Astrocyte targeted overexpression of Hsp72 or SOD2 reduces neuronal vulnerability to forebrain ischemia

Prolactin is an Endogenous Antioxidant Factor in Astrocytes That Limits Oxidative Stress-Induced Astrocytic Cell Death via the STAT3/NRF2 Signaling Pathway

Oxidative stress-induced death of neurons and astrocytes contributes to the pathogenesis of numerous neurodegenerative diseases. While significant progress has been made in identifying neuroprotective molecules against neuronal oxidative damage, little is known about their counterparts for astrocytes. Prolactin (PRL), a hormone known to stimulate astroglial proliferation, viability, and cytokine expression, exhibits antioxidant effects in neurons. However, its role in protecting astrocytes from oxidative stress remains unexplored. Here, we investigated the effect of PRL against hydrogen peroxide (H2O2)-induced oxidative insult in primary cortical astrocyte cultures. Incubation of astrocytes with PRL led to increased enzymatic activity of superoxide dismutase (SOD) and glutathione peroxidase (GPX), resulting in higher total antioxidant capacity. Concomitantly, PRL prevented H2O2-induced cell death, reactive oxygen species accumulation, and protein and lipid oxidation. The protective effect of PRL upon H2O2-induced cell death can be explained by the activation of both signal transducer and activator of transcription 3 (STAT3) and NFE2 like bZIP transcription factor 2 (NRF2) transduction cascades. We demonstrated that PRL induced nuclear translocation and transcriptional upregulation of Nrf2, concurrently with the transcriptional upregulation of the NRF2-dependent genes heme oxygenase 1, Sod1, Sod2, and Gpx1. Pharmacological blockade of STAT3 suppressed PRL-induced transcriptional upregulation of Nrf2, Sod1 and Gpx1 mRNA, and SOD and GPX activities. Furthermore, genetic ablation of the PRL receptor increased astroglial susceptibility to H2O2-induced cell death and superoxide accumulation, while diminishing their intrinsic antioxidant capacity. Overall, these findings unveil PRL as a potent antioxidant hormone that protects astrocytes from oxidative insult, which may contribute to brain neuroprotection.

Ginsenoside Re protects against kainate-induced neurotoxicity in mice by attenuating mitochondrial dysfunction through activation of the signal transducers and activators of transcription 3 signaling

It was demonstrated that ginsenosides exert anti-convulsive potentials and interleukin-6 (IL-6) is protective from excitotoxicity induced by kainate (KA), a model of temporal lobe epilepsy. Ginsenosides-mediated mitochondrial recovery is essential for attenuating KA-induced neurotoxicity, however, little is known about the effects of ginsenoside Re (GRe), one of the major ginsenosides. In this study, GRe significantly attenuated KA-induced seizures in mice. KA-induced redox changes were more evident in mitochondrial fraction than in cytosolic fraction in the hippocampus of mice. GRe significantly attenuated KA-induced mitochondrial oxidative stress (i.e. increases in reactive oxygen species, 4-hydroxynonenal, and protein carbonyl) and mitochondrial dysfunction (i.e. the increase in intra-mitochondrial Ca2+ and the decrease in mitochondrial membrane potential). GRe or mitochondrial protectant cyclosporin A restored phospho-signal transducers and activators of transcription 3 (STAT3) and IL-6 levels reduced by KA, and the effects of GRe were reversed by the JAK2 inhibitor AG490 and the mitochondrial toxin 3-nitropropionic acid (3-NP). Thus, we used IL-6 knockout (KO) mice to investigate whether the interaction between STAT3 and IL-6 is involved in the GRe effects. Importantly, KA-induced reduction of manganese superoxide dismutase (SOD-2) levels and neurodegeneration (i.e. astroglial inhibition, microglial activation, and neuronal loss) were more prominent in IL-6 KO than in wild-type (WT) mice. These KA-induced detrimental effects were attenuated by GRe in WT and, unexpectedly, IL-6 KO mice, which were counteracted by AG490 and 3-NP. Our results suggest that GRe attenuates KA-induced neurodegeneration via modulating mitochondrial oxidative burden, mitochondrial dysfunction, and STAT3 signaling in mice.

Efficacy and Mechanism Study of 6S-5-Methyltetrahydrofolate-Calcium Against Telencephalon Infarction Injury in Zebrafish Model of Ischemic Stroke

Ischemic stroke is a heterogeneous brain injury with complex pathophysiology and it is also a time sensitive neurological injury disease. At present, the treatment options for ischemic stroke are still limited. 6S-5-methyltetrahydrofolate-calcium (MTHF-Ca) is the calcium salt of the predominant form of dietary folate in circulation. MTHF-Ca has potential neuroprotective effect on neurocytes, but whether it can be used for ischemic stroke treatment remains unknown. We established zebrafish ischemic stroke model through photothrombotic method to evaluate the protective effect of MTHF-Ca on the ischemic brain injury of zebrafish. We demonstrated that MTHF-Ca reduced the brain damage by reducing motor dysfunction and neurobehavioral defects of zebrafish with telencephalon infarction injury. MTHF-Ca counteracted oxidative damages after Tel injury by increasing the activities of GSH-Px and SOD and decreasing the content of MDA. RNA-seq and RT-qPCR results showed that MTHF-Ca played a neuroprotective role by alleviating neuroinflammation, inhibiting blood coagulation, and neuronal apoptosis processes. Overall, we have demonstrated that MTHF-Ca has neuroprotective effect in ischemic stroke and can be used as a potential treatment for ischemic stroke.

Neuroprotective Effects of Water Extract from Brown Algae Petalonia binghamiae in an Experimental Model of Focal Cerebral Ischemia In Vitro and In Vivo

Focal cerebral ischemia (fCI) can result in brain injury and sensorimotor deficits. Brown algae are currently garnering scientific attention as potential therapeutic candidates for fCI. This study investigated the therapeutic effects of the hot water extract of Petalonia binghamiae (wPB), a brown alga, in in vitro and in vivo models of fCI. The neuroprotective efficacy of wPB was evaluated in an in vitro excitotoxicity model established using HT-22 cells challenged with glutamate. Afterward, C57/BL6 mice were administered wPB for 7 days (10 or 100 mg/kg, intragastric) and subjected to middle cerebral artery occlusion and reperfusion (MCAO/R) operation, which was used as an in vivo fCI model. wPB co-incubation significantly inhibited cell death, oxidative stress, and apoptosis, as well as stimulated the expression of heme oxygenase-1 (HO-1), an antioxidant enzyme, and the nuclear translocation of its upstream regulator, nuclear factor erythroid 2-related factor 2 (Nrf2) in HT-22 cells challenged with glutamate-induced excitotoxicity. Pretreatment with either dose of wPB significantly attenuated infarction volume, neuronal death, and sensorimotor deficits in an in vivo fCI model. Furthermore, the attenuation of oxidative stress and apoptosis in the ischemic lesion accompanied the wPB-associated protection. This study suggests that wPB can counteract fCI via an antioxidative effect, upregulating the Nrf2/HO-1 pathway.

Electrophysiological In Vitro Study of Long-Range Signal Transmission by Astrocytic Networks

Astrocytes are diverse brain cells that form large networks communicating via gap junctions and chemical transmitters. Despite recent advances, the functions of astrocytic networks in information processing in the brain are not fully understood. In culture, brain slices, and in vivo, astrocytes, and neurons grow in tight association, making it challenging to establish whether signals that spread within astrocytic networks communicate with neuronal groups at distant sites, or whether astrocytes solely respond to their local environments. A multi-electrode array (MEA)-based device called AstroMEA is designed to separate neuronal and astrocytic networks, thus allowing to study the transfer of chemical and/or electrical signals transmitted via astrocytic networks capable of changing neuronal electrical behavior. AstroMEA demonstrates that cortical astrocytic networks can induce a significant upregulation in the firing frequency of neurons in response to a theta-burst charge-balanced biphasic current stimulation (5 pulses of 100 Hz × 10 with 200 ms intervals, 2 s total duration) of a separate neuronal-astrocytic group in the absence of direct neuronal contact. This result corroborates the view of astrocytic networks as a parallel mechanism of signal transmission in the brain that is separate from the neuronal connectome. Translationally, it highlights the importance of astrocytic network protection as a treatment target.

