Toll-like receptors (TLRs) have emerged as crucial receptors on immune cells that mediate innate immunity against pathogens. TLRs signal through MyD88, an adaptor molecule containing the TLR-IL-1 receptor domain (TIR), to activate NF-KB and MAP kinases. Of the 11 members of the TLR family, TLR3 and TLR4 also signal through another TIR protein called TRIP that activates the key transcription factor IRF3 resulting in the production of IFNb. This sets off the induction of numerous IFN-stimulated genes, culminating in anti- viral immunity. TLR ligands and IL-1 are powerful activators of microglia and astrocytes modulating inflammatory and antiviral response genes, yet their role in anti-viral immunity and the signal transduction pathways involved are not known. We made a novel observation that the TLR3 ligand, synthetic dsRNA, poly-riboinosinic poly-ribocytidylic acid (PIC), limits HIV replication in microglia and astrocytes, whereas IL- 1, which also activates IRF3 and the arrays of genes similar to PIC, does not. In this competing renewal, we propose to study dsRNA signaling in primary human glia with the hypothesis that during HIV infection, TLR3 is upregulated but no effective dsRNA signaling occurs due to lack of available ligands and/or inhibition by HIV. We further propose that PIC can be used to boost antiviral immunity in vivo.
Three specific aims are proposed.
Specific Aim 1 is to elucidate TLRS signal transduction pathways in human astrocytes and microglia with respect to the mechanisms that lead to innate anti-viral immune response.
Specific Aim 2 is to determine PIC-induced modulation of HIV replication, glial inflammatory activation and neurotoxicity in human glia and neurons in vitro.
Specific Aim 3 is to characterize PIC- and HIV-induced gene expression and activity in vivo. We will study the efficacy of PIC to induce TLR3 and antiviral molecules in an HIV transgenic mouse model. In addition, the expression of TLRs and innate immune molecules in the brains of HIV encephalitis will be determined. These studies will provide molecular insights into the potential role of PIC and its downstream effectors such as indoleamine 2, 3-dioxygenase in modulating various aspects of HIV neuropathogenesis. These studies are relevant to public health because they will provide crucial information regarding how human brain cells fight against viral infections, and furthermore, they may lead to a new therapy for neuroAIDS. Since the brain harbors long-lived HIV- infected cells such as microglia, eradication of HIV from this site could also lead to cure of HIV/AID.
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