MONOSPLIT · Deciphering Split Monopoiesis Impact on Tissue Macrophages

Macrophages are key players in organ development, tissue maintenance, and the immune defense of vertebrate organisms. These cells are initially established during embryonic development, but most tissue-resident macrophage compartments are progressively seeded and often even replaced by monocyte-derived cells. Monocytes and their macrophage progeny critically contribute to a wide range of pathologies, including autoinflammatory, cardiovascular, and metabolic disorders, as well as cancer. Given their central role in physiology and pathophysiology, these cells are attractive targets for therapeutic intervention. This will, however, require an in-depth understanding of monocyte-to-macrophage trajectories, whose comprehensive study in mice and man is the goal of this proposal.Beyond these translational implications, our studies are particularly well-timed, given new exciting findings: thus, monocytes were recently shown to arise from distinct developmental trajectories, and we discovered that this developmental monocyte dichotomy translates into tissue macrophage heterogeneity with probable significant functional impact. Here, we propose to follow up on our recent intriguing finding and use murine fate mapping and novel Csf1r-targeted genetic perturbations, combined with a high-resolution single-cell-based imaging and omics analysis of murine and human blood, to explore the impact of developmental monocyte dichotomy on health and disease in man and mice. An in-depth understanding of the two monocyte trajectories, their differential dominance following infections, and differential fates in distinct tissues will have significant value for the future development of strategies for tissue macrophage manipulation. Moreover, our detailed analysis of human blood might incentivize routine monitoring of the monocyte-to-macrophage axis for diagnosis.