MRI-visible Enlarged Perivascular Spaces and the Alteration of Lymphatic Drainage System in CAA

Cerebral amyloid angiopathy (CAA) involves amyloid deposition in the vessel walls in the cerebral cortex and overlying leptomeninges, causing symptomatic intracerebral lobar intracerebral hemorrhage (ICH) in the elderly. CAA is considered as a form of cerebral small vessel disease, which refers to a group of vascular pathologies that affect the small vessels of the brain. In addition to lobar ICH, patients may present with other parenchymal injuries that can be detected on blood-sensitive MRI, such as multiple strictly lobar cerebral microbleeds, cortical superficial siderosis and leukoariosis. Recently, CAA has been suggested in association with MRI-visible enlarged perivascular space (EPVS) in centrum-semiovale (CSO), contrary to more severe MRI-visible EPVS in basal ganglia that is frequently found in chronic hypertension. The dilated perivascular space in CAA is suggestive of chronic poor perivascular drainage of the leptomeningeal arteries, predisposing individuals to impaired or altered meningeal lymphatic drainage and causing defect in amyloid clearance and subsequent CAA development. Nevertheless, it is unknown whether lymphatic drainage are the main routes for vascular amyloid clearance, and its relationship to the long-term outcome has not been clearly investigated in clinical patients yet.

In this three-year proposal, we will explore the MRI-visible EPVS in CAA and investigate its pathophysiology using animal models. Our specific aims include: (1) Establish the relationship of MRI-visible enlarged perivascular space and CAA, (2) Determine whether vascular amyloid clearance in CAA is associated with lymphatic drainage system, (3) Establish longitudinal data for MRI-visible enlarged perivascular space and cerebral amyloid angiopathy progression. In the first year, we will recruit spontaneous ICH patients for brain MRI, in vivo amyloid imaging and measuring their plasma Aβ40/42 levels. We aim to confirm EPVS in CSO as a specific marker for CAA, and to provide direct evidence that dilated perivascular space is worse with more advanced CAA; For the second year, we plan to use transgenic CAA mouse models to confirm that meningeal lymphatic drainage routes are crucial for clearance of vascular amyloid-β. We will manipulate the lymphatic drainage routes by either blockage or enhancement of the lymphatic vessels, to see if the vascular amyloid clearance is affected; For the third year, the main research focus will on be establishing the longitudinal data on amyloid and tau deposition in clinical ICH patients. We plan to repeat in vivo amyloid imaging in 2 years, for the purpose of validating our hypothesis in human that baseline worse lymphatic drainage function is associated with quicker cerebral vascular amyloid progression or prediction of future CAA development. We will also recruit patients for in vivo tau imaging to investigate long-term neuronal injury and neurodegeneration, namely tau-mediated neurofibrillary tangle, in relation to the impaired perivascular drainage in CAA.