Azobenzene-conjugated Propofol-derivatives for Light-control of GABA(A) Receptors in Vision Restoration
In many cases of retinal degeneration, the deterioration of photoreceptors leaves the downstream inner retinal neurons unstimulated, thus leading to vision loss. Re-initiating visual signaling by means of rendering photosensitivity to these inner retinal neurons could potentially restore vision in photoreceptor degenerated patients. Here, we investigated the feasibility of building nanoscale light-regulated neuromodulators that can attach to the inner retinal neurons at the sites of postsynaptic membrane receptors to enable photo-control of neuronal activity. Specifically, we focused on GABA(A) receptors given their importance in visual signaling and abundance in retinal neurons. The nanoscale structures consist of three main components: a receptor-interactive ligand, a light-sensitive photoswitch and an anchor for attachment. The ligand employed for this study is propofol (2,6-diisopropyl phenol), a well-known GABA(A) receptor modulator and activator. Our investigation of the action of propofol on retinal bipolar cells (RBCs) reveals a marked and selective potentiation of RBC GABA(A) receptor activity by propofol, thus encouraging its use as the prototype modulator for inner retinal neurons. Azobenzene, a chemical compound that undergoes bi-directional photo-conversion between trans- and cis-isomers upon photon absorption, was used as the photoswitch. A number of azobenzene-conjugated propofol derivatives were synthesized and tested on recombinant α1β2γ2 GABA(A) receptors. These studies demonstrate the photo-control of the receptor activity either by a freely diffusible agent (e.g. MPC088) or by a covalently tethered agent (e.g. maleimide-containing MPC100) that forms a stable carbon-sulfur bond with the cysteine substituted receptors. Further, we examined the activity of MPC088 on native GABA(A) receptors of retinal ganglion cells (RGCs), the output neuron of retina, and observed similar isomer-dependent regulation of membrane currents. Overall, this thesis study presents modulation of the native retinal GABA(A) receptors by propofol and the light-control of both recombinant and native GABA(A) receptors by propofol-azobenzene conjugates. Therefore it suggests the feasibility of using propofol-based nanoscale photoswitch to present light-sensitivity to retinal neurons as a vision restoration approach.