Unconjugated bilirubin modulates Th17-cell immunity by curbing glycolysis-related genes

Abstract

Abstract Unconjugated bilirubin (UCB) controls Th17-cell function by upregulating the ectonucleotidase CD39 and through activation of aryl-hydrocarbon-receptor (AhR), a modulator of adaptive immunity. UCB-induced CD39 upregulation is defective in Th17-cells of Crohn’s disease (CD) patients. Increasing evidence suggests a role for AhR in regulating glucose metabolism. In this study we tested whether UCB modulates Th17-cell metabolism and whether impaired Th17-cell response to UCB results in metabolic alterations in CD. Th17-cells were differentiated from circulating CD4-cells of 31 healthy controls (HC) and 22 CD patients. Using a multiplex gene expression panel including genes of 8 metabolic pathways, we found that UCB markedly downregulated glycolysis-related genes, particularly phosphoglycerate-kinase-1 (PGK1) and aldolase-A (ALDOA); this effect being prominent in Th17-cells derived from HC but not from CD patients. Reduced Pgk1 and AldoA was also noted in mesenteric-lymph-nodes of mice exposed to dextran-sulfate-sodium-induced colitis and treated with UCB. Functionally, UCB decreased the extracellular-acidification-rate and oxygen-consumption-rate of HC Th17-cells, while this effect was not noted in Th17-cells of CD patients. In vitro silencing of PGK1 and ALDOA further enhanced UCB immunoregulatory properties in HC Th17-cells, by boosting CD39 and Tim-3 while containing IL-17. In conclusion, UCB modulates Th17-cell immunity by downregulating glycolysis-related genes; this property being defective in cells obtained from CD patients. Strategies aimed at blocking/inhibiting glycolytic genes might represent a potential therapeutic tool to restore immune homeostasis in CD and other inflammatory conditions.