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Papers by John Parks

Research paper thumbnail of Minimal Lipidation of Pre- HDL by ABCA1 Results in Reduced Ability to Interact with ABCA1

Objectives-The aim of this study was to determine the role of ATP binding cassette transporter A1... more Objectives-The aim of this study was to determine the role of ATP binding cassette transporter A1 (ABCA1) on generation of different-sized nascent HDLs. Methods and Results-HEK293 cells stably-transfected with ABCA1 (HEK293-ABCA1) or non-transfected (control) cells were incubated with lipid free 125 I-apoA-I for 24 hours. Incubation of apoA-I with HEK293-ABCA1 cells, but not control cells, led to the formation of heterogeneous-sized, pre-␤ migrating nascent HDL subpopulations (pre-␤1 to -4) that varied in size (7.1 to 15.7 nm), lipid, and apoA-I content. Kinetic studies suggested that all subpopulations were formed simultaneously, with no evidence for a precursor-product relationship between smaller and larger-sized particles. When isolated nascent pre-␤ HDLs (pre-␤1 to -4) were added back to HEK293-ABCA1 cells, their ability to bind to ABCA1 and efflux lipid was severely compromised. Heat-denaturation of pre-␤1 HDL resulted in partial recovery of ABCA1 binding, suggesting that initial interaction of apoA-I with ABCA1 results in a constrained conformation of apoA-I that decreases subsequent binding. Conclusions-Interaction of apoA-I with ABCA1 results in the simultaneous generation of pre-␤ HDLs of discrete size and chemical composition. These nascent particles are poor substrates for subsequent lipidation by ABCA1 and presumably require additional non-ABCA1-mediated lipidation for further maturation. (Arterioscler Thromb Vasc Biol.

Research paper thumbnail of Determination of the tissue sites responsible for the catabolism of large high density lipoprotein in the African green monkey

The Journal of Lipid Research, Mar 1, 2000

In vivo multicompartmental modeling of the turnover of HDL subfractions has suggested that HDL co... more In vivo multicompartmental modeling of the turnover of HDL subfractions has suggested that HDL containing four molecules of apoA-I per particle and no other apolipoproteins (large LpA-I) are terminal particles in plasma. We hypothesized that these terminal particles were the end product of HDL metabolism and, as such, would be cleared preferentially by the liver. Thus, the purpose of this study was to determine: 1 ) the tissue sites of catabolism of large LpA-I in African green monkeys, and 2 ) whether saturated versus n-6 polyunsaturated dietary fat affected tissue accumulation. Large LpA-I were isolated, without ultracentrifugation, by size exclusion and immunoaffinity chromatography and radiolabeled with either the residualizing compound, 125 I-labeled tyramine cellobiose (TC), or with 131 I. After injection into recipient animals, the plasma die-away of the radiolabels was followed for 12 or 24 h, after which the animals were killed and tissues were collected for determining radiolabel sites of catabolism. The plasma die-away of the 125 I-labeled TC-LpA-I and 131 I-labeled LpA-I doses was similar suggesting that the TC radiolabeling did not modify the metabolism of the large LpA-I dose. The liver, adrenal, kidney, and spleen had the greatest accumulation of large LpA-I degradation products on a per gram tissue basis. On a whole organ basis, the liver was the major site of large LpA-I degradation in both the 12-h (15.4 ؎ 0.3% of injected dose) and 24-h (9.1 ؎ 0.6% of injected dose) catabolic studies. The kidney, compared to the liver, had less uptake of large LpA-I radioactivity in either study (1.3 ؎ 0.4% and 1.2 ؎ 0.3% of injected dose). There was no apparent influence of dietary fat type on the tissue accumulation of large LpA-I. We conclude that the liver is the primary site of catabolism of large LpA-I in the African green monkeyDetermination of the tissue sites responsible for the catabolism of large high density lipoprotein in the African green monkey. J. Lipid Res. 2000. 41: 384-394.

Research paper thumbnail of Apolipoprotein M expression increases the size of nascent preβ HDL formed by ATP binding cassette transporter A1

Journal of Lipid Research, Mar 1, 2010

This article is available online at http://www.jlr.org

Research paper thumbnail of Both Hepatic and Extrahepatic ABCA1 Have Discrete and Essential Functions in the Maintenance of Plasma High-Density Lipoprotein Cholesterol Levels In Vivo

Background-Extrahepatic tissues have long been considered critical contributors of cholesterol to... more Background-Extrahepatic tissues have long been considered critical contributors of cholesterol to nascent HDL particles in the reverse cholesterol transport pathway, in which ABCA1 plays the crucial role. Recent studies, however, including both overexpression and deletion of ABCA1 selectively in the liver, have highlighted the primary role of the liver in the maintenance of HDL levels in vivo.

Research paper thumbnail of Mechanisms responsible for dominant expression of human growth hormone gene mutations

Journal of Clinical Endocrinology Amp Metabolism, Dec 1, 1996

ABSTRACT Point mutations of the donor splice site of intron 3 of the human GH-1 gene cause autoso... more ABSTRACT Point mutations of the donor splice site of intron 3 of the human GH-1 gene cause autosomal dominant inherited isolated growth hor-mone deficiency (IGHD II). The mechanism by which a defect in one GH-1 allele results in GH deficiency is obscure. Previously ...

