Low levels of physiological interstitial flow eliminate morphogen gradients and guide angiogenesis

Abstract

Convective transport can significantly distort spatial concentration gradients. Interstitial flow is ubiquitous throughout living tissue, but our understanding of how interstitial flow affects concentration gradients in biological processes is limited. Interstitial flow is of particular interest for angiogenesis because pathological and physiological angiogenesis is associated with altered interstitial flow, and both interstitial flow and morphogen gradients (e.g., vascular endothelial growth factor, VEGF) can potentially stimulate and guide new blood vessel growth. We designed an in vitro microfluidic platform to simulate 3D angiogenesis in a tissue microenvironment that precisely controls interstitial flow and spatial morphogen gradients. The microvascular tissue was developed from endothelial colony forming cell-derived endothelial cells extracted from cord blood and stromal fibroblasts in a fibrin extracellular matrix. Pressure in the microfluidic lines was manipulated to control the interstitial flow. A mathematical model of mass and momentum transport, and experimental studies with fluorescently labeled dextran were performed to validate the platform. Our data demonstrate that at physiological interstitial flow (0.1-10 μm/s), morphogen gradients were eliminated within hours, and angiogenesis demonstrated a striking bias in the opposite direction of interstitial flow. The interstitial flow-directed angiogenesis was dependent on the presence of VEGF, and the effect was mediated by αvβ3 integrin. We conclude that under physiological conditions, growth factors such as VEGF and fluid forces work together to initiate and spatially guide angiogenesis.

Application of microscale culture technologies for studying lymphatic vessel biology

“…Together, these results suggest that biomolecular factors and interstitial flow cooperate in guiding lymphangiogenesis. It is noteworthy that the outcome described by Kim et al is similar to what was previously reported with the application of microfluidic systems on the directional bias of blood vessel angiogenesis when interstitial flow is oriented against the direction of sprouting …”

Computational modelling suggests complex interactions between interstitial flow and tumour angiogenesis

“…For both computations, time grows from left to right. The results show that our model predicts more prominent growth of the neovasculature against the flow, as observed in a recent experiment [18]. The VEGF was kept constant on the lateral boundaries with concentration f ¼ f HYC .…”

“…Interface 15: 20180415 uniform flow in horizontal direction is applied. When a controlled interstitial flow is applied, the experiments show a strikingly non-symmetric distribution of the neovasculature, while similar experiments without flow produce symmetric growth; see [18] for more details. The detailed mechanisms that control the symmetry breaking are not well understood.…”

“…since tumour angiogenesis is tightly regulated by soluble substances that are transported through the extracellular matrix (ECM), the influence of convective transport produced by interstitial flow may be significant, especially in the tumour micro-environment, where strong interstitial flows have been reported [16,17] (figure 1). Although recent noteworthy advances in microfabrication and microfluidic technology that allow the creation of in vitro multicellular microvascular tissues with simultaneous control of interstitial flow and the TAF spatial concentration gradient have demonstrated the importance of interstitial flow [18], the mechanistic understanding of the process has remained elusive. Achieving further progress requires controlling and/or measuring simultaneously TAF concentrations and interstitial flow in an experiment that recreates conditions similar to those encountered in vivo.…”

Consensus guidelines for the use and interpretation of angiogenesis assays

“…The VMO platform is fabricated from polydimethylsiloxane (PDMS), an optically clear, biologically inert polymer widely used in the microfluidics field [91]. The use of this polymer and the dimensions of the platform ensure that live, GFP-transduced endothelial progenitor cells (ECFC-EC) can be imaged and quantified throughout vessel formation.…”