Revealing Ionomycin As PPARγ Ligands For Improving2Type Diabetes

The nuclear hormone receptor peroxisome proliferator-activated receptor y (PPARy) plays central roles in adipogenesis and glucose homeostasis and is the molecular target for the thiazolidinediones(TZDs) class of antidiabetic drugs. Activation of PPARy by TZDs improve insulin sensitivity, however, this is accompanied with the induction of several undesirable side effects, such as weight gain, fluid retention and cardiovascular disease, it is important to find PPAR y ligands that retain the benefits in improving insulin resistance but with reduced side effects. We had identified that Ionomycin, an antibiotic produced by Streptomyces conglobatus metabolism, was a novel PPARy ligand by Alphascreen assay. Ionomycin was able to specifically bind and activate PPARy by recruiting coactivator and inhibiting the binding of auxiliary inhibitor, eventually induced PPARy transcriptional activity. The crystal structure showed that Ionomycin interacted with the PPARy ligand-binding domain in a unique binding mode with properties and epitopes distinct from those of TZD drugs. We explored the biological effects of Ionomycin on diabetic model mouse. Mice were treated with Ionomycin by intraperitoneal injection, the results showed that Ionomycin could significantly reduce blood glucose and insulin, it also reduced liver cholesterol and triglycerides, and improved glucose tolerance and insulin sensitivity. We analyzed the gene expression in epididymal adipose tissue and liver tissue from mice, Ionomycin suppressed the expression of genes associated with fatty acid synthesis and gluconeogenesis, but increased adiponectin (could enhance insulin sensitivity) gene expression. As a PPARy ligand, Ionomycin did not induce adipocyte fatty acid synthesis and gluconeogenesis and glycogenolysis. Furthermore, PPARy Ser273was phosphorylated by the activation of CDK5(cyclin-dependent kinase5) and led to reduce insulin sensitivity. Ionomycin effectively blocked the phosphorylation of PPAR y at Ser273by CDK5both in vitro and in vivo, showed that the improving diabetes of Ionomycin was connected with CDK5kinase signaling pathway. In addition, Ionomycin had no effects on the survival of HepG2, Cos7and mIMCD3cells by MTT assay, and it could reduce the expression of genes associated with fluid retention genes such as ion channel genes and water channel genes in mIMCD3cell. Meanwhile, the ability of Ionomycin to induce3T3-L1cell differentiation was obvious weaker than Rosiglitazone, suggested that Ionomycin neither induced adipogenesis and reabsorption of water capacity in mouse kidney medullary collecting duct cells, nor aroused other obvious side effects. As a result, Ionomycin bound to PPARy LBD, recruited cofactor of PPARy to improve the symptoms of diabetes and did not show obvious side effects, as a result, Ionomycin may represent a unique template for designing novel PPAR y ligands with advantages over current TZD drugs.