Motor and cognitive deficits in apolipoprotein E-deficient mice after closed head injury

Does apolipoprotein E genotype modify the clinical expression of ALS?

BACKGROUND

The presence of the apolipoprotein E (ApoE) 4 genotype is associated with an earlier age of onset for Alzheimer's disease (AD) and several other neurodegenerative disorders. The objective of this study was to investigate the effect of ApoE genotypes on the clinical course of amyotrophic lateral sclerosis (ALS).

METHODS

Eight hundred and fifty-two consecutive patients with sporadic ALS evaluated at a tertiary care center were investigated for the effect of ApoE genotype on age of onset, rate of motor disease progression, cognitive functioning, and survival in ALS.

RESULTS

The frequencies of individual ApoE genotypes did not differ between patients with ALS and ALS-free Caucasian populations. Patients with different ApoE genotypes did not differ in the age of onset for ALS (years) (ApoE2 = 57.8 ± 13.7, ApoE3 = 57.3 ± 13.7, ApoE4 = 57.7 ± 13.2; P = 0.97), the rate of disease progression (Appel ALS score/month) (ApoE2 = 2.91 ± 2.66, ApoE3 = 2.67 ± 2.66, ApoE4 = 2.61 ± 2.47; P = 0.89), cognitive status (% cognitively impaired) (ApoE2 = 31.7, ApoE3 = 26.8, ApoE4 = 34.3, P = 0.28), or survival in years (ApoE2 = 3.79 ± 3.70, ApoE3 = 3.17 ± 2.27, ApoE4 = 3.05 ± 1.75; P = 0.85).

CONCLUSIONS

Our results suggest that ApoE genotype does not modify clinical course of sporadic ALS, in stark contrast to the influence of ApoE genotype on the disease course of AD and other neurodegenerative disorders.

Apolipoproteins in the brain: implications for neurological and psychiatric disorders

The brain is the most lipid-rich organ in the body and, owing to the impermeable nature of the blood-brain barrier, lipid and lipoprotein metabolism within this organ is distinct from the rest of the body. Apolipoproteins play a well-established role in the transport and metabolism of lipids within the CNS; however, evidence is emerging that they also fulfill a number of functions that extend beyond lipid transport and are critical for healthy brain function. The importance of apolipoproteins in brain physiology is highlighted by genetic studies, where apolipoprotein gene polymorphisms have been identified as risk factors for several neurological diseases. Furthermore, the expression of brain apolipoproteins is significantly altered in several brain disorders. The purpose of this article is to provide an up-to-date assessment of the major apolipoproteins found in the brain (ApoE, ApoJ, ApoD and ApoA-I), covering their proposed roles and the factors influencing their level of expression. Particular emphasis is placed on associations with neurological and psychiatric disorders.

Abeta-independent roles of apolipoprotein E4 in the pathogenesis of Alzheimer's disease

Human apolipoprotein (APO) E has three common isoforms that differentially affect lipid and neuronal homeostasis. APOE4, the major known genetic risk factor for Alzheimer's disease (AD), increases the occurrence and lowers the age of onset of AD. APOE4 carriers account for 65-80% of all AD cases, highlighting the importance of APOE4 in AD pathogenesis. Emerging data suggest that APOE4 contributes to AD through various pathways, some of which are dependent on amyloid-beta (Abeta). Although these Abeta-dependent roles of APOE4 have been widely studied, APOE4 has detrimental effects on neurons independent of Abeta: aberrant proteolysis of APOE4 generates neurotoxic fragments, stimulates Tau phosphorylation, which disrupts the cytoskeleton, and impairs mitochondrial function.

Diffuse axonal injury induced by simultaneous moderate linear and angular head accelerations in rats

Diffuse axonal injury (DAI) is one of the most common and important pathologic features of human traumatic brain injury (TBI), accounting for high mortality and development of persistent post-traumatic neurologic sequelae. Although a relatively high number of therapies have been shown to be effective in experimental models, there are currently few treatments that are effective for improving the prognosis of clinical DAI. A major reason is the failure of current models to validly reproduce the pathophysiological characteristics observed after clinical DAI. In the present study, we employed a specially designed, highly controllable model to induce a sudden rotation in the coronal plane (75 degrees rotation at 1.6x10(4) degrees/s) combined with lateral translation (1.57 cm displacement at 3.4x10(2) cm/s) to the rat's head. We were interested in discovering whether the combined accelerations could reproduce the pathophysiological changes analogous to those seen in human DAI. The axonal injury as assessed with amyloid protein precursor (APP) as a marker was consistently present in all injured rats. The commonly injured brain regions included the subcortical regions, deep white matter, corpus callosum and brain stem. The evolution of APP accumulations in brain sections depicted the detailed progression of axonal pathology. Ultrastructural studies gave further insights into the presence and progression of axonal injury. All injured rats exhibited transient physiological dysfunction, as well as immediate and dramatic neurological impairment that still persisted at 14 days after injury. These results suggest that this model reproduced the major pathophysiological changes analogous to those observed after severe clinical TBI and provides an attractive vehicle for experimental brain injury research.

The apolipoprotein E ε4 allele and outcome in severe traumatic brain injury treated by an intracranial pressure–targeted therapy

Object

In this paper, the authors' goal was to study the influence of the apolipoprotein E ε4 allele on the clinical outcome in patients treated for severe traumatic brain injury (TBI) with an intracranial pressure (ICP)–targeted therapy based on the Lund concept.

Methods

The authors conducted a prospective double-blinded randomized trial in which they examined patients with severe TBI. Inclusion criteria consisted of a Glasgow Coma Scale (GCS) score ≤ 8 at the time of intubation and sedation, patient age between 15 and 70 years, an initial cerebral perfusion pressure > 10 mm Hg, and arrival to the hospital < 24 hours after trauma. Blood samples for the analysis of apolipoprotein E allele types were collected. Independent staff members evaluated outcomes by obtaining Glasgow Outcome Scale (GOS) scores at 3, 12, and 24 months.

Results

The occurrence of the ε4 allele was analyzed in 46 patients (mean age 35 ± 2.2 years with a median GCS score of 6 [range 3–8]). The ε4 allele was present in 39.1% of the patients. The ICP, cerebral perfusion pressure, and injury severity score were not statistically significantly different between the groups. The median GOS score at 3 months was 3.5, and at 12 and 24 months was 4 (range 1–5). Except for the GOS score at 3 months, which was dichotomized as favorable (GOS Score 4 or 5) and unfavorable (GOS Scores 1–3), no statistically significant differences in outcome, irrespective of GOS dichotomization used, were found between the patients with the ε4 allele and those without. The presence of the ε4 allele did not predict for clinical outcome, but GCS and ICP did.

Conclusions

The presence of ε4 is not associated with long-term clinical outcome in patients with severe TBI treated with an ICP targeted therapy, based on the Lund concept.

