Qingbo Guan

Significance of serum microRNAs in pre-diabetes and newly diagnosed type 2 diabetes: a clinical study

To explore the clinical significance of seven diabetes-related serum microRNAs (miR-9, miR-29a, miR-30d, miR34a, miR-124a, miR146a and miR375) during the pathogenesis of type 2 diabetes (T2D), 56 subjects were recruited to this study: 18 cases of newly diagnosed T2D (n-T2D) patients, 19 cases of pre-diabetes individuals (impaired glucose tolerance [IGT] and/or impaired fasting glucose [IFG]) and 19 cases of T2D-susceptible individuals with normal glucose tolerance (s-NGT). Serum miRNAs were determined by real-time RT-PCR. Expression levels of single miRNAs and the expression signatures of miRNAs as a panel were analysed among the three groups. In n-T2D, all 7 miRNAs were significantly up-regulated compared with s-NGT and five were significantly up-regulated compared with pre-diabetes, while miRNA expression was not significantly different between s-NGT and pre-diabetes. By Canonical discriminant analysis, 70.6% of n-T2D subjects (12/17) were recognized by canonical discriminant function, while s-NGT and pre-diabetes subjects could not be discriminated from each other. Similar results were found in Hierarchical Clustering analysis based on the expression levels of all seven miRNAs. In different statistical analysis, miR-34a always showed the most significant differences. We conclude that the expression levels of seven diabetes-related miRNAs in serum were significantly elevated in n-T2D compared with pre-diabetes and/or s-NGT, and the latter two groups featured similar expression patterns of these miRNAs, suggesting that during the pathogenesis of T2D, the peripheral diabetes-related miRNAs have not changed significantly from s-NGT at pre-diabetic stage.

A novel role for thyroid-stimulating hormone: Up-regulation of hepatic 3-hydroxy-3-methyl-glutaryl-coenzyme a reductase expression through the cyclic adenosine monophosphate/protein kinase A/cyclic adenosine monophosphate–responsive element binding protein pathway†

Elevated thyroid‐stimulating hormone (TSH) and hypercholesterolemia commonly coexist, as typically seen in hypothyroidism, but there is no known mechanism directly linking the two. Here, we demonstrated that in liver cells, TSH promoted the expression of 3‐hydroxy‐3‐methyl‐glutaryl coenzyme A reductase (HMGCR), a rate‐limiting enzyme in cholesterol synthesis, by acting on the TSH receptor in hepatocyte membranes and stimulating the cyclic adenosine monophosphate / protein kinase A / cyclic adenosine monophosphate–responsive element binding protein (cAMP/PKA/CREB) signaling system. In thyroidectomized rats, the production of endogenous thyroid hormone was eliminated and endogenous TSH was suppressed through pituitary suppression with constant administration of exogenous thyroid hormone, and hepatic HMGCR expression was increased by administration of exogenous TSH. These results suggested that TSH could up‐regulate hepatic HMGCR expression, which indicated a potential mechanism for hypercholesterolemia involving direct action of TSH on the liver. (HEPATOLOGY 2010)

Thyroid-Stimulating Hormone Levels within the Reference Range Are Associated with Serum Lipid Profiles Independent of Thyroid Hormones

CONTEXT AND OBJECTIVE Dyslipidemia in thyroid dysfunction has always been attributed to changes in thyroid hormone (TH) levels. We hypothesized that TSH plays an important role in lipid metabolism independent of TH. DESIGN AND SETTING We conducted a cross-sectional study to investigate the relationship between serum TSH levels and lipid profiles after controlling for free T(3), free T(4), total T(3), total T(4) and nonthyroid factors relevant to lipid metabolism in euthyroid Chinese subjects. MAIN OUTCOME MEASURES General linear analysis was performed to determine whether the impact of TSH on serum lipid levels is independent of the TH levels. Moreover, path analysis, an evolutionary multivariable regression technique, was conducted to test whether there is a direct and/or indirect effect between serum TSH and total cholesterol (TC) levels. Additionally, the odds ratios (95% confidence interval) for hypercholesterolemia in relation to TSH categories were calculated. RESULTS A total of 3664 euthyroid subjects were finally analyzed. There was a significant linear trend toward higher log TC (P = 0.021) and log triglyceride (P = 0.001) levels with increasing serum TSH levels within the reference range, which remained significant after adjusting for factors such as TH levels, age, and smoking. Most importantly, the total effect of TSH on TC levels (total effect(TC, TSH) = 0.05253) includes a direct effect (direct effect(TC, TSH) = 0.05979) and an indirect effect via TH. Compared with subjects in the lower part of the reference range (TSH level, 0.27-0.61 mIU/liter), the adjusted odds ratio for hypercholesterolemia was 3.239 (95% confidence interval, 1.392-7.538; P = 0.007) for those in the upper category (TSH level, 4.61-5.5 mIU/liter). CONCLUSIONS The variation in normal TSH levels is partially related to the lipid components and hypercholesterolemia in euthyroid subjects and includes both TH-dependent and TH-independent effects. Our study suggests the importance of controlling TSH in hypothyroid subjects.

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.

