Frontotemporal lobar degeneration with motor neuron disease (FTLD-MND) is characterized by neuronal cytoplasmic inclusions containing TDP-43. Apolipoprotein E4 (apoE4), derived from the apoE ε4 allele, enhances brain atrophy in FTLD through unknown mechanisms. Here, we studied two siblings with C9ORF72-linked familial FTLD-MND, an apoE ε4 homozygote and an apoE ε3 homozygote. The apoE ε4 homozygote had more cognitive-behavioral symptoms, fronto-insulo-temporal atrophy, and apoE fragments and aggregates in the anterior cingulate cortex. ApoE formed complexes with TDP-43 that were more abundant in the apoE ε4 homozygote. Although differences seen in a sibling pair could arise due to chance, these findings raise the possibility that apoE4 exacerbates brain pathology in FTLD through formation of neurotoxic apoE fragments and interactions with TDP-43.
Apolipoprotein E; TDP-43; Frontotemporal dementia; Motor neuron disease; Neuropathology
Genetic components controlling for echocardiographically determined left ventricular (LV) mass are still unclear in the Chinese population.
We conducted a family study from the Chin-San community, Taiwan, and a total of 368 families, 1145 subjects, were recruited to undergo echocardiography to measure LV mass. Commingling analysis, familial correlation, and complex segregation analysis were applied to detect component distributions and the mode of inheritance.
The two-component distribution model was the best-fitting model to describe the distribution of LV mass. The highest familial correlation coefficients were mother-son (0.379, P < .0001) and father-son (0.356, P < .0001). Genetic heritability (h2) of LV mass was estimated as 0.268 ± 0.061 (P < .0001); it decreased to 0.153 ± 0.052 (P = .0009) after systolic blood pressure adjustment. Major gene effects with polygenic components were the best-fitting model to explain the inheritance mode of LV mass. The estimated allele frequency of the gene was 0.089.
There were significant familial correlations, heritability and a major gene effect on LV mass in the population-based families.
In 1979 Steinberg and colleagues recognized a unique kindred with normotriglyceridemic hypobetalipoproteinemia (1979. J. Clin. Invest. 64:292-301). We have undertaken an intensive reexamination of this kindred and have studied 41 family members in three generations. In this family we document the presence of two distinct apo B alleles associated with low plasma concentrations of apolipoprotein (apo) B and low density lipoprotein (LDL) cholesterol and we trace the inheritance of these two alleles over three generations. One of the alleles resulted in the production of an abnormal, truncated apo B species, apo B-37. The other apo B allele was associated with reduced plasma concentrations of the normal apo B species, apo B-100. H.J.B., the proband, and two of his siblings had both abnormal apo B alleles and were therefore compound heterozygotes for familial hypobetalipoproteinemia. Their average LDL-cholesterol level was 6 +/- 9 mg/dl. All of the offspring of the three compound heterozygotes had hypobetalipoproteinemia, and each had evidence of only one of the abnormal apo B alleles. In the entire kindred, we identified six heterozygotes for familial hypobetalipoproteinemia who had only the abnormal apo B-37 allele and their average LDL cholesterol was 31 +/- 12 mg/dl. We identified 10 heterozygotes who had only the allele for reduced plasma concentrations of apo B-100 and their LDL cholesterol level was 31 +/- 15 mg/dl. Unaffected family members (n = 22) had LDL cholesterol levels of 110 +/- 27 mg/dl. This report describes the first kindred in which two distinct abnormal apo B alleles have been identified, both of which are associated with familial hypobetalipoproteinemia.
