Fast Photoswitchable Molecular Prosthetics Control Neuronal Activity in the Cochlea

Abstract

Artificial control of neuronal activity enables the study of neural circuits and restoration of neural functions. Direct, rapid, and sustained photocontrol of intact neurons could overcome the limitations of established electrical stimulation such as poor selectivity. We have developed fast photoswitchable ligands of glutamate receptors (GluRs) to enable neuronal control in the auditory system. The new photoswitchable ligands induced photocurrents in untransfected neurons upon covalently tethering to endogenous GluRs and activating them reversibly with visible light pulses of a few milliseconds. As a proof of concept of these molecular prostheses, we applied them to the ultrafast synapses of auditory neurons of the cochlea that encode sound and provide auditory input to the brain. This drug-based method afforded the optical stimulation of auditory neurons of adult gerbils at hundreds of hertz without genetic manipulation that would be required for their optogenetic control. This indicates that the new photoswitchable ligands are also applicable to the spatiotemporal control of fast spiking interneurons in the brain.

Reversible Photocontrol of Dopaminergic Transmission in Wild-Type Animals

“…Although there are clinical conditions that might take advantage of a dark-active drug that can be deactivated on demand (e.g., to reduce levodopa-induced dyskinesia in Parkinson’s disease) [ 63 ], light-activatable compounds are generally preferred for research and therapeutic purposes. Hence, new dopaminergic photoswitches must be developed that are active in the less thermodynamically stable configuration [ 64 ] and photoisomerize with visible [ 65 ] or infrared light [ 66 , 67 ] in order to unleash their full potential as photopharmacological tools.…”

A modular click ligand-directed approach to label endogenous aminergic GPCRs in live cells

“…We have adapted an heterogenous copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) chemistry, employing Cu2O as catalyst, which was developed for native tissue photopharmacology 24 and is compatible with in vivo testing. 25 In the CLD labeling, the use of copper-metal-chelating resins was required to eliminate traces of copper that may be toxic for cells and tissues. 22 On the other hand, this modular chemical approach allows us to employ affinity units with relatively nucleophilic character (such aminergic GPCR ligands), since the final labeling probe is built just before the labeling.…”

“…Similar approaches have been used in the field of tethered photopharamacology, enabling the covalent conjugation of glutamate derivatives directed to membrane receptors, even in vivo. 24,25 Additionally, the modular nature of our technology give us the opportunity to easily extend the application of the molecular unit 3a-c to label other receptors or proteins of interest. This only requires the development of an affinity unit module 4 specific for the new protein of interest.…”

Endogenous Proteins Modulation in Live Cells with Small Molecules and Light

“…With 45 , the kainate receptor channel (GluK1) was photo‐activated under violet‐light irradiation to yield the immediate photocurrents in the GluK1‐overexpressing cells [44] . After optimization, this method was applied to ultrafast synapses of the auditory system in live mice [45] . However, this method modified all four lysine residues of GluK1, and it was unsuitable for enzymes whose modified amino acid residues affect their native activity.…”

“…[44] After optimization, this method was applied to ultrafast synapses of the auditory system in live mice. [45] However, this method modified all four lysine residues of GluK1, and it was unsuitable for enzymes whose modified amino acid residues affect their native activity. The limitation of these PAL methods calls for new sitespecific protein photomodulation methods.…”