Multimodal imaging of the role of hyperglycemia following experimental subarachnoid hemorrhage

Hyperglycemia has been linked to worsening outcomes after subarachnoid hemorrhage (SAH). Nevertheless, the mechanisms involved in the pathogenesis of SAH have been scarcely evaluated so far. The role of hyperglycemia was assessed in an experimental model of SAH by T2 weighted, dynamic contrast-enhanced magnetic resonance imaging (T2W and DCE-MRI), [18F]BR-351 PET imaging and immunohistochemistry. Measures included the volume of bleeding, the extent of cerebral infarction and brain edema, blood brain barrier disruption (BBBd), neutrophil infiltration and matrix metalloprotease (MMP) activation. The neurofunctional outcome, neurodegeneration and myelinization were also investigated. The induction of hyperglycemia increased mortality, the size of the ischemic lesion, brain edema, neurodegeneration and worsened neurological outcome during the first 3 days after SAH in rats. In addition, these results show for the first time the exacerbating effect of hyperglycemia on in vivo MMP activation, Intercellular Adhesion Molecule 1 (ICAM-1) expression and neutrophil infiltration together with increased BBBd, bleeding volume and fibrinogen accumulation at days 1 and 3 after SAH. Notably, these data provide valuable insight into the detrimental effect of hyperglycemia on early BBB damage mediated by neutrophil infiltration and MMP activation that could explain the worse prognosis in SAH.

Transient Middle Cerebral Artery Occlusion Model of Stroke

Stroke stands as a major cause of death or chronic disability globally. Nevertheless, existing optimal treatments are limited to reperfusion therapies during the acute phase of ischemic stroke. To gain insights into stroke physiopathology and develop innovative therapeutic approaches, in vivo rodent models of stroke play a fundamental role. The availability of genetically modified animals has particularly propelled the use of mice as experimental stroke models. In stroke patients, occlusion of the middle cerebral artery (MCA) is a common occurrence. Consequently, the most prevalent experimental model involves intraluminal occlusion of the MCA, a minimally invasive technique that doesn't require craniectomy. This procedure involves inserting a monofilament through the external carotid artery (ECA) and advancing it through the internal carotid artery (ICA) until it reaches the branching point of the MCA. After a 45 min arterial occlusion, the monofilament is removed to allow reperfusion. Throughout the process, cerebral blood flow is monitored to confirm the reduction during occlusion and subsequent recovery upon reperfusion. Neurological and tissue outcomes are evaluated using behavioral tests and magnetic resonance imaging (MRI) studies.

Poststroke Lung Infection by Opportunistic Commensal Bacteria Is Not Mediated by Their Expansion in the Gut Microbiota

BACKGROUND

Respiratory and urinary tract infections are frequent complications in patients with severe stroke. Stroke-associated infection is mainly due to opportunistic commensal bacteria of the microbiota that may translocate from the gut. We investigated the mechanisms underlying gut dysbiosis and poststroke infection.

METHODS

Using a model of transient cerebral ischemia in mice, we explored the relationship between immunometabolic dysregulation, gut barrier dysfunction, gut microbial alterations, and bacterial colonization of organs, and we explored the effect of several drug treatments.

RESULTS

Stroke-induced lymphocytopenia and widespread colonization of lung and other organs by opportunistic commensal bacteria. This effect correlated with reduced gut epithelial barrier resistance, and a proinflammatory sway in the gut illustrated by complement and nuclear factor-κB activation, reduced number of gut regulatory T cells, and a shift of gut lymphocytes to γδT cells and T helper 1/T helper 17 phenotypes. Stroke increased conjugated bile acids in the liver but decreased bile acids and short-chain fatty acids in the gut. Gut fermenting anaerobic bacteria decreased while opportunistic facultative anaerobes, notably Enterobacteriaceae, suffered an expansion. Anti-inflammatory treatment with a nuclear factor-κB inhibitor fully abrogated the Enterobacteriaceae overgrowth in the gut microbiota induced by stroke, whereas inhibitors of the neural or humoral arms of the stress response were ineffective at the doses used in this study. Conversely, the anti-inflammatory treatment did not prevent poststroke lung colonization by Enterobacteriaceae.

CONCLUSIONS

Stroke perturbs homeostatic neuro-immuno-metabolic networks facilitating a bloom of opportunistic commensals in the gut microbiota. However, this bacterial expansion in the gut does not mediate poststroke infection.

CCR2 deficiency in monocytes impairs angiogenesis and functional recovery after ischemic stroke in mice

Inflammatory Ly6C^hiCCR2⁺ monocytes infiltrate the brain after stroke but their functions are not entirely clear. We report that CCR2⁺ monocytes and CCR2⁺ lymphocytes infiltrate the brain after permanent ischemia. To underscore the role of CCR2⁺ monocytes, we generated mice with selective CCR2 deletion in monocytes. One day post-ischemia, these mice showed less infiltrating monocytes and reduced expression of pro-inflammatory cytokines, markers of alternatively macrophage activation, and angiogenesis. Accordingly, Ly6C^hi monocytes sorted from the brain of wild type mice 24 h post-ischemia expressed pro-inflammatory genes, M2 genes, and pro-angiogenic genes. Flow cytometry showed heterogeneous phenotypes within the infiltrating Ly6C^hiCCR2⁺ monocytes, including a subgroup of Arginase-1⁺ cells. Mice with CCR2-deficient monocytes displayed a delayed inflammatory rebound 15 days post-ischemia that was not found in wild type mice. Furthermore, they showed reduced angiogenesis and worse behavioral performance. Administration of CCR2^+/+ bone-marrow monocytes to mice with CCR2-deficient monocytes did not improve the behavioral performance suggesting that immature bone-marrow monocytes lack pro-reparative functions. The results show that CCR2⁺ monocytes contribute to acute post-ischemic inflammation and participate in functional recovery. The study unravels heterogeneity in the population of CCR2⁺ monocytes infiltrating the ischemic brain and suggests that pro-reparative monocyte subsets promote functional recovery after ischemic stroke.

Dendritic Cells and Microglia Have Non-redundant Functions in the Inflamed Brain with Protective Effects of Type 1 cDCs

Brain CD11c⁺ cells share features with microglia and dendritic cells (DCs). Sterile inflammation increases brain CD11c⁺ cells, but their phenotype, origin, and functions remain largely unknown. We report that, after cerebral ischemia, microglia attract DCs to the inflamed brain, and astroglia produce Flt3 ligand, supporting development and expansion of CD11c⁺ cells. CD11c⁺ cells in the inflamed brain are a complex population derived from proliferating microglia and infiltrating DCs, including a major subset of OX40L⁺ conventional cDC2, and also cDC1, plasmacytoid, and monocyte-derived DCs. Despite sharing certain morphological features and markers, CD11c⁺ microglia and DCs display differential expression of pattern recognition receptors and chemokine receptors. DCs excel CD11c^- and CD11c⁺ microglia in the capacity to present antigen through MHCI and MHCII. Of note, cDC1s protect from brain injury after ischemia. We thus reveal aspects of the dynamics and functions of brain DCs in the regulation of inflammation and immunity.

High-density speckle contrast optical tomography of cerebral blood flow response to functional stimuli in the rodent brain

Noninvasive, three-dimensional, and longitudinal imaging of cerebral blood flow (CBF) in small animal models and ultimately in humans has implications for fundamental research and clinical applications. It enables the study of phenomena such as brain development and learning and the effects of pathologies, with a clear vision for translation to humans. Speckle contrast optical tomography (SCOT) is an emerging optical method that aims to achieve this goal by directly measuring three-dimensional blood flow maps in deep tissue with a relatively inexpensive and simple system. High-density SCOT is developed to follow CBF changes in response to somatosensory cortex stimulation. Measurements are carried out through the intact skull on the rat brain. SCOT is able to follow individual trials in each brain hemisphere, where signal averaging resulted in comparable, cortical images to those of functional magnetic resonance images in spatial extent, location, and depth. Sham stimuli are utilized to demonstrate that the observed response is indeed due to local changes in the brain induced by forepaw stimulation. In developing and demonstrating the method, algorithms and analysis methods are developed. The results pave the way for longitudinal, nondestructive imaging in preclinical rodent models that can readily be translated to the human brain.

