Effects of TDP-43 Pathology on Innate Antiviral Mechanisms in Neurodegenerative Disease

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Project Summary/Abstract Dysregulation of transactivating response region DNA-binding protein-43 (TDP-43) has been linked to many neurodegenerative diseases, including frontotemporal dementia, amyotrophic lateral sclerosis, and Alzheimer’s disease (AD). TDP-43 has a variety of functions linked to its RNA-binding motif, including regulation of transcription, splicing, and RNA transport. Along with these effects, TDP-43 alters expression of interferon (IFN)- related and other immune genes essential for antiviral responses. The relationship between viral pathogens and TDP-43 is bidirectional, as exposure to poly(I:C), which simulates viral pathogens, can promote subcellular mislocalization of TDP-43. Viral pathogens, like TDP-43 dysregulation, are linked to AD and other dementias; AD has been associated with increased presence of viral pathogens, like herpes simplex virus 1 (HSV-1), and altered IFN-related signaling and neuroimmune cascades. Our laboratory found that, like neuronal TDP-43, astrocytic TDP-43 can be mislocalized to the cytoplasm in AD. Dysregulation of astrocytic TDP-43 in mouse models caused neural deficits and cell-autonomous changes in antiviral and IFN-inducible factors. Further, dysregulated TDP-43 increased astrocytic susceptibility to HSV-1. Astrocytic susceptibility to HSV-1 associated with overexpression of human TDP-43 was reduced by blocking the ability of human TDP-43 to bind RNA. Previous studies also show that the RNA-binding domain on TDP-43 is necessary for its other disease-linked effects. Based on this evidence, I will test the hypothesis that dementia-related TDP-43 dysfunction affects antiviral pathways and increases neural susceptibility to HSV-1 by altering TDP-43 binding to host RNA, resulting in aberrant host antiviral and immune gene expression and impaired innate antiviral signaling. I propose to use a variety of cellular and molecular techniques to examine in vitro (Aim 1.1) and in vivo (Aim 1.2) susceptibility to HSV-1 following cell-specific expression of TDP-43 variants that either maintain nuclear localization, mislocalize to the cytoplasm, cannot bind to RNA, or both. I will also determine cell-specific molecular mechanisms that promote differences in antiviral pathways via single-cell RNA sequencing (Aim 2.1), and conduct targeted analysis of alternative splicing (ScISOr-Seq), transposable element expression (TEtranscripts), and protein levels (Western blotting). Finally, I will examine the physiological functions of differential genes of interest identified in Aim 2.1 using genetic and pharmacological approaches. Uncovering the mechanistic links that connect TDP-43 dysregulation to antiviral pathways and viral susceptibility may define new pathobiological mechanisms and therapeutic targets to prevent neurodegenerative disease onset and progression.