Thyrotropin increases hepatic triglyceride content through upregulation of SREBP-1c activity

BACKGROUND & AIMS Hallmarks of non-alcoholic fatty liver disease (NAFLD) are increased triglyceride accumulation within hepatocytes. The prevalence of NAFLD increases steadily with increasing thyrotropin (TSH) levels. However, the underlying mechanisms are largely unknown. Here, we focused on exploring the effect and mechanism of TSH on the hepatic triglyceride content. METHODS As the function of TSH is mediated through the TSH receptor (TSHR), Tshr(-/-) mice (supplemented with thyroxine) were used. Liver steatosis and triglyceride content were analysed in Tshr(-/-) and Tshr(+/+) mice fed a high-fat or normal chow diet, as well as in Srebp-1c(-/-) and Tshr(-/-)Srebp-1c(-/-) mice. The expression levels of proteins and genes involved in liver triglyceride metabolism was measured. RESULTS Compared with control littermates, the high-fat diet induced a relatively low degree of liver steatosis in Tshr(-/-) mice. Even under chow diet, hepatic triglyceride content was decreased in Tshr(-/-) mice. TSH caused concentration- and time-dependent effects on intracellular triglyceride contents in hepatocytes in vitro. The activity of SREBP-1c, a key regulator involved in triglyceride metabolism and in the pathogenesis of NAFLD, was significantly lower in Tshr(-/-) mice. In Tshr(-/-)Srebp-1c(-/-) mice, the liver triglyceride content showed no significant difference compared with Tshr(+/+)Srebp-1c(-/-) mice. When mice were injected with forskolin (cAMP activator), H89 (inhibitor of PKA) or AICAR (AMPK activator), or HeG2 cells received MK886 (PPARα inhibitor), triglyceride contents presented in a manner dependent on SREBP-1c activity. The mechanism, underlying TSH-induced liver triglyceride accumulation, involved that TSH, through its receptor TSHR, triggered hepatic SREBP-1c activity via the cAMP/PKA/PPARα pathway associated with decreased AMPK, which further increased the expression of genes associated with lipogenesis. CONCLUSIONS TSH increased the hepatic triglyceride content, indicating an essential role for TSH in the pathogenesis of NAFLD.

Thyrotropin and Obesity: Increased Adipose Triglyceride Content Through Glycerol-3-Phosphate Acyltransferase 3

Epidemiological evidence indicates that thyrotropin (TSH) is positively correlated with the severity of obesity. However, the mechanism remains unclear. Here, we show that TSH promoted triglyceride (TG) synthesis in differentiated adipocytes in a thyroid hormone-independent manner. Mice with subclinical hypothyroidism, which is characterized by elevated serum TSH but not thyroid hormone levels, demonstrated a 35% increase in the total white adipose mass compared with their wild-type littermates. Interestingly, Tshr KO mice, which had normal thyroid hormone levels after thyroid hormone supplementation, resisted high-fat diet-induced obesity. TSH could directly induce the activity of glycerol-3-phosphate-acyltransferase 3 (GPAT3), the rate-limiting enzyme in TG synthesis, in differentiated 3T3-L1 adipocytes. However, following either the knockdown of Tshr and PPARγ or the constitutive activation of AMPK, the changes to TSH-triggered GPAT3 activity and adipogenesis disappeared. The over-expression of PPARγ or the expression of an AMPK dominant negative mutant reversed the TSH-induced changes. Thus, TSH acted as a previously unrecognized master regulator of adipogenesis, indicating that modification of the AMPK/PPARγ/GPAT3 axis via the TSH receptor might serve as a potential therapeutic target for obesity.

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.

Insulin-like growth factor-1 promotes cell cycle progression via upregulation of cyclin D1 expression through the phosphatidylinositol 3-kinase/nuclear factor-κB signaling pathway in FRTL thyroid cells

AbstractAim:Insulin-like growth factor-1 (IGF-1) is an important hypertrophic and cell cycle progression factor for a number of cell types. It has been proven that IGF-1 is involved in the regulation of thyroid proliferation and cell cycle progression; however, the exact mechanism of this regulation has not been fully elucidated. In the present study, we investigated the effect of IGF-1 on the expression of cyclin D1, an important cell cycle regulatory protein, and a signaling pathway involved in IGF-1s effect on cyclinD1 expression in FRTL thyroid cells.Methods:FRTL thyroid cells were treated with IGF-1 or vector control for 24 h. As appropriate to individual experiments, a phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002, and/or a nuclear factor-κB (NF-κB) inhibitor, BAY11-7082, were added 1 h prior to IGF-1 treatment. Western blotting was used to detect cyclin D1 protein expression. Immunofluorescence was performed to analyze the expression of IκBα, an NF-κB inhibitory protein. Cell cycle analysis was performed by fluorescence activated cell sorting (FACS).Results:IGF-1 increased the cyclin D1 expression in thyroid cells. This increase was blocked by pretreatment with LY294002 or BAY11-7082. Further studies showed that IGF-1 specifically induced NF-κB activity. Treatment with IGF-1 could accelerate cell cycle progression from G0/G1 to S phase, whereas this progression was inhibited by the presence of LY294002 or BAY11-7082.Conclusion:In summary, the results of the present study show that in FRTL cells, IGF-1 promotes cell cycle progression via an upregulation of cyclin D1 expression, at least partially through the PI3K/NF-κB signaling pathway.

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.