Disruption of CSF-1 receptor-mediated metal ion homeostasis in the murine brain promotes neurodegenerative disease

Dominant-inactivating mutations in the colony stimulating factor-1 receptor (CSF1R) cause CSF-1R-related leukoencephalopathy (CRL), an adult-onset neurodegenerative disease that is modeled in the Csf1r+/- mouse. CRL is caused by microglial dysfunction. However, the primary microglial deficit is unknown. To address this question, we employed single-nucleus RNA sequencing of brains from young Csf1r+/- mice without pathological or behavioral alterations. Reduction of CSF-1R signaling caused metal ion accumulation in brain macrophages, with concomitant activation of cell death and stress response pathways in oligodendrocytes and neuronal subpopulations. Reduction of metallothionein 1 (Mt1) and 3 (Mt3) gene expression was a common feature in glial and neuronal cells of Csf1r+/- mice. Overexpression of Mt1 restored metal ion homeostasis, normalized ROS production in microglia, and prevented the development of behavioral deficits, while Mt3 deletion had disease-enhancing effects. These findings demonstrate CSF-1R regulation of metal ion homeostasis via metallothioneins in the brain.