Genetic mutations affecting human lipoproteins, their receptors, and their enzymes

Molecular Genetic Mechanisms in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is among the leading causes of irreversible blindness worldwide. In addition to environmental risk factors, such as tobacco use and diet, genetic background has long been established as a major risk factor for the development of AMD. However, our ability to predict disease risk and personalize treatment remains limited by our nascent understanding of the molecular mechanisms underlying AMD pathogenesis. Research into the molecular genetics of AMD over the past two decades has uncovered 52 independent gene variants and 34 independent loci that are implicated in the development of AMD, accounting for over half of the genetic risk. This research has helped delineate at least five major pathways that may be disrupted in the pathogenesis of AMD: the complement system, extracellular matrix remodeling, lipid metabolism, angiogenesis, and oxidative stress response. This review surveys our current understanding of each of these disease mechanisms, in turn, along with their associated pathogenic gene variants. Continued research into the molecular genetics of AMD holds great promise for the development of precision-targeted, personalized therapies that bring us closer to a cure for this debilitating disease.

GABAergic dysfunction, neural network hyperactivity and memory impairments in human aging and Alzheimer's disease

In this review, we focus on the potential role of the γ-aminobutyric acidergic (GABAergic) system in age-related episodic memory impairments in humans, with a particular focus on Alzheimer's disease (AD). Well-established animal models have shown that GABA plays a central role in regulating and synchronizing neuronal signaling in the hippocampus, a brain area critical for episodic memory that undergoes early and significant morphologic and functional changes in the course of AD. Neuroimaging research in humans has documented hyperactivity in the hippocampus and losses of resting state functional connectivity in the Default Mode Network, a network that itself prominently includes the hippocampus-presaging episodic memory decline in individuals at-risk for AD. Apolipoprotein ε4, the highest genetic risk factor for AD, is associated with GABAergic dysfunction in animal models, and episodic memory impairments in humans. In combination, these findings suggest that GABA may be the linchpin in a complex system of factors that eventually leads to the principal clinical hallmark of AD: episodic memory loss. Here, we will review the current state of literature supporting this hypothesis. First, we will focus on the molecular and cellular basis of the GABAergic system and its role in memory and cognition. Next, we report the evidence of GABA dysregulations in AD and normal aging, both in animal models and human studies. Finally, we outline a model of GABAergic dysfunction based on the results of functional neuroimaging studies in humans, which have shown hippocampal hyperactivity to episodic memory tasks concurrent with and even preceding AD diagnosis, along with factors that may modulate this association.

Arterial stiffening acts synergistically with APOE genotype and AD biomarker status to influence memory in older adults without dementia

BACKGROUND

Arterial stiffening has emerged as an important risk factor for Alzheimer's disease (AD) and related dementias. Carotid-femoral pulse wave velocity has been proposed as a non-invasive and reproducible method to assess arterial stiffness. However, the association of pulse wave velocity with performance across multiple cognitive domains as well as interactions with in vivo AD biomarkers and apolipoprotein E (APOE) genotype has received limited study.

METHOD

We studied 193 older adult volunteers (167 with normal cognition and 26 with mild cognitive impairment) who underwent comprehensive medical and neuropsychological evaluation at the University of California, San Diego Alzheimer's Disease Research Center. Cerebrospinal fluid (CSF) biomarkers were available on 123 participants (63%). Linear models examined whether pulse wave velocity significantly interacted with APOE ε4 status and CSF AD biomarker positivity (based on the ratio of total tau over beta-amyloid [tau/Aβ42]) on memory, language, executive functioning, attention, and visuospatial abilities.

RESULTS

After adjusting for demographic characteristics and vascular risk burden, across the entire sample, pulse wave velocity was associated with poorer executive functioning but not the performance in the other cognitive domains. When the modifying effects of AD genetic risk and CSF AD biomarkers were considered, pulse wave velocity interacted with APOE genotype and CSF tau/Aβ ratio such that a stronger association between elevated pulse wave velocity and poorer memory performance was found among those positive for CSF and genetic AD markers. There were no significant interaction effects for non-memory cognitive domains.

CONCLUSION

The findings suggest that pulse wave velocity, a non-invasive method to assess arterial wall properties, may be a useful marker of risk for cognitive decline, particularly among individuals who are APOE ε4 carriers or CSF AD biomarke0r-positive.

Alzheimer's Disease Animal Models: Elucidation of Biomarkers and Therapeutic Approaches for Cognitive Impairment

Alzheimer's disease (AD) is an age-related and progressive neurodegenerative disorder. It is widely accepted that AD is mainly caused by the accumulation of extracellular amyloid β (Aβ) and intracellular neurofibrillary tau tangles. Aβ begins to accumulate years before the onset of cognitive impairment, suggesting that the benefit of currently available interventions would be greater if they were initiated in the early phases of AD. To understand the mechanisms of AD pathogenesis, various transgenic mouse models with an accelerated accumulation of Aβ and tau tangles have been developed. However, none of these models exhibit all pathologies present in human AD. To overcome these undesirable phenotypes, APP knock-in mice, which were presented with touchscreen-based tasks, were developed to better evaluate the efficacy of candidate therapeutics in mouse models of early-stage AD. This review assesses several AD mouse models from the aspect of biomarkers and cognitive impairment and discusses their potential as tools to provide novel AD therapeutic approaches.

Apolipoprotein E ϵ4 allele and neuropsychiatric symptoms among older adults in Central Africa (EPIDEMCA study)

OBJECTIVES

To evaluate the association between neuropsychiatric symptoms and apolipoprotein E (APOE) ϵ4 allele among older people in Central African Republic (CAR) and the Republic of Congo (ROC).

DESIGN

Multicenter population-based study following a two-phase design.

SETTING

From 2011 to 2012, rural and urban areas of CAR and ROC.

PARTICIPANTS

People aged 65 and over.

MEASUREMENTS

Following screening using the Community Screening Interview for Dementia, participants with low cognitive scores (CSI-D ≤ 24.5) underwent clinical assessment. Dementia diagnosis followed the DSM-IV criteria and Peterson's criteria were considered for Mild Cognitive Impairment (MCI). Neuropsychiatric symptoms were evaluated through the brief version of the Neuropsychiatric Inventory (NPI-Q). Blood samples were taken from all consenting participants before APOE genotyping was performed by polymerase chain reaction (PCR). Logistic regression models were used to evaluate the association between the APOE ϵ4 allele and neuropsychiatric symptoms.

