A novel transgenic mouse model highlights molecular disruptions involved in the pathogenesis of Dent disease 1.

Dent disease (DD) is a hereditary renal disorder characterized by low molecular weight (LMW) proteinuria and progressive renal failure. Inactivating mutations of the CLCN5 gene encoding the 2Cl-/H+exchanger ClC-5 have been identified in patients with DD type 1. ClC-5 is essentially expressed in proximal tubules (PT) where it is thought to play a role in maintaining an efficient endocytosis of LMW proteins. However, the exact pathological roles of ClC-5 in progressive dysfunctions observed in DD type 1 are still unclear. To address this issue, we designed a mouse model carrying the most representative type of ClC-5 missense mutations found in DD patients. These mice showed a characteristic DD type 1 phenotype accompanied by altered endo-lysosomal system and autophagy functions. With ageing, KI mice showed increased renal fibrosis, apoptosis and major changes in cell metabolic functions as already suggested in previous DD models. Furthermore, we made the interesting new discovery that the Lipocalin-2-24p3R pathway might be involved in the progression of the disease. These results suggest a crosstalk between the proximal and distal nephron in the pathogenesis mechanisms involved in DD with an initial PT impairment followed by the Lipocalin-2 internalisation and 24p3R overexpression in more distal segments of the nephron. This first animal model of DD carrying a pathogenic mutation of Clcn5 and our findings pave the way aimed at exploring therapeutic strategies to limit the consequences of ClC-5 disruption in patients with DD type 1 developing chronic kidney disease.

The apical 70-pS potassium K channel in the thick ascending limb of Henle's loop is a large-conductance Na+-and Cl--activated, KNa1.1-like, channel.

Apical potassium channels are crucial for thick ascending limb (TAL) of Henle's loop transport function. The ROMK (KNCJ1) gene encodes a 30-pS K channel whose loss of function causes the reduced NaCl reabsorption in the TAL associated with Type 2 Bartter's syndrome. In contrast, the molecular basis of a functionally ROMK-related 70-pS K channel is still unclear. The aim of this study was to highlight new specific channel properties that may give insights on its molecular identity. Using the patch-clamp technique on the apical membrane of mouse split-open TAL tubules, we observed that 70-pS K channel activity, but not ROMK channel activity, increases with the internal Na+ and Cl- concentrations, with relative 50 % effective concentrations (EC50) and Hill coefficients (nH) of 40.6 mM (SD 1.65) and 2.4 (SD 0.28) for Na+, and of 29.3 mM (SD 2.35) and 2.2 (SD 0.39) for Cl-. Conversely, 70-pS K channel activity was inhibited by internal K+ with a relative EC50 of 64 mM (SD 13.5) and a nH of 3.5 (SD 2.3), and by internal NH4+ and Ca2+. The reevaluation of channel conductive properties revealed an actual inward conductance of ~ 170 pS, with multiple subconductance levels and an inward rectification, and a substantial permeability to NH4+ ( = 0.2). We conclude that the apical 70-pS K channel in TAL cells is a large-conductance Na+- and Cl--activated potassium channel functionally resembling a KNa1.1 channel and propose that ROMK determines its functional expression possibly at the level of channel protein synthesis or trafficking.