Apolipoprotein(a) [apo(a)], an apolipoprotein unique to lipoprotein(a) [Lp(a)], is highly polymorphic in size. Previous studies have indicated that the size of the apo(a) gene tends to be inversely correlated with the plasma level of Lp(a). However, several exceptions to this general trend have been identified. Individuals with apo(a) alleles of identical size do not always have similar plasma concentrations of Lp(a). To determine if these differences in plasma Lp(a) concentrations were due to sequence variations in the apo(a) gene, we examined the sequences of apo(a) alleles in 23 individuals homozygous for same-sized apo(a) alleles. We identified four single-strand DNA conformation polymorphisms (SSCPs) in the apo(a) gene. Of the 23 homozygotes, 21 (91%) were heterozygous for at least one of the SSCPs. Analysis of a family in which a parent was homozygous for the same-sized apo(a) allele revealed that each allele, though identical size, segregated with different plasma concentrations of Lp(a). These studies indicate that the apo(a) gene is even more polymorphic in sequence than was previously appreciated, and that sequence variations at the apo(a) locus, other than the number of kringle 4 repeats, contribute to the plasma concentration of Lp(a).
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 6 days 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 ≤ 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 to 28 P.I., a ~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.
HSV-1; apolipoprotein E; brain; cornea; herpetic stromal keratitis; trigeminal ganglia; transgenic mouse model; vascular endothelial growth factor
We describe a kindred in which the proband and 6 of his 12 children have hypobetalipoproteinemia. The plasma lipoproteins of the affected subjects contained a unique species of apolipoprotein (apo) B, apo B67, in addition to the normal species, apo B100 and apo B48. The size of apo B67 and immunochemical studies with a panel of apo B-specific antibodies indicated that apo B67 was a truncated species of apo B that contained approximately the amino-terminal 3,000-3,100 amino acids of apo B100. Sequencing of genomic apo B clones revealed that affected family members were heterozygous for a mutant apo B allele containing a single nucleotide deletion in exon 26 (cDNA nucleotide 9327). This frameshift mutation is predicted to result in the synthesis of a truncated apo B containing 3,040 amino acids. Apo B67 is present in low levels in the plasma but is easily detectable within the very low density lipoprotein and low density lipoprotein fractions. Examination of the proband's immediate family revealed seven normolipidemic subjects and seven subjects with hypobetalipoproteinemia. In the affected subjects, the mean total and low density lipoprotein cholesterol levels were 120 and 42 mg/dl, respectively. A significantly higher mean high density lipoprotein cholesterol level was found in the affected subjects (75 vs. 55 mg/dl). We hypothesize that the elevated high density lipoprotein cholesterol levels in subjects heterozygous for the apo B67 mutation may be metabolically linked to the low levels of apo B-containing lipoproteins in their plasma.
Genetic familial hypercholesterolemia (FH) and combined hyperlipidemia (FCH) are characterized by elevated plasma LDL (FH) and LDL/triglycerides (FCH), with mouse models represented by LDL receptor (LDLR) and apolipoprotein E (ApoE) gene deletion mice, respectively. Given the impact of FH and FCH on health outcomes, we determined the impact of FH/FCH on vascular structure in LDLR and ApoE mice. LDLR, ApoE and control mice were utilized at 12–13 and 22–23 weeks when gracilis arteries were studied for wall mechanics and gastrocnemius muscles were harvested for microvessel density measurements. Conduit arteries and plasma samples were harvested for biochemical analyses. Arteries from ApoE and LDLR exhibited blunted expansion versus control, reduced distensibility and left-shifted stress versus strain relation (LDLR>ApoE). Microvessel density was reduced in ApoE and LDLR (ApoE>LDLR). Secondary analyses suggested that wall remodeling in LDLR was associated with cholesterol and MCP-1, while rarefaction in ApoE was associated with TNF-α, triglycerides and vascular production of TxA2. Remodeling in ApoE and LDLR appears distinct; as that in LDLR is preferential for vascular walls, while that for ApoE is stronger for rarefaction. Remodeling in LDLR may be associated with cellular adhesion, while that in ApoE may be associated with pro-apoptotsis and constrictor prostanoid generation.
