The Relationship Between Pparγ And Steroid Receptors In Obesity

Objective:Obesity, characterized by excess adipose tissue, is a common health problem with increasing prevalence around the world. Obesity, particularly central obesity, is an important risk factor for type 2 diabetes and cardiovascular disease. Peroxisome-proliferator–activated receptorγ(PPARγ) and steroid receptors are nuclear receptors, which regulate transcriptional responses to diverse signaling pathways in adipose tissues. The insulin-sensitizing thiazolidinediones, which are selective ligands of PPARγ, have a side effect of body weight gain. It is attributed to expansion of the subcutaneous fat depot, and in some patients to edema, whereas the mass of visceral fat remains unchanged or decreases. Glucocorticoids, the ligand of glucocorticoid receptor and mineralocorticoid receptor induce fat redistribution and accumulation. And fat is shed from limbs and accumulates in truncal and visceral areas. To explore the relationship between PPARγand steroid receptors, we investigated the mechanisms of thiazolidinediones'adverse effects by using the ob/ob mice model and 33T3-L1 preadipocytes, and compared the different effects in adipose tissue with or without pioglitazone.Methods:1. After having balanced for 3d, the ob/ob mice were randomly divided into the normal group and pioglitazone-treatment group. And they were injected hypodermically with placebo or PGZ for two or six weeks. The weight and adipocyte distribution were observed. The mRNA expression levels MR, GR and the related gene from adipose tissue were analyzed by real-time quantitative PCR.2. Postconfluent 3T3-L1 preadipocytes were incubated with a cocktail of insulin, dexamethasone, and 3-isobutyl-1-methylxanthine (IBMX) in DMEM supplemented with 10% fetal calf serum (FCS) for 48 h, with the culture medium replaced next 48 h with DMEM, supplemented with 10% FCS and insulin, and then refeeding with standard medium. 3T3-L1 preadipocytes were treated with or without pioglitazone during differentiation. We observed the adipocytes on day0, day4, day8 and day14 under microscope, with the cells stained by oil red O. And real-time quantitative PCR was used to study the mRNA expression levels of MR, GR and the related gene.Results:1. The time-depended weight(P<0.05)were raised in PGZ-treatment group. The mass of subcutaneous adipose were raised in long-time treatment-group(P<0.01), and there were no statistical significance between the mass of visceral adipose tissues in two groups. Comparing to control group, the mRNA levels of MR, GR and 11β- HSD1 in PGZ groups were significantly raised in subcutaneous adipose tissues, and no change in visceral adipose tissues. In kidney, with the treatment of PGZ, the mRNA expressions of MR and 11β- HSD2 upregulated.2. With the process of adipose differentiation under classical conditions, 3T3-L1 fibroblasts were long-term exposure to 10μM pioglitazone, an agonist of PPARγ. After differentiation, the 3T3-L1 preadipocytes turned to be larger and round rather than of spindle shape, and contained large droplets of triglycerides. The cells were stained in day4, day8 and day 14 during the differentiation by oil red O, and quantitated by isopropyl alcohol method. Over 60% of the preadipocytes in control group and about 90% of the pioglitazone treatmented cells appeared to be differentiated into mature adipocyte. However, the single cell in PGZ group was smaller than control group's. The mRNA levels of MR and relative genes were detected by real-time quantitative PCR. Accompanied with pioglitazone induced adipogenesis, mRNA levels of MR and 11β-hydroxysteroid dehydrogenase type 1 were increased(P<0.01).Conclusion:3. PPARγagonist–pioglitazone could increase the weight of ob/ob mice, and improve the expansion of the subcutaneous fat depot, with the raise of the mRNA levels of steroid receptors. This study proved the relationship between side effects of pioglitazone and steroid receptors in vivo.4. Pioglitazone promote the differentiation of 3T3-L1 preadipocytes. 3T3-L1 preadipocytes express the mRNA of steroid receptors, which were increased during differentiation. Accompanied with pioglitazone induced adipogenesis, the mRNA levels of steroid receptors were increased. It is conclude that pioglitazone have the effect on steroid receptors.