Obesity provokes an imbalance in the immune system, including an aberrant type I interferon response during some viral infections and after TLR stimulation. SOCS3 overexpression and altered systemic leptin levels could be responsible for the reduced type I interferon production in people with obesity and, eventually, significantly increase the risk of viral infection. The aim of this study was to determine whether SOCS3- and leptin-induced tolerance are responsible for the reduced type I interferon production in people with obesity. SOCS3 overexpression in PBMCs from people with obesity was inhibited with the small interfering RNA (siRNA) assay, and leptin-induced tolerance was evaluated in PBMCs from non-obese volunte\ers and U937 cells treated with TLR ligands. SOCS3, but not SOCS1, gene silencing via siRNA increased the type I interferon response in PBMCs obtained from people with obesity. On the other hand, leptin induced SOCS3 expression and inhibited type I interferons in PBMCs from healthy donors and in U937 monocytes stimulated with TLR ligands. Taken together, these results demonstrate that reduced type I interferon production in obesity is caused by SOCS3 overexpression as well as tolerance induced by leptin. Here, we demonstrate a key role of leptin and SOCS3 in inhibiting the type I interferon response during obesity.

Human monocyte-derived dendritic cells (DCs) exposed to pathogen-associated molecular patterns (PAMPs) undergo bioenergetic changes that influence the immune response. We found that stimulation with PAMPs enhanced glycolysis in DCs, whereas oxidative phosphorylation remained unaltered. Glucose starvation and the hexokinase inhibitor 2-deoxy-d-glucose (2-DG) modulated cytokine expression in stimulated DCs. Strikingly, IL23A was markedly induced upon 2-DG treatment, but not during glucose deprivation. Since 2-DG can also rapidly inhibit protein N-glycosylation, we postulated that this compound could induce IL-23 in DCs via activation of the endoplasmic reticulum (ER) stress response. Indeed, stimulation of DCs with PAMPs in the presence of 2-DG robustly activated inositol-requiring protein 1α (IRE1α) signaling and to a lesser extent the PERK arm of the unfolded protein response. Additional ER stressors such as tunicamycin and thapsigargin also promoted IL-23 expression by PAMP-stimulated DCs. Pharmacological, biochemical, and genetic analyses using conditional knockout mice revealed that IL-23 induction in ER stressed DCs stimulated with PAMPs was IRE1α/X-box binding protein 1-dependent upon zymosan stimulation. Interestingly, we further evidenced PERK-mediated and CAAT/enhancer-binding protein β-dependent trans-activation of IL23A upon lipopolysaccharide treatment. Our findings uncover that the ER stress response can potently modulate cytokine expression in PAMP-stimulated human DCs.

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