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R W Mahley

Publications and source records attributed to R W Mahley.

At least 19 recordsLinked to original sources
PubMed1995

Stable expression and secretion of apolipoproteins E3 and E4 in mouse neuroblastoma cells produces differential effects on neurite outgrowth.

Previously, we demonstrated in cultured dorsal root ganglion neurons that, in the presence of beta-migrating very low density lipoproteins (beta-VLDL), apolipoprotein (apo) E4, but not apoE3, suppresses neurite outgrowth. In the current studies, murine neuroblastoma cells (Neuro-2a) were stably transfected with human apoE3 or apoE4 cDNA, and the effect on neurite outgrowth was examined. The stably transfected cells secreted nanogram quantities of apoE (44-89 ng/mg of cell protein in 48 h). In the absence of lipoproteins, neurite outgrowth was similar in the apoE3- and apoE4-secreting cells. The apoE4-secreting cells, when incubated with beta-VLDL, VLDL, cerebrospinal fluid lipoproteins (d < 1.21 g/ml), or with triglyceride/phospholipid (2.7:1 (w/w)) emulsions, showed a reduction in the number of neurites/cell, a decrease in neurite branching, and an inhibition of neurite extension, whereas in the apoE3-secreting cells in the presence of a lipid source, neurite extension was increased. Uptake of beta-VLDL occurred to a similar extent in both the apoE3- and apoE4-secreting cells. With low density lipoproteins or with dimyristoylphosphatidylcholine emulsions, either alone or complexed with cholesterol, no differential effect on neurite outgrowth was observed. A slight differential effect was observed with apoE-containing high density lipoproteins. The differential effect of apoE3 and apoE4 in the presence of beta-VLDL was blocked by incubation of the cells with heparinase and chlorate, with lactoferrin, or with receptor-associated protein, all of which prevent the uptake of lipoproteins by the low density lipoprotein receptor-related protein (LRP). The data suggest that the secreted and/or cell surface-bound apoE interact with the lipoproteins and facilitate their internalization via the heparan sulfate proteoglycan-LRP pathway. The mechanism by which apoE3 and apoE4 exert differential effects on neurite outgrowth remains speculative. However, the data suggest that apoE4, which has been shown to be associated with late onset familial and sporadic Alzheimer's disease, may inhibit neuronal remodeling and contribute to the progression of the disease.

Alzheimer Disease↗
PubMed1995

Low density lipoprotein receptor-related protein mediates apolipoprotein E-dependent neurite outgrowth in a central nervous system-derived neuronal cell line.

The epsilon 4 allele of apolipoprotein E (apoE) is a major risk factor for Alzheimer disease, suggesting that apoE may directly influence neurons in the aging brain. Recent data suggest that apoE-containing lipoproteins can influence neurite outgrowth in an isoform-specific fashion. The neuronal mediators of apoE effects have not been clarified. We show here that in a central nervous system-derived neuronal cell line, apoE3 but not apoE4 increases neurite extension. The effect of apoE3 was blocked at low nanomolar concentrations by purified 39-kDa protein that regulates ligand binding to the low density lipoprotein receptor-related protein (LRP). Anti-LRP antibody also completely abolished the neurite-promoting effect of apoE3. Understanding isoform-specific cell biological processes mediated by apoE-LRP interactions in central nervous system neurons may provide insight into Alzheimer disease pathogenesis.

Apolipoprotein E3↗
PubMed1995

The inhibitory effect of apolipoprotein E4 on neurite outgrowth is associated with microtubule depolymerization.

Evidence is presented for the differential effects of two isoforms of apolipoprotein (apo) E, apoE3 and apoE4, on neurite outgrowth and on the cytoskeleton of neuronal cells (Neuro-2a) in culture. In the presence of a lipid source, apoE3 enhances and apoE4 inhibits neurite outgrowth. Immunocytochemical studies demonstrate that there is a higher concentration of apoE3 than apoE4 in both the cell bodies and neurites. Cells treated with apoE4 showed fewer microtubules and a greatly reduced ratio of polymerized to monomeric tubulin than did cells treated with apoE3. The effect of apoE4 on depolymerization of microtubules was shown by biochemical, immunocytochemical, and ultrastructural studies. The depolymerization of microtubules and the inhibition of neurite outgrowth associated with apoE4 suggest a mechanism whereby apoE4, which has been linked to the pathogenesis of Alzheimer's disease, may prevent normal neuronal remodeling from occurring later in life, when this neurodegenerative disorder develops.

