Abstract 18430: Conditional Deletion of Aryl Hydrocarbon Nuclear Translocator (Hypoxia Inducible Factor 1-Beta) in the Adult Heart Results in Cardiomyopathy Associated with Autophagy
Background: Aryl hydrocarbon receptor nuclear translocator (ARNT) is a member of the basic helix-loop-helix Per/ARNT/Sim (bHLH-PAS) proteins and serves as a binding partner for a number of other family members. ARNT is also a required dimerization partner of HIF1alpha. Although HIF1alpha is essential for normal cardiac development, the role of ARNT in basal cardiac function in the adult heart is not known. We hypothesized that ARNT is necessary for normal cardiac physiology, and its deletion in adult heart results in cardiomyopathy.
Methods and Results: The deletion of ARNT gene in the hearts of 3 month old mice was achieved by crossing ARNTflox/flox mice with αMHC-MCM (tamoxifen-inducible heart specific Cre) transgenic mice followed by administration of tamoxifen by mouth. MHC-MCM/ARNT+/+ (WT) littermates were used as a control. The ARNT knock out (KO) mice exhibited enlarged left ventricle with a significant reduction in ejection fraction (KO vs. WT: 35.8 ± 3.6% vs. 61.2 ± 2.8%, n=12, p<0.01) and fractional shortening (KO vs. WT: 18.3 ± 1.5 % vs. 30.1 ± 1.1%, p<0.01), assessed by echocardiography. Closed-chest catheterization also demonstrated reduced +dP/dt (KO vs. WT: 4355 ± 538 vs. 9426 ± 180 mmHg, p<0.01) and increased left ventricular end diastolic pressure (KO vs. WT: 3.12 ± 1.1 vs. 8.47± 1.2 mmHg, P<0.05) in KO mice but not in WT mice. The worsened cardiac function in the KO mouse heart was associated with increases in ANF and BNP expression, interstitial fibrosis, and apoptosis as determined by TUNEL staining. Furthermore, electron microscopy revealed a variety of degenerative changes in the KO hearts. To determine the mechanism for cell death, we then assessed markers of autophagy in ARNT KO hearts. Beclin-1 expression was significantly higher in ARNT KO hearts than in WT hearts (p<0.01). Induction of autophagy in KO hearts was further confirmed by increased conversion of LC-3I to LC3-II.
Conclusion: ARNT is essential for the maintenance of structural and functional homeostasis in the adult heart, and its inactivation leads to cardiac contractile dysfunction. Our findings implicate a novel critical transcriptional requirement for ARNT in the maintenance of adult cardiac function.
- © 2010 by American Heart Association, Inc.