Synthesis and application of a photocaged-l-lactate for studying the biological roles of l-lactate

L-Lactate, once considered a metabolic waste product of glycolysis, is now recognized as a vitally important metabolite and signaling molecule in multiple biological pathways. However, exploring L-lactate's emerging intra- and extra-cellular roles is hindered by a lack of tools to perturb L-lactate concentration intracellularly and extracellularly. Photocaged compounds are a powerful way to introduce bioactive molecules with spatiotemporal precision using illumination. Here, we report the development of a photocaged derivative of L-lactate, 4-methoxy-7-nitroindolinyl-L-lactate (MNI-L-lac), that releases L-lactate upon illumination. We validated MNI-L-lac in cell culture by demonstrating that the photorelease of L-lactate elicits a response from genetically encoded extra- and intracellular L-lactate biosensors (eLACCO1, eLACCO2.1, R-iLACCO1.2). To demonstrate the utility of MNI-L-lac, we employed the photorelease of L-lactate to activate G protein-coupled receptor 81 (GPR81), as revealed by the inhibition of adenylyl cyclase activity and concomitant decrease of cAMP. These results indicate that MNI-L-lac may be useful for perturbing the concentration of endogenous L-lactate in order to investigate L-lactate's roles in metabolic and signaling pathways.