Role Of Aryl Hydrocarbon Receptor Nuclear Translocator Research Articles

Aryl-Hydrocarbon Receptor Nuclear Translocator (ARNT) in Human Skin with Aging

The goal of this study was to examine the content of aryl-hydrocarbon receptor nuclear translocator (ARNT) in fibroblasts of human dermis from 20 weeks of pregnancy to the age of 85 years and to define the role of ARNT in age-dependent changes in the fibroblast number in the dermis. ARNT and proliferating cell nuclear antigen (PCNA) were detected with an indirect immunohistochemical technique. The results showed that the proportion of fibroblasts with positive staining for ARNT in the dermis gradually decreased from 20 weeks of pregnancy to the age of 40 years. There is a sharp increase in the percentage of ARNT-positive fibroblasts in the dermis after the age of 41 years; it reaches the maximum in the 60- to 85-year-old age group. The total number and percentage of PCNA-positive fibroblasts in the dermis decreased with age, most significantly from the antenatal period until 40 years of life. Age-related changes in the ARNT content in fibroblasts are not statistically associated with an age-related decrease in total number or percentage of PCNA-positive fibroblasts in the dermis.

Down-regulation of ARNT promotes cancer metastasis by activating the fibronectin/integrin β1/FAK axis

The aryl hydrocarbon receptor nuclear translocator (ARNT) is broadly involved in regulating tumorigenesis by inducing genes that are involved in tumor growth and angiogenesis. Tumorigenesis usually involves normoxic conditions. However, the role of ARNT in tumor metastasis during normoxia remains unclear. Here, we demonstrate that ARNT protein levels were decreased in late-stage human colorectal cancer using immunohistochemical analysis. Down-regulation of ARNT protein promoted cancer cell migration and invasion, which was mediated by activation of the fibronectin/integrin β1/FAK signaling axis. In addition, the enhancement of migration and invasion in ANRT knockdown cells was blocked when ARNT was restored in the cells. In xenografts in severe combined immunodeficiency mice, tumor growth was significantly inhibited in the ARNT-knockdown condition. However, the tail-vein injection animal model revealed that the depletion of ARNT-induced metastatic lung colonies was further enhanced when ARNT expression was recovered post-injection. Interestingly, chemotherapeutic drugs inhibited ARNT expression and promoted the invasion of residual tumor cells. These results suggest that ARNT may play a positive role during tumor growth (either in early-stage tumor growth or in organ metastases), but plays a negative role in tumor migration and invasion. Therefore, the efficiency of ARNT-targeted therapy during different cancer stages should be carefully evaluated.

Abstract P121: Cardiac Deletion of Aryl Hydrocarbon Nuclear Translocator (Hypoxia-Inducible Factor 1-β) in the Adult Heart Results in Cardiomyopathy

Rongxue Wu, Kusum Chawla, Yoshihiko Ichikawa, Mohsen Granefar Hossein Ardehali Background: Aryl hydrocarbon receptor nuclear translocator (ARNT) is a member of 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 HIF1a. Although HIF1a is known to be required for normal cardiac development, the role of ARNT in basal cardiac function in the adult heart is not known. We hypothesized that ARNT is required for normal cardiac physiology, and its deletion in adult heart results in cardiomyopathy. Methods and Results: The deletion of ARNT gene in the heart of 3 month old mice was achieved by crossing ARNT flox/flox mice with αMHC-MCM (tamoxifen-inducible heart specific Cre) transgenic mice followed by administration of tamoxifen chow. 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 increase in ANF and BNP expression, interstitial fibrosis, and apoptosis as determined by TUNEL staining. Furthermore, electron microscopy reveals a variety of degenerative changes and some lipid droplet in the KO hearts, and histological studies demonstrated intramyocardial lipid accumulation in the perivascular area in the KO mouse hearts. Analysis of gene expression in the KO heart revealed up-regulation of peroxisome proliferator-activated receptor alpha. 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.

Abstract 16841: Cardiac Deletion of Aryl Hydrocarbon Nuclear Translocator (Hypoxia Inducible Factor 1-beta) in the Adult Heart Leads to Cardiomyopathy Due to Lipid Accumulation via Peroxisome Proliferator Activated Receptor Activation

Background: Aryl hydrocarbon receptor nuclear translocator (ARNT), also known as hypoxia-inducible factor 1-beta (HIF1-beta), serves as a binding partner for numerous basic helix-loop-helix Per/ARNT/Sim proteins, including HIF1alpha. Although HIF1alpha is known to be required for normal cardiac development, the role of ARNT in basal cardiac function in the adult is not known. We hypothesized that ARNT is required for normal cardiac physiology, and that ARNT deletion in the adult heart results in cardiomyopathy. Methods and Results: Cardiac-specific ARNT deletion was achieved by crossing ARNT flox/flox with αMHC-MCM (tamoxifen-inducible heart specific Cre) transgenic mice, followed by oral administration of tamoxifen. MCM/ARNT +/+ (WT) littermates were used as a control. Echocardiography of the ARNT knockout (KO) mice showed enlarged left ventricle with a reduction in ejection fraction (KO vs. WT: 35.8 ± 3.6% vs. 61.2 ± 2.8%, n=12, p<0.01). Closed-chest catheterization indicated that +dP/dt (KO vs. WT: 4355 ± 538 vs. 9426 ± 180 mmHg, p<0.01) was reduced in KO mice but not in WT mice. Electron microscopy revealed lipid droplets in ARNT KO heart tissues that were confirmed by oil-red staining. Furthermore, genes involved in fatty acid oxidation were up-regulated in KO hearts, as shown by microarray analysis and qRT-PCR. We further confirmed these results in vitro with siRNA-mediated knock down of ARNT in H9c2 cardiac myoblasts. Compared to control siRNA transfection, ARNT knockdown led to increases in PPAR-alpha (1.7-fold, p<0.001), fatty acid translocase (1.4-fold, P<0.01), and acyl-coenzyme A dehydrogenase (1.6-fold, p<0.0001) mRNA levels and to enhanced triglyceride accumulation (p<0.05). Moreover, insulin resistance was noted in ARNT knockdown cells, as demonstrated by significantly reduced glucose uptake in response to insulin stimulation. These results suggest that impaired fatty acid oxidation leads to lipid accumulation in response to a reduction in ARNT levels. Conclusion: ARNT is essential for normal cardiac function, and a reduction in ARNT levels leads to cardiomyopathy by increasing triglyceride accumulation through a PPAR-alpha pathway.