T Cells Prevent Hemorrhagic Transformation in Ischemic Stroke by P-Selectin Binding

Objective- Hemorrhagic transformation is a serious complication of ischemic stroke after recanalization therapies. This study aims to identify mechanisms underlying hemorrhagic transformation after cerebral ischemia/reperfusion. Approach and Results- We used wild-type mice and Selplg^-/- and Fut7^-/- mice defective in P-selectin binding and lymphopenic Rag2^-/- mice. We induced 30-minute or 45-minute ischemia by intraluminal occlusion of the middle cerebral artery and assessed hemorrhagic transformation at 48 hours with a hemorrhage grading score, histological means, brain hemoglobin content, or magnetic resonance imaging. We depleted platelets and adoptively transferred T cells of the different genotypes to lymphopenic mice. Interactions of T cells with platelets in blood were studied by flow cytometry and image stream technology. We show that platelet depletion increased the bleeding risk only after large infarcts. Lymphopenia predisposed to hemorrhagic transformation after severe stroke, and adoptive transfer of T cells prevented hemorrhagic transformation in lymphopenic mice. CD4⁺ memory T cells were the subset of T cells binding P-selectin and platelets through functional P-selectin glycoprotein ligand-1. Mice defective in P-selectin binding had a higher hemorrhagic score than wild-type mice. Adoptive transfer of T cells defective in P-selectin binding into lymphopenic mice did not prevent hemorrhagic transformation. Conclusions- The study identifies lymphopenia as a previously unrecognized risk factor for secondary hemorrhagic transformation in mice after severe ischemic stroke. T cells prevent hemorrhagic transformation by their capacity to bind platelets through P-selectin. The results highlight the role of T cells in bridging immunity and hemostasis in ischemic stroke.

Role of the S1P pathway and inhibition by fingolimod in preventing hemorrhagic transformation after stroke

Hemorrhagic transformation (HT) is a complication of severe ischemic stroke after revascularization. Patients with low platelet counts do not receive reperfusion therapies due to high risk of HT. The immunomodulatory drug fingolimod attenuated HT after tissue plasminogen activator in a thromboembolic stroke model, but the underlying mechanism is unknown. Fingolimod acts on several sphingosine-1-phosphate (S1P) receptors, prevents lymphocyte trafficking to inflamed tissues, and affects brain and vascular cells. This study aimed to investigate changes in S1P-signaling in response to brain ischemia/reperfusion and the effects of the S1P receptor modulator fingolimod on HT. We studied brain expression of S1P signaling components, S1P concentration, and immune cell infiltration after ischemia/reperfusion in mice. We administered fingolimod after ischemia to wild-type mice, lymphocyte-deficient Rag2^−/− mice, and mice with low platelet counts. Ischemia increased S1P-generating enzyme SphK1 mRNA, S1P concentration, and S1P receptor-1 (S1P1)⁺ T-cells in the brain. Fingolimod prevented lymphocyte infiltration, and attenuated the severity of HT in Rag2^−/− mice but it was ineffective under thrombocytopenia. Fingolimod prevented β-catenin degradation but not Evans blue extravasation. Ischemia/reperfusion upregulates brain S1P signaling pathway, and fingolimod exerts local effects that attenuate HT. Although fingolimod seems to act on the brain tissue, it did not prevent blood-brain barrier leakage.

Location of Neutrophils in Different Compartments of the Damaged Mouse Brain After Severe Ischemia/Reperfusion

Background and Purpose- Ischemia attracts neutrophils to the injured brain. However, neutrophil location and access to the damaged brain tissue is not yet entirely understood. We aimed to investigate neutrophil location in a mouse model of cerebral ischemia/reperfusion. Methods- Adult male C57BL/6 mice (n=52) received 45-minute intraluminal middle cerebral artery occlusion followed by 14, 24, 48, or 96 hours of reperfusion. Sham-operated mice (n=9) were subjected to the entire surgical procedure. We used wild-type mice and Catchup^IVM mice expressing a red fluorescent protein in neutrophils. In addition, fluorescent neutrophils obtained from reporter DsRed (discosoma red fluorescent protein) mice were transferred intravenously to wild-type mice after ischemia. Mice received transcardial paraformaldehyde perfusion, the brain was cryoprotected, frozen, and cryostat sections were studied by immunofluorescence and confocal microscopy. Results- Ischemia induced a time-dependent increase in brain neutrophil numbers versus sham operation. We detected neutrophils in the leptomeninges, ventricles, capillary lumen, perivascular spaces, and parenchyma within the infarcted core. Most ischemic mice showed neutrophils in the leptomeninges and perivascular spaces, whereas the presence and number of neutrophils in the parenchyma was variable among ischemic mice. During the first 24 hours, only a few mice showed parenchymal neutrophils, but the frequency of mice showing neutrophils in the parenchyma and neutrophil numbers increased at 48 and 96 hours. We also detected signs of basement membrane disruption and hints of occasional neutrophil degranulation and formation of neutrophil extracellular traps. Conclusions- After ischemia/reperfusion, neutrophils accumulate in the leptomeninges and perivascular spaces, and eventually can reach the infarcted brain parenchyma.

CNS-border associated macrophages respond to acute ischemic stroke attracting granulocytes and promoting vascular leakage

The central nervous system (CNS) contains several types of immune cells located in specific anatomic compartments. Macrophages reside at the CNS borders surrounding the brain vessels, in leptomeningeal spaces and the choroid plexus, where they interact with the vasculature and play immunological surveillance and scavenging functions. We investigated the phenotypic changes and role of these macrophages in response to acute ischemic stroke. Given that CD163 expression is a hallmark of perivascular and meningeal macrophages in the rat and human brain, we isolated CD163⁺ brain macrophages by fluorescence activated cell sorting. We obtained CD163⁺ cells from control rats and 16 h following transient middle cerebral artery occlusion, after verifying that infiltration of CD163⁺ peripheral myeloid cells is negligible at this acute time point. Transcriptome analysis of the sorted CD163⁺ cells identified ischemia-induced upregulation of the hypoxia inducible factor-1 pathway and induction of genes encoding for extracellular matrix components and leukocyte chemoattractants, amongst others. Using a cell depletion strategy, we found that CNS border-associated macrophages participate in granulocyte recruitment, promote the expression of vascular endothelial growth factor (VEGF), increase the permeability of pial and cortical blood vessels, and contribute to neurological dysfunction in the acute phase of ischemia/reperfusion. We detected VEGF expression surrounding blood vessels and in some CD163⁺ perivascular macrophages in the brain tissue of ischemic stroke patients deceased one day after stroke onset. These findings show ischemia-induced reprogramming of the gene expression profile of CD163⁺ macrophages that has a rapid impact on leukocyte chemotaxis and blood-brain barrier integrity, and promotes neurological impairment in the acute phase of stroke.

Longitudinal, transcranial measurement of functional activation in the rat brain by diffuse correlation spectroscopy

Neural activity is an important biomarker for the presence of neurodegenerative diseases, cerebrovascular alterations, and brain trauma; furthermore, it is a surrogate marker for treatment effects. These pathologies may occur and evolve in a long time-period, thus, noninvasive, transcutaneous techniques are necessary to allow a longitudinal follow-up. In the present work, we have customized noninvasive, transcutaneous, diffuse correlation spectroscopy (DCS) to localize changes in cerebral blood flow (CBF) induced by neural activity. We were able to detect changes in CBF in the somatosensory cortex by using a model of electrical forepaw stimulation in rats. The suitability of DCS measurements for longitudinal monitoring was demonstrated by performing multiple sessions with the same animals at different ages (from 6 to 18 months). In addition, functional DCS has been cross-validated by comparison with functional magnetic resonance imaging (fMRI) in the same animals in a subset of the time-points. The overall results obtained with transcutaneous DCS demonstrates that it can be utilized in longitudinal studies safely and reproducibly to locate changes in CBF induced by neural activity in the small animal brain.

A CNS-permeable Hsp90 inhibitor rescues synaptic dysfunction and memory loss in APP-overexpressing Alzheimer's mouse model via an HSF1-mediated mechanism

Induction of neuroprotective heat-shock proteins via pharmacological Hsp90 inhibitors is currently being investigated as a potential treatment for neurodegenerative diseases. Two major hurdles for therapeutic use of Hsp90 inhibitors are systemic toxicity and limited central nervous system permeability. We demonstrate here that chronic treatment with a proprietary Hsp90 inhibitor compound (OS47720) not only elicits a heat-shock-like response but also offers synaptic protection in symptomatic Tg2576 mice, a model of Alzheimer's disease, without noticeable systemic toxicity. Despite a short half-life of OS47720 in mouse brain, a single intraperitoneal injection induces rapid and long-lasting (>3 days) nuclear activation of the heat-shock factor, HSF1. Mechanistic study indicates that the remedial effects of OS47720 depend upon HSF1 activation and the subsequent HSF1-mediated transcriptional events on synaptic genes. Taken together, this work reveals a novel role of HSF1 in synaptic function and memory, which likely occurs through modulation of the synaptic transcriptome.

