Apolipoprotein E isoforms

SADP or sulfo-SADP also have been used to study the phenylalanine-methionine-arginine-phenylalanine-amide-activated sodium channel (Coscoy et al., 1998), various apolipoprotein E isoforms (Mann et al., 1995), the high-affinity phenylalkylamine Ca2+ antagonist binding protein from guinea pig (Moebius et al., 1994), the interaction of non-histone proteins with nucleosome core particles (Reeves and Nissen, 1993), and the interactions among cytochromes P-450 in the endoplasmic reticulum (Alston et al., 1991). See Chapter 28 for methods of using photoreactive heterobifunctional crosslinkers to study protein interactions. 

Mann, W.A., Meyer, N., Weber, W., Meyer, S., Greten, H., and Beisiegel, U. (1995) Apolipoprotein E isoforms and rare mutations parallel reduction in binding to cells and to heparin reflects severity of associated type III hyperlipoproteinemia./. Lipid Res. 36, 517. 

Cassel, D.L., et al., "The Conformation of Apolipoprotein E Isoforms in Phospholipid Complexes and Their Interaction with Human Hep G2 Cells," Atherosclerosis, 52, 203-218 (1984). 

Ji, Y., Gong, Y., Gan, W., Beach, T., Holtzman, D.M., Wisniewski, T. (2003) Apolipoprotein E isoform-specific regulation of dendritic spine morphology in apolipoprotein E mice and Alzheimer s disease patients. Neuroscience, 122, 305-315. 

Holtzman DM, Bales KR, Tenkova T, Pagan AM, Parsadanian M, Sar torius LJ, Mackey B, Olney J, McKeel D, Wozniak D, Paul SM (2000) Apolipoprotein E isoform-dependent amyloid deposition and neuritic degeneration in a mouse model of Alzheimer s disease. Proc Natl Acad Sci USA 97 2892-2897. 

Petrlova J, Hong HS, Bricarello DA, Harishchandra G, Lorigan GA, Jin LW et al (2011) A differential association of Apolipoprotein E isoforms with the amyloid-p oligomer in solution. Proteins 79 402-416... 

Meigs JB, Ordovas JM, Cupples LA, et al., Apolipoprotein E isoform polymorphisms are not associated with insulin resistance the Framingham Offspring Study, Diabetes Care, May 2000 23(5) 669-674. 

Apolipoprotein E (ApoE) A protein involved in cholesterol transport that has three major isoforms, one of which, ApoE4, significantly increases the risk of developing Alzheimer s disease. 

Gong, J.-S.,Kobayashi, M.,Hayashi,H. etal. Apolipoprotein E (apoE) isoform-dependent lipid release from astrocytes prepared from human apoE3 and apoE4 knock-in mice. /. Biol. Chem. 277 29919-29926, 2002. 

K15. Klausen, I. C., Berg Schmidt, E., Lervang, H. H., Gerdes, L. U., Ditzel, J., and Faergeman, O., Normal lipoprotein(a) concentrations and apolipoprotein(a) isoforms in patients with insulin-dependent diabetes mellitus. Eur. J. Clin. Invest. 22, 538-541 (1992). 

L5. Lackner, C., Boerwinkle, E., Leffert, C. C., Rahming, T., and Hobbs, H. H., Molecular basis of apolipoprotein(a) isoform heterogeneity as revealed by pulse-field electrophoresis. J. Clin. Invest. 87, 2153-2161 (1991). 

Production of LDL from VLDL in the plasma With these modifications, the VLDL is converted in the plasma to LDL. An intermediate-sized particle, the intermediate-density lipoprotein (IDL) or VLDL remnant, is observed during this transition. IDLs can also be taken up by cells through receptor-mediated endocytosis that uses apo E as the ligand. [Note Apolipoprotein E is normally present in three isoforms, E2, E3, and E4. Apo E2 binds poorly to receptors, and patients who are homozygotic for apo E2 are deficient in the clearance of chylomicron remants and IDLs. The individuals have familial type III hyperlipoproteinemia (familial dysbetalipoproteinemia, or broad beta disease), with hypercholesterolemia and premature atherosclerosis. Not yet understood is the fact that the E4 isoform confers increased susceptibility to late-onset Alzheimer disease.]... 

