RESEARCH ARTICLE The Journal of Clinical Investigation Type I interferon response drives neuroinflammation and synapse loss in Alzheimer disease Ethan R. Roy,1,2 Baiping Wang,1 Ying-wooi Wan,3 Gabriel Chiu,1 Allysa Cole,1 Zhuoran Yin,4 Nicholas E. Propson,1,5 Yin Xu,1 Joanna L. Jankowsky,6 Zhandong Liu,7 Virginia M.-Y. Lee,8 John Q. Trojanowski,8 Stephen D. Ginsberg,9,10 Oleg Butovsky,4,11 Hui Zheng,1,3 and Wei Cao1,3 1Huffington Center on Aging, 2Translational Biology & Molecular Medicine Program, and 3Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, USA. 4Ann Romney Center for Neurologic Diseases, Department of Neurology, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, USA. 5Molecular and Cellular Biology Program, Department of Molecular and Cellular Biology, 6Department of Neuroscience, and 7Department of Pediatrics-Neurology, Baylor College of Medicine, Houston, Texas, USA. 8Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA. 9Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York, USA. 10Departments of Psychiatry, Neuroscience & Physiology and the NYU Neuroscience Institute, New York University Langone Medical Center, New York, New York, USA. 11Evergrande Center for Immunologic Diseases, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, USA. Type I interferon (IFN) is a key cytokine that curbs viral infection and cell malignancy. Previously, we demonstrated a potent IFN immunogenicity of nucleic acid–containing (NA-containing) amyloid fibrils in the periphery. Here, we investigated whether IFN is associated with β-amyloidosis inside the brain and contributes to neuropathology. An IFN-stimulated gene (ISG) signature was detected in the brains of multiple murine Alzheimer disease (AD) models, a phenomenon also observed in WT mouse brain challenged with generic NA-containing amyloid fibrils. In vitro, microglia innately responded to NA- containing amyloid fibrils. In AD models, activated ISG-expressing microglia exclusively surrounded NA+ amyloid β plaques, which accumulated in an age-dependent manner. Brain administration of rIFN-β resulted in microglial activation and complement C3-dependent synapse elimination in vivo. Conversely, selective IFN receptor blockade effectively diminished the ongoing microgliosis and synapse loss in AD models. Moreover, we detected activated ISG-expressing microglia enveloping NA-containing neuritic plaques in postmortem brains of patients with AD. Gene expression interrogation revealed that IFN pathway was grossly upregulated in clinical AD and significantly correlated with disease severity and complement activation. Therefore, IFN constitutes a pivotal element within the neuroinflammatory network of AD and critically contributes to neuropathogenic processes. Introduction large panel of IFN-stimulated genes (ISGs) (4–6). IFN is predom- Accumulation of aggregated misfolded proteins is a pathologic inantly expressed by immune cells upon activation of intracel- hallmark of many neurodegenerative diseases, including Alz- lular innate immune sensors recognizing viral or self-derived heimer disease (AD), the most predominant form of dementia. nucleic acids (7–9). While best known for its ability to induce an Accompanying the formation of β-amyloid (Aβ) plaques and neu- antiviral state in cells via ISG induction, IFN is also involved in rofibrillary tangles, the brains of patients with AD are marked by immune modulation and pathology under infectious, autoim- conspicuous and chronic neuroinflammatory responses, mani- mune, and various other conditions (4, 10, 11). Despite exten- fested by reactive microgliosis, astrogliosis, and elevated levels of sive examination in peripheral responses, IFN has been largely proinflammatory cytokines (1–3). under-investigated in AD to date. The type I interferon (IFN) cytokines are innately produced In AD brain, Aβ plaques are structurally and biochemically in response to viral infections and include multiple IFN-α sub- heterogeneous (12, 13). Besides Aβ peptides, nonprotein con- types, IFN-β, IFN-ε, IFN-κ, and IFN-ϖ. All type I IFN species stituents, such as lipids, glycosaminoglycans, and nucleic acids, signal through a common receptor complex, which initiates the have been detected inside plaques (14–23). Previously, we have JAK-STAT signaling pathway and drives the transcription of a shown that soluble protein oligomers (i.e., amyloid precursors) have intrinsic affinity toward anionic cofactors, such as nucleic acids and glycosaminoglycans (GAGs), and that their interaction Related Commentary: p. 1622 expedites the formation of amyloid fibrils (24). In particular, amyloid fibrils containing nucleic acids potently induced IFN Conflict of interest: The authors have declared that no conflict of interest exists. production from peripheral immune cells by activating innate Copyright: © 2020, American Society for Clinical Investigation. immune Toll-like receptors in vitro and in vivo, a response Submitted: September 23, 2019; Accepted: January 3, 2020; Published: March 9, 2020. Reference information: J Clin Invest. 