Human cDC1s display constitutive activation of the UPR sensor IRE1

Abstract

The intracellular mechanisms safeguarding DC function are of biomedical interest in several immune-related diseases. Type 1 conventional DCs (cDC1s) are prominent targets of immunotherapy typified by constitutive activation of the unfolded protein response (UPR) sensor IRE1. Through its RNase domain, IRE1 regulates key processes in cDC1s including survival, ER architecture and function. However, most evidence linking IRE1 RNase with cDC1 biology emerges from mouse studies and it is currently unknown whether human cDC1s also activate the enzyme to preserve cellular homeostasis. In this work, we report that human cDC1s constitutively activate IRE1 RNase in steady state, which is evidenced by marked expression of IRE1, XBP1s, and target genes, and low levels of mRNA substrates of the IRE1 RNase domain. On a functional level, pharmacological inhibition of the IRE1 RNase domain curtailed IL-12 and TNF production by cDC1s upon stimulation with TLR agonists. Altogether, this work demonstrates that activation of the IRE1/XBP1s axis is a conserved feature of cDC1s across species and suggests that the UPR sensor may also play a relevant role in the biology of the human lineage.

The Unfolded Protein Response Sensor IRE1 Regulates Activation of In Vitro Differentiated Type 1 Conventional DCs with Viral Stimuli

“…Even though the IRE1/XBP1s axis is well-recognized to contribute to innate immune responses upon PRR engagement, most of these studies emerged from work in macrophages and DC subsets that do not belong to the cDC1 lineage [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. Reports on activated cDC1s include parasite infection [ 29 ], and we reported that human/mouse cDC1s use IRE1 for optimal proinflammatory cytokine production using pharmacological IRE1 inhibitors [ 10 , 14 ]. To extend these findings and identify efficient IRE1 activators in differentiated cDC1s, we stimulated OP9-DL1 cDCs from ERAI mice with agonists of major families of PRRs: LPS (TLR4 agonist), Poly(I:C) (TLR3 agonist), Curdlan (Dectin-1 agonist), DMXAA (STING agonist), MDP (NOD2 agonist), and CpG (TLR9 agonist).…”

“…The advent of this methodology prompted us to investigate whether IRE1 activation is a feature that can be modeled in cDC1s fully differentiated in vitro. Along these lines, we recently reported that human cDC1s generated under this methodology spontaneously activate IRE1 RNase [ 14 ], which opens novel avenues for expanding studies of the IRE1/XBP1s axis also in mouse models.…”

Mechanical Ventilation-Related High Stretch Mainly Induces Endoplasmic Reticulum Stress and Thus Mediates Inflammation Response in Cultured Human Primary Airway Smooth Muscle Cells

“…ASMCs cultured under the high-stretch or static conditions with or without pretreatment of TUDCA (ER stress inhibitor) were evaluated for mRNA expression levels of genes associated with ER stress and inflammation, which could verify whether ER stress mediated the effects of high stretch on ASMCs via ER stress signaling and airway inflammation [ 50 ]. The mRNA expression level was measured by quantitative PCR (qPCR) with the associated primers purchased from General Biosystems (Anhui, China), as shown in Table S5 [ 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 ]. These primer sequences used in this study are all obtained from the literature and then checked by NCBI Primer-BLAST ( , freely available for any user, accessed on 5 October 2022).…”

The unfolded protein sensor IRE1a is essential for homeostatic dendritic cell maturation

“…Several labs meanwhile noted that IRE1 shows a higher basal activity in cDC1s compared to cDC2s [11][12][13][14][15] , still the mechanism explaining this subset speci c activation of IRE1 has remained enigmatic. A recent study proposed that antigen-derived peptides can engage IRE1 in a TAP1-dependent manner by binding the IRE1 lumenal domain upon their import in the ER 14 .…”