Flow shear stress controls the initiation of neovascularization via heparan sulfate proteoglycans within biomimic microfluidic model

Endothelial cells (ECs) in vivo are subjected to three forms of shear stress induced by luminal blood flow, transendothelial flow and interstitial flow simultaneously. It is controversial that shear stress, especially the component induced by luminal flow, was thought to inhibit the initialization of angiogenesis but trigger arteriogenesis. Here, we combined microfabrication techniques and delicate numerical simulations to reconstruct the initially physiological microenvironment of neovascularization in vitro, where ECs experience high luminal shear stress, physiological transendothelial flow and various vascular endothelial growth factor (VEGF) distributions simultaneously. With the biomimic microfluidic model, cell alignment and endothelial sprouting assay were carried out. We found that luminal shear stress inhibits endothelial sprouting and tubule formation in a dose-dependent manner. Although high concentration of VEGF increases ECs sprouting, neither positive nor negative VEGF gradient additionally affect the degree of sprouting and luminal shear stress significantly attenuates neovascularization even in the presence of VEGF. Heparinase was used to selectively degrade heparan sulfate proteoglycans (HSPG) coating on ECs and messenger RNA profiles in ECs was analyzed. It turned out that HSPG could act as a mechanosensor to sense the change of fluid shear stress, modulate multiple ECs gene expression, and hence affect neovascularization. In summary, distraction from the stabilized state, such as decreased luminal shear stress, increased VEGF and destructed mechanotransduction of HSPG would induce the initiation of neovascularization. Our study highlights the key role of magnitude and forms of shear stress in neovascularization.