Cell: Tsinghua Ge Liang's team provides new therapeutic targets for neurodegenerative diseases | Cell Press Dialogue with Scientists

Life science On April 1, 2022, Ge Liang's team from the School of Life Sciences of Tsinghua University published a research paper entitled "CCT2 is an aggrephagy receptor for clearance of solid protein aggregates" in the Cell Press journal Cell
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This article is the first to report an autophagy receptor CCT2 that can specifically degrade solid protein aggregates, providing an important target for the treatment of diseases caused by protein aggregates, especially neurodegenerative diseases
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With the acceleration of the aging process of the world's population, neurodegenerative diseases are affecting more and more people
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The World Health Organization predicts that by 2040, neurodegenerative diseases will become the second leading cause of death in humans
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However, there is currently no drug in the world that can effectively treat neurodegenerative diseases
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The formation of toxic protein aggregates is an important factor leading to neurodegenerative diseases, and how to effectively remove toxic protein aggregates is also an important idea for the treatment of neurodegenerative diseases
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Autophagy is an important way to remove intracellular toxic protein aggregates, and the selectivity of autophagosomes for aggregates has not been well explained
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Known ubiquitin-binding receptors (P62, NBR1, and TAX1BP1) can mediate the recognition of aggregates by autophagosomes, but these receptors not only lack specificity, but are virtually incapable of more pathogenic solid-state aggregates
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Therefore, finding more specific receptors capable of degrading solid-state aggregates is the key to the treatment of neurodegenerative diseases by targeting the autophagy pathway
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Ge Liang's team found a protein CCT2 on aggregates that can recruit autophagosomes by establishing an ingenious in vitro screening system
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As a subunit of the chaperonin complex, CCT2 is known to bind and help misfolded proteins fold correctly
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In this study, the researchers found that CCT2 can bind aggregate proteins in a ubiquitin-independent manner and interact with LC3, a key protein on the autophagosome membrane, to mediate autophagosome-to-aggregate binding.
identification and degradation
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The binding of CCT2 to protein aggregates is independent of ubiquitin chains, which to a certain extent ensures the specificity of CCT2 as an autophagy receptor
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Further studies found that CCT2 is more inclined to promote the autophagic clearance of solid-state aggregates, which makes it more advantageous in disease treatment
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In the process of exploring the relationship between CCT2 as an autophagy receptor and its molecular chaperone function, the researchers found that the presence of protein aggregates increased the monomeric form of CCT2, and only the monomeric form of CCT2 could act as an autophagy receptor to promote Autophagic clearance of aggregates
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This suggests the transition of CCT2 from a complex to a monomeric form, enabling it to functionally switch from a molecular chaperone to an autophagy receptor
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This finding brings more thought to the link between molecular chaperones and autophagy
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Author's Interview Cell Press specially invited Associate Professor Ge Liang, the corresponding author of the paper, to conduct an exclusive interview on behalf of the team, and asked him to interpret it in detail
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CellPress: Autophagy is a key cellular process to clear protein aggregates, but how to achieve its selectivity has not been well explained.
What are the difficulties involved? Associate Professor Ge Liang: Aggregate autophagy, like many other selective autophagy, has the process of substrate ubiquitination, and some aggregate autophagy receptors found in mammalian cells contain ubiquitin binding sites.
This means that they can not only bind ubiquitinated aggregates, but some can also bind to other ubiquitinated substrates, such as mitochondria and lysosomes
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Therefore, the biggest challenge is to find receptors that can specifically target protein aggregates in mammalian cells
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Although in other types of selective autophagy, some specific receptors have been found to exist
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For example, anchor proteins with specificity in mitochondria and endoplasmic reticulum can directly act as receptors to mediate mitophagy or endoplasmic reticulum autophagy
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Given the specificity of aggregates, it is difficult to speculate whether specific aggregate receptors really exist and what are the properties of these receptors
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Previously, researcher Zhang Hong's laboratory discovered specific aggregate receptors in several nematode systems through genetic screening, but the intracellular clearance of protein aggregates in mammalian systems is not very thorough, and aggregate receptors may be essential genes.
Therefore, it is difficult to find specific aggregate receptors by means of genetic screening and cellular imaging
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The method we adopted was to simulate the process of autophagosome membrane-bound aggregates by in vitro reconstruction.
It was unexpectedly found that different aggregates recruited the autophagosome membrane protein LC3 differently.
Therefore, we thought that the difference in aggregate composition might lead to LC3 binds differently
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We then compared the composition of different aggregates using biochemical separation and protein profiling, and targeted CCT2 as a study subject
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It can be said that the discovery has a certain element of luck
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CellPress: How does CCT2 differ from known ubiquitin-binding receptors (P62, NBR1, and TAX1BP1) in the type selection of protein aggregates to be cleared? Associate Professor Ge Liang: First, CCT2 can bind to non-ubiquitinated protein aggregates, which ubiquitin-binding receptors cannot
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More importantly, they differ in the choice of protein aggregate state
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While traditional receptors are more prone to degrade fluid protein aggregates, CCT2 is more effective on pathogenic solid aggregates
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Finally, as stated by the answer to question 1, the specificity of P62, NBR1 and TAX1BP1 is for ubiquitin rather than aggregates, in contrast, CCT2, which is a molecular chaperone, is a specific collection of misfolded proteins and thus more specifically recognizes aggregates
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CellPress: How does CCT2 clear protein aggregates? Associate Professor Ge Liang: On the one hand, CCT2 binds protein aggregates through the apical domain, and on the other hand, it binds to LC3 protein on the autophagosome membrane through a site we call the VLIR motif, which acts like a porter to aggregate protein aggregates.
