title: White matter injury and microglia/macrophage polarization are strongly linked with age-related long-term deficits in neurological function after stroke.
abstract: Most of the successes in experimental models of stroke have not translated well to the clinic. One potential reason for this failure is that stroke mainly afflicts the elderly and the majority of experimental stroke studies rely on data gathered from young adult animals. Therefore, in the present study we established a reliable, reproducible model of stroke with low mortality in aged (18month) male mice and contrasted their pathophysiological changes with those in young (2month) animals. To this end, mice were subjected to permanent tandem occlusion of the left distal middle cerebral artery (dMCAO) with ipsilateral common carotid artery occlusion (CCAO). Cerebral blood flow (CBF) was evaluated repeatedly during and after stroke. Reduction of CBF was more dramatic and sustained in aged mice. Aged mice exhibited more severe long-term sensorimotor deficits, as manifested by deterioration of performance in the Rotarod and hanging wire tests up to 35d after stroke. Aged mice also exhibited significantly worse long-term cognitive deficits after stroke, as measured by the Morris water maze test. Consistent with these behavioral observations, brain infarct size and neuronal tissue loss after dMCAO were significantly larger in aged mice at 2d and 14d, respectively. The young versus aged difference in neuronal tissue loss, however, did not persist until 35d after dMCAO. In contrast to the transient difference in neuronal tissue loss, we found significant and long lasting deterioration of white matter in aged animals, as revealed by the loss of myelin basic protein (MBP) staining in the striatum at 35d after dMCAO. We further examined the expression of M1 (CD16/CD32) and M2 (CD206) markers in Iba-1(+) microglia by double immunofluorescent staining. In both young and aged mice, the expression of M2 markers peaked around 7d after stroke whereas the expression of M1 markers peaked around 14d after stroke, suggesting a progressive M2-to-M1 phenotype shift in both groups. However, aged mice exhibited significantly reduced M2 polarization compared to young adults. Remarkably, we discovered a strong positive correlation between favorable neurological outcomes after dMCAO and MBP levels or the number of M2 microglia/macrophages. In conclusion, our studies suggest that the distal MCAO stroke model consistently results in ischemic brain injury with long-term behavioral deficits, and is therefore suitable for the evaluation of long-term stroke outcomes. Furthermore, aged mice exhibit deterioration of functional outcomes after stroke and this deterioration is linked to white matter damage and reductions in M2 microglia/macrophage polarization.
authors.affiliation: Center of Cerebrovascular Disease Research, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Suenaga
authors.affiliation: Center of Cerebrovascular Disease Research, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA; The State Key Laboratory of Medical Neurobiology, The Institutes of Brain Science and the Collaborative Innovation Center for Brain Science, Fudan University, Shanghai 200032, China; Geriatric Research, Educational and Clinical Center, Veterans Affairs Pittsburgh Health Care System, Pittsburgh, PA 15261, USA.
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Hu
authors.affiliation: Center of Cerebrovascular Disease Research, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA; The State Key Laboratory of Medical Neurobiology, The Institutes of Brain Science and the Collaborative Innovation Center for Brain Science, Fudan University, Shanghai 200032, China.
authors.forename: Hongjian
authors.initials: H
authors.lastname: Pu
authors.affiliation: Center of Cerebrovascular Disease Research, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA; Geriatric Research, Educational and Clinical Center, Veterans Affairs Pittsburgh Health Care System, Pittsburgh, PA 15261, USA.
authors.forename: Yejie
authors.initials: Y
authors.lastname: Shi
authors.affiliation: Center of Cerebrovascular Disease Research, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
authors.forename: Sulaiman Habib
authors.initials: SH
authors.lastname: Hassan
authors.affiliation: The State Key Laboratory of Medical Neurobiology, The Institutes of Brain Science and the Collaborative Innovation Center for Brain Science, Fudan University, Shanghai 200032, China.
authors.forename: Mingyue
authors.initials: M
authors.lastname: Xu
authors.affiliation: Division of Pharmaceutical Sciences, Duquesne University, Pittsburgh, PA 15282, USA.
authors.forename: Rehana K
authors.initials: RK
authors.lastname: Leak
authors.affiliation: Center of Cerebrovascular Disease Research, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA; Geriatric Research, Educational and Clinical Center, Veterans Affairs Pittsburgh Health Care System, Pittsburgh, PA 15261, USA.
authors.forename: R Anne
authors.initials: RA
authors.lastname: Stetler
authors.affiliation: The State Key Laboratory of Medical Neurobiology, The Institutes of Brain Science and the Collaborative Innovation Center for Brain Science, Fudan University, Shanghai 200032, China. Electronic address: yqgao@shmu.edu.cn.
authors.forename: Yanqin
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Center of Cerebrovascular Disease Research, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA; The State Key Laboratory of Medical Neurobiology, The Institutes of Brain Science and the Collaborative Innovation Center for Brain Science, Fudan University, Shanghai 200032, China; Geriatric Research, Educational and Clinical Center, Veterans Affairs Pittsburgh Health Care System, Pittsburgh, PA 15261, USA. Electronic address: chenj2@upmc.edu.
authors.forename: Jun
authors.initials: J
authors.lastname: Chen
mesh_terms: D000375:Aging; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D020520:Brain Infarction / Q000209:etiology; D002452:Cell Count; D016764:Cell Polarity / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology; D004195:Disease Models, Animal; D056784:Leukoencephalopathies / Q000209:etiology*; D008264:Macrophages / Q000502:physiology*; D008297:Male; D018782:Maze Learning; D051379:Mice; D008810:Mice, Inbred C57BL; D017628:Microglia / Q000502:physiology*; D009043:Motor Activity / Q000502:physiology; D053580:Muscle Strength; D009422:Nervous System Diseases / Q000209:etiology*; D020521:Stroke / Q000150:complications*; D013997:Time Factors
chemical_list: D015703:Antigens, CD
keywords: Aging; Cerebral blood perfusion; Distal middle cerebral artery occlusion (dMCAO); Microglia
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