Astrocytes in cerebral ischemic injury: morphological and general considerations

Ca(2+) signaling in astrocytes and its role in ischemic stroke

Astrocytes have been found to play important roles in physiology being fundamental for ionic homeostasis and glutamate clearance from the synaptic cleft by their plasma membrane glutamate transporters. Astrocytes are electrically non-excitable, but they exhibit Ca(2+) signaling, which now has been demonstrated to serve as an indirect mediator of neuron-glia bidirectional interactions through gliotransmission via tripartite synapses and to modulate synaptic function and plasticity. Spontaneous astrocytic Ca(2+) signaling was observed in vivo. Intercellular Ca(2+) waves in astrocytes can be evoked by a variety of stimulations. Astrocytes are critically involved in many pathological conditions including ischemic stroke. For example, it is well known that astrocytes become reactive and form glial scar after stroke. In animal models of some brain disorders, astrocytes have been shown to exhibit enhanced Ca(2+) excitability featured as regenerative intercellular Ca(2+) waves. This chapter briefly summarizes astrocytic Ca(2+) signaling pathways under normal conditions and in experimental in vitro and in vivo ischemic models. It discusses the possible mechanisms and therapeutic implication underlying the enhanced astrocytic Ca(2+) excitability in stroke.

Optimal electroacupuncture frequency for maintaining astrocyte structural integrity in cerebral ischemia

The astrocyte is a critical regulator of neuronal survival after ischemic brain injury. Electroacupuncture may be an effective therapy for cerebral ischemia, as electroacupuncture frequency can affect the structural integrity of astrocytes. In this study, a rat model of middle cerebral artery occlusion established using the modified thread embolism method was treated with electroacupuncture of the bilateral Quchi (LI11) and Zusanli (ST36) at 15, 30, and 100 Hz frequencies. Behavioral testing, immunohistochemistry and electron microscopy were used to explore the effect of these electroacupuncture frequencies used on maintaining the structural integrity of ischemic brain tissue. Compared with the model and 100 Hz electroacupuncture groups, the 15 and 30 Hz electroacupuncture groups displayed decreased neurological deficit scores, as evaluated by the "Longa" method, significantly increased glial fibrillary acidic protein expression, and alleviated ultrastructural damage of astrocytes at the edge of the infarct. Our experimental findings indicate that 15 and 30 Hz electroacupuncture intervention can favorably maintain the structural integrity of astrocytes and play a protective role in cerebral ischemic injury. Astrocyte structural integrity may be the mechanism underlying acupuncture production of ischemic tolerance.

Cerebral malaria: gamma-interferon redux

There are two theories that seek to explain the pathogenesis of cerebral malaria, the mechanical obstruction hypothesis and the immunopathology hypothesis. Evidence consistent with both ideas has accumulated from studies of the human disease and experimental models. Thus, some combination of these concepts seems necessary to explain the very complex pattern of changes seen in cerebral malaria. The interactions between malaria parasites, erythrocytes, the cerebral microvascular endothelium, brain parenchymal cells, platelets and microparticles need to be considered. One factor that seems able to knit together much of this complexity is the cytokine interferon-gamma (IFN-γ). In this review we consider findings from the clinical disease, in vitro models and the murine counterpart of human cerebral malaria in order to evaluate the roles played by IFN-γ in the pathogenesis of this often fatal and debilitating condition.

Effects of activated protein C on the size of modeled ischemic focus and morphometric parameters of neurons and neuroglia in its perifocal zone

The effects of activated protein C (APC) on the quantitative parameters of neurons and neuroglia in the perifocal zone of infarction induced in the left hemispheric cortex were studied in two groups of rats. Group 1 animals served as control (control infarction). Group 2 rats were injected with APC (50 μg/kg) in the right lateral cerebral ventricle 3 h after infarction was induced, and after 72 h the infarction size was evaluated and the neurons and neuroglia in the perifocal zone were counted. APC reduced the infarction size 2.5 times in comparison with the control and reduced by 16% the neuronal death in the perifocal zone layer V, causing no appreciable changes in layer III, and did not change the size of neuronal bodies but increased (by 11%) the size of neuronal nuclei in layer III. The protein maintained the sharply increased count of gliocytes in the perifocal zone of infarction and promoted their growth. Hence, APC protected the neurons from death in the ischemic focus by increasing the gliocyte count and stimulating the compensatory reparative processes.

Glial fibrillary acidic protein in children with congenital heart disease undergoing cardiopulmonary bypass

OBJECTIVE

To determine whether blood levels of the brain-specific biomarker glial fibrillary acidic protein rise during cardiopulmonary bypass for repair of congenital heart disease.

METHODS

This is a prospective observational pilot study to characterise the blood levels of glial fibrillary acidic protein during bypass. Children <21 years of age undergoing bypass for congenital heart disease at Johns Hopkins Hospital and Texas Children's Hospital were enrolled. Blood samples were collected during four phases: pre-bypass, cooling, re-warming, and post-bypass.

RESULTS

A total of 85 patients were enrolled between October, 2010 and May, 2011. The median age was 0.73 years (range 0.01-17). The median weight was 7.14 kilograms (range 2.2-86.5). Single ventricle anatomy was present in 18 patients (22%). Median glial fibrillary acidic protein values by phase were: pre-bypass: 0 ng/ml (range 0-0.35); cooling: 0.039 (0-0.68); re-warming: 0.165 (0-2.29); and post-bypass: 0.112 (0-0.97). There were significant elevations from pre-bypass to all subsequent stages, with the greatest increase during re-warming (p = 0.0001). Maximal levels were significantly related to younger age (p = 0.03), bypass time (p = 0.03), cross-clamp time (p = 0.047), and temperature nadir (0.04). Peak levels did not vary significantly in those with single ventricle anatomy versus two ventricle repairs.

CONCLUSION

There are significant increases in glial fibrillary acidic protein levels in children undergoing cardiopulmonary bypass for repair of congenital heart disease. The highest values were seen during the re-warming phase. Elevations are significantly associated with younger age, bypass and cross-clamp times, and temperature nadir. Owing to the fact that glial fibrillary acidic protein is the most brain-specific biomarker identified to date, it may act as a rapid diagnostic marker of brain injury during cardiac surgery.

Progress on the protective effect of compounds from natural medicines on cerebral ischemia

The treatment of cerebral ischemic disease by natural medicines has a long history, and has accumulated a rich theoretical knowledge and treatment experience. The objective of this review is to critically evaluate the experimental research situation of the protective effect of the individual compounds from natural medicine on cerebral ischemia in the past ten years, emphasizing the major mechanisms underlying cerebral ischemic pathophysiology. Sixteen representative compounds from natural medicines which are often used to treat stroke are discussed. The results indicate that these components possess a protective effect on cerebral ischemia, and that these components have different mechanisms, including inhibiting excitotoxicity by ginkgolide B, antiapoptosis of breviscapine, influencing astrocytic activation and proliferation of tanshinone IIA, influencing free radicals by ginsenoside Rd, impairing blood-brain barrier disruption by baicalin, and the anti-inflammatory activity of tetramethylpyrazine. Moreover, some components have multiple neuroprotective mechanisms. Therefore, the combination of individual compounds from natural medicines, considering the mechanisms of cerebral ischemia, may be beneficial to patients with cerebral ischemia in the future. This approach will provide a direction for the further application and exploitation of new drug development in the treatment of cerebral ischemia.

Bioactive Agarose Carbon-Nanotube Composites are Capable of Manipulating Brain-Implant Interface

Composite electrodes made of the polysaccharide agarose and carbon nanotube fibers (A-CNE) have shown potential to be applied as tissue-compatible, micro-electronic devices. In the present work, A-CNEs were functionalized using neuro-relevant proteins (laminin and alpha-melanocyte stimulating hormone) and implanted in brain tissue for 1 week (acute response) and 4 weeks (chronic response). Qualitative and quantitative analysis of neuronal and immunological responses revealed significant changes in immunological response to implanted materials depending on the type of biomolecule used. The potential to manipulate tissue response through the use of an anti-inflammatory protein, alpha-melanocyte stimulating hormone, was shown in the reduction of astroglia presence near the implant site during the glial scar formation. These results suggest that A-CNEs, which are soft, flexible, and easily made bioactive, have the ability to modify brain tissue response through surface modification as a function of the biomolecule used.

