海馬におけるORP150の発現が遅延神経細胞死を抑制する

取得学位 : 博士（医学）, 学位授与番号 : 医博乙第1569号, 学位授与年月日 : 平成14年12月18日, 学位授与大学 : 金沢大

Transmission of cell stress from endoplasmic reticulum to mitochondria: enhanced expression of Lon protease

The rat homologue of a mitochondrial ATP-dependent protease Lon was cloned from cultured astrocytes exposed to hypoxia. Expression of Lon was enhanced in vitro by hypoxia or ER stress, and in vivo by brain ischemia. These observations suggested that changes in nuclear gene expression (Lon) triggered by ER stress had the potential to impact important mitochondrial processes such as assembly and/or degradation of cytochrome c oxidase (COX). In fact, steady-state levels of nuclear-encoded COX IV and V were reduced, and mitochondrial-encoded subunit II was rapidly degraded under ER stress. Treatment of cells with cycloheximide caused a similar imbalance in the accumulation of COX subunits, and enhanced mRNA for Lon and Yme1, the latter another mitochondrial ATP-dependent protease. Furthermore, induction of Lon or GRP75/mtHSP70 by ER stress was inhibited in PERK (−/−) cells. Transfection studies revealed that overexpression of wild-type or proteolytically inactive Lon promoted assembly of COX II into a COX I–containing complex, and partially prevented mitochondrial dysfunction caused by brefeldin A or hypoxia. These observations demonstrated that suppression of protein synthesis due to ER stress has a complex effect on the synthesis of mitochondrial-associated proteins, both COX subunits and ATP-dependent proteases and/or chaperones contributing to assembly of the COX complex

Expression of the endoplasmic reticulum molecular chaperone (ORP150) rescues hippocampal neurons from glutamate toxicity

金沢大学医薬保健研究域医学系A series of events initiated by glutamate-receptor interaction perturbs cellular homeostasis resulting in elevation of intracellular free calcium and cell death. Cells subject to such environmental change express stress proteins, which contribute importantly to maintenance of metabolic homeostasis and viability. We show that an inducible chaperone present in endoplasmic reticulum (ER), the 150-kDa oxygen-regulated protein (ORP150), is expressed both in the human brain after seizure attack and in mouse hippocampus after kainate administration. Using mice heterozygous for ORP150 deficiency, exposure to excitatory stimuli caused hippocampal neurons to display exaggerated elevation of cytosolic calcium accompanied by activation of μ-calpain and cathepsin B, as well as increased vulnerability to glutamate-induced cell death in vitro and decreased survival to kainate in vivo. In contrast, targeted neuronal overexpression of ORP150 suppressed each of these events and enhanced neuronal and animal survival in parallel with diminished seizure intensity. Studies using cultured hippocampal neurons showed that ORP150 regulates cytosolic free calcium and activation of proteolytic pathways causing cell death in neurons subject to excitatory stress. Our data underscore a possible role for ER stress in glutamate toxicity and pinpoint a key ER chaperone, ORP150, which contributes to the stress response critical for neuronal survival

Dynamic Assembly/Disassembly of Staphylococcus aureus FtsZ Visualized by High-Speed Atomic Force Microscopy

FtsZ is a key protein in bacterial cell division and is assembled into filamentous architectures. FtsZ filaments are thought to regulate bacterial cell division and have been investigated using many types of imaging techniques such as atomic force microscopy (AFM), but the time scale of the method was too long to trace the filament formation process. Development of high-speed AFM enables us to achieve sub-second time resolution and visualize the formation and dissociation process of FtsZ filaments. The analysis of the growth and dissociation rates of the C-terminal truncated FtsZ (FtsZt) filaments indicate the net growth and dissociation of FtsZt filaments in the growth and dissociation conditions, respectively. We also analyzed the curvatures of the full-length FtsZ (FtsZf) and FtsZt filaments, and the comparative analysis indicated the straight-shape preference of the FtsZt filaments than those of FtsZf. These findings provide insights into the fundamental dynamic behavior of FtsZ protofilaments and bacterial cell division

Expression of the endoplasmic reticulum molecular chaperone (ORP150) rescues hippocampal neurons from glutamate toxicity

A series of events initiated by glutamate-receptor interaction perturbs cellular homeostasis resulting in elevation of intracellular free calcium and cell death. Cells subject to such environmental change express stress proteins, which contribute importantly to maintenance of metabolic homeostasis and viability. We show that an inducible chaperone present in endoplasmic reticulum (ER), the 150-kDa oxygen-regulated protein (ORP150), is expressed both in the human brain after seizure attack and in mouse hippocampus after kainate administration. Using mice heterozygous for ORP150 deficiency, exposure to excitatory stimuli caused hippocampal neurons to display exaggerated elevation of cytosolic calcium accompanied by activation of μ-calpain and cathepsin B, as well as increased vulnerability to glutamate-induced cell death in vitro and decreased survival to kainate in vivo. In contrast, targeted neuronal overexpression of ORP150 suppressed each of these events and enhanced neuronal and animal survival in parallel with diminished seizure intensity. Studies using cultured hippocampal neurons showed that ORP150 regulates cytosolic free calcium and activation of proteolytic pathways causing cell death in neurons subject to excitatory stress. Our data underscore a possible role for ER stress in glutamate toxicity and pinpoint a key ER chaperone, ORP150, which contributes to the stress response critical for neuronal survival