Academic literature on the topic 'Apolipoprotein F'

Abstract Because lipoproteins containing apolipoprotein A (ApoA-I + ApoA-II) or apolipoprotein B (ApoB) seem to exert opposite effects as risk factors for coronary heart disease, we decided to determine the separability of these two major plasma lipoproteins by procedures originally designed to separate high-density from low- and very-low-density lipoproteins. The presumably ApoB-free lipoproteins isolated from normal plasma by (a) ultracentrifugation at d = 1.063; precipitation with (b) heparin-Mn2+ or (c) phosphotungstate-Mg2+; or (d) immunoprecipitation with antibodies to ApoB were characterized by quantifying cholesterol and apolipoproteins A-I, A-II, B, C-II, C-III, D, E, F, and Lp(a). ApoA- and ApoB-containing lipoproteins were completely separated only by immunoprecipitation with antibodies to ApoB. The ApoB-containing lipoproteins isolated by other procedures always contained 4% to 20% of total plasma ApoA-I and differed substantially from one another with respect to the content of some of the minor apolipoproteins. Measuring apolipoproteins was more reliable than measuring cholesterol for monitoring this separation and for expressing the concentrations of ApoA- and ApoB-containing lipoproteins.

A protein recognizing apolipoproteins AI, AII and AIV was purified from cultured mouse adipose cells of the Ob17MT18 clonal line. Apolipoprotein A binding sites were solubilized in the presence of proteinase inhibitors using the non-denaturating detergent CHAPS. Chromatography of the soluble extract on DEAE-Trisacryl was followed by immunoaffinity chromatography of the complex apolipoprotein AI-binding proteins on anti-(apolipoprotein AI) coupled to Sepharose 4B and then by h.p.l.c. on an RP-Select B column. A 1400-fold purification over the starting crude homogenate was achieved. The purified material contained two proteins that were both able to bind apolipoproteins AI, AII and AIV, but not low-density lipoprotein. Glycopeptidase F treatment showed the existence of a single protein bearing either N-linked high-mannose or complex oligosaccharide chains. The purified material showed an apparent molecular mass of 80 +/- 9 kDa by h.p.l.c. on a TSKG 3000 SW column. Rabbit polyclonal antibodies directed against the purified material revealed two protein bands of 80 and 92 kDa after SDS/PAGE under reducing conditions and immunoblotting. These bands were undetectable in growing Ob17PY cells previously shown not to bind the various apolipoproteins A and not to undergo cholesterol efflux, whereas they were conspicuous in growth-arrested Ob17PY cells which have recovered these properties.

Apolipoproteins govern lipoprotein metabolism and are promising biomarkers of metabolic and cardiovascular diseases. Unlike immunoassays, MS enables the quantification and phenotyping of multiple apolipoproteins. Hence, here, we aimed to develop a LC-MS/MS assay that can simultaneously quantitate 18 human apolipoproteins [A-I, A-II, A-IV, A-V, B48, B100, C-I, C-II, C-III, C-IV, D, E, F, H, J, L1, M, and (a)] and determined apoE, apoL1, and apo(a) phenotypes in human plasma and serum samples. The plasma and serum apolipoproteins were trypsin digested through an optimized procedure and peptides were extracted and analyzed by LC-MS/MS. The method was validated according to standard guidelines in samples spiked with known peptide amounts. The LC-MS/MS results were compared with those obtained with other techniques, and reproducibility, dilution effects, and stabilities were also assessed. Peptide markers were successfully selected for targeted apolipoprotein quantification and phenotyping. After optimization, the assay was validated for linearity, lower limits of quantification, accuracy (biases: –14.8% to 12.1%), intra-assay variability [coefficients of variation (CVs): 1.5–14.2%], and inter-assay repeatability (CVs: 4.1–14.3%). Bland-Altman plots indicated no major statistically significant differences between LC-MS/MS and other techniques. The LC-MS/MS results were reproducible over five repeated experiments (CVs: 1.8–13.7%), and we identified marked differences among the plasma and serum samples. The LC-MS/MS assay developed here is rapid, requires only small sampling volumes, and incurs reasonable costs, thus making it amenable for a wide range of studies of apolipoprotein metabolism. We also highlight how this assay can be implemented in laboratories.

ABSTRACT Mice contain a serum factor capable of inactivating some subgroups of murine leukemia viruses. This leukemia virus-inactivating factor (LVIF) is distinct from immunoglobulin and complement; it has been associated with lipoprotein serum fractions and may be an apolipoprotein. The present study demonstrates that some Swiss-derived inbred strains are LVIF negative. Genetic crosses show this factor to be under control of a single gene that maps to distal chromosome 10 at or near the gene encoding a minor serum apolipoprotein, apolipoprotein F (ApoF). To evaluate this gene as a potential candidate for LVIF, the mouse ApoF gene was cloned and sequenced and its expression was assessed in LVIF-positive and -negative mice; no obvious differences were detected, suggesting that LVIF is under the control of a distinct linked gene.

