Venue: Neurocentre Magendie – Conference room
Department of Chemistry of the University of Tokyo
Invited by Giovanni Marsicano (Neurocentre Magendie)
LACCO series: Genetically encoded fluorescent L-lactate biosensors for neuroscience
Organisms on Earth produce biologically-useful energy by catabolizing glucose to pyruvate which, in the absence of oxygen, is normally converted into L-lactate. Traditionally, L-lactate has been considered “waste” by-products of glucose metabolism. However, growing evidence suggests that L-lactate is better considered a biological “fuel currency”, that can be shuttled from cell-to-cell and plays a central role in the energy supply for organisms. For example, the astrocyte-to-neuron lactate shuttle (ANLS) hypothesis proposes that astrocytes metabolize glucose to produce L-lactate which is then released to the extracellular environment and taken up by neurons. In neurons, L-lactate is converted to pyruvate which is fed into the tricarboxylic acid cycle (TCA) for production of adenosine triphosphate (ATP) which provides energy necessary to sustain heightened neural activity. The ANLS hypothesis remains a controversial mystery, with recent reports of evidence both for and against it.
Fluorescent proteins (FPs) have been proven to be versatile scaffolds for development of biosensors (protein constructs that change their fluorescence intensity in response to changes in the environment). Specifically, GCaMP, a calcium ion (Ca2+) sensor based on green FP (GFP) and Ca2+ sensing domains, has been widely employed to monitor neural activities in live model organisms. In addition to GCaMP, various FP-based biosensors for non-Ca2+ target have been developed. However, few sensors have sensitivity as high as GCaMP, hampering their wide application in vivo.
Herein, we show that directed protein evolution can enable the engineering of FP-based biosensors for an important metabolite L-lactate with high sensitivity comparable to GCaMP. This study provides a powerful new optical toolbox, LACCO series, for the investigation of extracellular and intracellular L-lactate in neurons and astrocytes. We anticipate that the LACCO series will play a central role in investigations of L-lactate shuttles, including the controversial ANLS hypothesis.
Dr. Yusuke Nasu is an assistant professor in Robert E. Campbell’s lab at The University of Tokyo. His work focuses specifically on the protein engineering to develop high-performance genetically encoded fluorescent biosensors for neuroscience. In collaboration with neuroscientists, he aims to address mysteries in brain by applying these biosensors to living model animals.