Regulation of metabolism and diabetes mellitus by tristetraprolin

描述（由申请人提供）：糖尿病（DM）是发达国家发病率和死亡率的主要原因，但导致DM发生的分子机制尚不清楚。Tristetraprolin（TTP）是一种串联锌指蛋白，其与靶mRNA分子的3 '-非翻译区（3'-UTR）中的富含AU的元件结合，并促进其降解。TTP在炎症领域已被广泛研究，其中已显示其结合并降解肿瘤坏死因子α（TNFα）mRNA。我们最近的研究结果表明，在糖尿病小鼠肝脏中TTP mRNA和蛋白水平降低，肝细胞中TTP敲低（KD）增加了过氧化物酶体增殖物激活受体α（PPARα）（脂质代谢的主要调节因子）和丙酮酸脱氢酶激酶4（PDK 4）（葡萄糖利用的负调节因子）的mRNA水平。由于TTP KO小鼠在出生后不久由于TNFα循环水平升高而形成致死性炎症表型，因此我们获得了TTP和TNFα受体（TNFR 1/2）同时全身敲除（KO）的小鼠，这些小鼠缺乏TTP依赖性炎症。我的中心假设是，TTP通过分别调节PPARα和PDK 4水平介导其对肝脏脂质代谢和葡萄糖利用的影响，并且TTP通过其代谢作用防止DM的发展。在目的1中，我假设TTP KD通过上调PPARα介导脂质稳态的变化。我将从存在或不存在TTP缺失的小鼠中分离原代肝细胞，并通过RNA测序测量脂质摄取、脂质含量、β-氧化活性和代谢基因表达的变化来确定TTP对脂质代谢的影响。所有实验将在TTP KO/PPARα KD的设置下重复进行。我还将通过对PPARα内的3 '-UTR战神进行缺失研究来确定TTP是否直接调节PPARα。在目的2中，我假设TTP KD通过上调PDK 4介导葡萄糖稳态的变化。我将从有或没有TTP缺失的小鼠中分离原代肝细胞，并通过RNA测序测量葡萄糖摄取、葡萄糖产生、葡萄糖氧化和促生/糖酵解基因表达的变化，确定TTP对葡萄糖代谢的影响。所有实验将在TTP KO/PDK 4 KD的设置下重复。我还将通过对PDK 4内的3 '-UTR战神进行缺失研究来确定TTP是否直接调节PDK 4。最后，在目标3中，我假设TTP介导对II型糖尿病发展的保护作用。我将对TTP/TNFR 1/2 KO和TNFR 1/2 KO（对照）小鼠进行高脂饮食，并根据血糖和胰岛素水平评估这些小鼠的糖尿病进展。这些研究有望推进我们对TTP在糖尿病中作用的认识，并可能导致新的糖尿病治疗方法的开发。

DESCRIPTION (provided by applicant): Diabetes mellitus (DM) is a major cause of morbidity and mortality in the developed world, but the molecular mechanisms that lead to the development of DM are not well understood. Tristetraprolin (TTP) is a tandem zinc finger protein that binds to AU-rich elements in the 3'-untranslated region (3'-UTR) of target mRNA molecules, and promotes their degradation. TTP has been extensively studied in the field of inflammation, where it has been shown to bind to and degrade tumor necrosis factor α (TNFα) mRNA. Our recent results suggest that TTP mRNA and protein levels are reduced in diabetic murine livers, and that TTP knockdown (KD) in hepatocytes increases the mRNA levels of peroxisome proliferator-activated receptor alpha (PPARα), a major regulator of lipid metabolism, and pyruvate dehydrogenase kinase 4 (PDK4), a negative regulator of glucose utilization. Because TTP KO mice develop a lethal inflammatory phenotype shortly after birth due to elevated circulating levels of TNFα, we have obtained mice with simultaneous systemic knockout (KO) of TTP and TNFα receptors (TNFR1/2) which lack TTP-dependent inflammation. My central hypothesis is that TTP mediates its effects on hepatic lipid metabolism and glucose utilization by modulating the levels of PPARα and PDK4, respectively, and that TTP protects against the development of DM through its metabolic effects. In Aim 1, I hypothesize that TTP KD mediates changes in lipid homeostasis through up regulation of PPARα. I will isolate primary hepatocytes from mice with or without TTP deletion and determine the effects of TTP on lipid metabolism by measuring changes in lipid uptake, lipid content, beta- oxidation activity, and metabolic gene expression by RNA sequencing. All experiments will be repeated in the setting of TTP KO/PPARα KD. I will also determine whether TTP directly regulates PPARα by performing deletion studies of the 3'-UTR AREs within PPARα. In Aim 2, I hypothesize that TTP KD mediates changes in glucose homeostasis through up regulation of PDK4. I will isolate primary hepatocytes from mice with or without TTP deletion and determine the effects of TTP on glucose metabolism by measuring changes in glucose uptake, glucose production, glucose oxidation, and gluconeogenic/glycolytic gene expression by RNA sequencing. All experiments will be repeated in the setting of TTP KO/PDK4 KD. I will also determine whether TTP directly regulates PDK4 by performing deletion studies of the 3'-UTR AREs within PDK4. Finally, in Aim 3, I hypothesize that TTP mediates protective effects against the development of type II diabetes mellitus. I will subject TTP/TNFR1/2 KO and TNFR1/2 KO (control) mice to high-fat diet and assess the progression of diabetes in these mice in terms of blood glucose and insulin levels. These lines of investigation promise to advance our knowledge of the role of TTP in diabetes, and may potentially lead to the development of novel diabetic therapies.