Macrophage programming is regulated by a cooperative interaction between fatty acid binding protein 5 and peroxisome proliferator-activated receptor γ

Resolution of inflammation is an active process that is tightly regulated to achieve repair and tissue homeostasis. In the absence of resolution, persistent inflammation underlies the pathogenesis of chronic lung disease such as chronic obstructive pulmonary disease (COPD) with recurrent exacerbations. Over the course of inflammation, macrophage programming transitions from pro-inflammatory to pro-resolving, which is in part regulated by the nuclear receptor Peroxisome Proliferator-Activated Receptor gamma (PPAR gamma). Our previous work demonstrated an association between Fatty Acid Binding Protein 5 (FABP5) expression and PPAR gamma activity in peripheral blood mononuclear cells of healthy and COPD patients. However, a role for FABP5 in macrophage programming has not been examined. Here, using a combination of in vitro and in vivo approaches, we demonstrate that FABP5 is necessary for PPAR gamma activation. In turn, PPAR gamma acts directly to increase FABP5 expression in primary human alveolar macrophages. We further illustrate that lack of FABP5 expression promotes a pro-inflammatory macrophage programming with increased secretion of pro-inflammatory cytokines and increased chromatin accessibility for pro-inflammatory transcription factors (e.g., NF-kappa B and MAPK). And finally, real-time cell metabolic analysis using the Seahorse technology shows an inhibition of oxidative phosphorylation in FABP5-deficient macrophages. Taken together, our data indicate that FABP5 and PPAR gamma reciprocally regulate each other's expression and function, consistent with a novel positive feedback loop between the two factors that mediates macrophage pro-resolving programming. Our studies highlight the importance of defining targets and regulatory mechanisms that control the resolution of inflammation and may serve to inform novel interventional strategies directed towards COPD.