Zhiqi Xiong's team reveals the pathological mechanism of PRRT2 gene mutations leading to paroxysmal movement disorders

Life science On September 21, 2021, the Xiong Zhiqi team of the Chinese Academy of Sciences Brain Science and Intelligent Technology Excellence Innovation Center and the Shanghai Brain Science and Brain-like Research Center published a long article in the journal Cell Reports under the Cell Press titled "Cerebellum The research paper on "Cerebellar spreading depolarization mediates paroxysmal movement disorder" reveals the pathological mechanism of PRRT2 gene mutations leading to paroxysmal movement disorder
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Paroxysmal kinesigenic dyskinesia (PKD) is the most common paroxysmal dyskinesia disease, which is mainly manifested as chorea, athletes, and throwing syndrome induced by sudden movements.
, Dystonia and other involuntary movements
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Due to the similarity in symptoms with epileptic seizures, the disease is often misdiagnosed as epilepsy in clinical practice
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In 2011, Wu Zhiying's team cooperated with Wang Ning, Chen Wanjin's team and Xiong Zhiqi's team to report the first disease-causing gene PRRT2 of PKD internationally
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The discovery of the pathogenic gene laid the foundation for the construction of animal models and the study of disease mechanisms
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During the study of the pathological mechanism of paroxysmal dyskinesias, Xiong Zhiqi’s research team found that the cerebellar cortex of PKD model mice is extremely susceptible to spreading depolarization (SD), and dyskinesia always follows cerebellar depolarization.
Cloth happened
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Based on this discovery and the important role of the cerebellum in regulating movement and body posture, the research team proposed for the first time the hypothesis of "cerebellar depolarization spread" for paroxysmal dyskinesia
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Depolarization spread was first discovered and reported by Dr.
ARISTIDES AP LEÃO in the 1940s
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He found that after applying a series of local electrical stimulation (1-5 seconds) to the rabbit cerebral cortex, the recording positions arranged linearly away from the stimulating electrode will be recorded for several minutes until the disappearance of brain electrical activity, and the distance from the stimulation site The farther the position is, the later the disappearance of EEG will occur
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Based on this observation, Dr.
LEÃO speculated that electrical stimulation induced an event with transmission characteristics in the cerebral cortex, and named the event as spreading depression based on the consequence of its inhibition of brain electrical activity
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Subsequent studies have shown that it is the high concentration of excitatory substances outside the cell, such as potassium ions, that mediate the "spreading" in the cerebral cortex
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Such substances are produced during the depolarization of nerve cell populations and quickly accumulate in the intercellular space, and then diffuse outward to form reproducible depolarization waves
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In the area where the depolarization wave passes, the nerve cells will be forced to depolarize and accompanied by cell edema, which eventually leads to the inhibition of nerve activity
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The phenomenon observed by Dr.
LEAO is the consequence of depolarization waves
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In the cover of the latest issue of Cell Reports, in human brain tissue, depolarization and spreading generally only occur under pathological conditions
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It is usually induced by local stimulation and spreads slowly in the gray matter area of ​​the brain, often accompanied by acute brain injury, focal ischemia, and migraine with aura
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Studies based on experimental animals have shown that under certain conditions, depolarization can be induced in cerebral cortex, hippocampus, striatum, brainstem and cerebellum, but different brain regions are sensitive to depolarization.
There is a big difference in degree
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The cerebral cortex and hippocampus are more susceptible to depolarization, while the cerebellar cortex is very resistant to this event
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Why does the cerebellum become a "safe haven" for spreading depolarization? If depolarization spreads in the cerebellar cortex, what will be the behavioral consequences? This research by Xiong Zhiqi's team provides a convincing answer to the mystery
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This study shows that PRRT2 protein in cerebellar granule cells plays an important role in the process of cerebellar resistance to spreading depolarization
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PRRT2 reduces the continuous excitability of neurons by delaying the recovery of inactivated sodium ion channels, thereby preventing the occurrence and spread of depolarization in the cerebellar cortex induced by local stimulation
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On the contrary, knocking out the Prrt2 gene can make the cerebellar cortex in a state of depolarization and spreading sensitivity
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In this state, local stimulation of the cerebellar cortex can effectively induce depolarization and spreading
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The study further proves that the locally generated depolarization waves can almost spread throughout the entire cerebellar cortex, and interfere with the normal firing of neurons in this loop through the neural connections from Purkinje to the deep cerebellar nucleus, and eventually lead to dyskinesias.
