Apolipoprotein E isoform mediated regulation of nitric oxide release

Temporal Characterization of the Amyloidogenic APPswe/PS1dE9;hAPOE4 Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is a devastating disorder with a global prevalence estimated at 55 million people. In clinical studies administering certain anti-beta-amyloid (Aβ) antibodies, amyloid-related imaging abnormalities (ARIAs) have emerged as major adverse events. The frequency of these events is higher among apolipoprotein ε4 allele carriers (APOE4) compared to non-carriers. To reflect patients most at risk for vascular complications of anti-Aβ immunotherapy, we selected an APPswe/PS1dE9 transgenic mouse model bearing the human APOE4 gene (APPPS1:E4) and compared it with the same APP/PS1 mouse model bearing the human APOE3 gene (APOE ε3 allele; APPPS1:E3). Using histological and biochemical analyses, we characterized mice at three ages: 8, 12, and 16 months. Female and male mice were assayed for general cerebral fibrillar and pyroglutamate (pGlu-3) Aβ deposition, cerebral amyloid angiopathy (CAA), microhemorrhages, apoE and cholesterol composition, astrocytes, microglia, inflammation, lysosomal dysfunction, and neuritic dystrophy. Amyloidosis, lipid deposition, and astrogliosis increased with age in APPPS1:E4 mice, while inflammation did not reveal significant changes with age. In general, APOE4 carriers showed elevated Aβ, apoE, reactive astrocytes, pro-inflammatory cytokines, microglial response, and neuritic dystrophy compared to APOE3 carriers at different ages. These results highlight the potential of the APPPS1:E4 mouse model as a valuable tool in investigating the vascular side effects associated with anti-amyloid immunotherapy.

Vivaria housing conditions expose sex differences in brain oxidation, microglial activation, and immune system states in aged hAPOE4 mice

Apolipoprotein E ε4 allele (APOE4) is the predominant genetic risk factor for late-onset Alzheimer's disease (AD). APOE4 mouse models have provided advances in the understanding of disease pathogenesis, but unaccounted variables like rodent housing status may hinder translational outcomes. Non-sterile aspects like food and bedding can be major sources of changes in rodent microflora. Alterations in intestinal microbial ecology can cause mucosal barrier impairment and increase pro-inflammatory signals. The present study examined the role of sterile and non-sterile food and housing on redox indicators and the immune status of humanized-APOE4 knock-in mice (hAPOe4). hAPOE4 mice were housed under sterile conditions until 22 months of age, followed by the transfer of a cohort of mice to non-sterile housing for 2 months. At 24 months of age, the redox/immunologic status was evaluated by flow cytometry/ELISA. hAPOE4 females housed under non-sterile conditions exhibited: (1) higher neuronal and microglial oxygen radical production and (2) lower CD68+ microglia (brain) and CD8+ T cells (periphery) compared to sterile-housed mice. In contrast, hAPOE4 males in non-sterile housing exhibited: (1) higher MHCII+ microglia and CD11b+CD4+ T cells (brain) and (2) higher CD11b+CD4+ T cells and levels of lipopolysaccharide-binding protein and inflammatory cytokines in the periphery relative to sterile-housed mice. This study demonstrated that sterile vs. non-sterile housing conditions are associated with the activation of redox and immune responses in the brain and periphery in a sex-dependent manner. Therefore, housing status may contribute to variable outcomes in both the brain and periphery.

Oxidative damage in neurodegeneration: roles in the pathogenesis and progression of Alzheimer disease

Alzheimer disease (AD) is associated with multiple etiologies and pathological mechanisms, among which oxidative stress (OS) appears as a major determinant. Intriguingly, OS arises in various pathways regulating brain functions, and it seems to link different hypotheses and mechanisms of AD neuropathology with high fidelity. The brain is particularly vulnerable to oxidative damage, mainly because of its unique lipid composition, resulting in an amplified cascade of redox reactions that target several cellular components/functions ultimately leading to neurodegeneration. The present review highlights the "OS hypothesis of AD," including amyloid beta-peptide-associated mechanisms, the role of lipid and protein oxidation unraveled by redox proteomics, and the antioxidant strategies that have been investigated to modulate the progression of AD. Collected studies from our groups and others have contributed to unraveling the close relationships between perturbation of redox homeostasis in the brain and AD neuropathology by elucidating redox-regulated events potentially involved in both the pathogenesis and progression of AD. However, the complexity of AD pathological mechanisms requires an in-depth understanding of several major intracellular pathways affecting redox homeostasis and relevant for brain functions. This understanding is crucial to developing pharmacological strategies targeting OS-mediated toxicity that may potentially contribute to slow AD progression as well as improve the quality of life of persons with this severe dementing disorder.

APOE modulates microglial immunometabolism in response to age, amyloid pathology, and inflammatory challenge

The E4 allele of Apolipoprotein E (APOE) is associated with both metabolic dysfunction and a heightened pro-inflammatory response: two findings that may be intrinsically linked through the concept of immunometabolism. Here, we combined bulk, single-cell, and spatial transcriptomics with cell-specific and spatially resolved metabolic analyses in mice expressing human APOE to systematically address the role of APOE across age, neuroinflammation, and AD pathology. RNA sequencing (RNA-seq) highlighted immunometabolic changes across the APOE4 glial transcriptome, specifically in subsets of metabolically distinct microglia enriched in the E4 brain during aging or following an inflammatory challenge. E4 microglia display increased Hif1α expression and a disrupted tricarboxylic acid (TCA) cycle and are inherently pro-glycolytic, while spatial transcriptomics and mass spectrometry imaging highlight an E4-specific response to amyloid that is characterized by widespread alterations in lipid metabolism. Taken together, our findings emphasize a central role for APOE in regulating microglial immunometabolism and provide valuable, interactive resources for discovery and validation research.

LilrB3 is a putative cell surface receptor of APOE4

The three isoforms of apolipoprotein E (APOE2, APOE3, and APOE4) only differ in two amino acid positions but exert quite different immunomodulatory effects. The underlying mechanism of such APOE isoform dependence remains enigmatic. Here we demonstrate that APOE4, but not APOE2, specifically interacts with the leukocyte immunoglobulin-like receptor B3 (LilrB3). Two discrete immunoglobin-like domains of the LilrB3 extracellular domain (ECD) recognize a positively charged surface patch on the N-terminal domain (NTD) of APOE4. The atomic structure reveals how two APOE4 molecules specifically engage two LilrB3 molecules, bringing their intracellular signaling motifs into close proximity through formation of a hetero-tetrameric complex. Consistent with our biochemical and structural analyses, APOE4, but not APOE2, activates human microglia cells (HMC3) into a pro-inflammatory state in a LilrB3-dependent manner. Together, our study identifies LilrB3 as a putative immune cell surface receptor for APOE4, but not APOE2, and may have implications for understanding the biological functions as well as disease relevance of the APOE isoforms.

A multi-hit hypothesis for an APOE4-dependent pathophysiological state

The APOE gene encoding the Apolipoprotein E protein is the single most significant genetic risk factor for late-onset Alzheimer's disease. The APOE4 genotype confers a significantly increased risk relative to the other two common genotypes APOE3 and APOE2. Intriguingly, APOE4 has been associated with neuropathological and cognitive deficits in the absence of Alzheimer's disease-related amyloid or tau pathology. Here, we review the extensive literature surrounding the impact of APOE genotype on central nervous system dysfunction, focussing on preclinical model systems and comparison of APOE3 and APOE4, given the low global prevalence of APOE2. A multi-hit hypothesis is proposed to explain how APOE4 shifts cerebral physiology towards pathophysiology through interconnected hits. These hits include the following: neurodegeneration, neurovascular dysfunction, neuroinflammation, oxidative stress, endosomal trafficking impairments, lipid and cellular metabolism disruption, impaired calcium homeostasis and altered transcriptional regulation. The hits, individually and in combination, leave the APOE4 brain in a vulnerable state where further cumulative insults will exacerbate degeneration and lead to cognitive deficits in the absence of Alzheimer's disease pathology and also a state in which such pathology may more easily take hold. We conclude that current evidence supports an APOE4 multi-hit hypothesis, which contributes to an APOE4 pathophysiological state. We highlight key areas where further study is required to elucidate the complex interplay between these individual mechanisms and downstream consequences, helping to frame the current landscape of existing APOE-centric literature.

