Inflammatory bowel diseases are associated with dysregulated electrolyte and water transport and resultant diarrhea. Aquaporins are transmembrane proteins that function as water channels in ...intestinal epithelial cells. We investigated the effect of the inflammatory cytokine, interferon-gamma, which is a major player in inflammatory bowel diseases, on aquaporin-1 expression in a mouse colonic epithelial cell line, CMT93. CMT93 monolayers were exposed to 10 ng/mL interferon-gamma and aquaporin-1 mRNA and protein expressions were measured by real-time PCR and western blot, respectively. In other experiments, CMT93 cells were pretreated with inhibitors or were transfected with siRNA to block the effects of Janus kinases, STATs 1 and 3, or interferon regulatory factor 2, prior to treatment with interferon-gamma. Interferon-gamma decreased aquaporin-1 expression in mouse intestinal epithelial cells in a manner that did not depend on the classical STAT1/JAK2/IRF-1 pathway, but rather, on an alternate Janus kinase (likely JAK1) as well as on STAT3. The pro-inflammatory cytokine, interferon-gammaï¬ may contribute to diarrhea associated with intestinal inflammation in part through regulation of the epithelial aquaporin-1 water channel via a non-classical JAK/STAT receptor signalling pathway.
Abstract only
5‐HT
4
receptors are expressed in colonic epithelium, and activation with 5‐HT
4
receptor agonists causes mucus secretion from goblet cells, chloride secretion from enterocytes, and ...5‐HT release from enterochromaffin cells. We tested whether this receptor could serve a protective role in models of colitis and under basal conditions. CD‐1 mice were given DSS (4% w/v for 5 days in drinking water) or TNBS (7.5 mg/mL) on day 0. 5‐HT
4
receptor agonist (Tegaserod, 1mg/kg), vehicle, or antagonist (GR 113808) plus agonist was delivered by enema daily day 1–7 (prevention) or day 6–15 (recovery) to determine the effects of epithelial 5‐HT
4
receptor activation in colitis. To test the actions of 5‐HT
4
receptors under basal conditions, GR 113808 was administered to normal mice by enema for 10 days. Colitis was evaluated using disease activity index (DAI) and histological damage scores (HDS). Possible protective actions such as cell proliferation in colonic tissue and migration and resistance to oxidative stress in CaCo‐2 cell culture were also explored. To investigate function, we evaluated propulsive motility in the guinea pig distal colon. Intraluminal tegaserod treatment in both DSS and TNBS‐inflamed animals significantly attenuated the development of, and accelerated the recovery from, colitis in an antagonist‐sensitive manner. However, administration of Tegaserod (1 mg/kg) by intraperitoneal injection had no effect. TNBS‐induced dysmotility in guinea pigs was reversed by 5‐HT
4
receptor agonist treatment, and this action was blocked by the atagonist. Increased cell proliferation was detected in the form of increased Ki‐67 immunoreactivity in crypts of inflamed animals treated with Tegaserod. We also observed areas of accelerated healing of scratches and increased resistance to H
2
O
2
induced oxidative stress in CaCo‐2 cells. Interestingly, antagonist treatment alone in normal mice resulted in significant increases in DAI, HDS, and bacterial translocation in mice, as well as disrupted motility patterns in guinea pig colon. In summary, activation of 5‐HT
4
receptors on the colonic epithelium reduces the development of, and accelerates recovery from, colitis. It is likely acting through increased wound healing by increased cell migration and cell proliferation, as well as resistance to apoptosis. Additionally, 5‐HT
4
receptor activation protects colonic motility. Taken together, these data suggest that epithelial 5‐HT
4
receptors have a protective effect in the normal and inflamed colon.
