Leptin Transport across the BBB: The Role of ObR (+) astrocytes

描述（由申请人提供）：在第三个资助周期的“瘦素运输通过血脑屏障”，我们将集中在瘦素受体（ObR）阳性星形胶质细胞在传递瘦素从血液到中枢神经系统后穿过血脑屏障（BBB）的作用。我们推测，星形胶质细胞不仅调节瘦素运输的重要组成部分的血脑屏障，但也调节神经元瘦素信号，使更快的开始和更快的终止瘦素作用的神经元。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对瘦素受体（ObR）表达亚型和瘦素周转的影响。小鼠研究将测试星形胶质细胞活性和星形胶质细胞ObR对瘦素分布、细胞信号传导和肥胖发展的CNS动力学的作用。在目标1中，我们将测试的假设，反应性星形胶质细胞促进周转的瘦素在大脑中，通过加速细胞内降解的瘦素。在目标2中，我们将测试的假设，即反应性星形胶质细胞在文化和成年发病的肥胖症的小鼠表现出不平衡的ObR亚型的差异调节所造成的。目标3将集中在成年小鼠饮食诱导的肥胖或Avy突变，这两种表现出区域特异性增加星形胶质细胞ObR的调节变化。通过使用神经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转导的调节中发挥重要作用。这些结果将首次证明ObR（+）星形胶质细胞在连接BBB转运和CNS对瘦素的反应中的功能。对肥胖症中星形胶质细胞增生和星形胶质细胞ObR上调的后果的理解应该能够使星形胶质细胞靶向对抗肥胖受试者中的神经内分泌失调。 公共卫生相关性：瘦素是一种主要由脂肪组织产生的激素。高瘦素血症见于代谢综合征。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在美国和世界许多其他地区的患病率迅速增加。这项研究将主要集中在星形胶质细胞如何参与将瘦素从血液输送到大脑并调节其对神经元（最常见的效应细胞）的作用。星形胶质细胞是大脑中最丰富的细胞，但很少有研究涉及它们是否与瘦素和肥胖有关。我们最近发现瘦素受体的mRNA和蛋白质确实存在于星形胶质细胞中。此外，这些瘦素受体的表达水平在成年型肥胖小鼠模型中增加。这表明星形胶质细胞瘦素系统在肥胖受试者的调节变化中起重要作用。这可能是神经元-胶质细胞的相互作用，而不是神经元的直接激活，发挥重要的介导作用的血液传播的瘦素。因此，相关性在于（a）更好地理解星形胶质细胞如何影响肥胖症的发作和进展;（B）更好地理解大脑中的细胞-细胞相互作用;和（c）潜在的识别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.