Inhibition of glial D‐serine release rescues synaptic damage after brain injury

• Published in: Glia 2022-06, Vol.70 (6), p.1133-1152
• Main Authors: Tapanes, Stephen A., Arizanovska, Dena, Díaz, Madelen M., Folorunso, Oluwarotimi O., Harvey, Theresa, Brown, Stephanie E., Radzishevsky, Inna, Close, Liesl N., Jagid, Jonathan R., Graciolli Cordeiro, Joacir, Wolosker, Herman, Balu, Darrick T., Liebl, Daniel J.
• Format: Article
• Language: English
• Subjects: Agonists; Amino Acid Transport System ASC - metabolism; amino acid transporters; Amino acids; Animals; Astrocytes; Astrocytes - metabolism; Brain; Brain damage; Brain Injuries - drug therapy; Cognitive ability; D-Serine; Glial cells; Glutamic acid receptors; Glutamic acid receptors (ionotropic); Head injuries; Humans; Inflammation; L-Serine; Mice; Microglia; N-Methyl-D-aspartic acid receptors; Neuroglia - metabolism; Neuronal Plasticity - physiology; neuroprotection; Pharmacology; Receptors, N-Methyl-D-Aspartate - metabolism; Serine; Serine racemase; synaptic damage; Synaptic plasticity; Synaptic transmission; Synaptic Transmission - physiology; Traumatic brain injury
• ISSN: 0894-1491; 1098-1136
• DOI: 10.1002/glia.24161

Synaptic damage is one of the most prevalent pathophysiological responses to traumatic CNS injury and underlies much of the associated cognitive dysfunction; however, it is poorly understood. The D‐amino acid, D‐serine, serves as the primary co‐agonist at synaptic NMDA receptors (NDMARs) and is a critical mediator of NMDAR‐dependent transmission and synaptic plasticity. In physiological conditions, D‐serine is produced and released by neurons from the enzymatic conversion of L‐serine by serine racemase (SRR). However, under inflammatory conditions, glial cells become a major source of D‐serine. Here, we report that D‐serine synthesized by reactive glia plays a critical role in synaptic damage after traumatic brain injury (TBI) and identify the therapeutic potential of inhibiting glial D‐serine release though the transporter Slc1a4 (ASCT1). Furthermore, using cell‐specific genetic strategies and pharmacology, we demonstrate that TBI‐induced synaptic damage and memory impairment requires D‐serine synthesis and release from both reactive astrocytes and microglia. Analysis of the murine cortex and acutely resected human TBI brain also show increased SRR and Slc1a4 levels. Together, these findings support a novel role for glial D‐serine in acute pathological dysfunction following brain trauma, whereby these reactive cells provide the excess co‐agonist levels necessary to initiate NMDAR‐mediated synaptic damage. Main Points Enhanced D‐serine production by both astrocyte and microglia cells after brain injury leads to synaptic damage and cognitive impairments. Inhibiting glial D‐serine release improves outcomes, implicating glial D‐serine as a novel therapeutic target.