2020;130(4):1912–1930. capable of initiating lupus-like systemic autoimmunity (25, 26). https://doi.org/10.1172/JCI133737. Moreover, patients receiving systemic IFN treatment and those 1912 jci.org Volume 130 Number 4 April 2020 The Journal of Clinical Investigation RESEARCH ARTICLE with HIV-induced dementia display increased IFN activation in as Ifi27I2a and Oas1 (Figure 2A). Despite harboring bona fide amy- the central nervous system (CNS), which is associated with cog- loid fibril structure (24), heparin-containing amyloid was immu- nitive and psychiatric dysfunction (27–30). nologically inert. Primary mixed glial cells responded similarly Given its potential functional impact, we tested the hypoth- to RNA-containing amyloid fibrils, but not to heparin-containing esis that CNS IFN response to immunogenic amyloid may par- amyloid or nonfibril components (Supplemental Figure 2). In con- ticipate neuroinflammation and neuropathology in AD. First, we trast, primary neurons did not react to RNA-containing amyloid assessed IFN pathway expression in multiple Aβ models and pos- (Supplemental Figure 3). These findings revealed a potent immu- itively detected its upregulation in plaque-laden brains. Similar nogenicity of NA-containing amyloid fibrils toward the glial com- to periphery, NA+ amyloid elicited IFN response from CNS glial partment of the CNS milieu. cells in vitro and in vivo. Importantly, we detected NA+ Aβ plaques IFN response represents an immediate early event during accumulated in the brains of multiple Aβ models and activated viral infection. Accordingly, we detected both IFN-β transcript microglia expressing ISGs surrounding them. Additional analysis and protein secretion as early as 6 hours after exposure of cultured demonstrated that IFN activated microglia and induced synapse mixed glia to RNA-containing amyloid fibrils, in conjunction elimination in a complement-dependent manner. Conversely, IFN with significant CXCL10 release (Figure 2B). Heparin-containing blockade in mouse models of AD significantly dampened microg- amyloid was unable to induce IFN-β or CXCL10, and other IFN lia activation and rescued synapse loss in vivo. Furthermore, we subtypes were not significantly altered in the cultures with any examined NA+ neuritic plaques and their relation to microglia acti- treatment (Supplemental Figure 4). To examine the contribu- vation in human AD brains and conducted transcriptome analysis tion of microglia in the innate immune response to amyloids, we to reveal profound IFN pathway activation in clinical AD. Togeth- predepleted microglia from mixed glial cultures with liposome- er, our data identify an IFN-dependent program that is integral to encapsulated clodronate and found that the remaining cells sig- neuroinflammation and neuropathology in AD. nificantly diminished their reactivity to RNA-containing amyloid (Supplemental Figure 5A). In agreement with this finding, puri- Results fied primary microglia produced elevated levels of CXCL10 and Prevalent IFN pathway activation in Aβ models and amyloid-induced TNF-α in response to RNA-containing amyloid in a dose-depen- IFN response. To study IFN pathway activation in AD-relevant brain dent manner (Figure 2C), suggesting NA-containing amyloid can amyloidosis, we analyzed transcriptional profiles of the hippocam- directly activate microglia. To gain further insight into the immu- pus, a brain region crucial for learning and memory but vulnerable nogenicity of different Aβ amyloids, we stimulated primary mixed to pathology, in AD mouse models. Animal models with brain β glial cells with Aβ42 peptides preincubated with either heparin or amyloidosis differ in promoter usage, transgene products, genetic RNA, and detected increased levels of TNF-α and CXCL10 only background, and kinetics of disease progression (31, 32). To con- from cultures treated with Aβ42 complexed with RNA (Supplemen- duct an unbiased survey, we collected hippocampal tissues from tal Figure 5B). Together, NA-containing amyloid fibrils seemingly 4 distinct models: APPNL-G-F (33), 5XFAD, APP;tTa (34), and APP- elicit innate immune response primarily from microglia in vitro. PS1 (35) (Supplemental Table 1; supplemental material available To evaluate the brain’s response to NA+ amyloid in vivo, we online with this article; https://doi.org/10.1172/JCI133737DS1).