Inhibition of microRNA-200c preserves astrocyte sirtuin-1 and mitofusin-2, and protects against hippocampal neurodegeneration following global cerebral ischemia in mice

Memory impairment remains a leading disability in survivors of global cerebral ischemia, occurring secondary to delayed neurodegeneration of hippocampal cornu ammonis-1 (CA1) neurons. MicroRNA-200c (miR-200c) is induced following ischemic stress and we have previously demonstrated that pre-treatment with anti-miR-200c is protective against embolic stroke in mice. In the present study we assessed the role of miR-200c on CA1 neurodegeneration, sirtuin-1 (SIRT1), and mitochondrial dynamic protein expression in a mouse model of transient global cerebral ischemia and in vitro in primary mouse astrocyte cultures after simulated ischemia. Mice were subjected to 10 min bilateral common carotid artery occlusion plus hypotension with 5% isoflurane. After 2 h recovery mice were treated with intravenous injection of either anti-miR-200c or mismatch control. Memory function was assessed by Barnes maze at post-injury days 3 and 7. Mice were sacrificed at post-injury day 7 for assessment of brain cell-type specific expression of miR-200c, SIRT1, and the mitochondrial fusion proteins mitofusin-2 (MFN2) and OPA1 via complexed fluorescent in situ hybridization and fluorescent immunohistochemistry. Global cerebral ischemia induced significant loss of CA1 neurons, impaired memory performance and decreased expression of CA1 SIRT1, MFN2, and OPA1. Post-injury treatment with anti-miR-200c significantly improved survival, prevented CA1 neuronal loss, improved post-injury performance in Barnes maze, and was associated with increased post-injury expression of CA1 SIRT1 and MFN2 in astrocytes. In vitro, primary mouse astrocyte cultures pre-treated with miR-200c inhibitor prior to oxygen/glucose deprivation preserved expression of SIRT1 and MFN2, and decreased reactive oxygen species generation, whereas pre-treatment with miR-200c mimic had opposite effects that could be reversed by co-treatment with SIRT1 activator. These results suggest that miR-200c regulates astrocyte mitochondrial homeostasis via targeting SIRT1, and that CA1 astrocyte mitochondria and SIRT1 represent potential post-injury therapeutic targets to preserve cognitive function in survivors of global cerebral ischemia.

Pathophysiology of Ischemic Stroke: Noncoding RNA Role in Oxidative Stress

Stroke is a neurological disease that causes significant disability and death worldwide. Ischemic stroke accounts for 75% of all strokes. The pathophysiological processes underlying ischemic stroke include oxidative stress, the toxicity of excitatory amino acids, ion disorder, enhanced apoptosis, and inflammation. Noncoding RNAs (ncRNAs) may have a vital role in regulating the pathophysiological processes of ischemic stroke, as confirmed by the altered expression of ncRNAs in blood samples from acute ischemic stroke patients, animal models, and oxygen-glucose-deprived (OGD) cell models. Due to specific changes in expression, ncRNAs can potentially be biomarkers for the diagnosis, treatment, and prognosis of ischemic stroke. As an important brain cell component, glial cells mediate the occurrence and progression of oxidative stress after ischemic stroke, and ncRNAs are an irreplaceable part of this mechanism. This review highlights the impact of ncRNAs in the oxidative stress process of ischemic stroke. It focuses on specific ncRNAs that underlie the pathophysiology of ischemic stroke and have potential as diagnostic biomarkers and therapeutic targets.

Selective Ablation of Sod2 in Astrocytes Induces Sex-Specific Effects on Cognitive Function, d-Serine Availability, and Astrogliosis

Cognitive decline is a debilitating aspect of aging and neurodegenerative diseases such as Alzheimer's disease are closely associated with mitochondrial dysfunction, increased reactive oxygen species, neuroinflammation, and astrogliosis. This study investigated the effects of decreased mitochondrial antioxidant response specifically in astrocytes on cognitive performance and neuronal function in C57BL/6J mice using a tamoxifen-inducible astrocyte-specific knockout of manganese superoxide dismutase (aSOD2-KO), a mitochondrial matrix antioxidant that detoxifies superoxide generated during mitochondrial respiration. We reduced astrocyte SOD2 levels in male and female mice at 11-12 months of age and tested in an automated home cage (PhenoTyper) apparatus for diurnal patterns, spatial learning, and memory function at 15 months of age. aSOD2-KO impaired hippocampal-dependent spatial working memory and decreased cognitive flexibility in the reversal phase of the testing paradigm in males. Female aSOD2-KO showed no learning and memory deficits compared with age-matched controls despite significant reduction in hippocampal SOD2 expression. aSOD2-KO males further showed decreased hippocampal long-term potentiation, but paired-pulse facilitation was unaffected. Levels of d-serine, an NMDA receptor coagonist, were also reduced in aSOD2-KO mice, but female knockouts showed a compensatory increase in serine racemase expression. Furthermore, aSOD2-KO mice demonstrated increased density of astrocytes, indicative of astrogliosis, in the hippocampus compared with age-matched controls. These data demonstrate that reduction in mitochondrial antioxidant stress response in astrocytes recapitulates age-related deficits in cognitive function, d-serine availability, and astrogliosis. Therefore, improving astrocyte mitochondrial homeostasis may provide a therapeutic target for intervention for cognitive impairment in aging.SIGNIFICANCE STATEMENT Diminished antioxidant response is associated with increased astrogliosis in aging and in Alzheimer's disease. Manganese superoxide dismutase (SOD2) is an antioxidant in the mitochondrial matrix that detoxifies superoxide and maintains mitochondrial homeostasis. We show that astrocytic ablation of SOD2 impairs hippocampal-dependent plasticity in spatial working memory, reduces long-term potentiation of hippocampal neurons and levels of the neuromodulator d-serine, and increases astrogliosis, consistent with defects in advanced aging and Alzheimer's disease. Our data provide strong evidence for sex-specific effects of astrocytic SOD2 functions in age-related cognitive dysfunction.

Signaling pathways involved in ischemic stroke: molecular mechanisms and therapeutic interventions

Ischemic stroke is caused primarily by an interruption in cerebral blood flow, which induces severe neural injuries, and is one of the leading causes of death and disability worldwide. Thus, it is of great necessity to further detailly elucidate the mechanisms of ischemic stroke and find out new therapies against the disease. In recent years, efforts have been made to understand the pathophysiology of ischemic stroke, including cellular excitotoxicity, oxidative stress, cell death processes, and neuroinflammation. In the meantime, a plethora of signaling pathways, either detrimental or neuroprotective, are also highly involved in the forementioned pathophysiology. These pathways are closely intertwined and form a complex signaling network. Also, these signaling pathways reveal therapeutic potential, as targeting these signaling pathways could possibly serve as therapeutic approaches against ischemic stroke. In this review, we describe the signaling pathways involved in ischemic stroke and categorize them based on the pathophysiological processes they participate in. Therapeutic approaches targeting these signaling pathways, which are associated with the pathophysiology mentioned above, are also discussed. Meanwhile, clinical trials regarding ischemic stroke, which potentially target the pathophysiology and the signaling pathways involved, are summarized in details. Conclusively, this review elucidated potential molecular mechanisms and related signaling pathways underlying ischemic stroke, and summarize the therapeutic approaches targeted various pathophysiology, with particular reference to clinical trials and future prospects for treating ischemic stroke.

Application time and persistence of transcranial direct current stimulation (tDCS) against neuronal death resulting from transient cerebral ischemia

BACKGROUND

Transcranial direct current stimulation (tDCS) has been studied as a tool to stimulate the functional recovery of neurons after stroke. Although this device has recently begun to be utilized for providing neuroprotection in stroke, research on its application conditions is lacking. This study aimed to examine the effects of various tDCS application conditions on cerebral ischemia. Ischemia was induced for 5 min in a gerbil model. The application of tDCS comprised a 20 min stimulation-20 min rest-20 min stimulation protocol, which was implemented simultaneously with the induction of cerebral ischemia. Application time of the tDCS effect on ischemia was confirmed by sampling brain tissues after stimulation using 0.2 mA tDCS at 0, 5, 10 and 60 min after ischemia.

RESULTS

Persistence of the tDCS effect on ischemia was confirmed by sampling brain tissues 5, 7, and 10 days post stimulation, with 0.2 mA tDCS after ischemia. Furthermore, the tissues were stained with cresyl violet and Fluoro-Jade C so as to determine the reduction in neuronal death under all application conditions.

CONCLUSIONS

The application of tDCS can be used as a useful intervention for acute phase stroke due to its sustained neuroprotective effect.

HSP70 inhibition suppressed glioma cell viability during hypoxia/reoxygenation by inhibiting the ERK1/2 and PI3K/AKT signaling pathways

Heat shock protein 70 (HSP70) can regulate astrocyte viability under hypoxic and ischemic conditions. However, the protective mechanism involved is not completely clear. This study aimed to investigate whether HSP70 protects U87 glioma cells against hypoxic damage via the extracellular signal-regulated kinases 1/2 (ERK1/2) and phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) signaling pathways. Lentivirus-mediated HSP70-siRNA was used for HSP70 silencing. U87 glioma cells with lentiviral infection were exposed to hypoxia for 4, 8, 12, and 24 h, respectively, followed by a 24-h reoxygenation treatment. A Cell-Counting Kit-8 was then used to evaluate the viability of the U87 glioma cells. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) and western blotting were performed to determine the mRNA and protein levels, respectively. The expression of HSP70, p-ERK1/2, p-AKT, and U87 cell viability were increased after 8 h of hypoxia/24 h of reoxygenation (P < 0.01). However, HSP70 silencing significantly decreased the U87 cell viability after the hypoxia/reoxygenation treatment (P < 0.01). The protein expressions of p-ERK1/2 and p-AKT also decreased in HSP70-silenced U87 cells (P < 0.01). In conclusion, HSP70 inhibition suppressed the viability of U87 glioma cells during hypoxia/reoxygenation (at least partially) by inhibiting the ERK1/2 and PI3K/AKT signaling pathways. This study may help to understand the molecular mechanisms underlying the progression and development of cerebral hypoxia-ischemia.

