Interaction between glymphatic and vascular systems for waste clearance in brain

摘要 本申请的目的是首先开发和验证整个大脑的微血管测量， 使用超顺磁性氧化铁（SPIO）增强微血管检测灵敏度10倍 磁敏感加权成像（SWI，SPIO-SWI），然后研究胶质淋巴细胞和 糖尿病患者大脑中废物清除的血管系统。新的数据表明胶质淋巴系统 介导脑脊液（CSF）-间质（ISF）交换和溶质从脑中清除 在神经系统疾病中起重要作用1 -6。尽管取得了许多里程碑式的成就， 关于溶质外排途径的结论性发现相对有限。因此， 血管和胶质淋巴系统对废物清除的影响，特别是与神经系统疾病的关系尚不清楚。 外排途径研究的缺乏可能部分归因于技术困难，例如 具有挑战性的需求，对管状流入物进行微创体内、超高检测灵敏度， 外排途径和全脑成像。虽然MRI可以克服双光子共聚焦成像的缺点， 显微镜提供胶质淋巴系统的非侵入性全脑体内成像，常规MRI 灵敏度不足以满足研究胶质淋巴管微血管所需的空间分辨率 血管系统我们已经开发出高灵敏度的MRI方法（图1），它显著改善了 通过使用MRI试剂的高敏感性与晕染的组合来检测小血管的灵敏度 效果7 -9.新方法为研究废物清除的外排途径提供了出色的工具 在正常和病理生理条件下。最近提出了三种外排途径， 大脑中的淋巴细胞可以通过嗅球穿过筛骨板到达淋巴网络10，11或通过功能 脑膜中的常规淋巴管系统12.我们发现静脉系统中的示踪剂浓度 随着糖尿病的发生，脑组织中的蛋白质含量显著增加（图9），从而为脑废物的清除增加了一条新途径。基于我们 新的初步数据和其他人发表的研究，我们假设，新开发的SPIO-SWI 该技术显著提高了血管和胶质淋巴系统中微血管的检测灵敏度， 以及有无糖尿病的废物清除的外排途径可以通过使用 优化SPIO-SWI方法。为了验证这些假设，我们将首先（目标1）进一步开发、优化和 验证SPIO-SWI技术，以提高血管和胶质淋巴管的检测灵敏度 微血管我们将进行计算机模拟，优化SWI技术和实验条件， 动物实验，然后通过LSCM测量验证USPIO-SWI技术。我们将（目标2） 研究血管和胶质淋巴系统之间的相互作用，以清除糖尿病大脑中的废物， 优化的USPIO-SWI技术。从这个应用程序产生的数据将提供新的见解流出 糖尿病患者大脑中胶质淋巴系统和血管系统之间的通路。

ABSTRACT The objective of this application is to first develop and validate microvessel measurement for the entire brain to enhance detection sensitivity of microvessels by ten-fold using superparamagnetic iron oxide (SPIO) enhanced susceptibility weighted imaging (SWI, SPIO-SWI) and then to investigate the interaction between glymphatic and vascular systems for waste clearance in the diabetic brain. Emerging data indicate that the glymphatic system in the brain mediates the cerebrospinal fluid (CSF)-interstitial (ISF) exchange and solute clearance from the brain parenchyma and plays an important role in neurological diseases1-6. Despite many milestone achievements, conclusive findings on the solute efflux pathways are relatively limited. Consequently, the interaction between vascular and glymphatic systems on waste clearance, especially with neurological diseases, is unclear. The paucity of research into the efflux pathway may be attributed in part to technical difficulties, such as the challenging need to perform minimally invasive in-vivo, ultra-high detection sensitivity for tube-shaped influx and efflux pathways, and whole brain imaging. Although MRI can overcome the weak points of two-photon confocal microscopy to provide non-invasive whole brain in-vivo imaging of the glymphatic system, conventional MRI sensitivity is insufficient for the required spatial resolution for investigating microvessels of glymphatic and vascular systems. We have developed highly sensitive MRI methods (Fig. 1) which significantly improve the detection sensitivity of small vessels by using the combination of high susceptibility of MRI agents with blooming effects7-9. The new methods provide excellent tools for investigating the efflux pathways of waste clearance under normal and pathophysiological conditions. Three efflux routes have been recently proposed and solutes in the brain could reach the lymphatic network by the olfactory bulb across the ethmoid plate10, 11 or by functioning conventional lymphatic vasculature in the meninges12. We found that tracer concentration in the venous system significantly increased with diabetes (Fig. 9), thus adding a new route for brain waste clearance. Based on our novel preliminary data and published studies by others, we hypothesize that, the newly developed SPIO-SWI technique significantly increases detecting sensitivity of microvessels in both vascular and glymphatic systems, and the efflux pathways of waste clearance with and without diabetes can be identified and investigated using this optimized SPIO-SWI method. To test these hypotheses, we will first (Aim 1) further develop, optimize and validate SPIO-SWI techniques to enhance the detection sensitivity for both vascular and glymphatic microvessels. We will perform computer simulation, optimize SWI technique and experimental conditions in animal studies and then validate USPIO-SWI technique by LSCM measurements. We will then (Aim 2) investigate the interaction between vascular and glymphatic systems for waste clearance in diabetic brain using the optimized USPIO-SWI technique. Data generated from this application will provide new insights into the efflux pathways between glymphatic and vascular systems in diabetic brain.