Locus Coeruleus Biomarker Development for Early Detection of Alzheimers Disease in Humans

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Project Summary The advent of neuroimaging methods for measuring locus coeruleus (LC) structural integrity has generated intense interest from scientific fields focused on Alzheimer’s disease (AD), psychiatric disorders, as well as basic cognitive neuroscience. The LC is the brain’s primary generator of the neuromodulator norepinephrine (NE) and is one of the first brain regions to accumulate hyperphosphorylated tau protein, a hallmark pathological agent in AD. The ability to use magnetic resonance (MR) imaging to assess LC integrity opens up exciting possibilities for earliest detection of disease acceleration, and may also provide an MR measure that captures information about individual differences in neurochemical function. The ability to study neurochemical systems in vivo in humans is limited, with imaging approaches using radioactive tracers being the most established (e.g. positron emission tomography (PET)). However, due to the burden to subjects, as well as the infrastructural challenges, PET imaging is not a tool many researchers use despite the central role neuromodulatory systems like NE play in basic cognition and disease. We will take initial steps towards testing the validity of LC MR measures for predicting NE function by examining the correspondence between a neuromelanin-sensitive MR measure of LC integrity and a PET measure of catecholamine (norepinephrine/dopamine) synthesis capacity ([18F]Fluoro-l-m-tyrosine (FMT)) within subject in healthy young and older adults (Aim 1). Accumulating evidence in healthy aging, AD, and Parkinson’s disease suggests the catecholamine system responds to injury and shows compensatory capacity. Next, we will test the hypothesis that with advancing age, catecholamine synthesis goes up (Aim 2). Finally, to test the utility of LC neuroimaging measures as forecasters of the advancement of tau pathology, we will explore whether neuromelanin-sensitive MR and [18F]FMT predict the accumulation of tau in the medial temporal lobe using tau-sensitive [18F]flortaucipir imaging (Aim 3). Together, this research takes critical steps in establishing MR approaches as sensitive to neurochemical function, examines intriguing mechanisms of neurochemical compensation, and provides empirical testing of models of pathological spread in AD.