シンポジウム（Symposium）

Symposium New modes of neuronal translation regulation in health and disease シンポジウム神経細胞における翻訳制御の新たな地平

7月27日（土）8:45～9:10　第4会場（朱鷺メッセ　3F　301） 3S04m-1 Targeting RAN proteins improves phenotypes in C9orf72 BAC ALS/FTD mice Laura Ranum（Ranum Laura）¹，Lien Nyguen（Nyguen Lien）²，Fabio Montrasio（Montrasio Fabio）³，Olgert Bardhi（Bardhi Olgert）²，Shu Guo（Guo Shu）²，Solaleh Khoramian Tusi（Khoramian Tusi Solaleh）²，Katsuya Nakamura（Nakamura Katsuya），Monica Banez Coronel（Banez Coronel Monica）²，Nahum Sonenberg（Sonenberg Nahum）⁴，Jan Grimm（Grimm Jan）³，Tao Zu（Zu Tao）² ¹Center for NeuroGenetics, Department of Molec. Genet. Microb. University of Florida ²Center for NeuroGenetics, University of Florida ³Neurimmune AG ⁴McGill University Microsatellite expansion mutations cause more than 40 neurologic diseases. In 2011, we discovered that in the absence of an AUG or near cognate initiation codon, expanded CAG and CUG repeats can express homopolymeric proteins from all three reading frames. We and others have demonstrated that RAN translation occurs in a growing number of repeat expansion disorders including: spinocerebellar ataxia type 8 (SCA8), C9orf72 amyotrophic lateral sclerosis / frontotemporal dementia (ALS/FTD); Huntington’s disease (HD) and myotonic dystrophy (DM). An emerging theme is that coding and non-coding expansion mutations are bidirectionally expressed, producing two mutant RNAs and up to six mutant proteins. We now show that RAN translation can be regulated both in vitro and in vivo through the PKR/eIF2 phosphorylation pathway. In cells, steady state levels of several types of RAN proteins are increased by PKR overexpression and decreased by inhibiting PKR. In C9orf72 BAC transgenic ALS/FTD mice, inhibiting PKR through AAV expression of the dominant negative PKR-K296R protein decreases RAN protein pathology in vivo and improves behavioral phenotypes. These data are consistent with a model in which chronic activation of the PKR pathway by repeat expansion RNAs favor RAN translation and that blocking this pathway in mice reduces RAN protein accumulation and mitigates disease. These data suggest that targeting the PKR pathway may be a fruitful therapeutic approach to treat C9orf72 ALS/FTD and for other repeat expansion diseases. In a separate study we show that targeting RAN proteins with human antibodies improves behavior, decreases neurodegeneration and increases survival in C9orf72 ALS/FTD BAC transgenic mice. These data demonstrate RAN proteins play a central role in C9orf72 ALS/FTD and describe novel approaches for the treatment of C9 and other RAN-protein diseases.		7月27日（土）9:10～9:35　第4会場（朱鷺メッセ　3F　301） 3S04m-2 シナプスにおけるRNAエピジェンティクス制御 Dan Ohtan Wang（王丹）¹，Kei Iida（飯田慶）²，Ikumi Oomoto（大本育実）¹，Belinda Goldie（Goldie Belinda）³，Kelsey Martin（Martin Kelsey）⁴，Matteo Pelligrini（Pelligrini Matteo）⁴ ¹京都大学　高等研究院 ²京都大学　医学研究科 ³Monash University, Australia ⁴University of California, Los Angles, USA The brain is an intricate and complex organ that underlies our cognition and behavior. Although we are living in an era of privilege compared to other species where we can read our own genetic makeups, and may soon become capable of editing them at will, we remain woefully ignorant of what all this means for constructing brain function. Regulated translation has recently become an intense focus of studies to understand how experience-driven activities is integrated into circuit plasticity and functional adaptation of the brain. It has been shown that not only cell-wide, but local post-transcriptional regulation of RNA molecules at synapses, contribute to synaptic plasticity for learning and memory. Our recent work has revealed an unexplored regulatory mechanism of dynamic gene expression for the synthesis and modulation of tripartite synapses, and for brain pathways implicated in neurodevelopmental and neuropsychiatric diseases. This regulation involves dynamic RNA epigenetics at synapses. Thousands of localized mRNAs are identified to contain methylated adenosines and when the proteins that recognize and bind to these modifications are depleted from neurons, neurons failed to make mature synapses with each other and thus had weaker transmission. We propose that simple chemical modifications, such as an addition of a methyl group (-CH3) to the RNA molecules, can make critical contribution to building and remodeling neuronal connections in the brain. This function is mediated by the spatiotemporal control of protein synthesis such that not only what protein to be made, but also when, where, and how much of the proteins to be made are important for synapse function.

