Synaptic loss is accompanied by an increase in synaptic area in the dentate gyrus of aged human apolipoprotein E4 transgenic mice

To investigate the relationship between the three isoforms of apolipoprotein E (E2, E3 and E4) and the integrity of the synaptic circuitry in the dentate gyrus of the hippocampus, we have estimated the synapse per neuron ratio and mean apposition zone area per synapse at the electron microscope level in the dentate gyrus of apolipoprotein E knockout and human apolipoprotein E transgenic mice aged six to 24months. During ageing, only in human apolipoprotein E4 mice was there a decrease in synapse per neuron ratio, accompanied by an increase in synaptic size. When these mice were compared with human apolipoprotein E2, apolipoprotein E knockout and wild-type mice at old age, they displayed the lowest synapse per neuron ratio, but similar apposition zone area. In contrast, as in our previous study, aged apolipoprotein E knockout mice did not show any sign of synaptic degeneration.The functional consequences of such morphological changes remain to be determined. However, if such age-related loss of synapses occurred in the brain of Alzheimer apolipoprotein E4 patients, they might be additive to pathological processes and could contribute to greater cognitive impairment.     

Progressive loss of synaptic integrity in human apolipoprotein E4 targeted replacement mice and attenuation by apolipoprotein E2

Inheritance of the APOE4 allele is a well established genetic risk factor linked to the development of late onset Alzheimer's disease. As the major lipid transport protein in the central nervous system, apolipoprotein (apo) E plays an important role in the assembly and maintenance of synaptic connections. Our previous work showed that 7 month old human apoE4 targeted replacement (TR) mice displayed significant synaptic deficits in the principal neurons of the lateral amygdala, a region that is critical for memory formation and also one of the primary regions affected in Alzheimer's disease, compared to apoE3 TR mice. In the current study, we determined how age and varying APOE genotype affect synaptic integrity of amygdala neurons by comparing electrophysiological and morphometric properties in C57BL6, apoE knockout, and human apoE3, E4 and E2/4 TR mice at 1 month and 7 months. The apoE4 TR mice exhibited the lowest level of excitatory synaptic activity and dendritic arbor compared to other cohorts at both ages, and became progressively worse by 7 months. In contrast, the apoE3 TR mice exhibited the highest synaptic activity and dendritic arbor of all cohorts at both ages. C57BL6 mice displayed virtually identical synaptic activity to apoE3 TR mice at 1 month; however this activity decreased by 7 months. ApoE knockout mice exhibited a similar synaptic activity profile with apoE4 TR mice at 7 months. Consistent with previous reports that APOE2 confers protection, the apoE4-dependent deficits in excitatory activity were significantly attenuated in apoE2/4 TR mice at both ages. These findings demonstrate that expression of human apoE4 contributes to functional deficits in the amygdala very early in development and may be responsible for altering neuronal circuitry that eventually leads to cognitive and affective disorders later in life.     

Ultrastructural identification of cells with dendritic cell appearance in atherosclerotic aorta of apolipoprotein E deficient mice

The present electron microscopic study was undertaken to see whether cells with a dendritic cell appearance accumulate in atherosclerotic lesions of apolipoprotein E (apoE) deficient mice. Atherosclerotic aortas from 7 eight-month old apoE deficient mice were examined. In atherosclerotic plaques as well as in the underlying media and adventitia, cells with a dendritic cell appearance including the presence of a unique tubulovesicular system were detected. The tubulovesicular system was most hypertrophied in their cellular processes where the continuous cisterns sometimes formed circular structures. The cells containing the tubulovesicular system lacked lysosomes and phagolysosomes and their cytoplasm was free of lipid inclusions. The present observations suggest that dendritic cells are involved in apoE deficient mouse atherosclerosis. ApoE deficient mice might be a useful model for investigating functions of dendritic cells in atherogenesis.     

