The Relationship Between The Level Of RBP4 In Obese Mice And Insulin Resistance And The Influence Of Exercise Intervention

OBJECTIVE: Insulin resistance has a causal role in type 2 diabetes. Recent years many proteins secreted by adipocytes (e.g leptin, adiponectin, resisitin) were reported that may contribute to insulin resistance. Retinol-binding protein 4(RBP4), a protein secreted by heptocytes and adipocytes, are associated with insulin resistance. Mice and human experiments suggest elevated serum RBP4 levels cause insulin resistance. We sought to determine whether serum RBP4 levels correlated with insulin resistance in diet-induced-obesity mice model and change after exercise intervention that improves insulin sensitivity. We also investigated whether elevated serum RBP4 levels are associated with insulin levels and the relationship between serum RBP4 levels and the expression levels in liver and epididymal fat tissues.METHODS : We set up a diet-induced-obesity mice model and took up exercise intervention after 25 weeks on diets. The very high fat group was randomly divided into two groups: exercise group and non-exercise group, the exercise group can running voluntarily in a running machine. We measured weight, body content, serum RBP4 levels, serum insulin levels and plasma glucose concentrations. RBP4 protein was measured in liver and epididymal fat tissues.RESULTS: Serum RBP4 levels correlated with fat/lean ratio and serum insulin levels in mice. Exercise intervention was associated with body weight, body content, fat/lean ratio, serum insulin levels and serum RBP4 levels. RBP4 expression levels in liver and epididymal fat tissues were not influenced by diets or exercise.CONCLUSION: RBP4 is an adipocyte-secreted molecule that elevated in the serum when fat accumulating and appears to correlate with insulin resistance in diet-induced-obesity mice model. Exercise intervention not only loses weight (especially fat content) but also down-regulates serum RBP4 levels and serum insulin levels. That indicated improved insulin sensitivity. RBP4 expression levels in liver and epididymal fat tissues were not influenced by diets and exercise, suggested other factors contribute to the change of serum RBP4 levels.