Astrocytes expressing ALS‐linked mutant FUS induce motor neuron death through release of tumor necrosis factor‐alpha

Abstract

Mutations in fused in sarcoma (FUS) are linked to amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease affecting both upper and lower motor neurons. While it is established that astrocytes contribute to the death of motor neurons in ALS, the specific contribution of mutant FUS (mutFUS) through astrocytes has not yet been studied. Here, we used primary astrocytes expressing a N‐terminally GFP tagged R521G mutant or wild‐type FUS (WTFUS) and show that mutFUS‐expressing astrocytes undergo astrogliosis, damage co‐cultured motor neurons via activation of an inflammatory response and produce conditioned medium (ACM) that is toxic to motor neurons in isolation. Time lapse imaging shows that motor neuron cultures exposed to mutFUS ACM, but not WTFUS ACM, undergo significant cell loss, which is preceded by progressive degeneration of neurites. We found that Tumor Necrosis Factor‐Alpha (TNFα) is secreted into ACM of mutFUS‐expressing astrocytes. Accordingly, mutFUS astrocyte‐mediated motor neuron toxicity is blocked by targeting soluble TNFα with neutralizing antibodies. We also found that mutant astrocytes trigger changes to motor neuron AMPA receptors (AMPAR) that render them susceptible to excitotoxicity and AMPAR‐mediated cell death. Our data provide the first evidence of astrocytic involvement in FUS‐ALS, identify TNFα as a mediator of this toxicity, and provide several potential therapeutic targets to protect motor neurons in FUS‐linked ALS.

Mutant C9orf72 human iPSC‐derived astrocytes cause non‐cell autonomous motor neuron pathophysiology

“…MNs (Devlin et al, 2015). However, in the present study we found that patient iPSC-derived astrocytes caused a reduction in the func- (Re et al, 2014), proinflammatory cytokines and inflammatory mediators (Aebischer et al, 2011;Kia et al, 2018;Phatnani et al, 2013;Tripathi et al, 2017) as well as reactive oxygen species (ROS) (Marchetto et al, 2008;Rao & Weiss, 2004).…”

“…Fritz and colleagues showed that astrocyte conditioned medium, taken from primary cultures of mutant SOD1 expressing mouse astrocytes, induced changes in the output of wild‐type mouse MNs, thus implicating toxic factors released by astrocytes as mediators of altered MN function (Yamanaka & Komine, ). Factors released by astrocytes which may alter MN function include the effectors of necroptosis: receptor‐integrating serine/threonine‐protein kinase 1 (RIP1) and mixed lineage kinase domain‐like (MLKL) (Re et al, ), proinflammatory cytokines and inflammatory mediators (Aebischer et al, ; Kia et al, ; Phatnani et al, ; Tripathi et al, ) as well as reactive oxygen species (ROS) (Marchetto et al, ; Rao & Weiss, ).…”

“…Astrocyte pathology is prominent, with an emerging consensus, particularly from SOD1 based studies, that astrocytes appear critical to disease progression (Papadeas, Kraig, O'Banion, Lepore, & Maragakis, 2011;Wang, Gutmann, & Roos, 2011;Yamanaka et al, 2008). It has also been shown that astrocytes derived from sporadic or familial cases can, upon co-culture or upon exposure to astrocyte conditioned media (ACM), be directly toxic to MNs leading to cell death (Cassina et al, 2008;Di Giorgio, Carrasco, Siao, Maniatis, & Eggan, 2007;Fritz et al, 2013;Haidet-Phillips et al, 2011;Kia, McAvoy, Krishnamurthy, Trotti, & Pasinelli, 2018;Madill et al, 2017;Marchetto et al, 2008;Nagai et al, 2007;Phatnani et al, 2013;Re et al, 2014;Rojas, Cortes, Abarzua, Dyrda, & van Zundert, 2014). In contrast, the influence of astrocytes on MN function is unclear and comparatively understudied.…”

Enhanced SIRT6 activity abrogates the neurotoxic phenotype of astrocytes expressing ALS‐linked mutant SOD1

“…Astrocyte-mediated motor neuron toxicity is a feature observed in ALS animal models and is likely a pathogenic component of the human disease (5)(6)(7)(8)(9). Although the exact nature of the mechanism responsible for this toxicity remains under investigation, we have previously shown that several strategies aimed at modifying astrocyte antioxidant defenses are able to prevent astrocyte-mediated motor neuron death in cocultures (5,10,26,43).…”

“…Astrocytes play a key role in determining motor neuron fate in ALS models, and primary astrocytes overexpressing mutant human SOD1 (hSOD1) or mutant hFUS induce motor neuron death in coculture (5)(6)(7). In line with these observations, astrocytes differentiated from human post mortem ALS spinal cord-derived progenitor cells and astrocytes obtained from the transdifferentiation of fibroblasts from FALS and SALS patients are also toxic for motor neurons in coculture (8,9).…”