CX3CR1 deficiency suppresses activation and neurotoxicity of microglia/macrophage in experimental ischemic stroke.
BACKGROUND
Chemokine (C-X3-C motif) ligand 1 (CX3CL1)/ CX3C chemokine receptor 1 (CX3CR1) signaling is important in modulating the communication between neurons and resident microglia/migrated macrophages in the central nervous system (CNS). Although CX3CR1 deficiency is associated with an improved outcome following ischemic brain injury, the mechanism of this observation is largely unknown. The aim of this study was to investigate how CX3CR1 deficiency influences microglia/macrophage functions in the context of its protection following brain ischemia.


METHODS
Wild-type (WT) and CX3CR1-deficient (CX3CR1⁻/⁻) mice were subjected to transient middle cerebral artery occlusion (MCAO) and reperfusion. The ischemic brain damage was monitored by rodent high-field magnetic resonance imaging. Neurological deficit was assessed daily. Neuronal apoptotic death and reactive oxygen species (ROS) production were analyzed by immunostaining and live imaging. Activation/inflammatory response of microglia/macrophage were assessed using immunohistochemistry, flow cytometry, 5-bromo-2-deoxyuridine labeling, cytokine ELISA, and real-time PCR.


RESULTS
CX3CR1⁻/⁻ mice displayed significantly smaller infarcts and less severe neurological deficits compared to WT controls, following MCAO. In addition, CX3CR1⁻/⁻ MCAO mice displayed fewer apoptotic neurons and reduced ROS levels. Impaired CX3CR1 signaling abrogated the recruitment of monocyte-derived macrophages from the periphery, suppressed the proliferation of CNS microglia and infiltrated macrophage, facilitated the alternative activation (M2 state) of microglia/macrophages, and attenuated their ability to synthesize and release inflammatory cytokines.


CONCLUSIONS
Our results suggest that inhibition of CX3CR1 signaling could function as a therapeutic modality in ischemic brain injury, by reducing recruitment of peripheral macrophages and expansion/activation of CNS microglia and macrophages, resulting in protection of neurological function.
Zhiwei
Z
Tang
Yan
Y
Gan
Qiang
Q
Liu
Jun-Xiang
JX
Yin
Qingwei
Q
Liu
Jiong
J
Shi
Department of Neurology and the BNI-ASU Center for Preclinical Imaging, Barrow Neurological Institute, St, Joseph's Hospital and Medical Center, 350 West Thomas Road, Phoenix, Arizona 85013, USA. Fu-Dong.Shi@dignityhealth.org.
Fu-Dong
FD
Shi
D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D017209:Apoptosis / Q000235:genetics; D020520:Brain Infarction / Q000209:etiology / Q000235:genetics; D000073883:CX3C Chemokine Receptor 1; D049109:Cell Proliferation; D002490:Central Nervous System / Q000473:pathology*; D004195:Disease Models, Animal; D007839:Functional Laterality; D020244:Infarction, Middle Cerebral Artery / Q000150:complications* / Q000473:pathology*; D008264:Macrophages / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D017628:Microglia / Q000378:metabolism* / Q000473:pathology; D009422:Nervous System Diseases / Q000209:etiology; D017382:Reactive Oxygen Species / Q000378:metabolism; D019707:Receptors, Chemokine / Q000172:deficiency* / Q000235:genetics; D015424:Reperfusion; D015398:Signal Transduction / Q000235:genetics
D015703:Antigens, CD; D000073883:CX3C Chemokine Receptor 1; C471885:Cx3cr1 protein, mouse; D017382:Reactive Oxygen Species; D019707:Receptors, Chemokine