Slc9a8, encoding the sodium/hydrogen ion exchange protein NHE8, is an integral membrane protein crucial for multiple physiological processes. As a sodium/proton antiporter, it catalyzes the electroneutral exchange of Na⁺ and H⁺, contributing to functions like intracellular pH and cell volume regulation, and is involved in maintaining systemic electrolyte, acid-base, and fluid volume homeostasis [4].

In mouse models, Slc9a8 knockout leads to retinal defects due to retinal pigmented epithelium (RPE) dysfunction. The mutant retinas show separation of photoreceptors from the RPE, macrophage infiltration, reduced photoreceptor length, mislocalization of visual pigments, and deficits in rod and cone pathway function. The RPE has abnormal morphology, and conditional knockout in only RPE cells recapitulates the phenotype, suggesting that NHE8 in RPE is essential for endosomal volume and/or pH regulation, which is crucial for RPE cellular integrity and function [2].

In colorectal cancer cells, down-regulation of Slc9a8 promotes epithelial-mesenchymal transition (EMT) and metastasis via the IL6-JAK1/STAT3 signaling pathway. SLC9A8 protein is down-regulated in CRC tissues, and this down-regulation is associated with tumor size, lymph node status, pTNM stage, and poor prognosis [1]. Also, in vitamin D-deficient and VDR⁻/⁻ colitis mice, NHE8 expression is compromised, leading to more serious mucosal damage, indicating its role in maintaining intestinal barrier function [3].

In conclusion, Slc9a8 is essential for maintaining the integrity and function of multiple tissues. Its knockout or down-regulation in mouse models reveals its significance in retinal function, colorectal cancer progression, and intestinal barrier function. These findings suggest that Slc9a8 could be a potential therapeutic target for diseases related to these biological processes, such as retinal diseases, colorectal cancer, and colitis [1,2,3].