Expression of miR-200c corresponds with increased reactive oxygen species and hypoxia markers after transient focal ischemia in mice

Embolic stroke results in a necrotic core of cells destined to die, but also a peri-ischemic, watershed penumbral region of potentially salvageable brain tissue. Approaches to effectively differentiate between the ischemic and peri-ischemic zones is critical for novel therapeutic discovery to improve outcomes in survivors of stroke. MicroRNAs are a class of small non-coding RNAs regulating gene translation that have region- and cell-specific expression and responses to ischemia. We have previously reported that global inhibition of cerebral microRNA-200c after experimental stroke in mice is protective, however delineating the post-stroke sub-regional and cell-type specific patterns of post-stroke miR-200c expression are necessary to minimize off-target effects and advance translational application. Here, we detail a novel protocol to visualize regional miR-200c expression after experimental stroke, complexed with visualization of regional ischemia and markers of oxidative stress in an experimental stroke model in mice. In the present study we demonstrate that the fluorescent hypoxia indicator pimonidazole hydrochloride, the reactive-oxygen-species marker 8-hydroxy-deoxyguanosine, neuronal marker MAP2 and NeuN, and the reactive astrocyte marker GFAP can be effectively complexed to determine regional differences in ischemic injury as early as 30 min post-reperfusion after experimental stroke, and can be effectively used to distinguish ischemic core from surrounding penumbral and unaffected regions for targeted therapy. This multi-dimensional post-stroke immunofluorescent imaging protocol enables a greater degree of sub-regional mechanistic investigation, with the ultimate goal of developing more effective post-stroke pharmaceutical therapy.

Astrocyte Activation in Neurovascular Damage and Repair Following Ischaemic Stroke

Transient or permanent loss of tissue perfusion due to ischaemic stroke can lead to damage to the neurovasculature, and disrupt brain homeostasis, causing long-term motor and cognitive deficits. Despite promising pre-clinical studies, clinically approved neuroprotective therapies are lacking. Most studies have focused on neurons while ignoring the important roles of other cells of the neurovascular unit, such as astrocytes and pericytes. Astrocytes are important for the development and maintenance of the blood-brain barrier, brain homeostasis, structural support, control of cerebral blood flow and secretion of neuroprotective factors. Emerging data suggest that astrocyte activation exerts both beneficial and detrimental effects following ischaemic stroke. Activated astrocytes provide neuroprotection and contribute to neurorestoration, but also secrete inflammatory modulators, leading to aggravation of the ischaemic lesion. Astrocytes are more resistant than other cell types to stroke pathology, and exert a regulative effect in response to ischaemia. These roles of astrocytes following ischaemic stroke remain incompletely understood, though they represent an appealing target for neurovascular protection following stroke. In this review, we summarise the astrocytic contributions to neurovascular damage and repair following ischaemic stroke, and explore mechanisms of neuroprotection that promote revascularisation and neurorestoration, which may be targeted for developing novel therapies for ischaemic stroke.

New insights into targeting mitochondria in ischemic injury

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

Reactive astrocyte nomenclature, definitions, and future directions

Reactive astrocytes are astrocytes undergoing morphological, molecular, and functional remodeling in response to injury, disease, or infection of the CNS. Although this remodeling was first described over a century ago, uncertainties and controversies remain regarding the contribution of reactive astrocytes to CNS diseases, repair, and aging. It is also unclear whether fixed categories of reactive astrocytes exist and, if so, how to identify them. We point out the shortcomings of binary divisions of reactive astrocytes into good-vs-bad, neurotoxic-vs-neuroprotective or A1-vs-A2. We advocate, instead, that research on reactive astrocytes include assessment of multiple molecular and functional parameters-preferably in vivo-plus multivariate statistics and determination of impact on pathological hallmarks in relevant models. These guidelines may spur the discovery of astrocyte-based biomarkers as well as astrocyte-targeting therapies that abrogate detrimental actions of reactive astrocytes, potentiate their neuro- and glioprotective actions, and restore or augment their homeostatic, modulatory, and defensive functions.

In vitro P38MAPK inhibition in aged astrocytes decreases reactive astrocytes, inflammation and increases nutritive capacity after oxygen-glucose deprivation

Proper astroglial functioning is essential for the development and survival of neurons and oligodendroglia under physiologic and pathological circumstances. Indeed, malfunctioning of astrocytes represents an important factor contributing to brain injury. However, the molecular pathways of this astroglial dysfunction are poorly defined. In this work we show that aging itself can drastically perturb astrocyte viability with an increase of inflammation, cell death and astrogliosis. Moreover, we demonstrate that oxygen glucose deprivation (OGD) has a higher impact on nutritive loss in aged astrocytes compared to young ones, whereas aged astrocytes have a higher activity of the anti-oxidant systems. P38MAPK signaling has been identified to be upregulated in neurons, astrocytes and microglia after ischemic stroke. By using a pharmacological p38α specific inhibitor (PH-797804), we show that p38MAPK pathway has an important role in aged astrocytes for inflammatory and oxidative stress responses with the subsequent cell death that occurs after OGD.

TRPM2 in ischemic stroke: Structure, molecular mechanisms, and drug intervention

Ischemic stroke has a high lethality rate worldwide, and novel treatments are limited. Calcium overload is considered to be one of the mechanisms of cerebral ischemia. Transient receptor potential melastatin 2 (TRPM2) is a reactive oxygen species (ROS)-sensitive calcium channel. Cerebral ischemia-induced TRPM2 activation triggers abnormal intracellular Ca²⁺ accumulation and cell death, which in turn causes irreversible brain damage. Thus, TRPM2 has emerged as a new therapeutic target for ischemic stroke. This review provides data on the expression, structure, and function of TRPM2 and illustrates its cellular and molecular mechanisms in ischemic stroke. Natural and synthetic TRPM2 inhibitors (both specific and nonspecific) are also summarized. The three-dimensional protein structure of TRPM2 has been identified, and we speculate that molecular simulation techniques will be essential for developing new drugs that block TRPM2 channels. These insights about TRPM2 may be the key to find potent therapeutic approaches for the treatment of ischemic stroke.

Molecular Biology of Atherosclerotic Ischemic Strokes

Among the causes of global death and disability, ischemic stroke (also known as cerebral ischemia) plays a pivotal role, by determining the highest number of worldwide mortality, behind cardiomyopathies, affecting 30 million people. The etiopathogenetic burden of a cerebrovascular accident could be brain ischemia (~80%) or intracranial hemorrhage (~20%). The most common site when ischemia occurs is the one is perfused by middle cerebral arteries. Worse prognosis and disablement consequent to brain damage occur in elderly patients or affected by neurological impairment, hypertension, dyslipidemia, and diabetes. Since, in the coming years, estimates predict an exponential increase of people who have diabetes, the disease mentioned above constitutes together with stroke a severe social and economic burden. In diabetic patients after an ischemic stroke, an exorbitant activation of inflammatory molecular pathways and ongoing inflammation is responsible for more severe brain injury and impairment, promoting the advancement of ischemic stroke and diabetes. Considering that the ominous prognosis of ischemic brain damage could by partially clarified by way of already known risk factors the auspice would be modifying poor outcome in the post-stroke phase detecting novel biomolecules associated with poor prognosis and targeting them for revolutionary therapeutic strategies.

Riding the tiger - physiological and pathological effects of superoxide and hydrogen peroxide generated in the mitochondrial matrix

Elevated mitochondrial matrix superoxide and/or hydrogen peroxide concentrations drive a wide range of physiological responses and pathologies. Concentrations of superoxide and hydrogen peroxide in the mitochondrial matrix are set mainly by rates of production, the activities of superoxide dismutase-2 (SOD2) and peroxiredoxin-3 (PRDX3), and by diffusion of hydrogen peroxide to the cytosol. These considerations can be used to generate criteria for assessing whether changes in matrix superoxide or hydrogen peroxide are both necessary and sufficient to drive redox signaling and pathology: is a phenotype affected by suppressing superoxide and hydrogen peroxide production; by manipulating the levels of SOD2, PRDX3 or mitochondria-targeted catalase; and by adding mitochondria-targeted SOD/catalase mimetics or mitochondria-targeted antioxidants? Is the pathology associated with variants in SOD2 and PRDX3 genes? Filtering the large literature on mitochondrial redox signaling using these criteria highlights considerable evidence that mitochondrial superoxide and hydrogen peroxide drive physiological responses involved in cellular stress management, including apoptosis, autophagy, propagation of endoplasmic reticulum stress, cellular senescence, HIF1α signaling, and immune responses. They also affect cell proliferation, migration, differentiation, and the cell cycle. Filtering the huge literature on pathologies highlights strong experimental evidence that 30-40 pathologies may be driven by mitochondrial matrix superoxide or hydrogen peroxide. These can be grouped into overlapping and interacting categories: metabolic, cardiovascular, inflammatory, and neurological diseases; cancer; ischemia/reperfusion injury; aging and its diseases; external insults, and genetic diseases. Understanding the involvement of mitochondrial matrix superoxide and hydrogen peroxide concentrations in these diseases can facilitate the rational development of appropriate therapies.

