Yuantao Liu

Role of extrathyroidal TSHR expression in adipocyte differentiation and its association with obesity

BackgroundObesity is known to be associated with higher risks of cardiovascular disease, metabolic syndrome, and diabetes mellitus. Thyroid-stimulating hormone (TSHR) is the receptor for thyroid-stimulating hormone (TSH, or thyrotropin), the key regulator of thyroid functions. The expression of TSHR, once considered to be limited to thyrocytes, has been so far detected in many extrathyroidal tissues including liver and fat. Previous studies have shown that TSHR expression is upregulated when preadipocytes differentiate into mature adipocytes, suggestive of a possible role of TSHR in adipogenesis. However, it remains unclear whether TSHR expression in adipocytes is implicated in the pathogenesis of obesity.MethodsIn the present study, TSHR expression in adipose tissues from both mice and human was analyzed, and its association with obesity was evaluated.ResultsWe here showed that TSHR expression was increased at both mRNA and protein levels when 3T3-L1 preadipocytes were induced to differentiate. Knockdown of TSHR blocked the adipocyte differentiation of 3T3-L1 preadipocytes as evaluated by Oil-red-O staining for lipid accumulation and by RT-PCR analyses of PPAR-γ and ALBP mRNA expression. We generated obesity mice (C57/BL6) by high-fat diet feeding and found that the TSHR protein expression in visceral adipose tissues from obesity mice was significantly higher in comparison with the non-obesity control mice (P < 0.05). Finally, the TSHR expression in adipose tissues was determined in 120 patients. The results showed that TSHR expression in subcutaneous adipose tissue is correlated with BMI (body mass index).ConclusionTaken together, these results suggested that TSHR is an important regulator of adipocyte differentiation. Dysregulated expression of TSHR in adipose tissues is associated with obesity, which may involve a mechanism of excess adipogenesis.

Hydrogen sulfide protects against high-glucose-induced apoptosis in endothelial cells.

Hydrogen sulfide (H2S) is the third endogenous gaseous mediator identified after nitric oxide and carbon monoxide. It has been demonstrated that H2S has protective effects on myocardial ischemia/reperfusion-induced cell apoptosis. To date, little is known about the role of H2S in the pathophysiology of diabetic vascular complications. In this study, we investigated the effects of sodium hydrosulfide on high-glucose–induced apoptosis of primary human umbilical vein endothelium cells. Exposure to high glucose (25 mmole/L) for 48 hours resulted in the induction of apoptosis by 41.6% ± 1.01%, which was attenuated by pretreatment with sodium hydrosulfide (50 &mgr;mole/L) for 30 minutes. Further investigation of the apoptotic mechanisms in the cells demonstrated that high glucose upregulated the ratio of Bax/Bcl-2 and activated caspase-3 and also increased the levels of reactive oxygen species and malondialdehyde while reducing superoxide dismutase activity. All the above responses could be prevented by pretreatment with 50 &mgr;mole/L of sodium hydrosulfide. These results indicated that the protective effects of H2S on endothelial cells in the condition of high glucose might involve an antioxidative stress mechanism.

Hydrogen sulfide suppresses high glucose-induced expression of intercellular adhesion molecule-1 in endothelial cells.

Abstract: Hydrogen sulfide (H2S) is a newly identified endogenous gasotransmitter that has been implicated in the pathophysiology of several biologic systems. However, the role of H2S in the pathogenesis of diabetic vascular injury remains unclear. The aims of this study were to determine the effect of H2S on the high glucose (HG)–induced expression of intercellular adhesion molecule-1 (ICAM-1) in human umbilical vein endothelial cells and to explore the possible underlying mechanisms. Human umbilical vein endothelial cells were exposed either to a normal concentration of D-glucose (5.5 mmol/L) or to HG (16.7 mmol/L) in the absence or presence of NaHS for the indicated periods. The ICAM-1 protein and messenger RNA (mRNA) levels were analyzed by Western blotting and real-time reverse transcriptase–polymerase chain reaction, respectively. Exposure to HG for 48 or 72 hours significantly increased ICAM-1 expression at both the protein and mRNA levels, and these increases correlated with increases in both the production of intracellular reactive oxygen species and the activation of nuclear factor-&kgr;B. Pretreatment with NaHS inhibited HG-induced ICAM-1 expression at both the protein and mRNA levels and resulted in a reduction in the intracellular reactive oxygen species level and the suppression of nuclear factor-&kgr;B activity. NaHS also inhibited tumor necrosis factor-&agr;–induced ICAM-1 protein expression, which was similar to the effect of antioxidant N-acetyl-L-cysteine. These findings indicate that H2S might protect against HG-induced vascular damage by down-regulating ICAM-1 expression in endothelial cells.

