Rapid alteration of tau in oligodendrocytes after focal ischemic injury in the rat: involvement of free radicals

Post-Ischemic Permeability of the Blood-Brain Barrier to Amyloid and Platelets as a Factor in the Maturation of Alzheimer's Disease-Type Brain Neurodegeneration

The aim of this review is to present evidence of the impact of ischemic changes in the blood-brain barrier on the maturation of post-ischemic brain neurodegeneration with features of Alzheimer's disease. Understanding the processes involved in the permeability of the post-ischemic blood-brain barrier during recirculation will provide clinically relevant knowledge regarding the neuropathological changes that ultimately lead to dementia of the Alzheimer's disease type. In this review, we try to distinguish between primary and secondary neuropathological processes during and after ischemia. Therefore, we can observe two hit stages that contribute to Alzheimer's disease development. The onset of ischemic brain pathology includes primary ischemic neuronal damage and death followed by the ischemic injury of the blood-brain barrier with serum leakage of amyloid into the brain tissue, leading to increased ischemic neuronal susceptibility to amyloid neurotoxicity, culminating in the formation of amyloid plaques and ending in full-blown dementia of the Alzheimer's disease type.

Astrocytosis, Inflammation, Axonal Damage and Myelin Impairment in the Internal Capsule following Striatal Ischemic Injury

Secondary degeneration is defined as a set of destructive events that damage cells and structures that were initially spared or only peripherally affected by the primary insult, constituting a key factor for functional impairment after traumatic brain injury or stroke. In the present study, we evaluated the patterns of astrocytosis, inflammatory response, axonal damage and oligodendrocytes/myelin impairment in the internal capsule following a focal injection of endothelin-1 (ET-1) into the dorsal striatum. Animals were perfused at 1, 3 and 7 post-lesion days (PLD), and tissue was processed to immunohistochemistry for neutrophils (MBS1), macrophages/microglia (ED1), astrocytes (GFAP), axonal lesion (βAPP), oligodendrocytes (Tau) and myelin (MBP). A significant number of neutrophils was observed at 1PLD, followed by intense recruitment/activation of macrophages/microglia at 3PLD and astrocytic reaction with a peak at 7PLD. Oligodendrocyte damage was pronounced at 3PLD, remaining at 7PLD. Progressive myelin impairment was observed, with reduction of immunoreactivity at 7PLD. Axonal lesion was also identified, mainly at 7PLD. Our results indicate that acute inflammatory response elicited by the ischemic insult in the striatum can be associated with the axonal impairment and damage of both oligodendrocytes and myelin sheath identified in the internal capsule, which may be related to loss of tissue functionality observed in secondary degeneration.

Sex Differences in the Long-Term Consequences of Stroke

Stroke is the fifth leading cause of death and as healthcare intervention improves, the number of stroke survivors has also increased. Furthermore, there exists a subgroup of younger adults, who suffer stroke and survive. Given the overall improved survival rate, bettering our understanding of long-term stroke outcomes is critical. In this review we will explore the causes and challenges of known long-term consequences of stroke and if present, their corresponding sex differences in both old and young survivors. We have separated these long-term post-stroke consequences into three categories: mobility and muscle weakness, memory and cognitive deficits, and mental health and mood. Lastly, we discuss the potential of common preclinical stroke models to contribute to our understanding of long-term outcomes following stroke.

Inflammatory Response and Secondary White Matter Damage to the Corpus Callosum after Focal Striatal Stroke in Rats

Stroke is one of the leading causes of death and long-term disabilities worldwide, resulting in a debilitating condition occasioned by disturbances in the cerebral vasculature. Primary damage due to metabolic collapse is a quick outcome following stroke, but a multitude of secondary events, including excitotoxicity, inflammatory response, and oxidative stress cause further cell death and functional impairment. In the present work, we investigated whether a primary ischemic damage into the dorsal striatum may cause secondary damage in the circumjacent corpus callosum (CC). Animals were injected with endothelin-1 and perfused at 3, 7, 14, and 30 post-lesion days (PLD). Sections were stained with Cresyl violet for basic histopathology and immunolabeled by antibodies against astrocytes (anti-GFAP), macrophages/microglia (anti-IBA1/anti MHC-II), oligodendrocytes (anti-TAU) and myelin (anti-MBP), and Anti-Nogo. There were conspicuous microgliosis and astrocytosis in the CC, followed by later oligodendrocyte death and myelin impairment. Our results suggest that secondary white matter damage in the CC follows a primary focal striatal ischemia in adult rats.

Cross-Talk between Amyloid, Tau Protein and Free Radicals in Post-Ischemic Brain Neurodegeneration in the Form of Alzheimer’s Disease Proteinopathy

Recent years have seen remarkable progress in research into free radicals oxidative stress, particularly in the context of post-ischemic recirculation brain injury. Oxidative stress in post-ischemic tissues violates the integrity of the genome, causing DNA damage, death of neuronal, glial and vascular cells, and impaired neurological outcome after brain ischemia. Indeed, it is now known that DNA damage and repair play a key role in post-stroke white and gray matter remodeling, and restoring the integrity of the blood-brain barrier. This review will present one of the newly characterized mechanisms that emerged with genomic and proteomic development that led to brain ischemia to a new level of post-ischemic neuropathological mechanisms, such as the presence of amyloid plaques and the development of neurofibrillary tangles, which further exacerbate oxidative stress. Finally, we hypothesize that modified amyloid and the tau protein, along with the oxidative stress generated, are new key elements in the vicious circle important in the development of post-ischemic neurodegeneration in a type of Alzheimer’s disease proteinopathy.

The Many Faces of Post-Ischemic Tau Protein in Brain Neurodegeneration of the Alzheimer's Disease Type

Recent data suggest that post-ischemic brain neurodegeneration in humans and animals is associated with the modified tau protein in a manner typical of Alzheimer’s disease neuropathology. Pathological changes in the tau protein, at the gene and protein level due to cerebral ischemia, can lead to the development of Alzheimer’s disease-type neuropathology and dementia. Some studies have shown increased tau protein staining and gene expression in neurons following ischemia-reperfusion brain injury. Recent studies have found the tau protein to be associated with oxidative stress, apoptosis, autophagy, excitotoxicity, neuroinflammation, blood-brain barrier permeability, mitochondrial dysfunction, and impaired neuronal function. In this review, we discuss the interrelationship of these phenomena with post-ischemic changes in the tau protein in the brain. The tau protein may be at the intersection of many pathological mechanisms due to severe neuropathological changes in the brain following ischemia. The data indicate that an episode of cerebral ischemia activates the damage and death of neurons in the hippocampus in a tau protein-dependent manner, thus determining a novel and important mechanism for the survival and/or death of neuronal cells following ischemia. In this review, we update our understanding of proteomic and genomic changes in the tau protein in post-ischemic brain injury and present the relationship between the modified tau protein and post-ischemic neuropathology and present a positive correlation between the modified tau protein and a post-ischemic neuropathology that has characteristics of Alzheimer’s disease-type neurodegeneration.

