Fengying Li

Serum visfatin concentrations in obese adolescents and its correlation with age and high-density lipoprotein cholesterol

Visfatin was recently identified as an adipocytokine and has insulin mimetic properties, but its role in adolescents remains largely unknown. In this study, we examined the impact of adolescent obesity on circulating visfatin levels and the relationship between visfatin and anthropometric indices, insulin sensitivity, and blood lipids in Chinese adolescents (11-18 years). Serum visfatin, adiponectin, leptin, and blood lipids were measured in 76 non-obese and 72 obese adolescents. The medians of serum visfatin levels were significantly higher in obese subjects of 34.68ng/ml than in non-obese subjects of 28.67ng/ml (P=0.002). There were no significant correlations in the non-obese group between the serum visfatin concentration and the anthropometric indices or the lipid parameters. However, visfatin levels were negatively correlated with age, early insulin secretion index (EISI), Tanner stage, and positively correlated with HDL-c in the obese adolescents. These relationships, except that for EISI and Tanner stage, remained significant (P<0.05) after adjusting for age, gender, and body mass index. Moreover, unlike adiponectin and leptin, visfatin concentration did not correlate with testosterone in non-obese and obese boys. In conclusion, visfatin levels may decrease with age and be related to the HDL metabolism in obese adolescents.

Berberine Acutely Inhibits Insulin Secretion from β-Cells through 3′,5′-Cyclic Adenosine 5′-Monophosphate Signaling Pathway

Berberine, a hypoglycemic agent, has recently been shown to activate AMP-activated protein kinase (AMPK) contributing to its beneficial metabolic effects in peripheral tissues. However, whether berberine exerts a regulatory effect on beta-cells via AMPK or other signaling pathways and counteracts glucolipotoxicity remains uncertain. In the present study, the impact of berberine on beta-cell function was investigated in vivo and in vitro. In high-fat-fed rats, berberine treatment for 6 wk significantly decreased plasma glucose and insulin levels before and after an oral glucose challenge along with the reduction of body weight and improvement of blood lipid profile. In accordance with the in vivo results, berberine acutely decreased glucose-stimulated insulin secretion (GSIS) and palmitate-potentiated insulin secretion in MIN6 cells and rat islets. However, pretreated with berberine for 24 h augmented the response of MIN6 cells and rat islets to glucose and attenuated the glucolipotoxicity. Berberine acutely increased AMPK activity in MIN6 cells. However, compound C, an AMPK inhibitor, completely reversed troglitazone-suppressed GSIS, not berberine-suppressed GSIS. Otherwise, berberine decreased cAMP-raising agent-potentiated insulin secretion in MIN6 cells and rat islets. These results suggest that the activation of AMPK is required for troglitazone-suppressed GSIS, whereas cAMP signaling pathway contributes, at least in part, to the regulatory effect of berberine on insulin secretion.

Glucose-mediated repression of menin promotes pancreatic β-cell proliferation.

Menin, encoded by the Men1 gene, is responsible for β-cell tumor formation in patients with multiple endocrine neoplasia type 1. Recently, menin has been proven to negatively regulate β-cell proliferation during pregnancy. However, it is unclear whether menin is involved in pancreatic β-cell proliferation in response to other physiological replication stimuli, such as glucose. In this study, we found that the menin level was significantly reduced in high glucose-treated INS1 cells and primary rat islets, both with increased proliferation. A similar observation was found in islets isolated from rats subjected to 72-h continuous glucose infusion. The glucose-induced proliferation was inhibited by menin overexpression. Further molecular studies showed that glucose-induced menin suppression was blocked by PI3K/Akt pathway inhibitors. A major PI3K/Akt substrate, Foxo1, was shown to enhance menin transcription levels by binding the promoter region of the Men1 gene. Therefore, we conclude that glucose inhibits menin expression via the PI3K/Akt/Foxo1 pathway and hence promotes pancreatic β-cell proliferation. Our study suggests that menin might serve as an important intracellular target of glucose to mediate the mitogenic effect that glucose exerts in pancreatic β-cells.

Berberine attenuates cAMP-induced lipolysis via reducing the inhibition of phosphodiesterase in 3T3-L1 adipocytes ☆

