Impact of weight cycling on CTRP3 expression, adipose tissue inflammation and insulin sensitivity in C57BL/6J mice.

Impacts of weight cycling on C1q/tumor necrosis factor (TNF)-related protein-3 (CTRP3) expression, adipose tissue inflammation and insulin sensitivity in C57BL/6J mice were evaluated in the current study. A total of 30 male C57Bl/6J mice were divided randomly into three groups; normal control (n=10), high-fat diet (OB, n=10) and weight cycling (WC, n=10), which were fed with high-fat diet in the first and last 8 weeks and regular chow in between. Systemic glucose metabolic status and insulin sensitivity were detected by intraperitoneal glucose tolerance test and hyperinsulinemic-euglycemic clamp, respectively. Blood levels of interleukin (IL)-6 and TNF-α were determined using ELISA. Relative CTRP3, IL-6, TNF-α and glucose transporter (GLUT)4 mRNA expression in adipose tissue was detected using reverse transcription-quantitative polymerase chain reaction assays. Relative CTRP3, phosphatidylinositide 3-kinases (PI3K) and protein kinase B (PKB; Ser473) protein expression were detected by western blot analysis. Area under the curve of glucose and glucose infusion rate of the WC group were significantly increased compared with the OB group (P<0.01). CTRP3 mRNA and protein levels of the WC group were significantly decreased by 20.3 and 23.1%, respectively, compared with the OB group (P<0.01). IL-6 and TNF-α protein plasma levels and gene expression in adipose tissue of the WC group were significantly increased compared with the OB group (P<0.01). Expression and phosphorylation of insulin signaling molecules PI3K and PKB (Ser473), respectively and GLUT4 gene expression in adipose tissue of the WC group were significantly decreased compared with the OB group (P<0.01). In conclusion, weight cycling impaired glucose metabolism and insulin sensitivity by decreasing CTRP3, PI3K, phosphorylated-PKB (Ser473) and GLUT4 expression, and increasing IL-6 and TNF-α levels.

CTRP3 improves the insulin sensitivity of 3T3-L1 adipocytes by inhibiting inflammation and ameliorating insulin signalling transduction.

INTRODUCTION: C1q/TNF-related Protein-3 (CTRP3) is a novel adipokine with multiple effects such as lowering glucose levels, inhibiting glyconeogenesis in the liver, and increasing angiogenesis and anti-inflammation. But little is known about the effects of CTRP3 on insulin resistance in adipose tissue. This study aims to investigate the effects and mechanisms of CTRP3 on the insulin sensitivity of 3T3-L1 adipocytes. MATERIAL AND METHODS: Insulin resistant 3T3-L1 adipocytes were induced by palmic acid cultivation. Such adipocytes were treated with recombinant CTRP3 protein at different concentrations (0, 10, 50, 1,250 ng/mL) for 12 hours, and at a concentration of 250 ng/mL for differing times (2, 6, 12, and 24 h). Another group was pre-treated with wortmannin, the special inhibitor of phosphatidylinositol-4,5- bisphosphate 3-kinase (PI3K), for 20 minutes before the treatment with 250 ng/mL CTRP3. The glucose consumption, the glucose uptake, the expression and release of tumour necrosis factor α (TNF-α) and interleukin-6(IL-6) in supernatant, and the protein relative expression of PI3K and protein kinase B (PKB)(ser437) were detected. RESULTS: Compared to the control group, glucose consumption in the CTRP3 intervention group at concentrations of 10, 50, 250, and 1,250 ng/mL was increased by 22.1%, 42.9%, 76.6% and 80.5% respectively (all P < 0.01); the glucose uptake was increased by 39.0%, 68.0%, 108.0% and 111.0% respectively (all P < 0.01); the content of TNF-α in the culture media of CTRP3 (10, 50, 250 ng/mL) intervention group was decreased by 7.6% (P > 0.05), 13.0% (P < 0.05) and 17.4% (P < 0.01) respectively; the content of IL-6 was decreased by 7.1%, 12.4% and 17.1% respectively (all P < 0.01); the protein relative expression of PI3K was increased by 0.63-, 1.00- and 1.36-fold respectively (all P < 0.01), and PKB(ser437) increased by 0.65-, 1.61- and 1.93-fold respectively (all P < 0.01); the mRNA relative expression of GLUT-4 was increased by 23.0%, 47.0% and 62.0% respectively (all P < 0.01). After the treatment with wortmannin, glucose consumption, glucose uptake, PI3K and PKB(ser437) protein relative expression, as well as GLUT-4 mRNA relative expression, was decreased by 53.2%, 44.7%, 43.4%, 56.1 and 30.9% respectively (all P < 0.01). CONCLUSIONS: CTRP3 could improve insulin sensitivity of insulin resistant 3T3-L1 adipocytes by decreasing inflammation and ameliorating insulin signalling transduction, indicating that CTRP3 may be a new target for the prevention and cure of insulin resistance and type 2 diabetes.

Expression of CTRP3, a novel adipokine, in rats at different pathogenic stages of type 2 diabetes mellitus and the impacts of GLP-1 receptor agonist on it.

This study aimed to investigate the expression of C1q/TNF-related protein-3 (CTRP3) in rats at different pathogenic stages of type 2 diabetes mellitus (T2DM) and the impacts of glucagon-like peptide-1 (GLP-1) receptor agonist on it. Male wistar rats were fed with high-fat diet for 10 weeks to induce insulin resistance (IR) and then were given low-dose streptozotocin (STZ) intraperitoneal injection to induce T2DM. Exendin-4 (Ex-4), a GLP-1 receptor agonist, was subcutaneous injected to the IR rats and T2DM rats for 4 weeks. The expression of CTRP3 mRNA and protein in epididymis adipose tissue of rats at the stage of IR was lower significantly than that of normal control (NC) rats and decreased more when they were at the stage of overt T2DM (all P < 0.05 or P < 0.01). After the treatment with Ex-4, the mRNA and protein expressions of CTRP3 were increased by 15.5% (P < 0.01) and 14.8% (P < 0.05), respectively, in IR rats and increased by 20.6% (P < 0.01) and 16.5% (P < 0.05), respectively, in T2DM rats. Overall, this study found that the expression of CTRP3 in visceral adipose tissue was progressively decreased in a T2DM rat model from the pathogenic stage of IR to overt diabetes, while Ex-4 treatment increased its expression in such animals.