NHE3 Controls Proliferation and Migration of Colonic Epithelial Cells

Background In the gut, Na⁺/H⁺ exchanger 3 (NHE3; SLC9A3) plays important roles in pH regulation, absorption of Na⁺, and indirectly of other nutrients. NHE3-deficient mice develop inflammatory bowel disease (IBD)-like dysbiosis and spontaneous colitis, and rare mutations in the SLC9A3 gene may confer a risk factor for very early-onset IBD. However, the roles of NHE3 in the epithelial cell functions beyond the canonical ion transport, especially in the face of injury, remain poorly understood. Thus, we aimed to investigate the role of NHE3 in colonic epithelial cell proliferation and migration during wound healing. Methods Colonic organoids from NHE3^+/+ and NHE3^-/- mice and SK-CO-15 cells with shRNA-mediated NHE3 knockdown (NHE3KD) were used to assess the intrinsic role of NHE3 in cellular proliferation, migration, wound healing, adhesion to the extracellular matrix (ECM), activation status of focal adhesion kinase (pFAK^Y397), and in gene transcription. Results NHE3^-/- colonoids showed increased cell proliferation and reduced ECM adhesion. NHE3^-/- colonoids and NHE3KD cells showed increased spontaneous motility, enhanced migration in serum gradient, and in 2 models of wound healing. This was associated with FAK and Src activation and modulation of genes associated with cell-cell interactions, cell-ECM interactions, and the formation of focal adhesions. Inhibition of FAK autophosphorylation eliminated the effect of NHE3 deficiency on cell migration. Conclusions Inhibition of NHE3, unconfounded by chronic inflammatory or microbial pressure, may represent a permissible mechanism beneficial to the host by modulating cellular plasticity and promoting epithelial wound healing. These unexpected results provide a novel insight into the pleiotropic roles of NHE3 in mucosal homeostasis.