XIRP2 in Stereocilia F-Actin Repair

ABSTRACT Approximately one in seven adults in the United States (37.5 million) experience some degree of hearing loss, making it the third most common health condition among American adults. Hearing relies on the precise function of auditory hair cells, which possess specialized stereocilia that deflect in response to sound, activating mechanically-gated ion channels essential for mechanotransduction. Because mammalian auditory hair cells cannot regenerate, damage to stereocilia can lead to progressive hearing loss. Understanding endogenous mechanisms of damage repair is critical for identifying potential avenues for treating hearing loss. Recent findings from our lab reveal that noise exposure induces gaps in stereocilia F-actin, which are subsequently repaired, suggesting the presence of an active repair mechanism. A critical question remains: how do hair cells sense and repair F-actin damage, and how does this process prevent hearing loss? The actin-associated protein XIRP2 is highly enriched in hair cell stereocilia and accumulates at F-actin damage sites. Our lab has shown that Xirp2 knockout mice exhibit impaired stereocilia repair and progressive hearing loss, implicating XIRP2 in actin repair and hearing maintenance. I hypothesize that XIRP2 detects and mediates the repair of stereocilia F-actin damage, and this process is regulated by upstream signaling pathways. To test this hypothesis, I propose two complementary aims. Aim 1 investigates the mechanism by which XIRP2 detects F-actin damage in a heterologous cell system. Using laser ablation to induce actin damage, I will identify the protein domain responsible for XIRP2 recruitment and explore the regulation of its activation. Aim 2 examines the role of XIRP2 in hair cells using a transgenic mouse model enabling live imaging of endogenous XIRP2. I will determine XIRP2’s baseline dynamics, its recruitment to F-actin lesions, and the protein domain responsible for its recruitment in hair cells. By elucidating the upstream regulation of XIRP2 and its role in actin repair, this work will provide key insights into the molecular pathways enabling hair cells to respond to damage, offering potential therapeutic targets to mitigate progressive hearing loss.