Fig. 4: Lipid-droplets (LDs) act as scaffolds for glycogen synthesis.

A Representative hepatocyte SEM micrographs showing LDs and clustering of glycogen crystals around LDs in overnight-fasted mice or in mice at 1-, 2- and 4-hour [U-¹³C₆]-glucose-infusion timepoints. Blue arrows point to glycogen depots. B Representative electron tomography (eTOMO) micrographs of mouse hepatocytes after 1 hour of [U-¹³C]-glucose infusion, with mitochondria (Mito), lysosomes (Lys), lipid droplets (LD) in view. Yellow, blue, and green arrowheads point to the location of LD-tethered glycogen, smooth endoplasmic reticulum (ER), and rough ER, respectively. C, D 3D reconstruction of eTOMO volumes and organelle structures showing the close association between glycogen, ER, and LD. Two partial reconstructions of mitochondria and mitochondria cristae are also shown. E, F Representative scanning electron microscopy (SEM) images of a C. elegans intestinal cell and human male hepatocyte, respectively. SEM insets highlight the position of a single lipid droplet and blue arrowheads indicate the location of LD-associated glycogen particles. In the human micrograph, yellow arrowheads mark the position of smooth endoplasmic reticulum (sER) compartments. G Graph displaying reconstructed volume of n = 150 glycogen particles imaged with eTOMO and ranked according to their volume (blue dots). Dotted black line indicates the fit of an exponential curve with an observed r² = 0.946. Insets a, b, and c show representative glycogen particles of different sizes, and their location are marked in the micrographs shown in (B). In (B), scale bar = 50 nanometers, in (C, D and F), 100 nanometers. In (A, B and E, F), data representative of n = 3-to-5 mice per condition.