Achieving the control, by light, of native voltage-gated sodium channels (NaVs) by a nanoscale molecular device could prove valuable as a vision repair therapy for photoreceptor degenerative diseases as well as for fundamental neuroscience research. The effectiveness of gold nanoparticles (Au NPs) in collecting and locally dissipating (as heat) the energy of visible light is well established. This, together with recent evidence that a sudden application of photothermal energy can promote NaV-mediated action potential generation, and the availability of small proteins possessing high specific affiniy for the NaV extracellular face, raise the possibility that a Au NP localized at the NaV ectomain by conjugation with the protein ligand affinity reagent can mediate selective photothermal NaV activation. The proposed exploratory project is aimed at testing the feasibility of this technolog.
Aim 1 will provide the project's immediate foundation. Here we will determine the action of free Au NPs (i.e., not conjugated to protein ligand) on photo-induced transmembrane current in Xenopus oocytes, lipid bilayers, and isolated single ganglion cells of rat retina. The contributio of the Au NP to the light-elicited membrane current will be determined by comparing membrane currents elicited by photo-stimuli of similar intensity at wavelengths near to vs. distant from th nanoparticle's absorbance peak (~530 nm).
The Aim 1 experiments will also establish experimental conditions needed for suitable timing/duration of the pulsed stimulating light required for this photothermal approach, and for aqueous solubilization of the Au NPs.
In Aim 2 we will covalently couple the Au NP to the protein ligand Ts1, which has high affinity for the NaV domain II extracellular region. We hypothesize that close proximity of the Au NP to the membrane and its NaV target provided by attaching the Au NP to this NaV ligand will be key to minimizing the light level needed for NaV activation. We will construct Au NP-Ts1 conjugates in which a specific amino acid residue of the Ts1 is modified to serve as attachment site for the Au NP;we will determine the optimal structure of the conjugate by electrophysiological recording (experiments similar to those of Aim 1) and by analysis of cell-binding by fluorophore-tagged conjugate. Success in the project will establish feasibility of the investigated Au NP-based conjugate as a NaV photo-regulator. Specifically, it will encourage further development of this technology as a nano-prosthetic to enable NaV-mediated photo-signaling in ganglion cells of patients with advanced-stage photoreceptor degeneration. Leading the research will be David R. Pepperberg, PhD (Dept. of Ophthalmology and Visual Sciences, Univ. of Illinois at Chicago (UIC));Francisco Bezanilla, PhD, and Stephen B. H. Kent, PhD (Depts. of Chemistry, Biochemistry and Molecular Biology, Univ. of Chicago);and Karol S. Bruzik, PhD (Dept. of Medicinal Chemistry and Pharmacognosy, UIC).
Excitation and signal transmission in many types of nerve cells, including retinal ganglion cells, require the activation of voltage-gated sodium channels (NaVs), a protein that resides on the surfaces of these cells. A molecular device that enables photo-activation of native NaVs in specific cell types would represent a valuable research tool and, in particular, a major step toward development of vision-restoring nano-prosthetics for age- related macular degeneration and other photoreceptor degenerative diseases. Several types of evidence raise the possibility that structures employing a light-absorbing gold nanoparticle, localized near NaVs and close to the cell surface via covalent conjugation to a protein that tightly binds to the NaV, can activate the NaV with high photosensitivity. We propose to test the feasibility of this technology, by constructing structures of this type and determining their actio on NaV-expressing cells in vitro, including ganglion cells of rat retina.