Impact of apolipoprotein E (ApoE) polymorphism on brain ApoE levels

Inheritance of the apoE4 allele (epsilon4) increases the risk of developing Alzheimer's disease; however, the mechanisms underlying this association remain elusive. Recent data suggest that inheritance of epsilon4 may lead to reduced apoE protein levels in the CNS. We therefore examined apoE protein levels in the brains, CSF and plasma of epsilon2/2, epsilon3/3, and epsilon4/4 targeted replacement mice. These apoE mice showed a genotype-dependent decrease in apoE levels; epsilon2/2 >epsilon3/3 >epsilon4/4. Next, we sought to examine the relative contributions of apoE4 and apoE3 in the epsilon3/4 mouse brains. ApoE4 represented 30-40% of the total apoE. Moreover, the absolute amount of apoE3 per allele was similar between epsilon3/3 and epsilon3/4 mice, implying that the reduced levels of total apoE in epsilon3/4 mice can be explained by the reduction in apoE4 levels. In culture medium from epsilon3/4 human astrocytoma or epsilon3/3, epsilon4/4 and epsilon3/4 primary astrocytes, apoE4 levels were consistently lower than apoE3. Secreted cholesterol levels were also lower from epsilon4/4 astrocytes. Pulse-chase experiments showed an enhanced degradation and reduced half-life of newly synthesized apoE4 compared with apoE3. Together, these data suggest that astrocytes preferentially degrade apoE4, leading to reduced apoE4 secretion and ultimately to reduced brain apoE levels. Moreover, the genotype-dependent decrease in CNS apoE levels, mirror the relative risk of developing AD, and suggest that low levels of total apoE exhibited by epsilon4 carriers may directly contribute to the disease progression, perhaps by reducing the capacity of apoE to promote synaptic repair and/or Abeta clearance.

Clinical patterns and biological correlates of cognitive dysfunction associated with cancer therapy

Standard oncological therapies, such as chemotherapy and cranial radiotherapy, frequently result in a spectrum of neurocognitive deficits that includes impaired learning, memory, attention, and speed of information processing. In addition to classical mechanisms of neurotoxicity associated with chemo- and radiotherapy, such as radiation necrosis and leukoencephalopathy, damage to dynamic progenitor cell populations in the brain is emerging as an important etiologic factor. Radiation- and chemotherapy-induced damage to progenitor populations responsible for maintenance of white matter integrity and adult hippocampal neurogenesis is now believed to play a major role in the neurocognitive impairment many cancer survivors experience.

Does the apolipoprotein epsilon 4 allele predispose varsity athletes to concussion? A prospective cohort study

OBJECTIVE

To determine the association between the apolipoprotein epsilon 4 allele and concussion. We hypothesized that apolipoprotein epsilon 4 carriers may be more likely to sustain a concussion.

DESIGN

Prospective cohort study.

SETTING

University of Toronto varsity athletics.

PARTICIPANTS

Included 318 of 822 collegiate student athletes who participated in University of Toronto varsity sports from September 2002 to April 2006.

ASSESSMENT OF RISK FACTORS

The presence of apolipoprotein epsilon 4 was described dichotomously after genotyping blood samples collected from participants.

MAIN OUTCOME MEASUREMENTS

Concussions were identified by sport-medicine professionals present on the sidelines using on-field assessment forms. All concussion diagnoses were verified by a sports medicine physician. Survival analysis was used to determine the association between apolipoprotein epsilon 4 and first concussion.

RESULTS

The unadjusted hazard ratio for concussion in the apolipoprotein epsilon 4 carriers was 1.18 (95% CI: 0.52, 2.69) compared to noncarriers. Adjustment for sex, weight, height, and team type resulted in a hazard ratio of 1.06 (95% CI: 0.41, 2.72), indicating little effect from confounding factors.

CONCLUSIONS

There is no important association between carrying the apolipoprotein epsilon 4 allele and sustaining a concussion. At this time, we do not recommend preseason genetic testing for varsity athletes as a mechanism for targeting prevention strategies.

Neuropsychological sequelae of non-central nervous system cancer and cancer therapy

Cancer patients report numerous adverse symptoms associated with their disease and treatment including cognitive dysfunction, fatigue, and affective distress. Cognitive dysfunction is ubiquitous in patients with primary central nervous system (CNS) cancer and recent evidence has documented similar deficits in patients with non-CNS cancer as well. Both the cancer itself and treatments including chemotherapy, biological response modifiers, and hormonal therapies have been demonstrated to adversely impact cognitive and neurobehavioral function. Neuroimaging and neurophysiological investigations have likewise revealed alterations in brain function that are helping to account for the nature of these cognitive disorders. Similarly, preclinical animal research is assisting to identify the pathophysiological mechanisms that underlie treatment-related neurotoxicities. The coalescence of multidisciplinary clinical and research efforts hold promise for the development of interventions that may offer neuroprotection in addition to currently available symptomatic therapies and cognitive rehabilitation techniques.

Apolipoprotein E and neurological disease: therapeutic potential and pharmacogenomic interactions

The apolipoprotein E (apoE) polymorphism is emerging as a uniquely important genetic modifier that affects functional outcome from both acute and chronic neurological injuries. Recent attention has focused on common denominator mechanisms by which apoE might affect brain injury and/or brain repair responses in clinically diverse diseases. Although endogenous apoE likely serves several adaptive functions in the injured CNS, there is growing evidence that its effect on modifying brain inflammatory responses and providing protection from excitotoxic injury may be central to its protective properties. A more complete understanding of the role that apoE plays in the injured brain has led to novel therapeutic strategies for both acute and chronic neurological disease.

COG1410, a novel apolipoprotein E-based peptide, improves functional recovery in a murine model of traumatic brain injury

Traumatic brain injury (TBI) is a silent epidemic affecting approximately 1.4 million Americans annually, at an estimated annual cost of $60 billion in the United States alone. Despite an increased understanding of the pathophysiology of closed head injury, there remains no pharmacological intervention proven to improve functional outcomes in this setting. Currently, the existing standard of care for TBI consists primarily of supportive measures. Apolipoprotein E (apoE) is the primary apolipoprotein synthesized in the brain in response to injury, where it modulates several components of the neuroinflammatory cascade associated with TBI. We have previously demonstrated that COG133, an apoE mimetic peptide, improved functional outcomes and attenuated neuronal death when administered as a single intravenous injection at 30 min post-TBI in mice. Using the principles of rational drug design, we developed a more potent analog, COG1410, which expands the therapeutic window for the treatment of TBI by a factor of four, from 30 min to 2 h. Mice that received a single intravenous injection of COG1410 at 120 min post-TBI exhibited significant improvement on a short term test of vestibulomotor function and on a long term test of spatial learning and memory. This was associated with a significant attenuation of microglial activation and neuronal death in the hippocampus, the neuroanatomical substrate for learning and memory. Rationally derived apoE mimetic peptides have been demonstrated to exert neuroprotective and anti-inflammatory effects in vitro and in clinically relevant models of brain injury. This represents a novel therapeutic strategy in the treatment of TBI.