RESULTS

Overall, 322 participants had complete information on both neuropsychiatric symptoms and APOE status. Median age was 75.0 years and 81.1% were female. Neuropsychiatric symptoms were reported by 192 participants (59.8%) and at least 1 APOE ϵ4 allele was present in 135 (41.9%). APOE ϵ4 allele was not significantly associated with neuropsychiatric symptoms but showed a trend toward a protective effect in some models.

CONCLUSION

This study is the first one investigating the association between APOE ϵ4 and neuropsychiatric symptoms among older people in sub-Saharan Africa (SSA). Preliminary findings indicate that the APOE ϵ4 allele was not associated with neuropsychiatric symptoms. Further research seems, however, needed to investigate the protective trend found in this study.

APOE-ε4 Genotype and Dementia Before and After Transient Ischemic Attack and Stroke: Population-Based Cohort Study

Background and Purpose- APOE-ε4 genotype is a risk factor for sporadic Alzheimer disease and reduced recovery from brain injury. Since data on APOE genotype and dementia associated with transient ischemic attack/stroke are sparse, we determined the associations in a longitudinal population-based cohort. Methods- All patients with transient ischemic attack or stroke (2002-2012) in a defined population of 92 728 OxVASC (Oxford Vascular Study) had follow-up to 5-years. Pre-event and incident postevent dementia were ascertained through direct patient assessment and follow-up, supplemented by review of hospital/primary care records. Associations between pre- and post-event dementia and APOE genotype (ε4/ε4-homozygous and ε4/ε3-heterozygous versus ε3/ε3) were examined using logistic regression and Cox regression models, respectively, adjusted for age, sex, education, cerebrovascular burden (stroke severity, prior stroke, white matter disease), diabetes mellitus, and dysphasia. Results- Among 1767 genotyped patients (mean/SD age, 73.0/13.0 years, 901 [51%] male, 602 [34%] transient ischemic attack), 1058 (59.9%) were APOE-ε3/ε3, 403 (22.8%) were ε4/ε3 and 30 (1.7%) were ε4-homozygous. Homozygosity was associated with both pre-event (adjusted odds ratio, 5.81 [95% CI, 1.93-17.48]; P=0.002) and postevent dementia (adjusted hazard ratio, 3.64 [95% CI, 1.90-7.00]; P<0.0001). Association with postevent dementia was maintained after further adjustment for baseline cognitive impairment (hazard ratio, 2.41 [95% CI, 1.19-4.89]; P=0.01). There were no associations overall between ε4/ε3 and pre-event dementia (adjusted odds ratio, 1.47 [95% CI, 0.88-2.45]; P=0.14) or postevent dementia (hazard ratio, 1.11 [95% CI, 0.84-1.48]; P=0.47). Conclusions- In patients with transient ischemic attack and stroke, APOE-ε4 homozygosity was associated with both pre- and post-event dementia. Associations were independent of cerebrovascular burden and may be mediated through increased neurodegenerative pathology or vulnerability to injury.

Association between APOE4 and biomarkers in cerebral adrenoleukodystrophy

Cerebral adrenoleukodystrophy (cALD) is an inflammatory neurodegenerative disease associated with mutation of the ABCD1 gene. Proteomic analysis of cerebral spinal fluid (CSF) from young males with active cALD revealed markers of inflammation including APOE4. APOE4 genotype has been associated with an inferior prognosis following acute and chronic neurologic injury. We assessed APOE4 inheritance among 83 consecutive young males with cALD prior to hematopoietic cell transplant and its association with markers of cerebral disease. The allele frequency of APOE4 was not significantly different from that of the general population at 17%. Young males with cALD that were APOE4 carriers had similar CSF protein and chitotriosidase activity to that of non-carriers. In contrast, APOE4 carriers had an increased burden of cerebral disease involvement as determined by MRI severity score (10.5 vs 7.0 points, p = 0.01), higher gadolinium intensity score (2.0 vs 1.3 points, p = 0.007), inferior neurologic function (neurologic function score 2.4 vs 1.0, p = 0.001), and elevated CSF MMP2 levels compared to that of non-carriers (13168 vs 9472 pg/mL, p = 0.01). These are the first data showing that APOE4 is associated with increased severity of cerebral disease in cALD and suggest it may be a modifier of disease.

Placental secretion of apolipoprotein A1 and E: the anti-atherogenic impact of the placenta

High levels of atherogenic lipids in pregnancy are associated with health complications for the mother, the fetus and the newborn. As endocrine secretory tissue, the human placenta releases apolipoproteins (apos), particularly apoA1 and apoE. However, the magnitude and the directionality of the apo secretions remain unknown. We aimed to 1) determine the amount and orientation (apical-maternal versus basal-fetal) of placentally secreted apoA1 and apoE using human perfused placenta and primary trophoblast cell (PTC) culture, 2) compare apoA1 and apoE secretions of PTC with that of hepatocytes and 3) associate the obtained results with human blood levels by determining apoA1 and apoE concentrations in maternal and fetal serum samples. In perfused placenta and serum samples, apoA1 and apoE concentrations were significantly higher at the maternal compared to the fetal side. For apoE a similar trend was found in PTC. For apoA1, the secretion to the apical side declined over time while release to the basal side was stable resulting in significantly different apoA1 concentrations between both sides. Unexpectedly, PTC secreted significantly higher amounts of apoA1 and apoE compared to hepatocytes. Our data indicate that the placenta may play an important role in maternal and fetal cholesterol homeostasis via secretion of anti-atherogenic apos.

Identification of immunogenic proteins of the cysticercoid of Hymenolepis diminuta

Background

A wide range of molecules are used by tapeworm metacestodes to establish successful infection in the hostile environment of the host. Reports indicating the proteins in the cestode-host interactions are limited predominantly to taeniids, with no previous data available for non-taeniid species. A non-taeniid, Hymenolepis diminuta, represents one of the most important model species in cestode biology and exhibits an exceptional developmental plasticity in its life-cycle, which involves two phylogenetically distant hosts, arthropod and vertebrate.

