Mechanism Of Inflammatory Response Affecting Nerve Injury And Functional Recovery After Cerebral Ischemia In Aged Mice

Background and purpose:Stroke occurs mostly in patients with advanced age.The older patients have a less favorable prognosis than young patients.To understand the underlying mechanisms,we tested our hypothesis in mice that an increased inflammatory response to acute ischemic injury in older stroke victims leads to more severe brain damage and behavior dysfunction.We also tested ischemic brain response to vascular endothelial growth factor(VEGF)in aged mice.We further explored the underlying mechanisms.Methods:An ischemic stroke model was created in 2-and 12-month-old C57BL/6mice through permanent occlusion of the left distal middle cerebral artery(dMCAO).Infarct/atrophy volumes were quantified using Cresyl Violet staining brain sections.Sensorimotor function was assessed through corner test and adhesive removal test.CD68~+cells in the peri-infarct region were quantified at 1,3 and 14 days after dMCAO.Interleukin-6(IL-6),interleukin-1?(IL-1?)and vascular endothelial growth factor(VEGF)levels in the ischemic brain tissue were measured using ELISA.The expression of tight juncture protein,claudin-5 and ZO-1,were quantified by western blot analysis.Blood-brain barrier permeability was measured by Evans blue(EB)extravasation.Gelatinase B(MMP-9,type IV collagenase)was measured by gel zymography.To observe the level of VEGFR and MI/M2 phenotype expression after glucose oxygen deprivation,bone marrow-derived macrophages were co-cultured with HUVEC.Results:Compared to 2-month-old mice,12-month-old mice had more severe behavior deficits,at both acute and chronic stages of stroke.Twelve-month-old mice had larger infarct/atrophy volumes at 1 and 14 days after dMCAO,higher levels of IL-6 and IL-1?,higher MMP9 activity,and lower levels of Zonula Occludens(ZO-1)and Claudin-5 at 1 and 3 days after dMCAO then 2-month-old mice.Twelve-month-old mice also had more CD68~+cells in the peri-infarct region at 1,3 and 14 days after dMCAO and more EB leakage at 3 days after dMCAO.Postischemic gene transfer of VEGF significantly enhanced vascular density at 14 days after a stroke in the peri-infarct compared with AAV-LacZ.There was less increased vascular density in Twelve-month-old ischemic mice brain.Less ki67 positive endothelial cells were detected around peri-infarct area in Twelve-month-old ischemic mice brain.Twelve-month-old mice had lower levels of VEGFR-1,ARG and CD206 after OGD then2-month-old mice.Conclusion:A higher inflammatory response at the acute stage of ischemic stroke in older mice is associated with more severe neuronal injury and long-term behavior dysfunction.Impaired VEGF/VEGFR-1 signaling pathway after cerebral ischemia may be associated with severe neurological impairment in the aged brain.