vascular wall mechanics; microvascular density; vascular wall distensibility; rodent models of dyslipidemia
Apolipoprotein E (apoE) and apoE/amyloid-β (Aβ) transgenic (Tg) mouse models are critical to understanding apoE-isoform effects on Alzheimer's disease risk. Compared to wild type, apoE−/− mice exhibit neuronal deficits, similar to apoE4-Tg compared to apoE3-Tg mice, providing a model for Aβ-independent apoE effects on neurodegeneration. To determine the effects of apoE on Aβ-induced neuropathology, apoE−/− mice were crossed with Aβ-Tg mice, resulting in a significant delay in plaque deposition. Surprisingly, crossing human-apoE-Tg mice with apoE−/−/Aβ-Tg mice further delayed plaque deposition, which eventually developed in apoE4/Aβ-Tg mice prior to apoE3/Aβ-Tg. One approach to address hAPOE-induced temporal delay in Aβ pathology is an additional insult, like head injury. Another is crossing human-apoE-Tg mice with Aβ-Tg mice that have rapid-onset Aβ pathology. For example, because 5xFAD mice develop plaques by 2 months, the prediction is that human-apoE/5xFAD-Tg mice develop plaques around 6 months and 12 months before other human-apoE/Aβ-Tg mice. Thus, tractable models for human-apoE/Aβ-Tg mice continue to evolve.
Variation in APOE genotype is a determinant of Alzheimer disease (AD), but the risk associated with variation in plasma apoE levels has yet to be determined. Here, we studied offspring with and without a parental history of AD to identify the effect of plasma apoE levels at middle age on the risk of late-onset AD.
Some 203 offspring from 92 families with a parental history of AD were compared with 197 offspring from 97 families without a parental history of AD. APOE genotypes and plasma apoE levels were assessed in all offspring. Difference in plasma apoE level between subjects with and without a parental history of AD was calculated using robust linear regression, both stratified and adjusted for APOE genotype.
Offspring with a parental history of AD were more likely to be an APOE ɛ4 allele carrier (46% vs 21%, p < 0.001) than offspring without such a parental history. Mean plasma apoE levels strongly decreased from ɛ2 to ɛ3ɛ3 to ɛ4 carriers (p < 0.001). Offspring with a parental history of AD had lower plasma apoE levels than subjects without such a history, both in analyses adjusted for APOE genotype (difference: −0.21 mg/dL, p = 0.02) and when using standardized Z scores, when stratified for APOE genotype (difference: −0.22, p = 0.009).
Our findings suggest that lower plasma apoE levels in middle age could be a risk factor for Alzheimer disease in old age, independent of APOE genotype.
= Alzheimer disease;
= body mass index;
= confidence interval;
= cardiovascular disease;
= early-onset Alzheimer disease;
= high-density lipoprotein;
= low-density lipoprotein;
= late-onset Alzheimer disease;
= Mini-Mental State Examination;
= vascular dementia.
Brain alterations in structure and function have been identified in people with risk factors for sporadic type Alzheimer’s disease (AD), suggesting that alterations can be detected decades before AD diagnosis. While the effect of Apolipoprotein E (ApoE) ε4 on the brain is well studied, less is known about the effect of family history of AD. We examined the main effects of family history and ApoE ε4 on brain integrity, in addition to assessing possible additive effects of these two risk factors.
Diffusion tensor imaging was performed in 136 middle-aged asymptomatic participants stratified on family history and ApoE ε4. Mean diffusivity and fractional anisotropy (FA) were entered in factorial analyses to test the effect of AD risk on microstructural brain integrity. We performed a post hoc analysis of the three principle diffusivities (λ1, λ2, λ3) to provide potential additional insight on underlying tissue differences.
Parental family history of AD was associated with lower FA in regions of the brain known to be affected by AD, including cingulum, corpus callosum, tapetum, uncinate fasciculus, hippocampus, and adjacent white matter. Contrary to previous reports there was no main effect of ApoE ε4; however, there was an additive effect of family history and ApoE ε4 where family history positive participants who were also ApoE ε4 carriers had the lowest FA compared to the other groups.
The data indicate that unknown risk factors contained in family history are associated with changes in microstructural brain integrity in areas of the brain known be affected by AD. Importantly, the results provide further evidence that AD pathology may be detected prior to cognitive changes, perhaps decades before disease onset.
Alzheimer’s disease; family history; ApoE ε4; diffusion tensor imaging; MRI; white matter
To evaluate the longitudinal influence of family history (FH) of Alzheimer disease (AD) and apolipoprotein E ϵ4 allele (APOE4) on brain atrophy and cognitive decline over 4 years among asymptomatic middle-aged individuals.
