Biol Psychiatry︱ Tianming Gao's team reveals the regulation of astrocytes on adult hippocampal neurogenesis and memory through acetylcholine receptor M1

Written by Li Weipeng, editor in charge, Wang Sizhen, Zha Jiaxue The hippocampal dentate gyrus is one of the important brain regions for adult neurogenesis, and its neurogenesis is regulated by astrocytes in its local microenvironment [1,
Astrocytes are involved in regulating the proliferation and differentiation of adult hippocampal neural stem cells, the maturation of new neurons and the integration of local microcircuits [1-
Such as cytokines, e.
to achieve [1, 6,
Studies have shown that astrocytes express functional receptors for a variety of neurotransmitters, such as glutamate, γ-aminobutyric acid, adenosine triphosphate and acetylcholine receptors [8-1
However, it remains unclear how astrocytes receive and respond to external signals to regulate adult neurogenes.
 Acetylcholine is one of the important neurotransmitters involved in the regulation of adult hippocampal neurogenes.
Among them, the muscarinic acetylcholine receptor M1 (cholinergic receptor muscarinic 1, Chrm1) is one of the most abundant acetylcholine receptor subtypes expressed in the central nervous syst.
So, does Chrm1 on astrocytes play a role in adult hippocampal neurogenesis and learning and memory, and how? In response to these issues, researchers have carried out a series of studi.
 On May 13, 2022, Tianming Gao's team from Southern Medical University published a research paper titled "Astrocytes Mediate Cholinergic Regulation of Adult Hippocampal Neurogenesis and Memory through M1 Muscarinic Receptor" in the journal Biological Psychiatry
.
Li Weipeng and .
Su Xiaohong are the co-first authors of the paper, and Academician Gao Tianming and Associate Professor Yang Jianming are the corresponding autho.
This paper reveals for the first time how astrocytes, as a kind of niche cells of the local microenvironment, regulate adult hippocampal neurogenesis and learning and memory by receiving signals from the cholinergic syst.
(Extended reading: The research progress of Gao Tianming's research group, see "Logical Neuroscience" report: Biol Psychiatry︱ Academician Gao Tianming's team reveals the neural circuit mechanism of ATP regulating depression-like behavior; Mol Psychiatry | Gao Tianming's research group reveals fear memory extinction Mole Psychiatry︱ Gao Tianming’s research group revealed the different roles of astrocytes and neurons in synaptic plasticity and memory; JCI︱ Gao Tianming’s research group revealed that the prefrontal cortex plays an important role in regulating anxiety and fe.
Opposite neural circuits) First, we verified the expression of Chrm1 on astrocytes by immunofluorescence and two-photon calcium imaging (F.
1A-.

Next, in order to further specifically knock out Chrm1 on astrocytes, the team screened mouse strains that are currently commonly used for astrocyte research and found that ALDH1l1-CreERT2 is the most important factor for studying adult neurogenesis in the hippocampal dentate gyr.

Reliable mouse strain [1
Using the Cre-loxp recombination system, the researchers crossed ALDH1l1-creERT2 and Chrm1 fl/fl mice to obtain transgenic mice that specifically knocked out Chrm1 on astrocytes (hereinafter referred to as ALDH1l1-Chrm1fl/fl), ALDH1l1-Chrm1fl/fl mice were also verified at the mRNA, protein and functional levels (Figure 1E-.
 Figure 1 Construction of a transgenic mouse specifically knocking out Chrm1 on astrocytes (Source: Li, WP et .

, Biol Psychiatry, 2022) Next, the researchers used 5-bromo-2'-deoxynucleoside Uracil (5-Bromo-2'-deoxyuridine, BrdU) was used to label the new neurons, and the proliferation and survival/differentiation of the new neurons marked by BrdU in the hippocampal dentate gyrus were observed (Note: BrdU is a thymine analog, because of its molecular structure Similar to thymine T, it provides raw materials for DNA synthesis in the S phase of the cell proliferation cycle, so at this time BrdU can penetrate into the DNA of new cells without affecting the normal function of cells [14.

It was found that there was no significant difference between Nestin+ GFAP+ BrdU+ or Nestin+ GFAP+ Mcm2+ neural stem cells in ALDH1l1-Chrm1fl/fl mice compared with the control group (F.

2A-.

However, the survival (BrdU+) and the number and proportion of neurons differentiated into mature neurons (BrdU+ NeuN+) were significantly reduced in ALDH1l1-Chrm1fl/fl mice after 4 weeks (F.

