Activating transcription factor 6 derepression mediates neuroprotection in Huntington disease
José R. Naranjo, … , Jia-Yi Li, Britt Mellström
José R. Naranjo, … , Jia-Yi Li, Britt Mellström
Published January 11, 2016
Citation Information: J Clin Invest. 2016;126(2):627-638. https://doi.org/10.1172/JCI82670.
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Research Article Neuroscience

Activating transcription factor 6 derepression mediates neuroprotection in Huntington disease

Abstract

Deregulated protein and Ca2+ homeostasis underlie synaptic dysfunction and neurodegeneration in Huntington disease (HD); however, the factors that disrupt homeostasis are not fully understood. Here, we determined that expression of downstream regulatory element antagonist modulator (DREAM), a multifunctional Ca2+-binding protein, is reduced in murine in vivo and in vitro HD models and in HD patients. DREAM downregulation was observed early after birth and was associated with endogenous neuroprotection. In the R6/2 mouse HD model, induced DREAM haplodeficiency or blockade of DREAM activity by chronic administration of the drug repaglinide delayed onset of motor dysfunction, reduced striatal atrophy, and prolonged life span. DREAM-related neuroprotection was linked to an interaction between DREAM and the unfolded protein response (UPR) sensor activating transcription factor 6 (ATF6). Repaglinide blocked this interaction and enhanced ATF6 processing and nuclear accumulation of transcriptionally active ATF6, improving prosurvival UPR function in striatal neurons. Together, our results identify a role for DREAM silencing in the activation of ATF6 signaling, which promotes early neuroprotection in HD.

Authors

José R. Naranjo, Hongyu Zhang, Diego Villar, Paz González, Xose M. Dopazo, Javier Morón-Oset, Elena Higueras, Juan C. Oliveros, María D. Arrabal, Angela Prieto, Pilar Cercós, Teresa González, Alicia De la Cruz, Juan Casado-Vela, Alberto Rábano, Carmen Valenzuela, Marta Gutierrez-Rodriguez, Jia-Yi Li, Britt Mellström

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Figure 5

Repaglinide blocks DREAM-ATF6 interaction and regulates derepression of ATF6 targets.

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Repaglinide blocks DREAM-ATF6 interaction and regulates derepression of ...
(A) Coimmunoprecipitation of endogenous ATF6 and DREAM proteins in STHdhQ7/7 cell lysates. Immunoprecipitated band (arrowhead) corresponds to full-length ATF6. Coimmunoprecipitation was performed in the absence or presence of Ca2+ (2 mM) and/or repaglinide (200 nM). Bottom, optical density of the ATF6 band from 3 independent immunoprecipitations is shown as mean relative intensity to the immunoprecipitate in the absence of Ca2+. (B) Pull-down using GST (–) and GST-DREAM1-256 (+) proteins as bait and in vitro–translated Nt-ATF61–376 as target in the presence of EGTA, Mg2+, or Ca2+ (2 mM). The experiment was repeated twice. (C) Pull-down in the presence of Ca2+ using GST (–), GST-DREAM1–256 (D), or N-terminal GST-DREAM1–90 (ΔD) proteins as bait and in vitro–translated Nt-ATF61–376 as target, alone or with repaglinide (200 nM). b, empty beads. The experiment was repeated twice. Input for B and C was 3%. (D) Luciferase reporter assays in STHdhQ7/7 cells transiently transfected with reporter plasmid p5×ATF6-GL3 and stimulated with tunicamycin (T) (200 ng/ml) alone or with repaglinide (100 nM). *P < 0.05, ***P < 0.001, vs. control; ###P < 0.001 for tunicamycin-stimulated cells alone or with repaglinide (1-way ANOVA, Bonferroni’s post-test). (E) Luciferase reporter assay in WT or DREAM-overexpressing HeLa cells stimulated as in C. ####P < 0.0001, tunicamycin-stimulated HeLa cells alone and with DREAM; #P < 0.05, tunicamycin-stimulated DREAM-expressing HeLa cells alone or with repaglinide (1-way ANOVA, Bonferroni’s post-test). (F and G) Real-time qPCR analysis of XBP1 and BIP mRNAs after stimulation (14 hours) with thapsigargin (Tg) (200 nM) of STHdhQ7/7 cells alone or with repaglinide (200 nM; 1 hour). Values are normalized relative to HPRT mRNA levels. The experiment was repeated 3 times in triplicate. Significant differences were determined as in D: **P < 0.01, ****P < 0.0001, vs. control; #P < 0.05, ####P < 0.0001 for thapsigargin-stimulated cells alone or with repaglinide (1-way ANOVA, Bonferroni’s post-test).