Potential therapeutic agents for ischemic white matter damage

Ischemic white matter damage (WMD) is increasingly being considered as one of the major causes of neurological disorders in older adults and preterm infants. The functional consequences of WMD triggers a progressive cognitive decline and dementia particularly in patients with ischemic cerebrovascular diseases. Despite the major stride made in the pathogenesis mechanisms of ischemic WMD in the last century, effective medications are still not available. So, there is an urgent need to explore a promising approach to slow the progression or modify its pathological course. In this review, we discussed the animal models, the pathological mechanisms and the potential therapeutic agents for ischemic WMD. The development in the studies of anti-oxidants, free radical scavengers, anti-inflammatory or anti-apoptotic agents and neurotrophic factors in ischemic WMD were summarized. The agents which either alleviate oligodendrocyte damage or promote its proliferation or differentiation may have potential value for the treatment of ischemic WMD. Moreover, drugs with multifaceted protective activities or a wide therapeutic window may be optimal for clinical translation.

Brain Ischemia as a Prelude to Alzheimer's Disease

Transient ischemic brain injury causes massive neuronal death in the hippocampus of both humans and animals. This was accompanied by progressive atrophy of the hippocampus, brain cortex, and white matter lesions. Furthermore, it has been noted that neurodegenerative processes after an episode of ischemia-reperfusion in the brain can continue well-beyond the acute stage. Rarefaction of white matter was significantly increased in animals at 2 years following ischemia. Some rats that survived 2 years after ischemia developed severe brain atrophy with dementia. The profile of post-ischemic brain neurodegeneration shares a commonality with neurodegeneration in Alzheimer's disease. Furthermore, post-ischemic brain injury is associated with the deposition of folding proteins, such as amyloid and tau protein, in the intracellular and extracellular space. Recent studies on post-ischemic brain neurodegeneration have revealed the dysregulation of Alzheimer's disease-associated genes such as amyloid protein precursor, α-secretase, β-secretase, presenilin 1, presenilin 2, and tau protein. The latest data demonstrate that Alzheimer's disease-related proteins and their genes play a key role in the development of post-ischemic brain neurodegeneration with full-blown dementia in disease types such as Alzheimer's. Ongoing interest in the study of brain ischemia has provided evidence showing that ischemia may be involved in the development of the genotype and phenotype of Alzheimer's disease, suggesting that brain ischemia can be considered as a useful model for understanding the mechanisms responsible for the initiation of Alzheimer's disease.

Characterization of Tauopathy in a Rat Model of Post-Stroke Dementia Combining Acute Infarct and Chronic Cerebral Hypoperfusion

Post-stroke dementia (PSD) is a major neurodegenerative consequence of stroke. Tauopathy has been reported in diverse neurodegenerative diseases. We investigated the cognitive impairment and pathomechanism associated with tauopathy in a rat model of PSD by modeling acute ischemic stroke and underlying chronic cerebral hypoperfusion (CCH). We performed middle cerebral artery occlusion (MCAO) surgery in rats to mimic acute ischemic stroke, followed by bilateral common carotid artery occlusion (BCCAo) surgery to mimic CCH. We performed behavioral tests and focused on the characterization of tauopathy through histology. Parenchymal infiltration of cerebrospinal fluid (CSF) tracers after intracisternal injection was examined to evaluate glymphatic function. In an animal model of PSD, cognitive impairment was aggravated when BCCAo was combined with MCAO. Tauopathy, manifested by tau hyperphosphorylation, was prominent in the peri-infarct area when CCH was combined. Synergistic accentuation of tauopathy was evident in the white matter. Microtubules in the neuronal axon and myelin sheath showed partial colocalization with the hyperphosphorylated tau, whereas oligodendrocytes showed near-complete colocalization. Parenchymal infiltration of CSF tracers was attenuated in the PSD model. Our experimental results suggest a hypothesis that CCH may aggravate cognitive impairment and tau hyperphosphorylation in a rat model of PSD by interfering with tau clearance through the glymphatic system. Therapeutic strategies to improve the clearance of brain metabolic wastes, including tau, may be a promising approach to prevent PSD after stroke.

Participation of Amyloid and Tau Protein in Neuronal Death and Neurodegeneration after Brain Ischemia

Current evidence indicates that postischemic brain injury is associated with the accumulation of folding proteins, such as amyloid and tau protein, in the intra- and extracellular spaces of neuronal cells. In this review, we summarize protein changes associated with Alzheimer’s disease and their gene expression (amyloid protein precursor and tau protein) after brain ischemia, and their roles in the postischemic period. Recent advances in understanding the postischemic mechanisms in development of neurodegeneration have revealed dysregulation of amyloid protein precursor, α-, β- and γ-secretase and tau protein genes. Reduced expression of the α-secretase gene after brain ischemia with recirculation causes neuronal cells to be less resistant to injury. We present the latest data that Alzheimer’s disease-related proteins and their genes play a crucial role in postischemic neurodegeneration. Understanding the underlying processes of linking Alzheimer’s disease-related proteins and their genes in development of postischemic neurodegeneration will provide the most significant goals to date for therapeutic development.

Focal cerebral ischemia induces changes in oligodendrocytic tau isoforms in the damaged area

Ischemic stroke is a major cause of death and the first leading cause of long-term disability worldwide. The only therapeutic strategy available to date is reperfusion and not all the patients are suitable for this treatment. Blood flow blockage or reduction leads to considerable brain damage, affecting both gray and white matter. The detrimental effects of ischemia have been studied extensively in the former but not in the latter. Previous reports indicate that preservation of white matter integrity reduces deleterious effect of ischemia on the brain. Oligodendrocytes are sensitive to ischemic damage, however, some reports demonstrate that oligodendrogenesis occurs after ischemia. These glial cells have a complex cytoskeletal network, including tau, that plays a key role to proper myelination. 4R-Tau/3R-Tau, which differ in the presence/absence of Exon 10, are found in oligodendrocytes; but the precise role of each isoform is not understood. Using permanent middle cerebral artery occlusion model and immunofluorescence, we demonstrate that cerebral ischemia induces an increase in 3R-Tau versus 4R-Tau in oligodendrocytes in the damaged area. In addition, cellular distribution of Tau undergoes a change after ischemia, with some oligodendrocytic processes showing positive staining for 3R-Tau. This occurs simultaneously with the amelioration of neurological damage in ischemic rats. We propose that ischemia triggers an endogenous mechanism involving 3R-Tau, that induces colonization of the ischemic damaged area by oligodendrocytes in an attempt to myelinate-injured axons. Understanding the molecular mechanism of this phenomenon could pave the way for the design of therapeutic strategies that exploit glial cells for the treatment of ischemia.

Shared Genomic and Proteomic Contribution of Amyloid and Tau Protein Characteristic of Alzheimer's Disease to Brain Ischemia

Post-ischemic brain damage is associated with the deposition of folding proteins such as the amyloid and tau protein in the intra- and extracellular spaces of brain tissue. In this review, we summarize the protein changes associated with Alzheimer's disease and their gene expression (amyloid protein precursor and tau protein) after ischemia-reperfusion brain injury and their role in the post-ischemic injury. Recent advances in understanding the post-ischemic neuropathology have revealed dysregulation of amyloid protein precursor, α-secretase, β-secretase, presenilin 1 and 2, and tau protein genes after ischemic brain injury. However, reduced expression of the α-secretase in post-ischemic brain causes neurons to be less resistant to injury. In this review, we present the latest evidence that proteins associated with Alzheimer's disease and their genes play a key role in progressive brain damage due to ischemia and reperfusion, and that an ischemic episode is an essential and leading supplier of proteins and genes associated with Alzheimer's disease in post-ischemic brain. Understanding the underlying processes of linking Alzheimer's disease-related proteins and their genes in post-ischemic brain injury with the risk of developing Alzheimer's disease will provide the most significant goals for therapeutic development to date.

