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Intercalated cell depletion and vacuolar H+-ATPase mistargeting in an AE1 R607H knockin model


Mumtaz, Rizwan; Trepiccione, Francesco; Hennings, J Christopher; Huebner, Antje K; Serbin, Bettina; Picard, Nicolas; Ullah, A K M Shahid; Păunescu, Teodor G; Capen, Diane E; Lashhab, Rawad M; Mouro-Chanteloup, Isabelle; Alper, Seth L; Wagner, Carsten A; Cordat, Emmanuelle; Brown, Dennis; Eladari, Dominique; Hübner, Christian A (2017). Intercalated cell depletion and vacuolar H+-ATPase mistargeting in an AE1 R607H knockin model. Journal of the American Society of Nephrology (JASN), 28(5):1507-1520.

Abstract

Distal nephron acid secretion is mediated by highly specialized type A intercalated cells (A-ICs), which contain vacuolar H(+)-ATPase (V-type ATPase)-rich vesicles that fuse with the apical plasma membrane on demand. Intracellular bicarbonate generated by luminal H(+) secretion is removed by the basolateral anion-exchanger AE1. Chronically reduced renal acid excretion in distal renal tubular acidosis (dRTA) may lead to nephrocalcinosis and renal failure. Studies in MDCK monolayers led to the proposal of a dominant-negative trafficking mechanism to explain AE1-associated dominant dRTA. To test this hypothesis in vivo, we generated an Ae1 R607H knockin mouse, which corresponds to the most common dominant dRTA mutation in human AE1, R589H. Compared with wild-type mice, heterozygous and homozygous R607H knockin mice displayed incomplete dRTA characterized by compensatory upregulation of the Na(+)/HCO3(-) cotransporter NBCn1. Red blood cell Ae1-mediated anion-exchange activity and surface polypeptide expression did not change. Mutant mice expressed far less Ae1 in A-ICs, but basolateral targeting of the mutant protein was preserved. Notably, mutant mice also exhibited reduced expression of V-type ATPase and compromised targeting of this proton pump to the plasma membrane upon acid challenge. Accumulation of p62- and ubiquitin-positive material in A-ICs of knockin mice suggested a defect in the degradative pathway, which may explain the observed loss of A-ICs. R607H knockin did not affect type B intercalated cells. We propose that reduced basolateral anion-exchange activity in A-ICs inhibits trafficking and regulation of V-type ATPase, compromising luminal H(+) secretion and possibly lysosomal acidification.

Abstract

Distal nephron acid secretion is mediated by highly specialized type A intercalated cells (A-ICs), which contain vacuolar H(+)-ATPase (V-type ATPase)-rich vesicles that fuse with the apical plasma membrane on demand. Intracellular bicarbonate generated by luminal H(+) secretion is removed by the basolateral anion-exchanger AE1. Chronically reduced renal acid excretion in distal renal tubular acidosis (dRTA) may lead to nephrocalcinosis and renal failure. Studies in MDCK monolayers led to the proposal of a dominant-negative trafficking mechanism to explain AE1-associated dominant dRTA. To test this hypothesis in vivo, we generated an Ae1 R607H knockin mouse, which corresponds to the most common dominant dRTA mutation in human AE1, R589H. Compared with wild-type mice, heterozygous and homozygous R607H knockin mice displayed incomplete dRTA characterized by compensatory upregulation of the Na(+)/HCO3(-) cotransporter NBCn1. Red blood cell Ae1-mediated anion-exchange activity and surface polypeptide expression did not change. Mutant mice expressed far less Ae1 in A-ICs, but basolateral targeting of the mutant protein was preserved. Notably, mutant mice also exhibited reduced expression of V-type ATPase and compromised targeting of this proton pump to the plasma membrane upon acid challenge. Accumulation of p62- and ubiquitin-positive material in A-ICs of knockin mice suggested a defect in the degradative pathway, which may explain the observed loss of A-ICs. R607H knockin did not affect type B intercalated cells. We propose that reduced basolateral anion-exchange activity in A-ICs inhibits trafficking and regulation of V-type ATPase, compromising luminal H(+) secretion and possibly lysosomal acidification.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > Institute of Physiology
07 Faculty of Science > Institute of Physiology
Dewey Decimal Classification:570 Life sciences; biology
610 Medicine & health
Language:English
Date:2017
Deposited On:12 Jan 2017 10:27
Last Modified:06 Aug 2017 15:08
Publisher:American Society of Nephrology
ISSN:1046-6673
Free access at:PubMed ID. An embargo period may apply.
Publisher DOI:https://doi.org/10.1681/ASN.2016020169
PubMed ID:27932475

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