The roles of triiodothyronine and irisin in improving the lipid profile and directing the browning of human adipose subcutaneous cells

Triiodothyronine (T3) and irisin (I) can modulate metabolic status, increase heat production, and promote differentiation of white adipose tissue (WAT) into brown adipose tissue (BAT). Herein, human subcutaneous white adipocytes were treated with 10 nM T3 or 20 nM I for 24 h to evaluate intracellular lipid accumulation, triglyceride, and glycerol levels, oxidative stress, DNA damage, and protein levels of uncoupling protein 1 (UCP1), adiponectin, leptin, peroxisome proliferator-activated receptor gamma (PPARγ), and fibronectin type III domain-containing protein 5 (FNDC5). T3 and irisin improved UCP1 production, lipid profile, oxidative stress, and DNA damage. T3 elevated adiponectin and leptin levels with a concomitant decrease in PPARy and FNDC5 levels. However, irisin did not alter adipokine, PPARy, and FNDC5 levels. The results indicate that T3 may be used to increase leptin and adiponectin levels to improve insulin sensitivity, and irisin may be used to prevent obesity or maintain weight due to its impact on the lipid profile without altering adipokine levels.

Triiodothyronine activated extranuclear pathways upregulate adiponectin and leptin in murine adipocytes

Adiponectin and leptin, important for metabolic regulation, are synthesized and secreted by adipose tissue and are influenced by triiodothyronine (T3) that activates the MAPK/ERK and integrin αVβ3 pathways, modulating gene expression. Adipocytes were treated with T3 (10 nM), for 1 h, in the absence or presence of PD98059 (PD) and tetraiodothyroacetic acid (Tetrac), which are pathways inhibitors. The cells were incubated with Adipo Red/Oil Red O reagents, and intracellular lipid accumulation [glycerol and triacylglycerol (TAG)], MTT, 8-hydroxideoxyguanosine (8-OH-dG), and mRNA and protein expression were assessed. T3 increased leptin mRNA and protein expression, and, in contrast, there was a decrease in the Tetrac + T3 group. Adiponectin mRNA expression was not altered by T3, though it had increased its protein expression, which was terminated by inhibitors PD + T3 and Tetrac + T3. However, T3 did not alter PPARγ protein expression, lipid accumulation, TAG, glycerol, and DNA damage, but PD + T3 and Tetrac + T3 reduced these parameters. T3 activated the MAPK/ERK pathway on adipocytes to modulate the adiponectin protein expression and integrin αvβ3 to alter the leptin gene expression.

Adiponectin and Serine/Threonine Kinase Akt Modulation by Triiodothyronine and/or LY294002 in 3T3-L1 Adipocytes

Adipose tissue (AT), an endocrine organ that modulates several physiological functions by synthesizing and releasing adipokines such as adiponectin, is a metabolic target of triiodothyronine (T3). T3 and adiponectin play important roles in controlling normal metabolic functions such as stimulation of fatty acid oxidation and increase in thermogenesis. The phosphatidylinositol 3-kinase (PI3K) pathway is important for the differentiation of preadipocytes into adipocytes and can be activated by T3 for the transcription of specific genes, such as adiponectin. We examined the role of PI3K in adiponectin modulation by T3 action in murine adipocytes (3T3-L1). The 3T3-L1 adipocytes were treated with 1000 nM T3 for 1 h in the presence or absence of 50 μM LY294002 (LY), a PI3K inhibitor. Then, we assessed the expression of adiponectin and the phosphorylated serine/threonine kinase Akt (pAkt), a PI3K signaling protein, in the adipocytes. Adiponectin and pAKT levels were higher in the T3-adipocyte cells, whereas in the LY group adiponectin was elevated and pAKT was decreased compared to the control (C). PI3K pathway inhibition for 1 h and posterior treatment with T3, in LY + T3, reduced the adiponectin level and increased pAKT levels compared to those in LY. T3 stimulated adiponectin levels by PI3K pathway activation and T3 can compensate alteration in the PI3K pathway, because with inhibition of the pathway it is able to maintain the basal levels of adiponectin and pAKT.

The importance of estrogen for bone protection in experimental hyperthyroidism in human osteoblasts

Triiodothyronine (T₃) and estrogen (E₂) play important roles in the bone remodeling process and signaling of receptor activator of the nuclear factor-kappa β (RANKL) and osteoprotegerin (OPG) expressed by osteoblasts. However, little is known of the molecular action of these hormones in conditions of hyperthyroidism and associated E₂ in human cells.

AIMS

This study evaluated the effects of the physiological concentration of E₂ (10 nM), alone or in association with physiological (1 nM) and supraphysiological (10 nM) concentrations of T₃, on RANKL and OPG gene expression in human osteoblasts.

MAIN METHODS

Alkaline phosphatase and osteocalcin assays were performed to verify the presence of mature osteoblasts. After mimicking the experimental hyperthyroidism in osteoblasts untreated or treated with E₂, RANKL and OPG gene expression was analyzed by real-time PCR and protein expression by western Blot and ELISA. Alizarin Red staining analyzed the amount of bone matrix after hormonal treatments.

KEY FINDINGS

E₂ enhanced the gene expression of OPG when associated with 1 nM and 10 nM T₃. E₂ was able to restore the bone matrix after an initial decrease using 1 nM and 10 nM T₃. The protective effect of E₂ on the RANKL and OPG signaling pathway was demonstrated. E2 restored the bone matrix induced by experimental hyperthyroidism.

