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）对肥胖的病理后果具有保护作用，肥胖是一种危及生命的疾病的并发症。棕色脂肪细胞通过适应性产热耗散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生导致肥胖。除了对BAT有益作用的这一解释外，在啮齿类动物中，白色脂肪细胞向棕色脂肪细胞的转分化已被证明是对寒冷或其他交感神经系统刺激的反应。最近，通过正电子发射断层扫描（PET）检测到成年人的功能性BAT，为肥胖和相关疾病的治疗开辟了新的途径。大多数成年人似乎都有活组织检查显示的BAT，但它通常在肥胖和衰老个体中代谢不活跃，PET无法检测到。因此，BAT在人类中的分布特征仍然不完全，建立可靠的BAT库定位和定量方法是必要的。该项目的目标是建立一种方法来评估BAT仓库，而不考虑其代谢活性。我们建议鉴定针对成人BAT血管中差异表达标记物的探针，并将其用于BAT的非侵入性定位。首先，我们将使用小鼠模型分离与BAT脉管系统中特异性表达的受体结合的配体（小肽）。将噬菌体展示组合肽文库与本小组建立的生物信息学平台相结合，分离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肽共轭近红外（NIR）染料对BAT的无创成像。系统给药肽偶联物的BAT定位将通过常规PET、计算机断层扫描和BAT标记的组织免疫染色进行验证。在这些实验中，遗传背景对BAT数量和代谢活性的特异性调节将建立我们方法的敏感性以及与检测兼容的BAT仓库的特性。这种通过配体定向显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，本研究分离的BAT探针可用于鉴定目标受体并验证其作为BAT生物标志物的有效性。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，我们预测从小鼠中分离的肽将与可能也存在差异表达的人类血管BAT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BAT库的方法，这种方法将是强大的、负担得起的，并且可能具有高度特异性。

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.