced infarct size and improved motor function in mice. Free brain concentrations of DS2 were found to be lower than needed for robust modulation of central GABA _A receptors and were not affected by the presence and absence of elacridar, an inhibitor of both P-glycoprotein and breast cancer resistance protein (BCRP). Finally, as DS2 appears to dampen peripheral immune activation and only shows limited brain exposure, we assessed the role of DS2 to promote functional recovery after stroke when administered from 3-days after the stroke. Treatment with DS2 from 3-days post-stroke improved motor function on the grid-walking, but not on the cylinder task. These data highlight the need to further develop subunit-selective compounds to better understand change in GABA receptor signaling pathways both centrally and peripherally. Importantly, we show that GABA compounds such as DS2 that only shows limited brain exposure can still afford significant protection and promote functional recovery most likely via modulation of peripheral immune cells and could be given as an adjunct treatment.

The impact of sex and age on T cell immunity and ischemic stroke outcomes

Sex differences are well-recognized in ischemic stroke, a disease mainly affecting the elderly. Stroke results in robust activation of central and peripheral immune responses which contributes to functional outcome. Aging is associated with increased low-grade chronic inflammation known as "inflammaging" that renders aged males and females more susceptible to poor outcomes after ischemic stroke. Despite the fact that sex differences are well-documented in immunity and inflammation, few studies have focused on sex differences in inflammatory responses after ischemic stroke and even fewer have been performed in the context of aging. The role of T cell responses in ischemic stroke have gained increasing attention over the past decade as data suggest a major role in the pathophysiology/recovery after ischemic injury. T cells offer an attractive therapeutic target due to their relatively delayed infiltration into the ischemic brain. This review will focus on T cell immune responses in ischemic stroke, highlighting studies examining the effects of aging and biological sex.

Immunomodulatory Therapeutic Strategies in Stroke

The role of immunity in all stages of stroke is increasingly being recognized, from the pathogenesis of risk factors to tissue repair, leading to the investigation of a range of immunomodulatory therapies. In the acute phase of stroke, proposed therapies include drugs targeting pro-inflammatory cytokines, matrix metalloproteinases, and leukocyte infiltration, with a key objective to reduce initial brain cell toxicity. Systemically, the early stages of stroke are also characterized by stroke-induced immunosuppression, where downregulation of host defences predisposes patients to infection. Therefore, strategies to modulate innate immunity post-stroke have garnered greater attention. A complementary objective is to reduce longer-term sequelae by focusing on adaptive immunity. Following stroke onset, the integrity of the blood–brain barrier is compromised, exposing central nervous system (CNS) antigens to systemic adaptive immune recognition, potentially inducing autoimmunity. Some pre-clinical efforts have been made to tolerize the immune system to CNS antigens pre-stroke. Separately, immune cell populations that exhibit a regulatory phenotype (T- and B- regulatory cells) have been shown to ameliorate post-stroke inflammation and contribute to tissue repair. Cell-based therapies, established in oncology and transplantation, could become a strategy to treat the acute and chronic stages of stroke. Furthermore, a role for the gut microbiota in ischaemic injury has received attention. Finally, the immune system may play a role in remote ischaemic preconditioning-mediated neuroprotection against stroke. The development of stroke therapies involving organs distant to the infarct site, therefore, should not be overlooked. This review will discuss the immune mechanisms of various therapeutic strategies, surveying published data and discussing more theoretical mechanisms of action that have yet to be exploited.