High-density speckle contrast optical tomography (SCOT) for three dimensional tomographic imaging of the small animal brain

High-density speckle contrast optical tomography (SCOT) utilizing tens of thousands of source-detector pairs, was developed for in vivo imaging of blood flow in small animals. The reduction in cerebral blood flow (CBF) due to local ischemic stroke in a mouse brain was transcanially imaged and reconstructed in three dimensions. The reconstructed volume was then compared with corresponding magnetic resonance images demonstrating that the volume of reduced CBF agrees with the infarct zone at twenty-four hours.

Uric Acid Is Protective After Cerebral Ischemia/Reperfusion in Hyperglycemic Mice

Hyperglycemia at stroke onset is associated with poor long-term clinical outcome in numerous studies. Hyperglycemia induces intracellular acidosis, lipid peroxidation, and peroxynitrite production resulting in the generation of oxidative and nitrosative stress in the ischemic tissue. Here, we studied the effects of acute hyperglycemia on in vivo intercellular adhesion molecule-1 (ICAM-1) expression, neutrophil recruitment, and brain damage after ischemia/reperfusion in mice and tested whether the natural antioxidant uric acid was protective. Hyperglycemia was induced by i.p. administration of dextrose 45 min before transient occlusion of the middle cerebral artery. Magnetic resonance imaging (MRI) was performed at 24 h to measure lesion volume. A group of normoglycemic and hyperglycemic mice received an i.v. injection of micron-sized particles of iron oxide (MPIOs), conjugated with either anti-ICAM-1 antibody or control IgG, followed by T2*w MRI. Neutrophil infiltration was studied by immunofluorescence and flow cytometry. A group of hyperglycemic mice received an i.v. infusion of uric acid (16 mg/kg) or the vehicle starting after 45 min of reperfusion. ICAM-1-targeted MPIOs induced significantly larger MRI contrast-enhancing effects in the ischemic brain of hyperglycemic mice, which also showed more infiltrating neutrophils and larger lesions than normoglycemic mice. Uric acid reduced infarct volume in hyperglycemic mice but it did not prevent vascular ICAM-1 upregulation and did not significantly reduce the number of neutrophils in the ischemic brain tissue. In conclusion, hyperglycemia enhances stroke-induced vascular ICAM-1 and neutrophil infiltration and exacerbates the brain lesion. Uric acid reduces the lesion size after ischemia/reperfusion in hyperglycemic mice.

Immature monocytes recruited to the ischemic mouse brain differentiate into macrophages with features of alternative activation

Acute stroke induces a local inflammatory reaction causing leukocyte infiltration. Circulating monocytes are recruited to the ischemic brain and become tissue macrophages morphologically indistinguishable from reactive microglia. However, monocytes are a heterogeneous population of cells with different functions. Herein, we investigated the infiltration and fate of the monocyte subsets in a mouse model of focal brain ischemia by permanent occlusion of the distal portion of the middle cerebral artery. We separated two main subtypes of CD11b(hi) monocytes according to their expression of the surface markers Ly6C and CD43. Using adoptive transfer of reporter monocytes and monocyte depletion, we identified the pro-inflammatory Ly6C(hi)CD43(lo)CCR2(+) subset as the predominant monocytes recruited to the ischemic tissue. Monocytes were seen in the leptomeninges from where they entered the cortex along the penetrating arterioles. Four days post-ischemia, they had invaded the infarcted core, where they were often located adjacent to blood vessels. At this time, Iba-1(-) and Iba-1(+) cells in the ischemic tissue incorporated BrdU, but BrdU incorporation was rare in the reporter monocytes. The monocyte phenotype progressively changed by down-regulating Ly6C, up-regulating F4/80, expressing low or intermediate levels of Iba-1, and developing macrophage morphology. Moreover, monocytes progressively acquired the expression of typical markers of alternatively activated macrophages, like arginase-1 and YM-1. Collectively, the results show that stroke mobilized immature pro-inflammatory Ly6C(hi)CD43(lo) monocytes that acutely infiltrated the ischemic tissue reaching the core of the lesion. Monocytes differentiated to macrophages with features of alternative activation suggesting possible roles in tissue repair during the sub-acute phase of stroke.

High-speed multi-exposure laser speckle contrast imaging with a single-photon counting camera

Laser speckle contrast imaging (LSCI) has emerged as a valuable tool for cerebral blood flow (CBF) imaging. We present a multi-exposure laser speckle imaging (MESI) method which uses a high-frame rate acquisition with a negligible inter-frame dead time to mimic multiple exposures in a single-shot acquisition series. Our approach takes advantage of the noise-free readout and high-sensitivity of a complementary metal-oxide-semiconductor (CMOS) single-photon avalanche diode (SPAD) array to provide real-time speckle contrast measurement with high temporal resolution and accuracy. To demonstrate its feasibility, we provide comparisons between in vivo measurements with both the standard and the new approach performed on a mouse brain, in identical conditions.

Mannose-binding lectin promotes local microvascular thrombosis after transient brain ischemia in mice

BACKGROUND AND PURPOSE

Several lines of evidence support the involvement of mannose-binding lectin (MBL) in stroke brain damage. The lectin pathway of the complement system facilitates thrombin activation and clot formation under certain experimental conditions. In the present study, we examine whether MBL promotes thrombosis after ischemia/reperfusion and influences the course and prognosis of ischemic stroke.

METHODS

Middle cerebral artery occlusion/reperfusion was performed in MBL-deficient (n=85) and wild-type (WT; n=83) mice, and the brain lesion was assessed by MRI at days 1 and 7. Relative cerebral blood flow was monitored up to 6 hours after middle cerebral artery occlusion with laser speckle contrast imaging. Fibrin(ogen) was analyzed in the brain vasculature and plasma, and the effects of thrombin inhibitor argatroban were evaluated to assess the role of MBL in thrombin activation.

RESULTS

Infarct volumes and neurological deficits were smaller in MBL knockout mice than in WT mice. Relative cerebral blood flow values during middle cerebral artery occlusion and at reperfusion were similar in both groups, but decreased during the next 6 hours in the WT group only. Also, the WT mice showed more fibrin(ogen) in brain vessels and a better outcome after argatroban treatment. In contrast, argatroban did not improve the outcome in MBL knockout mice.

CONCLUSIONS

MBL promotes brain damage and functional impairment after brain ischemia/reperfusion in mice. These effects are secondary to intravascular thrombosis and impaired relative cerebral blood flow during reperfusion. Argatroban protects WT mice, but not MBL knockout mice, emphasizing a role of MBL in local thrombus formation in acute ischemia/reperfusion.

In vivo imaging of induction of heat-shock protein-70 gene expression with fluorescence reflectance imaging and intravital confocal microscopy following brain ischaemia in reporter mice

PURPOSE

Stroke induces strong expression of the 72-kDa heat-shock protein (HSP-70) in the ischaemic brain, and neuronal expression of HSP-70 is associated with the ischaemic penumbra. The aim of this study was to image induction of Hsp-70 gene expression in vivo after brain ischaemia using reporter mice.

METHODS

A genomic DNA sequence of the Hspa1b promoter was used to generate an Hsp70-mPlum far-red fluorescence reporter vector. The construct was tested in cellular systems (NIH3T3 mouse fibroblast cell line) by transient transfection and examining mPlum and Hsp-70 induction under a challenge. After construct validation, mPlum transgenic mice were generated. Focal brain ischaemia was induced by transient intraluminal occlusion of the middle cerebral artery and the mice were imaged in vivo with fluorescence reflectance imaging (FRI) with an intact skull, and with confocal microscopy after opening a cranial window.

