Apolipoprotein E allele-specific antioxidant activity and effects on cytotoxicity by oxidative insults and beta-amyloid peptides

Expanding the association between the APOE gene and the risk of Alzheimer's disease: possible roles for APOE promoter polymorphisms and alterations in APOE transcription

Alzheimer's disease (AD) is the most commonly diagnosed form of dementia in the elderly. Predominantly this disease is sporadic in nature with only a small percentage of patients exhibiting a familial trait. Early-onset AD may be explained by single gene defects; however, most AD cases are late onset (> 65 years) and, although there is no known definite cause for this form of the disease, there are several known risk factors. Of these, the epsilon4 allele of the apolipoprotein E (apoE) gene (APOE) is a major risk factor. The epsilon4 allele of APOE is one of three (epsilon2 epsilon3 and epsilon4) common alleles generated by cysteine/arginine substitutions at two polymorphic sites. The possession of the epsilon 4 allele is recognized as the most common identifiable genetic risk factor for late-onset AD across most populations. Unlike the pathogenic mutations in the amyloid precursor or those in the presenilins, APOE epsilon4 alleles increase the risk for AD but do not guarantee disease, even when present in homozygosity. In addition to the cysteine/arginine polymorphisms at the epsilon2/epsilon3/epsilon4 locus, polymorphisms within the proximal promoter of the APOE gene may lead to increased apoE levels by altering transcription of the APOE gene. Here we review the genetic and biochemical evidence supporting the hypothesis that regulation of apoE protein levels may contribute to the risk of AD, distinct from the well known polymorphisms at the epsilon2/epsilon3/epsilon4 locus.

Isoform-dependent cholesterol efflux from macrophages by apolipoprotein E is modulated by cell surface proteoglycans

OBJECTIVE

Apolipoprotein E (apoE) mediates cellular cholesterol efflux and plays a crucial role in the inhibition of atherogenesis. We investigated whether there is an isoform-specific difference in its function for cholesterol efflux from cholesterol-loaded RAW264.7 cells, a murine macrophage cell line that lacks endogenous apoE expression.

METHODS AND RESULTS

When human apoE was expressed in RAW264.7 cells, apoE2 reduced cellular total cholesterol (TC) and esterified cholesterol (EC) levels significantly, whereas apoE3 and apoE4 had no effect. However, treatment of cells with 4-methylumbelliferyl-7-beta-D-xyloside (beta-DX) resulted in all 3 isoforms' reducing cellular TC and EC contents significantly. We also investigated the effect of exogenously derived apoE on cholesterol efflux by utilizing the medium harvested from HeLa cells expressing apoE. ApoE2 and E3 reduced both cellular TC and EC contents significantly, whereas apoE4 did not. However, treatment of the cells with beta-DX resulted in all 3 exogenously derived apoE isoforms' reducing TC and EC contents significantly. The binding ability of apoE to heparan sulfate proteoglycans examined by heparinase I treatment revealed less binding ability of apoE2 compared with that of apoE3 or apoE4.

CONCLUSIONS

The present study clarified the differential cellular cholesterol-modulating effect of apoE isoforms in macrophages, which would be due to the difference in their binding to proteoglycans.

Effect of apolipoprotein E genotype on in-hospital mortality following intracerebral haemorrhage

OBJECTIVE

To determine the relationship between the apolipoprotein E (APOE) epsilon4 allele and in-hospital mortality from intracerebral haemorrhage (ICH).

MATERIAL AND METHODS

Patients admitted to two acute stroke units with ICH were prospectively evaluated and APOE genotyped. In-hospital survival was recorded in 176 patients.

RESULTS

There were 85 men and 91 women, mean age 68 years. Fifty-two (30%) of the 176 patients died in hospital. After adjusting for sex, age, hospital, and race, increased age (P = 0.009) and the presence of the APOEepsilon4 allele (P = 0.026) significantly reduced in-hospital survival.

CONCLUSION

The APOEepsilon4 allele in this population may be associated with poor survival following ICH.

Human apoE3 but not apoE4 rescues impaired astrocyte activation in apoE null mice

The allele E4 of apolipoprotein E (apoE) is an important risk factor for Alzheimer's disease (AD) and the chronic brain inflammation which is associated with AD is more pronounced in subjects who carry this allele. In the present study, we employed mice transgenic for the human apoE isoforms apoE3 or apoE4 on a null mouse apoE background and intracerebroventricular injection of LPS to investigate the possibility that the regulation of brain inflammation is affected by the apoE genotype. LPS treatment of control mice resulted in activation of brain astrocytes and microglia whose extent decreased with age. LPS treatment of 6-month-old apoE transgenic and control mice resulted in marked activation of brain astrocytes in the control and apoE3 transgenic mice but had no effect on astrogliosis of age-matched apoE-deficient and apoE4 transgenic mice. In contrast, there were no significant differences between the levels of activated microglia of the apoE3 and apoE4 transgenic mice following LPS treatment. Immunoblot assays revealed that the apoE4 and apoE3 transgenic mice had the same levels of brain apoE, which were similarly increased following LPS treatment. These results show that LPS-induced astrogliosis in apoE transgenic mice is regulated isoform-specifically by apoE3 and not by apoE4 and suggest that similar mechanisms may mediate the phenotypic expression of the apoE4 genotype in AD and in other neurodegenerative diseases.

Modulation of Alzheimer-like synaptic and cholinergic deficits in transgenic mice by human apolipoprotein E depends on isoform, aging, and overexpression of amyloid beta peptides but not on plaque formation

The most frequent human apolipoprotein (apo) E isoforms, E3 and E4, differentially affect Alzheimer's disease (AD) risk (E4 > E3) and age of onset (E4 < E3). Compared with apoE3, apoE4 promotes the cerebral deposition of amyloid beta (Abeta) peptides, which are derived from the amyloid precursor protein (APP) and play a central role in AD. However, it is uncertain whether Abeta deposition into plaques is the main mechanism by which apoE isoforms affect AD. We analyzed murine apoE-deficient transgenic mice expressing in their brains human APP (hAPP) and Abeta together with apoE3 or apoE4. Because cognitive decline in AD correlates better with decreases in synaptophysin-immunoreactive presynaptic terminals, choline acetyltransferase (ChAT) activity, and ChAT-positive fibers than with plaque load, we compared these parameters in hAPP/apoE3 and hAPP/apoE4 mice and singly transgenic controls at 6-7, 12-15, and 19-24 months of age. Brain aging in the context of high levels of nondeposited human Abeta resulted in progressive synaptic/cholinergic deficits. ApoE3 delayed the synaptic deficits until old age, whereas apoE4 was not protective at any of the ages analyzed. Old hAPP/apoE4 mice had more plaques than old hAPP/apoE3 mice, but synaptic/cholinergic deficits preceded plaque formation in hAPP/apoE4 mice. Moreover, despite their different plaque loads, old hAPP/apoE4 and hAPP/apoE3 mice had comparable synaptic/cholinergic deficits, and these deficits were found not only in the hippocampus but also in the neocortex, which in most mice contained no plaques. Thus, apoE3, but not apoE4, delays age- and Abeta-dependent synaptic deficits through a plaque-independent mechanism. This difference could contribute to the differential effects of apoE isoforms on the risk and onset of AD.

The apolipoprotein E epsilon4 haplotype is an important predictor for recurrence in ischemic cerebrovascular disease

OBJECTIVE

To determine whether a specific apolipoprotein E (APOE) allele is a predictor for ischemic cerebrovascular disease (ICVD).

BACKGROUND

The role of APOE in atherosclerosis has been a focus of intensive research. The APOE epsilon4 allele is overrepresented in Alzheimer's disease, atherosclerosis, ischemic heart disease, and ICVD. Also, epsilon4 carriers have higher cholesterol levels than non-epsilon4 carriers.

