The isolation and partial characterization of the serum lipoproteins and apolipoproteins of the rainbow trout.
1. VLD (very-low-density), LD (low-density) and HD (high-density) lipoproteins were isolated from the serum of trout (Salmo gairdneri Richardson). 2. Each lipoprotein class resembled that of the human in immunological reactivity, electrophoretic behaviour and appearance in the electron microscope. Trout LD lipoprotein, however, was of greater density than human LD lipoprotein. 3. The trout lipoproteins have lipid compositions which are similar to those of the corresponding human components, except for their high contents of long-chain unsaturated fatty acids. 4. HD and LD lipoproteins were immunologically non-identical, whereas LD lipoproteins possessed antigenic determinants in common with VLD lipoproteins. 5. VLD and HD lipoproteins each contained at least seven different apoproteins, whereas LD liprotein was composed largely of a single apoprotein which resembled human apolipoprotein B. 6. At least one, and possibly three, apoprotein of trout HD lipoprotein showed features which resemble human apoprotein A-1.7. The broad similarity between the trout and human lipoprotein systems suggests that both arose from common ancestral genes early in evolutionary history. (+info)
Transgenic rabbits as models for atherosclerosis research.
Several characteristics of the rabbit make it an excellent model for the study of lipoprotein metabolism and atherosclerosis. New Zealand White (NZW) rabbits have low plasma total cholesterol concentrations, high cholesteryl ester transfer protein activity, low hepatic lipase (HL) activity, and lack an analogue of human apolipoprotein (apo) A-II, providing a unique system in which to assess the effects of human transgenes on plasma lipoproteins and atherosclerosis susceptibility. Additionally, rabbit models of human lipoprotein disorders, such as the Watanabe Heritable Hyperlipidemic (WHHL) and St. Thomas' Hospital strains, models of familial hypercholesterolemia and familial combined hyperlipidemia, respectively, allow for the assessment of candidate genes for potential use in the treatment of dyslipoproteinemic patients. To date, transgenes for human apo(a), apoA-I, apoB, apoE2, apoE3, HL, and lecithin:cholesterol acyltransferase (LCAT), as well as for rabbit apolipoprotein B mRNA-editing enzyme catalytic poly-peptide 1 (APOBEC-1), have been expressed in NZW rabbits, whereas only those for human apoA-I and LCAT have been introduced into the WHHL background. All of these transgenes have been shown to have significant effects on plasma lipoprotein concentrations. In both NZW and WHHL rabbits, human apoA-I expression was associated with a significant reduction in the extent of aortic atherosclerosis, which was similarly the case for LCAT in rabbits having at least one functional LDL receptor allele. Conversely, expression of apoE2 in NZW rabbits caused increased susceptibility to atherosclerosis. These studies provide new insights into the mechanisms responsible for the development of atherosclerosis, emphasizing the strength of the rabbit model in cardiovascular disease research. (+info)
The heparin/heparan sulfate-binding site on apo-serum amyloid A. Implications for the therapeutic intervention of amyloidosis.
Serum amyloid A isoforms, apoSAA1 and apoSAA2, are apolipoproteins of unknown function that become major components of high density lipoprotein (HDL) during the acute phase of an inflammatory response. ApoSAA is also the precursor of inflammation-associated amyloid, and there is strong evidence that the formation of inflammation-associated and other types of amyloid is promoted by heparan sulfate (HS). Data presented herein demonstrate that both mouse and human apoSAA contain binding sites that are specific for heparin and HS, with no binding for the other major glycosaminoglycans detected. Cyanogen bromide-generated peptides of mouse apoSAA1 and apoSAA2 were screened for heparin binding activity. Two peptides, an apoSAA1-derived 80-mer (residues 24-103) and a smaller carboxyl-terminal 27-mer peptide of apoSAA2 (residues 77-103), were retained by a heparin column. A synthetic peptide corresponding to the CNBr-generated 27-mer also bound heparin, and by substituting or deleting one or more of its six basic residues (Arg-83, His-84, Arg-86, Lys-89, Arg-95, and Lys-102), their relative importance for heparin and HS binding was determined. The Lys-102 residue appeared to be required only for HS binding. The residues Arg-86, Lys-89, Arg-95, and Lys-102 are phylogenetically conserved suggesting that the heparin/HS binding activity may be an important aspect of the function of apoSAA. HS linked by its carboxyl groups to an Affi-Gel column or treated with carbodiimide to block its carboxyl groups lost the ability to bind apoSAA. HDL-apoSAA did not bind to heparin; however, it did bind to HS, an interaction to which apoA-I contributed. Results from binding experiments with Congo Red-Sepharose 4B columns support the conclusions of a recent structural study which found that heparin binding domains have a common spatial distance of about 20 A between their two outer basic residues. Our present work provides direct evidence that apoSAA can associate with HS (and heparin) and that the occupation of its binding site by HS, and HS analogs, likely caused the previously reported increase in amyloidogenic conformation (beta-sheet) of apoSAA2 (McCubbin, W. D., Kay, C. M., Narindrasorasak, S., and Kisilevsky, R. (1988) Biochem. J. 256, 775-783) and their amyloid-suppressing effects in vivo (Kisilevsky, R., Lemieux, L. J., Fraser, P. E., Kong, X., Hultin, P. G., and Szarek, W. A. (1995) Nat. Med. 1, 143-147), respectively. (+info)
Potent inhibition of CD4/TCR-mediated T cell apoptosis by a CD4-binding glycoprotein secreted from breast tumor and seminal vesicle cells.
