The Photoswitchable Cannabinoid Azo-HU308 Enables Optical Control of Ca2+ Signaling in Pancreatic β-Cells via a Non CB2 TRPC Channel Mechanism

Background and PurposeCa2+ plays a critical role in regulating insulin secretion from pancreatic {beta}-cells, a process modulated by various cell surface receptors, including cannabinoid receptors (CBRs). However, our understanding of cannabinoid signaling in {beta}-cells is complicated by the intricate pharmacology of cannabinoid ligands and their inherent hydrophobicity, which hinders precise control of receptor activation. This study aims to investigate the effects of the light-activatable CB2 receptor agonist, azo-HU308, on {beta}-cell Ca2+ dynamics. Experimental ApproachWe employ fluorescent Ca2+ imaging in INS-1 832/13 (INS-1) {beta}-cells to measure Ca2+ transients induced by azo-HU308 and photoactivation with UV-A light. We then apply a pharmacological screen using a various CBR and TRP channel antagonists to determine the mechanism by which azo-HU308 enables optical control of {beta}-cell Ca2+ levels. Key ResultsWe observed that azo-HU308 triggers a robust increase in intracellular Ca2+ when isomerized to the cis-form with UV-A light. The effect was repeatable over multiple cycles of irradiation and gradually desensitized on each sequential UV-light pulse. A pharmacological screen determined that the Ca2+ increase was not due to CB2 receptor activation and Ca2+ release from intracellular stores, but rather influx of extracellular Ca2+ through TRPC channels. Conclusions and Implicationsazo-HU308 enables robust, repeatable stimulation of Ca2+ in INS-1 pancreatic {beta}-cells when triggered by UV-A light. This study presents a novel tool to optically control {beta}-cell Ca2+ dynamics, and sheds light on a new mechanism by which synthetic cannabinoids affect Ca2+ signaling through non-GPCR targets.