Sex and APOE Genotype Alter the Basal and Induced Inflammatory States of Primary Microglia from APOE Targeted Replacement Mice

The sex and APOE4 genotype are significant risk factors for Alzheimer’s disease (AD); however, the mechanism(s) responsible for this interaction are still a matter of debate. Here, we assess the responses of mixed-sex and sex-specific APOE3 and APOE4 primary microglia (PMG) to lipopolysaccharide and interferon-gamma. In our investigation, inflammatory cytokine profiles were assessed by qPCR and multiplex ELISA assays. Mixed-sex APOE4 PMG exhibited higher basal mRNA expression and secreted levels of TNFa and IL1b. In sex-specific cultures, basal expression and secreted levels of IL1b, TNFa, IL6, and NOS2 were 2−3 fold higher in APOE4 female PMG compared to APOE4 males, with both higher than APOE3 cells. Following an inflammatory stimulus, the expression of pro-inflammatory cytokines and the secreted cytokine level were upregulated in the order E4 female > E4 male > E3 female > E3 male in sex-specific cultures. These data indicate that the APOE4 genotype and female sex together contribute to a greater inflammatory response in PMG isolated from targeted replacement humanized APOE mice. These data are consistent with clinical data and indicate that sex-specific PMG may provide a platform for exploring mechanisms of genotype and sex differences in AD related to neuroinflammation and neurodegeneration.

The Blood-Brain Barrier, Oxidative Stress, and Insulin Resistance

The blood–brain barrier (BBB) is a network of specialized endothelial cells that regulates substrate entry into the central nervous system (CNS). Acting as the interface between the periphery and the CNS, the BBB must be equipped to defend against oxidative stress and other free radicals generated in the periphery to protect the CNS. There are unique features of brain endothelial cells that increase the susceptibility of these cells to oxidative stress. Insulin signaling can be impacted by varying levels of oxidative stress, with low levels of oxidative stress being necessary for signaling and higher levels being detrimental. Insulin must cross the BBB in order to access the CNS, levels of which are important in peripheral metabolism as well as cognition. Any alterations in BBB transport due to oxidative stress at the BBB could have downstream disease implications. In this review, we cover the interactions of oxidative stress at the BBB, how insulin signaling is related to oxidative stress, and the impact of the BBB in two diseases greatly affected by oxidative stress and insulin resistance: diabetes mellitus and Alzheimer’s disease.

Reassessment of Pioglitazone for Alzheimer's Disease

Alzheimer's disease is a quintessential 'unmet medical need', accounting for ∼65% of progressive cognitive impairment among the elderly, and 700,000 deaths in the United States in 2020. In 2019, the cost of caring for Alzheimer's sufferers was $244B, not including the emotional and physical toll on caregivers. In spite of this dismal reality, no treatments are available that reduce the risk of developing AD or that offer prolonged mitiagation of its most devestating symptoms. This review summarizes key aspects of the biology and genetics of Alzheimer's disease, and we describe how pioglitazone improves many of the patholophysiological determinants of AD. We also summarize the results of pre-clinical experiments, longitudinal observational studies, and clinical trials. The results of animal testing suggest that pioglitazone can be corrective as well as protective, and that its efficacy is enhanced in a time- and dose-dependent manner, but the dose-effect relations are not monotonic or sigmoid. Longitudinal cohort studies suggests that it delays the onset of dementia in individuals with pre-existing type 2 diabetes mellitus, which small scale, unblinded pilot studies seem to confirm. However, the results of placebo-controlled, blinded clinical trials have not borne this out, and we discuss possible explanations for these discrepancies.

The Controversial Role of Glucose-6-Phosphate Dehydrogenase Deficiency on Cardiovascular Disease: A Narrative Review

Cardiovascular disorders (CVD) are highly prevalent and the leading cause of death worldwide. Atherosclerosis is responsible for most cases of CVD. The plaque formation and subsequent thrombosis in atherosclerosis constitute an ongoing process that is influenced by numerous risk factors such as hypertension, diabetes, dyslipidemia, obesity, smoking, inflammation, and sedentary lifestyle. Among the various risk and protective factors, the role of glucose-6-phosphate dehydrogenase (G6PD) deficiency, the most common inborn enzyme disorder across populations, is still debated. For decades, it has been considered a protective factor against the development of CVD. However, in the recent years, growing scientific evidence has suggested that this inherited condition may act as a CVD risk factor. The role of G6PD deficiency in the atherogenic process has been investigated using in vitro or ex vivo cellular models, animal models, and epidemiological studies in human cohorts of variable size and across different ethnic groups, with conflicting results. In this review, the impact of G6PD deficiency on CVD was critically reconsidered, taking into account the most recent acquisitions on molecular and biochemical mechanisms, namely, antioxidative mechanisms, glutathione recycling, and nitric oxide production, as well as their mutual interactions, which may be impaired by the enzyme defect in the context of the pentose phosphate pathway. Overall, current evidence supports the notion that G6PD downregulation may favor the onset and evolution of atheroma in subjects at risk of CVD. Given the relatively high frequency of this enzyme deficiency in several regions of the world, this finding might be of practical importance to tailor surveillance guidelines and facilitate risk stratification.

Fungal immunity and pathogenesis in mammals versus the invertebrate model organism Galleria mellonella

In recent decades, Galleria mellonella (Lepidoptera: Pyralidae) have emerged as a model system to explore experimental aspects of fungal pathogenesis. The benefits of the G. mellonella model include being faster, cheaper, higher throughput and easier compared with vertebrate models. Additionally, as invertebrates, their use is subject to fewer ethical and regulatory issues. However, for G. mellonella models to provide meaningful insight into fungal pathogenesis, the G. mellonella-fungal interactions must be comparable to mammalian-fungal interactions. Indeed, as discussed in the review, studies suggest that G. mellonella and mammalian immune systems share many similarities, and fungal virulence factors show conserved functions in both hosts. While the moth model has opened novel research areas, many comparisons are superficial and leave large gaps of knowledge that need to be addressed concerning specific mechanisms underlying G. mellonella-fungal interactions. Closing these gaps in understanding will strengthen G. mellonella as a model for fungal virulence in the upcoming years. In this review, we provide comprehensive comparisons between fungal pathogenesis in mammals and G. mellonella from immunological and virulence perspectives. When information on an antifungal immune component is unknown in G. mellonella, we include findings from other well-studied Lepidoptera. We hope that by outlining this information available in related species, we highlight areas of needed research and provide a framework for understanding G. mellonella immunity and fungal interactions.

