Organic Cation Transporter PMAT: Physiological Function and Role in Drug Disposit

说明(申请人提供)：多种药物(如双胍类抗高血糖药、组胺H2受体阻滞剂、铂类化疗药物等)毒素(如MPP、百草枯)是亲水性有机阳离子(OCs)，不容易被动扩散穿过细胞膜。有机阳离子转运体在这些有机化合物的处置、疗效和毒性中起着重要作用。这些转运蛋白还可能通过摄取内源性生物活性胺而参与各种生理途径。质膜单胺转运蛋白(PMAT)是本实验室首次克隆和鉴定的一种新的多特异性有机阳离子转运蛋白。PmAt的生理底物是单胺类神经递质，5-羟色胺(5-HT)是最首选的底物。PMAT还运输许多结构不同的阳离子异物，包括神经毒素MPP和治疗药物如二甲双胍。PMAT在脑和胃肠道中高度表达，与有机阳离子转运蛋白1-3(OCT1-3)具有重叠的底物特异性。我们以前的分子和细胞工作有力地支持了pmAt在5-羟色胺信号通路和OC在屏障组织(包括形成血-脑脊液屏障的脉络丛)转运中的作用。然而，这些研究受到体外设计的限制，pmAt的生理功能及其在脑内OC处置中的体内意义仍未确定。我们最近建立了一种新的pmAt基因敲除小鼠模型，它为评估pmAt在体内的作用和意义提供了独特的资源。利用化学生物学方法，我们还确定了一组有前景的pmAt特异性小分子抑制剂。更令人兴奋的是，pmAt基因缺失的小鼠表现出结肠的生理和组织学异常，这可能是与炎症性肠病发展相关的早期迹象。由于5-羟色胺是一种关键的胃肠激素，已知其参与炎症性肠病的发病机制，这些观察结果提示pmAt对结肠炎的保护作用可能是通过5-羟色胺介导的途径。在这种竞争性的更新应用中，我们建议使用我们的新的动物模型和独特的化学工具来研究pmAt的生理、药理和病理功能。在目标1中，我们将进一步表征和验证高效和选择性的pmAt小分子抑制剂。在目标2中，我们将使用我们的基因敲除动物模型和特定的化学抑制剂来研究pmAt在调节OC在血-脑脊液屏障中的外流中的作用。最后，在目标3中，我们将研究pmAt在肠道炎症反应发展中的致病作用。这些研究将极大地加深我们对新型有机阳离子转运蛋白在体内的作用和意义的理解。这些研究将为影响大脑处理OC药物和毒素的决定因素提供新的线索。最后，我们的研究将阐明pmAt在肠道中的病理生理作用，并为影响宿主对炎症性肠病易感性的遗传因素提供新的见解。

DESCRIPTION (provided by applicant): Many drugs (e.g. biguanide antihyperglycemics, histamine H2 receptor blockers, platinum-based chemotherapeutics etc.) and toxins (e.g. MPP+, paraquat) are hydrophilic organic cations (OCs) that do not readily cross cell membranes by passive diffusion. Organic cation transporters play important roles in the disposition, efficacy and toxicity of these OC xenobiotics. These transporters are also likely to be involved in various physiological pathways through their uptake of endogenous bioactive amines. The plasma membrane monoamine transporter (PMAT) is a new polyspecific organic cation transporter first cloned and characterized in our laboratory. The physiologic substrates of PMAT are the monoamine neurotransmitters with serotonin (5- HT) being the most preferred substrate. PMAT also transports many structurally diverse cationic xenobiotics including the neurotoxin MPP+ and therapeutic drugs such as metformin. PMAT is highly expressed in the brain and the gastrointestinal tract, and has overlapping substrate specificity with organic cation transporters 1- 3 (OCT1-3). Our previous molecular and cellular work strongly supports a role of PMAT in 5-HT signaling pathways and in OC transport at barrier tissues including choroid plexus that forms the blood- cerebrospinal fluid (CSF) barrier. However, these studies are limited by their in vitro design, and the physiological function of PMAT and its in vivo significance in brain OC disposition remain undefined. We have recently created a novel PMAT knockout mouse model, which provides a unique resource to evaluate the roles and significance of PMAT in vivo. Using a chemical biology approach, we also identified a set of promising specific small molecule inhibitors for PMAT. More excitingly, the PMAT null mice exhibited physiological and histological abnormalities in the colon which could represent early signs associated with the development of inflammatory bowel disease. Because 5-HT is a key gut hormone known to be involved in the pathogenesis of inflammatory bowel disease, these observations suggest a protective role of PMAT against colitis likely through 5-HT mediated pathway. In this competing renewal application, we propose to use our novel animal model and unique chemical tools to investigate the physiological, pharmacological and pathological function of PMAT. In Aim 1, we will further characterize and validate highly potent and selective small molecule inhibitors for PMAT. In Aim 2, we will use our knockout animal model and specific chemical inhibitors to investigate the role of PMAT in mediating OC efflux at the blood-CSF barrier. Lastly, in Aim 3, we will investigate the pathogenic role of PMAT in the development of inflammatory response in the gut. The proposed studies will greatly enhance our understandings of the in vivo roles and significance of a novel organic cation transporter. These studies will shed new light on the determinants influencing brain disposition of OC drugs and toxins. Finally, our studies will elucidate the pathophysiologic role of PMAT in the gut and offer new insights into genetic factors influencing host susceptibility to inflammatory bowel disease.