Despite the large number of viruses that can infect the human brain, and the growing suspicion that some neurotropic pathogens play a direct or contributory role in chronic neurodegenerative diseases, little is known about the fate of neurons following infection. It has been surmised that neurons can survive an infection and immunity event, resulting in cured cells that are functionally indistinguishable from the pre-infection phonotype, though this has not been experimentally tested. While there is abundant evidence that immunocompetent mice mount a protective response within the CNS that resolves a viral infection, leading to little overt inflammatory damage and apparent impairment-free survival, two critical questions remain unanswered, which are the basis for this proposal. First: do neurons, in fact, survive the anti- viral immune response? Second: If neurons can be cured of a virus, are they functionally competent? These questions will be addressed using a well-characterized mouse system (congenic Cre reporter mice) to follow the consequences of viral infection of neurons over time. Neurons that have been infected with one of two neurotropic RNA viruses (measles or rabies) will be "marked" by a permanent change in fluorescence signal from red to green. These neurons can then be monitored throughout the infection course in the presence or absence of a competent immune response. Moreover, marked (green) neurons can be isolated by laser capture microdissection for subsequent gene and protein expression analyses. The ability to identify, isolate and characterize actively infected neurons or previously infected neurons that have been cured by the host immune response will allow for more precise studies to define how variables including age, neuronal subtype, virus type, and immune effectors impact on CNS neuron survival and function. Finally, given that this system can be broadly applied to virtually any mouse model of CNS viral infection, we believe there is the potential to enable major advances in the fields of neurovirology and neuropathogenesis.
This proposal will explore the utility of a novel mouse model to explore neuronal survival and function following virus infection. In this model, neurons that have been infected by Cre- recombinase expressing viruses undergo a permanent, readily detectable color change from red to green, serving as a marker of previous infection. Using two well-characterized neurotropic viruses (measles and rabies), neuronal survival and function will be assessed during active infection and at various timepoints post-clearance. The information obtained from these studies will have direct translational links that will guide therapeutic strategies to prevent or resolve neurotropic infections in humans, aid viral vector-based gene therapy strategies, and elucidate what role, if any, viruses play in neurodegenerative diseases of unknown etiology.
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