Identification and optimization of channelrhodopsin variants for optogenetic hearing restoration

Background Recently, progress has been made towards the development of optical cochlear implants (oCI) which aim to overcome the limitations of electrical CI. Using spatially confined light instead of current, the oCI allows for precise stimulation of neurons enabling improved spectral selectivity. Optogenetic hearing restoration employs light-gated ion channels called channelrhodopsins (ChR) to render cells light sensitive. One of the remaining tasks before clinical application is the selection of the most suitable ChR variant. In this study, we investigated variants of the ChR f-Chrimson and ChRmine for their potential of future optogenetic hearing restoration.

Methods Characterization of the electrophysiological properties of f-Chrimson and ChRmine variants was performed by whole cell patch clamp recordings of transfected neuroblastoma glioma cells.

Results Recordings of f-Chrimson revealed a drop in photocurrent density following the removal of the adjacent fluorescent protein (FP) that could be rescued by modification of the C-terminus. ChRmine-FP displayed big peak photocurrents. However, its strong desensitization leads to a significantly reduced stationary photocurrent density. We constructed new ChRmine variants which feature significantly reduced desensitization.

Conclusion We consider f-Chrimson the currently most promising candidate for optogenetic hearing restoration due to the combination of the red-shifted action spectrum and fast closing kinetics. Our work further optimized f-Chrimson for clinical application by abolishing the need for additional expression of a jellyfish-derived protein with potential adverse effects in human. Furthermore, new ChRmine variants combine several of the required ChR properties for optimized optogenetic application.

Publication History

Article published online:
24 May 2022