Tmem59 deletion activates microglia and reduces phagocytic capacity

1300 Introduction: Neuroinflammation is widely regarded as a chronic innate immune response in the brain and apotentially pathogenic factor in a number of neurodegenerative diseases such as Alzheimer’s disease (AD), as well as traumatic brain injury. Recently, due to its key signaling steps in the initiation of immune activation, greater attention has been paid to the potential of neuroinflammation as a therapeutic target. Microglia, which comprise approximately 20% of all glial cells, serve as the principal immune cells and play crucial roles in the central nervous system, responding to neuroinflammation via migration and the execution of phagocytosis. The activation of microglia is characterized by an increase in the expression level of TSPO, which can be detected by PET. Transmembrane protein 59 (Tmem59) is a membrane protein that plays an important role in neural stem cell differentiation, glioma apoptosis, dendritic spine formation, and Alzheimer’s disease (AD), nevertheless, the involvement of the Tmem59 gene in the brain immune response has not yet been reported. In the current work, we investigated the effect of Tmem59 in neuroinflammation. Methods: 18F-DPA-714 imaging in WT and KO mice were performed using a micro PET/CT. Tmem59 down-expression models and vector controls of BV2 microglia cells were established by psiRNA-Tmem59 and Vehicle plasmid transfection, respectively. The change of gene expression was detected by western blotting analysis. Cell phagocytosis assay was used to study the effect of Dcf1 downregulation on the phagocytic ability of LPS-activated microglia Results: The activation of microglia is characterized by an increase in the expression level of TSPO and Iba1. Using this PET imaging technique, we found that TSPO expression was significantly increased in certain brain regions of Tmem59-KO mice, including the hippocampus, as compared with that of WT mice, indicating that Tmem59 deletion upregulated the ratio of activated microglia to resting microglia. Consistently, the expression level of Iba1 was also significantly increased in Tmem59-KO mice, as reflected by immunostaining and Western blotting analysis, which both show that the mean density in KO mice is 1.5 times that in WT mice. Furthermore, Western blotting analysis shows that the expression level of CD68 was significantly increased in Tmem59-KO mice. To explore the effect of Tmem59 downregulation on the phagocytic ability of LPS-activated microglia, a cell phagocytosis assay was performed. Image analysis shows that compared with the blank, the phagocytic capacity of BV2 cells following treatment with LPS was increased by approximately 10%. Moreover, downregulation of Tmem59 led to a significant decrease of approximately 50% in microglial phagocytic ability as compared with the LPS+vehicle group. Conclusion: In conclusion, our data indicates that Tmem59-deficient microglia induced aberrant proinflammatory cytokines release and subsequent microglial dysfunction, which blocked the phagocytic abilities of activated microglia. Taken together, these observations provide novel insight into the role of Tmem59 in activated microglial cells during the neuroimmune response, and further lay the foundation for the elucidation of the mechanism underlying neuroinflammatory-related diseases. Research Support: This study was supported by the National Natural Science Foundation of China (Project No. 81571345, 81701732), the Research Center on Aging and Medicine, Fudan University (Project No: IDF151006), National Key Research and Development Program Foundation of China(No: 2016YFC1306403), National Key Research and Development Program Foundation of China(No: 2016YFC1306403), Natural Science Foundation and Major Basic Research Program of Shanghai(No: 16JC1420100), Natural Science Foundation and Major Basic Research Program of Shanghai(No: 16JC1420502)