Happen
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The research work of Xiong Zhiqi's team not only deeply analyzes the pathological mechanism of PKD, but also provides a new cellular and molecular mechanism for the sensitivity regulation of depolarization spread
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The research was guided by researcher Xiong Zhiqi, and team members such as Lu Bin, Lou Sensen, Xu Ruoshui, Kong Delun, Wu Rongjie, and Zhang Jing collaborated to complete the research
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Graduate students Zhuang Ling, Wu Xuemei and He Junyan and Professor Wu Zhiying of Zhejiang University School of Medicine participated in the study
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The lack or functional defect of PRRT2 can make the cerebellar cortex susceptible to depolarization spreading by enhancing the function of sodium ion channels
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The spread of depolarization in the cerebellar cortex interferes with the function of the cerebellar Purkinje-deep nucleus loop and eventually leads to paroxysmal dyskinesia
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The author's interview with Cell Press Cell Press specially invited Professor Xiong Zhiqi to conduct an interview on behalf of the research team, and asked him to further explain it in detail
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CellPress: Paroxysmal movement-induced dyskinesia (PKD) is the most common paroxysmal dyskinesia, and PRRT2 has been identified as the main pathogenic gene of PKD
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How did you discover the association between PKD and cerebellar depolarization spread (SD)? Professor Xiong Zhiqi: The mouse PKD model does not show spontaneous dyskinesia similar to that of the patient
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We tried various stimulus induction methods
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The idea of ​​linking the two originally came from an accidental discovery in an experiment
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In the process of administering micro-administration to the cerebellar cortex of PKD model mice, we found that only a very fine injection needle needs to be inserted into the cerebellar cortex to induce dyskinesia in the model mice.
The dyskinesia has episodic characteristics and the mice are attacking.
After tens of seconds, normal operations can be resumed
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The same operation does not cause any movement abnormalities in normal mice
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And there is a 30-60 second delay from stimulation to exercise onset
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This phenomenon has aroused our great interest.
The operation of inserting an injection needle into the cortex is similar to the classic stimulation method (acupuncture) that induces SD events in the cerebral cortex
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So we speculated that similar SD events might have occurred in the cerebellar cortex of PKD model mice, and SD might have triggered the subsequent paroxysmal dyskinesia
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According to the classic SD detection method, we subsequently used electrophysiological and fluorescent calcium imaging technology to detect the stimulus-induced SD event in the PKD model mouse cerebellar cortex, and further confirmed the causal relationship between the cerebellar SD event and paroxysmal dyskinesia
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CellPress: How does the absence of PRRT2 promote SD? Professor Xiong Zhiqi: There are two main factors that affect the production and spread of SD.
One is the ability of nerve cells to release excitatory factors (such as potassium ions and glutamate neurotransmitters, etc.
) when they receive local stimulation, and the other is extracellular excitability.
The efficiency with which sex factors are eliminated
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Neuronal excitability is regulated by the extracellular potassium ion concentration
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Nerve cells will release potassium ions during the stimulation process, resulting in an increase in the concentration of extracellular potassium ions, and these extracellular potassium ions can further stimulate nerve cells and cause them to release more excitatory substances
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This form of excitatory positive feedback quickly amplifies the initial stimulation effect, and the local excitatory substance concentration rises sharply, and forms a chemical concentration gradient with the surrounding area, causing the excitatory factors to diffuse outward
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The excitatory substances spreading around again stimulate the nerve cells where it passes, and the expansion effect is repeated continuously, and finally a spreading depolarization wave is formed
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PRRT2 mainly affects the first factor, which is the ability of nerve cells to release excitatory substances when they are continuously stimulated
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We have found in our experiments that the lack of PRRT2 will increase the ability of cerebellar granule cells to continuously respond to stimuli, thereby releasing more potassium ions to the outside of the cell, making the cerebellar cortex more likely to produce SD
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CellPress: What function does sodium ion channel play in SD? Professor Xiong Zhiqi: Voltage-gated sodium ion channels are the basis for neuron action potential generation and play an important role in the process of neuron response to stimulation
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When the cell is stimulated to depolarize, the sodium channel undergoes a process of "close-open-inactivation", after which the sodium channel needs to be restored from the inactive state to the normal closed state before it can be activated again
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We found that PRRT2 plays an important role in regulating sodium ion channels from inactivation to recovery
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PRRT2 protein can delay the transition of sodium ion channels from inactive to normally closed state, thereby weakening the response of neurons to continuous stimulation, so that the concentration of local excitatory substances cannot reach the threshold induced by SD
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On the contrary, the lack of PRRT2 will accelerate the recovery of sodium ion channels from the inactive state, enhance the excitability of nerve cells, and promote the production of SD in the cerebellar cortex
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Our research also found that blocking sodium ion channels with drugs can effectively inhibit the production of SD and prevent the onset of dyskinesia in PKD model mice
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CellPress: How does SD affect movement disorders through deep cerebellar nucleus (DCN) neurons? Professor Xiong Zhiqi: The cerebellum is mainly composed of the cerebellar cortex and the deep cerebellar nucleus (DCN)
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Cerebellar granule cells-Purkinje cells-deep nucleus neurons constitute the main cerebellar neural circuit
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As an important node for the cerebellum to output regulatory information to the motor control loop, DCN plays an extremely important role in maintaining body posture and coordination of motion
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SD that starts in a local area of ​​the cerebellar cortex (distributed with granular cells and Purkinje cells) slowly spreads (1.