No evidence for cholinergic problems in apolipoprotein E knockout and apolipoprotein E4 transgenic mice

The varepsilon4 allele of the apolipoprotein E gene constitutes the major genetic risk factor to develop Alzheimer's disease. If and how this protein contributes to the pathological cascade of Alzheimer's disease is not known. The varepsilon4 allele particularly affects the cholinergic defect, which is one of the most consistent neurotransmitter problems in an Alzheimer's disease brain.We have analysed several parameters of the cholinergic system in brain of apolipoprotein E knockout mice as well as in transgenic mice overexpressing human apolipoprotein E4. We analysed the distribution of cholinergic fibers, the number and morphology of cholinergic neurons and the enzymatic activity of acetylcholinesterase and choline acetyltransferase in different brain regions. Finally, we analysed the distribution and the binding parameters of [3H]hemicholinium-3, a specific marker for the high affinity choline transporter in different brain sections and regions.This extensive effort failed to show any consistent difference in the cholinergic parameters studied, in either the apolipoprotein E4 transgenic mice or in the apolipoprotein E knockout mice, compared to age-matched non-transgenic mice. We conclude that the apolipoprotein E4 is not deleterious per se for the cholinergic system in mouse brain.     

Apolipoprotein E isoform-specific regulation of dendritic spine morphology in apolipoprotein E transgenic mice and Alzheimer's disease patients

Dendritic spines are postsynaptic sites of excitatory input in the mammalian nervous system. Apolipoprotein (apo) E participates in the transport of plasma lipids and in the redistribution of lipids among cells. A role for apoE is implicated in regeneration of synaptic circuitry after neural injury. The apoE4 allele is a major risk factor for late-onset familial and sporadic Alzheimer's disease (AD) and is associated with a poor outcome after brain injury. ApoE isoforms are suggested to have differential effects on neuronal repair mechanisms. In vitro studies have demonstrated the neurotrophic properties of apoE3 on neurite outgrowth. We have investigated the influence of apoE genotype on neuronal cell dendritic spine density in mice and in human postmortem tissue. In order to compare the morphology of neurons developing under different apoE conditions, gene gun labeling studies of dendritic spines of dentate gyrus (DG) granule cells of the hippocampus were carried out in wild-type (WT), human apoE3, human apoE4 expressing transgenic mice and apoE knockout (KO) mice; the same dendritic spine parameters were also assessed in human postmortem DG from individuals with and without the apoE4 gene. Quantitative analysis of dendritic spine length, morphology, and number was carried out on these mice at 3 weeks, 1 and 2 years of age. Human apoE3 and WT mice had a higher density of dendritic spines than human E4 and apoE KO mice in the 1 and 2 year age groups (P<0.0001), while at 3 weeks there were no differences between the groups. These age dependent differences in the effects of apoE isoforms on neuronal integrity may relate to the increased risk of dementia in aged individuals with the apoE4 allele. Significantly in human brain, apoE4 dose correlated inversely with dendritic spine density of DG neurons cell in the hippocampus of both AD (P=0.0008) and aged normal controls (P=0.0015). Our findings provide one potential explanation for the increased cognitive decline seen in aged and AD patients expressing apoE4.     

Apolipoprotein E inhibits neointimal hyperplasia after arterial injury in mice

The potential cytostatic function of apolipoprotein (apo) E in vivo was explored by measuring neointimal hyperplasia in response to vascular injury in apoE-deficient and apoE-overexpressing transgenic mice. Results showed a significant increase in medial thickness, medial area, and neointimal formation after vascular injury in both apoE knockout and wild-type C57BL/6 mice. Immunochemical analysis with smooth muscle alpha-actin-specific antibodies revealed that the neointima contained proliferating smooth muscle cells. Neointimal area was 3.4-fold greater, and the intima/medial ratio as well as stenotic luminal area was more pronounced in apoE(-/-) mice than those observed in control mice (P < 0.05). The human apoE3 transgenic mice in FVB/N genetic background were then used to verify a direct effect of apoE in protection against neointimal hyperplasia in response to mechanically induced vascular injury. Results showed that neointimal area was reduced threefold to fourfold in mice overexpressing the human apoE3 transgene (P < 0.05). Importantly, suppression of neointimal formation in the apoE transgenic mice also abolished the luminal stenosis observed in their nontransgenic FVB/N counterparts. These results documented a direct role of apoE in modulating vascular response to injury, suggesting that increasing apoE level may be beneficial in protection against restenosis after vascular surgery.     

