# Mechanism and function of intracellular sodium-proton exchangers

> **NIH NIH R01** · JOHNS HOPKINS UNIVERSITY · 2024 · $559,867

## Abstract

SUMMARY
 A growing number of serious disorders ranging from syndromic autism and intellectual disability to cancers
of the brain and gut have been linked to intracellular members of a family of electroneutral Na+/H+ exchangers,
including endosomal isoforms NHE6 and NHE9 (eNHE), that regulate pH and Na+ within the compartments of
the endo-lysosomal pathway. Plasma membrane NHE isoforms have been thoroughly characterized and
pharmaceutically targeted. In contrast, intracellular NHE remain poorly studied due to limitations and challenges
in sensing organelle-specific lumenal ions. Furthermore, overlapping distributions of eNHE isoforms and
contradictory reports on the direction of sodium and proton transport within organelles has hindered a
mechanistic understanding of transporter function and physiology. Case reports linking disease to eNHE genetic
variants are sporadic and genotype-phenotype correlations are incomplete. This proposal brings together three
research groups with unique and complementary expertise, together with powerful tools and resources to tackle
these problems. To overcome the technical challenges in measuring the activity of these transporters, we have
developed a multi-functional fluorescent reporter for both Na+ and H+ to precisely assay intracellular Na+/H+
exchange. This reporter can be targeted to specific organelles to simultaneously read out Na+ and H+ levels
therein using an imaging method called two-ion measurement. In Aim 1, we will deploy this reporter to specific
compartments along the endo-lysosomal pathway to quantify [Na+] and [H+] in both healthy and disease states.
We will determine the functional contribution and mode of transport of individual eNHE isoforms in key
organelles. This aim will lay the groundwork for functional analysis of clinically impactful gene variants in eNHE.
To capture the disease landscape for eNHE, in Aim 2 we will evaluate the clinical significance of rare and
common gene variants in SLC9A6 and SLC9A9. For these analyses, we will leverage large-scale exome
sequencing of a clinical cohort, paired with their de-identified electronic health records. Combining genetic
associations, gene expression and functional analysis will provide mechanistic insight on the biological basis of
disease associated with eNHE. In summary, our comprehensive biochemical mapping of the endo-lysosomal
pathway and disease-agnostic approach to link gene variants and expression to phenotypes will capture a broad
range of cellular and clinical correlates that will pave the way to successful therapeutic targeting of these
transporters in disease.

## Key facts

- **NIH application ID:** 10906806
- **Project number:** 5R01GM147197-03
- **Recipient organization:** JOHNS HOPKINS UNIVERSITY
- **Principal Investigator:** Yamuna Krishnan
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $559,867
- **Award type:** 5
- **Project period:** 2022-09-01 → 2026-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10906806

## Citation

> US National Institutes of Health, RePORTER application 10906806, Mechanism and function of intracellular sodium-proton exchangers (5R01GM147197-03). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10906806. Licensed CC0.

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