IFN-γ downregulates expression of Na⁺/H⁺ exchangers NHE2 and NHE3 in rat intestine and human Caco-2/bbe cells

Abstract

Diarrhea associated with inflammatory bowel diseases has traditionally been attributed to stimulated secretion. The purpose of this study was to determine whether chronic stimulation of intestinal mucosa by interferon-gamma (IFN-gamma) affects expression and function of the apical membrane Na(+)/H(+) exchangers NHE2 and NHE3 in rat intestine and Caco-2/bbe (C2) cells. Confluent C2 cells expressing NHE2 and NHE3 were treated with IFN-gamma for 2, 24, and 48 h. Adult rats were injected with IFN-gamma intraperitoneally for 12 and 48 h. NHE2 and NHE3 activities were measured by unidirectional (22)Na influx across C2 cells and in rat brush-border membrane vesicles. NHE protein and mRNA were assessed by Western and Northern blotting. IFN-gamma treatment of C2 monolayers caused a >50% reduction in NHE2 and NHE3 activities and protein expression. In rats, region-specific, time- and dose-dependent reductions of NHE2 and NHE3 activities, protein expression, and mRNA were observed after exposure to IFN-gamma. Chronic exposure of intestinal epithelial cells to IFN-gamma results in selective downregulation of NHE2 and NHE3 expression and activity, a potential cause of inflammation-associated diarrhea.

Coordinated epithelial NHE3 inhibition and barrier dysfunction are required for TNF-mediated diarrhea in vivo

“…Previous studies have shown that NHE3 can be downregulated by chronic IFN-g treatment (25). However, the lack of an effect of IFN-g alone on either water absorption or barrier function suggests that it does not play a role in the acute T cell-dependent diarrhea modeled here.…”

Traditional and emerging roles for the SLC9 Na+/H+ exchangers

“…Interferon-γ and TNF-α decrease NHE3 activity causing diarrhea [51,145,2]. Consistent with a role in inflammatory bowel disease, NHE3 expression and/or activity is decreased in mouse models and human disease [159,187] .…”

Role of epithelial ion transports in inflammatory bowel disease

“…Once again proinflammatory cytokines are partially to blame. IFN-␥ and TNF-␣ (but not IL-1␤) decrease NHE3 activity and mRNA expression (7,112,125). This reduction may result from cAMP-dependent PKAmediated phosphorylation of Sp1 and Sp3 (transcription factors), which decreases their affinity for the gene promoter region (7).…”