Apolipoprotein E4 (ApoE4) but not ApoE3 or ApoE2 potentiates beta-amyloid protein activation of complement in vitro

Role of Inflammatory Processes in Hemorrhagic Stroke

Hemorrhagic stroke is the deadliest form of stroke and includes the subtypes of intracerebral hemorrhage and subarachnoid hemorrhage. A common cause of hemorrhagic stroke in older individuals is cerebral amyloid angiopathy. Intracerebral hemorrhage and subarachnoid hemorrhage both lead to the rapid collection of blood in the central nervous system and generate inflammatory immune responses that involve both brain resident and infiltrating immune cells. These responses are complex and can contribute to both tissue recovery and tissue injury. Despite the interconnectedness of these major subtypes of hemorrhagic stroke, few reviews have discussed them collectively. The present review provides an update on inflammatory processes that occur in response to intracerebral hemorrhage and subarachnoid hemorrhage, and the role of inflammation in the pathophysiology of cerebral amyloid angiopathy-related hemorrhage. The goal is to highlight inflammatory processes that underlie disease pathology and recovery. We aim to discuss recent advances in our understanding of these conditions and identify gaps in knowledge with the potential to develop effective therapeutic strategies.

Inflammation—Cause or consequence of late onset Alzheimer’s disease or both? A review of the evidence

Accumulating evidence suggests that inflammation is involved in the development of late onset Alzheimer’s disease (LOAD). However, it is not clear whether inflammation is a cause or consequence, or both. The aim of this paper is to review the relationship between inflammation and LOAD. We also review the effect of anti-inflammation on the risk of LOAD to further elucidate the relationship between inflammation and LOAD.

Uncovering Disease Mechanisms in a Novel Mouse Model Expressing Humanized APOEε4 and Trem2*R47H

Late-onset Alzheimer's disease (AD; LOAD) is the most common human neurodegenerative disease, however, the availability and efficacy of disease-modifying interventions is severely lacking. Despite exceptional efforts to understand disease progression via legacy amyloidogenic transgene mouse models, focus on disease translation with innovative mouse strains that better model the complexity of human AD is required to accelerate the development of future treatment modalities. LOAD within the human population is a polygenic and environmentally influenced disease with many risk factors acting in concert to produce disease processes parallel to those often muted by the early and aggressive aggregate formation in popular mouse strains. In addition to extracellular deposits of amyloid plaques and inclusions of the microtubule-associated protein tau, AD is also defined by synaptic/neuronal loss, vascular deficits, and neuroinflammation. These underlying processes need to be better defined, how the disease progresses with age, and compared to human-relevant outcomes. To create more translatable mouse models, MODEL-AD (Model Organism Development and Evaluation for Late-onset AD) groups are identifying and integrating disease-relevant, humanized gene sequences from public databases beginning with APOEε4 and Trem2*R47H, two of the most powerful risk factors present in human LOAD populations. Mice expressing endogenous, humanized APOEε4 and Trem2*R47H gene sequences were extensively aged and assayed using a multi-disciplined phenotyping approach associated with and relative to human AD pathology. Robust analytical pipelines measured behavioral, transcriptomic, metabolic, and neuropathological phenotypes in cross-sectional cohorts for progression of disease hallmarks at all life stages. In vivo PET/MRI neuroimaging revealed regional alterations in glycolytic metabolism and vascular perfusion. Transcriptional profiling by RNA-Seq of brain hemispheres identified sex and age as the main sources of variation between genotypes including age-specific enrichment of AD-related processes. Similarly, age was the strongest determinant of behavioral change. In the absence of mouse amyloid plaque formation, many of the hallmarks of AD were not observed in this strain. However, as a sensitized baseline model with many additional alleles and environmental modifications already appended, the dataset from this initial MODEL-AD strain serves an important role in establishing the individual effects and interaction between two strong genetic risk factors for LOAD in a mouse host.

The complement cascade in Alzheimer's disease: a systematic review and meta-analysis

Genetic evidence implicates a causal role for the complement pathway in Alzheimer's disease (AD). Since studies have shown inconsistent differences in cerebrospinal fluid (CSF) and peripheral blood complement protein concentrations between AD patients and healthy elderly, this study sought to summarize the clinical data. Original peer-reviewed articles measuring CSF and/or blood concentrations of complement or complement regulator protein concentrations in AD and healthy elderly control (HC) groups were included. Of 2966 records identified, means and standard deviations from 86 studies were summarized as standardized mean differences (SMD) by random effects meta-analyses. In CSF, concentrations of clusterin (N_AD/N_HC = 625/577, SMD = 0.53, Z₈ = 8.81, p < 0.005; I² < 0.005%) and complement component 3 (C3; N_AD/N_HC = 299/522, SMD = 0.45, Z₃ = 3.21, p < 0.005; I² = 68.40%) were significantly higher in AD, but differences in C1q, C-reactive protein (CRP), serum amyloid protein (SAP), and factor H concentrations were not significant. In peripheral blood, concentrations of CRP were elevated in AD (N_AD/N_HC = 3404/3332, SMD = 0.44, Z₄₃ = 3.43, p < 0.005; I² = 93.81%), but differences between groups in C3, C4, C1-inhibitor, SAP, factor H and clusterin concentrations were not significant, and inconsistent between studies. Of 64 complement pathway proteins or regulators in the quantitative synthesis, trends in C1q, factor B, C4a, and late-stage complement pathway components (e.g. C9) in blood, C4 in CSF, and the membrane attack complex in blood and CSF, might be investigated further. The results collectively support elevated complement pathway activity in AD, which was best characterized by increased CSF clusterin concentrations and less consistently by CSF C3 concentrations. Complement activity related to an AD diagnosis was not reflected consistently by the peripheral blood proteins investigated.

