Complete cerebral ischemia with short-term survival in rat induced by cardiac arrest. II. Extracellular and intracellular accumulation of apolipoproteins E and J in the brain

A Look at the Etiology of Alzheimer's Disease based on the Brain Ischemia Model

Alzheimer's disease (AD) is the frequent form of dementia in the world. Despite over 100 years of research into the causes of AD, including amyloid and tau protein, the research has stalled and has not led to any conclusions. Moreover, numerous projects aimed at finding a cure for AD have also failed to achieve a breakthrough. Thus, the failure of anti-amyloid and anti-tau protein therapy to treat AD significantly influenced the way we began to think about the etiology of the disease. This situation prompted a group of researchers to focus on ischemic brain episodes, which, like AD, mostly present alterations in the hippocampus. In this context, it has been proposed that cerebral ischemic incidents may play a major role in promoting amyloid and tau protein in neurodegeneration in AD. In this review, we summarized the experimental and clinical research conducted over several years on the role of ischemic brain episodes in the development of AD. Studies have shown changes typical of AD in the course of brain neurodegeneration post-ischemia, i.e., progressive brain and hippocampal atrophy, increased amyloid production, and modification of tau protein. In the post-ischemic brain, the diffuse and senile amyloid plaques and the development of neurofibrillary tangles characteristic of AD were revealed. The above data evidently showed that after brain ischemia, there are modifications in protein folding, leading to massive neuronal death and damage to the neuronal network, which triggers dementia with the AD phenotype.

The Influence of Clusterin Glycosylation Variability on Selected Pathophysiological Processes in the Human Body

The present review gathers together the most important information about variability in clusterin molecular structure, its profile, and the degree of glycosylation occurring in human tissues and body fluids in the context of the utility of these characteristics as potential diagnostic biomarkers of selected pathophysiological conditions. The carbohydrate part of clusterin plays a crucial role in many biological processes such as endocytosis and apoptosis. Many pathologies associated with neurodegeneration, carcinogenesis, metabolic diseases, and civilizational diseases (e.g., cardiovascular incidents and male infertility) have been described as causes of homeostasis disturbance, in which the glycan part of clusterin plays a very important role. The results of the discussed studies suggest that glycoproteomic analysis of clusterin may help differentiate the severity of hippocampal atrophy, detect the causes of infertility with an immune background, and monitor the development of cancer. Understanding the mechanism of clusterin (CLU) action and its binding epitopes may enable to indicate new therapeutic goals. The carbohydrate part of clusterin is considered necessary to maintain its proper molecular conformation, structural stability, and proper systemic and/or local biological activity. Taking into account the wide spectrum of CLU action and its participation in many processes in the human body, further studies on clusterin glycosylation variability are needed to better understand the molecular mechanisms of many pathophysiological conditions. They can also provide the opportunity to find new biomarkers and enrich the panel of diagnostic parameters for diseases that still pose a challenge for modern medicine.

Myricetin as a Promising Molecule for the Treatment of Post-Ischemic Brain Neurodegeneration

The available drug therapy for post-ischemic neurodegeneration of the brain is symptomatic. This review provides an evaluation of possible dietary therapy for post-ischemic neurodegeneration with myricetin. The purpose of this review was to provide a comprehensive overview of what scientists have done regarding the benefits of myricetin in post-ischemic neurodegeneration. The data in this article contribute to a better understanding of the potential benefits of myricetin in the treatment of post-ischemic brain neurodegeneration, and inform physicians, scientists and patients, as well as their caregivers, about treatment options. Due to the pleiotropic properties of myricetin, including anti-amyloid, anti-phosphorylation of tau protein, anti-inflammatory, anti-oxidant and autophagous, as well as increasing acetylcholine, myricetin is a promising candidate for treatment after ischemia brain neurodegeneration with full-blown dementia. In this way, it may gain interest as a potential substance for the prophylaxis of the development of post-ischemic brain neurodegeneration. It is a safe substance, commercially available, inexpensive and registered as a pro-health product in the US and Europe. Taken together, the evidence available in the review on the therapeutic potential of myricetin provides helpful insight into the potential clinical utility of myricetin in treating neurodegenerative disorders with full-blown dementia. Therefore, myricetin may be a promising complementary agent in the future against the development of post-ischemic brain neurodegeneration. Indeed, there is a scientific rationale for the use of myricetin in the prevention and treatment of brain neurodegeneration caused by ischemia.

Dysregulation of Autophagy, Mitophagy, and Apoptotic Genes in the Medial Temporal Lobe Cortex in an Ischemic Model of Alzheimer's Disease

Ischemic brain damage is a pathological incident that is often linked with medial temporal lobe cortex injury and finally its atrophy. Post-ischemic brain injury associates with poor prognosis since neurons of selectively vulnerable ischemic brain areas are disappearing by apoptotic program of neuronal death. Autophagy has been considered, after brain ischemia, as a guardian against neurodegeneration. Consequently, we have examined changes in autophagy (BECN 1), mitophagy (BNIP 3), and apoptotic (caspase 3) genes in the medial temporal lobe cortex with the use of quantitative reverse-transcriptase PCR following transient 10-min global brain ischemia in rats with survival 2, 7, and 30 days. The intense significant overexpression of BECN 1 gene was noted on the 2nd day, while on days 7-30 the expression of this gene was still upregulated. BNIP 3 gene was downregulated on the 2nd day, but on days 7-30 post-ischemia, there was a significant reverse tendency. Caspase 3 gene, associated with apoptotic neuronal death, was induced in the same way as BNIP 3 gene after brain ischemia. Thus, the demonstrated changes indicate that the considerable dysregulation of expression of BECN 1, BNIP 3, and caspase 3 genes may be connected with a response of neuronal cells in medial temporal lobe cortex to transient complete brain ischemia.

Expression of Alzheimer's disease risk genes in ischemic brain degeneration

We review the Alzheimer-related expression of genes following brain ischemia as risk factors for late-onset of sporadic Alzheimer's disease and their role in Alzheimer's disease ischemia-reperfusion pathogenesis. More recent advances in understanding ischemic etiology of Alzheimer's disease have revealed dysregulation of Alzheimer-associated genes including amyloid protein precursor, β-secretase, presenilin 1 and 2, autophagy, mitophagy and apoptosis. We review the relationship between these genes dysregulated by brain ischemia and the cellular and neuropathological characteristics of Alzheimer's disease. Here we summarize the latest studies supporting the theory that Alzheimer-related genes play an important role in ischemic brain injury and that ischemia is a needful and leading supplier to the onset and progression of sporadic Alzheimer's disease. Although the exact molecular mechanisms of ischemic dependent neurodegenerative disease and neuronal susceptibility finally are unknown, a downregulated expression of neuronal defense genes like alfa-secretase in the ischemic brain makes the neurons less able to resist injury. The recent challenge is to find ways to raise the adaptive reserve of the brain to overcome such ischemic-associated deficits and support and/or promote neuronal survival. Understanding the mechanisms underlying the association of these genes with risk for Alzheimer's disease will provide the most meaningful targets for therapeutic development to date.

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.

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.

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.