Actins↗
PubMed1995

Chylomicron metabolism in normal, cholesterol-fed, and Watanabe heritable hyperlipidemic rabbits. Saturation of the sequestration step of the remnant clearance pathway.

The plasma clearance of radiolabeled chylomicrons was compared in normal, cholesterol-fed, and Watanabe heritable hyperlipidemic (WHHL) rabbits. Chylomicron clearance was rapid in normal rabbits but was significantly retarded in cholesterol-fed and WHHL rabbits. At 40 min after the injection of chylomicrons, 14-17% of the injected dose remained in the plasma of normal rabbits, whereas approximately 40-50% of the injected dose remained in the plasma of cholesterol-fed and WHHL rabbits. The differences were reflected in the reduced plasma clearance by the liver and bone marrow of the cholesterol-fed and WHHL rabbits. The hyperlipidemic rabbits expressed normal levels of low density lipoprotein (LDL) receptor-related protein/alpha 2-macroglobulin receptor in the liver. In contrast, the hepatic levels of LDL receptors were lower in hyperlipidemic rabbits; as expected, they were significantly lower in WHHL rabbits compared with normal and cholesterol-fed rabbits. Furthermore, it was demonstrated that lipoproteins accumulating in the plasma of the hyperlipidemic rabbits competed for and retarded the clearance of chylomicrons from the plasma. Competition was demonstrated by cross-circulation of normal and cholesterol-fed or normal and WHHL rabbits, in which the rapid influx of plasma containing the accumulated plasma lipoproteins from cholesterol-fed or WHHL rabbits was shown to impair the uptake of chylomicrons by the liver and bone marrow of normal rabbits. These observations were extended by infusing isolated lipoproteins into normal rabbits. The rabbit d < 1.02 g/ml (remnant) fraction and the canine cholesterol-rich high density lipoproteins (HDL) with apolipoprotein E (HDLc) inhibited chylomicron clearance, whereas human LDL and HDL from humans and rabbits did not. We conclude that the low LDL receptor activity in the cholesterol-fed and WHHL rabbits may contribute, at least in part, to the impaired clearance by decreasing remnant uptake and causing the accumulation of chylomicron and/or very low density lipoprotein remnants. The accumulated remnant lipoproteins then compete for and saturate the mechanism responsible for the initial rapid clearance of chylomicrons from the plasma. We speculate that saturation of the initial rapid clearance may occur at the sequestration step, which involves the binding of remnants to heparan sulfate proteoglycans in the space of Disse.

Animals↗
PubMed1995

Macrophage-specific expression of human apolipoprotein E reduces atherosclerosis in hypercholesterolemic apolipoprotein E-null mice.

apoE deficiency causes hyperlipidemia and premature atherosclerosis. To determine if macrophage-specific expression of apoE would decrease the extent of atherosclerosis, we expressed human apoE in macrophages of apoE-null mice (apoE-/-) and assessed the effect on lipid accumulation in cells of the arterial wall. Macrophage-specific expression of human apoE in normal mice was obtained by use of the visna virus LTR. These animals were bred with apoE-/- mice to produce animals hemizygous for expression of human apoE in macrophages in the absence of murine apoE (apoE-/-,hTgE+/0). Low levels of human apoE mRNA were present in liver and spleen and high levels in lung and peritoneal macrophages. Human apoE was secreted by peritoneal macrophages and was detected in Kupffer cells of the liver. Human apoE in the plasma of apoE-/-,hTgE+/0 mice (n = 30) was inversely correlated (P < 0.005) with the plasma cholesterol concentration. After 15 wk on a normal chow diet, atherosclerosis was assessed in apoE-/-,hTgE+/0 animals and in apoE-/-,hTgE0/0 littermates matched for plasma cholesterol level (approximately 450 mg/dl) and lipoprotein profile. There was significantly less atherosclerosis in both the aortic sinus and in the proximal aorta (P < 0.0001) in the animals expressing the human apoE transgene. In apo-E-/-,hTgE+/0 animals, which had detectable atherosclerotic lesions, human apoE was detected in the secretory apparatus of macrophage-derived foam cells in the arterial wall. The data demonstrate that expression of apoE by macrophages is antiatherogenic even in the presence of high levels of atherogenic lipoproteins. The data suggest that apoE prevents atherosclerosis by promoting cholesterol efflux from cells of the arterial wall.

