Liraglutide Activates Type 2 Deiodinase and Enhances β3-Adrenergic-Induced Thermogenesis in Mouse Adipose Tissue

Aims

Liraglutide is a long-acting glucagon-like peptide 1 (GLP-1) receptor agonist used as an anti-hyperglycemic agent in type 2 diabetes treatment and recently approved for obesity management. Weight loss is attributed to appetite suppression, but therapy may also increase energy expenditure. To further investigate the effect of GLP-1 signaling in thermogenic fat, we assessed adipose tissue oxygen consumption and type 2 deiodinase (D2) activity in mice treated with liraglutide, both basally and after β3-adrenergic treatment.

Methods

Male C57BL/6J mice were randomly assigned to receive liraglutide (400 μg/kg, n=12) or vehicle (n=12). After 16 days, mice in each group were co-treated with the selective β3-adrenergic agonist CL316,243 (1 mg/kg, n=6) or vehicle (n=6) for 5 days. Adipose tissue depots were assessed for gene and protein expression, oxygen consumption, and D2 activity.

Results

Liraglutide increased interscapular brown adipose tissue (iBAT) oxygen consumption and enhanced β3-adrenergic-induced oxygen consumption in iBAT and inguinal white adipose tissue (ingWAT). These effects were accompanied by upregulation of UCP-1 protein levels in iBAT and ingWAT. Notably, liraglutide increased D2 activity without significantly upregulating its mRNA levels in iBAT and exhibited additive effects to β3-adrenergic stimulation in inducing D2 activity in ingWAT.

Conclusions

Liraglutide exhibits additive effects to those of β3-adrenergic stimulation in thermogenic fat and increases D2 activity in BAT, implying that it may activate this adipose tissue depot by increasing intracellular thyroid activation, adding to the currently known mechanisms of GLP-1A-induced weight loss.

Abstract 4926: Loss of deiodinase type 3 expression distinguishes patients with poor prognosis in breast cancer

Background: Breast cancer is a highly heterogeneous disease and the identification of biomarkers that predict tumor biological behavior is warranted in improving patient survival. Thyroid hormones (THs) are critical regulators of cellular processes, and TH status alterations are known to contribute to cancer progression through all the hallmarks of cancer. Clinical studies associate THs levels with breast cancer mortality, and THs have been shown to influence breast cancer proliferation, apoptosis, and migration in in vitro models. Type 3 deiodinase (DIO3) is the main enzyme responsible for TH inactivation and disturbed DIO3 expression has been demonstrated in several human neoplasias. Here, we aimed to evaluate expression patterns and the prognostic significance of DIO3 in breast cancer.

Methods: The expression of DIO3 was assessed by immunohistochemistry in a primary cohort of 53 samples of breast tissue and was validated in a second cohort using the RNA-Seq data from TCGA database (BRCA study). We assessed DIO3 expression in both populations according to retrieved clinicopathological information. For methylation analysis, DNA methylation data from the TCGA-BRCA study were obtained. Regulation of DIO3 gene was investigated in MCF-7 and MDA-MB-231 cell lines.

Results: DIO3 expression was present in normal and tumoral breast glandular tissue. DIO3 mRNA expression was found to be reduced in tumor samples when compared to normal tissue (p<0.0001). Unexpectedly, loss of DIO3 expression was associated with increased mortality (HR 4.29; 95% CI 1.24-14.7) in the primary cohort. We then validated this finding in the secondary cohort. Patients with low DIO3 expression exhibited reduced overall survival (OS) when compared to those higher levels of DIO3 expression. Five-year OS rates were 90.4% and 77.4% in the high and low expression groups, respectively (p=0.0002). Among patients with metastasis, five-year OS rate was 70% in the high DIO3 group and 0% in the low DIO3 group (p=0.038). Additional experiments were performed to determine DIO3 regulation in breast cancer. In MCF-7 and MDA-MD-231 cells, DIO3 was subject to T3 stimulation and was under the regulation of MAPK pathway, as MAPK inhibition resulted in a 50% reduction of DIO3 expression (p=0.004). Methylation analysis revealed that DIO3 gene promoter is hypermethylated in tumoral cells when compared to normal tissue (p <0.0001).

Conclusions: DIO3 is expressed in normal and tumoral breast tissue. Here, we demonstrate a role for DIO3 as a prognostic marker in breast cancer, as loss of DIO3 expression distinguishes breast cancer patients with poor overall survival. Moreover, our fındings suggest the utility of DIO3 expression for stratifıcation of patients with metastasis. The finding that DIO3 gene is regulated by the MAPK pathway and that gene promoter is hypermethylated in breast cancer might have therapeutic implications.

Citation Format: Iuri M. Goemann, Vicente R. Marczyk, Mariana Recamonde-Mendoza, Marcia S. Graudenz, Simone M. Wajner, Ana Luiza Maia. Loss of deiodinase type 3 expression distinguishes patients with poor prognosis in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4926.

Dissecting thyroid hormone transport and metabolism in dendritic cells

We reported thyroid hormone (TH) receptor expression in murine dendritic cells (DCs) and 3,5,3'-triiodothyronine (T₃)-dependent stimulation of DC maturation and ability to develop a Th1-type adaptive response. Moreover, an increased DC capacity to promote antigen-specific cytotoxic T-cell activity, exploited in a DC-based antitumor vaccination protocol, was revealed. However, putative effects of the main circulating TH, l-thyroxine (T₄) and the mechanisms of TH transport and metabolism at DC level, crucial events for TH action at target cell level, were not known. Herein, we show that T₄ did not reproduce those registered T₃-dependent effects, finding that may reflect a homoeostatic control to prevent unspecific systemic activation of DCs. Besides, DCs express MCT10 and LAT2 TH transporters, and these cells mainly transport T₃ with a favored involvement of MCT10 as its inhibition almost prevented T₃ saturable uptake mechanism and reduced T₃-induced IL-12 production. In turn, DCs express iodothyronine deiodonases type 2 and 3 (D2, D3) and exhibit both enzymatic activities with a prevalence towards TH inactivation. Moreover, T₃ increased MCT10 and LAT2 expression and T₃ efflux from DCs but not T₃ uptake, whereas it induced a robust induction of D3 with a parallel slight reduction in D2. These findings disclose pivotal events involved in the mechanism of action of THs on DCs, providing valuable tools for manipulating the immunogenic potential of these cells. Furthermore, they broaden the knowledge of the TH mechanism of action at the immune system network.