Clusterin: a forgotten player in Alzheimer's disease

Clusterin, also known as apolipoprotein J, is a versatile chaperone molecule which contains several amphipathic and coiled-coil alpha-helices, typical characteristics of small heat shock proteins. In addition, clusterin has three large intrinsic disordered regions, so-called molten globule domains, which can stabilize stressed protein structures. Twenty years ago, it was demonstrated that the expression of clusterin was clearly increased in Alzheimer's disease (AD). Later it was observed that clusterin can bind amyloid-beta peptides and prevent their fibrillization. Clusterin is also involved in the clearance of amyloid-beta peptides and fibrils by binding to megalin receptors and enhancing their endocytosis within glial cells. Clusterin is a complement inhibitor and can suppress complement activation observed in AD. Clusterin is also present in lipoprotein particles and regulates cholesterol and lipid metabolism of brain which is disturbed in AD. Clusterin is a stress-induced chaperone which is normally secreted but in conditions of cellular stress, it can be transported to cytoplasm where it can bind to Bax protein and inhibit neuronal apoptosis. Clusterin can also bind to Smad2/3 proteins and potentiate the neuroprotective TGFbeta signaling. An alternative splicing can produce a variant isoform of clusterin which can be translocated to nuclei where it induces apoptosis. The role of nuclear clusterin in AD needs to be elucidated. We will review here the extensive literature linking clusterin to AD and examine the recent progress in clusterin research with the respect to AD pathology. Though clusterin can be viewed as a multipotent guardian of brain, it is unable to prevent the progressive neuropathology in chronic AD.

Brain ischemia and ischemic blood-brain barrier as etiological factors in sporadic Alzheimer's disease

The development of neuronal death and amyloid plaques is a characteristic feature of ischemic- and Alzheimer-type dementia. An important aspect of neuronal loss and amyloid plaques are their topography and neuropathogenesis. This review was performed to present the hypothesis that different fragments of blood-borne amyloid precursor protein are able to enter the ischemic blood-brain barrier. Chronic disruption of the blood-brain barrier after ischemic injury was shown. As an effect of chronic ischemic blood-brain barrier injury, a visible connection of amyloid plaques with neurovasculature was observed. This neuropathology appears to have similar distribution and mechanisms to Alzheimer's disease. The usefulness of rival ischemic theory in elucidating the neuropathogenesis of amyloid plaques formation and neuronal death in Alzheimer's disorder is discussed.

Up-regulation of low-density lipoprotein receptor expression in the ischemic core and the peri-ischemic area after transient MCA occlusion in rats

Low-density lipoprotein (LDL) receptor is involved in cholesterol metabolism of CNS as a receptor of apolipoprotein E (ApoE), which plays an important role in regenerative process after brain ischemia. Temporal and spatial changes of LDL receptor were investigated after 90 min of transient middle cerebral artery occlusion (MCAO) in relation to those of microtubule-associated protein 2 (MAP2) and ApoE. In the ischemic core, LDL receptor became positive at 1 d after transient MCAO, which was not double positive for MAP2 or ApoE, and disappeared in 7 and 56 d. In the peri-ischemic area, LDL receptor became observed at 7 d, which peaked at 21 d, most of which were double positive for MAP2. The number of LDL receptor and ApoE double-positive cells increased at 7 d and decreased at 21 d with the shift of LDL receptor immunoreactivity from cytoplasm at 7 d to dendrites at 21 d in the peri-ischemic area. These results suggest that LDL receptor, interacting with ApoE, is profoundly involved in lipid transport of CNS for tissue repair in the peri-ischemic area after brain ischemia.

Links between the pathology of Alzheimer's disease and vascular dementia

The major neuropathological lesions defining Alzheimer's disease (AD) include neurofibrillary tangles and amyloid plaques, which are mainly composed of abnormally phosphorylated tau and amyloid-beta (A beta), respectively. Numerous neuropathological and neuroimaging studies indicate that at least one-third of AD cases are complicated by some degree of vascular pathology, whereas in a similar proportion of patients clinically diagnosed with vascular dementia, AD pathology is also present. Many classical vascular risk factors such as hypertension, diabetes mellitus, and hypercholesterolemia have recently been shown also to increase the risk of AD. Growing evidence suggests that vascular pathology lowers the threshold for the clinical presentation of dementia at a given level of AD-related pathology and potentially directly promotes AD lesions such as A beta plaques. Cerebral ischemia, chronically up-regulates expression of the amyloid precursor protein (APP), which is the precursor to the amyloid beta peptide and damages the blood-brain barrier (BBB), affecting A beta peptide clearance from the brain. Recognition of the importance of these vascular risk factors for AD-related dementia and their treatment will be beneficial not only for preventing cardiac, cerebral, and peripheral complications of vascular disease, but also will likely have a direct impact on the occurrence of sporadic AD in older subjects. In this paper, we review some of the links between vascular risk factors and AD pathology and present data on the direct effect of ischemia on cognitive function and A beta deposition in a mouse model of AD.

Blood-brain barrier dysfunction and amyloid precursor protein accumulation in microvascular compartment following ischemia-reperfusion brain injury with 1-year survival

This study examined the late microvascular consequences of brain ischemia due to cardiac arrest in rats. In reacted vibratome sections scattered foci of extravasated horseradish peroxidase were noted throughout the brain and did not appear to be restricted to any specific area of brain. Ultrastructural investigation of leaky sites frequently presented platelets adhering to the endothelium of venules and capillaries. Endothelial cells demonstrated pathological changes with evidence of perivascular astrocytic swelling. At the same time, we noted C-terminal of amyloid precursor protein/beta-amyloid peptide (CAPP/betaA) deposits in cerebral blood vessels, with a halo of CAPP/betaA immunoreactivity in the surrounding parenchyma suggested diffusion of CAPP/betaA out of the vascular compartment. Changes predominated in the hippocampus, cerebral and entorhinal cortex, corpus callosum, thalamus, basal ganglia and around the lateral ventricles. These data implicate delayed abnormal endothelial function of vessels following ischemia-reperfusion brain injury as a primary event in the pathogenesis of the recurrent cerebral infarction.

Lipoprotein lipase and endothelial lipase expression in mouse brain: regional distribution and selective induction following kainic acid-induced lesion and focal cerebral ischemia

Lipoprotein and endothelial lipases are members of the triglyceride lipase gene family. These genes are expressed in the brain, where the encoded proteins are fulfilling functions that have yet to be elucidated. In this study, we examined the distribution of their respective mRNAs in the C57BL/6 mouse brain by in situ hybridization. In control mice, we observed widespread expression of lipoprotein lipase (LPL) mRNA mainly in pyramidal cells of the hippocampus (CA1, CA2 and CA3 areas), in the striatum and in several cortical areas. Endothelial lipase (EL) mRNA expression was restricted to CA3 pyramidal cells of the hippocampus, to ependymal cells in the ventral part of the third ventricle and to some cortical cell layers. To gain insight into the role played by lipases in the brain, neurodegeneration was induced by intraperitoneal injection of kainic acid (KA) or by occlusion of the middle cerebral artery (MCA). Upon injection of KA, a rapid increase in EL mRNA expression was observed in the piriform cortex, hippocampus, thalamus and neocortex. However, the levels of LPL mRNA were unaffected by KA injection. Remarkably, after focal cerebral ischemia, the expression of EL was unaffected whereas a dramatic increase in LPL expression was observed in neocortical areas of the lesioned side of the brain. These results show that LPL and EL transcripts are selectively upregulated in function of the type of brain injury. LPL and EL could thus fulfill a function in the pathophysiological response of the brain to injury.