Participants were cognitively healthy adults with (FH+) (n = 60) and without (FH−) (n = 48) a FH of AD (mean age at baseline 54 years) enrolled in the Wisconsin Registry for Alzheimer's Prevention. They underwent APOE genotyping, cognitive testing, and an MRI scan at baseline and 4 years later. A covariate-adjusted voxel-based analysis interrogated gray matter (GM) modulated probability maps at the 4-year follow-up visit as a function of FH and APOE4. We also examined the influence of parent of origin on GM atrophy. Parallel analyses investigated the effects of FH and APOE4 on cognitive decline.
Neither FH nor APOE4 had an effect on regional GM or cognition at baseline. Longitudinally, a FH × APOE4 interaction was found in the right posterior hippocampus, which was driven by a significant difference between the FH+ and FH− subjects who were APOE4−. In addition, a significant FH main effect was observed in the left posterior hippocampus. No significant APOE4 main effects were detected. Persons with a maternal history of AD were just as likely as those with a paternal history of AD to experience posterior hippocampal atrophy. There was no longitudinal decline in cognition within the cohort.
Over a 4-year interval, asymptomatic middle-aged adults with FH of AD exhibit significant atrophy in the posterior hippocampi in the absence of measurable cognitive changes. This result provides further evidence that detectable disease-related neuroanatomic changes do occur early in the AD pathologic cascade.
By the careful screening of familial dysbetalipoproteinemic (FD) patients, five probands showing heterozygosity for the APOE*3-Leiden allele were found. Genealogical studies revealed that these probands share common ancestry in the 17th century. In a group of 128 family members, spanning three generations, 37 additional heterozygous APOE*3-Leiden gene carriers were detected. Although with a variable degree of severity, all carriers exhibited characteristics of FD such as (a) elevated levels of cholesterol in the very low density lipoprotein (VLDL) and intermediate density lipoprotein (IDL) fractions, (b) elevated ratios of cholesterol levels in these density fractions over total plasma levels of triglycerides, and (c) strongly increased plasma levels of apolipoprotein E (apoE). Multiple linear regression analysis revealed that most of the variability in expression of FD in APOE*3-Leiden allele carriers can be explained by age. Body mass index showed a less significant influence on the expression of FD. Gender had no effect on the expression in E*3-Leiden allele carriers, nor did it influence the age of onset of FD. In the group of APOE*3-Leiden allele carriers, we found that the E*2 allele enhances the expression of FD, whereas the E*4 allele had the opposite effect. Isoelectric focusing of plasma and of isolated VLDL, IDL, and high density lipoprotein density fractions showed that in E*3-Leiden allele carriers the apoE3-Leiden variant largely predominates over its normal apoE counterpart, especially in the VLDL and IDL density fractions. We conclude that in APOE*3-Leiden allele carriers FD is dominantly inherited with a high rate of penetrance, i.e., the presence of normally functioning apoE molecules in the plasma does not prevent the age-related expression of this disease.
Children of Alzheimer's Disease (AD) patients are at heightened risk of developing AD due to genetic influences, including the apolipoprotein E4 (ApoE4) allele. In this study, we assessed the earliest cortical changes associated with AD in 71 cognitively healthy, adult children of AD patients (AD offspring) as compared with 69 with no family history of AD (non-AD offspring). Cortical thickness measures were obtained using FreeSurfer from 1.5T magnetic resonance (MR) scans. ApoE genotyping was obtained. Primary analyses examined family history and ApoeE4 effects on cortical thickness. Secondary analyses examined age effects within groups. All comparisons were adjusted using False Discovery Rate at a significance threshold of p < 0.05. There were no statistically significant differences between family history and ApoE4 groups. Within AD offspring, increasing age was related to reduced cortical thickness (atrophy) over large areas of the precuneus, superior frontal and superior temporal gyri, starting at around age 60. Further, these patterns existed within female and maternal AD offspring, but were absent in male and paternal AD offspring. Within non-AD offspring, negative correlations existed over small regions of the superior temporal, insula and lingual cortices. These results suggest that as AD offspring age, cortical atrophy is more prominent, particularly if the parent with AD is mother or if the AD offspring is female.
