Tissue mitochondrial activity dictates macrophage pool size by modulating CSF1 availability, ensuring efficient waste disposal.

Efficient cellular waste removal is crucial for tissue health, particularly in organs with high metabolic demands like the heart and skeletal muscle. Compromised mitochondrial function can impair tissue regeneration and nutrient delivery. Macrophages are key immune cells involved in clearing cellular debris, but the mechanisms coupling their abundance to tissue metabolic activity, specifically mitochondrial waste production, remain poorly understood. This gap limits strategies to optimize tissue repair and maintain metabolic fitness.

Researchers investigated the link between tissue mitochondrial activity and macrophage populations across various organs, including heart, skeletal muscle, and brown adipose tissue. They examined how myofiber mitochondrial activity influences macrophage abundance by modulating colony-stimulating factor 1 (CSF1) availability and the number of CSF1-producing fibroblasts. The study also involved inhibiting CSF1-CSF1 receptor (CSF1R) signaling to observe its impact on macrophage numbers and skeletal muscle mitochondrial activity.

The study revealed a prominent uptake of parenchyma-released mitochondria by macrophages in organs relying on oxidative respiration. Macrophage numbers were found to closely align with the mitochondrial activity of these organs, including heart, skeletal muscle, and brown adipose tissue. This suggests a direct relationship between a tissue's metabolic demands and its immune cell composition.

Myofiber mitochondrial activity directly dictates the abundance of macrophages by modulating colony-stimulating factor 1 (CSF1) availability and the number of CSF1-producing fibroblasts in the tissue. Consequently, inhibition of CSF1-CSF1 receptor (CSF1R) signaling led to a depletion of macrophages and a collapse in the mitochondrial activity of skeletal muscles. This mechanism suggests a fundamental coupling between tissue metabolic demands and immune cell regulation, ensuring efficient waste disposal and maintaining tissue fitness.