Purpose In systemic lupus erythematosus (SLE), lupus nephritis (LN) represents one of the most severe organ complications. LN is associated with persistent inflammation and perpetuated fibroblast activation, both determined by epigenetic mechanisms involving aberrant CpG DNA promoter methylation. During SLE progression, global methylation patterns are commonly lost. CpG DNA promoter methylation patterns are not limited to the kidney, circulating CpG-rich DNA is also detectable in the blood. However, little is known about its specific contribution to determining disease progression. In the kidney, CpG-rich DNA activates TLR9 signalling mechanisms involved in inflammation and fibrogenesis. Based on these observations, we hypothesised that CpG-rich DNA promoter fragments potentially accelerate renal inflammation and fibrogenesis in SLE-associated LN.
Methods First, CPG-rich DNA from blood samples of SLE patients with and without LN were collected. Then, we tested how these DNA promoter fragments influenced the LN phenotype in a TMPD (‘pristane’)-induced mouse model. The renal response to the administration of either human or synthetic methylated/unmethylated CpG-rich DNA oligodinucleotides (ODN) was observed. Downstream effects of the administration of circuclating CpG-rich DNA fragments on TLR9-signalling were analysed in endothelial cell cultures.
Results Circulating CpG-rich DNA promoter fragments are detectable in SLE patients‘ blood. LN was associated with accumulation of unmethylated CpG-rich DNA promoter fragments, implicating a mechanistic link. In a rodent model of pristane-induced lupus, administration of CpG-rich DNA (isolated from LN patients or synthetic unmethylated CpG-rich DNA ODN) worsened the renal phenotype. TLR9-mediated intrarenal inflammation can be therapeutically targeted by administration of synthetic methylated CpG-rich DNA oligonucleotides, ultimately associated with suppression of TLR9-mediated signalling responses and renal injury in experimental LN.
Conclusions Our results implicate accumulation of unmethylated CpG-rich promoter DNA fragments in LN. Furthermore. these unmethylated CpG-rich promoter DNA fragments causally contribute to TLR9-mediated inflammation and renal fibrogenesis and administration of methylated CpG-rich ODN attenuated intrarenal TLR9-mediated inflammatory signalling responses. Therefore, biomonitoring of CpG-rich promoter DNA fragments and modulation of intrarenal TLR9 signalling might be a promising therapeutical target in LN.
Statistics from Altmetric.com
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.