Apolipoprotein E protects against oxidative stress in mixed neuronal-glial cell cultures by reducing glutamate toxicity

Apolipoprotein E (ApoE) deficiency has been shown to adversely affect outcome after transient cerebral ischemia and head trauma. Since oxidative stress contributes to these injuries, the ability of ApoE to reduce irreversible oxidative damage was studied in primary mixed neuronal-glial cell cultures. Cells (13-16 days in vitro) were exposed to 50 microM hydrogen peroxide (H2O2) for 30 min, and toxicity was determined by the release of lactate dehydrogenase (LDH) 24 h after exposure. The presence of recombinant human ApoE2 (100, 300, or 1000 nM) in the culture media partially protected against oxidative injury. This protection was not reversed by pre-treatment with receptor associated protein. The NMDA receptor antagonist, MK-801, also provided partial protection against H2O2 toxicity. The degree of protection was similar to that conferred by ApoE treatment. The protective effects of ApoE and MK-801 were not additive; no ApoE protection was observed in cultures treated with MK-801 prior to H2O2 exposure. ApoE treatment had no effect on H2O2 stimulated glutamate release, but did increase the rate of glutamate uptake via the high affinity glutamate transporter in H2O2 treated cultures. Pre-treatment with ApoE also conferred partial protection against glutamate-induced LDH release. Taken together, these findings suggest that ApoE protects mixed neuronal-glial cell cultures against irreversible oxidative injury from H2O2 by reducing secondary glutamate excitotoxicity.

Spatiotemporal changes of apolipoprotein E immunoreactivity and apolipoprotein E mRNA expression after transient middle cerebral artery occlusion in rat brain

Apolipoprotein E (ApoE) is a constituent of lipoprotein and plays an important role in the maintenance of neural networks. However, spatiotemporal differences in ApoE expression and its long-term role in neural process after brain ischemia have not been studied. We investigated changes of ApoE immunoreactivity and ApoE mRNA expression both in the core and in the periischemic area at 1, 7, 21, or 56 days after 90 min of transient middle cerebral artery occlusion. Double stainings for ApoE plus NeuN or plus ED1 were performed in order to identify cell type of ApoE-positive stainings. The maximal increase of ApoE expression was observed at 7 days in the core and at 7 and 21 days in the periischemic area. In the core, ApoE plus NeuN double-positive cells increased at 1 and 7 days, without ApoE mRNA expression, whereas they increased in the periischemic area, with a peak at 21 days, with ApoE mRNA expression in glial cells but not in neurons. On the other hand, ApoE plus ED1 double-positive cells increased only in the core, with a peak in number at 7 and 21 days and marked ApoE mRNA expression in macrophages. The present study suggests that ApoE plays various important roles in different type of cells, reflecting spatiotemporal dissociation between degenerative and regenerative processes after brain ischemia, and that ApoE is profoundly involved in pathological conditions, such as brain ischemia.

Neuronal apolipoprotein E is not synthesized in neuron after focal ischemia in rat brain

Apolipoprotein E (ApoE) is a major apolipoprotein in the central nervous system (CNS) that plays an important role in Alzheimer's disease. It may also be involved in other CNS disorders including ischemic injury. We investigated the changes of ApoE protein and mRNA expression in the brain with middle cerebral artery occlusion (MCAO) to clarify its origin after focal ischemia in rats. Increased ApoE immunoreactivity was recognized in astrocytes 3-14 days after MCAO in the affected side of cortex, and in neurons 4-14 days after MCAO in the same area. ApoE immunoreactivity was also detected in macrophages in the ischemic core 3-14 days after MCAO. In contrast, ApoE mRNA was expressed in astrocytes and macrophages, but not in neurons. These results suggested that neuronal ApoE was not synthesized in neurons, but derived from astrocytes.

Glial expression of the beta-amyloid peptide in cardiac arrest

We have investigated in the rat, immunocytochemically, the expression of beta-amyloid peptide in glial cells following ischemia-reperfusion brain injury. The postischemic brain injuries were studied at survival times from 2 days to 12 months. The reactive astrocytes with indirect staining for beta-amyloid peptide were observed in brain till 7 days postischemia. beta-Amyloid positive astrocytes disappeared transiently on the 14 days and then reappeared in the 6 months and again disappeared at 9 months after brain injury. Transient ischemia temporarily induced beta-amyloid peptide expression in reactive astrocytes, but this expression peaked at 7 days and 6 months. A glial appearance of beta-amyloid peptide direct staining occurred at a time when extensive neuronal loss was evident.

Suppression of apolipoprotein C-II amyloid formation by the extracellular chaperone, clusterin

The effect of the extracellular chaperone, clusterin, on amyloid fibril formation by lipid-free human apolipoprotein C-II (apoC-II) was investigated. Sub-stoichiometric levels of clusterin, derived from either plasma or semen, potently inhibit amyloid formation by apoC-II. Inhibition is dependent on apoC-II concentration, with more effective inhibition by clusterin observed at lower concentrations of apoC-II. The average sedimentation coefficient of apoC-II fibrils formed from apoC-II (0.3 mg.mL-1) is reduced by coincubation with clusterin (10 microg x mL(-1)). In contrast, addition of clusterin (0.1 mg x mL(-1)) to preformed apoC-II amyloid fibrils (0.3 mg x mL(-1)) does not affect the size distribution after 2 days. This sedimentation velocity data suggests that clusterin inhibits fibril growth but does not promote fibril dissociation. Electron micrographs indicate similar morphologies for amyloid fibrils formed in the presence or absence of clusterin. The substoichiometric nature of the inhibition suggests that clusterin interacts with transient amyloid nuclei leading to dissociation of the monomeric subunits. We propose a general role for clusterin in suppressing the growth of extracellular amyloid.

Protective effect of apolipoprotein E against ischemic neuronal injury is mediated through antioxidant action

Recent studies have demonstrated that apolipoprotein E (APOE) deficiency worsened neuronal injuries after transient focal and global cerebral ischemia. However, the molecular mechanism underlying the protective effect of APOE remains uncertain, even though several mechanisms, including excitotoxicty, free radicals, and apoptosis, have been cited as causes of selective neuronal vulnerability in cerebral ischemia. In the present study, we first compared the vulnerability of cultured neurons prepared from APOE-knockout mice upon exposure to glutamate, hydrogen peroxide, and staurosporine. No significant difference in cell viability was observed after exposure to glutamate or staurosporine between APOE-deficient and wild-type mice. However, exposure to hydrogen peroxide significantly increased the level of cell death in APOE-deficient mice compared with that in wild-type mice. After transient forebrain ischemia for 12 min, APOE-deficient mice showed more neuronal death than wild-type mice. Pretreatment of APOE-deficient mice with vitamin E for 2 months markedly reduced neuronal death caused by ischemia. The results suggest that APOE exerted its neuroprotective effect against ischemia through its antioxidant action but not through mitigation of glutamate toxicity or blocking of apoptosis.