METHODS

We performed a prospective, longitudinal study on patients who have ICVD. The patients were recruited from St. Mary Hospital, Korea, and investigated for ICVD through interviews and by reviewing their medical records and neuroimaging studies. APOE genotypes were determined for each patient.

RESULTS

20 of the 91 enrolled patients had recurrent ICVD, yielding a 3-year cumulative recurrence rate of 22%. Carriers of the epsilon4 allele had a 3-year recurrence rate of 53%, as compared with only 16% for patients who had the APOE non-epsilon4 allele (the risk ratio was 4.11; the 95% CI was 1.49-11.32; P<0.01).

CONCLUSIONS

Our results make possible the identification of patients with ICVD who are at high risk for recurrence by assessing their APOE genotype. Also, this data might be clinically useful in methods for assessing potential strategies for prevention.

Folate quenches oxidative damage in brains of apolipoprotein E-deficient mice: augmentation by vitamin E

We demonstrate that folate and vitamin E can compensate for the diminished oxidative buffering capacity of brains of apolipoprotein E-deficient mice. Normal and ApoE(tmlUne) homozygous 'knockout' mice were maintained for 1 month on a diet either lacking or supplemented with folate, vitamin E or iron as a pro-oxidant after which brain tissue was harvested and analyzed for for thiobarbituric acid-reactive substances (TBARs) as an index of oxidative damage. Normal mice exhibited no significant difference in TBARs following iron challenge in the presence or absence of vitamin E, folic acid or both. Similarly, ApoE knockout mice exhibited no significant differences following dietary iron challenge in the presence or absence of vitamin E. However, ApoE knockout mice accumulated significantly increased TBARs following iron challenge when folic acid was withheld, and accumulated even more TBARs when both folic acid and vitamin E were withheld. These findings demonstrate that ApoE knockout mice during vitamin deficiency are less capable of buffering the consequences of dietary iron challenge than are normal mice. Since the apolipoprotein E4 allele, which exhibits diminished oxidative buffering capacity, is linked to Alzheimer's disease (AD), these data underscore the possibility that critical nutritional deficiencies may modulate the impact of genetic compromise on neurodegeneration in AD.

Apolipoprotein E kinetics: influence of insulin resistance and type 2 diabetes

BACKGROUNDS AND AIMS

Insulin resistance related to obesity and diabetes is characterized by an increase in plasma TG-rich lipoprotein concentrations. Apolipoprotein (apo) E plays a crucial role in the metabolism of these lipoproteins and particularly in the hepatic clearance of their remnants. The aim of this study was to explore apoE kinetics of obese subjects and to determine what parameters could influence its metabolism.

METHODS

Using stable-isotope labelling technique ([(2)H(3)]-leucine-primed constant infusion) and monocompartmental model (SAAM II computer software), we have studied the plasma kinetics of very-low-density lipoprotein (VLDL) and high-density lipoprotein (HDL) apoE in 12 obese subjects (body mass index (BMI) 27.4-36.6 kg/m(2)): Seven were type 2 diabetics (age 47-65 y; HbA1c 7.1-10.2%) and five were non-diabetics (age 40-51 y, HbA1c: 4.9-5.3%). Six of the diabetic subjects were insulin resistant as assessed by insulin sensitivity index (HOMA 2.6-10.0), while non-diabetic subjects were all insulin sensitive (HOMA 1.2-2.1).

RESULTS

Plasma VLDL and HDL apoE concentrations were significantly higher in diabetic than in non-diabetic subjects (5.74+/-1.60 vs 1.46+/-1.74 mg/l, P<0.01 and 17.81+/-6.67 vs 9.97+/-3.32 mg/l, P<0.05). These increased levels were associated with significantly higher absolute production rate (APR) of VLDL and HDL apoE (0.714+/-0.343 vs 0.130+/-0.200 mg/kg/day, P<0.01, and 0.197+/-0.087 vs 0.080+/-0.060 mg/kg/day, P<0.05, respectively) while no significant difference was found for fractional catabolic rate (FCR) of VLDL and HDL apoE (3.44+/-1.64 vs 1.97+/-0.84/day and 0.30+/-0.12 vs 0.19+/-0.09/day, respectively). In the whole population, BMI was not correlated with any of apoE kinetic data. HOMA was positively correlated with FCR of VLDL apoE (r=0.64, P<0.05) and tended to be correlated with APR of VLDL apoE (r=0.58, P=0.06). HbA1c was positively correlated with APR and FCR of both VLDL apoE (r=0.91 and 0.78, P<0.01, respectively) and HDL apoE (r=0.66 and 0.69, P<0.05, respectively).

CONCLUSION

Obese diabetics are characterized by elevated VLDL and HDL apoE levels associated with enhancement of VLDL and HDL apoE production rates. Whereas obesity did not influence apoE kinetic parameters in itself, insulin resistance may lead to an increase in VLDL apoE production and fractional catabolic rates. Diabetes and the glycemic control may also specifically influence the kinetics of both VLDL and HDL apoE. All together, these disorders should explain at least part of the increase in VLDL and HDL apoE observed in diabetes.

Neuroprotective effect of apolipoprotein E against ischemia

Apolipoprotein E (APOE) deficiency has been shown to worsen neuronal injuries after cerebral ischemia. However, the molecular mechanism underlying the protective effect of APOE remains uncertain, even though several mechanisms including excitotoxicity, free radicals, and apoptosis have been cited as causes of selective neuronal vulnerability in cerebral ischemia. In the present study, we compared the vulnerability of cultured neurons prepared from APOE-knockout mice upon exposure to glutamate, hydrogen peroxide, and staurosporine. No significant difference in cell viability was observed after exposure to glutamate or staurosporine between APOE-deficient and wild-type mice. However, exposure to hydrogen peroxide significantly increased the level of cell death in APOE-deficient mice compared with that in wild-type mice. In the adult mice, after transient forebrain ischemia for 12 min, APOE-deficient mice showed more neuronal death than wild-type mice. Pretreatment of APOE-deficient mice with vitamin E for 2 months markedly reduced neuronal death caused by ischemia. The results suggested that APOE exerted the neuroprotective effect against ischemia through its antioxidant action, but not through mitigation of glutamate toxicity or blocking of apoptosis.

Abeta as a bioflocculant: implications for the amyloid hypothesis of Alzheimer's disease

Research into Alzheimer's disease (AD) has been guided by the view that deposits of fibrillar amyloid-beta peptide (Abeta) are neurotoxic and are largely responsible for the neurodegeneration that accompanies the disease. This 'amyloid hypothesis' has claimed support from a wide range of molecular, genetic and animal studies. We critically review these observations and highlight inconsistencies between the predictions of the amyloid hypothesis and the published data. We show that the data provide equal support for a 'bioflocculant hypothesis', which posits that Abeta is normally produced to bind neurotoxic solutes (such as metal ions), while the precipitation of Abeta into plaques may be an efficient means of presenting these toxins to phagocytes. We conclude that if the deposition of Abeta represents a physiological response to injury then therapeutic treatments aimed at reducing the availability of Abeta may hasten the disease process and associated cognitive decline in AD.

Apolipoprotein E deficiency promotes increased oxidative stress and compensatory increases in antioxidants in brain tissue

The epsilon 4 allele of the apolipoprotein E gene (ApoE) is associated with Alzheimer's disease (AD). The extent of oxidative damage in AD brains correlates with the presence of the E4 allele of ApoE, suggesting an association between the ApoE4 genotype and oxygen-mediated damage in AD. We tested this hypothesis by subjecting normal and transgenic mice lacking ApoE to oxidative stress by folate deprivation and/or excess dietary iron. Brain tissue of ApoE-deficient mice displayed increased glutathione and antioxidant levels, consistent with attempts to compensate for the lack of ApoE. Folate deprivation and iron challenge individually increased glutathione and antioxidant levels in both normal and ApoE-deficient brain tissue. However, combined treatment with folate deprivation and dietary iron depleted antioxidant capacity and induced oxidative damage in ApoE-deficient brains despite increased glutathione, indicating an inability to compensate for the lack of ApoE under these conditions. These data support the hypothesis that ApoE deficiency is associated with oxidative damage, and demonstrate a combinatorial influence of genetic predisposition, dietary deficiency, and oxidative stress on oxidative damage relevant to AD.