RESULTS

Cells transfected with the Hsp70-mPlum construct showed mPlum fluorescence after stimulation. One day after induction of ischaemia, reporter mice showed a FRI signal located in the HSP-70-positive zone within the ipsilateral hemisphere, as validated by immunohistochemistry. Live confocal microscopy allowed brain tissue to be visualized at the cellular level. mPlum fluorescence was observed in vivo in the ipsilateral cortex 1 day after induction of ischaemia in neurons, where it is compatible with penumbra and neuronal viability, and in blood vessels in the core of the infarction.

CONCLUSION

This study showed in vivo induction of Hsp-70 gene expression in ischaemic brain using reporter mice. The fluorescence signal showed in vivo the induction of Hsp-70 in penumbra neurons and in the vasculature within the ischaemic core.

Abstract 2330: Citicoline Is A Strong Pro-angiogenic Molecule And Protects Brain Endothelial Cells From Apoptosis After Stroke

Background and purposes - Citicoline is neuroprotective agent used in stroke patients. Citicoline induces angiogenesis i n vitro ; however, the molecular mechanisms induced by citicoline have not been fully investigated. The present study was designed to investigate the key signalling mechanisms through which citicoline modulates angiogenesis-associated with stroke recovery.

Methods - In vitro angiogenesis assays: migration (Bodyen chamber, a chemotaxis assay and wound recovery), proliferation and differentiation into tube-like structures in Matrigel TM as well as spheroid development assays were carried out using human brain microvessel endothelial cells (HBMECs). Western blotting was performed on the protein extraction from HBMEC stimulated with citicoline. Citicoline signalling pathway was studied using a phospho-protein screening array performed by Kinexus. A Staurosporin/calcium ionophore-induced apoptosis assay was performed by seeding HBMEC on the glass coverslips. Cells were pre-incubated with citicoline and the apoptosis was induced by addition of the ionophore or staurosporin. Cells were examined by microscoy and/or stained using propidium iodide and Hoechst stain solution and then counted under fluorescence microscope. Transient MCAO was carried out on Sprague Dawley rats (n=4 per group) with and without citicoline treatment (1000mg/Kg) applied at the time of occlusion and subsequently every 3 days until euthanasia (21 days). Vascularity of the stroke-affected regions was examined with antibodies recognising the microvessels (CD34) and active cells (CD105).

Results - Citicoline presented no mitogenic and chemotactic effects on HBMEC; however, it significantly increased wound recovery, the formation of tube-like structures in Matrigel TM -with a stronger effect than FGF-2, and enhanced spheroid development and sprouting. Citicoline induced the expression of ERK-1/2, known to be involved in last step of signalling pathways of angiogenesis. Kinexus results showed an over-expression of ASK-1, HER2, IRS-1 and Jun and inhibition of Hsp27, Integrin alpha4, MEK1 (MAP2K1) and Histone H2B proteins. Knock-down of IRS-1 with targeted siRNA inhibited the pro-angiogenic effects (sprouting and tube-formation) of citicoline in HBMECs. The percentage of surviving cells was higher in the presence of citicoline after inducing apoptosis. Histology of infarcted regions showed that citicoline significantly increased the numbers of new active (CD105-positive) microvessels.

Conclusion - The findings demonstrate both a pro-angiogenic and protective effect of citicoline on HBMECs in vitro and following MCAO in vitro. Additionally, this molecule may play a key role in the modulation of angiogenesis thereby and ultimately, improving tissue function, revascularisation and neuronal survival after ischaemic stroke.

Stem cell mediation of functional recovery after stroke in the rat

BACKGROUND

Regenerative strategies of stem cell grafting have been demonstrated to be effective in animal models of stroke. In those studies, the effectiveness of stem cells promoting functional recovery was assessed by behavioral testing. These behavioral studies do, however, not provide access to the understanding of the mechanisms underlying the observed functional outcome improvement.

METHODOLOGY/PRINCIPAL FINDINGS

In order to address the underlying mechanisms of stem cell mediated functional improvement, this functional improvement after stroke in the rat was investigated for six months after stroke by use of fMRI, somatosensory evoked potentials by electrophysiology, and sensorimotor behavior testing. Stem cells were grafted ipsilateral to the ischemic lesion. Rigorous exclusion of spontaneous recovery as confounding factor permitted to observe graft-related functional improvement beginning after 7 weeks and continuously increasing during the 6-month observation period. The major findings were i) functional improvement causally related to the stem cells grafting; ii) tissue replacement can be excluded as dominant factor for stem cell mediated functional improvement; iii) functional improvement occurs by exclusive restitution of the function in the original representation field, without clear contributions from reorganization processes, and iv) stem cells were not detectable any longer after six months.

CONCLUSIONS/SIGNIFICANCE

A delayed functional improvement due to stem cell implantation has been documented by electrophysiology, fMRI and behavioral testing. This functional improvement occurred without cells acting as a tissue replacement for the necrotic tissue after the ischemic event. Combination of disappearance of grafted cells after six months on histological sections with persistent functional recovery was interpreted as paracrine effects by the grafted stem cells being the dominant mechanism of cell activity underlying the observed functional restitution of the original activation sites. Future studies will have to investigate whether the stem cell mediated improvement reactivates the original representation target field by using original connectivity pathways or by generating/activating new ones for the stimulus.

Genetically-defined deficiency of mannose-binding lectin is associated with protection after experimental stroke in mice and outcome in human stroke

BACKGROUND

The complement system is a major effector of innate immunity that has been involved in stroke brain damage. Complement activation occurs through the classical, alternative and lectin pathways. The latter is initiated by mannose-binding lectin (MBL) and MBL-associated serine proteases (MASPs). Here we investigated whether the lectin pathway contributes to stroke outcome in mice and humans.

METHODOLOGY/PRINCIPAL FINDINGS

Focal cerebral ischemia/reperfusion in MBL-null mice induced smaller infarctions, better functional outcome, and diminished C3 deposition and neutrophil infiltration than in wild-type mice. Accordingly, reconstitution of MBL-null mice with recombinant human MBL (rhMBL) enhanced brain damage. In order to investigate the clinical relevance of these experimental observations, a study of MBL2 and MASP-2 gene polymorphism rendering the lectin pathway dysfunctional was performed in 135 stroke patients. In logistic regression adjusted for age, gender and initial stroke severity, unfavourable outcome at 3 months was associated with MBL-sufficient genotype (OR 10.85, p = 0.008) and circulating MBL levels (OR 1.29, p = 0.04). Individuals carrying MBL-low genotypes (17.8%) had lower C3, C4, and CRP levels, and the proinflammatory cytokine profile was attenuated versus MBL-sufficient genotypes.

CONCLUSIONS/SIGNIFICANCE

In conclusion, genetically defined MBL-deficiency is associated with a better outcome after acute stroke in mice and humans.

MRI Detection of Secondary Damage After Stroke

Background and Purpose— Iron plays a central role in many metabolic processes. Under certain pathological situations it accumulates, producing negative effects such as increasing damage by oxidative stress. The present study examined long-term iron accumulation in a stroke model with secondary degeneration, using MRI and histological techniques.

Methods— Male Wistar rats (n=22) were subjected to 60 minutes MCA occlusion. MR images (T2- and T2*-weighted) were obtained weekly between weeks 1 and 7 after reperfusion, and at weeks 10, 14, 20, and 24. Histological iron detection and immunohistochemical examination for different markers (NeuN, GFAP, OX-42, HO-1, and APP) were performed at the 3 survival time points (3, 7, and 24 weeks).

Results— Infarcts affecting MCA territory were evident on T2-weighted imaging, and all animals showed deficits on behavioral tests. In the thalamus, T2 hyperintensity was detected 3 weeks after stroke, and disappeared around week 7 when T2*-weighted images showed a marked hypointensity in that area. Histology revealed neuronal loss in the thalamus, accompanied by strong microglial reactivity and microglial HO-1 expression. APP deposits were detected in the thalamus from week 3 on and persisted until week 24. Iron storage was detected in microglia at week 3, in the parenchyma at week 7, and around APP deposits at week 24.

Conclusions— T2*-weighted MRI allows the detection of secondary damage in the thalamus after MCAO. Iron accumulation in the thalamus is mediated by HO-1 expression in reactive microglia.

