Abstract 18667: Lipoprotein(a) Catabolism and Apolipoprotein(a) Secretion is Regulated by Sortilin

Circulation ◽  
2015 ◽  
Vol 132 (suppl_3) ◽  
Author(s):  
Rocco Romagnuolo ◽  
Matthew Gemin ◽  
Marlys Koschinsky
Keyword(s):  
Human Fibroblasts ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Coated Pits ◽  
Direct Role ◽  
Lipoprotein A ◽  
Hepatic Cells ◽  
Apolipoprotein A ◽  
Ability To Act ◽  
Ldl Catabolism

Elevated levels of lipoprotein(a) (Lp(a)) in plasma have been identified as an independent, causal risk factor for coronary heart disease. Lp(a) consists of a low-density lipoprotein (LDL)-like particle whose apolipoproteinB-100 (apoB-100) moiety is covalently linked to the unique glycoprotein apolipoprotein(a) (apo(a)). Recently, Lp(a) internalization by the LDL-receptor (LDLr) in hepatic cells and primary human fibroblasts has been shown to be regulated by proprotein convertase subtilisin/kexin type 9 (PCSK9). However, Lp(a)/apo(a) internalization still occurs even with a defective LDLr or in the presence of PCSK9 (in fibroblasts and hepatic cells, respectively), indicating a role for receptors other than the LDLr in Lp(a) catabolism. Hepatic sortilin has been identified as a potential receptor mediating LDL catabolism as well as the regulation of apoB-100 secretion. Sortilin localizes to the Golgi apparatus where it mediates trafficking of specific bound ligands to the lysosome. Sortilin also localizes to clathrin-coated pits in the plasma membrane where it can act as an internalization receptor. We demonstrate in the current study that Lp(a), but not apo(a), internalization in hepatic cells is influenced by sortilin overexpression. In the presence of PCSK9, Lp(a) internalization greatly increases with sortilin overexpression compared to control. These results suggest that hepatic sortilin has the ability to act as a receptor for Lp(a) catabolism, through the LDL-like moiety, in a manner that is not dependent on the LDLr. Furthermore, Lp(a) internalization increases with sortilin overexpression in primary human fibroblasts with a defective LDLr, again emphasizing an LDLr-independent role for sortilin as a receptor for Lp(a). Interestingly, an increase in apo(a) secretion is observed with sortilin overexpression in hepatic cells. Removal of the carboxyl-terminal tail of sortilin results in an inability to promote the secretion of apo(a), indicating a direct role for the sorting motifs present in this region of sortilin for the regulation of apo(a) secretion. Taken together, these results indicate novel roles for sortilin in both Lp(a) catabolism and apo(a) secretion.

scholarly journals Tissue-specific sorting of the human LDL receptor in polarized epithelia of transgenic mice.

1990 ◽  
Vol 111 (2) ◽  
pp. 347-359 ◽  
Author(s):  
R K Pathak ◽  
M Yokode ◽  
R E Hammer ◽  
S L Hofmann ◽  
M S Brown ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Transgenic Mice ◽  
Intestinal Epithelial Cells ◽  
Low Density Lipoprotein ◽  
Human Fibroblasts ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Intestinal Epithelial ◽  
Coated Pits ◽  
Ldl Receptors

The distribution of human low density lipoprotein (LDL) receptors was studied by immunofluorescence and immunoelectron microscopy in epithelial cells of transgenic mice that express high levels of receptors under control of the metallothionein-I promoter. In hepatocytes and intestinal epithelial cells, the receptors were confined to the basal and basolateral surfaces, respectively. Very few LDL receptors were present in coated pits or intracellular vesicles. In striking contrast, in the epithelium of the renal tubule the receptors were present on the apical (lumenal) surface where they appeared to be concentrated at the base of microvilli and were abundant in vesicles of the endocytic recycling pathway. Intravenously administered LDL colloidal gold conjugates bound to the receptors on hepatocyte microvilli and were slowly internalized, apparently through slow migration into coated pits. We conclude that (a) sorting of LDL receptors to the surface of different epithelial cells varies with each tissue; and (b) in addition to a signal for clustering in coated pits, the LDL receptor may contain a signal for retention in noncoated membrane that is manifest in hepatocytes and intestinal epithelial cells, but not in renal epithelial cells or cultured human fibroblasts.

