Abstract 11646: ATVB Outstanding Research Award : WDFY3 is Required for the Efficient Degradation of Engulfed Apoptotic Cells by Macrophages During Efferocytosis

Introduction: Defective clearance of apoptotic cells (ACs) by macrophages (efferocytosis) contributes to unresolved inflammation. Our recent genome-wide CRISPR screen has discovered WDFY3 as a novel regulator required for the efficient uptake of ACs during efferocytosis. WDFY3 is well known as a scaffold protein facilitating the autophagic degradation of aggregated proteins in neurons. Yet, if and how WDFY3 may also be required for the efficient degradation of engulfed ACs by macrophages have not been characterized. Hypothesis: WDFY3 is responsible for the efficient degradation of ACs by interacting with other autophagic proteins to facilitate phagosome-lysosome fusion, a process known as LC3-associated phagocytosis (LAP). Methods: Bone marrow-derived macrophages (BMDMs), peritoneal macrophages (PMs), and mice with myeloid-specific Wdfy3 knockout (LysMCre +/- Wdfy3 fl/fl ) or transgenic overexpression of human WDFY3 ( hWDFY3 Tg ) were used for in vitro and in vivo assays. Results: Wdfy3 knockout BMDMs and PMs showed impaired lysosomal acidification and degradation of engulfed ACs. Mechanistically, Wdfy3 knockout impedes efficient LC3 lipidation upon AC engulfment, the last step required for phagosome-lysosome fusion and subsequent lysosomal degradation. Pull-down assay supports that WDFY3 interacts with GABARAP, but not LC3B, to mediate LC3 lipidation, supporting the direct involvement of WDFY3 protein in the process. At the transcriptomic level, RNA-seq and pathway analyses further revealed that gene sets of ROS/RNS production by phagocytes, fatty acid oxidation, and autophagosome were enriched in differentially expressed genes downregulated in Wdfy3 knockout BMDM, supporting the secondary effects of WDFY3-deficiency on the mRNA expression of genes and pathways essential for cargo degradation. Intriguingly, BMDMs and PMs from hWDFY3 Tg mice showed enhanced AC uptake and degradation both in vitro and in vivo , suggesting that WDFY3 has a wide dynamic range in its regulatory capacity. Conclusion: We discovered a novel role of WDFY3 in the degradation of ACs during macrophage efferocytosis. Enhancing WDFY3 may represent a therapeutic approach to promote the resolution of inflammation in diseases due to defective efferocytosis.