Oxidation and biotinylation of beta 2 glycoprotein I glycan chains induce an increase in its affinity for anionic phospholipids similar to that obtained by the addition of anti-beta 2 glycoprotein I or anti-cardiolipin antibodies

Exosomes: Revisiting their role as "garbage bags"

In recent years, the term "extracellular vesicle" (EV) has been used to define different types of vesicles released by various cells. It includes plasma membrane-derived vesicles (ectosomes/microvesicles) and endosome-derived vesicles (exosomes). Although it remains difficult to evaluate the compartment of origin of the two kinds of vesicles once released, it is critical to discriminate these vesicles because their mode of biogenesis is probably directly related to their physiologic function and/or to the physio-pathologic state of the producing cell. The purpose of this review is to specifically consider exosome secretion and its consequences in terms of a material loss for producing cells, rather than on the effects of exosomes once they are taken up by recipient cells. I especially describe one putative basic function of exosomes, that is, to convey material out of cells for off-site degradation by recipient cells. As illustrated by some examples, these components could be evacuated from cells for various reasons, for example, to promote "differentiation" or enhance homeostatic responses. This basic function might explain why so many diseases have made use of the exosomal pathway during pathogenesis.

Plasma apolipoprotein H limits HCV replication and associates with response to NS3 protease inhibitors-based therapy

BACKGROUND & AIMS

Chronic infection with HCV remains a public health problem with approximately 150 million people infected worldwide. HCV intersects with lipid metabolism for replication and entry; and plasma concentrations of apolipoproteins have been identified as predictors for response to therapy. Herein, we conducted a screen of plasma proteins, including all apolipoproteins, to identify correlates of response to pegylated-interferon/ribavirin (PR) and HCV non-structural protein 3 (NS3) inhibitors (i.e., telaprevir/boceprevir) therapy in treatment-experienced cirrhotic patients from the ANRS CUPIC cohort.

METHODS

We analysed 220 baseline plasma protein concentrations in 189 patients using Luminex technology and analyzed results.

RESULTS

We identified baseline levels of apolipoprotein H (apoH) as a surrogate marker for sustained virological response (SVR). Notably, increased plasma concentration of apoH, used in combination with known clinical parameters, established a robust model with improved classification of patients as likely to achieve SVR (AUC = 0.77, Se = 66%, Sp = 72%, NRI = 39%). Moreover, we provide mechanistic information that indicates a previously unidentified role for apoH during viral entry. Using a human liver slices HCV infection model, we demonstrate that apoH limits replication.

CONCLUSION

These data support testing of new biomarker strategies for the management of cirrhotic HCV patients and expand our understanding of how apoH may intersect with HCV infection.

Apolipoprotein H expression is associated with IL28B genotype and viral clearance in hepatitis C virus infection

BACKGROUND & AIMS

HCV requires host lipid metabolism for replication, and apolipoproteins have been implicated in the response to treatment.

METHODS

We examined plasma apolipoprotein concentrations in three cohorts of patients: mono-infected patients with symptomatic acute hepatitis C (aHCV); those undergoing treatment for chronic hepatitis C (cHCV); and HIV/HCV co-infected patients being treated for their chronic hepatitis C. We also evaluated associations between apolipoproteins and IL28B polymorphisms, a defined genetic determinant of viral clearance.

RESULTS

Plasma apolipoprotein H (ApoH) levels were significantly higher in patients who achieved spontaneous clearance or responded to pegylated-interferon/ribavirin therapy. Strikingly, patients carrying the IL28B rs12979860 CC SNP correlated with the plasma concentration of ApoH in all three cohorts. Both ApoH and IL28B CC SNP were associated with HCV clearance in univariate analysis. Additional multivariate analysis revealed that the association between IL28B and HCV clearance was closely linked to that of Apo H and HCV clearance, suggesting that both belong to the same biological pathway to clearance. The association between IL28B CC SNP and ApoH was not observed in healthy individuals, suggesting that early post-infection events trigger differential ApoH expression in an IL28B allele dependent manner.

CONCLUSIONS

This relationship identifies ApoH as the first induced protein quantitative trait associated with IL28B, and characterises a novel host factor implicated in HCV clearance.

Biotinylation of glycan chains in beta2 glycoprotein I induces dimerization of the molecule and its detection by the human autoimmune anti-cardiolipin antibody EY2C9

Binding of beta2GPI (beta2 glycoprotein I), a human plasma protein, to AnPLs (anionic phospholipids) plays a key role in the formation of antiphospholipid antibodies involved in autoimmune diseases like antiphospholipid syndrome or systemic lupus erythematosus. We recently showed that binding of beta2GPI to AnPLs was enhanced by biotinylation of its glycan chains with biotin-hydrazide. In the present study, we investigated why this chemical modification of beta2GPI increased both its affinity for AnPLs and its recognition by anti-cardiolipin antibodies. Electrophoretic analysis showed that: (i) high molecular mass beta2GPI (dimers and other oligomers) covalently coupled by imine bonds, were present in variable amounts in oxidized beta2GPI and in beta2GPI-bh (beta2GPI-biotin-hydrazide), but were absent in native beta2GPI; (ii) binding of beta2GPI-bh to phosphatidylserine-coated microtitre plates generated high molecular mass polymers in a time-dependent manner. Native beta2GPI did not polymerize in these conditions. These polymers did not bind more strongly to AnPLs than the monomer beta2GPI. However, in solution at 1 microM beta2GPI-bh essentially appeared as a dimer as revealed by light-scattering analysis. SPR (surface plasmon resonance) analysis showed that the increased affinity of beta2GPI-bh for AnPL monolayers was due to a lower dissociation rate constant compared with native beta2GPI. Finally, the monoclonal human aCL (auto-immune anti-cardiolipin antibody) EY2C9 bound to beta2GPI-bh but did not bind to monomeric native and oxidized beta2GPI. It is likely that the dimeric quaternary structure of beta2GPI-bh is in fact responsible for the appearance of the epitopes targeted by the EY2C9 antibody.