Histone deacetylase expression patterns in developing murine optic nerve

Background

Histone deacetylases (HDACs) play important roles in glial cell development and in disease states within multiple regions of the central nervous system. However, little is known about HDAC expression or function within the optic nerve. As a first step in understanding the role of HDACs in optic nerve, this study examines the spatio-temporal expression patterns of methylated histone 3 (K9), acetylated histone 3 (K18), and HDACs 1–6 and 8–11 in the developing murine optic nerve head.

Results

Using RT-qPCR, western blot and immunofluorescence, three stages were analyzed: embryonic day 16 (E16), when astrocyte precursors are found in the optic stalk, postnatal day 5 (P5), when immature astrocytes and oligodendrocytes are found throughout the optic nerve, and P30, when optic nerve astrocytes and oligodendrocytes are mature. Acetylated and methylated histone H3 immunoreactivity was co-localized in the nuclei of most SOX2 positive glia within the optic nerve head and adjacent optic nerve at all developmental stages. HDACs 1–11 were expressed in the optic nerve glial cells at all three stages of optic nerve development in the mouse, but showed temporal differences in overall levels and subcellular localization. HDACs 1 and 2 were predominantly nuclear throughout optic nerve development and glial cell maturation. HDACs 3, 5, 6, 8, and 11 were predominantly cytoplasmic, but showed nuclear localization in at least one stage of optic nerve development. HDACs 4, 9 and10 were predominantly cytoplasmic, with little to no nuclear expression at any time during the developmental stages examined.

Conclusions

Our results showing that HDACs 1, 2, 3, 5, 6, 8, and 11 were each localized to the nuclei of SOX2 positive glia at some stages of optic nerve development and maturation and extend previous reports of HDAC expression in the aging optic nerve. These HDACs are candidates for further research to understand how chromatin remodeling through acetylation, deacetylation and methylation contributes to glial development as well as their injury response.

A Decade of Research on TLR2 Discovering Its Pivotal Role in Glial Activation and Neuroinflammation in Neurodegenerative Diseases

Toll-like receptors (TLRs) belong to a class of pattern recognition receptors that play an important role in host defense against pathogens. TLRs on innate immune cells recognize a wide variety of pathogen-associated molecular patterns (PAMPs) and trigger innate immune responses. Later, it was revealed that the same receptors are also utilized to detect tissue damage to trigger inflammatory responses in the context of non-infectious inflammation. In the nervous system, different members of the TLR family are expressed on glial cells including astrocytes, microglia, oligodendrocytes, and Schwann cells, implicating their putative role in innate/inflammatory responses in the nervous system. In this regard, we have investigated the function of TLRs in neuroinflammation. We discovered that a specific member of the TLR family, namely TLR2, functions as a master sentry receptor to detect neuronal cell death and tissue damage in many different neurological conditions including nerve transection injury, intracerebral hemorrhage, traumatic brain injury, and hippocampal excitotoxicity. In this review, we have summarized our research for the last decade on the role of TLR2 in neuroinflammation in the above neurological disorders. Our data suggest that TLR2 can be an efficient target to regulate unwanted inflammatory response in these neurological conditions.

Histological, cellular and behavioral assessments of stroke outcomes after photothrombosis-induced ischemia in adult mice

BACKGROUND

Following the onset of focal ischemic stroke, the brain experiences a series of alterations including infarct evolvement, cellular proliferation in the penumbra, and behavioral deficits. However, systematic study on the temporal and spatial dependence of these alterations has not been provided.

RESULTS

Using multiple approaches, we assessed stroke outcomes by measuring brain injury, dynamic cellular and glial proliferation, and functional deficits at different times up to two weeks after photothrombosis (PT)-induced ischemic stroke in adult mice. Results from magnetic resonance imaging (MRI) and Nissl staining showed a maximal infarction, and brain edema and swelling 1-3 days after PT. The rate of Bromodeoxyuridine (Brdu)-labeled proliferating cell generation is spatiotemporal dependent in the penumbra, with the highest rate in post ischemic days 3-4, and higher rate of proliferation in the region immediate to the ischemic core than in the distant region. Similar time-dependent generation of proliferating GFAP+ astrocytes and Iba1+ microglia/macrophage were observed in the penumbra. Using behavioral tests, we showed that PT resulted in the largest functional deficits during post ischemic days 2-4.

CONCLUSION

Our study demonstrated that first a few days is a critical period that causes brain expansion, cellular proliferation and behavioral deficits in photothrombosis-induced ischemic model, and proliferating astrocytes only have a small contribution to the pools of proliferating cells and reactive astrocytes.

3D Electrospun scaffolds promote a cytotrophic phenotype of cultured primary astrocytes

Astrocytes are a target for regenerative neurobiology because in brain injury their phenotype arbitrates brain integrity, neuronal death and subsequent repair and reconstruction. We explored the ability of 3D scaffolds to direct astrocytes into phenotypes with the potential to support neuronal survival. Poly-ε-caprolactone scaffolds were electrospun with random and aligned fibre orientations on which murine astrocytes were sub-cultured and analysed at 4 and 12 DIV. Astrocytes survived, proliferated and migrated into scaffolds adopting 3D morphologies, mimicking in vivo stellated phenotypes. Cells on random poly-ε-caprolactone scaffolds grew as circular colonies extending processes deep within sub-micron fibres, whereas astrocytes on aligned scaffolds exhibited rectangular colonies with processes following not only the direction of fibre alignment but also penetrating the scaffold. Cell viability was maintained over 12 DIV, and cytochemistry for F-/G-actin showed fewer stress fibres on bioscaffolds relative to 2D astrocytes. Reduced cytoskeletal stress was confirmed by the decreased expression of glial fibrillary acidic protein. PCR demonstrated up-regulation of genes (excitatory amino acid transporter 2, brain-derived neurotrophic factor and anti-oxidant) reflecting healthy biologies of mature astrocytes in our extended culture protocol. This study illustrates the therapeutic potential of bioengineering strategies using 3D electrospun scaffolds which direct astrocytes into phenotypes supporting brain repair. Astrocytes exist in phenotypes with pro-survival and destructive components, and their biology can be modulated by changing phenotype. Our findings demonstrate murine astrocytes adopt a healthy phenotype when cultured in 3D. Astrocytes proliferate and extend into poly-ε-caprolactone scaffolds displaying 3D stellated morphologies with reduced GFAP expression and actin stress fibres, plus a cytotrophic gene profile. Bioengineered 3D scaffolds have potential to direct inflammation to aid regenerative neurobiology.

Blast TBI Models, Neuropathology, and Implications for Seizure Risk

Traumatic brain injury (TBI) due to explosive blast exposure is a leading combat casualty. It is also implicated as a key contributor to war related mental health diseases. A clinically important consequence of all types of TBI is a high risk for development of seizures and epilepsy. Seizures have been reported in patients who have suffered blast injuries in the Global War on Terror but the exact prevalence is unknown. The occurrence of seizures supports the contention that explosive blast leads to both cellular and structural brain pathology. Unfortunately, the exact mechanism by which explosions cause brain injury is unclear, which complicates development of meaningful therapies and mitigation strategies. To help improve understanding, detailed neuropathological analysis is needed. For this, histopathological techniques are extremely valuable and indispensable. In the following we will review the pathological results, including those from immunohistochemical and special staining approaches, from recent preclinical explosive blast studies.

