Mechanical Regulation of Microvascular Angiogenesis

Neovascularization is a critical early step toward successful tissue regeneration during wound healing. While vasculature has long been recognized as highly mechanosensitive (to fluid shear, pulsatile luminal pressure, etc.), the effects of extracellular matrix strains on angiogenesis are poorly understood. Previously, we found that dynamic matrix compression in vivo potently regulated neovascular growth during tissue regeneration; however, whether matrix deformations directly regulate00 angiogenesis remained unknown. Here, we tested the effects of load initiation time, strain magnitude, and mode of compressive deformation (uniform compression vs. compressive indentation that also introduced shear stress) on neovascularization and key angiogenic and mechanotransduction signaling pathways by microvascular fragments in vitro. We hypothesized that neovascularization would be enhanced by delayed, moderate compression and inhibited by early, high magnitude compression and by compressive indentation. Consistent with our hypothesis, early, high magnitude loading inhibited vessel growth, while delayed loading enhanced vessel growth. Compressive indentation led to longer, more branched networks than uniform compression - particularly at high strain magnitude. Gene expression was differentially regulated by time of load initiation; genes associated with active angiogenic sprouts were downregulated by early loading but upregulated by delayed loading. Canonical gene targets of the YAP/TAZ mechanotransduction pathway were increased by loading and abrogated by pharmacological YAP inhibition. Together, these data demonstrate that neovascularization is directly responsive to dynamic matrix strain and is particularly sensitive to the timing of load initiation. This work further identifies putative mechanoregulatory angiogenic mechanisms and implicates a critical role for dynamic mechanical cues in vascularized tissue regeneration. Statement of SignificanceMechanical cues influence tissue regeneration, and although vasculature is known to be mechanically sensitive, remarkably little is known about the effects of bulk extracellular matrix deformation on the nascent vessel networks found in healing tissues. Here, we demonstrated that load initiation time, magnitude, and mode all regulate microvascular growth, as well as upstream angiogenic and mechanotransduction signaling pathways. Across all tested magnitudes and modes, microvascular network formation and upstream signaling were powerfully regulated by the timing of load initiation. This work provides a new foundational understanding of how extracellular matrix mechanics regulate angiogenesis and has critical implications for clinical translation of new regenerative medicine therapies and physical rehabilitation strategies designed to enhance revascularization during tissue regeneration.