Apolipoprotein E and Alzheimer's disease: The protective effects of ApoE2 and E3 (original) (raw)

ApoE in Alzheimer’s disease: pathophysiology and therapeutic strategies

Molecular Neurodegeneration

Alzheimer’s disease (AD) is the most common cause of dementia worldwide, and its prevalence is rapidly increasing due to extended lifespans. Among the increasing number of genetic risk factors identified, the apolipoprotein E (APOE) gene remains the strongest and most prevalent, impacting more than half of all AD cases. While the ε4 allele of the APOE gene significantly increases AD risk, the ε2 allele is protective relative to the common ε3 allele. These gene alleles encode three apoE protein isoforms that differ at two amino acid positions. The primary physiological function of apoE is to mediate lipid transport in the brain and periphery; however, additional functions of apoE in diverse biological functions have been recognized. Pathogenically, apoE seeds amyloid-β (Aβ) plaques in the brain with apoE4 driving earlier and more abundant amyloids. ApoE isoforms also have differential effects on multiple Aβ-related or Aβ-independent pathways. The complexity of apoE biology and pathob...

Impact of Apolipoprotein E (ApoE) Polymorphism on Brain ApoE Levels

Journal of Neuroscience, 2008

Inheritance of the apoE4 allele (4) increases the risk of developing Alzheimer's disease; however, the mechanisms underlying this association remain elusive. Recent data suggest that inheritance of 4 may lead to reduced apoE protein levels in the CNS. We therefore examined apoE protein levels in the brains, CSF and plasma of 2/2, 3/3, and 4/4 targeted replacement mice. These apoE mice showed a genotype-dependent decrease in apoE levels; 2/2 Ͼ3/3 Ͼ4/4. Next, we sought to examine the relative contributions of apoE4 and apoE3 in the 3/4 mouse brains. ApoE4 represented 30 -40% of the total apoE. Moreover, the absolute amount of apoE3 per allele was similar between 3/3 and 3/4 mice, implying that the reduced levels of total apoE in 3/4 mice can be explained by the reduction in apoE4 levels. In culture medium from 3/4 human astrocytoma or 3/3, 4/4 and 3/4 primary astrocytes, apoE4 levels were consistently lower than apoE3. Secreted cholesterol levels were also lower from 4/4 astrocytes. Pulse-chase experiments showed an enhanced degradation and reduced half-life of newly synthesized apoE4 compared with apoE3. Together, these data suggest that astrocytes preferentially degrade apoE4, leading to reduced apoE4 secretion and ultimately to reduced brain apoE levels. Moreover, the genotype-dependent decrease in CNS apoE levels, mirror the relative risk of developing AD, and suggest that low levels of total apoE exhibited by 4 carriers may directly contribute to the disease progression, perhaps by reducing the capacity of apoE to promote synaptic repair and/or A␤ clearance.

ApoE genotype accounts for the vast majority of AD risk and AD pathology

Neurobiology of Aging, 2004

In this review, evidence is provided that apolipoprotein E (apoE) genotype accounts for the majority of Alzheimer's disease (AD) risk and pathology. The three major human isoforms, apoE2, apoE3, and apoE4, are encoded by different alleles (ε2, ε3, ε4) and regulate lipid metabolism and redistribution. ApoE isoforms differ in their effects on AD risk and pathology. Clinical and epidemiological data have indicated that the ε4 allele may account for 50% of AD in the United States. Further, the rarity of AD among carriers of the ε2 allele suggests that allelic variations in the gene encoding this protein may account for over 95% of AD cases. ApoE4 disrupts memory function in rodents. Further studies have indicated that fragments of apoE may contribute to both plaque and tangle formation. Thus, the epidemiologic and basic science evidence suggest that apoE genotype accounts for the vast majority of AD risk and pathology.

Apolipoprotein E in Alzheimer's disease and other neurological disorders

The Lancet Neurology, 2011

Apolipoprotein E (ApoE) is a 299 amino acid protein encoded by the APOE gene. Three common polymorphisms in the APOE gene, ε2, ε3, and ε4, result in single amino changes in the ApoE protein. The APOEε2, ε3, and ε4 alleles strongly and dose-dependently alter the likelihood of developing Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA). In particular, APOE ε4 is associated with increased risk for AD, whereas APOEε2 is associated with decreased risk. The effects of APOE genotype on AD and CAA risk are likely mediated, in large part, by differential effects of the ApoE protein on amyloid-β (Aβ) accumulation in the brain and cerebrovasculature. Recent data indicate that responses to AD treatments may differ according to APOE genotype. The APOE ε4 allele is also associated with poor outcome following traumatic brain injury and brain hemorrhage, though the mechanisms underlying these associations are unclear. Given the convincing body of literature tying APOE genotype to AD and CAA risk, APOE has also been studied in relation to other neurological diseases. While the possibility that APOE plays a role in these diseases is of great interest, convincing associations have not yet emerged.

Current knowledge on the relationship between ApoE and Alzheimer’s disease

2018

Alzheimer ́s disease, the leading cause of dementia worldwide, is a progressive age-dependent neurological disease that mostly impacts seniors (>65). Currently an estimated 50 million people are living with dementia, this number will double every 20 years due to rising life expectancies. There is currently no cure to treat of slow down disease progression in AD. However, a lot of effort is put into research to expand the current knowledge of the pathogenesis ofand risk-factors involved in the origin and development of -AD. AD is mostly a sporadic disease, with only ~5% of patients suffering from familial AD (FAD). Amyloid beta (Aβ) plaques and neurofibrillary tau-tangles are hallmark features seen in AD patients brain. Moreover, chronic neuroinflammation, neuronal dystrophy and loss of neuronal connections are also signs of AD. Apolipoprotein E (ApoE) is a lipid transporter protein in the brain, humans can carry three ApoE genotypes, ApoE2, ApeE3 and ApoE4. ApoE4 is a well known ...

