Targeting TNFα produced by astrocytes expressing amyotrophic lateral sclerosis-linked mutant fused in sarcoma prevents neurodegeneration and motor dysfunction in mice

Genetic mutations that cause amyotrophic lateral sclerosis (ALS), a progressively lethal motor neuron disease, are commonly found in ubiquitously expressed genes. In addition to direct defects within motor neurons, growing evidence suggests that dysfunction of non-neuronal cells is also an important driver of disease. Previously, we demonstrated that mutations in DNA/RNA binding protein fused in sarcoma (FUS) induce neurotoxic phenotypes in astrocytes in vitro, via activation of the NF-κB pathway and release of pro-inflammatory cytokine TNFα. Here, we developed an intraspinal cord injection model to test whether astrocyte-specific expression of ALS-causative FUS^R521G variant (mtFUS) causes neuronal damage in vivo. We show that restricted expression of mtFUS in astrocytes is sufficient to induce death of spinal motor neurons leading to motor deficits through upregulation of TNFα. We further demonstrate that TNFα is a key toxic molecule as expression of mtFUS in TNFα knockout animals does not induce pathogenic changes. Accordingly, in mtFUS-transduced animals, administration of TNFα neutralizing antibodies prevents neurodegeneration and motor dysfunction. Together, these studies strengthen evidence that astrocytes contribute to disease in ALS and establish, for the first time, that FUS-ALS astrocytes induce pathogenic changes to motor neurons in vivo. Our work identifies TNFα as the critical driver of mtFUS-astrocytic toxicity and demonstrates therapeutic success of targeting TNFα to attenuate motor neuron dysfunction and death. Ultimately, through defining and subsequently targeting this toxic mechanism, we provide a viable FUS-ALS specific therapeutic strategy, which may also be applicable to sporadic ALS where FUS activity and cellular localization are frequently perturbed.