Induction of apolipoprotein E after traumatic brain injury in forensic autopsy cases

We investigated the dynamics of the induction of apolipoprotein E (apoE) in the human brain after death caused by traumatic brain injury (TBI). A striking difference in apoE immunoreactivity in the traumatised cortical hemisphere compared with the contralateral non-traumatised hemisphere was observed. ApoE was detected within the neurons of the traumatised cortical hemisphere in cases surviving only about 2 h, as well as in those surviving for extended periods. In contrast, no apoE staining within the neurons was seen in the contralateral cortical hemisphere. ApoE staining within astrocytes was faint in both traumatised and contralateral hemispheres of cases surviving only 2 h. However, staining was intense in the traumatised hemispheres in short as well as long surviving cases, even those surviving more than 1 month. ApoE immunoreactivity was also observed in areas adjacent to capillaries and surrounding the neuropil of the injured hemisphere. These observations corroborated the idea of a prolonged induction of apoE within the neurons and also in the extracellular matrix after TBI. Furthermore, the possibility is suggested that the alteration of apoE distribution may contribute to a cerebroprotective mechanism immediately after TBI.

Delayed, but marked, expression of apolipoprotein E is involved in tissue clearance after cerebral infarction

Clearance of infarct tissue would be an important process for tissue repair after a stroke. Delayed clearance may hamper reconstitution of the blood-brain barrier and glial boundary formation. Recent growing evidence has indicated that apolipoprotein E (APOE), a major apoprotein, plays an important role in lipid transport and homeostasis in the brain. The tissue in the infarction contains abundant lipids must be removed for tissue clearance. In the current study, the authors investigated APOE expression after focal ischemia and the functional role of APOE in tissue clearance using APOE-knockout mice. Expression of APOE was delayed, but marked, in immunohistochemistry and immunoblotting 7 days after permanent focal ischemia. Macrophages were found to express APOE in the infarct center. Infarct size was similar after focal ischemia between wild-type and APOE-knockout mice, although there was no APOE protein expression in knockout mice. However, clearance of infarct tissue 2 weeks after ischemia was significantly delayed in APOE-knockout mice compared with wild-type mice. The current study supports current thinking that APOE is a key molecule for tissue remodeling in the brain. Clearance of damaged tissue may be one of the important functions of APOE in the brain.

Association of apolipoprotein E polymorphism with outcome after aneurysmal subarachnoid hemorrhage: a preliminary study

BACKGROUND AND PURPOSE

Variation in the outcome after aneurysmal subarachnoid hemorrhage (SAH) is not fully explained by known prognostic factors. APOE genotype is the most important genetic determinant of susceptibility to Alzheimer's disease, and it is also shown to be associated with the outcome after traumatic brain injury. We studied the association of apolipoprotein E polymorphism with the outcome after aneurysmal SAH.

METHODS

A total of 160 consecutive patients were admitted after SAH to a neurosurgical unit. The clinical assessment after the SAH was performed with the Hunt and Hess grading scale. The severity of the bleeding as visualized on CT was assessed by Fisher's grading system. Outcome was assessed with the Glasgow Outcome SCALE: APOE genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

126 patients had aneurysmatic SAH, and detailed information on outcome and APOE genotype was available for 108 patients (86%). Sixteen (40%) of 40 patients with APOE epsilon4 had an unfavorable outcome compared with 13 (19%) of 68 without the APOE epsilon4 allele (OR 2.8, 95% CI 1.18 to 6.77). Association was more significant after adjustment for age, rebleeding, clinical status on admission, and CT scan findings (OR 7.1, 95% CI 1.9 to 26.3; P=0.0035).

CONCLUSIONS

Our findings show a significant genetic association of APOE polymorphism with outcome after spontaneous aneurysmal SAH. Genetic factors thus seem to explain a part of individual differences in the recovery of SAH.

Involvement of apolipoprotein E in herpes simplex encephalitis

APOE polymorphism may influence risk for cold sores and, by interacting with latent HSV-1, risk for Alzheimer's disease (AD). APOE genotype also influences outcome after brain injury. We sought to determine whether APOE genotype influences risk for herpes simplex encephalitis (HSE), whether apoE is involved in the response to HSE and if APOE genotype influences outcome from HSE. There was increased immunoreactivity of neurons, neuropil and glia for apoE areas of brain damaged by HSE. APOE genotypes for cases of HSE (n = 57) were similar to those of controls (n = 41). APOE genotypes for survivors of HSE were similar to those of patients who died. We conclude that apoE is involved in the response to damage associated with HSE, as in other forms of brain injury. However, APOE genotype does not appear to influence either the risk of developing HSE or subsequent mortality.

Apolipoprotein J (clusterin) and Alzheimer's disease

Apolipoprotein J (clusterin) is a ubiquitous multifunctional glycoprotein capable of interacting with a broad spectrum of molecules. In pathological conditions, it is an amyloid associated protein, co-localizing with fibrillar deposits in systemic and localized amyloid disorders. In Alzheimer's disease, the most frequent form of amyloidosis in humans and the major cause of dementia in the elderly, apoJ is present in amyloid plaques and cerebrovascular deposits but is rarely seen in NFT-containing neurons. ApoJ expression is up-regulated in a wide variety of insults and may represent a defense response against local damage to neurons. Four different mechanisms of action could be postulated to explain the role of apoJ as a neuroprotectant during cellular stress: (1) function as an anti-apoptotic signal, (2) protection against oxidative stress, (3) inhibition of the membrane attack complex of complement proteins locally activated as a result of inflammation, and (4) binding to hydrophobic regions of partially unfolded, stressed proteins, and therefore avoiding aggregation in a chaperone-like manner. This review focuses on the association of apoJ in biological fluids with Alzheimer's soluble Abeta. This interaction prevents Abeta aggregation and fibrillization and modulates its blood-brain barrier transport at the cerebrovascular endothelium.

Sodium dodecyl sulfate-resistant complexes of Alzheimer's amyloid beta-peptide with the N-terminal, receptor binding domain of apolipoprotein E

Immunocytochemical, biochemical, and molecular genetic studies indicate that apolipoprotein E (apoE) plays an important role in the process of amyloidogenesis-beta. However, there is still no clear translation of these data into the pathogenesis of amyloidosis-beta. Previous studies demonstrated sodium dodecyl sulfate (SDS)-resistant binding of apoE to the main component of Alzheimer's amyloid-A beta and modulation of A beta aggregation by apoE in vitro. To more closely characterize apoE-A beta interactions, we have studied the binding of thrombolytic fragments of apoE3 to A beta in vitro by using SDS-polyacrylamide gel electrophoresis and intrinsic fluorescence quenching. Here we demonstrate that SDS-resistant binding of A beta is mediated by the receptor-binding, N-terminal domain of apoE3. Under native conditions, both the N- and C-terminal domains of apoE3 bind A beta; however, the former does so with higher affinity. We propose that the modulation of A beta binding to the N-terminal domain of apoE is a potential therapeutic target for the treatment of amyloidosis-beta.

