Divergent TIR signaling domains in TLR7 and TLR9 control opposing effects on systemic autoimmunity
Claire Leibler, Kayla B. Thomas, Coralie Josensi, Russell C. Levack, Shuchi Smita, Shinu John, Daniel J. Wikenheiser, Sheldon Bastacky, Sebastien Gingras, Kevin M. Nickerson, Mark J. Shlomchik
Claire Leibler, Kayla B. Thomas, Coralie Josensi, Russell C. Levack, Shuchi Smita, Shinu John, Daniel J. Wikenheiser, Sheldon Bastacky, Sebastien Gingras, Kevin M. Nickerson, Mark J. Shlomchik
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Research Article Autoimmunity Immunology

Divergent TIR signaling domains in TLR7 and TLR9 control opposing effects on systemic autoimmunity

Abstract

Toll like receptor (TLR) 7 and 9, endosomal sensors for RNA and DNA, are key mediators of autoreactivity. Although generally considered homologous, they paradoxically have opposing effects on lupus: TLR7 exacerbates the disease while TLR9 protects from it How they mediate opposing effects in autoimmunity remains undetermined. We hypothesized that differences in signaling qualities of the Toll-Interleukin 1 Receptor (TIR) domains of TLR7 and TLR9 could be responsible for their opposing effects. To test this, we introduced the TIR domain of TLR9 into the endogenous Tlr7 locus and the TLR7 TIR domain into the endogenous Tlr9 locus of mice, creating chimeric molecules termed TLR779 and TLR997. Lupus-prone MRL/lpr mice carrying Tlr779 had greatly ameliorated disease, while MRL/lpr mice carrying Tlr997 had markedly exacerbated disease compared with respective TlrWT mice. These experiments establish that TLR7 and TLR9 TIR domains have divergent properties and control disease quality, thus explaining the longstanding “TLR paradox”.

Authors

Claire Leibler, Kayla B. Thomas, Coralie Josensi, Russell C. Levack, Shuchi Smita, Shinu John, Daniel J. Wikenheiser, Sheldon Bastacky, Sebastien Gingras, Kevin M. Nickerson, Mark J. Shlomchik

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Figure 5

Differences in B cell signaling qualities driven by TLR999 or TLR997.

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Differences in B cell signaling qualities driven by TLR999 or TLR997. Tr...
Transcriptome analysis of bead-purified B cells from 5-week-old Tlr9+/– Tlr7–/– or Tlr997 Tlr7–/– female MRL/lpr mice that were stimulated with TLR9 agonist (CpG, 10 μg/ml) for 4 hours. (A) Number of differentially expressed genes (DEGs) identified using the limma R package (log2 FC > 0.5, and FDR-corrected P value of < 0.05). (B) Bubble plots show the top 15 reactome pathways enriched in Tlr997 (purple bubbles) and Tlr9+/– (salmon bubbles) regulated genes from the Tlr997 (stim) vs Tlr9+/– (stim) comparison. Bubble size reflects the number of genes in the pathway that are also differentially expressed in Tlr997 vs Tlr9+/–. Enrichment was calculated using Fisher’s exact test (with all expressed genes as background) followed by Storey’s Q value FDR correction. (C) Volcano plot representing the DEGs between Tlr997 and Tlr9+/– CpG-stimulated B cells. The significant DEGs (log2 FC > 0.5) were annotated based on the reported functions of their corresponding proteins in B cell activation (green dots), cell death (yellow dots), TLR-mediated inflammation (red dots), negative regulation of TLR-mediated inflammation and/or B cell activation (blue dots), or if the genes were IFN-induced genes (pink dots). (D) Diagram depicting how proteins encoded by the curated DEGs in C could promote or regulate NF-κB, IRF, MAPK, IFN type 1 or 2 signaling pathways. In the cartoons of the chimeric TLR, TLR9-driven domains are in red and TLR7-derived domain in blue. (E) A TLR9-induced gene set signature for B cells of Tlr9+/+ BALB/c mice was generated. It comprises 1,724 upregulated genes (log2FC > 1 and FDR P value < 0.05) after a 4-hour in vitro CpG stimulation compared with unstimulated cells. Enrichment of this TLR9-induced gene set was assessed before and after TLR9 stimulation in Tlr9+/– B cells (left panel) and in Tlr997 (middle panel) B cells and between Tlr9+/– and Tlr997 stimulated B cells (right panel). The P value was calculated using the rankSumTestWithCorrelation function from the R limma package.