Extracellular mutant SOD1 induces microglial-mediated motoneuron injury.
Through undefined mechanisms, dominant mutations in (Cu/Zn) superoxide dismutase-1 (mSOD1) cause the non-cell-autonomous death of motoneurons in inherited amyotrophic lateral sclerosis (ALS). Microgliosis at sites of motoneuron injury is a neuropathological hallmark of ALS. Extracellular mutant SOD1 (mSOD1) causes motoneuron injury and triggers microgliosis in spinal cord cultures, but it is unclear whether the injury results from extracellular mSOD1 directly interacting with motoneurons or is mediated through mSOD1-activated microglia. To dissociate these potential mSOD1-mediated neurotoxic mechanisms, the effects of extracellular human mSOD1(G93A) or mSOD1(G85R) were assayed using primary cultures of motoneurons and microglia. The data demonstrate that exogenous mSOD1(G93A) did not cause detectable direct killing of motoneurons. In contrast, mSOD1(G93A) or mSOD1(G85R) did induce the morphological and functional activation of microglia, increasing their release of pro-inflammatory cytokines and free radicals. Furthermore, only when microglia was co-cultured with motoneurons did extracellular mSOD1(G93A) injure motoneurons. The microglial activation mediated by mSOD1(G93A) was attenuated using toll-like receptors (TLR) 2, TLR4 and CD14 blocking antibodies, or when microglia lacked CD14 expression. These data suggest that extracellular mSOD1(G93A) is not directly toxic to motoneurons but requires microglial activation for toxicity, utilizing CD14 and TLR pathways. This link between mSOD1 and innate immunity may offer novel therapeutic targets in ALS.
Zhao
Weihua
W
Department of Neurology, Methodist Neurological Institute, The Methodist Research Institute, The Methodist Hospital, Houston, Texas, USA.
Beers
David R
DR
Henkel
Jenny S
JS
Zhang
Wei
W
Urushitani
Makoto
M
Julien
Jean-Pierre
JP
Appel
Stanley H
SH
D000818:Animals; D016923:Cell Death / Q000502:physiology; D002478:Cells, Cultured; D018920:Coculture Techniques; D005110:Extracellular Space / Q000378:metabolism*; D006801:Humans; D018950:Lipopolysaccharide Receptors / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D017628:Microglia / Q000166:cytology / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology*; D020125:Mutation, Missense; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D013116:Spinal Cord / Q000166:cytology / Q000503:physiopathology; D013482:Superoxide Dismutase / Q000235:genetics* / Q000378:metabolism*; D000072105:Superoxide Dismutase-1; D051195:Toll-Like Receptor 2 / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000378:metabolism
D018950:Lipopolysaccharide Receptors; D011994:Recombinant Proteins; C000606290:SOD1 protein, human; C493486:Tlr2 protein, mouse; C493487:Tlr4 protein, mouse; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; C000606291:Sod1 protein, mouse; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1