Functional and mechanistic analysis of microtubule network architecture in pancreatic beta cells

Abstract

In pancreatic beta cells, molecular motors use cytoskeletal polymers microtubules as tracks for intracellular transport of secretory insulin granules. Beta-cell microtubule network has a complex architecture, which allows to provide insulin granules at the cell periphery for rapid secretion response, yet to avoid over-secretion and subsequent hypoglycemia. We have previously characterized a peripheral sub-membrane microtubule array, which is critical for withdrawal of excessive insulin granules from the secretion sites. Microtubules in beta cells originate at the Golgi in the cell interior, and how the peripheral array is formed is unknown. Using real-time imaging and photo-kinetics approaches in clonal mouse pancreatic beta cells MIN6, we now demonstrate that kinesin KIF5B, a motor protein with a capacity to transport microtubules as cargos, slides existing microtubules to the cell periphery and aligns them to each other along the plasma membrane. Moreover, like many physiological beta-cell features, microtubule sliding is facilitated by a high glucose stimulus. We have previously shown that in high glucose sub-membrane MT array is destabilized to allow for robust secretion. This work reported here indicate that MT sliding is another integral part of glucose-triggered microtubule remodeling, likely replacing destabilized peripheral microtubules to prevent their loss over time and beta-cell malfunction.