Tumor Necrosis Factor- Increases Claudin-1, 4, and 7 Expression in Tubular Cells: Role in Permeability Changes

Tumor necrosis factor- (TNF), is a pathogenic cytokine in kidney disease that alters expression of claudins in tubular cells. Previously we showed that in LLC-PK1 cells TNF caused a biphasic change in transepithelial resistance (TER) consisting of an early drop and recovery, followed by a late increase. However, the underlying mechanisms and the role of specific claudins in the TER effect remained incompletely understood. Here we sought to define how TNF affects claudins 1, 4, and 7 in tubular cells and to correlate their changes with the TER effect. We show that TNF elevates total and surface levels of Cldn-1, 4, and 7, and increases their mRNA expression through the ERK and JNK pathways. Further, JNK is also important for TNF-induced changes in claudin-2 expression. Continuous monitoring of TER using Electric cell-substrate impedance sensing (ECIS) reveals that the two phases of the TNF effect are differently regulated. Specifically, inhibition of the ERK or JNK pathways prevent the late TER increase, but not the early TER effect. Silencing experiments also show that Cldn-1 is necessary for the early TNF-induced TER change, while all three claudins appear to contribute to the late TER increase. In summary, we define a central role for ERK and JNK in TNF-induced altered claudin expression and barrier tightening. Together, our current and previous works show that the TNF-induced early TER effect requires claudin-1, while claudin-2 decrease is a significant mediator of the late TER increase, and elevation in claudin-1, 4, and 7 contribute to a smaller extent. J. Cell. Physiol. 232: 2210-2220, 2017. (c) 2016 Wiley Periodicals, Inc.