The role of astrocytes in oxidative stress of central nervous system: A mixed blessing

Central nervous system (CNS) maintains a high level of metabolism, which leads to the generation of large amounts of free radicals, and it is also one of the most vulnerable organs to oxidative stress. Emerging evidences have shown that, as the key homeostatic cells in CNS, astrocytes are deeply involved in multiple aspects of CNS function including oxidative stress regulation. Besides, the redox level in CNS can in turn affect astrocytes in morphology and function. The complex and multiple roles of astrocytes indicate that their correct performance is crucial for the normal functioning of the CNS, and its dysfunction may result in the occurrence and progression of various neurological disorders. To date, the influence of astrocytes in CNS oxidative stress is rarely reviewed. Therefore, in this review we sum up the roles of astrocytes in redox regulation and the corresponding mechanisms under both normal and different pathological conditions.

Inhibiting Caspase-12 Mediated Inflammasome Activation protects against Oxygen-Glucose Deprivation Injury in Primary Astrocytes

Stroke is one of the leading causes of death worldwide. Accumulating evidence suggests that NLRP3 inflammasome activation plays an important role in ischemic stroke injury. However, the existence of the NLRP3 inflammasome in astrocytes remains controversial. In this study, we demonstrated the presence of the NLRP3 inflammasome in primary mouse astrocytes and investigated the role of caspase-12 in NLRP3 inflammasome activation and cell injury in an in vitro astrocyte oxygen-glucose deprivation (OGD) model. Astrocytes exposed to 2, 3, and 4 h of OGD exhibited increased cell injury and apoptosis, and the protein levels of caspase-12, cleaved caspase-3, NLRP3 inflammasome components, and IL-1β were also significantly elevated. Interestingly, pretreatment with the caspase-12-specific inhibitor Z-ATAD-FMK attenuated cell injury and apoptosis and decreased the levels of NLRP3, caspase-1, IL-1β, and cleaved caspase-3 in the OGD group. In conclusion, Z-ATAD-FMK protected astrocytes against OGD-induced cell death and inhibited NLPR3-inflammasome activation. Our results indicate that caspase-12 and its potential regulation of NLRP3 inflammasome activation might be a promising target for treatment of ischemic stroke.

SOD2 Mediates Curcumin-Induced Protection against Oxygen-Glucose Deprivation/Reoxygenation Injury in HT22 Cells

Curcumin (Cur) induces neuroprotection against brain ischemic injury; however, the mechanism is still obscure. The aim of this study is to explore the potential neuroprotective mechanism of curcumin against oxygen-glucose deprivation/reoxygenation (OGD/R) injury in HT22 cells and investigate whether type-2 superoxide dismutase (SOD2) is involved in the curcumin-induced protection. In the present study, HT22 neuronal cells were treated with 3 h OGD plus 24 h reoxygenation to mimic ischemia/reperfusion injury. Compared with the normal cultured control group, OGD/R treatment reduced cell viability and SOD2 expression, decreased mitochondrial membrane potential (MMP) and mitochondrial complex I activity, damaged cell morphology, and increased lactic dehydrogenase (LDH) release, cell apoptosis, intracellular reactive oxygen species (ROS), and mitochondrial superoxide (P < 0.05). Meanwhile, coadministration of 100 ng/ml curcumin reduced the cell injury and apoptosis, inhibited intracellular ROS and mitochondrial superoxide accumulation, and ameliorated intracellular SOD2, cell morphology, MMP, and mitochondrial complex I activity. Downregulating the SOD2 expression by using siRNA, however, significantly reversed the curcumin-induced cytoprotection (P < 0.05). These findings indicated that curcumin induces protection against OGD/R injury in HT22 cells, and SOD2 protein may mediate the protection.

Ischemic stroke in neonatal and adult astrocytes

The objective of this paper is to review current information regarding astrocytes function after a stroke in neonatal and adult brain. Based on the current literature, there are some molecular differences related to blood brain barrier (BBB) homeostasis disruption, inflammation and reactive oxygen species (ROS) mediated injury between the immature and mature brain after an ischemic event. In particular, astrocytes, the main glial cells in brain, play a different role in neonatal and adult brain after stroke, as time course of glial activation is strongly age dependent. Moreover, the present review provides further insight into the therapeutic approaches of using neonatal and adult astrocytes after stroke. More research will be needed in order to translate them into an effective treatment against stroke, the second main cause of death and disability worldwide.

Involvement of d-amino acid oxidase in cerebral ischaemia induced by transient occlusion of the middle cerebral artery in mice

BACKGROUND AND PURPOSE

d-Amino acid oxidase (DAAO) is a flavine adenine dinucleotide-containing flavoenzyme and specifically catalyses oxidative deamination of d-amino acids. This study aimed to explore the association between increased cerebral DAAO expression or enzymic activity and the development of cerebral ischaemia.

EXPERIMENTAL APPROACH

A mouse model of transient (90 min) middle cerebral artery occlusion (MCAO) was established, and western blotting, enzymic activity assay, and fluorescent immunostaining techniques were used.

KEY RESULTS

The expression and enzymic activity of DAAO increased over time in the cortical peri-infarct area of the mice subjected to transient MCAO. The DAAO was specifically expressed in astrocytes, and its double immunostaining with the astrocytic intracellular marker, glial fibrillary acidic protein, in the cortical peri-infarct area was up-regulated following ischaemic insult, with peak increase on Day 5 after MCAO. Single intravenous injection of the specific and potent DAAO inhibitor Compound SUN reduced the cerebral DAAO enzymic activity and attenuated neuronal infarction and neurobehavioural deficits with optimal improvement apparent immediately after the MCAO procedure. The neuroprotective effect was dose dependent, with ED50 values of 3.9-4.5 mg·kg-1 . Intracerebroventricular injection of the DAAO gene silencer siRNA/DAAO significantly reduced cerebral DAAO expression and attenuated MCAO-induced neuronal infarction and behavioural deficits.

CONCLUSIONS AND IMPLICATIONS

Our results, for the first time, demonstrated that increased cerebral astrocytic DAAO expression and enzymic activity were causally associated with the development of neuronal destruction following ischaemic insults, suggesting that targeting cerebral DAAO could be a potential approach for treatment of neurological conditions following cerebral ischaemia.

Regional differences in the inflammatory and heat shock response in glia: implications for ALS

Preferential neuronal vulnerability is characteristic of several neurodegenerative diseases including the motor neuron disease amyotrophic lateral sclerosis (ALS). It is well established that glia play a critical role in ALS, but it is unknown whether regional differences in the ability of glia to support motor neurons contribute to the specific pattern of neuronal degeneration. In this study, using primary mixed glial cultures from different mouse CNS regions (spinal cord and cortex), we examined whether regional differences exist in key glial pathways that contribute to, or protect against, motor neuron degeneration. Specifically, we examined the NF-κB-mediated inflammatory pathway and the cytoprotective heat shock response (HSR). Glial cultures were treated with pro-inflammatory stimuli, tumour necrosis factor-ɑ/lipopolysaccharide or heat stressed to stimulate the inflammatory and HSR respectively. We found that spinal cord glia expressed more iNOS and produced more NO compared to cortical glia in response to inflammatory stimuli. Intriguingly, we found that expression of ALS-causing SOD1G93A did not elevate the levels of NO in spinal cord glia. However, activation of the stress-responsive HSR was attenuated in SOD1G93A cultures, with a reduced Hsp70 induction in response to stressful stimuli. Exposure of spinal cord glia to heat shock in combination with inflammatory stimuli reduced the activation of the inflammatory response. The results of this study suggest that impaired heat shock response in SOD1G93A glia may contribute to the exacerbated inflammatory reactions observed in ALS mice. Graphical abstract Mixed primary glial cultures were established from cortical and spinal cord regions of wild-type mice and mice expressing ALS-causing mutant human SOD1 and the inflammatory and heat shock responses were investigated in these cultures. In the absence of stress, all cultures appeared to have similar cellular composition, levels of inflammatory mediators and similar expression level of heat shock proteins. When stimulated, spinal cord glia were more reactive and activated the inflammatory pathway more readily than cortical glia; this response was similar in wild-type and SOD1G93A glial cultures. Although the heat shock response was similar in spinal cord and cortical glial, in SOD1G93A expressing glia from both the spinal cord and cortex, the induction of heat shock response was diminished. This impaired heat shock response in SOD1G93A glia may therefore contribute to the exacerbated inflammatory reactions observed in ALS mice.

