PROJECT SUMMARY/ABSTRACT Despite the fact that by the year 2050 older people at risk for cognitive decline and Alzheimer?s disease (AD) are predicted to reach 13 million, treatment approaches are woefully lacking. Although cholinergic dysfunction is a mainstay of AD, and cholinesterase inhibitors remain the drugs of choice for the management of mild to moderate AD, it does not prevent disease onset or modify its progression. Our goal is to elucidate the earliest molecular and cellular events underlying the selective neuronal vulnerability of the cholinergic basal forebrain (CBF) memory and executive function interactome in order to provide new and improved CBF interventions, to be used in combination with drugs that target other AD hallmarks, (e.g., tau and amyloid) during the preclinical stage of the disease. In AD, the magnitude of CBF neuron and volume loss and neurofibrillary tangle (NFT) formation displays a rostrocaudal pattern with greatest neurodegeneration in the posterior followed by the intermediate and then the anterior subfield, the least affected cholinergic (Ch4) subgroup. The Ch4 subfields were recently recognized as a as a critical subcortical regulatory node of the default mode network (DMN), which displays circuit-driven AD pathology associated with episodic memory and executive function deficits early in AD. CBF degeneration is not only manifested by specific post-translational tau modifications, but by a confluence of intracellular events that occur prior to the onset of clinical symptoms. We recently provided novel evidence that presplicing U1 small nuclear ribonucleoproteins (snRNPs) aggregate and are associated with NFTs in sporadic and familial AD, but not other neurologic diseases. We now report that defects in presplicing proteins are involved in CBF neuronal degeneration during the earliest preclinical stages of AD. Project 3 will translate information derived from a uniquely human condition, preclinical AD. Notwithstanding the conceptually and technically inventive approaches employed (i.e., oligomeric tau and presplicing antibodies, single population microarray and RNA sequencing approaches), studying the role(s) that presplicing plays in NFT evolution within vulnerable CBF neurons using clinically and neuropathological well-characterized same from preclinical, MCI and AD cases from the Rush Religious Orders Study (RROS) is highly innovative. Project 3 is posited to lay the groundwork for a wide range of potential interventions via transcriptionally aided drug design and suggest novel biomarkers for early AD diagnosis.