PCSK9 inhibition with alirocumab reduces lipoprotein(a) levels in nonhuman primates by lowering apolipoprotein(a) production rate

2018 ◽  
Vol 132 (10) ◽  
pp. 1075-1083 ◽  
Author(s):  
Mikaël Croyal ◽  
Thi-Thu-Trang Tran ◽  
Rose Hélène Blanchard ◽  
Jean-Christophe Le Bail ◽  
Elise F. Villard ◽  
...  
Keyword(s):  
Production Rate ◽  
Nonhuman Primates ◽  
Numerical Models ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Human Hepatocytes ◽  
Lipoprotein A ◽  
Apolipoprotein A ◽  
Pcsk9 Inhibition

Therapeutic antibodies targeting proprotein convertase subtilisin kexin type 9 (PCSK9) (e.g. alirocumab) lower low-density lipoprotein cholesterol (LDL-C) and lipoprotein (a) [Lp(a)] levels in clinical trials. We recently showed that PCSK9 enhances apolipoprotein(a) [apo(a)] secretion from primary human hepatocytes but does not affect Lp(a) cellular uptake. Here, we aimed to determine how PCSK9 neutralization modulates Lp(a) levels in vivo. Six nonhuman primates (NHP) were treated with alirocumab or a control antibody (IgG1) in a crossover protocol. After the lowering of lipids reached steady state, NHP received an intravenous injection of [2H3]-leucine, and blood samples were collected sequentially over 48 h. Enrichment of apolipoproteins in [2H3]-leucine was assessed by liquid chromatography–tandem mass spectrometry (LC–MS/MS). Kinetic parameters were calculated using numerical models with the SAAMII software. Compared with IgG1, alirocumab significantly reduced total cholesterol (TC) (−28%), LDL-C (−67%), Lp(a) (−56%), apolipoprotein B100 (apoB100) (−53%), and apo(a) (−53%). Alirocumab significantly increased the fractional catabolic rate of apoB100 (+29%) but not that of apo(a). Conversely, alirocumab sharply and significantly reduced the production rate (PR) of apo(a) (−42%), but not significantly that of apoB100, compared with IgG1, respectively. In line with the observations made in human hepatocytes, the present kinetic study establishes that PCSK9 neutralization with alirocumab efficiently reduces circulating apoB100 and apo(a) levels by distinct mechanisms: apoB primarily by enhancing its catabolism and apo(a) primarily by lowering its production.

scholarly journals Potent lipoprotein(a) lowering following apolipoprotein(a) antisense treatment reduces the pro-inflammatory activation of circulating monocytes in patients with elevated lipoprotein(a)

2020 ◽  
Vol 41 (24) ◽  
pp. 2262-2271 ◽  
Author(s):  
Lotte C A Stiekema ◽  
Koen H M Prange ◽  
Renate M Hoogeveen ◽  
Simone L Verweij ◽  
Jeffrey Kroon ◽  
...  
Keyword(s):  
Gene Expression ◽  
Ex Vivo ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Cvd Risk ◽  
Inflammatory Gene Expression ◽  
Lipoprotein A ◽  
Inflammatory Gene ◽  
Apolipoprotein A ◽  
Inflammatory Activation

Abstract Aims Elevated lipoprotein(a) [Lp(a)] is strongly associated with an increased cardiovascular disease (CVD) risk. We previously reported that pro-inflammatory activation of circulating monocytes is a potential mechanism by which Lp(a) mediates CVD. Since potent Lp(a)-lowering therapies are emerging, it is of interest whether patients with elevated Lp(a) experience beneficial anti-inflammatory effects following large reductions in Lp(a). Methods and results Using transcriptome analysis, we show that circulating monocytes of healthy individuals with elevated Lp(a), as well as CVD patients with increased Lp(a) levels, both have a pro-inflammatory gene expression profile. The effect of Lp(a)-lowering on gene expression and function of monocytes was addressed in two local sub-studies, including 14 CVD patients with elevated Lp(a) who received apolipoprotein(a) [apo(a)] antisense (AKCEA-APO(a)-LRx) (NCT03070782), as well as 18 patients with elevated Lp(a) who received proprotein convertase subtilisin/kexin type 9 antibody (PCSK9ab) treatment (NCT02729025). AKCEA-APO(a)-LRx lowered Lp(a) by 47% and reduced the pro-inflammatory gene expression in monocytes of CVD patients with elevated Lp(a), which coincided with a functional reduction in transendothelial migration capacity of monocytes ex vivo (−17%, P < 0.001). In contrast, PCSK9ab treatment lowered Lp(a) by 16% and did not alter transcriptome nor functional properties of monocytes, despite an additional reduction of 65% in low-density lipoprotein cholesterol (LDL-C). Conclusion Potent Lp(a)-lowering following AKCEA-APO(a)-LRx, but not modest Lp(a)-lowering combined with LDL-C reduction following PCSK9ab treatment, reduced the pro-inflammatory state of circulating monocytes in patients with elevated Lp(a). These ex vivo data support a beneficial effect of large Lp(a) reductions in patients with elevated Lp(a).

