Therapeutic efficacy of Ibudilast to attenuate inflammation at the synapse

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Abstract Despite earlier studies that have shown the overall impact of inflammation and excitotoxicity induced by HIV and methamphetamine (meth) in the progression of HIV-Associated Neurocognitive Disorders, a significant gap that remains is identifying synaptic protein targets including their modulation by therapeutic drugs to ameliorate such inflammatory responses and glutamate excitotoxicity at the synapse. This R21 proposal focuses on one such synaptic target phosphatidylethanolamine-binding protein 1 (PEBP1) which we have identified from a previous study and whose reduced expression by HIV (Tat, gp120) and meth was reversed by treatment with the anti- inflammatory drug Ibudilast, a phosphodiesterase inhibitor. Based on the synaptic localization of PEBP1, we tested a more causal effect of knock down of PEBP1 using siRNA on mixed cerebrocortical cultures that comprise of differentiating neurons and astrocytes. We treated 14 days in vitro (DIV14) mixed cerebrocortical cultures with siRNA against PEBP1 followed by Tat/meth treatments alone and in combination for 24h. In parallel, a subset of 24h Tat/meth treated cultures were given ibudilast treatment for 24h. Tat and meth in combination decreased the expression of the glutamate transporter EAAT2 and a concurrent increase in the vesicular glutamate transporter 1 (vGLUT1) in the lysates by western blot thus suggesting excitotoxicity. This increase in glutamate levels corroborated with increase in the levels of the proinflammatory cytokines IL6 and TNF-in the cell supernatants as determined by ELISA. Interestingly, these effects were attenuated in cultures treated with Ibudilast for 24h. Based on the well-established dogma of inflammation and excitotoxicity by HIV and meth, we hypothesize that PEBP1 down regulation by HIV and meth increases inflammation and glutamate toxicity thus exacerbating synaptodendritic damage which can be reversed by ibudilast treatment. We will examine our hypothesis in an in vitro model of mixed cerebrocortical cultures complemented by a tractable preclinical animal model system HIV-Tg rat using biochemical, molecular, imaging and electrophysiological approaches. To summarize, our studies have identified a potential synaptic protein target and an anti-inflammatory drug with a therapeutic efficacy to mitigate aberrations associated with its downregulation at the synapse during HIV and meth induced CNS dysfunction.