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HIV decreases glutamate transport in SK-N-MC neuroblastoma cells
T C Pappas1, S Alagarsamy, R B Pollard
1Department of Internal Medicine, University of Texas Medical Branch, Galveston 77555-0835, USA.
Abstract:
Autopsy studies of patients with AIDS dementia have shown neuronal loss consistent with a neurotoxic component of this disease. In vitro studies suggest that viral products or cytokines from HIV-infected macrophages (Mphi) may modulate or directly mediate excitotoxic cell death of neurons. Mphi differentiated from peripheral mononuclear blood cultures were infected with HIV, and conditioned media (CM) were harvested from these cultures. Exposure of SK-N-MC (neuroblastoma) cells to CM from HIV-infected Mphi for 4, 24 or > or = 48 h resulted in a mean suppression of 12-34% of the glutamate transport Vmax with no appreciable change in transport Km. An astrocytoma tumor cell, U373MG, showed similar CM-mediated glutamate uptake suppression. Changes were evident in total and Na+-dependent glutamate uptake, with significantly more suppression of Na+-dependent uptake. Similar effects were seen with the nonmetabolizable transporter agonist D-aspartate, indicating that the effect was on transport and not metabolism. No suppression was seen with CM from uninfected Mphi or Mphi infected with heat-inactivated HIV. The magnitude of uptake suppression was not correlated with CM p24 values, and removal of CM virions by ultracentrifugation and immunoprecipitation did not alter the uptake-suppressive properties of infected Mphi CM. Uptake suppression was seen when Mphi were infected with Mphi-tropic strains HIV(SF162), HIV(JR-CSF), HIV(NFN-SX) and a Mphi-tropic patient isolate, but not the lymphotropic strain HIV(LAI). HIV-infected Mphi may produce substances which suppress neuronal and glial glutamate neurotransmitter uptake, resulting in higher extracellular glutamate levels and leading possibly to deficits in cell signaling and neurotoxicity.
Insights
Human immunodeficiency virus (HIV)-infected macrophages release substances that impair glutamate transport in neurons and glial cells. This neurotoxic effect may contribute to neurological deficits seen in AIDS dementia.
Area of Science:
- Neuroscience
- Virology
- Cell Biology
Background:
- Autopsy studies reveal neuronal loss in AIDS dementia, suggesting a neurotoxic component.
- In vitro research indicates HIV products or cytokines from infected macrophages (Mphi) may cause excitotoxic neuronal death.
Purpose of the Study:
- To investigate the effect of HIV-infected Mphi on glutamate uptake in neuronal and glial cells.
- To determine if HIV-infected Mphi release factors that suppress glutamate transport.
Main Methods:
- Peripheral mononuclear blood cultures were differentiated into Mphi and infected with HIV.
- Conditioned media (CM) from HIV-infected Mphi were used to treat neuroblastoma (SK-N-MC) and astrocytoma (U373MG) cells.
- Glutamate transport was measured using Vmax and Km parameters, and D-aspartate uptake was assessed.
Main Results:
- CM from HIV-infected Mphi significantly suppressed glutamate transport Vmax (12-34%) in both cell types.
- Suppression was primarily of Na+-dependent glutamate uptake, indicating an effect on transport mechanisms.
- No suppression was observed with CM from uninfected Mphi or Mphi infected with heat-inactivated HIV.
- The effect was linked to Mphi-tropic HIV strains, not lymphotropic strains.
Conclusions:
- HIV-infected Mphi can produce substances that suppress neuronal and glial glutamate uptake.
- This suppression may lead to elevated extracellular glutamate levels, potentially causing neurotoxicity and neurological deficits in HIV-associated dementia.