Endothelial fenestrae are transcellular pores that pierce the capillary walls in endocrine glands such as the pituitary. The fenestrae are covered with a thin fibrous diaphragm consisting of the plasmalemma vesicle-associated protein (PLVAP) that clusters to form sieve plates. The basal surface of the vascular wall is lined by basement membrane (BM) composed of various extracellular matrices (ECMs). However, the relationship between the ECMs and the endothelial fenestrae is still unknown. In this study, we isolated fenestrated endothelial cells from the anterior lobe of the rat pituitary, using a dynabeads-labeled antibody against platelet endothelial cell adhesion molecule 1 (PECAM1). We then analyzed the gene expression levels of several endothelial marker genes and genes for integrin α subunits, which function as the receptors for ECMs, by real-time polymerase chain reaction (PCR). The results showed that the genes for the integrin α subunit, which binds to collagen IV, fibronectin, laminin-411, or laminin-511, were highly expressed. When the PECAM1-positive cells were cultured for 7 days on collagen IV-, fibronectin-, laminins-411-, or laminins-511-coated coverslips, the sieve plate structures equipped with probably functional fenestrae were maintained only when the cells were cultured on fibronectin. Additionally, real-time PCR analysis showed that the fibronectin coating was effective in maintaining the expression pattern of several endothelial marker genes that were preferentially expressed in the endothelial cells of the fenestrated capillaries. These results indicate that fibronectin functions as the principal factor in the maintenance of the sieve plate structures in the endothelial cells of the fenestrated capillary.

中文翻译：

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纤连蛋白对于有孔毛细血管内皮细胞中的窗孔形成至关重要

内皮窗孔是穿透内分泌腺（如垂体）毛细血管壁的跨细胞孔。窗孔被薄的纤维隔膜覆盖，该隔膜由聚集形成筛板的质膜囊泡相关蛋白 (PLVAP) 组成。血管壁的基底表面衬有由各种细胞外基质 (ECM) 组成的基底膜 (BM)。然而，ECMs 和内皮窗孔之间的关系仍然未知。在这项研究中，我们使用针对血小板内皮细胞粘附分子 1 (PECAM1) 的 dynabeads 标记抗体从大鼠垂体前叶中分离出有孔内皮细胞。然后我们分析了几种内皮标记基因和整合素 α 亚基基因的基因表达水平，这些基因作为 ECM 的受体，通过实时聚合酶链反应 (PCR)。结果表明，整合素 α 亚基与胶原蛋白 IV、纤连蛋白、层粘连蛋白 411 或层粘连蛋白 511 结合的基因高度表达。当 PECAM1 阳性细胞在胶原 IV、纤连蛋白、层粘连蛋白 411 或层粘连蛋白 511 包被的盖玻片上培养 7 天时，仅当细胞在纤连蛋白。此外，实时 PCR 分析表明，纤连蛋白涂层可有效维持几种内皮标记基因的表达模式，这些基因优先在有孔毛细血管的内皮细胞中表达。