Research paper thumbnail of Enhancement of Scavenger Receptor Class B Type I-mediated Selective Cholesteryl Ester Uptake from apoA-I-/- High Density Lipoprotein (HDL) by Apolipoprotein A-I Requires HDL Reorganization by Lecithin Cholesterol Acyltransferase

The Journal of Biological Chemistry, Mar 1, 2003

The severe depletion of cholesteryl ester (CE) in adrenocortical cells of apoA-I(-/-) mice sugges... more The severe depletion of cholesteryl ester (CE) in adrenocortical cells of apoA-I(-/-) mice suggests that apolipoprotein (apo) A-I plays an important role in the high density lipoprotein (HDL) CE selective uptake process mediated by scavenger receptor BI (SR-BI) in vivo. A recent study showed that apoA-I(-/-) HDL binds to SR-BI with the same affinity as apoA-I(+/+) HDL, but apoA-I(-/-) HDL has a decreased V(max) for CE transfer from the HDL particle to adrenal cells. The present study was designed to determine the basis for the reduced selective uptake of CE from apoA-I(-/-) HDL. Variations in apoA-I(-/-) HDL particle diameter, free cholesterol or phospholipid content, or the apoE or apoA-II content of apoA-I(-/-) HDL had little effect on HDL CE selective uptake into Y1-BS1 adrenal cells. Lecithin cholesterol acyltransferase treatment alone or addition of apoA-I to apoA-I(-/-) HDL alone also had little effect. However, addition of apoA-I to apoA-I(-/-) HDL in the presence of lecithin cholesterol acyltransferase reorganized the large heterogeneous apoA-I(-/-) HDL to a more discrete particle with enhanced CE selective uptake activity. These results show a unique role for apoA-I in HDL CE selective uptake that is distinct from its role as a ligand for HDL binding to SR-BI. These data suggest that the conformation of apoA-I at the HDL surface is important for the efficient transfer of CE to the cell.

Research paper thumbnail of Dietary Hydrogenated Fat Increases High-Density Lipoprotein apoA-I Catabolism and Decreases Low-Density Lipoprotein apoB-100 Catabolism in Hypercholesterolemic Women

Arteriosclerosis Thrombosis and Vascular Biology, Jun 1, 2004

Objective-To determine mechanisms contributing to decreased high-density lipoprotein cholesterol ... more Objective-To determine mechanisms contributing to decreased high-density lipoprotein cholesterol (HDL-C) and

Research paper thumbnail of Abstract 831: Selective Deficiency of Hepatic ABCA1 Results in Increased Susceptibility to Atherosclerosis

Circulation, Oct 31, 2006

Research paper thumbnail of Abstract 19183: Overexpression of Apom in Liver Stimulates Formation of Larger, Apom/S1P-Enriched Plasma HDL

Circulation, Nov 26, 2013

Research paper thumbnail of Hepatic ATP-Binding Cassette Transporter A1 Is a Key Molecule in High-Density Lipoprotein Cholesteryl Ester Metabolism in Mice

Objective-Mutations in ATP-binding cassette transporter A1 (ABCA1), the cellular lipid transport ... more Objective-Mutations in ATP-binding cassette transporter A1 (ABCA1), the cellular lipid transport molecule mutated in Tangier disease, result in the rapid turnover of high-density lipoprotein (HDL)-associated apolipoproteins that presumably are cleared by the kidneys. However, the role of ABCA1 in the liver for HDL apolipoprotein and cholesteryl ester (CE) catabolism in vivo is unknown. Methods and Results-Murine HDL was radiolabeled with 125 I in its apolipoprotein and with [ 3 H]cholesteryl oleyl ether in its CE moiety. HDL protein and lipid metabolism in plasma and HDL uptake by tissues were investigated in ABCA1-overexpressing bacterial artificial chromosome (BAC)-transgenic (BAC ϩ ) mice and in mice harboring deletions of total (ABCA1 Ϫ/Ϫ ) and liver-specific ABCA1 (ABCA1 ϪL/ϪL ). In BAC ϩ mice with elevated ABCA1 expression, fractional catabolic rates (FCRs) of both the protein and the lipid tracer were significantly decreased in plasma and in the liver, yielding a diminished hepatic selective CE uptake from HDL. In contrast, ABCA1 Ϫ/Ϫ or ABCA1 ϪL/ϪL mice had significantly increased plasma and liver FCRs for both HDL tracers. An ABCA1 deficiency was associated with increased selective HDL CE uptake by the liver under all experimental conditions. Conclusions-Hepatic ABCA1 has a critical role for HDL catabolism in plasma and for HDL selective CE uptake by the liver. (Arterioscler Thromb Vasc Biol. 2006;26:1821-1827.)

