Claudin-10a Deficiency Shifts Proximal Tubular Cl Permeability to Cation Selectivity Claudin-2 Redistribution.

Background: The tight junction proteins claudin-2 and claudin-10a form paracellular cation and anion channels, respectively, and are expressed in the proximal tubule. However, the physiologic role of claudin-10a in the kidney has been unclear.

Methods: To investigate the physiologic role of claudin-10a, we generated claudin-10a-deficient mice, confirmed successful knockout by Southern blot, Western blot, and immunofluorescence staining, and analyzed urine and serum of knockout and wild-type animals.

A Novel Claudinopathy Based on Claudin-10 Mutations.

Claudins are key components of the tight junction, sealing the paracellular cleft or composing size-, charge- and water-selective paracellular channels. Claudin-10 occurs in two major isoforms, claudin-10a and claudin-10b, which constitute paracellular anion or cation channels, respectively. For several years after the discovery of claudin-10, its functional relevance in men has remained elusive.

Transcription factor HNF1β regulates expression of the calcium-sensing receptor in the thick ascending limb of the kidney.

Mutations in hepatocyte nuclear factor 1β (HNF1β) cause autosomal dominant tubulointerstitial kidney disease (ADTKD-HNF1β), and patients tend to develop renal cysts, maturity-onset diabetes of the young (MODY), and suffer from electrolyte disturbances, including hypomagnesemia, hypokalemia, and hypocalciuria. Previous HNF1β research focused on the renal distal convoluted tubule (DCT) to elucidate the ADTKD-HNF1β electrolyte phenotype, although 70% of Mg is reabsorbed in the thick ascending limb of Henle's loop (TAL). An important regulator of Mg reabsorption in the TAL is the calcium-sensing receptor (CaSR).

Diuretic state affects ascending thin limb tight junctions.

The nephron segments in the inner medulla are part of the urine concentrating mechanism. Depending on the diuretic state, they are facing a large range of extracellular osmolality. We investigated whether water homeostasis affects tubular transport and permeability properties in inner medullary descending thin limb (IMdTL) and ascending thin limb (IMaTL).

Altered paracellular cation permeability due to a rare CLDN10B variant causes anhidrosis and kidney damage.

Claudins constitute the major component of tight junctions and regulate paracellular permeability of epithelia. Claudin-10 occurs in two major isoforms that form paracellular channels with ion selectivity. We report on two families segregating an autosomal recessive disorder characterized by generalized anhidrosis, severe heat intolerance and mild kidney failure.

A Novel Hypokalemic-Alkalotic Salt-Losing Tubulopathy in Patients with Mutations.

Mice lacking distal tubular expression of , the gene encoding the tight junction protein Claudin-10, show enhanced paracellular magnesium and calcium permeability and reduced sodium permeability in the thick ascending limb (TAL), leading to a urine concentrating defect. However, the function of renal Claudin-10 in humans remains undetermined. We identified and characterized mutations in two patients with a hypokalemic-alkalotic salt-losing nephropathy.

Tight junction strand formation by claudin-10 isoforms and claudin-10a/-10b chimeras.

Claudins are integral components of tight junctions (TJs) in epithelia and endothelia. When expressed in cell lines devoid of TJs, claudins are able to form TJ-like strands at contacts between adjacent cells. According to a current model of TJ strand formation, claudin protomers assemble in an antiparallel double row within the plasma membrane of each cell (cis-interaction) while binding to corresponding double rows from the neighboring cells (trans-interaction).

Heterogeneity of tight junctions in the thick ascending limb.

Renal tubular transport mechanisms are optimized to be energy efficient and tailored to local gradients and transport rates. The combined transcellular action of ion channels, transporters, and pumps, together with the paracellular pathway, enables kidney function. Monogenetic diseases and mouse models indicate that both trans- and paracellular proteins can become disease-causing candidates and may be targets for future therapeutic approaches.

ILDR1 is important for paracellular water transport and urine concentration mechanism.

Whether the tight junction is permeable to water remains highly controversial. Here, we provide evidence that the tricellular tight junction is important for paracellular water permeation and that Ig-like domain containing receptor 1 (ILDR1) regulates its permeability. In the mouse kidney, ILDR1 is localized to tricellular tight junctions of the distal tubules.

One gene, two paracellular ion channels-claudin-10 in the kidney.

Claudins are tight junction membrane proteins and regulate the paracellular passage of ions and water. They can seal the paracellular cleft against solute passage but also form paracellular channels. They are tetraspan proteins with two extracellular segments.

