Cell-generated traction forces and the resulting matrix deformation modulate microvascular alignment and growth during angiogenesis

Abstract

Underwood CJ, Edgar LT, Hoying JB, Weiss JA. Cell-generated traction forces and the resulting matrix deformation modulate microvascular alignment and growth during angiogenesis. Am J Physiol Heart Circ Physiol 307: H152-H164, 2014. First published May 9, 2014; doi:10.1152/ajpheart.00995.2013.-The details of the mechanical factors that modulate angiogenesis remain poorly understood. Previous in vitro studies of angiogenesis using microvessel fragments cultured within collagen constructs demonstrated that neovessel alignment can be induced via mechanical constraint of the boundaries (i.e., boundary conditions). The objective of this study was to investigate the role of mechanical boundary conditions in the regulation of angiogenic alignment and growth in an in vitro model of angiogenesis. Angiogenic microvessels within three-dimensional constructs were subjected to different boundary conditions, thus producing different stress and strain fields during growth. Neovessel outgrowth and orientation were quantified from confocal image data after 6 days. Vascularity and branching decreased as the amount of constraint imposed on the culture increased. In long-axis constrained hexahedral constructs, microvessels aligned parallel to the constrained axis. In contrast, constructs that were constrained along the short axis had random microvessel orientation. Finite element models were used to simulate the contraction of gels under the various boundary conditions and to predict the local strain field experienced by microvessels. Results from the experiments and simulations demonstrated that microvessels aligned perpendicular to directions of compressive strain. Alignment was due to anisotropic deformation of the matrix from cell-generated traction forces interacting with the mechanical boundary conditions. These findings demonstrate that boundary conditions and thus the effective stiffness of the matrix regulate angiogenesis. This study offers a potential explanation for the oriented vascular beds that occur in native tissues and provides the basis for improved control of tissue vascularization in both native tissues and tissue-engineered constructs.angiogenesis; strain; orientation; morphometry; image analysis; deformation ANGIOGENESIS, THE GROWTH OF new vessels from existing vessels, leads to the expansion of a microvascular bed. Sprouting angiogenic neovessels advance through the tissue space as they grow and extend away from the parent vessel. As angiogenic neovessels expand the vascular network to form a new vasculature, successful neovascularization requires that the topology of the new network meets the specific perfusion and functional requirements for that tissue (36). For example, alignment of both collagen fibers and blood vessels along the direction of loading is a critical step in tendon repair and healing (20). Additionally, neurons in peripheral tissues are aligned along blood vessels, and numerous molecular signals that regulate axonal guidance also affect blood vessel guidance as well, suggesting that blood ve...

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Mechanical Interaction of Angiogenic Microvessels With the Extracellular Matrix

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