Lupus autoimmunity altered by cellular methylation metabolism

Abstract

Modifications of both DNA and protein by methylation are key factors in normal T and B cell immune responses as well as in the development of autoimmune disease. For example, the failure to maintain the methylation status of CpG dinucleotides in DNA triggers T cell autoreactivity. Methylated proteins are known targets of autoimmunity, including the symmetrical dimethylarginine residues of SmD1 and SmD3 in SLE. Herein, we demonstrate that altering the metabolism of S-adenosylmethionine (SAM), the major methyl donor for transmethylation reactions, can suppress T cell immunity. A by-product of SAM metabolism, 5′-deoxy-5′-methylthioadenosine (MTA), and an indirect inhibitor of methyltransferases, inhibits T cell responses including T cell activation markers, Th1/Th2 cytokines and TCR-related signaling events. Moreover, treatment of the lupus-prone MRL/lpr mouse with MTA markedly ameliorates splenomegaly, lymphadenopathy, autoantibody titers as well as IgG deposition and cellular infiltration in the kidney. Incubation of cells with SAM, which increases intracellular MTA levels, inhibits both TCR-mediated T cell proliferation and BCR (anti-IgM)-triggered B cell proliferation in a dose-dependent manner. These studies define the central role of MTA and SAM in immune responses and provide a simple approach to altering lymphocyte transmethylation and T cell mediated autoimmune syndromes.

Keywords::

• Transmethylation
• methylthioadenosine
• S-adenosylmethionine
• CD4⁺ T cells
• SLE

Acknowledgements

We are grateful to the Abnova Corp. for providing the MTA phosphorylase recombinant protein for our present studies. We also thank Professor Mark Shlomchik for valuable suggestions and generous gift of anti-IgG1 antibody for B cell antibody class-switching assays.

Declaration of interests: The authors report no conflicts of interest. This work was supported by National Institutes of Health Grant (AI-48120 and AR-41032) and the Alliance for Lupus Research to M.J.M., National Institutes of Health Grant (GM-026020) to S.G.C., Arthritis Foundation Postdoctoral Fellowship to M-L. Y. and Research Engineering Apprenticeship Program from Department of Defense to A.J.P.G. The authors are responsible for the content and the writing of this paper.