New Tools for Genetically Targeting Myeloid Populations in the Central Nervous System

Abstract

As the resident macrophages of the brain and spinal cord, microglia are crucial for the phagocytosis of infectious agents, apoptotic cells and synapses. Developmentally, microglia originate from the embryonic yolk sac and serve important roles in the sculpting of neonatal neural circuits. During brain injury or infection, bone-marrow derived macrophages invade neural tissue, making it difficult to distinguish between invading macrophages and resident microglia. In addition to circulation-derived monocytes, other non-microglial central nervous system (CNS) macrophage subtypes include borderzone (meningeal and perivascular) and choroid plexus macrophages. To distinguish between resident microglia and these other CNS macrophage subtypes, we generated a P2ry12-CreER mouse line. P2RY12 is a microglialspecific nucleotide sensing GPCR that is important for microglial response to tissue damage. Using immunofluorescent labeling and flow cytometry experiments, we show that P2ry12-CreER recombination is exceptionally specific to parenchymal microglia. We also perform ribosome immunoprecipitations and transcriptional profiling of P2ry12-CreER recombined cells, using a Cre-dependent Rpl22-HA mouse line. By identifying genes enriched in this dataset that are not correspondingly enriched in a broader Cx3CR1-CreER; Rpl22 dataset, we isolate a number of borderzone macrophage-specific transcripts, including the gene PF4. Using a PF4-Cre mouse line, we show that PF4 expression robustly marks borderzone macrophages. Together, we demonstrate two new methods to genetically target distinct CNS macrophage subtypes.

Meta-Analysis of Leukocyte Diversity in Atherosclerotic Mouse Aortas

“…Pf4 expression was proposed to reflect platelet/macrophage conjugates. However, several studies in reporter mice driven by Pf4-Cre have demonstrated widespread macrophage expression of this gene, notably in peritoneal macrophages 152 and (peri)vascular macrophages 153 . Thus, Pf4 can no longer be considered platelet-specific.…”

Neuroimmune interaction in seizures and epilepsy: focusing on monocyte infiltration

“…Similarly, P2Y12 has also been shown to distinguish resident microglia from infiltrated monocytes [25,59]. As such, this marker is also being targeted for the development of genetic tools that can be utilized for the labeling and separation of microglia from monocytes [60]. However, it should be noted that under certain pathological conditions, microglia‐specific markers ( i.e., P2Y12) can be down‐regulated following activation [61,62].…”

“…Similarly, P2Y12 has also been shown to distinguish resident microglia from infiltrated monocytes [25,59]. As such, this marker is also being targeted for the development of genetic tools that can be utilized for the labeling and separation of microglia from monocytes [60]. However, it Fig.…”