Extremely low frequency magnetic field (50 Hz, 0.5 mT) reduces oxidative stress in the brain of gerbils submitted to global cerebral ischemia

Magnetic field as ecological factor has influence on all living beings. The aim of this study was to determine if extremely low frequency magnetic field (ELF-MF, 50 Hz, 0.5 mT) affects oxidative stress in the brain of gerbils submitted to 10-min global cerebral ischemia. After occlusion of both carotid arteries, 3-month-old gerbils were continuously exposed to ELF-MF for 7 days. Nitric oxide and superoxide anion production, superoxide dismutase activity and index of lipid peroxidation were examined in the forebrain cortex, striatum and hippocampus on the 7^th (immediate effect of ELF-MF) and 14^th day after reperfusion (delayed effect of ELF-MF). Ischemia per se increased oxidative stress in the brain on the 7^th and 14^th day after reperfusion. ELF-MF also increased oxidative stress, but to a greater extent than ischemia, only immediately after cessation of exposure. Ischemic gerbils exposed to ELF-MF had increased oxidative stress parameters on the 7^th day after reperfusion, but to a lesser extent than ischemic or ELF-MF-exposed animals. On the 14^th day after reperfusion, oxidative stress parameters in the brain of these gerbils were mostly at the control levels. Applied ELF-MF decreases oxidative stress induced by global cerebral ischemia and thereby reduces possible negative consequences which free radical species could have in the brain. The results presented here indicate a beneficial effect of ELF-MF (50 Hz, 0.5 mT) in the model of global cerebral ischemia.

The neglected co-star in the dementia drama: the putative roles of astrocytes in the pathogeneses of major neurocognitive disorders

Alzheimer's disease (AD) and vascular dementia are the major causes of cognitive disorders worldwide. They are characterized by cognitive impairments along with neuropsychiatric symptoms, and that their pathogeneses show overlapping multifactorial mechanisms. Although AD has long been considered the most common cause of dementia, individuals afflicted with AD commonly exhibit cerebral vascular abnormalities. The concept of mixed dementia has emerged to more clearly identify patients with neurodegenerative phenomena exhibiting both AD and cerebral vascular pathologies-vascular damage along with β-amyloid (Aβ)-associated neurotoxicity and τ-hyperphosphorylation. Cognitive impairment has long been commonly explained through a 'neuro-centric' perspective, but emerging evidence has shed light over the important roles that neurovascular unit dysfunction could have in neuronal death. Moreover, accumulating data have been demonstrating astrocytes being the essential cell type in maintaining proper central nervous system functioning. In relation to dementia, the roles of astrocytes in Aβ deposition and clearance are unclear. This article emphasizes the multiple events triggered by ischemia and the cytotoxicity exerted by Aβ either alone or in association with endothelin-1 and receptor for advanced glycation end products, thereby leading to neurodegeneration in an 'astroglio-centric' perspective.

Astrocyte-derived proinflammatory cytokines induce hypomyelination in the periventricular white matter in the hypoxic neonatal brain

Hypoxic exposure in the perinatal period causes periventricular white matter damage (PWMD), a condition associated with myelination abnormalities. Under hypoxic conditions, glial cells were activated and released a large number of inflammatory mediators in the PWM in neonatal brain, which may result in oligodendrocyte (OL) loss and axonal injury. This study aims to determine if astrocytes are activated and generate proinflammatory cytokines that may be coupled with the oligodendroglial loss and hypomyelination observed in hypoxic PWMD. Twenty-four 1-day-old Wistar rats were exposed to hypoxia for 2 h. The rats were then allowed to recover under normoxic conditions for 7 or 28 days before being killed. Another group of 24 rats kept outside the chamber was used as age-matched controls. Upregulated expression of TNF-α and IL-1β was observed in astrocytes in the PWM of P7 hypoxic rats by double immunofluorescence, western blotting and real time RT-PCR. This was linked to apoptosis and enhanced expression of TNF-R₁ and IL-1R₁ in APC⁺ OLs. PLP expression was decreased significantly in the PWM of P28d hypoxic rats. The proportion of myelinated axons was markedly reduced by electron microscopy (EM) and the average g-ratios were higher in P28d hypoxic rats. Upregulated expression of TNF-α and IL-1β in primary cultured astrocytes as well as their corresponding receptors in primary culture APC⁺ oligodendrocytes were detected under hypoxic conditions. Our results suggest that following a hypoxic insult, astrocytes in the PWM of neonatal rats produce inflammatory cytokines such as TNF-α and IL-1β, which induce apoptosis of OLs via their corresponding receptors associated with them. This results in hypomyelination in the PWM of hypoxic rats.

The role of astrocytes in mediating exogenous cell-based restorative therapy for stroke

Astrocytes have not been a major therapeutic target for the treatment of stroke, with most research emphasis on the neuron. Given the essential role that astrocytes play in maintaining physiological function of the central nervous system and the very rapid and sensitive reaction astrocytes have in response to cerebral injury or ischemic insult, we propose to replace the neurocentric view for treatment with a more nuanced astrocytic centered approach. In addition, after decades of effort in attempting to develop neuroprotective therapies, which target reduction of the ischemic lesion, there are no effective clinical treatments for stroke, aside from thrombolysis with tissue plasminogen activator, which is used in a small minority of patients. A more promising therapeutic approach, which may affect nearly all stroke patients, may be in promoting endogenous restorative mechanisms, which enhance neurological recovery. A focus of efforts in stimulating recovery post stroke is the use of exogenously administered cells. The present review focuses on the role of the astrocyte in mediating the brain network, brain plasticity, and neurological recovery post stroke. As a model to describe the interaction of a restorative cell-based therapy with astrocytes, which drives recovery from stroke, we specifically highlight the subacute treatment of stroke with multipotent mesenchymal stromal cell therapy.

De novo glioblastoma in the territory of a prior middle cerebral artery infarct

We report a case of a patient who developed glioblastoma in the territory of a previous infarction. Two years after an ischemic stroke, the patient presented with a cystic, necrotic, and heterogeneously enhancing mass. Open biopsy and debulking of the mass with histological analysis revealed the mass to be glioblastoma. Though several cases of posttraumatic GBM have been reported, this is the first proposed case of GBM after an ischemic stroke. From this case, we suggest that the ischemic stroke, like other forms of cortical injury, may predispose to glioblastoma formation.

In vivo molecular markers for pro-inflammatory cytokine M1 stage and resident microglia in trimethyltin-induced hippocampal injury

Microglia polarization to the classical M1 activation state is characterized by elevated pro-inflammatory cytokines; however, a full profile has not been generated in the early stages of a sterile inflammatory response recruiting only resident microglia. We characterized the initial M1 state in a hippocampal injury model dependent upon tumor necrosis factor (TNF) receptor signaling for dentate granule cell death. Twenty-one-day-old CD1 male mice were injected with trimethyltin (TMT 2.3 mg/kg, i.p.) and the hippocampus was examined at an early stage (24-h post-dosing) of neuronal death. Glia activation was assessed using a custom quantitative nuclease protection assay. We report elevated mRNA levels for glia response such as ionizing calcium-binding adapter molecule-1 and glial fibrillary acidic protein (Gfap); Fas, hypoxia inducible factor alpha, complement component 1qb, TNF-related genes (Tnf, Tnfaip3, Tnfrsfla); interleukin-1 alpha, Cd44, chemokine (C-C motif) ligand (Ccl)2, Cc14, integrin alpha M, lipocalin (Lcn2), and secreted phosphoprotein 1 (Spp1). These changes occurred in the absence of changes in matrix metalloproteinase 9 and 12, neural cell adhesion molecule, metabotropic glutamate receptor (Grm)3, and Ly6/neurotoxin 1 (Lynx1), as well as, a decrease in neurotrophin 3, glutamate receptor subunit epsilon (Grin)-2b, and neurotrophic tyrosine kinase receptor, type 3. The M2 anti-inflammatory marker, transforming growth factor beta-1 (Tgfb1) was elevated. mRNAs associated with early stage of injury-induced neurogenesis including fibroblast growth factor 21 and Mki67 were elevated. In the "non-injured" temporal cortex receiving projections from the hippocampus, Lynx1, Grm3, and Grin2b were decreased and Gfap increased. Formalin fixed-paraffin-embedded tissue did not generate a comparable profile.

