Alsin and SOD1G93A Proteins Regulate Endosomal Reactive Oxygen Species Production by Glial Cells and Proinflammatory Pathways Responsible for Neurotoxicity

Department of Anatomy and Cell Biology, The University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 09/2011; 286(46):40151-62. DOI: 10.1074/jbc.M111.279711
Source: PubMed


Recent studies have implicated enhanced Nox2-mediated reactive oxygen species (ROS) by microglia in the pathogenesis of motor neuron death observed in familial amyotrophic lateral sclerosis (ALS). In this context, ALS mutant forms of SOD1 enhance Rac1 activation, leading to increased Nox2-dependent microglial ROS production and neuron cell death in mice. It remains unclear if other genetic mutations that cause ALS also function through similar Nox-dependent pathways to enhance ROS-mediate motor neuron death. In the present study, we sought to understand whether alsin, which is mutated in an inherited juvenile form of ALS, functionally converges on Rac1-dependent pathways acted upon by SOD1(G93A) to regulate Nox-dependent ROS production. Our studies demonstrate that glial cell expression of SOD1(G93A) or wild type alsin induces ROS production, Rac1 activation, secretion of TNFα, and activation of NFκB, leading to decreased motor neuron survival in co-culture. Interestingly, coexpression of alsin, or shRNA against Nox2, with SOD1(G93A) in glial cells attenuated these proinflammatory indicators and protected motor neurons in co-culture, although shRNAs against Nox1 and Nox4 had little effect. SOD1(G93A) expression dramatically enhanced TNFα-mediated endosomal ROS in glial cells in a Rac1-dependent manner and alsin overexpression inhibited SOD1(G93A)-induced endosomal ROS and Rac1 activation. SOD1(G93A) expression enhanced recruitment of alsin to the endomembrane compartment in glial cells, suggesting that these two proteins act to modulate Nox2-dependent endosomal ROS and proinflammatory signals that modulate NFκB. These studies suggest that glial proinflammatory signals regulated by endosomal ROS are influenced by two gene products known to cause ALS.

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    • "Although it cannot be ruled out that some oligomeric form of SOD-1 could be the neurotoxic factor since it has been shown to be secreted (Urushitani et al., 2007) and taken up by cells (Munch et al., 2011), this has not yet been definitively proved. Equally, although some possible SOD-1 toxicity pathways or effects have been suggested as endosomal reactive oxygen species regulation (Li et al., 2011) or increased mitochondrial oxidative stress (Pehar et al., 2014), further research is needed in this direction using the available animal models. Moreover , assessing the neurotoxic species and mechanisms in ALS gets more complicated due to the involvement of other proteins as TDP-43, FUS or C9orf72 also showing neurotoxicity in animal models . "
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    • "Alsin is known to bind three components of the redoxosome: it possesses Rho-GEF domains for Rac1 and Rab5 and it also interacts with SOD1. When coexpressed with SOD1-G93A, alsin was shown to attenuate SOD1-dependent Rac1 activation, ROS generation by NOX2, NFκB induction, TNFα secretion and to protect neurons from toxicity in co-culture studies (Li et al., 2011). This protective effect is in line with the detrimental one exerted by alsin knockdown in motor neurons (Jacquier et al., 2006) and appears to be mediated by the ability of alsin to decrease Rac1 activation in the presence of SOD1-G93A. "
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    • "In line with this, we report a significant decrease of IL-1β and increase in BDNF and IL-10 levels upon treatment using the BBG100 protocol in SOD1-G93A mice. NF-κB mediates NOX2 expression in spinal cord microglia (Lim et al., 2013) and, at the same time, NF-κB is known to be modulated by NOX2 in SOD1- G93A microglia (Li et al., 2011), supporting the hypothesis that oxidative stress triggers a neuroinflammatory mechanism under the regulation of NF-κB transcription. However, we have demonstrated here that NOX2 is downregulated by treatment with BBG starting at both 40 and 100 days, therefore excluding a stringent dependency between NOX2 and NF-κB under our experimental conditions. "
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