Sigma-1 Receptor Radioligand for Translational Research in Alzheimer's Disease

Project Summary/Abstract In this grant application we propose to develop and validate an optimal 18F-labeled sigma-1 (σ1) receptor radioligand for translational research in Alzheimer's disease (AD) to further elucidate the role of σ1 receptor in AD pathogenesis and progression, to probe longitudinal changes in σ1 receptor in AD animal models, along with the synapse biomarker synaptic vesicle protein 2A (SV2A), and AD pathologic biomarkers b-amyloid (Ab) and tau, and to explore the potential of σ1 receptor imaging for early diagnosis of AD. AD is a progressive degenerative disorder that afflicts 6 million people in the USA. From a diagnostic perspective, AD is increasingly viewed along a continuum from preclinical AD, to mild cognitive impairment (MCI), and to AD-dementia. The clinical dementia of AD is coupled to a distinct pathology, with plaques composed of b-amyloid (Ab), neurofibrillary tangles of hyperphosphorylated tau protein, and synaptic loss. However, the molecular mechanism(s) of AD pathogenesis is complex and remains elusive. Several hypotheses have been put forward, including the b-amyloid hypothesis, the misfolded tau protein hypothesis, the cholinergic hypothesis, and the involvement of oxidative stress and calcium dyshomeostasis. Before the accumulation of plaques and tangles, the biochemical and morphological changes, such as altered calcium, cholesterol, and lipid metabolism, altered mitochondrial dynamics, and reduced bioenergetic interaction, are all closely associated with functions localized to the mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs). The σ1 receptor is situated at the MAM. The most recent research has located the earliest Ab generation in AD to neurons in the MAM, and its critical regulation by the σ1 receptor, thereby confirming the central role of σ1 receptor in AD pathogenesis. As such the σ1 receptor is considered an important target for AD therapeutic development. As a surrogate marker for mitochondria function and regulator of Ab production on the MAM, it also holds great promise as a biomarker for diagnosis of AD at its earliest stage. The research proposed in this application will bridge an important gap in the understanding of the σ1 receptor in AD pathogenesis and progression by leveraging the unique expertise and experience at Yale in novel PET radioligand development, AD mechanism study, and therapeutic target identification. Investigation of the σ1 receptor in AD animal models longitudinally in relation to biomarkers for synaptic density, Ab, and tau, is a natural extension of our ongoing research. When carried to completion, this project will provide further insights into the etiology of AD, and help identify a most sensitive and effective biomarker for early AD diagnosis, and for monitoring of disease progression and the efficacy of emerging AD therapies.