2G-.

To further study the changes of newborn neurons in ALDH1l1-Chrm1fl/fl mice during the intermediate stage of developing into neurons, the researchers also performed immunofluorescence staining for DCX (Doublecortion, a marker for immature neuron.

The results showed that the number of DCX-positive cells in ALDH1l1-Chrm1fl/fl mice was significantly lower than that in the control group; and from the immunofluorescence staining images, it could be seen that the branched protrusions in ALDH1l1-Chrm1fl/fl mice were sparser than those in the control group (Figure 2K-.


 Figure 2 Specific knockout of Chrm1 on astrocytes results in impaired survival and differentiation of new cells in the dentate gyrus of the hippocampus (Source: Li, WP et .

, Biol Psychiatry, 2022) In order to accurately observe the development of new neurons In this case, researchers used retrovirus to label newborn neurons (Note: Retrovirus retrovirus can only replicate in dividing cells, so it can be used to label newborn cells [15.

Morphological analysis and patch-clamp electrophysiological recordings revealed that retrovirus-labeled neonatal neurons in ALDH1l1-Chrm1fl/fl mice had reduced total dendritic branch length, reduced branch density, and reduced dendritic spine density; electrophysiologically The immature neurons exhibited reduced membrane properties and frequency of excitatory synaptic transmission, but no changes in inhibitory synaptic transmission (F.


The above results indicate that the maturation of neonatal neurons in ALDH1l1-Chrm1fl/fl mice is impaired, and the integration of neonatal neurons into the original neural network of the dentate gyrus is abnorm.

 Figure 3 Specific knockout of Chrm1 on astrocytes results in impaired maturation and integration of new neurons in the hippocampal dentate gyrus (Source: Li, WP et .

, Biol Psychiatry, 2022) Neurogenesis in the hippocampal dentate gyrus In the microenvironment, astrocytes play an important role, and the substances they secrete can affect the proliferation and differentiation of neural stem cells, such as FGF2, IL1β, WNT3 and BDNF [6,
So is it related to the impaired survival and maturation of new cells in the dentate gyrus of the hippocampus in ALDH1l1-Chrm1fl/fl mice? The researchers found that BDNF was significantly reduced in the hippocampus of ALDH1l1-Chrm1fl/fl mice by detecting the mRNA expression levels of various substances secreted by astrocytes (Figure 4A-.

Pharmacological experiments found that Chrm1 agonists could significantly increase the secretion of BDNF in cultured hippocampal astrocytes (F.

4I-.
Therefore, the above results suggest that Chrm1 on astrocytes can regulate the secretion of BD.

 Figure 4 Chrm1 on astrocytes regulates BDNF secretion (Source: Li, WP et .

, Biol Psychiatry, 2022) Next, the researchers used AAV virus vector to knock out Chrm1 astrocytes in the hippocampal dentate gyrus Chrm1 was re-overexpressed on cytoplasmic cells (F.

5A-.

Similarly, we found that Chrm1 overexpression on astrocytes increased the survival and the number of mature neurons differentiated from neonatal neurons in ALDH1l1-Chrm1fl/fl mice by labeling neonatal neurons with BrdU and retrovirus (F.

5D-H); also reversed the abnormal maturation and local microcircuit integration of neonatal neurons in ALDH1l1-Chrm1fl/fl mice (Figure 5I-.

 FigureOverexpression of Chrm1 in hippocampal dentate gyrus astrocytes of ALDH1l1-Chrm1fl/fl mice can reverse the impairment of adult hippocampal neurogenesis (Source: Li, WP et .

, Biol Psychiatry, 2022) The researchers further found that overexpression of Chrm1 on ALDH1l1-Chrm1fl/fl mouse astrocytes could increase the expression level of BDNF (F.

6A-.

Next, pharmacologically blocking the BDNF receptor TrkB was found to reverse the rescue effect caused by overexpression of Chrm1 on its astrocytes (F.

6D-.

Therefore, the above results suggest that Chrm1 on astrocytes can regulate their secreted BDNF, which in turn affects adult hippocampal neurogenes.
Figure 6 Chrm1 on astrocytes regulates the maturation and integration of newborn neurons through the BDNF-TrkB signaling pathway (Source: Li, WP et .

, Biol Psychiatry, 2022) In animal behavior, ALDH1l1-Chrm1fl/fl is small Mice exhibited impaired fear memory in conditioned contexts; overexpression of Chrm1 on astrocytes reversed the displayed behavioral abnormalities (F.


