Serum Gp96 is a chaperone of complement-C3 during graft-versus-host disease
Antoine Seignez, … , Evelyne Kohli, Carmen Garrido
Antoine Seignez, … , Evelyne Kohli, Carmen Garrido
Published March 23, 2017
Citation Information: JCI Insight. 2017;2(6):e90531. https://doi.org/10.1172/jci.insight.90531.
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Research Article Transplantation

Serum Gp96 is a chaperone of complement-C3 during graft-versus-host disease

Abstract

Better identification of severe acute graft-versus-host disease (GvHD) may improve the outcome of this life-threatening complication of allogeneic hematopoietic stem cell transplantation. GvHD induces tissue damage and the release of damage-associated molecular pattern (DAMP) molecules. Here, we analyzed GvHD patients (n = 39) to show that serum heat shock protein glycoprotein 96 (Gp96) could be such a DAMP molecule. We demonstrate that serum Gp96 increases in gastrointestinal GvHD patients and its level correlates with disease severity. An increase in Gp96 serum level was also observed in a mouse model of acute GvHD. This model was used to identify complement C3 as a main partner of Gp96 in the serum. Our biolayer interferometry, yeast two-hybrid and in silico modeling data allowed us to determine that Gp96 binds to a complement C3 fragment encompassing amino acids 749–954, a functional complement C3 hot spot important for binding of different regulators. Accordingly, in vitro experiments with purified proteins demonstrate that Gp96 downregulates several complement C3 functions. Finally, experimental induction of GvHD in complement C3–deficient mice confirms the link between Gp96 and complement C3 in the serum and with the severity of the disease.

Authors

Antoine Seignez, Anne-Laure Joly, Killian Chaumonnot, Adonis Hazoumé, Michel Sanka, Guillaume Marcion, Christophe Boudesco, Arlette Hammann, Renaud Seigneuric, Gaetan Jégo, Patrick Ducoroy, Patrice Delarue, Patrick Senet, Cristina Castilla-Llorente, Eric Solary, Marie-Agnès Durey, Marie-Thérèse Rubio, Olivier Hermine, Evelyne Kohli, Carmen Garrido

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Figure 6

Gp96 effect on complement C3 activity.

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Gp96 effect on complement C3 activity. (A) Gp96 inhibits C3b cleavage by...
(A) Gp96 inhibits C3b cleavage by factors I and H. Upper panel: Western blot analysis of the α’-chain (C3b) and the α2-chain (iC3b and C3c) both labeled with anti-C3c antibody, and of the α1-dg-chain (iC3b) labeled with anti-C3d antibody, after C3b incubation (0.3 μM) with normal human serum, supplemented with factors I and H with or without purified human Gp96 (1.2 μM). Lower panel: densitometry quantification. Cleavage without Gp96 is rationalized to 1. Statistical analysis performed using a 2-tailed Mann-Whitney U test. *P < 0.05; **P < 0.01 (n = 4 or 5). (B) Gp96 effect on opsonophagocytosis. Flow cytometry analysis of phagocytosis by human purified macrophages of Alexa Fluor 488–conjugated (AF 488–conjugated) E. coli bioparticles after opsonization by healthy human serum with or without Gp96 (1.5 mM). A representative image of AF 488 fluorescence in living cells is shown: the filled gray curve represents opsonization without serum, gray line with serum alone, black line with serum and Gp96, and dotted black line with serum and “BSA in buffer.” Histograms of mean fluorescence intensity ± SEM are shown. Statistical analysis performed using a one-tailed Mann-Whitney U test. *P < 0.05 (n = 3). (C) Gp96 effect on opsonization. AF 488–E. coli bioparticles were incubated with serum with or without Gp96 (1.5 mM). C3 and C4 were determined by Western blot in supernatants after deesterification of proteins tagged on bioparticles. One representative experiment is shown (n = 3). (D) Microscopy on AF 488–bioparticles after C3 AF568 staining. Right panel: C3 bioparticle quantification (median of fluorescence of AF 568 staining ± SEM). Statistical analysis performed using a one-tailed Mann-Whitney U test. *P < 0.05 (n = 3). (E and F) Gp96 effect on complement activation pathways. (E) Antibody-coated sheep erythrocytes (for classical pathway) (n = 6) and (F) rabbit erythrocytes hemolysis (for alternative pathway) (n = 4), in presence of Gp96 or controls. Percent of hemolysis are shown. Statistical analysis performed using a 2-tailed Mann-Whitney U test. *P < 0.05; **P < 0.01 (E: n = 6; F: n = 4).