Bifidobacterium bifidum prevents the IL-1B induced increase in intestinal permeability by a novel mechanism: TLR-2 dependent activation of PPAR-gamma and inhibition of NF-kB signaling pathway
Authors: Abdulqadir Raz , Al-Sadi Rana , Ma Thomas 
Published: May 2023

Background: Bifidobacterium bifidum (BB) is one of the most common probiotic bacteria strains that have been shown to have protective effects against intestinal inflammation, primarily by enhancing the intestinal epithelial tight junction (TJ) barrier function. IL-1β contributes to the development of intestinal inflammation in inflammatory bowel disease (IBD) in part by causing an increase in intestinal permeability. The IL-1β induced increase in intestinal epithelial TJ permeability is mediated by an NF-κB-dependent activation of myosin light chain kinase (MLCK) gene and disruption of the intestinal TJ barrier. The peroxisome proliferator-activated receptor gamma (PPAR-γ) is an important nuclear receptor in enterocytes which is known to have anti-inflammatory activity by interfering with NF-κB activation. However, the role of BB/PPAR-γ (and the possible mechanism involved) in protecting against IL-1β increase in intestinal permeability remain unclear. Aims: The major purpose of this study was to delineate the protective effect of BB against the IL-1β induced increase in intestinal TJ permeability and the intracellular mechanism involved. Methods: Filter-grown Caco-2 monolayers ( in vitro) and recycling intestinal perfusion of live mice ( in vivo) were used to assess intestinal permeability by using a paracellular marker (dextran-10kDa). Results: IL-1β caused a rapid activation of NF-κB and NF-κB and MLCK-dependent increase in intestinal epithelial TJ permeability in vitro and in vivo. A specific strain of BB (1x108 CFU/ml) referred to as BB1 strain inhibited the IL-1β increase in intestinal TJ permeability while strain BB4 had no effect. Other BB strains examined (5 total strains including BB4) did not inhibit the IL-1β increase in intestinal TJ permeability, suggesting that the BB enhancement of Caco-2 TJ barrier function was strain-specific. BB1, not BB4 enhancement of the TJ barrier was associated with an increase in TLR-2 expression, and PPAR-γ activation; BB1 also inhibited NF-kB activation and MLCK activity in Caco-2 monolayers and in mouse enterocyte. The inhibitory effect of BB on 1L-1β induced increase intestinal permeability, NF-κB activation, MLCK expression and activity was blocked by siRNA-induced knockdown of TLR-2 or PPAR-γ in Caco-2 monolayers. We also generated Villin-cre intestinal epithelial specific PPAR-γ knockout mice to study the involvement of enterocytes TLR-2/PPAR-γ on BB1 effect. BB1 did not inhibit the IL-1β-induced activation of NF-κB, increase in MLCK expression and increase in mouse intestinal permeability in TLR-2 or PPAR-γ intestinal deficient mice. Conclusion: These studies provide a novel insight into the BB the protective mechanism against the IL-1β-induced increase in intestinal TJ permeability in -vitro and in-vivo. Our data show that BB protects against the IL-1β induced increase in intestinal TJ permeability by a novel mechanism involving TLR-2/PPAR-g mediated inhibition of NF-kB and MLCK gene activatiation. NIH funding This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.