Kidney-specific claudin-2 deficiency leads to medullary nephrocalcinosis in mice
Christine V. Behm, Duuamene Nyimanu, Ony Araujo Galdino, Sadhana Kanoo, Young Chul Kim, Natalia Lopez, Helen Goodluck, Peter S. Rowe, Andrew P. Evan, André J. Sommer, Matthew N. Barr, Tracy Punshon, Volker Vallon, Brian P. Jackson, James C. Williams Jr., Alan S.L. Yu
Christine V. Behm, Duuamene Nyimanu, Ony Araujo Galdino, Sadhana Kanoo, Young Chul Kim, Natalia Lopez, Helen Goodluck, Peter S. Rowe, Andrew P. Evan, André J. Sommer, Matthew N. Barr, Tracy Punshon, Volker Vallon, Brian P. Jackson, James C. Williams Jr., Alan S.L. Yu
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Research Article Metabolism Nephrology

Kidney-specific claudin-2 deficiency leads to medullary nephrocalcinosis in mice

Abstract

Deposits of hydroxyapatite called Randall’s plaques are found in the renal papilla of calcium oxalate kidney stone formers and likely serve as the nidus for stone formation, but their pathogenesis is unknown. Claudin-2 is a paracellular ion channel that mediates calcium reabsorption in the renal proximal tubule. To investigate the role of renal claudin-2, we generated kidney tubule–specific claudin-2 conditional KO mice (KS-Cldn2 KO). KS-Cldn2 KO mice exhibited transient hypercalciuria in early life. Normalization of urine calcium was accompanied by a compensatory increase in expression and function of renal tubule calcium transporters, including in the thick ascending limb. Despite normocalciuria, KS-Cldn2 KO mice developed papillary hydroxyapatite deposits, beginning at 6 months of age, that resembled Randall’s plaques and tubule plugs. Bulk chemical tissue analysis and laser ablation–inductively coupled plasma mass spectrometry revealed a gradient of intrarenal calcium concentration along the corticomedullary axis in normal mice that was accentuated in KS-Cldn2 KO mice. Our findings provide evidence for the “vas washdown” hypothesis for Randall’s plaque formation and identify the corticomedullary calcium gradient as a potential target for therapies to prevent kidney stone disease.

Authors

Christine V. Behm, Duuamene Nyimanu, Ony Araujo Galdino, Sadhana Kanoo, Young Chul Kim, Natalia Lopez, Helen Goodluck, Peter S. Rowe, Andrew P. Evan, André J. Sommer, Matthew N. Barr, Tracy Punshon, Volker Vallon, Brian P. Jackson, James C. Williams Jr., Alan S.L. Yu

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Figure 3

Induction of hypercalciuria within a week in inducible kidney-specific Cldn2-KO mice.

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Induction of hypercalciuria within a week in inducible kidney-specific C...
(A) Western blot for claudin-2 in whole kidney lysates from KO mice (Cldn2fl/y, Pax8-LC1) treated with doxycycline (Dox) or vehicle (lane 1) and control littermates without the Pax8 and/or LC1 genes (lanes 4 and 5). (B) Immunofluorescence staining of kidney sections with antibodies to claudin-2 (green) and ZO-1 (red). The upper panels show kidney cortex, where claudin-2 is detectable at the tight junctions (arrowheads) and basolateral membrane (arrow) of PTs in the control mouse (left) and absent in the KO mouse (right). The lower panels show the inner stripe of outer medulla, where claudin-2 localized to the thin descending limbs (arrows) is only mildly reduced in the KO compared with control. Claudin-2 deletion in the thin descending limbs was incomplete even after 3 weeks of doxycycline induction (not shown). Scale bars: 50 μm. (C) Urine calcium/creatinine (Ca/Cr) ratio before and after 1 week of doxycycline or vehicle (Veh) in inducible KO mice (Cre+) or control littermates without LC1 (Cre–). Bars represent mean ± SEM. P value is shown for interaction of time with the group Cre+ Dox, by repeated-measures LMM.