Conclusion
These results suggest that suppression of diet-induced inflammation by IL-13 is an effective strategy in preventing diet-induced obesity and obesity-associated insulin resistance and fatty liver.
Methods
C57BL/6 mice were fed a high-fat diet and received hydrodynamic delivery of plasmids carrying the mouse Il-13 or Gfp (control) gene. IL-13 blood protein levels, food consumption and body weight of mice were continuously monitored for 8 weeks. Fat and lean masses of treated and control animals were determined at the end of the experiment. Serum concentrations of glucose, insulin and lipids were determined, and mRNA levels of macrophage marker genes in adipose tissue and genes involved in energy metabolism were examined using real-time PCR. Glucose tolerance and insulin sensitivity tests were performed to determine glucose homeostasis. Histochemistry and lipid assays were performed to determine the hepatic lipid accumulation.
Results
Blood concentration of IL-13 was 20 ng ml(-1) 1 week after gene delivery and declined with time. Overexpression of Il-13 prevented high-fat diet-induced weight gain without affecting food consumption. Mice that underwent Il-13 gene transfer showed regular body weight and normal serum concentrations of glucose and insulin, and less lipid accumulation in the liver. Overexpression of Il-13 blocked macrophage infiltration in adipose tissue and suppressed high-fat diet-induced expression of inflammatory F4/80, Cd68 and Mcp1, and elevated the expression of Ucp1 (uncoupling protein 1 gene) responsible for energy expenditure.