Treatment of acute ischemic stroke with the thrombolytic tissue plasminogen activator (tPA) can significantly improve neurological outcomes; however, thrombolytic therapy is associated with an increased risk of intra-cerebral hemorrhage (ICH). Previously, we demonstrated that during stroke tPA acting on the parenchymal side of the neurovascular unit (NVU) can increase blood-brain barrier (BBB) permeability and ICH through activation of latent platelet-derived growth factor-CC (PDGF-CC) and signaling by the PDGF receptor-α (PDGFRα). However, in vitro, activation of PDGF-CC by tPA is very inefficient and the mechanism of PDGF-CC activation in the NVU is not known. Here, we show that the integrin Mac-1, expressed on brain microglia/macrophages (denoted microglia throughout), acts together with the endocytic receptor LRP1 in the NVU to promote tPA-mediated activation of PDGF-CC. Mac-1-deficient mice (Mac-1-/-) are protected from tPA-induced BBB permeability but not from permeability induced by intracerebroventricular injection of active PDGF-CC. Immunofluorescence analysis demonstrates that Mac-1, LRP1, and the PDGFRα all localize to the NVU of arterioles, and following middle cerebral artery occlusion (MCAO) Mac-1-/- mice show significantly less PDGFRα phosphorylation, BBB permeability, and infarct volume compared to wild-type mice. Bone-marrow transplantation studies indicate that resident CD11b+ cells, but not bone-marrow-derived leukocytes, mediate the early activation of PDGF-CC by tPA after MCAO. Finally, using a model of thrombotic stroke with late thrombolysis, we show that wild-type mice have an increased incidence of spontaneous ICH following thrombolysis with tPA 5 h after MCAO, whereas Mac-1-/- mice are resistant to the development of ICH even with late tPA treatment. Together, these results indicate that Mac-1 and LRP1 act as co-factors for the activation of PDGF-CC by tPA in the NVU, and suggest a novel mechanism for tightly regulating PDGFRα signaling in the NVU and controlling BBB permeability.

中文翻译：

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小胶质细胞介导的PDGF-CC激活增加缺血性中风期间的脑血管通透性。

用溶栓组织纤溶酶原激活剂（tPA）治疗急性缺血性中风可以显着改善神经系统预后。但是，溶栓治疗会增加脑内出血（ICH）的风险。先前，我们证明了在卒中期间，tPA作用于神经血管单元（NVU）的实质侧，可以通过激活潜在的血小板衍生生长因子-CC（PDGF-CC）和信号传导来增加血脑屏障（BBB）的通透性和ICH由PDGF受体-α（PDGFRα）产生。但是，在体外，tPA激活PDGF-CC的效率非常低，并且NVU中PDGF-CC激活的机制尚不清楚。在这里，我们显示了在大脑小胶质细胞/巨噬细胞（在整个过程中均表示为小胶质细胞）上表达的整合素Mac-1，与NVU中的内吞受体LRP1共同起作用，以促进tPA介导的PDGF-CC活化。Mac-1缺陷小鼠（Mac-1-/-）不受tPA诱导的BBB渗透性的保护，但不受脑室内注射活性PDGF-CC诱导的渗透性的保护。免疫荧光分析表明，Mac-1，LRP1和PDGFRα均定位于小动脉的NVU，并且在大脑中动脉闭塞（MCAO）之后，Mac-1-/-小鼠的PDGFRα磷酸化，BBB通透性和梗死体积明显减少野生型小鼠。骨髓移植研究表明，MCAO后，tPA可以驻留CD11b +细胞，而不是源自骨髓的白细胞，从而介导PDGF-CC的早期活化。最后，使用血栓性中风伴晚期溶栓的模型，我们显示，野生型小鼠在MCAO后5小时用tPA溶栓后，自发性ICH发生率增加，而Mac-1-/-小鼠即使在tPA治疗后期也对ICH产生抵抗力。在一起，这些结果表明Mac-1和LRP1充当NVPA中tPA激活PDGF-CC的辅助因子，并提出了一种严格调节NVU中PDGFRα信号传导并控制BBB渗透性的新机制。