Berberine, a hypoglycemic agent, has been shown to decrease plasma free fatty acids (FFAs) level in insulin-resistant rats. In the present study, we explored the mechanism responsible for the antilipolytic effect of berberine in 3T3-L1 adipocytes. It was shown that berberine attenuated lipolysis induced by catecholamines, cAMP-raising agents, and a hydrolyzable cAMP analog, but not by tumor necrosis factor α and a nonhydrolyzable cAMP analog. Unlike insulin, the inhibitory effect of berberine on lipolysis in response to isoproterenol was not abrogated by wortmannin, an inhibitor of phosphatidylinositol 3-kinase, but additive to that of PD98059, an extracellular signal-regulated kinase kinase inhibitor. Prior exposure of adipocytes to berberine decreased the intracellular cAMP production induced by isoproterenol, forskolin, and 3-isobutyl-1-methylxanthine (IBMX), along with hormone-sensitive lipase (HSL) Ser-563 and Ser-660 dephosphorylation, but had no effect on perilipin phosphorylation. Berberine stimulated HSL Ser-565 as well as adenosine monophosphate-activated protein kinase (AMPK) phosphorylation. However, compound C, an AMPK inhibitor, did not reverse the regulatory effect of berberine on HSL Ser-563, Ser-660, and Ser-565 phosphorylation, nor the antilipolytic effect of berberine. Knockdown of AMPK using RNA interference also failed to restore berberine-suppressed lipolysis. cAMP-raising agents increased AMPK activity, which was not additive to that of berberine. Stimulation of adipocytes with berberine increased phosphodiesterase (PDE) 3B and PDE4 activity measured by hydrolysis of (3)[H]cAMP. These results suggest that berberine exerts an antilipolytic effect mainly by reducing the inhibition of PDE, leading to a decrease in cAMP and HSL phosphorylation independent of AMPK pathway.

Activation of SIRT1 protects pancreatic β-cells against palmitate-induced dysfunction☆

Sirtuin 1 (SIRT1), a nicotinamide adenosine dinucleotide-dependent histone deacetylase, is an important regulator of energy homeostasis in response to nutrient availability. In pancreatic β-cells, SIRT1 has been shown to up-regulate insulin secretion in response to glucose stimulation. However, the potential roles of SIRT1 in islet β-cells against lipotoxicity remain poorly understood. Here, we demonstrated that SIRT1 mRNA and protein expressions were markedly reduced in the islets isolated from rats infused with 20% Intralipid for 24h. Long-term exposure to 0.4mmol/L palmitate also decreased SIRT1 expression in cultured INS-1 cells and isolated rat islets, which was prevented by 10μmol/L resveratrol, a SIRT1 agonist. In addition, resveratrol improved glucose-stimulated insulin secretion decreased by palmitate, which was abrogated by EX527, a specific SIRT1 inhibitor. Furthermore, inhibition of SIRT1 activity by EX527 or a knockdown of SIRT1 suppressed insulin promoter activity, along with decreased insulin, v-maf musculoaponeurotic fibrosarcoma oncogene homolog A (MafA), and NK6 homeodomain 1 (NKX6.1) mRNA expressions. Activation of SIRT1 by resveratrol or overexpression of SIRT1 antagonized palmitate-inhibited insulin transcriptional activity. SIRT1 overexpression exerted an additive effect on pancreatic and duodenal homeobox 1 (PDX1)-stimulated insulin promoter activity and abolished forkhead box O1 protein (FOXO1)-decreased insulin transcriptional activity. Resveratrol reversed FOXO1 nuclear translocation induced by palmitate. Our findings indicate that SIRT1 protects against palmitate-induced β-cell dysfunction.

Berberine Suppresses Adipocyte Differentiation via Decreasing CREB Transcriptional Activity.

Berberine, one of the major constituents of Chinese herb Rhizoma coptidis, has been demonstrated to lower blood glucose, blood lipid, and body weight in patients with type 2 diabetes mellitus. The anti-obesity effect of berberine has been attributed to its anti-adipogenic activity. However, the underlying molecular mechanism remains largely unknown. In the present study, we found that berberine significantly suppressed the expressions of CCAAT/enhancer-binding protein (C/EBP)α, peroxisome proliferators-activated receptor γ2 (PPARγ2), and other adipogenic genes in the process of adipogenesis. Berberine decreased cAMP-response element-binding protein (CREB) phosphorylation and C/EBPβ expression at the early stage of 3T3-L1 preadipocyte differentiation. In addition, CREB phosphorylation and C/EBPβ expression induced by 3-isobutyl-1-methylxanthine (IBMX) and forskolin were also attenuated by berberine. The binding activities of cAMP responsive element (CRE) stimulated by IBMX and forskolin were inhibited by berberine. The binding of phosphorylated CREB to the promoter of C/EBPβ was abrogated by berberine after the induction of preadipocyte differentiation. These results suggest that berberine blocks adipogenesis mainly via suppressing CREB activity, which leads to a decrease in C/EBPβ-triggered transcriptional cascades.

