Thyroid hormone upregulates zinc-α2-glycoprotein production in the liver but not in adipose tissue - PubMed (original) (raw)
Thyroid hormone upregulates zinc-α2-glycoprotein production in the liver but not in adipose tissue
Rafael Simó et al. PLoS One. 2014.
Abstract
Overproduction of zinc-α2-glycoprotein by adipose tissue is crucial in accounting for the lipolysis occurring in cancer cachexia of certain malignant tumors. The main aim of this study was to explore whether thyroid hormone could enhance zinc-α2-glycoprotein production in adipose tissue. In addition, the regulation of zinc-α2-glycoprotein by thyroid hormone in the liver was investigated. We performed in vitro (HepG2 cells and primary human adipocytes) and in vivo (C57BL6/mice) experiments addressed to examine the effect of thyroid hormone on zinc-α2-glycoprotein production (mRNA and protein levels) in liver and visceral adipose tissue. We also measured the zinc-α2-glycoprotein serum levels in a cohort of patients before and after controlling their hyperthyroidism. Our results showed that thyroid hormone up-regulates zinc-α2-glycoprotein production in HepG2 cells in a dose-dependent manner. In addition, the zinc-α2-glycoprotein proximal promoter contains functional thyroid hormone receptor binding sites that respond to thyroid hormone treatment in luciferase reporter gene assays in HepG2 cells. Furthermore, zinc-α2-glycoprotein induced lipolysis in HepG2 in a dose-dependent manner. Our in vivo experiments in mice confirmed the up-regulation of zinc-α2-glycoprotein induced by thyroid hormone in the liver, thus leading to a significant increase in zinc-α2-glycoprotein circulating levels. However, thyroid hormone did not regulate zinc-α2-glycoprotein production in either human or mouse adipocytes. Finally, in patients with hyperthyroidism a significant reduction of zinc-α2-glycoprotein serum levels was detected after treatment but was unrelated to body weight changes. We conclude that thyroid hormone up-regulates the production of zinc-α2-glycoprotein in the liver but not in the adipose tissue. The neutral effect of thyroid hormones on zinc-α2-glycoprotein expression in adipose tissue could be the reason why zinc-α2-glycoprotein is not related to weight loss in hyperthyroidism.
Conflict of interest statement
Competing Interests: The authors have declared that no competing interests exist.
Figures
Figure 1. Treatment with T3 increases ZAG production by the liver but not in adipose tissue in C57BL/6 mice.
(A) ZAG blood levels increase in mice treated with T3 when compared with vehicle treated mice. (B) Analysis of ZAG mRNA expression in liver and adipose tissue of mice treated as in A. Mouse 18S was amplified as an internal control, and values are expressed as percentage relative to the untreated cells. Data are expressed as mean ± SD of triplicates.
Figure 2. Treatment with T3 increases ZAG production in HepG2 cells.
(A) ZAG media from HepG2 cells treated over the course of 3 days with vehicle (ethanol) or T3 (1, 10 and 100 nM) was measured by ELISA. Data are expressed as mean ± SD of triplicates. (B) ZAG mRNA levels from HepG2 cells treated as in A. Human 18S was amplified as an internal control, and values are expressed as percentage relative to the untreated cells. Data are expressed as mean ± SD of triplicates. (C) Western blot of ZAG and PPIA from extracts of HepG2 cells treated as in A.
Figure 3. Treatment with T3 do not change ZAG production in human adipocytes.
(A) ZAG media from human adipocytes treated over the course of 3 days with vehicle (ethanol) or T3 (10 and 100 nM) was measured by ELISA. Data are expressed as mean ± SD of triplicates. (B) ZAG mRNA levels from human adipocytes treated as in A. Human 18S was amplified as an internal control, and values are expressed as percentage relative to the untreated cells. Data are expressed as mean ± SD of triplicates.
Figure 4. Treatment with T3 increases ZAG promoter activity in HepG2 cells.
(A) ZAG promoter activity was analyzed in HepG2 cells in luciferase reporter gene assays. Data are expressed as mean ± SD of triplicates. (B) Scheme of the human ZAG promoter with 4 putative TR binding sites. (C) ZAG promoter activity was analyzed in HepG2 cells treated with vehicle or T3 (100 nM) in luciferase reporter gene assays. Data are expressed as mean ± SD of triplicates. (D) ChIP assays of TR binding to the human ZAG promoter in HepG2 cells treated with vehicle or T3 (100 nM) for 5 days. The GAPDH and PAI-1 promoters were used as a negative and positive control, respectively. Positive PCR controls of sheared genomic DNA templates indicated the integrity of the input DNA used in the ChIP reactions.
Figure 5. ZAG induces lipolysis in HepG2 cells.
Measurement of glycerol accumulation in the medium after treatment for 6(3 µM) and ZAG (1, 10 and 50 µg/ml). Data are expressed as mean ± SD of triplicates.
References
- Sanchez LM, Chirino AJ, Bjorkman P (1999) Crystal structure of human ZAG, a fat depleting factor related to MHC molecules. Science 283: 1914–1919. - PubMed
- Ceperuelo-Mallafré V, Näf S, Escoté X, Caubet E, Gomez JM, et al. (2009) Circulating and adipose tissue gene expression of zinc-α2-glycoprotein in obesity. Its relationship with adipokine and lipolytic gene markers in subcutaneous and visceral fat. J Clin Endocrinol Metab 94: 5062–5069. - PubMed
- Gong FY, Zhang SJ, Deng JY, Zhu HJ, Pan H, et al. (2009) Zinc-alpha2-glycoprotein is involved in regulation of body weight through inhibition of lipogenic enzymes in adipose tissue. Int J Obes (London) 33: 1023–30. - PubMed
- Rolli V, Radosavljevic M, Astier V, Macquin C, Castan-Laurell I, et al. (2007) Lipolysis is altered in MHC class I zinc-alpha(2)-glycoprotein deficient mice. FEBS Lett 581: 394–400. - PubMed
- Russell ST, Tisdale MJ (2011) Studies on the anti-obesity activity of zinc-α2-glycoprotein in the rat. Int J Obes (Lond) 35: 658–65. - PubMed
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