ABSTRACT A recent study showed that F-spondin, a protein associated with the extracellular matrix, interacted with amyloid precursor protein (APP) and inhibited β-secretase cleavage. F-spondin contains a thrombospondin domain that we hypothesized could interact with the family of receptors for apolipoprotein E (apoE). Through coimmunoprecipitation experiments, we demonstrated that F-spondin interacts with an apoE receptor (apoE receptor 2 [ApoEr2]) through the thrombospondin domain of F-spondin and the ligand binding domain of ApoEr2. Full-length F-spondin increased coimmunoprecipitation of ApoEr2 and APP in transfected cells and primary neurons and increased surface expression of APP and ApoEr2. Full-length F-spondin, but none of the individual F-spondin domains, increased cleavage of APP and ApoEr2, resulting in more secreted forms of APP and ApoEr2 and more C-terminal fragments (CTF) of these proteins. In addition, full-length F-spondin, but not the individual domains, decreased production of the β-CTF of APP and Aβ in transfected cells and primary neurons. The reduction in APP β-CTF was blocked by receptor-associated protein (RAP), an inhibitor of lipoprotein receptors, implicating ApoEr2 in the altered proteolysis of APP. ApoEr2 coprecipitated with APP α- and β-CTF, and F-spondin reduced the levels of APP intracellular domain signaling, suggesting that there are also intracellular interactions between APP and ApoEr2, perhaps involving adaptor proteins. These studies suggest that the extracellular matrix molecule F-spondin can cluster APP and ApoEr2 together on the cell surface and affect the processing of each, resulting in decreased production of Aβ.

La stéatohépatite métabolique (Non-Alcoholic Fatty Liver Disease, NAFLD) est une maladie hépatique chronique et progressive incluant plusieurs manifestations cliniques allant de la stéatose hépatique seule à la stéatohépatite (ou NASH). Ces changements dans le foie ont un impact significatif sur la physiologie globale et indiquent un risque important de mortalité par les maladies cardiovasculaires et le carcinome hépatocellulaire. Toutefois, les mécanismes moléculaires conduisant à l’évolution de la NAFLD vers la NASH restent mal connus. Grâce à une analyse transcriptomique non biaisée, nous avons identifié l’Apolipoprotéine F (ApoF) dont l’expression est inversement corrélée avec la stéatose et réduite de 50% chez les patients atteints de NASH. L’ApoF est secrétée exclusivement par le foie et est associée aux lipoprotéines de haute densité (HDL) et de basse densité (LDL). De précédentes études fonctionnelles ont montré que l’ApoF favorisait le transport inverse du cholestérol chez la souris. Ces résultats suggèrent que l’ApoF pourrait affecter le développement de la NAFLD et/ou de ses complications cardiovasculaires.Toutefois, le rôle précis de l’ApoF dans le métabolisme des lipoprotéines reste mal connu. Ainsi, au cours de ce projet, nous avons mis en évidence un nouveau rôle de l'ApoF. Nos résultats montrent que la surexpression de l'APOF chez la souris est associée à une diminution des taux plasmatiques de triglycérides (TG) à jeun. Elle favorise à la fois la sécrétion des VLDL et la clairance des particules riches en TG via l’augmentation de leur recapture hépatique probablement par l'activation de la voie SREBP2.Nous avons ensuite cherché à déterminer l’impact de la modulation de l’expression hépatique de l’ApoF sur le développement de la NAFLD chez des souris nourries avec un régime riche en gras supplémenté en sucrose et en cholestérol permettant d’induire la NASH. De manière surprenante, nos résultats montrent que la surexpression de l'APOF hépatique dans le contexte de la NAFLD semble être délétère. Nous observons, dans ce cas, une aggravation de l'inflammation hépatique et des changements défavorables dans les lipides plasmatiques (réduction du HDL-C et augmentation du LDL-C). A l’inverse, la délétion totale de l’ApoF semble protéger du développement de la pathologie. Ainsi, nos résultats suggèrent que la diminution de l’expression de l’APOF hépatique chez les patients atteints de NAFLD pourrait être un mécanisme compensatoire visant à empêcher un effet délétère de l’activité de l’ApoF. Toutefois, des études complémentaires sont indispensables pour confirmer le rôle de l’ApoF dans le développement de la NAFLD
Non-Alcoholic Fatty Liver Disease (NAFLD) is a chronic, progressive disease which includes a spectrum of disease states ranging from isolated hepatic steatosis to steatohepatitis (or NASH). These changes in the liver have a significant impact on overall physiology and indicate higher risk of mortality from cardiovascular disease and hepatocellular carcinoma. However, the molecular mechanisms driving NAFLD evolution to NASH remain poorly understood. Through an unbiased transcriptomic analysis, we identified Apolipoprotein F (ApoF) whose expression is inversely correlated with steatosis and reduced ~ 50% in subjects with NASH. ApoF is secreted exclusively from the liver and found associated with high-density (HDL) and low-density lipoprotein (LDL) particles. Previous functional studies of ApoF have shown that ApoF favors reverse cholesterol transport in mice. These results suggest ApoF could affect NAFLD development and/or its cardiovascular complications.However, the precise role of ApoF in lipoprotein metabolism remains poorly understood. In this project, we have identified a new role for ApoF. Our results show that overexpression of APOF in mice is associated with a decrease in fasting plasma triglycerides (TG) levels by promoting both VLDL secretion and clearance of TG-rich particles via an increase in their hepatic uptake, probably through activation of the SREBP2 pathway.Subsequently, we sought to determine the impact of modulating hepatic ApoF expression on the development of NAFLD in mice fed with a high fat diet supplemented with sucrose and cholesterol, which induces NASH. Surprisingly, our results show that raising the level of hepatic APOF in the context of NAFLD may rather be deleterious. We observed an aggravation of hepatic inflammation and unfavorable changes in plasma lipids (reduced HDL-C and increased LDL-C) in mice overexpressing APOF compared to GFP after being fed the NASH-inducing diet. Similarly, total deletion of ApoF does not seem to accelerate the development of the disease. Thus, our results suggest that the decrease in hepatic APOF expression in NAFLD patients may be a compensatory mechanism to prevent a deleterious effect of ApoF activity. However, further studies are needed to confirm the role of ApoF in the development of NAFLD