PROJECT SUMMARYAlzheimer's disease (AD) is the leading cause of dementia in the elderly characterized by neurofibrillarytangles senile plaques and a progressive loss of neuronal cells in neocortex and hippocampus. Currentlythere is no effective treatment for AD. Less than 10% of AD cases are early onset with only a small fractioncaused by autosomal dominantly inherited genetic changes in APP presenilin 1 (PS1) or presenilin 2 (PS2) allof which are responsible for the overproduction of A and the earlier formation of amyloid plaques. Thoughmore than 90% of AD cases are referred to as sporadic AD without family history they have the similar clinicaland pathologic phenotypes as sporadic AD. Despite a large body of evidence suggests that A deposition inthe brain as the likely culprit playing a critical role in the pathogenesis of AD or related dementia the molecularpathomechanisms of amyloid plaque formation remain largely elusive. Interestingly in our recent study wehave identified a novel protein Aggregatin specifically accumulated within the centers of amyloid plaques.Aggregatin is predominantly expressed in the central nervous system and increased in brains of patients withAD or amyloid precursor protein (APP) transgenic mice for AD. Excitingly Aggregatin physically interacts withA with very high affinity and remarkably facilitates A aggregation even under near-physiologic nanomolarconcentrations. Forced expression of Aggregatin resulted in increased amyloid deposition whereas ablation ofAggregatin suppressed the formation of amyloid plaques in APP transgenic mice further implying it as animportant factor for A aggregating to form amyloid plaques. These exciting and promising preliminary studiessuggest that a detailed investigation into the potential role of Aggregatin in the formation of amyloid plaques inAD is warranted. Using a novel transgenic mouse model with conditional ablation of Aggregatin this study willnot only study whether and how Aggregatin regulates amyloid plaque formation and disease progression butalso test the feasibility of targeting Aggregatin as a novel therapeutic approach for AD. Amyloid plaque is aprominent common histopathological feature of in various major neurodegenerative diseases including but notlimited to AD. Our proposed studies of Aggregatin and its connection with amyloid plaque will have very broadscientific and translational significance.