Abstract
BackgroundHypocatabolism of the amyloid β-protein (Aβ) by insulin-degrading enzyme (IDE) is implicated in the pathogenesis of Alzheimer disease (AD), making pharmacological activation of IDE an attractive therapeutic strategy. However, it has not been established whether the proteolytic activity of IDE can be enhanced by drug-like compounds.Methodology/Principal FindingsBased on the finding that ATP and other nucleotide polyphosphates modulate IDE activity at physiological concentrations, we conducted parallel high-throughput screening campaigns in the absence or presence of ATP and identified two compounds—designated Ia1 and Ia2—that significantly stimulate IDE proteolytic activity. Both compounds were found to interfere with the crosslinking of a photoaffinity ATP analogue to IDE, suggesting that they interact with a bona fide ATP-binding domain within IDE. Unexpectedly, we observed highly synergistic activation effects when the activity of Ia1 or Ia2 was tested in the presence of ATP, a finding that has implications for the mechanisms underlying ATP-mediated activation of IDE. Notably, Ia1 and Ia2 activated the degradation of Aβ by ∼700% and ∼400%, respectively, albeit only when Aβ was presented in a mixture also containing shorter substrates.Conclusions/SignificanceThis study describes the first examples of synthetic small-molecule activators of IDE, showing that pharmacological activation of this important protease with drug-like compounds is achievable. These novel activators help to establish the putative ATP-binding domain as a key modulator of IDE proteolytic activity and offer new insights into the modulatory action of ATP. Several larger lessons abstracted from this screen will help inform the design of future screening campaigns and facilitate the eventual development of IDE activators with therapeutic utility.
Highlights
Alzheimer disease (AD) is a devastating and increasingly common neurodegenerative disorder characterized by abnormal accumulation of the amyloid b-protein (Ab) in brain regions subserving memory and other cognitive functions [1]
Ab is a complex mixture of peptides ranging in size from 37 to 43 amino acids that are cleaved from the amyloid precursor protein by the successive action of aspartyl proteases known as b- and c-secretase [2]
During the assay development phase, we confirmed that ATP inhibited the degradation of Ab by insulin-degrading enzyme (IDE) at physiological concentrations (Fig. 1A)
Summary
Alzheimer disease (AD) is a devastating and increasingly common neurodegenerative disorder characterized by abnormal accumulation of the amyloid b-protein (Ab) in brain regions subserving memory and other cognitive functions [1]. A wealth of evidence from human molecular genetics, animal modeling studies and other fields supports the hypothesis that the proximal cause of AD is chronic elevations in cerebral Ab, either all forms or longer species, such as Ab42, which have a greater propensity to self-assemble into neurotoxic oligomers and higher-order aggregates, and which predominate in the amyloid plaques that characterize the disease [3,4,5,6] The latter findings have prompted extensive efforts to develop therapies aimed at achieving sustained reductions in cerebral Ab, thereby reducing the formation of neurotoxic Ab oligomers and plaques. It has not been established whether the proteolytic activity of IDE can be enhanced by drug-like compounds
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