The susceptibility of cochlear outer hair cells to cyclodextrin is not related to their electromotile activity

Abstract

Niemann-Pick Type C1 (NPC1) disease is a fatal neurovisceral disorder caused by dysfunction of NPC1 protein, which plays a role in intracellular cholesterol trafficking. The cholesterol-chelating agent, 2-hydroxypropyl-β-cyclodextrin (HPβCD), is currently undergoing clinical trials for treatment of this disease. Though promising in alleviating neurological symptoms, HPβCD causes irreversible hearing loss in NPC1 patients and outer hair cell (OHC) death in animal models. We recently found that HPβCD-induced OHC death can be significantly alleviated in a mouse model lacking prestin, an OHC-specific motor protein required for the high sensitivity and sharp frequency selectivity of mammalian hearing. Since cholesterol status is known to influence prestin’s electromotility, we examined how prestin contributes to HPβCD-induced OHC death in the disease context using the NPC1 knockout (KO) mouse model (NPC1-KO). We found normal expression and localization of prestin in NPC1-KO OHCs. Whole-cell patch-clamp recordings revealed a significant depolarization of the voltage-operating point of prestin in NPC1-KO mice, suggesting reduced levels of cholesterol in the lateral membrane of OHCs that lack NPC1. OHC loss and elevated thresholds were found for high frequency regions in NPC1-KO mice, whose OHCs retained their sensitivity to HPβCD. To investigate whether prestin’s electromotile function contributes to HPβCD-induced OHC death, the prestin inhibitor salicylate was co-administered with HPβCD to WT and NPC1-KO mice. Neither oral nor intraperitoneal administration of salicylate mitigated HPβCD-induced OHC loss. To further determine the contribution of prestin’s electromotile function, a mouse model expressing a virtually nonelectromotile prestin protein (499-prestin) was subjected to HPβCD treatment. 499-prestin knockin mice showed no resistance to HPβCD-induced OHC loss. As 499-prestin maintains its ability to bind cholesterol, our data imply that HPβCD-induced OHC death is ascribed to the structural role of prestin in maintaining the OHC’s lateral membrane, rather than its motor function.Electronic supplementary materialThe online version of this article (10.1186/s40478-018-0599-9) contains supplementary material, which is available to authorized users.

2-Hydroxypropyl-β-cyclodextrin Ototoxicity in Adult Rats: Rapid Onset and Massive Destruction of Both Inner and Outer Hair Cells Above a Critical Dose

“…However, the high doses of cyclodextrins needed to ameliorate NPC1 generally lead to high-frequency hearing loss. Studies of ototoxicity in cats and mice indicate that HPβCD mainly damages the outer hair cells (OHC) while sparing the inner hair cells (IHC) and spiral ganglion neurons (SGN) (Cronin et al, 2015, Crumling et al, 2017, Crumling et al, 2012, Takahashi et al, 2016, Ward et al, 2010, Zhou et al, 2018. Because the electromotile OHC provide the auditory system with its exquisite sensitivity and sharp tuning, the selective destruction of OHC by HPBCD results in a significant hearing loss (Liberman et al, 2002, Ryan andDallos, 1975).…”

Spatiotemporal Developmental Upregulation of Prestin Correlates With the Severity and Location of Cyclodextrin-Induced Outer Hair Cell Loss and Hearing Loss

“…In adult rats, the 4,000 mg/kg dose of HPβCD completely eliminated the DPOAE 2-days post-treatment ( Liu et al, 2020 ). Although several mechanisms have been suggested ( Crumling et al, 2017 ), selective cyclodextrin ototoxicity is believed to be correlated with prestin expression in OHCs because knockout mice missing this protein are more resistant to cyclodextrin damage than wild type mice ( Takahashi et al, 2016 ) or mutant mice with a non-electromotile form of prestin ( Zhou et al, 2018 ).…”

“…Much of the previous literature on HPβCD ototoxicity in mice has focused on its early, selective destruction of OHCs with little evidence of damage to IHCs, ANFs, or SGNs ( Crumling et al, 2012 , 2017 ; Takahashi et al, 2016 ; Zhou et al, 2018 ). However, recent studies from our lab have revealed that HPβCD unexpectedly causes massive, delayed degeneration of rat IHCs, PCs, ANFs, SGNs, and much of the organ of Corti ( Ding et al, 2020 ; Liu et al, 2020 ).…”

“…Because HPβCD initially destroys only OHCs and because cholesterol modulates OHC electromotility mediated by prestin ( Rajagopalan et al, 2007 ), it was assumed that this selective damage was related to the expression of the electromotile protein prestin located in the plasma membrane along the OHC lateral wall ( Takahashi et al, 2016 ; Crumling et al, 2017 ). Because mutant mice with a non-electromotile version of prestin continued to be vulnerable to HPβCD ototoxicity; it was concluded that electromotility per se was not a critical factor in HPβCD ototoxicity ( Zhou et al, 2018 ). On the other hand, OHCs in the middle and basal turn of prestin knockout mice were substantially less susceptible to HPβCD toxicity than wild type (WT) mice.…”

Experimental animal models of drug-induced sensorineural hearing loss: a narrative review

“…The mechanisms of the selective damage to OHCs remain undetermined. One factor at plays may be that prestin, the OHC motor protein and the main component of the OHC lateral membrane, is sensitive to changes in cholesterol levels (131)(132)(133). Compared to AABs' protocols, HPβCD seems to be a more effective agent to induce loss of OHCs selectively.…”