An overlooked subset of Cx3cr1 wt/wt microglia in the Cx3cr1 CreER-Eyfp/wt mouse has a repopulation advantage over Cx3cr1 CreER-Eyfp/wt microglia following microglial depletion

• Published in: Journal of neuroinflammation 2022, Vol.19 (1), p.20-18
• Main Authors: Zhou, Kai, Han, Jinming, Lund, Harald, Boggavarapu, Nageswara Rao, Lauschke, Volker M, Goto, Shinobu, Cheng, Huaitao, Wang, Yuyu, Tachi, Asuka, Xie, Cuicui, Zhu, Keying, Sun, Ying, Osman, Ahmed M, Liang, Dong, Han, Wei, Gemzell-Danielsson, Kristina, Betsholtz, Christer, Zhang, Xing-Mei, Zhu, Changlian, Enge, Martin, Joseph, Bertrand, Harris, Robert A, Blomgren, Klas
• Format: Article
• Language: English
• Subjects: Animals; Cre; CX3C Chemokine Receptor 1 - genetics; CX3C Chemokine Receptor 1 - metabolism; Cx3cr1; GFP; Mice; Mice, Transgenic; Microglia; Microglia - metabolism; Microglial depletion; Signal Transduction; YFP
• ISSN: 1742-2094
• DOI: 10.1186/s12974-022-02381-6

Fluorescent reporter labeling and promoter-driven Cre-recombinant technologies have facilitated cellular investigations of physiological and pathological processes, including the widespread use of the Cx3cr1 mouse strain for studies of microglia. Immunohistochemistry, Flow Cytometry, RNA sequencing and whole-genome sequencing were used to identify the subpopulation of microglia in Cx3cr1 mouse brains. Genetically mediated microglia depletion using Cx3cr1 Rosa26 mice and CSF1 receptor inhibitor PLX3397 were used to deplete microglia. Primary microglia proliferation and migration assay were used for in vitro studies. We unexpectedly identified a subpopulation of microglia devoid of genetic modification, exhibiting higher Cx3cr1 and CX3CR1 expression than Cx3cr1 Cre Eyfp microglia in Cx3cr1 mouse brains, thus termed Cx3cr1 Cre Eyfp microglia. This subpopulation constituted less than 1% of all microglia under homeostatic conditions, but after Cre-driven DTA-mediated microglial depletion, Cx3cr1 Cre Eyfp microglia escaped depletion and proliferated extensively, eventually occupying one-third of the total microglial pool. We further demonstrated that the Cx3cr1 Cre Eyfp microglia had lost their genetic heterozygosity and become homozygous for wild-type Cx3cr1. Therefore, Cx3cr1 Cre Eyfp microglia are Cx3cr1 Cre Eyfp . Finally, we demonstrated that CX3CL1-CX3CR1 signaling regulates microglial repopulation both in vivo and in vitro. Our results raise a cautionary note regarding the use of Cx3cr1 mouse strains, particularly when interpreting the results of fate mapping, and microglial depletion and repopulation studies.