Results

We identified H. diminuta cysticercoid proteins that were recognized by sera of H. diminuta-infected rats using two-dimensional gel electrophoresis (2DE), 2D-immunoblotting, and LC-MS/MS mass spectrometry. Proteomic analysis of 42 antigenic spots revealed 70 proteins. The largest number belonged to structural proteins and to the heat-shock protein (HSP) family. These results show a number of the antigenic proteins of the cysticercoid stage, which were present already in the insect host prior to contact with the mammal host. These are the first parasite antigens that the mammal host encounters after the infection, therefore they may represent some of the molecules important in host-parasite interactions at the early stage of infection.

Conclusions

These results could help in understanding how H. diminuta and other cestodes adapt to their diverse and complex parasitic life-cycles and show universal molecules used among diverse groups of cestodes to escape the host response to infection.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2519-4) contains supplementary material, which is available to authorized users.

Increased maternal and fetal cholesterol efflux capacity and placental CYP27A1 expression in preeclampsia

Preeclampsia is a pregnancy-specific condition that leads to increased cardiovascular risk in later life. A decrease in cholesterol efflux capacity is linked to CVD. We hypothesized that in preeclampsia there would be a disruption of maternal/fetal plasma to efflux cholesterol, as well as differences in the concentrations of both placental sterol 27-hydroxylase (CYP27A1) and apoA1 binding protein (AIBP). Total, HDL-, and ABCA1-mediated cholesterol effluxes were performed with maternal and fetal plasma from women with preeclampsia and normotensive controls (both n = 17). apoA1 and apoE were quantified by chemiluminescence, and 27-hydroxycholesterol (27-OHC) by GC-MS. Immunohistochemistry was used to determine placental expression/localization of CYP27A1, AIBP, apoA1, apoE, and SRB1. Maternal and fetal total and HDL-mediated cholesterol efflux capacities were increased in preeclampsia (by 10-20%), but ABCA1-mediated efflux was decreased (by 20-35%; P < 0.05). Maternal and fetal apoE concentrations were higher in preeclampsia. Fetal plasma 27-OHC levels were decreased in preeclamptic samples (P < 0.05). Placental protein expression of both CYP27A1 and AIBP were localized around fetal vessels and significantly increased in preeclampsia (P = 0.04). Placental 27-OHC concentrations were also raised in preeclampsia (P < 0.05). Increased HDL-mediated cholesterol efflux capacity and placental CYP27A1/27-OHC could be a rescue mechanism in preeclampsia, to remove cholesterol from cells to limit lipid peroxidation and increase placental angiogenesis.

The Neurobiology and Age-Related Prevalence of the ε4 Allele of Apolipoprotein E in Alzheimer's Disease Cohorts

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterised by amyloid beta (Aβ) plaques and tau neurofibrillary tangles in the brain. Human apolipoprotein E (ApoE) is a lipid transport protein coded by the polymorphic APOE gene, with three major alleles: ε2, ε3 and ε4. After age, the ε4 allele is the greatest risk factor for developing sporadic AD, conferring an increased risk of 3-4 and 8-12 times for one or two copies of the allele, respectively. This risk is reported to vary by demographic factors including sex, ethnicity and geography. In order to understand the risk of ApoE ε4 in relation to age, the primary risk factor for developing AD, we need to understand how the prevalence of APOE genotypes changes with age. Here, we present the first data on age-related prevalence of APOE ε4 in AD in three AD cohorts in Australia and the USA. There is a significant association between age and ε4 prevalence, particularly for ε4 homozygotes, such that as age increases the prevalence of ε4 decreases. Further studies on a random, population-based sample of the population are needed to provide more generalizable data, particularly in the >90-year-old age group.

apoE3[K146N/R147W] acts as a dominant negative apoE form that prevents remnant clearance and inhibits the biogenesis of HDL

The K146N/R147W substitutions in apoE3 were described in patients with a dominant form of type III hyperlipoproteinemia. The effects of these mutations on the in vivo functions of apoE were studied by adenovirus-mediated gene transfer in different mouse models. Expression of the apoE3[K146N/R147W] mutant in apoE-deficient (apoE(-/-)) or apoA-I-deficient (apoA-I(-/-))×apoE(-/-) mice exacerbated the hypercholesterolemia and increased plasma apoE and triglyceride levels. In apoE(-/-) mice, the apoE3[K146N/R147W] mutant displaced apoA-I from the VLDL/LDL/HDL region and caused the accumulation of discoidal apoE-containing HDL. The WT apoE3 cleared the cholesterol of apoE(-/-) mice without induction of hypertriglyceridemia and promoted formation of spherical HDL. A unique property of the truncated apoE3[K146N/R147W]202 mutant, compared with similarly truncated apoE forms, is that it did not correct the hypercholesterolemia. The contribution of LPL and LCAT in the induction of the dyslipidemia was studied. Treatment of apoE(-/-) mice with apoE3[K146N/R147W] and LPL corrected the hypertriglyceridemia, but did not prevent the formation of discoidal HDL. Treatment with LCAT corrected hypertriglyceridemia and generated spherical HDL. The combined data indicate that the K146N/R147W substitutions convert the full-length and the truncated apoE3[K146N/R147W] mutant into a dominant negative ligand that prevents receptor-mediated remnant clearance, exacerbates the dyslipidemia, and inhibits the biogenesis of HDL.

Genetic risk factors for perinatal arterial ischemic stroke

The cause of perinatal arterial ischemic stroke is unknown in most cases. We explored whether genetic polymorphisms modify the risk of perinatal arterial ischemic stroke. In a population-based case-control study of 1997-2002 births at Kaiser Permanente Northern California, we identified 13 white infants with perinatal arterial ischemic stroke. Control subjects included 86 randomly selected white infants. We genotyped polymorphisms in nine genes involved in inflammation, thrombosis, or lipid metabolism previously linked with stroke, and compared genotype frequencies in case and control individuals. We tested several polymorphisms: tumor necrosis factor-α -308, interleukin-6, lymphotoxin A, factor V Leiden, methyltetrahydrofolate reductase 1298 and 667, prothrombin 20210, and apolipoprotein E ε2 and ε4 alleles. Patients with perinatal arterial ischemic stroke were more likely than control subjects to demonstrate at least one apolipoprotein E ε4 allele (54% vs 25%, P = 0.03). More patients with perinatal arterial ischemic stroke carried two ε4 alleles than did control subjects (15% vs 2%, P = 0.09), although this finding lacked statistical significance. Proinflammatory and prothrombotic polymorphisms were not associated with perinatal arterial ischemic stroke. The apolipoprotein E polymorphism may confer genetic susceptibility for perinatal arterial ischemic stroke. Larger population-based studies are required to confirm this finding.

