Complex Processes Underlying the Dynamic Changes of D-serine Levels in AD Brains

Background: Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by extracellular β-amyloid (Aβ) plaques and cognitive impairments. D-Serine, produced by the enzyme serine racemase (SR) in the brain, functions as an endogenous co-agonist at the glycine-binding site of N-methyl-D-aspartate receptor (NMDAR), has been implicated in the pathophysiological progression of AD. Objectives: Evidence regarding the understanding of the role and dynamic modulation of D-serine during AD progression remains controversial. This literature review aims to offer novel research directions for studying the functions and metabolisms of D-serine in AD brains. Methods: We searched PubMed, using D-serine/SR and AD as keywords. Studies related to NMDAR dysfunction, neuronal excitotoxicity, D-serine dynamic changes and inflammatory response were included. Results: This review primarily discusses: (i) Aβ oligomers’ role in NMDAR dysregulation, and the subsequent synaptic dysfunction and neuronal damage in AD, (ii) D-serine’s role in NMDAR-elicited excitotoxicity, and (iii) the involvement of D-serine and SR in AD-related inflammatory pathological progression. Conclusion: We also presented supposed metabolism and dynamic changes of D-serine during AD progression and hypothesized that: (i) the possible modulation of D-serine levels or SR expression as an effective method of alleviating neurotoxicity during AD pathophysiological progression, and (ii) the dynamic changes of D-serine levels in AD brains possibly resulting from complex processes.