Physiopathology and Imaging of Neurological Disorders, Normandie Univ, UNICAEN, INSERM, INSERM UMR-S U1237, Institut Blood and Brain @ Caen-Normandie, GIP Cyceron, Boulevard Becquerel, 14074, Caen, France.
Department of Clinical Research, Caen-Normandie Hospital (CHU), Caen, France.
Fluids Barriers CNS. 2022 Oct 15;19(1):80. doi: 10.1186/s12987-022-00378-0.
In the vascular compartment, the serine protease tissue-type plasminogen activator (tPA) promotes fibrinolysis, justifying its clinical use against vasculo-occlusive diseases. Accumulating evidence shows that circulating tPA (endogenous or exogenous) also controls brain physiopathological processes, like cerebrovascular reactivity, blood-brain barrier (BBB) homeostasis, inflammation and neuronal fate. Whether this occurs by direct actions on parenchymal cells and/or indirectly via barriers between the blood and the central nervous system (CNS) remains unclear. Here, we postulated that vascular tPA can reach the brain parenchyma via the blood-cerebrospinal fluid barrier (BCSFB), that relies on choroid plexus (CP) epithelial cells (CPECs).
We produced various reporter fusion proteins to track tPA in primary cultures of CPECs, in CP explants and in vivo in mice. We also investigated the mechanisms underlying tPA transport across the BCSFB, with pharmacological and molecular approaches.
We first demonstrated that tPA can be internalized by CPECs in primary cultures and in ex vivo CPs explants. In vivo, tPA can also be internalized by CPECs both at their basal and apical sides. After intra-vascular administration, tPA can reach the cerebral spinal fluid (CSF) and the brain parenchyma. Further investigation allowed discovering that the transcytosis of tPA is mediated by Low-density-Lipoprotein Related Protein-1 (LRP1) expressed at the surface of CPECs and depends on the finger domain of tPA. Interestingly, albumin, which has a size comparable to that of tPA, does not normally cross the CPs, but switches to a transportable form when grafted to the finger domain of tPA.
These findings provide new insights on how vascular tPA can reach the brain parenchyma, and open therapeutic avenues for CNS disorders.
在血管腔中，丝氨酸蛋白酶组织型纤溶酶原激活物（tPA）促进纤维蛋白溶解，这使其在对抗血管阻塞性疾病的临床应用中具有合理性。越来越多的证据表明，循环 tPA（内源性或外源性）也控制着大脑的生理病理过程，如脑血管反应性、血脑屏障（BBB）稳态、炎症和神经元命运。这种情况是否通过对实质细胞的直接作用以及/或通过血液与中枢神经系统（CNS）之间的屏障间接发生尚不清楚。在这里，我们假设血管 tPA 可以通过血脑脊液屏障（BCSFB）到达脑实质，该屏障依赖于脉络丛（CP）上皮细胞（CPECs）。
我们制备了各种报告融合蛋白，以追踪原代 CPEC 培养物、CP 外植体和体内小鼠中的 tPA。我们还通过药理学和分子方法研究了 tPA 穿过 BCSFB 的转运机制。
我们首先证明 tPA 可被原代培养物中的 CPECs 和离体 CP 外植体内化。在体内，tPA 也可以在 CPEC 的基底和顶侧被内化。血管内给药后，tPA 可到达脑脊液（CSF）和脑实质。进一步的研究表明，tPA 的转胞吞作用是由 CPEC 表面表达的低密度脂蛋白相关蛋白-1（LRP1）介导的，并且依赖于 tPA 的指状结构域。有趣的是，大小与 tPA 相当的白蛋白通常不会穿过 CP，但当与 tPA 的指状结构域连接时，会转变为可转运的形式。
这些发现为血管 tPA 如何到达脑实质提供了新的见解，并为 CNS 疾病的治疗开辟了新的途径。