Apolipoprotein E Genotype and Response of Carbon Monoxide Poisoning to Hyperbaric Oxygen Treatment

RATIONALE

Hyperbaric oxygen (HBO2) reduced the incidence of cognitive sequelae 6 weeks after carbon monoxide (CO) poisoning compared with normobaric oxygen (NBO2). The apolipoprotein (APOE) epsilon4 allele predicts unfavorable neurologic outcome after brain injury and stroke.

OBJECTIVES

To assess the effects of the epsilon4 allele on 6-week cognitive sequelae after CO poisoning.

METHODS

We tested APOE genotypes in 86 of 152 CO-poisoned patients from our randomized trial. Logistic regression was used to control for risk factors while testing for effects with the epsilon4 allele or interactions with epsilon4 and treatment on 6-week and 6- and 12-month cognitive sequelae.

MEASUREMENTS AND MAIN RESULTS

We enrolled 86 patients: 44 received HBO2 and 42 NBO2 therapy. A total of 31 (36%) patients had at least one epsilon4 allele. Six-week cognitive sequelae rates for patients treated with HBO2 and NBO2, respectively: epsilon4 allele absent, 11% (3/27) and 43% (12/28); epsilon4 allele present, 35% (6/17) and 29% (4/14). The epsilon4 allele was not associated with 6-week cognitive sequelae, 27% (15/55) without and 32% (10/31) with the epsilon4 allele (P = 0.323). The interaction between the epsilon4 allele and treatment was significantly associated with 6-week cognitive sequelae (P = 0.048). The interaction between the epsilon4 allele and treatment was not associated with 6- and 12-month cognitive sequelae.

CONCLUSIONS

HBO2 therapy reduces cognitive sequelae after CO poisoning in the absence of the epsilon4 allele. Because apolipoprotein genotype is unknown at the time of poisoning, we recommend that patients with acute CO poisoning receive HBO2.

Apolipoprotein E modifies the CNS response to injury via a histamine-mediated pathway

Recent evidence demonstrates that apolipoprotein E (apoE) influences the central nervous system (CNS) response to both acute and chronic injury. To address the mechanisms by which apoE influences neurological disease, we examined differential gene expression in the brains of apoE transgenic mice after closed head injury. Apart from confirming the knockout of apoE, the largest differential gene expression occurred for the interleukin-9 receptor (IL-9R), which was > 100-fold up-regulated in apoE-deficient versus wild-type mice. We observed a similar pattern of posttraumatic IL-9R up-regulation in APOE4 targeted replacement mice as compared with their APOE3 counterparts. This difference in gene expression was associated with increased neuronal protein expression of IL-9R in E4 animals compared with E3 as demonstrated by immunohistochemistry. The consequence of IL-9R binding in mast cells is the induction of proliferation and differentiation. This indirectly favors degranulation and release of histamine and inflammatory mediators, which have previously been demonstrated to exacerbate secondary neuronal injury. We found that apoE-deficient animals had increased levels of systemic histamine after injury and that pre-treatment with antihistamines improved functional outcomes in apoE-deficient but not wild-type animals after head injury. These results suggest that apoE modifies secondary neuronal injury caused by histamine release and are consistent with previous observations that apoE affects the CNS inflammatory response in an isoform-specific manner.

Genetic influences on outcome following traumatic brain injury

Several genes have been implicated as influencing the outcome following traumatic brain injury (TBI). Currently the most extensively studied gene has been APOE. APOE can influence overall and rehabilitation outcome, coma recovery, risk of posttraumatic seizures, as well as cognitive and behavioral functions following TBI. Pathologically, APOE is associated with increased amyloid deposition, amyloid angiopathy, larger intracranial hematomas and more severe contusional injury. The proposed mechanism by which APOE affects the clinicopathological consequences of TBI is multifactorial and includes amyloid deposition, disruption of cytoskeletal stability, cholinergic dysfunction, oxidative stress, neuroprotection and central nervous system plasticity in response to injury. Other putative genes have been less extensively studied and require replication of the clinical findings. The COMT and DRD2 genes may influence dopamine dependent cognitive processes such as executive/frontal lobe functions. Inflammation which is a prominent component in the pathophysiological cascade initiated by TBI, is in part is mediated by the interleukin genes, while apoptosis that occurs as a consequence of TBI may be modulated by polymorphisms of the p53 gene. The ACE gene may affect TBI outcome via mechanisms of cerebral blood flow and/or autoregulation and the CACNA1A gene may exert an influence via the calcium channel and its effect on delayed cerebral edema. Although several potential genes that may influence outcome following TBI have been identified, future investigations are needed to validate these genetic studies and identify new genes that might influence outcome following TBI.

Candidate mechanisms for chemotherapy-induced cognitive changes

The mechanism(s) for chemotherapy-induced cognitive changes are largely unknown; however, several candidate mechanisms have been identified. We suggest that shared genetic risk factors for the development of cancer and cognitive problems, including low-efficiency efflux pumps, deficits in DNA-repair mechanisms and/or a deregulated immune response, coupled with the effect of chemotherapy on these systems, might contribute to cognitive decline in patients after chemotherapy. Furthermore, the genetically modulated reduction of capacity for neural repair and neurotransmitter activity, as well as reduced antioxidant capacity associated with treatment-induced reduction in oestrogen and testosterone levels, might interact with these mechanisms and/or have independent effects on cognitive function.

Apolipoprotein E4 polymorphism as a genetic predisposition to delirium in critically ill patients

OBJECTIVE

To test for an association between apolipoprotein E (APOE) genotypes and duration of intensive care unit delirium.

DESIGN

Prospective, observational cohort study.

SETTING

A 541-bed, community-based teaching hospital.

PATIENTS

Fifty-three mechanically ventilated intensive care unit patients.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

All patients were managed with standardized sedation and ventilator weaning protocols as part of an ongoing clinical trial and were evaluated prospectively for delirium with the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU). DNA was extracted from whole blood samples obtained on enrollment, and APOE genotype was determined using polymerase chain reaction followed by restriction enzyme digestion by investigators blinded to the clinical information. Delirium occurred in 47 (89%) patients at some point during the intensive care unit stay. Of the 53 patients, 12 (23%) had an APOE4 allele (APOE4+) and 41 (77%) had only APOE2 or APOE3 alleles (APOE4-). APOE4+ patients were younger (53.2 +/- 21.9 vs. 65.4 +/- 13.4, p = .08) and less often admitted for pneumonia (0% vs. 29.3%, p = .05) compared with APOE4- patients, yet they had a duration of delirium that was twice as long: median (interquartile range), 4 (3, 4.5) vs. 2 (1, 4) days (p = .05). No other clinical outcomes were significantly different between the APOE4+ and APOE4- patients. Using multivariable regression analysis to adjust for age, admission diagnosis of sepsis or acute respiratory distress syndrome or pneumonia, severity of illness, and duration of coma, the presence of APOE4 allele was the strongest predictor of delirium duration (odds ratio, 7.32; 95% confidence interval, 1.82-29.51, p = .005).