Small Vessel Disease-Related Dementia: An Invalid Neurovascular Coupling?

The arteriosclerosis-dependent alteration of brain perfusion is one of the major determinants in small vessel disease, since small vessels have a pivotal role in the brain's autoregulation. Nevertheless, as far as we know, endothelium distress can potentiate the flow dysregulation and lead to subcortical vascular dementia that is related to small vessel disease (SVD), also being defined as subcortical vascular dementia (sVAD), as well as microglia activation, chronic hypoxia and hypoperfusion, vessel-tone dysregulation, altered astrocytes, and pericytes functioning blood-brain barrier disruption. The molecular basis of this pathology remains controversial. The apparent consequence (or a first event, too) is the macroscopic alteration of the neurovascular coupling. Here, we examined the possible mechanisms that lead a healthy aging process towards subcortical dementia. We remarked that SVD and white matter abnormalities related to age could be accelerated and potentiated by different vascular risk factors. Vascular function changes can be heavily influenced by genetic and epigenetic factors, which are, to the best of our knowledge, mostly unknown. Metabolic demands, active neurovascular coupling, correct glymphatic process, and adequate oxidative and inflammatory responses could be bulwarks in defense of the correct aging process; their impairments lead to a potentially catastrophic and non-reversible condition.

Proteomic and Genomic Changes in Tau Protein, Which Are Associated with Alzheimer's Disease after Ischemia-Reperfusion Brain Injury

Recent evidence suggests that transient ischemia of the brain with reperfusion in humans and animals is associated with the neuronal accumulation of neurotoxic molecules associated with Alzheimer’s disease, such as all parts of the amyloid protein precursor and modified tau protein. Pathological changes in the amyloid protein precursor and tau protein at the protein and gene level due to ischemia may lead to dementia of the Alzheimer’s disease type after ischemic brain injury. Some studies have demonstrated increased tau protein immunoreactivity in neuronal cells after brain ischemia-reperfusion injury. Recent research has presented many new tau protein functions, such as neural activity control, iron export, protection of genomic DNA integrity, neurogenesis and long-term depression. This review discusses the potential mechanisms of tau protein in the brain after ischemia, including oxidative stress, apoptosis, autophagy, excitotoxicity, neurological inflammation, endothelium, angiogenesis and mitochondrial dysfunction. In addition, attention was paid to the role of tau protein in damage to the neurovascular unit. Tau protein may be at the intersection of many regulatory mechanisms in the event of major neuropathological changes in ischemic stroke. Data show that brain ischemia activates neuronal changes and death in the hippocampus in a manner dependent on tau protein, thus determining a new and important way to regulate the survival and/or death of post-ischemic neurons. Meanwhile, the association between tau protein and ischemic stroke has not been well discussed. In this review, we aim to update the knowledge about the proteomic and genomic changes in tau protein following ischemia-reperfusion injury and the connection between dysfunctional tau protein and ischemic stroke pathology. Finally we present the positive correlation between tau protein dysfunction and the development of sporadic Alzheimer’s disease type of neurodegeneration.

Substantiation for the Use of Curcumin during the Development of Neurodegeneration after Brain Ischemia

Currently available pharmacological treatment of post-ischemia-reperfusion brain injury has limited effectiveness. This review provides an assessment of the current state of neurodegeneration treatment due to ischemia-reperfusion brain injury and focuses on the role of curcumin in the diet. The purpose of this review was to provide a comprehensive overview of what was published about the benefits of curcumin influence on post-ischemic brain damage. Some data on the clinical benefits of curcumin treatment of post-ischemic brain in terms of clinical symptoms and adverse reactions have been reviewed. The data in this review contributes to a better understanding of the potential benefits of curcumin in the treatment of neurodegenerative changes after ischemia and informs scientists, clinicians, and patients, as well as their families and caregivers about the possibilities of such treatment. Due to the pleotropic properties of curcumin, including anti-amyloid, anti-tau protein hyperphosphorylation, anti-inflammatory, anti-apoptotic, and neuroprotective action, as well as increasing neuronal lifespan and promoting neurogenesis, curcumin is a promising candidate for the treatment of post-ischemic neurodegeneration with misfolded proteins accumulation. In this way, it may gain interest as a potential therapy to prevent the development of neurodegenerative changes after cerebral ischemia. In addition, it is a safe substance and inexpensive, easily accessible, and can effectively penetrate the blood–brain barrier and neuronal membranes. In conclusion, the evidence available in a review of the literature on the therapeutic potential of curcumin provides helpful insight into the potential clinical utility of curcumin in the treatment of neurological neurodegenerative diseases with misfolded proteins. Therefore, curcumin may be a promising supplementary agent against development of neurodegeneration after brain ischemia in the future. Indeed, there is a rational scientific basis for the use of curcumin for the prophylaxis and treatment of post-ischemic neurodegeneration.

Tau Protein Dysfunction after Brain Ischemia

Brain ischemia comprises blood-brain barrier, glial, and neuronal cells. The blood–brain barrier controls permeability of different substances and the composition of the neuronal cells ‘milieu’, which is required for their physiological functioning. Recent evidence indicates that brain ischemia itself and ischemic blood-brain barrier dysfunction is associated with the accumulation of neurotoxic molecules within brain tissue, e.g., different parts of amyloid-β protein precursor and changed pathologically tau protein. All these changes due to ischemia can initiate and progress neurodegeneration of the Alzheimer’s disease-type. This review presents brain ischemia and ischemic blood-brain barrier as a trigger for tau protein alterations. Thus, we hypothesize that the changes in pattern of phosphorylation of tau protein are critical to microtubule function especially in neurons, and contribute to the neurodegeneration following brain ischemia-reperfusion episodes with Alzheimer’s disease phenotype.

Small vessel disease to subcortical dementia: a dynamic model, which interfaces aging, cholinergic dysregulation and the neurovascular unit

Background

Small vessels have the pivotal role for the brain’s autoregulation. The arteriosclerosis-dependent alteration of the brain perfusion is one of the major determinants in small vessel disease. Endothelium distress can potentiate the flow dysregulation and lead to subcortical vascular dementia (sVAD). sVAD increases morbidity and disability. Epidemiological studies have shown that sVAD shares with cerebrovascular disease most of the common risk factors. The molecular basis of this pathology remains controversial.

Purpose

To detect the possible mechanisms between small vessel disease and sVAD, giving a broad vision on the topic, including pathological aspects, clinical and laboratory findings, metabolic process and cholinergic dysfunction.

Methods

We searched MEDLINE using different search terms (“vascular dementia”, “subcortical vascular dementia”, “small vessel disease”, “cholinergic afferents”, etc). Publications were selected from the past 20 years. Searches were extended to Embase, Cochrane Library, and LILIACS databases. All searches were done from January 1, 1998 up to January 31, 2018.

