Project #2. IGF-1 signaling pathway in HIV-1 CMS disorders. A significant number of HIV patients develop cognitive disorders and dementia. It is believed that cellular and viral factors released by the HIV-1 infected cells in the white matter, most notably TNFa , are responsible for neuronal injury seen in AIDS brains. Accordingly, we demonstrated that prolonged exposure of differentiated neurons to TNFoc leads to the retraction of neuronal processes in the absence of neuronal apoptosis. HIV-1 infection can also compromise neuroprotective pathways including the insulin-like growth factor 1 (IGF-1) signaling system. Accordingly, in earlier studies we demonstrated that IGF-1 protects neurons from TNFa-induced retraction of neuronal processes. We have demonstrated that TNFa triggers serine phosphorylation of IRS-1 (pS-IRS-1) at the membrane rafts of differentiated neurons, and that pSIRS- 1 interferes with integrin-mediated cellular responses, which are directly involved in the maintenance of neuronal processes and neuronal outgrowth. These observations led us to hypothesize that in HIV encephalitis degeneration of neuronal processes is caused by TNFa-induced interaction between pS-IRS-1 and neuronal integrins, which leads to detachment and retraction of neuronal processes. This detrimental action of TNFoc is counteracted by IGF-l-mediated tyrosine phosphorylation of IRS-1 (pY-IRS-1), which supports the binding of neuronal processes and facilitates tissue remodeling and neuronal outgrowth. We have addressed this hypothesis by experiments described in three Specific Aims.
In Aim#1. we will analyze density of neuronal processes in the regions of HIV encephalitis (HIVE) differentially affected by the accumulation of TNFoc.
In Aim#2. we will evaluate effects of TNFcc on subcellular localization and phosphorylation status of IRS-1;and will analyze molecular interactions between IRS-1, (31-integrin and ADAMs in primary neuronal cultures from the IGF-IR knockout embryos and from age-matching non-transgenic littermates. Finally, in Aim#3. we will examine effects of IGF-I stimulation on neuronal regeneration and tissue remodeling after TNFa -mediated retraction of neuronal processes in differentiated neurosphere cultures from the IGF-IR knockout embryos and from agematching non-transgenic littermates. The outcome of this project will identify and characterize new molecular events, which affect stability of neuronal processes in the paradigm of HIVE, and possibly other neurological disorders characterized by the accumulation of TNFcc. Understanding the cross interaction between IGF-1 and TNFa signaling pathways will help to develop new IGF-l-based therapeutic approaches against neurological disorders in which retraction/degeneration of neuronal processes is a common event.
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