Human Oral Isolate Lactobacillus fermentum AGR1487 Reduces Intestinal Barrier Integrity by Increasing the Turnover of Microtubules in Caco-2 Cells

Abstract

Lactobacillus fermentum is found in fermented foods and thought to be harmless. In vivo and clinical studies indicate that some L. fermentum strains have beneficial properties, particularly for gastrointestinal health. However, L. fermentum AGR1487 decreases trans-epithelial electrical resistance (TEER), a measure of intestinal barrier integrity. The hypothesis was that L. fermentum AGR1487 decreases the expression of intestinal cell tight junction genes and proteins, thereby reducing barrier integrity. Transcriptomic and proteomic analyses of Caco-2 cells (model of human intestinal epithelial cells) treated with L. fermentum AGR1487 were used to obtain a global view of the effect of the bacterium on intestinal epithelial cells. Specific functional characteristics by which L. fermentum AGR1487 reduces intestinal barrier integrity were examined using confocal microscopy, cell cycle progression and adherence bioassays. The effects of TEER-enhancing L. fermentum AGR1485 were investigated for comparison. L. fermentum AGR1487 did not alter the expression of Caco-2 cell tight junction genes (compared to L. fermentum AGR1485) and tight junction proteins were not able to be detected. However, L. fermentum AGR1487 increased the expression levels of seven tubulin genes and the abundance of three microtubule-associated proteins, which have been linked to tight junction disassembly. Additionally, Caco-2 cells treated with L. fermentum AGR1487 did not have defined and uniform borders of zona occludens 2 around each cell, unlike control or AGR1485 treated cells. L. fermentum AGR1487 cells were required for the negative effect on barrier integrity (bacterial supernatant did not cause a decrease in TEER), suggesting that a physical interaction may be necessary. Increased adherence of L. fermentum AGR1487 to Caco-2 cells (compared to L. fermentum AGR1485) was likely to facilitate this cell-to-cell interaction. These findings illustrate that bacterial strains of the same species can cause contrasting host responses and suggest that food-safe status should be given to individual strains not species.

Human oral isolate Lactobacillus fermentum AGR1487 induces a pro-inflammatory response in germ-free rat colons

“…Stimulation of the TLR2 pathway leads to activation of specific protein kinase C isoforms in vitro , ultimately leading to the sealing of tight junctions and an increase in TEER 28 or prevention of tight junction disruption 7 . Although AGR1487 activated TLR2, the strain disrupted tight junctions and caused a decrease in TEER of epithelial cell monolayers 21 . Caco-2 cells treated with AGR1487 had higher expression levels of genes involved in the p38 MAPK signalling pathway, which leads to tight junction disruption 29 .…”

“…Lactobacilli found in human faeces can originate from the mouth 19 20 , indicating that this oral isolate may reside in the intestines of the individual from whom it was isolated. AGR1487 was shown to increase intestinal epithelial barrier permeability in vitro , possibly by increasing the turnover of microtubules in the epithelial cells leading to tight junction disassembly 21 . In addition to reducing intestinal epithelial barrier integrity, the in vitro study also suggested that AGR1487 may have a pro-inflammatory effect 21 .…”

“…AGR1487 was shown to increase intestinal epithelial barrier permeability in vitro , possibly by increasing the turnover of microtubules in the epithelial cells leading to tight junction disassembly 21 . In addition to reducing intestinal epithelial barrier integrity, the in vitro study also suggested that AGR1487 may have a pro-inflammatory effect 21 .…”

“…To test the hypothesis that AGR1487 induces a pro-inflammatory response in the host we compared it with another human oral isolate of L. fermentum , AGR1485, which does not alter epithelial barrier integrity in vitro 21 . The effects of AGR1485 and AGR1487 on TLR activation and dendritic cell function were investigated in vitro as well as their effects on the mucosa of mono-colonized germ-free rats.…”

Giardia's Epithelial Cell Interaction In Vitro: Mimicking Asymptomatic Infection?

“…A mechanism that was proposed to link to acute symptoms was the breakdown of the intestinal barrier function of the epithelium, leading to increased permeability with bacterial invasion as a possible result (Buret, 2007 ; Ankarklev et al, 2010 ). This was probably inspired by the impressive in vitro phenotypes obtained with certain bacterial, gastrointestinal pathogens and their products/toxins/proteases (Malago et al, 2003 ; Fajdiga et al, 2006 ; Rees et al, 2008 ; Liu et al, 2012 ; Anderson et al, 2013 ; Fiorentino et al, 2013 ) as well as other parasitic protozoans like Entamoeba histolytica, Cryptosporidium parvum , or Blastocystis sp. (Li et al, 1994 ; Leroy et al, 2000 ; Buret et al, 2003 ; Betanzos et al, 2014 ; Wu et al, 2014 ).…”