ALL-OPTICAL ELECTROPHYSIOLOGY FOR NEUROSCIENCE AND CARDIOVASCULAR DRUG DISCOVERY

Graham Dempsey

Q-State Biosciences, Harvard University, Cambridge, MA, USA

Abstract

Human stem cell models have become a potentially powerful approach to modeling nervous system and cardiovascular disorders for drug discovery applications. Human induced pluripotent stem (iPS) cells derived from patient material can be differentiated into diverse cell types, including neurons and cardiomyocytes, which enable investigation of disease biology in the context of a human genetic background. HiPS cell systems will serve to complement existing rodent models in certain cases or supplant them where the human disease biology is not faithfully reproduced in the animal model. Novel assays with high information content are needed to characterize the phenotypic response of disease-relevant cellular models and to detect pharmacological effects on the observed phenotypes. To this end, we have created an optogenetic platform called Optopatch that rapidly and robustly characterizes the electrophysiological response of electrically excitable cells. Stimulation of action potentials (APs) was achieved with a blue light-activated channelrhodopsin (CheRiff). Fluorescent readout of transmembrane potential was enabled by an Archaerhodopsin variant (QuasAr2). QuaAr2 was also combined with the calcium indicator protein rCaMP to create a dual-reporter for simultaneous detection of APs and calcium transients. In neurons, we measured both intrinsic neuronal excitability and synaptic activity from thousands of neurons with single-cell spatial resolution, millisecond temporal resolution and vastly higher throughput than manual patch clamp. In cardiomyocytes, we measured both action potential and calcium transient properties under optically paced conditions, enabling extraction of waveform features as well as conduction properties. The Optopatch platform rapidly and robustly characterizes phenotypic response and provides an information-rich readout of pharmacological changes to the associated electrophysiology. This approach will prove effective for profiling of neurons and cardiomyocytes from individual patients and opens the path towards precision medicine.