Cardiac-specific ablation of ARNT leads to lipotoxicity and cardiomyopathy
Rongxue Wu, … , Gary Lopaschuk, Hossein Ardehali
Rongxue Wu, … , Gary Lopaschuk, Hossein Ardehali
Published October 20, 2014
Citation Information: J Clin Invest. 2014;124(11):4795-4806. https://doi.org/10.1172/JCI76737.
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Research Article Cardiology

Cardiac-specific ablation of ARNT leads to lipotoxicity and cardiomyopathy

Abstract

Patients with type 2 diabetes often present with cardiovascular complications; however, it is not clear how diabetes promotes cardiac dysfunction. In murine models, deletion of the gene encoding aryl hydrocarbon nuclear translocator (ARNT, also known as HIF1β) in the liver or pancreas leads to a diabetic phenotype; however, the role of ARNT in cardiac metabolism is unknown. Here, we determined that cardiac-specific deletion of Arnt in adult mice results in rapid development of cardiomyopathy (CM) that is characterized by accumulation of lipid droplets. Compared with hearts from ARNT-expressing mice, ex vivo analysis of ARNT-deficient hearts revealed a 2-fold increase in fatty acid (FA) oxidation as well as a substantial increase in the expression of PPARα and its target genes. Furthermore, deletion of both Arnt and Ppara preserved cardiac function, improved survival, and completely reversed the FA accumulation phenotype, indicating that PPARα mediates the detrimental effects of Arnt deletion in the heart. Finally, we determined that ARNT directly regulates Ppara expression by binding to its promoter and forming a complex with HIF2α. Together, these findings suggest that ARNT is a critical regulator of myocardial FA metabolism and that its deletion leads to CM and an increase in triglyceride accumulation through PPARα.

Authors

Rongxue Wu, Hsiang-Chun Chang, Arineh Khechaduri, Kusum Chawla, Minh Tran, Xiaomeng Chai, Cory Wagg, Mohsen Ghanefar, Xinghang Jiang, Marina Bayeva, Frank Gonzalez, Gary Lopaschuk, Hossein Ardehali

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Figure 5

ARNT regulates PPAR at the transcriptional level.

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ARNT regulates PPAR at the transcriptional level. (A) Schematic presenta...
(A) Schematic presentation of the Ppara promoter depicting its HRE sequences. (B) Relative luciferase activity in cells treated with control or ARNT siRNA and transfected with a Ppara promoter-luciferase reporter plasmid or constructs with a truncated Ppara promoter. Renilla luciferase activity was used as an internal control and for normalization of transfection efficiency (n = 6 independent experiments). Data are presented as the fold change of luciferase activity in ARNT siRNA–treated cells over control siRNA–treated cells and normalized to that of the empty vector reporter. Trunc, truncation. (C) Results of ChIP on the second HRE upstream of the PPARα initiation site and using ARNT antibody (n = 3 independent experiments). (D) Changes in Ppara mRNA levels in response to knockdown of ARNT and its partners in NRCMs (n = 6 independent experiments). (E) Sequential ChIP studies using HIF2α and ARNT antibodies. The first ChIP was performed with HIF2α antibody, and the subsequent ChIP was conducted with the indicated antibodies (n = 3 independent experiments). (F) Luciferase activity of WT and a construct with the deletion of the second HRE in cells treated with either control or ARNT siRNA (n = 6 independent experiments). (G) Luciferase activity of WT and a construct with mutations in the second HRE in cells treated with either control or ARNT siRNA (n = 6 independent experiments). Data in F and G are represented as fold change of luciferase activity in ARNT siRNA–treated cells over control siRNA–treated cells and normalized to that of the empty vector reporter. Data are presented as the mean ± SEM. *P < 0.01.