The Redox Activity of Protein Disulfide Isomerase Inhibits ALS Phenotypes in Cellular and Zebrafish Models

Abstract

Pathological forms of TAR DNA-binding protein 43 (TDP-43) are present in almost all cases of amyotrophic lateral sclerosis (ALS), and 20% of familial ALS cases are due to mutations in superoxide dismutase 1 (SOD1). Redox regulation is critical to maintain cellular homeostasis, although how this relates to ALS is unclear. Here, we demonstrate that the redox function of protein disulfide isomerase (PDI) is protective against protein misfolding, cytoplasmic mislocalization of TDP-43, ER stress, ER-Golgi transport dysfunction, and apoptosis in neuronal cells expressing mutant TDP-43 or SOD1, and motor impairment in zebrafish expressing mutant SOD1. Moreover, previously described PDI mutants present in patients with ALS (D292N, R300H) lack redox activity and were not protective against ALS phenotypes. Hence, these findings implicate the redox activity of PDI centrally in ALS, linking it to multiple cellular processes. They also imply that therapeutics based on PDI's redox activity will be beneficial in ALS.

Redox Post-translational Modifications of Protein Thiols in Brain Aging and Neurodegenerative Conditions—Focus on S-Nitrosation

“…The multifunctional protein PDI is also aberrantly S-nitrosated in neurodegenerative conditions as shown in postmortem spinal cords of ALS patients and transgenic SOD1 G93A mouse model of ALS as well as in postmortem brains of AD and PD patients (Uehara et al, 2006 ; Walker et al, 2009 ; Chen et al, 2013 ; Jeon et al, 2014 ; Conway and Harris, 2015 ; Figure 2D ). PDI is an ER protein, but in disease conditions, triggered by redox PTMs in particular, it can translocate to the cytoplasm where it localizes to inclusions containing ALS-associated proteins (Turano et al, 2002 ; Honjo et al, 2011 ; Walker and Atkin, 2011 ; Farg et al, 2012 ; Jeon et al, 2014 ; Valle and Carrì, 2017 ; Matsusaki et al, 2020 ; Parakh et al, 2020 ). PDI, as an oxidoreductase chaperone, catalyzes the maturation of disulfide bond-containing proteins through oxidation and isomerization functions (Gonzalez et al, 2010 ).…”

Emerging Evidence Highlighting the Importance of Redox Dysregulation in the Pathogenesis of Amyotrophic Lateral Sclerosis (ALS)

“…There is now growing evidence for a role of PDI in ALS (Parakh and Atkin, 2015 ; Parakh et al, 2020 ). PDI levels are upregulated in transgenic models of ALS and spinal cord tissues of ALS patients (Walker et al, 2010 ; Honjo et al, 2011 ; Jeon et al, 2014 ).…”

“…Mutations in PDI and ERp57 were also described in ALS patients, but are thought to be more of a risk factor than directly causative of neurodegeneration (Woehlbier et al, 2016 ). Recently, the redox function of PDI, in contrast to its chaperone function, was shown to be protective against multiple cellular processes that dysfunction in ALS; protein misfolding, mislocalization of TDP-43 to the cytoplasm, ER stress, inhibition of ER-Golgi transport, and apoptosis, in neuronal cells expressing pathological forms of TDP-43 or SOD1 (Parakh et al, 2020 ). Furthermore, the redox activity of PDI, but not its chaperone function, rescued motor dysfunction and axonopathy in zebrafish models of ALS expressing mutant SOD1, together implying that PDI has an important role both in vitro and in vivo (Parakh et al, 2020 ).…”

“…Recently, the redox function of PDI, in contrast to its chaperone function, was shown to be protective against multiple cellular processes that dysfunction in ALS; protein misfolding, mislocalization of TDP-43 to the cytoplasm, ER stress, inhibition of ER-Golgi transport, and apoptosis, in neuronal cells expressing pathological forms of TDP-43 or SOD1 (Parakh et al, 2020 ). Furthermore, the redox activity of PDI, but not its chaperone function, rescued motor dysfunction and axonopathy in zebrafish models of ALS expressing mutant SOD1, together implying that PDI has an important role both in vitro and in vivo (Parakh et al, 2020 ). In contrast, the PDI ALS-mutants (D292N and R300H) lack this redox activity and were not protective against ALS phenotypes, further confirming the importance of the redox activity of PDI in ALS (Parakh et al, 2020 ).…”

“…Also, several pathogenic mechanisms linked to ALS involve redox-sensitive proteins, including protein disulfide isomerase (PDI), thioredoxin, and glutathione (GSH), and recent evidence highlights their importance in neurodegeneration. However, whilst redox dysfunction has been associated with ALS for some time (Harraz et al, 2008 ; Cohen et al, 2012 ; Conrad et al, 2013 ; Parakh et al, 2020 ), a precise understanding of how cellular redox conditions are dysregulated has been lacking. Nevertheless, recent evidence implies that redox homeostasis is a central and primary mechanism in ALS and it may have greater importance than previously recognized (Sbodio et al, 2019 ; Parakh et al, 2020 ).…”