Innate Immune System Activation and Neuroinflammation in Down Syndrome and Neurodegeneration: Therapeutic Targets or Partners?

Innate immune system activation and inflammation are associated with and may contribute to clinical outcomes in people with Down syndrome (DS), neurodegenerative diseases such as Alzheimer's disease (AD), and normal aging. In addition to serving as potential diagnostic biomarkers, innate immune system activation and inflammation may play a contributing or causal role in these conditions, leading to the hypothesis that effective therapies should seek to dampen their effects. However, recent intervention studies with the innate immune system activator granulocyte-macrophage colony-stimulating factor (GM-CSF) in animal models of DS, AD, and normal aging, and in an AD clinical trial suggest that activating the innate immune system and inflammation may instead be therapeutic. We consider evidence that DS, AD, and normal aging are accompanied by innate immune system activation and inflammation and discuss whether and when during the disease process it may be therapeutically beneficial to suppress or promote such activation.

APOE ε4 genotype-dependent cerebrospinal fluid proteomic signatures in Alzheimer's disease

Background

Aggregation of amyloid β into plaques in the brain is one of the earliest pathological events in Alzheimer’s disease (AD). The exact pathophysiology leading to dementia is still uncertain, but the apolipoprotein E (APOE) ε4 genotype plays a major role. We aimed to identify the molecular pathways associated with amyloid β aggregation using cerebrospinal fluid (CSF) proteomics and to study the potential modifying effects of APOE ε4 genotype.

Methods

We tested 243 proteins and protein fragments in CSF comparing 193 subjects with AD across the cognitive spectrum (65% APOE ε4 carriers, average age 75 ± 7 years) against 60 controls with normal CSF amyloid β, normal cognition, and no APOE ε4 allele (average age 75 ± 6 years).

Results

One hundred twenty-nine proteins (53%) were associated with aggregated amyloid β. APOE ε4 carriers with AD showed altered concentrations of proteins involved in the complement pathway and glycolysis when cognition was normal and lower concentrations of proteins involved in synapse structure and function when cognitive impairment was moderately severe. APOE ε4 non-carriers with AD showed lower expression of proteins involved in synapse structure and function when cognition was normal and lower concentrations of proteins that were associated with complement and other inflammatory processes when cognitive impairment was mild. Repeating analyses for 114 proteins that were available in an independent EMIF-AD MBD dataset (n = 275) showed that 80% of the proteins showed group differences in a similar direction, but overall, 28% effects reached statistical significance (ranging between 6 and 87% depending on the disease stage and genotype), suggesting variable reproducibility.

Conclusions

These results imply that AD pathophysiology depends on APOE genotype and that treatment for AD may need to be tailored according to APOE genotype and severity of the cognitive impairment.

Apolipoprotein E Triggers Complement Activation in Joint Synovial Fluid of Rheumatoid Arthritis Patients by Binding C1q

We identified apolipoprotein E (ApoE) as one of the proteins that are found in complex with complement component C4d in pooled synovial fluid of rheumatoid arthritis (RA) patients. Immobilized human ApoE activated both the classical and the alternative complement pathways. In contrast, ApoE in solution demonstrated an isoform-dependent inhibition of hemolysis and complement deposition at the level of sC5b-9. Using electron microscopy imaging, we confirmed that ApoE interacts differently with C1q depending on its context; surface-bound ApoE predominantly bound C1q globular heads, whereas ApoE in a solution favored the hinge/stalk region of C1q. As a model for the lipidated state of ApoE in lipoprotein particles, we incorporated ApoE into phosphatidylcholine/phosphatidylethanolamine liposomes and found that the presence of ApoE on liposomes increased deposition of C1q and C4b from serum when analyzed using flow cytometry. In addition, posttranslational modifications associated with RA, such as citrullination and oxidation, reduced C4b deposition, whereas carbamylation enhanced C4b deposition on immobilized ApoE. Posttranslational modification of ApoE did not alter C1q interaction but affected binding of complement inhibitors factor H and C4b-binding protein. This suggests that changed ability of C4b to deposit on modified ApoE may play an important role. Our data show that posttranslational modifications of ApoE alter its interactions with complement. Moreover, ApoE may play different roles in the body depending on its solubility, and in diseased states such as RA, deposited ApoE may induce local complement activation rather than exert its typical role of inhibition.

