Regulation of brain glutamate metabolism by nitric oxide and S-nitrosylation

ly reduced in the brains of mice lacking endothelial nitric oxide synthase (eNOS �/� ) or neuronal nitric oxide synthase (nNOS �/� ). In particular, nNOS �/� animals showed decreased S-nitrosylation of proteins that participate in the glutamate/glutamine cycle, a metabolic process by which synaptic glutamate is recycled or oxidized to provide energy. 15 N-glutamine–based metabolomic profiling and enzymatic activity assays indicated that brain extracts from nNOS �/� mice converted less glutamate to glutamine and oxidized more glutamate than those from mice of the other genotypes. GLT1 [also known as EAAT2 (excitatory amino acid transporter 2)], a glutamate transporter in astrocytes, was S-nitrosylated at Cys 373 and Cys 561 in wild-type and eNOS �/� mice, but not in nNOS �/� mice. A form of rat GLT1 that could not be S-nitrosylated at the equivalent sites had increased glutamate uptake compared to wild-type GLT1 in cells exposed to an S-nitrosylating agent. Thus, NO modulates glutamatergic neurotransmission through the selective, nNOS-dependent S-nitrosylation of proteins that govern glutamate transport and metabolism.