Probiotic Bacteria Regulate Intestinal Epithelial Permeability in Experimental Ileitis by a TNF-Dependent Mechanism

Abstract

BackgroundWe previously showed that the probiotic mixture, VSL#3, prevents the onset of ileitis in SAMP/YitFc (SAMP) mice, and this effect was associated with stimulation of epithelial-derived TNF. The aim of this study was to determine the mechanism(s) of VSL#3-mediated protection on epithelial barrier function and to further investigate the “paradoxical” effects of TNF in preventing SAMP ileitis.MethodsPermeability was evaluated in SAMP mice prior to the onset of inflammation and during established disease by measuring transepithelial electrical resistance (TEER) on ex vivo-cultured ilea following exposure to VSL#3 conditioned media (CM), TNF or VSL#3-CM + anti-TNF. Tight junction (TJ) proteins were assessed by qRT-PCR, Western blot, and confocal microscopy, and TNFRI/TNFRII expression measured in freshly isolated intestinal epithelial cells (IEC) from SAMP and control AKR mice.ResultsCulture with either VSL#3-CM or TNF resulted in decreased ileal paracellular permeability in pre-inflamed SAMP, but not SAMP with established disease, while addition of anti-TNF abrogated these effects. Modulation of the TJ proteins, claudin-2 and occludin, occurred with a significant decrease in claudin-2 and increase in occludin following stimulation with VSL#3-CM or TNF. TNF protein levels increased in supernatants of SAMP ilea incubated with VSL#3-CM compared to vehicle, while IEC-derived TNFR mRNA expression decreased in young, and was elevated in inflamed, SAMP versus AKR mice.ConclusionsOur data demonstrate that the previously established efficacy of VSL#3 in preventing SAMP ileitis is due to direct innate and homeostatic effects of TNF on the gut epithelium, modulation of the TJ proteins, claudin-2 and occludin, and overall improvement of intestinal permeability.

Strain-Dependent Augmentation of Tight-Junction Barrier Function in Human Primary Epidermal Keratinocytes by Lactobacillus and Bifidobacterium Lysates

“…Certain probiotics, e.g., Lactobacillus salivarius, may ameliorate or prevent barrier disruption induced by pathogens or other noxious substances (9-11). Other probiotics can enhance TJ function in gut cells that have not been treated with any stressor (25). The mechanisms by which probiotics exert their effects on the gut barrier may vary, but they include both changes to the expression of individual TJ proteins and activation of signaling pathways involved in barrier formation or regulation.…”

Microbial Sensing and Regulation of Mucosal Immune Responses by Intestinal Epithelial Cells

“…Consistently, overexpression of hPepT1 in intestinal epithelial cells in villin-hPepT1 transgenic mice worsened the severity of inflammation induced by DSS, but not by TNBS (Dalmasso et al, 2011). This activity was dependent on NOD2, as mice bred in a NOD2-deficient background displayed a similar severity compared to nontransgenic mice (Dalmasso et al, 2011). Thus the expression of dipeptide transporters may aggravate innate colitis through the engagement of intracellular PRRs.…”

Epithelial Cells

“…IL-10 knockout mice may also be a powerful tool in studies of IBD-associated barrier loss because they display increased intestinal permeability long before disease presents (Madsen et al, 1999). In contrast to IL-10 knockout mice, which do not develop disease under germ-free conditions (Madsen et al, 1999), increased permeability that develops before clinical disease in the outbred SAMP1/YitFc model of spontaneous ileocolitis is independent of the presence of microbiota (Corridoni et al, 2012;Olson et al, 2006). In an effort to take advantage of the increased permeability that precedes onset in IL-10 knockout mice, one study treated these mice with a peptide that enhances small intestinal barrier function and found reduced mucosal TNF expression and neutrophil infiltration (Arrieta et al, 2009).…”