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

描述（由申请人提供）：炎症是身体对感染或损伤的最基本和最关键的反应。响应于炎性刺激，局部内皮被细胞因子和趋化因子激活以将循环白细胞募集到组织损伤区域。这涉及白细胞和构成血管系统的内皮细胞之间发生的粘附分子相互作用的复杂、逐步序列。可以说，炎症最重要的步骤是白细胞通过内皮屏障本身的运动，这一过程称为跨内皮迁移（TEM）。PECAM和CD99是已被证明对白细胞TEM至关重要的两种蛋白质。虽然PECAM在这一过程中的功能已被深入研究，但对CD99及其作用背后的机制知之甚少。 除了在白细胞上和沿着内皮边界表达外，PECAM和CD 99还部分存在于内皮质膜正下方的膜囊泡的互连网状网络中，称为侧缘再循环室（LBRC）。在TEM过程中，来自LBRC的膜（含有PECAM和CD99）在称为靶向再循环（TR）的过程中被运输到移行白细胞的位点。TR被认为向迁移的白细胞提供未连接的PECAM和CD99以接合细胞并促进其移出脉管系统。阻断PECAM功能可抑制TR的启动，从而阻止TEM。然而，尚不清楚CD99是否在这一复杂过程中发挥作用。通过定义CD99在分子水平上的运作方式，我们不仅可以深入了解TEM是如何调节的，还可以了解如何控制炎症的这一步骤。 虽然已经表明，CD99在体外TEM过程中在PECAM下游起作用，但迄今为止关于其在体内TEM中的功能和意义的报道在很大程度上是相互矛盾的。然而，这些研究的结论都是基于静态离体图像的解释，而不是通过观察真实的时间或活组织中的事件。为了充分了解CD99的功能，关键是要研究它是如何时空调节白细胞TEM。 凭借我们最先进的4维成像系统，我们拥有一个独特而强大的系统，用于以前所未有的分辨率在体内研究真实的TEM事件。通过利用这项技术，我们将更深入地了解这一重要分子，不仅对炎症的生理机制有了新的认识，而且能够为各种病理条件（如动脉粥样硬化，自身免疫性疾病和癌症）确定许多新的治疗靶点。

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.