Presence of apolipoprotein E immunoreactivity in degenerating neurones of mice is dependent on the severity of kainic acid-induced lesion

Apolipoprotein E (apoE) is a major apolipoprotein in the central nervous system (CNS) that may play a role in various CNS disorders. ApoE is primarily localised in astrocytes, but neuronal apoE mRNA expression has been demonstrated in normal and diseased human brain, as well as in ischaemic rat brain. To obtain further insight into the role of apoE in neuronal degeneration in the CNS and conditions of neuronal apoE localisation, we have investigated in mice the distribution of apoE following neuronal injury induced by kainic acid (n=35, 25 or 35 mg kainic acid/kg BW). Consecutive series of brain sections were immunostained for apoE and markers for astroglia (GFAP) and microglia/macrophage cells (CR3). Degenerating neurones were identified with a silver-degeneration staining technique. The intensity and cellular distribution of apoE-immunoreactivity (apoE-ir) was dependent on the severity of neuronal injury. Mice that developed mild neuronal degeneration, restricted to a subset of neurones in the hippocampus, showed increased apoE-ir in astrocytes concomitant with increased GFAP-ir and mild microgliosis. In these mice, no neuronal apoE-ir was detected. In contrast, mice developing severe neuronal injury in the hippocampus - frequently also showing degeneration in other brain regions including cortex, thalamus, striatum and amygdala - showed intense apoE-ir in degenerating neurones. Surrounding the lesion, apoE-ir was increased in neuropil recurrently whereas GFAP-ir astrocytes disappeared. Thus, in mice apoE accumulates in degenerating neurones in conditions of severe neuronal injury putatively in association with disruption of the glial network.

The role of apolipoprotein E in Alzheimer's disease, acute brain injury and cerebrovascular disease: evidence of common mechanisms and utility of animal models

The epsilon 4 allele of apolipoprotein E (APOE denotes gene; apoE denotes protein) is a major risk factor for Alzheimer's disease (AD). More recent evidence indicates an association with a poor outcome after acute brain injury including that due to head trauma and intracerebral hemorrhage. APOE gene polymorphism also influences the risk of hemorrhage in cerebral amyloid angiopathy. These diverse brain disorders seem to have some mechanisms in common. The multiplicity of the roles of apoE within the central nervous system is currently being unraveled. For example, apoE can interact with amyloid beta-protein and tau, proteins central to the pathogenesis of AD. In addition to these effects, it is proposed that one of the major functions of apoE is to mediate neuronal protection, repair and remodeling. In all of the different roles proposed, there are marked apoE-isoform specific differences. Although it remains to be clarified which is the most important mechanism(s) in each disorder in which apoE is involved, these isoform specific differences seem to underly a genetically determined susceptibility to outcome from acute brain injury and to AD with APOE epsilon 4 conferring relative vulnerability. This review focuses on apoE research, from clinical studies to animal models, in AD, acute brain injury and cerebrovascular disease and explores the common mechanisms that may explain some of the complex underlying neurobiology.

Apolipoprotein E expression by neurons surviving excitotoxic stress

In the adult brain, apolipoprotein E (apoE) mRNA is thought to be expressed by nonneuronal cells. Yet, when a brain damage has occurred, the protein is found in neurons. We have studied apoE expression following systemic kainic acid (KA), injected in rats to induce hippocampal neurodegeneration. We describe two effects. First, a moderate increase of apoE levels in astrocytes. Second, and unexpected, a very strong increase of apoE mRNA levels in clusters of CA1 and CA3 pyramidal neurons. Neuronal identity of these cells is supported by a series of observations. First, apoE hybridization signals were found in cells with morphological characteristics of pyramidal neurons. Second, the cells were positive for the neuronal marker MAP2. Third, the cells were negative for the astrocytic marker GFAP and for the microglia marker OX42. Fourth, the same distribution pattern was found with probes hybridizing to c-fos, a transcription factor transiently expressed in neurons under stress. At 48 and 72 h following KA, most of the excitotoxic cell death had already occurred. Since no morphological signs of programmed cell death were observed in apoE-positive pyramidal neurons, we suggest that expression of apoE by neurons may be part of a rescue program to counteract neurodegeneration.

Role of neuronal and endothelial nitric oxide synthase in nitric oxide generation in the brain following cerebral ischemia

Nitric oxide (NO) plays an important role in the pathogenesis of neuronal injury during cerebral ischemia. The endothelial and neuronal isoforms of nitric oxide synthase (eNOS, nNOS) generate NO, but NO generation from these two isoforms can have opposing roles in the process of ischemic injury. While increased NO production from nNOS in neurons can cause neuronal injury, endothelial NO production from eNOS can decrease ischemic injury by inducing vasodilation. However, the relative magnitude and time course of NO generation from each isoform during cerebral ischemia has not been previously determined. Therefore, electron paramagnetic resonance spectroscopy was applied to directly detect NO in the brain of mice in the basal state and following global cerebral ischemia induced by cardiac arrest. The relative amount of NO derived from eNOS and nNOS was accessed using transgenic eNOS(-/-) or nNOS(-/-) mice and matched wild-type control mice. NO was trapped using Fe(II)-diethyldithiocarbamate. In wild-type mice, only small NO signals were seen prior to ischemia, but after 10 to 20 min of ischemia the signals increased more than 4-fold. This NO generation was inhibited more than 70% by NOS inhibition. In either nNOS(-/-) or eNOS(-/-) mice before ischemia, NO generation was decreased about 50% compared to that in wild-type mice. Following the onset of ischemia a rapid increase in NO occurred in nNOS(-/-) mice peaking after only 10 min. The production of NO in the eNOS(-/-) mice paralleled that in the wild type with a progressive increase over 20 min, suggesting progressive accumulation of NO from nNOS following the onset of ischemia. NOS activity measurements demonstrated that eNOS(-/-) and nNOS(-/-) brains had 90% and < 10%, respectively, of the activity measured in wild type. Thus, while eNOS contributes only a fraction of total brain NOS activity, during the early minutes of cerebral ischemia prominent NO generation from this isoform occurs, confirming its importance in modulating the process of ischemic injury.

Expression of human apolipoprotein E3 or E4 in the brains of Apoe-/- mice: isoform-specific effects on neurodegeneration

Apolipoprotein (apo) E isoforms are key determinants of susceptibility to Alzheimer's disease. The apoE4 isoform is the major known genetic risk factor for this disease and is also associated with poor outcome after acute head trauma or stroke. To test the hypothesis that apoE3, but not apoE4, protects against age-related and excitotoxin-induced neurodegeneration, we analyzed apoE knockout (Apoe-/-) mice expressing similar levels of human apoE3 or apoE4 in the brain under control of the neuron-specific enolase promoter. Neuronal apoE expression was widespread in the brains of these mice. Kainic acid-challenged wild-type or Apoe-/- mice had a significant loss of synaptophysin-positive presynaptic terminals and microtubule-associated protein 2-positive neuronal dendrites in the neocortex and hippocampus, and a disruption of neurofilament-positive axons in the hippocampus. Expression of apoE3, but not of apoE4, protected against this excitotoxin-induced neuronal damage. ApoE3, but not apoE4, also protected against the age-dependent neurodegeneration seen in Apoe-/- mice. These differences in the effects of apoE isoforms on neuronal integrity may relate to the increased risk of Alzheimer's disease and to the poor outcome after head trauma and stroke associated with apoE4 in humans.

