STAT3 and STAT5 Signaling Thresholds Determine Distinct Regulation for Innate Receptor-Induced Inflammatory Cytokines, and STAT3/STAT5 Disease Variants Modulate These Outcomes.

Genetic variants in the STAT3/STAT5A/STAT5B region are associated with immune-mediated diseases, including inflammatory bowel disease (IBD). However, how STAT3 and STAT5 regulate the critical balance between pro- and anti-inflammatory cytokines and how common disease-associated genetic variants (e.g., rs12942547) in the region modulate this balance are incompletely understood. We found that upon pattern-recognition receptor (PRR) stimulation of human monocyte-derived macrophages (MDMs), decreasing STAT3, STAT5a, and STAT5b expression led to a progressive decrease in anti-inflammatory cytokines, whereas proinflammatory cytokines initially decreased but then increased when STAT3 or STAT5 expression fell below a critical threshold. Mechanisms regulating STAT3- and STAT5-dependent inflammatory cytokine outcomes included negative feedback from autocrine/paracrine IL-10, TGF-β, IL-4, IL-13, IL-22, and TSLP secretion and SOCS1/SOCS2/SOCS3 induction. MDMs from rs12942547 AA disease-risk carriers demonstrated increased STAT3, STAT5a, and STAT5b expression and increased PRR-induced STAT3 and STAT5 phosphorylation relative to GG MDMs. Both pro- and anti-inflammatory cytokine secretion was decreased in MDMs from GG carriers, as STAT3, STAT5a, and STAT5b expression was above the threshold for reciprocal regulation of these cytokines. Taken together, we identify that the threshold of STAT3, STAT5a, and STAT5b expression determines if PRR-induced proinflammatory cytokines are increased or decreased, define mechanisms for this reciprocal regulation, and elucidate consequences for disease variants in the STAT3/STAT5A/STAT5B region, indicating that considering signaling thresholds and targeting specific cell types might be beneficial when evaluating therapeutic interventions in this pathway.