Results

A total of 560 studies showed up, and appropriate studies were included. Associations between traditional vascular risk factors have been isolated. We remarked that SVD and white matter abnormalities are seen frequently with aging and also that vascular and endothelium changes are related with age; the changes can be accelerated by different vascular risk factors. Vascular function changes can be heavily influenced by genetic and epigenetic factors.

Conclusion

Small vessel disease and the related dementia are two pathologies that deserve attention for their relevance and impact in clinical practice. Hypertension might be a historical problem for SVD and SVAD, but low pressure might be even more dangerous; CBF regional selective decrease seems to be a critical factor for small vessel disease-related dementia. In those patients, endothelium damage is a super-imposed condition. Several issues are still debatable, and more research is needed.

Pathophysiology of Lacunar Stroke: History's Mysteries and Modern Interpretations

Since the term "lacune" was adopted in the 1800s to describe infarctions from cerebral small vessels, their underlying pathophysiological basis remained obscure until the 1960s when Charles Miller Fisher performed several autopsy studies of stroke patients. He observed that the vessels displayed segmental arteriolar disorganization that was associated with vessel enlargement, hemorrhage, and fibrinoid deposition. He coined the term "lipohyalinosis" to describe the microvascular mechanism that engenders small subcortical infarcts in the absence of a compelling embolic source. Since Fisher's early descriptions of lipohyalinosis and lacunar stroke (LS), there have been many advancements in the understanding of this disease process. Herein, we review lipohyalinosis as it relates to modern concepts of cerebral small vessel disease (cSVD). We discuss clinical classifications of LS as well as radiographic definitions based on modern neuroimaging techniques. We provide a broad and comprehensive overview of LS pathophysiology both at the vessel and parenchymal levels. We also comment on the role of biomarkers, the possibility of systemic disease processes, and advancements in the genetics of cSVD. Lastly, we assess preclinical models that can aid in studying LS disease pathogenesis. Enhanced understanding of this highly prevalent disease will allow for the identification of novel therapeutic targets capable of mitigating disease sequelae.

A novel therapeutic potential of cysteinyl leukotrienes and their receptors modulation in the neurological complications associated with Alzheimer's disease

Cysteinyl leukotrienes (cysLTs) are member of eicosanoid inflammatory lipid mediators family produced by oxidation of arachidonic acid by action of the enzyme 5-lipoxygenase (5-LOX). 5-LOX is activated by enzyme 5-Lipoxygenase-activating protein (FLAP), which further lead to production of cysLTs i.e. leukotriene C4 (LTC4), leukotriene D4 (LTD4) and leukotriene E4 (LTE4). CysLTs then produce their potent inflammatory actions by activating CysLT1 and CysLT2 receptors. Inhibitors of cysLTs are indicated in asthma, allergic rhinitis and other inflammatory disorders. Earlier studies have associated cysLTs and their receptors in several neurodegenerative disorders diseases like, multiple sclerosis, Parkinson's disease, Huntington's disease, epilepsy and Alzheimer's disease (AD). These inflammatory lipid mediators have previously shown effects on various aggravating factors of AD. However, not much data has been elucidated to test their role against AD clinically. Herein, through this review, we have provided the current and emerging information on the role of cysLTs and their receptors in various neurological complications responsible for the development of AD. In addition, literature evidences for the effect of cysLT inhibitors on distinct aspects of abnormalities in AD has also been reviewed. Promising advancement in understanding on the role of cysLTs on the various neuromodulatory processes and mechanisms may contribute to the development of newer and safer therapy for the treatment of AD in future.

Neurodegeneration and Glial Response after Acute Striatal Stroke: Histological Basis for Neuroprotective Studies

Stroke is a leading cause of death and neurological disability worldwide and striatal ischemic stroke is frequent in humans due to obstruction of middle cerebral artery. Several pathological events underlie damage progression and a comprehensive description of the pathological features following experimental stroke in both acute and chronic survival times is a necessary step for further functional studies. Here, we explored the patterns of microglial activation, astrocytosis, oligodendrocyte damage, myelin impairment, and Nogo-A immunoreactivity between 3 and 30 postlesion days (PLDs) after experimental striatal stroke in adult rats induced by microinjections of endothelin-1 (ET-1). The focal ischemia induced tissue loss concomitant with intense microglia activation between 3 and 14 PLDs (maximum at 7 PLDs), decreasing afterward. Astrocytosis was maximum around 7 PLDs. Oligodendrocyte damage and Nogo-A upregulation were higher at 3 PLDs. Myelin impairment was maximum between 7 and 14 PLDs. Nogo-A expression was higher in the first week in comparison to control. The results add important histopathological features of ET-1 induced stroke in subacute and chronic survival times. In addition, the establishment of the temporal evolution of these neuropathological events is an important step for future studies seeking suitable neuroprotective drugs targeting neuroinflammation and white matter damage.

Brain ischemia with Alzheimer phenotype dysregulates Alzheimer's disease-related proteins

There are evidences for the influence of Alzheimer's proteins on postischemic brain injury. We present here an overview of the published evidence underpinning the relationships between β-amyloid peptide, hyperphosphorylated tau protein, presenilins, apolipoproteins, secretases and neuronal survival/death decisions after ischemia and development of postischemic dementia. The interactions of above molecules and their influence and contribution to final ischemic brain degeneration resulting in dementia of Alzheimer phenotype are reviewed. Generation and deposition of β-amyloid peptide and tau protein pathology are essential factors involved in Alzheimer's disease development as well as in postischemic brain dementia. Postischemic injuries demonstrate that ischemia may stimulate pathological amyloid precursor protein processing by upregulation of β- and γ-secretases and therefore are capable of establishing a vicious cycle. Functional postischemic brain recovery is always delayed and incomplete by an injury-related increase in the amount of the neurotoxic C-terminal of amyloid precursor protein and β-amyloid peptide. Finally, we present here the concept that Alzheimer's proteins can contribute to and/or precipitate postischemic brain neurodegeneration including dementia with Alzheimer's phenotype.

Ameliorative Effects of Antioxidants on the Hippocampal Accumulation of Pathologic Tau in a Rat Model of Blast-Induced Traumatic Brain Injury

Traumatic brain injury (TBI) can lead to early onset dementia and other related neurodegenerative diseases. We previously demonstrated that damage to the central auditory pathway resulting from blast-induced TBI (bTBI) could be significantly attenuated by a combinatorial antioxidant treatment regimen. In the current study, we examined the localization patterns of normal Tau and the potential blast-induced accumulation of neurotoxic variants of this microtubule-associated protein that are believed to potentiate the neurodegenerative effects associated with synaptic dysfunction in the hippocampus following three successive blast overpressure exposures in nontransgenic rats. We observed a marked increase in the number of both hyperphosphorylated and oligomeric Tau-positive hilar mossy cells and somatic accumulation of endogenous Tau in oligodendrocytes in the hippocampus. Remarkably, a combinatorial regimen of 2,4-disulfonyl α-phenyl tertiary butyl nitrone (HPN-07) and N-acetylcysteine (NAC) resulted in striking reductions in the numbers of both mossy cells and oligodendrocytes positively labeled for these pathological Tau immunoreactivity patterns in response to bTBI. This treatment strategy represents a promising therapeutic approach for simultaneously reducing or eliminating both primary auditory injury and nonauditory changes associated with bTBI-induced hippocampal neurodegeneration.

tau protein, ischemic injury and vascular dementia

Clinical, neuroimaging and neuropathological studies have confirmed overlap between Alzheimer's disease (AD) and vascular dementia (VaD). Classical neuropathological changes of AD (plaques and tangles) can be present in VaD. We review neuroimaging, biochemical and animal studies to consider the role of tau protein in ischemic injury and VaD pathogenesis. The evidence comes largely from transgenic animal studies that confirm that tau transgenes influence cerebral vasculature. Clinicobiochemical studies in the cerebrospinal fluid (CSF) have, similarly, confirmed alterations in both total and phosphorylated tau protein in VaD. These data suggest that tau protein not only serves as a potential diagnostic tool for differential diagnosis of VaD from other types of dementia, but may also be a therapeutic target in ischemic stroke.

