Novel pathophysiological markers are revealed by iTRAQ-based quantitative clinical proteomics approach in vascular dementia

Abstract

Vascular dementia (VaD) is a leading cause of dementia in the elderly together with Alzheimer's disease with limited treatment options. Poor understanding of the pathophysiology underlying VaD is hindering the development of new therapies. Hence, to unravel its underlying molecular pathology, an iTRAQ-2D-LC–MS/MS strategy was used for quantitative analysis of pooled lysates from Brodmann area 21 of pathologically confirmed cases of VaD and matched non-neurological controls. A total of 144 differentially expressed proteins out of 2281 confidently identified proteins (false discovery rate = 0.3%) were shortlisted for bioinformatics analysis. Western blot analysis of selected proteins using samples from individual patients (n = 10 per group) showed statistically significant increases in the abundance of SOD1 and NCAM and reduced ATP5A in VaD. This suggested a state of hypometabolism and vascular insufficiency along with an inflammatory condition during VaD. Elevation of SOD1 and increasing trend for iron-storage proteins (FTL, FTH1) may be indicative of an oxidative imbalance that is accompanied by an aberrant iron metabolism. The synaptic proteins did not exhibit a generalized decrease in abundance (e.g. syntaxin) in the VaD subjects. This reported proteome offers a reference data set for future basic or translational studies on VaD.Biological significanceOur study is the first quantitative clinical proteomic study where iTRAQ-2D-LC–MS/MS strategy has been used to identify the differential proteome in the VaD cortex by comparing VaD and matched control subjects. We generate testable hypothesis about the involvement of various proteins in the vascular and parenchymal events during the evolution of VaD that finally leads to malfunction and demise of brain cells. This study also establishes quantitative proteomics as a complementary approach and viable alternative to existing neurochemical, electron microscopic and neuroimaging techniques that are traditionally being used to understand the molecular pathology of VaD. Our study could inspire fellow researchers to initiate similar retrospective studies targeting various ethnicities, age-groups or sub-types of VaD using brain samples available from brain banks across the world. Meta-analysis of these studies in the future may be able to shortlist candidate proteins or pathways for rationale exploration of therapeutic targets or biomarkers for VaD.

Identification of Pivotal Markers in Vascular Dementia Based on Proteomics Data

“…The protein expression profiles were obtained from the quantitative clinical proteomic study entitled ‘Novel pathophysiological markers are revealed by iTRAQ-based quantitative clinical proteomics approach in vascular dementia' [12]. A total of 20 data samples were enrolled, including 10 nondemented elderly controls and 10 age-matched VaD subjects.…”

“…Although some important proteins and some pathologic events in VaD samples have been found and illuminated through proteomics previously [12], more detailed information about proteins and pathways involved in the pathogenesis of VaD remains imperative. Using the same proteomics data, we aimed to further screen pivotal proteins and pathways occurring in VaD through protein and protein interaction (PPI) network and crosstalk analysis of the significant pathways.…”

Proteomic Study of Degenerative Protein Modifications in the Molecular Pathology of Neurodegeneration and Dementia

“…Proteomic technique enables the comprehensive analysis of the protein and its work flow involves the identification of proteins following their separation, digestion by trypsin, determination of the molecular weight of the resulting peptides, and database searching to make the identification and quantification of the proteins as well as the characterization of the DPMs. In addition to label-free proteomic methods, isobaric tags for relative and absolute quantitation (iTRAQ) and tandem mass tag (TMT) protein labeling are widely accepted approaches for quantitative profiling of cell lines and clinical brain tissue samples [24][25][26]. Proteomics has also been used for the accurate identification of protein modifications [26][27][28][29][30][31].…”

“…Applying two-dimensional (2D) liquid chromatography coupled with tandem mass spectrometry-based iTRAQ (2D-LC-MS/MS-iTRAQ) technique, Brodmann area 21 of pathologically confirmed cases of VaD and matched nonneurological controls were studied [25]. In the study, 144 differentially expressed proteins including superoxide dismutase, neural cell adhesion molecule, and ATP synthase subunit alpha were characterized to be significantly up-regulated in VaD patients, suggesting a state of hypometabolism and vascular insufficiency along with an inflammatory condition during vascular dementia.…”

“…Proteomic of pathological progression from hypoxiaischemia brain injury to clinical dementia revealed the dysregulation of energy metabolism, mitochondrial dysfunction, neuro-inflammation, synaptic failure, etc. [24][25][26]50]. Further, the activity of α-ketoglutarate dehydrogenase appears to be inhibited in the cerebral cortex of AD patients, and there are substantial evidences indicating that the function of the Krebs cycle is impaired in AD brains [51,52].…”