7月27日（土）9:35～10:00　第4会場（朱鷺メッセ　3F　301） 3S04m-3 RNG105 (caprin1) は神経樹状突起へのmRNA局在化を担い、長期記憶形成に不可欠である Nobuyuki Shiina（椎名伸之）^1,2,3 ¹基生研神経細胞生物学 ²生命創成探究センター ³総研大院基礎生物 Protein synthesis in the brain is required for the formation of long-term memory, but the mechanism involved is still poorly understood. Here, we show that RNG105 (also known as Caprin1) is essential for long-term memory formation. RNG105 is a major RNA-binding protein in RNA granules, which are involved in mRNA transport to dendrites and local translation in the vicinity of dendritic postsynapses (spines) in neurons. RNG105 conditional knockout in mice impaired the structural plasticity of spines and reduced synaptic transmission in hippocampal neurons. Furthermore, RNG105-deficient mice displayed unprecedentedly severe defects in long-term memory although they formed short-term memories of several minutes. Genome-wide profiling of mRNA distribution in the hippocampus revealed that RNG105 deficiency decreased the dendritic localization of mRNAs. Particularly, mRNAs encoding regulators of the cell surface expression of AMPA receptors were decreased in dendrites by RNG105 knockout. Labeling of cell surface AMPA receptors revealed that their surface expression was in fact decreased in dendrites by RNG105 knockout, which was consistent with the decrease in synaptic transmission in RNG105-deficient neurons. Thus, RNG105 plays an essential role in long-term memory formation as a key regulator of mRNA localization to dendrites. Recently, we found that RNG105 undergoes liquid-liquid phase separation and induces the formation of RNA granules with high liquidity to regulate RNA granule dynamics and translation in RNA granules. I would like to further discuss the relationship between these properties of RNG105 and the phenotype of RNG105 conditional knockout mice.		7月27日（土）10:00～10:20　第4会場（朱鷺メッセ　3F　301） 3S04m-4 タンパク質の凝集化による翻訳異常と精神障害発現機構の解明 Motomasa Tanaka（田中元雅）理研CBS タンパク質構造疾患 Protein aggregation is closely involved in a variety of neurodegenerative disorders, which are often associated with psychiatric symptoms. The molecular origin of these symptoms is unknown because the genetics of neurodegenerative disorders do not suggest overt overlap with psychiatric diseases. Although toxic protein aggregates may entrap proteins involved in psychiatric disorders and elicit deleterious effects, candidate mechanisms for this co-aggregation hypothesis remain unknown. Here, we report a novel cytosolic protein aggregate in frontotemporal lobar degeneration (FTLD) brain composed of TDP-43, the major protein constituent of insoluble inclusions in FTLD, and DISC1, a biological mediator of major mental conditions. TDP-43 and DISC1 co-aggregation disrupted activity-dependent dendritic local translation via impairment in translation initiation and peptide chain elongation, resulting in reduced synaptic protein expression. FTLD model mice with DISC1/TDP-43 co-aggregates in frontal cortex showed hyperactivity and social interaction deficits. Remarkably, these phenotypes were rescued by exogenous DISC1 expression to supplement endogenous functional DISC1 that is lost due to its sequestration into TDP-43 aggregates. These results support our hypothesis that co-aggregation of causal factors for neurodegenerative disorders with risk factors for psychiatric diseases represent a novel mechanism for mental conditions. Thus, our findings provide an insight into novel therapeutic approaches in devastating neuropsychiatric disorders.

7月27日（土）10:20～10:45　第4会場（朱鷺メッセ　3F　301） 3S04m-5 RPS25 regulates RAN translation of C9orf72 repeat expansions Shizuka Yamada（Yamada Shizuka） Stanford University A GGGGCC nucleotide repeat expansion in a non-coding portion of the C9orf72 gene is the most common cause of amyotrophic lateral sclerosis and frontotemporal dementia (c9ALS/FTD). The expanded nucleotide repeat is transcribed into sense and antisense RNAs, which are substrates for an unusual form of translation called RAN translation (repeat-associated non-AUG translation). RAN translation of the C9orf72 repeat expansion produces dipeptide repeat (DPR) proteins, some of which are toxic and may contribute to neurodegeneration. The mechanism of RAN translation remains poorly understood and key regulators have yet to be identified. Moreover, the relative contributions of sense and antisense RNAs and the RAN translated DPRs to neurodegeneration is unresolved, mainly because there lacks a way to selectively shut off RAN translation without affecting the repeat RNAs. We performed a genetic screen for RAN translation regulators and identified the small ribosomal subunit 25 (RPS25). Knockout of RPS25 in yeast and human cells reduced the levels of RAN translation without affecting levels of GGGGC repeat-containing RNA or global translation. Reduction of RPS25 in C9orf72 ALS patient-derived iPSCs decreased the production of DPRs while not affecting the formation of pathognomonic repeat-containing RNA foci. In a Drosophila C9orf72 model, in which neurodegeneration could be caused by repeat RNA or DPR toxicity, inhibiting Rps25 reduced DPR production and extended lifespan. These findings are consistent with DPRs being a major contributor to neurodegeneration and present a novel RAN translation regulator as a therapeutic target for c9ALS/FTD and perhaps other neurodegenerative diseases caused by nucleotide repeat expansions.