IL-37 increases in patients after ischemic stroke and protects from inflammatory brain injury, motor impairment and lung infection in mice

Post-stroke inflammation may contribute to secondary brain injury and systemic immunosuppression. Interleukin(IL)-37 is an immunosuppressive cytokine belonging to the IL-1 superfamily with no mouse homologue yet identified, the effects of which have not been studied in stroke. Here we report: (1) the effect of ischemic stroke on circulating IL-37 in humans; and (2) the effect of IL-37 on stroke outcome measures in mice transgenic for human IL-37 (IL-37tg). We found that in the first 3 days after ischemic stroke in 55 patients, the plasma abundance of IL-37 was ~2-fold higher than in 24 controls. In IL-37tg mice, cerebral ischemia-reperfusion resulted in marked increases in plasma IL-37 (~9-fold) and brain IL-37 mRNA (~7,000-fold) at 24 h compared with sham-operated IL-37tg mice. Further, compared with wild-type (WT) mice subjected to cerebral ischemia-reperfusion, IL-37tg mice exhibited less severe locomotor deficit, smaller cerebral infarcts and reduced bacterial lung infection. In the ischemic hemisphere, there were 60% fewer pro-inflammatory microglia-macrophages and up to 4-fold higher expression of anti-inflammatory markers in IL-37tg compared to WT mice. Our data show that IL-37 expression is increased following ischemic stroke in humans and IL-37tg mice, and may exert protective effects by modulating post-stroke inflammation in the brain and periphery.

Mechanism and Treatment Related to Oxidative Stress in Neonatal Hypoxic-Ischemic Encephalopathy

Hypoxic ischemic encephalopathy (HIE) is a type of neonatal brain injury, which occurs due to lack of supply and oxygen deprivation to the brain. It is associated with a high morbidity and mortality rate. There are several therapeutic strategies that can be used to improve outcomes in patients with HIE. These include cell therapies such as marrow mesenchymal stem cells (MSCs) and umbilical cord blood stem cells (UCBCs), which are being incorporated into the new protocols for the prevention of ischemic brain damage. The focus of this review is to discuss the mechanism of oxidative stress in HIE and summarize the current available treatments for HIE. We hope that a better understanding of the relationship between oxidative stress and HIE will provide new insights on the potential therapy of this devastating condition.

Substrain- and sex-dependent differences in stroke vulnerability in C57BL/6 mice

The C57BL/6 mouse strain is represented by distinct substrains, increasingly recognized to differ genetically and phenotypically. The current study compared stroke vulnerability among C57BL/6 J (J), C57BL/6JEiJ (JEiJ), C57BL/6ByJ (ByJ), C57BL/6NCrl (NCrl), C57BL/6NJ (NJ) and C57BL/6NTac (NTac) substrains, using a model of permanent distal middle cerebral artery and common carotid artery occlusion. Mean infarct volume was nearly two-fold smaller in J, JEiJ and ByJ substrains relative to NCrl, NJ and NTac (N-lineage) mice. This identifies a previously unrecognized confound in stroke studies involving genetically modified strain comparisons if control substrain background were not rigorously matched. Mean infarct size was smaller in females of J and ByJ substrains than in the corresponding males, but there was no sex difference for NCrl and NJ mice. A higher proportion of small infarcts in J and ByJ substrains was largely responsible for both substrain- and sex-dependent differences. These could not be straightforwardly explained by variations in posterior communicating artery patency, MCA anatomy or acute penumbral blood flow deficits. Their larger and more homogeneously distributed infarcts, together with their established use as the common background for many genetically modified strains, may make N-lineage C57BL/6 substrains the preferred choice for future studies in experimental stroke.

Impact of C57BL/6 substrain on sex-dependent differences in mouse stroke models

We have recently found significant variation in stroke vulnerability among substrains of C57BL/6 mice, observing that commonly used N-lineage substrains exhibit larger infarcts than C57BL/6J and related substrains. Parallel variation was also seen with respect to sex differences in stroke vulnerability, in that C57BL/6 mice of the N-lineage exhibited comparable infarct sizes in males and females, whereas infarcts tended to be smaller in females than in males of J-lineage substrains. This adds to the growing list of recognized phenotypic and genetic differences among C57BL/6 substrains. Although no previous studies have explicitly compared substrains with respect to sex differences in stroke vulnerability, unrecognized background mismatch has occurred in some studies involving control and genetically modified mice. The aims of this review are to: present the evidence for associated substrain- and sex-dependent differences in a mouse permanent occlusion stroke model; examine the extent to which the published literature in other models compares with these recent results; and consider the potential impact of unrecognized heterogeneity in substrain background on the interpretation of studies investigating the impact of genetic modifications on sex differences in stroke outcome. Substrain emerges as a critical variable to be documented in any experimental stroke study in mice.