Reproducible imaging of rat corticothalamic pathway by longitudinal manganese-enhanced MRI (L-MEMRI)

Manganese-enhanced MRI (MEMRI) has been described as a powerful tool to depict the architecture of neuronal circuits. The aim of the present study was to optimize the experimental conditions of MEMRI that permits the study of insult-induced alterations of the somatosensory pathway in a longitudinal way, and to provide functional information on rat corticothalamic connectivity or disturbances thereof. A guidance screw was implanted in the skull of the rats, over the forelimb representation area of the primary somatosensory cortex (S1fl), allowing repetitive injections at the same stereotactic coordinates. MnCl2 (200 nL, 0.3 M) was injected 1.5 mm below the dura using a calibrated microcapillary. Animals received MnCl2 injections 3 times at 15 day intervals. Spatiotemporal patterns showed a significant hyperintensity on T1-weighted images induced by manganese transport in structures related to the somatosensory pathway, i.e. globus pallidus, caudate putamen, thalamus and substantia nigra. 7 days after MnCl2 injection hyperintensity was only evident at some points surrounding the injection site. Complete loss of manganese-induced contrast was achieved after 15 days after injection. Functional MRI (fMRI) experiments were performed under the same conditions, 24 h after MnCl2 injection. Activation of S1fl was observed showing that fMRI and MEMRI studies are compatible and can be performed in parallel in the same animals. The present study shows, for the first time, a robust and reproducible technique to perform longitudinal MEMRI (L-MEMRI) experiments and to study the time course of alterations of the corticothalamic connections following stroke in the rat.

Cell tracking using magnetic resonance imaging

Cell tracking by in vivo magnetic resonance imaging (MRI) requires strategies of labelling the cells with MRI contrast agents. The principal routes to achieve efficient cell labelling for neurological applications are discussed with methodological advantages and caveats. Beyond temporo-spatial localization of labelled cells, the investigation of functional cell status is of great interest to allow studies of functional cell dynamics. The two major approaches to reach this goal, use of responsive contrast agents and generation of transgenic cell lines, are discussed.

Transient middle cerebral artery occlusion causes different structural, mechanical, and myogenic alterations in normotensive and hypertensive rats

Transient focal cerebral ischemia in the rat alters vessel properties, and spontaneously hypertensive rats (SHR) show a poorer outcome after ischemia. In the present study we examined the role of hypertension on vessel properties after ischemia-reperfusion. The right middle cerebral artery (MCA) was occluded (90 min) and reperfused (24 h) in SHR (n = 12) and Wistar-Kyoto rats (WKY; n = 11). Sham-operated rats (SHR, n = 10; WKY, n = 10) were used as controls. The structural, mechanical, and myogenic properties of the MCA were assessed by pressure myography. Nuclei distribution and elastin content and organization were analyzed by confocal microscopy. Infarct volume was larger in SHR than in WKY rats. Ischemia-reperfusion induced adventitial hypertrophy associated with an increase in the total number of adventitial cells. In addition, fenestrae area and arterial distensibility increased and myogenic tone decreased in the MCA of WKY rats after ischemia-reperfusion. Hypertension per se induced hypertrophic inward remodeling. Ischemia-reperfusion decreased the cross-sectional area of the MCA in SHR, without significant changes in distensibility, despite an increase in fenestrae area. In addition, MCA myogenic properties were not altered after ischemia-reperfusion in SHR. Our results indicate that in normotensive rats, MCA develops a compensatory mechanism (i.e., enhanced distensibility and decreased myogenic tone) that counteracts the effect of ischemia-reperfusion and ensures correct cerebral irrigation. These compensatory mechanisms are lost in hypertension, thereby explaining, at least in part, the greater infarct volume observed in SHR.

A responsive MRI contrast agent to monitor functional cell status

It has been shown that insoluble Gd chelates are suitable MRI contrast agents for conditional activation by intracellular lipases. The DTPA-based, insoluble, inactive contrast agent was internalized into dendritic cells by phagocytosis. Cleavage of long aliphatic side chains by intracellular lipase activity leads to the contrast agents solubility and hereby its activation depending on the enzyme expression. Uptake and activation of the contrast agent was much reduced in Flt3+ CD11b+ progenitor cells. Detectability limits in the T(1)-weighted MR images were estimated in phantoms and in vivo in the rat brain. Marginal toxic effects were only observed at very high concentrations of the contrast agent. The chelate can easily be modified to be targeted by enzymes expressed during specific change of cell status like activation or differentiation. Such a system is suitable for functional cellular in vivo MR imaging.

Modest MRI Signal Intensity Changes Precede Delayed Cortical Necrosis After Transient Focal Ischemia in the Rat

Background and Purpose— Diffusion-weighted imaging (DWI) hyperintensities and apparent diffusion coefficient (ADC) hypointensities are MRI features of acute stroke. DWI alterations during ischemia recover with early reperfusion, but they can reappear later. Pronounced signal abnormalities early after stroke are associated with infarction, but the significance of subtle changes is unclear. Here we evaluated the degree and time course of regional signal intensity changes during the first 24 hours of reperfusion after transient ischemia, and we related them to the progression of the histopathological damage.

Methods— Rats (n=54) were subjected to 1-hour intraluminal middle cerebral artery occlusion to assess the dynamics of MRI signal intensity changes during the initial 24 hours and their correspondent histopathological features: 2,3,5-triphenyltetrazolium chloride (TTC) staining, and hematoxylin and eosin, and immunoreactivity to 70-kDa heat shock protein and to astroglial and microglial markers.

Results— This model of ischemia caused early striatal infarction but delayed necrosis in the cortex. The striatum showed marked MRI changes from 4 hours of reperfusion. By 12 hours, the striatal ADC signal intensity ratio to the homologous contralateral region was 30% reduced, and the TTC staining evidenced infarction. Contrarily, the cortical ADC ratio was only 15% reduced, and TTC staining was normal at 12 hours. After this time, the cortex showed sudden and pronounced (>30%) ADC signal intensity changes coincidentally with the manifestation of infarction, accompanied with severe vacuolation and unambiguous signs of neuronal and astroglial death.

Conclusions— These findings suggest that minor changes in ADC signal intensity early after ischemia should not be underestimated because they may be harbingers of delayed infarction.

Anti-VCAM-1 antibodies did not protect against ischemic damage either in rats or in mice

Cerebral ischemia triggers an inflammatory process involving the infiltration of leukocytes to the parenchyma. Circulating leukocytes adhere to the vascular wall through adhesion molecules. Here we quantified the in vivo expression of vascular cell adhesion molecule-1 (VCAM-1) in the brain, heart and lungs from 6 to 48 h after transient middle cerebral artery (MCA) occlusion in rats, by intravenous injection of a tracer radiolabelled anti-VCAM-1 antibody. The vascular localization of VCAM-1 was verified by immunohistochemistry after in vivo injection of the antibody. Vascular cell adhesion molecule-1 was strongly induced (4-fold at 24 h) in the microvasculature of the ischemic area, and, to a lesser extent, in the contralateral hemisphere and in a remote organ, the heart, but not in the lungs, indicating that the inflammatory process propagates beyond the injured brain. We injected intravenously either blocking doses of anti-VCAM-1 antibodies or control antibodies after MCA occlusion in rats and mice. We evaluated the neurological score in rats, and infarct volume at 2 days in rats and at 4 days in mice. Anti-VCAM-1 did not protect against ischemic damage either in rats or in mice. Vascular cell adhesion molecule-1 blockade significantly decreased the number of ED1 (labeling monocytes /macrophages/reactive microglia)-positive cells in the ischemic rat brain. However, it did not reduce the numbers of infiltrating neutrophils and lymphocytes, and total leukocytes (CD45 positive), which showed a trend to increase. The results show vascular upregulation of VCAM-1 after transient focal ischemia, but no benefits of blocking VCAM-1, suggesting that this is not a therapeutical strategy for stroke treatment.

