Flow-induced modulations of endothelial glycocalyx are potential gateways for circulating tumor cell extravasation

Abstract

Background: One of the major events leading to cancer metastasis is extravasation - a process of circulating tumor cells (CTCs) exiting the blood stream across the endothelium and migrating into tissue at the secondary tumor site. Tethering, rolling and arrest of CTCs is mediated by the binding of the tumor cell adhesion ligands to endothelial cell (EC) adhesion receptors, embedded in the glycocalyx (GCX) layer of the endothelial cells. In vasculature, irregular vessel geometry such as bends, or bifurcations affect the blood flow and generate regions of disturbed flow. Endothelium is susceptible to the flow changes, which also damage the GCX layer, leading to the impairment of its barrier functions. Here, we hypothesized that disturbed flow induced reduction in endothelial GCX leads to increased attachment of CTCs to endothelial cells due to decrease of spacing between CTCs ligands and EC receptors. Methods: To investigate our hypothesis, we introduced human umbilical vein endothelial cell (HUVEC) monolayers to disturbed and uniform flow patterns in a customized parallel plate flow chamber and examined the correlation between the GCX remodeling and adhesion, clustering and migration of MCF-7 human breast cancer cells. Additionally, we investigated EC surface receptor E-Selectin expression under the same conditions. We also degraded GCX via neuraminidase in vivo, to support the hypothesis of the barrier role of GCX. Results: Results demonstrated that, in the regions of disturbed flow, GCX coverage and thickness were reduced significantly while the attachment of the cancer cells was increased, when compared to uniform flow. The expression of E-selectin between disturbed and uniform flow regions was non-differential. In vivo results showed increased attachment of 4T1 mouse breast cancer cells in the lungs of neuraminidase treated Balb/C mice compared to untreated group. Conclusion: We report for the first time the effects of disturbed flow induced endothelial GCX degradation and its importance in regulation of the attachment of CTCs to the endothelium, which results in increased adhesion of CTCs to the endothelium. Our result provides further insight into the mechanism of metastasis and suggest reinforcement of GCX as a new potential strategy for reducing the metastatic potential of CTCs.