The results suggest that Chrm1 on hippocampal dentate gyrus astrocytes is important for conditioned scene fear memo.

 Figure 7 Chrm1 on astrocytes in the hippocampal dentate gyrus regulates contextual fear memory (Source: Li, WP et .

, Biol Psychiatry, 2022) Figure 8 Work summary: astrocytes pass muscarinic acetylcholine The regulatory role of receptor M1 (Chrm1) on neurogenesis and memory in the adult hippocampus (Image source: Li, WP et .

, Biol Psychiatry, 2022) Conclusion and discussion, inspiration and prospect Transgenic mice specifically knocked out muscarinic acetylcholine receptor M1 (Chrm1) on glial cells, combined with immunofluorescence staining, retroviral labeling, primary astrocyte culture, electrophysiology, western blotting, and behavior From the molecular, cellular and overall levels, it has been revealed that astrocytes sense cholinergic signals mediated by Chrm1, thereby regulating the neurogenesis of the adult hippocampus, and the mechanism may be through the release of BDNF ( Figure
Of course, there are still some unresolved questions in this study, such as the decreased levels of astrocyte-derived BDNF in ALDH1l1-Chrm1fl/fl mice, but whether neuronal-derived BDNF is also altered, the experimental evidence still remains Further research is requir.

In the learning and memory mechanism, the evidence of the direct causal relationship of "astroglial Chrm1-adult hippocampal neurogenesis-conditioned scene fear memory" still needs further experiments to pro.
In conclusion, this study is the first to discover the regulatory function of astrocytes on adult hippocampal neurogenesis and learning and memory by sensing cholinergic signals, which provides a new perspective for the treatment of cholinergic diseases such as Alzheimer's disea.

Link to the original text: https://d.

org/11016.

biopsy.

2020019 Li Weipeng (left), .


, first author; Gao Tianming (right), professor, corresponding auth.
(Photo provided by: Gao Tianming's Laboratory, Southern Medical University) Special column: progress report of Gao Tianming's research group [1] Biol Psychiatry︱ Academician Gao Tianming's team reveals the neural circuit mechanism of ATP regulating depression-like behavior [2] Mol Psychiatry | Tianming's group reveals the local neural network mechanism of fear memory extinction 【3】Mol Psychiatry︱Gao Tianming's group reveals the different roles of astrocytes and neurons in synaptic plasticity and memory 【4】JCI︱Gao Tianming's group Revealing the neural circuits that prefrontal cortex has opposite roles in regulating anxiety and fear Review︱Fan Dongsheng's team focused on the interaction between peripheral and central immune systems in amyotrophic lateral sclerosis [2] NPP︱Lu Wei's team revealed a new mechanism of GABAA receptor auxiliary subunit phosphorylation to regulate neural behavior [3] Cereb Cortex︱ Pattern rigidity, the role of temporal dynamics of ventromedial prefrontal cortex on rumination and depression 【4】Front Aging Neurosci︱PTAFR as a novel biomarker for Alzheimer’s disease diagnosis and treatment 【5】PNAS︱Feng Guoping experiment The study reveals the important role of the anterior thalamic circuit in working memory【6】Mol Psychiatry︱ Keqiang Ye’s group revealed that inflammation-activated C/EBPβ/AEP signaling pathway mediates high-fat diet-induced diabetes and Alzheimer’s disease【7】 PNAS︱ Changhe Wang’s research group reveals a new mechanism of synaptic exocytosis-endocytosis balance [8] Autophagy︱ Ye Yihong’s research group reveals a new molecular mechanism of neuronal ceroid lipofuscin deposition: DNAJC5/CSPα gene mutation leads to lysosome stabilization State imbalance [9] J Neuroinflammation | Wang Yilong's team reported new evidence on the relationship between blood inflammatory markers and cerebral small vessel disease [10] Science︱Neural mechanism of non-cued goal-directed behavior Recommended for high-quality scientific research training courses [1] Academic paper writing practice Training class (live: 20221~22) [2] Symposium on Single-Cell Sequencing and Spatial Transcriptomic Data Analysis (Tencent Online Conference on June 11-12) [3] Seminar on Patch Clamp and Optogenetics and Calcium Imaging Technology on May 21-22 at Tencent Conference Symposium [1] Symposium Series︱Inside the Brain: Imaging Research References of the Amygdala Circuit (swipe up and down to read) [
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