Defective removal of ribonucleotides from DNA promotes systemic autoimmunity
Claudia Günther, et al.
Claudia Günther, et al.
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Research Article

Defective removal of ribonucleotides from DNA promotes systemic autoimmunity

Abstract

Genome integrity is continuously challenged by the DNA damage that arises during normal cell metabolism. Biallelic mutations in the genes encoding the genome surveillance enzyme ribonuclease H2 (RNase H2) cause Aicardi-Goutières syndrome (AGS), a pediatric disorder that shares features with the autoimmune disease systemic lupus erythematosus (SLE). Here we determined that heterozygous parents of AGS patients exhibit an intermediate autoimmune phenotype and demonstrated a genetic association between rare RNASEH2 sequence variants and SLE. Evaluation of patient cells revealed that SLE- and AGS-associated mutations impair RNase H2 function and result in accumulation of ribonucleotides in genomic DNA. The ensuing chronic low level of DNA damage triggered a DNA damage response characterized by constitutive p53 phosphorylation and senescence. Patient fibroblasts exhibited constitutive upregulation of IFN-stimulated genes and an enhanced type I IFN response to the immunostimulatory nucleic acid polyinosinic:polycytidylic acid and UV light irradiation, linking RNase H2 deficiency to potentiation of innate immune signaling. Moreover, UV-induced cyclobutane pyrimidine dimer formation was markedly enhanced in ribonucleotide-containing DNA, providing a mechanism for photosensitivity in RNase H2–associated SLE. Collectively, our findings implicate RNase H2 in the pathogenesis of SLE and suggest a role of DNA damage–associated pathways in the initiation of autoimmunity.

Authors

Claudia Günther, Barbara Kind, Martin A.M. Reijns, Nicole Berndt, Manuel Martinez-Bueno, Christine Wolf, Victoria Tüngler, Osvaldo Chara, Young Ae Lee, Norbert Hübner, Louise Bicknell, Sophia Blum, Claudia Krug, Franziska Schmidt, Stefanie Kretschmer, Sarah Koss, Katy R. Astell, Georgia Ramantani, Anja Bauerfeind, David L. Morris, Deborah S. Cunninghame Graham, Doryen Bubeck, Andrea Leitch, Stuart H. Ralston, Elizabeth A. Blackburn, Manfred Gahr, Torsten Witte, Timothy J. Vyse, Inga Melchers, Elisabeth Mangold, Markus M. Nöthen, Martin Aringer, Annegret Kuhn, Kirsten Lüthke, Leonore Unger, Annette Bley, Alice Lorenzi, John D. Isaacs, Dimitra Alexopoulou, Karsten Conrad, Andreas Dahl, Axel Roers, Marta E. Alarcon-Riquelme, Andrew P. Jackson, Min Ae Lee-Kirsch

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Figure 4

Reduced proliferation and increased DNA damage response activation in SLE and AGS patient fibroblasts.

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Reduced proliferation and increased DNA damage response activation in SL...
(A) Reduced proliferation rate of fibroblasts from patients with SLE (SLE1 and SLE2) and AGS (AGS1 and AGS2) compared with the mean of 5 WT control fibroblast lines (2 children, 3 adults). P < 0.05 (3 and 5 hours), P < 0.001 (7 hours), AGS1 vs. WT, t test. (B) Cell cycle analysis of propidium iodide–stained fibroblasts after synchronization in G1 by 24 hours of serum starvation. Representative flow cytometry images depict cell cycle delay in RNase H2–deficient fibroblasts. (C) Activation of a p53-dependent DNA damage response in patient fibroblasts in the absence of exogenous genotoxic stress, as shown by increased levels of phosphorylated p53 (Ser15). The same immunoblot probed for β-actin shows equal loading. (D) Increased number of p16-positive cells in RNase H2–deficient fibroblasts, measured by flow cytometry. (E) Increased senescence in patient fibroblasts, measured by β-galactosidase staining. Scale bar: 100 μm. (F) Increased dsDNA damage in RNase H2–deficient human fibroblasts. dsDNA breaks were visualized by immunostaining of γH2AX (red) and 53BP1 (green). The number of nuclei with 0–3 foci stained for both (yellow) among 50 randomly selected cells was quantified. Original magnification, ×400. Data are mean and SEM (D and E) or mean and SD (A, B, and F) of 3 independent experiments per patient and 5 independent WT control cell lines (A and B) or of 4 experiments per patient and 5 WT controls (D–F). (B–F) *P < 0.05, **P < 0.01, #P < 0.001 versus WT, t test.