STAT1 interacts with RXRα to upregulate ApoCII gene expression in macrophages

Apolipoprotein CII (apoCII) is a specific activator of lipoprotein lipase and plays an important role in triglyceride metabolism. The aim of our work was to elucidate the regulatory mechanisms involved in apoCII gene modulation in macrophages. Using Chromosome Conformation Capture we demonstrated that multienhancer 2 (ME.2) physically interacts with the apoCII promoter and this interaction facilitates the transcriptional enhancement of the apoCII promoter by the transcription factors bound on ME.2. We revealed that the transcription factor STAT1, previously shown to bind to its specific site on ME.2, is functional for apoCII gene upregulation. We found that siRNA-mediated inhibition of STAT1 gene expression significantly decreased the apoCII levels, while STAT1 overexpression in RAW 264.7 macrophages increased apoCII gene expression. Using transient transfections, DNA pull down and chromatin immunoprecipitation assays, we revealed a novel STAT1 binding site in the −500/−493 region of the apoCII promoter, which mediates apoCII promoter upregulation by STAT1. Interestingly, STAT1 could not exert its upregulatory effect when the RXRα/T3Rβ binding site located on the apoCII promoter was mutated, suggesting physical and functional interactions between these factors. Using GST pull-down and co-immunoprecipitation assays, we demonstrated that STAT1 physically interacts with RXRα. Taken together, these data revealed that STAT1 bound on ME.2 cooperates with RXRα located on apoCII promoter and upregulates apoCII expression only in macrophages, due to the specificity of the long-range interactions between the proximal and distal regulatory elements. Moreover, we showed for the first time that STAT1 and RXRα physically interact to exert their regulatory function.

Biophysical analysis of apolipoprotein E3 variants linked with development of type III hyperlipoproteinemia

Background

Apolipoprotein E (apoE) is a major protein of the lipoprotein transport system that plays important roles in lipid homeostasis and protection from atherosclerosis. ApoE is characterized by structural plasticity and thermodynamic instability and can undergo significant structural rearrangements as part of its biological function. Mutations in the 136–150 region of the N-terminal domain of apoE, reduce its low density lipoprotein (LDL) receptor binding capacity and have been linked with lipoprotein disorders, such as type III hyperlipoproteinemia (HLP) in humans. However, the LDL-receptor binding defects for these apoE variants do not correlate well with the severity of dyslipidemia, indicating that these variants may carry additional properties that contribute to their pathogenic potential.

Methodology/Principal Findings

In this study we examined whether three type III HLP predisposing apoE3 variants, namely R136S, R145C and K146E affect the biophysical properties of the protein. Circular dichroism (CD) spectroscopy revealed that these mutations do not significantly alter the secondary structure of the protein. Thermal and chemical unfolding analysis revealed small thermodynamic alterations in each variant compared to wild-type apoE3, as well as effects in the reversibility of the unfolding transition. All variants were able to remodel multillamelar 1,2-Dimyristoyl-sn-glycero-3-phosphocholine (DMPC) vesicles, but R136S and R145C had reduced kinetics. Dynamic light scattering analysis indicated that the variant R136S exists in a higher-order oligomerization state in solution. Finally, 1-anilinonaphthalene-8-sulfonic acid (ANS) binding suggested that the variant R145C exposes a larger amount of hydrophobic surface to the solvent.

Conclusions/Significance

Overall, our findings suggest that single amino acid changes in the functionally important region 136–150 of apoE3 can affect the molecule's stability and conformation in solution and may underlie functional consequences. However, the magnitude and the non-concerted nature of these changes, make it unlikely that they constitute a distinct unifying mechanism leading to type III HLP pathogenesis.

Opposite regulation of the human apolipoprotein M gene by hepatocyte nuclear factor 1 and Jun transcription factors

HDL is a negative risk factor for atherosclerosis because of its multiple atheroprotective functions. Inflammation converts HDL particles from anti-atherogenic to pro-atherogenic, and this transformation is associated with changes in HDL structure and composition. Apolipoprotein M (apoM) has been recently shown to play a role in the maturation of HDL in plasma and to protect from atherosclerosis. ApoM gene is expressed primarily in the liver and kidney and is down-regulated by pro-inflammatory signals. We now show that the human apoM promoter harbors a dual specificity regulatory element in the proximal region that binds hepatocyte nuclear factor 1 (HNF-1) and members of the AP-1 family of pro-inflammatory transcription factors (c-Jun and JunB). Overexpression of c-Jun or JunB repressed both the basal and the HNF-1-mediated transactivation of the human apoM promoter. Treatment of HepG2 cells with potent inflammation-inducing phorbol esters or overexpression of PKCα was associated with a marked inhibition of apoM gene expression in a c-Jun/JunB-dependent manner. We provide evidence for a novel mechanism of inflammation-induced transcriptional repression that is based on the competition between HNF-1 and Jun proteins for binding to the same regulatory region. A similar mechanism accounts for the down-regulation of the liver-specific apolipoprotein A-II gene by Jun factors. Our studies provide novel insights on the mechanisms that control the expression of liver-specific apolipoprotein genes during inflammation and could affect the maturation and the functionality of HDL particles.

SHORT COMMUNICATION: Apolipoprotein E genotype and cognition in bipolar disorder

Apolipoprotein E (APOE) has been extensively studied as a risk factor for sporadic and late onset Alzheimer's Disease (AD). APOE allele (∗)3, the most frequent variant, is not associated to cognitive dysfunction (CD) or to increased AD risk. Differently, the (∗)4 allele is a well-established risk factor for CD, while the (∗)2 allele is associated with survival and longevity. CD is an important feature of Bipolar Disorder (BD) and recent data suggest that CD may be one of its endophenotypes, although controversial results exist. The aim of this research is to study the association of APOE genotype (APOE) and neurocognitive function in a sample of drug free young BD-type I patients. Sample consisted of 25 symptomatic BD (type I) patients (age 18-35 years old). They were submitted to an extensive neuropsychological evaluation and genotyped for APOE. Subjects with allele (∗)2 presented better cognitive performance. The presence of allele (∗)4 was associated with worse performance in a few executive tasks. APOE (∗)3(∗)3 was associated with overall severe dysfunction on cognitive performance. In young individuals with nontreated BD-type I, APOE may predict cognitive performance. Further and larger studies on APOE and cognition in BD are required to clarify whether APOE is a BD cognitive endophenotype.

