Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement
Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.
DNA Damage, T Cell Lymphopenia and Immunosenescence in Rheumatoid Arthritis.
Shao1, Lan, Fujii2, Hiroshi, Goronzy1, Jorg J., Weyand1, Cornelia M.
In RA, immune aging is accelerated by 2530 years. The immune system is homeostatically controlled; lymphocyte regeneration/proliferation compensates for cell attrition. Lymphocytes age prematurely if they proliferate excessively; imposed by too much loss or too little cell input. We have examined whether RA patients have higher T cell loss than age-matched controls by focusing on naive CD4 T cells which have not yet been recruited into any immune response. Specifically, we have examined signals and molecular mechanisms regulating survival of naive T cells that build the immune reserve.
Naive CD4 T cells from sero-positive RA patients and demographically matched controls were tested ex vivo for their susceptibility to apoptosis by cytometric analysis of 7AAD and Annexin V with and without T cell receptor stimulation. The load of damaged DNA was quantified by Comet assay and telomeric length was measured by modified qPCR. Repair mechanisms for telomeric and non-telomeric DNA were assessed through the analysis of three enzymatic systems involved in DNA repair/telomeric maintenance; telomerase and the phosphoinositide-1079-kinase-related protein kinases Ataxia-telangiectasia mutated (ATM) and DNA-dependent protein kinase catalytic subunit (DNA-PKcs). DNA damage sensing enzymes were knocked down by si-RNA technology or forcefully overexpressed by transfection.
Summary of Results:
Naive human CD4 T cells, both resting and triggered with anti-CD3/CD28, died through the intrinsic death pathways, regulated by pro- and anti-apoptotic Bcl-2 family members. RA CD4 T cells freshly isolated from patients or kept without stimulation ex vivo were highly susceptible to apoptosis with doubling of death rates (28.2% RA T cells vs. 15.1% control T cells; p=0.01). Increased apoptotic susceptibility coincided with accumulation of DNA double strand breaks (p=0.0001), suggesting that unrepaired DNA and telomeres shorten survival of naive T cells. Induction of the telomere repair enzyme telomerase was impaired in RA T cells (p=0.0001). Also, RA T cells insufficiently upregulated the damage-sensing enzyme ATM (p=0.008) but expressed high levels of DNA-PKcs transcripts and protein (p=0.03). Forced overexpression of telomerase or ATM and blockade of DNA-PKcs rescued RA T cells from apoptosis (p=0.008, 0.001 and 0.005, respectively). The shift in apoptotic threshold setting was not a consequence of therapy but was equally present in untreated RA patients (p=NS, Tx vs. non-Tx).
Naive CD4 T cells in RA patients are under genotoxic stress. Telomeres are shortened and insufficiently repaired and DNA doubles strand breaks accumulate. Repair pathways involving the enzyme ATM are suppressed. Chronic repair activity signaled by the DNA-PKcs pathway sustains cell-internal stress signals that harm the cells and lead to apoptosis. Excessive T cell loss strains homeostatic mechanisms and, by depleting the proliferative reserve of long-lived T cells, leads to premature immune aging. Mechanisms regulating intactness of telomeric and non-telomeric DNA should be considered in attempts to reset the dysfunctional immune system of RA patients.
To cite this abstract, please use the following information:
Shao, Lan, Fujii, Hiroshi, Goronzy, Jorg J., Weyand, Cornelia M.; DNA Damage, T Cell Lymphopenia and Immunosenescence in Rheumatoid Arthritis. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :1079