In vivo astrocytic Ca2+ signaling in health and brain disorders

Astrocytes are the predominant glial cell type in the CNS. Although astrocytes are electrically nonexcitable, their excitability is manifested by their Ca2+ signaling, which serves as a mediator of neuron-glia bidirectional interactions via tripartite synapses. Studies from in vivo two-photon imaging indicate that in healthy animals, the properties of spontaneous astrocytic Ca2+ signaling are affected by animal species, age, wakefulness and the location of astrocytes in the brain. Intercellular Ca2+ waves in astrocytes can be evoked by a variety of stimulations. In animal models of some brain disorders, astrocytes can exhibit enhanced Ca2+ excitability featured as regenerative intercellular Ca2+ waves. This review first briefly summarizes the astrocytic Ca2+ signaling pathway and the procedure of in vivo two-photon Ca2+ imaging of astrocytes. It subsequently summarizes in vivo astrocytic Ca2+ signaling in health and brain disorders from experimental studies of animal models, and discusses the possible mechanisms and therapeutic implications underlying the enhanced Ca2+ excitability in astrocytes in brain disorders. Finally, this review summarizes molecular genetic approaches used to selectively manipulate astrocyte function in vivo and their applications to study the role of astrocytes in synaptic plasticity and brain disorders.

Evidence for miR-181 involvement in neuroinflammatory responses of astrocytes

Inflammation is a common component of acute injuries of the central nervous system (CNS) such as ischemia, and degenerative disorders such as Alzheimer's disease. Glial cells play important roles in local CNS inflammation, and an understanding of the roles for microRNAs in glial reactivity in injury and disease settings may therefore lead to the development of novel therapeutic interventions. Here, we show that the miR-181 family is developmentally regulated and present in high amounts in astrocytes compared to neurons. Overexpression of miR-181c in cultured astrocytes results in increased cell death when exposed to lipopolysaccharide (LPS). We show that miR-181 expression is altered by exposure to LPS, a model of inflammation, in both wild-type and transgenic mice lacking both receptors for the inflammatory cytokine TNF-α. Knockdown of miR-181 enhanced LPS-induced production of pro-inflammatory cytokines (TNF-α, IL-6, IL-1β, IL-8) and HMGB1, while overexpression of miR-181 resulted in a significant increase in the expression of the anti-inflammatory cytokine IL-10. To assess the effects of miR-181 on the astrocyte transcriptome, we performed gene array and pathway analysis on astrocytes with reduced levels of miR-181b/c. To examine the pool of potential miR-181 targets, we employed a biotin pull-down of miR-181c and gene array analysis. We validated the mRNAs encoding MeCP2 and X-linked inhibitor of apoptosis as targets of miR-181. These findings suggest that miR-181 plays important roles in the molecular responses of astrocytes in inflammatory settings. Further understanding of the role of miR-181 in inflammatory events and CNS injury could lead to novel approaches for the treatment of CNS disorders with an inflammatory component.

Fluoxetine-induced cortical adult neurogenesis

Adult neurogenesis in the hippocampal subgranular zone (SGZ) and the anterior subventricular zone (SVZ) is regulated by multiple factors, including neurotransmitters, hormones, stress, aging, voluntary exercise, environmental enrichment, learning, and ischemia. Chronic treatment with selective serotonin reuptake inhibitors (SSRIs) modulates adult neurogenesis in the SGZ, the neuronal area that is hypothesized to mediate the antidepressant effects of these substances. Layer 1 inhibitory neuron progenitor cells (L1-INP cells) were recently identified in the adult cortex, but it remains unclear what factors other than ischemia affect the neurogenesis of L1-INP cells. Here, we show that chronic treatment with an SSRI, fluoxetine (FLX), stimulated the neurogenesis of γ-aminobutyric acid (GABA)ergic interneurons from L1-INP cells in the cortex of adult mice. Immunofluorescence and genetic analyses revealed that FLX treatment increased the number of L1-INP cells in all examined cortical regions in a dose-dependent manner. Furthermore, enhanced Venus reporter expression driven by the synapsin I promoter demonstrated that GABAergic interneurons were derived from retrovirally labeled L1-INP cells. In order to assess if these new GABAergic interneurons possess physiological function, we examined their effect on apoptosis surrounding areas following ischemia. Intriguingly, the number of neurons expressing the apoptotic marker, active caspase-3, was significantly lower in adult mice pretreated with FLX. Our findings indicate that FLX stimulates the neurogenesis of cortical GABAergic interneurons, which might have, at least, some functions, including a suppressive effect on apoptosis induced by ischemia.

Neuroprotective effect of melatonin: a novel therapy against perinatal hypoxia-ischemia

One of the most common causes of mortality and morbidity in children is perinatal hypoxia-ischemia (HI). In spite of the advances in neonatology, its incidence is not diminishing, generating a pediatric population that will require an extended amount of chronic care throughout their lifetime. For this reason, new and more effective neuroprotective strategies are urgently required, in order to minimize as much as possible the neurological consequences of this encephalopathy. In this sense, interest has grown in the neuroprotective possibilities of melatonin, as this hormone may help to maintain cell survival through the modulation of a wide range of physiological functions. Although some of the mechanisms by which melatonin is neuroprotective after neonatal asphyxia remain a subject of investigation, this review tries to summarize some of the most recent advances related with its use as a therapeutic drug against perinatal hypoxic-ischemic brain injury, supporting the high interest in this indoleamine as a future feasible strategy for cerebral asphyctic events.

Endfeet serve as diffusion-limited subcellular compartments in astrocytes

Astrocytes extend their processes to make contact with neurons and blood vessels and regulate important processes associated with the physiology/pathophysiology of the brain. Their elaborate morphology, with numerous fine processes, could allow them to perform complex signal transductions with distinct compartments or to function as a spatial buffer depending on the diffusion properties of their intracellular molecules. Apart from calcium ions, however, the diffusion dynamics of molecules within astrocytes are poorly understood. In this study, we applied two-photon uncaging and fluorescence recovery after photobleaching of fluorescent molecules to acute cortical brain slices from mice to investigate the diffusion dynamics of molecules within astrocytes. We found that diffusion was significantly more restricted at the endfeet than at trunks and distal ends of other processes. Slow diffusion dynamics at the endfeet resulted in a large population of molecules being retained in a small region for tens of seconds, creating subcellular compartments that were isolated from other regions. In contrast, diffusion was fast and free at other processes. The same patterns were observed with the diffusions of a higher molecular weight (10 kDa) molecule and 2-NBDG, a fluorescent analog of glucose. These findings suggest that molecular diffusion is not uniform across the intracellular environment and that subcellular compartments are present in astrocytes. Therefore, similar to neurons, the elaborate and specialized structures of astrocytes may enable them to perform complex computations by providing distinct information storage/processing capacity among processes.

High-mobility group box 1: an amplifier of stem and progenitor cell activity after stroke

Stroke induces a highly complex web of pathophysiology that usually leads to serious long-term -disability. Molecules from the damage-associated molecular pattern (DAMP) family immediately increase after stroke. DAMPs are known to cause massive inflammation and brain damage. Thus, they may be targets for neuroprotection. However, emerging data now suggest that DAMPs may not always be detrimental. The high-mobility group box1 (HMGB1) protein is discussed as an example of this idea. During the acute phase after stroke, HMGB1 amplifies neuroinflammation. But during the brain remodeling phase of stroke recovery, HMGB1 can mediate beneficial plasticity and enhance stem and progenitor cell recruitment, proliferation, and differentiation within damaged brain. These emerging findings support the hypothesis that HMGB1 might be an important molecule for regulating stem and progenitor cell therapies in stroke patients.

