Chen Yelin from the Interdisciplinary Center of the Chinese Academy of Sciences and Shen Huazhi's team from Genentech discovered the neuronal signaling pathway that controls the proliferation of glial cells. Cell Press Dialogue with Scientists

Life science On March 29, 2022, researcher Chen Yelin from the Interdisciplinary Research Center of Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, and Dr.
Shen Huazhi (Morgan Sheng, now the Broad Institute) of Genentech Biotechnology Co.
, Ltd.
, were in Cell Press Cell.
A new study was published in the publisher's journal Cell Reports, titled "NMDA receptor-dependent Prostaglandin-Endoperoxide Synthase 2 induction in neurons promotes glial proliferation during brain development and injury"
.

The research group has defined a neuron-derived NMDAR-Ptgs2 signaling pathway, which can achieve transcellular control and regulation of glial cell proliferation during brain development and injury
.

▲Long press the picture to identify the QR code to read the original text In addition to neurons, the mammalian brain also contains abundant glial cells, the main one of which is astrocytes, which are involved in many key physiological and pathological processes , with important functions
.

From the perspective of brain development, embryonic astrocytes are derived from the differentiation of radial glial cells, and most of the radial glial cells disappear after birth
.

In the neonatal mouse brain, with synaptogenesis, the number of astrocytes in the cerebral cortex increases by 6-8 times, and most of them are generated by local proliferation, but the regulatory mechanism of local proliferation is not clear
.

Astrocytes are very important for the formation, elimination and plasticity of neuronal synapses, but it is unclear whether neurons can also influence the fate of glial cells under physiological conditions
.

In addition, brain injury and brain diseases can also lead to the activation and proliferation of glial cells, which is one of the main features of neuroinflammation and may have an extremely important impact on the disease process.
advance
.

Glutamate is the most important excitatory neurotransmitter
.

The N-methyl-D-aspartate receptor (NMDAR) is a major glutamate receptor, and its activation is an important component of excitatory synaptic activity
.

Activation of NMDAR also activates calcium signaling, which can lead to long-term changes in many neural functions, including changes in synaptic plasticity and regulation of gene expression
.

Previous studies have mainly focused on the effects of NMDAR on short-term (within a few hours) neural function, and NMDAR's regulation of long-term (more than one day) neural function has hardly been involved
.

In this study, the authors used microarrays to analyze the effect of prolonged (6 and 24 h) inhibition of NMDAR activity on mRNA expression profiles in hippocampus-derived primary cultured neurons
.

Surprisingly, it was found that the expression of a large number of cell division cycle genes was down-regulated after 24 hours of continuous NMDAR inhibition, while 6 hours of inhibition had no such effect.
In addition, enhancing NMDAR activity could also lead to up-regulation of related gene expression levels
.

Subsequent studies found that these genes are mainly expressed in astrocytes, and long-term changes in NMDAR activity can bidirectionally regulate astrocyte division
.

Further research found that the NMDAR receptor-mediated signaling pathway originates from neurons, and NMDAR induces prostaglandin-endoperoxide synthase 2 (Prostaglandin-endoperoxide Synthase 2; Ptgs2; the target of non-steroidal anti-inflammatory drugs) expression to promote astrocyte division
.

Pharmacologically altering NMDAR activity also significantly altered astrocyte division in the cerebral cortex during mouse development, suggesting that this signaling pathway also plays a role in brain development
.

In addition, traumatic brain injury (TBI) can very significantly activate the NMDAR-Ptgs2 pathway on neurons and cause the activation and proliferation of glial cells including astrocytes and microglia
.

When NMDAR was inhibited or the Ptgs2 gene was knocked out, TBI could no longer induce glial cell activation and proliferation, indicating that the neuronal NMDAR-derived signaling pathway is a key factor in brain injury-induced glial cell activation
.

In conclusion, this study defines a neuron-derived NMDAR-Ptgs2 signaling pathway that can achieve transcellular control and regulation of glial proliferation during brain development and injury
.

On the one hand, we expanded the scope of neuroplasticity in terms of time and cell type, and found that NMDAR can affect the nervous system by regulating the division of glial cells in a longer time axis; on the other hand, because the activation of glial cells under pathological conditions It is the main component of neuroinflammation in many brain diseases, and this discovery also provides a new direction for studying the occurrence and regulation mechanism of neuroinflammation
.