Diet-induced vitamin D deficiency has no effect on acute post-stroke outcomes in young male mice

Recent observational studies have reported that patients with low circulating levels of vitamin D experience larger infarct volumes and worse functional outcomes after ischemic stroke compared to those with sufficient levels. However, it is unknown whether a causal relationship exists between low vitamin D levels and poor stroke outcome. This study aimed to assess the effect of vitamin D deficiency on acute outcomes post-stroke. Male C57Bl6 mice (six week old) were assigned to either a control or vitamin D deficient diet for four weeks prior to stroke. Stroke was induced by 1 h middle cerebral artery occlusion (MCAO) with reperfusion. At 24 h, we assessed functional outcomes, infarct volume, quantified immune cells in the brain by immunofluorescence and examined susceptibility to lung infection. ELISAs showed that the plasma level of hydroxyvitamin D₃ was 85% lower in mice fed the vitamin D-deficient diet compared with the control group. Despite this, vitamin D deficiency had no impact on functional outcomes or infarct volume after stroke. Further, there were no differences in the numbers of infiltrating immune cells or bacterial load within the lungs. These data suggest that diet-induced vitamin D deficiency has no effect on acute post-stroke outcomes.

CXCL8 gene silencing promotes neuroglial cells activation while inhibiting neuroinflammation through the PI3K/Akt/NF-κB-signaling pathway in mice with ischemic stroke

OBJECTIVE

Ischemic stroke is known as a neurodegenerative disorder, which induces long-period tissue damage. Chemokine (C-X-C motif) ligand 8 (CXCL8) is involved in acute inflammation and tumor progression through the phosphoinositide-3-kinase/protein kinase B/nuclear factor-κB (PI3K/Akt/NF-κB)-signaling pathway. In this study, we aimed to explore the mechanism of CXCL8 in ischemic stroke in relation to the PI3K/Akt/NF-κB-signaling pathway.

METHODS

Microarray-based gene expression profiling of peripheral blood mononuclear cells was used to identify ischemic stroke-related differentially expressed genes and explore role of CXCL8 in ischemic stroke. Next, the ischemic mice model was successfully established, with transfection efficiency detected. After that, deflection index, recovery of nervous system, infarct sizes, ischemia-induced apoptosis, and neuroinflammatory response in ischemic stroke were measured. At last, the content of inflammatory factors as well as the expression of CXCL8, caspase-3, caspase-9, Bad, interleukin-6 (IL-6), IL-1β, tumor necrosis factor-α (TNF-α), Akt, PI3K, and NF-κB were determined.

RESULTS

Comprehensive gene expression profiling analysis identified that CXCL8 might affect the development of ischemic stroke through regulating the PI3K/Akt/NF-κB-signaling pathway. CXCL8 silencing significantly reduced deflection index and infarct size, improved neurological function, and suppressed neuroglial cell loss and apoptosis index. In addition, glial fibrillary acidic portein (GFAP) and ionized calcium-binding adapter molecule 1 (IBA-1) expressions were decreased following CXCL8 suppression, suggesting CXCL8 affected neuroglial activation. Importantly, we also found that CXCL8 silencing activated neuroglial cell and suppressed inflammatory cytokine production in ischemic stroke mice.

CONCLUSION

Taken together, these findings highlight that functional suppression of CXCL8 promotes neuroglial activation and inhibits neuroinflammation by regulating the PI3K/Akt/NF-κB-signaling pathway in mice with ischemic stroke, which might provide new insight for ischemic stroke treatment.

