Chiţu, Violeta

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.

AbstractMutations leading to colony‐stimulating factor‐1 receptor (CSF‐1R) loss‐of‐function or haploinsufficiency cause CSF1R‐related leukoencephalopathy (CRL), an adult‐onset disease characterized by loss of myelin and neurodegeneration, for which there is no effective therapy. Symptom onset usually occurs in the fourth decade of life and the penetrance of disease in carriers is high. However, familial studies have identified a few carriers of pathogenic CSF1R mutations that remain asymptomatic even in their seventh decade of life, raising the possibility that the development and severity of disease might be influenced by environmental factors. Here we report new cases in which long‐term glucocorticoid treatment is associated with asymptomatic status in elder carriers of pathogenic CSF‐1R mutations. The main objective of the present study was to investigate the link between chronic immunosuppression initiated pre‐symptomatically and resistance to the development of symptomatic CRL, in the Csf1r+/− mouse model. We show that chronic prednisone administration prevents the development of memory, motor coordination and social interaction deficits, as well as the demyelination, neurodegeneration and microgliosis associated with these deficits. These findings are in agreement with the preliminary clinical observations and support the concept that pre‐symptomatic immunosuppression is protective in patients carrying pathogenic CSF1R variants associated with CRL. Proteomic analysis of microglia and oligodendrocytes indicates that prednisone suppresses processes involved in microglial activation and alleviates senescence and improves fitness of oligodendrocytes. This analysis also identifies new potential targets for therapeutic intervention.

AbstractColony stimulating factor (CSF) receptor‐1 (CSF‐1R)‐related leukoencephalopathy (CRL) is an adult‐onset, demyelinating and neurodegenerative disease caused by autosomal dominant mutations in CSF1R, modeled by the Csf1r+/− mouse. The expression of Csf2, encoding granulocyte‐macrophage CSF (GM‐CSF) and of Csf3, encoding granulocyte CSF (G‐CSF), are elevated in both mouse and human CRL brains. While monoallelic targeting of Csf2 has been shown to attenuate many behavioral and histological deficits of Csf1r+/− mice, including cognitive dysfunction and demyelination, the contribution of Csf3 has not been explored. In the present study, we investigate the behavioral, electrophysiological and histopathological phenotypes of Csf1r+/− mice following monoallelic targeting of Csf3. We show that Csf3 heterozygosity normalized the Csf3 levels in Csf1r+/− mouse brains and ameliorated anxiety‐like behavior, motor coordination and social interaction deficits, but not the cognitive impairment of Csf1r+/− mice. Csf3 heterozygosity failed to prevent callosal demyelination. However, consistent with its effects on behavior, Csf3 heterozygosity normalized microglial morphology in the cerebellum and in the ventral, but not in the dorsal hippocampus. Csf1r+/− mice exhibited altered firing activity in the deep cerebellar nuclei (DCN) associated with increased engulfment of glutamatergic synapses by DCN microglia and increased deposition of the complement factor C1q on glutamatergic synapses. These phenotypes were significantly ameliorated by monoallelic deletion of Csf3. Our current and earlier findings indicate that G‐CSF and GM‐CSF play largely non‐overlapping roles in CRL‐like disease development in Csf1r+/− mice.