Is Alzheimer's disease a mitochondrial disorder?

Cell bodies of neurons at risk of death in Alzheimer's disease (AD) have increased lipid peroxidation, nitration, free carbonyls, and nucleic acid oxidation. These oxidative changes occur in all vulnerable neurons and are reduced in neurons that contain neurofibrillary pathology. In this review, the authors provide a summary of recent work that demonstrates key abnormalities that may play a part in initiating and promoting neuronal oxidative damage. Mitochondrial abnormalities are clearly involved as a source of reactive oxygen species that culminates in perikaryal oxidative damage. However, because mitochondria in AD do not exhibit striking evidence of oxidative damage, as would be expected if they produced free radicals directly, the authors suspected that abnormal mitochondria are responsible for supplying a key reactant, that once in the cytoplasm, releases radicals. Because abnormal mitochondria, H2O2 and redox-active iron are juxtaposed in the same AD neuron, it has all the markings of a "radical factory." The proximal causes of mitochondrial abnormalities likely involve reentry into the cell cycle, where organellokinesis and proliferation results in an increase of mitochondria and intermediately differentiated cells, with a consequent increase in turnover. Supporting this, the authors have considerable in vivo and in vitro evidence for mitotic disturbances in AD.

Apolipoprotein E protects against NMDA excitotoxicity

Preclinical and clinical evidence implicates a role for endogenous apolipoprotein E in modifying the response of the brain to focal and global ischemia. To investigate whether apoE modulates the neuronal response to glutamate excitotoxicity, we exposed primary neuronal glial cultures and a neuronal cell line to biologically relevant concentrations of apolipoprotein E prior to NMDA exposure. In both of these paradigms, apolipoprotein E exerted partial protective effects. At neuroprotective concentrations, however, apolipoprotein E failed to block NMDA-induced calcium influx to the same magnitude as the NMDA receptor antagonist MK-801. These results suggest that one mechanism by which apolipoprotein E modifies the central nervous system response to ischemia may be by reducing glutamate-induced excitotoxicity.

Regulation of macrophage ApoE expression and processing by extracellular matrix

Macrophage-derived apoE in the vessel wall has important effects on atherogenesis in vivo, making it important to understand factors that regulate its expression. Vessel wall macrophages are embedded in an extracellular matrix produced largely by arterial smooth muscle cells and endothelial cells. In this series of studies, we evaluated the influence of extracellular matrix on macrophage apoE expression. Subendothelial matrix, fibronectin, or collagen I stimulated macrophage apoE gene expression and apoE synthesis. Adhesion of macrophages to a polylysine substrate had no effect. An increase in apoE synthesis after plating on fibronectin could be observed by 2 h and was inhibited by blocking antibodies to the alpha(5)beta(1) integrin receptor for fibronectin. Fibronectin also regulated the post-translational processing of newly synthesized macrophage apoE by inhibiting its degradation. The increment in apoE resulting from suppressed degradation was retained in the cell-fibronectin monolayer in a pool that was resistant to release by exogenous high density lipoprotein subfraction 3. These observations establish a new pathway for the regulation of macrophage apoE expression in the vessel wall. The composition of the extracellular matrix changes after vessel wall injury and in response to locally produced cytokines and growth factors. The evolving composition of this matrix will, therefore, be important for regulating apoE expression and processing by vessel wall macrophages.

Apolipoprotein E structural requirements for the formation of SDS-stable complexes with beta-amyloid-(1-40): the role of salt bridges

Of the three major isoforms of human apolipoprotein E (apoE), apoE4 is a risk factor for the development of Alzheimer's disease. Among possible neurologically relevant differences in the properties of apoE3 and apoE4 is the fact that apoE3 forms an SDS-stable complex with beta-amyloid-(1-40) (Abeta40) with greater avidity than does apoE4. This interaction may sequester potentially toxic species of Abeta or facilitate clearance. To understand more about this difference, we examined whether differences in salt bridges between apoE domains influence the capacity of apoE isoforms to form complexes with Abeta. In apoE3 there is a salt bridge between Arg-61 and Asp-65, while in apoE4 there are salt bridges between Arg-61 and Glu-255, and Arg-112 and Glu-109. Mutation of position 112, which is Cys in apoE3 and Arg in apoE4, to Ala or Lys abolished complex formation, while mutant apoE with Ser at this position retained the capacity to form complex. Substituting Ala for Glu-109 had no effect on the ability of either apoE4 or apoE3 to form complexes. On the other hand, substitution of Thr for Arg-61 in apoE3 abolished, and truncation of apoE3 at position 201 substantially lowered, but did not abolish, complex formation. Neither of these mutations within apoE4 had any affect on its complex formation with Abeta. These results suggest that the nature of the cysteine residue in apoE3 and interactions between the N-terminal and C-terminal domains of human apoE are important for the ability of apoE3 to form an SDS-stable complex with Abeta40.

Carotid artery intima-media thickness and brachial artery flow-mediated vasodilation in asymptomatic Japanese male subjects amongst apolipoprotein E phenotypes

BACKGROUND

Epidemiological studies suggest that apolipoprotein E (apoE) polymorphism influences plasma lipoprotein levels and the development of cardiovascular disease.

OBJECTIVE

To clarify the role of apoE polymorphism as a risk factor for early atherosclerosis.

DESIGN

Using a high-resolution ultrasound method, we investigated the association between apoE phenotypes, carotid intima-media thickness (CCA-IMT), and flow-mediated dilation in the brachial artery (brachial-FMD) in 96 healthy asymptomatic Japanese men (mean +/- SD age, 50 +/- 8 years).

RESULTS

Serum cholesterol and LDL-cholesterol levels in subjects with E3E4 were highest and those with E2E3 were lowest (P < 0.05 and P < 0.05, respectively). The CCA-IMT in E3E4 subjects (0.76 +/- 0.17 mm) was greater than that in E2E3 and E3E3 (0.61 +/- 0.15 and 0.64 +/- 0.14 mm, respectively; P < 0.01). In contrast, there was no difference between brachial-FMD and apoE phenotypes (P=0.15). By univariate analysis, CCA-IMT was positively correlated with age (r=0.51, P < 0.01), LDL-chol/HDL-chol ratio (r=0.37, P < 0.01), triglycerides (r=0.23, P < 0.05), and negatively correlated with HDL-cholesterol (r=-0.31, P < 0.01). An association between CCA-IMT and the presence of E4 allele was also found (P < 0.05). Logistic regression analysis revealed that the presence of E4 allele was a higher risk for increased IMT (relative risk of 4.4, 95% CI 1.5-12.5), even after adjustment for age, LDL-cholesterol, blood pressure and other known risk factors. A negative correlation between brachial-FMD and CCA-IMT was also found in all subjects (r=-0.21, P < 0.05), being most apparent in the E3E4 subjects (r=-0.53, P < 0.02).

CONCLUSION

ApoE4 phenotype was independently associated with an increased risk of carotid atherosclerosis and elevated LDL-cholesterol levels in asymptomatic middle-aged Japanese men.

