The phospholipid scramblase PLSCR5 is regulated by POU4F3 and required for hair cell stereocilia homeostasis and auditory functions.

Hearing relies on the structural and functional integrity of cochlear hair cells, particularly their apical F-actin-filled stereocilia. Phospholipid scramblases are important for maintaining membrane asymmetry, but their roles in the stereocilia and auditory functions are not fully understood. Here, we identify Plscr5 as a downstream target of the transcription factor POU4F3 essential for hair cell function, whose mutation causes human DFNA15 deafness. Plscr5 knockout mice exhibit progressive hearing loss due to stereocilia degeneration and hair cell loss. Functional analyses reveal that PLSCR5 contributes to phosphatidylserine externalization in hair cell apical membranes, particularly in inner hair cells, and is important for outer hair cell and stereocilia maintenance. Our findings highlight PLSCR5 as an important downstream effector of POU4F3 and regulator of phosphatidylserine externalization and membrane dynamics required for auditory functions.