Ubiquitin Ligase COP1 Suppresses Neuroinflammation by Degrading c/EBPβ in Microglia

•Ubiquitin ligase COP1 promotes proteasomal degradation of c/EBPβ•Loss of COP1 triggers a pro-inflammatory gene expression program in microglia•COP1-deficient microglia exhibit c/EBPβ- and C1q-dependent neurotoxicity•COP1-deficient microglia exacerbate Tau-driven pathology in mice SummaryDysregulated microglia are intimately involved in neurodegeneration, including Alzheimer’s disease (AD) pathogenesis, but the mechanisms controlling pathogenic microglial gene expression remain poorly understood. The transcription factor CCAAT/enhancer binding protein beta (c/EBPβ) regulates pro-inflammatory genes in microglia and is upregulated in AD. We show expression of c/EBPβ in microglia is regulated post-translationally by the ubiquitin ligase COP1 (also called RFWD2). In the absence of COP1, c/EBPβ accumulates rapidly and drives a potent pro-inflammatory and neurodegeneration-related gene program, evidenced by increased neurotoxicity in microglia-neuronal co-cultures. Antibody blocking studies reveal that neurotoxicity is almost entirely attributable to complement. Remarkably, loss of a single allele of Cebpb prevented the pro-inflammatory phenotype. COP1-deficient microglia markedly accelerated tau-mediated neurodegeneration in a mouse model where activated microglia play a deleterious role. Thus, COP1 is an important suppressor of pathogenic c/EBPβ-dependent gene expression programs in microglia. Dysregulated microglia are intimately involved in neurodegeneration, including Alzheimer’s disease (AD) pathogenesis, but the mechanisms controlling pathogenic microglial gene expression remain poorly understood. The transcription factor CCAAT/enhancer binding protein beta (c/EBPβ) regulates pro-inflammatory genes in microglia and is upregulated in AD. We show expression of c/EBPβ in microglia is regulated post-translationally by the ubiquitin ligase COP1 (also called RFWD2). In the absence of COP1, c/EBPβ accumulates rapidly and drives a potent pro-inflammatory and neurodegeneration-related gene program, evidenced by increased neurotoxicity in microglia-neuronal co-cultures. Antibody blocking studies reveal that neurotoxicity is almost entirely attributable to complement. Remarkably, loss of a single allele of Cebpb prevented the pro-inflammatory phenotype. COP1-deficient microglia markedly accelerated tau-mediated neurodegeneration in a mouse model where activated microglia play a deleterious role. Thus, COP1 is an important suppressor of pathogenic c/EBPβ-dependent gene expression programs in microglia.