Vesiculo-vacuolar organelles and the regulation of venule permeability to macromolecules by vascular permeability factor, histamine, and serotonin.

Abstract

SummaryIn contrast to normal microvessels, those that supply tumors are strikingly hyperpermeable to circulating macromolecules such as plasma proteins. This leakiness is largely attributable to a tumor-secreted cytokine, vascular permeability factor (VPF). Tracer studies have shown that macromolecules cross tumor vascular endothelium by way of a recently described cytoplasmic organelle, the vesiculo-vacuolar organelle or WO (WOs are grapelike clusters of interconnected, uncoated vesicles and vacuoles). However, equivalent VVOs are also present in the cytoplasm of normal venules that do not leak substantial amounts of plasma protein. To explain these findings, we hypothesized that VPF increased the permeability of tumor blood vessels by increasing VVO function and that the WOs of normal venules were relatively impermeable in the absence of VPF stimulation. To test this hypothesis, VPF was injected intradermally in norreal animals after intravenous injection of a soluble macromolecular tracer, ferritin, whose extravasation could be followed by electron microscopy. VPF caused normal venules to leak ferritin, and, as predicted by our hypothesis, ferritin extravasated by way of WOs, just as in hyperpermeable tumor microvessels. Ultrathin (14-nm) serial electron microscopic sections and computer-aided three-dimensional reconstructions better defined VVO structure. VVOs occupied 16-18% of endothelial cytoplasm in normal venules. Individual VVOs were clusters of numerous (median, 124) interconnected vesicles and vacuoles that formed complex pathways across venular endothelium with multiple openings to both luminal and abluminal surfaces. Like VPF, histamine and serotonin also stimulated ferritin extravasation across venules by way of VVOs. Together, these data establish VVOs as the major pathway by which soluble plasma proteins exit venules in response to several mediators that increase venular hyperpermeability. These same mediators also increased the extravasation of colloidal carbon, but this large particulate nonphysiological tracer exited venules primarily through endothelial gaps.

Caveolar and intercellular channels provide major transport pathways of macromolecules across vascular endothelial cells

“…We may, therefore, reasonably conclude that the caveolar channels occur everywhere in the endothelial cells and in complicated profiles associated with large invaginations in their formation in the thick region. Recent transport studies have indicated that vesicle-tubule or vesicle-vacuole structures are responsible for the macromolecular transport in tumor-associated microvascular endothelial cells Feng et al, 1999;Kohn et al, 1992) and VEGF-, histamine-or serotonin-treated venular endothelial cells (Feng et al, 1996(Feng et al, , 1999. In this study and in a previous study , we observed HRP-positive deep invaginations.…”

In vivo myocardial gene transfer: optimization and evaluation of intracoronary gene delivery in vivo

“…This resulted in an increase in capillary permeability, as expected from previous work. [19][20][21][22][23] However, this did not increase gene transfer, nor did prior infusion of adenosine, a vasodilator, or changing the buffer to a nominal calcium-free Krebs-Henseleit solution, which has been demonstrated to increase gene delivery in vitro. 11 Similarly, the use of oxygenated perfluorocarbons, a blood substitute, to increase both the time the virus was in the coronary circulation and to exclude blood, did not improve gene delivery.…”

Ultrastructural Localization of Platelet Endothelial Cell Adhesion Molecule (PECAM-1, CD31) in Vascular Endothelium

“…VVOs represent an important pathway for transcellular passage of macromolecules and fluid in response to vascular permeabilizing mediators such as VEGF-A Feng et al 1996Feng et al ,1999. They may also have a role in neutrophil diapedesis (Feng et al 1998) and may provide a substantial store of membrane that can be rapidly mobilized to the cell surface early in angiogenesis to allow the rapid expansion in cell surface area that accompanies vessel enlargement (formation of "mother" vessels) (Pettersson et al 2000;Nagy et al 2002).…”