CONCLUSIONS

APOE4 allele represents the first demonstrated genetic predisposition to longer duration of delirium in humans.

Involvement of apolipoprotein E in excess fat accumulation and insulin resistance

Although apolipoprotein E (apoE) is well known to play a major role in lipid metabolism, its role in glucose and energy homeostasis remains unclear. Herein, we established apoE-deficient genetically obese Ay (apoE(-/-);Ay/+) mice. ApoE deficiency in Ay mice prevented the development of obesity, with decreased fat accumulation in the liver and adipose tissues. ApoE(-/-);Ay/+ mice exhibited better glucose tolerance than apoE(+/+);Ay/+ mice. Insulin tolerance testing and hyperinsulinemic-euglycemic clamp study revealed marked improvement of insulin sensitivity, despite increased plasma free fatty acid levels. These metabolic phenotypes were reversed by adenoviral replenishment of apoE protein, indicating circulating apoE to be involved in increased adiposity and obesity-related metabolic disorders. Uptake of apoE-lacking VLDL into the liver and adipocytes was markedly inhibited, but adipocytes in apoE(-/-);Ay/+ mice exhibited normal differentiation, suggesting that apoE-dependent VLDL transport is involved in the development of obesity, i.e., surplus fat accumulation. Interestingly, apoE(-/-);Ay/+ mice exhibited decreased food intake and increased energy expenditure. Pair-feeding experiments indicate these phenomena to both contribute to the obesity-resistant phenotypes associated with apoE deficiency. Thus, apoE is involved in maintaining energy homeostasis. ApoE-dependent excess fat accumulation is a promising therapeutic target for the metabolic syndrome.

Mechanisms of working memory dysfunction after mild and moderate TBI: evidence from functional MRI and neurogenetics

Cognitive complaints are a frequent source of distress and disability after mild and moderate traumatic brain injury (TBI). While there are deficits in several cognitive domains, many aspects of these complaints and deficits suggest that problems in working memory (WM) play an important role. Functional imaging studies in healthy individuals have outlined the neural substrate of WM and have shown that regions important in WM circuitry overlap with regions commonly vulnerable to damage in TBI. Use of functional MRI (fMRI) in individuals with mild and moderate TBI suggests that they can have problems in the activation and allocation of WM, and several lines of evidence suggest that subtle alterations in central catecholaminergic sensitivity may underlie these problems. We review the evidence from fMRI and neurogenetic studies that support the role of catecholaminergic dysregulation in the etiology of WM complaints and deficits after mild and moderate TBI.

An apolipoprotein E-based therapeutic improves outcome and reduces Alzheimer's disease pathology following closed head injury: evidence of pharmacogenomic interaction

Apolipoprotein E (apoE) modifies glial activation and the CNS inflammatory response in an isoform-specific manner. Peptides derived from the receptor-binding region of apoE have been demonstrated to maintain the functional activity of the intact protein, and to improve histological and functional deficits after closed head injury. In the current study, APOE2, APOE3, and APOE4 targeted replacement (TR) mice expressing the human apoE protein isoforms (apoE2, apoE3 and apoE4) were used in a clinically relevant model of closed head injury to assess the interaction between the humanized apoE background and the therapeutic apoE mimetic peptide, apoE(133-149). Treatment with the apoE-mimetic peptide reduced microglial activation and early inflammatory events in all of the targeted replacement animals and was associated with histological and functional improvement in the APOE2TR and APOE3TR animals. Similarly, brain beta amyloid protein (Abeta)(1-42) levels were increased as a function of head injury in all of the targeted replacement mice, while treatment with apoE peptide suppressed Abeta(1-42) levels in the APOE2TR and APOE3TR animals. These results suggest a pharmacogenomic interaction between the therapeutic effects of the apoE mimetic peptide and the human apoE protein isoforms. Furthermore, they suggest that administration of apoE-mimetic peptides may serve as a novel therapeutic strategy for the treatment of acute and chronic neurological disease.

Traumatic brain injury induces biphasic upregulation of ApoE and ApoJ protein in rats

Apolipoproteins play an important role in cell repair and have been found to increase shortly after traumatic brain injury (TBI). In addition, apolipoproteins reduce amyloid-beta (Abeta) accumulation in models of Alzheimer's disease. Considering that TBI induces progressive neurodegeneration including Abeta accumulation, we explored potential long-term changes in the gene and protein expression of apolipoproteins E and J (ApoE and J) over 6 months after injury. Anesthetized male Sprague-Dawley rats were subjected to parasagittal fluid-percussion brain injury and their brains were evaluated at 2, 4, 7, 14 days, and 1 and 6 months after TBI. In situ hybridization, Western blot, and immunohistochemical analysis demonstrated that although there was a prolonged upregulation in both the gene expression and protein concentration of ApoE and J after injury, these responses were uncoupled. Upregulation of ApoE and J mRNA expression lasted from 4 days to 1 month after injury. In contrast, a biphasic increase in protein concentration and number of immunoreactive cells for ApoE and ApoJ was observed, initially peaking at 2 days (i.e., before increased mRNA expression), returning to baseline by 2 weeks and then gradually increasing through 6 months postinjury. In addition, ApoE and J were found to colocalize with Abeta accumulation in neurons and astrocytes at 1-6 months after injury. Collectively, these data suggest that ApoE and J play a role in the acute sequelae of brain trauma and reemerge long after the initial insult, potentially to modulate progressive neurodegenerative changes.

Regulation of hippocampal cholesterol metabolism by apoE and environmental stimulation

Alzheimer's disease is associated with genetic risk factors, of which the allele E4 of apolipoprotein E (apoE4) is the most prevalent, and it is also affected by environmental factors such as early life education. We have recently shown, utilizing apoE-deficient and apoE transgenic mice, that synaptogenesis in the hippocampus following environmental stimulation is affected by apoE. In view of the pivotal role of cholesterol in synaptic plasticity, and of its suggested role in synaptogenesis, we presently examined the effects of apoE and environmental stimulation on brain cholesterol homeostasis. The hippocampal levels of cholesterol and its precursors and metabolites in control mice were not affected by exposure to environmental stimulation. In contrast, the hippocampal levels of cholesterol and its precursors lathosterol and desmosterol and metabolite 24S-hydroxycholesterol were lower in apoE-deficient mice that were maintained in a regular environmental than those of corresponding control mice, whereas they were markedly elevated following environmental stimulation. Histological and immunohistochemical experiments revealed that the combined stimulatory effects of apoE deficiency and environmental stimulation on cholesterol metabolism were associated with marked activation of hippocampal astrocytes and with the abnormal accumulation of cholesterol in neurons and astrocytes. These effects were rescued similarly in apoE3 and apoE4 transgenic mice. These findings suggest that apoE plays an important role in the translocation of cholesterol from astrocytes to neurons in vivo and in the regulation and homeostasis of this process.

