Redox proteomics analysis of HNE-modified proteins in Down syndrome brain: clues for understanding the development of Alzheimer disease

Abstract

Down syndrome (DS) is the most common genetic cause of intellectual disability, due to partial or complete triplication of chromosome 21. DS subjects are characterized by a number of abnormalities including premature aging and development of Alzheimer’s disease (AD) neuropathology after approximately 40 years of age. Several studies show that oxidative stress plays a crucial role in the development of neurodegeneration in DS population. Increased lipid peroxidation is one of the main events causing redox imbalance within cells through the formation of toxic aldehydes that easily react with DNA, lipids and proteins. In this study we used a redox proteomics approach to identify specific targets of 4-hydroxynonenal modifications in the frontal cortex from DS cases, with and without AD pathology. We suggest that a group of identified proteins followed a specific pattern of oxidation in DS vs. young controls (CTRY), likely indicating characteristic features of DS phenotype; a second group of identified proteins showed increased oxidation in DS/AD vs. DS, thus possibly playing a role in the development of AD. The third group of comparison, DS/AD vs. old controls (CTRO), identified proteins that may be considered specific markers of AD pathology. All the identified proteins are involved in important biological functions including intracellular quality control systems, cytoskeleton network, energy metabolism and antioxidant response. Our results demonstrate that oxidative damage is an early event in DS, as well as dysfunctions of protein degradation systems and cellular protective pathways, suggesting that DS subjects are more vulnerable to oxidative damage accumulation that might contribute to AD development. Further, considering that the majority of proteins have been already demonstrated to be oxidized in AD brain, our results strongly support similarities with AD in DS.

Polyubiquitinylation Profile in Down Syndrome Brain Before and After the Development of Alzheimer Neuropathology

“…Previous studies from our group demonstrate impairments of the proteasome system (17) and the reduction of autophagosome function in DS, before and after the development of AD, which suggests that accumulation of oxidized/misfolded protein is an early hallmark in DS brain (59). We showed that some members of the PQC are oxidatively modified in young DS cases before the development of AD and that oxidation of target proteins possibly leads to impaired activity of clearance systems (19). We hypothesize that reduced protein degradation contributes to the accumulation of polyubiquitinated proteins, which, in turn, may act to disturb other cellular functions.…”

“…The proteomic results for UCH-L1 indicated an increased polyubiquitinylation in DS and DS/AD compared with their respective controls and also when comparing DS/AD with DS. We previously reported that UCH-L1 was increasingly carbonylated and also HNE modified in DS and DS/AD (17,19) brains and in brains from AD cases (7). Data from the validation analysis on UCH-L1 confirmed the elevated poly-Ub K63 in DS and DS/AD compared with their age-matched controls (2-and 1.6-fold, Fig.…”

“…Previous results show that the level of DRP-2 is decreased in fetal DS brain (2) and increasingly polyubiquitinated both in DS versus Ctr Y and Ctr O versus Ctr Y in the current study. Furthermore, in adult DS brain, the level of DRP-2 is reduced either at protein l or at mRNA level; we also found this protein to be oxidatively modified (19). Indeed, DS is associated with a group of clinical manifestations of accelerated aging (31) that may ultimately culminate in the development of dementia.…”

Proteins that mediate protein aggregation and cytotoxicity distinguish Alzheimer's hippocampus from normal controls

“…In contrast, elongation factor 1α is far more oxidized in total aggregates (27–31%) than in Aβ‐ or tau‐IP aggregates (0–13%). Oxidized proteins are thought to be more vulnerable to aggregation and were found to be elevated in a C. elegans model of AD (Boyd‐Kimball et al ., 2006) and in hippocampi of AD and aging Down's patients (Butterfield et al ., 2014; Di Domenico et al ., 2014). However, this report is the first (to our knowledge) to identify and quantify proteins and modifications from specific affinity‐purified aggregates, and the first to show unequal distribution of oxidized proteins among aggregate types, which must reflect differing properties of those classes (see Discussion).…”

Chemistry and analysis of HNE and other prominent carbonyl-containing lipid oxidation compounds

“…For example, using MALDI-TOF specific targets of 4-hydroxy-2-nonenal modifications were identified in Down syndrome cases, supporting similarities with Alzheimer disease. Western blotting after 2D electrophoresis was carried out with a mouse monoclonal anti-HNE antibody, proteins in the corresponding digested spots were identified by MALDI-TOF peptide mass fingerprinting, and the data were searched using the Mascot search engine [113]. A similar method was also successfully applied in the identification of complex I subunits modified by HNE in mitochondria from diabetic kidney.…”