Involvement of CSE/ H2S in high glucose induced aberrant secretion of adipokines in 3T3-L1 adipocytes

BackgroundDeregulated secretion of adipokines contributes to subclinical systemic inflammation associated with type 2 diabetes mellitus (T2DM). However, the mechanisms underlying are not fully understood. Hydrogen sulfide (H2S), as an endogenous gasotransmitter, possesses an anti-inflammation activity. The aim of this study was to examine the possible involvement of H2S in high glucose induced adipokine secretion in 3T3-L1 adipocytes.MethodsThe expression of cystathionine-gamma-lyase (CSE), the H2S-forming enzyme, was evaluated by Western-blotting and real-time PCR. The secretion of TNF-α, MCP-1 and adiponectin was determined by radioimmunoassay and enzyme-linked immunosorbent assay (ELISA), respectively. Lentiviral empty vector and vector expressing mouse CSE were used for in vitro transduction.ResultsHigh glucose (HG) significantly decreased CSE expression at both protein and mRNA levels in mature 3T3-L1 adipocytes. In parallel, HG significantly increased secretion of MCP-1 while decreasing secretion of adiponectin, but had no effect on secretion of TNF-α. HG induced changes in MCP-1 and adiponectin secretion were partly attenuated by forced expression of CSE or sodium hydrosulfide (NaHS), a source of exogenous H2S.ConclusionHigh glucose induces aberrant secretion of adipokines in mature 3T3-L1 adipocytes, favoring inflammation. The mechanism is partly related to inhibition of CSE/ H2S system.

Thyroid-stimulating hormone maintains bone mass and strength by suppressing osteoclast differentiation

It has been suggested that pituitary hormone might be associated with bone metabolism. To investigate the role of thyroid-stimulating hormone (TSH) in bone metabolism, we designed the present study as follows. After weaning, TSH receptor (TSHR) null mice (Tshr(-/-)) were randomly divided into a thyroxine treatment group (n=10) or non-treatment group (n=10); the treatment group received a dose of desiccated thyroid extract at 100 ppm daily for 5 weeks. Age-matched wild-type (Tshr(+/+), n=10) and heterozygote mice (Tshr(+/-), n=10) served as controls. After 5 weeks, the animals were sacrificed, and the femurs were collected for histomorphometrical and biomechanical analyses. In addition, the effect of TSH on osteoclastogenesis was examined in the RAW264.7 osteoclast cell line. We found that compared with Tshr(+/+) mice, Tshr(-/-) and Tshr(+/-) mice had lower bone strength. The histomorphometric results showed that trabecular bone volume, osteoid surface, osteoid thickness and osteoblast surface were significantly decreased, whereas the osteoclast surface was significantly increased in both Tshr(-/-) and Tshr(+/-) mice compared with Tshr(+/+) mice. Bone resorption and formation in Tshr(-/-) mice were further enhanced by thyroxine replacement. bTSH inhibited osteoclast differentiation in vitro, as demonstrated by reduced development of TRAP-positive cells and down-regulation of differentiation markers, including tartrate-resistant acid phosphatase, matrix metallo-proteinase-9 and cathepsin K in RAW264.7 cells. Our results confirm that TSH increased bone volume and improved bone microarchitecture and strength at least partly by inhibiting osteoclastogenesis.

Regression to normoglycaemia by fenofibrate in pre-diabetic subjects complicated with hypertriglyceridaemia: a prospective randomized controlled trial

Diabet. Med. 27, 1312–1317 (2010)

The Orphan Nuclear Receptor NR4A1 Protects Pancreatic β-Cells from Endoplasmic Reticulum (ER) Stress-mediated Apoptosis

Background: It is not known whether NR4A1 plays a role in ER stress-induced β-cell apoptosis. Results: NR4A1 expression in β-cells or islets correlated positively with Survivin expression and negatively with CHOP expression and apoptosis rate upon treatment with ER stress inducers. Conclusion: NR4A1 protects β-cells from ER stress-induced apoptosis by up-regulating Survivin and down-regulating CHOP expression. Significance: Our findings provide clues to prevent diabetes. The role of NR4A1 in apoptosis is controversial. Pancreatic β-cells often face endoplasmic reticulum (ER) stress under adverse conditions such as high free fatty acid (FFA) concentrations and sustained hyperglycemia. Severe ER stress results in β-cell apoptosis. The aim of this study was to analyze the role of NR4A1 in ER stress-mediated β-cell apoptosis and to characterize the related mechanisms. We confirmed that upon treatment with the ER stress inducers thapsigargin (TG) or palmitic acid (PA), the mRNA and protein levels of NR4A1 rapidly increased in both MIN6 cells and mouse islets. NR4A1 overexpression in MIN6 cells conferred resistance to cell loss induced by TG or PA, as assessed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, and TUNEL assays indicated that NR4A1 overexpression also protected against ER stress-induced apoptosis. This conclusion was further confirmed by experiments exploiting siRNA to knockdown NR4A1 expression in MIN6 cells or exploiting NR4A1 knock-out mice. NR4A1 overexpression in MIN6 cells reduced C/EBP homologous protein (CHOP) expression and Caspase3 activation induced by TG or PA. NR4A1 overexpression in MIN6 cells or mouse islets resulted in Survivin up-regulation. A critical regulatory element was identified in Survivin promoter (−1872 bp to −1866 bp) with a putative NR4A1 binding site; ChIP assays demonstrated that NR4A1 physically associates with the Survivin promoter. In conclusion, NR4A1 protects pancreatic β-cells against ER stress-mediated apoptosis by up-regulating Survivin expression and down-regulating CHOP expression, which we termed as “positive and negative regulation.”