Effect of apolipoprotein E deficiency on reactive sprouting in the dentate gyrus of the hippocampus following entorhinal cortex lesion: role of the astroglial response

This study investigated the effect of apolipoporotein E (apoE) deficiency on hippocampal reactive sprouting responses of the septohippocampal cholinergic (SHC) and commissural/associational fibers (C/A) following an electrolytic lesion of the entorhinal cortex (ECL), using apoE knockout (apoEKO) and age-matched control wild-type mice. Based on recent evidence suggesting that apoE plays a role in the modulation of glial inflammation, we also tested the hypothesis that the pattern of the astroglial response to ECL might be related to the defective reinnervation previously reported in apoEKO mice. Consistent with our hypothesis, we report a differential pattern of astroglial response that concurred with impairments in the sprouting of the SHC and corresponding synaptic replacement in apoEKO mice at 14 and 30 days post-lesion (DPL), a time range covering the onset of axonal/terminal sprouting to synaptogenesis. We also report a limited sprouting of the C/A fiber system in apoEKO relative to control mice at 30 DPL, a period of active dendritic remodeling. The results of the present study confirm and extend previous findings that apoEKO mice display impaired regenerative capacity in response to ECL and argue that in addition to the effect of apoE on lipid trafficking, apoE may also influence the astroglial response to damage, and that both of these effects account for the defective reinnervation observed in apoEKO mice.

Intrathecal administration of a novel apoE-derived therapeutic peptide improves outcome following perinatal hypoxic–ischemic injury

Perinatal hypoxic-ischemic brain injury remains a significant clinical problem for which there remains no adequate therapeutic intervention. Apolipoprotein E (apoE) is a 299 amino acid protein that has been demonstrated to modify functional recovery following acute ischemic and traumatic brain injury. The aim of the current study was to evaluate whether administration of an apoE-derived peptide could reduce CNS injury in a rodent model of perinatal hypoxia and ischemia. We found that intrathecal delivery of an apoE-mimetic peptide caused a significant reduction in post-ischemic brain necrosis, as reflected by decreased reduction in ipsilateral brain weight 7 days following hypoxic-ischemic injury. These results suggest that administration of an apoE-derived therapeutic peptide represents a novel therapeutic strategy in the clinical setting of perinatal hypoxic-ischemic injury.

Lipid homeostasis and apolipoprotein E in the development and progression of Alzheimer's disease

Extracellular amyloid plaques, intracellular neurofibrillary tangles, and loss of basal forebrain cholinergic neurons in the brains of Alzheimer's disease (AD) patients may be the end result of abnormalities in lipid metabolism and peroxidation that may be caused, or exacerbated, by beta-amyloid peptide (Abeta). Apolipoprotein E (apoE) is a major apolipoprotein in the brain, mediating the transport and clearance of lipids and Abeta. ApoE-dependent dendritic and synaptic regeneration may be less efficient with apoE4, and this may result in, or unmask, age-related neurodegenerative changes. The increased risk of AD associated with apoE4 may be modulated by diet, vascular risk factors, and genetic polymorphisms that affect the function of other transporter proteins and enzymes involved in brain lipid homeostasis. Diet and apoE lipoproteins influence membrane lipid raft composition and the properties of enzymes, transporter proteins, and receptors mediating Abeta production and degradation, tau phosphorylation, glutamate and glucose uptake, and neuronal signal transduction. The level and isoform of apoE may influence whether Abeta is likely to be metabolized or deposited. This review examines the current evidence for diet, lipid homeostasis, and apoE in the pathogenesis of AD. Effects on the cholinergic system and response to cholinesterase inhibitors by APOE allele carrier status are discussed briefly.

A novel therapeutic derived from apolipoprotein E reduces brain inflammation and improves outcome after closed head injury

Although apolipoprotein E4 (APOE4) was initially identified as a susceptibility gene for the development of Alzheimer's disease, the presence of the APOE4 allele is also associated with poor outcome after acute brain injury. One mechanism by which apoE may influence neurological outcome is by downregulating the neuroinflammatory response. Because it does not readily cross the blood-brain barrier, the apoE holoprotein has limited therapeutic potential. We demonstrate that a single intravenous injection of a small peptide derived from the apoE receptor binding region crosses the blood-brain barrier and significantly improves histological and functional outcomes after traumatic brain injury (TBI). The development of an apoE-based intervention represents a novel therapeutic strategy in the management of acute brain injury.

Cognitive effects of cytotoxic cancer chemotherapy: predisposing risk factors and potential treatments

Increasing evidence suggests that systemic cancer chemotherapy can have significant long-term effects on cognition, particularly on verbal learning, memory, attention, and speed of information processing. These deficits can be a source of significant distress to survivors. There is much less known about the mechanisms, predisposing vulnerabilities, and treatment of these deficits. We will summarize current knowledge of chemotherapy-associated cognitive deficits. Emerging theories about the role of selected genetic polymorphisms in heightening the vulnerability to chemotherapy-induced cognitive decline will be described.

Alterations in cerebrospinal fluid apolipoprotein E and amyloid beta-protein after traumatic brain injury

There is evidence that apolipoprotein E (apoE) and amyloid beta-protein (Abeta), which are implicated in the pathology of chronic neurodegenerative disorders, are involved in the response of the brain to acute injury; however, human in vivo evidence is sparse. We conducted a prospective observational study to determine the magnitude and time-course of alterations in cerebrospinal fluid (CSF) apoE and Abeta concentrations after traumatic brain injury (TBI), and the relationship of these changes to severity of injury and clinical outcome. Enzyme linked immunosorbant assay (ELISA) was used to assay apoE, Abeta(1-40) and Abeta(1-42) in serial CSF samples from 13 patients with TBI and 13 controls. CSF S100B and tau were assayed as surrogate markers of brain injury. There was a significant decrease in CSF apoE (p < 0.001) and Abeta (p< 0.001) after TBI contrasting the observed elevation in CSF S100B (p < 0.001) and tau (p < 0.001) concentration. There was significant correlation (r = 0.67, p = 0.01) between injury severity and the decrease in Abeta(1-40) concentration after TBI. In vivo, changes in apoE and Abeta concentration occur after TBI and may be important in the response of the human 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.

