Bradykinin modulates mucin secretion but not synthesis from an intestinal goblet cell line

TRPM5-mediated calcium uptake regulates mucin secretion from human colon goblet cells

Mucin 5AC (MUC5AC) is secreted by goblet cells of the respiratory tract and, surprisingly, also expressed de novo in mucus secreting cancer lines. siRNA-mediated knockdown of 7343 human gene products in a human colonic cancer goblet cell line (HT29-18N2) revealed new proteins, including a Ca(2+)-activated channel TRPM5, for MUC5AC secretion. TRPM5 was required for PMA and ATP-induced secretion of MUC5AC from the post-Golgi secretory granules. Stable knockdown of TRPM5 reduced a TRPM5-like current and ATP-mediated Ca(2+) signal. ATP-induced MUC5AC secretion depended strongly on Ca(2+) influx, which was markedly reduced in TRPM5 knockdown cells. The difference in ATP-induced Ca(2+) entry between control and TRPM5 knockdown cells was abrogated in the absence of extracellular Ca(2+) and by inhibition of the Na(+)/Ca(2+) exchanger (NCX). Accordingly, MUC5AC secretion was reduced by inhibition of NCX. Thus TRPM5 activation by ATP couples TRPM5-mediated Na(+) entry to promote Ca(2+) uptake via an NCX to trigger MUC5AC secretion. DOI:http://dx.doi.org/10.7554/eLife.00658.001.

Intestinal tissue kallikrein-kinin system in inflammatory bowel disease

Tissue kallikrein cleaves kininogens to release kinins. Kinins mediate inflammation by activating constitutive bradykinin receptor-2 (BR2), which are rapidly desensitized, and induced by inflammatory cytokines bradykinin receptor-1 (BR1), resistant to desensitization. Intestinal tissue kallikrein (ITK) may hydrolyze growth factors and peptides, whereas kinins are responsible for capillary permeability, pain, synthesis of cytokines, and adhesion molecule-neutrophil cascade. Our and others results have demonstrated ITK in intestinal goblet cells and its release into interstitial space during inflammation. Kallistatin, an inhibitor of ITK, has been shown in epithelial and goblet cells, and was decreased in inflamed intestine as well as in plasma compared with noninflammatory controls. BR1 was upregulated in patients with inflammatory bowel disease (IBD), and it has expressed in an apical part of enterocytes in inflamed intestine, but in the basal part in normal intestine. ITK and BR1 were visualized in macrophages forming granuloma in Crohn's disease. In animal studies BR2 blockade decreased intestinal contraction, but had limited effect on inflammatory lesions. BR1 was found to be upregulated in animal inflamed intestine, in part dependent on tumor necrosis factor alpha (TNF-α). A selective BR1 receptor antagonist decreased morphological and biochemical features of experimental intestinal inflammation. Both BR1 and BR2 mediate epithelial ion transport that leads to secretory diarrhea. The upregulation of BR1 in inflamed intestine provides a structural basis for the kinins function, suggesting that a selective BR1 antagonist may have potential in therapeutic trial of IBD patients.

Sensory pathways and cyclooxygenase regulate mucus gel thickness in rat duodenum

We previously showed that the duodenal hyperemic response to acid occurs through activation of capsaicin-sensitive afferent nerves with subsequent release of vasodilatory substances such as calcitonin gene-related peptide (CGRP) and nitric oxide. We then tested the hypothesis that similar factors regulate duodenal mucus gel thickness. Gel thickness was optically measured using in vivo microscopy in anesthetized rats. Duodenal mucosae were superfused with pH 7.0 buffer with vanilloid receptor agonist capsaicin, bradykinin, or PGE(2) injection or were challenged with pH 2.2 solution, with or without the vanilloid antagonist capsazepine, human CGRP-(8-37), N(G)-nitro-L-arginine methyl ester, and indomethacin. Other rats underwent sensory ablation with high-dose capsaicin pretreatment. Acid, bradykinin, capsaicin, and PGE(2) all quickly thickened the gel. Antagonism of vanilloid and CGRP receptors, inhibition of nitric oxide synthase, and sensory deafferentation delayed gel thickening, suggesting that the capsaicin pathway mediated the initial burst of mucus secretion that thickened the gel. Indomethacin abolished gel thickening due to acid, bradykinin, and capsaicin. Inhibition of gel thickening by indomethacin in response to multiple agonists suggests that cyclooxygenase activity is essential for duodenal gel thickness regulation. Duodenal afferent neural pathways play an important role in the modulation of cyclooxygenase-mediated physiological control of gel thickness.

Dynamic regulation of mucus gel thickness in rat duodenum

We examined the dynamic regulation of mucus gel thickness (MGT) in vivo in rat duodenum in response to luminal acid, cyclooxygenase (COX) inhibition, and exogenous PGE(2). An in vivo microscopic technique was used to measure MGT with fluorescent microspheres in urethan-anesthetized rats. Duodenal mucosa was topically superfused with pH 7.0 or pH 2.2 solutions with or without PGE(2) and indomethacin treatments. Glycoprotein concentration of duodenal loop perfusates was measured with periodic acid/Schiff (PAS) or Alcian blue (AB) staining. MGT and perfusate glycoprotein concentration were stable during a 35-min perfusion with pH 7.0 solution. Acid exposure increased MGT and PAS- and AB-positive perfusate glycoprotein concentrations. Indomethacin pretreatment increased both PAS- and AB-positive perfusate glycoprotein at baseline; subsequent acid superfusion decreased perfusate glycoproteins and gel thickness. PGE(2) (1 mg/kg iv) simultaneously increased MGT and PAS-positive perfusate glycoprotein concentrations followed by a transient increase in AB-positive glycoprotein concentration, suggesting contributions from goblet cells and Brunner's glands. Parallel changes in MGT and perfusate glycoprotein concentration in response to luminal acid and PGE(2) suggest that rapid MGT variations reflect alterations in the balance between mucus secretion and exudation, which in turn are regulated by a COX-related pathway. Luminal acid and PGE(2) augment mucus secretion from goblet cells and Brunner's glands.