The rheumatoid arthritis shared epitope increases cellular susceptibility to oxidative stress by antagonizing an adenosine-mediated anti-oxidative pathway.
We have recently demonstrated that the rheumatoid arthritis (RA) shared epitope (SE) acts as a ligand that triggers nitric oxide (NO) signaling in opposite cells. Given the known pro-oxidative effect of NO and the proposed role of oxidative stress in the pathogenesis of RA, this study explores whether SE-triggered signaling can increase cellular oxidative stress. cAMP levels, adenylyl cyclase activity, and protein kinase A activity were measured using commercial kits. Generation of reactive oxygen species (ROS) was quantified using the fluorochrome dichlorofluorescein diacetate. Oxidative DNA damage was quantified using the single-cell electrophoresis technique. Here, we report that cells exposed to cell surface SE-positive HLA-DR (human leukocyte antigen-DR) molecules, to cell-free recombinant proteins genetically engineered to express the SE motif, or to SE-positive synthetic peptide showed diminished cAMP-dependent signaling, increased ROS levels, and higher vulnerability to oxidative DNA damage. Introduction of single amino acid substitutions into SE-positive peptides revealed a consensus five-amino acid sequence motif of Q/R-K/R-X-X-A that is necessary and sufficient for SE-triggered signaling. The pro-oxidative effect of the SE could be reversed by inhibiting NO production. We conclude that the SE acts as a signaling ligand that activates an NO-mediated pro-oxidative pathway. The potential contribution of this signaling aberration to RA pathogenesis is discussed.
Ling
Song
S
Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109-0680, USA. songlin@med.umich.edu
Li
Zhanguo
Z
Borschukova
Olga
O
Xiao
Liqun
L
Pumpens
Paul
P
Holoshitz
Joseph
J
D000241:Adenosine / Q000494:pharmacology*; D000975:Antioxidants / Q000378:metabolism / Q000494:pharmacology*; D001172:Arthritis, Rheumatoid / Q000276:immunology / Q000378:metabolism*; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D004198:Disease Susceptibility / Q000276:immunology / Q000378:metabolism; D018985:Epitopes, B-Lymphocyte / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D017382:Reactive Oxygen Species / Q000276:immunology / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*
D000975:Antioxidants; D018985:Epitopes, B-Lymphocyte; D017382:Reactive Oxygen Species; D000241:Adenosine