Testosterone modifies the effect of APOE genotype on hippocampal volume in middle-aged men

BACKGROUND

The APOE epsilon4 allele is an established risk factor for Alzheimer disease (AD), yet findings are mixed for how early its effects are manifest. One reason for the mixed results could be the presence of interaction effects with other AD risk factors. Increasing evidence indicates that testosterone may play a significant role in the development of AD. The aim of the present study was to examine the potential interaction of testosterone and APOE genotype with respect to hippocampal volume in middle age.

METHODS

Participants were men from the Vietnam Era Twin Study of Aging (n = 375). The mean age was 55.9 years (range 51-59). Between-group comparisons were performed utilizing a hierarchical linear mixed model that adjusted for the nonindependence of twin data.

RESULTS

A significant interaction was observed between testosterone and APOE genotype (epsilon4-negative vs epsilon4-positive). Those with both low testosterone (> or =1 SD below the mean) and an epsilon4-positive status had the smallest hippocampal volumes, although comparisons with normal testosterone groups were not significant. However, individuals with low testosterone and epsilon4-negative status had significantly larger hippocampal volumes relative to all other groups. A main effect of APOE genotype on hippocampal volume was observed, but only when the APOE-by-testosterone interaction was present.

CONCLUSIONS

These findings demonstrate an interaction effect between testosterone and the APOE epsilon4 allele on hippocampal volume in middle-aged men, and they may suggest 2 low testosterone subgroups. Furthermore, these results allude to potential gene-gene interactions between APOE and either androgen receptor polymorphisms or genes associated with testosterone production.

Molecular etiology of a dominant form of type III hyperlipoproteinemia caused by R142C substitution in apoE4

We have used adenovirus-mediated gene transfer in apolipoprotein (apo)E(-/-) mice to elucidate the molecular etiology of a dominant form of type III hyperlipoproteinemia (HLP) caused by the R142C substitution in apoE4. It was found that low doses of adenovirus expressing apoE4 cleared cholesterol, whereas comparable doses of apoE4[R142C] greatly increased plasma cholesterol, triglyceride, and apoE levels, caused accumulation of apoE in VLDL/IDL/LDL region, and promoted the formation of discoidal HDL. Co-expression of apoE4[R142C] with lecithin cholesterol acyltransferase (LCAT) or lipoprotein lipase (LPL) in apoE(-/-) mice partially corrected the apoE4[R142C]-induced dyslipidemia. High doses of C-terminally truncated apoE4[R142C]-202 partially cleared cholesterol in apoE(-/-) mice and promoted formation of discoidal HDL. The findings establish that apoE4[R142C] causes accumulation of apoE in VLDL/IDL/LDL region and affects in vivo the activity of LCAT and LPL, the maturation of HDL, and the clearance of triglyceride-rich lipoproteins. The prevention of apoE4[R142C]-induced dyslipidemia by deletion of the 203-299 residues suggests that, in the full-length protein, the R142C substitution may have altered the conformation of apoE bound to VLDL/IDL/LDL in ways that prevent triglyceride hydrolysis, cholesterol esterification, and receptor-mediated clearance in vivo.

Regulation of human apolipoprotein m gene expression by orphan and ligand-dependent nuclear receptors

Apolipoprotein M (apoM) plays an important role in the biogenesis and the metabolism of anti-atherogenic HDL particles in plasma and is expressed primarily in the liver and the kidney. We investigated the role of hormone nuclear receptors in apoM gene regulation in hepatic cells. Overexpression via adenovirus-mediated gene transfer and siRNA-mediated gene silencing established that hepatocyte nuclear factor 4 (HNF-4) is an important regulator of apoM gene transcription in hepatic cells. apoM promoter deletion analysis combined with DNA affinity precipitation and chromatin immunoprecipitation assays revealed that HNF-4 binds to a hormone-response element (HRE) in the proximal apoM promoter (nucleotides -33 to -21). Mutagenesis of this HRE decreased basal hepatic apoM promoter activity to 10% of control and abolished the HNF4-mediated transactivation of the apoM promoter. In addition to HNF-4, homodimers of retinoid X receptor and heterodimers of retinoid X receptor with receptors for retinoic acid, thyroid hormone, fibrates (peroxisome proliferator-activated receptor), and oxysterols (liver X receptor) were shown to bind with different affinities to the proximal HRE in vitro and in vivo. Ligands of these receptors strongly induced human apoM gene transcription and apoM promoter activity in HepG2 cells, whereas mutations in the proximal HRE abolished this induction. These findings provide novel insights into the role of apoM in the regulation of HDL by steroid hormones and into the development of novel HDL-based therapies for diseases such as diabetes, obesity, metabolic syndrome, and coronary artery disease that affect a large proportion of the population in Western countries.

Naturally occurring and bioengineered apoA-I mutations that inhibit the conversion of discoidal to spherical HDL: the abnormal HDL phenotypes can be corrected by treatment with LCAT