The axon-glia unit in white matter stroke: mechanisms of damage and recovery

Approximately one quarter of all strokes in humans occur in white matter, and the progressive nature of white matter lesions often results in severe physical and mental disability. Unlike cortical grey matter stroke, the pathology of white matter stroke revolves around disrupted connectivity and injured axons and glial cells, rather than neuronal cell bodies. Consequently, the mechanisms behind ischemic damage to white matter elements, the regenerative responses of glial cells and their signaling pathways, all differ significantly from those in grey matter. Development of effective therapies for white matter stroke would require an enhanced understanding of the complex cellular and molecular interactions within the white matter, leading to the identification of new therapeutic targets. This review will address the unique properties of the axon-glia unit during white matter stroke, describe the challenging process of promoting effective white matter repair, and discuss recently-identified signaling pathways which may hold potential targets for repair in this disease. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

A radical scavenger edaravone inhibits matrix metalloproteinase-9 upregulation and blood-brain barrier breakdown in a mouse model of prolonged cerebral hypoperfusion

Matrix metalloproteinase-9 (MMP-9) plays key roles in the brain pathophysiology, especially in blood-brain barrier (BBB) breakdown. Therefore, inhibiting MMP-9 activity may be a promising therapy for protecting brains in cerebrovascular diseases. Here we show that in a mouse prolonged cerebral hypoperfusion model, a clinically proven radical scavenger edaravone suppressed MMP-9 and reduced BBB damage in cerebral white matter. Prolonged cerebral hypoperfusion was induced by bilateral common carotid artery stenosis in male adult C57BL/6J mice (10 weeks old). After 7 days of cerebral hypoperfusion, white matter region (e.g. corpus callosum) exhibited significant BBB leakage, assessed by IgG staining. Correspondingly, immunostaining and western blotting showed that MMP-9 was upregulated in the white matter. Edaravone treatment (3mg/kg, i.p. at days 0 and 3) inhibited both BBB leakage and MMP-9 increase. Under the early phase of cerebral hypoperfusion conditions, oligodendrocyte precursor cells (OPCs) mainly contribute to the MMP-9 increase, but our immunostaining data showed that very little OPCs expressed MMP-9 in the edaravone-treated animals at day 7. Therefore, in vitro studies with primary rat OPCs were conducted to examine whether edaravone would directly suppressed MMP-9 expressions in OPCs. OPC cultures were exposed to sub-lethal CoCl2 for 7 days to induce prolonged chemical hypoxic stress. Prolonged chemical hypoxic stress increased MMP-9 expression in OPCs, and radical scavenging with edaravone (10μM for 7 days) ameliorated the increase. Taken together, our proof-of-concept study demonstrates that radical scavengers may provide a potential therapeutic approach for white matter injury by suppressing BBB damage.

Oligodendrocyte pathophysiology and treatment strategies in cerebral ischemia

Oligodendrocytes (OLs), the myelin-forming cells of the central nervous system, form a functional unit with axons and play a crucial role in axonal integrity. An episode of hypoxia-ischemia causes rapid and severe damage to these particularly vulnerable cells via multiple pathways such as overactivation of glutamate and ATP receptors, oxidative stress, and disruption of mitochondrial function. The cardinal effect of OL pathology is demyelination and dysmyelination, and this has profound effects on axonal function, transport, structure, metabolism, and survival. The OL is a primary target of ischemia in adult-onset stroke and especially in periventricular leukomalacia and should be considered as a primary therapeutic target in these conditions. More emphasis is needed on therapeutic strategies that target OLs, myelin, and their receptors, as these have the potential to significantly attenuate white matter injury and to establish functional recovery of white matter after stroke. In this review, we will summarize recent progress on the role of OLs in white matter ischemic injury and the current and emerging principles that form the basis for protective strategies against OL death.

Is the ischemic blood–brain barrier insufficiency responsible for full-blown Alzheimer's disease?

The goal of this paper is to provide scientists with a comprehensive review of the state-of-the-art influence the ischemic blood-brain barrier (BBB) has on the final development of Alzheimer's disease and to provide detailed food-for-thought which will hopefully stimulate more researchers in this area of neuroscience. Understanding new and fundamental concepts about the behavior of the BBB during long-term reperfusion after ischemia with a variety of new neuropathogenic factors can hopefully provide some interesting clues related to the pathologic processes issues that have been receiving considerable attention in the human clinic. We present the recent data to understand the role of the BBB in maturation of both diseases and try to differentiate between primary and secondary pathologic mechanisms. In conclusion, the neuropathogenesis of Alzheimer's disease involves an initial ischemic neuronal alterations leading to enhanced neuronal vulnerability to beta-amyloid peptide and the ischemic breakdown of the BBB with leakage of serum borne beta-amyloid peptide into brain parenchyma, activation of beta-amyloid peptide-dependent toxicity culminating in the formation of amyloid plaques and finally end in full-blown Alzheimer's disease. In summary, probably we have combined mechanism(s) of ischemia processes, ischemic and chronic BBB dysfunction and beta-amyloid peptide-dependent injury in pathology of neurodegeneration that is observed in Alzheimer's disease. We speculate that Alzheimer's disease may be caused by silent and sublethal ischemic episodes that attack and slowly steal the minds of its victims. Finally, our review proposes the ischemic BBB-dependent mechanism(s) that probably are responsible for full-blown Alzheimer's disease.