Immunosenescence in neurocritical care

BACKGROUND

Several advanced and developing countries are now entering a superaged society, in which the percentage of elderly people exceeds 20% of the total population. In such an aging society, the number of age-related diseases such as malignant tumors, diabetes, and severe infections including sepsis is increasing, and patients with such disorders often find themselves in the ICU.

MAIN BODY

Age-related diseases are closely related to age-induced immune dysfunction, by which reductions in the efficiency and specificity of the immune system are collectively termed "immunosenescence." The most noticeable is a decline in the antigen-specific acquired immune response. The exhaustion of T cells in elderly sepsis is related to an increase in nosocomial infections after septicemia, and even death over subacute periods. Another characteristic is that senescent cells that accumulate in body tissues over time cause chronic inflammation through the secretion of proinflammatory cytokines, termed senescence-associated secretory phenotype. Chronic inflammation associated with aging has been called "inflammaging," and similar age-related diseases are becoming an urgent social problem.

CONCLUSION

In neuro ICUs, several neuro-related diseases including stroke and sepsis-associated encephalopathy are related to immunosenescence and neuroinflammation in the elderly. Several advanced countries with superaged societies face the new challenge of improving the long-term prognosis of neurocritical patients.

IL-33 modulates inflammatory brain injury but exacerbates systemic immunosuppression following ischemic stroke

Stroke triggers a complex inflammatory process in which the balance between pro- and antiinflammatory mediators is critical for the development of the brain infarct. However, systemic changes may also occur in parallel with brain inflammation. Here we demonstrate that administration of recombinant IL-33, a recently described member of the IL-1 superfamily of cytokines, promotes Th2-type effects following focal ischemic stroke, resulting in increased plasma levels of Th2-type cytokines and fewer proinflammatory (3-nitrotyrosine+F4/80+) microglia/macrophages in the brain. These effects of IL-33 were associated with reduced infarct size, fewer activated microglia and infiltrating cytotoxic (natural killer-like) T cells, and more IL-10-expressing regulatory T cells. Despite these neuroprotective effects, mice treated with IL-33 displayed exacerbated post-stroke lung bacterial infection in association with greater functional deficits and mortality at 24 hours. Supplementary antibiotics (gentamicin and ampicillin) mitigated these systemic effects of IL-33 after stroke. Our findings highlight the complex nature of the inflammatory mechanisms differentially activated in the brain and periphery during the acute phase after ischemic stroke. The data indicate that a Th2-promoting agent can provide neuroprotection without adverse systemic effects when given in combination with antibiotics.

FasL incapacitation alleviates CD4+ T cells-induced brain injury through remodeling of microglia polarization in mouse ischemic stroke

Inflammation responses involving the crosstalk between infiltrated T cells and microglia play crucial roles in ischemia stroke. Recent studies showed that Fas ligand (FasL) mutation could reduce post-stroke T cell invasion and microglia activation. In this study, we demonstrated that CD4⁺ T cells could induce M1 microglia polarization through NF-κB signaling pathway, whereas FasL mutant CD4⁺ T cells significantly reversed this effect. Besides, Th17/Treg cells balance was skewed into Treg cells after FasL mutation. In addition, conditioned medium from co-culture of FasL mutant CD4⁺ T cells and microglia could alleviate neuronal injury. Collectively, FasL incapacitation could alleviate CD4⁺ T cells-induced inflammation through remodeling microglia polarization, suggesting a therapeutic potential for control of inflammation responses after ischemic stroke.

