PROJECT SUMMARY As the elderly population increases, the number of people with Alzheimer's disease (AD) is rising rapidly. There is, therefore, a growing interest in the development of in vitro human disease models to better understand and study the physiological and pathological mechanisms associated with AD. Emerging evidence has implicated an early breakdown of the BBB in AD patients, even before the cognitive decline and brain pathology. In addition, meningeal lymphatics are responsible for clearance of Aβ peptides from the brain parenchyma, and disruption of meningeal lymphatics in AD transgenic mice accelerates Aβ deposition in the meninges, aggravates parenchymal Aβ accumulation, and induces cognitive impairment. Yet, our understanding of the role of fluid transport across the BBB, through the brain parenchyma, and exiting via the lymphatic system is poorly understood. Therefore, the development of physiologically realistic human neural cell culture models of AD with a neurovascular unit and meningeal lymphatic vessels is urgently needed to dissect molecular mechanisms underlying the pathogenic cascade of AD and accelerate the discovery of new AD drugs. Building on our extensive set of preliminary and related studies, we propose to develop a three-dimensional (3D) in vitro model by integrating BBB, meningeal lymphatics, and stem-cell-derived AD cell culture to closely mimic the AD brain environment. With this model, we aim to identify AD-specific mechanisms underlying pathophysiological changes in the BBB, meningeal lymphatics, and Aβ clearance. Our 3D AD model will be useful for not only studying the mechanisms of AD progression but also for drug discovery in a human brain-like environment.