Antecedent biomarker; Familial risk; Alzheimer’s Disease; Dementia; Adult Children Study; Cortical thickness; Maternal risk
Apolipoprotein-E (apoE) plays important roles in neurobiology and the apoE4 isoform increases risk for Alzheimer's disease (AD). ApoE3 and apoE2 are known to form disulphide-linked dimers in plasma and cerebrospinal fluid whereas apoE4 cannot form these dimers as it lacks a cysteine residue. Previous in vitro research indicates dimerisation of apoE3 has a significant impact on its functions related to cholesterol homeostasis and amyloid-beta peptide degradation. The possible occurrence of apoE dimers in cortical tissues has not been examined and was therefore assessed. Human frontal cortex and hippocampus from control and AD post-mortem samples were homogenised and analysed for apoE by western blotting under both reducing and non-reducing conditions.
In apoE3 homozygous samples, ~12% of apoE was present as a homodimer and ~2% was detected as a 43 kDa heterodimer. The level of dimerisation was not significantly different when control and AD samples were compared. As expected, these dimerised forms of apoE were not detected in apoE4 homozygous samples but were detected in apoE3/4 heterozygotes at a level approximately 60% lower than seen in the apoE3 homozygous samples. Similar apoE3 dimers were also detected in lysates of SK-N-SH neuroblastoma cells and in freshly prepared rabbit brain homogenates. The addition of the thiol trapping agent, iodoacetamide, to block reactive thiols during both human and rabbit brain sample homogenisation and processing did not reduce the amount of apoE homodimer recovered. These data indicate that the apoE dimers we detected in the human brain are not likely to be post-mortem artefacts.
The identification of disulphide-linked apoE dimers in human cortical and hippocampal tissues represents a distinct structural difference between the apoE3 and apoE4 isoforms that may have functional consequences.
Plasma lipoprotein(a) [Lp(a)], a low density lipoprotein particle with an attached apolipoprotein(a) [apo(a)], varies widely in concentration between individuals. These concentration differences are heritable and inversely related to the number of kringle 4 repeats in the apo(a) gene. To define the genetic determinants of plasma Lp(a) levels, plasma Lp(a) concentrations and apo(a) genotypes were examined in 48 nuclear Caucasian families. Apo(a) genotypes were determined using a newly developed pulsed-field gel electrophoresis method which distinguished 19 different genotypes at the apo(a) locus. The apo(a) gene itself was found to account for virtually all the genetic variability in plasma Lp(a) levels. This conclusion was reached by analyzing plasma Lp(a) levels in siblings who shared zero, one, or two apo(a) genes that were identical by descent (ibd). Siblings with both apo(a) alleles ibd (n = 72) have strikingly similar plasma Lp(a) levels (r = 0.95), whereas those who shared no apo(a) alleles (n = 52), had dissimilar concentrations (r = -0.23). The apo(a) gene was estimated to be responsible for 91% of the variance of plasma Lp(a) concentration. The number of kringle 4 repeats in the apo(a) gene accounted for 69% of the variation, and yet to be defined cis-acting sequences at the apo(a) locus accounted for the remaining 22% of the inter-individual variation in plasma Lp(a) levels. During the course of these studies we observed the de novo generation of a new apo(a) allele, an event that occurred once in 376 meioses.
In this paper we report on the molecular defect underlying apolipoprotein CII (apoCII) deficiency in an Italian kindred. ApoCII serves as cofactor for lipoprotein lipase (LPL) in triglyceride hydrolysis of chylomicrons and very low density lipoproteins. Homozygous apoCII deficiency manifests with type I hyperlipoproteinaemia and is a rare disorder of lipoprotein metabolism. Until now, only 10 kindreds with apoCII deficiency have been published and all underlying mutations were unique. The proband was the offspring of a consanguineous mating. Sequencing of cloned DNA from the proband presented in this report showed homozygosity for a C-->A substitution at position 3002 in the apoCII gene, resulting in the introduction of a premature stop codon at residue 37 of the mature apoCII protein. Therefore, a truncated apoCII is synthesised, lacking the part of the apolipoprotein that activates LPL. This mutation has previously been described in another Italian family and is known as apoCIIPadova. We propose that apoCIIPadova is a frequent cause of apoCII deficiency in persons of Italian descent.
