Imaging liver and brain glycogen metabolism at the nanometer scale

In mammals, glycogen synthesis and degradation are dynamic processes regulating blood and cerebral glucose-levels within a well-defined physiological range. Despite the essential role of glycogen in hepatic and cerebral metabolism, its spatiotemporal distribution at the molecular and cellular level is unclear. By correlating electron microscopy and ultra-high resolution ion microprobe (NanoSIMS) imaging of tissue from fasted mice injected with 13C-labeled glucose, we demonstrate that liver glycogenesis initiates in the hepatocyte perinuclear region before spreading toward the cell membrane. In the mouse brain, we observe that 13C is inhomogeneously incorporated into astrocytic glycogen at a rate ~ 25 times slower than in the liver, in agreement with prior bulk studies. This experiment, using temporally resolved, nanometer-scale imaging of glycogen synthesis and degradation, provides greater insight into glucose metabolism in mammalian organs and shows how this technique can be used to explore biochemical pathways in healthy and diseased states.From the Clinical EditorBy correlating electron microscopy and ultra-high resolution ion microprobe imaging of tissue from fasting mice injected with 13C-labeled glucose, the authors demonstrate a method to image glycogen metabolism at the nanometer scale.

We present time-resolved nanometer-scale images of hepatic and cerebral glycogen formation following the injection of 13C-labeled glucose into awake animals. It is based on the combination of electron microscopy and ultra-high spatial resolution ion microprobe (NanoSIMS) imaging, which provides maps of isotopic ratios in thin-sections of biological tissue with a spatial resolution around 100 nm, enough to resolve all cellular compartments. These techniques permit precise localization of glucosyl residues forming within subcellular compartments. Spatially resolved, quantitative 13C/12C ratio mapping allows tracing precisely where, when, and how much glycogen is formed within a single cell during an isotopic labeling experiment.Figure optionsDownload high-quality image (71 K)Download as PowerPoint slide