Background: HIV-associated sensory neuropathy is the most common neurological complication of HIV infection, symptomatically affecting 1/3 of patients with AIDS. However as yet, little attention has been devoted to exploring the pathogenesis of this disorder. As there is no convincing evidence of neuronal infection, indirect neuro toxicity by secreted viral proteins such as the HIV-1 envelope glycoprotein, gp120, may play a role. We have established a robust in vitro model of gp120 peripheral neuro toxicity in order to elucidate pathogenic mechanisms and neuro-protective strategies.

Methods: Dissociated embryonic rat dorsal root ganglia (DRG) were co-cultured with Schwann cells, the cells that normally ensheath peripheral nerve axons. Varying doses of gp120-MN or vehicle control were then added to the cultures, and neuro toxicity was assessed using 4 parameters. These were neuronal mitochondrial membrane depolarization (using JC-1 labeling) at 6 hrs, evidence of neuritic toxicity (using b-III tubulin staining and digital image analysis) at 24 hrs, neuronal cytochrome c release into the cytosol (employing immunostaining) at 24 hrs, and neuronal nuclear DNA fragmentation (as judged by TUNEL) at 36 hrs. Moreover, the effects of co-administering DEVD, a caspase-3 inhibitor, anti-RANTES antibodies or anti-MIP-1b antibodies with gp120 were also assessed.

Results: Gp120, in the picogram/ml range, induced dose-dependent neuronal mitochondrial membrane depolarization, neuritic pruning and degeneration, neuronal cytochrome c release and neuronal nuclear DNA fragmentation. Furthermore, gp120-treated neurons were smaller than vehicle control—treated neurons under phase contrast microscopy. Of note, DEVD ameliorated both gp120-induced neuritic degeneration and neuronal DNA condensation. Whereas anti-MIP1b antibodies had no discernible effect when co-administered with gp120, anti-RANTES antibodies completely abrogated gp120-induced neuro toxicity.

Conclusions: We have developed a reliable in vitro model of gp120 peripheral neuro toxicity, in which gp120 causes caspase-3 dependent neuritic degeneration and apoptosis of primary sensory neurons. As part of this cell death process, there is early neuronal mitochondrial membrane depolarization and later mitochondrial cytochome c loss. Furthermore, we show that in this model, gp120-induced neuro toxicity is mediated by the beta chemokine, RANTES.