Increased vulnerability of hippocampal CA1 neurons to hypoperfusion in ataxia and male sterility (AMS) mouse

The nna1 gene mutation is associated with spontaneous degeneration of cerebellar Purkinje cells and germ cells in Ataxia and Male Sterility (AMS) mouse. Since nna1 is also expressed in hippocampal neurons, we investigated their vulnerability to hypoperfusion in AMS mouse. Eight-week-old male wild type (WT) and AMS mice were subjected to bilateral common carotid artery occlusion (BCCAO) for 10 min and sacrificed 1, 3, 7 and 28 days after BCCAO. Nissl staining revealed the neuronal cell loss and pyknotic change in the CA1 of AMS mice. TUNEL(+) apoptotic cells were found in the area at 7 days in AMS mice. Bcl-2 mRNA and protein in WT hippocampus were increased, while they were not increased in AMS. Bax mRNA was increased in AMS. Moreover, Bax activation was immunohistochemically demonstrated only in AMS at 3 and 7 days after BCCAO. An oxidative DNA damage marker, 8-hydroxydeoxyguanosine-positive cells were increased in both strains at 1 day; decreased in WT at 3 days but remained high in AMS. BCCAO increased glutathione, an antioxidant, in WT, but not in AMS at 3 days. The mRNA level of mitochondrial uncoupling protein 2, a regulator of oxidative stress, was increased only in WT at 1 day. Nna1 mRNA was similarly expressed in WT and AMS, but the protein was undetectable in AMS. Thus, our results indicate the increased vulnerability of hippocampal CA1 neurons of AMS mice to cerebral hypoperfusion could be due to an imbalance between oxidative stress and antioxidative defense system.

Ginkgolide B preconditioning on astrocytes promotes neuronal survival in ischemic injury via up-regulating erythropoietin secretion

Although ischemic preconditioning (IP) can provide powerful protection on brain against ischemic insult, it is rarely used in clinic to prevent the occurrence of ischemic stroke because of safety concerns. It is therefore necessary to seek the safer stimuli to initiate pharmacological preconditioning. Our previous work demonstrated that ginkgolide B (GB) could protect neurons against ischemia-induced apoptosis. Astrocytes are the most numerous cells in mammalian central nervous system and there is a close bi-directional communication between neurons and astrocytes in brain. Besides neurons, whether GB can exert the role of preconditioning on astrocytes through which to further improve neuronal survival under ischemic condition is not yet known. In the present study, primary cultured astrocytes were treated with GB for 24h or short-term ischemia (ischemia for 3h, as ischemic preconditioning/IP), and then cultured back to normoxia and normal medium for 24h to induce the preconditioning response. Astrocyte-conditioned medium (ACM) was then collected and used to incubate the cultured neurons for 24h before neurons were subjected to severe ischemia. Our results demonstrated that not only GB and IP increased astrocytic viability in ischemia, but also the conditioned medium from astrocytes treated with GB or IP increased cell viability and decreased the number of apoptosis of neurons in ischemia. We also found that GB and IP significantly stimulated astrocytes to express and secrete erythropoietin (EPO) into ACM, and the addition of anti-EPO antibody blocked the protective effect of GB or IP-treated astrocytes culture medium on neurons in ischemia. Further study of above protection revealed that ACM from astrocytes treated with GB or IP induced the inactivation of proapoptotic factor Bad by phosphorylation at serine 136 and 112 ((136)p-Bad and (112)p-Bad) in neurons. Together, our results suggest that GB is capable of preconditioning on astrocytes as IP and then protects neurons against ischemia-induced apoptosis, which is mediated by EPO.

AQP4 knockout aggravates ischemia/reperfusion injury in mice

BACKGROUND AND PURPOSE

The glial water channel aquaporin-4 (AQP4) has been shown to be involved in a wide range of brain disorders. Although its important role in stroke has already been documented, the underlying mechanism was not clarified yet. Therefore, this study was designed to investigate the impacts of AQP4 deletion in ischemia/reperfusion (I/R).

METHODS AND RESULTS

Herein we found a higher mortality and more severe neurological deficits in AQP4 knockout (AQP4(-/-)) mice after transient middle cerebral artery occlusion while no difference was observed in water content variation during I/R between two genotypes except a higher basal water content developed in AQP4(-/-) mouse brain, implying the same increment of water content over a higher basal level may provoke an even more elevated intracranial pressure, which might be an important cause of increased mortality in AQP4(-/-) mice. Moreover, AQP4 knockout aggravated I/R injury with enlarged infarct size and a more serious loss of CA1 neurons accompanied by a striking hypertrophy of astrocytes, suggesting an involvement of AQP4 in astrocytic dysfunction.

CONCLUSIONS

Our findings provide direct evidence that AQP4 plays a crucial role in the pathogenesis of I/R injury, which may confer a new option for stroke treatment.

The adenosine A3 receptor agonist Cl-IB-MECA induces cell death through Ca²⁺/ROS-dependent down regulation of ERK and Akt in A172 human glioma cells

Adenosine A(3) receptor (A3AR) is coupled to G proteins that are involved in a variety of intracellular signaling pathways and physiological functions. 2-Chloro-N(6)-(3-iodobenzyl) adenosine-5'-N-methylcarboxamide (Cl-IB-MECA), an agonist of A3AR, has been reported to induce cell death in various cancer cells. However, the effect of CI-IB-MECA on glioma cell growth is not clear. This study was undertaken to examine the effect of CI-IB-MECA on glioma cell viability and to determine its molecular mechanism. CI-IB-MECA inhibited cell proliferation and induced cell death in a dose- and time-dependent manner. Treatment of CI-IB-MECA resulted in an increase in intracellular Ca(2+) followed by enhanced reactive oxygen species (ROS) generation. EGTA and N-acetylcysteine (NAC) blocked the cell death induced by CI-IB-MECA, suggesting that Ca(2+) and ROS are involved in the Cl-IB-MECA-induced cell death. Western blot analysis showed that CI-IB-MECA induced the down-regulation of extracellular signal-regulated kinases (ERK) and Akt, which was prevented by EGTA, NAC, and the A3AR antagonist MRS1191. Transfection of constitutively active forms of MEK, the upstream kinase of ERK, and Akt prevented the cell death. CI-IB-MECA induced caspase-3 activation and the CI-IB-MECA-induced cell death was blocked by the caspase inhibitors DEVD-CHO and z-VAD-FMK. In addition, expression of XIAP and Survivin were decreased in cells treated with Cl-IB-MECA. Collectively, these findings demonstrate that CI-IB-MECA induce a caspase-dependent cell death through suppression of ERK and Akt mediated by an increase in intracellular Ca(2+) and ROS generation in human glioma cells. These suggest that A3AR agonists may be a potential therapeutic agent for induction of apoptosis in human glioma cells.

Bone marrow stromal cells induce cell cycle arrest in reactive astrocytes in vitro

Transplantation of bone marrow stromal cells (BMSCs) reduces astrogliosis, decreases scar thickness and improves neurological functional recovery after brain damage. It is believed that transplanted BMSCs have a profound influence on astrocytes. To obtain the possible mechanism in their interaction, a co-culture system between BMSCs and astrocytes were set to investigate whether BMSCs could modulate cell cycle machinery in reactive astrocytes. The results obtained showed cell cycle regulatory proteins, cdk4 along with its activator cyclin D1, and PCNA increased while p27, an endogenous cyclin-dependent kinase inhibitor, deceased in glutamate-treated astrocytes in vitro. However, BMSCs influenced cell cycle elements in the cocultured astrocytes: cyclin D1, cdk 4 and PCNA were downregulated, while p27 was unregulated. Flow cytometry showed astrocytes in the S phase after glutamate incubation increased to 17.4±2.0% while restored to a level of 7.8±1.1% when cocultured with BMSCs. l-Canavanine, an inhibitor of inducible nitric oxide synthase, partially reversed the S phase to 11.3±0.4% in the cocultured astrocytes. These data indicated that BMSCs might inhibit the cell cycle control system in reactive astrocytes and nitric oxide signaling was involved in this process. The decline of astrogliosis conferred by BMSCs may derive from their effect of inhibiting the cell cycle progression in astrocytes.