Research paper thumbnail of Influence of vesicle surface composition on the interfacial binding of lecithin:cholesterol acyltransferase and apolipoprotein A-I

Journal of Lipid Research, Jun 1, 1997

Interfacial binding affinities and capacities of lecithin:cholesterol acyltransferase (LCAT) and ... more Interfacial binding affinities and capacities of lecithin:cholesterol acyltransferase (LCAT) and apolipoprotein A-I (apoA-I) for surfaces of different phosphatidylcholine (PC) composition, cholesterol content, and apolipoprotein content were measured with a vesicle model system. Native polyacrylamide gel electrop was used to separate free protein from vesicle-bound . ApoA-I was isolated from human plasma and radiolabeled with iodine, whereas radiolabeled LCAT was purified from the media of Chinese hamster ovary cells that were transfected with human LCAT cDNA and incubated in the presence of ['4"S] cysteine and methionine. Bound and free radiolabeled LCAT arid apoA-I were quantified by phosphorimage analysis. ApoA-I binding was not influenced by cholesterol content (14 mole%) but was inflw enced by the PC fatty acyl composition of the vesicle. PC species containing long chain, polyunsaturated fatty acids (PUFA) in the sn-2 position resulted in increased binding affinity (K,l = 75-177 nM) but reduced capacity (0.1-0.3 apoA-

Research paper thumbnail of Apolipoprotein M expression increases the size of nascent pre HDL formed by ATP binding cassette transporter A1

J Lipid Res, 2010

This article is available online at http://www.jlr.org

Research paper thumbnail of Cloning and in vitro expression of rat lecithin:cholesterol acyltransferase

Biochimica et Biophysica Acta

Rat lecithin: cholesterol acyltransferase (LCAT) cDNA was obtained by reverse transcriptase/polym... more Rat lecithin: cholesterol acyltransferase (LCAT) cDNA was obtained by reverse transcriptase/polymerase chain reaction amplification of rat liver total RNA. A consensus sequence was derived from four independent clones from two strains of rats. In vitro ...

Research paper thumbnail of Thornburg JT, Parks JS & Rudel LL: Dietary fatty acid modification of HDL phospholipid molecular species alters lecithin: cholesterol acyltransferase reactivity in cynomolgus monkeys. J. Lipid Res. 36, 277-289

The Journal of Lipid Research

ABSTRACT

Research paper thumbnail of Production rate determines plasma concentration of large high density lipoprotein in non-human primates

The Journal of Lipid Research

Large LpAI HDL particles, containing only apoA-I without apoA-II, are reported to be the major an... more Large LpAI HDL particles, containing only apoA-I without apoA-II, are reported to be the major anti-atherogenic portion of HDL and to be increased in individuals with low risk for coronary heart disease. To determine whether the plasma concentration of large LpAI is modulated by the rate of production or catabolism of apolipoprotein A-I (apoA-I) in large LpAI, kinetic studies of large LpAI were performed in African green monkeys consuming an atherogenic diet with either high plasma HDL concentration (120 ؎ 36 mg/dl, mean ؎ SD, n ‫؍‬ 3) or low plasma HDL concentration (40 ؎ 13 mg/dl, n ‫؍‬ 3). Large LpAI was isolated, without ultracentrifugation, by immunoaffinity and gel filtration and radiolabeled. After injection, the specific activity of apoA-I in large HDL, consisting of both LpAI and LpAI:AII particles, was followed. A multicompartmental model was developed for the kinetics of apoA-I in large HDL, which indicated that a portion of large HDL is distributed to a sequestered pool, outside the circulating plasma, and reenters circulating plasma approximately 3 h after injection. There was no conversion of large LpAI to smaller HDL particles or transfer of radiolabeled apoA-I to smaller HDL particles. Although the mean fractional catabolic rate was not different comparing the high and low HDL group, the mean production rate of apoA-I in large HDL was 4-fold greater in the high HDL group compared with the low HDL group. These data support the hypothesis that the plasma concentration of large HDL is controlled primarily by the rate of production of apoA-I in large HDL.-Colvin, P., E. Moriguchi, H. Barrett, J. Parks, and L. Rudel. Production rate determines plasma concentration of large high density lipoprotein in non-human primates.

Research paper thumbnail of High level secretion of wild-type and mutant forms of human proapoA-I using baculovirus-mediated Sf-9 cell expression

The Journal of Lipid Research

To facilitate the investigation of apoA-I structure:function relationships as they relate to LCAT... more To facilitate the investigation of apoA-I structure:function relationships as they relate to LCAT acthation and lipid binding, we have developed an apo.4-I baculoviral expression and purification system that yields milligram quantities of wild-type or mutant proapo.4-I. Baculovirus-infected Sf-9 cells, grown in suspension, were found to secrete high levels of human wild-type (40-50 mg/l) or mutant apoA-I protein (1-38 mg/l), which was determined to be > 95% pure following a two-step purification procedure. In the case of wild-type apoA-I, ELISA showed that approximately 13-18% of the total protein secreted into the culture medium was apoA-I. To isolate pure protein from culture medium, 72 h post-infection medium was subjected to preparative reverse phase high performance liquid chromatography (HPLC), followed by DEAE ionsxchange chromatography. Purity and molecular size determination of wild-type proapoA-I protein was verified by SDS polyacrylamide gel electrophoresis, elcctrospray mass spectrometry, and N-terminal sequencing. In addition, recombinant discoidal apo.4-1:phospholipid complexes prepared from wild-type or plasma apoA-I showed similar particle size and LCAT activation properties. To fully characterize the utility of this expression system, the expression levels of various mutant apo.4-I proteins were compared to wild-type. Despite a lower production level seen with selected apoA-I mutants, milligram quantities of these purified mutant proteins were also obtained. DE In summary, we show that baculovirusderived wild-type proapoA-I shows properties similar to plasma apoA-I relative to recombinant HDL formation, LCAT reactivity, and a-helical content. In addition, we show that a variety of mutant forms of human proapoA-I can be expressed and purified in abundant quantity from baculoviral-infected Sf-9 cells.Sorci-Thomas, M. G., J. S. Parks, M. W. Keams, G. N. Pate, C. Zhang, and M. J. Thomas. High level secretion of wild-type and mutant forms of human proapoA-I using baculovirus-mediated Sf-9 cell expression. J. Lipid Res. 1996. 37: 673-683. Supplementary key words apolipoprotein A-I baculovirus expression high density lipoproteins 1ecithin:cholesterol acyltransferase discoidal complexes Sf-9 cells cholesterol cholesteryl ester Abbreviations: apo, apolipoprotein; HDL, high density lipoprotein; LCAT, 1ecithin:cholesterol acyltransferase; HPLC, high performance liquid Chromatography; MOI, multiplicity of infection; SDS, sodium dodecyl sulfate; ELISA, enqme-linked immunosorbent assay.

