Background: CNS consequences of AIDS are thought to reflect toxicity of HIV Tat and Env proteins for neurons, in which both neuronal CXCR4 and reactive oxygen species (ROS) have been implicated. No current therapy protects from this devastating complication. We hypothesized that HIV toxicity for neurons in part reflects gp120-induced apoptosis, in which free radical oxygen and neuron cell membrane CXCR4 are implicated. Decreasing CXCR4 in neurons and increasing the ability of neurons to detoxify peroxide and superoxide should protect from gp120-induced apoptosis. We tested the involvement CXCR4 and ROS in HIV-1 gp120 induced apoptosis, then tested whether neurons could be protected by gene delivery to decrease cell membrane CXCR4, or increase cellular ROS detoxification.

Methods: Cultured neurons (NT2-N) prepared from NT2 human embryonal carcinoma cells (Stratagene) were treated with HIV-1NL4-3 gp120, from the NIH AIDS Reference Reagent Repository Program. Apoptosis was measured by standard TUNEL and FACS analyses. Intracellular ROS were detected using dihydrorhodamine-123 indicator dye (DHR). Standard procedures were used to prepare and to transduce neurons with recombinant Tag-deleted SV40 vectors expressing human catalase (SVCatalase) and a single chain Fv antibody against CXCR4 (SV[HE]).

Results: Gp120 induced apoptosis in > 50% of NT2-N. SV(HE) both decreased cell membrane CXCR4 and virtually completely protected NT2-N from gp120-induced apoptosis by both FACS and TUNEL assays. Gp120 increased ROS in NT2-N, as assessed by DHR staining. SVCatalase treatment decreased gp120-induced ROS and protected neurons from apoptosis.

Conclusions: HIV Env causes neuronal apoptosis by mechanisms involving CXCR4 and implicating free radical oxygen species. NT2-N were protected from gp120-induced apoptosis by rSV40 gene delivery to decrease NT2-N cell membrane CXCR4, or to provide high levels of constitutive catalase expression. Although HIV encephalopathy is currently untreatable, these studies indicated that rSV40 gene delivery to neurons that may protect them from HIV Env-induced apoptosis.