Animals↗
PubMed1995

Intravenous heparinase inhibits remnant lipoprotein clearance from the plasma and uptake by the liver: in vivo role of heparan sulfate proteoglycans.

Heparan sulfate proteoglycans (HSPG) are involved in the binding and uptake of apolipoprotein (apo) E-enriched remnant lipoproteins by cultured cells in vitro. To define the role of hepatic HSPG in remnant lipoprotein clearance in vivo, heparinase (30 units) was infused intravenously into mice to hydrolyze the liver HSPG and determine the effect of HSPG hydrolysis on remnant clearance by the liver. Liver HSPG were prelabeled by peritoneal injection of [35S]Na2SO4. Injection of heparinase decreased the amount of 35S-labeled liver HSPG by approximately 20-40% within 10-15 min. Heparinase infusion significantly inhibited the clearance of chylomicrons, chylomicron remnants, chylomicron remnants + apoE, rabbit beta-very low density lipoproteins (beta-VLDL), and beta-VLDL + apoE. Compared with saline injection in control mice, heparinase injection retarded the plasma clearance of the remnants by 1.5- to 2-fold and decreased liver uptake by 1.3- to 1.6-fold. Confocal fluorescence microscopy of thick slices of liver from mice injected with 1,1'-dioctadecyl-3,3,3', 3'-tetramethylindocarbocyanine-labeled beta-VLDL + apoE revealed markedly less intense fluorescence from hepatocytes in heparinase-treated animals compared with those in saline-treated control animals. Intravenous heparinase infusion did not inhibit the clearance of mouse low density lipoproteins (LDL), a ligand for the LDL receptor, and did not affect the clearance of alpha 2-macroglobulin, a ligand for the LDL receptor-related protein. The results suggest an important role of the liver HSPG in remnant clearance in vivo.

Animals↗
PubMed1995

Turkish Heart Study: lipids, lipoproteins, and apolipoproteins.

We examined the plasma lipids, lipoproteins, and selected apolipoproteins in approximately 9,000 men and women from six different regions of Turkey with markedly different diets, ranging from an Aegean coast diet high in olive oil (plasma cholesteryl ester fatty acids enriched in monounsaturated fatty acids) to an inland Anatolian diet high in meat and dairy products (plasma cholesteryl esters enriched in saturated fatty acids). The rural population consuming an olive oil-rich diet had the lowest plasma cholesterol levels (men, 149 mg/dl; women, 150 mg/dl). The urban populations of Istanbul and Adana had higher plasma cholesterol levels (men, 202 and 184 mg/dl, respectively; women, 181 and 190 mg/dl, respectively). Affluent men had the highest cholesterol levels (207 mg/dl). The low density lipoprotein (LDL) cholesterol levels tended to parallel the total cholesterol levels (highest for Istanbul men at 136 mg/dl and lowest for Aegean coast men and women at approximately 100 mg/dl). Strikingly, the Turkish people were found to have very low levels of high density lipoprotein (HDL) cholesterol (HDL-C) (mean values for all six regions: men, 34-38 mg/dl; women, 37-45 mg/dl) and total cholesterol/HDL-C ratios that were high (mean values for all six regions: men, 4.5-5.5; women, 3.9-5.0). The low HDL-C levels appear to be caused, at least in part, by a genetic factor. Triglyceride levels also tended to be high in Turkish men (approximately 120-150 mg/dl) and women (approximately 90-110 mg/dl). Thus, even though the total plasma cholesterol levels are not excessively elevated in comparison to those in other populations, the presence of low HDL-C or low HDL-C coupled with mildly elevated triglyceride levels may represent a significant risk factor for heart disease in the Turkish population. Affluence and higher education were associated with higher cholesterol levels. Lack of physical activity, smoking, and alcohol consumption also tended to be associated with a detrimental lipid profile. Lipoprotein[a] levels were identical among the regions surveyed (mean: 11-15 mg/dl) and displayed the typical distribution with an increased number of individuals with low levels. The 90th percentile value for lipoprotein[a] was about 30 mg/dl for both men and women. Smoking, a major risk factor for heart disease, was very prevalent in the Turkish population, especially in men (50-70% smokers) and women in urban areas (30-40% smokers). Hypertension, defined as a systolic pressure > 140 or a diastolic pressure of > 90 occurred in approximately 17% and 26% of the men and women surveyed, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1994

