Potential Effect of S-Nitrosylated Protein Disulfide Isomerase on Mutant SOD1 Aggregation and Neuronal Cell Death in Amyotrophic Lateral Sclerosis

Abstract

Aggregation of misfolded protein and resultant intracellular inclusion body formation are common hallmarks of mutant superoxide dismutase (mSOD1)-linked familial amyotrophic lateral sclerosis (FALS) and have been associated with the selective neuronal death. Protein disulfide isomerase (PDI) represents a family of enzymatic chaperones that can fold nascent and aberrant proteins in the endoplasmic reticulum (ER) lumen. Recently, our group found that S-nitrosylated PDI could contribute to protein misfolding and subsequent neuronal cell death. However, the exact role of PDI in the pathogenesis of ALS remains unclear. In this study, we propose that PDI attenuates aggregation of mutant/misfolded SOD1 and resultant neurotoxicity associated with ER stress. ER stress resulting in PDI dysfunction therefore provides a mechanistic link between deficits in molecular chaperones, accumulation of misfolded proteins, and neuronal death in neurodegenerative diseases. In contrast, S-nitrosylation of PDI inhibits its activity, increases mSOD1 aggregation, and increases neuronal cell death. Specifically, our data show that S-nitrosylation abrogates PDI-mediated attenuation of neuronal cell death triggered by thapsigargin. Biotin switch assays demonstrate S-nitrosylated PDI both in the spinal cords of SOD1 (G93A) mice and human patients with sporadic ALS. Therefore, denitrosylation of PDI may have therapeutic implications. Taken together, our results suggest a novel strategy involving PDI as a therapy to prevent mSOD1 aggregation and neuronal degeneration. Moreover, the data demonstrate that inactivation of PDI by S-nitrosylation occurs in both mSOD1-linked and sporadic forms of ALS in humans as well as mice.

Global Analysis of S-nitrosylation Sites in the Wild Type (APP) Transgenic Mouse Brain-Clues for Synaptic Pathology

“…Despite thousands of SNO-proteins currently identified (ϳ3000), the observed specificity of S-nitrosylation in terms of target proteins and specific Cys residues is not entirely understood (81,82). S-nitrosylated proteins are implicated in the pathogenesis of various neurodegenerative diseases, including Alzheimer's, Parkinson's and Huntington's diseases, amyotrophic lateral sclerosis, Friedreich ataxia, and many others, where they influence the onset or development of neurodegeneration (8,23,(83)(84)(85).…”

The redox switch that regulates molecular chaperones

“…Cell models of AD pathology show that PDI inactivated through NO triggers an accumulation of poly-ubiquitinated proteins, an increase in ER stress, and induction of apoptosis (92,99). Similar reports using ALS and PD models show that overexpression prevents aggregation, whereas inhibition of PDI results in the accumulation of misfolded proteins (107,(116)(117)(118)(119). Further understanding of these metabolon, offering exciting new roles for these metabolic proteins as redox chaperones (Lee et al, unpublished observations).…”

S-nitrosylation of fatty acid synthase regulates its activity through dimerization

“…We next investigated whether protein S-nitrosylation, a major posttranslational modifi cation by NO, might have a unique role in adipogenesis. Protein S-nitrosylation can occur even at low levels of NO and can affect the activity and stability of specifi c proteins (36)(37)(38)(39). Immunofl uorescence assay using an antibody against nitroso-cysteine showed that protein S-nitrosylation was higher in differentiated adipocytes (day 9) than in undifferentiated preadipocytes ( Fig.…”

“…Protein S-nitrosylation is a major reversible posttranslational modifi cation by NO that regulates protein function and stability (36)(37)(38)(39)(51)(52)(53)(54)(55)(56). Interestingly, it has been reported that protein S-nitrosylation is increased in adipose tissue in a model of obesity ( 41 ).…”

“…A major mechanism mediating the biological function of NO is protein S-nitrosylation, a posttranslational modifi cation of proteins involving the addition of an NO + to a cysteine thiol group of the proteins. Therefore, under physiological conditions, S-nitrosylation can affect a number of cellular signaling pathways by inducing conformational changes of the protein and affecting protein-protein interactions and protein functions (36)(37)(38)(39). NO is reported to improve the ␤ -oxidation of fatty acids through reversible protein S-nitrosylation ( 40 ).…”