The Mechanisms About Mast Cells Regulating Insulin Resistance In Epididymal Adipose Tissues In Long- Standing Diet-induced Obese Mice

Obesity is defined as a chronic low-grade inflammatory disease. Obesity can lead to type 2 diabetes (T2D), cardiovascular disease, liver steatosis and a series of related metabolic diseases, which lower the quality of human lifespan and the quality of life severely. It has been reported that in long time high-fat diet-induced mice (LDIO), epididymal adipose tissue (EAT) expanded constantly during the first 16 weeks of high-fat diet, while reduced significantly after 16 weeks. Along with the EAT atrophying, the insulin resistance of mice reduced significantly. However, the molecular and cellular biology mechanisms of reducing insulin resistance remain unclear. To solve this problem, this thesis mainly studies the EAT inflammatory which is directly related to insulin resistance in the later period of LDIO mice.This study used 5-week-old male C57BL/6 mice given low-fat or high-fat diet treatment for 5,10,15,20 and 25 weeks respectively. And the results were as following:1) Between the 5 to 15 weeks, glucose tolerance and insulin sensitivity of high-fat group of mice became significantly worse. After 15 weeks, these mice showed improved glucose tolerance and insulin sensitive gradually.2) Because of the adipose tissue macrophages inflammatory polarization caused by obesity is a major reason for the deterioration of system glucose homeostasis, we used flow cytometry analysis and quantitative PCR to further study the EAT macrophages. Along with the change of insulin homeostasis, the proportion between pro-inflammatory M1 macrophages and anti-inflammatory M2 macrophages and the expression of inflammatory cytokines gradually changed in high-fat diet mice.3) Mast cells (MCs) as a kind of immune cells, aggregated in the adipose tissue of obese individuals and their roles in adipose tissue is still not clear yet. To explore the roles of MCs in improving insulin resistance and macrophages inflammatory polarization in EAT at the later period stage of high-fat diet mice, this thesis used flow cytometry to analyze the change of MCs’number. The results indicated that the number of MCs increased sharply during 15-25 weeks in high-fat diet mice. So we speculated MCs might be involved in the change of macrophages polarization in EAT.4) What’s more, BMMCs could inhibite GM-CSF-induced M1 polarization of bone marrow-derived macrophage in vitro.5) 5-HT, as a MCs important medium, could inhibit inflammatory macrophage polarization. LX1031, an inhibitor of 5-HT synthetase, lost the effect on BMDMs’ polarization. In addition, we found 5-HT in EAT mainly dervied from MCs by flow cytometry and quantitative PCR.In conclusion, MCs aggregated in EAT in the later period of high-fat diet LDIO mice. And 5-HT secreted by MCs could inhibit macrophage inflammatory polarization and reduce the inflammation of EAT, thus reduce the insulin resistance.