Invited Review: APOE at the interface of inflammation, neurodegeneration and pathological protein spread in Alzheimer's disease

Despite more than a century of research, the aetiology of sporadic Alzheimer's disease (AD) remains unclear and finding disease modifying treatments for AD presents one of the biggest medical challenges of our time. AD pathology is characterized by deposits of aggregated amyloid beta (Aβ) in amyloid plaques and aggregated tau in neurofibrillary tangles. These aggregates begin in distinct brain regions and spread throughout the brain in stereotypical patterns. Neurodegeneration, comprising loss of synapses and neurons, occurs in brain regions with high tangle pathology, and an inflammatory response of glial cells appears in brain regions with pathological aggregates. Inheriting an apolipoprotein E ε4 (APOE4) allele strongly increases the risk of developing AD for reasons that are not yet entirely clear. Substantial amounts of evidence support a role for APOE in modulating the aggregation and clearance of Aβ, and data have been accumulating recently implicating APOE4 in exacerbating neurodegeneration, tau pathology and inflammation. We hypothesize that APOE4 influences all the pathological hallmarks of AD and may sit at the interface between neurodegeneration, inflammation and the spread of pathologies through the brain. Here, we conducted a systematic search of the literature and review evidence supporting a role for APOE4 in neurodegeneration and inflammation. While there is no direct evidence yet for APOE4 influencing the spread of pathology, we postulate that this may be found in future based on the literature reviewed here. In conclusion, this review highlights the importance of understanding the role of APOE in multiple important pathological mechanisms in AD.

Insulin Signaling Impairment in the Brain as a Risk Factor in Alzheimer's Disease

Type 2 diabetes is a risk factor for developing Alzheimer’s disease (AD). The underlying mechanism that links up the two conditions seems to be the de-sensitization of insulin signaling. In patients with AD, insulin signaling was found to be de-sensitized in the brain, even if they did not have diabetes. Insulin is an important growth factor that regulates cell growth, energy utilization, mitochondrial function and replacement, autophagy, oxidative stress management, synaptic plasticity, and cognitive function. Insulin desensitization, therefore, can enhance the risk of developing neurological disorders in later life. Other risk factors, such as high blood pressure or brain injury, also enhance the likelihood of developing AD. All these risk factors have one thing in common – they induce a chronic inflammation response in the brain. Pro-inflammatory cytokines block growth factor signaling and enhance oxidative stress. The underlying molecular processes for this are described in the review. Treatments to re-sensitize insulin signaling in the brain are also described, such as nasal insulin tests in AD patients, or treatments with re-sensitizing hormones, such as leptin, ghrelin, glucagon-like peptide 1 (GLP-1),and glucose-dependent insulinotropic polypeptide (GIP). The first clinical trials show promising results and are a proof of concept that utilizing such treatments is valid.

Glial Contribution to Excitatory and Inhibitory Synapse Loss in Neurodegeneration

Synapse loss is an early feature shared by many neurodegenerative diseases, and it represents the major correlate of cognitive impairment. Recent studies reveal that microglia and astrocytes play a major role in synapse elimination, contributing to network dysfunction associated with neurodegeneration. Excitatory and inhibitory activity can be affected by glia-mediated synapse loss, resulting in imbalanced synaptic transmission and subsequent synaptic dysfunction. Here, we review the recent literature on the contribution of glia to excitatory/inhibitory imbalance, in the context of the most common neurodegenerative disorders. A better understanding of the mechanisms underlying pathological synapse loss will be instrumental to design targeted therapeutic interventions, taking in account the emerging roles of microglia and astrocytes in synapse remodeling.

CNS side effects of immune checkpoint inhibitors: preclinical models, genetics and multimodality therapy

Following cancer treatment, patients often report behavioral and cognitive changes. Novel cancer immunotherapeutics have the potential to produce sustained cancer survivorship, meaning patients will live longer with the side effects of treatment. Given the role of inflammatory pathways in mediating behavioral and cognitive impairments seen in cancer, we aim in this review to discuss emerging evidence for the contribution of immune checkpoint blockade to exacerbate these CNS effects. We discuss ongoing studies regarding the ability of immune checkpoint inhibitors to reach the brain and how treatment responses to checkpoint inhibitors may be modulated by genetic factors. We further consider the use of preclinical tumor-models to study the role of tumor status in CNS effects of immune checkpoint inhibitors and multimodality therapy.