We previously isolated a CD4 ligand glycoprotein, gp17, from human seminal plasma; this glycoprotein is identical with gross cystic disease fluid protein-15 (GCDFP-15), a factor specifically secreted from primary and secondary breast tumors. The function of gp17/GCDFP-15 in physiological as well as in pathological conditions has remained elusive thus far. As a follow up to our previous findings that gp17 binds to CD4 with high affinity and interferes with both HIV-1 gp120 binding to CD4 and syncytium formation, we investigated whether gp17 could affect the T lymphocyte apoptosis induced by a separate ligation of CD4 and TCR. We show here that gp17/GCDFP-15 is in fact a strong and specific inhibitor of the T lymphocyte programmed cell death induced by CD4 cross-linking and subsequent TCR activation. The antiapoptotic effect observed in the presence of gp17 correlates with a moderate up-regulation of Bcl-2 expression in treated cells. The presence of gp17 also prevents the down-modulation of Bcl-2 expression in Bcl-2bright CD4+ T cells that is caused by the triggering of apoptosis. Our results suggest that gp17 may represent a new immunomodulatory CD4 binding factor playing a role in host defense against infections and tumors. (+info)
Effects of alcohol and cholesterol feeding on lipoprotein metabolism and cholesterol absorption in rabbits.
Alcohol fed to rabbits in a liquid formula at 30% of calories increased plasma cholesterol by 36% in the absence of dietary cholesterol and by 40% in the presence of a 0.5% cholesterol diet. The increase was caused almost entirely by VLDL, IDL, and LDL. Cholesterol feeding decreased the fractional catabolic rate for VLDL and LDL apoprotein by 80% and 57%, respectively, and increased the production rate of VLDL and LDL apoprotein by 75% and 15%, respectively. Alcohol feeding had no effect on VLDL apoprotein production but increased LDL production rate by 55%. The efficiency of intestinal cholesterol absorption was increased by alcohol. In the presence of dietary cholesterol, percent cholesterol absorption rose from 34.4+/-2.6% to 44.9+/-2.5% and in the absence of dietary cholesterol, from 84.3+/-1.4% to 88.9+/-1.0%. Increased cholesterol absorption and increased LDL production rate may be important mechanisms for exacerbation by alcohol of hypercholesterolemia in the cholesterol-fed rabbit model. (+info)
Lipid transfer inhibitor protein defines the participation of lipoproteins in lipid transfer reactions: CETP has no preference for cholesteryl esters in HDL versus LDL.
Cholesteryl ester transfer protein (CETP) catalyzes the net transfer of cholesteryl ester (CE) between lipoproteins in exchange for triglyceride (heteroexchange). It is generally held that CETP primarily associates with HDL and preferentially transfers lipids from this lipoprotein fraction. This is illustrated in normal plasma where HDL is the primary donor of the CE transferred to VLDL by CETP. However, in plasma deficient in lipid transfer inhibitor protein (LTIP) activity, HDL and LDL are equivalent donors of CE to VLDL (Arterioscler Thromb Vasc Biol. 1997;17:1716-1724). Thus, we have hypothesized that the preferential transfer of CE from HDL in normal plasma is a consequence of LTIP activity and not caused by a preferential CETP-HDL interaction. We have tested this hypothesis in lipid mass transfer assays with partially purified CETP and LTIP, and isolated lipoproteins. With a physiological mixture of lipoproteins, the preference ratio (PR, ratio of CE mass transferred from a lipoprotein to VLDL versus its CE content) for HDL and LDL in the presence of CETP alone was approximately 1 (ie, no preference). Fourfold variations in the LDL/HDL ratio or in the levels of HDL in the assay did not result in significant preferential transfer from any lipoprotein. On addition of LTIP, the PR for HDL was increased up to 2-fold and that for LDL decreased in a concentration-dependent manner. Under all conditions where LDL and HDL levels were varied, LTIP consistently resulted in a PR >1 for CE transfer from HDL. Short-term experiments with radiolabeled lipoproteins and either partially purified or homogenous CETP confirmed these observations and further demonstrated that CETP has a strong predilection to mediate homoexchange (bidirectional transfer of the same lipid) rather than heteroexchange (CE for TG); LTIP had no effect on the selection of CE or TG by CETP or its mechanism of action. We conclude, in contrast to current opinion, that CETP has no preference for CE in HDL versus LDL, suggesting that the previously reported stable binding of CETP to HDL does not result in selective transfer from this lipoprotein. These data suggest that LTIP is responsible for the preferential transfer of CE from HDL that occurs in plasma. CETP and LTIP cooperatively determine the extent of CETP-mediated remodeling of individual lipoprotein fractions. (+info)
Levels of soluble cell adhesion molecules in patients with angiographically defined coronary atherosclerosis.
