Interaction between glymphatic and vascular systems for waste clearance in brain - Administrative Supplement

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ABSTRACT The objective of this current proposal is to investigate aging induced changes of brain waste clearance in the meningeal lymphatic and glymphatic systems using superparamagnetic iron oxide (SPIO)-enhanced susceptibility weighted imaging (SWI, SPIO-SWI) and fluorescent imaging. Emerging data indicate that the glymphatic system mediates the cerebrospinal fluid (CSF)-interstitial (ISF) exchange and solute clearance from the brain parenchyma and plays an important role in neurological diseases1-6. However, despite many milestone achievements, conclusive findings on the solute efflux pathways are relatively limited. In our funded RO1 (NS108463), we investigate the effects of diabetes on glymphatic and vascular system cerebral waste clearance. The recently discovered meningeal lymphatics has also been shown to be important for cerebral waste clearance. However, the interaction between the meningeal lymphatic and glymphatic systems on cerebral waste clearance has not been investigated. The paucity of research into the efflux pathways may be attributed, in part, to the technical difficulties of performing minimally invasive in vivo, ultra-high detection sensitivity measurements of influx and efflux pathways, and whole brain imaging. Although MRI can overcome the weak points of two-photon imaging (TPI), to provide non-invasive whole brain in vivo imaging of the glymphatic system, conventional MRI sensitivity is insufficient to investigate microvessels of the meningeal lymphatic and glymphatic systems. During the past funded period we have successfully optimized and validated highly sensitive MRI microvessel measurement. We have identified an optimal TE-dose index to greatly improve visualization of sub-voxel vessels (detecting ~10µm diameter microvessels), and have demonstrated that the parenchymal venous system also plays an important role in cerebral waste clearance7-9. The recently discovered meningeal lymphatics has been proposed to be an important efflux pathway for cerebral waste clearance, and the decrease in cerebral waste clearance mediated by a dysfunctional relationship between the meningeal lymphatics and the glymphatic system during, serves as an aggravating factor for Alzheimer’s disease pathology and age-associated cognitive decline10, 11. However, several critical issues for this important topic have not been addressed. Based on our novel preliminary data, and published studies, we hypothesize that the newly optimized SPIO-SWI method significantly increases detection sensitivity of microvessels in both the meningeal lymphatic and glymphatic systems, and that the efflux pathways of waste clearance can be identified and investigated using this optimized SPIO-SWI method. To test these hypotheses, we will investigate the effects of aging on the interaction between the meningeal lymphatic and glymphatic systems during waste clearance using the optimized USPIO-SWI method and fluorescent imaging. Data generated from this current proposal will provide new insights into the effects of aging on the efflux interactions between the meningeal lymphatic and glymphatic systems.