Neuronal TDP-43 pathology drives astrocytic interferon response in a mouse model of ALS

Neuroinflammation is implicated in the pathogenesis of Amyotrophic Lateral Sclerosis (ALS). Amongst potential innate immune mediators of disease, Type I interferon (IFN-I) could play an important role due to its ability to inhibit protein synthesis and affect neuronal synapses and metabolism. These effects could be cell intrinsic or non-cell autonomous mediated by glia or immune cells. We examined IFN-I in rNLS8 mice that have been engineered to express doxycycline suppressible human Transactive response DNA binding protein 43 kDa (hTDP-43) with a defective nuclear localization signal (hTDP-43ΔNLS) regulated by the neurofilament heavy chain (NEFH) promoter. Following induction of hTDP-43ΔNLS in rNLS8 mice, we observed upregulation of IFN-I stimulated genes (ISG) and, specifically, activation of the DNA sensor, cyclic GMP-AMP synthase (cGAS), as determined by mass spectrometry identification of the cyclic dinucleotide, cGAMP, in whole brain. To determine the cellular source of IFN-I, we performed single nucleus RNA sequencing of whole brain. We observed that ISG were most highly upregulated in astrocytes suggesting that astrocytes themselves were largely responsible for IFN-I production and / or response in rNLS8 mice. This observation was confirmed by immunohistochemical and immunofluorescence staining of IFN-I stimulated proteins in astrocytes in the cerebrum, especially in the hippocampus. These results point to a pivotal role of astrocytes in responding to cell damage at a relatively early phase of disease which prior studies have shown is partially reversible.