Cardiac-specific ablation of ARNT leads to lipotoxicity and cardiomyopathy
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
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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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 6

PPARα knockdown reverses the metabolic changes associated with Arnt deletion.

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PPARĪ± knockdown reverses the metabolic changes associated with Arnt dele...
(A) mRNA levels of genes involved in FAU and FAO in NRCMs treated with control, ARNT, PPARα, and ARNT plus PPARα siRNA. MCAD, medium-chain acyl-CoA dehydrogenase (n = 6 independent experiments). (B) FAO as determined by oxygen consumption with the exogenous addition of palmitate in NRCMs treated with control, ARNT, PPARα, and ARNT plus PPARα siRNA (n = 6 independent experiments). (C) Myocardial TAG levels in control, csArnt–/–, and csArnt–/– Ppara–/– mice (n = 6–8 independent experiments). (D) Myocardial FAO determined in isolated working hearts of csArnt–/–, csArnt–/– Ppara–/–, or littermate controls using 3H-labeled palmitate (n = 5 hearts). (E) mRNA levels of gene targets of Ppara in control, csArnt–/–, and csArnt–/– Ppara–/– hearts (n = 6 independent experiments). (F) Oil red O, TUNEL, MT, and H&E staining of hearts from control, csArnt–/–, and csArnt–/– Ppara–/– mice. Scale bar: 100 μm. Experiments were repeated in triplicate. (G) Summary of TUNEL+ cells normalized to the number of nuclei in hearts from control, csArnt–/–, and csArnt–/– Ppara–/– mice (n = 4 independent experiments). Data are presented as the mean ± SEM. *P < 0.01; #P < 0.01 for PPARα siRNA vs. ARNT plus PPARα siRNA.