Efficacy of vitamin E, phosphatidyl choline, and pyruvate on buffering neuronal degeneration and oxidative stress in cultured cortical neurons and in central nervous tissue of apolipoprotein E-deficient mice

Oxidative stress is a pivotal factor in neuronal degeneration. However, vitamin E was only marginally effective in clinical trials. We examined whether or not a mixture of vitamin E (as alpha-tocopherol), sodium pyruvate and phosphatidyl choline (PC), a mixture that promotes wound healing in non-neuronal systems, would provide neuroprotection beyond that observed with vitamin E alone. Combined treatment with these agents improved survival and neuritic spouting of murine embryonic cortical neurons in culture, and provided neuroprotection against oxidative damage following treatment with hydrogen peroxide. Dietary treatment with these three agents also compensated for the diminished oxidative buffering capacity of brains of apolipoprotein E-deficient mice, while vitamin E alone failed to do so. These data underscore the possibility that critical nutritional deficiencies may modulate the impact of genetic compromise on neurodegeneration.

Apolipoprotein E gene polymorphism in cerebrovascular disease: a case-control study

The association between apolipoprotein E (apo E) polymorphism and stroke has been controversial. So far there are no studies reported on the polymorphism of apolipoprotein E in cerebrovascular diseases in the Asian Indians. A blinded case-control study was therefore undertaken and the apo E genotypes and lipid profile of a total of 120 subjects (63 stroke patients and 57 healthy controls) were done. The frequency distribution of apo E alleles and genotypes were assessed and their relation with the occurrence of stroke in Asian Indian subjects was determined. A significantly high frequency of apo epsilon4 allele (30%) was observed in the stroke patients than the controls (11%) (p < 0.005), and patients with epsilon4 allele had a fourfold higher odds to develop stroke OR (95%CI) 4.2 (1.8-10.1) (p < 0.005). On multivariate analysis, after adjusting for age, triglycerides and hypertension, the association of epsilon4 allele with stroke was found to be no longer statistically significant, OR (95%CI) 1.2 (0.4-4.5) (p = NS). On multiple logistic regression analysis age, OR (95%CI) 1.1 (1.1-1.2) (p < 0.001), and hypertension OR (95%CI) 15.1 (2.6-89.1) (p < 0.005) were found to be independent risk factors for development of stroke. This is the first report to have examined the association of apo E gene polymorphism with stroke in the Asian Indians. This study suggests that apo epsilon4 allele, triglycerides, age and hypertension are the predictors for stroke development.

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

BACKGROUND AND PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Apolipoprotein E mediates the retention of high-density lipoproteins by mouse carotid arteries and cultured arterial smooth muscle cell extracellular matrices

Lipoprotein retention in the vascular extracellular matrix (ECM) plays a critical role in atherogenesis. Previous studies demonstrated the presence of apo A-I and E in atherosclerotic lesions, suggesting that HDL may be trapped by the artery wall. We sought to determine mechanisms by which HDL could be bound and retained by the arterial wall, and whether apo E was a principal determinant of this binding. We evaluated in situ accumulation of fluorescently labeled DiI-human HDL+/-apo E in perfused carotid arteries from apo E-null mice. Apo E was important in mediating HDL binding to the vascular wall, with a 48+/-16% increase in accumulation of DiI-labeled apo E-containing HDL (HDL3+E) compared with DiI-apo E-free HDL (HDL3-E) (P=0.003). To investigate possible mechanisms responsible for retention, we assessed binding of unlabeled HDL3-E and HDL3+E to ECM generated by cultured arterial smooth muscle cells. Similar to the in situ carotid artery data, HDL3+E bound better to the ECM than did HDL3-E (3-fold lower K(a) and 3.5-fold higher B(max) for HDL3+E versus HDL3-E). These differences were eliminated after either neutralization of arginine residues on apo E or digestion of matrix with chondroitin ABC lyase, suggesting that chondroitin and/or dermatan sulfate proteoglycans were responsible for apo E-mediated increased binding. These findings demonstrate that HDL can bind to both intact murine carotid arteries and smooth muscle cell-derived ECM, and that apo E is a principal determinant in mediating the ability of HDL to be trapped and retained via its interaction with ECM proteoglycans.

Inhibition of apolipoprotein E-related neurotoxicity by glycosaminoglycans and their oligosaccharides

Apolipoprotein E (apoE) has been genetically linked to late-onset Alzheimer's disease (AD). The role of this lipid-transport protein in AD remains to be established. One hypothesis is that apoE, particularly the apoE4 isoform, may have neurotoxic effects as demonstrated using apoE-related synthetic peptides and the N-terminal fragment of apoE. ApoE is a heparan-sulfate binding protein, and apoE peptide neurotoxicity can be blocked by heparin and prevented by degrading heparan sulfate or inhibiting its biosynthesis. The possibility that heparin inhibition of toxicity is mediated by a specific oligosaccharide sequence was investigated using a bioassay to determine the inhibition of apoE peptide toxicity by glycosaminoglycans and purified glycosaminoglycan oligosaccharides. Studies on modified heparins showed that the presence of N-sulfo groups and either 2- or 6-O sulfo groups were required for inhibition of toxicity. Heparin oligosaccharides with eight or more saccharide residues with seven O-sulfo groups and four N-sulfo groups exhibited potent inhibition. Larger oligosaccharides, and heparin and heparan sulfate polymers, afforded comparable, or somewhat better, protective effects but also caused clumping and detachment of cells when administrated alone.

Apolipoprotein E4 potentiates amyloid beta peptide-induced lysosomal leakage and apoptosis in neuronal cells

We assessed the isoform-specific effects of apolipoprotein (apo) E on the response of Neuro-2a cells to the amyloid beta peptide (Abeta1-42). As determined by the intracellular staining pattern and the release of beta-hexosaminidase into the cytosol, apoE4-transfected cells treated with aggregated Abeta1-42 showed a greater tendency toward lysosomal leakage than neo- or apoE3-transfected cells. Abeta1-42 caused significantly greater cell death and more than 2-fold greater DNA fragmentation in apoE4-secreting than in apoE3-secreting or control cells. H2O2 or staurosporine enhanced cell death and apoptosis in apoE4-transfected cells but not in apoE3-transfected cells. A caspase-9 inhibitor abolished the potentiation of Abeta1-42-induced apoptosis by apoE4. Similar results were obtained with conditioned medium from cells secreting apoE3 or apoE4. Cells preincubated for 4 h with a source of apoE3 or apoE4, followed by removal of apoE from the medium and from the cell surface, still exhibited the isoform-specific response to Abeta1-42, indicating that the potentiation of apoptosis required intracellular apoE, presumably in the endosomes or lysosomes. Studies of phospholipid (dimyristoylphosphatidylcholine) bilayer vesicles encapsulating 5-(and-6)-carboxyfluorescein dye showed that apoE4 remodeled and disrupted the phospholipid vesicles to a greater extent than apoE3 or apoE2. In response to Abeta1-42, vesicles containing apoE4 were disrupted to a greater extent than those containing apoE3. These findings are consistent with apoE4 forming a reactive molecular intermediate that avidly binds phospholipid and may insert into the lysosomal membrane, destabilizing it and causing lysosomal leakage and apoptosis in response to Abeta1-42.

Apolipoproteins and aging: emerging mechanisms

One of the goals of modern medicine is to foster successful aging. In order to age successfully, one must accomplish two things: first, survive; and second, survive with good health and a sharp mind. In this discussion of apolipoproteins and aging, the focus will be on apolipoprotein E (apoE), a protein with three common isoforms, which has a large impact on longevity and successful aging. One variant of apoE (E4) is associated with increased risk for heart disease, stroke and Alzheimer's disease (AD). In addition, some of the potential mechanisms for the observed effects of apoE on aging will be discussed.

