D-Serine Metabolic Enzymes as Potential Biomarkers for Alzheimer’s and Parkinson’s Diseases

다국어 초록 (Multilingual Abstract)

Alzheimer's disease (AD) and Parkinson's disease (PD) are caused by different proteins called amyloid-beta (Aβ) and α-synuclein (α-syn), respectively. Interestingly, AD and PD shared common pathophysiological features, such as Nmethyl-D-aspartate (NMDA) receptor dysfunction and excessive excitotoxicity. The homeostasis of D-Serine within the central nervous system could be a key mechanism controlling the activity of neuroregulators. This study aimed to show the possibility of a new biomarker capable of simultaneously identifying both AD and PD. D-amino acids from bacteria was suggested to be involved in neurodegenerative disease. As a defense mechanism, human genome contained Serine racemase (SR) and D-amino acid oxidase (DAAO), which were key enzymes for synthesizing and degrading DSerine and other D-amino acids.
Hence, the enzyme concentrations of SR and DAAO in blood plasma from patients with AD or PD pathology were measured and analyzed. In addition, the changes in enzyme concentrations were compared by analyzing the supernatant and lysate of the disease model using AD and PD cell models. In this process, D-aspartate oxidase (DDO), which decomposed D-aspartate amino acid, was used as a comparative control to verify the disease specificity of target enzymes.
From the results of plasma analysis, no significant difference of DDO was observed between the groups, supporting its role as a comparative control enzyme. Interestingly, the increased levels of SR and DAAO were observed in AD and PD patients. When SR and DAAO values from the same sample were multiplied, higher discrimination power was observed between both AD/PD patients than the control group than a single indicator.
In addition, the mechanism of above enzymes was explored by comparing SR and DAAO levels in cell supernatant and cell lysate of AD and PD cell models. The results demonstrated differential intracellular and extracellular alterations of SR and DAAO between AD and PD cell models, which suggested SR and DAAO as potential biomarkers in AD and PD, even with different etiology and involved proteins.The current results provided important evidence for the development of new
neuroprotective treatments targeting the increased D-Serine metabolic imbalance.

목차 (Table of Contents)

• CHAPTER 1. Introduction 1
• 1.1 Introduction 4
• 1.2 Pathological Mechanisms of AD and PD 6
• 1.2.1 Alzheimer’s Disease (AD) Pathology 6
• 1.2.2 Parkinson’s Disease (PD) Pathology 7
• 1.3 The Role of D-Serine in Glutamatergic System 9
• 1.3.1 Glutamatergic Dysfunction is Common Pathological Mechanisms of AD and PD 9
• 1.3.2 NMDA receptor Structure and D-Serine as a Co-agonist 12
• 1.3.3 Alterations in D-Serine Levels and Signaling in AD and PD 12
• 1.4 Enzymatic Regulation of SR and DAAO 14
• 1.4.1 Serine Racemase (SR) 14
• 1.4.2 D-Amino Acid Oxidase (DAAO) 14
• 1.4.3 The Role and Comparative enzyme DDO with DAAO 15
• 1.5 Conclusion 16
• CHAPTER 2. Measurement SR, DDO, DAAO Concentrations in Plasma 18
• 2.1 Introduction 20
• 2.2 Materials and Methods 21
• 2.2.1 Human Plasma Samples 21
• 2.2.2 Measurement of SR, DAAO, and DDO in Plasma 21
• 2.3 Results 23
• 2.4 Discussion 29
• 2.5 Conclusion 32
• CHAPTER 3. Measurement of SR, DDO, and DAAO concentrations in Cell Supernatant and Lysate 33
• 3.1 Introduction 35
• 3.2 Materials and Methods 37
• 3.2.1 Cell Lysate Extraction 37
• 3.2.2 Collection of Cell Supernatant 37
• 3.2.3 Measurement of SR, DAAO, and DDO in Cell Supernatant and Cell Lysate 38
• 3.3 Results 40
• 3.4 Discussion 42
• 3.5 Conclusion 46
• References 47
• 국문초록 58