BK21 Program of Bio-Molecular Seminar

 

▶ Subject : PPARg, phosphorylation and the anti-diabetic PPARg ligands: a new look at an old friend

▶ Speaker : Jang Hyun Choi, Ph.D.( Dana-Farber Cancer Institute, Harvard Medical School)

▶ Date : PM 5:00/ Aug. 3(Wed)/2011

▶ Place : Auditorium, Postech Biotech Center

*Abstract
Obesity is a major risk factor of Metabolic Syndromes such as type 2 diabetes, dyslipidemia and cardiovascular disease. In addition, it is now clear that increasing rates of obesity are contributing to increases in the incidence and mortality of certain cancers. To date, the number of patients with diabetes is rapidly increasing and reaching to infectious disease level. The world health organization (WHO) announced that in 2030, 0.3 billion people will become patients with diabetes. Therefore, understanding the molecular pathways that link adipose tissue biology to this staggering array of pathologies is scientifically and clinically crucial. The nuclear receptor PPARg is a master regulator of adipose cell differentiation and development. It is also the functioning receptor for the thiozolidinedione (TZD) class of anti-diabetic drugs such as rosiglitazone or pioglitazone. Here we showed that obesity induced in mice by high-fat feeding activates the protein kinase Cdk5, and this results in phosphorylation of PPARg at Ser273 in adipose tissues. This modification of PPARg does not alter its adipogenic capacity, but leads to dysregulation of a large number of genes whose expression is altered in obesity, including a reduction in the expression of the insulin-sensitizing adipokine, adiponectin. Unexpectedly, the phosphorylation of PPARg by Cdk5 is blocked by anti-diabetic PPARg ligands, such as rosiglitazone and MRL24. This inhibition works both in vivo and in vitro, and surprisingly, is completely independent of classical receptor transcriptional agonism. Similarly, inhibition of PPARg phosphorylation in obese patients by rosiglitazone is very tightly associated with the anti-diabetic effects of this drug. More recently, we have developed novel synthetic compounds that have a unique mode of binding to PPARg, completely lack classical transcriptional agonism and block the Cdk5-mediated phosphorylation in cultured adipocytes and in insulin-resistant mice. Moreover, one such compound, SR1664, has potent anti-diabetic activity while not causing the fluid retention and weight gain that are serious side effects of many of the PPARg drugs. Unlike TZDs, SR1664 also does not interfere with bone formation in culture. These data illustrate that Cdk5-mediated phosphorylation of PPARg is involved in the pathogenesis of insulin-resistance, and new classes of anti-diabetes drugs can be developed by specifically targeting the Cdk5-mediated phosphorylation of PPARg.

☎ Inquiry : Sung Ho Ryu (279-2292)