A.
Astrocytes in different mitotic stages (green/EdU is DNA, red/GFAP is astrocytes) when NMDAR is activated in primary cultured hippocampal neurons, the scale bar is 50 μm; B.
Schematic illustration of NMDAR regulating astrocyte proliferation by controlling Ptgs2 expression in neurons
.

The author's interview with the official account of Cell Press specially invited researcher Chen Yelin to accept the interview on behalf of the research team, and asked him to interpret it in detail
.

CellPress: The relationship between the proliferation of astrocytes and neurons is rarely reported.
How did you come up with this research direction? Researcher Chen Yelin: Simply put, this result was not what we thought of at the beginning, but was guided step by step by the experimental results
.

Research on this question stems from our curiosity about the function of NMDAR
.

For example, it is said in the field that synaptic plasticity is the basis of learning and memory, but the research on synaptic plasticity is mainly to analyze synaptic changes that can last for several hours, especially changes within an hour
.

And we all know that learning and memory can last for decades, so what mechanisms can mediate plastic changes that last so long? There is no answer to this question
.

Could the NMDAR receptor, a key molecule controlling synaptic plasticity, cause changes lasting well beyond a few hours? This is the starting point of our project
.

We know that NMDAR receptors regulate gene expression, but the physiological function of this regulation is unclear
.

Changes brought about by changes in gene expression can persist for longer periods of time, so we started from that perspective
.

First of all, we are very pleased to confirm that the expression of many genes is indeed changed after NMDAR inhibition in primary cultured neurons
.

However, after the excitement, I found another problem that must be faced.
Hundreds of genetic changes made us very confused about the follow-up research direction
.

Which gene function should be studied? After using gene enrichment analysis (Gene Ontology), we were surprised to find that genes with significantly altered expression levels were significantly enriched in cell cycle pathways, indicating altered cell division status
.

However, it is well known that healthy neurons do not divide
.

Morgan inadvertently asked, what cell division genes are regulated by NMDAR? Out of curiosity about this issue, we conducted in-depth research step by step and discovered this extremely surprising signaling pathway
.

If we look back, we did discover a new mechanism by which NMDAR regulates longer-term plastic changes in the nervous system, but the details were definitely not what we could have initially imagined
.

CellPress: There are many reports in the literature that Ptgs2 is mainly expressed in glial cells, which seems to contradict your results
.

How can this be explained? Researcher Chen Yelin: There are indeed many reports that Ptgs2 is mainly expressed in glial cells
.

But there are also some reports that Ptgs2 can be induced to express in neurons, which is consistent with our results
.

In fact, we were very concerned about the cell type in which Ptgs2 was expressed, and the specificity of the staining antibodies we used was validated using gold standard Ptgs2 knockout mice
.

It was found that Ptgs2 is mainly expressed in neurons under physiological conditions
.

In our model of acute brain injury, Ptgs2 expression was abundantly induced in neurons in an NMDAR-dependent manner, with only a very small amount of Ptgs2 induced in microglia and consistently undetected in astrocytes to the signal
.

These results fully indicate that Ptgs2 is mainly induced in neurons in the model we used
.

It should be emphasized, however, that we cannot rule out the possibility that Ptgs2 can be induced in certain types of glial cells in other disease models
.

Therefore, different experimental results may be caused by different disease models or cell culture methods.

.

CellPress: There are many genes downstream of NMDAR, how to lock Ptgs2 to play a role in NMDAR-promoted astrocyte proliferation? Researcher Chen Yelin: Our study found that NMDAR activity in neurons can regulate the proliferation of astrocytes transcellularly, so we hypothesized that there should be a secreted molecule that can be induced by NMDAR activity on neurons
.

Since astrocyte division can be bidirectionally regulated by NMDAR activity, this molecule should also be bidirectionally regulated by NMDAR activity
.

Subsequent analysis found that although 467 genes were regulated by NMDAR repression and 567 genes were regulated by NMDAR activation, only 34 genes were regulated by both NMDAR repression and activation (Chen et al.
, 2014)
.

Of these 34 genes, only two secreted factors directly: brain-derived neurotrophic factor (BDNF) and Ptgs2
.

Further research found that although both secreted molecules can promote the proliferation of astrocytes, only the inhibitor of Ptgs2 can block this process, indicating that Ptgs2 is more critical for NMDAR to regulate astrocyte division
.