transported to the autophagosome for subsequent degradation
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Moreover, CCT2 itself also enters the autophagosome and mediates the clearance of aggregates in a "suicide" manner
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CellPress: What is the relationship between the accumulation of aggregation-prone proteins and the formation of CCT2 monomers? How does CCT2 achieve the functional transition from a molecular chaperone to an autophagy receptor? Associate Professor Ge Liang: We found that the accumulation of aggregate proteins can increase the number of CCT2 monomers.
There are two explanations: one is that the formation of aggregate proteins hinders the formation of CCT complexes, which may be caused by the presence of aggregate proteins.
The disorder of protein homeostasis caused the 8 subunits of the CCT complex to be synthesized on demand, or some of the subunits had stronger binding ability to aggregate proteins and preferentially bound to aggregate proteins instead of participating in the CCT complex.
assembled
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The second is that the aggregated protein promotes the depolymerization of the already formed CCT complex, which may be related to the conformational change of the CCT complex: the CCT complex undergoes a conformational change when mediating protein folding, and is a loose one in the prepared state.
When the substrate is transported to the barrel-shaped center of the CCT complex, the complex will close the "lid" at both ends, showing a tight "closed" state, and the folding of the substrate is in such a closed environment.
carried out in
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If a protein with a certain degree of aggregation enters the barrel, the "lid" of the complex is likely to be unable to close because the substrate is too large.
At this time, the entire complex will be in a relatively loose state.
The conformational change of the CCT subunit caused by ATP hydrolysis is likely to cause the depolymerization of the complex, thereby releasing the monomer
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We need to explore more deeply for both hypotheses
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As a molecular chaperone, CCT2 must participate in the folding function of proteins together with the complex in the CCT complex
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At this time, the VLIR motif of the binding site of CCT2 with LC3 will be buried in the complex, and in this case, CCT2 cannot function as an autophagy receptor
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The presence of aggregate proteins enables the formation of CCT2 monomers, so that the VLIR motif is exposed on the surface of CCT2, enabling CCT2 to bind LC3, thereby becoming an autophagy receptor to mediate aggregate autophagy
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CellPress: This study identifies the function of CCT2 in clearing protein aggregates.
How will this help in understanding and treating human diseases associated with protein aggregation? Associate Professor Ge Liang: When it comes to protein aggregates, we can easily think of molecular chaperones, because molecular chaperones play an important role in preventing protein aggregation
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For the first time, we found that molecular chaperones represented by CCT2 can act as aggregate autophagy receptors to help the clearance of aggregates.
Molecular chaperones provide fuller considerations for the treatment of aggregate-related diseases
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We are also exploring the physiological function of CCT2 in mice with neurodegenerative disease models, looking forward to seeing the role of CCT2 in the treatment of neurodegenerative diseases and bringing hope to disease patients
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The author introduces the first author of Ma Xinyu's doctoral thesis, Ma Xinyu, a doctoral student in the School of Life Sciences of Tsinghua University, graduated from Nankai University with a bachelor's degree and entered the School of Life Sciences of Tsinghua University in 2017, under the tutelage of Associate Professor Ge Liang, dedicated to autophagic clearance of protein aggregation body research
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He has won the "Future Scholars Scholarship" and the National Scholarship for Doctoral Students of Tsinghua University
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The last corresponding author of Associate Professor Ge Liang's paper, Ge Liang, graduated from the School of Life Sciences of Shandong Normal University with a bachelor's degree
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He received his Ph.
D.
from the Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences
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He then worked as a postdoctoral researcher on autophagy at the University of California, Berkeley
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During this period, he received Jane Coffin Child Foundation Fellowship, Human Frontier Science Fellowship and NIH Pathway to Independence Award
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He returned to China in 2017 and worked in the School of Life Sciences of Tsinghua University.
He is now an associate professor, the vice president of the Subcellular Organ Branch of the Chinese Society of Biophysics, and the deputy secretary-general of the Organelle Branch of the Chinese Society of Cell Biology
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Representative research results 1: The endoplasmic reticulum Golgi intermediate (ERGIC) membrane protein TMED10 was found to be involved in the secretion of non-canonical proteins, and a molecular pathway (THU pathway) for the transmembrane transport of non-canonical secreted proteins mediated by TMED10 was revealed , answering the key question of how proteins without signal peptides in the non-classical secretory neighborhood enter the secretory pathway (Cell, 2020); 2: Discovering a novel endosome ERGIC-ERES interaction regulates the formation of autophagosomes, answering the field of autophagy Important questions about the origin and assembly of autophagosome membranes (Cell Research, 2021); 3.
Discovery of a novel autophagy receptor CCT2 to mediate autophagic degradation of solid-state aggregates (Cell, 2022)
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Related paper information▌Paper title: CCT2 is an aggrephagy receptor for clearance of solid protein aggregates▌Paper URL: https://▌DOI: https: //doi.
org/10.
1016/j.
cell.
2022.
03.
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