Enhancement of meningeal lymphatic structure and function through running exercise mitigates amyloidosis in an Alzheimer’s disease mouse model

Abstract

Background The meningeal lymphatic (mLym) system is a route for waste clearance from the brain to the periphery that has been implicated in the pathogenesis of Alzheimer’s disease (AD). While exercise has been linked to enhanced cognition and delay of AD progression, the effects of exercise on the mLym system have remain largely undescribed. Methods Three-month-old 5xFAD transgenic mice were subjected to a 3-month period of wheel running exercise. Before and after the exercise period, mLym function (i.e., bulk flow of cerebrospinal fluid from the lateral ventricles to the deep cervical lymph nodes) was monitored in real time using high-frequency ultrasound imaging with a nanoparticle contrast agent. The relationships between mLym structure and function, amyloidosis, and learning and memory were examined. Additionally, serum and extracellular vesicles (EVs) were obtained from exercised animals and used to treat lymphatic endothelial cells (HDLECs). Expression of lymphatic vessel-related genes (LYVE-1 and VEGFR3) was monitored. Results Compared to 3-month-old 5xFAD mice (without significant amyloidosis) and age-matched wild-type mice, 6-month-old 5xFAD mice (with robust amyloid plaque deposition in the brain) exhibited decreased mLym function, deterioration of mLym vessels, and impaired learning and memory performance. Reductions were observed in the expression of lymphatic vessel-related genes (LYVE-1 and VEGFR3) in the meninges and VEGF-C in the brain of 6-month-old 5xFAD mice. Subjecting 3-month-old 5xFAD mice to 3 months of running exercise improved mLym vessel structure and function, reduced amyloidosis, and enhanced learning and memory performance compared to non-exercised controls. Conversely, ligating mLym vessels accelerated amyloidosis in 3-month-old 5xFAD mice. Exercise also upregulated the expression levels of LYVE-1 and VEGFR3 in the meninges and VEGF-C in the brain. Further in vitro studies showed that Aβ oligomers decreased VEGFR3 gene expression in HDLECs, while serum and EVs from exercised mice antagonized this effect. Conclusions This study reveals beneficial effects of running exercise on the mLym system, suggesting a non-pharmacological strategy to improve Aβ clearance from the brain, delay AD progression, and enhance cognitive function.