There are three apolipoprotein E (apoE) isoforms involved in human lipid homeostasis. In the present study, truncated apoE2-, apoE3- and apoE4-(72-166) peptides that are tailored to lack domain interactions are expressed and elucidated the structural and functional consequences.
Methods & Results
Circular dichroism analyses indicated that their secondary structure is still well organized. Analytical ultracentrifugation analyses demonstrated that apoE-(72-166) produces more complicated species in PBS. All three isoforms were significantly dissociated in the presence of dihexanoylphosphatidylcholine. Dimyristoylphosphatidylcholine turbidity clearance assay showed that apoE4-(72-166) maintains the highest lipid-binding capacity. Finally, only apoE4-(72-166) still maintained significant LDL receptor binding ability.
Overall, apoE4-(72-166) peptides displayed a higher lipid-binding and comparable receptor-binding ability as to full-length apoE. These findings provide the explanation of diverged functionality of truncated apoE isoforms.
Domain interaction, a structural property of apolipoprotein E4 (apoE4), is predicted to contribute to the association of apoE4 with Alzheimer disease. Arg-61 apoE mice, a gene-targeted mouse model specific for domain interaction, have lower brain apoE levels and synaptic, functional, and cognitive deficits. We hypothesized that domain interaction elicits an endoplasmic reticulum (ER) stress in astrocytes and an unfolded protein response that targets Arg-61 apoE for degradation. Primary Arg-61 apoE astrocytes had less intracellular apoE than wild-type astrocytes, and unfolded protein response markers OASIS (old astrocyte specifically induced substance), ATF4, and XBP-1 and downstream effectors were up-regulated. ER stress appears to cause global astrocyte dysfunction as glucose uptake was decreased in Arg-61 apoE astrocytes, and astrocyte-conditioned medium promoted neurite outgrowth less efficiently than wild-type medium in Neuro-2a cell cultures. We showed age-dependent up-regulation of brain OASIS levels and processing in Arg-61 apoE mice. ER stress and astrocyte dysfunction represent a new paradigm underlying the association of apoE4 with neurodegeneration.
After age, the second largest risk factor for Alzheimer's disease (AD) is apolipoprotein E (APOE) genotype, where APOE4 is associated with lower apoE protein levels, more severer brain pathology, enhanced inflammation and disease. Small peptides corresponding to the receptor-binding region of apoE mimic the anti-inflammatory activity of the apoE holoprotein. These apoE mimetics greatly improve behavioral outcomes and neuronal survival in head trauma models that display AD pathology and neuronal loss. Objective: To determine whether apoE mimetics change behavior, inflammation and pathology in CVND-AD (SwDI-APP/NOS2–/–) transgenic mice.
Starting at 9 months, apoE peptides were subcutaneously administered 3 times per week for 3 months followed by behavioral, histochemical and biochemical testing.
Treatment with apoE mimetics significantly improved behavior while decreasing the inflammatory cytokine IL-6, neurofibrillary tangle-like and amyloid plaque-like structures. Biochemical measures matched the visible pathological results.
Treatment with apoE mimetics significantly improved behavior, reduced inflammation and reduced pathology in CVND-AD mice. These improvements are associated with apoE-mimetic-mediated increases in protein phosphatase 2A activity. Testing in additional AD models showed similar benefits, reinforcing this novel mechanism of action of apoE mimetics. These data suggest that the combination of anti-inflammatory and neuroprotective activities of apoE mimetics represents a new generation of potential therapeutics for AD.