Strittmatter WJ, Weisgraber KH, Huang DY, et al. Binding of human apolipoprotein E to synthetic amyloid beta peptide Isoform-specific effects and implications for late-onset Alzheimer disease. Proc Natl Acad Sci USA 1993 90 (17) 8098-8102. 

E Contiero, R Ferrari, GM Vaselli, M Folin. Apolipoprotein A1 isoforms in serum determined by isoelectric focusing and immunoblotting. Electrophoresis 18 122-126, 1997. 

An apolipoprotein E variant is the only unequivocal genetic risk factor for late-onset Alzheimer s disease in a variety of ethnic groups. Caucasians and Japanese with the apo-E-s4 isoform have between 10 and 30 times the risk of developing Alzheimer s by 75 years of age. While the exact mechanism is unknown, evidence suggests an interaction with amyloid. Alzheimer s disease is characterised by plaques consisting of the peptide beta-amyloid. Apolipoprotein E enhances proteolytic breakdown of this peptide. However, the isoform apo-E-e4 is much less effective, which might result in an increased vulnerability to Alzheimer s in individuals with that gene variation. 

Chylomicron remnants and very low density lipoprotein (VLDL) remnants are rapidly removed from the circulation by receptor-mediated endocytosis. ApoE, the major apolipoprotein of the chylomicron in the brain, binds to a specific receptor and is essential for the normal catabolism of triglyceride-rich lipoprotein constituents. Defects in apolipoprotein E result in familial dysbetalipoproteinemia, or type III hyperlipoproteinemia (HLP III), in which increased plasma cholesterol and triglycerides are the consequence of impaired clearance of chylomicron and VLDL remnants (Mahley et al., 1999). In the brain, lipidated apoE binds aggregated in a isoform-speciflc manner, apoE4 being much more effective than the other forms,... 

Michikawa M, Fan QW, Isobe I, Yanagisawa K (2000) Apolipoprotein E exhibits isoform-specific promotion of lipid efflux from astrocytes and neurons in culture. J Neurochem 74 1008-1016... 

Stratman NC, Castle CK, Taylor BM, Epps DE, Melchior GW, Carter DB (2005) Isoform-specific interactions of human apolipoprotein E to an intermediate conformation of human Alzheimer amyloid-beta peptide. Chem Phys Lipids 137 52-61... 

Fig. 3. Diagram of the isoelectric focusing patterns of the six common apolipoprotein E phenotypes. E, Protein e, apoE allele. Top Focusing position of the three common apoE isoforms, designated E2, E3, and E4, as they appear in the three homozygous and three heterozygous phenotypes. Bottom Effect of posttranslational sialylation on the isoform patterns. Sialylated derivatives are indicated as E,.

Fig. 8. Ability of apolipoprotein E-dimyristoylphosphatidylcholine (DMPC) complexes of the three major isoforms to compete with human I-labeled LDL for binding to normal human fibroblasts. Cells incubated in medium containing 10% human lipoprotein-deficient serum received 1 ml of the same medium with 2 of 1-labeled...

The function of apoE in lipoprotein metabolism is reviewed in the sixth chapter by Karl Weisgraber. The three-dimensional structure of a 22-kDa fragment of human apoE (34.2 kDa) has been solved by X-ray crystallography the relation of this structure to the role of apoE in lipoprotein metabolism is discussed in detail, together with a critical and extensive examination of the chemistry and biology of this apolipoprotein which plays such a central role in lipoprotein metabolism. Apolipoprotein E has three major isoforms in the human population which affect lipoprotein metabolism differently, resulting in different levels of the plasma lipoproteins. The impact of structure on function and how plasma lipid concentrations are affected by the different apoE isoforms are the themes of this important chapter. 

Apolipoprotein E, which has a direct influence on the development of cardiovascular and neurodegenerative diseases, exhibits no change in immunoreactivity upon freezedrying provided a bicarbonate buffer is used as the matrix [23]. As can be seen from Fig. 2.8, the immunological behaviour of various dilutions of reconstituted freeze-dried recombinant apo E, (one of the isoforms of apolipoprotein E) in relation to the frozen recombinant apo E the human VLDL (very low density lipoprotein) purified apo E, and fresh human serum samples, as determined using turbidimetric and ELISA methods, is similar. The stability of freeze-dried recombinant apo E, is acceptable, without any major alterations of its immunological reactivity. 