scholarly journals Galactose-specific asialoglycoprotein receptor is involved in lipoprotein (a) catabolism

2003 ◽  
Vol 376 (3) ◽  
pp. 765-771 ◽  
Author(s):  
Andelko HRZENJAK ◽  
Sasa FRANK ◽  
Xingde WO ◽  
Yonggang ZHOU ◽  
Theo van BERKEL ◽  
...  
Keyword(s):  
Physiological Function ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Asialoglycoprotein Receptor ◽  
Fractional Catabolic Rate ◽  
Wild Type ◽  
Lipoprotein A ◽  
Apolipoprotein A ◽  
Catabolic Rate ◽  
First Time

Lp(a) [lipoprotein (a)] is a highly atherogenic plasma lipoprotein assembled from low-density lipoprotein and the glycoprotein apolipoprotein (a). The rate of Lp(a) biosynthesis correlates significantly with plasma Lp(a) concentrations, whereas the fractional catabolic rate does not have much influence. So far, little is known about Lp(a) catabolism. To study the site and mode of Lp(a) catabolism, native or sialidase-treated Lp(a) was injected into hedgehogs or ASGPR (asialoglycoprotein receptor)-knockout (ASGPR−) mice or wild-type (ASGPR+) mice, and the decay of the plasma Lp(a) concentration was followed. COS-7 cells were transfected with high- (HL-1) and low-molecular-mass ASGPR subunits (HL-2), and binding and degradation of intact or desialylated Lp(a) were measured. In hedgehogs, one of the few species that synthesize Lp(a), most of the Lp(a) was taken up by the liver, followed by kidney and spleen. Lp(a) and asialo-Lp(a) were catabolized with apparent half-lives of 13.8 and 0.55 h respectively. Asialo-orosomucoide increased both half-lives significantly. In mice, the apparent half-life of Lp(a) was 4–6 h. Catabolism of native Lp(a) by wild-type mice was significantly faster compared with ASGPR− mice and there was a significantly greater accumulation of Lp(a) in the liver of ASGPR+ mice compared with ASGPR− mice. The catabolism of asialo-Lp(a) in ASGPR− mice was 8-fold faster when compared with native Lp(a) in wild-type mice. Transfected COS-7 cells expressing functional ASGPR showed approx. 5-fold greater binding and 2-fold faster degradation of native Lp(a) compared with control cells. Our results for the first time demonstrate a physiological function of ASGPR in the catabolism of Lp(a).

scholarly journals Metabolism of cationized lipoproteins by human fibroblasts: biochemical and morphologic correlations

1977 ◽  
Vol 74 (1) ◽  
pp. 119-135 ◽  
Author(s):  
SK Basu ◽  
RGW Anderson ◽  
JL Goldstein ◽  
MS Brown
Keyword(s):  
Electron Microscopy ◽  
Cholesteryl Ester ◽  
Lipid Droplets ◽  
Human Fibroblasts ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Turnover Time ◽  
Cholesteryl Esters ◽  
Light Microscope Level ◽  
Cellular Content

Human plasma low density lipoprotein (LDL) that had been rendered polycationic by coupling with N, N-dimethyl-1, 3-propanediamine (DMPA) was shown by electron microscopy to bind in clusters to the surface of human fibroblasts. The clusters resembled those formed by polycationic ferritin (DMPA-feritin), a visual probe that binds to anionic site on the plasma membrane. Biochemical studies with (125)I-labeled DMPA-LDL showed that the membrane-bound lipoprotein was internalized and hydrolyzed in lysosomes. The turnover time for cell bound (125)I-DMPA-LDL, i.e., the time in which the amount of (125)I-DMPA-LDL degraded was equal to the steady-state cellular content of the lipoprotein, was about 50 h. Because the DMPA-LDL gained access to fibroblasts by binding nonspecifically to anionic sites on the cell surface rather than by binding to the physiologic LDL receptor, its uptake failed to be regulated under conditions in which the uptake of native LDL was reduced by feedback suppression of the LDL receptor. As a result, unlike the case with native LDL, the DMPA-LDL accumulated progressively within the cell, and this led to a massive increase in the cellular content of both free and esterified cholesterol. Studies with (14)C-oleate showed that at least 20 percent of the accumulated cholesteryl esters represented cholesterol that had been esterified within the cell. After 4 days of incubation with 10 μg/ml of DMPA-LDL, fibroblasts had accumulated so much cholesteryl ester that neutral lipid droplets were visible at the light microscope level with Oil Red O staining. By electron microscopy, these intracellular lipid droplets were observed to lack a tripartite limiting membrane. The ability to cause the overaccumulation of cholesteryl esters within cells by using DMPA-LDL provides a model system for study of the pathologic consequences at the cellular level of massive deposition of cholesteryl ester.

