Single-cell RNA-sequencing of stria vascularis cells in the adult Slc26a4^-/- mouse

The primary pathological alterations of Pendred syndrome are endolymphatic pH acidification and luminal enlargement of the inner ear. However, the molecular contributions of specific cell types remain poorly characterized. Therefore, we aimed to identify pH regulators in pendrin-expressing cells that may contribute to the homeostasis of endolymph pH and define the cellular pathogenic mechanisms that contribute to the dysregulation of cochlear endolymph pH in Slc26a4^-/- mice.

We used single-cell RNA sequencing to identify both Slc26a4-expressing cells and Kcnj10-expressing cells in wild-type (WT, Slc26a4^+/+) and Slc26a4^-/- mice. Bioinformatic analysis of expression data confirmed marker genes defining the different cell types of the stria vascularis. In addition, specific findings were confirmed at the protein level by immunofluorescence.

We found that spindle cells, which express pendrin, contain extrinsic cellular components, a factor that enables cell-to-cell communication. In addition, the gene expression profile informed the pH of the spindle cells. Compared to WT, the transcriptional profiles in Slc26a4^-/- mice showed downregulation of extracellular exosome-related genes in spindle cells. Immunofluorescence studies in spindle cells of Slc26a4^-/- mice validated the increased expression of the exosome-related protein, annexin A1, and the clathrin-mediated endocytosis-related protein, adaptor protein 2.

Overall, cell isolation of stria vascularis from WT and Slc26a4^-/- samples combined with cell type-specific transcriptomic analyses revealed pH-dependent alternations in spindle cells and intermediate cells, inspiring further studies into the dysfunctional role of stria vascularis cells in SLC26A4-related hearing loss.