Apolipoprotein E receptors and amyloid expression are modulated in an apolipoprotein E-dependent fashion in response to hippocampal deafferentation in rodent

The entorhinal cortex lesion paradigm is a widely accepted and efficient method to provoke reactive synaptogenesis and terminal remodeling in the adult CNS. This approach has been used successfully to contrast the profile of reactivity from various proteins associated with Alzheimer's disease pathophysiology in wild-type and apolipoprotein E (apoE)-deficient (APOE ko) mice. Results indicate that the production of the beta-amyloid 1-40 peptide (A beta 40) is increased in response to neuronal injury, with a timing that is different between wild-type and APOE ko animals. Moreover, we report that baseline levels of the A beta 40 peptide are significantly higher in the APOE ko mice. The expression of the apolipoprotein E receptor type 2 (apoER2) is also modulated by the deafferentation process in the hippocampus, but only in APOE ko mice. These results provide novel insights as to the molecular mechanisms responsible for the poor plastic response reported in apoE4-expressing and apoE deficient mice in response to hippocampal injury.     

Marked regional differences of brain human apolipoprotein E expression in targeted replacement mice

We used three human apolipoprotein (apo) E targeted replacement mouse lines, each expressing one of the three common human apoE isoforms to study the pattern of apoE expression in the central nervous system (CNS). Immunocytochemistry on brain sections from all three lines of targeted replacement mice, wild type mice, African green monkeys, and humans show a predominantly glial pattern of apoE expression. The levels of human apoE protein in hippocampus and frontal cortex were similar between targeted replacement mice and non-demented human tissue. Within a given brain region, the levels of apoE were very similar amongst all three isoforms, which contrasts sharply with plasma, where apoE2 levels are 16-fold higher than apoE3 and E4 levels. Across brain regions, cerebellar apoE levels were significantly higher than cerebral apoE levels. In conclusion, we provide detailed analysis of a human apoE animal model system that recapitulates both the pattern and level of apoE expression in non-demented humans. The neurobiology of human apoE isoforms can now be studied in both the normal and post-injury state, since all apoE regulatory sequences are intact. Finally, the differences in apoE levels we observed may explain the regional vulnerability of neuronal degeneration in Alzheimer's disease.     

Mixed allogeneic chimerism with wild-type strains ameliorates atherosclerosis in apolipoprotein E-deficient mice

Atherosclerosis involves inflammatory processes between vascular tissues and hematocytes with a hyperlipidemic background. To examine whether variations of hematocytes constitute one of the genetic components in atherosclerosis, irradiated apolipoprotein E (apoE)-deficient (apoE(-/-)) mice with hypercholesterolemia and preexisting atherosclerotic lesions were reconstituted with mixed bone marrow cells (BMC) from syngeneic and wild-type (apoE(+/+); atherosclerosis-resistant SJL or -susceptible B10.S) mice. Stable mixed allogeneic chimeras with small amounts of serum apoE were established without any detrimental complications. Compared with untreated apoE(-/-) mice or apoE(-/-) mice transplanted with syngeneic BMC alone, significant reduction of the cholesterol level and significant lesion regression were observed in the mixed chimeras. Furthermore, mixed chimeras given SJL BMC showed marked reductions in numbers of lesions compared with those reconstituted with B10.S BMC. Cholesterol levels in the former SJL chimeras, however, were significantly higher than those in the latter B10.S chimeras. These findings indicate that the resistance of SJL to atherosclerosis resides in the bone marrow-derived cells.     

Overexpression of peroxiredoxin 4 attenuates atherosclerosis in apolipoprotein e knockout mice

Abstract Aim: A growing body of evidence has shown that increased formation of oxidized molecules and reactive oxygen species within the vasculature (i.e., the extracellular space) plays a crucial role in the initiation and progression of atherosclerosis and in the formation of unstable plaques. Peroxiredoxin 4 (PRDX4) is the only known secretory member of the antioxidant PRDX family. However, the relationship between PRDX4 and susceptibility to atherosclerosis has remained unclear. Results: To define the role of PRDX4 in hyperlipidemia-induced atherosclerosis, we generated hPRDX4 transgenic (Tg) and apolipoprotein E (apoE) knockout mice (hPRDX4(+/+)/apoE(-/-)). After feeding the mice a high-cholesterol diet, they showed fewer atheromatous plaques, less T-lymphocyte infiltration, lower levels of oxidative stress markers, less necrosis, a larger number of smooth muscle cells, and a larger amount of collagen, resulting in thickened fibrous cap formation and possible stable plaque phenotype as compared with apoE(-/-) mice. We also detected greater suppression of apoptosis and decreased Bax expression in hPRDX4(+/+)/apoE(-/-) mice than in apoE(-/-) mice. Bone marrow transplantation from hPRDX4(+/+) donors to apoE(-/-) mice confirmed the antiatherogenic aspects of PRDX4, revealing significantly suppressed atherosclerotic progression. Innovation: In this study, we demonstrated for the first time that PRDX4 suppressed the development of atherosclerosis in apoE(-/-) mice fed a high-cholesterol diet. Conclusion: These data indicate that PRDX4 is an antiatherogenic factor and, by suppressing oxidative damage and apoptosis, that it may protect against the formation of vulnerable (unstable) plaques. Antioxid. Redox Signal. 17, 1362-1375.     