Steady plasma concentration of unfractionated heparin reduces infarct volume and prevents inflammatory damage after transient focal cerebral ischemia in the rat

Unfractionated heparin (UH) decreases the extent of infarction after transient focal brain ischemia in the rat and abridges neuroinflammatory damage in patients with acute stroke. This study was aimed at assessing whether controlled and steady heparinemia in plasma can reduce infarct volume and exert neuroprotective effects after ischemia. Infarct volume was measured at 24 and 7 days following a 1-hr intraluminal middle cerebral artery (MCA) occlusion in rats treated with UH or with vehicle. After testing several UH administration protocols, we choose to give a bolus of 200 U/kg, which was started 3 hr after the occlusion, followed by a 24-hr intraperitoneal perfusion of 70 U/kg/hr, which maintained a 24-hr steady plasma heparinemia (0.3-0.6 U/ml) and caused no CNS or systemic bleeding. In addition, plasma IL-10 concentration was measured by ELISA, endothelial VCAM-1 expression was evaluated by i.v. injection of a (125)I-labeled monoclonal antibody against VCAM-1, and brain hemeoxygenase-1 (HO-1) expression was determined by Western blot. UH-treated rats showed smaller infarctions than rats treated with vehicle, as well as higher IL-10 plasma levels and HO-1 brain expression and lower endothelial VCAM-1 induction. The study shows that a stable plasma concentration of UH given at nonhemorrhagic doses reduces infarct volume after ischemia-reperfusion in the rat. It also shows that UH prevented the induction of cell adhesion molecules in the cerebral vasculature and increased the expression of molecules with antiinflammatory and prosurvival properties. These findings support further testing of the clinical value of parenteral, adjusted, high-dose UH in patients with acute stroke.

Neutrophil infiltration increases matrix metalloproteinase-9 in the ischemic brain after occlusion/reperfusion of the middle cerebral artery in rats

Matrix metalloproteinase-9 (MMP-9) activity increases in the brain during the first day after focal ischemia and might be involved in the pathogenesis of tissue damage. We previously showed MMP-9 in the extracellular space of brain parenchyma along with neutrophil recruitment after ischemia. In the present study, we tested whether neutrophils were a direct source of enhanced MMP-9 in the ischemic brain. Neutrophil infiltration was prevented either by injecting an antibody against ICAM-1, which abrogates neutrophil adhesion to the endothelial vessel wall, or by inducing neutropenia. One-hour intraluminal middle cerebral artery occlusion with reperfusion was induced, and studies were performed at 24 hours. Circulating neutrophils expressed 95-kDa MMP-9 and dimers, and infiltrated neutrophils stained positive for MMP-9. The expression of MMP-9 (mainly 95-kDa proform and dimers and, to a lesser extent, 88-kDa form) increased in brain after ischemia/reperfusion. Treatments preventing neutrophil infiltration failed to preclude the ischemia-induced increase in 88-kDa MMP-9 form and gelatinase activity in neurons and blood vessels. However, these treatments prevented the major increase in 95-kDa MMP-9 form and dimers. We conclude that neutrophil infiltration highly contributes to enhanced MMP-9 in the ischemic brain by releasing MMP-9 proform, which might participate in the tissular inflammatory reaction.

Caspase-dependent and caspase-independent signalling of apoptosis in the penumbra following middle cerebral artery occlusion in the adult rat

Transient focal ischaemia by middle cerebral artery occlusion (MCAO) may produce cell death, but the mechanisms leading to cell death differ in the infarct core and in the penumbra, the immediate zone surrounding the infarct core. In the present study, transient focal ischaemia to adult rats was produced by intraluminal occlusion of the middle cerebral artery for 1 h followed by 0 h (n=6), 1 h (n=10), 4 h (n=8), 6 h (n=2) and 12 h (n=3) of reperfusion. The present model of ischaemia causes a large cortico-striatal infarct extending through the mediolateral cortex and dorsolateral striatum at 12 h. The expression and subcellular distribution of several proteins involved in apoptosis have been examined in the penumbra and in the infarct core by using combined methods of immunohistochemistry, cell subfractionation and Western blotting. Transient focal ischaemia by MCAO results in activation of complex signal pathways for cell death in the penumbra. Increased expression of Bcl-2 and Bax, but not of Bcl-x, occurs in the penumbra at the time when Bax translocates from the cytosol to the mitochondria, cytochrome c is released to the cytoplasm and active caspase-3 is expressed. Bax translocation, cytochrome c release and active caspase-3 are observed at 4 h, but not at 1 h, following reperfusion, and together indicate activation of the caspase-dependent pathway of apoptosis in the penumbra. In contrast, reduced Bax expression but not Bax translocation and cytochrome c release occurs in the infarct core, thus suggesting apoptosis signals restricted to the penumbra. In addition, increased expression of an apoptosis-inducing factor in the cytoplasm and nuclei of selected cells shows, for the first time, activation of the caspase-independent mitochondrial pathway in the penumbra following transient focal ischaemia and reperfusion.

Activation of ERK and Akt signaling in focal cerebral ischemia: modulation by TGF-alpha and involvement of NMDA receptor

Cerebral ischemia activates ERK and Akt pathways. We studied whether these activations were affected by treatment with the protective growth factor transforming growth factor-alpha (TGF-alpha), and whether they were mediated through N-methyl D-aspartate (NMDA) receptors. The middle cerebral artery was occluded in rats and signaling was studied 1 h later. Noncompetitive NMDA receptor antagonist MK-801 was injected i.p. before the occlusion, whereas in other rats TGF-alpha was given intraventricularly before and after occlusion. Ischemia caused ERK phosphorylation in the nucleus, localized in the endothelium and neurons. Phosphorylation of ERK was prevented by TGF-alpha, but it was enhanced in the nucleus and cytoplasm by MK-801. Also, MK-801 but not TGF-alpha increased p-Akt. Results suggest that preventing ERK activation is related to the protective effect of TGF-alpha, whereas the protective effect of MK-801 is associated with activation of pro-survival Akt. While results support that NMDA receptor signaling precludes Akt activation, we did not find evidence to support that it underlies ischemia-induced ERK phosphorylation. This study illustrates that neuroprotection results from a fine balance between death and survival signaling pathways.

Certain forms of matrix metalloproteinase-9 accumulate in the extracellular space after microdialysis probe implantation and middle cerebral artery occlusion/reperfusion

Matrix metalloproteinases (MMPs) are activated in focal cerebral ischemia. The activation of MMP-9 is involved in blood-brain barrier breakdown and tissue remodeling. The MMPs are released to the extracellular space, but the form and fate of secreted enzymes in brain are unknown. Using microdialysis in vivo, the authors studied whether ischemia-induced MMP-9 in brain tissue was related to free MMP-9 in the extracellular fluid. A microdialysis probe was placed into the right striatum and microdialysis was initiated 24 hours later in controls (n = 7). One hour prior to microdialysis, a group of rats (n = 7) was subjected to 1-hour occlusion of the right middle cerebral artery, followed by reperfusion. Dialysates were collected at discrete time points up to 24 hours, and subjected to zymography and Western blot analysis. The MMP-9 was released after ischemia and accumulated in the extracellular space at 24 hours (P < 0.05). Free MMP-9 forms include mainly the 95-kd proform, and, to a lesser extent, dimers and cleaved active forms (70 kd), but not the 88-kd form found in tissue. Probe implantation and microdialysis increased free MMP-9 in the dialysate. This increase was concomitant with neutrophil infiltration after the mechanical lesion, as myeloperoxidase was found by means of Western blot analysis in the brain hemisphere subjected to microdialysis (P < 0.005), and immunohistochemistry revealed the presence of myeloperoxidase stain surrounding the site of probe implantation. The results suggest that certain forms of MMP-9 are released and accumulate in the extracellular space after brain injury, and that vascular alterations and neutrophil recruitment elicit MMP-9 activation in the brain after focal ischemia and trauma.

Focal cerebral ischemia causes two temporal waves of Akt activation

We studied whether pro-survival Akt was activated after transient focal cerebral ischemia and whether it inhibited pro-apoptotic Bad. Phosphorylation of Akt (serine-473) was enhanced in cortex after 1-hour ischemia, and also after 1h and 6 h of reperfusion, but it returned back to that in controls by 24 h. After this first wave of Akt activation, a second increase was observed between 4 and 7 days. In striatum, only the late Akt activation was seen. In contrast to Akt, no Bad phosphorylation (serine-136) was detected after ischemia. Therefore, injury spontaneously activated Akt, but this did not suppress Bad signalling. It is proposed that further pharmacological activation of Akt shortly after ischemia might promote cell survival, whereas Akt activation at longer time points is involved with glial reactivity.