The PI3K/AKT/mTOR Signaling Pathway Is Overactivated in Primary Aldosteronism

Background To date, the available non-invasive remedies for primary aldosteronism are not satisfactory in clinical practice. The phosphoinositide 3-kinase (PI3Ks)/protein kinase B (PKB or AKT)/mammalian target of rapamycin (mTOR) signaling pathway is essential for tumorigenesis and metastasis in many types of human tumors, including renal cancer, adrenal carcinoma and pheochromocytoma. The possibility that this pathway is also necessary for the pathogenesis of primary aldosteronism has not yet been explored. To answer this question, we investigated the activity of the PI3K/AKT/mTOR signaling pathway in normal adrenal glands (NAGs), primary aldosteronism (PA) patients and NCI-H295R cells. Methodology/Principal Findings Between January 2005 and December 2011, we retrospectively reviewed the records of 45 patients with PA. We compared clinical characteristics (age, gender and biochemical data) and the expression of phospho-AKT (p-AKT), phospho-mTOR (p-mTOR), phospho-S6 (p-S6) and vascular endothelial growth factor (VEGF) by immunohistochemical staining and western blotting, analyzing 30 aldosterone-producing adenomas (APAs), 15 idiopathic hyperaldosteronism (IHA) tissues and 12 NAGs following nephrectomy for renal tumors (control group). Compared with the control group, most of the PA patients presented with polydipsia, polyuria, resistant hypertension, profound hypokalemia, hyperaldosteronemia and decreased plasma renin activity. Compared with normal zona glomerulosa, the levels of p-AKT, p-mTOR, p-S6 and VEGF were significantly upregulated in APA and IHA. No significant differences were found between APA and IHA in the expression of these proteins. Additionally, positive correlations existed between the plasma aldosterone levels and the expression of p-AKT and p-mTOR. In vitro studies showed that mTOR inhibitor rapamycin could inhibit cell proliferation in NCI-H295R cells in a dose- and time-dependent manner. Furthermore, this inhibitor also decreased aldosterone secretion. Conclusions Our data suggest that the PI3K/AKT/mTOR signaling pathway, which was overactivated in APA and IHA compared with normal zona glomerulosa, may mediate aldosterone hypersecretion and participate in the development of PA.

Identification of suitable reference genes for quantitative RT-PCR during 3T3-L1 adipocyte differentiation

Quantitative reverse transcription PCR (qRT-PCR) is becoming increasingly important in the effort to gain insight into the molecular mechanisms underlying adipogenesis. However, the expression profile of a target gene may be misinterpreted due to the unstable expression of the reference genes under different experimental conditions. Therefore, in this study, we investigated the expression stability of 10 commonly used reference genes during 3T3-L1 adipocyte differentiation. The mRNA expression levels of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and transferrin receptor (TFRC) significantly increased during the course of 3T3-L1 adipocyte differentiation, which was decreased by berberine, an inhibitor of adipogenesis. Three popular algorithms, GeNorm, NormFinder and BestKeeper, identified 18 ribosomal RNA and hydroxymethylbilane synthase (HMBS) as the most stable reference genes, while GAPDH and TFRC were the least stable ones. Peptidylprolyl isomerase A [PIPA (cyclophilin A)], ribosomal protein, large, P0 (36-B4), beta-2-microglobulin (B2M), α1-tubulin, hypoxanthine-guanine phosphoribosyltransferase (HPRT) and β-actin showed relatively stable expression levels. The choice of reference genes with various expression stabilities exerted a profound influence on the expression profiles of 2 target genes, peroxisome proliferator-activated receptor (PPAR)γ2 and C/EBPα. In addition, western blot analysis revealed that the increased protein expression of GAPDH was markedly inhibited by berberine during adipocyte differentiation. This study highlights the importance of selecting suitable reference genes for qRT-PCR studies of gene expression during the process of adipogenesis.

Liraglutide protects pancreatic beta cells during an early intervention in Gato-Kakizaki rats.

Glucagon‐like peptide‐1 (GLP‐1) analogues have emerged as insulin secretagogues and are widely used in type 2 diabetic patients. GLP‐1 analogues also demonstrate a promotion of beta cell proliferation and reduction of apoptosis in rodents. In the present study, we investigated the protection of pancreatic beta cells by early use (at the age of 2 weeks) of GLP‐1 analogue, liraglutide in Gato‐Kakizaki (GK) rats and explored the underlying mechanisms.

Liraglutide protects pancreatic beta cells during an early intervention in Gato-Kakizaki rats (Gato-Kakizaki大鼠使用利拉鲁肽进行早期干预可以保护胰腺β细胞)

Glucagon‐like peptide‐1 (GLP‐1) analogues have emerged as insulin secretagogues and are widely used in type 2 diabetic patients. GLP‐1 analogues also demonstrate a promotion of beta cell proliferation and reduction of apoptosis in rodents. In the present study, we investigated the protection of pancreatic beta cells by early use (at the age of 2 weeks) of GLP‐1 analogue, liraglutide in Gato‐Kakizaki (GK) rats and explored the underlying mechanisms.