Sporadic Alzheimer's disease begins as episodes of brain ischemia and ischemically dysregulated Alzheimer's disease genes

The study of sporadic Alzheimer’s disease etiology, now more than ever, needs an infusion of new concepts. Despite ongoing interest in Alzheimer’s disease, the basis of this entity is not yet clear. At present, the best-established and accepted “culprit” in Alzheimer’s disease pathology by most scientists is the amyloid, as the main molecular factor responsible for neurodegeneration in this disease. Abnormal upregulation of amyloid production or a disturbed clearance mechanism may lead to pathological accumulation of amyloid in brain according to the “amyloid hypothesis.” We will critically review these observations and highlight inconsistencies between the predictions of the “amyloid hypothesis” and the published data. There is still controversy over the role of amyloid in the pathological process. A question arises whether amyloid is responsible for the neurodegeneration or if it accumulates because of the neurodegeneration. Recent evidence suggests that the pathophysiology and neuropathology of Alzheimer’s disease comprises more than amyloid accumulation, tau protein pathology and finally brain atrophy with dementia. Nowadays, a handful of researchers share a newly emerged view that the ischemic episodes of brain best describe the pathogenic cascade, which eventually leads to neuronal loss, especially in hippocampus, with amyloid accumulation, tau protein pathology and irreversible dementia of Alzheimer type. The most persuasive evidences come from investigations of ischemically damaged brains of patients and from experimental ischemic brain studies that mimic Alzheimer-type dementia. This review attempts to depict what we know and do not know about the triggering factor of the Alzheimer’s disease, focusing on the possibility that the initial pathological trigger involves ischemic episodes and ischemia-induced gene dysregulation. The resulting brain ischemia dysregulates additionally expression of amyloid precursor protein and amyloid-processing enzyme genes that, in addition, ultimately compromise brain functions, leading over time to the complex alterations that characterize advanced sporadic Alzheimer’s disease. The identification of the genes involved in Alzheimer’s disease induced by ischemia will enable to further define the events leading to sporadic Alzheimer’s disease-related abnormalities. Additionally, knowledge gained from the above investigations should facilitate the elaboration of the effective treatment and/or prevention of Alzheimer’s disease.

Brain ischemia activates β- and γ-secretase cleavage of amyloid precursor protein: significance in sporadic Alzheimer's disease

Amyloid precursor protein cleavage through β- and γ-secretases produces β-amyloid peptide, which is believed to be responsible for death of neurons and dementia in Alzheimer’s disease. Levels of β- and γ-secretase are increased in sensitive areas of the Alzheimer’s disease brain, but the mechanism of this process is unknown. In this review, we prove that brain ischemia generates expression and activity of both β- and γ-secretases. These secretases are induced in association with oxidative stress following brain ischemia. Data suggest that ischemia promotes overproduction and aggregation of β-amyloid peptide in brain, which is toxic for ischemic neuronal cells. In our review, we demonstrated the role of brain ischemia as a molecular link between the β- and the γ-secretase activities and provided a molecular explanation of the possible neuropathogenesis of sporadic Alzheimer’s disease.

Glial cell inclusions and the pathogenesis of neurodegenerative diseases

In this review, we discuss examples that show how glial-cell pathology is increasingly recognized in several neurodegenerative diseases. We also discuss the more provocative idea that some of the disorders that are currently considered to be neurodegenerative diseases might, in fact, be due to primary abnormalities in glia. Although the mechanism of glial pathology (i.e. modulating glutamate excitotoxicity) might be better established for amyotrophic lateral sclerosis (ALS), a role for neuronal-glial interactions in the pathogenesis of most neurodegenerative diseases is plausible. This burgeoning area of neuroscience will receive much attention in the future and it is expected that further understanding of basic neuronal-glial interactions will have a significant impact on the understanding of the fundamental nature of human neurodegenerative disorders.

Pathophysiologic cascades in ischemic stroke

Many advances have been achieved in terms of understanding the molecular and cellular mechanisms of ischemic stroke. But thus far, clinically effective neuroprotectants remain elusive. In this minireview, we summarize the basics of ischemic cascades after stroke, covering neuronal death mechanisms, white matter pathophysiology, and inflammation with an emphasis on microglia. Translating promising mechanistic knowledge into clinically meaningful stroke drugs is very challenging. An integrative approach that encompasses the multimodal and multicell signaling phenomenon of stroke will be required to move forward.

Ex vivo diffusion tensor imaging and neuropathological correlation in a murine model of hypoxia-ischemia-induced thrombotic stroke

Diffusion tensor imaging (DTI) is a powerful method to visualize white matter, but its use in patients with acute stroke remains limited because of the lack of corresponding histologic information. In this study, we addressed this issue using a hypoxia-ischemia (HI)-induced thrombotic model of stroke in adult mice. At 6, 15, and 24  hours after injury, animals were divided into three groups for (1) in vivo T2- and diffusion-weighted magnetic resonance imaging, followed by histochemistry, (2) ex vivo DTI and electron microscopy, and (3) additional biochemical or immunochemical assays. The temporal changes of diffusion anisotropy and histopathology were compared in the fimbria, internal capsule, and external capsule. We found that HI caused a rapid reduction of axial and radial diffusivities in all three axonal bundles. A large decrease in fractional anisotropy, but not in axial diffusivity per se, was associated with structural breakdown of axons. Furthermore, the decrease in radial diffusivity correlated with swelling of myelin sheaths and compression of the axoplasma. The gray matter of the hippocampus also exhibited a high level of diffusion anisotropy, and its reduction signified dendritic degeneration. Taken together, these results suggest that cross-evaluation of multiple DTI parameters may provide a fuller picture of axonal and dendritic injury in acute ischemic stroke.

Role of glial cells in neurotoxin-induced animal models of Parkinson's disease

Dopaminergic neurons are selectively vulnerable to oxidative stress and inflammatory attack. The neuronal cell loss in the substantia nigra is associated with a glial response composed markedly of activated microglia and, to a lesser extent, of reactive astrocytes although these glial responses may be the source of neurotrophic factors and can protect against oxidative stress such as reactive oxygen species and reactive nitrogen species. However, the glial response can also mediate a variety of deleterious events related to the production of pro-inflammatory, pro-oxidant reactive species, prostaglandins, cytokines, and so on. In this review, we discuss the possible protective and deleterious effects of glial cells in the neurodegenerative diseases and examine how these factors may contribute to the pathogenesis of Parkinson's disease. This review suggests that further investigation concerning glial reaction in Parkinson's disease may lead to disease-modifying therapeutic approaches and may contribute to the pathogenesis of this disease.

Tau as a potential novel therapeutic target in ischemic stroke

Stroke is associated with high mortality and major disability burdens worldwide, but there are few effective and widely available therapies. Tau plays an important role in promoting microtubule assembly and stabilizing microtubule networks with phosphorylation regulating these functions. Based on the "ischemia-reperfusion theory" of Alzheimer's disease, some previous studies have focused on the relationship of tau and Alzheimer lesions in experimental brain ischemia. Thus, we hypothesize that the alterations in phosphorylation of tau are critical to microtubule dynamics and metabolism, and contribute to the pathophysiologic mechanisms during brain ischemia and/or reperfusion processes. We infer that regulation of phosphorylation of tau may be considered as a potential new therapeutic target in ischemic stroke.

Alzheimer's mechanisms in ischemic brain degeneration

There is increasing evidence for influence of Alzheimer's proteins and neuropathology on ischemic brain injury. This review investigates the relationships between beta-amyloid peptide, apolipoproteins, presenilins, tau protein, alpha-synuclein, inflammation factors, and neuronal survival/death decisions in brain following ischemic episode. The interactions of these molecules and influence on beta-amyloid peptide synthesis and contribution to ischemic brain degeneration and finally to dementia are reviewed. Generation and deposition of beta-amyloid peptide and tau protein pathology are important key players involved in mechanisms in ischemic neurodegeneration as well as in Alzheimer's disease. Current evidence suggests that inflammatory process represents next component, which significantly contribute to degeneration progression. Although inflammation was initially thought to arise secondary to ischemic neurodegeneration, recent studies present that inflammatory mediators may stimulate amyloid precursor protein metabolism by upregulation of beta-secretase and therefore are able to establish a vicious cycle. Functional brain recovery after ischemic lesion was delayed and incomplete by an injury-related increase in the amount of the neurotoxic C-terminal of amyloid precursor protein and beta-amyloid peptide. Moreover, ischemic neurodegeneration is strongly accelerated with aging, too. New therapeutic alternatives targeting these proteins and repairing related neuronal changes are under development for the treatment of ischemic brain consequences including memory loss prevention.

