A179 MECHANISMS OF ACTION INVOLVED IN THE WOUND HEALING EFFECT OF THE DIETARY FIBRE RHAMNOGALACTURONAN

Background

Inflammatory bowel diseases (IBD) are chronic and relapsing inflammatory conditions associated with impaired intestinal epithelial barrier. Mucosal healing is the primary goal for IBD treatment since it is a good predictor of clinical remission. We previously showed the direct beneficial effects of rhamnogalacturonan (RGal), a polysaccharide isolated from the plant Acmella oleracea, on intestinal epithelial barrier function with participation of TLR4 and PKC activation. RNAseq data and pathway analysis have indicated the involvement of the canonical nuclear factor kB (NF-kB) signaling pathway.

Purpose

We hypothesize that RGal increases intestinal epithelial wound healing through FAK-Src/PI3K/NF-kB signaling pathways.

Method

Caco-2 and T84 cells, and human primary cell monolayers grown from ulcerative colitis patient-derived organoids, were wounded and treated with vehicle (media or 0.5% DMSO in media) or RGal (1000 μg/ml) for 48 h. Wound healing was assessed using either the IncuCyte or ImageXpress Pico live cell imaging systems. Proliferation and apoptosis of cells were evaluated using EdU and TUNEL assays, respectively. Inhibitors were added at the same time (transcription inhibitor Actinomycin D, 5 μg/ml) or 1 h (FAK inhibitor FAK-14, 10 μM, Src inhibitor PP2, 5 μM, PI3K inhibitor LY294002, 20 μM, NF-kB inhibitors Bay 11-7082 and JSH-23, 10 and 20 μM, respectively, or COX-2 inhibitor NS-398, 20 μM) before RGal treatment. Unwounded Caco-2 monolayers treated with RGal (1000 μg/ml) were collected for Western blotting for COX-2 protein.

Result(s)

In the wound healing assay, RGal (1000 μg/ml) enhanced wound healing by 12.5% at 48 h in Caco-2 cells and by 14.7% at 24 h in T84 cells, compared to control group. RGal (1000 μg/ml) also accelerated the wound closure in colonoid monolayers obtained from ulcerative colitis patient biopsies by 81.3% at 48 h. Neither proliferation nor apoptosis were involved in the RGal effect on wound healing. Treatment of cells with FAK14 (10 μM), PP2 (5 μM), and PI3K (20 μM) significantly prevented the RGal-induced wound healing. Actinomycin D (5 μg/ml), Bay 11-7082 (10 μM) or JSH-23 (20 μM) treatment significantly reversed the effect of RGal on wound healing, showing that the response was transcriptionally dependent and involved NF-kB signaling. Treatment of cells with NS-398 (20 μM) also reversed the effect of RGal on wound healing. COX-2 protein expression was significantly increased at 6 and 12 h after RGal addition to Caco-2 monolayers.

Conclusion(s)

These data suggest that the plant-based polysaccharide RGal increases intestinal epithelial cell wound healing by increasing cell migration. The RGal effect is dependent on the activation of the FAK-Src/PI3K signaling pathways and subsequently the transcription factor NF-kB and downstream COX-2 protein expression and activity. Our findings show a novel mechanism of action of RGal in wound healing that could help in the resolution of intestinal inflammation and mucosal healing.

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NSERC

Disclosure of Interest

None Declared

A275 MECHANOSENSITIVE KCA2 + 1.1 CHANNEL MEDIATES INTRALUMINAL DISTENSION-INDUCED CALCIUM INFLUX IN ENTERIC NEURONS

Background

The enteric nervous system (ENS) is the extensive neural network within the wall of the gastrointestinal (GI) tract that is essential for the control of gut function. However, the mechanisms whereby the ENS responds to the mechanical forces associated with distension are not well understood, and this has implications for gut function in health and disease.

Purpose

This study aims to determine the mechanisms underlying the responsiveness of enteric neural circuits in the myenteric plexus to intraluminal distension.

Method

Intact segments of the colon from mice expressing a genetically encoded fluorescent calcium reporter specifically in enteric neurons (Wnt-1-GCaMP6 mice) or cholinergic neurons (Chat-GCaMP6 mice) were bathed and luminally perfused with Krebs solution in a custom-designed chamber (35-37°C, 95% O₂ ,5% CO₂, pH 7.4). Intracellular Ca²⁺ fluorescence in enteric neurons was visualized by live-cell confocal microscopy and was analyzed using Imaris™ software. Intraluminal distension was accomplished either by increasing luminal perfusion pressure or using colonic preparations containing natural fecal pellets. The degree of intraluminal distension produced by perfusion was defined by the relative distance between identified neurons in preparation and is expressed as a percentage increase in the distance between them. Distension was studied over a range from 0-75%. The degree of distension produced by a fecal pellet in the distal colon is approximately 75%.

