Loss of TREM2 rescues hyperactivation of microglia, but not lysosomal deficits and neurotoxicity in models of progranulin deficiency

• Published in: The EMBO journal Vol. 41; no. 4; pp. e109108 - n/a
• Main Authors: Reifschneider, Anika, Robinson, Sophie, van Lengerich, Bettina, Gnörich, Johannes, Logan, Todd, Heindl, Steffanie, Vogt, Miriam A, Weidinger, Endy, Riedl, Lina, Wind, Karin, Zatcepin, Artem, Pesämaa, Ida, Haberl, Sophie, Nuscher, Brigitte, Kleinberger, Gernot, Klimmt, Julien, Götzl, Julia K, Liesz, Arthur, Bürger, Katharina, Brendel, Matthias, Levin, Johannes, Diehl‐Schmid, Janine, Suh, Jung, Di Paolo, Gilbert, Lewcock, Joseph W, Monroe, Kathryn M, Paquet, Dominik, Capell, Anja, Haass, Christian
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 15.02.2022; Blackwell Publishing Ltd; John Wiley and Sons Inc
• Subjects: Ablation; Animals; Antibodies; Antibodies - immunology; Antibodies - pharmacology; Biomarkers; Brain - diagnostic imaging; Brain - physiopathology; Cerebrospinal fluid; Degeneration; Deposition; Disease Models, Animal; EMBO19; EMBO27; Female; Frontotemporal dementia; frontotemporal lobar degeneration; Frontotemporal Lobar Degeneration - metabolism; Frontotemporal Lobar Degeneration - pathology; Haploinsufficiency; Humans; Hypometabolism; Light levels; Lipids; lysosomes; Lysosomes - metabolism; Lysosomes - pathology; Macrophages; Male; Membrane Glycoproteins - genetics; Membrane Glycoproteins - immunology; Membrane Glycoproteins - metabolism; Mice; Mice, Inbred C57BL; Mice, Knockout; Microglia; Microglia - drug effects; Microglia - physiology; Monocytes - drug effects; Monocytes - metabolism; Neurodegeneration; Neuroprotection; Neurotoxicity; Patients; Phagocytes; Pharmacology; Pluripotency; progranulin; Progranulins - deficiency; Receptors, Immunologic - genetics; Receptors, Immunologic - immunology; Receptors, Immunologic - metabolism; Signaling; Stem cell transplantation; Stem cells; Syk Kinase - metabolism; neurodegeneration; progranulin; lysosomes; microglia; frontotemporal lobar degeneration
• ISSN: 0261-4189; 1460-2075
• DOI: 10.15252/embj.2021109108

Haploinsufficiency of the progranulin (PGRN)‐encoding gene ( GRN ) causes frontotemporal lobar degeneration ( GRN ‐FTLD) and results in microglial hyperactivation, TREM2 activation, lysosomal dysfunction, and TDP‐43 deposition. To understand the contribution of microglial hyperactivation to pathology, we used genetic and pharmacological approaches to suppress TREM2‐dependent transition of microglia from a homeostatic to a disease‐associated state. Trem2 deficiency in Grn KO mice reduced microglia hyperactivation. To explore antibody‐mediated pharmacological modulation of TREM2‐dependent microglial states, we identified antagonistic TREM2 antibodies. Treatment of macrophages from GRN ‐FTLD patients with these antibodies led to reduced TREM2 signaling due to its enhanced shedding. Furthermore, TREM2 antibody‐treated PGRN‐deficient microglia derived from human‐induced pluripotent stem cells showed reduced microglial hyperactivation, TREM2 signaling, and phagocytic activity, but lysosomal dysfunction was not rescued. Similarly, lysosomal dysfunction, lipid dysregulation, and glucose hypometabolism of Grn KO mice were not rescued by TREM2 ablation. Synaptic loss and neurofilament light‐chain (NfL) levels, a biomarker for neurodegeneration, were further elevated in the Grn / Trem2 KO cerebrospinal fluid (CSF). These findings suggest that TREM2‐dependent microglia hyperactivation in models of GRN deficiency does not promote neurotoxicity, but rather neuroprotection. SYNOPSIS Patients suffering from progranulin (PGRN) associated frontotemporal lobar degeneration ( GRN ‐FTLD) exhibit hyperactivated microglia, lysosomal dysfunction and TDP‐43 deposition. Suppression of TREM2 reverses hyperactivation of microglia in models of PGRN deficiency. Hyperactivated microglia in models of PGRN deficiency retain neuroprotective functions. Lysosomal dysfunction is independent of microglia activation stages. Graphical Abstract TREM2‐dependent hyperactivated microglia retain neuroprotective functions in the neurodegenerative disorder GRN ‐FTLD.