Micro-Viscometric Studies of the Endothelial Surface Layer in Microvessels

本研究的长期目标是研究在微血管的血管内皮上表达的内皮表面层（ESL）对微血管和小动脉中的微血管血流动力学的影响及其作为微静脉中白细胞从自由流中自发滚动的屏障的作用。ESL在微血管生理学的广泛领域中的影响最近已经在我们实验室和其他实验室的工作中建立。这项研究的结果将解决微血管流动阻力和炎症领域的基本生理功能，因此将直接关系到健康和人类状况。由于在体内可视化和询问结构的实验挑战，我们对ESL及其在微血管生理学中的作用的理解进展缓慢。然而，最近，我们已经开发和验证了一套全面的新的分析工具，能够检测ESL的存在，并揭示其流体动力学相关的厚度在体内的准确性。利用活体微血管血流的微粒子图像测速数据，以及我们精确分析微血管血流动力学的新的微粘度测量方法，我们将（1）测试ESL是否增加微血管中的血流阻力，并定量确定小鼠体内肌肉微静脉中的Fahraeus和Fahraeus-Lindqvist效应，（2）测试体内小动脉上是否存在流体动力学相关的ESL，（3）测试在培养的内皮细胞的汇合单层的表面上是否存在生理学上典型的ESL，和（4）测试ESL是否作为抗炎屏障，其防止白细胞在体内从毛细血管后微静脉中的自由流的初级捕获和随后的滚动。我们的微观粘度测量方法将被广泛用于解释结果和指导实验研究。随着我们最近开发的新工具，我们准备最终解决长期存在的微血管血流动力学的不确定性，对培养的内皮细胞单层上ESL的存在进行必要的测试，并获得对ESL在炎症状态下的潜在屏障功能的新见解。

The long-term goal of this research is to study the endothelial surface layer (ESL) expressed on vascular endothelium of microvessels in the context of its influence on microvascular hemodynamics in venules and arterioles and its role as a barrier to spontaneous rolling of leukocytes from the free stream in venules. The implications of the ESL across a broad range of fields in microvascular physiology have recently been established in work from our laboratories and in that of others. Results of this research will address basic physiologic function in the areas of microvascular flow resistance and inflammation and will thus have direct bearing on health and the human condition. Progress on advancing our understanding of the ESL and its role in microvascular physiology has been slow owing to experimental challenges in visualizing and interrogating the structure in vivo. However, recently we have developed and verified the accuracy of a comprehensive set of novel analytical tools that are capable of detecting the presence of the ESL and revealing its hydrodynamically relevant thickness in vivo. Using micro-particle image velocimetry data of blood flow in microvessels in vivo, and our new microviscometric method for accurately analyzing microvascular hemodyna.mics, we will (1) test whether the ESL increases resistance to blood flow in microvessels and quantitatively determine the Fahraeus and Fahraeus-Lindqvist effects in mouse skeletal-muscle venules in vivo, (2) test whether a hydrodynamically relevant ESL exists on arterioles in vivo, (3) test whether a physiologically typical ESL exists on the surface of a confluent monolayer of cultured endothelial cells, and (4) test whether the ESL acts as an anti-inflammatory barrier that prevents primary capture and subsequent rolling of leukocytes from the free stream in post-capillary venules in vivo. Our micro-viscometric method will be used extensively to interpret results and direct the experimental studies. With the new tools we have recently developed, we are poised to definitively resolve long-standing uncertainties in microvascular hemodynamics, conduct essential tests for the presence of the ESL on cultured endothelial-cell monolayers, and gain new insight into the potential barrier function of the ESL in inflammatory states.