Brown Adipose Tissue Vasculature Probes for Non-Invasive Imaging

描述(申请人提供)：动物模型研究表明，棕色脂肪组织(BAT)对肥胖的病理后果具有保护作用，肥胖是一种使危及生命的疾病复杂化的医疗条件。棕色脂肪细胞通过适应性产热来消耗能量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殖是导致肥胖的原因。除了对BAT有益作用的这种解释外，啮齿类动物的白色脂肪细胞向棕色脂肪细胞的转分化也被证明是对寒冷或其他交感神经系统刺激的反应。最近，正电子发射断层扫描(PET)在成人中发现了功能性BAT，勾勒出了治疗肥胖和相关疾病的新途径。大多数成年人似乎都有BAT，但在肥胖和老年患者中，BAT往往代谢不活跃，PET无法检测到。因此，蝙蝠在人体内的分布仍然没有完全的特征，建立可靠的定位和量化蝙蝠仓库的方法是必要的。该项目的目标是建立一种评估BAT仓库的方法，而不考虑它们的代谢活动。我们建议找出在成年蝙蝠血管中差异表达的标志物的探针，并将其用于蝙蝠的非侵入性定位。首先，我们将使用小鼠模型来分离与蝙蝠血管系统中特定表达的受体结合的配体(小肽)。通过将体内展示的噬菌体组合多肽库的屏幕与我们团队建立的生物信息学平台相结合，将分离蝙蝠归巢的配体。接下来，我们将使用这些蝙蝠归宿多肽在小鼠模型中测试和优化BAT与多肽结合的近红外(NIR)染料的非侵入性成像。系统给药的多肽结合物的BAT定位将通过常规的PET、计算机断层扫描和BAT标记的组织免疫染色来验证。这些实验中对蝙蝠数量和代谢活动的遗传背景特异性调节将建立我们方法的敏感性和与检测兼容的蝙蝠储存库的特性。这种通过配基导向显像剂输送的非侵入性BAT成像将是有利的，因为它不是基于组织的代谢活动。最终，在本研究中分离的BAT探针可用于鉴定靶向受体，并验证其是否为BAT生物标志物。随后，可以设计改进的载体来靶向BAT中的这些生物标记物。由于通过组合多肽文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多肽将与可能也有差异表达的人类血管蝙蝠受体发生交叉反应。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量化人类蝙蝠储藏库的方法，该方法将是健壮的、负担得起的，并且可能具有高度的特异性。 公共卫生相关性：这里开发的BAT非侵入性成像的新方法将比目前使用PET检测BAT具有显著的优势：它不依赖于BAT的代谢活动，可能在其他代谢活跃的器官中产生较少的非特异性假阳性信号，并且将是更便宜和更普遍的。基于我们研究中产生的BAT靶向探针，可以开发将白色脂肪组织转化为BAT的新的药理学方法，作为一种治疗肥胖症的预期策略。

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.