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

Abstract

Acute T cell-mediated diarrhea is associated with increased mucosal expression of proinflammatory cytokines, including the TNF superfamily members TNF and LIGHT. While we have previously shown that epithelial barrier dysfunction induced by myosin light chain kinase (MLCK) is required for the development of diarrhea, MLCK inhibition does not completely restore water absorption. In contrast, although TNF-neutralizing antibodies completely restore water absorption after systemic T cell activation, barrier function is only partially corrected. This suggests that, while barrier dysfunction is critical, other processes must be involved in T cell-mediated diarrhea. To define these processes in vivo, we asked whether individual cytokines might regulate different events in T cell-mediated diarrhea. Both TNF and LIGHT caused MLCK-dependent barrier dysfunction. However, while TNF caused diarrhea, LIGHT enhanced intestinal water absorption. Moreover, TNF, but not LIGHT, inhibited Na + absorption due to TNF-induced internalization of the brush border Na + /H + exchanger NHE3. LIGHT did not cause NHE3 internalization. PKCa activation by TNF was responsible for NHE3 internalization, and pharmacological or genetic PKCa inhibition prevented NHE3 internalization, Na + malabsorption, and diarrhea despite continued barrier dysfunction. These data demonstrate the necessity of coordinated Na + malabsorption and barrier dysfunction in TNF-induced diarrhea and provide insight into mechanisms of intestinal water transport.

LIGHT Signals Directly to Intestinal Epithelia to Cause Barrier Dysfunction via Cytoskeletal and Endocytic Mechanisms

“…While a primary barrier defect may be present in IBD kindreds 12-14 , it is also clear that epithelial barrier defects can be induced by inflammatory cytokines [15][16][17][18][19][20][21][22][23][24] . Recent work has demonstrated that barrier dysfunction induced by inflammatory processes can be due to epithelial damage as well as non-apoptotic regulation of tight junction permeability 19,22,[25][26][27][28] .…”

Altered cGMP Dynamics at the Plasma Membrane Contribute to Diarrhea in Ulcerative Colitis

“…49,50 Many studies suggest that decreased gene expression/epithelial surface expression/activity of NHE3 and other sodium transporters relates to the incidence of absorptive diarrhea in IBD and animal colitis models. 39,51,52 However, other studies discount this to be the case. 51,53 CFTR remains critical to regulate electroneutral sodium chloride absorption and NHE3 regulation by augmenting its inhibition in a cAMP-dependent fashion.…”

Protein kinases are potential targets to treat inflammatory bowel disease

“…Constitutive MLCK activation in the intestinal epithelium increases intestinal paracellular permeability and aggravates the severity of colitis in mouse models. However, blockage of MLCK activation can increase significantly the intestinal barrier function and ameliorate DSS-induced colitis [100] . PKC: PKC has a variety of isoforms that are involved in the pathogenesis of IBD by their effect on the mucus layer [101] , microbiota [34][35][36][37] , cell junction [64,65] and immune system.…”