In the present study we have used adenovirus-mediated gene transfer of apoA-I (apolipoprotein A-I) mutants in apoA-I-/- mice to investigate how structural mutations in apoA-I affect the biogenesis and the plasma levels of HDL (high-density lipoprotein). The natural mutants apoA-I(R151C)Paris, apoA-I(R160L)Oslo and the bioengineered mutant apoA-I(R149A) were secreted efficiently from cells in culture. Their capacity to activate LCAT (lecithin:cholesterol acyltransferase) in vitro was greatly reduced, and their ability to promote ABCA1 (ATP-binding cassette transporter A1)-mediated cholesterol efflux was similar to that of WT (wild-type) apoA-I. Gene transfer of the three mutants in apoA-I-/- mice generated aberrant HDL phenotypes. The total plasma cholesterol of mice expressing the apoA-I(R160L)Oslo, apoA-I(R149A) and apoA-I(R151C)Paris mutants was reduced by 78, 59 and 61% and the apoA-I levels were reduced by 68, 64 and 55% respectively, as compared with mice expressing the WT apoA-I. The CE (cholesteryl ester)/TC (total cholesterol) ratio of HDL was decreased and the apoA-I was distributed in the HDL3 region. apoA-I(R160L)Oslo and apoA-I(R149A) promoted the formation of prebeta1 and alpha4-HDL subpopulations and gave a mixture of discoidal and spherical particles. apoA-I(R151C)Paris generated subpopulations of different sizes that migrate between prebeta and alpha-HDL and formed mostly spherical and a few discoidal particles. Simultaneous treatment of mice with adenovirus expressing any of the three mutants and human LCAT normalized plasma apoA-I, HDL cholesterol levels and the CE/TC ratio. It also led to the formation of spherical HDL particles consisting mostly of alpha-HDL subpopulations of larger size. The correction of the aberrant HDL phenotypes by treatment with LCAT suggests a potential therapeutic intervention for HDL abnormalities that result from specific mutations in apoA-I.

The carboxy-terminal region of apoA-I is required for the ABCA1-dependent formation of alpha-HDL but not prebeta-HDL particles in vivo

ATP-binding cassette transporter A-1 (ABCA1)-mediated lipid efflux to lipid-poor apolipoprotein A-I (apoA-I) results in the gradual lipidation of apoA-I. This leads to the formation of discoidal high-density lipoproteins (HDL), which are subsequently converted to spherical HDL by the action of lecithin:cholesterol acyltransferase (LCAT). We have investigated the effect of point mutations and deletions in the carboxy-terminal region of apoA-I on the biogenesis of HDL using adenovirus-mediated gene transfer in apoA-I-deficient mice. It was found that the plasma HDL levels were greatly reduced in mice expressing the carboxy-terminal deletion mutants apoA-I[Delta(185-243)] and apoA-I[Delta(220-243)], shown previously to diminish the ABCA1-mediated lipid efflux. The HDL levels were normal in mice expressing the WT apoA-I, the apoA-I[Delta(232-243)] deletion mutant, or the apoA-I[E191A/H193A/K195A] point mutant, which promote normal ABCA1-mediated lipid efflux. Electron microscopy and two-dimensional gel electrophoresis showed that the apoA-I[Delta(185-243)] and apoA-I[Delta(220-243)] mutants formed mainly prebeta-HDL particles and few spherical particles enriched in apoE, while WT apoA-I, apoA-I[Delta(232-243)], and apoA-I[E191A/H193A/K195A] formed spherical alpha-HDL particles. The findings establish that (a) deletions that eliminate the 220-231 region of apoA-I prevent the synthesis of alpha-HDL but allow the synthesis of prebeta-HDL particles in vivo, (b) the amino-terminal segment 1-184 of apoA-I can promote synthesis of prebeta-HDL-type particles in an ABCA1-independent process, and (c) the charged residues in the 191-195 region of apoA-I do not influence the biogenesis of HDL.

Novel changes in discoidal high density lipoprotein morphology: a molecular dynamics study

ApoA-I is a uniquely flexible lipid-scavenging protein capable of incorporating phospholipids into stable particles. Here we report molecular dynamics simulations on a series of progressively smaller discoidal high density lipoprotein particles produced by incremental removal of palmitoyloleoylphosphatidylcholine via four different pathways. The starting model contained 160 palmitoyloleoylphosphatidylcholines and a belt of two antiparallel amphipathic helical lipid-associating domains of apolipoprotein (apo) A-I. The results are particularly compelling. After a few nanoseconds of molecular dynamics simulation, independent of the starting particle and method of size reduction, all simulated double belts of the four lipidated apoA-I particles have helical domains that impressively approximate the x-ray crystal structure of lipid-free apoA-I, particularly between residues 88 and 186. These results provide atomic resolution models for two of the particles produced by in vitro reconstitution of nascent high density lipoprotein particles. These particles, measuring 95 angstroms and 78 angstroms by nondenaturing gradient gel electrophoresis, correspond in composition and in size/shape (by negative stain electron microscopy) to the simulated particles with molar ratios of 100:2 and 50:2, respectively. The lipids of the 100:2 particle family form minimal surfaces at their monolayer-monolayer interface, whereas the 50:2 particle family displays a lipid pocket capable of binding a dynamic range of phospholipid molecules.

Reduced hippocampal activation during episodic encoding in middle-aged individuals at genetic risk of Alzheimer's disease: a cross-sectional study

BACKGROUND

The presence of the apolipoprotein E (APOE) epsilon4 allele is a major risk factor for the development of Alzheimer's disease (AD), and has been associated with metabolic brain changes several years before the onset of typical AD symptoms. Functional MRI (fMRI) is a brain imaging technique that has been used to demonstrate hippocampal activation during measurement of episodic encoding, but the effect of the epsilon4 allele on hippocampal activation has not been firmly established.

METHODS

The present study examined the effects of APOE genotype on brain activation patterns in the medial temporal lobe (MTL) during an episodic encoding task using a well-characterized novel item versus familiar item contrast in cognitively normal, middle-aged (mean = 54 years) individuals who had at least one parent with AD.

RESULTS

We found that epsilon3/4 heterozygotes displayed reduced activation in the hippocampus and MTL compared to epsilon3/3 homozygotes. There were no significant differences between the groups in age, education or neuropsychological functioning, suggesting that the altered brain activation seen in epsilon3/4 heterozygotes was not associated with impaired cognitive function. We also found that participants' ability to encode information on a neuropsychological measure of learning was associated with greater activation in the anterior MTL in the epsilon3/3 homozygotes, but not in the epsilon3/4 heterozygotes.

CONCLUSION

Together with previous studies reporting reduced glucose metabolism and AD-related neuropathology, this study provides convergent validity for the idea that the MTL exhibits functional decline associated with the APOE epsilon4 allele. Importantly, these changes were detected in the absence of meaningful neuropsychological differences between the groups. A focus of ongoing work in this laboratory is to determine if these findings are predictive of subsequent cognitive decline.

