Interaction between Epithelial Sodium Channel γ-Subunit and Claudin-8 Modulates Paracellular Sodium Permeability in Renal Collecting Duct

Abstract

BackgroundWater and solute transport across epithelia can occur via the transcellular or paracellular pathways. Tight junctions play a key role in mediating paracellular ion reabsorption in the kidney. In the renal collecting duct, which is a typical absorptive tight epithelium, coordination between transcellular sodium reabsorption and paracellular permeability may prevent the backflow of reabsorbed sodium to the tubular lumen along a steep electrochemical gradient.MethodsTo investigate whether transcellular sodium transport controls tight-junction composition and paracellular permeability via modulating expression of the transmembrane protein claudin-8, we used cultured mouse cortical collecting duct cells to see how overexpression or silencing of epithelial sodium channel (ENaC) subunits and claudin-8 affect paracellular permeability. We also used conditional kidney tubule–specific knockout mice lacking ENaC subunits to assess the ENaC’s effect on claudin-8 expression.ResultsOverexpression or silencing of the ENaC γ-subunit was associated with parallel and specific changes in claudin-8 abundance. Increased claudin-8 abundance was associated with a reduction in paracellular permeability to sodium, whereas decreased claudin-8 abundance was associated with the opposite effect. Claudin-8 overexpression and silencing reproduced these functional effects on paracellular ion permeability. Conditional kidney tubule–specific ENaC γ-subunit knockout mice displayed decreased claudin-8 expression, confirming the cell culture experiments' findings. Importantly, ENaC β-subunit or α-subunit silencing or kidney tubule–specific β-ENaC or α-ENaC knockout mice did not alter claudin-8 abundance.ConclusionsOur data reveal the specific coupling between ENaC γ-subunit and claudin-8 expression. This coupling may play an important role in preventing the backflow of reabsorbed solutes and water to the tubular lumen, as well as in coupling paracellular and transcellular sodium permeability.

Clostridium butyricum Alleviates Enterotoxigenic Escherichia coli K88-Induced Oxidative Damage Through Regulating the p62-Keap1-Nrf2 Signaling Pathway and Remodeling the Cecal Microbial Community

“…Among them, p62 and Nrf2 specific primers were designed using primer 5 and the full sequences of their genes obtained from NCBI. p62 , Nrf2 , Heme oxygenase-1 ( HO-1 ) ( 22 ), GSH-Px ( 23 ), SOD1 ( 24 ), SOD2 ( 22 ), claudin 1 ( 25 ), claudin 8 ( 26 ), occludin ( 27 ), and zonula occludens-1 ( ZO-1 ) ( 25 ) mRNA expression levels were measured using LightCycler ® 480 real-time PCR and calculated based on 2 -ΔΔCt . Data are shown as ratios of abundance of target gene transcripts in the treated mice to those in the control group after normalization to Glyceraldehyde-3-phosphate dehydrogenase ( GAPDH ) ( 25 ).…”

Recent advances in understanding ion transport mechanisms in polycystic kidney disease

“…Tight junction composition was shown to be altered in the epithelium of polycystic kidneys: CLDNs normally expressed in the CD (3, 4, 7, 8, and 10) were localized in small cysts, while only CLDN7 persisted at substantive levels in the dedifferentiated epithelium of large, likely late-stage cysts, where it was found both at the TJ and basolaterally [ 59 ]. Sassi et al showed that CLDN8 interacts with the γ subunit of ENaC to regulate paracellular Na + permeability in the renal CD, which allows to speculate regarding the involvement of this interaction in cystic disease [ 60 ]. Therefore, it is possible that CLDNs may contribute to the pathogenesis of ADPKD, however, very little is known about the mechanisms that might be involved in their regulation in the disease state, or whether pharmacological targeting of these proteins could be beneficial for attenuating cystogenesis.…”

Expression of claudin-8 is induced by aldosterone in renal collecting duct principal cells

“…Stable cell lines were obtained after puromycin selection (2 μg/mL). Claudin-8 gene silencing was performed as previously described (5).…”

“…The expression profile of claudins in the kidney tubule is segment specific, and they can generate either a diffusion barrier or a paracellular permeability pathway (1). Claudin-8 is highly expressed in the CD (1)(2)(3), where it has been described to play a major role in Na þ barrier formation together with Cl À permeability and has been implicated in the generation of high electrical resistance (1,4,5). We recently showed that the ENaC c-subunit determines claudin-8 abundance, suggesting a coupling between paracellular and transcellular Na þ permeability (5).…”