Apolipoprotein E; Neuroprotection; Anti-inflammatory activity; SET (or I2PP2A); Protein phosphatase 2A; Dephosphorylation; Neurofibrillary tangles; Tau; Amyloid; Amyloid-β peptide; Alzheimer's disease
This study characterized the plasma lipoproteins of familial hyperalphalipoproteinemic patients with or without deficiency of cholesteryl ester transfer protein (CETP) activity. The subjects with CETP deficiency have increased levels of apolipoprotein (apo) E. The increased concentration of apo E in these subjects was correlated to the appearance of apo E-rich high density lipoproteins (HDL). Sodium dodecyl sulfate-polyacrylamide gel analysis revealed that these lipoproteins contained predominantly the apo E (82%) and little amount of apo A-I (18%). These apo E-rich HDL displayed a much higher affinity than human LDL in binding to LDL receptors on human fibroblasts. Furthermore, 3.5 times fewer apo E-rich HDL than LDL were required to saturate the receptors on fibroblasts. These data indicated that the apo E-rich HDL in CETP-deficient human subjects contained multiple copies of apo E and bound to the LDL receptor through multiple interactions. The apo E-rich HDL, with similar properties as cholesterol-induced apo E HDLc, were not detectable in normal human subjects or in hyperalphalipoproteinemic subjects with normal CETP activity. The apo E-containing HDL in the latter subjects were smaller and contained only small amounts of apo E (14%). The difference in apo E-containing HDL in these subjects suggests a correlation between CETP level and the appearance of apo E-rich HDL.
Although a high-resolution X-ray structure for the N-terminal domain of apolipoprotein E (apoE) in the lipid-free state has been solved, our knowledge of the structure of full-length apoE in a lipid-bound state is limited to an X-ray model fitting a molecular envelope at 10-Å resolution. To add molecular detail to the molecular envelope, we used cysteine mutagenesis to incorporate spin labels for analysis with electron paramagnetic resonance (EPR) spectroscopy. Twelve cysteine residues were introduced singly and in pairs at unique locations throughout apoE4 and labeled with an EPR spin probe. The labeled apoE4 was combined with dipalmitoylphosphatidylcholine, the particles were purified, and spectra were determined for 24 combinations (single and double) of the cysteine mutants. Data on the conformation, mobility, distance, and surface exposure of regions revealed by the cysteine probes were modeled into the molecular envelope of apoE bound to dipalmitoylphosphatidylcholine that had been determined by X-ray analysis. This EPR model of apoE in a native lipid-bound state validates the structural model derived from X-ray analysis and provides additional insight into apoE structure-function relationships.
protein structure; models; spin labels; lipoproteins
A unique kindred with premature cardiovascular disease, tubo-eruptive xanthomas, and type III hyperlipoproteinemia (HLP) associated with familial apolipoprotein (apo) E deficiency was examined. Homozygotes (n = 4) had marked increases in cholesterol-rich very low density lipoproteins (VLDL) and intermediate density lipoproteins (IDL), which could be effectively lowered with diet and medication (niacin, clofibrate). Homozygotes had only trace amounts of plasma apoE, and accumulations of apoB-48 and apoA-IV in VLDL, IDL, and low density lipoproteins. Radioiodinated VLDL apoB and apoE kinetic studies revealed that the homozygous proband had markedly retarded fractional catabolism of VLDL apoB-100, apoB-48 and plasma apoE, as well as an extremely low apoE synthesis rate as compared to normals. Obligate heterozygotes (n = 10) generally had normal plasma lipids and mean plasma apoE concentrations that were 42% of normal. The data indicate that homozygous familial apoE deficiency is a cause of type III HLP, is associated with markedly decreased apoE production, and that apoE is essential for the normal catabolism of triglyceride-rich lipoprotein constituents.