Oligovascular signaling in white matter stroke

Stroke is one of the leading causes of death and disability in developed countries. Since protecting neurons alone is not sufficient for stroke therapy, research has shifted to the rescue of multiple cell types in the brain. In particular, attention has focused on the study of how cerebral blood vessels and brain cells communicate with each other. Recent findings suggest that cerebral endothelial cells may secrete trophic factors that nourish neighboring cells. Although data are strongest in terms of supporting endothelial-neuronal interactions, it is likely that similar interactions occur in white matter as well. In this mini-review, we summarize recent advances in the dissection of cell-cell interactions in white matter. We examine two key concepts. First, trophic interactions between vessels and oligodendrocytes (OLGs) and oligodendrocyte precursor cells (OPCs) play critical roles in white matter homeostasis. Second, cell-cell trophic coupling is disturbed under diseased conditions that incur oxidative stress. White matter pathophysiology is very important in stroke. A deeper understanding of the mechanisms of oligovascular signaling in normal and pathologic conditions may lead us to new therapeutic targets for stroke and other neurodegenerative diseases.

Experimental models for analysis of oligodendrocyte pathophysiology in stroke

White matter damage is a clinically important part of stroke. However, compared to the mechanisms of neuronal injury in gray matter, white matter pathophysiology remains relatively understudied and poorly understood. This mini-review aims at summarizing current knowledge on experimental systems for analyzing the role of white matter injury relevant to stroke. In vitro platforms comprise primary cultures of both mature oligodendrocytes (OLGs) as well as oligodendrocyte precursor cells (OPCs). Tissue platforms involve preparations of optic nerve systems. Whole-animal platforms comprise in vivo models of cerebral ischemia that attempt to target white matter brain areas. While there is no single perfect model system, the collection of these experimental approaches have recently allowed a better understanding of the molecular and cellular pathways underlying OLG/OPC damage and demyelination. A systematic utilization of these cell, tissue and whole-animal platforms may eventually lead us to discover new targets for treating white matter injury in stroke and other CNS disorders.

Edaravone, a free radical scavenger, mitigates both gray and white matter damages after global cerebral ischemia in rats

Recent studies have shown that similar to cerebral gray matter (mainly composed of neuronal perikarya), white matter (composed of axons and glias) is vulnerable to ischemia. Edaravone, a free radical scavenger, has neuroprotective effects against focal cerebral ischemia even in humans. In this study, we investigated the time course and the severity of both gray and white matter damage following global cerebral ischemia by cardiac arrest, and examined whether edaravone protected the gray and the white matter. Male Sprague-Dawley rats were used. Global cerebral ischemia was induced by 5 min of cardiac arrest and resuscitation (CAR). Edaravone, 3 mg/kg, was administered intravenously either immediately or 60 min after CAR. The morphological damage was assessed by cresyl violet staining. The microtubule-associated protein 2 (a maker of neuronal perikarya and dendrites), the beta amyloid precursor protein (the accumulation of which is a maker of axonal damage), and the ionized calcium binding adaptor molecule 1 (a marker of microglia) were stained for immunohistochemical analysis. Significant neuronal perikaryal damage and marked microglial activation were observed in the hippocampal CA1 region with little axonal damage one week after CAR. Two weeks after CAR, the perikaryal damage and microglial activation were unchanged, but obvious axonal damage occurred. Administration of edaravone 60 min after CAR significantly mitigated the perikaryal damage, the axonal damage, and the microglial activation. Our results show that axonal damage develops slower than perikaryal damage and that edaravone can protect both gray and white matter after CAR in rats.

Selective adenosine A2a receptor antagonism reduces JNK activation in oligodendrocytes after cerebral ischaemia

Adenosine is a potent biological mediator, the concentration of which increases dramatically following brain ischaemia. During ischaemia, adenosine is in a concentration range (muM) that stimulates all four adenosine receptor subtypes (A(1), A(2A), A(2B) and A(3)). In recent years, evidence has indicated that the A(2A) receptor subtype is of critical importance in stroke. We have previously shown that 24 h after medial cerebral artery occlusion (MCAo), A(2A) receptors up-regulate on neurons and microglia of ischaemic striatum and cortex and that subchronically administered adenosine A(2A) receptor antagonists protect against brain damage and neurological deficit and reduce activation of p38 mitogen-activated protein kinase (MAPK) in microglial cells. The mechanisms by which A(2A) receptors are noxious during ischaemia still remain elusive. The objective of the present study was to investigate whether the adenosine A(2A) antagonist SCH58261 affects JNK and MEK1/ERK MAPK activation. A further aim was to investigate cell types expressing activated JNK and MEK1/ERK MAPK after ischaemia. We hereby report that the selective adenosine A(2A) receptor antagonist, SCH58261, administered subchronically (0.01 mg/kg i.p) 5 min, 6 and 20 h after MCAo in male Wistar rats, reduced JNK MAPK activation (immunoblot analysis: phospho-JNK54 isoform by 81% and phospho-JNK46 isoform by 60%) in the ischaemic striatum. Twenty-four hours after MCAo, the Olig2 transcription factor of oligodendroglial progenitor cells and mature oligodendrocytes was highly expressed in cell bodies in the ischaemic striatum. Immunofluorescence staining showed that JNK MAPK is maximally expressed in Olig2-stained oligodendrocytes and in a few NeuN stained neurons. Striatal cell fractioning into nuclear and extra-nuclear fractions demonstrated the presence of Olig2 transcription factor and JNK MAPK in both fractions. The A(2A) antagonist reduced striatal Olig 2 transcription factor (immunoblot analysis: by 55%) and prevented myelin disorganization, assessed by myelin-associated glycoprotein staining. Twenty-four hours after MCAo, ERK1/2 MAPK was highly activated in the ischaemic striatum, mostly in microglia, while it was reduced in the ischaemic cortex. The A(2A) antagonist did not affect activation of the ERK1/2 pathway. The efficacy of A(2A) receptor antagonism in reducing activation of JNK MAPK in oligodendrocytes suggests a mechanism of protection consisting of scarring oligodendrocyte inhibitory molecules that can hinder myelin reconstitution and neuron functionality.

