Department of Neurobiology, Harvard Medical School
Metabolic pathways provide essential energy and building blocks for the function of all cells, and dysregulation of these pathways is a central feature of cancer, diabetes, and obesity. The components of core metabolic pathways such as glycolysis have been very well understood for decades, but there are still major gaps in our understanding of their integrated behavior and regulation in the context of living cells.
A major challenge to understanding normal metabolism and its dysregulation in human disease is that metabolic behavior can vary dramatically from cell to cell, and over time within a single cell. For example, metabolic state can differ radically between neighboring cell types in a tissue: between neurons and astrocytes, or between a single metastatic cancer cell and the surrounding normal cells. Such spatial differences as well as dynamic changes in metabolism within a single cell are invisible to biochemical methods or even modern metabolomic methods, which require disruption of the living cell and homogenization of tissue.
Fluorescent sensors of metabolism, engineered by combining fluorescent proteins with metabolite binding proteins, can address this challenge by enabling us to monitor key metabolites in real time, in single living cells, or in hundreds of cells in parallel. We have developed novel sensors for two key metabolites (ATP and NADH), in order to address specific questions about how metabolism influences neuronal ion channels and can reduce susceptibility to epileptic seizures. They also offer a new window into the dynamic changes of metabolism in many other cell types.
Our lab is working to develop a series of metabolite biosensors, which can report the dynamics of metabolism in individual cells and can be used to complement the powerful tools of mass spec metabolomics. Using structural and functional data on metabolite binding proteins, we are designing and building new fluorescent metabolite sensors by gene synthesis, mutagenesis, and screening/optimization. We use state-of-the-art two-photon scanning microscopy and fluorescence lifetime imaging to image the sensors in living tissue (e.g. brain slices, and in the near future, in vivo recordings of rodent brain).
We also study how metabolic manipulation, through either dietary change or genetic alteration, can alter brain excitability, using mouse models and brain slice electrophysiology.
Díaz-García CM, Mongeon R, Lahmann C, Koveal D, Zucker H, Yellen G. Neuronal Stimulation Triggers Neuronal Glycolysis and Not Lactate Uptake. Cell Metab 2017; 26:361-374.e4.
Lutas A, Lahmann C, Soumillon M, Yellen G. The leak channel NALCN controls tonic firing and glycolytic sensitivity of substantia nigra pars reticulata neurons. Elife. 2016 May 13;5. pii: e15271. doi: 10.7554/eLife.15271.
Mongeon R, Venkatachalam V, Yellen G. Cytosolic NADH-NAD+ redox visualized in brain slices by two-photon fluorescence lifetime biosensor imaging. Antioxid Redox Signal. 2016 Mar 18.
Yellen G, Mongeon R. Quantitative two-photon imaging of fluorescent biosensors. Curr Opin Chem Biol. 2015 Jun 12;27:24-30.
Masia R, Krause DS, Yellen G. The inward rectifier potassium channel Kir2.1 is expressed in mouse neutrophils from bone marrow and liver. Am J Physiol Cell Physiol. 2015 Feb 1;308(3):C264-76.
Lutas A, Birnbaumer L, Yellen G. Metabolism regulates the spontaneous firing of substantia nigra pars reticulata neurons via KATP and nonselective cation channels. J Neurosci. 2014 Dec 3;34(49):16336-47.
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