Over-expression of NYGGF4 inhibits glucose transport in 3T3-L1 adipocytes via attenuated phosphorylation of IRS-1 and Akt

Aim： NYGGF4 is a novel gene that is abundantly expressed in the adipose tissue of obese patients. The purpose of this study was to investigate the effects of NYGGF4 on basal and insulin-stimulated glucose uptake in mature 3T3-L1 adipocytes and to understand the underlying mechanisms.
Methods： 3T3-L1 preadipocytes transfected with either an empty expression vector （pcDNA3.1Myc/His B） or an NYGGF4 expression vector were differentiated into mature adipocytes. Glucose uptake was determined by measuring 2-deoxy-D- [^3H]glucose uptake into the adipocytes. Immunoblotting was performed to detect the translocation of insulin-sensitive glucose transporter 4 （GLUT4）. Immunoblotting also was used to measure the phosphorylation and total protein contents of insulin signaling proteins such as the insulin receptor （IR）, insulin receptor substrate （IRS）-I, Akt, ERK1/2, p38, and JNK.
Results： NYGGF4 over-expression in 3T3-L1 adipocytes reduced insulin-stimulated glucose uptake and impaired insulinstimulated GLUT4 translocation. It also diminished insulin-stimulated tyrosine phosphorylation of IRS-1 and serine phosphorylation of Akt without affecting the phosphorylation of 1R, ERK1/2, p38, and JNK.
Conclusion： NYGGF4 regulates the functions of IRS-1 and Akt, decreases GLUT4 translocation and reduces glucose uptake in response to insulin. These observations highlight the potential role of NYGGP 4 in glucose homeostasis and possibly in the pathogenesis of obesity.     

Anti-ageing and rejuvenating effects of quercetin

Homeostasis is a key feature of the cellular lifespan. Its maintenance influences the rate of ageing and it is determined by several factors, including efficient proteolysis. The proteasome is the major cellular proteolytic machinery responsible for the degradation of both normal and damaged proteins. Alterations of proteasome function have been recorded in various biological phenomena including ageing and replicative senescence. Proteasome activities and function are decreased upon replicative senescence, whereas proteasome activation confers enhanced survival against oxidative stress, lifespan extension and maintenance of the young morphology longer in human primary fibroblasts. Several natural compounds possess anti-ageing/anti-oxidant properties. In this study, we have identified quercetin (QUER) and its derivative, namely quercetin caprylate (QU-CAP) as a proteasome activator with anti-oxidant properties that consequently influence cellular lifespan, survival and viability of HFL-1 primary human fibroblasts. Moreover, when these compounds are supplemented to already senescent fibroblasts, a rejuvenating effect is observed. Finally, we show that these compounds promote physiological alterations when applied to cells (i.e. whitening effect). In summary, these data demonstrate the existence of naturally occurring anti-ageing products that can be effectively used through topical application.     

Anti-Obesity Effect of an Ethanol Extract of Cheongchunchal In Vitro and In Vivo

Cheongchunchal (CE) is a developed crop more highly enriched in cyanidin-3-O-glucoside chloride (anthocyanin) than conventional waxy corn. Anthocyanin has been proven to have anti-oxidant, anti-inflammatory, anti-obesity, and anti-cancer effects. In this study, using high-performance liquid chromatography (HPLC), Cheongchunchal was confirmed to contain 8.99 mg/g anthocyanin. The inhibitory effect of an ethanol extract of Cheongchunchal (CE) on adipocyte differentiation was demonstrated using Oil Red O staining and a triglyceride assay. By conducting Western blotting, we also confirmed the regulatory effect of CE on adipocyte differentiation factors by assessing changes in the levels of factors that play a significant role in the differentiation of 3T3-L1 preadipocytes. A C57BL/6N mouse model of obesity was induced with a high-fat diet, and CE (400, 600, and 800 mg/kg/day) or Garcinia (245 mg/kg/day) was orally administered to verify the anti-obesity effect of CE. As a result of CE administration, the food efficiency ratio (FER), weight gain, and weight of tissues decreased. Additionally, blood biochemical changes were observed. Furthermore, the inhibitory effect of CE on adipocytes was confirmed through morphological observation and the expression of adipocyte differentiation-related factors in the liver and fat tissues. Therefore, in this study, we verified the anti-obesity effects of anthocyanin-rich CE both in vitro and in vivo.     

GLP-1 amplifies insulin signaling by up-regulation of IRbeta, IRS-1 and Glut4 in 3T3-L1 adipocytes

Glucagon-like peptide-1 (7–36) amide (GLP-1) is an insulin secretagogue. Recently, many studies have shown GLP-1 can improve insulin resistance in peripheral tissues. In the present study, we investigated glucose uptake in 3T3-L1 adipocytes in either basal or insulin resistant state and dissected insulin signaling pathway in order to elucidate the molecular mechanisms of GLP-1 mediated improvement of insulin resistance. We found GLP-1 and its long lasting analogue, exendin 4 up-regulated basal IR, IRS-1 and Glut 4 expressions although they did not increase basal glucose uptake alone. However, GLP-1 and exendin-4 increased insulin mediated glucose uptake in intact and TNF-α treated 3T3-L1 adipocytes by up-regulation of phophorylated IRβ, IRS-1, Akt and GSK-3β. These results indicate that GLP-1 and its analogue exendin-4 can amplify insulin signaling in 3T3-L1 adipocytes by up-regulation of some crucial insulin signaling molecules. Hong Gao and Xinjun Wang equally contributed to this work.     

