Although insulin resistance is a key component of type II diabetes, the molecular mechanisms controlling insulin sensitivity have not been fully elucidated. Understanding the etiology of insulin resistance will therefore be of tremendous importance for developing better screening, treatment and prevention targets to combat the rising threat of metabolic disorders. Peroxisome proliferator-activated receptor gamma (PPARg) has been implicated in the insulin signaling pathway as the target of thiazolidinediones, drugs that have recently been employed in the management of insulin-resistant disorders for their insulin-sensitizing effects. PPARg is a ligand-activated nuclear receptor with a well-characterized structure that binds PPAR response elements and regulates transcription of target genes by recruiting coactivators and/or corepressors. Although many PPARg-regulated genes have been identified, the exact set of PPARg target genes that mediate improvements in insulin sensitivity in vivo is largely unknown. The goal of this project is to shed light on this issue by studying a unique, recently discovered PPARg mutation that causes familial partial lipodystrophy (FPLD), an extreme form of type II diabetes. This project will take advantage of the particular properties of this mutation, which makes a conservative single change (E157D) in the DNA binding domain of the receptor. Our preliminary data show that this mutation alters the DNA sequence recognition specificity of the receptor, resulting in a distinctly different pattern of transcription of several known PPARg target genes. These findings led to the hypothesis that forms the basis for this proposal: the E157D PPARg causes diabetes through misregulation of key metabolic genes. There are two specific aims: 1) Characterize the effects of the E157D mutation on DNA binding and transcriptional activation of a set of known PPARg target genes, and 2) Identify the global set of genes that are misregulated by E157D PPARg. Standard in vitro techniques for DNA binding and transcriptional activity will be used to compare mutant and wild type PPARg function. Human cell lines expressing wild-type and mutant PPARg will be generated, and microarray analysis of gene expression as well as chromatin immunoprecipitation analysis of selected genes will be used to identify genes misregulated by E157D PPARg.
. Results from this study will identify genes or sets of genes that were not previously recognized as being involved in the etiology of metabolic diseases such as lipodystrophy and in particular diabetes. This knowledge may advance possibilities for screening, treatment and prevention of diabetes and other metabolic diseases.