Exercise-induced irisin ameliorates cognitive impairment following chronic cerebral hypoperfusion by suppressing neuroinflammation and hippocampal neuronal apoptosis.

Abstract

Background: Chronic cerebral hypoperfusion (CCH) is a pathophysiological hallmark of vascular dementia, the second most common form of dementia. CCH exerts complex and subtle detrimental effects on both the brain and peripheral systems. Irisin is a polypeptide primarily expressed in contracting skeletal muscle and the brain. However, its role in CCH remains unclear. This study aimed to investigate the effects of CCH on irisin metabolism and whether increasing endogenous irisin levels through forced aerobic exercise (FAE) could confer neuroprotection against secondary brain injury induced by CCH.

Methods: A total of 212 adult (8-week-old) male C57BL/6 mice were randomly assigned to either sham or CCH groups. CCH was induced by bilateral common carotid artery stenosis. FAE consisted of daily swimming (1 h/day, 5 days/week, for 5 weeks). Two subgroups of CCH mice received daily intraperitoneal injections of either DMSO or cilengitide trifluoroacetate (CT), a selective inhibitor of integrin αV and β5 (the irisin receptor), during FAE. ELISA and western blotting were used to assess irisin expression, while western blotting, TUNEL, immunofluorescence staining, and neurobehavioral tests were conducted to evaluate neurofunctional outcomes.

Results: Hippocampal and serum irisin levels were progressively reduced in CCH mice. Additionally, expression of integrins αV and β5 in hippocampal neurons, microglia, and astrocytes decreased post-CCH. FAE effectively enhanced both peripheral and central irisin expression. Increased endogenous irisin levels inhibited CCH-induced hippocampal neuronal apoptosis and microglial activation, thereby promoting neuronal survival and partially ameliorating white matter injury. These changes led to improvements in memory, motor function, and anxiety- and depression-like behaviors. Mechanistically, the neuroprotective effects of irisin were mediated by enhanced hippocampal neuronal and microglial autophagy through increased AMPK phosphorylation and decreased mTOR phosphorylation-effects abolished by CT treatment.

Conclusion: Our findings demonstrate that enhancing endogenous irisin via FAE mitigates CCH-induced neuronal apoptosis, microglial activation, cognitive impairment, and affective behavioral deficits by promoting autophagy through the integrin αVβ5/AMPK/mTOR signaling pathway.