Gain- and Loss-of-Function Variants in Epithelial Sodium (Na+) Channel Delta Subunit

Background: Epithelial Na+ channels (ENaCs) are trimeric complexes composed of one to three homologous subunits encoded by four distinct genes. Canonical ENaCs consist of α, β, and γ subunits, while δ subunits can form functional channels either alone or in combination with β and γ subunits. However, the physiological roles of δENaC remain unclear. In this study, we investigated the functional impact of selected missense variants in the δ subunit. Methods: Point mutations corresponding to selected common (minor allele frequency (MAF) > 0.05), low frequency (MAF, 0.01-0.05) and rare (MAF < 0.01) variants in δ subunit were introduced into human δENaC cDNA. Wild type (WT) or mutant human δENaC were co-expressed with WT β and γ subunits in Xenopus oocytes via RNA injection. ENaC activity was assessed using two-electrode voltage clamp recordings. Amiloride-sensitive currents (0.1 mM) representing ENaC activity were measured and compared within the same baches of oocytes expressing the WT or mutant channels. Results: Three common δENaC variants exhibited channel activity similar to WT. Among four low-frequency variants, R297C produced significantly greater amiloride-sensitive current than WT (relative current to WT: 1.7 ± 0.6, n = 40, p < 0.0001) and abolished the Na+ self-inhibition response, potentially explaining the increased activity. Of the 12 rare variants, two (G71S and C370R) showed significantly reduced amiloride-sensitive currents compared to WT (G71S: 0.2 ± 0.1, n = 46, p < 0.0001; C370R: 0.5 ± 0.4, n = 40, p < 0.0001). Conclusion: Our results suggest that R297C is a gain-of-function low-frequency variant and G71S and C370R are loss-of-function rare variants of δENaC. These and other δENaC variants may contribute to the reported association between δENaC and blood pressure. Funding: NIDDK Support - NIDDK Support, NIDDK Support