Inhibition of IRF5 hyperactivation protects from lupus onset and severity
Su Song, Saurav De, Victoria Nelson, Samin Chopra, Margaret LaPan, Kyle Kampta, Shan Sun, Mingzhu He, Cherrie D. Thompson, Dan Li, Tiffany Shih, Natalie Tan, Yousef Al-Abed, Eugenio Capitle, Cynthia Aranow, Meggan Mackay, William L. Clapp, Betsy J. Barnes
Su Song, Saurav De, Victoria Nelson, Samin Chopra, Margaret LaPan, Kyle Kampta, Shan Sun, Mingzhu He, Cherrie D. Thompson, Dan Li, Tiffany Shih, Natalie Tan, Yousef Al-Abed, Eugenio Capitle, Cynthia Aranow, Meggan Mackay, William L. Clapp, Betsy J. Barnes
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Research Article Autoimmunity Immunology

Inhibition of IRF5 hyperactivation protects from lupus onset and severity

Abstract

The transcription factor IFN regulatory factor 5 (IRF5) is a central mediator of innate and adaptive immunity. Genetic variations within IRF5 are associated with a risk of systemic lupus erythematosus (SLE), and mice lacking Irf5 are protected from lupus onset and severity, but how IRF5 functions in the context of SLE disease progression remains unclear. Using the NZB/W F1 model of murine lupus, we show that murine IRF5 becomes hyperactivated before clinical onset. In patients with SLE, IRF5 hyperactivation correlated with dsDNA titers. To test whether IRF5 hyperactivation is a targetable function, we developed inhibitors that are cell permeable, nontoxic, and selectively bind to the inactive IRF5 monomer. Preclinical treatment of NZB/W F1 mice with an inhibitor attenuated lupus pathology by reducing serum antinuclear autoantibodies, dsDNA titers, and the number of circulating plasma cells, which alleviated kidney pathology and improved survival. Clinical treatment of MRL/lpr and pristane-induced lupus mice with an inhibitor led to significant reductions in dsDNA levels and improved survival. In ex vivo human studies, the inhibitor blocked SLE serum–induced IRF5 activation and reversed basal IRF5 hyperactivation in SLE immune cells. We believe this study provides the first in vivo clinical support for treating patients with SLE with an IRF5 inhibitor.

Authors

Su Song, Saurav De, Victoria Nelson, Samin Chopra, Margaret LaPan, Kyle Kampta, Shan Sun, Mingzhu He, Cherrie D. Thompson, Dan Li, Tiffany Shih, Natalie Tan, Yousef Al-Abed, Eugenio Capitle, Cynthia Aranow, Meggan Mackay, William L. Clapp, Betsy J. Barnes

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Figure 3

N5-1 is predicted to bind to the C-terminal IAD of an inactive IRF5 monomer and inhibit phosphorylation of Ser462.

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N5-1 is predicted to bind to the C-terminal IAD of an inactive IRF5 mono...
(A) Schematic diagram of N5-1 (pink) binding to the C-terminal IAD of IRF5 from peptide docking using the Schrodinger suite (see Supplemental Methods). N5-1 stabilizes the nonphosphorylated, inactive IRF5 monomer. Serine phosphorylation sites are shown by orange circles. (B) PBMCs were preincubated with 10 μM inhibitor for 1 hour and stimulated with R848. p-IRF5 phosphorylation at Ser462 was detected by flow cytometry following gating on CD14+ monocytes. The fold change in p-IRF5 relative to unstimulated mock samples is shown. n = 5 independent samples from healthy donors. Data represent the mean ± SD. *P ≤ 0.05 and **P ≤ 0.01, by 1-way ANOVA. (C) On the basis of the binding of N5-1 to full-length inactive IRF5, we propose that the DBD masks the IAD of IRF5 and that the AID masks the C-terminal phosphorylation sites, thus stabilizing a closed, unphosphorylated conformation of the IRF5 monomer (left panel). In this conformation, the DBD α3 helix, which contains all the conserved residues and is responsible for protein-DNA contacts, is shielded. Upon phosphorylation, the AID unfolds, which unmasks the C-terminal phosphorylation sites and frees helix 5 for dimerization (right panel). The DBD will also be released from this folded, inactive position and exposed to DNA for binding. The colors correspond to the specified regions of IRF5 in the crystal structure (above) and the stick model (below). The DBD is indicated in green, the IAD in blue, and the AID in purple. The N5-1 sequence is shown in red in both models.