TNFa hinders FGF4 efficacy to mitigate ALS astrocyte dysfunction and cGAS-STING pathway-induced innate immune reactivity

Astrocytes play an important role in the onset and progression of amyotrophic lateral sclerosis (ALS), a fatal disorder characterized by the relentless degeneration of motor neurons (MNs) in the central nervous system. Despite evidence showing that ALS astrocytes are toxic to MNs, little is understood about the earliest pathological changes that lead to their neurotoxic phenotype. In this study, we generated human astrocytes from induced pluripotent stem cells (iPSCs) harboring the ALS-associated A4V mutation in superoxide dismutase 1 (SOD1), to examine cellular pathways and network changes similar to early stages of the disease. By using proteomics as a molecular indicator, we observed significant alterations in the levels of proteins linked to ALS pathology and the cGAS-STING pathway-induced innate immunity. Interestingly, we found that the protein profile of reactive ALS astrocytes differed from that of wildtype astrocytes treated with the pro-inflammatory cytokine TNF. Notably, we showed that fibroblast growth factor 4 (FGF4) reversed ALS astrocyte dysfunction and reactivity, but failed to provide protection to MNs when expressed in the spinal cord of the SOD1G93A mouse model of ALS. Further analysis showed that ALS astrocyte reactivity which was rescued by FGF4 was abrogated by TNF. The latter is capable of exacerbating the dysfunction and reactivity of ALS astrocytes compared to control. Our data show that iPSC-derived ALS astrocytes are dysfunctional and spontaneously exhibit a reactive phenotype when generated from iPSCs. This suggests that this phenotype may resemble the early stages of the disease. Our data also demonstrate that reducing mutant astrocyte reactivity in vivo using FGF4 is not sufficient to prevent MN death in a mouse model of ALS. To mitigate ALS, future studies should investigate whether dual therapies that both lower astrocyte reactivity and reverse disease-associated cellular dysfunction could prevent MN death. Graphic abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=193 SRC="FIGDIR/small/566131v1_ufig1.gif" ALT="Figure 1"> View larger version (48K): org.highwire.dtl.DTLVardef@9490b5org.highwire.dtl.DTLVardef@1a897e5org.highwire.dtl.DTLVardef@18c4578org.highwire.dtl.DTLVardef@24da7d_HPS_FORMAT_FIGEXP M_FIG C_FIG Highlights- ALS astrocytes are dysfunctional and reactive compared to wildtype astrocytes - FGF4 reverses ALS astrocyte dysfunction and reactivity - FGF4 lowers ALS astrocyte reactivity in vivo but fails to protect ALS motor neurons from death - ALS astrocyte reactivity rescued by FGF4 is attenuated by TNF