Effects of insulin and IGF-I on growth hormone- induced STAT5 activation in 3T3-F442A adipocytes

BackgroundGrowth hormone (GH) and insulin signaling pathways are known important regulators of adipose homeostasis. The cross-talk between GH and insulin signaling pathways in mature adipocytes is poorly understood.MethodsIn the present study, the impact of insulin on GH-mediated signaling in differentiated 3T3-F442A adipocytes and primary mice adipocytes was examined.ResultsInsulin alone did not induce STAT5 tyrosine phosphorylation, but enhanced GH-induced STAT5 activation. This effect was more pronounced when insulin was added 20 min prior to GH treatment. The above results were further confirmed by in vivo study, showing that insulin pretreatment potentiated GH- induced STAT5 tyrosine phosphorylation in visceral adipose tissues of C57/BL6 mice. In addition, our in vitro results showed that IGF-I had similar potentiating effect as insulin on GH-induced STAT5 activation. In vitro, insulin and IGF-I had an additive effect on GH- induced MAPK activation.ConclusionThese results indicate that both insulin and IGF-I specifically potentiated GH mediated STAT5 activation in mature adipose cells. These findings suggest that insulin and GH, usually with antagonistic functions, might act synergistically to regulate some specific functions in mature adipocytes.

TSH/TSHR Signaling Suppresses Fatty Acid Synthase (FASN) Expression in Adipocytes

TSH/TSHR signaling plays a role in the regulation of lipid metabolism in adipocytes. However, the precise mechanisms are not known. In the present study, we determined the effect of TSH on fatty acid synthase (FASN) expression, and explored the underlying mechanisms. In vitro, TSH reduced FASN expression in both mRNA and protein levels in mature adipocytes and was accompanied by protein kinase A (PKA) activation, cAMP‐response element binding protein (CREB) phosphorylation, as well as extracellular signal‐regulated kinase 1/2 (ERK1/2) and c‐Jun NH2‐terminal kinase (JNK) activation. TSH‐induced downregulation of FASN was partially abolished by inhibition of PKA and ERK, but not JNK. TSHR and FASN expression in visceral tissue was significantly increased in C57BL/6 mice with diet‐induced obesity compared with control animals, whereas thyroid TSHR expression was normal. These findings suggest that activation of TSHR directly inhibits FASN expression in mature adipocytes, possibly mediated by PKA and ERK. In obese animals, this function of TSHR seems to be counteracted. The precise mechanisms need further investigation. J. Cell. Physiol. 230: 2233–2239, 2015.

Signal transducer and activator of transcription 5B (STAT5B) modulates adipocyte differentiation via MOF

The role and mechanism of signal transducer and activator of transcription 5B (STAT5B) in adipogenesis remain unclear. In this study, our data showed that Males absent on the first (MOF) protein expression was increased during 3 T3-L1 preadipocytes differentiation accompanied with STAT5B expression increasing. Over-expression STAT5B enhanced MOF promoter trans-activation in HeLa cells. Mutagenesis assay and ChIP analysis exhibited that STAT5B was able to bind MOF promoter. Knocking-down STAT5B in 3 T3-L1 preadipocytes led to decreased expression of MOF, but resulted in increased expression of peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer-binding protein α (C/EBPα) and fatty acid-binding protein 4 (Fabp4), which were important factors or enzymes for adipogenesis. We also found that knocking-down MOF in 3 T3-L1 preadipocytes resulted in increased expression of PPARγ, C/EBPα and Fabp4, which was in the same trend as STAT5B knocking-down. Over-expression MOF resulted in reduced promoter trans-activation activity of C/EBPα. These results suggest that STAT5B and MOF work as negative regulators in adipogenesis, and STAT5B modulates preadipocytes differentiation partially by regulating MOF expression.