We are interested in manipulating the biology of dendritic cells (DCs) in order to enhance or inhibit their ability to induce T cell immunity, which underpins both protective and sometimes deleterious (as is the case in autoimmunity or asthma, for example) immune responses. DCs stand at the interface between innate and adaptive immunity. They express receptors (such as Toll-like receptors, TLRs) that allow them to sense and respond to infection. Following exposure to TLR agonists, which typically are pathogen-derived, quiescent DCs become activated through a process that encompasses changes in expression of genes including those that initiate inflammation and allow DCs to activate naive T cells and thereby stimulate adaptive immune responses. The impact of activated DCs, which is potentially dangerous, is tightly regulated by cytokines such as IL-10, and by a poorly understood mechanism through which cellular lifespan is limited following exposure to TLR agonists. It is increasingly clear that changes in cellular longevity and activation are coupled to profound changes in metabolism. Consistent with this, we have found that the transition of mouse bone marrow-derived DCs from quiescent to activated states involves a significant and prolonged upregulation of aerobic glycolysis and a concomitant decrease in mitochondrial oxidative phosphorylation. Importantly, depriving DCs of glucose or promoting mitochondrial metabolism inhibits activation, suggesting that glycolysis is permissive for DC activation whereas mitochondrial metabolism is not. Collectively, our data implicate DC metabolic reprogramming as an integral component of the activation process. However, we have yet to experimentally address why activation requires such a metabolic switch, or why cellular lifespan is shortened once this switch has occurred, or whether the observed metabolic changes occur in mouse DCs that develop in vivo, or in human DCs. Based on our published and preliminary data, we hypothesize that either: 1) glycolysis is the only type of metabolism that can support the demands of activation, or 2) activated DCs switch to glycolysis because mitochondrial metabolism shuts down as a result of activation. We plan to explore these possibilities in detail through the following specific aims: 1) To determine why TLR-mediated activation of DCs is accompanied by a switch to glycolysis;2) To explore the role of mitochondrial function and AMP-kinase in DC activation and survival;3) To promote DC lifespan and sustained expression of costimulatory molecules through the manipulation of metabolic pathways. Our long term goal is to be able to manipulate metabolic processes in DCs in order to promote or inhibit their activation and/or longevity, and in so doing develop novel approaches for improving vaccination strategies, and limiting immune responses in chronic, pathological conditions.
Dendritic cells (DCs) are required to activate T cells, and thus are a key element for targeting in approaches that aim to develop prophylactic or therapeutic vaccines, or treatments that inhibit autoimmunity. Our research to understand basic changes in DC cellular metabolism that are linked to DC activation promises to open new avenues for manipulating these cells and therefore the immune responses that they control.
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