Oxidized low-density lipoprotein induces neuronal death: implications for calcium, reactive oxygen species, and caspases

Low-density lipoprotein (LDL) exists within the brain and is highly vulnerable to oxidative modifications. Once formed, oxidized LDL (oxLDL) is capable of eliciting cytotoxicity, differentiation, and inflammation in nonneuronal cells. Although oxLDL has been studied primarily for its role in the development of atherosclerosis, recent studies have identified a possible role for it in neurological disorders associated with oxidative stress. In the present study application of oxLDL, but not LDL, resulted in a dose- and time-dependent death of cultured rat embryonic neurons. Studies using pharmacological inhibitors implicate the involvement of calcium, reactive oxygen species, and caspases in oxLDL-induced neuronal death. Coapplication of oxLDL with either amyloid beta-peptide or glutamate, agents that enhance oxidative stress, resulted in increased neuronal death. Taken together, these data demonstrate that oxLDL induces neuronal death and implicate a possible role for oxLDL in conditions associated with increased levels of reactive oxygen species, including Alzheimer's disease.

Hippocampal alterations of apolipoprotein E and D mRNA levels in vivo and in vitro following kainate excitotoxicity

Alteration in the expression of apolipoprotein E (ApoE) and apolipoprotein D (ApoD) genes was evaluated in rat, 7 days following status epilepticus (SE) induced by intra-amygdala injection of kainate (KA), and in organotypic hippocampal cultures, 2 days after a single 1 h exposure to KA. Global polyadenylated RNA (poly A+) steady state, assessing global regulation of mRNA transcription was first measured in cortices and hippocampi from each animal and in the organotypic cultures. No alteration due to KA treatment was observed and individual concentrations of ApoE and ApoD mRNA species were therefore measured and comparative analysis performed. In the cortices of KA-treated animals, ApoE and ApoD mRNA levels did not show statistically significant changes. In contrast, in hippocampi, 7 days after SE, ApoE and ApoD mRNA levels were significantly increased, respectively, by 123 and 138%. This in vivo effect was confirmed in vitro on organotypic cultures, where KA treatment increased ApoE and ApoD mRNA expressions, respectively, by 72 and 61%. These observations indicate that lipidic metabolism is modified in the lesioned structure and suggest an increased traffic of lipids and a need for more ApoE and D in the hippocampus during the period of recovery and restructuration that follows severe seizures.

Apolipoprotein E deficiency worsens outcome from global cerebral ischemia in the mouse

BACKGROUND AND PURPOSE

Apolipoprotein E (apoE) has been found relevant in a variety of central nervous system disorders. This experiment examined the effect of endogenous murine apoE on selective neuronal necrosis resulting from a transient forebrain ischemia insult.

METHODS

ApoE deficient (n=16) and wild type (n=17) halothane-anesthetized mice were subjected to severe forebrain ischemia (10 minutes of bilateral carotid occlusion and systemic hypotension). After 3 days' recovery, brain injury was determined histologically. In other apoE-deficient and wild-type mice, regional cerebral blood flow (CBF) was determined by 14C-iodoantipyrine autoradiography 10 minutes before, 5 minutes after onset of, and 30 minutes after reperfusion from 10 minutes of forebrain ischemia.

RESULTS

The percentage of dead hippocampal CA1 neurons (mean+/-SD) was greater in the apoE-deficient group (apoE deficient=67+/-30%; wild type=37+/-33%; P=0.011). A similar pattern was observed in the caudoputamen (P=0.002) and neocortex (P=0.014). Cerebral blood flow was similar between groups at each measurement interval. Marked hypoperfusion persisted in both groups at 30 minutes after ischemia.

CONCLUSIONS

ApoE deficiency worsens ischemic outcome. This is not attributable to effects on CBF. A role of apoE in the cerebral response to global ischemia is consistent with prior reports that murine apoE deficiency increases infarct size resulting from focal cerebral ischemia.

Specific regional transcription of apolipoprotein E in human brain neurons

In central nervous system injury and disease, apolipoprotein E (APOE, gene; apoE, protein) might be involved in neuronal injury and death indirectly through extracellular effects and/or more directly through intracellular effects on neuronal metabolism. Although intracellular effects could clearly be mediated by neuronal uptake of extracellular apoE, recent experiments in injury models in normal rodents and in mice transgenic for the human APOE gene suggest the additional possibility of intraneuronal synthesis. To examine whether APOE might be synthesized by human neurons, we performed in situ hybridization on paraffin-embedded and frozen brain sections from three nondemented controls and five Alzheimer's disease (AD) patients using digoxigenin-labeled antisense and sense cRNA probes to human APOE. Using the antisense APOE probes, we found the expected strong hybridization signal in glial cells as well as a generally fainter signal in selected neurons in cerebral cortex and hippocampus. In hippocampus, many APOE mRNA-containing neurons were observed in sectors CA1 to CA4 and the granule cell layer of the dentate gyrus. In these regions, APOE mRNA containing neurons could be observed adjacent to nonhybridizing neurons of the same cell class. APOE mRNA transcription in neurons is regionally specific. In cerebellar cortex, APOE mRNA was seen only in Bergmann glial cells and scattered astrocytes but not in Purkinje cells or granule cell neurons. ApoE immunocytochemical localization in semi-adjacent sections supported the selectivity of APOE transcription. These results demonstrate the expected result that APOE mRNA is transcribed and expressed in glial cells in human brain. The important new finding is that APOE mRNA is also transcribed and expressed in many neurons in frontal cortex and human hippocampus but not in neurons of cerebellar cortex from the same brains. This regionally specific human APOE gene expression suggests that synthesis of apoE might play a role in regional vulnerability of neurons in AD. These results also provide a direct anatomical context for hypotheses proposing a role for apoE isoforms on neuronal cytoskeletal stability and metabolism.

Is there a genetic basis for the deposition of beta-amyloid after fatal head injury?

1. Alzheimer's disease is a heterogeneous disorder that may be caused by genetic or environmental factors or by a combination of both. Abnormalities in chromosomes 1, 14, and 21 have all been implicated in the pathogenesis of the early-onset form of the disease, while the epsilon 4 allele of the apolipoprotein E gene (on chromosome 19) is now recognized as a risk factor for early- and late-onset sporadic and familial Alzheimer's disease. 2. The best-established environmental trigger for the disease is a head injury, based on epidemiological and neuropathological evidence. Approximately 30% of patients who die after a single episode of severe head injury show intracerebral deposition of beta-amyloid protein (A beta), a protein that is thought to be central to the pathogenesis of Alzheimer's disease. 3. Recent studies have revealed an over-representation of the apoE epsilon 4 allele in those head-injured patients displaying A beta pathology, thus providing the first evidence for a link between a genetic susceptibility (apoE epsilon 4) and an environmental trigger (head injury) in the development of Alzheimer-type pathology.

