Immature monocytes recruited to the ischemic mouse brain differentiate into macrophages with features of alternative activation.
Acute stroke induces a local inflammatory reaction causing leukocyte infiltration. Circulating monocytes are recruited to the ischemic brain and become tissue macrophages morphologically indistinguishable from reactive microglia. However, monocytes are a heterogeneous population of cells with different functions. Herein, we investigated the infiltration and fate of the monocyte subsets in a mouse model of focal brain ischemia by permanent occlusion of the distal portion of the middle cerebral artery. We separated two main subtypes of CD11b(hi) monocytes according to their expression of the surface markers Ly6C and CD43. Using adoptive transfer of reporter monocytes and monocyte depletion, we identified the pro-inflammatory Ly6C(hi)CD43(lo)CCR2(+) subset as the predominant monocytes recruited to the ischemic tissue. Monocytes were seen in the leptomeninges from where they entered the cortex along the penetrating arterioles. Four days post-ischemia, they had invaded the infarcted core, where they were often located adjacent to blood vessels. At this time, Iba-1(-) and Iba-1(+) cells in the ischemic tissue incorporated BrdU, but BrdU incorporation was rare in the reporter monocytes. The monocyte phenotype progressively changed by down-regulating Ly6C, up-regulating F4/80, expressing low or intermediate levels of Iba-1, and developing macrophage morphology. Moreover, monocytes progressively acquired the expression of typical markers of alternatively activated macrophages, like arginase-1 and YM-1. Collectively, the results show that stroke mobilized immature pro-inflammatory Ly6C(hi)CD43(lo) monocytes that acutely infiltrated the ischemic tissue reaching the core of the lesion. Monocytes differentiated to macrophages with features of alternative activation suggesting possible roles in tissue repair during the sub-acute phase of stroke.
Àrea de Neurociències, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), 08036 Barcelona, Spain.
Francesc
F
Miró-Mur
Àrea de Neurociències, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), 08036 Barcelona, Spain; Departament d'Isquèmia Cerebral i Neurodegeneració, Institut d'Investigacions Biomèdiques de Barcelona (IIBB), Consejo Superior de Investigaciones Científicas (CSIC), 08036 Barcelona, Spain.
Isabel
I
Pérez-de-Puig
Àrea de Neurociències, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), 08036 Barcelona, Spain; Departament d'Isquèmia Cerebral i Neurodegeneració, Institut d'Investigacions Biomèdiques de Barcelona (IIBB), Consejo Superior de Investigaciones Científicas (CSIC), 08036 Barcelona, Spain.
Maura
M
Ferrer-Ferrer
Àrea de Neurociències, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), 08036 Barcelona, Spain; Functional Stroke Unit of Cerebrovascular Diseases, Hospital Clínic, 08036 Barcelona, Spain.
Xabier
X
Urra
Àrea de Neurociències, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), 08036 Barcelona, Spain; Departament d'Isquèmia Cerebral i Neurodegeneració, Institut d'Investigacions Biomèdiques de Barcelona (IIBB), Consejo Superior de Investigaciones Científicas (CSIC), 08036 Barcelona, Spain.
Carles
C
Justicia
Àrea de Neurociències, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), 08036 Barcelona, Spain; Functional Stroke Unit of Cerebrovascular Diseases, Hospital Clínic, 08036 Barcelona, Spain.
Angel
A
Chamorro
Àrea de Neurociències, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), 08036 Barcelona, Spain; Departament d'Isquèmia Cerebral i Neurodegeneració, Institut d'Investigacions Biomèdiques de Barcelona (IIBB), Consejo Superior de Investigaciones Científicas (CSIC), 08036 Barcelona, Spain. Electronic address: anna.planas@iibb.csic.es.
Anna M
AM
Planas
D019264:Adoptive Transfer; D000818:Animals; D002545:Brain Ischemia / Q000276:immunology* / Q000378:metabolism / Q000473:pathology / Q000628:therapy; D002454:Cell Differentiation / Q000276:immunology; D004195:Disease Models, Animal; D007958:Leukocyte Count; D008264:Macrophages / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D017628:Microglia / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D009000:Monocytes / Q000276:immunology* / Q000378:metabolism / Q000473:pathology / Q000637:transplantation; D011897:Random Allocation; D054390:Receptors, CCR2 / Q000378:metabolism; D020521:Stroke / Q000276:immunology / Q000378:metabolism / Q000473:pathology / Q000628:therapy
D054390:Receptors, CCR2
Alternative M2 phenotype; Cerebral ischemia; Macrophages; Microglia; Monocytes