RT Journal Article
SR Electronic
T1 Impaired Extracellular Secretion of Mutant Superoxide Dismutase 1 Associates with Neurotoxicity in Familial Amyotrophic Lateral Sclerosis
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 108
OP 117
DO 10.1523/JNEUROSCI.4253-04.2005
VO 25
IS 1
A1 Bradley J. Turner
A1 Julie D. Atkin
A1 Manal A. Farg
A1 Da Wei Zang
A1 Alan Rembach
A1 Elizabeth C. Lopes
A1 Justin D. Patch
A1 Andrew F. Hill
A1 Surindar S. Cheema
YR 2005
UL http://www.jneurosci.org/content/25/1/108.abstract
AB Mutations in the intracellular metalloenzyme superoxide dismutase 1 (SOD1) are linked to neurotoxicity in familial amyotrophic lateral sclerosis (ALS) by an unclear mechanism. Golgi fragmentation and endoplasmic reticulum stress are early hallmarks of spinal motor neuron pathology in transgenic mice overexpressing mutant SOD1, suggesting that dysfunction of the neuronal secretory pathway may contribute to ALS pathogenesis. We therefore proposed that mutant SOD1 directly engages and modulates the secretory pathway based on recent evidence of SOD1 secretion in diverse human cell lines. Here, we demonstrate that a fraction of active endogenous SOD1 is secreted by NSC-34 motor neuron-like cells via a brefeldin-A (BFA)-sensitive pathway. Expression of enhanced green fluorescent protein-tagged mutant human SOD1 (hSOD1-EGFP) in NSC-34 cells induced frequent cytoplasmic inclusions and protein insolubility that correlated with toxicity. In contrast, transfection of non-neuronal COS-7 cells resulted in mutant hSOD1-EGFP cytoplasmic inclusions, oligomerization, and fragmentation without detectable toxicity. Importantly, impaired secretion of hSOD1-EGFP was common to all 10 SOD1 mutants tested relative to wild-type protein in NSC-34 cells. Treatment with BFA inhibited hSOD1-EGFP secretion with pronounced BFA-induced toxicity in mutant cells. Extracellular targeting of mutant hSOD1-EGFP via SOD3 signal peptide fusion attenuated cytoplasmic inclusion formation and toxicity. The effect of elevated extracellular SOD1 was then evaluated in a transgenic rat model of ALS. Chronic intraspinal infusion of exogenous wild-type hSOD1 significantly delayed disease progression and endpoint in transgenic SOD1G93A rats. Collectively, these results suggest novel extracellular roles for SOD1 in ALS and support a causal relationship between mutant SOD1 secretion and intraneuronal toxicity.