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ObjectivesAnticitrullinated 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.MethodsWith 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.ResultsIgM 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.ConclusionsBy 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.

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. 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. 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). 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.

Mitochondrial Reactive Oxygen Species Are Required for Hypothalamic Glucose Sensing Corinne Leloup 1 , Christophe Magnan 2 , Alexandre Benani 1 , Emilie Bonnet 1 , Thierry Alquier 1 , Géraldine Offer 1 , Audrey Carriere 1 , Alain Périquet 1 , Yvette Fernandez 1 , Alain Ktorza 2 , Louis Casteilla 1 and Luc Pénicaud 1 1 Laboratoire de Neurobiologie, Plasticité Tissulaire et Métabolisme, Institut L. Bugnard, Toulouse, France 2 Laboratory of the Physiopathology of Nutrition, Universite Paris, Paris, France Address correspondence and reprint requests to Corinne Leloup, UMR 5018-CNRS UPS, Institut L. Bugnard, IFR31, BP 84432, 31 432 Toulouse cedex 4, France. E-mail: coleloup{at}toulouse.inserm.fr Abstract The physiological signaling mechanisms that link glucose sensing to the electrical activity in metabolism-regulating hypothalamus are still controversial. Although ATP production was considered the main metabolic signal, recent studies show that the glucose-stimulated signaling in neurons is not totally dependent on this production. Here, we examined whether mitochondrial reactive oxygen species (mROS), which are physiologically generated depending on glucose metabolism, may act as physiological sensors to monitor the glucose-sensing response. Transient increase from 5 to 20 mmol/l glucose stimulates reactive oxygen species (ROS) generation on hypothalamic slices ex vivo, which is reversed by adding antioxidants, suggesting that hypothalamic cells generate ROS to rapidly increase glucose level. Furthermore, in vivo, data demonstrate that both the glucose-induced increased neuronal activity in arcuate nucleus and the subsequent nervous-mediated insulin release might be mimicked by the mitochondrial complex blockers antimycin and rotenone, which generate mROS. Adding antioxidants such as trolox and catalase or the uncoupler carbonyl cyanide m -chlorophenylhydrazone in order to lower mROS during glucose stimulation completely reverses both parameters. In conclusion, the results presented here clearly show that the brain glucose-sensing mechanism involved mROS signaling. We propose that this mROS production plays a key role in brain metabolic signaling. CCCP, carbonyl cyanide m-chlorophenylhydrazone ETC, electron transport chain KATP channel, ATP-sensitive K+ channel mROS, mitochondrial reactive oxygen species ROS, reactive oxygen species Footnotes The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “ advertisement ” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Accepted April 12, 2006. Received January 19, 2006. DIABETES

Enhanced Hypothalamic Glucose Sensing in Obesity: Alteration of Redox Signaling Anne-Laure Colombani 1 , Lionel Carneiro 1 , Alexandre Benani 1 , Anne Galinier 1 , Tristan Jaillard 1 , Thibaut Duparc 1 , Géraldine Offer 1 , Anne Lorsignol 1 , Christophe Magnan 2 , Louis Casteilla 1 , Luc Pénicaud 1 and Corinne Leloup 1 1 Métabolisme, Plasticité et Mitochondrie, Unité Mixte de Recherche 5241, Centre National de la Recherche Scientifique, Université Paul Sabatier, Toulouse, France; 2 Physiopathologie de la Nutrition, Unité Mixte de Recherche 7059, Centre National de la Recherche Scientifique, Université Denis Diderot, Paris, France. Corresponding author: Corinne Leloup, leloup{at}cict.fr . Abstract OBJECTIVE Recent data demonstrated that glucose sensing in different tissues is initiated by an intracellular redox signaling pathway in physiological conditions. However, the relevance of such a mechanism in metabolic disease is not known. The aim of the present study was to determine whether brain glucose hypersensitivity present in obese Zücker rats is related to an alteration in redox signaling. RESEARCH DESIGN AND METHODS Brain glucose sensing alteration was investigated in vivo through the evaluation of electrical activity in arcuate nucleus, changes in reactive oxygen species levels, and hypothalamic glucose-induced insulin secretion. In basal conditions, modifications of redox state and mitochondrial functions were assessed through oxidized glutathione, glutathione peroxidase, manganese superoxide dismutase, aconitase activities, and mitochondrial respiration. RESULTS Hypothalamic hypersensitivity to glucose was characterized by enhanced electrical activity of the arcuate nucleus and increased insulin secretion at a low glucose concentration, which does not produce such an effect in normal rats. It was associated with 1 ) increased reactive oxygen species levels in response to this low glucose load, 2 ) constitutive oxidized environment coupled with lower antioxidant enzyme activity at both the cellular and mitochondrial level, and 3 ) overexpression of several mitochondrial subunits of the respiratory chain coupled with a global dysfunction in mitochondrial activity. Moreover, pharmacological restoration of the glutathione hypothalamic redox state by reduced glutathione infusion in the third ventricle fully reversed the cerebral hypersensitivity to glucose. CONCLUSIONS The data demonstrated that obese Zücker rats' impaired hypothalamic regulation in terms of glucose sensing is linked to an abnormal redox signaling, which originates from mitochondria dysfunction. Footnotes The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Received January 25, 2009. Accepted June 22, 2009. © 2009 by the American Diabetes Association.