RESUMEN
Mitochondria require nicotinamide adenine dinucleotide (NAD+) to carry out the fundamental processes that fuel respiration and mediate cellular energy transduction. Mitochondrial NAD+ transporters have been identified in yeast and plants1,2, but their existence in mammals remains controversial3-5. Here we demonstrate that mammalian mitochondria can take up intact NAD+, and identify SLC25A51 (also known as MCART1)-an essential6,7 mitochondrial protein of previously unknown function-as a mammalian mitochondrial NAD+ transporter. Loss of SLC25A51 decreases mitochondrial-but not whole-cell-NAD+ content, impairs mitochondrial respiration, and blocks the uptake of NAD+ into isolated mitochondria. Conversely, overexpression of SLC25A51 or SLC25A52 (a nearly identical paralogue of SLC25A51) increases mitochondrial NAD+ levels and restores NAD+ uptake into yeast mitochondria lacking endogenous NAD+ transporters. Together, these findings identify SLC25A51 as a mammalian transporter capable of importing NAD+ into mitochondria.
Asunto(s)
Mitocondrias/metabolismo , Proteínas Mitocondriales/metabolismo , NAD/metabolismo , Animales , Transporte Biológico , Línea Celular , Respiración de la Célula/genética , Prueba de Complementación Genética , Humanos , Ratones , Mitocondrias/genética , Mitocondrias/patología , Proteínas Mitocondriales/deficiencia , Proteínas Mitocondriales/genética , Proteínas de Transporte de Nucleótidos/genética , Proteínas de Transporte de Catión Orgánico/deficiencia , Proteínas de Transporte de Catión Orgánico/genética , Saccharomyces cerevisiae/citología , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genéticaRESUMEN
Flow cytometry approaches combined with a genetically encoded targeted fluorescent biosensor are used to determine the subcellular compartmental availability of the oxidized form of nicotinamide adenine dinucleotide (NAD+ ). The availability of free NAD+ can affect the activities of NAD+ -consuming enzymes such as sirtuin, PARP/ARTD, and cyclic ADPR-hydrolase family members. Many methods for measuring the NAD+ available to these enzymes are limited because they cannot determine free NAD+ as it exists in various subcellular compartments distinctly from bound NAD+ or NADH. Here, an approach to express the sensor in mammalian cells, monitor NAD+ -dependent fluorescence intensity changes using flow cytometry approaches, and analyze data obtained is described. The benefit of flow cytometry approaches with the NAD+ sensor is the ability to monitor compartmentalized free NAD+ fluctuations simultaneously within many cells, which greatly facilitates analyses and calibration. © 2018 by John Wiley & Sons, Inc.