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

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.

Toll-like receptors in immunity and inflammatory diseases: Past, present, and future

“…Furthermore, quinazoline derivative called CPG-52364 is a specific inhibitor of TLR7, TLR8, and TLR9 that has shown efficacy in SLE and other cancers [464]. Most recently, an aminoguanidine compound called guanabenz (2,6-dichlorobenzylidene aminoguanidine acetate) that is used as an antihypertensive drug is shown to prevent the activation of TLR9 upon stimulation with CpG ODNs or DNA immunoglobulin complexes in endosomes [465]. The drug inhibited TLR9 activation in both murine and human DCs and B cells in vitro [465].…”

“…Most recently, an aminoguanidine compound called guanabenz (2,6-dichlorobenzylidene aminoguanidine acetate) that is used as an antihypertensive drug is shown to prevent the activation of TLR9 upon stimulation with CpG ODNs or DNA immunoglobulin complexes in endosomes [465]. The drug inhibited TLR9 activation in both murine and human DCs and B cells in vitro [465]. Under in vivo conditions, guanabenz showed protection against CpG ODN induced systemic cytokine shock and a chemically induced autoimmune disease called SLE in mice [465].…”

“…The drug inhibited TLR9 activation in both murine and human DCs and B cells in vitro [465]. Under in vivo conditions, guanabenz showed protection against CpG ODN induced systemic cytokine shock and a chemically induced autoimmune disease called SLE in mice [465]. In addition to these direct agonists and antagonists of TLR signaling, future TLR based therapeutics will be comprised of miRNAs regulating TLR signaling and the host-derived negative regulators of TLR signaling (i.e.…”

Developmentally regulated PERK activity renders dendritic cells insensitive to subtilase cytotoxin-induced integrated stress response

“…Given the lack of ATF4 synthesis and the resistance of active DCs to mount an acute ISR, we investigated their capacity to produce pro-inflammatory cytokines and type-I IFN in a perturbed eIF2a-phosphorylation context. Importantly, we have previously shown that GADD34deficient GM-CSF BM-derived and spleen DCs, have a reduced capacity to produce different cytokines, like IFN-β (Clavarino et al, 2012b, Perego et al, 2018, further suggesting that GADD34 activity and potentially eIF2a dephosphorylation is an important process for TLR signaling and cytokine production in DCs, although contrasting with the data obtained in macrophages (Abdel-Nour et al, 2019). LPS and the dsRNA synthetic mimic polyriboinosinic:polyribocytidylic acid (poly(I:C)), that is recognized by TRIFdependent TLR3 and the MAVS-dependent cytosolic RNA helicases RIG-I and MDA5 (RLRs) Kagan, 2020, Ablasser andHur, 2020) were used to stimulate DCs (Fig.…”

Type I interferons and endoplasmic reticulum stress in health and disease

“…CHOP facilitates apoptosis via transcription of various pro-apoptotic genes like, growth arrest and DNA-damage inducible protein (GADD34), and ER oxidoreductase 1 alpha (ERO1α) (amongst others) (Brush et al, 2003;Fransson et al, 2014;Hollander et al, 2003;Kojima et al, 2003;Novoa et al, 2001). For instance, GADD34 directs protein phosphatase 1 (PP1) to de-phosphorylate the eIF2α protein thereby causing recommencement of (Cap-dependent) protein synthesis (Choy et al, 2015;Perego et al, 2018;Rojas et al, 2015). This resumption of protein synthesis overwhelms the protein-folding capacity of the ER, which is already dealing with proteotoxicity, thereby amplifying ER stress and pushing the cell toward cell death (Han et al, 2013;Haynes et al, 2004;Malhotra and Kaufman, 2011;Sano and Reed, 2013;Sovolyova et al, 2014;Thomas et al, 2013).…”