Apolipoprotein E-promoter single-nucleotide polymorphisms affect the phenotype of primary open-angle glaucoma and demonstrate interaction with the myocilin gene

Primary open-angle glaucoma (POAG) is an optic neuropathy that has a high worldwide prevalence and that shows strong evidence of complex inheritance. The myocilin (MYOC) gene is the only one that has thus far been shown to have mutations in patients with POAG. Apolipoprotein E (APOE) plays an essential role in lipid metabolism, and the APOE gene has been involved in neuronal degeneration that occurs in Alzheimer disease (AD). Here, we report that two APOE-promoter single-nucleotide polymorphisms (SNPs) previously associated with AD also modify the POAG phenotype. APOE(-219G) is associated with increased optic nerve damage, as reflected by increased cup:disk ratio and visual field alteration. In addition, APOE(-491T), interacting at a highly significant level with an SNP in the MYOC promoter, MYOC(-1000G), is associated with increased intraocular pressure (IOP) and with limited effectiveness of IOP-lowering treatments in patients with POAG. Together, these findings establish APOE as a potent modifier for POAG, which could explain the linkage to chromosome 19q previously observed by use of a genome scan for this condition and an increased frequency of glaucoma in patients with AD. The findings also shed new light on potential mechanisms of optic nerve damage and of IOP regulation in POAG.

Genetic polymorphisms and oxidative stress in heart failure

Heart failure results from various known cardiovascular diseases, such as coronary artery disease, or can be the result of an idiopathic dilated cardiomyopathy. It is of utmost importance for diagnostic, preventive, and therapeutic purposes to understand the cellular events that trigger the cascade of functional and structural changes that result in the development and progression of heart failure. Progress in unraveling the genetic background in both ischemic and nonischemic cardiomyopathies has been slow compared with that for monogenic diseases, such as some forms of hypertrophic cardiomyopathy or familial dilated cardiomyopathies. It is likely that susceptibility to and risk of progression of heart failure are both influenced by many genes acting in concert or independently. Among the diverse subcellular mechanisms implicated in the pathogenesis and progression of heart failure, reactive oxygen species play a major role. The search for genetic polymorphisms in clinical association studies in order to identify genotypes susceptible to develop and affect the progression to heart failure has been the focus of many investigations over the past several years. In this review, the authors summarize the current data in support of the role of various polymorphisms of genes related to oxidative stress in the susceptibility to develop heart failure, and its progression.

Defective neuronal sprouting by human apolipoprotein E4 is a gain-of-negative function

The apolipoprotein E (apoE) epsilon 4 allele (apoE4) is a major risk factor for neurodegenerative conditions, including Alzheimer's disease (AD). A role for apoE in regeneration of synaptic circuitry after neural injury has been shown in several in vitro studies in which apoE3 supports neuronal sprouting better than apoE4. We evaluated sprouting in an in vitro mouse organotypic hippocampal slice culture system derived from transgenic mice expressing apoE3 or apoE4, in which apoE-dependent granule cell mossy fiber sprouting in the presence of apoE4 is only 51% of the level of apoE3. Sprouting supported by apoE4 had a dose response opposite that by supported by apoE3: although increasing E3 expression increased sprouting, increasing E4 expression decreased sprouting, suggesting that the defect in E4 in supporting neuronal sprouting is a gain-of-negative activity. These results may have important pharmacogenomic implications for AD therapies that modulate apoE expression levels.

Protective effect of apolipoprotein E against ischemic neuronal injury is mediated through antioxidant action

Recent studies have demonstrated that apolipoprotein E (APOE) deficiency worsened neuronal injuries after transient focal and global cerebral ischemia. However, the molecular mechanism underlying the protective effect of APOE remains uncertain, even though several mechanisms, including excitotoxicty, free radicals, and apoptosis, have been cited as causes of selective neuronal vulnerability in cerebral ischemia. In the present study, we first compared the vulnerability of cultured neurons prepared from APOE-knockout mice upon exposure to glutamate, hydrogen peroxide, and staurosporine. No significant difference in cell viability was observed after exposure to glutamate or staurosporine between APOE-deficient and wild-type mice. However, exposure to hydrogen peroxide significantly increased the level of cell death in APOE-deficient mice compared with that in wild-type mice. After transient forebrain ischemia for 12 min, APOE-deficient mice showed more neuronal death than wild-type mice. Pretreatment of APOE-deficient mice with vitamin E for 2 months markedly reduced neuronal death caused by ischemia. The results suggest that APOE exerted its neuroprotective effect against ischemia through its antioxidant action but not through mitigation of glutamate toxicity or blocking of apoptosis.

Atherosclerosis in C3H/HeJ mice reconstituted with apolipoprotein E-null bone marrow

Previous studies showed that reconstitution of atherosclerosis-susceptible C57BL/6 (B6) female mice with apolipoprotein E (apoE)-deficient (apoE(-/-)) bone marrow resulted in markedly increased atherosclerosis, despite the fact that plasma lipid levels were unchanged. To determine whether apoE(-/-) bone marrow would increase atherosclerosis in an atherosclerosis-resistant strain, female C3H/HeJ (C3H) mice were lethally irradiated and reconstituted with bone marrow from either C3H.apoE(-/-) mice or wild-type C3H mice. Four weeks after transplantation, the mice were fed an atherogenic diet for 12 weeks. We found that reconstitution of C3H mice with apoE(-/-) bone marrow resulted in a slight reduction in plasma apoE levels and a dramatic reduction in apoE and apolipoprotein B (apoB) in the aortic wall. Plasma apoB and cholesterol levels were unchanged, as were atherosclerotic lesions at the aortic root. These data indicate that reconstitution of C3H mice with apoE(-/-) bone marrow has no effect on atherosclerosis susceptibility and that apoE promotes accumulation of apoB in the vessel wall.

Oxidative protein damage in cells engaged in beta-amyloidosis is related to apoE genotype

The epsilon4 allele of apolipoprotein E (apoE) is a risk factor for Alzheimer's disease. The reduced antioxidant defense in epsilon4 carriers is suggested to contribute to beta-amyloidosis. We found that oxidative stress induced by treatment with Fe2+ ions raised more protein carbonyls in vascular smooth muscle cells isolated from human brains with apoE genotype epsilon4/epsilon4 than with 3epsilon/epsilon3 and epsilon3/epsilon4. Antioxidant vitamin E prevented formation of carbonyls but not in cells with genotype epsilon4/epsilon4. Treatment with Fe2+ ions induced cellular accumulation of amyloid-beta protein (Abeta)-immunoreactive material that co-localized with heme oxygenase, a marker of oxidative stress, and apoE. We hypothesize that the damage caused by oxidation in epsilon4/epsilon4 carriers facilitates development of beta-amyloidosis.

Apolipoprotein E: far more than a lipid transport protein

First recognized as a major determinant in lipoprotein metabolism and cardiovascular disease, apolipoprotein (apo) E has emerged as an important molecule in several biological processes not directly related to its lipid transport function, including Alzheimer's disease and cognitive function, immunoregulation, and possibly even infectious diseases. ApoE is a polymorphic protein arising from three alleles at a single gene locus. The three major isoforms, apoE4, apoE3, and apoE2, differ from one another only by single amino acid substitutions, yet these changes have profound functional consequences at both the cellular and molecular levels. ApoE3 seems to be the normal isoform in all known functions, while apoE4 and apoE2 can each be dysfunctional. Isoform (allele)-specific effects include the association of apoE2 with the genetic disorder type III hyperlipoproteinemia and with both increased and decreased risk for atherosclerosis and the association of apoE4 with increased risk for both atherosclerosis and Alzheimer's disease, impaired cognitive function, and reduced neurite outgrowth; isoform-specific differences in cellular signaling events may also exist. Functional differences in the apoE isoforms that affect (or did affect) survival before the reproductive years probably account, at least in part, for the allele frequencies of the present day.

