Reduced Tie2 in Microvascular Endothelial Cells Is Associated with Organ-Specific Adhesion Molecule Expression in Murine Health and Endotoxemia

Endothelial cells (ECs) in the microvasculature in organs are active participants in the pathophysiology of sepsis. Tyrosine protein kinase receptor Tie2 (Tek; Tunica interna Endothelial cell Kinase) is thought to play a role in their inflammatory response, yet data are inconclusive. We investigated acute endotoxemia-induced changes in the expression of Tie2 and inflammationassociated endothelial adhesion molecules E-selectin and VCAM-1 (vascular cell adhesion molecule-1) in kidneys and lungs in inducible, EC-specific Tie2 knockout mice. The extent of Tie2 knockout in healthy mice differed between microvascular beds, with low to absent expression in arterioles in kidneys and in capillaries in lungs. In kidneys, <em>Tie2</em> mRNA dropped more than 70% upon challenge with lipopolysaccharide (LPS) in both genotypes, with no change in protein. In renal arterioles, tamoxifen-induced Tie2 knockout was associated with higher VCAM-1 protein expression in healthy conditions. This did not increase further upon challenge of mice with LPS, in contrast to the increased expression occurring in control mice. Also, in lungs, <em>Tie2</em> mRNA levels dropped within 4 h after LPS challenge in both genotypes, while Tie2 protein levels did not change. In alveolar capillaries, where tamoxifen-induced Tie2 knockout did not affect the basal expression of either adhesion molecule, a 4-fold higher E-selectin protein expression was observed after exposure to LPS compared to controls. The here-revealed heterogeneous effects of absence of Tie2 in ECs in kidney and lung microvasculature in health and in response to acute inflammatory activation calls for further in vivo investigations into the role of Tie2 in EC behavior.

器官微血管系统中的内皮细胞（Endothelial Cells，ECs）是脓毒症病理生理过程中的积极参与者。酪氨酸蛋白激酶受体Tie2（Tyrosine protein kinase receptor Tie2，Tek，即内皮细胞酪氨酸激酶，Tunica interna Endothelial cell Kinase）被认为在内皮细胞的炎症反应中发挥作用，但现有研究数据尚无定论。本研究以诱导型内皮细胞特异性Tie2基因敲除小鼠为模型，探究了急性内毒素血症对其肾脏和肺组织中Tie2以及炎症相关内皮黏附分子E-选择素（E-selectin）和血管细胞黏附分子-1（vascular cell adhesion molecule-1，VCAM-1）表达的影响。健康小鼠体内Tie2基因敲除的程度因微血管床而异，肾脏小动脉及肺毛细血管中Tie2表达水平较低甚至缺失。在肾脏组织中，两种基因型小鼠经脂多糖（Lipopolysaccharide，LPS）刺激后，<em>Tie2</em> mRNA水平均下降70%以上，但蛋白水平无变化。在肾小动脉中，他莫昔芬诱导的Tie2基因敲除在健康状态下与更高的VCAM-1蛋白表达水平相关；经LPS刺激后，该表达水平未进一步升高，这与对照组小鼠的表达上调现象形成鲜明对比。同样在肺组织中，两种基因型小鼠经LPS刺激后4小时内，<em>Tie2</em> mRNA水平均出现下降，但Tie2蛋白水平未发生改变。在肺泡毛细血管中，他莫昔芬诱导的Tie2基因敲除未影响两种黏附分子的基础表达，但经LPS暴露后，E-选择素蛋白表达水平较对照组升高4倍。本研究揭示了健康状态及急性炎症激活时，肾脏和肺微血管系统中内皮细胞缺失Tie2所产生的异质性效应，这要求进一步开展体内研究以探究Tie2在内皮细胞行为中的作用。