Abstract
Author summary
These studies further demonstrate that regulation of dendritic cell metabolism is mediated by SIRT1, a critical cellular sensor that controls both cellular and mitochondrial protein activation that facilitates proper innate immune activation. The absence of SIRT1 in DC leads to inappropriate metabolic processes, including fatty acid synthesis through Acetyl Co A pathways, which enhances the pathogenic immune responses leading to inappropriately modified acquired immunity. The present studies have identified several modified pathways in the absence of SIRT1 that may be relevant targets for intervention to avoid altered innate immunity. Inhibiting acetyl Co A activation by blocking ACC1 with a specific inhibitor corrected the altered metabolic state and resulted in the more appropriate innate and acquired immune responses during RSV infection. By identifying specific metabolic pathways in this manner, new therapeutics for RSV may be identified and allow interruption of the pathogen immune responses.
Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract infection in children worldwide. Sirtuin 1 (SIRT1), a NAD+ dependent deacetylase, has been associated with induction of autophagy, reprogramming cellular metabolism, and regulating immune mediators. In this study, we investigated the role of SIRT1 in bone marrow dendritic cell (BMDC) function during RSV infection. SIRT1 deficient (SIRT1 -/-) BMDC showed a defect in mitochondrial membrane potential (Delta & x2366;m) that worsens during RSV infection. This defect in Delta & x2366;m caused the generation of elevated levels of reactive oxygen species (ROS). Furthermore, the oxygen consumption rate (OCR) was reduced as assessed in Seahorse assays, coupled with lower levels of ATP in SIRT1-/- DC. These altered responses corresponded to altered innate cytokine responses in the SIRT1-/- DC in response to RSV infection. Reverse Phase Protein Array (RPPA) functional proteomics analyses of SIRT1-/- and WT BMDC during RSV infection identified a range of differentially regulated proteins involved in pathways that play a critical role in mitochondrial metabolism, autophagy, oxidative and ER stress, and DNA damage. We identified an essential enzyme, acetyl CoA carboxylase (ACC1), which plays a central role in fatty acid synthesis and had significantly increased expression in SIRT1-/- DC. Blockade of ACC1 resulted in metabolic reprogramming of BMDC that ameliorated mitochondrial dysfunction and reduced pathologic innate immune cytokines in DC. The altered DC responses attenuated Th2 and Th17 immunity allowing the appropriate generation of anti-viral Th1 responses both in vitro and in vivo during RSV infection thus reducing the enhanced pathogenic responses. Together, these studies identify pathways critical for appropriate DC function and innate immunity that depend on SIRT1-mediated regulation of metabolic processes.