Modulation of THP-1 macrophage and cholesterol-loaded foam cell apolipoprotein E levels by glycosphingolipids

Macrophages synthesize and secrete apolipoprotein E (apoE) constitutively. This process is upregulated under conditions of cholesterol loading. The response to cholesterol is antiatherogenic as it is believed to promote cholesterol efflux from the artery wall. The concentration of lactosyl ceramide (LacCer), a glycosphingolipid recently discovered to regulate cellular signaling, proliferation, and expression of adhesion molecules, is also increased in atherosclerotic tissues. Here we have investigated the effect of exogenous LacCer on macrophage apoE levels. We show that increasing macrophage LacCer levels sevenfold led to reductions in cellular and secreted apoE (15 and 30%, respectively, over a 24-h period) as determined by enzyme-linked immunosorbent assay. A similar effect was also induced by glucosyl ceramide (GlcCer) but not by ganglioside species. When macrophages were converted to cholesterol-loaded foam cells by incubation with acetylated LDL, the resulting increase in cellular apoE levels was inhibited by 26% when the cells were subsequently enriched with LacCer. After metabolic labeling of cellular glycosphingolipids with [14C]palmitate, we also discovered that high-density lipoprotein (HDL) stimulates the efflux of glycosphingolipids from foam cells. These data imply that LacCer and GlcCer may be proatherogenic due to the suppression of macrophage apoE production. Furthermore, the efflux of glycosphingolipids from macrophage foam cells to HDL could indicate a potential pathway for their removal from the artery wall and subsequent delivery to the liver.

Identifying disease modifying genes in multiple sclerosis

Evidence is mounting that genetic variation influences not only susceptibility to multiple sclerosis (MS), but also its course and severity. Identification of disease modifying genes, however, poses unique challenges, especially on how to classify the course and outcome of the disease in ways that may be relevant to analysis of biological factors that might be influenced by genes. The power of the statistical approaches to detect small effects of individual genes in complex disorders such as MS is problematic, and approaches to estimate power must be appropriate for the data. Nonetheless, using contemporary schemes of classification, genetic variants that influence disease course have been found; in fact, a small number have been confirmed to influence disease course in two or more independent studies. This review addresses strategies relevant to identification of disease modifying genes in MS, and summarizes and critically evaluates the current state of knowledge in this area.

Neurotoxic effects of apolipoprotein E4 are mediated via dysregulation of calcium homeostasis

The association of the E4 allele of apolipoprotein E (apoE4) as a genetic risk factor for Alzheimer's disease (AD) has been well established. Although recent studies in neuronal cell lines and transgenic mice have shown that apoE4 promotes neurodegeneration, the mechanisms through which apoE4 impairs neuronal viability are not completely understood. In this context, the main objective of the present study was to determine whether the neurotoxic effects of apoE4 are mediated by an alteration in calcium homeostasis. For this purpose, effects of recombinant apoE3 and apoE4 on cell viability and intracellular calcium levels were analyzed in a murine hippocampal cell line (HT22) and in primary rat cortical neurons, in the presence or absence of calcium inhibitors. Under basal conditions, apoE4-treated cells displayed increased levels of cytosolic calcium associated with cell death in a dose-dependent manner. Furthermore, apoE4 treatment potentiated the rise in cytosolic calcium and cell death following the administration of a calcium ionophore. The effects of apoE4 on cell viability and calcium homeostasis were inhibited by calcium chelators or by blocking calcium channels, but not by inhibitors of intracellular calcium reserves. Taken together, these results indicate that the neurotoxic effects of apoE4 are dependent on extracellular calcium influx via calcium channels.

Apolipoprotein E modulates Alzheimer's Abeta(1-42)-induced oxidative damage to synaptosomes in an allele-specific manner

Several functional differences have been reported among the three human e2, e3, and e4 alleles of apolipoprotein E (apoE). One functional difference lies in the antioxidant potential of these alleles; e4 has the poorest potential. Interestingly, e4 also correlates with increased oxidative damage in the Alzheimer's disease (AD) brain, which may explain why the inheritance of the e4 allele is a risk factor for the onset of AD. Beta-amyloid (Abeta) is also intimately involved in AD and promotes oxidative damage in vitro; therefore, we have examined the role of the different apoE alleles in modulating Abeta(1-42)-induced oxidation to synaptosomes. Measurement of specific markers of oxidation in synaptosomes isolated from mice that express one of the human apoE alleles indicates that Abeta-induced increases of these markers can be modulated by apoE in an allele-dependent manner (e2>e3>e4). Increases in reactive oxygen species formation and protein and lipid oxidation were always greatest in e4 synaptosomes as compared to e2 and e3 synaptosomes. Our data support the role of apoE as a modulator of Abeta toxicity and, consistent with the antioxidant potentials of the three alleles, suggest that the e4 allele may not be as effective in this role as the e2 or e3 alleles of apoE. These results are discussed with reference to mechanistic implications for neurodegeneration in the AD brain.

Inhibition of atherosclerosis in apolipoprotein-E-deficient mice following muscle transduction with adeno-associated virus vectors encoding human apolipoprotein-E

Apolipoprotein E (apoE) is a multifunctional plasma glycoprotein involved in lipoprotein metabolism and a range of cell signalling phenomena. ApoE-deficient (apoE(-/-)) mice exhibit severe hypercholesterolaemia and are an excellent model of human atherosclerosis. ApoE somatic gene transfer and bone marrow transplantation in apoE(-/-) mice results in reversal of hypercholesterolaemia, inhibition of atherogenesis and regression of atherosclerotic plaque density. Replication defective adeno-associated virus vectors (rAAVs) are an attractive system currently in clinical trial for muscle-based heterologous gene therapy to express secreted recombinant plasma proteins. Here we have applied rAAV transduction of skeletal muscle to express wild-type (epsilon3) and a defective receptor-binding mutant (epsilon2) human apoE transgene in apoE(-/-) mice. In treated animals, apoE mRNA was present in transduced muscles and, although plasma levels of recombinant apoE fell below the detection levels of our ELISA (ie <10 ng/ml), circulating antibodies to human apoE and rAAV were induced. Up to 3 months after a single administration of rAAV/apoE3, a significant reduction in atherosclerotic plaque density in aortas of treated animals was observed (approximately 30%), indicating that low-level rAAV-mediated apoE3 expression from skeletal muscle can retard atherosclerotic progression in this well-defined genetic model.

Mitochondrial genetic variants and Alzheimer disease: a case-control study of the T4336C and G5460A variants

The T4336C mitochondrial genetic variant was associated with Alzheimer disease in several previous studies. Recent investigations, however, failed to confirm this association. We tested this association in newly diagnosed Alzheimer disease cases and controls of similar age and gender recruited from an established HMO serving Seattle, Washington and surrounding areas. In this, the largest case-control study reported to date, the T4336C variant was not associated with Alzheimer disease overall (present in 6 of 236 cases and 7 of 328 controls; odds ratio = 1.20, 95% CI 0.33 to 4.22). There was evidence of effect modification by Apolipoprotein E (APOE) status--among subjects with an APOE epsilon 4 allele, the T4336C variant was associated with disease (present in 5 of 139 cases and none of 82 controls; odds ratio = infinity, 95% CI 0.73 to infinity). APOE may be an important modifier of the T4336C effect, potentially explaining variable findings across previous studies. Alternatively, the positive findings reported to date may simply reflect the problem of "type I" error inherent in genetic association studies. Substantially larger samples than are currently available would be required to resolve this question. G5460(A/T) variants were also investigated and found not to be associated with Alzheimer disease.