Expression and activation of matrix metalloproteinase-2 and -9 in rat brain after transient focal cerebral ischemia

Matrix metalloproteinases (MMPs) degrade the extracellular matrix and carry out key functions during development and after injury. By means of zymography, Western blot and immunohistochemistry, we studied MMP-2 (gelatinase A) and MMP-9 (gelatinase B) in rat brain after focal cerebral ischemia. The control rat brain showed constitutive MMP-2 and, to a lesser extent, MMP-9, which were mainly present as prozymogens. MMP-2 protein was located in the cell body of neurons, glia, and endothelium, whereas MMP-9 was associated to neurons and myelinated fibre tracts. Ischemia greatly increased MMP activation in two temporal waves, in the first one, MMP-9 protein was induced from 4 h to 4 days, and also a small and short-lasting increase in MMP-2 was detected at 4 h. The second wave showed a massive increase in MMP-2 protein expression and activation by day 4, which was compatible with abundant MMP-2 in reactive microglia/macrophages. Our results are compatible with progressive induction of MMP-9 proform, likely in neurons, shortly after ischemia. For MMP-2, the results suggest a discrete production immediately after reperfusion, while a very enhanced expression and activation of MMP-2 attributable to microglia/macrophages occurs on day 4, and it might contribute to the phagocytic action of these reactive cells.

Temporospatial expression of HSP72 and c-JUN, and DNA fragmentation in goat hippocampus after global cerebral ischemia

The role of gene induction (expression of HSP72 and c-JUN proteins) and delayed ischemic cell death (in situ labeling of DNA fragmentation) have been investigated in the goat hippocampus after transient global cerebral ischemia. The animals were subjected to 20-min ischemia (bilateral occlusion of the external carotid arteries plus bilateral jugular vein compression) and allowed to reperfuse for 2 h, and then 1, 3, and 7 days. Histological signs of cell loss were not found in the hippocampus at 2 h, 1 day, or 3 days of reperfusion. However, such an ischemic insult produced extensive, selective, and delayed degeneration in the hippocampus, as 68% of the neurons in CA1 had died at 7 days, but cell loss was not detected in CA3 and dentate gyrus fields. Concomitantly, a high percentage of TUNEL-positive CA1 neurons (60+/-9%, mean +/- SEM) was seen at 7 days, but not at the earlier time points. Mild induction of HSP72 was detected in the goat hippocampus after ischemia. The maximum percentage of HSP72-positive neurons (10-15%) was shown at 3 days of reperfusion and was concentrated mainly in the CA3 field, subiculum, and hilus, rather than in the CA1 field, whereas HSP72 expression was hardly detected at 7 days. At this later time point, scattered induction of nuclear c-JUN was found in a few neurons. The results show that: 1) postischemic delayed neuronal death selectively affects the CA1 field in the goat hippocampus, a phenomenon which seems to take longer to develop than in previously reported rodent models; and 2) postischemic expression of c-JUN does not appear to be related to cell death or survival, while the inability of most CA1 neurons to express HSP72 could contribute to neuronal death.

Administration of transforming growth factor-alpha reduces infarct volume after transient focal cerebral ischemia in the rat

Growth factors promote cell growth and survival and protect the brain from developing injury after ischemia. In this article, the authors examined whether transforming growth factor-alpha (TGF-alpha) was protective in transient focal ischemia and whether alteration of cerebral circulation was involved. Rats received intraventricular TGF-alpha (50 ng, either split into 2 doses given 30 minutes before and 30 minutes after middle cerebral artery occlusion (MCAO), or 1 dose given 30 minutes after MCAO) or vehicle. Rats were subjected to 1-hour intraluminal MCAO and cerebral blood flow was recorded continuously by laser-Doppler flowmetry. Infarct volume was measured 1 and 4 days later. The effects of TGF-alpha on arterial tone were assessed in isolated rabbit basilar and common carotid arteries. Transforming growth factor-alpha before and after ischemia reduced infarct volume by 70% at 1 day and 50% at 4 days. Transforming growth factor-alpha given only after ischemia also did reduce infarct volume by 70% at 1 day and 80% at 4 days. The protective effect was more marked in cortex than in striatum. Transforming growth factor-alpha did not change cortical microvascular perfusion and did not modify arterial passive tone nor agonist-induced active tone. It can be concluded that TGF-alpha reduces infarct volume, even when the factor is exclusively administered at reperfusion, and that this effect is not mediated by changes in microvascular perfusion or cerebral arteries. It is therefore suggested that TGF-alpha has a protective effect against neuronal cell death after transient focal ischemia.

Estimation of gelatinase content in rat brain: effect of focal ischemia

Matrix metalloproteinases degrade the extracellular matrix and are involved in a variety of diseases, including inflammatory diseases of the central nervous system. Here we estimated the content of gelatinase in rat brain under control conditions and 4 h after transient focal ischemia using gelatinolytic extraction and zymographic analysis. We also examined the expression of the MMP-9 and MMP-2 proteins by Western blot. Using the zymographic apparent gelatinase activity we estimated that brain gelatinase content was 0.44 ng/mg of protein. Ischemia induced a 1.7-fold increase at 4 h, thus showing an early MMP response to the ischemic injury. The main increase was seen for the MMP-9 proform, which was accompanied by enhanced MMP-9 protein expression. We suggest that basal cerebral MMP-9 and MMP-2 activities are involved in the maintenance of the extracellular matrix and prevent substrate accumulation, while enhanced postischemic MMP activity before cell death may contribute to edema formation and blood-brain barrier breakdown.

Activation of the JAK/STAT pathway following transient focal cerebral ischemia: signaling through Jak1 and Stat3 in astrocytes

JAK/STAT is one of the pathways bearing signals from the cell membrane to the nucleus in response to extracellular growth factors and cytokines. In the present study, we examined the cellular distribution of Jak1 and Stat3, and activation of the JAK/STAT pathway following transient focal cerebral ischemia in the rat. Jak1 was mainly seen in white matter astrocytes and in certain neurons. Notably, large pyramidal neurons of cortical layer V showed the highest neuronal Jak1 expression within cerebral cortex and, in addition, expressed Stat3 indicating that the JAK/STAT pathway is involved in signaling in the corticofugal projection system. Shortly following ischemia, Jak1 immunoreactive astrocytes located in the ipsilateral neighbouring white matter and ischemic cortex and striatum showed nuclear translocation of Stat3. These features were maintained in large reactive astrocytes that surrounded the infarct from 3 to 7 days. At these later times, the abundant reactive microglia/macrophages were strongly immunoreactive to Stat3 and, to a lesser extent, Jak1. Two main protein complexes showing DNA binding activity at the sis-inducible element site were found under basal conditions, followed by changes in this pattern following ischemia concomitant with neuronal cell loss and activation of glia. This study showed basal cerebral activity of JAK/STAT signaling pathway, involving Jak1 and Stat3 proteins, and selective activation following ischemia. It is suggested that the kinase activity of Jak1 mediates nuclear translocation of Stat3 in astrocytes, and that this signaling pathway is involved in the astroglial response to focal cerebral ischemia.

Induction of cyclooxygenase-2 in the rat brain after a mild episode of focal ischemia without tissue inflammation or neural cell damage

Cyclooxygenase-2, a key enzyme in prostanoid synthesis, is induced by inflammatory stimuli and it is associated with cell death after cerebral ischemia. Here we evaluated whether cyclooxygenase-2 was induced after a short (10-min) episode of focal ischemia, mild enough not to cause inflammation or cell death. One-hour ischemia leading to brain infarct was studied for comparative purposes. Induction of cyclooxygenase-2 mRNA and protein was detected after both 10-min and 1-h ischemia. However, signs of edema were only apparent after 1-h, but not 10-min ischemia, and only rats subjected to 1-h ischemia had developed brain infarct at 4 days. Therefore, cyclooxygenase-2, not linked with neural cell death or inflammation, is induced after focal ischemia.

Activation of nuclear factor-kappaB in the rat brain after transient focal ischemia

Nuclear factor-kappaB (NF-kappaB) becomes activated under inflammatory conditions and triggers induction of gene expression. Here, activation of NF-kappaB was studied after transient middle cerebral artery occlusion in the rat. Expression of p65 and p50, protein subunits of NF-kappaB, was examined by Western blotting, and immunohistochemistry for p65 was carried out. Double-labelling with specific markers for astroglia and microglia was used for cell type identification. Neurons located within and surrounding the ischemic core were identified during the first 24 h post-ischemia by using an antibody against 72-kDa heat shock protein. NF-kappaB binding activity was evaluated at different times post-ischemia with electrophoretic mobility gel shift assays. The results showed constitutive expression of p65 and p50, and NF-kappaB binding activity. Basal p65 was seen in certain neurons and resting astrocytes. Constitutive NF-kappaB binding activity was attributable to one main protein complex possibly formed in neurons and astrocytes, although two minor complexes were also detected. At 1 day post-ischemia selective induction of p65 was seen in neurons located in a penumbra-like area. At this time, however, no disturbances of basal NF-kappaB binding activity were found. Western blotting showed delayed induction of p65 several days after ischemia, whereas no changes were detected for p50. From 4 days post-ischemia, a substantial increase in the amount of p65 was detected due to induction in reactive astrocytes and microglia/macrophages. This was correlated with a robust enhancement of NF-kappaB binding activity with formation of three major specific complexes binding DNA. It is proposed that the highly inducible NF-kappaB complexes resulted from induction of p65 and activation of NF-kappaB in post-ischemic reactive glia.

