Fundamental principles of glial transdifferentiation: NeuroD1 cannot mediate microglia-neuron reprogramming

A joint research by researchers from Peng Bo's research group from the Translational Institute of Brain Science, Fudan University, Mao Ying's research group from Huashan Hospital Affiliated to Fudan University, and Yuan Tifei's research group from Shanghai Mental Health Center uses live-cell imaging, rigorous lineage tracing, and pharmacology.
The phenomenon of NeuroD1-mediated microglia-neuron reprogramming has been systematically explored by multiple approaches
.

On December 6, 2021, the related research results were published in Neuron, a top journal of neuroscience, with the title NeuroD1 induces microglial apoptosis and cannot induce microglia-to-neuron cross-lineage reprogramming

Ideas for microglia-neuron reprogramming

The central nervous system (CNS) is mainly composed of neurons and glial cells
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Unlike peripheral tissues and organs, neurons in the mammalian central nervous system hardly regenerate in adulthood

Microglia are the most regenerative glial cells in the central nervous system
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A preliminary study by Peng Bo's research group at Fudan University found that microglia can regenerate an average of 20% of the cells per day through self-proliferation under repopulation conditions6

Demonstrating three basic principles of glial reprogramming

Astonishing and significant conclusions must be rigorously verified
.

In this study, the researchers propose three basic principles required to fully demonstrate glial-neuron reprogramming: (1) A rationally designed control group (well- designed control) to prove and rule out the possibility of virus leakage; (2) through unambiguous in vivo/live cell imaging evidence, observe the glial-neuron transition process; (3) if the type is killed glial cells, then the glial cell-neuron transdifferentiation mediated by this factor will not occur

The first is lineage tracing, where the researchers used tamoxifen to induce tdTomato-specific expression in almost all microglia of CX3CR1-CreER::Ai14 mice (a permanent marker that expresses tdTomato even if cell fates are shifted)
.

Next, microglia were infected by lentivirus hCAG-NeuroD1-T2A-GFP or hCD68-NeuroD1-T2A-GFP

In observing the microglia-neuron transition process, the researchers observed by live-cell imaging and did not find a morphological transition from neuroD1-expressing microglia to neurons
.

On the contrary, the researchers found that expression of NeuroD1 caused mass death of microglia

Finally, the researchers killed 99% of the microglia in the brain through the CSF1R inhibitor PLX5622, and found that even in this case, there would still be a high proportion of "microglia-derived neurons", and the proportion was different from the same The control group that killed microglia was comparable
.

Therefore, the results of the study further confirm that the previously observed "microglia-neuron reprogramming" is not a real situation, but an experimental artifact generated by the non-specific leakage of the virus

NeuroD1 molecular switch to prevent runaway replacement/transplantation of microglia

The Peng Bo team from Fudan University developed three protocols (Mr BMT, Mr PB and Mr MT) by exploiting the regenerative capacity of microglia, realizing the first efficient exogenous transplantation/replacement of microglia at the whole brain scale9 -12
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This protocol can be used to treat diseases caused by mutations in microglia

Dr.
Rao Yanxia from Shanghai Mental Health Center is the first author and co-corresponding author of the paper
.
Prof.
Peng Bo from the Translational Institute of Brain Science, Fudan University, Prof.
Mao Ying from Huashan Hospital Affiliated to Fudan University, and Prof.
Yuan Tifei from Shanghai Mental Health Center are the co-corresponding authors
.
Many people on the team contributed to this research
.

Paper link: https://