SUMMARY Alzheimer disease (AD), the most common form of dementia, is characterized by the extracellular deposition of parenchymal and vascular ß-amyloid (Aß), intracellular accumulation of tau as neurofibrillary tangles (NFTs), neuronal cell loss, and significant inflammation1,2. During the past decades, a major focus of research has been the understanding of the connection between parenchymal Aß, NFT, and neurodegeneration, with the contribution of vascular pathology to NFT and neurodegeneration remaining under studied. Cerebral amyloid angiopathy (CAA) is typified by the cerebrovascular deposition of Aß and has a close molecular relationship with AD. Unfortunately, there is no clear understanding of the molecular and cellular mechanisms and targets that underlie the contribution of CAA to neurodegeneration and dementia. Therefore, the main goal of this proposal is to dissect the mechanism(s) by which CAA leads to neuroinflammation, abnormal tau accumulation, and neurodegeneration. CAA has been associated to an active immune response and perivascular deposition of hyperphosphorylated tau; yet these three pathological entities have never been linked in a spatio-temporal context in relation to cognitive decline. Hence, we propose to determine if a disease- associated form of tau, catalyzed by a pro-inflammatory response, plays a major role on behavioral deficit and the synaptotoxicity observed in dementias associated to CAA, using a well-established genetic mouse model for CAA (Tg-FDD)12. We will also determine if the triggering receptor expressed on myeloid cells 2 (TREM2) plays a preponderant role in vascular amyloid deposition and vascular integrity in vivo during CAA progression. Furthermore, we will identify the potential role of tau on CAA and subsequent neurotoxicity by determining if the ablation of functional endogenous tau suppresses behavioral deficit and toxicity in our genetic mouse model for CAA. The proposed studies will provide a platform for the understanding of the role of CAA in neurodegeneration. Information gained from these studies might lead to the development of effective therapeutics not only for CAA and AD, but also for a number of neurodegenerative diseases characterized by the vascular accumulation of amyloid peptides.