Biomechanical control of vascular morphogenesis by the surrounding stiffness

Sprouting angiogenesis is a form of morphogenesis which expands vascular networks from the preexisting ones in both developmental and postnatal settings. During this process, endothelial cells (ECs) collectively elongate new branches via their directional movement. Almost simultaneously, the vessel lumen develops internally with blood flowing into it. Our recent study has suggested lumen expansion induced by blood inflow to be an inhibitory factor for branch elongation. However, the precise mechanism governing efficient angiogenic branch elongation during lumen development under the influence of blood inflow remains unknown. Herein, we show perivascular stiffening to be a major factor that integrates branch elongation and lumen development during angiogenic morphogenesis. We found that the circumferential expansion seen during lumen development inhibits directional EC movement driving angiogenic branch elongation, as clarified by an approach combining in vitro on-chip reconstitutions and in vivo validation experiments. This process was counter-regulated by perivascular stiffening that prevents excessive lumen expansion. We also found that appropriate collagen-IV (Col-IV) deposition on the vascular basement membrane (VBM) from ECs driven by pericytes accounts for spatiotemporal perivascular stiffening. Our results demonstrate how ECs elongate branches while developing the lumen by properly building the surrounding physical environment in coordination with pericytes during angiogenesis. These findings provide insights enhancing our understanding of principles biomechanically integrating different morphogenetic processes not only in angiogenesis but also other forms of tissue development, and may in addition provide insights that open avenues to novel applications in clinical management as well as regenerative medicine.