Research paper thumbnail of Fish oil decreases hepatic cholesteryl ester secretion but not apoB secretion in African green monkeys

The Journal of Lipid Research

Two groups of African green monkeys were fed diets containing 40 % of calories as fat with half o... more Two groups of African green monkeys were fed diets containing 40 % of calories as fat with half of the fat calories as either fish oil or lard. The fish oil-fed animals had lower cholesterol concentrations in blood plasma (33 %) and low density lipoproteins (LDL) (34%) than did animals fed lard. Size and cholesteryl ester (CE) content of LDL, strong predictors of coronary artery atherosclerosis in monkeys, were significantly less for the fish oil-fed animals although the apoB and LDL particle concentrations in plasma were similar for both diet groups. We hypothesized that decreased hepatic C E secretion led to the smaller size and reduced C E content of LDL in the fish oil-fed animals. Hepatic C E secretion was studied using recirculating perfusion of monkey livers that were infused during perfusion with fatty acids (85% 18:l and 15% n-3) at a rate of 0.1 pmoll min per g liver. The rate of cholesterol secretion was less Abbreviations: VLDL, very low density lipoprotein(s); LDL, low density lipoprotein(s); CE, cholesteryl ester(s); ACAT, acyl CoA:cholesterol acyltransferase; LCAT, 1ecithin:cholesterol acyltransferase; M'NB, 5,5'-dithiobis-(2-nitrobenzoic acid); IDL, intermediate density lipoprotein(s).

Research paper thumbnail of Dietary polyunsaturated fat modifies low-density lipoproteins and reduces atherosclerosis of nonhuman primates with high and low diet responsiveness

American Journal of Clinical Nutrition

We tested the hypothesis that an increased content of n-6 polyunsaturated fatty acids (principall... more We tested the hypothesis that an increased content of n-6 polyunsaturated fatty acids (principally linoleic acid) in an atherogenic diet of nonhuman primates would decrease atherosclerosis by modifying the composition and decreasing the concentration of plasma low-density lipoprotein (LDL). A species readily susceptible to diet-induced atherosclerosis (cynomolgus monkey) was compared with a less-susceptible species (African green monkey) with dietary cholesterol concentration and saturated or polyunsaturated fat (40% of energy) as variables. In both species, cholesterol concentrations in whole plasma, LDL, and high-density lipoprotein (HDL) were 20-30% lower when polyunsaturated fat was fed, whereas dietary cholesterol increased LDL cholesterol three- to fourfold. LDL was enriched in cholesteryl oleate when saturated fat and cholesterol were fed. Dietary linoleic acid prevented cholesteryl oleate enrichment and promoted cholesteryl linoleate accumulation in LDL. At the same plasma c...

Research paper thumbnail of Determining the Hypotriglyceridemic Effect of Echium Oil

Arteriosclerosis Thrombosis and Vascular Biology

Research paper thumbnail of Biogenesis and cytotoxicity of APOL1 renal-risk variant proteins in hepatocytes and hepatoma cells

Journal of lipid research, Jan 18, 2015

Two apolipoprotein L1 (APOL1) gene variants, which likely evolved to protect individuals from Afr... more Two apolipoprotein L1 (APOL1) gene variants, which likely evolved to protect individuals from African sleeping sickness, are strongly associated with non-diabetic kidney disease in individuals with recent African ancestry. Consistent with its role in trypanosome killing, the pro-death APOL1 protein is toxic to most cells, but its mechanism of cell death is poorly understood and little is known regarding its intracellular trafficking and secretion. Because liver appears to be the main source of circulating APOL1, we examined its secretory behavior and mechanism of toxicity in hepatoma cells and primary human hepatocytes. APOL1 is poorly secreted in vitro, even in the presence of chemical chaperones; however, it is efficiently secreted in wild-type transgenic mice, suggesting that APOL1 secretion has specialized requirements that cultured cells fail to support. In hepatoma cells, inducible expression of APOL1 and its risk variants promoted cell death, with the G1 variant displaying th...

