Surgical patients with critical disorders such as thermal injury, sever trauma, shock, and sepsis are commonly complicated with the gastrointestinal mucosal injury, which can lead to the development of systemic infection, septic shock, and multiple organ failure. Restitution is an important process for repair of disrupted intestinal lining. Previous studies have suggested that intestinal epithelial restitution is delayed in critically ill individuals. Our recent work has revealed that milk fat globule-EGF factor 8 (MFG-E8) is a macrophage-derived intestinal epithelial restitution factor. MFG-E8 promotes intestinal epithelial wound-healing via a PKC5 dependent manner. In sepsis, intestinal injury is associated with downregulation of MFG-E8, which contributes to the impairment of restitution. In this proposal, therefore, we will test a central hypothesis that under the physiological state, MFG-E8 maintains intestinal epithelial cell migration via a typical signal pathway, whereas under the septic condition, inflammatory mediators down-regulate MFG-E8 expression, which in turn impairs intestinal epithelial cell restitution.
In Specific Aim 1, we will define the molecular and signaling mechanism through which MFG-E8 enhances intestinal epithelial restitution. Our preliminary data suggest that MFG-E8 activates several PKC5-associated intracellular signal molecules. Therefore, we will investigate the role of these molecules in MFG-E8-induced intestinal epithelial cell migration using molecular biology and gene knockdown approaches.
In Specific Aim 2, we will focus on understanding the cause of down-regulation of intestinal MFG-E8 gene expression and impairment of MFG-E8-dependent intestinal restitution in sepsis. Our preliminary data suggest that a sepsis-derived inflammatory mediator mimics septic effect on intestinal MFG-E8 gene expression and restitution. Thus, we will test the hypothesis that this mediator inhibits intestinal MFG-E8 gene expression, which subsequently results in impairment of intestinal restitution.
In Specific Aim 3, we will investigate the molecular mechanism underlying the inhibition of MFG-E8 expression in macrophages by septic insult-derived inflammatory stimulus. Our preliminary data show that repression of MFG-E8 gene expression by an inflammatory stimulus is involved in affecting the activities of promoter and mRNA 3'-untranslated region (3'-UTR) of MFG-E8. To follow up on these findings, we will characterize binding motifs in the MFG-E8 gene promoter and their binding proteins, and study their role in suppression of MFG-E8 gene expression during inflammation. The standard approach for analysis of the gene promoter function will be applied. In addition, we will use the microRNA and site-directed mutagenesis technologies to study the role of 3'-UTR and microRNAs in regulation of MFG-E8 gene expression by an inflammatory stimulus. Achievement of these specific aims and confirmation of our hypotheses will provide the novel mechanistic information that allows us to understand the crucial role of MFG-E8 in the gut and its physio/pathological implications. Our studies will ultimately lead to development of novel strategies for management and treatment of intestinal injury in critically ill patients.
Acute intestinal injury contributes to morbidity and mortality of hospitalized patients in the intensive care unit and surgical department. However, despite the medical advances of the past few decades, there remain few effective treatments for this common disorder. Our recent findings demonstrate that milk fat globule-EGF factor 8 (MFG-E8) promotes repair of intestinal lining in sepsis. Achievement of aims of this proposal will not only provide the novel mechanistic information that allows us to understand the crucial role of MFG-E8 in the gut and its physio/pathological implications, but also are likely to suggest novel therapeutic strategies aimed at preserving intestinal barrier function for critically ill patients.
|Asai, Akihiro; Chou, Pauline M; Bu, Heng-Fu et al. (2014) Dissociation of hepatic insulin resistance from susceptibility of nonalcoholic fatty liver disease induced by a high-fat and high-carbohydrate diet in mice. Am J Physiol Gastrointest Liver Physiol 306:G496-504|
|Wang, Xiao; Bu, Heng-Fu; Zhong, Wei et al. (2013) MFG-E8 and HMGB1 are involved in the mechanism underlying alcohol-induced impairment of macrophage efferocytosis. Mol Med 19:170-82|
|Eaves-Pyles, Tonyia; Bu, Heng-Fu; Tan, Xiao-di et al. (2011) Luminal-applied flagellin is internalized by polarized intestinal epithelial cells and elicits immune responses via the TLR5 dependent mechanism. PLoS One 6:e24869|
|Chogle, Ashish; Bu, Heng-Fu; Wang, Xiao et al. (2011) Milk fat globule-EGF factor 8 is a critical protein for healing of dextran sodium sulfate-induced acute colitis in mice. Mol Med 17:502-7|
|Zhou, Huiping (2011) HIV protease inhibitors induce endoplasmic reticulum stress and disrupt barrier integrity in intestinal epithelial cells. Methods Enzymol 490:107-19|
|Bu, Heng-Fu; Wang, Xiao; Tang, Yi et al. (2010) Toll-like receptor 2-mediated peptidoglycan uptake by immature intestinal epithelial cells from apical side and exosome-associated transcellular transcytosis. J Cell Physiol 222:658-68|
|Wu, Xudong; Sun, Lixin; Zha, Weibin et al. (2010) HIV protease inhibitors induce endoplasmic reticulum stress and disrupt barrier integrity in intestinal epithelial cells. Gastroenterology 138:197-209|
|Wang, Xiao; O'Gorman, Maurice R G; Bu, Heng-Fu et al. (2009) Probiotic preparation VSL#3 alters the distribution and phenotypes of dendritic cells within the intestinal mucosa in C57BL/10J mice. J Nutr 139:1595-602|
|Bu, Heng-Fu; Zuo, Xiu-Li; Wang, Xiao et al. (2007) Milk fat globule-EGF factor 8/lactadherin plays a crucial role in maintenance and repair of murine intestinal epithelium. J Clin Invest 117:3673-83|
|Bu, Heng-Fu; Wang, Xiao; Zhu, Ya-Qin et al. (2006) Lysozyme-modified probiotic components protect rats against polymicrobial sepsis: role of macrophages and cathelicidin-related innate immunity. J Immunol 177:8767-76|
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