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


CONCLUSIONS
Our 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.
Department of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
Arnab
A
Datta
School of Biological Sciences, Nanyang Technological University, Singapore.
Jingru
J
Qian
Department of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
Ruifen
R
Chong
Institute for Ageing Health, Newcastle University, Campus for Ageing and Vitality, Newcastle upon Tyne, UK.
Raj N
RN
Kalaria
Wolfson Centre for Age-related Diseases, King's College London, London, UK.
Paul
P
Francis
Department of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore; Memory, Aging and Cognition Centre, National University Health System, Singapore.
Mitchell K P
MK
Lai
Department of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore; Memory, Aging and Cognition Centre, National University Health System, Singapore. Electronic address: phccclh@nus.edu.sg.
Christopher P
CP
Chen
School of Biological Sciences, Nanyang Technological University, Singapore. Electronic address: sksze@ntu.edu.sg.
Siu Kwan
SK
Sze
D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000378:metabolism; D015140:Dementia, Vascular / Q000378:metabolism* / Q000473:pathology; D005260:Female; D006801:Humans; D008297:Male; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D020543:Proteome / Q000378:metabolism*; D040901:Proteomics / Q000295:instrumentation / Q000379:methods*
D015415:Biomarkers; D009419:Nerve Tissue Proteins; D020543:Proteome
Clinical proteomics; Mass spectrometry; Oxidative stress; Vascular dementia; Vascular dysfunction; iTRAQ