Neuroglial activation and Cx43 expression are reduced upon transplantation of human umbilical cord blood cells after perinatal hypoxic-ischemic injury

Glial cells play a crucial role in the pathomechanism of perinatal hypoxic-ischemic brain injury (HI) and are involved in the maintenance of a chronic state of inflammation that causes delayed neuronal damage. Activation of astrocytes is one factor prolonging brain damage and contributing to the formation of a glial scar that limits neuronal plasticity. In this context, the major astrocytic gap junction protein Connexin 43 (Cx43) has been ascribed various functions including regulation of astrocytic migration and proliferation. Here, we investigate glial responses like microglia/macrophages and astrocytic activation in a rat model of neonatal HI and characterize changes of these parameters upon transplantation of human umbilical cord blood cells (hUCB). As an alleviation of motor function in lesioned rats has previously been described in transplanted animals, we analyze the putative correlation between motor function and glial activation over time. The lesion-induced impairment of motor function, assessed by forelimb use bias, muscle strength and distal spasticity, was alleviated upon transplantation of hUCB short and long term. HI induced an acute inflammatory reaction with activation of microglia/macrophages and reactive astrogliosis associated with perilesional upregulation of Cx43 that slowly declined during the chronic post-ischemic phase. hUCB transplantation accelerated the regression of inflammatory events, narrowed the perilesional astrocytic wall and led to a downregulation of the investigated astrocytic proteins. Thus, in the immature brain, hUCB may indirectly reduce secondary cell death upon hypoxia-ischemia and facilitate post-ischemic plasticity through the attenuation of reactive gliosis. This article is part of a Special Issue entitled Electrical Synapses.

Diffusion properties of molecules at the blood-brain interface: potential contributions of astrocyte endfeet to diffusion barrier functions

Molecular diffusion in the extracellular space (ECS) plays a key role in determining tissue physiology and pharmacology. The blood-brain barrier regulates the exchange of substances between the brain and the blood, but the diffusion properties of molecules at this blood-brain interface, particularly around the astrocyte endfeet, are poorly characterized. In this study, we used 2-photon microscopy and acute brain slices of mouse neocortex and directly assessed the diffusion patterns of fluorescent molecules. By observing the diffusion of unconjugated and 10-kDa dextran-conjugated Alexa Fluor 488 from the ECS of the brain parenchyma to the blood vessels, we find various degrees of diffusion barriers at the endfeet: Some allow the invasion of dye inside the endfoot network while others completely block it. Detailed analyses of the time course for dye clearance support the existence of a tight endfoot network capable of acting as a diffusion barrier. Finally, we show that this diffusion pattern collapses under pathological conditions. These data demonstrate the heterogeneous nature of molecular diffusion dynamics around the endfeet and suggest that these structures can serve as the diffusion barrier. Therefore, astrocyte endfeet may add another layer of regulation to the exchange of molecules between blood vessels and brain parenchyma.

Protective efficacy of an Ecklonia cava extract used to treat transient focal ischemia of the rat brain

Phlorotannins (marine algal polyphenols) have been reported to exhibit beneficial biological activities, serving as both antioxidants and anti-inflammatory agents. Among marine algae, Ecklonia cava, a member of the Laminariaceae, is a very popular food regarded as healthy in Korea and Japan. Recently, benefits afforded by phlorotannins in the treatment of various clinical conditions have been reported, but any therapeutic effects of such materials in the treatment of neurodegenerative diseases such as stroke remain unclear. Also, the mechanisms of action of the algal components remain poorly understood. In the present in vivo study, administration of Ecklonia cava polyphenols (ECP) at 10 mg/kg and 50 mg/kg intraperitoneally (i.p.) significantly decreased infarct size and the extent of brain edema in the rat after induction of transient focal ischemia via middle cerebral artery occlusion (MCAO). Further, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay revealed dose-dependent blockage of neuronal apoptosis upon intravenous ECP treatment. Neurobehavioral tests performed over the 6 days after MCAO revealed a reduction in neurological motor performance in control animals, but administration of ECP (50 mg/kg i.p.) prevented this decline. In vitro, a significant neuroprotective effect of ECP was evident when cell viability was assayed after induction of H₂O₂-mediated oxidative stress, upon retinoic acid treatment, in the differentiated neuroblastoma cell line SH-SY5Y. Interestingly, ECP blocked the rise in cytosolic calcium, in a dose-dependent manner, in differentiated SH-SY5Y cells exposed to H₂O₂. Together, the results suggest that ECP exerts neuroprotective effects in the focally ischemic brain by reducing Ca²⁺-mediated neurotoxicity.

Response of hippocampal neurons and glial cells to alternating magnetic field in gerbils submitted to global cerebral ischemia

The purpose of this study was to determine whether exposure to an extremely low-frequency magnetic field (ELF-MF, 50 Hz) affects the outcome of postischemic damage in the hippocampus of Mongolian gerbils. After 10-min bilateral carotid occlusion, the gerbils were continuously exposed to ELF-MF (average magnetic induction at the center of the cage was 0.5 mT) for 7 days. The impact of ELF-MF was estimated immediately (the 7th day after reperfusion) and 7 days after cessation of exposure (the 14th day after reperfusion) compared with ischemic gerbils without ELF-MF exposure. Applying stereological methods, histological evaluation of changes in the hippocampus was done for determining its volume, volume densities of degenerating neurons and astrocytes, as well as the number of microglial cells per unit area. ELF-MF per se did not induce any morphological changes, while 10-min global cerebral ischemia led to neuronal death, especially in CA1 region of the hippocampus, as expected. Ischemic gerbils exposed to ELF-MF had significantly a lower degree of cell loss in the examined structure and greater responses of astrocytes and microglial cells than postischemic gerbils without exposure on the seventh day after reperfusion (immediate effect of ELF-MF). Similar response was observed on the 14th day after reperfusion (delayed effect of ELF-MF); however, differences in measured parameters were low and insignificant. Applied ELF-MF has possible neuroprotective function in the hippocampus, as the most sensitive brain structure in the model of global cerebral ischemia, through reduction of neuronal death and activation of astrocytes and microglial cells.

Intracerebral chondroitinase ABC and heparan sulfate proteoglycan glypican improve outcome from chronic stroke in rats

Physical and chemical constraints imposed by the periinfarct glial scar may contribute to the limited clinical improvement often observed after ischemic brain injury. To investigate the role of some of these mediators in outcome from cerebral ischemia, we treated rats with the growth-inhibitory chondroitin sulfate proteoglycan neurocan, the growth-stimulating heparan sulfate proteoglycan glypican, or the chondroitin sulfate proteoglycan-degrading enzyme chondroitinase ABC. Neurocan, glypican, or chondroitinase ABC was infused directly into the infarct cavity for 7 d, beginning 7 d after middle cerebral artery occlusion. Glypican and chondroitinase ABC reduced glial fibrillary acidic protein immunoreactivity and increased microtubule-associated protein-2 immunoreactivity in the periinfarct region, and glypican- and chondroitinase ABC-treated rats showed behavioral improvement compared with neurocan- or saline-treated rats. Glypican and chondroitinase ABC also increased neurite extension in cortical neuron cultures. Glypican increased fibroblast growth factor-2 expression and chondroitinase ABC increased brain-derived neurotrophic factor expression in these cultures, whereas no such effects were seen following neurocan treatment. Thus, treatment with glypican or enzymatic disruption of neurocan with chondroitinase ABC improves gross anatomical, histological, and functional outcome in the chronic phase of experimental stroke in rats. Changes in growth factor expression and neuritogenesis may help to mediate these effects.

