The transcription factor PU.1 regulates a network of innate and adaptive immune mediators in primary human microglia: implications for Alzheimer's disease Justin Rustenhoven1,2, Amy M. Smith3, Leon C. Smyth1,2, Deidre Jansson1,2, Emma Scotter1,2, Molly Swanson1,4, Miranda Aalderink1,2, Natacha Coppieters1,4, Pritika Narayan5, Thomas IH1,2,4, Patrick Schweder6, Peter Heppner6, Maurice A1,4, Richard LM Faull1,4 and Mike Dragunow1,2 1Department of Pharmacology, University of Auckland, NZ; 2Centre for Brain Research, University of Auckland, NZ; 3Department of Physiology, Anatomy and Genetics, University of Oxford, UK; 4Department of Anatomy and Medical Imaging, University of Auckland, NZ; 5Department of Biology Science, University of Auckland, NZ; 6Auckland City Hospital, NZ
Microglia play critical roles in the brain during homeostasis and pathological conditions. Understanding the molecular events underpinning microglial functions will further enable us to target these cells for the treatment of various neurological disorders. The transcription factor PU.1 is critical in the development of myeloid cells and a major regulator of microglial gene expression. In the brain, PU.1 is specifically expressed in microglia and recent evidence from GWAS suggest that reductions in PU.1 contribute to a delayed onset of AD, possibly through limiting neuroinflammatory responses. In order to understand how PU.1 contributes to immune activation in human microglia, microarray analysis was performed on mixed glial cultures subjected to siRNA-mediated knockdown of PU.1. Bioinformatic analysis of PU.1 silencing in mixed glial cultures revealed a network of modified microglial transcripts involved in the innate and adaptive immune systems, particularly those involved in antigen presentation and phagocytosis. These changes were confirmed using isolated microglial cultures. Utilising high throughput screening of 1280 FDA approved compounds in mixed glial cultures we identified the HDAC inhibitor vorinostat as an effective attenuator of PU.1 expression in human microglia. Further characterisation in isolated microglial cultures revealed changes partially recapitulating those seen following siRNA-mediated PU.1 knockdown. Lastly, we demonstrate that several of these PU.1-regulated genes display microglial expression in the human AD brain in situ, suggesting that attenuating PU.1 may be a valid therapeutic target to limit microglial-mediated inflammatory responses in AD.
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