The apolipoprotein E e4 polymorphism is strongly associated with poor mobility performance test results but not self-reported limitation in older people

BACKGROUND

The apolipoprotein E (ApoE) e4 polymorphism is linked to increased mortality rates, Alzheimer's disease, and cardiovascular disease in older people, but previous studies have largely failed to detect an effect on self-reported mobility disability. We hypothesized that poor performance on mobility-related tests may provide a better measure of effects, and we aimed to estimate the extent to which the ApoE e4 allele increases risks of poor performance on measured mobility and self-reported mobility disability compared to e3/3, in a medium-sized population cohort.

METHODS

Data were from 1262 people at baseline older than 65 years from the Longitudinal Aging Study Amsterdam (LASA), followed up for 6 years. Age- and sex-adjusted logistic regression models were used to explore associations.

RESULTS

At baseline, those individuals with an e4 allele had an odds ratio of 2.26 (95% confidence interval, 1.31-3.90) for poor performance on gait speed testing (<0.4 m/s) and 1.94 (95% confidence interval, 1.19-3.16) for five chair stands (> or =20 s), compared to those with e3/3 status. At follow-up, associations between e4 status and incident poor performance on the chair stand test was significant. Associations with self-reported inability or need for help walking for 5 minutes or for climbing 15 steps were nonsignificant throughout.

CONCLUSIONS

The ApoE e4 polymorphism is associated with a substantial excess of mobility limitation. The impact is detectable by performance testing, but not by self-reports. Poor results on mobility performance tests may provide a phenotype of ageing.

Synergism between nuclear receptors bound to specific hormone response elements of the hepatic control region-1 and the proximal apolipoprotein C-II promoter mediate apolipoprotein C-II gene regulation by bile acids and retinoids

We have shown previously that the hepatic control region 1 (HCR-1) enhances the activity of the human apolipoprotein C-II (apoC-II) promoter in HepG2 cells via two hormone response elements (HREs) present in the apoC-II promoter. In the present paper, we report that the HCR-1 selectively mediates the transactivation of the apoC-II promoter by chenodeoxycholic acid (CDCA) and 9- cis -retinoic acid. CDCA, which is a natural ligand of farnesoid X receptor alpha (FXRalpha), increases the steady-state apoC-II mRNA levels in HepG2 cells. This increase in transcription requires the binding of retinoid X receptor alpha (RXRalpha)-FXRalpha heterodimers to a novel inverted repeat with one nucleotide spacing (IR-1) present in the HCR-1. This element also binds hepatocyte nuclear factor 4 and apoA-I regulatory protein-1. Transactivation of the HCR-1/apoC-II promoter cluster by RXRalpha-FXRalpha heterodimers in the presence of CDCA was abolished by mutations either in the IR-1 HRE of the HCR-1 or in the thyroid HRE of the proximal apoC-II promoter, which binds RXRalpha-thyroid hormone receptor beta (T3Rbeta) heterodimers. The same mutations also abolished transactivation of the HCR-1/apoC-II promoter cluster by RXRalpha-T3Rbeta heterodimers in the presence of tri-iodothyronine. The findings establish synergism between nuclear receptors bound to specific HREs of the proximal apoC-II promoter and the HCR-1, and suggest that this synergism mediates the induction of the HCR-1/apoC-II promoter cluster by bile acids and retinoids.

Generation and characterization of two transgenic mouse lines expressing human ApoE2 in neurons and glial cells

Apolipoprotein E (apoE) isoforms are key determinants of susceptibility to late-onset Alzheimer's disease (AD). The epsilon 4 and epsilon 2 alleles have been associated with increased and decreased risk for AD, respectively. We have generated and characterized transgenic mice in which the human apoE2 gene is expressed under the control of the platelet-derived growth factor B-chain (PDGF-B) promoter, or the transferrin (TF) promoter. S1 nuclease analysis and immunoblotting showed that the PDGF-B apoE2 mice express apoE2 exclusively in the brain whereas the TF apoE2 mice express apoE2 in the liver and in the brain. In the TF apoE2 mouse line, apoE2 is also detected in the plasma. The PDGF-B apoE2 and the TF apoE2 transgenic mice were bred back to apoE(-)(/)(-) background. Immunohistochemical analysis showed that the PDGF apoE2 x apoE(-)(/)(-) and the TF apoE2 x apoE(-)(/)(-) mice express human apoE2 within the neocortex in hippocampal neurons and glial cells, respectively. ApoE(-)(/)(-) mice have been shown to develop age-dependent loss of synaptophysin. Immunoblotting of mouse brain extracts and immunohistochemical analysis of brain sections showed that apoE expression in both apoE2 x apoE(-)(/)(-) transgenic lines was associated with significant recovery of brain synaptophysin levels as compared to the levels of apoE(-)(/)(-) littermates of the same age. These apoE2-expressing mice, when bred back on amyloid precursor protein (APP) transgenic mice or other mouse lines featuring alterations in lipoprotein metabolism, may provide new mouse models for elucidating the role of apoE2 in lipid homeostasis in the brain and in the pathogenesis of AD.

Genetics of menopause-associated diseases

Menopause is the permanent cessation of menstruation resulting from the loss of ovarian follicular activity. It is estimated that perhaps 50 million women worldwide will go into menopause annually. Atherosclerotic cardiovascular disease, osteoporotic fractures and Alzheimer's dementia are common chronic disorders after menopause, representing major health problems in most developed countries. Apart from being influenced by environmental factors, these chronic disorders recognize a strong genetic component, and there are now considerable clinic evidences that these disorders are related to low hormonal milieu of postmenopausal women. Here, we review up-to-date available data suggesting that genetic variation may contribute to higher susceptibility to four sporadic chronic syndromes such as osteoporosis (OP), osteoarthritis (OA), Alzheimer's disease (AD) and coronary artery disease (CAD). For these four syndromes candidate genes that today appear as major loci in genetic susceptibility encode for proteins specific of a given system, as the vitamin D receptor (VDR) gene for the skeleton and, therefore, OP or angiotensin converting enzyme (ACE) for the cardiovascular system and, therefore, CAD. The investigation of gene polymorphisms in various pathological conditions typical of postmenopause offer an explanation not only of their genetic inheritance but also of their co-segregation in given individuals. In this view, it may be possible to identify a common set of genes whose variants contribute to a common genetic background for these different disorders. Ideal candidates appear genes of the estrogen response cascade [i.e. estrogen receptor (ERs), enzymes involved in estrogen metabolism or co-activators and co-inhibitors]. All together this information may represent the basis both for future recognition of individuals at risk and for the pharmacogenetic driving of drug responsiveness.