Support or Funding Information
Funded by DK62267
Inflammatory diseases of the gut are associated with altered electrolyte and water transport, leading to the development of diarrhea. Epithelially expressed aquaporins (AQPs) are downregulated in ...inflammation, although the mechanisms involved are not known. We hypothesized that AQP3 expression in intestinal epithelial cells is altered in intestinal inflammation and that these changes are driven by tumor necrosis factor (TNF) α. Human colonic adenocarcinoma (HT‐29) cells were treated with TNFα to investigate signaling mechanisms in vitro. AQP3 expression was assessed by real‐time PCR and radiolabeled glycerol uptake, with select inhibitors and a luciferase reporter construct used to further elucidate intracellular signaling. AQP3 expression was downregulated in HT‐29 cells treated with TNFα. Luciferase reporter construct experiments revealed that TNFα downregulated constitutive transcriptional activity of the AQP3 promoter, and inhibition of MEK/ERK and nuclear factor κB (NF‐κB) signaling prevented the decrease in AQP3 mRNA expression. Constitutive AQP3 expression was suppressed by specificity protein (Sp) 3, and knockdown of this transcription factor bound to the AQP3 promoter was able to partially prevent the TNFα‐induced downregulation of AQP3. TNFα signals through MEK/ERK and NF‐κB to enhance the negative transcriptional control of AQP3 expression exerted by Sp3. Similar mechanisms regulate numerous ion channels, suggesting a common mechanism by which both ion and water transport are altered in inflammation.
Aquaporins (AQPs) are water channels critical for a variety of functions in epithelia, including water and small solute transport, proliferation, and apoptosis. AQP3 is downregulated in colonic inflammation, with important physiological consequences, but the mechanism underlying this decreased expression remains unknown. We have discovered the signaling mechanisms whereby tumor necrosis factor suppresses AQP3 expression in intestinal epithelium. TNF activation of MAP kinases and NFB to mediate suppression of gene expression via the Sp3 transcription factor.
Background & Aims: Cyclooxygenase-2 (COX-2) has been implicated as contributing to mucosal defense. Acetylation of COX-2 by aspirin can result in production of an antiinflammatory substance, ...15(R)-epi-LXA4. We determined whether aspirin-triggered lipoxin (LX) production via COX-2 diminishes aspirin-induced damage in the rat stomach. Methods: Rats were treated with aspirin plus or minus celecoxib or rofecoxib. Gastric generation of LXA4 was measured. Effect of exogenous LXA4 or an LXA4 receptor antagonist on gastric resistance to aspirin-induced damage was examined. Aspirin-induced leukocyte adherence in mesenteric venules, and the effects of LXA4, were examined by intravital microscopy. Results: Celecoxib and rofecoxib significantly increased the severity of aspirin-induced gastric damage. Aspirin rapidly up-regulated COX-2 expression in the stomach and caused a significant increase in gastric 15(R)-epi-LXA4 production, which was abolished by celecoxib. LXA4 dose dependently (0.25–2.5 μg/kg, intraperitoneally) reduced the severity of aspirin-induced gastric damage and suppressed aspirin-induced leukocyte adherence, whereas an LXA4 antagonist had the opposite effects. Conclusions: Aspirin administration results in elevated production of 15(R)-epi-LXA4 via COX-2. LXA4 exerts very potent protective actions on the gastric mucosa. Co-administration of aspirin and a selective COX-2 inhibitor results in substantially more severe gastric injury than is produced with either agent alone.
