RESUMEN
Colitis in interleukin-2-deficient (IL-2(-/-)) mice resembles ulcerative colitis in humans. We studied epithelial transport and barrier function in IL-2(-/-) mice and used this model to characterize mechanisms of diarrhea during intestinal inflammation. (22)Na(+) and (36)Cl(-) fluxes were measured in proximal colon. Net Na(+) flux was reduced from 4.0 +/- 0.5 to 0.8 +/- 0.5 micromol.h(-1).cm(-2), which was paralleled by diminished mRNA and protein expression of the Na(+)/H(+) exchanger NHE3. Net Cl(-) flux was also decreased from 2.2 +/- 1.6 to -2.7 +/- 0.6 micromol.h(-1).cm(-2), indicating impaired Na(+)-Cl(-) absorption. In distal colon, aldosterone-induced electrogenic Na(+) absorption was 6.1 +/- 0.9 micromol.h(-1).cm(-2) in controls and was abolished in IL-2(-/-) mice. Concomitantly, mRNA expression of beta- and gamma-subunits of the epithelial sodium channel (ENaC) was reduced. Epithelial barrier was studied in proximal colon by impedance technique and mannitol fluxes. In contrast to ulcerative colitis, epithelial resistance was increased and mannitol fluxes were decreased in IL-2(-/-) mice. This was in accord with the findings of reduced ion transport as well as increased expression of tight junction proteins occludin and claudin-1, -2, -3, and -5. In conclusion, the IL-2(-/-) mucosa exhibits impaired electroneutral Na(+)-Cl(-) absorption and electrogenic Na(+) transport due to reduced mRNA and protein expression of NHE3 and ENaC beta- and gamma-subunit mRNA. This represents a model of early intestinal inflammation with absorptive dysfunction due to impaired transport protein expression/function while epithelial barrier is still intact. Therefore, this model is ideal to study regulation of transporter expression independent of barrier defects.
Asunto(s)
Colitis/complicaciones , Colitis/etiología , Diarrea/etiología , Interleucina-2/deficiencia , Animales , Northern Blotting , Western Blotting , Cloruros/metabolismo , Colitis/patología , Colitis/fisiopatología , Colon/metabolismo , Colon/patología , Colon/fisiopatología , Impedancia Eléctrica , Electrofisiología , Canales Epiteliales de Sodio , Interleucina-2/genética , Absorción Intestinal , Manitol/farmacocinética , Proteínas de la Membrana/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados/genética , Ocludina , Isoformas de Proteínas/metabolismo , ARN Mensajero/metabolismo , Sodio/metabolismo , Canales de Sodio/metabolismo , Intercambiador 3 de Sodio-Hidrógeno , Intercambiadores de Sodio-Hidrógeno/metabolismo , Uniones Estrechas/metabolismoAsunto(s)
Rechazo de Injerto/tratamiento farmacológico , Hepatitis C/cirugía , Inmunosupresores/uso terapéutico , Trasplante de Hígado/inmunología , Ácido Micofenólico/uso terapéutico , Alanina Transaminasa/sangre , Aspartato Aminotransferasas/sangre , Ciclosporina/efectos adversos , Quimioterapia Combinada , Hepatitis C/prevención & control , Humanos , Inmunosupresores/efectos adversos , Trasplante de Hígado/patología , Ácido Micofenólico/análogos & derivados , Recurrencia , Estudios Retrospectivos , Tacrolimus/efectos adversos , Carga ViralRESUMEN
On the basis of recently observed high levels of iNOS expression that correlated with intestinal inflammation in interleukin-2-deficient [IL-2(-/-)] mice, it was postulated that nitric oxide may damage colonic epithelial cells or impair intestinal epithelial barrier function. This damage may result in an increased permeability of the colonic epithelium leading to high antigenic exposure of the intestinal immune system, which may perpetuate chronic inflammation. Our data demonstrate that high expression of iNOS in IL-2(-/-) mice is correlated with the length/weight ratio (L/W ratio), a widely accepted marker for intestinal inflammation. However, no reduction of epithelial resistance was observed, as would be expected in case of a damaged, leaky epithelium. Our results suggest that enhanced formation of NO in IL-2(-/-) mice does not cause impairment of epithelial barrier function.
Asunto(s)
Colon/enzimología , Colon/inmunología , Interleucina-2/genética , Mucosa Intestinal/enzimología , Mucosa Intestinal/inmunología , Óxido Nítrico Sintasa/genética , Animales , Colitis/inmunología , Colitis/metabolismo , Conductividad Eléctrica , Impedancia Eléctrica , Electrofisiología , Regulación Enzimológica de la Expresión Génica , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Óxido Nítrico Sintasa/metabolismo , Óxido Nítrico Sintasa de Tipo IIRESUMEN
Severely inflamed colonic sections of IL-2 (-/-) mice showed up to 19-fold increased iNOS mRNA levels. The level of iNOS protein expression corresponded to the increased iNOS mRNA levels as detected by means of Western blot analysis. There was a clear, positive relationship between the level of iNOS expression and the degree of inflammation in the colonic tissue of IL-2 (-/-) and wild-type mice. Our data suggest that iNOS may play a key role in the pathogenesis of ulcerative colitis-like disease in IL-2 (-/-) mice. Further investigation should elucidate the impact of NO on the regulation of the inflammatory process in this model and might contribute to a better understanding of the role iNOS expression in human immune-mediated diseases.