The cholesterol-lowering drug probucol increases apolipoprotein E production in the hippocampus of aged rats: implications for Alzheimer's disease

Several recent epidemiological studies have proposed that cholesterol-lowering drug Statin may provide protection against Alzheimer's disease (AD). Probucol is a non-Statin cholesterol-lowering drug and a potent inducer of apolipoprotein E (apoE) production in peripheral circulation. A recent clinical study using Probucol in elderly AD subjects revealed a concomitant stabilisation of cognitive symptoms and significant increases in apoE levels in the cerebral spinal fluid in these patients. To gain insight into the mechanisms underlying these effects, we treated a cohort of aged male rats (26-month-old) with oral dose of Probucol for 30 days. Specifically, we examined the effects of Probucol on apoE production and its receptors (low density lipoprotein receptor [LDLr] and low density lipoprotein receptor-related protein [LRP]), astroglial marker of cell damage (glial fibrillary acidic protein [GFAP]), markers of neuronal synaptic plasticity and integrity (synaptosomal associated protein of 25 kDa [SNAP-25] and synaptophysin) as well as cholesterol biosynthesis (3-hydroxy-3-methylglutaryl coenzyme A reductase [HMGCoAr]) in the hippocampus. We report that Probucol induces the production of apoE and one of its main receptors, LRP, increases HMGCoAr (rate-limiting enzyme in cholesterol synthesis), substantially attenuates age-related increases in glial activation, and induces production of synaptic marker SNAP-25, a molecule commonly associated with synaptogenesis and dendritic remodeling. These findings suggest that Probucol could promote neural and synaptic plasticity to counteract the synaptic deterioration associated with brain aging through an apoE/LRP-mediated system. Consistent with the beneficial effects of other cholesterol-lowering drugs such as the Statin, Probucol could also offers additional benefits based on apoE neurobiology.

Apolipoprotein e4 decreases whereas apolipoprotein e3 increases the level of secreted amyloid precursor protein after closed head injury

Apolipoprotein E (apoE4) and head trauma are important genetic and environmental risk factors for Alzheimer's disease. Furthermore, apoE4 increases both the acute and chronic consequences of head trauma. The latter are associated with the deposition of amyloid-beta, which is particularly elevated in apoE4 subjects. The short-term effects of head injury are associated with transiently increased metabolism of amyloid precursor protein (APP) and its secreted fragment, APPs. In the present study, we examined the possibility that the acute, short-term pathological effects of apoE4 following head trauma and the corresponding neuroprotective effects of apoE3 are related to isoform-specific effects of apoE on APP metabolism. Accordingly, male transgenic mice expressing human apoE3 or apoE4 on a null mouse apoE background and apoE-deficient and control mice were subjected to closed head injury (CHI). The resulting effects on brain APP, and on its secreted products, APPs and secreted product of the alpha-cleavage of APP (APPsalpha) were then determined 24 h following injury. Immunoblotting revealed no significant differences between the basal APP, APPs and APPsalpha levels of the hippocampus or the cortex of the control and the apoE3 and ApoE4 transgenic mice. The apoE-deficient mice also had similar cortical basal levels of APP and its metabolites, whereas their corresponding basal hippocampal APP and APPs levels were lower than those of the other groups. CHI lowered the hipppocampal APPs and APPsalpha levels of the apoE4 transgenic mice, whereas those of the apoE3 transgenic mice and of the control and apoE-deficient mice were not affected by this insult. In contrast, CHI raised the cortical APP and APPs levels of the apoE3 transgenic mice but had no significant effect on those of the other mice groups. These animal model findings suggest that the acute, short-term pathological effects of apoE4 following CHI and the corresponding neuroprotective effects of apoE3 may be mediated by their opposing effects on the expression and cleavage of cortical and hippocampal APP. Similar isoform-specific interactions between apoE and APP may play a role in the acute, short-term effects of head trauma in humans.

APOE genotype and an ApoE-mimetic peptide modify the systemic and central nervous system inflammatory response

Human apolipoprotein E is the major apolipoprotein expressed in the brain and exists as three isoforms, designated E2, E3, and E4. Although evidence suggests that apolipoprotein E plays an important role in modifying systemic and brain inflammatory responses, there is little data investigating apoE isoform-specific effects in vivo. In this study, we compared the inflammatory responses of targeted-replacement mice expressing the human APOE3 and APOE4 genes after intravenous administration of lipopolysaccharide. Animals expressing the E4 allele had significantly greater systemic and brain elevations of the pro-inflammatory cytokines TNFalpha and IL-6 as compared with their APOE3 counterparts, suggesting an isoform-specific effect of the immunomodulatory properties of apoE. Furthermore, intravenous administration of a small apoE-mimetic peptide derived from the receptor-binding region of the apoE holoprotein (apoE-(133-149)) similarly suppressed both systemic and brain inflammatory responses in mice after lipopolysaccharide administration. These results suggest that apoE plays an isoform-specific role in mediating the systemic and brain inflammatory responses. Moreover, because exogenous administration of this apoE mimetic peptide is effective at suppressing both systemic and brain inflammation, it may represent a novel therapeutic strategy for diseases characterized by systemic or central nervous system inflammation, such as septic shock, multiple sclerosis, and traumatic brain injury.

Relationship between apoE4 allele and excitatory amino acid levels after traumatic brain injury

OBJECTIVE

Apolipoprotein E isoform (E4) has been posited to affect outcomes after central nervous system injury. This project sought to determine the relationship between the apoE4 allele and the recovery of amino acid neurotransmitters (aspartate, glutamate, and lactate/pyruvate ratio [L/P]) following a traumatic brain injury (TBI) after controlling for patient characteristics.

DESIGN

This prospective clinical study examined neurotransmitters and L/P within the cerebrospinal fluid and compared the trends by apoE genotypes.

SETTING

Adults with TBI were recruited from a neurotrauma intensive care unit within a trauma I university medical center.

PATIENTS

Ninety-one patients were enrolled into the study after a severe TBI (Glasgow Coma Scale [GCS] score, </=8). Cerebrospinal fluid was serially sampled from a ventriculostomy every 4 hrs for the first 24 hrs and every 6 hrs for 25-120 hrs after injury.

MEASUREMENTS AND MAIN RESULTS

Hierarchical linear modeling analyses were used to compare the change of glutamate, aspartate, and L/P over time by the presence or absence of the apoE4 allele, with GCS score, sex, race, and therapeutic hypothermias included as covariates. There was a significant apoE4 allele group effect on both the linear and quadratic slopes in aspartate. In glutamate, the rate of change in glutamate was statistically related to GCS score. There was no significant difference in the glutamate response over time by the presence of the apoE4 allele. There was a significant difference in the change in L/P across time, with faster recovery when the apoE4 allele was absent.

CONCLUSIONS

Recovery of aspartate and L/P differed depending on the presence of the apoE4 allele. Patients with the allele had significant increased and sustained levels of aspartate and L/P after TBI. Changes in glutamate were related to severity of illness and were independent of the presence of the apoE4 allele.