5-3 mm/min) in the gray matter area of ​​the cerebellar cortex, so that a large number of granular cells and Purkinje cells continue to disappear Polarization, and causes Purkinje cells to depolarize and stop the regular neuron firing
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Since the nerve fibers of Purkinje cells project directly to the deep nucleus of the cerebellum, SD interferes with the activity of neurons in the deep nucleus through this neural connection, which eventually leads to the occurrence of dyskinesia
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It is worth noting that SD cannot cross the white matter area between the cerebellar cortex and the deep nucleus.
Therefore, the effect of SD on the neurons of the deep cerebellar nucleus is different from the effect on Purkinje cell neurons
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CellPress: This study found that SD plays an important role in PKD.
How can the results of this study help understand the pathogenesis and treatment of PKD? Professor Xiong Zhiqi: PKD is a paroxysmal neurological disease.
The clinical symptoms of patients have been comprehensively explained, but the pathological mechanism of the onset, development and termination of PKD disease has been unclear
.

The discovery of cerebellar SD events in PKD model animals provides theoretical guidance for the study of the pathological mechanism of PKD, as well as new ideas for the intervention and treatment of PKD diseases
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The means and methods to inhibit SD will be able to effectively control the symptoms of PKD
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CellPress: What is the focus of your team's work next? Professor Xiong Zhiqi: PRRT2 has important clinical and basic scientific significance for the regulation of neural activity-dependent sodium channels
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Overexcitement of neurons is involved in the occurrence and development of many neurological diseases, including epilepsy and neuralgia
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At present, our understanding of the PRRT2 molecule is still very preliminary.
One of the focus of our team’s follow-up work will be on the analysis of the biological function of PRRT2.
This part of the work is very important for understanding its mechanism of action and can also play a role in the subsequent development of new drugs.
Guiding role
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In addition, there are still some PKD patients in clinical practice, especially more than half of sporadic patients, and PRRT2 gene mutations have not been detected, which means that PKD and other pathogenic genes have not yet been discovered
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Just this year, we and Wu Zhiying's team worked together again and discovered the second disease-causing gene TMEM151A of PKD
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Another focus of our follow-up work is to conduct in-depth research on the pathological mechanism of PKD related to TMEM151A
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Corresponding author: Professor Xiong Zhiqi, Professor Xiong Zhiqi, received his Ph.
D.
in Pharmacology and Neuroscience from Baylor College of Medicine in 2000; Postdoctoral in Department of Neurobiology, Duke University from 2000 to 2003; From 2003 to present, he has been a researcher and doctoral supervisor of the Institute of Neuroscience, Chinese Academy of Sciences, 2012 Promoted to senior researcher
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Since 2014, he has been an adjunct professor at the University of Chinese Academy of Sciences and ShanghaiTech University
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Served as an editorial board member of Developmental Neurobiology, Neurobiology of Disease and other journals
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The research group uses genetic manipulation of mice and non-human primate model animals to study the molecular, synaptic and neural circuit mechanisms of brain diseases
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Published more than 80 papers
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The research results of related paper information are published in the journal Cell Reports under Cell Press.
Click "Read Full Text" or scan the QR code below to view the paper
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▌Paper title: Cerebellar spreading depolarization mediates paroxysmal movement disorder▌Paper URL: https://▌DOI: https://doi.
org /10.
1016/j.
celrep.
2021.
109743 Long press the picture to identify the QR code to read the original text.
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