Showing papers by "Fumihiko Urano published in 2015"

Beta cells transfer vesicles containing insulin to phagocytes for presentation to T cells.

Abstract: Beta cells from nondiabetic mice transfer secretory vesicles to phagocytic cells. The passage was shown in culture studies where the transfer was probed with CD4 T cells reactive to insulin peptides. Two sets of vesicles were transferred, one containing insulin and another containing catabolites of insulin. The passage required live beta cells in a close cell contact interaction with the phagocytes. It was increased by high glucose concentration and required mobilization of intracellular Ca2+. Live images of beta cell-phagocyte interactions documented the intimacy of the membrane contact and the passage of the granules. The passage was found in beta cells isolated from islets of young nonobese diabetic (NOD) mice and nondiabetic mice as well as from nondiabetic humans. Ultrastructural analysis showed intraislet phagocytes containing vesicles having the distinct morphology of dense-core granules. These findings document a process whereby the contents of secretory granules become available to the immune system.

IRE1 prevents endoplasmic reticulum membrane permeabilization and cell death under pathological conditions

Abstract: The endoplasmic reticulum (ER) has emerged as a critical regulator of cell survival. IRE1 is a transmembrane protein with kinase and RNase activities that is localized to the ER and that promotes resistance to ER stress. We showed a mechanism by which IRE1 conferred protection against ER stress-mediated cell death. IRE1 signaling prevented ER membrane permeabilization mediated by Bax and Bak and cell death in cells experiencing ER stress. Suppression of IRE1 signaling triggered by its kinase activity led to the accumulation of the BH3 domain-containing protein Bnip3, which in turn triggered the oligomerization of Bax and Bak in the ER membrane and ER membrane permeabilization. Consequently, in response to ER stress, cells deficient in IRE1 were susceptible to leakage of ER contents, which was associated with the accumulation of calcium in mitochondria, oxidative stress in the cytosol, and ultimately cell death. Our results reveal a role for IRE1 in preventing a cell death-initializing step that emanates from the ER and provide a potential target for treating diseases characterized by ER stress, including diabetes and Wolfram syndrome.

Research resource: Monitoring endoplasmic reticulum membrane integrity in β-cells at the single-cell level.

Abstract: Endoplasmic reticulum (ER) membrane integrity is an emerging target for human chronic diseases associated with ER stress. Despite the underlying importance of compromised ER membrane integrity in disease states, the entire process leading to ER membrane permeabilization and cell death is still not clear due to technical limitations. Here we describe a novel method for monitoring ER membrane integrity at the single-cell level in real time. Using a β-cell line expressing ER-targeted redox sensitive green fluorescent protein, we could identify a β-cell population undergoing ER membrane permeabilization induced by palmitate and could monitor cell fate and ER stress of these cells at the single-cell level. Our method could be used to develop a novel therapeutic modality targeting the ER membrane for ER-associated disorders, including β-cell death in diabetes, neurodegeneration, and Wolfram syndrome.

10. Dantrolene as a Therapeutic Option for Wolfram Syndrome (134-OR)

Abstract: Wolfram syndrome is a genetic disorder characterized by diabetes and neurodegeneration and considered as an endoplasmic reticulum (ER) disease. Despite the underlying importance of ER dysfunction in Wolfram syndrome and the identification of two causative genes, WFS1 and WFS2, a molecular mechanism linking the ER to death of β cells and neurons was not clear. We have recently discovered that calpain 2 is involved in death of β cells and neurons in Wolfram syndrome.