ApoE4 impairs hippocampal plasticity isoform-specifically and blocks the environmental stimulation of synaptogenesis and memory

Alzheimer's disease (AD) is associated with genetic risk factors, of which the allele E4 of apolipoprotein E (apoE4) is the most prevalent, and is affected by environmental factors that include education early in life and socioeconomic background. The extent to which environmental factors affect the phenotypic expression of the AD genetic risk factors is not known. Here we show that the neuronal and cognitive stimulations, which are elicited by environmental enrichment at a young age, are markedly affected by the apoE genotype. Accordingly, exposure to an enriched environment of young mice transgenic for human apoE3, which is the benign AD apoE allele, resulted in improved learning and memory, whereas mice transgenic for human apoE4 were unaffected by the enriched environment and their learning and memory were similar to those of the nonenriched apoE3 transgenic mice. These cognitive effects were associated with higher hippocampal levels of the presynaptic protein synaptophysin and of NGF in apoE3 but not apoE4 transgenic mice. In contrast, cortical synaptophysin and NGF levels of the apoE3 and apoE4 transgenic mice were similarly elevated by environmental enrichment. These findings show that apoE4 impairs hippocampal plasticity and isoform-specifically blocks the environmental stimulation of synaptogenesis and memory. This provides a novel mechanism by which environmental factors can modulate the function and phenotypic expression of the apoE genotype.

Cholesterol: from heart attacks to Alzheimer's disease

The accumulation and aggregation of the amyloid-beta peptide (Abeta) in the brain are important contributing factors to Alzheimer's disease (AD). Consequently, blocking the generation of Abeta is a potentially important treatment strategy. Recent work on the metabolism of Abeta has identified several cellular proteins and proteases that collectively promote or prevent the generation of Abeta. In addition, accumulating in vitro and in vivo evidence suggests a role for cholesterol in modulating the cellular processing of Abeta with the potential to affect AD.

Closed-head minimal traumatic brain injury produces long-term cognitive deficits in mice

Victims of minimal traumatic brain injury (mTBI) do not show clear morphological brain defects, but frequently suffer lasting cognitive deficits, emotional difficulties and behavioral disturbances. In the present study we adopted a non-invasive closed-head weight-drop mouse model to produce mTBI. We examined the effects of 20, 25, or 30 g weight drop 7, 30, 60 and 90 days following injury on mice's ability to perform the Morris water maze. The mice suffered profound long-lasting learning and memory deficits that were force- and time-dependent. Although the injured mice could acquire the task, they could not improve their initial escape latency by more than 50%, while normal mice improved by up to 450% (P<0.001). In order to directly compare the learning ability of individual mice following our mTBI we have devised a new measure which we term learning rate. We define learning rate as the rate the mouse improved its own performance in consecutive trials in a given experimental day. The learning rate of control mice increased linearly throughout the testing period with a slope of approximately 0.9. Injured mice that sustained 20 and 25 g weight drop could also improve their learning rate linearly but with a slope of only 0.2. Mice who sustained 30 g weight drop could not improve their learning rate linearly and reached a plateau after the third experimental learning day. These results indicate that the severity of injury may correlate with the degree of integration of the learning task. These cognitive deficits occurred without any other clear neurological damage, no evident brain edema, no notable damage to the blood-brain barrier and no early anatomical changes to the brain (observed by magnetic resonance imaging imaging). These results demonstrate that persistent deficits of cognitive learning abilities in mice, similar to those observed in human post-concussive syndrome, can follow mTBI without any anatomical damage to the brain and its surrounding tissue.

Genetic vulnerability following traumatic brain injury: the role of apolipoprotein E

Apolipoprotein E (APOE) is thought to be responsible for the transportation of lipids within the brain, maintaining structural integrity of the microtubule within the neurone, and assisting with neural transmission. Possession of the APOE epsilon4 allele has also been shown to influence neuropathological findings in patients who die from traumatic brain injury, including the accumulation of amyloid beta protein. Previous clinical studies reporting varying outcome severities of traumatic brain injury, including cognitive and functional recovery, all support the notion that APOE epsilon4 allele possession is associated with an unfavourable outcome. Evidence from experimental and clinical brain injury studies confirms that APOE plays an important role in the response of the brain to injury.

Experimental models of head trauma

Traumatic brain injury is one of the most common causes for chronic disability in young people. Despite this there are currently no widely available modes of therapy that would limit the extent of brain damage secondary to trauma. Therefore, new insights into the pathological mechanisms involved in head trauma possibly leading to the identification of new therapeutic targets are urgently needed. In order to attain these goals adequate animal models for traumatic brain injury are needed. In the following paper the authors will review the various animal models for head trauma and emphasize their potential strengths and weaknesses.

Apolipoprotein E polymorphism and outcome after closed traumatic brain injury: influence of ethnic and regional differences

OBJECT

The presence of the apolipoprotein E-epsilon4 (APOE-epsilon4) allele is reported to be associated with poor outcome after traumatic brain injury (TBI). This study was performed to determine if the presence of the APOE-epsilon4 allele influenced outcome in a cohort of black patients with TBI who had homogeneous neuropathological findings.

METHODS

Venous blood was collected at the time of admission to determine the APOE genotype in black Zulu-speaking patients who presented with traumatic cerebral contusions. The frequency of the APOE-epsilon4 allele's appearance was correlated with outcome at a minimum of 6 months of follow up. Univariate and multivariate analyses were performed to determine independent risk factors and to control for confounding factors. In 110 black Zulu-speaking patients with traumatic cerebral contusions, genotypes for APOE were analyzed. Eleven of 45 (24.4%) with the APOE-epsilon4 allele experienced a poor outcome, compared with 10 (15.4%) of 65 without this allele (p = 0.34). Both patients with homozygous APOE-epsilon4 alleles experienced a good outcome (Glasgow Outcome Score 5). Univariate and multivariate analysis revealed no significant relationship in patients with the APOE-epsilon4 allele with regard to age, admission Glasgow Comas Scale score, contusion volume, type of neurosurgical management, and outcome. The risk of a poor outcome was, however, greater in patients with the APOE-epsilon4 allele (relative risk 1.59; 95% confidence interval 0.74-3.42).

CONCLUSIONS

The authors recorded no relationship between APOE-epsilon4 allele status and outcome after TBI in black patients. Given the high regional susceptibility to the APOE gene, further studies, possibly even community-based investigations and studies conducted in other geographic areas, are probably warranted.