Human apolipoprotein E. Role of arginine 61 in mediating the lipoprotein preferences of the E3 and E4 isoforms.

Human apolipoprotein (apo) E4 (arginine at residue 112) preferentially associates with very low density lipoproteins (VLDL), and apoE3 (cysteine at 112) associates with high density lipoproteins. It has been postulated that the amino-terminal domain, which contains residue 112, influences the lipoprotein preference by interacting with the carboxyl-terminal domain, which contains the lipid-binding region. To delineate the region in the carboxyl-terminal domain mediating lipoprotein binding and involved in isoform preference, we produced truncated apoE3 and apoE4 variants (terminating at residues 251, 260, 266, or 272) in Escherichia coli and assessed them for lipoprotein association. This analysis suggested that residues 260-272 contain important determinants for complete lipoprotein association and isoform preferences. To determine whether positive charge at residue 112 was an absolute requirement for the apoE4 VLDL preference, we compared the distributions of rabbit apoE (equivalent to apoE3, with cysteine at a position corresponding to 112), canine apoE (arginine at the corresponding site), and cysteamine-treated rabbit apoE (cysteine converted to a positively charged residue). Surprisingly, all distributed like human apoE3, suggesting that positive charge at a position corresponding to 112 was not directly responsible for the isoform preference and that other residues in the amino-terminal domain were involved. To determine which residues were involved, the structure of the apoE4 22-kDa fragment (the amino-terminal two-thirds of the molecule) was determined to 2.5 A by x-ray crystallography. Compared with the known four-helix bundle structure of apoE3, the only significant differences in the apoE4 structure were that glutamic acid 109 formed a salt bridge with arginine 112 and that the arginine 61 side chain was displaced to a new position. Site-directed mutagenesis of glutamic acid 109 in apoE3 and arginine 61 in apoE4 demonstrated that the position of the arginine 61 side chain in apoE4 was critical in determining apoE4 lipoprotein distribution, suggesting that arginine 61 interacted with the carboxyl-terminal domain to direct binding to VLDL.

Animals↗
PubMed1994

Overexpression of hepatic lipase in transgenic rabbits leads to a marked reduction of plasma high density lipoproteins and intermediate density lipoproteins.

To elucidate the precise metabolic roles of hepatic lipase (HL), a human HL cDNA in a liver-specific expression vector was used to generate transgenic lines in the rabbit, an animal that normally expresses low levels of this enzyme. HL was detected in the plasma of all rabbits only after the administration of heparin; HL activity in transgenic rabbits was found at levels up to 80-fold greater than that in nontransgenic littermates. This increase in enzyme activity was associated with as much as a 5-fold decrease in total plasma cholesterol levels. Expression of the transgene resulted in a dramatic reduction in the level of large high density lipoproteins (HDL1 and HDL2) as well as dense HDL3. A reduction in the quantity of intermediate density lipoproteins (IDL) was also observed. These results demonstrate that HL functions in the metabolism of HDL and IDL, thereby playing a key role in plasma cholesterol homeostasis.

Animals↗
PubMed1994

Salt bridge relay triggers defective LDL receptor binding by a mutant apolipoprotein.

