Guanabenz inhibits TLR9 signaling through a pathway that is independent of eIF2α dephosphorylation by the GADD34/PP1c complex.

Jessica Perego,Manuel A S Santos,Nathalie Bardin,Hong Liu,Evelina Gatti,Thien-Phong Vu Manh,Voahirana Camosseto,Philippe Pierre,Alexis Combes,Lionel Spinelli,Clarisse Bourbon,Laurent Chiche,Lionel Chasson,Andreia Mendes,Alexandre Dalet

doi:10.1126/scisignal.aam8104

Abstract

Endoplasmic reticulum (ER) stress triggers or amplifies inflammatory signals and cytokine production in immune cells. Upon the resolution of ER stress, the inducible phosphatase 1 cofactor GADD34 promotes the dephosphorylation of the initiation factor eIF2α, thereby enabling protein translation to resume. Several aminoguanidine compounds, such as guanabenz, perturb the eIF2α phosphorylation-dephosphorylation cycle and protect different cell or tissue types from protein misfolding and degeneration. We investigated how pharmacological interference with the eIF2α pathway could be beneficial to treat autoinflammatory diseases dependent on proinflammatory cytokines and type I interferons (IFNs), the production of which is regulated by GADD34 in dendritic cells (DCs). In mouse and human DCs and B cells, guanabenz prevented the activation of Toll-like receptor 9 (TLR9) by CpG oligodeoxynucleotides or DNA-immunoglobulin complexes in endosomes. In vivo, guanabenz protected mice from CpG oligonucleotide-dependent cytokine shock and decreased autoimmune symptom severity in a chemically induced model of systemic lupus erythematosus. However, we found that guanabenz exerted its inhibitory effect independently of GADD34 activity on eIF2α and instead decreased the abundance of CH25H, a cholesterol hydroxylase linked to antiviral immunity. Our results therefore suggest that guanabenz and similar compounds could be used to treat type I IFN-dependent pathologies and that CH25H could be a therapeutic target to control these diseases.

Highlights

The immunomodulating functions of dendritic cells (DCs), such as antigen presentation, are considerably enhanced after detection of cell damage–associated or pathogen-associated molecular patterns (PAMPs)
GBZ treatment partially phenocopies GADD34 genetic inactivation in DCs We have previously shown that IFN-b and IL-6 production in response to the double-stranded RNA (dsRNA) mimic polyriboinosinic:polyribocytidylic acid [poly(I:C)] is defective in granulocytemacrophage colony-stimulating factor (GM-CSF)–induced bone marrow (BM)– derived DCs from GADD34DC/DC mice [14]
We investigated whether this observation could be extended to other DC subsets and other Toll-like receptors (TLRs) ligands

Summary

Introduction

The immunomodulating functions of dendritic cells (DCs), such as antigen presentation, are considerably enhanced after detection of cell damage–associated or pathogen-associated molecular patterns (PAMPs). Most TLRs detect their ligand at the cell surface, except for TLR3, TLR7, TLR8, and TLR9, which are found in endosomes [2], where they are proteolytically activated and mediate nucleic acid recognition and signal transduction [3, 4]. TLR7 and TLR9, whose ligands are, respectively, single-stranded RNA and DNA with unmethylated cytosine-phosphate-guanine (CpG) motifs [5, 6], are expressed in a restricted subset of immune cells, including B cells or plasmacytoid DCs (pDCs), which specialize in the production of type I interferon (IFN) [7]. TLR9 and its DNA ligands must have access to specific endosome subsets to allow the recruitment and activation of the MyD88/IFN regulatory factor 7(IRF7)–dependent signaling pathway and to initiate type I IFN production [8]. TLR7and TLR9-expressing pDCs and B cells are key cellular players in the establishment and progression of several type I IFN– dependent diseases such as systemic lupus erythematosus (SLE) or Sjögren syndrome [9, 10]

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Conclusion