Background/Purpose: Accumulation of apoptotic cells leads to excessive autoantigen presentation and autoantibody formation in autoimmunity, whereas mandatory to avoid apoptosis is the efficient repair of DNA double-strand breaks (DSBs). Herein, we tested the hypothesis that in patients with lupus nephritis, a severe complication of the prototypic systemic autoimmune disease, the DSBs repair is deficient and linked with increased apoptosis in peripheral blood mononuclear cells.

Methods: The intrinsic DNA damage and the DNA repair capacity using γH2Ax foci measurement by confocal microscopy and comet assay, as well as the induction of apoptosis following ex vivo treatment with genotoxic drugs (cisplatin, melphalan) were evaluated in peripheral blood mononuclear cells from lupus nephritis patients (n=6). Healthy individuals (n=10), age- and gender-matched to patients were served as controls.

Results: We found that the intrinsic DNA damage was significantly higher in lupus patients than in healthy volunteers (p<0.01). Particularly, using comet assay, lupus patients showed Olive Tail Moment values of 15.8+2.3 arbitrary units, while healthy controls only 3.0+1.4 units. Also, using confocal microscopy, the percentage of the γH2AX positive cells was 13.6+1.8 in lupus patients and 4.6+0.9 in healthy controls. Moreover, the genotoxic agent-induced apoptosis rates were significantly higher in lupus than in control cells (p<0.01). That is, melphalan dose as low as 9.9+4.8μg/ml was sufficient to induce detectable levels of apoptosis in lupus patients, while healthy controls required doses of 32.3+7.7μg/ml. The corresponding values for cisplatin treatment were 29.8+8.3μg/ml and 67.7+5.5μg/ml, respectively. Finally, following ex vivo treatment of mononuclear cells with a genotoxic agent, DSBs repair efficiency was inversely correlated with the apoptosis rates of these cells, being significantly lower in lupus than in control cells (p<0.01). That is, melphalan-induced DNA damage was removed with t_1/2=9.1+2.4h in healthy controls and 51.3+7.6h in lupus patients, with the corresponding values for cisplatin-induced damage being 4.2+1.5h and 25.4+5.9h, respectively. Results in lupus cells were not associated with individual disease activity level or treatment modalities at the time of study.

Conclusion: We demonstrated that circulating mononuclear cells from lupus nephritis patients are characterized by higher intrinsic DNA damage and profoundly reduced DSBs repair capacity. Since failure to repair DNA lesions such as DSBs leads to mutations, genomic instability and induction of apoptosis, these results suggest a novel mechanism by which deficient repair of DSBs may contribute to the induction of systemic autoimmunity.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/deficient-repair-of-dna-double-strand-breaks-and-increased-apoptosis-in-patients-with-lupus-nephritis/