Outer Hair Cell Lateral Wall Structure Constrains the Mobility of Plasma Membrane Proteins

Abstract

Nature’s fastest motors are the cochlear outer hair cells (OHCs). These sensory cells use a membrane protein, Slc26a5 (prestin), to generate mechanical force at high frequencies, which is essential for explaining the exquisite hearing sensitivity of mammalian ears. Previous studies suggest that Slc26a5 continuously diffuses within the membrane, but how can a freely moving motor protein effectively convey forces critical for hearing? To provide direct evidence in OHCs for freely moving Slc26a5 molecules, we created a knockin mouse where Slc26a5 is fused with YFP. These mice and four other strains expressing fluorescently labeled membrane proteins were used to examine their lateral diffusion in the OHC lateral wall. All five proteins showed minimal diffusion, but did move after pharmacological disruption of membrane-associated structures with a cholesterol-depleting agent and salicylate. Thus, our results demonstrate that OHC lateral wall structure constrains the mobility of plasma membrane proteins and that the integrity of such membrane-associated structures are critical for Slc26a5’s active and structural roles. The structural constraint of membrane proteins may exemplify convergent evolution of cellular motors across species. Our findings also suggest a possible mechanism for disorders of cholesterol metabolism with hearing loss such as Niemann-Pick Type C diseases.

Susceptibility of outer hair cells to cholesterol chelator 2-hydroxypropyl-β-cyclodextrine is prestin-dependent

“…Yamashita et al . recently suggested that the OHC’s trilaminate structure, which consists of PM, actin-spectrin cortical lattice (CL), and the subsurface cisternae (SSC), limits prestin’s mobility 53 . It is also reported that salicylate, a prestin inhibitor that reversibly alters the SSC 54 , can increase prestin’s mobility in the presence MβCD 53 .…”

Direct administration of 2-Hydroxypropyl-Beta-Cyclodextrin into guinea pig cochleae: Effects on physiological and histological measurements

“…Recent studies on the chronic effects of HPβCD administered systemically or directly into cerebrospinal fluid found graduated losses of outer hair cells (OHC) along the cochlear spiral, with more severe losses at the cochlear base than the apex [5–6]. While the origins of HPβCD toxicity within the ear remain uncertain, its effects can modulate cochlear or OHC electromechanics in excised cochleae [7–8]. In experiments reported here we used a variety of physiological measurements to understand the effects of acute administration of HPβCD, and HPβCD analog methyl-β-cyclodextrin (MβCD), directly into cochlear perilymph.…”

Membrane prestin expression correlates with the magnitude of prestin-associated charge movement

“…Changes in cholesterol can alter OHC membrane lipid fluidity, which may affect prestin function (Organ and Raphael, 2009). A recent study using a prestin-YFP knockin mouse model showed that disrupting lateral wall membrane structure with a cholesterol-depleting agent and salicylate increased lateral mobility of prestin, which would have functional consequences for both normal development and disorders of cholesterol metabolism (Yamashita et al, 2015). Increased expression of other OHC membrane, cytoskeletal, and prestin-associated proteins, may provide additional maturation mechanisms for the full development of adult OHC electromotility, either by direct association with prestin or by altering membrane material properties such as stiffness and tension (Jensen-Smith and Hallworth, 2007; Santos-Sacchi et al, 1998; R.…”