Modulation of D-serine levels in brains of mice lacking PICK1.

D-serine is an endogenous coagonist of the N-methyl-D-aspartate subtype glutamate receptor. Genetic association studies have implicated genes coding for enzymes associated with D-serine metabolism in schizophrenia and bipolar disorder. Protein expression of serine racemase (SR) and its binding partner, protein interacting with C-kinase (PICK1), were examined by Western blotting in brains from wildtype and PICK1 knockout mice. Levels of D-serine in wildtype and PICK1 mice were also examined by an established high-pressure liquid chromatography protocol. Expression of SR and PICK1 proteins was developmentally regulated. Although no change was observed in the level of SR protein, levels of D-serine were selectively decreased in the forebrain of neonatal PICK1 knockout mice, compared with those in wildtype mice. PICK1 may be involved in the regulation of brain D-serine levels and SR in a spatially and temporally specific manner.