Liddelow Shane A, Dzięgielewska Katarzyna M, Møllgård Kjeld, Whish Sophie C, Noor Natassya M, Wheaton Benjamin J, Gehwolf Renate, Wagner Andrea, Traweger Andreas, Bauer Hannelore, Bauer Hans-Christian, Saunders Norman R
Department of Pharmacology & Therapeutics, University of Melbourne, Melbourne, Australia; Department of Neurobiology, Stanford University, Stanford, California, United States of America.
Department of Pharmacology & Therapeutics, University of Melbourne, Melbourne, Australia.
PLoS One. 2014 Sep 11;9(9):e106592. doi: 10.1371/journal.pone.0106592. eCollection 2014.
To maintain the precise internal milieu of the mammalian central nervous system, well-controlled transfer of molecules from periphery into brain is required. Recently the soluble and cell-surface albumin-binding glycoprotein SPARC (secreted protein acidic and rich in cysteine) has been implicated in albumin transport into developing brain, however the exact mechanism remains unknown. We postulate that SPARC is a docking site for albumin, mediating its uptake and transfer by choroid plexus epithelial cells from blood into cerebrospinal fluid (CSF). We used in vivo physiological measurements of transfer of endogenous (mouse) and exogenous (human) albumins, in situ Proximity Ligation Assay (in situ PLA), and qRT-PCR experiments to examine the cellular mechanism mediating protein transfer across the blood-CSF interface. We report that at all developmental stages mouse albumin and SPARC gave positive signals with in situ PLAs in plasma, CSF and within individual plexus cells suggesting a possible molecular interaction. In contrast, in situ PLA experiments in brain sections from mice injected with human albumin showed positive signals for human albumin in the vascular compartment that were only rarely identifiable within choroid plexus cells and only at older ages. Concentrations of both endogenous mouse albumin and exogenous (intraperitoneally injected) human albumin were estimated in plasma and CSF and expressed as CSF/plasma concentration ratios. Human albumin was not transferred through the mouse blood-CSF barrier to the same extent as endogenous mouse albumin, confirming results from in situ PLA. During postnatal development Sparc gene expression was higher in early postnatal ages than in the adult and changed in response to altered levels of albumin in blood plasma in a differential and developmentally regulated manner. Here we propose a possible cellular route and mechanism by which albumin is transferred from blood into CSF across a sub-population of specialised choroid plexus epithelial cells.
为维持哺乳动物中枢神经系统精确的内环境，需要对分子从外周进入大脑的过程进行良好控制。最近，可溶性和细胞表面白蛋白结合糖蛋白SPARC（富含半胱氨酸的酸性分泌蛋白）被认为与白蛋白向发育中的大脑转运有关，但其确切机制仍不清楚。我们推测SPARC是白蛋白的停靠位点，介导脉络丛上皮细胞将其从血液摄取并转运至脑脊液（CSF）中。我们使用体内对内源（小鼠）和外源（人）白蛋白转运的生理学测量、原位邻近连接分析（原位PLA）和qRT-PCR实验，来研究介导蛋白质跨血脑屏障转运的细胞机制。我们报告称，在所有发育阶段，小鼠白蛋白和SPARC在血浆、脑脊液以及单个脉络丛细胞内的原位PLA实验中均给出阳性信号，提示可能存在分子相互作用。相比之下，在注射人白蛋白的小鼠脑切片上进行的原位PLA实验显示，血管腔中的人白蛋白呈阳性信号，而仅在较老的年龄段才在脉络丛细胞内很少见到。我们估计了血浆和脑脊液中内源性小鼠白蛋白和外源性（腹腔注射）人白蛋白的浓度，并以脑脊液/血浆浓度比表示。人白蛋白穿过小鼠血脑屏障的程度不如内源性小鼠白蛋白，这证实了原位PLA的结果。在出生后发育过程中，Sparc基因表达在出生后早期高于成年期，并以差异且受发育调节的方式响应血浆中白蛋白水平的变化。在此，我们提出了一种可能的细胞途径和机制，通过该途径白蛋白可从血液穿过特定亚群的特化脉络丛上皮细胞进入脑脊液。