SIGNIFICANCE

The data highlight the importance of E₂ to maintain OPG expression and osteoblast activity against possible loss of bone mass, especially in conditions where T₃ is in excess.

Disruptive Effect of Organotin on Thyroid Gland Function Might Contribute to Hypothyroidism

A considerable increase in endocrine abnormalities has been reported over the last few decades worldwide. A growing exposure to endocrine-disrupting chemicals (EDCs) can be one of the causes of endocrine disorders in populations, and these disorders are not only restricted to the metabolic hormone system but can also cause abnormal functions. Thyroid hormone (TH) disruption is defined as an abnormal change in TH production, transport, function, or metabolism, which results in some degree of impairment in body homeostasis. Many EDCs, including organotin compounds (OTCs), are environmental contaminants that are commonly found in antifouling paints used on ships and in several other industrial procedures. OTCs are obesogenic and can disrupt TH metabolism; however, abnormalities in thyroid function resulting from OTC exposure are less well understood. OTCs, one of the most prevalent EDCs that are encountered on a daily basis, modulate the thyroid axis. In most toxicology studies, it has been reported that OTCs might contribute to hypothyroidism.

Triiodothyronine modulates the expression of leptin and adiponectin in 3T3-L1 adipocytes

Objective

To study the effect of different doses of triiodothyronine on gene expression of the adipokines leptin and adiponectin, at different times, and to evaluate the difference in expression between the two adipokines in each group.

Methods

3T3-L1 adipocytes were incubated with triiodothyronine at physiological dose (10nM) and supraphysiological doses (100nM or 1,000nM), or without triiodothyronine (control, C) for 0.5, 6, or 24 hours. Leptin and adiponectin mRNA was detected using real-time polymerase chain reaction (RT-PCR). One-way analyses of variance, Tukey’s test or Student’s t test, were used to analyze data, and significance level was set at 5%.

Results

Leptin levels decreased in the 1,000nM-dose group after 0.5 hour. Adiponectin levels dropped in the 10nM-dose group, but increased at the 100nM dose. After 6 hours, both genes were suppressed in all hormone concentrations. After 24 hours, leptin levels increased at 10, 100 and 1,000nM groups as compared to the control group; and adiponectin levels increased only in the 100nM group as compared to the control group.

Conclusion

These results demonstrated fast actions of triiodothyronine on the leptin and adiponectin expression, starting at 0.5 hour, at a dose of 1,000nM for leptin and 100nM for adiponectin. Triiodothyronine stimulated or inhibited the expression of adipokines in adipocytes at different times and doses which may be useful to assist in the treatment of obesity, assuming that leptin is increased and adiponectin is decreased, in obesity cases.

Short-term effects of triiodothyronine on thyroid hormone receptor alpha by PI3K pathway in adipocytes, 3T3-L1

Objective The present study aimed to examine the effects of thyroid hormone (TH), more precisely triiodothyronine (T3), on the modulation of TH receptor alpha (TRα) mRNA expression and the involvement of the phosphatidyl inositol 3 kinase (PI3K) signaling pathway in adipocytes, 3T3-L1, cell culture. Materials and methods: It was examined the involvement of PI3K pathway in mediating T3 effects by treating 3T3-L1 adipocytes with physiological (P=10nM) or supraphysiological (SI =100 nM) T3 doses 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 level. Results T3 increased TRα mRNA expression in P (1.91±0.13, p<0.001), SI (2.14±0.44, p<0.001) compared to C group (1±0.08). This increase was completely abrogated by LY294002 in P (0.53±0.03, p<0.001) and SI (0.31±0.03, p<0.001). To examine whether TRα is directly induced by T3, we used the translation inhibitor cycloheximide (CHX). The presence of CHX completely abrogated levels TRα mRNA in P (1.15±0.05, p>0.001) and SI (0.99±0.15, p>0.001), induced by T3. Conclusion These results demonstrate that the activation of the PI3K signaling pathway has a role in T3-mediated indirect TRα gene expression in 3T3-L1 adipocytes.

Triiodothyronine and breast cancer

The thyroid hormones (THs), triiodothyronine (T3) and thyroxine (T4), are essential for survival; they are involved in the processes of development, growth, and metabolism. In addition to hyperthyroidism or hypothyroidism, THs are involved in other diseases. The role of THs in the development and differentiation of mammary epithelium is well established; however, their specific role in the pathogenesis of breast cancer (BC) is controversial. Steroid hormones affect many human cancers and the abnormal responsiveness of the mammary epithelial cells to estradiol (E2) in particular is known to be an important cause for the development and progression of BC. The proliferative effect of T3 has been demonstrated in various types of cancer. In BC cell lines, T3 may foster the conditions for tumor proliferation and increase the effect of cell proliferation by E2; thus, T3 may play a role in the development and progression of BC. Studies show that T3 has effects similar to E2 in BC cell lines. Despite controversy regarding the relationship between thyroid disturbances and the incidence of BC, studies show that thyroid status may influence the development of tumor, proliferation and metastasis.

Triiodothyronine increases mRNA and protein leptin levels in short time in 3T3-L1 adipocytes by PI3K pathway activation

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.