IgM and IgA Rheumatoid Factors Purified from Rheumatoid Arthritis Sera Boost the Fc Receptor– and Complement-Dependent Effector Functions of the Disease-Specific Anti–Citrullinated Protein Autoantibodies

International audienceRheumatoid factors (RF) and the disease-specific anti-citrullinated protein autoantibodies (ACPA) coexist in the joints of rheumatoid arthritis (RA) patients where they probably contribute to synovitis. We investigated the influence of IgM and IgA RF on the FcR- and complement-dependent effects of ACPA immune complexes (ACPA-IC). When stimulated by ACPA-IC formed in the presence of IgM RF or IgA RF fractions purified from RA serum pools, M-CSF-generated macrophages skewed their cytokine response toward inflammation, with increases in the TNF-α/IL-10 ratio and in IL-6 and IL-8 secretion, and decreases in the IL-1Ra/IL-1β ratio. In the IgM RF-mediated amplification of the inflammatory response of macrophages, the participation of an IgM receptor was excluded, notably by showing that they did not express any established receptor for IgM. Rather, this amplification depended on the IgM RF-mediated recruitment of more IgG into the ACPA-IC. However, the macrophages expressed FcαRI and blocking its interaction with IgA inhibited the IgA RF-mediated amplification of TNF-α secretion induced by ACPA-IC, showing its major implication in the effects of RF of the IgA class. LPS further amplified the TNF-α response of macrophages to RF-containing ACPA-IC. Lastly, the presence of IgM or IgA RF increased the capacity of ACPA-IC to activate the complement cascade. Therefore, specifically using autoantibodies from RA patients, the strong FcR-mediated or complement-dependent pathogenic potential of IC including both ACPA and IgM or IgA RF was established. Simultaneous FcR triggering by these RF-containing ACPA-IC and TLR4 ligation possibly makes a major contribution to RA synovitis

La fission mitochondriale induite par le glucose est indispensable à la signalisation ROS lors de la détection hypothalamique de l'hyperglycémie / The mitochondrial fission induced by glucose is essential to the ROS signaling in hypothalamic detection of hyperglycemia

International audienceNous avons montré que la détection hypothalamique de l'hyperglycémie (HG) fait intervenir une signalisation ROS d'origine mitochondriale, laquelle est. indispensable aux réponses effectrices, dont la sécrétion d'insuline. Par ailleurs, des études récentes montrent que la morphologie des mitochondries. varie lors de l'HG, morphologie qui est dépendante de la dynamique mitochondriale, modifiant alors la production de ROS. Ainsi, l'inhibition de la fission. mitochondriale diminue la production de ROS lors d'une hyperglycémie dans l'hépatocyte par exemple. Objectif : Comprendre si, in vivo, la. signalisation par les ROS lors du « glucose sensing » hypothalamique, implique la dynamique mitochondriale, et plus particulièrement la fission. Matériels et Méthodes. L'inhibition de Drp1 (fission), est réalisée par transfection de siRNA en cultures hypothalamiques pour la validation des siRNA, soit par injection dans. le noyau arqué de rat, les animaux témoins sont transfectés par un siRNA contrôle. L'inhibition est évaluée par l'étude du réseau mitochondrial (in. vitro) et Western blot (in vivo). La prise alimentaire (PA), le poids, la glycémie et l'insulémie sont suivis avant et après transfection (5 jours). La. détection du glucose dans l'hypothalamus est évaluée par cfos, marqueur d'activation cellulaire, et en termes de production de ROS après injection. d'un bolus de glucose par la carotide, laquelle déclenche un pic de sécrétion d'insuline. Résultats. L'inhibition de la fission mitochondriale dans le noyau arqué entraine une inhibition de la sensibilité au glucose. Ceci se traduit par la diminution de. production de ROS lors de l'injection de glucose vers le cerveau dont la conséquence est une diminution de la sécrétion d'insuline. Ceci entraîne. également des défauts de régulation de la PA : les animaux ayant reçu les siRNA Drp1 présentent une augmentation de leur prise alimentaire, qui se. traduit par un gain de poids plus important que chez les rats siRNA témoins. Discussion. Conclusion. Ces résultats montrent que la morphologie mitochondriale est requise pour la détection du glucose par le NA hypothalamique, en termes de régulation. de la PA et de sécrétion d'insuline

IgM rheumatoid factor amplifies the inflammatory response of macrophages induced by the rheumatoid arthritis-specific immune complexes containing anticitrullinated protein antibodies