Expression and secretion of apoE isoforms in astrocytes and microglia during inflammation

Neuroinflammation is a common feature in neurodegenerative diseases, modulated by the Alzheimer's disease risk factor, apolipoprotein E (APOE). In the brain, apoE protein is synthesized by astrocytes and microglia. We examined primary cultures of astrocytes and microglia from human APOE (E2, E3, and E4) targeted-replacement mice. Astrocytes secreted two species of apoE, whereas cellular apoE consisted of only one. Both forms of secreted astrocytic apoE were bound during glycoprotein isolation, and enzymatic removal of glycans produced a convergence of the two forms of apoE to a single form; thus, the two species of astrocyte-secreted apoE are differentially glycosylated. Microglia released only a single species of apoE, while cellular apoE consisted of two forms; the secreted apoE and one of the two forms of cellular apoE were glycosylated. We treated the primary glia with either endogenous (TNFα) or exogenous (LPS) pro-inflammatory stimuli. While LPS had no effect on astrocytic apoE, APOE2, and APOE3 microglia increased release of apoE; APOE4 microglia showed no effect. APOE4 microglia showed higher baseline secretion of TNFα compared to APOE2 and APOE3 microglia. TNFα treatment reduced the secretion and cellular expression of apoE only in APOE4 astrocytes. The patterns of apoE species produced by astrocytes and microglia were not affected by inflammation. No changes in APOE mRNA were observed in astrocytes after both treatments. Together, our data demonstrate that astrocytes and microglia differentially express and secrete glycosylated forms of apoE and that APOE4 astrocytes and microglia are deficient in immunomodulation compared to APOE2 and APOE3.

Apolipoprotein E and oxidative stress in brain with relevance to Alzheimer's disease

Inheritance of apolipoprotein E4 (APOE4) is a major risk factor for development of Alzheimer's disease (AD). This lipoprotein, in contrast to apoE2, has arginine residues at positions 112 and 158 in place of cysteines in the latter isoform. In apoE3, the Cys at residue 158 is replaced by an arginine residue. This differential amino acid composition of the three genotypes of APOE have profound influence on the structure, binding properties, and multiple functions of this lipoprotein. Moreover, AD brain is under a high degree of oxidative stress, including that associated with amyloid β-peptide (Aβ) oligomers. Lipid peroxidation produces the highly reactive and neurotoxic molecule, 4-hydroxynonenal (HNE) that forms covalent bonds with cysteine residues (Cys) [as well as with Lys and His residues]. Covalently modified Cys significantly alter structure and function of modified proteins. HNE bound to Cys residue(s) on apoE2 and apoE3 lessens the chance of HNE damage other proteins. apoE4, lacking Cys residues, is unable to scavenge HNE, permitting this latter neurotoxic molecule to lead to oxidative modification of neuronal proteins and eventual cell death. We posit that this lack of HNE scavenging activity in apoE4 significantly contributes to the association of APOE4 inheritance and increased risk of developing AD. Apoe knock-out mice provide insights into the role of this lipoprotein in oxidative stress. Targeted replacement mice in which the mouse gene of Apoe is separately replaced by the human APOE2, APOE3, or APOE4 genes, while keeping the mouse promoter assures the correct location and amount of the human protein isoform. Human APOE targeted replacement mice have been used to investigate the notion that oxidative damage to and death of neurons in AD and its earlier stages is related to APOE genotype. This current paper reviews the intersection of human APOE genotype, oxidative stress, and diminished function of this lipoprotein as a major contributing risk factor for development of AD. Discussion of potential therapeutic strategies to mitigate against the elevated risk of developing AD with inheritance of the APOE4 allele also is presented.

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.

The Role of APOE4 in Disrupting the Homeostatic Functions of Astrocytes and Microglia in Aging and Alzheimer's Disease

APOE4 is the greatest genetic risk factor for late-onset Alzheimer’s disease (AD), increasing the risk of developing the disease by 3-fold in the 14% of the population that are carriers. Despite 25 years of research, the exact mechanisms underlying how APOE4 contributes to AD pathogenesis remain incompletely defined. APOE in the brain is primarily expressed by astrocytes and microglia, cell types that are now widely appreciated to play key roles in the pathogenesis of AD; thus, a picture is emerging wherein APOE4 disrupts normal glial cell biology, intersecting with changes that occur during normal aging to ultimately cause neurodegeneration and cognitive dysfunction. This review article will summarize how APOE4 alters specific pathways in astrocytes and microglia in the context of AD and the aging brain. APOE itself, as a secreted lipoprotein without enzymatic activity, may prove challenging to directly target therapeutically in the classical sense. Therefore, a deeper understanding of the underlying pathways responsible for APOE4 toxicity is needed so that more tractable pathways and drug targets can be identified to reduce APOE4-mediated disease risk.

Interactions between inflammation, sex steroids, and Alzheimer's disease risk factors

Alzheimer's disease (AD) is an age-related neurodegenerative disorder for which there are no effective strategies to prevent or slow its progression. Because AD is multifactorial, recent research has focused on understanding interactions among the numerous risk factors and mechanisms underlying the disease. One mechanism through which several risk factors may be acting is inflammation. AD is characterized by chronic inflammation that is observed before clinical onset of dementia. Several genetic and environmental risk factors for AD increase inflammation, including apolipoprotein E4, obesity, and air pollution. Additionally, sex steroid hormones appear to contribute to AD risk, with age-related losses of estrogens in women and androgens in men associated with increased risk. Importantly, sex steroid hormones have anti-inflammatory actions and can interact with several other AD risk factors. This review examines the individual and interactive roles of inflammation and sex steroid hormones in AD, as well as their relationships with the AD risk factors apolipoprotein E4, obesity, and air pollution.

Influence of the APOE genotype on hepatic stress response: Studies in APOE targeted replacement mice and human liver cells

Apolipoprotein E (APOE) is a multifunctional plasma protein mainly acting in lipid metabolism. Human APOE is polymorphic with three major isoforms (APOE2, APOE3 and APOE4). Up to 75% of the body's APOE is produced by the liver. There is increasing evidence from studies in brain-derived cells that APOE4 affects mitochondrial function and biogenesis as well as stress and inflammatory responses - processes, whose disturbances are considered hallmarks of the ageing process. However, although the liver is the main production site of APOE, knowledge about the impact of the APOE genotype on hepatic stress response-related processes is rather limited. Therefore, we studied biomarkers of oxidative status (glutathione levels, 3-nitrotyrosine adducts, protein carbonyl concentration), ER stress (XBP1(S), BiP, DDIT3), proteasome activity, mitochondrial function (respiratory complexes, ATP levels and mitochondrial membrane potential as well as biomarkers of mitochondrial biogenesis, fission and fusion), autophagy (LC3, LAMP2A), apoptosis (BCL2, BAX, CYCS) and DNA damage in the liver of APOE targeted replacement (TR) mice and in Huh7 hepatocytes overexpressing the APOE3 and the APOE4 isoform, respectively. APOE4 mice exhibited a lower chymotrypsin-like and a higher trypsin-like proteasome activity. Levels of protein carbonyls were moderately higher in liver tissue of APOE4 vs. APOE3 mice. Other biomarkers of oxidative stress were similar between the two genotypes. Under basal conditions, the stress-response pathways investigated appeared largely unaffected by the APOE genotype. However, upon stress induction, APOE4 expressing cells showed lower levels of adenosine triphosphate (ATP) and lower mRNA levels of the ATP-generating complex V of the mitochondrial respiratory chain. Overall, our findings provide evidence for a rather low influence of the APOE genotype on the hepatic stress response processes investigated in this study.

