Novel Approach to Visualize Microglia Death and Proliferation After Intracerebral Hemorrhage in Mice

Abstract

Background: Microglia are important brain immune cells. However, it is difficult to differentiate microglia from monocyte-derived macrophages. To visualize microglia changes following intracerebral hemorrhage (ICH), we utilized a genetic knock-in mouse line, Tmem119 (transmembrane protein 119)-EGFP (enhanced green fluorescent protein), which expresses EGFP specifically in microglia. Methods: There were 2 parts in this study. First, autologous blood was injected into the right basal ganglia to model ICH in Tmem119-EGFP mice. Mice were euthanized at 4 hours, days 1, 3, and 7 after ICH. Sham animals were used as controls. Second, Tmem119-EGFP mice were injected with iron or thrombin, factors involved in ICH-induced injury, and were euthanized at 4 hours. Naïve mice were controls. Brains were harvested for histology. Results: The number of perihematomal microglia significantly decreased 1 day after ICH, but markedly increased by days 3 and 7. Microglia death was also induced by intracerebral iron injection while microglia proliferation was found with intracerebral thrombin injection. Conclusions: Perihematomal microglia death and proliferation after ICH are visualized in vivo with a Tmem119-EGFP transgenic mouse line. Iron and thrombin may contribute to ICH-induced microglia death and proliferation, respectively.

Characteristics of activation of monocyte-derived macrophages versus microglia after mouse experimental intracerebral hemorrhage

“…In our previous study, 19 we were able to detect an enhanced green fluorescent signal in perihematomal microglia at day 3 and day 7 after experimental ICH in Tmem119-EGFP mice, along with an increased number of microglia. Similarly, microglia can be found with enhanced fluorescence signals after intracerebral thrombin injection.…”

“…17 Previously, we have used the Tmem119-EFGP mice to demonstrate the microglia death after ICH by day 1 and proliferation by days 3 and 7 as a natural history of microglia response to ICH. 19 In this study, we focused on the changes of MDMs versus microglia and, in particular, their phagocytic activity, as well as their response to phagocyte depletion with clodronate liposomes and phagocytic enhancement by CD47 blocking antibody. With the microglia identified with gene editing, the MDMs population can subsequently be established with a generalized macrophage marker (such as F4/80).…”

“…We found the number of perihematomal microglia decreased 1 day after ICH, while markedly increasing in number and being highly activated by day 3 and day 7. 19…”

Iron homeostasis imbalance and ferroptosis in brain diseases

“…Timeline of microglia and iron after hemorrhage stroke (A) and ischemic stroke (B). These timelines are based on the data from the male rat model of AIS and HS 95–98 . Iron deposition in hemorrhage stroke is more rapid than in ischemic stroke due to the release of iron by the dissolution of mass red blood cells.…”

Peripheral macrophages causally contribute to disease onset and progression in theNdufs4(KO) model of Leigh syndrome

“…In our recent work, we found that low doses of the pexidartinib (sufficient to deplete microglia but not peripheral macrophages) fail to substantially alter disease course while high doses prevent disease. Moreover, staining of lesions using a TMEM119-GFP reporter revealed that a substantial fraction of IBA1(+) cells in CNS lesions do not express this microglia-specific marker [24, 30]. Defining the roles of individual phagocytic cell populations is important for developing immune-targeting strategies into therapies, as CNS microglia and peripheral macrophages have distinct pharmacological properties and targets.…”