Protective effects of Lingguizhugan decoction on amyloid-beta peptide (25-35)-induced cell injury: Anti-inflammatory effects

In the present study, a human neuroblastoma cell line (SH-SY5Y) and BV-2 microglia were treated with amyloid-β peptide (25-35), as a model of Alzheimer's disease, to evaluate the protective effects of 10-3-10-8 g/mL Lingguizhugan decoction and to examine the underlying anti-inflammatory mechanism. Lingguizhugan decoction significantly enhanced the viability of SH-SY5Y cells with amyloid-β peptide-induced injury, and lowered levels of interleukin-1β, interleukin-6, tumor necrosis factor-α and nitric oxide in the culture supernatant of activated BV-2 microglia. The effects of 10-3 g/mL Lingguizhugan decoction were more significant. These results suggest that Lingguizhugan decoction can protect SH-SY5Y cells against amyloid-β peptide (25-35)-induced injury in a dose-dependent manner by inhibiting overexpression of inflammatory factors by activated microglia.

Exploring the potential benefits of vaccinia virus complement control protein in controlling complement activation in pathogenesis of the central nervous system diseases

Aging is a major risk factor for the development of diseases related to the central nervous system (CNS), such as Alzheimer's disease (AD) and age-related macular degeneration (AMD). In both cases, linkage studies and genome-wide association studies found strong links with complement regulatory genes and disease risk. In AD, both CLU and CR1 genes were implicated in the late-onset form of the disease. In AMD, polymorphisms in CFH, CFB and C2 were similarly implicated. The cost of caring for patients with AD or AMD is approaching billions of dollars, and with the baby boomers reaching their 60's, this amount is likely to increase further. Intervention using complement inhibitors for individuals in their early 50s who are at a higher risk of disease development, (testing positive for genetic risk factors), could slow the progression of AD or AMD and possibly prevent the severity of late stage symptoms. Although we have used the vaccinia virus complement control protein (VCP) to elucidate the role of complement in CNS diseases, it has merely been an investigational tool but not the only possible potential therapeutic agent.

Apolipoprotein E, amyloid-beta, and neuroinflammation in Alzheimer's disease

Alzheimer's disease (AD) is characterized by the accumulation and deposition of amyloid-beta (Aβ) peptides in the brain. Neuroinflammation occurs in the AD brain and plays a critical role in the neurodegenerative pathology. Particularly, Aβ evokes an inflammatory response that leads to synaptic dysfunction, neuronal death, and neurodegeneration. Apolipoprotein E (ApoE) proteins are involved in cholesterol transport, Aβ binding and clearance, and synaptic functions in the brain. The ApoE4 isoform is a key risk factor for AD, while the ApoE2 isoform has a neuroprotective effect. However, studies have reached different conclusions about the roles of the isoforms; some show that both ApoE3 and ApoE4 have anti-inflammatory effects, while others show that ApoE4 causes a predisposition to inflammation or promotes an inflammatory response following lipopolysaccharide treatment. These discrepancies may result from the differences in models, cell types, experimental conditions, and inflammatory stimuli used. Further, little was known about the role of ApoE isoforms in the Aβ-induced inflammatory response and in the neuroinflammation of AD. Our recent work showed that ApoE isoforms differentially regulate and modify the Aβ-induced inflammatory response in neural cells, with ApoE2 suppressing and ApoE4 promoting the response. In this article, we review the roles, mechanisms, and interrelations among Aβ, ApoE, and neuroinflammation in AD.

A shift in microglial β-amyloid binding in Alzheimer's disease is associated with cerebral amyloid angiopathy

Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA) are two common pathologies associated with β-amyloid (Aβ) accumulation and inflammation in the brain; neither is well understood. The objective of this study was to evaluate human post-mortem brains from AD subjects with purely parenchymal pathology, and those with concomitant CAA (and age-matched controls) for differential expression of microglia-associated Aβ ligands thought to mediate Aβ clearance and the association of these receptors with complement activation. Homogenates of brain parenchyma and enriched microvessel fractions from occipital cortex were probed for levels of C3b, membrane attack complex (MAC), CD11b and α-2-macroglobulin and immunoprecipitation was used to immunoprecipitate (IP) CD11b complexed with C3b and Aβ. Both C3b and MAC were significantly increased in CAA compared to AD-only and controls and IP showed significantly increased CD11b/C3b complexes with Aβ in AD/CAA subjects. Confocal microscopy was used to visualize these interactions. MAC was remarkably associated with CAA-affected blood vessels compared to AD-only and control vessels. These findings are consistent with an Aβ clearance mechanism via microglial CD11b that delivers Aβ and C3b to blood vessels in AD/CAA, which leads to Aβ deposition and propagation of complement to the cytolytic MAC, possibly leading to vascular fragility.

