Mutant superoxide dismutase 1-induced IL-1β accelerates ALS pathogenesis

Abstract

ALS is a fatal motor neuron disease of adult onset. Neuroinflammation contributes to ALS disease progression; however, the inflammatory trigger remains unclear. We report that ALS-linked mutant superoxide dismutase 1 (SOD1) activates caspase-1 and IL-1β in microglia. Cytoplasmic accumulation of mutant SOD1 was sensed by an ASC containing inflammasome and antagonized by autophagy, limiting caspase-1-mediated inflammation. Notably, mutant SOD1 induced IL-1β correlated with amyloid-like misfolding and was independent of dismutase activity. Deficiency in caspase-1 or IL-1β or treatment with recombinant IL-1 receptor antagonist (IL-1RA) extended the lifespan of G93A-SOD1 transgenic mice and attenuated inflammatory pathology. These findings identify microglial IL-1β as a causative event of neuroinflammation and suggest IL-1 as a potential therapeutic target in ALS.A LS is a fatal neurodegenerative disorder characterized by progressive loss of motor neurons causing paralysis and finally death within 1-5 years after diagnosis. Dominant gain of function mutations of SOD1 are the most common genetic cause of ALS and also lead to motor neuron disease in mutant SOD1 transgenic mice (1). Mutations induce toxic misfolding and aggregation of SOD1 and interfere with cellular homeostasis in neurons and glia cells (2, 3). Neurodegeneration in ALS is accompanied by glia mediated neuroinflammation, which accelerates disease progression non-cell-autonomously (2, 4). One of the inflammatory markers found in the CNS of ALS mice is active caspase-1, which is also implicated in amyloid-β-mediated inflammation (5-7). Caspase-1 is activated in response to danger signals by cytosolic protein complexes called inflammasomes and proteolytically matures IL-1β and IL-18 (8). Accordingly, IL-1β levels are elevated in the CNS of mutant SOD1 transgenic mice and ALS patients (7). Extracellular mutant SOD1 has been shown to induce an inflammatory reaction by microglia (9, 10); however, the underlying mechanisms are poorly understood. ResultsMutant SOD1 Activates Caspase-1 in Microglia. To test whether mutant SOD1 can act as a danger signal that activates caspase-1 in resident microglia, we stimulated these cells with purified WT or mutant G93A-SOD1. G93A-SOD1, but not the WT protein, activated caspase-1 in microglia and macrophages in a dose-dependent manner ( Fig. 1 A and B). Consistently, time-and dose-dependent secretion of mature IL-1β was observed specifically upon G93A-SOD1 stimulation of microglia or macrophages (Figs. 1C and S1). G93A-SOD1 induced IL-1β maturation was dependent on caspase-1 and could not be observed in astrocytes (Fig. 1 D and E). Notably, caspase-1-mediated IL-1β release in response to G93A-SOD1 was independent of nonproteinaceous contaminants, LPS priming or transgenic mutant SOD1 expression in microglia or macrophages (Figs. S2 and S3). The inflammasome adaptor protein apoptosisassociated speck-like protein containing a caspase recruitment domain (ASC) was essential for IL-1β release in response to G93A-SOD1, whereas the ...

IFNγ triggers a LIGHT-dependent selective death of motoneurons contributing to the non-cell-autonomous effects of mutant SOD1

“…Recently, interleukin (IL)-1b has been proposed to promote a microglial-mediated neuroinflammation process contributing to disease progression in SOD1 G93A mice. 42 In our study, the timing of IFNg expression in SOD1 G93A mice suggests that IFNg participates in the progression rather than the onset of disease, and Light deletion in SOD1 G93A mice delayed progression, but not onset, of motoneuron disease. Cooperation between IFNg and IL-1b provides a potential pathological mechanism for initiating and/or expanding the neuroinflammatory response in ALS.…”

Fingolimod: A Disease-Modifier Drug in a Mouse Model of Amyotrophic Lateral Sclerosis

“…CD11b microglia expression is considered an histological marker for disease progression in animal model of ALS [35], as it is already detectable at clinical onset to further increase at end-stage disease [14]. Inhibition of both iNOS and IL-1β have been proposed as potential therapeutic approach to ALS, as in ALS mice upregulation of iNOS occurs in parallel with motor neuron loss [36], and treatment of presymptomatic ALS mice with IL-1 blocker anakinra increases survival without affecting the time of disease onset [37]. M1 microglia-mediated motor neuron death, driven by nuclear factor kB-dependent mechanisms, has been shown in mSOD1 G93A mice and heterozygous inhibition of nuclear factor kB specifically in the myeloid lineage of mSOD1 G93A mice significantly delayed disease progression and increased survival [4], further supporting the hypothesis that a dampened M1 response might contribute to protective action of fingolimod.…”

Blocking IL-1β to slow down progression of ALS?

“…Meissner et al (2) show that purified mutant SOD1 can directly stimulate microglia to activate caspase-1 and increase secretion of mature IL-1β, after cytoplasmic accumulation. They reproduced the findings of Friedlander et al (7) that SOD1 transgenic mice crossed with mice that are caspase-1 deficient (completely, not selectively in the neurons) had similar disease onset but longer survival.…”

“…Although it is the most common adult motor neuron disease, with a prevalence of 2 per 100,000 individuals, the pathogenesis of ALS has not been unraveled thus far, and there is no cure (1). The PNAS paper by Meissner et al (2) focuses on mutant superoxide dismutase 1 (SOD1) and links this to the proinflammatory cytokine interleukin 1β (IL-1β). The number of specific therapies that block IL-1β signaling is growing, so how optimistic should we be for a therapy for ALS?…”