Dissecting the regulation of macrophage metabolic wiring in response to efferocytosis

Abstract

Clearance of dying cells is a pivotal function of the immune system. During the phagocytosis of apoptotic cells (efferocytosis), some components of the autophagy machinery can be directly recruited to the phagosome membrane. This recruitment catalyzes the lipidation of proteins from the LC3-GABARAP family onto phosphatidylethanolamine and phosphatidylserine residues on the phagosome membrane containing internalized apoptotic cells, inducing its maturation and fusion with the lysosome. As a consequence, LAP deficiency is associated with a reduction in anti-inflammatory responses during efferocytosis while simultaneously inducing various inflammatory genes in macrophages. Our hypothesis is that the inflammatory activation of LAP-deficient macrophages during efferocytosis may be triggered by a metabolic shift regulated by the transcription factor HIF-1±. Supporting this hypothesis, we observed an increase in glycolytic activity coupled with increased stabilization of HIF1± in response to efferocytosis in LAP-deficient macrophages. Our data indicate that deficiency in LAP components leads to the stabilization of HIF1±, but whether upstream components that regulate the recognition and internalization of dying cells are involved still needs to be elucidated. For this BEPE, we propose a collaboration with Drs. Carla V. Rothlin and Sourav Ghosh, experts in the field of efferocytosis, to investigate the molecular mechanisms by which LAP regulates the stabilization of HIF-1±. We will focus on four main points: 1) To investigate the involvement of the TAM family of phosphatidylserine recognition receptors in LAP activation in response to efferocytosis. 2) To assess whether HIF1± stabilization in response to efferocytosis is dependent on TAM receptors. 3) To characterize the involvement of metabolites derived from apoptotic cells in macrophage modulation and how LAP and HIF-1± may be involved in this process. 4) To test how recognition the type of cell death affects corpse recognition and degradation, focusing on TAM receptors, LAP and HIF-1±. Thus, this proposal may elucidate the mechanisms by which LAP is modulated and shapes macrophages function during efferocytosis.