APOE-modulated Aβ-induced neuroinflammation in Alzheimer's disease: current landscape, novel data, and future perspective

Chronic glial activation and neuroinflammation induced by the amyloid-β peptide (Aβ) contribute to Alzheimer's disease (AD) pathology. APOE4 is the greatest AD-genetic risk factor; increasing risk up to 12-fold compared to APOE3, with APOE4-specific neuroinflammation an important component of this risk. This editorial review discusses the role of APOE in inflammation and AD, via a literature review, presentation of novel data on Aβ-induced neuroinflammation, and discussion of future research directions. The complexity of chronic neuroinflammation, including multiple detrimental and beneficial effects occurring in a temporal and cell-specific manner, has resulted in conflicting functional data for virtually every inflammatory mediator. Defining a neuroinflammatory phenotype (NIP) is one way to address this issue, focusing on profiling the changes in inflammatory mediator expression during disease progression. Although many studies have shown that APOE4 induces a detrimental NIP in peripheral inflammation and Aβ-independent neuroinflammation, data for APOE-modulated Aβ-induced neuroinflammation are surprisingly limited. We present data supporting the hypothesis that impaired apoE4 function modulates Aβ-induced effects on inflammatory receptor signaling, including amplification of detrimental (toll-like receptor 4-p38α) and suppression of beneficial (IL-4R-nuclear receptor) pathways. To ultimately develop APOE genotype-specific therapeutics, it is critical that future studies define the dynamic NIP profile and pathways that underlie APOE-modulated chronic neuroinflammation. In this editorial review, we present data supporting the hypothesis that impaired apoE4 function modulates Aβ-induced effects on inflammatory receptor signaling, including amplification of detrimental (TLR4-p38α) and suppression of beneficial (IL-4R-nuclear receptor) pathways, resulting in an adverse NIP that causes neuronal dysfunction. NIP, Neuroinflammatory phenotype; P.I., pro-inflammatory; A.I., anti-inflammatory.

A non-invasive, rapid method to genotype late-onset Alzheimer's disease-related apolipoprotein E gene polymorphisms

The apolipoprotein E gene ε4 allele is considered a negative factor for neural regeneration in late-onset Alzheimer's disease cases. The aim of this study was to establish a non-invasive, rapid method to genotype apolipoprotein E gene polymorphisms. Genomic DNA from mouth swab specimens was extracted using magnetic nanoparticles, and genotyping was performed by real-time PCR using TaqMan-BHQ probes. Genotyping accuracy was validated by DNA sequencing. Our results demonstrate 100% correlation to DNA sequencing, indicating reliability of our protocol. Thus, the method we have developed for apolipoprotein E genotyping is accurate and reliable, and also suitable for genotyping large samples, which may help determine the role of the apolipoprotein E ε4 allele in neural regeneration in late-onset Alzheimer's disease cases.

Lack of association between APOE gene polymorphisms and amyotrophic lateral sclerosis: a comprehensive meta-analysis

Several studies have evaluated the association between APOE gene polymorphisms and the risk for amyotrophic lateral sclerosis (ALS), with inconclusive results. The aim of our study was to further define the risk associated with carriage of the APOE alleles and development and clinical characteristics of ALS. We performed a comprehensive meta-analysis of all existing studies investigating the association between the APOE gene and ALS published up to September 2013, comprising a total of 4249 ALS patients and 10,397 controls. Pooled odds ratios (OR) were estimated using the random effect (RE) model. Results showed that the carriage of different APOE alleles had no effect on disease risk. In particular, the ϵ4 allele was not associated with a significantly increased disease risk (ϵ4 carriers vs. non-ϵ4 carriers: RE OR 1.18; 95% CI 0.91-1.53). In conclusion, our study suggests that the APOE gene does not have a significant effect in ALS aetiopathogenesis.

Antioxidant gene therapy against neuronal cell death

Oxidative stress is a common hallmark of neuronal cell death associated with neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, as well as brain stroke/ischemia and traumatic brain injury. Increased accumulation of reactive species of both oxygen (ROS) and nitrogen (RNS) has been implicated in mitochondrial dysfunction, energy impairment, alterations in metal homeostasis and accumulation of aggregated proteins observed in neurodegenerative disorders, which lead to the activation/modulation of cell death mechanisms that include apoptotic, necrotic and autophagic pathways. Thus, the design of novel antioxidant strategies to selectively target oxidative stress and redox imbalance might represent important therapeutic approaches against neurological disorders. This work reviews the evidence demonstrating the ability of genetically encoded antioxidant systems to selectively counteract neuronal cell loss in neurodegenerative diseases and ischemic brain damage. Because gene therapy approaches to treat inherited and acquired disorders offer many unique advantages over conventional therapeutic approaches, we discussed basic research/clinical evidence and the potential of virus-mediated gene delivery techniques for antioxidant gene therapy.

Apolipoprotein E gene polymorphism and risk for coronary heart disease in the Chinese population: a meta-analysis of 61 studies including 6634 cases and 6393 controls

BACKGROUND

Numerous studies have evaluated the association between the apolipoprotein E (apoE) gene polymorphisms in coronary heart disease (CHD). However, the results remain uncertain. We carried out a meta-analysis to derive a more comprehensive estimation of the association in Chinese population.

METHODS

Case-control studies in Chinese and English publications were identified by searching databases of PubMed, EMBASE, Web of Science, CNKI, CBM, Wanfang, VIP and hand searching of relevant journals and the reference lists of retrieved articles. Odds ratio (OR) and 95% confidence interval (CI) were applied to assess the strength of the associations. Subgroup analysis and sensitivity analysis were performed to explore the between-study heterogeneity.

RESULTS

We finally identified 61 relevant studies which comprised 6634 case-patients and 6393 controls. The pooled OR for ε4 carriers was 96% higher than the ε3/3 genotype for CHD (OR, 1.96; 95% CI, 1.70 to 2.24; P<0.001). However, there was no evidence of statistically significant association between ε2 carriers and risk of CHD (OR, 1.02; 95% CI, 0.91 to 1.13; P = 0.729). In the subgroup analysis, different endpoints may partially account for the heterogeneity. No publication bias was found.

CONCLUSIONS

Our meta-analysis suggests that the apoE ε4 allele may be a risk factor for CHD in the Chinese population, however, ε2 allele has no significant association.

Apolipoprotein E as a β-amyloid-independent factor in Alzheimer's disease

APOE, which encodes apolipoprotein E, is the most prevalent and best established genetic risk factor for late-onset Alzheimer’s disease. Current understanding of Alzheimer’s disease pathophysiology posits an important role for apolipoprotein E in the disease cascade via its interplay with β-amyloid. However, evidence is also emerging for roles of apolipoprotein E in the disease process that are independent of β-amyloid. Particular areas of interest are lipid metabolism, tau pathology, neuroenergetics, neurodevelopment, synaptic plasticity, the neurovasculature, and neuroinflammation. The intent of this article is to review the literature in each of these areas.

Apolipoprotein E Mimetic Promotes Functional and Histological Recovery in Lysolecithin-Induced Spinal Cord Demyelination in Mice

Objective

Considering demyelination is the pathological hallmark of multiple sclerosis (MS), reducing demyelination and/or promoting remyelination is a practical therapeutic strategy to improve functional recovery for MS. An apolipoprotein E (apoE)-mimetic peptide COG112 has previously demonstrated therapeutic efficacy on functional and histological recovery in a mouse experimental autoimmune encephalomyelitis (EAE) model of human MS. In the current study, we further investigated whether COG112 promotes remyelination and improves functional recovery in lysolecithin induced focal demyelination in the white matter of spinal cord in mice.

Methods

A focal demyelination model was created by stereotaxically injecting lysolecithin into the bilateral ventrolateral funiculus (VLF) of T8 and T9 mouse spinal cords. Immediately after lysolecithin injection mice were treated with COG112, prefix peptide control or vehicle control for 21 days. The locomotor function of the mice was measured by the beam walking test and Basso Mouse Scale (BMS) assessment. The nerve transmission of the VLF of mice was assessed in vivo by transcranial magnetic motor evoked potentials (tcMMEPs). The histological changes were also examined by by eriochrome cyanine staining, immunohistochemistry staining and electron microscopy (EM) method.