MAP kinases and mTOR mediate insulin-induced phosphorylation of Insulin Receptor Substrate-1 on serine residues 307, 612 and 632

Aim/hypothesis Insulin-induced IRS-1 serine phosphorylation could be physiologically important to regulate insulin action. In a hyperinsulinaemic state such as obesity or Type 2 diabetes, this phosphorylation could be modified and exacerbate insulin resistance. We aimed at identifying serine residues in IRS-1 phosphorylated in response to insulin stimulation and at determining the involved kinases.Methods 3T3-L1 adipocytes, muscle and adipose tissue of mice were subjected to Western Blot analysis with phosphospecific antibodies to identify phosphorylation sites in IRS-1 following insulin treatment. Pharmacological inhibitors were used to determine the serine kinases involved in this phosphorylation.Results In 3T3-L1 adipocytes, insulin promoted the phosphorylation of serine 307, 612 and 632 with Serine^612/632 more rapidly phosphorylated than Serine³⁰⁷. Insulin-induced phosphorylation of Serine³⁰⁷ was dependent on the activation of a PI 3-kinase/mTOR pathway. The phosphorylation of Serine^612/632 required the activation of the MAP kinase pathway following short-term insulin stimulation and activation of the PI 3-kinase/mTOR pathway following prolonged insulin stimulation. Phosphorylation of Serine³⁰⁷ and Serine⁶³² occurred in vivo in skeletal muscle and white adipose tissue of mice injected with insulin and was dependent on the activation of mTOR. Moreover, inhibition of mTOR led to a persistent PI 3-kinase activation by insulin.Conclusion/Interpretation Insulin-induced IRS-1 serine phosphorylation is a complex process involving different sites and kinases. This complexity could be physiologically important to accurately regulate insulin signalling. Abnormal phosphorylation of these serine residues in hyperinsulinaemic state could participate in the down-regulation of insulin signalling.Abbreviations PI 3-kinase phosphatidylinositol 3-kinase - mTOR mammalian target of rapamycin - APS adaptor with a PH and SH2 domains - Shc Src Homology Collagen - SH2 Src Homology 2 - PTB phosphotyrosine binding - MAP mitogen-activated protein - MEK mitogen-activated protein kinase kinase - PKB protein kinase B - PDGF platelet derived growth factor - JNK c-Jun NH2 terminal kinase - PMA phorbol myristate acetate - PIP3 phosphatidylinositol 3,4,5 triphosphates     

Alterations of insulin sensitivity by the implantation of 3T3-L1 cells in nude mice. A role for TNF-alpha?

Aims/hypothesis. Visceral adipocytes have different functions than those from the subcutaneous fat area. These differences could contribute to the pathological significance of excessive visceral fat accumulation for accompanying insulin resistance and hyperinsulinaemia. This study addresses this hypothesis and describes a unique method to clarify whether the functional differences between visceral and subcutaneous adipocytes depend on their anatomical location. Methods. 3T3-L1 cells or TNF-α overexpressing CHO cells were implanted into subcutaneous fat area or mesenteric area as visceral fat area in athymic mice of BALB/C strain. Then, serum insulin, glucose, TNF-α, and several markers of lipid metabolism were measured in the fasting condition. OGTT was also analysed. Results. During the course of glucose loading, the mice which had 3T3-L1 cells implanted into mesenteric area but not into subcutaneous fat area showed remarkably increased serum insulin and TMF-α concentrations, compared to the control mice. Moreover, serum insulin concentrations of the mice, implanted with TNF-α overexpressing cells into subcutaneous fat area, were apparently higher than that of control mice. Conclusion/interpretation. This method of implanting adipose cells into subcutaneous or visceral fat area showed high TNF-α concentration and insulin resistance by the adipose cells in visceral area of nude mice. Furthermore, we found that the functional significance of visceral fat accumulation for TNF-α-induced insulin resistance is partly caused by the interaction of adipocytes with surrounding conditions in mesenteric area. [Diabetologia (2002) 45: ▪–▪] Received: 15 February 2001 and in revised form: 21 December 2001     

高糖高脂肪酸环境下维生素D对分化后前脂肪细胞脂肪合成的影响

目的 探讨在高糖、高脂肪酸环境下维生素D的活性形式1,25（OH）2 D3（VD3）对分化后前脂肪细胞脂肪合成的影响.方法 将前脂肪细胞3T3-L1细胞分为对照组（C组）、高糖组（G组）和高糖高脂肪酸组（GF组）后进行诱导分化,观察加入VD3后最终成熟脂肪细胞中脂肪含量的改变,采用油红O染色和异丙醇萃取法半定量检测细胞内脂肪含量;用RT-PCR法检测各组细胞维生素D受体（VDR）、固醇调节元件结合蛋白-1c（SREBP-1c）和激素敏感脂肪酶（HSL） mRNA的表达水平.结果 与C组比较,G组和GF组脂肪细胞内脂肪含量明显增高（P＜0.05）,VD3可减少C组脂肪含量（P＜0.05）,但是对G组和GF组脂肪含量无影响（P＞0.05）.与C组比较,G组和GF组VDR mRNA表达降低（P＜0.05）,VD3可提高三组细胞VDR mRNA的表达（P＜0.05）.与C组比较,G组和GF组的SREBP-1c、HSL mRNA表达升高（P＜0.05）;VD3减少C组SREBP-1c mRNA水平,对G组和GF组的SREBP-1c、HSL以及C组的HSL mRNA无影响（P＞0.05）.结论 在高糖、高脂肪酸的环境下,VD3已失去对前脂肪细胞脂肪合成的抑制作用.