Hammond TR, Dufort C, Dissing-Olesen L, Giera S, Young A, Wysoker A, Walker AJ, Gergits F, Segel M, Nemesh J, Marsh SE, Saunders A, Macosko E, Ginhoux F, Chen J, Franklin RJM, Piao X, McCarroll SA, Stevens B.Single-Cell RNA Sequencing of Microglia throughout the Mouse Lifespan and in the Injured Brain Reveals Complex Cell-State Changes. Immunity. 2018 Nov 21. pii: S1074-7613(18)30485-0. doi: 10.1016/j.immuni.2018.11.004. [Epub ahead of print]
Complex cell-state changes revealed by single cell RNA sequencing of 76,149 microglia throughout the mouse lifespan and in the injured brain. Timothy R Hammond, Connor Dufort, Lasse Dissing-Olesen, Stefanie Giera, Adam Young, Alec Wysoker, Alec J Walker, Michael Segel, James Nemesh, Arpiar Saunders, Evan Macosko, Robin JM Franklin, Xianhua Piao, Steve McCarroll, Beth Stevensdoi: https://doi.org/10.1101/406140
comprising 10% of brain cells. Not only are microglia active in
injury and disease, but they also play critical roles in brain
maintenance and development.
different morphologies and are distributed unevenly in the
brain (Karperien et al., 2013). They congregate in specific areas,
including the ventricular zone and around growing axon tracts,
and not in other areas, like the developing cortex (Squarzoni et
al., 2014), suggesting that transcriptionally and functionally
different subpopulations of microglia exist.
states across all ages and conditions, including injury .
Cluster sizes ranged from 0.2% of all microglia to as many as
24% of all microglia
diversity at the youngest ages (E14.5 (embryonic day 14.5. A mouse is born on E20-E21and P5 (5 days after birth) and considerably
less diversity in juveniles (P30 a month old. Mice mature at 5-6 weeks) and adults (P100 about 3 moths old)
highly expressed by most of the analyzed cells, but
interestingly, only three (C1qa, Fcrls, Trem2) were uniformly
expressed in all clusters (Fig 1e), suggesting existing tools and
marker definitions need to be updated.
definitions were previously established in adult animals and they found that
P2ry12, Cx3cr1 (often used in conditional knockouts), and Tmem119 were expressed at
much lower levels or not at all in certain clusters of microglia
from the developing brain.
Gene expression patterns show that each microglial state reflects a specific and definable transcriptional program, rather than a simple modulation of commonly expressed microglial genes.
the most enriched subpopulation was defined by the gene
chemokine (C-C motif) ligand 4 (Ccl4,
expressed the genes coagulation factor XIII, A1 subunit (F13a1,
macrophage), histocompatibility 2, class II antigen A, alpha
(H2-Aa, macrophage), chemokine (C-C motif) receptor 2 (Ccr2,
monocyte), lymphatic vessel endothelial hyaluronan receptor 1
(Lyve1, macrophage), and macrophage galactose N-acetylgalactosamine
specific lectin 2 (Mgl2, macrophage), genes that
were barely expressed, if at all, by microglia
identified as being enriched in aging mice
Injury Cluster–specific genes were variably upregulated
among the microglia , suggesting the existence of
subpopulations within the cluster. To delineate these genes, they created three categories: broadly responsive genes that were
upregulated in greater than 60% of Injury Cluster 2 microglia,
responsive genes that were upregulated in 30–60%, and
selectively responsive genes that were upregulated in less than
30%. Broadly responsive genes included
apolipoprotein E (Apoe), Ifi27l2a, and the major
histocompatibility complex II (MHC-II) genes H2-Aa and H2-K1
(Fig 6d). Responsive genes included several interferon response
genes (Irf7, Oasl2, and Ifit3), Ccl3, and lipoprotein lipase (Lpl)
(Fig 6d). Selectively responsive genes included AXL receptor
tyrosine kinase (Axl), Ccl4, chemokine (C-X-C motif) ligand 10
(Cxcl10), and Birc5 (Fig 6d).
I am sorry I don’t have the time to fully explore this paper. Maybe when it is printed, it will have an editorial. We have seen how M1 become M2 as cell subsets are not static, etc. This shows that the simplistic one-two subsets of cells is far off the biology.