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 2

DISC1, but not PDE4B, is sequestered into insoluble HTT aggregates in HD.

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DISC1, but not PDE4B, is sequestered into insoluble HTT aggregates in HD...
(A) Filter trap assay with homogenates of cerebral cortex or striatum from 12-week-old R6/2 mice showed significantly increased levels of HTT (EM48) (top) and DISC1 (m317C) (middle) but not PDE4B (pan-PDE4B) (bottom) in the SDS-resistant fraction, compared with those from WT mice. A negative control with rabbit secondary antibody alone is also shown (middle). Data represent mean + SEM. *P < 0.05, **P < 0.01; unpaired 2-tailed t test. n = 3 per group. (B) Filter trap assay with homogenates of cerebral cortex or striatum showed significantly increased levels of HTT (EM48) (top) and DISC1 (h316C) (middle) but not PDE4B (pan-PDE4B) (bottom) in the SDS-resistant fraction from HD patients (HD), compared with those from controls (Con). A negative control with rabbit secondary antibody alone is also shown (middle). Data represent mean + SEM. *P < 0.05, **P < 0.01; unpaired 2-tailed t test. n = 3 per group. (C) Immunostaining of frozen sections of cerebral cortex (left) or striatum (right) demonstrated that DISC1 was colocalized with intranuclear inclusions of mutant HTT in 12-week-old R6/2 mice. Green, HTT (EM48); red, DISC1 (m317C); blue, DAPI (the nucleus). Arrowheads show intranuclear inclusions. Scale bar: 10 μm. n = 3 per group. (D) Immunostaining of paraffin sections of cerebral cortex (left half) or striatum (right half) in HD patients (HD) and human controls (Con) was performed with anti-HTT (EM48) (green, left) and anti-DISC1 (h316C) (red) antibodies. Nucleus was stained by DAPI (blue). Merged images are shown on the right. Arrowheads show intranuclear inclusions. Scale bar: 10 μm. n = 3 (Con), 6 (HD).