GABA selectively increases mucin-1 expression in isolated pig jejunum

Abstract

The inhibitory neurotransmitter GABA (γ-aminobutyric acid) is synthesized by glutamic acid decarboxylase, which is expressed in the central nervous system and in various other tissues including the intestine. Moreover, GABA can be ingested in vegetarian diets or produced by bacterial commensals in the gastrointestinal tract. As previous studies in lung have suggested a link between locally increased GABA availability and mucin 5AC production, the present study sought to test whether the presence or lack of GABA (and its precursor glutamine) has an effect on intestinal mucin expression. Porcine jejunum epithelial preparations were incubated with two different amounts of GABA or glutamine on the mucosal side for 4 h, and changes in the relative gene expression of seven different mucins, enzymes involved in mucin shedding, GABA B receptor, enzymes involved in glutamine/GABA metabolism, glutathione peroxidase 2, and interleukin 10 were examined by quantitative PCR (TaqMan(®) assays). Protein expression of mucin-1 (MUC1) was analyzed by Western blot. On the RNA level, only MUC1 was significantly up-regulated by both GABA concentrations compared with the control. Glutamine-treated groups showed the same trend. On the protein level, all treatment groups showed a significantly higher MUC1 expression than the control group. We conclude that GABA selectively increases the expression of MUC1, a cell surface mucin that prevents the adhesion of microorganisms, because of its size and negative charge, and therefore propose that the well-described positive effects of glutamine on enterocytes and intestinal integrity are partly attributable to effects of its metabolite GABA.

The GadX regulon affects virulence gene expression and adhesion of porcine enteropathogenic Escherichia coli in vitro

“…As expected, the lowest pH was found in the digesta fluid of the stomach (4.1±0.3, average pH of N=6), whereas the jejunum appeared to have the highest pH (6.5±0.1), decreasing again in the cecum (6.0±0.2, see additional file 1). These findings are very much in line with the results of our previous study ( Braun et al, 2015 ): highest concentrations of GABA were found in the stomach whereas the lowest GABA concentration was detected in the jejunum, increasing again towards the hindgut.…”

“…In accordance with our recent hypothesis that GABA levels influence mucin-1 expression, McGuckin, Linden, Sutton and Florin (2011) described that the mucus layer is thickest in the stomach and colon. Apparently this does not only correlate with the number and distribution of mucus-producing cells throughout the gastrointestinal tract but also with our finding that GABA levels are highest in the stomach and colon ( Braun et al, 2015 ). These GABA levels were derived from the same animals and correlate well with measured pH levels.…”

“…The subsequent release of GABA via a GABA-glutamate antiporter represents the factual extrusion of protons and stabilizes the bacteria's inner pH milieu ( Foster, 2004 , Hersh et al, 1996 , Richard and Foster, 2003 ). In a previous study, we have shown that luminal GABA has significant local effects in the small intestine, namely a selective upregulation of mucin 1 (MUC1) ( Braun, Sponder, Pieper, Aschenbach, & Deiner, 2015 ). The MUC1 protein is the best characterized transmembrane mucin and is an important player of intestinal defense.…”

Overexpression of Na+/Mg2+ exchanger SLC41A1 attenuates pro-survival signaling

“…The TGX Stain-Free TM FastCast TM Kit (Bio-Rad) was used to prepare 10% SDS-PAA gels. Protein detection with this technique is based on trihalo-compound modification of tryptophan residues and has proven to be superior to the conventional detection of housekeeping-proteins [ 68 – 70 ]. Loaded protein amounts were as described previously and gels for the detection of total and phosphorylated Erk1/2 were run in parallel.…”

Intake of Fish Oil Specifically Modulates Colonic Muc2 Expression in Middle‐Aged Rats by Suppressing the Glycosylation Process

“…Braun et al. also mentioned that such enzyme could promote mucin expression . Phosphoinositide phospholipase C (Plch1) is an enzyme that cleaves phosphatidylinositol 4,5‐bisphosphate to generate inositol 1,4,5‐trisphosphate and diacylglycerol.…”