The goal of this new-investigator application is to study Alzheimer's disease (AD) pathogenesis in the brain and ocular lens. Age-dependent cerebral B-amyloid (AB) accumulation is a cardinal feature of Alzheimer's disease. We have recently identified AB in human lenses and detected AB deposition, amyloid pathology, and co-localizing equatorial supranuclear cataracts (SNC) in lenses from aged individuals with AD but not in those without the disorder. Because these unusual cataracts are located at the lens periphery behind the iris, this phenotype is neither visually disabling nor observable by routine examination. We have identified similar SNC and human AB overexpression in Tg2576 AD transgenic mouse lenses. AB localizes to the lens fiber cell cytoplasm, where this peptide interacts with cytosolic lens proteins such as AB-crystallin, an abundant lens structural protein/molecular chaperone that is upregulated in AD brain. AB promotes metal-dependent lens protein aggregation and light scattering. This data supports a model in which AIS-mediated lens protein aggregation increases supranuclear light scatter that ultimately manifests as cataracts. We hypothesize that the SNC phenotype and its molecular antecedents may be detectable as an early, organ-specific expression of the AD disease process. To investigate this hypothesis, we will conduct biochemical analyses of AB-mediated lens protein aggregation and examine the potential for non-invasive in vivo monitoring of lens AI5 as a putative AD biomarker. The proposed studies will utilize in vitro model systems, ex vivo human AD lenses, and Tg2576 transgenic mice.
Aim 1 tests the hypothesis that lens AB accumulation is associated with localized lens protein aggregation, light scattering, and biometal accumulation. We will determine AB and biometal concentrations, localization, and composition in human AD/control and Tg2576/WT mice lenses.
Aim 2 tests the hypothesis that AB interacts with other lens proteins to promote protein aggregation via metalloprotein redox reactions. We will investigate AB binding to cytosolic structural proteins (a-, b-, and y-crystallins) and study lens protein aggregation in the presence of AB species, metal chelators, and gases (air, 02, Ar).
Aim 3 tests the hypothesis that AB-mediated lens protein aggregation may serve as a peripherally-accessible AD biomarker. We will construct purpose-built optical instruments for quantitative, non-invasive in vivo detection of AB-associated lens protein aggregation. We will utilize these instruments to examine AD/non-AD lenses ex vivo and Tg2576/WT mice in vivo. We will conduct a longitudinal in vivo assessment of lens protein aggregation in four groups of mice (Tg2576, Ctrl+/- Cu-deficit knockouts, Tg2576 x Ctrl+/- crosses, WT controls) and correlate index lens measurements with age, lens/brain AB burden, metal concentration, and histopathology. The resulting data may provide insights into fundamental mechanisms of AD-associated protein aeration and support development of novel AD diagnostic and monitoring technology.
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