Adherens Junction Proteins in Cochlear Lateral Wall Capillaries are Altered by Loud Sound‐induced Stress to the Ear

Abstract

BackgroundThe capillaries of the cochlear lateral wall are part of the blood‐labyrinth‐barrier (BLB) that separates the inner ear fluid from systemic circulation. The BLB controls the exchange of solutes, protein, and water, and plays an essential role in maintaining inner ear homeostasis and the endocochlear potential. Compromise of the BLB's integrity is a contributing factor in various hearing disorders including presbycusis, noise‐induced hearing loss, and autoimmune inner ear disease. This crucial barrier's function relies on endothelial cell‐cell junctions including those formed by the adherens junction (AJ) proteins. However, the mechanisms which regulate the function of AJs in the cochlear lateral wall capillaries remain largely unknown.ObjectiveTo characterize the role of AJ protein complexes and the associated signaling pathways in modulating the integrity of lateral wall capillaries under normal and loud sound‐induced stress conditions.Methods and ResultsThe spiral ligament and stria vascularis were isolated from the cochlea of 10 week old CBA/CaJ mice and immunolabeled for VE‐cadherin, β‐catenin, and FAK. Confocal imaging revealed that the fluorescent signals for VE‐cadherin and β‐catenin overlapped at endothelial cell to cell contacts whereas FAK revealed nuclear, cytoplasmic, and focal adhesion distribution without overlap with VE‐cadherin. To evaluate the dynamic changes of VE‐cadherin and its associated signaling pathway components under stress conditions, we exposed the CBA/CaJ mice to loud sound (106 dB SPL, 8–16 kHz, 2 hours). The following immunofluorescence analysis of the capillaries revealed an increase of specific phosphorylation sites for β‐catenin and FAK in the endothelial cells of noise exposed mice. Airyscan imaging showed alterations of the AJ proteins at the cell membrane as well as increased translocation of FAK to the endothelial cell‐cell junctions.ConclusionsAdherens junctions are dynamic structures that allow for rapid and specific responses to changes in the perivascular microenvironment. Loud sound‐induced alterations of AJ components and intracellular partners may reduce the integrity of the BLB. Unraveling the molecular mechanisms and signaling pathways that modulate the function of AJ complexes will contribute to the future discovery of breakthrough therapeutic treatments that maintain inner ear barrier integrity.Support or Funding InformationSupported by grants 5R01DC000105 (ALN) and P30DC005983.