Research paper thumbnail of Minimal Lipidation of Pre- HDL by ABCA1 Results in Reduced Ability to Interact with ABCA1

Objectives-The aim of this study was to determine the role of ATP binding cassette transporter A1... more Objectives-The aim of this study was to determine the role of ATP binding cassette transporter A1 (ABCA1) on generation of different-sized nascent HDLs. Methods and Results-HEK293 cells stably-transfected with ABCA1 (HEK293-ABCA1) or non-transfected (control) cells were incubated with lipid free 125 I-apoA-I for 24 hours. Incubation of apoA-I with HEK293-ABCA1 cells, but not control cells, led to the formation of heterogeneous-sized, pre-␤ migrating nascent HDL subpopulations (pre-␤1 to -4) that varied in size (7.1 to 15.7 nm), lipid, and apoA-I content. Kinetic studies suggested that all subpopulations were formed simultaneously, with no evidence for a precursor-product relationship between smaller and larger-sized particles. When isolated nascent pre-␤ HDLs (pre-␤1 to -4) were added back to HEK293-ABCA1 cells, their ability to bind to ABCA1 and efflux lipid was severely compromised. Heat-denaturation of pre-␤1 HDL resulted in partial recovery of ABCA1 binding, suggesting that initial interaction of apoA-I with ABCA1 results in a constrained conformation of apoA-I that decreases subsequent binding. Conclusions-Interaction of apoA-I with ABCA1 results in the simultaneous generation of pre-␤ HDLs of discrete size and chemical composition. These nascent particles are poor substrates for subsequent lipidation by ABCA1 and presumably require additional non-ABCA1-mediated lipidation for further maturation. (Arterioscler Thromb Vasc Biol.

Research paper thumbnail of Determination of the tissue sites responsible for the catabolism of large high density lipoprotein in the African green monkey

The Journal of Lipid Research, Mar 1, 2000

In vivo multicompartmental modeling of the turnover of HDL subfractions has suggested that HDL co... more In vivo multicompartmental modeling of the turnover of HDL subfractions has suggested that HDL containing four molecules of apoA-I per particle and no other apolipoproteins (large LpA-I) are terminal particles in plasma. We hypothesized that these terminal particles were the end product of HDL metabolism and, as such, would be cleared preferentially by the liver. Thus, the purpose of this study was to determine: 1 ) the tissue sites of catabolism of large LpA-I in African green monkeys, and 2 ) whether saturated versus n-6 polyunsaturated dietary fat affected tissue accumulation. Large LpA-I were isolated, without ultracentrifugation, by size exclusion and immunoaffinity chromatography and radiolabeled with either the residualizing compound, 125 I-labeled tyramine cellobiose (TC), or with 131 I. After injection into recipient animals, the plasma die-away of the radiolabels was followed for 12 or 24 h, after which the animals were killed and tissues were collected for determining radiolabel sites of catabolism. The plasma die-away of the 125 I-labeled TC-LpA-I and 131 I-labeled LpA-I doses was similar suggesting that the TC radiolabeling did not modify the metabolism of the large LpA-I dose. The liver, adrenal, kidney, and spleen had the greatest accumulation of large LpA-I degradation products on a per gram tissue basis. On a whole organ basis, the liver was the major site of large LpA-I degradation in both the 12-h (15.4 ؎ 0.3% of injected dose) and 24-h (9.1 ؎ 0.6% of injected dose) catabolic studies. The kidney, compared to the liver, had less uptake of large LpA-I radioactivity in either study (1.3 ؎ 0.4% and 1.2 ؎ 0.3% of injected dose). There was no apparent influence of dietary fat type on the tissue accumulation of large LpA-I. We conclude that the liver is the primary site of catabolism of large LpA-I in the African green monkeyDetermination of the tissue sites responsible for the catabolism of large high density lipoprotein in the African green monkey. J. Lipid Res. 2000. 41: 384-394.

Research paper thumbnail of Apolipoprotein M expression increases the size of nascent preβ HDL formed by ATP binding cassette transporter A1

Journal of Lipid Research, Mar 1, 2010

This article is available online at http://www.jlr.org

Research paper thumbnail of Both Hepatic and Extrahepatic ABCA1 Have Discrete and Essential Functions in the Maintenance of Plasma High-Density Lipoprotein Cholesterol Levels In Vivo

Background-Extrahepatic tissues have long been considered critical contributors of cholesterol to... more Background-Extrahepatic tissues have long been considered critical contributors of cholesterol to nascent HDL particles in the reverse cholesterol transport pathway, in which ABCA1 plays the crucial role. Recent studies, however, including both overexpression and deletion of ABCA1 selectively in the liver, have highlighted the primary role of the liver in the maintenance of HDL levels in vivo.

Research paper thumbnail of Mechanisms responsible for dominant expression of human growth hormone gene mutations

Journal of Clinical Endocrinology Amp Metabolism, Dec 1, 1996

ABSTRACT Point mutations of the donor splice site of intron 3 of the human GH-1 gene cause autoso... more ABSTRACT Point mutations of the donor splice site of intron 3 of the human GH-1 gene cause autosomal dominant inherited isolated growth hor-mone deficiency (IGHD II). The mechanism by which a defect in one GH-1 allele results in GH deficiency is obscure. Previously ...

