The blood-cerebrospinal fluid barrier (BCSFB), formed by the choroid plexus epithelial (CPE) cells, plays an active role in removing drugs and metabolic wastes from the brain. Recent functional studies in isolated mouse choroid plexus (CP) tissues suggested the presence of organic anion transporting polypeptides (OATPs, encoded by SLCOs) at the apical membrane of BCSFB, which may clear large organic anions from the cerebrospinal fluid (CSF). However, the specific OATP isoform involved is unclear. Using quantitative fluorescence imaging, we showed that the fluorescent anions sulforhodamine 101 (SR101), fluorescein methotrexate (FL-MTX), and 8-fluorescein-cAMP (fluo-cAMP) are actively transported from the CSF to the subepithelial space in CP tissues isolated from wild-type mice. In contrast, transepithelial transport of these compounds across the CPE cells was abolished in Oatp1a/1b^−/− mice due to impaired apical uptake. Using transporter-expressing cell lines, SR101, FL-MTX, and fluo-cAMP were additionally shown to be transported by mouse OATP1A5 and its human counterpart OATP1A2. Kinetic analysis showed that estrone-3-sulfate and SR101 are transported by OATP1A2 and OATP1A5 with similar Michaelis-Menten constants (K_m). Immunofluorescence staining further revealed the presence of OATP1A2 protein in human CP tissues. Together, our results suggest that large organic anions in the CSF are actively transported into CPE cells by apical OATP1A2 (OATP1A5 in mice), then subsequently effluxed into the blood by basolateral multidrug resistance-associated proteins (MRPs). As OATP1A2 transports a wide array of endogenous compounds and xenobiotics, the presence of this transporter at the BCSFB may imply a novel clearance route for drugs and neurohormones from the CSF.

中文翻译：

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有机阴离子转运多肽介导的血脑脊液屏障有机阴离子清除的分子机制

血脑脊液屏障（BCSFB）由脉络丛上皮（CPE）细胞形成，在清除大脑中的药物和代谢废物方面发挥着积极作用。最近对离体小鼠脉络丛 (CP) 组织的功能研究表明，BCSFB 顶膜存在有机阴离子转运多肽（OATP，由 SLCO 编码），这可能会清除脑脊液 (CSF) 中的大有机阴离子。然而，具体涉及的 OATP 同工型尚不清楚。使用定量荧光成像，我们发现荧光阴离子磺基罗丹明 101 (SR101)、荧光素甲氨蝶呤 (FL-MTX) 和 8-荧光素-cAMP (fluo-cAMP) 主动从脑脊液转运到分离的 CP 组织中的上皮下空间来自野生型小鼠。相比之下，由于顶端摄取受损，这些化合物跨 CPE 细胞的跨上皮转运在 Oatp1a/1b ^{−/−小鼠中被取消。}使用表达转运蛋白的细胞系，还显示 SR101、FL-MTX 和 Fluo-cAMP 可以由小鼠 OATP1A5 及其人类对应物 OATP1A2 转运。动力学分析表明，雌酮3-硫酸酯和SR101由OATP1A2和OATP1A5转运，具有相似的米氏常数(K _m )。免疫荧光染色进一步揭示了人CP组织中OATP1A2蛋白的存在。总之，我们的结果表明，CSF 中的大有机阴离子通过顶端 OATP1A2（小鼠中的 OATP1A5）主动转运到 CPE 细胞中，然后通过基底外侧多药耐药相关蛋白 (MRP) 流出到血液中。由于 OATP1A2 转运多种内源性化合物和外源性物质，这种转运蛋白在 BCSFB 上的存在可能意味着药物和神经激素从 CSF 中清除的新途径。