In sum, #tissues tune #macrophage_numbers to their #mitochondrial_activity through a #CSF1 + #fibroblast niche, matching waste-clearance capacity to metabolic demand. This immune-metabolic coupling is essential to preserve mitochondrial fitness and tissue function

Notably, #CSF1 levels across tissues closely correlated with macrophage numbers. Blocking #CSF1 strongly depleted macrophages across cardiac and skeletal muscles, whereas loss of IL-34, the alternative #CSF1R ligand, had no effect.

Finally, we asked: what mediates this coupling between mitochondrial activity and macrophage❓ scRNA-seq across muscles with different metabolic states pointed to #CSF1 - #CSF1R signaling—a key pathway controlling macrophage survival and proliferation.