Reinforcing endothelial junctions prevents microvessel permeability increase and tumor cell adhesion in microvessels in vivo.

Bingmei M Fu,Lin Zhang,Min Zeng,Bin Cai,Jinlin Yang,Jie Fan

doi:10.1038/srep15697

Abstract

Tumor cell adhesion to the microvessel wall is a critical step during tumor metastasis. Vascular endothelial growth factor (VEGF), a secretion of tumor cells, can increase microvessel permeability and tumor cell adhesion in the microvessel. To test the hypothesis that inhibiting permeability increase can reduce tumor cell adhesion, we used in vivo fluorescence microscopy to measure both microvessel permeability and adhesion rates of human mammary carcinoma MDA-MB-231 cells in post-capillary venules of rat mesentery under the treatment of VEGF and a cAMP analog, 8-bromo-cAMP, which can decrease microvessel permeability. By immunostaining adherens junction proteins between endothelial cells forming the microvessel wall, we further investigated the structural mechanism by which cAMP abolishes VEGF-induced increase in microvessel permeability and tumor cell adhesion. Our results demonstrate that 1) Pretreatment of microvessels with cAMP can abolish VEGF-enhanced microvessel permeability and tumor cell adhesion; 2) Tumor cells prefer to adhere to the endothelial cell junctions instead of cell bodies; 3) VEGF increases microvessel permeability and tumor cell adhesion by compromising endothelial junctions while cAMP abolishes these effects of VEGF by reinforcing the junctions. These results suggest that strengthening the microvessel wall integrity can be a potential approach to inhibiting hematogenous tumor metastasis.

Highlights

For transient increase in microvessel permeability induced by Vascular endothelial growth factor (VEGF), Fu and Shen[5] suggested that the most likely structural changes would be a ~2.5-fold increase in the width of the cleft between endothelial cells forming the microvessel wall and partial degradation of endothelial surface glycocalyx
Perfusion with solutions containing 2 mM 8-bromo-cAMP elicited a consistent decrease in apparent permeability P for all three molecules, and abolished the transient increase induced by 1 nM VEGF
Elevation of endothelial cAMP appeared effective in reducing the permeability of endothelial cells both in vitro and in vivo[15,17,26,27,29,37,38]

Summary

Introduction

Junctions appear as discrete sites of fusion between the outer plasma membrane of adjacent cells when visualized in ultra-thin section electron microscopy. They create an intercellular barrier for material transport across the microvessel wall and can be regulated by response to physiological and tissue-specific requirements[25]. To investigate the structural mechanism by which elevated intracellular cAMP levels regulate microvessel permeability in vivo, Adamson et al.[33] quantified the number of junction strands in the interendothelial cleft from the same frog mesenteric microvessel on which permeability was determined[33].

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