Results

The area of demyelination in the spinal cord was significantly reduced in the COG112 group. EM examination showed that treatment with COG112 increased the thickness of myelin sheaths and the numbers of surviving axons in the lesion epicenter. Locomotor function was improved in COG112 treated animals when measured by the beam walking test and BMS assessment compared to controls. TcMMEPs also demonstrated the COG112-mediated enhancement of amplitude of evoked responses.

Conclusion

The apoE-mimetic COG112 demonstrates a favorable combination of activities in suppressing inflammatory response, mitigating demyelination and in promoting remyelination and associated functional recovery in animal model of CNS demyelination. These data support that apoE-mimetic strategy may represent a promising therapy for MS and other demyelination disorders.

ApoE genotype: from geographic distribution to function and responsiveness to dietary factors

ApoE is a key protein in lipid metabolism with three major isoforms.ApoEallele frequencies show non-random global distribution especially in Europe with highapoEε3frequency in the Mediterranean area, whereas theapoEε4genotype is enriched in Northern Europe. TheapoEε4genotype is one of the most important genetic risk factors for age-dependent chronic diseases, including CVD and Alzheimer's disease (AD). The apoE polymorphism has been shown to impact on blood lipids, biomarkers of oxidative stress and chronic inflammation, which all may contribute to the isoform-dependent disease risk. Studies in mice and human subjects indicate that theapoEε3but not theapoEε4genotype may significantly benefit from dietary flavonoids (e.g. quercetin) andn-3 fatty acids. Metabolism of lipid soluble vitamins E and D is likewise differentially affected by theapoEgenotype. Epidemiological and experimental evidence suggest a better vitamin D status inapoEε4than ε3subjects indicating a certain advantage of ε4over ε3. The present review aims at evaluation of current data available on interactions between apoE polymorphism and dietary responsiveness to flavonoids, fat soluble vitamins andn-3 fatty acids. Likewise, distinct geographic distribution and chronic disease risk of the different apoE isoforms are addressed.

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.

Apolipoprotein E polymorphism and the progression of diabetic nephropathy in type 2 diabetes

BACKGROUND/AIMS

Three different apo E alleles (E2, E3 and E4) produce apo E isoproteins, which regulate the metabolism of lipoproteins. This study investigated the apo E polymorphisms as a prognostic factor for the development of diabetic nephropathy (DN).

METHODS

A total of 525 type 2 diabetic patients were enrolled to participate in this prospective observational study. Apo E gene polymorphisms were analyzed by polymerase chain reaction. The progression of DN was defined as a shift to a higher stage of DN or a doubling of the baseline serum creatinine level by the end of the study.

RESULTS

The mean follow-up period was 42.4 months. The patients whose DN progressed had significantly higher urine albumin/creatinine ratios and fewer used diuretics than those in whom DN did not progress. In the Cox regression analysis, the apo E4 carriers were found to be at greater risk of progression of DN than non-apo E4 carriers (p = 0.007, hazard ratio 2.252). After adjusting for confounding factors, apo E4 carriers remained at increased risk of progression to more severe DN (p = 0.002, hazard ratio 2.820).

CONCLUSION

Our study suggests the apo E4 carrier might serve as a predictor of DN progression in Taiwan.

Rosuvastatin reduces microglia in the brain of wild type and ApoE knockout mice on a high cholesterol diet; implications for prevention of stroke and AD

We have previously shown that a high cholesterol (HC) diet results in increases in microglia load and levels of the pro-inflammatory cytokine interleukin-6 (IL-6) in the brains of wild type (WT) and apolipoprotein E knockout (ApoE-/-) mice. In the present investigation, we analyzed whether treatment with rosuvastatin, an inhibitor of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, would prevent the increases in inflammatory microglia and IL-6 levels in the brain and plasma of WT and ApoE-/- mice. We report that a HC diet resulted in an increased microglia load in the brains of WT and ApoE-/- mice, in support of our previous study. Treatment with rosuvastatin significantly decreased the microglia load in the brains of WT and ApoE-/- mice on a HC diet. Rosuvastatin treatment resulted in lowered plasma IL-6 levels in WT mice on a HC diet. However, in the present study the number of IL-6 positive cells in the brain was not significantly affected by a HC diet. A recent clinical study has shown that rosuvastatin reduces risk of ischemic stroke in patients with high plasma levels of the inflammatory marker C-reactive protein by 50%. The results from our study show that rosuvastatin reduces inflammatory cells in the brain. This finding is essential for furthering the prevention and treatment of neurodegenerative diseases such as Alzheimer's disease (AD) and stroke.

An apolipoprotein E-mimetic stimulates axonal regeneration and remyelination after peripheral nerve injury

Elevated apolipoprotein E (apoE) synthesis within crushed sciatic nerves advocates that apoE could benefit axonal repair and reconstruction of axonal and myelin membranes. We created an apoE-mimetic peptide, COG112 (acetyl-RQIKIWFQNRRMKWKKCLRVRLASHLRKLRKRLL-amide), and found that postinjury treatment with COG112 significantly improved recovery of motor and sensory function following sciatic nerve crush in C57BL/6 mice. Morphometric analysis of injured sciatic nerves revealed that COG112 promoted axonal regrowth after 2 weeks of treatment. More strikingly, the thickness of myelin sheaths was increased by COG112 treatment. Consistent with these histological findings, COG112 potently elevated growth associated protein 43 (GAP-43) and peripheral myelin protein zero (P0), which are markers of axon regeneration and remyelination, respectively. Electron microscopic examination further suggested that the apoE-mimetic COG112 may increase clearance of myelin debris. Schwann cell uptake of cholesterol-containing low-density lipoprotein particles was selectively enhanced by COG112 treatment in a Schwann cell line S16. Moreover, COG112 significantly promoted axon elongation in primary dorsal root ganglion cultures from rat pups. Considering that cholesterol and lipids are needed for reconstructing myelin sheaths and axon extension, these data support a hypothesis where supplementation with exogenous apoE-mimetics such as COG112 may be a promising strategy for restoring lost functional and structural elements following nerve injury.

The role of apolipoprotein E in Guillain-Barré syndrome and experimental autoimmune neuritis

Apolipoprotein E (apoE) is a 34.2 kDa glycosylated protein characterized by its wide tissue distribution and multiple functions. ApoE has been widely studied in lipid metabolism, cardiocerebrovascular diseases, and neurodegenerative diseases like Alzheimer's disease and mild cognitive impairment, and so forth. Recently, a growing body of evidence has pointed to nonlipid related properties of apoE, including suppression of T cell proliferation, regulation of macrophage function, facilitation of lipid antigen presentation by CD1 molecules to natural killer T (NKT) cells, and modulation of inflammation and oxidation. By these properties, apoE impacts physiology and pathophysiology at multiple levels. The present paper summarizes updated studies on the immunoregulatory function of apoE, with special focus on isoform-specific effects of apoE on Guillain-Barré syndrome (GBS) and its animal model experimental autoimmune neuritis (EAN).