Result(s)

Intraluminal distension significantly increased intracellular Ca²⁺ fluorescence in most (>85%) of neurons of the myenteric plexus. When the colon was distended, the response to depolarization by KCl, a general cell depolarization activator, and DMPP, a nicotinic receptor agonist in Wnt1-cre GCaMP6 mice and Chat GCaMP6 mice, respectively was substantially inhibited. To identify how distention induced an increase in intracellular Ca²⁺ fluorescence and inhibited depolarization, pharmacological inhibitors of mechanosensitive ion channels were used. The nonspecific mechanosensitive channel inhibitor, gadolinium (50 mM) and the Kca_1.1 channel inhibitor, paxilline (10 mM), both significantly reduced the luminal distension-induced increase in intracellular Ca²⁺ fluorescence. The effect of luminal distension-inhibited cell depolarization by KCl recovered in the presence of paxilline. This was not observed in the Ca²⁺ responses evoked by DMPP, suggesting that other mechanisms may play a role in the inhibition of neuronal responses in cholinergic enteric neurons.

Conclusion(s)

The majority of neurons of the colonic myenteric plexus are mechanosensitive and show an increase in intracellular Ca²⁺ when the gut is distended. Myenteric neurons do not respond to nicotinic receptor activation when the gut is distended through a mechanism that is dependent on the activity of Kca_1.1 channel.

Supported by CIHR

Disclosure of Interest

None Declared

A62 PROTEASE-ACTIVATED RECEPTOR-2 ACTIVATION ENHANCES EPITHELIAL WOUND HEALING THROUGH SRC PATHWAY-DEPENDENT CELL MIGRATION

Background

Protease-activated receptors (PARs) and their activating enzymes play a role in inflammatory bowel disease (IBD) pathogenesis, but the specific roles of PAR2 in disease initiation and progression remain unclear. Interestingly, PAR2 activation has both pro-proliferative and pro-migratory effects and could be involved with restoration of the epithelial barrier following injury. We previously showed that the PAR2 activation increase the epithelial wound healing through ERK, PI3K and JNK pathways. However, the role of Src kinase, which is also activated by PAR2, is not known.

Aims

We hypothesized that PAR-2 activation induces a wound healing response in intestinal epithelial cells through Src activity.

Methods

Circular wounds were made in T84 colonic epithelial cells monolayers. Wounded monolayers were treated with the PAR2 activating peptide, 2-furoyl-LIGRLO (2fLI, 5 μM), or the inactive control reverse-sequence peptide, 2-furoyl-OLRGIL (2fO, 5 μM), and live cell imaging was used to record wound closure over a 12 or 24-hr period. The specificity of PAR2 was assessed with a PAR2 inhibitor (GB88). Proliferation and cytotoxicity were measured using EdU and TUNEL assays. The mechanism of action was evaluated using inhibitors of FAK (PF57328 and FAK14) and Src (PP2) and western blot (WB) was used to confirm the protein levels [p-FAK (Y397; Y576/577) and p-Src (Y416)]. For immunofluorescence, images of E-cadherin and F-actin or p-FAK were taken to capture the entire wound border and surrounding cells.

Results

PAR2 activation by 2fLI promoted wound closure compared to 2fO or vehicle control at the 12 and 24 hr timepoints ( p<0.05). PAR2’s ability to enhance wound closure was blocked with the PAR2 inhibitor, GB88 ( p<0.01). PAR2 activation had no effect on proliferation at the wound-edge and did not cause apoptosis, but enhanced lamellipodia/filopodia formation ( p<0.001), indicating that PAR2 might program the cells toward a migratory phenotype rather than a proliferative phenotype. When we investigated the mechanisms of action, PAR2 activation did not induce focal adhesion kinase (FAK) expression in T84 cells and inhibition of FAK by selective inhibitors (PF573288 and FAK14) did not alter PAR2-induced wound healing. The immunofluorescence for p-FAK (Y397) and WB (Y937 and Y576/577) confirmed these results. However, the Src tyrosine kinase inhibitor (PP2, p<0.0001) inhibited PAR2-induced wound healing. PAR2 activation increased Src phosphorylation (Y416, p<0.05).