BACKGROUND: Apolipoprotein-E (apo-E), a 34kDa blood plasma protein, plays a key role in directing cholesterol transport via its interaction with the low density lipoprotein (LDL) receptor. The amino-terminal domain of apo-E forms an unusually elongated four-helix bundle arranged such that key basic residues involved in LDL receptor binding form a cluster at the end of one of the helices. A common apo-E variant, apo-E2, corresponding to the single-site substitution Arg158-->Cys, displays minimal LDL receptor binding and is associated with significant changes in plasma cholesterol levels and increased risk of coronary heart disease. Surprisingly, the site of mutation in this variant is physically well removed (> 12A) from the cluster of LDL receptor binding residues. RESULTS: We now report the refined crystal structure of the amino-terminal domain of apo-E2, at a nominal resolution of 3.0A. This structure reveals significant conformational changes relative to the wild-type protein that may account for reduced LDL receptor binding. Removal of the Arg158 side chain directly disrupts a pair of salt bridges, causing a compensatory reorganization of salt bridge partners that dramatically alters the charge surface presented by apo-E to its receptor. CONCLUSIONS: It is proposed that the observed reorganization of surface salt bridges is responsible for the decreased receptor binding by apo-E2. This reorganization, essentially functioning as a mutationally induced electrostatic switch to turn off receptor binding, represents a novel mechanism for the propagation of conformational changes over significant distances.

Apolipoprotein E2↗
PubMed1994

Differential effects of apolipoproteins E3 and E4 on neuronal growth in vitro.

Apolipoprotein E4 (apoE4), one of the three common isoforms of apoE, has been implicated in Alzheimer's disease. The effects of apoE on neuronal growth were determined in cultures of dorsal root ganglion neurons. In the presence of beta-migrating very low density lipoproteins (beta-VLDL), apoE3 increased neurite outgrowth, whereas apoE4 decreased outgrowth. The effects of apoE3 or apoE4 in the presence of beta-VLDL were prevented by incubation with a monoclonal antibody to apoE or by reductive methylation of apoE, both of which block the ability of apoE to interact with lipoprotein receptors. The data suggest that receptor-mediated binding or internalization (or both) of apoE-enriched beta-VLDL leads to isoform-specific differences in interactions with cellular proteins that affect neurite outgrowth.

Animals↗
PubMed1994

Variable heparan sulfate proteoglycan binding of apolipoprotein E variants may modulate the expression of type III hyperlipoproteinemia.

The initial step in the clearance of apolipoprotein (apo) E-enriched remnant lipoproteins from the plasma appears to be sequestration within the liver mediated by their binding to heparan sulfate proteoglycans (HSPG). The surface-bound remnants are believed to be internalized by their interaction with the low density lipoprotein (LDL) receptor-related protein or by the LDL receptor. Cholesterol-induced rabbit beta-very low density lipoproteins (beta-VLDL) enriched in human apoE3 display 4-5-fold enhanced binding to cultured cells. The present study attempts to determine whether recessive versus dominant type III hyperlipoproteinemia might be explained, at least in part, by a variable interaction of the mutant forms of apoE with the HSPG and impaired uptake. The beta-VLDL+apoE2(Arg158-->Cys), which is associated with recessive type III hyperlipoproteinemia, bound more poorly than beta-VLDL+apoE3 but still possessed significant enhanced binding (approximately 2-2.5-fold compared with beta-VLDL without added apoE) to HepG2 and McA-RH7777 cells. In comparison, beta-VLDL+apoE(Arg142-->Cys), beta-VLDL+apoE(Arg145-->Cys), and beta-VLDL+apoE-Leiden, which are associated with dominant type III hyperlipoproteinemia, bound more poorly. This same hierarchy of binding and uptake was determined by [14C]oleate incorporation into cholesteryl esters in LDL receptor-negative cells and by secretion of apoE3 and the variant apoE forms from McA-RH7777 cells. Furthermore, the enhanced binding of the apoE-enriched beta-VLDL was almost totally inhibited by heparinase treatment of the cells, and the basal binding activity was inhibited by 80-90% following addition of an LDL receptor antibody capable of blocking receptor-ligand interaction. The beta-VLDL enriched in apoE or apoE-dimyristoylphosphatidylcholine complexes bound to isolated HSPG from McA-RH7777 cells or the rat liver to a very similar degree. Likewise, the binding of beta-VLDL plus the various forms of apoE to the LDL receptor-related protein on ligand blots paralleled the results of other studies. In conclusion, all of the type III hyperlipoproteinemic apoE variants are defective in displaying enhanced binding to HSPG and in the cellular uptake initiated by HSPG. However, apoE2(Arg158-->Cys) displayed more activity than the variants associated with the dominant forms of type III hyperlipoproteinemia. The hierarchy of binding and uptake was as follows: apoE3 > apoE2(Arg158-->Cys) > apoE(Arg145-->Cys) > apoE(Arg142-->Cys) approximately apoE-Leiden (the latter two usually displaying very little, if any, enhanced binding and uptake). Thus, a correlation exists between the mode of expression of type III hyperlipoproteinemia and the binding and uptake of the specific apoE mutation.

