D-Serine Production, Degradation, and Transport in ALS : Critical Role of Methodology

Abstract EN

In mammalian systems, D-serine is perhaps the most biologically active D-amino acid described to date.

D-serine is a coagonist at the NMDA-receptor, and receptor activation is dependent on D-serine binding.

Because D-serine binding dramatically increases receptor affinity for glutamate, it can produce excitotoxicity without any change in glutamate per se.

D-serine is twofold higher in the spinal cords of mSOD1 (G93A) ALS mice, and the deletion of serine racemase (SR), the enzyme that produces D-serine, results in an earlier onset of symptoms, but with a much slower rate of disease progression.

Localization studies within the brain suggest that mSOD1 and subsequent glial activation could contribute to the alterations in SR and D-serine seen in ALS.

By also degrading both D-serine and L-serine, SR appears to be a prime bidirectional regulator of free serine levels in vivo.

Therefore, accurate and reproducible measurements of D-serine are critical to understanding its regulation by SR.

Several methods for measuring D-serine have been employed, and significant issues related to validation and standardization remain unresolved.

Further insights into the intracellular transport and tissue-specific compartmentalization of D-serine within the CNS will aid in the understanding of the role of D-serine in the pathogenesis of ALS.