Novel aspirin-triggered neuroprotectin D1 attenuates cerebral ischemic injury after experimental stroke

Acute ischemic stroke triggers complex neurovascular, neuroinflammatory and synaptic alterations. Aspirin and docosahexaenoic acid (DHA), an omega-3 essential fatty acid family member, have beneficial effects on cerebrovascular diseases. DHA is the precursor of neuroprotectin D1 (NPD1), which downregulates apoptosis and, in turn, promotes cell survival. Here we have tested the effect of aspirin plus DHA administration and discovered the synthesis of aspirin-triggered NPD1 (AT-NPD1) in the brain. Then we performed the total chemical synthesis of this molecule and tested in the setting of 2h middle cerebral artery occlusion (MCAo) in Sprague-Dawley rats. Neurological status was evaluated at 24h, 48 h, 72 h, and 7 days. At 3h post-stroke onset, an intravenous administration of 333 μg/kg of AT-NPD1 sodium salt (AT-NPD1-SS) or methyl-ester (AT-NPD1-ME) or vehicle (saline) as treatment was given. On day 7, ex vivo magnetic resonance imaging (MRI) of the brains was conducted on 11.7 T MRI. T2WI, 3D volumes, and apparent diffusion coefficient (ADC) maps were generated. In addition, infarct volumes and number of GFAP (reactive astrocytes), ED-1 (activated microglia/macrophages) and SMI-71-positive vessels were counted in the cortex and striatum at the level of the central lesion. All animals showed similar values for rectal and cranial temperatures, arterial blood gases, and plasma glucose during and after MCAo. Treatment with both AT-NPD1-SS and AT-NPD1-ME significantly improved neurological scores compared to saline treatment at 24h, 48 h, 72 h and 7 days. Total lesion volumes computed from T2WI images were significantly reduced by both AT-NPD1-SS and AT-NPD1-ME treatment in the cortex (by 44% and 81%), striatum (by 61% and 77%) and total infarct (by 48% and 78%, respectively). Brain edema, computed from T2WI in the cortex (penumbra) and striatum (core), was elevated in the saline group. In contrast, both AT-NPD1 decreased water content in the striatum on day 7. 3D volumes, computed from T2WI, were dramatically reduced with both AT-NPD1 and the lesion was mostly localized in the subcortical areas. Treatment with both AT-NPD1-SS and AT-NPD1-ME significantly reduced cortical (by 76% and 96%), subcortical (by 61% and 70%) and total (69% and 84%, respectively) infarct volumes as defined by histopathology. In conclusion, a novel biosynthetic pathway that leads to the formation of AT-NPD1 mediator in the brain was discovered. In addition, administration of synthetic AT-NPD1, in either its sodium salt or as the methyl ester, was able to attenuate cerebral ischemic injury which leads to a novel approach for pharmaceutical intervention and clinical translation.

Regulator of calcineurin 1 (Rcan1) has a protective role in brain ischemia/reperfusion injury

Background

An increase in intracellular calcium concentration [Ca²⁺]_i is one of the first events to take place after brain ischemia. A key [Ca²⁺]_i-regulated signaling molecule is the phosphatase calcineurin (CN), which plays important roles in the modulation of inflammatory cascades. Here, we have analyzed the role of endogenous regulator of CN 1 (Rcan1) in response to experimental ischemic stroke induced by middle cerebral artery occlusion.

Methods

Animals were subjected to focal cerebral ischemia with reperfusion. To assess the role of Rcan1 after stroke, we measured infarct volume after 48 h of reperfusion in Rcan1 knockout (KO) and wild-type (WT) mice. In vitro studies were performed in astrocyte-enriched cortical primary cultures subjected to 3% oxygen (hypoxia) and glucose deprivation (HGD). Adenoviral vectors were used to analyze the effect of overexpression of Rcan1-4 protein. Protein expression was examined by immunohistochemistry and immunoblotting and expression of mRNA by quantitative real-time Reverse-Transcription Polymerase Chain Reaction (real time qRT-PCR).

Results

Brain ischemia/reperfusion (I/R) injury in vivo increased mRNA and protein expression of the calcium-inducible Rcan1 isoform (Rcan1-4). I/R-inducible expression of Rcan1 protein occurred mainly in astroglial cells, and in an in vitro model of ischemia, HGD treatment of primary murine astrocyte cultures induced Rcan1-4 mRNA and protein expression. Exogenous Rcan1-4 overexpression inhibited production of the inflammatory marker cyclo-oxygenase 2. Mice lacking Rcan1 had higher expression of inflammation associated genes, resulting in larger infarct volumes.

Conclusions

Our results support a protective role for Rcan1 during the inflammatory response to stroke, and underline the importance of the glial compartment in the inflammatory reaction that takes place after ischemia. Improved understanding of non-neuronal mechanisms in ischemic injury promises novel approaches to the treatment of acute ischemic stroke.

Phenolic alkaloids from Menispermum dauricum rhizome protect against brain ischemia injury via regulation of GLT-1, EAAC1 and ROS generation

Menispermum dauricum rhizome has been widely used in China to treat various cardiovascular and thrombosis disorders. Some studies have reported that the phenolic alkaloids of Menispermum dauricum rhizome (PAM) have protective effects against brain ischemia injury, but the mechanism of this action remains to be clarified. In the present study, we investigated the possible mechanisms of action of PAM on experimental brain ischemia injury. Oxygen and glucose deprivation (OGD) in rat primary cortical cultures and middle cerebral artery occlusion in rats were used to mimic ischemia-reperfusion injury, respectively. The results suggested that PAM protected rat primary cortical cultures against OGD-reoxygenation induced cytotoxicity. PAM decreased extracellular glutamate content and markedly prevented the effects induced by OGD on protein level of GLT-1 and EAAC1 glutamate transporters. In addition, it reduced intracellular ROS generation. In vivo, PAM significantly reduced cerebral infarct area and ameliorated neurological functional deficits at different time points. Our findings revealed that the possible mechanism of action of PAM protected against brain ischemia injury involves regulation of GLT-1, EAAC1 and ROS generation.

Cerebral microglial activation in patients with hepatitis C: in vivo evidence of neuroinflammation

Patients with chronic hepatitis C infection may exhibit neuropsychological symptoms and cognitive impairment. Post-mortem studies of hepatitis C virus HCV quasispecies and replicative intermediates indicate that the brain might act as a separate compartment for viral replication and microglia may be the locus for infection and subsequent neuroinflammatory activity. We sought to use two independent in vivo imaging techniques to determine evidence of neuroinflammation in patients with histologically mild chronic hepatitis C. Using positron emission tomography (PET) with a ligand for microglial/brain macrophage activation, (11)C-(R)-PK11195 (PK11195) and cerebral proton magnetic resonance spectroscopy, we determined whether there was evidence of neuroinflammation in a pilot study of 11 patients with biopsy-proven mild chronic hepatitis C, compared to healthy volunteers. Patients were characterized by cognitive testing and the fatigue impact scale to assess for CNS impairment. PK11195 binding potential was significantly increased in the caudate nucleus of patients, compared to normal controls (P = 0.03). The caudate and thalamic binding potential were more significantly increased in six patients with genotype 1 infection (P = 0.007) and positively correlated with viraemia (r = 0.77, P = 0.005). Basal ganglia myo-inositol/creatine and choline/creatine ratios were also significantly elevated in patients with chronic hepatitis C compared to normal controls (P = 0.0004 and P = 0.01, respectively). Using PET, we demonstrated evidence of microglial activation, which positively correlated with HCV viraemia and altered cerebral metabolism in the brains of patients with mild hepatitis C. This provides further in vivo evidence for a neurotropic role for HCV.