APOE genotype-specific differences in the innate immune response

Apolipoprotein-E protein is an endogenous immunomodulatory agent that affects both the innate and the adaptive immune responses. Since individuals with the APOE4 gene demonstrate worsened pathology and poorer outcomes in many neurological disorders, we examined isoform-specific differences in the response of microglia, the primary cellular component of the brain's innate immune response, in detail. Our data demonstrate that microglia derived from APOE4/4 targeted replacement mice demonstrate a pro-inflammatory phenotype that includes altered cell morphology, increased NO production associated with increased NOS2 mRNA levels, and higher pro-inflammatory cytokine production (TNFalpha, IL-6, IL12p40) compared to microglia derived from APOE3/3 targeted replacement mice. The effect is gene dose-dependent and increases with the number of APOE4 gene alleles. The APOE genotype-specific immune profile observed in the microglial immune response is also observed in the cortex of aged APOE3/3 and APOE4/4 mice treated with lipopolysacchride (LPS) and in peripheral (peritoneal) macrophages. To determine if APOE4's action resulted from an isoform-specific difference in effective levels of the apolipoproteins, we generated mice expressing only a single allele of APOE3. Immune-stimulated macrophages from APOE3/0 mice demonstrated an increased inflammatory response compared to APOE3/3 mice, but less than in APOE4/4 mice. These data suggest that inhibition of inflammation depends upon the dose of apoE3 protein available and that apoE4 protein may alter inflammation partly by dose effects and partly by being qualitatively different than apoE3. Overall, these data emphasize the important role of apolipoprotein E and of the APOE genotype on the immune responses that are evident in most, if not all, neurological disease.

Apolipoprotein E modifies neurological outcome by affecting cerebral edema but not hematoma size after intracerebral hemorrhage in humans

INTRODUCTION

To address the mechanisms by which apoE polymorphism affects functional outcome after intracerebral hemorrhage in humans, we tested the hypothesis that the presence of the APOE4 allele results in amplified inflammatory responses and increased cerebral edema.

METHODS

We prospectively enrolled and collected data on 21 adult patients consecutively admitted to Duke University Hospital with supratentorial intracerebral hematoma including hemorrhage volume, midline shift, modified Rankin Score, Glasgow Outcome Score, and APOE genotype. Hemorrhage size (cm(3)) and midline shift (mm), at the level of the thalamus, were measured by computed tomography within 36 hours of admission. Rankin and Glasgow Scores were determined at discharge. Student's t-test was used to analyze hemorrhage size, midline shift, and Glasgow Outcome Score and logistical regression were used to measure allele affect on modified Rankin Score. When analyzing modified Rankin Score, patients were grouped by favorable outcome (0-2) or unfavorable (3-6).

RESULTS

Out of 21 patients, 11 possessed at least 1 APOE4 allele (APOE4+). There was no difference in hemorrhage volume (25.8 v 38.3 mm for APOE4- v APOE4+, respectively) between the groups, but there was a significant difference in midline shift (P = .04, 0.7 v 4 mm). Functional outcomes were worse for the patients possessing at least 1 APOE4 allele (P = .04)

CONCLUSION

The presence of APOE4 is associated with poor functional outcomes in humans after intracerebral hemorrhage. Our data suggest that the mechanism for this may be increased cerebral edema and not larger hematoma volume.

Immunotherapy, vascular pathology, and microhemorrhages in transgenic mice

Alzheimer's disease (AD) is a progressive, neurodegenerative disorder that results in severe cognitive decline. Amyloid plaques are a principal pathology found in AD and are composed of aggregated amyloid-beta (Abeta) peptides. According to the amyloid hypothesis, Abeta peptides initiate the other pathologies characteristic for AD including cognitive deficits. Immunotherapy against Abeta is a potential therapeutic for the treatment of humans with AD. While anti-Abeta immunotherapy has been shown to reduce amyloid burden in both mouse models and in humans, immunotherapy also exacerbates vascular pathologies. Cerebral amyloid angiopathy (CAA), that is, the accumulation of amyloid in the cerebrovasculature, is increased with immunotherapy in humans with AD and in mouse models of amyloid deposition. CAA persists in the brains of clinical trial patients that show removal of parenchymal amyloid. Mouse model studies also show that immunotherapy results in multiple small bleeds in the brain, termed microhemorrhages. The neurovascular unit is a term used to describe the cerebrovasculature and its associated cells-astrocytes, neurons, pericytes and microglia. CAA affects brain perfusion and there is now evidence that the neurovascular unit is affected in AD when CAA is present. Understanding the type of damage to the neurovascular unit caused by CAA in AD and the underlying cause of microhemorrhage after immunotherapy is essential to the success of therapeutic vaccines as a treatment for AD.

Searching for genes that matter in acute kidney injury: a systematic review

BACKGROUND AND OBJECTIVES

Identifying patients who may develop acute kidney injury (AKI) remains challenging, as clinical determinants explain only a portion of individual risk. Another factor that likely affects risk is intrinsic genetic variability. Therefore, a systematic review of studies was performed that related the development or prognosis of AKI to genetic variation.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

MEDLINE, EMBASE, HuGEnet, SCOPUS, and Web of Science were searched for articles from 1950 to Dec 2007. Two independent researchers screened articles using predetermined criteria. Studies were assessed for methodological quality via an aggregate scoring system.

RESULTS

The 16 included studies were of cohort or case-cohort design and investigated 35 polymorphisms in 21 genes in association with AKI. Fifteen gene-gene interactions were also investigated in four separate studies. Study populations were primarily premature infants or adults who were critically ill or postcardiac bypass patients. Among the studies, five different definitions of AKI were used. Only one polymorphism, APO E e2/e3/e4, had greater than one study showing a significant impact (P < 0.05) on AKI incidence. The mean quality score of 5.8/10 (range four to nine), heterogeneity in the studies, and the dearth of studies precluded additional meta-analysis of the results.

CONCLUSIONS

Current association studies are unable to provide definitive evidence linking genetic variation to AKI. Future success will require a narrow consensus definition of AKI, rigorous epidemiologic techniques, and a shift from a priori hypothesis-driven to genome-wide association studies.

Polymorphism in apolipoprotein E among migraineurs and tension-type headache subjects

Nitric oxide plays an important role in the pathogenesis of migraine as well as tension-type headache. Studies suggest that the expression of molecules involved in the pathogenesis of headache, i.e., nitric oxide and interleukin, is influenced by apolipoprotein E (APOE) and is gene specific. Hence, we hypothesized that APOE polymorphism may be associated with migraine as well as tension-type headache.The study sample comprised of three groups: migraineurs, tension-type headache subjects as well as a healthy control group. A total of 50 subjects in each group were included after screening for the inclusion and exclusion criteria. None of the subjects was a blood relative of any other subject included in the present study. Their venous blood was drawn and stored at −20°C. Genomic DNA extraction was performed with a commercial kit and simple sequence-specific primer PCR was performed to assess the APOE polymorphism. Data were analyzed with the help of SPSS V11.0 for Windows. χ² test and logistic regression analysis were run. The results of the study showed that APOE ε2 gene increases the risk of migraine as compared to the control group and the tension-type headache group (OR = 4.85; 95% CI = 1.92–12.72; P < 0.001 and OR = 2.31; 95% CI = 1.08–4.94; P = 0.01, respectively). Interestingly, APOE ε4 gene was protective against migraine as well as tension-type headache. This study shows that APOE ε2 gene increases the risk of migraine, while APOE ε4 gene is protective against migraine and tension-type headache. Further research is required to confirm the findings of the present study in a larger sample and to elucidate the role of APOE polymorphism in headache.

Apolipoprotein E genotype is related to nitric oxide production in platelets

The presence of the epsilon4 allele of apolipoprotein E (APOE) is considered a risk factor for sporadic Alzheimer's disease (AD). Our recent data demonstrated that the systemic modulation of oxidative stress in platelets and erythrocytes is disrupted in aging and AD. In this study, the relationship between APOE genotype and oxidative stress markers, both in AD patients and controls, was evaluated. The AD group showed an increase in the content of thiobarbituric acid-reactive substances (TBARS) and in the activities of nitric oxide synthase (NOS) and Na, K-ATPase, when compared to controls. Both groups had a similar cGMP content and superoxide dismutase activity. APOE epsilon4 allele carriers showed higher NOS activity than non-carriers. These results suggest a possible influence of APOE genotype on nitric oxide (NO) production that might enhance the effects of age-related specific factor(s) associated with neurodegenerative disorders.

