Intranasal Tat alters gene expression in the mouse brain

Intranasal (IN) delivery of HIV-1 Tat in aging mice was investigated as a possible model for HIV-1 infection in the brain. After IN administration, the distribution of [I-125]-labeled Tat in the brains of Swiss Webster mice was evaluated by autoradiography and gamma counting. [I-125]-labeled Tat was detected at the highest concentrations in the olfactory bulb, cervical nodes, and trigeminal nerve tract. In another experiment, APPSw transgenic mice were used to model chronic Tat exposure. The mice were treated intranasally with 6 mu g Tat (n=4) or vehicle (n=4) three times per week for 4 weeks. Total RNA was isolated from the frontal cortex, and differential gene expression analysis was performed using gene microarrays. Gene ontology profiles indicated innate immunity, inflaminatory and apoptotic responses. Five genes of interest in the Tat-treated mice that were significantly elevated in the microarrays were validated by RT-PCR. One gene, the Toll-like receptor 9 (Tlr9), has previously been shown to activate signaling cascades leading to innate immunity and enhanced HIV-1 gene expression. A second gene, Fas, plays a key role in neuroinflammation. Two cysteine-rich cytokines associated with chemotaxis were elevated: MCP1 (Cc12), which is chemotactic for monocytes, and Ccl 17 (TARC), which is chemotactic for lymphocytes. Finally, the gene sestrin was significantly elevated and has been associated with oxidative stress, in particular amyloid beta-induced oxidative stress. This IN Tat model of neuroinflammation may be useful to study HIV-1-induced neurodegeneration.