Long‐term effects of tumor necrosis factor on LLC‐PK₁ transepithelial resistance

Abstract

Renal epithelial LLC-PK1 cell sheets incubated with tumor necrosis factor (TNF) undergo an acute, spontaneous, and rapidly reversible decrease in transepithelial resistance (TER). (Mullin et al., 1992). However, 24 to 72 h following TNF exposure, TER across the cell sheet increases 2-fold. This later effect of TNF is also reversible, albeit slowly. The TER of TNF-treated cell sheets then declines toward initial levels between 72 and 144 h following exposure to the cytokine. Whereas the long-term increase in TER following TNF exposure is not associated with a decreased transepithelial 14C-mannitol flux (size selectivity), the charge (anionic) selectivity of the LLC-PK1 tight junction is decreased. Basal-lateral (ouabain and bumetanide-insensitive) Rb+ and apical Na+-dependent alpha-methylglucoside (AMG) uptake into the cell are both reduced in cultures exposed to TNF 24 h earlier. Correspondingly, this long-term effect on TER is accompanied by a 30% decrease in short circuit current (iscc). Along with an observed increase in basal-lateral methylamino-isobutyric acid (MeAIB) influx into the cells, an increased incorporation of [3H]-thymidine into DNA indicates increased cell cycling after exposure to TNF. While the increase in cell cycling is not sustained for the duration of the elevation in TER, it does appear to initiate a sequence of events that lead to the sustained increase in TER. A decrease in the lateral intercellular space, observed between these epithelial cells after long-term TNF exposure, may be a mechanism for the elevated TER following from the mitogenesis and/or transport changes. This overall long-term tightening of an epithelium in response to TNF may function, in part, as a compensatory action of the epithelium to reestablish its effectiveness as a physiological barrier, following the acute effect of TNF.

Probiotic Bacteria Regulate Intestinal Epithelial Permeability in Experimental Ileitis by a TNF-Dependent Mechanism

“…In addition, treatment with infliximab (anti-TNF) has been reported to restore barrier function in CD, and some UC, patients [51]–[53]. However, conflicting studies exist regarding the interpretation of the effects of TNF that may reflect differences in the specific epithelial cell line used or variations in the dose and length of the treatment with TNF [54]. For example, in the intestinal epithelial cell line, Caco-2, TNF stimulation results in a delayed effect on permeability by increasing small molecule flux within 24 hrs, but reduction in TEER is not observed until 48 hrs post treatment [55].…”

Role for TGF-β in Cyclosporine-Induced Modulation of Renal Epithelial Barrier Function

“…There have been several conflicting theories regarding the relationship between tight junction function and cell proliferation. Some investigators reported that a rise in cell number could generate an increase in TER (25)(26)(27)(28). However, contrasting reports suggested that overgrowth of cells could result in enhanced transepithelial permeability.…”

Gliovascular and cytokine interactions modulate brain endothelial barrier in vitro

“…TNF-α increases permeability of bovine pulmonary artery endothelial (BPAEC) monolayers, human colonic adenocarcinoma (Caco-2), HT29/B6 and cholangiocytes, but decreased solute permeability of uterine epithelial cells (UECs) [47]. Further, TNF-α can either increase or decrease solute exchange depending on the type of insult in porcine renal epithelial cells (LLC-PK1) [48,49]. These effects are mediated by diverse mechanisms involving actin reorganization, monolayer motility, NF-kβ activation, apoptosis and reorganization of junctional proteins [49-54].…”