Transduction Pathways Regulating The Trophic effects of Saccharomyces boulardii in Rat small intestinal mucosa

S . boulardii is a probiotic yeast widely prescribed in a lyophilized form that determines in human and rat small intestine several effects including endoluminal secretion of enzymes and of polyamines, stimulation of microvillous enzymes, of sIgA ,increased production of the receptor for polymeric immunoglobulins by crypt cells, and enhanced D-glucose uptake.Aim: The objective of this study was to determine the pathway(s) by which these effects generated by the yeast are transduced into the cell. Litters of 6 growing Wistar rats each (30 days post partum) were treated with S .boulardii (50[micro]g per g body wt) or with saline during 72 hours. For each animal, the cytosol was prepared from the whole mucosa after the fat cake was discarded. Several known intestinal substrates were immunoprecipitated and immunoblotted using specific antibodies recognizing the non-, mono- or diphosphorylated forms of these substrates. The signals were detected using ECL and were measured by optodensitometry. treatement with S.boulardii enhanced markedly the RAS-GAP-RAF-ERK1,2 pathway with participation of GRB2, SHC, SOS, and CRKII. Unit p85a of Pi-3 kinase ,tested in its phosporylated form, was also enhanced by the probiotic compared to control samples. In rats treated with an inhibitor of RAF-1 and of ERK 1,2 (PD098059) the expression of mucosal disaccharidases was inhibited by about 50%. Conclusion: The probiotic S. boulardii generates in vivo mitogen and metabolic signals which are transduced into intestinal cells downstream from the apical membrane to the nuclei, using recruitment substrates and serine, threonine, or tyrosine kinases .