Effects of 137Cs gamma irradiation on cognitive performance and measures of anxiety in Apoe-/- and wild-type female mice

Mice deficient in apoE (Apoe-/-) can be used to assess the potential role of apoE in the effects of cranial irradiation on hippocampal function. Radiation-induced impairments in hippocampal function may be more pronounced in female Apoe-/- mice and more pronounced in mice irradiated and tested cognitively later in life. To assess this possibility, female wild-type and Apoe-/- mice were irradiated at 6 months of age with 10 Gy 137Cs gamma rays and tested cognitively 3 months later. Sham-irradiated wild-type female mice showed enhanced hippocampal-dependent novel location recognition compared to sham-irradiated Apoe-/- female mice. However, cranial irradiation impaired novel location recognition similarly in both genotypes. Cranial irradiation also impaired hippocampal-dependent spatial memory retention similarly in wild-type and Apoe-/- female mice in the water maze. Because novel location recognition was not affected after 137Cs gamma irradiation in younger mice, these data support the possibility that older mice are more susceptible to the effects of gamma radiation on novel location recognition. Together with the impairments in spatial memory retention in the water maze after irradiation, these data support the existence of detrimental effects of cranial irradiation on hippocampal function. In addition, compared to wild-type female mice, Apoe-/- female mice showed enhanced levels of anxiety, and in Apoe-/-, but not in wild-type, female mice, radiation decreased levels of anxiety. Because levels of anxiety during the hidden session of the water maze were associated with ability to locate the hidden platform, assessments of anxiety need to be considered in evaluating the effects of cranial irradiation on cognitive performance after cranial irradiation.

The APOE4 genotype alters the response of microglia and macrophages to 17beta-estradiol

The apolipoprotein E4 (APOE4) gene is a well-known risk factor for Alzheimer's disease (AD) and other neurological disorders. Post-menopausal women with AD who express at least one APOE4 gene have more severe neuropathology and worsened cognitive scores than their non-expressing counterparts. Since 17beta-estradiol down-regulates inflammation as part of its neuroprotective role, we examined the effect of 17beta-estradiol on the response of microglia to immune activation as a function of APOE genotype. Our data show that the anti-inflammatory activity of 17beta-estradiol is significantly reduced in APOE4 targeted replacement mice compared to APOE3 mice. A significant interaction between APOE genotype and the response to 17beta-estradiol was observed for NO and cytokine production by immune activated microglia. The genotype specific effect was not restricted to brain macrophages since peritoneal macrophages from APOE4 ovariectomized mice also demonstrated a significant difference in 17beta-estradiol responsiveness. ERbeta protein levels in APOE4 microglia were higher than APOE3 microglia, suggesting a difference in post-translational protein regulation in the presence of the APOE4 gene. Overall, our data indicate that the APOE genotype may be a critical component in assessing the effectiveness of 17beta-estradiol's action and may impact the neuroprotective role of 17beta-estradiol and of hormone replacement therapy on brain function when the APOE4 gene is expressed.

SJL mice exposed to cuprizone intoxication reveal strain and gender pattern differences in demyelination

The role of mouse strain and the influence of gender on demyelination were explored for the first time in SJL mice using the cuprizone intoxication model. We document here that SJL mice display a unique pattern of demyelination that did not follow the profile that is well-characterized in C57BL/6 mice. The SJL mice did not readily demyelinate at the midline within the corpus callosum but showed greater demyelination immediately lateral to midline. During continuous exposure to cuprizone, demyelination was not complete and appeared to plateau after week 7. Importantly, female mice were partially resistant to demyelination, whereas male mice were more severely demyelinated. Differences in the number of mature oligodendrocytes were consistent with the extent of demyelination; however, microglia, astrocyte and oligodendrocyte precursor cell populations did not differ between male and female mice. Thus, genetic factors and gender influence susceptibility to demyelinating disease in the cuprizone model, which may provide additional insights into the variability observed in human demyelinating diseases such as multiple sclerosis.

Meta-analysis of APOE4 allele and outcome after traumatic brain injury

There is conflicting evidence regarding a possible association between the apolipoprotein E4 (APOE4) allele and the consequences of traumatic brain injury (TBI). Our aim was to carry out a meta-analysis of cohort studies of sufficient rigor to determine whether the presence of the APOE4 allele contributes to initial injury severity and/or poor outcome following TBI. MEDLINE, EMBase, CBMdisc, and CNKI databases were searched for literature published from January 1993 to October 2007. Of the 100 identified studies, 14 cohort studies were selected for analysis based on comprehensive quality assessment using a standardized scale. Data from the 14 eligible cohort studies included a total of 2527 participants, 736 with and 1791 without the APOE4 allele. The APOE4 allele was not associated with initial injury severity of TBI. The pooled RR were 1.11 (95% confidence interval [CI], 0.91 to 1.35) for severe injury, 1.06 (95% CI, 0.86-1.31) for moderate injury and 0.93 (95% CI, 0.81-1.06) for mild injury. However, the APOE4 allele was significantly associated with a poor outcome of TBI at 6 months after injury (RR = 1.36; 95% CI, 1.04-1.78). The association remained significant in sensitivity tests. This meta-analysis indicates that the presence of the APOE4 allele is not associated with the initial severity of brain injury following TBI but is associated with increased risk of poor long-term outcome at 6 months after injury.

Effect of human apolipoprotein E genotype on the pathogenesis of experimental ocular HSV-1

The isoform-specific role of human apolipoprotein E (apoE) has been assessed in a mouse model of ocular herpes. Female, age-matched transgenic mice knocked-in for the human allele apoE3 or apoE4 and their parent C57Bl/6 mice were inoculated corneally with HSV-1 strain KOS. Ocular HSV-1 pathogenesis was monitored through viral replication and clinical progression of stromal opacity and neovascularization by slit-lamp examination. Establishment of latency was determined by analysis of HSV-1 DNA (copy number) by specific real-time PCR in the cornea, trigeminal ganglia (TG), and brain. Representative groups of transgenic mice were sacrificed for the analysis of gene expression of vascular endothelial growth factor (VEGF) by reverse-transcription PCR, and apoE expression by Western blot analysis. At 6days post-infection (P.I.), the ocular infectious HSV-1 titer was significantly higher (p<0.05) in apoE4 mice compared with apoE3 and C57Bl/6 mice. Corneal neovascularization in apoE4 mice was significantly higher (p<0.05) than apoE3 and C57Bl/6 mice. The onset of corneal opacity in apoE4 mice was accelerated during days 9-11 P.I.; however, no significant difference in severity was seen on P.I. days 15 and beyond. At 28 days P.I., infected mice of all genotypes had no significant differences in copy numbers (range 0-15) of HSV-1 DNA in their corneas, indicating that HSV-1 DNA copy numbers in cornea are independent of apoE isoform regulation. At 28 days P.I., both apoE4 and C57Bl/6 mice had a significantly higher (p=0.001) number of copies of HSV-1 DNA in TG compared with apoE3. ApoE4 mice also had significantly higher (p=0.001) copies of HSV-1 DNA in their TGs compared with C57Bl/6 mice. In brain, both apoE4 and C57Bl/6 mice had significantly higher numbers (p<or=0.03) of copies of HSV-1 DNA compared with apoE3 mice. However, the number of HSV-1 DNA copies in the brain of C57Bl/6 mice was not significantly different than that of apoE4 (p=0.1). Comparative molecular analysis between apoE3 and apoE4 mice on selected days between 7 and 28 P.I., inclusive, revealed that the corneas of apoE4 mice expressed VEGF. None of the corneas in the apoE3 mice expressed VEGF during this time. Western blot analysis showed proteolytic cleavage of the apoE protein in the corneas of the apoE4 mice. Through days 14-28 P.I., a approximately 29 kDa C-terminal truncated apoE fragment was present in the corneas of apoE4 mice, but not in apoE3 mice. ApoE4 is a risk factor for ocular herpes, in part, through increased replication of virus in the eye, an earlier onset in clinical opacity, significantly higher neovascularization, and increased HSV-1 DNA load in TG and brain than that of apoE3. Increased pathogenesis of ocular herpes in apoE4 mice was also mediated, in part through up-regulated expression of VEGF and apoE proteolysis in the cornea. This is the first report linking a human gene, apoE4, as a risk factor for ocular herpes pathogenesis in a transgenic mouse model.

