Nanotracer Development to Track Stem Cell Therapy

描述（由申请人提供）：在美国，大约有800万至1200万人患有外周动脉疾病（PAD），这是一种动脉粥样硬化性疾病。PAD可以减少下肢的血液流动，导致疼痛、运动能力丧失、足部溃疡和潜在的肢体丧失。这种最终结果被称为严重肢体缺血（CLI），通过手术或内窥镜治疗，以增强肢体的血流量。在受CLI影响的患者中，20-30%不适合进行血运重建术，可能不得不截肢。这促进了临床研究的医学治疗，以实现治疗性血运重建和细胞治疗。我们首次描述了不溶性基质可以在没有额外可溶性信号的情况下控制间充质干细胞（MSCs）向血管细胞的细胞分化。我们的初步研究表明，在水凝胶基质中培养的间充质干细胞在缺乏额外细胞因子的情况下表达内皮细胞和周细胞的基因型、表型和形态学特征。体内实验结果表明，这些表型变化导致新生血管的增加，这可能是骨骼肌等可再生组织功能改善的一个有利步骤。因此，我们有兴趣了解从祖细胞血管生成的过程，以实现肌肉再生。我们对这一过程的理解的核心是能够追踪干细胞和由此形成的新血管系统的必要性。干细胞标签的一个基本要求是它们不会随着时间的推移而产生毒性。同样重要的是，成像不能改变标记干细胞群的行为或命运。我们建议利用球形金纳米粒子，等离子体纳米示踪剂，因为它们具有良好的生物相容性，以及高和可调的光吸收特性。有几种方法可用于跟踪干细胞或测量新生血管，但没有一种方法可以同时监测两者。因此，当前提案的总体目标是使用纳米示踪剂增强，高分辨率超声和光声（US/PA）联合成像来量化血管生长动力学和体内功能。第二个目标是能够在模型系统中量化血运重建，其中我们能够将血管的范围和结构与肌肉功能的定量测量相关联。纳米示踪剂与US/PA成像的结合产生了一种独特的单一系统方法，能够定量祖细胞的血管发育。这将使我们能够回答关于MSC参与血管生长的基本问题，并验证临床可翻译的组织再生解决方案。

DESCRIPTION (provided by applicant): In the United States, approximately 8 to 12 million people are affected with peripheral artery disease (PAD), a form of atherosclerotic disease. PAD can reduce blood flow in the lower limbs, resulting in pain, loss of motility, foot ulcers and the potential for loss of limb. This end result, termed critical limb ischemia (CLI), is treated surgiclly or endoscopically in an effort to enhance blood flow to the limb. Of patients affected by CLI, 20-30% are not suitable for revascularization procedures and may have to be amputated. This has prompted clinical investigation into both medical therapies to achieve therapeutic revascularization as well as cellular therapies. We have described for the first time that an insoluble matrix can control cellular differentiation of mesenchymal stem cells (MSCs) towards vascular cells without additional soluble signals. Our preliminary studies show that MSCs cultured in a hydrogel matrix express genotypic, phenotypic and morphologic characteristics of endothelial cells and pericytes in the absence of additional cytokines. In vivo results indicate that these phenotypic changes lead to increased neovascularization, which may be an enabling step for the functional improvement of a regenerable tissue like skeletal muscle. Therefore, we are interested in understanding the process of vasculogenesis from progenitor cells for the purpose of enabling muscle regeneration. Central to our understanding of this process is the necessity of being able to track stem cells and the resulting newly formed vasculature. An essential requirement for stem cell labels is that they are not toxic over time. It is also essentil that imaging must not alter the behavior or fate of marked stem cell populations. We propose here to utilize spherical gold nanoparticles, plasmonic nantracers, due to their excellent biocompatibility, as well as high and tunable optical absorption properties. Several approaches are available to either track stem cells or to measure neovascularization, but none of the approaches can monitor both simultaneously. Therefore, the overall goal of the current proposal is to quantify blood vessel growth kinetics and function in vivo using nanotracer-enhanced, high-resolution combined ultrasound and photoacoustic (US/PA) imaging. A secondary goal is to be able to quantify revascularization in a model system in which we are able to correlate the extent and structure of blood vessels with quantitative measures of muscle function. The combination of nanotracers with US/PA imaging results in a unique single system approach capable of quantifying blood vessel development from progenitor cells. This will allow us to answer fundamental questions regarding MSC involvement in blood vessel growth as well as validate a clinically translatable solution for tissue regeneration.