MECHANISMS FOR THE INTESTINAL PROBIOTIC EFFECTS OF S. BOULARDII

博拉氏酵母菌是一种非致病性酵母菌，几十年来一直被安全地用于预防肠道损伤、炎症和肠道分泌物，这些肠道损伤是由多种肠道细菌病原体引起的，包括艰难梭状芽胞杆菌和志贺氏菌。该项目的长期目标是明确博氏沙门氏菌等益生菌制剂对肠道感染和炎症的保护和治疗作用的特定细胞和分子机制。博氏弧菌广泛的有益作用使我们假设这种益生菌酵母可能通过调节宿主肠道炎症反应途径起作用。我们的初步数据表明，博氏弧菌产生一种可溶因子来阻止IkappaBalpha

Saccharomyces boulardii is a non-pathogenic yeast that has been used safely for many decades to protect against intestinal injury, inflammation and secretion caused by a variety of bacterial enteric pathogens including Ciostridium difficile and Shigellae. The longterm goal of this project is to define specific cellular and molecular mechanisms for the protective and therapeutic effects of probiotic agents such as S. boulardii in intestinal infection and inflammation. The broad-ranging beneficial effects of S. boulardii led us to hypothesize that this probiotic yeast may act through modulation of host intestinal inflammatory response pathways. Our preliminary data demonstrate that S. boulardii produces a soluble factor that prevents IkappaBalpha degradation, NF-kappaB nuclear translocation and NF-kappaB-mediated IL-8 gene expression in human intestinal epithelial cells or monocytes. Purification and characterization studies indicate that the S. boulardii antiinflammatory factor (SAIF) is a small (approximately 1 kDa), heat stable, water soluble glycan. The Specific Aims of this proposal are: Aim 1: To determine the mechanism whereby S. boulardii and SAIF modulate NF-kappaB activation and pro-inflammatory gene expression in monocytes and intestinal epithelial cells exposed to bacterial products (C. difficile toxin A, LPS), or endogenous inflammatory mediators (IL-1betap, TNFalpha). In collaboration with project 1 we will also examine the ability of S. boulardii to modulate NF-kappaB signaling in response to the gut neuropeptides CRH and urocortin II. Aim 2: To determine whether and by which mechanism S. boulardii and SAIF prevent MAP kinase activation and signaling. This aim will also test the hypothesis that S. boulardii blocks Ras/Erk MAP kinase signaling through an inhibitory effect on EGF receptor kinase activation. Aim 3: To elucidate the mechanisms whereby S. boulardii and SAIF augment intestinal epithelial barrier function in polarized T84 monolayers and in murine small intestinal mucosal strips (in collaboration with projects 3 and 4). Aim 4: To determine whether S. boulardii and SAIF can prevent intestinal injury, inflammation and loss of barrier function in both murine and human xenograft intestinal mucosa exposed to C. difficile toxin A (in collaboration with Core B). Examination of these specific aims will advance our understanding of the cellular and in vivo mechanisms whereby a probiotic yeast and/or its soluble products can prevent and treat gastrointestinal infectious and inflammatory diseases in humans.