Disease-Associated Microglia Are Implicated in Neuropsychiatric Manifestations of Systemic Lupus Erythematosus

Abstract Systemic lupus erythematosus (SLE) is an autoimmune disease affecting multiple organs, including the brain. Though 50% of patients may experience neuropsychiatric symptoms (NPSLE), disease mechanisms remain largely unknown. Microglia, the resident innate immune cell of the brain, have recently been implicated in NPSLE. Microglia are heterogenous and may be associated with a homeostatic microglia (CD11clo) or a disease-associated microglia (DAM; CD11chi) state common to neurodegenerative disease and aging. Yet, few studies have examined microglia subsets in NPSLE. We showed that expression of a shared NPSLE transcriptional signature and DAM-associated genes correlates with the severity of behavioral deficits in microglia isolated from two NPSLE models prior to overt systemic disease. Further, our single-cell RNA-seq data identify homeostatic microglia and DAM states in control and NPSLE-prone mice. DAM in NPSLE are enriched for genes associated with antigen presentation but depleted for genes associated with phagocytosis, which is in contrast to DAM in neurodegenerative disease that are critical for phagocytic functions. Moreover, NPSLE CD11clo microglia upregulate genes linked to synapse pruning and phagocytosis, consistent with exacerbated synaptic pruning by microglia in models of NPSLE. We also find that restricted expression of the DAM transcriptional program in NPSLE DAM corresponds to improved behavioral outcomes in NPSLE-prone mice following treatment with fingolimod, a sphingosine-1-phosphate receptor modulator that reduces microglia activation and improves blood brain barrier integrity. These discoveries mark the first to implicate DAM as a potentially pathogenic microglia subset in NPSLE.