Extrarenal Signs of Proximal Renal Tubular Acidosis Persist in Nonacidemic Nbce1b/c-Null Mice.

Journal Article (Journal Article)

Background

The SLC4A4 gene encodes electrogenic sodium bicarbonate cotransporter 1 (NBCe1). Inheritance of recessive mutations in SLC4A4 causes proximal renal tubular acidosis (pRTA), a disease characterized by metabolic acidosis, growth retardation, ocular abnormalities, and often dental abnormalities. Mouse models of pRTA exhibit acidemia, corneal edema, weak dental enamel, impacted colons, nutritional defects, and a general failure to thrive, rarely surviving beyond weaning. Alkali therapy remains the preferred treatment for pRTA, but it is unclear which nonrenal signs are secondary to acidemia and which are a direct consequence of NBCe1 loss from nonrenal sites (such as the eye and enamel organ) and therefore require separate therapy. SLC4A4 encodes three major NBCe1 variants: NBCe1-A, NBCe1-B, and NBCe1-C. NBCe1-A is expressed in proximal tubule epithelia; its dysfunction causes the plasma bicarbonate insufficiency that underlies acidemia. NBCe1-B and NBCe1-C exhibit a broad extra-proximal-tubular distribution.

Methods

To explore the consequences of Nbce1b/c loss in the absence of acidemia, we engineered a novel strain of Nbce1b/c-null mice and assessed them for signs of pRTA.

Results

Nbce1b/c-null mice have normal blood pH, but exhibit increased mortality, growth retardation, corneal edema, and tooth enamel defects.

Conclusions

The correction of pRTA-related acidemia should not be considered a panacea for all signs of pRTA. The phenotype of Nbce1b/c-null mice highlights the physiologic importance of NBCe1 variants expressed beyond the proximal tubular epithelia and potential limitations of pH correction by alkali therapy in pRTA. It also suggests a novel genetic locus for corneal dystrophy and enamel hypomineralization without acidemia.

Full Text

Duke Authors

Cited Authors

  • Salerno, EE; Patel, SP; Marshall, A; Marshall, J; Alsufayan, T; Mballo, CSA; Quade, BN; Parker, MD

Published Date

  • June 2019

Published In

Volume / Issue

  • 30 / 6

Start / End Page

  • 979 - 989

PubMed ID

  • 31040187

Pubmed Central ID

  • PMC6551787

Electronic International Standard Serial Number (EISSN)

  • 1533-3450

International Standard Serial Number (ISSN)

  • 1046-6673

Digital Object Identifier (DOI)

  • 10.1681/asn.2018050545

Language

  • eng