Brain-immune interactions in perinatal hypoxic-ischemic brain injury

Perinatal hypoxia-ischemia remains the primary cause of acute neonatal brain injury, leading to a high mortality rate and long-term neurological deficits, such as behavioral, social, attentional, cognitive and functional motor deficits. An ever-increasing body of evidence shows that the immune response to acute cerebral hypoxia-ischemia is a major contributor to the pathophysiology of neonatal brain injury. Hypoxia-ischemia provokes an intravascular inflammatory cascade that is further augmented by the activation of resident immune cells and the cerebral infiltration of peripheral immune cells response to cellular damages in the brain parenchyma. This prolonged and/or inappropriate neuroinflammation leads to secondary brain tissue injury. Yet, the long-term effects of immune activation, especially the adaptive immune response, on the hypoxic-ischemic brain still remain unclear. The focus of this review is to summarize recent advances in the understanding of post-hypoxic-ischemic neuroinflammation triggered by the innate and adaptive immune responses and to discuss how these mechanisms modulate the brain vulnerability to injury. A greater understanding of the reciprocal interactions between the hypoxic-ischemic brain and the immune system will open new avenues for potential immunomodulatory therapy in the treatment of neonatal brain injury.

NADPH Oxidase-Related Pathophysiology in Experimental Models of Stroke

Several experimental studies have indicated that nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (Nox) exert detrimental effects on ischemic brain tissue; Nox-knockout mice generally exhibit resistance to damage due to experimental stroke following middle cerebral artery occlusion (MCAO). Furthermore, our previous MCAO study indicated that infarct size and blood-brain barrier breakdown are enhanced in mice with pericyte-specific overexpression of Nox4, relative to levels observed in controls. However, it remains unclear whether Nox affects the stroke outcome directly by increasing oxidative stress at the site of ischemia, or indirectly by modifying physiological variables such as blood pressure or cerebral blood flow (CBF). Because of technical problems in the measurement of physiological variables and CBF, it is often difficult to address this issue in mouse models due to their small body size; in our previous study, we examined the effects of Nox activity on focal ischemic injury in a novel congenic rat strain: stroke-prone spontaneously hypertensive rats with loss-of-function in Nox. In this review, we summarize the current literature regarding the role of Nox in focal ischemic injury and discuss critical issues that should be considered when investigating Nox-related pathophysiology in animal models of stroke.

Role of microglia in ischemic focal stroke and recovery: focus on Toll-like receptors

Stroke is the leading cause of disability in adults. Drug treatments that target stroke-induced pathological mechanisms and promote recovery are desperately needed. In the brain, an ischemic event triggers major inflammatory responses that are mediated by the resident microglial cells. In this review, we focus on the microglia activation after ischemic brain injury as a target of immunomodulatory therapeutics. We divide the microglia-mediated events following ischemic stroke into three categories: acute, subacute, and long-term events. This division encompasses the spatial and temporal dynamics of microglia as they participate in the pathophysiological changes that contribute to the symptoms and sequela of a stroke. The importance of Toll-like receptor (TLR) signaling in the outcomes of these pathophysiological changes is highlighted. Increasing evidence shows that microglia have a complex role in stroke pathophysiology, and they mediate both detrimental and beneficial effects on stroke outcome. So far, most of the pharmacological studies in experimental models of stroke have focused on neuroprotective strategies which are impractical for clinical applications. Post-ischemic inflammation is long lasting and thus, could provide a therapeutic target for novel delayed drug treatment. However, more studies are needed to elucidate the role of microglia in the recovery process from an ischemic stroke and to evaluate the therapeutic potential of modulating post-ischemic inflammation to promote functional recovery.

Central Modulation of Neuroinflammation by Neuropeptides and Energy-Sensing Hormones during Obesity

Central nervous system (CNS) senses energy homeostasis by integrating both peripheral and autonomic signals and responding to them by neurotransmitters and neuropeptides release. Although it is previously considered an immunologically privileged organ, we now know that this is not so. Cells belonging to the immune system, such as B and T lymphocytes, can be recruited into the CNS to face damage or infection, in addition to possessing resident immunological cells, called microglia. In this way, positive energy balance during obesity promotes an inflammatory state in the CNS. Saturated fatty acids from the diet have been pointed out as powerful candidates to trigger immune response in peripheral system and in the CNS. However, how central immunity communicates to peripheral immune response remains to be clarified. Recently there has been a great interest in the neuropeptides, POMC derived peptides, ghrelin, and leptin, due to their capacity to suppress or induce inflammatory responses in the brain, respectively. These may be potential candidates to treat different pathologies associated with autoimmunity and inflammation. In this review, we will discuss the role of lipotoxicity associated with positive energy balance during obesity in proinflammatory response in microglia, B and T lymphocytes, and its modulation by neuropeptides.

