Mitochondrial glutaminase enhances extracellular glutamate production in HIV‐1‐infected macrophages: Linkage to HIV‐1 associated dementia

Dysfunction in mononuclear phagocyte (MP, macrophages and microglia) immunity is thought to play a significant role in the pathogenesis of HIV‐1 associated dementia (HAD). In particular, elevated extracellular concentrations of the excitatory neurotransmitter glutamate, produced by MP as a consequence of viral infection and immune activation, can induce neuronal injury. To determine the mechanism by which MP‐mediated neuronal injury occurs, the concentration and rates of production of extracellular glutamate were measured in human monocyte‐derived macrophage (MDM) supernatants by reverse phase high‐performance liquid chromatography (RP‐HPLC). Measurements were taken of supernatants from MDM infected with multiple HIV‐1 strains including ADA and DJV (macrophage tropic, M‐tropic), and 89.6 (dual tropic). High levels of glutamate were produced by MDM infected with M‐tropic viruses. AZT, an inhibitor of HIV‐1 replication, inhibited glutamate generation, demonstrating a linkage between HIV‐1 infection and enhanced glutamate production. In our culture system, glutamate production was dependent upon the presence of glutamine and was inhibited by 6‐diazo‐5‐oxo‐l‐norleucine, a glutaminase inhibitor. Supernatants collected from HIV‐1‐infected MP generated more glutamate following glutamine addition than supernatants isolated from uninfected MP. These findings implicate the involvement of a glutamate‐generating enzyme, such as phosphate‐activated mitochondrial glutaminase (PMG) in MP‐mediated glutamate production.