Corticomedullary difference in the effects of dietary Ca²⁺ on tight junction properties in thick ascending limbs of Henle's loop.

The thick ascending limb of Henle's loop (TAL) drives an important part of the reabsorption of divalent cations. This reabsorption occurs via the paracellular pathway formed by the tight junction (TJ), which in the TAL shows cation selectivity. Claudins, a family of TJ proteins, determine the permeability and selectivity of this pathway.

Probing the cis-arrangement of prototype tight junction proteins claudin-1 and claudin-3.

Claudins form a large family of TJ (tight junction) proteins featuring four transmembrane segments (TM1-TM4), two extracellular loops, one intracellular loop and intracellular N- and C-termini. They form continuous and branched TJ strands by homo- or heterophilic interaction within the same membrane (cis-interaction) and with claudins of the opposing lateral cell membrane (trans-interaction). In order to clarify the molecular organization of TJ strand formation, we investigated the cis-interaction of two abundant prototypic claudins.

In tight junctions, claudins regulate the interactions between occludin, tricellulin and marvelD3, which, inversely, modulate claudin oligomerization.

Tight junctions seal the paracellular cleft of epithelia and endothelia, form vital barriers between tissue compartments and consist of tight-junction-associated marvel proteins (TAMPs) and claudins. The function of TAMPs and the interaction with claudins are not understood. We therefore investigated the binding between the TAMPs occludin, tricellulin, and marvelD3 and their interaction with claudins in living tight-junction-free human embryonic kidney-293 cells.

Claudin-3 acts as a sealing component of the tight junction for ions of either charge and uncharged solutes.

The paracellular barrier of epithelia and endothelia is established by several tight junction proteins including claudin-3. Although claudin-3 is present in many epithelia including skin, lung, kidney, and intestine and in endothelia, its function is unresolved as yet. We therefore characterized claudin-3 by stable transfection of MDCK II kidney tubule cells with human claudin-3 cDNA.

Claudin-2, a component of the tight junction, forms a paracellular water channel.

Whether or not significant amounts of water pass the tight junction (TJ) of leaky epithelia is still unresolved, because it is difficult to separate transcellular water flux from TJ-controlled paracellular water flux. Using an approach without differentiating technically between the transcellular and paracellular route, we measured transepithelial water flux with and without selective molecular perturbation of the TJ to unequivocally attribute changes to the paracellular pathway. To this end, MDCK C7 cells were stably transfected with either claudin-2 or claudin-10b, two paracellular cation-channel-forming TJ proteins that are not endogenously expressed in this cell line.

Tight junction proteins as channel formers and barrier builders.

Tight junctions form the paracellular barrier for ions and uncharged solutes not only in "tight" but also in "leaky" epithelia. In the premolecular era of tight junction research, this was believed to be achieved in a perfect or less perfect way, depending mainly on the amount of horizontally oriented tight junction strands. During the past decade it emerged that tight junction molecules, such as claudin-1 and many others, strengthen the barrier, while a few claudins, such as claudin-2 or -10, weaken it.

Claudin function in the thick ascending limb of Henle's loop.

During the past decade, claudins have been established as major determinants of paracellular permeablilty in epithelia. In the kidney, each nephron segment expresses a distinct pattern of claudins. Cells of the thick ascending limb of Henle's loop (TAL), which is characterized by high paracellular cation permeability, co-express an unusually large number of different claudins: claudin-10, -16, and -19 and, depending on the species, also claudin-3, -4, -8, and/or -11.

Tricellulin forms a barrier to macromolecules in tricellular tight junctions without affecting ion permeability.

Tricellulin is a tight junction protein localized in tricellular tight junctions (tTJs), the meeting points of three cells, but also in bicellular tight junctions (bTJs). To investigate its specific barrier functions in bTJs and tTJs, TRIC-a was expressed in low-level tricellulin-expressing cells, and MDCK II, either in all TJs or only in tTJs. When expressed in all TJs, tricellulin increased paracellular electrical resistance and decreased permeability to ions and larger solutes, which are associated with enhanced ultrastructural integrity of bTJs toward enhanced strand linearity.

Na+ absorption defends from paracellular back-leakage by claudin-8 upregulation.

In distal colon, the limiting factor for Na(+) absorption is represented by the epithelial sodium channel (ENaC). During absorption, high transepithelial Na(+) gradients are observed. In human colon and in HT-29/B6-GR cells, we investigated whether Na(+) back-leakage is prevented by paracellular sealing.