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

ABSTRACT 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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    ABSTRACT: Prion diseases or Transmissible Spongiform Encephalopathies (TSEs) are a group of fatal neurodegenerative disorders affecting several mammalian species being Creutzfeldt-Jacob Disease (CJD) the most representative in human beings, scrapie in ovine, Bovine Spongiform Encephalopathy (BSE) in bovine and Chronic Wasting Disease (CWD) in cervids. As stated by the "protein-only hypothesis", the causal agent of TSEs is a self-propagating aberrant form of the prion protein (PrP) that through a misfolding event acquires a β-sheet rich conformation known as PrP(Sc) (from scrapie). This isoform is neurotoxic, aggregation prone and induces misfolding of native cellular PrP. Compelling evidence indicates that disease-specific protein misfolding in amyloid deposits could be shared by other disorders showing aberrant protein aggregates such as Alzheimer's Disease (AD), Parkinson's Disease (PD), Amyotrophic lateral sclerosis (ALS) and systemic Amyloid A amyloidosis (AA amyloidosis). Evidences of shared mechanisms of the proteins related to each disease with prions will be reviewed through the available in vivo models. Taking prion research as reference, typical prion-like features such as seeding and propagation ability, neurotoxic species causing disease, infectivity, transmission barrier and strain evidences will be analyzed for other protein-related diseases. Thus, prion-like features of amyloid β peptide and tau present in AD, α-synuclein in PD, SOD-1, TDP-43 and others in ALS and serum α-amyloid (SAA) in systemic AA amyloidosis will be reviewed through models available for each disease. Copyright © 2015. Published by Elsevier B.V.
    Virus Research 04/2015; 207. DOI:10.1016/j.virusres.2015.04.014 · 2.32 Impact Factor
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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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    ABSTRACT: Rac1 is a major player of the Rho family of small GTPases that controls multiple cell signaling pathways, such as the organization of cytoskeleton (including adhesion and motility), cell proliferation, apoptosis and activation of immune cells. In the nervous system, in particular, Rac1 GTPase plays a key regulatory function of both actin and microtubule cytoskeletal dynamics and thus it is central to axonal growth and stability, as well as dendrite and spine structural plasticity. Rac1 is also a crucial regulator of NADPH-dependent membrane oxidase (NOX), a prominent source of reactive oxygen species (ROS), thus having a central role in the inflammatory response and neurotoxicity mediated by microglia cells in the nervous system. As such, alterations in Rac1 activity might well be involved in the processes that give rise to Amyotrophic Lateral Sclerosis (ALS), a complex syndrome where cytoskeletal disturbances in motor neurons and redox alterations in the inflammatory compartment play pivotal and synergic roles in the final disease outcomes. Here we will discuss the genetic and mechanistic evidence indicating the relevance of Rac1 dysregulation in the pathogenesis of ALS.
    Frontiers in Cellular Neuroscience 09/2014; 8:279. DOI:10.3389/fncel.2014.00279 · 4.29 Impact Factor
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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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    ABSTRACT: In recent years there has been an increasing awareness on the role of P2X7 receptor for extracellular ATP in modulating physiopathological mechanisms in the CNS. In particular, P2X7 was shown to be implicated in neuropsychiatry, chronic pain, neurodegeneration, neuroinflammation. Remarkably, P2X7 was shown to be a "gene modifier" in amyotrophic lateral sclerosis (ALS): the receptor is up-regulated in spinal cord microglia in human and rat at advanced stages of the disease; in vitro, activation of P2X7 exacerbates pro-inflammatory responses in ALS-microglia, as well as toxicity towards neuronal cells. Despite this detrimental in vitro role of P2X7, in P2X7(-/-)/SOD1-G93A mice the clinical onset of ALS was significantly accelerated and disease progression worsened, thus indicating that the receptor might have some beneficial effects at least at certain stages of disease. In order to clarify this dual action of P2X7 in ALS pathogenesis, in the present work we used the antagonist Brilliant Blue G (BBG), a blood-brain barrier permeable and safe drug already proven to reduce neuroinflammation in traumatic brain injury, cerebral ischemia/reperfusion, neuropathic pain and experimental autoimmune encephalitis. We tested BBG in SOD1-G93A ALS mouse model at asymptomatic, pre-symptomatic and late pre-symptomatic phases of disease. BBG at late pre-onset significantly enhances motoneuron survival and reduces microgliosis in lumbar spinal cord, modulating inflammatory markers such as NF-κB, NADPH oxidase 2, interleukin-1β, interleukin-10 and brain-derived neurotrophic factor. This is accompanied by delayed onset and improved general conditions and motor performance, in both male and female mice, although survival appears not affected. Our results prove the twofold role of P2X7 in the course of ALS, and establish that P2X7 modulation might represent a promising therapeutic strategy by interfering with the neuroinflammatory component of the disease.
    Disease Models and Mechanisms 07/2014; 7(9). DOI:10.1242/dmm.017038 · 4.97 Impact Factor
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