Research paper thumbnail of Enhancement of Scavenger Receptor Class B Type I-mediated Selective Cholesteryl Ester Uptake from apoA-I-/- High Density Lipoprotein (HDL) by Apolipoprotein A-I Requires HDL Reorganization by Lecithin Cholesterol Acyltransferase

The Journal of Biological Chemistry, Mar 1, 2003

The severe depletion of cholesteryl ester (CE) in adrenocortical cells of apoA-I(-/-) mice sugges... more The severe depletion of cholesteryl ester (CE) in adrenocortical cells of apoA-I(-/-) mice suggests that apolipoprotein (apo) A-I plays an important role in the high density lipoprotein (HDL) CE selective uptake process mediated by scavenger receptor BI (SR-BI) in vivo. A recent study showed that apoA-I(-/-) HDL binds to SR-BI with the same affinity as apoA-I(+/+) HDL, but apoA-I(-/-) HDL has a decreased V(max) for CE transfer from the HDL particle to adrenal cells. The present study was designed to determine the basis for the reduced selective uptake of CE from apoA-I(-/-) HDL. Variations in apoA-I(-/-) HDL particle diameter, free cholesterol or phospholipid content, or the apoE or apoA-II content of apoA-I(-/-) HDL had little effect on HDL CE selective uptake into Y1-BS1 adrenal cells. Lecithin cholesterol acyltransferase treatment alone or addition of apoA-I to apoA-I(-/-) HDL alone also had little effect. However, addition of apoA-I to apoA-I(-/-) HDL in the presence of lecithin cholesterol acyltransferase reorganized the large heterogeneous apoA-I(-/-) HDL to a more discrete particle with enhanced CE selective uptake activity. These results show a unique role for apoA-I in HDL CE selective uptake that is distinct from its role as a ligand for HDL binding to SR-BI. These data suggest that the conformation of apoA-I at the HDL surface is important for the efficient transfer of CE to the cell.

Research paper thumbnail of Dietary Hydrogenated Fat Increases High-Density Lipoprotein apoA-I Catabolism and Decreases Low-Density Lipoprotein apoB-100 Catabolism in Hypercholesterolemic Women

Arteriosclerosis Thrombosis and Vascular Biology, Jun 1, 2004

Objective-To determine mechanisms contributing to decreased high-density lipoprotein cholesterol ... more Objective-To determine mechanisms contributing to decreased high-density lipoprotein cholesterol (HDL-C) and

Research paper thumbnail of Abstract 831: Selective Deficiency of Hepatic ABCA1 Results in Increased Susceptibility to Atherosclerosis

Circulation, Oct 31, 2006

Research paper thumbnail of Abstract 19183: Overexpression of Apom in Liver Stimulates Formation of Larger, Apom/S1P-Enriched Plasma HDL

Circulation, Nov 26, 2013

Research paper thumbnail of Hepatic ATP-Binding Cassette Transporter A1 Is a Key Molecule in High-Density Lipoprotein Cholesteryl Ester Metabolism in Mice

Objective-Mutations in ATP-binding cassette transporter A1 (ABCA1), the cellular lipid transport ... more Objective-Mutations in ATP-binding cassette transporter A1 (ABCA1), the cellular lipid transport molecule mutated in Tangier disease, result in the rapid turnover of high-density lipoprotein (HDL)-associated apolipoproteins that presumably are cleared by the kidneys. However, the role of ABCA1 in the liver for HDL apolipoprotein and cholesteryl ester (CE) catabolism in vivo is unknown. Methods and Results-Murine HDL was radiolabeled with 125 I in its apolipoprotein and with [ 3 H]cholesteryl oleyl ether in its CE moiety. HDL protein and lipid metabolism in plasma and HDL uptake by tissues were investigated in ABCA1-overexpressing bacterial artificial chromosome (BAC)-transgenic (BAC ϩ ) mice and in mice harboring deletions of total (ABCA1 Ϫ/Ϫ ) and liver-specific ABCA1 (ABCA1 ϪL/ϪL ). In BAC ϩ mice with elevated ABCA1 expression, fractional catabolic rates (FCRs) of both the protein and the lipid tracer were significantly decreased in plasma and in the liver, yielding a diminished hepatic selective CE uptake from HDL. In contrast, ABCA1 Ϫ/Ϫ or ABCA1 ϪL/ϪL mice had significantly increased plasma and liver FCRs for both HDL tracers. An ABCA1 deficiency was associated with increased selective HDL CE uptake by the liver under all experimental conditions. Conclusions-Hepatic ABCA1 has a critical role for HDL catabolism in plasma and for HDL selective CE uptake by the liver. (Arterioscler Thromb Vasc Biol. 2006;26:1821-1827.)

