Spatiotemporal Developmental Upregulation Of Prestin Correlates With The Severity And Location Of Cyclodextrin-Induced Outer Hair Cell Loss And Hearing Loss

2-Hyroxypropyl-beta-cyclodextrin (HP beta CD) is being used to treat Niemann-Pick C1, a fatal neurodegenerative disease caused by abnormal cholesterol metabolism. HPKD slows disease progression, but unfortunately causes severe, rapid onset hearing loss by destroying the outer hair cells (OHC). HP beta CD-induced damage is believed to be related to the expression of prestin in OHCs. Because prestin is postnatally upregulated from the cochlear base toward the apex, we hypothesized that HP beta CD ototoxicity would spread from the high-frequency base toward the low-frequency apex of the cochlea. Consistent with this hypothesis, cochlear hearing impairments and OHC loss rapidly spread from the high-frequency base toward the low-frequency apex of the cochlea when HP beta CD administration shifted from postnatal day 3 (P3) to P28. HP beta CD-induced histopathologies were initially confined to the OHCs, but between 4- and 6-weeks post-treatment, there was an unexpected, rapid and massive expansion of the lesion to include most inner hair cells (IHC), pillar cells (PC), peripheral auditory nerve fibers, and spiral ganglion neurons at location where OHCs were missing. The magnitude and spatial extent of HP beta CD-induced OHC death was tightly correlated with the postnatal day when HP beta CD was administered which coincided with the spatiotemporal upregulation of prestin in OHCs. A second, massive wave of degeneration involving IHCs, PC, auditory nerve fibers and spiral ganglion neurons abruptly emerged 4-6 weeks post-HP beta CD treatment. This secondary wave of degeneration combined with the initial OHC loss results in a profound, irreversible hearing loss.