Effect of apolipoprotein E genotype on hematoma volume after trauma

OBJECT

The apolipoprotein E-epsilon4 (APOE-epsilon4) allele is associated with poor outcome after head injury and spontaneous intracerebral hemorrhage (SICH). The aims of this study were to determine if patients in whom one or more APOE-epsilon4 alleles are present are more likely to sustain intracranial mass lesions after head injury and to determine whether there is an isoform-specific effect on the size of the intracranial hematoma.

METHODS

The authors performed a computerized volumetric analysis of 142 hematomas visible on computerized tomography (CT) scans obtained in 129 patients. The APOE genotype was determined by subjecting buccal smear samples to polymerase chain reaction and restriction enzyme digestion. Allele frequencies were similar in head-injured patients with and without intracranial hematomas (p = 0.36). Univariate analysis revealed that in those patients with one or more APOE-epsilon4 alleles hematoma volume was greater (cube root-transformed values) than that found in patients without the APOE-epsilon4 allele (3.1 cm compared with 2.5 cm, p = 0.0039). The results of univariate analysis also suggested significant effects of patient age, injury severity (mild, moderate, or severe according to admission Glasgow Coma Scale scores) and hematoma location (extraaxial, intraaxial, or both) on hematoma volume. The mechanism of injury (assault, fall, or other) was marginally associated with hematoma volume (p = 0.052). Time from injury to CT scan, hypoxia, and hypotension had no significant effect on hematoma volume. The results of multiple linear regression analysis showed that the presence of an APOE-epsilon4 allele and an extraaxial hematoma location were independent predictors of hematoma volume, after adjusting for patient age, hours between injury and CT scan, injury severity, and injury mechanism.

CONCLUSIONS

Larger hematomas were found in head-injured patients with one or more APOE-epsilon4 alleles than in patients without the allele. This may contribute to the poorer outcomes observed in these patients.

A protective role for kidney apolipoprotein E. Regulation of mesangial cell proliferation and matrix expansion

Mesangial expansion is a key feature in the pathogenesis of numerous renal diseases involving the glomerulus. Studies indicate that mutations in apolipoprotein E (apoE) might independently contribute to kidney dysfunction. Although the role of apoE as an atheroprotective molecule is well established, its role in kidney is unclear. In this study, we sought to explore whether apoE has a protective function in kidney. Northern blotting and reverse transcriptase-polymerase chain reaction showed apoE expression in kidney, and mesangial cell is a major source of apoE in kidney. In the kidneys of 14-16-month-old apoE-null mice, hematoxylin-eosin (HE) staining revealed increased mesangial cell proliferation and matrix formation compared with wild type mice or apoB-overexpressing mice, which have elevated plasma cholesterol and triglycerides. These data suggest that lack of apoE, rather than hyperlipidemia, contributes to increased mesangial expansion. We isolated mesangial cells from mouse kidney and determined the effect of apoE on cell growth. ApoE (E3, 10 microg/ml) completely inhibited serum, platelet-derived growth factor (10 ng/ml), as well as low density lipoprotein-induced mesangial cell proliferation. Among the three isoforms, E3 was found to be most effective in inhibiting mesangial cell proliferation. ApoE did not show any cytotoxic effect, and moreover, inhibited mesangial cell apoptosis induced by oxidized low density lipoprotein. These data suggest that apoE regulates growth as well as survival of mesangial cells. We previously showed that apoE induces matrix heparan sulfate proteoglycan (HSPG) in vascular cells, which has an antiproliferative effect. Similarly, apoE induced the mesangial matrix HSPG. Perlecan is the major HSPG of mesangial matrix and subendothelial space, and consistent with this, blockade of perlecan reversed the antiproliferative effect of apoE. Immunohistochemistry revealed reduced staining of perlecan in kidney from apoE-null mice. Because the loss of anionic HSPG in the basement membrane and mesangial matrix is associated with disruption of filtration barrier, these data suggest a novel role for kidney apoE in preserving the filtration barrier. In summary, apoE has a protective function in kidney as an autocrine regulator of mesangial expansion and kidney function.

Cell-derived apolipoprotein E (ApoE) particles inhibit vascular cell adhesion molecule-1 (VCAM-1) expression in human endothelial cells

Sub-endothelial infiltration of monocytes occurs early in atherogenesis and is facilitated by cell adhesion molecules that are up-regulated on activated endothelium. Apolipoprotein E (apoE) helps protect against atherosclerosis, in part, because apoE particles secreted by macrophages have local beneficial effects at lesion sites. Here, we hypothesize that such protection includes anti-inflammatory actions and investigate whether cell-derived apoE can inhibit tumor necrosis factor-alpha-mediated up-regulation of vascular cell adhesion molecule-1 (VCAM-1) in human umbilical vein endothelial cells (HUVECs). Two models were used to mimic endothelial exposure to macrophage-derived apoE. In the first, HUVECs were transiently transfected to secrete apoE; VCAM-1 induction inversely correlated with secretion of apoE into the media (r = -0.76, p < 0.001). In the second, incubation of HUVECs with media from recombinant Chinese hamster ovary (CHO) cells expressing apoE (CHO(apoE)) also reduced VCAM-1 in a dose-dependent manner (r = -0.70, p < 0.001). Characterization of CHO(apoE) cell-derived apoE revealed several similarities to apoE particles secreted by human blood monocyte-derived macrophages. The suppression of endothelial activation by apoE most likely occurs via stimulation of endothelial nitric oxide synthase; apoE increased levels of intracellular nitric oxide and its surrogate marker, cyclic guanosine monophosphate, while the nitric oxide synthase inhibitor, ethyl-isothiourea, blocked its effect. We propose that apoE secreted locally at lesion sites by macrophages may be anti-inflammatory by stimulating endothelium to release NO and suppress VCAM-1 expression.

Pathophysiology of apolipoprotein E deficiency in mice: relevance to apo E-related disorders in humans

Apolipoprotein E (apo E) deficiency (or its abnormalities in humans) is associated with a series of pathological conditions including dyslipidemia, atherosclerosis, Alzheimer's disease, and shorter life span. The purpose of this study was to characterize these conditions in apo E-deficient C57BL/6J mice and relate them to human disorders. Deletion of apo E gene in mice is associated with changes in lipoprotein metabolism [plasma total cholesterol (TC) (>+400%), HDL cholesterol (-80%), HDL/TC, and HDL/LDL ratios (-93% and -96%, respectively), esterification rate in apo B-depleted plasma (+100%), plasma triglyceride (+200%), hepatic HMG-CoA reductase activity (-50%), hepatic cholesterol content (+30%)], decreased plasma homocyst(e)ine and glucose levels, and severe atherosclerosis and cutaneous xanthomatosis. Hepatic and lipoprotein lipase activities, hepatic LDL receptor function, and organ antioxidant capacity remain unchanged. Several histological/immunohistological stainings failed to detect potential markers for neurodegenerative disease in the brain of 37-wk-old male apo E-KO mice. Apo E-KO mice may have normal growth and development, but advanced atherosclerosis and xanthomatosis may indirectly reduce their life span. Apo E plays a crucial role in regulation of lipid metabolism and atherogenesis without affecting lipase activities, endogenous antioxidant capacity, or appearance of neurodegenerative markers in 37-wk-old male mice.