International audienceObjectives: Anticitrullinated protein antibodies (ACPA) are specifically associated with rheumatoid arthritis (RA) and produced in inflamed synovial membranes where citrullinated fibrin, their antigenic target, is abundant. We showed that immune complexes containing IgG ACPA (ACPA-IC) induce FcγR-mediated tumour necrosis factor (TNF)-α secretion in macrophages. Since IgM rheumatoid factor (RF), an autoantibody directed to the Fc fragment of IgG, is also produced and concentrated in the rheumatoid synovial tissue, we evaluated its influence on macrophage stimulation by ACPA-IC.Methods: With monocyte-derived macrophages from more than 40 healthy individuals and different human IgM cryoglobulins with RF activity, using a previously developed human in vitro model, we evaluated the effect of the incorporation of IgM RF into ACPA-IC. Results: IgM RF induced an important amplification of the TNF-α secretion. This effect was not observed in monocytes and depended on an increase in the number of IgG-engaged FcγR. It extended to the secretion of interleukin (IL)-1β and IL-6, was paralleled by IL-8 secretion and was not associated with overwhelming secretion of IL-10 or IL-1Ra. Moreover, the RF-induced increased proinflammatory bioactivity of the cytokine response to ACPA-IC was confirmed by an enhanced, not entirely TNF-dependent, capacity of the secreted cytokine cocktail to prompt IL-6 secretion by RA synoviocytes. Conclusions: By showing that it can greatly enhance the proinflammatory cytokine response induced in macrophages by the RA-specific ACPA-IC, these results highlight a previously undescribed, FcγR-dependent strong proinflammatory potential of IgM RF. They clarify the pathophysiological link between the presence of ACPA and IgM RF, and RA severity

In Rheumatoid Arthritis Patients, HLA-DRB1*04:01 and Rheumatoid Nodules Are Associated With ACPA to a Particular Fibrin Epitope

International audienceObjectives Rheumatoid arthritis (RA) is associated with HLA-DRB1 genes encoding the shared epitope (SE), a 5-amino acid motive. RA is usually preceded by the emergence of anti-citrullinated protein/peptide antibodies (ACPAs). Citrulline is a neutral amino acid resulting from post-translational modification of arginine involved in peptidic bounds (arginyl residue) by PeptidylArginine Deiminases (PADs). ACPAs recognize epitopes from citrullinated human fibrin(ogen) (hFib) and can be specifically detected by the AhFibA assay. Five citrullinated peptides derived from hFib together represent almost all of the epitopes recognized by patients with ACPA-positive RA, namely: α36–50cit, α171–185cit, α501–515cit, α621–635cit, and β60–74cit. The use of antibody fine specificities as markers of clinical phenotypes has become a major challenge. Our objective was to study whether RA clinical characteristics and HLA-DRB1 genetic background were associated with a specific reactivity against the epitopes borne by the five peptides. Methods 184 ACPA-positive RA patients fulfilling the 2010 ACR/EULAR criteria were studied. Patient characteristics including HLA-DRB1 genotype, were collected from their medical files. Anti-CCP2 antibodies, AhFibA, and antibodies against the five citrullinated hFib (hFib-cit) peptides were analyzed by ELISA. Results Anti-α505-515cit antibodies were associated with HLA-DRB1*04:01 (OR = 5.52 [2.00 – 13.64]; p = 0.0003). High level anti-α505-515cit antibodies were associated with rheumatoid nodules (OR = 2.71 [1.00 – 7.16], p= 0.044). Conclusion Immune complexes containing anti-α501-515cit antibodies and rheumatoid factors might be involved in the development of rheumatoid nodules on the HLA-DRB1*04:01 background. Apheresis of these epitope-specific antibodies might be a new therapeutic opportunity for patients with rheumatoid nodules

Importance of mitochondrial dynamin-related protein 1 in hypothalamic glucose sensitivity in rats.

International audienceAIMS: Hypothalamic mitochondrial reactive oxygen species (mROS)-mediated signaling has been recently shown to be involved in the regulation of energy homeostasis. However, the upstream signals that control this mechanism have not yet been determined. Here, we hypothesize that glucose-induced mitochondrial fission plays a significant role in mROS-dependent hypothalamic glucose sensing. RESULTS: Glucose-triggered translocation of the fission protein dynamin-related protein 1 (DRP1) to mitochondria was first investigated in vivo in hypothalamus. Thus, we show that intracarotid glucose injection induces the recruitment of DRP1 to VMH mitochondria in vivo. Then, expression was transiently knocked down by intra-ventromedial hypothalamus (VMH) DRP1 siRNA (siDRP1) injection. 72 h post siRNA injection, brain intracarotid glucose induced insulin secretion, and VMH glucose infusion-induced refeeding decrease were measured, as well as mROS production. The SiDRP1 rats decreased mROS and impaired intracarotid glucose injection-induced insulin secretion. In addition, the VMH glucose infusion-induced refeeding decrease was lost in siDRP1 rats. Finally, mitochondrial function was evaluated by oxygen consumption measurements after DRP1 knock down. Although hypothalamic mitochondrial respiration was not modified in the resting state, substrate-driven respiration was impaired in siDRP1 rats and associated with an alteration of the coupling mechanism. INNOVATION AND CONCLUSION: Collectively, our results suggest that glucose-induced DRP1-dependent mitochondrial fission is an upstream regulator for mROS signaling, and consequently, a key mechanism in hypothalamic glucose sensing. Thus, for the first time, we demonstrate the involvement of DRP1 in physiological regulation of brain glucose-induced insulin secretion and food intake inhibition. Such involvement implies DRP1-dependent mROS production