Research paper thumbnail of Influence of vesicle surface composition on the interfacial binding of lecithin:cholesterol acyltransferase and apolipoprotein A-I

Journal of Lipid Research, Jun 1, 1997

Interfacial binding affinities and capacities of lecithin:cholesterol acyltransferase (LCAT) and ... more Interfacial binding affinities and capacities of lecithin:cholesterol acyltransferase (LCAT) and apolipoprotein A-I (apoA-I) for surfaces of different phosphatidylcholine (PC) composition, cholesterol content, and apolipoprotein content were measured with a vesicle model system. Native polyacrylamide gel electrop was used to separate free protein from vesicle-bound . ApoA-I was isolated from human plasma and radiolabeled with iodine, whereas radiolabeled LCAT was purified from the media of Chinese hamster ovary cells that were transfected with human LCAT cDNA and incubated in the presence of ['4"S] cysteine and methionine. Bound and free radiolabeled LCAT arid apoA-I were quantified by phosphorimage analysis. ApoA-I binding was not influenced by cholesterol content (14 mole%) but was inflw enced by the PC fatty acyl composition of the vesicle. PC species containing long chain, polyunsaturated fatty acids (PUFA) in the sn-2 position resulted in increased binding affinity (K,l = 75-177 nM) but reduced capacity (0.1-0.3 apoA-

Research paper thumbnail of Apolipoprotein M expression increases the size of nascent pre HDL formed by ATP binding cassette transporter A1

J Lipid Res, 2010

This article is available online at http://www.jlr.org

Research paper thumbnail of Cloning and in vitro expression of rat lecithin:cholesterol acyltransferase

Biochimica et Biophysica Acta

Rat lecithin: cholesterol acyltransferase (LCAT) cDNA was obtained by reverse transcriptase/polym... more Rat lecithin: cholesterol acyltransferase (LCAT) cDNA was obtained by reverse transcriptase/polymerase chain reaction amplification of rat liver total RNA. A consensus sequence was derived from four independent clones from two strains of rats. In vitro ...

Research paper thumbnail of Thornburg JT, Parks JS & Rudel LL: Dietary fatty acid modification of HDL phospholipid molecular species alters lecithin: cholesterol acyltransferase reactivity in cynomolgus monkeys. J. Lipid Res. 36, 277-289

The Journal of Lipid Research

ABSTRACT

Research paper thumbnail of Production rate determines plasma concentration of large high density lipoprotein in non-human primates

The Journal of Lipid Research

Large LpAI HDL particles, containing only apoA-I without apoA-II, are reported to be the major an... more Large LpAI HDL particles, containing only apoA-I without apoA-II, are reported to be the major anti-atherogenic portion of HDL and to be increased in individuals with low risk for coronary heart disease. To determine whether the plasma concentration of large LpAI is modulated by the rate of production or catabolism of apolipoprotein A-I (apoA-I) in large LpAI, kinetic studies of large LpAI were performed in African green monkeys consuming an atherogenic diet with either high plasma HDL concentration (120 ؎ 36 mg/dl, mean ؎ SD, n ‫؍‬ 3) or low plasma HDL concentration (40 ؎ 13 mg/dl, n ‫؍‬ 3). Large LpAI was isolated, without ultracentrifugation, by immunoaffinity and gel filtration and radiolabeled. After injection, the specific activity of apoA-I in large HDL, consisting of both LpAI and LpAI:AII particles, was followed. A multicompartmental model was developed for the kinetics of apoA-I in large HDL, which indicated that a portion of large HDL is distributed to a sequestered pool, outside the circulating plasma, and reenters circulating plasma approximately 3 h after injection. There was no conversion of large LpAI to smaller HDL particles or transfer of radiolabeled apoA-I to smaller HDL particles. Although the mean fractional catabolic rate was not different comparing the high and low HDL group, the mean production rate of apoA-I in large HDL was 4-fold greater in the high HDL group compared with the low HDL group. These data support the hypothesis that the plasma concentration of large HDL is controlled primarily by the rate of production of apoA-I in large HDL.-Colvin, P., E. Moriguchi, H. Barrett, J. Parks, and L. Rudel. Production rate determines plasma concentration of large high density lipoprotein in non-human primates.

Research paper thumbnail of High level secretion of wild-type and mutant forms of human proapoA-I using baculovirus-mediated Sf-9 cell expression

The Journal of Lipid Research

To facilitate the investigation of apoA-I structure:function relationships as they relate to LCAT... more To facilitate the investigation of apoA-I structure:function relationships as they relate to LCAT acthation and lipid binding, we have developed an apo.4-I baculoviral expression and purification system that yields milligram quantities of wild-type or mutant proapo.4-I. Baculovirus-infected Sf-9 cells, grown in suspension, were found to secrete high levels of human wild-type (40-50 mg/l) or mutant apoA-I protein (1-38 mg/l), which was determined to be > 95% pure following a two-step purification procedure. In the case of wild-type apoA-I, ELISA showed that approximately 13-18% of the total protein secreted into the culture medium was apoA-I. To isolate pure protein from culture medium, 72 h post-infection medium was subjected to preparative reverse phase high performance liquid chromatography (HPLC), followed by DEAE ionsxchange chromatography. Purity and molecular size determination of wild-type proapoA-I protein was verified by SDS polyacrylamide gel electrophoresis, elcctrospray mass spectrometry, and N-terminal sequencing. In addition, recombinant discoidal apo.4-1:phospholipid complexes prepared from wild-type or plasma apoA-I showed similar particle size and LCAT activation properties. To fully characterize the utility of this expression system, the expression levels of various mutant apo.4-I proteins were compared to wild-type. Despite a lower production level seen with selected apoA-I mutants, milligram quantities of these purified mutant proteins were also obtained. DE In summary, we show that baculovirusderived wild-type proapoA-I shows properties similar to plasma apoA-I relative to recombinant HDL formation, LCAT reactivity, and a-helical content. In addition, we show that a variety of mutant forms of human proapoA-I can be expressed and purified in abundant quantity from baculoviral-infected Sf-9 cells.Sorci-Thomas, M. G., J. S. Parks, M. W. Keams, G. N. Pate, C. Zhang, and M. J. Thomas. High level secretion of wild-type and mutant forms of human proapoA-I using baculovirus-mediated Sf-9 cell expression. J. Lipid Res. 1996. 37: 673-683. Supplementary key words apolipoprotein A-I baculovirus expression high density lipoproteins 1ecithin:cholesterol acyltransferase discoidal complexes Sf-9 cells cholesterol cholesteryl ester Abbreviations: apo, apolipoprotein; HDL, high density lipoprotein; LCAT, 1ecithin:cholesterol acyltransferase; HPLC, high performance liquid Chromatography; MOI, multiplicity of infection; SDS, sodium dodecyl sulfate; ELISA, enqme-linked immunosorbent assay.

