AXL-mediate GEF-H1 phosphorylation was involved in microglia synapse phagocytosis in 5xFAD mice

Studies indicated that microglial synapse phagocytosis played a critical role in synapse loss and pathogenesis in Alzheimer's disease. AXL was one of key phagocytic receptors and was upgraded in disease associated microglia. This study aimed to investigate the role of AXL-mediated microglial synapse phagocytosis in AD mice model. Our data indicated that AXL was increased in microglia in 5xFAD mouse AD model. The lentivirus PLV-CXC3CR1-shAXl was applied to especially knockdown the AXL expression in microglia and the shAXL treatment ameliorated the cognitive impairment in 5xFAD mice. AXL knockdown decreased the 6E10 positive amyloid plaques, the diffusion index of amyloid plaques and the level of phosphorylated Tau. shAXL treatment increased microglial complexity and reduced the microglial synapse phagocytosis. This study further demonstrated that GEF-H1 was identified as a substrate of AXL and mainly phosphorylated at Y470 by AXL. The AXL-mediated GEF-H1-Y470 phosphorylation enhanced the phagocytic capacity of BV2. It seems paradoxical that amyloid plaque load and microglial phagocytosis were both decreased at the same time when the AXL was knockdown, but these indicated that microglia phagocytosis related synapse loss played a more critical role in cognitive impairment and AD pathogenesis than amyloid plaque load. Our study demonstrated that the activated AXL in microglia in 5xFAD enhanced synapse phagocytosis via phosphorylating GEF-H1 at Y470, which led to synapse loss and cognitive impairment. The application of AXL blockage would be a potential therapeutic strategy for AD treatment.