Date Published: January 31, 2014
Publisher: Public Library of Science
Author(s): Debjyoti Bandyopadhyay, Austin Cyphersmith, Jairo A. Zapata, Y. Joseph Kim, Christine K. Payne, Xiaochen Wang.
Lysosomes are membrane-bound organelles responsible for the transport and degradation of intracellular and extracellular cargo. The intracellular motion of lysosomes is both diffusive and active, mediated by motor proteins moving lysosomes along microtubules. We sought to determine how lysosome diameter influences lysosome transport. We used osmotic swelling to double the diameter of lysosomes, creating a population of enlarged lysosomes. This allowed us to directly examine the intracellular transport of the same organelle as a function of diameter. Lysosome transport was measured using live cell fluorescence microscopy and single particle tracking. We find, as expected, the diffusive component of intracellular transport is decreased proportional to the increased lysosome diameter. Active transport of the enlarged lysosomes is not affected by the increased lysosome diameter.
Lysosomes are membrane-bound organelles essential for endocytosis, phagocytosis, and autophagy –. Fusion of endosomes, phagosomes, and autophagosomes with lysosomes exposes the cargo in these organelles to the hydrolytic enzymes and low pH of the lysosomes resulting in the degradation of cargo. Like many organelles, the diameters of lysosomes are heterogeneous. The canonical lysosome diameter ranges from 50 nm to 500 nm . A fundamental question is how the size of the lysosome affects intracellular transport.
The goal of this research was to determine how lysosome diameter affects lysosome transport. Early research in the field of intracellular transport examined transport of small (100 nm – 200 nm), medium (200 nm – 600 nm), and large (800 nm –5 µm) organelles in squid axons and found slower mean velocities for the larger organelles . However, these were not all the same organelles. The largest organelles were mitochondria, the smaller organelles were not identified. Incubating cells with sucrose results in enlarged lysosomes (Figure 1), allowing us to compare transport of identical organelles with different diameters within live cells.