The enteric nervous system (ENS) can control the behavior of the bowel without input from brain or spinal cord. A functioning ENS is essential for life and, when abnormal, causes discomfort and may contribute to the pathophysiology or severity of disorders of gastrointestinal motility, secretion, and inflammation. We have recently discovered that varicella zoster virus (VZV) establishes latency within human enteric neurons in most individuals who have experienced natural varicella or received varicella vaccine. VZV, moreover, has been linked to the occurrence of lethal pseudoobstruction in immunocompromised individuals. Neither the route by which VZV gains access to the ENS, nor the frequency or consequences of its reactivation in enteric neurons (""""""""enteric zoster"""""""") has previously been explored. The current proposal is designed to test the hypotheses that transport in visceral afferent nerves conducts VZV to the ENS, that cell- free virions establish latency in enteric neurons, and that the non-structural VZV ORF61 protein must be expressed in neurons to enable VZV to manifest lytic infection or to reactivate from latency. Although VZV displays a marked preference for human cells, we have developed animal models that permit VZV infection of the ENS to be studied in vitro and in vivo. Depending on conditions, VZV recapitulates latent, lytic, and reactivating infection in enteric neurons isolated from guinea pigs or mice and, when introduced to the bowel, VZV establishes latency in the guinea pig ENS in situ. The proposal has 3 specific aims: (1) Can VZV travel from the skin to the ENS in sensory nerve fibers? Preliminary studies have identified neurons in dorsal route ganglia that project both to skin and gut. We will determine whether latent infection is established in the ENS when VZV is introduced to the skin and whether VZV-infected nerve terminals release infectious cell-free VZV that crosses synaptic gaps to transfer latent infection to target neurons. (2) Can a viremia establish latent VZV infection of enteric neurons? We will determine whether VZV-infected T lymphocytes release infectious cell-free VZV and whether they can establish latency directly in enteric neurons or indirectly via infections of the mucosal epithelium or skin. Preliminary studies have shown that VZV DNA is present in guinea pig enteric neurons following the iv injection of VZV-infected peripheral blood mononuclear cells. (3) Is VZV ORF61 protein expression necessary for the manifestation of lytic infection in enteric neurons? We will study the ability of a VZV mutant that lacks ORF61 to establish lytic infection of enteric neurons or reactivate from latency. The significance of understanding VZV infection of the ENS is enhanced by the possibility that unsuspected reactivation of VZV in enteric neurons might contribute to the pathogenesis of GI disorders such as irritable bowel syndrome, inflammatory bowel disease, idiopathic gastroparesis, and chronic intestinal pseudoobstruction.
The gut contains a large and complex network of nerve cells, known as the enteric nervous system (ENS), which is able to control the behavior of the bowel without input from the brain or spinal cord. The ENS contributes to the underlying basis of a number of disorders that disturb the functioning of ENS, such as irritable bowel syndrome, inflammatory bowel disease, idiopathic gastroparesis, and chronic intestinal pseudoobstruction are currently not understood. We have recently discovered that varicella zoster virus (VZV) establishes latency within nerve cells of the human ENS. Neither the cause nor the consequences of this phenomenon have previously been explored because latent VZV in enteric nerve cells was not known to occur. The current proposal is designed to determine how VZV gains access to the ENS and we will utilize enteric nerve cells to test the hypotheses that only the cell-free particle form of VZV is able to establish of latency in enteric or other nerve cells and that a viral protein that is produced in infected cells but which is not incorporated into viral particles (ORF61p) is required for VZV to give rise to an infection that produces more virus and kills infected cells (lytic infection) or to reactivate from latency in nerve cells.
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