Although the complement system has been implicated in atherosclerosis, the influence of membrane-bound complement regulators in this process has not been well understood. We studied the role of two membrane complement regulators, decay-accelerating factor (DAF) and CD59, in a murine model of atherosclerosis. DAF−/− and CD59−/− mice were crossed with apolipoprotein E (ApoE)-deficient mice to generate DAF−/−ApoE−/− and CD59−/−ApoE−/− mice. Mice were fed a high fat diet (HFD) for 8 or 16 weeks. En face analysis showed that CD59 deficiency led to more extensive lesions in female ApoE−/− mice both at 8 weeks (2.07±0.27 % vs.1.34±0.21%, P=0.06) and 16 weeks (17.13±1.14% vs. 9.72±1.14%, P<0.001). Similarly, lesions measured by aortic root sectioning were larger in female CD59−/−ApoE−/− mice than in controls at 8 weeks of HFD feeding (20.74±1.33% vs. 13.12±1.46%, P<0.005). On the other hand, DAF deficiency did not significantly influence atherosclerosis in ApoE−/− mice. Immunohistochemistry revealed more abundant membrane attack complex (MAC) deposition and more collagen staining in the aortic roots of CD59−/−ApoE−/− mice. Unexpectedly, total plasma cholesterol levels in female CD59−/−ApoE−/− mice were found to be elevated compared with CD59+/+ApoE−/− mice. We conclude that CD59 but not DAF offered protection in atherosclerosis in the context of ApoE deficiency. The protective role of CD59 was gender-biased and most likely involved prevention of MAC-mediated vascular injury, with possible contribution from an undefined effect on plasma cholesterol homeostasis.
The apolipoprotein E family consists of three major protein isoforms: apolipoprotein E4 (ApoE4), ApoE3 and ApoE2. The isoforms, which contain 299 residues, differ only by single amino acid changes but of the three only ApoE4 is a risk factor for Alzheimer’s Disease. At μM concentrations lipid-free ApoE exists predominantly as tetramers. In more dilute solutions, lower molecular weight species predominate. Using Fluorescence Correlation Spectroscopy (FCS), intermolecular Fluorescence Resonance Energy Transfer (FRET) and sedimentation methods we find that the association-dissociation reaction of ApoE can be modeled with a monomer-dimer-tetramer process. Equilibrium constants have been determined from the sedimentation data while the individual rate constants for association and dissociation are determined by measuring the kinetics of dissociation of ApoE and are in agreement with the equilibrium constants. Dissociation kinetics as measured by intermolecular FRET show two phases reflecting the dissociation of tetramer to dimer and of dimer to monomer with dissociation from tetramer to dimer being more rapid than the dimer to monomer dissociation. The rate constants differ for the different ApoE isoforms showing that the association-dissociation process is isoforms specific. Strikingly, the association rate constants are almost two orders of magnitude slower than expected for a diffusion controlled process. Dissociation kinetics were also monitored by tryptophan fluorescence in presence of acrylamide and the data found to be consistent with the monomer-dimer-tetramer model. The approach combining multiple methods establishes the reaction scheme of ApoE self-association.
Protein-protein interaction; monomer-dimer-tetramer; rate constants; intermolecular FRET; sedimentation velocity; sedimentation equilibrium
The apolipoprotein E4 allele (APOE4) contributes to Alzheimer’s disease (AD) risk and APOE2 is protective, but the relevant cellular mechanisms are unknown. We have used flow cytometry analysis to measure apolipoprotein E (apoE) and amyloid beta peptide (Aβ) levels in large populations of synaptic terminals from AD and aged cognitively normal controls, and demonstrate that modest but significant increases in soluble apoE levels accompany elevated Aβ in AD cortical synapses and in an APP/PS1 rat model of AD. Dual labeling experiments document co-localization of apoE and Aβ in individual synapses with concentration of Aβ in a small population of apoE-positive synapses in both AD and controls. Consistent with a clearance role, the apoE level was higher in Aβ-positive synapses in control cases. In aged targeted replacement mice expressing human apoE, apoE2/4 synaptic terminals demonstrated the highest level of apoE and the lowest level of Aβ compared to apoE3/3 and apoE4/4 lines. In apoE2/4 terminals, the pattern of immunolabeling for apoE and Aβ closely resembled the pattern in human control cases, and elevated apoE was accompanied by elevated free cholesterol in apoE2/4 synaptic terminals. These results are consistent with a role for APOE in Aβ clearance in AD synapses, and suggest that optimal lipidation of apoE2 compared to E3 and E4 makes an important contribution to Aβ clearance and synaptic function.
Synaptosome; Flow cytometry; Filipin; Ganglioside GM1; Triple transgenic mouse; Triple transgenic rat