Clusterin (apolipoprotein J) protein levels are increased in hippocampus and in frontal cortex in Alzheimer's disease

We studied the multifunctional protein clusterin (apolipoprotein J, SGP-2, SP-40,40) in brain tissue using quantitative Western blotting and immunohistochemistry. The material included postmortem brains from 19 patients with Alzheimer's disease (AD), 6 with vascular dementia (VAD), and 7 age-matched control subjects. Intense clusterin staining was found in the soma of both neuronal and astroglial cells. In addition, positive staining was found in a portion of senile plaques (SP) in AD brains. Quantitative analysis showed that clusterin levels were significantly increased in AD, both in frontal cortex (150% of the control value, P = 0.002) and in the hippocampus (179% of the control value, P < 0.001), while normal clusterin levels were found in cerebellum (104% of the control value). No significant changes were found in VAD. Within the AD group, there was a significant negative correlation between clusterin levels in hippocampus and severity of dementia (r = -0.40), while no such correlation was found in frontal cortex (r = 0.12). No significant correlations were found between clusterin levels and the number of SP or neurofibrillary tangles. No significant differences in clusterin levels were found in any brain region between AD patients possessing different numbers of the ApoE4 allele. The increased clusterin levels in AD brain, together with the absence of a correlation between SP counts and clusterin levels, and the finding that clusterin is only found in a smaller portion of SP do not suggest a link between clusterin and beta-amyloid dependence. Instead we hypothesize that the increase is part of a regional response in AD brain.

Changes in oxidative stress in the rat brain during post-cardiac arrest reperfusion, and the effect of treatment with the free radical scavenger idebenone

The study was designed to determine the effect of idebenone, an electron-trapping agent and free radical scavenger capable of crossing the blood-brain barrier, on cardiac arrest-induced oxidative brain stress. Stress indices used were the brain contents of thiobarbituric acid-reactive material (TBAR), conjugated dienes and protein and non-protein thiols. Twenty-four hours after receiving one oral dose of placebo or 100 mg kg(-1) idebenone, the rats were anaesthetized with diethyl ether and either decapitated immediately, or subjected to 7.5 min cardiac arrest induced by compression of the heart vessel bundle. The next groups of rats were sacrificed at the end of the cardiac arrest session, or resuscitated by external chest compression and artificial ventilation with air and sacrificed 15 min, 60 min, 24 h, and 72 h later while re-anesthetized with diethyl ether. Subsequent placebo or idebenone (100 mg kg(-1)) doses were given to the appropriate surviving rats once daily, beginning 8-10 min after the end of cardiac arrest session. Compared to pre-arrest values, TBAR and conjugated dienes' contents increased, respectively, by 339 and 286%, and protein and non-protein thiol contents decreased, respectively, by 69 and 85% within 60 min after the resuscitation in placebo-treated rats. Normalization of all oxidative stress indices in these rats was slow and incomplete even at 72 h. Idebenone treated rats showed no increase in TBAR contents, and a marked attenuation of changes in the other indices. These results show that oral idebenone greatly reduces oxidative brain stress following transient circulatory arrest in the rat. This effect could not be explained by simple stoichiometric scavenging of free radicals. Possible mechanisms of idebenone action are discussed.

Isoform-specific effects of human apolipoprotein E on brain function revealed in ApoE knockout mice: increased susceptibility of females

Apolipoprotein E (apoE) mediates the redistribution of lipids among cells and is expressed at highest levels in brain and liver. Human apoE exists in three major isoforms encoded by distinct alleles (epsilon2, epsilon3, and epsilon4). Compared with APOE epsilon2 and epsilon3, APOE epsilon4 increases the risk of cognitive impairments, lowers the age of onset of Alzheimer's disease (AD), and decreases the response to AD treatments. Besides age, inheritance of the APOE epsilon4 allele is the most important known risk factor for the development of sporadic AD, the most common form of this illness. Although numerous hypotheses have been advanced, it remains unclear how APOE epsilon4 might affect cognition and increase AD risk. To assess the effects of distinct human apoE isoforms on the brain, we have used the neuron-specific enolase (NSE) promoter to express human apoE3 or apoE4 at similar levels in neurons of transgenic mice lacking endogenous mouse apoE. Compared with NSE-apoE3 mice and wild-type controls, NSE-apoE4 mice showed impairments in learning a water maze task and in vertical exploratory behavior that increased with age and were seen primarily in females. These findings demonstrate that human apoE isoforms have differential effects on brain function in vivo and that the susceptibility to apoE4-induced deficits is critically influenced by age and gender. These results could be pertinent to cognitive impairments observed in human APOE epsilon4 carriers. NSE-apoE mice and similar models may facilitate the preclinical assessment of treatments for apoE-related cognitive deficits.

Apolipoprotein E genotype, atherosclerosis, and cognitive decline: the Rotterdam Study

The apolipoprotein E4 allele (APOE epsilon 4) and atherosclerosis are risk factors for cognitive decline. We investigated whether the effects of APOE epsilon 4 and atherosclerosis on cognitive decline are independent. A population-based follow-up study was performed on 838 subjects who were non-demented at baseline. The Mini Mental State Examination (MMSE) score at follow-up was studied as a function of APOE epsilon 4 and atherosclerosis. Mild, non-significant effects on the MMSE score were found for atherosclerosis in the absence of APOE epsilon 4 and for APOE epsilon 4 in the absence of atherosclerosis. APOE epsilon 4 carriers with two or more indicators of atherosclerosis positive, had a significantly lower MMSE score at follow-up (mean difference -0.7 points; 95% confidence interval -1.1 to -0.2) relative to non-APOE epsilon 4 carriers with no evidence of atherosclerosis. Our findings suggest that the consequences of APOE epsilon 4 and atherosclerosis are not independent, and that particularly APOE epsilon 4 carriers with atherosclerosis are at increased risk of cognitive decline.

Behavioural, physiological and morphological analysis of a line of apolipoprotein E knockout mouse

Using apolipoprotein E knockout mice derived from the Maeda source [Piedrahita J. A. et al. (1992) Proc. natn. Acad Sci. US.A. 89, 4471 4475], we have studied the influence of apolipoprotein E gene deletion on normal CNS function by neurological tests and water maze learning, hippocampal ultrastructure assessed by quantitative immunocytochemistry and electron microscopy, CNS plasticity, i.e. hippocampal long-term potentiation and amygdaloid kindling, and CNS repair, i.e. synaptic recovery in the hippocampus following deafferentation. In each study there was little difference between the apolipoprotein E knockout mice and wild-type controls of similar age and genetic background. Apolipoprotein E knockout mice aged eight months demonstrated accurate spatial learning and normal neurological function. Synaptophysin and microtubule-associated protein 2 immunohistochemistry and electron microscopic analysis of these animals revealed that the hippocampal synaptic and dendritic densities were similar between genotypes. The induction and maintenance of kindled seizures and hippocampal long-term potentiation were indistinguishable between groups. Finally, unilateral entorhinal cortex lesions produced a marked loss of hippocampal synaptophysin immunoreactivity in both groups and a marked up-regulation of apolipoprotein E in the wild-type group. Both apolipoprotein E knockout and wild-type groups showed immunohistochemical evidence of reactive synaptogenesis, although the apolipoprotein E knockout group may have initially shown greater synaptic loss. It is suggested that either apolipoprotein E is of no importance in the maintenance of synaptic integrity and in processes of CNS plasticity and repair, or more likely, alternative (apolipo)proteins may compensate for the loss of apolipoprotein E in the knockout animals.

Apolipoprotein E and the CNS response to injury

Apolipoprotein E (apoE) is a multifunctional protein with an expanding role in the neurobiology of disease. Although originally described in the context of cholesterol metabolism, interest in the neurobiology of apoE has intensified following the association between apoE genotype and risk of developing Alzheimer's disease. Recent clinical observations also suggest that apoE genotype may influence recovery after a variety of neurological insults. Thus, in addition to the study of disease-specific mechanisms by which apoE may modulate susceptibility of developing Alzheimer's disease, there has been an increasing focus on its role in modulating the CNS response to acute injury. Although the neurobiology of apoE in the injured brain remains incompletely defined, there is evidence to suggest neurotrophic, immunomodulatory, and antioxidant effects.

