# Distinct Roles of SLC26A3 and CFTR in Surface pH Regulation and Bicarbonate Secretion in Human Intestinal Epithelium

## TL;DR

This study shows that SLC26A3 can compensate for CFTR dysfunction in intestinal cells by regulating pH and mucin distribution, but cannot restore fluid secretion.

## Contribution

The study reveals distinct and complementary roles of SLC26A3 and CFTR in pH regulation and bicarbonate secretion in human intestinal epithelium.

## Key findings

- SLC26A3 overexpression normalizes surface pH and mucin distribution in CF organoids.
- SLC26A3 cannot rescue CFTR-dependent fluid secretion defects.
- CF organoids have lower surface pH compared to healthy controls.

## Abstract

Colonic bicarbonate secretion is mediated by the chloride/bicarbonate exchanger SLC26A3 and the cystic fibrosis transmembrane conductance regulator (CFTR). Dysfunction of either causes luminal acidosis, altered mucus properties, and inflammation. While physical and functional interactions have been demonstrated in heterologous systems, their relationship in native epithelium is not fully established. We investigated the distinct roles of SLC26A3 and CFTR using human intestinal organoids with inducible SLC26A3 overexpression.

Human colonic and rectal organoids from healthy controls and cystic fibrosis patients with F508del mutations were studied in the proliferative state with high endogenous CFTR expression and inducible SLC26A3 overexpression. Real‐time surface pH measurements, electrophysiological analysis, forskolin‐induced swelling assays, and confocal microscopy were employed.

Steady‐state surface pH was lower in CF versus healthy organoids (7.23 ± 0.03 vs. 7.34 ± 0.03). SLC26A3 overexpression normalized surface pH in CF organoids and CFTR‐inhibited organoids, equalizing responses between genotypes. SLC26A3 overexpression corrected abnormal morphology and significantly improved intracellular MUC2 distribution in CF organoids. However, SLC26A3 did not restore fluid secretion in CF organoids or enhance CFTR‐mediated electrogenic anion secretion in Ussing chambers.

SLC26A3 and CFTR perform distinct yet complementary functions. SLC26A3 dominates surface pH regulation and maintains bicarbonate efflux independently of CFTR, while CFTR drives agonist‐stimulated fluid secretion. SLC26A3's ability to restore pH homeostasis and normalize mucin intracellular distribution in CF organoids demonstrates its critical importance for maintaining colonic mucosal health.

SLC26A3 independently maintains colonic surface pH and can compensate for CFTR dysfunction in cystic fibrosis.SLC26A3 overexpression normalized abnormal mucin distribution in CF intestinal organoids.Despite restoring surface pH, SLC26A3 cannot rescue CFTR‐dependent fluid secretion defects.

SLC26A3 independently maintains colonic surface pH and can compensate for CFTR dysfunction in cystic fibrosis.

SLC26A3 overexpression normalized abnormal mucin distribution in CF intestinal organoids.

Despite restoring surface pH, SLC26A3 cannot rescue CFTR‐dependent fluid secretion defects.