In vivo investigation of f-Chrimson variants for optogenetic hearing restoration

Worldwide, 0.5 billion people suffer from disabling sensorineural hearing loss requiring rehabilitation by hearing aid or cochlear implant (CI). One of the key bottlenecks of current CIs is wide-spread electrical neural excitation, which could be overcome by optogenetics that offers more spatial selectivity. f-Chrimson is one of the most promising candidate channelrhodopsin (ChR) variants for optogenetic hearing restoration by future optical CIs. f-Chrimson provides ultrafast kinetics, high light sensitivity, as well as low phototoxicity due to its red-light-shifted activation. For scientific purposes, fluorescent proteins such as EYFP were fused to the C-terminus of ChRs. It turned out, that these reporting proteins are required for opsin functionality as their removal decreases photocurrent density. Yet, these reporters otherwise are not strictly required for optogenetic hearing restoration and might cause adverse effects. Therefore, less complex C-terminal modifications of f-Chrimson serving comparable benefits regarding photocurrent density would be preferable and were the aim of the present in vivo experiments in mice. The cochleae of neonatal mice were injected with adeno-associated viruses serving as a vector for transducing the f-Chrimson transgene into SGNs. Functional expression of modified f-Chrimson was probed by recording optically evoked auditory brainstem responses (oABR) using a laser (Obis TTL 594nm)-coupled 200 µm optical fiber positioned into the cochlea´s round window. We compared oABRs mediated by the modified f-Chrimson and the original f-Chrimson-EYFP and found comparable results regarding waveform, amplitudes and latencies. In conclusion, our C-terminal modification further optimizes f-Chrimson for clinical applications.

Publication History

Article published online:
24 May 2022