Dominant negative effects of apolipoprotein E4 revealed in transgenic models of neurodegenerative disease

Apolipoprotein E fulfills fundamental functions in lipid transport and neural tissue repair after injury.(6,8) Its three most common isoforms (E2, E3, and E4) are critical determinants of diverse human diseases, including major cardiovascular and neurodegenerative disorders.(8,14) Apolipoprotein E4 is associated with an increased risk for Alzheimer's disease(3,5) and poor clinical outcome after head injury or stroke.(11,16) The precise role of apolipoprotein E4 in these conditions remains unknown. To characterize the effects of human apolipoprotein E isoforms in vivo, we analysed transgenic Apoe knockout mice that express apolipoprotein E3 or E4 or both in the brain. Hemizygous and homozygous apolipoprotein E3 mice were protected against age-related and excitotoxin-induced neurodegeneration, whereas apolipoprotein E4 mice were not. Apolipoprotein E3/E4 bigenic mice were as susceptible to neurodegeneration as apolipoprotein E4 singly-transgenic mice. At eight months of age neurodegeneration was more severe in homozygous than in hemizygous apolipoprotein E4 mice consistent with a dose effect. Thus, apolipoprotein E4 is not only less neuroprotective than apolipoprotein E3 but also acts as a dominant negative factor that interferes with the beneficial function of apolipoprotein E3. The inhibition of this apolipoprotein E4 activity may be critical for the prevention and treatment of neurodegeneration in APOE varepsilon4 carriers.     

Apolipoprotein E4 decreases whereas apolipoprotein E3 increases the level of secreted amyloid precursor protein after closed head injury

Apolipoprotein E (apoE4) and head trauma are important genetic and environmental risk factors for Alzheimer's disease. Furthermore, apoE4 increases both the acute and chronic consequences of head trauma. The latter are associated with the deposition of amyloid-beta, which is particularly elevated in apoE4 subjects. The short-term effects of head injury are associated with transiently increased metabolism of amyloid precursor protein (APP) and its secreted fragment, APPs. In the present study, we examined the possibility that the acute, short-term pathological effects of apoE4 following head trauma and the corresponding neuroprotective effects of apoE3 are related to isoform-specific effects of apoE on APP metabolism. Accordingly, male transgenic mice expressing human apoE3 or apoE4 on a null mouse apoE background and apoE-deficient and control mice were subjected to closed head injury (CHI). The resulting effects on brain APP, and on its secreted products, APPs and secreted product of the alpha-cleavage of APP (APPsalpha) were then determined 24 h following injury. Immunoblotting revealed no significant differences between the basal APP, APPs and APPsalpha levels of the hippocampus or the cortex of the control and the apoE3 and ApoE4 transgenic mice. The apoE-deficient mice also had similar cortical basal levels of APP and its metabolites, whereas their corresponding basal hippocampal APP and APPs levels were lower than those of the other groups. CHI lowered the hipppocampal APPs and APPsalpha levels of the apoE4 transgenic mice, whereas those of the apoE3 transgenic mice and of the control and apoE-deficient mice were not affected by this insult. In contrast, CHI raised the cortical APP and APPs levels of the apoE3 transgenic mice but had no significant effect on those of the other mice groups. These animal model findings suggest that the acute, short-term pathological effects of apoE4 following CHI and the corresponding neuroprotective effects of apoE3 may be mediated by their opposing effects on the expression and cleavage of cortical and hippocampal APP. Similar isoform-specific interactions between apoE and APP may play a role in the acute, short-term effects of head trauma in humans.     

Differential neurotrophic effects of apolipoprotein E in aged transgenic mice.