CellPress: How can we understand the role of neurons in the inflammatory response through this study? Researcher Chen Yelin: It is generally believed that the occurrence of neuroinflammation mainly originates from and is dominated by glial cells, leading to the up-regulation of many inflammatory molecules, which in turn causes a series of nerve damage
.

In this process, past studies have believed that the contribution of neurons mainly comes from the debris or excreted metabolites after their death
.

Our study found that healthy neurons can activate glial cells through the NMDAR-Ptgs2 pathway: mild brain injury models did not cause neuronal cell death, but glial cells were still activated through this pathway
.

This suggests that not only dead neurons, but active neurons can also be the source of neuroinflammation
.

This finding is extremely important for understanding the occurrence of neuroinflammation, and reminds everyone that when talking about neuroinflammation, you can't just think of glial cells, and neurons may also play a key role in it
.

Neuroinflammation may be the result of interactions between neurons and glial cells
.

CellPress: What guidance and help does this study have for the development of clinical treatments for post-traumatic brain injury? Researcher Chen Yelin: Post-traumatic brain injury can be divided into two stages: primary injury originates from direct mechanical injury; secondary injury is caused by a series of physiological and biochemical changes including excitotoxicity and inflammation
.

Because primary damage is uncontrollable, treatment of brain injury usually focuses on the mitigation of secondary damage
.

From this perspective, NMDAR is known to be a key molecule mediating excitotoxicity, and our findings suggest that NMDAR can also cause neuroinflammation, suggesting that NMDAR is a core signaling molecule in secondary injury
.

The inhibitors we currently use in animals require larger doses to effectively shut down the NMDAR-Ptgs2 pathway, which causes larger side effects and is less feasible
.

If NMDAR inhibitors with fewer side effects can be developed, it may have a good therapeutic effect on brain injury
.

In addition, the use of Ptgs2 inhibitors may be an effective method: our experiments on Ptgs2 knockout mice found that Ptgs2 is the core molecule that controls glial cell activation, although the Ptgs2 at work comes from neurons or other There is no direct evidence for this issue of cells, and more in-depth research is still needed
.

It should be noted that Ptgs2 inhibitors are common non-steroidal anti-inflammatory drugs, but such drugs are not very successful in clinical treatment of brain injury, and the reasons need further analysis
.

References Chen, Y.
, Wang, Y.
, Modrusan, Z.
, Sheng, M.
, and Kaminker, JS (2014).
Regulation of neuronal gene expression and survival by basal NMDA receptor activity: a role for histone deacetylase 4.
The Journal of neuroscience : the official journal of the Society for Neuroscience 34, 15327-15339.
The author introduces Chen Yelin, researcher Chen Yelin, researcher and doctoral supervisor of the Interdisciplinary Research Center of Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences
.

He graduated from Peking University with a bachelor's degree in biochemistry and molecular biology, and then entered Vanderbilt University in the United States to conduct research and development of new psychotropic drugs targeting glutamate receptors, and obtained a doctorate degree in neurobiology.
The Faculty and Genentech Biotechnology conduct postdoctoral training in the same research area
.

In 2015, he joined the Interdisciplinary Research Center of Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences as research team leader and researcher, focusing on the pathogenesis of mental diseases and neurodegenerative diseases
.

The research group mainly uses molecular cell neurobiology and pharmacology to study the pathogenic mechanism of brain diseases
.

Professor Huazhi Shen Huazhi Shen (Morgan Sheng), Fellow of the Royal Society; Co-Director of the Stanley Center for Psychiatry at Harvard University and the Broad Institute of MIT; Professor of the Department of Brain and Cognitive Sciences, MIT
.

From 2001 to 2008, he was a professor of the Department of Neuroscience at the Massachusetts Institute of Technology; from 2008 to 2019, he was the senior vice president of neuroscience at Genentech Biotechnology; in 2019, he joined the Broad Institute as the co-director of the Stanley Center for Psychiatry
.

He has served on the editorial boards of Neuron, Journal of Neuroscience, and Current Opinions in Neurobiology, and has published more than 200 peer-reviewed articles to date
.

His main research interests are the molecular mechanisms of synaptic structure and plasticity and the molecular and cellular biology of neurodegenerative diseases
.

Zhou Jia Ph.
D.
candidate at the Interdisciplinary Research Center of Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences
.

In 2016, he entered Chen Yelin's research group to study for a doctoral degree.
His main research direction is NMDA receptor function and brain diseases
.

Related paper information The original paper was published in Cell Reports, a journal of CellPress Cell Press.