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

描述（由申请人提供）：在“瘦素跨血脑屏障运输”的第三个资助周期中，我们将重点关注瘦素受体（ObR）阳性星形胶质细胞在穿过血脑屏障（BBB）后将瘦素从血液传递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运输，而且还通过使神经元中的瘦素作用更快地开始和更快地终止来调节神经元中的瘦素信号传导。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形成对瘦素受体（ObR）亚型表达和瘦素转换的影响。小鼠研究将测试星形细胞活性和星形细胞ObR在瘦素分布、细胞信号传导和肥胖发展的中枢神经系统动力学中的作用。在Aim 1中，我们将检验反应性星形胶质细胞通过加速细胞内瘦素降解来促进大脑中瘦素周转的假设。在Aim 2中，我们将验证一种假设，即在培养和成年型肥胖小鼠中，反应性星形胶质细胞都表现出由于调节差异而导致的ObR亚型失衡。Aim 3将关注饮食诱导肥胖或Avy突变的成年小鼠的调节变化，这两种小鼠都表现出星形细胞ObR的区域特异性增加。通过使用胶质代谢抑制剂和新生成的星形胶质细胞特异性ObR敲除小鼠，我们将证明这些ObR（+）星形胶质细胞在调节神经元瘦素信号传导中发挥重要作用。该结果将提供ObR（+）星形胶质细胞连接血脑屏障运输和中枢神经系统对瘦素反应的功能的第一个证据。了解星形胶质细胞形成的后果和肥胖中星形胶质细胞ObR的上调，应该能够靶向星形胶质细胞来抵消肥胖受试者的神经内分泌失调。

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.