The rs225017 polymorphism in the 3'UTR of the human DIO2 gene is associated with increased insulin resistance

The Thr92Ala (rs225014) polymorphism in the type 2 deiodinase (DIO2) gene has been associated with insulin resistance (IR) and decreased enzyme activity in human tissues but kinetic studies failed to detect changes in the mutant enzyme, suggesting that this variant might be a marker of abnormal DIO2 expression. Thus, we aimed to investigate whether other DIO2 polymorphisms, individually or in combination with the Thr92Ala, may contribute to IR. The entire coding-region of DIO2 gene was sequenced in 12 patients with type 2 diabetes mellitus (T2DM). Potentially informative variants were evaluated in 1077 T2DM patients and 516 nondiabetic subjects. IR was evaluated using the homeostasis model assessment (HOMA-IR) index. DIO2 gene sequencing revealed no new mutation but 5 previously described single nucleotide polymorphisms (SNPs). We observed that all T2DM patients displaying high HOMA-IR index (n = 6) were homozygous for the rs225017 (T/A) polymorphism. Further analysis showed that the median fasting plasma insulin and HOMA-IR of T2DM patients carrying the T/T genotype were higher than in patients carrying the A allele (P = 0.013 and P = 0.002, respectively). These associations were magnified in the presence of the Ala92Ala genotype of the Thr92Ala polymorphism. Moreover, the rs225017 and the Thr92Ala polymorphisms were in partial linkage disequilibrium (|D'| = 0.811; r2 = 0.365). In conclusion, the rs225017 polymorphism is associated with greater IR in T2DM and it seems to interact with the Thr92Ala polymorphism in the modulation of IR.

Type 2 deiodinase Thr92Ala polymorphism is associated with disrupted placental activity but not with dysglycemia or adverse gestational outcomes: a genetic association study

OBJECTIVE

To study whether the D2 Thr92Ala polymorphism-a genetic marker that is associated with reduced thyroid type 2 deiodinase (D2) activity, increased insulin resistance, and risk for type 2 diabetes-is associated with disrupted placental D2 activity and with glycemic control and gestational outcomes.

DESIGN

Cross-sectional study.

SETTING

Tertiary hospital in Brazil.

PATIENT(S)

Consecutive singleton-pregnancy patients, 18-45 years old.

INTERVENTION(S)

Clinical examination and genotyping of the D2 Thr92Ala polymorphism, with placental samples collected and assayed for D2 mRNA and activity.

MAIN OUTCOME MEASURE(S)

Glucose homeostasis and gestational outcomes.

RESULT(S)

A total of 294 patients were included in the study. The clinical and laboratory characteristics were similar among the D2 genotypes. No differences were observed in D2 placental mRNA levels, but D2 activity was decreased in patients with the Ala92Ala genotype (0.35 ± 0.15 vs. 1.96 ± 1.02 fmol/mg/min.). Newborn serum thyroid-stimulating hormone levels (TSHneo) did not differ according to maternal D2 Thr92Ala genotype. Also, maternal glucose control, insulin resistance evaluated by the homeostasis model assessment (HOMA-IR), and gestational outcomes did not differ across D2 genotypes.

CONCLUSION(S)

The D2 Ala92Ala genotype is associated with reduced placental D2 activity but is not associated with dysglycemia, increased insulin resistance, or worse gestational outcomes.

Regulation of Dio2 gene expression by thyroid hormones in normal and type 1 deiodinase-deficient C3H mice

The C3H/HeJ mouse presents an inherited type 1 deiodinase (D1) deficiency that results in elevated serum thyroxine (T(4)), whereas TSH and tri-iodothyronine (T(3)) concentrations are normal when compared with those in the C57BL/6J strain. Here, we evaluated the expression of the type 2 (D2), the other T(4)-activating enzyme, in C3H mice. A comparative analysis revealed that D2 mRNA levels in C3H are similar to those in C57 animals. The D2 activity in C3H pituitary and brain are reduced when compared with those in the C57 strain (3.75 +/- 1.08 vs 5.78 +/- 0.33 and 0.17 +/- 0.05 vs 0.26 +/- 0.07 fmol/min per mg protein respectively). However, no differences on D2 activity levels were observed in the brown adipose tissue (BAT) between both strains (0.34 +/- 0.06 vs 0.36 +/- 0.09 fmol/min per mg protein). Experiments using different T(4) doses showed that higher levels of serum T(4) than those of the C3H mouse are required to downregulate D2 activity in this tissue. T(3) administration to euthyroid mice resulted in a two- to four-fold increase on D2 activity in BAT and brain of both strains, despite a marked decrease in BAT D2 transcripts and no changes in brain D2 mRNA levels. The increase in D2 activity was preceded by a decrease in serum T(4) levels, which appears to reduce D2 degradation. Indeed, administration of T(3) plus T(4) abolished the T(3)-induced D2 upregulation. In conclusion, our results demonstrated that D2 activity is mainly regulated at posttranslational level in a tissue-specific manner. These observations further characterize and provide insights into the complex and dual regulatory role of the iodothyronines in D2 regulation.