Role of small leucine zipper protein in hepatic gluconeogenesis and metabolic disorder.

Hepatic gluconeogenesis is the central pathway for glucose generation in the body. The imbalance between glucose synthesis and uptake leads to metabolic diseases such as obesity, diabetes, and cardiovascular diseases. Small leucine zipper protein (sLZIP) is an isoform of LZIP and it mainly functions as a transcription factor. Although sLZIP is known to regulate the transcription of genes involved in various cellular processes, the role of sLZIP in hepatic glucose metabolism is not known. In this study, we investigated the regulatory role of sLZIP in hepatic gluconeogenesis and its involvement in metabolic disorder. We found that sLZIP expression was elevated during glucose starvation, leading to the promotion of phosphoenolpyruvate carboxylase and glucose-6-phosphatase expression in hepatocytes. However, sLZIP knockdown suppressed the expression of the gluconeogenic enzymes under low glucose conditions. sLZIP also enhanced glucose production in the human liver cells and mouse primary hepatic cells. Fasting-induced cyclic adenosine monophosphate impeded sLZIP degradation. Results of glucose and pyruvate tolerance tests showed that sLZIP transgenic mice exhibited abnormal blood glucose metabolism. These findings suggest that sLZIP is a novel regulator of gluconeogenic enzyme expression and plays a role in blood glucose homeostasis during starvation.

Effect of Rosuvastatin on Cholesterol Efflux Capacity and Endothelial Function in Type 2 Diabetes Mellitus and Dyslipidemia.

BACKGROUND: Quality and quantity of high-density lipoprotein cholesterol (HDL-C) may be associated with cardiovascular risk. We investigated the effect of rosuvastatin on cholesterol efflux (CE) for HDL function and vascular health.Methods and Results:We enrolled 30 dyslipidemic patients with type 2 diabetes mellitus and 20 healthy subjects as controls. Vascular health was assessed on flow-medicated dilation (FMD), nitroglycerin-induced dilatation of the brachial artery and carotid artery intima-media thickness (cIMT). These parameters were compared between patients and controls, and between baseline and at 12 weeks of treatment with rosuvastatin 20 mg. Age and body mass index were 49.8±11.3 years and 25.8±3.7 kg/m2in the patients, and 28.8±3.2 years and 22.4±2.4 kg/m2in the controls, respectively. The biomarkers related to lipid and glucose metabolism and lipoprotein (a), high-sensitivity C-reactive protein, and cIMT were significantly higher, and CE and FMD were significantly lower in the patients than in the controls. In the patients, rosuvastatin 20 mg decreased low-density lipoprotein cholesterol by 54.1% and increased HDL-C by 4.8%. The CE increased significantly after rosuvastatin treatment (12.26±2.72% vs. 14.05±4.14%). FMD also increased, and lipoprotein (a) and cIMT decreased significantly and were associated with changes of CE. CONCLUSIONS: Rosuvastatin-induced changes in HDL function are significantly associated with cardiovascular benefit.

Association between thyroid function and lipid profiles, apolipoproteins, and high-density lipoprotein function.

BACKGROUND: Thyroid hormone regulates lipid metabolism. In particular, it has been reported to regulate plasma high-density lipoprotein cholesterol (HDL-C) levels and the activity of molecules involved in HDL metabolism. OBJECTIVE: We investigated changes in the concentrations of lipids and apolipoproteins and in the function of HDL according to acute dynamic changes in thyroid function. METHODS: Concentrations of plasma lipids and apolipoproteins, paraoxonase-1 activity, and cholesterol efflux were measured in 27 patients with differentiated thyroid carcinoma who underwent total thyroidectomy and radioactive iodine (RAI) treatment, at 3 distinct times: After surgery (baseline subclinical hyperthyroid state), on the day of undergoing RAI treatment (overt hypothyroid state), and 3 months post-RAI treatment (subclinical hyperthyroid state). RESULTS: The mean free T4 and thyroid-stimulating hormone concentrations were 0.24 ± 0.06 ng/dL and 91.2 (77.8-118.2) µIU/mL, respectively, on the day of RAI treatment. Total cholesterol, triglyceride, low-density lipoprotein cholesterol, and apoB levels, and the apoA-I/II ratio were significantly increased in the overt hypothyroid state and recovered to baseline values with levothyroxine replacement. HDL-C and apoE levels were persistently elevated despite levothyroxine replacement. Paraoxonase-1 activity, corrected for apoA-I, decreased in the overt hypothyroid state but recovered with levothyroxine replacement (P = .009). Cholesterol efflux also decreased significantly in the overt hypothyroid state (21.5 ± 5.1% vs 18.9 ± 2.9%, P = .005), but remained low despite recovery of thyroid function. CONCLUSION: Changes in thyroid function are associated not only with changes in the concentrations of various plasma lipid components but also with changes in HDL function.