Conclusions

PAR2 activation drives wound healing in part via Src tyrosine kinase activity, but independently of FAK activity. These findings provide a further mechanism whereby PAR2 can participate in the resolution of intestinal wounds in gastrointestinal inflammatory diseases.

Funding Agencies

CAG, CIHR

A64 THE DIETARY FIBRE RHAMNOGALACTURONAN PROMOTES INTESTINAL EPITHELIAL CELL MIGRATION THROUGH THE NF-κB SIGNALING PATHWAY

Background

Damaged intestinal epithelial barrier is characteristic of inflammatory bowel diseases (IBD) and mucosal healing is the primary goal for IBD treatment. We previously showed the direct beneficial effects of rhamnogalacturonan (RGal), a polysaccharide isolated from the plant Acmella oleracea, on intestinal epithelial barrier function with participation of TLR4 and PKC activation. We also observed that RGal accelerates wound healing in human colonic epithelial Caco-2 cells. RNAseq data and pathway analysis have indicated the involvement of the canonical nuclear factor kB (NF-kB) signaling pathway.

Aims

We hypothesize that RGal increases intestinal epithelial wound healing through NF-kB signaling pathway.

Methods

Caco-2 cells monolayers were scratched and treated with vehicle (media or 0.5% DMSO in media) or RGal (1000 mg/ml) for 48 h. Wound healing was assessed using the IncuCyte live cell imaging system. Proliferation and apoptosis of cells were evaluated using EdU and TUNEL assays, respectively. Inhibitors were added at the same time (transcription inhibitor Actinomycin D, 5 mg/ml) or 1 h (NF-kB inhibitors Bay 11–7082 and JSH-23, 10 and 20 mM, respectively, or COX-2 inhibitor NS-398, 20 mM) before RGal treatment. Unwounded Caco-2 monolayers treated with RGal (1000 mg/ml) were collected for Western blotting for COX-2 protein.

Results

In the wound healing assay, RGal at a concentration of 1000 µg/ml enhanced wound healing by 12.5% at 48 h compared to control group, under 10% serum conditions. Neither proliferation nor apoptosis were involved in the RGal effect on wound healing, suggesting the response was due solely to cell migration. Actinomycin D (5 mg/ml), Bay 11–7082 (10 mM) or JSH-23 (20 mM) treatment significantly reversed the effect of RGal on wound healing, showing that the response was transcriptionally dependent and involved NF-kB signaling. Treatment of cells with NS-398 (20 mM) also reversed the effect of RGal on wound healing. COX-2 protein expression was significantly increased at 6 and 12 h after RGal addition to Caco-2 monolayers.

Conclusions

These data suggest that the plant-based polysaccharide RGal increases intestinal epithelial cell wound healing by increasing cell migration. The RGal effect is dependent on the activation of the transcription factor NF-kB and downstream COX-2 protein expression and activity. Our findings show a novel mechanism of action of RGal in wound healing that could help in the resolution of intestinal inflammation and mucosal healing.

Funding Agencies

NSERC

Cellular pathways mediating tachykinin-evoked secretomotor responses in guinea pig ileum

This study characterized tachykinin-evoked secretomotor responses in in vitro submucosal and mucosal-submucosal preparations of the guinea pig ileum using combined intracellular and Ussing chamber recording techniques. Superfusion of endogenous tachykinins substance P (SP), neurokinin A (NKA), and neurokinin B depolarized single submucosal neurons and evoked increased short-circuit current (Isc) responses in Ussing chamber preparations. The NK1-receptor agonist [Sar9,Met(O2)11]SP [50% effective concentration (EC50) = 2 nM] depolarized all submucosal neurons examined. The NK3-receptor agonist senktide (EC50 = 20 nM) depolarized approximately 50% of neurons examined, whereas the NK2-receptor agonist [Ala5,beta-Ala8]NKA-(4-10) had no effect on membrane potential. [Sar9,Met(O2)11]SP and senktide evoked similar increases in Isc that were tetrodotoxin sensitive (91 and 100%, respectively) and were selectively blocked by the NK1 antagonist CP-99,994 and the NK3 antagonist SR-142,801, respectively. Capsaicin-evoked increases in Isc were significantly inhibited (54%, P < 0.05) by CP-99,994 but not by SR-142,801. Neither antagonist inhibited slow excitatory postsynaptic potentials. These findings suggest that tachykinin-evoked secretion in guinea pig ileum is mediated by NK1 and NK3 receptors on submucosal secretomotor neurons and that capsaicin-sensitive nerves release tachykinin(s) that activate the NK1 receptors.