Transcriptional mechanism of IRF8 and PU.1 governs microglial activation in neurodegenerative condition

Abstract

Microglial activation occurs in divergent neuropathological conditions. Such microglial event has the key involvement in the progression of CNS diseases. However, the transcriptional mechanism governing microglial activation remains poorly understood. Here, we investigate the microglial response to traumatic injuryinduced neurodegeneration by the 3D fluorescence imaging technique. We show that transcription factors IRF8 and PU.1 are both indispensible for microglial activation, as their specific post-developmental deletion in microglia abolishes the process. Mechanistically, we reveal that IRF8 and PU.1 directly target the gene transcription of each other in a positive feedback to sustain their highly enhanced expression during microglial activation. Moreover, IRF8 and PU.1 dictate the microglial response by cooperatively acting through the composite IRF-ETS motifs that are specifically enriched on microglial activation-related genes. This action of cooperative transcription can be further verified biochemically by the synergetic binding of IRF8 and PU.1 proteins to the composite-motif DNA. Our study has therefore elucidated the central transcriptional mechanism of microglial activation in response to neurodegenerative condition.

Key words： microglia; 3D fluorescence imaging technique; neurodegeneration; IRF8; PU.1

References

1 Aguzzi A, Barres BA, Bennett ML (2013) Microglia: scapegoat, saboteur, or something else? Science 339:156–161

2 Arthur JS, Ley SC (2013) Mitogen-activated protein kinases in innate immunity. Nat Rev Immunol 13:679–692

3 Biber K, Moller T, Boddeke E, Prinz M (2016) Central nervous system myeloid cells as drug targets: current status and translational challenges. Nat Rev Drug Discov 15:110–124

4 Colonna M, Butovsky O (2017) Microglia function in the central nervous system during health and neurodegeneration. Ann Rev Immunol 35:441–468

5 Colonna M, Wang Y (2016) TREM2 variants: new keys to decipher Alzheimer disease pathogenesis. Nat Rev Neurosci 17:201–207

6 Finsen B, Owens T (2011) Innate immune responses in central nervous system inflammation. FEBS Lett 585:3806–3812

7 Fu R, Shen Q, Xu P, Luo JJ, Tang Y (2014) Phagocytosis of microglia in the central nervous system diseases. Mol Neurobiol 49:1422–1434

8 Ginhoux F, Prinz M (2015) Origin of microglia: current concepts and past controversies. Cold Spring Harbor Perspect Biol 7:a020537

9 Ginhoux F, Lim S, Hoeffel G, Low D, Huber T (2013) Origin and differentiation of microglia. Front Cell Neurosci 7:45

10 Goldmann T, Wieghofer P, Muller PF, Wolf Y, Varol D, Yona S, Brendecke SM, Kierdorf K, Staszewski O, Datta M (2013) A new type of microglia gene targeting shows TAK1 to be pivotal in CNS autoimmune inflammation. Nat Neurosci 16:1618–1626

11 Heppner FL, Ransohoff RM, Becher B (2015) Immune attack: the role of inflammation in Alzheimer disease. Nat Rev Neurosci 16:358–372

12 Herz J, Filiano AJ, Smith A, Yogev N, Kipnis J (2017) Myeloid cells in the central nervous system. Immunity 46:943–956

13 Hollenhorst PC, McIntosh LP, Graves BJ (2011) Genomic and biochemical insights into the specificity of ETS transcription factors. Ann Rev Biochem 80:437–471

14 Hong S, Dissing-Olesen L, Stevens B (2016) New insights on the role of microglia in synaptic pruning in health and disease. Curr Opin Neurobiol 36:128–134

15 Horiuchi M, Wakayama K, Itoh A, Kawai K, Pleasure D, Ozato K, Itoh T (2012) Interferon regulatory factor 8/interferon consensus sequence binding protein is a critical transcription factor for the physiological phenotype of microglia. J Neuroinflamm 9:227

16 Inoue K, Tsuda M (2018) Microglia in neuropathic pain: cellular and molecular mechanisms and therapeutic potential. Nat Rev Neurosci 19:138–152

17 Kalin S, Heppner FL, Bechmann I, Prinz M, Tschop MH, Yi CX (2015) Hypothalamic innate immune reaction in obesity. Nat Rev Endocrinol 11:339–351