The present study seeked to determine whether the neurodegenerative and cognitive alterations in aged apolipoprotein E-deficient mice are differentially reversed by transgenic overexpression of human apolipoprotein-E3 vs. apolipoprotein-E4 in the background of deficient endogenous apolipoprotein E. These studies showed dendritic alterations in pyramidal neurons of apolipoprotein-E4 transgenic mice, similar to the ones observed in apolipoprotein E-deficient mice. However, these mice had a preserved density of synaptophysin-immunoreactive presynaptic terminals. In contrast, mice overexpressing apolipoprotein-E3 showed no synapto-dendritic alterations. Analysis of behavioral performance in the Morris water maze showed that while apolipoprotein E-deficient mice performed poorly, overexpression of apolipoprotein-E3 and, to a lower extent apolipoprotein-E4, resulted in an improved performance. This study supports the contention that, compared with apolipoprotein-E4, apolipoprotein-E3 might have a greater neurotrophic in vivo effect in aged mice.     

Susceptibility of transgenic mice expressing human apolipoprotein E to closed head injury: the allele E3 is neuroprotective whereas E4 increases fatalities

Apolipoprotein E, the major brain lipid-binding protein, is expressed in humans as three common isoforms (E2, E3 and E4). Previous studies revealed that the allele apolipoprotein E4 is a major genetic risk factor of Alzheimer's disease and that traumatic brain injury is associated with increased risk for developing this disease. Furthermore, it has been suggested that the effects of traumatic head injury and apolipoprotein E4 in Alzheimer's disease are synergistic. To test the hypothesis that the apolipoprotein E genotype affects susceptibility to brain injury, we subjected transgenic mice, expressing either human apolipoprotein E3 or human apolipoprotein E4 on a null mouse apolipoprotein E background and apolipoprotein E-deficient knockouts, to closed head injury and compared mortality, neurological recovery and the extent of brain damage of the survivors. More than 50% of the transgenic mice expressing human apolipoprotein E4 died following closed head injury, whereas only half as many of the transgenic mice expressing human apolipoprotein E3, and of the control and apolipoprotein E-deficient mice died during this period (P<0.02). A neurological severity score used for clinical assessment of the surviving mice up to 11 days after closed head injury revealed that the four mouse groups displayed similar severity of damage at 1h following injury. At three and 11 days post-injury, however, the neurological severity scores of the transgenic mice expressing human apolipoprotein E3 were significantly lower than those of the other three groups whose scores were similar, indicating better recovery of the transgenic mice expressing human apolipoprotein E3. Histopathological examination of the mice performed 11 days post-injury revealed, consistent with the above neurological results, that the size of the damaged brain area of the transgenic mice expressing human apolipoprotein E3 was smaller than that of the other head-injured groups.These findings show that transgenic mice expressing human apolipoprotein E4 are more susceptible than those expressing apolipoprotein E3 to closed head injury. We suggest that this effect is due to both a protective effect of apolipoprotein E3 and an apolipoprotein E4-related pathological function.     

Use of transgenic mice to study the role of apolipoprotein E in lipid metabolism and atherosclerosis

Insight into the role of apolipoprotein (apo) E in lipoprotein metabolism and atherosclerosis has increased dramatically with the generation and analysis of novel transgenic, knockout and knockin mouse models. Moreover, the recent development and application of somatic gene and cell transfer technologies which can express (or delete) apoE in specific tissues of virtually any mouse model have further added to this increase in knowledge. It is now well established that apoE plays a role in virtually every step in the metabolism of very low-density lipoproteins and in the efflux of cholesterol from macrophages. In this review we will discuss recent insights into the role of apoE in these processes with particular emphasis on the specific effects of variation in apoE structure and quantity.     

Similar promotion of Abeta1-42 fibrillogenesis by native apolipoprotein E epsilon3 and epsilon4 isoforms