Thyroid-stimulating hormone improves insulin sensitivity in skeletal muscle cells via cAMP/PKA/CREB pathway-dependent upregulation of insulin receptor substrate-1 expression.

Thyroid-stimulating hormone (TSH) receptor is expressed in extrathyroidal tissues such as hepatocytes, adipocytes, and skeletal muscle, which suggests a possible novel role of TSH in various metabolic processes in extrathyroidal tissues independent of thyroid hormones. We investigated whether TSH has any effects on glucose tolerance and insulin sensitivity in the skeletal muscle using diet-induced obesity (DIO) mouse models and rodent skeletal muscle cells. TSH improved glucose tolerance in DIO mice and this was associated with an improvement of skeletal muscle insulin sensitivity resulting from the increased expression of insulin receptor substrate (IRS)-1 protein and mRNA therein. TSH significantly increased both basal and insulin-stimulated glucose transport in rat L6 myotubes and increased the expression of IRS-1 protein and mRNA in these cells as well. TSH also stimulated Irs1 promoter activation; this stimulation was abolished by protein kinase A (PKA) inhibition using H89 or by mutation of the cAMP-response element site located at -1155 to -875 bp of the Irs1 promoter region, supporting a novel role of TSH activated-cAMP/PKA/CREB signaling in the regulation of Irs1 expression. In conclusion, TSH improves insulin sensitivity in skeletal muscle by increasing Irs1 gene expression. This regulatory effect is mediated by a PKA-CREB-dependent pathway.

Therapeutic potential of metformin in papillary thyroid cancer in vitro and in vivo.

Metformin, an anti-diabetic drug used in type 2 diabetes treatment, is reported to have oncopreventive or therapeutic roles in several human cancers. The present study investigated the therapeutic potential of physiologic dose of metformin in PTC. Metformin inhibited PTC cell viability and increased cell apoptosis in various doses (0.5-20mM) in BCPAP and BHP10-3SC cells. Western blot analysis demonstrated that the p-AMPK/AMPK ratio increased with increased metformin treatment. The ectopic tumor experiment was performed using BHP10-3SC cells and athymic nude mice. Oral metformin treatment via drinking water significantly delayed tumor growth in both tumor development model and established tumor models. Necrotic area in tumors significantly increased with metformin treatment. Western blot analysis revealed an increase in p-AMPK/AMPK ratio and suppressions of mTOR and Akt expressions in metformin-treated mice compared to the results in mock-treated control mice. Our results indicate that a physiologic dose of metformin has anti-tumorigenic effects that result from activation of AMPK signaling and inhibition of Akt signaling.

Expression of Thyroid Stimulating Hormone Receptor mRNA in Mouse C2C12 Skeletal Muscle Cells.

BACKGROUND: We analyzed whether thyroid stimulating hormone receptor (TSH-R) is expressed in a skeletal muscle cell line and if TSH has influence on the differentiation of muscle cells or on the determination of muscle fiber types. METHODS: TSH-R gene expression was detected with nested real-time polymerase chain reaction (RT-PCR) in C2C12, a mouse skeletal muscle cell line. The effect of TSH on myotube differentiation was assessed by microscopic examination of myotube formation and through the measurement of expression of muscle differentiation markers, i.e., myogenin and myoD, and muscle type-specific genes, i.e., MyHC1, MyHC2a, and MyHC2b, with quantitative RT-PCR before and after incubation of C2C12 myotube with TSH. RESULTS: TSH-R was expressed in the mouse skeletal muscle cell line. However, treatment with TSH had little effect on the differentiation of muscle cells, although the expression of the muscle differention marker myogenin was significantly increased after TSH treatment. Treatment of TSH did not affect the expression of muscle type-specific genes. CONCLUSION: TSH-R is expressed in a mouse skeletal muscle cell line, but the role of TSH receptor signaling in skeletal muscle needs further investigation.