18 Kettenmann H, Hanisch UK, Noda M, Verkhratsky A (2011) Physiology of microglia. Physiol Rev 91:461–553

19 Kettenmann H, Kirchhoff F, Verkhratsky A (2013) Microglia: new roles for the synaptic stripper. Neuron 77:10–18

20 Kierdorf K, Prinz M (2013) Factors regulating microglia activation. Front Cell Neurosci 7:44

21 Kierdorf K, Erny D, Goldmann T, Sander V, Schulz C, Perdiguero EG, Wieghofer P, Heinrich A, Riemke P, Holscher C (2013) Microglia emerge from erythromyeloid precursors via Pu.1- and Irf8-dependent pathways. Nat Neurosci 16:273–280

22 Lall D, Baloh RH (2017) Microglia and C9orf72 in neuroinflammation and ALS and frontotemporal dementia. J Clin Invest 127:3250–3258

23 Li Q, Barres BA (2018) Microglia and macrophages in brain homeostasis and disease. Nat Rev Immunol 18:225–242

24 Li Y, Okuno Y, Zhang P, Radomska HS, Chen H, Iwasaki H, Akashi K, Klemsz MJ, McKercher SR, Maki RA (2001) Regulation of the PU.1 gene by distal elements. Blood 98:2958–2965

25 Lum FM, Low DK, Fan Y, Tan JJ, Lee B, Chan JK, Renia L, Ginhoux F, Ng LF (2017) Zika virus infects human fetal brain microglia and induces inflammation. Clin Infect Dis 64:914–920

26 Masuda T, Tsuda M, Yoshinaga R, Tozaki-Saitoh H, Ozato K, Tamura T, Inoue K (2012) IRF8 is a critical transcription factor for transforming microglia into a reactive phenotype. Cell Rep 1:334–340

27 McKercher SR, Torbett BE, Anderson KL, Henkel GW, Vestal DJ, Baribault H, Klemsz M, Feeney AJ, Wu GE, Paige CJ (1996) Targeted disruption of the PU.1 gene results in multiple hematopoietic abnormalities. EMBO J 15:5647–5658

28 Meertens L, Labeau A, Dejarnac O, Cipriani S, Sinigaglia L, Bonnet-Madin L, Le TCharpentier ML, Hafirassou A, Zamborlini VM, Cao-Lormeau (2017) Axl mediates ZIKA virus entry in human glial cells and modulates innate immune responses. Cell Rep 18:324–333

29 Meyer-Luehmann M, Prinz M (2015) Myeloid cells in Alzheimer’s disease: culprits, victims or innocent bystanders? Trends Neurosci 38:659–668

30 Michell-Robinson MA, Touil H, Healy LM, Owen DR, Durafourt BA, Bar-Or A, Antel JP, Moore CS (2015) Roles of microglia in brain development, tissue maintenance and repair. Brain 138:1138–1159

31 Minten C, Terry R, Deffrasnes C, King NJ, Campbell IL (2012) IFN regulatory factor 8 is a key constitutive determinant of the morphological and molecular properties of microglia in the CNS. PLoS ONE 7:e49851

32 Nayak D, Roth TL, McGavern DB (2014) Microglia development and function. Ann Rev Immunol 32:367–402

33 Neumann H, Kotter MR, Franklin RJ (2009) Debris clearance by microglia: an essential link between degeneration and regeneration. Brain 132:288–295

34 Okuno Y, Huang G, Rosenbauer F, Evans EK, Radomska HS, Iwasaki H, Akashi K, Moreau-Gachelin F, Li Y, Zhang P (2005) Potential autoregulation of transcription factor PU.1 by an upstream regulatory element. Mol Cell Biol 25:2832–2845

35 Osterloh JM, Yang J, Rooney TM, Fox AN, Adalbert R, Powell EH, Sheehan AE, Avery MA, Hackett R, Logan MA (2012) dSarm/Sarm1 is required for activation of an injury-induced axon death pathway. Science 337:481–484

36 Parkhurst CN, Yang G, Ninan I, Savas JN, Yates JR III, Lafaille JJ, Hempstead BL, Littman DR, Gan WB (2013) Microglia promote learning-dependent synapse formation through brain-derived neurotrophic factor. Cell 155:1596–1609

37 Perry VH, Holmes C (2014) Microglial priming in neurodegenerative disease. Nat Rev Neurol 10:217–224

38 Perry VH, Nicoll JA, Holmes C (2010) Microglia in neurodegenerative disease. Nat Rev Neurol 6:193–201

39 Prinz M, Priller J (2014) Microglia and brain macrophages in the molecular age: from origin to neuropsychiatric disease. Nat Rev Neurol 15:300–312