Role and mechanism of Unc119b in the regulation of glucose homeostasis - Summary While several pharmaceuticals are available of the treatment of type II diabetes, they generally fail to achieve long term glycemic control. Insulin sensitizers that would reverse insulin resistance and restore insulin-dependent glucose uptake in storage tissues are urgently needed. TZDs, the only currently available family of drugs that improves insulin sensitivity, also cause serious cardiovascular side effects due to their agonism at PPARg. Using a new HTS assay that allows real time monitoring of GLUT4 translocation in live cells we identified new insulin sensitizers. Compound C59 enhances insulin-stimulated GLUT4 translocation but has no activity in the absence of insulin. Additionally, this compound does not activate PPARg. Treatment of insulin resistant DIO mice with C59 results in a drastic decrease in blood glucose and plasma insulin concentration, a significant improvement in glucose tolerance and a reversal of insulin resistance. Proteome wide thermal shift assay identified Unc119b as the target of C59 and deletion of Unc119b results in a loss of C59-mediated insulin sensitization. Additionally, deletion of Unc119b in mice results in protection from diet induced glucose intolerance, demonstrating that Unc119b plays a role in the development of insulin resistance and identifying this protein as a new promising target for the treatment of type II diabetes. While Unc119b is known to be a chaperone for myristoylated proteins and a regulator of small G-protein activity, it has not previously been implicated in the regulation of insulin function. As such, understanding the role and mechanism of Unc119b-mediated regulation of GLUT4 translocation and glucose homeostasis represents a critical step towards developing new treatments for type II diabetes. The goal of this proposal is to 1) investigate the importance of Unc119b in each glucose storing tissue for the maintenance of glucose homeostasis; 2) Determine if improving insulin sensitivity using either C59 or by deleting Unc119b results in protection from b-cell damage. 3) Identify the proteins that interact with Unc119b and the molecular mechanism involved in Unc119b-mediated regulation of GLUT4 translocation. Studies in aim 1 will identify the role of Unc119b for glucose homeostasis in skeletal muscle, adipose tissue and the heart using Unc119b KO and Unc119b flox mice as well as the reporter mouse we engineered that allows measurement of GLUT4 translocation in live animals. Studies in aim 2 will focus in determining if the improved insulin sensitivity and lowered circulating glucose concentration brought about by C59 treatment or Unc119b deletion result in protection from b-cell damage and b-cell loss in the genetic model of obesity and diabetes BKS Db/Db mouse. This will be achieved using clamps assays, ex-vivo glucose stimulated insulin secretion assay in isolated islets and IDISCO imaging of whole cleared pancreas. Studies in aim 3 will focus on identifying the domains of Unc119b required for the regulation of GLUT4 translocation, the mechanism of action of Unc119b and its protein interactome. Overall, this project will identify Unc119b as a new and important component of the insulin signaling cascade in glucose storage tissues, identify its molecular mechanism of action and evaluate the beneficial effect of C59 treatment and Unc119b deletion on insulin sensitivity and b-cell protection.
