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

The resolution of inflammation is an active process that is tightly regulated to achieve repair and tissue homeostasis. In the absence of resolution, chronic inflammation underlies the pathogenesis of chronic lung disease including Chronic Obstructive Pulmonary Disease (COPD) with recurrent exacerbations. Over the course of inflammation, macrophage programming transitions from inflammatory to pro-resolving, and is in part regulated by the nuclear receptor Peroxisome Proliferator-Activated Receptor γ (PPARγ). In our previous work, we demonstrated an association between Fatty Acid Binding Protein 5 (FABP5) expression and PPARg activity in PBMCs. However, the role of FABP5 in macrophage programming is not yet defined, thus, we further investigated its interaction with PPARγ and its role in macrophage programming. Here, we demonstrate that FABP5 is necessary to initiate PPARγ activation and macrophage pro-resolving programming. We used the RNAscope tool in combination with co-immunofluorescence, immunoprecipitation, PPARγ activity assay, and chromatin immunoprecipitation to show that FABP5 and PPARγ not only interact but also regulate one another. By integrating flow cytometry, ELISA, assay for transposase-accessible chromatin by sequencing (ATAC-seq) and the Seahorse technology, we extend our findings to illustrate that lack of FABP5 expression promotes a glycolytic pro-inflammatory macrophage programming. Taken together, these data provide evidence that FABP5 and PPARγ reciprocally regulate each other’s expression and function, consistent with a positive feedback regulatory loop between the two to promote macrophage pro-resolving programming. The Omni method for the Assay for transposase-accessible chromatin by sequencing (Omni-ATAC-seq) was performed in primary mouse bone marrow-derived macrophages for WT or FABP5-deficient mice. All samples were sequenced in duplicate.