Rev-ERBa Regulates Mitochondrial Biogenesis, Adiposity, and Insulin Action

描述（由申请人提供）：在过去的三十年里，美国肥胖和2型糖尿病的患病率急剧上升。识别调节肥胖和胰岛素作用的基因对于开发新型抗肥胖和胰岛素增敏化合物至关重要。通过用锰四苯甲酸（MnTBA）卟啉治疗肥胖小鼠，我们发现血红素的核受体Rev-ERBa是一种新的抗肥胖靶点，也能改善胰岛素的作用。Rev-ERBa是一种转录抑制因子，其活性在与其配体血红素结合时增强。在负反馈回路中，血红素调节Rev- ERBa的表达。我们的初步数据显示，用MnTBA卟啉治疗小鼠增加了Rev-ERBa的表达，表明卟啉模拟低水平的血红素。Rev-ERBa抑制过氧化物酶体增殖物激活受体γ (PPAR?)协同激活因子1 α (PGC1a)的表达，PGC1a是线粒体生物发生的主要调节因子。我们的初步数据表明，PGC1a在MnTBA卟啉处理的小鼠中增加。与线粒体生物发生的增加一致，解偶联蛋白2和3 （UCP2和UCP3）在MnTBA卟啉处理的小鼠中增加，这一反应可能解释了我们在这些小鼠中观察到的肥胖的大幅减少。由于我们的初步研究表明MnTBA卟氨酸不会与血红素竞争Rev-ERBa的结合位点，但会增加血红素加氧酶-1 (HO-1)，我们的假设是HO-1产物一氧化碳抑制Rev-ERBa。具体目标#1将确定用血红素样卟啉或一氧化碳治疗野生型和HO-1敲除小鼠是否会减少Rev-ERBa与PGC1a启动子的结合，这一过程将刺激线粒体生物发生并减少肥胖（增加UCP2/3）。由于我们观察到用MnTBA卟啉治疗的小鼠肥胖减少，因此我们也表明MnTBA卟啉逆转饮食诱导的胰岛素抵抗也就不足为奇了。然而，MnTBA卟啉诱导的胰岛素敏感性的增加与Akt/PKB表达的增加有关，这一发现与热量限制引起的体重减轻不同。我们的假设是，在MnTBA卟啉处理的小鼠中，Akt/PKB水平的增加是由于该化合物降低Rev-ERBa活性的能力。这一假设得到了Rev-ERBa抑制IL-6的证据的支持，这一过程将抑制STAT3依赖性诱导Akt/PKB启动子。因此，Specific Aim #2将确定用血红素样卟啉或一氧化碳喂养高脂肪饮食的小鼠是否通过增加STAT3介导的Akt/PKB表达来逆转胰岛素抵抗。通过完成这项R15提案的具体目标，我们将建立一种新的机制，解释卟啉或一氧化碳如何与Rev-ERBa相互作用以改变代谢，可能导致肥胖和2型糖尿病的新治疗方法。

DESCRIPTION (provided by applicant): The prevalence of obesity and type 2 diabetes in the United States has increased dramatically over the last three decades. Identifying genes that regulate adiposity and insulin action is essential for the development of novel anti-obesity and insulin sensitizing compounds. By treating obese mice with the manganese tetrakis benzoic acid (MnTBA) porphyrin, we have identified heme's nuclear receptor, Rev-ERBa, as a novel anti- obesity target that also improves insulin action. Rev-ERBa is a transcriptional repressor whose activity is enhanced upon binding its ligand, heme. In a negative feedback loop, heme regulates the expression of Rev- ERBa. Our preliminary data shows that treating mice with MnTBA porphyrin increases Rev-ERBa expression indicating that the porphyrin mimics low levels of heme. Rev-ERBa represses the expression of peroxisome proliferator-activated receptor-gamma (PPAR?) coactivator 1 alpha (PGC1a), a master regulator of mitochondrial biogenesis. Our preliminary data demonstrates that PGC1a is increased in mice treated with MnTBA porphyrin. Consistent with an increase in mitochondrial biogenesis, uncoupling protein 2 and 3 (UCP2 and UCP3) are increased in mice treated with MnTBA porphyrin, a response that likely explains the large reductions in adiposity we observed in these mice. Because our preliminary studies show that MnTBA porphyrin does not compete with heme for Rev-ERBa's binding site, but increases heme oxygenase-1 (HO-1), our hypothesis is that the HO-1 product, carbon monoxide, inhibits Rev-ERBa. Specific aim #1 will determine if treating wildtype and HO-1 knockout mice with heme-like porphyrins or carbon monoxide decreases the binding of Rev-ERBa to the PGC1a promoter, a process that would stimulate mitochondrial biogenesis and reduces adiposity (increased UCP2/3). Since we observed a reduction in adiposity in mice treated with MnTBA porphyrin, it is not surprising that we also show that MnTBA porphyrin reverses diet-induced insulin resistance. However, the MnTBA porphyrin-induced increase in insulin sensitivity is associated with an increase in Akt/PKB expression, a finding that is distinct from caloric restriction induced weight loss. Our hypothesis is that the increase in Akt/PKB levels in mice treated with MnTBA porphyrin is due to the compound's ability to decrease Rev-ERBa activity. This hypothesis is supported by the evidence that Rev-ERBa represses IL-6, a process that would restrain STAT3 dependent induction of the Akt/PKB promoter. Therefore, Specific Aim #2 will determine if treating mice fed a high fat diet with heme-like porphyrins or carbon monoxide reverses insulin resistance by increasing STAT3 mediated Akt/PKB expression. By completing the specific aims of this R15 proposal, we will establish a novel mechanism explaining how porphyrins or carbon monoxide interact with Rev-ERBa to alter metabolism, possibly leading to novel treatments for obesity and type 2 diabetes. PUBLIC HEALTH RELEVANCE: The prevalence of obesity and type 2 diabetes in the United States has increased dramatically in the last three decades. We have identified the transcriptional repressor, Rev- ERBa, as a potential anti-obesity target that improves type 2 diabetes. The overall goal of this proposal is to learn more about how Rev-ERBa reduces adiposity and enhances insulin action.