Growth-associated protein-43 and ephrin B3 induction in the brain of adult SIV-infected rhesus macaques
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Understanding the mechanisms of neuronal regeneration and repair in the adult central nervous system is a vital area of research. Using a rhesus lentiviral encephalitis model, we sought to determine whether recovery of neuronal metabolism after injury coincides with the induction of two important markers of synaptodendritic repair: growth-associated protein-43 (GAP-43) and ephrin B3. We examined whether the improvement of neuronal metabolism with combined anti-retroviral therapy (cART) after simian immunodeficiency virus (SIV) infection in rhesus macaques involved induction of GAP-43, also known as neuromodulin, and ephrin B3, both implicated in axonal pathfinding during neurodevelopment and regulation of synapse formation, neuronal plasticity, and repair in adult brain. We utilized magnetic resonance spectroscopy to demonstrate improved neuronal metabolism in vivo in adult SIV-infected cART animals compared to untreated and uninfected controls. We then assessed levels of GAP-43, ephrin B3, and synaptophysin, a pre-synaptic marker, in three brain regions important for cognitive function, cortex, hippocampus, and putamen, by quantitative real-time RT-PCR and immunohistochemistry. Here we demonstrate that (1) GAP-43 mRNA and protein are induced with SIV infection, (2) GAP-43 protein is higher in the hippocampus outer molecular layer in SIV-infected animals that received cART compared to those that did not, and (3) activated microglia and infiltrating SIV-infected macrophages express abundant ephrin B3, an important axonal guidance molecule. We propose a model whereby SIV infection triggers events that lead to induction of GAP-43 and ephrin B3, and that short-term cART results in increased magnitude of repair mechanisms especially in the hippocampus, a region known for high levels of adult plasticity.
KeywordsRhesus Macaque SIV GAP-43 Ephrin B3 Neuronal injury Synaptophysin Plasticity Microglia
We would like to thank Dr. Larry Benowitz for supplying the anti- GAP-43 antibody and protocol, Ron Desrosiers for supplying the virus inoculum SIVmac251, Keith Reimann for providing anti-CD8 cM-T807, Raymond Schinazi for supplying Racivir (RCV), and Norbert Bischofberger of Gilead Sciences for providing PMPA. In addition, we thank Elizabeth Curran, Michael O’Connell, and Doug Pauley for pathology assistance, and Drs. Prabhat Sehgal, Angela Carville, and Elisabeth Moeller for veterinary expertise. We also thank Hayley Dirscherl, Alexis Denysyk, Heather Knight, and Karen Boisvert Dalecki for their contribution with immunohistochemistry and Hong Yang for real-time PCR contribution. This work was supported by RR00168 (NEPRC Base Grant), R01NS050041 (RGG), DA025697 (GMM), and the NEPRC Microscopy and Primate Genetics Cores.
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