Neurotoxic effects of feline immunodeficiency virus, FIV-PPR

FIV is a lentivirus of domestic cats that causes neurologic disorders which are remarkably similar to those found in HIV-1 infected people. Using feline neuron cultures, we investigated the potential of both FIV virus and FIV-Env protein to cause neuronal damage through the excitotoxicity mechanism. The neuron swelling and lactate dehydrogenase (LDH) release assays were used as measures of cellular damage. The effects of FIV Env protein on glutamate receptor mediated increases in intracellular calcium were also examined. We found that FIV virus and FIV-Env protein significantly increased LDH release from the neuron cultures. Additionally, an increase in neuron size was detected in the cultures exposed to the virus, while swelling did not occur with exposure to either saline, denatured virus, or FIV-Env by itself. However, when both 20 μM glutamate and the FIV-PPR Env protein were added to the culture, a significant increase in neuron cell size was observed. The NMDA calcium signals were similar in general form between the control and FIV-PPR Env exposed cultures. However, the FIV-PPR Env protein treated cultures resulted in significant enhancement of the NMDA induced calcium signal. Our results indicate that FIV Env protein (either within the virion or baculovirus expressed) induced neurotoxicity as measured by neuron swelling and LDH release assays and that exposure of feline neurons to FIV Env protein alters the handling of intracellular calcium. These findings help to validate the FIV/cat system as a potential animal model for evaluating therapeutic approaches that target the excitotoxicity mechanisms of lentivirus induced CNS disease.