Development of Hypothalamic Neurons That Control Energy Balance

 描述（由申请人提供）：下丘脑在体内平衡和能量代谢中起关键作用，因此下丘脑发育缺陷会导致严重的病理状况，包括糖尿病和肥胖症（1）。然而，下丘脑细胞类型的多样性如何被指定和组织仍然不清楚，部分原因是由于这个重要脑区的解剖复杂性。本提案的中心主题是解决这一关键问题，重点关注下丘脑弓状核（ARC）中的两种神经元亚型，AgRP-和POMC-神经元，它们直接感知来自外周的能量可用性的营养和激素信号，并将此信息传递给中枢神经系统（CNS）中的其他神经元。AgRP-神经元的关键功能是响应能量缺乏条件，通过增加刺激摄食行为和减少能量消耗的食欲相关肽（AgRP）和神经肽Y（NPY）的表达来实现。相比之下，POMC神经元通过抑制摄食和增加能量消耗来响应能量丰富的条件，主要是通过α-黑素细胞刺激激素（αMSH）的上调，α MSH是阿黑皮素原（POMC）的蛋白水解产物（1）。Islet-1（Isl 1）是LIM-homeodomain（LIM-HD）转录因子家族的成员，在几种器官（如脊髓运动神经元和内分泌胰岛细胞（x））的发育过程中在决定细胞命运中起关键作用。Isl 1的表达已在下丘脑的几个区域中报道（xx，xx）。我们还发现Isl 1在胚胎和出生后小鼠大脑的ARC中高度表达。我们对条件性Isl 1缺失小鼠的分析表明，下丘脑中Isl 1的缺失导致出生后死亡，与ARC神经元的AgRP、NPY和POMC表达的急剧减小和废除相关。我们还发现Isl 1在AgRP神经元的出生后代谢功能中的关键作用。基于这些开创性的发现，我们将测试的假设，Isl 1作为一个关键的双重调节器的1）规格/发展和2）出生后的功能的AgRP和POMC神经元协调一组基因，建立身份，成熟和能量稳态的行动，这些神经元在发展和出生后的下丘脑。我们将在以下三个具体目标中使用细胞，生物化学，遗传和无偏全基因组方法的合奏来测试这一假设。在第一个目标中，我们希望确定Isl 1在发育和出生后小鼠下丘脑中表达的时间和空间模式。在第二个目标中，我们将定义Isl 1在AgRP-和POMC-神经元的发育和能量平衡功能中的作用。在最后的目标，我们将定义的Isl 1和其合作伙伴的转录因子，指导弓状AgRP-和POMC-神经元的发育规范，成熟和功能的靶基因。

 DESCRIPTION (provided by applicant): The hypothalamus plays critical roles in homeostasis and energy metabolism, and thus defects in hypothalamic development result in serious pathological conditions, including diabetes and obesity (1). However, how the diverse array of hypothalamic cell types is specified and organized remains poorly defined, partly due to the anatomical complexity of this essential brain region. The central theme of this proposal is to address this critical issue with a focus on two neuronal subtypes in the hypothalamic arcuate nucleus (ARC), AgRP- and POMC- neurons, which directly sense nutrient and hormonal signals of energy availability from the periphery and relay this information to other neurons in the centra nervous system (CNS). The key function of AgRP-neurons is to respond to energy scarcity conditions, accomplished by increased expression of the orexigenic agouti-related peptide (AgRP) and neuropeptide Y (NPY) that stimulate feeding behavior and reduce energy expenditure. In contrast, POMC-neurons respond to conditions of energy abundance by suppressing feeding and increasing energy expenditure primarily via the upregulation of α-melanocyte-stimulating hormone (αMSH), a proteolytic product of pro-opiomelanocortin (POMC) (1). Islet-1 (Isl1), a member of the LIM-homeodomain (LIM-HD) transcription factor family, plays crucial roles in determining cell fates during the development of several organs, such as spinal motor neurons and endocrine pancreatic islet cells (x). Expression of Isl1 has been reported in several regions of the hypothalamus (xx, xx). We also discovered that Isl1 is highly expressed in the ARC of both embryonic and postnatal mouse brains. Our analyses of conditional Isl1-null mice revealed that deletion of Isl1 in the hypothalamus results in postnatal death, associated with drastically reduced body size and abrogation in the expression of AgRP, NPY and POMC by ARC neurons. We also found critical roles of Isl1 in postnatal metabolic function of AgRP-neurons. Based on these seminal findings, we will test the hypothesis that Isl1 acts as a critical dual regulator of 1) the specification/development and 2) the postnatal function of AgRP- and POMC-neurons by coordinating a cohort of genes that establish the identity, maturation and energy homeostasis action of these neurons in developing and postnatal hypothalamus. We will test this hypothesis in the following three specific aims using an ensemble of cellular, biochemical, genetic, and unbiased genome-wide approaches. In the first aim, we wish to determine the temporal and spatial pattern of Isl1 expression in the developing and postnatal mouse hypothalamus. In the second aim, we will define the roles of Isl1 in the development and the energy balance function of AgRP- and POMC-neurons. In the final aim, we will define the target genes of Isl1 and its partner transcription factors that direct the developmental specification, maturation and function of the arcuate AgRP- and POMC-neurons.