Selective oestrogen receptor modulators decrease the inflammatory response of glial cells

Neuroinflammation comprises a feature of many neurological disorders that is accompanied by the activation of glial cells and the release of pro-inflammatory cytokines and chemokines. Such activation is a normal response oriented to protect neural tissue and it is mainly regulated by microglia and astroglia. However, excessive and chronic activation of glia may lead to neurotoxicity and may be harmful for neural tissue. The ovarian hormone oestradiol exerts protective actions in the central nervous system that, at least in part, are mediated by a reduction of reactive gliosis. Several selective oestrogen receptor modulators may also exert neuroprotective effects by controlling glial inflammatory responses. Thus, tamoxifen and raloxifene decrease the inflammatory response caused by lipopolysaccharide, a bacterial endotoxin, in mouse and rat microglia cells in vitro. Tamoxifen and raloxifene are also able to reduce microglia activation in the brain of male and female rats in vivo after the peripheral administration of lipopolysaccharide. In addition, tamoxifen decreases the microglia inflammatory response induced by irradiation. Furthermore, treatment with tamoxifen and raloxifene resulted in a significant reduction of the number of reactive astrocytes in the hippocampus of young, middle-aged and older female rats after a stab wound injury. Tamoxifen, raloxifene and the new selective oestrogen receptor modulators ospemifene and bazedoxifene decrease the expression and release of interleukine-6 and interferon-γ inducible protein-10 in cultured astrocytes exposed to lipopolysaccharide. Ospemifene and bazedoxifene exert anti-inflammatory effects in astrocytes by a mechanism involving classical oestrogen receptors and the inhibition of nuclear factor-kappa B p65 transactivation. These data suggest that oestrogenic compounds are candidates to counteract brain inflammation under neurodegenerative conditions by targeting the production and release of pro-inflammatory molecules by glial cells.

Acute effects of all-trans-retinoic acid in ischemic injury

All-trans-retinoic acid (ATRA) is a vitamin A derivative that is important in neuronal patterning, survival, and neurite outgrowth. Neuroprotective effects of ATRA in ischemia have been demonstrated but its effects on glial swelling are not known. We investigated the relatively acute effects of ATRA on cell swelling in ischemic injury and on key features hypothesized to contribute to cell swelling including increased reactive oxygen species/reactive nitrogen species (ROS/RNS), depolarization of the inner mitochondrial membrane potential (ΔΨm), and increased intracellular calcium ([Ca2+]i). C6 glial cultures were subjected to 5 hr oxygen-glucose deprivation (OGD). ATRA was added to separate groups after the end of OGD. OGD increased cell volume by 43%, determined at 90 min after the end of OGD, but this increase was significantly attenuated by ATRA. OGD induced an increase in ROS/RNS production in the whole cell and mitochondria, as assessed by the fluorescent dyes CM-H2DCFDA and MitoTracker CM-H2-XROS at the end of OGD. The increase in mitochondrial ROS, but not cellular ROS, was significantly attenuated by ATRA. OGD also induced a 67% decline in mitochondrial ΔΨm but this decline was significantly attenuated by ATRA. OGD-induced increase in [Ca2+]i was also significantly attenuated by ATRA. Taken together with our previous results where calcium channel blockers reduced cell swelling, the effects of ATRA in attenuating swelling are possibly mediated through its effects in regulating [Ca2+]i. Considering the paucity of agents in attenuating brain edema in ischemia, ATRA has the potential to reduce brain edema and associated neural damage in ischemic injury.

Complete transglutaminase 2 ablation results in reduced stroke volumes and astrocytes that exhibit increased survival in response to ischemia

Transglutaminase 2 (TG2) is a very multifunctional protein that is ubiquitously expressed in the body. It is a Ca(2+)-dependent transamidating enzyme, a GTPase, as well as a scaffolding protein. TG2 is the predominant form of transglutaminase expressed in the mammalian nervous system. Previously, it was shown that TG2 can affect both cell death and cell survival mechanisms depending on the cell type and the stressor. In the case of ischemic stress, TG2 was previously shown to play a protective role in the models used. For example in hTG2 transgenic mice, where TG2 is overexpressed only in neurons, middle cerebral artery ligation (MCAL) resulted in smaller infarct volumes compared to wild type mice. In this study TG2 knock out mice were used to determine how endogenous TG2 affected stroke volumes. Intriguingly, infarct volumes in TG2 knock out mice were significantly smaller compared to wild type mice. As expected, primary neurons isolated from TG2 knock out mice showed decreased viability in response to oxygen-glucose deprivation. However, primary astrocytes that were isolated from TG2 knock out mice were resistant to oxygen-glucose deprivation in situ. Both wild type and knock out neurons were protected against oxygen glucose deprivation when they were co-cultured with astrocytes from TG2 knockout mice. Therefore, the decreased stroke volumes observed in TG2 knock out mice after MCAL, can be correlated with the protective effects of TG2 knock out in astrocytes in response to oxygen glucose deprivation in situ. These findings suggest that neuron-astrocyte crosstalk plays a significant role in mediating ischemic cell death and that TG2 differentially impacts cell survival depending on cell context.

A procyanidin type A trimer from cinnamon extract attenuates glial cell swelling and the reduction in glutamate uptake following ischemia-like injury in vitro

Dietary polyphenols exert neuroprotective effects in ischemic injury. The protective effects of a procyanidin type A trimer (trimer 1) isolated from a water soluble cinnamon extract (CE) were investigated on key features of ischemic injury, including cell swelling, increased free radical production, increased intracellular calcium ([Ca(2+)](i)), mitochondrial dysfunction, and the reduction in glutamate uptake. Astrocyte (glial) swelling is a major component of cytotoxic brain edema in ischemia and, along with vasogenic edema, may contribute to increased intracranial pressure, brain herniation, and additional ischemic injuries. C6 glial cultures were exposed to oxygen-glucose deprivation (OGD) for 5 h, and cell swelling was determined at 90 min after the end of OGD. OGD-induced increases in glial swelling were significantly blocked by trimer 1, but not by the major nonpolyphenol fractions of CE including cinnamaldehyde and coumarin. Increased free radical production, a contributing factor in cell swelling following ischemic injury, was also significantly reduced by trimer 1. Mitochondrial dysfunction, another key feature of ischemic injury, is hypothesized to contribute to glial swelling. Depolarization of the inner mitochondrial membrane potential (ΔΨ(m)) was assessed using a fluorescent dye (tetramethylrhodamine ethyl ester [TMRE]), and was significantly attenuated by trimer 1 as was OGD-induced increased [Ca(2+)](i). Taken together with our previous observation that blockers of [Ca(2+)](i) reduce cell swelling, our results indicate that trimer 1 may attenuate cell swelling by regulating [Ca(2+)](i). Trimer 1 also significantly attenuated the OGD-induced decrease in glutamate uptake. In addition, cyclosporin A, a blocker of the mitochondrial permeability pore (mPT), but not FK506 (that does not block the mPT), reduced the OGD-induced decline in glutamate uptake indicating a role of the mPT in such effects. Thus, the effects of trimer 1 in attenuating the reduction in glutamate uptake are likely mediated through their action on the mitochondria.

Effect of polyphenols on oxidative stress and mitochondrial dysfunction in neuronal death and brain edema in cerebral ischemia

Polyphenols are natural substances with variable phenolic structures and are elevated in vegetables, fruits, grains, bark, roots, tea, and wine. There are over 8000 polyphenolic structures identified in plants, but edible plants contain only several hundred polyphenolic structures. In addition to their well-known antioxidant effects, select polyphenols also have insulin-potentiating, anti-inflammatory, anti-carcinogenic, anti-viral, anti-ulcer, and anti-apoptotic properties. One important consequence of ischemia is neuronal death and oxidative stress plays a key role in neuronal viability. In addition, neuronal death may be initiated by the activation of mitochondria-associated cell death pathways. Another consequence of ischemia that is possibly mediated by oxidative stress and mitochondrial dysfunction is glial swelling, a component of cytotoxic brain edema. The purpose of this article is to review the current literature on the contribution of oxidative stress and mitochondrial dysfunction to neuronal death, cell swelling, and brain edema in ischemia. A review of currently known mechanisms underlying neuronal death and edema/cell swelling will be undertaken and the potential of dietary polyphenols to reduce such neural damage will be critically reviewed.