Apolipoprotein E isoforms and regulation of the innate immune response in brain of patients with Alzheimer's disease

The largest genetic risk for late-onset Alzheimer's disease (AD) resides at the apolipoprotein E gene (APOE) locus, which has three common alleles (ɛ2, ɛ3, ɛ4) that encode three isoforms (apoE2, apoE3, apoE4). The very strong association of the APOE ɛ4 allele with AD risk and its role in the accumulation of amyloid β in brains of people and animal models solidify the biological relevance of apoE isoforms but do not provide mechanistic insight. The innate immune response is consistently observed in AD and is a likely contributor to neuronal injury and response to injury. Here we review emerging data showing that apoE isoform regulation of multiple facets of the innate immune response in the brain may alter AD not only through amyloid β-dependent mechanisms, but also through other, amyloid β-independent mechanisms.

Aging, Neurodegenerative Disease and the Brain

L'eorganisation anatomique et chimique du cerveau humain subit de nombreux changements au cours du vieillissement. Certains neurons meurent, d'autres s'atrophient et ily a une réduction marquée du nombre de synapses dans des régions spécifiques du cerveau. Des diminutions du métabolisme du glucose et des effets pré- et post-synaptiques des neurotransmetteurs ont aussi été rapportées. À l'exception de certaines structures sous-corticales, il existe cependant une controverse quant à la sévérité des changements dans l'ensemble du cerveau. De plus, les effets du vieillissement sont très variables d'une région du cerveau à l'autre ainsi que d'un individu à l'autre. Certains phénomènes observès dans le vieillissement normal, tels la perte des neurones dopaminergique de la substance noire et celle des neurones cholinergiques du prosencé;phale basal, apparaissent sous une forme grandement exacerbées dans diverses pathologies neurodégénératives comme les maladies de Parkinson et d'Alzeimer. Les faibles altérations qui surviennent au niveau de ces systémes lors du vieillissement normal pourraient étre responsables des troubles d'équilibre, de la pauvreté de mouvement et des pertes de mémoires que l'on observent chez les gens âgés. Cependant, l'inflammation chronique du cerveau semble être une caractéristique typique des individus atteints de maladies neurodégénératives. L'hypothèse voulant que cette inflammation puisse être ralentie par un traitement avec des agents anti-inflammatoires a été supportée par les résultats de 19 études épidémiologiques ainsi que par un essai clinique de moindre envergure. Cependant, d'Autres études cliniques devront ètre réalisées et une attention particulière devra être portée aux effets secondaires de la thérapie anti-inflammatoire conventionnelle afin d'en arriver à une conclusion définitive.

Clearance mechanisms of Alzheimer's amyloid-beta peptide: implications for therapeutic design and diagnostic tests

Currently, the 'amyloid hypothesis' is the most widely accepted explanation for the pathogenesis of Alzheimer's disease (AD). According to this hypothesis, altered metabolism of the amyloid-beta (Abeta) peptide is central to the pathological cascade involved in the pathogenesis of AD. Although Abeta is produced by almost every cell in the body, a physiological function for the peptide has not been determined, and the pathways by which Abeta leads to cognitive dysfunction and cell death are unclear. Numerous therapeutic approaches that target the production, toxicity and removal of Abeta are being developed worldwide. Although therapeutic treatment for AD may be imminent, the value and effectiveness of such treatment are largely dependent on early diagnosis of the disease. This review summarizes current knowledge of Abeta clearance, transport and degradation, and evaluates the use of such information in the development of diagnostic tools. The conflicting results of plasma Abeta ELISAs are discussed, as are the more promising results of Abeta imaging by positron emission tomography. Current knowledge of Abeta-binding proteins and Abeta-degrading enzymes is analysed in the context of a potential therapy for AD. Transport across the blood-brain barrier by the receptor for advanced glycation end products and efflux via the multi-ligand lipoprotein receptor LRP-1 is also reviewed. Enhancing clearance and degradation of Abeta remains an attractive therapeutic strategy, and improved understanding of Abeta clearance may lead to advances in diagnostics and interventions designed to prevent or delay the onset of AD.

Complement activation by islet amyloid polypeptide (IAPP) and alpha-synuclein 112

Complement can damage host tissue when overactivated. Evidence of complement self damage exists for Alzheimer disease (AD), age-related macular degeneration, type 1 diabetes mellitus (T1DM), and Parkinson disease (PD). Known complement activators include Abeta, found in AD, and IgG found in T1DM. We compared their complement activating ability in vitro with those of islet amyloid polypeptide (IAPP), which aggregates in the pancreas of T2DM, and alpha-synuclein (alpha-Syn), which aggregates in PD. We found that IAPP and the alternatively spliced alpha-Syn 112 form, but not full-length alpha-Syn 140, activated complement in vitro. Complement activation may contribute to death of insulin-secreting cells in T2DM or to neuronal death in Parkinson disease (PD) and related synucleinopathies where alpha-Syn 112 occurs. This suggests the possibility of anti-inflammatory treatment in these pathologies. It also suggests that blockers of complement activation may be an appropriate therapeutic target for a range of age-related degenerative diseases.

