The Role of CD99 in Leukocyte Transendothelial Migration in vitro and in vivo

描述(申请人提供)：炎症是身体对感染或损伤最基本和最关键的反应。作为对炎症刺激的反应，局部内皮细胞被细胞因子和趋化因子激活，将循环中的白细胞招募到组织损伤区域。这涉及到白细胞和构成血管系统的内皮细胞之间发生的一系列复杂的、循序渐进的黏附分子相互作用。可以说，炎症最重要的一步是白细胞通过内皮屏障本身的运动，这一过程被称为跨内皮细胞迁移(TEM)。PECAM和CD99是两种已被证明对白细胞透射电子显微镜起关键作用的蛋白质。虽然PECAM在这一过程中的作用已被深入研究，但对CD99及其作用机制知之甚少。PECAM和CD99除了表达在白细胞和内皮细胞边缘外，还部分存在于内皮细胞质膜下相互连接的膜泡网状网络中，称为侧缘循环隔室(LBRC)。在透射电子显微镜下，来自LBRC的膜(包含PECAM和CD99)在一个被称为靶向循环(TR)的过程中被输送到白细胞迁移的部位。TR被认为为迁移的白细胞提供未连接的PECAM和CD99，以接触细胞并促进其移出血管系统。阻断PECAM功能会抑制TR的启动，并随后阻止TEM。然而，目前尚不清楚CD99是否在这一复杂的过程中发挥了作用。通过定义CD99在分子水平上的运作方式，我们不仅将对TEM是如何调控的，而且对如何可能控制这一炎症步骤有了很好的了解。虽然已有研究表明，CD99在体外的透射电子显微镜中发挥着PECAM下游的功能，但到目前为止，关于其在体内透射电子显微镜中的功能水平和意义的报道很大程度上是相互矛盾的。然而，这些研究的结论都是基于对静态体外图像的解释，而不是通过实时或在活组织中观察事件。为了全面了解CD99的功能，准确地研究它在时空上如何调节白细胞的透射电子显微镜是至关重要的。 凭借我们最先进的四维成像系统，我们拥有一套独特而强大的系统，可以在体内以前所未有的分辨率实时研究事件的瞬变电磁。通过利用这项技术，我们将对这一重要分子有更深入的了解，不仅对炎症的生理机制有新的见解，而且能够识别出许多针对各种病理情况的新的治疗靶点，如动脉粥样硬化、自身免疫性疾病和癌症。

DESCRIPTION (provided by applicant): Inflammation is the body's most fundamental and critical response to infection or injury. In response to inflammatory stimuli, the local endotheliu is activated by cytokines and chemokines to recruit circulating leukocytes to the areas of tissue damage. This involves a complex, stepwise sequence of adhesive molecular interactions that occur between leukocytes and the endothelial cells comprising the vasculature. Arguably the most important step of inflammation is the movement of leukocytes through the endothelial barrier itself, in a process known as transendothelial migration (TEM). PECAM and CD99 are two proteins that have proven to be critical for leukocyte TEM. While PECAM's function in this process has been studied in depth, very little is known about CD99 and the mechanisms behind its actions. In addition to being expressed on leukocytes and along endothelial borders, PECAM and CD99 also partially reside in an interconnected reticular network of membrane vesicles just underneath the endothelial plasma membrane, known as the lateral border recycling compartment (LBRC). During TEM, membrane from the LBRC (containing PECAM and CD99) is trafficked to sites of transmigrating leukocytes in a process known as targeted recycling (TR). TR is thought to supply the migrating leukocyte with unligated PECAM and CD99 to engage the cell and facilitate its movement out of the vasculature. Blocking PECAM function inhibits TR from being initiated and subsequently prevents TEM. However, it is not known if CD99 plays a role in this complex process. By defining how CD99 operates on a molecular level, we will gain great insight into not only how TEM is regulated but also how to possibly control this step of inflammation. While it has been shown that CD99 functions downstream of PECAM during TEM in vitro, the reports thus far regarding its level of function and significance in TEM in vivo have been largely conflicting. However, the conclusions from these studies have all been based on the interpretations of static ex vivo images and not by viewing the events in real time or in living tissue. In order to fully understand the function of CD99, it is critical to study exactly how it functions spatio-temporally to regulate leukocyte TEM. With our state-of-the-art 4- dimensional imaging system, we possess a unique and powerful system for studying the events TEM in real time in vivo at unprecedented resolution. By utilizing this technology, we will gain a more thorough understanding of this important molecule and gain novel insight into not only the physiologic mechanism of inflammation, but be able to identify a number of novel therapeutic targets for various pathologic conditions such as atherosclerosis, autoimmune diseases, and cancer.