Abstract
The present study aimed to examine the effects of thyroid hormone (TH), more precisely triiodothyronine (T3), on the modulation of leptin mRNA expression and the involvement of the phosphatidyl inositol 3 kinase (PI3K) signaling pathway in adipocytes, 3T3-L1, cell culture. We examined the involvement of this pathway in mediating TH effects by treating 3T3-L1 adipocytes with physiological (P=10nM) or supraphysiological (SI=100 nM) T3 dose during one hour (short time), in the absence or the presence of PI3K inhibitor (LY294002). The absence of any treatment was considered the control group (C). RT-qPCR was used for mRNA expression analyzes. For data analyzes ANOVA complemented with Tukey’s test was used at 5% significance. T3 increased leptin mRNA expression in P (2.26 ± 0.36, p< 0.001), SI (1.99 ±0.22, p< 0.01) compared to C group (1± 0.18). This increase was completely abrogated by LY294002 in P (1.31±0.05, p< 0.001) and SI (1.33±0.31, p< 0.05). Western blotting confirmed these results at protein level, indicating the PI3K pathway dependency. To examine whether leptin is directly induced by T3, we used the translation inhibitor cycloheximide (CHX). In P, the presence of CHX maintained the levels mRNA leptin, but was completely abrogated in SI (1.14±0.09, p> 0.001). These results demonstrate that the activation of the PI3K signaling pathway has a role in TH-mediated direct and indirect leptin gene expression in 3T3-L1 adipocytes.
Highlights
Thyroid hormones (THs) actions are especially important during development, this actions regulate the growth and maturation of many organs and tissues during the fetal and neonatal life [1,2]
We have found that T3 increases the leptin expression levels in one hour of treatment, and such increase occurs directly in T3 physiological dose and indirectly in supraphysiological dose, but both depend on the activation of phosphatidyl inositol 3 kinase (PI3K) pathway
Since the adipose tissue is a target of thyroid hormones [19,20], some authors suggest that the leptin and thyroid might have a parallel response [21]
Summary
Thyroid hormones (THs) actions are especially important during development, this actions regulate the growth and maturation of many organs and tissues during the fetal and neonatal life [1,2]. Studies from our group showed that a T3 physiological dose increases leptin gene expression in obese animals subjected to diet restriction [13]. Animals subjected to supraphysiological doses of T3 showed a diminishment in leptin mRNA expression [14] These findings suggest that THs physiological levels might be necessary for the adequate leptin secretion [13]. The present study assessed the effect of physiological and supraphysiological T3 doses in leptin mRNA and protein expression levels at 3T3-L1, adipocytes culture, after one hour of treatment. We have found that T3 increases the leptin expression levels in one hour (short time) of treatment, and such increase occurs directly in T3 physiological dose and indirectly in supraphysiological dose, but both depend on the activation of PI3K pathway
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