Visualizing physiological parameters in cells and tissues using genetically encoded indicators for metabolites.

The study of metabolism is undergoing a renaissance. Since the year 2002, over 50 genetically-encoded fluorescent indicators (GEFIs) have been introduced, capable of monitoring metabolites with high spatial/temporal resolution using fluorescence microscopy. Indicators are fusion proteins that change their fluorescence upon binding a specific metabolite.

Imaging of the Lactate/Pyruvate Ratio Using a Genetically Encoded Förster Resonance Energy Transfer Indicator.

The ratio between the cytosolic concentrations of lactate and pyruvate is a direct readout of the balance between glycolysis and mitochondrial oxidative metabolism. Current approaches do not allow detection of the lactate/pyruvate ratio in a single readout with high spatial/temporal resolution in living systems. Using a Förster resonance energy transfer (FRET)-based screening strategy, we found that the orphan transcriptional factor from is an endogenous sensor of the lactate/pyruvate ratio, suitable for use as a binding moiety to develop a lactate/pyruvate ratio FRET-based genetically encoded indicator, Lapronic.

Fluid Brain Glycolysis: Limits, Speed, Location, Moonlighting, and the Fates of Glycogen and Lactate.

Glycolysis is the core of intermediate metabolism, an ancient pathway discovered in the heydays of classic biochemistry. A hundred years later, it remains a matter of active research, clinical interest and is not devoid of controversy. This review examines topical aspects of glycolysis in the brain, a tissue characterized by an extreme dependence on glucose.

A highly responsive pyruvate sensor reveals pathway-regulatory role of the mitochondrial pyruvate carrier MPC.

Mitochondria generate ATP and building blocks for cell growth and regeneration, using pyruvate as the main substrate. Here we introduce PyronicSF, a user-friendly GFP-based sensor of improved dynamic range that enables real-time subcellular quantitation of mitochondrial pyruvate transport, concentration and flux. We report that cultured mouse astrocytes maintain mitochondrial pyruvate in the low micromolar range, below cytosolic pyruvate, which means that the mitochondrial pyruvate carrier MPC is poised to exert ultrasensitive control on the balance between respiration and anaplerosis/gluconeogenesis.

Monocarboxylate transporter 4 (MCT4) is a high affinity transporter capable of exporting lactate in high-lactate microenvironments.

Monocarboxylate transporter 4 (MCT4) is an H-coupled symporter highly expressed in metastatic tumors and at inflammatory sites undergoing hypoxia or the Warburg effect. At these sites, extracellular lactate contributes to malignancy and immune response evasion. Intriguingly, at 30-40 mm, the reported of MCT4 for lactate is more than 1 order of magnitude higher than physiological or even pathological lactate levels.