Crosstalk between CES1 and PPAR gamma and LXR alpha in macrophages

摘要

Abstract The intersection of bioactive lipids and inflammation is a central feature of immune cells during tissue injury, particularly in macrophages. When homeostatic mechanisms fail to resolve inflammatory responses and/or become maladaptive, chronic low-grade inflammatory conditions or excessive wound healing events can be established. For example, lung fibrosis and atherosclerosis, in part, results from overactive tissue repair and defective inflammation resolution, respectively. There are major knowledge gaps regarding the nature of the lipid interactome in health and disease, and how it modulates inflammation to either exacerbate tissue damage or promote resolution/repair. Thus, ‘defects in inflammation resolution programs’ is a major theme that runs through this proposal. The specific goal of this grant is to mechanistically understand the immunoregulatory crosstalk we have observed between a metabolic serine hydrolase – termed human carboxylesterase 1 (CES1) – and the lipid-sensing nuclear receptors PPARgamma and LXRalpha, which can affect macrophage phenotype and function after exposure to ‘danger-associated molecules’, such as cytokines and oxidized low-density lipoproteins (oxLDL). To attack this problem, we hypothesize that one function of CES1 in macrophages is to regulate the levels of endogenous ligands that are sensed by PPARgamma and LXRalpha in the setting of resolving inflammation, thus modulating the activity of these putative anti-inflammatory receptors. This will be tested with two aims that will: (i) Characterize the cross talk between CES1 and the lipid-sensing receptors PPARgamma and LXRalpha; (ii) Evaluate the mechanisms by which murine Ces1d (the mouse ortholog of human CES1) in lung regulates the activity of ‘alternatively polarized’ macrophages in a pulmonary fibrosis model. Human monocyte- derived macrophages with key genes knocked out and an innovative mouse model will be used to study the effects of macrophage-activating stimuli on biochemical, genomic, and lipidomic outputs. The impact of this project is that it will demonstrate how CES1 transduces extracellular signals that shape the immunophenotype of macrophages. At this stage, the links between CES1 and the nuclear receptors PPARgamma and LXRalpha are unclear; however, obtaining this knowledge would allow new and innovative ways to therapeutically temper the activities of M1 and M2 macrophages that exacerbate atherosclerosis and lung fibrosis, respectively. Following the successful completion of this project, we will better understand the mechanisms by which CES1 regulates cellular levels of oxidized chemicals (oxylipins and oxysterols) that are formed in the context of lipid- and chemical-driven inflammation. Further, we will have a better view of the subsequent interactions of these compounds with proteins (e.g., ligand-activated transcription factors) in macrophages that ultimately shape their cellular response to immune-polarizing stimuli in health and injury.