A kinase-dead Csf1r mutation associated with adult-onset leukoencephalopathy has a dominant-negative impact on CSF1R signaling

Amino acid substitutions in the kinase domain of the human CSF1R gene are associated with autosomal dominant adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP). To model the human disease, we created a disease-associated mutation (Glu631Lys; E631K) in the mouse Csf1r locus. Homozygous mutation ( Csf1r E631K/E631K ) phenocopied the Csf1r knockout; with prenatal mortality or severe postnatal growth retardation and hydrocephalus. Heterozygous mutation delayed the postnatal expansion of tissue macrophage populations in most organs. Bone marrow cells from Csf1r E631K/+ mice were resistant to CSF1 stimulation in vitro , and Csf1r E631K/+ mice were unresponsive to administration of a CSF1-Fc fusion protein which expands tissue macrophage populations in controls. In the brain, microglial cell numbers and dendritic arborization were reduced in the Csf1r E631K/+ mice as in ALSP patients. The microglial phenotype is the opposite of microgliosis observed in Csf1r +/- mice. However, we found no evidence of brain pathology or impacts on motor function in aged Csf1r E631K/+ mice. We conclude that disease-associated CSF1R mutations encode dominant negative repressors of CSF1R signaling. We speculate that leukoencephalopathy associated with human CSF1R mutations requires an environmental trigger and/or epistatic interaction with common neurodegenerative disease-associated alleles. Summary Statement This study describes the effect of a human disease-associated mutation in the mouse CSF1R gene on postnatal development and growth factor responsiveness of cells of the macrophage lineage.