Non-cell Autonomous Toxicity in Motor Neuron Disease: Evidence and Mechanisms of Astrocyte-Driven Neurotoxicity in FUS-ALS
Amyotrophic Lateral Sclerosis is a progressively lethal motor neuron disease with no known cure. Genetic evidence suggests a diverse set of underlying causes with broad links to protein quality control and DNA/RNA homeostasis. Cellular evidence suggests that ALS is not only caused by defects within motor neurons but also through significant contributions from non-neuronal cells. In particular, astrocytes have been proposed to gain properties that greatly accelerate disease progression. The most common ALS-causative genes are widely expressed throughout the nervous system, including in astrocytes. While many studies have focused on cell-autonomous defects in ALS motor neurons, less is known about mechanisms by which non-neuronal cells such as astrocytes contribute to motor neuron degeneration. The studies presented here explore the behavior of astrocytes in models of ALS caused by mutations in the DNA/RNA binding protein Fused in Sarcoma (FUS). Here, we studied whether over-expression of wild-type FUS or of mutant FUS disrupts astrocyte function. We further analyzed how FUS-induced alterations in astrocytes alter communication between astrocytes and two cell-types highly relevant to neurodegenerative disease: motor neurons and endothelial cells. To carry out these studies we coupled gene-profiling, quantitative protein assays, microscopy, functional assays, and pharmacological manipulations in cultures of relevant cell-types from rodents and humans, and in an acute mouse model. Through these studies we demonstrate the first evidence that astrocytes expressing mutant FUS are toxic to wild-type motor neurons in vitro. Further we demonstrate that this toxicity is mediated by activation of astrocytic NF-κB transcription factors, elevated production of the pro-inflammatory cytokine TNFα by astrocytes, and TNFα induced changes to motor neuron AMPA receptors that sensitize motor neurons to excitotoxic cell-death. Further we show that FUS patient-derived iPSC astrocytes similarly release increased quantities of TNFα in a blood-brain-barrier model system. Astrocytic TNFα additionally signals onto endothelial cells to increase drug-efflux properties which drive pharmaco-resistance. Lastly, we demonstrate in an acute in vivo model that over-expression of wild-type and mutant FUS in astrocytes causes pathological changes and neurodegeneration. Taken together these studies extend evidence from different genetic models of ALS that astrocytes contribute to disease, provide novel findings that FUS-ALS astrocytes induce pathogenic changes to motor neurons and endothelial cells of the blood-brain-barrier, and provide new mechanistic insights into these phenomena which warrant future studies.
McAvoy, Kevin James, "Non-cell Autonomous Toxicity in Motor Neuron Disease: Evidence and Mechanisms of Astrocyte-Driven Neurotoxicity in FUS-ALS" (2019). ETD Collection for Thomas Jefferson University. AAI13425948.