TOP ＞ Symposia

Symposia Physiological and pathological controls of the central nervous system by multifunctional organelle-endoplasmic reticulum／多機能性細胞小器官－小胞体による脳・神経系の生理病態制御 1S2-1 Enhancement of inflammatory response by ATF6alpha in the activated microglia Osamu Hori Dept Neuroanat. Grad Sch Medi Sci, Kanazawa Univ Activating transcription factor 6alpha (ATF6alpha is a transducer of the unfolded protein response (UPR) required for the functioning of the endoplasmic reticulum (ER). We have reported critical roles of this molecule in both neuronal survival and glial activation in different pathological situations. In this symposium, we report the activation status and roles of ATF6alpha after hypoglossal nerve axotomy (HNA), a peripheral nerve-injury model that is characterized by slowly progressive motor neuron death and glial activation in mice. The expression of ATF6alpha-target molecular chaperones was observed in hypoglossal neurons under normal conditions, and it was extensively increased in the activated microglia after HNA. Comparative analysis using Atf6alpha+/+and Atf6alpha-/- mice revealed no significant difference in the level of early neuronal damage after HNA. However, microglial activation, reflected by enlarged size of Iba1-positive cells as well as the induction of inflammatory genes, was repressed in Atf6alpha-/- mice after HNA. The number of CD68-positive microglia was also diminished in Atf6alpha-/- mice after HNA. Furthermore, HNA-induced motor neuron death in the chronic phase was reduced in Atf6alpha-/- mice. These results suggest that regulation of ATF6α may be critical for controlling microglial activation and protecting motor neurons from nerve injury-induced cell death. 1S2-2 Molecular mechanism of neurodegenerative diseases triggered by the dysfunction of ER quality control Hideki Nishitoh Lab Biochem and Mol Biol, Dept Med Sci, Univ Miyazaki The endoplasmic reticulum (ER) is an organelle in which newly synthesized secretory and transmembrane proteins are assembled and folded into their correct tertiary structures. The accumulation of misfolded proteins disrupts the function of the ER and induces ER stress. Mammalian cells possess a highly conserved signaling pathway, termed the unfolded protein response (UPR), to adapt and respond to ER stress conditions. However, in the case of prolonged ER stress or UPR malfunction, cell death signaling is activated. Dysfunction of the UPR causes numerous conformational diseases, including familial or sporadic neurodegenerative diseases. We have previously reported the importance of ER quality control system to maintain the function of neurons. Especially, the dysfunction of ER-associated degradation leads to many of neurodegenerative diseases, such as polyglutamine diseases (Genes Dev, 2002), dementing disorder (Cell Death Differ, 2005) and amyotrophic lateral sclerosis (Genes Dev, 2008; Hum Mol Genet, 2016). In this symposium, I would like to discuss the point that the UPR and ER stress-induced signaling pathways may serve as potent therapeutic targets of ER stress-related neurodegenerative diseases. 1S2-3 Dendritic expansion and spine formation regulated by signaling pathways of unfolded protein response Atsushi Saito1，Kazunori Imaizumi2 1Dept. Stress Protein., Inst. BioMed. Health Sci., Hiroshima Univ.，2Dept. Biochem., Inst. BioMed. Health Sci., Hiroshima Univ. Endoplasmic reticulum (ER) stress transducers IRE1, PERK and ATF6 recognize unfolded proteins and transduce signals from ER to cytoplasm or nucleus (unfolded protein response: UPR). The signaling is involved not only in dealing with unfolded proteins but also in biological regulations. The dendritic ER network is complexly extended from cell soma to distal dendrites of neurons, indicating that ER functions may orchestrate local events contributing to dendritic capabilities. We focused on dendritic machineries mediated by ER-derived signaling including UPR. To assess the induction of UPR in response to neuronal activities, primary cultured mouse hippocampal neurons were pretreated with tetrodotoxin subsequently the washout to induce spontaneous excitatory synaptic activities. The phosphorylation levels of IRE1 and PERK were transiently upregulated after the washout. The