Loss of Claudin-15, but Not Claudin-2, Causes Na+ Deficiency and Glucose Malabsorption in Mouse Small Intestine

doi:10.1053/j.gastro.2010.08.006

Gastroenterology

Volume 140, Issue 3, March 2011, Pages 913-923

https://doi.org/10.1053/j.gastro.2010.08.006 Get rights and content

Background & Aims

In the small intestine, the paracellular transport of Na⁺ is thought to be critical for luminal Na⁺-homeostasis and the transcellular absorption of nutrients by Na⁺-driven transporters. Na⁺ is supplied to the intestinal lumen from the submucosa and serum through tight junctions, which form a paracellular barrier between the cells of epithelial sheets. However, the molecular basis for this paracellular transport of Na⁺ is not well understood. Here, we examined this mechanism by performing loss-of-function studies of claudin-2 and claudin-15, two tight-junctional membrane proteins that are specifically and age-dependently expressed in the villi and/or crypts of small intestinal epithelia.

Methods

Knockout mice for claudin-2 or claudin-15 were subjected to histologic, cell biologic, electrophysiologic, and physiologic analyses.

Results

Examination of the knockout mice revealed that both claudin-2 and claudin-15 play crucial roles in the transepithelial paracellular channel-like permselectivity for extracellular monovalent cations, particularly Na⁺, in infants and adults. Especially in Cldn15^−/− adults, the luminal Na⁺ concentration in the small intestine measured directly in vivo was abnormally low, and glucose absorption was impaired, as assessed by the oral glucose tolerance test and estimation of unabsorbed glucose.

Conclusions

We propose that the “Na⁺-leaky” claudin-15 is indispensable in vivo for the paracellular Na⁺ permeability, luminal Na⁺-homeostasis, and efficient glucose absorption in the small intestine, but claudin-2 is indispensable for only the first of these functions. Claudin-15 knockout leads to Na⁺ deficiency and glucose malabsorption in the mouse adult small intestine.

Section snippets

Animals

Claudin-2- and claudin-15-deficient mice were generated in Shoichiro Tsukita's laboratory33, 34 and given by Shoichiro Tsukita to Sachiko Tsukita and Tetsuo Noda. All animal experiments were performed in accordance with protocols approved by the Osaka University School of Medicine Animal Studies Committee.

Antibodies

The following antibodies were used: rabbit polyclonal anti-claudin-2, anti-claudin-15, and anti-ZO-1; rat monoclonal anti-occludin,33, 38 anti-claudin-3 (Zymed Laboratories, San Francisco,

Characterization of Cldn2^−/− and Cldn15^−/− Small Intestines in Comparison With Wild Type

We compared the intestinal physiology of knockout mice for claudin-2 and claudin-15 because the luminal Na⁺-homeostasis is thought to be critical for small intestinal functions such as glucose absorption. First, we used immunofluorescence to examine the specific localization of claudin-2 and claudin-15 in the small intestines of wild-type mice. Consistent with previous studies,³⁶ the specific staining for claudin-2 and claudin-15 was confirmed by their disappearance in intestinal villi and

Discussion

Our current results show that claudin-2 and claudin-15 function as paracellular monovalent cation-selective pores at zTJs and thereby mediate the long known but molecularly undefined high paracellular permeability to Na⁺ and K⁺ in the small intestinal epithelium. This permeability permits Na⁺, the main submucosal extracellular ion, access to the lumen to support the Na⁺-dependent absorption of nutrients. The permeability to K⁺ is higher than to Na⁺, most likely to maintain the ionic balance

Acknowledgments

The authors thank the members of their laboratories and Drs Grace Gray and Leslie Miglietta for proofreading the manuscript.

This paper is dedicated to the late Dr Shoichiro Tsukita, who asked Tetsuo Noda and Sachiko Tsukita to keep and use the frozen embryos of the knockout mice to continue and develop the work he had intended.

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: Conflicts of interest The authors disclose no conflicts.

: Funding Supported by a Grant-in-Aid for Creative the Scientific Research from the Ministry of Education, Science and Culture of Japan (to S.T.).

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Basic—Alimentary TractLoss of Claudin-15, but Not Claudin-2, Causes Na+ Deficiency and Glucose Malabsorption in Mouse Small Intestine

Background & Aims

Methods

Results

Conclusions

Section snippets

Animals

Antibodies

Characterization of Cldn2−/− and Cldn15−/− Small Intestines in Comparison With Wild Type

Discussion

Acknowledgments

Prog Histochem Cytochem

Biochim Biophys Acta

J Biol Chem

Cell

Cell

Gene Expr Patterns

Lab Invest

Coupled transport of sodium and organic solutes

Physiol Rev

Intestinal barrier: an interface between health and disease

J Gastroenterol Hepatol

Coupling between apical and paracellular transport processes

Biochem Cell Biol

A family of mammalian Na+-dependent L-ascorbic acid transporters

Nature

Sodium chloride absorption by the small intestine and the relationships between salt transport and the absorption of water and some organic molecules

Proc Nutr Soc

Fracture faces of zonulae occludentes from “tight” and “leaky” epithelia

J Cell Biol

Barrier function of epithelia

Am J Physiol

Diffusion potentials across the small intestine

Nature

Ionic conductances of extracellular shunt pathway in rabbit ileumInfluence of shunt on transmural sodium transport and electrical potential differences

J Gen Physiol

Electrical properties and active solute transport in rat small intestineII. Conductive properties of transepithelial routes

J Membr Biol

Regulation of the movement of solutes across tight junctions

Annu Rev Physiol

Multifunctional strands in tight junctions

Nat Rev Mol Cell Biol

Claudins and epithelial paracellular transport

Annu Rev Physiol

Tight junction-based epithelial microenvironment and cell proliferation

Oncogene

Basic—Alimentary Tract
Loss of Claudin-15, but Not Claudin-2, Causes Na⁺ Deficiency and Glucose Malabsorption in Mouse Small Intestine

Characterization of Cldn2^−/− and Cldn15^−/− Small Intestines in Comparison With Wild Type