Spatio-temporal profile, phenotypic diversity, and fate of recruited monocytes into the post-ischemic brain.

TitleSpatio-temporal profile, phenotypic diversity, and fate of recruited monocytes into the post-ischemic brain.
Publication TypeJournal Article
Year of Publication2016
AuthorsGarcia-Bonilla L, Faraco G, Moore J, Murphy M, Racchumi G, Srinivasan J, Brea D, Iadecola C, Anrather J
JournalJ Neuroinflammation
Date Published2016 Nov 04
KeywordsAnimals, Brain, Calcium-Binding Proteins, Cell Movement, Disease Models, Animal, Endothelial Cells, Gene Expression Regulation, Glucose Transporter Type 1, Infarction, Middle Cerebral Artery, Male, Mice, Mice, Inbred C57BL, Mice, Transgenic, Microfilament Proteins, Monocytes, Myocytes, Smooth Muscle, Nerve Tissue Proteins, Neurons, Nuclear Receptor Subfamily 4, Group A, Member 1, Receptors, CCR2, Receptors, Interleukin-8A

BACKGROUND: A key feature of the inflammatory response after cerebral ischemia is the brain infiltration of blood monocytes. There are two main monocyte subsets in the mouse blood: CCR2+Ly6Chi "inflammatory" monocytes involved in acute inflammation, and CX3CR1+Ly6Clo "patrolling" monocytes, which may play a role in repair processes. We hypothesized that CCR2+Ly6Chi inflammatory monocytes are recruited in the early phase after ischemia and transdifferentiate into CX3CR1+Ly6Clo "repair" macrophages in the brain.

METHODS: CX3CR1GFP/+CCR2RFP/+ bone marrow (BM) chimeric mice underwent transient middle cerebral artery occlusion (MCAo). Mice were sacrificed from 1 to 28 days later to phenotype and map subsets of infiltrating monocytes/macrophages (Mo/MΦ) in the brain over time. Flow cytometry analysis 3 and 14 days after MCAo in CCR2-/- mice, which exhibit deficient monocyte recruitment after inflammation, and NR4A1-/- BM chimeric mice, which lack circulating CX3CR1+Ly6Clo monocytes, was also performed.

RESULTS: Brain mapping of CX3CR1GFP/+ and CCR2RFP/+ cells 3 days after MCAo showed absence of CX3CR1GFP/+ Mo/MΦ but accumulation of CCR2RFP/+ Mo/MΦ throughout the ischemic territory. On the other hand, CX3CR1+ cells accumulated 14 days after MCAo at the border of the infarct core where CCR2RFP/+ accrued. Whereas the amoeboid morphology of CCR2RFP/+ Mo/MΦ remained unchanged over time, CX3CR1GFP/+ cells exhibited three distinct phenotypes: amoeboid cells with retracted processes, ramified cells, and perivascular elongated cells. CX3CR1GFP/+ cells were positive for the Mo/MΦ marker Iba1 and phenotypically distinct from endothelial cells, smooth muscle cells, pericytes, neurons, astrocytes, or oligodendrocytes. Because accumulation of CX3CR1+Ly6Clo Mo/MΦ was absent in the brains of CCR2 deficient mice, which exhibit deficiency in CCR2+Ly6Chi Mo/MΦ recruitment, but not in NR4A1-/- chimeric mice, which lack of circulating CX3CR1+Ly6Clo monocytes, our data suggest a local transition of CCR2+Ly6Chi Mo/MΦ into CX3CR1+Ly6Clo Mo/MΦ phenotype.

CONCLUSIONS: CX3CR1+Ly6Clo arise in the brain parenchyma from CCR2+Ly6Chi Mo/MΦ rather than being de novo recruited from the blood. These findings provide new insights into the trafficking and phenotypic diversity of monocyte subtypes in the post-ischemic brain.

Alternate JournalJ Neuroinflammation
PubMed ID27814740
PubMed Central IDPMC5097435
Grant ListR01 NS034179 / NS / NINDS NIH HHS / United States
R01 NS081179 / NS / NINDS NIH HHS / United States
R37 NS034179 / NS / NINDS NIH HHS / United States