Postinjury Inhibition of miR-181a Promotes Restoration of Hippocampal CA1 Neurons after Transient Forebrain Ischemia in Rats

The cellular and molecular mechanisms regulating postinjury neurogenesis in the adult hippocampus remain undefined. We have previously demonstrated that preinjury treatment with anti-microRNA (miR)-181a preserved neurons and prevented astrocyte dysfunction in the hippocampal cornu ammonis-1 (CA1) following transient forebrain ischemia. In the present study, we assessed postinjury treatment with anti-miR-181a on recovery of CA1 neurons following transient forebrain ischemia in rats. Stereotactic CA1 injection of miR-181a antagomir at either 2 h or 7 d postinjury resulted in improved restoration of CA1 measured at 28 d postinjury. Treatment with antagomir was associated with overexpression of the mir-181a target cell adhesion-associated, oncogene-related protein and enhanced expression of the neuroprogenitor cell marker doublecortin (DCX) in the CA1. Assessment of GFAP+ cell fate by Cre/Lox-mediated deletion demonstrated that some GFAP+ cells in CA1 exhibited de novo DCX expression in response to injury. In vitro experiments using primary neuronal stem cells confirmed that miR-181a inhibition augmented the expression of DCX and directed cellular differentiation toward a neuronal fate. These results suggest that miR-181a inhibition plays a central role in the restoration of CA1 neurons via augmentation of early latent neurogenic gene activation in neural progenitor cells, including some reactive astrocytes. Therapeutic interventions targeting this restorative process may represent a novel postinjury approach to improve clinical outcomes in survivors of forebrain ischemia.

FGF21 Protects Against Hypoxia Injury Through Inducing HSP72 in Cerebral Microvascular Endothelial Cells

Background: Fibroblast growth factor 21 (FGF21), a member of a family of atypical FGFs, functions as cytokine to control endocrinology and metabolism. Recently, the roles of FGF21 in cardio-cerebral-vascular diseases have been gradually uncovered. In the present study, we investigated the effect of FGF21 on bEnd.3 cerebral microvascular endothelial cells (CMECs) upon hypoxia stress.

Methods and Results: CMECs were cultured in the condition of 1% O₂ for 8 h to induce hypoxia stimuli. For FGF21 treatment, recombinant FGF21 (50 nM) was added into the culture medium. Various biomedical assays were used to evaluate the hypoxia-induced injury in CMECs. Under normoxia condition, FGF21 had no obvious effect on cell viability and did not cause any cytotoxicity on CMECs. Under hypoxia condition, FGF21 significantly attenuated the hypoxia-induced injury, evidenced by the influences of FGF21 on CMEC viability and LDH release. TUNEL staining assay and immunoblotting of caspase-3 showed that FGF21 reduced hypoxia-induced apoptosis in CMECs. Mechanistically, FGF21 treatment compromised the hypoxia-induced changes of reactive oxygen species, malondialdehyde, total antioxidant activity, and total superoxide dismutase levels. FGF21 administration decreased hypoxia-induced matrix metalloprotein 3 and matrix metalloprotein 2/9 activity in CMECs. Activities of cyclooxygenase-2 and NF-κB-p65, two pro-inflammatory factors, were also upregulated by hypoxia but suppressed by FGF21. At last, we found that FGF21 increased heat shock protein family A member 1A (HSP72) mRNA and protein expression. Blockade of HSP72 by a pharmacological inhibitor VER155008 or specific siRNA-mediated knockdown abrogated the protection of FGF21 against hypoxia in CMECs.

Conclusion: These data demonstrate that FGF21 protects against hypoxia stress-induced injury in CMECs by inducing HSP72 expression, suggesting a therapeutic value of FGF21 in hypoxia-related brain diseases such as ischemic stroke and acute mountain sickness.

Stem cell-based cell therapy for neuroprotection in stroke: A review

Neurological disorders, such as stroke, are triggered by a loss of neurons and glial cells. Ischemic stroke remains a substantial problem for industrialized countries. Over the previous few decades our understanding about the pathophysiology of stroke has enhanced, nevertheless, more awareness is required to advance the field of stroke recovery. Existing therapies are incapable to adequately relief the disease outcome and are not appropriate to all patients. Meanwhile, the majority of patients continue to show neurological deficits even subsequent effective thrombolysis, recuperative therapies are immediately required that stimulate brain remodeling and repair once stroke damage has happened. Cell therapy is emergent as a hopeful new modality for increasing neurological recovery in ischemic stroke. Numerous types of stem cells from various sources have been identified and their possibility and efficiency for the treatment of stroke have been investigated. Stem cell therapy in patients with stroke using adult stem cells have been first practiced in clinical trials since 15 years ago. Even though stem cells have revealed a hopeful role in ischemic stroke in investigational studies besides early clinical pilot studies, cellular therapy in human is still at a primary stage. In this review, we summarize the types of stem cells, various delivery routes, and clinical application of stem cell-based therapy for stroke treatment.

Chick Embryo: A Preclinical Model for Understanding Ischemia-Reperfusion Mechanism

Ischemia-reperfusion (I/R)-related disorders, such as stroke, myocardial infarction, and peripheral vascular disease, are among the most frequent causes of disease and death. Tissue injury or death may result from the initial ischemic insult, primarily determined by the magnitude and duration of the interruption in blood supply and then by the subsequent reperfusion-induced damage. Various in vitro and in vivo models are currently available to study I/R mechanism in the brain and other tissues. However, thus far, no in ovo I/R model has been reported for understanding the I/R mechanisms and for faster drug screening. Here, we developed an in ovo Hook model of I/R by occluding and releasing the right vitelline artery of a chick embryo at 72 h of development. To validate the model and elucidate various underlying survival and death mechanisms, we employed imaging (Doppler blood flow imaging), biochemical, and blotting techniques and evaluated the cell death mechanism: autophagy and inflammation caused by I/R. In conclusion, the present model is useful in parallel with established in vitro and in vivo I/R models to understand the mechanisms of I/R development and its treatment.

Potentially Common Therapeutic Targets for Multiple Sclerosis and Ischemic Stroke

Ischemic stroke (IS) and multiple sclerosis (MS) are two pathologies of the central nervous system (CNS). At the first look, this appears to be the only similarity between the two diseases, as they seem quite different. Indeed IS has an acute onset compared to MS which develops chronically; IS is consecutive to blood clot migrating to cerebral blood vessels or decrease in cerebral blood flow following atherosclerosis or decreases in cardiac output, whereas MS is an immune disease associated with neurodegeneration. However, both pathologies share similar pathologic pathways and treatments used in MS have been the object of studies in IS. In this mini-review we will discuss similarities between IS and MS on astrocytes and neuroinflammation hallmarks emphasizing the potential for treatments.

Hsp72 protects against liver injury via attenuation of hepatocellular death, oxidative stress, and JNK signaling

BACKGROUND & AIMS

Heat shock protein (Hsp) 72 is a molecular chaperone that has broad cytoprotective functions and is upregulated in response to stress. To determine its hepatic functions, we studied its expression in human liver disorders and its biological significance in newly generated transgenic animals.

METHODS

Double transgenic mice overexpressing Hsp72 (gene Hspa1a) under the control of a tissue-specific tetracycline-inducible system (Hsp72-LAP mice) were produced. Acute liver injury was induced by a single injection of acetaminophen (APAP). Feeding with either a methionine choline-deficient (MCD; 8 weeks) or a 3,5-diethoxycarbonyl-1,4-dihydrocollidine-supplemented diet (DDC; 12 weeks) was used to induce lipotoxic injury and Mallory-Denk body (MDB) formation, respectively. Primary hepatocytes were treated with palmitic acid.

RESULTS

Patients with non-alcoholic steatohepatitis and chronic hepatitis C infection displayed elevated HSP72 levels. These levels increased with the extent of hepatic inflammation and HSP72 expression was induced after treatment with either interleukin (IL)-1β or IL-6. Hsp72-LAP mice exhibited robust, hepatocyte-specific Hsp72 overexpression. Primary hepatocytes from these animals were more resistant to isolation-induced stress and Hsp72-LAP mice displayed lower levels of hepatic injury in vivo. Mice overexpressing Hsp72 had fewer APAP protein adducts and were protected from oxidative stress and APAP-/MCD-induced cell death. Hsp72-LAP mice and/or hepatocytes displayed significantly attenuated Jnk activation. Overexpression of Hsp72 did not affect steatosis or the extent of MDB formation.