Animals↗
PubMed1994

Enhanced binding and uptake of remnant lipoproteins by hepatic lipase-secreting hepatoma cells in culture.

Rat hepatoma McA-RH7777 cells transfected with a human hepatic lipase (HL) cDNA synthesized and secreted 50-80 ng of human HL/mg of cell protein at 4 h, approximately 50% of which was bound to cell-surface heparan sulfate proteoglycans (HSPG). The newly synthesized HL possessed enzymatic activity. When rabbit beta-very low density lipoproteins (beta-VLDL) and canine chylomicrons or chylomicron remnants were incubated with HL-secreting cells, remnant binding and uptake were enhanced 3-fold compared with nontransfected cells. Furthermore, fluorescence microscopy showed enhanced uptake of 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine-labeled beta-VLDL by the HL-transfected cells. When 125I-beta-VLDL were added to conditioned medium from HL-secreting cells, the HL in the media enhanced the binding and uptake of the remnant lipoproteins by nontransfected cells about 3-fold. Likewise, surface-bound HL (without HL in the medium) also was able to mediate the enhanced binding of the remnants. This HL-enhanced binding was shown to be mediated by an interaction with cell-surface HSPG. Heparinase treatment to remove cell-surface HSPG or chlorate treatment to prevent HSPG sulfation of the HL-secreting cells abolished all the HL-mediated enhanced binding and uptake. Furthermore, heparinase pretreatment of nontransfected cells prevented the enhanced binding and uptake of beta-VLDL incubated with conditioned medium from HL-secreting cells. As binding was not enhanced in the absence of HSPG, an HL-HSPG initial interaction appears essential. Addition of apolipoprotein (apo) E to the beta-VLDL did not facilitate HL-mediated binding and uptake; in fact, beta-VLDL from apoE-null mice demonstrated a similar degree of enhanced binding as did rabbit beta-VLDL with or without added apoE. On the other hand, beta-VLDL from transgenic mice overexpressing binding-defective apoE(Arg142-->Cys) did not display any enhanced binding and uptake by the HL-secreting cells, and it appears that the apoE(Arg142-->Cys) actually inhibited the HL-mediated interaction. This mutant form of apoE is associated with a dominant mode of expression of type III hyperlipoproteinemia in contrast to the more commonly occurring recessive disorder. Impaired HL interaction with the apoE(Arg142-->Cys) beta-VLDL may contribute to remnant lipoprotein accumulation in the plasma of patients with this mutant form of apoE. Thus, HL contributes to the enhanced cell association of specific types of remnant lipoproteins by initiating their binding to cell-surface HSPG.

Animals↗
PubMed1994

Susceptibility to diet-induced atherosclerosis in transgenic mice expressing a dysfunctional human apolipoprotein E(Arg 112,Cys142).

