Background/Purpose: Recent data highlight that patients with Systemic Lupus Erythematosus (SLE) have defects in two main DNA repair pathways, namely nucleotide excision repair (NER) and DNA double-strand break repair and that increased apoptosis observed in SLE may be partly attributed to the deregulated DNA damage response (DDR) network. Herein, we tested the hypothesis that ongoing DNA damage is present in patients with systemic autoimmune rheumatic diseases.

Methods: Peripheral blood mononuclear cells (PBMCs) were isolated from patients with SLE (n=14), Rheumatoid Arthritis (RA) (n=23), Systemic Sclerosis (SSc) (n=8) and 34 healthy controls (HC). Endogenous DNA damage levels were assessed using single-cell gel electrophoresis (comet assay) of untreated PBMCs. Repairing capacity of the two subpathways of NER, i.e. global genome repair (GGR) and transcription-coupled repair (TCR), as well as interstrand cross-links (ICL) repair were assessed after ex vivo treatment of PBMCs with genotoxic agents. Chromatin organization and expression of critical DNA repair-associated genes were also examined.

Results: Higher levels of endogenous DNA damage were present in patients compared to HC [Olive Tail Moment units of HC: 4.0 (1.5-9.9), SLE: 9.0 (2.4-23.0), RA: 11.5 (3.4-35.6) and SSc: 12.1 (5.4-29.3, all p<0.01]. SLE patients and HC displayed similar DNA repair efficiencies of the transcribed strand of the active N-ras gene (repaired by TCR), but in SLE the repair in the non-transcribed strand of the active N-ras gene was slower, as well as in both strands of a non-coding DNA region located outside the N-ras gene (repaired by GGR, all p<0.001), showing that the previously observed deficiency of NER in SLE patients may be specifically attributed to reduced GGR capacity while TCR is preserved. Of interest, we found that the repair efficiency of GGR in different genomic loci was inversely correlated with the local chromatin condensation, with autoimmune disease patients exhibiting more condensed chromatin structures. Moreover, critical molecular components of NER [such as DDB1 and XPC genes (associated with the GGR subpathway) and XPA, LIG1, RPA1, ERCC2 genes (associated with both NER subpathways)] were significantly down-regulated in SLE, RA and SSc patients versus HC. Finally, although the repairing capacity of cytotoxic ICL-lesions was similar in both HC and autoimmune disease patients, higher accumulation of these lesions was observed in patients’ PBMCs, possibly due to the higher burden of unrepaired NER lesions (precursors of ICLs). Interestingly, individual ICL repair efficiencies were inversely correlated with apoptosis rates in the same cells, underlying the cytotoxic character of this lesion.

Conclusion: Our study demonstrates that increased ongoing, spontaneous DNA damage is present in SLE, RA and SSc, possibly due to epigenetically regulated defective DNA repair mechanisms. Further studies to uncover a potentially crucial role of these mechanisms in the pathogenesis of systemic autoimmunity are underway.

« Back to 2018 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/ongoing-dna-damage-chromatin-deregulation-and-defective-dna-damage-response-in-systemic-autoimmune-rheumatic-diseases/