The apolipoprotein E epsilon4 allele contributes to the genetic susceptibility underlying a large proportion (~40-60%) of typical, sporadic Alzheimer disease. Apolipoprotein E deficient mice made transgenic for human apolipoprotein E epsilon4 accumulate excess cerebral amyloid when compared to similarly prepared mice expressing human apolipoprotein E epsilon3. Therefore, it is important to search for relevant interactions(s) between apolipoprotein E epsilon4 and Abeta in order to clarify the biological role for apolipoprotein E epsilon4 in Alzheimer disease. Using a thioflavine T (ThT)-based assay, we have investigated the effects of native human apolipoprotein E isoforms on the kinetics of Abeta fibrillogenesis. No obvious profibrillogenic activity was detected in Abeta1-40-based assays of any native apolipoprotein E isoform. However, when ThT assays were repeated using Abeta1-42, modest, but statistically significant, profibrillogenic activity was detected in both apolipoprotein E epsilon3- and apolipoprotein E epsilon4-containing media and was similar in magnitude for the two isoforms. These data demonstrate that native apolipoprotein E possesses "pathological chaperone"-type activity for Abeta: in other words, the data indicate that a chaperone-like misfolding reaction can occur between native apolipoprotein E and Abeta. However, the equipotent activities of the apolipoprotein E epsilon3 and epsilon4 isoforms suggests the possibility that either extended co-incubation of apolipoprotein E and Abeta, or, perhaps, the inclusion in the reaction of other fibrillogenesis-modulation co-factors (such as metal ions, or inflammatory mediators such as reactive oxygen species, alpha2-macroglobulin, apolipoprotein J, etc.) may be required for modeling in vitro the apolipoprotein E-isoform-specific-regulation of extracellular Abeta accumulation that occurs in vivo. Alternatively, other events, such as differential apolipoprotein E-isoform-mediated clearance of Abeta or of apolipoprotein E/Abeta complexes may underlie apolipoprotein E-isoform-dependent Abeta accumulation.     

Reversal of presynaptic deficits of apolipoprotein E-deficient mice in human apolipoprotein E transgenic mice

Apolipoprotein E genotype is an important risk factor of Alzheimer's disease, which is associated with the degeneration of distinct brain neuronal systems. In the present study we employed apolipoprotein E-deficient mice and human apolipoprotein E3 and apolipoprotein E4 transgenic mice on a null mouse apolipoprotein E background, to examine the extent to which distinct brain neuronal systems are affected by apolipoprotein E and the isoform specificity of this effect. This was pursued by histological and autoradiographic measurements utilizing neuron specific presynaptic markers. The results thus obtained revealed significant reductions in the levels of brain cholinergic and noradrenergic nerve terminals in young apolipoprotein E-deficient mice and no changes in brain dopaminergic nerve terminals. These cholinergic and noradrenergic presynaptic derangements were ameliorated similarly in human apolipoprotein E3 and apolipoprotein E4 transgenic mice. In the case of the cholinergic system, this resulted in complete reversal of the presynaptic deficits, whereas in the case of the noradrenergic neurons the amelioration was partial.These findings suggest that brain cholinergic and noradrenergic neurons are markedly more dependent on brain apolipoprotein E than brain dopaminergic neurons and that the isoform specificity of these effects is not apparent at a young age under non-challenged conditions.     

Cells of human aminopeptidase N (CD13) transgenic mice are infected by human coronavirus-229E in vitro, but not in vivo

Aminopeptidase N, or CD13, is a receptor for serologically related coronaviruses of humans, pigs, and cats. A mouse line transgenic for the receptor of human coronavirus-229E (HCoV-229E) was created using human APN (hAPN) cDNA driven by a hAPN promoter. hAPN-transgenic mice expressed hAPN mRNA in the kidney, small intestine, liver, and lung. hAPN protein was specifically expressed on epithelial cells of the proximal convoluted renal tubules, bronchi, alveolar sacs, and intestinal villi. The hAPN expression pattern within transgenic mouse tissues matched that of mouse APN and was similar in mice heterozygous or homozygous for the transgene. Primary embryonic cells and bone marrow dendritic cells derived from hAPN-transgenic mice also expressed hAPN protein. Although hAPN-transgenic mice were resistant to HCoV-229E in vivo, primary embryonic cells and bone marrow dendritic cells were infected in vitro. hAPN-transgenic mice are valuable as a source of primary mouse cells expressing hAPN. This hAPN-transgenic line will also be used for crossbreeding experiments with other knockout, immune deficient, or transgenic mice to identify factors, in addition to hAPN, that are required for HCoV-229E infection.     

Human APOE protein localized in brains of transgenic mice

Transgenic mice carrying the three common human apolipoprotein E (APOE) alleles have been developed. In this study, brains of the transgenic mice have been analyzed by in situ histohybridization, immunohistochemistry, and immunoblots to determine sites of gene expression, to identify specific brain cells associated with human apoE protein, and to determine the relative concentrations of the human apoE. Results indicate that (1) human APOE mRNA and apoE protein occur in the gray and white matter of transgenic mouse brains; (2) in the hippocampus of transgenic brains, human apoE protein reacts immunologically within the same cells as the glial fibrillary acidic protein (GFAP), a specific marker for astrocytes; and (3) concentrations of the apoE isoforms determined in three heterozygous transgenic brains range from 22 to 250 pmol/g wet weight of brain.