Molecular Control of Brown Adipose Cell Fate and Energy Metabolism

描述（由申请人提供）：当能量摄入长期超过总能量消耗时，就会发生肥胖。目前，大多数抗肥胖药物通过抑制食欲或抑制肠道脂肪吸收来抑制能量摄入。然而，由于副作用，包括抑郁症，油性排便和脂肪酸，迫切需要替代方法。由于棕色脂肪组织（BAT）消耗能量产生热量作为抵御寒冷和肥胖的防御，改变分子途径以增加BAT的量或产热活性可能导致替代和有效的治疗干预来对抗人类肥胖和代谢紊乱。我们的长期目标是了解调节棕色脂肪细胞命运的分子回路，并研究它们在能量稳态中的生理作用。我们以前已经表明，棕色脂肪细胞产生于一个子集的皮细胞前体通过转录因子，PRDM 16的作用，但是，目前还不清楚PRDM 16的作用在成肌细胞到棕色脂肪开关的调节。我们确定了赖氨酸甲基转移酶，EHMT 1作为PRDM 16转录复合物的关键组成部分。EHMT 1在BAT中的表达最高，并受到PRDM 16的高度诱导。值得注意的是，EHMT 1似乎是棕色脂肪细胞相对于肌细胞的发育开关。重要的是，EHMT 1基因的缺失与小鼠和人类的肥胖有关;然而，其潜在机制仍然完全未知。因此，我们目前的目标是研究EHMT 1的生理功能和机制，控制棕色脂肪细胞的命运在体内。基于我们的初步数据，我们将测试EHMT 1在能量稳态中起着关键作用的假设，作为一个发育开关，通过调节PRDM 16复合物的功能来控制棕色脂肪细胞的命运。为了验证这一假设，我们将追求以下具体目标：在Aim 1中，我们将确定EHMT 1在体外和体内棕色脂肪细胞的命运规范和维持中的遗传要求。在Aim 2中，我们将分析脂肪特异性EHMT 1基因敲除小鼠和EHMT 1杂合子无效小鼠的代谢表型，并严格表征EHMT 1在体内控制能量消耗和葡萄糖稳态中的生理作用。在Aim 3中，我们将进行生化分析，并使用培养的细胞来阐明EHMT 1作为棕色脂肪谱系发育开关的机制。这些研究的预期结果是表征棕色脂肪细胞命运特化的一种全新的上游调控途径。我们的发现将产生重大影响，因为据我们所知，这项研究将描述第一种控制棕色脂肪与骨骼肌之间细胞命运转换的酶。所确定的机制将使我们能够通过药理学方法操纵这一发育途径，这可能提供一个可能的治疗靶点。

DESCRIPTION (provided by applicant): Obesity develops when energy intake chronically exceeds total energy expenditure. Currently, most anti- obesity medications act to repress energy intake, either by suppressing appetite or by inhibiting intestinal fat absorption. However, due to side effects including depression, oily bowel movements and steatorrhea, there is an urgent need for alternative approaches. Because brown adipose tissue (BAT) dissipates energy to produce heat as a defense against cold and obesity, altering the molecular pathway to increase the amount or thermogenic activity of BAT may lead to an alternative and effective therapeutic intervention to counteract human obesity and metabolic disorders. Our long-term goals are to understand the molecular circuits that regulate the fate specification of brown adipose cells and to investigate their physiological roles in energy homeostasis. We have previously shown that brown adipocytes arise from a subset of dermomytomal precursors through the action of a transcription factor, PRDM16; however, it remains unclear how the PRDM16 action in the myoblast-to-brown fat switch is regulated. We identified a lysine methyltransferase, EHMT1 as a critical component of the PRDM16 transcriptional complex. EHMT1 is expressed at its highest in BAT and is highly induced by PRDM16. Notably, EHMT1 appears to act as a developmental switch of brown adipocytes versus myocytes. Importantly, loss of the EHMT1 gene is associated with obesity in mice and in humans; however, its underlying mechanism remains completely unknown. Our current objective is thus to investigate the physiological function and mechanism of EHMT1 that controls brown adipose cell fate in vivo. Based on our preliminary data, we will test the hypothesis that EHMT1 plays a pivotal role in energy homeostasis as a developmental switch that controls brown adipose cell fate through modulating the function of the PRDM16 complex. To test this hypothesis, we will pursue the following specific aims: In Aim1, we will determine the genetic requirement of EHMT1 in the fate specification and maintenance of brown adipose cells in vitro and in vivo. In Aim2, we will analyze the metabolic phenotypes of adipose-specific EHMT1 knockout mice and EHMT1 heterozygous null mice and critically characterize EHMT1's physiological role in controlling energy expenditure and glucose homeostasis in vivo. In Aim3, we will conduct biochemical analyses and use cultured cells to elucidate the mechanism by which EHMT1 acts as a developmental switch of brown fat lineage. The expected outcome of these studies is to characterize a completely novel upstream regulatory pathway of brown adipose cell fate specification. Our findings will have a significant impact, because, to our knowledge, this study will characterize the first enzyme that controls the cell fate switch between brown adipose versus skeletal muscle. The identified mechanism will allow us to manipulate this developmental pathway by pharmacological approaches, which may provide a possible therapeutic target.