GASTROENTEROLOGY 2002;123:1598-1606
Aceylation of cyclooxygenase (COX)-2 by aspirin can trigger the formation of 15(R)-epilipoxin A4, or aspirin-triggered lipoxin (ATL). ATL exerts protective effects in the stomach. Selective COX-2 ...inhibitors block ATL synthesis and exacerbate aspirin-induced gastric damage. Nitric oxide-releasing aspirins, including NCX-4016, have antiplatelet effects similar to aspirin but do not cause gastric damage. In the present study, we examined whether or not NCX-4016 triggers ATL synthesis and/or upregulates gastric COX-2 expression and the effects of coadministration of NCX-4016 with a selective COX-2 inhibitor on gastric mucosal injury and inflammation. Rats were given aspirin or NCX-4016 orally and either vehicle or a selective COX-2 inhibitor (celecoxib) intraperitoneally. Gastric damage was blindly scored, and granulocyte infiltration into gastric tissue was monitored through measurement of myeloperoxidase activity. Gastric PG and ATL synthesis was measured as was COX-2 expression. Whereas celecoxib inhibited gastric ATL synthesis and increased the severity of aspirin-induced gastric damage and inflammation, coadministration of celecoxib and NCX-4016 did not result in damage or inflammation. NCX-4016 did not upregulate gastric COX-2 expression nor did it trigger ATL synthesis (in contrast to aspirin). Daily administration of aspirin for 5 days resulted in significantly less gastric damage than that seen with a single dose, as well as augmented ATL synthesis. Celecoxib reversed this effect. In contrast, repeated administration of NCX-4016 failed to cause gastric damage, whether given alone or with celecoxib. These studies support the notion that NCX-4016 may be an attractive alternative to aspirin for indications such as cardioprotection, including in individuals also taking selective COX-2 inhibitors.
Nonsteroidal anti‐inflammatory drugs have been reported to exacerbate hypertension and to interfere with the effectiveness of some anti‐hypertensive therapies. In this study, we tested the effects of ...a gastric‐sparing, nitric oxide‐releasing derivative of aspirin (NCX‐4016) on hypertension in rats.
Hypertension was induced by administering L‐NAME in the drinking water (400 mg l−1). Groups of rats were treated daily with aspirin, NCX‐4016 or vehicle.
NCX‐4016 significantly reduced blood pressure relative to the aspirin‐treated group over the 2‐week period of treatment. Aspirin and, to a lesser extent, NCX‐4016 suppressed whole blood thromboxane synthesis.
In anaesthetized rats, acute intravenous administration of NCX‐4016 caused a significant fall in mean arterial pressure in hypertensive rats, but was devoid of such effects in normotensive controls.
In vitro, NCX‐4016 relaxed phenylephrine‐pre‐contracted aortic rings obtained from both normotensive and hypertensive rats, and significantly reduced their responsiveness to the contractile effects of phenylephrine.
These results suggest that NCX‐4016 reduces blood pressure in hypertensive rats, not simply through the direct vasodilatory actions of the nitric oxide released by this compound, but also through possible interference with the effects of endogenous pressor agents. These properties, added to its anti‐thrombotic effects, suggest that NCX‐4016 may be a safer alternative to aspirin for use by hypertensive patients.
British Journal of Pharmacology (2001) 133, 1314–1322; doi:10.1038/sj.bjp.0704209
Inflammatory bowel diseases are associated with dysregulated electrolyte and water transport and resultant diarrhea. Aquaporins are transmembrane proteins that function as water channels in ...intestinal epithelial cells. We investigated the effect of the inflammatory cytokine, interferon- gamma , which is a major player in inflammatory bowel diseases, on aquaporin-1 expression in a mouse colonic epithelial cell line, CMT93. CMT93 monolayers were exposed to 10 ng/mL interferon- gamma and aquaporin-1 mRNA and protein expressions were measured by real-time PCR and western blot, respectively. In other experiments, CMT93 cells were pretreated with inhibitors or were transfected with siRNA to block the effects of Janus kinases, STATs 1 and 3, or interferon regulatory factor 2, prior to treatment with interferon- gamma . Interferon- gamma decreased aquaporin-1 expression in mouse intestinal epithelial cells in a manner that did not depend on the classical STAT1/JAK2/IRF-1 pathway, but rather, on an alternate Janus kinase (likely JAK1) as well as on STAT3. The pro-inflammatory cytokine, interferon- gamma may contribute to diarrhea associated with intestinal inflammation in part through regulation of the epithelial aquaporin-1 water channel via a non-classical JAK/STAT receptor signalling pathway.
![Interferon-[gamma] Suppress...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1932-6203/small "Interferon-[gamma] Suppresses Intestinal Epithelial Aquaporin-1 Expression via Janus Kinase and STAT3 Activation")
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