Reversal of Alpha-Synuclein Fibrillization by Protein Disulfide Isomerase

Abstract

Aggregates of α-synuclein contribute to the etiology of Parkinson's Disease. Protein disulfide isomerase (PDI), a chaperone and oxidoreductase, blocks the aggregation of α-synuclein. An S-nitrosylated form of PDI that cannot function as a chaperone is associated with elevated levels of aggregated α-synuclein and is found in brains afflicted with Parkinson's Disease. The protective role of PDI in Parkinson's Disease and other neurodegenerative disorders is linked to its chaperone function, yet the mechanism of neuroprotection remains unclear. Using Thioflavin-T fluorescence and transmission electron microscopy, we show here for the first time that PDI can break down nascent fibrils of α-synuclein. Mature fibrils were not affected by PDI. Another PDI family member, ERp57, could prevent but not reverse α-synuclein aggregation. The disaggregase activity of PDI was effective at a 1:50 molar ratio of PDI:α-synuclein and was blocked by S-nitrosylation. PDI could not reverse the aggregation of malate dehydrogenase, which indicated its disaggregase activity does not operate on all substrates. These findings establish a previously unrecognized disaggregase property of PDI that could underlie its neuroprotective function.

C-terminal truncation modulates α-Synuclein’s cytotoxicity and aggregation by promoting the interactions with membrane and chaperone

“…This result points to an autoinhibitory role for the C-terminus on fibrillation, consistent with the previous studies 20,23,60 . As expected, the presence of PDI inhibits FL-α-syn aggregation 52,61,62 , but inhibits CT-α-syn aggregation to a somewhat smaller extent, as reflected by an over 3-fold increase in lag time for FL-α-syn whereas less than 2-fold for CT-α-syn. Besides, half-time of aggregation (t 1/2 ) clearly shows that PDI exerted a less inhibitory effect on CT-αsyn aggregation (Fig.…”

ERp57 chaperon protein protects neuronal cells from Aβ‐induced toxicity

“…its neuroprotective action resides in ERp57 impairment of peptide aggregation, rather than in disaggregation of existing fibrils. The inhibition of the aggregation was induced by low amounts of ERp57 protein, present in the reaction mixture in a very low molar ratio compared to the peptide (1:250), in line with the experiments conducted by Serrano and coworkers, who demonstrated that ERp57 is able to reduce the aggregation of α-synuclein in a very efficient manner, in a 1:50 molar ratio(Serrano et al, 2020). The efficiency ofERp57, even at a low molar ratio compared to Aβ 25−35 , indicates that ERp57 may bind oligomeric Aβ 25−35 .…”

“…Many literature reports indicate that ERp57 is a multifunctional protein with a high propensity to interact with peptides and proteins prone to misfolding, such as PrP (Hetz et al, 2005; Thapa et al, 2018; Torres et al, 2015) and α‐synuclein (Serrano et al, 2020). Moreover, other members of the PDI family are able to bind tau protein (Xu et al, 2013) and proteins without disulfide bonds (Cai et al, 1994).…”

“…ERp57 is able to guarantee the correct folding of APP after glycosylation, but it could also be able to perform a regulatory function It could be speculated that in AD patients this regulation is lost, possibly because less ERp57 is secreted or the oxidative environment is not favorable, because of the aging process (Ghosh & Brewer, 2014) and therefore the Aβ, released outside the cell, is no longer digested by enzymes such as neprilysin (Campos et al, 2020) and Insulin Degrading Enzyme (Bulloj et al, 2010), triggering a fibrillation process that will eventually lead to the formation of amyloid aggregates (Erickson et al, 2005;Zhao et al, 2012). To date, it was reported that neuronal (Fontana et al, 2020) and SH-SY5Y cells are able to internalize Aβ (Ida et al, 1996) and pre-formed alpha-synuclein fibrils (Pantazopoulou et al, 2021) through endocytosis and clear them, so it could be hypothesized that ERp57, which is able to bind alpha-synuclein (Serrano et al, 2020), is released from the neuronal cells in order to bind the Aβ, prevent its aggregation and favor the endocytosis of this complex.…”

CNS Redox Homeostasis and Dysfunction in Neurodegenerative Diseases

“…They also confirmed inhibited fibrillization by PDI. Later, it was also shown that PDI can break down nascent α-Syn fibrils, yet not mature fibrils [ 114 ]. The redox balance in the ER impacts the S-nitrosylation state of PDI [ 115 ].…”