Apolipoprotein E isoform-specific differences in outcome from focal ischemia in transgenic mice

Apolipoprotein E (apoE), a 34-KD glycosylated lipid-binding protein, is expressed as three common isoforms in humans (E2, E3, or E4). Clinical evidence suggests that the apoE genotype (APOE) may be a risk factor for poor outcome after acute central nervous system injury. This was examined further in transgenic mice constructed with the human APOE3 or APOE4 gene under the control of human promoter and tissue expression elements. Presence of human apoE3 and apoE4 proteins in brains of human APOE homozygous transgenic mice was confirmed by Western blotting. APOE3 (n = 12) and APOE4 (n = 10) mice underwent 60 minutes of middle cerebral artery occlusion. After 24-hour recovery, infarct size was measured. Infarct volumes (mean +/- standard deviation) were smaller in the APOE3 group (cortex: APOE3 = 18 +/- 4 mm3; APOE4 = 30 +/- 11 mm3, P = 0.04; subcortex: APOE3 = 12 +/- 4 mm3; APOE4 = 18 +/- 4 mm3, P = 0.003). Hemiparesis was less severe in APOE3 mice (P = 0.02). These data indicate that human isoform-specific effects of apoE are relevant to acute pathomechanisms of focal ischemic brain damage when examined in the mouse. APOE transgenic mice may provide an appropriate model to examine the mechanistic basis for the differential effects of human apoE isoforms in acute central nervous system injury.

Deleterious actions of chronic ethanol treatment on the glycosylation of rat brain clusterin

Clusterin is a N-glycosylated sialoglycoprotein present in rat brain cells. Clusterin, which elicits aggregation in a wide variety of cells, has been suggested to play an important role in synaptic remodeling through its cell adhesion property or lipid transport capacity in the brain. Sialic acid residues in clusterin may be responsible for its structural conformation, stability and functional ability. Maturation of clusterin is governed by the relative actions of sialyltransferases and sialidases that are present in brain microsomes, golgi bodies, cytosol and plasma membranes. We have earlier reported that chronic ethanol treatment in rats has a damaging effect on the hepatic glycosylation machinery. Others have reported increased hydrolysis of brain sialoconjugates in rats following chronic ethanol administration. Specificity of the effects of chronic ethanol treatment in the brain in relation to the glycosylation process, is still obscure. Therefore, in this investigation, we have studied the specific effects of chronic ethanol treatment on the glycosylation of rat brain clusterin and the causes that may lead to any possible defects in the glycosylation process. We have determined the effects of chronic ethanol treatment on (i) the incorporation of labeled leucine and N-acetylmannosamine into immunoprecipitable clusterin in whole brain homogenate, microsomes, golgi, cytosol, plasma membrane and synaptosomes, (ii) enzymatic activities of sialyltransferases in golgi and synaptosomes, and sialidase in brain cytosol and plasma membranes, and (iii) de novo synthetic rate of rat brain cytosolic sialidase. Our results showed that chronic ethanol treatment in rats resulted in (1) a decreased sialation index of brain clusterin by 47. 2% (p<0.001), 56.7% (p<0.05), 51.7% (p<0.05), 64.8% (p<0.001), and 54.5% (p<0.05), respectively, in whole brain homogenate, golgi, cytosol, plasma membranes, and synaptosomes; (2) a 46.1% (p<0.05) and 12.5% (p<0.05) decreased activities of brain sialyltransferases, respectively, in the golgi and the synaptosomal fractions; (3) a 70. 1% (p<0.05) and 42.6% (p<0.05) increased activities of sialidases, respectively, in the cytosol and plasma membrane fractions; and (4) a 22.2%-64.3% (p<0.001) increased incorporation of labeled leucine into brain cytosolic sialidase. Our findings have clearly established that long-term ethanol treatment in rats leads to a marked impairment in the glycosylation of rat brain clusterin as a result of altered activities of brain sialation and desialation enzymes. In particular, the specific increase noted in brain sialidase activity was due to concomitant increases in its synthetic rate. These defects in the glycosylation of brain clusterin may lead to changes in the molecular conformation of clusterin, and thus, may result in its structural instability and/or functional impairment.

Stress-induced transcription of the clusterin/apoJ gene

Clusterin/apoJ is an intriguing gene frequently isolated by differential screening in laboratories from different areas of molecular biology, since it is overexpressed in numerous cases of degenerative diseases such as Alzheimer's disease and scrapie. While the dramatic increase of clusterin expression in injured tissues is well established, the molecular basis of the gene induction remains unclear. In this study, we have focused our attention on the only DNA region strictly conserved between clusterin gene proximal promoters from different vertebrate classes. We show that this 14-bp DNA element is specifically recognized by the HSF1 transcription factor and can mediate heat-shock-induced transcription in transient expression assays. Conversely, the avian clusterin proximal promoter, point-mutated at the level of this element, no longer transmits heat-shock activation. These findings provide a possible explanation for the high sensitivity of clusterin expression to environmental changes and allow the classification of clusterin as an extracellular version of heat-shock protein.

Association of apolipoprotein E polymorphism with outcome after head injury

BACKGROUND

Variation in outcome after head injury is not fully explained by known prognostic features. Polymorphism of the apolipoprotein E gene (APOE) influences neuropathological findings in patients who die from head injuries. More people who die from head injuries than non-head-injured controls have deposits of amyloid beta-protein in the cerebral cortex, with amyloid beta-protein deposits present predominantly in patients with the APOE epsilon4 allele. We report a prospective clinical study to test the hypothesis that patients with APOE epsilon4 have a worse clinical outcome 6 months after head injury than those without APOE epsilon4.

METHODS

We studied a prospectively recruited series of patients admitted after a head injury to a neurosurgical unit (n=93). Assessment of severity of the initial injury was by means of the Glasgow Coma Score (GCS). Outcome 6 months after injury was assessed by means of the Glasgow Outcome Scale. APOE genotypes were determined from blood samples by standard methods.

FINDINGS

Detailed information on outcome was available for 89 patients. 17 (57%) of 30 patients with APOE epsilon4 had an unfavourable outcome (dead, vegetative state, or severe disability) compared with 16 (27%) of the 59 patients without APOE epsilon4 (p=0.006). The association remained significant when adjustment was made to control for age, GCS, and computed tomography scan findings (p=0.024).

INTERPRETATION

Our findings show a significant genetic association of APOE polymorphism with outcome after head injury supporting the hypothesis of a genetically determined influence. Patients with APOE epsilon4 are more than twice as likely as those without APOE epsilon4 to have an unfavourable outcome 6 months after head injury. Further studies are under way to confirm and further evaluate this association.

Changes in amyloid precursor protein and apolipoprotein E immunoreactivity following ischemic brain injury in rat with long-term survival: influence of idebenone treatment

We observed in extra- and intracellular space accumulation of different fragments of amyloid precursor protein (APP) and apolipoprotein E (Apo E) in rat brain after cardiac arrest with long-term survival. Idebenone treatment did not affect APP and Apo E alterations in this condition.