CONCLUSIONS

Our results demonstrate that HSP72 induction occurs in human liver disease, thus, HSP72 represents an attractive therapeutic target owing to its broad hepatoprotective functions.

LAY SUMMARY

HSP72 constitutes a stress-inducible, protective protein. Our data demonstrate that it is upregulated in patients with chronic hepatitis C and non-alcoholic steatohepatitis. Moreover, Hsp72-overexpressing mice are protected from various forms of liver stress.

Hypothermia and brain inflammation after cardiac arrest

The cessation (ischemia) and restoration (reperfusion) of cerebral blood flow after cardiac arrest (CA) induce inflammatory processes that can result in additional brain injury. Therapeutic hypothermia (TH) has been proven as a brain protective strategy after CA. In this article, the underlying pathophysiology of ischemia-reperfusion brain injury with emphasis on the role of inflammatory mechanisms is reviewed. Potential targets for immunomodulatory treatments and relevant effects of TH are also discussed. Further studies are needed to delineate the complex pathophysiology and interactions among different components of immune response after CA and identify appropriate targets for clinical investigations.

Curcumin Inhibits Monocyte Chemoattractant Protein-1 Expression in TNF-α induced Astrocytes Through AMPK Pathway

Curcumin, a phenolic pigment, plays an inhibitory role in astrocytes activation, a key step for neuropathic pain (NP). The present study aimed to investigate the mechanism behind the therapeutic effect of Curcumin on NP in vitro. Specifically, we investigated the inhibitory effect of Curcumin on tumor necrosis factor-α (TNF-α)-induced astrocyte migration. We also studied the effects of Curcumin on monocyte chemoattractant protein-1(MCP-1) expression and activity, as well as super oxide dismutase-2 (SOD2) expression and activity in TNF-α-induced astrocytes. Additionally, we investigated whether the adenosine-monophosphate-activated protein kinase signaling (AMPK) pathway was involved in this process. Our data demonstrated that Curcumin inhibited TNF-α-induced astrocytes migration, decreased MCP-1 expression, and up-regulated SOD2 expression in TNF-α-induced astrocytes in vitro. Our study also indicated that this process was mediated through the AMPK signaling pathway, as addition of Curcumin significantly increased the level of phosphorylated AMPK protein. Furthermore, the specific AMPK activator AICAR (5-aminoimidazole-4-carboxamide 1-D-ribofuranoside) mimicked the effects of Curcumin, whereas a selective AMPK inhibitor Compound C (also called dorsomorphin) partially blocked its function. These results could shed light on understanding of the molecular basis for the inhibition of Curcumin on MCP-1 expression during the process of astrocyte activation, and provide a molecular mechanism for using Curcumin in neuropathic pain.

Expression of functional inhibitory neurotransmitter transporters GlyT1, GAT-1, and GAT-3 by astrocytes of inferior colliculus and hippocampus

Neuronal inhibition is mediated by glycine and/or GABA. Inferior colliculus (IC) neurons receive glycinergic and GABAergic inputs, whereas inhibition in hippocampus (HC) predominantly relies on GABA. Astrocytes heterogeneously express neurotransmitter transporters and are expected to adapt to the local requirements regarding neurotransmitter homeostasis. Here we analyzed the expression of inhibitory neurotransmitter transporters in IC and HC astrocytes using whole-cell patch-clamp and single-cell reverse transcription-PCR. We show that most astrocytes in both regions expressed functional glycine transporters (GlyTs). Activation of these transporters resulted in an inward current (I_Gly) that was sensitive to the competitive GlyT1 agonist sarcosine. Astrocytes exhibited transcripts for GlyT1 but not for GlyT2. Glycine did not alter the membrane resistance (R_M) arguing for the absence of functional glycine receptors (GlyRs). Thus, I_Gly was mainly mediated by GlyT1. Similarly, we found expression of functional GABA transporters (GATs) in all IC astrocytes and about half of the HC astrocytes. These transporters mediated an inward current (I_GABA) that was sensitive to the competitive GAT-1 and GAT-3 antagonists NO711 and SNAP5114, respectively. Accordingly, transcripts for GAT-1 and GAT-3 were found but not for GAT-2 and BGT-1. Only in hippocampal astrocytes, GABA transiently reduced R_M demonstrating the presence of GABA_A receptors (GABA_ARs). However, I_GABA was mainly not contaminated by GABA_AR-mediated currents as R_M changes vanished shortly after GABA application. In both regions, I_GABA was stronger than I_Gly. Furthermore, in HC the I_GABA/I_Gly ratio was larger compared to IC. Taken together, our results demonstrate that astrocytes are heterogeneous across and within distinct brain areas. Furthermore, we could show that the capacity for glycine and GABA uptake varies between both brain regions.

Effects of over-expression of SOD2 in bone marrow-derived mesenchymal stem cells on traumatic brain injury

Intravenous administration of bone marrow-derived mesenchymal stem cells (BM-MSCs) has been shown to promote nerve cell regeneration following traumatic brain injury (TBI). As the anti-oxidant defense systems in neuronal tissue including superoxide dismutase 2 (SOD2) are crucial to defend cell against oxidative stress. We proposed a new stratege to increase the therapeutic effect of MSCs by preventing cells death from oxidative stress. We overexpressed SOD2 in BM-MSCs, transplanted these MSCs into TBI model mice, assessed the protective effect of SOD2 against oxidation-induced apoptosis in BM-MSCs both in vitro and in vivo, evaluated brain functional recovery by the rotarod behavioral test, and tested the oxidation status of TBI mice brain after BM-MSCs transplantation by monitoring the superoxide dismutase, glutathione and malonaldehyde level. We found over-expression of SOD2 protected BM-MSCs from H₂O₂-induced cell apoptosis. Injection of SOD2 over-expressed BM-MSCs attenuated neuro-inflammation in the ipsilateral cortex of TBI mice, and protected TBI mice against loss of blood-brain barrier integrity. Furthermore, the rotarod behavioral test showed functional recovery of TBI mice after MSC treatment. Our experiments indicated that SOD2-over-expressed BM-MSCs have an improved therapeutic effect on brain injury treatment in TBI mice.

Inhibition of miR-181a protects female mice from transient focal cerebral ischemia by targeting astrocyte estrogen receptor-α

Whether the effect of miR-181a is sexually dimorphic in stroke is unknown. Prior work showed protection of male mice with miR-181a inhibition. Estrogen receptor-α (ERα) is an identified target of miR181 in endometrium. Therefore we investigated the separate and joint effects of miR-181a inhibition and 17β-estradiol (E2) replacement after ovariectomy. Adult female mice were ovariectomized and implanted with an E2- or vehicle-containing capsule for 14d prior to 1h middle cerebral artery occlusion (MCAO). Each group received either miR-181a antagomir or mismatch control by intracerebroventricular injection 24h before MCAO. After MCAO neurologic deficit and infarct volume were assessed. Primary male and female astrocyte cultures were subjected to glucose deprivation with miR-181a inhibitor or transfection control, and E2 or vehicle control, with/without ESRα knockdown with small interfering RNA. Cell death was assessed by propidium iodide staining, and lactate dehydrogenase assay. A miR-181a/ERα target site blocker (TSB), with/without miR-181a mimic, was used to confirm targeting of ERα by miR-181a in astrocytes. Individually, miR-181a inhibition or E2 decreased infarct volume and improved neurologic score in female mice, and protected male and female astrocyte cultures. Combined miR-181a inhibition plus E2 afforded greater protection of female mice and female astrocyte cultures, but not in male astrocyte cultures. MiR-181a inhibition only increased ERα levels in vivo and in female cultures, while ERα knockdown with siRNA increased cell death in both sexes. Treatment with ERα TSB was strongly protective in both sexes. In conclusion, the results of the present study suggest miR-181a inhibition enhances E2-mediated stroke protection in females in part by augmenting ERα production, a mechanism detected in female mice and female astrocytes. Sex differences were observed with combined miR-181a inhibition/E2 treatment, and miR-181a targeting of ERα.

Emerging Roles of microRNAs in Ischemic Stroke: As Possible Therapeutic Agents

Stroke is one of the leading causes of death and physical disability worldwide. The consequences of stroke injuries are profound and persistent, causing in considerable burden to both the individual patient and society. Current treatments for ischemic stroke injuries have proved inadequate, partly owing to an incomplete understanding of the cellular and molecular changes that occur following ischemic stroke. MicroRNAs (miRNA) are endogenously expressed RNA molecules that function to inhibit mRNA translation and have key roles in the pathophysiological processes contributing to ischemic stroke injuries. Potential therapeutic areas to compensate these pathogenic processes include promoting angiogenesis, neurogenesis and neuroprotection. Several miRNAs, and their target genes, are recognized to be involved in these recoveries and repair mechanisms. The capacity of miRNAs to simultaneously regulate several target genes underlies their unique importance in ischemic stroke therapeutics. In this Review, we focus on the role of miRNAs as potential diagnostic and prognostic biomarkers, as well as promising therapeutic agents in cerebral ischemic stroke.