activation of these ER stress transducers was observed at post-synaptic sites. We found the reduction of the phosphorylation levels by inhibiting calcium ion release from ER. These data suggest that the acceleration of the calcium ion release and its depletion in ER lumen by the excitatory synaptic activation triggers the induction of UPR at post-synaptic sites. The blocking of UPR by the knockdown of UPR-related genes using lentiviruses expressing shRNA inhibited the extension and branching of dendrites. Furthermore, the impaired dendritic spine formation was shown in these knockdown-neurons. Immunofluorescence analysis in the knockdown-neurons revealed that the ER failed to elongate and invaginate into spine segments. Thus, UPR signaling may regulate the development of intricately branched dendrites and the dendritic spine formation through the spatio-temporal fine-tuning of the dendritic ER-dynamics. 1S2-4 Control of pathological condition via endoplasmic reticulum stress by Sigma 1 receptor Takashi Kudo Dept Mental Heaith Promotion, Grad Sch Med, Osaka Univ Since the sigma 1 receptor (Sig1R) is located in the mitochondria-associated endoplasmic reticulum (ER) membrane (MAM), we have examined the relationship between Sig1R and ER stress. First, we found that ER stress induces expression of Sig1R. Furthermore, it was revealed that this expression occurs downstream of the PERK-ATF4 pathway, one of the unfolded protein responses (UPR).What is the physiological significance of Sig1R induced by this ER stress? As the answer, it was revealed that cells with high expression by transfection of Sig1R show anti-ER stress effect. This is considered to be the physiological role of Sig1R. In some neuropsychiatric disorders such as schizophrenia, genetic polymorphisms are reported in the promoter region of Sig1R. In our reporter assay with these polymorphisms, the induction of Sig1R by ER stress was decreased, suggesting that the physiological role of Sig1R was attenuated leading to these onset.Fluvoxamine is a conventional SSRI, but it is known for its high affinity with Sig1R. Our study revealed that fluvoxamine induces expression of Sig1R. It was revealed that the induction occurs by directly acting on ATF4 of the PERK-ATF4 pathway. It was found that induction of Sig1R expression by fluvoxamine leads to anti-ER stress effect as expected. The effect was proved by not only neuronal cell experiments but also the prevention of infarction development in mice with cerebral ischemia.Thus, it is shown that Sig1R is a player who is responsible for pathological condition control associated with ER stress. 1S2-5 Collapse of mitochondria-associated membrane as common pathomechanism for ALS Koji Yamanaka Res Inst Environ Med, Nagoya Univ Contacting site of endoplasmic reticulum (ER) and mitochondria, called as the mitochondria-associated membrane (MAM), regulates various functions including calcium (Ca2+) transfer from ER to mitochondria. Sigma 1 receptor (Sig1R), a gene product of SIGMAR1, is a chaperone specifically localized in the MAM and recessive mutations for SIGMAR1 gene were causative for juvenile amyotrophic lateral sclerosis (ALS), ALS16. In addition, mutant SOD1 (Cu/Zn superoxide dismutase) protein, a gene product of ALS causative gene, SOD1, is known to accumulate in mitochondria and ER. However, the role of the MAM in the pathomechanism for ALS is not elucidated. We identified a novel recessive mutation c.283dupC/p.L95fs in SIGMAR1 gene, which causes juvenile inherited ALS (ALS16). The mutant Sig1R proteins were unstable, and unable to regulate the intracellular Ca2+ flux. The loss of Sig1R function accelerated the disease onset by more than 20 % in mutant SOD1 mice. Moreover, collapse of the MAM structure was observed both in Sig1R deficient mice and mutant SOD1 mice. Collapse of MAM induced neuronal cell death through deregulation of inositol 1,4,5-triphosphate receptor type 3 (IP3R3), a MAM-specific Ca2+ channel enriched in motor neurons. Our findings indicate that collapse of the MAM is a common pathomechanism in both Sig1R- and SOD1-linked ALS. Furthermore, our result of the selective enrichment of IP3R3 in motor neurons suggests that integrity of the MAM is crucial for the selective vulnerability in ALS.