Effects of insulin on pigment epithelium-derived factor expression in adipocytes of type 2 diabetic mellitus in rats

Abstract

To explore the effects of insulin therapy on the expression of pigment epithelium-derived factor (PEDF) in adipocytes of type 2 diabetic mellitus (T2DM) in rats. A total of 22 newly diagnosed type 2 diabetics received a 2-week intensive insulin therapy. The levels of fasting plasma glucose (FPG), serum triglyceride and PEDF were measured before and after therapy. T2DM was induced by a high-fat diet and a low-dose streptozotocin (STZ). The Spraque-Dawley rats were divided randomly into diabetic, insulin treatment and gliclazide treatment groups. Another group with a chow diet was designated as normal controls. Differentiated 3T3-L1 adipocytes were then incubated with tumor necrosis factor-alpha (TNF-α) and (or) insulin for 24 h. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and Western blot were used to detect the expression of PEDF in adipose tissue or adipocytes. The PEDF levels in both sera and cell supernatant were measured by enzyme-linked immunosorbent assay (ELISA). Glucose uptake was detected after treatment of PEDF or anti-PEDF antibody simultaneously together with insulin in mature 3T3-L1 adipocytes. Insulin therapy decreased the serum levels of FPG and triglyceride of T2DM patients ((12.9 ± 2.8) vs (5.9 ± 1.4) mmol/L, (3.1 ± 1.8) vs (1.7 ± 0.8) mmol/L, P < 0.05) while the serum level of PEDF decreased significantly after therapy ((22.85 ± 5.73) vs (18.38 ± 5.28) µg/L, P < 0.05). Consistently the serum level of PEDF of diabetic rats was remarkably higher than that of normal controls and insulin-treated group ((28.6 ± 0.5) vs (25.4 ± 0.6) and (25.3 ± 0.6) µg/L, P < 0.05). And the elevated levels of PEDF, TNF-α mRNA and protein in adipose tissue (P < 0.05) could be reduced by insulin treatment (P < 0.05). However, no obvious change was detected in gliclazide treatment group. Further evidences suggested that TNF-α could induce more secretion and expression of PEDF in 3T3-L1 adipocyte while this effect became ameliorated by insulin treatment. Furthermore, decreased capacity of glucose uptake by PEDF might be reversed by anti-PEDF antibody in 3T3-L1 adipocytes (P < 0.05). Insulin can down-regulate the expression of PEDF in adipocytes of T2DM and improve the glucose uptake of adipocytes. It may be one of the mechanisms through which insulin therapy improves peripheral insulin resistance.