Abstract
The CAG repeat expansion that elongates the polyglutamine tract in huntingtin is the root genetic cause of Huntington’s disease (HD), a debilitating neurodegenerative disorder. This seemingly slight change to the primary amino acid sequence alters the physical structure of the mutant protein and alters its activity. We have identified a set of G-quadruplex-forming DNA aptamers (MS1, MS2, MS3, MS4) that bind mutant huntingtin proximal to lysines K2932/K2934 in the C-terminal CTD-II domain. Aptamer binding to mutant huntingtin abrogated the enhanced polycomb repressive complex 2 (PRC2) stimulatory activity conferred by the expanded polyglutamine tract. In HD, but not normal, neuronal progenitor cells (NPCs), MS3 aptamer co-localized with endogenous mutant huntingtin and was associated with significantly decreased PRC2 activity. Furthermore, MS3 transfection protected HD NPCs against starvation-dependent stress with increased ATP. Therefore, DNA aptamers can preferentially target mutant huntingtin and modulate a gain of function endowed by the elongated polyglutamine segment. These mutant huntingtin binding aptamers provide novel molecular tools for delineating the effects of the HD mutation and encourage mutant huntingtin structure-based approaches to therapeutic development.
Highlights
Huntington’s disease (HD) is a dominantly inherited neurodegenerative disorder with motor, cognitive, and psychiatric features caused by expanded HTT CAG trinucleotide repeats that extend a polyglutamine tract in the amino terminus of huntingtin.[1]
Because we expect subtle structural changes in mutant huntingtin that are correlated to polyglutamine tract size,[8] we chose Q78-huntingtin to maximize the possibility to find out mutant huntingtin-specific DNA aptamers
We have identified a specific set of DNA aptamers that preferentially bind to full-length huntingtin with an expanded polyglutamine tract, providing novel molecular tools that may modulate the structure and function of the mutant protein, unlike the previously reported guanine-rich oligonucleotides that bind to the exon 1-encoded short amino-terminal huntingtin fragments inhibiting their aggregation.[25,26,27]
Summary
Huntington’s disease (HD) is a dominantly inherited neurodegenerative disorder with motor, cognitive, and psychiatric features caused by expanded HTT CAG trinucleotide repeats that extend a polyglutamine tract in the amino terminus of huntingtin.[1]. Extending the length of the polyglutamine tract enhances the ability of recombinant human mutant huntingtin to stimulate the basal histone H3 lysine 27 trimethylation (H3K27me3) activity of polycomb repressive complex 2 (PRC2), as measured in a cell-free chromatin-nucleosome assay.[9] This quantitative biochemical assay, which serves to monitor the effect of the polyglutamine tract length on a functional activity of huntingtin, emerged from huntingtin’s critical role in regulating PRC2
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