Brown Adipose Tissue Vasculature Probes for Non-Invasive Imaging

描述（由申请人提供）：动物模型研究表明，棕色脂肪组织（BAT）对肥胖症的病理后果具有保护作用，肥胖症是一种危及生命的疾病并发症。棕色脂肪细胞通过适应性产热在能量耗散中的独特功能与白色脂肪细胞的作用相反，白色脂肪细胞的肥大和增生是肥胖的原因。除了对BAT的有益作用的这种解释之外，已经显示白色脂肪细胞向棕色脂肪细胞的转分化在啮齿动物中响应于冷或其他症状性神经系统刺激而发生。最近，正电子发射断层扫描（PET）检测到成年人的功能性BAT，概述了治疗肥胖症和相关疾病的新途径。大多数成年人似乎有BAT显示活检，但它往往是代谢不活跃的肥胖和老龄化的个人，是无法检测到的PET。因此，BAT在人体中的分布仍然不完全，有必要建立可靠的BAT库定位和量化方法。该项目的目标是建立一种方法来评估BAT库，无论其代谢活动。我们建议确定探针靶向标记差异表达的成人BAT血管和使用它们的非侵入性定位BAT。首先，我们将使用小鼠模型来分离与BAT脉管系统中特异性表达的受体结合的配体（小肽）。本课题组建立的生物信息学平台将通过筛选噬菌体展示的组合肽库来筛选BAT归巢配体。接下来，我们将使用这些BAT归巢肽在小鼠模型中测试和优化BAT与肽缀合的近红外（NIR）染料的非侵入性成像。将通过常规PET、计算机断层扫描和BAT标志物的组织免疫染色验证全身给药肽缀合物的BAT定位。在这些实验中，BAT量和代谢活性的遗传背景特异性调节将建立我们方法的灵敏度和与检测相容的BAT库的性质。这种通过配体导向的成像剂递送的非侵入性BAT成像将是有利的，因为它不基于组织代谢活性。最终，本研究中分离的BAT探针可用于鉴定靶向受体及其作为BAT生物标志物的验证。随后，可以设计改进的载体来靶向BAT中的这些生物标志物。由于通过组合肽库筛选发现的血管配体/受体系统在哺乳动物中往往是保守的，我们预测在小鼠中分离的肽将与人血管BAT受体交叉反应，这些受体也可能是差异表达的。这项研究的长期目标是将这里开发的工具转化为设计一种方法来量化人体中的BAT库，这种方法将是稳健的，负担得起的，并且可能具有高度特异性。 公共卫生相关性：本文开发的BAT非侵入性成像的新方法将对目前使用PET进行的BAT检测具有显着优势：它不依赖于BAT代谢活性，可能在其他代谢活性器官中产生较少的非特异性假阳性信号，并且更便宜且更普遍可用。基于我们研究中产生的BAT靶向探针，将白色脂肪组织转化为BAT的新药理学方法可以被开发为治疗肥胖的前瞻性策略。

DESCRIPTION (provided by applicant): Studies in animal models indicate that brown adipose tissue (BAT) has a protective effect against the pathological consequences of obesity, a medical condition complicating life-threatening diseases. The unique function of brown adipocytes in energy dissipation through adaptive thermogenesis opposes the action of white adipocytes, hypertrophy and hyperplasia of which are responsible for obesity. In addition to this explanation for the beneficial effect of BAT, transdifferentiation of white adipocytes into brown adipocytes has been shown to take place in response to cold or other symphatetic nervous system stimuli in rodents. Recently, functional BAT in adult humans has been detected by positron emission tomography (PET), outlining new avenues in treatment of obesity and the associated disorders. Most adults appear to have BAT revealed by biopsy, however it is often metabolically inactive in obese and aging individuals and is undetectable by PET. Therefore, distribution of BAT in humans remains incompletely characterized, and the establishment of approaches for reliable localization and quantification of BAT depots is necessary. The goal of this project is to establish an approach to assess BAT depots irrespective of their metabolic activity. We propose to identify probes targeting markers differentially expressed in adult BAT vasculature and to use them for non-invasive localization of BAT. First, we will use the mouse model to isolate ligands (small peptides) that bind to receptors specifically expressed in the BAT vasculature. BAT-homing ligands will be isolated by integrating a screen of a phage-displayed combinatorial peptide library in vivo with the bioinformatics platform established by our group. Next, we will use these BAT-homing peptides to test and optimize non-invasive imaging of BAT with a peptide-conjugated near-infrared (NIR) dye in the mouse model. BAT localization of systemically administered peptide conjugates will be validated via conventional PET, computed tomography, and tissue immunostaining for BAT markers. Genetic background-specific modulation of BAT amount and metabolic activity in these experiments will establish the sensitivity of our approach and the properties of BAT depots compatible with detection. This non-invasive BAT imaging through ligand-directed imaging agent delivery will be advantageous because it is not based on tissue metabolic activity. Eventually, BAT probes isolated in this study could be used for identification of the targeted receptors and their validation as BAT biomarkers. Subsequently, improved vectors could be designed to target these biomarkers in BAT. Because vascular ligand/receptor systems uncovered through combinatorial peptide library screens tend to be conserved among mammals, we predict that peptides isolated in mice will cross-react with human vascular BAT receptors that are likely to also be differentially expressed. The long-term goal of this study is to translate the tools developed here for designing a method for quantifying BAT depots in humans that will be robust, affordable and potentially highly specific. PUBLIC HEALTH RELEVANCE: The novel approach to non-invasive imaging of BAT developed here will have significant advantages to currently practiced BAT detection with PET: it will not depend on BAT metabolic activity, is likely to produce less non-specific false positive signals in other metabolically active organs, and will be cheaper and more generally available. Based on the BAT-targeting probes generated in our study, new pharmacological approaches to convert white adipose tissue to BAT could be developed as a prospective strategy to treat obesity.