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

描述（由申请人提供）：许多药物（例如双胍类降糖药、组胺H2受体阻滞剂、铂类化疗药等）和毒素（如MPP+、百草枯）是亲水性有机阳离子（OC），不易通过被动扩散穿过细胞膜。有机阳离子转运蛋白在这些OC外源性物质的处置、功效和毒性中起着重要作用。这些转运蛋白也可能通过摄取内源性生物活性胺参与各种生理途径。质膜单胺转运蛋白（PMAT）是本实验室首次克隆并鉴定的一种新的多特异性有机阳离子转运蛋白。PMAT的生理底物是单胺神经递质，其中5-羟色胺（5- HT）是最优选的底物。PMAT还转运许多结构多样的阳离子外源性物质，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，并与有机阳离子转运蛋白1- 3（OCT 1 -3）具有重叠的底物特异性。我们先前的分子和细胞工作强烈支持PMAT在5-HT信号通路和OC在屏障组织（包括形成血液-脑脊液（CSF）屏障的脉络丛）的转运中的作用。然而，这些研究受到其体外设计的限制，PMAT的生理功能及其在脑OC处置中的体内意义仍不明确。我们最近建立了一种新的PMAT基因敲除小鼠模型，这为评价PMAT在体内的作用和意义提供了独特的资源。使用化学生物学方法，我们还确定了一组有前途的PMAT特异性小分子抑制剂。更令人兴奋的是，PMAT敲除小鼠在结肠中表现出生理学和组织学异常，这可能代表与炎症性肠病发展相关的早期体征。由于5-HT是已知参与炎症性肠病发病机制的关键肠道激素，因此这些观察结果表明PMAT可能通过5-HT介导的途径对结肠炎具有保护作用。在这个竞争性的更新应用中，我们建议使用我们的新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PMAT的高效和选择性小分子抑制剂。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在介导OC流出血-CSF屏障中的作用。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一种新型有机阳离子转运蛋白在体内作用和意义的理解。这些研究将为影响OC药物和毒素大脑处置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.