Abstract
Aptamers are useful molecular recognition tools in research, diagnostics, and therapy. Despite promising results in other fields, aptamer use has remained scarce in amyloid research, including Alzheimer's disease (AD). AD is a progressive neurodegenerative disease believed to be caused by neurotoxic amyloid β-protein (Aβ) oligomers. Aβ oligomers therefore are an attractive target for development of diagnostic and therapeutic reagents. We used covalently-stabilized oligomers of the 40-residue form of Aβ (Aβ40) for aptamer selection. Despite gradually increasing the stringency of selection conditions, the selected aptamers did not recognize Aβ40 oligomers but reacted with fibrils of Aβ40, Aβ42, and several other amyloidogenic proteins. Aptamer reactivity with amyloid fibrils showed some degree of protein-sequence dependency. Significant fibril binding also was found for the naïve library and could not be eliminated by counter-selection using Aβ40 fibrils, suggesting that aptamer binding to amyloid fibrils was RNA-sequence-independent. Aptamer binding depended on fibrillogenesis and showed a lag phase. Interestingly, aptamers detected fibril formation with ≥15-fold higher sensitivity than thioflavin T (ThT), revealing substantial β-sheet and fibril formation undetected by ThT. The data suggest that under physiologic conditions, aptamers for oligomeric forms of amyloidogenic proteins cannot be selected due to high, non-specific affinity of oligonucleotides for amyloid fibrils. Nevertheless, the high sensitivity, whereby aptamers detect β-sheet formation, suggests that they can serve as superior amyloid recognition tools.
Highlights
Alzheimer’s disease (AD) is a progressive neurodegenerative disorder that initially presents as episodic memory lapses and culminates in the decline of mental faculties, dementia, and death
RNA pools for reactivity with the target—oligomeric Ab40, and the unintended, cross-reactive species—Ab40 fibrils. We found that both the 3rd and the 6th RNA pools reacted with Ab40 fibrils but not with oligomeric Ab40 indicating that the counterselection against fibrils was inefficient (Fig. 6A)
Because our sequencing and motif analyses showed high G content in KM aptamers, we tested a biased library with reduced G ratio (A:C:G:T = 30:30:10:30%). We found that both libraries reacted with fibrils of Ab40, Ab42, and the other amyloid proteins (Fig. 8A, B) in a fashion similar to all the selected aptamers tested (Figs. 4 and 5)
Summary
Alzheimer’s disease (AD) is a progressive neurodegenerative disorder that initially presents as episodic memory lapses and culminates in the decline of mental faculties, dementia, and death. According to the Alzheimer’s Association, an estimated 5.3 million Americans have AD in 2009 and this number will increase to 11–16 million by 2050 [1]. The annual cost of care for AD in the US is more than $ 148 billion and will increase dramatically if effective prevention and/or cure are not found. Definite diagnosis of AD is achieved only by postmortem neuropathological examination. Because the onset of AD occurs insidiously many years before emergence of the initial symptoms [3], early diagnosis is important for effective therapeutic intervention before progression to symptomatic disease [4]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