Apolipoprotein E epsilon 4 is associated with an increased vulnerability to cell death in Alzheimer’s disease

The presumption to suffer from Alzheimer's disease (AD) accelerates with aging. One important risk factor seems to be the isoform epsilon 4 of the apolipoprotein E gene (Apo epsilon 4), which increases the risk to develop AD at an earlier age. Furthermore, convincing evidence is provided that apoptotic cell death mechanisms play an important role in neuronal cell death in AD. In the present study, we investigated whether abnormalities in apoptosis and caspase-3 activity can be found at the level of lymphocytes and a T cell subtype, CD4 T cells, from AD patients compared to aged sex- and ApoE genotype-matched non-demented controls. Under different experimental conditions (at baseline or after in vitro incubation in the presence of proapoptotic stimuli) increased levels of apoptosis and enhanced caspase-3 activity were detected in lymphocytes from AD patients. This difference was most pronounced in the CD4(+) T cell subtype. Notably, we found a significant increase of apoptotic cells and caspase-3 activity in lymphocytes from AD patients bearing one or two alleles of the ApoE4 compared to non-E4 carriers. Again, these effects were strongest in CD4(+) T cells. Circulating amyloid-beta (A beta) levels did not differ between AD patients bearing ApoE4 and non-ApoE4 and age-matched controls. Therefore, it is likely that circulating A beta is not responsible for the observed effects, which might rather reflect an ongoing systemic response in AD, e.g. an increase in CD95 expression.

Lack of apolipoprotein-E exacerbates experimental allergic encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) was found to have a chronic and significantly worse course in apolipoprotein-E (apoE) deficient female mice when compared with matched controls. Disease measures compared included incidence of EAE (64% versus 31%, P < 0.05, chi2 test), maximal clinical score (average +/- SD 2.81 +/- 2.5 versus 0.75 +/- 1.1, P < 0.01, Mann-Whitney test) and mortality (27.3% versus 0%, P = 0.02, Mann-Whitney test and chi2 test). ApoE deficient mice had significantly increased lymphocyte proliferation responses to both myelin antigens and mitogens and significantly more infiltrating lesions in the central nervous system (CNS) in histopathology. Defective neuronal repair mechanisms and enhanced immune reactivity in apoE deficient mice may explain our findings. Clinical implications for MS are discussed.

Clinical manifestations of cerebral amyloid angiopathy-related inflammation

To explore the clinical effects of inflammation associated with vascular deposits of the amyloid beta peptide (A beta), we analyzed 42 consecutive patients with pathologically diagnosed cerebral amyloid angiopathy (CAA) for evidence of an inflammatory response. Inflammation with giant-cell reaction surrounding amyloid-laden vessels was identified in 7 of the 42 cases. The clinical symptoms in each of the seven were subacute cognitive decline or seizure rather than hemorrhagic stroke, the primary clinical presentation in 33 of 35 patients with noninflammatory CAA (p < 0.001). Inflammatory CAA also was associated with radiographic white matter abnormalities, significantly younger age at presentation, and a marked overrepresentation of the apolipoprotein E epsilon 4/epsilon 4 genotype (71% vs 4%, p < 0.001). Of the six inflammatory CAA patients with available follow-up information, five demonstrated clinical and radiographic improvement after immunosuppressive treatment. The syndrome of CAA-related perivascular inflammation appears to represent a subset of CAA with clinically distinct symptoms that may respond to immunosuppressive treatment. These data add to evidence that inflammation against A beta can cause vascular dysfunction, a potential mechanism for the toxic response recently observed in clinical trials of A beta immunization.

Meat‐Adaptive Genes and the Evolution of Slower Aging in Humans

The chimpanzee life span is shorter than that of humans, which is consistent with a faster schedule of aging. We consider aspects of diet that may have selected for genes that allowed the evolution of longer human life spans with slower aging. Diet has changed remarkably during human evolution. All direct human ancestors are believed to have been largely herbivorous. Chimpanzees eat more meat than other great apes, but in captivity are sensitive to hypercholesterolemia and vascular disease. We argue that this dietary shift to increased regular consumption of fatty animal tissues in the course of hominid evolution was mediated by selection for "meat-adaptive" genes. This selection conferred resistance to disease risks associated with meat eating also increased life expectancy. One candidate gene is apolipoprotein E (apoE), with the E3 allele evolved in the genus Homo that reduces the risks for Alzheimer's and vascular disease, as well as influencing inflammation, infection, and neuronal growth. Other evolved genes mediate lipid metabolism and host defense. The timing of the evolution of apoE and other candidates for meat-adaptive genes is discussed in relation to key events in human evolution.

Effect of apolipoprotein E genotype on cerebral autoregulation during cardiopulmonary bypass

BACKGROUND AND PURPOSE

The presence of the apolipoprotein E epsilon4 (apoE4) allele has been associated with cognitive decline after cardiac surgery. We compared autoregulation of cerebral blood flow (CBF), cerebral metabolic rate for oxygen (CMRO(2)), and arterial-venous oxygen content difference [C(A-V)O(2)], during cardiopulmonary bypass (CPB) in patients with and without the apoE4 allele to help define the mechanism of association with cognitive decline.

