Within the cytosol of the cell, glucose is converted into pyruvate that is used as a fuel for mitochondria. The latter supply the cell with energy in the form of ATP (adenosine triphosphate) and also play an important role in many other cellular functions like calcium homeostasis. Glucose-to-pyruvate conversion is mediated by the glycolysis pathway, which also generates ATP. Interestingly, the balance between glycolytic and mitochondrial ATP production differs between cell types and metabolic conditions. Moreover, this balance is often altered during pathological conditions.
In this paper, researchers from the Dept. of Biochemistry (Dania C. Liemburg-Apers (photo up), Peter H.G.M. Willems, Werner J.H. Koopman (photo below) and Pharmacology/Toxicology (Tom J.J. Schirris, Frans M.G. Russel) aimed to gain insight into the kinetic properties of this adaptive mechanism. This work was selected to appear on the cover of Biophysical Journal and features on the official Blog of the Biophysical Society (https://biophysicalsociety.wordpress.com/).
A strategy was presented to analyze the uptake and consumption rate of glucose in single living muscle cells (C2C12 cells) using a FRET-based glucose nanosensor (FLII), which consisted of a glucose binding domain sandwiched between two fluorescent proteins (CFP and Citrine). As exemplified by the cover illustration, glucose binding to FLII triggers a conformational change that increases the energy transfer from CFP to Citrine. This is reflected by an increase in Citrine fluorescence intensity (CitrineFRET; upper panel), paralleled by a decrease in CFP fluorescence intensity (middle panel). As a consequence, the ratio between these signals (CitrineFRET/CFP; lower panel) increases and can be used as a readout of free cytosolic glucose concentration. Calibration of the ratio signal and the use of specific inhibitors of glucose uptake/consumption allowed construction of a quantitative mathematical model to predict the steady-state glucose flux (in mM/min). We demonstrated that this flux was rapidly increased upon mitochondrial malfunction, and that this increase fully compensated for the loss in mitochondrial ATP production. The latter suggests that cells can alter the balance between glycolytic and mitochondrial ATP production on demand, to prevent energy crisis and maintain their viability.
Paper: Liemburg-Apers, D.C., Schirris, T.J.J, Russel, F.G.M., Willems, P.H.G.M. and Koopman, W.J.H. (2015) Mitoenergetic dysfunction triggers a rapid compensatory increase in steady-state glucose flux. Biophys. J. 109:1372-1386.
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