Endothelin-1 in Obesity and Insulin Resistance

点击翻译按钮获取中文摘要

Project Summary Insulin resistance (IR) is a major health problem in the U.S. It precludes type II diabetes and is often present in patients suffering from obesity, both being major risk factors for cardiovascular disease. Currently, mechanisms leading to IR are not fully understood. ET-1 is a vasoactive peptide primarily released by endothelial cells. It is increased in patients with obesity and associated with IR. ET-1 is elevated in response to hypoxia, which occurs in individuals with obesity. It activates two receptors, ETA and ETB, which typically oppose each other physiologically. Our preliminary data indicate that inhibiting ETB receptors in rodents, either genetically or pharmacologically, improves insulin tolerance and reduces fasting blood glucose. This improvement in glucose control is associated with an increase in plasma adiponectin and adipose adiponectin and peroxisome proliferator-activated receptor gamma (PPAR-γ) mRNA. In addition, adipocyte specific ETB gain of function mice have exacerbated glucose intolerance in response to high fat feeding, while adipocyte ETB knockout mice have improved glucose and insulin tolerance compared to floxed control littermates. These data suggest the adipose tissue as a possible target for ET-1 induced reduction in insulin signaling. It has been previously shown that activation of ETB receptors on cultured adipocytes inhibits the anti-lipolytic effects of insulin. Furthermore, blockade of ETB receptors improves insulin sensitivity in a rodent model of sleep apnea. These data suggest that increased ET-1 observed in patients with obesity may promote IR via the ETB receptor. Thus, we hypothesize that that obesity induced tissue hypoxia promotes ET-1/ETB receptor activation in adipose leading to IR on adipocytes, PPAR-γ inhibition and reduced Adiponectin release by adipocytes thereby causing IR in muscle and liver tissue. To test this hypothesis, we will utilize both in vivo and in vitro techniques. First, using cultured adipocytes, we will determine whether activation of ETB receptors inhibits PPAR-γ, reduces adiponectin secretion, and causes insulin resistance on adipocytes. Next, we will used clinically approved inhibitors of ET-1 receptors in a model of diet induced obesity and IR, and we will utilize two novel mouse models that were produced by our lab that allow us to over-express or knockout the ETB. To test this hypothesis, the following specific aims will be tested: Specific aim 1: To test the hypothesis that ETB receptor activation directly inhibits insulin signaling on adipocytes and reduces adiponectin production by inhibiting PPAR-γ. Specific aim 2: To test the hypothesis that ETB receptor activation on adipocytes promotes insulin resistance by inhibiting PPAR-γ and reducing adiponectin release in mice. Specific aim 3: To test the hypothesis that ETB receptor blockade increases plasma adiponectin and improves insulin resistance in obese mice.