scholarly journals Resistance of lipoprotein(a) to lipid peroxidation induced by oxygenated free radicals produced by γ radiolysis: a comparison with low-density lipoprotein

1996 ◽  
Vol 314 (1) ◽  
pp. 277-284 ◽  
Author(s):  
Jean-Louis BEAUDEUX ◽  
Monique GARDES-ALBERT ◽  
Jacques DELATTRE ◽  
Alain LEGRAND ◽  
François ROUSSELET ◽  
...  
Keyword(s):  
Lipid Peroxidation ◽  
Free Radicals ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Peroxyl Radicals ◽  
Low Density ◽  
Lipoprotein A ◽  
Acetylneuraminic Acid ◽  
Paired Samples ◽  
Apolipoprotein A

Lipid peroxidation of lipoprotein(a) [Lp(a)] by defined oxygen-centred free radicals (O2-· /OH·, O2-·, O2-· /HO2·) produced by γ radiolysis was compared with that of paired samples of low-density lipoprotein (LDL). Lp(a) appeared to be more resistant to oxidation than LDL, as indicated by the kinetic study of four markers of lipid peroxidation: decrease in vitamin E, formation of conjugated dienes and aldehydic products, and modification of electrophoretic mobility. In contrast, similar kinetics of lipid peroxidation were obtained for LDL and Lp(a-), which is the lipoparticle issued following the reductive cleavage of apolipoprotein(a) from Lp(a), thus suggesting that the greater resistance of Lp(a) to lipid peroxidation was due to the presence of apolipoprotein(a). Lipid peroxidation of Lp(a) and LDL induced by peroxyl radicals, which were produced by an azo compound [2,2′-azobis-(2-amidinopropane)dihydrochloride], confirmed both the resistance of Lp(a) to lipid peroxidation and the propensity of Lp(a-) to exhibit a greater susceptibility to oxidation than intact Lp(a). Our findings also indicated that the high content of apolipoprotein(a) in N-acetylneuraminic acid residues was only partly responsible for the resistance of Lp(a) to oxidation.

The NHLBI Twin Study: heritability of apolipoprotein A-I, B, and low density lipoprotein subclasses and concordance for lipoprotein(a)

1991 ◽  
Vol 91 (1-2) ◽  
pp. 97-106 ◽  
Author(s):  
Stefania Lamon-Fava ◽  
Dolores Jimenez ◽  
Joe C. Christian ◽  
Richard R. Fabsitz ◽  
Terry Reed ◽  
...  
Keyword(s):  
Twin Study ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Low Density ◽  
Lipoprotein A ◽  
Lipoprotein Subclasses ◽  
Apolipoprotein A

Analysis of strneture–fonction relationships in human apolipoprotein(a)

1994 ◽  
Vol 72 (3) ◽  
pp. 304-310 ◽  
Author(s):  
Ytje Y. van der Hoek ◽  
John J. P. Kastelein ◽  
Marlys L. Koschinsky
Keyword(s):  
Recombinant Expression ◽  
Low Density Lipoprotein ◽  
Expression System ◽  
Density Lipoprotein ◽  
Site Directed Mutagenesis ◽  
Human Populations ◽  
Low Density ◽  
Covalent Linkage ◽  
Lipoprotein A ◽  
Apolipoprotein A

Elevated levels of lipoprotein(a) (Lp(a)) have been strongly correlated with the development of atherosclerosis in human populations. Lp(a) is distinguishable from low density lipoprotein by the presence of the unique protein component apolipoprotein(a) (apo(a)), which contains repeated domains that closely resemble that of plasminogen kringle IV. Using human embryonic kidney cells, we have expressed a recombinant form of apo(a) (r-apo(a)) containing 17 kringle IV-like domains. We have utilized this recombinant expression system to study the assembly of Lp(a) particles. We have demonstrated that Lp(a) particles containing r-apo(a) can be assembled extracellularly in plasma by covalent linkage to low density lipoprotein. Using site-directed mutagenesis, we have demonstrated that a cysteine residue present at position 4057 of the apo(a) protein (i.e., in the penultimate kringle IV repeat) mediates this covalent linkage. Using polymerase chain reaction amplification of liver apo(a) complementary DNA, we have demonstrated the presence of a polymorphism in apo(a) kringle IV type 10, which results in the substitution of a threonine for a methionine. Preliminary studies indicate that the presence of a threonine at this position may enhance the interaction of Lp(a) with lysine–Sepharose.Key words: apolipoprotein(a), lipoprotein(a), kringles, lipoprotein(a) assembly, polymorphism.

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