Inhibitory Effect of Selenoprotein P on Cu⁺/Cu²⁺-Induced Aβ₄₂ Aggregation and Toxicity

It has been suggested that the aggregation and cytotoxicity of amyloid-β (Aβ) peptide with transition-metal ions in neuronal cells is involved in the progression of Alzheimer’s disease (AD). Selenoproteins are a group of special proteins that contain the 21st amino acid selenocysteine in their sequence, and they are found to be involved in the onset and progression of AD. Here, we report that the histidine-rich domain of selenoprotein P (SelP-H) is capable of binding Cu ions in both oxidation states of Cu⁺ and Cu²⁺ with high affinity and of modulating Cu⁺ and Cu²⁺-mediated Aβ aggregation, reactive oxygen species (ROS) production, and neurotoxicity. SelP-H was found to coordinate 1 and 2 mol equiv of Cu⁺ and Cu²⁺ with sub-picomolar and nanomolar affinities, respectively. Cu⁺/Cu²⁺ binding to Aβ₄₂ inhibited the fibrillization of Aβ₄₂ but induced it to form amorphous aggregates, which could be significantly restored by SelP-H, as observed by thioflavin T fluorescence and transmission electron microscopy. Interestingly, SelP-H inhibited Cu⁺/Cu²⁺-Aβ₄₂-induced neurotoxicity and the intracellular ROS production in living cells. These studies suggest that SelP may play certain roles in regulating redox balance as well as metal homeostasis

Blocking the Thiol at Cysteine-322 Destabilizes Tau Protein and Prevents Its Oligomer Formation

Abnormal accumulation of tau protein into oligomers contributes to neuronal dysfunction. Reduction of tau level is potentially able to prevent its accumulation. Here we uncover a critical role of the free thiol at Cys-322 in determining tau stability. We found that the application of thiol-blocking agents like NEM or MMTS blocks this thiol, by which it destabilizes tau protein and prevents its oligomer formation. Furthermore, we identified a tau-interacting protein, selenoprotein W, which attenuates tau accumulation by forming disulfide linkage between SelW Cys-37 and tau Cys-322. These findings provide a promising strategy to prevent tau accumulation and oligomer formation

Sodium selenate regulated Aβ production in N2aSW culture medium.

<p>The expression levels of APP (A) and BACE1 (B) proteins did not change significantly between the selenate-treated and the control cells. While extracellular Aβ concentration was down-regulated when treated with selenate (C). <i>**</i>, <i>P<0.01</i>.</p

Representative 2-DE images of the phosphor-enriched proteins from the untreated (control) and selenate-treated N2aSW cells.

<p>Gels were stained with Pro-Q Diamond (A, B) and SYPRO ruby (C, D) fluorescent dyes, respectively. Arrows indicate the identified proteins whose phosphorylation levels were altered.</p

Phosphoproteomic Profiling of Selenate-Treated Alzheimer's Disease Model Cells

<div><p>The reversible phosphorylation of proteins regulates most biological processes, while abnormal phosphorylation is a cause or consequence of many diseases including Alzheimer's disease (AD). One of the hallmarks of AD is the formation of neurofibrillary tangles (NFTs), which is composed of hyperphosphorylated tau proteins. Sodium selenate has been recently found to reduce tau hyperphosphorylation and NFTs formation, and to improve spatial learning and motor performance in AD mice. In the current study, the phosphoproteomics of N2aSW cells treated with selenate were investigated. To avoid missing low-abundance phosphoproteins, both the total proteins of cells and the phosphor-enriched proteins were extracted and subjected to the two-dimensional gel electrophoresis with Pro-Q diamond staining and then LC-MS/MS analysis. A total of 65 proteins were altered in phosphorylation level, of which 39 were up-regulated and 26 were down-regulated. All identified phosphoproteins were bioinformatically annotated according to their physiochemical features, subcellular location, and biological function. Most of these significantly changed phosphoproteins are involved in crucial neural processes such as protesome activity, oxidative stress, cysteine and methionine metabolism, and energy metabolism. Furthermore, decreases were found in homocysteine, phosphor-tau and amyloid β upon selenate treatment. Our results suggest that selenate may intervene in the pathological process of AD by altering the phosphorylation of some key proteins involved in oxidative stress, energy metabolism and protein degradation, thus play important roles in maintaining redox homeostasis, generating ATP, and clearing misfolded proteins and aggregates. The present paper provides some new clues to the mechanism of selenate in AD prevention.</p></div

Effect of selenate on tau phosphorylation in N2aSW cells.

<p>Levels of total tau protein expression (A), phosphorylation of tau at pS404 (B) or at pT231 (C) were not altered in the cells treated with/without selenate. However, the phosphorylation level of tau at pS422 and pS396 were reduced by selenate-treatment (D). <i>*</i>, <i>P</i><0.05.</p

PANTHER gene ontology enrichment analysis of phosphoproteins altered in the N2aSW cells treated with sodium selenate.

<p>Enrichment analyses were performed in terms of cellular component (A), molecular function (B) and biological process (C).</p

Representative 2-DE images of the total proteins extracted from the untreated (control) and selenate-treated N2aSW cells.

<p>Gels were stained with Pro-Q Diamond (A, B) and SYPRO ruby (C, D) fluorescent dyes, respectively. Arrows indicate the identified proteins whose phosphorylation levels were altered.</p

Differentially phosphorylated proteins identified from the total proteins by 2-DE-LC-MS/MS between the selenate-treated and untreated N2aSW cells.

a<p>Protein IDs were assigned manually.</p>b<p>Protein names were identified by MS.</p>c<p>Theoretical molecular weight and isoelectric point of the protein(s).</p>d<p>The ratio in spot density from the Rubby stained gel of the selenate treated cells compared to the control (untreated cells).</p>e<p>The ratio in spot density from the Pro-Q diomand stained gel of the selenate treated cells compared to the control (untreated cells).</p><p>Differentially phosphorylated proteins identified from the total proteins by 2-DE-LC-MS/MS between the selenate-treated and untreated N2aSW cells.</p

La Toque blanche : organe professionnel hebdomadaire des chefs de cuisine de France et de l'étranger

02 mars 19281928/03/02 (N157)