Apolipoprotein E and apolipoprotein E receptors modulate A beta-induced glial neuroinflammatory responses

Large numbers of activated glia are a common pathological feature of many neurodegenerative disorders, including Alzheimer's disease (AD). Several different stimuli, including lipopolysaccharide (LPS), dibutyryl (db)cAMP, and aged amyloid-beta 1-42 (A beta), can induce glial activation in vitro, as measured by morphological changes and the production of pro-inflammatory cytokines and oxidative stress molecules. Only A beta-induced activation is attenuated by the addition of exogenous apolipoprotein E (apoE)-containing particles. In addition, only A beta also induces an increase in the amount of endogenous apoE, the primary apolipoprotein expressed by astrocytes in the brain. The functional significance of the increase in apoE appears to be to limit the inflammatory response. Indeed, compared to wild type mice, glial cells cultured from apoE knockout mice exhibit an enhanced production of several pro-inflammatory markers in response to treatment with A beta and other activating stimuli. The mechanism for both the A beta-induced glial activation and the increase in apoE appears to involve apoE receptors, a variety of which are expressed by both neurons and glia. Experiments using receptor associated protein (RAP), an inhibitor of apoE receptors with a differential affinity for the low-density lipoprotein receptor (LDLR) and the LDLR-related protein (LRP), revealed that LRP mediates A beta-induced glial activation, while LDLR mediates the A beta-induced changes in apoE levels. In summary, both an apoE receptor agonist (apoE) and an antagonist (RAP) inhibit A beta-induced glial cell activation. Thus, apoE receptors appear to translate the presence of extracellular A beta into cellular responses, both initiating glial cell activation and limiting its scope by inducing apoE, an anti-inflammatory agent.

Amyloid-beta: an antioxidant that becomes a pro-oxidant and critically contributes to Alzheimer's disease

Elevated production of amyloid-beta (A beta) as a preventive antioxidant for brain lipoproteins under the action of increased oxidative stress in aging is postulated to represent a major event in the development of Alzheimer's disease (AD). Increase in A beta production is followed by chelation of transition metal ions by A beta, accumulation of A beta-metal lipoprotein aggregates, production of reactive oxygen species and neurotoxicity. Chelation of copper by A beta is proposed to be a most important part of this pathway, because A beta binds copper stronger than other transition metals and because copper is a more efficient catalyst of oxidation than other metals. This amyloid-binds-copper (ABC) model does not remove A beta peptide from its central place in our current thinking of AD, but rather places additional factors in the center of discussion. Most importantly, they embrace pathological mechanisms known to develop in aging (which is the major risk factor for AD), such as increased production of reactive oxygen species by mitochondria, that are positioned upstream relative to the generation of A beta.

Brain region-specific up-regulation of mouse apolipoprotein E by pharmacological estrogen treatments

Cerebral apolipoprotein E (apoE) has been implicated in neuronal protection and repair. Due to the variable levels and types of estrogen receptors within different brain regions, the effect of estrogen on apoE and the mechanism of this effect may vary within different regions. Ovariectomized female C57BL/6 mice were treated with pharmacological levels of 17 beta-estradiol or placebo for 5 days, resulting in supraphysiological plasma levels of estradiol in the treated mice. ApoE and glial fibrillary acidic protein (GFAP) levels were measured in the cortex, hippocampus and diencephalon. 17 beta-Estradiol up-regulated apoE but not GFAP in the cortex and diencephalon, whereas in the hippocampus, GFAP and apoE were equally up-regulated. Treatment of estrogen receptor (ER) alpha knockout mice with 17 beta-estradiol or treatment of C57BL/6 mice with 17 alpha-estradiol, a poor estrogen receptor agonist, specifically induced apoE in the cortex, but not in the diencephalon. These results indicate that 17 beta-estradiol effects on apoE are either directly or indirectly mediated by ER alpha in the diencephalon, while the effects in the cortex may be mediated by a non-classical mechanism or by ER beta. Measurement of mRNA levels in estrogen versus placebo-treated wild-type mice indicated that the effect of 17 beta-estradiol on apoE was not associated with changes in apoE mRNA levels.

Purification and characterization of astrocyte-secreted apolipoprotein E and J-containing lipoproteins from wild-type and human apoE transgenic mice

The varepsilon4 allele of apolipoprotein E (apoE) is a genetic risk factor for Alzheimer's disease (AD). In order to gain a better understanding of the molecular mechanisms by which apoE and possibly other apolipoproteins produced in the central nervous system (CNS) influence AD pathogenesis, we have purified and characterized the two most abundant apolipoproteins produced in the CNS, apoE and apoJ. We purified apoE and apoJ from primary cultures of mouse astrocytes, which were derived from transgenic mice expressing human apoE isoforms in the absence of mouse apoE. Utilizing antibody affinity columns, we were able to purify both human apoE3 and apoE4, as well as mouse apoJ-containing lipoproteins. Astrocyte-secreted human apoE was present in high density-like lipoproteins of three predominant sizes ranging from 8 to 15 nm in diameter. Mouse apoJ was in particles between 10 and 17 nm in diameter with a peak size range of approximately 11 nm. ApoE and apoJ were in distinct lipoproteins. Utilization of quick-freeze, deep-etch electron microscopy revealed the apoE particles were discs while the apoJ particles were smaller and more irregular in appearance. The lipid composition of apoE particles was very different from those containing apoJ. ApoE-particles contained a similar mass of apoE and lipid, with cholesterol and phospholipid being about equal in mass per particle. ApoJ-particles were relatively lipid poor (three parts protein, one part lipid), with phospholipids being much more abundant than cholesterol. Detailed characterization of phospholipid composition by electrospray ionization mass spectrometry analysis revealed ethanolamine glycerophospholipids to be the most abundant phospholipid present in both apoE and apoJ particles. Analysis of cerebrospinal fluid from apoE3 and apoE4 transgenic mice revealed that human and mouse apoE were in particles the same size as those secreted by astrocytes. Further use of physiological preparations of CNS-derived lipoproteins may allow for a detailed understanding of the role of these molecules in the normal brain and in diseases such as AD.

Heart failure in beta thalassemia: a 5-year follow-up study

PURPOSE

To evaluate the survival of patients with beta thalassemia and heart failure who were treated with iron chelation therapy.

SUBJECTS AND METHODS

Fifty-two consecutive patients with beta thalassemia and heart failure were followed in a prospective 5-year study. All patients underwent a full clinical examination with chest radiograph, electrocardiogram, and echocardiographic investigation performed at 6-month intervals or when a new symptom developed.

RESULTS

Of the 52 patients (mean [+/- SD] age, 24 +/- 5 years), 25 (48%) survived 5 years after the onset of heart failure. Forty-three patients had left-sided heart failure, and 9 had right-sided heart failure. Those with left-sided heart failure were younger at presentation with heart failure (22 +/- 4 years vs. 31 +/- 6 years; P <0.001), had lower ejection fractions (36% +/- 9% vs. 64% +/- 10%; P <0.001), and had a lower mean serum ferritin level (3355 +/- 1241 ng/mL vs. 6,397 +/- 1,613 ng/mL; P <0.001).

CONCLUSION

The 5-year survival rate in patients with beta thalassemia with heart failure was greater than previously reported. There are clinical characteristics that may make patients more likely to develop left- or right-sided heart failure.

Delayed, but marked, expression of apolipoprotein E is involved in tissue clearance after cerebral infarction

Clearance of infarct tissue would be an important process for tissue repair after a stroke. Delayed clearance may hamper reconstitution of the blood-brain barrier and glial boundary formation. Recent growing evidence has indicated that apolipoprotein E (APOE), a major apoprotein, plays an important role in lipid transport and homeostasis in the brain. The tissue in the infarction contains abundant lipids must be removed for tissue clearance. In the current study, the authors investigated APOE expression after focal ischemia and the functional role of APOE in tissue clearance using APOE-knockout mice. Expression of APOE was delayed, but marked, in immunohistochemistry and immunoblotting 7 days after permanent focal ischemia. Macrophages were found to express APOE in the infarct center. Infarct size was similar after focal ischemia between wild-type and APOE-knockout mice, although there was no APOE protein expression in knockout mice. However, clearance of infarct tissue 2 weeks after ischemia was significantly delayed in APOE-knockout mice compared with wild-type mice. The current study supports current thinking that APOE is a key molecule for tissue remodeling in the brain. Clearance of damaged tissue may be one of the important functions of APOE in the brain.