Sunday, May 18, 2025
5/18/2025
Lipid Flippases in the Function and Degeneration of Sensory Hair Cells - Project Abstract The cochlea of the inner ear houses sensory hair cells responsible for detecting auditory signals. Since hair cells do not regenerate, their loss leads to permanent hearing impairment, making it essential to understand the molecular mechanisms underlying their degeneration to develop effective therapies. At the apex of each hair cell is the hair bundle, a specialized structure that detects sound-induced mechanical vibrations. These vibrations open mechanosensitive ion channels, leading to hair cell depolarization. While the roles of proteins within the hair bundle are well-studied, the importance of the plasma membrane's lipid composition in hair bundle function and maintenance remains poorly understood. Of particular interest is the asymmetric distribution of phosphatidylserine (PS), which is typically confined to the inner leaflet of the membrane. Ototoxic insults, such as loud noise and aminoglycosides, disrupt lipid homeostasis in the hair bundle, though the exact mechanisms and their effects on hair cell function are unclear. This proposal investigates how phospholipid homeostasis regulates hair cell function and health using mice deficient in the phospholipid flippase ATP8B1 or its cofactor TMEM30B, which experience rapid hearing loss. These models provide a framework to explore the link between lipid dynamics and auditory function. Previous research suggests that ATP8B1 deficiency leads to hair cell degeneration and deafness, though the underlying mechanisms remain unknown (Stapelbroek et al., 2009). We hypothesize that ATP8B1 is essential for maintaining the lipid environment required for proper mechanotransduction. To address this hypothesis, we will first define the developmental timeline of ATP8B1 and TMEM30B expression and investigate whether their localization to the stereocilia depends on mechanotransduction (MET) or TMC1 activity. We will also determine how ATP8B1 loss impacts hair cell function, plasma membrane asymmetry, MET currents, and cell survival, aiming to uncover ATP8B1’s role in stereocilia and its contribution to the proper lipid environment for hair cell MET. Lastly, we will assess whether TMEM30B alone qualifies as a deafness gene by conducting auditory brainstem response and distortion product otoacoustic emission testing, alongside evaluations of hair bundle morphology and plasma membrane asymmetry. This research will illuminate the critical role of the lipid membrane environment in hair cell function and longevity. Insights gained could advance our understanding of how disruptions in lipid homeostasis contribute to hearing loss, paving the way for innovative therapeutic strategies.
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