Serine 421 regulates mutant huntingtin toxicity and clearance in mice
Ian H. Kratter, … , Eliezer Masliah, Steven Finkbeiner
Ian H. Kratter, … , Eliezer Masliah, Steven Finkbeiner
Published September 1, 2016; First published August 15, 2016
Citation Information: J Clin Invest. 2016;126(9):3585-3597. https://doi.org/10.1172/JCI80339.
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Research Article Neuroscience

Serine 421 regulates mutant huntingtin toxicity and clearance in mice

Abstract

Huntington’s disease (HD) is a progressive, adult-onset neurodegenerative disease caused by a polyglutamine (polyQ) expansion in the N-terminal region of the protein huntingtin (HTT). There are no cures or disease-modifying therapies for HD. HTT has a highly conserved Akt phosphorylation site at serine 421, and prior work in HD models found that phosphorylation at S421 (S421-P) diminishes the toxicity of mutant HTT (mHTT) fragments in neuronal cultures. However, whether S421-P affects the toxicity of mHTT in vivo remains unknown. In this work, we used murine models to investigate the role of S421-P in HTT-induced neurodegeneration. Specifically, we mutated the human mHTT gene within a BAC to express either an aspartic acid or an alanine at position 421, mimicking tonic phosphorylation (mHTT-S421D mice) or preventing phosphorylation (mHTT-S421A mice), respectively. Mimicking HTT phosphorylation strongly ameliorated mHTT-induced behavioral dysfunction and striatal neurodegeneration, whereas neuronal dysfunction persisted when S421 phosphorylation was blocked. We found that S421 phosphorylation mitigates neurodegeneration by increasing proteasome-dependent turnover of mHTT and reducing the presence of a toxic mHTT conformer. These data indicate that S421 is a potent modifier of mHTT toxicity and offer in vivo validation for S421 as a therapeutic target in HD.

Authors

Ian H. Kratter, Hengameh Zahed, Alice Lau, Andrey S. Tsvetkov, Aaron C. Daub, Kurt F. Weiberth, Xiaofeng Gu, Frédéric Saudou, Sandrine Humbert, X. William Yang, Alex Osmand, Joan S. Steffan, Eliezer Masliah, Steven Finkbeiner

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Figure 3

mHTT-S421D mice, but not mHTT-S421A mice, have less severe motor and psychiatric-like behavioral deficits than BACHD mice.

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mHTT-S421D mice, but not mHTT-S421A mice, have less severe motor and psy...
(A) Analysis of motor performance on the accelerating rotarod of a cohort of BACHD (n = 7), mHTT-S421D (n = 17), and WT (n = 31) mice at 3, 6, and 12 months of age. (B) Analysis of hind-limb gaits of BACHD, mHTT-S421D, and WT mice at 12 months of age with the CatWalk XT (Noldus). (C and D) Comparison of total activity (C) and rearing activity (D) in BACHD, mHTT-S421D, and WT mice in the open field for 10 minutes at 12 months of age. (E) Comparison of anxiety-like behavior in the light-dark box over 10 minutes in BACHD, mHTT-S421D, and WT mice at 12 months of age. (F) Analysis of motor performance on the accelerating rotarod of a cohort of mHTT-S421A (n = 13) and WT (n = 19) mice at 6 and 12 months of age. In A and F, 2-way repeated-measures ANOVA statistical analyses were used, with 1-way ANOVA used for B–E. Bonferroni post hoc tests were used for all pairwise comparison. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001.