Research paper thumbnail of Fish oil decreases hepatic cholesteryl ester secretion but not apoB secretion in African green monkeys

The Journal of Lipid Research

Two groups of African green monkeys were fed diets containing 40 % of calories as fat with half o... more Two groups of African green monkeys were fed diets containing 40 % of calories as fat with half of the fat calories as either fish oil or lard. The fish oil-fed animals had lower cholesterol concentrations in blood plasma (33 %) and low density lipoproteins (LDL) (34%) than did animals fed lard. Size and cholesteryl ester (CE) content of LDL, strong predictors of coronary artery atherosclerosis in monkeys, were significantly less for the fish oil-fed animals although the apoB and LDL particle concentrations in plasma were similar for both diet groups. We hypothesized that decreased hepatic C E secretion led to the smaller size and reduced C E content of LDL in the fish oil-fed animals. Hepatic C E secretion was studied using recirculating perfusion of monkey livers that were infused during perfusion with fatty acids (85% 18:l and 15% n-3) at a rate of 0.1 pmoll min per g liver. The rate of cholesterol secretion was less Abbreviations: VLDL, very low density lipoprotein(s); LDL, low density lipoprotein(s); CE, cholesteryl ester(s); ACAT, acyl CoA:cholesterol acyltransferase; LCAT, 1ecithin:cholesterol acyltransferase; M'NB, 5,5'-dithiobis-(2-nitrobenzoic acid); IDL, intermediate density lipoprotein(s).

Research paper thumbnail of Dietary polyunsaturated fat modifies low-density lipoproteins and reduces atherosclerosis of nonhuman primates with high and low diet responsiveness

American Journal of Clinical Nutrition

We tested the hypothesis that an increased content of n-6 polyunsaturated fatty acids (principall... more We tested the hypothesis that an increased content of n-6 polyunsaturated fatty acids (principally linoleic acid) in an atherogenic diet of nonhuman primates would decrease atherosclerosis by modifying the composition and decreasing the concentration of plasma low-density lipoprotein (LDL). A species readily susceptible to diet-induced atherosclerosis (cynomolgus monkey) was compared with a less-susceptible species (African green monkey) with dietary cholesterol concentration and saturated or polyunsaturated fat (40% of energy) as variables. In both species, cholesterol concentrations in whole plasma, LDL, and high-density lipoprotein (HDL) were 20-30% lower when polyunsaturated fat was fed, whereas dietary cholesterol increased LDL cholesterol three- to fourfold. LDL was enriched in cholesteryl oleate when saturated fat and cholesterol were fed. Dietary linoleic acid prevented cholesteryl oleate enrichment and promoted cholesteryl linoleate accumulation in LDL. At the same plasma c...

Research paper thumbnail of Determining the Hypotriglyceridemic Effect of Echium Oil

Arteriosclerosis Thrombosis and Vascular Biology

Research paper thumbnail of Biogenesis and cytotoxicity of APOL1 renal-risk variant proteins in hepatocytes and hepatoma cells

Journal of lipid research, Jan 18, 2015

Two apolipoprotein L1 (APOL1) gene variants, which likely evolved to protect individuals from Afr... more Two apolipoprotein L1 (APOL1) gene variants, which likely evolved to protect individuals from African sleeping sickness, are strongly associated with non-diabetic kidney disease in individuals with recent African ancestry. Consistent with its role in trypanosome killing, the pro-death APOL1 protein is toxic to most cells, but its mechanism of cell death is poorly understood and little is known regarding its intracellular trafficking and secretion. Because liver appears to be the main source of circulating APOL1, we examined its secretory behavior and mechanism of toxicity in hepatoma cells and primary human hepatocytes. APOL1 is poorly secreted in vitro, even in the presence of chemical chaperones; however, it is efficiently secreted in wild-type transgenic mice, suggesting that APOL1 secretion has specialized requirements that cultured cells fail to support. In hepatoma cells, inducible expression of APOL1 and its risk variants promoted cell death, with the G1 variant displaying th...