Apolipoprotein E (apoE) is a genetic risk factor for AD. There are four distinct isoforms of apoE, which is involved in transport of cholesterol and lipids in blood. Although all the isoforms function equally well, individuals who are homozygous for the apoE 4 allele ( 4/4 ) have a much higher lifetime risk of AD than do those homozygous for the apoE 2 allele ( 2/2 ). The mechanism by which the apoE 4 protein increases the risk of AD is not known. 

The etiology of the majority of the cases still remains unknown, although it appears to be depending on multiple factors. Familial AD, although rare, can be inherited. The patients in this group have an earlier onset (age 30 to 60) than the common form of AD. The one risk factor for the more common form is a protein involved in cholesterol transport known as apolipoprotein E (apoE). The allele frequency of an isoform of apoE (apoE4) was found to be 40% in either familial or common form AD compared to 15% in patients without AD [11]. 

Apolipoprotein E (APOE) is the major lipoprotein within the CNS it is synthesized by astrocytes (Pitas et al., 1987) and by neurons under physiological and pathological conditions (Harris et al., 2004). APOE is a polymorphic 299-amino acid protein. The gene is located on chromosome 19 and has three possible alleles, s2, s3, and s4. APOE-zi is the most common (frequency in population 60-70%), followed by APOE-zA with a frequency of 15-20%, mAAPOE-z2 with a frequency of 5-10%. The three isoforms differ by single amino acid substitutions (cysteine to arginine) at two positions. APOE-e4 lacks both cysteine residues (Cys" and Cys ), while APOE-e3 and APOE-e2 contain 1 and 2 cysteine residues, respectively (Mahley and Huang, 2006). 

ApoD is found in association with LCAT and with apoA-I in the HDL fraction. Albers et al. used a specific antibody to apoD to remove all apoD by immunoadsorption chromatography from plasma about 64% of LCAT activity and 11% of apoA-I were also removed from plasma (A14). Purified apoD has an apparent Mr of 32,500, and appears as three isoforms on isoelectric focusing (pi 5.20, 5.08, and 5.00) (A14). An HDL apolipoprotein, Mr 35,000, has been thought to be apoD, and to be a cholesteryl ester transfer protein (i.e., to transfer newly synthesized esterified cholesterol from HDL to LDL) (C8). Cholesteryl ester transfer activity in plasma was removed by polyclonal immunoglobulin to apoD (C8, F10). However, Morton and Zilversmit (M41) were able to separate apoD and lipid transfer protein (i.e., the cholesteryl ester transfer protein, or lipid transfer protein I) by chromatography, and they showed that the removal of apoD from plasma by precipitation with specific antisera did not remove any lipid transfer activity. Albers et al. (A14) also showed that immunoadsorption with antibody specific for apoD removed all the apoD from plasma without removing any cholesteryl ester transfer activity. 

The isoforms of apoE were first clearly demonstrated by Utermann et al., who showed on one-dimensional isoelectric focusing of VLDL apolipoproteins that there were four major isoforms of apoE (U3— U5). These were named, from acidic to basic, apoE-1, apoE-2, apoE-3, and apoE-4. Patients with Type I1 hyperlipoproteinemia (dysbetalipoproteinemia) were, in virtually all cases, deficient in apoE-3 (U3-U6). Only 27% of subjects had apoeE-4, but this band was not associated with any particular abnormality. However, individuals deficient in apoE-3 were also deficient in apoE-4 (U6). Utermann suggested that the genetic pattern of apoE isoforms could be explained if there was a single genetic locus for apoE which could produce three apoE phenotypes, i.e., apoE-N (normal), apoE-D (deficient, associated particularly with the Type III disorder), and apoE-ND (U4, U6). 

Apo-E An apolipoprotein principally associated with VLDL and chylomicrons responsible for the receptor-mediated clearance of IDL and chylomicron remnants. It is a ligand for most members of the LDL receptor superfamily. The apo-E4 isoform is associated with increased risk of Azheimer s disease. 

---