Abstract
Hearing relies on two major kind of sensory auditory hair cells in the cochlea: the outer hair cells (OHCs), which amplify sound stimulation, and the inner hair cells (IHCs), which transduce sound stimulation into release of neurotransmitter. Thus, cochlear activity sets high demands on the cellular metabolism. Ferritin, which belongs to the iron-binding protein family, stores the intracellular iron, require for several metabolic processes. Here, we probed the role of ferritin in the cochlea by phenotyping the ferritin light-chain subunit knock-out mouse. Wild-type and heterozygous mice showed similar ABR and auditory thresholds. In contrast, in the FTL1 knock-out mouse, we found-out a threshold shift in 20% of the homozygous mice associated with the loss of the distortion product of otoacoustic emissions, reflecting the OHC’s activity. Consistently, light and electron microscopy show a massive degeneration of the OHCs. In addition, we found-out splayed hair bundle in IHCs in the fraction of FTL1-/- with threshold shift. Although the loss of FTL1 did not change the number and size of the hair cell synaptic ribbons, we found-out a larger proportion of hair cells with altered calcium current in the FTL1-/- mice. We propose that ferritin may protect to some extent the hair cells and notably the ribbon synapse against iron-induced hydroxyl radicals.