Dysfunctional D-aspartate metabolism in BTBR mouse model of idiopathic autism

Background: Autism spectrum disorders (ASD) comprise a heterogeneous group of neurodevelopmental conditions characterized by impairment in social interaction, deviance in communication, and repetitive behaviors. Dysfunctional ionotropic NMDA and AMPA receptors, and metabotropic glutamate receptor 5 activity at excitatory synapses has been recently linked to multiple forms of ASD. Despite emerging evidence showing that D-aspartate and D-serine are important neuromodulators of glutamatergic transmission, no systematic investigation on the occurrence of these D-amino acids in preclinical ASD models has been carried out. Methods: Through HPLC and qPCR analyses we investigated D-aspartate and D-serine metabolism in the brain and serum of four ASD mouse models. These include BTBR mice, an idiopathic model of ASD, and Cntnap2^−/−, Shank3^−/−, and 16p11.2^+/− mice, three established genetic mouse lines recapitulating high confidence ASD-associated mutations. Results: Biochemical and gene expression mapping in Cntnap2^−/−, Shank3^−/−, and 16p11.2^+/− failed to find gross cerebral and serum alterations in D-aspartate and D-serine metabolism. Conversely, we found a striking and stereoselective increased D-aspartate content in the prefrontal cortex, hippocampus and serum of inbred BTBR mice. Consistent with biochemical assessments, in the same brain areas we also found a robust reduction in mRNA levels of D-aspartate oxidase, encoding the enzyme responsible for D-aspartate catabolism. Conclusions: Our results demonstrated the presence of disrupted D-aspartate metabolism in a widely used animal model of idiopathic ASD. General significance: Overall, this work calls for a deeper investigation of D-amino acids in the etiopathology of ASD and related developmental disorders.