Transgenic mice expressing apolipoprotein (apo) E(Cys 142), a human defective variant of apo E, have elevated levels of plasma cholesterol, triglycerides, and very-low-density lipoproteins (VLDL); beta-VLDL, the biochemical hallmark of the human genetic disease type III hyperlipoproteinemia (HLP), is also present in these mice. This study was designed to determine whether these type III HLP mice have an increased susceptibility to spontaneous or diet-induced atherosclerosis. Three 4-month-old male transgenic mice and three male nontransgenic littermates were assessed for the presence of atherosclerotic lesions in the proximal aorta. No lipid-stained microscopic lesions were visible in the aortas of nontransgenic mice, whereas minimal lesions were observed on the aortic valve stumps of transgenic mice. To magnify the effect of the mutant apo E on the susceptibility of the transgenic animals to atherosclerosis, 8 transgenic and 8 nontransgenic mice were fed a synthetic diet containing 1% cholesterol, 16% fat, and 0.5% cholic acid for 3 months. The diet induced an increase in plasma cholesterol level in both transgenic and nontransgenic mice. However, the increase in plasma cholesterol level in the transgenic mice was all in the VLDL fraction, whereas in nontransgenic mice it was due to increases in both VLDL and high-density lipoprotein (HDL) fractions. Plasma triglyceride levels fell in both groups of mice. After 3 months on the diet, there were compositional changes in the VLDL of both groups, characterized mainly by higher cholesteryl ester content, that resulted in beta-migration on agarose gel electrophoresis. Despite similar VLDL lipid compositions, the extent of atherosclerosis differed markedly in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Lactoferrin binding to heparan sulfate proteoglycans and the LDL receptor-related protein. Further evidence supporting the importance of direct binding of remnant lipoproteins to HSPG.

Bovine lactoferrin inhibits the clearance of remnant lipoproteins from the plasma and competes with the cell-surface binding of apolipoprotein (apo) E-enriched remnants. We established that lactoferrin inhibits remnant binding and uptake by interacting with both heparan sulfate proteoglycans (HSPG) and the low-density lipoprotein receptor-related protein (LRP). The binding of 125I-lactoferrin was inhibited 45% to 60% in HepG2 hepatocytes and wild-type Chinese hamster ovary (CHO) cells treated with heparinase to remove HSPG. In mutant CHO cells (pgsD-677) lacking HSPG, the level of 125I-lactoferrin binding was approximately 50% that seen with wild-type CHO cells; thus, about one half of lactoferrin binding appears to be mediated through cell-surface HSPG. A significant fraction of the residual binding of the lactoferrin appears to be mediated through the LRP. The 39-kd protein known to bind to the LRP and to block ligand interaction inhibited 125I-lactoferrin degradation in wild-type CHO cells by 60% to 65%. The addition of the 39-kd protein plus heparinase treatment reduced the binding by 85% to 90% (this combination blocks direct interaction with both the LRP and HSPG). However, it was also shown that the 39-kd protein bound to HSPG and the LRP. Heparinase treatment of wild-type CHO cells decreased the binding of the 125I-39-kd protein by approximately 40%, and the mutant CHO cells lacking HSPG bound half as much 125I-39-kd protein as wild-type CHO cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Apolipoprotein E associates with beta amyloid peptide of Alzheimer's disease to form novel monofibrils. Isoform apoE4 associates more efficiently than apoE3.

Late-onset and sporadic Alzheimer's disease are associated with the apolipoprotein E (apoE) type 4 allele expressing the protein isoform apoE4. Apolipoprotein E binds avidly to beta amyloid (A beta) peptide, a major component of senile plaque of Alzheimer's disease, in an isoform-specific manner. The apoE4 isoform binds to A beta peptide more rapidly than apoE3. We observed that soluble SDS-stable complexes of apoE3 or apoE4, formed by coincubation with A beta peptide, precipitated after several days of incubation at 37 degrees C with apoE4 complexes precipitating more rapidly than apoE3 complexes. A beta(1-28) and A beta(1-40) peptides were incubated in the presence or absence of apoE3, apoE4, or bovine serum albumin for 4 d at 37 degrees C (pH 7.3). Negative stain electron microscopy revealed that the A beta peptide alone self-assembled into twisted ribbons containing two or three strands but occasionally into multistranded sheets. The apoE/A beta coincubates yielded monofibrils 7 nm in diameter. ApoE4/A beta coincubates yielded a denser matrix of monofibrils than apoE3/A beta coincubates. Unlike purely monofibrillar apoE4/A beta coincubates, apoE3/A beta coincubates also contained double- and triple-stranded structures. Both apoE isoforms were shown by immunogold labeling to be uniformly distributed along the A beta peptide monofibrils. Monofibrils appeared earlier in apoE4/A beta than in apoE3/A beta in time-course experiments. Thus apoE3 and apoE4 each interact with beta amyloid peptide to form novel monofibrillar structures, apoE4 more avidly, a finding consistent with the biochemical and genetic association between apoE4 and Alzheimer's disease.

Alzheimer Disease↗