Aggregation of scaffolding protein DISC1 dysregulates phosphodiesterase 4 in Huntington’s disease
Motomasa Tanaka, … , Miles D. Houslay, Akira Sawa
Motomasa Tanaka, … , Miles D. Houslay, Akira Sawa
Published March 6, 2017
Citation Information: J Clin Invest. 2017;127(4):1438-1450. https://doi.org/10.1172/JCI85594.
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Research Article Cell biology Neuroscience

Aggregation of scaffolding protein DISC1 dysregulates phosphodiesterase 4 in Huntington’s disease

Abstract

Huntington’s disease (HD) is a polyglutamine (polyQ) disease caused by aberrant expansion of the polyQ tract in Huntingtin (HTT). While motor impairment mediated by polyQ-expanded HTT has been intensively studied, molecular mechanisms for nonmotor symptoms in HD, such as psychiatric manifestations, remain elusive. Here we have demonstrated that HTT forms a ternary protein complex with the scaffolding protein DISC1 and cAMP-degrading phosphodiesterase 4 (PDE4) to regulate PDE4 activity. We observed pathological cross-seeding between DISC1 and mutant HTT aggregates in the brains of HD patients as well as in a murine model that recapitulates the polyQ pathology of HD (R6/2 mice). In R6/2 mice, consequent reductions in soluble DISC1 led to dysregulation of DISC1-PDE4 complexes, aberrantly increasing the activity of PDE4. Importantly, exogenous expression of a modified DISC1, which binds to PDE4 but not mutant HTT, normalized PDE4 activity and ameliorated anhedonia in the R6/2 mice. We propose that cross-seeding of mutant HTT and DISC1 and the resultant changes in PDE4 activity may underlie the pathology of a specific subset of mental manifestations of HD, which may provide an insight into molecular signaling in mental illness in general.

Authors

Motomasa Tanaka, Koko Ishizuka, Yoko Nekooki-Machida, Ryo Endo, Noriko Takashima, Hideyuki Sasaki, Yusuke Komi, Amy Gathercole, Elaine Huston, Kazuhiro Ishii, Kelvin Kai-Wan Hui, Masaru Kurosawa, Sun-Hong Kim, Nobuyuki Nukina, Eiki Takimoto, Miles D. Houslay, Akira Sawa

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Figure 1

PDE4 activity could be regulated by the newly identified HTT-DISC1-PDE4 ternary protein complex.

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PDE4 activity could be regulated by the newly identified HTT-DISC1-PDE4 ...
(A) PDE4 activities of the homogenates of cerebral cortex (left) and striatum (right) in R6/2 mice were increased compared with those in WT at 8 and 12 weeks (w) of age. Data represent mean + SEM. *P < 0.05, **P < 0.01, ***P < 0.001; unpaired 2-tailed t test. Cortex: 4 weeks, n = 4 per group; 8 weeks, n = 5 per group; 12 weeks, n = 9 (WT), 6 (R6/2). Striatum: 4, 8, and 12 weeks, n = 4 per group. (B) Protein complex of HTT-DISC1-PDE4B in cerebral cortex of WT mice. Brain homogenates were immunoprecipitated by an anti-PDE4B (pan-PDE4B) or anti-DISC1 (mEx3) antibody or IgG control, followed by immunoblotting with an anti-HTT (MAB2144), anti-DISC1 (m317C), or anti-PDE4B (pan-PDE4B) antibody. Representative immunoblots are shown from 3 independent sample sets. (C) Formation of HTT-DISC1-PDE4B tertiary protein complex in cerebral cortex of WT mice was detected with sequential coimmunoprecipitation. Brain homogenates were immunoprecipitated by PDE4B antibody (pan-PDE4B) (1st IP), then the immunoprecipitates were immunoprecipitated by an anti-DISC1 (mEx3) antibody (2nd IP), followed by immunoblotting with an anti-HTT (MAB2166), anti-DISC1 (m317C), or anti-PDE4B (pan-PDE4B) antibody. Negative control was immunoprecipitated by IgG. Representative immunoblots are shown from 3 independent sample sets. (D) Increased binding of HTT513 and DISC1 with expansion of polyQ (Q18 or Q82) in HEK293T cells by coimmunoprecipitation. Data represent mean + SEM (5 independent sample sets). *P < 0.05; 1-way ANOVA followed by Bonferroni post hoc corrections. (E) Increased binding of HTT67 and DISC1 with expansion of polyQ (Q18 or Q82) in HEK293T cells by coimmunoprecipitation. Data represent mean + SEM (3 independent sample sets). ***P < 0.001; 1-way ANOVA followed by Bonferroni post hoc corrections.