Prenatal expression of D-aspartate oxidase causes early cerebral D-aspartate depletion and influences brain morphology and cognitive functions at adulthood.

The free D-amino acid, D-aspartate, is abundant in the embryonic brain but significantly decreases after birth. Besides its intracellular occurrence, D-aspartate is also present at extracellular level and acts as an endogenous agonist for NMDA and mGlu5 receptors. These findings suggest that D-aspartate is a candidate signaling molecule involved in neural development, influencing brain morphology and behaviors at adulthood. To address this issue, we generated a knockin mouse model in which the enzyme regulating D-aspartate catabolism, D-aspartate oxidase (DDO), is expressed starting from the zygotic stage, to enable the removal of D-aspartate in prenatal and postnatal life. In line with our strategy, we found a severe depletion of cerebral D-aspartate levels (up to 95%), since the early stages of mouse prenatal life. Despite the loss of D-aspartate content, Ddo knockin mice are viable, fertile, and show normal gross brain morphology at adulthood. Interestingly, early D-aspartate depletion is associated with a selective increase in the number of parvalbumin-positive interneurons in the prefrontal cortex and also with improved memory performance in Ddo knockin mice. In conclusion, the present data indicate for the first time a biological significance of precocious D-aspartate in regulating mouse brain formation and function at adulthood.