RIG-I Mediated Neuron-Specific IFN Type 1 Signaling in FUS-ALS Induces Neurodegeneration and Offers New Biomarker-Driven Individualized Treatment Options for (FUS-)ALS.

Recent research demonstrated activation of the innate immune system in ALS models. This pathway can be activated by cGAS-STING sensing of cytosolic DNA that accumulates as a result of chronic DNA damage and defective mitochondria, both of which was identified as pathology in FUS-ALS. Therefore, we analyzed innate immune pathways in FUS-ALS, which revealed upregulation of interferon-stimulated genes (ISGs) and activation of the TBK1-IRF3 pathway in FUSmut iPSC-derived spinal motor neurons (sMNs). Accumulation of cytosolic dsRNA and its sensor RIG-I, but not MDA5, was found to be significantly upregulated in FUSmut sMNs, which was abolished upon siRNA-mediated knockdown of RIG-I. RIG-I was highly expressed in FUS-ALS post-mortem α-MNs. IFN treatment of FUSwt sMNs phenocopied the axonal degeneration of FUSmut sMNs. Mitochondrial transcription, a known source of dsRNA, was found to be upregulated in compartmental axonal RNAseq analysis and its inhibition reduced ISGs in FUS-ALS sMNs. The JAK-STAT inhibitor ruxolitinib alleviated the upregulated ISG expression and reversed the axonal degeneration of sMNs. Finally, we analyzed ISG expression in peripheral blood from 18 FUS-ALS patients, eight of whom had a significantly elevated interferon signature. RIG-I-mediated innate immune activation in sMNs may be an interesting novel individualized biomarker-driven therapeutic target in (FUS-) ALS. A one-sentence summary of your paper: RIG-I-mediated innate immune activation is found in FUS-ALS spinal motor neurons caused by cytosolic dsRNA accumulation due to mitochondrial transcriptional activation and is amenable to JAK-STAT inhibition and might thus be an interesting novel individualized biomarker-driven therapeutic approach in (FUS-) ALS.