Regulation of brain endothelial cell physiology by the TAM receptor tyrosine kinase Mer

The receptor tyrosine kinase Mer (gene name Mertk) acts in vascular endothelial cells (ECs) to tighten the blood-brain barrier (BBB) subsequent to viral infection. Correspondingly, we found that Mer regulates the expression and activity of a large cohort of cytoskeletal and BBB proteins, together with endothelial nitric oxide synthase, in brain ECs. We further found that Mer controls the expression of multiple angiogenic genes, and that EC-specific Mertk gene inactivation results in perturbed vascular sprouting and a compromised BBB after induced photothrombotic stroke. Unexpectedly, stroke lesions in the brain were also markedly reduced in the absence of EC Mer, which was linked to reduced plasma expression of fibrinogen, prothrombin, and other effectors of blood coagulation. Together, these results demonstrate that Mer is a central regulator of angiogenesis, BBB integrity, and blood coagulation in the mature vasculature. They may also account for disease severity following infection with the coronavirus SARS-CoV-2. Overall design: Primary brain endothelial cells from WT and Mertk-/- mice were treated with the Mer inhibitor UNC2025 or vehicle alone (PBS) for 20h, after which RNA was harvested and used for bulk RNAseq

受体酪氨酸激酶Mer（基因名Mertk）可在血管内皮细胞（endothelial cells, ECs）中发挥功能，在病毒感染后收紧血脑屏障（blood-brain barrier, BBB）。相应地，我们发现Mer可调控脑内皮细胞中一大批细胞骨架蛋白、血脑屏障相关蛋白以及内皮型一氧化氮合酶的表达与活性。我们进一步发现，Mer可调控多种血管生成基因的表达；而内皮细胞特异性Mertk基因失活，会导致光血栓性脑卒中诱导后血管出芽异常以及血脑屏障受损。出人意料的是，在缺失内皮细胞Mer的小鼠中，脑部脑卒中病灶也显著减少，这与血浆中纤维蛋白原、凝血酶原及其他凝血效应因子的表达水平降低相关。综上，这些结果证实Mer是成熟脉管系统中血管生成、血脑屏障完整性及凝血过程的核心调控因子。该发现或可解释新型冠状病毒SARS-CoV-2感染后的疾病严重程度。整体实验设计：将野生型（wild type, WT）和Mertk敲除（Mertk-/-）小鼠的原代脑内皮细胞用Mer抑制剂UNC2025或仅溶剂（磷酸盐缓冲液, PBS）处理20小时，随后收集RNA并进行批量RNA测序（bulk RNAseq）