Apolipoprotein D is elevated in oligodendrocytes in the peri-infarct region after experimental stroke: influence of enriched environment

Injury to the brain (e.g., stroke) results in a disruption of neuronal connectivity and loss of fundamental sensori-motor functions. The subsequent recovery of certain functions involves structural rearrangements in areas adjacent to the infarct. This remodeling of the injured brain requires trafficking of macromolecular components including cholesterol and phospholipids, a transport carried out by apolipoproteins including apolipoprotein D (apoD). We investigated the changes in the levels of apoD mRNA and protein, and its cellular localization during a recovery period up to 30 days after experimental stroke in the rat brain. In the core of the brain infarct, apoD immunoreactivity but not mRNA increased in dying pyramidal neurons, indicative of cellular redistribution of lipids. During 2 to 7 days of recovery after stroke, the apoD levels increased in the peri-infarct and white matter areas in cells identified as mature oligodendrocytes. The apoD expressing cells were conspicuously located along the rim of the infarct, suggesting a role for apoD in tissue repair. Furthermore, housing animals in an enriched environment improved sensori-motor function and increased the apoD levels. Our data strongly suggest that apoD is involved in regenerative processes and scar formation in the peri-infarct area presumably by enhancing lipid trafficking.

Increasing in situ nick end labeling of oligodendrocytes in white matter of patients with Binswanger's disease

Increasing evidence suggests the presence of apoptotic cell death in many neurodegenerative diseases. However, in Binswanger's disease (BD), no information is available concerning the apoptosis-related pathologic changes that may occur in the white matter. To investigate whether apoptotic cell death is included in the pathophysiology of the white matter changes in BD, autopsied brains from patients with BD (n = 5) were compared with those of non-neurologic controls (n = 5). Terminal deoxynucleotidyl transferase-mediated dUTP in situ nick end labeling (TUNEL) was used as a marker for cell damage with DNA fragmentation. A proteolipid protein (PLP) messenger RNA (mRNA) hybridization signal was also used as a sensitive and specific marker of oligodendrocytes as well as glial fibrillary acidic protein (GFAP) immunoreactivity as a marker of astrocytes. There were frequent TUNEL-positive cells in the rarefied white matter of patients with BD. TUNEL-positive cells were found 15-fold more numerously in BD than in controls (P < .01). TUNEL-positive cells were presumably oligodendrocytes because of their coexpression with PLP mRNA. The numbers of GFAP-positive astrocytes were significantly decreased in BD compared with those in control subjects. The reduction in numbers of PLP mRNA-positive oligodendrocytes were also seen in BD, but these changes did not reach the level of significance. The pathologic alterations in BD brains include increased TUNEL-positive oligodendrocytes, associated with degradation of myelin. Although TUNEL-positive glial cells did not show typical apoptotic morphologic features, these findings suggest that increase in in situ nick end labeling of oligodendrocytes in white matter may play an important role in the pathophysiology of BD.

Damage to oligodendrocytes in the striatum after MPTP neurotoxicity in mice

We investigated the alteration of oligodendrocytes in comparison with that of astrocytes and microglia in the mouse striatum after MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropridine) treatment under the same conditions using Western blot analysis and Immunohistochemistry. In our Western blot analysis, four administrations of MPTP at 2-h intervals to mice produced the remarkable loss of TH (tyrosine hydroxylase) protein levels in the striatum after 3 and 7 days. In contrast, GFAP (glial fibrillary acidic protein) and Iba-1 protein in the striatum showed a significant increase of GFAP and Iba-1 protein levels 3 and 7 days after MPTP treatment. On the other hand, the levels of CNPase (2', 3'-cyclic nucleotide 3'-phosphodiesterase) protein were decreased significantly in the striatum 3 and 7 days after MPTP treatment. In our immunohistochemical study, a significant decrease in the area of expression of CNPase-positive profiles was observed in the striatum 3 and 7 days after MPTP treatment. These results demonstrate that oligodendrocytes in the striatum are damaged after MPTP treatment. Thus our present findings provide valuable information for the pathogenesis of Parkinson's disease.

Time-dependent increase in Nogo-A expression after focal cerebral ischemia in marmoset monkeys

Nogo-A is a myelin-associated protein that has been shown to inhibit axonal sprouting after lesions to the CNS. Several studies have demonstrated that blocking the activity or expression of this inhibitor can induce structural and functional recovery after CNS lesions. However, there are limited and contradictory data on the expression of Nogo-A after CNS lesions. In the present study, marmoset monkeys received permanent occlusion of the middle cerebral artery (MCAo). Two, 3, or 4 months after the onset of injury brain sections were stained for Nogo-A protein. Two sham operated marmosets were included as a control. Nogo-A protein expression was quantified in white matter and grey matter in the areas adjacent to the lesion (or the equivalent areas in the intact side). At 2 months after injury, but not at 3 or 4 months, there was a significant increase in the number of oligodendrocytes that were Nogo-A immunopositive. This increase was observed in white matter structures that were adjacent to the lesion (e.g. corona radiate (CR)); but not in: white matter structures distal to the lesion (e.g. corpus callosum (CC)); cortical regions adjacent to the lesion; contralateral regions or in sham operated marmosets. These data suggest that Nogo-A levels are significantly increased within oligodendrocytes in areas adjacent to the lesion up to 2 months following cerebral ischaemia. Future studies will determine whether this offers the opportunity to promote plasticity by targeting Nogo-A weeks or months following stroke.

Injury to axons and oligodendrocytes following endothelin-1-induced middle cerebral artery occlusion in conscious rats

Injury to axons and oligodendrocytes has been poorly characterized in most animal models of stroke, and hence has been difficult to target therapeutically. It is therefore necessary to characterize axonal and oligodendroglial injury in these models, in order to rationally design putative protective compounds that minimize this injury. This study aims to characterize injury to axons and oligodendrocytes in the endothelin-1 (ET-1) model of middle cerebral artery occlusion (MCAO) in conscious rats. Transient forebrain ischemia was induced in conscious adult male Long Evans rats by the perivascular microinjection of ET-1. Quantitative histopathology was performed on forebrain sections at 6, 24, 48 and 72 h after ET-1 administration, using ballistic light analyses and immunohistochemistry for amyloid precursor protein (APP), SMI32, and Tau-1. Ballistic light analyses of cortical and striatal lesions revealed that the infarct volume was maximal in these regions by 6 h. APP and SMI32 immunohistochemistry demonstrated that axonal injury was maximal by 6 h in this model; however, some injured axons appeared to maintain good structural integrity up to 72 h after insult. Density measurements for Tau-1-immunopositive oligodendrocytes were significantly elevated within the corpus callosum from 48 h, but reductions in total oligodendrocyte numbers were not apparent up 72 h after ET-1 injection. These results indicate that axonal and oligodendroglial injury should be investigated as potential targets for delayed therapeutic intervention after MCAO.

Identification of neuroprotective properties of anti-MAG antibody: a novel approach for the treatment of stroke?

The inhibitory activity of myelin-associated glycoprotein (MAG) on neurons is thought to contribute to the lack of regenerative capacity of the CNS after injury. The interaction of MAG and its neuronal receptors mediates bidirectional signaling between neurons and oligodendrocytes. The novel finding that an anti-MAG monoclonal antibody not only possesses the ability to neutralise the inhibitory effect of MAG on neurons but also directly protects oligodendrocytes from glutamate-mediated oxidative stress-induced cell death is reported here. Furthermore, administration of anti-MAG antibody (centrally and systemically) starting 1 hour after middle cerebral artery occlusion in the rat significantly reduced lesion volume at 7 days. This neuroprotection was associated with a robust improvement in motor function compared with animals receiving control IgG1. Together, these data highlight the potential for the use of anti-MAG antibodies as therapeutic agents for the treatment of stroke.