Charting the fate of the "good cholesterol": identification and characterization of the high-density lipoprotein receptor SR-BI

Risk for cardiovascular disease due to atherosclerosis increases with increasing concentrations of low-density lipoprotein (LDL) cholesterol and is inversely proportional to the levels of high-density lipoprotein (HDL) cholesterol. The receptor-mediated control of plasma LDL levels has been well understood for over two decades and has been a focus for the pharmacologic treatment of hypercholesterolemia. In contrast, the first identification and characterization of a receptor that mediates cellular metabolism of HDL was only recently reported. This receptor, called scavenger receptor class B type I (SR-BI), is a fatty acylated glycoprotein that can cluster in caveolae-like domains on the surfaces of cultured cells. SR-BI mediates selective lipid uptake from HDL to cells. The mechanism of selective lipid uptake is fundamentally different from that of classic receptor-mediated endocytic uptake via coated pits and vesicles (e.g. the LDL receptor pathway) in that it involves efficient receptor-mediated transfer of the lipids, but not the outer shell proteins, from HDL to cells. In mice, SR-BI plays a key role in determining the levels of plasma HDL cholesterol and in mediating the regulated, selective delivery of HDL-cholesterol to steroidogenic tissues and the liver. Significant alterations in SR-BI expression can result in cardiovascular and reproductive disorders. SR-BI may play a similar role in humans; thus, modulation of its activity may provide the basis of future approaches to the treatment and prevention of atherosclerotic disease.

Contribution of cysteine 158, the glycosylation site threonine 194, the amino- and carboxy-terminal domains of apolipoprotein E in the binding to amyloid peptide beta (1-40)

Recent studies have shown that at physiological conditions (pH 7.6, 37 degrees C), the reactivity of recombinant apoE isoforms secreted by mammalian cells toward amyloid peptide beta (Abeta40) follows the order apoE2 > apoE3 > apoE4 for the apoE monomer and apoE2 > apoE3 for apoE dimer that is formed via that intramolecular disulfide bridges. Different Abeta binding properties have been reported for the plasma-derived apoE and commercially available apoE preparations that differ from the native apoE forms in the degree of their O-glycosylation. To define structural elements of apoE involved in the interaction with Abeta, we have introduced point mutations as well as amino- and carboxy-terminal deletions in the apoE structure. The mutant apoE forms were expressed transiently using the Semliki Forest Virus system, and the culture medium was utilized to study the reactivity of the mutated proteins with Abeta 40. This analysis showed that a mutation in the O-glycosylation site of apoE2 (Thr194-Ala) did not affect the SDS-stable binding of apoE to Abeta. In contrast, introduction of cysteine at position 158 of apoE4 (Arg112, Cys158) increased the SDS-stable binding of apoE to Abeta to the levels similar to those observed in apoE2. Similar analysis showed that apoE truncated at residues 259, 249, 239, and 229 retains the SDS-stable binding to Abeta40, whereas apoE truncated at residues 185 and 165 does not bind to Abeta. The deletion of aminoterminal residues 2-19 reduced the SDS-stable binding of apoE2 to Abeta and deletion of residues 2-81 abolished binding to Abeta. It is also noteworthy that the (Delta2-81) apoE mutant exists predominantly as a dimer, suggesting that removal of residues 2-81 promoted dimerization of apoE. These findings suggest that the amino- and carboxy-terminal residues of apoE are required for SDS-stable binding of apoE to Abeta and that the presence of at least one cysteine contributes to the efficient Abeta binding.

Two regulatory elements of similar structure and placed in tandem account for the repressive activity of the first intron of the human apolipoprotein A-II gene

Recent reports indicate that apolipoprotein (apo) A-II, the second most abundant protein of high-density lipoproteins, plays a crucial role in counteracting the beneficial effect of apo A-I against atherogenesis. Transcription of the human apo A-II gene is controlled by an enhancer comprising 14 regulatory elements located upstream of its promoter whereas the first intron of this gene behaves as a silencer. Here we show that two sequence elements account for the repressive activity of this intron and correspond to negative regulatory elements termed NRE I and NRE II. The activity of intron I and the nuclear proteins binding to NRE I and II are encountered in hepatic cells but not in non-hepatic cells studied here. Both NREs form nucleoprotein complexes of very similar physicochemical characteristics and bind the same or closely related proteins. Site-directed mutagenesis, transient transfection and gel-shift analysis experiments indicate that both NREs exhibit similar structures, being composed of two sites required for maximal activity and optimal binding of transcription factors. Therefore two negative regulatory elements of similar structure and function, placed in tandem, account for the repressive activity of the first intron of the human apo A-II gene. These NREs do not exhibit structural similarity with known NREs of other genes.

Concentration of intracellular hepatic apolipoprotein E in Golgi apparatus saccular distensions and endosomes

The intrahepatic distribution of apolipoprotein E has been assessed by immunogold labeling of cryosections as well as by Western blotting of organelles isolated from liver homogenates. Both techniques supported the prior analytical fractionation studies of Wong (1989) who concluded that intrahepatic apoE was largely endosomal. All endosomal components decorated by gold particles indicative of apoE antigenicity in cryosections appeared filled with lipoprotein-like particles thereby accounting for this prominent morphological feature of isolated liver endosomes. The distribution of gold particles about the hepatic Golgi apparatus revealed a high content of apoE in closely apposed endosomes, ca. 400 nm in diameter, double labeled for apoE and internalized HRP. Remarkably, apoE (but not internalized HRP) was also observed within saccular distensions of all saccules of stacked Golgi cisternae but absent from the flattened saccular components as was also observed for apoB. This contrasted with albumin, the major secretory protein, which was uniformly distributed throughout the hepatic Golgi apparatus. These observations support a growing body of evidence for intra-Golgi sorting of secretory material in hepatic Golgi apparatus. The lack of any immunoreactive apoE or albumin in small 70-90 nm vesicles about the Golgi cisternae suggests limits to current models of vesicle-mediated intra-Golgi transport.