UDP-glucose Regulates Dendritic Cell Mitochondrial Respiration via a Nitric Oxide-dependent Mechanism

Abstract

Abstract Dendritic cells (DCs) are key innate immune cells specialized in fine tuning an immune response. Activation of DCs through Toll-Like Receptors (TLRs) is accompanied by a metabolic switch to increased use of glycolytic metabolism fueled by carbohydrates glucose and glycogen. Our lab has shown that DCs require glucose and glycogen to perform their immune effector functions including: production of cytokines and inflammatory mediators, antigen presentation to T cells, and initiation of the T cell-mediated immune response. Recent studies in inflammatory macrophages showed a secondary metabolite in the glycogen synthetic pathway, uridine diphosphate glucose (UDP-glucose), is upregulated through TLR4 stimulation. UDP-glucose exits the cell and signals in an autocrine manner through its specific purinergic receptor P2Y 14. Additionally, P2Y 14R signaling modulates the expression of proinflammatory pathways including upregulation of inducible nitric oxide synthase (iNOS). Activated bone marrow-derived DCs (BMDCs) upregulate iNOS and produce nitric oxide (NO), which has pleiotropic effects, including inhibiting mitochondrial respiration. Therefore, we hypothesized that the UDP-glucose/P2Y 14R/iNOS axis regulates BMDC metabolism, which has further ramifications on DC cell survival and proinflammatory phenotypes. To investigate the impact of UDP-glucose as an autocrine signaling molecule, we characterized proinflammatory gene transcript and protein levels, as well as the functional outcomes of increased iNOS protein in the cell. These studies showed that DCs use the UDP-glucose/P2Y 14R/iNOS axis to bolster inflammatory phenotypes including inhibition of mitochondrial respiration leading to exacerbated cell death. Supported by grants from NIH (R01 AI158710-01, 1R21AI135385-01A1) and UVM (COBRE VCIID Funding Support and Pilot Project)