Adhesion molecules on the endothelial cell membrane play an important role in the pathogenesis of atherosclerosis. Levels of soluble forms of cell adhesion molecules are reportedly elevated in patients with peripheral artery vessel disease and in patients with an atherosclerotic aorta. The present study investigated the association of serum levels of soluble vascular cell adhesion molecule 1 (sVCAM-1), soluble intercellular adhesion molecule 1 (sICAM-1), and soluble P-selectin (sP-selectin) with coronary heart disease (CHD) and the extent of coronary atherosclerosis, and examined the influence of serum levels of lipids, lipoproteins and apolipoproteins (apo) in subjects with (n=52, M/F:43/9) and without (controls, n=40, M/F:25/15) angiographically proven coronary atherosclerosis. After controlling for age and gender, levels of sVCAM-1 (least squares mean +/- std error: 565+/-36 ng/ml vs 540+/-41 ng/ml, ns), sICAM-1 (261+/-17ng/ml vs 247+/-19ng/ml, ns), and sP-selectin (142+/-8ng/ml vs 149+/-10 ng/ml, ns) in patients with coronary atherosclerosis were not different from those in controls, as assessed by an analysis of covariance. After also adjusting for body mass index, hypertension, diabetes mellitus, and smoking by a multiple logistic function analysis, the association of sVCAM-1, sICAM-1, and sP-selectin with CHD was still not significant. Levels of sVCAM-1, sICAM-1, and sP-selectin were also not related to the extent of coronary atherosclerosis as judged by the number of stenosed vessels. However, inverse (p<0.05) relationships were observed between sVCAMs and serum levels of HDL3-cholesterol, apo A-II, and lipoprotein containing apo A-I and A-II, between sICAMs and levels of apo A-II and Lp A-I/A-II (Lp A-I/A-II), and between sP-selectin and lipoprotein containing only apo A-I. In conclusion, serum levels of soluble VCAM-1, ICAM-1, and P-selectin were not related to CHD or the extent of coronary atherosclerosis, but were inversely related to serum levels of high-density lipoprotein-related lipoproteins. (+info)
CREB-binding protein is a transcriptional coactivator for hepatocyte nuclear factor-4 and enhances apolipoprotein gene expression.
Hepatocyte nuclear factor-4 (HNF-4) is a liver-enriched transcription factor that is crucial in the regulation of a large number of genes involved in glucose, cholesterol, and fatty acid metabolism and in determining the hepatic phenotype. We have previously shown that HNF-4 contains transcription activation functions at the N terminus (AF-1) and the C terminus (AF-2) which work synergistically to confer full HNF-4 activity. Here, we show that HNF-4 recruits the CREB-binding protein (CBP) coactivator on promoters of genes that contain functional HNF-4 sites. HNF-4 interacts with the N-terminal region of CBP (amino acids 1-771) and the C-terminal region of CBP (amino acids 1812-2441). The two activating functions of HNF-4, AF-1 and AF-2, interact with the N terminus and the N and C terminus of CBP, respectively. In addition, we show that in contrast to the other nuclear hormone receptors the interaction between HNF-4 and CBP is ligand-independent. Recruitment of CBP by HNF-4 results in an enhancement of the transcriptional activity of the latter. CBP does not activate gene expression in the absence of HNF-4, and dominant negative forms of HNF-4 prevent transcriptional activation by CBP, suggesting that the mere recruitment of CBP by HNF-4 is not sufficient for enhancement of gene expression. These findings demonstrate that CBP acts as a transcriptional coactivator for HNF-4 and provide new insights into the regulatory function of HNF-4. (+info)