AR, apoE, and cognitive function

Reduced androgen levels in aged men and women might be risk factors for age-related cognitive decline and Alzheimer's disease (AD). Ongoing clinical trials are designed to evaluate the potential benefit of estrogen in women and of testosterone in men. In this review, we discuss the potential beneficial effects of androgens and androgen receptors (ARs) in males and females. In addition, we discuss the hypothesis that AR interacts with apolipoprotein (apoE)4, encoded by epsilon4 and a risk factor for age-related cognitive decline and AD, and the potential consequences of this interaction.

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.

ApoE4 disrupts sterol and sphingolipid metabolism in Alzheimer's but not normal brain

The epsilon 4 allele of ApoE is associated with an earlier onset and faster progression of Alzheimer's disease in patients with the familial form of this neurodegenerative condition. Although ApoE4 has been repeatedly associated with altered sphingomyelin and cholesterol levels in tissue culture and rodent models, there has not been a direct quantification of sphingomyelin or sterol levels in the brains of patients with different forms of ApoE. We measured the sphingolipid and sterol content of human brain tissues and found no evidence of perturbed sterol or sphingolipid biochemistry in the brains of individuals expressing ApoE4 who did not have a preexisting neurodegenerative condition. Nevertheless, ApoE4 was associated with gross abnormalities in the sterol and sphingolipid content of numerous brain regions in patients with Alzheimer's disease. The findings suggest that ApoE4 may not by itself alter sterol or sphingolipid metabolism in the brain under normal conditions, but that other neuropathologic changes of Alzheimer's are required to unmask the effect of ApoE4, and to perturb sterol and sphingolipid biochemistry.

Vascular oxidative stress in Alzheimer disease

Alzheimer disease and cerebrovascular dementia are two common causes of dementia and, by present diagnostic criteria, are mutually exclusive using vascular pathology as an arbitrary demarcation in differential diagnosis. However, evidence from epidemiological, neuropathological, clinical, pharmacological, and functional studies suggest considerable overlap in risk factors and pathological changes suggesting shared common pathogenic mechanisms between these two diseases such that vascular factors play a vital role in the pathogenesis of Alzheimer disease. A high energy demand and lack of an endogenous fuel reserve make the brain highly dependent upon a continuous blood supply where disruption of cerebral blood vessels and blood flow can have serious consequences on neural activities. Indeed, many studies implicate metabolic defects in Alzheimer disease, such a reduced brain metabolism is one of the best documented abnormalities in the disease. Notably, since endothelial reactive oxygen species such as nitric oxide act as vasodilators at low concentrations, increased production coupled with elevated reactive oxygen species scavenging of nitric oxide, can lead to reduced bioavailability of nitric oxide and increased oxidative stress that damage sensitive vascular cells. In this respect, we and others have demonstrated that oxidative stress is one of the earliest pathological changes in the brain of Alzheimer disease patients and plays a critical role in the vascular abnormalities underlying metabolic defects in Alzheimer disease. Here, we discuss vascular factors in relation to Alzheimer disease and review hypoperfusion as a potential cause by triggering mitochondrial dysfunction and increased oxidative stress initiating the pathogenic process.

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.

Apolipoprotein E isoform-dependent dendritic recovery of hippocampal neurons following activation of innate immunity

Background

Innate immune activation, including a role for cluster of differentiation 14/toll-like receptor 4 co-receptors (CD14/TLR-4) co-receptors, has been implicated in paracrine damage to neurons in several neurodegenerative diseases that also display stratification of risk or clinical outcome with the common alleles of the apolipoprotein E gene (APOE): APOE2, APOE3, and APOE4. Previously, we have shown that specific stimulation of CD14/TLR-4 with lipopolysaccharide (LPS) leads to greatest innate immune response by primary microglial cultures from targeted replacement (TR) APOE4 mice and greatest p38MAPK-dependent paracrine damage to neurons in mixed primary cultures and hippocampal slice cultures derived from TR APOE4 mice. In contrast, TR APOE2 astrocytes had the highest NF-kappaB activity and no neurotoxicity. Here we tested the hypothesis that direct activation of CD14/TLR-4 in vivo would yield different amounts of paracrine damage to hippocampal sector CA1 pyramidal neurons in TR APOE mice.

Methods

We measured in vivo changes in dendrite length in hippocampal CA1 neurons using Golgi staining and determined hippocampal apoE levels by Western blot. Neurite outgrowth of cultured primary neurons in response to astrocyte conditioned medium was assessed by measuring neuron length and branch number.

Results

Our results showed that TR APOE4 mice had slightly but significantly shorter dendrites at 6 weeks of age. Following exposure to intracerebroventricular LPS, there was comparable loss of dendrite length at 24 hr among the three TR APOE mice. Recovery of dendrite length over the next 48 hr was greater in TR APOE2 than TR APOE3 mice, while TR APOE4 mice had failure of dendrite regeneration. Cell culture experiments indicated that the enhanced neurotrophic effect of TR APOE2 was LDL related protein-dependent.

Conclusion

The data indicate that the environment within TR APOE2 mouse hippocampus was most supportive of dendrite regeneration while that within TR APOE4 hippocampus failed to support dendrite regeneration in this model of reversible paracrine damage to neurons from innate immune activation, and suggest an explanation for the stratification of clinical outcome with APOE seen in several degenerative diseases or brain that are associated with activated innate immune response.

Apolipoprotein E-derived peptides ameliorate clinical disability and inflammatory infiltrates into the spinal cord in a murine model of multiple sclerosis

Apolipoprotein E (apoE), well known to play a role in lipid transport and cholesterol metabolism, also exerts anti-inflammatory and neuroprotective effects in the central nervous system. Recent clinical and genetic studies display an association between apoE genotype (APOE) and the progression and severity of multiple sclerosis, raising the possibility that modulation of apoE may be a novel treatment for multiple sclerosis. Using a murine experimental autoimmune encephalomyelitis (EAE) model of human multiple sclerosis, we found that a peptidomimetic of apoE protein, COG133, substantially reduces the clinical symptoms of EAE and promotes remission from the disability when administered before or after onset of disease. Most notably, fusion of COG133 to a protein transduction domain creates COG112, a modified apoE-mimetic peptide with significantly enhanced anti-inflammatory bioactivities in vitro, and improved therapeutic effects on EAE in vivo, which renders a nearly full remission from the disability. Histopathological analysis showed that COG112 and COG133 attenuated demyelination and significantly diminished the number of peripheral cells infiltrating into the spinal cord. ApoE mimetics also interfered with several mechanisms relevant to the pathogenesis of EAE and multiple sclerosis, including activation of macrophages, subsequent production of nitric oxide and inflammatory cytokines, and lymphocyte proliferation. These data suggest that apoE mimetics represent a multidimensional therapeutic for multiple sclerosis capable of inhibiting the inflammatory cascade, modulating immune cell function, and reducing clinical signs, which may have novel utility for the treatment of inflammatory autoimmune diseases.