Postoperative ileus (POI) following gastrointestinal (GI) surgery leads to significant patient morbidity and prolonged hospitalizations. POI is a major health problem and a significant burden on the health care system, which is estimated at $750 million to $1 billion per year in the United States. Currently, no treatments have been completely successful in reducing POI's significant impacts on patients and health care system. Recent studies have demonstrated that intestinal manipulation and surgical trauma activate inflammatory macrophages (M?) and release inflammatory mediators such as nitric oxide (NO) to inhibit intestinal smooth muscle cells in POI. Therefore, suppression of the immune function has been considered as a promising means to treat POI. However, inhibition of the intestinal immune system could elicit severe side effects because intestinal immune system hosts near 70% of the entire immune system and is critical to immune homeostasis. Intestinal M? are a highly heterogeneous and dynamic population in the innate immune system. Preliminary studies show that transient receptor potential vanilloid 4 (TRPV4) channel, a molecular sensor of tissue damage and inflammation, is exclusively expressed by the F4/80+/CD206+ intestinal anti-inflammatory M2 M?. Activation of TRPV4 produces an intestinal contractile response and improves GI transit in a mouse model of POI. The current proposal aims to elucidate the cellular and molecular mechanisms underlying the activation of TRPV4 in the intestinal M2 M?. Ca2+ imaging and patch-clamp studies will be used to study the function of TRPV4 in intestinal M?. The requirement of bone marrow (BM)-derived M? in TRPV4-mediated contractile response will be determined by constructing chimeric mice by reciprocal BM transplantation in lethally irradiated Trpv4+/+ and Trpv4-/- mice as well as using macrophage-deficient op/op mice and transgenic mice expressing the human diphtheria toxin receptor (DTR) in CD11b+ intestinal M? (itgam-DTR). Pharmacological and genetic ablation studies will be used to test if TLR4-mediated release of serotonin from mucosal enterochromaffin cells and/or mast cells is required for potentiation of TRPV4-mediated intestinal contractile response by bacterial lipopolysaccharides (LPS). More importantly, a mouse model of POI will be generated to investigate if selective activation of TRPV4 can improve or reverse POI in vivo. Successful completion of these studies will advance our understanding of the previously unrecognized role of TRPV4 and intestinal M? in regulating GI motility. More importantly, the proposed studies will define novel therapeutic targets for future clinical studies for the treatment of POI by directly targeting both intestinal innate immune system and the TRPV4 channels.
Postoperative ileus (POI) resulting from intestinal manipulation and surgical trauma leads to significant patient morbidity and prolonged hospitalizations, and has become a major health problem and a significant burden on the health care system, which is estimated at $750 million to $1 billion per year in the United States. Currently, no treatments have been completely successful in reducing POI's significant impacts on patients and health care system. The proposed studies will investigate the mechanisms underlying regulation of intestinal motility by TRPV4 channels expressed exclusively in intestinal macrophages in the hopes of exploring novel therapeutic interventions to improve POI.
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