Leptin Transport Across the BBB: The Role of ObR (+) Astrocytes

描述(申请人提供)：在“瘦素跨血脑屏障转运”的第三个资助周期中，我们将重点研究瘦素受体(OBR)阳性的星形胶质细胞在跨越血脑屏障(BBB)后将瘦素从血液中转送到中枢神经系统中的作用。我们假设星形胶质细胞不仅作为血脑屏障的重要组成部分调节瘦素的运输，而且通过使神经元中的瘦素更快地开始和终止来调节神经元的瘦素信号。对小鼠原代星形胶质细胞的细胞研究将确定反应性星形胶质细胞增生症对瘦素受体亚型(OBR)表达和瘦素更新的影响。小鼠研究将测试星形细胞活动和星形细胞OBR在瘦素分布、细胞信号和肥胖发展的中枢神经系统动力学中的作用。在目标1中，我们将检验这一假设，即反应性星形胶质细胞通过加速瘦素在细胞内的降解来促进瘦素在大脑中的周转。在目标2中，我们将检验这样的假设，即培养中的反应性星形胶质细胞和成年肥胖症小鼠的反应性星形胶质细胞显示出由于不同调控而导致的OBR亚型失衡。目标3将侧重于饮食诱导肥胖或Avy突变的成年小鼠的调节变化，这两者都表现出星形细胞OBR的区域性特异性增加。通过使用胶质代谢抑制剂和新产生的星形胶质细胞特异性OBR基因敲除小鼠，我们将证明这些OBR(+)星形胶质细胞在神经元瘦素信号的调节中发挥重要作用。这一结果将为OBR(+)星形胶质细胞在BBB转运与中枢神经系统对瘦素的反应之间的联系提供第一个证据。了解肥胖者星形胶质细胞增多症和星形胶质细胞OBR上调的后果，可以靶向星形胶质细胞来对抗肥胖者的神经内分泌失调。 公共卫生意义：瘦素是一种主要由脂肪组织产生的荷尔蒙。代谢综合征表现为高瘦素血症。肥胖及其相关的高脂血症、心血管并发症、癌症和睡眠呼吸暂停症在美国和世界其他许多地区的患病率正在迅速上升。这项研究将主要关注星形胶质细胞如何参与将瘦素从血液输送到大脑，以及如何调节其对神经元的作用，神经元是最常见的效应细胞。星形胶质细胞是大脑中含量最丰富的细胞，但很少有研究表明它们是否与瘦素和肥胖有关。我们最近发现瘦素受体的mRNA和蛋白确实存在于星形胶质细胞中。此外，在成年肥胖症小鼠模型中，这些瘦素受体的表达水平增加。这表明星形细胞瘦素系统在肥胖者的调节变化中起着重要作用。可能是神经元-胶质细胞的相互作用，而不是神经元的直接激活，对血源性瘦素起着重要的中介作用。因此，相关性在于：(A)更好地了解星形胶质细胞如何影响肥胖的发生和发展；(B)更好地了解大脑中细胞与细胞的相互作用；以及(C)潜在地确定新的治疗靶点，以更好地对抗肥胖症。

DESCRIPTION (provided by applicant): In the third grant cycle of "leptin transport across the BBB", we will focus on the role of leptin receptor (ObR)-positive astrocytes in relaying leptin from blood to the CNS after crossing the blood-brain barrier (BBB). We hypothesize that astrocytes not only regulate leptin transport as vital components of the BBB, but also modulate neuronal leptin signaling by enabling a more rapid onset and faster termination of leptin action in neurons. The cellular studies with primary astrocytes from mice will determine the effects of reactive astrogliosis on subtypes of leptin receptor (ObR) expression and leptin turnover. The mouse studies will test the role of astrocytic activity and astrocytic ObR on CNS kinetics of leptin distribution, cellular signaling, and development of obesity. In Aim 1, we will test the hypothesis that reactive astrocytes facilitate the turnover of leptin in the brain by accelerating intracellular degradation of leptin. In Aim 2, we will test the hypothesis that reactive astrocytes both in culture and in mice with adult-onset obesity show an imbalance of ObR subtypes resulting from differential regulation. Aim 3 will focus on regulatory changes in adult mice with diet-induced obesity or the Avy mutation, both of which exhibit regional specific increases of astrocytic ObR. By use of glial metabolic inhibitors and newly generated astrocyte-specific ObR knockout mice, we will show that these ObR(+) astrocytes play an essential role in the regulation of neuronal leptin signaling. The results will provide the first evidence of the functions of ObR(+) astrocytes in linking BBB transport to the CNS response to leptin. An understanding of the consequence of astrogliosis and upregulation of astrocytic ObR in obesity should enable the targeting of astrocytes to counteract the neuroendocrine dysregulation in obese subjects. PUBLIC HEALTH RELEVANCE: Leptin is a hormone mainly produced by fat tissue. Hyperleptinemia is seen in the metabolic syndrome. Obesity and its associated hyperlipidemia, cardiovascular complications, cancer, and sleep apnea have a rapidly increasing prevalence in the US and many other parts of the world. This study will mainly focus on how astrocytes participate in delivering leptin from blood to brain and modulating its actions on neurons, the most commonly considered effector cells. Astrocytes are the most abundant cells in the brain, but very few studies have addressed whether they have anything to do with leptin and obesity. We recently found that both the mRNA and protein of leptin receptors are indeed present in astrocytes. Moreover, the expression level of these leptin receptors increases in mouse models of adult-onset obesity. This suggests an important role of the astrocytic leptin system in the regulatory changes in obese subjects. It is possible that it is neuron-glial interactions, rather than direct activation of neurons, that play important mediatory roles for blood-borne leptin. Thus, the relevance lies in (a) better understanding of how astrocytes affect obesity onset and progression; (b) better understanding of cell-cell interactions in the brain; and (c) potential identification of novel therapeutic targets to better combat obesity.