Pathogenic mechanisms following ischemic stroke

Stroke is the second most common cause of death and the leading cause of disability worldwide. Brain injury following stroke results from a complex series of pathophysiological events including excitotoxicity, oxidative and nitrative stress, inflammation, and apoptosis. Moreover, there is a mechanistic link between brain ischemia, innate and adaptive immune cells, intracranial atherosclerosis, and also the gut microbiota in modifying the cerebral responses to ischemic insult. There are very few treatments for stroke injuries, partly owing to an incomplete understanding of the diverse cellular and molecular changes that occur following ischemic stroke and that are responsible for neuronal death. Experimental discoveries have begun to define the cellular and molecular mechanisms involved in stroke injury, leading to the development of numerous agents that target various injury pathways. In the present article, we review the underlying pathophysiology of ischemic stroke and reveal the intertwined pathways that are promising therapeutic targets.

Astrocyte-specific insulin-like growth factor-1 gene transfer in aging female rats improves stroke outcomes

Middle aged female rats sustain larger stroke infarction and disability than younger female rats. This older group also shows age-related reduction of insulin like growth factor (IGF)-1 in serum and in astrocytes, a cell type necessary for poststroke recovery. To determine the impact of astrocytic IGF-1 for ischemic stroke, these studies tested the hypothesis that gene transfer of IGF-1 to astrocytes will improve stroke outcomes in middle aged female rats. Middle aged (10-12 month old), acyclic female rats were injected with recombinant adeno-associated virus serotype 5 (AAV5) packaged with the coding sequence of the human (h)IGF-1 gene downstream of an astrocyte-specific promoter glial fibrillary acidic protein (GFAP) (AAV5-GFP-hIGF-1) into the striatum and cortex. The AAV5-control consisted of an identical shuttle vector construct without the hIGF-1 gene (AAV5-GFAP-control). Six to eight weeks later, animals underwent transient (90 min) middle cerebral artery occlusion via intraluminal suture. While infarct volume was not altered, AAV5-GFAP-hIGF-1 treatment significantly improved blood pressure and neurological score in the early acute phase of stroke (2 days) and sensory-motor performance at both the early and late (5 days) acute phase of stroke. AAV5-GFAP-hIGF-1 treatment also reduced circulating serum levels of GFAP, a biomarker for blood brain barrier permeability. Flow cytometry analysis of immune cells in the brain at 24 hr poststroke showed that AAV5-GFAP-hIGF-1 altered the type of immune cells trafficked to the ischemic hemisphere, promoting an anti-inflammatory profile. Collectively, these studies show that targeted enhancement of IGF-1 in astrocytes of middle-aged females improves stroke-induced behavioral impairment and neuroinflammation.

Soluble cpg15 from Astrocytes Ameliorates Neurite Outgrowth Recovery of Hippocampal Neurons after Mouse Cerebral Ischemia

The present study focuses on the function of cpg15, a neurotrophic factor, in ischemic neuronal recovery using transient global cerebral ischemic (TGI) mouse model and oxygen-glucose deprivation (OGD)-treated primary cultured cells. The results showed that expression of cpg15 proteins in astrocytes, predominantly the soluble form, was significantly increased in mouse hippocampus after TGI and in the cultured astrocytes after OGD. Addition of the medium from the cpg15-overexpressed astrocytic culture into the OGD-treated hippocampal neuronal cultures reduces the neuronal injury, whereas the recovery of neurite outgrowths of OGD-injured neurons was prevented when cpg15 in the OGD-treated astrocytes was knocked down, or the OGD-treated-astrocytic medium was immunoadsorbed by cpg15 antibody. Furthermore, lentivirus-delivered knockdown of cpg15 expression in mouse hippocampal astrocytes diminishes the dendritic branches and exacerbates injury of neurons in CA1 region after TGI. In addition, treatment with inhibitors of MEK1/2, PI3K, and TrkA decreases, whereas overexpression of p-CREB, but not dp-CREB, increases the expression of cpg15 in U118 or primary cultured astrocytes. Also, it is observed that the Flag-tagged soluble cpg15 from the astrocytes transfected with Flag-tagged cpg15-expressing plasmids adheres to the surface of neuronal bodies and the neurites. In conclusion, our results suggest that the soluble cpg15 from astrocytes induced by ischemia could ameliorate the recovery of the ischemic-injured hippocampal neurons via adhering to the surface of neurons. The upregulated expression of cpg15 in astrocytes may be activated via MAPK and PI3K signal pathways, and regulation of CREB phosphorylation.SIGNIFICANCE STATEMENT Neuronal plasticity plays a crucial role in the amelioration of neurological recovery of ischemic injured brain, which remains a challenge for clinic treatment of cerebral ischemia. cpg15 as a synaptic plasticity-related factor may participate in promoting the recovery process; however, the underlying mechanisms are still largely unknown. The objective of this study is to reveal the function and mechanism of neuronal-specific cpg15 expressed in astrocytes after ischemia induction, in promoting the recovery of injured neurons. Our findings provided new mechanistic insight into the neurological recovery, which might help develop novel therapeutic options for cerebral ischemia via astrocytic-targeting interference of gene expression.

TRPC3/6/7 Knockdown Protects the Brain from Cerebral Ischemia Injury via Astrocyte Apoptosis Inhibition and Effects on NF-кB Translocation

Ischemia contributes significantly to morbidity and mortality associated with many common neurological diseases. Calcium overload is an important mechanism of cerebral ischemia and reperfusion (I/R) injury. Despite decades of intense research, an effective beneficial treatment of stroke remains limited; few therapeutic strategies exist to combat the consequences of cerebral ischemia. Traditionally, a "neurocentric" view has dominated research in this field. Evidence is now accumulating that glial cells, especially astrocytes, play an important role in the pathophysiology of cerebral ischemia. Here, we show that transient receptor potential (TRP)C3/6/7 knockout (KO) mice subjected to an I/R procedure demonstrate ameliorated brain injury (infract size), compared to wild-type (WT) control animals. This is accompanied by reduction of NF-кB phosphorylation and an increase in protein kinase B (AKT) phosphorylation in I/R-injured brain tissues in TRPC3/6/7 KO mice. Also, the expression of pro-apoptotic protein Bcl-2 associated X (Bax) is down-regulated and that of anti-apoptotic protein Bcl-2 is upregulated in TRPC3/6/7^-/- mice. Astrocytes isolated from TRPC3/6/7 KO mice and subjected to oxygen/glucose deprivation and subsequent reoxygenation (OGD-R, mimicking in vivo I/R injury) also exhibit enhanced Bcl-2 expression, reduced Bax expression, enhanced AKT phosphorylation, and reduced NF-кB phosphorylation. Furthermore, apoptotic rates of TRPC3/6/7 KO astrocytes cultured in OGD-R conditions were reduced significantly compared to WT control. These findings suggest TRPC3/6/7 channels play a detrimental role in brain I/R injury. Deletion of these channels can interfere with the activation of NF-кB (pro-apoptotic), promote activation of AKT (anti-apoptotic), and ultimately, ameliorate brain damage via inhibition of astrocyte apoptosis after cerebral ischemia/reperfusion injury.

Targeting Glial Mitochondrial Function for Protection from Cerebral Ischemia: Relevance, Mechanisms, and the Role of MicroRNAs

Astrocytes and microglia play crucial roles in the response to cerebral ischemia and are effective targets for stroke therapy in animal models. MicroRNAs (miRs) are important posttranscriptional regulators of gene expression that function by inhibiting the translation of select target genes. In astrocytes, miR expression patterns regulate mitochondrial function in response to oxidative stress via targeting of Bcl2 and heat shock protein 70 family members. Mitochondria play an active role in microglial activation, and miRs regulate the microglial neuroinflammatory response. As endogenous miR expression patterns can be altered with exogenous mimics and inhibitors, miR-targeted therapies represent a viable intervention to optimize glial mitochondrial function and improve clinical outcome following cerebral ischemia. In the present article, we review the role that astrocytes and microglia play in neuronal function and fate following ischemic stress, discuss the relevance of mitochondria in the glial response to injury, and present current evidence implicating miRs as critical regulators in the glial mitochondrial response to cerebral ischemia.

Glycyrrhizin protects against focal cerebral ischemia via inhibition of T cell activity and HMGB1-mediated mechanisms

Background

Glycyrrhizin (Gly) protects against brain injury induced by stroke. We studied whether Gly achieves its protection by inhibiting T cell activity and high-mobility group box 1 (HMGB1) release in the ischemic brain.

Methods

Stroke was induced by transient middle cerebral artery occlusion in rats and mice. Gly was injected intraperitoneally before or after stroke. We measured infarction, neuroinflammatory cells, gene expressions of interferon-γ (IFNγ), IL-4, and IL-10 in CD4 T cells, HMGB1 release, and T cell proliferation in cultured splenocytes.

