SYK coordinates neuroprotective microglial responses in neurodegenerative disease [Bulk RNA-seq]

Many neurodegenerative diseases are thought to be caused by impaired containment and/or disposal of neurotoxic material such as amyloid beta (Ab) and myelin debris. Indeed, recent human genome-wide association studies (GWAS) and animal model studies have begun to reveal critical roles for the brain's professional phagocytes, microglia, as well as various innate immune receptors expressed by microglia in the control of neurotoxic material and subsequent neurodegenerative disease pathogenesis. Yet, the critical intracellular molecules that orchestrate the neuroprotective functions of microglia in degenerative disorders remain poorly understood. In our studies, we have identified the innate immune signaling molecule spleen tyrosine kinase (SYK) as a key regulator of microglial phagocytosis in neurodegenerative disease. We find that targeted deletion of SYK in microglia leads to exacerbated Ab deposition, aggravated neuropathology, and cognitive defects in the 5xFAD mouse model of Alzheimer's disease (AD). Furthermore, disruption of SYK signaling in this AD model was also shown to impede the development of disease-associated microglia (DAMs), alter AKT/GSK3b-signaling in microglia, and to cause severe deficits in the ability of microglia to phagocytose Ab. Importantly, these critical neuroprotective functions of SYK in microglia were not only restricted to Ab-driven models of neurodegeneration, as we found that SYK is also a critical regulator of microglial phagocytosis and DAM phenotype acquisition in demyelinating disease. Collectively, these results help to break new ground in our understanding of the key innate immune signaling molecules that instruct beneficial microglial functions in response to neurotoxic material. Moreover, these findings suggest that targeting SYK may offer a therapeutic strategy to treat a spectrum of neurodegenerative disorders. Overall design: Comparison of 5xFAD severity and microglial response with or without SYK function. 4 replicates per group of non disase (control), SYK-deficient, 5xFAD, and 5xFAD Syk deficient