The Pathophysiological Role of NOX2 in Hypertension and Organ Damage

NADPH oxidases (NOXs) represent one of the major sources of reactive oxygen species in the vascular district. Reactive oxygen species are responsible for vascular damage that leads to several cardiovascular pathological conditions. Among NOX isoforms, NOX2 is widely expressed in many cells types, such as cardiomyocytes, endothelial cells, and vascular smooth muscle cells, confirming its pivotal role in vascular pathophysiology. Studies in mice models with systemic deletion of NOX2, as well as in transgenic mice overexpressing NOX2, have demonstrated the undeniable involvement of NOX2 in the development of hypertension, atherosclerosis, diabetes mellitus, cardiac hypertrophy, platelet aggregation, and aging. Of note, the inhibition of NOX2 has been found to be protective for cardiovascular homeostasis. Here, we review the evidence demonstrating that the modulation of NOX2 activity is able to improve vascular physiology, suggesting that NOX2 may be a potential target for therapeutic applications.

The opposing roles of NO and oxidative stress in cardiovascular disease

Nitric oxide (NO) plays a pivotal role in the maintenance of cardiovascular homeostasis. A reduction in the bioavailability of endogenous NO, manifest as a decrease in the production and/or impaired signaling, is associated with many cardiovascular diseases including hypertension, atherosclerosis, stroke and heart failure. There is substantial evidence that reactive oxygen species (ROS), generated predominantly from NADPH oxidases (Nox), are responsible for the reduced NO bioavailability in vascular and cardiac pathologies. ROS can compromise NO function via a direct inactivation of NO, together with a reduction in NO synthesis and oxidation of its receptor, soluble guanylyl cyclase. Whilst nitrovasodilators are administered to compensate for the ROS-mediated loss in NO bioactivity, their clinical utility is limited due to the development of tolerance and resistance and systemic hypotension. Moreover, efforts to directly scavenge ROS with antioxidants has had limited clinical efficacy. This review outlines the therapeutic utility of NO-based therapeutics in cardiovascular diseases and describes the source and impact of ROS in these pathologies, with particular focus on the interaction with NO. Future therapeutic approaches in the treatment of cardiovascular diseases are highlighted with a focus on nitroxyl (HNO) donors as an alternative to traditional NO donors and the development of novel Nox inhibitors.

Oxidative Stress in Hypoxic-Ischemic Encephalopathy: Molecular Mechanisms and Therapeutic Strategies

Hypoxic-ischemic encephalopathy (HIE) is one of the leading causes of morbidity and mortality in neonates. Because of high concentrations of sensitive immature cells, metal-catalyzed free radicals, non-saturated fatty acids, and low concentrations of antioxidant enzymes, the brain requires high levels of oxygen supply and is, thus, extremely sensitive to hypoxia. Strong evidence indicates that oxidative stress plays an important role in pathogenesis and progression. Following hypoxia and ischemia, reactive oxygen species (ROS) production rapidly increases and overwhelms antioxidant defenses. A large excess of ROS will directly modify or degenerate cellular macromolecules, such as membranes, proteins, lipids, and DNA, and lead to a cascading inflammatory response, and protease secretion. These derivatives are involved in a complex interplay of multiple pathways (e.g., inflammation, apoptosis, autophagy, and necrosis) which finally lead to brain injury. In this review, we highlight the molecular mechanism for oxidative stress in HIE, summarize current research on therapeutic strategies utilized in combating oxidative stress, and try to explore novel potential clinical approaches.