The overall goal of these studies is to understand the mechanisms of enteric neuroregeneration in order to develop therapies targeted toward endogenous repopulation of the enteric nervous system (ENS) for the treatment of enteric neuropathy. Enteric neuropathy, which contribute to numerous digestive diseases including idiopathic gastroparesis, chronic intestinal pseudoobstruction (CIPO) Hirshsprung's disease, Chagas' disease, achalasia, and possibly slow transit constipation, are characterized by damage or loss of enteric neurons. Existing animal models of enteric neuropathy, i.e., genetic aganglionosis are characterized by complete loss of neural crest cells including neurons and glia. This complete loss, while recapitulating severe congenital human enteric neuropathy, is in contrast to most enteric neuropathy in humans, which are characterized by less severe neuronal loss, and importantly essentially precludes endogenous neural regeneration by neural crest precursors. Overcoming this limitation, we developed a novel low-dose, instead of the traditional high-dose, benzalkonium chloride (BAC) model in the murine small intestine to induce a loss of 50% of neurons, and robust neuroregeneration. It is the only animal model to date that demonstrates robust endogenous neuroregeneration. Using this model with novel transgenic mouse strains and additional in vitro approaches, we will test the overall hypothesis that regeneration of the myenteric plexus is mediated by transdifferentiation of enteric glia to neurons via a SRY-related homeobox transcription factor 2 (SOX2)- dependent mechanism. Our overall hypothesis will be tested by experiments directed at two specific aims.
Specific Aim 1 will determine the source and functionality of new neurons following BAC treatment because currently, the cellular origin and function of regenerating neurons are not understood.
This aim will be met by testing three hypotheses: 1.1) new neurons derive from enteric cells that express glial fibrillary acidic protein (GFAP); 1.2) glia directly transdifferentiate into neurons; and 1.3 neurons derived from enteric glia are functional and diverse. Enteric glia as a manipulable endogenous source of enteric neurons would be a significant advance because glia outnumber neurons 4:1 in the ENS and are continually replenished by constitutive gliogenesis.
Specific Aim 2 will determine the signaling pathways that contribute to enteric neuroregeneration.
This aim will be met by testing three hypotheses: 2.1) SOX2 expression in glia is necessary and sufficient to generate new neurons; 2.2) bone morphogenic protein 2 (BMP2) induces SOX2 expression in enteric glial cells; and 2.3) SOX2 reprograms enteric glia to neurons by removing RE1-silencing transcription factor (REST)-mediated repression of neural genes. Results of the proposed studies, involving morphological and molecular characterization of novel transgenic mouse strains for genetic lineage tracing, clonal analysis, and molecular targeting, will provide a mechanistic understanding of enteric neuroregeneration and provide the basis for novel therapeutic approaches for the treatment of enteric neuropathy.
Changes in the structure and function of the nerves that supply the gastrointestinal tract can contribute to symptoms of diseases that affect the bowel. These diseases are characterized by damage or loss of nerve cells and current therapies only target symptoms, involve major surgery and often require life-long medical management. We have developed a new animal model that provides insights to ways to treat bowel disease by manipulating the natural ability of the bowel to regenerate the nerve cells that are lost.
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