A Quarter Century of APOE and Alzheimer’s Disease: Progress to Date and the Path Forward

Neuron, 2019

Alzheimer's disease (AD) is considered a polygenic disorder. This view is clouded, however, by lingering uncertainty over how to treat the quasi ''monogenic'' role of apolipoprotein E (APOE). The APOE4 allele is not only the strongest genetic risk factor for AD, it also affects risk for cardiovascular disease, stroke, and other neurodegenerative disorders. This review, based mostly on data from human studies, ranges across a variety of APOE-related pathologies, touching on evolutionary genetics and risk mitigation by ethnicity and sex. The authors also address one of the most fundamental question pertaining to APOE4 and AD: does APOE4 increase AD risk via a loss or gain of function? The answer will be of the utmost importance in guiding future research in AD. (A) The three main APOE isoforms APOE2, APOE3, and APOE4, respectively, encoded by the Apolipoprotein E2, E3, and E4 alleles, are the result of non-synonymous polymorphisms that cause amino acid changes at position 112 and 158 of the APOE protein (Rall et al., 1982; Weisgraber et al., 1981). APOE3 is the most common variant in the general population. The APOE4 variant is a major genetic risk factor for AD, while APOE2 is protective (Farrer et al., 1997). (B) Structural models of lipid-free APOE are shown for each major isoform, based on X-ray crystallography, structure prediction, and circular dichroism spectroscopy (Zhong and Weisgraber, 2009). The N-terminal domain contains APOE's low-density lipoprotein receptor (LDLR) region at amino acid residues 134-150, while the C-terminal holds the lipid-binding region at residues 244-272. Amino acid substitutions in APOE4 promote a salt bridge between Arg61 and Glu255, which, compared to the APOE2 and APOE3 variants, drives increased domain interaction between the N-and C-terminal domains. In (A), APOE allele frequencies are obtained, with permission, from American

Apolipoprotein E and Alzheimer disease: an update on genetic and functional analyses

Journal of neuropathology and experimental neurology, 2000

Exceptional advances have been made in understanding the genetics of how common polymorphisms of the apolipoprotein E gene influence the risk and age of onset of Alzheimer disease (AD). The major genetic susceptibility locus for the common forms of AD, there are 3 common alleles, designated epsilon2, epsilon3, and epsilon4. The inheritance of each dose of APOE4 increases the risk of disease and decreases the age of onset; conversely, the APOE2 allele appears to be protective, by lowering the risk of disease and increasing the age of onset. Testing for the APOE4 allele can be a clinically useful tool in the early diagnosis of cognitively impaired patients suspected of having AD. The APOE4 allele also negatively influences functional recovery following a variety of brain insults. What remains in the study of apolipoprotein E is an explanation of how minor changes in a protein can produce such striking differences in risk and age of onset. In vitro and animal model studies strongly sug...

Apolipoprotein E isoforms in Alzheimer's disease pathology and etiology

Microscopy Research and Technique, 2000

The apolipoprotein E (apoE) ⑀4 allele increases risk of Alzheimer's disease (AD), perhaps by accelerating plaque formation, or by impairing neuron repair. Considerable evidence supports both mechanisms. AD patients with ⑀4 have more and earlier amyloid deposits than do patients without ⑀4. The same is true of non-demented control subjects. In vitro, all apoE isoforms inhibit amyloid ␤ protein (A␤) aggregation, but apoE4 less effectively than apoE3. Transgenic amyloid-producing mice expressing apoE3 or apoE4 develop less A␤ deposition than apoE knockout mice. These observations are consistent with an effect of apoE isoforms on A␤ aggregation in AD. ApoE is important for neurite maintenance since apoE knockout mice lose neurites and suffer behavioral deficits with aging or treatment with excitotoxins. ApoE4 mice show similar defects, but apoE3 mice are normal. AD patients with ⑀4 show more neuritic deficits than ⑀3 carriers. ApoE ⑀4 also worsens neurological impairment in head injury, stroke, and multiple sclerosis. Thus, apoE4 is less effective at neurite maintenance. Perhaps ⑀4 increases AD risk by both mechanisms: allowing amyloid deposition and failing to repair neurites. In either case, introducing apoE3 or apoE2 into the brain, for example by gene therapy or cell grafts, might delay AD progression.

Apolipoprotein e: essential catalyst of the Alzheimer amyloid cascade

International journal of Alzheimer's disease, 2012

The amyloid cascade hypothesis remains a robust model of AD neurodegeneration. However, amyloid deposits contain proteins besides Aβ, such as apolipoprotein E (apoE). Inheritance of the apoE4 allele is the strongest genetic risk factor for late-onset AD. However, there is no consensus on how different apoE isotypes contribute to AD pathogenesis. It has been hypothesized that apoE and apoE4 in particular is an amyloid catalyst or "pathological chaperone". Alternatively it has been posited that apoE regulates Aβ clearance, with apoE4 been worse at this function compared to apoE3. These views seem fundamentally opposed. The former would indicate that removing apoE will reduce AD pathology, while the latter suggests increasing brain ApoE levels may be beneficial. Here we consider the scientific basis of these different models of apoE function and suggest that these seemingly opposing views can be reconciled. The optimal therapeutic target may be to inhibit the interaction of a...