Fatty acid-binding protein 5 deficiency impairs alveolar macrophage function and metabolism

Macrophages are large mononuclear immune cells that participate in host protection, not only by phagocytosing foreign or infected cells and initiating inflammatory responses, but also by contributing to the resolution of inflammation. Chronic Obstructive Pulmonary Disease (COPD) is characterized by increased numbers of macrophages in lung tissue, with altered engulfment capabilities. However, the molecular pathways leading to macrophage dysfunction in COPD remain unclear. Using integrated genetics and genomics approaches, we previously identified Fatty Acid Binding Protein 5 (FABP5) as a key target in the resolution of airway inflammation that exhibits decreased expression in COPD patients. The objective is to define the significance of alveolar macrophage FABP5 by comparing the resolution of inflammation in WT and Fabp5^-/- mice following nontypeable Haemophilus influenzae (NTHi) infection or LPS sterile inflammation. Immune and metabolic responses were analyzed using functional assays, flow cytometry, ELISA, cell metabolic profiling and tracing, as well as ATAC-seq. Fabp5^-/- mice exhibited impaired efferocytosis, reflected by a reduction of apoptotic cell engulfment by alveolar macrophages. This was accompanied by a reduction in fatty acid uptake and fatty acid β-oxidation, a reduction in mitochondrial respiration, an accumulation of TCA cycle and glycolysis metabolites, and an increased chromatin accessibility for AP-1 family members. Fabp5-deficient alveolar macrophages failed to initiate reparative metabolic programming, which is critical for the resolution of inflammation. Our data suggest that increasing FABP5 expression could provide a metabolic switch that facilitates macrophage conversion to a pro-resolving phenotype and restores alveolar macrophage efferocytic functions in the lungs of COPD patients.