Transforming growth factor-alpha acting at the epidermal growth factor receptor reduces infarct volume after permanent middle cerebral artery occlusion in rats

Transforming growth factor-alpha (TGF-alpha) is a ligand for the epidermal growth factor (EGF) receptor (EGFR), and is more abundant than EGF in the brain. The authors studied whether administration of exogenous TGF-alpha into the brain can protect neurons against ischemia in a model of permanent middle cerebral artery (MCA) occlusion in the rat, and whether any effect of TGF-alpha was mediated by EGFR by administering 4,5-dianilinophthalimide (DAPH), a protein-tyrosine kinase inhibitor with high selectivity for EGFR. Rats received either TGF-alpha (10 or 25 ng), DAPH (100 ng), DAPH plus TGF-alpha (25 ng), or vehicle in the ipsilateral first ventricle. Drugs were administered twice: 30 minutes before and 30 minutes after MCA occlusion, and infarct volume was evaluated 24 hours later. Transforming growth factor-alpha at the dose of 25 ng caused a statistically significant reduction of infarct volume (60%) in relation to ischemic rats administered vehicle. This reduction was no longer seen when TGF-alpha was administered in combination with DAPH. The present results show that TGF-alpha can protect neurons from ischemic damage, and that this effect is mediated by EGFR. It is suggested that activation of EGFR-mediated intracellular signalling pathways contributes to the survival of neural cells susceptible to ischemic injury.

Epidermal growth factor receptor in proliferating reactive glia following transient focal ischemia in the rat brain

Severe transient focal cerebral ischemia causes brain infarction with a strong glial reaction. We have studied whether postischemic reactive glial cells express epidermal growth factor receptor (EGFR) following middle cerebral artery occlusion in the rat. We have also looked for signs of proliferating activity, as EGFR is known to be involved in cell growth and proliferation in certain non-neural cells. EGFR was studied using three different antibodies which were found to stain for a tyrosine-phosphorylated protein (p170) corresponding to the membrane-anchored EGFR. Neurons of the control brain were strongly immunoreactive to EGFR, but a decrease of EGFR-immunoreactivity was seen in the ipsilateral brain side from 24 h postischemia due to neuronal loss. However, the presence of abundant glial cells strongly immunoreactive to EGFR became apparent in this area from 4 days postischemia onward. The use of microglial (lectin or OX-42) and astroglial (GFAP) markers showed that these postischemic EGFR-stained cells were reactive microglia/macrophages and astroglia. The subcellular localization of EGFR in reactive microglia/macrophages was compatible with the network of the Golgi apparatus, as revealed with an antibody against a peripheral membrane-bound protein of the Golgi. The presence of abundant proliferating cells in the ischemic brain was detected from 4 days postischemia with an antibody against proliferating cell nuclear antigen. Proliferating reactive microglia/macrophages were abundant within the infarcted brain side, whereas proliferating astrocytes were found mainly in the immediate periphery of the infarct limiting the necrotic area from the undamaged tissue. These proliferating cells were immunoreactive to EGFR. The results show the presence of EGFR in postischemic reactive glial cells and suggest that EGFR-dependent pathways mediate signal transduction in reactive glia following transient focal cerebral ischemia.

Striatal infarction in the rat causes a transient reduction of tyrosine hydroxylase immunoreactivity in the ipsilateral substantia nigra

Dopaminergic neurons of the substantia nigra pars compacta were examined in the rat brain following striatal infarction subsequent to transient focal cerebral ischemia. Rats had the middle cerebral artery occluded for 2 h or were sham-operated, and tyrosine hydroxylase immunoreactivity was evaluated by Western blot and immunohistochemistry at different times ranging from 1 to 60 days after ischemia. The number of tyrosine hydroxylase-immunoreactive cells in the substantia nigra pars compacta was counted under the light microscope and compared to that in the contralateral side and controls. No changes of tyrosine hydroxylase immunoreactivity were detected in the ipsilateral versus the contralateral substantia nigra of sham-operated rats or 1 day after ischemia. However, a statistically significant reduction of tyrosine hydroxylase-immunoreactive cells became apparent in the ipsilateral compared with the contralateral substantia nigra at 7 and 14 days after ischemia. This reduction showed a clear recovery at 30 days after ischemia, and no signs of difference between the ipsilateral and the contralateral side were apparent by 60 days. Therefore, the reduction of tyrosine hydroxylase immunoreactivity in the ipsilateral substantia nigra was only transiently seen from 1 to 2 weeks following ischemia. The observed loss of tyrosine hydroxylase was not accompanied by signs of cell death or gliosis in the ipsilateral pars compacta. The present results show a transitory reduction of tyrosine hydroxylase immunoreactivity in the ipsilateral substantia nigra pars compacta after focal ischemia and suggest that striatal infarction causes a transient deficit of dopaminergic function.

Stat1 in developing and adult rat brain. Induction after transient focal ischemia

Stat1 has a dual function as signal transducer and activator of transcription, and is activated in response to growth factors and cytokines. We examined Stat1 in the rat brain during development and following transient focal ischemia, using Western immunoblotting. Two bands of 91 and 84 kDa, corresponding to Stat1 alpha and Stat1 beta forms, were found with an intensity that increased from postnatal day 0 to adulthood in cerebellum and cerebral cortex. Ischemia caused a strong induction of Stat1 in the ipsilateral cortex after 4, 7 and 15 days, but not at 6 or 24 h. These results show that Stat1 is normally expressed in the postnatal and adult rat brain and is induced under brain infarction.

Stat3 is present in the developing and adult rat cerebellum and participates in the formation of transcription complexes binding DNA at the sis-inducible element

Stat3 is a member of a recently identified family of proteins named STATs for their ability to act as signal transducers and activators of transcription. Stimulation of epidermal growth factor or cytokine receptors can cause activation of Stat3 and transduction of specific responses to the nucleus. Here the presence of Stat3 has been examined in the rat cerebellum at different times during postnatal development and adulthood by means of immunohistochemistry and western blotting. In addition, DNA binding activity at the sis-inducible element that is present in the promoter of the c-fos gene has been studied by electrophoretic mobility shift assay. The results have shown that Stat3 p92 is abundant in the rat cerebellum. Stat3 was found in the external granule cell layer and also within the molecular layer from postnatal day (P) 0 to P7. From P15 to the adult, the internal granule cell layer and Purkinje cells were also stained for Stat3. Nuclear extracts were found to contain DNA binding activity to the sis-inducible element during development and adulthood. Supershift assays demonstrated that Stat3 mediates the formation of one protein-DNA complex. The present results suggest that Stat3 participates in intracellular signaling and is involved in maintaining basal c-fos expression in the cerebellum of the developing and adult rat under physiological conditions.

Induction of Stat3, a signal transducer and transcription factor, in reactive microglia following transient focal cerebral ischaemia

Stat3, a member of the family of cytoplasmic signal transducers and activators of transcription, was found in the rat brain in vivo under physiological conditions and was stimulated following transient focal cerebral ischaemia. A transient episode of middle cerebral artery occlusion induced a strong microglial response in the areas undergoing neural cell death from 4 days after middle cerebral artery occlusion. This was accompanied by increased expression of Stat3 in the ipsilateral cortex and striatum, as revealed by Western blotting of tissue extracts. Immunohistochemistry showed strong induction of Stat3 in reactive microglial cells 4, 7 and 15 days after cerebral ischaemia. Stat3 was seen in the microglia cytoplasm, but in many microglial cells immunoreactivity was also distributed within the nucleus. These results suggest that Stat3 mediates signal transduction and activates transcription in reactive microglia in vivo following brain ischaemia.