Cell-targeted Gold Nanoparticles for Photo-excitation fo Retinal Ganglion Cells
ABSTRACT Retinal ganglion cells (RGCs) convey visual signals to the brain in the form of action potentials, the initiation and axonal propagation of which depend on the activation of RGC voltage-gated sodium channels (NaVs). In photoreceptor degenerative diseases such as age-related macular degeneration (AMD), inner retinal neurons including RGCs in many cases remain intact and capable of generating action potential responses. RGCs thus represent a logical target for approaches aimed at restoring vision in advanced-stage AMD and related retinal diseases, by bypassing the nonfunctioning rod and cone photoreceptors and establishing direct RGC responsiveness to light. In a recent study of dorsal root ganglion cells (a non-retinal neuron widely studied as a model action-potential-generating cell type) and in hippocampal slice preparations, we have shown that gold nanoparticles (AuNPs) conjugated with a cell-targeting biomolecule enable robust light-induced NaV activation and resulting action potential generation. Essential features of the cell-targeted AuNP technique are: (i) functionalization of the light-absorbing AuNPs to localize them at or near the NaVs; (ii) upon the AuNP?s plasmon absorption of a millisecond/submillisecond light flash, AuNP radiation of the light energy as a nondamaging pulse of heat that creates a localized, transient, depolarizing capacitive current across the plasma membrane; and (iii) resulting activation, i.e., channel opening, of neighboring NaVs and thus action potential initiation by this depolarization. In this application we propose exploratory research to apply this AuNP approach to RGCs in the living eye of the rat. The project?s goal is to establish AuNP treatment conditions that achieve robust AuNP-mediated RGC photo-responsiveness in vivo. In rats for which rod and cone photoreceptor signaling to RGCs has been suppressed pharmacologically, we will intra-vitreally deliver AuNP conjugates designed for binding to the immediate vicinity of the RGC NaVs. Following treatment with the AuNP conjugates, we will employ in vivo recording of electroretinographic (ERG) signals associated with RGC activity, and of visual evoked potentials (VEPs), to analyze properties of RGC electrophysiological responses to AuNP photo-excitation. The research will involve variation of the size/structure of the AuNP, of the AuNP- conjugated RGC-targeting component, and of the duration and energy [(intensity) x (duration)] of AuNP- excitatory flashes. Accompanying the in vivo experiments will be all-optical stimulation/recording of AuNP- mediated action potentials in isolated rat retina, and histological analysis of retinas treated in vivo and in vitro with AuNPs. Results of the in vitro retina experiments will guide the selection of in vivo treatment conditions to be systematically investigated and facilitate interpretation of the in vivo data. Leading the research will be David R. Pepperberg, PhD (Univ. of Illinois at Chicago) and Francisco Bezanilla, PhD (Univ. of Chicago).