METHODS

One hundred fifty-four patients underwent coronary artery bypass grafting with CPB, nonpulsatile flow, and alpha-stat management. CBF was measured by using (133)Xe washout methods. C(A-V)O(2), CMRO(2), and oxygen delivery were calculated. Pressure-flow autoregulation was tested by using 2 CBF measurements at stable hypothermia: the first at stable mean arterial pressure (MAP) and the second 15 minutes later, when MAP had increased or decreased >/=20%. Metabolism-flow autoregulation was tested by varying the temperature and measuring the coupling of CBF and CMRO(2).

RESULTS

In patients with (n=41) or without (n=113) the apoE4 allele, there were no differences in CBF, CMRO(2), C(A-V)O(2), pressure-flow and metabolism-flow autoregulation corrected for age, gender, non-insulin-dependent diabetes, hemoglobin, CPB time, and temperature.

CONCLUSIONS

We conclude that apoE genotype does not affect global CBF and oxygen delivery/extraction during CPB, which suggests that other mechanisms are responsible for the apoE isoform-related neurocognitive dysfunction seen in patients undergoing CPB.

A unifying hypothesis of Alzheimer's disease. III. Risk factors

Normal ageing and Alzheimer's disease (AD) have many features in common and, in many respects, both conditions only differ by quantitative criteria. A variety of genetic, medical and environmental factors modulate the ageing-related processes leading the brain into the devastation of AD. In accordance with the concept that AD is a metabolic disease, these risk factors deteriorate the homeostasis of the Ca(2+)-energy-redox triangle and disrupt the cerebral reserve capacity under metabolic stress. The major genetic risk factors (APP and presenilin mutations, Down's syndrome, apolipoprotein E4) are associated with a compromise of the homeostatic triangle. The pathophysiological processes leading to this vulnerability remain elusive at present, while mitochondrial mutations can be plausibly integrated into the metabolic scenario. The metabolic leitmotif is particularly evident with medical risk factors which are associated with an impaired cerebral perfusion, such as cerebrovascular diseases including stroke, cardiovascular diseases, hypo- and hypertension. Traumatic brain injury represents another example due to the persistent metabolic stress following the acute event. Thyroid diseases have detrimental sequela for cerebral metabolism as well. Furthermore, major depression and presumably chronic stress endanger susceptible brain areas mediated by a host of hormonal imbalances, particularly the HPA-axis dysregulation. Sociocultural and lifestyle factors like education, physical activity, diet and smoking may also modulate the individual risk affecting both reserve capacity and vulnerability. The pathophysiological relevance of trace metals, including aluminum and iron, is highly controversial; at any rate, they may adversely affect cellular defences, antioxidant competence in particular. The relative contribution of these factors, however, is as individual as the pattern of the factors. In familial AD, the genetic factors clearly drive the sequence of events. A strong interaction of fat metabolism and apoE polymorphism is suggested by intercultural epidemiological findings. In cultures, less plagued by the 'blessings' of the 'cafeteria diet-sedentary' Western lifestyle, apoE4 appears to be not a risk factor for AD. This intriguing evidence suggests that, analogous to cardiovascular diseases, apoE4 requires a hyperlipidaemic lifestyle to manifest as AD risk factor. Overall, the etiology of AD is a key paradigm for a gene-environment interaction. Copyright 2000 John Wiley & Sons, Ltd.

Complement activation by the amyloid proteins A beta peptide and beta 2-microglobulin

Complement activation (CA) has been reported to play a role in the pathogenesis of Alzheimer's disease (AD). To investigate whether CA may contribute to amyloidogenesis in general, the CA potential of different amyloid fibril proteins was tested. CA induced by A beta preparations containing soluble protein, protofilaments and some fibrils or only fibrils in a solid phase system (ELISA) was modest with a slow kinetics compared to the positive delta IgG control. Soluble A beta induced no detectable CA in a liquid phase system (complement consumption assay) while fibrillar A beta caused CA at 200 mg/ml and higher concentrations. Soluble beta 2-microglobulin (beta 2M) purified from peritoneal dialysates was found to be as potent a complement activator as A beta in both solid and liquid phase systems while beta 2M purified from urine exhibited lower activity, a difference which may be explained by differences observed in SDS-resistant oligomers and isoforms. Soluble Amyloid A-protein caused no significant CA. A beta and beta 2M activated complement via the classical pathway. The modifying influence by amyloid-associated molecules on A beta-induced CA was also investigated, but neither serum amyloid P component nor heparan sulfate did significantly alter the A beta-induced CA. The results indicate that not only fibrillar A beta but also oligomers of, in particular, beta 2M from patients with dialysis-associated amyloidosis are capable of inducing CA at supra-physiological concentrations.

