Conversion of <i>Zonulae Occludentes</i> from Tight to Leaky Strand Type by Introducing Claudin-2 into Madin-Darby Canine Kidney I Cells

TLDR

MDCK I cells exhibit much higher transepithelial electric resistance than MDCK II cells despite having similar numbers of tight junction strands. The authors introduced dog claudin‑2 cDNA into MDCK I cells to replicate the claudin expression pattern of MDCK II cells. Introducing claudin‑2 into MDCK I cells reduced transepithelial resistance by over 20‑fold to MDCK II levels, without altering tight junction density or strand number, whereas claudin‑3 had no effect, indicating that claudin‑2 incorporation weakens claudin‑1/4‑based strands and that claudin composition governs barrier properties.

Abstract

There are two strains of MDCK cells, MDCK I and II. MDCK I cells show much higher transepithelial electric resistance (TER) than MDCK II cells, although they bear similar numbers of tight junction (TJ) strands. We examined the expression pattern of claudins, the major components of TJ strands, in these cells: claudin-1 and -4 were expressed both in MDCK I and II cells, whereas the expression of claudin-2 was restricted to MDCK II cells. The dog claudin-2 cDNA was then introduced into MDCK I cells to mimic the claudin expression pattern of MDCK II cells. Interestingly, the TER values of MDCK I clones stably expressing claudin-2 (dCL2-MDCK I) fell to the levels of MDCK II cells (&amp;gt;20-fold decrease). In contrast, when dog claudin-3 was introduced into MDCK I cells, no change was detected in their TER. Similar results were obtained in mouse epithelial cells, Eph4. Morphometric analyses identified no significant differences in the density of TJs or in the number of TJ strands between dCL2-MDCK I and control MDCK I cells. These findings indicated that the addition of claudin-2 markedly decreased the tightness of individual claudin-1/4–based TJ strands, leading to the speculation that the combination and mixing ratios of claudin species determine the barrier properties of individual TJ strands.