Decoding PGC-1a1 Control of Energy Metabolism

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Project Summary A major challenge for combating obesity is to identify targetable pathways that can decrease energy intake or increase energy expenditure. One of the most promising biological systems that can be exploited to increase energy expenditure is the thermogenic brown adipose tissue. Unlike white adipose tissue that stores energy in the form of triglycerides, brown adipose tissue oxidize fuels and dissipate energy as heat by uncoupling ATP synthesis from the electron transport chain in a process known as non-shivering thermogenesis. The overall goal of our studies is to understand the molecular mechanisms underlying non-shivering thermogenesis and to exploit these mechanisms to antagonize obesity and associated diseases including Type 2 Diabetes. PGC1α1 is a key transcriptional coactivator that facilitates mitochondrial biogenesis and thermogenesis in brown and adipose tissue. Indeed better understanding novel signal integration points into PGC1α1 are much needed. Identification and characterization of these mechanisms could lead to the discovery of novel ways to boost energy expenditure and antagonize obesity. The objective of this study is to delineate the role protein synthesis plays in regulating PGC1α1 protein expresion in adipose tissue thermogenesis and metabolism. Our preliminary data suggest that insulin strongly induces PGC1α1 protein indepdently of mRNA levels and it is important for adipose tissue thermogenesis. Genetic studies have revealed that insulin signaling is important for brown fat function, but its role in regulating PGC1α1 translation has never been explored. Thus, we hypothesize that a major mode of signal integration into PGC1α1 comes at the level of translation and we aim to decode these mechanisms and biological outcomes in brown adipocytes. We propose the following aims to test this hypothesis: 1. Aim 1 will define the role of the of the PGC1α1 untranslated region (UTR) in regulating its insulin- dependent translation in primary brown adipose tissue (BAT) cells. The PGC1α1 mRNA transcript has not been fully studied and the function of the UTR is currently unknown. Since we have data strongly suggesting that PGC1α1 is regulated by translation, we are going to test the role of the UTR in this process. 2. Aim 2 will study the in vivo regulation of PGC1α1 translation by polysome analysis in BAT. The gold standard for measuring translation is the transition of mRNA to translating polyribosomes by the polysome assay. We will delineate the upstream signals that initiate the translation of PGC1α1 in vivo by this assay. 3. Aim 3 will identify and characterize mRNA binding proteins (RBPs) of PGC1α1 using mRNA capture and mass spectrometry. An open biological question is why are certain mRNAs translated and not others. One hypothesis that we are pursuing is that RBPs allow this specificity by binding certain mRNAs and allowing them to bind the translation complex under preferetial conditions. Here, we are using PGC1α1 as a test case for this and search for novel RBPs.