The Effect Of Insulin On Expression Of Adiponectin Gene In 3T3-L1 Adipocyte

BackgroundThe view of the adipocyte as simply a storage depot for fat is no longer tenable. Adipose tissue represent an important and very active endocrine organ that produces a number of hormones and other substances with the significant roles in the regulation of the insulin sensitivity and other physiological processes. Adiponectin is a novel and important member of the adipocytokines discovered in recent years. It is a collagen-like protein that is exclusively synthesized in white adipose tissue, is induced during adipocyte differentiation, and circulates at relatively high (microgram/milliliter) concentrations in the serum, appears to play a very important role in carbohydrate and lipid metabolism and vascular biology. Adiponectin has significant insulin-sensitizing as well as anti-inflammatory properties. Adiponectin production and concentrations actually decrease in obese and insulin resist subjects. In hypertension, diabetes mellitus and coronary artery disease patients, the expression of adiponectin is inhibited too. Adiposetissue are found to be the source of other hormones such as TNF- a , PAI-1, resistin and others that are increased in obesity and that, at least under experimental settings, are companying and possibly induce obesity-related insulin resistance. Adiponectin gene regulation includes a number of hormonal and environmental factors. Adiponectin gene expression is decreased by obesity, glucocorticoids, -adrenergic agonist and TNF- a and increased by leanness, cold exposure, adrenolectomy, and IGF-1. Adiponectin appears to be a major modulator of insulin action and its levels are reduced in type 2 diabetes, which could contribute to peripheral insulin resistance in this condition. Adiponectin knock-out mice had insulin resistance. Adenovirus-mediated adiponectin expression in adiponectin knockout mice completely reversed the phenotype. Administration of the globular domain of the adiponectin was accompanied by a weight loss and a decrease of plasma glucose, free fatty acids and triglycerides in mice consuming a high-fat/high sucrose diet. Thus replenishment of adiponectin might represent a novel treatment strategy for insulin resistance and type 2 diabetes.The mechanisms through which adiponectin exerts its actions are largely unknown and controversial. It is not yet established whether decreased adiponectin levels are the cause or effect of this dysregulated metabolic state. Insulin resistance is usually accompanied by hyperglycemia and hyperinsulinemia. What the effects of hyperglycemia or hyperinsulinemia on the adiponectin expression are during development of insulin resistance?We have studied the effect of glucose on expression of adiponectin gene in 3T3-L1 adipocyte and have found hyperglycemia inhibitedadiponectin gene expression in vitro. In the current study, we examined the effect of insulin on the adiponectin mRNA expression in 3T3-L1 adipocytes in vitro in order to elucidate the mechanism of adiponectin act in diabetes mellitus.Materials and methodsThe murine 3T3-L1 preadipocyte cell line (provided by Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences) were grown in DMEM containing 25mmol/L glucose as normal anchoring cells. Confluent preadipocytes were cultured for 2 days in culture medium further supplemented with 10ug/ml insulin, 0.5mmol/L isobutylmethylxanthine and 0.25umol/L dexamethasone and 2 days in culture medium with 10ug/ml insulin. After additional 4 to 6 days in culture medium , more than 90% of the cells had accumulated fat droplets.Insulin was diluted to desired concentrations with culture medium. The major working solution concentration of Insulin was from 1 nmol/L to 1000 nmol/L. The time of Insulin effecting on 3T3-L1 is 48 hours. Then adiponectin gene expression was measured by semi-quantitative RT-PCR, the adiponectin mRNA levels was controlled with those of -actin.ResultsTreatment of 3T3-L1 cells with different insulin concentrations for 48 hours suppressed adiponectin gene expression. At the lower i...