Apolipoprotein E4 influences amyloid deposition but not cell loss after traumatic brain injury in a mouse model of Alzheimer's disease

The epsilon4 allele of apolipoprotein E (APOE) and traumatic brain injury (TBI) are both risk factors for the development of Alzheimer's disease (AD). These factors may act synergistically, in that APOE4+ individuals are more likely to develop dementia after TBI. Because the mechanism underlying these effects is unclear, we questioned whether APOE4 and TBI interact either through effects on amyloid-beta (Abeta) or by enhancing cell death/tissue injury. We assessed the effects of TBI in PDAPP mice (transgenic mice that develop AD-like pathology) expressing human APOE3 (PDAPP:E3), human APOE4 (PDAPP:E4), or no APOE (PDAPP:E-/-). Mice were subjected to a unilateral cortical impact injury at 9-10 months of age and allowed to survive for 3 months. Abeta load, hippocampal/cortical volumes, and hippocampal CA3 cell loss were quantified using stereological methods. All of the groups contained mice with Abeta-immunoreactive deposits (56% PDAPP:E4, 20% PDAPP:E3, 75% PDAPP:E-/-), but thioflavine-S-positive Abeta (amyloid) was present only in the molecular layer of the dentate gyrus in the PDAPP:E4 mice (44%). In contrast, our previous studies showed that in the absence of TBI, PDAPP:E3 and PDAPP:E4 mice have little to no Abeta deposition at this age. After TBI, all of the Abeta deposits present in PDAPP:E3 and PDAPP:E-/- mice were diffuse plaques. In contrast to the effect of APOE4 on amyloid, PDAPP:E3, PDAPP:E4, and PDAPP:E-/- mice did not differ in the amount of brain tissue or cell loss. These data support the hypothesis that APOE4 influences the neurodegenerative cascade after TBI via an effect on Abeta.

Apolipoprotein E knockout mice display procedural deficits in the Morris water maze: analysis of learning strategies in three versions of the task

Apolipoprotein E knockout (apoEKO) mice have been shown to be impaired in the spatial Morris water maze (MWM). However, several groups failed to replicate this finding. One reason for this inconsistency may stem from variations in the experimental protocols and environment between laboratories. In the present study, we have tested if age and variations in protocol implementation that specifically affect salience of the visual extramaze cues influence performance and navigational strategies in the MWM. We tested three- and 12-month-old apoEKO and wild type mice in three versions of the MWM differing on the availability of visual extramaze cues: (1) salient cues, (2) diffuse cues, and (3) absence of cues. Our results show that the presence of salient cues enhances acquisition performance of wild type, but not apoEKO mice in the MWM. This effect was restricted to the acquisition phase since apoEKO mice reached a level of performance that was comparable to that of controls toward the end of the task. No significant differences were detected between apoEKO and controls in either the diffuse cues or absence of cues paradigms. Thigmotaxic tendencies were observed in apoEKO mice and correlated high latency scores. Thigmotaxis may have interfered with the initial ability to engage in a proficient navigational strategy. These findings suggest that, in contrast to what has been proposed in the past, apoEKO mice appear not to be impaired in spatial memory per se but are deficient in a procedural component of the MWM. Furthermore, the procedural deficit and corresponding thigmotaxic tendencies of apoEKO mice appeared to increase with age. Taken together, these findings confirm our hypothesis that age and variations in experimental protocols can influence MWM performances.

Neuroplasticity in Alzheimer's disease

Ramon y Cajal proclaimed in 1928 that "once development was ended, the founts of growth and regeneration of the axons and dendrites dried up irrevocably. In the adult centers the nerve paths are something fixed, ended and immutable. Everything must die, nothing may be regenerated. It is for the science of the future to change, if possible, this harsh decree." (Ramon y Cajal, 1928). In large part, despite the extensive knowledge gained since then, the latter directive has not yet been achieved by 'modern' science. Although we know now that Ramon y Cajal's observation on CNS plasticity is largely true (for lower brain and primary cortical structures), there are mechanisms for recovery from CNS injury. These mechanisms, however, may contribute to the vulnerability to neurodegenerative disease. They may also be exploited therapeutically to help alleviate the suffering from neurodegenerative conditions.

2002 Refshauge Lecture. When to retire after concussion?

The management of an athlete with recurrent concussions, whether persistently symptomatic or not, remains anecdotal. There are no evidence-based guidelines upon which a team physician can advise the athlete. All doctors involved in athlete care need to be aware of the potential for medicolegal problems if athletes are inappropriately returned to sport prematurely or in the case of professional athletes held out of sport or retired on the basis of non-scientific recommendations.

Expression of human apolipoprotein E downregulates amyloid precursor protein-induced ischemic susceptibility

BACKGROUND AND PURPOSE

Epidemiological findings and experimental data on transgenic mice show that Alzheimer's disease-related changes render the brain more susceptible to ischemic damage. We studied whether the previously observed vulnerability in mice overexpressing the 751-amino-acid isoform of human amyloid precursor protein (APP751) is regulated by human apolipoprotein E (apoE) alleles, which determine the relative risk for Alzheimer's disease and the susceptibility to various forms of acute brain damage.

METHODS

Aged apoE knock out (KO) mice, mice overexpressing APP751 in the apoE KO background and mice expressing either human apoE3 or apoE4 and APP751 in the apoE KO background were exposed to permanent occlusion of the middle cerebral artery (MCA). Infarct volumes were quantified from T2-weighted magnetic resonance images 24 hours after the MCA occlusion. Local cortical blood flow was monitored by laser Doppler flowmetry. Ischemia-induced microgliosis was detected by immunohistochemistry.

RESULTS

Overexpression of human APP751 significantly increased the infarct volumes in apoE KO mice. Furthermore, this APP751-induced ischemic vulnerability was attenuated by the coexpression of either human apoE isoform. MCA occlusion resulted in a similar relative reduction in cortical blood flow in all mouse groups. Vascular anatomy showed no variation in the MCA territory between the groups. Instead, the expression of human apoE isoforms reduced the ischemia-induced microgliosis.

CONCLUSIONS

Expression of either the human apoE3 or apoE4 isoform protects against the increased ischemic vulnerability observed in aged mice overexpressing human APP751, probably by modulating the inflammatory response induced by MCA occlusion.

The behavioural effect of middle cerebral artery occlusion on apolipoprotein-E deficient mice

The behavioural effects of middle cerebral artery occlusion (MCAO) in apolipoprotein-E deficient (Apo-E KO) mice were investigated using a modified SHIRPA protocol and compared with effects in wild type littermate controls. The MCA was permanently occluded by insertion of an intraluminal filament to its origin on the Circle of Willis and behavioural responses were observed 24 h later. MCAO treatment caused a range of changes in the wild type mice whereas, few differences were observed in the Apo-E KO mice in the behavioural observation. In the rotarod task, MCAO operated wild type mice showed a significant reduction in performance compared with sham-operated and non-operated animals. In contrast, both sham and MCAO operated Apo-E KO mice showed significant impairment compared with non-operated controls. A significant reduction in performance was also observed in sham-operated Apo-E KO compared with sham-operated wild type mice. In locomotor activity tests, no significant reduction in activity was observed between non-operated and sham-operated wild type controls, whereas a significant reduction was found between sham operated and MCAO operated mice. In the Apo-E KO mice, both sham and MCAO-operated animals showed a reduction in locomotor activity compared with non-operated mice. Furthermore, Apo-E KO MCAO mice showed a worsened deficit in locomotor activity, which was significantly correlated with exacerbated cortical lesion volume, unlike wild-type MCAO mice. This study shows that Apo-E KO animals demonstrate an impaired functional recovery post surgery which may be further compounded by post experimental stroke and also demonstrates the utility of the SHIRPA test system for investigating behavioural changes in functional outcome post stroke.