TDP-43 Triggers Mitochondrial DNA Release via mPTP to Activate cGAS/STING in ALS

Chien-Hsiung Yu,Kate Mcarthur,Bradley J Turner,Fiona Moghaddas,Dominic De Nardo,Christopher J Tonkin,Sophia Davidson,Shiraz Tyebji,Cassandra R Harapas,Peter J Crouch,Seth L Masters,Michael P Gantier,Dale J Calleja,Erya Ni,Michael J Mlodzianoski,Jonas Moecking,Cynthia Louis,Kelly L Rogers,Pawat Laohamonthonkul,Katherine R Balka,Ronnie Ren Jie Low,James B Hilton,Geneviève Pépin ,Chris R Bye ,André L Samson ,Catriona Mclean

doi:10.1016/j.cell.2020.09.020

Abstract

SummaryCytoplasmic accumulation of TDP-43 is a disease hallmark for many cases of amyotrophic lateral sclerosis (ALS), associated with a neuroinflammatory cytokine profile related to upregulation of nuclear factor κB (NF-κB) and type I interferon (IFN) pathways. Here we show that this inflammation is driven by the cytoplasmic DNA sensor cyclic guanosine monophosphate (GMP)-AMP synthase (cGAS) when TDP-43 invades mitochondria and releases DNA via the permeability transition pore. Pharmacologic inhibition or genetic deletion of cGAS and its downstream signaling partner STING prevents upregulation of NF-κB and type I IFN induced by TDP-43 in induced pluripotent stem cell (iPSC)-derived motor neurons and in TDP-43 mutant mice. Finally, we document elevated levels of the specific cGAS signaling metabolite cGAMP in spinal cord samples from patients, which may be a biomarker of mtDNA release and cGAS/STING activation in ALS. Our results identify mtDNA release and cGAS/STING activation as critical determinants of TDP-43-associated pathology and demonstrate the potential for targeting this pathway in ALS.

Highlights

TDP-43 is a nuclear DNA/RNA binding protein that is mutated in 4% of familial amyotrophic lateral sclerosis (ALS) (Kabashi et al, 2008; Sreedharan et al, 2008); its cytoplasmic accumulation is observed in neurons of almost all patients with sporadic ALS and defines the major pathological subtype of frontotemporal lobar degeneration (FTLD) (Neumann et al, 2006)
Inflammatory Signaling from TDP-43 Is Dependent on cyclic guanosine monophosphate (GMP)-AMP synthase (cGAS)/STING To examine inflammation triggered by TDP-43, we employed inducible expression of empty vector, wild-type (WT), or ALS mutant (Q331K) TDP-43 in a mouse neuronal cell line, which confirmed upregulation of nuclear factor kB (NF-kB) and type I IFN pathways in vitro (Figures S1A–S1C)
Deletion of cGAS, a sensor of cytoplasmic DNA, returned activation of these pathways to baseline (Figure 1A). cGAS signals via generation of a specific cyclic dinucleotide, cGAMP, which we could detect in response to TDP-43 (Figure S1F). cGAMP acts to trigger STING, which, as we confirmed using genetically deficient MEFs, prevents TDP-43-induced inflammation (Figure 1A)

Summary

Introduction

TDP-43 is a nuclear DNA/RNA binding protein that is mutated in 4% of familial amyotrophic lateral sclerosis (ALS) (Kabashi et al, 2008; Sreedharan et al, 2008); its cytoplasmic accumulation is observed in neurons of almost all patients with sporadic ALS and defines the major pathological subtype of frontotemporal lobar degeneration (FTLD) (Neumann et al, 2006). Aside from two RNA binding domains, TDP-43 encodes a nuclear localization sequence and nuclear export sequence, which mediate shuttling between the nucleus and cytosol, and a low-complexity glycine-rich region, which is where missense mutations (e.g., A315T, Q331K, or M337V) have been found to cause ALS (Kabashi et al, 2008; Sreedharan et al, 2008). Recent studies demonstrate that ALSassociated mutations enhance TDP-43 accumulation in the cytoplasm but within mitochondria (Magraneet al., 2014; Wang et al, 2013, 2017) and that preventing its translocation through the inner mitochondrial membrane can prevent neurotoxicity (Wang et al, 2016).

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