FS2-Samak etal-OS/LC/EGF study

Osmotic stress plays a crucial role in the pathogenesis of many gastrointestinal diseases. <em>Lactobacillus casei</em> and epidermal growth factor (EGF) effects on the osmotic stress-induced epithelial junctional disruption and barrier dysfunction were investigated. Caco-2 cell monolayers were exposed to osmotic stress in the presence or absence of <em>L. casei</em> or EGF, and the barrier function was evaluated by measuring inulin permeability. Tight junction (TJ) and adherens junction integrity were assessed by immunofluorescence confocal microscopy. The role of signaling molecules in the <em>L. casei</em> and EGF effects was determined by using selective inhibitors. Data show that pretreatment of cell monolayers with <em>L. casei</em> or EGF attenuates osmotic stress-induced TJ and adherens junction disruption and barrier dysfunction. EGF also blocked osmotic stress-induced actin cytoskeleton remodeling. U0126 (MEK1/2 inhibitor), the MAP kinase inhibitor, blocked EGF-mediated epithelial protection from osmotic stress. In contrast, the <em>L. casei</em>-mediated epithelial protection from osmotic stress was unaffected by U0126, AG1478 (EGFR tyrosine kinase inhibitor), SP600125 (JNK1/2 inhibitor), or SB202190 (P38 MAP kinase inhibitor). On the other hand, Ro-32-0432 (PKC inhibitor) blocked the <em>L. casei</em>-mediated prevention of osmotic stress-induced TJ disruption and barrier dysfunction. The combination of EGF and <em>L. casei</em> is more potent in protecting the barrier function from osmotic stress. These findings suggest that <em>L. casei</em> and EGF ameliorate osmotic stress-induced disruption of apical junctional complexes and barrier dysfunction in the intestinal epithelium by distinct signaling mechanisms.