Results

Gly treatment reduced infarctions and neuroinflammation characterized by the infiltration of CD68-positive macrophages and myeloperoxidase-positive neutrophils, which corresponds to a reduction in the number of T cells and their subsets, CD4 and CD8 T cells, in the ischemic brain, as measured by flow cytometry. Unlike in wild-type animals, Gly did not offer protection in nude rats and severe combined immunodeficient (SCID) mice who had no T cells, while Gly reduced infarction in both nude rats and SCID mice whose T cells were reconstituted, suggesting that T cells should be the target of Gly. In addition, Gly administration inhibited T cell proliferation stimulated by ConA in in vitro assays and inhibited HMGB1 release from the ischemic brain. Furthermore, Gly attenuated gene expression of IFNγ, but not IL-4 and IL-10 in CD4 T cells. Lastly, HMGB1 promoted T cell proliferation stimulated by ConA, which was inhibited by the addition of Gly.

Conclusions

Gly blocks infarction by inhibiting IFNγ-mediated T cell activity, which is at least partly modulated by HMGB1 activity.

miR-29a differentially regulates cell survival in astrocytes from cornu ammonis 1 and dentate gyrus by targeting VDAC1

Neurons in the cornu ammonis 1 (CA1) region of the hippocampus are vulnerable to cerebral ischemia, while dentate gyrus (DG) neurons are more resistant. This effect is mediated by local astrocytes, and may reflect differences in subregional hippocampal expression of miR-29a. We investigated the role of miR-29a on survival of hippocampal astrocytes cultured selectively from CA1 and DG in response to glucose deprivation (GD). CA1 astrocytes exhibited more cell death and a greater decrease in miR-29a than DG astrocytes. A reciprocal change was observed in the mitochondrial voltage dependent cation channel-1 (VDAC1), a regulator of mitochondria and target of miR-29a. In CA1 astrocytes, increasing miR-29a decreased VDAC1 and improved cell survival, while knockdown of VDAC1 improved survival. Finally, the protective effect of miR-29a was eliminated by inhibition of miR-29a/VDAC1 binding. These findings suggest that the selective vulnerability of the CA1 to injury may be due in part to a limited miR-29a response in CA1 astrocytes, allowing a greater increase in VDAC1-mediated cellular dysfunction in CA1 astrocytes.

Astrocytes as new targets to improve cognitive functions

Astrocytes are now viewed as key elements of brain wiring as well as neuronal communication. Indeed, they not only bridge the gap between metabolic supplies by blood vessels and neurons, but also allow fine control of neurotransmission by providing appropriate signaling molecules and insulation through a tight enwrapping of synapses. Recognition that astroglia is essential to neuronal communication is nevertheless fairly recent and the large body of evidence dissecting such role has focused on the synaptic level by identifying neuro- and gliotransmitters uptaken and released at synaptic or extrasynaptic sites. Yet, more integrated research deciphering the impact of astroglial functions on neuronal network activity have led to the reasonable assumption that the role of astrocytes in supervising synaptic activity translates in influencing neuronal processing and cognitive functions. Several investigations using recent genetic tools now support this notion by showing that inactivating or boosting astroglial function directly affects cognitive abilities. Accordingly, brain diseases resulting in impaired cognitive functions have seen their physiopathological mechanisms revisited in light of this primary protagonist of brain processing. We here provide a review of the current knowledge on the role of astrocytes in cognition and in several brain diseases including neurodegenerative disorders, psychiatric illnesses, as well as other conditions such as epilepsy. Potential astroglial therapeutic targets are also discussed.

Targeted activation of CREB in reactive astrocytes is neuroprotective in focal acute cortical injury

The clinical challenge in acute injury as in traumatic brain injury (TBI) is to halt the delayed neuronal loss that occurs hours and days after the insult. Here we report that the activation of CREB-dependent transcription in reactive astrocytes prevents secondary injury in cerebral cortex after experimental TBI. The study was performed in a novel bitransgenic mouse in which a constitutively active CREB, VP16-CREB, was targeted to astrocytes with the Tet-Off system. Using histochemistry, qPCR, and gene profiling we found less neuronal death and damage, reduced macrophage infiltration, preserved mitochondria, and rescued expression of genes related to mitochondrial metabolism in bitransgenic mice as compared to wild type littermates. Finally, with meta-analyses using publicly available databases we identified a core set of VP16-CREB candidate target genes that may account for the neuroprotective effect. Enhancing CREB activity in astrocytes thus emerges as a novel avenue in acute brain post-injury therapeutics.

Paradoxical Roles of Antioxidant Enzymes: Basic Mechanisms and Health Implications

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from aerobic metabolism, as a result of accidental electron leakage as well as regulated enzymatic processes. Because ROS/RNS can induce oxidative injury and act in redox signaling, enzymes metabolizing them will inherently promote either health or disease, depending on the physiological context. It is thus misleading to consider conventionally called antioxidant enzymes to be largely, if not exclusively, health protective. Because such a notion is nonetheless common, we herein attempt to rationalize why this simplistic view should be avoided. First we give an updated summary of physiological phenotypes triggered in mouse models of overexpression or knockout of major antioxidant enzymes. Subsequently, we focus on a series of striking cases that demonstrate "paradoxical" outcomes, i.e., increased fitness upon deletion of antioxidant enzymes or disease triggered by their overexpression. We elaborate mechanisms by which these phenotypes are mediated via chemical, biological, and metabolic interactions of the antioxidant enzymes with their substrates, downstream events, and cellular context. Furthermore, we propose that novel treatments of antioxidant enzyme-related human diseases may be enabled by deliberate targeting of dual roles of the pertaining enzymes. We also discuss the potential of "antioxidant" nutrients and phytochemicals, via regulating the expression or function of antioxidant enzymes, in preventing, treating, or aggravating chronic diseases. We conclude that "paradoxical" roles of antioxidant enzymes in physiology, health, and disease derive from sophisticated molecular mechanisms of redox biology and metabolic homeostasis. Simply viewing antioxidant enzymes as always being beneficial is not only conceptually misleading but also clinically hazardous if such notions underpin medical treatment protocols based on modulation of redox pathways.

Cell-Permeable Peptide Targeting the Nrf2-Keap1 Interaction: A Potential Novel Therapy for Global Cerebral Ischemia

The current study examined efficacy of a small Tat (trans-activator of transcription)-conjugated peptide activator of the Nrf2 (nuclear factor-E2-related factor-2) antioxidant/cell-defense pathway as a potential injury-specific, novel neuroprotectant against global cerebral ischemia (GCI). A competitive peptide, DEETGE-CAL-Tat, was designed to facilitate Nrf2 activation by disrupting interaction of Nrf2 with Keap1 (kelch-like ECH-associated protein 1), a protein that sequesters Nrf2 in the cytoplasm and thereby inactivates it. The DEETGE-CAL-Tat peptide contained the critical sequence DEETGE for the Nrf2-Keap1 interaction, the cell transduction domain of the HIV-Tat protein, and the cleavage sequence of calpain, which is sensitive to Ca(2+) increase and allows injury-specific activation of Nrf2. Using an animal model of GCI, we demonstrated that pretreatment with the DEETGE-CAL-Tat peptide markedly decreased Nrf2 interaction with Keap1 in the rat hippocampal CA1 region after GCI, and enhanced Nrf2 nuclear translocation and DNA binding. The DEETGE-CAL-Tat peptide also induced Nrf2 antioxidant/cytoprotective target genes, reduced oxidative stress, and induced strong neuroprotection and marked preservation of hippocampal-dependent cognitive function after GCI. These effects were specific as control peptides lacked neuroprotective ability. Intriguingly, the DEETGE-CAL-Tat peptide effects were also injury specific, as it had no effect upon neuronal survival or cognitive performance in sham nonischemic animals. Of significant interest, peripheral, postischemia administration of the DEETGE-CAL-Tat peptide from days 1-9 after GCI also induced robust neuroprotection and strongly preserved hippocampal-dependent cognitive function. Based on its robust neuroprotective and cognitive-preserving effects, and its unique injury-specific activation properties, the DEETGE-CAL-Tat peptide represents a novel, and potentially promising new therapeutic modality for the treatment of GCI.

SIGNIFICANCE STATEMENT

The current study demonstrates that DEETGE-CAL-Tat, a novel peptide activator of a key antioxidant gene transcription pathway in the hippocampus after global cerebral ischemia, can exert robust neuroprotection and preservation of cognitive function. A unique feature of the peptide is that its beneficial effects are injury specific. This feature is attractive as it targets drug activation specifically in the site of injury, and likely would lead to a reduction of undesirable side effects if translatable to the clinic. Due to its injury-specific activation, robust neuroprotection, and cognitive-preserving effects, this novel peptide may represent a much-needed therapeutic advance that could have efficacy in the treatment of global cerebral ischemia.