Mitochondria-targeted melatonin photorelease supports the presence of melatonin MT1 receptors in mitochondria inhibiting respiration

Abstract

The presence of signaling-competent G protein-coupled receptors in intracellular compartments is increasingly recognized. Recently, the presence of G_i/o protein-coupled melatonin MT₁ receptors in mitochondria has been revealed, in addition to the plasma membrane. Melatonin is highly cell permeant, activating plasma membrane and mitochondrial receptors equally. Here, we present MCS-1145, a melatonin derivative bearing a triphenylphosphonium cation for specific mitochondrial targeting and a photocleavable o-nitrobenzyl group releasing melatonin upon illumination. MCS-1145 displayed low affinity for MT₁ and MT₂ but spontaneously accumulated in mitochondria, where it was resistant to washout. Uncaged MCS-1145 and exogenous melatonin recruited β-arrestin 2 to MT₁ in mitochondria and inhibited oxygen consumption in mitochondria isolated from HEK293 cells only when expressing MT₁ and from mouse cerebellum of WT mice but not from MT₁-knockout mice. Overall, we developed the first mitochondria-targeted photoactivatable melatonin ligand and demonstrate that melatonin inhibits mitochondrial respiration through mitochondrial MT₁ receptors.

Keywords: G protein-coupled receptors; intracellular signaling; melatonin; melatonin receptors; mitochondria; mitochondria-targeted caged melatonin ligand; mitochondrial respiration; photopharmacology.