Nagy Janice A, Feng Dian, Vasile Eliza, Wong Wendy H, Shih Shu-Ching, Dvorak Ann M, Dvorak Harold F
Department of Pathology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, USA.
Lab Invest. 2006 Aug;86(8):767-80. doi: 10.1038/labinvest.3700436. Epub 2006 May 29.
Malignant tumors generate new blood vessels by secreting growth factors, particularly members of the vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) family. Overall, the new blood vessels that form are hyperpermeable to plasma proteins, a property that is thought to be important for generating new stroma. However, tumor blood vessels are structurally heterogeneous and include microvessels of at least the following distinct types: mother vessels (MV), glomeruloid microvascular proliferations (GMP), arterio-venous-like vascular malformations and capillaries. Our goal was to determine whether macromolecular tracers leaked from all or from only a subset of these vessel types and to elucidate the extravasation pathways. As blood vessels are only a minor component of tumors, and therefore, difficult to study in situ, we used an adenoviral vector to express VEGF-A164, the most important member of the VPF/VEGF family, in mouse tissues. So expressed, VEGF-A164 induces large numbers of surrogate vessels of each type found in tumors in a highly reproducible manner. Overall permeability to plasma proteins was assessed qualitatively with Evan's blue dye and quantitatively with a dual tracer method employing radioactive albumin. Leaky vessels were identified by confocal microscopy (FITC-dextran) and by electron microscopy (ferritin). MV, and to a lesser extent GMP, were found to be hyperpermeable but capillaries and vascular malformations were not. Ferritin extravasated primarily by two trans-cellular routes, vesiculo-vacuolar organelles (VVOs) and fenestrae. This occurred despite a considerable reduction in VVO frequency as VVO membranes translocated to the plasma membrane during MV formation. However, reduction in the number and complexity of VVOs was offset by extensive endothelial cell thinning and a greatly shortened extravasation pathway. Extrapolating these findings to tumors predicts that only a subset of tumor vessels, MV and GMP, is hyperpermeable, and that measures of overall vessel permeability greatly underestimate the permeability of individual MV and GMP.
恶性肿瘤通过分泌生长因子，特别是血管通透性因子/血管内皮生长因子（VPF/VEGF）家族的成员来生成新血管。总体而言，形成的新血管对血浆蛋白具有高通透性，这一特性被认为对生成新的基质很重要。然而，肿瘤血管在结构上是异质性的，至少包括以下不同类型的微血管：母血管（MV）、肾小球样微血管增殖（GMP）、动静脉样血管畸形和毛细血管。我们的目标是确定大分子示踪剂是从所有这些血管类型中泄漏，还是仅从其中一部分泄漏，并阐明渗出途径。由于血管只是肿瘤的一个次要成分，因此难以在原位进行研究，我们使用腺病毒载体在小鼠组织中表达VPF/VEGF家族中最重要的成员VEGF - A164。如此表达的VEGF - A164以高度可重复的方式诱导肿瘤中发现的每种类型的大量替代血管。用伊文思蓝染料定性评估对血浆蛋白的总体通透性，并用放射性白蛋白的双示踪剂方法进行定量评估。通过共聚焦显微镜（FITC - 葡聚糖）和电子显微镜（铁蛋白）鉴定渗漏血管。发现MV，以及程度较轻的GMP，具有高通透性，但毛细血管和血管畸形则不然。铁蛋白主要通过两种跨细胞途径渗出，即囊泡 - 液泡细胞器（VVO）和窗孔。尽管在MV形成过程中VVO膜转移到质膜时VVO频率显著降低，但仍发生这种情况。然而，VVO数量和复杂性的减少被内皮细胞广泛变薄和大大缩短的渗出途径所抵消。将这些发现外推到肿瘤中预测，只有一部分肿瘤血管，即MV和GMP，具有高通透性，并且总体血管通透性的测量大大低估了单个MV和GMP的通透性。