Abnormalities of protein kinases in neurodegenerative diseases

In neurodegenerative diseases such as ALS and AD there is evidence for abnormal regulation of protein kinases. In these diseases, altered activities and protein levels of several specific kinases suggest that abnormal phosphorylation is present and this aberrant phosphorylation may be involved in the pathogenesis of these diseases. The observation that regulation of the NMDA receptor ion channel is altered in tissue from ALS patients may arise from the abnormal phosphorylation state of the protein kinase regulating NMDA receptor function. Whether the abnormalities of these protein kinases is a primary event leading to altered receptor regulation or vice versa is still poorly understood. The seemingly multiple pathogenic mechanisms of ALS and AD create complexity in assessing a primary cause that may lead to cell death. The mechanisms causing cell death (apoptosis or necrosis) may be overlapping with integrated events among the components interacting and contributing to a final pathway for neuron death. Thus, evidence of impairment in protein kinase signalling in these diseases may be a primary cause, a secondary event, or a compensatory mechanism. To further study this issue, different model systems could be beneficial to obtain a better understanding of these diseases.

Enhanced upregulation of the Fc gamma receptor IIIa (CD16a) during in vitro differentiation of ApoE4/4 monocytes

We recently reported a positive correlation of the pool size of lipopolysaccharide receptor (CD14)dim and Fc gamma receptor IIIa (CD16a)+ monocytes in peripheral blood to the apolipoprotein E4 (apoE4) phenotype and a negative correlation to high density lipoprotein (HDL) cholesterol levels (Arterioscler Thromb Vasc Biol. 1996;16:1437-1447). In this study, the in vitro differentiation of mononuclear phagocytes derived from healthy blood donors homozygous for the E3/3 or the E4/4 phenotype was analyzed during 7 days of culture in serum-free medium supplemented with macrophage colony-stimulating factor (M-CSF). The CD16a expression, which indicates Fc receptor-dependent phagocytic activity, increased to a significantly higher level in apoE4/4 monocytes than in apoE3/3 cells. The costimulatory molecule CD40, which indicates antigen-presenting capacity, was upregulated more strongly in apoE3/3 monocytes compared with E4/4 cells, but the difference did not reach a significant level. The expression of differentiation-associated surface proteins (CD14, CD33, CD45) and adhesion molecules (CD11a, CD11b, CD11c, CD49d) was not significantly different between apoE3/3 and apoE4/4 monocytes. However, a significantly decreased intracellular apoE concentration and a reduced amount of secreted apoE were found in apoE4/4 monocytes during in vitro differentiation. No differences were found in the surface expression of the low density lipoprotein receptor-related protein (CD91) and the uptake of fluorescence labeled low density lipoprotein between apoE3/3 and apoE4/4 monocytes. These data indicate that the apoE4/4 phenotype significantly influences the M-CSF-dependent differentiation of monocytes toward a more CD16a-positive phagocytic phenotype.

Biology of A beta amyloid in Alzheimer's disease

The genetic associations with the pathological features of AD are diverse: A rapidly growing number of mutations in presenilin 1 and 2 on chromosomes 14 and 1, respectively, are found in many early-onset FAD patients (Lendon et al., 1997). In addition, beta PP mutations are found in a small percentage of early-onset FAD kindreds. The apoE4 allele on chromosome 19 is associated with the presence of the most common form of AD, sporadic AD (Wisniewski & Frangione, 1992; Namba et al., 1991). However, it is clear that other proteins are also involved in the pathogenesis of AD, since some early-onset FAD kindreds do not have linkage to PS1, PS2, apoE, or beta PP, while at least 50% of late-onset AD is unrelated to apoE. Other proteins which have been implicated in the formation of senile plaques, but so far are not known to have any genetic linkage to AD, include proteoglycans (Snow et al., 1987), apoA1 (Wisniewski et al., 1995a), alpha 1-antichymotrypsin (Abraham et al., 1988), HB-GAM (Wisniewski et al., 1996a), complement components (McGeer & Rogers, 1992), acetylcholinesterase (Friede, 1965), and NAC (Ueda et al., 1993). Which of these proteins will be the most important for the etiology of the most common form of AD, late-onset sporadic AD, remains an open question. Three of the genes which are now known to be linked to AD, including PS1, beta PP, and apoE, have been established immunohistochemically and biochemically to be components of senile plaques (see Fig. 1). This raises at least two possibilities: either each of these proteins is part of one pathway with A beta-related amyloid formation as a final causative pathogenic event or amyloid deposition in AD is a reactive process related to dysfunction of a number of different CNS proteins. Whether or not amyloid formation is directly causative in the pathogenesis of AD, current data suggest that new therapeutic approaches which may inhibit the aggregation and/or the conformational change of sA beta to A beta fibrils (Soto et al., 1996) have the greatest likelihood to make a significant impact on controlling amyloid accumulation in AD.